TRIUMF: Canada's national laboratory for particle and nuclear physics

Annual report scientific activities, 1983 TRIUMF Apr 30, 1984

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TRIUMFANNUAL REPORT SCIENTIFIC ACTIVITIES 1983MESON F A C I L I T Y  OF:U N IV E R S IT Y  OF ALBERTA  SIMON FRASER U N IV E R S IT Y  U N IV E R S IT Y  OF V IC T O R IA  U N IV E R S IT Y  OF B R I T I S H  COLUMBIAOPERATED UNDER A CONTR IBUTION  FROM THE NAT IONAL RESEARCH COUNCIL  OF CANADATRIUMF > TRIUMF LIBRARYANNUAL REPORT SCIENTIFIC ACTIVITIES1983TRIUMF4004 WESBROOK MALL VANCOUVER, B.C. CANADA V6T 2A3CHEMISTRYANNEX-2C  -1A (P)THERMAL NEUTRON FACI LITYINTERIM RADIOISOTOPE LABORATORYNEUTRON TIVATION  ANALYSIS)URCEZED)URCEBAT HO BIOMEDICAL LABORATORYISOTOPEPRODUCTIONCYCLOTRON(P) /BLIB(P)MESON HALLM9(n/jj) 2 0 ( j j  )This annual report is dedicated to the memory ofDr. Edward P. HincksTed Hincks was one of Canada's great leaders in subatomic physics and he played a crucial role in the development of TRIUMF. He began Canada's participation as a user of major high-energy facilities abroad and established a group of scientists in Ottawa for that purpose. He was the first in Canada to promote the idea of a Canadian meson factory and was a strong advocate of the ideas which culminated in TRIUMF. At TRIUMF he was an early participant in experiments, a found­ing member of the National Research Council's Advisory Board on TRIUMF and a long-term and respected member of TRIUMF's Experiments Evalua­tion Committee. At the time of his death here on June 21, 1983, he was the key organizer of the first international workshop on time projection chambers. He will be remembered by everyone associated with the science of our project for his lively and friendly interest in all aspects of intermediate-energy physics and for his ideas and his humour.FOREWORDThis past year, 1983, has been the second full year of science at TRIUMF. Again, as in 1982, the cyclotron delivered beam to experi­ments for three-quarters of the year. Opera­tion at this level is highly satisfactory for a major international accelerator facility.The high volume of science emerging from TRIUMF can be measured both by the papers published and the number of people involved in the TRIUMF program. The number of publications in 1983 emerging from TRIUMF (approaching 150) was double that for any preceding year. The Board of Management has derived a considerable satisfaction out of the series of scientific achievements of the past year.TRIUMF began as a very interesting regional facility centred on its four founding universities. Although it remains a Joint Venture of the four it is now clearly the National Laboratory which the National Research Council of Canada intended. Inter­national participation has grown beyond all initial expectations.A measure of the national and international involvement in TRIUMF is a count of those scientists who were associated with TRIUMF's experiments during 1983 and who spent at least two weeks at the main site during the year. The number includes about 200 scientists (excluding students) of whom just over 40% have been based at TRIUMF or at the four founding universities, about 20% from the other Canadian provinces - including almost all of the major Canadian universities - and just under 20% each from the United States and the remaining countries of the world combined. In addition, about 50 graduate students are presently carrying out their thesis work at TRIUMF. It is a mixture of people and ideas very appropriate for the highest levels of scientific excellence.The TRIUMF applied program made great progress throughout the year and continued to achieve a high public profile. The pion therapy program treated many more patients. TRIUMF's positron emission tomograph (PET) was dedicated by the Queen in March and by fall was being used regularly for brain scans of patients. The new isotope-producing cyclotron of Atomic Energy of Canada Limited began full operation late in the year.It is a difficult task to maintain the operation of a complex cyclotron such as that of TRIUMF free of major problems, almost on a daily basis. Our extraordinary success in this regard is clearly due to the scientists, engineers, operators, technicians and support staff who attended to these problems and achieved a very high performance for the facility. Without doubt the exceptionally high morale and research vigour of TRIUMF is due largely to its energetic and imaginative Director, Dr. Erich Vogt.The TRIUMF project owes a great debt of gratitude to the National Research Council of Canada not only for its provision of operat­ing funds but also for the continued lively interest in all aspects of the project. The scientific achievements recorded in this Annual Report may be regarded as the begin­ning of the repayment of that investment by the National Research Council.The Board of Management was also pleased to note, among the recognitions received by the project, the award of honorary degrees to TRIUMF's two principal founding fathers,Dr. J.R. Richardson (D.Sc., University of Victoria, November 1982), and Dr. J.B. Warren (D.Sc., University of British Columbia, May 1983) - and also to the present Director,Dr. E.W. Vogt (D.Sc., University of Manitoba, October 1982).Chairman of the Board of ManagementvTRIUMF was established in 1968 as a laboratory operated and to be used jointly by the University of Alberta, Simon Fraser University, the University of Victoria and the Uni­versity of British Columbia. The facility is also open to other Canadian as well as foreign users.The experimental programme is based on a cyclotron capable of producing three simultaneous beams of protons, two of which are individually variable in energy, from 180-520 MeV, and the third fixed at 70 MeV. The potential for high beam currents - 100 pA at 500 MeV to 300 pA at 400 MeV - quali­fied this machine as a 'meson factory'.Fields of research include basic science, such as medium- energy nuclear physics and chemistry, as well as applied research, such as isotope research and production and nuc­lear fuel research. There is also a biomedical research facility which uses mesons in cancer research and treatment.The ground for the main facility, located on the UBC campus, was broken in 1970. Assembly of the cyclotron started in 1971. The machine produced its first full-energy beam in 1974 and its full current in 1977.The laboratory employs approximately 380 staff at the main site in Vancouver and 18 based at the four universities.The number of university scientists, graduate students and support staff associated with the present scientific pro­gramme is about 345.viCONTENTSINTRODUCTION 1SCIENCE DIVISION 3Introduction 3Particle Physics 5Photon asymmetry in radiative muon capture 5Search for muon electron conversion 6Test of charge symmetry in n-p elastic scattering at 500 MeV 7Measurement of the n parameter in muon decay 102S muonium production from thin foils 11Precise measurement of the polarization parameter E, 12Low energy, electromagnetic pion form factors 13Muonic molecule formation rates 16Precise measurement of muon decay asymmetry parameter 6 16Nuclear Physics and Chemistry 17Fragments 17A study of (p,y) reactions on 3H and 5Li at intermediate energies 17Pion production 18Non-evaporative fragment emission 18Measurement of the 1/E dependence in 7 Li(p,n)7Be reaction 18Cross section and analysing power measurement of giant resonances 19Neutron-nuclear structure with pions 20Broad pionic X-rays 21Inclusive one-pion production in proton-nucleus collisions 21Radiative polarized neutron capture on protons 23Search for 1 2C+12C "molecular" resonances in inelastic scatteringof protons from 21+Mg 23Isospin dependence of pion absorption on nucleon pairs at T^ = 65 MeV 24Tensor analysing power in pion deuterium scattering 26A study of (p,n) and related reactions 27Proton-proton bremsstrahlung 27The neutron y-ray correlations in the p“ and ir“ capture inmedium heavy nuclei 29In search of a tredecabaryon resonance 30Absorption at rest of n~ in light nuclei 31Pion production from 12C and 13 B with polarized protons at 350 MeV 31Search for evidence of a delta-nucleus intermediate state inproton elastic scattering 32The (p,2p) reaction and momentum distribution of the deuteron 32Inclusive inelastic pion scattering from light elements at 100 MeV 34Pion double charge exchange at 50 MeV on 35Studies of the A(p,Tr- )A+l reaction 35Energy and angle dependence of the 6Li(7r+ ,3He)3He reaction 37Research in Chemistry and Solid-State Physics 40Transfer effects for stopping tt~ in H2~D2 mixtures 40Formation and reactivity of muonium in gases 41Utilization of backward muons to study muonium reaction intermediates 45The chemistry of muonium atoms in condensed media 47pSR in amorphous spin glasses 49Muons and muonium on surfaces 50The chemistry of pionic hydrogen atoms 51Muonium spin exchange 52Giant muon Knight shifts 52viipSR study of critical spin fluctuationspSR in magnetic superconductors 55Coulomb capture of negative muons and pions 55A bibliography on exotic atoms 56Neutron diffraction at TRIUMF 57Theoretical program 60Introduction 60The nucleon-nucleon potential and applications to nuclear matter 60Nucleon-nucleon interaction 60Theoretical predictions for the n-p spin correlationparameter Ann 61Two-meson exchange three-nucleon potentials 61Relativistic nuclear matter calculations 61Bremsstrahlung and off-shell processes 62Proton-proton bremsstrahlung 62Amplitude structure of off-shell processes 62Nuclear reactions and electromagnetic effects 63Intermediate energy proton-12C elastic scattering 63Electromagnetic effects in the ratios (pd*tir+)/(pd->3Heir°) and(nd>3Hen“)/(nd+tir0 ) 63Large angle inclusive nuclear reactions 64Pion photoproduction and the structure of light nuclei 64The role of the A(1232) in the (y,p) reaction 64Electron scattering 65Pion effect in deep inelastic polarized lepton polarizednucleon scattering 65Quasi-elastic scattering of polarized electrons on polarized 3He 66Final state interaction in eA ■*■ e'X reactions 67Electro-disintegration of 2H with polarized beam and target 67Pion nucleus interactions 68Pion nucleus optical potential 68Pion scattering on ^2C at 100 MeV 68The role of three-nucleon absorption processes in theA(ir+ ,d)A-2 reaction 69The quark model and QCD 69Gluon effects in isospin-violating meson mixing 69Convergence behaviour in chiral bag models and the pion-nucleonscattering amplitude 70Quantum fluctuations in the bag and nucleon observables 70Order as corrections to nucleon axial form factors in the bag model 71Decay of the p-meson 71Meson-meson scattering in a non-relativistic quark model 72Coulombic confinement model 72The structure of the A(1232) resonance 73Baryon spectrum 73Lattice QCD 74Kaon physics and hypernuclei 74The KN interaction near threshold 74Kaon-induced deuteron disintegration 74K--ltHe scattering at low energies 75Hypernuclei 75Hypernuclei at a kaon factory 75Weak interactions and high energy physics 76Possible supersymmetry breaking in 1+1 dimensional supersymmetricquantum electrodynamics 76Spin 0 boson production in Z° decays and tests for compositenessof Higgs boson 76Higgs production in high energy pp collisions 76Quark fragmentation and Higgs decays 76viiiZ° decays into lepton pairs and quark pairs 76The mixings of heavy neutrinos in muon decays 76Charged Higgs production and their effects in ve scattering 76Extended electroweak models 77Fermions in Kaluza-Klein theories 7 7The effective potential in supersymmetric theories 77Theoretical chemistry 7 7Charge exchange of muons in gases 77APPLIED PROGRAMS DIVISION 78Introduction 78Biomedical program 7842 MeV cyclotron 80Radioisotope processing (AECL) 82500 MeV radioisotope production facility 83Positron emission tomography 83Novatrack 86TRIM program 86CYCLOTRON DIVISION 88Introduction 88Beam production 91Cyclotron 92Cyclotron development 92RF system 9 5Probes and diagnostics 98Vacuum 98Cyclotron engineering physics 99Ion sources and injection system 99Primary beam lines 101Thermal neutron facility (TNF) 102Control system 103Operational services 104EXPERIMENTAL FACILITIES DIVISION 107Introduction 107Experimental support 108Data acquisition systems and CFAT 108Nucleonics and IAC 109Detectors facility 109MWPC facility H OMeson hall H OMil channel H OM13 low energy ir-p channel mM15 channel H IQQD spectrometer H 3M9 channel and rf separator H 3M20 channel H 4Beam line IB H 5Beam line 2C n 6Proton hall H 7Beam line 4A H 7Neutron facility H 7MRS U 7Targets H 9Experimental facilities engineering 120ixACCELERATOR RESEARCH DIVISION 123IntroductionBeam development -*-24Cyclotron 124Primary beam lines 127Secondary channels 129Beam line diagnostics 130Computing services 131Kaon factory studies 133TECHNOLOGY DIVISION i 4 7Introduction I47Site services I47Safety program I47Building program 149Mechanical engineering 130Design office 131Planning 131Controls, electronics and computing 153Electronics development 153Electronics shop 157VAX computing centre 157CONFERENCES, WORKSHOPS AND MEETINGS 159ORGANIZATION 161APPENDICESA. Publications 104B. Users group 123C. Experiment proposals 175xINTRODUCTIONThis Annual Report for 1983 records the accomplishments of the TRIUMF project for a highly satisfactory year of major science production. Such a record does not chronicle the daily triumphs, the monthly traumas or the euphoric waves which yield the year's accomplishments. Without attempting such a history a brief overview here of the whole year may provide a perspective for the whole report.The achievement of record beam delivery (243,000 pAh) was a case of deliberate brinksmanship - with most of the high inten­sity operation occurring in the final third of the year. The first third of the year was devoted primarily to the installation of major new facilities, especially the M20 beam line.The resilience of the TRIUMF project received its severest test in mid-summer at the beginning of the long cycle of high-intensity operation. A water leak occurred inside the vacuum tank of the cyclotron in the system feeding cooling water to the rf resonators. The system includes very thin-walled stainless-steel bellows which had always been regarded as vulnerable to such leaks. The recovery from this trauma was magnificent largely as the result of extraordinary effort by the cyclotron maintenance and operations staff and by the remote handling group. A minute leak in a vast tank had to be located. The afflicted resonator had to be removed with remote handling manipulators and properly leak checked. The offending feeding system and bellows had to be extracted, repaired and reinstalled. The whole operation, from initial vacuum loss to resumed operation at high intensity, was only two weeks - a small fraction of the time which had been envisaged for such an event.As a by-product of this breakdown a great deal of confidence was gained in carrying out major repairs with remote handling.Subsequently the balance of the year produced operation as free of problems as any heretofore. The overall record of beam delivery for the year was highly satisfactory.The experimentalists were kept busy not only with the considerable beam time provided but also with writing up and reporting the previous year's work. 1982 had been thethe first year of major year-round beam delivery at TRIUMF and as a result the number of publications - in refereed journals and invited conference papers, as listed in this Annual Report - is nearly double that of any earlier year.It is difficult, from this year's work and publications, to extract a few items which epitomize the program. Several experiments in fundamental interactions received considerable recognition at international conferences on particle physics. Partly because of the excitement generated by the discovery at CERN of the intermediate gauge bosons, W~ and Z°, there was great interest in the result of Mark Strovink's group at TRIUMF for the Michel parameters of muon decay. This experiment implied a much higher mass limit than all earlier experiments combined on the mass of any possible right-handed gauge bosons; if such particles exist their mass should be at least seven times greater than that of the left- handed W~ and Z° just discovered.Another experiment, by Oram et al., also on TRIUMF's M13 beam line, provided the first definite measurement of the Lamb shift in muonium. These atomic experiments are always beautiful. This one could set the stage for a future accurate measurement of this Lamb shift as a definitive test of quantum electrodynamics.TRIUMF's time projection chamber (TPC) ran smoothly through the year in the relentless pursuit of rare modes for muon conversion.The TPC as a detector received international kudos and was the focus of an international workshop on TPCs held at TRIUMF in June. It is capable of analysing the decay of muons captured on nuclei, one after another, at a rate of almost a million stopped muons per second. The energy of the emerging electrons is measured to a few MeV in the search for any rare events in which the electron carries off the full muon energy so that the muon conversion is neutrinoless. During the year the world lower limit on such neutrinoless muon conversion was lowered to the vicinity of 10-11. This is a major achievement and the experiment is widely regarded as an extremely important test for the Standard Model of subatomic particles and their interactions which has emerged during the past decade.The work on usR is growing as rapidly as any sector of TRIUMF's activities. Major new results are recorded in this Annual Report including Knight shifts of record size and important work on gases, liquids and solids. The completion of the improved M20 beam line and the progress being made toward a new M15 beam line are stimulating the development of the whole ysR field.In the proton hall the achievement of a frozen spin target for the charge-symmetry experiment was a major technical accomplish­ment. Also important for this experiment was the major improvement in the delivery of polarized beam. Through a great deal of effort by the Ion Source group - and the insistence on Swiss standards of cleanliness - it appears possible to count on the delivery of about 500 nA of polarized beam on target. The charge-symmetry experiment thus ended the year in a position for significant production runs in early 1984.Buildings completed at TRIUMF during the year included the new machine shop building, the M15 hall and the third ion-source addition. Unfortunately much of TRIUMF's staff continues to operate out of inferior trailer space, in part as a result of new experimental space winning out, in priority, over office and workshop space. Perhaps this should be viewed as a sign of the youth and vitality of the project.Among the greatest milestones achieved during the year were those of the applied program. Apart from the schedule interruption caused by the water leak in the tank, there was a very smooth schedule for patient treatment with pions. 24 new patients were treated during the year in a program which added to the 15 patients treated during 1982. The main clinical trials for this very hopeful new cancertreatment lie ahead in the next few years.Isotope production at TRIUMF made a major step forward with the successful commissioning of AECL's CP-42 cyclotron. At the end of the year it was in full operation for AECL and was also producing isotopes for TRIUMF's PET brain scanner. TRIUMF now possesses an unmatched combination of beams for accelerator-produced isotopes. Almost the entire energy range from 15 to 520 MeV is available with proton beam intensities exceeding 100 pA. The CP-42 spans the energy interval from 15 to 42 MeV which is most useful for (p,n) and (p,2n) reactions. The main cyclotron's beam line 2C operates from 70 to 110 MeV, allowing reactions in which a few more neutrons are emitted. Finally beam line 1A covers the energy interval from 180- 520 MeV, although it operates primarily at the highest energy. A great deal of fundamental work remains to be done to delineate the optimum reactions and energies - and concomitant chemical techniques - for commercial isotope production.The positron emission tomograph (PET) was dedicated by the Queen in March and was used to obtain brain scans for research with patients throughout much of the fall. Design work on a new whole-body PET has begun with a grant from the Province of B.C.Our Board of Management, under the able stewardship of Dr. John M. Webster, remained nearly constant in membership. Prof. Alfred Fischer stepped down, after a short but valued term, and has been replaced by Dean R.R. Davidson. Closer ties were established during the year between the Board of Management and the National Research Council's Advisory Board on TRIUMF (ABOT).The chairman of ABOT, Dr. Paul Redhead, will henceforth attend Board meetings as an ex­officio member.2SCIENCE DIVISIONINTRODUCTIONForty-two experiments received beam in 1983, of which twenty-one completed the data-taking phase. The number of weeks of beam time (33) was down slightly from last year, because of a long shutdown for M20 upgrade, although this was compensated by higher beam currents. Thirteen proposals were presented at the July meeting of the EEC, and twenty-two at the December meeting, an increase of one third over last year, while the number of TRIUMF preprints more than doubled.Three workshops were sponsored by TRIUMF during the year on the topics of:Polarized Ion SourcesTime Projection ChambersIntermediate Energy Physics and ProtonBeamsThe first two were held at TRIUMF, the third in Edmonton, and all three were very suc­cessful in attracting speakers and partici­pants who are leading experts in these fields from around the globe.The user community at TRIUMF continued to expand, with about two-thirds coming from Canada and one-third from abroad. Of Canadian users, more than one-third now come from outside the four founding universities.During 1983 great progress was made in Expt. 104, a search for the reaction p“+Tc -*• e“+Tc , a process forbidden by the standard electroweak theory (though allowed in many extensions to the simplest model). Improve­ments to the time projection chamber (TPC) built for this experiment increased its over­all efficiency by more than 50% and its rate capability by a factor of two. The number of muon stops recorded in 1983 was 2 . 8 x 1012, a factor of three more than in 1982. The TPC was also used in a measurement of the cross section for pionic double charge exchange on 14C at 50 MeV. The cross section for this process is extremely small and the large solid angle of the TPC very advantageous.Experiment 104 will continue to run through 1984 in order to reach the sensitivity goal of <5 x 10~12; further improvements to the apparatus are being planned and proposals for new experiments are already being prepared.A notable event in TRIUMF's year was the pub­lication of the measurement of the Michel muon decay parameter £ carried out by a group from LBL/Berkeley, TRIUMF and Northeastern. This experiment, which sets limits on the masses of right-handed intermediate vector bosons, attracted considerable attention in the particle physics community. Another muon decay measurement, this time of the Michel parameter n (Expt. 134), completed data- taking, as did a measurement of the radiative muon capture rate in 40Ca (Expt. 47). Two experiments on pion decay, Expt. 217 which is a measurement of the ir° form factor, and Expt. 268, a measurement of the it -*• ev decay rate, had successful test runs.The pion scattering group continued to make progress with commissioning and improving the QQD spectrometer. Using a MWPC installed at an intermediate focus, the M13 channel reso­lution has been improved to ~300 keV with the full acceptance for it-, and the overall reso­lution of the whole system is now ~800 keV. Elastic scattering measurements have been completed on 36,34>32g^ 26,24Mg # 16Bj 12c>ll|N and 160 (Expt. 177), giving information on neutron and proton distribution differ­ences. Inelastic it- scattering has been measured on 26Mg, 180 (Expt. 166), and 32’34S (Expt. 203). During the coming year, the overall resolution will be improved to better than 600 keV; inelastic scattering measurements will be continued (Expts. 202, 264), and double charge exchange experiments (Expt. 246) and (tt,tt'y ) experiments (Expt. 263) have been approved by the EEC.Inclusive pion scattering on very light nuclei was measured by a group from Univers­ity of Washington in Expt. 224, while it3" absorption on 3He was compared in Expt. 199 by an Israeli/TRIUMF collaboration. A group from Trieste completed a study of it" absorp­tion on light nuclei at rest (Expt. 213), and neutron and gamma-ray correlations were studied in medium and heavy nuclei (Expt. 211) by a Johns Hopkins group. Experiment 205 began a study of the tensor polarization T2Q in pion deuteron elastic scattering using a 3He polarimeter.In the proton hall the biggest experiment continues to be a search for charge symmetry3breaking in the neutron-proton system (Expt. 121). It is mainly for this experi­ment that TRIUMF has constructed a large polarized proton frozen spin target. This target was brought to successful completion this year and attained polarizations close to the theoretical limit. The detection equip­ment for this experiment was installed on the neutron beam and commissioned during the year. The experiment will complete data-tak- ing during 1984. The polarized neutron beam was also used in a study of radiative capture (Expt. 190) which finished data-taking at two energies below the pion threshold.Upgrade of the MRS to achieve an energy reso­lution better than 100 keV is now nearing completion. In order to achieve dispersion matching a six-quadrupole dispersion plane twister was installed and commissioned in the spring. A "continuous vacuum" target has also been installed. The remaining elements needed were installed in the December shut­down. During the year the MRS was used in several proton scattering and pion production experiments (Expts. 212, 223, 165, 194 and 234).In the TT-mesic X-ray program the University of Victoria group completed data-taking on 4f 3d and 5g -+■ 4f transitions in 208Pb and 209Bi with a new BgO Compton suppression spectrometer which reduced background substantially. The 2p -»■ Is transitions wereobserved in Na, Mg and AJl with this system. Another highlight was the completion of Expt. 168, the first measurement of the Lamb shift in muonium. Although the precision of the measurement was not sufficient to be a test of QED, it represents an important first step towards such a goal.With the completion of the M20 upgrade in the spring 1983 has been a busy year for ySR users. Experiment 147 is studying formation and reactivity of muonium molecular ions in noble gases while Expt. 150 is looking at muonium relaxation rates in single crystals of ice. Muonium absorption trapping and dif­fusion in surfaces is the subject of Expt. 191, while Expt. 157 surveys p SR in liquid and solid phases and in solution.Spin glasses and giant muon Knight shifts in antimony alloys are the subjects of Expt. 239 and 232.Running schedule for 1984Jan 4-Feb 11 8 weeks unpolarizedFeb 22-Mar 5 2 weeks polarizedMar 6-May 2 9 weeks shutdownMay 3-Aug 3 13 weeks unpolarizedAug 4-Sep 2 4.5 weeks polarizedSep 3-0ct 2 4 weeks shutdownOct 3-0ct 17 2 weeks polarizedOct 18-Nov 27 6 weeks unpolarizedNov 28-Dec 24 3.5 weeks polarizedThe contributions on individual experiments in this Report are outlines intended to demonstrate the extent of scientific activity at TRIUMF during the past year. The outlines are not publications, and often contain preliminary results not intended, or not yet ready for publication. Material from these reports should not be reproduced or quoted without permission of the authors.4PARTICLE PHYSICSExperim ent 47Photon asym m etry in radiative muon capture (M. Hasinoff, UBC)There has been considerable interest lately in the values of the basic coupling constants of the weak interaction (gA , gM , gp) for the case of a nucleon bound inside a nucleus. Large renormalizations due to mesonic effects have already been observed for the axial and weak magnetism coupling constants, g» and gM [Weise, Nucl. Phys., A396, 373 (1983)]. Since the pseudoscalar coupling constant gp is related to the axial current by PCAC a large renormalization of gp is also expected. Moreover, Ericson [Mesons in Nuclei, vol. 3, ed. Rho and Wilkinson (North-Holland, Amsterdam, 1979) p. 905] has predicted that the value for gp in a nucleus might also provide some information on the effective nuclear polarizability through the effective mass term in the virtual pion propagator. Because most ordinary capture experiments in nuclei are quite insensitive to gp/gA , the experimental work has been concentrated mostly on measurements of the inclusive radi­ative muon capture (RMC) rate or the partial capture rates to various nuclear levels. Several theoretical calculations have been performed and there is general agreement that inclusive RMC is much more sensitive to gp/g^ than to details of the nuclear response function or existing uncertainties in the RMC Hamiltonian. Moreover, the photon-muon spin angular correlation is predicted to be even less sensitive than the ratio of the RMC/ordinary muon capture rate to the syste­matic uncertainties of the nuclear models [Christillin, Nucl. Phys. A362, 391 (1981)].Thus we have undertaken a measurement of both the photon asymmetry and energy spectrum fol­lowing RMC in Ca using the new M20 backward- muon channel at TRIUMF with the goal of sig­nificantly increasing the statistical sample over that obtained by the SREL group. Our technique is similar to that employed at SREL except that we have replaced the passive lead-scintillator y-ray converter with a 5 cm thick segmented Nal converter (25x33 cm2)(see Fig. 1). We also utilized a much larger Nal (46 cm cf> x 51 cm) as the total energy counter, thus ensuring a better energy resolution. The use of a converter is essen­tially to reduce our sensitivity to the flux of high energy neutrons emitted in direct muon capture. In order to provide evengreater n/y discrimination we also placed a 1.25 thick lucite C detector and a triplet of layered scintillators (3x3.2 mm) between the main Nal and the thin Nal converter to detect the e+e" pair. These counters were not required in the hardware trigger. The p~ stopping rate in our metallic Ca target (10x10x3.6 cm3) was typically » 2.80xl05/s at 76 MeV/c incident muon momentum. The target, defining beam counters and pole tip counters were all situated in a transverse magnetic field of =500 G over a gap of 16 cm. Because of the rather high beam rate and long inspec­tion time for the RMC event considerable attention was paid to the "pre-history" of the beam. The stop, the (S0 )*(S1) and the TINA signals were each delayed by =1000 ns of coaxial cable and then passed through a logic pulse separator (6 ns pulse pair reso­lution which routed up to 4 sequential pulses on each input signal line to separate channels of a CAMAC TDC. In this way we were able to ensure that no early muon could be residing in the target without unnecessarily sacrificing a high muon stopping rate.Prompt events were removed by a 50 ns hard­ware veto on the (S0 )*(S1) signal and further reduced by a software cut on the energy deposited in S2 at the time of the event. A full 200 ns of early time data was collectedFig. 1. Experimental apparatus.51 , apj apps.ENERGY (MeV)Fig. 2. Preliminary energy spectrum from a partial analysis of the data. Contributions to this spectrum are from the following sources 1) bremsstrahlung from decay elec­trons from ordinary p decay, below 55 MeV, falling sharply; 2) RMC, up to 90 MeV;3) radiative pion capture, up to 130 MeV, peaking around 100 MeV; 4) cosmic-ray back­ground, at all suitably delaying the respective energy and time signals into CAMAC. Time and energy information were also recorded for all scin­tillators surrounding the target. A short run with a carbon target substituted for the Ca target confirmed that none of our events were coming from p stopping in the magnet pole tips.An examination of our preliminary on-line energy histogram for neutral events >55 MeV (see Fig. 2) shows a residual pion background which is still not removed by our hardware and software cuts on the "PROMPT" events.Both counters S0 and Sx were clipped to provide pulses <20 ns at FWTM so the discrim­inators should have been able to recover for the next cyclotron beam burst (TCyC = 43 ns). However, because the rate for it- radiative capture is = 2% a very small counter ineffici­ency can produce a y rate which is comparable to the (p“,y). Tests were performed with the hardware prompt veto disabled and these indicate a tt/ p  ratio <10-3. Another source of prompt ir-induced background was the other leg of the M20 channel which received the forward -it/p beam while we were running (because of a faulty beam blocker). This source was reduced by shielding it with =30 cm of iron and 8 cm of lead midway through the run. The analysis of these data should be completed within the next six months.Experiment 104Search fo r muon electron conversion(D. Bryman, Victoria/TRIUMF)A system employing a time projection chamber (TPC) has been developed to search for lepton flavour violation. The reactions under study at TRIUMF are muon-electron conversion p“Z +■ e-Z, in which single electrons with momentum p 5 100 MeV/c are searched for following nuclear muon capture, and p“z •> e+ (Z-2), a double charge exchange process producing positrons with <100 MeV/c. Muons with momen­tum 71 MeV/c are degraded and stopped in a Ti foil target (2g/cm2) at a rate of ~ 5 x 105 /s. Surrounding the target are an inner set of scintillators and wire chambers, followed by the TPC and an outer set of scintillators and wire chambers.The TPC is a large volume drift chamber operated with a gas mixture of 80% argon and 20% methane at 1 atm. A magnetic field, which is typically B = 9 kG with <0.3% uni­formity, bends charged particles as they traverse the chamber, so that their momenta may be determined, while the parallel elec­tric field of approximately E0= 250 V/cm causes the ionization electrons to drift onto position-sensing devices. The magnetic field reduces the transverse diffusion of the ionization electrons during the drift.The best spatial resolution in the TPC, a - 200 pm, occurs at the minimum drift length (Z=0) and for an optimum track-to-anode crossing angle (6 ) determined by the magnetic field. The observed resolution is dependent on the diffusion of the drifting electrons, the track-to-anode crossing angle, ExB effects near the anode wire and the discrete nature of the ionization process.The parametrizations of the charge distribu­tions and of the spatial resolution were used in a Monte Carlo simulation of electron tracks in the TPC. A momentum resolution (FWHM) of about 5 MeV/c was predicted for 70 MeV/c positrons, from it+ -*■ e+ve, in a 6 kG magnetic field. This is in good agree­ment with the observed resolution.In the TPC and other similar drift chambers space charge effects due to positive ions created in the avalanche process at the end- cap wires can result in significant track distortions and gain modifications at high rates. Positive ion leakage into the drift volume of the TPC was measured to be approxi­mately 6% at an anode voltage of V^ = 1750 VCATHODE  PADANODE"Icm1.6 m mFig. 3. The anode wire region showing the dual gating grids.pulse. It was found to be advantageous to pulse G2 by approximately 3 V relative to the normal drift potential in the opposite polarity to G1 to cancel the induced charge on the wires and pads.The induced pulses observed at the anode amp­lifiers for the outer wires are <2% of mini­mum ionizing particle signals. When only one sector is pulsed the induced cathode pulses are <1 ADC channel, compared to ~300 channels for the peak pad in a minimum ionizing event. When all twelve sectors are pulsed simultane­ously the induced cathode signal is typically -2 ADC channels, which is comparable to the ambient noise. Most of the observed pick-up appears to originate in the cabling external to the TPC.and a drift field of E0 = 250 V/cm. In the muon-electron conversion experiment the radial distribution of positive ions is non- uniform. Under high rate conditions with a particle flux through the chamber of approxi­mately 6xl05 ,* distortions of order 5 mm were observed for track segments on the inner wires of the TPC. These distortions were consistent with the presence of radial elec­tric fields corresponding to Er ~ 0.02 x E0, estimated using the particle flux, the wire gain and the leakage factor.In order to significantly reduce the leakage of positive ions into the drift volume, a dual grid structure consisting of 0.006 cm wires spaced at 0.06 cm has been installed at the entrance to the anode wire slots as shown in Fig. 3. Under normal operation the grid closest to the drift region G1 is positively biased by approximately 48 V relative to the drift potential. It collects all primary ionization and thus prevents the creation of positive ions by blocking the entrance to the anode wire slot. When the trigger logic external to the TPC identifies a potential track of interest G1 is pulsed down to the normal drift potential allowing transmission of the primary ionization.The voltage on G1 is returned to the non­transmitting value after the maximum drift time ~5 ps. The second grid G2 is present to shield the anode wire and cathode pads from induced charges developed during the G1*This is approximately 6 x the normal operating flux.By January 1, 1983 the experiment had sampled lxlO12 muon stops and no event was seen.These data were taken at an average p“ stopping rate of approximately 3 . 0  x 105 /s, limited by space charge effects in the TPC. Following the improvements to the system described above, distortions due to positive ions leaking back into the drift volume from the anode wire region have been nearly eliminated by the use of the pulsed grid system. Thus, data taken in the June- November period used the maximum muon stop rate available of ~ 6 x 1 0^/s at a proton current of 125 pA to accumulate approximately 3 x 1012 p“ stops. In addition to more than doubling the data acquisition rate the system acceptance was also improved by nearly a factor of two. These data are presently being analysed.Experiment 121Test o f charge sym m etry in n-p elastic scattering a t 500 M eV  (W.T.H. van Oers, Manitoba)During calendar year 1983 a series of five test runs were devoted to electronics check­out, evaluation of instrumentation perfor­mance and calibrations. A sixth run saw first data-taking. All that is left of the originally envisaged program of calibrations is a measurement of the frozen spin target polarization other than using NMR techniques and a measurement of the ratio of the polari­zation transfer coefficients Dt/Rt for the D(p,n)2p reaction at 9°lab and 500 MeV. Analysis of the data taken to determine the crossover angle of the analysing power in n-p elastic scattering is in progress.G 10SPACERSCu CLADDING7Test Run #9Neutron beam profiles were studied for the laterally shifted neutron collimator. The observed neutron intensity distributions were trapezoidal in shape in both the horizontal and vertical directions with flat tops of 7.0 cm and 4.5 cm, respectively. There remained some uncertainty about the vertical position of the neutron collimator. Instru­mental asymmetries of the neutron polarimeter were investigated. For zero up-down asym­metry the proton beam at the LD2 target, as observed on the wire profile monitor 4AM5, has to be rather low (5 1/2 wires below the central wire) indicating some offset in the vertical position of the neutron collimator (see also Fig. 4).Precession curves for the three spin pre­cession magnets were measured. The super­conducting solenoid Janis precesses the transverse polarization component of the polarized proton beam into the horizontal plane (cw rotation). The required excitation Prot of the solenoid is with I = -82.5 ± 3.6 A^ corresponding to a rotation of 90.3 ± 3.9 .The horizontal polarization component of the polarized neutron beam is precessed by the first spin precession dipole magnet Clyde into a longitudinal direction (with negative helicity if the proton spin direction leaving the cyclotron was "up" and with positive helicity when the proton spin direction was "down"). The required excitation corresponds to By = 9.903 ±0.23 kG or a rotation of 61.7 ± 1.4°. The longitudinal polarization component of the polarized neutron beam is precessed into the vertical direction by the second spin precession dipole magnet Bonnie ("up" for a polarized proton beam with spin "up") while the unwanted vertical polariza­tion component produced in the D(p,n)2p reac­tion is precessed into the longitudinal direction (negative helicity) where parity conservation makes it ineffective for left- right and up-down scattering. The required excitation corresponds to Bx = 15.71 ±0.76 kG or a rotation of 88.2 ± 4.3°.Test run #10Linearities and efficiencies were determined for all eight delaiy line chambers. The deviations from linearity are on the order of 1 to 2 mm over the length of the delay line (60 cm). The measured linearity curves provide first-order corrections so that x-y coordinates can be determined to a fraction of a millimetre. Intrinsic efficiencies wereon range countert.o.f. start counter- x-y wire chambers-Proton beam-Proton polarimeter & energy monitor-Spin precession solenoid Split plate s.e.m.'s Liquid deuterium targetrClearing magnetLead collimator9° port -H - dipole magnetLead collimator -V - dipole magnet•Frozen spin targetdetector// ii leter rofileFig. 4. Experimental layout of the test of charge symmetry in n-p elastic scattering.found to be typically 0.997, uniform over the active area of each chamber.Radiation damage to thin CH2 foils in the proton polarimeter forced evaluation of other alternatives. A kapton foil having a H:C ratio about 5.5:1 less favourable than for CH2 was tested. In comparison with a “ mg/cm2 CH2 foil and a 3.9 mg/cm2 kaptonfoil at 600 nA it was found:ch2p-p yield 5.24Instrumental -0.0166±0.0001 asymmetry / randoms 9.3%% (p,2p) 0.9%Scattered energy error 0kapton-0.0162±0.000222%4.0%+150 keVIn a two-day period with the kapton foil, there was a monotonic loss of hydrogen at 3.6%. The large random rate does not appear to affect the measured instrumental8asymmetry, which was stable to better than ±0.01 during the 48 h test. The left beam energy monitor operated satisfactorily. The energy spread in the stopping proton beam was less than 3 MeV. Over a 24 h period, includ­ing several accesses, the detected average beam energy was stable to better than 100 keV. There is a change of about 150 keV in the detected beam energy when kapton and CH2 targets are interchanged. This is due to increased background from heavy nuclei in the kapton foil. Correction of a geometrical misalignment in one counter in the right BEM eliminated an apparent inefficiency, but the stopping distributions are still incorrect for scatters to the right and some mechanical problems must still be resolved. The right beam energy monitor gives proper stopping distributions if it is physically moved to the left side.Test run #11Subsequent to modifications in the frozen spin target and the addition of the pattern counter to the proton booms, it was found necessary to reduce the thickness of the brass absorber wedges in order to ensure that all particles of interest traversed the wedge and gave a uniform signal in the E-counter. The wedges were therefore remachined so that protons would emerge with energies up to approximately 90 MeV. The proton range counters were tested for various trigger arrangements and with various amounts of brass absorber between the E counter and the veto counter.The neutron detector array efficiency has been calculated using a Monte Carlo program. Incorporating the experimental kinematical configuration an average efficiency of 29.1% and 27.7% was obtained with the detector threshold for all photomultipliers set at 1 MeV and 3 MeV, respectively. No obvious dependence of the efficiency on the position and direction of neutron incidence was observed over the energy region of interest (280-360 MeV).The position resolution of the neutron bars is one of the parameters which influence the degree of rejection of unwanted background due to quasifree scattering in the target material and surrounding walls of the refrig­erator. The position resolution of the neutron bars for charged particles was determined by selecting only particles trig­gering narrow ( 1 cm) overlap regions of two adjacent veto counter paddles in front of theneutron array. The additional requirement that the particle comes from the target region gives a very well-defined geometry. The width of the corresponding peaks in the neutron was found to be of the order of 4 cm (±0.5 cm variation in different bars). This resolution in turn translates into a time resolution of ~180 ps at both ends of the neutron bars. The position resolution for neutrons is probably slightly worse because of the character of the pulse height dis­tribution for neutrons (continuous, down to discriminator threshold).Test run #12An upward shift of the neutron collimator aperture allowed better centring of proton beams on to the LD2 target. The delay lines on the delay line chambers received new covers. Consecutively, linearities and efficiencies were remeasured. The high volt­age settings for all photomultiplier tubes on both neutron array detectors have been iterated to obtain the same gain on the basis of the pulse height centroids of passing charged particles in the button detectors. After several iterations the gains were equalized to within better than 2% for all photomultiplier tubes on the upstream neutron-array banks and 4% for those on the downstream banks. With the same high voltage settings significant shifts (~1 0%) in the pulse height centroids were, however, observed for 10 tubes in a later run.Various magnet elements were tried with the SEM feedback system. The most reliable combination consists of 4ASM3/4VB1 for horizontal steering and 4ASM2/4ASMI for vertical steering of the proton beam. With the frozen spin target a measurement was made of the crossover angle. Analysis of these data is still in progress.Test run #13The polarized ion source after extensive servicing produced the highest intensity ever of polarized protons on the LD2 target. Currents of 650 nA of p for all three spin states up", "off", and "down" were measured. Polarizations varied between 0.65 and 0.70. The frozen spin polarized target reached positive polarizations of 0.87 and negative polarizations in the 90% region. A calibration of the frozen spin target polari­zation still has to be made, n-p coincidence data were taken for the first time with the data acquisition program MIDAS and written on9to magnetic tape. Various data-taking sequences were tried. The measurement of the precession curve for the first spin preces­sion dipole magnet Clyde was repeated. The result was in agreement with the earlier value for the required excitation of the magnet. Combining the two results gives By = 9.964 ± 0.11 kG or a rotation of 62.1 ±0 .7 °, close to the calculated value based upon magnetic field measurements. The amplitude of the precession curve provides a calibra­tion of the effective analysing power of the neutron polarimeter assuming the transfer coefficients Rt and R{- for the (p,n) reaction to be known. The effective up-down and left- right analysing powers were found to be*UDeffand iLR = eff±0.003 stat.= 0.215 +0 . 0 1 2 sys.-0.007 sys.±0.004 stat.= 0.209 +0 . 0 1 2 sys.-0.007 sys.Run #14First data-taking took place. There appeared to be some instability in the room tempera­ture coil current providing the holding field which will be corrected by installing a better regulated power supply (stable to one part in lO4). Also randomization of the sequence of spin states of the polarized source "up", "off", "down", and off will be introduced. Data analysis is in progress.Experim ent 134M easurem ent o f the q param eter in muon decay(K. Crowe, California Berkeley)Despite the recent progress in the under­standing of weak interactions substantial deviations from the V-A vertex interaction have not yet been ruled out. The successes of the Weinberg-Salam model should not be misunderstood: the model takes the V-Avertex as input and does not predict it.Other models have other expectations, such as the prediction by S0(10) of a V+A component. Further, despite the recent efforts by many experimenters there has not been any con­vincing evidence that neutrinos are massless and this would allow S and/or P vertex coup­lings. Thus, the present situation demands that one keep an open mind about weak inter­actions and provides the motivation to make accurate measurements to constrain the theory.Muon decay provides an excellent way to study the weak interaction: it is free from the complications of strong interactions and excellent statistics are possible due to the copious numbers of muons available at TRIUMF. Experiment 134 is an accurate measurement of the low end of the positron spectrum from unpolarized muon decay. This yields a value of the so-called Michel parameter, n , which is a function of the V,A,S,P coupling con­stants. In the V-A theory q = 0.0, exactly. The only experimental determination to date is q = 0.12 ± 0.21 [Derenzo, 1969] which makes q the most poorly determined of the Michel parameters. Experiment 134 expects to reduce this error to ±0.05 but it must be recognized that improvement to the level of accuracy to the other parameters is probably impossible since the effect of n upon the spectrum is suppressed by a factor of (electron mass)/(muon mass). Also, since q affects mostly that part of the spectrum with energies less than about 304 of the maximum, any measurement must contend with the need to reject showers from higher energy positrons with very high efficiency (of order 1 part in 105).Experiment 134 uses an axial focusing beta spectrometer which samples the positron spec­trum in 2 .5% momentum bites, up to momenta in excess of the maximum from muon decay. The spectrometer differs from the conventional in that it uses a large number of active collim­ators to reject shower events. Other features include NMR monitoring to provide the calibration, plastic and Nal scintillator to measure the energy of accepted particles, and a plastic scintillator stopping target to provide a TOF measurement of events (Fig. 5). The only major change in the spectrometer in the past year was the addition of T5 plastic counter before the Nal. The purpose of this counter, which is 3.7 cm thick, was toFig. 5. Spectrometer layout (C0M0S).10Fig. 6 . Positron spectrum from unpolarized muon decay.improve the energy measurement for accepted particles: low energy positrons tend tobackscatter from the Nal or its window and T5, due to its low-Z composition, helps ensure that positrons with energies up to about 15 MeV deposit most of their energy in active material. The composite detector provides better energy resolution than could a detector made of a single material.The data-taking phase of the experiment was completed with a run during the summer of 1983 which greatly improved our statistics. The data are now adequate to give ±0.04 statistical uncertainty for n. Analysis of the data is still under way but as shown in Fig. 6 , the V-A theory curve (corrected for experimental effects) provides a reasonable fit to the data. The data plotted represent most of our data taken before 1983 and have a statistical uncertainty for q of ±0 .1 0 .Experim ent 1682S muonium production from thin foils (C. Oram, TRIUMF)This year has seen the successful completion of this experiment by having measured the Lamb shift in muonium to be 1070+12/-15 MHz. The theoretical value is 1047.03 MHz.Early in the year we installed a new rf cavity in our apparatus (see Fig. 7) and a new 63 pm incident scintillator. Improve­ments were made to the electronics to minimize noise on our microchannel plate detectors (MCP). These improvements increased our signal-to-noise ratio consid­erably from that which we had obtained in December 1982.Data were taken in an 8-day period on the M13 beam line. The beam line was tuned so that 15.4 MeV/c muons were incident on the evacuated apparatus through a 50 pm mylar window. A 63 pm plastic scintillator (X) detected particles incident on a 0 . 7 5  pm aluminum foil. Muons and muonium emerging from the foil passed through an rf transmission line into a static electric Stark quench field (~300 V/cm) and were detected by a rectangular (92 x 75 mm) microchannel plate (MCPB). Transitions from 2S to 2P states induced in the 3.4 cm wide rf transmission line region depopulate the n=2 state. At resonance with 12.5 W of rf power approximately one third of the 2S muonium moving at c/70 would survive the rf region. The lifetime of the surviving 2S muonium in the quench region was reduced to about 8 ns due to Stark mixing. The resulting Lyman a radiation was detected by two (40 mm diameter) Csl-coated microchannel plates (MCP1 and MCP2).After adjusting beam parameters for optimum flux between X and MCPB of particles with velocity near c/70, data were accumulated in runs of approximately eight hours over an eight-day period. Rf power was maintained at either 2, 12.5 or 25 W during a run, and the frequency was changed every few minutes.Off-line analysis started by requiring the following criteria for the time relationship between X, MCP1 or MCP2, and MCPB:Fig. 7. A schematic of the apparatus, show­ing a good event in which a Lyman a photon is detected in microchannel plate (MCP1) from de-excitation of p+e“(2S) in the quench region.111. The time of flight between X and MCPB corresponded to a velocity between c/55 and c/200.2. MCP1 or MCP2 fired after the particle entered the quench region, but more than 5 ns prior to striking MCPB.3. The interval between entry into the quench region and detection of a Lyman a photon was less than 20 ns.4. No muon arrived in X before the preceding muon had reached MCPB.The remaining number of events was normalized by the X-MCPB coincidences at each frequency and power. To check for the effect of stray rf fields on the efficiencies of MCP1 and MPC2 and to check the normalization of the data, the total (i.e. before imposing time requirements) number of events at each fre­quency and power was normalized in the same way. The data are shown in Fig. 8 . Also shown are fits consisting of a power inde­pendent flat background plus the resonance curve. Consistent values were obtained when the data for MCP1 and MCP2 were analysed separately.The sensitivity of the measurement to systematic effects gives a total systematic error of 2 MHz. We find that about 31 2S muonium emerge from the foil for an incident p+ flux of 4 x loVs in agreement with the IS data of Bolton et al. [Phys. Rev. Lett. 47, 1441 (1981)] (after correcting for our reduced stopping rate at the surface of the foil and assuming l/1 0th of the neutrals were in 2S state), and slightly less than Oram et al. [J. Phys. B. L14, 789 (1981)].The main limitation in this type of experi­ment is the low stopping density of available muon beams. Using present beams, the statis­tical uncertainty in future experiments could in principle be reduced, for instance by a larger angular acceptance from the foil; however, it appears that such improvements result in larger systematic uncertainties.Experim ent 185Precise measurem ent o f the polarization  param eter E, (M. Strovink, Berkeley)During 1983 Expt. 185 completed and published the analysis of the data from our highly suc­cessful initial run in the spring of 1982, and made major strides toward completing the analysis of data taken in our main data col­lection run in the fall of 1982. A final period of data collection, focusing on theFig. 8 . The intensity of the muonium 2P-1S signal is plotted (triangles) for the measured rf frequencies and powers. The circles, representing the background intensi­ties, give an independent test of the normalization. The smooth curve is a of the final systematic error assign­ments, will take place in January 1984. Even with the statistics obtained from our earliest run TRIUMF data now impose the major constraint both on the mass and mixing phase of a possible right-handed W boson coupling to light neutrinos.The final version of the Berkeley- Northwestern-TRIUMF muon polarimeter is depicted in Fig. 9. Surface p+ from the M13 channel enter from the top and stop in a pure metal foil target with a 1.1 T longitudinal magnetic field. Decay e+ with the maximum momentum are prevented by the usual left- handed weak interactions from being emitted in the beam direction. Careful study of the spectrum in e+ angle and momentum, measured to 0.2% by the 98° spectrometer (D3, magnet, D4, S3), provides a powerful method of searching for the possible effects of a right-handed weak boson Wr . This very heavy particle is predicted in many models of the weak interaction but as yet is not observed.12N(Wr ) (GeV/c2)600 400 300  250 220 200Fig. 9. Plan view of Expt. 185 muon polarim­eter in the M13 channel. P1-P3 are propor­tional wire chambers, D1-D4 are drift chambers and S1-S3 are scintillators.As reported [Carr et al., Phys. Rev. Lett.51, 727 (1983)], the precision achieved by Expt. 185 in its initial run is shown in Fig. 10. The bold curve is the TRIUMF result; other curves are from a wide variety of experiments at low and high energies. The region in W mass-squared ratio a and mixing angle r, that is allowed by these curves includes the origin, which is the point predicted by the conventional weak- interaction theory. If the two bosons are assumed not to mix, the TRIUMF data require the Wr to be more massive than 450 GeV.The quality of the data from our main run has been verified also to be quite high, and we are aiming for improved precision on the pub­lished result using two nearly independent analysis methods. The final study of systematic errors scheduled for early 1984 should provide the basis for timely com­pletion of the full analysis.a- M 2(WL)/M2(WR)Fig. 10. Experimental 90% confidence limits on the WLjR mass-squared ratio a and mixing angle £ describing possible right-handed charged currents. The bold curve is the new TRIUMF result.Experim ent 217Low  energy, electrom agnetic pion form  factors  (J.-M. Poutissou, TRIUMF/UBC)The tt° meson being the lightest of the known hadrons is stable vis-A-vis strong interactions and decays mainly through electromagnetic processes:YYye+e“e+e_e+e"e+e"98.8% 1.15xl0-2 3.32xl0"5 1.7 xlO- 71 )2 )3)4)In first approximation the it0 couples to 2 photons and estimates for these decay rates can be obtained from purely electromagnetic interaction. The effect of tt° structure is absorbed in a form factor.13The electromagnetic form factor of the ir° represents the real part of the simplest electromagnetic vertex for their decayit0 y y ■ - - - awhen one or both of the photons are off their mass-shell.Dalitz et al. [Phys. Rev. 98, 1355 (1955); Proc. Phys. Soc. (London) A64, 667 (1951)] have calculated the distribution of the lepton pairs produced in reaction (2 ) for the case where one assumes a contact interaction {F(k2 ,k2=0 ) = l} , modified to take into account a possible form factor parametrized byF(k2 ,0) = 1 + a(£'where "a" is called the slope parameter of the it0 form factor.In the it0 + e+e“Y decay the effect of the structure of the tt° can be seen by looking at the rate for events corresponding to a large k1, the photon invariant mass. The total integrated rate is very insensitive to the structure effect.The primary objective of the proposed experiment is to determine the momentum dependence of the ir° form factor in the region of small, (q2 < mjj) timelike momentum transfer. The measurement is made by stopping a ir~ beam in a liquid hydrogen target and observing the distribution of Dalitz decays:TT p Lir°ne+ e_YThe differential decay rate do/dx can becalculated for a point-like pion usingordinary QED. The form factor T(x) modifies this distribution as follows:d£.= (d£l | T (x) | 2dx (dx) QED 1 1where x is the invariant mass of the e+ e" pair.Over the small range of momentum transfer considered here it is customary to parametrize T(x) as:T(x) = 1 + ax + 9(x2 )and assume that high order terms are negligible.The variable x, the invariant mass of the e+e_ pair, is then determined from:x = (2Me2 + 2E+E- - 2q+q_ cos9)where E+, q+, E_ and q_, the energies and momentum of the electron and positron, are determined by the Nal detectors, and 0, the opening angle of the pair, is determined by the wire chambers.The differential decay rate has been calcu­lated by Kroll and Wada [Phys. Rev. 98, 1355 (1955); Dalitz, Proc. Phys. Soc. (London)A64, 667 (1951)]. It can be shown that, to be sensitive to a, an experiment has to detect pairs e+ e_ with large x, which in turn implies large opening angles.To realize this, the two Nal detectors are placed in the configuration shown in Fig. 11. The electrons and positrons are required to pass through three scintillators and a three wire chamber telescope on each side and then be totally absorbed in the large Nal detectors. A valid event must have triggered each of the scintillators and produced tracks which could be traced back to a common inter­action point in the active volume of the target.Both large sodium iodide detectors (TINA and MINA) to be used in this experiment have beenFig. 11. Experimental set-up for Expt. 217.14I  15si10Va (0,20°)■ r (0,15°) •  •  (0 ,0°)0 30 60 90 120 150ENERGY (MeV)Fig. 12. Resolution of MINA vs. energy for two angles of incidence (0 ° lower curve, 2 0° upper curve).8CO£-90.4MeV/0° ■-135 MeV/0° a■ ••• ••0 5 10 15POSITION (CM)Fig. 13. Resolution of MINA vs. position from axis in centimetres for 2 energies (90.6 and 135 MeV).sent back to their original manufacturers with the goal of recompensating the light collection system and providing much better uniformity of the light output. New photo­tubes and bases have also been installed.In a test run in May we measured the response function of the recompensated detectors and established a map of the dependence of the response function on the incident energy.The position and direction of the incident electron beam was also varied. Some of the results are presented in Figs. 12 and 13.The main conclusion from these studies is that we feel confident we will be able to maintain a 5% FWHM energy resolution for the e+ and e" pairs detected in the geometry that we have proposed for our experiment, reducing the contamination from the radiative decay tt“p e+e“n.The effect of a is to modify the shape of the spectrum in the region of steeply varying rate and to change the absolute number of events above a given energy cut-off. Absolute energy calibration and stability are essen­tial because of the steep variation of da/da at large x.On-line monitoring of the calibration and stability is done by studying the copious number of uncharged events (singles and coincidents). We have tested a new prototype CAMAC module designed by E. Cairns at the University of Alberta which when used in conjunction with a L.R.S. spectroscopic ADC 3512 allows us to tag our valid event with the mean average of the peak position of the monoenergetic photons from radiative capture, averaged over a selectable number of events.The calibration for charged leptons can be done using the ir+ev decay. Stability ismonitored via diode light pulsers which have been implemented on each of our Nal detectors and scintillation counters.In 1983 considerable effort went into the design, drafting and manufacturing of the telescope assemblies which were installed on a large scattering table available at TRIUMF. This work was completed successfully for our September run and has been carried out by the TRIUMF design office and machine shop. It proved to be adequate during our test run with only minor improvements to be incorpo­rated in future runs. Six delay line wire chambers were used during the run but two out of six showed marginal reliability. We are working on a new design to improve the electronics so that we can operate these chambers at a lower high voltage.The design of the liquid hydrogen flask has been completed and manufacturing is in progress with a target date of February 1/84 for first operation in the M13 beam line. It consists of a vertical cylindrical mylar vessel 7.5 cm in diameter and 12 cm high housed in a vacuum chamber presenting a 150° unobstructed view with only a 0 . 2 mm thick mylar window (to minimize external conversion of real photons).A pile-up detection system based on succes­sive sampling of the Nal linear pulse has been tested during our September run.We are now ready to take data on tt° + e+e~Y and this should happen in February 1984 when the liquid hydrogen target becomes operational.15Experiment 230Muonic molecule form ation rates(K. Aniol, UBC)The experiment ran parasitically in April on M20B to gain experience with the problems that could arise and to measure background rates. As the M20 channel was modified in the spring shutdown there was a great improvement in the neutron background rates. The results of that run showed that the back­ground rate satisfying the trigger conditions was a factor of two lower than the event rate. This ratio should improve further with the target that was designed to be used with 60 MeV/c muons. Beam tuning of the new M20A showed that a usable flux of negative muons is available at 60 MeV/c. It should be possible to stop most of the muons in the gas.The target has been built and is currently undergoing mechanical tests. A few days have been scheduled for early in 1984 to do on-line tests, mainly to establish that thegas purity is sufficient for observation of the fusion neutrons. If that test is success ful the time remaining to complete this experiment will be requested in spring 1984.The experimental group will be joined by some staff members from the Idaho Falls National Engineering Laboratory who have expressed an interest in collaborating on this experiment.Experiment 247Precise measurem ent o f muon decay asymm etry param eter 5 (J. Carr, Berkeley)Our proposal to extend the present precision in the measurement of this basic y-decay parameter to 0.004 was accepted in mid-1983. The experiment is an extension of the techniques we have developed for Expt. 185 and will also be run in January of 1984. The preparations have progressed smoothly and we are looking forward to a productive data collection period.16NUCLEAR PHYSICS AND CHEMISTRYExperim ent 117Fragments (R. Green, Simon Fraser)Reduction and analysis of the data taken for Expt. 117 is proceeding. The vast majority of the allowed kinematic range for the He isotopes has been surveyed. Figure 14 shows an invariant cross section plot for 4He pro­duced from 300 MeV protons on Ag. Two devi­ations from the behaviour observed at lower fragment energies are evident. First, the nearly linear relationships between |3r and 6S [see Green and Korteling, Phys. Rev. C 18, 311 (1978) and TRI-PP-83-116] observed at lower fragment energies and for all fragments seems to break down at higher energies. Secondly, the circular contours, indicative of isotopic emission from single moving sources, also no longer fit at higher frag­ment energies. Therefore the analysis used for lower momentum fragments cannot be trivi­ally extended to the very high fragment ener­gy regions. Various interpretations of these findings are being considered.Experim ent 131A study o f (p,y) reactions on 3H a n d 6Li a tintermediate energies (J. Cameron, Alberta)The studies of radiative proton capture on isotopes of hydrogen have now been completed. Final data for radiative capture on deuterium at five energies have been obtained and a paper has been submitted describing the work. The cross sections at all energies are in excellent agreement with the most recent data for the reverse reaction; thus in spite of substantial remaining disaccord with older data sets the most recent results from TRIUMF and MIT/Bates show no evidence for time-reversal violation when detailed balance is invoked. The analysing powers at lower energies are in reasonable accord with the microscopic model calculations which explic­itly include meson exchange currents; however, at tp = 500 MeV the model seems, somewhat surprisingly, to be much less successful.Fig. 14. Sets of data points of constant invariant cross section [nanobarns/(MeV/c) (MeV’sr)] in the plane of parallel and perpendicular fragment momentum (divided by fragment mass) for 4He fragments from 300 MeV protons incident on Ag. For each set of points along a radial line from the origin successive points of larger radius are lower in invariant cross section by one decade.The 1 nb points are enclosed by an additional ring. The outer circle is the kinematic limit for these fragments. The inner circu­lar contours are fits for isotropic emission from moving sources to P ^  < 0 points at the 1 , 1 0 - 2 and lO-4 nb level.Fig. 15. Cross section as function of photon angle.17A test of detailed balance can also be made for the four-nucleon system as a result of the new data which we have obtained for the 3H(p,y)ltHe reaction. In this case the data are compared to the photodisintegration data from Bonn. Data for both reactions at Ep = 300 MeV are shown in Fig. 15.In this case we have excellent agreement with the Bonn data, again somewhat surprising as our data for the 3-nucleon systems appear to be systematically about 25% above the Bonn measurements for that system. The solid lines are impulse approximation calculations from Fearing without (top) and with (bottom line) distortion.Fig. 16. The preliminary differential cross section results for the pp*n+d reaction at 425 MeV. 9* is the centre-of-mass angle of the pion. The magnitude of the statistical errors is approximately the size of the data points.Experiments 132 and 192Pion production (P. Walden, TRIUMF/UBC)During the past year analysis of the Expt. 192 analysing power data at 375, 450 and 500 MeV has been completed with the desired statistical accuracy of ±0 . 0 1  achieved, and the results published. Pre­liminary analysis of the Expt. 132 differ­ential cross section data at proton energies of 350, 425 and 475 MeV is also complete. Final values for these cross sections, however, require a detailed Monte Carlo evaluation of the acceptance solid angle of the detection system, work which is currently under way. An example of the results obtained to date, assuming approximate values for the solid angles, is shown in Fig. 16. The exper­imental aim of obtaining values for the dif­ferential cross section to a precision of a few per cent appears likely to be achieved.Experim ent 142Non-evaporative fragm ent em ission (R. Korteling, Simon Fraser)A new scattering chamber was built during the last year by TRIUMF for 4BT1 which will permit the measurement of out-of-plane as well as in-plane correlations between highenergy protons and other fragments. It is basically a 25 cm radius thin-walled Al sphere. Hydrogen isotopes are detected in air outside the sphere with wire chambers coupled to plastic-Nal telescopes while heavier fragments are measured inside the vacuum with Si and Ge detectors.An initial test of the system in November with only the exterior detector systems indicated that more than adequate energy and angular resolution can be obtained for the needs of Expt. 142 but that it will be desir­able to improve the beam quality. Reduction of beam halos will improve the single rates in the detectors and permit faster data collection. The angular resolution is limited by the beam spot and its stability but was less than 20 mr. Multiple scattering of the protons through the 340 mg/cm2 Al sphere is of negligible consequence in the planned close geometry. This geometry, possible with the new chamber, has yielded a twenty-fold improvement in the true-to-random ratio from our earlier measurements and it is now better than 50 to 1.Initial Ag(p,2p)X measurements indicate that although there is an increase at high energies in the summed energy spectrum of the outgoing protons, there is no dominant coher­ent recoil peak as observed in the simpler Be(p,2p)X reaction. Further measurements of both proton-proton and proton-fragment cor­relations await the completion of the experimental set-up. Serious data-taking is expected to begin in May 1984 with both (p,2p) and (p,pa) reactions being studied on a selection of targets.Experiment 164M easurem ent o f the 1/E dependence in 7L i (p ,n )7Bereaction (J. D ’Auria, Simon Fraser)The total production cross section for the 7 Li(p,n)7 Be(g.s. and 0.429 MeV) reaction was measured by observing the 478 keV y-xay following the 10.4±0.1% electron capture branch of 7Be(53.29 d) . Proton beams of energies 190, 250, 301, 349, 400 and 480 MeV were used with irradiations performed in vacuum in the isotope production area (beam line 4A) using Li metal targets. These targets ranged in thicknesses from 7 to 60 mg/cm2 (to explore recoil losses) and were fabricated using either 99.994% enriched 7Li or natural lithium metal. Behind each target was a stack of three thin (~5 mg/cm2 ) Al metal18foils used both to monitor the incident proton flux from 21+Na production and to estimate losses due to recoiling 7 Be from the lithium targets. In addition these were used to obtain cross sections for the production of 7 Be in AI .Irradiated targets and catchers containing the ;Be activity were counted periodically in standard geometry for several months using an ORTEC Ge(Li) detector whose resolution is 1.8 keV FWHM at 1.313 MeV and whose efficien­cy was determined within ±1 0% using standard precision y-ray reference IAEA sources.Table I presents tentative cross sections for the total, angle-integrated production of 7Be from 7Li following an initial analysis of these data.Table IEp (MeV) a (mb)190 2.7 ± 0.2250 2.6 ± 0.3301 1.7 ± 0.1349 1.5 ± 0.3400 1 . 6  ± 0 . 2480 1.1 ± 0.07Experim ent 165Cross section and analysing pow er measurementso f g iant resonances(D. McDaniels, Oregon)The major accomplishment of the past year has been the observation of L=4 strength in the giant resonance region of 2 0 8Pb. This strength has been determined by stripping out a peak at an excitation energy of 12.0±0.3 MeV. The measured angular distribu­tion for this peak shown in Fig. 17 is con­sistent with L=4 excitation depleting 10%±3% of the T=0, L=4 EWSR. We interpret this peak as arising from the excitation of 2 hw, hexa- decapole strength. The location, width and magnitude of this 2 hio, L=4 strength are in excellent agreement with recent calculations [Bortingnon et al., Nucl. Phys. A371, 405 (1981); Serr et al., Nucl. Phys., A393, 109 (1983] in 2 0 8Pb.In addition to the above, the entire giant resonance region in 288Pb has been studied using inelastic scattering of 200 MeV pola­rized and unpolarized protons. Both differ­ential cross section o(0) and analysing power Ay(9) measurements were made. The isoscalarquadrupole resonance at 10.6±0.5 MeV, the isovector dipole resonance at 13.6±0.5 MeV and the isoscalar monopole resonance at 14.1±0.5 MeV were clearly observed. Data for a peak at 20.9±1.0 MeV are found to be consistent with an isoscalar giant octupole resonance. This conclusion is based on a comparison of the o(9) and Ay(9) data with distorted wave Born approximation (DWBA) predictions as shown in Fig. 18.All of our 288Pb spectra show visible peaks from the excitation of several giant resonances. The continuum underlying the resonances exhibits a broad peaked structure which we attribute to quasifree scattering. The centroid of this broad structure shifts monotonically to higher excitation energy as the scattering angle is increased. The inelastic proton spectra for other nuclei are similar in appearance; the broad structure shows the same kinematical shift as the scattering angle is increased.Fig. 17. Experimental angular distribution for the 12.0 MeV peak and the GQR peak (for­ward angles only) compared with L=4, 3 and 2 DWBA calculations which are denoted by the solid, long-dash and short-dash curves, res­pectively. The EWSR depletions shown were obtained by normalizing the L=2 calculation to the GQR cross section.19"0  4 6 12 16 20A *"10 5 10 15 20 25 306l (deg)Fig. 18. Angular distribution for the giant resonance peak located at 20.9 MeV of excita­tion. The solid curve is the prediction of the collective DWBA theory for an L=3 transi­tion. The insert shows our measured Ay(9) along with a DWBA calculation for a multi­polarity of L=3.56> 48 0>E  40e> 32 a:UJzUJoh-<(_>X— i----- 1------1 rCONTINUUM PEAK8 12 16 20 8 l (DEG)24Fig. 19. Plot of the excitation energy of the quasifree structure as a function of scattering angle for 88Ni, 98 Zr and 208Pb targets. The ordinate on the right refers to the 80Ni data. The smooth curves were calcu­lated assuming NN kinematics and subtracting out a constant energy shift as indicated.The kinematical shifting of the quasifree peak is shown in detail in Fig. 19 for all three targets. Each point was obtained by determining the excitation energy corresponding to the maximum for the continuum in the inelastic proton spectra measured at each scattering angle. For each target the curves were calculated utilizing free NN kinematics. To the difference between the incident proton energy and the scattered energy at each angle (for the NN case) an additional amount of energy was added, assumed to represent some type of constant shift dependent only upon mass number. From Fig. 19 it is seen that the kinematic plots are best fit by modifying the free NN kinematics to include binding energy shifts of 9 MeV for 2 0 8Pb, 15 MeV for 90Zr and 16 MeV for 60Ni. The large uncertainties in the individual centroid determinations render these energy shifts uncertain by at least ±4 MeV.There are several possible explanations for the observed shift of the quasifree peak from free NN kinematics. First there is a kinematic factor which can be thought of as arising from the consideration of free NN scattering within a well depth V . it can be shown [Wolff, Phys. Rev. 87, 434 (1952); Cladis et al., Phys. Rev. 87_, 425 (1952)] that this gives rise to an angle- dependent shift with a maximum magnitude ofonly 4 MeV at 20°. More likely, the observed shifts are due to binding energy effects [Wall et al., Phys. Rev. 150, 811 (1966); Peele et al., Phys. Rev. 167, 981 (1968)] or to higher-order particle-hole configurations [Bertsch et al., Phys. Rev. 26_, 1323 (1982)]. The identification of the observed broad structure in the continuum as being due to a quasifree process is further strengthened by our measurement of analysing powers for this region of excitation. The Ay(0) data for the quasifree peak follow the same trend exhibited by free NN scattering.Experim ent 166Neutron-nuclear structure with pions  (R. Johnson, UBC/TRIUMF)An experiment measuring tt* scattering from ISO and 28Mg was completed this summer. The data were taken with the QQD spectrometer on the M13 channel. The combined channel-spec- trometer resolution at the time was =1.1 MeV, which was sufficient to clearly separate the first 2+ state in both nuclei.The data can be compared with DWBA calcula­tions which allow for separate deformations of the neturon and proton nuclear densities. These deformations can be varied in order to fit the data. Figure 20 shows the measured differential cross sections for it -  inelastic206  cmFig. 20. it* scattering from 26Mg*(21+ ).scattering to the 2j+ state of 2 6Mg, along with some of the calculations. The solid curves use the best fit values of the defor­mations, from which we can extract the ratio of neutron to proton matrix elements, Mn/Mp = 0.83±0.06, for this state. This is in agree­ment with the values obtained from (p,p'), (a,a'), and other experiments. The short (long) dashed curves represent the calcula­tions with the neutron (proton) deformations varied by 30% from their best fit values.This shows both the sensitivity and the selectivity of the pion as a probe of nuclear structure.Experiments 173, 196 and 204Broad pion ic X-rays(A. Olin, Victoria/TRIUMF)The broadest pionic X-ray lines observed so far have had anomalously narrow widths and at­tempts to describe this phenomenon within the framework of the optical model have not been successful. This experiment aims at remea­suring some of these lines (1 8 ,180, 2 2Ne,23Na 2p-ls and 209Bi 4f-3d) and extending the range of these measurements to other nuclei (2LfMg, 27AA 2p-ls and 208Pb 4f-3d). These lines are very weak as well as broadened, so a segmented BGO Compton suppression spectrom­eter [Olin et al., TRI-PP-83-112] was devel­oped to reduce the background. Data-taking is now completed except for 2 2Ne. The X-rays from Mg, AZ and Pb were clearly observed for the first time. So far, the analysis effort has been concentrated on the Pb and Na data.The fit to the 208Pb 4f-3d X-ray is shown in Fig. 21. A preliminary value of the strong interaction shift of 23.2 (2.5) keV and width of 40 (10) keV has been obtained. These values are approximately a factor 2 smaller than predicted by theory. For the 5g-4f transition the shift is 1.6 (0.1) keV and the width 1.20 (0.1) keV, in reasonable agreement with theory. A 3d width of 40 keV is required to obtain the predicted ratio of the 5g-4f and 4f-3d intensities. Similar results have been obtained for 2 0 9Bi, where, however, the systematic uncertainty is larger because of the more complex background structure.Preliminary values for the shift and width in 23Na are 51.7 ± 0.8 keV and 17.4 ± 2.5 keV. While the statistics are somewhat worse than our previous result, the peak to background has been improved by a factor of 4, and the Compton edge that lies under the peak was greatly suppressed, allowing a better estima­tion of the systematic uncertainties. The fit obtained in the previous measurement did give an acceptable fit to the same region of the new data, but significantly underesti­mated the backgrounds in a wider fit region. The present results are consistent with optical model predictions.Experim ent 175Inclusive one-pion production in proton- nucleus collisions (W. Sondheim, Los Alamos)Our group has been involved in an extensive program to acquire a comprehensive set of data on the inclusive pion production fromENERGY (keV)Fig. 21. Prompt photon spectrum in coinci­dence with ir~ stopping in 2 0 8Pb. The fit (solid line) includes the broad it 4-3 X-ray together with a number of narrower X-rays and gammas from it- absorption.21proton-nucleus collisions, and to use them to refine the data base used in intranuclear cascade calculations. The long-range goal of the program is to contribute, through a detailed knowledge of elementary processes, to a better understanding of high energy heavy ion-nucleus collisions.To this effect we have constructed and tested a novel spectrometer, and developed an appropriate hardware-software data acquisi­tion system for it. The spectrometer con­sists of a dipole magnet (Calliope), 81 cm in diameter, with a 7.5 cm pole gap and a uniform field of up to 2.1 T. The target is located at the centre of the magnet, whose polefaces are surrounded by six detector assemblies. Each detector consists of two planes of x,y position-sensitive gas counters placed 10 cm apart, one Pilot-F A-E scintil­lator, and one Cherenkov counter built of a 0.16 cm layer of Pilot 425 laminated on a2.5 cm lucite slab (Fig. 22). The number of beam particles on target is counted by a 0.16 cm scintillation counter. The beam intensity is therefore limited to a few 106 p/s. This results in a produced pion rate well matched to the performance of the data acquisition electronics. This spectrometer can detect and analyse, over a range of scattering angles from 0 to 360°, mesons (and light ions) in the momentum range 0.05 < p <1 GeV/c. The CAMAC-based data acquisition system is centred around a M0DC0MP 7860 com­puter, with a variety of peripherals includ­ing a bulk memory processor with a 1 megaword histogram memory. The system can process a sustained event rate of 1 kHz, a typical event consisting of 25 to 30 16-bit words.The electronics and the computer are housed in a mobile trailer.Fig. 22. Schematic diagram of the Calliope spectrometer system.After debugging this system at LAMPF in 1981 we acquired some data there at 330 MeV in the summer of 1982 prior to moving the entire system to TRIUMF where data were acquired at 330, 400 and 500 MeV incident proton energy in January 1983. These data have been anal­ysed and the necessary software developed and debugged this summer. The analysis is nearly complete and two comprehensive papers, one on the spectrometer system, the other on the p+A tt+X (A(p,ir)X) reactions, are in progress. Some preliminary results are presented below.In Fig. 23 we present our data on the ratio as a function of the incident kinetic energy. In Figs. 24 and 25, we show the integrated pion production cross section for tt+ and it- , respectively. Our data were taken with targets of C and U. The data of Crawford et al. at 585 MeV are from C and Pb targets, while Cochran et al. used C and Th targets at 730 MeV. In Fig. 26 we show a typical angle integrated pion momentum distribution.•  C TARGET  i U  TARGETPROTON ENERGY(MeV)Fig. 23. Cross section ratios for tt+ to tt“ production. The circles are for a C target, the triangles for a U target (Pb at 585 MeV, Th at 730 MeV).•  C TARGET  A U  TARGETFig. 24. Total it+ production cross section.CHERENKOV COUNTER UVT LUCITE 8 PILOT 425MAGNETRETURNYOKE81.28cm DIA.MAGNETPOLE FACEX Y POSITION WIRE CHAMBERSPROTON BEAM PATH22•  C TARGET  a  U TARGETPROTON ENERGY(MeV)Fig. 25. Total tt“ production cross section.The results are in good agreement with the earlier work, giving us confidence in the operation and understanding of the "Calliope" system. They extend the existing data base toward the pion production threshold.Nuclear cascade calculations to compare with the data are in progress.Experim ent 190Radiative polarized neutron capture onprotons (J. Cameron, Alberta)Using the polarized neutron beam and a liquid hydrogen target we have measured the cross section and analysing power for radiative polarized neutron capture on protons at En = 180 and 270 MeV. This initial phase of our investigation was made by detecting photons in the lead glass scintillation counters used for Expt. 131. The recoil deuterons, detected in coincidence, were identified using time of flight. Their direction in the laboratory was determined using multiwire proportional chambers and their energy measured in thick plastic detectors.Our analysing power results at a neutron energy of 270 MeV are shown in Fig. 27. The solid line is a calculation with no meson exchange currents by Greben and Woloshyn and the dashed curve from Arenhovel including meson exchange and isobar currents. The data clearly favour the latter calculation.We have investigated the possibility of making measurements at En = 500 MeV, parasitically to Expt. 121, with encouraging results. At energies above the pion produc­tion threshold we plan to add gamma position information to further constrain the event type. It is hoped to have the equipment in place to start these measurements by mid- 1984. Data at En = 350 and 425 MeV will beFig. 26. Angle integrated tt+ momentum dis­tribution for 400 MeV protons incident on C.added as soon as neutron beam time can be obtained in prime user mode.Experim ent 195Search fo r 12C + 12C “m olecu lar”  resonances in inelastic scattering o f protons from 24Mg  (R. Abegg, Alberta/TRIUM F)The 1 2C+12C system has exhibited a wealth of resonant phenomena from the Coulomb barrier to considerably higher excitation energies in 21tMg. Recently this system has been studied through electrofission [Sandorfi et al.,Phys. Rev. Lett. 45_, 615 (1980)] and inelastic scattering of 120 MeV alpha particles [Wilczynski et al., Nucl. Phys,A34, 317 (1980)]. The work along with radiative 12C+12C capture has the advantage over heavy ion scattering and reaction studies in that it relates these "molecular" resonances to the 2LfMg ground state. Thus,If well-defined states can be identified in the 1 2C+12C break-up of 24Mg by inelastic scattering and angular distributions obtained, one hopes to understand the structure of these states.Qy  (cm)Fig. 27. Analysing power as a function of photon angle.233o io-no n ^  nnn hnnr- in nn II r I n n-3 0  -20  -10MISSING EN ERGY (MeV)Fig. 28. Spectrum of carbon-carbon events as a function of "missing" energy, i.e. Q-value + energy losses. The small peak at - 8 MeV is due to the 1&0(p,poc)12C reaction from oxygen contamination in the target. Not all of the alphas are eliminated by software carbon- carbon cuts.The TRIUMF MRS was used to detect inelastic- ally scattered protons at 6iab = 15.3°(beam energy was 190 MeV) coming from a 195 pg/cm2 99.9% enriched 2LfMg target. Frag­ments coming from the target were detected in two solid state surface barrier detectors at 20 cm and at angles of 82° and 88.5° to the right and left with respect to the beam direction. Thus the energies of the proton and both fragments are known and the time of flight of both fragments relative to the pro­ton is measured, allowing the identification of the 3 2C+12C break-up of 2 4Mg. After the particles have been identified their energies are summed as presented in Fig. 28. The amount by which this sum is less than the beam energy, the "missing" energy, is explained by the Q-value of the reaction (13.9 MeV for both carbons in the ground state) and carbon ion energy losses in the largest (~1 MeV). The 1 2C+12C break-up is then seen clearly at -15 MeV. The peak at -19.5 MeV is attributed to the break-up channel 1 2C(g.s.)+12C (4.44 MeV).The excitation energy spectrum in 21tMg is shown in Fig. 29 for the 1 2C+12C break-up.The events are localized around Ex «22 MeV, somewhat lower than the centroid of events seen in alpha inelastic scattering but on a strong though narrow resonance observed in radiative capture. There is little evi­dence for structure above 25 MeV excitation energy.In summary, we have observed "molecular" resonances In Inelastic proton scattering from 21tMg, in a region consistent with previ­ous inelastic scattering work. The yield isFig. 29. Spectrum of carbon-carbon ground state events as a function of excitation energy in 21+Mg.too small under present experimental condi­tions to obtain complete angular distribu­tions both as a function of carbon and proton angle.Experim ent 199Isospin dependence o f pion absorption onnucleon pa irs a t T„ =  65 M eV(K. Aniol, UBC)In September we ran tt~ at 65 and 85 MeV on Mil using the new cryogenic 3He target. This new target has cylindrical symmetry and allows for nearly 2ir viewing at one time. Because of this symmetry and the substan­tially thinner vessel walls we were able to obtain proton-proton and proton-neutron coincidence spectra at off-conjugate angle combinations. During any particular run, while one telescope was at the deuteron conjugate angle with respect to the neutron bars, two other telescopes at 30° and 60° away from the conjugate angle were also registering coincidences with the neutron bars.Our first task was to measure the 65 MeV data again. We repeated all of the ir+ data and remeasured 3 angles with ir-. In Fig. 30 we present our ir+ differential cross section from 1982 taken with the NASA target (•) and preliminary results from the September run with the new targets (X). We used both the ir“+3He->-n+d and the 65 MeV tt+ elastic scat­tering data to establish the target thick­ness. This is the same procedure we followed with the 1982 data. There Is an absolute uncertainty of ±15% in the p+d>t-hr cross sections that we used. In addition we performed a range curve measurement with the target and a dummy target. This gave a target thickness about 25% larger than that24-Qa.c?■oNbTO= 65 MeV4000300020001000#-1982X-PRELIMINARYRESULTS FROM 1983An = 67 + 4®cm <DEG>Fig. 30. Differential cross sections for pion absorption on nucleon pairs in 3He. The Legendre polynomial coefficients are in yb/sr. Tp (MeV)Fig. 31. Off-conjugate coincidence spectra at 65 MeV for tt+ (a) and it- (b). The angles in the diagrams correspond to (9tel> 0bars)•determined from the it 3He+n+d and ir+ elastic scattering method. It may be that the range measurement sampled a different portion of the target than did the beam during data runs. We have not yet found the cause for the difference. However, from Fig. 30 we observe that we obtain the same differ­ential cross sections for the two runs if we use the same normalization technique (i.e. the n*d coincidence and ir+ elastic scat­tering). The results of the 1982 measurement are therefore being submitted for publica­tion.As an example of what the new target allows us to do we show in Fig. 31 some off-conju­gate spectra. For these angle pairs the two-body process is strongly suppressed and we can see evidence for non-two-body (3-body) absorption. In the case of it-, Fig. 31(b), for example, it is sufficient to go 30° off conjugate to eliminate the two-body part of the spectrum. It will be seen that the shape of the energy spectrum in Fig. 31(b) is rea­sonably reproduced by the phase space factor. In the spirit of our previous analysis we assume that the three-body absorption matrix element is a constant and that the variation of the three-body absorption cross section as a function of angles and particle (reaction product) energy is given by the phase space factor. In the case of ir” we get at 65 MeV,dadflj dfl2dE1= 0.13±0.03p 2p 2 1 2  _ y b(E1*E2*E3) I sr2 MeVIn the case of tt+ we see the tail of the two- body process for some combinations of angles which are 30° off conjugate, for example,Fig. 31(a). From those combinations where the shape of the energy spectrum clearly shows the absence of the two-body absorption process we get at 65 MeV for tt+dadfij dfi2dE30.13±0.03yb P 2P 2 *1 2sr2MeVJ (E1*E2«E3)With this phase space factor we are then able to go to the conjugate spectrum and deduce how much of the cross section is attributable to the three-body process. This procedure treats the two-body and three-body processes incoherently, when in fact they add coher­ently. When calculations are published for the it- absorption we shall, perhaps, be in a better position to judge the adequacy of our procedure. The task of a good theory is then to explain the shapes of the it- spectra rather than just the ratios of ir+ to ir” total absorption cross sections. In Fig. 32 we show a it” proton energy spectrum for the (1 2 0°, -45°) conjugate condition (9proton = 120°). The spectrum has been corrected for proton reaction losses and for neutron detection efficiency. Superimposed on this spectrum is25250Ox200=>ooFig. 32. Proton energy spectrum for coinci­dent events in ir“+ 3He (p*n)+n for 8proton =120°, eneutron -45° at T™ = 65 MeV. Thephase space is deduced from the off-conjugate angles and the it+ shape comes from 65 MeV ir+ on 3He at the same angles.the deduced three-body portion and the shape of the ir+ spectrum taken at the same angle (120°).We have started the analysis of the 83 MeV data and already we can make some interesting observations on the gross features of the data. In Fig. 33 we compare the 65 and 85 MeV data for the (120°-45°) conjugate position.In Fig. 33(a) for tt+ bombardment we see that the yield of event per pion is about 30% bigger at 85 MeV as compared to 65 MeV. For the ir++d reaction the increase at 1 2 0° is about 20%. For ir~ the spectra look very simi­lar but we need to analyse the rest of the data to make a definitive comparison.t=toh-o<_>Tp (MeV)Fig. 33. Comparison of the -ir“+3He (n)*P+P proton spectra at 1 2 0° 9iab f°r the conjugate condition. (a) ir+ data for 65 and 85 MeV with reaction loss corrections, (b) tt“ data at 65 MeV; no reaction loss or neutron effi­ciency corrections made. (c) ir~ data at 85 MeV; no reaction loss or neutron efficien­cy corrections made.We will be able to extract differential cross sections for the two-body process and the magnitude of the three-body absorption at 85 MeV. At 65 MeV we find that the three- body piece in the conjugate spectrum for tt+ contributes 4% to 10% (angle dependent) of the total yield. This is of interest because at 165 MeV Lee and Ohta [Phys. Rev. Lett. 47, 1079 (1983)] calculate a contribution on the order of 0.2% in the conjugate spectrum. It will also be interesting to trace the influ­ence of the three-body absorption as a function of bombarding energy. It apparently is becoming bigger relative to the two-body piece as the energy decreases. An energy dependence of this reaction will provide understanding of pion absorption on a T=1 nuclear pair as well as yield insight into the three-body absorption.Experiment 205Tensor analysing pow er in pion deuterium  scattering (Y. Shin, Saskatchewan)A preliminary run in beam line IB, examining proton deuterium scattering, took place dur­ing the summer. Protons at 237 MeV were used on a CD2 target to examine the performance of the triplet in focusing the deuterons onto the 3He polarimeter cell. Subsequently the effects of tuning the 3 quadrupole magnets, effects of absorbers and background (using a CH2 target) were examined.In October/November a three-week run in Mil using 140 MeV pions on a 2 mm D20 (or ^ 0 )26target enabled the Initial setting up of the complete apparatus. The scattered pions were detected in MINA. During the final week the liquid deuterium target was installed. An on-line examination of the ability to separate clean rrd events from the surrounding inelastic distributions was made and subse­quently data were taken at 5 deuteron arm angles - 20°, 25°, 30°, 35° and 40°. Paral­lel off-line analysis is now under way at TRIUMF and the University of Saskatchewan.Experiment 206A study o f(p ,n ) and re lated reactions(J. D ’Auria, Simon Fraser)The main objective of this study is to measure and compare inclusive neutron and proton emission above the evaporation region (>30 MeV) from proton-induced reactions on a series of targets (Be, Ag, Ta) as a function of angle (20-150°) and incident proton energy (190, 500 MeV). Aside from providing information on reactions for which data do not exist, these results will also be useful in assessing the applicability of the several models which have been advanced to account for the angular and energy dependence of energetic nucleon and fragment emission observed in intermediate energy reactions, including light ion induced reactions.This year beam time was used both to build up and test the final configuration of the experiment, as well as to initiate the data- taking phase. During these tests one extra­ordinary problem was encountered. While attempting to ascertain the optimum detector shielding which consisted of iron (~2xl0 3 kg) and lead blocks, it was observed that the photomultiplier tubes on which the time-of- flight neutron detectors (12.7 cm x 12.7 cm long BC501 liquid scintillators) were mounted exhibited large gain shifts both in energy and in the transit time of the photoelectron through the tube.These shifts were observed as the detectors were subjected to differing shielding configurations or as the entire configuration was moved from one location (e.g. scattering angle) to another. They were apparently due to axial components of the ambient fringe field of the main cyclotron magnet and not easily eliminated with mu-metal detector shields arranged for perpendicular magnetic fields. Finally a combination of thicker mu- metal shielding and an empirically determined iron shielding configuration was found whichallowed movement of the neutron detectors with tolerable time ( < 1 0 0 ps) and energy shifts. The use of a LED was incorporated appropriately to monitor such shifts during the experiment.Further a more satisfactory approach to deriving a time-of-flight reference signal was developed utilizing an rf phase correcting module supplied by TRIUMF. The rf signal which is used as the reference signal is corrected by comparing it with a signal that is derived from the proton beam striking the target.Approximately 10 shifts were used to collect (p,n) and (p,p') data at 190 MeV from Be, Ag and Ta targets and at several angles. These data are presently under analysis.Experiment 208 Proton-proton bremsstrahlung  (P. Kitching, Alberta/TRIUMF)Test runs in the IB area in November have shown that the count rate from beam halo striking the walls of the 1 m long hydrogen target will be ~5-10% of the count rate from the hydrogen itself. Background for the beam dump was also investigated.Another test run with major elements of the apparatus in place (certainly the vacuum chamber, plastic scintillators and front drift chamber) is planned for February 1984. This run will establish the conditions for the major data-taking run in July 1984.Progress in theoretical calculations and construction of apparatus is given in more detail below.Theoretical progressWork has continued on the program of theore­tical calculations being carried out to understand the ppy process and to provide reliable predictions for comparison with the data to be obtained. A great deal of prog­ress has been made and the calculations, which are being performed in large part by a student, R. Workman, are just beginning to show some interesting results. The main aim is to develop a modern potential model cal­culation which uses one of the newer poten­tials such as the Paris or the Bonn potential and a number of refinements which have been shown to be important in individual investi­gations but which have never been combined27into one calculation. Our approach is to solve the momentum space Lippmann-Schwinger equation to obtain the on-shell NN amplitudes and the half-off-shell extension functions for a given potential. These off-shell amplitudes are combined with vertex and prop­agator factors and a gauge term to get the full ppy amplitude. We have so far included relativistic spin corrections which are known to be important at these energies, Coulomb effects, and one-pion exchange in higher partial waves. All kinematics are done rel- ativistically, and frame transformations of the NN amplitudes, which are not normally included, have been incorporated. The calcu­lation is done in the centre of mass so as to minimize gauge corrections but can also be done in the lab. Both cross section and analysing powers are calculated and coplanar or non-coplanar geometries can be used.At present the calculation is working for the usual Reid soft core (RSC) potential, which is valuable for test purposes, and for a RSC potential extended to higher J, in both cases supplemented by one-pion exchange in the higher partial waves. The code for the Paris potential is almost finished. We have also had preliminary discussions with R. Machleidt, who is on sabbatical at TRIUMF, as to how the Bonn potential can be incor­porated. This potential would have the advantage of giving a specific model of the off-shell behaviour as opposed to the Paris potential for which only a phenomenological extension off shell is possible.Preliminary results are rather interesting and indicate a lot of sensitivity in both cross section and analysing power to the various ingredients. Relativistic spin cor­rections are very important at these energies as is the inclusion of one-pion exchange for the higher partial waves. Coulomb correc­tions are not too important, however, and at least for the cases tried so far there are still the large differences between the predictions of potential models and those of the model-independent soft photon calcula­tions which in part motivated this experiment.Several further refinements are intended once the program is complete for the various potentials. Double scattering terms are at present incorporated only to 0 (k°) via the gauge term, and gauge terms coming from the momentum-dependent pieces of the potential have not yet been included. Eventually we also want to explore more carefully off-shellsensitivity by using phase-equivalent trans­formations.Progress in experimental apparatus contributionHydrogen target. This now consists of a 5 mm thick liquid cell in a 1 m long x 50 mm diameter stainless steel tube containing cold hydrogen gas. The end windows welded to the tube are 25 ym of stainless steel, and are far enough away from the liquid hydrogen that the detectors may be shielded from viewing them directly. Low energy protons exit on one side through a 25 ym kapton window glued to the inside of the stainless steel tube. This target assembly is now under construc­tion in Edmonton and the hydrogen liquefier will be supplied by TRIUMF.Vacuum chamber. Design has been esentlally completed and construction is under way in Edmonton. The chamber will have kapton windows A, B and C (Fig. 34). Window A allows the high energy protons to exit to the magnetic spectrometer. Window B allows elas­tically scattering protons, which pass through the low energy proton detectors, to exit from the chamber, pass through the absorber, and be vetoed by the 5 plastic scintillator veto counters behind the absorber. Window C will allow protons re­coiling from protons elastically scattered into the magnetic spectrometer to escape from the chamber. They can then be vetoed if necessary (though this will require some mod­ification of the end window shielding on thatside) to reduce to the random coincidence rate. The chamber will be completed and installed for the February 1984 test run.The "C" magnet. The design of this magnet is complete and contracts for the steel andcoils are at the point of being signed. Themagnet will be assembled and tested at TRIUMF and field maps measured, hopefully by February 1984.Vertical drift chambers. The chambers are basically of the same design as those used for the upgrade of the TRIUMF medium resolu­tion spectrometer. They are now under con­struction at the TRIUMF wire chamber assembly facility in Edmonton. The first chamber will be completed for the February run and we expect to have the remainder before the following polarized beam run in July.Cerenkov counters. Eight lead glass Cerenkov counters from the np+dy and pd-^Hey28CHERENKOVCOUNTERSPOLARISED PROTON BEAMH2 LIQUID (5mm)PP7PROTONS DRIFT CHAMBERS\  XELASTICALLY SCATTERED PROTONSFig. 34. Experimental apparatus for Expt. 208.experimenters already exist at TRIUMF and can be used for this experiment. Eight new counters, with twice the solid angle accept­ance, are presently under construction in Edmonton.Target chamber support. The structure has been designed and is being constructed at TRIUMF. It will be supported by the concrete shielding blocks in the BL1B experimental area and were installed in dealing with large nuclear excitations, correlated pairs of nucleons play an impor­tant role. At large energy transfer the capture of a p must occur on a correlated pair of nucleons, with kinematics similar to it capture. This work extends the energy range of spectra to 100 MeV for neutrons from y- capture in medium to heavy nuclei by using a detector system with good energy resolution from a time-of-flight technique.During the current year data from the latest run with 185Ho target were analysed and the results were accepted for publication in Phys. Lett. A, and new measurements with 27AH and 28 Si were initiated. The detector system consisted of an in-beam y stop telescope, large Ge(Li) detectors and high purity Ge planar detectors for singles y-ray, Nal crystals and 12 large scintillators for coin­cidence measurements. Each counter was accompanied by dE/dx detector for charged particles. A 55 MeV/c y~ beam in M13 channel was used for 185Ho target and 75 MeV/c beam in the M20 for 27AH and 28 Si targets.The y-ray singles measurement carried out with Ge(Li) detectors identified various nuclear de-excitation y-rays from 185 Ho tar­get including the 6+ -*• 4+ transitions in 16L+ , 1 62d an(j 4+ 2+ transitions in164,162,16Opyt Transitions in '■8 0Dy, cor­responding to five neutron emission, were clearly seen at 197 and 297 keV with inten­sities far greater than expected. Transi­tions corresponding to proton emission could not be identified because the decay schemes for l8 2 »l6i+Tb are not known. No signifi­cant intensity of ^88Dy gamma-rays was observed.Plastic scintillation counters. The low energy proton scintillators which are mounted inside the vacuum chamber are being con­structed in Edmonton, as are the Cerenkov veto counters. The remaining plastic scintillators will be made at TRIUMF. All counters should be ready by February 1984.Experim ent 211The neutron y-ray correlations in the p ~  and  n r  capture in medium heavy nuclei (Y.K. Lee, Johns Hopkins)The measurements of spectra in the range beyond 50 MeV for both protons and neutrons confirmed the existence of energetic parti­cles which cannot be explained within the impulse approximation. As is often the caseThe neutron spectra from 188Ho are shown in Fig. 35 which contains four spectra differing in the final nuclear states (as defined by the Nal pulse height cuts). The change in intensity is due to the differing intensities of the required coincident y-ray. The spectra obtained for the 2.5 MeV equivalent electron baseline is shown together with the 10 MeVee case. The errors are statistical.The spectra from the two baseline cuts agree for each Nal pulse height cut, indicating that most of the background was removed. All the spectra (corresponding to the 2.5 MeVee baseline data) were fitted to an exponential exp(-E/E0 ) between 13 and 50 MeV. These fits are shown in Fig. 35. In Fig. 35(a) which corresponds to cut including all the Nal pulse heights, the fit to the data gives29an exponential constant of E0 = 10.5±1 MeV. Above 50 MeV the spectra do not follow the simple exponential. There are more neutrons in the 50-100 MeV region than predicted by the fitted curve. Above 40 MeV there are0.019±0.004 neutrons per p-stop, correspond­ing to 1 .2% production of neutrons above 40 MeV.The most detailed calculation within the impulse approximation [Lifshitz et al., Phys.Neutron Energy (MeV)Fig. 35. Neutron spectra from 100 to 200 MeV coincident with different final nuclear states. Data associated with the 2.5 MeVee neutron counter baseline cut are plotted as crosses, data in the 10 MeVee cut as boxes.A fit to exp(-E/E0) in the energy range from 13 to 50 MeV is plotted for each spectra, (a) is associated with the entire Nal spectrum; (b) is associated with 16l*Dy and therefore has a neutron multiplicity of one; (c) is associated with neutron multi­plicities of 1 through 5; (d) is associated with the continuum between 0.3 and 1.3 MeV of y-ray energy.Rev. C 22_, 2135 (1980)] fails to account for this strength above 50 MeV even with the use of phenomenological nucleon momentum distri­bution which may overestimate the contribu­tion of the high momentum tail. The results of the current experiment can be taken as evidence favouring non-impulse approximation based models [Bernabfeu et al., Phys. Lett.69B, 161 (1977)].During the November run with 2 7 AI and 2®Si targets we were able to employ 5'x5' Nal crystal with a vastly increased counting efficiency. This was possible because the final product nuclides of these targets involved only y-rays with energy around 1 MeV and much simpler y-ray transition schemes near 1 MeV. Furthermore, measurement of charged particle spectra was significantly improved compared to 165Ho target. These data are now undergoing analysis.Experiment 212In search o f a tredecabaryon resonance(K.P. Jackson, SFU/TRIUMF)The acquisition of data has begun in the search for possible resonance structure in the compound nucleus ^ N  at excitation energies in the range from 200 to 500 MeV.The differential cross sections for proton elastic and inelastic scattering from 12C are being measured at very large values of momen­tum transfer (q > 1 GeV/c) as the incident proton energy is varied in 1 MeV steps throughout the TRIUMF energy range. This experiment puts exceptional demands on both the operation of the cyclotron and the per­formance of the medium resolution spectro­meter (MRS) in the efficient measurement of sub-nanobarn cross sections.Brief runs in May and June were used to test the performance of a new low-mass wire chamber installed at the entrance to the MRS quadrupole and to explore the procedures by which the energy of the incident beam could be expeditiously changed In small steps. Measurements of the angular distributions at Ep = 300 MeV were carried out as part of Expt. 221 and are shown in Figs. 36 and 37 (p. 33).Following the completion of these prepara­tions the detailed measurements of the exci­tation functions were initiated in August.The BL4 stripper was moved to step the energy of the beam in 3 MeV intervals and at each of these energies the beam line elements were30retuned as required. The finer increments (AE = ±1 MeV) were achieved using the approp­riate cyclotron harmonic coils. By these means the energy of the incident proton beam was varied from 185 to 210 MeV and from 299 to 337 MeV in 1 MeV intervals. The angle of the MRS was adjusted to measure the yield of protons populating the ground and first excited states of 12C for fixed values of the momentum transfer (0.99 GeV/c for the lower energy interval, 1.295 GeV/c in the measure­ments at the higher incident energies). The gap in the excitation functions above 210 MeV resulted from difficulties tuning BL4B while delivering high currents to BL1A. The over­heads involved in each energy change decreased significantly during the experi­ment but remained somewhat excessive.Further measurements await the final completion of the MRS upgrade.Experim ent 213Absorption a t rest o f  n~ in light nuclei(C. Cernigoi, Trieste)In September the experiment concerning the ir” absorption at rest in 4He, 9Be, 6Li, 160 and 27 Al was completed.The absorption in 9He has been investigated in a kinematically complete experiment in which the correlated pairs of the emitted protons, neutrons, and deuterons were detected. Relative emission branching ratios, energy spectra and angular distribu­tions were measured. The energy resolution and counting statistics allowed valuable data to be obtained in connection with the problem of the possible a-clustering in nuclei as well as with the problem of the ir-absorption mechanism. A liquid helium cryostat was used as the 4He target. This had no liquid reservoir at temperatures intermediate between room temperature and that of liquid helium. The gas consumption was only 300 l/h. A target thickness of about 0.2 g/cm2 was realized in order to minimize the energy losses of the outgoing charged particles.The measurements were performed on the M13 p —nr channel.The analysis of the experimental data is now in progress at the Institute of Physics of the University of Trieste and at the National Laboratory of Legnaro.For the 6Li, 9Be, 160 and 27Al only the inclusive spectra of neutrons and protonswere measured. Measurements of neutron spectra for 160 and 27Al were performed on the Mil channel late in 1982. Because of the biological Importance of 160 [Jackson and Brenner, Prog. Part. & Nucl. Phys. 5., ed.D. Wilkinson (Pergamon, Oxford, 1981) p. 143] the measurements were repeated this year on the M13 channel.These inclusive spectra, as well as that for 12C [Cernigoi et al., Report INFN/AE-82/13], are providing very important information on the single-nucleon emission process. As far as the single-neutron emission process is concerned, rates of 1.7 x 10“ 2 per stopped pion for 12C and of (2-3) x 10- 3 per stopped pion for 1 6 0 and 27Al were obtained.It is worth while to note that the inclusive neutron and proton spectra, apart from geometrical factors, have been normalized to the same incident pion beam. This is a peculiar feature of this experiment with respect to other experiments in this field, and it was achieved by using a detector called a range telescope [Cernigoi et al., Nucl. Instrum. Methods 211, 129 (1983)] specifically designed to detect, discriminate and measure the kinetic energy of protons, deuterons, tritons and neutrons at the same time.For the above-mentioned nuclei target thicknesses of 0 .2-0 .4 g/cm2 , depending on the nucleus under investigation, were used.In spite of the thinness of targets the pion stopping rate was (2-4) x 105 pions/s, with target-in to target-out ratios of the order of 2. This has to be considered a particular figure of merit of the M13 channel, notwith­standing a displacement of the focus of the incoming beam from the standard value of 80 cm to 275 cm; this was necessary because of the floor position of the counters.Experiment 218Pion production from  ,2C and 10B with po larized protons o f 350 M eV  (G. Lolos, UBC)During the past years the (|,ir^  group has completed measurements of (p,ir- ) exclusive reactions on selected light nuclei, e.g. 1 2C, 10B and 9Be in the 200 to 250 MeV incident proton range. Recent theoretical progress in microscopic two-nucleon model calculations have pinpointed the importance of the A reso­nance in such a model. In order to test these models at an energy range where the contribu-31tion of the A is at its maximum, Expt. 218 obtained data on the 1 2C(p,ir+)l3Cg.s. >13Cg 50 MeV reaction. At 350 MeV incident proton energy it is expected that the s-wave and the non-resonant p-wave pion production contribution to the da/dft will be small compared to resonant terms contribution, thus simplifying the theoretical interpretation of the results.We have obtained data in the forward angles at present where comparison with theory is more meaningful. The data are under analysis at this time. We plan to complete Expt. 218 with large-angle measurements in the summer of 1984 and thus provide a complete da/dn(6 ) distribution at 350 MeV as well as a total cross-section measurement of the (p,ir+) reaction for transitions leading to sp states (13r ) and stretched neutron 2p-lh states13 *( C9.50 MeV).Experim ent 221Search fo r evidence o f a delta-nucleus  intermediate state in proton elastic scattering (H. Meyer, IUCF)The applicability of the optical model in describing medium energy proton-nucleus elastic scattering has been amply demon­strated. Before data at angles larger than say 0 = 80° were available, the standard Woods-Saxon form for the radial dependence of the potentials was found to be adequate. The inclusion of large-angle (high-momentum transfer) data near 200 MeV bombarding energy made it necessary to modify the radial poten­tial shapes. The most striking change required by the new data is a considerable reduction of the attractive real part of the central potential in the nuclear interior, a feature also predicted by microscopic potentials.While adjustments in the shape of the optical potential have brought significant improve­ment in the agreement with the data, large discrepancies remain, especially at very large angles where generally the calculation falls off much faster than the measurements. It may be argued that at very large angles the direct potential scattering cross section is so small ( < 1 nb/sr) that other small effects contribute or even dominate the measured value. We postulated the formation of an intermediate state in proton elastic scattering whereby the projectile picks up a tt meson from the nuclear medium and propa­gates as a A before decaying back to theelastic channel. The contribution of such a process has been calculated in a coupled channels approach. Fits to elastic scat­tering data from IUCF (p+1 2C) at 122, 160 and 200 MeV worked rather well. The energy dependence of the potential parameters was then used to predict cross sections and analysing powers at higher energies (250- 350 MeV), where the A contributions should be stronger. These predicted cross sections are 1 to 2 orders of magnitude larger than the ones calculated with the "standard" model when comparing at angles 6iab * 1 0 0°.The cross sections in the angular range16°<9lab < 120° at Tp = 300 MeV ^see Fig. 36), which were measured with the MRS spectrometer, are in closer agreement with a standard optical model prediction; thus, the postulated mechanism to explain the observed discrepancies at lower energies does not seem to be confirmed by our new data. Further theoretical analysis is still in progress.In a 11-shift run cross sections for elastic proton scattering from the 12C ground and 1st excited states (2+ , 4.444 MeV) as low as 100 pb/sr were measured (see Figs. 36 and 37). Initial feasibility studies to measure such low cross sections with MRS were undertaken in collaboration with the TREDEC group (Expt. 212). It is planned to continue the measurements in 1984 with polarized beam to take analysing power data at high momentum transfers.Experim ent 223The (p,2p) reaction and momentum distribution  o f the deuteron (W.T.H. van Oers, Manitoba and C.F. Perdrisat, William and Mary)Several investigations of the neutron recoil distribution [Perdrisat et al. (1969), Witten et al. (1975), Felder et al. (1976)] have indicated large and systematic deviations from the impulse approximation (IA). In lowest order the differential cross section for the process is given by:d5a/dfi3 df2ltdp3 = k x (da/dfi)pp x |<(>(q) | 2where dfl3 and dfl^  are the solid angles for the two protons and dp3 is the momentum bite of one of them. In the impulse approxima­tion, neglecting binding energy effects, q is assumed to be equal to p5 , the unobserved recoil momentum (here of the neutron) given by32Fig. 36. Laboratory differential cross sec­tions of 1 2C(p,p) 12C elastic scattering at 300 MeV.Fig. 37. Laboratory differential cross sec­tions 1 2C(p,p')12C (2+, 4.44 MeV) at 300 MeV._ ■> f + ■> VP5 - Pi (P3-Pit) •Whereas these experiments have given results in agreement with the shape of the |<j> |2 cal­culated from typical NN-potentials deuteron wave functions up to p5 ~ 250 MeV/c, even after scattering corrections have been applied [Wallace (1972)], the magnitude of |<|>|2 has been typically 20% too small. Above 250 MeV/c definite deviations are seen, typ­ically in excess of what expected by one order of magnitude. In the similar reaction D(e,e'p)n, recently studied by Bernheim et al. (1982), excellent agreement with the the- retical | <(> | 2 is obtained [Arenhovel (1982)] after extensive calculations to correct for final state interactions, rescattering, pion exchange currents and isobar (delta) excita­tion. The goals of Expt. 223 were defined as: (a) verify the absolute value of thecross sections at small recoils to definitely establish the status of the 2 0% defect found in previous experiments, (b) measure a complete recoil distribution in the complete­ly symmetric configuration with |p3 | = |pjJ and 0 3 = 0  ^ to confirm the large recoil behaviour seen in past experiments, and (c) investigate special geometries corre­sponding to regions of phase space in which virtual and real delta excitation should become dominant (A. Yano Is calculating several of the relevant diagrams).A first run occurred from July 27 to August 3 A new liquid hydrogen-liquid deuterium target built specifically for this experiment by the Technological University Delft was used for the first time at 4BT2. Three Nal detec­tors were used together with the MRS in a double coincidence arrangement. The MRS was in coincidence with one Nal detector at 41.52, 50, 52, 57 and 6 6° symmetrically. The two other Nal detectors were in coincidence at 66-6 6° in permanence. A large fraction of the run was spent measuring the pp cross sec­tion at 506 MeV for 90° c.m. in order to es­tablish the efficiency of the system and the thickness of the target (by comparison with existing and recent precision pp data [Chatelain et al. (1982), Ottewell et al. (1983)]). Additional pp data were also obtained to determine the energy calibration of the 3 Nal detectors in the relevant energy range. The D(p,2p)n data obtained cover in principle all symmetric configurations antic­ipated. A preliminary analysis for the zero recoil cross section from the 41.52°-41.52° data gives encouraging results. We do not yet have cross-section values either for hydrogen or deuterium, as several higher-order correc­tions still need to be considered carefully.The analysis of the present data is now entering its routine phase, and should be largely finished in two months. The data at each angle combination will give us an energy-sharing recoil spectrum; the data at33each angle for the minimum recoil condition will give us a recoil spectrum for p5 along the beam direction. We have enough data to achieve goal (b). Additional pp data will be needed before we can achieve a level of accuracy as low as 2-3% but the analysis does not indicate any basic difficulty in this respect. The third part of the program, asymmetric angles in the delta-excitation region, has yet to be carried out.Experim ent 224Inclusive inelastic p ion scattering from  light elements a t 100 MeV  (I. Halpern, Washington)The main goal of Expt. 224 is to study the inclusive inelastic scattering of pions which suffer large energy loss and are emitted at forward angles. Our earlier work in carbon and heavier elements suggests that there is an excess of yield in this region beyond that expected from quasielastic scattering. In Expt. 224 we study the scattering from light targets such as deuterium, 3He and 4He using the QQD spectrometer. The lighter targets should help unravel the basic patterns since they provide features not so available in heavy targets (e.g. variations in mean nucleon separations and in the ratio of neutrons to protons).The experiment was approved in the summer of 1982 and we had a run on deuterium and 4He in May 1983 and another which included 3He In July 1983. Unfortunately, there were severe machine problems during the second run. As a result the total main beam charge for the 3 He runs corresponds to only a little over one day at the normal proton current of 100 pA. The high pressure gas targets and target supports for these runs were designed and tested by Dr. M. Doss of our group and Mr. M. Khandaker, the graduate student whose thesis project this experiment is.We are currently analysing the results obtained last summer. In the region of small energy loss at middle-range angles (this is the easy region where the signal is high and the background is low) we find a number of expected features:1. Quasielastic peaks in the right place with reasonable (and different) widths from deuterium 3He and ^He.2. A fairly clear picture of the gaps in 3He and ^He to the first excited states.3. Roughly 2:1 ratios of the ir+ scattering cross sections from the He isotopes comparedwith deuterium (as one might expect for quasielastic scattering).4. Roughly 2:1 ratios for the scatterings from 3He for tt+ compared with tv" (and ~1:1 ratios for ^He).These various features of our data are reassuring and give us general confidence in the measurements.During the year a survey of inclusive scat­tering of pions from helium has been pub­lished by Baumgartner et al. of SIN. Their analysis of their own results in terms of quasielastic scattering described by a A-hole formalism fits their observations at 200 MeV and above. Their fits are not successful at lower energies close to that of our measurement.In our experiment the full outgoing spectrum is covered in four settings of the spectrom­eter field. A set of spectra at one of the intermediate field settings is given in Fig. 38. We cannot yet say very much about the data at forward angles and large energy loss. The statistical accuracy so far is relatively poor and we must be particularly careful at the lower field settings about the acceptance criteria that are used to elimin­ate backgrounds. Moreover, at forward direc­tions muon rejection becomes important. This is done in our measurements by means of a crude range determination using absorbers placed behind the focal plane of the spectrom­eter. We are carefully examining the opera­tion of this system in preparation for the next run.V)Fig. 38. Pion spectra - uncorrected for spectrometer efficiency, T^-*" = 100 MeV,0 = 100° .34In February we plan to finish the experiment outlined in our original proposal. This will require repeating some points and taking data that we failed to obtain with 3He at all angles and with the other targets at forward angles. If the machine were running at 100 pA of protons we should be able to complete the necessary runs in one week of steady running. In addition, we would need four to five days for set up and adequate testing.Experiment 229Pion double charge exchange a t 50 M eV on 14C(I. Navon, Victoria)Pion double charge exchange (DCX) is a reaction with very low cross section for which data are scarce, and no low energy measurement exists. It is a reaction which necessarily involves at least two nucleons and therefore probes nucleon correlations in the nucleus, matter distribution and isotensor components of every term of the optical potential. At low energies one expects to probe the interior of the nucleus.The TPC is well suited for the measurement of the DCX cross section l‘tC(Tr+ ,7r~)ll+N(g.s.) because of: a) its large acceptance, b) its trigger selectivity on the outgoing tt“ , and c) its e- background rejection capability through dE/dx measurement in the TPC chamber. The 11+C target was chosen because a) the ground state of is its double isobaric analog (DIAS) state and was expected to be highly populated, b) the level separation from the ground state is more than 5 MeV, and c) the Q value of the reaction is low (-4 MeV) for ^ C  and very high for the *2C (-31 MeV) which is present in the target.The l^C target (82% enriched) was enclosed in two thin copper boxes. Special handling procedures, approved by the TRIUMF Safety Advisory Committee, were used.Two l^C boxes were placed upstream and downstream from the centre of the TPC chamber in such a way that an overlap of the angular distributions occurred in the range 70°-100°. Absolute normalization was obtained from measurements of the elastic cross sections tt- +  ^2 C and TT“ + 14C and their compari­son with existing data. Background from incorrectly identified electrons and from DCX in the copper box was evaluated from runson *2 C, where DCX yields it- of at most 18 MeV, and from empty target runs. An average of about 7% background under the DIAS peak was thus estimated. Figures 39 and 40 show the final results. Comparison is made with calculations of E. Siciliano involving isotensor Lorentz-Lorenz (ILL) terms in the optical potential.Experiment 234Studies o f the A(p,n~) A + 1  reaction(R. Bent, IUCF)The aim of Expt. 234 is to study the A(p,ir )A+1 reaction in the previously unexplored 33 resonance region to see if the striking selectivity of the (p,ir-) reaction observed at IUCF energies (Tp < 200 MeV) persists at higher energies and, if so, to use this simplifying feature of the (p ,tt-) reaction to test current microscopic models of proton-induced nuclear pion production.The first data were taken in the summer of 1983 (June 29-July 5). This run utilized 11 shifts of polarized beam. The background was low, the particle identification was clean, and the resolution was good (~350 keV) considering that the twister was not yet operational in a dispersion matching mode on BL4B. However, during most of the run the beam current was limited to < 10 nA by the maximum counting rate (2 0 0,0 0 0/s) that could be tolerated in the multiwire chamber at the front end of the MRS spectrometer and conse­quently less data were obtained than was planned in the proposal, which assumed an average beam current of 25 nA.Figure 41 shows an 1 80(p,ir~) spectrum ob­tained during a 24 h run at Tp = 350 MeV and 0^ = 30°. This spectrum is similar to that obtained at IUCF, except that the peak at Ex = 4.6 MeV is somewhat less pro­nounced relative to the continuum.Differential cross sections and analysing powers were measured at the following energies and angles:Tp(lab) 01r(lab) q(MeV) (deg) (MeV/c)350 60 73030 587250 60 608350 10 20 30 40 50 60E 7T [ MFig. 39. Angle integrated spectra of it" scat­tering at 45 MeV (dotted line) and (it"*",it ) at 50 MeV (solid line). The scattering spectrum was normalized to the DIAS and shifted by 1 MeV to match the DIAS energy of 46 MeV.During the course of this experiment, 1 2C(p,ir+)13C spectra were taken before and after each (p,tt~) run (except for the last one) for efficiency and energy calibration of the (p,tt-) spectra, and to ensure that all the electronics was working. The latter was essential because of the very low (p,ir“) counting rates. Figure 42 shows 1 2C(p,ir+) spectrum obtained at Tp = 250 MeV and 0-^ = 60°. The energy resolution for this spectrum (~ 350 keV) is the best ever achieved in (p,ir) experiments at TRIUMF. For the first time the 3.09 and 3.77 MeV peaks are clearly resolved.The 1 2C(p,ir+ )1 3C(9.5 MeV) transition is of special interest in relation to (p,tt~)Fig. 41. Spectrum of events for 180(p,ir )X at 30° in the lab and 350 MeV.Fig. 40. Angular distribution of 14 C(tt+ ,tt-) at 50 MeV. The errors are the full angle- dependent errors (including the acceptance errors). The two solid lines are results of theoretical calculations with (LLIT=1) and without (LLIT=0) isotensor terra in the potential.experiments. In general, the (p ,tt+) reaction is more complex than (p,w“) because positive pions can be produced in both pp and pn interactions whereas for ir production the incident proton must interact with a target neutron. Consequently, more diagrams can contribute to tt+ production. However, thisFig. 42. 1 2C(P,ir+ )X event spectrum taken at250 MeV for a pion angle of 60° lab. The energy resolution is ~350 keV.3610Tp(MeV)•  2 0 0  (IUCF) - ¥ 2 5 0  (E234)/ /101350 (E234) / /  ///IZC(p,ir+) l3C(9.5) - q = 605 MeV/cl80(p,Tr-)l9Ne(4.6) 1  q = 6 0 8  MeV/cTp (MeV)0 2 0 0  (IUCF) _ x 2 50  (E234)A  350 (E234)(MeV/c)1.0 2.0 3.0Fig. 43. Comparison of the (p,ir+ ) differen­tial cross section on carbon with the ( p , tt“ )  on oxygen as a function of momentum transfer to the 2p-lh states.Fig. 44. Comparison of the cross sections on carbon and oxygen (for equal momentum trans­fer) as a function of the pion c.m. momentum (in units of i%c).is not the case for the ( p , tt+ )  reaction on 12C leading to the 9/2+ state at 9.5 MeV in 1 3C. The large ratio observed in pioninelastic scattering experiments [Denhard et al., Phys. Rev. Lett. 43, 1091 (1979)] suggests that this state has the stretched neutron configuration [(vPi / 2 , v p 3 /2- 1>2+ *5/2^9/2+* which can be reached from the 32C ground state [assumed to be pure(ttP3/2 )1+(vP3/2 )1+] via the ( P . O  reaction in a two-nucleon mechanism only if the incident proton interacts with a target neutron. Thus, in the two-nucleon model, this particular (p,ir+) transition is similar to ( p , tt“ )  tran­sitions to stretched 2p-lh states, and should provide a complementary test of the TNM.Figure 43 shows the differential cross sections for the (p,ir“) and (p,ir+) reactions leading to the stretched 2p-lh states at4.6 MeV in 19Ne and 9.5 MeV in 1 3C, respec­tively, plotted as a function of momentum transfer q, together with corresponding data obtained at IUCF at lower energies. In Fig. 44 the differential cross sections at q = 608 MeV are plotted vs the pion centre-of- mass momentum (in units of m^c). The influence of the A-resonance is seen in bothreactions but may be somewhat weaker for (p,7r“) than for (p,ir+).Further studies of the 1 2C(p,ir+)1 3C(9.5) and 1 80(p,ir“)19Ne(4.6) excitation functions in the 33-resonance region are planned.Experim ent 243Energy and angle dependence o f the 6Li(n+,3He)3He reaction  (G. Lolos, Regina)In order to determine the angular dependence of da/dft for pion-induced fission of lithium,i.e. ir++6Li+3He+3He Expt. 243 was proposed. Recent experiments at Orsay, LAMPF, TRIUMF and Saclay have determined to a certain extent the energy dependence of the reaction for T^ = 15-120 MeV. Most of the measure­ments, however, are at different angles so angular distributions cannot be compared to theory. In addition large differences exist between the results reported by LAMPF, TRIUMF and Saclay and they are all in variance with theoretical predictions (see Fig. 45). Experiment 243 will measure the angular dis­tribution at 15°, 30°, 45°, 60°, 75° and 90°37and at various incident pion energies from 20 to 100 MeV, and thus will not only pin down the angular dependence of da/dfl(E) but will also help resolve the normalization differ­ences between the different measurements.The experimental apparatus consists of six AE1-AE2~E veto telescopes with plastic scintillator counters arranged in three pairs (see Fig. 46). The two 3He products will be detected in the forward and backward directions in coincidence and three angles at a time will be simultaneously measured. The 3He nuclei will stop in the 2.54 cm thick E counters providing good particle identifica­tion while lighter particles will trigger the veto counters, thus greatly reducing the proton, deuteron and triton background.In a recent test run at T^ = 80 MeV the extracted 3He spectra exhibited clean particle identification and the preliminary do/dft is in good agreement with other results reported in the literature. Particularly satisfactory was the performance of the plastic scintillator counters coupled to fibre optic light guides, in the first such application in a telescope design with parti­cle identification capability (see Fig. 47).Fig. 45. World data on the 6Li(ir+ , 3He)3He reaction as a function of 1^+ (for:A-ORSAY, A-LAMPF, »-TRIUMF and B-Saclay. Solid line is da/dft calculated in the (KDH) model while dotted line is for the (GW) model.Fig. 46. A schematic diagram of the tele­scopes (not drawn to scale).The use of flexible fibre optic light guides was dictated by the severe spatial con­straints facing the four counter telescopesFig. 47. Energy loss histogram for 109 MeV protons and 80 MeV pions in the AE2 counter with fibre optic light guide.38in addition to the mechanical stress imposed on the thin (0.5 and 1.0 mm) AE counters when coupled to standard plexiglass UVT light guides.We plan to complete the experiment with ~10% precision and thus provide the necessary experimental input to the theoretical models that have been proposed for this reaction.39RESEARCH IN CHEMISTRY AND SOLID-STATE PHYSICSExperiment 140 Transfer effects fo r stopping n~ in H2-D2 m ixtures (D. Measday, UBC)The results from Expt. 140 were published this year [Aniol et al. in Phys. Rev. A 28, 2684 (1983)]. In this work we investigated the influence of molecular structure on the nuclear capture probability of stopped negative pions in gaseous hydrogen isotopes. The comparison was made at several pressures between HD to a mixture of equal amounts of H2 plus D2 . The fraction of stopped pions that suffer nuclear capture by the proton in the H2+D2 mixture is fh2D2 = 0.417 ± 0.004, while for HD it is fnD = 0.338 ± 0.008 and is independent of gas pressure between 6 and 90 atm. The ratio fH2D2/fHD = ± °*03.In Fig. 48 we present the yield of pir- gammas over the region 12 < Ey < 145 MeV. It will be seen that the yield of pir- gammas, i.e. those from the reactionsp-hr- & n+YoU- n-Hr° ■> n+Y1,+Y2,is consistently larger at all pressures measured for H2+D2 compared to HD. A sample gamma-ray spectrum from 50 atm HD is shown in Fig. 49. The yield of the characteristic ir° gamma rays from the pion charge exchange on the proton (40 < Ey < 90 MeV) essentiallyFig. 48. Yield of piT- y - r a y s  obtained by fitting the region 12 < Ey < 145 MeV.fixes the fraction f^p when the spectra are fitted with measured pir- and dir- gamma ray spectra. Note that the charge exchange branch in deuterium, i.e. ir“+d + ir°+n+n, for stopped pions is much suppressed (1.45xl0-1+) [MacDonald et al., Phys. Rev.Lett. 18, 746 (1977)] .In Fig. 50 we present schematic diagrams of the possible reaction mechanisms. Our results clearly show that the pion is aware that the proton is bound to the deuteron in a giant molecular complex (giant on the scale of the pir or dir atoms). Its preferential capture on the deuteron can be explained either by a larger rate X^ ir > xpir tsee Fig. 50(a)] and/or by direct nuclear cagti^re from the mesic molecular state Ad > Ap •It is clear though from the fact that fH d * 1 /2 , among other reasons, that the di£e£t capture from the molecular levels can­not be much bigger than the molecular break-. . v v . mox, mu a/up rates. If we assume A ,AdlT Ad ,athen our results show 1.46 < A^/Ap^ < 1.54. No currently published models can explain such a large effect. It is not unreasonable though to suppose that some of the preference for the capture on the deuteron comes from direct capture from the mesic molecular state [Aniol, op. cit.].Ev (MeV)Fig. 49. Fitted spectrum for 50 atm HD using measured spectral shapes for gammas from pir and dir- .Fig. 50. Schematic rate diagrams for ir stop­ping in (a) HD and (b) H2+D2.Experim ent 147 Formation and reactivity o f  muonium in gases (D. Fleming, UBC)ApparatusIn studies of muonium formation in gases it is often necessary to measure diamagnetic muon signals accurately as well as muonium signals. For the proper analysis of muon signals we must be able to account for the muon signal coming from the wall of the target vessel. The wall signal becomes troublesome especially at low pressures. In order to reduce wall signals we have designed and constructed a new target vessel with a large diameter (50 cm). This target vessel together with the large homogeneous Helmholtz coils mentioned in last year's annual report allow us to investigate problems which we could not easily study until a few years ago. It turns out this new apparatus is essential to the work described below. Also the new upgraded M20 beam line with a dc separator which provides a clean surface muon beam free of positron background contributes greatly to the better quality of our data.Formation and reactivity of muonium molecular ionWe started muonium molecular ion studies in noble gases as part of R. Mikula's thesis project. Last year we decided to look at this subject again with the new Helmholtz coils and discovered that the diamagnetic muon signal in Ne doped with a small amount of Xe (order of one hundred ppm) consists of two components with different relaxation rates (A a n d  X2) for fast and slow compon­ents, respectively (Figs. 51 and 52). Since muons show 100% muonium formation in pure Xe because of its low ionization energy, this fast relaxation is most likely to be due to thermal muonium formation. We have extended the measurements to other noble gases and dopants. The fast reaction rate constants (K2) available so far are summarized in Table II (Fig. 53).Fast relaxations are observed in He and Ne but not in Ar. This fact strongly reinforces our belief that the muon cannot be free in these noble gases. Instead it must be bound in a diamagnetic environment. As discussed in detail in last year's annual report and in publications [Phys. Rev. A 26_, 2527 (1982) and Chem. Phys. 82, 75 (1983)] the muon is most likely to be in the form of a molecular ion like NeMu+ . The argument based on the exothermicity of various muonium formation processes has led us to the conclusion that the observed fast relaxation is due to muonium formation from the vibrationally excited states of the molecular ion,(NeMu+ )* + X + Mu + Ne + X+ .The fast rate constant in Ne/NH3 is indepen­dent of total pressure, implying that the fast relaxation is due to simple two-body collisions between a Xe atom and diamagnetic muon species. An interesting point to note is that the amplitudes of slow and fast components (Aj and Ag, respectively) are total-pressure dependent (Tables III and IV). The tendency is that the higher the total pressure, the larger the fast amplitude can be clearly seen. The amplitudes of the slow and fast components and of muonium signal (A^u) are a slowly varying function of the dopant concentration [X] in the concentration region investigated and the total asymmetry Aj+ Ag + 2A^U stays roughly constant within the experimental accuracy. This confirms that two kinds of muonium formation processes exist in Ne/NH3 (1 ) muonium formation at epithermal energies41Fig. 51. The ySR signal in pure Ne at 288 G Fig. 52. The MSR signal at 288 G in Ne atand 1300 Torr pressure. 1300 Torr with 200 ppm of added Xe. Twodifferent relaxations are visible:X, (slow) = 0.044 ± 0.008 us-1 X2 (fast) = 3.18 ± 0.35 ys“l.Table II. Reaction rate constant for the fast relaxation component [in units of 10-1° cm3 molecule- 1s-1]Host Xedopantnh3 CH^ KrHe 12(4) at 1500 torr 60(20) at 1500 torrNe 3.6(6) at 1300 torr 28(6) at 1300 torr no fast component no fast component26(2) at 1300 torrAr no fast component no fast componentTable III. The amplitudes of ySR signals on the addition of dopant NH3 to Ne(800 torr total pressure)Concentration(1 0 14 cm-3) 3.4 6 . 2 8 . 2 13.1 100Aj (slow) 0.130(0.005) 0.115(0.005) 0.151(0.004) 0.124(0.04) 0.047(0.01)A^ (fast) 0 .1 0 2(0 .0 1 ) 0 .1 1 2(0 .0 2) 0.086(0.01) 0.092(0.01) —A-Mu 0.040(0.005) 0.043(0.004) 0.043(0.002) 0.046(0.003) 0.115(0.003)0.272 0.3130.323 0.288 0.27742Table IV. The amplitudes of ySR signals in Ne/NH3 (1300 torr total pressure).Concentration of NH3(1 0 14 molecule cm 3 ) 5.6 10 13.4 21.3A 1 0.105(0.006) 0.08(0.005) 0.089(0.006) 0.069(0.06)a2 0.181(0.006) 0.186(0.006) 0.183(0.009) 0.183(0.01)Table V. The amplitude (A2) and relaxation rate (X2) of the fast relaxing seen in He/NH3. A strong correlation can be seen between [NH3] and A^ which is to be compared with Ne/NH3 (Tables III, IV).Concentration of NH3(lO14 molecule cm-3) 1.1 3.0 5.6 120.043(0.007) 0.120(0.02) 0.088(0.01) 0.176(0.07)x2 2 .6 5 (1 .2 ) 5 .2 (1 .3 ) 7 .0 (1 .0 ) 11 .3 (3 .0 )We have observed fast relaxation also in He/Xe and He/NH3 . The corresponding rate constant for He/NH3 is 6(2)xl0- 9 cm3 mole­cule- 1 s-1, more than three times higher than in Ne/NH3 . This difference is further sup­porting evidence for molecular ion formation. The A2 in He/NH3 is, unlike in Ne/NH3 , strong­ly dependent on the concentration of the dopant (Table V). In fact A2 and the relaxa­tion rate (X2) are roughly proportional to [NH3 ]. Here we must exercise extreme caution in fitting the data because in case of very fast relaxation, strong but unreal correla­tion between amplitude and relaxation rate may complicate the data analysis. Careful analysis of the fast component, however, seems to confirm the above-mentioned correla­tion between A and [NH3 ]. At present we do not have an explanation for this. In order to fully understand the formation and reac­tion mechanism of muonium molecular ions further extensive studies will be needed.So far we have established the formation of muonium molecular ions in noble gases. We are planning further: (1 ) measurements ofK2 , Aj, A2 and Aj^ at various total pressures; (2 ) temperature dependence of the fast relaxation rate in a few of these systems, which could tell us something about the thermal muonium formation mechanism;(3) search for a fast component in Ar host;(4) adding a second dopant to the systemsin which the muon spin coherence is maintained, (2 ) muonium formation at thermal energies where the spin coherence is lost which manifests itself as fast relaxation of a diamagnetic signal.Co[NH3] (10“ /cmJ ]Fig. 53. A plot of the fast relaxation rate (X2^) of the ySR signal seen in Ne at 1300 torr with added NH3. The slope of this straight line gives the reaction rate con­stant K2 = 26(2) x 1 0 - 1 9 cm3 molecule- 1 s-1.43ARGONPressure(atm  )Fig. 54. The pressure dependence of the muon amplitude in Ar. Here the normalized amplitudes, i.e. A(observed)/A(A£) are plot­ted where A(M) is the absolute asymmetry observed in Ail. □: our earlier data; ®: our latest data; £ : data from SIN.already studied, hoping that this will alter the population distribution of the molecular ion over vibrational excited states.Charge exchange of muons in gasesAs a muon slows down in a moderator gas, it passes three distinct regimes:(1) Bethe-Bloch ionization of moderator atoms which has no effect on the spin dynamics of the muon;(2 ) charge exchange regime where the muon undergoes a series of electron pick-up (Kp) and loss (%) cycles, where Kc and K^ are respective rates;(3) thermalization.The second regime, because of the strong hyperfine interaction between the electron and the muon spin, is known to have a pro­found impact on the muon spin dynamics. If the time between charge exchange becomes comparable with the hyperfine period, muon spin depolarization becomes substantial.Recently, R.E. Turner, a member of TRIUMF's Theory Group, calculated the muon spin dy­namics in the charge exchange regime using a density operator formalism starting from the Boltzmann equation. He calculated furtherARGONPressure(atm  )Fig. 55. The muonium amplitude corresponding to Fig. 54. The upper solid line at high pressure is the triplet signal.the pressure dependence of the muon and muonium signal amplitudes in pure gas. The calculation has two rates (Kp and ) and a parameter which relates pressure to the time between charge exchange. Interesting predic­tions of this calculation are: (1 ) dependingon the Kp and K^ there is oscillatory behaviour at low pressures; (2 ) triplet and singlet muonium amplitudes are in general different. Intuitively the first prediction can be seen as follows. If the time between charge exchanges is such that the hyperfine interaction rotates the muon spin by just 180° or integer multiples of it, the muon spin coherence is recovered in the same or opposite direction to the original spin direction. This might be thought to be a (remote) analog of spin echoes.We have measured the pressure dependence of Ay and A in Ar, Ne, and He. The amplitude Ay also shows monotonical decrease with decreasing pressure. Experiments in Ne turned out to be extremely tricky because the muonium signal (should be very small in pure Ne) changed in amplitude depending on how long the target gas was left in the target vessel before measurements. Therefore, we baked the target vessel at about 100°C for three days until just before measurements.This procedure largely eliminated the problem. The amplitude Ay also shows monotonical behaviour as a function of pressure. Ar is the case where both muon and muonium signals are detectable. Figure 54 is a fit to Ay4 4data. Using the best parameters obtained from the fit in Fig. 54, one can calculate unambiguously the pressure dependence of Am u as shown in a solid line in Fig. 55 together with experimental points. Agreement between the calculation and experiments is reasonable. Further refinements of experi­ment and theory are in progress.Experim ent 150 Utilization o f  backw ard muons to study muonium  reaction interm ediates (P. Percivai, Simon Fraser)During the past year the SFU muonium chemistry group has concentrated on the study of muonium in ice. This work was a natural outcome of the previous year's discovery and characterization of two-frequency precession of muonium in single crystals of H2 0 and D2 0 . In 1983 detailed studies were made of both relaxation rates and signal amplitudes as a function of temperature (90-262 K) in H20.The relaxation rates are presented in Fig. 56.For ease and reliability in fitting the muonium signals the H„0 crystal was oriented with its c-axis at 55 to the magnetic field, so that the two frequency components were degenerate. However, this practice was only employed for temperatures <200 K, where any error due to misorientation would not be significant. At higher temperatures the crystal c-axis was aligned with the field, and the full expression for split muonium precession was used in the data analysis.The range of relaxation rates (XM) dis­played in Fig. 56 represents the most practi­cal range of values which can be determined by the pSR technique. At the low end limi­tations of field homogeneity and stability put a limit at about 0 . 1  ps-1, while at theother extreme the signal is so short lived that counting statistics suffer. The latter problem is serious below 120 K, and so it is not clear from Fig. 56 if continues to rise at still lower temperatures, or if a plateau has been reached. Clearly Mu signals must be sought in H2 0 at lower temperatures, and such experiments are planned.Preliminary measurements of XM for a D20 crystal also show temperature dependence:0.8, 0.4 and 0.1 ps- 1 for 102, 145 and 250 K, respectively. These low values are in accord with identification of the relaxation process as electron-nuclear dipolar coupling of muonium to the lattice protons (deuterons), modulated by translational diffusion of muonium. A full study of X in D20 would not only constitute an excellent test of the relaxation mechanism, but it would also show up any temperature independence in the diffu­sion rate below 120 K. Furthermore, if such a situation is found to exist, the ratio of X in 11,0 and D20 should serve to distinguish between the possibilities of trapping (i.e. diffusion rate < relaxation rate) and the dominance of tunnelling (i.e. constant fast diffusion).Our original purpose in studying muonium in ice was to measure the muonium and diamagnetic fractions as a function of temp­erature. The discovery of the anisotropic muonium hyperfine interaction and the information on Mu diffusion provided by the relaxation measurements were "spin-offs".But just as the study of single crystals proved invaluable in the relaxation study, so too for the signal amplitudes. To date we have only studied in detail H2 0 crystals above 90 K, but already the results have profound implications.1DDO_.OOOc 1—50 100— I---- 1---- 1---- 1150 200 250 300Temperature /K  Fig. 56. Relaxation rates of muonium in a single crystal of H20. The crystal c-axis was oriented either parallel to the field (circles) or at 55° (squares).The results are gathered in Figs. 57 and 58. As an aid to comparison of diamagnetic (Pp) and muonium (P^) fractions a smooth curve has been drawn through the points in Fig. 57, and is reproduced in the form of 1-Pp in Fig. 58. Two sets of data are displayed. The earlier results were so surprising that a different, more thorough calibration proced­ure was employed in the detailed survey. The good agreement between the data sets for Pp suggests we were successful in eliminating potential systematic errors. The two most important features of the results are:1) Comparison of with l“Pp shows that there is a missing fraction in ice at temp­eratures >200 K. This is in marked contrast to the findings of the earlier study on451.0 -0 .8 -0.6 -0.4-0.2 -0.0crf^ 050 100 150 200 250 300Temperature /KFig. 57. Muon polarization (Pp) in H20 single crystals (circles and squares) and the liquid (triangle).1.0- H0.0  1---- 1---- 1 I I50 100 150 200 250 300Temperature /KFig. 58. Muonium polarization (Pp) in 1^0 single crystals compared with 1-Pp (solid line for ice, triangle for the liquid).polycrystalline ice [Percival et al., Chem. Phys. 32_, 353 (1978)] .2) In agreement with the polycrystalline ice study the Pjq fraction increases at the ex­pense of Pp for temperature below 150 K. It is unclear whether or not Pp levels off below 90 K, but a single measurement at 77 K [Byakov et al., Khim. Vys. Energ. 12, 279 (1978)] suggests a further decline.In a different aspect of Expt. 150, reintro­duced at the December EEC meeting as a sepa­rate proposal (Expt. 260), the reaction of muonium with hydrogen peroxide is being studied to clarify the mechanism of the corresponding H atom reaction. Two pathways are known for the gas phase reaction:( 1 ) (2)H + H202 -*■ H20 + *0H R + H202 > H2 + •00H ,but there is ambiguity as to which dominates in aqueous solution.In 1982 it was established that:1) The rate constant for Mu + H202 in natural pH iskM (H202 ) = (1.79 ± 0.16) x 109 M_1 s- 1 .2) A residual polarization study of concen­trated li2 0 2 solutions shows that diamagnetic muon products are formed, i.e. the possibil­ity of MuO* has been excluded.3) The rate constant for Mu + D202 in natural pH iskM (D2 02) = (0.92 ± 0.06) x 109 M- 1 s- 1 .In the latest work the pH dependence of Mu kinetics was investigated. The rationale for this was that H02“, the basic form of H202 , has only one H atom available for abstraction so that the rate of reaction (2 )would be reduced accordingly. Our results took an unexpected turn, however: Fasterdecay was apparent at high pH (Fig. 59), more so than could be accounted for by the contribution ofk3Mu + OH -2-+ MuOH + eaq • (3)Five separate kinetic studies (3 or 4 l^ O,, concentrations each) were carried out at different pH's. The results are gathered in Fig. 60, where the variation in slopes clear­ly demonstrates the pH dependence of k^. A formal quantitative analysis was carried out by simultaneously fitting all the decay rates, asssuming a competition between reaction (3) and separate reactions of Mu with and H02 :k,.Mu + H202 Mu + HOTproductsproducts(4)(5)Combination of the rate equations for reac­tions (3), (4) and (5) with the relations[HO"] [11+][h2o2]Kw = [H+ ][0H-] = 1 x 10-19 and [H2°2 ]tot = tH2°2  ^ + [H0 2 ]leads to an expression for the muonium decay rate XM in terms of total peroxide concen­tration, [H202]tot and acidity, [H+]:k[H+] + k,Ka k, KwX = 9 ,  ---§_a [H202 ]tot + 3 - W[H ] + Ka Z Z [H+] + X°where XQ is the (instrument limited) decay rate measured in the absence of reaction. Since Ka is known from the literature46Muonium Asymmetry in 2mM H202Time / j , sFig. 59. Muonium decays at different pH's.(2.A x 10“ 12 M), this only leaves k3, k^, and k5 as fit variables. An excellent fit (reduced chi-square = 0.92) was found giving values:k3 = (3.4 ± 0.4) x 107 M- 1 s_1 k^ = (1.54 ± 0.08) x 109 M” 1 s" 1k5 = (4.9 ± 0.6) x 109 M_1 s" 1k^ is consistent with the value of k^ found at neutral pH ("1." above). k3 is a factor of 2 higher than literature values but this is probably not significant given the high [0H“] used and the presence of other solutes. The important outcome of this study is the high value of k5 compared with k^. The analogous situation with H is not known since H atom studies in basic media are so problematic. Its introduction might have important consequences in computer modelling of the radiolysis of aqueous systems.Experim ent 157 The chem istry o f  muonium atoms in condensed  media (D. Walker, UBC)A broadly based series of muon spin rotation experiments has been conducted during the past few years under the 'umbrella' of Expt. 157. These have been concerned with the chemical reactivity of muonium, its mode of formation from muons, and the specificity of muon-containing free radicals. Many of[ H202 ]/mMFig. 60. pH dependent muonium decay inH2 0 2 solutions.these studies have involved the reactants dissolved in water, but others have focused directly on organic materials as pure liquids or solids. Some attempt was made to explore the potential of pSR in studying molecules of basic biological importance such as porphy­rins or model structures such as micelles and cyclodextrins. These studies have mainly been published in chemical journals, with progress reports given at various confer­ences, some of which are recorded as Proceed­ings. A book has also been written with a broad chemical audience in mind to try to show the potential use of this rare, man-made particle in chemical research. Expt. 157 has now been completed.During 1983 it received some 20 shifts of high-intensity beam time on M20 and was involved in the following specific projects.1) Muonium reaction rate constants (k^) were determined for a variety of aromatic organic solutes in dilute aqueous solution. The results were analysed in accordance with the Hammett equation, where a quantative measure of the electronic effect of the reagent (muonium, in this case) is determined by reference to the established electron- withdrawing power of substituent groups at­tached to the benzene ring. The results are shown in Fig. 61, plotted as log k^ versus a. The latter gives the Hammett substituent factor for both ortho/para and meta directing effects, so that the slope (p = 0 . 6 ± 0 .2)47Fig. 61. The logarithm of the muonium rate constant ky as a function of a , the Hammett electron-withdrawing substituent effect, for a variety of substituted benzenes in dilute aqueous solution at ~295 K.suggests a weak nucleophilic character for muonium. This contrasts with both H-atoms and hydrated electrons, for which p = -0.45 and 4.8 are the literature values, respec­tively. It highlights some of the important differences between these species and sug­gests a mechanism for the reaction. An important question now is whether muonium- containing free radicals are produced with similar or quite different Hammett p factors in these compounds and their concentrated solutions (part of the new Expt. 262 proposal).2) Muonium provides a unique opportunity to study the rather tenuous interaction between two paramagnetic species that results simply in electron spin conversion, sometime specif­ically assigned as "electron spin exchange". Such subtle processes can be followed by pSR because the rate of conversion of 'triplet' tMu to 'singlet' sMu is readily followed as a relaxation of the muonium precession signal. Such spin-exchange inter­actions are usually observable only under rather ambiguous conditions, because paramag­netic species also generally interact (i) by transferring an electron (electron-exchange, or in chemical terms, oxidation-reduction) and (ii) by combining to form an ordinary a bond. To avoid these ambiguities, Expt. 157 chose nickel cyclam, which has a Ni2+ (d8) ion coordinated in the planar 4N organic ligand. Under ordinary dilute aqueous solu­tion conditions this complex coordinates two axial 11,0 molecules, resulting in a distorted octahedral geometry with Jahn-Teller split­F.Fig. 62. The observed muonium rate constant kf4 dependence on the fraction of the reac­tant (nickel cyclam) in a paramagnetic state.ting. It is, however, distinctly paramagnet­ic. But when an inert salt (Na2 S01+ and NaGiO^ in this study) is added at high concentration, the H2 0 ligands are removed, resulting in a square planar (D^) diamagnetic complex.The conversion from a paramagnetic species to a diamagnetic one is thus accomplished by the simple addition to the solution of an inert salt. There is no change in the principal ligand nor in the oxidation state of the central metal ion. Only the d-electron con­figuration is altered, with its resulting change in magnetism. Using this system it was shown that k{4 for reaction of Mu with the complex had a value of only 2 x 108 M- 1  s_1 with the diamagnetic state, but was 10 0- fold faster (essentially at the diffusion- controlled limit) with the paramagnetic state. These results are presented in Fig. 62, plotted as k^ versus the fraction of complex present in the paramagnetic state (as determined by optical spectroscopy of solutions containing various inert salt con­centrations) . This is a delightfully simple and unambiguous demonstration of an electron spin-exchange interaction.3) With regard to muon and muonium chemistry in organic media: (i) it was discovered thatthe fractional diamagnetic yield in CCl^ (the standard calibrant of the stopped-beam asym­metry) fell from Pp = 1.0 to Pp = 0.5 upon crystallization of CCi.^  at -45°C even though no change occurred at the liquid-to- glass transition at -23°C; (ii) the anti- inhibitary effect of CgF& on the Pp of a one molar solution of CCJl^  in cyclohexane48contrasted sharply with the analogous situ­ation in ortho-positronium formation studies; and (iii) yields and relaxations of both muonium and diamagnetic species were measured and compared to cyclohexane, n-hexane, and neopentane at their glass-transition and crystallization temperatures. Solutions of muonium scavengers in these media are presently under study.Experim ent 161pS R  in am orphous spin glasses  (C. Huang, Los Alamos)Muon relaxation functionsInterpretation of zero-field (ZF) muon spin relaxation functions G(t) in terms of the local field distributions and spin dynamics that generate them is rapidly becoming one of the most powerful (and unique) tools of pSR. We have now developed general-purpose pSR data analysis software to fit every known variety of G(t) as well as new tabulated functions which cannot be expressed analytically, an example of which is shown in Fig. 63. This will allow us to realize the full potential of the high statistics, low background data now available from the new M20 and M15.SGT50.TBLFig. 63. Tabulated relaxation function for spin glass model of Y.J. Uemura (zero static component).P d „F e ,S i„  A m o rp h o u s  Sp in  G la ssTemperature (K)Fig. 64. Temperature dependence of "order parameter" Q in Pdy5Fe5 Si20.Amorphous spin glassesThe amorphous alloys PD7 5Fe5 Si2g and Fe5Niy5P1LfB6 have proved to be ’model" spin glasses, including an onset of the "order parameter" Q below Tg, first observed by Uemura in the dilute-alloy spin glasses.Q is a measure of the fraction of the randomly oriented local field which is static, as opposed to fluctuating - a sort of microscopic local magnetization parameter. The temperature dependence of Q in PdygFe5 Si2Q is shown in Fig. 64, and the T- dependence of the extracted local field correlation time Tc is shown in Fig. 65.The curve through the T > Tg points in Fig. 65 is given by:T (s) = 1.8(3)xl0-l° (   ■)c \T — 15.5(3)K/in agreement with the power law observed for all the dilute-alloy spin glasses studied earlier. A paper in preparation discusses the implications of this "classic" spin glass behaviour in a random amorphous system."Metglas" (Fe5Ni?5P 11+B5) has several interesting and useful properties, one of which is that it appears to be a typical spin glass like Pdy5Fe5 Si2Q but with a larger "static width ’ > 100 ys_1 . This isevident from the very fast initial relaxation at low temperature in the preliminary data shown in Fig. 6 6 .49PdjjFesSia, A m o rp h o u s  S p in  G la ssTemperature (K)Fig. 65. Temperature dependence of local field correlation time in Pd7 5 Fe5 Si20.Experim ent 191 M uons and muonium on surfaces  (J. Brewer, UBC)Muonium relaxation on silica surfacesOur investigation of muonium absorption, trapping and diffusion on the surfaces of 7 nm silica powder grains has been intensi­fied, with several interesting results.First, as shown in Fig. 67, while the quali­tative features of diffusion and trapping at different temperatures are independent of sample preparation, it is possible to repro- ducibly change the transverse-field (TF) muonium relaxation rates by vacuum heat treatment to remove the normally plentiful surface hydroxyl groups. This supports the hypothesis that the proton moments of OH groups provide the principal relaxation mechanism.This picture is further borne out by detailed zero-field (ZF) and longitudinal-field (LF) relaxation measurements, which reveal a relaxation function G(t) similar to that observed for muons in dilute magnetic alloys, where the random local magnetic fields have an approximately Lorentzian distribution.This is just what one would expect for relaxation of the more sensitive Mu atom by randomly interspersed proton dipole moments.Surprising results were obtained with the surfaces coated with 4He films. First, theZF-/uSR in METGLAS (Fe,N i„PHB.)T I M E  (m icrosec)Fig. 6 6 . Spin-glass relaxation in "Metglas".Mu relaxation rate at constant temperature is dramatically dependent upon the 4He coverage, as shown in Fig. 6 8 . Second, this behaviour is in turn critically dependent upon the preparation of the surfaces. At certain coverages well below monolayer completionTemperature (K)20 10 5 41/T ( OFig. 67. Muonium relaxation rate on Si02 surfaces (7 nm powder grains) as a function of temperature and sample preparation, for 7 Oe applied transverse field. Circles: sample baked at 110°C in vacuum for 10 h. Squares: sample baked at 600°C in vacuum for10 h (110°C removes only H2 0; 600°C removes more than half of chemisorbed OH from surface).50Mu Relax, in He C o a te d  SiO , at 6 K B a re  and 4H e—c o a te d  S iO , Z F — and T F —MSRXJoDoser Volume Pressure (to rr)<Qu-1a>.24.22.2-b .18 v1 16 f  .14I  -12cr.1.08.06\ *■ Bare, 2. \ ••A\Coated, 6' I ZF5 KrA v* /’A tf / \ /?+:V V V/  \VDoser Volume Pressure (to rr)Fig. 6 8. TF (7 Oe) Mu relaxation in Si02 powders at 6 K vs fractional coverage of surfaces by ^He films, for sample baked at 100°C (top) and 600°C (bottom). Helium vapour pressure (right hand scale) begins to increase at monolayer completion.the ^He actually seems to assist the Mu atoms in reaching depolarization sites.Finally, with completely He-coated surfaces one sees only very slow relaxation in 7 G transverse fields, but in zero field a re­markable relaxation effect is seen, as shown in Fig. 69. This is especially surprising inasmuch as H atoms are known to have very low affinity for He-coated glass surfaces.Supported and unsupported platinum catalystsMicrocyrstalline (3.5 nm) Pt powder and Pt microplatelets supported on a silica gel substrate (two genuine industrial catalysts) were both investigated by TF-p+SR with0 .5 1 1.5 2 2.5 3T I M E  (Microsec)Fig. 69. TF-p+SR (80 Oe, diamonds) and ZF-MSR (circles) in Si02 powder with several mono­layers of 4 He on the surfaces. TF-MSR (7 Oe) shows very slow Mu relaxation (not shown). ZF-MSR (squares) in the same powder without ^He coating at 2.5 K is shown for contrast.various amounts of 02 , H2 and Ar gas deposited on the surfaces. The sudden decrease of the y+ signal below 55 K (the temperature at which oxygen freezes onto the Pt surfaces) was confirmed with the untreated supported catalyst, indicating formation of Mu atoms at the Pt surfaces.Experim ent 219The chem istry o f pionic hydrogen atoms(D. Horvath, Budapest)The aim of Expt. 219 is to carry on the study of hydrogen-bonded systems by measuring the W probability of pir" formation in normal and deuterated methanol (CHjOH, CDgOH, CHgOD) at various temperatures. As the W probability is very low in CDjOH this experiment would be extremely difficult using the Dubna setup. During a short preliminary run in May we measured a clear pn- ■* mr° -*■ nyy energy spectrum from CHjOH in 2.5 h in Mil, and as a first estimation also measured the probabili­ty W in CDjOH: W(CD30H) = (1.0 ± 0.3)*10-3.We also plan to measure the effect of phase transitions on pion capture by hydrogen in metallic hydrides, as a first step in the NbHx system. For these measurements we obtained the target materials, deuterated plastic scintillators for hydrogen-free beam counters, high pressure target vessels, and a hot air heating system.51Experim ent 220 Muonium spin exchange (M. Senba, TRIUMF/UBC)Under Expt. 147 we have measured the temperature dependence of the spin exchange cross section for Mu-02 and Mu-NO systems. A theoretical calculation, motivated by our work, agrees with our measurements to within a factor of about two but shows the wrong trends with temperature. This is probably due to the fact that in molecular systems the rotational anisotropies in the scattering potential are poorly known. This state of affairs, in part, prompted our interest in the pure atom-atom spin exchange problem, notably Mu + Cs, and ultimately with other alkali metal vapours.In Expt. 220 our runs to date have been unsuccessful. Upon the addition of Cs vapour to Ar modulator we have observed an increase in the muonium relaxation rate corresponding to roughly 1 / 1 0  of the spin exchange cross section between H and Cs. The real problem was that after pumping out the target vessel again we would not restore the background relaxation we had obtained before the addition of Cs. This is probably due to the absorption of Cs on the wall of the stainless target vessel. We are currently implementing two modifications which will hopefully overcome this problem; a flow system so that Cs vapour (at ~250°C) is constantly being replenished and an optical absorption device to monitor the absolute concentration of Cs atoms•Experiment 232  Giant muon Knight shifts (D. Williams, UBC)Giant muon Knight shifts in Sb alloysA "giant" anisotropic muon Knight shift (Kp~l%) is observed in pure antimony crystals; to understand this phenomenon is the motivation for our studies of Ky in Sb alloys. Our early work (recently published) demonstrated that alloying 6.3 at.% Bi with Sb causes a reduction of Ky by about a factor of 2 , presumably due to the reduction of the number of sixth-band electrons caused by such alloying. At 15% Bi concentration Ky becomes small (<0 .2%) and the monotonic decrease of Ky with T is replaced by a complicated temperature dependence (results from SIN, in press) which is not yet understood.Preliminary work with SbSn alloys showed that as little as 0.3 at.% Sn reduced Ky to <0 .2%; this again was consistent with the idea that the sixth-band electrons were responsible for the giant Knight shift in Sb, since the addition of Sn decreases their number drastically. These findings prompted a study of Sb with Te, in which the number of sixth-band electrons is known to increase as a function of Te concentration. This might be expected to result in an increased Ky. However, recent measurements on a single crystal of SbTe (0.1 at.%) have revealed no detectable Knight shift!These surprising results led us to investigate lower Sn and Te concentrations in Sb, with the following preliminary results:0.2 at.% gives Ky < 0.2%, but both 0.03% and 0.06% Sn show Knight shifts which are larger than that in pure Sb. On the other hand, 0.06% Te still shows no giant Knight shift. We are now checking the impurity content of these crystals by independent methods; preliminary results confirm the nominal concentrations.In any case it is clear that Ky first increases, and then decreases, as a function of dilute Sn concentration in Sb. This suggests that the same may occur with Bi impurities, which has not yet been checked.We have also checked the Knight shift in polycrystalline As, which has a band structure much like that of Sb, but found Ky < 100 ppm.Muon diffusion and trapping in pure antimonyIn high transverse fields inhomogeneous Knight shifts also cause relaxation.However, this effect can be masked by the diffusive motion and/or trapping behaviour of the muon (leading to T-dependent dipolar relaxation) which has not previously been studied in this crystal. We have therefore made the first zero field (ZF) relaxation study of muons in pure Sb, with interesting results (see Fig. 70.).The relaxation function at 6 K is a typical "dynamic Kubo-Toyabe" G(t) associated with a static gaussian local field distribution (from the Sb nuclear moments), amongst which the muon "hops" only about once per muon lifetime. At higher T the G(t) functions observed indicate a monotonic increase of the muon hop rate (within the same local field distribution) up to around 150 K, above which52Pure Sb crystal in Zero FieldT I M E  (microsec)Fig. 70. Zero field p+ relaxation in pure Sb at several temperatures.this model breaks down completely and there is clear evidence for trapping at imperfections (either impurities or lattice defects).We conclude that the Knight shift data below about 100 K is truly representative of muon located interstitially in the pure Sb lattice, but that above 150 K the Knight shift is a combination of that experienced by muons in pure Sb (at early times) and that associated with muons trapped at imperfec­tions (at later times) where the local electronic density will surely be distorted.These measurements must be repeated for the Sb alloys, in which the muons may trap at much lower temperatures; it would be especially interesting to learn whether the exotic T-dependence of K^ in SbBi (15%) is actually related to muons trapped in different sites with various configurations of Sb and Bi neighbours.Development of the "vernier" pSR techniqueBy routing events to n separate histograms Nj(t) depending upon j = mod(i,n), where i= the bin number of the original time interval measurement, we generate data displaying the "vernier" frequency Av = - v0 wherev0 = nAt (At = bin size). A judicious choice of n (for a given aplied field) produces a very small Av so that the data canFig. 71. "Vernier" pSR spectrum in SbSn (0.06 at.%).be "packed" and fitted very efficiently; moreover, as is evident from a typical spectrum shown in Fig. 71, it is a simple matter to distinguish frequencies, ampli­tudes, and relaxation behaviour of several signals at once. This now makes 100 ppm accuracy readily available in multi-frequency situations with available fields of 8 kOe.When combined with a new high-field (3T) superconducting magnet and our new LRS 4204 TDC with a time resolution of 156.25 ps this technique will allow easy measurement of frequencies at the 10 ppm level with resolution of frequencies separated by as little as 200 ppm (presently impossible with any existing techniques).Experiment 239 pSR  study o f critica l spin fluctuations (Y. Uemura, Japan Society)Hybrid relaxation mechanism in MnSiThis itinerant helimagnet is among the most exhaustively studied crystals in pSR, largely because of its very interesting properties and the fact that the muon is the only probe sensitive to its critical behaviour in the most important time range.In a recent study of the zero field (Zf) muon relaxation function G(t) near Tc = 29.7 K (see Fig. 72) we found that the exponential G, (t) seen at low T, caused by spin-exchange scattering between muons and itinerant con­duction electrons (believed to be described correctly by Moriya's self-consistent renormalization theory, or SCR), becomes53Z F -/u S R  in MnSi nea r Tc = 29 .7  K Muon R e la xa tio n  in M nF, N ea r T ,=  67  K.3.25<uEE.15oi r .05-.0545 K29.6 K 33 K.35EE.25.2.15T I M E  (microsec)Fig. 72. ZF-pSR in MnSi near Tc = 29.7 K."mixed" with the high temperature "Kubo- Toyabe" G2 (t) (due to the local dipolar fields of Mn nuclear moments) in a narrow temperature range near 33 K.One might expect the "mixed" G(t) at 33 K to be simply the product of the exponential G^(t) times the more Gaussian-shaped G2 (t). When analysed using this model, the data reveal a dynamical Kubo-Toyabe G2 (t) under­lying the exponential G^t). This is very unlikely to be due to a sudden onset of muon hopping just above Tc (29.7 K), and is more likely due to the fact that the Mn nuclei, like the p+ , are being "spin-flipped" by the same itinerant conduction electrons. This behaviour is qualitatively apparent from the fact that for t > 3 ps the 33 K spectrum rises above the low-T and high-T functions, and has a shallower slope - either of which is mathematically impossible for the product of two functions which are everywhere < 1 and monotonically decreasing on the range observed. Therefore the Kubo-Toyabe G2 (t) must be drastically "exchange-narrowed" due to relaxation of the Mn nuclear spins by the conduction electrons.These results are still being analysed, but it is clear that pSR has for the first time directly revealed the relaxation of the host nuclei themselves in what might be termed "double relaxation" (a process in which the muon is a pure spectator). It is likely that the nuclear relaxation times measured in this way are far shorter than can be accurately determined by (e.g.) NMR.T I M E  (Microsec)Fig. 73. Muon relaxation in MnF2 near Tn = 67 K.Critical behaviour in MnF2Recent ZF- and TF-pSR measurements on a single crystal of the antiferrogmagnetic insulator MnF2 are shown in Fig. 73.One conclusion may be immediately drawn from the data shown in Fig. 73: there are two muon sites in this crystal which see different local fields. This is evident from the fact that the "envelope" of the transverse field (TF) p+ precession at 68 K is the same as the zero field (ZF) relaxation function G(t) at the same temperature, which has a "fast component" and a "slow component". This "fast-slow" behaviour is normally charac­teristic of magnetic order with slow fluctu­ations (as in spin glasses) but in that case there is always only one (fast) relaxation rate in the TF data.Another conclusion from very recent data (not obvious from Fig. 73 by itself) is that the critical spin fluctuations which set in below T become temperature independent above Tn . The ZF G(t) spectra between 68 and 90 K are all indistinguishable from that shown in Fig. 73 (triangles) for 68 K. This is rather unexpected above the ordering temperature, and is not yet understood.Muon relaxation functionsInterpretation of zero-field (ZF) muon spin relaxation functions G(t) in terms of the local field distributions and spin dynamics that generate them is rapidly becoming one of the most powerful (and unique) tools of pSR. We have now developed general-purpose pSR54data analysis software to fit every known variety of G(t) as well as new tabulated functions which cannot be expressed analytically. This will allow us to realize the full potential of the high statistics, low background data now available from the new M20 and M15.Experim ent 244 liSR  in m agnetic superconductors  (E. Ansaldo, Saskatchewan)Ternary magnetic superconductorsNew zero field (ZF) ySR data in ErRh^B^ (superconducting below 3.6 K and ferromagnet­ic below 0 . 8 K) show fast paramagnetic relax­ation at high temperatures (30 K > T > 300 K), whereas in SmRh^B^ and the nonmagnetic YRh^B^ the relaxation function is a static gaussian Kubo-Toyabe G(t) (due to B nuclear moments) above about 40 K (Fig. 74)..6 i i i r i5 5 _4 4*♦ 4-.5\  +\  + l°° K * * V a  H  + 4.177 K4 5.43555 K'_^Z*L%s..3 - I I I i 10 .05 .1 .15 .2 .25 .3T I M E  (Microsec)Fig. 74. ZF muon relaxation in ErRh^B^ at high temperatures.falling off at t = 0 but actually rounded, as a Gaussian relaxation should be.In SmRh^B^ at T>40 K the paramagnetic moments are still present, but they are fluctuating so fast that the muon "sees" the much weaker nuclear moments; thus the ErRh^B^ results indicate a remarkably slow fluctuation rate for the Er spins, even at room temperature.Additional light is shed on this phenomenon by the almost "root-exponential" shape of the high-T relaxation function, which is characteristic of several muon sites with different random local field distributions. This shape reverts to a spin glass-like G(t) at low temperatures, where the initial component of the relaxation becomes too fast to see (<10 ns). This helps to explain both the earlier ErRh^B^ data and the similar behaviour of SmRh^B^ at very low T.However, both the "root exponential" and the low-T limits of "spin glass relaxation" behaviour are characteristic of random locations of large magnetic moments, giving an instantaneously Lorentzian local field distribution; this is an unphysical picture for the regular array of moments in ErRh^B^, which must produce, in the static limit, a Gaussian local field distribution for a given muon site. Moreover, although the data shown above can be fitted into the spin glass relaxation functions, the fitted values of the initial asymmetry become unphysically large for the fast-relaxing cases, indicating that the very early part of the spectrum (to which we are uniquely sensitive with our surface muon technique) is not sharplyThese results suggest that the correct relaxation function is in fact the familiar Gaussian Kubo-Toyabe G(t), but that there are (at least) two different muon sites in the complicated unit cell, one of which is nearer to the Er sites and "sees" a larger (but still Gaussian) local field distribution.The overall G(t) is then the sum of the G(t) for the various sites; but all must share a common Er spin fluctuation rate v.Coulomb capture o f negative muons and pions  (D. Horvath, Budapest)The various models of atomic capture of negative mesonic particles have been tested against 321 experimental Coulomb-capture ratios measured on binary systems: gas mix­tures, alloys and simple compounds. The com­parison has shown that the general agreement between theory and experiment is not satis­factory. We tried to improve on the models of Fermi and Teller [Phys. Rev. 72^ , 399 (1947)], Daniel [Phys. Rev. Lett. 35, 1649(1975)], Vasilyev et al. [JINR-R1-10222, Dubna, 1976], and Schneuwly, Pokrovsky and Ponomasar (SPP) [Nucl. Phys. A312, 419(1978)]. We have shown [Horvath and Entezami, Nucl. Phys. A407, 297 (1983)] that the pre­dictions of the SPP model are closest to the atomic capture ratios for alloys and com­pounds while the data measured in gas mix­tures are better approximated by the empiri­cal formula of Vasilyev et al. (see Fig. 75).55Rtonic capture ratio2 4 6 8 10 12Z1/Z2Fig. 75. Atomic capture ratios A(Z1 ,Z2) measured in oxides, fluorides and chlorides againt the ratio of the corresponding atomic numbers /Z2 . Note the characteristic oscillations in each case. The upper solid line corresponds to the Fermi-Teller Z-law and the lower one to our modified Z-law.The dashed curve represents the predictions of the SPP model with the fitted parameter values [from Horvath and Entezami, Nucl. Phys., A407, 297 (1983)].A systematic analysis is made of the possible elementary processes determining the fate of negative pions stopping in hydrogen-contain­ing samples. Using a phenomenological des­cription in comparison with the available experimental information on pion capture in hydrogen, it is shown that the formation and decay of pir- atoms in compounds ZmHn are determined mainly by the processes of Auger- capture in a molecular orbit ZHtr", transition from molecular to atomic orbit, transfer ofpions to atoms Z in collisions pm + Z, and nuclear capture by protons in collisions pm- + H (see Fig. 75) [Horvath, TRI-PP-83-13 (submitted to Phys. Rev. A) and TRI-PP-83-31, to be published in Hyp. Int.]. A recent assumption [Jackson et al., Phys. Rev. A25, 3262 (1982)] of a considerable role of the processes of radiative atomic capture in bound hydrogen atoms, nuclear capture of pions by protons from the ZHm~ molecularFig. 76. The fate of a slow m“-meson in a compound ZmHn . The pion is captured in a molecular state ZHir“ or in atomic orbits of pm“ and Zm“ with probabilities D, P and (1-P-D), respectively. The pionic molecule may decay via pion capture in a proton or by pion transition to atomic orbits pm“ and Zm“ .The pion can be transferred from pm“ to Z, orabsorbed by a proton [from Horvath, TRI-PP- 83-13] .state, or the "inner" transfer of the pion via tunnelling through the Z-H bond (see Fig. 76) is not supported by the theory andcontradicts the experimental data.A bib liography on exotic atoms (D. Horvath, Budapest)Exotic atoms - atoms in which one (or more) of the electrons or the nucleus is replaced by another appropriately charged particle - can be considered as new nuclear probes in the physical, chemical, biological and materials sciences.We recognized the exponential growth of pub­lication dealing with exotic atoms in 1975. Knowing that scientific literature in this esoteric field was weakly indexed and often appeared in obscure sources, we decided to attempt the compilation of a complete bibli­ography on exotic atoms [Horvath and Lambrecht, to be published by Elsevier, Amsterdam, cca. 650 pp]. It is our hope that the document will stimulate new chemical and physical applications of exotic atoms and aid researchers entering the field.56The analysis of nearly 4000 publications [Lambrecht et al., paper presented at the Yamada Conference on Muon Spin Rotation and Associated Problems, Shimoda, Japan, 1983, TRIUMF preprint TRI-PP-83-30] demonstrated that (see Figs. 77 and 78):- exotic atoms are nuclear probes used in every field of physics, from the test of quantum electrodynamics (QED) to chemical physics, to materials sciences;- the role of nuclear and atomic physics in exotic atom research is decreasing (although it is still significant), while that of materials science and chemical physics is exponentially increasing,- prior to 1980 most investigators were mainly interested in atoms with negative muons, while during the last few years the positive muon (pSR) studies have dominated exotic atom research.Neutron diffraction at TRIUMF  (A. Arrott, Simon Fraser)The neutron diffraction spectrometer at the thermal neutron facility is used to study quantitative aspects of the propagation of neutrons in real crystals, as opposed to the extreme limits of 'perfect' crystals and 'ideally imperfect' crystals. Only in these limiting cases is theory adequate to accurately describe the results of elastic scattering of neutrons. The 'real' crystals used in these studies are almost perfect crystals which can be elastically distorted to produce strain gradients that change the scattering toward the limit of 'ideally imperfect' crystals. The aims of this research are to provide more suitable crystals for the monochromation of thermal neutron beams, to better understand the corrections needed in crystallographic studies and to develop the field of precision measurements of static magnetic induction waves in ferromagnetic materials. Most of the work is focussed on the materials silicon and iron.Three different methods of producing a superior neutron monochromator have been invented and developed using the principle of mechanically creating elastic strain gradients in single crystal silicon wafers. The wafers (7.5 mm diam by 0.3 to 0.5 mm thick) are readily and cheaply available on the reject market for electronic component manufacture. In the first method the circular wafers are separated by thin aluminum Belleville washers. When the stackis compressed, the washers act as springs in series which elastically deform the wafers into spherical caps. The orientation of the wafers is changed slightly from wafer to wafer by canting the end supports by a small angle. The second method achieves the same objective but uses a different arrangement to produce elastic deformation in the form of cylindrical bends, generally a preferable arrangement, as it avoids the curvature in the scattering plane.The third method uses a thermal treatment to create a permanent cylindrical curve by systematically introducing dislocations into the crystals. These curved crystals are then stacked with the sign of the curvature alternating from crystal to crystal. The stack is then easily compressed to form a set of flat crystals, a process in which each is elastically deformed with a uniform strain gradient. This third method has been most successful, matching the best efforts to produce monochromators by plastically deforming large ingots very close to the silicon melting temperature.From the studies of curved crystals an explanation has been found for the often observed lack of symmetry in scattering experiments where symmetry is to be expected crystallographically. In general the orien­tation of a crystal is not constant across a crystal nor is it randomly distributed about a constant mean orientation. The leading term in the variation of orientation or mean orientation with position is equivalent to a curvature which destroys the symmetry of the scattering experiment. Such effects are usually observed as several percent changes in peak intensity on turning crystals through 180°. Understanding this effect has permitted a demonstration of an extreme case where the effect is a factor of five change in intensity on reversing the scattering path.The crystallographic problem of primary extinction, which arises from having too large regions of crystal perfection, is that it is difficult to know to what extent it is present. Making crystals thinner will elimi­nate secondary extinction problems, which arise from multiple scattering of neutrons, but the thinnest crystals are still much thicker than needed to eliminate primary extinction. Elastic strain gradients elimi­nate primary extinction in brittle materials such as silicon where it is possible to reach large elastic strains. But in metallic crystals such as iron quite small strains57Y E A R  Y E A RFig. 77. Annual publication rates on exotic atoms with the following particles: positive muon (y+), negative muon (y-), pion (ir-), kaon (K“), antiproton, E~ hyperon, etc. (p, I- ...) and with unspecified particles: (a) in absolute numbers, (b) in per cents.Y E A R  Y E A RFig. 78. Annual publication rates on exotic atoms concerning the following topics: test of quantum electrodynamics (QED), particle physics, atomic physics, solid state physics and chemistry, and methodical problems including review articles.58give plastic rather than elastic deforma­tions. The effect of primary extinction in magnetic measurements is such that it is rather certain that no magnetic intensity measurements are reliable to the level of one per cent. A demonstration of the effect of primary extinction has been made using iron crystals which are thin by the standards of secondary extinction. When the primary extinction is severe not only is the answer in error, but it even has the wrong sign.The magnetic contribution to scattering can be turned on and off by turning a magnetic field from perpendicular to parallel to the scattering vector. The intensity, whichdepends on the square of the magnetization, should be highest when the magnetic contribu­tion is turned on, but the result goes the other way because of the primary extinction. The presence of primary extinction can also be detected by producing small elastic strain gradients within the elastic limit. The present program is to increase the disloca­tion densities to reduce the primary extinc­tion while using the elastic strain gradient method to follow that reduction. The aim of this research is to accurately determine the temperature dependence of the static magnetic induction waves in ferromagnetic materials and in iron in particular.59THEORETICAL PROGRAMIntroductionThere has always been a commitment at TRIUMF to provide a core group of theoretical physicists. The intention is then that such a group will provide both a centre for high quality theoretical research and resource people for the various experimental groups.The research activities of the group members cover a wide variety of topics in nuclear and particle physics, many of which are directly related to the TRIUMF experimental program or the proposed kaon factory. In addition to their research activities the theorists are also involved in a number of other laboratory activities.Currently there are three permanent staff members in the group: H.W. Fearing, B.K.Jennings and R.M. Woloshyn. A fourth posi­tion is currently being advertised. J.N. Ng holds an NSERC University Research Fellowship. Research associates, some of whom are sup­ported through NSERC grants, are C.Y. Cheung, R.G. Ellis, G. Fogleman, P.A. Kalyniak (to September), K. Masutani (from October), O.V. Maxwell, L. Tiator (to October), R.E. Turner, W. Wilcox (from September). Long-term visitors who have been with the theory group are: R. Barrett, N. de Takacsy, S. Gurvitz,Q. Li, R. Machleidt, E. Veit, M. Zahir and J. Zofka. In addition there is regular interaction with theorists from the four associated universities.Several members of the theory group taught courses at UBC and supervised graduate students. Current graduate students are D. Hamilton, R. Workman and P. Zakarauskas.In addition we have had an NSERC summer student G. Starkman.Members of the theory group have been in­volved with the Long Range Planning Committee and the Kaon Factory Steering Committee. Organization of the regular TRIUMF seminars has also been handled by the theory group. This and the summer theoretical visitors program has brought a large number of visit­ing theorists to TRIUMF including:D. Atkinson J.M. Greben F.C. Khanna B. Blankleider K. Hashimoto R. LandauR. Crewther K. Holinde B. LawsonS. DasGupta A.N. Kamal V. MandelzweigM. Dillig J. Kapusta P. MeierM. Gomm B. Kayser M. MoravcsikM. Morita S. Rudaz H. TokiY. Nogami J. Shepard I. TownerT. Oka H. Sherif V. VentoK. Olynk D.W.L. Sprung H.V. Von GerambJ. Parmentola M. Stone H.A. WeldonA. Rinat R. Tegen S.S.M. WongR. Rodenburg A.W. Thomas M. YumawakiG. RossSpecific research activities undertaken during the past year are outlined below.Some of this work has been done in collaboration with theorists at other institutions, not all of whom are mentioned.The nucleon-nucleon potential and applications to nuclear matterNucleon-nucleon interaction (R. Machleidt, Bonn and TRIUMF; K. Holinde, Bonn and LAMPF)The oldest idea for a possible "fundamental" (or better "effective" from today's QCD point of view) mechanism mediating the nuclear force is the exchange of mesons between the two nucleons [Yukawa, (1935)]. In contrast to this historical fact the idea had never been carried through consistently. Therefore a meson-exchange model for the NN-interaction has been developed which is as consistent as by all means possible. It includes all meson exchanges (one meson and multiple meson) up to a total exchanged mass of about 1 GeV,i.e. up to the cutoff region.The set of diagrams considered contains in particular an explicit determination of the 2ir-exchange contribution to the NN-interac- tion taking into account virtual A-excitation and direct Tnr-interaction.This part of the model agrees quantitatively with results obtained from dispersion theory which in turn are based on the analysis of irN- and inr-scattering data. A detailed description of the lower partial wave phase shifts of NN-scattering requires, however, (apart from the well-known OBE contributions) the contribution of further irreducible dia­grams containing also heavy boson exchange, in particular the combination of it and p .  In the framework of the consistently extended model an accurate description of the NN-scat­tering data below 300 MeV laboratory energy as well as the deuteron data is achieved.60The quantitative results are definitely superior to well-known simplified boson- exchange models i.e. the one-boson exchange.Theoretical pred ictions fo r the n-p spin correlation param eter Ann (R. Machleidt, Bonn and TRIUMF)The measurement of the spin correlation parameter Ann has been proposed by an experi­mental group at TRIUMF. Therefore the theoretical predictions for this particular observable of NN-scattering at 210 and 325 MeV laboratory energy is evaluated for two modern meson-exchange NN-interactions, namely the Paris and the Bonn potential.It turns out that the predictions of these two models deviate appreciably for the observable under consideration. The reason for the discrepancy can be traced back to an appreciable difference in the fit of the 3D2 phase shift. The Paris potential (as well as all other meson-theoretic models, except the most recent complete Bonn model) overshoots the 3D2 phase shift in the range of 2 00- 300 MeV lab energy by “5-7° compared to the latest phase-shift analyses of Arndt et al. and of Bugg and coworkers. The reason for the quantitative fit of the 3D2 phase shift in the Bonn model is due to the inclusion of irreducible two-boson-exchange diagrams of ir- and p-exchange. Therefore, in turn, the dif­ferent predictions for the Ann demonstrate the effect of the irp diagrams in a directly measurable observable. The experimental re­sult will therefore give an indication about the physical relevance of those diagrams being omitted in most theoretical models.Two-meson exchange three-nucleon potentials  (R. Ellis; S. Coon, Washington; B. McKellar, Melbourne)In recent years considerable attention has been devoted to the study of three-nucleon potentials, in particular the two-pion- exchange three-nucleon potential, denoted it—irE3BF. Much of the reason for this inter­est is the hope that 3BF's may help to cure several outstanding problems in nuclear physics: the triton binding energy, the 3He form factor and the binding energy of nuclear matter. A comprehensive treatment of the imE3BF has been made by Coon et al. [Nucl. Phys. A317, 242 (1979)] using the techniques of current algebra and PCAC. We have recent­ly made an analogous treatment of the irpE3BF and the ppE3BF [Ellis et al., TRI-PP-83-77] and have studied their effects on the bindingenergy of nuclear matter.The irpE3BF was constructed using the tech­niques of current algebra, PCAC, VMD and Ward identities to obtain a low energy extrapola­tion for the off-mass-shell pN + irN amplitude to which the irpE3BF is proportional. To first order in a typical momentum over mass expansion the pN -*■ ttN amplitude was uniquely and model independently determined (in fact it was the p analog of the Kroll Ruderman result). At higher order in such an expan­sion the A (1232) contributions were impor­tant. The A(1232) entered the pirE3BF by the assumption that it dominated the dispersion integral for the pN + axial vector N ampli­tude. This is a well-justified, but never­theless, model-dependent assumption. Conse­quently the pirE3BF has model-independent and model-dependent contributions.The pp3BF was also constructed using similar techniques and the same general structure was observed: lower-order terms were model inde­pendent while the higher-order terms are model dependent again introducing theA(1232).In order to estimate the importance of the tttt , pTT and ppE3BF's we calculated their con­tribution to the binding energy of nuclear matter at the empirical density (kf=1.36 fm-1) using first- and second-order perturbation.The three-nucleon potential was considered a perturbation on the usual two-nucleon potential. The results are displayed below:model first secondindependent? order order■miE3BF yes -2 . 1 1 -2.03pirE3BF yes 0.45 -no (A) -0.43 1.96ppE3BF yes -0.16 -no (A) 0.03 -0.08Total -2 . 2 2 -0.15We observe that the contributions to nuclear matter seem to be converging quite well with respect to the mass of the exchanged mesons. Consequently future calculations should not be concerned with heavier exchange mesons. However, the pirE3BF provides a significant reduction to the itttE3BF and it should be included in future 3BF calculations.R elativistic nuclear m atter calculations  (R. Machleidt, Bonn and TRIUMF; R. Brockmann, Regensburg)The longstanding problem of nuclear matter is reflected in the fact that no theories nor61calculations to date can reproduce the cor­rect empirical binding energy and saturation density simultaneously; the theoretical satu­ration points are lying on a band (the 'Coester line') which does not contain the empirical point.In usual nuclear structure calculations applying meson-exchange forces the origin of the NN potential is forgotten once the stage of the application of that potential to the nuclear many-body problem is reached. This may be the origin of the problem outlined in the first paragraph.The meson-exchange diagrams building up the nuclear force are evaluated for the case of NN scattering using - correctly - free Dirac spinors for the interacting nucleons.However, in the nuclear many-body problem the nucleons are not free; a common attractive potential, to be determined selfconsistently, is felt by the nucleons and is to be taken into account in the Dirac equation determin­ing the Dirac spinors to be used. First results for nuclear matter following the scheme sketched here show that in the frame­work of this extended nuclear matter theory the empirical binding and density can be explained simultaneously. A similar approach to nuclear matter can be found in the work of Shakin and coworkers.Bremsstrahlung and off-shell processesProton-proton brem sstrahlung(H. Fearing, R. Workman)Work has continued this past year on the pro­gram of theoretical calculations outlined last year which is being carried out to understand the proton-proton bremsstrahlung (ppy) process and to provide reliable predic­tions for comparison with data to be obtained in the new TRIUMF experiment (208). A great deal of progress has been made and the calcu­lations are just beginning to show some interesting results. Recall that the main aim is to develop a modern potential model calculation which uses one of the newer potentials such as the Paris or Bonn poten­tial and which includes a number of refine­ments which have been shown to be important in individual investigations but which have never been combined into one calculation.Our approach is to solve the momentum space Lippmann-Schwinger equation to obtain the on- shell NN amplitudes and the half-off-shell extension functions for a given potential.These off-shell amplitudes are combined with vertex and propagator factors and a gauge term to get the full ppy amplitude. We have so far included relativistic spin corrections which are known to be important at these en­ergies, Coulomb effects and one-pion exchange in higher partial waves. All kinematics are done relativistically, and frame transforma­tions of the NN amplitudes, which are not normally included, have been incorporated.The calculation is done in the centre of mass so as to minimize gauge corrections, but can also be done in the lab. Both cross section and analysing powers are calculated and co- planar or non-coplanar geometries can be used.At present the calculation is working for the usual Reid soft core (RSC) potential, which is valuable for test purposes, for a RSC potential extended to higher partial waves, and for the Paris potential as parametrized by the Paris group [Lacombe et al., Phys.Rev. C 2l_, 861 (1980)]. In each case the potentials are supplemented by one-pion exchange in the higher partial waves.Preliminary results are rather interesting and indicate a lot of sensitivity in both cross section and analysing power to the various ingredients. Relativistic spin cor­rections are very important at these energies as is the inclusion of one-pion exchange for the higher partial waves. Coulomb is not too important, however, and, at least for the cases tried so far, there are still the large differences between the potential model cal­culations and the on-shell soft photon calcu­lations, particularly in the analysing power, which were seen at lower energies and which in part motivated the new TRIUMF experiment.Several further refinements are intended once the program is complete for the various potentials. Double scattering terras are at present incorporated only to 0 (k°) via the gauge term, and gauge terms coming from the momentum-dependent pieces of the potential have not yet been included. Eventually also we want to explore more carefully off-shell sensitivity by using phase-equivalent transformations.Am plitude structure o f off-shell processes  (H. Fearing; M. Moravcsik, Oregon; G. Goldstein, Tufts)Off-shell processes play an important role in many areas of atomic, nuclear and particle physics; in particular all of nuclear physics is based on the two-nucleon interaction off62shell. To learn about the off-shell interac­tion a number of reactions have been suggested as, for example, for the nucleon- nucleon case, (p,2p) reactions, pd breakup and pp bremsstrahlung. In view of this it is important to explore the amplitude structure of off-shell processes and to see if the dif­ference in on- and off-shell amplitude struc­ture can be used to obtain off-shell informa­tion in an isolated manner as has been sug­gested [Moravcsik, Phys. Lett. 65B, 409(1976); Fearing Phys. Rev. Lett. 42, 1394(1979)].First we have examined the meaning of off- shell amplitudes in relativistic field theory and in a nonrelativistic potential approach. Then we investigate how the general structure of the transition amplitude changes off shell. There are three possible ways in which such changes might manifest themselves.First there will be additional scalar variables, one extra for each off-shell leg. Secondly there may be additional amplitudes off shell. It turns out that in the nonrela­tivistic approach there are actually no addi­tional amplitudes. The correct number can be obtained by counting helicity amplitudes. In the relativistic field theory approach, how­ever, additional amplitudes can be formed off shell. These arise because of the additional degrees of freedom due to the particle-anti- particle nature of a virtual particle and because in a field theory approach a virtual particle of spin S actually contains spin components S, (S-l), (S-2) ... . The correct number of amplitudes can still be obtained by counting helicity amplitudes, but all spin components must be included in the count as well as a factor of two to account for the antiparticle part of virtual fermion lines.The third way amplitudes can differ off shell is in the way various symmetry constraints apply. Parity applies in the same way on or off shell. However, time reversal invariance is different off shell since time reversal relates processes with initial and final states interchanged. Thus for on-shell elas­tic amplitudes there are relations among the amplitudes which constrain them. For the off-shell case, just as for reactions, time reversal simply relates amplitudes for different processes and so does not reduce the number of amplitudes. Thus we find that there may be amplitudes appearing in the general off-shell amplitudes which vanish on shell by time reversal, but which are present off shell, even when time reversal holds.Finally we have investigated how one might extract off-shell information from an actual physical process. Our conclusion is that it is impossible to do this in a model-independ­ent way. One must always have some sort of model for embedding the desired off-shell amplitudes in the physical amplitude for the overall process. However, given such a model, the off-shell amplitudes can be extracted. Details are given in TRI-PP-83-44.Nuclear reactions and electromagnetic effectsIntermediate energy p ro ton-12C elastic scattering (Q. Li; S. Wong, Toronto)Recent experimental data on intermediate energy p-12C elastic scattering [Meyer et al., Phys. Rev. C 27_, 459 (1983)] show an anomalous rise in the differential cross section at back angles. This phenomenon is not explainable by a Woods-Saxon type optical potential, no matter how one adjusts the parameters. Also a KMT optical potential, which uses an antisymmetrized on-shell NN t- matrix as input, fails to reproduce the back- angle data.Large-angle behaviour seems to be sensitive to a variety of mechanisms such as nucleon exchange, Pauli effect, nucleon-nucleon correlation, isobar excitation, and so on.On the other hand, when we examine the differential cross sections for p-^He elas­tic scattering in the same energy region, we also find a similar rise at back angles.This indicates that the mechanisms above mentioned are also present in the large angle behaviour of p-'+He scattering. Therefore, if we utilize the p-^He amplitude as a basic input to calculate p-12C scattering, it might be possible to explain the phenomenon of rising differential cross sections at large angles. This calculation is in progress.Electrom agnetic effects in the ratios  (pd~tK +)/(pd^H en0) and (nd-3H en-)/(nd~tnc) (H. Fearing, L. Tiator)A recent measurement of the cross section ratio R i cr(nd •* 2Heir-)/0 (nd tir°) has been made [Dutty et al., Proc. Few Body X, Karlsruhe, p.102 (1983)] giving the result R = 1.76±0.09 averaged over an energy range 330 < Tn < 570 MeV. Isospin invariance, however, would predict R = 2. It is thus of interest to try to understand the reasons for this discrepancy.63Before looking for exotic effects it is necessary to examine a number of well known electromagnetic correction effects which would lead to a deviation of R from 2. We have examined some of these effects in the context of a distorted wave impulse approximation model of pd * tir+ which was developed earlier [Fearing, Phys. Rev. C _U, 1210 (1975)].Most such "known" effects can be traced to the mass differences between the ir+/ir-, p/n, or 3He/t pairs, which affect all of the in­gredients of the calculation. When the proper masses are put in there are small differences in the phase space, in the kine­matics leading to the choice of energy at which to evaluate the impulse cross section pp -* ir+d or np ■> ir°d and thus in the value of the cross section used and in the kinemat­ics used for calculating nucleon and pion distortion. The difference in size of 3He and t also affects the pion distortion. The major effect, however, according to the one previ­ous calculation [Kohler, Phys. Rev. 118, 1345 (I960)] arises from the differences in 6He and t wave functions: this must be put in with care, however. The 3He and t form factors are quite different, but most of the difference is due to the different combina­tions of isoscalar and isovector form factors appearing, rather than due to the real dif­ference in the wave functions, which arises only from Coulomb effects.So far all of these effects have been included in a preliminary way and all produce variations in R at the few per cent level.In the coming year we intend to complete this calculation of "known" effects and compare with the experiment in a more detailed way than just via an average R to see if there is any residual isospin symmetry-breaking effect.Large angle inclusive nuclear reactions  (S. Gurvitz)We have analysed inclusive nuclear reactions tt+A •* tt '+X and p+A -*■ p'+X for the incident energies 200-300 MeV and scattering angles > 90° in the kinematical region below pion production but above the discrete excitation of the nucleus. Assuming the single scattering mechanism we extracted the one- nucleon momentum distribution from these data. We found that the proton and pion data reproduce the same momentum distribution which coincides with that found from the electron data. It strongly indicates that in the region of large momentum but small energy transfer the projectile behaves like a weakprobe which undergoes only one scattering on the target nucleon. Predictions for the analysing power for 300 MeV proton-nucleus inclusive scattering have been done.Pion photoproduction and the structure o f  light nuclei (L. Tiator; L. Wright, Ohio)Pion photoproduction and the inverse reaction of radiative pion capture are of particular interest in medium energy nuclear physics because they show a sensitivity on both nuclear and pion wave functions which cannot be reached by more direct methods like electron and pion scattering. Furthermore medium effects on the elementary y ,ir-reaction from bound nucleons can be studied. We have investigated a momentum space calculation for a distorted wave impulse approximation. In this way all operator non-localities arising from nucleon- and pion-pole diagrams as well as A-excitation can be treated exactly. The pion waves are distorted by an optical poten­tial parametrized in the way of Strieker, McManus and Carr. A new way of analysing such reactions over a wide range of light nuclei has been developed which decomposes the differential cross section in partial cross sections classified by a specific transition spin S', angular momentum L and total multipolarity J. This method is well suited for proposing further experiments which can filter out different multipolari­ties in nuclear transitions. As an applica­tion we have studied 1 3C(y ,ir“)1 3Ng.s> which was recently measured at NIKHEF and is a combination of EO and Ml multipoles. There we found indications that in monopole transitions the Blomqvist-Laget amplitudes, which are in wide use as input for the elementary process, drastically overestimate the A-excitation for 50 MeV pion energy.The role o f the A(1232) in the (y,p) reaction  (C. Y. Cheung; B. Keister, Carnegie-Mellon)Except for the d(y,p)n data, other data of (y,p) reactions on heavier targets show no characteristic peak of the A (1232) resonance at intermediate energies. This raises the question of whether the A plays an important role in the (y,p) reaction mechanism. On the theory side, two major calculations reported contradictory conclusions [see Londergan and Nixon, Phys. Rev. C 1J9, 998 (1979); Gari and Hebach, Phys. Rep. 72_, 1 (1981)]. In this work we investigate the role of the A (1232) resonance in the reactions ‘+He(y,p)3H and 1 60(y,p)1 5N. Our approach is similar to the isobar-doorway model used to calculate the64(p,ir) reaction by Keister and Kisslinger [Carnegie-Mellon preprint (1983)]. We include both the one-nucleon term and the two-nucleon A-rescattering term. The A non­locality is neglected by fixing the A sub­energy. The outgoing proton wave is calculated with an optical potential. We include only those contributions which are individually gauge invariant, i.e. the mag­netic currents. The reason is two fold. On the one hand it is not clear how to include other contributions in a gauge invariant way. On the other hand, we feel that what we do is adequate for the purpose of our work.Preliminary results indicate that at Ey K 300 MeV the A-rescattering contribution is comparable with the data, implying that A ex­citation is indeed an important ingredient of the (y »p ) reaction mechanism. We also find that the one-nucleon contribution, while dominant at Ey < 100 MeV, is negligible in the resonance region. Similar conclusions have been reached by Londergan and Nixon. However, our result about the A contradicts that of Gari and Hebach, who have claimed the A contribution is small at all energies.Electron scatteringPion effect in deep inelastic polarized  lepton polarized nucleon scattering  (C. Y. Cheung)The lepton-nucleon asymmetry measured in a deep inelastic polarized experiment is con­ventionally defined as_ dg(H - H )  (1)N dcr (++ + ++) *where ++ and ft indicate respectively anti­parallel and parallel beam and target spins. Determination of the asymmetry in the scaling region yields knowledge about the distribu­tion of the target spin among different quarkspecies; it is thus very useful in testing various theoretical models of nucleon spin structure. We note that in various models the effect of the pion cloud surrounding the proton has been ignored. Pionic contribu­tions have been discussed in unpolarized deep inelastic lepton-nucleon scattering [Sullivan Phys. Rev. D 5_, 1732 (1972); Thomas,Phys. Lett. 126B, 97 (1983)]. In this work we show that the effect of the pion is also important in deep inelastic polarized lepton- polarized nucleon scattering. In the follow­ing we shall for simplicity restrict ourselves to the case of electron-proton scattering.Fig. 79. Dilution of the nucleon polariza­tion due to pion emission in deep inelastic polarized electron-polarized nucleon scattering.The basic idea of this work is depicted in Fig. 79. That is, before the proton absorbs the virtual photon it can emit a pion, and at the same time flips its spin. (Note that in a deep inelastic process the pion does not have to be on its mass shell.) The net effect would be an effective dilution of the proton target polarization. We shall examine the above situation from a slightly different point of view. Since a proton is surrounded by a pion cloud, we can expand a polarized physical proton state by states of definite numbers of pions. ThusIp+ V ys . = a |p+> + B° ° lir° p+> ++ 8_0 |tr+n+> + 8__|ir+n4.> , (2 )where we have truncated the expansion at one pion, which is a good approximation. The normalization condition implies I ^  = 1-a2 and it is_not_ hard to see that 80 0 :80 _:8_0 : 3__ = l:v'2 :/2 :2 .Because the pion has zero spin, the process in which the virtual photon is absorbed by the pion does not contribute to the electron- proton asymmetry. It is then immediately clear that, due to the incoherent nature of deep-inelastic scattering, the proton (or valence quark) polarization is effectively diluted by the pion cloud. That is, the effective polarization of the proton, as seen by the photon, is actually cx2-B2 0 < 1 .  With a bag radius of =0.9 fm in the cloudy bag model the dilution factor a2 -f32 0 - 0.7, which is a large effect. The pionic dilution effect is strongest at small values of the scaling variable x < 0 .2 ), where the sea density is significant. In this region the pion cloud alone would reduce the valence quark polarization by about 30%. As x + 1 only the zero pion state is expected to con­tribute in a deep inelastic process, so that the pion cloud effect becomes negligible [see Cheung, TRIUMF preprint TRI-PP-120 (1983)].65OJ (MeV)Fig. 80. (a) The differential cross sectionat = 1.5 GeV and 9 = 60° for inclusive electron scattering from 3He as a function of energy transfer w. (b) The corresponding longitudinal asymmetry for two values of the target polarization angle 8 . The different curves (labelled by values of p) correspond to different choices of the neutron electric form factor.Fig. 81. Asymmetries as a function of target polarization angle 8 for (a) polarized elec­tron-polarized neutron scattering, (b) inclu­sive polarized electron scattering from polarized 3He at the quasi-free peak. In both cases E^ = 1.5 GeV and 9 = 60°, and the different curves (labelled by values of n) correspond to different choices of the neutron electric form factor.Quasi-elastic scattering o f po larized electrons  on polarized 3He (B. Blankleider, Indiana; Ft. Woloshyn)Cross sections and asymmetries for quasi­elastic scattering of longitudinally polarized electrons on polarized 3He were calculated in a model consisting of impulse approximation plus closure approximation to sum over final states. At the quasi-elastic peak the asymmetry is found to be dominated by scattering from the neutron and judicious choice of target polarization allows sensitivity to either the neutron's electric or magnetic form factor to be maximized.Away from the quasi-elastic peak the protons contribute to the asymmetry.Near the quasi-elastic peak the contribution of the protons to the asymmetry is very small. Effectively 3He looks like a neutron target except that the asymmetry is reduced in magnitude due to the large proton contribution to the spin averaged cross section. Typical results (at incident electron energy 1.5 GeV) are shown in Fig. 80 for different choices of the neutron electric form factor which was parameterized by(l+pnx)(l+Q2 /B) 2with B = 0.71 (GeV/c) 2 and x = Q2 /4M2 .By choosing the direction in which the 3He target is polarized it is possible to enhance the sensitivity of the asymmetry at the quasi-elastic peak to either the neutron electric form factor Gg or the magnetic form factor Gjj. Furthermore the asymmetry goes through zero as a function of 3He polariza­tion direction (Fig. 81) precisely in the region where it is least sensitive to uncertainties in G^ J. The zero crossing of the asymmetry depends essentially only on Gg which could provide a new way of determining this form factor.As one moves out into the tail of the quasi­elastic peak the contribution of the protons to the asymmetry increases. This contribu­tion depends on the fact that the probability of finding a proton of high momentum in 3He with spin parallel to the total spin is not equal to the probability of having a proton with antiparallel spin. We find that this66difference in momentum distributions is determined by only two small components of the 3He wave function, one mixed symmetry S- state (La = £. = 3 = 0 ) and one D-state (La = 2, £a = 0). The contribution of these two states to the asymmetry tend to cancel. At lower incident electron energies (a few hundred MeV), and at low energy transfer the D-state contribution wins out and the asymmetry approaches 0.3, the largest we have found in any of our calculations.Final state interaction in e A ~ e ’X  reactions (S. Gurvitz; J. Tjon, Utrecht; S. Wallace, Maryland)Electron-nucleus inclusive scattering is usually treated in the plane wave impulse approximation which neglects the interaction between the struck nucleon and (A-l) spectator nucleons in the final state. Using this approximation one obtains a simple formula for inclusive cross section which allows the extraction of one nucleon momentum distribution, n(p), directly from eA+e'X date. In particular, one extracts the tail of n(p) (p > 200 MeV/c) from the measurements in the kinematical region of small energy transfer (D) and large momentum transfer (q) to the nucleus. The tail of n(p) provides direct information on the nucleon correlation function. However, it is known that the plane wave approximation cannot be used for analysis of the data in this kinematical region.We developed a new approach to eA -*■ e'X reactions which accounts for the final state nuclear interaction. It is based on a general relation between the off-shell scat­tering amplitude and the ground state nuclear wave function. For the momentum transfers q > R- 1 (R is the nuclear radius) our final result has the same simple form as that in the plane wave approximation. However, the dependence on the external variables (v, q, ...) is quite different. We have analysed available e+(3He,LtHe,litN)-»-e,+X data and extracted the tail of n(p) (p>200 MeV/c) for 3He, ^He, ll*N. We found that n(p) falls down with p much faster than n(p) extracted from old analysis without final state interaction. In the case of 3He, our n(p) is in agreement with the results of the three- body calculations.Electro-disintegration o f 2H with po larized  beam and target (C. Y. Cheung, R. Woloshyn)Due to the lack of free neutron targets, measurement of neutron electromagnetic form factors, particularly the neutron electron electric form factor (Gg), is quite difficult. In this study we calculate the asymmetry:_ dg(-H )-dq(-H ) do(if)+d0 (++)for the exclusive and inclusive reactions ci(e,e'n)p and cl(e,e')np. Since we are interested in the neutron electric form factor, we want to minimize the sensitivity to the nuclear wave function. The calcula­tion of an asymmetry (i.e. ratio of cross sections) helps and we further choose quasi- free scattering kinematics. This in combination with high momentum transfer also reduces the importance of final state interactions, exchange current and off-shell effects [see e.g. Arenhovel, Nucl. Phys.A384, 287 (1982)]. In particular, we note that for the exclusive reaction, with the detected neutron momentum equals that of the electron momentum transfer, the deuteron D- wave component does not contribute, and off- mass-shell effects are minimal. In this situation the deuteron essentially provides a free neutron target. We adopt the parametrization:CT5 = “hnT (l+nT)- 1 (l+Q2 /B) - 2 (1)where t=Q2 /4M2 , B=0.71 (GeV/c)2 , and n is a parameter. The asymmetry for the exclusive reaction at fixed kinematics is shown in Fig. 82 [Cheung and Woloshyn, Phys. Lett. 12715, 147 (1983)]. We see that A is large, and there is considerable sensitivity in Gg. Note also that A changes sign at a certain deuteron polarization angle a0. This is desirable because the zero crossing of A may be determined more accurately than its abso­lute value and thereby make a better determi­nation of gJ}. In the inclusive case thensensitivity of the asymmetry to Gg is suppressed by the large proton contribution.67aFig. 82. Exclusive electron-deuteron asym­metry at fixed kinematics (k = 1 GeV, k' = 0.65 GeV, 6 = 60°) as a function of direction a of polarization of the deuteron target. Different curves correspond to different choices for the neutron form factors (see Eq. 1).Pion nucleus interactionsPion nucleus optical potential (Q. Li)It has been known for some time that the Kisslinger potential works well in the resonance region and fails to agree with the data in the low energy region. This is because the nuclei are "black" in the res­onance region and various effects of nuclear structure as well as the pion true absorption become more important in the low energy region. From the point of view of the clus­ter structure of the nucleus, we can con­struct multiple scattering theory by using the clusters as scatterers instead of the nucleons and utilize the w-cluster amplitudes as the basic input, so the various effects above mentioned can be "automatically" in­cluded a certain extent. Therefore, it is expected that better results can be obtained than the one from tt-N amplitudes. We have constructed the optical potential in the a- particle model of the nucleus. The calcu­lated results show better agreement with the data, particularly in the low energy region, than those calculated with the Kisslinger potential. [Nucl. Phys. A, in press]Pion scattering on 12C at 100 MeV(K. Masutani; T Takaki, NIKHEF)The measurement of ir~ scattering on 12C at an incident energy of 100 MeV has been recently performed at SIN [Antonuk et al., SIN PR-83-12]. In addition to elastic scattering, the data of inelastic scattering to several excited states such as 2+ (4.4 MeV) and 3” (9.6 MeV) have been taken for a large angular range. We have analysed these data with the A-h formalism, which has been applied successfully to various ir-nucleus reactions in the A-resonance region.Following Lenz, Thies and Horikawa [Ann.Phys. 140, 266 (1982)], the inelastic scat­tering amplitude is given in the "modified” distorted wave impulse approximation (modi­fied DWIA), in which medium corrections are included in the same way for both elastic scattering (distorted wave) and the transi­tion operator. This is one of the main dif­ferences between the A-h formalism and more conventional phenomenological DWIA approaches. Note that the description of the inelastic scattering does not contain any free parameters, once phenomenological "spreading potential", which accounts for the coupling of the A-h states to more complicated states, is fixed using the elastic scattering data.We have calculated elastic and inelastic scattering using the standard energy- independent spreading potential given by Horikawa et al. [Nucl. Phys., A345, 386 (1980)]. The theoretical predictions for 2+ and 3" excitations are in surprisingly good agreement with the experimental measurements. However, the description of elastic scat­tering is unsatisfactory as was already seen to some extent in the previous work.We have investigated the origin of the discrepancy in elastic scattering. We have varied the spreading potential so that it accurately reproduces the elastic scattering data. The experimental measurements require a strong positive imaginary spin-orbit inter­action. However, this interaction destroys the agreement with inelastic scattering, and strong energy dependence makes the interpre­tation of the spreading potential difficult.One additional mechanism we have considered is a strong repulsive ir-2N interaction, which is frequently used in the analysis of pionic atoms and low energy scattering. This non­resonant correction improves the theoretical results for elastic scattering very much.When we treat elastic and inelastic scat­tering consistently, however, this inter­action also destroys the agreement with inelastic scattering.68We emphasize that the simultaneous analysis of elastic and inelastic scattering provides severe constraints in the theoretical description. Our theoretical results suggest that other additional important dynamical ef­fects beyond those contained in the standard A-h calculations exist.The role of three-nucleon absorption processes In the A(jt+,d)A -2 reaction (C. Y. Cheung, O. Maxwell)After several years of intense study of (x,p) reactions in nuclei, there has recently been an awakening of interest in more complex pion absorption processes, involving, for example, deuteron production. Angular distributions have been obtained for the reaction 1 2C(TT+ ,d)10C at laboratory pion energies of 47 and 65 MeV [Doss, doctoral thesis, Carnegie-Mellon University, 1980]. This reaction has also been the subject of theo­retical investigations, along with the analogous reactions on 1 6 0 , 1 8 0 , and several isotopes of nickel. To date these theoret­ical investigations have concentrated on the impulse contribution, where absorption of the incident pion on a single nucleon line leads directly to the ejection of a deuteron from the target nucleus, and where momentum and energy balance are provided by the Fermi motion of the ejected nucleon pair in the target. The strength of this contribution is extremely sensitive to distortion effects. Betz and Kerman [Nucl. Phys. A345, 493 (1980)] found in a DWBA calculation that the combined influence of pion and deuteron dis­tortions can reduce da/dfi at forward angles by as much as two orders of magnitude. It also appears from this calculation that the impulse term primarily involves nucleon pairs coupled to spin zero in the target nucleus.In view of the large momentum transfers characterizing (Tr+ ,d) reactions (~750 MeV/c at threshold), three-nucleon processes, involving excitation of a A resonance at the initial absorption vertex followed by a vir­tual meson exchange with one of the nucleons in the residual nucleus prior to the ejec­tion of the deuteron, could be an important, if not the dominant, ingredient of the reac­tion mechanism. By involving three nucleons, such a process provides a more efficient means for transferring momentum and thus may be considerably less sensitive to distortion effects than the impulse term. Moreover, the rather different spin structure of the three- nucleon absorption operator, compared withthat of the impulse term, could modify the spin dependence of the reaction matrix ele­ments. A numerical investigation of three- nucleon absorption contributions to the A(Tr+ ,d)A-2 reaction, specifically addressed to these questions, is currently in progress.The quark model and QCDGluon effects in isospin-violating meson mixing (C. Y. Cheung)It is now well known that the quark- (anti)quark effective potential from one- gluon exchange is important in understanding the hadronic spectrum [DeRujula et al., Phys. Rev. D 12_, 147 (1975)]. In particular, it has been shown that the spin-spin hyperfine piece of the one-gluon-exchange potential is crucial In explaining the origin and signs of the A-N and A-E mass differences. The effective one-gluon-exchange potential is actually charge asymmetric, because it depends explicitly on quark masses which are themselves flavour dependent. Recently, it has been shown that the spin-spin hyperfine interaction, because of its quark mass dependence, is very important in under­standing mass differences within isomultiplets [Chan, Phys. Rev. Lett. 51, 253 (1983)]. Furthermore, since the effective one-gluon-exchange potential is charge asymmetric, it also contributes to the isospin-violating mixings of neutral mesons. However, this fact is often ignored in most recent works [Jones et al., Nucl. Phys. B 155 409 (1979); Coon et al., Phys. Rev. C 26, 562(1982); Langacken et al., Phys. Rev. C 25_1194 (1982)]. The purpose of this work is to present a more careful and self-consistent analysis of the role of gluon induced charge symmetry breaking (CSB) mechanisms in AI = 1 meson mixings.Particle mixing is a well known phenomenon in particle physics; it usually signals the breaking of certain symmetries. For instance, the p-w, n-n and ir-n' mixings are examples of mixing due to the breaking of isospin symmetry. These three mixings are important in nuclear physics because they involve low-lying mesons that can be exchanged between two nucleons. The exchange of mesons of mixed isospins gives rise to charge asymmetric nuclear forces. Of the three mixings mentioned above, experimental evidence is well established only for the p-w mixing.69In this work the relatively well known p-to mixing matrix element is used as an input to fix the CSB parameters in our calculation.The tt —n and it —n' mixing matrix elements are predicted to be M^n = -5.79±1.21 MeV and M ^ ' = -1.66±0.76 MeV. We have included all important CSB mechanisms on the quark level, and it is found that charge symmetry induced by quark-gluon interactions plays an impor­tant role in all of the three mixings examined [see Cheung, TRIUMF preprint TRI-PP-83-115 (1983)].Convergence behaviour in chiral bag models and the pion-nucleon scattering amplitude  (B. Jennings, O. Maxwell)In recent years chiral bag models and related models have generated considerable theoretical activity in intermediate energy physics, in part by providing a natural description of pion-nucleon scattering and, in the SU(3) generalization, kaon-nucleon scattering. Many of the results obtained with these models have been based on the assumptions that (i) terms in the Lagrangian of lowest order in the quark-pion coupling strength suffice for the evaluation of physical observables, even when amplitudes are evaluated to higher order; and (ii) only conventional baryon states, such as the nucleon and the A33 resonance, need be included in intermediate state sums. To date, neither of these assumptions has received a convincing justification in the literature; nor has the degree to which chiral bag model successes depend upon them been adequately investigated.In an attempt to partially rectify this situation, two versions of the chiral bag, involving surface and volume quark-pion interactions respectively, have been examined in connection with the pion-nucleon (ttN) scattering amplitude. The two interaction Lagrangians are related by a unitary chiral transformation of the quark fields, which, when the Lagrangians are expanded in powers of the interaction strength, f^1, guarantees their equivalence at the tree level. By means of successive partial integrations employing the Dirac equation and the bag boundary conditions, this equivalence has been demonstrated explicitly for the lowest order (order f^2) ttN amplitude.Despite their equivalence, the convergence behaviour exhibited by the two Lagrangians with respect to intermediate state sums is quite different. To make the differencesexplicit, the lowest order ttN amplitude was studied numerically in some detail with both versions of the Lagrangian. We found for the surface interaction Lagrangian that intermediate radial and orbital excitations and intermediate antiparticle states are both important; without cancellations provided by the latter, in fact, the intermediate state sums do not even converge. By contrast, the volume Lagrangian exhibits much better convergence behaviour in the ttN amplitude due to the presence of a contact term which partially sums up the intermediate state series associated with the surface interaction. This contact term, which represents a second order contribution to the volume Lagrangian, actually makes the largest contribution to the order f^ 2 s-wave ampli­tude, a contribution substantially exceeding that from first-order terms in the Lagrangian in apparent contradiction with the first of the assumptions mentioned above.Quantum fluctuations in the bag and nucleon observables (O. Maxwell; V. Vento, Valencia)Since its original conception, the hadronic bag model has received a good deal of attention as an alternative to nonrela- tivistic quark models of hadron structure.To date, most of the theoretical work has been connected with the restoration of chiral invariance in the model. Quantum fluctua­tions in the quark fields induced by gluon- mediated processes have received much less attention, although they are no less significant.The effect of such fluctuations on static nucleon observables - weak current coupling constants, charge radii, and magnetic moments - have been investigated within a time-dependent, perturbative formalism using the static, spherical cavity approximation. This treatment differs from previous work in that (1) all relevant contributions to second order in the QCD coupling are generated systematically from the time-ordered perturbation series and included in the numerical treatment; and (2 ) the intermediate state sums are carried out over a complete set of states consistent with parity and SU(2) coupling rules. The diagrams which are evaluated include 2-body diagrams involving a gluon exchange between two different valence quarks and 1-body vertex correction diagrams. The latter diagrams exhibit the same sort of logarithmic divergences that are associated with loop integrals in the continuum theory and thus require regularization and70renormalization. The regularization is effected by means of a regularization mass introduced into the gluon spectrum. After isolating and removing the cut-off dependent contributions, the finite part of the renormalization is fixed by requiring that the renormalized vector and axial vector quark-current couplings be free of gluonic radiative corrections inside the bag where a global SU(2) x SU(2) chiral symmetry is exactly realized in the Wigner-Weyl mode (for zero mass quarks with Goldstone fields excluded from the interior).This procedure yields results for the nucleon axial vector coupling strength and the squared EM and axial charge radii that are non-negligible, but small compared with the zeroth order (MIT) results. This supports the concept of the bag as a bounded, perturbative region within a non-perturbative vacuum. The results obtained for the magnet­ic moment corrections, however, are much too large. Through an explicit consideration of counter terms in the Lagrangian, the large magnitude of the magnetic moment corrections can be traced to a violation of the Ward- Takahashi identity, which, in turn, indicates a breakdown in the Lorentz covariance of the renormalization prescription utilized. If this breakdown is associated with the static nature of the bag model as it is usually employed, it represents a fundamental diffi­culty for the bag model in suggesting that meaningful finite results cannot be obtained for all observables beyond zeroth order in perturbation theory on the basis of a single renormalization.Order as corrections to nucleon axial form  factors in the bag m odel (B. Loiseau, Orsay; O. Maxwell; W. Cottingham, Bristol)Recently, the nucleon axial form factors, defined by the relation between nucleon spinors,< s ' I Ay ( P , P ' ) | = U ( p ' , s ' ) | G A ( q 2 ) y ] iY5 +  G p (q2 )x Im t5 + 1 Gx(q2) “ 2iT “  y5] u (p>s> »where q is a momentum transfer, have become the subject of bag model calculations that attempt to account for the observed q2-dependence in terms of the underlying quark structure of the hadrons. Generally, the role of the quark-pion interaction in chirally invariant models has beenemphasized, but it is of interest also to ascertain the effect of gluon-mediated interactions on the form factors.As a step in this direction, a model has been evolved in which the form factor q2- dependences are attributed to lowest-order valence quark contributions (without pions) supplemented with first-order (in a c) gluon exchange corrections. A fixed cavity approximation is employed in which the cavity wave functions represent superpositions of nucleon states in relative motion. The QCD corrections consist of finite, 2-body gluon exchange terms plus 1-body vertex corrections, which diverge logarithmically.The latter divergences are handled by means of a Pauli-Villars regularization followed by a finite renormalization in which gluonic radiative corrections to the renormalized axial vector quark-current vertex are required to vanish in the limit q2 0 .Our results indicate that the axial vectorform factor, GA , is well represented, both in its magnitude and in its q2 -dependence, by such a model. In particular, the calculated q2-dependence is consistent with a dipole form with mass MA ~ 1.4 GeV and is, thus, in rough agreement with the data. Among the QCD corrections to GA , the 2-body terms, which are finite and consequently independent of the renormalization procedure, dominate. By contrast, the results obtained for the induced pseudoscalar form factor, Gp, do notexhibit the expected pion pole structure andare much too small. Evidently, perturbative QCD processes inside the bag cannot simulate the pionic contribution to Gp(q2 ), which appears to require some kind of non-perturb- ative treatment (at the QCD level), such as the introduction of explicit Goldstone fields.Decay o f the p-m eson  (O. Maxwell, B. Jennings)Since its discovery, the width of the p-meson has been a topic of active theoretical interest, most recently in connection with chiral bag models and related models of hadronic structure. Several calculations of the p width within such models have been carried out on the basis of certain approxi­mations. In an early calculation, Vento [doctoral thesis, SUNY at Stony Brook (1980)] interpreted p-meson decay as the transition of a p bag to a pion bag plus a Goldstone pion. Although this picture yields the correct empirical width, the asymmetric71treatment of the two decay pions is aesthetically unpleasing. More recently, Miller and Singer [CERN preprint TH 3609(1983)] have evaluated the contribution to the p width from the contact term in the volume interaction version of the cloudy bag Lagrangian, treating the bag as a wave packet superposition of momentum states. Again the empirical value for the width is obtained, but contributions from lower order terms in the Lagrangian, which involve an intermediate fermion (or antifermion) line correcting a pair of single pion vertices, have not been taken into account. Inclusion of these terms in the p width presents a possible double counting problem in that the Goldstone pion and a bagged qq pair with pionic quantum numbers presumably represent the same state. Nevertheless, it is of interest to determine what effect such contributions would have if included in the decay amplitude. It should also be observed that to second order in the quark-pion coupling, the original cloudy bag Lagrangian with surface interactions does not have a contact term.Motivated by these considerations, we have embarked upon a study of p-meson decay using both the surface and volume interaction versions of the cloudy bag Lagrangian. Contributions from the contact term (with the volume interaction Lagrangian) and from diagrams with intermediate fermion lines are incorporated, and in the latter, a complete set of states is included in the intermediate sums, which converge without the need for additional form factors. On the basis of preliminary results, it appears that the surface interaction yields a somewhat larger width than the volume interaction. In the latter case, cancellations occur among the contributions with intermediate lines, so that the net result is mainly due to the contact term alone.M eson-m eson scattering in a non-relativistic  quark m odel (K. Masutani)Phenomenological non-relativistic quark models have given quite satisfactory explana­tion of various ground state properties and excited spectra of hadrons. This success has encouraged many authors to apply them to the low energy hadron-hadron interaction. They have a nice feature that the centre-of-mass motion is clearly separated from the internal motion, which is very important in the scattering problem. However, they have a difficulty related to the long range Van der Waals force, which is inevitablycaused by the naive sum of the two-body confining potential.Recently, a new type of confining interaction has been proposed by Lenz and co-workers. Their interaction is completely free from Van der Waals problem and it is very similar to the string flip-flop model. Furthermore, their model becomes exactly solvable in some cases and we can investigate this rich and interesting scattering system without any approximations. One of the interesting results is that their model gives a finite scattering in the limit N •+■ 00, using SU(N) colour group; for simplicity, other internal degrees of freedom are suppressed. However, we can show that there is a way of modifying the so-called "hidden colour" part of the interaction, for which the scattering amplitude behaves as 1/N for large N. It should be noted that such a feature is also obtained by the 1/N expansion phenomenology of the SU(N) gauge theory. Since our modified confining interaction gives weak force between two mesons for large N, we can develop an appropriate approximation and investigate the effect of more complicated residual interactions. The work is still in progress.Coulombic confinem ent m odel (W. Wilcox)Recently, a promising new model of heavy- light quark systems representing the D, D B, F, etc. mesons (the s-states of which may be viewed, neglecting gluon-gluon couplings, as confined hydrogen-like systems) has been proposed [Wilcox and Milton, Confined Coulombic Model for Heavy-Light Quark Systems, Oklahoma State Univ. Research Note 147 (1983)]. The great advantage of studying these systems is the absence to a large extent of any centre-of-mass corrections, which are large in the traditional application to the low-lying hadrons. Thus, a cleaner phenomenological testing ground for the MIT fixed cavity description of mesons (baryons also if one of the quarks is significantly heavier than the other two) should eventually be provided. The wave functions should enable one to address nonspectator influences as well as purely radiative decays such as D Dy.Eventually, one would also hope to try to fit the overall mass spectrum of such states. As a first step in this direction, I have recently considered the contribution of fermions to the Casimir energy of such a system [Wilcox, Fermionic Zero-Point Energy in the Confined Coulombic Model, in72preparation]; however, much work remains to be accomplished in this direction.The structure o f  the A(1232) resonance C. Y. Cheung)In this work we investigate the structure of the physical A(1232) resonance within a model which contains pion (ir) interacting with nucleon (N) and A. The ttNN form factor is obtained from quark models of hadronic structure. It is pointed out that by fitting the static properties of the nucleon, the size of the three-quark nucleon core (or bag) is constrained to be about 1 fm. This result has been obtained both in the nonrelativistic constituent model and the "relativistic" bag model. Using a irNN form factor which corresponds to a nucleon bag size of 1 fm, we demonstrate explicitly that the perturbation series of ir-N scattering converges rapidly. Thus a crossing symmetric solution to the ir-N scattering problem can be obtained reliably by perturbation expansion. We expand the tt-N scattering series consistently to fourth order in renormalized coupling constants, and then the (3,3) phase shift is calculated. It is found that the A-contribution is dominant in generating the observed resonance at 1232 MeV (see Fig. 83) [Cheung, TRIUMF preprint TRI-PP-83-82 (1983)]. The contribu­tion from the conventional Chew-Low series is small but not negligible, i.e. its inclusion is necessary to fit the data. It is pointed out that the inclusion of the nucleon recoil energy is important in obtaining a reliable fit to the data. The general feature of our0 100 200 300kcm (MeV/c)Fig. 83. Results from the T-matrix approach. The solid line represents the best fit to the data. The dash line corresponds to the A- contribution, and the dash-dotted line the Chew-Low contribution. The experimental data are from Rowe et al., [Phys. Rev. C 18, 584 (1978)].solution is similar to that of the CBM [Th&berge et al., Phys. Rev. D 22_, 2838(1980)]. However, the values of the param­eters obtained in this work are quite differ­ent from those in CBM. The differences can be attributed to the fact that in the CBM calculation R is treated as a free parameter, instead of fixing it by the baryon static properties; also, nucleon recoil energies have been neglected. In addition, the ttNN and ttNA vertex corrections have not been included properly in the CBM solution, and the CBM solution is not crossing symmetric.Baryon spectrum  (B. Jennings; R. Bhaduri, J.C. Waddington, McM aster)A striking feature in the excitation spectra of the nucleon and the delta is the appear­ance of low-lying even parity states. In the quark model, the energy spectrum of a baryon is generated by exciting one or more quarks to excited orbitals which appear in groups of alternating parity. This feature is true both in the bag model and in the nonrelati­vistic constituent quark model. Since the odd-parity states are seen at excitations of about 500 MeV one should expect the even- parity single-particle states to appear at roughly twice this energy. Yet the N(1440)l/2+ and A(1600)3/2+ are all found to be lower than the lowest odd parity states.In the Isgur-Karl nonrelativistic quark model the even parity states are lowered by splitting the 2 fico states using a local two- body potential in a first-order perturbation calculation while arbitrarily ignoring higher- order terms in the perturbation expansion.We are proposing that the low-lying even parity excited states are deformed and that this leads naturally to the low excitation energy of the N(1440) and D(1600). If these states are deformed it then follows that there should be rotational bands built on them. In fact the known even parity baryon resonances can be fit into such bands.In the bag model, the nonlinear boundary conditions will cause the bag to deform for excited states but not for the ground states. Further the even parity excited states will deform than the 1 ftw odd parity states. Thus we have evidence both from the experimental spectrum and theoretical considerations that the excited states will be deformed.73Lattice QCD (R. Woloshyn, W. Wilcox)A program of lattice QCD calculations has been started. Monte Carlo codes to calculate SU(2) gauge fields (heat bath algorithm) and SU(3) gauge fields (Metropolis algorithm) have been implemented on the TRIUMF VAX 11/780. Codes for fermion matrix inversion using Gauss-Seidhel and conjugate-gradient methods have been developed. Calculations aimed at elucidating the structure of lattice hadrons are under way. These include determination of hadron sizes and electric and magnetic polarizability.Kaon physics and hypernucleiThe KN interaction near threshold  (R. Jennings, E. Veit; R. Barrett, Surrey; A. Thomas, CERN)The cloudy bag model has been generalized to SU(3) symmetry in order to dscribed kaon- nucleon scattering. This model has been applied to low energy s-wave 1=0 KN scattering and to describing the A(1405).With only modest adjustments of the input parameters we find that it is possible to describe the low energy scattering data indicating that in spite of the relatively large mass of the kaon the SU(3) chiral bag model is a useful starting point. In agreement with K-matrix analysis of KN scattering data, but in disagreement with kaonic hydrogen experiments we get a negative scattering length.In the present model the A(1405) comes out as KN bound state and not as an elemen­tary quark state. This has important implications in the interpretation of baryon spectroscopy.Currently the model is being extended by including the 1=1 channel and p-waves. We are also investigating the importance of crossed graphs and additional channels.Kaon-induced deuteron disintegration  (O. Maxwell)With the possibility that high quality kaon beams will become available in the not too distant future, the simple K~ absorption reactionsK"d -> Z-p, An, (1)which have generated little interest to date,may be worth examining in some detail. These reactions are kinematically similar to the well-studied reaction,ir+d pp (2 )and like pion absorption are most probably dominated by resonance rescattering processes. This similarity suggests that models that have achieved semi-quantitative success in describing reaction (2 ) could be adapted to an analysis of reactions (1 ) and possibly provide information concerning the low-lying KN resonances to supplement that obtained from KN scattering.In pursuit of this goal, a simple resonance rescattering model, analogous to that employed successfully by Brack, Riska and Weise to describe pion absorption [Nucl.Phys. A287, 425 (1977); see also Maxwell et al., Nucl. Phys. A348, 388 (1980) and Chai and Risha, Nucl. Phys. A338, 349 (1980)], has been developed to study K" absorption, reactions (1). The model is based ugon the diagrams in Fig. 84, which involve Yexcitation (Y* = E* or A*) at the initial K- absorption vertex followed by de-excitation through a virtual meson exchange that transfers momentum to the other nucleon.Both strange and non-strange pseudoscalar mesons may participate in this exchange, as well as vector mesons; but for the sake of simplicity, the latter are neglected. Among the full spectrum of E and A resonances, we have included in the reaction mechanism the eight well-established resonances (3 or 4 star status) below 1700 MeV in the K-N c.m. Two of these, the E(1385) and the A (1405), lie below the K~N threshold and dominate the absorption cross section at low energy. The required coupling strengths are estimated using empirical widths and branching ratios74or SU(3) symmetry relations. In addition to the neglect of vector meson exchanges, two further simplifying approximations have been made: (i) impulse terras are omitted and (ii)final state correlations are ignored.The resulting cross sections, as functions of the K~ lab momentum, exhibit two structures of interest: a strong, narrow peak near400 MeV/c due almost exclusively to the A(1520) and a smaller, broader structure around 700 MeV/c associated with a spectrum of higher lying resonances. In the absence of vertex form factors, the strengths of the two peaks are about 25 mb and 4 mb, respec­tively for the 2~p final state, compared with a background of 1-2 mb. Unfortunately, form factors exert a rather drastic influence on these peaks, greatly reducing their strength relative to the background. Similar results are obtained for the An final state.K  - 4He scattering a t low  energies (K. Masutani)There have been several phenomenological studies on K--l*He scattering at low energies. Although they have succeeded to reproduce the experimental data quite well by adjusting the parameters of the optical potential, there is no direct connection to the analysis of the KN system which has a A(1405), 1=0, J77 1/2" resonance only about 30 MeV below KN threshold, with a width of “40 MeV.It is very interesting to investigate the importance of this resonance in the low ener­gy K“-nucleus scattering in a microscopic fashion. To this end, we construct the energy-dependent separable KN interaction using the A propagator and the KNA and ttIA vertex functions, and we apply it to the K-_ltHe scattering with the method which has been developed in the analysis of Tr-nucleus scattering around the A-resonance region. In order to treat the threshold effect correct­ly, we have to refine the original method.In addition to the non-locality due to the A propagation, various medium corrections such as nucleon binding, Pauli blocking, and rescattering effects can be calculated with­out unjustified approximations. The study of kaonic atoms in this method can also give useful information on the properties of the A in the nuclear medium. This work is still in progress.Hypernuclei (J. Zofka, NPI, Rez-Prague)The influence of the target nucleon motion on the production reaction (K“ ,ir) has been studied in distorted wave impulse approxima­tion. It has been demonstrated [Zofka, Sofona, Fetisov, submitted to Nucl. Phys. A] that the change in the cross sections does not exceed a few tens of percent for strongly excited states when the elementary amplitude is taken fully into account. Also the role of various approximations (plane waves, 1/A terms of excitation energies neglected) has been disentangled for 12C as an example. Further, possible dynamical effects of schematic three-body ANN interaction on the structure of p- and s-d-shell hypernuclei have been investigated in a selfconsistent scheme. The single particle spectrum exhibits the greatest sensitivity to it and might be used to extract information on this supposedly important component of A-hyperon- nucleon interaction.Hypernuclei a t a kaon factory  (J. Zofka, NPI, Rez-Prague)In connection with the kaon factory proposal, the interest of various hypernuclear topics, their impact and feasibility were studied, compared and commented on. Among them (tt+ , K+ ) and (K“ ,tt-) with stoped K- may become an important new source of low-lying A(I) hypernuclear states needed for precision of hyperon-nucleon interaction characteristics and of widths of states. For the same purpose and for the understanding of the coexistence of a hyperon with nuclear medium, studies of hypernuclear y-emission (both low- energy and -10 MeV) and nucleon decays of hypernuclear resonances are very useful. Due to a small hypernuclear polarization (changes in nuclear core caused by the added hyperon), the hypernuclear data also yield nuclear information which is difficult to obtain elsewhere (nuclear incomprehensibility, neutron distributions and spectra). Baryon substructure in medium might be revealed by experiments on hypernuclear lifetimes and by extracting spin-orbit component of hyperon- nucleon interaction. The reaction (K“ ,K+ ) is a source of S=-2 hypernuclei and intensive K_-beam would yield unique data on AA inter­action and H particle. Strange dibaryons might even be produced in decays of some hypernuclear resonances. An important nuclear physics topic, propagation of resonances through nuclear medium, may be efficiently simulated by production and study of a A*(1520) narrow resonance.All of the above topics become experimentally accessible when intensive beams of K-mesons with momenta around 400-500 MeV/c and 1500- 2000 MeV/c and tt+ mesons with momenta around 1200 MeV/c become available from a K-factory.75Weak interactions and high energy physicsPossible supersym m etry breaking in 1 +  1 dimensional supersym metric quantum electro­dynamics (J. Ng; L. Chang, VPI)The massless Schwinger model is known to break chiral symmetry via the anomaly and the photon gets a mass dynamically. It is of interest to study whether this so-called Schwinger mechanism remains after supersym­metry is introduced into the system. We have constructed the Lagrangian for this case us­ing the superspace technique; as in the case of four-dimensional supersymmetry the fermion has a scalar partner and the photon obtains a spin 1 / 2 majorana partner as well as a scalar partner. We have constructed the Lagrangian in terms of these physical fields using the Wess-Zumino gauge. We also notice that by counting the number of bosons and number of fermions in the ground state the Witten index Tr(-1)F vanishes signalling supersymmetry is broken in the theory.Spin 0 boson production in Z °  decays and  tests fo r com positeness o f H iggs boson  (P. Kalyniak, J. Ng, P. Zakarauskas)Recently there are non-perturbative lattice calculations on the parts of the standard model involving the scalar potential that indicate the Higgs boson must be light com­pared to 1 TeV in order that the theory be consistent. For a light enough Higgs boson, the cleanest way of producing it will be at LEP using Z° + H°£+£- decays. Also there are other schemes of mass generation such as technlcolour scenarios that replace the Higgs boson in gauge theories. Typically they pre­dict both parity even and parity odd bosons. Composite models of gauge bosons also have spin 0 resonances, with both parities. We calculated the scattered plots of the ener­gies and invariant mass of the dilepton pair in the above reaction and showed that Higgs production can be separated from technihadron but harder to distinguish it from composite spin 0 hadrons. The distinction between tech- nipion and composite models is even smaller. This is of great importance to experimental­ists as well as to the study of the models.Higgs production in high energy pp  collisions  (J. Ng, P. Zakarauskas)We have calculated in QCD parton model the production cross section of pp" H° + Q + Tf + X where Q(Q) is a hadron (charge conjugate) with a heavy quark flavour. The cross sec­tion as a function of Mq, Mjj and /s are given. Preliminary study of the sequential weak decays of H°, Q and Q indicates that spectacular signatures of up to eight charged leptons with large transverse momenta can be obtained. More detailed studies of using quark fragmentation models are under way.Quark fragmentation and Higgs decays (P. Kalyniak and J. Ng)We have calculated the first-order QCD cor­rection to the rate of the Higgs boson decay­ing into two heavy quarks. Our corrections are found to be numerically smaller than pre­viously obtained. By constructing a hybrid heavy quark fragmentation model we calculated the average momentum fraction carried off by rank one and two mesons in the decay. We also found that the average charge multici- plicity from Higgs boson decay is high and is estimated to be ~17 charged particles for a Higgs with mass of 20 GeV/c2 .Z ° decays into lepton pairs and quark pairs  (P. Kalyniak, J. Ng, P. Zakarauskas)We have calculated the electroweak radiative correction to fermion and antifermion pairs in the standard Glashow-Weinberg-Salam model. They are found to be at the level of 10- 5 in branching ratio and hence form important background for Higgs boson searches in Z° decays. Characteristics of the fermion spectra are given.The m ixings o f heavy neutrinos in muon decays (M. Dixit, NRC; P. Kalyniak, J. Ng)We set limits on the mixings of heavy neu­trinos into the muon family for neutrinos in the mass range of 30 to 70 MeV/c2 using the Michel parameter and the e+ spectrum. The mixing parameter is found to be <7 x 103 for mv = 40 MeV / c2 .Charged Higgs production and their effects in ve scattering (J. Ng, P. Zakarauskas)We have studied the production of charged Higgs bosons in e+e~ and pp collisions. Charged Higgs bosons are important ingredi­ents in most gauge models extending beyond the Glashow-Weinberg Salam model. A novel interference effect between the charge Higgs exchange and the Z° exchange in 'v£e- scat­tering is found. For a 1 TeV/c2 Higgs boson this can lead to a few per cent contribution to neutrino electron scattering.76Extended electroweak models (G. Fogleman,P. Kalyniak, P. Zakarauskas)The observability of additional neutral weak bosons from proton-antiproton collisions at SPS energies is being investigated. This study is done within the framework of extended electroweak models such as SU(2)xU(l)xU(l) and SU(2)LxSU(2)RxU(l) .We will discuss the signatures of extra Z0,s from these models and the dependence of these signatures on the generalized parameters of extended electroweak models. How heavy a second neutral boson would have to be before it is lost in the background is one of the issues that will be studied. Efforts to extend this analysis to additional charged weak bosons are also under way.Fermions in Kaluza-Klein theories(G. Fogleman)One of the outstanding problems in Kaluza- Klein theories is obtaining zero-mass chiral fermions. With this problem in mind we are currently examining the effects of an Einstein-Cartan torsion on the mass spectrum of the Dirac and Rarita-Schwinger operators in higher dimensional theories. The usual restrictions on the masses of Kaluza-Klein fermions are not applicable in theories with torsion. These calculations, still in a preliminary stage, also have applicability to theories of supergravity.The effective potentia l in supersym metrictheories (G. Fogleman, G. Starkman;K.S. Viswanathan, Simon Fraser)The effective potential is useful in the study of spontaneous symmetry breaking. In theories of supersymmetry the effective potential should be positive-definite. Some analysis of 0(N) symmetric Wess-Zumino mod­els, however, have found that the effective potential is negative at a stationary point [see, for example, Zanon, Phys. Lett. 10415, 127 (1981)]. The simplest Wess-Zumino model, which is the prototype for all supersymmetric chiral models, displays this same usual be­haviour in its effective potential if a naive minimal subtraction type renormalization pre­scription is used. This renormalization prescription, it turns out, leads to negative kinetic energy terms in the effective action[Amati and Chou, Phys. Lett. 114B, 129 (1982)]. We computed the Wess-Zumino effec­tive potential off shell to two loops (TRI-PP -83-80). A renormalization prescription which preserves the positivity of the kinetic terms, and which is easly extended to higher order, was implemented. After the auxiliary field was eliminated the two loop effective potential was shown to be positive definite. Thus supersymmetry is not broken by radiative corrections in the Wess-Zumino model to two loops.Theoretical chemistryCharge exchange o f m uons in gases(R. Turner, M. Senba)Kinetic equations for the spin-density ope­rators of the diamagnetic and paramagnetic states of the positive muon have been ob­tained [Turner, Phys. Rev. A28, 3300 (1983)] for the description of the stopping process encountered when high-energy muons thermalize in single component gases. The motion of this two-species system is generated by the Liouville superoperators associated with the free flight spin Hamiltonians and by time- dependent rate superoperators which depict the probabilities per collision that an electron is captured or lost. Using a time independent rate constant approximation, analytic solutions of these rate equations have been presented [Turner and Senba, Hyp. Int. (in press); Phys. Rev. A (in press)] and related to the observable muon spin polariza­tions of the diamagnetic and paramagnetic species. Line shapes have been obtained from the amplitudes of these polarizations as a function of the length of the charge exchange region (which is inversely proportional to the number density of the gas). The line shapes have two general features, namely (i) they are constants when the duration of the charge exchange region is short (high number densities) and (ii) they have resonances for long durations. As well, in general, the amplitudes of the "singlet" (hyperfine frequency) term and the "triplet" (muonium Larmor frequency) term are not equal. These theoretical line shapes suggest further experimental studies be made, in particular to see if the resonances are experimentally resolvable or not.77APPLIED PROGRAMS DIVISIONINTRODUCTIONThe TRIUMF Applied Program exploits the technologies available at TRIUMF for projects outside the pure research activities. The technical support here has facilitated the commissioning of the CP-42 cyclotron. Now both the AECL and the PET groups have isotope production runs on a regular basis. Users of this facility must submit a proposal similar to proposals for experiments on the 500 MeV cyclotron beam lines. The proposals are then used as a basis for scheduling isotope pro­duction time. Likewise there are isotope production facilities on the 500 MeV cyclo­tron beam lines as well as a neutron activa­tion program. These facilities are available to users when an accepted proposal can be incorporated into their schedule.The TRIUMF pion radiotherapy program has had a steady year of evolution toward routine tumour treatment, treating 24 patients with negative pions. The reliability and greater beam intensity of the 500 MeV cyclotron has allowed a regular treatment schedule.BIOMEDICAL PROGRAMThe year 1983 has been a year of rapid expansion of the TRIUMF pion radiotherapy program after the successful initiation of deep-seated tumour therapy in May 1982. The Batho Biomedical Facility is rapidly being transformed into a routine radiotherapy treatment centre equipped with reception, waiting area and examination rooms. In the past year a total of 90 days of high inten­sity beam were available for patient treat­ment. This was separated into three blocks of 8 , 8 and 4 weeks each, the last two runs being separated by a break of only 1 week. Compared to the 4-week blocks available in 1982 these long runs have significantly improved the rate of patient accrual, since patients have to be treated over a period of 10 to 15 days and therefore no new patient can be accepted during the last 2 weeks of the run. However, these long treatment blocks also present a serious challenge to the whole staff, especially the physics team which has to keep the biomedical channel in good condition and ready to deliver pions on demand over months. With excellent support from the TRIUMF service groups, such as the Vacuum group, the Magnet group and the Elec­tronics group, we were able to handle all the major and minor repairs on the maintenance days during the runs and hence not a single patient treatment day was lost in 1983 due to channel failure.There has been a significant increase in the average M8 pion flux during patient treatment in 1983, mainly due to the improved cyclo­tron stability and higher maximum operating current of 130 yA, instead of 110 pA as in the previous year, and also partly due to the better beam tune available with the new M8Q1 magnet power supply which was installed in the spring shutdown. This increase in flux, however, was somewhat compromised by the 1983 revised BL1A beam intensity calibration factor, which effectively reduces the flux by about 1 0%.After clinical follow-up studies in patients treated in 1982 we were able to improve on the treatment regime for the past year. The pelvic tumour dose was increased from 10 to 12 daily fractions of 2.5 Gy each. Many of these treatments were monitored by endoscopic bowel examination with intraluminal photo­graphy before and after irradiation using a flexible fibreoptic sigmoidoscope. The original protocol for brain tumours was a primary tumour site pion boost on top of a whole brain megavoltage photon irradiation.It was decided in December 1982 to increase the primary pion boost gradually to eliminate the whole brain photon irradiation. The pion boost dose used for the past year was there­fore increased to 15 fractions of 1.7 Gy each, while the whole brain photon dose was reduced to 10 fractions of 2 Gy each. This escalation of pion dose has increased the brain tumour treatment time to an average of 45 min, which was still well tolerated by all the patients treated.Twenty-four patients were treated in the past year (Table VI), making the total number of patients with deep-seated tumours treated since May 1982 to be 39. One of the patients had skin melanoma over a relatively large area of his leg and was treated three separate times over three different areas of his skin. Of the other 23 patients treated this year 14 had pelvic malignancies, including prostate, rectum and sigmoid colon tumours, and of the 9 brain tumours treated 2 patients could not complete their treatments due to medical reasons. Most patients were78transported to TRIUMF by relatives or by our volunteer drivers. The rest were originally from the B.C. Interior, but arranged to stay in Vancouver during the whole treatment.The technique of patient immobilization with reasonable comfort has been developed using thermal-plastic shells for the brain tumour and polyurethane molds for the pelvic tumours. The patient alignment system has also been upgraded with a new 7 mW laser which is bright enough for the patient to be set up without the inconvenience of having to dim the room light during alignment. The bright laser beam spot was also used routine­ly to monitor the scanning position during treatment using a newly installed close-up camera system. Patients were able to listen to high quality music of their choice or relaxation narratives during their treatment through a stereo sound system implemented in March by three practicum students from the B.C. Institute of Technology. This system is totally independent of the regular sound system in order that the attending staff can still be in direct sound contact with the patient for instructions and complaints.All pelvic patients were set up outside the treatment room on a simulated table in order to minimize patient change-over time as well as to reduce staff radiation dose. The general neutron background in the treatment room when beam was on the 1AT1 target re­mained at a level of 10-50 mrem/h in the past year. The plastic sheet that was installed over the whole BL1A tunnel earlier this year to block the radioactive gases from rising into the meson hall actually helped to channel more radioactive gas into the M8 treatment room during the summer months.With the installation of an improved venti- ation system in BL1A in the fall the air activity in our treatment room was consider­ably reduced, although more work is required to reduce the level.During the high beam intensity period the day shift on the biomedical channel was entirely dedicated to patient irradiation and related activities, such as dosimetry calculation and equipment testing. A maximum of 7 patients were treated on a single day, taking up to 8 h of beam time during which all the other TRIUMF beam users would help to minimize disturbances on the cyclotron operation.With increasing patient workload and longer irradiation times due to use of higher doses for more patients, the understanding and co-operation of the other high beam intensityusers has been a major factor in our smooth running for the past year.The night shifts on the biomedical channel were also being used actively for basic studies with the pion beam as a continuation of preclinical studies to provide more input to the ongoing clinical program. Dosimetry measurements were made using an ionization chamber with an electrode made of gelatine, which is a much closer approximation to human tissue than the standard material used in commercial ionization chambers. Dosimetric measurements for microscopic ionization den­sity variation (microdosimetry) were carried out in both polarized and high intensity beam periods. Significant differences in beam quality have been observed for beam tunes with and without scanning. High spatial- resolution cellular in vitro measurements were made using CHO cells suspended in gela­tine for some beam tunes developed for actual patient treatment to monitor biological effects throughout the treatment field. Several in vivo animal experiments were also made using scanned beam tunes which have much more uniform dose profiles than those previously available. In particular, a high­ly difficult 12 h interval 20 fraction mouse experiment was successfully completed this summer.Table VI. Summary of TRIUMF pion patient 1983.treatment forRunFraction Total Patient finished/intended daysDose/fraction (it- rad)Apr 29-Jun 20 X rectum 12/12 17 250X rectum 12/12 17 250X rectum 12/12 19 250X skin 10/10 15 250X brain 15/15 23 170X brain 15/15 22 170X colon 12/12 17 250X prostate 12/12 18 250Aug 22-Nov 20 X skin 10/10 17 250X brain 15/15 25 170X prostate 12/12 21 250X prostate 12/12 20 250X prostate 12/12 21 250X prostate 12/12 17 250X skin 12/12 17 250X prostate 12/12 17 250X brain 7/12 16 170X brain 12/15 28 170X brain 15/15 34 170X brain 15/15 31 170X brain 15/15 23 170X rectum 12/12 17 250X brain 15/15 22 170X colon 12/12 17 250X rectum 12/12 17 250X colon 10/10 15 2507942 MeV CYCLOTRON CommissioningStatusAt the end of 1983 the 42 MeV cyclotron facility had been in "operation" for two months. Much of this operation, however, is still for the purpose of product development and evaluation.The layout of the facility is shown in Fig. 85. It illustrates the relative loca­tions of the cyclotron with a solids target station and a gas target in the vault and another solids target station and gas target in series in the target cave. 7.5 cm diam­eter rabbit lines connect the solid target stations to the chemistry hot cells and 3 mm gas lines connect the gas targets to hot cells and shielded fume cabinets. It should be noted that all available space in the cyclotron area is now occupied.On January 21 the Cyclotron Corporation (TCC), who supplied the 42 MeV cyclotron for radioisotope production, applied for "suspension of operation" under Chapter 11 of the U.S. Bankruptcy Act. At that time the machine was capable of delivering 100 yA to a fixed energy 30 MeV target and from 11 to 42 MeV into the variable energy beam line. How­ever, the beam loss at energies below 35 MeV varied from 30 to 70%, and the machine stability left much to be desired.During the following two months the machine was in operation three out of every six working days with an actual running time of up to 10% during the operational days. The operational days were used primarily for product development by AECL and gas target development by both AECL and PET. The other three days were used for maintenance andTARGET CAVE\ — -----\ GAS TARGETGAS TARGETSOLIDSTARGETFUTUREEXTENSIONSOLIDSTARGETCYCLOTRON VAULTACTIVE WASTE STORAGE □ FUTURECONTROL ROOM EXTENSIONCOOLINGSYSTEM CONTROLROOMPOWER SUPPLY ROOMAECLHOT CHEMISTRY LABORATORYAECL DEVELOPMENTAECLSHIPPINGFig. 85. The 42 MeV radioisotope production area.80repairs, as well as for improving the reliability and stability of the machine and the various target assemblies. This mode of operation was continued with increased beam delivery during the second quarter of 1983.Early in July the Insurance Company of North America (the bonding company) on behalf of TCC, and AECL (who funded the cyclotron) on behalf of TRIUMF, reached agreement on com­pletion of the contract. The agreement gave TCC absolute priority on the machine for further commissioning towards meeting the performance specifications. Irradiations for the users were not completely stopped, how­ever, but were carried out whenever they did not interfere with the commissioning opera­tions, often during the early hours, evenings or on Saturdays.The TCC effort resulted in a series of acceptance tests between September 15 and October 25. The following tests were run:1) One hour at 200 pA on each of the following targets: a) a silver production target in the MeV target station; b) an aluminum test target at the 26 MeV beam port; c) a silver production target at 42 MeV in the variable energy target station.2) 16 h at 200 pA and "full energy" on a silver production target in the variable energy target station.3) A series of 10 min runs at 200 pA at 12,20 and 30 MeV on a silver production target station in the variable energy station.With respect to the specifications as per contract the following deficiencies were noted:1) Energy: There is a 10% beam loss between41 and 42 MeV. Therefore the one-hour test at 200 pA was run at 42 MeV, but the 16-hour test was run at 41 MeV. In practice this means that we should only run 42 MeV at low beam currents to prevent undue activation of the machine.2) Emittance and beam line loss: At 12 MeV the external beam loss far exceeds the specified 10%. The emittance, therefore, also does not meet the specified value . In practice this means that beams at the lower end of the energy range will not be available at 200 pA at the target station and one has to be careful with beam spill in the beam line.3) Operator intervention: The frequency ofoperator intervention is greater than specified. Instead of 0.25 per hour it was on an average 2 per hour.However, it should also be noted that some of the tests were not required in the original specifications. The one-hour tests were also run at the 27 MeV target station and 26 MeV exit port, which is beyond what the specifi­cations called for. Also, the one-hour and 16-hour tests were run on a production tar­get, which is more difficult, and more useful than on the target specified by TCC.The successful performance during acceptance tests proves only that the equipment con­cerned is capable of a certain specified performance. It does not guarantee reliable performance during actual operation. This has been abundantly apparent during the ope­ration of the target stations. These passed the specified acceptance tests in September1982 as reported in last year's Annual Report. They have failed numerous times ever since, thereby causing serious delays in the cyclotron acceptance program. An improved design for the target stations was completed by TRIUMF in December.Operation1983 was primarily a year of cyclotron commissioning, hampered with many delays due to poor performance of the manufacturer. In spite of this a substantial amount of cyclo­tron performance has been devoted to the users. Only during the months of October and November was the cyclotron run primarily in an operating mode, albeit almost exclusively for product development and evaluation. Downtime as a fraction of scheduled operating time was approx. 1 0%, most of it caused by a computer failure. Figure 86 displays the weekly beam delivery during the year. It reflects the period of reduced production, due to TCC machine priority during the latesummer and the increasing productivity nearthe end of the year. The lower productionduring the last few weeks of Decemberreflects the computer failure during that period and the fact that the cyclotron was shut down from Dec. 25-31.The operation of the 42 MeV isotope producing cyclotron differs vastly from that of the 500 MeV machine. While the latter runs con­tinuously on a number of targets that are permanently installed in the beam lines, the former has to be turned on and off and tuned81BEAM DELIVERY OJA HOURS1 f ik  Hour=3.6X10'* CoulombFig. 8 6 . Weekly 42 MeV beam delivery.frequently on a multitude of targets that have to be inserted in four different locations and subsequently withdrawn for delivery to the user.The following table lists the number and kinds of targets irradiated during 1983, a total of 248, of which 74 were irradiated during November and December.Most of the 74 20Ne irradiations were uti­lized for development of 18FDG processing techniques, but 27 were actually used for PET patient scans. All patient runs were run as per schedule without failure.Figures 87 and 88 show the beam delivery and machine time consumed by each users. While the PET targets do not consume much beam, they do use a fair amount of machine time.Targetmaterial IsotopeType of target User Number58 ni 87 Co solid AECL20 3 20 1 Ti. solid AECL129Xe 123]; solid AECL 1282°Ne 18p solid AECLH 2Cd Ulln gas AECL88Zn 8 7Gu gas PET1 6o2 15q gas PET 89Misc. solid Others 31Total 248RADIOISOTOPE PROCESSING (AECL)About 144,000 pAh were delivered to 500 MeV production targets during three beam periods. 127Xe for lung ventilation studies was the major product and some business has been lost because of lengthy periods without beam. A similar situation will exist in 1984 when two long intervals of 11 and 15 weeks without high intensity beam are planned. The balance of the production was made up with 1 0 9Cd, which is not affected by such scheduling, together with spot shipments of 88Ge and 82 Sr.The CP-42 cyclotron was accepted based on mod­ified tests early in November and has been operating steadily since that time. For the rest of the year beam was available with poor reliability but considerable development workUSER■  DOSEFig. 87. Beam delivery for each user.700USER■  MACHINE TIMEFig. 8 8. Machine time consumed by each user.82was completed. Procedures are now in place for the production of 2 0 1Ti,, 6(,Ga and 87Co - all from the CP-42 cyclotron. Regular com­mercial shipments of these isotopes will start in January 1984. Development of 111 In which may be used to label monoclonal anti­bodies for tumour imaging applications is under way and will be available commercially in the first quarter of 1984.In October AECL demonstrated that commercial quantities of high purity 123I (1 Ci at end of processing) could be produced using the compact CP42 cyclotron and 124Xe target gas. The recommended production route for 1231 is that employing the 123Xe parent and beam line 2C will one day be used to produce 1231 em­ploying the 127l (p,5n) 123Xe •* 123l reaction. However, beam line 2C will never provide the reliability that is required for commercial operations and so an alternative route for this most important isotope was required.Some development work is still required to optimize product yields but commercial shipments will start in January 1984.500 MeV ISOTOPE PRODUCTION FACILITYThe year 1983 was the fourth year of opera­tion for the 500 KeV isotope production faci­lity. The facility performed without failures and was able to cope with the increasing maximum beam current run during some periods. It received ~142 mAh, slightly more than during 1982. The use of the facility is illustrated in the following table:TargetsYearmAh to facilityTargetsirradiateddelivered to AECL1980 51 40 261981 56 53 381982 120 49 421983 142 70 74The isotope production of the facility isdetailed as follows:Number ofNumber of targetsTarget targets deliveredmaterial Isotope irradiated to AECLCsC£ 127Xe 51 58In 109Cd 7 5Zn 67Cu 6 5As 68 Ge 0 1Mo 83 Sr 6 5Any discrepancies between the number of targets irradiated and the number delivered to AECL are due to delays in delivery at the beginning and end of each calendar year.The facility was also used to irradiate some stainless steel samples to study radiation damage effects for the cyclotron vacuum tankPOSITRON EMISSION TOMOGRAPHYLast year's annual report chronicled the building of a positron emission tomograph at TRIUMF for the UBC/TRIUMF PET Program. This device represents essentially a development of the PETT IV design, originated at Washington University, St. Louis, Missouri. Just before Christmas of 1982 the tomograph was installed in the Acute Care Unit of the Health Sciences Centre Hospital on the UBC campus, and some of its engineering details were the subject of a publication [Evans et al., IEEE Trans. NS-30, 707 (1983)].The first few weeks of 1983 were spent verifying correct operation of the tomograph, and continued measurement of its operational parameters by means of measurements on "phan­toms". Additional software was developed for the LSI 11-23 microcomputer, used to control the data acquisition process plus gantry wobble motion and the like, as well as for the VAX 11/750 computer system (located in the Electrical Engineering Department at UBC) used to reconstruct, by means of filtered back projection, the seven brain-slice images obtained from the machine. Correlation and simultaneous region-of-interest analysis of PET, NMR and CT tomographic images was also achieved [Martin et al., submitted to AAN Scientific Program, October 1983], Studies of PET tomograph physics continued throughout this year, particularly on the variation of in-slice resolution (varying between about 8 and 9 mm depending on the reconstruction filter used) and on effective slice thick­ness, as a function of distance from the gantry axis [Buschmann et al., TRIUMF internal report (TRI-DN-83-38].The first scanning agent produced by the TRIUMF PET Chemistry group for the measure­ment program (2-fluoro-2-deoxy-D-glucose, or FDG, to measure regional cerebral glucose metabolism) was approved for use in human subjects in January, and the first subject was scanned on February 24. On March 9 Her Majesty Queen Elizabeth II visited the UBC Imaging Research Centre and inspected the83UBC TRIUMF PET Scanner which was demonstrated to her by the PET team.Performance of the tomograph has been highly satisfactory throughout its first year of operation. The performance characteristics have been shown to be quite stable, and failures, both of the cesium fluoride radiation detectors and of other electronic components, have been fewer than expected.Work has also continued towards a second tomograph, with an aperture suitable for whole-body measurements, and with higher resolution. Earlier design studies [Yao and Rogers, submitted to Nucl. Instr. and Methods] have been extended [TRIUMF internal report, TRI-DN-83-39] with grant support from the B.C. Science Council.The development of scanning agents continued throughout the year. Two significant innovations [Adam, abstract, 10th Int. Symp. of Fluorine Chemistry, August; Adam et al., submitted to J. Nucl. Med., November 1983] in the chemistry for production of FDG (see above) were introduced, to simplify and accelerate the synthetic procedure. In addi­tion, at year's end the chemistry for the production of water labelled with oxygen-15 (for measurement of regional cerebral blood flow) was essentially complete. The synthe­sis of oxygen gas labelled with oxygen-15 and of carbon-monoxide labelled with oxygen-15 or carbon-11 was also well advanced. These agents together will permit the measurement of regional cerebral oxygen metabolism, of importance particularly in studies of stroke.In the latter months of the year an accele­rated program of development of dopa and dopa analogues labelled with fluorine-18 and carbon-11 was instituted. These agents are expected to allow imaging of various aspects of dopamine synthesis in the brain and hence permit measurement of the metabolic activity of dopaminergic neurons implicated in move­ment disorders and some psychiatric condi­tions. This activity was in addition to general research on techniques for the label­ling of complex molecules with positron emit­ting radionuclides, needed for future chem­istry development [Adam et al., Can. J. Chem. 61, 658 (1983); Adam et al., presented to ACS National Mtg., March, Seattle; Adam et al., submitted to J. Org. Chem.; Nickles et al., Int. J. Appl. Radiat. Isot. (to be published)],The 110 min half-life of fluorine-18 used to label FDG and subsequently fluorodopa per­mitted transport of the scanning agents over the 2.A km distance from TRIUMF to the Acute Care Unit Hospital by vehicle. The inception of scans with agents labelled with 2 min oxygen-15, however, necessitated more rapid transport techniques. Accordingly, a pneumatic transport or rabbit system was installed during the course of this year [Gelbart et al., TRIUMF internal report TRI- DN-83-27, presented at CAP Mtg., Victoria, June]. It consists of a concrete-encased 6 in. drainpipe buried 4 ft below the ground surface and containing four polyethylene tubes. Capsules are propelled through these tubes by compressed air (at 80 psi) with a transit time slightly over two minutes. A rabbit system of this length is believed to be unique, and presented a number of minor engineering problems. At the time of writing the majority of these have been successfully solved.In this year of the PET program its applica­tion to medical research was concentrated in a few selected areas. In studies of movement disorders patients suffering from Parkinson's disease and Huntington's disease were scanned with FDG, and the first medical research pub­lication from the program resulted from this work [Martin et al., Can. J. Neuro. Sci. (in press)]. In psychiatric disease, studies of schizophrenia were begun; subjects suffering from Alzheimer's disease (senile dementia) were also scanned, with characteristic changes in the glucose metabolism pattern being observed and quantified.In November studies of patients suffering from stroke were initiated, with techniques being developed to accommodate subjects for scanning within a few hours of the initial infarct event.By year's end some 30 subjects had been examined, being a mixture of patients suffer­ing from the above diseases, and normal volunteers for comparison. Progress was severely limited during August, September and October, owing to firmly scheduled beam time on the CP-42 cyclotron being unavailable for the program, for reasons discussed elsewhere in this report. In November and December, however, the rate of scanning subjects had accelerated to three per week.84UBC IMAGING R E S E A R C H  CENTRE PETT Ur»f*ftgiFig. 89. Fourteen slice images of glucose metabolism in a normal brain. These were taken in two measurement, each giving 7 slices, with the subject displaced one half of a slice thickness between scans. The grey matter (primarily around the outside of the brain) is brain) is seen to metabolize more glucose (shown in red and green) than the white matter regions and the brain ventricles, shown in blue.85Fig. 90. TRIUMF/UBC scanner. Fig. 91. A patient undergoing a PET brainscan. The face ask assists the subject in remaining immobile during the scan, which may last for several minutes.NOVATRACKA  com parison of the different sources of radiation and their associated doses.PET StudiesAbsorbed Radiation Dose (in millirem)Radiopharma­ceutical used Whole Body Ovary Kidney Brain77Kr 8 6 20 35150 2 4.4 11 13 8.2C,50 2 15 36 44 2813NH3 60 50 1.080 68018FDG 215 315 385 33018FDG 430 630 770 660X-Ray StudiesAbsorbed Radiation Dose (in millirem)Procedure Skin Bone & Marrow Ovary Kidney ChestAbdomen(Abdominal Flat Film) 600 35 60 120 120Back(Lumbo-sacral Spine) 4,500 1,400 700 900 45Stomach(Upper F.l. Fluoroscopy) 20,000 500 600 4,000 600Nuclear Medicine Procedures Absorbed Radiation Dose (in millirem)Type of scan Whole Body Ovary KidneyBrain 200 300 1,500Kidney 200 300 400Lung 30 30 200Bone 240 450Typical Ionizing Radiation Exposures received in one year (in millirem)From the environmentMedical (X-rays etc.)Naturally occuring radioisotopes within the bodyMiscellaneous70203These can add to your exposure:Altitude of residence (higher altitude increases dose) 25 - 75 Brick, stone or concrete residence 30Sleeping with partner 3Watching T.V. up to 0.3Flying to England & back 10Fig. 92. A comparison of the different sources of radiation and their associated doses.1983 was a year of consolidation for Novatrack. The number of samples analysed in 1983 was virtually the same as 1982. Again only about 30% of the samples were irradiated at TRIUMF; the other 70% was irradiated at the University of Washington (Seattle) and at Washington State University (Pullman).During the winter shutdown period a new multisample rotating irradiation device was installed in the TNF in conjunction with the overhaul of the entire thermal neutron facility. Unfortunately, even though the design of this new device was a simplified version of the original rotating irradiation facility, which was successfully operated for a couple of years, the new device did not perform nearly as well. After a number of breakdowns in the first few months of operation, a large water leak developed in the drum assembly which made further operation of the device impossible as of October.Until new irradiation facilities have been installed in the TNF operation of the neutron activation analysis facility will rely heavily on the use of reactor facilities in the State of Washington.TRIM PROGRAMA sodium iodide target is now in place in BL2C which will enable TRIM to deliver 123 j and other radiohalogens. The receiving lab­oratory in the TRIM trailer is also prepared86to receive 123Xe from the new target. The TRIM trailer and hot cell incorporate many outstanding features including an extensive automatic control system and a redesigned 1 2 3 1 delivery system. The controls system has a resident microprocessor, which contains all the safety requirements and some autonomous programs, viz. liquid nitrogen controls. The command sequences, however, are received from the BL2C computer over the serial CAMAC link for arbitration and execu­tion. The delivery system includes automated radiogas deposition in sterile glass vials, radiochemical stabilization with hydrogen sulphide, and the ability to flame seal the final 123 I. The overall advantages of this scheme are as follows: radioisotope contami­nation will be less likely with l23i in a form with no solvent added; the user can use the optimal solvent for his labelling; we believe hydrogen sulphide will stabilize the iodide form of 1 2 3 1 ; the system will also produce 1 2 2Xe, which is a generator for short-lived 1 2 2I.TRIM members have long concerned themselves with the supply and clinical application of 123i-iabelled fatty acids, as these sub­stances are important worldwide for imaging the diseased human myocardium. We discovered this year that omega-labelled 123I fattyacids can generally be prepared from macro- cyclic lactones. Scores of such lactones are obtainable from industry where each is a va­riety of perfume. We gained the co-operation of the perfume industry and began preparing new fatty acid analogues for testing in animals. A patent application was submitted for this efficient and widely applicable process. We hope this research will encour­age use and experimentation with known fatty acids and that new analogues will emerge with superior diagnostic characteristics.During the latter part of 1983 construction of the 127Xe recycling clinical prototype unit was begun. This is a collaboration between BCRC (Techwest Enterprises Ltd.), VGH and TRIUMF under a grant from the Science Council of B.C. Earlier work at TRIUMF in the spring indicated that we could recover about 99% of *27Xe used in pulmonary venti­lation studies for reuse. This is an important development for widespread applica­tion of 127Xe in clinical practice, as it should improve the effective availability while lowering the effective cost. TRIUMF is one of only three facilities currently pro­ducing *2 7Xe. After a short testing period at TRIUMF the unit will be moved to VGH for clinical testing and evaluation in the spring of 1984.87CYCLOTRON DIVISIONReliable beam production was the highest priority for the Cyclotron Division. The effort has proved effective with last year's record of 229 mAh being exceeded by 14 mAh. Refer to the Beam Production section for various details.The monthly production, yearly production, hours per year of operation over the history of the cyclotron are shown in Fig. 93. It should be noted that the hours of operation for 1983 were less than 1982; however, more beam production was realized. This is mainly due to the fact that high current operation is now routinely 125 pA.There were three planned shutdowns during the year as well as three major equipment failures: 1 ) a water leak in the resonator cooling system in the tank; 2) inflector insulator breakdowns; 3) BL4 extraction probe. Details of each appear in their respective sections of the report.A highlight during 1983 was the extraction of more than 600 nA of polarized beam at 500 MeV which doubled the record previously achieved. This level of polarized current could be maintained over periods of a few weeks and was the result of a careful overhaul and tuning of the H- polarized Lamb-shift source. A program of laboratory tests to ensure thatthis level of current is easily reproduced is now under way on a test-stand Lamb-shift polarized source.The good operational behaviour was achieved through a patient day-to-day optimization of conditions and, where possible, through a constant gradual elimination of causes of problems. Nevertheless, for many aspects the situation is still marginal, especially at higher currents where beam losses and beam heating effects could not always be kept under proper control due to the inadequacy or malfunctioning of some of the beam loss diagnostics systems. Other marginal elements include the electrostatic elements in the central region (inflector and correction plates) and the cyclotron probes. The resonators, however, operated fairly well during the year with no appreciable sagging of the tips and the temperatures of the structures were kept well under control. No major problems occurred along the injection line and along the primary extraction beam lines.Two major projects were completed by the end of the spring shutdown: the vault improve­ment program and the thermal neutron facility upgrading. The vault improvement program was aimed at making the front end of the beam lines adequate for high intensity by40>3i20Fig. 93. Beam charge delivered (broken line) and hours of operation (solid line) over the past several years. Milestones in extracted peak current are also indicated. The histogram shows the charge delivered per month.20002 2 5^A  @  10%h/yr-60004000mAh—  200100mAh /  m100/xA 120/xAI I170 f j .A (§, 100%88completing the remote handling capability and by increasing the radiation resistance of all elements. The vacuum chambers of the combination magnets were welded to the main cyclotron vacuum chamber to eliminate the risk of a vacuum leak at the seal between the two chambers. The combination magnets were modified to permit remote servicing and several beam monitors were made compatible with the higher radiation environment. The vault floor was reinforced near the vault entrance to facilitate the transport of heavy elements.The benefits of the vault improvement program for a high yearly beam charge production are already obvious. The vacuum in the cyclotron tank has reached the 10- 9 Torr range with RF off and a few 10- 8 Torr with RF on, with increased beam transmission and reduced beam losses in the machine. It is also noteworthy that no problem occurred during the year in the front end region of the beam lines, a primary source of downtime during previous years. With the addition of the remote handling annex the servicing of the vault is more efficient resulting in a reduction of dose exposure per task to personnel.The upgrading of the thermal neutron facility makes it now possible to extract currents above the previous limit of 150 pA. The new lead target is designed to absorb =>125 kW of beam power. Taking into account the beam power irradiated from the lead target and the power dissipated in the meson production targets 1AT1 and 1AT2 upstream of the TNF, one finds a corresponding upper limit of about 400 pA for the beam extracted from the machine. Initial tests aimed at increasing the maximum extracted beam current resulted in a maximum of 170 pA. The limiting factor was an excessive beam loss in the vertical electrostatic injection line. A redistribu­tion of the polarity of quadrupoles in this beam line is required to overcome this limit. This will be done during the spring 1984 shutdown. The maximum current tolerated by the present 1AT2 meson production target is about 200 pA. For the thin target at 1AT1 the limit is now 140 pA. Target development effort is well in progress as described in the Experimental Facilities report. Some development shifts were dedicated to increasing the peak beam current in the 1 0% duty cycle pulsed mode. Currents equivalent to 225 pA extracted were demonstrated again but could not be increased. The reason for this limit is at present not completely known but seems related to factors depending on thebrightness of the ion source and on the longitudinal space charge debunching in the inflector region at the bottom of the vertical injection line. A third buncher to overcome this limitation is planned. A cw H- ion source capable of higher brightness is being studied.Two new major projects were initiated towards the end of the year: the alternative H-extraction project and the new vertical injection line project. The first project is aimed at defining a scheme by which H~ ions are directly extracted from the cyclotron at operating intensities of about 100 pA. These beams could then be used for injection in an accumulator, a storage ring, an energy booster, or other post-accelerator. The importance of studying and testing the capa­bility of the cyclotron to produce this type of beam is obvious at the moment where a great deal of studies are made toward possible future expansions of the facility. Two principal schemes are being investigated. A special task force was formed with members of the Accelerator Research Division and of the Cyclotron Division to oversee and finalize the definition of these concepts and implement the realisation and testing of these schemes in the machine. One should refer to the Accelerator Research Division section for details.Another task force was formed to oversee and implement the design and the construction of the extension of the present injection line toward the third ion source. As soon as this work is completed it will be followed by the design and construction of the lower part of the vertical injection line with the aim of making this line more accessible for servicing and adapting it to the new high intensity and high beam quality requirements.The resonator improvement program was the centre of the cyclotron development activity throughout the year. The prototype of the replacement resonator segment was completed and tested at full power in the vacuum chamber test-stand which was assembled for this purpose. The test showed that the segment is suitable as a replacement reso­nator. It has the cooling characteristics and the alignment characteristics required for reliable operation under existing condi­tions. Other significant achievements of the resonator improvement program are the increase in understanding of the RF leakage outside of the resonating cavity, and the increased number of RF diagnostics. As a89consequence the existing resonator system has become more reliable. In this scenario it is our intention that the replacement resonators not only answer the reliability requirements, established as the main design criteria at the beginning of the program, but also the requirements of high voltage and phase stability as dictated by the alternative extraction program and by the development programs for higher intensity and higher split ratios between simultaneously extracted high and low intensity beams. The feasibil­ity of a stable flat-topped RF voltage by the superposition of the third harmonic component on the fundamental was studied extensively and new more stringent criteria for the new resonator systems were derived.As described in the report from the RF group a new tuning scheme to regulate the frequency of the fundamental RF and at the same time maintain the ratios between the frequency of the fundamental and the third harmonic con­stant was developed and mechanically tested in a prototype test in the laboratory. RF tests of the flat-topping concept will be performed at power in the test-stand cavity (containing only a pair of opposite seg­ments). A third harmonic power amplifier is being built for this purpose. The controls of the fundamental and of the third harmonic components are being designed to meet the stability requirements for voltage and phase of the two components.Intrinsic instabilities in the resonating field can be reduced by improving themechanical stability of the segments. Simplecalculations based on the requirement for separated turns at extraction radius show that a vibration amplitude of the order of a hundredth of a millimetre would be desirable at the tips of the resonators. If this cannot be achieved mechanically, a control feedback system is required which willmaintain the voltage stable to a few parts in10- 5 and the phase difference between fundamental and third harmonic, stable within 0.15° at the fundamental frequency. Mechan­ical stability of the resonator system and sophisticated controls have received a high priority in the studies. Fruitful consulta­tions with RF experts from CERN, SIN and GANIL have taken place. The construction of a second prototype segment with improved dynamic stability of the cantilevered three metre long hot arm is awaiting the decision for the best material to be used. This design is being evaluated in consultation with experts from NAE (National AeronauticEstablishment) and in consultation with CAP (Canadian Aircraft Products). A series of measurements are planned in the main machine to define the parameters required for low RF leakage and third harmonic flat-topping. In parallel, the prototype testing will proceed on the test-stand and with model studies in the 1 : 1 0 scale cavity model as described in the Cyclotron section of this report.Significant progress was made in the areas of diagnostics, probes and controls. New monitors were inserted in strategic positions along the various beam lines. Several improvements to the existing probes were introduced for reliability as described in the Probes-Diagnostics report. The improve­ments introduced at the controls during 1982 paid their dividends in terms of machine reliability. A new feature which should be highlighted is availability in the control room of the VAX 730 development computer.This computer will have access to all cyclo­tron data and will be used to upgrade the high level language programs to aid opera­tions, to make the existing information easily understandable and to analyse the data for stability and reproducibility studies.For both diagnostics and controls more effort is needed, especially in light of the new machine developments which require new and more sophisticated beam measurements in the cyclotron and the control of additional systems like third harmonic flat-topping, RF boosters, electrostatic or magnetic channels. The lack of expert manpower is at present slowing down the progress in these areas.This will hopefully be remedied during the coming year so that these systems will be at the level required for the next several years of TRIUMF's operation.The two major projects designed to upgrade the capability of the polarized and non­polarized ion source are proceeding well.The third ion source terminal is being erected and its volume is such as to be able to contain both an unpolarized and a polarized source at the same time.The engineering of the power services, the cooling services and the control services inside the terminal is well ahead. As soon as the injection line joining the third terminal to the existing horizontal line is installed, it will be possible to test the third terminal system at high current using the high intensity H“ Ehlers source presently mounted in the laboratory for improvement studies. The power and the cooling to the90<0DC.<1o2  <LlI00WEEK_3 |  SCHEDULEDI llA h = 3.6 xIO C it,“  [/] ACTU ALFig. 94. Beam production, scheduled vs. actual.third terminal are, however, adequate to supply other types of sources. If the planned ion source tests are successful, a cusp source will be eventually installed for operational purposes.The high-intensity polarized source program is now definitely aiming at demonstrating the feasibility of cw current in the order of 15 to 30 yA of H“ polarized beam through an optically pumped source similar to the one which has already produced extremely good results in a 2% pulse mode at KEK in Japan. The ion source development group at TRIUMF is proceeding on this challenging project. The emittances of the beam have been measured at KEK and are acceptable to TRIUMF. The whole program is being conducted in collaboration with physicists from Japan and from other countries, and there is a great deal of interest in this research. The H- high intensity polarized source workshop organized by TRIUMF during the summer has been extreme­ly successful in terms of attendance and con­clusions. The panel has agreed on the limits of the Lamb-shift type H- sources and reviewed the most promising projects for high intensity polarized H“ sources including the one mentioned above.To summarize the situation of the cyclotron at the end of 1983, one can state that the day-to-day beam production and reliability have been substantially improved over previ­ous years, sometimes at the cost of a slow­down in developments or major projects. Towards the end of 1983 new major projects were started and existing ones were givenhigher emphasis. Also, it should be empha­sized that most of the present developments are inter-related and have to be brought ahead in parallel. The next challenge for the Cyclotron Division is to be able to bring ahead the developments successfully and at the same time maintain or improve the present level of operational reliability. It is clear that most of the developments described and being pursued are extremely important and critical for the operation and the potential of the cyclotron during the next ten years and therefore should have the highest priority.BEAM PRODUCTIONThe operation of the cyclotron during the year was quite successful, with records being set in both polarized and unpolarized opera­tion. There were 843 actual hours of on- target polarized operation and 2932 h of unpolarized. This compares to 985 and 2900 the previous year. The total hours of injected beam for the year was 4166 h.Figure 94 shows the unpolarized beam de­livered for the year and the amount delivered each week. The total for the year was 243,000 pAh compared with 229,000 pAh in 1982.The polarized operation in June saw 275 nA being delivered continuously over a two-week period with only one hour of downtime due to the source. Later operation was not as successful but the efforts being made to91improve polarized operation, both in relia­bility and intensity, are showing signs of fruition.Although the year's operation overall was considered a successful one, it was not without problems, and continuous effort was required to keep the cyclotron operational. After each shutdown period equipment failures continually plagued the operation of the machine for about two weeks. There seemed to be no specific type of equipment failure which one could predict or prepare for.Three specific major failures accounted for most of the lost time. One was sparking of the inflectors. It was found that an inferior batch of insulators had been received and installed. These insulators were changed out and small modifications were also made in the insulator area to help out- gassing. The second major failure was the breaking of the beam line 4 extraction probe azimuth drive tape. This was repaired and a new design is in progress which will change this drive to a cable system. The third major failure was a water leak in a stainless steel bellows between the header and the connecting block in the resonator cooling system inside the vacuum tank. It took one week to replace and a complete analysis of the faulty bellows was done by the UBC Metallurgical Engineering Department (see RF system section).Figure 95 shows the yearly total of beam pro­duction lost due to equipment failure, by group. This lost time is time lost while operating. It does not show any downtime1983( 2900 )(413) MAINTENANCE (686) DOWNTIME (135) OVERHEADINFLECTOR (64) SAFETY (30) CONTROLS(50) MAGNETS(49) VACUUM (47)RF (144)(170)DOWNTIMEFig. 95. Operating record for 1983.where rescheduling occurred and a major downtime was required to repair the damage, for instance the repair of the bellows in the resonator cooling system. The total scheduled time of cyclotron operation was 5300 h and the total of the downtime due to equipment failure was 650 h plus 237 h off due to various machine trips and unscheduled tuning. The total equipment failure rate was 12% of the scheduled operating time. The two systems causing the most downtime were ISIS and the RF system.Table VII shows the scheduled and delivered microampere hours to each experiment during the year. A 'P' in the hours column indicates polarized operation.CYCLOTRON Cyclotron development RF studiesDuring 1983 efforts to reduce the leakage of RF radiation into the cyclotron tank con­tinued on the 1 : 1 0  scale model of the cyclo­tron. A number of improvements were made to the model to enhance the agreement with the main machine. The resonator segments, in­cluding the ground arms, were reconstructed using copper sheet. The central region was modelled as in the main machine to correctly simulate the cyclotron capacitance in that region. An experiment to determine whether "lossy" or resistive M-foils connecting adjacent segments should be used was per­formed, as well as a test simulating a stain­less steel surface on the beam side of the hot arms. The results did not indicate a clear choice of material and more tests with the main machine are required.On the main machine an attempt was made to reduce the leakage by using a limited number of short M-foils. The frequency of the para­sitic TM310 mode changed by about 1/3 of the amount predicted from the model and therefore did not produce the expected reduction in the leakage. This discrepancy is thought to be due to the detailed nature of the strongback ribs. Experiments are being carried out to verify this on the model.Measurements taken of the voltage profile of the lower half of the south dee are shown in Fig. 96. At segments 2 and 8 large departures from the "smooth" curve are evident. Subse­quent tests in the 1 : 1 0  model showed that92Table VII. Beam to experiments - total 1983.Experiment* Channel Scheduled h p AhDeliveredh pAhQQD Mil 150 14 404 131.25 12 263.05Tune M20 92 10 580 78.03 9184.03Tune Mil 265+46P 17 430 238.70+22.85P 12 742.2247 M20 486 57 720 463.00 53 127.4854 Mil 12 960 3.25 347.0788 M20 150 10 170 122.90 5481.94104 M9 2650 278 965 2304.80 231 798.72134 Ml 3 803 65 865 631.00 48 170.55147 M2 0B 368 34 060 334.40 28 387.64150 M20A 230 23 000 193.05 18 040.79157 M20A 265 26 665 212.00 21 818.99160 M20 35 3500 25.38 2212.72161 M2 0B 35 4550 34.30 3967.99166 M13 334 32 020 310.25 25 545.24167 Mil 231 23 100 211.80 20 561.23168 M13 242 24 200 194.25 18 783.60178 M13 69 8970 61.30 7281.17191 M20 353 42 560 294.79 33 424.34196 M13 127 12 700 98.46 9178.51199 Mil 380 41 615 316.65 33 190.89202 M13 452 51 470 408.75 46 619.29204 M13 208 23 920 191.18 22 780.94205 Mil 474 61 620 427.05 53 062.21211 M20 219 28 470 177.40 21 150.85213 M13 243 31 050 228.47 25 660.53217 Mil 384 39 840 324.35 26 151.98219 Mil 127 12 700 104.80 10 027.73220 M20B 263 18 180 175.29 10 563.43224 Mil 554 41 470 416.81 25 570.37229 M9 139 9840 105.48 7206.88232 M20 243 26 040 213.75 22 549.74233 Mil 92 10 580 78.03 9184.03239 M2 0B 161 18 320 136.48 13 748.18243 Mil 127 16 510 125.05 15 374.70246 M13 150 19 500 116.10 13 869.68248 Mil 104 11 870 99.55 11 328.49175 IB 242+300P 146.40+174.60P205 IB 346P 168.87P208 IB 128 30.85Perm, magnet 4A 323 221.15SEM development 4A/2 46 0121 4A/2 531+266P 329.75+131.45P189 4A 81 34.70190 4A/2 311+323P 204.15+241.55PMRS development 4B 280 162.80Phlons 4B 0 4.70131 4B 23 10.90142 4B 69 55.40165 4B 104P 87.10P194 4B 150P 92.70P+9.0195 4B 127 83.90206 4b 463 285.35212 4B 347 219.80215 4B 69 61.20218 4B 104 79.70221 4B 127 113.85223 4B 125 90.25234 4B 127 98.60236 4B 127 56.00238 4B 127 0*See Appendix C for experiment title and spokesman.93-  80 S .strooCO60QUADRANT 3 QUADRANT 4LOWER DEE x x UPPER  DEE20o 4 l-L- _1_ _L9 5 I I  5 9RESONATOR SEGMENT NUMBERFig. 96. Measurements of the tip-to-ground RF voltage profiles for one of the TRIUMF dees.this effect could be explained by a poor RF contact at the root segment. This also produced higher RF leakage in the tank model,which is more consistent with the leakageobserved in the tank. During the nextshutdown the main resonator roots will beinspected and replaced where necessary. As well, new RF probes will be installed so that all possible segments will contain a voltage probe.An experiment was carried out to determine whether the RF phase of a given segment is affected by the vibrational movement of that segment tip. It was found that although the phase of the entire cavity varied by as much as ±5° relative to the master oscillator phase, the phase difference between any two segments was very small (<0.6°). There was a constant phase difference of 2 1° between the north and south dees.Studies of third harmonic tuning mechanisms were carried out on the model using shorted A/4 tuning stubs to shift the third harmonic resonant frequency. The RF cavity could be successfully tuned to resonate at both the fundamental and third harmonic. By using only two tuning stubs the amplitude of the third harmonic varied considerably along the RF gap. The effect of the central region on the third harmonic voltage along the dee was greatly reduced when the properly modelled central region was installed. An alternative method of providing third harmonic tuning, in which the cavity itself is perturbed, is discussed in the RF section.DiagnosticsNew cyclotron diagnostic developments occurred in a number of areas. A prototype system was tested that allowed the simultane­ous measurement of the current on a high energy probe and the time of flight in the cyclotron. Work continues on the development of low noise amplifiers for current readout of the emittance apparatus current harps. Development has begun on a split plate posi­tion monitor for ISIS. Tests to date indi­cate that the beam may be positioned success­fully for currents of 30 pA (peak) at any duty cycle.New capacitive RF voltage probes were devel­oped to measure cavity voltage profiles. The frequency response of the probes was cali­brated using a constant impedance parallel plate split transmission line designed specifically for these probes. This tech­nique enables us to make absolute voltage measurements in the TRIUMF cavity.Due to the pulsed nature of the beam injected into the cyclotron, the beam loading of the resonant cavity will have a similar modula­tion. For extracted beam currents of 130 pA this results in a RF voltage modulation of ~400 V. If the ISIS pulser frequency is increased so that the pulser period equals the time of flight, then the beam loading in the cavity will be approximately constant. When one of the spare ISIS pulse width modulators was modified to allow control of both pulse width and pulse frequency, it was possible to reduce the beam loading effect by more than a factor of 5. Work is proceeding on a new design for the ISIS pulse modulator. A control algorithm will be required to match the pulse frequency to the time of flight of the beam in the machine, which varies accord­ing to machine tune and resonator voltage.Magnet stabilityIn order to provide separated turn operation drifts in the main magnet must be reduced to <1 ppm. This stability has been achieved for short periods of time with modifications to the main magnet power supply. To reduce longer-term drifts a high resolution NMR sys­tem is being developed. The system uses a digital frequency synthesizer controlled by a CAMAC-based microprocessor and has been shown, on a test bench, to measure the mag­netic field with a resolution of 0 . 1  ppm and a 10 Hz bandwith. This system should allow94the beam phase to be stabilized directly from the magnetic field measurement, rather than using the measured phase excursions of the extracted beam. A second NMR probe has been installed on hill #6 to determine whether long-term drifts occur equally for all hills.Data acquisitionThe VAX-11/730 computer acquired last year has now been moved to the central control room. This will allow testing and develop­ment of a direct read/write interface to the expanded executive crate (see controls sec­tion) . At present the VAX communicates with the cyclotron data base by means of an RS232 link with the HLL Eclipse. This allows acquisition of cyclotron data directly into the VAX for further analysis. An interactive analysis and graphics plotting package has been installed on the VAX, and provides imme­diate display of trends, correlations, etc. of data acquired. In parallel with the CAMAC interface to the central control system a separate serial/parallel highway CAMAC inter­face has been installed and commissioned.The software drivers for both the serial and parallel highways are operational. This will allow studies and acquisition of data from devices not directly connected to the control system, such as the 1:10 RF model and diagnostic devices in their test phases.RF systemR esonator im provem ent program  GeneralLast year saw the manufacturing of a proto­type resonator segment and the building of an RF test facility. The major effort this year was focused on testing the prototype reso­nator and improving the engineering design for future requirements such as third harmon­ic operation and alternative extraction systems.Prototype resonator programThe Mark I prototype resonator segment was mechanically tested prior to installation in­to the RF test facility. The concept of pre­stressing the two major structural members was successful in producing a flat hot arm panel profile. A tip stiffness of 30 lb/in. and a natural mechanical frequency of 2.4 Hz was measured. This compares to 55 lb/in. and 4.9 Hz, respectively, for the existing reso­nators. Although the tip stiffness of the prototype resonator is less than the existing resonator, it is less sensitive to cooling water pressure changes, and the combined ef­fect is an amplitude vibration of 0.0015 in. on either resonator as measured in the test facility.Planned improvements such as separated turns and third harmonic operation demand that the amplitude of the tip vibrations of the new resonator segment be improved by almost an order of magnitude. In order to achieve this improvement emphasis was placed on achieving a maximum hot arm stiffness to control the effect of dynamic vibrations. Several improved conceptual designs and various manu­facturing techniques have been investigated and are still under investigation.In parallel with the engineering design effort the acquisition of a FFT vibration analyser and sensitive piezoelectric accel­erometers has enabled us to perform vibration measurements on the existing resonator system. We now have available the vibration characteristics of a resonator segment and an octant of segments, the magnitude of segment tip vibration as a function of cooling water parameters and the effectiveness of the existing resonator segment dampers on reduc­ing tip vibration amplitude. The results of these measurements will provide valuable input into the design concepts of the new resonator segment.Work has continued on the root tuning foil and actuation system. A life test rig for the root tuning foil was commissioned early in the year and was run the equivalent of 20 years cyclic operation without a problem. Other designs currently being examined will exhibit a reduced operational load and shorter current path for reduced heat genera­tion. The root tuning actuation system test rig has been operational for several months and has highlighted some fatigue sensitive areas. In conjunction with a softer root tuning foil steps are also being taken to decrease load levels in the actuation system.With the help of the Engineering Physics group a survey program to check tank align­ment and the subsequent effect on resonator alignment was begun this year. In the December shutdown 150 targets were placed at grid points on the floor and lid of the tank and their elevation measured using the alignment periscopes which are used for95resonator tip alignments. 150 more targets will be installed in the March 1984 shutdown to complete the measurements of the array of grid points.Model workMeasurements on the 1:10 scale model con­tinued to give further understanding of the RF leakage at the fundamental frequency, but with emphasis this year on the third harmon­ic. The measurements were expanded to include not only leakage but also voltage distribution along the dee gap and possible tuning mechanisms for third harmonic operation. The results are discussed in the Cyclotron Development section of this report.Test facilityThe prototype resonator segment and a spare se