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

Annual report, 1978 TRIUMF Jul 31, 1979

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T R I U M FANNUAL REPORT 1978MESON F A C I L I T Y  OF:UN IV ERS I T Y  OF ALBERTA  SIMON FRASER UN IVERS I T Y  UN IV ERS I T Y  OF V IC TOR IA  UN IV ERS I T Y  OF BR I T ISH  COLUMBIATRIUMFANNUAL REPORT 1978TRIUMFUNIVERSITY OF BRITISH COLUMBIA VANCOUVER, B.C.CANADA V6T 1W5EXISTINGPROPOSEDH" POLARIZED ION SOURCEBLAA(p) BLA(p)SERVICEBRIDGECYCLOTRONVAULTPROTONHALLBLAB(p)MRS SPECTROMETER BL1(p) H~ ION SOURCEFUTURE NEUTRON THERAPY FAC I LIT IESto—‘  'oTrBLlB(p)70-90 MeV BEAMBATHOBIOMEDICALLABORATORYTHERMAL NEUTRON FAC ILITY7 ' ' h4-ISOTOPEPRODUCTIONCYCLOTRONRADIOISOTOPELABORATORYNEUTRONACTIVATIONANALYSISFOREWORDThe experimental program and facility development at TRIUMF grew in 1978 beyond reasonable expectations.In 1978 TRIUMF produced a total of about 5 x 1020 protons, which is yust under a milligram of 500 MeV protons. The protons in turn pro­duced a slightly smaller number of pions— or under one ten-thousandth of a gram of pions. But that was three times more than the year before. The same growth rate continued for twenty years would see TRIUMF pro­duce about 100 kG of pions in a single year, but that would take more electric power than Canada produces. At present the aims of the orig­inally planned meson factory are being fully realized with the annual production of a fraction of a milligram of pions.The success of TRIUMF is chronicled in this annual report in the large number of experiments under way and completed. It is reflected in the very satisfactory growth of grant support. The rewards of TRIUMF are manifest in the extraordinary growth of the applied program dur­ing 1978.The momentum of TRIUMF is clearly evident in the design steps now be­ing taken under the leadership of TRIUMF's former director, Dr. J.R. Richardson, to add a kaon factory to TRIUMF in the mid 1980's by using TRIUMF's cyclotron as an injector for a synchrotron to be built. The worldwide interest in TRIUMF is evident in the many scientists from around the world who work here. The arrangements for them are varied and perhaps epitomized by the successful initiation in Vancouver of a major support fund from generous private donors in the city to help exchange between TRIUMF and the Weizmann Institute in Israel.The director of TRIUMF, Dr. J.T. Sample, and his colleagues are to be warmly congratulated on their accomplishments during 1978.E.W. VogtChairman of the Board of ManagementvTRIUMF was established in 1968 as a laboratory operated and to be used jointly by the Universityof Alberta, Simon Fraser Uni­versity, the Universityof Victoria and the University of British Columbia. The facility is also open to other Canadian as well as foreign users.The experimental program is based on a cyclotron capable of pro­ducing two simultaneous beams of protons, individually variable in energy, from 180-520 M e V . The potential for high beam cur­rents— 100 yA at 500 MeV to 300 yA at 400 MeV— qualified this machine as a 'meson factory1.Fie1ds of research include basic science, such as medium-energy nuclear physics and chemistry, aswell asapplied research, such as isotope research and production and nuclear fuel research. There is also a bi omed ical research facility which will use 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 1 9 7 7 -The laboratory employs approximately 215 staff at the main site in Vancouver and 12 based at the four universities. The number of university scientists and support staff associated with the present scientific program is about 175-CONTENTSPageINTRODUCTION 'OPERATION AND DEVELOPMENT OF FACILITIES 3Cyclotron 3Beam Development 10RESEARCH PROGRAM 26Introduction 26Particle Physics 28BASQUE 28Measurements of p-p and p-4He analysing powers at medium energies 31Etude de la disintegration EEX e+vey 31Charge exchange of stopped IES in nuclei 33Muon radiative capture 3^ tBound muon decay in nuclei 35Rare electromagnetic decays of pionic atoms 36Pion production by proton bombardment of hydrogen and other light nuclei 38A survey of proton-proton bremsstrahlung 38The time projection chamber 39Reduction of multiple scattering displacement by a magnetic fieldparallel to the beam ^0Daresbury-Mainz-TR1UMF collaboration at CERN ^1Nuclear Physics and Chemistry ^2Pi scattering and total cross-section measurements ^2Strong interaction shift in 7i3He ^Variation of pionic X-ray intensity with atomic number ^6Strong interaction effects in pionic atoms ^7Elastic scattering of protons from 4He ^7Quasi-elastic scattering ^8Studies of the (p,2p) reaction on 4He ^9Studies of (p,d) reactions in nuclei 50Inclusive scattering of 500 MeV polarized protons on helium 51The characteristics of fragments emitted from silver with 200-500 MeV protons 51I ntermediate-energy fission 53Neutral pion production 56A study of the production and decay of 1]-Be with intermediate-energy protons 57Research in Chemistry and Solid-State Physics 58ySR i n soli ds 58Muoniurn chemistry 62Muonium formation in insulating powders 67Applied Research 68Biomedical experimental program 68Proton radiography 71Isotope production 71Ferti1e-to-fissile conversion (FERFIC0N) 72Theoretical Program 73v i  iCYCLOTRON SYSTEMSIon Source and Injection SystRF SystemProbesVacuum System Remote Hand ling Safety ControlsData Interface Task Force I nstrumentat ionEXPERIMENTAL FACILITIESI ntroduct ion Meson Ha 11 M9 ExtensionMl 3 Low-Energy Pion ChannelBeam Line IBTargetsThermal Neutron Facility Proton Ha 11ORGANIZATIONAPPENDICESA. Publi cationsB. StaffC. Users GroupD. Experiment ProposalsINTRODUCTIONDuring 1978 TRIUMF continued to increase service to experimenters, with higher beam current delivered and cyclotron availability increased to 8A%. At the same time develop­ment continued of the cyclotron and experi­mental facilities. In particular:1) Several shifts were provided with extracted beams in excess of 100 yA.2) Operation at 30 yA became routine.3) The total beam delivered to targets wasincreased by a factor of 3 over 1977-A) A polarized proton beam of 200 nA was provided on a regular basis.During this period measurements of cyclotron parameters were continued with the aim of improving energy resolution, beam stability and beam spill. The reduction of leakage of radio-frequency power in the cyclotron great­ly increased stability and reliability of the cyclotron. Integrated beam output con­tinues to be limited by radioactivity of machine components not fully remotely serviceable, although great progress toward remotely controlled removal and replacement of such components as RF resonators makes many operations 'almost remote1. A new microprocessor-based safety interlock system was developed to permit extensions and changes in configuration on relatively short notice without compromising safety standards.The experimental programs begun in 1976 and 1977 gained momentum through 1978 with new results in all fields; the large program in n u c 1eon-nuc1 eon scattering changed course upon the completion of measurement of Wolfenstein parameters at several energies. The installation of shielding beams overmuch of the proton hall enabled angular ad­justment of the medium resolution spectro­graph and many experiments awaiting this facility will be completed during 1979- The continuation of researchon 'forbidden' decay modes of muons and pions, an exciting field in which TRIUMF experiments have made fore­front contributions, will be accelerated during 1979 because of the completion of the design and much of the construction of a Berkeley-style time projection chamber during 1978. The thermal neutron facility, essen­tially completed in 1 9 7 7 , has been fully commissioned for experiments, some of which are under way. While a flux in the neighbourhood of 1012 per square centimetre per second is unimpressive by reactor standards, it attracts users in an area without research reactors.The increase in integrated beam intensity has caused the applied science program to burgeon. Advances in ir" dosimetry will per­mit the beginning of a clinical experiment in cancer therapy during 1979- A grant from the federal Department of Health and Welfare provided support for a pilot program supply­ing iodine-123 to several hospitals distributed across Canada with generally enthusiastic response concerning the prefera­bility of 123I to the commonly used 131I.A contract was completed between TRIUMF and Novatrack Analysts Ltd. who began a commer­cially oriented program in neutron activa­tion analysis based on the newly commissioned thermal neutron facility. The Commercial Products Division of Atomic Energy of Canada, Ltd. completed a contract with TRIUMF and other agencies for the commercial production of radiopharmaceuticals made as a byproduct by the various beams extracted from the TRIUMF cyclotron. A $3.5 M construction program was begun.The TRIUMF Board of Management, the govern­ing body of the joint venture called TRIUMF by the four founding partners (the Univers­ity of Alberta, Simon Fraser University, the University of Victoria and the University of British Columbia), elected Dr. E.W. Vogt for a further term as Chairman. Two universities chose to change their representation on the Board: Dr. Peter Larkin, Dean of Graduate Studies at UBC has replaced Dr. Michael Shaw, and Dr. Bruce d a y m a n ,  Associate Dean of Graduate Studies, Simon Fraser University has replaced Dr. Brian Wilson whose long service to TRIUMF deserves special notice.The University of Alberta nominated replace­ments for both of its representatives on the Operating Committee: Dr. W.C. Olsen and Dr. P. Kitching have been replaced by Dr. G. Roy and Dr. J.A. Cameron. The Experiments Evaluation Committee met twice during 1978 to consider new proposals and review progress on previously approved ex­periments. The scientists and management atTRIUMF wish to thank retiring members M.D. Hasinoff and E.W. Vogt for providing their expertise to the committee. We welcome A.D. Bacher, G.A. Beer and F.C. Khanna as new members of the EEC.In spite of budget cuts by the Federal Government in many areas, support for TRIUMF increased for fiscal 1978-79 as shown in the f o 11owing tab 1e :Fund i ngOperat i ng CapitalResearch grants1977/78$ 5 , 360,000 1 , 702 ,000  1 , 113,6001978/79$ 7 , 176 , 0 0 0  1 ,519,000 1 , 8 1 8 , 0 0 0The National Research Council and the Natural Sciences and Engineering Research Council were able to provide increased funds to a growing organization even though their overall budget increase was slight.J.T. Sample Di rector2OPERATION AND DEVELOPMENT OF FACILITIESCYCLOTRONDuring 1978 the cyclotron performance con­tinued the trend of improvement over the preceding year, with more hours of scheduled beam operation, more hours of beam delivered and more microampere-hours. The highlight of the year's operation was the successful commissioning of the beam line 1 extension and the thermal neutron facility (TNF). The shutdown for the installation of the TNF started in the fall of 1977, and most of the details of this facility are described in last year's annual report. First beam to the TNF was obtained in early January, and the commissioning culminated in a successful high-current test run of one hour at over 100 yA on February 13- Since then there have been 8 beam shifts with currents in ex­cess of 80 yA for meson production. Later inspection of the lead target in the TNF has revealed no apparent damage. More details of the commissioning results are covered in a later section (p.93).There were two major shutdowns during the year: a six-week shutdown in May-June forwork in the cyclotron and the proton hall and a shutdown in October for improvements in the proton hall and the installation of two new beam lines in the meson hall. The cyclotron and proton hall resumed operation in December.During the May shutdown beam line AA was up­graded for routine operation at the 10 yA level. This was partly motivated by the in­stallation of a cesium target near the 4A dump for the production of 123I. During the last three months of beam operation a 12-hour iodine production run was scheduled once per week.The microampere-hours of beam increased by a factor of three over 1977 to a total of27,000 yAh. The best week of operation pro­duced 2700 yAh. Figure 1 shows the total number of microampere-hours of beam delivered per month over the past three years. A sig­nificant result of the higher-current opera­tion, which augers well for future intensity increases, has been the reduction in residu­al activity induced in the cyclotron tank per microampere-hour. This has come about from a number of improvements: beam tuning to correct the vertical excursions; reducedvacuum pressure in the cyclotron tank to lessen the beam loss in the cyclotron; and addition of removable beam stops for the e 1ectromagnetica11y stripped beam to reduce activation. This reduction in activation can be seen in Fig. 2 which shows the micro­ampere-hours per year and the residual activity at the cyclotron tank centre since first beam. Also shown is the total dose to personnel in man-rem, which indicates a similar relative reduction.Although much of the effort in cyclotron development was aimed at improving the beam performance for high-current operation, several significant steps were taken towards gaining a better understanding of the factors affecting beam stability and resolution.The simultaneous extraction feature of the TRIUMF cyclotron puts very stringent require­ments on the beam stability, especially for operation at high circulating beam intensi­ties. Typical extraction requirements are currents of tens of microamperes for meson production simultaneous with currents of a few nanoamperes on beam line AB for nuclear physics experiments. Improved beam energy resolution from the cyclotron is important for the optimum performance of the medium resolution spectrometer. Studies of beam resolution were possible during 1978 after the commissioning of two centring probes and four pairs of internal slits. The use of in­ternal slits with a well-centred beam allowedFig. 1. Cyclotron beam current.3cr<UJ>-5$, 2crz<5IxJGOO0_J1Fig. 2. Microampere-hours per year and residual activity in the cyclotron since first beam.identifiable separate turns to be observed to 200 MeV and the extraction of a 400 MeV beam with an energy spread of less than 500 keV. This work and the studies of the factors affecting beam stability are described in the section on Beam Development.Polarized beam was operated for about 23% of the time during the year compared with 38% for 1977- The outputof the source continued to improve, with typical source currents of1.0 yA and currents up to 200 nA on the ex­perimenters' targets. With the completion of the polarized beam phase of the BASQUE ex­periment in April the current capability of the polarized source is not fully utilized by the remaining experiments. However, the installation of a new primary proton line beam line IB, intended primarily for polar­ized beam operation, will increase the polarized beam capability by enabling two experiments to use polarized beam simultane­ous 1 y ear 1y in 1 9 7 9 •Operation and performanceThere were no significant changes in the cyclotron operation other than the fact that higher currents are being delivered. Opera­tion at beam currents up to 30 yA is consid­ered routine, with existing beam diagnostics and machine protect interlocks able to cope satisfactorily at this current level. At currents of 100 yA assistance from beam physicists is required to set up the tune, in particular along the injection line. How­ever, as more experience is gained in this mode of operation, and with the commission­ing of further beam protection interlocks, it is anticipated that this current level will be routine in the near future.The performance of the cyclotron is summar­ized in Table I. Machine availability for the year was 8 3 .8%, a slight improvement over the corresponding figure for 1977. The division of the beam time between polarized and unpolarized operation is shown in Fig. 3- The period from June 13 to October 26 repre­sents the longest stretch of continuous operation since start-up.The operating record for the year showing the breakdown of machine downtime is illus­trated in Fig. b . The downtime in almost all cases represents the accumulation of many short periods of machine off due to component failures. A better understanding of the RF problems has come about with the capability of adjusting eight of the resonator ground arms remotely. During the fall shutdown the upper and lower resonator arrays were elec­trically connected at the flux guides lead­ing to cons iderable reduction in the RF leakage. One problem which caused little downtime but some concern was a water leak which developed in the TNF target chamber. This leak was traced to a corroded burst disc on the con­crete/steel reflector shield tank, which was eas i1y repa i red.S  160UJ5COCT 120^  8 0<crUJ Q.o4 0<UJm□  TOTAL HOURS OPERATION EZ) POLARIZED BEAM OPERATION/I n2 1ruTIUiJAN FEB MAR APR MAY JUNE JUL AUG SEPT OCT NOV DECFig. 3. Beam operation in 1978.bFig. 4. Operating record for 1978.Table I. Summary of machine performance 1978.hoursScheduled operating time 6014Scheduled maintenance 723Injected beam Unpolarized 2862Polarized 849371 1Cyclotron Tune-up, development and training 707yA hours 26950Beam line 1 Tune-up and development 186Experiment 2456Beam line 4 Tune-up and development 248Experiment 2564Downtime 860ISIS 143POL I S I S 96RF 225Controls 71Probes 37Vacuum 36Magnet ^7Services 86Safety 18Other 103Machine availability (average) 83-8%5Table II. Beam time to experiments 1973.Area / Beam Line Exper i ment Short Title SpokesmanNumber of 12-hour shifts scheduled(P) polarized beamBEAM LINE 1Development - - 14M8 61 B i omed i c a 1 L.D. Skarsgard 19515 (P)1 ,53 EE scattering and R.R. Johnson 17-5heavy fragments1,54 IE scattering R.R. Johnson AM9 M9 development - - 10Alb EE EE0 charge exchange M.S. Hasinoff 53M. SalomonA2a 7T3He G.R. Mason 856b tt ■+ evy P. Depommier 50.513,89 p-fission, p-X-rays S.N. Kaplan 1630 Pionic X-ray R.M. Pearce 17,0 M u o niumi n insulators J.B. Warren 871 pSR J. Brewer 2591 Muoniurn in semi­ J . Brewer 10conductors83 Bound muon decay M.D. Hasinoff 1097 Rare decay of pionic M.D. Hasinoff 24.5a toms1,53 EE sea t ter i ng and R.R. Johnson 16heavy fragments108 Meson cascade R.M. Pearce 3M20 35,71,78,91 pSR J. Brewer 222BEAM LINE 4AD e v e 1opment - - A3 Fragments R.G. Korteli ng 206 F i ss i on B.D. Pate 1411 Gas jet J.M. D'Auria 1 1120 Production of 1JBe K.P. Jackson 393 1 n-a i r i rrad iat ion B.D. Pate pa ras i t i c115 EE production J.M. D 'Aur ia paras i t ic48 FERFIC0N 1 .M . Thorson 677 1^3I production J .S . Vi ncent 826 np differential D.A. Axen 61cross-sect ion27,40 np scattering D.A. Axen 45 (P)D .V . Bugg 687 Proton radiography E.W. Blackmore 12BEAM LINE 4BDevelopment - J .G . Rogers 23S MRS comm.58 Polarized (p,2p) P . Ki tch i ng 11 (p)Q59 (p,2p) on ^He W.T.H. van Oers0198 (P)99 (p,d) reactions J . Ka 1 1 ne 14.51A Proton elastic G.A. Moss 6.5scatteri ng W.T.H. van Oers 21 (P)15 Quasi-free scattering W.J. McDonald 31105 Backward inclusive G . Roy 7scatteri ng 10 (P)10 PP -> TTd G. Jones 4 (P)3CYCLOTRON D e v e 1opment - - 366Beam time to experimentsTable II shows the number of 12 h beam shifts scheduled to experiments during 1978.Cyclotron improvements and developmentsReliability, availability of 100 yA on demand, new extracted beams, beam resolution, beam stability and special beam time struc­tures have been the directions toward which improvements and developments have been performed. The previous 100 yA Task Force and the Separated Turns Task Force were suspended, and a new Cyclotron Development Group was created to co-ordinate the devel­opment efforts and to take direct initia­tives for developments not covered by the trad i t i o n a 1 groups.A major step toward reliability was achieved by the RF Group, which was able to reduce the RF leakage from the cavity into the beam gap by at least an order of magnitude. Previously this leakage had been responsible for overheating and melting of several ex­posed components and for RF noise or arcing phenomena on low-energy probes and other central region elements. Due to overheating the resonator structure was gradually sag­ging, posing a difficult long-term problem to the mechanical engineers. The reduction in leakage was achieved mainly by connecting the upper and lower resonators together in the neighbourhood of the accelerating gap at outside radii. The system is presently being carefully tested to determine whether a further reduction in leakage is possible.It appears that heating effects have been substantially reduced.Particularly beneficial for the stability and reliability of the 100 yA operation were the improvements in the H" Ehlers type source, which produced an increase in bright­ness by a factor of five and allowed a corresponding reduction in the emittance of the externally injected beam at equal values of injected current. The size of the slits in the 12 keV beam formation region could be reduced, and the transport along the 300 keV injection line became less marginal. In the improved ion source plasma oscillations can now be reduced below 10%, simply by control­ling the gas pressure and the arc voltage.The rate of sparking across the 12 kV gap, between the source and the surrounding elec­trodes, is down to a few per hour or less.The increasing residual activity in the tank, a function of the increasing average production current, requires that the maintenance time required for the tank com­ponents be reduced correspondingly. One of the two high-energy probes was replaced with a more reliable system, and two sets of central region steering plates were substi­tuted with new sets more easily removable.At the resonator tip in the central region two aluminum quadrants were replaced with copper ones to complete the work initiated during 1977 after melting damage had been caused by stray electron beam in that reg i o n .The remote handling equipment for the tank components was upgraded to include a new trolley for the upper resonator panels, an outrigger and a 'nut-runner' trolley. The trolley for the lower resonator panels was successfully used, and the commissioning of other equipment for various elements is well in progress. Some elements are being redesigned for easier remote handling; the most significant examples are the central resonator panels and some of the central region equipment lying on these panels.The vacuum is now normally below 10-7 Torr during operation, with optimum values, after a few weeks of pumping, of 6 x 10-8 Torr. Most of the residual pressure is due to hydrogen which is induced when the RF power is applied to the resonators and which is not pumped by the 20° cryopanels.A 25,000 £/sec 3°K He cryopump was in­stalled to pump the hydrogen gas load. The initial tests confirmed the expected three­fold increase in hydrogen pumping speed over the previous diffusion pumping system. However, the helium consumption is higher than expected and the causes are being in­vestigated. The benefit of the helium pumping will be not only the reduced H” gas stripping, especially after shutdowns, but also the elimination of the need for diffu­sion pumps in steady vacuum conditions.Major installations in the vacuum tank for increased future machine capability have to be performed before the average current and the residual activity are allowed to reach too high a value. This constraint, and pressure from the users, have accelerated the program toward new extraction lines.Two new ports were added to the vacuum tank in the region of port 2 for low-energy7RESONATORSFig. 5. Trajectories of extracted proton beams for beam lines 2A (400-520 MeV), 2B (100-180 MeV) and 2C (65-100 MeV).extracted beams (65-IOO MeVand 100-180 MeV) [see Fig. 5 ]• Extraction foils were posi­tioned in the machine and beams were e x ­tracted at 70 MeV and 90 MeV. The external beam line for the low-energy beams is being developed. It is planned to have the 65- 100 MeV beam delivered for isotope produc­tion and isotope research at an experimental station in the vault simultaneously with the meson hall and proton hall beams. The con­ceptual design for an extraction mechanism for a 400-500 MeV beam from port 2 has been developed. This beam could well become the fourth beam extracted simultaneously from TRIUMF and be used for a high-flux muon or pion channel, and hopefully be used to feed the 1kaon factory1 recently proposed as a post-accelerator for TRIUMF. The possi­bility of extracting a beam from port 5 has also been kept open by installing a vacuum chamber capable of housing the extraction mechanism. More details are given in the probes section in this report (p.8 3 ).The work toward improved beam stability and energy resolution resulted from the close collaboration between the Beam Development, Probes, RF, Controls and Magnet Groups.The stability achieved for the RF system using an improved reference signal extracted from two voltage pick-up probes is better than ±6 x 10-t+ and the stability for the main magnet is around ±2 x 10- 6 . Recently a tighter mechanical connection between resonator panels appears to have improved the RF stability even further. However, a precise measurement on the effects of the new improvements is not yet in hand. Feed­back from an NMR probe is being considered for improving magnetic field stability or for stabilizing the beam phase through RFfrequency correction. In the former case the feedback would act on one of the external trim coils which has an action on the beam similar to that of the main coil. Feedback between beam phase and the RF frequency has been successfully tested by using an external beam phase signal. More details are given in the Beam Development section (p.15). Separated turns at 500 MeV require an im­provement by only a factor of three in mag­net stability and by a factor of ten in RF stability. The prospects for 100 keV energy resolution beam appear, therefore, very promising, especially if one takes into account that separated turns have already been achieved at 200 MeV energies. The effort toward flat-topping the fundamental RF with third harmonic is again being given priority, and the amplifier is under con­struct i o n .The pulse duration in the extracted beam microstructure was reduced to 0.5 nsec by using a flag and three sets of slits in the region below 30 MeV. In another effort toward special time structures four out of five beam pulses can now be eliminated and the duration between beam pulses can be in­creased from 43 nsec to 215 nsec. This is accomplished by eliminating four out of five 'spokes' in the cyclotron— fifth harmonic mode— accelerated beam. A sinusoidal voltage is applied to two deflection plates in the injection line, with a frequency one-fifth of the main RF frequency, and the beam is injected during only one RF cycle out of five. A suppression factor better than 2 x 10-7 was achieved. The effect on the secondary beam as measured in the M9 channel is shown in Fig. 6. This mode of operation will be particularly useful for rare pion decay and p~ capture experiments and is being used for background subtraction in neutron time-of-f1 ight experiments.The use of selecting devices for improved beam resolution, lower duty cycle, and more convenient time structures obviously reduces the beam current available to the users. Extraction of a significant fraction of beam at 70 MeV would also lower the avail­able operating current unless an effort were made toward more intense injected beams. This effort was initiated last year and a model H_ ion source was set up in the lab for source studies. At present the model is operating and currents similar to the ones of the operating source have been extracted. Studies to understand8_J I _ J _____ — I— L L _20 60 100Channel NumberFig. 6. Effect of the 5:1 selector on a time- of-flight spectrum with the secondary channel tuned for 100 MeV/c particles.and improve the functioning of the H" Ehlers source have started and are planned to continue during the coming year.9BEAM RESEARCH AND DEVELOPMENT CyclotronIn the cyclotron, a major milestone reached this year has been the observation of iso­lated turns at an energy high enough to be extractable (200 MeV or 226 in. radius— see Fig. 7). A great improvement in the energy resolution of the extracted beam has also been seen at 200 MeV. This turn pattern was ach i eved using the internal slits to restrict the beam and then optimizing the centring, but without any third harmonic RF flat- topping. This augers well for obtaining separated turns at 500 MeV when third har­monic RF is available.Important progress has also been made in im­proving the stability of the beam by regula­tion of both RF voltage and frequency with beam-derived signals. Simultaneous beams are now available with stable split ratios of 1/10,000. Improved tuning has led to lower beam losses, and with the buncher on more than 30% of the dc beam is now normally expected to reach 500 MeV.Regarding proton beam lines, beams of 70 and 90 MeV have been extracted for line 2C, beam line IX has been commissioned up to the thermal neutron facility, tunes have been developed suitable for the new 1AT1 target in line 1A, and the design of line IB has been completed. Additional beam monitors have been installed and others upgraded to deal with higher proton currents.Work on secondary channel optics has been centralized in the Beam Development Group for the first time this year. The design for Ml 3 (slow pion/muon channel) was com­pleted, and those for Mil (high resolution pions) and the M9 extension (stopping muons using a dc separator) are complete except for minor details. Experimental work has resulted in some progress in understanding the operation of the existing section of M 9 ■Operation at increased intensities, the recent commissioning of the medium resolu­tion spectrometer (MRS) and the eventual aim of separated turn operation have made it necessary to increase the effort to under­stand the factors determining the emittance, energy resolution and stability of the beam.This work has been facilitated during the last fifteen months by the commissioning of two centring probes, four pairs of internal slits and a 'radial flag' (Fig. 8). The centring probes consist of single fingers 0.2 in. wide which can be raised into the beam plan and run along the accelerating gaps between radii of 17 in. and 80 in. The slits consist of pairs of tantalum plates which can be raised into the beam plane and driven independently to define apertures adjustable in both width and radius. One slit runs between 27 in. and 39 in. radius, the remaining three between 72 in. and 112 in.; all run perpendicular to the ac­celerating gap. The radial flag can be rotated to intercept the innermost ions on the first turn in order to restrict the phase acceptance.Radial centring o f the beamThe turn patterns of the central orbits have been studied by moving the centring probes or slits radially while observing the in­tensity modulation on a fixed current mea­suring probe at larger radius. The slits yield a positive image of the radial beam profile, while the centring probes provide a shadow scan (Fig. 9)- With the phase ac­ceptance restricted to 15“20° by use of the chopper or radial flag it can be seen that the turn separation is virtually complete over the first 60 turns. The usefulness of this data is directly related to the speedFig. 7. Radial turn pattern between 65 MeV and 520 MeV obtained using slits. Single turns can be detected up to 200 MeV (226 in.). 1 ! 11 601 5010; o u w w u u u m i20 .0 40 .0 60 .0 R CCP)80.0Fig. 9. Centring probe turn pattern obtained big digitizing beam currents at 20 pts/in.l m n n m m m n rF ig . 8. Layout o f  d iagnostic  probe and defin in g  s l i t s  in  the cen tra l reg ion .9 0 . 08 0 . 07 0 . 06 0 . 05 0 . 0V c o *  ( $  )P R O B E S0 . 0  ' 8 0 . 0T I M E  OF F L I G H T1 60 .0  2 4 0 . 0  3 2 0 . 0R C IN)F ig . 10. Vfi cos$ measured by various techniques. F ig . 11. Centring e rro r  to 30 MeV obtained using  both cen trin g  probes and s l i t s .  The curve la b elled  2 /9 /7 8  was taken with a harmonic c o i l  powered to optimize cen trin g  a t 70 MeV.1 60 1 70 1 80 1 90with which it can be analysed and the effects of altering machine parameters observed. The beam intensity signals are therefore digi­tized every 0.050 in. and transmitted to the UBC Computing Centre. The positions of the turns are then determined by an automatic peak-finding algorithm, and the data from the two probes (or slits) analysed together to determine the energy gain per turn and the coherent centring error.The energy gain indicates Vj cos<J) ^  80 kV (or more recently 85 kV) near the centre, where V<j is dee voltage and <ji phase. This is somewhat higher than observed at larger radii by time-of-f1 ight measurements to the HE2 probe, but consistent with the tendency of the dee voltage to decrease with radius there (Fig. 10). [This effect is perhaps as­sociated with the RF impedance of the vacuum tank, as seen from the beam gap, passing through zero at large radius.]The (coherent) centring error along the dee gap varies according to the matching between the injection line and the central region (Fig. 11). It can be smaller than 0.1 in. between 1(0 and 70 in., but then increases from 70 to 78 in. (the cyclotron is most sensitive to first harmonic errors near 60 in.). The recent use of the slits to de­termine the centring error perpendicular to the dee gap shows that it can be as large as 0.4 in. in the 80-110 in. region. However, shadow measurements show that it can be <0.1 in. at 160 in. radius, where the motion is finally ad i abat i c .The effects of harmonic coils HC2 and HC3 on the centring along the dee gap have been measured and are in good agreement with theoretical predictions (Fig. 12).A fitting routine has also been developed to compute the harmonic coil currents and phases needed to correct the centring error through­out the centra 1 region. Initial work suggests_ 0.08-0.16 *-Fig. 12. Change in beam eentring along the dee gap (6°/186°) caused by harmonic coil No. 3 (radius 54 ■* 71 in., amplitude 150 AT, phase 96° or 186°). The points are experimental and the curves theoretical.that it should be possibleto reduce the error amplitude A r from 0.3 in. to 0.1 in. every­where between 70 in. and 112 in. radius. Power supplies are being connected to more of the ha rmon ic coil sets so that it shouldbepossible to effect this reduction in the near future.Radial-longitudinal coupling e ffectWhen an ion's centre of curvature is dis­placed in a direction perpendicular to the dee gap, the ion crosses successive dee gaps at different phases and in general receives a higher energy gain on one side of the dee than on the other side. Simple analytic theory shows that this effect causes the radial width of the beam at 1 80° azimuth to be nearly independent of the centring error, while at the 0° azimuth (the injection gap) the radial width increases as the centring error is increased. Figure 13 shows thd radial width obtained from centring probe scans as a function of deflector voltage. Adjusting the deflector voltage displaces the orbit centre normal to the dee gap by 0.12 in./kV. The optimum setting occurs1 9 0 2202 0 0 2  1 012RADIUS ( IN .)F ig . 13. R adia l-longitudinal coupling e f f e c t  as observed in  the rad ia l width o f  indiv idual turns  along the dee gap.when the radial widths on both sides are equal, in this case about 1 kV from the nominal setting.Use o f defining slits to improve energy resolutionFour sets of movable slits are used to re­strict and define the radial betatron ampli­tude of the accelerated beam. Their primary purpose is to provide an extracted beam with an energy spread of less than 500 keV. The radial flag and slit H2 near the centre restrict the phase acceptance of the cyclo­tron to about 10° and eliminate extreme phases which could be transmitted through the outer slits. Two of the outer slits HI and H3 are set about turns separated by one quarter of a precession cycle (about 5 turns at 30 MeV). The third slit H4 is also set about the fifth turn but on the opposite side of the dee gap to clean up some parti­cles at the extreme ends of the phase range.Due to its large size and low magnetic field the TRIUMF cyclotron is extremely sensitive to a first harmonic component in the magnet­ic field and the radial motion is not adia­batic until approximately 30 MeV. A procedure has been developed to adjust thephase and amplitude of harmonic coils between 15 and 30 MeV to centre the narrow phase band produced by the inner slit.A harmonic coil produces a coherent dis­placement of the beam in (x,px ) space with an amplitude and phase linearly related to the amplitude and phase of the first harmon­ic component of the coil currents. The centring can be determined by observing the turn pattern on a differential probe at 70 MeV. The difference between the maximum and minimum turn separation is noted and the experiment repeated several times with the harmonic coil powered with a fixed amplitude and different phases. From the results the optimum setting for centring the beam is determined by a geometrical construction. Typically the predicted setting centres the beam to 0.020 in.The coherent amplitude has remained quite stable for several hours. A turn pattern taken with a slit H2 aperture of 0.2 in. and the outer slits at 0.1 in. shows identifi­able separate turns at 200 MeV (an energy which can be extracted) [Fig. 7]- The cir­culating beam current is reduced by a factor 20. Shadow measurements have shown that the use of the slits produces a factor 3 reduc­tion in the incoherent amplitude. The resulting total betatron amplitude of typi­cally 0.125 in. corresponds to a calculated energy spread of ^60 keV. With this slit- selected beam the measured energy spread using the MRS is 900 keV FWHM at 400 MeV and 650 keV FWHM at 200 MeV. However, the spec­trometer resolution in its present configu­ration is calculated to be ^50 KeV at A00 MeV.Cyclotron stabilityThe simultaneous extraction feature of the TRIUMF cyclotron puts very stringent require­ments on the stability of the beam both spatially and in intensity. Typical250220 230 24016MAGNET TC 54Fig. 14. Stability of the extracted, beams at a high split ratio.requirements for operation require a split ratio of 1:10,000, i.e. currents of a few nanoamperes or less extracted down one beam line (primarily for nuclear physics experi­ments) while currents of tens of microamperes are extracted down the second beam line to the meson production target. This split is achieved by using as the extraction foil a 0.001 in. diam carbon wire and by inserting it from above into the 'halo' of the circu­lating beam. The success of our efforts to date can be seen in Fig. 14.Measurements of the beam fluctuations in the cyclotron show that there are two main causes, the magnetic field and the dee volt­age. These fluctuations are characterized by distinct frequency components, the former at 0.2 to 0.5 Hz and the latter at 5-0 to7.0 Hz, the mechanical vibration frequency of the resonator structure. One or both of these frequency components can be seen in the intensity fluctuations of an internal slit-selected beam or an extracted beam at high split ratio, in the energy fluctuationsFig. 15. Time of flight to 500 MeV showing components due to RF voltage and magnetic field variations.of an extracted beam (using a range tele­scope as the monitor) and in the total time of flight through the cyclotron. This latter quantity, obtained by pulsing the in­jected beam at 1 msec intervals and measur­ing the length of time for the beam to arrive at an internal probe at 500 MeV or a capacitive probe along the extracted beam line, is inversely proportional to Vj cos<j) and therefore contains contributions from both dee voltage and magnetic field.Figure 15 shows the correlation between this time-of-flight signal, the magnetic field variations as determined by integrating the voltage induced in the outer of the 54 circu­lar trim coils, and an RF voltage signal.This recording was made with the magnet tuned slightly off resonance to accentuate the effect of the beam phase fluctuations.At present the amplitude of the RF voltage induced fluctuations is about 0.4 ysec peak- peak in a 350 ysec time of flight, corre­sponding to an effective dee voltage stabili­ty of ±0 .06%.Although the RF voltage stabilization system is capable of achieving 1 part in 10l+ sta­bility, the effective stability depends on how well the reference voltage correlates with the actual accelerating voltage seen byI second/divi i i i i i i i  ....................................................i l l  i i l 1. I I l l 1 I 1250 260 28027014At  ■ I n« /  8 3 • A f  fts 6 0 - 7 0  Hx/nsFig. 16. Block diagram of the beam phase stabilization system.the beam. This is a special problem for the TRIUMF cyclotron where the dee structure consists of 80 separate resonators coupled loosely together mechanically. A number of RF voltage reference signals are available, either from capacitive pickups at the high voltage tip or inductive pickups near the short circuit end. At present the RF control system can average two of these signals to provide the reference for voltage stabiliza­tion. Initially the inductive pickups were used for this purpose but measurements of beam stability have shown that the optimum combination of signals, two voltage probes on outer resonators and on opposite corners of the dee structure, results in a factor four improvement in effective dee voltage stability. As the mechanical vibrations of the resonator are water flow induced, addi­tional improvements have been made by reduc­ing the flow velocity in the cooling channels.The RF voltage can be further stabilized by an external beam-derived signal. The total time-of-f1 ight signa1 has been used for this purpose, resulting in a further factor of four improvement in the time-of-f1ight sta­bility. However, as this signal contains beam phase variations due to the main magnet which should not be compensated with dee voltage corrections, this feedback system is not a practical option until the magnet fluc­tuations have been removed independently.Fig. 17. Beam phase stabilization using the RF frequency to compensate for magnetic field variations.Magnet stabilityAs mentioned previously the magnetic field variations can be measured by integrating the voltage induced in trim coil 5^- The present field stabilization uses this same signal as part of a slow feedback system (time constant A min) to compensate for tempera­ture-dependent drifts in the current monitor shunt. With this feedback operational the field is stable to ±2 x 10-6 corresponding to a beam phase variation at 500 MeV of ±5° or ±0.6 nsec. A phase stability of ±2° is required for separated turn operation. One method being investigated to improve on this stability is to use the beam phase to con­trol the RF frequency. A frequency shift of ±50 Hz in 23 MHz corrects for the observed magnet fluctuations. The block diagram of this arrangement is shown in Fig. 16. Con­ventional nuclear instrumentation is used except that the time-to-pu1se height con­verter is modified to output a dc voltage rather than a pulse. The cyclotron computer is used to read this voltage and generate the necessary frequency correction. The result of closing this loop is shown in Fig. 17- An intentional magnet adjustment of 15 ppm was made while the feedback was280 290 300 3 1 □15operating. The residual phase variation has been traced to lack of sufficient time response in the loop, a relatively simple improvement to make. In spite of this the stability is close to that required for separated turns.This solution has the disadvantage that it relies on a beam-derived signal. The RF frequency could also be controlled directly from the magnetic field. The trim coil 5^ signal is not satisfactory for this purpose as it is not an absolute measurement, being subject to integrator drift. However, an NMR probe capable of better than 1 ppm reso­lution and with a convenient error signal output is being built for this purpose.Transmission and e lectric strippingThe transmission through the central region is, in optimum conditions, above 40% and the phase acceptance has been measured to be as high as 45°. This transmission is in close agreement with the value that can be deduced from the measured time distribution of the bunched beam shown in Fig. 18. The current accepted by a 10° wide phase interval, de­fined by the chopper system installed just above the inf lector, was recorded as a func­tion of the buncher phase. The area within A5° around the peak is, in fact, about 45% of the total for both a 10 and a 350 yA beam. At higher intensities, with the bunching voltage kept constant at 3 k V , the peak is obviously wider due to longitudinal2eo IQBUNCHED BEAM TIME DISTRIBUTION-1 0  >iA - 350>iAI-90’ 0 90*BUNCHER PHASE(DEGREES)space charge, but it is still substantially within the cyclotron phase acceptance.Recent measurements of transmission to the HE2 probe show the radial drop-off due to electric stripping of the H" ions at large radius very clearly (Fig. 19). The curve is a fit to the data based on the expected variation of stripping cross-section with energy, with the dee voltage Vj as the only free variable. The optimum value of Vj was 67 k V , consistent with the measurements of V(-| cos<j> quoted above.Transmission curves through the cyclotron for a low intensity beam have been published previously. At 100 yA the transmission is not substantially different and the total loss between central region and 500 MeV is between 15 and 20% of the accelerated beam, including magnetic stripping (11%), gas stripping (4%), and vertical beam loss (0-5%)Since the fractional beam acceptance of the central region is above 40%, the overall transmission between the exit of the 300 keV injection line and 500 MeV is well above 30%. Taking into account the 85% transmis­sion through the injection line, the overall transmission between the injection line entrance and 500 MeV is above 25%.Extracted proton beamsLow-energy extracted beamsIn 1977 low-energy extracted beam ports were added to beam port 2 on the cyclotron tank (Fig. 5)• Beams to these ports have been suc­cessful ly extracted from the inner orbits ofFig . 18. The time d is tr ibu tio n  o f  the beam at in je c t io n  fo r  two d i f fe r e n t  in t e n s it ie s .F ig . 19. Beam loss due to H suppressed  z e ro ).E (MEV)s tr ipp in g  (note1670 MeV>- t  to -5UJQHORIZ. VERT.■ v / . '  ’••■.-•vH ------------ 1------------ 1-- L------------ 1------------0  5 - 5 090 MeV5 (cm)I-ZsHORIZ..V-VERT.-5 -5  0 5 (cm)F ig . 20. P ro file s  o f  ex tra cted  70 and 90 MeV beams. Wire spacing 3 mm.the cyclotron at 70 and 90 MeV. The beams were measured at the new extraction ports by profile monitors, and the profiles are seen in Fig. 20.The beams were viewed on wire chambers with a 3 mm wire spacing positioned at the ex­traction port. The amplitude of the current on each wire is seen in the oscilloscope picture. The external beam lines for these ports have not been installed but the suc­cessful extraction has now made TRIUMF the only cyclotron that has simultaneously ex­tracted three beams of different energy and i ntens i t y .A port has also been installed for the e x ­traction of 100-180 MeV beams, so that even­tually it will be possible to extract beams from the cyclotron with continuous variations of energy from 65 to 525 MeV.Beam line 1AThe beginning of the year saw the commis­sioning of the rebuilt high-intensity proton line (lA) and its extension from the tempor­ary beam dump at the thick target 1AT2 to the thermal neutron facility (TNF). One A50 MeV and one 500 MeV tune were commis­sioned, the beam sizes being in fair agree­ment with theory. Using a temporary monitor at the TNF and various targets in 1AT2 the 1AT2 TNF focus condition was set up suc­cessfully. Beam spills along the line for the ^50 MeV tune were about half those for 500 MeV. Spills measured upstream of 1AT2 were, as expected, very small. Downstream of 1AT2 the spills on the collimators weremuch higher (xA) than expected, due to mis­alignment of the second collimator. Subse­quent calculations using the REVM0C Monte Carlo code confirmed that the extra spill was consistent with the measured misalign­ment; the effects of various corrective actions were also investigated.Spill calculations have also been invoked upstream of 1AT2, where the line had been reconfigured to allow installation of the thin target IATI feeding the secondary lines Mil and M13 - (Fig. 21, see below.) Because the Ml 1 septum magnet was not ready for installation this year it was decided to remove the 1AQ9 quadrupole (only powered when Mil is operating) to avoid activating it unnecessarily and to measure its harmonic content in more detail. A spill study was therefore made to determine a suitable design for a collimator to replace 1 AQ.9 • An iron collimator 25 cm long of constant bore was decided upon; no significant advantage was found in using copper, or a greater length, or a conical bore. Calculations also indicated that BL1A could be tuned for either a horizontal or a vertical beam spot at 1AT2 without affecting the spill along the line appreciably.Beam line 4AREVMOC calculations were used to design a collimator to go downstream of the 10 cm liquid deuterium (LD2 ) target. This has now been built and installed and has per­mitted the maximum current through this target to be increased from 0.2 to over 1 y A , without exceeding the previous radia­tion limits downstream of the collimator. With the LD2 target out it has been possible to raise the maximum current through the beam line to the 10 yA design aim with only minor changes to the master tunes developed last year.Beam line 4BMost effort has been directed in support of commissioning the medium resolution spec­trometer. The cyclotron internal slits were used to restrict beam quality and give beam spots at ABT2of 0.25 cmand 0.20 cm d i am at 200 and ^00 MeV. The energy spread should have been reduced to the order of 0.5 MeV; the beam current was less than 1 yA. An attempt is being made to develop a beam line tune which disperses the beam horizon­tally across a vertical ribbon target to17enable good resolution spectrometer experi­ments to be performed while high currents are run in BL1A. However, initial measure­ments have shown an imperfect horizontal focus and only half the expected dispersion (12 cm/% Ap/p). Calculations have shown that tolerances for quadrupole strength and location are tighter than achieved in in­stallation. An optimization program is being developed to converge on a solution.Secondary channelsChannel M9Two beam development runs were completed on the channel. In the second of these four position-sensitive detectors were used to study the horizontal and vertical phase planes. Measurements of the dispersion and magnification were in fairly good agreement with theory, as were measurements of resolu­tion (<2.4% pQ ), momentum acceptance (23% p0) and angular acceptance (~20 m s r ) . Diffi­culties were experienced when trying to set up the achromatic and focus conditions.These were found to be due to second- and higher-order aberrations (chromatic domi nated).Pion beam phase space measurements were in good agreement with theory for the vertical plane but were much larger in the horizontal plane, presumably again due to high-order aberrations. Measurements of the cloud muon phase space indicated that the apparent source size lies between that of the target and the spatial acceptance dimensions.Channel M9 extensionThe present M9 channel provides a nearly achromatic double focus F2 about 1 m down­stream from the last quadrupole; the total length is 8.5 m. This channel is presently being extended with a crossed field (velocity filter) separator to obtain a muon beam uncontaminated by pions and electrons. The gap in the separator is 3 m long, 30 cm wide and 10 cm high, and the separation takes place vertically.After installation of the dc separator is completed there will be three modes of operation (see Fig. 86, p.92):1) a pion beam at F2;2) a clean 77 MeV/c cloud muon beam at waist W3; and3) a clean 77 MeV/c cloud muon beam at wa i st W 4 .The time projection chamber is situated at waist W4 (20 m from the production target) with its field in the direction of the beam line.Calculations for a 77 MeV/c cloud muon beam have been performed for a 10 cm long beryl­lium production target. The separator volt­age assumed was 400 kV and the magnetic field 226 G. Because of the small vertical apei—  ture of the separator and its great length, its phase acceptance is much smaller than that of M9- In particular the area at the production target seen by the extension is 1 . 2 5  cm (vertically) x 10 cm (horizontally) whereas the area seen by M9 is 2.5 cm 7 10 cm. The cloud muons resulting from pion decay near the production target come from the whole area seen by M 9 . Furthermore, large drift spaces between the magnetic elements increase second-order distortions. As a result only 40% of the muons in a 10% momen­tum bite at F2 is transmitted to W3/W4. For 77 MeV/c negative muons the expected flux for a 10% momentum bite is 500,000/sec for a 100 yA proton beam and a 10 cm beryllium target. There is no electron contamination. The pion contamination is 1-2% and can be influenced by operation of the horizontal and vertical slits at FI.Channel M 1 1By the end of 1978 modification of the opti­cal design of the Mil pion channel was virtually complete. The present design, shown in Fig. 21, differs from that consid­ered previously in the following manner:1) The wedge angles of dipole 11B1 have been altered from 0° to +7-7° and the coil has been redesigned to prevent the field shape changing with magnet excitation and to permit the tune to be scaled with momentum.2) Two quadrupoles, 1 1 Q.5 and 1 1 Q.6 , have been added to the system.3) Both the doubly achromatic and 'normal' dispersed beams are bent 60° to the left by dipole 11B2. The bend angle to the 'reversed' dispersed target position has been reduced from 60° to 30°. (With this change the existing 11B2 yoke can beut i1i zed .)134) Sextupoles, the 1 11S X ' elements, have been added for second-order bend-plane correction at the target positions.Predicted parameters at the target positions are listed inTable III. In all cases there is a double focus (Rjo = R31+ = 0) at the target.Table III. Mil channel design parameters.Doubly achromat i c1 Norma 1 ' d i spersed1 Reverse 1 d i spersedR 11 (Mx ) + 1 .65 + 1.14 + 5253R 16 (c m / % ) 0.0 -3.30 +12.10^33 ( % ) -2.00 -2.00 + 1 .73AQ Ap (msr-MeV/c) 50 200 88Ap (MeV/c) 26 25 10A ( m s r ) 10.41 7.76 8.74in the achromatic mode the use of sextupoles reduces the contribution of second-order ef­fects to the final beam size to 25%. In the normal dispersed mode they contribute 0.37 cm1 Reversed 1at the final target position (0.11% in momentum); doubling the J 'B 'dS L of the last sextupole would reduce this by a factor three. In both cases the focal plane is normal to the optic axis. Second-order coi—  rections for the 'reversed' dispersed target position are still under investigation.Channel M l 3A new low-energy meson channel Ml 3 has been designed and installed. A layout is given in Fig. 87 (p.90). The channel takes off at an angle of 1 3 5 ° with respect to the proton beam direction from production target 1AT1 which will typically be 3 cm beryllium. The channel runs horizontally and has two rec­tangular bending magnets, each bending the beam through an angle of 60°. The first bend is clockwise, the second bend counter-clock­wise. There are seven quadrupoles— doublets at entrance and exit and a triplet between the bending magnets.The magnetic elements have the functions DF-B-FDF-B-FD, where F means horizontally focusing, D horizontally defocusing and B bending magnet. There is a horizontally dis­persed focus FI 50 cm after the first bend, which is imaged symmetrically with respect to the centre of the triplet at F2, 50 cm beforethe second bend. The channel is doublyachromatic after the second bend. The verti­cal beam is largest in the centre of the triplet and smallest at FI and F2.There are horizontal as well as vertical slits at three locations, viz., between the first doublet and first bend, at FI and atF2. There is no dividing window between theproton beam line and this secondary line.A vacuum valve made from 1 in. tungsten is placed between the first bend and FI, and serves as a beam blocker.The calculated channel characteristics are:Fig. 21. Proposed layout of Mil channel.Length:Momentum range:Solid ang1e :Angular acceptance:Hor i zonta1 Vert i ca1 Momentum acceptance (Ap/p): Momentum resolution:Spot size (80% flux):1 cm target & 1% Ap/p3 cm target & 2% Ap/p3 cm target & 10% Ap/pFlux (30 MeV pions, from3 cm Be target)9.5 m<130 MeV/c (50 MeV pions) 30 msr±60 mrad ±155 mrad 10% FWHM 1% FWHM for 1 cm target 2% FWHM for 3 cm target1.53x 1.5 cm2x 2 cm26 x 2 . 5  cm2 5X 106 ir+/sec/100 yA/% Ap/p 1 x 1 06 7T_/sec/100 yA/% Ap/p19High flux muon channelThe beam optical properties of axisymmetric magnetic fields have been investigated with the goal of obtaining a muon beam of high flux and high purity. Such a channel is illustrated in Fig. 22. The proton beam strikes a thick target at A on the system axis. Annular slits located between A and B define a momentum band of trajectories trans­mitted to B. At B an 8.2 g/cm2 A1 degrader separates the momentum band of the muons from that of the unwanted particles (pions and electrons) such that only the muons will pass through the annular slits between B andC. At C the muon beam will have a small radial spot size: 90% of the muons will be within a 5 cm rad i u s .A fourth coil can be added in a Helmholtz configuration with respect to coil 3 to pro­duce a region of uniform axial field near Z = ^62.5 cm. Suitable current settings will produce a cylindrical region, coaxial with the system axis, 65 cm long and 80 cm in diameter, within which the magni­tude of the radial field component is <0 .50% of the maximum axial field within the reg i o n .This channel has a peak solid angle of ac­ceptance >1 sr, an integrated solid angle of acceptance >5 sr • MeV/c, and would deliver a cloud muon flux about 25 times that presently obtainable with the existing M9 channel; this channel can be expected to deliver about 7 x 107 y~/sec to a target.© © © I  _-5 0 0( Nl)  ( AMP TURNS) 1.98 x 10j (AM P /cm 2 ) 198MAXIMUM AXIAL B, ( 0 , 0 , - 3 9 7 )  -  9.34 FIELDS (kG)            - 3 0 0-  250-  170-  50 111.93 x  10 4816Bz ( 0 . 0 . - 0 . 7 )  ■ 10.09 49 .2s  rs  70.9 55.6 S rs  71.6 59 .7s rs  73.0 38 .5s  rs 61.7 r 5 3.0                 1002002653004000.86 x  10° 2152Bz ( 0 , 0 , 3 9 8  ) -  4.63         44.3S rs  64.6 OS rs  73.4 59 .0s  r 57 .7s  r S 80.1 41 .0s  rs  69 .5F ig . 22. An axisymmetria high f lu x  muon channel. The  axis is  the axis o f  symmetry and a l l  dimensions are in  centim etres .20Beam line diagnosticsAs the facility matures a much larger frac­tion of the man-hours devoted to diagnostics has been spent in maintenance and in recon­figuring existing systems to permit the construction of new beam lines and other facilities rather than in building novel devices. However, it has been possible to make performance measurements and to improve the engineering.Several gas-filled multi-wire ionization chambers (MWIC), which give profiles for beam currents of 0.1 to 10.0 nA, were assem­bled for the new low current beam line IB.As other beam lines operate at higher cur­rents (120 yA in beam line 1A and 12 yA in beam line AA) more secondary emission (SEM) devices have been installed.Both types of monitor deteriorate in use.The wires of the MWIC are enclosed in an isolated chamber filled with argon; after about one year, depending on the radiation environment, a coating appears on the wires which inhibits collection of the ionization electrons and distorts the profile. It is hoped to lengthen the useful life of these monitors by passing through them gases of the type used in proportional chambers.Our MWICsalso appear to overestimate the width of the beam at the level of 1% of the total current. Figure 23 compares the MWIC profile with that portion observed by steer­ing the beam sideways into the jaws of a SEM halo monitor.X IculF ig . 22. Multi-wire ion ization  chamber pro­f i l e  compared with ta i ls  seen  by a secondary  emission halo monitor.It is well known that the secondary emission coefficient of devices exposed to a working vacuum, with periodic venting and pumpdown, changes with time and beam exposure.Figure24 shows some profiles displayed by a carbon wire SEM monitor when a beam was steered across its surface. The monitor was placed directly in front of the meson pro­duction target 1AT2 and after exposure to17,000 y A h o f  beam, including periods with more than 100 yA, the SEM current/yA of beam is seen to be reduced for those wires normal­ly hit by the beam, thus distorting the profile. The design of a new meson produc­tion target has allowed us to incorporate a monitor that will normally be retracted and can be inserted when the target is in the blank pos i t i o n .SEM halo monitors, consisting of four jaws around a central aperture, have been placed in front of production targets to protect the latter from a mis-steered beam hitting welds or from the beam density on the target being too high. The density signal is derived from the difference in the total beam current in the line and that hitting the four jaws. Jaws have been made from stainless steel, aluminum and aluminum with gold evaporated onto the surface. All show similar aging effects, about 30% reduction in response. Aging will necessitate occa­sional adjustment of the set-points, but does not affect the usefulness as a protec­tion device since it would tend to give a more pessimistic response to a mistuned beam.STEERING  MAGNET (DAC)Fig . 24. Response o f  a TRIUMF carbon wire secondary  emission p ro f i le  monitor, exposed to 17,000 \iAh, to beam s tee red  across the su rfa ce .21A SEM total current monitor has been con­structed for beam line 4A. It consists of five aluminum emitting foils flashed with gold enclosed in a vacuum system independent of the rest of the beam line and maintained by a dedicated ion pump. The monitor and pump can be moved together from one location to another; the ion pump can be restarted after being off for 2k h. The device has been exposed to — 1000 yAh, including periods with more than 10 yA, and still shows a uni­form response to a beam of about 2 cm diam steered in a raster fashion over its accep­tance area of about 10 cm diam. The device is useful for beam currents of order 1 nA to 10 yA. The dark current has fallen from 0.3 nA (equivalent to 1 nA beam) after a few days of operation to <0.1 nA after one year. Dark current fluctuations are smaller than this, and a similar device, using a getter pump, is being constructed for the low current beam line 4B.The experiment shown in Fig. 25 calibrated the monitor SEM against a Faraday cup FC [Annual Report 1976] and a cyclotron high- energy probe HE2 [Annual Report 197*0 which measures the electron current stripped from the circulating H" ion beam. PM was a pro­file monitor, AF and NF were aluminum activation foil sandwiches (NF measuring neutron-induced activity). The currents read by HE2 and the Faraday cup agreed to within ± k % , and the SEM coefficient varied with beam energy as the stopping power, dE/dx, of gold, as shown in Table IV. The beam flux estimated from the 22Na activity produced in the foil AF by about 1 yA of k82 MeV protons over two days was compared with the integrated output of the SEM moni­tor, and the two measurements agreed within 1%. The 22Na activity in NF was 1% of that in AF. A calibration facility has been designed for beam line 4B; it will allow beam to be passed through a target, ion chamber of SEM monitor and stopped in the Faraday cup.The amplified pulses from the non-intercept- ing capacitive pick-up probe in beam line 1A, normally used for timing, have been 'teed' into a detector. The rectified output was found to be linearly proportional to currents above 1 yA and will provide a feedback signal for automatic gain control of the amplifier and permit more precise timing.Since the MWIC and SEM monitors need to be replaced periodically the monitors have beenF CFig. 25. Experiment to aross-oalibrate various TRIUMF probes and monitors.fitted with guides and simple tools and clamps so that they can be removed and replaced rapidly and, where necessary, remote 1y .The profile monitors required for the new beam lines (IB, 2C) presented us with a problem of finding rack space for the electronics; however, we were able to both redesign the readout system and build new units within the budget allotted for the old units. The new units [TRI-DN-78-18] take advantage of modern C-Mos multiplexers to reduce the size of a 64-wire readout from k NIM slots to 1, with a corresponding saving in cost. Both old and new units collect the current from each wire on indi­vidual input capacitors for a time determined by the gain setting. The old unit multiplexed the 64 resulting voltage sequentially to the output. The new unit multiplexes the charge on each input capacitor to a single charge-to-voltage converter, thereby improving wire-to-wire consistency. The charge-to-vo1tage con­vertor is followed by an absolute amplifier to give positive output signals for both MWIC and SEM monitors, and the gain of a unit can now be changed remotely from the control room.Table IV. Secondary emission c a 1 i brat i o n .SEM coefficient/ SEM coefficient/Proton energy surface (dE/dx)Au(MeV) (%)210 5-5 2.4350 4.1 2.5482 3.5 2.422Kaon factoriesAs outlined in the 1977 annual report both fast-cycling synchrotrons and isochronous ring cyclotrons are being considered for the acceleration of an intense beam of protons from the TRIUMF cyclotron to 8-10 GeV, the aim being to produce beams of kaons and other particles a hundred times more intense than available from present accelerators.In the case of synchrotrons the chief design problem is in matching the time structure of the two machines, the synchrotron being pulsed at, say, 20 Hz, while the 500 MeV cyclotron operates cw at 23 MHz. Of the various options available, the most promis­ing at the moment, because it would provide an intermediate pulse frequency, appears to be the extraction of '100 turn stacks' from TRIUMF. The beam would be allowed to drift90° out of phase at 450 MeV, after which itwould begin decelerating back towards the centre; the outermost 50 accelerating and 50 decelerating turns, which would be located in a 25 mm wide radial interval,could then be extracted in one bunch0.44 ysec long by pulsing an axial electric field. The repetition period would be 22 ysec, corresponding to 14 synchrotron turns. Fast bumper magnets and RF accelera­tion would be used to move the equilibrium orbit away from the injection system.200 macropulses per synchrotron cycle would be adequate to achieve an intensity of 2 x ]0 lk p sec-1 (32 y A ) , assuming 400 yA in the present cyclotron. To accommodate the long injection time (9% duty factor) the magnet cycle would be flat-bottomed using60 Hz third harmonic. This machine in turn could act as injector to a high-intensity 40 GeV synchrotron. Some of the parameters of the injection-capture system are shown in Tabl  !2The alternative proposal is for a two-stage isochronous ring cyclotron to accelerate protons to 8.5 GeV. There being no incom­patibility in time structure the beam cur­rent would in principle be limited only by what was available from the present cyclo­tron (400 yA?). The first stage of 15 sectors and 10 m radius would take a 450 MeV beam from TRIUMF to 3 GeV, the acceleration being completed by a second stage of 30 sectors and 20 m radius. Superconducting magnets would be used, the weight of steel being estimated to be 2000 tonnes for the first stage and 1800 tonnes for the second, less in total that in the present 500 MeV machine. Numerical orbit tracking through simulated magnetic fields has confirmed that the focusing properties of the design are satisfactory and has emphasized the impor­tance of using small pole-gaps to prevent fringing field effects weakening the edge focusing. Steel is provided outside the coils on the focusing edge (Fig. 26) to pro­vide a reverse field, keeping the edge hard and increasing the flutter. Several integer and half-integer radial resonances would have to be crossed, but with a high energy gain per turn (3 MeV and 8 MeV, respectively) this should cause no difficulty. The most difficult technical problem will be that of extracting the beam efficiently. Here again the high energy gain per turn will beTable V. TRIUMF -* fast-cycling synchrotron.Number of stacked turns - TRIUMF Energy spread of extracted beam Injected beam microstructure macrostructure Beam loss - stacking in TRIUMF Phase space ratio Synchrotron frequency Space charge limit Phase space limit Synchrotron orbit time Macropulses per synchrotron cycle Injection time Mean synchrotron radius Average energy gain per turn Radio frequencyBeam loss - extraction, injection and capture Final energy~100 450 + 2.5 MeV 10 each pulses of 14 nsec 0.4 ysec every 21 ysec <5%~105 20 Hz 8 x 101I+ p se c -1 1015 p s e c" 1 1.5-1.14 ysec 500 4.4 msec 50 m 0.45 MeV 0.67-0.93 MHz <5%8-10 GeV230 50 100F ig . 26. Superconducting magnet design  fo r  second  stage 3 to 8 .5  GeV 30 s e c to r  cyclotron .important; certain resonances will also be of assistance in exciting coherent radial oscillations. The accelerating system con­sists of SIN-style cavities, with flat- topping provided by operating some at the second harmonic (first stage) or third har­monic (second stage). The phase compression effect is also utilized to allow higher fundamental frequencies (and hence smaller cavities) to be used on successive stages. The ring configurations are shown in Fig. 27- The design parameters are listed in Table V I .Table VI. Ring cyclotron kaon factoryFirst Stage Second StageInjection energy (MeV) 1(50 3000Extraction energy (MeV) 3000 8500rc = c/Wp (m) 10.3 20.6Number of sectors 15 30Primary cavities 8 at 46 MHz 15 at 69 MHzHa rmon i c cav i t i es 4 at 92 MHz 6 at 207 MHzApprox. dimensions ofprimary cavities (m2 ) 5-9 x 3.6 4 x 2.6secondary cavities (m2 ) 5.9 x 1.6 4 x 1 . 5Total RF power (MW) 2.0 1.7Peak energy gain/turn (MeV)at injection 1 .2 7-9at extraction 3.6 7-9AE/Ar (MeV/mm)at injection 0.23 1 -9at extraction 5-6 30Radius gain per turn (mm)at injection 5-3 4.2at extraction 0.64 0.26Crude estimate of magnetweight (m tons) 2000 1800Approx. number of turns "00 700F ig . 27. 3 GeV and 8 GeV (2 0 .7  m rad ius) r in gcyclotron  with superconducting magnets and SIN- s ty le  RF ca v it ie s . (TRIUMF magnet po les  drawn to the same s c a le .)2kComputingREVMOC, the Monte Carlo partic1e-tracking code for beam line design, has been further improved by allowing dumping and inputting of rays (for 'continue' and 'backward' run capability), filtering of unwanted particles in mass and momentum space (vastly reducing the cost of some studies), and misalignment of beam line components (for studies of the effect on beam spill).New features in our general purpose array- manipulating program OPDATA include dynamic array management, optimization of storage requirements and allowance for very large (>100 kwords) arrays. Expressions input by the user are no longer limited to 80 charac­ters (now 256), are now evaluated ~ 5  times faster using reverse polish notation (RPN) expressions and decoder evaluation routines (as opposed to the FORTRAN compilation scheme). These routines, capable of decod­ing into RPN any general expression contain­ing arbitrary operators, have been found useful in a compiler which converts Boolean logic into assembler (8080) code.The graphics-plotting package has been con­siderably improved to allow logarithmic axes, superior axis ticking and labelling, upper, lower and Greek character labelling with cursor control positioning, control of x:y aspect ratio, editing of errors with the cursor, and error bars on data. Finally, the user can now control the scales on Cal- comp plots produced from plots on the CRT screen.TRIUMF Committee on Computing Systems (TRICCS)Business on the asynchronous links to the UBC Computing Centre has continued to expand this year, as detailed in Table VII. Two of the lines are now fully multiplexed, rather than one, allowing the number of terminals to be raised from 9 to 15- To cope with the increased traffic the Computing Centre has allocated TRIUMF 3 ports in addition to the 6 previously available. Transmission speeds on these lines had been limited to 1200 b d ; how­ever, with the provision of more powerful modems, two of these lines are now operating at 9600 bd. Scope for further improvements is limited chiefly by the number of telephone lines available; more lines are scheduled to be installed in the summer of 1 9 7 9 -The Computing Centre has offered replacement of our Terminal 1 card reader and line printer by a group of four conversational terminals plus a printer with resolution sufficient for plotting. The suggestion was approved by TRIUMF computer users, and a suitable room to house the new equipment is to be constructed on the CRC mezzanine. The terminal is expected to be in operation by spring 1 9 7 9 •The Computing Centre is making progress with the SDLC protocol for synchronous communica­tions. Work at TRIUMF has been at a stand­still due to other commitments, but will be resumed in January 1979-The possibility of a very high speed (1 Mbd) link to the Computing Centre is under active study. Coax or optical fibre would seem to be the most suitable medium, and negotia­tions are under way to lay a cable with either the new telephone lines or the radio­gas line. The Computing Centre is already working on a megabaud link to Computing Science Department.Table VII.Nov 1 , 1977Nov 1 , 1978Telephone circuits 7 8Asynchronous facilitiesUBC CC ports 6 9UBC CC 1i nes 9 15TRIUMF stations 8 12Mu 11 i p 1exed 1i nes 1 29600 bd 1 i nes 0 2Synchronous facilitiesSynch ronous 1 i nes 3 325INTRODUCTIONRESEARCH PROGRAMThe year 1978 was marked by continued good availability of the cyclotron beam as a per­centage of scheduled time (84%), but in addition there was a hefty increase of a factor of three to 27,000 y A h  in the accel­erated beam. This resulted in a further expansion of the variety and significance of the experimental research performed at the facility. The continuing availability of a 200 nA polarized proton beam was crucial to some experiments.One of the more intriguing results of 1977 continued to be a puzzle in 1978. This was the large asymmetry observed from the p,ir+ reaction with polarized protons leading to specific nuclear states in light nuclei.(Much larger asymmetries were observed than for the p(p,ir+ )d reaction.) The only new experimental data obtained this year were asymmetry values of 0.6 in pion production leading to the 3-37 MeV state in 10Be. It appears that more extensive experimental results will be required, both for heavier nuclei and for the (p,tr- ) reaction, before the process involved can be elucidated.In pion nuclear scattering, the TRIUMF group is finding interesting differences between the angular distributions for tt+ and tt~ nuclear scattering, reflecting to some ex­tent the difference in the Coulomb-nuclear interference, but also reflecting the energy change of the tt" in the nuclear field. It appears that the relative neutron and proton nuclear radii can probably be ob­tained from the ratio of the tt' scattering distributions for adjacent isotopes, but the question as to whether or not the result (e.g. a difference of 0.06 fm for 13C) is model independent has not yet been estab­lished. Information on the difference in neutron and proton radii (rn -Tp) is also coming from the group measuring the pionic 2p-ls X-rays in the light nuclei. Assuming first, (as above) the proton radius given by electron elastic scattering, and second that rn and rp are equal in 10B, they find for n B that rp-rp = 0.04 ± 0.02 fm. An interesting feature of similar measurements of the pionic X-rays in F and Na is that the ratio of the line widths is r(Na)/f(F) = 1.20 ± 0.15 compared to an optical model prediction of 1.9 ± 0.1. All of these mea­surements show promise for the use of pions in investigating the properties of nuclei.In particle physics, the fundamental work at TRIUMF on nucleon-nucleon scattering was continued in 1978. The work on the Wolfen- stein spin correlation parameters was com­pleted with the addition of data on A t and Rt , the polarization transferred to the recoil proton when the incident spin is longitudinal or transverse in the reaction plane, to last year's data on P and Dj-. The results of this program, together with all other world data, are incorporated in Table IX of the report, showing the 1=1 and 1=0 phase shifts for four energies from 200 to 500 MeV. The unique­ness and definition of the phase-shift solu­tions are a tribute to the excellence of the TRIUMF variable energy, polarized neutron facility, as well as to the skill of the exper i menters.The charge exchange TEENGEE0 ) reaction has been observed for the first time in nuclei heavier than 3He. In another experiment, preliminary results have been obtained com­paring the decay electron spectrum and asymmetry of the y~ in carbon, titanium and lead with that from the y+ decaying in the same materials. Two large Nal crystals were used in an experiment to measure the branch­ing ratio in the decay of pionic atoms resulting in the emission of an electron- positron pair or two high-energy gamma-rays.In view of the large variation with atomic number of X-ray intensity observed with K." mesons, it was of interest to find out if a similar effect could be observed with pions. Such was indeed found to be the case. The variation in the intensity of the 4-3 trans­ition in the pionic atoms, for example, was found to be quite regular, with a reduction by a factor of 2 in going from Z = 32 to Z = 24.The anomalously high cross-section for 12C(p,pn) at TRIUMF energies compared with 12C(p,2p) was reported last year. The normalization of the neutron detection ef­ficiency had used the assumption that the ratio a(p,pn)/a(p,2p) for deuterium depended only on the pn-to-pp cross-section ratio. Experimental results have now confirmed the validity of this assumption, and there are still 50% too many (p,pn) events relative to (p,2p). This is still an intriguing puzzle with no clear-cut explanation yet forthcoming. Further studies were also26conducted on the L*He(p,2p)3H reaction at several energies.In nuclear chemistry a general survey of the fragments emitted from silver by 500 MeV protons has made it clear that both evapora­tive and non-evaporative processes are involved. Further work was also done on the nuclear spectroscopic parameters of the short-lived radioactive products of proton bombardment, with the results being shown in several tables in this report.The activities of the group using muons for research in chemistry and solid-state physics have continued to be vigorous and varied. An outstanding example of this work comes from muonium-spin-rotation experiments in a-quartz. The precession of triplet muoniurn in the crystal is split into two clearly resolved frequencies with a separa­tion some 100 times larger than would be expected from the quadratic Zeeman effect in the low magnetic field (3 G ) . This effect is the first clear-cut evidence for the i n t v i n s i e  electric quadrupole moment of the ground state of the muoniurn atom.Some research has been done using the magnet­ic field oriented parallel to the initial muon spin direction. Among the results o b ­tained with this orientation are the follow­ing: confirmation of the stochastic relaxa­tion theory of the spin alignment in weak magnetic fields and the theory of spin fluctuations in weak itinerant ferromagnets, evidence that in MnSi the y+ does not move within four lifetimes, even at room tempera­ture, while in MnO there appears to be very fast diffusion in the paramagnetic region. Studies in muoniurn chemistry in the gas phase have been continued, and new results have been obtained on muonium formation in gases at atmospheric pressure. Critical ex­periments have shown that the y+ relaxation signal which remains after therma1 ization cannot be due to wall effects and is unlike­ly to be due to bare muons. Hence the sig­nal is most probably due to a molecular ion such as Ney+ . Further studies on the liquid phase have shown that the magnitude of the kinetic isotope effect (k^/k^) depends sharply on the type of reaction involved, and that muonium is neutral at the point of react i o n .The small but important theoretical group has made major contributions to the TRIUMF research effort. Significant theoretical work is being done on N-N scattering abovethe threshold for pion production. Linear integral equations, based on field theory, have been obtained. These equations couple the NN elastic scattering amplitude to the various pion production amplitudes and have a number of advantages. In particular, double counting problems are avoided, and two- and three-body unitarity is guaranteed.A comparison of the two current (and equally successful) theoretical treatments of the pion-nucleus scattering has been made— on the one hand there is the Kiss1 inger-type potential in co-ordinate space with a EEP interaction of zero range and on the other hand a separable potential, used in momentum space, having a range of order 0.6 fm. Con­siderations on the location of the Chew-Low pole, and of unitarity, indicate that the t-matrix for the pion-nucleus interaction must have a fairly long range, so that the latter treatment is favoured. The general formalism has been worked out for obtaining an effective Hamiltonian operator from a known relativistic amplitude, applicable to an arbitrary, time-dependent second-order interaction, and has been applied, for example, to the radiative capture of muons by nuclei and to the TR GEEO reaction.One important mission of the theory group—  which has been pursued very successfully in 1978— is to help in the interpretation of the results of the experimental groups and to advise those groups on the most fruitful directions for their future research. For example, in the proton-proton bremsstrah 1ung calculations to higher orders in the soft photon approximation have been compared to the TRIUMF 200 MeV experiment and to other experimental results. In addition, important considerations have been developed for the guidance of future experiments in the crite­ria of 'off-shell effects' and remoteness from the 'soft photon' region.27PARTICLE PHYSICSExperiments 2 6 ,2 7 , 40BASQUEExperiment 26n-p differentia l cross-sectionsThe BASQUE group is in the process of mea­suring free n-p differential cross-sections at 210, 325, 425 and 500 MeV. Following the successful measurements of n-p Woifenstein parameters over a large angular range, this observable will form the last in a 'complete set' of n-p experiments at the above ener­gies. Phase-shift pred ictions [Bugg, TRIUMF report TRI -75“5 (1975) 1 indicated that an accuracy of 1-2% is required over the full angular range, with the backward region (elastic proton detection) having the same absolute normalization as the forward region (elastic neutron detection).Equipment was set up originally at the 9° port of TRIUMF's fast neutron facility (Fig. 28) to measure forward scattered neu­trons. A 20 cm LD2 target produced an in­tense flux of quasi-elastica11y scattered neutrons collimated at 3° intervals from 0°-27° lab. Monitors at the 0° and 9° ports indicated that the primary beam sweep magnet (4AB2) had left an unacceptably high charged particle flux in the 9° port, whereas the 0° port was extremely clean. Higher neutron flux at 0° and a more monoenergetic beam prompted the move to 0° where the apparatus is presently set up.A collimated neutron beam, produced at 0° by charge exchange scattering off deuterium, was monitored at the port exit by detecting protons scattered left, right and forward from a (CH2 )n converter. These monitors tracked together to better than 0.5% without need for randoms correction. Further colli- mation downstream reduced the neutron beam 'wings' at the LH2 target. A sweep magnet immediately upstream of the LH2 target re­moved charged particles produced by the monitor and by (n,p) reactions in the col­limator. A thin scintillator vetoed charged particles passing into the 20 cm long x 14 cm diam LH2 target. To reduce air scattering a helium bag was interposed between the LH2 target and the shielded beam dump. A wide angle monitor, at 20°, monitored the target status.Neutrons were detected by conversion in a53x53x10 cm block of carbon. Knockout charged particles traversed a 0.50 m2 timing counter, seven 1 m 2 multi-wire proportional chambers (MWPC) that gave the conversion co-ordinates, 1 m2 aluminum degrader giving the detector an energy threshold of 80 MeV and a final 1 m 2 trigger counter. Charged particles were vetoed by a 1 m2 MWPC and scintillator arranged before the converter. Neutron time of flight (T0F) to PI (Fig. 28) were recorded, with respect to the cyclotron RF, to identify elastic events. An interval P1-P2 T0F was recorded to eliminate y-ray background and charged particles traversing the detector, in a backward direction, but stopping in the converter.Preliminary data have been recorded to test the on-line software, off-line event recon­struction, equipment status and the effec­tiveness of secondary beam line collimation. On the basis of these measurements improved collimation was installed during the Christmas shutdown. By using the TRIUMF 5:1 selector a chopped beam structure, having a period of 215 nsec, can be produced. This facility was an invaluable tool for unfold­ing the inelastic background, from under the elastic peak, in the Pl-RF T0F spectra [Figs. 29(a),(b)]. Neutrons arriving modulo 2 1 5  nsec were ranged out in the detector. Cosmic rays arriving randomly gave a flat T0F spectra.Experiments 27, 40Triple scattering parameters in n-p scatteringThe series of experiments to measure nucleon' nucleon spin correlation parameters at low energies between 200 and 500 MeV over a wide angular range has been completed. Proton- proton experiments were reported in 1976- Measurements of P, the polarization produced in neutron-proton scattering, and Dt, the polarization transfer to the recoil proton where the incident and scattered spin are perpendicular to the reaction plane, were reported last year. This year's report pre­sents the measurements of A t and R^, the pol arization transferred to the recoil proton when the incident spin is longitudinal or transverse in the reaction plane, respective ly, and the scattered particle spin is mea­sured transverse to the direction of motion in the reaction plane. The statistical accu­racy of these data is of the order of ±0.05.53Fig . 28. Plan view o f  the BASQUE experimental area showing the neutron d etec to r  at 0 ° , the LD2 neutron production ta rget and the LHZ sca tte rin g  ta rget.F ig . 29. R elative neutron t im e -o f- f l ig h t  sp ectra  as recorded  in  the neutron d etec to r , i l lu s t ra t in g  a) the 43 n sec  RF p eriod  o f  TRIUMF, b) the e f f e c t  o f  using the 215 nsec p eriod  capability  o f  TRIUMF.23For the neutron experiments a polarized monoenergetic neutron beam was produced by charge exchange scattering of polarized pro­tons in a 20 cm liquid deuterium traget at 9° using the R configuration. The neutron beam line consisted of a 3-25 rn lead collim­ator, two spin precession magnets at right angles for precessing the neutron spin into any one of the three orthogonal directions, a 53 cm long liquid hydrogen target, and a neutron polarimeter at the end of the beam line. The recoil proton polarization was measured by vertical scattering in the car­bon polarimeter. The neutron was detected in a position-sensitive detector 1 m square which had a detection efficiency of approxi­mately 30%.The polarization transfer parameter at 9° lab is given in Table VIII. The measured values of Rt and A t are shown in Fig. 30 where the solid curves are phase-shift fits.Single energy phase-shift analyses have been carried out of the pp and np data simultane­ously at 210, 325, ^25 and 515 MeV using the BASQUE data and the previously existing world data. The solutions obtained (listed in Table IX) are now unique and well defined at all energies. The values shown in paren-F ig . 30. The po la riza tion  t ra n s fe r  parameters a) and b) at fo u r  en e rg ie s .theses had been fixed at the theoretical values calculated from one-pion exchange and heavy-boson exchange (2EEGR GDHO"Analysis of these spin correlation data yields spin-orbit and tensor combinations of phase shifts that vary smoothly with energy. The central combination of phase shifts varies less smoothly, as these terms are less sensitive to spin effects. The central terms will be constrained considerably when the differential cross-section data are ava i1a b l e .Table VIII. Rt at 9° lab np scattering.Proton beam energy (MeV)®c.m.(deg)225 160.97 -0235 ,  ± 0.025332.5 160.50 -0.799 ± 0.024434.7 160.06 -0.772 ± 0.023506.4 159-76 -0211 ± 0.021Table IX. 1=1 and 1=0 phase shiftsEnergy (MeV) 510 65# $5# #1#6%El3D112#6%236 0216&0230 ', 21, 702"5 '16206&1266$ 30,(02$ 206&02#$ 266702,$ 3 2367 120,' 1323(02,3 '5,2$5&02$ '5#2,#&02#$ '5320$70 23)*1LAZ'56'60(023, '66'6$702"1 '632507 1211 '6#', 712#$5'6+02,6 5621#&021 552,0702,# 1"2"571201LA L #20$702$5 5 237026, $2157026# 5230702$06 #2107025  26, 7025, '657025" 2""&02$1LU L '6215(026 '62#57,2$3 '#201&02$1 '#2&02#353 5 '5 266+02$0 '#2$#70265 '#20,7025 ',2,0&02666-. $ 2"3+02$5 ,206702$$ ,230702$3 3213702#3LU C 26#+0266 '021&025$ '12$(025" '125&02656&#1 2"1 523# 6'$ 6'33'02#5 '1200 '126" '12160 6, '1253 '12 '5216 '526 ,6 1, 12$ , 52#1 6'60 6'"56* '1235702#, '1621,702,$ '502$"&02#" '532,0702"6/ 0 0 $ 2 #6+02#" '"2,#702#0 '1"2,702$0'552657,23$6*1 '5521&0251 '602137026 '6,20670260 '$625702,"3p2 1,21"7021, 121570250 1325"7021 1326702$160 '5 23370 210 '5 2, 7021 '5 26#70 21, '023070265531 12067025$ 0267025$ 02537021" '026070265B A Z 26$70250 " 23670 21, 112#370 21$ 15231702503 1 6 '52,#7021 '52,7026$ '52,07021, '12,, 702#5612 12,"(0216 5 2"70210 6'#672%/ $21170210'1217020, '12#$70203 '12,"70211 '12"702166 3 %4 0266+020# 02,37020 02,7020 0 20702101 -24 120,7020" 126,70210 5251&0211 5 2,6 70 21$63# '023,7020# '12107020" '125370211 ' 125#70 21063, 021"&020# 02#$7020 02,7020 0257020'0263 '02,1 '02# '023 ,0 b 3Kfa 020 021 025# 0261'Ic 025" 02$" 02, 02365 16 1 02"""#&020015 02"361 7 ,200$ 023"567020060x3 65,23 $525 ,052" $3'"Degrees of6""freedom 22 A 6# $$#30Experiment 24Measurements o f p-p and p - 4He analysing powers  at medium energiesHigh precision proton-proton and proton-^He analysing power measurements have been made using incident proton beam energies of 2 2 5 , 327 and 520 MeV. A secondary polarized proton beam was obtained by elastic scatter­ing of polarized protons at 1 5 ° from a liquid ^He target. This secondary beam was incident on a CH2 target, where p-p elastic scattering events at 0 ] a i-, = 1 7 ° were observed. Measurement of the three scatter­ing asymmetries as a function of the inci­dent beam polarization allowed the following analysing powers to be determined:A pp at 17° for (225, 327, 520) MeVA p at 2 k ° for (205, 308, 499) MeVA pHe at 15° for (222, 325, 518) MeVThe differences of effective scattering ener­gies from those of the primary beam are dueto kinematic effects and target thicknesses. Details of the experiment have been described [Dubois, M.Sc. thesis, Univ. of British Columbia (unpublished); Greeniaus e t  a t . ,  Nucl. Phys. (in press)]. A description also appeared in the TRIUMF 1977 annual report.A short summary of the results is presented in Table X .Table X. p-p and p-^He analysing powers.Nominal beam energy Ap p ( 2 4 ° ) A p p ( 1 7 ° ) ApHe 0  5 ° )225 0 . 2 7 3  ± 0 . 011 0 . 3 3 9  ± 0 . 0 0 3 0 . 9 5 8  ± 0 . 0 0 7327 0 . 3 5 8  ± 0 . 0 1 0 0 . 4 2 6  ± 0 . 0 0 4 0 . 7 91  ± 0 . 0 0 7520 0.1)26 ± 0 . 0 1 3 0 . 5 2 3  ± 0 . 0 1 0 0 . 4 9 6  ± 0 . 0 1 0Experiment 23bEtude de la d is in tegra tion  n+  - *  e + v e yLa d#s i nt#grat ion ir+ -> e+vey a #te #tudiee en grands details sur le plan th#orique [Bardin et Ivanov, Sov. J. Part. Nucl. 7_, 286 (1976). Cet article contient de nom- breuses r#f#rences aux travaux ant#rieurs] Elle a et# consideree comme un moyen d'at- teindre le facteur de forme axial du pion en supposant le facteur de forme vectoriel deduit de la largeur de la d#sint#gration tt° -*■ yy. Les experiences faites jusqu'ici [Depommier e t  a t . ,  Phys. Lett. ]_, 285 (1963); A. Stetz e t  a t . ,  Nucl. Phys. B13 8 , 285 (1978)] ont et# utilis#es pourdeterminer le rapport y de ces deux facteurs de forme. A cause de la grande simplicit# de la d#s i nt#grat ion ir+ -* e+vey (un seul hadron y contribue), cette derni#re a #t# consider#e comme un excellent banc d'essai pour plusieurs ingr#dients th#oriques tels que PCAC, l'algebre des courants, les th#- orfemes de pions mous et pour des modules, tels que la dominance du p et du A j , les modeles des quarks. R#cemment, Bernabeu e t  a t .  [Phys. Lett. 7 9 B , 464 (1978)] ont fait remarquer que cette desint#gration pourrait constituer un cas unique pour la mise en #vidence de la violation de l'isospin 1 i#e h la difference de masse entre quarks u et d. Le parametre interessant est 4 = md/mu et la contribution des effets de structure au taux de desintegration est directement propoi—  tionnelle a |f(4)|2 , ou f(?) est une fonction calculable de 4. La violation d 1isospin pourrait conduire a un effet de 50% sur les effets de structure.Des I'ete 1976 nous avions commence a TRIUMF une experience visant a mesurer le taux de des i n teg rat i on tt+ a- e+vey en fonction des energies du positron et du photon. Cette experience a ete interrompue au debut de 1977 pour faire place a la recherche de la desinteg ration y+ -> e+y. Nous avons repris 1 'experience tt+ -> e+v£y en mars 1978 et avons obtenu du temps de faisceau en mars et en juin. La detection du positron et du photon a ete faite au moyen des deux cris- taux d'iodure de sodium TINA et MINA, dans une g#om#trie propre a favoriser les effets de structure par rapport au freinage interne. La figure 3 1 montre le dispositif de detection. La discrimination entre particules chargees et particules neutres etait faite par des detecteurs plastiques places devant les cristaux INa. Plusieurs detecteurs plastiques entouraient les detecteurs TINA et MINA pour deceler les evenements dus aux rayons cosmiques. Le dispositif experimental etait, dans son e n ­semble, assez semblable a celui qui fut utilise pour la recherche de la desintegra- tion y -> ey [Depommier e t  a t . ,  Phys. Rev. Lett. 39, 1113 (1977)]■L 'electronique etait arrangee pour accepter diverses classes d 'evenements. Chacun de ces evenements etait enregistre comme une liste de parametres: nature de l'evenement (neutre-charge, charge-neutre, neutre- neutre cosmiques, etc...); intervalles de temps entre les differents compteurs, y compris le telescope d'entree; energies dans les INa et dans certains compteurs31ENERGIE DU POSITRON (MINA)plastiques. Afin d'obtenir un etalonnage de l'energie 'en ligne1, on enregistrait un echantillon (choisi du hasard) de disintegra­tions ir+ -y e+ve et u+ -y e+ veV y . Des dispo­sitions etaient prises pour identifier des impulsions resultant d'empilement dans les cristaux INa.L'analyse des donnees, enregistrees sur bandes magnetiques, est en cours. Apres avoir ramene tous les evenements a une echelle d'energie commune, nous avons deter­mine les coupures en temps pour eliminer les evenements 'prompts', et pour isoler le pic de coincidences. Les figures 32(a) et 32(b) montrent les evenements ir+ -> e+vey recueillis au cours du run de mars 1978. Les energies du photon et du positron sont portees res- pectivement en abscisses et en ordonnees.La figure 32(a) est relative a la configuration y(TINA)-e+ (MINA) alors que la figure 32(b) est relative a la configuration y(MINA)-e+ (TINA). Aucune soustraction de bruit de fond n'a ete faite. Nous poursuivons l'analyse par la determination du fruit de fond et par celle de la determination de l'efficacite de detect i o n .L E A DI R O NFig . 31. Les compteurs a s c in t i l la t io n  AJo 1-10 ( I 'epa isseu r n 'e s t  pas a I ’e ch e lle )  ont e te  u ti-  l i s e e s  pour id e n t i f i e r  les  p a rt icu le s  chargees.MeV9070503010....  1..... 1- a)---r i ii. ’..,. , £ 1---; - - "112 1 311'' 11'I 1" r:, - : "2 1 2 "i 12 1 ' .11 1- n3-!iUliflt"l|l1 l\' 'l1 2 11 1 1-?'l 1 1 1i i 1 1 1 1 110 30 50ENERGIE DU PHOTON (TINA)70 MeVMeV90<P  70ocrt/5 50 OCL3072^  10' ..r--  - . ■ ----i ■ ■ i i- b)t 1 i1 i 1i "ir  --i.'.i2ii M 121' , C " 1 1 i, 1 1 1 11 -i I" 2-1 1 1 1 1 1 110 30 50 70ENERGIE DU PHOTON (MINA)MeVF ig . 32. Evenements Fig -y  (7 8 pour la con figuration  a) 8 (TINA)-e+ (MINA), h) y (MINA)-e+ (TINA). Les evenements avea Ey e t  Ee+ < 53 MeV proviennent de la d is in teg ra tion  yd e+ vevyT■32Experiment 41bCharge exchange o f s topped n in nucle iAlthough the TEE( G EEp ) reaction for stopped EE) is energetically possible in many nuclei, it is known to occur only in the three lightest nuclei, H, D, 3He. Only upper limits for this process in heavier nuclei have been published [Petrukhin and Prokoshkin, Nucl. Phys. 5 A , AlA (1965)]. These indicate that the reaction, if it does occur, has a branching ratio -6 10- 4 .A search for this reaction in heavier nuclei has been conducted at TRIUMF using the two large Nal crystals (TINA and MINA) in a 180° coincidence geometry to detect the it0 -> 2y decays. Pion beams of 20 and 30 MeV from the stopped ir/y channel (M9) were stopped in several targets: 6 L i, 7 L i, C, A 1, Ti, Cu,Nb and Pb. The 7Li and C targets were used to investigate sources of background, since the TIE) GIE0 ) reaction has Q values of -7-1 and -9.3 MeV, respectively, in these nuclei. The data were collected during a week's run in February with a 10 pA proton beam current (1^ ~  5 x 105 ir_/sec) after the low statis­tics data taken by the group a year earlier showed some indications of the process in 6L i .Scintillators were placed in front of TINA and MINA to reject charged particle events, and time of flight was used to separate y's and n's. The true stopping rate was mea­sured using a veto counter placed directly behind the target, but this counter was re­moved during the run and only the incident EEN flux was monitored. This was done toreduce the background from hydrogen tt° ' s in the wrapping of the scintillator. The scintillators upstream of the target were carefully shielded with lead so that any tt° ' s produced in them could not 8  decay into TINA and MINA. The target thickness was ~A g/cm2 and no degrader was used.The two-dimensional time-of-f1 ight spectrum TINA-STOP versus MINA-STOP in shown in Fig. 33 for the coincident events observed from the A1 target. A coincident peak with a rather small random background (<10%) is clearly observed. Calibration of the flight time with the singles spectrum of y's and n's in each crystal clearly establishes this peak as a y-y coincidence.The two-dimensional energy spectrum Ey|na vs E^i^a is shown in Fig. 3A for those events which occur in the y-y time window shown in Fig. 33- Almost all the events lie on the st ra i ght line Ey + E^ ~  135 MeV i nd i cat i ng that they arise from the ( tt- , tt° ) reaction.The major backgrounds in this experiment are random coincidences, neutrons from the (u- ,2n) reaction, IE0 1 s from hydrogen in the targets and charge exchange in-flight. The last background is the most uncertain as the low energy TEE) GEEpO cross section is not known.Preliminary values for the branching ratios for the TEENGEEpO reaction at rest in 6Li and 27A1 are (2.8 ± 0.6) x 10"6 and (A.8 ± 1.5) x 10- 5 , respectively. These measurements represent the first observation of this pro­cess in nuclei having A > A .TAK7T ,7T ° )-8 --12' Hi-,',,2 2 11  1 1 1 2  1 15556  151  5 116 1516551a1 'ii3 11- 8  - 4  0TOF (TINA) in nsecI IF ig . 33. Two-dimensional t im e -o f- f l ig h t  spectrum  fo r  TWA and MW A.<z2-//-  5$I 2 I I 12 II ' 1 ' I2I I - IAI(7r T 7T 0)2  1 ti 1-TINAFig . 24. Two-dimensional energy spectrum fo r  co inciden t  8 events in  TINA and MINA.33Experiment 4 7 Muon radiative captureThe muon radiative capture reaction is of considerable interest in that it provides one of the most sensitive measurements of the value of the induced pseudoscalar coup­ling constant of the weak intereaction in­side the nucleus. However, the experiments are difficult to perform because of the low rate for radiative capture and the high neutron background. Many of the early ex­periments have been incorrect because of the neglect or improper determination of the neutron contribution to the photon spectrum. A recent experiment by a SREL group [Hart e t  a i l . , Phys. Rev. Lett. 3 9 ,399 (1 9 7 7 )] has shown that the neutron background can be significantly reduced by the use of a gamma-ray converter.A bar of Nal (2. 5"x2" x 10") with tubes at either end was recently tested at TRIUMF as a prototype Nal converter. The advantage of a Nal converter over a lead scintillator stack or lead-glass sinctillator is that a rather thick converter can be used with no significant loss in energy resolution. By employing two phototubes, one at either end and treating the surface of the bar so that the pulse height in each tube is a sensitive function of position, a versatile position- sensitive converter can be produced.F ig . 35. Measured position  reso lu tion  fo r  various sources as a function  o f  po sition  along the bar. The so lid  lin es  are merely to guide the eye.F ig . 36. The ra tio  ER-EL/ER+EL measured at the cen tre  o f  the bar fo r  high-energy beam e le c tro n s .  The so lid  curve i s  the convolution o f  a rectangu­la r d is tribu tio n  o f  width 2 .5  cm with a Gaussian o f  width 1 .5  cm (FWHM).The test bar was produced by the Harshaw Chemical Company and has RCA 6342A tubes mounted at each end. It was tested with both sources (y 1 s and electrons) and high- energy beam electrons from the M9 stopped ir/y channel. The energy resolution for the summed energy signals i s — 8^ for a e0Co source (1.33 MeV) and the pulse height from a single tubes varies from 100% to ~30% as the source is moved along the bar away from the tube.Figure 35 shows the position sensitivity o b ­tained with this bar using a ®®Co source which was positioned at 2.5 cm intervals along the bar. For each measurement the ratio (ER-EL)/(ER+EL), where ER and EL are the respective pulse heights in the left and right tubes, was computed. The ful1-width at half-maximum (FWHM) obtained was 1.5 cm for the e0Co source and 1.0 cm for electrons of energy > 1.4 MeV from a 106Ru source.For the high-energy electron measurements (Ee <  90 MeV) a 2.5 cm defining counter was placed in front of the test bar. Hence the true position resolution has to be unfolded from the data. Figure 36 shows the function (ER-EL)/(ER+EL) for the electron beam data with the scintillator positioned 18 cm from one end of the bar. The solid line is a calculated curve obtained by convoluting a rectangle of width 2.5 cm with a Gaussian of width 1.5 cm. (This Gaussian represents the intrinsic Nal position resolution.) A good34fit to the data is obtained and thus we are confident that a position resolution of 1.5"2.0 cm can be obtained for high-energy y's or electrons.A large Nal converter consisting of several such position-sensitive bars is now being purchased, and this will be used in the y - radiative capture experiment when the average proton intensity at TRIUMF is raised above ~30 yA.Experiment 83Bound muon decay in nucle iThe energy spectrum for negative muons which decay while orbiting an atomic nucleus is predicted to differ from that of a free y+ because o f  several effects: the reduced phase space due to the y" binding energy; the time dilation produced by the orbital motion; the attractive Coulomb interaction between the decay e _ and the nucleus; and the finite nuclear size in heavy nuclei.Although there have been several calcula­tions of the decay rates and energy spectra for bound y “ decay, there have been no mea­surements performed with sufficient energy resolution to observe the differences pre­dicted in the shapes of the energy spectra [Beilin, Nuovo Cimento 5 ^ A , 871 (1968)].During a short run in September the large TRIUMF Nal detector (TINA) was used to mea­sure the energy spectrum and also the energy dependence of the asymmetry of the decay electrons from y" decay in 12C, Ti and Cu targets. Except for the case of y_ decay in Pb where only the energy spectrum was measured, the targets were maintained in a uniform transverse magnetic field ( B < 7 0 0  G) and the differential asymmetry of the decay electrons was measured simultaneously. A three-detector scintillator telescope was used to assure that the electrons origi­nated from y “ decays in the target.Measurements were also made on the free y decay in order to check the systematics of the technique— a time differential analysis using the ySR method to eliminate backgrounds having lifetimes different than that of the target element. In three separate runs totalling =^12 h of beam time the group recorded ~2 x 106 decay positrons or — 4 times the existing data for the differential y+ asymmetry in 5Li and 9Be [Fryberger, Phys. Rev. 166, 1379 (1968)].ENERGY CHANNELFig. 27. a) Corrected, energy spectrum of e+ from decay, b) y+ decay asymmetry vs positron energy.Figure 37(a) shows the preliminary y+ decay energy spectrum corrected for background (mainly at low energies) from y+ decay in a carbon target at a field of 338 G. The large error bar on the low-energy point is due to a very large RF time component in the data within this energy bin. Figure 37(b) shows the differential asymmetry P^a(Ee ) which varies from +1 at the highest energy to -0.10 at the lowest energy where the sig­nal can be observed in the decay curve.Figure 38 shows the energy spectra measured for bound y“ decay in Ti and Pb. The solid line represents the spectrum for the free y+ decay which is almost equal to the y -- 12C spectrum. For pB the data are shifted con­siderably towards lower energies, as expected, but here the low-energy background has not been completely eliminated. This low-energy background is thought to be due to showers produced by high-energy beam electrons striking the collimator, and this can be reduced either by using a separated y- beam or by considerably increasing the lead shielding between the collimator and TINA.35ENERGY  (MeV)Fig. 38. Corrected energy spectrum of e~ from p- decay.ENERGY (MeV)Fig. 39. y~ decay asymmetry vs electron energy in titanium.The differential asymmetries for y - decay in 12C and Ti are shown in Fig. 39- These were obtained by binning the decay-time data into 32 separate histograms based on the electron energy and then fitting the decay curve with the express ion A [1 + a(Ee )Pu cos wt] to determine the asymmetry. Although the shape of the differential asymmetry in Ti is essentially the same as that in 12C, sub­stantially more depolarization of the y “ is observed; the reason for this is not immedi­ately obvious at the present time.Further measurements are planned in the next year to reduce the RF-related background at low electron energies and to improve the statistical errors on the differential asymmetry for the heavier targets.Experiment 9 7Rare electromagnetic decays o f pionic atomsRecently there has been a suggestion by Ericson and Wilkin [Phys. Lett. 5 7 B , 3A5 (1975)] that pionic atoms might decay with an observable branching ratio by the emis­sion of two high-energy gamma-rays or an electron-positron pair. Two mechanisms for this rare electromagnetic decay of pionic atoms were proposed: the charge exchange ofthe bound EE) to a virtual EEp TEE) VH SEEYB )H2y or e+e “ ) , or the annihilation of the ini­tial tt- on a virtual tt+ inside the nucleus (tt- +  l 7T+ l  -*■ 2y or e+e - ) . Their qualitative estimate for the branching ratio for the (7r",2y) process w a s ~ 0 . 2  x 10-5 for virtual charge exchange and ~ 5  * 10-6 for the pion annihilation process. Other authors[Migdal, Lee, Sawyer, Barshay] have sug­gested the (iT- ,2y) reaction as a method of testing for a pion condensate in nuclei.An upper limit for this process has been published by a SREL group [Roberson e t  a t . ,  Phys. Lett. 7 0 B , 35 (1977)], and the first observation of the y-y pairs was reported recently by Deutsch e t  a l .  [Phys. Lett. 8 0 B , 3A7 (1979)]- In this last experiment the angular distribution of the y-y pairs emitted after tt-  capture in C and Be was observed with a total B.R. = ( 1 . 0 ± 0 . 1 ) x l 0 -5 and (1.4 ± 0.2) x 10- 5 , respectively.In two separate runs in April and September we have looked at y-y and e-e pairs at TRIUMF using two large Nal crystals (TINA and MINA) and two lead-glass Cerenkov counters as detectors. These counters were positioned as shown in Fig. AO to provide the following opening angles: 50°, 80°, 110°, 120°, 160° and 170°. The pion beam from the stopped ir/y channel (M9) was tuned for 20 MeV pions; the average rate through S3 (A in. x A in.) was8 x lo5 iT-/sec. The timing signal was de­rived from S3 and the energy loss in S3 was used to reject second pion events. A 1-cm- thick carbon target was used to reduce the unwanted background from charge exchange (Q = -9-3 M e V ) . Scintillators (S5~S10) were placed in front of the y counters in order to identify charged particle events. A veto counter was used to measure the true ir stop rate, but this was removed during the run to reduce the tt° background from the hydrogen content in the counter. Time of flight wasused to separate the y's and n's in the Nalcrystals (resolutions^ nsec FWHM). The36Fig. 40. Experimental layout.  ^ TIEA and MINA are two large Nal deteetors. Cl and C2 are two Serenkov counters.cosmic-ray background in the Nal crystals was reduced by covering them with large plastic counters. Steel shielding was placed between the y-ray counters to reduce cross-talk and other sources of background.Although the analysis of the data is not yet complete preliminary results are in reason­able agreement with those of Deutsch e t  a t .  for a carbon target. The following software cuts have been imposed on the data in the off-line analysis: timing with respect tothe proton beam, timing between S3 and counter Nj, the energy deposited in S3, and a summed energy < 135 MeV.Figure 41(a ) shows the TINA-STOP time-of- flight spectrum for neutral events in coin­cidence with MINA {Qyy = 120°) after cutting on the proton timing signal and the energy deposited in S3. The peak at the right of the spectrum corresponds to neutron coinci­dences and is cut by the timing of the hard­wired coincidence. The y peak is easily identified along with a small random back­ground at early times. Figure ^l(b) shows a two-dimensional scatter-plot of the TOF in MINA versus the TOF in C2 for e+e _ coinci­dences. The region of the coincidences is easily identified. The random background for the e-e coincidences is <10% of the real events. In the case of the y-y events the random background is never more than 30% of the real events.The summed energy distribution for the e-e pairs in the TINA-MINA coincidence (9ee = 120°) is shown in Fig. h i .  This dis­tribution peaks at ~95 MeV (observed energy in Nal) and is rather narrow (r ~  30 M e V ) . However, this energy must be increased by — 20 MeV due to the energy loss experienced by the electrons in the target, the veto scintillators and the front faces of the Nal crystals. Detailed Monte Carlo calculations of these effects are presently under way.Fig. 41. a) Time of flight of particles incident on TINA. The peak on the right is produced by a hardware cut on the neutron events. The other peak corresponds to y-ray events, b) Plot of coincident events vs the time of flight of C2 and MINA for charged particles.b)I I IIII I I 156  15  515        / / 5 5 1    6 1       55  5#$655151 5   95   155165665,1#$5115  51 5         5 1   1$65,$66$##15$ 151    9 91$556$#5$6#,663#$6,655151    1$6 1 66$$$#,##3$66#$1 51511  151     55,5 55655161 51       151615  11$16$56 11 5  5   151   155 5     9 % 5  9211 I 12 I I |I 21 I I I II ITOF (MINA) •37EVENTS BBefp,Tr)'0Be (2^3-37)F ig . 42. Histogram o f  y-y co incident events vs the sum energy E8 + Ey at 120°.The branching ratio for e-e pairs at 120° is similar to that observed for y-y pairs which, in turn, is in reasonable agreement with the predictions of Ericson and Wilkin and the experimental results of Deutsch e t  a l .Experiment 10Pion production by proton bombardment o fhydrogen and o ther light nucle i1978 has been a year occupied by the design and assembly of a new magnetic spectrograph facility (named 'Resolution' after one of the ships of Captain Cook, our tribute to the B.C. Bicentennial celebrations of Cook's pioneering voyages to British Columbia).This spectrograph is a 65 cm Browne-Buechner instrument previously used by the Atomic Energy of Canada Ltd. at Chalk River. It has been reassembled on the new proton beam line (IB) at TRIUMF and is being instru­mented with 'helical' multiwire proportional chambers and scintillation counters for pion detection. Initial operation of both the beam line and the spectrograph are planned early in 1979•The only experimental data obtained during 1978 arose from a run using the MRS on beam line AB. The 9Be (p-, ir+ ) 1 °Be reaction was investigated at 0 = 22.5° for incident pro­ton energies of 200 and 3AA MeV. As a result we have thereby extended the angular range of our differential cross-section and analysing power measurements at 200 MeV and have the first point of the angular distri­j  2 0 0  MeV (reported previously) ^  2 00  MeV MRS ^  3 4 4  MeV MRS•6•42■0-•2- . 4—  6 — 8 -10I ,  i_J______ I______ I______ I______ I______ I______ I-----------L_0  2 0  4 0  6 0  8 0  100 120  140  160B,F ig . 43. Analysing power fo r  pion production  from the rea ction  Be(p,T\+ ) 10Be* as a functiono f  pion angle (labo ra to ry ).butions for an incident proton energy of 3AA MeV. Transitions to several excited states of 10Be were clearly observed, with some yielding positive values of the analys­ing power (Ay) in agreement with expecta­tions based on a simple impulse approximation model (Fig. A3).Experiment 66A survey o f proton-proton bremsstrahlungData analysis has been completed for the 200 MeV ppy experiment. The final publica­tion will shortly be available as a TRIUMF preprint [Anderson e t  a t . ,  submitted for publication]. A careful analysis of the efficiency and normalization has resulted in a reduction in the final cross-section values compared to the preliminary data [Beveridge e t  a t .  in l l u c t e o n - n u c le o n  I n t e r ­a c t io n s —1 9 7 7 , AIPCP#Al, AA6 (1978)].Figure AA shows the final data along with several calculations. The final data agree best with the soft photon approximation (SPA) calculation of Fearing [ i b i d . .  506]38F ig . 44. The measured ::8 cro ss-s ection s  (with e rro r  bars) and oalaulated th eo retica l c ro ss-sec tio n s . The ca lcu la tions are d iscussed  in  the tex t .Experiment 104The time pro jection chamberThe breaking of conservation laws has played a crucial role in the development of the theory of weak interactions. The discovery in 1 957 that parity and charge conjugation are maximally violated in beta decay has led to a careful study of many conservation laws. Small violations, such as the charge- parity nonconservation of order 10-3 dis­covered in K£ decays, are extremely signifi­cant and further emphasize the importance of establishing conservation principles with high precision.Lepton number conservation is another impor­tant law that has attracted much attention recently. In particular muon number conser­vation has been investigated in several major experiments at the new meson facili­ties and has come under intense theoretical scrutiny. The activity has focused on the question: Is muon number conserved absolute­ly, as charge and baryon number appear to be, or is there a small but observable v i olat ion?The answer is being sought within the frame­work of non-Abelian gauge theories, which led to the discovery of neutral currents and to the detection of charmed particles and which provide for the successful unification of weak and electromagnetic interactions. Many gauge theoretical approaches lead to the conclusion that the present experimental absence of muon number nonconserving pro­cess, 1 i ke y -> ey and p"+Z -* e _+Z, need not indicate that muon number is conserved in afundamental sense, since these processes are automatically suppressed by other mechanisms. Thus, muon number conservation should be treated as an open question.The basic SU(2) x U(l) model of Weinberg and Salam correctly describes many weak interac­tion phenomena. In this minimal model muon number conservation is effectively preserved. However, recent experimental information such as the discovery of the t lepton indi­cates that this theory may not provide the whole picture, and many attempts at generali­zation have been proposed; these require additional quarks, bosons, Higgs particles and/or leptons. Experiments testing the limits of muon number conservation can pro­vide important information and constraints necessary for discriminating among these theories and could lead to an understanding of important features such as the existence, mass mixing and currents of new particles.At TRIUMF preparations are under way for a new search for the reactions y _+Z e “+Z and y-+Z -+ e+Z - 2 .The features of the detector required for this experiment are (i) large solid angle, (ii) high resolution, and (iii) good back­ground rejection. These requirements are met by a system based on the time projection chamber (TPC) being developed at Berkeley by D. Nygren e t  d l .  [Proposal for a PEP facili­ty based on the time projection chamber, LBL].The TPC (shown in Fig. ^5) is a large volume drift chamber sitting in a uniform magnetic field. Charged particles which traverse the central region of the TPC are bent by theMAGNETCOILFig . 45. TRIUMF time p ro jection  chamber.39from protons emitted following muon capture.Fig. 46. TPC end cap detectors.magnetic field and leave a trail of electrons produced by ionization of the gas in their path.Good momentum resolution is possible because the only material intercepted by the par­ticle inside the chamber is the gas. An electric field aligned with the magnetic field C? x ^  = o) forces the ionization electrons to drift onto the end caps. There, proportional wire detectors are used to measure co-ordinates of track segments orthogonal to the drift direction and to ob­tain the drift time to determine their original position along the drift direction. The three spatial co-ordinates are measured with one plane of detectors and are determined unambiguously for each point with one measurement. This greatly simplifies reconstruction of mu 11ipartic1e events. In addition to bending the particles the mag­netic field is used to reduce the transverse diffusion of the ionization electrons as they drift through the gas along the direc­tion of E and B, thereby maintaining the precision of the r<j> position measurement.Another feature of the system is the capa­bility of obtaining the rate of energy loss of charged particles in the gas by measuring the charge deposited at many points on the trajectory. This capability is useful in the 8 -* e experiment, since particle identi­fication is required to distinguish electronsThe TRIUMF TPC will be operated at atmos­pheric pressure with an A r ^ H ^  mixture and an electric-fie1d-to-pressure ratio E / p ~  0.2 (for 80% Ar, 20% CHy) , where E is in V/cm and p is in Torr. Each of the hexagonal end cap detectors shown in Fig. A6 has 12 anode proportional wires spaced radially by 2.5^ cm. The charge produced on the wire by gas amplification of the of the drifting track segments induces a charge distributed along a row of cathode pads which runs above the anode wire. The centre of the distribution determines the position of the track segment along the anode wi r e .Final design and much of the construction of the TRIUMF TPC system was completed during 1978.Reduction o f multiple scattering displacement by a magnetic field parallel to the beamA charged particle of mass m moving with velocity V through a continuous medium approximately parallel to a uniform magnetic field H suffers many smal1-angle Coulomb scatterings. The net square deflection in air traversal can be expressed as a sum of4> — -F ig . 47. The fa c to r  F by which a magnetic f i e l d  reduces the rms displacement due to multip le s ca tte r in g  vs the h e l ic a l  angle ;:2kothe square deflections from single scatter­ings occurring in many independent traver­sals. These single displacements have been evaluated by beam transport methods. The ratio of the rms displacement projected on a plane perpendicular to the magnetic field (which is along the z-axis) to the zero field displacement isF = 1— 5-*2 [(' -1 / 2where <j> = eHz/(mVc) is the angle of the helical trajectory (see Fig. h~J) , e.g. for a single-turn helical trajectory F(2tt) =O.A, and the effect of the magnetic field is to reduce the multiple scattering to A0%. This confirms a previous [Farley e t  a l .  , Nucl. Instr. S Meth. 152, 353 (1978)] solu­tion of the diffusion equation for Fermi's distribution function.Daresbury-Mainz-TRIUMF collaboration at CERNResults achieved by a TRIUMF group and their collaborators working at the CERN PS are described in the following quotation from CERN Builetin No. 5/79:'With the development of the proton-anti- proton collider for the SPA, high-energy antiprotons are much in fashion these days at CERN. However, important physics results have already been obtained at the other end of the antiproton energy range. One of the major achievements at CERN in 1978 was the discovery, by a Daresbury-Mainz-TRIUMF (Canada) group working at the PS, of the spectral lines of antiprotonic hydrogen.This discovery was largely due to the group's specially developed X-ray detector, and now a new device is planned for a second genera­tion of experiments to further explore the structure of this exotic atom. In anti­protonic atoms the usual orbital electrons of everyday atoms are replaced by anti­protons. Spectra from such atoms were first seen at CERN back in 1970, but difficulties prevented experimentalists from getting at the simplest antiproton atom of all— anti­protonic hydrogen. Thanks to their detector, the Daresbury-Mainz-TRIUMF group were able to pick up and identify the low-energy X-rays given off by antiprotonic hydrogen.The details of the spectra are not yet com­plete, but the hope is that the missing details will be filled in by the next generation of experiments. The study of this rare breed of atoms reveals details of subnuclear particle interactions in a way that is different from ordinary scattering experiments at accelerators, and provides physicists with an important additional tool for extending our knowledge of particle behaviour.' [Auld e t  a l .  , Phys. Lett. 7 7 B , A5A (1978).AlNUCLEAR PHYSICS AND CHEMISTRYExperiments 1, 53, 54Pi scattering and tota l cross-section measurementsThe group has completed a series of  elas­tic scattering experiments on carbon, oxygen and lead, and has observed enhanced nuclear p-wave effects in the differential cross- sections. Though  and  elastic scatter­ing differential cross-sections appear with similar shapes at resonance energies, the profound Coulomb effects at low energies make angular distributions there quite dif­ferent. When  elastic scattering experi­ments on different nuclear isotopes are compared, very clear differences are noted. Nuclear neutron-proton radius difference can account for these isotope effects but this interpretation may be model dependent.Differential cross-section measurements of negative pion elastic scattering on 12C, 13C,    ancj 208Pb have been completed. A letter describing the interpretation of the general ir" angular distribution shape for 12C at T^- = 29 MeV has been published [Johnson e t  a t . ,  Phys. Lett. 75B , 560 (1978)]. The difference in angular distribution shapes between ir+ and ir” scattering is due to Coulomb-nuclear interference. In the region around A0° the Coulomb-nuclear inter­ference is constructive for  scattering causing the cross-section to be larger than the Rutherford cross-section. At 70° phase- shift analysis of the data shows that this interference has become destructive giving rise to the deep minimum observed in the cross-section. The opposite is true for the  data at 70° and the corresponding cross- section is much larger than for it” scattering.Likewise, the Coulomb effects yield quite different results for 208Pb scattering.Though one would expect diffraction minima to be apparent with such a large nucleus, the AO MeV ir+ data show little indication of such minima [Preedom, Proc. 7th Int. C o n f . on High-Energy Physics and Nuclear Structure, Zurich (Birkhauser, Zurich, 1977), p -119)]- On the other hand the 29 MeV  data clearly exhibit such minima and are shown in Fig. ^8. This is due to a nuclear p-wave enhancement caused essentially by the effective energy change of the  in the attractive Coulomb field and was anticipated by McManus [Strieker, McManus and Carr, to be published]. This data and its interpretation have been submitted for publication.Resonance energy pion scattering has been used to estimate neutron radii by taking into account the very strong ir--n p-wave scattering. The resonance differential elastic cross-sections of u" and tt+ differ, since the diffractive nature of the scat­tering is determined by the neutron or the proton distribution, respectively. Recall that low-energy pion elastic scattering for light nuclei is not diffractive in character [Johnson e t  a t . ,  Nucl. Phys. A 2 9 6 , k k k  (1978)]. One can observe proton-neutron radius difference effects at low energies from the large s-wave isovector parts of the N interaction. The s-wave isovector term contributes over 25% to the s-wave scattering amplitudes and will interfere destructively with the larger p-wave amplitude, especially at back angles. By using proton radii determined from electron scattering and com­paring the optical potential, ratio calcula­tions with differential cross-section ratios of similar Z target nuclei, considerable experimental uncertainties are eliminated.ANGLE  (c .  m.)F ig . 48. %<  208Pb e la s t ic  d i f f e r e n t ia l  cross-  section s  at 29 MeV. The no ticeable  d i f f ra c t iv e  s tru ctu re  is  due to nuclea r p-wave e f f e c t s  enhanced by the Coulomb in te ra ctio n .h2  =  /> 0 2%  'ir/cr2 < > 2 %,1.6Oh—;12$cr1.21.01)2? 5 " !J I 1 L l l20 ,0 100 1$0 ©F ig . 49. The d i f f e r e n t ia l  e la s t ic  c ro ss-section  ra t io  o f  carbon isotopes at 29 MeV. The proton ra d ii  o f  the ca lcu la ted  curves were f ix e d  to e lec tro n  sca tte rin g  re su lts  while the neutron  radius on 16 was varied .3(X/'2<J Ot—<F ig . SO. The experim ental 22' e la s t i c  sca tte rin g  re su lts  on 12C and 16 at 49 .5  MeV are compared with a ra t io  ca lcu la tion  where the neutron  proton radius d i f fe r e n c e  fo r  13C was taken as 0 .0 6  f .and the proton-neutron radius effects are emphasized in both the experimental and cal­culated ratios. The results of the 13C - 12C experiment and theoretical curves are shown in Fig. 49- The results indicate rn - fp0.06 f for 13C. These ratios are quite dif­ferent from the 50 MeV ir+ results of Dytman e t  a t .  [Phys. Rev. C _[8, 2316 (1978)]. The rr+ differential cross-section structure is destructively modified by the Coulomb ef­fects while the  differential cross-sec­tion structure is enhanced. Nuclear effects are thus enhanced in it- elastic scattering at low energies, so that nuclear parameters such as neutron-proton radius differences may be observable in  scattering at low energ i e s .Though the range telescopes used were de­signed to operate best at 30 MeV, they have been used to study EE) 13C and 12C scattering at 50 MeV. The differential cross-section ratios are presented in Fig. 50. Likewise 160 and 180 elastic scattering cross- sections have been measured and the results are displayed in Fig. 51.0CMF ig . 51. The experim ental FF  e la s t i c  d i f f e r e n t ia l  sca tte r in g  ra t io  r e s u lt s  on 1,0 and 130 at 29 MeV.43As can be observed from the figures, the neutron-proton radius difference affects the ratio curves quite significantly. Before any definitive statement can be made, though, mode 1-dependence studies now under way must be completed. There is some indication that more than the nuclear surface is sampled by these low-energy scattering experiments than with similar resonance energy experiments since the ratios that have been calculated are not sensitive to the parameter > in the modified Gaussian density, p(r) = p0 [1 + a (r/a)2 ] exp[-(r/a)2 ] .Experiment 42aStrong interaction sh ift in n3HeBecause two previous experiments (one at TRIUMF, one at SIN) to measure the strong interaction shift and width of the Is state in ir3He gave differing values for the width, it was decided to repeat the experiment in March. The experimental set-up was essen­tially the same as that described and shown in Fig. 29 of the 1977 Annual Report; the same liquid 3He target and the same Kevex Si (Li) X-ray detector were used. However, a new 200 MHz ADC (TN-1213)andgain stabilizer from Northern Scientific gave better spec­trum stability, and a Nova minicomputer was used more extensively for control of the ex­periment and for some on-line analysis. The recorded spectrum was extended to about 35 keV (starting from about 5 keV) in order to help identify background contaminants. Calibration sources covering the wider range of energies gave a somewhat better energy c a 1 i b rat ion.While the helium target was being cooled with ^He, a muonic spectrum was collected, and is shown in Fig. 52. The resulting values for the y^He Ka and Kg X-ray energies, 8223 + 5  eV and 9740 ± 6 e V , respectively, are in good agreement with theory and with the only published experimental data, as shown in Table XI.Table XI. y^He energies, eVTrans i t i on Ka M1Present experiment 8223 ± 5 9740 ± 6Theory 8223.7 9 7 4 4 . 1CERN experiment 8228 ± k 9742 ± 3a G. Backenstoss et at. , Nucl. Phys. A232,519 (1974)A n^He spectrum was also obtained, which is similar to that shown later for 7r3He. The weighted average for the Is strong interac­tion shift as determined from the Ka and Kg ir^He transition energies is AEjs = -71 ±5 eV, while the Lorentzian width was de­termined to be F|s = 51 ± 9  e V . These results for n^He are consistent with those (A E 1 s = - 7 6  ± 2  eV and Tjs = 45 ± 3 eV) o b ­tained by Backenstoss et at. [Nucl . Phys. A 2 3 2 , 519 (1974)].Figure 53 shows the summed ir3He X-ray spec­trum which was obtained by adding 20 separate runs over a total net acquisition time of about 2k h. Using the computer program JAGSPOT seven energy calibration lines (four source lines and three prominent pionic X-ray lines) were fitted to Gaussian line shapes modified by two-parameter low-energy tails with a straight-line background. The calibration lines and their energies are listed in Table XII. The resolutions for the 7r3He X-ray lines were obtained from a quadratic fit of the experimental energy resolution versus energy for the calibration lines. The positions, Lorentzian widths and intensities of the Tr3He Ka and Kg X-ray lines were found by fitting several closely spaced peaks simultaneously, making use of the TT^He and target-empty spectra to identi­fy interfering lines.Table XII. Energies of the calibration linesCalibration line Energy (eV)57 Fe Ka 6399 + 157 Fe Kg 7058 + 2119 4--3 1 1 470 + (57Fe Y 1 k 412 + V117 3--2 18 401 ± r119 3--2 32 843 ± 21 2 5 x Y 35 492 ± rIn determining the relative intensities of the ir3He K transitions, the positions and Lorentzian widths of the Ky and Kg lines were fixed and other parameters were allowed to vary. The relative intensities of the pionic Ka , Kg, Ky and Kg transitions in 1 i qu i d 3He were observed to be 100, 109 ± 8, 2k ± 2, and 8 + 2 ,  respectively, in agree­ment with the previous measurement at TRIUMF. The measured energies and Lorentzian widths of the Tr3He Ka and Kg lines arekkcounts per channelchannel numberF ig . 52. v^He X-ray speatrum.F ig . 53. -n^ He X-ray speatrum.^5Table XIII. ir3He results, eVTrans i t ion M 1Experimental energy 10679-0 12647.5Statistical uncertainty 1.5 1.5Total uncertainty 4.3 4.3Electromagnetic energy 10646 1261 3Shift 33-0 34.5Gauss ian width 229 238Lorentzian width 34.8 37-5listed in Table XIII, where the strong interaction energy shift of the Is level is the difference between the measured energy and the calculated electromagnetic energy. The electromagnetic energies are the Klein- Gordon values for 7r3He, corrected for nuclear finite size (a Gaussian charge dis­tribution was used, with ( r 2y 1/ 2 = 1.88 fm), vacuum polarization, and pion form factor. The quoted total uncertainties were obtained by combining in quadrature the statistical uncertainties with the systematic uncertain­ties which included the effects of instru­mental resolution, fitting procedures, position and intensity parameters of inter­fering lines, Compton scattering in the target, and spectrometer non 1inearity.As seen in Table XIV, the agreement is good between the value obtained in this experi­ment for the strong interaction shift and those values already published. However, the present value for the Lorentzian line width for the Is level agrees better with the published SIN value than with the pre­vious TRIUMF value. There is the possi­bility that the source spectrum in the previous TRIUMF experiment was not taken exactly under 'in-beam' conditions so thatTable XIV. Comparison of results for the ir3He 1 s level , eVShift Wi dthPresent experiment 34 ± 4 36 ± 7Previous TRIUMF expt.a 27 ± 5 65 ± 12SIN experiment'3 44 ± 5 42 ± 14the Gaussian widths deduced sured calibration lines are would result in too large a previous Lorentzian width.from the mea- too narrow; this value for theExperiment 108Variation o f pionic X-ray in tensity with atomic numberThe intensity of pionic X-rays per pion stop has been observed to vary with the atomic number of the stopping material. One of the largest variations occurs in the case of the 4-3 transition where the intensity has a maximum at Z = 32 which is twice the value at the minimum at Z = 24 (see Fig. 54). Results are also available for 2-3, 5_4, 6-5, 7-6, 4-2, 5-3, 6-4, 7-5, 5-2, 6-3 and 7-4.Pions from the 100 MeV/c channel at TRIUMF were stopped in 57 materials, all in elemen­tal form, and the X-rays were detected in a hyperpure germanium detector. For the main transitions the total relative error due to statistical uncertainties, target position­ing, deadtime correction, etc. typically amount to 5%. In addition there are uncer­tainties in the absolute value of thea G.R. Mason e t  a t . ,  Phys. Lett. 74B , 179 , (1978)R. Abela e t  a t . , Phys. Lett. 6 8 B , 429 (1977)F ig . 54. In ten sity  o f  4-3 X-ray tran sition s  p er  pion stop as a function  o f  atomic number.46intensities from the detector efficiency, the efficiency of the stop signal, and from self-absorption corrections. Similar effects have been observed wi th kaons [Godfrey and Wiegand, Phys. Lett. 5 6 B , 255 (1978)].Experiment 80Strong interaction effects in p ion ic atomsMeasurements of pionic 2p-ls X-rays using separated isotope targets of 1 0 B, i:lB and 13C have continued. The spectrum of 11B is shown in Fig. 55- Preliminary values for the transition energies and widths are:1 0 B : E = 65844 ± 13 (65942) eVr = 2011 ± 33 (1640) eV1 1 B : E = 65269 ± 24 (65356) e\ir = 1995 ± 68 (1840) eV1 3 C: E = 92249 ± 40 eVr = 2400 ± 140 eVValues in parentheses are from an optical model calculation. The measurements are accurate enough to give information about the neutron distribution in the nucleus. Assuming that the proton and neutron radii are equal in 1 0 B, one finds rn (1 1 B) - rp( 1 ]-B) = 40 ± 20 mfm. Important contri­butions to the error come from the uncer­tainty in the isovector scattering length (bj = 0.087 ± 0.007 m) and from the proton charge radius (rp = 2450 ± 120 mfm) determined from electron scattering. It is not very sensitive to other details of the opt i c a 1 m odel.The tt 1 3 C is quite preliminary but it is expected of sufficient accuracy for per­formance of the same sort of analysis. The new low-energy scattering data (Expt. 54) will allow another stringent test of the method of analysis. This confirms the early promise of pionic atoms as a tool for the study of nuclei.Analysis of the F and Na X-ray data has been completed, and the results have been published. An interesting feature of these results is the ratio of the widths:R = T(Na)/r(F) = 1.20 ± 0.15- Optical model calculations give R = 1.9 ± 0.1, the error being estimated conservatively for a wide variation of optical model parameters, and for different formulations of the opti­ca 1 potent ia 1 .Fig . 55. Spectrum o f  p ion ic  11@2 The energy d isp er­sion  i s  54 eV /channel. The d etec to r  reso lu tion  was 7 .33  channels FWHM.Measurements of 20Ne and 21+Mg are planned for 1979 to further investigate this large width region. A cryogenic 20Ne target is being prepared. Analysis of a short run on magnesium failed to find definite evidence for the 2-1 X-ray. A novel Compton suppres­sion system is being designed to ameliorate the severe background problems.Experiment 14Elastic scattering o f pro tons from 4 HeMeasurements of differential cross-sections and analysing powers arising in proton-^He scattering have taken place in three dis­tinct regimes: the forward scattering (3-5°“ l6° laboratory angle), large-angle scattering (l45°-l72° laboratory), and the intermediate angular range (13°-150° laboratory). The first two investigations have been published [Stetz e t  a l . ,  Nucl.Phys. A 2 9 0 , 285 (1977); McCamis e t  a t . ,Nucl. Phys. A 3 0 2 , 388 (1978)], and data analysis is in progress for the third (inter­mediate angle) region. Data on the inelas­tic process p + 4He -> d + 3He which came simultaneously in the backward angle measure­ments have been published as well [Cameron  2  a l .  , Phys. Lett. 74B, 31 (l978)A .The large-angle differential cross-section and analysing power results have been useful as tests for reaction models at TRIUMF energies. Preliminary results from the intermediate angular domain (Tp = 200, 350, 500 MeV) indicate large magnitudes for47F ig . 56. Cross sec tio n  and analysing power angular d is tribu tio n s  fo r  the p+^He e la s t ic  s ca tte r in g  at 200 MeV.and rapid variations to analysing power angular distributions (see Fig. 56). Theoretical investigation [Alexander, private communication] of this behaviour is presently under way at 200 MeV.Experiment 15 Quasi-elastic scatteringThere were 30 shifts of beam time at TRIUMF ABT2 target positions over the summer, and data were taken for 160(p,pn) and 150(p,2p) using the MRS spectrometer and a counter array of 16 neutron detectors. The spec­trometer was fixed at an angle of 22.5° while the neutron counters covered the angu­lar range from 35° to 75°• The analysis of this data is under way and proceeding well.It appears that the resolution will be ade­quate to resolve the ground state in 15N and 150. The results are of interest in order to help determine the cause of the anomalous­ly high cross-section for 12C(p,pn) compared with 12C(p,2p) reported last year. It should be recalled that the latter result was obtained by using the (p,pn) and (p,2p) cross-sections for deuterium to obtain the neutron detection efficiency. It was assumed that the ratio R = [a(p,pn)]/ c ( p ,2p) ] for deuterium depended only on the pn-to-pp cross-section ratio. To check thisassumption data were obtained from np scat­tering with the BASQUE apparatus. The results have now been analysed and do con­firm that the assumption is valid. This is in contrast to the results of Felder e t  a l .  [Nucl. Phys. A 2 6 4 , 397 (1976)] who found the cross-section for 2H(p,pn) to be larger than expected by as much as 60% depending on the geometry. The authors indicated that back­ground may have contributed.For carbon there are about 50% too many (p,pn) events relative to (p,2p). Three possible explanations which may be invoked to account for the observation of too many neutrons are:1) Differences in the nuclear structure of 12C between neutrons and protons. Knock-out reactions are strongly surface localized due to the absorptive nature of the optical potentials. The observed reduction factor in 12C(p,2p) i s ~ 0 . 2  which in a simple model suggests that only the outer 20% of protons contribute to the reaction. The 50% enhance­ment of the (p,pn) reaction then suggests that 10% of all the neutrons are 'outside' the protons in 12C. A difference of 0.1 fm would be required between the neutron and proton radii which is unlikely [Allardyce e t  a l .  , Nucl. Phys. A209, 1 (1973)].k82) An enhancement of the nuc1eon-nuc1 eon interaction for (p,pn) relative to (p,2p). It is unlikely that the balance between nucleon interaction processes could be altered to change the forward and backward proton-neutron scattering in the same way while altering the proton-proton scattering i n a d i fferent w a y .3) An isospin dependence in the optical potentials. The simplest modification would require that the overall absorption for (p,2p) reactions be 10% greater than that for (p,pn) reactions. Alternatively, isospin flipping transitions betweenp + 11B and n + l:LC could be introduced which couple (p,2p) and (p,pn) cross- sections. In the first case the departures from charge independence due to Coulomb and Pauli effects are most likely for the lowest energy (— 100 MeV) particle of the three. In the second case the exchange probability is expected [Balashov e t  a l .  , Nucl. Phys. A 2 16, 517 (1976); Sternheim and Silbar, Phys. Rev. Lett. 34_> 824 (1975)] to decrease like E- 1 , and again the effect is strongest for the low-energy particle. However, the same effect has been observed for two geometries in which the neutron and proton exchanged the role of 'low-energy pa rt i c 1 e 1 .Experiment 59Studies o f the (p,2p) reaction on 4HeThe investigation of the 4He(p,2p)3H reac­tion with unpolarized protons was completed in 1978. Data were taken at incident ener­gies of 350 and 500 MeV. For each energy measurements were made of an energy-sharing spectrum at k 0 ° - k 0 ° ,  a pair of angles for which zero recoil momentum is allowed, and the symmetric angular distribution. The energies of the outgoing particles were measured with Nal(TJl) detectors, while pass­ing counters provided dE/dx values and time signals, and multiwire proportional chambers measured the emission angles.The energy-sharing spectrum at 350 MeV is shown in Fig. 57- By measuring consecutive energy bites— corresponding to varying amounts of copper degrader in the detector telescopes— this spectrum could be extended to recoil 3H momenta of 270 MeV/c. The value for the cross-section at zero recoil momentum at 500 MeV is close to the one o b ­tained at 350 MeV. Since earlier results inI 8 12,1 41.2 1 10 0.8if)|  0 6  0.402 00100 140 180 220 260 300T0 (MeV)Fiq. 57. Enerqu-sharinq spectrum at 250 MeV and 03 = e„ = 40°.this energy region— the SREL data at 590 MeV [Perdrisat e t  a l .  , Phys. Rev. 187, 1201 (1969)] and the Chicago data at 460 MeV [Tyr^n e t  a t . ,  Nucl. Phys. 79_, 321 (1966)] —  differ in absolute magnitude by a factor of 1.6, it was felt important to check the 500 MeV cross-section measured previously. The new measurement corroborates the normal­ization of the previous TRIUMF data and thus confirms the agreement with the 590 MeV resu1t from SREL.Figure 58 shows the world data for the q=0 point of the distorted momentum distribution p(q) obtained from the ltHe(p,2p)3H reaction at various incident energies. The TRIUMFicr7rowos>0)2o5.0 100 200  300  400  500  600T0 (MeV)F ig . 58. Momentum d is tr ibu tio n  o f a proton in **He fo r  zero r e c o i l  momentum as function  o f  energy  compared to DWIA p red ic t io n s .n n 1 1 1 1 n  r109 61 14 7 37 88 141 201 272 381 q(MeV/c)3174He(p,2p)3H350 MeV§5 40°-40°5 *5 §49F ig . 59. D istorted  momentum d istribu tion s  at 500 MeV and 600 MeV compared with DWIA p red ic t io n s .data at 350 and 500 MeV and the SREL measure­ment are close to the existing DWIA calcula­tions [Roos, Phys. Rev. C 9_, 2437 (1974); Frascaria e t  a l .  , Phys. Rev. C J_2, 243 (1975)], while the low-energy data [Pugh e t  a l .  , Phys. Lett. 4 6 B , 192 (1973)] (and the 460 MeV point) disagree by a factor of two.It would thus be interesting to obtain data at 225 MeV incident energy to fill the gap between the 350 MeV data point and the point at 150 MeV.The symmetric angular distributions at 350 and 500 MeV were measured at laboratory angles ranging between 30° and 65°. With the exception of the angular settings corre­sponding to the highest recoil momenta, cross-section values were extracted at 2-3 angular pairs from each setting of the tele­scopes by division of the angular range subtended by the multiwire chambers into appropriate regions. The data at 350 and 500 MeV extend to momenta of 410 and 490 MeV/c, respectively, which is consider­ably further out in the tail of the momentum distribution than in any previous 1+He(p,2p) exper i m e n t .While DWIA calculations in connection with the results are still in a preliminary stage, the importance of probing the high- momentum region can be illustrated by com­parison of the data with an earlier calcula­tion performed by Roos [Phys. Rev. C %  2437(1974); Frascaria e t  a l .  , Phys. Rev. C 12,243 (1975)] for an incident energy of 600 MeV with an Eckart-type wave function.Figure 59 compares the distorted momentum distribution extracted from the TRIUMF 500 MeV data, together with the SREL results, with this DWIA calculation (solid curve). Horizontal bars represent the momentum inter­vals corresponding to the angular bins accepted in the analysis. Up to 150 MeV/c the TRIUMF data are in better agreement with the calculation than the SREL data, which show a pronounced asymmetry between recoil momenta parallel and anti-para 11 el to the beam. At higher momenta the experimental data fall off much more slowly than predicted by the DWIA. It remains to be investigated whether this apparent excess of high-momentum components is entirely due to the insuffi­ciencies in the DWIA description or whether it indicates a strong high-momentum part in the nuclear wave function, as predicted by recent coupled-cluster calculations [Zabolitsky and Ey, private communication].Experiment 99Studies of(p ,d) reactions in nucle iThe experiment began taking data in January—  the first experimental group to collect data using TRIUMF's medium resolution spectrome­ter (MRS). Cross-sections were measured as a function of beam energy from 200 to 500 MeV for various targets at the 'TRIUMF' angle of 22.5°, the angle at which the MRS had been locked by beam line shielding. With an overall energy resolution of 1.5 to 2.0 MeV, the group obtained data on the tar­gets 4He, 7 L i, 12C and 160. Brief survey runs were also made on 6 Li and 12C targets.On-line data acquired for 4He(p,d)3He have been analysed and published [Kallne e t  a l . , Phys. Rev. Lett. 4j_, 1638 (1978)]. An anal­ysis program has been written and de-bugged to replay the remaining data. Replay is progressing, along with studies of MRS dis­persion and acceptance, wire chamber effi­ciencies, and beam monitor normalizations. Present plans for the first half of 1979 include the measurement of angular distribu­tions at several energies for the targets 4H e , 7Li, 1 3C and 150 .50Experiment 105Inclusive scattering o f 500  MeV polarized protonson heliumMeasurements of inclusive scattering of 500 MeV polarized protons on a liquid helium target were completed at lab angles of 65°, 90°, 120° and 160°. Range counters were used to detect the reaction protons, deuterons and pions. Particle identifica­tion was achieved by using time-of-f1ight and energy loss information. The inclusive spectra extended out to the elastically scattered protons at the angles of 90°, 120° and 160°. Preliminary analysis shows analysing powers of 10% to 20% for inclusive scattering at 160°. Analysing powers appear smaller at 90° and 120°. The 65° data appear more difficult to analyse and will be attempted again at a later date.Experiments 3, 116, 117The characteristics o f fragments em itted fromsilver with 200 -500  MeV protonsGeneral survey. As a result of a general survey of fragment emission it has become clear that both an evaporative and a non- evaporative process are involved. The evap­orative component is a strong function of the emitted fragment where features such as the number of particle stable states, sepa­ration energies, Coulomb barriers and the distribution of the evaporating systems are important. With the wide range of emitted particles observed in these experiments, it is possible to place constraints on the prop­erties of the equilibrated emitting systems generated from the initial interaction and an evaporation calculation based on the Weisskopf-Ewing formula has been able to reproduce the relative emission probabili­ties for the He-Be isotopes. However, a better inverse cross-section calculation is required to extend the calculation beyond B in an accurate quantitative manner.The remaining non-evaporative component is a slowly varying function of mass but strongly forward peaked. Although the non- evaporative spectra have some features con­sistent with an evaporative process, they cannot be described by any conventional evaporation calculation. Furthermore, a rapidity analysis clearly shows them to be inconsistent with the notion of emission from an equilibrated large mass nucleus.Figure 60 shows the angular distributions for the isotopes of He-Be at 480 MeV. The evaporative and non-evaporative components have been resolved and illustrate the gen­eral trends.Detailed study of inclusive fragment emi ss ion. Addition of TOF has permitted isotopic resolution for fragments to beyond Mg. Measurement with A80 MeV protons and at six angles (20°, A0° , 60°, 90°, 120°, 160°) are in progress with approximately two thirds of the data collected. This added information is permitting a more detailed analysis of both the evaporative and non- evaporative components. The availability of isotopic spectra for the heavier fragments such as C and 0 is proving very useful in the development of the evaporation calcula­tion and in obtaining a description of the systems leading to fragment evaporation.The strong dependence of the evaporation probability on isotopic characteristics is illustrated in Fig. 61 where 20° carbon iso­topic spectra are displayed. In addition, the radically different slopes between 10-11C and 12-lkC is indicative of the fact that the non-evaporative processes are still important in the emission of C, and it is found that they are still discernible in the heaviest fragments.Search for polarization effect in fragment emi ss ion. The group also pursued a sug­gestion of the IEP committee and mounted a parasitic experiment to measure the left- right asymmetries of light fragments emitted from Ag using polarized protons at several energies up to 518 MeV. This experiment concentrated on the spectra of 3He and ^He, but limited data were obtained for the H and Li isotopes. The data analysis is incomplete, but it is apparent that, if non-zero, the asymmetries are very small.Correlation studies of fragment emission. A considerable amount of effort has been ex­pended to determine what experimental infor­mation is required to specify the non- evaporative processes and how this informa­tion can be efficiently obtained. It is becoming clear that it is theoretically important to characterize the protons emitted in coincidence with the fragments by determining their identity, energy, position and multiplicity. Such an experiment is being planned.51measu red— •  — e v a p o r a t i v e  — -*■ — n o n - e v a p o r a t i v ecos  0F ig . 60. Angular d is tribu tio n s  o f  isotopes o f  He to Be from 480 MeV protons on s i lv e r .ene rg y  ( M eV )F ig . 61. Smooth f i t s  to energy spectra  fo r  carbon isotopes at 20° from 480 MeV protons on s i lv e r .52Experiment 6Intermediate-energy fissionDuring 1978 data-taking on this experiment was completed. It is believed that the data presently in hand represent the best which can be taken on this experiment with the existing instrumentation.The experimental configuration used this year is shown in Fig. 62. The fission de­tectors were increased in area to 400 mm2 and the target-to-detector distances were decreased to 10 cm. These measures resulted in an improved true-to-random ratio, and with uranium and bismuth target thicknesses in the order of 100 to 200 pg per cm2 rates for triple fission-fission-te1escope events increased to about one per second, for beam currents of 100-200 nA.F  M O N I T O RFig . 62. Experimental arrangement.Measurement of emitted charged particles at 135° to the beam in coincidence with binary fission events were made at two angles: first with the charged particles detected at approximately 90° to the fission axis and second at approximately 2 5 ° to the axis.The telescope data were of good enough quality to permit the resolution of helium and lithium ions from each other and from other evaporated particles, and it is e x ­pected that helium-3 can be resolved from helium-4 particles upon further analysis. Figure 63(a) shows the energy spectra mea­sured for emitted helium ions from a Bi tar­get, and Fig. 63(b) those from a U target, from the few data thus far analysed.Preliminary analysis of these data reveals the absence of a statistically significant energy shift between the spectra at 25 and at 90° in both cases, and also the absence of a significant intensity difference (that is, the data appear indistinguishable from isotropy of emission). This result is con­sistent with charged particle emission occurring entirely before fission, in con­trast with the predictions of the conven­tional statistical model.This conclusion is supported by further analysis of the data, presented in Fig. 64, where the relative helium ion emission probability is displayed as a function of the respective fission fragment energies.The data show perhaps the effect of centre- of-mass motion of the emitting system, but are otherwise consistent with an unchanged helium ion intensity with changing fission fragment energy, which is in turn consistent with charged particle emission before fission.Analysis of these data will be concluded in 1979-Experiment 11Nuclear spectroscop ic studies o f short-livedradioactive products o f high-energy reactionsThis experimental program is intended to collect information on the production and properties of nuclides far from stability. The techniques available have been described briefly in the 1977 Annual Report.The survey of the properties of very neu­tron-rich fission fragments produced with intermediate-energy protons on uranium is essentially completed, and a total of 35 isotopes have been studied. Table XV pre­sents a comparison of some of the Eg results measured here and elsewhere.Table XVI displays new (reported here for the first time) beta end-point energies in coincidence with specific gamma rays in the decay of indicated isotopes. For those nuclei whose decay is reasonably well known, Q.g values have been extracted and compared to various mass formulae theories. In general the predictions of the Liran-Zeldes approach [Li ran and Zeldes, in Atomic and Nuclear Data Tables J_7, 474 (1976)] gave the best agreement with all of the species cons i d ered.53F ig . 62. Helium ion energy spectra  measured from a) Bi+444 MeV protons, b) UFi,+444 MeV protons: a l l  helium ions em itted , helium ions em itted  in  co incidence with binary f i s s io n  events at 25° to the f is s io n  a x is , and helium ions em itted  in  co incidence with f is s io n  fragments at 90° to the f i s s io n  ax is .F ig . 64. R elative helium ion emission p robab ility  at 90° to the f is s io n  axis as a function  o f  the f i s s io n  fragment energy a) Bi+444 MeV protons, b) UFk+444 MeV protons.54Table XV. Beta end-point energies in coin­cidence with indicated y-gates.Table XVI. New beta end-point energies for isotopes indicated.y-gate T 1/2 1 sotope ~ 1 (lit) Ass i gnment T l/2 y-gate E e(keV) (sec) (MeV) (MeV) (sec) (keV) (MeV)925 2 3 21 121ln9 2.41±0.08 2.48+0.05 100Nbm 3-1 1530 4. 27 ± 0 . 16504 7.1 100Zr 5 .30±0 210 2.81 ±0.1 5 ,00 4.2 9 ± 0 .08400 7.1 100Zr 2 . 8 8 ± 0 . 10 5 ." , ±0 21 5 523 4 . 0 9 ± 0 2 151131 6.0 123In 3.23+0.09 3.3 0 ± 0 .07 535 4.07±0.08137-7 14.0 " N b m 3.3 9 ± 0 .05 3-38±0.02546 2. 1 99Zr 3-63±0.07 3.55+0.15 103Nb 1.8 102.7 4. 7 8 ± 0 .12594 2.1 99Zr 3.55±0.09 3-61±0.15 103Nb 4.3 1"525 5-3 +0.3915 10.0 96ym 4.2 2 ± 0 .08 4 . 3 4 ± 0 .20 BYLFt 66 45-8 3 . 14±0.121750 10.0 96ym 4.2 3 ± 0 .08 4 . 3 4 ± 0 25# 83.4 3.50±0 21#1633 4.3 1 0 2 N b m $ .3+0210 4 . 7 8 ± 0 .17159.6 1.5 100Nb9 5.40±0.05 5 . 5 7 ± 0 . 15 103 Mo 60 , 3 2 5 .0 0 ± 0 .03535 3.1 100Nbm 5.56±0.08 5.72+0.181 0 5 Mo55-0 2.03±0.0435.6 85.4147-776.64.58±0.08 4 . 4 5 ± 0 .09 4 . 10±0.11I po— Y 8.6 53.9 3-01+0.121 0 7 T c 21 102.7106.65 .3"10210  2. 84 ±0 . 171 0 8 T c145-5 3.3810.035.0 242 5-79±0.06110Rh 3.3 373.3 4.9010.0811°Rhm 28.5 373.3 2.89+0.09n s P d 31 48.5 4.57+0.151 1  6 pd 13 114.7 2.4110.05Table XVII. Calculated and measured cross-sections for the reaction of 480 MeV protons with targets indicated.Target Product React i on Cross-sect ion (pb)aCa1cu1 a ted S-Tbc ross-sect ions I-Ecnatural HoTBoC‘t O 153Tm (p, EEN 1 3n) ^ 4.6 — 715ATm (p T RRI  12n) d 15 — 12151Er P. 1 5n 240 — 1331 52E r p , 14n 130 — 5611 5 3 E r P, 13n 280 — 6371 5 0 H o p,pl5n 640 62 84715lHo+151Hom p,pi4n 1200 270 1750152Ho+152Hom p, pi3n 2200 790 3300150Dy p,2pl4n 4340 360 6100151 Dy p,2pl3n 5700 1640 6800natural gold1 8 3Hg p , 1 5n 320 — 1000B'LrD p,pi4n 1600 — 15001 7 5 p t p ,2p20n 43 0.2 30176Pt p,2pl9n 220 1 2501  7 7 p t p ,2 p18n 480 3 5001 7 8 p t p,2pl7n 1500 15 175015l*Tm+15‘*Tmm P,11P33n 7.6 0.4 <101 5 2 E r P,12p33n 14.5 I <101 5 3 E r p,12p32n 54 2.6 <101 5 1 H o P,13p34n 75 4.2 <10152Ho+152Hom p,13p33n 120 11 <10aThe error on these values is about ±50% i1berberg-Tsao semi-empirical approach cComputer codes ISOBAR and EVAdThe contribution from secondary alpha reactions has not been determined and deducted; the reaction path indicated is the one used for the theoretical calculations.55Experiment 115  Neutral pion production■ ioo80CC 4064  66 68 78 80Z of productsF ig . 65. R elative e f f ic ie n c y  fo r  the transport o f  proton-induced rea ction  products using  the ethylene  g a s - je t  r e c o i l  transport system as a function  o f  the product element.This new experiment represents a collabora­tive effort between co-workers from the Indiana University Cyclotron Facility, Tel- Aviv University and SFU/TRIUMF. The primary purpose is to study the angle-integrated cross-section for the 2 0 9 B i (p , tt°+y) 2 1 °Po reaction at incident proton energies from 185 to 500 MeV through measurements of the residual polonium alpha activities resulting from radiochemical separations. These represent a continuation of similar studies performed at IUCF up to about 200 MeV. In addition it is intended to apply similar techniques to measure relative excitation functions for the (p,Tr+ ), (p,ir- ) and (p,7r0+Y) reactions on 209Bi through measure­ment of the respective heavy reaction prod­ucts 210B i, 21°At and 210Po.The measurements of the absolute cross- sections of known short-lived alpha emit­ters resulting from the irradiation of a variety of targets (Tb, Ho, Tm, Ta, Re, Ir,Au and Bi) with A80 MeV protons has been completed and these data compared to certain theoretical approaches, i.e., semi-empirica1 approach of S i 1berberg-Tsao [Partial cross- sections in high-energy nuclear reactions, Astrophys. J. Suppl. Series 25_, 373 (1973); computer code written by W. Wiesehahn] and a more fundamental approach using the ISOBAR and EVA computer codes [Computer programs provided by Z. Fraenkel, Weizmann Institute]. Some of these are displayed in Table X V I I .  Indications are that the fundamental approach provides reasonable accuracy for products of low AA, but the discrepancy in­creases remarkably for deep spallation prod­ucts (high A A ) , which are far from stability, e.g. Ho, Er, alpha emitters from the gold target. The applicability of this program for such products needs to be examined further.In the process of studying these cross- sections it was necessary to measure the transport efficiency of the ethylene gas jet recoil system used to carry the products for a large range of elements. This relative efficiency is a function of Z o f  the products displayed in Fig. 65; the results for the different targets were combined appropriate­ly-Preliminary experiments were performed in 1978 to assess the feasibility of this ex­periment and assess the contributions of various interfering reactions. Reasonably intense (0.2-1 pA) proton beams at energies of 210, 3^3 and 480 MeV were used to bombard 209Bi foils (typically ~2 h) of va ry i ng thicknesses (~3 mg/cm2 ) and in addition a relatively thick foil (18 mg/cm2 ), the latter to assess effects of secondary alpha reactions. Polonium and in one case astatine were chemically separated and residual alpha activity studied over a period of several months. These separations were performed within 1.5 h after bombard­ment to minimize decay contributions of 229At (8.3 h) and 219Bi (5-5 d) into the polonium samples. In addition the irradi­ated Bi targets were divided into two equal parts, only one of which the proton beam intercepted, to study the contribution from neutrons in the system.If one combines data from various labora­tories, including recent unpublished results from IUCF and the preliminary TRIUMF measure­ments, the excitation functions for the produc­tion of 205Po, 208Pband 210Pb from 209Bi wi th intermediate-energy protons can be compared. The spallation yield of the 2n and ^n prod­ucts (208Po and 208Po) display expected dependencies with increasing proton energies. There are indications, however, of either interesting structure or experimental incon­sistencies in the observed excitation func­tion for the production of 210Po in the region of 200 MeV. Further experiments are required to complete this investigation.56Experiment 120A study o f the production and decay o f 11 Bewith intermediate-energy protonsPreliminary data acquisition for this ex­periment has been initiated following its approval at the June meeting of the EEC.The original objectives included the follow­ing: (i) to obtain new spectroscopic infor­mation on the decay of n Be (t1(/2 = 13-8 sec) particularly from 3" delayed alpha emission; (ii) to provide a critical test of the application of the gas jet recoil transport system to the study of the decay of neutron- rich light nuclei; and (iii) to investigate the mechanism involved in the production of l:lBe in the 11B (p , pir+ ) 11 Be reaction.In pursuit of these objectives initial ex­periments were concentrated on optimizing the yield of 31Be produced in the 13C(p,3p) reaction. The activity, transported to the counting area by a jet of helium saturated with methanol, was observed using a Ge(Li) detector. With a beam of 0.9 yA at 480 MeV incident on a thick (~40 mg/cm2 ) 13C target a detection rate of 1.5 sec-1 has been observed for the photopeak of the 2125 keV transition in 13B. These observations indicate that under these conditions thel:lBe activity delivered by the transport system is maintained at a level o f ~ 0 . 2  yC i. Further effort will be required to reduce the levels of background activity (attrib­uted primarily to the windows of the target cell) and ensure the collection of sources thin enough to permit observation of delayed alpha particles of e n e r g y < 1 MeV.A second approach to the study of the (p,pTr+ ) reaction mechanism has been ini­tiated while dealing with the problems of background reduction and the fabrication of a target suitable for the gas jet sys­tem. Spectra of the lithium and beryllium isotopes emitted at 35° and 60° from the interaction of 480 MeV protons in a beryllium target have been observed using the semiconductor telescope of Experiment 3 mounted in the 60 in. scattering chamber.The intention is to study the role of the (( in the reaction by inferring the missing mass of the (pir+ ) system from the observed energy of 9Li. 9Be is a more suitable tar­get than H b  for this aspect of the investi­gation of the (p,pn+ ) reaction. The data obtained are being used to assess the feasibility of this approach to the study of the reaction mechanism.57RESEARCH IN CHEMISTRY AND SOLID-STATE PHYSICSExperiments 71, 78, 91 pSR in solidsInt roducti onLast year's annual report described in some detail the characteristic features of ySR (muon spin rotation) and the potential im­pact of these experimental techniques on solid-state physics. In 1978 more of that potential has been realised. Before focus­ing on TRIUMF's special role in these advances, it is best to summarize the world­wide progress of ySR in the past year.The First International Topical Meeting on Muon Spin Rotation was held in September at Rorschach, Switzerland (proceedings to be published in Hyperfine Interactions). The second meeting will be held in Vancouver in 1980. At Rorschach 86 participants pre­sented 73 papers, of which about one quarter were theoretical and the rest experimental or review talks. There were 26 papers on diffusion and trapping of y+ and other hydro­gen isotopes in metals with and without defects; 22 on interstitial magnetism and the electronic structure of hydrogenlike im­purities in metals; 14 on muonium chemistry;9 on muonium states in semiconductors and insulators; and 2 on y -SR. In total, 17 were based on the work of the TRIUMF ySR program.At least two general conclusions can be drawn from the discussions at Rorschach. First, most theorists working in this and associated fields now regard the 'extrinsic' behaviour of the y+ -lattice system as the most intriguing aspect of y+ SR, since the y+ has now begun to fulfill its promise as the 'prototype interstitial impurity'. For instance, explicit calculations of spin- dependent electronic structure, using such theoretical tools as nonlinear self-con­sistent density functional formalism, are now being widely used to predict hyperfine fields and Knight shifts at the y+ in metals. Similarly, the quantum theory of diffusion of light interstitials in metals can fairly be said to have been revolution­ized by new work on y+ diffusion.Second, thanks in part to clarifying work on such extrinsic problems, there are an in­creasing number of cases where ySR provides unique and valuable information about theintrinsic properties of the medium. Several of the most gratifying examples of this type came from TRIUMF in 1978.y_SR (Experiment 71)Because of the inherent difficulty of y"SR relative to y+ SR [3~4 times less intense beams, 3"5 times less muon polarization in the ground state of muonic atoms, and up to 30 times lower probability of muon decay (as opposed to nuclear y - capture) in the high-Z elements where y-SR tends to be most inter­esting], this branch of ySR will probably never have as broad a scope as y+ SR. How- ever, the promise of a measurement of the hyperfine anomaly has motivated the Tokyo ySR group to overcome experimental diffi­culties and external scepticism. In 1978 their determination paid off: after prelimi­nary experiments at TRIUMF, a high-statistics run on the LAMPF muon channel gave a success­ful measurement of the y ” Knight shift in Pd. The result, K(y“Pd in Pd) = -9-0(7)%, when compared with the Knight shift of the analogous nucleus K(Rh in Pd) = -15-0%, gives a hyperfine anomaly of -40(5)%- This and other new Knight-shift measurements of y — S i in MnSi (reported at Rorschach) demon­strate the feasibility of y~SR as an adjunct to NMR studies of 'Z — 1 in Z' in cases where the spatial distribution of the hyperfine field near the nucleus is needed.Longitudina1-fie1d (B^) y+SR (Experiments 71,78)Forward/backward decay asymmetries in a field applied along the initial muon spin direction can provide information about longitudinal relaxation rates and other new phenomena in ySR; these 1B//' techniques have been known for decades, but have been neglected until recently in favour of trans- verse-field 'Bx ' methods, where precession frequencies, etc. provide more information per run. However, in 1978 the method was resurrected at TRIUMF and shown to be a powerful complement to Bj_ techniques when careful attention is given to target posi­tioning and counter geometry.Zero-Field Stochastic Relaxation. One particularly interesting result with the B// apparatus was the observation of longitudi­nal y+ relaxation due to static random di­polar fields in MnSi with zero applied58/X + in MnSi (T  = 2 8 5  K)3 0  Oe\  10 Oe J\  0  Oe1 1 ^ 1  12  4  6  8  T IME  t /xsec)10F ig . 66. Longitudinal re laxa tion  o f  B( decay asymmetry in  MnSi in  zero and weak longitudinal magnetic f i e ld s .field, where the observed relaxation func­tion (see Fig. 66) gave unambiguous con­firmation of the stochastic relaxation theory of Kubo and Toyabe [M a g n e t ic  r e s o n ­an ce <? r e l a x a t i o n  (North-Hol 1 a n d , Amsterdam, 1967) p.810]. The experiment also shows that the y in MnSi is frozen at a vacancy or an interstitial site even at room temperature.Itinerant Magnetism. When a 'holding field1 B// > 30 Oe is applied, this relaxation by static dipole moments is quenched. However, as the temperature approaches T c (where MnSi acquires helical magnetic order), the spin fluctuations of itinerant electrons slow down until their large contact fields on the y+ begin to cause an exponential spin-lattice relaxation rate, 1/Tj ~ T / ( T - T C ) according to the self-consistent renormali­zation theory of spin fluctuations in weak itinerant ferromagnets [Moriya, Solid State Comm. J_5, 169 (1974)]. In 1978 y+ SR (B„) experiments at TRIUMF confirmed both the linear dependence of Tj on 1/T above T c (see Fig. 6 7 ) and the divergence of the relaxa­tion rate at T c (see Fig. 68) predicted by this theory. NMR studies have been unable to detect the latter effect due to the short relaxation times involved..Magnetic Insulators. Longitudinal y+ relax­ation in MnO is purely exponential above and below the Neel temperature, as y+ SR(B//) data from TRIUMF show (see Fig. 69)- The absolute value and temperature dependence of T^ (see Fig. 7 0 ) indicate that this relaxation isdue to dipolar fields from d-electrons on neighbouring Mn2+ ions, and that it is quenched by motional narrowing and/or temp­erature dependence of the spin fluctuations as the temperature rises.y+ Diffusion and Defect Trapping. In 1977 exotic temperature dependence of the y+ relaxation rate in transverse field (Bj_) was seen in numerous metals. This certainly had to do with 'motional narrowing' of the re­laxation due to host nuclear dipole moments—  and thus with the fast diffusion of the muon— but the unexpected dips and bumps in the relaxation rate as a function of temp­erature were somewhat mysterious. Several theories were proposed, all involving 'quantum tunneling' as a diffusion mechanism. By the time of this year's Rorschach confer­ence these models had been refined consider­ably, and new data were also available. It now appears that muons move by 'quantum diffusion' (usually of the 'incoherent' variety) in most metals, and are t r a p p e d  with widely varying degrees of efficiency by different species of impurities. About 50% of the ySR efforts at LAMPF, SIN and CERN are now devoted to this topic. This is understandable in view of the apparent sens­itivity of the muon to minute impurities and the controversial phenomenon of quantum diffusion, and the direct relevance to the practical problems of H in metals.One of the first indications of this remark­able sensitivity of the y+SR technique was the purity-dependence of the transverse relaxation rate in Fe crystals as a function of temperature, demonstrated at TRIUMF last year. This technique allowed measurement of 'hop times' down to 10_12sec. This year's development of the B// technique at TRIUMF extended the experimentally access­ible region in the other direction. The stochastic zero-field longitudinal relaxa­tion seen in Fig. 66 (for example) applied only for strictly static dipolar relaxation. That is, if the y+ 'hopped' even once during the 10 ysec period of observation, the return of the asymmetry to +1/3 after the initial dip to zero would be quenched. This technique is therefore sensitive to 'hop times' as long as 10-5 sec— at least ten times longer than transverse-fie1d (Bd ) methods.These techniques have provided the following information: (1) in MnSi the y+ does not move within four lifetimes, even at room59TEMPERATURE T ( K)$0 63 6, 6$ 65 60Fig . 67. L inear dependence o f  longitudinal relaxa tion  time o f  8C spin upon inverse  temperature in  MnSi in  longitudinal f i e ld .F ig . 68. Temperature dependence o f  ra te  o f  longitudinal relaxa tion  o f  8( spin in  MnSi in  longitudinal f i e l d ,  showing d ivergence at magnetic o rdering  temperature.1 8T R  I UM sec )F ig . 69. Longitudinal relaxa tion  o f  8( decay asymmetry in  MnO in  zero and weak longitudinal magnetic f i e ld s .F ig . 70. Temperature dependence o f y+ spin  re laxa tion  time (e f f e c t iv e  exchange frequency ) upon inverse  temperature in MnO in  longitudinal f i e l d .  Dashed lin e  shows assumed exchange frequency o f  magnetic ions.—i--------- 1----------1----------rp.* IN MnOTEMPERATURE T (K )500  400  300  200 150 125— I— I---1-------1------- 1----- 1—500- T, OF pd IN MnO,0temperature. (2) In MnO there appears to be very fast diffusion in the paramagnetic region. (3) In the non-stoichiometric inter metallic compounds Al-Ni and Cu-Al, where the y+ relaxation is sensitive to fast dif­fusion between traps for nearly pure Al samples in B, experiments, B// experiments provide a measure of the diffusion of the muon between traps in a crystal which is supersaturated with vacancies. (4) In FeS i (3 at.%) there is a sudden change in the longitudinal relaxation rate between room temperature and -10°C, perhaps indicating a change in the preferred interstitial muon site.Transverse-field (Bx ) y+ SR (Experiments 71,78,91)Notwithstanding the successes of the 1 B //' technique, for practical and historical reasons the more familiar ' Bj_' ySR tech­nique is still the mainstay of the TRIUMF program.Ferromagnetic Alloys. The hyperfine field at the y+ in dilute alloys N i C r (0.9 at.%) and FeS i (5 at.%) was found to be 'diluted' compared to that in the pure host, as is known to be true for the saturation magne­tization M s . However, the fractional dilution of B^f at the y+ is twice [1/4] as big as that of M s in N i Cr [FeS i], sug­gesting that the muon is 'repelled' by some impurities and 'attracted' by others, even when clearly not trapped.Kn i ght Shifts. This topic was quite popu­lar at Rorschach. TRIUMF presented new values for Ky (Pd), Kp (MnSi) and K (MnO), among others. The linear relationship between K and x 'n MnSi demonstrates the 'itinerant' nature of its magnetism. A sign reversal of Ky (MnO) between 130 K and 300 K suggests a change in prefered y+ site. The Knight shift of y+ in Pd was remeasured in September, with an improved magnetic field homogeneity, and the value (-13 ± 28 ppm) was found; this result conflicts with pro­ton Knight-shift measurements, indicating (for once) a difference between muon and H hyperfine interactions in a metal.Longitudinal vs Transverse Relaxation in Z r H z . This system exhibits approximate­ly the same sort of stochastic 'Kubo-Toyabe re 1axation'by static nuclear dipolar broad­ening in zero field as does MnSi (see Fig. 66). However, the Gaussian 'Van Vleckrelaxation' in transverse field is 2.4 times slower. This turns out to be in accord with the theoretical prediction of a factor of 2.5, due to quenching of non-secular terms in the relaxation Hamiltonian when one works in the rotating reference frame. That is, the precession of nuclear dipoles in a strong external field averages out the depol­arizing effects of those components of their spins which lie in the plane of precession.Muonium in Semiconductors and Insulators. A session was devoted to this topic at Rorschach, where several new discoveries were reported, among which was the TRIUMF study of Mu precession in quartz crystals, which showed a small splitting in low field (3~6 G) that depends upon the orientation of the crystal's c-axis in the magnetic field (as shown in Fig. 71).ANISOTROPY OF SPLITTING IN QUARTZ3 COS2 9 - 1Fig . 71. Dependence o f  the s p l i t t in g  o f  the t r ip le t -  muonium p recession  frequency in  weak f i e ld s  upon the angle 3 between the magnetic f i e l d  and the c ry s ta l 's  c-a x is . Round points - 6 . 3  G; triangu la r points  ' 3 .3  G; square points  ' 1 .5  G.This previously undetected behaviour is de­scribed by an anisotropic spin Hamiltonian= ~ ^ y b y I  + 9e^B^) * ^  + hv0 (l-S)+ hAv0 (lzSz ) ,where I and S are the muon and electron spins, v0 «  4463 Mhz is the isotropic part of the hyperfine frequency, and Av0 =0.79 ± 0.03 MHz is the hyperfine anisotropy with respect to the z (c) axis of the crys­tal. This Hamiltonian is formally identical to that shown by the SIN group to describethe Mu* state in silicon [Phys. Rev. Lett.*>0. 1347 (1978)], except that the magn i tude of the anisotropic term is 100 times weaker! The most important consequence of this dif­ference is that ~80% of the splitting in Si0g is due to the interaction of the61i n t r i n s i c  electric quadrupole moment of Mu [Beder, Nucl. Phys. A 3 0 5 , ^11 (1978); Baryshevsky and Kuten, Phys. Lett. 6 7 A , 355 (1978)], whereas the anisotropy of Mu* in Si must be almost entirely due to second-order effects of 1attice-induced distortions. A paper on this work has just been submitted to Phys. Rev. Letters.New ySR TechnologyLongitudinal and Transverse Field y S R . It should be clear from the above menu of longitudinal and zero-field ySR results that the revival of 1B//1 techniques makes new physics accessible to ySR. Since the information from B// experiments is often quite different from that obtained in trans­verse field (BjJ ySR, the combination of B// and Bx ySR techniques makes for a tool of great power and versatility. This combina­tion should be applied to virtually all ySR work in the future, but it should be espe­cially useful for studying the dynamics of magnetic systems— the topic it was developed to explore.The Surface Muon Facility. Many of the studies the TRIUMF group hopes to perform on small, thin, or rare targets can only be done properly using a surface y+ beam delivered to a low-temperature target in a strong magnetic field— i.e., the surface muon facility. This versatile and unique tool, when operational, will permit a host of qualitatively new y+SR experiments. In 1978 tests of a prototype version exposed several features necessitating a new design. First, the huge e+ contamination in the M20 surface y+ beam creates a severe background problem at the high intensities required for these experiments. Second, the cramped geometry of the solid pole-tip magnet used thus far for high-field runs limits flexi­bility, restricts the solid angle, and pro­hibits the use of a vacuum chamber to reduce beam scattering. Finally, for trans- verse-field experiments such as these, the inherent positive helicity of the y+ beam requires that the beam enter the target region perpendicular to the field; since the radius of curvature of surface muons is at most 1 m in 1 kG, this makes the attractive high-field region (2-5 kG) practically i naccess i ble.Solutions to these problems are now almost ready for commissioning: a large Helmholtz coil from Lawrence Berkeley Laboratory,capable of 3-5 kG, has been mounted in a new ySR apparatus incorporating counters, target, collimators, and cryostat into one large vacuum chamber contiguous with beam line vacuum. This apparatus, provided by K.M. Crowe of Berkeley, will permit effec­tive use of A.l MeV muons on small, thin targets. The positron contamination problem will be solved when the M9 dc separator operates; furthermore, this facility will provide TRIUMF with a quali­tatively unique feature: the y+ spins, un­affected by the electric field, will precess through ~90° when the magnetic field of the separator is set at 500 G. The resultant 29.8 MeV/c beam will not only be pure y+(for the first time at TRIUMF) but will be t r a n s v e r s e l y  p o la r i z e d .— thus allowing (among other things) insertion of surface muons into an experimental target along mag­netic field lines while still producing precession for high-field y+ SR. This capa­bility combined with the surface muon facility will for the first time give TRIUMF a practical advantage over other labora­tories with high-performance muon channels.Experiment 35Muonium chem istryThe muonium atom (y+e~) offers a multitude of exciting possibilities for study in the realm of chemical physics and physical chemistry. With a mass only 1/9 that of hydrogen it can be regarded as the ultimate light H 'isotope1, extending the most sen­sitive end of the mass scale in studies of isotope effects from the present factor of 3 (comparing T and H) to a factor of 27 (comparing T and Mu). This anomalously large mass difference has important (pos­sibly even crucial) applications in the fields of charge and spin exchange and chemical reaction dynamics. Experimentally, the presence and reactivity of Mu is usual­ly determined by monitoring the 1 M S R 1 sig­nal [e.g. see Garner e t  a l .  , Chem. Phys. Lett. 55., 163 (1978)] in which the coherent precession of 'triplet' Mu is monitored in weak (<10 G) magnetic fields by the basic y+ SR technique. The work at TRIUMF has been exploiting the high stopping density of surface y+ (primarily on the M20 channel) in studies of both gases and liquids.Gas phase studiesGas phase studies of muonium chemistry are particularly facilitated by the use of a62surface y+ beam, with its concomitant high stopping density. In 1 atm Ar, for example, the entire beam (after passing through a single counter and the target window) stops in a distance of ~ 35  cm, enabling investiga- tions in the 'ideal gas' regime. This is an important consideration in comparisons of experiment and theory, and at present the TRIUMF program is unique in the world.y+ charge exchange and muonium formation. During its slowing-down process from MeV to thermal energies the y+ undergoes a series of charge exchange cycles,_  °10. . yT + e , " M u ,a 01ultimately thermalizing as either 'free' y+ or Mu depending on the specific velocity dependence of ct^q o r  CT01 'n the moderator gas. Available data on proton charge ex­change (forming H) suggest that the frac­tion of y+ thermalizing as Mu (fflu ) should be large in N2 and Ar, for example, but small in He and Ne, an expectation in good agreement with both present TRIUMF results and earlier results from LAMPF (in He, Ne and Ar) obtained at much higher gas pres­sures [Stambough e t  a l .  , Phys. Rev. Lett.3 3 , 568 (197*01■ The y+ , however, offers a distinct advantage over the proton— it stops in the gas and thus probes the lowest energy regions of lEI7 and a 01 (proton charge exchange studies are invariably transmission experiments at 'high' energies, >1 keV) .To date f^u has been determined in pure He, Ne, N2 , CH^, and Ar, all at ~1 atm pressure. The TRIUMF and LAMPF data are compared in Table XVIII. A recent run on pure Xe yielded a very small, and quickly relaxing, Mu signal (f^u •«£ 5%) with no y+ signal at all. Such a tiny Mu amplitude is not expected since the charge exchange process on Xe, y+ + Xe -y Mu + Xe+ , is actually exothermic by l.A eV (as is CH4 , by 1.0 eV) and thus could proceed even at thermal energies. Impurities are suspected, principally 0 2 (see below), and the experiment will be repeated early in 1979- A major problem in studies of this nature is evaluating the importance of 'wall effects'— this contrib­utes about A0% of the y+ signal in the LAMPF experiment. As part of a run at TRIUMF last October essentially no signal at all was found in 1 atm air (in accord­ance with a much earlier observation atTable XVIII. Muonium formation in gases.Target Gas P ressu re (atm)fy f mu Ref.He 50 99(5) 1(5) a)1 .2 96(9) 4(9) b)Ne 26 1 0 0 (2 ) 0 (2 ) a)1 . 2 94(6) 6 (6) b)Ar 30 35(5) 65(5) a)3 85(9) c)0.9 37(7) 63(7) b)n 2 1 . 0 2 0 (A) 8 0 (A) b)ch4 1 . 0 2 0 (8) 80(8) b)Xe A.A 10(5) (100?) a)0.9 0 7 b)a) R.D. Stambough, Ph.D. Thesis, Yale Univ., 197A; R.D. Stambough e t  a l .  ,Phys. Rev. Lett. 3_3, 568 (197*0 [LAMPF].b) R.J. Mikula, Thesis in progress [TRIUMF] ; R.J. Mikula e t  a l . , 1st Int. ySR Conf. Proc., Rorschach, Hyp. Int.,1 979 (in press).c) B.A. Barnett e t  a l .  , Phys. Rev. A l 1 ,39 (1975) [SREL].LBL) suggesting a negligible fraction of y+ scattered into the walls. This result is important and demonstrates the existence of an appreciable 'free' y signal in all gases (except Xe) studied, being essential­ly 100% in He and Ne. The origin of this signal is not clear but it is probably primarily due to y+ molecular ions (e.g. yHe+ ) formed during the slowing-down process.Since the ionization potentials of N2 and Ar are both greater than Mu (13-6 e V ) , it is clear that the process of Mu formation must be an epithermal one in these gases; indeed, considerations of cfio(v) ar,8 1 (v ) from proton charge exchange indicate that Mu formation should be an epithermal process in all gases. In order to further elucidate the nature of the charge exchange process, trace amounts of Xe, CH4 and Ar impurities have been added to He and Ne moderators.The effect on the initial amplitude of the Mu and y+ signals is shown in the 1977 Annual Report (Fig. 52) for the case of Xe63added to Ne; similar curves have now been obtained for the other gases. The observed loss in amplitude of the y+ SR signal, mirrored by a corresponding increase in the Mu signal, provides confirmation of the epi- thermal nature of the charge exchange pro­cess, since any Mu formed thermally would not lead to coherent precession. The thermal relaxation of the 'free' muon signal is shown in Fig. 72 as a function of impuri­ty concentration C (C = X e , CH^ and A r ) . The slopes yield the bimolecular rate constant for the thermal process y+ + C -+ Mu + C+ ; k = (1-7 ± 0.3) x 1CT11 cc/atom sec with Xe, (5-6 ± 2.2) x 10-12 cc/atom sec in CH and zero in Ar. These rates correlate well with the difference in ionization potential between the impurity C and Mu (1.A , 1.0 and -2.0 eV, respectively). Two important con­clusions can be drawn from these data: first, the y+ relaxation cannot be due to wall effects and second, it is unlikely to be due to bare muons, since these would be expected to exhibit a collision controlled rate (k^y + 0 2 = (2.6 ± 0.2) x 10-10 cc/atom sec). Hence it is concluded that the relax­ing signal is most probably due to a molecular ion, e.g., either Ney+ or Xey+ or b oth.Muonium spin exchange. In collisions with a paramagnetic molecule (e.g., NO), Mu may undergo a 'spin-exchange' process, repre­sented by Mu(t) + N0(f) -+ Mu( + ) + N0(f), the effect of which is to depolarize the y+ .This effect manifests itself in a relaxation of the MSR signal, much akin to that shown in Fig. 72 for the y+ signal. The only spin-exchange process measured at TRIUMF to date is Mu + O 2 , which was actually completed in 1976, yielding a bimolecular rate constant k = (2.6 ± 0.2) x IO - 1 0  cc/atom sec at room temperature, the fastest reaction yet o b ­served. This result has in turn been used to establish the presence of Mu in the voids between powder grains, as part of Expt. 60 last year [Marshall e t  a l .  , Phys. Lett. 65A_, 351 (1978)]. In 1979 measurements will be made of the spin-exchange cross-sections (k = cfv, where V  is the mean velocity) for Mu + O2 , Mu + NO and possibly Mu + NO2 as a function of both T and P, in order to dis­criminate spin exchange from chemical react i o n .Chemical reaction dynamics. Since the muon mass is only 1/9 that of the proton, measure­ments of the chemical reaction rates of Mu provide a u n iq u e  set of data with which toImpurity in atom-crrr3x 10'16F ig . 72. Thermal re laxa tion  o f  the signa l  due to muonium formation in  the p resence o f  added gases.confront current theories of isotope ef­fects in chemical reaction dynamics, par­ticularly quantum mechanical tunnelling.The basis of D. Garner's Ph.D thesis in chemistry is a measurement of the reaction rates of Mu + X2 (F2C£2 Br2 ) and Mu + HX, as outlined in last year's annual report. No new data have been taken while this thesis is being written but in 1979 it is intended to measure the activation energies for Mu + Br2 , I2 and all the HX gases.Liquid Phase StudiesUse of the MSR technique to study muonium atoms (Mu) in water was started in earnest at TRIUMF in February, and during the year four beam periods of 6 to 10 shifts each were assigned to these liquid phase experi­ments. Five projects were undertaken, four of which are now essentially complete and have been published or submitted for publi­cation. The fifth project was a recon­naissance investigation of model biological systems (in this case, the influence of a micellar enclosure on a muonium reaction), which is where many of these studies are ultimately heading. The completed projects fall into three natural divisions:6AChemical identity of muonium in w a t e r .Prior to 1978 the SIN group had identified Mu in water and a few other pure solvents, measured its lifetime and some of its rate constants with added solutes. From a chemi­cal point of view it was not obvious that Mu behaved 1 ike a light isotope of H because the kinetic isotope effect varied from 10-2 to 102 . Therefore, the first TRIUMF experi­ments were chosen to compare Mu with the pattern of chemical reactivity already known for hydrogen atoms, solvated electrons (eljq) and positronium (Ps). Typical muonium pre­cession signals are shown in Fig. 73 for (a) pure water, (b) 1.0 x lO-4 M phenol and (c) 5-0 x 10-1+ M phenol. From the decay of the high frequency muonium precession signal the bimolecular rate constant can be found. Table XIX shows the comparison of the values of k^u obtained with published data for H, egq and Ps. These data helped to es­tablish that the magnitude of the kinetic isotopic effect (k^/k^) depends sharply on the type of reaction involved— be it addition, abstraction or reduction, etc.Further confirmation of the neutral character of Mu was obtained in the second series of experiments, in which Mu was made to react with positive (Cu2+) , neutral (phenol) and negative (CNS~) solute molecules in the presence of high concentrations of an inert salt (Na2 S0i+) . By use of the Bronsted- Bjerrum treatment of ionic solutions it was possible to show that Mu is neutral at the point of reaction and hence charge-transfer does not occur until the activated complex is formed, as with H.Spin-exchange reactions of Mu in w a t e r .The third project was to examine an inter­action (electron spin-exchange), which is difficult to observe for the H atom but which with Mu may prove to be a sensitive analytical probe of the spin state of d 6 ions, such as Fe2+ and Co3 + , in biologically important molecules. The rate constant for muonium spin depolarization (kp) was mea­sured for twelve transition metal ions, half of which were paramagnetic. It transpired that all the paramagnetic ions gave kg at about the diffusion-controlled limit (10 10 M ” 1 sec-1) while the diamagnetic ions were<108 M -1 sec-1 (negligible spin-exchange) These results are collected in Table XX.It is interesting to note, for instance, the difference between Fe(ll) in the aquatic Fe2+ state (weak field, high spin, paramag­netic) with it in the hexacyano complex %0 ' > *. A WiiiPURE URTERcrUJ2,CC0-F~ -P — 9~eF ig . 73. Muonium p recession  signa l in  a) pure water, b) 1 .0  x 10D2 M phenol and o) 5 .0  x 10~h M phenol in  aqueous so lutions at ~29 5 K. These data were obtained  on the r ig h t  hand s id e  positron  d etecto r , c o lle c t in g  10-20 m illion  events , with a magnetic f i e l d  o f  7 .6  G. The constant background and exponential muon decay have been removed leaving the p lo tted  signa l A lt) =Av cos (w^t+i^) + Apju exp(-X t) cos (wpiut+§MU) . The decay o f  the high frequency muonium p recess ion , superimposed on a slow muon p recess ion , can read ily  be seen  to be much more rapid  the h igher the phenol concentration .Fe(CN)g- (strong ligand field, low spin, d iamagnet i c state).Muonium formation by 'hot' or 'spur' processes. The fourth completed project was to see if: (i) Mu was formed by combination of thermalized p+ with free electrons pro­duced in the spurs of the muon track; and (ii) some of its primary chemistry arises from intra-spur processes with radiation- produced electrons, free-radica1s and ions, as proposed by the SIN group. Thus, the yields of Mu and of diamagnetic muon species were measured in the presence and absence65Table XIX. Comparison of k(M u ) with k(H ), k(e - ) and k(Ps) (in M- 1 sec-1).Solute k (Mu) k (H) k (eiq) k (Ps)phenol 7 x lo9 2 x  10 9 3-5 1 . 8  x  io7 < 1 0 8p-n i trophenol 8 x  1 0 9 (3± 1 ) x  io9 2.7 V-O VJ-I X o o VO X O COTl +COoXCXD [1 .2 x  IO8 ] » 7 3 x  io 10 < 1 0 8CNS- 6 x io7 [2 x  1 08 ] w 0 . 3 <I06 < 1 0 8Zn2+ < 1 0 7 < 1 0 5 — 1 . 5  x  1 0 9 < 1 0 7Na+ /S0^" <107 v . sma11 — <106 <107Table XX. Calculated values of kD , the spin-conversion rate constant.1 on kobs (/I 0 1°M"1 sec- 1)Spin kMu/kH ^Mu(/10 10M - 1 sec- 1)kD(/10 1°M- 1 sec- 1)(Fe3+) 0.55 5/2 (3) 0.15 0.1*0Fe2+ 1 .22 2 (3) 0.006 1 .2(Cr3+) 0.53 3/2 (3) 0.006 0.52N i2+ 1.7 1 (3) <10-1+ 1.7Cu2+ 0.65 1/2 (3) 0.02 0.63Fe(CN)3- 2.0 1/2 (3) - 0.60 1 .kFe(CN)g" 0.03 0 - 0.03 « 1 0 -2Zn2+ <10-3 0 - <10-3 <10-3Cd2 + <10-3 0 - <10-3 <10-3HgC 1 2 0.20 0 (-0.2) 0.20 « 1 0 -2T1 + 0.082 0 - 7 0.08 « 1 0 -2Ag+ 1 .6 0 0.5 1 .6 « 1 0 -266of high concentrations of solutes (1M Cd2 + ,1M 2-propanol and 0.2M NaOH) which are known to intercept 69~90% of intra-spur species.It was concluded that spur reactions involv­ing Mu occur to the extent of only ~ 1 5% and therefore that this 'spur model' is inap­propriate in muonium chemistry. (in the ‘hot model', some— perhaps as much as 1 5 %—  of the muonium atoms may, by chance, be backscattered into the spurs).Solid State ChemistryThe statement made in last year's annual report that a muonic radical may have been identified in solid CO2 has been shown now to be incorrect— high statistics runs reveal only the characteristic 'two-frequency' pre­cession of normal muonium at those fields (<70 G) where splittings were observed.Such radicals have recently been identified though in the liquid phase at SIN [Roduner e t  a t . ,  Chem. Phys. Lett. 57_, 37 (1978)] but in high magnetic fields (>1.5 k G ) . It is still of considerable interest to search for y+ radicals in the solid state (as well as extending the present studies in liquids); it is planned that such a program should get under way at TRIUMF in 1979, employing also high magnetic fields.A continuing search for chirality-dependent Mu formation in quartz crystals has, to date, yielded inconclusive results. The motivation for the experiment comes from measurements of e+ annihilation in various chiral media, in which a sensitivity in 3y/2y annihilation to the 1D 1 vs 'L ' nature of the stopping medium has been reported [Garay, Nature 250, 332 (197*0]- Positive muons were stopped in D-quartz with the ini­tial momentum and hence the spin direction both parallel and perpendicular to the principal optic axis. The sign of the opti­cal rotation is opposite for two orienta­tions. The results of a preliminary analysis of several measurements of the Mu amplitude yield an orientation difference of 0.8 ±l.A%. TRIUMF has recently received a crys­tal of L-quartz, as well as a fused quartz sample of the same geometry, and a 'defini­tive' measurement of any difference between D and L is planned early in 1979-Experiment 60Muonium formation in insulating powdersIt is to be expected that the formation and chemical behaviour of muonium and hydrogen atoms would be very closely similar as their binding energies differ only through the reduced mass correction. In contrast, positronium atoms, where this correction reduces the ionization potential from 13-6 eV to 6.8 eV, while similar to hydro­gen, might be expected to show some sub­stantial divergence in these properties.Since it was known that a substantial amount of the long-lived orthopositroniurn was formed in finely divided insulating materials such as Si2 and MgO, and apparently diffused to the voids, MSR experiments were performed with a polarized muon beam with substantially comparable results.During the past year the behaviour of posi­trons and positronium in a number of fine insulating powders has been studied using time delay spectra, Doppler broadening of the annihilation radiation and the shape of the gamma-ray spectrum arising from the presence of 3~quantum annihilation from orthopositroniurn. These same materials were studied as to muonium formation— the fraction formed, for example, being larger with the smallest particle size Si02 powder.From this work several targets were made and tested to achieve a substantial fraction of muonium atoms in the voids; with a view, in due course, of looking for y+ e~ -> y~e+ conversion, the appearance of the y - to be signalled by the muonic X-ray cascade from the subsequent capture of the y ” . For this purpose a large Helmholtz coil assembly has been built to provide a magnetic field-free region at the target to ensure that any M formed does remain in a state degenerate with respect to transitions to M. Two tar­gets using 50 A Si02 powder in layers have been constructed. Finally the H 13 beam line is nearing completion which is, in part, designed to provide a large flux of positive surface muons with little positron contami nat ion.67APPLIED RESEARCHAn agreement was concluded in 1978 between TRIUMF, Atomic Energy of Canada, Ltd. Com­mercial Products Division, University of British Columbia and the British Columbia Development Corporation to permit the com­mercial distribution of medical radioiso­topes produced at TRIUMF. A loan of $3-5 million from BCDC to UBC will permit con­struction of radioisotope facilities and installation of a compact cyclotron at TRIUMF; the loan will be repaid over 25 years by AECL from the proceeds of radioiso­tope sales. The radioisotopes of initial interest are 201T1, 67Ga, 123I, 111In, 127Xe, 109Cd and 53Ge.Detailed plans and specifications for exten­sion of the Chemistry Annex building at TRIUMF and redevelopment of the present space in the Annex as radioisotope laboratory facilities were prepared this year and sub­mitted for scrutiny to the Atomic Energy Control Board, the local municipal regula­tory authorities, and the TRIUMF Safety Advisory Committee. Tenders for construc­tion will be received early in 1979, with a projected completion date of November 1979 -An order was placed with the Cyclotron Corp­oration for a model CP-A2 compact cyclotron for delivery in 1980. A contribution to the total purchase price of $^00,000 was received from the British Columbia Provincial Govern­ment, in view of the machine's potential ap­plication in neutron therapy of cancer. Ini­tial planning for a program in this area was started with the B.C. Cancer Control Agency.Detailed design continued on a facility for isotope production via high-power irradia­tion in beam line lAatTRIUMF. A full-scale mock-up of the bottom and top of the target insertion apparatus has been built to permit study of transport mechanics, target cooling and target unloading. Conceptual design has proceeded of a hot cell to be installed on the TNF roof shielding, to permit transfer of the irradiated targets to a wheeled flask for transport to the Chemistry Annex.An extraction port was installed on exit horn 2 of the TRIUMF cyclotron to accommodate the beam for isotope production (described last year) with an energy variable between 65 and 100 MeV. A beam intensity of 10 yA was extracted through this port.A small radioisotope laboratory facility was built to the east of the main accelerator building, via joint funding with the UBC Fac­ulty of Pharmaceutical Sciences. This labora­tory permitted a start to be made this year on the chemical processing procedures required for the commercial isotope production program, by D. Graham, the first of the AECL-CPD staff to arrive on site. The laboratory was also used for separation of 52Fe from irradiated nickel targets, as described below.An agreement was also brought to final draft in 1978 between TRIUMF and Novatrack Analysts Limited, a sub-group of PANARA who, as de­scribed last year, have proposed the use of the TRIUMF thermal neutron facility for neu­tron activation analysis. Novatrack secured this year funding from the B.C. Provincial Government permitting installation at TRIUMF of a trai1e r - 1aboratory, the purchase of radiation detection apparatus, and the pur­chase (jointly with TRIUMF) of pneumatic transfer systems for samples between the TNF and the Novatrack trailer. Discussions pro­ceeded with representatives from departments of the TRIUMF universities interested in re­search use of the NAA facilities, inaddition to the commercial use planned by Novatrack.A proposal has been formulated by a committee of representatives from TRIUMF and the Uni­versity of British Columbia Faculties of Medicine and Pharmaceutical Sciences for a pro­gram of pos i tron tomography based on l:LC, 13N, 50 and 18F, produced at TRIUMF and applied to problems in brain and heart research.Experiment 61Biomedical experimental programDuring 1978 a limited amount of operation at currents of 80 yA made it possible to begin that part of the program which involves tt-- irradiation of experimental animals. Prelim­inary studies of the reaction of mouse skin to   beams were carried out during two running periods of approximately 2k h each. These studies, though preliminary, gave results that are consistent with the cultured cell studies which preceded them, although more detailed studies are required; these are planned for 1979- Cultured cell experiments during 1978 have been directed at mapping the relative biological effectiveness (RBE) of68extended tt~ peaks and the deve 1 opment of dose profiles shaped so as to give the uniform cell inactivation throughout the peak region which is required for tumour treatment. Pre­liminary measurements of the oxygen enhance­ment ratio (OER) in 770  beams have also been made, though these are hampered by currents less than 100 yA. Substantial increases in scheduled 100 yA will be required if patient treatment with 7 70  beams is to commence in 1979- The 100 yA operation is needed for further cultured cell experiments, animal studies (mice and pigs) as well as for the patient irradiations.The lack of prolonged high-intensity opera­tion during 1978 has allowed more detailed characterization of the pion beam in terms of its physical parameters. Measurements of the EEx stopping power, the response of ion cham­bers under varying conditions in a pion radi­ation field, and the details of the energy deposition spectra by microdosimetry have been made.Adequate determination of the pion stopping position in a non-homogeneous human body re­quires a knowledge of the stopping power ratio with respect to water for a variety of materia 1s at better than 2% accuracy. Precise determi­nations, using a differential range telescope of the shift in the range when different materials were inserted into the beam, have given experimental determinations of the mass stopping power ratios with respect to waterr\XwUJCOooUJ>HI -<D/UJacF ig . 74. Microdosimetry spectra  measured at depths from 3 .0  to 40 .5  am along the axis o f  a pion beam in  a water phantom show changes in  the energy deposition  pa ttern s , p a rt icu ­la rly  in  the peak region  18-28 am.for 62 MeV positive and negative pions to an accuracy of 1%. The measured values have been shown to be in agreement with the values published by Anderson and Zeigler.The measured values for compounds support the use of the Bragg additivity rule to with­in the accuracy of the measurements.Studies of the responseof ionization chambers with different wall materials, gases, pres­sures and dimensions have been undertaken to refine our understanding of the absolute dose in a pion beam as determined from ioni­zation measurements. These experiments have shown that Bragg Gray cavity theory does not hold for certain gas wall combinations in chambers of the 1 cc volume range and pres­sures from 0 to 10 atm. In fact, for a CO2 - filled graphite chamber as the pressure varies from 1 to 8 kg/cm2 the charge collected per unit massof gas (an invariant under Bragg Gray cavity theory) decreases by 30%. Such measurements show the need for detailed calculations of the response of ion chambers in pion radiation fields, if reliable abso­lute dosimetry is to be based on ionization measurements. Such calculations, coupled with further experiments, w i 11 be performed in 1979-Mi crodos imetry measurements with a spherical proportional counter of 2 y effective diam­eter have shown the varied energy deposition patterns along the axis of a pion radiation field (Fig. l h )  . At depths shallower than 18 cm, the energy is deposited predominantlyDEPTH (cm )69e 8 <0 00 $ 4>1.8 Q id to o0 8Q0 2 i0 A>8^Id</>6 oId>4?<_JD25O0 01 0 r\>0.8 Q K 0 8 2Y w M a0 2§o0 0I 08 °Me2Fig . 75. The to ta l depth dose curve i s  d iv ided  into  fo u r components on the basis  o f  the lin ea l en erg ies  as measured by m events with lineal energies less than 10 keV/ym. In the peak region pion stars deliver energy in the 10 to 1000 keV/ym range. Such measurements allow the total depth dose profile to be broken into differ­ent components corresponding to the size of the individual events, as is shown inFig. 75. Microdosimetery combined with time of flight has allowed the lineal energy deposition spectrum for a pure pion beam to be measured. The effectively dc structure of the pion beam at TRIUMF makes it ideally suited for these types of microdosimetry.70Experiment 8 7 Proton radiographyThe objective of the proton radiography work at TRIUMF is to investigate various tech­niques for using 200 MeV protons for imaging purposes. The experimental arrangement has been described in previous annual reports.Two different methods are used to produce radiographic images, both exploiting the rapid decrease in proton transmission near the end of the range of a monoenergetic pro­ton beam. One technique uses a well- collimated beam which is scanned over the sample in a raster fashion with the protons detected by means of large plastic scintil­lators forming a range telescope. The other technique uses fast X-ray film as the proton detector with the sample exposed to a broad uniform beam as in conventional X-ray rad iography.During this past year most of the effort has been aimed at studying the factors affecting the spatial and density resolution of the techniques. The ultimate resolution is determined by the stability of the proton energy from the cyclotron and by the diameter of the collimated beam in the case of the raster scan technique. For instance an en­ergy shift of 100 keV in 200 MeV would pro­duce an apparent density change of 0.1%. The range telescope provides a rapid measurement of the instantaneous beam energy, and corre­lations between energy and cyclotron param­eters such as the main magnetic field and resonator voltage can be seen. Improvements to the cyclotron stability have been made and the possibility of providing feedback loops for increased stability investigated. While some of this work was initiated by the requirements for improved energy stability for p r o t o n  r a d i o g r a p h y ,  the i m p r o v e d  e n e r g y  resolution is part of the general cyclotron development program and is described else­where in this report.An improvement to increase the data-taking rate using the Eclipse computer system was made operational, and presently the scan rate is 10 steps per second. The rate is partly limited by settling times for the scanning magnets. The design of a fast scanning magnet for this work has been ini­tiated. All of the proton radiography work to date was done in beam line ^A. A section of the recently installed beam line IB has been designed for rapid installation of the radiography equipment, and future work will be carried out in this area.Experiments 77, 93  Isotope productionThe medical radioisotope program proceeded as outlined in last year's annual report, with the introduction of no new target proj e c t s .A facility has now been installed for 123I production. This program, named TRIM (TRIUMF radioiod ine for medicine), has been implemented as a result of support from Health and Welfare Canada. Major equipment is now in place. A caesium target (20 g/cm2 ) was installed in the beam line k /\ dump. The target has shown entirely satisfactory thermodynamic behaviour in full beam tests. TRIM has a remotely operable receiving station designed to handle about 20 Ci of spallation products from 12 h runs. A DEC 11-40 computer and CAMAC system have been incorporated to support the TRIM pro­cess. TRIM is housed in a b x 1k m trailer 1 a b .Much effort has been devoted to design of hardware and establishment of protocols for safe recovery, processing and packaging of the products. Techniques have been developed to assay and control the chemical as well as nuclidic purity of the 123I.Safety and operational requirements have now been satisfied sufficiently for low- power operation of the complete system. Shipments of the 123i have been sent to participating hospitals in Toronto, Winnipeg, Edmonton and Vancouver. This material has been used for the investigation of thyroid disease as well as thyroid metastases (Fig. 76).Substantial by-products are also collected f r o m  th e  T R I M  p r o c e s s .  T h e s e  m a t e r i a l s  (125i, 1 2 1 -j-e ancj 127xe ) are recovered in a form usable for medical or industrial purposes.The 52Fe program has been continued. An improved target system and hot cell are presently being completed to permit safe chemical separations of 1 mCi 52Fe from other by-products.Work has progressed on the low-energy beam system for isotope production. During the mid-year shutdown two simple extraction mechanisms, developed by the Probes group, were placed in the cyclotron at the calcu­lated locations. A new port (2C) was added to the tank wall to allow energies between71Experiment 48Fertile-to-fissile conversion (FERFICON)Experiments were concluded this year on measurement of neutrons leaking from mass­ive heavy element targets bombarded with 350 and 480 MeV protons. Detailed scrutiny this year was applied to the data analysis procedures employed, and calibration of the detector systems used, in collaboration with Los Alamos Scientific Laboratory.Table XXI shows the final data values o b ­tained for the target configurations listed.Experiments continued this year on measure­ment of the conversion, fission, and the n,2n reactions via gamma spectroscopy of samples removed from the irradiated target assemblies. These data are in the course of ana lysis.Fig . 76. Whole body d is tr ibu tio n  o f  156  sodium iodide in  man. The in crea sed  a ctiv ity  in  the lungs ind ica tes  metastases.65 and 100 MeV to be extracted. Each of two beams at 70 and 90 MeV, 3 yA, were extracted simultaneously with production runs on lines 1 and 4. Efforts were made to investigate interference of the new beams with other ex­periments, especially through alteration of beam time structure. Present indications are that the three beams are truly orthogonal except for sharing of the cyclotron ion source. As the year closed full-scale design of the new beam line and target systems was started.72THEORETICAL PROGRAMThe theory group at TRIUMF was formed so as to provide an active group of researchers at the main site who are interested in the kinds of medium-energy physics problems which are under experimental investigation here. Hopefully the existence of such a group will provide opportunities for inter­change of ideas between experimentalists and theorists, which cannot help but be of bene­fit to the long-term research program at TRIUMF.The group is currently very small, especial­ly considering the large variety and number of experiments under way. However, there are hopes for expansion. Permanent members are H.W. Fearing and A.W. Thomas. Research associates include R. Woloshyn, A. Saharia, J. Greben and J. Ng, the latter two being formally associated with UBC. Graduate students G. Brookfield, N. Shrimpton,R. Sloboda and S. Theberge and visitor to SFU, H. von Baeyer, have also been involved with some of the projects described below.A number of the theoretical faculty at mem­ber universities also have been active par­ticipants in group activities including D.S. Beder, M. McMillan, E.W. Vogt (UBC),A .N . Kamal, H. Sherif (Univ. of Alberta),C. Picciotto (Univ. of Victoria) andD. Boal (SFU).Members of the group have been involved in the planning of the International Conference on High-Energy Physics and Nuclear Structure to be held in Vancouver in 1979 as well as in several workshops and discussion sessions dealing with the experimental program.They are responsible for the TRIUMF seminar series which together with the theoretical visitors program has made possible the visits of a number of theorists includingI. Afnan, I.T. Cheon, W. Gibbs, B. Gibson,T. Goldman, B. Goulard, G. Goulard,A. loannides, M. Krel1, R. Landau,T. McMullen, G. Miller, M. Morita, J. Noble, W-Y.P. Hwang, A. Rinat, A. Sanda,R. Schaeffer, P. Tandy, E. Tomusiak,I. Wilets and many others passing through.Specific areas of research which have been of interest in the past year include:Proton-proton bremsstrahlungMajor effort during the past year has been devoted to further analysis of various a s ­pects of proton-proton bremsstrahlung (ppy)and comparison of calculations [Fearing, AIPCP #4 1 (1978), p.506] in soft photon ap­proximation (SPA) with a variety of data.In SPA the ppy cross-section can be written as da ~  A 2/k + 2AB + (B2+2AC)k + ... where the amplitudes A and B are given in terms of purely on-shel1 information. The amplitude C, which is not calculated, contains the more interesting off-shell information as well as higher-order on-shel1 corrections. Hence one hopes to find regions where the SPA fails, thus suggesting the possibility of off-shell information.SPA calculations have now been compared with the TRIUMF 200 MeV experiment [Anderson e t  a l .  , to be published and AIPCP #41 (1978), p.446], and the experiments of Manitoba at 42 MeV [Jovanovich e t  a l .  , Manitoba preprint and Phys. Rev. Lett. 37_, 631 (1976)], Orsay at 156 MeV [Willis e t  a l .  , Phys. Rev. Lett. 16, 1063 (1972)], and UCLA at 730 MeV iNefkens e t  a l .  , Phys. Rev. C (in press)]. For the TRIUMF experiment the data fall sig­nificantly below standard potential model calculations and are in fair agreement with SPA. A similar situation holds for the Orsay data. At 42 MeV the data fall in between SPA and the results of a potential model calculation which are higher but, when all data are considered, fit the two calculations equally well (see Fig. 77).Thus it seems to be a general result that in this region potential model calculations are too high, with the data fitting SPA as wellF ig . 77. An example o f  a comparison o f the Manitoba ppy data at 42 MeV with a Hamada-Johnston po ten tia l  model ca lcu la tion  (so lid  lin e )  and with the SPA ca lcu la tion  (dashed l in e ) .  The data typ ica lly  f a l l  between the two curves.73or better. For the UCLA experiment SPA de­scribes the data up to photon energies of about 100 MeV. Above 100 MeV something ad­ditional is required, perhaps some contribu­tion from the A (1236).In view of these cross-section results it is important to examine other situations which might be more sensitive to off-shel1 effects. We have looked particularly at the asymme­tries. Comparison of SPA calculations [Fearing, Few Body Systems... vol. 1, Graz Conference (1978), p.9*0 with potential model calculations [Bohannon, AIPCP § k \  (1978), p .1482 and private communication] of the usual transverse asymmetry shows that SPA and potential model results are quite different and in addition that potential model results are sensitive to off-shel1 variations of the potential, thus suggesting that measurements of such asymmetries might be particularly useful.Another very interesting suggestion made recently by Moravcsik [AIPCP § h \ (1978), p.5 1 5 ] dealt with the so-called 'forbidden' asymmetries. These are asymmetries which vanish in the elastic limit because of a general selection rule such as parity and thus are presumedly particularly sensitive to off-shel1 effects. We have analysed this suggestion in detail and find that the 'for­bidden' asymmetries are suppressed in ppy by only one power of k [Fearing, TRIUMF pre­print TRI-PP-78-2 8 ] . They thus contain sub­stantial on-shell contributions as well as off-shel1 o n e s .For both cross-section and asymmetry mea­surements it is important to know where to look, i.e. what kinematical conditions are most likely to lead to off-shel1 information. At least two constraints must be met for a geometry to be a 'good' one, and it has not been fully appreciated in the past that these constraints are favoured by d i f f e r e n t  geometries. First, to see off-shel1 effects one must have a nucleon off shell and hence a parameter Am2 can be defined to measure the average amount by which the nucleons are off shell. Am2 increases with increasing energy. Second, one must be out of the soft-photon region, i.e. a parameter k/T must be large where T is some not very well defined parameter which sets the scale of the expansion. Figure 78 shows a plot in the Am2 vs k/T plane of the regions reached by various current and possible ex­periments. The geometry in which bothFig . 78. P lot o f  kinematic regions obtained by sev era l e x is t in g  and proposed ppy experiments in  the plane o f  o f f - s h e l l  parameter m2 vs s o ft -  photon parameter k/T.protons are measured (TRIUMF, Manitoba) favours large k/T whereas the UCLA experiment, because of its higher energy, reaches large Am2 but fairly small k/T. The proposed e x ­periments at 350 and bSO MeV would be possible at TRIUMF and could reach previous­ly unexplored regions of the Am2 vs k/T piane.Radiative muon captureOur program of calculating radiative muon capture (RMC) consistently through 0(l/m2 ) is now essentially complete. Such a calcu­lation was originally motivated by the ob­servation [Fearing, Phys. Rev. Lett. 35., 79(1975)] that the photon asymmetry in RMC was given effectively by the 0(l/m2 ) terms and the fact that such a calculation had never been carried out consistently.Figure 79 shows some of our results for the contributions of the various terms in a simple shell model-harmonic oscillator cal­culation. One can see that the 0(l/m) and 0(l/m2 ) terms are non-neg1 igib1e . However,l bFig . 79. Photon speatrum in  RMC in  ti0Ca showing e f f e c t s  o f  h igher-ordev  terms. Curves la b e lled  0 (1 ) ,  0 (l/m ) and 0 (l/m 2) contain a l l  terms in  the ra te  through 0 (1 ) ,  0 (l /m ), 0 (l/m 2) ,  r e sp e c t iv e ly .the largest of the 0(l/m2 ) terms have been included in at least some other calculations, and the new 0(l/m2 ) terms calculated here, while making the calculation consistent, do not make large numerical changes in either photon spectrum or asymmetry.Calculations were made also using improved nuclear wave functions obtained using a Hartree-Fock technique [Shao e t  a l .  , Phys. Rev. C 8_, 53 (1973)] and also in the giant dipole resonance model. In all cases the relative rate proved to be rather insensi­tive to the details of the nuclear model. Highei order corrections to the closure ap­proximation were also calculated, using sum rules, and found to be important [Sloboda and Fearing, Phys. Rev. C J_8, 2265 (1978)].In a related but different investigation we have begun looking at RMC in hydrogen. This was motivated by a new calculation [Hwang and Primakoff, Phys. Rev. C J_8, 411+ (1978)] which seems to obtain results quite differ-erent than previous ones. We now understand at least part of the reason for the differ­ences and have started numerical calculations to investigate it further.Bound muon decayProcesses which violate muon number conser­vation such as y -* ey and neutrinoless u e conversion have generated a lot of excite­ment over the past couple of years, and the y -> e conversion process is the subject of a new experiment at TRIUMF (Expt. 1 0 )  . The signature of such a process is a high-energy electron which, however, can also be obtained from the ordinary decay of a muon bound in a nucleus which absorbs the necessary recoil momentum. Thus it is very important to have an extremely accurate calculation of the high-energy end of the electron spectrum from bound decay. The process is of intrin­sic interest as well and is the subject of Expt. 83. Furthermore, the electron asym­metry is also an important quantity since it is used for determining the residual muon polarization in muon capture experiments such as Expt. h i .We have thus begun a calculation of the electron spectrum and asymmetry from bound muon decay which will use accurate muon and electron wave functions obtained by solving the Dirac equation for a finite charge dis­tribution and which will include all recoil and binding effects exactly in so far as possible. It should thus be a significant improvement over the only previous asymmetry calculation [Gil insky and Matthews, Phys.Rev. 120, 1450 (i960)] which uses simple wave functions and over previous spectrum calculations [Hanggi e t  a l .  , Phys. Lett.51B , 1 1 9 (1974)] which include recoil in an approximate way, but find that it can be an important effect in the region of interest of Expt. 104.So far most of the basic formalism for the calculation has been derived, and some of the computer programs required have been written. Preliminary numerical results have been obtained for very simple wave functions. The next step will be to include further recoil corrections and more realis­tic wave functions.Lepton number violationViolation of number by two units in gauge theories has been investigated in models75containing a Majorana spinor. A systematic study of 0+ mesons decaying into y+ u+ + hadron is completed. The conversion of y" -> e+ in nuclei is studied in Sll(2) x U(l) gauge models where the reaction occurs as a second-order weak process mediated by a Majorana lepton. The effects of the mass of the new lepton from very light to ultra­heavy > Mw is given in conventional SU(2) x U (1) gauge theories.The radiative capture of y~ where one member of the e+e" pair from the photon is not de­tected forms an important background for any ye conversion experiment. This rate and the leptonic spectra are being calculated.(p,d) reactionsIn a recent TRIUMF experiment (Expt. 99) data [Kallne e t  a l .  , Phys. Rev. Lett. 41 ,I638 (1978)] were obtained on the reaction p + ^He -* d + 3He for forward-going deuterons at several incident energies. The data seem not to be well explained by the simplest pick-up or one-nucleon-exchange diagrams, but require some additional mechanism to en­hance the cross-section at the higher ener­gies. A possible alternative mechanism is a triangle diagram in which the incoming pro­ton knocks out a 'deuteron' in the ^He and is captured on the remaining 'deuteron1.Such a diagram has been analysed in the im­pulse approximation using exactly the same procedures used previously for (p,ir) reac­tions [Fearing, Phys. Rev. C 16, 313 (1977) 1 - Thus the cross-section is given by the elastic p-d cross-section times a form factor which involves wave function overlaps and an integration over the triangle momen­tum. Preliminary indications are that this mechanism may give the required enhancement at higher energies though the absolute normalization and some spin complications still must be calculated. It is also necessary to understand the connection of this diagram with the usual pick-up diagram, which is at least partially included in the triangle diagram, and perhaps to include a deuteron exchange diagram which could con­tribute in the backward direction.Effective nuclear HamiltoniansIt is often necessary to obtain from a pre­sumedly known relativistic amplitude or interaction an effective Hamiltonian opera­tor which can be used in impulse approxima­tion in a nuclear problem. Radiative muoncapture, (p ,EEO , (p,y), Ts GEEO and (p,mr)reactions in nuclei are all examples of such situations. We have now worked out the general formalism for obtaining such an ef­fective operator for an arbitary, time- dependent, second-order interaction. The general results have been applied to radia­tive muon capture and to the question of the appropriate effective operator to use in (p, t t ) and (p,nir) reactions. This has made possible a better understanding of the ori­gin of the so-called 'Galilean invariant1 term in the usual effective operator used for M e V 7 7 9 reactions and the possible ambi­guities in such an operator.The range o f the nN interactionOne of the underlying differences between the co-ordinate space and momentum space treatments of pion-nucleus scattering is the assumed behaviour of the ttN  interaction. Fundamental to the Kiss1inger-type of poten­tial, and its refinements which include the classical Lorentz-Lorenz (L2 E2 ) effect [Ericson and Ericson, Ann. Phys. N.Y. 3 8 ,323 (1966)], is the assumption that the t tN interaction has essentially zero range. On the other hand, the solution of the inverse scattering problem for the ttN  system yields a separable interaction with a range of order 0.6 fm [Londergan e t  a l . , Ann. Phys.8 6 , 1A7 (1974)]. It is the latter type of interaction which has been used in recent momentum space studies of pion-nucleus scattering [Landau and Thomas, Nucl. Phys. A 3 0 2 , 461 (1978)]. A major qualitative dif­ference for such a long-range interaction is that the classical L2 E2 effect is known to be very small in that case.The evidence so far is that neither elastic nor inelastic pion-nucleus scattering seems capable of distinguishing between optical models constructed under these two different assumptions. Thus we are forced for the present to rely on theoretical guidance as to which is the more realistic model. Some insight on this problem came out of recent considerations by Myhrer and Thomas of a somewhat different problem. These authors ['An important contribution to ttD  scattering in the resonance region', NORDITA preprint(1978)] found rather different answers for the triple scattering diagram (Fig. 80), with two different P 33 interactions. The reason for this difference could be traced to the presence in one model [Myhrer and Koltun, Nucl. Phys. B8 6 , 441 (1975), and76T T s  P  —  Pv  r-ji b  x\ 3 '  \  3 Vd=a A = d "i ‘ - x - - 1 ''p.Fig . 80. A t r ip le  s ca tte rin g  contribution  to F ig . 81. The crossed  Bom graph which contributes%2D sca tte rin g  considered  by Myhrer and Thomas. a pole at ,=0 in  the Chew-Low model.Mandelzweig e t  a l .  , Nucl. Phys. A 2 5 6 , 461(1976)] of a pole, near the nucleon mass (i.e. s ~  mjjj) corresponding to the Chew-Low pole, Fig. 8 l . Such a pole does not occur naturally in the separable potential model [Thomas, Nucl. Phys. A 2 5 8 , 417 (1976)]. Furthermore, one can show on the grounds of unitarity that the ttN t-matrix should n o t  have an s-channel pole corresponding to the process in Fig. 81 below the two-pion produc­tion threshold.In fact, if we use s-channel unitarity as the guide in determining the most reasonable phenomenological structure for a ttN  t-matrix to be used in a multiple scattering theory, the conclusion concerning its range becomes self evident. That is, both the nucleon pole (at w = 0) and the left-hand cut [we (-<*>,-[%) ] must occur in the m om entim  de­pendence (k,k') of the off-shell t-matrix t£ ( k ',k ;e) , with only the right-hand cut [we(m7r,°°)] occurring in the energy variable. Since the range of such a t-matrix is in­versely related to the distance to the near­est singularity in the momentum variable, it will necessarily have a fairly long range. Clearly there is no contradiction with Chew- Low theory where all this structure is in one function ha (w), because that is purely a two-particle theory and there is no need to distinguish off-shell from on-shell behav i ou r .Pion-nucleus scatteringThe momentum-space treatment of pion-nucleus scattering [Landau and Thomas, op . a i t . ] ,  which has been discussed in previous reports in connection with the data of Johnson e t  a l .  for tt+12C scattering, has been extended in several directions. In particular it has been verified that the predictions for 9He and 12C scattering lengths are consistent with experiment. The results of the calcu­lations for 150, 40Ca and 90Zr at 50 MeV are in fair agreement with the data of Dytmane t  a l .  [to be published] at 50 MeV. How­ever, the recent u+208Pb data from TRIUMF and LAMPF have provided problems which are under investigation.Work is also under way (in collaboration with M. Krell) on the co-ordinate space description. While it should be clear from the discussion of the ttN interaction above that on theoretical grounds we favour the momentum space optical model, the phenomeno­logical success of (e.g.) the Michigan State work [Strieker e t  a l .  , Phys. Rev., in press] has been very impressive. We are currently studying the dependence on vari­ous parameters of that potential, of neutron radius differences estimated from tt” scattering off 1 2 >12C and 1 6 ’180. Pre­liminary results of this analysis are reported elsewhere in this report (p .43)- If it seems that the neutron radii are well determined in the co-ordinate space optical model, the full momentum space calculation will be applied (in collaboration with R.H. Landau). Finally, if and only if both methods agree, we may at last have learned something new (and model independent) about the structure of nuclei using pions.nD scatteringTwo major steps have been taken towards our aim of a complete theoretical description of this system. The equations of Rinat (Nucl. Phys. A 2 8 7 , 399 (1977)], which pro­vide a means to include the effect of ab­sorption on EEi elastic scattering, have been applied in the resonance region.Figure 82 shows the effect of this correc­tion [Rinat e t  a l . , Phys. Lett. 8 0 B , 166(1979)]- Unfortunately there is no signi­ficant improvement vis-l-vis the 256 MeV data— which incidentally is being remeasured at SIN.The second aspect of some interest in the context of the pion-nucleus interaction is77®CMF ig . 82. A comparison o f  data in  the (3 ,3 )  resonance reg ion  with the three-body ca lcu la tions o f  Rinat e t  a l . (see  t e x t ) ,  fo r  %2D sca tte rin g .that p-exchange has been included to all orders by the replacementin the usual relativistic three-body equa­tions [Rinat and Thomas, Nucl. Phys. A 2 8 2 , 365 (1977)]. In agreement with the earlier work of Levin and Eisenberg [Nucl. Phys. A 2 9 2 , 459 (1977)] this was found to be a very small correction.NN scatteringThe description of NN scattering above the threshold for pion production is currently a topic of great interest, both because of the results of the BASQUE group and because of the reports of possible NN resonances from Argonne [Auer e t  a l .  , Phys. Lett. 67B , 113 (1977)]. In collaboration with A.S. Rinat linear integral equations have been derived (starting from an underlying field theory) which couple the amplitude for NN elastic scattering to the various pion pro­duction amplitudes (e.g. NN -> NA and NN -»■ ttD) . Because the starting point is a field theory of the NNir system, doublecounting problems are avoided. Moreover, the non-static nature of the pion exchange means that the theory is unitary (unlike some coup 1ed-channels potential models). As a matter of historical interest we note that the form of these equations is identical to those of Afnan and Thomas [Phys. Rev. C 10, 109 (1974)]— although the motivation and actual content is somewhat different. This theory is currently being employed in calcu­lations of the NN interaction above pion production threshold.The 4He(p,nn+ )4He reactionGiven the present theoretical difficulties associated with the interpretation of the (p,ir) reaction, it was recently suggested that some study of the (p,niT+ ) reaction, leaving the residual nucleus in its ground state, could be of interest [Sherif e t  a l . , TRIUMF preprint, TRI-UAE-5013 (1978)].While the nuclear structure information contained in such a reaction is necessarily small, this is actually an advantage if one wants to investigate the pion production process itself. Of prime importance in this reaction is the fact that the momentum transfer involved can be kept as low as 200 MeV/c. To investigate the sensitivity of this reaction to details of the pion production process we varied the coefficient a in the effective non-rel at i v i st ic PPEE vertex operatorH'  =  (4tt) j/ 2 (f/m^) O '  [k^ - a(p|+pf)]T • cj>,which has been used in many calculations of the M e V 77■ 9 reaction in the one-nucleon model [e.g. Noble, AIPCP #33, 221 (1976)]. We take the sensitivity to this parameter, shown in Fig. 8 3 , as an indication that this reaction should provide a strong test of any more spohisticated model.Nucleon quasi-free scatteringThe sensitivity of the (p,2p) and (p,pn) reactions to the off-shel1 behaviour of the N-N interaction has been tested for both the TRIUMF geometry and the more sophisticated fixed condition geometry recently proposed by loannides and Jackson [Nucl. Phys. A308, 305 (1978)]. It was possible to retain complete phase-shift equivalence by using the Kowa1 ski-Noyes half-shell functions, in­cluding the generalization to coupled channels [Mongan, Phys. Rev. 184, 1888 (1969)]- While the half-shell calculations78F ig . 83. The c ro ss-s ec tio n  fo r  {*He(p,nn+ ) liHe at 560 MeV fo r  outgoing pion k in e t ic  energy of 130 MeV, and neutron angles o f  0° (upper) and 10° (low er), as a function  o f  the outgoing pion angle. The fou r  curves in  each case show the s en s it iv ity  o f  the rea ction  to the parameter a (see  t e x t ) .never consistently agreed with either the initial- or final-state on-shell prescrip­tions, we were unable to find significant differences in observable polarizations or differential cross-sections between the Reid soft-core and Mongan potentials when the half-shell prescription was used! More details of these calculations may be found in the discussion under Expt. 15 (p.48).The (7i+, n+pj reactionThe possibility of choosing an ideal experi­mental configuration for coincidence studies of this reaction has been studied recently [Jackson, loannides and Thomas, Univ. of Surrey/TRIUMF preprint TRI-PP-78 - 2 9  (1978)]. It has been shown that it will be essential­ly impossible to learn about the off-shel1 behaviour of the  t-matrix from this reaction— even under ideal circumstances.On the other hand, it was found that underspecial geometrical conditions the angu­lar distribution showed a strong qualitative dependence of the 11F interaction on the effect of the medium. This is currently being investigated further.Phenomenology o f inclusive reactionsThe analysing power of proton-induced nuclear inclusive reactions has been found to deviate from the prediction of the single scattering model [Kallne e t  a l . , Phys. Lett. 7 4 B , 170 (1978) and Frankel e t  a l .  , Phys. Rev. Lett. 4J_, 148 (1978)]. The implication of these results is that the production mechanism for backward-going protons is much more complicated than naive quasi-two-body scaling suggests. During the past year a model has been developed to take some of these complications into account. The cluster recoil model [Woloshyn, Nucl. Phys. A 3 0 6 , 333 (1978)] assumes that the inclusive cross-section is the incoherent sum of con­tributions from final states in which the (unobserved) recoil energy and momentum is carried off by different numbers of nucle­ons. A satisfactory description of the inclusive cross-section as a function of energy and angle is achieved even though quasi- two-body scaling now holds only in an average sense. It is suggested that semi- inclusive quantities such as average recoil multiplicity would be useful in revealing the nature of the reaction mechanism.Strangeness-conserving non-leptonic weak interactionsThe weak interaction induced scalar pion- nucleon coupling is particularly sensitive to neutral currents in the weak Hamiltonian [Koiner e t  a l . , DESY preprint 78/61], A reliable determination of the weak pion- nucleon coupling constant a^ would provide, therefore, very useful information on the non-leptonic neutral current. Unfortunate­ly, nuclear physics complications and the importance of vector meson exchange in the parity-violating n u c 1eon-nuc1 eon interac­tion make it difficult to extract a^ from data on parity-violating effects in nuclear transitions [Branderburg e t  a l . , Phys. Rev. Lett. 4l_, 618 (1978)] .It is suggested that measurement of pseudo­scalar asymmetries in low-energy pion photoproduction or radiative capture would provide a direct determination of a,,-. Parity-violating asymmetries have been cal­culated for yp ir+ n in a pole model and79found to be of order 10~7 . Effects due to vector meson exchange and weak interactions at the yNN vertex [Paar e t  a l .  , Nucl. Phys. A 3 0 8 , 439 (1978)] were found to be small. Short distance pieces of the three- and four-current correlations are presently under investigation. These will be compared to the pole model calculation.A study o f bound-state approximations in athree-body model o f rearrangement collisionsA common approximation in atomic and nuclear rearrangement processes is the neglect of n-body breakup contributions (n > 3) by re­placing the full wave function by products of internal and relative wave functions, each product corresponding to a certain asymptotic two-body channel. This bound- state approximation (BSA) is tested in a simple three-body model of the (d,p) reac­tion on a heavy nucleus by comparing BSA calculations with exact and DWBA-type calcu­lations. For energies below the deuteron breakup threshold the BSA provides an ex­cellent fit in the forward direction, and a qualitative fit in other directions. For energies above breakup the BSA is only reliable in the forward direction and becomes increasingly bad for larger angles. This indicates that even for energies as low as 12 MeV one has to take into account the continuum, e.g. by a DWBA calculation where the distorted waves incorporate some continuum effects, or by an impulse approx­imation for the elastic process. The quality of the BSA and DWBA in the various kinematical regions can be explained interms of the momentum dependence of the bound-state wave functions.Pion-nucleus interaction in the resonance regionUsing the isobar-doorway model which is a phenomenological version of isobar-doorway theory, the pion elastic scattering for 12C and 150has recently been completed [Saharia, Ph.D. thesis CMU (1978, unpublished) and Kisslinger and Saharia (to be published)]. The model includes the effects of many-body dynamics in pion-nucleon TEEPO 3_3 channel in terms of phenomenological parameters which have simple physical interpretation. Using this model the effect of pion true absorp­tion on elastic scattering has been esti­mated. Using a very simple model for nuclear wave function, it was found that the true absorption in EEP non-resonance channels is unable to give the large 'S-wave' repul­sion needed to explain the low-energy elastic scattering data. It is planned to improve these estimates by using more realistic nuclear wave functions.It is further planned to generalize the code for I DM to generate elastic scattering wave functions for any arbitrary nucleus. These wave functions can then be used to study nuclear reactions involving pions, in DWBA and DWIA. Also the generalization of the I DM to the single charge exchange scattering [Hiruta (preprint 1978) and Auerbach, Phys. Rev. Lett. _38_, 80A (1977)] will be extended to double charge exchange scattering.30CYCLOTRON SYSTEMSION SOURCE AND INJECTION SYSTEMUnpolarized source and injection lineThe operational experience during 1973 has confirmed the validity of the instrumenta­tion previously installed in order to pro­tect the 300 keV line from high-current thermal beam damage. Whereas during 1977 part of the vertical line had to be over­hauled to repair ground faults and damage to the electrical insulators, this was not the case during 1978, although beam currents between 100 and 500 yA (for extracted cur­rents between 20 and 100 yA) were run quite frequently. Setting-up times of one to two hours for the 100 yA extracted beam were recorded, and the 100 yA running was suffi­ciently reliable to be entrusted to the operators.Largely responsible for the improved relia­bility was an improvement in the H~ Ehlers source which allowed a brighter beam to be produced in a smaller emittance. With an arc current of 0.8 yA a stable current of 800 yA could be produced in an emittance of 0.2tt mm-mrad horizontally and 0. 1 EE mm-mrad verti­cally. This was achieved through minor modifications in the arc chamber geometry. Also, the beam modulations deriving from arc- plasma oscillations in the ion source were reduced to a few per cent and can now be easily controlled by tuning the arc voltage and the H 2 gas flow. The sparking between the -12 kV ion source and the surrounding electrodes was kept within a few sparks per hour by installing a copper shroud around the anode block to disperse the electrons drain­ing from the source-pu11er region. The filament lifetime is now above 150 h in normal operating conditions.With the smaller beam emittance, smaller de­fining slits could be used in the 12 keV region. This made sudden beam deflections in the injection line less likely to occur and trips caused by the beam loss protection system less frequent. The beam cross- section along the injection line became smaller by at least a factor of two, allow­ing several additional cooled collimators,0.5 in. diam, to be installed along the line. The advantage of the cooled collimators, with respect to the non-cooled 'skimmer' electrodes protecting the electrostatic ele­ments from excessive beam spills, is that they can be used to localize beam losses andto reduce them by tuning, before any substan­tial spill will hit the skimmers and cause a source trip. Both skimmers and cooled collimators can be displayed in form of a bar chart on a 611 scope in the Control Room and provide a powerful diagnostic tool.Successful was the installation and testing along the injection line of a A .6 MHz RF sys­tem which was used to provide a special 5:1 time structure of the beam. As a matter of fact, by eliminating four out of five beam pulses injected into the cyclotron one eliminates four out of five beam spokes nor­mally present into the fifth harmonic mode of acceleration in the machine. As a conse­quence the time between extracted pulses is increased from 43 nsec to 215 nsec. This can be very useful for background considera­tions in several experiments and has been requested by pion, muon and neutron users.Polarized sourceEarly this year, influenced by experimental requests for an intense polarized beam, it was possible to upgrade the source and to extract 200 nA at 500 MeV. During this run, a record 1 yA of polarized H~ was measured at the source, 80% of which was injected into the cyclotron. Completion of the BASQUE experiment has reduced the requested beam intensities and the effort has shifted to­wards i mprov i ng the re 1 i ab i1 i ty of the source.A substantial increase in the length of time the source could run between maintenance periods was realized when the plastic insu­lators on the accel lens were replaced by ceramic insulators. During the fall shut­down the source was dismantled in order to install a sturdier frame. Gate valves, sus­pended from this frame, were installed above each of the four diffusion pumps. This not only offers some protection against vacuum accidents but also has considerably decreased the time required for an overall source clean-up. A freon refrigerator was in­stalled in the source and connected to baf­fles above the diffusion pumps in order to reduce an oil contamination problem. A rudi­mentary interlock system has been installed; however, the polarized source remains essen­tially unprotected from many conceivable failures and a more thorough interlocking system needs to be implemented.81RF SYSTEMRF amplifiersThe RF amplifiers performed very reliably during the past year. Four major areas were the cause of considerable machine downtime:1) Failure of the ACW100000E I PA tetrode. Considering it was the original tube and had 1 7 , 000 h of filament elapsed time, it served us w e l 1 .2) SCR fai 1 ure in the filament power sup­plies have always been a source of major downtime. The SCRs are in a very inacces­sible place and physically replacing the SCRs accounts for most of the downtime. A more reliable SCR has now been found (the original SCRs are no longer manufactured), and modifications have been made to the power supplies to make the SCR assemblies plug-in units to facilitate replacement.3) Mechanical problems with water valves, water seals, drive motors, etc. in the cool­ing systems and in the liquid waster loads have caused major downtime, but they seem to be mostly maintenance problems.A) RF control problems were a major contri­bution to downtime this year. Most of the breakdowns seem to be due to components heating up. Some of the problems have been solved while others are intermittent and are still present. The Electronics Group is presently working on a new RF control system using a microprocessor.RF resonatorsAn important milestone was reached in under­standing and controlling the RF leakage and resonator strongback heating. In 1977 we were able to correlate the RF leakage and resonator strongback heating to the RF beam gap impedance and up-down voltage asymmetry. The results revealed quite clearly how sensitive resonator tip alignment was to RF leakage in the beam gap. Early in 1978 much effort was devoted to straightening reson­ators and mechanical tip alignment. Although this improved the situation, the resonator strongbacks were still becoming quite warm, and the RF leakage was still very sensitive 


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