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Efficiency calibration of a neutron long counter. MacFarlane, Tracy Lynn 1968

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EFFICIENCY CALIBRATION OF A NEUTRON LONG COUNTER by TRACY LYNN MacFARLANE B . S c , The U n i v e r s i t y of New Brunswick, 19&5  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of PHYSICS We accept t h i s t h e s i s as conforming to required standard  THE UNIVERSITY OF BRITISH COLUMBIA May, 1968  the  In  presenting  for  an  that  advanced  thesis  shall  I further  agree  for scholarly  Department  or by  publication  without  thesis  degree  the Library  Study.  or  this  my  hits  make  i t freely  that  may  be  thesis  Department Columbia  the  granted  by  requirements  Columbia,  t h e Head  shall  and  copying  It i s understood  gain  I agree  for reference  for extensive  for financial  permission.  of  of B r i t i s h  available  permission  representatives.  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada  fulfilment  the U n i v e r s i t y  purposes  of this  written  at  in partial  of  of  this  my  that  n o t be  copying  allowed  ABSTRACT The U.B.C. Hanson-McKibben type Long Counter has been modified to permit  i n s e r t i o n of a larger diameter BF^ proportional counter.  An  i n v e s t i g a t i o n was made to determine the e f f e c t s of the m o d i f i c a t i o n on the neutron detection c h a r a c t e r i s t i c s of the counter.  2.60 MeV and •3  3.09 MeV neutrons were obtained from the reaction D(d,n) He and 4.5 MeV 241 neutrons from a standard  AmBe source.  The e f f i c i e n c y of the Long Counter was determined in terms of counting rate per unit neutron f l u x occurring at the e f f e c t i v e centre of the counter.  The count rate used was that due to the ^ B ( n , a ) ^ L i  pulses from the BF^ counter located in the centre of the Long Counter. The e f f e c t i v e centre was defined as that point inside the counter such that the counting rate varied as the inverse square of the distance of the source from the e f f e c t i v e c e n t r e .  The following table l i s t s the  neutron energy, e f f i c i e n c y and distance from the front reference face of the Long Counter to the e f f e c t i v e centre. Neutron Energy MeV  Efficiency counts / neutron per cm at the e f f e c t i v e centre 26.6 ( ± 2 0 % ) . 29.4 ( ± 1 9 % ) 14.1 (±2.2%) 2  2.580  (±.06%)  3.004  (±.3%)  4.5  (±10%)  Distance to E f f e c t i v e Centre cm 12.6 {±3%) 10.3  (±7*)  10.8 (±6%)  The e f f i c i e n c y f o r 4.5 MeV neutrons was found to have increased  i ii by at least an order of magnitude from that of the o r i g i n a l  Long Counter.  However, the dependence of the e f f i c i e n c y on energy has been increased, varying by 50% over the range of energies measured. The s h i e l d i n g on the sides of the Long Counter was found to reduce the i n t r i n s i c e f f i c i e n c y for neutrons incident from the side to O.A of that for neutrons  incident on the front f a c e .  TABLE OF CONTENTS ABSTRACT . . . . . . . . LIST OF FIGURES • •  ii • • • • o » « * o * « 0 o » o o * o « * « o o o * « * « « » o o o « « « « « * o » « * o o  ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CHAPTER I  CHAPTER II  v vi  INTRODUCTION 1.1.  General Introduction  1.2.  The Long Counter  „  1 A  MEASUREMENT OF THE LONG COUNTER EFFICIENCY USING AN A m B e NEUTRON SOURCE 2ltl  CHAPTER III  2.1.  The Standard Neutron Source  ..........  2.2.  Measurements  2.3.  C a l c u l a t i o n of E f f i c i e n c y . . . . . . . . . . . . . . . . .  6 7 10  MEASUREMENT OF LONG COUNTER EFFICIENCY USING THE REACTION D(d,n) He 3  3.1.  The Reaction D(d,n)^He . . .  13  3.2.  The Gas Target  14  3.3.  Current Integration . . . . . . . . . . . . . . . . . . . . . . .  16  3.4.  Measurements  19  3.6.  Gas Target Thickness . . . . . . . . . . . . . . . . . . . . . .  22  3.7.  Beam Energy in the Gas Cell  ...............  23  3.8.  Neutron Flux from the Gas Target . . . . . . . . . .  23  3.9.  C a l c u l a t i o n of E f f i c i e n c y . . . . . . . . . . . . . . . . .  26  Iv  CHAPTER IV  CONCLUSIONS  BIBLIOGRAPHY . . . . . . . . . . . . . . . APPENDIX  ........................... ........  ...............  28 30  LONG COUNTER ELECTRONICS A.1.  Proport iona 1 Counter  A.2.  E l e c t r o n i c s for  AmBe C a l i b r a t i o n . . . . . . .  31  A.3-  E l e c t r o n i c s for D(d,n) He C a l i b r a t i o n . . . . .  32  241  • o « # » o o » » « o » o o » o «  3^  LIST OF FIGURES Figure  Follows Page  1.  U.B.C. Long Counter  ......  ..........  4  2. 3.  Comparison of RaBe and AmBe spectra ............ Arrangement of Long Counter and neutron source f o r e f f i c i e n c y measurement . in text p.  5  4.  Long Counter spectrum for AmBe neutrons  7  5.  Arrangement of Long Counter and neutron source for side s h i e l d i n g i n v e s t i g a t i o n  7  in text p.  9  6.  Inverse square plot for AmBe source at end of counter .  9  7.  Inverse square plot for AmBe source at side of counter.  10  8.  V a r i a t i o n of energy with angle for neutrons from 12  9.  the reaction D(d,n) He . . . . . . . 3 V a r i a t i o n of D(d,n) He cross section with incident deuteron energy  12  10.  Gas target and beam c o l l i m a t i o n system  13  11.  Current measurement system for study of  3  current d i s t r i b u t i o n  in target  16  12.  Results of current d i s t r i b u t i o n study . . . . . . . . . . . . . . . . .  17  13.  E l e c t r o n i c s for D(d,n) He c a l i b r a t i o n  18  1h.  Beam dependent background increase with running time . .  20  •3  15.  Inverse square plot for D(d,n) He runs  25  16.  E f f i c i e n c y v a r i a t i o n with neutron energy . . . . . . . . . o . . . .  27  17.  E f f e c t i v e centre v a r i a t i o n with neutron energy  27  ACKNOWLEDGEMENTS I wish to express my sincere gratitude to Dr. G„M.  Griffiths  for his supervision and assistance throughout the course of t h i s work. I am a l s o grateful  to the students, s t a f f and f a c u l t y of the  Van de Graaff Group for t h e i r generous help in the  laboratory,  e s p e c i a l l y Duncan Hepburn, Dr. Grahame B a i l e y , Richard Helmer and Miguel 01ivo.  CHAPTER I INTRODUCTION 1.1.  General Introduction The Hanson-McKibben (19^7) Long Counter developed at Los Alamos  is probably the most widely used of a l l neutron d e t e c t o r s . It c o n s i s t s of a long BF^ proportional counter placed in a c y l i n d r i c a l moderator of p a r a f f i n .  The moderator is surrounded a l l but on  one end by a thermal neutron absorber, u s u a l l y a t h i n sheet of cadmium, and a second fast neutron moderating layer surrounds the absorber. Neutrons incident on the open end are thermalized in the center moderator and have a high p r o b a b i l i t y of entering the BF^ counter, where they produce ^ B ( n , a ) ^ L i reactions in the counter gas.  In general the gas is  enriched to about 90% in ^ B , compared to the 19-8% of natural boron.  found in  Ions produced by the charged p a r t i c l e s from the reactions  are c o l l e c t e d and produce an e l e c t r i c a l pulse which is amplified and counted e l e c t r o n i c a l l y .  Neutrons incident from the side are l a r g e l y  thermalized in the outer moderator and e i t h e r escape or are captured in the absorber.  Therefore they have a small p r o b a b i l i t y of entering the  center region and do not contribute s i g n f i c a n t l y to the counting r a t e . Thus, the counter has the highest s e n s i t i v i t y only to those neutrons that enter the center region at one end. Pangher and Nichols (1966) at the P a c i f i c Northwest Laboratory in Richland, Washington have made an improvement by replacing the p a r a f f i n  2 with polyethylene, supported by aluminum rather than steel used by McKibben.  The r e s u l t was a highly reproducible detector with considerably  better r e s o l u t i o n on the neutron peak than the McKibben model. The Long Counter is much used in the neutron range from 25 keV to 14 MeV.  The absolute c a l i b r a t i o n is u s u a l l y based on observing the  counting rate for a neutron source with a known neutron output. neutron sources are made of a natural or a r t i f i c i a l l y emitter  Standard  produced alpha-  intimately mixed with beryllium in which the neutron y i e l d a r i s e s  from the reaction  9  Be(a,n)  12 C.  Typical sources such as Ra-Be or  241  Am-Be  produce a broad spectrum of neutrons from a few MeV to 10 or 11 MeV, with a tendency to peaking in the 3 to 6 MeV range.  This provides a reasonable  c a l i b r a t i o n over the energy range in which the counters are used because the neutron detection e f f i c i e n c y of the counter with the usual dimensions is r e l a t i v e l y  independent of neutron energy.  (Hanson and McKibben, 1947;  Pangher and N i c h o l s , 1966) The o r i g i n a l U.B.C. Long Counter was constructed by Heiberg (1954) using a Chalk River one inch diameter BF^ counter.  In 1966, when  the counter began to f a i l , a d e c i s i o n was made to introduce gas counters of larger diameter and higher pressure containing e i t h e r BF^ or  He.  The  aim of the present work was to investigate the properties of these counters and in p a r t i c u l a r to make a more accurate measurement of the absolute e f f i c i e n c y for neutron detection using both accurately c a l i b r a t e d neutron sources and monoenergetic neutrons produced by the Van de Graaff generator.  Using monoenergetic neutrons from reactions of known cross  section in has been possible to investigate the e f f i c i e n c y of the detector  as a function of neutron energy. A major disadvantage with the Long Counter is i t s slow response to incoming neutrons, making i t of l i t t l e use in time of f l i g h t or concidence measurements. used.  In these cases a s c i n t i l l a t i o n detector is often  This type of detector c o n s i s t s of a s c i n t i l l a t i n g material mounted  on a p h o t o m u l t i p l i e r .  Some materials used are ^ L i - I ( T l ) c r y s t a l , ^ L i  loaded g l a s s , a compound of 15% Zn-S a c t i v a t e d with s i l v e r and dispersed in l u c i t e (Hornyak 1952), and various l i q u i d and p l a s t i c s c i n t i l l a t o r s . These however require elaborate pulse shape a n a l y s i s to separate the pulses o r i g i n a t i n g from neutrons and those o r i g i n a t i n g from gamma ray f l u x . The major advantege of the Long Counter, i t s r e l a t i v e l y constant e f f i c i e n c y with varying energy, is not always a d e s i r a b l e f e a t u r e . a case is health monitoring of neutrons.  Such  The r e l a t i v e health hazard for  a given f l u x of neutrons increases with energy.  It was found by Bramlett,  Ewing and Bonner (1960) that a ^ L i - l ( E u ) c r y s t a l placed in the center of a 12 inch polyethylene sphere exhibited an e f f i c i e n c y v a r i a t i o n with energy of the incident neutrons which c l o s e l y approximated the energy v a r i a t i o n of the health hazard of neutrons.  4  1.2.  The Long Counter The Long Counter depends on the d e t e c t i o n . o f the alpha p a r t i c l e s  emitted by the reaction ^ B ( n , a ) ^ L i produced in boron t r i f l u o r i d e gas in a c y l i n d r i c a l proportional counter. ^B(n,a)^Li  is 2.79 MeV.  The energy release in the reaction  This is considerably greater than the energy  l o s t by electrons traversing the counter volume.  Proportional operation  then ensures that processes leading to a s i n g l e electron e j e c t i o n , such as gamma i n t e r a c t i o n s , produce pulses considerably smaller than the reaction pulses.  This is important f o r a neutron detector since a neutron  f l u x i s often accompanied by a large gamma ray f l u x . Table 1 shows the cross section of the reaction ^ B ( n , a ) ^ L i as taken from Hughes and Schwartz (1958). TABLE 1 ^B(n,cx)^Li Cross Sections Neutron Energy  Cross Section  0.0235 eV 6.0 eV 10.0 keV  3820 barns 85 barns 7 barns  C l e a r l y the e f f i c i e n c y of the proportional counter depends strongly on the energy of the incident neutrons.  The counter developed by Hanson  and McKibben (19^7) had a p a r a f f i n moderator arrangement to give a counting r a t e , as nearly as p o s s i b l e , proportional f l u x and independent Of the neutron energy.  to the incident neutron  By making the moderator  appreciably longer than the mean free path of f a s t neutrons, neutrons  k  ' 0 >J ft «J >  <L<fc  -mi OJ  S \ N..  <L 'J.  t o CL  ft ct  d  0  (J  (0  'L 0 C9  entering the moderator are slowed by successive c o l l i s i o n s in the moderator so that the f r a c t i o n that d r i f t s into the counting tube at thermal energies v a r i e s l i t t l e with energy. The U.B.C. Long Counter, shown in F i g . 1, is based on the Hanson - McKibben d e s i g n , however the present version has a larger BF^ counter( 2 inches in diameter) f i l l e d to 70 cm of Hg with 96% ^ B enriched BF^.  Further d e t a i l s concerning the counter and operating conditions are  given in the Appendix.  CHAPTER I I MEASUREMENT OF THE LONG COUNTER EFFICIENCY USING AN * Am-Be NEUTRON SOURCE 2i  2.1.  1  The Standard Neutron Source The e f f i c i e n c y of the long counter shown in F i g . 1 was  measured using an accurately c a l i b r a t e d neutron source placed at various distances from the counter ranging from 10 cm to 150 cm. The neutron source (type AMN-18) obtained from the Radiochemical Center, Amersham, England consisted of the alpha-emitter Americium-241 fused with beryllium metal. 9 reaction  Be(a,n)  It produces neutrons by the  12 C.  The absolute neutron output was measured by  K.W. Geiger at the National Research Council of Canada by a d i r e c t intercomparison with the Canadian Standard source #118 using a P r e c i s i o n Long Counter (Pangher and Nichols 1966).  The Canadian standard had been  absolutely c a l i b r a t e d by the manganese bath method (Geiger and Baerg, 1965), and intercompared with the standards of other c o u n t r i e s .  The neutron  output f o r the present source was 7.62 x 10^ (±2%) neutrons per second. ( C a l i b r a t i o n Report APXNR-2095, January 1968) Some data on the alpha p a r t i c l e s emitted by 237 Y~rays from the daughter product strongest  l i n e s underlined.  2h1  Am and on the  Np are given in Table 2 with the  The neutron energy spectrum is compared with  that from a Ra-Be source in F i g / 2 .  7 TABLE 2 241 'Am *\m --> >-• a a + + a-Energy MeV a a 3 a 0  3  6 0  p \ (T, "N Np i  2 3 7  = 458 years) Y~ n 9y (%) MeV  %  5-545 5.513 5.486  0.25 0.12 85.5  aio  3  5.443  12.7  ai5  9  5.389  1.3  E  er  0 0.0332 (100) 0.0594,(94) 0.026 (6) 0.1029 (22) 0.043 (78) 0.125 (11) 0.099 (50) 0.055 (39)  plus 18 other alpha groups, a l l less than 0.02%.  The complex alpha spectrum, combined with the fact that alpha p a r t i c l e s of a l l energies slowing down in the source can produce neutrons 12 which leave  C either  in the ground state or in the f i r s t excited state  at 4.43 MeV, gives r i s e to a broad neutron energy spectrum. 2.2.  Measurements  d tfiBICHT-  Figure 3-  SOURCE  Arrangement of Long Counter and Neutron Source. The Long Counter and source were arranged as shown in Figure 3,  such that wall s c a t t e r i n g of the neutrons was much less than from the f l o o r .  scattering  The pulses from the Long Counter were analyzed in an  ND-101 256 channel k i c k s o r t e r , using the a m p l i f i c a t i o n  system described  0 \  8  in Appendix A. 1 . A t y p i c a l neutron spectrum is shown in Figure 4 .  This spectrum  resulted from a 3 0 minute exposure of the Long Counter to the Am-Be source at a distance  d=60  cm.  The lop-sided appearance of the peak is explained by Pangher and Nichols  ( 1 9 6 6 ) - i n  t h e i r work on an accurately reproducable long counter  using polyethylene rather than p a r a f f i n .  Their P r e c i s i o n Long Counter had  better r e s o l u t i o n than the Hanson-McKibben type;  as a r e s u l t two d i s t i n c t  peaks, a main peak and a smaller one at s l i g h t l y higher energy, could be c l e a r l y resolved.  The main peak was a t t r i b u t e d to the case when the alpha  p a r t i c l e from the reaction ° B ( n , a ) ^ L i 1  (Q. = 2 i 3 1  MeV) leaves the  \ i  nucleus in i t s f i r s t excited state ( 4 7 8 keV above the ground s t a t e ) , and the second small peak, which produces the hump on the high energy side of Figure 4 ,  to the case when the ^ L i nucleus i s l e f t in the ground state  ( Q = 2 . 7 9 MeV ) ( about 5% of the t i m e - ) . To determine the number of counts in the spectrum due to neutrons, the background was subtracted and the spectrum integrated from a bias level to the point where the spectrum returned to background l e v e l . So as to make the operation independent of the p a r t i c u l a r neutron source being used, a bias level was chosen to cut off a l l pulses r e s u l t i n g from gamma rays.  This gives a bias unnecessarily high for such  sources as Am-Be which produce l i t t l e accompanying gamma f l u x , however it  is appropriate for the many high gamma f l u x s i t u a t i o n s in which the  counter may be used in f u t u r e .  The bias was determined by running a spectrum s i m i l a r to the Am Be one of F i g . 4 . but using a Ra Be source with neutron f l u x of 5  7 . 5 x 10  neutrons per second accompanied by a high gamma f l u x .  The  spectrum was s i m i l a r to that for Am Be but with a very high low energy t a i l , as dotted in on F i g . 4 . The effectiveness of the s h i e l d i n g layers around the sides of the Long Counter was investigated by determining the e f f i c i e n c y of the Long Counter for neutrons from the Am Be neutron source placed at various distances along a l i n e at r i g h t angles to the axis of the Long Counter. The arrangement  is shown in F i g . 5 .  Figure 5. Arrangement of Long Counter and neutron source for effectiveness i n v e s t i g a t i o n .  shielding  10 2.3.  C a l c u l a t i o n of E f f i c i e n c y In order to define an e f f i c i e n c y independent of the distance  from the source to the Long Counter, a plot of C  2  against the distance  from the counter face to the source was made as shown in F i g . 6, where C is the count rate from the Long Counter.  In the range of distances  d $ 100 cm t h i s produced a reasonable approximation to a s t r a i g h t  line.  Beyond t h i s point the room scattered neutron background became s i g n i f i c a n t as indicated by the deviation of the data from the inverse square law. This l i n e was extrapolated back to cross the distance a x i s at a point " e " cm from the o r i g i n , c a l l e d the e f f e c t i v e centre. The Long Counter count rate can be related to i t s  intrinsic  e f f i c i e n c y and the neutron source strength as f o l l o w s : C = n where:  A 4TT (d+e)  Eff 2  C = counts per unit time from Long Counter. n = neutrons per unit time emitted into 4TT sterradians by the neutron source. A = area presented by the counter to the incident neutrons, d = distance from the counter face to the source, e = distance from the counter face to the e f f e c t i v e centre of the Long Counter. D = d + e e = the p r o b a b i l i t y of obtaining a count when a neutron enters the s o l i d angle of the counter. Eff = Ae-= e f f i c i e n c y of. the Long Counter in terms of counts per unit neutron f l u x at the e f f e c t i v e centre.  This can be rearranged to give the e f f i c i e n c y Eff =  explicitly  c  n or in terms of the slope S of the inverse square p l o t , where S -  - 1 =  the e f f i c i e n c y can be expressed as  Eff =  4  IT  The slope S of F?g„ 6 f o r d £ 100 cm was found to be 2„549 x 10  5  of 7-62 x 10  ( ± 0.1% ).  This combined with the neutron source strength  ( ±2% ) neutrons per second, gives an effeciency  5  Eff = 14.1 ( ±2.2% ) counts per neutron per cm at the e f f e c t i v e centre  2  Using the same s l o p e , the e f f e c t i v e centre was found to be at e = 10.8  ( ±5.5% ) cm behind the front reference face of the counter  shown in F i g . 3. The e f f i c i e n c y can a l s o be stated in terms of the f r a c t i o n of neutrons emitted by a source which produce counts in the counter. c l e a r l y depends on the distance of the source from the counter.  This The  present counter can be compared with the counter in i t s o r i g i n a l form in terms of the relateve number of counts obtained when the source was placed at 150 cm from the f a c e .  The o r i g i n a l U.B.C. Long Counter  contained a 1 inch diameter BF^ counter as described on page 2.  Using  a RaBe neutron source at 150 cm t h i s counter gave 4.6 x 10 ^ counts per neutron emitted by the source (Heiberg, 1954).  For an AmBe source of  approximately the same strength, at the same d i s t a n c e , the new counter gave 4.74 x 10  counts per neutron emitted by the source, more than an  order of magnitude improvement. Results for the source at the side of the counter are shown in F i g . 7 where the inverse square root of the counting rate is plotted against the distance  from the counter centre l i n e to the source.  12 The slope of t h i s plot for d  s  $100 cm was found to be 7.74 x 10  _c  Using t h i s slope and the method described previously ( page 10 ),  ± 1.6%„ the  Long Counter e f f i c i e n c y for neutrons incident from the side was c a l c u l a t e d to be centre.  15.3 ± 5-2% counts per unit neutron f l u x at the e f f e c t i v e  The e f f e c t i v e centre in t h i s case was obtained by extrapolation  of the plot  in F i g . 7 to the distance a x i s , and found to be  1.6 ( ±2% )cm  behind the centre l i n e of the counter. The e f f i c i e n c y per unit f l u x for neutrons incident on the side is thus s l i g h t l y larger than that previously c a l c u l a t e d for the same flux  incident on the end.  However, since the cross sectional area of the  s e n s i t i v e region from the s i d e , A , is 2.7 times that from the end,A , 3  S  t h i s implies a lower i n t r i n s i c e f f i c i e n c y e for neutrons incident on the side.  From the data we have for the end (Eff) = A e = 14.1 a a a  and for the side  (Eff)  s  = A e = 15-3 s s  Therefore the r a t i o of the i n t r i n s i c e f f i c i e n c i e s is — £  S  a  = 15.3 14.1  A = A° 3  14.1  x — = 0.402 2.7  This indicates that the s h i e l d i n g on the Long Counter reduces the i n t r i n s i c e f f i c i e n c y for neutrons incident from the side compared to the e f f i c i e n c y for those entering the front end. background and room scattered neutrons.  This reduces the e f f e c t of  I  O  .  1  -do  ,  .  _l  I  80  I  1_  ISO  :_t  I  /60  t  /so  90  o C EN  77/?£T  0/=  rt&SS  /V'£OCTew  Ft CURE  SH/FT£-E>  £zj  p.  DCJhJ/V  J>> 0.99 SYe V  JDCJj n) ffe  £3.y • • S~ fnti/sti HRS  r3G£M  RNCLS o//=/=e R e^TS^u  firs  &  GFtCht-  ^Hi>=-r{^D  UP  of:  Gy  c/foss  T H E  S  CURVES  /sZ  s=-f?ot-t  CHAPTER  III  MEASUREMENT OF LONG COUNTER EFFICIENCY USING THE REACTION D(d,n) He 3  3.1•  The Reaction D(d,n) He At low energies, c o l l i s i o n s between two deuterons r e s u l t in the  two reactions D(d,n) He and D(d,p)T with approximately equal and Q-values of 3.268 MeV and 4.033 MeV r e s p e c t i v e l y .  probability  If the input  energy of the reaction is increased, a t e r t i a r y process, involving the breakup of the deuteron, occurrs with a Q-value of -2.225 MeV. F i g . 8 shows the v a r i a t i o n in neutron energy with the neutron angle and incident deuteron energy f o r the reaction D(d,n) He (Fowler and B r o l l e y , 1956). F i g . 9 shows the d i f f e r e n t i a l  cross section f o r the reaction  D(d,n) He f o r various incident deuteron energies as a function of the centre of mass angle.  The data shown were obtained by Hunter and  Richards (19^9) using a c a l i b r a t e d Hanson-McKibben Long Counter to detect the neutrons produced in a gas target 2 cm in length. 3 observed rather than the  The neutrons were  He in order that measurements could include a l l  angles in centre of mass from 0° to nearly 180°. Background neutrons from the f o i l and c o l l i m a t i n g apertures amounted to only 2% of the D(d,n) He y i e l d at a deuteron energy of 0.7 MeV.  The data shown in F i g . 9  have been corrected f o r the v a r i a t i o n of Long Counter e f f i c i e n c y with neutron energy using the curve given in McKibben (19^7) and converted to  14 centre of mass. differential  The appearance in the data of the symmetry of the  cross section about 90° in the centre of mass system as  required by the i d e n t i t y of the i n i t i a l  p a r t i c l e s , v e r i f i e s the  a p p l i c a b i l i t y of McKibben's curve to the Long Counter used. The s t a t i s t i c a l errors in the data were ^ ±5% and the Long Counter c a l i b r a t i o n was accurate to cross sections of 3•2.  ±5% g i v i n g a t o t a l error on the  10%.  The Gas Target The gas target system used is i l l u s t r a t e d  in F i g . 10.  The Nickel F o i l Entrance Window Manufacturer: Specifications:  Chromium Corporation of America, Waterbury, Conn.,U.S.A. Grade C, Dimensions  x i " x 50yinches  The f o i l thickness was determined for =0.9 MeV protons by i n v e s t i g a t i n g the s h i f t  in the 0.873 MeV gamma resonance from proton  bombardment of f l u o r i n e .  S u f f i c i e n t f l u o r i n e contamination was present  on the gas target backstop and on the metal backing of a beamstop in the beamline before the c o l l i m a t o r s to make actual deposition of a f l u o r i n e target unnecessary.  The f l u o r i n e gamma peak before the window was  centered about 876 ±2 keV with a half-width of 7 keV, and that a f t e r  the  window , at 1015 ±4 keV with half width 12 keV, i n d i c a t i n g a window thickness of 139 ±6 keV for =0.9 MeV protons. The f o i l was soldered over the end of the brass support tube using " S t a y - B r i t e " s o l d e r .  The^nd of the tube was dipped in a puddle  of molten solder and f l u x on an aluminum plate so as to r e t a i n a small  15 amount of solder on the end. up, a n i c k e l f o i l  The tube was then clamped  solder end  l a i d across the end and a small aluminum block set on  the f o i l . The block was then heated, melting the s o l d e r .  F o i l s attached  in t h i s manner were found to withstand pressure differences of =740 mm Hg, the lower pressure being inside the support tube, before r u p t u r i n g . Using an e l e c t r i c a l contact system, a pressure d i f f e r e n c e of 300 mm Hg was found to cause a depression in the f o i l of 0.012 cm from the p o s i t i o n of the f o i l with equal pressures on both s i d e s .  This represents a 1,4%  change in the 0.833 cm length of the beam path in the gas eel 1 . Target Thickness The purpose in using a gas target was the ease of determination of the number of target n u c l e i , which can be c a l c u l a t e d using the path length in the gas from the entrance f o i l  to the backstop, the gas  pressure in the t a r g e t , and the temperature in the beam region of the gas. The pressure of the target gas was measured using a 0 to 800 mmHg Wallace and Tiernan absolute pressure meter, and the target region length was measured with a t r a v e l l i n g telescope. Because of the power d i s s i p a t e d by the incident deuteron beam, the temperature in the beam region is generally s l i g h t l y greater than that in the bulk of the gas in the target.  The extent of t h i s e f f e c t has  been measured and plotted for various beam currents by Robertson et al (1961) using the same gas target being used in the present experiment. Due to the large copper backstop' it was assumed that the temperatures of the bulk of the gas in the target and that of the backstop would be  16 e s s e n t i a l l y the same.  This temperature was measured using a copper-  constantan thermocouple a f f i x e d to the backstop.  The e f f e c t i v e  temperature in the beam region i s described in terms of the temperature T of the bulk of the g'as as T  effV  (  P  i / o > P  T  where ( P./P ) is given by Robertson's plot as q  Beam Current  ( P./P ) i o 1 .001 1.005 1.012  .02 yamp .1  .2 3-3.  Current Integration Even at very low beam currents the target gas w i l l experience  considerable ion z a t i o n .  This was confirmed by the fact that a d i s t i n c t  blue glow was seen in the beam region in the gas, which in f a c t was used to check the centering of the beam in the f o i l window support tube.  The  s l i g h t e s t potential d i f f e r e n c e between the window and backstop portions of the target would cause charge s e p a r a t i o n , making current measurements from the backstop completely u n r e l i a b l e . The only way to eliminate errors in the current measurement r e s u l t i n g from charge separation in the gas, or from p r e f e r e n t i a l c o l l e c t i o n of secondary electron emission, was to connect the window and backstop portions e l e c t r i c a l l y and measure the t o t a l current and stopped in the gas c e l l .  entering  This method, however, presents the problem  that i f some of the deuteron beam is l o s t on the sides of the tube holding the window, p o s i t i v e current  is measured which does not a c t u a l l y  /  SfiCKS-roP  FOIL. \~>IN-DOVJ  U L  9° V- . 'OO  A--Ti-  go  /.  )0 v.  300  V.  17 pass through the target gas. To prevent any current f a l l i n g on the tube supporting the f o i l at the entrance to the gas c e l l , the beam c o l l i m a t i o n system was designed such that a p a r t i c l e passing through the c o l l i m a t o r s at even the most extreme angle would pass through the window into the gas without the w a l l s of the entrance tube.  hitting  A l s o , the focussing was arranged to give  as nearly as p o s s i b l e a p a r a l l e l beam and rule out any chance of a focus i n s i d e the c o l l i m a t i o n system. These precautions were shown to be e f f e c t i v e in a current d i s t r i b u t i o n check using the apparatus described in F i g . 11.  The f i n a l  col 1imator.nwas held at +300 v in order to r e t a i n any electrons knocked out of i t by the incident beam.  The window portion was held at +90 v  so that the potential d i f f e r e n c e between i t and the backstop could be varied from +90 v to -90 v continuously.  Using t h i s arrangement an  i n v e s t i g a t i o n was made, with no gas in the t a r g e t , of the currents on different  parts of the target chamber and c o l l i m a t i o n system, r e s u l t i n g  from both a proton beam d i r e c t l y and the secondary electron emission. The t o t a l current was measured, with a +300 v b i a s , on a removable metal beam stop j u s t in fromt of the f i n a l c o l l i m a t o r .  Then,  with the beam stop removed, simultaneous currents were measured on the f i n a l c o l l i m a t o r , the f o i l window and i t s supporting tube, and on the backstop, as shown in F i g . 11, f o r various r e l a t i v e p o t e n t i a l s on the f o i l window and backstop. To 10% the net current' agreed with the t o t a l current measured on the removable stop, i n d i c a t i n g that no beam was being lost other than  18  on the three parts considered. window current  is zero further  This agreement at the point where the indicates that a l l current that goes  through the c o l l i m a t o r , passes through the f o i l window and the gas c e l l and h i t s the backstop with none being l o s t on the sides of the entrance tube. The high saturation currents at negative backstop b i a s , indicate a higher rate of secondary electron emission from the backstop than from the foi1  window. The t o t a l charge entering and stopped in the gas c e l l was  measured on the connected window and backstop using an Eldorado E l e c t r o n i c s model CI-110 current The trip-meter  integrator  ( Eldorado E l e c t r o n i c s , Berkeley, C a l i f . ) .  pointer was set to f u l l scale before the runs with the  Long Counter were begun and was l e f t unchanged u n t i l a l l runs and the current  integrator c a l i b r a t i o n check had been completed. The current  integrator c a l i b r a t i o n on the range used during  the runs was checked using a 1.01902 (±0.01%) v o l t standard c e l l , and an accurately measured 5.0116 (±0.005%) ohm r e s i s t o r .  These gave an  input current of 0.20303 ya which was measured by the current for 52'' V , or 14 cycles of kS ycoulombs each.  Comparison of the input  charge and the charge integrated indicated the current read w i t h i n 1.25%.  integrator  integrator  to  X  k  HI  si  Q:  •A  U ,1  O  ft.  0  u  ft Jl s  •o  o  o  o  0  ^ 0.  •HI  o  k  0 it 0  \  1  i  Q a:  J '41 31  3  19 3.4.  Measurements The experimental arrangement was that shown in F i g . 3 (page 7),  the neutron source in t h i s case being the gas target. The pulses from the BF^ tube were amplified and analyzed as shown in F i g . 13  :  The l i n e a r i t y of the k i c k s o r t e r was checked, and the  window l i m i t s of the s i n g l e channel analyzer were set using a pulse generator which was able to produce pulses very the BF^ tube.  s i m i l a r to those from  These test pulses were injected with a 51 fl termination  at the p r e a m p l i f i e r test  input.  Using a 776 keV  deuteron beam of 250±20 nanoamps at the gas  c e l l from the U.B.C. Van de Graaff generator, a s e r i e s of 44 runs were made, each having a t o t a l c o l l e c t e d charge of 45 u c o u l . or 90 an even one or two c y c l e s of the current  integrator.  ycoul.,  For each run the  Long Counter was placed at a distance between 30 cm and 200 cm, measured from the front face of the centre p a r a f f i n region to the centre of the gas c e l l , and along one of two l i n e s drawn at 60° and 90° to the d i r e c t i o n of the incident deuteron beam in the gas c e l l . target was f i l l e d with 200  The gas  t o r r of e i t h e r deuterium or hydrogen, the  l a t t e r for background runs. Table 3 gives an o u t l i n e of the run schedule.  20 TABLE 3 Run Schedule Run 1 9  16 23  26  33 38 42  Long Counter Direction  Target Gas  8  15 22 25 32 37 41 44  The r e s u l t i n g spectra were punched on paper tape d i r e c t l y from the kick sorter memory and l a t e r converted to cards by the U.B.C. computing centre f o r use with a neutron peak integrating program.  A l l spectra  had the same c h a r a c t e r i s t i c shape shown in F i g . 4 . A short computer program was used to integrate a l l the s p e c t r a , with the bias set as shown in F i g . 4 , and the accumulated running time at the beginning of each run.  A beam-off run was made to determine the time dependent  room background.  A l l counts were corrected for k i c k s o r t e r dead time,  which only twice exceeded k%, and for time dependent background, which never exceeded 3% of the t o t a l count rate and was almost always considerably less than 3%. 3-5.  Background The accumulated time was used as a c l o c k to study the background  increase with time due to neutrons from deuterium build-up on the c o l l i m a t o r s and backstop.  The neutron counts remaining in the H, runs  21 a f t e r subtraction of the time dependent background represented the background due to deuterium contamination in the target chamber and c o l l i m a t i o n system.  These count rates were plotted against the ' c l o c k '  time of the midway point of the run, to produce a family of curves showing the background buildup with beam-on time at Long Counter distances of 30 cm, 50 cm, 75 cm, 100 cm, 130 cm, 150 cm, and 200 cm at 90°; and 35 cm, 75 cm, and 130 cm at 60°. Two of these curves were normalized to produce F i g . 14.  It can be seen that even a f t e r almost  3 hours with actual beam on t a r g e t , or 2385 ucoulombs of deuterium stopped in the gas c e l l , the neutron y i e l d due to build-up of deuterium on the surfaces shows no tendency to level- o f f as would r e s u l t from s a t u r a t i o n of the s u r f a c e s . will  The greatest portion of t h i s background  be from the backstop where most of the beam i s stopped. The  f a i l u r e to saturate is in agreement with a c a l c u l a t i o n based on a d i s c u s s i o n by J . H . Coon in Marion and Fowler (i960), which indicates that f o r the beam current and c o n f i g u r a t i o n , and the gold backstop used in t h i s experiment, a t o t a l charge of about 4200 ucoulombs would be c o l l e c t e d by the backstop before saturation became s i g n i f i c a n t . The o r i g i n a l curves f o r individual distances were used to read o f f the background seen by the Long Counter at a p a r t i c u l a r d i s t a n c e , angle and time.  These backgrounds were then subtracted from the  determine the count rate due to the target gas alone.  runs to To determine  the beam dependent background f o r runs at Long Counter distances where no background data was taken, suth as 100 cm at 90°, plots were made  22 of  B(d,t)  and at t,  2  , where B(d,t) is the background count rate at distance d  the mid-time of the run in question, versus the distance d.  Interpolation then gave the background at the desired d i s t a n c e s . 3.6„  Gas Target Thickness The thickness of gas traversed by the deuteron beam is defined by  the pressure and temperature of the gas in the beam region, and the geometrical distance between the entrance window and the backstop. The gas c e l l length was measured, using a t r a v e l l i n g telescope, to be 0.833 ( ±0.3% ) cm.  Thus, including the f o i l depression, the  beam path length was 0.845 ( ±0.5% ) cm. The gas pressure for a l l runs was 200 t o r r (±2%).  Any d i f f e r e n c e  between the meter pressure and the gas pressure in the beam region was corrected for by the e f f e c t i v e temperature c o r r e c t i o n . The temperatures measured on the backstop cooling f i n varied by ± 0.24% about an average of 295-2°K.  For the current  range  250 ± 20 nanoamps used in the runs, the temperature c o r r e c t i o n for gas heating in the beam region is 1.001 a l , 1961 ).  factor  ( ±0.1% ) ( Robertson et  This gives an e f f e c t i v e temperature in the beam region of  295-5 (±0.34%) ° K .  Using these parameters, N^, the number of target nuclei per square centimeter  in the gas c e l l was: N = ~° x L x £ t v K 0  x i > = 1.11 x 10 c  1  19  ( ±2.8% )  target nuclei / cm  2  23 where: L P  T  3.7.  Avagadro's number. Volume of one mole of gas at STP. Length of beam path in gas c e l l . Gas pressure. 760 t o r r . 273°K E f f e c t i v e temperature in beam region.  Beam Energy in the Gas C e l l A check of the Van de Graaff energy c a l i b r a t i o n indicated that  the meter read 3 keV h i g h , so that the meter energy reading of 776 keV used during the runs indicated a beam energy of 773 ( ±0.4% ) keV entering the f o i l window.  The f o i l window thickness was 138 ( ±2.3% ) keV  for 900 keV protons, which corresponds to a thickness of 228 ( ±3.6% ) keV for 773 keV deuterons ( page 683, Marion and Fowler, 1960 ).  Thus the  deuteron beam entered the gas c e l l with an energy of 5^5 ( ±2.0% ) keV. Deuterons of t h i s energy are slowed in deuteriom gas at the rate of -15 3.1 x 10  2 ev per gas atom per cm  (page 681, Marion and Fowler, i960 ).  Thus the approximate energy of the deuteron beam midway across the gas c e l l would be 528 ( ±2.1% ) keV.  R e c a l c u l a t i n g , using t h i s approximate  energy in the gas to determine a better average energy loss r a t e ,  the  beam energy midway through the gas was found to be 527 ( ±2.1% ) keV. 3.8.  Neutron Flux from the Gas Target The number of neutrons emitted from the target in the d i r e c t i o n  of the Long Counter can be c a l c u l a t e d using the reaction cross section for the appropriate angle and deuteron beam energy, the thickness of gas in the gas c e l l , and the number of deuterons incident on the target  2h  gas.  The average beam energy in the gas c e l l was found in section 3.7  t o be 527 ( ±2.1% ) keV.  Interpolating  o f F i g . 9, the d i f f e r e n t i a l  to t h i s energy using the curves  cross sections for the reaction D(d,n) He  a t 60° and 90° in the laboratory system were found to be 3.18 m i l l i b a r n s per sterradian and 3.03 respectively. 1.11 x 10  19  ( ±10% )  ( ±10% ) m i l l i b a r n s per s t e r r a d i a n ,  The gas target thickness was found in section 3.6 to be  2 ( ±2.8% ) target nuclei per cm .  during each c y c l e of the current be 45 ( ±1.25% ) ucoulombs.  The charge c o l l e c t e d  integrator was found, on page 18, to  Thus, during each c y c l e , the number of  deuterons entering the gas eel 1 was 45-ycoui  .1 N =  Zyi  d  1.6 x 10 = 2.81 x 10 The d i f f e r e n t i a l  :  y c o u l . / deuteron ( ±1.25% ) deuterons  cross section at angle 8 is defined as N N, x N d t  where:  N = Number of neutrons per sterradian emitted per integrator c y c l e at angle 0. = Number of deuterons incident orj the target per c y c l e . N^ = Number of target nuclei per cm .  Thus  N = a_ N . N . n 6 d t  In order to use the method described in section  2.3 to c a l c u l a t e the e f f i c i e n c y , the number of neutrons emitted by the reaction must be expressed as the number of neutrons emitted into 4TT sterradians by an i s o t r o p i c source.  In s p i t e of the f i n i t e s o l i d angle  subtended at the gas c e l l by the Long Counter, i t was found that the neutron energy and cross sect i o n ' v a r i e d l i t t l e across the s e n s i t i v e  25 region, so that no c o r r e c t i o n was necessary for the spread in angles due to the f i n i t e s i z e of the detector at 60° and 90°. was therefore s u f f i c i e n t l y  The  reaction  i s o t r o p i c over the range of angles included  by the counter at e i t h e r 60° or 90° that n in the effeciency c a l c u l a t i o n on page 10 could be expressed as n. = 0 Therefore  " n^  8 = 1.25 x 10  and  n  = 1.19 * 10  ATT  g  q Q  N = 4TT a. N , N n 0 d t  ( ±14% ) neutrons per integrator c y c l e emitted in a l l d i r e c t i o n s ( ±14% ) neutrons per integrator c y c l e emitted in a l l directions,,  Due to the geometry of the gas c e l l , at angles d i f f e r e n t from 90° the counter face w i l l  be p a r t i a l l y shadowed by the backstop.  When the Long Counter is at 60° to the d i r e c t i o n of the deuteron beam in the gas c e l l , 32.7% of the beam path length is shadowed by the backstop.  The neutrons emitted in the d i r e c t i o n of the Long Counter  by t h i s shadowed portion of the beam pass through an average of 0.276 cm of copper in the backstop. copper i s . 4 barns (  The total cross section for neutrons in  Hughes and Schwartz, 1958  the neutrons entering the backstop w i l l fractions, it  ), so that 9.2% of  be l o s t .  Combining these  is estimated that at 60°, 3.01% of a l l the neutrons  emitted into the s o l i d angle of the Long Counter w i l l backstop.  be l o s t in the  Applying t h i s c o r r e c t i o n to n ^ gives n ^ = 1.21 x 10  neutrons per integrator c y c l e , emitted in a l l  directions.  ( ±14% )  26 C a l c u l a t i o n of E f f i c i e n c y  3.9.  Following the procedure used in section 2.3 for the AmBe c a l i b r a t i o n , a plot was made of C  2  against the distance from the counter  face to the centre of the gas c e l l , where C is the number of counts per integrator c y c l e from the Long Counter.  The slope of t h i s p l o t , shown  in F i g . 15, was found to be S^ = 5-94 x 10~  5  Q  Counter at 60°, and S  = 6.3 x 10~  5  ( ±2.4% ) for the Long  ( ±2.8% ) for the counter at 90°,  and the corresponding e f f e c t i v e centres were found" to be at -10.3 ( ±7% ) cm and -12.6 ( ±9% ) cm, r e s p e c t i v e l y .  Both slopes  represent the region d^100 cm, as the room scattered neutron background becomes s i g n i f i c a n t beyond that p o i n t , as indicated by the d e v i a t i o n of the data from the inverse square law.  The e f f i c i e n c y was then c a l c u l a t e d  as  • E f f .6 =  where n  6  k  «  "71 •  is the number of neutrons emitted by the reaction in a l l  directions", assuming isotropy.  It was found in section 3.8 that  g  n^Q = 1.21 x 10  ( ±14% ) neutrons per c y c l e into 4TT assuming isotropy  and  n  ( ±14% ) neutrons per c y c l e into 4TT assuming isotropy  so that  Eff  - 1.19 x 10  q f )  =  6 Q  « x (V.?-* Y x 10-!° l  l o 2 1  x  10  = 29-4 ( ±19% ) counts per neutron per cm at the e f f e c t i v e centre 2  a n d  Eff  90  =  1.19 x 10 x U.30' ) x 10-^ y  2  = 26.6 ( ±20% ) counts per neutron per cm effective centre.  at the  27 The uncertainty on these e f f i c i e n c i e s would be considerably reduced by more accurate measurement of the d i f f e r e n t i a l  cross s e c t i o n s ,  which in t h i s c a l c u l a t i o n accounted for 10% of the 19% or 20% u n c e r t a i n t y .  _J  ,  !  1  3 A /-LTD S3-VOi/j'  1  1  „ 3> ^  ^  ll  fV &  S  —inj  / C7  VJ Oc  CHAPTER IV CONCLUSIONS In F i g . 16 the Long Counter e f f i c i e n c i e s are plotted against neutron energy.  The energy of the AmBe neutrons was determined from  F i g . 2 to be approximately 4.5 MeV.  The neutron energies produced  at 60° and 90° by the reaction D(d,n) He were interpolated from the 3  data of Fowler and B r o l l e y ( 1956 ) shown in F i g . 8, to be  F i g . 16 indicates considerable v a r i a t i o n of the e f f i c i e n c y of the modified Long Counter with energy.  This is due to the fact that  the larger diameter BF^ counter displaced a considerable amount of p a r a f f i n , thus reducing the amount of moderating material and leading to the loss of a higher proportion of high energy neutrons than with the smaller BF^ counter.  This reduction of p a r a f f i n would, on the other  hand, allow a higher proportion of those neutrons that have been thermalized to reach the BF^ tube and be counted.  F i g . 17 shows the  e f f e c t i v e centre p o s i t i o n plotted against neutron energy. Thus for a gain of an order of magnitude in e f f i c i e n c y for high energy neutrons, and even more for low energy neutrons, one has s a c r i f i c e d energy independence of the Long Counter.  This is acceptable,  however, as the neutron evergy spectrum is generally known in an experiment.  29 By modifying the o r i g i n a l counter, the old c a l i b r a t i o n was destroyed, but a f a c t o r of ten increase in e f f i c i e n c y was achieved and the modified counter has been c a l i b r a t e d to better accuracy than the o r i g i n a l „  BIBLIOGRAPHY Bramlett, R . L . , R . l Ewing, and T.W. Bonner, N u c l . I n s t r . Methods 9, 1 (1960). c  de Pangher, J . , and L . L . N i c h o l s , BNWL-260, P a c i f i c Northwest Laboratory, Richland, Washington, 1966. Fowler, J . L . , and J . E . B r o l l e y J r . , Rev. Mod. Phys. 28,112 (1956). Geiger, K.W., and A . P . Baerg, Can. J . Phys. 43,373 (1965). Hanson, A . O . , and J . L . McKibben, Phys. Rev. 72,673 (1947) Heiberg, S . A . , Ph D Thesis, U n i v e r s i t y of B r i t i s h Columbia, 1954. Hornyak, W . F . , Rev. S c i . I n s t r . 23,264 (1952). Hughes, J . D . , and R.B. Schwartz, Neutron Cross Sect ions, Brookhaven National Laboratory, Upton, New York, 1958. Hunter, G . T . , and H.T. Richards, Phys. Rev. 7_6, 1445 (1949). Marion, J . B . , and J . L . Fowler, Fast Neutron Physics Part Interscience Publishers I n c . , New York, i960.  I,  Robertson, L . P . , B . L . White, and K . L . Erdman, Rev. S c i . I n s t r . 32., 1405 (1961).  APPENDIX LONG COUNTER ELECTRON ICS A.1.  Proportional Counter Reuter Stokes, Model # RSN 44A  F i l l i n g Gas: BF^ (96% °B)  F i l l i n g Pressure: 70 cm Hg  Outside Diameter: 2 1/32 "  S e n s i t i v e Length: 12"  Operating Voltage: +2200 v  Maximum Voltage: +3500 v  1  Max. Neutron Flux:2.5x10  13  2 o n/cm sec Maximum Temperature: 150 C  12  Res stance: £ 10 A.2.  ft  Capacitance: 8 pf  E l e c t r o n i c s f o r AmBe C a l i b r a t i o n  D.C. Power Supply for Proportional  Counter:  Hewlett-Packard, Harrison 6I56A (Hewlett-Packard C o . , Palo A l t o , California) Preamplifier  PRO  CO  Input:  PORT/0£SRL_  UMT£~R  -Ih  /oo -o  - V W -  O U T P U T  -170  •+•'2 2.0 0 vr-  T  H  -O-  3 2  Preamplif i e r : Atomic Instruments, model 205 B (Atomic Instruments C o . , Cambridge, Mass.) Gain: 24  Limiting occurrs for input £ 0.2 v  Linear A m p l i f i e r : Atomic Instruments, model 204 C (Atomic Instruments C o . , Cambridge, Mass.) Input Time Constant: 7  Feedback: 1  Gain: 16 (x700 a m p l i f i c a t i o n ) 32 (x1200 a m p l i f i c a t i o n ) Output: High Level Kicksorter: Nuclear Data, model ND 101,  (Nuclear Data Inc.,  Palatine,  California)  A.3o  3  E l e c t r o n i c s for D(d,n) He C a l i b r a t i o n See F i g . 13.  Pulse Generator: B.N.C. model PB-2, (Berkeley Nucleonics C o . , Berkeley, C a l i f . ) Frequency: 10-100 cps  Fine Frequency: 10  Width: 1-10 usee  Fine Width: 0.0  P o l a r i t y : negative  Amplitude: 10-560  Attenuator:  Rise Time: 0.5 ysec  100  33 Linear  Amplifier: C . I . Linear A m p l i f i e r ,  model # 1410, (Canberra  Industries,  Middleton, Conn.) Input Mode: neg unterm  Integration: 1  Coarse Gain: 28  Fine Gain: 7  First Differentiation: 1  Second D i f f e r e n t i a t i o n :  Output: p o s . , u n i p o l a r ,  prompt  Kicksorter: ND-160 (Nuclear Data Inc.,  Palatine,  California)  Input: bipolar 10 v  Conversion Gain: 1024  Zero L e v e l : 8.0  Threshold:  Coarse Gain: external Experimental  1.0  amp Fine Gain: 0.0  Configuration:  IQ24  X  LOW  Single Channel Analyzer: C . I . Timing Single Channel Analyzer, model # 1435 (Canberra I n d u s t r i e s , Middleton,  Conn.)  Window Width: 0.94  B a s e l i n e : 0.31  V a r i a b l e Delay: 0.0  Input Mode: uni  Analyzer Mode: window  Output: f a s t  P r e a m p l i f i e r and Preamplidier See A . 2 .  Input:  off  

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