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The gamma rays of radium (B and C) Pearce, Michael 1949

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THE OF  GAMMA RADIUM  Michael  RAYS (B + C)  Pearce  Thesis Submitted i n P a r t i a l F u l f i l l m e n t o f the Requirements  f o r t h e Degree o f  Master o f A r t s i n t h e Department o f P h y s i c s  - 3 -  ABSTRACT: Several tics  of  counting  spectrometer concile  the  transitions been  met  are  small  new  techniques  peaks  presented.  on  large  These i n  in  1.02  with.  (B  +  0)  above  improving the  backgrounds  arose  c o n f l i c t i n g reports Ra  for  the  from an  Some  a  beta-  attempt  l i t e r a t u r e  Mev.  i n  s t a t i s -  of  to  gamma-  success  has  re-  - 1 -  ACKNOWLEDGMENT: T h i s work was c a r r i e d o u t u n d e r a G r a n t - i n - A i d o f R e s e a r c h t o D r . K.C. Mann f r o m t h e N a t i o n a l R e s e a r c h C o u n c i l . The  a u t h o r would l i k e  t o acknowledge  theNational  Research  C o u n c i l S c h o l a r s h i p w h i c h made t h e i n v e s t i g a t i o n p o s s i b l e . The B r i t i s h C o l u m b i a  I n d u s t r i a l Research Council k i n d l y  a 5 0 0 mc, r a d i u m s o u r c e a t o u r d i s p o s a l . would l i k e  t o acknowledge  placed  L a s t l y , the author  t h e c o n t i n u e d a s s i s t a n c e o f D r . K. C.  Mann, w i t h o u t whose i n t e r e s t t h e p r o j e c t c o u l d n o t h a v e b e e n undertaken.  - 2 -  TABLE OF CONTENTS: Acknowledgment  Page  1  Contents  2  Abstract  3  Introduction  4  E x p e r i m e n t a l T e c h n i q u e s <(1)  The S p e c t r o m e t e r  5  The G e l g e r C o u n t e r  5  (iii)  The S o u r c e  9  (iv)  The C u r r e n t R e g u l a t o r  9  (v)  The C o u n t i n g E q u i p m e n t  10  ,(ii)  Results  10  Conclusions  13  Bibliography  14  -  4-  -  INTRODUCTION; A l e c h a n o v and L a t y s h e v  1  using internal  pair  p r o d u c t i o n r e p o r t , e l e v e n g a m m a - l i n e s o f RaB a n d R a C V o f  energy  more t h a n 1.02  report  six  Mev.  lines i n this region.  techniques.  The  m e t e r and 10 mc. thin  latter o f Ra  Ellis  used i n t e r n a l c o n v e r s i o n  group used a t h i n l e n s b e t a - s p e c t r o (B -f C) w i t h a l e a d r a d i a t o r  l e a d l a m i n a as a source o f p h o t o e l e c t r o n s . ) *  500 mc. the  E l l i s ? a n d Mann a n d O z e r o f f ^ e a c h  s o u r c e o f Ra  (i.e.  a  Because  a  (B + C) h a s s i n c e b e e n made a v a i l a b l e  B r i t i s h C o l u m b i a R e s e a r c h C o u n c i l , t h e s p e c t r u m has been  r e p e a t e d i n an a t t e m p t t o c o n f i r m t h e w o r k o f A l e c h a n o v Latyshev. the  by  and  T h i s h a s b e e n done i n a t h i n l e n s s p e c t r o m e t e r o f  t y p e d e s c r i b e d by D e u t s c h , E l l i o t t ,  and Evans^.  The  spec-  t r o m e t e r i s shown i n F i g . / a n d i s shown s c h e m a t i c a l l y i n Fig.  7 . A r e d u c t i o n o f background  count t o improve  the  c o u n t i n g s t a t i s t i c s has been a t t e m p t e d i n t h e f o l l o w i n g ways: (i)  C o i n c i d e n c e c o u n t e r s w e r e c o n s t r u c t e d so a s t o count o n l y those p a r t i c l e s which e n t e r e d the c o u n t e r window i n t h e p r o p e r d i r e c t i o n fined  (ii)  by t h e s p e c t r o m e t e r b a f f l e s ,  E x t r a l e a d was  added t o b a f f l e  A  as  de-  ( s e e F i g . 2)  ( s e e F i g . 7)  a t t h e s o u r c e end t o r e d u c e t h e b a c k g r o u n d  from  Compton e l e c t r o n s . ( i i i ) Compton e l e c t r o n s p r o d u c e d i n t h e s o u r c e c o n -  - 5 t a i n e r made a l a r g e c o n t r i b u t i o n t o t h e b a c k g r o u n d c o u n t . attempt  An  was made t o d e f l e c t t h e s e e l e c t r o n s away f r o m t h e l i n e  o f f o c u s e d e l e c t r o n s b y means o f a magnet p l a c e d b e t w e e n t h e source  c o n t a i n e r and r a d i a t o r .  EXPERIMENTAL TECHNIQUES: (1)  The S p e c t r o m e t e r , The s p e c t r o m e t e r  t y p e d e s c r i b e d by D e u t s c h ,  ( s e e F i g s . 1 a n d 7) u s e d was o f t h e t h i n  Elliot  and Evans.  The  lens  spectrometer  t u b e was 4 0 i n c h e s i n l e n g t h a n d 8 i n c h e s i n d i a m e t e r . aligned parallel  t o the magnetic meridian i n order that t h e  h o r i z o n t a l component o f t h e e a r t h ' s f i e l d the b e t a - p a r t i c l e s . field  The v e r t i c a l  should not defocus  component o f t h e e a r t h ' s  was e l i m i n a t e d b y p a s s i n g a c u r r e n t t h r o u g h  Helmholtz  c o i l s above and b e l o w t h e s p e c t r o m e t e r ,  horizontal ( s e e F i g . 1)  The magnet c o n s i s t s o f f o u r w a t e r c o o l e d ( s e e F i g . 7) used.  I t was  In this  coils,  spectrum o n l y t h e three o u t e r c o i l s  T h i s has t h e advantage o f l o w e r i n g t h e s p h e r i c a l  were  aber-  r a t i o n and thus i n c r e a s i n g t h e r e s o l u t i o n . (ii)  The G e i g e r In  Counter.  t h e o p e r a t i o n o f any c o u n t e r  where i t i s d e -  s i r e d t o measure a c o u n t i n g r a t e N w h i c h i s s u p e r i m p o s e d upon a background counting r a t e N ^ ^ , i t i s apparent  t h a t two s e p -  a r a t e m e a s u r e m e n t s b e made - t h e t o t a l  N^Q^Q^.  a c  count and  Ni s  then o b t a i n e d by s u b t r a c t i o n . Thus N = N  t  o  t  a  l  + Nback  (1)  I t f o l l o w s that t h e standard d e v i a t i o n of N i s CT and  = ( T t o t a l + <T back ,  2  2  assuming a Poisson <T =  2  distribution  V t o t a l t Nback  , and from (1)  N  = V N b a c k +• N  (2)  2  To r e d u c e OTand accuracy  i t was n e c e s s a r y  thereby  t o reduce N  D a c  improve t h e s t a t i s t i c a l k.  T h i s was accomp-  l i s h e d b y two c o u n t e r s o p e r a t i n g i n c o i n c i d e n c e so a s t o r e cord only focussed beta-rays.  The a r r a n g e m e n t i s shown i n  Fig.  are cut i n brass  2.  The two c o u n t e r  a n g l e s t o one a n o t h e r  tubes  stock at right  and t o t h e a x i s o f t h e s p e c t r o m e t e r  tube.  The h o l e b e t w e e n c o u n t e r s a n d t h e m i c a window l a y on t h e a x i s of the tube.  Maximum t r a n s m i s s i o n was o b t a i n e d b y f o c u s s i n g  on t h e w i r e o f c o u n t e r No. 2. Kovar-glass tubes.  s e a l s were u s e d t o p l u g t h e c o u n t e r  No. 4 0 c o p p e r w i r e was t h r e a d e d  f o r t h e anode.  mg./cm? m i c a window was s e a l e d w i t h P l i c e n e c e m e n t . tional  A conven-  f i l l i n g o f 9 cm. o f a r g o n a n d 1 cm. o f a l c o h o l was u s e d .  Each counter than  A 2.5  e x h i b i t e d a 100 v o l t p l a t e a u w i t h a r i s e o f l e s s  0.2^ p e r v o l t .  However, t h e e f f i c i e n c y o f t h e c o u n t e r s  went down s e v e r a l p e r c e n t  i n a few hours o f o p e r a t i o n at a  c o u n t i n g r a t e o f 10,000 p e r m i n u t e .  T h i s was t h o u g h t t o r e s u l t  -  from the r e l a t i v e l y tubes.  7  -  s m a l l volume o f a l c o h o l a v a i l a b l e i n t h e  H o w e v e r , when a s i m i l a r c o u n t e r was o p e r a t e d w i t h a  c o u n t i n g g a s r e s e r v o i r , t h e same b e h a v i o u r was o b s e r v e r e d . T h i s suggests t h a t t h e i n s t a b i l i t y I s a cathode e f f e c t , and some e v i d e n c e t o s u p p o r t t h i s v i e w was o b t a i n e d b y t h e w r i t e r at  the Chalk R i v e r l a b o r a t o r i e s o f the N a t i o n a l  Research  Council. A t e s t was c o n d u c t e d t o i n s u r e  that the opera-  t i o n o f one t u b e was i n d e p e n d e n t o f t h e o p e r a t i o n o f t h e o t h e r . The  possibility  e x i s t e d t h a t when one t u b e r e c o r d e d an i o n i z -  ing  e v e n t , t h a t a photon from t h e e l e c t r o n a v a l a n c h e i n t h i s  tube should pass t h r o u g h t o t h e second tube, c a u s i n g a s p u r i ous c o u n t .  T h i s was I n v e s t i g a t e d b y o b s e r v i n g t h e c o u n t i n g  r a t e o f t u b e No. 1 w i t h t h e v o l t a g e o n a n d w i t h t h e v o l t a g e off ical  t u b e No. 2 ( i . e .  w i t h a n d w i t h o u t No. 2 c o u n t i n g . ) .  Typ-  f i g u r e s f o r t u b e No. 1 w e r e 1 8 2 4 ( s . d . = 6 ) c o u n t s p e r  m i n u t e w i t h t u b e No. 2 o f f a n d 1882 ( s . d . = 8 ) c o u n t s p e r m i n ute  w i t h t u b e No. 2 r e c o r d i n g 3 0 0 0 c o u n t s p e r m i n u t e .  ing  t h a t t h e c h a n g e i n r g t e o f 58 comes f r o m t u b e No. 2, we  Assum-  may s a y t h a t 2% o f t h e a v a l a n c h e s s p r e a d f r o m t u b e No. 2 t o t u b e No.  1. The u s e o f t h e c r o s s e d c o u n t e r s i n c o i n c i d e n c e  a s c o m p a r e d t o t h e u s e o f t u b e No. 2 b y i t s e l f was f o u n d t o r e duce t h e background  count by a f a c t o r o f n i n e .  A t t h e same  t i m e h o w e v e r , t h e n e t c o u n t was r e d u c e d b y a f a c t o r o f t h r e e .  /  - 8 -  The c h a n g e I n t h e s t a t i s t i c a l a c c u r a c y , w h i c h c o u n t i n g r a t e s b r i n g about,  i s investigated  C o n s i d e r ^/fras  these, two  new  below.  a f i g u r e o f m e r i t , where  0~"ls  t h e s t a n d a r d d e v i a t i o n o f t h e n e t c o i n c i d e n c e c o u n t N. <T and  - V N  N  therefore  ^/N  Let  t  o  t  a  Since  + Nback  l  -  Ntotal+ N  = V  N +2Nb ck  D a c  k  »  /N.  a  t h e net count  f o r t h e s i n g l e c o u n t e r be Nt?,  and l e t t h e b a c k g r o u n d f o r t h e s i n g l e c o u n t e r b e N o a c k . putting N  1  - 3N a n d Nfeack  s  9N  D A C  Then  ^ we o b t a i n f o r t h e s i n g l e  counter  <VN« = V N « 4 2 N V^N  88  +  b  l 8 N  a  c  b  /N«  k  a  c  k  ,.  /3N  (3)  where XT i s t h e s t a n d a r d d e v i a t i o n o f N'. Examination  <*7N  <  shows t h e r e i s no N  <T/N'.  T h a t i s , no b e t t e r s t a t i s t i c s t h e two c o u n t e r s ' . N  r  sueh- t h a t  1  a r e o b t a i n a b l e from  the use o f  However i f i t w e r e t h a t =  2 N ,  '  then o b v i o u s l y  " -  <?7N <°7N*  fora l l N^5N  b  a  c  k  .  So t h e e f f i c i e n c y o f t h e c o i n c i d e n c e for  f o c u s s e d e l e c t r o n s must be s l i g h t l y  istics  a r e t o be i m p r o v e d .  counters  increased i f the s t a t -  T h i s m i g h t be a c c o m p l i s h e d b y  c a r e f u l f o c u s s i n g and b e t t e r c o l l i m a t i o n .  I f the counting  more  -  9  -  l o s s e s w e r e due t o s c a t t e r i n g i n t h e window, t h i n n e r  mica  might improve t h e e f f i c i e n c y . ( i i i ) The  Source.  The 500 mc. r a d i u m s o u r c e was i n a s i l v e r  con-  t a i n e r whose w a l l s were o f s u f f i c i e n t t h i c k n e s s t o s t o p t h e primary beta-rays.  An a t t e m p t t o s e p a r a t e t h e Compton  elec-  t r o n s o f t h e c o n t a i n e r f r o m t h e gamma-rays b y means o f a s t r o n g p e r m a n e n t magnet was made.  The gap o f t h e m a g n e t ,  w h i c h h a d a f l u x o f 1,500  g a u s s , was p l a c e d b e t w e e n t h e l e a d  r a d i a t o r and t h e s o u r c e .  I t was n e c e s s a r y t o s h i e l d t h e s p e c t -  r o m e t e r t u b e f r o m t h e p e r m a n e n t magnet b y a n i r o n perpendicular to the axis of the spectrometer.  sheet p l a c e d  T h i s s h e e t had  a 5/16 i n c h h o l e o p p o s i t e t h e l e a d r a d i a t o r , w h i c h was inches i n diameter.  3/16  H o w e v e r , t h e magnet was u n a b l e t o remove  b e t a - p a r t i c l e s s c a t t e r e d from the p o l e f a c e s and from the i r o n sheet, w i t h the r e s u l t t h a t t h e background  was n o t s u c c e s s f u l l y  eliminated. The b a c k g r o u n d was v e r y e f f e c t i v e l y r e d u c e d b y e n l a r g i n g t h e b a f f l e a t t h e c o u n t e r end o f t h e s p e c t r o m e t e r "tube a n d b y b e t t e r c o l l i m a t i o n a t t h e s o u r c e e n d , (iv)  The C u r r e n t R e g u l a t o r . The magnet c u r r e n t was r e g u l a t e d i n a c o n v e n t i o n -  a l manner b y p a s s i n g i t t h r o u g h 38 t w i n t r i o d e s parallel,  ( s e e F i g . 3)  (6AS7's) i n  A s i g n a l i s t a k e n from a c o n s t a n t r e -  -  10  -  s i s t a n c e I n t h e magnet c i r c u i t , D.  C.  (see P i g . 4 )  amplifier,  g r i d s of the 6AS7's.  onto the  a m p l i f i e d by  an A.  then a p p l i e d 180° The  C.  out  and  of  i n p u t o f t h e D.C.  a  phase  is a  Brown c o n v e r t e r w h i c h d e t e c t s t h e d i f f e r e n c e b e t w e e n t h e nal  and  may  be  a potentiometer  voltage.  cheeked a g a i n s t a standard (v)  s e t t i n g ;.  cell.  done w i t h t h e  i n s e c t i o n ( i i ) and  A conventional an  potentiometer  Counting Equipment. C o u n t i n g was  described  The  sig-  counter  a regulated high tension  c a t h o d e f o l l o w e r was  " A t o m i c " s c a l e r and  coincidence  set.  used i n conjunction  a p r e a m p l i f i e r , (see F i g .  with  5)  RESULTS: The u p p e r c u r v e was  taken  of photoelectrons from the rometer.  curves  obtained  shown i n F i g . 6.  w i t h t h e l e a d r a d i a t o r and  i s the  The sum  f r o m t h e l e a d r a d i a t o r , Compton e l e c t r o n s  s o u r c e h o l d e r , and The  are  e l e c t r o n s scattered i n the  l o w e r c u r v e was  taken  without  the l e a d r a d i a t o r .  The  0 , 6 0 7 Mev  The  r e s u l t s appear i n Table I together  g a m m a - l i n e was  spect-  used  for.calibra-  tion.  r e s u l t s of E l l i s , shev.  Mann and  I t s h o u l d be  r e p o r t e d by  Ozeroff,  noted that the  Alichanov  and  and  with  o f A l e c h a n o v and  gamma l i n e o f e n e r g y  L a t y s h e v has  been c o n f i r m e d .  the  Laty1.52 The  11  v a l u e o b t a i n e d was 1.54 Mev. Mev may b e t h e 1.82 Mev l i n e  A faint  l i n e detected  a t 1.94  r e p o r t e d b y A l e c h a n o v and L a t y -  shev. The gamma l i n e r e p o r t e d a t 0.448 Mev b y Mann • and O z e r o f f  has n o t been  found.  N o t e t h a t i n t h e r e g i o n b e l o w 1.02 Mev, l i n e s r e p o r t e d a t 0.498 Mev a n d 0.933 Mev b y E l l i s a t 0.511 Mev a n d 0.950 Mev r e s p e c t i v e l y .  have been  found  - 12 TABLE I GAMMA Ellis  0.0529 0.2406 0.8571 0.2937 0.3499 0.4260 0*4980 0.6067 0.766 0.933 1*120 1*238 1.379 1*414  1.761 2.193  LIMES  OF  RADIUM  • • • • •  • •  • •  • • • • • • * • •  • • • • • • • • • • • • •  0.606 0.766 • 0.933 • 1.11 • 1.120 • 1.21 (23). 1.234 • • 1.370 • • 1.39 ( 4 9 ) . 1.414 • • 1.52 (29). 1.62 (22). 1.69 ( 1 7 ) . 1.75 (100). 1.761 • • 1.82 ( 1 7 ) . 2.09 (15). 2.20 ( 4 1 ) . 2.40 (21).  Mann a n d Pearce  Mann a n d Ozeroff  Alechanov and L a t y s h e v • • * • •  I N MEV.  .. .. .. .. 0.291 . . . . . . . .  •  •  • • •  • <• •  • •  • •  0.352 0.426 ( 9 ) . 0.450 ( 4 ) . 0.496 ( 1 4 ) . 0.607 (74). 0.781 (13).  ... ..1.12 .. . 1.22  (9). (24). • •  • •  • •  • •  • •  • • * •  • • • •  • • • •  • • • •  • • • •  • •  • • •  • • •  • • •  • • •  . 1.40  (23).  . 1.77 (100).  . 2.21 . 2.40  Figures i n parentheses a r e r e l a t i v e  (25). •  • • •  • • •  • • •  •  •  •  • •  • •  • •  •  •  •  •  t  •  . . . . . . . .  0.283 0.351 0.425 0.483 0.511 0.697 0.780 0.950  . 1.12 . 1.22  . . . . 1.54 .1.38  . . .  . 1.79 .1.94 •  •  •  . 2.23  •  intensities.  - 13 -  CONCLUSIONS: The p r e s e n t i n v e s t i g a t i o n h a s I n d e n t i f i e d  gamma  r a y s w h i c h a r e i n agreement w i t h t h e o v e r a l l p i c t u r e o f E l l i s . One,  and p r o b a b l y two, l i n e s o f A l e c h a n o v  to unconfirmed  have been  found.  and L a t y s h e v  hither-  - 14  -  BIBLIOGRAPHY: 1.  A l e c h a n o v , A., a n d L a t y s h e v , G. D., s c i . U . S. S. R. 2 0 : 2 4 9 .  Compt. r e n d . a c a d .  1948.  P r o c . R o y . S o c . ( L o n d o n ) , A , 143:350.  2.  Ellis,  3.  Mann, K. C , a n d O z e r o f f , M. J . , C a n . J o u r , o f R e s . , A , V o l . 27, p. 164. 1949.• D e u t s c h , M., E l l i o t t , L. G., a n d E v a n s , R . , R e v . S c i . I n s t r u m e n t s , 15:7. 1944.  4.  CD.,  1934.  -  15  -  Fig.  1  The Thin Lens Beta Spectrometer  - 16 -  - 17 -  4 v -  <>  n  W W  -18 -  Fig. 4  -  1 9  -  ^ 1  9 •^T-JJ  - OS  -  MAGNETIC  WATER  

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