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On the decay scheme of ZN"65" Rankin, David 1949

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65  ON THE DECAY SCHEME OP ZN by David Rankin  A thesis submitted i n p a r t i a l f u l f i l m e n t of the requirements f o r the degree of MASTER OF ARTS i n the Department of PHYSICS  The University of B r i t i s h Columbia September 1949.  ABSTRACT  65 The r a d i a t i o n from Zn thin lens beta ray spectrometer.  has "been investigated i n a A s p i r a l b a f f l e was used  to discriminate between positrons and negatrons.  Gamma ray  energies of 1.12 and 1.4 mev have been measured as well as . a n n i h i l a t i o n radiation of .51 mev.  A positron end point at  .32 mev has also been measured. F a i r l y intense Internal conversion was found. A decay scheme has been proposed i n 65 which Zn decays by K-capture to a 1.4 mev excited state from which i t proceeds to an Intermediary state by emission of a gamma ray.  The a l t e r n a t i v e positron emission i s to the  intermediary stage from which both paths descend to the 65 ground state of Cu ray.  with the emission o f a 1.1 mev gamma  ACKNOWLEDGEMENTS  This study has been made possible through the Grants-in-AId-of-Research to Professor K. C. Mann from the  65  National Research Council, as well as the loan of the Zn source, without which so detailed a study would have been impossible.  The award of a bursary and.a summer scholarship  to the author have also greatly f a c i l i t a t e d t h i s work. The author wishes to express h i s deep gratitude to Professor K. C. Mann f o r h i s guidance and encouragement during the progress of t h i s research.  TABLE OF CONTENTS I.  Page 1  INTRODUCTION  I I . APPARATUS AND PROCEDURE Spectrometer Current Regulator Geiger Counter Amplifier Compensating C o i l s Source Arrangement Calibration.. S t a t i s t i c a l Accuracy... I I I . RESULTS Negatron Spectrum Positron Spectrum Gamma-ray Spectrum  -  A 4 8 8 10 11 11 12 12  *  13 13 13  ,  13  IV.  CONCLUSIONS  18  V.  BIBLIOGRAPHY  20 TABLE OF ILLUSTRATIONS  Figure 1 2 3 A 5 6 7 8 9  Spectrometer Complete Assembly Spiral Baffle Geiger Counter Source Arrangement Negatron Spectrum Positron Spectrum Fermi Plot Gamma-Ray Spectrum  5 5 7 9 9 15 16 16 17  (1) INTRODUCTION  Zn  65  i s an a r t i f i c i a l l y radio-active isotope which  has been investigated by various methods.  This isotope has  been produced by the following reactions: Zn Cu Cu Zn  64  64 65 64 65  Ga  65  (d,p) Zn  '  65  (d,2n) Zn  65  (p,n) Zn  65  (n,y) Zn  65  (K-capture) Zn  A good deal of confusion attended the e a r l i e r invest i g a t i o n of the Cu-Zn-Ga compounds which were produced i n the cyclotron by deuteron bombardment. Livingood ^  reporting on one such element,  suggests the p o s s i b i l i t y of a Zn isotope decaying through positron emission with a h a l f - l i f e of 12 hrs.  This was un-  doubtedly one of the short l i f e a c t i v i t i e s which i s found i n conjunction with Zn a c t i v i t i e s . (2) P e r r i e r , Santangelo, and Segre  v  ' report, on t h e i r  examination of the f i l i n g s from the copper d e f l e c t i o n plate of the Berkeley Cyclotron, the existence of a 245 day h a l f l i f e a c t i v i t y . They do not a t t r i b u t e t h i s to Z n ^ s i n c e they quote Livingood »s 12 h r . h a l f - l i f e a c t i v i t y as being Z n ^ . Barnes and Valley(3) report an a c t i v i t y produced i n Cu by proton bombardment with a h a l f - l i f e of approximately  (2) 210 days.  They suggest a positron and negatron emission i n  the r a t i o of 2:1.  There i s also a strong gamma radiation  with a gainma to beta r a t i o of 60 to 1. The maximum energy of the Beta group i s .7 mev as indicated by i t s absorption i n aluminum. Delsasso et alUO report on a C u ^ (p,n) Zn*-' decay 1  with both positron and negatron a c t i v i t y i n addition to strong gamma r a d i a t i o n .  They suggest that the decay Is Zn 5  Cu 5  6  6  The f a i r l y intense X radiation i s attributed to both i n t e r n a l conversion of the gamma rays and K-capture with the negatrons due e n t i r e l y to i n t e r n a l conversion. Livingood and Seaborg (5), using the reaction Zn  30 and  D +" 1 6 4  Cu 5  -H  6  2  Q  and either ^ or  2  Q  +  Cu 5 6  Cu63  +  + l D  Zn H 3 0 + 1  2  6 5  Zn * ^ n 6  1 3  0  ^ 2  ^  1  Zn * ^ n 6  z-65  3 Q  1  +  1  -  suggest the decay as both 30 and 3 Z n 0  250 days.  6 5  Z n 6 5  + e~  29 29  C u 6 5  C u 6 5  ^' w  i  t  h  a  t  o  t  a  l  h a l f - l i f e of  They point to the small number of p a r t i c l e s as  compared to gamma-rays as evidence of the existence of Kcapture as an alternative to positron emission.  From a con-  sideration of positron and gamma-rays i n equilibrium, the  (3)  i o n i z a t i o n produced by the positron rays should be approximately t h i r t y times as great i s that produced by the gamma radiation.  Livingood and Seaborg f i n d however, that the  gamma-radiation produces the greater part of the i o n i z a t i o n . This demonstrates the predominance of K-capture as the mode of decay.  From absorption measurements i n Pb, a high i n t e n s i t y  gamma-ray with an energy o f 1.0 mev together with an inappreci a b l e amount of .5 mev a n n i h i l a t i o n radiation tends to confirm the low rate of positron emission to K-capture. Alvarez(6)measured the absorption of the x-rays produced i n t h i s reaction.  From a comparison of absorption  i n n i c k e l and copper he deduced that the x-rays were the characteristic C u ^ lines. Sagane et a l ^ u s i n g cloud chamber measurements have found end points f o r positron emission of .39 and .19 mev.  These upper l i m i t s were calculated from K.U. p l o t s . Watase et alWhowever, found a single positron  with an end point of .47 mev and f a i r l y intense gamma radi a t i o n of 1.0, .65, and .A5 mev i n the r a t i o s approximately 1:1:1. Deutsch, Roberts and E l l i o t t ^ ) r e p o r t on Zn^5 with a h a l f - l i f e of 250 days, and give a gamma-ray energy of 1.1A to better than 1%. Good and Peacock (10).  using a c a l i b r a t e d gamma-ray counter, measured X-gamma and positron-gamma  coincidences.  They found that 5A% of K-capture occurs i n the ground state and A6# i n the I.I4 mev excited state; also that 2.2% of the  U)  t r a n s i t i o n s are by positron emission d i r e c t l y to the ground state of Cu 4. 6  W. C. P e a c o c k r e p o r t s a positron end point of .320  mev. Jensen, L a s l e t t , and P r a t t C ) using a high r e s o l 1 2  ution beta-ray spectrometer, give a corrected value f o r the gamma-ray energy of 1 . 1 1 mev as measured from the photo-elect-, rons ejected from a t h i n lead radiator. D a y k i n ^ ^ , using the same thin lens spectrometer as 1  the present investigator, found a gamma-ray energy of  1.11  mev as measured from the photo-electric peak i n both lead and uranium and a positron end point of .32 mev.  Since t h i s work  was done with a source of very low s p e c i f i c a c t i v i t y i t was deemed a t t r a c t i v e to repeat t h i s investigation, using a stronger source with a view to a more detailed study of Zn ^ 6  activity.  APPARATUS AND EXPERIMENTAL TECHNIQUE Spectrometer The spectrometer used i n t h i s research i s of the "thin lens" type introduced by Deutsch, E l l i o t t and Evans A l i n e diagram i s shown i n f i g . 1 and a photograph of the complete assembly i n f i g . 2 . evacuated brass tube 8  n  The spectrometer consists of ah  i n diameter and A0  n  long, with a short  F i g u r e 2 - Complete  Assembly  (6) magnetic c o i l wound around i t s c e n t r e s e c t i o n .  A system o f  b a f f l e s d e f i n e s the t r a j e c t o r i e s o f the p a r t i c l e s from the source.  These p a r t i c l e s a r e bent through a s p i r a l bath t o  focus a t the window o f a b e l l - t y p e Geiger c o u n t e r . c e n t r e b a f f l e , which i s shown i n f i g . 3, e i t h e r p o s i t i v e or negative  The  i s designed to  b e t a p a r t i c l e s from passing  the spectrometer, depending on the d i r e c t i o n of the which i s passed through the f o c u s s i n g c o i l s . have shown t h a t the p i t c h i s almost constant having d i f f e r e n t r a d i i . t h i s b a f f l e has  through  current  Deutsch e t a l (U) for trajectories  In t h e course o f the present  research  proven t o be most e f f i c i e n t i n the e l i m i n a t i o n  o f the e l e c t r o n s of the o p p o s i t e  sign.  Daykin (12).  r e p o r t s a 25%  stop  l o s s in:-the counting  however,  r a t e of the d e s i r e d s i g n o f  e l e c t r o n s w i t h the s p i r a l b a f f l e , probably due  to too l a r g e a  pitch. The which may  magnet c o i l i s made up  i n four c o - a x i a l layers  be used i n d i v i d u a l l y or i n s e r i e s .  It i s easily  shown t h a t the s i g n of the g r a d i e n t of the f i e l d i n the r a d i a l d i r e c t i o n Is o p p o s i t e momentum d i s c r i m i n a t i o n .  to t h a t r e q u i r e d f o r the  T h i s e f f e c t can be minimized  best by  u s i n g o n l y the outermost l a y e r of the c o i l , which o f course r e q u i r e s much h e a v i e r  currents.  Therefore  a compromise must  be made between the c o n s i d e r a t i o n of f o c u s s i n g and i e n c e o f c o v e r i n g an ample range o f momenta. o n l y the two  outermost s e c t i o n s were u t i l i z e d .  the  conven-  In t h i s work  (7)  (8) Current Regulator Only those p a r t i c l e s , t r a v e l l i n g i n the correct d i r e c t i o n , with momenta such that they w i l l he focussed at the counter window, w i l l satisfy, the focussing conditions determined .by the strength of the magnetic f i e l d of the focussing magnet.  Since there Is no ferro-magnetic material  i n or near the spectrometer the strength of the f i e l d  will  be d i r e c t l y proportional to the current through a standard manganin resistance of approximately .08 ohms i n series with the c o i l .  The voltage drop across t h i s resistance i s compared  to the voltage set on a Rubicon Potentiometer and the unbalanced voltage used to drive the current s t a b i l i z e r described by Lindenfeld, Mathews, Ozeroff and Daykin(H).  Geieer Counter The t h i n window Geiger Counter shown i n f i g . 4 was designed i n t h i s laboratory to eliminate as much as possible the use of wax s e a l s .  The only wax used i s the very t h i n layer  which seals the mica window between the brass flanges. copper anode i s f " i n diameter.  The  The .005" tungsten anode wire  i s hard soldered to an advance wire which i n turn i s soft soldered to the top end of the Kovar seal through which i t projects and which i n turn Is soldered to the top of the metal outer case of the counter.  A short section of Nonex glass tube i s fastened  to the glass sleeve of the Kovar seal which i s then soldered upside down onto the outer case of the counter.  This assembly  (9)  Figure  GEIGER COUNTER  4  BRASS CASING  FILUNG TUBE  COPPER ANODE MICA _ WINDOW  ADVANCE  FLANGE*  Figure 5  F i g u r e 5(b)  URANIUM RADIATOR -SOURCE  -SOURCE  BRASS ABSORBERS  FOR  ELECTRONS  FOR  GAMMAS  (10) i s used to f i l l the counter and the glass tube Is then sealed off,  thus eliminating the use of a stopcock and the possible  leakage thereof.  The 2.8 mg/cm  mica window i s sealed to the  base of the counter with Plicene wax which has been dissolved i n b o i l i n g turpentine and peinted onto the brass flanges. The counter was f i l l e d with 1.5 cm. of alcohol and 8.5 cm. of argon.  Amplifier The arrangement of the laboratory required the use of a ten foot cable to carry the counter pulses to the amplifier.  To avoid the loading of the counter by the cable, a  cathode follower i s used to feed the pulses through the cable Into the a m p l i f i e r . A matching resistance of 100 ohms Is used at the putput end of the cable.  Amplifier i s a two-stage  grounded g r i d triode type preceded by a cathode follower.  The  pulse i s s u f f i c i e n t l y amplified by the f i r s t stage to saturate the second stage and provide 60 v o l t pulses of equal amplitude for  the s c a l a r .  This amplitude of pulse allows a scalar d i s -  crimination bias of 15 v o l t s which i s quite s u f f i c i e n t to eliminate most of the counts due to stray pickup, while at the same time keeping the counting rate completely  independent of  discriminator bias f l u c t u a t i o n s . The plateau obtained  with  t h i s c i r c u i t and the counter described above has been s a t i s f a c t ory and has remained stable over the whole period during which t h i s research has been c a r r i e d out.  (11) Compensating  Coils  The horizontal component o f the earth's magnetic f i e l d is,compensated f o r by a pair of Helmholtz c o i l s wound on a frame about the spectrometer table.  The current i s  regulated against l i n e voltage variations by the use of two b a l l a s t tubes i n series with the 10 ohm c o i l s .  The excess  of the normal 1.7 amps above the required .94 amps i s shunted through a rheostat.  This regulation i s s u f f i c i e n t to care f o r  normal hour to hour l i n e voltage f l u c t u a t i o n .  Source  Arrangement The 1 m i l l i c u r i e Zn ? source was produced by slow 6  neutron i r r a d i a t i o n i n the Chalk River p i l e of a sample of pure Z n * i n the form of a thin square f o i l , 25 mg/cm . 6  2  This form  of a source was most adaptable f o r the various types of investigation which were required i n t h i s research.  For counting  positrons and negatrons the source was fastened to a 2 mg/cm  2  mica backing as i l l u s t r a t e d i n f i g . 5a. For counting the photoelectrons ejected from a uranium radiator, the source was fastened to one side of a 1/16" thick brass plate with the uranium radiator of 90 mg/cm on the other side. 2  The thickness  of the brass absorber was calculated from the Feather formula to be s u f f i c i e n t l y thick to stop the most energetic beta p a r t i c l e s which were observed i n the negatron spectrum. In order t o obtain the Compton background an i d e n t i c a l brass absorber was i n s t i t u t e d without the uranium radiator.  This  (12) arragement  i s shown i n f i g . 5b. Care was taken to ensure that  the position o f the source for beta counting was i d e n t i c a l to the position of the uranium radiator i n order to provide a cross check f o r the calculations of energies.  Calibration of the Instrument This instrument was c a l i b r a t e d on the basis of the .607 mev gamma l i n e of radium.  This energy was obtained by  Ozeroff(3) n the basis of the well known F l i n e of thorium B 0  as measured i n a s i m i l a r instrument.  The potentiometer read-  ing corresponds then to the energy of gamma l i n e minus the binding energy of the correct l e v e l of the radiator, since the photo-electric e f f e c t i s used.  In the above cases the K  s h e l l of lead with a binding energy of 87.5 kev i s appropriate. The potentiometer setting can then be translated d i r e c t l y into Ef values.  S t a t i s t i c a l Accuracy The s t a t i s t i c a l accuracy of a l l points on the spectra was better than 2%, while those points i n the regions from which important data might be expected, had a s t a t i s t i c a l accuracy approaching 1$.  This entailed a minimum of 20 minutes counting  per point i n the f i r s t case and as much as 60 minutes i n the latter.  (13)  RESULTS  Negatron Spectrum The negatron spectrum i s shown i n the graph i n f i g . 6.  A Fermi plot of t h i s spectrum was prepared and nof  dist-  ribution could be recognized, indicating the continuum was due l a r g l e y to Compton r e c o i l electrons.  In other words any (5~  emission must be of so low an a c t i v i t y as to be l o s t i n the Compton d i s t r i b u t i o n which i s produced by gamma-rays i n the Zn source. A very pronounced spectral l i n e i s i n evidence which can be i d e n t i f i e d as an i n t e r n a l conversion l i n e of C|i^.  With the binding energy f o r Cu as calculated, from the  data i n the Handbook o.f Physics and Chemistry at .088 mev, t h i s leads to a gamma-ray energy of 1.13 mev Hi .005.  Positron Spectrum The positron spectrum i s shown i n f i g . 7 and the Fermi plot of t h i s spectrum i s shown i n f i g . 8.  The extrapol-  ated end point i s f i t t e d by the method of least squares, using the 11 points indicated by the arrows i n f i g . 8.  The r e s u l t s  indicate an end point energy of .320 _T .003 mev.  Gamma-Ray Spectrum  The gamma-ray spectrum shown i n f i g . 9 displays the  (14) high i n t e n s i t y photo-electric peak from the K s h e l l of uranium, as well as the less pronounced L s h e l l peak.  A rather  weak peak at .3 V. corresponding to a gamma-ray energy of .513  .003 mev i s i d e n t i f i e d as a n n i h i l a t i o n r a d i a t i o n .  Using the value .114 mev for the binding energy of the K s h e l l and .020 mev for the L s h e l l , the gamma-ray energy Is i n both cases 1.12  .005 mev.  A close examination of the high energy end of the Compton d i s t r i b u t i o n i n f i g . 9 shows a spectral configuration which may be due to a low intensity gamma-ray.  Using a r e -  arranged version of the well-known Compton scattering formula, we can determine the gamma-ray energy responsible for the maximum r e c o i l electron.  This may be expressed as:  where  = energy of the gamma-ray Em  =  maximum energy of the Compton r e c o i l electron i n  the forward d i r e c t i o n (which i n t h i s case i s 1.14 mev). This leads to the result that: E  y  = 1.4  - »1 mev.  COUNTS  PER  MINUTE  (16) Figure 7 80c|  POSITRON OF  SPECTRUM ZN  6 5  POTENTIOMETER  VOLTAGE  Figure. 8 °  o  X  FERMI  PLOT  OF  THE  POSITRON  SPECTRUM  601  40  fNp  hfl 20  •180 •  « 0 0  ENERGY  2 2 0  IN  M "  MEV-  280  3 0 0  320  340  cm  GAMMA" SPECTRUM 1  POTENTIOMETER  VOLTAGE  OF Z N  6 S  •»  4 (D  (18)  CONCLUSIONS The results obtained i n this research agree i n t h e i r main features with those of the most recent investigations. The rather high i n t e n s i t y i n t e r n a l conversion electrons found, confirm i n part the assumptions of Delasso et a l ^ regarding the presence of negatrons. The positron end point agrees with the results of W. C. Peacock^ ) and i s 7$ lower than that of P.N. 11  Daykin^ } 13  The gamma-ray energies .513 - .002 mev and 1.12 - .005 agree well with those of Jensen, L a s l e t t and P r a t t b u t  are  s l i g h t l y lower than the results of Deutch, E l l i o t t and Roberts ^).  However the gamma energy as measured from the i n t -  ernal conversion l i n e 1.13  .005 agrees closer with the r e s u l t  of the l a t t e r i n v e s t i g a t o r s . The findings of Sagane et a l ^ w i t h respect to the positron end points seem most u n l i k e l y , i n view of the results of t h i s investigation, while the three gamma-ray energies reported by Watase et a l (8) i n the r a t i o 1:1:1 improbable, since the energies 1.0,  are even more  .65, and .4.5 mev are well  within the p o s s i b i l i t y of detection i n the i n t e n s i t i e s claimed, with our instrument. The gamma-ray energy of 1.4. t .1 mev f i r s t reported here must be considered with caution i n view of the low a c t i v i t y source a v a i l a b l e for the measurement of t h i s reaction.  (19) T h i s gamma l i n e i s i n h e r e n t l y weaker t h a n t h e 1.1 mev. l i n e i f t h e h y p o t h e s i s w h i c h i s p u t f o r w a r d below has any s i g n i f i c a n c e The c o n f i r m a t i o n of t h e 1.4 mev l i n e must a w a i t e i t h e r a b e t a , ray spectrometer i n v e s t i g a t i o n w i t h a stronger source, o r perhaps b e t t e r , an i n v e s t i g a t i o n u s i n g a p a i r s p e c t r o m e t e r w i t h t h e source i n a s t r o n g f l u x o f n e u t r o n s . A decay scheme based on t h e s e r e s u l t s c a n be tentatively  advanced: Cu°5  Zn 5 6  K-capture .51 mev - N ) 1.4 mev V Positron .32 +.51 mev 1.1 mev V  B e f o r e t h i s scheme c a n be a c c e p t e d w i t h l e s s t h a n the utmost c a u t i o n , f u r t h e r r e s e a r c h must be u n d e r t a k e n .  The r a t i o o f  gamma t o p o s i t r o n e m i s s i o n must be re-examined.'  I t s h o u l d be  n o t e d t h a t t h e arrangement o f t h e s o u r c e m i l i t a t e s a g a i n s t c o u n t i n g t h e a n n i h i l a t i o n r a d i a t i o n , a l s o the presence o f s t r o n g i n t e r n a l c o n v e r s i o n must a f f e c t t h e r a t i o p r e v i o u s l y accepted.  Not o n l y X-gamma and positron-gamma-but a l s o gamma-  gamma c o i n c i d e n c e s must be measured, b e f o r e a a n a l y s i s o f t h e decay scheme o f Z n  6 5  comprehensive  c a n be v e r i f i e d .  (20)  BIBLIOGRAPHY 1. 2.  J . J . Livingood P h y s . Rev.,  5 0 , 4-25, 1 9 3 6  -C. P e r r i e r , M. S a n t a n g e l o , E . S e g r e P h y s . Rev., 5 3 , 104, 1 9 3 8  3.  S. W.  4-  L. A. D e l s a s s o , L . N. R i d e n o u r , R. S h e r r , M. P h y s . Rev., 5 5 , 1 1 3 , 1 9 3 9  5.  J . J . L i v i n g o o d , G. T. S e a b o r g P h y s . Rev., 5 5 , 4 5 7 , 1 9 3 8  6.  L . W.  7.  R.  8.  Y. W a t a s e , J . I t o h , E. T a k e d a P r o c . Phys. Math. Soc. Japan, 2 2 , 9 0 , 1 9 4 0  9.  M. D e u t s c h , A. R o b e r t s , L. G. E l l i o t t P h y s . Rev., 6 1 , 3 8 9 , 1 9 4 2  10.  W.  11.  W.  B a r n e s , G. V a l l e y P h y s . Rev., 5 3 , 9 4 6 , 1 9 3 8  Alvarez P h y s . Rev.  White  54, 486, 1938  S a g a n e , S. K o j i m a , G. M i y a m o t o P r o c . Phys. Math. Soc. Japan, 2 1 , 7 2 8 , 1 9 3 9  M. C.  Good and W. P h y s . Rev.,  C. P e a c o c k 69, 680, 1946  Peacock P l u t o n i u m P r o j e c t R e p o r t , Mon. (prob. r e s t r i c t e d c i r c u l a t i o n )  N - 4 3 2 ,  12.  E. N. J e n s e n , L. J . L a s l e t t , W. W. P h y s . Rev., 7 5 , 5 2 9 , 1 9 4 9  13.  P. N. D a y k i n M. A. T h e s i s , U n i v e r s i t y o f B r i t i s h P. L i n d e n f e l d , M.  14.  G.  A.  56,  Pratt  Columbia  Thesis, U n i v e r s i t y of B r i t i s h  Columbia  M. J . O z e r o f f , M. A. T h e s i s , U n i v e r s i t y o f B r i t i s h  Columbia  M. D e u t s c h , L. G. E l l i o t t , R. S. I . , 1 5 , 178,  R. D. 1944.  1942.  Evans,  

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