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The decay scheme of Zn65 Daykin, Philip Norman 1949

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( H I ftSf  6*  THE DECAY SCHEME OF ZN  by PHILIP NORMAN DAYKIN  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE HEQUIHEMEHTS FOR THE DEGREE OF MASTER OF ARTS IN THE: DEPARTMENT OF PHYSICS;  1  fHEL UNXVERSITr OF BRITISH COLOMBIA \  APRIL,  I 9 4 9  ABSTRACT  65 Radiations from Zn  have been studied by means o f  a t h i n l e n s b e t a r a y spectrometer* A s p i r a l b a f f l e waa used to separate p o s i t r o n s from negatrons* The gamma r a y spectrum i n the energy range above 100 k e r was found t o consist o f one gamma r a y at 1.11 mev and a n n i h i l a t i o n r a d i a t i o n at 0.^1 mer. One p o s i t r o n group was found w i t h maximum energy a t 0*327 mev. No i n t e r n a l conversion e l e c t r o n s were found. 65 A decay scheme has been proposed i n whieh Zn decays e i t h e r  65 by K-capture t o a 1.11 mev e x c i t e d s t a t e o f Gu 65 p o s i t r o n emission t o the ground state of Cu •  o r by  ACKCTOWIEIIGEMEMT  This researah was carried out w i t h the a i d of National Research Council Sc3u?larahlp>  (1)  Introduction  65  R a d i a t i o n s from the Zn  nucleus hare been studied  65  by s e v e r a l methods.  The samples o f Zn (1) produced by the f o l l o w i n g r e a c t i o n s *  used have been  64 65 (d,p) Zn 6? 65 Cu (d,2n) Zn 65 65 Cu (p,n) Zn 64 65 Zn ( n , Y ) Zn 65 65 Zn  Ga  Barnes and V a l l e y  (K-decay) Zn  (2)  i n v e s t i g a t e d r a d i a t i o n s from  copper bombarded by- p r o t o n s , u s i n g absorption and cloud chamber techniques*  They reported ah a c t i v i t y w i t h a h a l f  l i f e o f about f months* c o n s i s t i n g o f both p o s i t r o n and negatron emission i n the r a t i o o f 2:1 and gamma r a d i a t i o n w i t h a gamma to p o s i t r o n r a t i o e f about 6 0 , A b s o r p t i o n measurements i n aluminum i n d i c a t e d an end p o i n t o f 0*7 mev A A f o r the p o s i t r o n group* Through the Cu Cp n) Zn r e a c t i o n  63  both Zn  65  and Zn  63  r  could be produced from the two s t a b l e  65  i s o t o p e s Ca ^and Cu by proton bombardment* Livingood and Seahorg , however, found a s i m i l a r a c t i v i t y i n an isotope o f z i n c produced b y deuteron bombardment o f z i n c . 64  They i d e n t i f i e d the r e a c t i o n a s Zn  62  there i s no stable isotope Zn  65 • 63  (d,p) Zn  , from which Zn  Since could r  s i m i l a r l y be produced, they assigned the a c t i v i t y t o n 2  6'5  (2) (4)  Doleasao et a l  also Investigated the r a d i a t i o n s  from copper bombarded by protons, by absorption measurements in aluminum* The absorption curve was separated i n t o three components which were i d e n t i f i e d as: one positron group;, one i n t e r n a l conversion electron and one gamma ray. The The lowest end point only waa reported at 0»55 mev.  This  value could be assigned to e i t h e r the positron group o r the i n t e r n a l converson e l e c t r o n .  F a i r l y intense X-radiation  found by them was a t t r i b u t e d to both the K-capture and i n t e r n a l conversion  processes.  Livingood and Seaborgf^ reported X-ray a appropriate approximately  to the CuK^ l i n e *  Previously Alvarez  had  showed that there was ho large difference i n the absorption of these X-rays i n n i c k e l and copper.  Livingood and Seaborg  concluded from t h i s that the X-rays were from an element of atomic number lese than that of zinc, and assigned them to the GuK^ l i n e .  The K-eapture process f o r the decay Zn -^Cu v  waa therefore postulated. They used magnetic separation o f the p a r t i c l e s and gamma raye and confirmed the high r a t i o o f gamma rays to particles.  Their absorption measurement a In aluminum i n d i c -  ated one -ray a t 1*0 mev and a weak a n n i h i l a t i o n r a d i a t i o n at 6 . 5 mev.  The h a l f l i f e waa given aa 250*5 days* P e r r i e r  Santangelo and Segre^^ reported a h a l f l i f e of 245 days f o r a Zn isotope obtained from copper which had been bombarded by both protons and deuterohs.  (3) Since the GuE^ X-rays could a r i s e from e i t h e r K-eapture process:,or i n t e r n a l conversion o f gamma rays from the e x c i t e d C u ^ i coincidence s t u d i e s are r e q u i r e d .  Good and peacock  i n v e s t i g a t e d X-ray Jf-ray and @"V-»ray coincidences*. They concluded that $4% of the K-capture process leads t o the ground s t a t e o f G u ^ , w h i l e 4-6% l e a d s t o the 1.14 mev^ ^ e x c i t e d 11  s t a t e , and 2*2% o f the d i s i n t e g r a t i o n s go by p o s i t r o n emission '*'"  d i r e c t l y t o the ground s t a t e .  Watase, I t o h and Takeda  (8)  also found some evidence by X-ray Jf-ray coincidence that some part o f the K-capture process goes t o the ground s t a t e . The Table of I s o t o p e s ^ l i s t s G.4 mev f o r thefl*end  (9) point from cloud chamber measurements and 0*32 mev, u s i n g a b e t a r a y spectrometer • The existence o f i n t e r n a l conversi v e r s i o n e l e c t r o n s i s also l i s t e d from the work of Livingood (a) and Seaborg  , but no energies are given.  For the gamma r a y energies, 1.14mev - 3^  w  by Deutsch, Hoberts and E l l i o t t (12) Jensen, L a s l e t t and Pratt-  s  a  reported  and l . l l m e v ± O.J% by  . , both from spectrometer studies;*  The l a t t e r found a weak a n n i h i l a t i o n r a d i a t i o n at O.51 mev* v* The existence of both K-eapture and p o s i t r o n emission w i t h the former process h i g h l y favored i s reasonably c e r t a i n * At l e a s t one y-ray has been found at 1.11 mev and at l e a s t one (3 -group w i t h end point at O.32 mev, both by spectrometer f  methods*  I n view o f the work* o f Good and Peacock, there  should be a weaker ^ - g r o u p w i t h higher end p o i n t energy* The presence o f i n t e r n a l conversion e l e c t r o n s has not been  (4)  confirmed "by spectrometer methods, and the energies are therefore not Known with any certainty. In view of these uncertainties i t was deemed advisable to repeat the spectrometer study of the gamma ray spectrum. and further, te investigate bath positron and negatron spectra  65  64  separately.  The isotope used was obtained by the Zn  (n.y)Zn  reaction from the Chalk River Laboratories of the National Research Council. Equipment Spectrometer The spectrometer la of the thin lens type whieh has (13)  been used in previous researches: in this laboratory elsewhere^ 1 4 f l 5 » l 6 ) ^ In figure I •  A  and  diagram of the spectrometer i s shown  Electrons from the source are selected by the  baffle B and f'ocussed by the magnetic f i e l d on the thin window cf the beta ray counter.  The baffles A , C, D, and E are added  to reduce scattered, radiation and prevent direct radiation from reaching the counter*  For study of positron spectra an  additional s p i r a l baffle was inserted between C and the f i e l d (14)  coils*  Deutsch et a l  have calculated the pitch of the  focuseed electrons i n their s p i r a l path through the spectrometer.  The baffle shown in figure 2 is based on these c a l -  culations.  Since the pitch Is almost a oonstant for paths  (5)  Figure 1*  I  311  "H  Diagram of the spectrometer*  II W CMS.  H  II 1  %  Figure 2. S p i r a l b a f f l e Used with the spectrometer f o r studying positron spectra*  having d i f f e r e n t r a d i i , r a d i a l b a f f l e plates of constant p i t c h may  be used.  Electrons of either sign may  be selected  by choosing the d i r e c t i o n of the magnet c o i l current; t h i s b a f f l e transmitted 75%  o f  d i r e c t i o n of c o i l current  the focussed  while i t reduced the count to  background with the opposite transmission  electrons with one  d i r e c t i o n . The  l o s s of 25%  caused by i n s e r t i o n of the b a f f l e must be a t t r i b -  uted to a difference between the p i t c h of the b a f f l e plates and that of the electrons, since the geometric cross section of the p l a t e s i s much l e s s than 25% of the spectrometer cross section*  Plate I.  Assembled spectrometer.  (7) P l a t e I shows: the assembled spectrometer*  The axis  of the instrument i s aligned with the magnetic meridian and the v e r t i c a l component of the earth*s magnetic f i e l d i s e f f e c t i v e l y cancelled by a current through the p a i r of compensating c o i l s surrounding the instrument*  The effect o f  the remaining a x i a l component may he found by reversing the (11)  magnet c o i l current (with the s p i r a l b a f f l e removed)  •  I t was found that, with the present resolution of 3 to 4% obtained with t h i s spectrometer, no effect could be observed* By use of non-ferromagnetic materials throughout, proportiona l i t y between the momentum of the focussed electrons and c o l l current i s therefore preserved* (1*) Deutsch et a l have shown the r e l a t i o n between spherical aberration and mean c o i l radius*  Spherical aberration may  be minimized by operating with the largest radius permitted by the momentum of the electrons being studied* The magnet c o i l I s therefore wound i n four layers having separate terminals, so that the inner layers may be disconnected*  Counters The t h i n window Geiger counter, sketched i n figure 3, was d e s i g n e d to u s e a minimum of wax seals.  Unstable oper-  ation peculiar to wax sealed counters has been experienced i n t h i s laboratory* Anode wire and f i l l i n g tube are brought through the brass envelope with Kovar seals, whioh are  (8)  FLANGES  * BRASS  TUNOSTtN  Figure  3.  ENVELOPE  AN0O6  Counter  hard  s o l d e r e d and c o a t e d w i t h s o f t t a p was  H ' H A H O  5 0 L D E  S - S O F T  S O L0 C R  R  A l l other soldered j o i n t s are  omitted; waa  after a satisfactory f i l l i n g  S E A L S  construction  soldered t o the envelope.  tube  KO.VAR  . C O S ' f l A .  soft  usual f i l l i n g  •  oiwolopo  solder.  t h e t u b e was  The  sealed o f f  obtained. 2  The  mica  window,  2»8mg/cm  >$hick,  t h e f l a n g e s u s i n g Cenco P l i c e n e , a wax with the following technique.  was  s e a l e d between  insoluble  i n alcohol,  P l i c e n e , d i s s o l v e d i n turpen-  t i n e was p a i n t e d s m o o t h l y on b o t h f l a n g e s and a l l o w e d t o d r y . t h e s e were t h e n h e a t e d on t h e c o u n t e r ; tube  t o melt  a i r bubbles  t h e wax and t h e m i c a  were p r e s s e d  out w i t h a  dropped rubber  and t h e o u t e r f l a n g e b o l t e d t o t h e f i r s t . The  counter d e s c r i b e d has operated  during the present  work.  satisfactorily  (9)  Amplifiers The l a b o r a t o r y a r r a n g e m e n t foot  pulse cable to  avoid direct  use o f a  ten  scalar.  To  c a r r y counter p u l s e s to the  l o a d i n g of the  counter by the  f o l l o w e r was c o n n e c t e d t o t h e shown i n f i g u r e 4.  cable,  counter w i t h short  The c a b l e c o n n e c t e d t o t h e  a p p r o x i m a t e l y matched at resistor*  r e q u i r e d the  t i t s output  end b y t h e  The f o l l o w i n g p r e a m p l i f i e r i s  a  cathode  leads,  cathode  as is  100 ohm  a two s t a g e  grounded  g r i d t r i o d e a m p l i f i e r , , each stage of which i s preceded by a cathode f o l l o w e r . cathode  The t h r e e v o l t p u l s e s  f o l l o w e r are  whose o u t p u t  consists  obtained from  s u f f i c i e n t to saturate the of sixty volt pulses  The s c a l a r d i s c r i m i n a t o r was s e t s t r a y ; p i c k u p and n o i s e ,  at  and t h e n t h e  amplitude.  eliminate  c o u n t i n g r a t e was  pendent o f d i s c r i m i n a t o r b i a s f l u c t u a t i o n s . obtained with t h i s  preamplifier,  of equal  15 v o l t s t o  c o u n t e r and c i r c u i t a r e  the  Counter  inde-  plateaus  shown i n f i g u r e  5*  Cio)  Figure 4. Schematic of cathode f o l l o w e r and p r e a m p l i f i e r .  IIOO  IISO COUNTER  Figure  IIOO  1250  VOLTAGE  Counting rate of p u l s e s from p r e a m p l i f i e r o f amplitude g r e a t e r than 1$  volts.  (11) Regulators  Magnet Current  Regulator  The r e g u l a t o r i s the same as used i n previous research(13a)  es  except f o r the f o l l o w i n g m o d i f i c a t i o n s . The D.  C.  power i s taken from the "building supply, whose negative t e r m i n a l i s grounded, i n s t e a d of from t h e f l o a t i n g " M  supply*  generator  The A. C. e r r o r v o l t a g e ±a then taken between the  standard r e s i s t o r and ground.  T h i s m o d i f i c a t i o n required snth  a d d i t i o n a l stage o f A * C. a m p l i f i c a t i o n to o b t a i n b o t h e r r o r s i g n a l i n v e r s i o n and i n c r e a s e d voltage g a i n .  The d r i v e r stage  was m o d i f i e d so that, i t operated as a t e t r o d e w i t h normal b i a s f o r a l l b i a s s e t t i n g s of the type 6AS7 c o n t r o l tubes. B i a s c o n t r o l f o r the l a t t e r was obtained from a 100,000 ohm: potientiometer Connected across the d r i v e r B  supply, w i t h  the movable arm grounded; the negative b i a s supply was then not r e q u i r e d * Magnet current was determined as before by s e t t i n g the d i a l box potentiometer.  S t a b i l i t y was 0.01^  at, 10 amperes  and 0.1^ at 1 ampere w i t h t h i s arrangement. Compensating C o i l Current  Regulator  The current c a r r i e d by the p a i r of compensating f i e l d efifils i s regulated against l i n e voltage v a r i a t i o n s by the use o f two b a l l a s t tubes (type CRC876") i n a e r i e s w i t h the 10  ohm  C12) field coils.  Since these operate normally w i t h .1.7 amperes,  whereas only 1 ampere i s required f o r f i e l d  compensation,  the excess current was shunted "by the c o i l s through a rheostat. Current regulation: o f 0+2$% par v o l t was obtained, which value Is s u f f i c i e n t f o r normal hourly l i n e voltage v a r i a t i o n s .  Experimental  Technique  Arrangement o f Sources A diagram of the source arrangement i s shown: i n f i g u r e 6. For gamma ray spectra the active m a t e r i a l i s inserted into the brass cup from' the outside. A screw cap holds t h i s f i r m l y i n p l a c e . S u f f i c i e n t brass I s l e f t between the a c t i v e material and the r a d i a t o r to absorb the beta r a y s . The radiator, a t h i n d i s c o f lead o r uranium oxide I s cemented to the front face. For b e t a ray/ spectra, f i l i n g s fwom the a c t i v e material wewe cemented with collodion t o a t h i n d i s c o f mica, which f i t s ilnto the brass cup.  The brass i s removed from Immed-  i a t e l y behind the mica to> reduce r e f l e c t i o n s o f beta r a y s . Owing to the low s p e c i f i c activity, o f the Zn  , the deposit  could not be made as t h i n as was desired} sufficients was added to produce roughly/ twice background count In the spectrometer*  (1%)  Figure 6 * Arrangement o f sources* A, Gamma ray source* B, Beta ray source*  Calibration The spectrometer was calibrated d i r e c t l y In terms of d i a l box potentiometer reading, which i s proportional to the momentum of the fo cussed electrons. Phot ©electrons ejected from the E s h e l l of lead by the 0 . 6 0 7 mev/ gamma ray o f radium  (13c) were used*  This energy value was obtained by Ozeroff  from a s i m i l a r spectrometer c a l i b r a t e d i n terms o f the * l i n e of thorium B* The momentum of the photo electrons was obtained by subtracting the binding energy fo.0875mev) of the K s h e l l . The c a l i b r a t i o n curves i n figure 7 show that both resolution and transmission are improved by using- only the magnet c o i l s of large r a d i i .  Below/ are l i s t e d the c a l i b r a t i o n  correspond-  (14) Ing to peak values and the resolution f o r each c o i l combination used*  Ciiils i n  Width at  Calibration i n  series  h a l f maximum  gauss-em* per v o l t  4 coils  4 %  9600  3 outer  3-6*  6600  2 outer  3-5#  4090  1 outer  2.000  1915  OUTER COIL  ^  1-56 VOLTS Ic^SOMA  0-730 VOLTS 140 MA  UJ r—  D  0 4-55 VOLTS  1800  I,= <H0M A  UJ  0-3)1 VOLTS  a. ^  h-wo 1600  MA RADIATOR *0 M ^ /  PB  ZD O  U  1+00  J  O-IG  Pigure 7.  L  0<>?  I-0O  I  J_  J-*?^-  C a l i b r a t i o n curves.  M  Z  (15) The compensating current, I , had to be adjusted f o r c  maximum peak i n t e n s i t y with each c o i l combination.  Pre-  sumably, the difference i s due t o s l i g h t misalignment of the separate c o i l axes In the horizontal plane.  The resolu-  t i o n possibly could be improved f o r the outer c o i l alone by realignment of the spectrometer axis w i t h the outer c o i l  (14) axis, i n the v e r t i c a l plane(  , but t h i s was not  attempted  because the outer c o l l alone was i n s u f f i c i e n t f o r most energies.  Experimental  Results  Gamma Ray Spectrum The gamma ray spectrum i s shown i n f i g u r e 8 .  Compt on  background, obtained w i t h the radiator removed, i s dotted under the main curve; the difference gives the photoeleetrona ejected from the r a d i a t o r .  Several radiators and magnet c o i l s  were t r i e d both to obtain high peak i n t e n s i t y and resolution and to eliminate spurious peaks.  The two peaks obtained with  lead radiators show that l i t t l e i s gained by using a radiator t h i c k e r than 50 mg/cm • Several small peaks appear on the mala curve obtained by using; the lead r a d i a t o r .  These could  be interpreted e i t h e r as spurious peaks a r i s i n g from unusually large s t a t i s t i c a l deviations o r as photoelectron peaks from weak gamma r a y s .  To remove the ambiguity, the region con-  t a i n i n g these peaks was repeated with the uranium radiator.  020  040 POTENTIOMETER  VOLTAGE  65 F i g u r e 8.  Gamma r a y s p e c t r u m of  Zn  0-60  (16)  Since the binding: energy of the uranium E - s h e l l i s 2 7 . 5 kev higher than t h a t o f the lead K - s h e l l , a photoeloctron peak obtained w i t h the l e a d r a d i a t o r must reappear when the uranium radiator i s used, but art 2 7 • 5 kev lower energy* Only one such peak s a t i s f i e d t h i s condition. T h i s peak i s indicated i n f i g u r e 8 at 0 . 2 6 v o l t s . The Compton background seemed rather excessive* I t was shown that the high i n t e n s i t y was due to the large source A lead' cylinder  area required by the low s p e c i f i c a c t i v i t y .  2 cm. long and 2 cm. i n diameter, with a c o n i c a l hole  drilled  to f i t over the radiator, reduced the Compton background to £ but l e f t the photoelectron peak unchanged.  The work  however was not repeated since r e p e t i t i o n was not considered worthwhile f o r a f a c t o r o f 2 . I t i s therefore recommended that fungi! sources of high s p e c i f i c a c t i v i t y , when a v a i l a b l e , be placed d i r e c t l y behind the radiator; and the lead cylinder b a f f l e be used only when necessary, since a d d i t i o n a l s c a t t e r i n g i s undoubtedly produced by i t s use. Gamma Ray Energies The gamma ray energies were obtained by adding the K s h e l l binding energies, l l j f kev f o r uranium and 8 7 . 5 kev U7) for  lead(  below.  , t o the photo electron peaks.  These are tabulated  The center of the photoelectron peak was chosen  generally, except i n the case o f the 100 mg/cm  lead radiator*  Since t h i s had a d e f i n i t e f l a t top, the high energy end of (12)  the f l a t top/ was chosen .  Cl7). Gamma Ray (1)  Radiator  Polls  U, 80mg/cm  4 coils  0.$1  U, 80  2 outer  0.?08  P b 50  4 coils  1.107  Pb,100  4 coils  1.104  2  (2)  r  Positron  By i n Mev  U,  80  4 colls  1.109  U,  80  2. outer  1.109  Spectrum  The p o s i t r o n spectrum, shown i n f i g u r e 9 , was obtained from the beta ray source w i t h the magnet current r e v e r s e d i the s p i r a l b a f f l e e f f e c t i v e l y removed negative particles.  The counter was shielded fsrom other sources  ( i n c l u d i n g a £00 m i l l i c u r i e radium source i n a second spectrometer i n an a d j o i n i n g room) w i t h Vy cm. o f l e a d . ground was reduced t o 10 counts p e r minute.  Back-  The source  t h i c k n e s s required t o o b t a i n twice background count was 130 mg/cm . The Fermi p l o t o f the p o s i t r o n spectrum, shown i n f i g u r e 10, was obtained "by use o f the f o l l o w i n g approximations.  The Fermi r e l a t i o n i s given by  F=  Ff  ~  max "  K  E  (17a)  15  04  0-5  OX  P O T E N T / 0 M E T E R  OS  V O L T A G E  6?  Figure 9 . Positron spectrum of Zn  0  0-1  0-1  •  .  r  ENERfiy  .  IN MEV  Ori  0-+  Figure 10. Fermi plot of positron spectrum  (IS)  where  T\ ~ momentum of electron i n u n i t s of n^e H -  r e l a t i v e number of electrons w i t h momentum 7 ^  try l  2S  end  t{Zj\) = r\  where  S =J T  z  e  l  Z  -  n  j] ( 1 + S i y ) +  Wl$7Y  Jl f Tj  137  -1  2  71  The approximation discussed concerns the expansion of the gamma function.  T h i s was expanded In a Taylor series, to  the f i r s t power o f S only*  By a second approximation to  the f i r s t power, the expression  The expression i n brackets was expanded i n s e r i e s , using a w e l l known expansion f o r PC'Z.) • The s e r i e s involved, o f the form  00  y  ("HZ)  1  . 0 0  , was approximated by /  ^nTn^TpT  dn  •  The  j n U * + y*J  r e s u l t used i n the calculations i s  IPCl f S f. Iy)| I  2  1  TT v (l 28^ 4 8 log(l • yj )} sinhTTy ( 2  A commonly used approximate expansion f o r t h i s gamma function is  TT y  sinhTjy  fl t 0 . 4 ( p ( z ) ) . 2  (  {  This formula can be obtained from ours by two further approximations.  (19) The Fermi p l o t of the positron spectrum indicates one postron group with end point a t 0«32?  Bier**  with a  standard deviation o f 0.0037 mev f o r the 14 p o i n t s used.  Internal Conversion Electrons A negatron spectrum was attempted, using the beta ray source.  P a r t i c u l a r attention was paid t o the low energy  end i n a search f o r i n t e r n a l conversion l i n e s .  Bone were  found* hut a d i s t r i b u t i o n was obtained which was i d e n t i f i e d as a Compton d i s t r i b u t i o n .  The existence of Compton electrons  i s attributed to the high surface density o f the source Cl30 mg/cm ) and to the r e l a t i v e l y Intense 1.11 mev gamma 2  radiation.  Conclusions The average values of the gamma ray energies, taken to the number of v a l i d s i g n i f i c a n t figures, are? O.51 mev and 1.11 mev.  The 0*51 mev radiation i s i d e n t i f i e d with  annihilation radiation.  These r e s u l t s are s i m i l a r , within  (12)  1%, t o those reported by Jensen et a l  • The gamma ray  energy i s 3$ lower than that reported by Deutsch, and E l l i o t t  (11)  Boberts  The end point of the positron group i s 0.327 mev.  (20) (10),  T h i s value i s 2% h i g h e r than that reported by Peacock  from spectrometer measurements, and I s considerably l e s s than a l l values reported from cloud chamber and absorption (2,4,91  measurements Decay  •  Scheme The f o l l o w i n g decay scheme based on these r e s u l t s  i s proposed. Cu  65  Zn  65  The K-capture process i s e n e r g e t i c a l l y p o s s i b l e i f the energy d i f f e r e n c e between the i n i t i a l and f i n a l s t a t e s I s l e s s than the r e s t energy of the e l e c t r o n .  This c o n d i t i o n  i s s a t i s f i e d by the decay scheme. The statement made i n the i n t r o d u c t i o n — that a second (J^-group of higher end p o i n t (7)  energy was required by the r e s u l t s of Good and Peacock  —  i s t h e r e f o r e i n c o r r e c t . According to t h e i r r e s u l t s there i s a second K-capture process, approximately e q u a l l y favored, 65 l e a d i n g to the ground s t a t e of Cu  • They f u r t h e r concluded  that. 2% of a l l d i s i n t e g r a t i o n s go by p o s i t r o n emission d i r e c t l y t o the ground s t a t e .  Therefore, i f only one ^  -  (21)  group e x i s t s , the r a t i o o f gamma t o p o s i t r o n emission would he approximately 25-  Barnes and vTalleyt  , however, reported  a r a t i o of 60. F u r t h e r , the reported presence o f i n t e r n a l (1.2,3.)  conversion e l e c t r o n s  has not "been confirmed.  65  I t would he p o s s i b l e t o estimate the mass o f Zn , assuming that the p o s i t r o n emission leads t o the ground state.  However, owing t o the c o n f l i c t i n g r e s u l t s , f u r t h e r  work w i t h a source o f much higher s p e c i f i c a c t i v i t y i s recommended, t o determine f i r s t the decay scheme w i t h greater certainty*  (22)  ACKNOWI3Ja36EMENTS  Acknowledgement i s g r a t e f u l l y made t o Dr. K. C. Mann under whose d i r e c t i o n the p r o j e c t was e s t a b l i s h e d and c a r r i e d out. The N a t i o n a l Research Council made t h i s work p o s s i b l e by a G r a n t - i n - A i d  t o D r . K. G* Mann i n a d d i t i o n t o a Student-  s h i p granted t o the author* The author wishes t o thank Dr." J * B. Warren f o r making a v a i l a b l e the z i n c isotope used and Dr. A* van der Z i e l f o r h i s valuable discussions on t h e current r e g u l a t o r * The author extends h i s g r a t i t u d e t o Mr* A* J . F r a s e r . f o r h i s u s e f u l advice oh the machine work connected w i t h the counter and b a f f l e c o n s t r u c t i o n , and t o Mr. A . Win. Eye f o r c o n s t r u s t i n g the counter f i l l i n g systems*  (23) References 1. 2. 3. 4. 5. 6. 7. 8. 9.  G. T. Seahorg and I . Perlman Rev. Mod. P h y s i c s , 20, 597, 1948 S. W. Barnes and G. V a l l e y • Phys. Rev., 53, 946(A), 1938 J . J . Livingood and 6. IT. Seahorg Phys. Rev. 5i, 459, 1939 L. A. Delsasso, L. N. Ridenour, R. Shear and M. G. $ h i t e . Phys. Rev., i i , 113, 1939 L. W. A l v a r e z Phys. ReV., £4, 486, 0 . P e r r i e r , M. Phys. W. ffi. Good and Phys.  1938  Santangelo and E. Segre Rev., 53, 104, 1938 W. C. peacock Rev., 6 2 , 680, 1946  Y. Watase, Z. I t o h and E. Take da Proa. Physico-Math. S o c , Japan, 22, 90, L. A. Dubridge P r i v a t e communication to^ G. T. Seahorg  10.  ¥ . C . Peacock Plutonium P r o j e c t Report, Hon. ir-432, 56, 1947. (probably r e s t r i c t e d c i r c u l a t i o n )  11.  II. Deutsch, A. Roberts and L. G. E l l i o t t Phys. Rev., 6l> 389(A), 1942 E. N. Jensen, 1. J . L a s l e t t and W. wT. P r a t t Phys. Rev., 7£, 458, 1949  12. 13.  1940  Dec.  (a) P . L i n d e n f e l d H. A. T h e s i s , U n i v e r s i t y of B r i t i s h GoIambia,1948 Cb) P. Mathews M. A. t h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1948 (c) M. J . Ozeroff M. A. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia,1948  14. M. Deutsch, L. G. E l l i o t t and R. D. Evans R. S. I . , i i , 178, 1944  (24)  1^.  16.  17.  ¥• R a i l and R. G. Wilkinson Phys. Rev., 2i» 321.  1947  L. C. M i l l e r and L. P. Curtis J . Research, Hat. Bur. Stds., 38, 359, International C r i t i c a l Tables, 6> 35,  i929  1947  

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