2 ] Nuclear Ph3~stcs A100 (1967) 416--424, (~) ,North-HollandPubhshtng Co, Amsterdam B 2 G I

N o t to be reproduced by photoprlnt or m~crohlm ,a ~thout ~ruten permtsslon from the puohsher

T H E R E A C T I O N S 64Zn(aHe, d)6SGa AND 64Zn(aHe, ~)6aZn

M G BETIGERI~, H H DUHM**, R SANTO, R STOCK +** and R BOCK Max-Planck-lnstltut [ur Kernphvsd,, HeMelberg, Germany

Recmved 11 Aprd 1967

Abstract The reactmns e'aZn(aHe, d) 65Ga and 6~Zn(aHe, ~)6~Zn have been studied at incident ~He energy of 18 MeV using a broad range magnetic spectrograph and an E-dE telescope Angular d~stnbutmns have been obtained and are analysed by the DWBA theory The results g~*e mformatmn about the ~Zn ground state configuratmn as well as the neutron hole states m ~aZn and the single proton states in nSGa, respectively

NUCLEAR REACTIONS 64Zn(aHe, d), (~He, ~) E = 18 MeV, measured ~(E, Ot, E "aZn, ('~Ga deduced levels, l, spectroscopic factors Enrmhed target

1. Introduction

The nucleus 64Zn has two protons and six neutrons filhng the 2p}, 2p} and If,

single particle states with the closed fx shell as its core F rom the small spacing of

these shell model orbttals, a considerable mlxmg ts expected for the pro ton as well

as the neu t ron conf igmat lons in the ground state o f Z n ~sotopes Most of the prevtous

work on 65Ga consisted m the study of ground-sta te fl-decay *) to levels in 65Zn,

leading to a ground-state spin assignment of 2 a-- It was, therefore, of mtel est to study

the reachon 64Zn(aHe, d)6SGa and to obta in mformat lon regarding the posmons

of the single pro ton states and their strengths

Recent (p, d) work 2) on Zn Isotopes has provided some mstght into the neut ron

configuratton in these isotopes In the (a He, :~) reaction, higher/-wtlues are kmemat>

cally favoured and as such the f , hole states can be expected to be more eastly detected

m the (3He, J) reaction than m the (p, d) reactton, so that m some sense the t\~o

reactions ate complementary The prevtously knm~n ln fo rmatmn was hmtted to

a) fi-decay a) of 63Zn b) energtes of some low-lying levels m 63Zn thzough the

study~ s) of the reaction 63Cu(p ,n ) In the present study, the low-lying levels m

63Zn upto an exmtat~on of 3 2 MeV have been investigated

2 Experimental method and results

The (3He, d) and (~He :~) reactions o n 64Zn were studied ~ l th the Heidelberg

Tandem Van-de-G~aaff accelerator using a 3He beam of 18 MeV The zeactlon prod-

* On lea~e of absence of Atomic Energy Estabhshment Bombay,, India ** Present address Lax~tence Radiation Laboratory, Berkeley, U S

iF+ Present address Nlels Bohr Institute, Copenhagen, Denmark

416

6 4 Z ; ( 3 I t e ) REACTIONS 417

aE 200 E

o ~1C2,

L)

I i i

e4Zn(SHe m)~Zn E 3 H e = 1 8 M e V 2 5 °

I 2

i !' ]~,

45 bO 55

1AOa 12 C I o a o

is

"~ Ji s 1 i I 1~

I' ,., '~ ~/~

i I

L I I I 1 I i 60 65 70 75 80 85 90

Distance along the photo plate

Fig l The s p e c t r u m o f f - p a r t i c l e s r e su l t i ng f r o m 6~Zn(aHe, ~)6aZn at 25 ° T h e n u m b e r s on the hnes c o r r e s p o n d to the levels m 63Zn The s a m e n u m b e r i n g ~s a l so to be f o u n d m t ab l e I

1 ~ I I I I I I I

0 4 - ~' 64 Zn (3He,°O63Zn

i ~ ' ~ E3He=18MeV 01~ ',

,J_,

0 4

m B ,E, 1

o41:,,,"

f ~ •~t_,,_. O1 '~ u, " / - - .

004~ ~ ~

O 0 1 L I ~ I I ~ I

0 o 20 ° 4 0 ° 6 0 °

i%

I I i

E <=0000 (1/2-)

£=1

z z

Fig 2 A n g u l a r d l s t n b u t m n s to the first t h r ee levels m 6aZn The c losed circles refer to the m a g n e t da ta , the crosses refer to tl~e t e l e scope d a t a a n d the o p e n circles refer to the c o u n t e r d a t a The dashed

l ines refer to the D W B A c a l c u l a n o n s

Ex= 0192 5/2-

. 1:=3 q

\ 1 x

\

c

c

E x = 0641 (3/2-) . '

I ! I I i [ _ _ 8 0 ° 100 ° 120 °

e C M ~

4 1 8 M G BET1GERI e ta l

ucts were analysed by a single gap magnet ic spectrograph at forward angles and sam-

ul taneously by a dE-E telescope at larger angles The resulting magnet spectrum

for c~-parUcles at 25 ° w~th respect to the mcadent beam as shown m fig 1 The numbers

on the peaks an the spectrum correspond to the levels m 6 3Zn In figs 2 and 3, the

6 4 Z n ( 3 H e , ( x ) l ~ 3 Z n , E 3 H e = 1 8 M e V

'1 I I I I I

1

O4 E x = 1 0 6 5

[=1÷3

01 ""

0 2 : ~ " . ~ -

0 1 ~q ~,,:

~ - ~ Ex=1216 0 0 4 ,~',~

2 0 - ~, t=3

10 ~'- 11.1 |

0 4 "~'. Ex=1704

0 2 L -~-. [=3 I-E-1

o Ot 0 0 4 {~ Ex=1924

,~1~ 002 ' ~ ' ' , ~"~-gF t" 1 0 * , , "'L

0 4 - - - - ' 4 , , • E x = 2 651

0 2 , ~ ¢=3

01 " ' - ~ =

\

0 0 4 ~ ' -

- E x = 2 764

. . . . . -,% t=3

\

" ' t ~ £=3 Z

- , # EX=2936

"-~'" ~:~ l __ l ' I ' I I o E x = 3 0 2 4 -: - x \ O

\ \ £:3 - =

_ " ; , ' . q

. . . . " l l I \ \ - \ \ z ~ \

E x =3 372

£=3

0 0 1 ; I J I [ i 0 0 1 ~ 10" 3(7 50 ~ eCM 10 = 30 ° 50* eCM

Fig 3 Angular dlstrlbut]ons to the rest of levels m e3Zn The closed circles represent the magnet data and the crosses refer to the telescope data, the dashed curves being the DWBA calculations

angular dB tnbu t l ons for the first 14 levels upto an excltaUon energy of 3 23 MeV m

63Zn are shown The closed circles are the magnet data and the crosses represent the

telescope data The open circles m fig 2 result from an a d d m o n a l scattering chamber

measurement employing 8 surface barrier detectors Since both the elasncally scattered

3He parncles and the ~-parUcles resulting from the (3He, ~) r eacnon are samultane-

ously recorded an the telescope measurements , normahzataon to absolute umts of

cross section was relaUvely easy The error associated with each point in the forward

6 a Z n ( 3 H e ) R E A C T I O N S 419

10 f ~ ,

64Zn (3He d)65Ga ] i t I

1()

4

2

10

O4

2

10

O4

O2

01

4 2 r-ci

t h

,E, O4

oC:~ -ol-o

2

1

0 ,4

O 2

Ex C~ D

r £ 1

r ~, E x 0 0 6 2 ,r

'.

, - ,~ Ex-O 191

/ ',~ ~ 3

i l

E x = 0 6 5 5

Xi

~ ~ ~ Ex :O 822

%1 £=1

01~- ,, "~ ' , Ex=1083

0 0 4 ~ ,,/f ",.__.,, e:4

oo2b' ] / k " ~ 4 ~ l I I I I I I

O° 20° 40° 60° co4

1

04

O2

1 t 0 4 /

0 2 ',

01

E3He=18 MeV i I J I I I i I

E x - ~ ~,70

X £ 1

E x - 1867

1

4

2

1

04

02

01

04

02

01

E x - 2 0 3 4

d 1~ 4 / ' c

E x 2 206

/

1

4

2 E× - 2 819

04 "',,

2 ~ w, Ex=2 922 'Z

" ' - . - g 2

04

02

° ° 2o° 4o° 6o° %M

Fig 4 Angular dlstribuhons to the levels in ~SGa, the dashed curves being the DWBA calculations

420 M G B E T I G E R I el a[

TA~CE 1

S u m m a r y of results obta ined in G~Zn(JHe, c~)~3Zn

Level E,~e l J= S No (MeV) (assumed) (N ~ l 8)

0 0 1 1 - 2 6O 1 0 192 3 5 6 20 2 0 641 1 ~ 1 70 3 1 065 1 + 3 ~ I " 0 3 7 / 0 4 5

( 4 5 ~ , ' , 1 5 5 ° ) 4 1 216 3 7 0 36 5 1 704 3 ~ - 0 69 6 1 924 1 ~ - 0 23 7 2 160 weak 8 2 520 weak -- 9 2 650 3 7 1 90

10 2 760 3 7 - 0 50 11 2 850 3 7,- 0 25 12 2 940 3 r - 0 26 13 3 020 3 7- 0 55 14 3 370 3 ~- 0 87

Eex e (p, d) S (MeV)

0 1 35 0 20 2 80 0 64 0 84 1 04 0 70

1 22 0 25 I 68 0 85 1 91 0 3 0

2 64 0 40

A no rmahza t lon factor N ~ 18 2 was used m the calculations

TABLE 2

S u m m a r y of results obta ined m G~Zn(~He, d)~oGa

Level E~xe l J'~ (2Jr - 1 )5 No (MeV) (assumed)

0 0 000 1 ~,- 1 34 1 0 062 l }- 1 04 2 0 192 3 ) - 5 05 3 0 655 1 1.~ 0 63 4 0 82l 1 ~ ~ 0 24 5 1 08~ 4 ~ ~ 0 39 6 1 670 1 ~ 0 14 7 1 867 I ~- 0 10 8 2 034 4 q ~ 3 90 9 2 206 3 ~- 0 58

10 2 819 2 ~+ 0 16 11 2 922 2 2, ~ 0 59

A n o r m a h z a t m n factor N -- 4 4 was used m the calculat tons

d l l e c t l o n is a p p r o x i m a t e l y 10~,~, w i t h t h e e r r o l s in t h e b a c k w a l d a n g l e s b e i n g o f t i le

o r d e r o f 2 0 ° , ; T h e r e s u l t s f o r 6 a z n , u e s u m m a r i z e d m t a b l e 1

T h e a n g u l a r d t s m b u t J o n s f o r t h e l o w - l y i n g l e v e l s m ° S G a r e s u l t i n g f r o m t h e 6 a Z n

( 3 H e , d ) r e a c t i o n a r e s h m ~ n m f ig 4 T h e c h a ~ a c t e r l s t l c d e p e n d e n c e o f t h e s h a p e o f

t h e a n g u l a r d ~ s t r l b u t ~ o n s o n t h e a n g u l a r m o m e n t u m I r a n s f e r c a n b e s e e n c l e a r l y , w~th

l = 1 d t s m b u t J o n s p e a k i n g a t l 0 ~, / = 2 d l s t r l b t m o n s p e a k i n g a t 17 5 ~, l = 3 p e a k i n g

a t 25 ~ a n d I = 4 d ~ s t ~ l b u t l o n s a t 30" T h e r e a s o n x~hy t h i s c h a r a c t e l l s t l c d e p e n d e n c e

64Zn(3He) REACTIONS 4 2 1

of the shape o f the angu l a r d i s t r l b u n o n s ~s absen t m the case o f the (3He, ~) reac t ion

has been discussed e l sewhere 6) T h e resul ts for 65Ga are co l lec ted m table 2

In e i the r case, the energy ca l ib ra t ion is accura te to _ 15 keV

3 . D W B A c a l c u l a t i o n s

T h e o r e n c a l p r ed l c tmns for the reac t ions 6a 'Zn(3He, 3 { ) 6 3 Z n and 64Zn(3He , d ) g s G a

angu l a r d i s t n b u U o n s were o b t a i n e d by p e r f o r m i n g D W B A c a l c u l a t m n s using the

O a k R i d g e code J U L 1 E t These are shown in figs 2, 3 and 4 as dashed curves T h e

T A B L E 3

Sets of potentml parameters for aHe, ~ and deuterons used m the DWBA calculatmns

Particles V W r o r e a Vs o r,~ a w 4X W' (Mev) (Mev) (fm) (fro) (fro) (Mev) (fro) (fm) (MeV)

aHe 165 24 I 3 1 4 0 723 8 1 6 0 81 -- d 87 -- I 15 1 15 0 81 5 1 34 0 68 77 :~ 180 26 1 48 1 46 0 56 - - - - -

op tmal m o d e l p a r a m e t e r s used in the ca l cu l a tmns are l is ted in tab le 3 The aHe

p a r a m e t e r s were o b t a i n e d by f i t t ing the elastm sca t te r ing d a t a 7) on 64Zn at 19 5 M e V

T h e s ta r t ing va lues o f the p a r a m e t e r s were t aken f r o m ref 7 and were ad jus ted to Dye

C - T " ' - V - - - - ~ - - " - F - - - - " ' - F - - ' r " " ~ - ~ i i --Y-- '-7 - ' 3 - " - 7 - r ' ' ~

C4~ 2~ 3 64 _ ,_.n( ' a H c ) ,_q

0 4

0 2

01

-~E, 0 0 4

~ , ,~ 0 0 2

C01

OO04

0 0 0 2 ~

.... O o

X.~\

2

Es,~, I t 5"deV

%-..~ t;\ \

I I I

i q

q

-i

~ ' < L [ - I

t I 1 I I I ] ]

120 ° 150 ° C~- M L . I I I I I I I I I

3(,'° 60 ° 9 0 °

Fig 5 Angular distribution of elasncally scattered 3He parncles on b4Zn ESHe = 19 5 MeV The continuous curve is the optical model calculation with the parameters shown in table 3

the best fit, the resu l t ing angu l a r d i s t r i bu t ion for the 3He elastm sca t te r ing is seen in

fig 5 F o r the emt channe l , an ~-poten t la l was used w h m h was close to the po ten t i a l 8)

desc r ib ing the e las t ic c~-scattermg f l o m 63Cu at 24 7 M e V T h e d e u t e r o n p a r a m e t e r s

h a v e been t aken f r o m Percy 9) Since the angu la r d i s t r ibu t ion c o r r e s p o n d i n g to an

t We thank Dr Drisko for making the export versmn of JULIE available

422 M G BETIGERI et a[

l = 1 transfer seemed to be not very sensmve to the various deuteron potent ia l sets,

the present set was chosen to fit an l = 3 dlstr lbutton No radial cut-off was used

Inclus ion of sptn-orb, t interact ion In both the channels did no t br ing any difference

In the structure of the (3He, d) angular dis t r ibut ions for ½- and 2 a - except that the

cross section for ~ - was higher than that of 21 - by 14 ~a/o

4. Discussion

4 l THE 64Zn(3He, d)°~Ga REACTION

In the absence of any other data on 65Ga, the spin assignments can only be ten-

tatlve The first two l = I distr ibutions, corresponding to the 0 000 and 0 062 MeV

levels, are interpreted to be 2p~ and 2p~, respectively The ground state ass ignment

of 23-- is suggested by the fl-decay measurement ~) leading to 65Zn and also by the

simple shell model The l = 3 character of the angular dis t r ibut ion and the strong

excltatton of the level at 0 192 MeV suggest a lf~ assignment to this level A strong

l = 4 t ransi t ion is found to the state at 2 034 MeV whtch seems to conta in most of

the lg~ strength A much weaker 1 -- 4 t ransi t ion is seen to the 1 083 MeV state

Smce in N = 31 nuclei the lg} neut ron strength is usually concentrated in one smgle

level, the origin of this addl tmnal 1 = 4 transt t lon in the 64Zn(3He, d)6SGa leact lon

Is not clear The low excitat ion energy and the small cross section may point to an

explanat ion of this level m terms of core-exota tmn Some indicat ion for this is pro- vided by the results of 64 66Zn(t ' ~)6s, 6SCu measurements ~0)

TABLE 4

Total strength of the single pamcles as compared with the theoretical ~alues

2pg 2p_~ lf~ lg3

S(experlmental) 1 9 1 67 5 63 4 29

S(theoretlcal) 2 0 I 6 2 0 5 2-4 8 8 0

Since the sum-rule values for proton capture in T< states depend on the average number of neutrons in the corresponding shells, only the upper and lower hmlts can be given for the theoretical lf~ and 2p~ proton strength because ot the nuxmg of If1_ and 2p~. neutron states m the "4Zn ground state (see subsect 4 1)

The excitation energies and the strengths for the various single particle states are

given m table 4 Using the D W B A normal iza t ion cons tant of Bassel ~ 1 ), the t ransi t ion

strengths for 2p~, 2p~ and lf~_ ale in good agreement with the predicted values,

implying a relatively pu le (2p~)o 2 p lo ton configurat ion of the 64Zn ground state

4 2 THE e'~Zn(~He, ~)63Zn REACTION

In 63Zn, both the ground state and the second excited state at 0 641 MeV show

1 = 1 pattern However, the angular d is t r ibut ion corresponding to the ground

state t ransi t ion has more structure In investigations of (~, p) leactlons lz), the

t r ansmons with j = l - ½ wele found to have more structure than transi t ions with

°4Zn(3He) REACTIONS 423

j = 1+½ in their angular d lsmbut ions This j-effect was quahtatwely reproduced by the D W B A theory with the inclusion of spin-orblt coupling In the (3He, ~) reaction, we expect a similar j-effect to be produced m D W B A calculations With parameters o f table 3, on inclusion o f spin-orbit coupling in the 3He channel, the calculations lead

to the curves shown In fig 2 1 e the 1 = ½ t ransmon turned out to be more structured than t h e j = ~z transition m its angular distribution, favouring a ½- assignment to the ground state o f 63Zn On the other hand, the fl-decay data 3) as well as j-effect arguments f rom the (p, d) work 2) suggest j = 3 - for the ground state of 63Zn

In addition, results of investigation o f j -dependence in some (3He, c0 reactxons i3)

indicate that experimental j = 2 ~ - transitions may have more structure than ½- transitions, so that further measurements are needed to clarify the situation The strong transit ion to the level at 0 192 MeV shows an l = 3 shape, which is in agree- ment with the assignment of ~ - to this level f rom 63Cu(p, n)63Zn work 5) Most o f

lf~ strength is exhausted by this level alone The level number 3, corresponding to an excitation energy of I 065 MeV, seems to be a doublet, since the line width is higher than for the nelghbourmg lines and shows an asymmetry which varies with angle Indicating that two different/-values contribute to this peak Wxth the exception of the 1 92 MeV level, which exhibits an l = 1 d l smbutmn, all other levels favour an

/ = 3 assignment Of course, l = 4 cannot be ruled out In ref 2) the centre o f gravity of lf~ hole states in 63Zn IS calculated to lie at

2 64 MeV A strong l = 3 transition is observed at an excitation energy of 2 65 MeV in our measurement Since the If? states are expected to be much more split than lf~ states, all l = 3 transitions to levels beyond 1 MeV have been assumed to be ½- For getting spectroscopic factors we used a normahzat ion factor N = 18 2, which was obtained by normahzlng the I f I_ strength to its sum rule value considering only T< states With this normahza tmn, however, the sum of 2p~, 2p~ and lf~: spectroscopic factors exceed the expected sum by about a factor of two On the other hand, a reasonable value for the summed 2p~, 2pi_ and lf~ strength is found in the (p, d) work of ref 2, where only one I f I state was detected at 2 64 MeV Renormahzmg our spectroscopic factors with N = 40, our results are pretty close to the (p, d) results Using this renormahzat lon the summed 2p~, 2p~. and lf~ strength o f levels 0, 1, 2, 3 and 6 amounts to ~ S = 5 8, whlch is in agreement with the expected

strength 5 6

5 Conclusion

The results of the reaction 64Zn(3He, ~)63Zn reveal appreciable admixtures of

2p~, 2p+ and I f , single particle components m the neutron configuration of the ground state o f 64Zn, m agreement with the (p, d) work 2) The average number of neutrons outside the core, however, exceeds the expected value by a factor o f two when normahzed to the strength of I f : hole states This behavlour seems to be con- fined not only to the 64Zn(3He, ~)63Zn reaction but is also observed in SaCr(3He, ~) and S4Cr(p, d) reactions 6,14) as well as the 64 66Zn(t ' 7) reactions 10) A similar

424 r~ G BETIGERI et a l

difficulty amses in the 64Zn(3He, d) reaction, where the l = 4 strength is found to have only half o f the expected value when the no lmahzat lon constant N = 4 4 is used Since, in the present study, the range of the excitation energy is large enough to cover most of the 1 = 3 strength in the 64Zn(3He, ~) reacnon, the observed discrep- ancies must be atmbuted to the shortcomings of the D W B A analysis Investigation of 66zn(aHe, d) and 66zn(aHe, :~) reactions are underway to study these m,tttels in detail

The authors wish to thank Plofessor Gentner for his cont inued interest m this ~01 k

References

1) K Way et a l , Nuclear Data Sheets 2) L C Mclntyre, Phys Rev 152 (1966)1013 3) J B Cummmg and N T Porfle, Phys Rev 122 (1961) 1267 4) J D Anderson, C Wong and J McClure, Nuclear Physics 36 (1962) 161 5) L Blrstem, M Harchol, A A Jaffe and A Tsukrovltz, Nuclear Physics 84 (1966) 81 6) R Stock, P David, H H Duhm, R Bock and T Tamura, to be published 7) R Bock, P David, H H Duhm, H Hefele, U Lynen and R Stock, Nuclear Physics A92 (1967)

539 8) A Budzanowskl, K Grotowskl, S Mlcek, H Nlewodmczanskl, J Shz, A Strzalkowskt and

H Wojclechowskl, Inst of Nucl Phys, Krakow, Report Number 347 (1964) Phys Lett 11 (1964) 74

9) C M Perey and F co Perey, Phys Rev 132 0963)755 10) D Bachner, S Hinds, H H Duhm, R Stock, R Santo and R Bock, to be pubhshed 11) C Glashausser, thesis, Princeton University, 1965 12) R H Bassel, Phys Rev 149 (1966)791 13) C Mayer-Boncke, R H Slemssen and L L Lee, Phys Rev 147 (1966) 797 14) C A Whltten, thesis, Princeton Umverslty, 1965