HIGH SPIN STATES OF 232Th, 234U AND 236U+

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Submitted on 1 Jan 1980

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HIGH SPIN STATES OF 232Th, 234U AND 236U+

H. Ower, Th. Elze, J. Idzko, K. Stelzer, H. Emling, P. Fuchs, E. Grosse, D.

Schwalm, H. Wollersheim, N. Kaffrell, et al.

To cite this version:

H. Ower, Th. Elze, J. Idzko, K. Stelzer, H. Emling, et al.. HIGH SPIN STATES OF 232Th, 234U AND 236U+. Journal de Physique Colloques, 1980, 41 (C10), pp.C10-102-C10-105.

�10.1051/jphyscol:19801011�. �jpa-00220630�

JOURNAL

DE PHYSIQUE

_{CoZZoque CZO,} supplkrnent au n012, Tome 41, d&cernbre 1980, page

C10-102

H I G H S P I N STATES OF 2 3 2 ~ h , ^234"

A N D

236,,+

H.

Ower, Th. W. glze,

J.

Idzko%*K. Stelzer,

H.

~m&in~*,

P.

~uchs*, E. ~rosse*, D. ~chwalm*,

H.J.

Wollersheim ,

^N.

Kaffrell and

N.

Trautmann .

.Institut fiir Kemphysik, Universitat Frankfurt am Main, R.F.A.

.*GeseZZschaft fur Schwerionenforschung, Darmstadt, R.F.A.

f n s t i t u t fiir Kemchemie, Universitiit Mainz, R.F.A.

Mu1 t,iple Coulomb excitation with 5.3 MeV/u 'OBPb ions supplied by the U N I L A C at GSI has been used to study high-spin states in the actinide nuclei 2 3 2 T h ,

2 3 2 ~

and 2 3 6 U . De-excitation gamma rays were observed with two Ge(Li)-detectors 'positioned at

( B y , q y ) =

(30°,00) and ( 1 5 0 ~ , 1 8 0 ~ ) with respect to the beam. By detecting the gamma rays in coincidence with the recoiling target nuclei and/or the scattered projectiles and measur- ing their time of flight and scattering angle by means of two large-area, positron-sensi- tive parallel plate counters1), we were able to correct for the sizeable Doppler shifts of the observed gamma rays. The particle detectors covered an angular range of (1709ir280) 2 ( 0 , ~ ) 2 (58°,+280'), and (51°,1800+300) 2

( 8

,Q) 2 (89°,18~0+300), respectively. Thus we were able to measure the dependence of the gamma yields on the c.m. scattering angle of the projectile,

0 ,

between 33' and 144'. This allows one to determine i(~2)-values, at.least for the ground-state band, in a model-independent way.

Doppler-corrected spectra are shown in

F i g . 1.

Excitation of the ground-state band

Fig. 1 : Doppler-correctedgamma s

ectra

obtained b Coulomb

excitation

of '=h,

2 3 4 ~and 2Y6U with " ~ b ions.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801011

i s o b s e r v e d u p t o s p i n I" = 28' i n 2 3 2 T h a n d 2 3 4 U a n d 1' = 30' i n " 6 U . H i g h - s p i n l e v e l s o f t h e K" = 0 - o c t u p o l e v i b r a t i o n a l b a n d a r e a l s o i d e n t i f i e d . The s p i n a s s i g n - m e n t s shown a r e p r i m a r i l y b a s e d o n e n e r g y s y s t e m a t i c s a n d t h e @ - d e p e n d e n c e o f t h e gamma y i e l d s . P a r t i a l l e v e 1 schemes s h o w i n g t h e e x c i t a t i o n e n e r g i e s o f t h e g r o u n d - b a n d l e v e l s d e d u c e d f r o m t h e m e a s u r e d t r a n s i t i o n e n e r g i e s a r e p r e s e n t e d i n F i g . 2 .

Fig. 2 : Partial level schemes as deduced from the present study for 2 3 2 ~ h , 2 3 4 ~and

2 3 6 u .

I n F i g . 3, t h e e f f e c t i v e moment o f i n e r t i a o f t h e g r o u n d b a n d i s p l o t t e d v s . t h e s q u a r e o f . t h e r o t a t i o n a l f r e q u e n c y f o r t h e t h r e e n u c l e i ' i n v e s t i g a t e d , t o g e t h e r w i t h 2 3 8 U ( r e f . 1) a n d 2 4 8 C m ( r e f . 2 ) , a l s o . s t u - d i e d a t G S I . A l l n u c l e i e x h i b i t t h e . g e n e r a 1 t r e n d o f a s m o o t h i n c r e a s e o f t h e moment o f

Fig. 3 : Effective moment of inertia deduced from the level schemes shown in Fig. 2. The data for 2 3 8 ~and 2 C 8 ~ m are taken from ref. 1 and 2, respectively.

i n e r t i a w i t h i n c r e a s i n g r o t a t i o n a l f r e q u e n - c y . H o w e v e r , a m o r e d e t a i l e d e x a m i n a t i o n o f t h e s e c u r v e s shows t h a t t h e i r s l o p e s r e a c h a maximum ( l e s s d i s t i n c t f o r 2 3 4 U ) a t f r e - q u e n c i e s a r o u n d ( h a ) ' ^M 0 . 0 5 M ~ V ' (I 2 0 . .

.

2 2 ) .

I t i s w e l l known t h a t t h e y r a s t s t a t e s o f many s t r o n g l y d e f o r m e d r a r e - e a r t h n u c l e i b e h a v e i n a s i m i l a r way. T h e r e , t h i s p a r t i c - u l a r d e p e n d e n c e

o f

3 o n w2 i s u s u a l l y r e - f e r r e d t o as " u p b e n d i n g " a n d i s i n t e r p r e t - e d 3 ) a s b e i n g c a u s e d b y t h e c r o s s i n g o f t w o s t r o n g l y i n t e r a c t i n g b a n d s , n a m e l y t h e g r o u n d - s t a t e b a n d a n d a n e x c i t e d b a n d b u i l t o n a r o t a t i o n - a 1 i g n e d t w o - q u a s i p a r t i c l e c o n - f i g u r a t i o n .

I n t h e a c t i n i d e r e g i o n , t h e n u c l e o n s e x p e c t e d 4 ) t o a l i g n f i r s t w i t h i n c r e a s i n g r o t a t i o n a l f r e q u e n c y , a r e t h e j15,2 n e u t r o n s a n d i13,2 p r o t o n s . Our r e s u l t s , t o g e t h e r w i t h t h o s e f o r 2 3 8 U a n d 2 4 8 C m , c a n b e i n t e r -

c10-104 JOURNAL DE PHYSIQUE

U s i n g t h e r o t a t i o n - v i b r a t i o n model 5, t o d e - s c r i b e t h e c o l l e c t i v e r o t a t i o n o f t h e c o r e , a r o t a t i o n a l i g n e d a n g u l a r momentum i ( w ) = I e X p ( w )

-

I R V M ( w ) , o f a p p r o x i m a t e l y 5 'ii c a n be d e d u c e d a t t h e h i g h e s t o b s e r v e d f r e q u e n - c i e s ( F i g . 4 ) .

The a n a l y s i s o f t h e gamma y i e l d s i n t e r m s o f i n d i v i d u a l B ( E 2 ) - v a l u e s i s p r e s e n t - l y b e i n g p e r f o r m e d . So f a r , t h e e x p e r i m e n - t a l l y d e t e r m i n e d gamma y i e l d s o f t r a n s i t i o n s w i t h i n t h e g r o u n d b a n d f o r 2 3 2 T h h a v e b e e n c o m p a r e d w i t h r e s u l t s o f s e m i - c l a s s i c a l C o u l o m b - e x c i t a t i o n c a l c u l a t i o n s u s i n g g r o u n d - b a n d m a t r i x e l e m e n t s o b t a i n e d f r o m t h e r i g i d - r o t o r , i n t e r a c t i n g - b o s o n ( S U ( 3 ) l i m i t ) 6 ) a n d r o t a t i o n - v i b r a t i o n m o d e l 5 ) . The r i g i d - r o t o r c a l c u l a t i o n s i n c l u d e d a l s o E l a n d E4 e x c i t a - t i o n s , a s w e l l a s t h e e x c i t a t i o n o f o c t u - p o l e , 8- a n d y - b a n d s . The o b s e r v e d gamma y i e l d s i n t h e g r o u n d b a n d o f 2 3 2 T h a r e r e a - s o n a b l y w e l l r e p r o d u c e d when r i g i d - r o t o r v a l u e s p r e u i e d f o r t h e i n - b a n d m a t r i x e l e - m e n t s ; a r e s u l t w h i c h was a l s o f o u n d f o r

2 3 8 U

( r e f . 1 ) . On t h i s b a s i s i t seems

u n -

l i k e l y t h a t t h e o b s e r v e d " u p b e n d i n g " i s c a u s e d b y t h e i n t e r a c t i o n o f t h e g r o u n d

p r e t e d a s " u p b e n d i n g " , t o o . The assumed

Fig. 4 : The aligned angular momentum i = I

,

,

-

^IRm a s a function of the rotational freGuency w (2Rw = E ( 1 ) - E ( 1 - 2 ) ) .

For details, see text.

b a n d w i t h a n * e x c i t e d b a n d b u i l t o n a much m o r e s t r o n g l y d e f o r m e d c o n f i g u r a t i o n .

The i n t e r a c t i n g - b o s o n m o d e l , w h i c h p r e - d i c t s a c u t - o f f i n t h e g r o u n d b a n d s a t s p i n 24+, 26+, 28' f o r 2 3 2 T h ,

P 3 4 U

a n d 2 3 6 U , r e - s p e c t i v e l y , a n d s t r o n g l y r e d u c e d gamma y i e l d s i n t h e h i g h - s p i n r e g i o n i s i n c o n t r a s t t o o u r d a t a . P r e s e n t l y , i t i s n o t o b v i o u s how t h e c o l l e c t i v e p r o p e r t i e s o f t h e y r a s t s t a t e s a r e c h a n g e d i f r o t a t i o n - a l i g n e d b a n d s a r e i n c l u d e d i n t h e i n t e r a c t i n g b o s o n m o d e l . I t i s f e l t , h o w e v e r , t h a t b y m a k i n g t h i s s t r o n g i n t e r a c t i o n b e t w e e n t h e c r o s s i n g b a n d s 6

g u a r a n t e e s t h a t t h e Coulomb e x c i t a t i o n f o l -

5 - l o w s t h e a l i g n e d b a n d a b o v e t h e c r o s s i n g

p o i n t . T h i s i n t e r p r e t a t i o n i s c o n s i s t e n t 4 -

5

w i t h t h e e x p e r i m e n t a l B ( E 2 ) - v a l u e s , w h i c h ,

;

³

so f a r , h a v e b e e n d e t e r m i n e d f o r ' 3 2 T h ( s e e

-"

^{1 0 1} X ²

b e l o w ) a n d h a v e b e e n f o u n d t o b e c l o s e t o

t h e r i g i d - r o t o r v a l u e s , a s i n 2 3 8 U ( r e f . 1 ) . 1 The a m o u n t o f t h e a l i g n e d s p i n c a n b e e s t i -

e x t e n s i o n t h e e f f e c t o f t h e p r e d i c t e d 6 ) c u t - o f f on t h e B ( E 2 ) - v a l u e s b e t w e e n t h e y r a s t s t a t e s c a n h a r d l y b e r e m o v e d a n d a g r e e m e n t b e o b t a i n e d w i t h t h e o b s e r v e d r i g i d - r o t o r b e h a v i o u r o v e r t h e e n t i r e s p i n r e g i o n .

I I

-

D 2 3 2 ~ h

A 2 3 h ~

0 2 3 6 ~

0 2 3 8 u

- 1" -

-

- J ¹

0-- _I

-

I

Work s u p p o r t e d b y t h e B u n d e s m i n i s t e r i u m f u r F o r s c h u n g u n d T e c h n o l o g i e

m a t e d b y s u b t r a c t i n g t h e s p i n o f t h e r o t a t - 100 200 300 400 500 E ( I ) -E(I-2) [ k e V I i n g c o r e f r o m t h e m e a s u r e d a n g u l a r momentum3).

R e f e r e n c e s :

1 ) P . F u c h s e t a l . , GSI Annual R e p o r t 1 9 7 7 4 ) S . F r a u e n d o r f a n d R . S . S i m o n , p r i v a t e 2 ) R . P i e r c e y e t a l . , P r o c . I n t . C o n f . on c o m m u n i c a t i o n

Band S t r u c t u r e a n d N u c l e a r D y n a m i c s , 5 ) M . S e i w e r t a n d P . Hes's, U n i v e r s i t a t New O r l e a n s , 1 9 8 0 t o be pub1 i s h e d F r a n k f u r t , p r i v a t e c o m m u n i c a t i o n 3 ) R . B e n g t s s o n a n d S . F r a u e n d o r f , N u c l . 6 ) A . Arima a n d F . I a c h e l l o , Ann. P h y s .

P h y s .

A314

( 1 9 7 9 ) 2 7 a n d

A327

( 1 9 7 9 ) 1 3 9 ( N . Y . ) 1 1 1 ( 1 9 7 8 ) 2 0 1