Elastic scattering of polarized deutrons from 4He between 18 and 22 MeV

Volume 22, number 4

ELASTIC

PH Y S I C S LE T T E RS

1 September 1966

SCATTERING OF POLARIZED DEUTERONS FROM 4He BETWEEN 18 A N D 22 M e V

J . ARVIEUX, P . D A R R I U L A T , D. GARRETA, A. P A P I N E A U , A. TARRATS and J . TESTONI * Centre d'Etudes Nucl~aires de Saclay

Received 4 July 1966 Angular distributions of polarized deuterons scattered from 4He have been measured for 17.7, 19.7 and 21.4 MeV incident energy. Vector- and tensor-polarization parameters are presented.

E l a s t i c s c a t t e r i n g of d e u t e r o n s f r o m 4He in the v i c i n i t y of the 3He + 3H t h r e s h o l d has r e c e n t l y b e e n the s u b j e c t of s e v e r a l e x p e r i m e n t a l i n v e s t i gations; the d a t a d i s a g r e e s l i g h t l y but show an i m p o r t a n t e n e r g y d e p e n d e n c e of the d i f f e r e n t i a l c r o s s s e c t i o n [1-4]. P h a s e shift a n a l y s i s of low e n e r g y d a t a [5, 6] a p p e a r s to b e a p o w e r f u l tool in u n d e r s t a n d i n g the l e v e l s c h e m e of 6Li, to which t h e o r e t i c a l i n t e r e s t i s a t t a c h e d , due to the s i m p l i c i t y of i t s s h e l l m o d e l [7] and c l u s t e r m o d e l [8] descriptions. Furthermore, polarization parame t e r s can be c o m p u t e d f r o m the p h a s e shifts a l lowing d e u t e r o n - a l p h a s c a t t e r i n g to be u s e d e i t h e r a s an a n a l y z e r o r a s a g e n e r a t o r of p o l a r i z e d deuterons. Towards higher energies, extraction of p h a s e s h i f t s f r o m the c r o s s s e c t i o n d a t a b e c o m e s quickly a m b i g u o u s : a b s o r p t i o n i s s o i m p o r t a n t that the s e n s i t i v i t y of the s c a t t e r i n g a m p l i t u d e s to the r e a l p a r t s of the p h a s e s h i f t s is weakened; on the o t h e r hand, v a r i o u s s e t s of p h a s e s h i f t s can g e n e r a t e the s a m e c r o s s s e c t i o n and a knowledge of the p o l a r i z a t i o n p a r a m e t e r s i s n e e d e d to d i s c r i m i n a t e b e t w e e n t h e m [9, 10]. The p u r p o s e of t h i s note is to r e p o r t on a m e a s u r e m e n t of t h e s e p a r a m e t e r s at 17.7, 19.7 and 21.4 MeV i n c i d e n t d e u t e r o n e n e r g y . The 22 MeV p o l a r i z e d d e u t e r o n b e a m (2 × 108 p a r t i c l e s p e r second; e n e r g y s p r e a d 300 keY) of the S a c l a y f i x e d f r e q u e n c y c y c l o t r o n i s b r o u g h t to a focus in a h e l i u m t a r g e t , the p r e s s u r e of which (2 k g / c m 2) i s kept c o n s t a n t by m e a n s of a m e r cury manostat. A carbon polarimeter located d o w n s t r e a m a l l o w s continuous m o n i t o r i n g of the b e a m p o l a r i z a t i o n . Two a l u m i n i u m a b s o r b e r s , 0.2 m m thick, a r e u s e d in such a way that the * I . A . E . A . F e l l o w . Permanent address: C . N . E . A . , Laboratorio del Sincrociclotron, Buenos Aires (Argentina).

e n e r g y r e m a i n s the s a m e in the p o l a r i m e t e r but can take, in the c e n t e r of the g a s t a r g e t , the v a l u e s 17.7, 19.7 and 21.4 MeV. Two c o u n t e r t e l e s c o p e s (2.2 ° a n g u l a r r e s o l u t i o n ) can be r o t a t e d a r o u n d the g a s t a r g e t on e a c h s i d e of the b e a m . E a c h c o u n t e r i s m a d e of a p a i r of s o l i d s t a t e s i l i con d e t e c t o r s (one s u r f a c e b a r r i e r , one l i t h i u m d r i f t e d ) in o r d e r to d i s c r i m i n a t e b e t w e e n the s c a t t e r e d d e u t e r o n s and the b r e a k u p p r o t o n s . In a few i n s t a n c e s ( f o r w a r d a n g l e s ) , the ~ r e c o i l s can be d e t e c t e d . A f t e r a m p l i f i c a t i o n through s t a n d a r d e l e c t r o n i c c i r c u i t r y , the p u l s e s a r e a n a l y s e d in a 4 0 0 0 - c h a n n e l k i c k s o r t e r . A b s o r b e r s l o c a t e d in f r o n t of the p o l a r i m e t e r c o u n t e r s (lithium d r i f t e d s i l i c o n d e t e c t o r s at 50o lab angle) allow s e l e c t i o n of the p r o t o n group in the 12C(d,p)13C r e a c t i o n , the p u l s e s being r e c o r d e d on s c a l e r s a f t e r a m p l i fication. The incident d e u t e r o n b e a m i s p o l a r i z e d b e f o r e a c c e l e r a t i o n [11], the sign of i t s t e n s o r - and v e c t o r - c o m p o n e n t s b e i n g r e v e r s e d e v e r y 0.2 s e c o n d . This a l l o w s , by d e t e c t i n g the s c a t t e r e d p a r t i c l e s in both h o r i z o n t a l and v e r t i c a l p l a n e s , to m e a s u r e the following q u a n t i t i e s ltl P

= : ~ " 1- -

Q

=

~

,

¢0 +

=

-q~ 2),

the t~ b e i n g the h e l i c i t y c o m p o n e n t s on the i r r e d u c i b l e t e n s o r o p e r a t o r s [12]

1 D , ,,~-1~1-m' T ixt =-~ mm

(llm-m'lxu) llm>(lm'[ 439

Volume 22, number 4

P HYSI CS L E T T E RS

1 September 1966

~) @ @ T~) @ @ @ 179T~@ @ @ 1~o1~ 10.

!

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Fig. 1. A s y m m e t r y p a r a m e t e r s P, Q and R as defined in the text for 17.7, 19.7 and 21.4 MeV incident energy. The solid curves are the results of a preliminary phase shift analysis. of the d e n s i t y m a t r i x

-i~

P - 3 Xg

(_i)~ t ~x T _ ~

w h i c h w o u l d d e s c r i b e the s c a t t e r e d p a r t i c l e s if the incident beam were unpolarized. They are r e l a t e d to S e n h o u s e ' s ' [9] t h r o u g h the r o t a tion matrices = (0, 0, 0 ) t k. ,

where O is the center-of-mass scattering angle. The results are presented in fig. I. Error bars include statistical and systematic uncertainties. Absolute normalization is achieved by comparing the polarimeter data with previous results of Beurtey [II]; an uncertainty of 6% is attached to this normalization. No important energy dependence, as could be expected from ref. 4, is found. The asymmetries are smaller than at lower energies: helium does 440

not a p p e a r a s v e r y e f f i c i e n t a n a l y z e r of d e u t e r o n s in the 20 M e V r e g i o n . A p r e l i m i n a r y p h a s e s h i f t a n a l y s i s of the d a t a ( i n c l u d i n g c r o s s s e c t i o n m e a s u r e m e n t s [2, 3 , 4 ] ) s h o w s that F and G w a v e s c o n t r i b u t e to the s c a t t e r i n g . The P w a v e s r e m a i n u n s p l i t t e d and the c o u p l i n g p a r a m e t e r s a r e s m a l l . High a b s o r p t i o n c o e f f i c i e n t s a r e n e e d e d to fit the l a r g e f o r w a r d differential cross sections, generating reaction c r o s s s e c t i o n s of the o r d e r of 3 to 4 b a r n . A m o r e d e t a i l e d a c c o u n t of t h i s w o r k w i l l b e published later.

_T~efe~'~ces 1. K . P . A r t e m o v and N.A. Vlasov, Soviet Phys. - J E T P 12 (1961) 1124. 2. H . J . . E r r a m u s p e and R. J. Slobodrian, Nucl. Phys. 49 (1963) 65. 3. H.W. Broek and J. L. Yntema, Phys. Rev• 135 (1964) B678.

Volume 22, number 4

P HYSICS L E T T E RS

4. W.T.H..Van Oers and K.W.Broclmmn J r . , Nucl. Phys. 44 (1963) 546. 5. T.Lauritsen, T.Huus and S.G. Nflsson, Phys.Rev. 92 (1953) 1501. 6. A. Galonsky and M. T. Me Ellistrem, Phys. Rev. 98 (1955) 590. 7. D.R.Inglis, Phys.Rev.87 (1952) 915. 8. J . L . G ~ m m e l , B . J . H i l l and R.M.Thaler, Helv.Phys.

ON

THE

1 September 1966

Acta-Supp. VI (1961) 409. 9. L.S. Senhouse Jr. and ~ . A . ~ m b r e l l o , Nucl. Phys. 57 (1964) 624. 10. L.C.Me/ntyre andW~Hmiherli, BulLAm. Phys.

Soc.9 (1964) 627. I I . R. Beurtey, I~,mm~CF_,A-~ 2 ~ C . E . N . Saclay. 12. J. Raynal, ~ r t ~ C E A - ~ Z5~11~ C. E. N. Saelay.

ENERGIES OF THE OCTUPOLE STATES OF EVEN-EVEN IN THE ENERGY REGION 2 2 8 ~ A -.< 2 5 4

NUCLEI

L . A . M A I , O V , V.G.SOLOVIEV and P . V O G E L Joi~t Institute f o r Nuclear Research, Laboratory of Theoretical tT!tysic~, Dubna, USSR Received 15 June 1966

More accurate calculations of the energies of octupole states of even nuclei in the region 228 ~
The n u c l e a r model with p a i r i n g and octupoleoctupole i n t e r a c t i o n was used in ref. 1 to c a l c u late the e n e r g i e s of the octupole s t a t e s of e v e n even d e f o r m e d n u c l e i and t h e i r s t r u c t u r e . The r e s u l t s of the c a l c u l a t i o n s a r e in s a t i s f a c t o r y a g r e e m e n t with the c o r r e s p o n d i n g e x p e r i m e n t a l data including those obtained a f t e r p e r f o r m i n g c a l c u l a t i o n s , e . g . ref. 2. The only f r e e p a r a m e t e r - the o c t u p o l e - o c t u p o l e i n t e r a c t i o n c o n s t a n t K(3) - was chosen so as to obtain the b e s t a g r e e m e n t between the c a l c u l a t e d and e x p e r i m e n t a l e n e r g i e s of the KIr = 0 - s t a t e s in the r e g i o n 228 --< ~
further experimental investigations. The e n e r g i e s and the s t r u c t u r e of .the K ~ = 1and 2- s t a t e s a r e c a l c u l a t e d for ~(3) = 0.00045 ~ o while for the K~r = 0- s t a t e s the value of K(3) is taken by 10% s m a l l e r in o r d e r to i m p r o v e effectively the a c c u r a c y of the method. The twot h r e e f i r s t poles a r e equal to the e n e r g i e s of the t w o - q u a s i - p a r t i c l e s t a t e s given i n ref. 4. The value of K(3) is d e c r e a s e d as c o m p a r e d to the c a l c u l a t i o n s in ref, 1; b e c a u s e of the i n c r e a s e of the n u m b e r of the a v e r a g e field l e v e l s the c a l culations a r e made a c c o r d i n g the s c h e m e II given in ref. 5. The r e s u l t s of c a l c u l a t i o n s a r e t a b u lated. F r o m table 1 it is s e e n that the c a l c u l a t e d e n e r g i e s a g r e e sufficiently well with e x p e r i m e n tal data. By making K(3) m o r e a c c u r ~ t e one has obtained s o m e i m p r o v e m e n t of a g r e e m e n t with e x p e r i m e n t as c o m p a r e d with the r e s u l t s of p a p e r 1. We d i s c u s s the p e c u l i a r i t i e s of the octupole s t a t e s in s o m e n u c l e i . The PrK =1-1 s t a t e in 234U p o s s e s s e s an e n e r g y of 1438 keV [6], the c a l c u lated e n e r g y of the f i r s t PrK =1-1 s t a t e is 940 keV and of the second one is 1450 keV, It may be t h e r e f o r e a s s u m e d that the e x p e r i m e n t a l l y obs e r v e d / T r K = l - 1 s t a t e of e n e r g y 1438 keV is the second f~K = 1-1 s t a t e . An i n t e r e s t i n g s i t u a t i o n takes p l a c e in 246Cm. In ref. 2 t h r e e octupole s t a t e s a r e o b s e r v e d , two with PrK--1-1 and e n e r g i e s 1080 and 1351 keV and one w i t h / ~ K = 2 - 2 and e n e r g y 842 keV. According 441