Volume 32B. number 8 P H Y S I C S L E T T E R S 14 September 19~

C O R E E X C I T A T I O N I N 3 0 p

M. WAYNE G R E E N E *, L. L. G R E E N and G. D. J O N E S

O l i v e r Lodge L a b o r a t o r y , Un iver s i t y o f L i v e r p o o l , UK **

Received I0 August 1970

A study of 30p by the 29Si(3He, d) reaction indicates that the level at 2.84 MeV excitation has J?T= 1 + in conflict with a previous JY = 3 + assignment. Spectroscopic factors obtained for levels below 3.5 MeV excitation are compared with predictions from collective and shell model calculations.

The l o w - l y i n g s t a t e s in 3 0 p h a v e b e e n e x t e n - s i v e l y s t u d i e d by the 27A1(~, ny), 28Si (3He, pv) and 29Si(p, 7) r e a c t i o n s [1-4] . We h a v e s t u d i e d t h e s e s t a t e s wi th the 29Si(3He, d ) 3 0 p (Q = 0 .099 MeV) r e a c t i o n and p r e s e n t the r e s u l t s a s wel l a s p o i n t ou t an i n c o n s i s t e n c y wi th a p r e v i o u s sp in Ex a s s i g n m e n t . (MeV)

A 3He++ b e a m of 15 MeV f r o m the O x f o r d [2] U n i v e r s i t y t a n d e m a c c e l e r a t o r w as u s e d to b o m - b a r d s e l f - s u p p o r t i n g 65 g g / c m 2 e n r i c h e d 29Si t a r g e t s (28Si 4.7%, 2 9 S i 95% and 30Si 0.3%) in 0 c o n j u n c t i o n wi th a m u l t i g a p m a g n e t i c s p e c t r o - m e t e r . T h e e x p o s u r e s w e r e m a d e at 3.75 ° i n t e r - 0.677 v a l s a n d a c h a r g e of 500 ~C w a s c o l l e c t e d . 2.538 2

T h e d e u t e r o n a n g u l a r d i s t r i b u t i o n s shown in 2.937 2 f ig. 1 h a v e b e e n c o m p a r e d wi th D W B A c a l c u l a - t i o n s a n d the e x t r a c t e d s p e c t r o s c o p i c i n f o r m a - 0.708 O+2 t i o n i s g i v e n in t a b l e 1. T he o p t i c a l p a r a m e t e r s w e r e t a k e n f r o m M o r r i s o n [5] and J o n e s e t al . [6]. N o n - l o c a l c o r r e c t i o n s w e r e u s e d in the en - 1.454 2 t r a n c e and ex i t c h a n n e l s bu t no t in the b o u n d - 1.972 2 s t a t e c h a n n e l . The b o u n d - s t a t e wave f u n c t i o n s w e r e g e n e r a t e d wi th a S a x o n - W o o d s p o t e n t i a l of

2.723 r a d i u s 1.33 fm and d i f f u s e n e s s of 0.5 fro. T h e (3He, d) o v e r l a p n o r m a l i z a t i o n of 4 .42 c a l c u l a t e d 2.839 by B a s s e l [7] w a s u s e d in d e t e r m i n i n g the s p e c - 3.018 t r o s c o p i c f a c t o r s . T he DWBA f i t s w e r e in g e n - e r a l v e r y good wi th the e x c e p t i o n of the two 3 + l e v e l s at 1 .98 and 2.54 MeV. F o r the 0.71 M e V s t a t e i s was n e c e s s a r y to i n c l u d e s o m e /p = 2 s t r e n g t h to the p r e d o m i n a n t /p = 0 s t r e n g t h .

The l e v e l a t 2.84 M e V h a s an lp = 0 a n g u l a r

* Nuclear Physics Research Fellow. Univers i ty of Liverpool.

** This work was supported by grants f rom the U.K. Science Research Council.

Table 1

Summary of spect roscopic information from the

29Si(3He, d)30p react ion

Sp

lp Jf~ T K Exper i - Collective Shell model mental [9] [101

0.177 (/p=0) 0.464 (lp=0)

0 1 + 0 0 0.961 0.036(lp=2) 0.749 (lp=2)

0 0 + 1 0 1.00 0.533 1.452

3 + 0 0 0.059 0.051 0 +

2 1 0 0.656 0.093 0.934

1 + 0 1 0.107 (/p=0) 0.355 (/p=0) 1.536 (/p=0)

0.044 (/p=2) 0.018 (/p=2) 0.222 (/p=2)

2 + 0 1 0.645 0.080 1.000

3 + 0 1 0.037 0.068

2 2 + 0 - 0.080

0 1 + 0 - 0.089

0 1 + 0 - 0.167

Summed s t rength for lp = O, T = O, ~(2J f+l )Sp = 3.97 (experimental) ,

" = 6.0 (theoretical),

d i s t r i b u t i o n w h i c h r e s t r i c t s i t s j v v a l u e s to 0 + o r 1 +. T h i s s t a t e ]ms p r e v i o u s l y b e e n a s s i g n e d

j v = 3 + f r o m ~ g S i ( p , y ) 3 0 p c o r r e l a t i o n s t u d i e s [4]. V e r m e t t e e t al . [3] m e a s u r e d t he p - ~ c o r r e l a t i o n f r o m the 28Si (3He , p-r )30p r e a c t i o n fo r t h i s s t a t e and found a l a r g e a 2 / a 0 c o e f f i c i e n t f o r the L e g e n -

680

Volume 32B, number 8 P H Y S I C S L E T T E R S 14 September 197(

so( \ 29Si(3He.d )30p

lp =0 E ( ~ e ) =15.00 MeV

IQ(

• j n = 1"

I0.I - ~s.s [ p = 2

so " " I'-~" ~ I~ ~.., j.°2"

\ ,o L_

{ \

0. I \1 _ ¢ x

\

VI"

I I I 4 I i i I ~s 3o ~s eo is 3o ~:~ 6o

O~m 8cm

Fig. 1. Comparison of deuteron angular distributions measured in the 295i(3He, d)30p reaction for E(3He) = 15.00 MeV and the DWBA calculations. The parameters for the 3He potential are: U= 173.0 MeV, W= 18.6 MeV, ru=l.07 fro, rw= 1.657 fm, au=0.795 fm and aw= 0. 762 fm. The deuteron optical parameters are: U= 91.08 MeV, W=27.40 MeV, ru=l.20 fro, rw=l.51 fm, au=0.78 fm and t~v= 0.48 fro. The parity assignments are from the present work and the indicated spin assignments are a combination of the present and previous work [1-4].

d r e p o l y n o m i a l f i t w h i c h would e l i m i n a t e a J = 0 a s s i g n m e n t . T h e y c o n c l u d e d t h a t the sp in f o r t h i s s t a t e w a s J = 1, 2 o r 3 b u t r u l e d out J = 1 a s i t w a s t h r e e t i m e s l e s s p r o b a b l e t h a n J= 2 o r 3. The

m e a n l i f e t i m e m e a s u r e d by J a m e s e t al . [2] of 1.25 + 0 .20 p s l e a d s to M1 s t r e n g t h s (if one a s - s u m e s 6 ( E 2 / M 1 ) = 0) of 0.22 + 0.04, 1.3 + 0.2 an t 3 . 0 ± 0.5 m W . u . f o r the 2 . 8 4 - 0, 2 . 8 4 - 0.71 an~ 2 .84 ~ 1.45 M e V t r a n s i t i o n s , r e s p e c t i v e l y . Thes , v a l u e s a r e c o n s i s t e n t w i th t a b u l a t e d v a l u e s [8] fo: s e l f - c o n j u g a t e n u c l e i wi th A < 40 and f u r t h e r s u p p o r t the J ~ = 1 + a s s i g n m e n t fo r the 2 .84 M e V sta~

The e x p e r i m e n t a l s p e c t r o s c o p i c f a c t o r s a r e s u m m a r i z e d in t a b l e 1 a s we l l a s the t h e o r e t i c a l v a l u e s c a l c u l a t e d wi th N i l s s o n wave f u n c t i o n s by W a l s h [9] a n d s h e l l m o d e l v a l u e s c a l c u l a t e d by G l a u d e m m l s et a l . [10]. The N i l s s o n m o d e l s p e c - t r o s c o p i c f a c t o r s w e r e c a l c u l a t e d by c o u p l i n g the c a p t u r e s p r o t o n to a d i s t o r t e d 29Si c o r e . T h e d is t o r t i o n w a s a s s u m e d to be o b l a t e [11] a n d fl = -0 . w a s c h o s e n [12]. It was not ~ o s s i b l e to d e s c r i b e a l l t he l o w - l y i n g l e v e l s in 3 U l wi th s i m p l e m o d e l B o t h m o d e l s a r e on ly p a r t i a l l y s u c c e s s f u l in de s . c r i b i n g t h e s e l e v e l s . P a r t of t h i s d i s c r e p a n c y , a t t r i b u t e d to the p r e s e n c e of c o r e e x c i t a t i o n in 29Si , i s e v i d e n c e d by the p r e s e n c e of the two 3 + l e v e l s a t 1 .97 and 2.54 MeV. Iu s u m m a r y , i t i s o b v i o u s t h a t m o r e s o p h i s t i c a t e d m o d e l c a l c u l a t i o : w h i c h i n c l u d e c o r e e x c i t a t i o n a r e n e e d e d to e x - p l a i n the l o w - l y i n g s t a t e s in 30p .

We would l ike to t h a n k Dr . I. M. Naq ib a n d Dr . B. C. W a l s h f o r he lp fu l d i s c u s s i o n s . We a r e g ra t{ ful to Dr . W. D a r c e y , Dr . K. J o n e s and M r . J . Mo: ton f o r t h e i r h o s p i t a l i t y whi l e the e x p e r i m e n t wa~, b e i n g p e r f o r m e d at O x f o r d U n i v e r s i t y .

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[3] C, W. Vermette, W. C. Olsen, D. A. Hutcheon and D. H. Sykes, Nuel. Phys. Al l l (1968) 39.

[4] G. I. Harris and A. K. Hyder, Phys. Rev. 157 (1967) 9 G. I. Harris, A.K. Hyder and J. Walinga, Phys. Rev. 187 (1969) 1413.

[5] R. A. Morrison, Nucl. Phys. A140 (1970) 97. [6] G. D. Jones, R.R. Johnson and R. J. Griffiths, Nuel°

Phys. AI07 (1968) 659. [7] R.H, Bassel, Phys. Rev. 149 (1966) 791. [8] S. J. Skorka, J. Hertel and T. W. Retz-Sehmidt,

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