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The s e l e c t i v i t y and t h e s u r p r i s i n g s i m p l i c i t y of response function f o r spin-isospin t r a n s i t i o n s with t h e (p,n) r e a c t i o n a t intermediate energies has been AL=O t r a n s f e r s f o r 5 4 9 5 6~e t a r g e t s . I n t h e case of used t o study the spin-isospin c o r r e l a t i o n s i n n u c l e i t h e N i i s o t o p e s , a comparison may be made with t h e M1 (see Ref. 1 and o t h e r references within). The zero s p e c t r a obtained from e l e c t r o -e x c i t a t i o n . 3 9 degree s p e c t r a have been used t o o b t a i n t h e AL = 0 The experimental r e s u l t s and a n a l y s i s f o r the response function of n u c l e i while t h e measured2 energy 5 8~i ( p , n ) 5 8~u r e a c t i o n have been published3; t h e dependence of the e f f e c t i v e n u c l e o n n u c l e u s i n t e r a c t i o n a n a l y s i s f o r t h e o t h e r i s o t o p e s is i n progress.r e s u l t i n g from the spin-isospin terms i n the The double d i f f e r e n t i a l c r o s s s e c t i o n of L = 0 nucleonnucleon f o r c e has been employed t o i d e n t i f y t h e s t r e n g t h observed a t ( 3~ = 0' f o r t h e 5 8~i ( p , n ) 5 8~u spin-isospin o r Gamow-Teller strength. Other r e a c t i o n is presented i n Fig. l b and i s compared i n multipoles observed a t higher e x c i t a t i o n energies Fig. l c with the B(M1)C s t r e n g t h reported4 f o r t h e i n d i c a t e a maximum d i f f e r e n t i a l c r o s s s e c t i o n a t 5 8~i ( e , e ' ) reaction. The l o c a t i o n s of known 1+ e x c i t e ds l i g h t l y higher angles and have been i n t e r p r e t e d a s s t a t e s i n A = 58 n u c l e i a r e shown i n Fig. la. (AL = 1, AS = 1) and (AL = 2, AS = 1) e x c i t a t i 0 n s . l *permanent address: C e n t r a l Research I n s t i t u t e f o r W e have obtained 160 MeV (p,n) d a t a on 5 4 * 5 6~e and Physics, Budapest, Hungary.5 8 * 6 0~i and 120 MeV d a t a f o r t h e 5 8~i ( p , n ) 5 8~u r e a c t i o n 1) C. Gaarde e t a l . , Nucl. Phys. A369, 258 (1981).i n order t o study t h e response function of 5 8 * 6 0~i 2) T.N. Taddeucci e t a l . , Phys. Rev. C 25, 1094 (1981).t a r g e t s t o spin-isospin t r a n s i t i o n s characterized with 3) J. Rapaport e t al., Phys. Lett. 119B, 61 (1982). AL = 0, AL = 1 and AL = 2 t r a n s f e r s and t o study t h e 4) R.A. Lindgren e t a l . , Phys. Rev. C 3, 1789 (1976).

At intermediate energies, the differential cross quantity R(Ep) thus represents very nearly the ratio of sections at 8=0° for hJJE=l+ and O+ (p,n) transitions interaction strengths I Ja,/J, 1. In Fig. 1 we plot are proportional to the reduced transition probabilities B(GT) and B(F) for the analogous Gamow-Teller (GT) and Fermi (F) beta decays, respectively. This proportionality may be exploited to gain information about the isovector effective i n t e r a c t i o n s t r e n g t h s . For even-A t a r g e t s wed e f i n e the empirical quantity [R(E~)]* = [C~~~(O")/B(GT)][B(F)/C~(~~)] where B(GT) and B(F) are obtainable from measured beta-decay ft values according to1 B(F)+(~ .~5)~~(~~)=(6163.4 sec)/ft . A

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The 28 Si͑a, 8 He͒ 24 Si reaction has been used to measure the energies of the first two excited states in 24 Si. The excitation energies were found to be 1.879 6 0.011 and 3.441 6 0.010 MeV. These data allow for the first time the calculation of the stellar reaction rate of 23 Al͑ p, g͒ 24 Si on the basis of experimental information. This reaction is of considerable interest, since it might lead to a decrease of the 22 Na production in nova explosions, and solve the discrepancy between the 22 Na yield predictions of nova models and recent COMPTEL observations. We show, however, that the temperatures and densities required for a significantly reduced 22 Na yield are not reached in current nova models. [S0031-9007(97)04602-4]

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