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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).

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The Gamow-Teller strength function in 71 Ge has been measured by use of the reaction 71 Ga(/?,/2 ) at E p = 120 and 200 MeV. While a significant fraction of the total strength is associated with excited states located below particle-emission threshold, the first excited state exhibits little strength. Excited-state contributions to the total solar-neutrino capture rate for a 71 Ga detector are about 14 solar neutrino units for the neutrino spectrum of the standard solar model and about 3-4 solar neutrino units for representative nonstandard solar models.PACS numbers: 25.40. Ep, 23.40.Hc, 27.50. + e, 96.60.Kx The discrepancy between the solar-neutrino capture rate observed in the 37 C1 experiment 1 and that predicted by the standard solar model 2 (SSM) has been a problem for almost two decades. The 37 C1 detector is sensitive only to neutrino energies above 814 keV, resulting in a response which is primarily dependent on the higher-energy (0-14 MeV) 8 B neutrinos. 3 Solar-neutrino capture via the reaction 71 Ga(v e , e~) ll Ge has a threshold 4 of only 233 keV and has been proposed 5 as a way to determine whether the 37 C1 discrepancy is caused by an inadequacy in our understanding of the solar interior (astrophysics) or by neutrino oscillations or decay (neutrino propagation). The flux of low-energy (0-420 keV) neutrinos arising from the reaction p +p -> 2 H + e + + v is relatively insensitive to the solar model, but neutrino oscillations would for some range of neutrino masses reduce solar electron-neutrino fluxes by factors which depend upon neutrino energy. 4,6 The neutrino-capture cross section to the ground state (g.s.) of 71 Ge can be calculated reliably by use of the ft value for 71 Ge(/3 + ) 71 Ga. On the basis of betadecay systematics in the neighboring mass region, Bahcall 7 estimated small contributions to the total capture cross section from low-lying excited states in 71 Ge. It follows that 63% of the capture events on 71 Ga would come from p+p neutrinos if the SSM flux is assumed. Transitions to highly excited states would enhance the overall response of the Ga detector but thereby dilute its relative sensitivity to p +p neutrinos. Since electron capture (EC) half-lives cannot be measured for the excited states and theoretical calculations 8,9 are model dependent, we have utilized the established relationship 10 between /3-decay Gamow-Teller transition strength B(GT) and (p,n) zero-degree differential cross section cr(0°) for E P ~~ 100-200 MeV to mea-

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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