High energy-resolution measurement of the Se82(He3,t)Br82 reaction for double- β decay and for solar neutrinos

For this study, a high-resolution (³He,t) charge-exchange experiment at an incident energy of 420 MeV has been performed on the double beta (ββ) decay nucleus ⁸²Se. A detailed Gamow-Teller (GT^-) strength distribution in ⁸²Br has been extracted, which provides information to the ββ-decay nuclear matrix elements. Three strong and isolated transitions, which are to the 75, 1484 and the 2087 keV states in ⁸²Br, are found to dominate the low-excitation region below ≈ 2.1 MeV. Above 2.1 MeV a sudden onset of a strong GT fragmentation is observed. The degree of fragmentation resembles a situation found in the neighboring A = 76 system ⁷⁶Ge, whereas the observed concentration of strength in the three low-lying states is reminiscent of the heavier neighbors ⁹⁶Zr and ¹⁰⁰Mo. The strong GT transition to the 75 keV (1⁺) state makes ⁸²Se interesting for solar neutrino detection. The ⁸²Se(ν_e,e^-) ⁸²Br solar neutrino capture rate in a nonoscillation scenario is therefore evaluated to 668 ± 12(stat) ± 60(sys) SNU, and some of the advantages of using selenium for solar neutrino studies are discussed.