High energy-resolution measurement of the Se 82 (He 3,t) Br 82 reaction for double- β decay and for solar neutrinos

A high-resolution (He3,t) charge-exchange experiment at an incident energy of 420 MeV has been performed on the double beta (ββ) decay nucleus Se82. A detailed Gamow-Teller (GT-) strength distribution in Br82 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 Br82, 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 Ge76, whereas the observed concentration of strength in the three low-lying states is reminiscent of the heavier neighbors Zr96 and Mo100. The strong GT transition to the 75 keV (1+) state makes Se82 interesting for solar neutrino detection. The Se82(νe,e-)Br82 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.