High Energy-Resolution Measurement of These82(he3,t)br82

A high-resolution ($^{3}\mathrm{He},t$) charge-exchange experiment at an incident energy of 420 MeV has been performed on the double beta ($\ensuremath{\beta}\ensuremath{\beta}$) decay nucleus $^{82}\mathrm{Se}$. A detailed Gamow-Teller (${\mathrm{GT}}^{\ensuremath{-}}$) strength distribution in $^{82}\mathrm{Br}$ has been extracted, which provides information to the $\ensuremath{\beta}\ensuremath{\beta}$-decay nuclear matrix elements. Three strong and isolated transitions, which are to the 75, 1484 and the 2087 keV states in $^{82}\mathrm{Br}$, are found to dominate the low-excitation region below $\ensuremath{\approx}2.1$ 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 $^{76}\mathrm{Ge}$, whereas the observed concentration of strength in the three low-lying states is reminiscent of the heavier neighbors $^{96}\mathrm{Zr}$ and $^{100}\mathrm{Mo}$. The strong GT transition to the 75 keV $({1}^{+})$ state makes $^{82}\mathrm{Se}$ interesting for solar neutrino detection. The $^{82}\mathrm{Se}({\ensuremath{\nu}}_{e},{e}^{\ensuremath{-}})^{82}\mathrm{Br}$ solar neutrino capture rate in a nonoscillation scenario is therefore evaluated to $668\ifmmode\pm\else\textpm\fi{}12\text{(stat)}\ifmmode\pm\else\textpm\fi{}60\text{(sys)}$ SNU, and some of the advantages of using selenium for solar neutrino studies are discussed.