He3(α,γ)Be7cross section at low energies

The flux of ${}^7\mathrm{Be}$ and ${}^8\mathrm{B}$ neutrinos from the Sun and the production of ${}^7\mathrm{Li}$ via primordial nucleosynthesis depend on the rate of the ${}^3\mathrm{He}$($\alpha ,\gamma$)${}^7\mathrm{Be}$ reaction. In an extension of a previous study showing cross section data at 127–167 keV center-of-mass energy, the present work reports on a measurement of the ${}^3\mathrm{He}$($\alpha ,\gamma$)${}^7\mathrm{Be}$ cross section at 106 keV performed at Italy's Gran Sasso underground laboratory by the activation method. This energy is closer to the solar Gamow energy than ever reached before. The result is $\sigma =0.567\pm 0.{029}_{\mathrm{stat}}\pm 0.{016}_{\mathrm{syst}}$ nb. The data are compared with previous activation studies at high energy, and a recommended $S(0)$ value for all ${}^3\mathrm{He}$($\alpha ,\gamma$)${}^7\mathrm{Be}$ activation studies, including the present work, is given.