New Precision Measurement of theHe3(He4,γ)Be7Cross Section

The ${}^3\mathrm{H}\mathrm{e}({}^4\mathrm{H}\mathrm{e},\gamma ){}^7\mathrm{B}\mathrm{e}$ reaction plays an important role in determining the high energy solar neutrino flux and in understanding the abundances of primordial ${}^7\mathrm{L}\mathrm{i}$. This Letter reports a new precision measurement of the cross sections of this direct capture reaction, determined by measuring the ensuing ${}^7\mathrm{B}\mathrm{e}$ activity in the region of $E_{\mathrm{c}.\mathrm{m}.}=420$ to 950 keV. Various recent theoretical fits to our data result in a consistent extrapolated value of $S_{34}(0)=0.53(2)(1)\mathrm{k}\mathrm{e}\mathrm{V}\mathrm{b}$.