Low-EnergyHe3(α, γ)Be7Cross-Section Measurements

The cross section and branching ratio for ${}_{}{}^3{}_{}{}^{}\mathrm{He}(\alpha , \gamma ){}_{}{}^7{}_{}{}^{}\mathrm{Be}$ have been measured from $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=165\mathrm{} \mathrm{to} 1170$ keV by counting prompt $\gamma$ rays from a windowless, recirculating, ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ gas target. Absolute cross sections were also measured at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=945\mathrm{} \mathrm{and} 1250$ keV by measuring the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ activity produced in a ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ gas cell with a Ni entrance foil. The inferred zero-energy intercept is $S_{34}\mathrm{}\left(0\right)=0.52\mathrm{}\pm 0.03$ keV b. The effect of this extrapolated value on the solar-neutrino problem is discussed.