The absolute total cross section for the reaction ${}_{}{}^7{}_{}{}^{}\mathrm{Be}(p, \gamma ){}_{}{}^8{}_{}{}^{}\mathrm{B}$ has been measured for $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=117-1230\mathrm{}$ keV by detecting the delayed $\alpha$ particles following the ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ $\beta$ decay. Two independent methods have been used to determine the areal density of the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ target. The inferred zero-energy $S$ factor from the present experiment is $S_{17}\mathrm{}\left(0\right)=0.0216\mathrm{}\pm 0.0025$ keV b. This value reduces the predicted ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ solar-neutrino capture rate by ∼25%.

• Received 4 November 1982

DOI:https://doi.org/10.1103/PhysRevLett.50.412