New measurement of the proton capture rate on7Beand theS17(0)factor

The 7Be(p,gamma)8B reaction plays a central role in the evaluation of solar neutrino fluxes. We report on a new precision measurement of the cross section of this reaction, following our previous experiment with an implanted target, a raster scanned beam and the elimination of backscattering losses. The new measurement incorporates a higher activity 7Be target and a number of improvements in design and procedure. The cross section at Ec.m. = 850 keV was measured several times under varying expermental conditions, yielding a value of S17(Ec.m.=850 keV) = 24.0 +/- 0.5 eV b. Measurements were carried out at lower energies as well. We obtain from the entire set of measurements an extrapolated value of S17(0) = 21.2 +/- 0.7 eV b.