A New precision measurement of the Be-7(p,gamma) B-8 cross-section with an implanted Be-7 target

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 7Be target, a raster scanned beam and the elimination of the backscattering loss. The new measurement incorporates a more abundant 7Be target and a number of improvements in design and procedure. The point at Elab=991 keV was measured several times under varying conditions, yielding a value of S17(Ec.m. =850 keV) = 24.0(5) eV b. Measurements were carried out at lower energies as well. Due to the precise knowledge of the implanted 7Be density profile it was possible to reconstitute both the off- and on resonance parts of the cross section and to obtain from the entire set of measurements an extrapolated value of S17(0)=21.2(7) eV b.