A new measurement of the 7Be(p,γ)8B cross-section with an implanted 7Be target

The 7Be(p,γ)8B capture reaction is of major importance to the physics of the sun and the issues of the “solar neutrino puzzle”. We report here on a new determination of the absolute cross section of this reaction, using a novel method which overcomes some of the major experimental uncertainties of previous measurements. We utilize a 7Be target implanted into a Cu substrate and a uniformly scanned particle beam larger than the target spot, eliminating issues of target homogeneity and backscattering loss of 8B reaction products. The target was produced using a beam of 1.8·1010/s 7Be nuclei extracted at ISOLDE (CERN) from a graphite target bombarded by 1 GeV protons in a two-step resonant laser ionization source. The 7Be nuclei were directly implanted into a copper substrate to obtain a target of 2 mm diameter with a total of 3.1015 atoms. The measurement of the 8B production cross section was carried out at the Van de Graaff laboratory of the Weizmann Institute of Science. We obtain for the S factor of the reaction: S17(Ecm = 1.09 MeV) = 22.7(1.2) eV. barn and S17(Ecm = 1.29 MeV) = 23.8(1.5) eV. barn, somewhat higher than other recent measurements. The present results can serve as a benchmark for further measurements of this cross section.