A new measurement of the Be p , g B cross - section with an implanted 7 Be target

7 Ž .8 The Be p,g B 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 Be 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 B reaction products. The target was produced using a beam of 1.8P10rs Be nuclei extracted at Ž . ISOLDE CERN from a graphite target bombarded by 1 GeV protons in a two-step resonant laser ionization source. The Be nuclei were directly implanted into a copper substrate to obtain a target of 2 mm diameter with a total of 3.10 atoms. The measurement of the B production cross section was carried out at the Van de Graaff laboratory of the Weizmann Ž . Ž . Ž Institute of Science. We obtain for the S factor of the reaction: S E s 1.09 MeV s 22.7 1.2 eV. barn and S E 17 cm 17 cm . Ž . s 1.29 MeV s 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. q 1999 Published by Elsevier Science B.V. All rights reserved. PACS: 25.40.Lw; 26.65.q t; 27.20.qm 7 Ž .8