An exclusive measurement of the Coulomb breakup of B8 into Be7+p at 254A MeV was used to infer the low-energy Be7(p,γ)B8 cross section. The radioactive B8 beam was produced by projectile fragmentation of 350A MeV C12 and separated with the FRagment Separator (FRS) at Gesellschaft für Schwerionenforschung in Darmstadt, Germany. The Coulomb-breakup products were momentum-analyzed in the KaoS magnetic spectrometer; particular emphasis was placed on the angular correlations of the breakup particles. These correlations demonstrate clearly that E1 multipolarity dominates within the angular cuts selected for the analysis. The deduced astrophysical S17 factors exhibit good agreement with the most recent direct Be7(p,γ)B8 measurements. By using the energy dependence of S17 according to the recently refined cluster model for B8 of P. Descouvemont [Phys. Rev. C 70, 065802 (2004)], we extract a zero-energy S factor of S17(0)=20.6±0.8(stat)±1.2(syst) eV b. These errors do not include the uncertainty of the theoretical model to extrapolate to zero relative energy, estimated by Descouvemont to be about 5%.
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