An exclusive measurement of the Coulomb breakup of ${}^8\mathrm{B}$ into ${}^7\mathrm{Be}$$+p$ at 254A MeV was used to infer the low-energy ${}^7\mathrm{Be}$($p,\gamma$)${}^8\mathrm{B}$ cross section. The radioactive ${}^8\mathrm{B}$ beam was produced by projectile fragmentation of 350A MeV ${}^{12}\mathrm{C}$ 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 $S_{17}$ factors exhibit good agreement with the most recent direct ${}^7\mathrm{Be}$($p,\gamma$)${}^8\mathrm{B}$ measurements. By using the energy dependence of $S_{17}$ according to the recently refined cluster model for ${}^8\mathrm{B}$ of P. Descouvemont [Phys. Rev. C 70, 065802 (2004)], we extract a zero-energy S factor of $S_{17}(0)=20.6\pm 0.8(\mathrm{stat})\pm 1.2(\mathrm{syst})$ 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%.

• Received 15 August 2005

DOI:https://doi.org/10.1103/PhysRevC.73.015806