Uncertainties in extracting S₁₇ from transfer reactions

The transfer reaction ⁷Be(d,n)⁸B is modeled for the recent low experimental energies using the distorted-wave Born approximation (DWBA). Tests of the validity of the asymptotic normalization constant method for the extraction of the S₁₇ astrophysical factor are performed. We show that a peripheral assumption is no longer accurate for center-of-mass energies greater than approximately 15 MeV. In all cases we found that core deformation and/or excitation effects to be small as long as the optical potential for the entrance channel is not strongly surface peaked. Multistep corrections to the DWBA were found to be small. We also emphasize that the lack of knowledge of the optical potentials for the entrance and outgoing channels induces severe uncertainties in the extracted S₁₇ astrophysical factor.