Optical-Model Analysis of "Quasielastic" (p, n) Reactions

Measured differential cross sections for ($p, n$) transitions between isobaric analog states are compared with the predictions of an optical model which includes an isobaric spin-dependent potential proportional to t·${\mathrm{T}}_0$, where t and ${\mathbf{T}}_0$ are the isobaric spins of projectile and target, respectively. The magnitudes of the measured cross sections indicate a strength for this potential which is close to the symmetry potential found from analysis of elastic proton scattering. The shapes of the angular distributions give strong evidence for the radial shape of this potential to be peaked at the nuclear surface. The calculations are made in the distorted-wave Born approximation using optical potential parameters determined by fits to elastic scattering. Numerical studies are made of the sensitivity of the predictions to various parameter changes to determine the significance of the fits obtained to experiment. Finally, some discussion is given of the "quasi-inelastic" transitions to excited isobaric states, in terms of the collective-model description of inelastic scattering.