Diffraction Model for Direct Reactions

Abstract

A diffraction model for direct reactions which we proposed earlier is extended. The simple model provides physical insight into the effects of nuclear optical-model potential distortions without the necessity of performing complex numerical integrations. It is particularly useful, and can be qualitatively justified, for direct reactions when (1) strong absorption is present in both the incident and exit channels and (2) the center-of-mass wave function of the bound state involved corresponds to a small binding energy or to a long exponential tail. Thus, it is expected to be especially applicable to intermediate-energy complex-particle reactions such as the (${\mathrm{He}}^{3}$, $d$) and ($\ensuremath{\alpha}, t$) processes. In this paper, the forward-angle approximations made earlier are removed so that time-reversal symmetry is restored. Proper bound-state wave functions outside the nucleus are employed. Coulomb effects are briefly discussed. The assumptions of the model are thus made less drastic, but at the expense of decreasing mathematical simplicity. Predictions based on the earlier version are essentially unaffected, so that the simple forward-angle model remains useful up to moderately large angles. This is illustrated by comparisons with experiments.