Surface-peaked medium effects in the interaction of nucleons with finite nuclei

TL;DR

This paper analyzes how the optical model potential for nucleon-nucleus scattering separates into medium-independent and surface-sensitive parts, revealing surface-peaked effects at energies 30-100 MeV.

Contribution

It introduces a decomposition of the optical potential that isolates surface effects and demonstrates its effectiveness in reproducing scattering observables.

Findings

Surface sensitivity is mainly due to proton-neutron coupling.

The decomposition accurately predicts scattering observables within 10%.

The approach links medium dependence with shell-model densities.

Abstract

We investigate the asymptotic separation of the optical model potential for nucleon-nucleus scattering in momentum space, where the potential is split into a medium-independent term and another depending exclusively on the gradient of the density-dependent g matrix. This decomposition confines the medium sensitivity of the nucleon-nucleus coupling to the surface of the nucleus. We examine this feature in the context of proton-nucleus scattering at beam energies between 30 and 100 MeV and find that the pn coupling accounts for most of this sensitivity. Additionally, based on this general structure of the optical potential we are able to treat both, the medium dependence of the effective interaction and the full mixed density as described by single-particle shell models. The calculated scattering observables agree within 10% with those obtained by Arellano, Brieva and Love in their momentum-space g-folding approach.