Deuteron effects in nucleon-nucleus scattering at intermediate energies.

%e investigate the role of the full dynamical dependence of the free off-shell nucleon-nucleon t matrix on the optical potential for proton-nucleus elastic scattering in the 100—400 MeV incident energy range within a full-folding model context. Particular emphasis is placed on the effects of deuteron formation by explicitly taking into account pole singularities in the free nucleon-nucleon t matrix. The full-folding model for the optical potential provides a Bexible framework for this purpose as it allows the sampling of the internucleon effective force both off shell and as a function of the energy available in the center of mass for the interacting nucleon pair. A comparison of calculated and measured scattering observables for proton elastic scattering on Ca and Pb leads to the conclusion that the full off-shell free t matrix is a poor approximation for that part of the nucleonnucleon effective force required for calculating optical potentials below 250 MeV. Medium effects and higher order corrections to the optical potential are necessary to improve our understanding of nucleon scattering.