Nonlocal potentials and the energy dependence of the optical model for neutrons

Abstract

The energy dependence of the nuclear optical model potential for neutrons is derived from a nonlocal formalism. The imaginary part of the potential changes continuously from purely surface absorption at zero energy to purely volume absorption at energies beyond 100 MeV. Most of the parameters are determined by demanding that the equivalent local potential at zero energy coincide with the Moldauer potential while the remaining parameters are varied to fit the total and nonelastic cross sections of various spherical nuclei between 30 and 150 MeV. The resulting potential also produces good fits to elastic angular distributions, and, when an appropriate spin-orbit potential is added, to polarization measurements in this energy region as well as the intermediate region between 7 and 24 MeV. This shows that the energy dependence could be described in terms of nonlocality of the interaction and provides a simple local potential which can be used over the whole energy range from 0 to 150 MeV and probably even beyond.