Some fundamental aspects of the optical potential for the interaction of fast neutrons with cobalt

Differential elastic- and inelastic-scattering cross sections, measured from approx. 1.5 to 10.0 MeV, are interpreted in terms of spherical-optical-statistical (OM) and coupled-channels models. A successful description of the differential elastic scattering below 10 MeV and the total cross section to 20.0 MeV is achieved using the spherical OM with energy-dependent strengths and geometries. These energy dependencies are large below approx. 7.0 MeV, but become smaller and similar to those reported for ''global'' potentials at higher energies. This change in the energy dependence of the parameters probably marks the onset of the Fermi surface anomaly approx. 19 MeV above the Fermi energy. Inelastic scattering to the levels below 1.8 MeV displays a forward peaked behavior. This non-statistical component is interpreted using the weak coupling model in which the f7/2 proton hole is coupled to the 2+ state in 60Ni. This model provides an explanation of the unusual energy dependence and relatively small radius found for the imaginary OM potential. The coupling also contributes to the large value of this potential. The real spherical OM potential derived from the neutron-scattering results is extrapolated to bound energies using the dispersion relationship and the method of moments. The resulting real-potential strength and radius peak at approx. -10.0 MeV, whereas the real diffuseness is at a minimum at this energy. The extrapolated potential is approx. 8% larger than that implied by reported particle-state energies, and approx. 13% smaller than indicated by hole-state energies. (author). 42 refs, 8 figs