DISPERSION-RELATION APPROACH TO THE OPTICAL-POTENTIAL RESONATING-GROUP FORMULATION OF THE N-40 REACTION(CA)

The scattering of neutrons by Ca-40 is studied in the energy region fr om 11 to 40 MeV with a semimicroscopic optical model, taking the dispe rsion relation into account. The real part of the internuclear interac tion is mainly the equivalent local potential of a single-channel appr oximation based on the resonating group formulation. It contains dispe rsive contributions which are derived from the imaginary potential by means of a dispersion relation. The imaginary part is purely phenomeno logical and it is parametrised to fit the empirical data. The importan ce of the dispersive contribution is examined and the reliability of t his model is confirmed by comparison with the experimental data and wi th similar optical model studies. The results obtained for the differe ntial and total cross sections are quite satisfactory. It is found tha t the dispersion relation can indeed be accommodated in the resonating group optical model with phenomenological absorptive parts. This can be done by small energy-dependent variations of the effective nucleon- nucleon force, as in similar previous studies, which however ignored t he dispersion relation.