Neutron scattering on nuclei near A=60 and A=90

Over a wide range of incident energies, the total cross section and angular distributions for elastic scattering of neutrons from nuclei in these mass regions are analyzed using the spherical-optical-statistical model. The effect of a real-surface-peaked potential, predicted by dispersion relations, is considered. It is found that when the data on a given nucleus between say, 4.5 and 10 MeV, are analyzed simultaneously one obtains a smooth energy variation of the optical model parameters. Moreover, this parameterization may be used to predict, quite accurately, at least the total cross sections up to 20 MeV. The parameters characterizing the model are quite different in the two mass regions. However, a comparison of the optical model results for 89Y and 93Nb indicates that near A=90 the well parameters are nearly the same for the two nuclei and that the volume integrals of the imaginary potentials are similar. (author). 16 refs, 9 figs, 2 tabs