Energy dependence of the optical model parameters for α-particles scattered from 40Ca and 58Ni

The differential cross sections for α-particles elastically scattered from 40Ca and 58Ni at seven different bombarding energies up to 85.6 MeV are reported. The results of optical model analyses yielded energy dependent optical potential parameter sets which are given, as well as individual best-fit parameters. For a given real radius parameter, an analytical expression is found to explain satisfactorily the difference in energy dependence of the real potential depth between two discrete potential families. For α-particle energies less than 80 MeV, the potential parameters and especially the individual best-fit parameters for the two discrete potential families vary strongly but systematically with energy. Similar anomalous energy dependence in the potential parameters was also observed when an improved form for the real potential was used. The analysis of the data indicated that the potential family which has the normalized volume integral of the real potential Jsub(R) approximately 350 MeV . fm3 is the most appropriate for α-particle scattering. (Auth.)