Optical models from low-energy s-, p- and d-wave cross sections

Abstract

From transmission measurements with good resolution at low energies one can obtain data on the optical model potential (OMP) for individual partial waves by first making a multilevel analysis to isolate the partial waves and then averaging for comparison to the OMP. For each Jπ the averaging yields two quantities which are related to the amplitude and phase of the OMP scattering function or, alternatively, to the volume integrals of the real and imaginary potentials. Historically, the experimental averages have been represented by the s‐ and p‐wave strength functions, S0 and S1, and the s‐wave scattering radius R’. To make full use of data from modern time‐of‐flight facilities such as ORELA it is necessary to re‐examine the averaging procedure in order to extend it upward both in energy and neutron l‐value. This averaging is discussed and applied to data on 30Si, 32S, 34S, 40Ca, 48Ca, 60Ni, 86Kr and 208Pb. The resulting OMP shows a systematic real potential with some indication of a parity dependence. The imaginary potential shows considerable fluctuations indicating the importance of nuclear structure at neutron energies below 1 MeV. A coupled channel OMP is also discussed for some of the nuclei.