Coupled-Channel Optical-Model Calculations for Evaluating Neutron Cross Sections of Odd-Mass Actinides

Abstract

As coupled-channel calculations are very time consuming when applied to odd-mass target nuclei using the actual level schemes, the adequacy of the following approximation is studied. Calculations are performed for a fictitious even-even nucleus with the same mass number as the odd-mass target of interest. Deformation parameters are obtained from a systematic available in this mass region, and the optical model parameters used are extrapolated from those determined for the neighboring even-even nuclei. Direct elastic and inelastic scattering cross sections resulting from such calculations are distributed among the true ground-state band levels of the odd-mass nucleus. Comparisons of calculations made with a fixed set of optical parameters, but using either the actual or the fictitious level scheme, are presented for ground-state bands of K = 1/2 and K = 5/2. The approximation proposed can be applied with great confidence over the energy range 10 keV to 20 MeV in case of K = 1/2. In case of K = 5/2, the approximation gives satisfactory results in the limited energy range 4 to 20 MeV.