Optical model with multiple band couplings using soft rotator structure

¹ Nuclear Evaluation Lab, Joint Institute for Energy and Nuclear Research, Minsk, Belarus
² NAPC–Nuclear Data Section, International Atomic Energy Agency, Vienna, Austria
³ Departamento de Física Atómica, Molecular y Nuclear, Universidad de Sevilla, Sevilla, Spain
⁴ Laboratory for Advanced Nuclear Energy, Institute of Innovative Research, Tokyo Institute of Technology, Japan, and National Astronomical Observatory of Japan, Tokyo, Japan

^a e-mail: dmart@sosny.bas-net.by

Published online: 13 September 2017

Abstract

A new dispersive coupled-channel optical model (DCCOM) is derived that describes nucleon scattering on ²³⁸U and ²³²Th targets using a soft-rotator-model (SRM) description of the collective levels of the target nucleus. SRM Hamiltonian parameters are adjusted to the observed collective levels of the target nucleus. SRM nuclear wave functions (mixed in K quantum number) have been used to calculate coupling matrix elements of the generalized optical model. Five rotational bands are coupled: the ground-state band, β-, γ-, non-axial- bands, and a negative parity band. Such coupling scheme includes almost all levels below 1.2 MeV of excitation energy of targets. The “effective” deformations that define inter-band couplings are derived from SRM Hamiltonian parameters. Conservation of nuclear volume is enforced by introducing a monopolar deformed potential leading to additional couplings between rotational bands. The present DCCOM describes the total cross section differences between ²³⁸U and ²³²Th targets within experimental uncertainty from 50 keV up to 200 MeV of neutron incident energy. SRM couplings and volume conservation allow a precise calculation of the compound-nucleus (CN) formation cross sections, which is significantly different from the one calculated with rigid-rotor potentials with any number of coupled levels.