Direct and compound interactions for the neutron-induced fission cross section determination

Joint Institute for Nuclear and Energy Research, 220109 Minsk-Sosny, Belarus

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

Abstract

Recent ratio surrogate data for the neutron-induced fission cross sections are inter-compared for the chain of Th and U nuclides. The structure of the fission barrier and the angular moments of the entrance channel states are shown to be significant. The excitation/position of the K^π = 2⁺ abnormal rotational band-head at the inner saddle of even-even U fissioning nuclide like ²⁴⁰U is shown to be critically important. At ²³¹Th nuclide medium excitations of 10–20 MeV, when pre-fission neutron emission is possible in the reaction ²³²Th(³He, ⁴He), the excitation of K^π = 0⁻ states depends on the mass-asymmetry of the even nuclide ²³⁰Th saddle shapes. Octupole band states are shown to be relevant for the ²³²Th(³He, ³He′) reaction. The consistency of surrogate, ratio surrogate and neutron-induced fission data is revisited.