Manifestation of pairing effects in the cross section for 238Pu fission induced by neutrons

Abstract

The cross section for 238Pu fission induced by neutrons with energies between 1 keV and about 5 MeV is described within the statistical model. It is shown that the stepwise structure observed above the fission threshold (at incident-neutron energies of Es>1 MeV) is due to the step in the level density of the fissile 239Pu nucleus at deformations corresponding to the inner fission barrier. In turn, the step in the level density of the odd nucleus 239Pu is associated with the excitation of internal single-and three-quasiparticle states. The level density is described with allowance for collective, pairing, and shell effects.