0.04?4.0 Mev neutron fission cross section of Pu240

Abstract

A detailed investigation of the Pu240 nucleus cross section is of interest with regard to an experimental verification of theoretical concepts of the energy dependence of fission probability as well as regarding possible uses of Pu240 as a nuclear fuel in fast neutron reactors. We measured the energy dependence of the fast neutron fission cross section of Pu240 for neutrons with the energy En = 0.04–4.0 Mev. The T(p, n)He3 reaction served as the neutron source. The Pu240 fission cross section in the plateau region (1–4 Mev) amounts to ~ 1.6 barn and is equal to only one-half of this value for the neutron energy En ≃ 0.7 Mev. A sharp decrease in the fission cross section value occurs as En decreases to 0.3 Mev; for a further decrease in En, the cross section value drops less sharply, and it remains practically constant (~ 0.065 barn) for 0.04 < En < 0.15 Mev. The correlation between the irregularities in fission cross section values and the levels of Pu240 nuclei which correspond to inelastic scattering channels is discussed.