Fission cross-section evaluations in the frame of the multi-modal fission model for 237Np(n, f)

Abstract

The statistical model for fission cross-section evaluation is extended by including the concept of multi-modality of the fission process. The three most dominant fission modes, the two asymmetric standard I (S1) and standard II (S2) modes and the symmetric superlong (SL) mode are taken into account. Based on calculations of the nuclear surface in the frame of the multi-modal random neck-rupture model, separate outer fission barriers are considered for each mode, while the inner barriers and isomeric wells are assumed to be the same. Deconvoluted fission cross sections for S1, S2 and SL modes for 237Np(n, f), based on experimental branching ratios, were calculated for the first time in the incident energy range 0.01 to 5.5 MeV providing good agreement with the experimental fission cross-section data. Including the concept of multi-modal fission into nuclear reaction models could lead to a better understanding and provides a more consistent description of the fission process.