Sub-barrier resonance fission and its effects on fission fragment properties

Abstract

The correlation between the sub-barrier resonant behavior of fission cross-section of non-fissile actinides (pre-scission stage) and the visible fluctuations of their fission fragment and prompt neutron data (post-scission stage) around the incident energies of sub-barrier resonances is outlined and supported by quantitative results in the case of 238U(n,f). A particular focus in our fission cross-section calculation was put on vibrational resonances at sub-threshold neutron energies. The incorporation of the multi-modality in fission led to an integrative description of the sub-barrier resonant behavior of fission cross-sections and of the fluctuations in the fission fragment properties. Through the Point-by-Point (PbP) treatment of prompt neutron emission and the multi-modal fission concept we arrived at a quantitative explanation of the observed fluctuations. The quantitative results refers to both stages of the fission process as following: (a) The pre-scission stage including the neutron induced cross-section calculations with focus on the fission cross-section. Calculations are done in the frame of the refined statistical model for fission with sub-barrier effects, also extended to take into account the multi-modal fission. (b) The post-scission stage including the prompt neutron emission treated in the frame of the PbP model. Total fission fragment and prompt neutron quantities as a function of incident neutron energy, obtained by averaging the PbP model results as a function of fragment over the fission fragment distributions, reveal variations around the energies of sub-barrier resonances in the fission cross-section.