Prescission neutron multiplicity and fission probability from Langevin dynamics of nuclear fission

Abstract

A theoretical model of one-body nuclear friction, which was developed earlier, namely, the chaos-weighted wall formula, is applied to a dynamical description of compound nuclear decay in the framework of the Langevin equation coupled with statistical evaporation of light particles and photons. We have used both the usual wall formula friction and its chaos-weighted version in the Langevin equation to calculate the fission probability and prescission neutron multiplicity for the compound nuclei ${}^{178}\mathrm{W},$ ${}^{188}\mathrm{Pt},$ ${}^{200}\mathrm{Pb},$ ${}^{213}\mathrm{Fr},$ ${}^{224}\mathrm{Th},$ and ${}^{251}\mathrm{Es}.$ We have also obtained the contributions of the presaddle and postsaddle neutrons to the total prescission multiplicity. A detailed analysis of our results leads us to conclude that the chaos-weighted wall formula friction can adequately describe the fission dynamics in the presaddle region. This friction, however, turns out to be too weak to describe the postsaddle dynamics properly. This points to the need for a suitable explanation for the enhanced neutron emission in the postsaddle stage of nuclear fission.