Inferring fission timescales from prescission neutron multiplicity using a Langevin dynamical model

Background: In the theoretical analysis of nuclear fission observables, dissipation strength is often adjusted locally to reproduce the experimental data. The global trend of the dissipation strength over the whole mass range of fissioning nuclei is still not known convincingly. Also, its connection with fission timescales is essential to understand the reaction dynamics.Purpose: We extracted the nuclear dissipation strength by reproducing the experimental prescission neutron multiplicities for reactions forming compound nuclei in the mass range of $168\ensuremath{\le}A\ensuremath{\le}256$. Subsequently, we predicted the systematics of fission lifetime over this range of compound nuclear mass.Method: We employed a one-dimensional Langevin dynamical model for fission, where shape-dependent shell correction and one-body dissipation are used. The dissipation strengths for different compound systems are extracted by reproducing the measured prescission neutron multiplicities. Obtained strengths are shown to consistently reproduce the average total kinetic energy of the fission fragments. Subsequently, dynamical fission-time distributions were simulated in coincidence with these neutron multiplicities.Results: We identified three different mass regions depending on the required dissipation strength: (i) for compound nuclear mass number $A<210$, the role of dissipation is minimal, (ii) in $210⪅A⪅244$, shell correction is found to influence the dissipation strength strongly, and (iii) for $A⪆244$ the dynamics is strongly driven by dissipation. Further, for lighter masses with a fission barrier height between $18\phantom{\rule{4.pt}{0ex}}\text{and}\phantom{\rule{4.pt}{0ex}}30$ MeV, fission time appeared to depend very weakly on the fission barrier, whereas, for heavy nuclei, fission time is shown to be well correlated with the barrier height of the primary compound nucleus.Conclusion: Our paper provides a global understanding of the nuclear dissipation strength and the fission lifetime based on the experimental neutron multiplicities. These systematics will be helpful in estimating fission time in heavy ion-induced reactions.