Fission dynamics within time-dependent Hartree-Fock: deformation-induced fission

TL;DR

This study uses time-dependent Hartree-Fock methods to simulate nuclear fission dynamics in $^{240}$Pu, revealing how initial deformation influences fission pathways and outcomes, thus advancing microscopic understanding of fission processes.

Contribution

It demonstrates the capability of dynamic mean-field methods to describe fast fission processes beyond the fission barrier, including non-adiabatic effects and initial deformation dependence.

Findings

Dynamic states show giant-resonance behaviour when starting below the barrier.

Fission occurs only when initial deformation exceeds the barrier and crosses the two-fragment pathway.

Time-dependent Hartree-Fock accurately models fast fission dynamics with sufficient initial deformation.

Abstract

Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic density functional studies of fission have previously concentrated on adiabatic approaches based on constrained static calculations ignoring dynamical excitations of the fissioning nucleus, and the daughter products. Purpose: To explore the ability of dynamic mean-field methods to describe fast fission processes beyond the fission barrier, using the nuclide $^{240}$Pu as an example. Methods: Time-dependent Hartree-Fock calculations based on the Skyrme interaction are used to calculate non-adiabatic fission paths, beginning from static constrained Hartree-Fock calculations. The properties of the dynamic states are interpreted in terms of the nature of their collective motion. Fission product properties are compared to data. Results: Parent nuclei constrained to begin dynamic evolution with a deformation less than the fission barrier exhibit giant-resonance-type behaviour. Those beginning just beyond the barrier explore large amplitude motion but do not fission, whereas those beginning beyond the two-fragment pathway crossing fission to final states which differ according to the exact initial deformation. Conclusions: Time-dependent Hartree-Fock is able to give a good qualitative and quantitative description of fast fission, provided one begins from a sufficiently deformed state.