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

TL;DR

This study investigates how time-dependent Hartree-Fock methods can simulate induced fission in heavy nuclei, revealing that boost-induced fission produces more asymmetric fragments compared to traditional deformation-induced approaches.

Contribution

It demonstrates the capability of dynamic mean-field methods to model induced fission processes with different excitation techniques, highlighting differences in fragment distributions.

Findings

Instantaneous boosts cause rapid shape changes leading to fission.

Finite-time boosts induce gentler excitations and fission with less energy deposition.

Boost-induced fission results in more asymmetric fragments.

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 induced fission processes, using quadrupole boosts in the nuclide $^{240}$Pu as an example. Methods: Quadrupole constrained Hartree-Fock calculations are used to create a potential energy surface. An isomeric state and a state beyond the second barrier peak are excited by means of instantaneous as well as temporally extended gauge boosts with quadrupole shapes. The subsequent deexcitation is studied in a time-dependent Hartree-Fock simulation, with emphasis on fissioned final states. The corresponding fission fragment mass numbers are studied. Results: In general, the energy deposited by the quadrupole boost is quickly absorbed by the nucleus. In instantaneous boosts, this leads to fast shape rearrangements and violent dynamics that can ultimately lead to fission. This is a qualitatively different process than the deformation-induced fission. Boosts induced within a finite time window excite the system in a relatively gentler way, and do induce fission but with a smaller energy deposition. Conclusions: The fission products obtained using boost-induced fission in time-dependent Hartree-Fock are more asymmetric than the fragments obtained in deformation-induced fission, or the corresponding adiabatic approaches.