Fission Dynamics of 240Pu from Saddle-to-Scission and Beyond

TL;DR

This study uses advanced density functional theory to simulate the fission process of 240Pu, revealing highly dissipative collective motion and consistent energy sharing patterns between fragments, supporting statistical models of fission.

Contribution

It demonstrates that the fission dynamics are predominantly overdamped and insensitive to pairing strength variations, validating the use of statistical models and extending understanding of energy sharing in fission.

Findings

Fission dynamics are highly dissipative with little inertial contribution.

The energy sharing between fragments varies with initial excitation energy, matching experimental data.

Varying pairing strength has minor effects on the fission process.

Abstract

Calculations are presented for the time evolution of $^{240}$Pu from the proximity of the outer saddle point until the fission fragments are well separated, using the time-dependent density functional theory extended to superfluid systems. We have tested three families of nuclear energy density functionals and found that all functionals exhibit a similar dynamics: the collective motion is highly dissipative and with little trace of inertial dynamics, due to the one-body dissipation mechanism alone. This finding justifies the validity of using the overdamped collective motion approach and to some extent the main assumptions in statistical models of fission. This conclusion is robust with respect to the nuclear energy density functional used. The configurations and interactions left out of the present theory framework only increase the role of the dissipative couplings. An unexpected finding is varying the pairing strength within a quite large range has only minor effects on the dynamics. We find notable differences in the excitation energy sharing between the fission fragments in the cases of spontaneous and induced fission. With increasing initial excitation energy of the fissioning nucleus more excitation energy is deposited in the heavy fragment, in agreement with experimental data on average neutron multiplicities.