Microscopic description of the torque acting on fission fragments

TL;DR

This study investigates the angular momentum transfer in nuclear fission fragments using time-dependent Hartree-Fock theory, revealing the dominant role of Coulomb interactions and the nature of rotational modes at scission.

Contribution

It introduces a microscopic analysis of torque and angular momentum in fission fragments, combining TDHF and Frozen Hartree-Fock methods for detailed insights.

Findings

Coulomb interaction mainly generates collective angular momentum after fission.

Angular momentum at scission is not predominantly collective.

Angular momentum is mainly perpendicular to the fission axis.

Abstract

When two fragments are created in a fission decay, any torque due to nuclear and Coulomb interaction can change the fragment's angular momentum. This article explores the character and magnitude of the angular momentum as a function of the initial conditions around the scission point using the time-dependent Hartree-Fock theory. To understand the torque acting on the fragments, the Frozen Hartree-Fock method is also used to determine the collective potential at scission. Two $^{240}$Pu fission channel ( $^{132}$Sn+$^{108}$Ru and $^{144}$Ba+$^{96}$Sr ) are studied. These two channels cover different shapes (spherical, quadrupole, and octupole deformation) of the fragments. It is found that the angular momentum generated by the Coulomb interaction after fission is mainly collective, while this is not the case for the angular momentum generated at scission. The competition between rotational modes (bending, wriggling, and twisting) is discussed and shows that the angular momentum is generated mainly perpendicular to the fission axis.