Collective aspects deduced from time-dependent microscopic mean-field with pairing: application to the fission process

TL;DR

This paper introduces a method to derive collective momenta and masses from microscopic time-dependent mean-field theories, applied to nuclear fission, revealing dynamical effects beyond adiabatic approximations.

Contribution

A versatile approach to connect microscopic mean-field dynamics with macroscopic collective variables, demonstrated on nuclear fission of Fm-258.

Findings

Off-diagonal inertia matrix elements are crucial for multi-variable analysis.

Dynamical effects extend the scission point beyond adiabatic predictions.

Effective nucleus-nucleus potential is extracted from microscopic data.

Abstract

Given a set of collective variables, a method is proposed to obtain the associated conjugated collective momenta and masses starting from a microscopic time-dependent mean-field theory. The construction of pairs of conjugated variables is the first step to bridge microscopic and macroscopic approaches. The method is versatile and can be applied to study a large class of nuclear processes. An illustration is given here with the fission of $^{258}$Fm. Using the quadrupole moment and eventually higher-order multipole moments, the associated collective masses are estimated along the microscopic mean-field evolution. When more than one collective variable are considered, it is shown that the off-diagonal matrix elements of the inertia play a crucial role. Using the information on the quadrupole moment and associated momentum, the collective evolution is studied. It is shown that dynamical effects beyond the adiabatic limit are important. Nuclei formed after fission tend to stick together for longer time leading to a dynamical scission point at larger distance between nuclei compared to the one anticipated from the adiabatic energy landscape. The effective nucleus-nucleus potential felt by the emitted nuclei is finally extracted.