Uncertainty Principle and Angular Momentum Generation in Microscopic Fission Models

TL;DR

This paper explores the quantum origins of angular momentum in fission fragments, demonstrating that the uncertainty principle largely explains the observed spin distributions in microscopic models.

Contribution

It introduces a simple uncertainty-based model to explain the spin distribution of fission fragments within a microscopic TDDFT framework, clarifying the physical origin of their angular momentum.

Findings

Spin distribution can be largely explained by the uncertainty principle.

Angular fluctuations are mainly due to quadrupole deformation.

Projection methods and uncertainty estimates show consistent results.

Abstract

The generation of angular momentum (intrinsic spin) in fission fragments has recently attracted renewed attention. While several microscopic approaches reproduce the spin distribution qualitatively using projection techniques, the physical origin of the fragments' angular momentum in density functional theory remains unclear. In this work, we investigate the mechanisms responsible for the spin distribution of fission fragments within a microscopic TDDFT framework. We compare spin distributions obtained from projection operators with those predicted by a simple expression derived from the uncertainty relation between angle and angular momentum, where angular fluctuations are estimated using a Monte Carlo sampling of nucleon positions. We find that a large portion of the spin distribution obtained from projection methods can be explained by the uncertainty principle. Our results thus show that, within microscopic approaches, the spin of fission fragments originates primarily from quantum uncertainty associated with their orientation angle with respect to the fission axis, mainly due to quadrupole deformation and, to a lesser extent, octupole deformation.