Spatial orientation of the fission fragment intrinsic spins and their correlations

TL;DR

This paper investigates the spatial orientation and correlations of fission fragment intrinsic spins using microscopic evaluations, revealing complex 3D spin dynamics and highlighting limitations of previous semi-phenomenological models.

Contribution

It provides the first detailed microscopic analysis of fission fragment spins and their correlations, uncovering twisting spin modes absent in earlier models.

Findings

Identification of well-defined 3D spin dynamics

Discovery of twisting spin modes in fission fragments

Limitations of semi-phenomenological models

Abstract

New experimental and theoretical results obtained in 2021 made it acutely clear that more than 80 years after the discovery of nuclear fission we do not understand the generation and dynamics of fission fragment (FF) intrinsic spins well, in particular their magnitudes, their spatial orientation, and their correlations. The magnitude and orientation of the primary FFs have a crucial role in defining the angular distribution and correlation between the emitted prompt neutrons, and subsequent emission of statistical (predominantly E1) and stretched E2 {\gamma}-rays, and their correlations with the final fission fragments. Here we present detailed microscopic evaluations of the FF intrinsic spins, for both even- and odd-mass FFs, and of their spatial correlations. These point to a well-defined 3D FF intrinsic spin dynamics, characteristics absent in semi-phenomenological studies, due to the presence of the twisting spin modes, which artificially were suppressed in semi-phenomenological studies.