Quantification of spin alignment in fission by simultaneous treatment of gamma and conversion electron angular distributions

TL;DR

This paper presents a novel method to quantify the spin alignment of fission fragments by simultaneously analyzing gamma-ray and conversion-electron angular distributions, providing insights into the fission process.

Contribution

It introduces an event-by-event calculation approach using FIFRELIN to predict electron and gamma angular distributions, advancing the study of fragment spin alignment.

Findings

Predicted electron angular distribution relative to the fission axis.

Estimated average spin alignment for 252Cf fission fragments.

Method offers a new way to analyze spin alignment in fission studies.

Abstract

The study of the angular momentum properties of fission fragments can shed light about the complex mechanisms that characterize the fission process. One quantity that is of significant interest, and has not yet been studied adequately, is the alignment of the fragments, which is the cause of anisotropy of the {\gamma} rays along the fission axis and has been observed in various past and recent experiments. In this work, we have performed calculations using the FIFRELIN code, in an attempt to quantify the alignment of the nuclear spins after neutron-emission. Under the statistical tensor formalism of angular distributions, the conversion-electron and the {\gamma}-ray angular distributions can be treated simultaneously in an event-by-event calculation. This enables a first prediction of the conversion-electron angular distribution with respect to the fission axis. An average value for the alignment of fission fragments is deduced for 252Cf, with the use of recent experimental data. The method used for the present work can serve as a starting point for future theoretical and experimental studies in terms of {\gamma} and conversion-electron spectroscopy in view of studying the spin alignment of individual fission fragments, which could further improve our understanding on the process of fission.