Structure in the Event-by-Event Energy-Dependent Neutron-Gamma Multiplicity Correlations in $^{252}\text{Cf}$(sf)

TL;DR

This paper introduces a new analysis method for neutron-gamma correlations in fission, revealing energy-dependent structures linked to rotational band transitions and angular momentum generation.

Contribution

It presents a novel analysis technique that uncovers structured correlations in neutron-gamma emission data from 252Cf(sf), enhancing understanding of fission fragment properties.

Findings

Enhanced neutron-gamma correlations at specific gamma-ray energies.

Correlation structures linked to rotational band gamma-ray transitions.

Agreement with model predictions suggests a positive spin-energy correlation.

Abstract

The emission of neutrons and gamma rays by fission fragments reveal important information about the properties of fragments immediately following scission. The initial fragment properties, correlations between fragments, and emission competition give rise to correlations in neutron-gamma emission. Neutron-gamma correlations are important in nonproliferation applications because the characterization of fissionable samples relies on the identification of signatures in the measured radiation. Furthermore, recent theoretical and experimental advances have proposed to explain the mechanism of angular momentum generation in fission. In this paper, we present a novel analysis method of neutrons and gamma rays emitted by fission fragments that allows us to discern structure in the observed correlations. We have analyzed data collected on \ce{^{252}Cf}(sf) at the Chi-Nu array at the Los Alamos Neutron Science Center. Through our analysis of the energy-differential neutron-gamma multiplicity covariance, we have observed enhanced neutron-gamma correlations, corresponding to rotational band gamma-ray transitions, at gamma-ray energies of $0.7$ and $1.2$ MeV. To shed light on the origin of this structure, we compare the experimental data with the predictions of three model calculations. The origin of the observed correlation structure is understood in terms of a positive spin-energy correlation in the generation of angular momentum in fission.