# Fissile material detection using neutron time-correlations from photofission

## TL;DR

This study demonstrates that neutron time-correlations from photofission can rapidly identify fissile materials like HEU in cargo, using a combination of experiments, simulations, and ROC analysis.

## Contribution

The paper introduces a method using two-neutron time-correlations from photofission with empirical and computational analysis to distinguish fissile from fissionable materials in seconds.

## Key findings

- 10-second screening differentiates HEU from DU in cargo scenarios.
- Neutron time-correlations effectively identify fissile materials under shielding.
- Simulation and empirical data align to predict detection performance.

## Abstract

The detection of special nuclear materials (SNM) in commercial cargoes is a major objective in the field of nuclear security. In this work we investigate the use of two-neutron time-correlations from photo-fission using the Prompt Neutrons from Photofission (PNPF) detectors in Passport Systems Inc.'s (PSI) Shielded Nuclear Alarm Resolution (SNAR) platform~\cite{pnpf} for the purpose of detecting $\sim$5~kg quantities of fissionable materials in seconds. The goal of this effort was to extend the secondary scan mode of this system to differentiate fissile materials, such as highly enriched uranium, from fissionable materials, such as low enriched and depleted uranium (LEU and DU). Experiments were performed using a variety of material samples, and data were analyzed using the variance-over-mean technique referred to as $Y_{2F}$ or Feynman-$\alpha$. Results were compared to computational models to improve our ability to predict system performance for distinguishing fissile materials. Simulations were then combined with empirical formulas to generate receiver operating characteristics (ROC) curves for a variety of shielding scenarios. We show that a 10 second screening with a 200~$\mu$A 9~MeV X-ray beam is sufficient to differentiate kilogram quantities of HEU from DU in various shielding scenarios in a standard cargo container.