Isotopic Measurements of SNM using a Portable Neutron Resonance Transmission System for Arms Control

TL;DR

This paper demonstrates a portable neutron resonance transmission system capable of rapidly identifying and quantifying isotopic compositions of nuclear materials for arms control verification, with high accuracy in a short measurement time.

Contribution

It introduces a compact, portable neutron ToF system for isotopic analysis of SNM, enabling rapid, accurate measurements suitable for arms control verification.

Findings

Successfully identified isotopic signatures within 2 hours

Predicted uranium enrichment within 5% accuracy

Determined plutonium composition within 6% accuracy

Abstract

Neutron Resonance Transmission Analysis (NRTA) was explored as an arms control verification approach to support potential future nuclear weapon limiting treaties. A compact and portable neutron Time of Flight (ToF) system was developed to enable proof-of-concept NRTA measurements of special nuclear material (SNM). Using a short 2-meter flight path, the NRT system is sensitive to cross-section resonances of isotopes such as 235U, 238U, 239Pu and 240Pu between 1-100 eV incident neutron energies due to their physical nuclear structure. The detected neutron ToF spectrum exhibits transmission dips at resonance energies that are characteristic of SNM isotopic composition in the inspected item. The proof-of-concept measurements of Highly Enriched Uranium (HEU), Depleted Uranium (DU), and Reactor Grade Plutonium (RGPu) confirmed the characteristic resonance features within two hours of data collection time. Analysis via the REFIT resonance fitting tool accurately predicted the 235U enrichment and Pu isotopic composition within 5% and 6% of the known values, respectively.