Time-dependent hydride correction for accurate 240Pu/239Pu isotopic ratio measurements in µm-sized Pu-bearing particles using large geometry-secondary ion mass spectrometry

Abstract

This paper describes a new methodology based on a time-dependent hydride correction for measuring the isotopic composition of micrometer sized plutonium bearing particles using large geometry secondary ion mass spectrometry. This methodology allows the mitigation of the effect of the hydride interferences on ²³⁶U, ²³⁹Pu and ²⁴⁰Pu on weapon grade plutonium particles, which contain a low amount of the ²⁴⁰Pu isotope, and on MOX particles, which contain a low amount of plutonium at the weight% level. We successfully applied it on six different samples and demonstrated that the deviations from the reference values of the ²⁴⁰Pu/²³⁹Pu isotopic ratios were reduced from +4.6% to +0.24% for the MP2 sample (weapon grade Pu) and from −7% to +0.75% for the UKMOX-100 sample (MOX). We also demonstrated the capabilities for simultaneously measuring the uranium and plutonium isotopic compositions in MOX particles using the dynamic multi-collection mode of LG-SIMS. Moreover, we determined the Pu/U relative sensitivity factor using Pu particles of known ages and applied it to measure the ²³⁹Pu/²³⁸U atomic ratio in MOX particles. At last, the imaging capabilities of the instrument allowed the detection and discrimination of different types of nuclear particles within the same sample, such as U, Pu or MOX particles. This methodology enhances the range of methods applicable to particle analysis in the field of nuclear safeguards and nuclear forensics.