Accurate measurement of uranium isotope ratios in solid samples by laser ablation multi-collector inductively coupled plasma mass spectrometry

Abstract

A multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) coupled to a 213 nm ns-laser was used to measure uranium isotope ratios (²³⁴U/²³⁸U, ²³⁵U/²³⁸U, and ²³⁶U/²³⁸U) in six solid nuclear certified reference materials (CRMs). The powdered CRMs, containing depleted, natural and low enriched uranium (U), were pressed into pellets, for straightforward handling of the nuclear material. Being analysed without dissolution, the experimental U isotope ratios of the solid materials were in good agreement with the corresponding certified values. The measured U isotope ratios in the samples were corrected for mass bias using a pelletised CRM containing nominally 2% enriched ²³⁵U. Scanning electron microscopy investigations of an actual sample from which material was previously ablated revealed that only 5 ng of sample is consumed during a single measurement. As such laser ablation MC-ICP-MS can be regarded as quasi-non-destructive and therefore is an ideal technique for the rapid but still accurate and precise determination of the uranium isotopic composition in solid samples for nuclear safeguards and forensic purposes. The proposed analytical procedure essentially assists the characterisation of the illicit nuclear material for hazard and origin assessment. Moreover, as the sample is also an evidence, it can be analysed with further techniques.