Nuclear forensics: determining the origin of uranium ores and uranium ore concentrates via radiological, elemental and isotopic signatures

Abstract

There is increasing demand for the development of rapid and effective analytical tools to support nuclear forensic investigations of seized suspect materials to determine sample origins and ownership. New methods are sometimes simply adapted from other scientific disciplines and can be effectively used to rapidly prepare complex materials for analysis. The adaptation and re-implementation of such techniques for rapid nuclear forensic characterisation is the focus of this thesis with emphasis on geolocating uranium ore concentrates (UOC) whilst preserving as much of the original sample as possible.

A rapid sample solubilisation technique was developed to overcome significant and unpredictable photon self-attenuation observed in U-bearing matrices caused by variable matrix compositions containing dense uranium-bearing particles. The technique enables collection of accurate gamma spectrometric measurements of U-bearing compounds where no photon self-absorption corrections, photon detection efficiency adjustments or sample specific matrix matching are required due to the reproducible and predictable aqueous matrix. The technique was used to prepare and measure 19 UOCs via gamma and alpha spectrometry and the data were statistically analysed by Principal Components Analysis. Half of the UOCs were statistically unique whilst the remaining samples grouped together. The UOCs were re-prepared, re-measured and incorporated into the PCA and plotted in close proximity to the original 3D modelled data. This validates the effectiveness of the procedures to obtain accurate and reliable data and that statistical analysis of the data is able to infer possible sample origins.

A second sample preparation technique was developed and tested using U-bearing samples which allows for 1.5 mg of sample to be formed in to a small glass bead after dilution with pure MgSiO3 instead of using a specific flux (usually determined with prior knowledge of sample composition) and could over-dilute the sample and introduce contaminants. The glass was prepared using an iridium-strip resistive fusion device and is produced in less than 10 minutes. The resulting homogeneous flux-free bead of glass was then analysed via laser-ablation ICPMS and the rare earth element (REE) patterns were obtained for reference materials and 9 UOCs. The REEs can be used to infer UOC provenance. The patterns were convincingly similar to chondrite normalised reference values and data from chemically purified UOCs and offer a rapid and effective approach to obtaining REE data and other trace element data.

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ORCID for David George Reading: orcid.org/0000-0002-6697-8525

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