Expanding the nuclear forensic toolkit: chemical profiling of uranium ore concentrate particles by synchrotron X-ray microanalysis

Abstract

Nuclear forensic trace evidence may include particles of unknown nuclear or radiological substances which would need to be indentified in an investigation. In this study we report the novel application of synchrotron X-ray microanalysis techniques to characterise the chemistry of particles derived from several uranium ore concentrates (UOCs). Using a combination of micro-focused X-ray diffraction and X-ray absorption spectroscopy, the uranium speciation in particles of 12 UOCs from different geographical sources was identified. Particles were classified based on their composition; four samples were found to contain only U₃O₈, four samples were comprised of various U(VI) species and the final four were binary mixtures. In addition to U₃O₈, the identified materials included ammonium, sodium and copper uranate species, and various hydroxide and sulphate phases. Differences in the crystal structure of UOCs which contained the same material were identifiable by μ-XRD, and were hypothesised to be as a result of differences in process conditions. Consistency in particle speciation was assessed in several samples, some of which were found to contain variable levels of two component materials and minor crystalline impurities. Although this variability limits the intrinsic interpretation of single particle microanalysis data in terms of sample provenance, the non-destructive and highly specific analysis of nuclear fuel cycle materials demonstrated in this study will be of value to complex nuclear forensic investigations.