Determination of nuclear forensic signatures from lead ratios and REEs in uranium ore samples using ICP‐MS and LIBS

Abstract

The aim of this study was to determine nuclear forensic signatures from lead ratios and resolve rare earth elements (REE) signatures in uranium samples and water using inductively coupled plasma mass spectroscopy (ICP-MS) and laser induced breakdown spectroscopy (LIBS), as well as comparing resolved REEs and lead isotopic ratios from South Africa with the Namibian results. A set of water samples were collected from underground in the Namibian area and another set of uranium ore samples were collected in the mine tailings from both South Africa and Namibia. The uranium ore samples were digested in a microwave and diluted with distilled water. Both the water and uranium ore samples were analyzed using the ICP-MS and LIBS. For ICP-MS, the instrument was set to isotopic ratio method, operated in the collision mode for mass energy discrimination and filtration against interferences and it was also set to total quantitative method to analyze REEs. For LIBS, no sample preparation was required so the sample was directly ablated by the laser to analyze REEs. Principal component analysis (PCA) was performed using the results obtained from both techniques in order to identify patterns in the samples. Enriched light rare earth elements and depleted heavy rare earth elements were exhibited in both samples analyzed using the LIBS and ICP-MS. 206Pb/204Pb isotope ratio was greater than 20 thus, indicating a uranium rich ore. However, lead ratios from South Africa exhibited a uranium rich ore compared to lead ratios of Namibia. The PCA displayed identical patterns for samples analyzed by ICP-MS whereas distinct patterns were observed in the samples analyzed by LIBS. These characteristics can be used as a fingerprint and this study will promote and improve nuclear safety in the fight against theft of nuclear material, thereby promoting the non-violent use of nuclear material. That is why nuclear forensic signatures of uranium or nuclear materials need to be established and stored in a nuclear forensic library database.