Precise and accurate isotopic analysis of uranium and thorium in uranium ore concentrates using ICP-MS and their age dating for nuclear forensic analysis

• Published in: Journal of analytical atomic spectrometry 2024-01, Vol.39 (1), p.178-189
• Main Authors: Wang, Wei, Xu, Jiang, Xi, Ruiyang, Guo, Siqi, Su, Yongyang, Fang, Sui, Zhang, Haitao, Wang, Yalong, Fan, Jinlong, Feng, Lei, Wang, Yufeng, Li, Zhiming
• Format: Article
• Language: English
• Subjects: Inductively coupled plasma mass spectrometry; Isotope ratios; Mass spectrometry; Measuring instruments; Ratios; Scientific imaging; Thorium; Thorium isotopes; Uranium; Uranium ores
• ISSN: 0267-9477; 1364-5544
• DOI: 10.1039/d3ja00196b

Isotope ratios and age dating of uranium ore concentrates (UOCs) are of great significance in nuclear forensic analysis. This paper presents accurate and precise isotopic analysis of uranium and thorium in 15 different UOCs using two types of ICP-MS instruments. 235 U/ 238 U, 234 U/ 238 U and 230 Th/ 232 Th isotope ratios were determined by Multi-Collector Inductively Coupled-Plasma Mass Spectrometry (MC-ICP-MS), while 230 Th/ 234 U and 234 U/ 232 Th atom ratios were determined by triple quadruple Inductively Coupled-Plasma Mass Spectrometry (ICP-MS/MS). Results show that the relative uncertainties in the determined values of 235 U/ 238 U, 234 U/ 238 U and 230 Th/ 234 U ratios for CRM124-1 are 0.0014%, 0.02% and 3.2%, respectively. It has been proved that an aliquot containing 1.12 μg of 238 U was the minimum sample amount to obtain the representative 235 U/ 238 U ratios of the UOC samples for bulk analysis by MC-ICP-MS, especially when the sample of UOCs was inhomogeneous or a mixture of several UOCs. No correlation between the measured 238 U/ 235 U and 235 U/ 234 U ratios is observed in the UOC samples. It is possible to distinguish a single UOC sample from others by synthesizing 235 U/ 238 U ratio, 234 U/ 238 U ratio and 230 Th/ 234 U ratio simultaneously. The 230 Th- 234 U model ages estimated using a 230 Th- 234 U chronometer lie between 3.5 a and 4435 a. However, it is usually not reliable to determine the age over 100 a of UOCs, mainly because the material was not completely purified from relevant decay products during production. To overcome this problem, an alternative approach for age dating is proposed using multiple measurements of the ratios of 230 Th/ 232 Th and 232 Th/ 234 U at an interval of about 2 a to 5 a. This work demonstrates that multiple parameters obtained from a combination of multiple analytical techniques, including bulk analysis, imaging and microanalysis techniques, can be used to narrow the range of potential origins for nuclear forensic purpose. Precise and accurate analysis of 235 U/ 238 U, 234 U/ 238 U, 230 Th/ 234 U and 230 Th/ 232 Th in 15 uranium ore concentrates (UOCs) was achieved using ICP-MS for nuclear forensic applications. A novel method was developed to dating UOCs.