Certification of Uranium Isotope Amount Ratios in a Suite of Uranium Ore Concentrate Certified Reference Materials

In this study, data from thirteen laboratories from around the world are presented for a successful certification of uranium isotope ratios in uranium ore concentrate (UOC) certified reference materials from the National Research Council Canada. Different mass spectrometric measurement principles (including SF-ICP-MS, quadruple ICP-MS, TIMS, MC-ICP-MS, SIMS and AMS) and measurement procedures were employed. In general, data from all sources exhibit good consistency with TIMS and MC-ICP-MS showing superior performance. The three candidate UOC CRMs (UCLO-1, UCHI-1 and UPER-1) have natural uranium isotope ratios with certified values of 0.5304(7) × 10⁻⁴, 0.5475(2) × 10⁻⁴ and 0.5361(4) × 10⁻⁴ for n(²³⁴U)/n(²³⁸U) and 0.007 2563(13), 0.007 2563(10) and 0.007 2542(11) for n(²³⁵U)/n(²³⁸U), respectively, with expanded uncertainty (k = 2) applicable to the last digit of the value given in the parentheses. Information values for n(²³⁶U)/n(²³⁸U) in these three CRMs, measured by AMS, are also provided: 10 × 10⁻¹², 200 × 10⁻¹² and 22 × 10⁻¹². The uncertainties of the proposed certified values of uranium isotope ratios in UOC CRMs are superior to available reference materials, and the values of n(²³⁴U)/n(²³⁸U) and n(²³⁶U)/n(²³⁸U) show significant variation among the three CRMs.