²³⁰Th heterogeneity in a CMX-7 depleted uranium metal sample

LA-(QQQ)ICP-MS was used to investigate the sources of inconsistent ²³⁰Th/²³⁴U radiochronometry results obtained during CMX-7 for depleted uranium (DU) oxide powder, ES-1, and DU metal, ES-4, samples. The stability of the (QQQ)ICP-MS was greatly improved using a modified “broad peak” technique to enable a more precise and accurate analysis of the samples. Whereas ES-1 was found to be homogeneous in both U and Th, ES-4 was homogeneous in U but inhomogeneous in Th. The ratio of ²³⁰Th/²³⁴U decreased with depth of the metal sample, whereas ²³⁴U/²³⁵U remained constant, leading to an apparently higher age on the surface of the sample.