Production of radioactive traceable reference materials for measuring radioactive pollutants in the environment

There are very few radioactive environmental reference materials (RM) traceable to the International System of Units. Existing radioactive RMs for environmental samples that can be measured by mass spectrometry are even more limited and their characterisation does not always include relevant parameters such as isotopic ratios. This paper focuses on the development of two environmentally relevant candidate RMs, one liquid and one solid, which could be used for routine quality control measurements. The liquid RM was prepared by spiking seawater sampled from the North Sea, and therefore the matrix is representative of a real environmental sample, while the solid RM was prepared using a synthetic approach by spiking a mixture of silica precursors before a sol-gel reaction. The homogeneity, between-bottles and within-bottles, of both RMs was assessed using gamma-ray spectrometry and mass spectrometry. For the liquid RM, the variation among sub-samples was due mainly to the within-bottle variance, and was lower than 1 %, for all the radionuclides tested. For the solid RM, the ²⁴¹Am content measured with gamma-ray spectrometry revealed a statistically significant variation between-bottles, but was lower than 1 %. The ²³⁸U and ²³⁹Pu contents, measured by mass spectrometry, showed higher measurement variability (∼5 %), with the main contribution coming from within the bottles.