REIMEP-22 inter-laboratory comparison: “U Age Dating – determination of the production date of a uranium certified test sample”

Abstract The REIMEP-22 inter-laboratory comparison aimed at determining the production date of a uranium certified test sample (i.e. the last chemical separation date of the material). Participants in REIMEP-22 on “U Age Dating – Determination of the production date of a uranium certified test sample” received one low-enriched 20 mg uranium sample for mass spectrometry measurements and/or one 50 mg uranium sample for α-spectrometry measurements, with an undisclosed value for the production date. They were asked to report the isotope amount ratios n(230Th)/n(234U) for the 20 mg uranium sample and/or the activity ratios A(230Th)/A(234U) for the 50 mg uranium sample in addition to the calculated production date of the certified test samples with its uncertainty. Reporting of the 231Pa/235U ratio and the respective calculated production date was optional. Eleven laboratories reported results in REIMEP-22. Two of them reported results for both the 20 mg and 50 mg uranium certified test samples. The measurement capability of the participants was assessed against the independent REIMEP-22 reference value by means of z- and zeta-scores in compliance with ISO 13528:2005. Furthermore a performance assessment criterion for acceptable uncertainty was applied to evaluate the participants' results. In general, the REIMEP-22 participants' results were satisfactory. This confirms the analytical capabilities of laboratories to determine accurately the age of uranium materials with low amount of ingrown thorium (young certified test sample). The Joint Research Centre of the European Commission (EC-JRC) organised REIMEP-22 in parallel to the preparation and certification of a uranium reference material certified for the production date (IRMM-1000a and IRMM-1000b).