REIMEP-22 : U age dating - Determination of the production date of a uranium certified test sample

The REIMEP-22 inter-laboratory comparison (ILC) "U Age Dating - Determination of the production date of a uranium certified test sample" was organised by JRC-IRMM as support to the Nuclear Forensics International Technical Working Group (ITWG) This ILC was organised prior to the release of the candidate certified reference material IRMM-1000, produced in cooperation with JRC-ITU. The aim of REIMEP-22 was to determine the production date of the uranium certified test sample (i.e. the last chemical separation date of the material) using the disequilibrium between the 230Th-234U and 231Pa-235U nuclides as chronometers. The first was compulsory, the latter optional. Participants in REIMEP-22 received either a 20 mg or 50 mg low-enriched uranium sample of known age in solid uranyl nitrate form, depending on the type of analytical technique they used. Participating laboratories were asked to measure and report either the isotope amount ratio n(230Th)/n(234U) for the 20 mg uranium samples or the activity ratio A(230Th)/A(234U) for the 50 mg uranium samples and to report the calculated production date of the certified test samples. The participants were asked to apply their standard analytical procedures and report the results with the associated uncertainties. REIMEP-22 was announced to participants in June 2013 and fourteen laboratories registered for REIMEP-22 by October 2013. The shipment of the samples to the participants took place between December 2013 and late January 2014. Finally, by May 2014, nine laboratories reported results for the 20 mg uranium sample (using mass spectrometry and reporting amount ratios) and four laboratories for the 50 mg uranium sample (using a-spectrometry and reporting activity ratios). The reported measurement results have been evaluated against the certified reference value by means of zeta-scores in compliance with international guidelines. In general the REIMEP-22 participants' results were satisfactory. This report presents the REIMEP-22 participants' results; including the evaluation of the questionnaire.