IRMM-1000a and IRMM-1000b uranium reference materials certified for the production date. Part I: Methodology, preparation and target characteristics

The paper describes the preparation and production of the reference materials, IRMM-1000a and IRMM-1000b, certified for the production date based on the 230Th/234U radiochronometer. The production date of the reference materials corresponds to the last separation of 230Th from 234U, i.e. when the initial daughter nuclide content in the material was finally removed. The certified reference materials were produced jointly by the European Commission Joint Research Centre Institute for Transuranium Elements (EC-JRC-ITU) and Institute for Reference Materials and Measurements (EC-JRC-IRMM) in compliance with ISO Guide 34:2009. For the preparation low-enriched uranium was used, which was purified using a unique methodology to guarantee high U recovery and high Th separation efficiency. The complete elimination of Th from the initial material was verified by gamma spectrometry, by the addition of 232Th tracer to the starting material and its re-measurement from the final product and by the age dating of the freshly prepared material a few days after preparation. The reference material was produced in two sizes containing 20 mg uranium and 50 mg uranium, distributed by EC-JRC-IRMM as IRMM-1000a and IRMM-1000b. The CRM is intended for calibration of methods, quality control, and assessment of method performance with isotope mass spectrometry and radiometry techniques for uranium materials in nuclear forensics and safeguards.JRC.E.7-Nuclear Safeguards and Forensic