Certification of a Uranium Micro-particle Reference Material and Results of the NUSIMEP-9 Inter-Laboratory Comparison on Uranium Isotope Amount Ratios and Mass in Uranium Micro-Particles

Measurements of the uranium and plutonium isotopic ratios in small amounts, such as typically found in environmental swipe samples and particles, are required for nuclear safeguards, for the control of environmental contamination and for the detection of nuclear proliferation. The JRC-Geel, the Forschungzentrum Jülich (FZJ, Germany) and the IAEA-Safeguards Analytical Service, SGAS (Seibersdorf, Austria) are collaborating on the production and characterisation of a certified uranium oxide micro-particle reference material for quality control and method validation in nuclear safeguards.The μm-sized uranium oxide particles were produced using a vibrating orifice aerosol generator (VOAG) at the FZJ and deposited on carbon planchets. The uranium nitrate input solution was prepared and characterized for uranium isotopic composition by Thermal Ionization Mass Spectrometry (TIMS) at JRC-Geel. At the IAEA, \"process control measurements\" were performed by leaching the particles from the planchets and confirming the isotopic composition using MC-ICPMS.The certification is combined with the interlaboratory comparison NUSIMEP-9 (Nuclear Signatures Inter-laboratory Measurement Evaluation Programme) external quality control programme, organised by the G.2 unit at JRC-Geel, which aims at providing materials for measurements of trace amounts of nuclear materials in environmental matrices. In this context, NUSIMEP-9 was targeting particularly the IAEA-NWAL, a worldwide network of analytical laboratories, but was as well open to other laboratories from various scientific fields. Finally, 30 laboratories worldwide registered in NUSIMEP-9. They received one certified test planchet with some thousands of U3O8 particles of about 1 µm diameter-size deposited on it.Participants were asked to measure, using their routine analytical procedures, and report the 234U/238U, 235U/238U and 236U/238U isotope amount ratios of ten particles, which belong to the main particle population. Moreover, participants were also encouraged to measure and report the uranium mass per particle by measuring at least ten particles. The participants’ measurement results were evaluated against the certified reference values in accordance to ISO 17043 and ISO 13528, while guaranteeing full confidentiality with respect to the link between measurement results and the participants’ identity.This paper will present both the different steps of the certification process of the Uranium Micro-particle Reference Material and results of the NUSIMEP-9 interlaboratory comparison.