The NUSIMEP (Nuclear Signatures Inter-laboratory Measurement Evaluation Programme) is an external quality control programme organised by the European Commission - Joint Research Centre, Directorate G - Nuclear Safety and Security, Unit G.2 for Standards for Nuclear Safety, Security and Safeguards (JRC-Geel, former IRMM), which aims at providing materials for measurements of trace amounts of nuclear materials in environmental matrices. Measurements of the uranium and plutonium isotopic ratios in small amounts, such as typically found in environmental samples, are required for nuclear safeguards, for the control of environmental contamination and for the detection of nuclear proliferation. The JRC-Geel, the Forschungszentrum Jülich (Germany) and the IAEA-SGAS (Seibersdorf, Vienna) joined forces to produce and characterise micrometre-sized uranium oxide particles, which can be used for safeguards purposes as Reference Materials (RM). In this context, JRC-Geel organised a new NUSIMEP proficiency test round, targeting more particularly the IAEA-NWAL network of analytical laboratories. However, NUSIMEP-9 was opened to all laboratories in various scientific fields. Thirty participants in NUSIMEP-9 received one certified test item, a carbon planchet on which were deposited some thousands U3O8 particles of about 1 μm diameter-size of single isotopic composition. They were requested to use their routine analytical procedures and report the n(234U)/n(238U), n(235U)/n(238U) and n(236U)/n(238U) isotope amount ratios of ten particles. Participants were also encouraged to measure and report the uranium mass per particle by measuring at least ten particles. At the end, 25 participants reported results for NUSIMEP-9. These results were evaluated against the certified reference values in accordance with ISO 13528:2015, while guaranteeing full confidentiality with respect to the link between measurement results and the participants' identity. In general, laboratory's performances in measuring and reporting major and minor uranium isotope amount ratios in the NUSIMEP-9 particles were satisfactory. A few participants undertook to measure and report the uranium mass per particle in NUSIMEP-9 and their overall performance was satisfactory, although with a large scatter of the reported results. The final evaluation of the participant's performances in the uranium particle analysis of the NUSIMEP-9 test item, the findings and feedback of this proficiency test are presented in this report.
