[en] Quality Assurance and Control (QC) of analytical measurements on safeguards samples are of utmost importance to maintain the International Atomic Energy’s credibility with its Member States. For measurements of individual micrometer-sized particles, collected by inspectors on swipe samples, reference materials in particulate form are needed to implement a robust QC system. For this purpose, trilateral cooperation between the Office of Safeguards Analytical Services of the International Atomic Energy Agency (IAEA-SGAS), the European Commission - Joint Research Centre Unit G.2, Geel, Belgium (JRC-Geel) and Forschungszentrum Jülich, Germany (Jülich) was established. The overall aim of the cooperation is to qualify Forschungszentrum Jülich as a laboratory for the provision of reference materials under the IAEA’s Network of Analytical Laboratories (NWAL). One essential milestone in the qualification process is the development and implementation of a reliable procedure for producing uranium microparticles. Meeting the IAEA’s requirements with respect to uranium microparticle production, the procedure established in Jülich over the past six years now produces samples that consist of uranium microparticles with well-defined properties; such as monodisperse particle size distribution and consistent isotopic composition. The role of the JRC-Geel in this cooperation is twofold: First, JRC-Geel prepares and certifies the uranyl nitrate base solutions used in particle production, taking into account the specifications provided by the IAEA. The isotopic compositions of the base solutions are first verified by IAEA-SGAS and then used at Jülich as a feed solution to produce the microparticles. Second, samples prepared by the Jülich procedure can then be certified for the uranium isotopic composition and possibly content by a team of JRC-Geel and IAEA analysts. Future research activities will focus on the production and characterisation of microparticles with defined mixed elemental compositions, such as Ln/U, Th/U and Pu/U microparticles. (author)

[en] A major task in nuclear forensics and safeguards investigations is the detection and analysis of small particles containing fissile isotopes that may be present at low concentration within particulate environmental samples. These radioactive particles-of-interest (POIs) are usually in the micro-metric size range, and intermixed within large populations of other particles, such as dust, soil, or industrial exhaust pollutants. A commonly used method for the detection of particles of single POIs containing fissile isotopes is to embed a dispersion of particles within a thin polymer layer ('catcher'), attach a 'detector' sheet (for example, LEXAN^®) to the catcher, irradiate this structure with thermal neutrons, and then separate the two and chemically etch the detector to 'develop' fission track (FT) clusters. The resulting FT clusters are visible under light microscopy, and indicate the presence of ²³⁵U or other fissile isotopes within the POI. Measuring the coordinates of the FT cluster in the detector image enables the POI to be retrieved from the corresponding location in the catcher for further analysis. The main challenge in this procedure is imaging a large area detector (typically 100-400 mm²), at a resolution ≤1 μm, and automatically scan and locate the FT clusters while rejecting artifacts. This paper reports a novel approach which enhances the ability of the Particle Analyst to accurately identify and locate FT clusters. (author)