Micro Particle Suspensions for Preparation of Reference Materials for Particle Analysis Methods in Safeguards

In order to produce micro particle reference materials for nuclear safeguards particle analysis, a dedicated facility has been established at Forschungszentrum Jülich. This includes an aerosol-based particle production setup which is capable of producing uranium micro particles with consistent isotopic compositions and uranium contents. While the produced particles could be used as reference materials as obtained after production, further options for packaging the particles are being considered to simplify handling of the particles and to open new possibilities, such as the preparation of particle mixtures.The transfer of the collected particles into a suspension has several advantages. For example, particles in suspension stored in a bottle would be amenable to extraction of an aliquot, which could be dried on a substrate of interest, such as silicon wafers, glass-like carbon disks or cotton-swipes, to obtain test samples. Also, various suspensions could be mixed in different ratios followed by drying on the desired substrates to obtained particle mixtures of two or more different particle types. However, while the particles are dispersed in suspension, various reactions could have an influence on the stability of the micro particle property values. In order to assess the stability of uranium micro particles in a suspension, experiments have been conducted using synthetic powders and uranium micro particles. Our results from dissolution and uranium isotope exchange studies show that ethanol is a suitable medium for the storage of particles over a period of a few months. Using particles produced with the particle production setup at Forschungszentrum Jülich, particle suspensions have been produced by transfer of collected particles into ethanol and distribution on silicon wafers and cotton-swipes produced consistent results. It was demonstrated that the production of particle mixtures is feasible. It was also shown that particles in suspension could represent a suitable packaging for a particle reference material which permits a quick and flexible preparation of various types of test samples