Uranium oxide based microparticulate reference materials for analytical measurements in nuclear safeguards – Status & perspective

The analysis of individual micrometre- and submicrometre-sized particles collected by IAEA safeguards inspectors on swipe samples during in-field verification activities requires the implementation of a sustainable quality control system. This system needs to be further optimised by developing advanced mass spectrometric analytical methods and suitable reference materials. For the design of these microparticulate reference materials well-defined tuning of elemental and isotopic composition is required. Additionally, a refined understanding on material science aspects, such as morphology, chemistry, and structure is essential. This paper is throwing a retrospective glance on the historical evolution of the microparticle production task and its safeguards implementation during the last 25 years addressing (i) the requirements and IAEA needs on microparticle reference materials; (ii) the developments and advancements of relevant particle production routes and of analytical tools for particle analysis in nuclear safeguards and nuclear forensics. Exemplarily, the way from the idea of developing and establishing a sustainable reference particle production route in the laboratories of Forschungszentrum Juelich (FZJ) to the officially certified reference material, over the application of these reference particles in an international interlaboratory exercise and finally to the qualification of FZJ as a member within the IAEA’s Network of Analytical Laboratories (NWAL) for the provision of microparticulate reference materials will be highlighted. The main focus will be spent on the production of monodisperse pure and lanthanide (Ln) doped uranium-oxide based microparticles utilising an aerosol-based particle production process as well as on the importance of material science aspects for an explicit description of the particles’ properties. Electron microscopy and X-ray absorption spectroscopy confirm the monodispersity of the produced microspheres as well as the presence of Ln (lanthanides) in the compound particles. Complementarily conducted structural investigations reveal a refined insight into the mechanism on the formation of U3O8 microparticles for both compounds as well as on shelf-life and storage conditions of these reference materials. These results demonstrate that the process established in Juelich allows for a very flexible and reliable preparation of reference materials for particle analysis methods applied in nuclear safeguards and nuclear forensics