Using a Redesigned TSI FMAG 1520 to Produce Uranium Oxide Microparticles Collected Directly on Swipes to Strengthen the IAEA’s Quality Control System for Particle Analyses

During the last decade the IAEA (International Atomic Energy Agency) expressed an increasing demand for sub- and micrometre-sized uranium oxide-based reference particles. These particles are used by the IAEA and its connected Network of Analytical Laboratories (NWAL) for machine calibration, method development and proficiency testing. In this context, an aerosol-based approach to produce uranium oxide-based microparticulate reference materials was implemented in the laboratories of Forschungszentrum Jülich (FZJ). Since 2020 the Safeguards Laboratories at FZJ have been first qualified member of IAEA’s dedicated NWAL for the provision of microparticle reference materials for particle analysis in nuclear safeguards. The centrepiece for the production of these uranium oxide-based microparticles at FZJ is a modified aerosol generator, TSI® VOAG 3450 (Vibration Orifice Aerosol Generator), which was acquired in 2012. Unfortunately, TSI® has ceased the production of the VOAG and will soon also cease servicing and procuring spare parts. In addition, chemical composition of the microparticles will be extended to more complex systems, e.g. Pu- doped uranium oxide, and the demand for new advanced reference materials, e.g. for nuclear forensics and age-dating including the research and development required for this purpose will also increase the technical requirements on the particle production. Therefore, a new aerosol generator, the TSI® FMAG 1520 (Flow Focussing Monodisperse Aerosol Generator) was purchased and installed. In order to produce particles of comparable quality to those produced with the FZJ’s VOAG setup the original setup of FMAG was significantly modified according to the experiences gained during the design of the VOAG-based setup. Additional changes were made to enable a broader range of the process parameters, i.e. temperature by the installation of two furnaces which are connected in line and are individually controllable. Finally, care was taken to ensure that the handling of the system was kept as simple as possible, for example by using gas-tight quick couplings of the gas tubes to simplify the cleaning process and replacement of parts, as it is planned to operate the system in a glove box. An encouraging additional result of the redesign is that, compared to the VOAG setup, these modifications lead to a much higher particle yield and additionally allows a higher flexibility in the methods of particle collection. For instance, slight modifications on the FMAG setup allow for a direct collection of microparticles on cotton swipes, like those used by IAEA inspectors, instead of the usage of inert vacuum impactors. These microparticles deposited on swipes, can be easily detached by vacuuming the swipe and then collected with a standard inert impactor. A previous or subsequent addition of a second type of microparticles or dust to the swipe is also feasible to simulate a more realistic “in-field” sample. This means, that, after deposition of uranium oxide-based microparticles with known isotopic composition, these swipes are fit for purpose as materials for proficiency testing like round robin tests. An overview of the status of these activities and first results will be presented.