Physical Characterization of Actinide Particles - A Study on Novel Techniques for Radiological and Nuclear Safeguard Investigations

Sammanfattning: This thesis presents a study of advanced analytical techniques, for the characterization of actinide particles originating from the non-peaceful use of nuclear technology and from international inspections of the nuclear fuel cycle associated with non-proliferation agreements. The thesis is based on five papers, which will be referred to by Paper I-V in the text. Individual particle analysis has several advantages over bulk analysis as it can give detailed information on elemental surface and internal compositions, elemental distributions, and compositional information. This information is valuable in tracing the source of the material, and in modelling and predicting the transport of radionuclides in the environment, for instance, in a release scenario. In bulk sample analysis, these characteristics are largely masked. The specific objectives of this work, which was aimed at improving the techniques used in actinide particle analysis, were: 1) the analysis of microscopic materials from nuclear weapons tests and an accidental release involving nuclear weapons (Papers I and II) and materials from nuclear inspection samples (Paper III) in order to obtain elemental and isotopic fingerprints. Single-particle analysis were performed using techniques such as secondary ion mass spectrometry (SIMS) and scanning electron microscopy (SEM) to characterize the particles, regarding elemental, isotopic, size and morphology structures, and fundamental limitations were identified; 2) the optimization of SIMS analysis of uranium particles by tuning the instrument to obtain the highest obtainable efficiency (Paper III); 3) the investigation of large-geometry SIMS applied to inspection samples to allow isotopic analysis of particles that is not possible with conventional SIMS (Paper III); 4) the production and characterization of new particle materials suitable for calibration purposes (Papers IV and V); and 5) the application of the calibration material produced for the evaluation of SIMS and SEM (Papers III and V).