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Study on the applicability of structural and morphological parameters on selected uranium compounds for nuclear forensic purposes

Ho, Doris Mer Lin

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Nuclear forensic science or nuclear forensics, is a relatively young discipline which evolved due to the need of analysing interdicted nuclear or radioactive material, necessary for determining its origin. Fundamentally, nuclear forensic science makes use of measurable material properties, referred to as "signatures", which provide hints on the history of the material. As part of the advancement in this multi-faceted field, new signatures are constantly sought after and as well as analytical techniques to efficiently and accurately determine the signatures. The work carried out in this study is part of this fulfilment to investigate new structural and morphological parameters as possible new nuclear forensic signatures for selected uranium compounds. The scientific goals have been oriented into three parts for investigations in this study. Firstly, five different compositions of uranium ore concentrates (UOCs) were prepared in the laboratory under well-defined conditions. These materials were subsequently characterized by several techniques such as X-ray diffraction, thermogravimetry/differential thermal analysis, Infrared and Raman spectroscopy, mass spectrometry, scanning electron microscopy etc. Such materials were pivotal for comparison with the industrial samples. Secondly, several uranium compounds, mainly UOCs were measured using Raman spectroscopy. At least three different Raman spectrometers were used and a comparison made in their performance and suitability for nuclear forensics. Raman spectra of industrial uranium materials were interpreted with regard to compound identification and to determination of (anionic) impurities. Anionic impurities that were present were identified and they could provide clues to the processing history of the samples. Statistical techniques such as principal component analysis (PCA) and partial least square-discriminant analysis (PLS-DA) were applied to several Raman spectra. The analysis showed that different compositions of uranium compounds could be discerned based on their spectra. Apart from bulk analysis of the samples, Raman was also used to measure single particles. Results showed that although particle analysis could be slightly less precise in terms of the peak positions, it could still distinguish the different form of ore concentrates. Raman spectroscopy is therefore, a useful technique for probing the molecular structure of different uranium compounds. It can be used not just for forensic purposes, but for nuclear safeguards as well. Last but not the least, microstructural fingerprints were investigated as part of the search for ways to differentiate different forms of UOCs. Currently, forensic investigations involve studying the morphology of interdicted samples using scanning electron microscope (SEM). This approach has remained qualitative and more quantitative ways are needed to study the variety of samples available. In this study, the concept of morphological fingerprint was explored by studying the sizes and shapes of dispersed particles. Although this method can be tedious, it can be applied to small number of samples. Two samples were shown to have different sizes but similar shapes and therefore they could be distinguished. A different property of the sample, known as image texture was studied for the first time, using Angle Measure Technique algorithm. SEM images were taken and transformed into numeric data using the algorithm. The data processed by PCA and PLS-DA indicated that image texture could differentiate the samples. Both structural (Raman spectroscopy) and morphological (using SEM) aspects of UOCs have been studied at great lengths, demonstrating that these signatures may provide useful hints on the history of the material. The data provided in this thesis can serve as a good reference for future nuclear forensic investigations.

Document type: Dissertation
Supervisor: Fanghänel, Prof. Dr. Thomas
Date of thesis defense: 13 March 2015
Date Deposited: 07 Apr 2015 13:03
Date: 2015
Faculties / Institutes: Fakultät für Chemie und Geowissenschaften > Institute of Physical Chemistry
DDC-classification: 540 Chemistry and allied sciences
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