The aim of this thesis is to investigate the vibrational properties of a range of uranium based materials and to demonstrate the benefit of using vibrational data to identify and distinguish these materials in a forensic scenario. The ability to rapidly detect and identify radioactive samples is of particular importance to countries interested in controlling the distribution of nuclear material, as well as environmental scientists investigating the remediation of nuclear sites. The materials of interest to this study are U3O8 and UO3, which are the two primary oxidation products of UO2, and a range of minerals containingthe uranyl (UO2)2+ cation that readily form from UO2 in the environment. Raman spectroscopy is a promising technique, with experimental data indicating that it may be used to distinguish between uranyl minerals, hence it is a particular focus of this thesis.Earlier work used group theory to interpret the spectra, whereas in this study the vibrational properties have been compared with density functional theory (DFT) simulations. This strategy has provided both an interpretation of vibrational modes and insight into how the vibrational properties change in response to structural or compositional changes.Chapter 1 provides background information on binary uranium oxides, uranyl minerals and strategies that may be used to study them. Furthermore, the aims of this thesis are discussed. A summary of the theory of Raman and IR spectroscopy is described inChapter 2 and the computational methods used are detailed in Chapter 3. Chapters 4 and 5 are focused on the simulation of vibrational spectra for the various polymorphs of U3O8 and UO3, with comparisons made to experimental Raman and IR spectra. In Chapter 6 experimental Raman spectra for a range of uranyl minerals from Cornwall,UK are presented, with an emphasis on identifying differences that may be used to discriminate between samples. In Chapter 7 DFT is used to simulate the vibrational spectra for a set of uranyl phosphate and arsenate minerals, known as autunite minerals, with systematic variations in composition. Finally, the conclusions from all chapters are collated and discussed in Chapter 8, alongside possible areas of continued research.
|Date of Award||13 Sep 2016|
|Sponsors||Atomic Weapons Establishment|
|Supervisor||Steve Parker (Supervisor) & Daniel Wolverson (Supervisor)|
- Raman spectroscopy
- computational chemistry
- Density functional theory