Microscale synchrotron radiation-based x-ray fluorescence (SR-XRF) chemical analyses can provide a unique capability for chemical signature recognition and classification capabilities for actinide micro-particle analysis. SR-XRF is well suited to forensic type analyses of small particles because it is rapid, non-destructive, highly sensitive, has good spatial resolution, and can provide chemical information on the elements that are present when combined with x-ray absorption spectroscopy (XAS). The combination of spatially resolved distribution and chemical information, often known as chemical imaging, effectively provides a “chemical morphology” of the sample of interest and can show how chemical states are distributed within and among a series of particles. This type measurement is critical for understanding particle origin and history, as the spectroscopy, and its spatial distribution, can provide unique and complementary chemical signatures that may not be elucidated with other forms of measurement.

However, the conventional XAS capability in the near edge region as commonly implemented is often inadequate for systems that require high sensitivity or require a higher detail of spectroscopic information. This can be overcome with the combination of traditional micro SR-XRF and XAS, integrated with a high energy resolution fluorescence detector (HERFD) crystal analyzer. This has been recently implemented at BL 6-2b at SSRL and applied in the determination of the micron-scale oxidation state of uranium in particles. A discussion of the image and data processing techniques that can be applied using spatially resolved HERFD to obtain chemical and structural information, as well as the distribution of phases across different particles at the micro-scale, will also be presented.

The exceptional properties of transition metal nitrides for coatings, as well as photo- and electrochemical applications have opened the doors for more detailed studies of their structure and synthesis. Mn- and Cr- nitrides are strong candidates to showcase the application of spintronic and magnetic sensing applications partially because of their ability to form several different metastable phases. Similarly, rare-earth nitrides have been studied for over 50 years due to their optical properties and strong electron correlations, leading to behaviors that range from insulating to metallic. This study uses molecular beam epitaxy to synthesize epitaxial thin films of different Mn-, Cr-, Ga-, and Ce-nitride phases. The electrical and magnetic properties of these films are investigated with the rocksalt MnN and CrN both showing metallic behavior, with the latter showing a magnetic transition ~280K. However, when combining these materials at similar growth conditions, instead of maintaining the rocksalt structure, a new ternary cubic phase of Mn_xCr_yN is obtained which shows narrow-gap semiconducting behavior. Additionally, density functional theory calculations show potential new phases where lanthanoid ternary phases are experimentally realizable. This work presents an avenue for the epitaxial integration of metallic, magnetic, and semiconductor materials via transition metal and lanthanoid compounds, en route to the synthesis of actinoid compounds.

Nanomaterials of uranium and thorium oxides and their mixtures are of significance to the development of advanced nuclear fuels with properties such as self-healing and greater fission gas retention. They also serve as a means for furthering our understanding of spent nuclear fuel behaviors. Furthermore, thorium incorporation into the uranium sublattice induces changes in oxidation behavior, which would be a promising means to provide additional redox resistance. Coupling this with the possible application in fast neutron reactors presents a potential fuel for the Th fuel cycle, which is inherently proliferation resistant. However, these possible applications are purely hypothetical given that, compared to nanomaterials from the rest of the periodic table, actinide nanomaterials are heavily understudied. Therefore, it will be imperative to interrogate the properties of these nanomaterials. This work aims to explore three key areas. (1) How careful kinetic control through variations in synthetic methods can be used to produce particles with different sizes, shapes, and heterogeneities of mixing. (2) Elucidation of the structural and thermodynamic properties of these nanomaterials and how characteristic size, shape, and heterogeneity of mixing affect them through a variety of X-ray characterization and calorimetry techniques. X-ray characterization techniques such as X-ray absorption spectroscopy (XAS) is used to evaluate the heterogeneity of mixing, local structure, and oxidation state of particles while small-angle X-ray scattering (SAXS) is used to determine statistical values on particle size, shape, and polydispersity. Calorimetry techniques like high temperature drop calorimetry are used to determine enthalpies of formation for nanoparticles and the contribution surface effects have on the thermodynamics or thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), which can be used to evaluate oxidation behaviors. (3) How sintered nanoparticles behave in in-situ reactor conditions as nuclear fuels and how particle characteristics can be chosen to achieve more desirable radiation-resistance and thermal properties for nuclear fuel, through irradiation studies performed at the 1-MW TRIGA reactor on the campus of Washington State University. Overall, the work presented provides initial evidence for the benefits of nanomaterials in the production of advanced reactor fuels and outlines important fundamental properties of actinides on the nanoscale.