Micro-Focused X-Ray Absorption Spectroscopy Studies of Plutonium Materials

Synchrotron X-ray absorption spectroscopy (XAS) is an established technique for studying the local structure of plutonium materials, including oxides and metals. Modern imaging and high-resolution techniques provide detailed information that may elucidate questions regarding the fate of impurities with different Pu oxidation conditions and may also find utility in nuclear forensics investigations. Combining XAS with x-ray fluorescence (XRF) mapping provides the ability to quickly locate particles or areas of interest with up to 1 μm spatial resolution and then obtain local structure information from individual points. In this work, we apply micro-focused XRF+XAS techniques to the study of common impurities in plutonium oxides, such as gallium, iron, and nickel. We investigate the distribution and local structure of these impurities in plutonium oxides made from various synthetic routes, including corrosion and high temperature calcination of Pu metal. The results show that for some impurities, like Ga, local structure and distribution are highly dependent on processing conditions, such as temperature. We also discuss developments in micro-focused high energy resolution fluorescence detection (HERFD) XAS techniques and their applications to Pu particulate samples. Using a HERFD spectrometer significantly increases the resolution of the near-edge spectrum, providing greater confidence in oxidation state determination, and combining this technique with a micro-focused beam enables the generation of oxidation state distribution maps. Here, we present results for heterogeneous plutonium samples, demonstrating the utility of this technique for distinguishing between phases of interest (e.g. oxide and metal) and their distribution within a sample. Characterization using these advanced methods provides insight into impurity fate with plutonium processing and possible nuclear forensics signatures of plutonium materials.