Identification of uranium hexavalent compounds using X-ray photoelectron spectroscopy

Abstract

X-ray photoelectron spectroscopy (XPS) has applications in many fields ranging from development of thin films for semi-conductors to post failure analysis of organic coatings and structural adhesives. The current work expands on that versatility by applying XPS to the growing field of nuclear forensics. This was achieved by the synthesis and characterisation of several uranium compounds, predominantly in the hexavalent state associated with the nuclear fuel cycle, and by X-ray diffraction and Raman spectroscopy analysis prior to XPS. Spectral characteristics for each compound are discussed, and interpretations made through observations in the binding energy of the U4f region as well as secondary energy loss features such as shake up satellites. The interpretation of such features is related to the stoichiometry, oxidation state and bonding structure of a range of uranium compounds. As XPS is typically insensitive to structural (crystallographic) variations, a rationale is provided for the relationship between structural variations, as measured by Raman and X-ray diffraction and compared to the open literature, and the XPS satellite to parent peak intensity of uranium compounds, providing a novel and useful approach for uranium compound characterisation. In addition to the novel approach described, Wagner chemical state plots have also been generated to provide another comparison tool.