Hydride Mapping in Uranium Using MLLS Fitting of Electron Energy-Loss Spectra

Previous studies of the reaction of hydrogen gaswith uranium metal have been mainly limited to microscale or higher observations of uranium surfaces. We have characterized subsurface features of uranium hydride structures formed in a depleted uranium pellet aged for over 9 years under a controlled atmosphere with an initial H2 partial pressure of 0.667 kPa (5 torr) using electron energy-loss spectroscopy (EELS), giving information at lower length scales than previously reported. We demonstrate that multiple linear least-squares fitting of the O4,5 edge of the uranium EEL spectrum, with input spectra generated from the dataset being analyzed, can be used to map hydride and metal phases in aged uranium metal at the nanometer scale. While the interface between the bulk metal and the subsurface hydride structures is sharp and well defined, the interior of the reacted region is heterogeneous,containing a mix of polycrystalline UH3 and stranded, apparently unreacted, U metal.