Engineering topics
Publications and source records attributed to Weng, T. -C..
A quantitative analysis method has been developed that allows the cross calibration of separate Uranium M 4 and M 5 X-ray absorption spectra (XAS), in particular those collected with the new High Energy Resolution Fluorescence Detection (HERFD) method. With this method, it is now possible to generate experimental Branching Ratio (BR) values from the U M 4,5 XAS HERFD data.
Delocalization of the 5f states in the early actinides in general and U metal in particular is significantly important and yet poorly understood. Here, extant spectroscopic techniques have failed to resolve the situation. Here it will be shown that X-Ray Emission Spectroscopy (XES) of the M 4,5 levels can provide the needed information, with a distinct difference between the delocalized U metal and localized uranium dioxide and uranium tetrafluoride cases. A Peak Ratio (PR) model, built upon electric dipole selection rules, has been developed and utilized, with quantitative agreement between experiment and theory. Possible expansion to other types of 5f mixing systems will be discussed.
Recently, it was demonstrated that an empirical model based on bremsstrahlung isochromat spectroscopy of elemental thorium (Th) could be used to explain the experimental results and unoccupied 5f electronic structure for simple localized actinide systems with n = 2/3, 2, 3, and 5, where n is the 5f occupancy. In this work, the thorium model will be extended to provide an understanding of the observed behavior and unoccupied 5f electronic structure in the uranium monochalcogenide systems of uranium sulfide and uranium telluride, in terms of weak 5f delocalization.
Ligand field density functional theory calculations of the dioxides of thorium, uranium, and plutonium have been combined with high-energy-resolution fluorescence detection (HERFD) in x-ray absorption spectroscopy and inverse photoelectron spectroscopy (IPES) measurements to provide powerful insight into the underlying composition of the unoccupied 5f electronic structure in these 5f localized systems. Fine structure in the 5f 5/2 transitions in HERFD can be directly correlated with the fine structure in the leading edge of the IPES. The shapes, intensities, and systematics in HERFD and IPES are explained in a consistent and rigorous fashion in terms of the j-specific 5f electronic structure.
Abstract not provided.