Electrical Characterization of Crystalline UO2, ThO2, and U0.71Th0.29O2
Technical Report,01 Oct 2015,20 Dec 2018
AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH WRIGHT-PATTERSON AFB United States
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Uranium dioxide UO2, thorium dioxide ThO2, and UxTh1-xO2 alloys are characterized for suitability in uranium-based neutron detectors. ThO2 was studied for an envisioned UO2ThO2 heterojunction. A U0.71Th0.29O2 alloy was studied because of its resistance to oxidation and potential use in surface passivation. The U0.71Th0.29O2 effective Debye temperature of 217 24 K was measured using temperature-dependent x-ray photoemission spectroscopy XPS. The specific heat capacity for the U0.71Th0.29O2 alloy was calculated from the Debye temperature and compared to the heat capacity obtained from modulated-temperature differential scanning calorimetry MDSC. The XPS derived Debye temperature specific heat capacity was lower than with MDSC due to effects of a vacuum reduced crystal surface. Angle resolved XPS provides depth profiling of a UO2 surface. The U 4f72 peaks are evident of U4 and U6 oxidation states with an increase in the U4 oxidation state further from the surface. The presence of U 5f peaks in the valence band spectra provided evidence of U4 but does not preclude the presence of U6, while the electronic band-gap energy remained at 2.2 eV, confirming the presence of UO2. These surface characteristics indicated a vacuum reduced UO2 surface and excess oxygen incorporated into the lattice forming a UO2x selvedge region.
- Metallurgy and Metallography