Electrical Characterization of Crystalline UO2, ThO2, and U0.71Th0.29O2
Abstract
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 UO2/ThO2 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 4f7/2 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 UO2+x selvedge region.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 20, 2018
- Accession Number
- AD1067727
Entities
People
- Christina Dugan
Organizations
- Air Force Institute of Technology