Date of Award

12-17-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Engineering Physics

First Advisor

James C. Petrosky, PhD

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.

AFIT Designator

AFIT-ENP-DS-18-D-007

DTIC Accession Number

AD1067727

Comments

Plain-text title: Electrical Characterization of Crystalline UO(2), ThO(2) AND U(0.71)Th(0.29)O(2)

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