Date of Award
Master of Science in Applied Physics
Department of Engineering Physics
Robert L. Hengehold, PhD.
The Department of Defense has expressed interest in thorium dioxide (ThO2) and uranium dioxide (UO2) as possible candidates for use as special nuclear material in designing neutron detectors. Both materials have large neutron interaction cross sections. Uranium dioxide is particularly attractive due to its semiconducting properties and a relatively small band gap of 2 eV. Both materials fluoresce under ionizing radiation making them candidates for scintillating detectors. Three Ux:Th1-xO2 (x= 0.00, 0.01, 0.22) hydrothermally grown single crystals were examined using cathodoluminescence to interrogate the changing electronic properties of ThO2 as it became an alloy. Both depth-resolved and temperature- dependent cathodoluminescence studies were performed to examine the crystal structure and the defects present. An ultra-high vacuum system operating at 10 to the minus 8th power Torr was used with electron beam energies ranging from 2 to 14 keV. Spectra were taken on all three samples before and after a proprietary chemical cleaning process involving a crown ether/picric acid solution was applied to the crystals to remove surface contaminants. Spectral deconvolution of the spectra showed evidence of both direct and indirect gap photon transitions from the O 2p to Th 6d at 4.2 eV and 4.8 eV respectively. Uranium-doped spectra showed evidence of the midgap O 2p to U 5f quadrupole transition and O 2p to U 6d transition at 5 eV.
DTIC Accession Number
Reding, Joshua D., "Band Gap Transition Studies of U:ThO2 Using Cathodoluminescence" (2014). Theses and Dissertations. 659.