Cathodoluminescent Study of ThO$_{2}$

Single crystal thorium dioxide (ThO$_{2})$ samples were hydrothermally grown and studied using depth-resolved cathodoluminescence (CL) to characterize the surface and bulk electronic states. X-ray diffraction (XRD) measurements confirmed that these crystals were ThO$_{2}$ in the fluorite structure. Understanding the chemical and structural quality of ThO$_{2}$ will aid in the fabrication of better neutron detectors as well as in commercial power production with thorium breeder reactors. Monte Carlo simulations were used to predict the expected energy-dependent electron interaction depths in the ThO$_{2}$ crystals. CL was conducted using 1.5 - 12 keV electrons at vacuums of 5x10$^{-7}$ to 1.2x10$^{-9\, }$Torr, and sample temperatures of 24 K -- 297 K. The CL measurements indicated that the as-grown sample exhibited definite surface effects. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) conducted on the samples appeared to partially clean the surface as indicated by CL spectra taken following TOF-SIMS.