Assessing UO2 sample quality with μ-Raman spectroscopy

Abstract

μ-Raman spectroscopy of UO2 has demonstrated its value as a tool in nuclear forensics and for analyzing nuclear fuels, but its ability to evaluate UO2 sample quality has been relatively unexplored. To investigate this potential, a three-pronged study that uses Raman spectroscopy to analyze 1) three distinct qualities of UO2 single crystals with two different excitation lasers, 2) a high quality single crystal UO2 sample that is progressively damaged with a laser, and 3) a single crystal of UO2 grown on top of a ThO2 substrate was undertaken. The results demonstrate that the peak height ratio between the second order longitudinal optical phonon signal near 1145 cm−1 and the T2g peak located near 450 cm−1 is directly correlated with crystal quality when a 532 nm excitation source is used. Furthermore, this observed pattern relies upon the two most intense peaks that are present in the Raman spectra, making it more robust to lower signal-to-noise ratios than similar trends present in the peak height ratio between the first order longitudinal optical phonon signal near 565 cm−1 and the T2g peak. Both peak height ratios are more sensitive indicators of the crystal quality than the width ratios of the same signals or the associated wavenumber shift in the T2g peak location. The correlation between the 2LO and T2g peak heights and the overall crystal quality offers the potential to directly assess and compare the quality of different samples of single crystal UO2.