Raman/SEM Chemical Imaging of a Residual Gallium Phase in a Mixed Oxide Feed Surrogate

Abstract

An integrated analytical approach, which combines elemental [scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS)] and molecular (Raman) chemical imaging techniques, has been utilized for the characterization of a residual phase of gallium in mixed oxide (MOX) surrogate material. Surrogate MOX materials are comprised of CeO₂ in place of PuO₂. In real MOX materials, PuO₂ is mixed with UO₂ as a commercial fuel source. A Ga phase remains in the surrogate sample following reductive heating experiments designed to explore the removal of gallium from weapons-grade plutonium. The SEM/EDS data reveal the concentration of Ga within the grain boundaries of the sample and a distribution of Ce and O throughout the sample matrix. Molecular analysis provided by Raman chemical matrix imaging correlates with the SEM/EDS elemental imaging results. Specifically, the Raman data suggest that the matrix is comprised of CeO₂ and grain boundaries are a mixed phase comprised of CeO₂ with a form of Ga, most likely a CeGaO3 perovskite phase having a cubic structure.