Activation of uranyl peroxides by ionizing radiation prior to uranyl carbonate formation.

The solid form of the uranyl peroxide cage (UPC) cluster LiU (Li[(UO)(O)]) was irradiated by 5 MeV He ions to achieve doses up to 42 MGy. An intermediate compound formed that reacts with atmospheric CO to form uranyl carbonates. The role of water in the UPC to uranyl carbonate transformation was studied by flowing either dry or hydrated Ar over samples during He irradiation, and by storing samples in dry and humid environments before and after irradiation. Raman, infrared, and X-ray photoelectron spectroscopies and electrospray ionization mass spectrometry were used to characterize solid Li-U salts before and after He irradiation. The highest yield of uranyl carbonates occurred when hydrated Ar gas was flowed across the sample during He irradiation. Electron paramagnetic resonance spectroscopy provided evidence of hydroxyl and superoxide radicals in both unirradiated and γ-irradiated Li-U.