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

Abstract

The solid form of the uranyl peroxide cage (UPC) cluster LiU₂₈ (Li₂₈[(UO₂)₂₈(O₂)₄₂]) was irradiated by 5 MeV He²⁺ ions to achieve doses up to 42 MGy. An intermediate compound formed that reacts with atmospheric CO₂ 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 He²⁺ 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–U₂₈ salts before and after He²⁺ irradiation. The highest yield of uranyl carbonates occurred when hydrated Ar gas was flowed across the sample during He²⁺ irradiation. Electron paramagnetic resonance spectroscopy provided evidence of hydroxyl and superoxide radicals in both unirradiated and γ-irradiated Li–U₂₈.