Solid state characterization of oxidized actinides co-crystallized with uranyl nitrate hexahydrate

Abstract

Characterization of the penta- and hexavalent dioxo cations of NpO₂⁺, NpO₂²⁺, PuO₂²⁺, and AmO₂²⁺ has been carried out by diffuse reflectance UV-Vis-NIR spectroscopy, with the first observations of NpO₂⁺, NpO₂²⁺, and AmO₂²⁺ in the solid state. Absorbance measurements confirmed the presence of the higher actinides of Np, Pu, and Am, with shifts in their absorbance bands indicating the formation of the dinitrate species in the crystalline phase. The oxidized actinides were prepared in the solid state by co-crystallization with UO₂(NO₃)₂·6H₂O by a simple reduction in temperature. The hexavalent species were all co-crystallized in near proportion to UO₂²⁺ and the pentavalent species was co-crystallized in a slightly less efficient manner, roughly 83% of that of UO₂²⁺.