Chemical Studies of Rutherfordium (Rf) and Nobelium (No) on an Atom-at-a-time Scale

Abstract

Hexafluoro comlexation of rutherfordium (Rf) and successful oxidation of the divalent state of nobelium (No) recently carried out at JAEA are reviewed. The ²⁶¹Rf and ²⁵⁵No isotopes were produced in the ²⁴⁸Cm(¹⁸O, 5n) and ²⁴⁸Cm(¹²C, 5n) reactions, respectively, at the JAEA tandem accelerator. Anion-exchange behavior of Rf in HF and HNO₃ (HF/HNO₃) mixed solution was studied together with short-lived Zr and Hf isotopes using an automated chemistry apparatus to characterize anionic fluoride species of Rf and to evaluate its formation constants. It was found that the hexafluoro complex of Rf is present in the HF/HNO₃ solutions under the given conditions where the same complexes of Zr and Hf are existing. The formation constant of the Rf complex was evaluated to be at least one order of magnitude smaller than those of Zr and Hf, which suggests a larger ionic radius of Rf⁴⁺ than those of Zr⁴⁺ and Hf⁴⁺. Oxidation experiments of No²⁺ were conducted in 0.1 M α-hydroxyisobutyric (α-HIB) acid using a newly developed electrolytic column chromatography apparatus on a single atom scale. The result clearly demonstrated that stable No²⁺ is successfully oxidized to the trivalent state, No³⁺, which is held in the α-HIB solution.