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.

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For the recovery of nuclear materials from spent fuel with more effective and convenient methods comparing with conventional process, the sulfurization and dissolution behavior of fission products, such as rare-earths, alkali, alkalline-earth and platinum group elements were studied. The sulfurization experiment was carried out using tracer doped U₃O₈. The samples were reacted with CS₂ at temperatures from 573 to 773 K for 1 hour followed by dissolution with 1M nitric acid solution for 1 hour at 323 K. The dissolution ratio for each element was obtained by α- and γ-ray spectrometry. The alkali and alkaline-earth elements show higher dissolution ratios as well as trivalent lanthanide elements. On the other hand, U, Zr, Ce, and Ru showed lower dissolution ratios. These results were in good agreement with those expected from the thermodynamic consideration.

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To measure radioactivities in soil contaminated by the accident of the Fukushima Daiichi Nuclear Power Plant, efficiency calibration of Ge detectors for ¹³¹I, ¹³⁴Cs, and ¹³⁷Cs in volume sources was investigated. Gamma-ray detection efficiencies for these nuclei were determined precisely using standard soil samples containing ¹³⁴Cs, ¹³⁷Cs, ¹⁷⁵Hf, and ⁸⁸Zr. These standard sources were prepared by admixing radioactive solutions with soil, and point sources were made from the same solutions to determine their radioactivity concentrations. The efficiency for the 364 keV γ ray of ¹³¹I was extracted from the experimental efficiencies of ¹³⁷Cs and ¹⁷⁵Hf. Cascade summing corrections for γ rays of ¹³⁴Cs in soil samples were evaluated experimentally. To easily calculate the cascade summing corrections for volume sources, we examined a simplified method using averaged efficiencies, and evaluated its validity through a comparison of the calculated correction factors with the experimental ones.

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