Extraction of U (VI) and Th (IV) from chloride and nitrate solutions with tri-n-dodecylamine impregnated on Amberlite XAD4, was investigated. The distribution of U (VI) and Th (IV) was studied at different concentrations of acid, salting-out agent, extractant, aqueous metal ion and other parameters. Absorption spectral studies have been investigated for uranium species in both aqueous HC1 solution and the resin phase. From these studies, it is suggested that the tetrachloro complex of U (VI) is formed in the extraction of uranium (VI) from hydrochloric acid solutions by TDA impregnated resin. Stripping of the extracted U (VI) and Th (IV) was assayed with HC1 and HNO₃. Finally, the separation of uranium from thorium and fission products in HC1 media was achieved.

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Supercritical fluid extraction of silicone oil from urania microspheres prepared through sol-gel route was investigated. The influence of pressure, temperature, and flow rate on the extraction efficiency was studied. Experimental conditions were optimised for the complete removal of silicone oil from urania microspheres.

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Hydrogen gas evolution from water induced with γ-ray irradiation of silica gels and metal oxides dispersed in water is studied by examining the hydrogen gas evolved. Hydrogen gas is detected by gas chromatography after ⁶⁰Co γ-ray irradiation of the sample solution in a closed vial at room temperature. Water adsorbed on the surface of metal oxides shows more evolution of hydrogen gas than pure water. Hydrogen gas evolution is maximized in the silica gels when the size of a silica gel cavity is about 2 nm, being on the order of spur size. The most active surface toward the decomposition of water upon γ-ray irradiation is that of SiO₂ dried at 100°C after sample preparation.

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Concentration of organically-bound ¹⁴C in the tree-ring cellulose of a pine tree grown in Shika-machi, Ishikawa prefecture, Japan (37.1°N, 136.5°E), was measured for the ring-years from 1949 to 1999 and compared with those in several trees from East Asia region reported by other researchers. The difference of . Δ¹⁴C values was found during the period of 1970-1981 between our data and those of other reports, in addition to the difference during the period of 1963-1967 caused by the so-called latitude dependence of the ¹⁴C variations in the northern troposphere. These results suggest that the ¹⁴C concentration in atmospheric CO₂ was considerably disturbed during the period of 1970-1981, especially in 1970, 1976, and 1978-1981, in the East Asia region. This phenomenon may be interpreted by the possibility of the several times of injections of ¹⁴C originated from a series of Chinese thermonuclear bomb tests.

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Five manganese nodules obtained from different locations with varying water depths of the Indian Ocean were analysed by k₀-based instrumental neutron activation analysis (k₀-INAA) method. A total of 22 elements were estimated including nineeee rare earth elements (REE). The accuracy of the method has been evaluated by analysing USGS manganese nodule reference material NOD P1. The nodules have been classified into hydrogenous and diagenetic on the basis of their Mn/Fe ratios. Data on elemental concentrations were used to explain the possible differences in the trace element distribution. The minor elements were found to be enriched in the hydrogenous nodules compared to the diagenetic one. An attempt was made to characterise the distribution of these minor elements in the light of known geochemical evidences of Pacific Ocean nodules. The dissimilarity of the geochemistry of Ce and Mn in the Indian Ocean nodules has been discussed. The manganese nodules under investigation exhibit a positive cerium anomaly, indicating an oxidising environment. The possible mechanism of incorporation of elements like REE into the iron oxyhydroxide phase has been discussed.

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The improved Cascade-Exciton Model (CEM) code CEM2k+GEM2 and the Los Alamos version of the Quark-Gluon String Model code LAQGSM are extended to describe photonuclear reactions. First, we incorporate new evaluations of elementary cross sections based on the latest experimental data into CEM2k+GEM2 and also make several improvements in the description of the de-excitation of nuclei remaining after the cascade stage of reactions induced by arbitrary projectiles. Next, for photonuclear reactions we include a normalization to evaluated experimental absorption cross sections based on the recent systematics by Kossov in CEM2k+GEM2. Then, we extend our high-energy code LAQGSM by adding the photonuclear mode which was ignored in all its previous versions, and add to it the photonuclear part from our improved CEM2k+GEM2. Presently, these codes do not include a calculation for GDR and describe properly photonuclear reactions only at intermediate energies from∼30 MeV to∼1.5 GeV. In this work we present a short description of the photonuclear mode as incorporated into our codes, show several illustrative results, and point out some unresolved problems.

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⁸⁵Zr, ¹⁶⁹Hf, and ²⁶¹Rf were produced simultaneously from ^natGe (¹⁸O, xn), ^natGd (¹⁸O, xn), and ²⁴⁸Cm (¹⁸O, 5n) reactions, respectively, and the volatility of their chlorides was examined using an isothermal gas chromatographic system. The observed gas chromatogram indicated that ZrCl₄, HfCl₄, and RfCl₄ had almost similar volatility.

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Radiochemical studies of element 104, rutherfordium (Rf), at JAAERI (Japan Atomic Energy Research Institute) are reviewed. The transactinide nuclide ²⁶¹Rf has been successfully produced in the reaction ²⁴⁸Cm (¹⁸O, 5n) at the JAERI tandem accelerator. The excitation function of the reaction has been measured with a rotating wheel catcher apparatus and the maximum production cross section has been determined to be about 13 nb. On-line ionexchange experiments on Rf together with the group-4 elements Zr and Hf in acidic solutions have been conducted with a rapid ion-exchange separation apparatus. From the systematic study of the anion-exchange behavior of Rf, it has been found that the properties of Rf in HCI and HNO₃ solutions are quite similar to those of Zr and Hf, definitely confirming that Rf is a member of the group-4 elements. However, we have observed an unexpected chemical behavior of Rf in HF solutions; the fluoride complex formation of Rf is significantly different from those of Zr and Hf. The current progress in the Rf aqueous chemistry is briefly summarized and prospects of extending chemical studies of transactinide elements at JAERI are considered.

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