A thick cobalt foil has been irradiated consecutively with ¹⁶O, ⁷Li, and ¹²C beams to produce the 'tracer packet' containing carrier free radiotracers of Cu, Zn, Ga, Ge, As, and Se. The present work describes sequential separation of these product radionuclides by liquid-liquid extraction method.

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The alpha-decay half-life of ¹⁴⁷Sm has been reevaluated. Known amounts of natural Sm and an alpha-emitter standard (²¹⁰Po, ²³⁸U, or ²⁴¹Am) were mixed well to prepare thin sources for the simultaneous counting of ¹⁴⁷Sm and the alpha-emitter standard by means of an alpha-spectrometer using a silicon surface barrier detector. The alpha-dis-integration rate of known amounts of ¹⁴⁷Sm was determined by reference to the alpha activity of the standard. The source preparation and counting were repeated to establish the reproducibility of the present half-life determination, and supplementary alpha spectrometry was carried out by a liquid-scintillation spectrometer. The arithmetic mean of the experimental half-life values was obtained to be (1.17±0.02) ×10¹¹ y. This value is about 10% longer than the currently adopted value, (1.06±0.02) ×10¹¹ y, and the possible factors for this difference are dis-cussed.

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²³⁷Np oxide targets irradiated in the experimental fast reactor JOYO were analyzed by applying sophisticated radiochemical technique. Pu and Np were isolated from the irradiated targets by anion exchange chromatography. Total fission events of each target were estimated by ¹³⁷Cs method. ²³⁷Np and ²³⁶Pu were determined by alpha spectrometry. The isotopic ratio of Pu and the content of Pu were determined by thermal ionization mass spectroscopy and isotope dilution mass spectrometry, respectively. From these analytical results, the transmutation behavior of ²³⁷Np in a fast reactor was discussed. Up to about 528 EFPD (Effective Full Power Days) irradiation, the transformation through capture reaction was much larger than the incineration through fission reaction, although the latter increased comparatively in case of irradiation in hard neutron spectrum. ²³⁶Pu was clearly observed in all irradiated ²³⁷Np samples but its quantity was much smaller than the estimated value on the basis of present nuclear data library.

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Using an ion implantation method, we introduced cerium nuclei in highly oriented pyrolytic graphite (HOPG), and have studied their behavior by means of the time-differential perturbed angular correlation technique. The timevariant directional anisotropy for the present pseudo-single crystalline sample is little different from that for polycrystalline graphite. Temperature dependence has been observed on the electric quadrupole interaction between the probe nuclei and the extranuclear charge distribution: the anisotropy shows gradual attenuation at room temperature, whereas the effect of an electrostatic perturbation is implied in the spectrum at 10 K. For the chemical state of the probe atom in HOPG, the trivalent state is suggested from the large magnitude of the electric field gradient at the probe nucleus.

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Obtaining data on ⁹⁹Tc in the rice paddy field environment is important because Tc is a redox sensitive element. The behavior of Tc is expected to be different under upland field and rice paddy field conditions since the redox conditions in the soil environment differ. However, most of the data on the nuclide behavior in soil were obtained under upland field conditions. To understand the global fallout ⁹⁹Tc distributions in soil samples collected in Japan, a simple and rapid separation method was developed in order to determine low-levels of ⁹⁹Tc in soil samples by an inductively coupled plasma mass spectrometry. Also, radiotracer experiments using soils under aerobic and anaerobic conditions were carried out to clarify the Tc behavior under paddy field conditions. The results of determination of global fallout ⁹⁹Tc in Japanese soils indicated that the radionuclide had been accumu-lating in rice paddy fields. The mechanisms can be explained by the immobilization of Tc in soil under anaerobic conditions. From the radiotracer experiments, it was clear that under waterlogged conditions, the highly mobile TcO₄^- in soil was readily changed to other immobilized forms, such as TcO₂, TcS₂ and organically bound forms. To this immobilization, the microbial activity seemed to have an important role in Tc sorption reactions. When the soil, which was once kept in anaerobic conditions, was air-dried again and kept in aerobic conditions, the chemical forms of immobilized Tc did not change remarkably. Interestingly, the similar Tc behavior was observed in a real wet forest near the Chernobyl Reactor.

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A novel technetium (IV) complex of a tetradentate Schiff base ligand was synthesized from the reaction of H₂dmsalen [dmsalen; N, N'-ethylenebis (3, 5-dimethylsalicylideniminato) ] and trans-⁹⁹Tc^IVCl₄ (PPh₃) ₂ [PPh₃; triphenylphosphin]. The complex ⁹⁹Tc^IVCl₂ (dmsalen), the structure of which was determined by X-ray crystallography, has an octahedral coordination geometry. The dmsalen ligand coordinates to the technetium atom through two N and two O atoms of the tetradentate ligand in the equatorial plane. Two chloro ligands are in the trans apical position with an average Tc-Cl bond length of 2.35 Å.

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The nuclear shell model predicts that the next doubly magic shell-closure beyond ²⁰⁸Pb is at a proton number Z = 114, 120, or 126 and at a neutron number N = 172 or 184. The outstanding aim of experimental investigations is the exploration of this region of spherical 'SuperHeavy Elements' (SHEs). Experimental methods are described which allowed for the identification of elements 107 to 112 in studies of cold fusion reactions based on lead and bismuth targets. Also presented are data which were obtained on the synthesis of elements 112, 114, and 116 in investigation of hot fusion reactions using actinide targets. The decay data reveal that for the heaviest elements, the dominant decay mode is alpha emission, not fission. Decay properties as well as reaction cross-sections arecompared with the results of theoretical studies. Finally, plans are presented for the further development of the experimental set-up and the application of new techniques. At a higher sensitivity, the exploration of the region of spherical SHEs now seems to become feasible, more than thirty years after its prediction.

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