Frontiers in fundamental research on both nuclear and chemical properties and prospects for future advances were highlighted in this two-day Symposium. The following four areas were especially emphasized: Superheavy elements-production, chemical and nuclear properties, and potential use of the unique techniques developed to solve applied problems; Nuclear processes as chemical probes to explore environmental and ecological radionuclide distributions; Application of nuclear and radiochemical techniques to geochemical, pharmaceutical, and biological sciences, and even information technology; Environmental radiochemistry and fundamental actinide sciences and practical applications in nuclear waste storage and remediation. These topics were explored in both invited lectures and poster presentations. The Global Nuclear Energy Program recently proposed by the U. S. is briefly described and the potential need for scientists with expertise in nuclear and radiochemistry and actinide science, and the opportunities for synergistic interactions are highlighted.

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The synthesis of new nuclides has been performed with the use of the gas-filled recoil separator; in a number of experiments some radio-chemical methods have been employed. The experimental data point to a substantial increase in the nuclear stability with a growing neutron number. For all the nuclei in decay chains undergoing α decay or spontaneous fission the energies and half-lives have been measured. The obtained data are in agreement with predictions of microscopic theory on the deciding role of the nuclear shells in the stability of heaviest elements.

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Superheavy elements have been synthesized and chemically characterized one-atom-at-a-time up to element 108. Presently, the quest for element 112 is one of the hottest topics in this field. The transactinide elements 104 to 108 are members of group 4 to 8 of the Periodic Table and element 112 belongs into group 12. Chemical properties of some of these elements, like elements 104 and 105, show stunning deviations from simple extrapolations within their respective group while others exhibit great similarities with their lighter homologues elements. First experiments to investigate seaborgium (Sg, element 106) in aqueous solution were performed. Again, in large international collaborations at the GSI, several gas-phase chemistry experiments were performed with hassium (Hs, element 108). Recently, the highly efficient and very clean separation of Hs was applied for nuclear studies of various Hs nuclides investigating their cross section and their nuclear decay properties in the region of the doublymagic ²⁷⁰Hs (Z=108, N=162). To overcome certain limitations of the presently used on-line chemical separations the new TransActinide Separator and Chemistry Apparatus (TASCA) - with a gas-filled recoil separator as a front-end tool - was designed and built at the GSI in a collaborative effort. Presently in its commissioning phase, TASCA shall be a key instrument for a big leap into quantitatively and qualitatively new experiments in the region of superheavy elements.

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A gas-jet transport system for the superheavy element chemistry was coupled to the gas-filled recoil ion separator GARIS at the RIKEN Linear Accelerator. The performance of the system was investigated using ²⁰⁶Fr and ²⁴⁵Fm produced in the ⁴⁰Ar-induced reactions on ¹⁶⁹Tm and ²⁰⁸Pb targets, respectively. Alpha particles of ²⁰⁶Fr and ²⁴⁵Fm separated with GARIS and transported by the gas-jet were measured with a rotating wheel system for α spectrometry under low background condition. The high gas-jet efficiency of over 80% was found to be independent of the beam intensity up to 2 particle μA. These results suggest that the GARIS/gas-jet system is a promising tool for future superheavy element chemistry at RIKEN.

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A technique of microchip chemistry was introduced into an on-line solvent extraction system for studies of chemical behaviors of heavy elements, and the performance of the system was investigated with some rare earth elements as their homologues. It was confirmed that the extraction equilibria of the elements between the aqueous (acetic acid-sodium acetate buffer solution) and organic (2-thenoyltrifluoroacetone-toluene solution) phases were attained in the microchip within about one second. Using the system, on-line solvent extraction experiments were performed for the short-lived ^{150, 151}Dy as model experiments of heavy actinides at the AVF cyclotron facility of the Research Center for Nuclear Physics (RCNP), Osaka University. All the chemical stages from the RI production to their detections were completed within about three minutes, signifying that this system is applicable to studies of heavy actinides having half-lives of a few minutes.

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The role of entrance channel for reactions with massive nuclei is discussed by comparison of experimental data of reactions with different mass (charge) asymmetry and leading to different isotopes of the superheavy element Z = 112. Three stages (capture, complete fusion, and formation of evaporation residues) of the so called “cold” and “hot” fusion reactions are considered for ⁷⁰Zn + ²⁰⁸Pb and ⁴⁸Ca + ²³⁸U reactions which were used to synthesize superheavy elements Z =112. It is shown that the collisions by the orientation angles 30°<α_P< 60° for projectile and 30°<α_T<45° for the target nucleus lead to the largest cross section in synthesis of superheavy element in the ⁴⁸Ca + ²³⁸U reaction at E^*_CN = 35 MeV.

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To find suitable conditions for the experimental study of anion-exchange behavior of element 105, dubnium (Db), we have investigated anion-exchange behavior of the group-5 elements Nb, Ta, and their pseudo homologue Pa in HF/HNO₃ media by a batch method using radiotracers of ⁹⁵Nb, ¹⁷⁹Ta, and ²³³Pa. Clearly different adsorption behavior was observed among those homologues in the fluoride ion concentrations of 1 × 10^-6 M < [F^-] < 2 × 10^-2 M, suggesting that each element forms different anionic complexes. Based on the observed distribution coefficients of these elements, we propose appropriate experimental conditions to investigate fluoride complexation of Db.

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Effects of the prolate deformation of ²³⁸U on fusion were studied in the reaction ³⁰Si + ²³⁸U at bombarding energies close to the Coulomb barrier. The fission (capture) cross sections were measured at the JAEA tandem accelerator to see the enhancement of the cross sections in the subbarrier energy due to the lower Coulomb barrier in the collisions of projectile at the polar sides of ²³⁸U. In order to obtain the direct evidence for complete fusion, evaporation residue cross sections were measured at UNILAC of GSI. At the subbarrier energy of E_c.m. = 133. 0 MeV, where only polar collisions to ²³⁸U occur, we measured three spontaneously fissioning nuclei which we assigned to the isotope ²⁶⁴Sg. The obtained cross section (10⁺¹⁰_-6) pb was smaller than the calculation that the system captured at the polar collisions results in complete fusion, suggesting the competition between fusion and quasifission. At the above barrier energy of E_c.m. = 144.0 MeV, where collisions on the equatorial side of ²³⁸U start to contribute, we observed α-decay chains starting from ²⁶³Sg and the cross section was determined to be (67⁺⁶⁷_-37) pb. The data was reproduced by the calculation that the system captured from the equatorial side of ²³⁸U results in complete fusion .

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Time-differential perturbed angular correlation (TDPAC) is a powerful tool in material science for measuring the local electromagnetic fields at probe nuclei through hyperfine interactions. We have been applying this technique with reactor-made radioactive nuclei to several different material systems. In this paper, following a brief descrip-tion of the TDPAC technique, our recent results are reviewed.

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⁵⁷Fe Mössbauer spectroscopy has provided detailed information about the low-spin/high-spin transition in two types of two-dimensional Fe (II) complexes, [Fe^IIH₃L^Me][Fe^IIL^Me]X (X^-=BF₄^-, ClO₄^-, PF₆^-, NO₃^-) 1-4 and [Fe^IIH₃L^Me] Cl·X (X^-=PF₆^-, AsF₆^-, SbF₆^-) 5-7, where H₃L^Me denotes a hexadentate N₆ tripod-like ligand containing three imidazole groups, tris [2- ( ( (2-methylimidazol-4-yl) methylidene) amino) ethyl] amine. The molar fraction of high-spin Fe^II versus total Fe^II (γ_HS) was estimated from Mössbauer area intensities of each compound in different temperatures. The γ_HS-T plots for 1-4 indicated that these compounds exhibit a two-step spin crossover corresponding to (LS-[Fe^IIH₃L^Me]²⁺ + LS-[Fe^IIL^Me]^-) ↔ (HS-[Fe^IIH₃L^Me]^2- + LS-[Fe^IIL^Me]^-) ↔ (HS-[Fe^IIH₃L^Me]²⁺ + HS-[Fe^IIL^Me]^-). The larger size of the counter anion separated the first and second spin crossover transitions in the [Fe^IIH₃L^Me] [Fe^IIL^Me]X system well. A variety of γ_HS-T curves depending on the counter anion was observed for [Fe^IIH₃L^Me] Cl·X. It was suggested that a smaller counter anion stabilizes the 1/2 (LS-[Fe^IIH₃L^Me]²⁺ + HS-[Fe^IIH₃L^Me]²⁺) state in this system.

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The time-differential perturbed angular correlation method with the ¹⁴⁰Ce probe was applied to a microscopic investigation on a perovskite manganite, La_0.7Ca_0.3MnO₃. A drastic change was observed in the time evolution of the directional anisotropies around the Curie temperature (T_c∼245K), reflecting the paramagnetic-ferromagnetic phase transition. The internal magnetic field at the probe nucleus stabilized at the A site was estimated to be B_int=6.9±0.3T at 240K, whereas no appreciable magnetic field was observed at 260 K. From a comparative study using two different probe-introduction methods, in addition, we found that ascendant ions of the probe, ¹⁴⁰Ba and ¹⁴⁰La, can be located at the A site by heat treatment.

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The use of radioisotopes and radiation is essential in the research field of life science. This article describes the studies on the usefulness of radioisotope in pharmaceutical sciences, especially focusing on the results of our research group as follows. (i) Mixed disulfide formation catalyzed by Cu (II) in relation to the radioprotective ability of a radioprotector, cysteamine (2-mercaptoethylamine). (ii) Suppression of reactive oxygen species (ROS) in the skin of live animals given oral administrations of Zn (II) and its complexes in relation to the skin damage under ultra-violet (UV) light. (iii) Improvement of diabetes mellitus by insulin-mimetic vanadyl (IV) (VO (II) ) complexes.

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The Oklo uranium deposit at the Republic of Gabon, central Africa, had partly functioned as natural fission reac-tors. Many elements of the Oklo reactor zones and the related samples show the variations in the isotopic compo-sition caused by a combination of nuclear fission, neutron capture, and radioactive decay. Isotopic studies provide useful information to estimate reactor conditions and to understand behavior of radionuclides in geological media. In my recent work, in-situ REE, Pb, and U isotopic analyses of individual tiny minerals in and around reactor zones have been performed using a Sensitive High Resolution Ion Micro-Probe (SHRIMP). The data suggest the adsorption property of apatite in trapping fissiogenic LREE and Pu migrated from the reactor zone, and distribution of fissiogenic REE under oxidizing atmosphere.

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Hydrophilic endohedral ¹³³Xe-fullerenols [¹³³Xe@C₇₆ (OH) _x and ¹³³Xe@C84 (OH) _x] were synthesized from hydrophobic endohedral ¹³³Xe-fullerenes. The yields were found to depend on the solubility of endohedral ¹³³Xe-fullerenols in ο-dichlorobenzene and water phases, reflecting the number of OH groups of the product. The endohedral ¹³³Xe-fullerenols stored in 0.9% NaCl solution at 20°C were stable enough for the use in nuclear medicine.

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Techniques for the measurement of the ¹⁴⁶Sm nuclide, which is known as an extinct nuclide on the present Earth, were developed in order to determine its half-life. The nuclide was produced in three reactions of ¹⁴⁷Sm (γ, n) ¹⁴⁶Sm, ¹⁴⁷Sm (n, 2n) ¹⁴⁶Sm, and ¹⁴⁷Sm (p, 2n) ¹⁴⁶Eu (→¹⁴⁶Sm). The Sm fraction in the target was chromatographically purified to prepare α counting samples as hydroxide. The ¹⁴⁶Sm/¹⁴⁷Sm α-activity ratios in the samples were measured using a Si surface barrier detector. The ¹⁴⁶Sm²²⁺/¹⁵²Sm²³⁺ and ¹⁴⁷Sm²²⁺/¹⁵²Sm²³⁺ ratios were measured by accelerator mass spectrometry using the ECR-ATLAS-GFM system. The ¹⁴⁶Sm ions were distinguished clearly from the other ions such as the abundant isobar, ¹⁴⁶Nd in the samples.

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Trace amount of manganese in high-purity iron samples was determined by INAA using Tc-Pn at KUR, ICP-MS, and ICP-AES. It was confirmed that the INAA using Tc-Pn was able to determine several tens of ppb Mn as an impurity in iron samples without correcting a contribution of the ⁵⁶Mn produced by the fast neutron-induced reaction on ⁵⁶Fe. Based on the results, the INAA using Tc-Pn was applied to the determination of trace amount of manganese in some fragments of the Gibeon iron meteorite in order to estimate cosmogenic ⁵⁵Mn in those fragments.

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Three chemical forms of atmospheric tritium, i. e., tritiated water vapor (HTO), hydrogen gas (HT), and hydrocarbons (CH₃T), were measured at Kumamoto, Japan during the period between 2003 and 2005. The average concentrations were in the order of HT, CH₃T, and HTO. The yearly average HT concentrations were not so different in each year, while that of CH₃T showed a large variation. The concentrations of all chemical species have decreased compared to those measured during the period between 1984 and 1995 at Fukuoka, about 100 km north of the present sampling location, suggesting a decrease in emissions of HT and CH₃T from their sources for these 8-10 years. The decrease in HTO concentration would be attributed to the decrease of the bomb-produced tritium and to a regional characteristic of the sampling locations; Kumamoto showed lower tritium concentrations in rain than Fukuoka.

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Microorganisms have been detected in transuranic- and low-level radioactive wastes, Pu-contaminated soils, and in nuclear waste-repository sites. Microbial activity could affect the chemical nature of the Pu by altering the speciation, solubility, and sorption properties and thus could affect the stability and mobility of Pu in the environment. We investigated the biotransformation of Pu (IV) -citrate by Pseudomonas fluorescens under aerobic conditions. Characterization of ²⁴²Pu (IV) -citrate by electrospray ionization-mass spectrometry (ESI-MS) showed the presence of 1:1 mononuclear, 1:2 mononuclear biligand, and 2:2 dinuclear complex. X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) analysis of Pu-citrate confirmed Pu in the IV oxidation state and predominantly present as a 1:2 mononuclear biligand complex. Citric acid was rapidly metabolized by P. fluorescens resulting in the formation of Pu polymer. Under anaerobic conditions, reductive dissolution of Pu (IV) to Pu (III) by Clostridium sp. was observed. The presence of Pu (III) was confirmed by XANES. Addition of Pu (VI) to a mixture consisting of bacterial cells an kaolinite clay showed that the Pu was preferentially associated with bacterial cells as Pu (IV) and that Pu (VI) was reduced to Pu (V) and Pu (IV) only in the presence of bacteria. Studies with Pu contaminated soils from Nevada Test Site showed remobilization of Pu and other radionuclides due to enhanced microbial activity.

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The association properties of Am and Pu with aquatic fulvic acid in a 0.01 M NaClO₄ solution at pH 6-7 were studied on the basis of molecular size distribution. Seven fulvic acids (FA) were isolated from river, lake, and groundwater samples using XAD extraction technique. They were used for comparison of their effects on the association of Am and Pu. In the absence of FA, about 80% of Am and 75% of Pu were found to have molecular size greater than 450 nm (particulate forms). On the other hand, in the presence of FA, particulate forms of Am and Pu decreased with increasing FA concentration, and were negligible at the FA concentration of 10 mg/L. Both Am and Pu were associated mainly with aquatic FA having two size fractions of 30-10 kDa or less than 5 kDa. The differences between Am and Pu were rather small and the association patterns were divisible into two groups: size-selective and non-size-selective. Complexation of FA with Am and Pu was controlled by the amount of FA, the percentage, and characteristics of each size fraction of FA.

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Protein expression of Saccharomyces cerevisiae grown in the medium containing ²³⁸U (VI) and ²³³U (VI) was examined by two-dimensional gel electrophoresis. Saccharomyces cerevisiae of BY4743 was grown in yeast nitrogen base medium containing glucose and glycerol 2-phosphate and ²³⁸U of 0, 2.0, and 5.0×10^-4 M or ²³³U of 2.5×10^-6 M (radioactivity was higher by 350 times than 2.0×10^-4 M ²³⁸U) and 5.0×10^-6 M for 112 h at 30°C. The growth of Saccharomyces cerevisiae was monitored by measuring OD₆₀₀ at 112 h after the inoculation. Uranium concentrations in the media also were measured by radiometry using a liquid scintillation counter. The growths of the yeast grown in the above media were in the following order: control > 2.5×10^-6 M ²³³U > 2.0×10^-4 M ²³⁸U > 5.0×10^-6 M ²³³U > 5.0×10^-4 M ²³⁸U. This result indicated that not only radiological but also chemical effect of U reduced the growth of the yeast. The concentrations of U in the medium containing ²³⁸U or ²³³U decreased, suggesting U accumulation by the yeast cells. The 2-D gel electrophoresis analysis showed the appearance of several spots after exposure to ²³⁸U or to ²³³U but not in the control containing no uranium. These results show that the yeast cells exposed to U express several specific proteins.

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The concentrations of ²²⁶Ra in upland field crops (e. g., cabbage, leek, onion, potato. and so on) and associated soils collected from 45 locations throughout Japan were determined in order to obtain soil-to-crop transfer factors (TFs). Concentrations of ²²⁶Ra in the soils collected in southwestern Japan were higher than those in northeastern Japan; however, no correlations between ²²⁶Ra concentrations in crops and soils were observed. The TFs ranged from <1.1 × 10^-3 to 5.8 × 10^-2 with a geometric mean of 6.4 × 10^-3. These data were within the 95% confidential range of TF-Ra for several crops as reported in the IAEA Technical Reports Series No. 364. Among the alkaline earth metals, TF-Ba was similar to TF-Ra.

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The average concentrations of ²²⁶Ra and ²²⁸Ra in the water in hot springs in and around metropolitan Tokyo were 39 mBq L^-1 and 55 mBq L^-1 for NaCl-type water and 0.6 mBq L^-1 and 0.8 mBq L^-1 for simple alkaline-type water, respectively. From the chemical characteristics, the hot spring waters from the Kazusa and Miocene formations are classified as NaCl and that from the Shimanto and Chichibu formations is simple alkaline. This indicates that the concentrations of Ra isotopes are high for the NaCl type and low for the simple alkaline type and are correlated with the relevant sedimentation layer from which the hot spring water is welled up. Good correlation was observed for the ratios in the concentrations of Ra/Na and Ra/Cl in both types of hot spring water. The correlation patterns of Ra/Na and Ra/Cl for the simple alkaline type and sedimentary rock were different from those for the NaCl type and seawater, suggesting that the origin of the Ra isotopes may be different. The ²²⁸Ra/²²⁶Ra activity ratio was found to be related with Si concentration, showing that the activity ratio decreased with an increase of H₂SiO₃ for both the NaCl and the simple alkaline type. Assuming that the Ra isotopes in hot spring water were supplied from the relevant rock in the aquifer together with Si, the activity ratio of ²²⁸Ra/²²⁶Ra in hot spring water might be different between the NaCl and simple alkaline type, suggesting that the (²²⁸Ra/²²⁶Ra) _t=0 activity ratio for residence time at t = 0 might be different for the two types.

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High-resolution measurements of temporal variations of airborne ²¹⁰Pb and ⁷Be were performed by ultralow background γ-spectrometry at Ogoya Underground Laboratory (OUL). Moreover, high-resolution measurements of ²¹⁰Po were also made by α-spectrometry at Low Level Radioactivity Laboratory (LLRL). In this paper, the results focusing mainly on cyclic variation with ∼1 week period observed in winter season, and the high resolution measurements conducted at the time of approach of typhoon and Kosa events are reported.

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