In April and May of 1999 the Berkeley Gas-filled Separator was used to search for the production and decay of element 118 from the ⁸⁶Kr + ²⁰⁸Pb reaction, according to Smolañczuk's predictions of relatively large production rates. Three decay chains, each consisting of an implanted heavy ion, followed by a rapid (ms) succession of high-energy (> 10 MeV) alpha-particle decays were detected. These chains are consistent with the production and decay of element 118 with mass number 293. These results a) show experimental evidence for the existence of shell-stabilized superheavy elements, b) provide experimental values for refinement of nuclear mass models in the superheavy element region, and, most importantly, c) present a “new” reaction pathway for the production of superheavy elements.

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The distributions of the naturally occurring radionuclides ²³⁸U, ²³⁴U, ²³²Th, ²³⁰Th, ²²⁸Th, ²²⁸Ra, and ²²⁶Ra in river and hot spring water within the Peitou hot spring basin at the northern part of Taiwan were studied by using alph-and gamma-spectrometric methods and liquid scintillation counting method. The respective concentration ranges of ²³⁸U, ²³⁴U, ²³²Th, ²³⁰Th, ²²⁸Th, and ²²⁶Ra in river and hot spring water were 0.80-48, 1.2-51, 0.05-44, 0.09-39, 0.19-342, 3.0-22.5 mBq/L and 2.3-85, 2.9-91, 0.67-73, 1.14-66, 1.01-630, and 4. 5-36.5 mBq/L, respectively. In general, the distributions of uranium-series and thorium-series nuclides in river water, hot spring water were all pH dependent. The respective radioactivity ratios of ²³⁴U/²³⁸U in river and hot spring water are observed to be 1. 0-1.5 and 1.03-1.5, however, the radioactivity ratios of ²²⁸Th/²³²Th in river and hot spring water are 1.4-19 and 1.5-8.8, respectively. The high ²²⁸Th/²³²Th activity ratios showed that besides the recoil effect, enrichment of ²²⁸Ra to ²³²Th in the waters was another possible factor causing an excess of ²²⁸Th. Because radium may exist as (Pb, Ba, Ra) (SO₄) _x pseudo-colloid in hot spring water, which is the same as the more famous mineral of Peitoustone (Hukutolite), therefore, ²²⁸Ra and ²²⁶Ra are more abundant in the hot spring sediments, which radioactivity arel8-3010 and 16-230 Bq/kg (dry), respectively.

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The relation between free volume size and the lifetime of ortho-Ps trapped in that volume is usually described in the framework of simplified model, proposed by Tao and Eldrup et al. In that model the positronium trap has spherical shape and the potential is rectangular one with infinite depth. In spite of its simplicity in most cases the model gives proper values of o-Ps lifetime and its zero-point energy in the trap. It can be also easily extended toward nonspherical and large-size free volumes. In that last case the population of particle states lying above the zero-point energy has to be taken into account.

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In the past 15 years our research activities covered the following four aspects: (1) Labeling of monoclonal antibodies (McAb) with radionuclides. Both direct and indirect labeling methods by using various radionuclides were studied. (2) Designing and synthesis of radiopharmaceuticals used for myocardial imaging. Two types of Tc compounds were intensively studied: BATOs and complexes containing [^99mTc≡N]²⁺ core and [^99mTc=NAr]³⁺ core. (3) Synthesis and screening of boron-and gadolinium-containing compounds for use in neutron capture therapy. (4) Investigation of the coordination chemistry of Tc.

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The earliest activities of nuclear analytical techniques (NATs) in China were much later than those in the developed countries, but since the late fifties a vast progress in the development of NATs has been made. This paper will describe some latest achievements in the field of modern nuclear analytical techniques, including molecular activation analysis, scanning proton microscope, accelerator mass spectrometry, synchrotron radiation-based X-ray analytical techniques, and position sensitive spectrometry, etc. and their applications in environmental, biological, geological, and material science. The analytical quality assurance and related topics, like new type reference materials for microbeam analysis, biological and environmental specimen banking, and biological monitor for environmental quality survey, will be outlined as well.

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Several periods in radiochemistry development history are observed. In the report the sources of radionuclide income into environment are examined including long-lived transuranic elements on the different stages of full nuclear fuel cycle. Radioactive substance contamination analysis is given for different regions of Russia from natural and man-caused sources. Potential danger of long-livad radionuclide and transuranic element presence in the wastes of nuclear fuel cycle plants is shown. Data related with the sequences of nuclear weapon testing on the proving grounds near Semipalatinsk, and Novaya Zemlya are presented. The modern radioecological situation around the reprocessing plant “Mayak”, which was constructed more than 40 years ago for the production of plutonium for military purposes, is overviewed. The following topics are considered: lake Karachay; artificial water reservoirs contaminated by radionuclides; solid radioactive wastes and their vitrification. Some new approaches, methods and tools developed at the Vernadsky Institute of Russian Academy of Sciences for determination of dif-ferent radionuclides in various environmental samples from the impact zone of the facility are discussed. The data on distribution, occurrence forms and migration processes of ⁹⁰Sr, ¹³⁷Cs, ²³⁷Np, ²³⁹Pu, and ²⁴¹Am in aquatic and terrestrial ecosystems are presented.

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Some of the important aspects of the radiochemical research carried out in India during the past 40 years are presented in this article. The major part of this work was carried out in the field of nuclear fission which has been one of the most important discoveries of the 20th century and in which radiochensts have played the pivotal role. Radiochemical work carried out on mass, charge, and kinetic energy distribution in fission of actinide nuclei by neutron and charged particles has been described. During the past one decade major part of the work carried out is, using medium energy heavy ions in both nuclear fission and nuclear reactions. Recently work has been initiated on neutron activation analysis using single comparative (K₀) method. Basic actinide chemistry programme deals with the thermodynamics/kinetics of complexation of these metal ions with novel ligands as extractants viz. cryptands, polyazapolycarboxylate crown ethers, pyrazolones, isoxazolones, sulphoxides, phosphine oxides, and amides. Particular attention has been paid during last two decades to investigate synergism and develop separation procedures for actinides employing solvent extraction, ion exchange, extraction chromatography, and supported liquid membranes. Focus has shifted in recent years to the evaluation of a) N, N dialkyl amides as alternate extractants to TBP in PUREX/THOREX process and b) CMPO/diamides for actinide partitioning from high level waste.

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Exotic atoms are the interesting object as a new probe in material science and a new chemical species in future chemistry. Our group (πAX) has recognized the mesoatomic and mesomolecular phenomena as a subject of chemistry, and continued the experimental study for the capture process of negative pions since 1982. In the recent study, we have investigated the pion capture process mainly in liquid and gas phases, focusing to the behavior of pionic hydrogen atoms. A novel method to measure selectively the pion capture for a particular hydrogen in a molecule revealed the effect of the chemical state of the hydrogen on the transfer process. A proposed model, which combines a LMM model with a transfer process, was useful to wholly understand the capture process observed. The outline of the formation process of pionic atoms and its behavior in material is described briefly, and the main results of our studies are reviewed.

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Nuclear chemistry studies in Japan are briefly reviewed. Main topics are concerned with the works related to nuclear fission and discoveries of new radioisotopes. The other works, such as photonuclear reaction, high energy light ion-induced reaction, intermediate energy heavy ion-induced reaction, and neutron-induced reaction, are just outlined. The future plan for transactinide elements is also briefly introduced.

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Understanding of environmental radioactivity has progressed by investigation of undesirable events: nuclear explosion tests and nuclear accidents. Now the importance of the research on environmental radioactivity has realized widely because of an increasing use of nuclear energy. One of the tops of the current research is construction of models, which explain and predict behavior of radionuclides released to the environment . Parameters of mathematical equations used in the model require reliable values, which must be determined by environmental analysis and laboratory experiments. Development of analytical instruments and techniques would make possible to obtain more reliable values of the parameters.

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In all quartz samples having different origins, radiation-induced hydrogen radicals (atomic hydrogens) were observed in ESR measurement at 77K in addition to intense Al-centers. An obvious positive correlation was recognized between the hydrogen radical intensities and the reduction of the Al-centers after warming up to room temperature, although there was no clear relationship between hydrogen signals and initial Al-centers at 77K. In isochronal annealing treatments the hydrogen radicals were gradually decreased with increments of temperature and completely disappeared after warming up to room temperature. Similar behavior was shown in the Al-centers, but a few percentages of which were still remained at room temperature. The Al-centers remained gave a linear relation to the blue thermoluminescence (BTL) intensity. We concluded that the hydrogen radicals arising from radiolytic products of OH and molecular water impurities could operate as a “killer” of radiation-induced Alcenters related intimately to emission of BTL in natural quartz.

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