Uranium isotopes are naturally occurring radionuclides with long half-lives and are possibly released from nuclear industries to the environment. Therefore, behavior of U in the environment is important to be studied both for radiation protection and geochemical view points. This paper focuses on the difference between environmental natural U and enriched U on their behaviors in soil-plant systems. As the concentration of U fluctuates in the environment, the U-235/U-238 ratio is used to detect the enriched U by human activity.Soil and plant samples collected near the uranium conversion facilities were analyzed after acid digestion. Chemical extractions with different solutions were also applied, in order to obtain information about the chemical form of U in soil. High-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) was mainly used for the determination of U isotopes.The U-235/U-238 ratios in soils collected around the uranium conversion facilities were higher than the natural ratio. The U-235/U-238 ratio in leachate was higher than the ratio obtained for the total U in the soil. The amount of U leached from the soil was increased with increasing HNO3 concentration. On the other hand, the U-235/U-238 ratio decreased with increasing HNO3 concentration. The U-235/U-238 ratios in plants were higher than those in soils collected in the same sampling places. These facts suggest that the enriched U added to the soil was more soluble (more bio-available) compare with the natural U originally contained in the soil.

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For the development of the modelling technique in prediction of the ⁹⁹Tc concentrations in marine biota, temporal and space distributions of ⁹⁹Tc concentrations in marine organisms are important especially in case of short-term introduction to coastal area. We developed a basic model being composed of nuclide transfer both from seawater and food chain in imaginary coastal area, expressing the temporal ⁹⁹Tc concentrations in marine organisms accompanied with the habitat location. The result of simulation by model in case of short term introduction exhibits the following information; 1) The introduced ⁹⁹Tc in seawater is diluted and disappeared quickly by current advection and diffusion, 2) ⁹⁹Tc in organisms increased according to the ⁹⁹Tc in seawater is increased, mainly from the contribution from ⁹⁹Tc transfer from seawater. 2) The ⁹⁹Tc concentration plateau in algae continues approximately 1 months later, and the concentration ratio (⁹⁹Tc in organism / ⁹⁹Tc in seawater) at that time is larger than the BCF in equilibrium state. This result indicates that 1) monitoring of ⁹⁹Tc concentration in algae must be continued until 3 months after acute introduction even it is weekly term.

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Marine organisms sometimes show a high affinity specifically to a chemical element or a radionuclide and accumulate it to the extent up to 100,000 in terms of so-called concentration factor. These organisms could be defined as hyperaccumulator and used as a biological monitor in the environmental surveillance programme not only for just monitoring the release of radionuclides or contaminant elements but also for tracing the temporal and spatial changes of their distribution in the marine environment, whereas the levels of contaminants released under control are usually too low to be detected directly in seawater and other medium materials. Such hyperaccumulators often accumulate chemical elements other than the element of concern itself and show a unique mineral composition. The present study reports the result of a screening analysis for determining mineral composition in marine organisms by the ICP-AES, ICP-MS and PIXE methods. Special concern was directed to the chemical properties of the candidate organisms for biological monitor in the environmental monitoring.

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New method using Ag-108m with half-life of 4l8 y was developed for the evaluation of neutron dose due to Atomic Bomb in Hiroshima and Nagasaki. This nuclide has never been paid attention not only because neutron capture cross section of target nuclei Ag-107 is only about 1.barn but also because rather long half-life of Ag-108m. Extremely higher elemental abundance of silver up to 100 %, which corresponds to 2 million times higher than typical abundance of in granite (0.5 ppm), compensate the disadvantage of Ag-108m measurement. Furthermore 3 abundant gamma-rays (434, 615 and 723 keV) from Ag-108m can be measured without interfering different from the case of Eu-152. Overall advantage of Ag-108m over Eu-152 is estimated to be > 1000. We tried to measure silver medal and some other metalic samples lent from Hiroshima and Nagasaki Atomic Bomb Museum and confirmed sufficient amout of Ag-108m for the evaluation of neutron fluence by A-Bomb. Great importance of Ag-108m measurement is that neutron dosimetry of the A-Bomb victim is possible if finger ring and/or a rosary containing silver exposed are available as counting samples and that this nuclide can be used more than 2000 years.

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As fungi play important roles as decomposer in ecosystems, effects of toxicants including radiation on fungi may result in a change of ecosystem. However, there is rare information of the influence of radiation on fungi. In this work, the &gamma ray irradiation experiment with high dose in short time was carried out for clarifying radiation effect on fungous growth. Four species of fungi, Flammulina velutipes (NRBC4901), Aspergillus niger (NRBC4066), Cladosporium cladosporioides (NRBC4459) and Cladosporium resinae (NRBC8588) were used. After adjusting the growth condition, the hyphae were irradiated with &gamma ray (⁶⁰Co) with different irradiation time. Then, the hyphae were cultured in a incubator at 22 ° C and extension of hyphae were measured every day. The hypha growth of F. velutipes was not affected by radiation less than 50 Gy. On the other hand, hypha growth was stopped by 0.6 kGy irradiation, then the hypha started re-growing after 1 day. In case of 1 kGy irradiation, the hypha started re-growing after two days. Positive correlation was observed between a delay period of hypha growth and radiation dose. The delay of hypha growth was caused by the temporal stopping of hypha extension at circumference of the colony. The similar effect was also observed in the other fungi, although the delay periods were different depending on the species. This delay of hyphae growth might be used as the indicator of radiation effect on fungi at high dose.

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The first commercial nuclear fuel reprocessing plant in Japan locates in Rokkasho Village, Aomori Prefecture, and is now under the uranium test. Since the plant will release small amount of Tc-99 to the ocean, the concentration of Tc-99 in seawater nearby the plant will possibly increase in the future. Seaweeds are important food items in Japan, and concentrate some radionuclides in seawater. Therefore, the Tc-99 concentration level in edible seaweeds before the plant full operation is important for investigate the effect of the plant to the local environmental radioactivity. We measured concentrations of Tc-99 and Cs-137 in edible seaweeds and report the results here. Fifteen edible seaweeds (Konbu) samples, 11 samples of Laminaria japonica and one each sample of L. ochotensis, L. angustata L. diabolica and L. longissama, were obtained from fishermen's cooperative associations in Aomori, Iwate and Hokkaido in 2004. The concentration of Tc-99 in L. japonica ranged from 3.9 to 74 mBq/kg-dry, and mean value was 31 mBq/kg-dry. The concentrations in other edible seaweeds in Hokkaido were 3.4 - 6.2 mBq/kg-dry except for L. longissama which is lower than detection limit (2.4 mBq/kg-dry). Mean Tc-99/Cs-137 activity ratio in the samples was 0.07±0.04, which is larger than that (0.0003) reported for seawater around Kyushu, Japan. It is implied that Tc is selectively accumulated by Konbu compared with Cs-137. This work was supported by Aomori Prefectural Gorvernment.

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High concentrations of thoron (²²⁰Rn) have been investigated in various living environments. However, many unclear points related to the exposure to thoron remain as an issue to be clarified. This report focuses on the behavior of thoron and its decay products which could influence on the exposure of public. The measurements of long-term averaged concentrations of thoron and its decay products were carried out with passive detectors in traditional Japanese houses with soil walls. RADOPOT® and a deposition monitor were used for thoron and its decay products, respectively. To investigate the temporal change of their concentration, active methods,RAD7® and WLx® were employed. From the results of the measurements over 1 year, thoron concentrations ranged from almost 0 to more than several thousands Bq m^-3. High concentrations were found in the places near wall surface, and they decrease drastically as distance from the wall surface increases. Large diurnal changes of the thoron concentration were found in some houses. The changes due to air turbulence by fan were also investigated. The equilibrium equivalent thoron concentrations (EETC) ranged from nearly 0 to about 6 Bq m^-3. No large change of the EETC with distance from the surface of the wall and no diurnal change of EETC were found. Large spatial and temporal changes exist in the indoor thoron concentrations, while the temporal change in concentrations of the decay products was found to be small, and the concentration would be changed due to complicated factors.

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The mean Rn concentration in the residents of Hiroshima was approximately two times of that in Nagasaki (Yonehara H., Aoyama T., et al., 1995). One of the plausible reasons of the high concentration is that many granite stones were used in the surroundings of Hiroshima City. The granite stones are mainly produced in the quarries around Hiroshima City. Kato measured the gamma-rays from the granites at 11 locations around Hiroshima City, and the K, U and Th contents were determined (Kato K., 2004). The content of K strongly relates to depth of the place where the granitizations occurred. In order to reveal what kinds of granites around Hiroshima City were rich in U and Th, 3 quarries were newly surveyed, and the K, U and Th contents in many granite stones were measured. The U and Th contents in 51 granite samples measured until now ranged widely from 0.85 ppm to 6.7 ppm of U and from 5.7 ppm to 55 ppm of Th. All the data were analyzed in this study. Moreover, microscopic examinations were performed in order to examine the visible characteristics of the granites with high U and Th contents.

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Microdosimetric single event spectra as a function of depth in phantom for the therapeutic carbon beam from HIMAC have been measured by two ways: one is a fragment particle identification measurement (PID-mode) using a tissue equivalent proportional counter (TEPC) coupled with scintillation counter system and the other is an in-phantom measurement (IPM-mode) which a TEPC is actually positioned in phantom.For the PID-mode, fragments produced by carbon beam in phantom are identified by ΔE-TOF distribution between two scintillation counters. Lineal energy distribution for carbon and five fragments of proton, helium, lithium, beryllium and boron ions are obtained in the lineal-energy range of 0.1-1000keV/mm at eight depths (6.9-146.9mm).For the IPM-mode, the total lineal energy distributions at eight depths (59.9-295.9 mm) are measured and compared with the result of PID-mode measurement. Both spectra are consistent with each other. It shows that the PID-mode measurement can be discussed as in phantom measurement. The dose distribution of the carbon beam and fragments are obtained separately. The depth dose curve has consistent with the Bragg peak. And also, it can clearly be seen that the fragment-dose contributions dominated at the deeper position of the Bragg peak.Relative biological effectiveness for the carbon beam in the phantom has been calculated using a response function. RBE of the carbon beam is maximized at the Bragg peak. The maximum value of RBE is about 4.5 and then rapidly decreases at the deeper position of the peak.

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