Wastes containing high concentrations of radiocaesium released from the Fukushima Dai-ichi Nuclear Power Plant have been disposed in controlled landfill sites. In these landfill sites, soil layers were installed around the waste to prevent leaching of radiocaesium from the waste via precipitation. The objective of this study was to enhance Cs retention in the soil layers by mixing clay minerals. In andosol and brown forest soil, the amount of Cs fixed in the soil increased with the mineral mixing ratio; however, the amount of Cs fixed in gray lowland soil was independent of the mineral mixing ratio. In addition, the inhibition of Cs sorption by organic matter dissolved from each soil was examined by comparing the estimated amount with the actual amount of sorbed Cs. The obtained results suggest that the inhibition of Cs sorption onto clay minerals mixed with soil occurred due to the organic matter sorbed by the minerals.
Log cultivation of shiitake mushrooms has been declining in Fukushima Prefecture and its surrounding areas due to the Fukushima Dai-ichi Nuclear Power Plant accident. The Forestry Agency has set a maximum concentration limit for radioactive caesium of 50 Bq/kg for bed logs to cultivate safe shiitake mushrooms (<100 Bq/kg). The development of a portable radioactivity detection system that can be operated outdoors is necessary to detect safe bed logs at cultivation locations that are potentially contaminated. In this study, we developed a low-cost portable radioactivity detection system without radiation shielding material. The safe bed logs were selected using a screening test with the portable radioactivity detection system even at a for low-levels of contamination (~0.1 µSv/h).
Radon collectors (e.g., PicoRad collectors) based on activated-charcoal have been used for screening and measuring radon. However, researchers at the U. S. Environmental Protection Agency reported that they could not verify the proper functioning of some commercially available radon detectors, including PicoRad collectors. In this study, we exposed two lots (with different expiration dates) of PicoRad collectors to the reference conditions at a controlled radon concentration within a radon chamber because the calibration factors were derived for use by a semi-empirical equation. Further, we exposed the PicoRad collectors to an uncontrolled radon atmosphere for conducting validity evaluation. The radon concentration results obtained by the PicoRad collectors using the semi-empirical equation were observed to be in good agreement with the conventional true radon concentration value. It denoted the optimal value of a quantity determined using a reference instrument. These experiments revealed that different values were required for the factors of the conversion equation of each radon collector lot with a different expiration date.
Fukushima Dai-ichi Nuclear Power Plant Accident in Japan caused a severe environmental pollution by the radioactive nuclides such as 137Cs and 90Sr. In this study, adsorption and removal of Cs+ in aqueous solution have been developed by using the hydrogel composed of poly(2-acrylamido-2-methyl-1-propanesulfonic acid), abbreviated as PAMPS. By optimizing the degree of cross-linking of the PAMPS gel, higher adsorption capacity of Cs+ ion and lower water adsorption were achieved. Sulfo groups (−SO3−) in the PAMPS hydrogel coordinate to Cs+ ions to remove them from the waste water. It proved that the newly developed PAMPS hydrogel could be a highly potential candidate for the Cs+-removal material.
Our research group has attempted to introduce a micropattern on the surface of thermo-responsive cell culture membranes in order to improve the affinity between cultured cells and body tissues and control the direction three-dimensionally. Therefore, Poly(N-isopropylacrylamide) (PNIPAAm) was partially grafted to Ethylene-tetrafluoroethylene copolymer (ETFE) by electron beam graft polymerization method under N2 gas atmosphere at room temperature, using a Si-made mask that is microfabricated with µm order grid shapes. Roundish micro level unevenness of approximately 3 µm, which is due to electron beam diffusion and graft chain elongation, could be observed on the surface by evaluation using a confocal laser microscope. Distribution of PNIPAAm corresponding to the uneven shape was confirmed by microscopic FT-IR. Moreover, wettability change due to temperature change was observed from evaluation of water contact angles around the lower critical solution temperature. From these result, controllability of cell attachment / detachment properties was suggested.
We measured 137Cs concentrations in the young persimmon fruit of each tree in 4 orchards in Fukushima prefecture. We found that the 137Cs concentrations in the young fruit differed even within the same orchard, and it was revealed that there were a few trees that yielded fruit with high 137Cs concentration. In addition, the radioactive contamination density on the ground surface as measured by the walking type radioactivity measurement system ‘KURAMA-II,’ the radiation count rate on the surface of the tree trunk, and the stem perimeter of the tree were measured. These results were compared with the 137Cs concentrations of the young fruit. As a result, no relation was observed between each measured value and the 137Cs concentration of the young fruit, and it was shown that it is difficult to estimate which trees have a high risk of radioactive contamination by these methods.