A Sr adsorption fiber was prepared for rapid analysis of 90Sr content in the fiber using radiation-induced emulsion graft polymerization and subsequent chemical modification. A polyethylene fiber with a diameter of 13 μm was first immersed in a methanol solution of an epoxy-group-containing vinyl monomer, glycidyl methacrylate (GMA), and polyoxyethylene sorbitol ester (Tween20) as a surfactant for the graft-polymerization of GMA. Octadecylamine was then bound to a polymer chain extending from the fiber surface, providing hydrophobicity to the polymer chain. Dicyclohexano-18-crown-6 (DCH18C6) was finaly impregnated onto the polymer chain via a hydrophobic interaction between the octadecyl moiety of the polymer chain and the cyclohexyl moiety of DCH18C6. The fiber surface structure, characterized by DCH18C6 molecules loosely entangled with polymer chains, allowed for the rapid adsorption of Sr ions at an adsorption rate of approximately 100-times higher than that of a commercially available Sr-selective resin (Sr Resin®).
The accident of the Fukushima Dai-ichi Nuclear Power Plant in March, 2011, released large amounts of radiocesium into the atmosphere, and contaminated the environment of Gunma Prefecture in eastern Japan. In particular, 640 Bq kg–1-wet of radiocesium concentration was found in wakasagi (Hypomesus nipponensis) in Lake Onuma on Mt. Akagi in August, 2011. Thus, to elucidate the body-size effect in weight-dependent and dynamics of radiocesium in the ecosystem of Lake Onuma, we determined the age of wakasagi, the body-weight class of the radiocesium concentration in wakasagi and the effective ecological half-life (Teff) of radiocesium in wakasagi 0+ from 2012 to 2016. The body-size effect was found for the 137Cs concentration of wakasagi fished from 2012 to 2015, i.e., the concentration of 137Cs increased with the increase in its body weight. On the other hand, no body size effect was found in 2016. This result may be caused by the following two factors: the 137Cs concentration of the lake water reached a steady state after May 2014; wakasagi is a small plankton-feeding fish, while it is known that larger piscivorous fishes show the strong body size effect. Teff of the 137Cs concentration in wakasagi 0+ consists of two components, fast- and slow-term ones, and the decay rate of the 137Cs concentration in wakasagi 0+ was greatly reduced. As stated above, the radiocesium contamination in Lake Onuma has still been lasting; we are thus continuing our monitoring studies.
Passed five and a half years from the Great East Japan Earthquake, a large number of research papers on the distribution of radioactive material have been published. In this work, based on the monitoring value of the air-dose rate and the radioactive cesium concentration in Tokyo City University Atomic Energy Research Laboratory, we focused on the temporal change of these values and indicated the attenuation of the dose rate. According to the long-term monitoring results, before the Fukushima NPP accident the average of air-dose rate, which is the background level of the laboratory, was 0.034 μSv h–1. In Aug. 2013, the measured data was close to the background value. On the other hand, the concentration of radioactive cesium (Cs-137) decreased drastically until Sep. 2011, and after that the attenuation speed had been quite slow. We focused on the slow pace of the attenuation region, and indicated the correlation coefficient between the air-dose rate and the Cs-137 concentration of airborne particulate matter. As a result, we considered that the magnitude of the correlation coefficients might be related to the existence form of Cs-137.