2017 年 66 巻 3 号 p. 201-204
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.