Measures to protect against radiation due to a large-scale nuclear accident of distant place - radioactive materials in Nagasaki from the Fukushima Daiichi nuclear power plant indicate

摘要

Objective: To investigate human health effects of radiation exposure due to possible future nuclear accidents in distant places and other various findings of analysis of the radioactive materials contaminating the atmosphere of Nagasaki due to the Fukushima Daiichi Nuclear Power Plant accident. Methods: The concentrations of radioactive materials in aerosols in the atmosphere of Nagasaki were measured using a germanium semiconductor detector from March 2011 to March 2013. Internal exposure dose was calculated in accordance with ICRP Publ. 72. Air trajectories were analyzed using NOAA and METEX web-based systems. Results: 134Cs and 137Cs were repeatedly detected. The air trajectory analysis showed that 134Cs and 137Cs flew directly from the Fukushima Daiichi Nuclear Power Plant from March to April 2011. However, the direct air trajectories were rarely detected after this period even when 134Cs and 137Cs were detected after this period. The activity ratios (134Cs/137Cs) of almost all the samples converted to those in March 2011 were about unity. This strongly suggests that the 134Cs and 137Cs detected mainly originated from the Fukushima Daiichi Nuclear Power Plant accident in March 2011. Although the 134Cs and 137Cs concentrations per air volume were very low and the human health effects of internal exposure via inhalation is expected to be negligible, the specific activities (concentrations per aerosol mass) were relatively high. Conclusion: It was found that possible future nuclear accidents may cause severe radioactive contaminations, which may require radiation exposure control of farm goods to more than 1000 km from places of nuclear accidents.