Fukushima mapping project after the Fukushima Dai ichi nuclear power station accident

In the so-called Fukushima mapping project, a series of large-scale environmental monitoring with diverse methods have been conducted, aiming to obtain information on contamination conditions in different aspects. Several radionuclides released from the accident were observed in soil over wide areas soon after the accident. However, it turned out from rough estimation that radiocesium was far more important than other observed radionuclides from a viewpoint of long-term exposure doses. This article presents the measurement methodologies for distribution mapping of air dose rates and radionuclides deposition density adopted in our mapping project, and also discuss the temporal change in air dose rate and radiocesium deposition density through repeatedly conducted measurements. The distribution maps on air dose rate and radiocesium deposition density were constructed on the measured data at different occasions. Then, the time-dependent deceasing tendency of air dose rate, and that of deposition density were shown on the basis of the monitoring results