Radiation monitoring using an unmanned helicopter in the evacuation zone around the Fukushima Daiichi nuclear power plant

The Great East Japan Earthquake that occurred on 11 March 2011 generated a series of large tsunami waves that caused serious damage to the Fukushima Daiichi nuclear power plant, following which a large amount of radioactive material was discharged from the nuclear power plant into the environment. In recent years, technologies for unmanned helicopters have been developed and applied in various fields. In expectation of the application of unmanned helicopters in airborne radiation monitoring, in this study we developed a radiation monitoring system for aerial use. We then measured the radiation level by using unmanned helicopters in areas where the soil had been contaminated by radioactive caesium emitted from the nuclear power plant to evaluate the ambient dose rate distribution around the site. We found that in dry riverbeds near the nuclear power plant, the dose rate was higher than that in the surrounding areas. The results of our measurements show that radiation monitoring using this system was useful in measuring radioactivity in contaminated areas.