A GM-tube detector was calibrated with a standard cesium-137 (137Cs) source and used for measuring radioactive contamination from the Fukushima Daiichi Nuclear Power Plant. The GM-tube detector used in this study was calibrated up to 4 μSv/h based on a quadratic equation. This GM-tube detector yielded the same result as a NaI scintillation counter, and its practical use was validated under calibration.
Air dose rates were measured in Fukushima City, Iwaki City, Shirakawa City, and Samegawa Village and along the Tohoku and Banetsu Expressways during our screening activity in Fukushima Prefecture from March 19 to 22, 2011. Those rates in Fukushima City were highest, followed by those along Tohoku Expressway, whereas those in Samegawa Village and along Banetsu Expressway (both located in the Abukuma highlands) were relatively low. This radioactive distribution agreed with the MEXT reports consisted of airborne monitoring in April 2011. The radioactivity on masks used and the external and internal exposure was substantially low.
Acknowledgement We thank the Matsushimaya Ryokan staff for their support despite difficulties following the Great East Japan Earthquake and the subsequent nuclear accident. We thank Mr. Yukihiro Mizuochi for measuring the dose rates. This work was supported by KUR Research Program for Scientific Basis of Nuclear Safety.
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