Compton camera measurements of radiation distribution images at Hamadori, Fukushima Prefecture

Kawahara, Rika*; Ochi, Kotaro   ; Yamaguchi, Katsuhiko*; Torii, Tatsuo*  

As a result of the Fukushima Daiichi Nuclear Power Station accident, radioactive materials were dispersed into the environment from inside the nuclear reactor. Now that the difficult-to-return zone is being lifted, it is important to understand the radiation distribution in the surrounding area. At two locations in the difficult-to-return zone (Okuma Town), measurements were taken with a Compton camera and video was recorded with an optical camera. The locations of radionuclides were confirmed by combining the measurement data and video. The measurement equipment used included a Compton camera using a CZT (CdZnTe) semiconductor (H420 manufactured by H3D), a survey meter with a wand-type GPS (Gamma Plotter H manufactured by Japan Radiation Engineering Co., Ltd.) and an optical camera. Air dose rates at 1 m above ground level ranged from 4 to 46 Sv/h at the first location and from 6 to 12 Sv/h at the second location. By photographing the high-dose points from various positions and angles, the three-dimensional spatial extent of the radiation source could be confirmed.