Development of a gamma camera to image radiation fields

Measurement of radioactive contamination and confirmation of the decontamination effects are important for the recovery from the nuclear accident at the Fukushima Dai-ichi Nuclear Power Plant. We have developed a gamma camera which can visualize the gamma-ray intensity distribution in real time. Experiments were conducted to investigate its performance. An energy resolution of 2.3 % and spatial resolution of 0.68 m at a distance of 5 m were confirmed. In addition, field tests were conducted in the Fukushima Dai-ichi Nuclear Power Plant. The gamma-ray intensity distribution was successfully visualized within as short a time as 10 seconds in an environment with an air dose rate of 1 - 10 mSv/h. Prominent gamma-ray radiation was found from the penetration holes, which connect the inside and outside of the primary containment vessel. From this result, it was found that shielding the penetration holes will improve the work environment during decontamination and cleanup activities. These results indicate the gamma camera will contribute to decontamination work and radiation exposure reduction for workers.