Estimation of ¹³⁷Cs Contamination Density of Wall, Ceiling, and Floor at Unit 2 Operation Floor in Fukushima Daiichi Nuclear Power Station Using Pinhole Gamma Camera

The pinhole gamma camera is a simple and useful device for determining the radiation distribution in a certain region. Using this device, we developed a method to measure the distribution of ¹³⁷Cs contamination density on surfaces using the total energy absorption peak count rate of gamma rays, where each camera pixel was projected onto the surface to determine the corresponding measured area and distance to the surface. We applied this method to measure the ¹³⁷Cs contamination density of the wall, ceiling, and floor of the Unit 2 Operation Floor at the Fukushima Daiichi Nuclear Power Station in 2020 and 2022 and compared the results obtained in 2020 to those of a robot-operated, conventional, high-dose-area smear test. We found a pinhole gamma camera with the proposed method is useful for obtaining contamination density distribution results quickly, without the complexities of using a robot.