Estimation of ¹³⁷Cs Contamination Density of Unit 1 SGTS Outdoor Pipe Using Pinhole Gamma Camera and Dosimeters in Fukushima Daiichi Nuclear Power Station

Knowledge of radioactivity distribution is important for the decommissioning of postaccident plants. We derived methods to obtain the ¹³⁷Cs contamination density of the inner surface of a pipe using a pinhole-type gamma camera, surface dose rate measurements using a Teletector, a GF10, and a lead-shielded ionization chamber. Using these methods, we obtained the ¹³⁷Cs contamination density distribution of a Unit 1 standby gas treatment system outdoor pipe at the Fukushima Daiichi nuclear power station. Considering the characteristics of each method, these results were consistent. We obtained useful data for the decommissioning program.