Decommissioning of Nishina Memorial Cyclotron Center

We decommissioned the Nishina Memorial Cyclotron Center that was mainly used for PET/PIXE study until 2019. The main body of the cyclotron and peripheral equipment were separated as radioactive waste. For the concrete in the accelerator room building, radioactivity analysis of concrete core samples using a Ge detector, dose measurement of concrete surface using a CsI scintillation survey meter with a lead shield, and activation calculation using PHITS code were performed. The PHITS calculation with detailed modeling well reproduced the measurement result. The activated part was evaluated to have a depth of 21 to 41 cm, and the scraped concrete was treated as radioactive waste. All the work took 22 months. A practical procedure is proposed for the estimation of activated part of the concrete.