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内容記述 |
NanoTerasu is the first synchrotron radiation facility in Japan designed to exclude most of the Experimental Hall from radiation-controlled areas by optimizing its shielding design and radiation safety systems. This unique approach allows users who have completed radiation safety training to access and operate synchrotron radiation beamlines without the need for licensing as radiation workers.The shielding design was performed based on semi-empirical approaches, supported by detailed Monte Carlo simulations using PHITS. In addition to the structural concrete shielding that encloses the 3 GeV electron linear accelerator and the electron storage ring, supplementary local shields were installed at specific locations to suppress high-energy bremsstrahlung photons, based on the simulation results. The Experimental Hall is designed to ensure that the effective dose does not exceed 1.3 mSv over a three-month period, assuming 500 hours of working time, even under maximum operating conditions.The radiation safety system consists of two major components: (1) access control and (2) beam current and secondary radiation monitoring, to protect users from radiation exposure. Access is managed using personal dosimeters with QR codes, which radiation workers scan at entry points for authentication. Prior to beam injection, an evacuation confirmation sequence ensures that each interlocked area is unoccupied and securely closed. If an interlock door is opened during operation, the system immediately halts the accelerator. Ambient dose rates behind the shielding are continuously monitored every 10 seconds using several gamma-ray and neutron detectors installed around the radiation-controlled areas and at the site boundary. If the dose rate exceeds a predefined threshold, the system triggers an automatic shutdown. Integrated dose throughout the entire facility is also monitored using several hundred passive dosimeters.This paper reports the radiation monitoring results and dose control measures implemented during accelerator commissioning, following the commencement of user operations in FY2024. |
