SIMPLIFIED METHOD FOR DETERMINING RESIDUAL SPECIFIC ACTIVITY IN ACTIVATED CONCRETE OF A PET-CYCLOTRON ROOM USING A SURVEY METER

摘要

An in situ method to determine the specific activity in concrete structures using a survey meter was established in this study for decommissioning accelerator rooms.This method is much simpler than the conventional sampling method that requires core boring.A survey meter(T-SP2,TAC Inc.,Japan)was customised and equipped with a small detector probe,whose size allowed the design of a light-weight Pb shield.For dose rate measurement,a Pb shield thickness of 4.5 cm was enough to shield ambient γ-rays,and its weight(16 kg)was low enough for the device to be carried by a human.A calibration curve was obtained to quickly and easily convert the net contact dose rate on concrete into the specific activity in a PET cyclotron room.The specific activity detection limit for this device was lower than the clearance limit of ~(152)Eu and ~(60)Co in activated materials.Therefore,this method can be used for separating non-activated concrete from activated concrete during decommissioning.A general correction factor for the slope of the calibration curve was also obtained for use at other accelerator facilities.