Detecting intake of radionuclides: In vivo screening measurements with conventional radiation protection instruments

Internal contamination monitoring of a large number of workers is challenging, especially when dealing with various radionuclides. This work presents an approach for a pragmatic internal monitoring programme at CERN that is compatible with the Swiss regulation and features quick in vivo screening measurements. These are intended to be performed by the workers themselves using conventional radiation protection instruments. The programme ensures that the yearly committed effective dose does not exceed 1 mSv. This is done by defining screening intervals and coordinating the workers activity according to the minimum detectable committed effective dose associated to each screening. We elaborated a procedure to determine whether a radiation protection instrument is suitable to perform screening measurements and ensure the compliance with the annual E$_{50}$≤1 mSv limit. Seven conventional radiation protection instruments were characterised with reference sources of $^{57}$Co, $^{133}$Ba, $^{137}$Cs and $^{60}$Co. For these instruments, values ranging between tens and hundreds of μ Sv were found for the minimum detectable committed effective dose when performing the screening measurement the day after the intake. The approach provides local radiation protection officers with basic tools to efficiently set up an internal monitoring programme.