Geiger–Müller counter tube survey metres with resolving times greater than approximately 2000 µs should not be used for contamination inspection at Operational Intervention Level 4

The International Atomic Energy Agency sets standards for the decontamination of radioactive materials adhering to the body surface at Operational Intervention Level 4. Contamination is determined using instruments designed to measure surface contamination, such as the Geiger-Müller counter tube survey metre (GM survey metre). This study was performed to evaluate the validity of using GM survey metres to inspect the surface contamination of evacuees during a nuclear disaster. We measured the resolving time (RT) of GM survey metres and examined the relationship between the corrected count rate and surface contamination density. The RTs of all objects were longer than the Japanese Industrial Standards standard value of 250 μs. Our study suggests that the RT should be maintained at <2000 µs to avoid overestimation during contamination inspection. Close attention is required to maintain the RT within this time, and GM survey metres with long RTs should be excluded from inspections to maintain the adequacy of contamination estimation.