High sensitive airborne radioiodine monitor

• Highly sensitive airborne radioiodine monitor was designed.
• The characteristics of the monitor were investigated using air including radioiodine.
• The monitor was proven to have enough sensitivity to detect low-level radioiodines in the air.

Airborne radioiodine monitoring includes a problem in that commercial radioactive gas monitors have inadequate sensitivity. To solve this problem, we designed a highly sensitive monitoring system. The higher counting efficiency and lower background made it possible to perform the low-level monitoring. The characteristics of the system were investigated using gaseous 125I. The minimum detectable activity concentration was 1×10−4 Bq cm−3 for 1 min counting, which is one tenth of the legal limit for the radiation controlled areas in Japan.