Development of emergency-use stack gas monitor.

In case of reactor accidents, it is desirable that a stack gas monitor for high-concentration mixed radioactive rare gases measurement should indicate a value directly proportional to the exposure rates in the environment. In a stack monitor based on a new method which enables the easy estimation of exposures in the environment, the radioactive rare gases at a release source is partly allowed to flow through a limited space where two detectors are mounted, one having a flat γ-ray energy response and the other having a sensitivity dependency with energy. The detector having a flat response is made by a high-pressure argon filled ionization chamber covered with thin copper filter and the other is made by a xenon filled one using the same way. Accordingly, a special unit of exposure rate (μR/h·mm2·l/h) and an average γ-ray energy of the released mixed radioactive rare gases are measured by use of the two detectors, thereby providing the exhaust-stack gas monitor with a capability of directly predicting exposure rate in the environment. The new method is suitable for the emergency-use stack gas monitor.