Wide-range krypton gas monitor using a plastic scintillation detector operated in current mode with a gate circuit

Takasaki, Koji  ; Kobayashi, Hirohide ; Suzuki, Hideki; Ushigome, Sadaharu*

The wide-range krypton-85 detector was developed for monitoring of krypton-85 gas, which was discharged from the stack of a nuclear fuel reprocessing plant and varied largely in concentration. The detector combined a current-mode-operated plastic scintillation counter with a gated photomultiplier. The discrimination voltage of gated photomultiplier was determined, and the effects of temperature and humidity were examined on the background measurement. The detector was calibrated by krypton-85 gas and the decision threshold was estimated. These examinations showed that the wide-range krypton-85 detector worked in the measurement range as wide as 10-10 Bq/cm in linearity and the decision threshold of krypton-85 concentration was 1.310 Bq/cm for 10-minute measurement. The parallel measurement was made between this detector and a GM counter in the reprocessing laboratory. Both concentrations showed a good agreement with each other.