Performance test of passive radon–thoron discriminative detectors on environmental parameters

This paper describes how humidity, wind and ambient aerosols in air influence the detection responses of passive detectors. Two types of alpha track detectors based on a passive radon (222Rn)–thoron (220Rn) discriminative measurement technique were used: the Raduet and Radopot detectors that were developed and calibrated by the National Institute of Radiological Sciences, Japan. The initial experiment showed that the infiltration rate of 220Rn onto sponges with a high air exchange rate for the Raduet detectors was one third lower than that onto filters for the Radopot detectors. Little distinct dependence on humidity was observed for the 222Rn detection responses of both detectors. For 220Rn, the detection responses of both detectors for the high air exchange rate seemed to decrease slightly at high humidity conditions. The 220Rn detection responses of the Radopot detectors had little influence from wind speed. The 220Rn detection responses of the Raduet detectors for the high air exchange rate seemed to decrease at low wind speeds. Furthermore, there was little difference between the detection responses in the presence and absence of ambient aerosol particles because the ambient aerosols were filtered out during their passive diffusion through the sponges and filters for the Raduet and Radopot detectors, respectively.

► Influence of humidity, wind and ambient aerosols on the passive detectors.
► Two passive radon–thoron discriminative measurement techniques were used.
► Little distinct dependence on humidity was observed for 222Rn detection responses.
► Thoron detection responses for high air exchange rate decreased at high humidity.
► Radon detection responses had little influence from wind speed.