Influence of the presence of humidity, ambient aerosols and thoron on the detection responses of electret radon monitors

This paper describes how the presence of humidity, ambient aerosols and thoron influences the detection responses of an electret passive environmental radon monitor (commercially E-PERM®) using radon and thoron chambers of National Institute of Radiological Sciences (NIRS). From the initial experiments, the linear correlation between the conversion factor for radon and the midpoint voltage for the short-term and long-term electrets was determined. As a result, it was observed that the conversion factors were approximately 10% lower for the short-term electrets and 3% higher for the long-term electrets than those reported by the manufacturer. The evaluation of different magnitudes of radon concentration showed that the presence of humidity and ambient aerosols had little influence on the detection response for radon, with less than 10% relative standard deviation. In the case of thoron detection response, net voltage drop values increased linearly with time-integrated concentrations for both short-term and long-term electrets, as was the case with radon. The thoron responses to radon were less than 5% for both the electrets from the results of experiments and calculations.