A practical E-PERM (electret passive environmental radon monitor) system for indoor 222Rn measurement.

The technical and scientific basis for the measurement of indoor 222Rn concentration using an E-PERM (Electret passive environmental radon monitor) has been described in our earlier work. The purpose of this paper is to describe further development of a practical and convenient system that can be used routinely for indoor 222Rn measurement. The ion chamber is now made of electrically conducting plastic to minimize the response from natural gamma radiation. A spring-loaded shutter method is used to cover and uncover the electret from outside the chamber. The electret voltage reader has been modified to improve the accuracy and the ease in operation. The calibration, performance, error analysis, and lower limits of detection for these standardized versions of E-PERMs are also described.