Electret ion chamber-based passive radon-thoron discriminative monitor
Electret ion chambers (EICs), commercially available under brand name E-PERM®, are widely used for measuring indoor and outdoor 222Rn concentrations in air. These are designed to respond only to 222Rn and not to 220Rn by restricting diffusional entry area. Such radon EIC (R EIC) monitors are modified by increasing the entry area to allow 220Rn, in addition to 222Rn. Such modified units are called RT EIC. When a set of R and RT EICs are collocated, it is possible to discriminate and measure both radon and thoron concentrations, using appropriate calibration factors (CFs) and algorithms. The EICs come in different volumes, providing different sensitivities. The thoron CFs for 58-, 210- and 960-ml volume R and RT pairs are, respectively, 2.8-, 18.7- and 89-V drop per (kBq m-3 d), respectively. These provide much wider sensitivities and ranges compared to alpha track-based passive radon-thoron discriminative monitors.
Kotrappa P, Steck DJ. 2010. Electret ion chamber-based passive radon-thoron discriminative monitor. Radiation Protection Dosimetry 141(4): 386-389.