ELECTRET ION CHAMBER-BASED PASSIVE RADON–THORON DISCRIMINATIVE MONITORS
Radiation Protection Dosimtetry (2010) Vol.141, No. 4, pp. 386-389
P.Kotrappa 1,* and D. Steck 2
1Rad Elec Inc., 5716-A Industry Lane Frederick, MD 21704, USA
2Physics Department, St John’s University, Collegeville, MN 56321, USA
*Corresponding author: pkotrappa@aol.com
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 to222Rn. 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.