US EPA

8802977 

Book/Book Chapter 

Electret ion chambers for characterizing indoor, outdoor, geologic and other sources of radon 

Kotrappa, P 

2015 

Nova Science Publishers, Inc. 

Radon: Geology, Environmental Impact and Toxicity Concerns 

1-42 

English 

Electret Ion Chambers (EICs) are portable, passive, accurate integrating ionization chambers that do not require a battery or any external source of power. An EIC consists of an electret, a charged Teflon®1 disk, enclosed inside an electrically conducting plastic enclosure. The electret serves both as a source of electrostatic field for ion collection and also as a sensor for quantifying the ions collected. The passive EICs, also popularly known as E-PERM®2 (electret passive environmental radon/radiation monitors) are widely used passive radon detectors in US, Europe, Canada and other countries for the measurement of indoor and outdoor radon concentrations and other applications. Figure 1 illustrates how a radon measuring EIC works. The radon gas passively diffuses into the chamber through small filtered holes into the volume of the chamber, and the alpha particles emitted by the decay process ionize the air molecules inside the chamber. Negative ions produced inside the chamber are collected on the positively charged electret, causing a reduction of its surface charge. The reduction in charge (initial charge minus the final charge of the electret) is a function of the radon concentration, the test duration, and the chamber volume. The charge on the electret surface is measured by using a specially designed portable electret reader. The collected data is analyzed by software using algorithms obtained by appropriate calibrations. The EICs are used not only for indoor and outdoor measurements, but also for characterizing a number of geologically important radon related parameters. Such parameters include, radon in water, radon flux from ground and other surfaces, radon progeny concentration in air, and for geophysical prospecting for uranium. This article further provides historic development and standardization of EIC system. The article also provides the theory and practice of measuring geologically important parameters of radon. Bibliography provides a list of publications for those who wish to pursue the technology further. © 2015 by Nova Science Publishers, Inc. All rights reserved.