Radon Testing Systems uses E-PERM brand electret ion chamber technology to test for radon levels. Our test typically consists of leaving two small E-PERM canisters in the lowest level of the testing site for 2-5 days. Each canister's electret is read before placing, then read after pickup to determine the level of radon.
What exactly is an E-PERM®? How is it different from an electret?
An E-PERM® (which stands for electret passive environmental radon/radiation monitor) is an electret ion chamber. This means that an E-PERM® is comprised of two components: (1) an electret, and (2) a special chamber that will allow ionization to occur. Although electrets are an important component of an E-PERM®, they cannot measure radon by themselves. As soon as an electret is paired with an ionization chamber, the resulting configuration is known as an E-PERM®, which is also synonymous with an electret ion chamber.
How do Electret Ion Chambers measure radon?
Electret Ion Chambers are comprised of both an electret and an ionization chamber. The ionization chamber is constructed of electrically-conductive plastic, with a volume and shape that has been very accurately characterized. Because the ionization chamber is conductive, it displays strong anti-static properties (that prevents an electrical charge from accumulating on the chamber's exterior and interior surfaces). It also functions as a makeshift Faraday cage, which offers some protection against stray electromagnetic fields.
The second component of an Electret Ion Chamber -- the electret -- consists of a positively charged Teflon® disk, which is housed in an electrically-conductive plastic holder. When the electret is loaded into an ionization chamber, an Electret Ion Chamber (known as an E-PERM®) is created. As radon and its daughters decay inside the ionization chamber, they release alpha and beta particles; the alpha particle is like a tiny atomic cannonball, and the beta particles are the subatomic equivalent of bullets. As these particles fly through the ionization chamber, they strike other molecules in the air. Whenever this happens, an effect called ionization occurs -- and the resulting air molecule is left with either a positive or negative charge.
These negatively charged ions are attracted to the positively charged electret surface, and a reduction in voltage occurs. The radon concentration of a given environment is a direct function of the reduction in voltage over a known time period.