E-perm® passive integrating electret ionization chambers for measuring radon in air, thoron in air, radon in water and radon flux from surfaces/building materials

Electret ion chamber (EIC) for monitoring radon consists of a stable electret (electrically chargedTeflon disc) mounted inside an electrically conducting chamber. PERM? passive integrating electretionization chambers for measuring radon in air has a restricted filtered passive access to radon (222Rn), allowing it to respond only to radon and not to thoron(220Rn) A modified unit called thoron monitor, with unrestricted access to thoron responds to both radon and thoron. Radon monitor and thoron monitor when used side by side allows measurement of both radon and thoron concentrations in air. Taking a small sample of water into a four-liter glass jar containing a radon monitor and measuring radon in air phase allows an accurate measurement of radon in water. Such arrangement can also be used for a quantitative measurement of radium in soil, by taking a soil sample in the place of watersample and measuring radon emanated from the soil or the building materials. Special monitors calledradon flux monitors with vents are modified radon monitors having a large window lined with a thinsheet of material that allows unrestricted entry of radon. Such a chamber is positioned on the surfacein question for a known duration. Using appropriate calibration constants radon flux from the surfacecan be calculated. The paper reviews the design and performance of these monitors.