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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

Carolyn Allen, Paul Kotrappa - Rad Elec Inc.

Electret ion chamber (EIC) for monitoring radon consists of a stable electret (electrically charged
Teflon disc) mounted inside an electrically conducting chamber. PERM . passive integrating electret
ionization chambers for measuring radon in air has a restricted filtered passive access to radon ( 222 Rn),
allowing it to respond only to radon and not to thoron(220 Rn) 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 water
sample and measuring radon emanated from the soil or the building materials. Special monitors called
radon flux monitors with vents are modified radon monitors having a large window lined with a thin
sheet of material that allows unrestricted entry of radon. Such a chamber is positioned on the surface
in question for a known duration. Using appropriate calibration constants radon flux from the surface
can be calculated. The paper reviews the design and performance of these monitors.

Key words: Radon. Thoron, Flux, Radon in water, Electret, Ion chamber