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6. ES - Electret Ion Chamber: Short-Term
For this method, an electrostatically charged disk detector
(electret) is situated within a small container (ion chamber). During
the measurement period, radon diffuses through a filter-covered
opening in the chamber, where the ionization resulting from the
decay of radon and its progeny reduces the voltage on the
electret. A calibration factor relates the measured drop in voltag
to the radon concentration. Variations in electret design deter
whether detectors are appropriate for making long-term or short-term measurements. ES
detectors may be deployed for 2 to 7 days. Since electret-ion chambers are true integrating
detectors, the ES type can be exposed at longer intervals if radon levels are sufficiently low.
LHI Analytical utilizes only Electret Ion chambers for testing. Since we analyze in-house test
results are available the same day the devices are closed. Testing devices have to be accurate
with-in +/- 25%. Eperm devises are statistically are accurate with-in 5%.