Page 36 - Summer2011

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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. Radon testing devices have to be accurate with-in +/- 25%. Eperm devises are statistically accurate with-in 5%.