Radon Mitigation >> Radon Gas Measurement Methods

AC - Activated Charcoal Adsorption For this method, an airtight container with activated charcoal is opened in the area to be sampled and radon in the air adsorbs onto the charcoal granules. At the end of the sampling period, the container is sealed and may be sent to a laboratory for analysis.The gamma decay from the radon adsorbed to the charcoal is counted on a scintillation detector and a calculation based on calibration information is used to calculate the radon concentration at the Radon Gas Measurement Methods sample site.

Charcoal adsorption detectors, depending on design, are deployed from 2 to 7 days. Because charcoal allows continual adsorption and desorption of radon, Radon Gas Measurement Methods the method does not give a true integrated measurement over the exposure time. Use of a diffusion barrier over the charcoal reduces the effects of drafts and high humidity. 

All applicants and participants in the Program are responsible for developing their own calibration curves. Use of curves developed by EPA for its own charcoal canister (AC) Programs is not appropriate; Radon Gas Measurement Methods do not use the information contained in EERF Standard Operating Procedures for Rn-222 Measurement Using Charcoal Canisters (EPA 520/5-87-05, as amended, October 1989). 

AT - Alpha Track Detection (filtered)For this method, Radon Gas Measurement Methods the detector is a small piece of special plastic or film inside a small container. Air being tested diffuses through a filter covering a hole in the container. When alpha particles from radon and its decay products strike the detector, they cause damage tracks. 

At the end of the test the container is sealed and returned to a laboratory for reading.The plastic Radon Gas Measurement Methods or film detector is treated to enhance the damage tracks and then the tracks over a predetermined area are counted using a microscope or optical reader. The number of tracks per area counted is used to calculate the radon concentration of the site tested. 

Exposure of alpha track detectors is usually 3 to 12 months, but because they are true integrating devices, Radon Gas Measurement Methods alpha track detectors may be exposed for shorter lengths of time when they are measuring higher radon concentrations. UT - Unfiltered Track Detection The unfiltered alpha track detector operates on the same principle as the alpha track detector, except that there is no filter present to remove radon decay products and other alpha particle emitters. 

Without a filter, the concentration of radon decay products decaying within the "striking range" of the detector depends on the equilibrium ratio of radon decay products to radon present in the area being tested, Radon Gas Measurement Methods not simply the concentration of radon. Unfiltered detectors that use cellulose nitrate film exhibit an energy dependency that causes radon decay products that plate out on the detector not to be recorded.

This phenomenon lessens, but does not totally compensate for the dependency of the calibration factor on equilibrium ratio. For this reason, Radon Gas Measurement Methods EPA currently recommends that these devices not be used when the equilibrium fraction is less than 0.35 or greater than 0.60 without adjusting the calibration factor. EPA is currently evaluating this device further to determine more precisely the effects of equilibrium fraction and other factors on performance. 

These evaluations will lead to a determination as to whether to finalize the current protocol or Radon Gas Measurement Methods remove the method from the list of Program method categories.4. LS - Charcoal Liquid Scintillation This method employs a small vial containing activated charcoal for sampling the radon. After an exposure period of 2 to 7 days (depending on design) the vial is sealed and returned to a laboratory for analysis. 

While the adsorption of radon onto the charcoal is the same as for the AC method, analysis is accomplished by treating the charcoal with a scintillation fluid, Radon Gas Measurement Methods then analyzing the fluid using a scintillation counter. The radon concentration of the sample site is determined by converting from counts per minute.

CR - Continuous Radon Monitoring This method category includes those devices that record real-time continuous measurements of radon gas. Air is either pumped or diffuses into a counting chamber. The counting chamber is typically a scintillation cell or ionization chamber. Scintillation counts are processed by electronics, Radon Gas Measurement Methods and radon concentrations for predetermined intervals are stored in the instrument's memory or transmitted directly to a printer.

EL - Electret Ion Chamber: Long-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, Radon Gas Measurement Methods 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 voltage to the radon concentration. 

Variations in electret design determine whether detectors are appropriate for making long-term or short-term measurements. EL detectors may be deployed for 1 to 12 months. Since the electret-ion chambers are true integrating detectors, Radon Gas Measurement Methods the EL type can be exposed at shorter intervals if radon levels are sufficiently high. 

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, Radon Gas Measurement Methods 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 voltage to the radon concentration. Variations in electret design determine 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, Radon Gas Measurement Methods the ES type can be exposed at longer intervals if radon levels are sufficiently low.

GC - Grab Radon/Activated Charcoal This method requires a skilled technician to sample radon by using a pump or a fan to draw air through a cartridge filled with activated charcoal. Depending on the cartridge design and airflow, Radon Gas Measurement Methods sampling takes from 15 minutes to 1 hour. After sampling, the cartridge is placed in a sealed container and taken to a laboratory where analysis is approximately the same as for the AC or LS methods.

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