Radon Glossary A-E

AARST: American Association of Radon Scientists and Technologists, the professional association of the radon industry.

Absorbed Dose: The amount of radiation energy absorbed, especially by human tissue; measured in rads.

Activated Carbon: A material manufactured from the combustion of fibrous materials such as coconut shells or wood under low oxygen conditions. This process makes "sites" within the material upon which radon can be adsorbed. This material is used in activated carbon measurement devices and in activated carbon adsorption units for removing radon from water.

Active radon/radon decay product measurement device: A radon test or radon decay product measurement system which uses a sampling device, detector, and measurement system integrated as a complete unit or as separate, but portable, components. Active devices include continuous radon monitors, continuous working level monitors, and grab radon gas and grab working level measurement systems, but does not include devices such as electret ion chamber devices, activated carbon or other adsorbent systems, or alpha track devices.

Adsorption: where radon molecules are retained on the surface of the charcoal in a charcoal canister.

Air Pressure Differentials: Differences in air pressure that exist over short distances, e.g. between the interior of a home and below slab or between inside and outside the building shell. Air moves from areas of higher pressure to lower pressure. Air flow caused by pressure differentials is a major force for radon entry into buildings.

Alpha Decay: The radioactive decay of an atom in which the nucleus loses two protons and two neutrons.

Alpha Track Detector: A long term detector for radon. It consists of a plastic material or celluloid film, in which alpha radiation leaves damage tracks that can be counted under a microscope after the plastic material is etched in NaOH (sodium hydroxide) solution.

Background count rate: The counting rate obtained on a given instrument with a background counting sample. Typical reference background counting samples are:

  • Empty planchet: for G-M detectors, internal proportional counters, low background beta counters, alpha spectrometers.
  • Scintillation vial containing scintillant and sample known to contain no radioactivity: for liquid scintillation counters.
  • Container filled with distilled water: for gamma spectrometers.

Background measurements: Measurements made with either active instruments exposed to a radon-free gas, such as aged air or nitrogen, or for passive detectors by analyzing unexposed detectors. Results are subtracted from the actual field measurements before calculating the reported concentration. Background levels may be due to electronic noise of the analysis system, leakage of radon into the detector, detector response to gamma radiation, or other causes.

Background radiation: Radiation arising from radioactive material other than that under consideration. Background radiation due to cosmic rays and natural radioactivity is always present; background radiation may also be due to the presence of radioactive substances in building materials.

Becquerel (Bq): A unit of radiation equal to one disintegration per second (the SI unit).

BEIR: Biological Effects of Ionizing Radiation A report by the National Research Council that provides the basis for determining lung cancer risks for individuals from the Uranium Miner data.

Beta Decay: Radioactive decay in which a nucleus is transformed by the emission of an electron or positron. In either case, the atomic mass remains unchanged, but the atomic number either increases or decreases by 1.

Blank sample: A control sample in which the detector is unexposed and submitted for analysis. Often used to determine detector background values.

Blind spikes: Detectors exposed to known radon or decay product concentrations and submitted for analysis without being labeled as such. Used to evaluate the accuracy of the measurement.

Check source: A radioactive source, not necessarily calibrated, which is used to confirm the continuing satisfactory operation of an instrument.

Curie (Ci): A standard measurement for radioactivity, specifically the rate of decay for a gram of radium - 37 billion decays per second. A unit of radioactivity equal to 3.7 x 1010 disintegrations per second.

Decay: Decrease in activity of a radioactive substance due to the disintegration of an atomic nucleus resulting in the release of alpha or beta particles or gamma radiation.

Electret Ion Chamber: A device for measuring radon. Radon diffuses into the chamber where it goes through its normal decay process emitting ionizing radiation. The ions created alter the charge on an electret surface. Measurements of the charge on the electret surface before and after deployment of the device can be used to calculate the radon concentrations in the room in which the detector was placed.

Equilibrium, Secular: A state in which the formation of atoms by decay of a parent radioactive isotope is equal to its rate of disintegration by radioactive decay.

Equilibrium Ratio, Dynamic: A total concentration of radon decay products (RDPs) present divided by the concentration that would exist if the RDPs were in radioactive equilibrium with the radon gas concentration which is present. At 100% equilibrium (i.e., at an equilibrium ratio of 1.0), 1 WL of RDPs would be present when the radon concentration was 100 pCi/L. The ratio is never 1.0 in a house. Due to ventilation and plate out, a commonly assumed equilibrium ratio is 0.5 in which case 1 WL corresponds to 200 pCi/L. However, equilibrium ratios vary with time and location, and ratios of 0.3 to 0.7 are commonly observed. Large buildings, including schools, often contain equilibrium ratios less than 0.5.

Exposure time: The length of time a specific mail-in device must be in contact with radon or radon decay products to get an accurate radon measurement. Also called exposure period, exposure parameters, or duration of exposure.

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