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.


Field Blank: A quality control measurement made using a detector which has not been exposed to radon or progeny. The purpose of this procedure is to determine the bias associated with the storage and shipping of devices.


Follow Up Measurements: Measurements made to evaluate typical long term radon concentrations. They are conducted after an initial measurement indicates the potential for unacceptable radon levels.


Gamma radiation: Short-wavelength electromagnetic radiation of nuclear origin, with energies between 10 keV to 9 MeV.


Gamma Rays: Gamma rays are an example of electromagnetic radiation, as is visible light. Gamma rays originate from the nucleus of an atom. They are capable of traveling long distances through air and most other materials. Gamma rays require more “shielding” material, such as lead or steel, to reduce their numbers than is required for alpha and beta particles.


Geiger Counter: A device for detecting beta and gamma radiation.


Half-Life: The time required for a population of atoms of a given radionuclide to decrease, by radioactive decay, to exactly one-half of its original number is called the radionuclide’s half-life. No operation, either chemical or physical, can change the decay rate of a radioactive substance. Half-lives range from much less than a microsecond to more than a billion years. The longer the half-life the more stable the nuclide. After one half-life, half the original atoms will remain; after two half-lives, one fourth (or 1/2 of 1/2) will remain; after three half-lives one eighth of the original number (1/2 of 1/2 of 1/2) will remain; and so on.


Ionizing radiation: Any type of radiation capable of producing ionization in materials it contacts; includes high-energy charged particles such as alpha and beta rays, and nonparticulate radiation such as gamma rays and X-rays. In contrast to wave radiation (e.g., visible light and radio waves) in which waves do not ionize adjacent atoms as they move.


Non-Ionizing Radiation: Low energy radiation such as radio and television waves.


Passive radon/radon decay product measurement device: A radon or radon decay product measurement system in which the sampling device, detector, and measurement system do not function as a complete, integrated unit. Passive devices include electret ion chamber devices, activated carbon or other adsorbent systems, or alpha track devices, but does not include continuous radon/radon decay product monitors, or grab radon/radon decay product measurement systems.


PicoCurie (pCi): One pCi is one trillionth of a Curie, 0.037 disintegrations per second, or 2.22 disintegrations per minute.


PicoCurie per liter (pCi/L): A unit of radioactivity corresponding to one decay every 27 seconds in a volume of one liter, or 0.037 decays per second in every liter of air.


Plating Out: The process whereby small particles or dust attach to walls, carpets, furniture, lung tissue, and so forth.


Rad (Radiation Absorbed Dose): A measurement of the energy deposited in any material by ionizing radiation. One rad is equal to the absorption of 100 ergs of energy in every gram of the material exposed to the radiation.


Radiation: The emission and propagation of energy by means of electromagnetic waves or sub-atomic particles.


Radiation Types: Radiation is energy in the form of waves or particles. X-rays and gamma rays are electromagnetic waves of radiation, as is visible light. Particulate radiation includes alpha and beta radiation. The energy associated with any radiation can be transferred to matter. This transfer of energy can remove electrons from the orbit of atoms leading to the formation of ions. The types of radiation capable of producing ions in matter are collectively referred to as “ionizing radiation”.


Radioactive Decay: Radioactive decay describes the process where an energetically unstable atom transforms itself to a more energetically favorable, or stable, state. The unstable atom can emit ionizing radiation in order to become more stable. This atom is said to be “radioactive”, and the process of change is called “radioactive decay”.


Radioactive Decay Series: A series of isotopes that result following the decay of a parent radionuclide. There are three natural radioactive decay series, uranium 238, uranium 235, and thorium 232.


Radioactivity: The spontaneous decay of an unstable atomic nucleus, giving rise to the emission of radiation.


Radiotoxicity: The adverse health effect of a radionuclide due to its radioactivity.


Radium: An element often found in uranium ore. It has several radioactive isotopes. Radium-226 decays to Radon-222.


Radon (Rn): A colorless, odorless, naturally occurring, radioactive, inert, gaseous element formed by radioactive decay of radium (Ra) atoms. The atomic number is 86. Although other isotopes of radon occur in nature, radon in indoor air is almost exclusively Rn-222.


Radon chamber: An airtight enclosure in which operators can induce and control different levels of radon gas and radon decay products. Volume is such that samples can be taken without affecting the levels of either radon or its decay products within the chamber.


Radon Daughters: Radioactive decay products of radon-222.


Radon Source Strength: The intensity, power, or concentration of radon action from its point of origin.


Reading Prong: A geographical area stretching throughout Pennsylvania, New Jersey, and New York known to have a large number of homes with high radon concentrations.


Rem: A unit of exposure to ionizing radiation in human tissue; an estimate of the health risk that exposure to ionizing radiation could have on human tissue.


Scintillation Cell: A metal cylinder or flask coated with a material that will fluoresce or scintillate (give of a light flash) when contacted by alpha radiation. This device is used to measure radon concentrations in air samples collected in the cell.


Sensitivity Checks: Sensitivity checks are used to determine the lower limit of detection for a particular measurement system. Background radiation and inherent instrument design often limit the ability to measure very low concentrations of radon.


Soil Gas (Air): Gas which is always present underground, in the small spaces between particles of the soil or in crevices in rock. Major constituents of soil gas include nitrogen and oxygen (from the outdoor air), water vapor, and carbon dioxide. Since radium 226 is essentially always present in the soil or rock, trace levels of radon 222 will exist in the soil gas.


Time integrated sampling: Sampling conducted over a specific time period (e.g., from two days to a year or more) producing results representative of the average value for that period.


Unattached Fraction: Refers to radon decay products which have not yet adhered to other, larger dust particles in the air (or to other surfaces, such as walls). Unattached RDPs might result in a higher lung cancer risk than will RDPs that are attached to larger particles, because they can selectively deposit in small areas of the lung.


Uranium: A naturally occurring radioactive element with the atomic number 92 and an atomic weight of approximately 238.  


Working level (WL): Any combination of short-lived radon decay products in one liter of air that will result in the ultimate emission of 1.3 x 105 MeV of potential alpha energy. This number was chosen because it is approximately the alpha energy released from the decay products in equilibrium with 100 pCi of Ra-222. Exposures are measured in working level months (WLM).


WORKING LEVEL MONTH (WLM): Exposure resulting from the inhalation of air with a concentration of 1 working level of radon decay products for 170 hours. This is approximately the number of working hours in a month. Since a month of 30 days has 720 hours, exposure to a concentration of 1WL for 24 hours a day for 30 days corresponds to 4.235 WLM