• activity: number of disintegration per second or decays per second. Both the number of atoms and the activity follow an exponential decay law.
• AEC: Atomic Energy Commission. The responsibilities of the AEC are now conducted by the Department of Energy (DOE).
• aerosol: a system of solid or liquid particles which are dispersed in a gaseous medium and are suspended in the medium for a relatively long time compared to the time scale of interest.
• air exchange ration: the rate at which fresh air entering a home replaces the existing air supply.
• alpha particle: particle emitted in the decay of some radioactive nuclei; a nucleus of the helium isotope of mass 4.
• alveoli: the small sacs in the lung where gases are exchanged with the bloodstream.
• atom: fundamental particle of matter consisting of at least one proton and zero or more neutrons surrounded by an electron cloud equal to the number of protons.
• attached fraction: the fraction of a set of radon daughters adsorbed onto or absorbed into the aerosol particles.
• becquerel (Bq): S.I. unit of radioactive decay; 1 Bq = 1 disintegration per second.
• Beta particle: an electron with a positive or negative charge emitted in the decay of some radioactive nuclei.
• BPA: Bonneville Power Administration, and agency of the D.O.E. which oversees the sale of electric power generated by dams in the Pacific Northwest.
• charcoal canister: radon measurement device that absorbs dust and radon.
• cilia: hair like projections of some cells of the bronchial walls, which move in such a way as to help the elimination of particulate matter via the muco-ciliary escalator.
• curie: unit of radioactive decay; 1 Ci = 37,000,000,000 disintegration per second.
• daughter: an atom chemically different from the radioactive parent atom which changed to produce it.
• decay chain: a radioactive isotope and the series of radioactive daughters which are generated from it through a series of radioactive decays. Production of a non radioactive daughter terminates the chain.
• DNA (deoxyribonucleic acid): the genetic material controlling the maintenance and reproduction of the cell.
  
• electron volt: a unit of energy; 1 eV = 1.6x10^12 ergs = 1.6x10^19 Joules.
• equilibrium factor (F): The ratio of the number of working levels actually present to the number of working levels which would be present if the short-lived daughters were in equilibrium with the radon present.
• equivalent equilibrium concentration (EEC): That concentration of radon in equilibrium with its daughters which would produce the same number of working level as are actually present. The ratio of the EE to the actual radon concentration is equal o the equilibrium factor F.
• ERDA: U.S. Energy Research and Development Administration.
• EPA: The Environmental Protection Agency.
• gamma ray: radiation emitted in the radioactive decay of some nuclei, similar to light and x-rays.
• generation: a division of the airway in the lung from the trachea. Each division of a lung airway usually produces two smaller airways, and another generation.
• grab-sample: type of sampling method which collects a small sample of air in a scintillation cell over a short time span. The sample is analyzed for radioactive decay to determine the concentrations of radon or radon decay products.
• gray: S.I. unit of physical dose; the unit of deposition of energy in material due to the passage of ionizing radiation; 1 Gray = 1 Joule per kg.
• half-life (biologic): time required for the body to eliminate half of a dose of any substance.
• half-life (effective): time required for elimination of 50% of a radioactive element by the combination of biological elimination processes and the element's rate of decay.
• half-life (radioactive):the time required for the radioactive nuclei present to decrease by a factor of two by radioactive decay.
• ICRP: International Commission on Radiobiological Protection.ionizing radiation: radiation with the ability to interact with and remove electrons from the atoms of material, ionizing the atom.
• isotopes: nuclides having equal numbers of protons, but different numbers of neutrons and therefore mass numbers although similar characteristics.
• Jacobi-Eisfeld model: dosimetric model for radon daughters based on the Weibel "A" model of the lung.
• James-Birchall model: dosimetric model for radon daughters based on both the Weibel and Yeh-Schum models of the lung.
• kerma (Kinetic Energy Released in Material): unit of quantity representing the kinetic energy transferred by uncharged particles to the charged particles per unit mass of the irradiated medium.
• laminar flow: non-turbulent, smooth flow of a fluid.
• LET (linear energy transfer): average amount of energy lost per unit of particle spur-track length. low LET : radiation characteristic of electrons, x-rays, and gamma rays. high LET: radiation characteristic of protons and fast neutrons.
• linearity hypothesis: assumption that the biological damage from radiation is linearly proportional to the radiation dose.
• NAS: National Academy of Science.
• NCRP: The National Council on Radiation Protection and Measurements.
• noble gas: a gaseous element with a full octet and therefore unreactive nature.
• NIH: National Institute of Health.
• NRC: The Nuclear Regulatory Commission, or the National Research Council.
• precursor: a precursor of a radioactive isotope is a radioactive chain member which occurs earlier in the decay chain.
• NURE: National Uranium Resource Evaluation.
• quadratic-dose model: model that assumes that excess risk is proportional to the square of the dose.
• quality factor (QF or Q): correction factor use to obtain a common basis for the health hazard from different radiations. The value of Q increases with increasing density of energy deposition in the tissue effected by radiation.
• Rad: traditional unit of physical radiation dose; the unit of deposition of energy in material due to the tissue through which the radiation passes.
• radioactivity: the process of spontaneous change of an atom by the emission of an energetic particle from the nucleus.
• radium: naturally occurring radioactive element whose decay chain includes radon and begins with uranium.
• radon daughters: the short-lived radioisotopes in the decay chain of radon down to lead-210. They are polonium-218, lead-214, bismuth-214, and polonium-214.
• radon: noble gas generated by the decay of radium.
• Reading Prong: geological area near Reading, Pennsylvania characterized by high levels of radon in buildings.
• Rem: traditional unit of "dose equivalent" used to express on a common basis the health hazard from various forms of radiation; the dose equivalent in rem is equal to the product of the quality factor and the physical dose in rad (1 rem = 0.01 sieverts).
• risk coefficient: mortality rate due to lung cancer per unit of exposure after a suitable latent interval.
• secular equilibrium: in the chain of radioactive daughters, secular equilibrium is reached when the activity of each radioactive daughter is equal to the activity of the radioactive parent.
• Sievert (Sv): The S.I. unit of "dose equivalent" used to express on a common basis the health hazard from different kinds of radiations; the dose equivalent in sieverts is equal to the product of the quality factor and the physical dose in grays. (1 Sv = 100 rem).
• synergism: the combination of two (or more) factors that often produce multiplicative health effects.
• threshold hypothesis: hypothesis that below some threshold of radiation the body's DNA repair systems can repair all induced damage and neutralize any effects.
• thoron: radon isotope.
• trachea: main airway of the respiratory system connecting the throat and lungs.
• unattached fraction: 1. the ratio of the specific activity of RaX which is not attached to the atmospheric aerosol to the total specific activity of RaX present in the atmosphere; 2. the ratio of the number of working levels contributed by the unattached RaA, RaB, and RaC to the total number of working levels; 3. the ratio of the specific activity of RaX not attached to the atmospheric aerosol to the total specific activity of RaX which would be present in equilibrium with the specific activity of radon present.
• uranium: naturally occurring radioactive nucleus with a long half-life. The ultimate parent of radon, U-238 makes up 99.3% of all naturally occurring uranium (the remaining 0.7% is U-235).
• working level month (WLM): A unit of exposure to short-lived radon daughters equal to the exposure to one WL for one working month of 170 hours.
• working level (WL): the amount of potential alpha-particle energy dissipated in air by the daughters in equilibrium with 100 pCi/L of radon. One WL = 130,000 MeV (milli electron volts) of alpha-particle energy deposited per liter of air.