• 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.