Radon Glossary R-Z

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.

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