Radon Glossary 



  • Absolute risk:  Expression of excess risk due to exposure as the arithmetic difference between the risk among those exposed and that obtained in the absence of exposure.

  • Actinide:  Element with an atomic number from 90 through 103.

  • Action levels:  The inner-most level around the operating level on a control chart.  Any corrective action is intended to bring the measured values back toward the operating level and within the action levels.

  • Active detector:  A radiation detector which processes and displays a signal at the time of detection.

  • Activity:  The rate of decay of a radioactive material.  The traditional unit is the curie (Ci).  The SI unit is the becquerel (Bq).

  • Acute exposure:  Radiation exposure in a short period of time (e.g. hours).

  • Aerosol:  Any material (liquid or solid) of fine enough particle size that when dispersed in air will remain suspended.

  • Agreement State:  Any state with which the U.S. Nuclear Regulatory Commission (NRC) has entered into an effective licensing agreement under Section 274(b) of the Atomic Energy Act of 1954, as amended, to enable the state to regulate source, special nuclear, and byproduct materials.

  • ALARA (As Low As Reasonably Achievable):  A principle of radiation protection philosophy that requires that exposures to ionizing radiation be kept as low as reasonably achievable, economic and societal factors being taken into account. The ALARA principle is satisfied when the expenditure of further resources would be unwarranted by the reduction in exposure that would be achieved.

  • Alpha (α) decay:  A process of radioactive decay wherein the mass number of the original atom decreases by 4 and the atomic number decreases by two with the difference made up via the emission of an alpha particle.

  • Alpha (α) particle:  A completely-ionized nucleus of a helium-4 (He-4) atom which results from the radioactive decay of heavy elements.  Alpha particles have a mass of 4 amu, a charge of +2 ec, but relatively low penetrating powers.  Alpha particles can be completely stopped by a few inches of air, a sheet of paper, or the dead outer layers of skin.

  • Aquifer:  A saturated geologic feature that is permeable and capable of transmitting usable quantities of water under ordinary hydraulic gradients. 

  • Atomic Energy Act (AEA):  Law passed originally in 1946 and extensively revised in 1954 that governs production and use of radioactive materials (i.e., byproduct material, source material, and special nuclear material) for defense and peaceful purposes and regulation of such radioactive materials to protect public health and safety. The Act provides authority for licensing of nuclear activities by the U.S. Nuclear Regulatory Commission or Agreement States and regulation by the U.S. Department of Energy of its atomic energy defense, research and development activities.

  • Atomic number (Z):  The number of protons in a nucleus.  An element is defined by the number of protons.


  • Background:  A value associated with a null exposure.

  • Background level:  The ambient concentration of radon.

  • Background radiation:  The ambient, natural radiation from terrestrial sources (e.g. radon) or extraterrestrial sources (e.g. solar radiation, cosmic rays).  Also includes artificial sources, such as from fallout from the atmospheric testing of nuclear weapons or nuclear reactor accidents.

  • Becquerel (Bq):  The SI unit for radioactivity with the dimensions of disintegrations per second (s-1).

  • Beta (β) decay / beta-plus/minus (β) decay:  A process of radioactive decay wherein the atomic number changes by one with no change in mass number with the difference in charge made up by the emission of a beta particle.

  • Beta (β) particle:  An energetic electron emitted by a nucleus during radioactive decay.  Usually refers to a beta-minus (β-) particle, which is an electron, but may be generally used to indicate either beta-minus or beta-plus emission.

  • Beta-minus (β-) particle:  An energetic electron emitted during radioactive decay.

  • Beta-plus (β+) particle:  An energetic positron (anti-electron) during radioactive decay.


This page is under construction.  We apologize for any inconvenience. 


Order Radon Test Kits

Check Your Results

< Back to Radon Page                                 


Copyright ©2015 Radiation Safety Services, Inc.

HACKER SAFE certified sites prevent over 99.9% of hacker crime.

Home | Consulting | Laboratory | Calibration | Radon | Contact Us