Guidance for Radiation Accident Management


Definition of Radiation



Safety Around Radiation Sources

Types of Radiation Exposure

Managing Radiation Emergencies

Basics of Radiation


Alpha particle: A specific particle ejected from a radioactive atom. It has low penetrating power and short range. Alpha particles will generally fail to penetrate the skin. Alpha-emitting atoms can cause health effects if introduced into the lungs or wounds.

Atom: The smallest piece of an element that cannot be divided or broken up by chemical means.

Background radiation: The radiation in man's natural environment, including cosmic rays and radiation from the naturally radioactive elements, both outside and inside the bodies of humans and animals. It is also called natural radiation. Man-made sources of radioactivity contribute to total background radiation levels.

Becquerel: The SI unit of activity 1 disintegration per second; 37 billion Bq = 1 curie. (See conversion factors in the Measurement section.)

Beta particle: A small particle ejected from a radioactive atom. It has a moderate penetrating power and a range of up to a few meters in air. Beta particles will penetrate only a fraction of an inch of skin tissue.

Controlled area: An area where entry, activities, and exit are controlled to help ensure radiation protection and prevent the spread of contamination.

Cosmic rays: High-energy radiation that originates outside the Earth's atmosphere.

Contamination: Deposition of radioactive material in any place where it is not desired, particularly where its presence can be harmful.

Curie: A unit of measure used to describe the amount of radioactivity in a sample of material.

Decontamination: The reduction or removal of contaminating radioactive material from a structure, area, object, or person.

Detector: A device that is sensitive to radiation and can produce a response signal suitable or measurement or analysis. A radiation detection instrument.

Dose: A general term for the quantity of radiation or energy absorbed.

Dose rate: The dose delivered per unit of time. It is usually expressed as rads per hour or in multiples or submultiples of this unit such as millirads per hour. The dose rate is commonly used to indicate the level of hazard from a radioactive source.

Dosimeter: A small, pocket-sized device used for monitoring radiation exposure of personnel. Before use, it is given a charge, and the amount of discharge that occurs is a measure of the accumulated radiation exposure.

Electromagnetic radiation: A traveling wave motion that results from changing electric and magnetic fields. Types of electromagnetic radiation range from those of short wavelength, like x rays and gamma rays, through the ultraviolet, visible, and infrared regions, to radar and radio waves of relatively long wavelengths.

Exposure: A quantity used to indicate the amount of ionization in air produced by x- or gamma-ray radiation. The unit is the roentgen (R). For practical purposes, one roentgen is comparable to 1 rad or 1 rem for X and gamma radiation. The SI unit of exposure is the coulomb per kilogram (C/kg). One R = 2.58 x 10-4 C/kg.

Gamma rays, or gamma radiation: Electromagnetic radiation of high energy. Gamma rays are the most penetrating type of radiation and represent the major external hazard.

Geiger counter or G-M meter: An instrument used to detect and measure radiation.

Gray: The SI unit of absorbed dose; 1 gray = 100 rads.

Inverse square law: The relationship that states that electromagnetic radiation intensity is inversely proportional to the square of the distance from a point source.

Ionization: Production of charged particles in a medium. An orbital electron is stripped from a neutral atom, producing an ion pair (a negatively charged electron and a positively charged atom).

Ionizing radiation: Electromagnetic (X ray and gamma) or particulate (alpha, beta) radiation capable of producing ions or charged particles.

Irradiation: Exposure to ionizing radiation.

Monitoring: Determining the amount of ionizing radiation or radioactive contamination present. Also referred to as surveying.

Rad: The unit of radiation absorbed dose.

Radiation: Energy traveling through space. Some types of radiation associated with radioactivity are alpha and beta particles and gamma and X rays.

Radioactivity: The spontaneous emission of radiation from the nucleus of an unstable atom. As a result of this emission, the radioactive atom is converted, or decays, into an atom of a different element that might or might not be radioactive.

Rem: A measure of radiation dose related to biological effect.

Roentgen: The unit of exposure from X or gamma rays (see exposure).

Sealed source: A radioactive source, sealed in an impervious container that has sufficient mechanical strength to prevent contact with and dispersion of the radioactive material under the conditions of use and wear for which it was designed. Generally used for radiography or radiation therapy. May be classified "Special Form" on shipping papers and packages.

Sievert: The SI unit of dose equivalent; 1 Sv = 100 rem.

X rays: Penetrating electromagnetic radiation whose wavelengths are shorter than those of visible light.

Next | REAC/TS Home