Half-life is the time required for half of any quantity of identical radioactive atoms to undergo radioactive decay, so that half of the atoms in the substance are no longer emitting radiation and are no longer considered to be radioactive. Doses to an individual are usually measured in millirem. Radiation, as used in this section, does not include non-ionizing radiation, such as radio or microwaves, or visible, infrared, or ultraviolet light. Radioactive decay is the spontaneous natural process by which an unstable radioactive nucleus releases energy or particles. Residual radioactivity means radioactive contamination or activation products that remain following decontamination and dismantlement of the facility.
Radioactive contamination is radioactive material that is deposited on a nonradioactive surface.
The material may be deposited from the air, or it may be dissolved in water and subsequently deposited into material such as concrete. Radioactive contamination is generally located on or near the surface of materials like metal or high-density concrete or painted walls. It would travel farther into unpainted surfaces or lower density concrete. Radioactive contamination can usually be removed from surface areas by washing, scrubbing, spraying, or, in extreme cases, by removing the outer surface of the material. Contaminated materials are transported through the facility by workers, equipment, and to some degree through the air.