Chemistry & Environmental Dictionary

Radiation - RTECS

Radiation (radiant energy)

energy in the form of electromagnetic waves. Different forms of radiation comprise the electromagnetic spectrum and are characterized by their different wave frequency and wavelength. Radiation is emitted from matter in the form of photons. The following types of radiation make up the electromagnetic spectrum (in order of decreasing energy and increasing wavelength): cosmic rays, gamma rays, x-rays, UV (ultraviolet) rays, visible light rays, infrared, microwave, radio (Hertzian) waves and electric waves. These electromagnetic waves have no mass and are not electrically charged. The shortest wavelength forms of radiation are most penetrating and are the most damaging to living tissue.


the spontaneous emission of radiation and atomic particles from unstable elements. Radioactivity is measured in terms of half-lives and is not affected by physical state or chemical combination.

Rare Earth Metals

see Lanthanides

Rare Gasses

see Noble Gasses

RCRA (Resource Conservation and Recovery Act)

The principle law in the United States that governs the disposal of solid waste and the management of both solid and hazardous waste.

RDF (refuse derived fuel)

a product of a mixed waste processing system from which some recycleable wastes and som non-combustible materials have been removed. The remaining material is used as a fuel to create energy.

Recommended Exposure Limit (REL)

The maximum recommended exposure limit. With the occasional exception in some jurisdictions, REL's are only suggested industry practices and are not enforced by legal regulations (as are PEL's, which are regulated in the U.S. by OSHA under 29 CFR).

Relative Error

the ratio of the absolute error to the exact value.

Relative error =(exact value - observed value)/(exact value)


Registry of Toxic Effects of Chemical Substances.

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