gamma radiation, high-energy photons emitted as one of the three types of radiation resulting from natural radioactivity . It is the most energetic form of electromagnetic radiation , with a very short wavelength (high frequency). Wavelengths of the longest gamma radiation are less than 10 −10 m, with frequencies greater than 10 18 hertz (cycles per sec). Gamma rays are essentially very energetic X rays ; the distinction between the two is not based on their intrinsic nature but rather on their origins. X rays are emitted during atomic processes involving energetic electrons. Gamma radiation is emitted by excited nuclei (see nucleus ) or other processes involving subatomic particles; it often accompanies alpha or beta radiation, as a nucleus emitting those particles may be left in an excited (higher-energy) state. The applications of gamma radiation are much the same as those of X rays, both in medicine and in industry. In medicine, gamma ray sources are used for cancer treatment and for diagnostic purposes. Some gamma-emitting radioisotopes are also used as tracers (see radioactive isotope ). In industry, principal applications include inspection of castings and welds. Data from artificial satellites and high-altitude balloons have indicated that a flux of gamma radiation is reaching the earth from outer space, thus opening up the field of research known as gamma-ray astronomy .
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
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