Cherenkov radiation

Cherenkov radiation or Cerenkov radiation [for P. A. Cherenkov], light emitted by a transparent medium when charged particles pass through it at a speed greater than the speed of light in the medium. The effect, discovered by Cherenkov in 1934 while he was studying the effects of gamma rays on liquids and explained in 1937 by I. E. Tamm and I. M. Frank, is analogous to the creation of a sonic boom when an object exceeds the speed of sound in a medium. The light is emitted only in directions inclined at a certain angle to the direction of the particles' motion dependent upon the particles' momentum. Thus, by simply measuring the angle between the radiation and the path of the particles, the particles' speed may be determined. The effect is used in the Cherenkov counter, a device for detecting fast particles and determining their speeds or distinguishing between particles of different speeds.

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Cherenkov radiation

Light produced by charged particles when they pass through an optically transparent medium at speeds greater than the speed of light in that medium. For example, when electrons from a nuclear reactor travel through shielding water, they do so at a speed greater than that of light through water and they displace some electrons from the atoms in their path. This causes emission of electromagnetic radiation that appears as a weak bluish-white glow. The phenomenon is named for Pavel A. Cherenkov (1904–1990), who discovered it; he shared a 1958 Nobel Prize with Igor Y. Tamm (1895–1971) and Ilya M. Frank (1908–1990), who interpreted the effect.