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electromagnetic radiation

(Encyclopedia)CE5 Electromagnetic spectrum electromagnetic radiation, energy radiated in the form of a wave as a result of the motion of electric charges. A moving charge gives rise to a magnetic field, and if ...

Cherenkov radiation

(Encyclopedia)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. ...

ultraviolet radiation

(Encyclopedia)ultraviolet radiation, invisible electromagnetic radiation between visible violet light and X rays; it ranges in wavelength from about 400 to 4 nanometers and in frequency from about 1015 to 1017 hert...

adaptive radiation

(Encyclopedia)CE5 Adaptive radiation in Hawaiian honey-creepers adaptive radiation, in biology, the evolution of an ancestral species, which was adapted to a particular way of life, into many diverse species, e...

radiation chemistry

(Encyclopedia)radiation chemistry: see radiochemistry. ...

radiation sickness

(Encyclopedia)radiation sickness, harmful effect produced on body tissues by exposure to radioactive substances. The biological action of radiation is not fully understood, but it is believed that a disturbance in ...

radiation weapon

(Encyclopedia)radiation weapon or radiological weapon, a bomb or warhead that uses conventional chemical explosives to disperse radioactive material, sometimes called a “dirty bomb.” Designed to produce radiati...

synchrotron radiation

(Encyclopedia)synchrotron radiation, in physics, electromagnetic radiation emitted by high-speed electrons spiraling along the lines of force of a magnetic field (see magnetism). Depending on the electron's energy ...

Cerenkov radiation

(Encyclopedia)Cerenkov radiation: see Cherenkov radiation. ...

Johnson, Allen

(Encyclopedia)Johnson, Allen, 1870–1931, American historian, b. Lowell, Mass. He was professor of history at Iowa (now Grinnell) College (1898–1905), Bowdoin College (1905–10), and Yale (1910–26). He achiev...