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gamma-ray astronomy

(Encyclopedia)gamma-ray astronomy, study of astronomical objects by analysis of the most energetic electromagnetic radiation they emit. Gamma rays are shorter in wavelength and hence more energetic than X rays (see...

pacemaker, artificial

(Encyclopedia)pacemaker, artificial, device used to stimulate a rhythmic heartbeat by means of electrical impulses. Implanted in the body when the heart's own electrical conduction system (natural pacemaker) does n...

magnetic resonance

(Encyclopedia)magnetic resonance, in physics and chemistry, phenomenon produced by simultaneously applying a steady magnetic field and electromagnetic radiation (usually radio waves) to a sample of atoms and then a...

photoelectric effect

(Encyclopedia)photoelectric effect, emission of electrons by substances, especially metals, when light falls on their surfaces. The effect was discovered by H. R. Hertz in 1887. The failure of the classical theory ...

Prokhorov, Aleksandr Mikhailovich

(Encyclopedia)Prokhorov, Aleksandr Mikhailovich əlyĭksänˈdər mēkhīˈləvĭch prôˈkhərəf [key], 1916–2002, Russian physicist, b. Atherton, Queensland, Australia. In 1923 he was taken to the Soviet Union...

Planck, Max

(Encyclopedia)Planck, Max mäks plängk [key], 1858–1947, German physicist. Seeking to explain the experimental spectrum (distribution of electromagnetic energy according to wavelength) of blackbody radiation, he...

pulsar

(Encyclopedia)pulsar, in astronomy, a neutron star that emits brief, sharp pulses of energy instead of the steady radiation associated with other natural sources. The study of pulsars began when Antony Hewish and h...

liquid crystal

(Encyclopedia)liquid crystal, liquid whose component particles, atoms or molecules, tend to arrange themselves with a degree of order far exceeding that found in ordinary liquids and approaching that of solid cryst...

laser

(Encyclopedia)CE5 Ordinary light sources produce incoherent light, while a laser produces a beam of coherent light. laser [acronym for light amplification by stimulated emission of radiation], device for the cr...

X ray

(Encyclopedia)CE5 Typical X-ray composite spectrum (intensity as a function of frequency) X ray, invisible, highly penetrating electromagnetic radiation of much shorter wavelength (higher frequency) than visibl...