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Cherenkov, Pavel Alekseyevich

effect speed glow frank

[che reng kof] (1904–90) Russian physicist: discoverer of the Cherenkov effect.

A graduate of Voronezh State University, Cherenkov worked at the Lebedev Institute of Physics from 1930. In 1934 he first saw the blue light emitted from water exposed to radioactivity from radium, which had been observed by many earlier workers who had assumed it to be fluorescence. Cherenkov soon found that this could not be the explanation because the glow is shown by other liquids; and he found it was caused by fast electrons (beta rays) from the radium and that it was polarized. By 1937, working with I M Frank (1908–90) and I E Tamm (1895–1971), he was able to explain the effect. They showed that in general the effect arises when a charged particle traverses a medium (liquid or solid) when moving at a speed greater than the speed of light in that medium, and they were able to predict its direction and polarization. The effect is dramatically visible in the blue glow in a uranium reactor core containing heavy water; and it is used in a method for detecting high-energy charged particles. A counter of this type, using a photomultiplier, can detect single particles. The effect has some analogy with the shock wave and sonic boom produced when an aircraft exceeds the speed of sound in air. Cherenkov, Frank and Tamm shared a Nobel Prize in 1958.

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