Il´ja Mikhailovich Frank
Born: 23 October 1908, Leningrad (now Saint Petersburg), Russia
Died: 22 June 1990, Moscow, USSR (now Russia)
Affiliation at the time of the award: University of Moscow, Moscow, USSR, P.N. Lebedev Physical Institute, Moscow, USSR
Prize motivation: "for the discovery and the interpretation of the Cherenkov effect"
Prize share: 1/3
In certain media the speed of light is lower than in a vacuum and particles can travel faster than light. One result of this was discovered in 1934 by Pavel Cherenkov, when he saw a bluish light around a radioactive preparation placed in water. Ilya Frank and Igor Tamm explained the phenomenon in 1937. On their way through a medium, charged particles disturb electrons in the medium. When these resume their position, they emit light. Normally this does not produce any light that can be observed, but if the particle moves faster than light, a kind of backwash of light appears.