Tuesday, July 15, 2014

Pavel Cherenkov and the Blue Light

Pavel Cherenkov
(1904 - 1990)
On July 15, 1904, Soviet physicist Pavel Alekseyevich Cherenkov was born. He shared the Nobel Prize in physics in 1958 with Ilya Frank and Igor Tamm for the discovery of Cherenkov radiation, made in 1934. Cherenkov radiation is a faint blue light emitted by electrons passing through a transparent medium when their speed exceeds the speed of light in that medium. This sounds pretty weird, doesn't it. With Einstein he have learned that nothing exceeds the speed of light. But Cherenkov radiation caused by particles faster than the speed of light? Well, it depends of the medium in which the light is distributing. In water as e.g. the speed of light is slower than in vacuum. But, let's get back to Cherenkov...

Cherenkov was born in 1904 in present day Voronezh Oblast, Russia. He enrolled at Voronezh State University, where he graduated in 1928, and became senior researcher at the Lebedev Institute of Physics two years later. In 1959, the professor of experimental phyiscs was appointed head of the institute's photo-meson processes laboratory. He remained a professor for fourteen years. In 1970, he became an Academician of the USSR Academy of Sciences.

Cherenkov made his most important discovery in 1934. He observed the emission of blue light from a bottle of water subjected to radioactive bombardment. This sounds trivial at first, but associated with charged atomic particles moving at velocities faster than the speed of light in the local medium, it proved to be of great importance in subsequent experimental work in nuclear physics, and for the study of cosmic rays. It was later on named the Cherenkov effect.

Cherenkov radiation is widely used to facilitate the detection of small amounts and low concentrations of biomolecules. Also, it can be used to detect high-energy charged particles. In pool-type nuclear reactors, high-energy electrons are released as the fission products decay. The glow continues after the chain reaction stops, dimming as the shorter-lived products decay. Furthermore, when a high-energy gamma photon or cosmic ray interacts with the Earth's atmosphere, it may produce an electron-positron pair with enormous velocities. The Cherenkov radiation from these charged particles is used to determine the source and intensity of the cosmic ray or gamma ray. Cherenkov radiation can also be used to determine properties of high-energy astronomical objects that emit gamma rays, such as supernova remnants and blazars.

Pavel Cherenkov also shared in the development and construction of electron accelerators and in the investigation of photo-nuclear and photo-meson reactions. He passed away on January 6, 1990.

At yovisto, you may be interested in a video lecture on the "High Energy Universe" by Rene Ong.



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