Cherenkov Radiation

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Cherenkov radiation is a form of radiation that is emitted from a medium when a charged particle moves through the medium at a speed greater than the speed of light in the medium (also called phase velocity of light in the medium). When the charged particle moves at this rate, it energizes the surrounding particles, and as those particles decay into their ground state, they lose energy in the form of Cherenkov radiation, which often takes the form of visible light.

Cherenkov radiation is often explained by analogy with a sonic boom. When a plane accelerates faster than the speed of sound, the sound waves cannot move faster than the plane, so the plane ends up pushing the waves themselves forward, causing a build up that results in a sonic boom. Similarly, Cherenkov radiation can be viewed as a build-up of photonic energy by the superluminal radiation, which is released in the form of visible light.

Discovery of Cherenkov Radiation

Cherenkov radiation gets its name from the Russian physicist Pavel Alekseyevich Cherenkov, who was one of the physicists credited with discovering the effect. Cherenkov first discovered the effect in 1934, when he noticed a blue glow emanating from a bottle of water as it was bombarded with radiation. He received the 1958 Nobel Prize in Physics for the discovery and subsequent work on the interpretation of the phenomenon, sharing the Nobel Prize with colleagues Il´ja Mikhailovich Frank and Igor Yevgenyevich Tamm.

Cherenkov Radiation & Relativity

This is not a case of violating the theory of relativity!

The theory of relativity indicates that nothing can accelerate faster than the speed of light in a vacuum. (Or, more specifically, the theory of relativity indicates that it would require an infinite amount of energy to accelerate faster than the speed of light.) However, this situation doesn't involve accelerating in this way, so it is allowed by and consistent with the theory of relativity.

The key piece of information to understand is that the speed of light in different media is different. A charged particle, such as an electron, which is moving at very nearly the speed of light within a vacuum can leave the vacuum, entering into a gas-filled chamber, and the speed of light within the chamber is slightly lower. The electron retains the bulk of its energy, momentum, and speed during this movement ... and therefore if all the variables are right, the electron is now moving at superluminal speeds within the medium, though not moving faster than the speed allowed by relativity. 

Also Known As: Vavilov-Cherenkov radiation, Cerenkov radiation, Cherenkov effect, Vavilov-Cherenkov effect
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