General, Research, Technology

The Vavilov-Cherenkov effect: what you need to know?

In science fiction films, nuclear reactorsand nuclear materials always glow blue. For example, in the first Iron Man movie, Robert Downey Jr.'s Tony Stark character assembles a small nuclear reactor that powers the suit. Interestingly, the characteristic blue glow emanating from the reactor (be it real) is a real phenomenon called the Vavilov-Cherenkov effect. It is because of him that the water surrounding nuclear reactors really glows bright blue. This glow was first noticed by physicist Sergei Vavilov and his graduate student Pavel Cherenkov in the laboratory of the Physics and Mathematics Institute in 1933, when they saw that a bottle of water, exposed to radiation, glowed blue. In 1958, for this discovery, Cherenkov received the Nobel Prize in Physics, sharing it with Ilya Frank and Igor Tamm, who experimentally confirmed the existence of the effect. Although it was possible to explain the Vavilov-Cherenkov radiation only after Albert Einstein published the special theory of relativity, its existence was predicted by the English polymath Oliver Heaviside back in 1888.

When certain particles, for example, cosmic particles, move faster than the speed of light in a certain medium, Vavilov-Cherenkov radiation appears.

What is Vavilov-Cherenkov radiation?

It is impossible to exceed the speed of light in a vacuum.But when an elementary particle is in a dense medium, it can exceed this limit. So, a particle accelerated in a vacuum can fly into water at a speed of, for example, 299,799 kilometers per second: since the laws of physics prohibit an instantaneous change in speed, a particle, being in a medium, flies some distance faster than the local limit. During the flight, the particle slows down by losing energy, which needs to go somewhere.

As Tass writes in an article on the NobelPrize in physics in 1958, when the car brakes, kinetic energy goes into heating the brakes, and superluminal particles give off an excess in the form of quanta of radiation, that is, light. One of the features of Cherenkov radiation is that it is mainly in the continuous ultraviolet spectrum, and not in bright blue.

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Interestingly, Cherenkov radiation is similar tosound boom effect. For example, if an airplane in the air moves slower than the speed of sound, then the deflection of the air around the wings of the airplane occurs smoothly. However, if the speed of movement exceeds the average speed of sound, then a sudden change in pressure occurs and shock waves propagate from the aircraft in a cone at the speed of sound.

You've probably noticed that Tony Stark's nuclear reactor shines with a blue light.

How exactly the radiation appears, in detailchecked by Vavilov, Cherenkov, Tamm and Frank. Since Vavilov died in 1951, three physicists received the Nobel Prize seven years later. Thanks to their work, today you can observe the Vavilov-Cherenkov radiation almost anywhere. When. provided, of course, that you know where to look.

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Eerie blue light

When Cherenkov radiation passes through water,charged particles move faster than light through this medium. Thus, the light you see has a higher frequency (or shorter wavelength) than the normal wavelength. Insofar as in Cherenkov radiation, light with a short wavelength predominates, the glow appears to be blue... This is because the fast movingthe charged particle excites the electrons of the water molecules, which absorb energy and release it as photons of light, returning to equilibrium. Usually some of these photons cancel each other out (destructive interference) so that the glow is not visible. But when a particle moves faster than light can pass through water, the shock wave creates constructive interference, which we see as glow.

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The Cherenkov radiation spectrum is continuous, and its intensity increases with frequency; this is what gives it the eerie blue that you see in photographs of swimming pool reactors.

Fortunately, the Vavilov-Cherenkov radiation can beuse it not only to make the water in the nuclear laboratory glow blue. Thus, in a pool-type reactor, the amount of blue glow can be used to measure the radioactivity of spent fuel rods. Radiation is used in particle physics experiments - physicists hope that it will help them determine the nature of the particles under study.

Moreover, Cherenkov radiation arises whenWhen cosmic rays and charged particles interact with the Earth's atmosphere, detectors are used to measure these phenomena, detect neutrinos, and study gamma-ray emitting astronomical objects such as supernova remnants.

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Interestingly, if the relativistic chargedparticles hit the vitreous body of the human eye, then you can see flashes of Cherenkov radiation, for example, from exposure to cosmic rays or as a result of a nuclear accident, so it is probably best to refrain.