What is Cherenkov radiation

During the passage of a particle through a certain material medium at a speed that exceeds the speed of light for a given medium, one can observe characteristic radiation, which has received the name Cherenkov radiation (but it is more correct to call it the Cherenkov effect - Vavilov). This phenomenon will be discussed in this material.

Vavilov - Cherenkov radiation in the coolant of the ATR research reactor at Idaho National Laboratory. By Argonne National Laboratory - originally posted to Flickr as Advanced Test Reactor core, Idaho National LaboratoryUploaded using F2ComButton, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php? curid = 27024528

Cherenkov radiation and the history of its discovery

So, during the passage of light, for example, through glass (or any material that transmits light), light passes through it much slower than light passes in a vacuum.

Here you can draw an analogy with air travel. So any passenger still spends time on intermediate landings, when compared with a direct flight.

Roughly the same thing happens with light rays, they are slowed down, interacting with the atoms of the medium, and are simply unable to move as fast as in a vacuum.

So, according to the theory of relativity, not a single material body, including fast high-energy elementary particles that are unable to move at a speed corresponding to the speed of propagation of a light flux in an airless space.

But this limitation has nothing to do with the speed of movement in transparent environments. So, for example, in glass, light rays propagate at a speed of 60% to 70% of the speed of propagation of a light flux in an airless space.

And it turns out that there are no obstacles for a sufficiently fast particle (say, for a proton or an electron) to move faster than the speed of the light flux in such a medium.

So in the already distant 1934 P. Cherenkov under the leadership of S.I. Vavilov luminescence of liquids under the influence of gamma radiation.

In the course of scientific experiments, a faint bluish glow was discovered, which is currently called the Cherenkov radiation (but it would be more correct to call it the Cherenkov-Vavilov effect).

This radiation was triggered by the so-called fast electrons, which were knocked out of the atoms of the material by gamma radiation. As it turned out later, such electrons moved at a speed greater than the speed of light in the medium under consideration.

In fact, this is a kind of optical type of shock wave, which is provoked in the atmosphere by a supersonic aircraft, which overcomes the sound barrier.

To understand the process, you can recall the Huygens Principle, according to which literally every point on the path of wave propagation can be taken as a source of secondary waves.

So, according to the Huygens principle, let's imagine that the waves diverge outward in concentric circles, while their speed of propagation is equal to the speed of light. In addition, each subsequent wave emanates from the next point located on the path of the particle.

And if, in this case, a particle with a speed greater than the speed of light in the medium, then it is ahead of the waves, and the peaks of the amplitude of these waves are responsible for the formation of the wavefront of Cherenkov radiation.

In this case, the radiation propagates in a cone around the path of the particle, and this angle directly depends on the initial velocity of the particle and on the speed of the light flux in the medium under consideration.

Where is Cherenkov radiation used in the modern world

This observed effect is extremely useful for the physics of elementary particles, since having learned the magnitude of the angle, physicists can quite easily determine the speed of the particle that caused this radiation.

Note. For his discovery in 1958, Cherenkov, together with I. Tamm, as well as with I. Frank received the Nobel Prize in Physics. So in 1937, Tamm and Frank finally figured out the mechanism of the formation of glow, and then also made an assumption about its presence in solids and gases.

So the combination with other measurement methods makes it possible to register elementary particles in laboratory facilities.

At the moment, Cherenkov radiation is actively used in modern laboratory detectors.

In addition, Cherenkov radiation can be observed even with the naked eye in small reactors, which are often mounted on the bottom of the pool to guarantee radiation protection. In this case, the core of the reactor is surrounded by a blue glow, which is the Cherenkov radiation.

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