A Cherenkov detector (pronunciation: /tʃɛrɛnˈkɔv/; Russian: Черенко́в) is a type

particle detector In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify ionizing elementary particle, particles, such as t ...

designed to detect and identify particles by the

Cherenkov Radiation Cherenkov radiation () is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium (such as distilled water) at a speed greater than the phase velocity (speed of propagation of a wavefro ...

produced when a charged particle travels through the medium of the detector.

Fundamental

A particle passing through a material at a velocity greater than that at which light can travel through the material emits light. This is similar to the production of a

sonic boom A sonic boom is a sound associated with shock waves created when an object travels through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding similar to an explosion or a thunderclap to ...

when an airplane is traveling through the air faster than sound waves can move through the air. The direction this light is emitted is on a cone with angle θ_c about the direction in which the particle is moving, with cos(θ_c) = (c = the vacuum

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time i ...

, n = the

refractive index In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...

of the medium, and v is the speed of the particle). The angle of the cone θ_c thus is a direct measure of the particle's speed. The Frank–Tamm formula gives the number of photons produced.

Aspects

Most Cherenkov detectors aim at recording the Cherenkov light produced by a primary charged particle. Some sensor technologies explicitly aim at Cherenkov light produced (also) by secondary particles, be it incoherent emission as occurring in an electromagnetic

particle shower In particle physics, a shower is a cascade of secondary particles produced as the result of a high-energy particle interacting with dense matter. The incoming particle interacts, producing multiple new particles with lesser energy; each of these t ...

or by coherent emission, for example Askaryan effect. Cherenkov radiation is not only present in the range of visible light or UV light but also in any frequency range where the emission condition can be met i.e. in the radiofrequency range. Different levels of information can be used. Binary information can be based on the absence or presence of detected Cherenkov radiation. The amount or the direction of Cherenkov light can be used. In contrast to a

scintillation counter A scintillation counter is an instrument for detecting and measuring ionizing radiation by using the Electron excitation, excitation effect of incident radiation on a Scintillation (physics), scintillating material, and detecting the resultant li ...

the light production is instantaneous.

Detector types

In the simple case of a threshold detector, the mass-dependent threshold energy allows the discrimination between a lighter particle (which does radiate) and a heavier particle (which does not radiate) of the same energy or momentum. Several threshold stages can be combined to extend the covered energy range. Cherenkov threshold detectors have been used for fast timing and

time of flight Time of flight (ToF) is the measurement of the time taken by an object, particle or wave (be it acoustic, electromagnetic, etc.) to travel a distance through a medium. This information can then be used to measure velocity or path length, or as a w ...

measurements in particle detectors. More elaborate designs use the amount of light produced. Recording light from both primary and secondary particles, for a Cherenkov calorimeter the total light yield is proportional to the incident particle energy.

Examples

Cherenkov detectors are primarily used in

Particle Physics Particle physics or high-energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the s ...

experiments:

LHCb

The

LHCb The LHCb (Large Hadron Collider beauty) experiment is a particle physics detector collecting data at the Large Hadron Collider at CERN. LHCb specializes in the measurements of the parameters of CP violation in the interactions of b- and c-hadro ...

experiment at

CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...

employs the

RICH Rich may refer to: Common uses * Rich, an entity possessing wealth * Rich, an intense taste, flavor, color, sound, texture, or feeling **Rich (wine), a descriptor in wine tasting Places United States * Rich, Mississippi, an unincorporated c ...

detector. As a charged particle travels through the medium of the detector (C4F10 for RICH-1 and CF4 for RICH-4) it emits Cherenkov radiation in a ring pattern. Photon detectors are then used to detect the Cherenkov photons and by measuring the angle at which the Cherenkov photons are produced the velocity of the particle is determined. This can then be used along with information obtained from other parts of the detector (e.g. momentum and charge of the particle) to identify the particle type.

Super-Kamiokande

The

Super-Kamiokande Super-Kamiokande (abbreviation of Super-Kamioka Neutrino Detection Experiment, also abbreviated to Super-K or SK; ) is a neutrino detector, neutrino observatory located Kamioka Observatory, under Mount Ikeno near the city of Hida, Gifu, Hida, ...

detector in Japan is Cherenkov detector used to detect

neutrinos A neutrino ( ; denoted by the Greek letter ) is an elementary particle that interacts via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small ('' -ino'') that it ...

. It consists of 50,220 tonnes of ultrapure water which is used as the medium. As neutrinos pass through the water they have a small chance to interact with the

electrons The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

or nuclei in the water, producing either an

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

or a

muon A muon ( ; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 '' e'' and a spin of ''ħ'', but with a much greater mass. It is classified as a ...

. These are highly energetic and produce a cone of Cherenkov radiation as they travel through the water. The Cherenkov light is detected as a circular feature by the photomultiplier tubes placed around the detector and it is possible to distinguish between muons and electrons by the fuzziness of the rings. Muons are weakly interacting particles and can travel through the detector un-impeded, producing sharp rings, while electrons will scatter in the water producing rings that are much more fuzzy.

References

Particle detectors Russian inventions Soviet inventions Particle physics