Cerenkov radiation


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Related to Cerenkov radiation: Chernobyl, Tachyons

Cerenkov radiation:

see Cherenkov radiationCherenkov radiation
or Cerenkov radiation
[for P. A. Cherenkov], light emitted by a transparent medium when charged particles pass through it at a speed greater than the speed of light in the medium.
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Cerenkov radiation

Light emitted by a high-speed charged particle when the particle passes through a transparent, nonconducting, solid material at a speed greater than the speed of light in the material. The blue glow observed in the water of a nuclear reactor, close to the active fuel elements, is radiation of this kind. The emission of Cerenkov radiation is analogous to the emission of a shock wave by a projectile moving faster than sound, since in both cases the velocity of the object passing through the medium exceeds the velocity of the resulting wave disturbance in the medium.

Particle detectors which utilize Cerenkov radiation are called Cerenkov counters. They are important in the detection of particles with speeds approaching that of light, such as those produced in large accelerators and in cosmic rays, and are used with photomultiplier tubes to amplify the Cerenkov radiation. These counters can emit pulses with widths of about 10-10 s, and are therefore useful in time-of-flight measurements when very short times must be measured. They can also give direct information on the velocity of the passing particle. See Particle detector

The properties of Cerenkov radiation have been exploited in the development of a branch of gamma-ray astronomy that covers the energy range of about 105–108 MeV. A high-energy gamma ray from a source external to the Earth creates in the atmosphere a cascade of secondary electrons and positrons. This cascade is generated by the interplay of two processes: electron-positron pair production from gamma rays, and gamma-ray emission as the electrons and positrons are accelerated by the electric fields of nuclei in the atmosphere (bremsstrahlung). For a primary gamma ray having an energy of 1012 eV (1 teraelectronvolt), as many as 1000 or more electrons and positrons will contribute to the cascade. The combined Cerenkov light of the cascade is beamed to the ground over an area a few hundred meters in diameter and marks the arrival direction of the initiating gamma ray to about 1°. On a clear, dark night this radiation may be detected as a pulse of light lasting a few nanoseconds, by using an optical reflector. See Bremsstrahlung, Electron-positron pair production

This technique offers a means to study regions of the universe where charged particles are accelerated to extreme relativistic energies. Such regions involve highly magnetized, rapidly spinning neutron stars; supernova remnants; and active galactic nuclei. These same motivations drive the satellite observations of the EGRET instrument of the Compton Gamma-Ray Observatory at lower gamma-ray energies (up to about 104 MeV).

Cerenkov radiation

[chə′reŋ·kəf rād·ē′ā·shən]
(electromagnetism)
Light emitted by a high-speed charged particle when the particle passes through a transparent, nonconducting material at a speed greater than the speed of light in the material.
References in periodicals archive ?
The conclusion is that the tachyonic kinematics do not exclude any range of [q.sup.2] from the kinematically allowed range of permissible momentum transfers, and neutrino pair Cerenkov radiation (or, more generally, tachyon-antitachyon pair production) is allowed in the entire range
Parametrically, they are of the same order-of-magnitude as those given in [35] for (charged) lepton pair Cerenkov radiation, but the threshold is zero for the neutrino pair emission.
Here, we calculate the decay rate and energy loss rate, for a hypothetically tachyonic neutrino flavor, against neutrino pair Cerenkov radiation. It needs to be checked if the absence of a threshold would lead to a disagreement with high-energy data on neutrinos of cosmic origin.
The results given in (27a) and (27b) for the decay rate and energy loss rate due to neutrino pair Cerenkov radiation are not subject to a threshold energy; parametrically they are of the same order-of-magnitude as those given for lepton pair Cerenkov radiation in [35], but the threshold energy is zero.
The neutrino pair Cerenkov radiation process, even if threshold-less, has such a low probability due to the weak-interaction physics involved that it cannot constrain the tachyonic models.
We thus take the opportunity here to correct claims recently made by one of us (U.D.J.) in [35], where a hypothetical cutoff of cosmic neutrino spectrum at the Big Bird energy was related to the threshold energy for (charged) lepton pair Cerenkov radiation and thus to a neutrino mass parameter.
The new data should also help scientists refine models of microwave Cerenkov radiation, says George M.
The enhancement of Lorentz-violating effects with the neutrino energy makes also the study of neutrino velocity and Cerenkov radiation a sensitive probe of Lorentz invariance with high-energy neutrinos.
In particular, some decays with neutrinos in the final state can become forbidden above certain threshold energy; similarly, some forbidden processes can become allowed, including Cerenkov radiation of one or more particles.