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Cherenkov Radiation

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Photons of light are produced when a charged particle travels through a transparent medium at a speed greater than the speed of light in that medium. The medium may be a gas, liquid or solid. These photons are referred to as Cherenkov radiation in honor of the Russian physicist Pavel A. Cherenkov for his discovery of this unique radiation and his basic research to measure the properties of the radiation and the phenomenon upon which the radiation finds its origin, now referred to as the Cherenkov effect.

Definition

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In order for a charged particle to radiate electromagnetic waves, it must generally undergo an accelerated motion.However, a charged particle moving uniformly in a material medium can also emit radiation if it is moving with a velocity greater than that of light in the medium. This radiation is possible only if the speed of light in the material medium is less than that in a vacuum or equivalently, the refractive index of the medium is greater than unity. The radiation due to a charged particle moving uniformly in a material medium was first observed by Cherenkov in 1934. After his name, this radiation is called the Cherenkov radiation.
Cherenkov radiation is produced when the charged particles pass through any matter with a velocity larger than the velocity of light in the medium. The major problem of Cherenkov radiation is the energy loss due to ionization or excitation.

  • The yield of Cherenkov radiations per unit wavelength is proportional to $\frac{1}{\lambda^{2}}$. Therefore, the emission is concentrated in the short wavelength region of the spectrum. At extremely short wavelengths, the yield gradually drops off because the refractive index (as a function of wavelength) approaches to unity.
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Detectors

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The Cherenkov radiation detector is a category of radiation detectors is based on the light that is emitted by a sufficiently fast charged particle passing through an optically transparent medium with index of refraction greater than 1. The light is emitted whenever the velocity of a charged particle exceeds that of light in the medium through which it is passing. Detectors based on sensing the Cherenkov light are widely used in high energy physics experiments but have only limited use for the lower energy radiations of interest. For particles in the tens of MeV range or lower, electrons are the only category to achieve sufficiently high velocity to emit Cherenkov light in available materials. Applications therefore involve either fast primary electrons such as beta particles or energetic secondary electrons produced in gamma ray interactions. Cherenkov detectors bear some similarity to common scintillation detectors, in that the emitted light is converted into an electrical signal by a photomultiplier tube in optical contact with the Cherenkov medium. However, several important properties are quite different.