History

• Discovered by Mallet in 1926
  • Observed that the light had a continuous spectrum, no band structure like fluorescent light.
• Studied by Cerenkov from 1934-1938
  • Proved that it was not a fluorescence effect
  • Found that the light was partially polarized
• Classical theoretical explanation by Frank and Tamm in 1937
  • First to correctly explain the phenomena

Physics

• When a fast moving charged particle moves through an dielectric medium it causes local, non-isotropic polarizations in the atoms of the dielectric.
• These atoms return to normal states by emitting light.
• If the velocity of the particle is less than the velocity of light in the medium, the light is destroyed by destructive interference.
• If the velocity of the particle is greater than the velocity of light in the medium, the light remains due to constructive interference.
• Wavelength and direction of light are governed by the Cerenkov equation:

  

  Where theta=direction of light, _=v/c, c=speed of light in vacuum, v=velocity of particle, and n=refractive index of dielectric

• From this equation one can see that there is a critical velocity below which Cerenkov radiation cannot occur.

  

Conditions for Cerenkov in Reactor

• Water has an index of refraction of about 4/3, so only particles traveling faster than .75c will produce Cerenkov radiation.
• .75c corresponds to threshold energies of:

  260keV electrons
      475MeV protons 960MeV deuterons 2GeV Alpha particles 

• Many electrons in the reactor will satisfy this condition and produce Cerenkov radiation, but no protons or heavier particles will.
• Cerenkov radiation in water has a peak intensity at about 400nm, which is at the extreme blue end of the visible light spectrum.
• In different materials, the threshold energies will usually be much higher for electrons:

  Helium 61MeV Argon 21MeV Air
      21MeV Nitrogen 21MeV CO2 16MeV 

References

1. Jelley, J.V. Cerenkov Radiation and its Applications, New York, Pergamon Press, 1958.
2. Madey, Robert W. Cerenkov Light Production in a Water Moderated Nuclear Reactor, Ann Arbor, 1964.
3. Ypsilantis81 T. Ypsilantis, Cherenkov ring imaging, Physica Scripta 23 (1981) 371.
4. Ypsilantis94 T. Ypsilantis and J. Seguinot, Theory of ring imaging Cherenkov counters, Nucl. Instrum. Meth. Phys. Res. A343 (1994) 30.