Named for the Russian
physicist Pavel Alekseyevich Cherenkov, Cherenkov
radiation is emitted by any
particle travelling faster than the
speed of light in the
medium in which it is travelling. As it
collides with
particles, it slows down and the lost
kinetic energy is released in the form of
photons. When the
particle slows down enough to be travelling at exactly the
speed of light in the
medium, it emits an
optical boom, exactly analogous to the
sonic boom emited by an object passing the
speed of sound in its
medium.
This radiation is emitted in a forward cone, and can be seen with the naked eye (as a blue glow) if there are enough particles creating it. The Cherenkov radiation
emitted by even a single such particle can be detected by devices such as photomultiplier tubes, and is crucial for measurements made at neutrino observatories, such as SNO.