Cerenkov radiation

[Zweistein]

Quote:

Reading the thread about the fate of Louis Slotin, following phrase :

<The "blue glow" is Cerenkov radiation which occurs when subatomic charged particles move "through a medium at a speed greater than the velocity of light in the medium.">

Can someone explain this phrase, I don't understand it.

[Bosda Di'Chi of Tricor]

Could you please provide a link?

[Zweistein]

Thread about Louis Slotin:

http://www.nukes.org/MAp/slotin.html

[Ankh_Too]

Most Cerenkov radiation is found at water cooled nuclear reactors such as the one pictured here. The speed of light in water is (I think) .7 C, and Cerenkov radiation occurs when charged particles move through the water faster than the photons are travelling. Since the photons are not travelling at the "normal" speed of light through a vaccum, relativity is not violated by the beta particles travelling faster than the photons. The page referenced above goes into much greater detail about the polarization and interferences that actually create the radiation.

[Homer]

Why does it emit light in the blue wavelength? What circumstances would be required to obtain a red-shift in Cerenkov radiation? Don't say move it away fast.

--Tim

[Pleonast]

Cerenkov radiation is analogous to a sonic boom. When a particle (say, a bullet) moves through air faster than the speed of sound in air, it emits a sonic boom. When a particle (say, a neutron) moves through water faster than the speed of light in water, it emits Cerenkov radiation. In case it isn't clear, the speed of light in most substances is less than Eistein's constant (the speed of light in a vacuum). Which is how you can have a particle going faster than light in the first place (but still slower than Einstein's constant).

IIRC, most of the energy from Cerenkov radiation is at UV frequencies. We only see the low-frequency tail of the distribution (i.e. blue). I don't think you can get a red Cerenkov radiation, because more energy is always going to go into the higher frequencies. But if the speed of light in the substance were low enough, all visible frequencies could be equally excited. That would give a white effect.