For 10 points, name this often-blue radiation emitted by charged particles traveling faster than the speed of light in their medium.
One device that measures this phenomenon uses a perfluorohexane radiator and measures uses an image of a 2-dimensional ring produced by it to measure the angle at which it occurs. Water-medium devices that measure this phenomenon may employ a fluorophore like carbostyril as a wavelength shifter to improve detection efficiency. (*) Cosmic-ray detectors that use an air medium must reconstruct the cosmic ray from this phenomenon as produced by the ray's secondaries; such detectors are used in CRID and VERITAS. The energy emitted in this process per unit length and angular frequency is proportional to one, minus one over the square of "beta times the index of refraction", according to the Frank-Tamm formula. For 10 points, name this often-blue radiation emitted by charged particles traveling faster than the speed of light in their medium.
One device that measures this phenomenon uses a perfluorohexane radiator and measures uses an image of a 2-dimensional ring produced by it to measure the angle at which it occurs.
Cherenkov radiation