When a charged particle is emitted in radioactive decay
with velocity greater than c/n (the speed of light in the medium),
where c is the speed of light in vacuum
and n is the index of refraction of the medium,
a "shock wave" of photons is generated in the blue light range,
analogous to the sonic boom of a jet flying faster than the speed of sound.
Applications of this effect include:
- in physics: detection of elementary particles;
- in nuclear medicine: in the assaying of P-32, which in a water solution has a detectable (by liquid scintillator apparatus) Cherenkov emission.