Cherenkov radiation
Cherenkov radiation, also known as Vavilov–Cherenkov radiation (; Russian: Черенков) is a type of electromagnetic radiation produced by charged particles when they pass through an optically transparent medium at a speed which is greater than the speed of light in that medium. (It doesn't violate special relativity because the refractive index slows down the speed of light in a medium. So, the particle doesn't have to travel at the speed of light in a vacuum.) It is named after Pavel Alekseyevich Čerenkov, who discovered this phenomenon in 1934 under the supervision of Sergey Vavilov. Igor Tamm and Ilya Frank developed a theory on this effect in 1937. Pavel Čerenkov, Igor Tamm and Ilya Frank shared the 1958 Nobel Prize in physics because of their contribution in cherenkov radiation.