Čerenkov Radiation

Abstract

Electrons of two million volts energy from an electrostatic generator were used to investigate the properties of the asymmetric radiation discovered by Čerenkov. This radiation is produced when electrons traverse a material medium with a velocity greater than the velocity of light in that medium. It was found for several solids and liquids that the direction of the emission of the radiation is accurately expressed by the relation, $cos\theta =\frac{1}{\beta n}$, and that the intensity maximum is quite sharp. The nature of the radiation from all solids and liquids investigated was found to be continuous and identical in appearance. The radiation apparently extends with increasing intensity from the infra-red to the ultraviolet absorption limit of the medium in which it is produced. Rough quantitative measurements of its intensity indicate that one 1.9 million volt electron in being brought to rest in water produces 40 quanta in a wave-length range 4000A to 6700A. These results are in good agreement with the classical explanation of the phenomenon given by Frank and Tamm.