The Askaryan radiation[1][2][3][4] also known as Askaryan effect is the phenomenon whereby a particle traveling faster than the phase velocity of light in a dense dielectric (such as salt, ice or the lunar regolith) produces a shower of secondary charged particles which contains a charge anisotropy and emits a cone of coherent radiation in the radio or microwave part of the electromagnetic spectrum.
Wavelengths greater than the extent of the shower interfere constructively and thus create a radio or microwave signal which is strongest at the Cherenkov angle.
So far the effect has been observed in silica sand,[5] rock salt,[6] ice,[7] and Earth's atmosphere.
[8] The effect is of primary interest in using bulk matter to detect ultra-high energy neutrinos.
The Antarctic Impulse Transient Antenna (ANITA) experiment uses antennas attached to a balloon flying over Antarctica to detect the Askaryan radiation produced by showers of particles when cosmic neutrinos interact in the ice.