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
lunarregolith) 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. The signal is a result of the
Cherenkov radiation from individual particles in the shower. 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. The effect is named after
Gurgen Askaryan, a Soviet-Armenian physicist who postulated it in 1962.
The radiation was first observed experimentally in 2000, 38 years after its theoretical prediction. So far the effect has been observed in
silicasand,[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 as cosmic neutrinos travel through the ice.[9][10] Several experiments have also used the
Moon as a
neutrino detector based on detection of the Askaryan radiation.[11][12][13][14]
^Buitink, Stijn; Corstanje, A.; Falcke, H; Hörandel, J. R; Huege, T; Nelles, A; Rachen, J. P; Rossetto, L; Schellart, P; Scholten, O; Ter Veen, S; Thoudam, S; Trinh, T. N. G; Anderson, J; Asgekar, A; Avruch, I. M; Bell, M. E; Bentum, M. J; Bernardi, G; Best, P; Bonafede, A; Breitling, F; Broderick, J. W; Brouw, W. N; Brüggen, M; Butcher, H. R; Carbone, D; Ciardi, B; Conway, J. E; et al. (2016). "A large light-mass component of cosmic rays at 1017–1017.5 electronvolts from radio observations". Nature. 531 (7592): 70–3.
arXiv:1603.01594.
Bibcode:
2016Natur.531...70B.
doi:
10.1038/nature16976.
PMID26935696.
S2CID205247687.