The Askaryan radiation also known as Askaryan effect is the phenomenon whereby a particle traveling faster than the
phase velocity of
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
in a dense
dielectric
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...
(such as salt, ice or the
lunar
Lunar most commonly means "of or relating to the Moon".
Lunar may also refer to:
Arts and entertainment
* ''Lunar'' (series), a series of video games
* "Lunar" (song), by David Guetta
* "Lunar", a song by Priestess from the 2009 album ''Prior t ...
regolith
Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestr ...
) produces a shower of secondary charged particles which contains a charge
anisotropy
Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physic ...
and thus emits a cone of
coherent radiation in the
radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmi ...
or
microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...
part of the
electromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging fro ...
. It is similar to the
Cherenkov radiation. It is named after
Gurgen Askaryan
Gurgen Ashotovich Askaryan ( hy, Գուրգեն Ասկարյան; russian: Гурген Аскарьян or Гурген Аскарян) (14 December 1928 – 2 March 1997) was a prominent Soviet - Armenian physicist, famous for his discovery of ...
, 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
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class o ...
, rock salt, ice, and Earth's atmosphere.
The effect is of primary interest in using bulk matter to detect ultra-high energy
neutrino
A neutrino ( ; denoted by the Greek letter ) is a fermion (an elementary particle with spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass ...
s. The
Antarctic Impulse Transient Antenna The Antarctic Impulsive Transient Antenna (ANITA) experiment has been designed to study ultra-high-energy (UHE) cosmic neutrinos by detecting the radio pulses emitted by their interactions with the Antarctic ice sheet. This is to be accomplished u ...
(ANITA) experiment uses antennas attached to a balloon flying over
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
to detect the Askaryan radiation produced as cosmic neutrinos travel through the ice. Several experiments have also used the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
as a
neutrino detector
A neutrino detector is a physics apparatus which is designed to study neutrinos. Because neutrinos only weakly interact with other particles of matter, neutrino detectors must be very large to detect a significant number of neutrinos. Neutrino d ...
based on detection of the Askaryan radiation.
RESUN project
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See also
* Cherenkov radiation
References
{{reflist
External links
RADHEP-2000 Write-ups
Physical phenomena
Particle physics