Askaryan effect
Encyclopedia
The 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 contain a charge anisotropy
and thus emits a cone of coherent
radiation in the radio
or microwave
part of the electromagnetic spectrum
. It is similar to the Cherenkov effect. It is named after Gurgen Askaryan
, a Soviet-Armenian physicist who postulated it in 1962.
The effect was first observed experimentally in 2000, 38 years after its theoretical prediction. So far the effect has been observed in silica
sand
, rock salt, and ice.
The effect is of primary interest in using bulk matter to detect ultra-high energy neutrino
s. 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. Several experiments have also used the Moon
as a neutrino detector
based on detection of the Askaryan radiation.
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
(such as salt, ice or the lunar
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
regolith
Regolith
Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...
) produces a shower of secondary charged particles which contain a charge anisotropy
Anisotropy
Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...
and thus emits a cone of coherent
Coherence (physics)
In physics, coherence is a property of waves that enables stationary interference. More generally, coherence describes all properties of the correlation between physical quantities of a wave....
radiation in the radio
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
or microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
part of the electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
. It is similar to the Cherenkov effect. It is named after Gurgen Askaryan
Gurgen Askaryan
Gurgen Askaryan was a prominent Soviet physicist, famous for his discovery of the self-focusing of light, pioneering studies of light-matter interactions, and the discovery and investigation of the interaction of high-energy particles with condensed matter...
, a Soviet-Armenian physicist who postulated it in 1962.
The effect was first observed experimentally in 2000, 38 years after its theoretical prediction. So far the effect has been observed in silica
Silicon dioxide
The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...
sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
, rock salt, and ice.
The effect is of primary interest in using bulk matter to detect ultra-high energy neutrino
Neutrino
A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
s. The Antarctic Impulse Transient Antenna
ANtarctic Impulse Transient Antenna
The AA experiment has been designed to study ultra-high-energy cosmic neutrinos by detecting the radio pulses emitted by their interacting with the Antarctic ice sheet...
(ANITA) experiment uses antennas attached to a balloon flying over Antarctica to detect the Askaryan radiation produced as cosmic neutrinos travel through the ice. Several experiments have also used the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
as a neutrino detector
Neutrino detector
A neutrino detector is a physics apparatus designed to study neutrinos. Because neutrinos are only weakly interacting with other particles of matter, neutrino detectors must be very large in order to detect a significant number of neutrinos. Neutrino detectors are often built underground to isolate...
based on detection of the Askaryan radiation.