Askaryan effect is termed for a phenomenon where a particle traveling faster than the velocity of light in a dense substance (salt, ice or the lunar regolith), produces a sprinkler shower of some secondary charged particles which may contain a charge anisotropy and thus it emits a ray that has constant phase difference. It also has the same frequency that is produced in the radio or microwave part of the electromagnetic spectrum. Due to this reason, it is also called ‘Askaryan Radiation’. It is just similar to the ‘Cherenkov radiation’ (radiation produced by a charged particle that passes through a dielectric medium with a speed greater than the speed of light).
The ‘Askaryan Effect’ is named after a Soviet-Armenian physicist, Gurgen Askaryan, who postulated this effect in the year 1962. According to the internet, Askaryan was also famous for his discovery of the self-focusing nature of light. He also performed great studies on the interactions of light and matter. History postulates his great contributions for his investigation on the interaction of high-energy particles with the condensed matter as well.
The Askaryan radiation was for the first time observed experimentally in around 2000, which is 38 years after this effect has its theoretical prediction. Till now, the effect has been observed in substances such as silica sand, rock salt, ice, and also in the Earth’s atmosphere.
The first observation of the Askaryan effect was made when ice was taken as a medium. It further showed that the coherent impulsive radio along with the Cherenkov radiation is given out from the charged particle in that electromagnetic shower. Such radiations have also been observed in silica sand and rock salt, but this was regarded as the first direct observation from an electromagnetic shower in ice. These measurements are important because the majority of the experiments to date rely on this effect. Thus, it was clear that the first direct experimental evidence that was given for the charge excess in high energy particle showers was predicted to nearly 40 years ago by the famous physicist, Askaryan.
‘ICE’ AS A MEDIUM
Despite the confirmation of the Askaryan’s theory for sand and salt, there are important reasons as well to test this in ice as well, since so much research and experimental efforts have been directed towards ice as the target medium. Although the effect is primarily determined more by shower physics, the properties like the radio production and transmission occur only under the conditions where the properties of the medium could play an efficient role in modifying the behavior of the emission. The Cherenkov method that is somewhat just similar to the Askaryan effect is most effective at shower energies where the cosmic ray backgrounds are almost negligible, and the method is stated for having no natural backgrounds with and to collaborate with the Cherenkov intensity.
There are some advantages associated with the radio detection of Ultra high energy particles as provided by the Askaryan effect. Some of the primary advantages are that large detection volumes always give clear signals and also they have low attenuation. By this effect, we can also observe the distant events or the events that are taking place far from our eyes.
It gives good statistics in a lesser amount of time.
It has a relatively lower cost when compared to the area that it covers.
It is available for neutrons or other particles (charged & charge-less both).
When Askaryan first described this effect, he suggested that it should lead to strong coherent radio and microwave emission for the showers that are propagating within the dielectric. Since the dimensions of the bunch of the charged particles are small when compared to the wavelength of the radio waves, the shower radiates coherent radio radiation whose power is said to be in proportion to the square of the altogether net charge in the shower. The Askaryan effect matters a lot since it allows for the detection of ultra-high energy neutrons, and it is said to be universal in nature even for those particles that do not have any charge like neutrons.
RELATION WITH CHERENKOV EFFECT
The Askaryan effect works the same way as the Cherenkov effect is universal for charged particles. And here the tracking ultra-high-energy neutrons is important because they collectively point out towards a source, and it is also stated that they can help us to solve the confusion of the origin of cosmic rays and also the composition of the cosmic rays, here the acceleration mechanism of cosmic radiation can also be studied by this effect, the nuclear interactions of objects such as sun, stars, planets, galaxies also called the astrophysical objects can be studied and helps in tracking of the highest energy emissions from anywhere in the universe. Thus, we now do know that the charged particles that tend to move faster than the speed of light moving through the vacuum emit Cherenkov radiation that was considered to be similar to the Askaryan effect.
This Askaryan’s hypothesis has now been confirmed in detail in the laboratory experiments for all of the stated dielectric materials such as ice, salt, and sand. It is now concluded that the Askaryan theory is one of the best media in a way to exploit the coherent radio Cherenkov emission from the particles that give out high energy showers. Askaryan’s main intension was to give in a methodology by which the particles having ultra-high-energy could be made observable through some methods or by the use of huge volumes of natural materials.