What is an Ultra-High Energy Cosmic Ray?

Ultra-high energy cosmic rays are the entire extended atmospheric shower (EAS) energy region or the energy region that cannot be reached by the most powerful modern accelerator.

Ultra-high energy cosmic rays refer to the higher energy part of the cosmic rays. The energy range of cosmic rays is very wide. The low-energy part only has thousands of electron volts. The high-energy part has measured up to 10 ²⁰ eV per nucleus. According to related theories, the highest energy can reach 10 ²¹ ev per nucleus. Some people even suggested that it can reach 10 ²³ eV ^[1]

The level of cosmic ray energy is relative, referring to different occasions

As the most important nucleus in the composition of cosmic rays, its origin still has no place for the generation of angular high-energy gamma-rays, high-energy neutrinos, and extremely high-energy cosmic rays, as well as the indirect detection of dark matter particles, to study the evolution of the universe and new physical laws.

In 1912, the Austrian physicist Hess took a hot air balloon to rise to an altitude of more than 5,350 meters. During a 6-hour flight, through the measurement of the current in the ionization chamber, it was found that the ionization rate of high-altitude air is several times that of the ground, thus explaining this. This kind of ionization in the air is caused by "radiation" (later called cosmic rays) outside the earth. It is worth mentioning that from 1931 to 1914, German physicist Col Horst repeated Hess's The experiment, the balloon flight in 1914 actually reached an altitude of 9000m. The Hess experiment was later considered to be an experiment that marked the discovery of cosmic rays. High altitude and space experiments have since become inextricably linked to the study of cosmic rays. ^{[2 ]}

For a long time, people have studied high-energy cosmic rays by means of detectors (observing Cherenkov light or fluorescence). In order to determine the energy and orientation of cosmic rays, large-scale detectors (such as those from Tibet Yangbajing), high cost and difficult maintenance, exploring new cosmic ray detection technology has always been the wish of scientists. As early as the 1960s, people realized that atmospheric showers would occur when cosmic rays entered the earth, and the decay of their secondary particles would generate positron-negative electron pairs. When these electrons moved at nearly the speed of light, they were caused by the Earth s magnetic field. The synchrotron radiation will produce weak electromagnetic radiation, and the radiated energy falls near the low frequency of 20-100MHz, which manifests itself as a nanosecond-level radio pulse in this band. Therefore, as long as low-frequency radio observation with high time resolution and various interference signals can be realized, radio detection of cosmic rays is possible. This is because all methods reconstruct the original cosmic ray characteristics by detecting the secondary effects of cosmic rays ^[2] .