Cosmic rays are particles from outer space. It is being observed that there are subatomic particles that fall on the Earth continuously. They can reach energies much higher than the most massive machine.
The Austrian physicist Victor Hess is famous for having made a historic balloon flight that changed the existing knowledge of the matter. This flight was done in August 1912. He ascended to 5300 meters, and he measured the level of ionization.
He found out that at that height, the ionization was three times more than that at the sea level. That way, he concluded that radiation has been penetrating the atmosphere. He discovered the cosmic rays.
What are the cosmic rays?
As we have already mentioned, the cosmic rays are high-energy particles that come from outer space They are mainly protons (89%) – nuclei of hydrogen; there are also nuclei of helium (10%), as well as some heavier nuclei (1%) like uranium.
When these particles come to Earth, they meet the nuclei of atoms in the upper atmosphere, and thus they create new particles called pions. The charged pions decay very quickly, and they emit other particles called muons.
Pions and muons do not interact with matter. This fact allows them to travel further down to Earth and below the ground.
The particles of antimatter
Since the discovery of cosmic rays, other particles beyond the limits of the atoms came to our knowledge. The positron, the first particle of antimatter, got discovered in 1932, the muon – in 1937, then the pion, the kaon, and several others.
Before the age of the high-energy accelerators in the 1950s, the radiation particles were the only way to explore the growing world of particles. When they founded CERN in 1954, one of its targets was to examine cosmic rays. Even after the appearance of the accelerators, cosmic rays are still a matter of interest to scientists.
The energies of the cosmic rays vary from 1 GeV (of the microscopic particles) to 108 TeV (which is much higher than the beam energy). When these particles come to the top of the atmosphere, they fall with increasing energy. Some very high energy cosmic rays generate enormous showers of 10 billion secondary particles. These showers can be observed by particle detectors scattered over 20 km areas.
How do cosmic rays reach such high energies? Which are the natural accelerators? What is the solar wind? The lowest energy cosmic rays come from the Sun in the form of the so-called solar wind. The solar wind is a stream of charged particles. However, it is difficult to identify the high-energy particles because they swirl in the magnetic fields of space.
High-energy gamma rays are fewer than cosmic rays, but the magnetic fields don’t influence them as they are electrically neutral. They make showers of particles that can be identified on Earth. The sources of these high-energy gamma rays are the remains after supernovae. The shock waves from these explosions are believed to be the natural accelerators.