August 15, 2022
Gamma radiation or gamma rays is a type of electromagnetic radiation, and therefore constituted by photons, generally produced by radioactive elements or by subatomic processes such as the annihilation of a positron-electron pair. It is also generated in astrophysical phenomena of great violence. Due to their high energies, gamma rays are a type of ionizing radiation capable of penetrating matter more deeply than alpha and beta radiation. They can cause serious damage to the nucleus of cells, which is why they are used to sterilize medical equipment and food. Energy of this nature is measured in megaelectronvolts (MeV). One MeV corresponds to gamma photons with wavelengths less than 10-11 m or frequencies greater than 1019 Hz. Gamma rays are produced by deexcitation of a nucleon from one excited level or state to another of lower energy and by decay of radioactive isotopes. They differ from X-rays in their origin. These are generated at an extranuclear level, by electronic braking phenomena. Radioactivity is generally linked to nuclear energy and nuclear reactors, although it exists in the natural environment: to cosmic rays, expelled from the sun and from outside our solar system: from galaxies; radioactive isotopes in rocks and minerals. In general, gamma rays produced in space do not reach the Earth's surface, as they are absorbed by the upper atmosphere. To observe the universe at these frequencies it is necessary to use high-altitude balloons or exospace observatories. To detect them, in both cases the Compton effect is used. These gamma rays originate from high-energy astrophysical phenomena, such as supernova explosions or the nuclei of active galaxies. In astrophysics, GRBs (gamma ray bursts) are called gamma ray sources that last a few seconds or a few hours, followed by a decreasing brightness of the X-ray source for a few days. They occur at random positions in the sky. Its origin is still under scientific discussion. In any case, they seem to constitute the most energetic phenomena in the universe. Exceptional are gamma rays with energy greater than a few gigaelectronvolts (GeV, thousands of MeV) which, when they hit the atmosphere, produce thousands of particles (extensive atmospheric cascade), which, as they travel at speeds close to light in the air, generate Cherenkov radiation. This radiation is detected at the Earth's surface using a Cherenkov telescope.