Air shower (physics)

An air shower is an extensive (many kilometres wide) cascade of ionized particles and electromagnetic radiation produced in the atmosphere when a primary cosmic ray (i.e. one of extraterrestrial origin) enters the atmosphere. The term cascade means that the incident particle, which could be a proton, a nucleus, an electron, a photon, or (rarely) a positron, strikes an atom's nucleus in the air so as to produce many energetic hadrons. The unstable hadrons decay in the air speedily into other particles and electromagnetic radiation, which are part of the shower components. The secondary radiation rains down, including x-rays, muons, protons, antiprotons, alpha particles, pions, electrons, positrons, and neutrons.

The dose from cosmic radiation is largely from muons, neutrons, and electrons, with a dose rate that varies in different parts of the world and based largely on the geomagnetic field, altitude, and solar cycle. Airline crews receive more cosmic rays if they routinely work flight routes that take them close to the North or South pole at high altitudes, where this type of radiation is maximal.

The air shower was discovered by Bruno Rossi in 1934. By observing the cosmic ray with the detectors placed apart from each other, Rossi recognized that many particles arrive simultaneously at the detectors. This phenomenon is now called an air shower.

After the primary cosmic particle has collided with the air molecule, the main part of the first interactions are pions. Also kaons and baryons may be created. Pions and kaons are not stable, thus they may decay into other particles.

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