Air shower (physics)

An air shower is a shower particles in the atmosphere, which is generated by a high-energy photon or particle of cosmic radiation. It involves a lot of miles broad " avalanche " of elementary particles and electromagnetic radiation. The original (primary) particles initially hits an atom of air with which it interacts. As a result of this interaction more particles are formed ( secondary particles), which in turn react with the air atoms and generate more particles. The formation of this cascade stimulates the nitrogen atoms, which emit the excitation energy in a row as fluorescent light.

Formation and properties of the air shower

The primary particles can be a proton, electron, nucleus, photon, or more rarely a positron. The Teilchenkaskade consists predominantly of electrons, positrons and photons. The electrons and positrons generated by deflection in the Coulomb field of the atomic nuclei and orbital electrons bremsstrahlung. The high-energy photon produced by pair production, in turn, an electron -positron pair.

As long as the energy of electrons and positrons is greater than the critical energy ( 80 MeV ), the number of particles in the air nearby increases. Decreases the average energy of the electrons and positrons below the critical energy, the electrons and positrons lose energy mainly by ionization of atoms, with no more high-energy photons are generated: The shower maximum is reached and the Teilchenkaskade dies out.

Depending on the type and energy of the primary particle varies the shape of the shower, the number of particles produced and the location of the shower maximum. For a normally incident to the surface particles with an energy of 107GeV hadrons, muons and electrons can be detected at sea level. They form from a few meters thick shower front, the lateral to the original direction of incidence of the primary particle has a radius of about 100 m. Air showers of primary particles with energies less than 100 GeV, however, are not directly detectable at sea level.

Detection methods

Air showers can be detected by various methods:

  • Air showers fields: Here, the charged particles and photons are detected. By measuring the relative delay at various points of the shower front, the direction of incidence of the initial particle can be reconstructed. By measuring the number of particles can be close to the initial energy of the primary particle.
  • Air - Cherenkov detectors: The charged particles in the shower front moving at a speed corresponding to nearly the speed of light in vacuum. Since the propagation speed of light in the atmosphere to approximately 1/ 1000 is smaller than that in vacuum, some of the particles move with a velocity that is greater than that of light in air. This leads to a coherent polarization of the medium along the trajectory, which is detectable as Cherenkov radiation. The light appears as a bluish flash with a time length of a few billionths of a second ( nanosecond ). With the human eye this flash is not perceptible, with a correspondingly fast photodetector, however, air - Cherenkov light detected.
  • Radio antennas: the electrons and positrons in air showers are easily distracted in the Earth's magnetic field, so that synchrotron radiation is emitted. Due to the high density of electrons in front of the shower, this effect is coherently amplified. The resulting radio signal is detectable and can be used for observation of air showers.

A part of the cosmic radiation is responsible for the aurora (without cascades, since lower energy).

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