.
Extensive Air Showers
of the
Cosmic Radiation
are caused by nucleon-nucleon collisions of high-energy primary cosmic
radiation particles with atoms of the Earth's atmosphere. The collision
products are pions and nucleons emerging in a well-collimated beam. The
decay of neutral pions into two gamma quanta can be regarded as the
initial stage of photon-electron cascades. The decay of charged pions into
muons and the decay of the latter into electrons and positrons contribute
to the photon-electron cascades.
The electrons of the cascade produce additional quanta by radiation losses,
the positrons of the cascade give annihilation quanta, and the photons of the
cascade produce electrons and positrons by various interactions with the
atoms of the atmosphere. Thus, in the initial stages of an Extensive Air
Shower, the number of particles keeps increasing with the propagation of the
shower front. The maximum number of particles depends on the energy of the
primary cosmic ray particle. The energy range of cosmic radiation that is
being investigated by the showers that they produce lies between
1013
eV and
1020
eV.
As the number of electrons and photons in a shower increases, their average
energy decreases and eventually reaches a level where the cascading process
can no longer be maintained and the particle numbers in a shower start to
decrease due to absorption in the atmosphere. Most showers that reach the
Earth's surface are at this stage. Thus, the total number of particles in a
shower and the area density of these particles can be used for an estimation
of the energy of the primary cosmic ray particle that initiated
the shower.
The charged pions from the original nucleon-nucleon collision are of very
high energy. Thus, while they have a near isotropic distribution in the
center-of-mass system, they will propagate in a very narrow solid angle when
viewed in a Earth-centered coordinate system. The narrow beam of pions
arriving at the Earth is well aligned with the direction of incidence of the
primary particle. Through successive inelastic collisions with air nuclei
the pions produce a meson-nucleon cascade which is still well collimated
when arriving at the Earth's surface. Due to the high energies of the
particles of the photon-electron cascade, the cascade particles also
propagate in directions that deviate only by small angles (plus or minus)
from the direction of the generating particles. Thus, measurements of the
direction of incidence of both the penetrating particles of an Extensive Air
Shower and of the particles of the photon-electron cascade can be used for
the determination of the direction of incidence of the primary particle
that originated the shower.
Very important astrophysical conclusions can be derived from the study of the
energy spectrum and the non-isotropy of the Extensive Air Showers of the
cosmic radiation.
More details can be found in the following paragraphs:
of Extensive Air Showers
Density Spectrum of Extensive Air Showers
Number Spectrum of Extensive Air Showers
Direction of Arrival of Extensive Air Showers
Measurement of Extensive Air Showers
Modeling of Extensive Air Showers
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Edited on 10 July 2002 - E-mail to the
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