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An air shower is an extensive (many kilometres wide)
cascade Cascade, Cascades or Cascading may refer to: Science and technology Science *Cascade waterfalls, or series of waterfalls * Cascade, the CRISPR-associated complex for antiviral defense (a protein complex) * Cascade (grape), a type of fruit * Bioc ...
of ionized particles and
electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...
produced in the
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...
when a ''primary''
cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
(i.e. one of extraterrestrial origin) enters the atmosphere. When a particle, which could be a
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
, a
nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: * Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...
, an
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...
, a
photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alwa ...
, or (rarely) a
positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 '' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. When a positron collide ...
, strikes an atom's nucleus in the air it produces many energetic
hadrons In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the ele ...
. The unstable hadrons decay in the air speedily into other particles and electromagnetic radiation, which are part of the particle shower components. The secondary radiation rains down, including
x-rays An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nbs ...
,
muon A muon ( ; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 '' e'' and a spin of , but with a much greater mass. It is classified as a lepton. As w ...
s,
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
s, antiprotons,
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be prod ...
s,
pion In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: ) is any of three subatomic particles: , , and . Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more gene ...
s,
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...
s,
positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 '' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. When a positron collide ...
s, and
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...
s. 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 Bruno Benedetto Rossi (; ; 13 April 1905 – 21 November 1993) was an Italian experimental physicist. He made major contributions to particle physics and the study of cosmic rays. A 1927 graduate of the University of Bologna, he became in ...
in 1934. In 1937 Pierre Auger, unaware of Rossi's earlier report, detected the same phenomenon and investigated it in some detail. He concluded that high-energy primary cosmic-ray particles interact with air nuclei high in the atmosphere, initiating a cascade of secondary interactions that ultimately yield a shower of electrons, and photons that reach ground level. 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.


Air shower formation

After the primary cosmic particle has collided with the air molecule, the main part of the first interactions are
pion In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: ) is any of three subatomic particles: , , and . Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more gene ...
s. Also
kaon KAON (Karlsruhe ontology) is an ontology infrastructure developed by the University of Karlsruhe and the Research Center for Information Technologies in Karlsruhe. Its first incarnation was developed in 2002 and supported an enhanced version of ...
s and
baryon In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron family of particles; hadrons are composed of quarks. Baryons are also classifie ...
s may be created. Pions, kaons, and heavy
baryon In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron family of particles; hadrons are composed of quarks. Baryons are also classifie ...
s are unstable, and decay into lighter and more stable particles relatively high in the atmosphere. Neutral pions \ \pi^0\ decay by the electroweak interaction into pairs of oppositely spinning photons \ \gamma\ in the process \ \pi^0 \rightarrow \gamma + \gamma\ . The photons produced form an electromagnetic cascade by creating more photons, protons, antiprotons, electrons, and positrons. Charged pions \ \pi^\pm\ preferentially decay into
muons A muon ( ; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 '' e'' and a spin of , but with a much greater mass. It is classified as a lepton. As wi ...
and (anti) neutrinos via the
weak interaction In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction ...
\ \pi^ \rightarrow \mu^ + \nu\ and \ \pi^ \rightarrow \mu^ + \overline\ . This is how the muons and neutrinos that eventually reach the ground are produced in the air shower. The same holds true for kaons which can produce muons in the process \ K^ \rightarrow \mu^ + \nu\ and \ K^ \rightarrow \mu^ + \overline\ In addition, kaons can produce also pions via the decay mode K^\pm \rightarrow \pi^\pm + \pi^0\ .


Detection

The original particle arrives with high energy and hence a velocity near the
speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit fo ...
, so the products of the collisions tend also to move generally in the same direction as the primary, while to some extent spreading sidewise. In addition, the secondary particles produce a widespread flash of light in forward direction due to the Cherenkov effect, as well as fluorescence light that is emitted isotropically from the excitation of nitrogen molecules. The particle cascade and the light produced in the atmosphere can be detected with surface detector arrays and optical telescopes. Surface detectors typically use
Cherenkov detector A Cherenkov detector (pronunciation: /tʃɛrɛnˈkɔv/; Russian: Черенко́в) is a particle detector using the speed threshold for light production, the speed-dependent light output or the speed-dependent light direction of Cherenkov rad ...
s or
Scintillation counter A scintillation counter is an instrument for detecting and measuring ionizing radiation by using the excitation effect of incident radiation on a scintillating material, and detecting the resultant light pulses. It consists of a scintillator wh ...
s to detect the charged secondary particles at ground level. The telescopes used to measure the fluorescence and Cherenkov light use large mirrors to focus the light on PMT clusters. Finally, air showers emit radio waves due to the deflection of electrons and positrons by the geomagnetic field. As advantage over the optical techniques, radio detection is possible around the clock and not only during dark and clear nights. Thus, several modern experiments, e.g.,
TAIGA Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic and Turkic languages), generally referred to in North America as a boreal forest or snow forest, is a biome characterized by coniferous forests consisting mostly of pines, sp ...
, LOFAR, or the
Pierre Auger Observatory The Pierre Auger Observatory is an international cosmic ray observatory in Argentina designed to detect ultra-high-energy cosmic rays: sub-atomic particles traveling nearly at the speed of light and each with energies beyond 1018  eV. In Ear ...
use radio antennas in addition to particle detectors and optical techniques. The longitudinal profile of the number of charged particles can be parameterized by the Gaisser–Hillas function.


See also

*
Cosmic-ray observatory A cosmic-ray observatory is a scientific installation built to detect high-energy-particles coming from space called cosmic rays. This typically includes photons (high-energy light), electrons, protons, and some heavier nuclei, as well as antimat ...


References

{{Reflist


External links


Extensive Air Showers

Haverah Park Detection SystemHiRes Detector SystemPierre Auger ObservatoryHiSPARC
(High School Project on Astrophysics Research with Cosmics)
AIRES
(AIRshower Extended Simulations) : Large and well documented Fortran package for simulating cosmic ray showers by Sergio Sciutto at the Department of Physics of the
Universidad Nacional de La Plata The La Plata National University ( es, Universidad Nacional de La Plata, UNLP) is one of the most important Argentine national universities and the biggest one situated in the city of La Plata, capital of Buenos Aires Province. It has over 9 ...
, Argentina *
CORSIKA CORSIKA (COsmic Ray SImulations for KAscade) is a physics computer software for simulation of extensive air showers induced by high energy cosmic rays, i.e. protons and atomic nuclei, as well as Gamma rays (photons), electrons, and neutrinos. ...

CORSIKA
Another code for simulating cosmic ray air showers by Dieter Heck of the Forschungszentrum Karlsruhe, Germany
COSMUS
: Interactive animated 3d models of several different cosmic ray air showers, and instructions on how to make your own using AIRES simulations. From the COSMUS group at the University of Chicago.

: Movies and instructions for how to make them, showing how air showers interact with the Milagro detector. By Miguel Morales.
CASSIM Animations
: Animations of different cosmic ray air showers by Hajo Dreschler of New York University.
SPASE2 Experiment
: South-Pole Air Shower Experiment (SPASE).
GAMMA Experiment
: High mountain Air Shower Experiment. Atmosphere Earth phenomena Cosmic rays