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The positron or antielectron is the antiparticle
Antiparticle

Corresponding to most kinds of particle physics, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay....
 or the antimatter
Antimatter

In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles....
 counterpart of the electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
. The positron has an electric charge
Electric charge

Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields....
 of +1, a spin
Spin (physics)

In quantum mechanics, spin is a fundamental property of atomic nucleus, hadrons, and elementary particles. For particles with non-zero spin, spin direction is an important intrinsic degrees of freedom ....
 of 1/2, and the same mass as an electron. When a low-energy positron collides with a low-energy electron, annihilation
Annihilation

Annihilation is defined as "total destruction" or "complete obliteration" of an object; having its root in the Latin nihil . A literal translation is "to make into nothing"....
 occurs, resulting in the production of two gamma ray
Gamma ray

Gamma rays are a form of electromagnetic radiation produced by atom particle interactions, such as electron-positron annihilation or radioactive decay....
 photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
s (see electron-positron annihilation
Electron-positron annihilation

Electron-positron annihilation occurs when an electron and a positron collide. The result of the collision is the conversion of the electron and positron and the creation of gamma ray photons or, less often, other particles....
). The first scientist deemed to have detected positrons through electron-positron annihilation was Chung-Yao Chao
Chung-Yao Chao

Chung-Yao Chao was a China physicist. Chung-Yao Chao studied the scattering of gamma rays in lead by pair production in 1930, without knowing that positrons were involved in the anomalously high scattering cross-section....
, a graduate student at Caltech in 1930, though he did not realize what they were at that time.

Positrons may be generated by positron emission
Positron emission

Positron emission is a type of beta decay, sometimes referred to as "beta plus" . In beta plus decay, a proton is converted, via the weak force, to a neutron, a positron , and a neutrino....
 radioactive decay (a weak interaction
Weak interaction

The weak interaction is one of the four fundamental interactions of nature. In the Standard Model of particle physics, it is due to the exchange of the heavy W and Z bosons....
), or by pair production
Pair production

Pair production refers to the creation of an elementary particle and its antiparticle, usually from a photon . This is allowed, provided there is enough energy available to create the pair ? at least the total rest mass energy of the two particles ? and that the situation allows both energy and momentum to be conserved ....
 from a sufficiently energetic photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
.

The existence of positrons was first postulated in 1928 by Paul Dirac
Paul Dirac

Paul Adrien Maurice Dirac, Order of Merit , Royal Society was a United Kingdom theoretical physicist. Dirac made fundamental contributions to the early development of both quantum mechanics and quantum electrodynamics....
 as a consequence of the Dirac equation
Dirac equation

In physics, the Dirac equation is a theory of relativity quantum mechanics wave equation formulated by British physicist Paul Dirac in 1928 and provides a description of elementary particle spin-? particles, such as electrons, consistent with both the principles of quantum mechanics and the theory of special relativity....
.






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The positron or antielectron is the antiparticle
Antiparticle

Corresponding to most kinds of particle physics, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay....
 or the antimatter
Antimatter

In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles....
 counterpart of the electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
. The positron has an electric charge
Electric charge

Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields....
 of +1, a spin
Spin (physics)

In quantum mechanics, spin is a fundamental property of atomic nucleus, hadrons, and elementary particles. For particles with non-zero spin, spin direction is an important intrinsic degrees of freedom ....
 of 1/2, and the same mass as an electron. When a low-energy positron collides with a low-energy electron, annihilation
Annihilation

Annihilation is defined as "total destruction" or "complete obliteration" of an object; having its root in the Latin nihil . A literal translation is "to make into nothing"....
 occurs, resulting in the production of two gamma ray
Gamma ray

Gamma rays are a form of electromagnetic radiation produced by atom particle interactions, such as electron-positron annihilation or radioactive decay....
 photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
s (see electron-positron annihilation
Electron-positron annihilation

Electron-positron annihilation occurs when an electron and a positron collide. The result of the collision is the conversion of the electron and positron and the creation of gamma ray photons or, less often, other particles....
). The first scientist deemed to have detected positrons through electron-positron annihilation was Chung-Yao Chao
Chung-Yao Chao

Chung-Yao Chao was a China physicist. Chung-Yao Chao studied the scattering of gamma rays in lead by pair production in 1930, without knowing that positrons were involved in the anomalously high scattering cross-section....
, a graduate student at Caltech in 1930, though he did not realize what they were at that time.

Positrons may be generated by positron emission
Positron emission

Positron emission is a type of beta decay, sometimes referred to as "beta plus" . In beta plus decay, a proton is converted, via the weak force, to a neutron, a positron , and a neutrino....
 radioactive decay (a weak interaction
Weak interaction

The weak interaction is one of the four fundamental interactions of nature. In the Standard Model of particle physics, it is due to the exchange of the heavy W and Z bosons....
), or by pair production
Pair production

Pair production refers to the creation of an elementary particle and its antiparticle, usually from a photon . This is allowed, provided there is enough energy available to create the pair ? at least the total rest mass energy of the two particles ? and that the situation allows both energy and momentum to be conserved ....
 from a sufficiently energetic photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
.

The existence of positrons was first postulated in 1928 by Paul Dirac
Paul Dirac

Paul Adrien Maurice Dirac, Order of Merit , Royal Society was a United Kingdom theoretical physicist. Dirac made fundamental contributions to the early development of both quantum mechanics and quantum electrodynamics....
 as a consequence of the Dirac equation
Dirac equation

In physics, the Dirac equation is a theory of relativity quantum mechanics wave equation formulated by British physicist Paul Dirac in 1928 and provides a description of elementary particle spin-? particles, such as electrons, consistent with both the principles of quantum mechanics and the theory of special relativity....
. In 1932, positrons were discovered by Carl D. Anderson, who gave the positron its name. The positron was the first evidence of antimatter
Antimatter

In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles....
 and was discovered by passing cosmic ray
Cosmic ray

Cosmic rays are energetic particles originating from space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are protons, about 9% are helium nuclei and about 1% are electrons ....
s through a cloud chamber
Cloud chamber

[Image:Cloud_chamber_bionerd.jpg|thumb|Cloud chamber with visible tracks from ionizing radiation The cloud chamber, also known as the Wilson chamber, is used for detecting particles of ionizing radiation....
 and a lead plate surrounded by a magnet to distinguish the particles by bending differently charged particles in different directions.

Today, positrons, created through the decay of a radioactive tracer, are detected in positron emission tomography
Positron emission tomography

Positron emission tomography is a nuclear medicine medical imaging technique which produces a three-dimensional image or picture of functional processes in the body....
 (PET) scanners used in hospitals and in accelerator physics laboratories used in electron-positron collider experiments. In the case of PET scanners, positrons provide a mechanism to show areas of activity within the human brain. In addition to the two above-mentioned applications of positrons in medicine and fundamental physics, an experimental tool called positron annihilation spectroscopy
Positron annihilation spectroscopy

Positron annihilation spectroscopy or Positron lifetime spectroscopy is a non-destructive spectroscopy technique to study voids and defects in solids....
 (sometimes referred to as PAS
PAS

Pas or PAS may be:* Pas River, in Spain* PAS Giannina, a Greek football club from Ioannina* PAS Tehran F.C., a defunct Iranian football club from Tehran...
) is used in materials research.

New research has dramatically increased the quantity of positrons capable of being created through experimental processes. Physicists at the Lawrence Livemore National Laboratory in California have used a short, ultra-intense laser to irradiate a millimetre-thick gold target and produce more than 100 billion particles of antimatter by causing the electrons to emit energy packets which decay into matter and anti-matter.

See also

  • Beta particle
    Beta particle

    Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive Atomic nucleus such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays....
  • Radioactive decay
    Radioactive decay

    Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide....
  • List of particles
    List of particles

    This is a list of the different types of particles found or believed to exist in nature. For individual lists of the different particles, see the individual pages given below....
  • Positron emission tomography
    Positron emission tomography

    Positron emission tomography is a nuclear medicine medical imaging technique which produces a three-dimensional image or picture of functional processes in the body....
  • Positronium
    Positronium

    Positronium is a system consisting of an electron and its antimatter, a positron, bound together into an "exotic atom". The orbit of the two particles and the set of energy levels is similar to that of the hydrogen atom ....
  • Electron
    Electron

    The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
  • proton
    Proton

    The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+....


External links

  • (from the Frequently Asked Questions Center for Antimatter-Matter Studies)
  • [https://publicaffairs.llnl.gov/news/news_releases/2008/NR-08-11-03.html New production method to produce large quantities of positrons]