positron (redirected from Positrons)

positron: see antiparticle.

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positron

Subatomic particle having the same mass as an electron but with an electric charge of +1 (an electron has a charge of −1). It constitutes the antiparticle (see antimatter) of an electron. The existence of the positron was a consequence of the electron theory of P.A.M. Dirac (1928), and the particle was discovered in cosmic rays by Carl D. Anderson (1905–1991) in 1932. Though they are stable in a vacuum, positrons react quickly with the electrons of ordinary matter, producing gamma rays by the process of annihilation. They are emitted in positive beta decay of proton-rich radioactive nuclei and are formed in pair production.

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positron

Physics the antiparticle of the electron, having the same mass but an equal and opposite charge. It is produced in certain decay processes and in pair production, annihilation occurring when it collides with an electron

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positron [′päz·ə‚trän]

(particle physics)

An elementary particle having mass equal to that of the electron, and having the same spin and statistics as the electron, but a positive charge equal in magnitude to the electron's negative charge. Also known as positive electron.

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Positron

An elementary particle with mass equal to that of the electron, and positive charge equal in magnitude to the electron's negative charge. The positron is thus the antiparticle (charge-conjugate particle) to the electron. The positron has the same spin and statistics as the electron. Positrons, like electrons, appear as decay products of many heavier particles; electron-positron pairs are produced by high-energy photons in matter. See Antimatter, Electron, Electron-positron pair production, Elementary particle

A positron is, in itself, stable, but cannot exist indefinitely in the presence of matter, for it will ultimately collide with an electron. The two particles will be annihilated as a result of this collision, and photons will be created. However, a positron can first become bound to an electron to form a short-lived “atom” termed positronium. See Positronium

Quantum field theory predicts the occurrence of a fundamental positron creation process in the presence of strong, static electric fields. For a bare nucleus with atomic number Z > 173, it becomes energetically favorable to transform the electron binding energy of larger than 2m₀c², where m₀ is the electron rest mass and c is the speed of light, into simultaneously creating an electron bound to the nucleus and a positron that escapes from the nucleus. This process of spontaneous positron emission has not been observed since atoms with Z > 173 are not available in nature. However, with the introduction of heavy-ion accelerators, it has become possible to simulate such an atom for a short period in a high-energy collision between two stable heavy atoms such as uranium. Experiments have utilized a variety of such collision systems with total Z ranging from 180 to 188 to search for spontaneous positron emission. A number of these experiments reproduce the salient features expected for this process. However, some inconsistencies with the predictions of the theory have yet to be resolved before spontaneous positron emission is established experimentally. See Nuclear molecule, Quasiatom, Supercritical fields