positron

n.

An elementary particle having the same mass and magnitude of charge as an electron but exhibiting a positive charge; a positive electron. Also called antielectron.

[POSI(TIVE) + (ELEC)TRON.]

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 also 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 also 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 also Nuclear molecule; Quasiatom; Supercritical fields.

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(poz-i-tron)

The antiparticle for an electron; it has the same mass as an electron, but carries a positive charge.

Positrons are found in collisions initiated by cosmic rays.

The antiparticle of the electron. When a positron is emitted by a radionuclide it combines with an electron and both undergo annihilation, producing two 511 keV gamma rays traveling in opposite directions. This effect is used in positron emission tomography (PET).

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Dansk (Danish)
n. - positron

Nederlands (Dutch)
positron

Français (French)
n. - positron

Deutsch (German)
n. - Positron

Ελληνική (Greek)
n. - (φυσ.) ποζιτρόνιο

Italiano (Italian)
positrone

Português (Portuguese)
n. - pósitron (m) (Fís.)

Русский (Russian)
позитрон

Español (Spanish)
n. - positrón

Svenska (Swedish)
n. - positron, positiv elektron

中文（简体）(Chinese (Simplified))
正电子

中文（繁體）(Chinese (Traditional))
n. - 正電子

한국어 (Korean)
n. - 양전자

日本語 (Japanese)
n. - 陽電子

العربيه (Arabic)
‏(الاسم) البوزترون : جسم موجب ذو كتله تعادل كتله الالكترون‏

עברית (Hebrew)
n. - ‮חלקיק תת-אטומי בעל מטען חיובי, פוזיטרון‬

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