The antimatter counterpart of the electron is its antiparticle, the positron. The positron has the same amount of electrical charge as the electron, except that the charge is positive. It has the same mass and spin as the electron. When a positron annihilates with an electron, their mass is converted into energy in the form of two gamma ray photons. (See electron-positron annihilation)
A positron may be generated by positron emission radioactive decay, or the interaction of photon with a charged particle (such as an atom's nucleus) with energy greater than 2 mec2 = 2×0.511 MeV = 1.022 MeV with matter (me represents the mass of one electron and c is the speed of light in vacuum). This process is called pair production, as it generates one electron and one positron from the energy of the photon.
The existence of positrons was first postulated in 1928 by Paul Dirac as an inevitable consequence of the Dirac equation. In 1932, positrons were observed by Carl D. Anderson, who gave the positron its name. Anderson also unsuccessfully suggested renaming electrons "negatrons." The positron was the first evidence of antimatter and was discovered by passing cosmic rays through a gas chamber and a lead plate surrounded by a magnet to distinguish the particles by bending differently charged particles in different directions.
Today, positrons are produced in enormous numbers in accelerator physics laboratories and used in electron-positron colliders.
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