antielectron

An antielectron, also called a positron, is the antiparticle of the electron. It has the same mass as an electron but carries a positive electric charge and the same magnitude of spin (½). In interactions, it behaves as the electron’s antimatter counterpart.

The existence of the antielectron was predicted by Paul Dirac’s relativistic quantum theory and was experimentally discovered by Carl D. Anderson in 1932 in cosmic-ray exposures. The discovery confirmed that Dirac's equation implied antiparticles.

Positrons can be produced in various processes, notably electron-positron pair production by high-energy photons in the field of a nucleus, and in beta-plus decay of certain radionuclides. When a positron encounters ordinary matter, it typically annihilates with an electron, producing gamma rays, most commonly two photons of 511 keV emitted in opposite directions. Positronium, a bound state of an electron and a positron, can form and decay into either two or three gamma rays depending on its spin state.

In medicine, positrons are used in positron emission tomography (PET) to image metabolic processes. In physics and astronomy, positrons are observed in cosmic rays and various astrophysical environments. Their study helps probe antimatter interactions and fundamental symmetries.