positron Particle that is identical to the electron, except that it is positively charged, making it the antiparticle of the electron. It was observed (1932) in cosmic radiation by US physicist Carl Anderson. It is also emitted from certain radioactive nuclei. Electron-positron pairs can be produced when gamma radiation interacts with matter. See also antimatter; elementary particle

pos·i·tron / ˈpäzəˌträn/ • n. Physics a subatomic particle with the same mass as an electron and a numerically equal but positive charge.

positron (poz-i-tron) n. an electrically charged particle, released in some radioactive decays, that has the same mass as an electron but opposite charge. It has a very short lifetime as it quickly reacts with an electron to produce gamma rays.