Positron

The positron is the electron’s antiparticle, with the same mass and spin but opposite electric charge. It annihilates with an electron into other particles, often photons.

Electron–positron annihilation: A process in which an electron and positron convert into other particles, commonly two gamma-ray photons. This is the characteristic fate of a positron meeting an electron at low energy.
Paul Dirac: A British theoretical physicist whose work established relativistic quantum mechanics and predicted antimatter. His relativistic electron theory implied a positively charged counterpart.
Positron emission tomography: A medical imaging method that maps radioactive tracer distributions by detecting paired photons from positron annihilation. PET turns positron annihilation inside the body into images of tracer activity.
Electron: A stable elementary particle with negative electric charge and spin one-half. It has the positron’s mass and spin but the opposite electric charge.
Pair production: The creation of a particle and its antiparticle from energy or another particle’s interaction. A sufficiently energetic photon can produce an electron–positron pair near a nucleus.
Carl David Anderson: An American physicist who discovered the positron in cosmic-ray tracks in 1932. His cloud-chamber observations supplied the first clear evidence for the particle.
Fluorine-18: A radioactive fluorine isotope that decays by positron emission and is widely used in PET tracers. Its positrons enable common PET scans using fluorodeoxyglucose.
Proton: A positively charged composite particle found in atomic nuclei, made of quarks and gluons. Its positive charge can resemble a positron’s, but its mass and internal structure differ greatly.
Dirac equation: A relativistic quantum equation describing spin-½ particles such as electrons and positrons. Its negative-energy solutions helped predict the existence of the positron.
Cloud chamber: A particle detector that reveals charged-particle paths as trails of condensed droplets. A magnetic-field cloud-chamber image showed a positive particle with an electron-like mass.

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