Paul Dirac’s 1928 equation predicted the positron before it was observed. The positron is the electron’s antimatter counterpart, with the same mass and spin but positive electric charge.
Dirac developed a relativistic wave equation that combined quantum mechanics with special relativity. Its mathematical solutions included states that seemed to have negative energy. Dirac’s interpretation led to the prediction that a particle with electron-like properties but opposite charge should exist.
Carl Anderson discovered the positron in 1932 while studying cosmic-ray tracks in a cloud chamber. Its curved path in a magnetic field showed a positive charge, while its mass matched that expected for an electron. The discovery provided striking support for Dirac’s theory.
When a positron meets an electron, the pair can annihilate, commonly producing two gamma-ray photons in a suitable frame. Positrons are also used in medical positron-emission tomography, or PET, imaging.