What is the anti-matter equivalent of an electron?

The antimatter equivalent of an electron is a positron. Also called an antielectron, it has the same mass and spin as an electron but carries a positive electric charge instead of the electron’s negative charge.

The positron was predicted by physicist Paul Dirac’s relativistic theory of the electron in 1928. Its existence was confirmed in 1932 by American physicist Carl Anderson, who observed the particle’s track in a cloud chamber while studying cosmic rays. Anderson received the 1936 Nobel Prize in Physics for the discovery.

A positron is not simply a positively charged proton. Protons are much heavier composite particles found in atomic nuclei, whereas positrons are elementary particles with the same mass as electrons. This distinction is a common source of confusion when people first encounter antimatter.

When a positron meets an electron, the pair can annihilate, converting their mass into energy, usually producing two gamma-ray photons when the particles collide at low energies. Positrons are also used in medical imaging, especially positron-emission tomography, or PET scans.