Body face
- antiparticle of the electron: same mass and spin, charge +e
- annihilate with electrons → two 511 keV gamma-ray photons, emitted back to back
- produced in β⁺ decay: p → n + e⁺ + νₑ (in proton-rich nuclei)
- PET scans (positron emission tomography): tracer with a positron emitter (usually fluorine-18), detectors record coincident photon pairs