Elektronpositron

Elektronpositron is the system formed by the elementary particle electron and its antiparticle, the positron. The electron and positron have the same mass (about 9.109 × 10^-31 kilograms) and opposite electric charges (−e and +e). They are leptons with spin 1/2 and are described by quantum electrodynamics.

When an electron and a positron meet, they annihilate, converting their mass into energy in the form of photons. In free space, annihilation typically yields two gamma rays of 511 keV emitted in nearly opposite directions to conserve momentum. A bound state of an electron and a positron, called positronium, can form briefly before annihilation. Positronium exists in two spin configurations: para-positronium, which decays into two photons, and ortho-positronium, which decays into three photons; their lifetimes in vacuum are about 125 picoseconds and 142 nanoseconds, respectively.

Positrons are produced naturally in beta-plus decay and can be generated artificially by radioactive sources or particle accelerators. They can be created through pair production when high-energy photons interact with nuclei, requiring energy above 1.022 MeV. In applied science, positron-emitting isotopes are used in positron emission tomography (PET) for medical imaging, and in materials science for positron annihilation spectroscopy to study electron density and defects. In fundamental physics, electron-positron collisions test quantum electrodynamics and probe for new phenomena.

The concept dates to the discovery of the positron by Carl D. Anderson in 1932, supporting Dirac’s prediction of antimatter. Electron-positron interactions remain central to particle physics, astrophysics, and modern medical technology.