Annihilation

Annihilation is a phenomenon in which a particle and an antiparticle come together. By combining, both original particles disappear and particles of a different type are created.

In medicine, this phenomenon is commonly observed when a positron and an electron interact, emitting two photons of energy 0.51 MeV flying in opposite directions. An example of this radiation is the β⁺ emitter in PET or electron-positron pairs diagnostics.