The destruction of a particle and its antiparticle as a result of a collision between them. The annihilation radiation produced is carried away by photons or mesons. For example, in a collision between an electron and a positron the energy produced is carried away by two photons, each having an energy of 0.511 MeV, which is equivalent to the rest-mass energies of the annihilated particles plus their kinetic energies. When nucleons annihilate each other, the energy is carried away by mesons and antimesons.