ANNIHILATION (Latin: annihilatio)—destruction, annihilation)—the action of particles with their anti-particles. As a result they change into other particles of the same total energy and the same total momentum, spin, etc. For example, the result of the annihilation of a negatron with a positron (of relatively small energies) is the appearance of two photons. The annihilation of a proton with an antiproton results in π+ and π- mesons. The particles that result from annihilation may possess zero inertial mass (π mesons). The kind of particles that result from annihilation depend on the energy of the annihilating particles. For example, with sufficiently great energy (>1 GeV) a negatron and a positron as the result of annihilation may change into μ+ and μ- mesons.

Annigiliacya in Fizičeskaya encyklopedya, Mwa 1960, 1998² I 85–87; E. H. Wichmann, Quantum Physics, NY 1967 (Fizyka Kwantowa, Wwa 1973, 1975², 181–183); M. Kubiak, Antymateria we wszechświece [Antimatter in the universe], in: Encyclopedia fizyki współczesnej [Encyclopedia of contemporary physics], Wwa 1983, 908–912; M. Swięcki, Oddziaływania elektromagnetyczne [Electromagnetic reactions], ibid. 143–155.

Henryk Piersa

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