pion | charge multiplet | -has source: Hopkins, J. 1976 Glossary of Astronomy and Astrophysics, University of Chicago Press | π-meson | 270 me | An unstable nuclear particle of mass intermediate between that of a proton and an electron. The pions are believed to be the particles exchanged by nucleons, resulting in the strong nuclear force; they play a role in the strong interactions analogous to that of the photons in electromagnetic interactions. | -has source: Hopkins, J. 1976 Glossary of Astronomy and Astrophysics, University of Chicago Press |