The elementary antiparticle of an electron with mass equal to that of an electron but with positive rather than negative charge. Its existence was theoretically predicted by P. A. M. Dirac in 1928. It was first observed by C. D. Anderson in 1932. Positrons and electrons have the same spin and statistics. Positrons are naturally produced by radioactive decay of many heavier particles; this is referred to as beta-plus decay. Electron-positron pairs are also produced when high-energy photons or electrons interact with matter.