This Day In History: 1932-08-02
American physicist Carl Anderson discovered positrons. He was examining chamber photographs of cosmic rays when he realised that the tracks orientation revealed the existence of positively charged particles too small to be protons. The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1 e, a spin of 1/2, and has the same mass as an electron. When a positron collides with an electron, annihilation occurs.