Electron-positron annihilation occurs when an electron and a positron (the electron's anti-particle) collide. The result of the collision is the conversion of the electron and positron and the creation of gamma ray photons or, less often, other particles. The process must satisfy a number of conservation laws, including: * Conservation of charge. The net charge before and after is zero. * Conservation of linear momentum and total energy. This forbids the creation of a single gamma ray. * Conservation of angular momentum.