For example, an electron and a positron, each with a mass of 0.511 MeV/ c, can annihilate to yield 1.022 MeV of energy. A proton has a mass of 0.938 GeV/ c. In general, the masses of all hadrons are of the order of 1 GeV/ c, which makes the GeV/ c a convenient unit of mass for particle physics: