The energy that holds the protons together in an atomic nucleus. Since protons are positively charged, they exert strong mutually repulsive forces and tremendous energy is required to keep them from flying apart. This energy is so great that it results in a slightly lower value for the mass of a nucleus taken as a whole than for the sum of its constituents taken individually. This phenomenon is of vast significance, for it means that a small fraction of mass has been converted into energy within the nucleus, as shown by Einstein's equivalence equation E = mc2. Thus, when a 235U nucleus (92 protons) is split, as in the fission process, a portion of its binding energy (equivalent to the mass difference) is released. It amounts to approximately 200 million electron volts per nucleus. Binding energy may also be defined as the minimum energy required to dissociate a nucleus into its component neutrons and protons. The neutron or proton binding energy is that required to remove a neutron or a proton from a nucleus; the electron binding energy is that required to remove an electron from an atom or molecule.See Mass Defect; Fission.
