Binding energy

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The energy required to separate particles which are bound by electromagnetic or nuclear forces (infinitely far apart). In the case of the nucleus of an atom, these particles are protons and neutrons held together by the nuclear binding energy. The neutron and proton binding energies are the energies necessary to release a neutron or proton from the nucleus. Electron binding energy is the energy required to completely remove an electron from an atom or a molecule. The binding energy of nucleons in the nucleus of an atom amounts for most nuclei (i.e. Z>5) to around 8 MeV per nucleon. However in the case of the heaviest nuclei of an atom, such as uranium, the binding energy per nucleon is slightly less negative than for nuclei with medium mass numbers. Therefore, the fission of an uranium nucleus into two nuclei of medium mass number results in a total more negative binding energy leading to energy being released to the outside (See also 'nuclear fission'). Similarly the binding energy of the light nuclei of the hydrogen isotopes deuterium and tritium is significantly less negative than that of the helium nucleus He-4. Thus, energy is released during the fusion of deuterium and tritium to helium (See also 'fusion').

Diagram binding energy

Nucleus binding energy per nucleon as a function of the mass number

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