nuclear binding energy

Nuclear binding energy in experimental physics is the minimum energy that is required to fully disassemble the nucleus of one atom into its constituent protons and neutrons, known collectively as nucleons. The binding energy for stable nuclei is always a positive number, as the nucleus must gain energy for the nucleons to move apart from each other. Nucleons are attracted to each other by the strong nuclear force. In theoretical nuclear physics, the nuclear binding energy is considered a negative number. In this context it represents the energy of the nucleus relative to the energy of the constituent nucleons when they are infinitely far apart. Both the experimental and theoretical views are equivalent, with slightly different emphasis on what the binding energy means.

The mass of an atomic nucleus is less than the sum of the individual masses of the free constituent protons and neutrons. The difference in mass can be calculated by the Einstein equation, E = mc, where E is the nuclear binding energy, c is the speed of light, and m is the difference in mass. This "missing mass" is known as the mass defect, and represents the energy that was released when the nucleus was formed.