the binding energy of a nucleus is the amount of energy needed to
Nuclear binding energy Nuclear binding energy is the minimum energy that would be required to disassemble the nucleus of an atom into its component parts. These component parts are neutrons and protons, which are collectively called nucleons. The binding energy is always a positive number, as we need to spend energy in moving the nucleons away from each other (attracted by nuclear force). The mass of an atomic nucleus is less than the sum of the individual masses of the free constituent protons and neutrons (according to Einstein's equation E=mc2) and this 'missing mass' is known as the mass defect, and represents the energy that was released when the nucleus was formed.