Binding energy

The binding energy of an assembly of particles is the energy required to separate the particles. It is calculated from the internal energies and masses, using the Einstein relationship E = mc², applied separately to the assembly and its constituents. The result in a mass defect : the assembly is lighter than its constituents. In the case of a nucleus, the mass defect is about 1%. Translating masses into energies by multiplying by the square of the speed of light (300 000 km/s, a huge number), this leads to binding energies of around 8 million electronvolts per nucleon. In the fission of uranium nuclei, a fraction of this impressive hidden energy is released.