Binding Energy

Nuclei are bound together due to the short range attractive nuclear force which overcomes the longer range repulsive coulomb force.

Therefore the attractive nuclear potential has to be overcome to release a nucleon. This is known as the Binding Energy and the value is roughly independent of the Mass Number, A, but the small variation is responsible for the possibility of nuclear energy. Nuclei can be fissioned apart or fused together with the resulting nuclei being more stable, i.e. nuclei with a higher Binding Energy.