Mass Defect and Binding Energy

The mass defect of a bound nucleus is the sum of the masses of its separate protons and neutrons minus the mass of the nucleus. The corresponding binding energy is E = Δm c²: the energy needed to separate the nucleus completely into free nucleons.

Binding energy per nucleon compares the average binding of nuclei of different sizes. It is greatest in the iron–nickel region and generally decreases for heavier nuclei. Total binding energy alone is not a reliable comparison of nuclear stability. Calculations using atomic masses must account for electrons consistently.

Key terms

• mass defect (Δm)

• binding energy

• nucleon

• atomic mass unit (u)