The energy released when protons and neutrons bind together to form an atomic nucleus, or the energy required to break up that nucleus. The binding energy per proton or neutron is greatest for atoms with mass numbers in the range 50–65 (the iron peak). Energy is released when lighter atoms combine to form heavier ones (as in nucleosynthesis inside stars), provided the products are no heavier than iron. Conversely, when heavy atoms break down to lighter ones (e.g. in fission reactors) energy is also released, provided the products remain heavier than iron. The binding energy is the equivalent of the mass defect.
Subjects: Physics — Astronomy and Astrophysics.