Binding Energy per Nucleon

Binding energy is the energy needed to disassemble a nucleus into its constituent protons and neutrons.

Equivalently, it is the ENERGY RELEASED when free nucleons assemble into a nucleus (mass-energy equivalence).

Mass defect: Δm = Zm_p + (A−Z)m_n − m_nucleus. The nucleus weighs LESS than its parts.

Binding energy: B = Δm · c². Often quoted in MeV using 1 u = 931.5 MeV/c².

Binding energy per nucleon B/A is the most useful quantity: nuclei with larger B/A are more stable.

B/A peaks at A ≈ 56 (Fe-56, Ni-62) with ~8.8 MeV/nucleon. Falls off for heavier and lighter nuclei.

Fission of heavy nuclei (A > 56) and fusion of light nuclei (A < 56) BOTH release energy because the products have higher B/A.

Iron-56 is the most stable nucleus per nucleon — endpoint of stellar nucleosynthesis.