Binding energy per nucleon
The binding energy of a nucleus divided by the number of nucleons (A). This quantity varies with A in a characteristic curve: it increases from hydrogen to iron (A ≈ 56), then decreases for heavier nuclei. Maximum binding energy per nucleon (~8.8 MeV) occurs for iron-56.
Formula
Binding energy per nucleon = BE / A
Real World
Iron-56, produced in the cores of massive stars like Betelgeuse, sits at the peak of the binding energy curve — stars cannot release energy by fusing or splitting it, which is why iron cores collapse in supernovae.
Exam Focus
When asked to 'explain' why fusion or fission releases energy, explicitly reference the binding energy per nucleon curve and state that products are more stable than reactants.
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