Student Physics FAQ: How Does Binding Energy per…

How Does Binding Energy per Nucleon Vary with Nucleon Number; and What Does That Curve Tell You?

Binding energy per nucleon rises rapidly for light nuclei, reaches a maximum in the iron-nickel region around nucleon number $A \approx 56$ to $62$ , and then decreases slowly for heavier nuclei. The curve shows nuclear stability and explains why fusion of light nuclei and fission of heavy nuclei can release energy.

How the curve varies

Binding energy is the energy required to separate a nucleus completely into its individual nucleons. Dividing the total binding energy by the nucleon number $A$ gives the average energy needed to remove one nucleon.

Region of curve	Variation and meaning

How Does Binding Energy per Nucleon Vary with Nucleon Number; and What Does That Curve Tell You?

How the curve varies

Region of curve	Variation and meaning

Very light nuclei	Binding energy per nucleon increases steeply as $A$ increases. Adding nucleons allows each nucleon to experience more attractive strong nuclear force interactions.
Medium-mass nuclei	The curve reaches about $8.8\ \text{MeV}$ per nucleon in the iron-nickel region. These nuclei are among the most tightly bound and therefore most stable.
Heavy nuclei	Binding energy per nucleon decreases gradually. The strong nuclear force is short-range, while electrostatic repulsion acts between all protons and becomes increasingly significant.

How Does Binding Energy per Nucleon Vary with Nucleon Number; and What Does That Curve Tell You?

How the curve varies

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How Does Binding Energy per Nucleon Vary with Nucleon Number; and What Does That Curve Tell You?

How the curve varies

What the curve predicts

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