E.3.3—Binding energy curve

Read the curve

Binding energy per nucleon rises for light nuclei, reaches a broad maximum for medium-mass nuclei, then decreases gradually for very heavy nuclei. The curve compares average nuclear stability per nucleon, not total binding energy.

Predict energy release

Fusion of light nuclei can move products upward toward the maximum. Fission of very heavy nuclei can also move products upward. In either case, the increase in binding energy per nucleon corresponds to released energy.

Sketch the trend

Show a rise from the light-nucleus region, a maximum between roughly A=50 and A=100, and a slow decline for larger A. Exact numerical values are not required for the qualitative graph.

Common trap

Do not claim that the heaviest nucleus is most stable simply because it has the largest total binding energy. Use binding energy per nucleon to compare stability.

How it is assessed

Questions draw the qualitative graph of binding energy per nucleon against A.

Command terms

Draw

What earns marks

Draw a rising curve, a maximum between A≈50 and 100, and a declining tail; exact vertical scale is unnecessary.

Watch for

Drawing a monotonic increase or placing the main maximum at the largest A.

Retrieve the nuclear structure

Isotopes differ in neutrons; mass defect becomes binding energy; the binding-energy curve explains why fusion and fission can release energy; and the strong force competes with electromagnetic repulsion.

Retrieve the decay model

Alpha, beta and gamma decays change A and Z differently. Radioactive decay is random but statistically predictable; use half-life, count-rate scaling and background correction carefully.

E.3.3—Binding energy curve

Read Binding Energy Curve

E.3.3 Exam Analysis

Assessment in practice

Retrieve the SL Nuclear Model