Answer: A resonance energy (sharp peak in cross-section).
- A Mainly the reaction threshold energy, with little peak elsewhere
- B A resonance energy (sharp peak in cross-section)
- C All energies uniformly, with a perfectly flat cross-section curve
- D Mainly thermal neutron energies, with little dependence elsewhere
Correct answer: B. A resonance energy (sharp peak in cross-section)
Explanation: Breit-Wigner formula: sigma(E) = sigma_max × Gamma²/4 / [(E-E<sub>R</sub>)² + Gamma²/4] near resonance energy E<sub>R</sub>. Gamma is the width.
Binding energy per nucleon rises sharply for light nuclei, peaks around iron-56 (the most stable nucleus), then slowly declines for heavier nuclei - which is exactly why fusing light nuclei or splitting heavy nuclei both release energy: each moves the products toward this stability peak.
Concept context
Radioactivity, nuclear reactions, fission, fusion, and binding energy.