Answer: Effective target area for reaction probability (in barns = 10⁻²⁴ cm²).
- A The literal physical geometric size of the target nucleus
- B Effective target area for reaction probability (in barns = 10⁻²⁴ cm²)
- C The kinetic energy carried by the incoming projectile particle
- D The mass defect of the nucleus formed after the reaction
Correct answer: B. Effective target area for reaction probability (in barns = 10⁻²⁴ cm²)
Explanation: Cross-section sigma: effective area for nuclear reaction. 1 barn = 10⁻²⁴ cm² = 10⁻²⁸ m². Reaction rate R = n × phi × sigma × N<sub>target</sub>.
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.