Estimate reaction rates and interaction probabilities from cross-section data in barns.
The nuclear cross-section is a measure of the probability that a specific nuclear reaction will occur. It has units of area (typically barns, where 1 barn = 10⁻²⁴ cm²) but represents an effective target area rather than a physical one. A larger cross-section means a higher probability of interaction.
The reaction rate R equals the beam flux times the target number density times the cross-section times the target thickness: R = Φ × n × σ × d. This is fundamental to reactor physics, particle physics experiments, and radiation shielding calculations.