reaction cross-section

Reaction cross-section is a measure of the probability that a specific nuclear or particle interaction will occur when two particles collide. Imagine it as the "effective size" or target area that one particle presents to another for a particular reaction to happen. The larger the cross-section, the more likely the particles are to interact. It is usually expressed in units called "barns" (1 barn = 10^-24 cm²). This concept helps scientists predict reaction rates in processes like nuclear fusion, radioactive decay, or particle collisions in accelerators.