The term cross-section is used in an unusual sense in the nuclear jargon. What does it really mean?
The term cross-section generally refers to a plane surface or area of a cut-out section. The basic meaning of cross-section remains the same in the nuclear jargons as well. However, it is used to represent the probability of interaction between a projectile (a particle, say neutron that impinges on a target) and a target (say, an atom, that is hit by the projectile). Imagine a projectile approaching a target as in the figure below. Obviously the chance (probability) of a collision depends on the surface area projected by the target. i.e. The probability of collision is larger if the area is larger. If there are a large number of projectiles, the number of projectiles that could hit the surface is larger if the surface area is larger. Arguing in this manner, it is easy to visualize that the probability of collision (i.e. interaction) between the target and the projectile could be expressed by the effective surface area available for the collision. The idea is extended to represent proba
