Collision Cross-Sections and Related Quantities

Consider a collision between particles A and B (see Fig. 3.1). Here B is a target fixed in space and A is a projectile incident along z-axis. (Collisions between two moving particles are treated in Sect. 3.4.) The flux of the incident particle is denoted by jin. The number of particles coming out per unit time and per unit solid angle in the direction (θ, φ) is denoted by Jout(θ, φ). (Note that Fig. 3.1 shows a case of axial symmetry and the φ-dependence is omitted.) The quantity Jout is proportional to the incident flux jin.