In a gas of finite-sized particles there are collisions among particles that depend on their cross-sectional size. The average distance that a particle travels between collisions depends on the density of gas particles. These … See more

If a beam of particles enters a thin layer of material of thickness dz, the flux Φ of the beam will decrease by dΦ according to
where σ is the total … See more

In the time-independent formalism of quantum scattering, the initial wave function (before scattering) is taken to be a plane wave with definite See more

For light, as in other settings, the scattering cross section for particles is generally different from the geometrical cross section of the particle, and it depends upon the See more

Consider a classical measurement where a single particle is scattered off a single stationary target particle. Conventionally, a spherical coordinate system is used, with the target placed at the origin and the z axis of this coordinate system aligned with the incident beam. … See more

Although the SI unit of total cross sections is m , a smaller unit is usually used in practice.
In nuclear and particle physics, the conventional unit is the barn b, where 1 b = 10 m = 100 fm . Smaller prefixed units such as See more

Elastic collision of two hard spheres
The following equations apply to two hard spheres that undergo a perfectly elastic collision. Let R and r denote the radii of the scattering center and scattered sphere, respectively. The differential cross section is See more