The scattering amplitude describes the amplitude of an outgoing, elementary, spherical wave relative to a plane, incoming wave scattered on a point size particle. Since the spherical wave amplitude varies with 1/R (note, the intensity is the |square| of the amplitude), R being the distance to the point scatterer, the unit of the scattering amplitude includes the unit of a length with respect to the units of the incoming wave. Therefore, the scattering amplitude is often also called scattering length. Look up length, width, breadth in Wiktionary, the free dictionary. ...

Cross section

The scattering amplitude f relates to the scattering cross section s = 4 * π * f². Cross section may refer to the following In geometry, Cross section is the intersection of a 3-dimensional body with a plane. ...

X-rays

The scattering length for X-rays is the Thompson scattering length or classical electron radius r0. The classical electron radius, also known as the Compton radius or the Thomson scattering length is based on a classical (i. ... The classical electron radius, also known as the Compton radius or the Thomson scattering length is based on a classical (i. ...

Neutrons

The nuclear neutron scattering process involves the coherent neutron scattering length, often described by b.

Quantum mechanical formalism

A quantum mechanical approach is given by the S matrix formalism. The S-matrix is the matrix in quantum mechanics or quantum field theory that relates the final state in the infinite future and the initial state in the infinite past. ...