An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Same as → cross section.

→ collisional; → cross; → section.

1) Math: The intersection of a plane with a geometric figure, usually at right angles to an axis of symmetry.
2) Physics: A quantity that expresses the effective area that a given particle presents as a target to another incident particle, giving a measure of the probability that the incident particle will induce a particular atomic or nuclear reaction. Also called collision cross section. The cross section has the dimensions of a surface. In nuclear and particle physics, the commonly used units for the cross section are the barn and cm².

In classical mechanics, the cross section for the collision of a point particle with a hard sphere is just be the surface of a section through the middle of the sphere. This explains the name "cross section." → cross; → section.

The → cross section involved the → Thomson scattering of electromagnetic waves by a free electron. It is defined by: σ_T = 8πr_e²/3, where r_e is the classical → electron radius. Its value is 0.665 245 x 10^-28 m².

→ Thomson; → cross; → section.