Nuclear cross section

A measure of the likelihood that a specified nuclear interaction occurs, expressed as an effective area. It depends on the incident particle, its energy, and the target nucleus.

Scattering cross section: A cross section describing the probability and angular distribution of particles scattered by a target. It measures interactions that redirect particles rather than necessarily changing the nucleus.
Barn (unit): A unit of area equal to 10⁻²⁸ square metres, commonly used for nuclear cross sections. Nuclear interaction areas are often conveniently expressed in barns and submultiples.
Neutron capture: A nuclear reaction in which an atomic nucleus absorbs a neutron. Capture cross sections determine how readily materials absorb neutrons in reactors and detectors.
Total cross section: The cross section for all specified interactions between an incident particle and a target. It combines the channels counted by a chosen interaction definition.
Differential cross section: A cross section specified per unit solid angle, energy, or another interval of final states. It resolves which scattering angles or reaction outcomes contribute to a nuclear interaction.
Particle flux: The number of particles crossing a unit area per unit time. Flux is needed alongside cross section to calculate how often a beam induces reactions.
Fission cross section: The cross section for an incident particle to induce nuclear fission in a target nucleus. Its energy dependence helps determine whether fissile material sustains a chain reaction.
Elastic scattering: Scattering in which the particles' internal states remain unchanged, though their directions may change. Its cross section counts a different outcome from reactions that alter nuclear states or composition.
Resonance: A temporary excited state formed when an incoming particle's energy matches a system's allowed energy level. Resonances can produce sharp peaks in a nuclear cross section at particular energies.
Target thickness: The amount of target material encountered by an incident particle beam, often expressed as nuclei per unit area. Reaction yields depend on how many target nuclei the beam passes through.

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