Neutron cross section

A measure of the probability that a neutron will interact with a particular nucleus. It is expressed as an effective area, usually in barns, and depends on neutron energy and interaction type.

Barn (unit): A unit of area equal to 10⁻²⁸ square metres, commonly used for nuclear cross sections. Neutron cross sections are conventionally reported in barns.
Neutron: An electrically neutral subatomic particle found in atomic nuclei and produced in nuclear reactions. Its energy and interactions with nuclei set the conditions for a cross section.
Nuclear reactor: A system that sustains a controlled nuclear fission chain reaction to produce energy or neutrons. Reactor calculations rely on cross sections to predict neutron balance and fuel consumption.
Total cross section: The sum of cross sections for all possible interactions between an incident particle and a target. It combines the neutron interaction channels represented by partial cross sections.
Neutron flux: The number of neutrons crossing a unit area per unit time, often resolved by energy. Multiplying flux by a cross section gives an interaction rate per target nucleus.
Nucleus: The compact, positively charged central part of an atom, composed of protons and neutrons. A cross section is defined for a neutron interacting with a specified target nucleus.
Neutron shielding: Materials and structures used to reduce neutron radiation reaching people or equipment. Shielding design depends on scattering and absorption cross sections of candidate materials.
Scattering cross section: A measure of the probability that an incident particle is deflected by a target. It counts neutron scattering, unlike absorption-only measures.
Macroscopic cross section: A material-level measure of neutron interaction probability per unit path length, combining number density and microscopic cross section. It converts the nucleus-level quantity into attenuation through bulk material.
Neutron energy: The kinetic energy carried by a neutron, commonly grouped into thermal, epithermal, and fast ranges. The same nucleus can have very different cross sections at different neutron energies.

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