cross section (redirected from cross-sectional)

cross section

In nuclear physics, a measure of the probability that a given atomic nucleus will exhibit a specific reaction (absorption, scattering, or nuclear fission) in relation to a particular incident particle. Cross section is expressed in terms of area, and its value is chosen so that, if the bombarding particle hits a circular target of this size perpendicular to its path and centred at the nucleus, the given reaction occurs. If it misses the area, the reaction does not occur. The unit of cross section is the barn, which equals 10⁻²⁴ sq cm. Cross-section values for a given nucleus depend on the energy of the bombarding particle and the kind of reaction and are often different from the actual cross-sectional area of the nucleus.

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cross section

1. Maths a plane surface formed by cutting across a solid, esp perpendicular to its longest axis

2. a section cut off in this way

3. Physics a measure of the probability that a collision process will result in a particular reaction. It is expressed by the effective area that one participant presents as a target for the other