In
nuclear and
particle physics, the concept of a
neutron cross section is used to express the likelihood of interaction between an incident
neutron and a target nucleus. In conjunction with the
neutron flux, it enables the calculation of the reaction rate, for example to derive the thermal
power of a
nuclear power plant. The standard unit for measuring the cross section is the
barn, which is equal to 10
-28 m
2 or 10
-24 cm
2. The larger neutron cross section, the more likely a neutron will react with the nucleus.