The neutron cross section is defined for a given type of target particle. its relative angle between the incident neutron and the target nuclide,.the incident particle energy, also called speed or temperature (thermal, fast…),.the type of nuclear reaction (scattering, fission…).The neutron cross section, and therefore the probability of an neutron-nucleus interaction, depends on: 4 Microscopic versus macroscopic cross section.3 Continuous versus average cross section.2 Link to reaction rate and interpretation.1.3 Incident particle energy dependence.A poison that is purposely inserted into a nuclear reactor for controlling its reactivity in the long term and improve its shutdown margin is called a burnable poison. Nuclides which have a large absorption cross section are neutron poisons if they are neither fissile nor undergo decay. Isotopes which have a large scatter cross section and a low mass are good neutron moderators (see chart below). Some isotopes, like uranium-238, have nonzero cross sections of all three. The remaining isotopes will simply scatter the neutron, and have a scatter cross section. Isotopes that undergo fission are fissionable fuels and have a corresponding fission cross section. Nuclides that tend to absorb a neutron and either decay or keep the neutron in its nucleus are neutron absorbers and will have a capture cross section for that reaction. The larger the neutron cross section, the more likely a neutron will react with the nucleus.Īn isotope (or nuclide) can be classified according to its neutron cross section and how it reacts to an incident neutron. The standard unit for measuring the cross section is the barn, which is equal to 10 −28 m 2 or 10 −24 cm 2. 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 neutron cross section σ can be defined as the area in cm 2 for which the number of neutron-nuclei reactions taking place is equal to the product of the number of incident neutrons that would pass through the area and the number of target nuclei. In nuclear physics, the concept of a neutron cross section is used to express the likelihood of interaction between an incident neutron and a target nucleus. JSTOR ( September 2011) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed.įind sources: "Neutron cross section" – news Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.
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