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Neutron moderators are used to produce thermal neutrons, which have kinetic energies below 1 eV (T < 500K). [1] Thermal neutrons are used to maintain a nuclear chain reaction in a nuclear reactor, and as a research tool in neutron scattering experiments and other applications of neutron science (see below). The remainder of this article ...
The wavelength, λ, is on the order of a few angstroms (Å). Because a thermal neutron cannot “see” the internal structure of a nucleus, the scattering is considered to be isotropic. This interaction is thus characterized by a scattering length of b, which is on the same order of the size of a nucleus (10 −15 m). Therefore, nuclear ...
A thermal neutron is a free neutron with a kinetic energy of about 0.025 eV (about 4.0×10 −21 J or 2.4 MJ/kg, hence a speed of 2.19 km/s), which is the energy corresponding to the most probable speed at a temperature of 290 K (17 °C or 62 °F), the mode of the Maxwell–Boltzmann distribution for this temperature, E peak = k T.
Reactions with neutrons are important in nuclear reactors and nuclear weapons. While the best-known neutron reactions are neutron scattering, neutron capture, and nuclear fission, for some light nuclei (especially odd-odd nuclei) the most probable reaction with a thermal neutron is a transfer reaction:
Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material. A sample to be examined is placed in a beam of thermal or cold neutrons to obtain a diffraction pattern that provides information of the structure of the material.
The Debye–Waller factor (DWF), named after Peter Debye and Ivar Waller, is used in condensed matter physics to describe the attenuation of x-ray scattering or coherent neutron scattering caused by thermal motion. [1] [2] It is also called the B factor, atomic B factor, or temperature factor.
¯ is the average lethargy gain per scattering event. Lethargy is defined as decrease in neutron energy. (fast utilization) is the probability that a fast neutron is absorbed in fuel. is the probability that a fast neutron absorption in fuel causes fission.
Thermal neutrons are described by both the free gas and S(α,β) models. For photons, the code accounts for incoherent and coherent scattering, the possibility of fluorescent emission after photoelectric absorption, absorption in pair production with local emission of annihilation radiation, and bremsstrahlung.