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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 concentrates on the scattering of thermal neutrons.
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.
In neutron scattering, neutrons interact with nuclei and the interaction depends on the isotope; some light elements like deuterium show similar scattering cross section as heavy elements like Pb. In zero order dynamical theory of diffraction the refractive index is directly related to the scattering length density and is a measure of the ...
The first type of interaction is nuclear scattering occurs when neutrons interact with nuclei through the very short range nuclear force. 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.
Fast neutrons are often detected by first moderating (slowing) them to thermal energies. However, during that process the information on the original energy of the neutron, its direction of travel, and the time of emission is lost. For many applications, the detection of "fast" neutrons that retain this information is highly desirable. [64]
It was applied to thermal neutron scattering since the early 1960s, notably in an article by Leon van Hove [1] and in a highly cited one by Pierre Gilles de Gennes. [2] QENS is typically investigated on high-resolution spectrometers (neutron backscattering, neutron time-of-flight scattering, neutron spin echo). It is used to investigate topics like
Neutron scattering allows scientists to count scattered neutrons, measure their energies and the angles at which they scatter, and map their final positions. This information can reveal the molecular and magnetic structure and behavior of materials, such as high-temperature superconductors , polymers , metals, and biological samples.
Spin echo small angle neutron scattering (SESANS) measures structures from around 20 to 2000 nm in size. The information is presented as a real-space (similar to g(r)) as opposed to a reciprocal space (q(r)) mapping.