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neutron scattering
Neutron scattering, the scattering of free neutrons by matter, can refer to either the physical process or the experimental technique which uses this process for the investigation of materials. Neutron scattering as a physical process is of primordial importance in nuclear engineering. Neutron scattering as an experimental technique is used in crystallography, physics, physical chemistry, biophysics, and materials research. It is practiced at research reactors and spallation neutron sources that provide neutron radiation of sufficient intensity. Neutron diffraction (elastic scattering) is used for determining structures; Inelastic neutron scattering is used for the study of atomic vibrations and other excitations.
== Scattering of fast neutrons ==
"Fast neutrons" (see neutron temperature) have a kinetic energy above 1 MeV. Their scattering by condensed matter (with nuclei having kinetic energies far below 1 eV) is in a good approximation an elastic collision with a particle at rest. At each collision the fast neutron transfers a significant part of its kinetic energy to the scattering nucleus; the more so the lighter the nucleus. In this way the neutron is slowed down until it reaches thermal equilibrium with the material in which it is scattered.
Neutron moderators are used to produce "thermal neutrons" that have kinetic energies below 1 eV (T < 500K).〔
〕 Thermal neutrons are used to maintain a nuclear chain reaction in a nuclear reactor, and as a research tool in neutron science comprising scattering experiments and other applications (see below). The remainder of this article concentrates on the scattering of thermal neutrons.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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