In quantum physics, neutrons are particles that can occur as building blocks of atomic nuclei. In a nuclear reactor, neutrons can be set free when nuclei decay (fission, radioactivity). All quantum particles can exhibit wave phenomena we typically associate with light or sound. Diffraction is one of those phenomena; it occurs when waves encounter obstacles whose size is comparable with the wave length. If the wave length of a quantum particle is short enough, atoms or their nuclei can serve as diffraction obstacles. When neutrons from a reactor are slowed down and selected properly, their wave length lies near one Angstrom, the typical separation between atoms in a solid material.
A neutron diffraction measurement requires a neutron source (e.g. a reactor), a target (the material to be studied), and a detector. Other components may be needed to select the desired neutron wavelength. Some parts of the setup may also be movable.
Neutron diffraction then reveals structural details of the target material, which are measured by recording the way in which neutrons are deflected. Neutrons can also change their speed during the scattering experiment; this is used to study the types of vibrations that can occur in the solid. An important difference between neutron and X-ray diffraction is that neutrons are sensitive to magnetic forces in the material.\n
