4. Dynamics

In condensed matter, atoms and molecules are bound together by forces that help to organize the overall structure of the material. They are therefore not immobile, but animated by movements. The study of these movements provides information on the interactions they undergo. Neutron scattering is a powerful tool here too, since the kinetic energy of thermal neutrons is of the order of magnitude of the interactions in matter.

Traditionally, a distinction is made between two situations: on the one hand, collective modes involve very large numbers of atoms or molecules, generally distributed over a crystal lattice; on the other hand, diffusive modes or excited levels tend to involve individual entities. Two particularly effective types of instrument are used for each of these situations: the three-axis spectrometer for collective modes, and the quasi-elastic time-of-flight...