In a more strict meaning, it denotes scattering processes where dynamics in the sample (such as diffusive dynamics) lead to a broadening of the incident neutron spectrum, in contrast to, e.g., the scattering from a diffusionless crystal, where the scattered neutron energy spectrum consists of an elastic line (corresponding to no energy transfer with the sample) and a number of well-separated inelastic lines due to the creation or annihilation of phonons with specific energies.
The term quasielastic scattering was originally coined in nuclear physics.
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.
It is used to investigate topics like Starting in 1992, there is a conference series entitled QENS.
Since 2012, it is being held together with the Workshop on Inelastic Neutron Spectrometry (WINS).