Quasielastic neutron scattering (QENS) designates a
limiting case of
inelastic neutron scattering
Neutron scattering, the irregular dispersal of free neutrons by matter, can refer to either the naturally occurring physical process itself or to the man-made experimental techniques that use the natural process for investigating materials. Th ...
, characterized by energy transfers being small compared to the incident energy of the scattered particles. 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
phonon
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids. A type of quasiparticle, a phonon is an excited state in the quantum mechanical ...
s with specific energies.
The term
quasielastic scattering was originally coined in nuclear physics. It was applied to thermal
neutron scattering
Neutron scattering, the irregular dispersal of free neutrons by matter, can refer to either the naturally occurring physical process itself or to the man-made experimental techniques that use the natural process for investigating materials. Th ...
since the early 1960s, notably in an article by
Leon van Hove and in a highly cited one by
Pierre Gilles de Gennes.
QENS is typically investigated on high-resolution spectrometers (
neutron backscattering,
neutron time-of-flight scattering,
neutron spin echo
Neutron spin echo spectroscopy is an inelastic neutron scattering technique invented by Ferenc Mezei in the 1970s, and developed in collaboration with John Hayter. In recognition of his work and in other areas, Mezei was awarded the first Walt ...
).
It is used to investigate topics like
*
solid-state diffusion (e.g. hydrogen in metals)
*
slow mode
In everyday use and in kinematics, the speed (commonly referred to as ''v'') of an object is the magnitude of the change of its position over time or the magnitude of the change of its position per unit of time; it is thus a scalar quantity ...
s in crystals (e.g.
methyl group rotation)
*
relaxation of viscous liquids
Conference Series
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).
Textbooks
* M. Beé, ''Quasielastic Neutron Scattering'', Adam Hilger: Bristol (1988).
* R. Hempelmann, ''Quasielastic Neutron Scattering and Solid State Diffusion'', Clarendon Press: Oxford (2000).
References
{{Reflist
Neutron scattering