CRG - thermal neutron backscattering spectrometer
- The incoming polychromatic neutron beam (wavelength around 2.2 Å) is backscattered on the monochromator (Bragg reflexion on a crystal lattice) with a high monochromaticity (energy resolution 10 µeV).
- The beam is reflected so as to hit the sample. The scattered neutrons are analysed by a Bragg reflexion on the analysers.
- A chopper creates "bursts" of neutrons, so as only those neutrons who have travelled from the sample to the analysers and back to the detectors are counted.
- The energy transfer between the neutron hitting the sample and the neutrons scattered by the sample is monitored by varying the monochromator temperature (with reference to the analysers temperature which remains almost constant).
- Elastic scattering (energy transfer = 0) or inelastic scattering (energy transfer up to ca. 200 µeV) is analysed as a function of the scattering angle.
- This gives access to the dynamical characteristics of the scattering sample, and mostly to the hydrogen atoms it contains.