The Time-of-flight and High-Resolution (TOF/HR) group of the ILL operates three distinct kinds of instruments that measure the atomic, molecular and crystal motions of samples in powder, glass or liquid form:
- time-of-flight spectrometers which analyse the change of velocity of neutrons interaction with the sample by measuring their time of arrival;
- backscattering spectrometers, a special version of the three-axis spectrometer with very high resolution, achieved by reflecting the scattered neutrons under normal incidence from perfect crystals
- spin-echo spectrometers which measure small changes in neutron velocities very precisely by analising how their spins precess - like the axis of a spinning top - before and after interaction with the sample.
In Time-of-Flight instruments, series of bursts of monochromatized neutrons is send upon the sample.
The energy of the scattered neutrons is then analysed by measuring their time of arrival at the detectors which cover a wide angular range. The monochromatization of the beam is performed either by a set of disc choppers turning at high speed (IN5) or by a set of crystals with the beam being pulsed by a Fermi chopper (BRISP, IN4 and IN6).
These instruments are mainly used to study stochastic motions of atoms, molecules, ions and chemical entities, spins, on a microscopic level. They are also useful to study low frequency vibrations, in glasses for example.