In spectroscopic (inelastic) neutron scattering techniques, energy exchange between the incident neutron beam and the atomic and magnetic vibrations is accurately resolved as reciprocal lattice scans. The change in excitation state within the sample leads to modification of both the energy of the neutron and the internal state of the sample such that the total energy is conserved. A wide variety of different physical phenomena can be probed such as the motions of atoms (diffusional or hopping), the rotational modes of molecules, sound modes and molecular vibrations, recoil in quantum fluids, magnetic and quantum excitations or even electronic transitions. Neutron polarisation analysis additionally grants the ability to separate the components of the neutron scattering cross section, thereby permitting the isolation of weak magnetic or structural signals, as well as giving direct access to the directional components of the sample magnetization.
In time-of-flight spectrometers the neutron beam is pulsed using a rotating mechanical chopper and the neutron energies can then be measured simply by timing their arrival at the detector. A broad spectrum of energies is recorded simultaneously. TOFS are used in chemistry and in studies of soft matter, as well as for studies of polycrystalline, glassy and liquid samples.
The triple axis spectrometer (TAS) is the most widely used instrument in the study of materials with neutron scattering. It enables measurement of the inelastic scattering of neutrons due to energy or momentum exchange with the sample dynamics in a single crystal by determining (and measuring) the initial and final neutron energies using Bragg reflections. The spectrometer is called triple axis due to the three vertical axes of rotation located at the monochromator, sample stage as well as analyser goniometer. Independent control of the momentum (Q) and energy transfer (E) is routine.
Cold TAS: Cold -Triple Axis Spectrometer
Cold TAS is a spectrometry technique which utilizes cold neutrons (0.0 - 0.025 eV) for material investigations of nuclear and magnetic structures, quasi-elastic scattering, and lattice and magnetic dynamics in a variety of materials, including superconductors, transition metal oxides, multiferroics, thermoelectric materials, and low-dimensional quantum magnets. Compared to thermal TAS, this enables study of energy transfers from -4 meV < ∆E < 9 meV with quite good energy resolution (50 μeV and upwards to 1meV or so) and is good for high-resolution studies of diffusing molecules (diffusing both translationally and rotationally), molecules tunnelling between different orientational states and other large-scale motions of whole units within molecules.
Thermal TAS: Thermal Triple Axis Spectrometer
Thermal TAS is a spectrometry technique which utilises thermal neutrons (0.025 eV) for material investigations. This provides spectroscopic information with much more detail than obtained from optical spectroscopy methods like infra-red or Raman spectroscopy. The difference is that, in addition to thermal neutrons having wavelenghts comparable with interatomic spacings, they also have energies comparable to vibrational energies in solids and inelastic neutron scattering provides additional information on the spatial nature of the modes or excitations. Application of the technique includes spin and lattice dynamics investigation in high-temperature superconductors, magnetic excitations in low-dimensional magnetic model systems, spin waves in magnetically ordered systems, phonon anharmocities and linewidths in thermoelectric materials and alloys, magnetic critical scattering in phase transitions and crystalline electric fields amongst others.
SES: Spin Echo Spectrometer
Neutron Spin-Echo spectroscopy is the neutron scattering technique that processes high energy resolution (neV). It uses the spin precession of polarized neutrons in magnetic field to measure tiny velocity changes of the individual neutrons during the scattering process. It is ideal to investigate slow relaxations processes in polymers, fluctuations in soft colloidal systems or proteins functions.