Cold neutron backscattering spectrometer IN10

The IN10 backscattering spectrometer is designed for inelastic or quasielastic scattering experiments requiring very high energy resolution and moderate momentum transfer resolution. IN10 owes its high energy resolution to the use of nearly perfect backscattering both at the monochromator and at the analyser crystals.

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Applications

Typical applications of the instrument include studies of:

  • Microscopic motions in polymers and biological systems.
  • Diffusive processes in supercooled liquids and dynamic correlations near the liquid glass transition, as well as in confined systems.
  • Rotational or conformational motions in plastic crystals.
  • Solid state diffusion (diffusion of hydrogen in metals, self diffusion in metal and alloys, diffusive processes in intercalated compounds, ...)
  • Quantum tunnelling.
  • Nuclear hyperfine splitting.
  • Magnetism in disordered materials.

Selected examples

Dynamics of conducting polymers

The dynamics of doped polyaniline has been studied in detail by means of quasielastic neutron scattering using a combination of backscattering and time-of-flight spectrometers. Fixed windows scans performed on IN10 on polyaniline doped with different agents reveal the onset of molecular motions by the decrease in the elastic intensity. The change happens at the same temperatures at which the conductivity changes, revealing a correspondence between dynamical and electrical transitions. The analysis of the quasielastic scans allows to study in detail the nature of these motions and to determine their geometry and their characteristics times.

References: D. Djurado et al, Phys. Rev. B 65, 184202 (2002);
M. Bee et al., Chem. Phys.277, 211 (2002) and Appl.Phys. A 74, S402 (2002).

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Helium roton peak

The roton peak is a sharp excitation that appears in superfluid 4He at energies about 0.74 meV.Its linewidth changes very fast with increasing temperature, disappearing completely about the superfluid transition temperature T_lambda = 2.17 K. The temperature dependence of the position and linewidth of the roton peak have been determined with unprecedented precision by measuring it on IN10B using a NaF(111) monochromator that gives access to the energy and momentum transfer region of interest. The linewidths agree with some theoretical results, but the roton energy varies more slowly with temperature than predicted by the same theory. Similar measurements have also been performed in confined superfluid 4He.

References: K. H. Andersen et al., Phys. Rev. Lett. 77, 4043 (1996); C. R. Anderson et al., Phys. Rev. B 59, 13588 (1999).

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