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Cold neutron backscattering spectrometer IN16

The backscattering spectrometer IN16 uses neutron optical focusing in the primary spectrometer. As a consequence IN16 has a higher flux than IN10 and maintains perfect backscattering condition in the primary spectrometer at the expense of Q-resolution.

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Applications

  • A classical field backscattering is rotational tunneling spectroscopy. New developments in this field have arisen from combining neutron spectroscopy and molecular dynamics simulations. Only recently methyl group tunneling has been found in amorphous systems
  • Among other classical fields of application are relaxation processes in glasses, H-diffusion in metals or proton and ionic conductors as well as diffusion processes in matrices
  • Of growing interest is the study of complex materials like polymers and biological samples
  • An increasing interest can also be observed for magnetic investigations
  • Further applications of IN16 arise from the possibility to do backscattering and diffraction simultaneously.This option can for instance be used to study the adsorption of molecules from a solvent on to crystals for diffusion studies near phase transitions or other structural re-arrangements

Selected examples

Fixed window scans

Elastic or inelastic fixed window scans give a quick overview of the onset of motions faster than the time scale corresponding to the energy resolution (~4 ns). The elastic scans shown illustrate how local methyl group dynamics and extended segmental dynamics of a polymer are differently influenced by spatial restrictions in a porous material. It can also be seen that the crystallisation (upwards jump for bulk) is suppressed when confinement volume is sufficiently small. (see figure).

 

Reference: Schönhals, A., Goering, H., Schick, C., Frick, B. & Zorn, R., European Physical Journal E 2003. 12, 173-178

Quasielastic Spectroscopy

The high energy resolution of IN16 allows the separation of elastic and quasielastic contributions and helps to understand the microscopic dynamics by the analysis of the Q-dependence of the intensities and linewidth.

The example shows IN16 measurements on a miscible polymer blend of the more mobile PEP with the less mobile HPPP and using for the blend D-labeling to enhance the scattering of one of the components. The understanding of dynamic miscibility of blends is a topical issue in physical chemistry (see figure).

Reference: R. Perez, A. Arbe, J. Colmenero, L.Willner, D. Richter, B. Frick; Macromolecules 2005, to be published.

Inelastic Spectroscopy

Inelastic excitations can be measured on IN16 with extremely high energy resolution.

Many examples for backscattering on rotational tunneling systems can be found in Prager, M. & Heidemann A., Chemical Reviews 1997, 97, 2933-2966.
Similarly, low energy nuclear spin excitations, which arise in the example shown from nuclear hyperfine splitting of Nd nuclei in NdGaO3, can only be resolved with sub-μeV energy resolution (see figure).

Reference: Chatterji,T. & Frick, B., Solid State Communications 2004, 131, 453.

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