Breakthrough in neutron backscattering spectroscopy: A tenfold enhanced energy resolution using GaAs

Start Date
20-11-2018 14:00
End Date
20-11-2018 15:00
Room 337, Central Building
Speaker's name
Kristijan Kuhlmann
Speaker's institute
Friedrich-Alexander University Erlangen-Nürnberg, Germany - Institut Laue-Langevin
Contact name
Anaïs Fernandes
Host name
Marine Cotte - Tobias Schulli
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A prototype neutron backscattering spectrometer using the GaAs 200 Bragg reflection has been developed to bring about a substantial increase in energy resolution. Commissioning has yielded an unprecedented resolution of δE = 77 neV FWHM [1], an order of magnitude smaller than the current standard of 750 neV FWHM.

Crystal quality is paramount in order to retain the high resolution offered by the narrow intrinsic line width of GaAs 200. This includes variations of the lattice parameter to (Δa/a) < 10-6, the influence of dislocations on the energetic line width as well as avoiding sawing damage by using the “scribing and cleaving” technique to single the crystals into 4x4 mm2 facets.

Furthermore, several other parameters need to be controlled to a high degree of precision, like temperature inhomogeneities to ΔT < 0.3 K over 10 m2 of crystal surface, the co-alignment of more than 500 000 crystal facets to ε < 0.1°, or mechanical strain to γ < 10-6.

In this talk, I will give an introduction into neutron backscattering spectroscopy, discuss our extensive study of the structural properties of commercially available GaAs crystals and present the design of our prototype that has yielded the first significant gain in resolution since the invention of backscattering 50 years ago.


[1] K. Kuhlmann, M. Appel, B. Frick and A. Magerl, ILL Annual Report 2017, pp. 82–83

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