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SPHERES (spectrometer for high energy resolution) is a third-generation backscattering instrument with focussing optics and a phase-space-transform chopper. It is a versatile spectrometer for the investigation of atomic and molecular dynamics on a GHz scale.
The necessary filtering of neutron energies is achieved by Bragg reflection from perfect monochromator and analyzer crystals under angles close to 180°. The backscattering geometry makes it unavoidable to use a primary beam deflector and a duty-cycle chopper. At SPHERES, these two functions are both realised by a chopper that bears deflector crystals on its circumference. This leads to a particularly compact spectrometer layout so that full use can be made of the focussing neutron guide. As an additional advantage, the fast motion of the deflector crystals achieves a phase-space transform of the primary spectrum, thereby enhancing the flux at the sample.
The principal figures of merit qualify SPHERES as one of the best of its class . Count rates and signal-to-noise ratio have been improved by filling the instrument housing with argon, thereby avoiding air scattering in the secondary spectrometer. Another gain in flux will be achieved by a more efficient phase-space transform chopper which is in the commissioning phase. The new designed chopper will be more efficient due to optimised rotation speed and higher reflectivity and mosaicity of the graphite crystals. The resolution of the small angle detectors have been improved by reducing the azimuth angle range of the analyzers .
As a multi-detector instrument with relaxed angular resolution, SPHERES is particularly suited for studying tagged-particle motion by incoherent scattering. Typical applications include for example dynamical processes in polymers and biological systems . The high resolution of the spectrometer allows to investigate the dynamics of water in confined geometry. The unprecedented sensitivity of SPHERES helps us to detect the onset of quasielastic scattering deep in the supercooled state . Other important applications are hyperfine splitting in magnetic materials  and rotational tunneling . The high count rates allow inelastic temperature scans  and real-time kinetic experiments .
Raw histograms are accumulated on an equidistant ω grid. A script driven program, SLAW , is provided to normalise the raw counts, to perform optional binning, and to deliver S(q,ω) in a variety of output formats so that users are not bound to any specific data analysis program. In data fitting, it is critcially important to convolute theoretical models with the measured resolution function in an efficient and numerically stable way. We strive to support best practice through our FRIDA package .
 Wuttke, J. et al., Rev. Sci. Instrum. 83, 075109 (2012).
 Wuttke, J. , Zamponi, M., Rev. Sci. Instrum. 84, 115108 (2013).
 Gallat, F.-X. et. al., J. Am. Chem. Soc. 134, 13168 (2012).
 Doster, W. et al., Phys. Rev. Lett. 104, 098101 (2010).
 Chatterji, T. at al., Phys. Rev. B 78, 012411 (2008).
 Bator, G. et al., Chem. Phys. 410, 55 (2013).
 Häußler, W. et al., Neutron News 22, 24 (2011).
 Leon, A., Wuttke, J., J. Phys.: Condens Matter 23, 254214 (2011).
 Wuttke, J.: SLAW – a neutron histogram to scattering law converter, http://apps.jcns.fz-juelich.de/slaw
 Wuttke, J.: FRIDA – fast reliable interactive data analysis, http://apps.jcns.fz-juelich.de/doku/frida/start
|Neutron wavelength||6.27 Å|
|Neutron energy||2.08 meV|
|Resolution FWHM||0.62 – 0.65 µeV|
|Dynamic range||± 31 µeV|
|Q range||0.2 – 1.8 Å-1|
|Flux after selector||1010 s-1|
|Flux at sample||1.8·106 s-1|
|Illuminated area||40 × 30 mm2|
Dr. Michaela Zamponi
Dr. Marina Khaneft
Find the latest publications regarding SPHERES in our publication database iMPULSE:
Heinz Maier-Leibnitz Zentrum. (2015). SPHERES: Backscattering spectrometer. Journal of large-scale research facilities, 1, A30. http://dx.doi.org/10.17815/jlsrf-1-38
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