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MLZ (eng)

85748 Garching


Backscattering spectrometer


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 [1]. 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 [2].

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 [3]. 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 [4]. Other important applications are hyperfine splitting in magnetic materials [5] and rotational tunneling [6]. The high count rates allow inelastic temperature scans [7] and real-time kinetic experiments [8].

Raw histograms are accumulated on an equidistant ω grid. A script driven program, SLAW [9], 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 [10].

[1] Wuttke, J. et al., Rev. Sci. Instrum. 83, 075109 (2012).
[2] Wuttke, J. , Zamponi, M., Rev. Sci. Instrum. 84, 115108 (2013).
[3] Gallat, F.-X. et. al., J. Am. Chem. Soc. 134, 13168 (2012).
[4] Doster, W. et al., Phys. Rev. Lett. 104, 098101 (2010).
[5] Chatterji, T. at al., Phys. Rev. B 78, 012411 (2008).
[6] Bator, G. et al., Chem. Phys. 410, 55 (2013).
[7] Häußler, W. et al., Neutron News 22, 24 (2011).
[8] Leon, A., Wuttke, J., J. Phys.: Condens Matter 23, 254214 (2011).
[9] Wuttke, J.: SLAW – a neutron histogram to scattering law converter,
[10] Wuttke, J.: FRIDA – fast reliable interactive data analysis,

Typical Applications
  • Hyperfine splitting
  • Molecular reorientations and rotational tunneling
  • Dynamic signature of phase transitions
  • Hydrogen diffusion
  • Liquid dynamics
  • Polymer relaxation
  • Protein aggregation
Sample Environment
  • Cryofurnace 3…700 K
  • Dilution inset 20 mK
  • Furnace
Technical Data
Primary beam
Neutron guideNL6-S
Neutron wavelength6.27 Å
Neutron energy2.08 meV

Main parameters
Resolution FWHM0.62 – 0.65 µeV
Dynamic range± 31 µeV
Q range0.2 – 1.8 Å-1
Flux after selector1010 s-1
Flux at sample1.8·106 s-1
Illuminated area40 × 30 mm2

Instrument Scientists

Dr. Michaela Zamponi
Phone: +49 (0)89 289-10793

Dr. Daria Noferini
Telefon: +49 (0)89 289-11676

Phone: +49 (0)89 289-14875

Operated by



Find the latest publications regarding SPHERES in our publication database iMPULSE:

Citation of the instrument

Heinz Maier-Leibnitz Zentrum. (2015). SPHERES: Backscattering spectrometer. Journal of large-scale research facilities, 1, A30.

For citation please always include the DOI.


© Andreas Heddergott/ TU Muenchen
Resolution at SPHERES
Resolution at SPHERES

Figure 1: A resolution of 0.65 ueV, a dynamic range of ±31 µeV, and a signal-to-noise ratio of 1000 : 1 or better are routinely achieved in user experiments [5].

Inelastic temperature scan
Inelastic temperature scan

Figure 2: This inelastic temperature scan, measured during 23 h,
revealed a hitherto unknown phase transition in Mg(NH3)6Cl2 [5].

MLZ is a cooperation between:

Technische Universität München> Technische Universität MünchenHelmholtz-Zentrum Geesthacht> Helmholtz-Zentrum GeesthachtForschungszentrum Jülich> Forschungszentrum Jülich