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Neutron spin echo spectrometer
In the last cycle of 2017 the refurbished J-NSE (“PHOENIX”) started first operation with new field shape optimized superconducting main solenoids, new powersupplies and associated reconfiguration. Thereby the resolution is increased by a factor of 2.5.
The neutron spin echo technique uses the neutron spin as an indicator of the individual velocity change the neutron undergoes when scattered by the sample. Due to usage of the spins as individual timekeepers for each neutron the instrument accepts a broad wavelength band (incoming velocity spread) while at the same time maintaining sensitivity to the individual scattering induced velocity changes down to 10-5. However the information is carried by the spins as intensity modulation proportional to the cosine of a precession angle difference. Thus the measured signal is the intermediate scattering function, i.e. the cosine transform S(Q,τ) of the scattering function S(Q, ω) for small velocity (i.e. energy) changes and a symmetric scattering function. All spin manipulations only serve to establish this special type of velocity analysis. For details see “Neutron Spin Echo”, ed. F. Mezei, Lecture Notes in Physics, Vol. 128, Springer Verlag, Heidelberg, 1980.
Due to the intrinsic Fourier transform property of the NSE instrument it is especially suited for the investigation of relaxation-type motions that contribute at least several percent to the entire scattering intensity at the momentum transfer of interest. In those cases the Fourier transform property yields the desired relaxation function directly without numerical transformation and tedious resolution deconvolution. The resolution of the NSE may be corrected by a simple division.
For a given wavelength the Fourier time range is limited to short times (about 2 ps for the MLZ-setup) by spin depolarization due to vanishing guide field and to long times by the maximum achievable field integral J. The time is proportional to J x λ3. The new superconducting main solenoids are able to create field integrals up to 1.5 Tm, currently
the available correction scheme applied on the new optimized field shape coils allows “real-world” experiments with τ= 100 ns at λ = 8 Å corrsponding to J=1Tm.
In a major upgrade in 2017, the instrument has been equipped with superconducting main precession coils which increased the achievable field integral by a factor of 3 compared to the previously used normal conducting copper coils. The field shape of the main solenoids has been optimized in order to guarantee the required field homogeneity of the different neutron paths passing through the instrument thereby extending the regime with acceptable field integral homogeneity by a factor of 2.5 compared to the previous coils. With this new design, Fourier times up to 500 ns will be accessible for user experiments, or shorter wavelengths can be used to increase the intensity (and with it the statistics).
The spin echo spectrometer J-NSE is especially suited for the investigation of slow (~ 1 to 100 ns) relaxation processes. Typical problems from the fields of “soft matter” and glass transition are:
• Thermal fluctuations of surfactant membranes in microemulsions
• Polymer chain dynamics in melts
• Thermally activated domain motion in proteins, which is an important key for understanding the protein function.
The intermediate scattering function S(Q,τ) of a polymer in solution (PEP in deuterated decane) is shown in Figure 1, where the segmental dynamics of the Gaussian polymer chain is measured. A representative spin echo group is shown on the right of Figure 1, for a setting of τ= 80 ns at λ = 8 Å only achievable due to the upgrade of the instrument. The amplitude of the echo group normalized to the difference between maximum and minimum intensity is the intermediate scattering function at this point.
• Circulation thermostat furnace (260 – 360 K)
• Cryofour (3 – 650 K)
• Furnace (300 – 510 K)
• CO2-pressure cell (500 Bar)
Other specialised sample environments on request.
• Polarised neutron flux at sample position (10% selector)
o 7 Å: 1·107 n cm-2 s-1
o 12 Å: 6.8·105 n cm-2 s-1
• Momentum transfer range: 0.02 – 1.8 Å-1
• Fourier time range: 2 ps (4.5 Å) < τ < 500 ns (16 Å)
• Max. field integral: 1.2 Tm
• Useful max. Fouriertime: 100ns×(λ/8Å)2 for λ > 6 Å ; 45ns × (λ/6Å)3 λ < 6 Å
• Scattering angle: 2.50 < Φ < 850
*Primary beam *
• Neutron guide NL2a
o FeSi m=5 single reflection polarizer at entrance of the spectrometer
• Cross section of guide: 6 cm × 6 cm
• Max. sample size: 3 cm × 3 cm
• Collimation: By source and sample size 0.5° × 0.5°
• 30 × 30 cm2 CoTi supermirror Venetian blind
• 32 × 32 1 cm² cells 3He multidetector
Dr. Olaf Holderer
Phone: +49 (0)89 289-10707
Dr. Stefano Pasini
Phone: +49 (0)89 289-54810
Phone: +49 (0)89 289-14903
Find the latest publications regarding J-NSE in our publication database iMPULSE:
Heinz Maier-Leibnitz Zentrum. (2015). J-NSE: Neutron spin echo spectrometer. Journal of large-scale research facilities, 1, A11. http://dx.doi.org/10.17815/jlsrf-1-34
For citation please always include the DOI.