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Neutrons

V5: spin echo spectrometer - SPAN

enlarged view

V5 SPAN at HZB


Neutron spin echo spectroscopy reaches the highest energy resolution from all neutron spectroscopic techniques by decoupling the value of the minimal neutron velocity changes that may be detected from the width of the velocity distribution of the incoming neutrons. This is achieved by using polarized neutrons and the neutron spin as a kind of stop-watch carried by each neutron individually.

The SPAN spectrometer is the first and, currently, only wide angle neutron spin echo spectrometer in operation and is located in the new neutron guide hall of the HZB. The unique open configuration, the improved neutron optics and the novel magnetic field configuration (high symmetry and homogeneity) realised with SPAN enables simultaneous measurements over a wide angular, resp. momentum transfer range. The instrument can be operated as a combination of high resolution neutron spin echo (NSE) technique and a poor resolution time‑of‑flight (TOF) analysis on the same instrument. The wide dynamic range of SPAN makes it a multipurpose instrument. It is particularly well adapted for studies of glass forming polymers above the glass transition, water dynamics, localized dynamics in porous media, macromolecules and biological macromolecules as well as magnetic materials.

Neutron guide

Polarizing cavity NL4 with FeCo-Si supermirrors, cross section 100mm x 58mm

Monochromatization

Mechanical velocity selector (Dornier, NVS 030, (2000)), 15% FWHM

Wavelength range

2.5Å - 9Å

Scattering plane

Horizontal

Distance sample – detectors

3.5m

Maximum sample area

4cm x 4cm

Detectors

96 3He detectors (5 cm diameter, 15 cm height, mounted vertically) in three detector banks (opening of 25.7°)

Precession Coils

Two Coils, Diameter 3 m, Distance between the coils 0.9 m, Imax = 380 A, 220 windings/coil

Secondary Coils

Two Coils, Diameter 1 m, Distance between the coils 1 m, Imax = 60 A, 288 windings/coil

Compensation Coils for the p/2 flipper

Two Coils, Diameter 4.8 m, Distance between the coils 0.7 m, Imax = 80 A, 100 windings/coil

Maximum magnetic field integral

6·104 Oe cm

Angular range

£150°

Range of momentum transfer

0.06Å-1 – 3.2Å-1(3.8Å), 0.025Å-1 – 1.35Å-1 (9Å)

Fourier time range

2.2ps – 0.66ns (3.8Å), 27ps – 8.2ns (9Å)

Energy range (NSE)

1meV - 300meV (3.8Å), 80neV - 24meV (9Å)

Typical flux at sample

3∙106n/cm2/s (3.8Å), 0.5∙106 n/cm2/s (9Å)