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Lichtenbergstr.1
85748 Garching

KWS-3

Very small angle scattering diffractometer with focusing mirror

KWS-3 scheme KWS-3 scheme

KWS-3 is a very small angle neutron scattering (VSANS) instrument running on the focusing mirror principle at the Research Neutron Source Heinz-Maier Leibnitz (FRM-II) in Garching. Standard configuration of the instrument with 9.5 m sample-to-detector distances allows performing scattering experiments with a wave vector transfer resolution between 10−4 and 3 · 10−3 Å−1, bridging a gap between Bonse-Hart and pinhole cameras. Second sample position at 1.3 m distances has extended Q-range of the instrument to 2 · 10−2 Å−1 and reached more than one-decade overlapping with the classical pinehole SANS instruments. The principle of this instrument is a one-to-one image of an entrance aperture onto a 2D position sensitive detector by neutron reflection from a double-focusing toroidal mirror.
Small-angle scattering is used for the analysis of structures with sizes just above the atomic scale, between 1 and about 100 nm, which cannot be assessed or sufficiently characterized by microscopic techniques. KWS-3 is an important instrument, which extends the accessible range of scattering angles to very small angles with a superior neutron flux when compared with a conventional instrumental setup with pinhole geometry. Thus the length scale that can be analyzed is extended beyond 10 µm for numerous materials from physics, chemistry, materials science and life science, such as alloys, diluted chemical solutions and membrane systems.

Typical Applications
  • High-flux bridge between Bonse-Hart and conventional SANS diffractometers
  • Colloid science: mixtures of particles, particles of micron size, silicon macropore arrays, …
  • Materials science: filled polymers, cements, microporous media, …
  • Polymer science: constrained systems, emulsion polymerization, …
  • Bio science: aggregations of bio-molecules, protein complexes, crystallization of proteins, …
  • Hierarchical structures
  • Multilamellar vesicles

The instrument covers the Q range of small angle light scattering instruments. Especially when samples are turbid due to multiple light scattering, V-SANS gives access to the structural investigation. Thus, the samples do not need to be diluted. The contrast variation method allows for highlighting of particular components. In figure 2 the VSANS measurement of water solution of polystyrene (PS) particles with a diameter of 760 nm is depicted. The spherically shaped polymer particles with a diameter of about were measured at both sample positions covering standard Q-range.

Technical Data

Overall performance

  • Resolution: δQ = 10-4 Å-1 (extension to 4 · 10-5 Å-1 possible)
  • Q-range:
    • 1.0 · 10-4 – 3 · 10-3 Å-1 at 9.5 m distance
    • 1.5 · 10-3 – 2 · 10-2 Å-1 at 1.3 m distance
  • Neutron flux:
    • high-resolution mode: > 10000 [n s-1]
    • high-intensity mode: > 60000 [n s-1]

Monochromator

  • MgLi velocity selector
  • Wavelength spread Δλ/λ = 0.2
  • Wavelength range λ = 10 – 30 Å (maximal flux at 12.8 Å)

Aperture size (focus)

1 × 1 mm2 – 5 × 5 mm2

Beam size at 9.5 m

0 × 0 mm2 – 100 × 25 mm2

Beam size at 1.3 m

0 × 0 mm2 – 15 × 10 mm2

Instrument Scientists

Dr. Vitaliy Pipich
Phone: +49.(0)89.289.10710
E-Mail:

Dr. Zhendong Fu
Phone: +49.(0)89.289.10716
E-Mail:

KWS-3
Phone: +49.(0)89.289.14873

Operated by

JCNS

Gallery

Principle of KWS-3
Principle of KWS-3

The principle of KWS-3 instrument is a one-to-one image of an entrance aperture onto a 2D position sensitive detector by neutron reflection from a double-focusing toroidal mirror; (right) photo of the mirror installed in vacuum its chamber. Length scales up to 10 μm are accessible.

Measurement of polystyrene spheres
Measurement of polystyrene spheres

Polystyrene spheres of 7600 Å diameter measured at 9.5 and 1.2 m at KWS-3 (black symbols: concentration of spheres in water 0.2wt %). The red curve is the theoretical scattering curve (form factor of 7600 Å spheres). The instrumental resolution and sample polydispersity were not taken into account. Mismatching of the measured curve and model at low Q is due to the presence of the structure factor.

KWS-3
KWS-3

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