D22 - State of the Art

Roland P. May Institut Max von Laue - Paul Langevin, F-38042 Grenoble Cedex 9

SANS is produced by heterogeneities in matter (that can be as well defined as identical viruses in aqueous solution). If these are randomly oriented, every atom pair contributes a sin (Qd) / (Qd) term to the scattering of a sample, where d is the distance between the two atoms of the pair, and Q the momentum transfer, Q = (4π/λ) sin Θ, with 2Θ, the full scattering angle and λ, the wavelength.

Inhomogeneities of sizes larger than atomic distances (10 to 1000 Å) produce scattering patterns with interesting Q ranges 1/D < Q < 10/D, if D is the dimension of the inhomogeneities. The scattering angle 2Θ corresponding to the upper Q limit for D=100 Å is about 9.1 ° for neutrons of 10 Å wavelength.

In most cases, the sample and/or the sample environment are rather bulky. Therefore, SANS instruments usually have to be large themselves in order to yield the desired resolution. Small SANS instruments can only serve a very limited number of applications. For reasons of intensity, a relatively large beam divergence, i.e. a beam cross-section larger than the sample size is accepted as well as wavelength resolutions Δλ/λ of up to about 20 %.

Discovered by Chadwick in 1932

Total reflection: Ultra-cold neutrons, neutron guides

    1983: Proposal (R.P. May, R. Oberthür, P.A. Timmins and A.F.Wright)

    1987 (September): Final proposal (R.P. May, M. Thomas) endorsed by Instrument Subcommittee

    1989 (December): Delivery of detector tube and collimation by ABT (SIGRI)

    1992 (December): Delivery of detector by CERCA (after 24 months)

    1995 (February): First tests after reactor overhaul: first users in April

    1996 (April): Start of permanent operation after repair of detector

"Classical" pin-hole small-angle scattering instrument
 

Wavelength selection

• DORNIER velocity selector 25 cm long, 28 300 rpm, resolution 10% (fwhm), 4.6 < l < 42 Å for 0 ° tilt
  

Collimation system

• guide cross-section 55 x 40 mm

• 8 drums of lengths varying as a geometical series to yield free flight paths of 1.4 to 17.6 m

•  three positions: guide in / apertures (/ optical elements)

• 3 attenuators and 4 round apertures (5, 10, 20, 30 mm diameter), computer controlled

• manually remotely controlled aperture at 19.1 m from sample

• 3He, 2 bars; sensitive surface: 0.96 m x 0.96 m

• 16 K pixels of 0.75 x 0.75 cm

• minimal distance 1.35 m, maximal distance 18 m

• can be translated by half its width, i.e. 50 cm

• can be rotated around its vertical axis (25 °)

• Q-range: 0.7x10-3 Å-1< Q < 1 Å -1
  
  • Qmax/Qmin up to 50, typically 20 with offset, 10 without

• table for mounting equipment in air, e.g. sample changer, shear apparatus

• vessel ("cloche") for working in vacuum

• electromagnets (1.4 T)

• furnace (up to 1300 °C)
  

• "orange" cryostats with support permitting direct-beam and reference measurements

• remotely controlled heating/cooling bath (about -10 / +80 °C)

The small-angle neutron-scattering from SiO2 precipitates in a single crystal of silicon which has been heat treated for 500 hours at 600°C; the neutron beam was incident along a <100> direction. The central cross arises from the cushion shaped SiO2 precipitates lying on (100) planes with their edges along <110> directions.

Homogeneous nucleation and growth of oil droplets studied by time-resolved small-angle neutron-scattering

S.U. Egelhaaf (ILL), P. Schurtenberger (ETH Zürich), J. Morris, U. Olsson, H. Wennerström (Lund University)

and many others...

... the  D22 "Yellow Book" page (pdf) and the  D22 documentation.