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The neutron small-angle scattering system at the high-flux reactor in Grenoble consists of three major parts: the supply of cold neutrons via bent neutron guides; the small-angle camera D11; and the data handling facilities. The camera D 11 has an overall length of 80 m. The effective length of the camera is variable. The full length of the collimator before the fixed sample position can be reduced by movable neutron guides; the secondary flight path of 40 m full length contains detector sites in various positions. Thus, a large range of momentum transfers can be used with the same relative resolution. Scattering angles between 5 x 10-'* and 0.5 rad and neutron wavelengths from 0.2 to 2.0 nm are available. A large-area position-sensitive detector is used which allows simultaneous recording of intensities scattered at different angles; it is a multiwire proportional chamber. 3808 elements of 1 cm 2 are arranged in a two-dimensional matrix.

The use of neutrons in small-angle scattering has opened a wide field of applications for investigations in magnetism, polymeric science, for certain problems in biology, and in metallurgy. In the first part, this review deals with the experimental aspects of neutron small-angle scattering. In particular, the compensation of the relatively small luminosity of neutron sources as compared to X-ray tubes will be discussed in detail. This is mainly achieved by large beam cross sections, leading to correspondingly long instruments, and by an optimization of the intensity with respect to the different contributions to the resolution width of the scattering vector K(~: = 27r0/2, 0 = scattering angle, 2 = wavelength). Instruments which have been developed along these lines are described, especially the 40 m instrument in Ji~lich and the 80 m instrument at the high-flux reactor in Grenoble. The Grenoble instrument covers a range of scattering vectors between 1 .~-1 and 3.10 -4 A-~; the maximum possible resolution is about 10 -4 A-1. Typical applications are reviewed and discussed, namely those dealing with (i) density and compositional fluctuations in solids (alloys, defect clusters, dislocations, grains), (ii) magnetic inhomogeneities in solids (alloys, magnetic domains), (iii) flux-line lattices in type-II superconductors (form factors, imperfections and morphology), (iv) polymers in the solid state, and (v) biological substances.

Small angle neutron scattering experiments (SANS) on solutions of cetylpyridiniumsalicylate (CPS) in D2O over a large concentration range show a characteristic scattering maximum due to mutual interactions between the rodlike micelles. From the scattering rates structure factors S(Q), pair correlation functions g(r) and corresponding mean potentials W(r) are derived. Furthermore it is shown, that the length L of the scatterers decreases in a concentration range from 20 mM to 160 mM CPS. To study the influence of interaction on the rods, increasing amount of salt (NaCl and NaSal) was added to a 5 mM solution of CPS. As one would expect, the scattering maximum decreases, while the length of the micelles increases. It is shown, that the rods remain rather stiff when small amounts of salt are added. In the case of 32 mM NaCl it was also possible to fit the data with a persistence length model showing that the rods may become flexible when large amounts of salt are added. A persistence length of 8000 – 12000 Å was evaluated for these conditions.

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