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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 κ(κ = 2πθ/λ, θ = scattering angle, λ = wavelength). Instruments which have been developed along these lines are described, especially the 40 m instrument in Jülich and the 80 m instrument at the high-flux reactor in Grenoble. The Grenoble instrument covers a range of scattering vectors between 1 Å−1 and 3.10−4Å−1; the maximum possible resolution is about 10−4 Å−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.
