Spin-echo small-angle neutron scattering (SESANS) is, in contrast to conventional small-angle neutron scattering (SANS), a real-space technique. SESANS measures the projection of the density-density correlation function of a sample, rather than, as in SANS, its Fourier transform. This paper introduces a toolkit for interpretion and analysis of a SESANS measurement. Models that are used in SANS are discussed and translated into a SESANS formalism. These models can be used to analyse and fit the data obtained by SESANS. Dilute, concentrated, random, fractal and anisotropic density distributions are considered. Numerical methods used to calculate the projection from numerical data are presented, either by using Fourier transformation or via the real-space pair correlation function. research papers J. Appl. Cryst. (2008). 41, 868-885 Robert Andersson et al. Analysis of SESANS measurements 869

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A systematic analysis of grazing incidence synchrotron X-ray diffraction data of uncompressed amphiphilic alcohols C,H2,+ ,OH (n = 31, 30, 23, 20. 19, 18, 16, 14. 13) on a water subphase at 5 "C is presented. Pronounced structural changes were observed on reduction of chain length from n = 31 to 13. The relative amount of two dimensional (2-D) crystalline material formed fell drastically; shorter crystalline coherence lengths were also observed. For n = 31-18 the molecules are arranged in a rectangular cell (a z 5 A, b increases from ca. 7.4 to ca.8.2 A) with plane symmetry p l g l . For

We describe two spin-echo instruments for neutron small angle scattering, which have been installed at the reactor institute in Delft. The first setup is using a monochromatic beam and magnetized foils as spin flippers, while the second uses resonant spin flippers in a pulsed neutron beam. The components that play an essential role for operation are described in some detail. Each setup has specific advantages in its range of spin-echo lengths that covers the range of correlation lengths that could be measured. This is demonstrated in a comparative measurement, the setup with magnetized foils measuring at spin-echo-lengths up to 20 μm and the setup with resonant flippers measuring in the range up to 0.5 μm.

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