Collimation effects in small-angle X-ray and neutron scattering

To obtain adequate intensity in small-angle X-ray and neutron scattering measurements, the apertures that define the incident and scattered beams often must be made so large that the measured intensity is an average over an appreciable interval of scattering angles. Allowance must frequently be made for the resulting distortion of the measured scattering curve. A technique previously developed by Hendricks & Schmidt [Acta Phys. Austriaca (1967), 26, 96-112; Acta Phys. Austriaca (1973), 37, 20-30] for describing collimation effects is outlined. This method makes use of a function called the `weighting function', which specifies the width of the interval over which the intensity is averaged and indicates the emphasis given to scattering angles within this interval. A new calculation of the weighting function for `pinhole' collimating systems, which employ circularly symmetric apertures instead of long narrow slits, is presented. Several techniques for performing collimation corrections are described, and a review is given of results that several workers have recently obtained in studies of collimation effects in pinhole systems.