Improving sensitivity of a small angle x-ray scattering camera with pinhole collimation using separated optical elements

Abstract

We show that a significant improvement in the sensitivity of a Huxley–Holmes design for a small angle x-ray scattering camera is obtained by separating the mirror and the monochromator. The design of the camera involves a long x-ray mirror close to a point x-ray source associated with a curved focusing crystal located close to the sample. The sample area is located at half the distance between the source and detector planes. Diffuse scattering produced by the mirror is not incident on the focusing crystal, thus reducing the background signal. Complete elimination of hard x rays allows precise calibration and hence absolute determination of sample cross section by means of a semitransparent beam stop. In pinhole geometry, the flux corresponds to a ∼107 photons/s through the sample, collimated to 10−2 Å−1 in q range. This allows determination of scattered intensities on the order of 10−3 cm−1, corresponding to the scattering related to isothermal compressibility of less than 0.1 mm of pure water. As a reference sample, the widely used Lupolen™, a semicrystalline polymer, is calibrated. The high-q limit (q≈4.5 nm−1) of a porous calcite sample can be used as a secondary standard for specific area determination of solid/solid or solid–liquid dispersions.