A high-sensitivity pinhole camera for soft condensed matter

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 separated optics camera described in this paper 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 semi-transparent beam-stop. In pinhole geometry, the flux corresponds to a ca. 10(7) photons/s through the sample, collimated to q= 10(-2) Angstrom(-1) in scattering vector range. This allows determination of scattered intensities of the order of 10(-3) cm(-1), corresponding to the scattering related to isothermal compressibility of less than 0.1 mm of pure water. Values of absolute intensities for water as well as convenient widespread buffer solutions are shown, in order to be usable for calibration as secondary standards. As solid reference sample, the widely studied Lupolen(tm) - a semi-crystalline polymer-is calibrated. The high-q limit (q approximate to 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.