Two-dimensional focusing of high-energy X-rays by thermal-gradient crystals for small-angle X-ray scattering

摘要

A novel method for focusing X-rays in two dimensions by thermal-gradient crystals in symmetrical Laue geometry is described. A 225 kV stationary tungsten tube delivers an X-ray beam with a source diameter of about 1.0 mm (full width at half-maximum). The focal point at the detector at a distance up to 16 m from the source is of the same size. The beam at the focusing crystals at half the distance between the source and the detector has typical dimensions of 30 x 30 mm. The intensity of the focal point can be increased by more than 200 times by applying a thermal gradient of about 2.2 K mm(-1) on the focusing crystals. The described method and apparatus are designed for small-angle X-ray scattering at high photon energies up to 60 keV, where the high penetration power allows experiments on strongly absorbing materials in transmission mode. Particle sizes up to 3000 angstrom can be detected. First measurements on nanocrystalline tungsten carbide and Teflon yield radii of gyration of 540 angstrom and 815 angstrom, respectively.