Whereas wide angle scattering WAXS yields information about atomic lattices spacing, or the structure factor respectively, small angle scattering is applied for the analysis of the form factor, i.e. particle form and size, boundary surfaces and anisotropy, resp. orientation. When analyzing SAXS scattering images a purely elastic scattering is assumed. The entire intensity is dependent on the photon flux irradiating the sample, the dihedral angle of the detector and the scattering behavior of the sample, resp. the differential cross section.
Since the X-ray beam produced by an X-ray source does not have coherence it is monochromatized and parallelized by a Montel mirror. Thus, the beam can be formed and its divergence reduced (ca.0.24 mrad) by applying three collimators and two-axes hybrid blade systems. With the moveable Medipix detector the system can be used in SAXS or ultra-small scattering (USAXS) mode.
Since SAXS measurements are displaying the structure in reciprocal space smaller angles have to be used for imaging larger structures. Structural information in the range of 2 – 100 nm can be gained by conventional SAXS methods.
By applying USAXS sizes up to 2 µm can be analyzed at LRM. Due to the necessary collimation measurement periods for USAXS are considerably longer. As an example a sample of silver behenate usually used for calibration purposes was chosen. It is nano crystalline and has a large lattice spacing of 5.84 nm facilitating the precise assignment of the scattering angles (<100> and <200> in this case). Thus e.g. the detector-sample-distance can be calibrated.