Small-angle X-ray scattering is a powerful means to study nanoparticles. With its help it is possible to determine their shape or size distribution with higher accuracy than other methods, e.g. from TEM images. The reason for this is that the number of investigated particles is much higher in SAXS (because of the typically 1 mm3 irradiated sample volume) than TEM (only a few hundreds of particles in each image), and the measurement is free from artifacts introduced by sample preparation and measurements inherent in the latter method.
By varying the sample-to-detector distance different ranges in the scattering variable, $q$ (or the scattering angle, $2\theta$) can be reached. Scattering curves measured at different experimental geometries (commonly denoted as "short" or "long" geometry) can be united to form a single curve covering a wide range in $q$. The uniting involves finding a common interval of $q$, which is present in both the short and long distance curves, and determining a scaling factor, which, applied to one of the curves, makes it overlap the other on the selected interval.
Glassy carbon is a secondary standard sample for absolute intensity calibration. It is an ideal material for this goal, since it is stable, easy to handle (1 mm thick small, solid plate), and withstands environmental stress well (not sensitive for temperature, humidity, effets of radiation damage are negligible). Its scattering curve (presented in the figure below) features a long, shallow plateau, which renders a scaling operation numerically stable.
Silver behenate is a widely used calibration sample in X-ray scattering measurements. Its lamellar structure (one-dimensional periodicity) manifests itself as several orders of Bragg peaks in the scattering curve (Bragg rings in the scattering image). The next figure shows a typical scattering image of silver behenate and the scattering curve resulting thereof by azimuthal averaging.