The Absolute Calibration of a Small-Angle Scattering Instrument with a Laboratory X-ray Source

Absolute calibration of small-angle scattering data (in units of differential cross-section per unit sample volume per unit solid angle) is necessary for the determination of molecular weights, the number density of particles, the scattering-length densities of phases in multiphased systems, volume fraction, the specific surface area of the scatterers and to restrict the parameters of a given model to the set which reproduces the observed intensity. It is also a useful means for the detection of artefacts in SAS experiments. Absolute intensities from the same sample also allows intercalibration among different instruments. This work details the absolute calibration procedure of a small-angle X-ray scattering instrument, the Rigaku S-Max3000. Absolute calibration is achieved by using two standards: homogeneous and stable glassy carbon and water. The scattering intensity of glassy carbon is calibrated by comparison with the absolute-calibration measurements taken on the USAXS instrument located at the 32ID beamline of the Advanced Photon Source in Argonne National Laboratory. This instrument has primary calibration capability. Scattering from water is angle-independent and only depends on the physical property of isothermal compressibility. Absolute calibrations using two standards were compared. The agreement of scale factors obtained using two standards suggests that precalibrated glassy carbon can serve as a convenient standard for all types of materials under study.