A unified theory of absolute intensity measurements in small-angle X-ray scattering

A general equation relating the intensity (in electron units) scattered at small angles by a sample to the power received by the X-ray detector in a small-angle collimation system is developed which includes the effects of a nonuniform incident beam and of a nonuniformly sensitive detector. The theoretical bases for various experimental methods of measurement of the power in the incident beam are discussed. These include primary methods such as ionization chambers and attenuation by multiple foils or mechanical devices, and secondary methods which involve the measurement of scattering from standards such as gases, liquids, or amorphous scatterers for which the scattering may also be computed in absolute units.