Relationship between counting modes, absolute noise term and the errors of structure functions in the interpretation of small-angle X-ray scattering data

The requirements imposed on the magnitude of the noise in a scattering curve in order to minimize the corresponding error in the structure functions are estimated for a given value of the time T in which the scattering curve is recorded. Typical small-angle X-ray scattering (SAXS) curves have been used to check how these conditions are fulfilled when different counting modes are applied for the measurement. It is shown that fixed-time counting is the most practical technique and produces error bands in the structure functions with magnitudes close to the smallest values attainable in SAXS investigations.