Background subtraction and moments of the microscopic density fluctuation

Some models of microscopic density fluctuations are numerically analysed in order to study the behaviour of the related background contribution. The results suggest that this contribution can be described by an algebraic expression depending on only the moments of the microscopic density fluctuation. In this way, the parameter values, determined by a best-fit procedure to account for background contributions in the case of real samples, acquire a definite physical meaning. The procedure is applied to the small-angle X-ray intensities of a polymer sample analysed at different temperatures and yields satisfactory results.