The effect of finite slit heights on the determination of systematic deviations from Porod's law

Systematic deviations from Porod's law have often to be studied in angular regions in which the infinite-slit approximation is no longer valid. It is shown that this is not a serious limitation as long as the lower limit of the validity of Porod's law is smaller than a certain dimension of the slit height and that the method of evaluation proposed in an earlier paper [Ruland (1971). J. Appl. Cryst. 4, 70-73] can be modified to allow for the effect of finite slit heights. An example of application is given for the small-angle scattering of glassy carbons.