The effect of refraction in the small-angle diffraction of X-rays from stacked lamellae

An expression for the scattering of X-rays from a regular stack of lamellae is developed, releasing the prior restraint that no refraction may occur. The effect of refraction is to cause deviations from the classical Bragg condition. Further, a condition of total reflection is shown to occur within systems whose lamellar spacings are greater than a critical value.