Scattering intensity limit value at very small angles

The existence of a limit of the sample scattering intensity, as the scattering vector approaches zero, requires and is ensured by the property that the mean value of the scattering density fluctuation over a volume V behaves asymptotically, at large V, as νV^−1/2, ν being an appropriate constant. The limit of the normalized scattering intensity is then equal to ν². The implications of this result are also analysed in the case of samples made up of two homogeneous phases.