Fig. 1.
Pictorial presentation of small-angle scattering in the case of the particles of different size. 2θ1 and 2θ2 are the angles between incident and scattered waves from two particles, λ is a wavelength of incident radiation and is a path difference between two waves scattered from two arbitrary points within a particle. Since the scattering is elastic, the wavelength of the scattered radiation is unchanged and also equals to λ. Red dashed arrows show the direction of the scattered radiation to the detector.