Some details of the superatomic structure evolution in silver azide during its decomposition under the action of soft X-ray radiation are revealed by Small Angle X-ray Scattering techniques (SAXS). The functions of particle size distribution are computed from SAXS intensity curves. It is found that several types of inhomogeneities are formed in the process of decomposition : density fluctuations on atomic scale (probably silver centers), small silver particles with bimodal size distribution and their aggregates.