AbstractA probability method is used to describe the processes of characteristic x‐ray fluorescence excitation and absorption in a heterogeneous monolayer of particles. Based on this the analytical dependence of the characteristic x‐ray peak intensity on the sizes and shape of particles, and the distribution of elements among the particles is inferred, for two kinds of spectrum excitation. Theoretical evaluations for applying boundaries of the ‘thin’ homogeneous layer model to a heterogeneous monolayer are given. The elements to be determined in unknown compositions are S, Fe