A method of calculation of the random fractionXR(l) in a disordered channel containing host and foreign atoms is described. According to this method dechanneling caused by single scattering as well as multiple scattering at defects is calculated taking into account positions of the selfinterstitials and foreign atoms with respect to the lattice rows. The results demonstrate that the transverse energy distribution, flux peaking and, hence,XR(l) and depth profiles of defectsc(l) depend drastically on the defect position, concentration of implanted atoms, their position and the rechanneling process. The method is applied to experimental data for GaAs irradiated by He+and N-implanted Si. The obtainedXR(l) andc(l) are compared with those obtained using other methods.