A simulation method of charged particle scattering in a crystal lattice is described. Angular distributions of protons and positrons leaving the crystal are calculated and the orientational distributions of axial channeling particles are received. The influence of the experimental geometry and the crystal condition on the obtained results is discussed. It is shown that binary collision calculation gives agreement with experimental results. I n the present paper the first results of a computer simulation of the scattering of positrons in a single crystal are given. Since the applicability of the classical mechanics to the description of the channeling phenomena of light p-particles is under discussion, we choose a computer model allowing for the most exact simulation of the experimental conditions, without the usually applied methods of computing time minimization. I n our calculation the particle trajectory is observed from the first collision point until the particle leaves the certain geometrical dimension of the single crystal. The calculation thus yields the angular distributions of the particles leaving the single crystal in dependence on the rotation angle of the single crystal relative to the incident beam axis. The angular distributions are integrated over the detector aperture of the simulated experiment geometry and these values depending on the crystal rotation angle are compared with the experimental data.

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A new technique is applied to determine the sites of implanted substitutional impurities in GaAs. Since the 2 values are nearly equal, G a and As substitutions cannot be distinguished from a measurement of the width of channeling dips, but the asymmetry of a scan in the {llO} plane is opposite for backscattering from the two types of atoms, and a comparison with the observed asymmetry for backscattering from the impurity determines the site. As expected, In is found to replace G a and Sb to replace As. In addition, the preferential site of implanted Sn atoms is shown to be a G a site. These results confirm earlier assignments based on isomer shifts in Mossbauer experiments.