The trajectories of Kr ions in the energy range 50 eV to 5 keV incident on the (100) and (110) surfaces of W have been followed using digital computational techniques, in which the interaction was treated as a multiparticle process rather than a sequence of binary collisions. At the higher energies (>2 keV), the latter process was found to be a good description also of the multiparticle event but at lower energies, many atoms were involved simultaneously in the ion scattering process. Probabilities of ion penetration into the surfaces were derived and compared with experimental data of Kornelsen and Sinha and penetration probability-energy functions shown to be similar. For the (100) surface penetration was prohibited below an ion energy of∼400 eV and angular and energy distributions of backscattered particles in this energy range were determined. Angular analysis showed a pattern illustrative of surface atomic symmetry but the energy distribution shows a sharply defined probability of backscattering in narrow energy range which lies between the maximum recoil energy in a binary collision and recoil from an infinitely hard surface. This indicates that, as energy decreases, the multiple collision process can be approximately characterised as a ‘soft’ surface of effective mass greater than the target atom mass. Because of the sharply defined energy of recoil and a quite well defined narrow cone of backscattering, these results suggest a method of producing quite mono-energetic neutral atomic beams by recoil of ions from surfaces, since neutralization is usually highly efficient at low ion energies. The energy of ions recoiling in a collision on an axis of symmetry between surface atoms is compared with the theoretical non-binary scattering model of Andersen and Sigmund.