The experimental and theoretical data on energy distributions of reflected hydrogen atoms are compared with computer simulations based on BCA Monte Carlo code. It is shown that analytical theories fail to describe the dependence of energy spectra parameters on the angle of incidence for small angle scattering of the beam at the energy about few tens of keV. The computer simulations reasonably agree with experimental data. The restriction in computation of the maximum value of scattering angle in each collision results in good agreement of energy spectra of reflected particles with an analytical model.
Nuclear Instruments and Methods in Physics Research B 212 (2003) 270–273

The discovery that many trans-neptunian objects exist in pairs, or binaries, is proving invaluable for shedding light on the formation, evolution and structure of the outer Solar system. Based on recent systematic searches it has been estimated that up to 10% of Kuiper-belt objects might be binaries. However, all examples discovered to-date are unusual, as compared to near-Earth and main-belt asteroid binaries, for their mass ratios of order unity and their large, eccentric orbits. In this article we propose a common dynamical origin for these compositional and orbital properties based on four-body simulations in the Hill approximation. Our calculations suggest that binaries are produced through the following chain of events: initially, long-lived quasi-bound binaries form by two bodies getting entangled in thin layers of dynamical chaos produced by solar tides within the Hill sphere. Next, energy transfer through gravitational scattering with a low-mass intruder nudges the binary into a nearby non-chaotic, stable zone of phase space. Finally, the binary hardens (loses energy) through a series of relatively gentle gravitational scattering encounters with further intruders. This produces binary orbits that are well fitted by Kepler ellipses. Dynamically, the overall process is strongly favored if the original quasi-bound binary contains comparable masses. We propose a simplified model of chaotic scattering to explain these results. Our findings suggest that the observed preference for roughly equal mass ratio binaries is probably a real effect; that is, it is not primarily due to an observational bias for widely separated, comparably bright objects. Nevertheless, we predict that a sizeable population of very unequal mass Kuiper-belt binaries is likely awaiting discovery.