Universal expression for blocking cone size based on the ZBL potential

Calculations of blocking cone sizes for the “blocking geometry” of the scattering and recoiling imaging spectrometry (SARIS) technique have been performed. By fitting calculated points in the space of the parameters of the interacting atomic species, a universal formula for calculating the blocking cone size for arbitrary energies and interacting species has been derived. This provides a “blocking cross-section” and an estimate of the total scattering cross-section of the process under consideration. The results obtained from the formula are compared with experimental SARIS blocking cone data for He+ and Ne+ scattering from a Pt(1 1 1) surface in the energy range 3–20 keV. The blocking cones in this low-energy range are appreciably asymmetric with respect to the interatomic axis. At small interatomic distances and low-projectile energies, the difference in angular size of the upper and lower halves of the blocking cone can be as large as 15%. The results of scattering and recoiling imaging code simulations and molecular dynamics blocking cone trajectory simulations using the Ziegler–Biersack–Littmark potential are in good agreement with experimental blocking cone sizes. Comparison is also made to the results of other formulas for the critical blocking angle found in the literature.