Applications of invariant embedding: positron backscattering from surfaces

An effective invariant-embedding technique is developed for the detailed description of charged-particle backscattering from solids, with example calculations concentrating on quasielastic positron backscattering. The invariant-embedding formalism considered incorporates elastic and inelastic interactions, as well as particle annihilation effects, and allows a very efficient numerical scheme (based upon a recurrence in the number of elastic collisions) for accurate and fast evaluation of various distributions of backscattered particles, including those resolved at once in numerous variables. Not invoking drastic simplifications characteristic for existing analytical-based approaches and easily handling realistic collision cross-sections, the calculation scheme allows to test the accuracy of simulation programs and within its (albeit more narrow) range of validity - offers significant advantages compared to those as regards accuracy, computing speed, and resolution. Capabilities of the approach are illustrated by calculation results pertaining to elastic and inelastic positron backscattering for various targets and energies in the keV range. Distributions in (dependences on) numerous variables (incidence and/or emission directions, numbers of elastic and/or inelastic collisions, path length, energy, target atomic number) and their combinations are exemplified, and their nontrivial features are briefly discussed. (C) 2003 Elsevier B.V. All rights reserved.