Mixed simulation of the multiple elastic scattering of electrons and positrons using partial-wave differential cross-sections

We describe an algorithm for mixed (class II) simulation of electron multiple elastic scattering using numerical differential cross-sections (DCS), which is applicable in a wide energy range, from similar to 100 eV to similar to1 GeV. DCSs are calculated by partial-wave analysis, or from a suitable high-energy approximation, and tabulated on a grid of scattering angles and electron energies. The size of the required DCS table is substantially reduced by means of a change of variable that absorbs most of the energy dependence of the DCS. That is, the scattering angle theta is replaced by a variable u, whose probability distribution function Varies smoothly with the kinetic energy of the electron. A fast procedure to generate random values of u in restricted intervals is described. The algorithm for the simulation of electron transport in pure elastic scattering media (with energy-loss processes switched off) is obtained by combining this sampling procedure with a simple model for space displacements. The accuracy and stability of this algorithm is demonstrated by comparing results with those from detailed, event by event, simulations using the same DCSs. A complete transport code, including energy losses and the production of secondary radiations, is obtained by coupling the present elastic scattering simulation algorithm to the general-purpose Monte Carlo program PENELOPE. Simulated angular distributions of MeV electrons backscattered in aluminium and gold are in good agreement with experimental data. (C) 2001 Elsevier Science B.V. All rights reserved.