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 multip le elastic scattering using numerical differential cross-sections (DCS), wh ich 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 red uced by means of a change of variable that absorbs most of the energy depen dence of the DCS. That is, the scattering angle theta is replaced by a vari able u, whose probability distribution function Varies smoothly with the ki netic energy of the electron. A fast procedure to generate random values of u in restricted intervals is described. The algorithm for the simulation o f electron transport in pure elastic scattering media (with energy-loss pro cesses 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, ev ent by event, simulations using the same DCSs. A complete transport code, i ncluding energy losses and the production of secondary radiations, is obtai ned by coupling the present elastic scattering simulation algorithm to the general-purpose Monte Carlo program PENELOPE. Simulated angular distributio ns of MeV electrons backscattered in aluminium and gold are in good agreeme nt with experimental data. (C) 2001 Elsevier Science B.V. All rights reserv ed.