PENELOPE - AN ALGORITHM FOR MONTE-CARLO SIMULATION OF THE PENETRATIONAND ENERGY-LOSS OF ELECTRONS AND POSITRONS IN MATTER

A mixed algorithm for Monte Carlo simulation of relativistic electron and positron transport in matter is described. Cross sections for the different interaction mechanisms are approximated by expressions that permit the generation of random tracks by using purely analytical meth ods. Hard elastic collisions, with scattering angle greater than a pre selected cutoff value, and hard inelastic collisions and radiative eve nts, with energy loss larger than given cutoff values, are simulated i n detail. Soft interactions, with scattering angle or energy loss less than the corresponding cutoffs, are simulated by means of multiple sc attering approaches. This algorithm handles lateral displacements corr ectly and completely avoids difficulties related with interface crossi ng. The simulation is shown to be stable under variations of the adopt ed cutoffs; these can be made quite large, thus speeding up the simula tion considerably, without altering the results. The reliability of th e algorithm is demonstrated through a comparison of simulation results with experimental data. Good agreement is found for electrons and pos itrons with kinetic energies down to a few keV.