INCORPORATION OF SINGLE ELASTIC-SCATTERING IN THE EGS4 MONTE-CARLO CODE SYSTEM - TESTS OF MOLIERE THEORY

To avoid prohibitively long computation times, conventional Monte Carl o e- transport algorithms (e.g. EGS4, ETRAN, ITS) employ multiple scat tering theories and ''condensed history'' methods to model e- transpor t. Although highly successful for many calculations, these techniques do not model backscatter very well, particularly for high-Z materials. In an attempt to correct for this shortcoming, we have extended the E GS4 Monte Carlo code to allow for the simulation of single elastic sca ttering. The single scattering method also allows quantities to be sco red in submicrometer dimension geometries where the Moliere multiple s cattering theory fails and the Goudsmit-Saunderson multiple scattering equations converge very slowly. Two single scattering schemes have be en implemented: (i) Screened Rutherford cross sections which form the basis of Moliere's multiple scattering theory, (ii) Single scattering cross sections based upon phase-shift data. In this work we describe t he implementation of single elastic scattering in the EGS4 Monte Carlo code system and employ it to verify the Moliere multiple scattering t heory in its range of validity. We demonstrate that the Moliere multip le scattering formalism provides a good description of multiple scatte ring despite its use of a relatively crude cross section and that it m ay be employed with semi-quantitative accuracy in the plural scatterin g regime, where electron step-lengths are so short that only as few as five atoms participate in the angular deflection. However, the remain ing differences of the Moliere distributions with the phase-shift data motivate the use of more accurate fundamental data, in particular, fo r applications involving high-Z elements.