Gaussian approximation for multiple scattering in infinite medium

Lewis theory of the Coulomb multiple scattering is considered in the Gauss approximation for small scattering angles. The model is similar to the Yang theory expressed in terms of the projectile particle true path length. A mixed algorithm of the Coulomb elastic scattering simulation based on condensed along step consideration of small angles and single post step scattering for the rest of angular spectrum is discussed for Monte-Carlo simulation of multiple scattering. The model is in satisfactory agreement with experimental data for electrons and protons.