ABSTRACT
Low-Energy Electron Transport in EGS4 ......................................................... 175 Models of Basic Physics Processes in EGSnrc and EGS5 ............................... 177
Electron Transport Models ............................................................................ 177 Discrete Collisions with Atomic Electrons ............................................. 177 Electron Impact Ionization ....................................................................... 178 Discrete Bremsstrahlung Interactions..................................................... 178 Two Photon Positron Annihilation ......................................................... 179 Stopping Powers ........................................................................................ 179 Multiple Elastic Scattering ....................................................................... 179
Photon Transport Models .............................................................................. 180 Pair Production .......................................................................................... 180 Compton Scattering .................................................................................. 181 Rayleigh Scattering .................................................................................... 181 Photoelectric Effect .................................................................................... 182 Atomic Relaxation ..................................................................................... 182
Electron Transport Mechanics of EGSnrc and EGS5 ...................................... 182 EGSnrc Transport Mechanics ........................................................................ 183 EGS5 Transport Mechanics ........................................................................... 184
EGSnrc and EGS5 Code Packages .................................................................... 186 Installation and Structure of Packages ........................................................ 187 Preparing Material Data Files with PEGS ................................................... 188 Basic Structure of an EGS User Code .......................................................... 188 Writing EGSnrc User Code ........................................................................... 189
Macros, MORTRAN .................................................................................. 189 EGSnrc C++ Library .................................................................................. 190 Step Size Control........................................................................................ 190 Additional Features ................................................................................... 190 EGSnrc Sample User Codes ..................................................................... 191
Writing EGS5 User Codes .................................................................................. 191 FORTRAN “include” Extension ................................................................... 192 Step Size Control ............................................................................................ 192 Auxiliary Geometry and Scoring Routines ................................................ 193
The electron gamma shower (EGS) Monte Carlo particle transport simulation code system was originally developed by researchers at the Stanford Linear Accelerator Center as a platform for modeling high-energy physics experiments, and through the release of version 3 of the code (EGS3) in 1978 [1], developmental work on EGS focused on modeling physics processes at very high energies. This changed with the release of EGS4 in 1985 [2], whose authors cited the “many requests to extend EGS3 down to lower energies” as a major reason for the creation of EGS4 [2]. Much of the impetus for this extension of the dynamic range of EGS was provided by medical physics investigators, who also contributed a great deal of the effort required to modify the code system for low-energy simulations.
