RSICC CODE PACKAGE CCC-733
1. NAME AND TITLE
PENELOPE2006: Code System for Monte Carlo Simulation of Electron and Photon Transport.
2. CONTRIBUTORS
Facultat de Fisica (ECM), Universitat de Barcelona and Universitat Politècnica de Catalunya de Barcelona, Spain,
through the Nuclear Energy Agency Data Bank, Issy-les-Moulineaux, France.
3. CODING LANGUAGE AND COMPUTER
Fortran; PC under Windows or Linux (RSICC ID: C00733PC58600).
This is the same version that the NEADB distributes as NEA-1525/12.
4. NATURE OF PROBLEM SOLVED
PENELOPE performs Monte Carlo simulation of coupled electron-photon transport in arbitrary materials and complex quadric geometries. A mixed procedure is used for the simulation of electron and positron interactions (elastic scattering, inelastic scattering and bremsstrahlung emission), in which 'hard' events (i.e. those with deflection angle and/or energy loss larger than pre-selected cutoffs) are simulated in a detailed way, while 'soft' interactions are calculated from multiple scattering approaches. Photon interactions (Rayleigh scattering, Compton scattering, photoelectric effect and electron-positron pair production) and positron annihilation are simulated in a detailed way. PENELOPE reads the required physical information about each material (which includes tables of physical properties, interaction cross sections, relaxation data, etc.) from the input material data file. The material data file is created by means of the auxiliary program MATERIAL, which extracts atomic interaction data from the database of 767 ASCII files.
PENELOPE mailing list archives can be found on the web: http://www.nea.fr/lists/penelope.html.
The following features are specific to the 2001 and later versions of the code:
1) The simulation parameters (Eabs, C1, C2, Wcc and Wcr) are defined independently for each material. This allows the user to specify regions of interest where the simulation is performed in greater detail.
2) The argument DSMAX of subroutine JUMP specifies the maximum allowed path length between hard interactions of electrons and positrons. By selecting a suitably small value for this parameter, the user can control the number of hinges in thin regions (which must be larger that 10 or so, to ensure accuracy). This argument is also used for simulating the transport of charged particles in the presence of static external electric and magnetic fields. DSMAX has no effect when set equal to a very large number (e.g. 10**35).
3) The structure of the common /TRACK/ differs from previous versions. The variable ILB(5), which describes the origin of secondary particles, can be used to study partial contributions from particles originated by a given process.
The following features are specific to the 2003 and later versions of the code:
1) The generation of fluorescent radiation (x rays and Auger electrons) resulting from ionization of inner shells by impact of electrons and positrons is described as an independent process. The adopted ionization cross sections were calculated by using the relativistic Born approximation with a generalized oscillator strength model built from the partial photoelectric cross section of the active electron shell. This gives a more accurate description of the generation of characteristic x rays by electron and positron impact.
2) The energies of characteristic x rays are set equal to their experimental values (in previous versions of the code they were calculated from the ionization energies of the active electron shells).
3) The simulation algorithm for electron and positron inelastic collisions has been re-coded to allow more flexibility in the description of the physics and also to improve the simulation speed. Apart from a certain gain in speed (which is higher for heavy elements) this feature is not "visible" from the user's main program.
4) The program TABLES.F, which produces tables of interaction properties (photon mass attenuation coefficients, electron/positron mean free paths, stopping powers, radiation yields, ranges,...) for arbitrary materials, has been included in the distribution package.
The following features have been added to the 2005 version of the code:
1) Version 2005 includes the new program PENMAIN, that works like a blackbox for solving a large variety of problems with quadric geometries. With PENMAIN occasional (and normal) users can solve problems without having to write a single program line.
2) The program TABLES gives access to additional details of the interactions physics, both in a numeric and graphical way, e.g. the energy loss of electrons, or the photon attenuation coefficients in a material.
3) TIMER subroutines have been modified, according to a suggestion from a user from the NEA Data Bank, and are portable now (so far these work correctly with all compilers, under Windows or Linux).
4) Also following a suggestion from a NEA Data Bank user, unit 6 is no longer the standard output unit, except when the program makes a fatal error and stops. Now it is possible to write messages on the screen (like number of simulated showers) at predefined intervals, and consequently, it is possible to follow the program execution.
5) The electron elastic differential cross-sections are now obtained through partial wave analysis (PWA). Before only the total cross-section and the two first momenta of the differential cross-sections were considered..
6) The atomic disexcitation process following the vacancies in the M layer is now described. Before only the X rays and Auger electrons resulting from the vacancies in the K and L layers were described.
7) Some improvements have introduced in the geometry subroutine (PENGEOM). For instance, now it is possible to clone objects.
8) Consequently, some changes had to be made in the geometry viewers. For instance GVIEW allows to visualise materials and shapes (before only materials).
Improvements in the 2006 version compared to version 2005.
1) The correction for the energy dependence of the stopping power and the energy straggling parameter for soft interactions of electrons and positrons has been improved.
2) The sampling algorithm for Rayleigh scattering (which caused the g77 compiler to issue multiple warning messages) has been reformulated and improved.
3) Numerical interpolations, particularly those of elastic-scattering differential cross sections, are more accurate.
4) The structure of several common blocks has been modified to make interaction properties accessible from the program TABLES, and to facilitate future extensions of the interaction database. The names of interaction physics routines have been modified to allow the use of multiple models for each interaction mechanism.
5) The geometry package PENGEOM has been expanded. The present version can handle complex quadric geometries with up to 9,999 surfaces and 5,000 bodies. This extension required slight changes in the FORMAT of the geometry definition files (old files can be adapted with little editing work).
The geometry enclosure is defined as a sphere of 1.0e7 cm radius. This corrects a bug in the 2005 version (which caused inconsistencies when the whole material system was enclosed in a single module and this module was not simply connected).
6) The manual (penelope-2006-NEA.pdf) has been expanded and adapted to the present structure of the code.
5. METHOD OF SOLUTION
The Monte Carlo method is used. A sufficiently large number of particle histories is simulated, and relevant quantities are obtained as averages. The mixed simulation algorithm for electrons and positrons implemented in PENELOPE reproduces the actual transport process to a high degree of accuracy and is very stable even at low energies. This is partly due to the use of a sophisticated transport mechanics model based on the so-called random hinge method, with energy-loss corrections for soft events. Other differentiating features of the simulation are a consistent description of angular deflections in inelastic collisions and of energy-loss straggling in soft stopping events. Binding effects and Doppler broadening in Compton scattering are also taken into account.
6. RESTRICTIONS OR LIMITATIONS
Electron and positron kinetic energies must be in the range from 100 eV to 1 GeV, and plural or multiple scattering conditions have to be fulfilled, i.e. the number of both elastic and inelastic interactions in the material must be larger than about 10. Photon energies should be in the range from 100 eV (or the M-shell absorption edge, whichever is the largest) to 1 GeV. Photo-nuclear reactions are disregarded.
7. TYPICAL RUNNING TIME
The running time largely depends on the number of histories to be simulated, the kind of incident particle, its initial energy and the considered geometry. The adopted simulation parameters (energy cutoffs, etc.) also influence the computing time. As an example, a broad-beam depth-dose distribution of 10 MeV electrons incident on a water phantom, obtained by simulating 100.000 histories, can be obtained with a running time of some 320 s on an Intel Pentium III at 733 MHz with 128 MB RAM. Some example problems run for days unless dump and time parameters are modified. This demonstrates stability of the code with the user’s compiler.
8. COMPUTER HARDWARE REQUIREMENTS
PENELOPE 2006 runs on personal computers.
9. COMPUTER SOFTWARE REQUIREMENTS
PENELOPE 2006 runs on Pentium personal computers under either Windows XP or Linux. The code will run on almost any operating system supporting a FORTRAN 77 compiler and is FORTRAN 90 compatible. There are no specific requirements for the PENELOPE kernel. However the time subroutine, which is used in the example programs, must be adapted to the user’s operating system. Included time routines are standard Fortran 90.
A Fortran compiler is required on all computers as the user must supply the main program for his particular problem. Editing the included PENMAIN generally allows users to define their source characteristics without writing a single line of source code. The authors recommend GNU Fortran 77 or GNU Fortran 95 compilers. Some other compilers which have been used include Compaq Visual Fortran 6.6, Intel 9.0, Lahey/Fujitsu 5.5h and Absoft. To plot the results, you need a plotting program. GNUPLOT is recommended.
In addition to PENELOPE 2006 source code, data files and example problems, some graphic tools are included. GVIEW2D, GVIEW3D and GVIEWC are geometry viewers/debuggers that display 2- or 3-dimensional images of the geometry. SHOWER displays showers produced by primary particles of a given kind and energy in a slab. These graphic tools are operable only under MS-Windows 9x/NT/2000/XP. Windows executables are included for these viewers, but source codes are not provided.
10. REFERENCES
F.Salvat, J.M. Fernandez-Varea, and J.Sempau, “PENELOPE-2006, A Code System for Monte Carlo Simulation of Electron and Photon Transport ,” Workshop Proceedings Barcelona, Spain, OECD ISBN 92-64-02301-1 (July 2006).
Tutorial for PENELOPE (version 2006) written by code developers.
11. CONTENTS OF CODE PACKAGE
The package is transmitted on a CD which includes the referenced documents in PDF files, Penelope source codes, graphic tools, data files and example problems. The code system is distributed in two formats: a self-extracting Windows file and a Unix tar file.
12. DATE OF ABSTRACT
March 2007.
KEYWORDS: MONTE CARLO; BREMSSTRAHLUNG; HIGH ENERGY; GAMMA-RAY; POSITRON