Code characteristics

Transcription

1 The PENELOPE Computer code M.J. Anagnostakis Nuclear Engineering Department National Technical University of Athens

2 The PENELOPE code system PENetration and Energy LOss of Positrons and Electrons in matter performs Monte Carlo simulation of coupled electron and photon transport in arbitrary materials It was developed by: F. Salvat, J.M. Fernandez-Varea and J. Sempau from Facultat de Fisica (ECM). Universitat de Barcelona. Diagonal Barcelona. Spain

3 Code characteristics The simulation algorithm is based on a scattering model that combines numerical databases with analytical cross-section models for the different interaction mechanisms and is applicable to energies (kinetic energies in the case of electrons and positrons) from 50 ev to 1 GeV. PENELOPE generates random electron-photon showers in complex material structures consisting of any number of distinct homogeneous regions (bodies) of different compositions.

4 Code characteristics The considered interactions and the corresponding differential cross sections are the following: ¾ ¾ ¾ ¾ ¾ ¾ ¾ ¾ ¾ Elastic scattering of electrons and positrons. Inelastic collisions of electrons and positrons. Bremsstrahlung emission by electrons and positrons. Positron annihilation. Inner-shell ionisation by electron and positron impact. Coherent (Rayleigh) scattering of photons. Incoherent (Compton) scattering of photons. Photoelectric absorption of photons. Electron-positron pair production.

5 Code characteristics The simulation of photon transport follows the usual detailed procedure, i.e. all the interaction events in a photon history are simulated in chronological succession. The simulation of electron and positron tracks is performed by means of a mixed (class II) algorithm. Individual hard elastic collisions, hard inelastic interactions and hard bremsstrahlung emission are simulated in a detailed. The track of a particle between successive hard interactions, or between a hard interaction and the crossing of an interface is generated as a series of steps of limited length.

6 Code structure Main program (User code) PENELOPE subroutines

7 Example of MAIN programs In principle, the user should provide the MAIN program for each specific geometry. The distribution package includes various examples of MAIN programs for simple geometries (slab and cylindrical) and for general quadric geometries, with limited scoring and variance reduction options. The 2005 version includes the MAIN programs: Penslab Pencyl Penmain the 2006 version.

8 The MAIN program penslab The program PENSLAB simulates electron/photon showers within a material slab. It illustrates the use of the simulation routines for the simplest geometry (as geometry operations are very simple, this program is faster). PENSLAB generates detailed information on many quantities and distributions of physical interest. The slab is limited by two planes. Primary particles of a given kind are emitted from a point source either with fixed energy or with a specified energy spectrum. The initial direction of the primary particles is sampled uniformly inside a cone and with central axis in the specific direction.

9 The MAIN program pencyl The program PENCYL simulates electron-photon showers in multilayered cylindrical structures. The system consists of one or several layers of given thicknesses. Each layer contains a number of concentric homogeneous rings. The geometrical structure is symmetrical about the Z-axis. Primary particles of a given kind are emitted from the active volume of the source, either with fixed energy or with a specified energy spectrum. The initial direction of the primary particles is sampled uniformly inside a cone of and with central axis in a specific direction. The program can simulate two different types of sources: An external source with uniform activity over a cylindrical volume. A set of internal sources spread over specified bodies, each one with uniform activity concentration.

10 The MAIN program penmain This is a generic main program that performs simulations of electron-photon transport in complex material structures. PENMAIN is devised to allow occasional users to employ PENELOPE without having to write their main program. The geometry of the material system is described by means of the package PENGEOM, which is able to handle complicated geometries very efficiently The operation of PENMAIN is completely controlled from the input data files. Although it is impossible to cover all possible cases with a ''closed'' program, PENMAIN is flexible enough to solve a broad class of practical problems.

11 How to run the code Write (in fortran) or modify the Main program. Prepare the necessary input data files (to describe the geometry, the materials etc). The program material is used for the material data file preparation. Auxiliary programs such as gview2d and gview3d may be used to check the correctness of the geometry data file (ASCII file). Compile and link the Main program with the PENELOPE subroutines. Run the code with the input data files.

12 How to run the code A dump/resume option allows the user to stop the simulation at any time and to resume it from the last dumping point in a completely consistent way. The program can also write simulation results in the output files at regular time intervals. This option is useful to check the progress of long simulations. It also allows running the program with a long execution time and stopping it when the required statistical uncertainty has been reached.

13 Input data files The input data file the user has to prepare are: The file.mat to describe the materials used. The file.geo to describe the geometry of the system The file.in to initiate various parameters (number of showers, detectors used, source type and energy, number of bins etc)

14 Main input data file TITLE Response of a Ge detector. >>>>>>>> Source definition. SKPAR 2 [Primary particles: 1=electron, 2=photon, 3=positron] SENERG 4.5e4 [Initial energy (monoenergetic sources only)] SPOSIT [Coordinates of the source] SDIREC 0 0 [Beam axis direction angles, in deg] SAPERT 180 [Beam aperture, in deg] >>>>>>>> Material data and simulation parameters. NMAT 2 [Number of different materials,.le.10] SIMPAR 1 4.5e2 4.5e1 4.5e e2 4.5e1 [M,EABS,C1,C2,WCC,WCR] SIMPAR 2 4.5e2 4.5e1 4.5e e2 4.5e1 [M,EABS,C1,C2,WCC,WCR] The following material data file must be copied from directory. to the working directory. PFNAME Ge_geom3.mat [Material definition file, 20 chars] >>>>>>>> Geometry definition file. GEOMFN Ge_geom3.geo [Geometry definition file, 20 chars] >>>>>>>> Emerging particles. Energy and angular distributions. NBE 1e3 4.5e4 100 [E-interval and no. of energy bins] NBTH 45 [No. of bins for the polar angle THETA] NBPH 18 [No. of bins for the azimuthal angle PHI] >>>>>>>> Energy deposition detectors (up to 5). ENDDET 1e3 4.5e4 100 [Energy window and number of channels] EDBODY 1 [Active body; one line for each body] >>>>>>>> Job properties RESUME dump1.dat [Resume from this dump file, 20 chars] DUMPTO dump1.dat [Generate this dump file, 20 chars] DUMPP 60 [Dumping period, in sec] TIME 6.0e5 [Allotted simulation time, in sec]

15 Typical Geometry input file 3in*3in cylindrical NaI detector, with Al case and Al2O3 reflecting layer SURFACE ( 1) Cylinder R=3.81 INDICES=( 1, 1, 0, 0,-1) X-SCALE=( E+00, 0) Y-SCALE=( E+00, 0) SURFACE ( 6) Plane Z=0.00 INDICES=( 0, 0, 0, 1, 0) BODY ( 1) NaI CRYSTAL. MATERIAL( 1) SURFACE ( 1), SIDE POINTER=(-1) SURFACE ( 6), SIDE POINTER=(+1) SURFACE ( 7), SIDE POINTER=(-1) MODULE ( 2) Al2O3 reflecting layer. MATERIAL( 2) SURFACE ( 2), SIDE POINTER=(-1) SURFACE ( 5), SIDE POINTER=(+1) SURFACE ( 7), SIDE POINTER=(-1) BODY ( 1) END

16 For the description of complicated geometries several types of surfaces are used

17 View of a geometry file

18 Complicated geometries The code is able to handle complicated geometries

19 The detectors Several types of detectors are included in the code in order to record various parameters and distributions: Impact detectors. The main characteristics of the particles coming in the detector are recorded. Energy deposition detectors. The energy of a particle that is deposited in the detector is recorded. Dose enclosure. To record the dose distribution within a specific system volume.

20 Output data files Two general types of files are produced: Files with the main parameters of the simulation and several useful information such as average values (e.g. penmain.dat) Files with space or energy distribution for various parameters, such as energy distribution of the deposited energy on a detector (e.g. pm_spc_enddet.dat)

21 The pm_spc_enddet.dat file # Results from PENMAIN. Output from energy-deposition detector # 1 # 1st column: deposited energy (ev). # 2nd column: probability density (1/(eV*particle)). # 3rd column: statistical uncertainty (3 sigma) E E E E E E E E E E E E E E E E E E E E E-09

22 Energy deposition spectrum in an energy detector Energy spectrum from energy-deposition detector # 'pm_spc_enddet_1.dat' u 1:2:3 1e-005 1e-006 1e-007 P(E) 1e-008 1e-009 1e-010 1e-011 1e E

23 Typical graph output file of the pendoses user code 3.4e e+006 3e+006 Depth dose distribution 'psddose.dat' u 1:2:3 dose (ev/(g/cm**2)) 2.8e e e e+006 2e e e depth (cm)

24 Auxiliary programs The PENELOPE package includes some auxiliary programs such as: The program shower for the visual representation of the simulation in real time. The program tables for the creation of tables of energy dependent quantities such as linear attenuation coefficients etc. The program wgnuplot for the the graphical representation of the energy dependent quantities.

25 The program shower

26 Typical graph from program tables 1e Photon mass attenuation coefficients Rayleigh Compton Photoabsorption Pair production Total mu (cm**2/g) e-006 1e e+006 Energy (kev)

27 Thank you very much for your attention