Packages for Monte Carlo simulation of radiation interaction with matter Sergey Ananko Saint-Petersburg State University Department of Physics Division of Computational Physics JASS-06

Outline Actuality Short description of physical model Monte Carlo method Geant4 Fluka Comparison of packages Conclusions Future plans JASS-06

Actuality Particular General Nuclear physics Necessity to have several ways of the solution of the same problem General Nuclear physics High-energy physics Cosmic rays Neutrino physics Medicine JASS-06

Gamma-rays Physics review Gamma-rays – high-frequency electromagnetic oscillations: and above Gamma-particles characteristics: velocity: energy: momentum: wave length: Gamma photons energy range: Effects: photoelectrical absorption, Compton effect and pair production JASS-06

Scattering cross-section Physics review - number of photons through unit square per unit of time - number of scattered photons - cross-section - number of scattered gamma photons - probability of photons scattering JASS-06

Photoelectrical effect Physics review Photoelectrical effect is a process of gamma photon absorption by atom of substance - photoelectron energy - photon energy - binding energy JASS-06

Compton effect Physics review Compton effect is a process of gamma photon scattering on electron of atom - scattered photon energy - incident photon energy - electron rest-energy - wave length after interaction - wave length before interaction - Compton electron energy JASS-06

Compton effect - minimal value of scattered photon energy Physics review - minimal value of scattered photon energy - maximum photoelectron energy - gamma-quantum scattering angle - Compton electron scattering angle JASS-06

Pair production Physics review Pair production is a process of generation electron-positron pair in nucleus or atom field JASS-06

Total interaction coefficient Physics review Number of photons lost by the beam: where - cross-sections of Compton effect, photo effect, pair production - atom number per unit of volume - flux density - beam cross-section - total interaction cross-section per one atom of matter Quantum energy loss per unit of time: JASS-06

Total interaction coefficient Physics review mass absorption coefficient for air - linear absorption coefficient - mass absorption coefficient - matter density JASS-06

Energy and angular distribution of secondary particles Model Physics review Air-filled cubic volume: Detecting plane Gamma energy range: Point-like source Energy and angular distribution of secondary particles JASS-06

Deterministic methods Two approaches The Monte Carlo Method Deterministic methods Finite difference method Finite element method The Monte Carlo method JASS-06

Model: probability estimation The Monte Carlo Method Source – anisotropic point-like monoenergetic gamma photon source Shield – relatively thick spherical shell, only one sort of atom Effects: Elastic scattering Absorption Effects are characterized by: Cross-section Probability density function for path length JASS-06

Simulation steps First step: free path length The Monte Carlo Method First step: free path length Second step: scattering or absorption Third step: scattering angle Further steps: repeating - number of generated trajectories - number of escaped gamma photons - score Estimated probability of escape: Variance of the : Relative error z JASS-06

Variance reduction Brute-force approach Truncation Population control: The Monte Carlo Method Brute-force approach Truncation Population control: Splitting Russian roulette Probability modification Pseudodeterministic methods JASS-06

Geometry description Combinatorial object Surface-sense object The Monte Carlo Method Combinatorial object Surface-sense object JASS-06

Monte Carlo packages Main aspirations: Examples: The Monte Carlo Method Main components: Data base of cross-sections and other parameters Theoretical base Random number generator Tool for geometry description Main aspirations: Extended range of ability Flexibility Examples: MNCP, Fluka, Geant, Geant4, Vulcanu, PYTHIA, ARIADNE and so on JASS-06

Geant4: status Geant4 is a detector description and simulation tool Application areas: High-energy physics, nuclear experiment, medical, accelerator and space physics studies History: 1974 – GEANT first version 1982 – the appearance of GEANT3 1998 December – first release of GEANT4 Geant4 is a free software It can be downloaded from URL: http://geant4.cern.ch Operating systems: Unix, Linux, Windows JASS-06

Main features GEANT4 is written in C++ GEANT4 is based on an object-oriented technology Experiment stages: Detector description Source description Physics description Detector reaction description JASS-06

Fluka: status Fluka JASS-06 Fluka is a general purpose tool for calculations of particle transport and interactions with matter, covering an extended range of applications spanning from proton and electron accelerator shielding to target design, calorimetry, activation, dosimetry, detector design, Accelerator Driven Systems, cosmic rays, neutrino physics, radiotherapy etc. Fluka is distributed under the licence as a tar file It can be downloaded from its web-site: www.fluka.org Supported platforms: - Hewlett-Packard 9000 Series 700/800 running HP-UX - Sun running SunOS - Intel PCs running LINUX: - RedHat 7.3 - RedHat 9.0 - Scientific Linux 4.1 ` - Fedora Core History: First generation – the Fluka of the 70th Second generation – the Fluka of the 80th Third generation – the Fluka of today JASS-06

Main features Fluka is written in Fortran Package consists of compiled libraries, user routing in source form, INCLUDE files, various unformatted and formatted data and a number of scripts for compiling, linking and running the program. Structure of input file: particle source, geometry, transport options, detectors Example: source (kind of particle, energy, location in space, distribution) BEAM 50.E+00 PROTON BEAMPOS 0.0 0.0 -50.0 JASS-06

Comparison: main features Geant4 Fluka photoelectric effect: Compton effect: - recommended value for threshold for Fluka pair production: multiple scattering: threshold energy

Conclusion Both Fluka and Geant4 provide with ability of simulation particles transport in a very extended energy range. JASS-06

Future plans To receive results from Fluka To process them To compare them with Geant4 To parallel both Fluka and Geant4 JASS-06

Thank you for attention