Gabriele Cosmo
310 lines
10 KiB
Plaintext
310 lines
10 KiB
Plaintext
-------------------------------------------------------------------
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=========================================================
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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=========================================================
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gammaray_telescope
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------------------
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F.Longo, R.Giannitrapani & G.Santin
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June 2003
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--------------------------------------------------------------
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Acknowledgments to GEANT4 people, in particular to R.Nartallo,
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A.Pfeiffer, M.G.Pia and G.Cosmo
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--------------------------------------------------------------
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GammaRayTel is an example of application of Geant4 in a space
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envinronment. It simulates a typical telescope for gamma ray analysis;
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the detector setup is composed by a tracker made with silicon planes,
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subdivided in ladders and strips, a CsI calorimeter and an
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anticoincidence system. In this version, the three detectors are made
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sensitive but only the hits on the tracker strips are registered and relevant
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information (energy deposition, position etc) are dumped to an external
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ASCII file for subsequent analysis.
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Relevant information from the simulation is processed in the GammarayTelAnalysis
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class and saved, through the G4AnalysisManager interface, to Histograms and
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Tuples.
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a) Macros for the visualization of geometry and tracks with
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OpenGL, VRML and DAWN drivers
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b) Implementation of messengers to change some parameters of
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the detector geometry, the particle generator and the analysis
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manager (if present) runtime
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c) Readout geometry mechanism to describe an high number of
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subdivisions of the planes of the tracker (strips) without
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affecting in a relevant way the simulation performances
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d) Histogramming facilities are presently provided through the G4AnalysisManager class.
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e) User interfaces via Xmotif or normal terminal provided
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1. Setting up the environment variables
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---------------------------------------
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- Setup for storing ASCII data
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If you want to store the output data in an ASCII file 'Tracks_x.dat'
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where x stays for the run number. You should specify the environment
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variable:
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setenv G4STORE_DATA 1
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- Setup for Visualization
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IMPORTANT: be sure that your Geant4 installation has been done
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with the proper visualization drivers; for details please see the
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file geant4/source/visualization/README.
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To use the visualization drivers set the following variables in
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your local environment:
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setenv G4VIS_USE_OPENGLX 1 # OpenGL visualization
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setenv G4VIS_USE_DAWNFILE 1 # DAWN file
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setenv G4VIS_USE_VRMLFILE 1 # VRML file
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setenv G4VRMLFILE_VIEWER vrmlview # If installed
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- Setup for Xmotif user interface
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setenv G4UI_USE_XM 1
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- Set up for analysis
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To compile the GammaRayTel example with the analysis tools activated,
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set the following variables
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setenv G4ANALYSIS_USE 1 # Use the analysis tools
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2. Sample run
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-------------
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To run a sample simulation with gamma tracks interacting with
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the detector in its standard configuration and without any
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visualization, execute the following command in the example main
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directory:
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$G4WORKDIR/bin/$G4SYSTEM/GammaRayTel
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It is possible also to run three different configuration defined in
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macro1.mac, macro2.mac and macro3.mac for visualization (OpenGL, VRML
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and DAWN respectively) with the following command
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$G4WORKDIR/bin/$G4SYSTEM/GammaRayTel macroX.mac
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where X can be 1, 2 or 3. Be sure to have the right environment (see
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the preceding section) and the proper visualization driver enabled in
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your local G4 installation (see geant4/source/visualization/README for
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more information).
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3. Detector description
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-----------------------
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The detector is defined in GammaRayTelDetectorConstruction.cc
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It is composed of a Payload with three main detectors, a Tracker (TKR), a
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Calorimeter (CAL) and an Anticoincidence system (ACD).
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The standard configuration is made of a TKR of 15 Layers of 2 views made of
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4*4 Si single sided silicon detectors with Lead converter, and a CAL of
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5 layers of CsI, each made of 2 views of 12 CsI bars orthogonally posed.
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4 lateral panels and a top layer of plastic scintillator (ACL and ACT)
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complete the configuration.
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The Si detectors are composed of two silicon planes subdivided in strips
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aligned along the X axis in one plane and along the Y axis for the other.
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The following baseline configuration is adopted:
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GEOMETRICAL PARAMETER VALUE
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Converter thickness 300 microns
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Silicon Thickness 400 microns
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Silicon Tile Size XY 9 cm
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Silicon Pitch 200.micrometer
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Views Distance 1. mm
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CAL Bar Thickness 1.5 cm
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ACD Thickness 1. cm
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It is possible to modify in some way this configuration using the
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commands defined in GammaRayTelDetectorMessenger.
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This feature is available in the UI throught the commands subtree
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"/payload/" (see the help command in the UI for more information).
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4. Physics processes
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--------------------
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This example uses a modular physics list, with a sample of Hadronic processes
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(see the web page http://cmsdoc.cern.ch/~hpw/GHAD/HomePage/ for more adeguate
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physics lists), the Standard or the LowEnergy Electromagnetic processes.
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5. Particle Generator
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---------------------
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The GammaRayTelParticleGenerationAction and its Messenger let the user define
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the incident flux of particles, from a specific direction or from an
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isotropic background. In the first case particles are generated on a spherical
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surface which diameter is perpendicular to the arrival direction. In the second
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case the arrival directions are isotropic.
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The user can define also between two spectral options:
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monochromatic or with a power-law dependence. The particle
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generator parameters are accessible throught the UI tree "/gun/" (use the
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UI help for more information). We are planning to include, in the next
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releases of this example, the General Particle Source module of G4.
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6. Hit
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------
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In this version the hits from the TKR the CAL and the ACD are generated.
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Only the hit from the TRK are saved. Each TKR hit contains the following
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information
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a) ID of the event (this is important for multiple events run)
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b) Energy deposition of the particle in the strip (keV)
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c) Number of the strip
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d) Number of the plane
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e) Type of the plane (1=X 0=Y)
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f) Position of the hit (x,y,z) in the reference frame of the payload
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The hit information are saved on an ASCII file named Tracks_N.dat, where
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N is the progressive ID number associated to the run.
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7. Analysis
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----------------
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Relevant information from the simulation is processed in the GammarayTelAnalysis
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class and saved, through the G4AnalysisManager interface, to Histograms and
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Tuples. The output file is written in ROOT format, but one can easily switch to
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XML (or Hbook) by changing the appropriate #include in GammarayTelAnalysis.hh
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No external software is required (apart from the hbook case, in which the CERNLIB
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must be installed and a FORTRAN compiler must be present)
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Keep in mind that the actual implementation of the analysis tools in GammaRayTel
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is of a pedagogical nature, so we kept it as simple as possible.
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The actual analysis produces some histograms (see next section) and an ntuple.
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Both the histograms and the ntuple are saved at the end of the run in the file
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"gammaraytel.root". Please note that in a multiple run session,
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the last run always override the root file.
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8. Histogramming
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----------------
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The 1D histograms contain the energy deposition in the last X plane of
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the TKR and the hits distribution along the X planes of the TKR
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(note again that these histograms have been chosen more for pedagogical
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motivation than for physical one).
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These histograms are filled and updated at every event and are initialized
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with each new run; the scale of the histograms is automatically derived from
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the detector geometry.
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Throught a messenger it is possible to set some options with
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the UI subtree "/analysis/" (use the UI help for more info);
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In this example we only show the use of very basic feature of this new
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simulation/analysis framework.
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9. Digi
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--------
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For the TKR also the digits corresponding to the Hits are generated.
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A digi is generated when the hit energy deposit is greater than a threshold
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(in this example setted at 120 keV).
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The TKR digi information are stored on the same file Tracks_N.dat and contain:
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a) ID of the event (this is important for multiple events run)
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b) Number of the strip
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c) Number of the plane
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d) Type of the plane (1=X 0=Y)
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10. Classes Overview
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-------------------
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This is the overview of the classes defined in this example
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GammaRayTelPrimaryGeneratorAction
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User action for primaries generator
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GammaRayTelPrimaryGeneratorMessenger
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Messenger for interactive particle generator
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parameters modification via the User Interface
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GammaRayTelPhysicsList
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Determination of modular physics classes
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GammaRayTelGeneralPhysics
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Decay processes
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GammaRayTelEMPhysics
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Std and LowE physics processes (for gamma & e-/e+)
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GammaRayTelMuonPhysics
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Muon & its processes
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GammaRayTelIonPhysics
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Ions and their processes
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GammaRayTelHadronPhysics
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Sample of hadronic processes
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GammaRayTelTelVisManager
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Visualization manager class
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GammaRayTelDetectorConstruction
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Geometry and material definitions for the detector
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GammaRayTelDetectorMessenger
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Messenger for interactive geometry parameters
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modification via the User Interface
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GammaRayTelAnalysis
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Analysis manager class (experimental)
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GammaRayTelAnalysisMessenger
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Messenger for interactive analysis options modification
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via the User Interface
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GammaRayTelRunAction
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User run action class
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GammaRayTelEventAction
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User event action class
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GammaRayTelTrackerHit
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Description of the hits on the tracker
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GammaRayTelDigi
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Description of the digi on the tracker
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GammaRayTelDigitizer
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Description of the digitizer for the tracker
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GammaRayTelTrackerSD
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Description of the TKR sensitive detector
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GammaRayTelAnticoincidenceHit
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Description of the hits on the anticoincidence
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GammaRayTelAnticoincidenceSD
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Description of the ACD sensitive detector
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GammaRayTelCalorimeterHit
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Description of the hits on the calorimeter
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GammaRayTelCalorimeterSD
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Description of the CAL sensitive detector
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