Authors: F.Longo (Ferrara), R.Giannitrapani (Udine) & G.Santin (Trieste) -- December 2000
Acknowledgments to GEANT4 people, in particular to R.Nartallo, A.Pfeiffer, M.G.Pia and G.Cosmo
Introduction
GammaRayTel is an example of application of Geant4 in a space envinronment. It simulates a typical telescope for gamma ray analysis; the detector setup is composed by a tracker made with silicon planes, subdivided in ladders and strips, a CsI calorimeter and an anticoincidence system. In this version, only the tracker is made sensitive; the hits on the tracker strips are registered and relevant information (energy deposition, position etc) are dumped to an external ASCII file for subsequent analysis. If Lizard is available on the user platform, than some histograms with relevant hits information are displayed and saved as PostScript files. The main features of this example are
Macros for the visualization of geometry and tracks with OpenGL, VRML and DAWN drivers
Implementation of messengers to change some parameters of the detector geometry, the particle generator and the analysis manager (if present) runtime
Readout geometry mechanism to describe an high number of subdivisions of the planes of the tracker (strips) without affecting in a relevant way the simulation performances
Histogramming for Linux and Solaris platform via the Lizard system (tested on Linux platform); this is a preliminary feature of GEANT4, so expect some changes and/or improvements in future releases
User interfaces via Xmotif or normal terminal provided
Setting up the environment variables
Setup for Visualization
IMPORTANT: be sure that your Geant4 installation has been done with the proper visualization drivers; for details please see the file geant4/source/visualization/README. To use the visualization drivers set the following variables in your local environment:
setenv G4VIS_USE_OPENGLX 1 # OpenGL visualization
setenv G4VIS_USE_DAWNFILE 1 # DAWN file
setenv G4VIS_USE_VRMLFILE 1 # VRML file
setenv G4VRMLFILE_VIEWER vrmlview # If installed
Setup for Xmotif user interface
setenv G4UI_USE_XM 1
Set up for analysis using Lizard:
IMPORTANT: be sure that your G4 installation has been done properly; in particular be sure that the following environment variables are set prior to build the library (this is working only on Linux and Solaris platform)
setenv G4ANALYSIS_BUILD 1 # Build the analysis tools
setenv G4ANALYSIS_BUILD_LIZARD 1 # Build the Lizard interface
setenv LIZARDROOT /usr/local/freeLizard/3.2.0 #get correct path
For example at CERN the path is
setenv LIZARDROOT /afs/cern.ch/project/asddat/lhcxx/3.2.0/freeLizard/3.2.0
To compile the GammaRayTel example with the analysis tools activated, set the following variables
setenv G4ANALYSIS_USE 1 # Use the analysis tools
setenv G4ANALYSIS_USE_LIZARD 1 # Use the Lizard one
and be sure to have the right path to the Lizard library
#add to the LD_LIBRARY_PATH (get correct path)
setenv LD_LIBRARY_PATH /usr/local/freeLizard/3.2.0/Linux/lib
For example at CERN the path is
setenv LD_LIBRARY_PATH /afs/cern.ch/project/asddat/lhcxx/3.2.0/freeLizard/3.2.0/Linux/lib
Sample run
To run a sample simulation with gamma tracks interacting with the detector in its standard configuration and without any visualization, execute the following command in the example main directory:
$G4WORKDIR/bin/$G4SYSTEM/GammaRayTel
It is possible also to run three different configuration defined in macro1.mac, macro2.mac and macro3.mac for visualization (OpenGL, VRML and DAWN respectively) with the following command
$G4WORKDIR/bin/$G4SYSTEM/GammaRayTel macroX.mac
where X can be 1, 2 or 3. Be sure to have the right environment (see the preceding section) and the proper visualization driver enabled in your local G4 installation (see geant4/source/visualization/README for more information).
Detector description
The detector is defined in GammaRayTelDetectorConstruction.cc It is composed of a Payload with three main detectors, a Tracker (TKR), a Calorimeter (CAL) and an Anticoincidence system (ACD). The standard configuration is made of a TKR of 15 Layers of Si detectors, with Lead converter, and a CAL of 8 layers of CsI. 4 lateral panels and a top layer of plastic scintillator (ACT and ACL) complete the configuration. The Si detectors are composed of two silicon planes subdivided in strips aligned along the X axis in one plane and along the Y axis for the other. It is possible to modify in some way this configuration using the commands defined in GammaRayTelDetectorMessenger. This feature is available in the UI throught the commands subtree "/payload/" (see the help command in the UI for more information).
Physics processes
This example uses the standard Electromagnetic processes.
Particle Generator
The GammaRayTelParticleGenerationAction and its Messenger let the user define the incident flux of particles, from a specific direction or from an isotropic background. The user can define also between two spectral options: monochromatic or with a power-law dependence. The particle generator parameters are accessible throught the UI tree "/gun/" (use the UI help for more information). We are planning to include, in the next release of this example, the new General Particle Source module of G4.
ReadOutGeometry
The tracker is made of Silicon Microstrips detectors. The ReadOut geometry provides the description of the strips.
Hit
In this version only the hits from the TKR are recorded. Each hit contains the following information
ID of the event (this is important for multiple events run)
Energy deposition of the particle in the strip (keV)
Number of the strip
Number of the plane
Type of the plane (1=X 0=Y)
Position of the hit (x,y,z) in the reference frame of the payload
The hit information are saved on an ASCII file named Tracks_N.dat, where N is the progressive ID number associated to the run.
Histogramming
Some hits information can be visualized runtime using Lizard (if it is available on the user platform); two 2D histograms and two 1D histograms can be visualized and saved (as PostScript files) during the simulation run. The 2D histograms contain the hits positions on the TKR projected on the XZ plane and the YZ plane; the 1D histograms contain the energy deposition in the last X plane of the TKR and the hits distribution along the X planes of the TKR (note that this histograms have been chosen more for pedagogical motivation than for physical one). These histograms are filled and updated at every event and are initialized with each new run; the scale of the histograms is automatically derived from the detector geometry. Throught a messenger it is possible to set some options with the UI subtree "/analysis/" (use the UI help for more info); in particular it is possible to enable or disable the drawing of the 1D and 2D histograms at every event and to enable or disable the saving of PostScript files at the end of each run. If you feel that the simulation is too slow with the histograms updated every event, you can disable the drawing and retain the saving. Please note that the updating of the histograms is triggered only when there is some hit in an event. In this example we only show the use of very basic feature of this new simulation/analysis framework; histogramming and analysis in Geant4 are in an evolving phase, so expect some changes and/or improvements for next releases.
Classes Overview
This is the overview of the classes defined in this example
GammaRayTelPrimaryGeneratorAction User action for primaries generator
GammaRayTelPrimaryGeneratorMessenger Messenger for interactive particle generator parameters modification via the User Interface
GammaRayTelPhysicsList Determination of particles and processes active in this example
GammaRayTelTelVisManager Visualization manager class
GammaRayTelDetectorConstruction Geometry and material definitions for the detector
GammaRayTelDetectorMessenger Messenger for interactive geometry parameters modification via the User Interface
GammaRayTelAnalysisManager Analysis manager class with Lizard tool (experimental)
GammaRayTelAnalysisMessenger Messenger for interactive analysis options modification via the User Interface
GammaRayTelRunAction User run action class
GammaRayTelEventAction User event action class
GammaRayTelPayloadHit Description of the hits on the tracker
GammaRayTelPayloadROGeometry Description of the readout geometry for strips subdivision
GammaRayTelPayloadSD Description of the sensitive detector
