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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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gammaray_telescope
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F. Longo, R. Giannitrapani & G. Santin
June 2003
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Acknowledgments to GEANT4 people, in particular to R. Nartallo,
A. Pfeiffer, M. G. Pia and G. Cosmo
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GammaRayTel is an example of application of Geant4 in a space
environment. 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, the three detectors are made
sensitive but only 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.
Relevant information from the simulation is processed in the GammarayTelAnalysis
class and saved, through the G4AnalysisManager interface, to Histograms and
Tuples.
a) Macros for the visualization of geometry and tracks with
OpenGL, VRML and DAWN drivers
b) Implementation of messengers to change some parameters of
the detector geometry, the particle generator and the analysis
manager (if present) runtime
c) 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
d) Histogramming facilities are presently provided through the G4AnalysisManager class.
e) User interfaces via Xmotif or normal terminal provided
1. Setting up the environment variables
---------------------------------------
- Setup for storing ASCII data
If you want to store the output data in an ASCII file 'Tracks_x.dat'
where x stays for the run number. You should specify the environment
variable:
setenv G4STORE_DATA 1
- 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
To compile the GammaRayTel example with the analysis tools activated,
set the following variables
setenv G4ANALYSIS_USE 1 # Use the analysis tools
2. 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).
3. 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 2 views made of
4 * 4 Si single sided silicon detectors with Lead converter, and a CAL of
5 layers of CsI, each made of 2 views of 12 CsI bars orthogonally posed.
4 lateral panels and a top layer of plastic scintillator (ACL and ACT)
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.
The following baseline configuration is adopted:
GEOMETRICAL PARAMETER VALUE
Converter Thickness 300 micron
Silicon Thickness 400 micron
Silicon Tile Size XY 9 cm
Silicon Pitch 200. micrometer
Views Distance 1. mm
CAL Bar Thickness 1.5 cm
ACD Thickness 1. cm
It is possible to modify in some way this configuration using the
commands defined in GammaRayTelDetectorMessenger.
This feature is available in the UI through the commands subtree
"/payload/" (see the help command in the UI for more information).
4. Physics processes
--------------------
This example uses a modular physics list, with a sample of Hadronic processes
(see the web page http://cmsdoc.cern.ch/~hpw/GHAD/HomePage/ for more adeguate
physics lists), the Standard or the LowEnergy Electromagnetic processes.
5. 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. In the first case particles are generated on a spherical
surface which diameter is perpendicular to the arrival direction. In the second
case the arrival directions are isotropic.
The user can define also between two spectral options:
monochromatic or with a power-law dependence. The particle
generator parameters are accessible through the UI tree "/gun/" (use the
UI help for more information). We are planning to include, in the next
releases of this example, the General Particle Source module of G4.
6. Hit
------
In this version the hits from the TKR the CAL and the ACD are generated.
Only the hit from the TRK are saved. Each TKR hit contains the following
information
a) ID of the event (this is important for multiple events run)
b) Energy deposition of the particle in the strip (keV)
c) Number of the strip
d) Number of the plane
e) Type of the plane (1=X 0=Y)
f) 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.
7. Analysis
-----------
Relevant information from the simulation is processed in the GammarayTelAnalysis
class and saved, through the G4AnalysisManager interface, to Histograms and
Tuples. The output file is written in ROOT format, but one can easily switch to
XML (or Hbook) by changing the appropriate #include in GammarayTelAnalysis.hh
No external software is required (apart from the hbook case, in which the CERNLIB
must be installed and a FORTRAN compiler must be present)
Keep in mind that the actual implementation of the analysis tools in GammaRayTel
is of a pedagogical nature, so we kept it as simple as possible.
The actual analysis produces some histograms (see next section) and an ntuple.
Both the histograms and the ntuple are saved at the end of the run in the file
"gammaraytel.root". Please note that in a multiple run session,
the last run always override the root file.
8. Histogramming
----------------
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 again that these 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.
Through a messenger it is possible to set some options with
the UI subtree "/analysis/" (use the UI help for more info);
In this example we only show the use of very basic feature of this new
simulation/analysis framework.
9. Digi
-------
For the TKR also the digits corresponding to the Hits are generated.
A digi is generated when the hit energy deposit is greater than a threshold
(in this example setted at 120 keV).
The TKR digi information are stored on the same file Tracks_N.dat and contain:
a) ID of the event (this is important for multiple events run)
b) Number of the strip
c) Number of the plane
d) Type of the plane (1=X 0=Y)
10. 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 modular physics classes
GammaRayTelDetectorConstruction
Geometry and material definitions for the detector
GammaRayTelDetectorMessenger
Messenger for interactive geometry parameters
modification via the User Interface
GammaRayTelAnalysis
Analysis manager class (experimental)
GammaRayTelAnalysisMessenger
Messenger for interactive analysis options modification
via the User Interface
GammaRayTelRunAction
User run action class
GammaRayTelEventAction
User event action class
GammaRayTelTrackerHit
Description of the hits on the tracker
GammaRayTelDigi
Description of the digi on the tracker
GammaRayTelDigitizer
Description of the digitizer for the tracker
GammaRayTelTrackerSD
Description of the TKR sensitive detector
GammaRayTelAnticoincidenceHit
Description of the hits on the anticoincidence
GammaRayTelAnticoincidenceSD
Description of the ACD sensitive detector
GammaRayTelCalorimeterHit
Description of the hits on the calorimeter
GammaRayTelCalorimeterSD
Description of the CAL sensitive detector
Gabriele Cosmo