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Geant4 examples
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Geant4 examples
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This example simulates a simple Sampling Calorimeter setup. To demonstrate several possible ways of data scoring, the example is provided in four variants: B4a, B4b, B4c, B4d. (See also examples/extended/electromagnetic/TestEm3)
The calorimeter is a box made of a given number of layers. A layer consists of an absorber plate and of a detection gap. The layer is replicated.
Four parameters define the geometry of the calorimeter :
In addition a transverse uniform magnetic field can be applied (see B4DetectorMessenger class) and set via the interactive command. For example:
/B4/det/setMagField 0.2 tesla
|<----layer 0---------->|<----layer 1---------->|<----layer 2---------->|
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==========================================================================
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beam || absorber | gap || absorber | gap || absorber | gap ||
======> || | || | || | ||
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==========================================================================
A more general version of this geometry can be found in: examples/extended/electromagnetic/TestEm3 where all the geometry parameters, the absorber and gap materials can be modified interactively via the commands defined in the DetectorMessenger class.
The particle's type and the physic processes which will be available in this example are set in the FTFP_BERT physics list. This physics list requires data files for low energy electromagnetic processes which path is defined via the G4LEDATA envirnoment variable.
In addition the build-in interactive command:
/process/(in)activate processName
allows to activate/inactivate the processes one by one.
The primary beam consists of a single particle which hits the calorimeter perpendicular to the input face. The type of the particle and its energy are set in the B4PrimaryGeneratorAction class, and can be changed via the G4 build-in commands of the G4ParticleGun class (see the macros provided with this example).
A run is a set of events.
The user can choose the frequency of printing from B4aEventAction (or event action classes in other options) via the interactive command defined in B4aEventActionMessenger (or messengers classes in other options), for example:
/B4/event/setPrintModulo 100
The energy deposit and track lengths of the charged particles are recorded on an event by event basis in the Absober and Gap layers.
In order to demonstrate several possible ways of data scoring, the example is provided in four variants:
These 4 quantities are data members of the B4aEventAction class. They are collected step by step in B4aSteppingAction::UserSteppingAction(), and passed to the event action via two methods: B4aEventAction::AddAbs() and B4aEventAction::AddGap().
In B4aEventAction::EndOfEventAction(), these quantities are printed and filled in H1D histograms and ntuple to accumulate statistic and compute dispersion.
In order to avoid dependencies between action classes, a user object B4bRunData is defined with data members needed to the accounted information. In order to reduce the number of data members a 2-dimensions array is introduced for each quantity. Then the quantities are collected step by step in user action classes: B4bSteppingAction::UserSteppingAction() and B4bEventAction::EndOfEventAction() in a similar way as in variant a.
In this option, the physics quantities are accounted using the hits and sensitive detectors framework defined in the Geant4 kernel. The physics quantities are stored in B4cCalorHit via two B4cCalorimeterSD objects, one associated with the Absorber volume and another one with Gap in B4cDetectorConstruction.
In contrary to the B2 example (Tracker) where a new hit is created with each track passing the sensitive volume (in the calorimeter), only one hit is created for each calorimeter layer and one more hit to account for the total quantities in all layers. In addition to the variants a and b, the quantities per each layer are also available in addition to the total quantities.
In this option, the Geant4 scorers which are defined on the top of hits and sensitive detectors Geant4 framework are used. In practice this means that the user does not need to define hits and sensitive detector classes but rather uses the classes already defined in Geant4. In this example, the G4MultiFunctionalDetector with G4PSEnergyDeposit and G4PSTrackLength primitive scores are used (see B4dDetectorConstruction class).
Also with this approach, the quantities per each layer are available in addition to the total quantities.
The analysis tools are used to accumulate statistics and compute the dispersion of the energy deposit and track lengths of the charged particles. H1D histograms are created in B4RunAction::BeginOfRunAction() for the following quantities:
The accumulated statistic and computed dispersion is printed at the end of run, in B4RunAction::EndOfRunAction().
The histograms and ntuple are saved in the output file in a format according to a technology selected in B4Analysis.hh.
Additional visualization tutorial macros are available in the visTutor subdirectory. They can be tried as:
% cd B4/B4[a,b,c,d] % ln -s ../macros/visTutor visTutor % exampleB4[a,b,c,d] Idle > /control/execute visTutor/exN03VisX.mac
For details, see comment lines described in the macro files. These macros are designed to help your understanding of the User's Guide.
The following paragraphs are common to all basic examples
The visualization manager is set via the G4VisExecutive class in the main () function in exampleB4a.cc (or in b, c, d variants). The initialisation of the drawing is done via a set of /vis/ commands in the macro vis.mac. This macro is automatically read from the main () function when the example is used in interactive running mode.
By default, vis.mac opens an OpenGL viewer. The user can switch to other graphics systems by commenting out this line and instead uncommenting one of the other /vis/open statements, such as HepRepFile or DAWNFILE (which produce files that can be viewed with the HepRApp and DAWN viewers, respectively).
The DAWNFILE, HepRepFile drivers are always available (since they require no external libraries), but the OGL driver requires:
For more information on visualization, including information on how to install and run DAWN, OpenGL and HepRApp, see the visualization tutorials, for example,
The tracks are automatically drawn at the end of each event, accumulated for all events and erased at the beginning of the next run.
The user command interface is set via the G4UIExecutive class in the the main () function in exampleB4a.cc The selection of the user command interface is then done automatically according to the Geant4 configuration. The default command interface, called G4UIterminal, is done via a standard G4cin/G4cout. On Linux and Sun-cc one can use a smarter command interface G4UItcsh. It is enough to set the environment variable G4UI_USE_TCSH before compiling exampleB4a.cc
% cd B4/B4a % make
% exampleB4a and type in the commands from run1.mac line by line: Idle> /tracking/verbose 1 Idle> /run/beamOn 1 Idle> ... Idle> exit
Idle> /control/execute run1.mac .... Idle> exit
% exampleB4a run2.mac % exampleB4a exampleB4.in > exampleB4.out
1.7.4