Geant4 examples: Example B1

This example demonstrates a very simple application where an energy deposit is accounted in user actions and a dose in a selected volume is calculated.

GEOMETRY DEFINITION

The geometry is constructed in the B1DetectorConstruction class. The setup consists of a an envelope of box shape containing two volumes: a spherical cone and a trapezoid.

In this example we use some common materials materials for medical applications. The envelope is made of water and the two inner volumes are made from tissue and bone materials. The materials are created with the help of the G4NistManager class, which allows to build a material from the NIST database using their names. All available materials can be found in the Geant4 User's Guide for Application Developers, Appendix 9: Geant4 Materials Database .

PHYSICS LIST

The particle's type and the physic processes which will be available in this example are set in the QGSP_BIC_EMY physics list. This physics list requires data files for low energy electromagnetic processes which path is defined via the G4LEDATA environment variable.

In addition the build-in interactive command:

/process/(in)activate processName

allows to activate/inactivate the processes one by one.

PRIMARY GENERATOR

The primary generator is defined in the B1PrimaryGeneratorAction class. The default kinematic is a 6 MeV gamma, randomly distributed in front of the envelope across 80% of the (X,Y) envelope size. This default setting can be changed via the Geant4 built-in commands of the G4ParticleGun class.

DETECTOR RESPONSE

This example demonstrates a simple scoring implemented directly in the user action classes. Alternative ways of scoring via Geant4 classes can be found in the other examples.

Here, the energy deposit in a selected volume is accumulated step by step in B1SteppingAction and the event energy deposit deposit is done event by event in B1EventAction. The dose is then computed in B1RunAction::EndOfRunAction() and and its value is printed on the screen.

The following paragraphs are common to all basic examples

VISUALISATION

The visualization manager is set via the G4VisExecutive class in the main () function in exampleB1.cc. 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:

the visualisation & interfaces categories have been compiled with the environment variable G4VIS_BUILD_OPENGLX_DRIVER.
exampleB1.cc has been compiled with G4VIS_USE_OPENGLX. (This is best done through Configure or CMake.)

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.

USER INTERFACES

The user command interface is set via the G4UIExecutive class in the the main () function in exampleB1.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 exampleB1.cc

HOW TO RUN

compile and link to generate an executable
```
% cd B1
% make
```

execute exampleB1 in the 'interactive mode' with visualization

% exampleB1
and type in the commands from run1.mac line by line:
Idle> /control/verbose 2
Idle> /tracking/verbose 1
Idle> /run/beamOn 10 
Idle> ...
Idle> exit

Idle> /control/execute run1.mac
....
Idle> exit

execute exampleB1 in the 'batch' mode from macro files (without visualization)
```
% exampleB1 run2.mac
% exampleB1 exampleB1.in > exampleB1.out
```