$Id$
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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Example B3
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This example simulates schematically a Positron Emitted Tomography system.
1- GEOMETRY DEFINITION
The support of gamma detection are scintillating crystals. A small number
of such crystals are optically grouped in a matrix of crystals. In
this example, individual crystals are not described; only the matrix of
crystals is and it is still called 'Crystal' hereafter.
Crystals are circularly arranged to form a ring. Few rings make up the full
detector (gamma camera). This is done by positionning Crystals in
Ring with an appropriate rotation matrix. Several copies of Ring are
then placed in the full detector.
The head of a patient is schematised as a homogeneous cylinder of brain
tissue, placed at the center of full detector.
The Crystal material, Lu2SiO5, is not included in the G4Nist database.
Therefore, it is explicitly built in DefineMaterials().
2- PHYSICS LIST
The physics list contains standard electromagnetic processes and the
radioactiveDecay module for GenericIon. It is defined in the B3PhysicsList
class as a Geant4 modular physics list with registered physics builders
provided in Geant4:
- G4DecayPhysics - defines all particles and their decay processes
- G4RadioactiveDecayPhysics - defines radioactiveDecay for GenericIon
- G4EmStandardPhysics - defines all EM standard processes
This physics list requires data files for:
- low energy electromagnetic processes which path is defined via
the G4LEDATA envirnoment variable
- radioactive decay hadronic processes which path is defined via
the G4RADIOACTIVEDATA envirnoment variable.
See more on installation of the datasets in Geant4 Installation Guide,
Chapter 3.3: Note On Geant4 Datasets:
http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/InstallationGuide/html/ch03s03.html
3- PRIMARY GENERATOR
The default particle beam is an ion (F18), at rest, randomly distributed
within a zone inside a patient and is defined in
B3PrimaryGeneratorAction::GeneratePrimaries().
The type of a primary particle can be changed with G4ParticleGun commands
(see run2.mac).
4- DETECTOR RESPONSE: scorers
A 'good' event is an event in which an identical energy of 511 keV is
deposited in two separate Crystals. A count of the number of such events
corresponds to a measure of the efficiency of the PET system.
The total dose deposited in a patient during a run is also computed.
Scorers are defined in DetectorConstruction::CreateScorers(). There are
two G4MultiFunctionalDetector objects: one for the Crystal (EnergyDeposit),
and one for the Patient (DoseDeposit)
EventAction::EndOfEventAction() collects informations event per event
from the hits collections, and accumulates statistic for
RunAction::EndOfRunAction().
5- STACKING ACTION
Beta decay of Fluor generates a neutrino. One wishes not to track this
neutrino; therefore one kills it immediately, before created particles
are put in a stack.
The function B3StackingAction::ClassifyNewTrack() is invoked by G4 kernel
each time a new particle is created.
The following paragraphs are common to all basic examples
A- VISUALISATION
The visualization manager is set via the G4VisExecutive class
in the main() function in exampleB3.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 (/vis/open OGL).
The user can change the initial viewer 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). Note that one can always
open new viewers at any time from the command line. For example, if
you already have a view in, say, an OpenGL window with a name
"viewer-0", then
/vis/open DAWNFILE
then to get the same view
/vis/viewer/copyView viewer-0
or to get the same view *plus* scene-modifications
/vis/viewer/set/all viewer-0
then to see the result
/vis/viewer/flush
The DAWNFILE, HepRepFile drivers are always available
(since they require no external libraries), but the OGL driver requires
that the Geant4 libraries have been built with the OpenGL option.
For more information on visualization, including information on how to
install and run DAWN, OpenGL and HepRApp, see the visualization tutorials,
for example,
http://geant4.slac.stanford.edu/Presentations/vis/G4[VIS]Tutorial/G4[VIS]Tutorial.html
(where [VIS] can be replaced by DAWN, OpenGL and HepRApp)
The tracks are automatically drawn at the end of each event, accumulated
for all events and erased at the beginning of the next run.
B- USER INTERFACES
The user command interface is set via the G4UIExecutive class
in the main() function in exampleB3.cc
The selection of the user command interface is then done automatically
according to the Geant4 configuration or it can be done explicitly via
the third argument of the G4UIExecutive constructor (see exampleB4a.cc).
C- HOW TO RUN
- Execute exampleB3 in the 'interactive mode' with visualization
% exampleB3
and type in the commands from run1.mac line by line:
Idle> /control/verbose 2
Idle> /tracking/verbose 2
Idle> /run/beamOn 1
Idle> ...
Idle> exit
or
Idle> /control/execute run1.mac
....
Idle> exit
- Execute exampleB3 in the 'batch' mode from macro files
(without visualization)
% exampleB3 run2.mac
% exampleB3 exampleB3.in > exampleB3.out
Gabriele Cosmo