Gabriele Cosmo
191 lines
8.0 KiB
Plaintext
191 lines
8.0 KiB
Plaintext
$Id: README 94957 2016-01-08 13:27:26Z gcosmo $
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-------------------------------------------------------------------
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=========================================================
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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=========================================================
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Example B3
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----------
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This example simulates schematically a Positron Emitted Tomography system.
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1- GEOMETRY DEFINITION
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The support of gamma detection are scintillating crystals. A small number
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of such crystals are optically grouped in a matrix of crystals. In
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this example, individual crystals are not described; only the matrix of
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crystals is and it is still called 'Crystal' hereafter.
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Crystals are circularly arranged to form a ring. Few rings make up the full
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detector (gamma camera). This is done by positionning Crystals in
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Ring with an appropriate rotation matrix. Several copies of Ring are
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then placed in the full detector.
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The head of a patient is schematised as a homogeneous cylinder of brain
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tissue, placed at the center of full detector.
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The Crystal material, Lu2SiO5, is not included in the G4Nist database.
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Therefore, it is explicitly built in DefineMaterials().
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2- PHYSICS LIST
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The physics list contains standard electromagnetic processes and the
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radioactiveDecay module for GenericIon. It is defined in the B3PhysicsList
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class as a Geant4 modular physics list with registered physics builders
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provided in Geant4:
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- G4DecayPhysics - defines all particles and their decay processes
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- G4RadioactiveDecayPhysics - defines radioactiveDecay for GenericIon
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- G4EmStandardPhysics - defines all EM standard processes
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This physics list requires data files for:
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- low energy electromagnetic processes which path is defined via
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the G4LEDATA envirnoment variable
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- nuclides properties which path is defined via
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the G4ENSDFSTATEDATA envirnoment variable
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- radioactive decay hadronic processes which path is defined via
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the G4RADIOACTIVEDATA envirnoment variable.
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See more on installation of the datasets in Geant4 Installation Guide,
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Chapter 3.3: Note On Geant4 Datasets:
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http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides
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/InstallationGuide/html/ch03s03.html
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3- ACTION INITALIZATION
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B3[a,b]ActionInitialization class instantiates and registers to Geant4 kernel
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all user action classes.
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While in sequential mode the action classes are instatiated just once,
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via invoking the method:
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B3[a,b]ActionInitialization::Build()
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in multi-threading mode the same method is invoked for each thread worker
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and so all user action classes are defined thread-local.
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A run action class is instantiated both thread-local
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and global that's why its instance is created also in the method
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B3[a,b]ActionInitialization::BuildForMaster()
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which is invoked only in multi-threading mode.
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4- PRIMARY GENERATOR
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The default particle beam is an ion (F18), at rest, randomly distributed
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within a zone inside a patient and is defined in
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B3PrimaryGeneratorAction::GeneratePrimaries().
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The type of a primary particle can be changed with G4ParticleGun commands
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(see run2.mac).
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5- DETECTOR RESPONSE: scorers
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A 'good' event is an event in which an identical energy of 511 keV is
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deposited in two separate Crystals. A count of the number of such events
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corresponds to a measure of the efficiency of the PET system.
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The total dose deposited in a patient during a run is also computed.
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Scorers are defined in B3DetectorConstruction::ConstructSDandField(). There are
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two G4MultiFunctionalDetector objects: one for the Crystal (EnergyDeposit),
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and one for the Patient (DoseDeposit)
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Two variants of accumulation event statistics in a run are demonstrated
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in this example:
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B3a:
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At the end of event, the values acummulated in B3aEventAction are passed
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in B3aRunAction and summed over the whole run (see B3aEventAction::EndOfevent()).
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In multi-threading mode the data accumulated in G4Parameter objects per
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workers is merged to the master in B3aRunAction::EndOfRunAction() and the final
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result is printed on the screen.
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G4Parameter<> type instead of G4double and G4int types is used for the B3aRunAction
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data members in order to facilitate merging of the values accumulated on workers
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to the master. Currently the parameters have to be registered to G4ParametersManager
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and G4ParametersManager::Merge() has to be called from the users code. This is planned
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to be further simplified with a closer integration of G4Parameter classes in
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the Geant4 kernel next year.
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B3b:
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B3bRun::RecordEvent(), called at end of event, collects informations
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event per event from the hits collections, and accumulates statistic for
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B3bRunAction::EndOfRunAction().
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In multi-threading mode the statistics accumulated per workers is merged
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to the master in B3bRun::Merge().
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6- STACKING ACTION
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Beta decay of Fluor generates a neutrino. One wishes not to track this
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neutrino; therefore one kills it immediately, before created particles
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are put in a stack.
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The function B3StackingAction::ClassifyNewTrack() is invoked by G4 kernel
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each time a new particle is created.
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The following paragraphs are common to all basic examples
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A- VISUALISATION
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The visualization manager is set via the G4VisExecutive class
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in the main() function in exampleB3.cc.
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The initialisation of the drawing is done via a set of /vis/ commands
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in the macro vis.mac. This macro is automatically read from
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the main function when the example is used in interactive running mode.
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By default, vis.mac opens an OpenGL viewer (/vis/open OGL).
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The user can change the initial viewer by commenting out this line
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and instead uncommenting one of the other /vis/open statements, such as
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HepRepFile or DAWNFILE (which produce files that can be viewed with the
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HepRApp and DAWN viewers, respectively). Note that one can always
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open new viewers at any time from the command line. For example, if
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you already have a view in, say, an OpenGL window with a name
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"viewer-0", then
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/vis/open DAWNFILE
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then to get the same view
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/vis/viewer/copyView viewer-0
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or to get the same view *plus* scene-modifications
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/vis/viewer/set/all viewer-0
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then to see the result
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/vis/viewer/flush
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The DAWNFILE, HepRepFile drivers are always available
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(since they require no external libraries), but the OGL driver requires
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that the Geant4 libraries have been built with the OpenGL option.
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For more information on visualization, including information on how to
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install and run DAWN, OpenGL and HepRApp, see the visualization tutorials,
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for example,
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http://geant4.slac.stanford.edu/Presentations/vis/G4[VIS]Tutorial/G4[VIS]Tutorial.html
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(where [VIS] can be replaced by DAWN, OpenGL and HepRApp)
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The tracks are automatically drawn at the end of each event, accumulated
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for all events and erased at the beginning of the next run.
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B- USER INTERFACES
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The user command interface is set via the G4UIExecutive class
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in the main() function in exampleB3.cc
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The selection of the user command interface is then done automatically
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according to the Geant4 configuration or it can be done explicitly via
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the third argument of the G4UIExecutive constructor (see exampleB4a.cc).
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C- HOW TO RUN
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- Execute exampleB3a in the 'interactive mode' with visualization
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% exampleB3a
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and type in the commands from run1.mac line by line:
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Idle> /control/verbose 2
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Idle> /tracking/verbose 2
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Idle> /run/beamOn 1
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Idle> ...
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Idle> exit
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or
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Idle> /control/execute run1.mac
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....
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Idle> exit
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- Execute exampleB3a in the 'batch' mode from macro files
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(without visualization)
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% exampleB3a run2.mac
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% exampleB3a exampleB3.in > exampleB3.out
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