Gabriele Cosmo
151 lines
5.8 KiB
Plaintext
151 lines
5.8 KiB
Plaintext
$Id: README 93735 2015-10-30 11:00:28Z 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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TestEm1
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-------
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How to count processes.
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How to activate/inactivate processes.
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How to survey the tracking, in particular the range of charged particles.
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How to define a maximum step size.
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1 - GEOMETRY DEFINITION
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It is a simple box which represents a 'semi infinite' homogeneous medium.
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Two parameters define the geometry :
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- the material of the box,
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- the full size of the box.
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In addition a transverse uniform magnetic field can be applied.
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e.g. /globalField/setValue 0 0 5 tesla
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The default geometry is constructed in DetectorConstruction class, but all of
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the above parameters can be changed interactively via the commands defined in
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the DetectorMessenger class.
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2 - PHYSICS LIST
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Physics lists are based on modular design. Several modules are instantiated:
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1. Transportation
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2. EM physics
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3. Decays
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4. StepMax - for step limitation
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EM physics builders can be local (eg. in this example) or from G4 kernel
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physics_lists subdirectory.
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Local physics builder:
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- "local" standard EM physics with current 'best' options setting.
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these options are explicited in PhysListEmStandard
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From geant4/source/physics_lists/builders:
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- "emstandard_opt0" recommended standard EM physics for LHC
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- "emstandard_opt1" best CPU performance standard physics for LHC
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- "emstandard_opt2" similar fast simulation
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- "emstandard_opt3" best standard EM options - analog to "local" above
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- "emstandard_opt4" best current advanced EM options standard + lowenergy
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- "emstandardSS" standard EM physics and single scattering model
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- "emlivermore" low-energy EM physics using Livermore data
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- "empenelope" low-energy EM physics implementing Penelope models
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- "emlowenergy" low-energy EM physics implementing experimental
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low-energy models
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Physics lists and options can be (re)set with UI commands
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Please, notice that options set through G4EmProcessOptions are global, eg
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for all particle types. In G4 builders (geant4/source/physics_lists/builders)
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it is shown how to set options per particle type.
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A few commands have been added to PhysicsList, in order to set the production
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threshold for secondaries for gamma and e-/e+.
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3 - AN EVENT : THE PRIMARY GENERATOR
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The primary kinematic consists of a single particle starting at the left face
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of the box. The type of the particle and its energy are set in the
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PrimaryGeneratorAction class, and can be changed via the G4 build-in commands
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of G4ParticleGun class (see the macros provided with this example).
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In addition one can choose randomly the impact point of the incident particle.
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The corresponding interactive command is built in PrimaryGeneratorMessenger.
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4 - VISUALIZATION
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The Visualization Manager is set in the main () (see TestEm1.cc).
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The initialisation of the drawing is done via the commands /vis/... in the
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macro vis.mac. To get visualisation:
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> /control/execute vis.mac
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The detector has a default view which is a longitudinal view of the box.
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The tracks are drawn at the end of event, and erased at the end of run.
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5 - PHYSICS SURVEY
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The particle's type and the physics processes which will be available in this
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example are set in PhysicsList class.
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A set of macros defining various run conditions are provided. The processes
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are actived/inactivated together with differents cuts, in order to survey the
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processes one by one.
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The number of produced secondaries are counted, the number of steps, and the
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number of process calls responsible of the step.
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6 - HOW TO START ?
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- execute TestEm1 in 'batch' mode from macro files
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% TestEm1 runs.mac
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- execute TestEm1 in 'interactive mode' with visualization
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% TestEm1
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....
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Idle> type your commands
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....
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Idle> exit
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7 - TRACKING : StepMax
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In order to control the accuracy of the deposition, the user can limit
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'by hand' the maximum step size of charged particles.
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As an example, this limitation is implemented as a 'full' process :
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see StepMax class and its Messenger. The 'StepMax process' is registered
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in the Physics List.
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8 - HISTOGRAMS
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Testem1 produces several histo which are saved as testem1.root by default.
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Content of these histo:
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1 : track length of primary particle
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2 : number of steps primary particle
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3 : step size of primary particle
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4 : total energy deposit
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5 : energy of charged secondaries at creation
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6 : energy of neutral secondaries at creation
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The histograms are managed by G4AnalysisManager class and its Messenger.
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The histos can be individually activated with the command :
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/analysis/h1/set id nbBins valMin valMax unit
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where unit is the desired unit for the histo (MeV or keV, deg or mrad, etc..)
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One can control the name of the histograms file with the command:
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/analysis/setFileName name (default testem1)
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It is possible to choose the format of the histogram file : root (default),
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hbook, xml, csv, by using namespace in HistoManager.hh
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It is also possible to print selected histograms on an ascii file:
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/analysis/h1/setAscii id
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All selected histos will be written on a file name.ascii (default testem1)
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Using hbook format
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------------------
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Need a special treatement : the Cern Library must be installed and the
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environment variable CERNLIB correctly set. Then, *before* compiling,
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activate G4_USE_HBOOK in GNUmakefile and g4hbook.hh in HistoManager.hh
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