$Id: README,v 1.26 2008/10/23 12:20:13 maire Exp $
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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TestEm1
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How to count processes.
How to activate/inactivate processes.
How to survey the tracking, in perticular the range of charged particles.
How to define a maximum step size.
1 - GEOMETRY DEFINITION
It is a simple box which represente an 'semi infinite' homogeneous medium.
Two parameters define the geometry :
- the material of the box,
- the full size of the box.
In addition a transverse uniform magnetic field can be applied.
The default geometry is constructed in DetectorConstruction class, but all of
the above parameters can be changed interactively via the commands defined in
the DetectorMessenger class.
2 - PHYSICS LIST
Physics lists can be local (eg. in this example) or from G4 kernel
physics_lists subdirectory.
Local physics lists:
- "standard" standard EM physics with current 'best' options setting.
these options are explicited in PhysListEmStandard
- "livermore" low-energy EM physics using Livermore data
- "penelope" low-energy EM physics implementing Penelope models
Physics lists and options can be (re)set with UI commands
Please, notice that options set through G4EmProcessOPtions are global, eg
for all particle types. In G4 builders (geant4/source/physics_lists/builders)
it is shown how to set options per particle type.
Few commands have been added to PhysicsList, in order to set the production
threshold for secondaries for gamma and e-/e+.
3 - AN EVENT : THE PRIMARY GENERATOR
The primary kinematic consists of a single particle starting at the left face
of the box. The type of the particle and its energy are set in the
PrimaryGeneratorAction class, and can be changed via the G4 build-in commands
of ParticleGun class (see the macros provided with this example).
In addition one can choose randomly the impact point of the incident particle.
The corresponding interactive command is built in PrimaryGeneratorMessenger.
4 - VISUALIZATION
The Visualization Manager is set in the main().
The initialisation of the drawing is done via the commands /vis/... in the
macro vis.mac. To get visualisation:
> /control/execute vis.mac
The detector has a default view which is a longitudinal view of the box.
The tracks are drawn at the end of event, and erased at the end of run.
Optionaly one can choose to draw all particles, only the charged, or none.
This command is defined in EventActionMessenger class.
5 - PHYSICS SURVEY
The particle's type and the physic processes which will be available in this
example are set in PhysicsList class.
A set of macros defining various run conditions are provided. The processes
are actived/inactived together with differents cuts, in order to survey the
processes one by one.
The number of produced secondaries are counted, the number of steps, and the
number of process calls responsible of the step.
6 - HOW TO START ?
- compile and link to generate an executable
% cd geant4/examples/extended/electromagnetic/TestEm1
% gmake
- execute TestEm1 in 'batch' mode from macro files
% TestEm1 run10.mac
- execute TestEm1 in 'interactive mode' with visualization
% TestEm1
....
Idle> type your commands
....
Idle> exit
7 - TRACKING : StepMax
In order to control the accuracy of the deposition, the user can limit
'by hand' the maximum step size of charged particles.
As an example, this limitation is implemented as a 'full' process :
see StepMax class and its Messenger. The 'StepMax process' is registered
in the Physics List.
8 - HISTOGRAMS
Testem1 produces several histo which are saved as testem1.root by default.
Content of these histo:
1 : track length of primary particle
2 : number of steps primary particle
3 : step size of primary particle
The histograms are managed by the HistoManager class and its Messenger.
The histos can be individually activated with the command :
/testem/histo/setHisto id nbBins valMin valMax unit
where unit is the desired unit for the histo (MeV or keV, deg or mrad, etc..)
One can control the name of the histograms file with the command:
/testem/histo/setFileName name (default testem1)
It is possible to choose the format of the histogram file (hbook, root, XML)
with the command /testem/histo/setFileType (root by default)
It is also possible to print selected histograms on an ascii file:
/testem/histo/printHisto id
All selected histos will be written on a file name.ascii (default testem1)
Note that, by default, histograms are disabled. To activate them, uncomment
the flag G4ANALYSIS_USE in GNUmakefile.
Before compilation of the example it is optimal to clean up old files:
gmake histclean
gmake
9 - USING HISTOGRAMS
To use histograms, at least one of the AIDA implementations should be
available. See the file InstallAida.txt
Gabriele Cosmo