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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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TestEm18
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This example allows to study the various contributions of the energy lost
by a charged particle in a single layer of an homogeneous material.
See any textbook of interactions of charged particles with matter, in particular :
1- geant4.web.cern.ch --> UserSupport --> Physics Reference Manual
2- lappweb.in2p3.fr/~maire/tutorials/index.html
1- GEOMETRY DEFINITION
It is a simple cubic box of homogeneous material.
Two parameters define the geometry :
- the material of the box,
- the thickness of the box.
The default geometry (1 cm of water) is constructed in DetectorConstruction,
but the above parameters can be changed interactively via the commands
defined in DetectorMessenger.
2- PHYSICS
The physics list contains the 'standard' electromagnetic processes.
However the MultipleScattering is not registered, in order to focuse on
fluctuations of to energy loss alone.
3- BEAM
The primary kinematic is a single particle starting at the edge
of the box. The type of the particle and its energy are set in
PrimaryGeneratorAction (e- 10 MeV), and can be changed via the G4
build-in commands of ParticleGun class.
4- RUN
During the tracking of the incident particle, by default, the secondary
particles are immediately killed, after that their energy has been registered
(see SteppingAction and StackingAction).
Therefore, we study here the various components of the total energy lost
by the incident particle, not the energy deposited in a layer of finite
thickness.
With the option /testEm/trackSecondaries one can compute and plot the energy
deposited in the layer. See edep.mac
At EndOfRun, the above results are compared with 'reference' values,
i.e. the input data read from EnergyLoss and Range tables.
See reference 2 : Energy-Range relation, slide 4.
5- HISTOGRAMS
The test contains 13 built-in 1D histograms, which are managed by
G4AnalysisManager and its Messenger.
1 step size of primary track
2 energy continuously deposited along primary track
3 energy transfered to secondaries by ionisation
4 energy transfered to secondaries by Bremsstrahlung
5 energy transfered to secondaries by (e+,e-) production
6 total energy transfered to secondaries
7 total energy lost by primary track
8 total energy lost by primary track from energy balance
9 energy continuously deposited along secondary tracks
10 total energy deposited
11 energy spectrum of gamma
12 energy spectrum of e-
13 energy spectrum of e+
The histograms are defined in HistoManager.
The histos can be activated individually with the command :
/analysis/h1/set id nbBins valMin valMax unit
where 'unit' is the desired unit for the histo (MeV or KeV, cm or mm, etc..)
One can control the name of the histograms file with the command:
/analysis/setFileName name (default testem18)
It is possible to choose the format of the histogram file : root (default),
xml, csv, by using namespace in HistoManager.hh
For convenience, few simple Root macros are provided : plotHisto.C pixe.C
It is also possible to print selected histograms on an ascii file:
/analysis/h1/setAscii id
All selected histos will be written on a file name.ascii (default testem18)
6- 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.
7- HOW TO START ?
execute TestEm18 in 'batch' mode from macro files :
% TestEm18 electron.mac
execute TestEm18 in 'interactive mode' with visualization :
% TestEm18
Idle> control/execute vis.mac
....
Idle> type your commands
....
Idle> exit
Macros provided in this example:
- csda.mac: test independance of user step max
- edep.mac: track secondary particles and plot energy deposited
- electron.mac: e- (10 MeV) on 1 cm of water
- ion.mac: ion C12 (4 GeV) on 1 cm of water
- muon.mac: mu+ (1 TeV) on 1 m of water
- pixe.mac: proton (20 MeV) on 50 um of gold. Plot gamma pixe
- proton.mac: proton (1 GeV) on 10 cm of water
- plotHisto.C, pixe.C: Root macros
Macros to be run interactively:
- vis.mac: To activate visualization