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Example TestEm18

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

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.

PHYSICS

The physics list, PhysicsList, contains the 'standard' electromagnetic processes. However the MultipleScattering is not registered, in order to focuse on fluctuations of to energy loss alone.

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 G4ParticleGun class.

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.

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 locally 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/sweAscii id

All selected histos will be written on a file name.ascii (default testem18)

VISUALIZATION

The Visualization Manager is set in the main () (see TestEm18.cc). 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.

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

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