Example TestEm11

How to plot a depth dose profile in a rectangular box.

GEOMETRY DEFINITION

The geometry consists of a stack of one or several blocks of homogenous material, called absorbers. Optionally, each absorber can be divided in thinner layers (replica)

A minimum of 5 parameters define the geometry :

• the number of absorbers (NbOfAbsor)
  
• the material of each absorber,
• the thickness of each absorber,
• the tranverse dimension of the stack (sizeYZ),
• the number of divisions of each absorber (NbOfDivisions)

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.

PHYSICS LIST

Physics Lists are based on modular design. Several modules are instantiated:

1. Transportation
2. EM physics
3. Decays
4. StepMax - for step limitation

The following options for EM physics using builders from physics_lists sub-package are available:

• "emstandard_opt0" recommended standard EM physics for LHC
• "emstandard_opt1" best CPU performance standard physics for LHC
• "emstandard_opt2" similar fast simulation
• "emstandard_opt3" best standard EM options - analog to "local" above
• "emstandard_opt4" best current advanced EM options standard + lowenergy
• "emstandardWVI" standard EM physics and WentzelVI multiple scattering
• "emstandardSS" standard EM physics and single scattering model
• "emstandardGS" standard EM physics and Goudsmit-Saunderson multiple scatt.
• "emlivermore" low-energy EM physics using Livermore data
• "empenelope" low-energy EM physics implementing Penelope models
• "emlowenergy" low-energy EM physics implementing experimental low-energy models

A local builder, PhysListEmStandard "local" (similar to opt3) is also available.

Physics lists and options can be (re)set with UI commands

ACTION INITIALIZATION

A newly introduced class, ActionInitialization, instantiates and registers to Geant4 kernel all user action classes.

While in sequential mode the action classes are instantiated just once, via invoking the method: ActionInitialization::Build() in multi-threading mode the same method is invoked for each thread worker and so all user action classes are defined thread-local.

A run action class (if present) has to be instantiated both thread-local and global, which is why its instance has to be created also in the method ActionInitialization::BuildForMaster() which is invoked only in multi-threading mode.

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 G4ParticleGun 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 class.

A RUN is a set of events.

VISUALIZATION

The Visualization Manager is set in the main () (see TestEm11.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. Optionally one can choose to draw all particles, only the charged one, or none. This command is defined in EventActionMessenger class.

HOW TO START ?

• Execute TestEm11 in 'batch' mode from macro files

  % TestEm11   run01.mac
  

• Execute TestEm11 in 'interactive mode' with visualization

  % TestEm11
  ....
  Idle> type your commands
  ....
  Idle> exit
  

  Macros provided in this example:

  • alpha.mac: alpha (400 MeV) on water
  • ionC12.mac: ion C12 (2.4 GeV) on water
  • multiLayers.mac: gamma (6 MeV) on multi layers
  • radioactive.mac: radioactive ion on multi layers
  • range.mac: compute csda range of primary particle
  • run01.mac: e- (500 keV) on silicon. Step max from histo 1
  • run02.mac: e- (500 keV) on silicon. Step max from geometry
  • sandia.mac: to compare with Sandia data
  • water.mac: e- (4 MeV) on water. No constraint on tracking step
    

  Macros to be run interactively:

  • vis.mac: To activate visualization

TRACKING and STEP MAX

TestEm11 computes the distribution of energy deposited along the trajectory of the incident particle : the so-called longitudinal energy profile, or depth dose distribution. The energy deposited (edep) is randomly distribued along the step (see SteppingAction).

In order to control the accuracy of the deposition, the maximum step size of charged particles is computed automatically from the binning of histograms 1 and 8 (see RunAction).

As an example, this limitation is implemented as a 'full' process : see StepMax class and its messenger, StepMaxMessenger. The 'StepMax process' is registered in the Physics List.

StepMax is evaluated at RunAction::BeginOfRunAction(), and passed to the StepMax process. A boolean UI command allows to deactivate this mechanism. Another UI command allows to define directly a stepMax value.

HISTOGRAMS

TestEm11 has several predefined 1D histograms :

• 1 : longitudinal energy profile (in MeV/mm and per event)
• 2 : total energy deposited in the absorber
• 3 : total track length of the primary track
• 4 : step size of the primary track
  
• 5 : projected range of the primary track
• 6 : total track length of charged secondary tracks
• 7 : step size of charged secondary tracks
  
• 8 : longitudinal energy profile (in MeV.cm2/g), as a function of x/r0 where r0 is the range of the primary particle
• 9 : total energy leakage
• 10 : total energy : Edep + Eleak
• 11 : energy deposited in absorber 1
• 12 : energy deposited in absorber 2 ...etc........

The histograms are managed by G4Analysis classes; The histos can be individually activated with the command :

/analysis/h1/set 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:

/analysis/setFileName  name  (default testem11)

It is possible to choose the format of the histogram file : root (default), hdf5, xml, csv, by changing the default file type in HistoManager.cc

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 testem11)