Gabriele Cosmo
147 lines
5.6 KiB
Plaintext
147 lines
5.6 KiB
Plaintext
-------------------------------------------------------------------
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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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fanoCavity2
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This program computes the dose deposited in an ionization chamber by an
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extended (one dimensional) monoenergetic electron source.
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The geometry of the chamber satisfies the conditions of charged particle
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equilibrium. Hence, under idealized conditions, the ratio of the dose
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deposited over the beam energy fluence must be equal to 1.
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This variante of the Fano cavity test make use of an reciprocity theorem.
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J.Sempau and P.Andreo, Phys. Med. Biol. 51 (2006) 3533
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1- GEOMETRY
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The chamber is modelized as a cylinder with a cavity in it.
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5 parameters define the geometry :
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- the radius of the chamber (must be big)
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- the material of the wall
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- the thickness of the wall
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- the material of the cavity
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- the thickness of the cavity
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Wall and cavity must be made of the same material, but with different
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density.
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Radius must be bigger than range of electrons in cavity.
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All above parameters can be redifined via the UI commands built in
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DetectorMessenger class.
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_________________
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radius (infinite) | | | |
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| | <-+-----+--- cavity
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---------------------------- cylinder axis = e- source
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|wall | |wall |
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-----------------
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2- BEAM
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Monoenergetic (E0) incident electron source is uniformly distribued along
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cylinder axis, within wall and cavity, with constant lineic density
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per mass: I.
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An effective wall thickness is defined from the range of e- at energy E0.
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Beam_energy_fluence is E0*I
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3- PURPOSE OF THE PROGRAM
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The program computes the dose deposited in the cavity and the ratio
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Dose/Beam_energy_fluence. This ratio must be 1.
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The program needs high statistic to reach precision on the computed dose.
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The UI command /run/printProgress allows to survey the convergence of
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the dose calculation.
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The simplest way to study the effect of e- tracking parameters on dose
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deposition is to use the command /testem/stepMax.
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4- PHYSICS
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The physics list contains the standard electromagnetic processes, with few
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modifications listed here.
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- Bremsstrahlung : Fano conditions imply no energy transfer via
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bremsstrahlung radiation. Therefore this process is not registered in the
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physics list. However, it is always possible to include it.
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See PhysListEm classes.
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- Ionization : In order to have same stopping power in wall and cavity, one
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must cancel the density correction term in the dedx formula. This is done in
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a specific MollerBhabha model (MyMollerBhabhaModel) which inherites from
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G4MollerBhabhaModel.
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To prevent explicit generation of delta-rays, the default production
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threshold (i.e. cut) is set to 10 km (CSDA condition).
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The finalRange of the step function is set to 10 um, which more on less
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correspond to a tracking cut in water of about 20 keV. See emOptions.
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Once again, the above parameters can be controled via UI commands.
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- Multiple scattering : is switched in single Coulomb scattering mode near
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boundaries. This is selected via EM options in PhysicsList, and can be
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controled with UI commands.
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- All PhysicsTables are built with 100 bins per decade.
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5- HISTOGRAMS
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fanoCavity2 has several predefined 1D histograms :
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1 : emission point of e+-
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2 : energy spectrum of e+-
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3 : theta distribution of e+-
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4 : emission point of e+- hitting cavity
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5 : energy spectrum of e+- when entering in cavity
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6 : theta distribution of e+- before enter in cavity
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7 : theta distribution of e+- at first step in cavity
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8 : track segment of e+- in cavity
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9 : step size of e+- in wall
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10 : step size of e+- in cavity
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11 : energy deposit in cavity per track
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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 fanocavity2)
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It is possible to choose the format of the histogram file :
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root(default), xml, hbook. See 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
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(default fanocavity2)
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6- HOW TO START ?
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- execute fanoCavity2 in 'batch' mode from macro files
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% fanoCavity2 run01.mac
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- execute fanoCavity2 in 'interactive mode' with visualization
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% fanoCavity2
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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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