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0002
0003 =========================================================
0004 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
0005 =========================================================
0006
0007 fanoCavity
0008 ----------
0009
0010 This program computes the dose deposited in an ionization chamber by a
0011 monoenergetic photon beam.
0012 The geometry of the chamber satisfies the conditions of charged particle
0013 equilibrium. Hence, under idealized conditions, the ratio of the dose
0014 deposited over the beam energy fluence must be equal to the
0015 mass_energy_transfer coefficient of the wall material.
0016
0017 E.Poon and al, Phys. Med. Biol. 50 (2005) 681
0018 I.Kawrakow, Med. Phys. 27-3 (2000) 499
0019
0020 1- GEOMETRY
0021
0022 The chamber is modelized as a cylinder with a cavity in it.
0023
0024 6 parameters define the geometry :
0025 - the material of the wall of the chamber
0026 - the radius of the chamber and the thickness of the wall
0027 - the material of the cavity
0028 - the radius and the thickness of the cavity
0029
0030 Wall and cavity must be made of the same material, but with different
0031 density
0032
0033 All above parameters can be redifined via the UI commands built in
0034 DetectorMessenger class
0035
0036 -----------------
0037 | |
0038 | wall |
0039 | ----- |
0040 | | | |
0041 | | <-+-----+--- cavity
0042 ------> | | | |
0043 ------> | | | |
0044 beam -------------------------------- cylinder axis
0045 ------> | | | |
0046 ------> | | | |
0047 | | | |
0048 | | | |
0049 | ----- |
0050 | |
0051 | |
0052 -----------------
0053
0054 2- BEAM
0055
0056 Monoenergetic incident photon beam is uniformly distribued, perpendicular
0057 to the flat end of the chamber. The beam radius can be controled with an
0058 UI command built in PrimaryGeneratorMessenger; the default is full wall
0059 chamber radius.
0060
0061 Beam regeneration : after each Compton interaction, the scattered photon is
0062 reset to its initial state, energy and direction. Consequently, interaction
0063 sites are uniformly distribued within the wall material.
0064
0065 This modification must be done in the ParticleChange of the final state
0066 of the Compton scattering interaction. Therefore, a specific model
0067 (MyKleinNishinaCompton) is assigned to the ComptonScattering process in
0068 PhysicsList. MyKleinNishinaCompton inherites from G4KleinNishinaCompton;
0069 only the function SampleSecondaries() is overwritten.
0070
0071 3- PURPOSE OF THE PROGRAM
0072
0073 The program computes the dose deposited in the cavity and the ratio
0074 Dose/Beam_energy_fluence. This ratio is compared to the mass_energy_transfer
0075 coefficient of the wall material.
0076
0077 The mass_energy_transfer coefficient needs :
0078 - the photon total cross section, which is read from the PhysicsTables
0079 by G4EmCalculator (see EndOfRunAction).
0080 - the average kinetic energy of charged secondaries generated in the
0081 wall during the run.
0082
0083 The program needs high statistic to reach precision on the computed dose.
0084 The UI command /run/printProgress allows to survey the convergence of
0085 the kineticEnergy and dose calculations.
0086
0087 In addition, to increase the program efficiency, the secondary particles
0088 which have no chance to reach the cavity are immediately killed (see
0089 StackinAction). This feature can be switched off by an UI command (see
0090 StackingMessenger).
0091
0092 The simplest way to study the effect of e- tracking parameters on dose
0093 deposition is to use the command /testem/stepMax.
0094
0095 4- PHYSICS
0096
0097 The physics lists contains the standard electromagnetic processes, with few
0098 modifications listed here.
0099
0100 - Compton scattering : as explained above, the final state is modified in
0101 MyKleinNishinaCompton class.
0102
0103 In order to make the program more efficient, one can increase the Compton
0104 cross section via the function SetCSFactor(factor) and its
0105 associated UI command. Default is factor=1000.
0106
0107 - Bremsstrahlung : Fano conditions imply no energy transfer via
0108 bremsstrahlung radiation. Therefore this process is not registered in the
0109 physics list. However, it is always possible to include it.
0110 See PhysListEmStandard class.
0111
0112 - Ionisation : In order to have same stopping power in wall and cavity, one
0113 must cancel the density correction term in the dedx formula. This is done in
0114 a specific MollerBhabha model (MyMollerBhabhaModel) which inherites from
0115 G4MollerBhabhaModel.
0116
0117 To prevent explicit generation of delta-rays, the default production
0118 threshold (i.e. cut) is set to 10 km (CSDA condition).
0119
0120 The finalRange of the step function is set to 10 um, which more on less
0121 correspond to a tracking cut in water of about 20 keV. See emOptions.
0122 Once again, the above parameters can be controled via UI commands.
0123
0124 - Multiple scattering : is switched in single Coulomb scattering mode near
0125 boundaries. This is selected via EM options in PhysicsList, and can be
0126 controled with UI commands.
0127
0128 - All PhysicsTables are built with 100 bins per decade.
0129
0130 5- HISTOGRAMS
0131
0132 fanoCavity has several predefined 1D histograms :
0133
0134 1 : emission point of e+-
0135 2 : energy spectrum of e+-
0136 3 : theta distribution of e+-
0137 4 : emission point of e+- hitting cavity
0138 5 : energy spectrum of e+- when entering in cavity
0139 6 : theta distribution of e+- before enter in cavity
0140 7 : theta distribution of e+- at first step in cavity
0141 8 : track segment of e+- in cavity
0142 9 : step size of e+- in wall
0143 10 : step size of e+- in cavity
0144 11 : energy deposit in cavity per track
0145
0146 The histograms are managed by G4AnalysisManager class and its messenger.
0147 The histos can be individually activated with the command :
0148 /analysis/h1/set id nbBins valMin valMax unit
0149 where unit is the desired unit for the histo (MeV or keV, deg or mrad, etc..)
0150
0151 One can control the name of the histograms file with the command:
0152 /analysis/setFileName name (default fanoCavity)
0153
0154 It is possible to choose the format of the histogram file : root (default),
0155 hdf5, xml, csv, by changing the default file type in HistoManager.cc
0156
0157 It is also possible to print selected histograms on an ascii file:
0158 /analysis/h1/setAscii id
0159 All selected histos will be written on a file name.ascii (default fanocavity)
0160
0161 6- HOW TO START ?
0162
0163 - execute fanoCavity in 'batch' mode from macro files
0164 % fanoCavity run01.mac
0165
0166 - execute fanoCavity in 'interactive mode' with visualization
0167 % fanoCavity
0168 ....
0169 Idle> type your commands
0170 ....
0171 Idle> exit
0172
0173 Alternative macro file:
0174 basic.mac - disabled multiple scattering and fluctuations of energy loss
