| 1 | $Id: README,v 1.16 2009/10/25 19:06:26 maire Exp $
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| 2 | -------------------------------------------------------------------
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| 3 |
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| 4 | =========================================================
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| 5 | Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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| 6 | =========================================================
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| 7 |
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| 8 | fanoCavity
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| 9 | ----------
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| 10 |
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| 11 | This program computes the dose deposited in an ionization chamber by a
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| 12 | monoenergetic photon beam.
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| 13 | The geometry of the chamber satisfies the conditions of charged particle
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| 14 | equilibrium. Hence, under idealized conditions, the ratio of the dose
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| 15 | deposited over the beam energy fluence must be equal to the
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| 16 | mass_energy_transfer coefficient of the wall material.
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| 17 |
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| 18 | E.Poon and al, Phys. Med. Biol. 50 (2005) 681
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| 19 | I.Kawrakow, Med. Phys. 27-3 (2000) 499
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| 20 |
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| 21 | 1- GEOMETRY
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| 22 |
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| 23 | The chamber is modelized as a cylinder with a cavity in it.
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| 24 |
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| 25 | 6 parameters define the geometry :
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| 26 | - the material of the wall of the chamber
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| 27 | - the radius of the chamber and the thickness of the wall
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| 28 | - the material of the cavity
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| 29 | - the radius and the thickness of the cavity
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| 30 |
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| 31 | Wall and cavity must be made of the same material, but with different
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| 32 | density
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| 33 |
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| 34 | All above parameters can be redifined via the UI commands built in
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| 35 | DetectorMessenger class
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| 36 |
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| 37 | -----------------
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| 38 | | |
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| 39 | | wall |
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| 40 | | ----- |
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| 41 | | | | |
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| 42 | | | <-+-----+--- cavity
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| 43 | ------> | | | |
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| 44 | ------> | | | |
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| 45 | beam -------------------------------- cylinder axis
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| 46 | ------> | | | |
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| 47 | ------> | | | |
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| 48 | | | | |
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| 49 | | | | |
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| 50 | | ----- |
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| 51 | | |
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| 52 | | |
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| 53 | -----------------
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| 54 |
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| 55 | 2- BEAM
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| 56 |
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| 57 | Monoenergetic incident photon beam is uniformly distribued, perpendicular
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| 58 | to the flat end of the chamber. The beam radius can be controled with an
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| 59 | UI command built in PrimaryGeneratorMessenger; the default is full wall
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| 60 | chamber radius.
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| 61 |
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| 62 | Beam regeneration : after each Compton interaction, the scattered photon is
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| 63 | reset to its initial state, energy and direction. Consequently, interaction
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| 64 | sites are uniformly distribued within the wall material.
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| 65 |
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| 66 | This modification must be done in the ParticleChange of the final state
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| 67 | of the Compton scattering interaction. Therefore, a specific model
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| 68 | (MyKleinNishinaCompton) is assigned to the ComptonScattering process in
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| 69 | PhysicsList. MyKleinNishinaCompton inherites from G4KleinNishinaCompton;
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| 70 | only the function SampleSecondaries() is overwritten.
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| 71 |
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| 72 | 3- PURPOSE OF THE PROGRAM
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| 73 |
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| 74 | The program computes the dose deposited in the cavity and the ratio
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| 75 | Dose/Beam_energy_fluence. This ratio is compared to the mass_energy_transfer
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| 76 | coefficient of the wall material.
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| 77 |
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| 78 | The mass_energy_transfer coefficient needs :
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| 79 | - the photon total cross section, which is read from the PhysicsTables
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| 80 | by G4EmCalculator (see EndOfRunAction).
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| 81 | - the average kinetic energy of charged secondaries generated in the
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| 82 | wall during the run.
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| 83 |
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| 84 | The program needs high statistic to reach precision on the computed dose.
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| 85 | The UI command /testem/event/printModulo allows to survey the convergence of
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| 86 | the kineticEnergy and dose calculations.
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| 87 |
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| 88 | In addition, to increase the program efficiency, the secondary particles
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| 89 | which have no chance to reach the cavity are immediately killed (see
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| 90 | StackinAction). This feature can be switched off by an UI command (see
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| 91 | StackingMessenger).
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| 92 |
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| 93 | The simplest way to study the effect of e- tracking parameters on dose
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| 94 | deposition is to use the command /testem/stepMax.
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| 95 |
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| 96 | 4- PHYSICS
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| 97 |
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| 98 | The physics lists contains the standard electromagnetic processes, with few
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| 99 | modifications listed here.
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| 100 |
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| 101 | - Compton scattering : as explained above, the final state is modified in
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| 102 | MyKleinNishinaCompton class.
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| 103 |
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| 104 | In order to make the program more efficient, one can increase the Compton
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| 105 | cross section via the function SetCSFactor(factor) and its
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| 106 | associated UI command. Default is factor=1000.
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| 107 |
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| 108 | - Bremsstrahlung : Fano conditions imply no energy transfer via
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| 109 | bremsstrahlung radiation. Therefore this process is not registered in the
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| 110 | physics list. However, it is always possible to include it.
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| 111 | See PhysListEmStandard class.
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| 112 |
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| 113 | - Ionisation : In order to have same stopping power in wall and cavity, one
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| 114 | must cancel the density correction term in the dedx formula. This is done in
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| 115 | a specific MollerBhabha model (MyMollerBhabhaModel) which inherites from
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| 116 | G4MollerBhabhaModel.
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| 117 |
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| 118 | To prevent explicit generation of delta-rays, the default production
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| 119 | threshold (i.e. cut) is set to 10 km (CSDA condition).
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| 120 |
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| 121 | The finalRange of the step function is set to 10 um, which more on less
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| 122 | correspond to a tracking cut in water of about 20 keV. See emOptions.
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| 123 | Once again, the above parameters can be controled via UI commands.
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| 124 |
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| 125 | - Multiple scattering : is switched in single Coulomb scattering mode near
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| 126 | boundaries. This is selected via EM options in PhysicsList, and can be
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| 127 | controled with UI commands.
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| 128 |
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| 129 | - All PhysicsTables are built with 100 bins per decade.
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| 130 |
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| 131 | 5- HISTOGRAMS
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| 132 |
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| 133 | fanoCavity has several predefined 1D histograms :
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| 134 |
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| 135 | 1 : emission point of e+-
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| 136 | 2 : energy spectrum of e+-
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| 137 | 3 : theta distribution of e+-
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| 138 | 4 : emission point of e+- hitting cavity
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| 139 | 5 : energy spectrum of e+- when entering in cavity
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| 140 | 6 : theta distribution of e+- before enter in cavity
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| 141 | 7 : theta distribution of e+- at first step in cavity
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| 142 | 8 : track segment of e+- in cavity
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| 143 | 9 : step size of e+- in wall
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| 144 | 10 : step size of e+- in cavity
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| 145 | 11 : energy deposit in cavity per track
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| 146 |
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| 147 | The histograms are managed by the HistoManager class and its Messenger.
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| 148 | The histos can be individually activated with the command :
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| 149 | /testem/histo/setHisto id nbBins valMin valMax unit
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| 150 | where unit is the desired unit for the histo (MeV or keV, deg or mrad, etc..)
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| 151 |
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| 152 | One can control the name of the histograms file with the command:
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| 153 | /testem/histo/setFileName name (default fanoCavity)
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| 154 |
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| 155 | It is possible to choose the format of the histogram file (hbook, root, XML)
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| 156 | with the command /testem/histo/setFileType (root by default)
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| 157 |
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| 158 | It is also possible to print selected histograms on an ascii file:
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| 159 | /testem/histo/printHisto id
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| 160 | All selected histos will be written on a file name.ascii (default fanocavity)
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| 161 |
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| 162 | Note that, by default, histograms are disabled. To activate them, uncomment
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| 163 | the flag G4ANALYSIS_USE in GNUmakefile.
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| 164 |
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| 165 | 6- HOW TO START ?
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| 166 |
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| 167 | - compile and link to generate an executable
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| 168 | % cd geant4/examples/extended/medical/fanoCavity
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| 169 | % gmake
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| 170 |
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| 171 | - execute fanoCavity in 'batch' mode from macro files
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| 172 | % fanoCavity run01.mac
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| 173 |
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| 174 | - execute fanoCavity in 'interactive mode' with visualization
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| 175 | % fanoCavity
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| 176 | ....
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| 177 | Idle> type your commands
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| 178 | ....
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| 179 | Idle> exit
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| 180 |
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| 181 | 7- USING HISTOGRAMS
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| 182 |
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| 183 | To use histograms, at least one of the AIDA implementations should be
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| 184 | available. See InstallAida.txt
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| 185 |
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