| 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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