| Geant4 Cross Reference |
1 ------------------------------------------------------------------- 2 3 ========================================================= 4 Geant4 - an Object-Oriented Toolkit for Simulation in HEP 5 ========================================================= 6 7 fanoCavity 8 ---------- 9 10 This program computes the dose deposited in an ionization chamber by a 11 monoenergetic photon beam. 12 The geometry of the chamber satisfies the conditions of charged particle 13 equilibrium. Hence, under idealized conditions, the ratio of the dose 14 deposited over the beam energy fluence must be equal to the 15 mass_energy_transfer coefficient of the wall material. 16 17 E.Poon and al, Phys. Med. Biol. 50 (2005) 681 18 I.Kawrakow, Med. Phys. 27-3 (2000) 499 19 20 1- GEOMETRY 21 22 The chamber is modelized as a cylinder with a cavity in it. 23 24 6 parameters define the geometry : 25 - the material of the wall of the chamber 26 - the radius of the chamber and the thickness of the wall 27 - the material of the cavity 28 - the radius and the thickness of the cavity 29 30 Wall and cavity must be made of the same material, but with different 31 density 32 33 All above parameters can be redifined via the UI commands built in 34 DetectorMessenger class 35 36 ----------------- 37 | | 38 | wall | 39 | ----- | 40 | | | | 41 | | <-+-----+--- cavity 42 ------> | | | | 43 ------> | | | | 44 beam -------------------------------- cylinder axis 45 ------> | | | | 46 ------> | | | | 47 | | | | 48 | | | | 49 | ----- | 50 | | 51 | | 52 ----------------- 53 54 2- BEAM 55 56 Monoenergetic incident photon beam is uniformly distribued, perpendicular 57 to the flat end of the chamber. The beam radius can be controled with an 58 UI command built in PrimaryGeneratorMessenger; the default is full wall 59 chamber radius. 60 61 Beam regeneration : after each Compton interaction, the scattered photon is 62 reset to its initial state, energy and direction. Consequently, interaction 63 sites are uniformly distribued within the wall material. 64 65 This modification must be done in the ParticleChange of the final state 66 of the Compton scattering interaction. Therefore, a specific model 67 (MyKleinNishinaCompton) is assigned to the ComptonScattering process in 68 PhysicsList. MyKleinNishinaCompton inherites from G4KleinNishinaCompton; 69 only the function SampleSecondaries() is overwritten. 70 71 3- PURPOSE OF THE PROGRAM 72 73 The program computes the dose deposited in the cavity and the ratio 74 Dose/Beam_energy_fluence. This ratio is compared to the mass_energy_transfer 75 coefficient of the wall material. 76 77 The mass_energy_transfer coefficient needs : 78 - the photon total cross section, which is read from the PhysicsTables 79 by G4EmCalculator (see EndOfRunAction). 80 - the average kinetic energy of charged secondaries generated in the 81 wall during the run. 82 83 The program needs high statistic to reach precision on the computed dose. 84 The UI command /run/printProgress allows to survey the convergence of 85 the kineticEnergy and dose calculations. 86 87 In addition, to increase the program efficiency, the secondary particles 88 which have no chance to reach the cavity are immediately killed (see 89 StackinAction). This feature can be switched off by an UI command (see 90 StackingMessenger). 91 92 The simplest way to study the effect of e- tracking parameters on dose 93 deposition is to use the command /testem/stepMax. 94 95 4- PHYSICS 96 97 The physics lists contains the standard electromagnetic processes, with few 98 modifications listed here. 99 100 - Compton scattering : as explained above, the final state is modified in 101 MyKleinNishinaCompton class. 102 103 In order to make the program more efficient, one can increase the Compton 104 cross section via the function SetCSFactor(factor) and its 105 associated UI command. Default is factor=1000. 106 107 - Bremsstrahlung : Fano conditions imply no energy transfer via 108 bremsstrahlung radiation. Therefore this process is not registered in the 109 physics list. However, it is always possible to include it. 110 See PhysListEmStandard class. 111 112 - Ionisation : In order to have same stopping power in wall and cavity, one 113 must cancel the density correction term in the dedx formula. This is done in 114 a specific MollerBhabha model (MyMollerBhabhaModel) which inherites from 115 G4MollerBhabhaModel. 116 117 To prevent explicit generation of delta-rays, the default production 118 threshold (i.e. cut) is set to 10 km (CSDA condition). 119 120 The finalRange of the step function is set to 10 um, which more on less 121 correspond to a tracking cut in water of about 20 keV. See emOptions. 122 Once again, the above parameters can be controled via UI commands. 123 124 - Multiple scattering : is switched in single Coulomb scattering mode near 125 boundaries. This is selected via EM options in PhysicsList, and can be 126 controled with UI commands. 127 128 - All PhysicsTables are built with 100 bins per decade. 129 130 5- HISTOGRAMS 131 132 fanoCavity has several predefined 1D histograms : 133 134 1 : emission point of e+- 135 2 : energy spectrum of e+- 136 3 : theta distribution of e+- 137 4 : emission point of e+- hitting cavity 138 5 : energy spectrum of e+- when entering in cavity 139 6 : theta distribution of e+- before enter in cavity 140 7 : theta distribution of e+- at first step in cavity 141 8 : track segment of e+- in cavity 142 9 : step size of e+- in wall 143 10 : step size of e+- in cavity 144 11 : energy deposit in cavity per track 145 146 The histograms are managed by G4AnalysisManager class and its messenger. 147 The histos can be individually activated with the command : 148 /analysis/h1/set id nbBins valMin valMax unit 149 where unit is the desired unit for the histo (MeV or keV, deg or mrad, etc..) 150 151 One can control the name of the histograms file with the command: 152 /analysis/setFileName name (default fanoCavity) 153 154 It is possible to choose the format of the histogram file : root (default), 155 hdf5, xml, csv, by changing the default file type in HistoManager.cc 156 157 It is also possible to print selected histograms on an ascii file: 158 /analysis/h1/setAscii id 159 All selected histos will be written on a file name.ascii (default fanocavity) 160 161 6- HOW TO START ? 162 163 - execute fanoCavity in 'batch' mode from macro files 164 % fanoCavity run01.mac 165 166 - execute fanoCavity in 'interactive mode' with visualization 167 % fanoCavity 168 .... 169 Idle> type your commands 170 .... 171 Idle> exit 172 173 Alternative macro file: 174 basic.mac - disabled multiple scattering and fluctuations of energy loss