1 | // |
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2 | // ******************************************************************** |
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3 | // * License and Disclaimer * |
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4 | // * * |
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5 | // * The Geant4 software is copyright of the Copyright Holders of * |
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6 | // * the Geant4 Collaboration. It is provided under the terms and * |
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7 | // * conditions of the Geant4 Software License, included in the file * |
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8 | // * LICENSE and available at http://cern.ch/geant4/license . These * |
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9 | // * include a list of copyright holders. * |
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10 | // * * |
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11 | // * Neither the authors of this software system, nor their employing * |
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12 | // * institutes,nor the agencies providing financial support for this * |
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13 | // * work make any representation or warranty, express or implied, * |
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14 | // * regarding this software system or assume any liability for its * |
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15 | // * use. Please see the license in the file LICENSE and URL above * |
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16 | // * for the full disclaimer and the limitation of liability. * |
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17 | // * * |
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18 | // * This code implementation is the result of the scientific and * |
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19 | // * technical work of the GEANT4 collaboration. * |
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20 | // * By using, copying, modifying or distributing the software (or * |
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21 | // * any work based on the software) you agree to acknowledge its * |
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22 | // * use in resulting scientific publications, and indicate your * |
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23 | // * acceptance of all terms of the Geant4 Software license. * |
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24 | // ******************************************************************** |
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25 | // |
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26 | // -------------------------------------------------------------------- |
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27 | /// |
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28 | // $Id: G4LowEnergyGammaConversion.cc,v 1.39 2009/06/11 15:47:08 mantero Exp $ |
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29 | // GEANT4 tag $Name: geant4-09-03 $ |
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30 | // |
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31 | // |
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32 | // -------------------------------------------------------------- |
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33 | // |
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34 | // Author: A. Forti |
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35 | // Maria Grazia Pia (Maria.Grazia.Pia@cern.ch) |
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36 | // |
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37 | // History: |
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38 | // -------- |
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39 | // 02/03/1999 A. Forti 1st implementation |
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40 | // 14.03.2000 Veronique Lefebure; |
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41 | // Change initialisation of lowestEnergyLimit from 1.22 to 1.022. |
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42 | // Note that the hard coded value 1.022 should be used instead of |
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43 | // 2*electron_mass_c2 in order to agree with the value of the data bank EPDL97 |
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44 | // 24.04.01 V.Ivanchenko remove RogueWave |
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45 | // 27.07.01 F.Longo correct bug in energy distribution |
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46 | // 21.01.03 V.Ivanchenko Cut per region |
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47 | // 25.03.03 F.Longo fix in angular distribution of e+/e- |
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48 | // 24.04.03 V.Ivanchenko - Cut per region mfpt |
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49 | // |
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50 | // -------------------------------------------------------------- |
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51 | |
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52 | #include "G4LowEnergyGammaConversion.hh" |
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53 | |
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54 | #include "Randomize.hh" |
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55 | #include "G4ParticleDefinition.hh" |
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56 | #include "G4Track.hh" |
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57 | #include "G4Step.hh" |
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58 | #include "G4ForceCondition.hh" |
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59 | #include "G4Gamma.hh" |
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60 | #include "G4Electron.hh" |
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61 | #include "G4DynamicParticle.hh" |
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62 | #include "G4VParticleChange.hh" |
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63 | #include "G4ThreeVector.hh" |
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64 | #include "G4Positron.hh" |
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65 | #include "G4IonisParamElm.hh" |
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66 | #include "G4Material.hh" |
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67 | #include "G4VCrossSectionHandler.hh" |
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68 | #include "G4CrossSectionHandler.hh" |
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69 | #include "G4VEMDataSet.hh" |
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70 | #include "G4VDataSetAlgorithm.hh" |
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71 | #include "G4LogLogInterpolation.hh" |
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72 | #include "G4VRangeTest.hh" |
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73 | #include "G4RangeTest.hh" |
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74 | #include "G4MaterialCutsCouple.hh" |
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75 | |
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76 | G4LowEnergyGammaConversion::G4LowEnergyGammaConversion(const G4String& processName) |
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77 | : G4VDiscreteProcess(processName), |
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78 | lowEnergyLimit(1.022000*MeV), |
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79 | highEnergyLimit(100*GeV), |
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80 | intrinsicLowEnergyLimit(1.022000*MeV), |
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81 | intrinsicHighEnergyLimit(100*GeV), |
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82 | smallEnergy(2.*MeV) |
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83 | |
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84 | { |
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85 | if (lowEnergyLimit < intrinsicLowEnergyLimit || |
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86 | highEnergyLimit > intrinsicHighEnergyLimit) |
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87 | { |
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88 | G4Exception("G4LowEnergyGammaConversion::G4LowEnergyGammaConversion - energy limit outside intrinsic process validity range"); |
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89 | } |
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90 | |
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91 | // The following pointer is owned by G4DataHandler |
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92 | |
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93 | crossSectionHandler = new G4CrossSectionHandler(); |
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94 | crossSectionHandler->Initialise(0,1.0220*MeV,100.*GeV,400); |
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95 | meanFreePathTable = 0; |
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96 | rangeTest = new G4RangeTest; |
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97 | |
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98 | if (verboseLevel > 0) |
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99 | { |
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100 | G4cout << GetProcessName() << " is created " << G4endl |
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101 | << "Energy range: " |
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102 | << lowEnergyLimit / MeV << " MeV - " |
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103 | << highEnergyLimit / GeV << " GeV" |
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104 | << G4endl; |
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105 | } |
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106 | |
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107 | G4cout << G4endl; |
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108 | G4cout << "*******************************************************************************" << G4endl; |
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109 | G4cout << "*******************************************************************************" << G4endl; |
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110 | G4cout << " The class G4LowEnergyGammaConversion is NOT SUPPORTED ANYMORE. " << G4endl; |
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111 | G4cout << " It will be REMOVED with the next major release of Geant4. " << G4endl; |
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112 | G4cout << " Please consult: https://twiki.cern.ch/twiki/bin/view/Geant4/LoweProcesses" << G4endl; |
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113 | G4cout << "*******************************************************************************" << G4endl; |
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114 | G4cout << "*******************************************************************************" << G4endl; |
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115 | G4cout << G4endl; |
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116 | } |
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117 | |
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118 | G4LowEnergyGammaConversion::~G4LowEnergyGammaConversion() |
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119 | { |
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120 | delete meanFreePathTable; |
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121 | delete crossSectionHandler; |
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122 | delete rangeTest; |
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123 | } |
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124 | |
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125 | void G4LowEnergyGammaConversion::BuildPhysicsTable(const G4ParticleDefinition& ) |
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126 | { |
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127 | |
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128 | crossSectionHandler->Clear(); |
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129 | G4String crossSectionFile = "pair/pp-cs-"; |
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130 | crossSectionHandler->LoadData(crossSectionFile); |
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131 | |
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132 | delete meanFreePathTable; |
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133 | meanFreePathTable = crossSectionHandler->BuildMeanFreePathForMaterials(); |
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134 | } |
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135 | |
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136 | G4VParticleChange* G4LowEnergyGammaConversion::PostStepDoIt(const G4Track& aTrack, |
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137 | const G4Step& aStep) |
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138 | { |
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139 | // The energies of the e+ e- secondaries are sampled using the Bethe - Heitler |
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140 | // cross sections with Coulomb correction. A modified version of the random |
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141 | // number techniques of Butcher & Messel is used (Nuc Phys 20(1960),15). |
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142 | |
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143 | // Note 1 : Effects due to the breakdown of the Born approximation at low |
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144 | // energy are ignored. |
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145 | // Note 2 : The differential cross section implicitly takes account of |
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146 | // pair creation in both nuclear and atomic electron fields. However triplet |
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147 | // prodution is not generated. |
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148 | |
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149 | aParticleChange.Initialize(aTrack); |
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150 | |
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151 | const G4MaterialCutsCouple* couple = aTrack.GetMaterialCutsCouple(); |
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152 | |
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153 | const G4DynamicParticle* incidentPhoton = aTrack.GetDynamicParticle(); |
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154 | G4double photonEnergy = incidentPhoton->GetKineticEnergy(); |
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155 | G4ParticleMomentum photonDirection = incidentPhoton->GetMomentumDirection(); |
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156 | |
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157 | G4double epsilon ; |
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158 | G4double epsilon0 = electron_mass_c2 / photonEnergy ; |
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159 | |
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160 | // Do it fast if photon energy < 2. MeV |
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161 | if (photonEnergy < smallEnergy ) |
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162 | { |
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163 | epsilon = epsilon0 + (0.5 - epsilon0) * G4UniformRand(); |
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164 | } |
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165 | else |
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166 | { |
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167 | // Select randomly one element in the current material |
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168 | const G4Element* element = crossSectionHandler->SelectRandomElement(couple,photonEnergy); |
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169 | |
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170 | if (element == 0) |
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171 | { |
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172 | G4cout << "G4LowEnergyGammaConversion::PostStepDoIt - element = 0" << G4endl; |
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173 | } |
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174 | G4IonisParamElm* ionisation = element->GetIonisation(); |
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175 | if (ionisation == 0) |
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176 | { |
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177 | G4cout << "G4LowEnergyGammaConversion::PostStepDoIt - ionisation = 0" << G4endl; |
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178 | } |
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179 | |
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180 | // Extract Coulomb factor for this Element |
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181 | G4double fZ = 8. * (ionisation->GetlogZ3()); |
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182 | if (photonEnergy > 50. * MeV) fZ += 8. * (element->GetfCoulomb()); |
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183 | |
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184 | // Limits of the screening variable |
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185 | G4double screenFactor = 136. * epsilon0 / (element->GetIonisation()->GetZ3()) ; |
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186 | G4double screenMax = std::exp ((42.24 - fZ)/8.368) - 0.952 ; |
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187 | G4double screenMin = std::min(4.*screenFactor,screenMax) ; |
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188 | |
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189 | // Limits of the energy sampling |
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190 | G4double epsilon1 = 0.5 - 0.5 * std::sqrt(1. - screenMin / screenMax) ; |
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191 | G4double epsilonMin = std::max(epsilon0,epsilon1); |
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192 | G4double epsilonRange = 0.5 - epsilonMin ; |
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193 | |
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194 | // Sample the energy rate of the created electron (or positron) |
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195 | G4double screen; |
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196 | G4double gReject ; |
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197 | |
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198 | G4double f10 = ScreenFunction1(screenMin) - fZ; |
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199 | G4double f20 = ScreenFunction2(screenMin) - fZ; |
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200 | G4double normF1 = std::max(f10 * epsilonRange * epsilonRange,0.); |
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201 | G4double normF2 = std::max(1.5 * f20,0.); |
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202 | |
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203 | do { |
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204 | if (normF1 / (normF1 + normF2) > G4UniformRand() ) |
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205 | { |
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206 | epsilon = 0.5 - epsilonRange * std::pow(G4UniformRand(), 0.3333) ; |
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207 | screen = screenFactor / (epsilon * (1. - epsilon)); |
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208 | gReject = (ScreenFunction1(screen) - fZ) / f10 ; |
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209 | } |
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210 | else |
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211 | { |
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212 | epsilon = epsilonMin + epsilonRange * G4UniformRand(); |
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213 | screen = screenFactor / (epsilon * (1 - epsilon)); |
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214 | gReject = (ScreenFunction2(screen) - fZ) / f20 ; |
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215 | } |
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216 | } while ( gReject < G4UniformRand() ); |
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217 | |
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218 | } // End of epsilon sampling |
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219 | |
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220 | // Fix charges randomly |
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221 | |
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222 | G4double electronTotEnergy; |
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223 | G4double positronTotEnergy; |
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224 | |
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225 | if (CLHEP::RandBit::shootBit()) |
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226 | { |
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227 | electronTotEnergy = (1. - epsilon) * photonEnergy; |
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228 | positronTotEnergy = epsilon * photonEnergy; |
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229 | } |
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230 | else |
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231 | { |
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232 | positronTotEnergy = (1. - epsilon) * photonEnergy; |
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233 | electronTotEnergy = epsilon * photonEnergy; |
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234 | } |
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235 | |
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236 | // Scattered electron (positron) angles. ( Z - axis along the parent photon) |
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237 | // Universal distribution suggested by L. Urban (Geant3 manual (1993) Phys211), |
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238 | // derived from Tsai distribution (Rev. Mod. Phys. 49, 421 (1977) |
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239 | |
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240 | G4double u; |
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241 | const G4double a1 = 0.625; |
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242 | G4double a2 = 3. * a1; |
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243 | // G4double d = 27. ; |
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244 | |
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245 | // if (9. / (9. + d) > G4UniformRand()) |
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246 | if (0.25 > G4UniformRand()) |
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247 | { |
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248 | u = - std::log(G4UniformRand() * G4UniformRand()) / a1 ; |
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249 | } |
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250 | else |
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251 | { |
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252 | u = - std::log(G4UniformRand() * G4UniformRand()) / a2 ; |
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253 | } |
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254 | |
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255 | G4double thetaEle = u*electron_mass_c2/electronTotEnergy; |
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256 | G4double thetaPos = u*electron_mass_c2/positronTotEnergy; |
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257 | G4double phi = twopi * G4UniformRand(); |
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258 | |
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259 | G4double dxEle= std::sin(thetaEle)*std::cos(phi),dyEle= std::sin(thetaEle)*std::sin(phi),dzEle=std::cos(thetaEle); |
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260 | G4double dxPos=-std::sin(thetaPos)*std::cos(phi),dyPos=-std::sin(thetaPos)*std::sin(phi),dzPos=std::cos(thetaPos); |
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261 | |
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262 | |
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263 | // Kinematics of the created pair: |
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264 | // the electron and positron are assumed to have a symetric angular |
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265 | // distribution with respect to the Z axis along the parent photon |
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266 | |
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267 | G4double localEnergyDeposit = 0. ; |
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268 | |
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269 | aParticleChange.SetNumberOfSecondaries(2) ; |
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270 | G4double electronKineEnergy = std::max(0.,electronTotEnergy - electron_mass_c2) ; |
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271 | |
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272 | // Generate the electron only if with large enough range w.r.t. cuts and safety |
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273 | |
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274 | G4double safety = aStep.GetPostStepPoint()->GetSafety(); |
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275 | |
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276 | if (rangeTest->Escape(G4Electron::Electron(),couple,electronKineEnergy,safety)) |
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277 | { |
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278 | G4ThreeVector electronDirection (dxEle, dyEle, dzEle); |
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279 | electronDirection.rotateUz(photonDirection); |
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280 | |
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281 | G4DynamicParticle* particle1 = new G4DynamicParticle (G4Electron::Electron(), |
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282 | electronDirection, |
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283 | electronKineEnergy); |
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284 | aParticleChange.AddSecondary(particle1) ; |
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285 | } |
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286 | else |
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287 | { |
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288 | localEnergyDeposit += electronKineEnergy ; |
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289 | } |
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290 | |
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291 | // The e+ is always created (even with kinetic energy = 0) for further annihilation |
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292 | G4double positronKineEnergy = std::max(0.,positronTotEnergy - electron_mass_c2) ; |
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293 | |
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294 | // Is the local energy deposit correct, if the positron is always created? |
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295 | if (! (rangeTest->Escape(G4Positron::Positron(),couple,positronKineEnergy,safety))) |
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296 | { |
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297 | localEnergyDeposit += positronKineEnergy ; |
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298 | positronKineEnergy = 0. ; |
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299 | } |
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300 | |
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301 | G4ThreeVector positronDirection (dxPos, dyPos, dzPos); |
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302 | positronDirection.rotateUz(photonDirection); |
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303 | |
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304 | // Create G4DynamicParticle object for the particle2 |
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305 | G4DynamicParticle* particle2 = new G4DynamicParticle(G4Positron::Positron(), |
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306 | positronDirection, positronKineEnergy); |
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307 | aParticleChange.AddSecondary(particle2) ; |
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308 | |
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309 | aParticleChange.ProposeLocalEnergyDeposit(localEnergyDeposit) ; |
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310 | |
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311 | // Kill the incident photon |
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312 | aParticleChange.ProposeMomentumDirection(0.,0.,0.) ; |
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313 | aParticleChange.ProposeEnergy(0.) ; |
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314 | aParticleChange.ProposeTrackStatus(fStopAndKill) ; |
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315 | |
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316 | // Reset NbOfInteractionLengthLeft and return aParticleChange |
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317 | return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep); |
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318 | } |
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319 | |
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320 | G4bool G4LowEnergyGammaConversion::IsApplicable(const G4ParticleDefinition& particle) |
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321 | { |
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322 | return ( &particle == G4Gamma::Gamma() ); |
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323 | } |
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324 | |
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325 | G4double G4LowEnergyGammaConversion::GetMeanFreePath(const G4Track& track, |
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326 | G4double, // previousStepSize |
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327 | G4ForceCondition*) |
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328 | { |
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329 | const G4DynamicParticle* photon = track.GetDynamicParticle(); |
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330 | G4double energy = photon->GetKineticEnergy(); |
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331 | const G4MaterialCutsCouple* couple = track.GetMaterialCutsCouple(); |
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332 | size_t materialIndex = couple->GetIndex(); |
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333 | |
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334 | G4double meanFreePath; |
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335 | if (energy > highEnergyLimit) meanFreePath = meanFreePathTable->FindValue(highEnergyLimit,materialIndex); |
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336 | else if (energy < lowEnergyLimit) meanFreePath = DBL_MAX; |
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337 | else meanFreePath = meanFreePathTable->FindValue(energy,materialIndex); |
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338 | return meanFreePath; |
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339 | } |
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340 | |
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341 | G4double G4LowEnergyGammaConversion::ScreenFunction1(G4double screenVariable) |
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342 | { |
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343 | // Compute the value of the screening function 3*phi1 - phi2 |
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344 | |
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345 | G4double value; |
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346 | |
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347 | if (screenVariable > 1.) |
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348 | value = 42.24 - 8.368 * std::log(screenVariable + 0.952); |
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349 | else |
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350 | value = 42.392 - screenVariable * (7.796 - 1.961 * screenVariable); |
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351 | |
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352 | return value; |
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353 | } |
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354 | |
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355 | G4double G4LowEnergyGammaConversion::ScreenFunction2(G4double screenVariable) |
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356 | { |
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357 | // Compute the value of the screening function 1.5*phi1 - 0.5*phi2 |
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358 | |
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359 | G4double value; |
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360 | |
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361 | if (screenVariable > 1.) |
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362 | value = 42.24 - 8.368 * std::log(screenVariable + 0.952); |
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363 | else |
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364 | value = 41.405 - screenVariable * (5.828 - 0.8945 * screenVariable); |
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365 | |
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366 | return value; |
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367 | } |
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