1 | // |
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2 | // ******************************************************************** |
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3 | // * License and Disclaimer * |
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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 | // $Id: G4eeToTwoGammaModel.cc,v 1.15 2009/04/09 18:41:18 vnivanch Exp $ |
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27 | // GEANT4 tag $Name: geant4-09-04-beta-01 $ |
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28 | // |
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29 | // ------------------------------------------------------------------- |
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30 | // |
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31 | // GEANT4 Class file |
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32 | // |
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33 | // |
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34 | // File name: G4eeToTwoGammaModel |
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35 | // |
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36 | // Author: Vladimir Ivanchenko on base of Michel Maire code |
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37 | // |
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38 | // Creation date: 02.08.2004 |
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39 | // |
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40 | // Modifications: |
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41 | // 08-04-05 Major optimisation of internal interfaces (V.Ivanchenko) |
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42 | // 18-04-05 Compute CrossSectionPerVolume (V.Ivanchenko) |
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43 | // 06-02-06 ComputeCrossSectionPerElectron, ComputeCrossSectionPerAtom (mma) |
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44 | // 29-06-06 Fix problem for zero energy incident positron (V.Ivanchenko) |
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45 | // 20-10-06 Add theGamma as a member (V.Ivanchenko) |
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46 | // |
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47 | // |
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48 | // Class Description: |
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49 | // |
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50 | // Implementation of e+ annihilation into 2 gamma |
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51 | // |
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52 | // The secondaries Gamma energies are sampled using the Heitler cross section. |
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53 | // |
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54 | // A modified version of the random number techniques of Butcher & Messel |
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55 | // is used (Nuc Phys 20(1960),15). |
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56 | // |
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57 | // GEANT4 internal units. |
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58 | // |
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59 | // Note 1: The initial electron is assumed free and at rest. |
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60 | // |
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61 | // Note 2: The annihilation processes producing one or more than two photons are |
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62 | // ignored, as negligible compared to the two photons process. |
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63 | |
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64 | |
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65 | |
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66 | // |
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67 | // ------------------------------------------------------------------- |
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68 | // |
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69 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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70 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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71 | |
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72 | #include "G4eeToTwoGammaModel.hh" |
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73 | #include "G4TrackStatus.hh" |
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74 | #include "G4Electron.hh" |
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75 | #include "G4Positron.hh" |
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76 | #include "G4Gamma.hh" |
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77 | #include "Randomize.hh" |
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78 | #include "G4ParticleChangeForGamma.hh" |
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79 | |
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80 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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81 | |
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82 | using namespace std; |
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83 | |
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84 | G4eeToTwoGammaModel::G4eeToTwoGammaModel(const G4ParticleDefinition*, |
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85 | const G4String& nam) |
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86 | : G4VEmModel(nam), |
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87 | pi_rcl2(pi*classic_electr_radius*classic_electr_radius), |
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88 | isInitialised(false) |
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89 | { |
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90 | theGamma = G4Gamma::Gamma(); |
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91 | } |
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92 | |
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93 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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94 | |
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95 | G4eeToTwoGammaModel::~G4eeToTwoGammaModel() |
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96 | {} |
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97 | |
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98 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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99 | |
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100 | void G4eeToTwoGammaModel::Initialise(const G4ParticleDefinition*, |
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101 | const G4DataVector&) |
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102 | { |
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103 | if(isInitialised) return; |
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104 | fParticleChange = GetParticleChangeForGamma(); |
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105 | isInitialised = true; |
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106 | } |
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107 | |
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108 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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109 | |
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110 | G4double G4eeToTwoGammaModel::ComputeCrossSectionPerElectron( |
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111 | const G4ParticleDefinition*, |
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112 | G4double kineticEnergy, |
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113 | G4double, G4double) |
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114 | { |
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115 | // Calculates the cross section per electron of annihilation into two photons |
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116 | // from the Heilter formula. |
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117 | |
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118 | G4double tau = kineticEnergy/electron_mass_c2; |
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119 | G4double gam = tau + 1.0; |
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120 | G4double gamma2= gam*gam; |
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121 | G4double bg2 = tau * (tau+2.0); |
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122 | G4double bg = sqrt(bg2); |
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123 | |
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124 | G4double cross = pi_rcl2*((gamma2+4*gam+1.)*log(gam+bg) - (gam+3.)*bg) |
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125 | / (bg2*(gam+1.)); |
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126 | return cross; |
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127 | } |
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128 | |
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129 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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130 | |
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131 | G4double G4eeToTwoGammaModel::ComputeCrossSectionPerAtom( |
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132 | const G4ParticleDefinition* p, |
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133 | G4double kineticEnergy, G4double Z, |
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134 | G4double, G4double, G4double) |
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135 | { |
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136 | // Calculates the cross section per atom of annihilation into two photons |
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137 | |
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138 | G4double cross = Z*ComputeCrossSectionPerElectron(p,kineticEnergy); |
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139 | return cross; |
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140 | } |
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141 | |
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142 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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143 | |
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144 | G4double G4eeToTwoGammaModel::CrossSectionPerVolume( |
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145 | const G4Material* material, |
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146 | const G4ParticleDefinition* p, |
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147 | G4double kineticEnergy, |
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148 | G4double, G4double) |
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149 | { |
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150 | // Calculates the cross section per volume of annihilation into two photons |
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151 | |
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152 | G4double eDensity = material->GetElectronDensity(); |
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153 | G4double cross = eDensity*ComputeCrossSectionPerElectron(p,kineticEnergy); |
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154 | return cross; |
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155 | } |
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156 | |
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157 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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158 | |
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159 | void G4eeToTwoGammaModel::SampleSecondaries(vector<G4DynamicParticle*>* vdp, |
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160 | const G4MaterialCutsCouple*, |
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161 | const G4DynamicParticle* dp, |
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162 | G4double, |
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163 | G4double) |
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164 | { |
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165 | G4double PositKinEnergy = dp->GetKineticEnergy(); |
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166 | |
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167 | // Case at rest |
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168 | if(PositKinEnergy == 0.0) { |
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169 | G4double cost = 2.*G4UniformRand()-1.; |
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170 | G4double sint = sqrt((1. - cost)*(1. + cost)); |
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171 | G4double phi = twopi * G4UniformRand(); |
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172 | G4ThreeVector dir (sint*cos(phi), sint*sin(phi), cost); |
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173 | G4DynamicParticle* aGamma1 = new G4DynamicParticle(theGamma, |
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174 | dir, electron_mass_c2); |
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175 | G4DynamicParticle* aGamma2 = new G4DynamicParticle(theGamma, |
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176 | -dir, electron_mass_c2); |
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177 | vdp->push_back(aGamma1); |
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178 | vdp->push_back(aGamma2); |
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179 | |
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180 | } else { |
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181 | |
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182 | G4ThreeVector PositDirection = dp->GetMomentumDirection(); |
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183 | |
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184 | G4double tau = PositKinEnergy/electron_mass_c2; |
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185 | G4double gam = tau + 1.0; |
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186 | G4double tau2 = tau + 2.0; |
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187 | G4double sqgrate = sqrt(tau/tau2)*0.5; |
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188 | G4double sqg2m1 = sqrt(tau*tau2); |
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189 | |
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190 | // limits of the energy sampling |
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191 | G4double epsilmin = 0.5 - sqgrate; |
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192 | G4double epsilmax = 0.5 + sqgrate; |
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193 | G4double epsilqot = epsilmax/epsilmin; |
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194 | |
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195 | // |
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196 | // sample the energy rate of the created gammas |
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197 | // |
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198 | G4double epsil, greject; |
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199 | |
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200 | do { |
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201 | epsil = epsilmin*pow(epsilqot,G4UniformRand()); |
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202 | greject = 1. - epsil + (2.*gam*epsil-1.)/(epsil*tau2*tau2); |
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203 | } while( greject < G4UniformRand() ); |
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204 | |
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205 | // |
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206 | // scattered Gamma angles. ( Z - axis along the parent positron) |
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207 | // |
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208 | |
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209 | G4double cost = (epsil*tau2-1.)/(epsil*sqg2m1); |
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210 | if(std::abs(cost) > 1.0) { |
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211 | G4cout << "### G4eeToTwoGammaModel WARNING cost= " << cost |
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212 | << " positron Ekin(MeV)= " << PositKinEnergy |
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213 | << " gamma epsil= " << epsil |
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214 | << G4endl; |
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215 | if(cost > 1.0) cost = 1.0; |
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216 | else cost = -1.0; |
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217 | } |
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218 | G4double sint = sqrt((1.+cost)*(1.-cost)); |
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219 | G4double phi = twopi * G4UniformRand(); |
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220 | |
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221 | G4double dirx = sint*cos(phi) , diry = sint*sin(phi) , dirz = cost; |
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222 | |
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223 | // |
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224 | // kinematic of the created pair |
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225 | // |
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226 | |
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227 | G4double TotalAvailableEnergy = PositKinEnergy + 2.0*electron_mass_c2; |
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228 | G4double Phot1Energy = epsil*TotalAvailableEnergy; |
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229 | |
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230 | G4ThreeVector Phot1Direction (dirx, diry, dirz); |
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231 | Phot1Direction.rotateUz(PositDirection); |
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232 | G4DynamicParticle* aGamma1 = |
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233 | new G4DynamicParticle (theGamma,Phot1Direction, Phot1Energy); |
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234 | vdp->push_back(aGamma1); |
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235 | |
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236 | G4double Phot2Energy =(1.-epsil)*TotalAvailableEnergy; |
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237 | G4double PositP= sqrt(PositKinEnergy*(PositKinEnergy+2.*electron_mass_c2)); |
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238 | G4ThreeVector dir = PositDirection*PositP - Phot1Direction*Phot1Energy; |
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239 | G4ThreeVector Phot2Direction = dir.unit(); |
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240 | |
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241 | // create G4DynamicParticle object for the particle2 |
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242 | G4DynamicParticle* aGamma2= |
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243 | new G4DynamicParticle (theGamma,Phot2Direction, Phot2Energy); |
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244 | vdp->push_back(aGamma2); |
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245 | /* |
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246 | G4cout << "Annihilation in fly: e0= " << PositKinEnergy |
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247 | << " m= " << electron_mass_c2 |
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248 | << " e1= " << Phot1Energy |
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249 | << " e2= " << Phot2Energy << " dir= " << dir |
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250 | << " -> " << Phot1Direction << " " |
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251 | << Phot2Direction << G4endl; |
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252 | */ |
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253 | } |
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254 | fParticleChange->SetProposedKineticEnergy(0.); |
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255 | fParticleChange->ProposeTrackStatus(fStopAndKill); |
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256 | } |
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257 | |
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258 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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