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15 | // * use. Please see the license in the file LICENSE and URL above * |
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24 | // ******************************************************************** |
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25 | // |
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26 | // $Id: G4PenelopeAnnihilationModel.cc,v 1.4 2009/06/10 13:32:36 mantero Exp $ |
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27 | // GEANT4 tag $Name: geant4-09-03 $ |
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28 | // |
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29 | // Author: Luciano Pandola |
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30 | // |
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31 | // History: |
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32 | // -------- |
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33 | // 29 Oct 2008 L Pandola Migration from process to model |
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34 | // 15 Apr 2009 V Ivanchenko Cleanup initialisation and generation of secondaries: |
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35 | // - apply internal high-energy limit only in constructor |
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36 | // - do not apply low-energy limit (default is 0) |
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37 | // - do not use G4ElementSelector |
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38 | |
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39 | #include "G4PenelopeAnnihilationModel.hh" |
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40 | #include "G4ParticleDefinition.hh" |
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41 | #include "G4MaterialCutsCouple.hh" |
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42 | #include "G4ProductionCutsTable.hh" |
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43 | #include "G4DynamicParticle.hh" |
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44 | #include "G4Gamma.hh" |
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45 | |
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46 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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47 | |
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48 | |
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49 | G4PenelopeAnnihilationModel::G4PenelopeAnnihilationModel(const G4ParticleDefinition*, |
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50 | const G4String& nam) |
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51 | :G4VEmModel(nam),isInitialised(false) |
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52 | { |
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53 | fIntrinsicLowEnergyLimit = 0.0; |
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54 | fIntrinsicHighEnergyLimit = 100.0*GeV; |
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55 | // SetLowEnergyLimit(fIntrinsicLowEnergyLimit); |
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56 | SetHighEnergyLimit(fIntrinsicHighEnergyLimit); |
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57 | |
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58 | //Calculate variable that will be used later on |
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59 | fPielr2 = pi*classic_electr_radius*classic_electr_radius; |
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60 | |
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61 | verboseLevel= 0; |
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62 | // Verbosity scale: |
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63 | // 0 = nothing |
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64 | // 1 = warning for energy non-conservation |
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65 | // 2 = details of energy budget |
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66 | // 3 = calculation of cross sections, file openings, sampling of atoms |
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67 | // 4 = entering in methods |
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68 | |
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69 | } |
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70 | |
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71 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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72 | |
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73 | G4PenelopeAnnihilationModel::~G4PenelopeAnnihilationModel() |
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74 | {;} |
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75 | |
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76 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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77 | |
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78 | void G4PenelopeAnnihilationModel::Initialise(const G4ParticleDefinition*, |
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79 | const G4DataVector&) |
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80 | { |
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81 | if (verboseLevel > 3) |
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82 | G4cout << "Calling G4PenelopeAnnihilationModel::Initialise()" << G4endl; |
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83 | |
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84 | if(verboseLevel > 0) { |
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85 | G4cout << "Penelope Annihilation model is initialized " << G4endl |
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86 | << "Energy range: " |
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87 | << LowEnergyLimit() / keV << " keV - " |
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88 | << HighEnergyLimit() / GeV << " GeV" |
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89 | << G4endl; |
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90 | } |
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91 | |
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92 | if(isInitialised) return; |
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93 | fParticleChange = GetParticleChangeForGamma(); |
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94 | isInitialised = true; |
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95 | } |
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96 | |
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97 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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98 | |
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99 | G4double G4PenelopeAnnihilationModel::ComputeCrossSectionPerAtom( |
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100 | const G4ParticleDefinition*, |
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101 | G4double energy, |
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102 | G4double Z, G4double, |
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103 | G4double, G4double) |
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104 | { |
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105 | if (verboseLevel > 3) |
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106 | G4cout << "Calling ComputeCrossSectionPerAtom() of G4PenelopeAnnihilationModel" << |
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107 | G4endl; |
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108 | |
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109 | G4double cs = Z*ComputeCrossSectionPerElectron(energy); |
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110 | |
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111 | if (verboseLevel > 2) |
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112 | G4cout << "Annihilation cross Section at " << energy/keV << " keV for Z=" << Z << |
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113 | " = " << cs/barn << " barn" << G4endl; |
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114 | return cs; |
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115 | } |
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116 | |
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117 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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118 | |
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119 | void G4PenelopeAnnihilationModel::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect, |
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120 | const G4MaterialCutsCouple*, |
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121 | const G4DynamicParticle* aDynamicPositron, |
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122 | G4double, |
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123 | G4double) |
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124 | { |
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125 | // |
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126 | // Penelope model to sample final state for positron annihilation. |
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127 | // Target eletrons are assumed to be free and at rest. Binding effects enabling |
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128 | // one-photon annihilation are neglected. |
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129 | // For annihilation at rest, two back-to-back photons are emitted, having energy of 511 keV |
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130 | // and isotropic angular distribution. |
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131 | // For annihilation in flight, it is used the theory from |
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132 | // W. Heitler, The quantum theory of radiation, Oxford University Press (1954) |
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133 | // The two photons can have different energy. The efficiency of the sampling algorithm |
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134 | // of the photon energy from the dSigma/dE distribution is practically 100% for |
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135 | // positrons of kinetic energy < 10 keV. It reaches a minimum (about 80%) at energy |
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136 | // of about 10 MeV. |
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137 | // The angle theta is kinematically linked to the photon energy, to ensure momentum |
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138 | // conservation. The angle phi is sampled isotropically for the first gamma. |
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139 | // |
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140 | if (verboseLevel > 3) |
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141 | G4cout << "Calling SamplingSecondaries() of G4PenelopeAnnihilationModel" << G4endl; |
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142 | |
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143 | G4double kineticEnergy = aDynamicPositron->GetKineticEnergy(); |
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144 | |
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145 | // kill primary |
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146 | fParticleChange->SetProposedKineticEnergy(0.); |
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147 | fParticleChange->ProposeTrackStatus(fStopAndKill); |
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148 | |
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149 | if (kineticEnergy == 0.0) |
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150 | { |
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151 | //Old AtRestDoIt |
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152 | G4double cosTheta = -1.0+2.0*G4UniformRand(); |
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153 | G4double sinTheta = std::sqrt(1.0-cosTheta*cosTheta); |
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154 | G4double phi = twopi*G4UniformRand(); |
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155 | G4ThreeVector direction (sinTheta*std::cos(phi),sinTheta*std::sin(phi),cosTheta); |
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156 | G4DynamicParticle* firstGamma = new G4DynamicParticle (G4Gamma::Gamma(), |
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157 | direction, electron_mass_c2); |
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158 | G4DynamicParticle* secondGamma = new G4DynamicParticle (G4Gamma::Gamma(), |
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159 | -direction, electron_mass_c2); |
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160 | |
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161 | fvect->push_back(firstGamma); |
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162 | fvect->push_back(secondGamma); |
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163 | return; |
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164 | } |
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165 | |
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166 | //This is the "PostStep" case (annihilation in flight) |
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167 | G4ParticleMomentum positronDirection = |
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168 | aDynamicPositron->GetMomentumDirection(); |
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169 | G4double gamma = 1.0 + std::max(kineticEnergy,1.0*eV)/electron_mass_c2; |
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170 | G4double gamma21 = std::sqrt(gamma*gamma-1); |
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171 | G4double ani = 1.0+gamma; |
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172 | G4double chimin = 1.0/(ani+gamma21); |
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173 | G4double rchi = (1.0-chimin)/chimin; |
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174 | G4double gt0 = ani*ani-2.0; |
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175 | G4double test=0.0; |
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176 | G4double epsilon = 0; |
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177 | do{ |
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178 | epsilon = chimin*std::pow(rchi,G4UniformRand()); |
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179 | G4double reject = ani*ani*(1.0-epsilon)+2.0*gamma-(1.0/epsilon); |
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180 | test = G4UniformRand()*gt0-reject; |
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181 | }while(test>0); |
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182 | |
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183 | G4double totalAvailableEnergy = kineticEnergy + 2.0*electron_mass_c2; |
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184 | G4double photon1Energy = epsilon*totalAvailableEnergy; |
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185 | G4double photon2Energy = (1.0-epsilon)*totalAvailableEnergy; |
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186 | G4double cosTheta1 = (ani-1.0/epsilon)/gamma21; |
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187 | G4double cosTheta2 = (ani-1.0/(1.0-epsilon))/gamma21; |
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188 | |
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189 | //G4double localEnergyDeposit = 0.; |
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190 | |
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191 | G4double sinTheta1 = std::sqrt(1.-cosTheta1*cosTheta1); |
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192 | G4double phi1 = twopi * G4UniformRand(); |
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193 | G4double dirx1 = sinTheta1 * std::cos(phi1); |
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194 | G4double diry1 = sinTheta1 * std::sin(phi1); |
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195 | G4double dirz1 = cosTheta1; |
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196 | |
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197 | G4double sinTheta2 = std::sqrt(1.-cosTheta2*cosTheta2); |
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198 | G4double phi2 = phi1+pi; |
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199 | G4double dirx2 = sinTheta2 * std::cos(phi2); |
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200 | G4double diry2 = sinTheta2 * std::sin(phi2); |
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201 | G4double dirz2 = cosTheta2; |
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202 | |
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203 | G4ThreeVector photon1Direction (dirx1,diry1,dirz1); |
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204 | photon1Direction.rotateUz(positronDirection); |
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205 | // create G4DynamicParticle object for the particle1 |
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206 | G4DynamicParticle* aParticle1= new G4DynamicParticle (G4Gamma::Gamma(), |
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207 | photon1Direction, |
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208 | photon1Energy); |
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209 | fvect->push_back(aParticle1); |
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210 | |
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211 | G4ThreeVector photon2Direction(dirx2,diry2,dirz2); |
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212 | photon2Direction.rotateUz(positronDirection); |
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213 | // create G4DynamicParticle object for the particle2 |
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214 | G4DynamicParticle* aParticle2= new G4DynamicParticle (G4Gamma::Gamma(), |
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215 | photon2Direction, |
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216 | photon2Energy); |
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217 | fvect->push_back(aParticle2); |
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218 | |
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219 | if (verboseLevel > 1) |
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220 | { |
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221 | G4cout << "-----------------------------------------------------------" << G4endl; |
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222 | G4cout << "Energy balance from G4PenelopeAnnihilation" << G4endl; |
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223 | G4cout << "Kinetic positron energy: " << kineticEnergy/keV << " keV" << G4endl; |
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224 | G4cout << "Total available energy: " << totalAvailableEnergy/keV << " keV " << G4endl; |
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225 | G4cout << "-----------------------------------------------------------" << G4endl; |
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226 | G4cout << "Photon energy 1: " << photon1Energy/keV << " keV" << G4endl; |
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227 | G4cout << "Photon energy 2: " << photon2Energy/keV << " keV" << G4endl; |
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228 | G4cout << "Total final state: " << (photon1Energy+photon2Energy)/keV << |
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229 | " keV" << G4endl; |
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230 | G4cout << "-----------------------------------------------------------" << G4endl; |
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231 | } |
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232 | if (verboseLevel > 0) |
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233 | { |
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234 | G4double energyDiff = std::fabs(totalAvailableEnergy-photon1Energy-photon2Energy); |
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235 | if (energyDiff > 0.05*keV) |
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236 | G4cout << "Warning from G4PenelopeAnnihilation: problem with energy conservation: " << |
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237 | (photon1Energy+photon2Energy)/keV << |
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238 | " keV (final) vs. " << |
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239 | totalAvailableEnergy/keV << " keV (initial)" << G4endl; |
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240 | } |
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241 | return; |
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242 | } |
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243 | |
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244 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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245 | |
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246 | G4double G4PenelopeAnnihilationModel:: ComputeCrossSectionPerElectron(G4double energy) |
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247 | { |
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248 | // |
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249 | // Penelope model to calculate cross section for positron annihilation. |
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250 | // The annihilation cross section per electron is calculated according |
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251 | // to the Heitler formula |
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252 | // W. Heitler, The quantum theory of radiation, Oxford University Press (1954) |
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253 | // in the assumptions of electrons free and at rest. |
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254 | // |
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255 | G4double gamma = 1.0+std::max(energy,1.0*eV)/electron_mass_c2; |
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256 | G4double gamma2 = gamma*gamma; |
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257 | G4double f2 = gamma2-1.0; |
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258 | G4double f1 = std::sqrt(f2); |
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259 | G4double crossSection = fPielr2*((gamma2+4.0*gamma+1.0)*std::log(gamma+f1)/f2 |
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260 | - (gamma+3.0)/f1)/(gamma+1.0); |
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261 | return crossSection; |
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262 | } |
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