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2 | // ******************************************************************** |
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15 | // * use. Please see the license in the file LICENSE and URL above * |
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18 | // * This code implementation is the result of the scientific and * |
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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 | // $Id: G4PolarizedComptonScattering.cc,v 1.16 2006/06/29 19:53:30 gunter Exp $ |
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28 | // GEANT4 tag $Name: geant4-09-01-patch-02 $ |
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29 | // |
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30 | // |
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31 | //---------- G4PolarizedComptonScattering physics process ---------------------- |
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32 | // by Vicente Lara, March 1998 |
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33 | // |
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34 | // ----------------------------------------------------------------------------- |
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35 | // Corrections by Rui Curado da Silva (Nov. 2000) |
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36 | // - Sampling of Phi |
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37 | // - Depolarization probability |
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38 | // |
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39 | // 13-07-01, DoIt: suppression of production cut for the electron (mma) |
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40 | // 20-09-01, DoIt: fminimalEnergy = 1*eV (mma) |
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41 | // 04-05-05, Inheritance from ComptonScattering52 (V.Ivanchenko) |
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42 | // 30-01-06, DoIt : return G4ComptonScattering52::PostStepDoIt(aTrack,aStep) mma |
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43 | // |
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44 | // ----------------------------------------------------------------------------- |
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45 | |
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46 | #include "G4PolarizedComptonScattering.hh" |
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47 | |
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48 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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49 | |
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50 | using namespace std; |
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51 | |
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52 | G4PolarizedComptonScattering::G4PolarizedComptonScattering( |
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53 | const G4String& processName) |
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54 | : G4ComptonScattering52 (processName) |
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55 | { } |
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56 | |
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57 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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58 | |
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59 | G4VParticleChange* G4PolarizedComptonScattering::PostStepDoIt( |
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60 | const G4Track& aTrack, |
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61 | const G4Step& aStep) |
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62 | // |
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63 | // The scattered gamma energy is sampled according to Klein - Nishina formula. |
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64 | // The random number techniques of Butcher & Messel are used |
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65 | // (Nuc Phys 20(1960),15). |
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66 | // GEANT4 internal units |
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67 | // |
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68 | // Note : Effects due to binding of atomic electrons are negliged. |
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69 | |
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70 | { |
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71 | aParticleChange.Initialize(aTrack); |
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72 | |
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73 | const G4DynamicParticle* aDynamicGamma = aTrack.GetDynamicParticle(); |
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74 | |
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75 | G4ThreeVector GammaPolarization0 = aDynamicGamma->GetPolarization(); |
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76 | |
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77 | if (std::abs(GammaPolarization0.mag() - 1.e0) > 1.e-14) |
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78 | return G4ComptonScattering52::PostStepDoIt(aTrack,aStep); |
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79 | |
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80 | G4double GammaEnergy0 = aDynamicGamma->GetKineticEnergy(); |
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81 | G4double E0_m = GammaEnergy0 / electron_mass_c2; |
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82 | |
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83 | G4ParticleMomentum GammaDirection0 = aDynamicGamma->GetMomentumDirection(); |
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84 | |
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85 | // |
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86 | // sample the energy rate of the scattered gamma |
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87 | // |
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88 | G4double epsilon, epsilonsq, onecost, sint2, greject; |
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89 | |
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90 | G4double epsilon0 = 1./(1. + 2*E0_m) , epsilon0sq = epsilon0*epsilon0; |
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91 | G4double alpha1 = - log(epsilon0) , alpha2 = 0.5*(1.- epsilon0sq); |
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92 | |
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93 | do { |
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94 | if (alpha1/(alpha1+alpha2) > G4UniformRand()) |
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95 | { epsilon = exp(-alpha1*G4UniformRand()); // epsilon0**r |
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96 | epsilonsq = epsilon*epsilon; } |
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97 | else { |
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98 | epsilonsq = epsilon0sq + (1.- epsilon0sq)*G4UniformRand(); |
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99 | epsilon = sqrt(epsilonsq); |
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100 | }; |
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101 | onecost = (1.- epsilon)/(epsilon*E0_m); |
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102 | sint2 = onecost*(2.-onecost); |
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103 | greject = 1. - epsilon*sint2/(1.+ epsilonsq); |
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104 | } while (greject < G4UniformRand()); |
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105 | |
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106 | |
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107 | // |
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108 | // Phi determination |
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109 | // |
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110 | G4double minimum=0., maximum=twopi, middle=0., resolution=0.001; |
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111 | G4double Rand = G4UniformRand(); |
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112 | |
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113 | int j = 0; |
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114 | while ((j < 100) && (std::abs(SetPhi(epsilon,sint2,middle,Rand)) > resolution)) |
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115 | { |
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116 | middle = (maximum + minimum)/2; |
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117 | if (SetPhi(epsilon,sint2,middle,Rand)* |
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118 | SetPhi(epsilon,sint2,minimum,Rand)<0) maximum = middle; |
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119 | else minimum = middle; |
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120 | j++; |
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121 | } |
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122 | |
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123 | // |
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124 | // scattered gamma angles. ( Z - axis along the parent gamma) |
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125 | // |
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126 | G4double cosTeta = 1. - onecost , sinTeta = sqrt (sint2); |
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127 | G4double Phi = middle; |
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128 | G4double dirx = sinTeta*cos(Phi), diry = sinTeta*sin(Phi), dirz = cosTeta; |
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129 | |
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130 | // |
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131 | // update G4VParticleChange for the scattered gamma |
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132 | // |
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133 | G4double GammaEnergy1 = epsilon*GammaEnergy0; |
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134 | |
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135 | // New polarization |
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136 | // |
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137 | G4ThreeVector GammaPolarization1 = SetNewPolarization(epsilon,sint2,Phi, |
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138 | cosTeta, |
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139 | GammaPolarization0); |
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140 | // Set new direction |
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141 | G4ThreeVector GammaDirection1 ( dirx,diry,dirz ); |
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142 | |
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143 | // Change reference frame. |
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144 | SystemOfRefChange(GammaDirection0,GammaDirection1, |
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145 | GammaPolarization0,GammaPolarization1); |
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146 | |
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147 | G4double localEnergyDeposit = 0.; |
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148 | |
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149 | if (GammaEnergy1 > fminimalEnergy) |
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150 | { |
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151 | aParticleChange.ProposeEnergy(GammaEnergy1); |
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152 | } |
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153 | else |
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154 | { |
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155 | localEnergyDeposit += GammaEnergy1; |
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156 | aParticleChange.ProposeEnergy(0.) ; |
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157 | aParticleChange.ProposeTrackStatus(fStopAndKill); |
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158 | } |
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159 | |
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160 | // |
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161 | // kinematic of the scattered electron |
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162 | // |
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163 | G4double ElecKineEnergy = GammaEnergy0 - GammaEnergy1; |
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164 | |
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165 | if (ElecKineEnergy > fminimalEnergy) |
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166 | { |
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167 | G4double ElecMomentum = sqrt(ElecKineEnergy* |
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168 | (ElecKineEnergy+2.*electron_mass_c2)); |
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169 | G4ThreeVector ElecDirection ( |
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170 | (GammaEnergy0*GammaDirection0 - GammaEnergy1*GammaDirection1) |
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171 | *(1./ElecMomentum)); |
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172 | |
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173 | // create G4DynamicParticle object for the electron. |
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174 | G4DynamicParticle* aElectron= new G4DynamicParticle ( |
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175 | G4Electron::Electron(),ElecDirection,ElecKineEnergy); |
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176 | aParticleChange.SetNumberOfSecondaries(1); |
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177 | aParticleChange.AddSecondary( aElectron ); |
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178 | } |
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179 | else |
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180 | { |
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181 | aParticleChange.SetNumberOfSecondaries(0); |
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182 | localEnergyDeposit += ElecKineEnergy; |
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183 | } |
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184 | |
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185 | aParticleChange.ProposeLocalEnergyDeposit(localEnergyDeposit); |
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186 | |
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187 | // Reset NbOfInteractionLengthLeft and return aParticleChange |
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188 | return G4VDiscreteProcess::PostStepDoIt( aTrack, aStep); |
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189 | } |
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190 | |
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191 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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192 | |
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193 | G4double G4PolarizedComptonScattering::SetPhi(G4double EnergyRate, |
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194 | G4double sinsqrth, |
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195 | G4double phi, |
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196 | G4double rand) |
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197 | { |
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198 | G4double cosphi = cos(phi), sinphi = sin(phi); |
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199 | G4double PhiDetermination = ((twopi*rand - phi) |
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200 | *(EnergyRate + 1./EnergyRate - sinsqrth)) |
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201 | + (sinsqrth*sinphi*cosphi); |
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202 | return PhiDetermination; |
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203 | } |
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204 | |
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205 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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206 | |
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207 | G4ThreeVector G4PolarizedComptonScattering::SetNewPolarization( |
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208 | G4double EnergyRate, |
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209 | G4double sinsqrth, |
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210 | G4double phi, |
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211 | G4double costheta, |
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212 | G4ThreeVector&) |
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213 | { |
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214 | G4double cosphi = cos(phi), sinphi = sin(phi); |
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215 | //// G4double ParallelIntensityPolar = EnergyRate + 1./EnergyRate |
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216 | //// + 2. - 4.*sinsqrth*cosphi*cosphi; |
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217 | G4double ParallelIntensityPolar = EnergyRate + 1./EnergyRate |
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218 | - 2.*sinsqrth*cosphi*cosphi; |
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219 | G4double PerpendiIntensityPolar = EnergyRate + 1./EnergyRate - 2.; |
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220 | G4double PolarizationDegree = sqrt(sinsqrth*sinphi*sinphi+costheta*costheta); |
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221 | G4double sintheta = sqrt(sinsqrth); |
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222 | |
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223 | G4ThreeVector GammaPolarization1; |
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224 | // depolarization probability (1-P) |
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225 | if ( G4UniformRand() > (PerpendiIntensityPolar/ParallelIntensityPolar) ) |
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226 | { |
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227 | // Parallel to initial polarization |
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228 | GammaPolarization1.setX(PolarizationDegree); |
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229 | GammaPolarization1.setY(-sinsqrth*sinphi*cosphi/PolarizationDegree); |
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230 | GammaPolarization1.setZ(-sintheta*costheta*cosphi/PolarizationDegree); |
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231 | |
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232 | } |
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233 | else |
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234 | { |
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235 | // Perpendicular to initial polarization |
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236 | GammaPolarization1.setX(0.); |
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237 | GammaPolarization1.setY(costheta/PolarizationDegree); |
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238 | GammaPolarization1.setZ(-sintheta*sinphi/PolarizationDegree); |
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239 | |
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240 | }; |
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241 | |
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242 | return GammaPolarization1; |
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243 | } |
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244 | |
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245 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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246 | |
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247 | void G4PolarizedComptonScattering::SystemOfRefChange(G4ThreeVector& Direction0, |
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248 | G4ThreeVector& Direction1, |
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249 | G4ThreeVector& Polarization0, |
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250 | G4ThreeVector& Polarization1) |
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251 | { |
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252 | // Angles for go back to the original RS |
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253 | G4double cosTeta0 = Direction0.cosTheta(), sinTeta0 = sin(Direction0.theta()); |
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254 | G4double cosPhi0 = cos(Direction0.phi()), sinPhi0 = sin(Direction0.phi()); |
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255 | |
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256 | |
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257 | |
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258 | G4double cosPsi, sinPsi; |
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259 | |
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260 | if (sinTeta0 != 0. ) |
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261 | { |
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262 | cosPsi = -Polarization0.z()/sinTeta0; |
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263 | if (cosPhi0 != 0.) |
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264 | sinPsi = (Polarization0.y() - cosTeta0*sinPhi0*cosPsi)/cosPhi0; |
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265 | else sinPsi = -Polarization0.x()/sinPhi0; |
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266 | |
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267 | } |
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268 | else |
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269 | { |
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270 | cosPsi = Polarization0.x()/cosTeta0; |
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271 | sinPsi = Polarization0.y(); |
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272 | } |
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273 | G4double Psi = atan(sinPsi/cosPsi); |
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274 | |
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275 | // Rotation along Z axe |
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276 | Direction1.rotateZ(Psi); |
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277 | // |
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278 | Direction1.rotateUz(Direction0); |
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279 | aParticleChange.ProposeMomentumDirection(Direction1); |
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280 | |
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281 | // 3 Euler angles rotation for scattered photon polarization |
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282 | Polarization1.rotateZ(Psi); |
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283 | Polarization1.rotateUz(Direction0); |
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284 | aParticleChange.ProposePolarization(Polarization1); |
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285 | |
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286 | } |
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287 | |
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288 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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