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: G4BetheHeitlerModel.cc,v 1.15 2010/10/25 19:02:32 vnivanch Exp $ |
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27 | // GEANT4 tag $Name: emstand-V09-03-24 $ |
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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: G4BetheHeitlerModel |
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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: 15.03.2005 |
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39 | // |
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40 | // Modifications: |
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41 | // 18-04-05 Use G4ParticleChangeForGamma (V.Ivantchenko) |
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42 | // 24-06-05 Increase number of bins to 200 (V.Ivantchenko) |
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43 | // 16-11-05 replace shootBit() by G4UniformRand() mma |
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44 | // 04-12-05 SetProposedKineticEnergy(0.) for the killed photon (mma) |
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45 | // 20-02-07 SelectRandomElement is called for any initial gamma energy |
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46 | // in order to have selected element for polarized model (VI) |
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47 | // 25-10-10 Removed unused table, added element selector (VI) |
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48 | // |
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49 | // Class Description: |
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50 | // |
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51 | // ------------------------------------------------------------------- |
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52 | // |
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53 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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54 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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55 | |
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56 | #include "G4BetheHeitlerModel.hh" |
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57 | #include "G4Electron.hh" |
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58 | #include "G4Positron.hh" |
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59 | #include "G4Gamma.hh" |
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60 | #include "Randomize.hh" |
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61 | #include "G4ParticleChangeForGamma.hh" |
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62 | |
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63 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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64 | |
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65 | using namespace std; |
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66 | |
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67 | G4BetheHeitlerModel::G4BetheHeitlerModel(const G4ParticleDefinition*, |
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68 | const G4String& nam) |
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69 | : G4VEmModel(nam) |
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70 | { |
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71 | fParticleChange = 0; |
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72 | theGamma = G4Gamma::Gamma(); |
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73 | thePositron = G4Positron::Positron(); |
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74 | theElectron = G4Electron::Electron(); |
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75 | } |
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76 | |
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77 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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78 | |
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79 | G4BetheHeitlerModel::~G4BetheHeitlerModel() |
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80 | {} |
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81 | |
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82 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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83 | |
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84 | void G4BetheHeitlerModel::Initialise(const G4ParticleDefinition* p, |
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85 | const G4DataVector& cuts) |
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86 | { |
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87 | if(!fParticleChange) { fParticleChange = GetParticleChangeForGamma(); } |
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88 | InitialiseElementSelectors(p, cuts); |
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89 | } |
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90 | |
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91 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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92 | |
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93 | G4double |
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94 | G4BetheHeitlerModel::ComputeCrossSectionPerAtom(const G4ParticleDefinition*, |
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95 | G4double GammaEnergy, G4double Z, |
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96 | G4double, G4double, G4double) |
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97 | // Calculates the microscopic cross section in GEANT4 internal units. |
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98 | // A parametrized formula from L. Urban is used to estimate |
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99 | // the total cross section. |
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100 | // It gives a good description of the data from 1.5 MeV to 100 GeV. |
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101 | // below 1.5 MeV: sigma=sigma(1.5MeV)*(GammaEnergy-2electronmass) |
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102 | // *(GammaEnergy-2electronmass) |
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103 | { |
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104 | static const G4double GammaEnergyLimit = 1.5*MeV; |
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105 | G4double CrossSection = 0.0 ; |
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106 | if ( Z < 0.9 || GammaEnergy <= 2.0*electron_mass_c2 ) { return CrossSection; } |
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107 | |
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108 | static const G4double |
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109 | a0= 8.7842e+2*microbarn, a1=-1.9625e+3*microbarn, a2= 1.2949e+3*microbarn, |
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110 | a3=-2.0028e+2*microbarn, a4= 1.2575e+1*microbarn, a5=-2.8333e-1*microbarn; |
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111 | |
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112 | static const G4double |
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113 | b0=-1.0342e+1*microbarn, b1= 1.7692e+1*microbarn, b2=-8.2381 *microbarn, |
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114 | b3= 1.3063 *microbarn, b4=-9.0815e-2*microbarn, b5= 2.3586e-3*microbarn; |
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115 | |
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116 | static const G4double |
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117 | c0=-4.5263e+2*microbarn, c1= 1.1161e+3*microbarn, c2=-8.6749e+2*microbarn, |
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118 | c3= 2.1773e+2*microbarn, c4=-2.0467e+1*microbarn, c5= 6.5372e-1*microbarn; |
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119 | |
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120 | G4double GammaEnergySave = GammaEnergy; |
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121 | if (GammaEnergy < GammaEnergyLimit) { GammaEnergy = GammaEnergyLimit; } |
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122 | |
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123 | G4double X=log(GammaEnergy/electron_mass_c2), X2=X*X, X3=X2*X, X4=X3*X, X5=X4*X; |
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124 | |
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125 | G4double F1 = a0 + a1*X + a2*X2 + a3*X3 + a4*X4 + a5*X5, |
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126 | F2 = b0 + b1*X + b2*X2 + b3*X3 + b4*X4 + b5*X5, |
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127 | F3 = c0 + c1*X + c2*X2 + c3*X3 + c4*X4 + c5*X5; |
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128 | |
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129 | CrossSection = (Z + 1.)*(F1*Z + F2*Z*Z + F3); |
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130 | |
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131 | if (GammaEnergySave < GammaEnergyLimit) { |
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132 | |
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133 | X = (GammaEnergySave - 2.*electron_mass_c2) |
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134 | / (GammaEnergyLimit - 2.*electron_mass_c2); |
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135 | CrossSection *= X*X; |
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136 | } |
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137 | |
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138 | if (CrossSection < 0.) { CrossSection = 0.; } |
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139 | return CrossSection; |
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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 | void G4BetheHeitlerModel::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect, |
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145 | const G4MaterialCutsCouple* couple, |
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146 | const G4DynamicParticle* aDynamicGamma, |
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147 | G4double, |
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148 | G4double) |
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149 | // The secondaries e+e- energies are sampled using the Bethe - Heitler |
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150 | // cross sections with Coulomb correction. |
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151 | // A modified version of the random number techniques of Butcher & Messel |
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152 | // is used (Nuc Phys 20(1960),15). |
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153 | // |
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154 | // GEANT4 internal units. |
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155 | // |
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156 | // Note 1 : Effects due to the breakdown of the Born approximation at |
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157 | // low energy are ignored. |
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158 | // Note 2 : The differential cross section implicitly takes account of |
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159 | // pair creation in both nuclear and atomic electron fields. |
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160 | // However triplet prodution is not generated. |
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161 | { |
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162 | const G4Material* aMaterial = couple->GetMaterial(); |
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163 | |
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164 | G4double GammaEnergy = aDynamicGamma->GetKineticEnergy(); |
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165 | G4ParticleMomentum GammaDirection = aDynamicGamma->GetMomentumDirection(); |
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166 | |
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167 | G4double epsil ; |
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168 | G4double epsil0 = electron_mass_c2/GammaEnergy ; |
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169 | if(epsil0 > 1.0) { return; } |
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170 | |
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171 | // do it fast if GammaEnergy < 2. MeV |
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172 | static const G4double Egsmall=2.*MeV; |
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173 | |
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174 | // select randomly one element constituing the material |
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175 | const G4Element* anElement = SelectRandomAtom(aMaterial, theGamma, GammaEnergy); |
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176 | |
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177 | if (GammaEnergy < Egsmall) { |
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178 | |
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179 | epsil = epsil0 + (0.5-epsil0)*G4UniformRand(); |
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180 | |
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181 | } else { |
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182 | // now comes the case with GammaEnergy >= 2. MeV |
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183 | |
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184 | // Extract Coulomb factor for this Element |
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185 | G4double FZ = 8.*(anElement->GetIonisation()->GetlogZ3()); |
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186 | if (GammaEnergy > 50.*MeV) { FZ += 8.*(anElement->GetfCoulomb()); } |
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187 | |
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188 | // limits of the screening variable |
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189 | G4double screenfac = 136.*epsil0/(anElement->GetIonisation()->GetZ3()); |
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190 | G4double screenmax = exp ((42.24 - FZ)/8.368) - 0.952 ; |
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191 | G4double screenmin = min(4.*screenfac,screenmax); |
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192 | |
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193 | // limits of the energy sampling |
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194 | G4double epsil1 = 0.5 - 0.5*sqrt(1. - screenmin/screenmax) ; |
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195 | G4double epsilmin = max(epsil0,epsil1) , epsilrange = 0.5 - epsilmin; |
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196 | |
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197 | // |
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198 | // sample the energy rate of the created electron (or positron) |
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199 | // |
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200 | //G4double epsil, screenvar, greject ; |
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201 | G4double screenvar, greject ; |
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202 | |
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203 | G4double F10 = ScreenFunction1(screenmin) - FZ; |
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204 | G4double F20 = ScreenFunction2(screenmin) - FZ; |
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205 | G4double NormF1 = max(F10*epsilrange*epsilrange,0.); |
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206 | G4double NormF2 = max(1.5*F20,0.); |
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207 | |
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208 | do { |
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209 | if ( NormF1/(NormF1+NormF2) > G4UniformRand() ) { |
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210 | epsil = 0.5 - epsilrange*pow(G4UniformRand(), 0.333333); |
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211 | screenvar = screenfac/(epsil*(1-epsil)); |
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212 | greject = (ScreenFunction1(screenvar) - FZ)/F10; |
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213 | |
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214 | } else { |
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215 | epsil = epsilmin + epsilrange*G4UniformRand(); |
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216 | screenvar = screenfac/(epsil*(1-epsil)); |
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217 | greject = (ScreenFunction2(screenvar) - FZ)/F20; |
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218 | } |
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219 | |
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220 | } while( greject < G4UniformRand() ); |
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221 | |
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222 | } // end of epsil sampling |
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223 | |
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224 | // |
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225 | // fixe charges randomly |
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226 | // |
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227 | |
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228 | G4double ElectTotEnergy, PositTotEnergy; |
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229 | if (G4UniformRand() > 0.5) { |
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230 | |
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231 | ElectTotEnergy = (1.-epsil)*GammaEnergy; |
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232 | PositTotEnergy = epsil*GammaEnergy; |
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233 | |
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234 | } else { |
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235 | |
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236 | PositTotEnergy = (1.-epsil)*GammaEnergy; |
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237 | ElectTotEnergy = epsil*GammaEnergy; |
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238 | } |
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239 | |
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240 | // |
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241 | // scattered electron (positron) angles. ( Z - axis along the parent photon) |
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242 | // |
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243 | // universal distribution suggested by L. Urban |
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244 | // (Geant3 manual (1993) Phys211), |
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245 | // derived from Tsai distribution (Rev Mod Phys 49,421(1977)) |
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246 | |
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247 | G4double u; |
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248 | const G4double a1 = 0.625 , a2 = 3.*a1 , d = 27. ; |
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249 | |
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250 | if (9./(9.+d) >G4UniformRand()) u= - log(G4UniformRand()*G4UniformRand())/a1; |
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251 | else u= - log(G4UniformRand()*G4UniformRand())/a2; |
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252 | |
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253 | G4double TetEl = u*electron_mass_c2/ElectTotEnergy; |
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254 | G4double TetPo = u*electron_mass_c2/PositTotEnergy; |
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255 | G4double Phi = twopi * G4UniformRand(); |
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256 | G4double dxEl= sin(TetEl)*cos(Phi),dyEl= sin(TetEl)*sin(Phi),dzEl=cos(TetEl); |
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257 | G4double dxPo=-sin(TetPo)*cos(Phi),dyPo=-sin(TetPo)*sin(Phi),dzPo=cos(TetPo); |
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258 | |
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259 | // |
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260 | // kinematic of the created pair |
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261 | // |
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262 | // the electron and positron are assumed to have a symetric |
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263 | // angular distribution with respect to the Z axis along the parent photon. |
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264 | |
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265 | G4double ElectKineEnergy = max(0.,ElectTotEnergy - electron_mass_c2); |
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266 | |
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267 | G4ThreeVector ElectDirection (dxEl, dyEl, dzEl); |
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268 | ElectDirection.rotateUz(GammaDirection); |
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269 | |
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270 | // create G4DynamicParticle object for the particle1 |
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271 | G4DynamicParticle* aParticle1= new G4DynamicParticle( |
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272 | theElectron,ElectDirection,ElectKineEnergy); |
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273 | |
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274 | // the e+ is always created (even with Ekine=0) for further annihilation. |
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275 | |
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276 | G4double PositKineEnergy = max(0.,PositTotEnergy - electron_mass_c2); |
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277 | |
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278 | G4ThreeVector PositDirection (dxPo, dyPo, dzPo); |
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279 | PositDirection.rotateUz(GammaDirection); |
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280 | |
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281 | // create G4DynamicParticle object for the particle2 |
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282 | G4DynamicParticle* aParticle2= new G4DynamicParticle( |
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283 | thePositron,PositDirection,PositKineEnergy); |
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284 | |
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285 | // Fill output vector |
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286 | fvect->push_back(aParticle1); |
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287 | fvect->push_back(aParticle2); |
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288 | |
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289 | // kill incident photon |
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290 | fParticleChange->SetProposedKineticEnergy(0.); |
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291 | fParticleChange->ProposeTrackStatus(fStopAndKill); |
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292 | } |
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293 | |
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294 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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