[819] | 1 | // |
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| 2 | // ******************************************************************** |
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| 3 | // * License and Disclaimer * |
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| 4 | // * * |
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| 5 | // * The Geant4 software is copyright of the Copyright Holders of * |
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| 6 | // * the Geant4 Collaboration. It is provided under the terms and * |
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| 7 | // * conditions of the Geant4 Software License, included in the file * |
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| 8 | // * LICENSE and available at http://cern.ch/geant4/license . These * |
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| 9 | // * include a list of copyright holders. * |
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| 10 | // * * |
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| 11 | // * Neither the authors of this software system, nor their employing * |
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| 12 | // * institutes,nor the agencies providing financial support for this * |
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| 13 | // * work make any representation or warranty, express or implied, * |
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| 14 | // * regarding this software system or assume any liability for its * |
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| 15 | // * use. Please see the license in the file LICENSE and URL above * |
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| 16 | // * for the full disclaimer and the limitation of liability. * |
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| 17 | // * * |
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| 18 | // * This code implementation is the result of the scientific and * |
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| 19 | // * technical work of the GEANT4 collaboration. * |
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| 20 | // * By using, copying, modifying or distributing the software (or * |
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| 21 | // * any work based on the software) you agree to acknowledge its * |
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| 22 | // * use in resulting scientific publications, and indicate your * |
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| 23 | // * acceptance of all terms of the Geant4 Software license. * |
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| 24 | // ******************************************************************** |
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| 25 | // |
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[1340] | 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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[819] | 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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[1340] | 45 | // 20-02-07 SelectRandomElement is called for any initial gamma energy |
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[819] | 46 | // in order to have selected element for polarized model (VI) |
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[1340] | 47 | // 25-10-10 Removed unused table, added element selector (VI) |
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[819] | 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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[1340] | 69 | : G4VEmModel(nam) |
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[819] | 70 | { |
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[961] | 71 | fParticleChange = 0; |
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[819] | 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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[1340] | 80 | {} |
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[819] | 81 | |
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| 82 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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| 83 | |
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[1340] | 84 | void G4BetheHeitlerModel::Initialise(const G4ParticleDefinition* p, |
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| 85 | const G4DataVector& cuts) |
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[819] | 86 | { |
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[1340] | 87 | if(!fParticleChange) { fParticleChange = GetParticleChangeForGamma(); } |
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| 88 | InitialiseElementSelectors(p, cuts); |
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[819] | 89 | } |
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| 90 | |
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| 91 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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| 92 | |
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[1340] | 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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[819] | 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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[1340] | 106 | if ( Z < 0.9 || GammaEnergy <= 2.0*electron_mass_c2 ) { return CrossSection; } |
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[819] | 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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[1340] | 121 | if (GammaEnergy < GammaEnergyLimit) { GammaEnergy = GammaEnergyLimit; } |
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[819] | 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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[1340] | 138 | if (CrossSection < 0.) { CrossSection = 0.; } |
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[819] | 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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[1340] | 169 | if(epsil0 > 1.0) { return; } |
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[819] | 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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[1340] | 186 | if (GammaEnergy > 50.*MeV) { FZ += 8.*(anElement->GetfCoulomb()); } |
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[819] | 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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