[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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[1055] | 26 | // $Id: G4eeToTwoGammaModel.cc,v 1.15 2009/04/09 18:41:18 vnivanch Exp $ |
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| 27 | // GEANT4 tag $Name: geant4-09-03-beta-cand-01 $ |
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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: G4eeToTwoGammaModel |
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| 35 | // |
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| 36 | // Author: Vladimir Ivanchenko on base of Michel Maire code |
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| 37 | // |
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| 38 | // Creation date: 02.08.2004 |
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| 39 | // |
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| 40 | // Modifications: |
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| 41 | // 08-04-05 Major optimisation of internal interfaces (V.Ivanchenko) |
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| 42 | // 18-04-05 Compute CrossSectionPerVolume (V.Ivanchenko) |
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| 43 | // 06-02-06 ComputeCrossSectionPerElectron, ComputeCrossSectionPerAtom (mma) |
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| 44 | // 29-06-06 Fix problem for zero energy incident positron (V.Ivanchenko) |
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| 45 | // 20-10-06 Add theGamma as a member (V.Ivanchenko) |
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| 46 | // |
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| 47 | // |
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| 48 | // Class Description: |
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| 49 | // |
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| 50 | // Implementation of e+ annihilation into 2 gamma |
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| 51 | // |
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| 52 | // The secondaries Gamma energies are sampled using the Heitler cross section. |
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| 53 | // |
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| 54 | // A modified version of the random number techniques of Butcher & Messel |
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| 55 | // is used (Nuc Phys 20(1960),15). |
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| 56 | // |
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| 57 | // GEANT4 internal units. |
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| 58 | // |
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| 59 | // Note 1: The initial electron is assumed free and at rest. |
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| 60 | // |
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| 61 | // Note 2: The annihilation processes producing one or more than two photons are |
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| 62 | // ignored, as negligible compared to the two photons process. |
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| 63 | |
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| 64 | |
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| 65 | |
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| 66 | // |
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| 67 | // ------------------------------------------------------------------- |
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| 68 | // |
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| 69 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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| 70 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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| 71 | |
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| 72 | #include "G4eeToTwoGammaModel.hh" |
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| 73 | #include "G4TrackStatus.hh" |
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| 74 | #include "G4Electron.hh" |
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| 75 | #include "G4Positron.hh" |
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| 76 | #include "G4Gamma.hh" |
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| 77 | #include "Randomize.hh" |
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| 78 | #include "G4ParticleChangeForGamma.hh" |
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| 79 | |
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| 80 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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| 81 | |
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| 82 | using namespace std; |
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| 83 | |
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| 84 | G4eeToTwoGammaModel::G4eeToTwoGammaModel(const G4ParticleDefinition*, |
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| 85 | const G4String& nam) |
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| 86 | : G4VEmModel(nam), |
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| 87 | pi_rcl2(pi*classic_electr_radius*classic_electr_radius), |
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| 88 | isInitialised(false) |
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| 89 | { |
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| 90 | theGamma = G4Gamma::Gamma(); |
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| 91 | } |
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| 92 | |
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| 93 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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| 94 | |
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| 95 | G4eeToTwoGammaModel::~G4eeToTwoGammaModel() |
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| 96 | {} |
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| 97 | |
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| 98 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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| 99 | |
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| 100 | void G4eeToTwoGammaModel::Initialise(const G4ParticleDefinition*, |
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| 101 | const G4DataVector&) |
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| 102 | { |
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| 103 | if(isInitialised) return; |
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[1055] | 104 | fParticleChange = GetParticleChangeForGamma(); |
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[819] | 105 | isInitialised = true; |
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| 106 | } |
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| 107 | |
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| 108 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 109 | |
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| 110 | G4double G4eeToTwoGammaModel::ComputeCrossSectionPerElectron( |
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| 111 | const G4ParticleDefinition*, |
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| 112 | G4double kineticEnergy, |
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| 113 | G4double, G4double) |
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| 114 | { |
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| 115 | // Calculates the cross section per electron of annihilation into two photons |
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| 116 | // from the Heilter formula. |
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| 117 | |
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| 118 | G4double tau = kineticEnergy/electron_mass_c2; |
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| 119 | G4double gam = tau + 1.0; |
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| 120 | G4double gamma2= gam*gam; |
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| 121 | G4double bg2 = tau * (tau+2.0); |
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| 122 | G4double bg = sqrt(bg2); |
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| 123 | |
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| 124 | G4double cross = pi_rcl2*((gamma2+4*gam+1.)*log(gam+bg) - (gam+3.)*bg) |
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| 125 | / (bg2*(gam+1.)); |
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| 126 | return cross; |
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| 127 | } |
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| 128 | |
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| 129 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 130 | |
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| 131 | G4double G4eeToTwoGammaModel::ComputeCrossSectionPerAtom( |
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| 132 | const G4ParticleDefinition* p, |
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| 133 | G4double kineticEnergy, G4double Z, |
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| 134 | G4double, G4double, G4double) |
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| 135 | { |
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| 136 | // Calculates the cross section per atom of annihilation into two photons |
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| 137 | |
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| 138 | G4double cross = Z*ComputeCrossSectionPerElectron(p,kineticEnergy); |
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| 139 | return cross; |
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| 140 | } |
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| 141 | |
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| 142 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 143 | |
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| 144 | G4double G4eeToTwoGammaModel::CrossSectionPerVolume( |
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| 145 | const G4Material* material, |
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| 146 | const G4ParticleDefinition* p, |
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| 147 | G4double kineticEnergy, |
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| 148 | G4double, G4double) |
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| 149 | { |
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| 150 | // Calculates the cross section per volume of annihilation into two photons |
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| 151 | |
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| 152 | G4double eDensity = material->GetElectronDensity(); |
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| 153 | G4double cross = eDensity*ComputeCrossSectionPerElectron(p,kineticEnergy); |
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| 154 | return cross; |
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| 155 | } |
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| 156 | |
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| 157 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 158 | |
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| 159 | void G4eeToTwoGammaModel::SampleSecondaries(vector<G4DynamicParticle*>* vdp, |
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| 160 | const G4MaterialCutsCouple*, |
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| 161 | const G4DynamicParticle* dp, |
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| 162 | G4double, |
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| 163 | G4double) |
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| 164 | { |
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| 165 | G4double PositKinEnergy = dp->GetKineticEnergy(); |
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| 166 | |
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| 167 | // Case at rest |
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| 168 | if(PositKinEnergy == 0.0) { |
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| 169 | G4double cost = 2.*G4UniformRand()-1.; |
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| 170 | G4double sint = sqrt((1. - cost)*(1. + cost)); |
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| 171 | G4double phi = twopi * G4UniformRand(); |
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| 172 | G4ThreeVector dir (sint*cos(phi), sint*sin(phi), cost); |
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| 173 | G4DynamicParticle* aGamma1 = new G4DynamicParticle(theGamma, |
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| 174 | dir, electron_mass_c2); |
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| 175 | G4DynamicParticle* aGamma2 = new G4DynamicParticle(theGamma, |
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| 176 | -dir, electron_mass_c2); |
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| 177 | vdp->push_back(aGamma1); |
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| 178 | vdp->push_back(aGamma2); |
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| 179 | |
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| 180 | } else { |
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| 181 | |
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| 182 | G4ThreeVector PositDirection = dp->GetMomentumDirection(); |
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| 183 | |
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| 184 | G4double tau = PositKinEnergy/electron_mass_c2; |
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| 185 | G4double gam = tau + 1.0; |
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| 186 | G4double tau2 = tau + 2.0; |
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| 187 | G4double sqgrate = sqrt(tau/tau2)*0.5; |
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| 188 | G4double sqg2m1 = sqrt(tau*tau2); |
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| 189 | |
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| 190 | // limits of the energy sampling |
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| 191 | G4double epsilmin = 0.5 - sqgrate; |
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| 192 | G4double epsilmax = 0.5 + sqgrate; |
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| 193 | G4double epsilqot = epsilmax/epsilmin; |
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| 194 | |
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| 195 | // |
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| 196 | // sample the energy rate of the created gammas |
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| 197 | // |
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| 198 | G4double epsil, greject; |
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| 199 | |
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| 200 | do { |
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| 201 | epsil = epsilmin*pow(epsilqot,G4UniformRand()); |
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| 202 | greject = 1. - epsil + (2.*gam*epsil-1.)/(epsil*tau2*tau2); |
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| 203 | } while( greject < G4UniformRand() ); |
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| 204 | |
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| 205 | // |
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| 206 | // scattered Gamma angles. ( Z - axis along the parent positron) |
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| 207 | // |
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| 208 | |
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| 209 | G4double cost = (epsil*tau2-1.)/(epsil*sqg2m1); |
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| 210 | if(std::abs(cost) > 1.0) { |
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| 211 | G4cout << "### G4eeToTwoGammaModel WARNING cost= " << cost |
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| 212 | << " positron Ekin(MeV)= " << PositKinEnergy |
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| 213 | << " gamma epsil= " << epsil |
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| 214 | << G4endl; |
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| 215 | if(cost > 1.0) cost = 1.0; |
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| 216 | else cost = -1.0; |
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| 217 | } |
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| 218 | G4double sint = sqrt((1.+cost)*(1.-cost)); |
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| 219 | G4double phi = twopi * G4UniformRand(); |
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| 220 | |
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| 221 | G4double dirx = sint*cos(phi) , diry = sint*sin(phi) , dirz = cost; |
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| 222 | |
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| 223 | // |
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| 224 | // kinematic of the created pair |
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| 225 | // |
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| 226 | |
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| 227 | G4double TotalAvailableEnergy = PositKinEnergy + 2.0*electron_mass_c2; |
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| 228 | G4double Phot1Energy = epsil*TotalAvailableEnergy; |
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| 229 | |
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| 230 | G4ThreeVector Phot1Direction (dirx, diry, dirz); |
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| 231 | Phot1Direction.rotateUz(PositDirection); |
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| 232 | G4DynamicParticle* aGamma1 = |
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| 233 | new G4DynamicParticle (theGamma,Phot1Direction, Phot1Energy); |
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| 234 | vdp->push_back(aGamma1); |
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| 235 | |
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| 236 | G4double Phot2Energy =(1.-epsil)*TotalAvailableEnergy; |
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| 237 | G4double PositP= sqrt(PositKinEnergy*(PositKinEnergy+2.*electron_mass_c2)); |
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| 238 | G4ThreeVector dir = PositDirection*PositP - Phot1Direction*Phot1Energy; |
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| 239 | G4ThreeVector Phot2Direction = dir.unit(); |
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| 240 | |
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| 241 | // create G4DynamicParticle object for the particle2 |
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| 242 | G4DynamicParticle* aGamma2= |
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| 243 | new G4DynamicParticle (theGamma,Phot2Direction, Phot2Energy); |
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| 244 | vdp->push_back(aGamma2); |
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| 245 | /* |
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| 246 | G4cout << "Annihilation in fly: e0= " << PositKinEnergy |
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| 247 | << " m= " << electron_mass_c2 |
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| 248 | << " e1= " << Phot1Energy |
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| 249 | << " e2= " << Phot2Energy << " dir= " << dir |
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| 250 | << " -> " << Phot1Direction << " " |
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| 251 | << Phot2Direction << G4endl; |
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| 252 | */ |
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| 253 | } |
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| 254 | fParticleChange->SetProposedKineticEnergy(0.); |
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| 255 | fParticleChange->ProposeTrackStatus(fStopAndKill); |
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| 256 | } |
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| 257 | |
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| 258 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... |
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