Geant4 Cross Reference |
1 // 1 2 // ******************************************* 3 // * License and Disclaimer 4 // * 5 // * The Geant4 software is copyright of th 6 // * the Geant4 Collaboration. It is provided 7 // * conditions of the Geant4 Software License 8 // * LICENSE and available at http://cern.ch/ 9 // * include a list of copyright holders. 10 // * 11 // * Neither the authors of this software syst 12 // * institutes,nor the agencies providing fin 13 // * work make any representation or warran 14 // * regarding this software system or assum 15 // * use. Please see the license in the file 16 // * for the full disclaimer and the limitatio 17 // * 18 // * This code implementation is the result 19 // * technical work of the GEANT4 collaboratio 20 // * By using, copying, modifying or distri 21 // * any work based on the software) you ag 22 // * use in resulting scientific publicati 23 // * acceptance of all terms of the Geant4 Sof 24 // ******************************************* 25 // 26 // 27 // GEANT4 Class file 28 // 29 // 30 // File name: G4AllisonPositronAtRestModel 31 // 32 // Author: Vladimir Ivanchenko 33 // 34 // Creation date: 14 May 2024 35 // 36 // ------------------------------------------- 37 // 38 39 #include "G4AllisonPositronAtRestModel.hh" 40 #include "G4DynamicParticle.hh" 41 #include "G4Material.hh" 42 #include "Randomize.hh" 43 #include "G4Gamma.hh" 44 #include "G4RandomDirection.hh" 45 #include "G4ThreeVector.hh" 46 #include "G4PhysicalConstants.hh" 47 #include "G4SystemOfUnits.hh" 48 49 //....oooOO0OOooo........oooOO0OOooo........oo 50 51 G4AllisonPositronAtRestModel::G4AllisonPositro 52 : G4VPositronAtRestModel("Allison") 53 {} 54 55 //....oooOO0OOooo........oooOO0OOooo........oo 56 57 void G4AllisonPositronAtRestModel::SampleSecon 58 std::vector<G4DynamicParticle*>& 59 G4double&, const G4Material* mate 60 { 61 const G4double eGamma = CLHEP::electron_mass 62 63 // In rest frame of positronium gammas are b 64 const G4ThreeVector& dir1 = G4RandomDirectio 65 const G4ThreeVector& dir2 = -dir1; 66 auto aGamma1 = new G4DynamicParticle(G4Gamma 67 auto aGamma2 = new G4DynamicParticle(G4Gamma 68 69 // In rest frame the gammas are polarised pe 70 // Pryce and Ward, Nature No 4065 (1947) p.4 71 // Snyder et al, Physical Review 73 (1948) p 72 G4ThreeVector pol1 = (G4RandomDirection().cr 73 G4ThreeVector pol2 = (pol1.cross(dir2)).unit 74 75 // A positron in matter slows down and combi 76 // make a neutral atom called positronium, a 77 // atom. I expect that when the energy of th 78 // less than the binding energy of positroni 79 // energetically favourable for an electron 80 // nearby atom or molecule to transfer and b 81 // ionic bond, leaving behind a mildly ionis 82 // would expect the positronium to come away 83 // few eV on average. In its para (spin 0) s 84 // photons, which in the rest frame of the p 85 // (back-to-back) due to momentum conservati 86 // positronium, photons will be not quite ba 87 88 // The positroniuim acquires an energy of or 89 // doesn't have time to thermalise. Neverthe 90 // energy distribution by a Maxwell-Boltzman 91 // of a more familiar concept of temperature 92 // of energy of translational motion, <KE>=3 93 // has a distribution exp(-mv^2/2kT), which 94 // and variance kT/m=2<KE>/3m, where m is th 95 96 const G4double meanEnergyPerIonPair = materi 97 const G4double& meanKE = meanEnergyPerIonPai 98 99 if (meanKE > 0.) { // Positronium has motio 100 // Mass of positronium 101 const G4double mass = 2.*CLHEP::electron_m 102 // Mean <KE>=3kT/2, as described above 103 // const G4double T = 2.*meanKE/(3.*k_Bolt 104 // Component velocities: Gaussian, varianc 105 const G4double sigmav = std::sqrt(2.*meanK 106 // This is in units where c=1 107 const G4double vx = G4RandGauss::shoot(0., 108 const G4double vy = G4RandGauss::shoot(0., 109 const G4double vz = G4RandGauss::shoot(0., 110 const G4ThreeVector v(vx,vy,vz); // In un 111 const G4ThreeVector& beta = v; // so be 112 aGamma1->Set4Momentum(aGamma1->Get4Momentu 113 aGamma2->Set4Momentum(aGamma2->Get4Momentu 114 115 // Rotate polarisation vectors 116 const G4ThreeVector& newDir1 = aGamma1->Ge 117 const G4ThreeVector& newDir2 = aGamma2->Ge 118 const G4ThreeVector& axis1 = dir1.cross(ne 119 const G4ThreeVector& axis2 = dir2.cross(ne 120 const G4double& angle1 = std::acos(dir1*ne 121 const G4double& angle2 = std::acos(dir2*ne 122 pol1.rotate(axis1, angle1); 123 pol2.rotate(axis2, angle2); 124 } 125 126 // use constructors optimal for massless par 127 aGamma1->SetPolarization(pol1); 128 aGamma2->SetPolarization(pol2); 129 130 secParticles.push_back(aGamma1); 131 secParticles.push_back(aGamma2); 132 } 133 134 //....oooOO0OOooo........oooOO0OOooo........oo 135 136 void G4AllisonPositronAtRestModel::PrintGenera 137 { 138 G4cout << "\n" << G4endl; 139 G4cout << "Allison AtRest positron 2-gamma a 140 G4cout << "Takes into account positronium mo 141 } 142 143 //....oooOO0OOooo........oooOO0OOooo........oo 144