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25 //
26 //
27 // -------------------------------------------------------------------
28 //
29 // GEANT4 Class file
30 //
31 //
32 // File name: G4DipBustGenerator
33 //
34 // Author: Vladimir Grichine
35 //
36 // Creation date: 17 May 2011
37 //
38 // Modifications:
39 //
40 // 17.07.2018 optimisations, using G4Pow in SampleCosTheta() method M.Novak
41 //
42 // Class Description:
43 //
44 // Bremsstrahlung Angular Distribution Generation
45 // suggested the dipole approximation in the rest frame of electron
46 // busted in the laboratory frame.
47 //
48 // Class Description: End
49 //
50 // -------------------------------------------------------------------
51 //
52
53 #include "G4DipBustGenerator.hh"
54 #include "Randomize.hh"
55 // #include "G4Log.hh"
56 // #include "G4Exp.hh"
57 #include "G4Pow.hh"
58 #include <CLHEP/Units/PhysicalConstants.h>
59
60 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
61
62 G4DipBustGenerator::G4DipBustGenerator(const G4String&)
63 : G4VEmAngularDistribution("DipBustGen")
64 {}
65
66 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
67
68 G4DipBustGenerator::~G4DipBustGenerator() = default;
69
70 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
71
72 G4double G4DipBustGenerator::SampleCosTheta(const G4double kinEnergy)
73 {
74 const G4double c = 4. - 8.*G4UniformRand();
75 const G4double delta = 0.5*(std::sqrt(c*c+4.) + std::abs(c));
76 const G4double signc = (c < 0.) ? -1.0 : 1.0;
77 // const G4double cofA = -signc*G4Exp(G4Log(delta)/3.0);
78 const G4double cofA = -signc*G4Pow::GetInstance()->A13(delta);
79 const G4double cosTheta = std::min(1.,std::max(-1.,cofA - 1./cofA));
80 const G4double tau = kinEnergy/CLHEP::electron_mass_c2;
81 const G4double beta = std::sqrt(tau*(tau + 2.))/(tau + 1.);
82
83 return (cosTheta + beta)/(1. + cosTheta*beta);
84 }
85
86 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
87
88 G4ThreeVector&
89 G4DipBustGenerator::SampleDirection(const G4DynamicParticle* dp, G4double,
90 G4int, const G4Material*)
91 {
92 const G4double cosTheta = SampleCosTheta(dp->GetKineticEnergy());
93
94 const G4double sinTheta = std::sqrt((1. - cosTheta)*(1. + cosTheta));
95 const G4double phi = CLHEP::twopi*G4UniformRand();
96
97 fLocalDirection.set(sinTheta*std::cos(phi), sinTheta*std::sin(phi),cosTheta);
98 fLocalDirection.rotateUz(dp->GetMomentumDirection());
99
100 return fLocalDirection;
101 }
102
103 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
104
105 G4double G4DipBustGenerator::PolarAngle(G4double eTkin,
106 G4double, // final_energy
107 G4int ) // Z
108 {
109 const G4double cosTheta = SampleCosTheta(eTkin);
110 G4double theta = std::acos(cosTheta);
111 theta = std::min(std::max(theta, 0.), CLHEP::pi);
112 return theta;
113 }
114
115 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
116
117 void G4DipBustGenerator::SamplePairDirections(const G4DynamicParticle* dp,
118 G4double elecKinEnergy,
119 G4double posiKinEnergy,
120 G4ThreeVector& dirElectron,
121 G4ThreeVector& dirPositron,
122 G4int, const G4Material*)
123 {
124 const G4double phi = CLHEP::twopi * G4UniformRand();
125 const G4double sinp = std::sin(phi);
126 const G4double cosp = std::cos(phi);
127
128 G4double cost = SampleCosTheta(elecKinEnergy);
129 G4double sint = std::sqrt((1. - cost)*(1. + cost));
130
131 dirElectron.set(sint*cosp, sint*sinp, cost);
132 dirElectron.rotateUz(dp->GetMomentumDirection());
133
134 cost = SampleCosTheta(posiKinEnergy);
135 sint = std::sqrt((1. - cost)*(1. + cost));
136
137 dirPositron.set(-sint*cosp, -sint*sinp, cost);
138 dirPositron.rotateUz(dp->GetMomentumDirection());
139 }
140
141 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
142
143 void G4DipBustGenerator::PrintGeneratorInformation() const
144 {
145 G4cout << "\n" << G4endl;
146 G4cout << "Angular Generator based on classical formula from" << G4endl;
147 G4cout << "J.D. Jackson, Classical Electrodynamics, Wiley, New York 1975"
148 << G4endl;
149 }
150
151 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
152