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G4DipBustGenerator.cc
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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()
69 {}
70 
71 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
72 
73 G4double G4DipBustGenerator::SampleCosTheta(const G4double kinEnergy)
74 {
75  const G4double c = 4. - 8.*G4UniformRand();
76  const G4double delta = 0.5*(std::sqrt(c*c+4.) + std::abs(c));
77  const G4double signc = (c < 0.) ? -1.0 : 1.0;
78  // const G4double cofA = -signc*G4Exp(G4Log(delta)/3.0);
79  const G4double cofA = -signc*G4Pow::GetInstance()->A13(delta);
80  const G4double cosTheta = std::min(1.,std::max(-1.,cofA - 1./cofA));
81  const G4double tau = kinEnergy/CLHEP::electron_mass_c2;
82  const G4double beta = std::sqrt(tau*(tau + 2.))/(tau + 1.);
83 
84  return (cosTheta + beta)/(1. + cosTheta*beta);
85 }
86 
87 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
88 
89 G4ThreeVector&
90 G4DipBustGenerator::SampleDirection(const G4DynamicParticle* dp, G4double,
91  G4int, const G4Material*)
92 {
93  const G4double cosTheta = SampleCosTheta(dp->GetKineticEnergy());
94 
95  const G4double sinTheta = std::sqrt((1. - cosTheta)*(1. + cosTheta));
96  const G4double phi = CLHEP::twopi*G4UniformRand();
97 
98  fLocalDirection.set(sinTheta*std::cos(phi), sinTheta*std::sin(phi),cosTheta);
99  fLocalDirection.rotateUz(dp->GetMomentumDirection());
100 
101  return fLocalDirection;
102 }
103 
104 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
105 
106 G4double G4DipBustGenerator::PolarAngle(G4double eTkin,
107  G4double, // final_energy
108  G4int ) // Z
109 {
110  const G4double cosTheta = SampleCosTheta(eTkin);
111  G4double theta = std::acos(cosTheta);
112  theta = std::min(std::max(theta, 0.), CLHEP::pi);
113  return theta;
114 }
115 
116 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
117 
118 void G4DipBustGenerator::SamplePairDirections(const G4DynamicParticle* dp,
119  G4double elecKinEnergy,
120  G4double posiKinEnergy,
121  G4ThreeVector& dirElectron,
122  G4ThreeVector& dirPositron,
123  G4int, const G4Material*)
124 {
125  const G4double phi = CLHEP::twopi * G4UniformRand();
126  const G4double sinp = std::sin(phi);
127  const G4double cosp = std::cos(phi);
128 
129  G4double cost = SampleCosTheta(elecKinEnergy);
130  G4double sint = std::sqrt((1. - cost)*(1. + cost));
131 
132  dirElectron.set(sint*cosp, sint*sinp, cost);
133  dirElectron.rotateUz(dp->GetMomentumDirection());
134 
135  cost = SampleCosTheta(posiKinEnergy);
136  sint = std::sqrt((1. - cost)*(1. + cost));
137 
138  dirPositron.set(-sint*cosp, -sint*sinp, cost);
139  dirPositron.rotateUz(dp->GetMomentumDirection());
140 }
141 
142 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
143 
144 void G4DipBustGenerator::PrintGeneratorInformation() const
145 {
146  G4cout << "\n" << G4endl;
147  G4cout << "Angular Generator based on classical formula from" << G4endl;
148  G4cout << "J.D. Jackson, Classical Electrodynamics, Wiley, New York 1975"
149  << G4endl;
150 }
151 
152 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....