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25 //
26 //
27 // -------------------------------------------------------------------
28 //
29 // GEANT4 Class header file
30 //
31 //
32 // File name: G4BetheHeitlerModel
33 //
34 // Author: Vladimir Ivanchenko on base of Michel Maire code
35 //
36 // Creation date: 19.04.2005
37 //
38 // Modifications by Vladimir Ivanchenko, Michel Maire, Mihaly Novak
39 //
40 // Class Description:
41 //
42 // Implementation of gamma conversion to e+e- in the field of a nucleus
43 // For details see Physics Reference Manual
44
45 // -------------------------------------------------------------------
46 //
47
48 #ifndef G4BetheHeitlerModel_h
49 #define G4BetheHeitlerModel_h 1
50
51 #include "G4VEmModel.hh"
52 #include "G4PhysicsTable.hh"
53 #include "G4Log.hh"
54
55 #include <vector>
56
57 class G4ParticleChangeForGamma;
58 class G4Pow;
59 class G4EmElementXS;
60
61 class G4BetheHeitlerModel : public G4VEmModel
62 {
63
64 public:
65
66 explicit G4BetheHeitlerModel(const G4ParticleDefinition* p = nullptr,
67 const G4String& nam = "BetheHeitler");
68
69 ~G4BetheHeitlerModel() override;
70
71 void Initialise(const G4ParticleDefinition*, const G4DataVector&) override;
72
73 void InitialiseLocal(const G4ParticleDefinition*,
74 G4VEmModel* masterModel) override;
75
76 G4double ComputeCrossSectionPerAtom(const G4ParticleDefinition*,
77 G4double kinEnergy,
78 G4double Z,
79 G4double A=0.,
80 G4double cut=0.,
81 G4double emax=DBL_MAX) override;
82
83 void SampleSecondaries(std::vector<G4DynamicParticle*>*,
84 const G4MaterialCutsCouple*,
85 const G4DynamicParticle*,
86 G4double tmin,
87 G4double maxEnergy) override;
88
89 // hide assignment operator
90 G4BetheHeitlerModel & operator=(const G4BetheHeitlerModel &right) = delete;
91 G4BetheHeitlerModel(const G4BetheHeitlerModel&) = delete;
92
93 protected:
94
95 inline G4double ScreenFunction1(const G4double delta);
96
97 inline G4double ScreenFunction2(const G4double delta);
98
99 inline void ScreenFunction12(const G4double delta, G4double &f1, G4double &f2);
100
101 void InitialiseElementData();
102
103 struct ElementData {
104 G4double fDeltaMaxLow;
105 G4double fDeltaMaxHigh;
106 };
107
108 static const G4int gMaxZet;
109
110 G4Pow* fG4Calc;
111 const G4ParticleDefinition* fTheGamma;
112 const G4ParticleDefinition* fTheElectron;
113 const G4ParticleDefinition* fThePositron;
114 G4ParticleChangeForGamma* fParticleChange;
115 G4EmElementXS* fXSection{nullptr};
116
117 G4bool isFirstInstance{false};
118 G4bool useEPICS2017{false};
119
120 static std::vector<ElementData*> gElementData;
121 };
122
123 //
124 // Bethe screening functions for the elastic (coherent) scattering:
125 // Bethe's phi1, phi2 coherent screening functions were computed numerically
126 // by using (the universal) atomic form factors computed based on the Thomas-
127 // Fermi model of the atom (using numerical solution of the Thomas-Fermi
128 // screening function instead of Moliere's analytical approximation). The
129 // numerical results can be well approximated (better than Butcher & Messel
130 // especially near the delta=1 limit) by:
131 // ## if delta <= 1.4
132 // phi1(delta) = 20.806 - delta*(3.190 - 0.5710*delta)
133 // phi2(delta) = 20.234 - delta*(2.126 - 0.0903*delta)
134 // ## if delta > 1.4
135 // phi1(delta) = phi2(delta) = 21.0190 - 4.145*ln(delta + 0.958)
136 // with delta = 136mc^2kZ^{-1/3}/[E(Eg-E)] = 136Z^{-1/3}eps0/[eps(1-eps)] where
137 // Eg is the initial photon energy, E is the total energy transferred to one of
138 // the e-/e+ pair, eps0 = mc^2/Eg and eps = E/Eg.
139
140 // Compute the value of the screening function 3*PHI1(delta) - PHI2(delta):
141 inline G4double G4BetheHeitlerModel::ScreenFunction1(const G4double delta)
142 {
143 return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
144 : 42.184 - delta*(7.444 - 1.623*delta);
145 }
146
147 // Compute the value of the screening function 1.5*PHI1(delta) +0.5*PHI2(delta):
148 inline G4double G4BetheHeitlerModel::ScreenFunction2(const G4double delta)
149 {
150 return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
151 : 41.326 - delta*(5.848 - 0.902*delta);
152 }
153
154 // Same as ScreenFunction1 and ScreenFunction2 but computes them at once
155 inline void G4BetheHeitlerModel::ScreenFunction12(const G4double delta,
156 G4double &f1, G4double &f2)
157 {
158 if (delta > 1.4) {
159 f1 = 42.038 - 8.29*G4Log(delta + 0.958);
160 f2 = f1;
161 } else {
162 f1 = 42.184 - delta*(7.444 - 1.623*delta);
163 f2 = 41.326 - delta*(5.848 - 0.902*delta);
164 }
165 }
166
167 #endif
168