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G4BetheHeitlerModel.hh
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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 convertion 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 
58 class G4Pow;
59 
61 {
62 
63 public:
64 
65  explicit G4BetheHeitlerModel(const G4ParticleDefinition* p = 0,
66  const G4String& nam = "BetheHeitler");
67 
68  virtual ~G4BetheHeitlerModel();
69 
70  virtual void Initialise(const G4ParticleDefinition*,
71  const G4DataVector&) override;
72 
73  virtual void InitialiseLocal(const G4ParticleDefinition*,
74  G4VEmModel* masterModel) override;
75 
77  G4double kinEnergy,
78  G4double Z,
79  G4double A=0.,
80  G4double cut=0.,
81  G4double emax=DBL_MAX) override;
82 
83  virtual void SampleSecondaries(std::vector<G4DynamicParticle*>*,
84  const G4MaterialCutsCouple*,
85  const G4DynamicParticle*,
86  G4double tmin,
87  G4double maxEnergy) override;
88 
89 protected:
90 
91  inline G4double ScreenFunction1(const G4double delta);
92 
93  inline G4double ScreenFunction2(const G4double delta);
94 
95  inline void ScreenFunction12(const G4double delta, G4double &f1, G4double &f2);
96 
97  void InitialiseElementData();
98 
99  struct ElementData {
102  };
103 
104 private:
105 
106  // hide assignment operator
108  G4BetheHeitlerModel(const G4BetheHeitlerModel&) = delete;
109 
110 protected:
111 
112  static const G4int gMaxZet;
113 
119 
120  static std::vector<ElementData*> gElementData;
121 };
122 
123 
124 //
125 // Bethe screening functions for the elastic (coherent) scattering:
126 // Bethe's phi1, phi2 coherent screening functions were computed numerically
127 // by using (the universal) atomic form factors computed based on the Thomas-
128 // Fermi model of the atom (using numerical solution of the Thomas-Fermi
129 // screening function instead of Moliere's analytical approximation). The
130 // numerical results can be well approximated (better than Butcher & Messel
131 // especially near the delta=1 limit) by:
132 // ## if delta <= 1.4
133 // phi1(delta) = 20.806 - delta*(3.190 - 0.5710*delta)
134 // phi2(delta) = 20.234 - delta*(2.126 - 0.0903*delta)
135 // ## if delta > 1.4
136 // phi1(delta) = phi2(delta) = 21.0190 - 4.145*ln(delta + 0.958)
137 // with delta = 136mc^2kZ^{-1/3}/[E(Eg-E)] = 136Z^{-1/3}eps0/[eps(1-eps)] where
138 // Eg is the initial photon energy, E is the total energy transferred to one of
139 // the e-/e+ pair, eps0 = mc^2/Eg and eps = E/Eg.
140 
141 // Compute the value of the screening function 3*PHI1(delta) - PHI2(delta):
143 {
144  return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
145  : 42.184 - delta*(7.444 - 1.623*delta);
146 }
147 
148 
149 // Compute the value of the screening function 1.5*PHI1(delta) +0.5*PHI2(delta):
151 {
152  return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
153  : 41.326 - delta*(5.848 - 0.902*delta);
154 }
155 
156 
157 // Same as ScreenFunction1 and ScreenFunction2 but computes them at once
159  G4double &f1, G4double &f2)
160 {
161  if (delta > 1.4) {
162  f1 = 42.038 - 8.29*G4Log(delta + 0.958);
163  f2 = f1;
164  } else {
165  f1 = 42.184 - delta*(7.444 - 1.623*delta);
166  f2 = 41.326 - delta*(5.848 - 0.902*delta);
167  }
168 }
169 
170 
171 #endif