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27 // -------------------------------------------------------------------
28 //
29 // GEANT4 Class header file
30 //
31 //
32 // File name: G4PairProductionRelModel
33 //
34 // Author: Andreas Schaelicke
35 //
36 // Creation date: 02.04.2009
37 //
38 // Modifications:
39 // 28-05-18 New version with improved screening function approximation, improved
40 // LPM function approximation, efficiency, documentation and cleanup.
41 // Corrected call to selecting target atom in the final state sampling.
42 // (M. Novak)
43 //
44 // Class Description:
45 //
46 // Implementation of gamma conversion to e+e- in the field of a nucleus
47 // relativistic approximation
48 //
49
50 // -------------------------------------------------------------------
51 //
52
53 #ifndef G4PairProductionRelModel_h
54 #define G4PairProductionRelModel_h 1
55
56 #include <CLHEP/Units/PhysicalConstants.h>
57
58 #include "G4VEmModel.hh"
59 #include "G4Log.hh"
60 #include <vector>
61
62 class G4ParticleChangeForGamma;
63 class G4Pow;
64
65 class G4PairProductionRelModel : public G4VEmModel
66 {
67
68 public:
69
70 explicit G4PairProductionRelModel(const G4ParticleDefinition* p = nullptr,
71 const G4String& nam = "BetheHeitlerLPM");
72
73 ~G4PairProductionRelModel() override;
74
75 void Initialise(const G4ParticleDefinition*, const G4DataVector&) override;
76
77 void InitialiseLocal(const G4ParticleDefinition*,
78 G4VEmModel* masterModel) override;
79
80 G4double ComputeCrossSectionPerAtom(const G4ParticleDefinition*,
81 G4double kinEnergy,
82 G4double Z,
83 G4double A=0.,
84 G4double cut=0.,
85 G4double emax=DBL_MAX) override;
86
87 void SampleSecondaries(std::vector<G4DynamicParticle*>*,
88 const G4MaterialCutsCouple*,
89 const G4DynamicParticle*,
90 G4double tmin,
91 G4double maxEnergy) override;
92
93 void SetupForMaterial(const G4ParticleDefinition*,
94 const G4Material*,G4double) override;
95
96 inline void SetLPMflag(G4bool val) { fIsUseLPMCorrection = val; }
97 inline G4bool LPMflag() const { return fIsUseLPMCorrection; }
98
99 G4PairProductionRelModel & operator=
100 (const G4PairProductionRelModel &right) = delete;
101 G4PairProductionRelModel(const G4PairProductionRelModel&) = delete;
102
103 protected:
104
105 // for evaluating screening related functions
106 inline void ComputePhi12(const G4double delta,
107 G4double &phi1, G4double &phi2);
108 inline G4double ScreenFunction1(const G4double delta);
109 inline G4double ScreenFunction2(const G4double delta);
110 inline void ScreenFunction12(const G4double delta,
111 G4double &f1, G4double &f2);
112 // helper methods for cross-section computation under different approximations
113 G4double ComputeParametrizedXSectionPerAtom(G4double gammaEnergy, G4double Z);
114 G4double ComputeXSectionPerAtom(G4double gammaEnergy, G4double Z);
115 G4double ComputeDXSectionPerAtom(G4double eplusEnergy, G4double gammaEnergy,
116 G4double Z);
117 G4double ComputeRelDXSectionPerAtom(G4double eplusEnergy,
118 G4double gammaEnergy, G4double Z);
119
120 private:
121
122 // for creating some data structure per Z
123 void InitialiseElementData();
124 struct ElementData {
125 G4double fLogZ13;
126 G4double fCoulomb;
127 G4double fLradEl;
128 G4double fDeltaFactor;
129 G4double fDeltaMaxLow;
130 G4double fDeltaMaxHigh;
131 G4double fEtaValue;
132 G4double fLPMVarS1Cond;
133 G4double fLPMILVarS1Cond;
134 };
135 // for precomputing comp. intensive parts of LPM suppression functions and
136 // using them at run-time
137 void InitLPMFunctions();
138 void ComputeLPMGsPhis(G4double &funcGS, G4double &funcPhiS,
139 const G4double varShat);
140 void GetLPMFunctions(G4double &lpmGs, G4double &lpmPhis, const G4double sval);
141 void ComputeLPMfunctions(G4double &fXiS, G4double &fGS, G4double &fPhiS,
142 const G4double eps, const G4double egamma,
143 const G4int izet);
144 struct LPMFuncs {
145 LPMFuncs() : fIsInitialized(false), fISDelta(100.), fSLimit(2.) {}
146 G4bool fIsInitialized;
147 G4double fISDelta;
148 G4double fSLimit;
149 std::vector<G4double> fLPMFuncG;
150 std::vector<G4double> fLPMFuncPhi;
151 };
152
153 protected:
154 static const G4int gMaxZet;
155 //
156 static const G4double gLPMconstant;
157 //
158 static const G4double gXGL[8];
159 static const G4double gWGL[8];
160 static const G4double gFelLowZet[8];
161 static const G4double gFinelLowZet[8];
162 //
163 static const G4double gXSecFactor;
164 static const G4double gEgLPMActivation;
165 //
166 static std::vector<ElementData*> gElementData;
167 static LPMFuncs gLPMFuncs;
168 //
169 G4bool isFirstInstance{false};
170 G4bool fIsUseLPMCorrection;
171 G4bool fIsUseCompleteScreening;
172 //
173 G4double fLPMEnergy;
174 //
175 G4double fParametrizedXSectionThreshold;
176 G4double fCoulombCorrectionThreshold;
177 //
178 G4Pow* fG4Calc;
179 G4ParticleDefinition* fTheGamma;
180 G4ParticleDefinition* fTheElectron;
181 G4ParticleDefinition* fThePositron;
182 G4ParticleChangeForGamma* fParticleChange;
183 };
184 //
185 // Bethe screening functions for the elastic (coherent) scattering:
186 // Bethe's phi1, phi2 coherent screening functions were computed numerically
187 // by using (the universal) atomic form factors computed based on the Thomas-
188 // Fermi model of the atom (using numerical solution of the Thomas-Fermi
189 // screening function instead of Moliere's analytical approximation). The
190 // numerical results can be well approximated (better than Butcher & Messel
191 // especially near the delta=1 limit) by:
192 // ## if delta <= 1.4
193 // phi1(delta) = 20.806 - delta*(3.190 - 0.5710*delta)
194 // phi2(delta) = 20.234 - delta*(2.126 - 0.0903*delta)
195 // ## if delta > 1.4
196 // phi1(delta) = phi2(delta) = 21.0190 - 4.145*ln(delta + 0.958)
197 // with delta = 136mc^2kZ^{-1/3}/[E(Eg-E)] = 136Z^{-1/3}eps0/[eps(1-eps)] where
198 // Eg is the initial photon energy, E is the total energy transferred to one of
199 // the e-/e+ pair, eps0 = mc^2/Eg and eps = E/Eg.
200
201 inline void G4PairProductionRelModel::ComputePhi12(const G4double delta,
202 G4double &phi1,
203 G4double &phi2)
204 {
205 if (delta > 1.4) {
206 phi1 = 21.0190 - 4.145*G4Log(delta + 0.958);
207 phi2 = phi1;
208 } else {
209 phi1 = 20.806 - delta*(3.190 - 0.5710*delta);
210 phi2 = 20.234 - delta*(2.126 - 0.0903*delta);
211 }
212 }
213
214 // Compute the value of the screening function 3*PHI1(delta) - PHI2(delta):
215 inline G4double G4PairProductionRelModel::ScreenFunction1(const G4double delta)
216 {
217 return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
218 : 42.184 - delta*(7.444 - 1.623*delta);
219 }
220
221 // Compute the value of the screening function 1.5*PHI1(delta) +0.5*PHI2(delta):
222 inline G4double G4PairProductionRelModel::ScreenFunction2(const G4double delta)
223 {
224 return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
225 : 41.326 - delta*(5.848 - 0.902*delta);
226 }
227
228 // Same as ScreenFunction1 and ScreenFunction2 but computes them at once
229 inline void G4PairProductionRelModel::ScreenFunction12(const G4double delta,
230 G4double &f1, G4double &f2)
231 {
232 if (delta > 1.4) {
233 f1 = 42.038 - 8.29*G4Log(delta + 0.958);
234 f2 = f1;
235 } else {
236 f1 = 42.184 - delta*(7.444 - 1.623*delta);
237 f2 = 41.326 - delta*(5.848 - 0.902*delta);
238 }
239 }
240
241 #endif
242