include/Geant4/G4BetheHeitlerModel.hh

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0025 //
0026 //
0027 // -------------------------------------------------------------------
0028 //
0029 // GEANT4 Class header file
0030 //
0031 //
0032 // File name:     G4BetheHeitlerModel
0033 //
0034 // Author:        Vladimir Ivanchenko on base of Michel Maire code
0035 //
0036 // Creation date: 19.04.2005
0037 //
0038 // Modifications by Vladimir Ivanchenko, Michel Maire, Mihaly Novak
0039 //
0040 // Class Description:
0041 //
0042 // Implementation of gamma conversion to e+e- in the field of a nucleus
0043 // For details see Physics Reference Manual
0044
0045 // -------------------------------------------------------------------
0046 //
0047
0048 #ifndef G4BetheHeitlerModel_h
0049 #define G4BetheHeitlerModel_h 1
0050
0051 #include "G4VEmModel.hh"
0052 #include "G4PhysicsTable.hh"
0053 #include "G4Log.hh"
0054
0055 #include <vector>
0056
0057 class G4ParticleChangeForGamma;
0058 class G4Pow;
0059 class G4EmElementXS;
0060
0061 class G4BetheHeitlerModel : public G4VEmModel
0062 {
0063
0064 public:
0065
0066   explicit G4BetheHeitlerModel(const G4ParticleDefinition* p = nullptr,
0067                                const G4String& nam = "BetheHeitler");
0068
0069   ~G4BetheHeitlerModel() override;
0070
0071   void Initialise(const G4ParticleDefinition*, const G4DataVector&) override;
0072
0073   void InitialiseLocal(const G4ParticleDefinition*,
0074                G4VEmModel* masterModel) override;
0075
0076   G4double ComputeCrossSectionPerAtom(const G4ParticleDefinition*,
0077                       G4double kinEnergy,
0078                       G4double Z,
0079                       G4double A=0.,
0080                       G4double cut=0.,
0081                       G4double emax=DBL_MAX) override;
0082
0083   void SampleSecondaries(std::vector<G4DynamicParticle*>*,
0084              const G4MaterialCutsCouple*,
0085              const G4DynamicParticle*,
0086              G4double tmin,
0087              G4double maxEnergy) override;
0088
0089   // hide assignment operator
0090   G4BetheHeitlerModel & operator=(const G4BetheHeitlerModel &right) = delete;
0091   G4BetheHeitlerModel(const  G4BetheHeitlerModel&) = delete;
0092
0093 protected:
0094
0095   inline G4double ScreenFunction1(const G4double delta);
0096
0097   inline G4double ScreenFunction2(const G4double delta);
0098
0099   inline void ScreenFunction12(const G4double delta, G4double &f1, G4double &f2);
0100
0101   void     InitialiseElementData();
0102
0103   struct ElementData {
0104     G4double fDeltaMaxLow;
0105     G4double fDeltaMaxHigh;
0106   };
0107
0108   static const G4int                gMaxZet;
0109
0110   G4Pow*                            fG4Calc;
0111   const G4ParticleDefinition*       fTheGamma;
0112   const G4ParticleDefinition*       fTheElectron;
0113   const G4ParticleDefinition*       fThePositron;
0114   G4ParticleChangeForGamma*         fParticleChange;
0115   G4EmElementXS*                    fXSection{nullptr};
0116
0117   G4bool isFirstInstance{false};
0118   G4bool useEPICS2017{false};
0119
0120   static std::vector<ElementData*>  gElementData;
0121 };
0122
0123 //
0124 // Bethe screening functions for the elastic (coherent) scattering:
0125 // Bethe's phi1, phi2 coherent screening functions were computed numerically
0126 // by using (the universal) atomic form factors computed based on the Thomas-
0127 // Fermi model of the atom (using numerical solution of the Thomas-Fermi
0128 // screening function instead of Moliere's analytical approximation). The
0129 // numerical results can be well approximated (better than Butcher & Messel
0130 // especially near the delta=1 limit) by:
0131 // ## if delta <= 1.4
0132 //  phi1(delta) = 20.806 - delta*(3.190 - 0.5710*delta)
0133 //  phi2(delta) = 20.234 - delta*(2.126 - 0.0903*delta)
0134 // ## if delta  > 1.4
0135 //  phi1(delta) = phi2(delta) = 21.0190 - 4.145*ln(delta + 0.958)
0136 // with delta = 136mc^2kZ^{-1/3}/[E(Eg-E)] = 136Z^{-1/3}eps0/[eps(1-eps)] where
0137 // Eg is the initial photon energy, E is the total energy transferred to one of
0138 // the e-/e+ pair, eps0 = mc^2/Eg and eps = E/Eg.
0139
0140 // Compute the value of the screening function 3*PHI1(delta) - PHI2(delta):
0141 inline G4double G4BetheHeitlerModel::ScreenFunction1(const G4double delta)
0142 {
0143   return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
0144                        : 42.184 - delta*(7.444 - 1.623*delta);
0145 }
0146
0147 // Compute the value of the screening function 1.5*PHI1(delta) +0.5*PHI2(delta):
0148 inline G4double G4BetheHeitlerModel::ScreenFunction2(const G4double delta)
0149 {
0150   return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
0151                        : 41.326 - delta*(5.848 - 0.902*delta);
0152 }
0153
0154 // Same as ScreenFunction1 and ScreenFunction2 but computes them at once
0155 inline void G4BetheHeitlerModel::ScreenFunction12(const G4double delta,
0156                                                   G4double &f1, G4double &f2)
0157 {
0158   if (delta > 1.4) {
0159     f1 = 42.038 - 8.29*G4Log(delta + 0.958);
0160     f2 = f1;
0161   } else {
0162     f1 = 42.184 - delta*(7.444 - 1.623*delta);
0163     f2 = 41.326 - delta*(5.848 - 0.902*delta);
0164   }
0165 }
0166
0167 #endif