Gabriele Cosmo
168 lines
6.0 KiB
C++
168 lines
6.0 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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// -------------------------------------------------------------------
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//
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// GEANT4 Class header file
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//
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//
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// File name: G4BetheHeitlerModel
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//
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// Author: Vladimir Ivanchenko on base of Michel Maire code
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//
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// Creation date: 19.04.2005
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//
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// Modifications by Vladimir Ivanchenko, Michel Maire, Mihaly Novak
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//
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// Class Description:
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//
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// Implementation of gamma conversion to e+e- in the field of a nucleus
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// For details see Physics Reference Manual
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// -------------------------------------------------------------------
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//
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#ifndef G4BetheHeitlerModel_h
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#define G4BetheHeitlerModel_h 1
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#include "G4VEmModel.hh"
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#include "G4PhysicsTable.hh"
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#include "G4Log.hh"
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#include <vector>
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class G4ParticleChangeForGamma;
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class G4Pow;
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class G4EmElementXS;
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class G4BetheHeitlerModel : public G4VEmModel
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{
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public:
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explicit G4BetheHeitlerModel(const G4ParticleDefinition* p = nullptr,
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const G4String& nam = "BetheHeitler");
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~G4BetheHeitlerModel() override;
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void Initialise(const G4ParticleDefinition*, const G4DataVector&) override;
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void InitialiseLocal(const G4ParticleDefinition*,
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G4VEmModel* masterModel) override;
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G4double ComputeCrossSectionPerAtom(const G4ParticleDefinition*,
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G4double kinEnergy,
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G4double Z,
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G4double A=0.,
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G4double cut=0.,
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G4double emax=DBL_MAX) override;
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void SampleSecondaries(std::vector<G4DynamicParticle*>*,
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const G4MaterialCutsCouple*,
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const G4DynamicParticle*,
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G4double tmin,
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G4double maxEnergy) override;
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// hide assignment operator
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G4BetheHeitlerModel & operator=(const G4BetheHeitlerModel &right) = delete;
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G4BetheHeitlerModel(const G4BetheHeitlerModel&) = delete;
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protected:
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inline G4double ScreenFunction1(const G4double delta);
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inline G4double ScreenFunction2(const G4double delta);
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inline void ScreenFunction12(const G4double delta, G4double &f1, G4double &f2);
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void InitialiseElementData();
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struct ElementData {
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G4double fDeltaMaxLow;
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G4double fDeltaMaxHigh;
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};
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static const G4int gMaxZet;
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G4Pow* fG4Calc;
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const G4ParticleDefinition* fTheGamma;
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const G4ParticleDefinition* fTheElectron;
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const G4ParticleDefinition* fThePositron;
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G4ParticleChangeForGamma* fParticleChange;
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G4EmElementXS* fXSection{nullptr};
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G4bool isFirstInstance{false};
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G4bool useEPICS2017{false};
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static std::vector<ElementData*> gElementData;
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};
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//
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// Bethe screening functions for the elastic (coherent) scattering:
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// Bethe's phi1, phi2 coherent screening functions were computed numerically
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// by using (the universal) atomic form factors computed based on the Thomas-
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// Fermi model of the atom (using numerical solution of the Thomas-Fermi
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// screening function instead of Moliere's analytical approximation). The
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// numerical results can be well approximated (better than Butcher & Messel
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// especially near the delta=1 limit) by:
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// ## if delta <= 1.4
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// phi1(delta) = 20.806 - delta*(3.190 - 0.5710*delta)
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// phi2(delta) = 20.234 - delta*(2.126 - 0.0903*delta)
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// ## if delta > 1.4
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// phi1(delta) = phi2(delta) = 21.0190 - 4.145*ln(delta + 0.958)
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// with delta = 136mc^2kZ^{-1/3}/[E(Eg-E)] = 136Z^{-1/3}eps0/[eps(1-eps)] where
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// Eg is the initial photon energy, E is the total energy transferred to one of
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// the e-/e+ pair, eps0 = mc^2/Eg and eps = E/Eg.
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// Compute the value of the screening function 3*PHI1(delta) - PHI2(delta):
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inline G4double G4BetheHeitlerModel::ScreenFunction1(const G4double delta)
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{
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return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
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: 42.184 - delta*(7.444 - 1.623*delta);
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}
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// Compute the value of the screening function 1.5*PHI1(delta) +0.5*PHI2(delta):
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inline G4double G4BetheHeitlerModel::ScreenFunction2(const G4double delta)
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{
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return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
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: 41.326 - delta*(5.848 - 0.902*delta);
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}
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// Same as ScreenFunction1 and ScreenFunction2 but computes them at once
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inline void G4BetheHeitlerModel::ScreenFunction12(const G4double delta,
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G4double &f1, G4double &f2)
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{
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if (delta > 1.4) {
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f1 = 42.038 - 8.29*G4Log(delta + 0.958);
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f2 = f1;
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} else {
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f1 = 42.184 - delta*(7.444 - 1.623*delta);
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f2 = 41.326 - delta*(5.848 - 0.902*delta);
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}
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}
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#endif
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