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db49709b532cdbe4a21775b0b28ce7fdf435e735
geant4/source/processes/electromagnetic/standard/include/G4PairProductionRelModel.hh
T
Gabriele Cosmo db49709b53 Import Geant4 10.5.0 source tree
2018-12-07 15:15:39 +01:00

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//
// ********************************************************************
// * License and Disclaimer *
// * *
// * The Geant4 software is copyright of the Copyright Holders of *
// * the Geant4 Collaboration. It is provided under the terms and *
// * conditions of the Geant4 Software License, included in the file *
// * LICENSE and available at http://cern.ch/geant4/license . These *
// * include a list of copyright holders. *
// * *
// * Neither the authors of this software system, nor their employing *
// * institutes,nor the agencies providing financial support for this *
// * work make any representation or warranty, express or implied, *
// * regarding this software system or assume any liability for its *
// * use. Please see the license in the file LICENSE and URL above *
// * for the full disclaimer and the limitation of liability. *
// * *
// * This code implementation is the result of the scientific and *
// * technical work of the GEANT4 collaboration. *
// * By using, copying, modifying or distributing the software (or *
// * any work based on the software) you agree to acknowledge its *
// * use in resulting scientific publications, and indicate your *
// * acceptance of all terms of the Geant4 Software license. *
// ********************************************************************
//
//
// -------------------------------------------------------------------
//
// GEANT4 Class header file
//
//
// File name: G4PairProductionRelModel
//
// Author: Andreas Schaelicke
//
// Creation date: 02.04.2009
//
// Modifications:
// 28-05-18 New version with improved screening function approximation, improved
// LPM function approximation, efficiency, documentation and cleanup.
// Corrected call to selecting target atom in the final state sampling.
// (M. Novak)
//
// Class Description:
//
// Implementation of gamma convertion to e+e- in the field of a nucleus
// relativistic approximation
//
// -------------------------------------------------------------------
//
#ifndef G4PairProductionRelModel_h
#define G4PairProductionRelModel_h 1
#include <CLHEP/Units/PhysicalConstants.h>
#include "G4VEmModel.hh"
#include "G4Log.hh"
#include "G4Exp.hh"
#include "G4Pow.hh"
#include <vector>
class G4ParticleChangeForGamma;
class G4PairProductionRelModel : public G4VEmModel
{
public:
explicit G4PairProductionRelModel(const G4ParticleDefinition* p = nullptr,
const G4String& nam = "BetheHeitlerLPM");
virtual ~G4PairProductionRelModel();
virtual void Initialise(const G4ParticleDefinition*,
const G4DataVector&) override;
virtual void InitialiseLocal(const G4ParticleDefinition*,
G4VEmModel* masterModel) override;
virtual G4double ComputeCrossSectionPerAtom(
const G4ParticleDefinition*,
G4double kinEnergy,
G4double Z,
G4double A=0.,
G4double cut=0.,
G4double emax=DBL_MAX) override;
virtual void SampleSecondaries(std::vector<G4DynamicParticle*>*,
const G4MaterialCutsCouple*,
const G4DynamicParticle*,
G4double tmin,
G4double maxEnergy) override;
virtual void SetupForMaterial(const G4ParticleDefinition*,
const G4Material*,G4double) override;
inline void SetLPMflag(G4bool val) { fIsUseLPMCorrection = val; }
inline G4bool LPMflag() const { return fIsUseLPMCorrection; }
protected:
// for evaluating screening related functions
inline void ComputePhi12(const G4double delta, G4double &phi1, G4double &phi2);
inline G4double ScreenFunction1(const G4double delta);
inline G4double ScreenFunction2(const G4double delta);
inline void ScreenFunction12(const G4double delta, G4double &f1, G4double &f2);
// helper methods for cross-section computation under different approximations
G4double ComputeXSectionPerAtom(G4double gammaEnergy, G4double Z);
G4double ComputeDXSectionPerAtom(G4double eplusEnergy, G4double gammaEnergy,
G4double Z);
G4double ComputeRelDXSectionPerAtom(G4double eplusEnergy, G4double gammaEnergy,
G4double Z);
private:
// for creating some data structure per Z with often used comp. intensive data
void InitialiseElementData();
struct ElementData {
G4double fLogZ13;
G4double fCoulomb;
G4double fLradEl;
G4double fDeltaFactor;
G4double fDeltaMax;
G4double fEtaValue;
G4double fLPMVarS1Cond;
G4double fLPMILVarS1Cond;
};
// for precomputing comp. intensive parts of LPM suppression functions and
// using them at run-time
void InitLPMFunctions();
void ComputeLPMGsPhis(G4double &funcGS, G4double &funcPhiS,
const G4double varShat);
void GetLPMFunctions(G4double &lpmGs, G4double &lpmPhis, const G4double sval);
void ComputeLPMfunctions(G4double &fXiS, G4double &fGS, G4double &fPhiS,
const G4double eps, const G4double egamma,
const G4int izet);
struct LPMFuncs {
LPMFuncs() : fIsInitialized(false), fISDelta(100.), fSLimit(2.) {}
G4bool fIsInitialized;
G4double fISDelta;
G4double fSLimit;
std::vector<G4double> fLPMFuncG;
std::vector<G4double> fLPMFuncPhi;
};
private:
// hide assignment operator
G4PairProductionRelModel & operator=
(const G4PairProductionRelModel &right) = delete;
G4PairProductionRelModel(const G4PairProductionRelModel&) = delete;
protected:
static const G4int gMaxZet;
//
static const G4double gLPMconstant;
//
static const G4double gXGL[8];
static const G4double gWGL[8];
static const G4double gFelLowZet[8];
static const G4double gFinelLowZet[8];
//
static const G4double gXSecFactor;
static const G4double gEgLPMActivation;
//
static std::vector<ElementData*> gElementData;
static LPMFuncs gLPMFuncs;
//
G4bool fIsUseLPMCorrection;
G4bool fIsUseCompleteScreening;
//
G4double fLPMEnergy;
//
G4Pow* fG4Calc;
G4ParticleDefinition* fTheGamma;
G4ParticleDefinition* fTheElectron;
G4ParticleDefinition* fThePositron;
G4ParticleChangeForGamma* fParticleChange;
};
//
// Bethe screening functions for the elastic (coherent) scattering:
// Bethe's phi1, phi2 coherent screening functions were computed numerically
// by using (the universal) atomic form factors computed based on the Thomas-
// Fermi model of the atom (using numerical solution of the Thomas-Fermi
// screening function instead of Moliere's analytical approximation). The
// numerical results can be well approximated (better than Butcher & Messel
// especially near the delta=1 limit) by:
// ## if delta <= 1.4
// phi1(delta) = 20.806 - delta*(3.190 - 0.5710*delta)
// phi2(delta) = 20.234 - delta*(2.126 - 0.0903*delta)
// ## if delta > 1.4
// phi1(delta) = phi2(delta) = 21.0190 - 4.145*ln(delta + 0.958)
// with delta = 136mc^2kZ^{-1/3}/[E(Eg-E)] = 136Z^{-1/3}eps0/[eps(1-eps)] where
// Eg is the initial photon energy, E is the total energy transferred to one of
// the e-/e+ pair, eps0 = mc^2/Eg and eps = E/Eg.
inline
void G4PairProductionRelModel::ComputePhi12(const G4double delta, G4double &phi1,
G4double &phi2)
{
if (delta > 1.4) {
phi1 = 21.0190 - 4.145*G4Log(delta + 0.958);
phi2 = phi1;
} else {
phi1 = 20.806 - delta*(3.190 - 0.5710*delta);
phi2 = 20.234 - delta*(2.126 - 0.0903*delta);
}
}
// Compute the value of the screening function 3*PHI1(delta) - PHI2(delta):
inline G4double G4PairProductionRelModel::ScreenFunction1(const G4double delta)
{
return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
: 42.184 - delta*(7.444 - 1.623*delta);
}
// Compute the value of the screening function 1.5*PHI1(delta) +0.5*PHI2(delta):
inline G4double G4PairProductionRelModel::ScreenFunction2(const G4double delta)
{
return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
: 41.326 - delta*(5.848 - 0.902*delta);
}
// Same as ScreenFunction1 and ScreenFunction2 but computes them at once
inline void G4PairProductionRelModel::ScreenFunction12(const G4double delta,
G4double &f1, G4double &f2)
{
if (delta > 1.4) {
f1 = 42.038 - 8.29*G4Log(delta + 0.958);
f2 = f1;
} else {
f1 = 42.184 - delta*(7.444 - 1.623*delta);
f2 = 41.326 - delta*(5.848 - 0.902*delta);
}
}
#endif
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