G4eplusTo2GammaOKVIModel.cc

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// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:   G4eplusTo2GammaOKVIModel
//
// Author:      Vladimir Ivanchenko and Omrame Kadri
//
// Creation date: 29.03.2018
//
// -------------------------------------------------------------------
//
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#include "G4eplusTo2GammaOKVIModel.hh"
#include "G4eplusTo3GammaOKVIModel.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4EmParameters.hh"
#include "G4TrackStatus.hh"
#include "G4Electron.hh"
#include "G4Positron.hh"
#include "G4Gamma.hh"
#include "G4DataVector.hh"
#include "G4PhysicsVector.hh"
#include "G4PhysicsLogVector.hh"
#include "Randomize.hh"
#include "G4ParticleChangeForGamma.hh"
#include "G4Log.hh"
#include "G4Exp.hh"
 
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using namespace std;
 
G4PhysicsVector* G4eplusTo2GammaOKVIModel::fCrossSection   = nullptr;
G4PhysicsVector* G4eplusTo2GammaOKVIModel::fCrossSection3G = nullptr;
G4PhysicsVector* G4eplusTo2GammaOKVIModel::f3GProbability  = nullptr;
 
G4eplusTo2GammaOKVIModel::G4eplusTo2GammaOKVIModel(const G4ParticleDefinition*,
                                                   const G4String& nam)
  : G4VEmModel(nam),
    fDelta(0.001),
    fGammaTh(MeV)
{
  theGamma = G4Gamma::Gamma();
  fParticleChange = nullptr;
  fCuts = nullptr;
  f3GModel = new G4eplusTo3GammaOKVIModel();
  SetTripletModel(f3GModel);
}
 
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G4eplusTo2GammaOKVIModel::~G4eplusTo2GammaOKVIModel() = default;
 
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void G4eplusTo2GammaOKVIModel::Initialise(const G4ParticleDefinition* p,
                      const G4DataVector& cuts)
{
  f3GModel->Initialise(p, cuts); 
  fCuts = &cuts;
  fGammaTh = G4EmParameters::Instance()->LowestTripletEnergy();
  f3GModel->SetDelta(fDelta);
  
  if(IsMaster()) {
    if(!fCrossSection) {
      G4double emin = 10*eV;
      G4double emax = 100*TeV;
      G4int nbins = 20*G4lrint(std::log10(emax/emin));
      fCrossSection   = new G4PhysicsLogVector(emin, emax, nbins, true);
      fCrossSection3G = new G4PhysicsLogVector(emin, emax, nbins, true);
      f3GProbability  = new G4PhysicsLogVector(emin, emax, nbins, true);
      for(G4int i=0; i<= nbins; ++i) {
        G4double e = fCrossSection->Energy(i);
        G4double cs2 = ComputeCrossSectionPerElectron(e);
        G4double cs3 = f3GModel->ComputeCrossSectionPerElectron(e);
    cs2 += cs3;
    fCrossSection->PutValue(i, cs2);
    fCrossSection3G->PutValue(i, cs3);
    f3GProbability->PutValue(i, cs3/cs2);
      }
      fCrossSection->FillSecondDerivatives();
      fCrossSection3G->FillSecondDerivatives();
      f3GProbability->FillSecondDerivatives();
    }
  }
  // here particle change is set for the triplet model
  if(fParticleChange) { return; }
  fParticleChange = GetParticleChangeForGamma();
}
 
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G4double 
G4eplusTo2GammaOKVIModel::ComputeCrossSectionPerElectron(G4double kinEnergy)
{
  // Calculates the cross section per electron of annihilation into two 
  // photons from the Heilter formula with the radiation correction to 3 gamma 
  // annihilation channel. (A.A.) rho is changed
 
  G4double ekin   = std::max(eV,kinEnergy);   
  G4double tau    = ekin/electron_mass_c2;
  G4double gam    = tau + 1.0;
  G4double gamma2 = gam*gam;
  G4double bg2    = tau * (tau+2.0);
  G4double bg     = sqrt(bg2);
  G4double rho = (gamma2+4.*gam+1.)*G4Log(gam+bg)/(gamma2-1.) 
    - (gam+3.)/(sqrt(gam*gam - 1.));   
 
  static const G4double pir2 = pi*classic_electr_radius*classic_electr_radius;
  G4double cross = (pir2*rho + alpha_rcl2*2.*G4Log(fDelta)*rho*rho)/(gam+1.);
 
  return cross;  
}
 
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G4double G4eplusTo2GammaOKVIModel::ComputeCrossSectionPerAtom(
                                    const G4ParticleDefinition*,
                                    G4double kineticEnergy, G4double Z,
                    G4double, G4double, G4double)
{
  // Calculates the cross section per atom of annihilation into two photons
  G4double cross = Z*fCrossSection->Value(kineticEnergy);
  return cross;  
}
 
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G4double G4eplusTo2GammaOKVIModel::CrossSectionPerVolume(
                    const G4Material* material,
                    const G4ParticleDefinition*,
                          G4double kineticEnergy,
                          G4double, G4double)
{
  // Calculates the cross section per volume of annihilation into two photons
  G4double eDensity = material->GetElectronDensity();
  G4double cross = eDensity*fCrossSection->Value(kineticEnergy);
  return cross;
}
 
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// Polarisation of gamma according to M.H.L.Pryce and J.C.Ward, 
// Nature 4065 (1947) 435.
 
void 
G4eplusTo2GammaOKVIModel::SampleSecondaries(vector<G4DynamicParticle*>* vdp,
                        const G4MaterialCutsCouple* mcc,
                        const G4DynamicParticle* dp,
                        G4double, G4double)
{
  G4double posiKinEnergy = dp->GetKineticEnergy();
  CLHEP::HepRandomEngine* rndmEngine = G4Random::getTheEngine();
 
  if(rndmEngine->flat() < f3GProbability->Value(posiKinEnergy)) {
    G4double cutd = std::max(fGammaTh,(*fCuts)[mcc->GetIndex()])
      /(posiKinEnergy + electron_mass_c2);
    // check cut to avoid production of 3d gamma below 
    if(cutd > fDelta) {
      G4double cs30 = fCrossSection3G->Value(posiKinEnergy);
      f3GModel->SetDelta(cutd);
      G4double cs3 = f3GModel->ComputeCrossSectionPerElectron(posiKinEnergy);
      if(rndmEngine->flat()*cs30 < cs3) {
    f3GModel->SampleSecondaries(vdp, mcc, dp);
    return;
      }
    } else {
      f3GModel->SampleSecondaries(vdp, mcc, dp);
      return;
    }
  }
 
  G4DynamicParticle *aGamma1, *aGamma2;
 
  // Case at rest
  if(posiKinEnergy == 0.0) {
    G4double cost = 2.*rndmEngine->flat()-1.;
    G4double sint = sqrt((1. - cost)*(1. + cost));
    G4double phi  = twopi * rndmEngine->flat();
    G4ThreeVector dir(sint*cos(phi), sint*sin(phi), cost);
    phi = twopi * rndmEngine->flat();
    G4double cosphi = cos(phi);
    G4double sinphi = sin(phi);
    G4ThreeVector pol(cosphi, sinphi, 0.0);
    pol.rotateUz(dir);
    aGamma1 = new G4DynamicParticle(theGamma, dir, electron_mass_c2);
    aGamma1->SetPolarization(pol.x(),pol.y(),pol.z());
    aGamma2 = new G4DynamicParticle(theGamma,-dir, electron_mass_c2);
    pol.set(-sinphi, cosphi, 0.0);
    pol.rotateUz(dir);
    aGamma2->SetPolarization(pol.x(),pol.y(),pol.z());
 
  } else {
 
    G4ThreeVector posiDirection = dp->GetMomentumDirection();
 
    G4double tau     = posiKinEnergy/electron_mass_c2;
    G4double gam     = tau + 1.0;
    G4double tau2    = tau + 2.0;
    G4double sqgrate = sqrt(tau/tau2)*0.5;
    G4double sqg2m1  = sqrt(tau*tau2);
 
    // limits of the energy sampling
    G4double epsilmin = 0.5 - sqgrate;
    G4double epsilmax = 0.5 + sqgrate;
    G4double epsilqot = epsilmax/epsilmin;
 
    //
    // sample the energy rate of the created gammas
    //
    G4double epsil, greject;
 
    do {
      epsil = epsilmin*G4Exp(G4Log(epsilqot)*rndmEngine->flat());
      greject = 1. - epsil + (2.*gam*epsil-1.)/(epsil*tau2*tau2);
      // Loop checking, 03-Aug-2015, Vladimir Ivanchenko
    } while( greject < rndmEngine->flat());
 
    //
    // scattered Gamma angles. ( Z - axis along the parent positron)
    //
 
    G4double cost = (epsil*tau2-1.)/(epsil*sqg2m1);
    if(std::abs(cost) > 1.0) {
      G4cout << "### G4eplusTo2GammaOKVIModel WARNING cost= " << cost
         << " positron Ekin(MeV)= " << posiKinEnergy
         << " gamma epsil= " << epsil
         << G4endl;
      if(cost > 1.0) cost = 1.0;
      else cost = -1.0; 
    }
    G4double sint = sqrt((1.+cost)*(1.-cost));
    G4double phi  = twopi * rndmEngine->flat();
 
    //
    // kinematic of the created pair
    //
 
    G4double TotalAvailableEnergy = posiKinEnergy + 2.0*electron_mass_c2;
    G4double phot1Energy = epsil*TotalAvailableEnergy;
 
    G4ThreeVector phot1Direction(sint*cos(phi), sint*sin(phi), cost);
    phot1Direction.rotateUz(posiDirection);
    aGamma1 = new G4DynamicParticle (theGamma,phot1Direction, phot1Energy);
    phi = twopi * rndmEngine->flat();
    G4double cosphi = cos(phi);
    G4double sinphi = sin(phi);
    G4ThreeVector pol(cosphi, sinphi, 0.0);
    pol.rotateUz(phot1Direction);
    aGamma1->SetPolarization(pol.x(),pol.y(),pol.z());
 
    G4double phot2Energy =(1.-epsil)*TotalAvailableEnergy;
    G4double posiP= sqrt(posiKinEnergy*(posiKinEnergy+2.*electron_mass_c2));
    G4ThreeVector dir = posiDirection*posiP - phot1Direction*phot1Energy;
    G4ThreeVector phot2Direction = dir.unit();
 
    // create G4DynamicParticle object for the particle2
    aGamma2 = new G4DynamicParticle (theGamma,phot2Direction, phot2Energy);
 
    //!!! likely problematic direction to be checked
    pol.set(-sinphi, cosphi, 0.0);
    pol.rotateUz(phot1Direction);
    cost = pol*phot2Direction;
    pol -= cost*phot2Direction;
    pol = pol.unit();
    aGamma2->SetPolarization(pol.x(),pol.y(),pol.z());
  }
  /*
    G4cout << "Annihilation in fly: e0= " << posiKinEnergy
    << " m= " << electron_mass_c2
    << " e1= " << phot1Energy 
    << " e2= " << phot2Energy << " dir= " <<  dir 
    << " -> " << phot1Direction << " " 
    << phot2Direction << G4endl;
  */
 
  vdp->push_back(aGamma1);
  vdp->push_back(aGamma2);
 
  // kill primary positron
  fParticleChange->SetProposedKineticEnergy(0.0);
  fParticleChange->ProposeTrackStatus(fStopAndKill);
}
 
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