G4LivermoreGammaConversionModel.cc

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//
// Author: Sebastien Incerti
//         22 January 2012
//         on base of G4LivermoreGammaConversionModel

#include "G4LivermoreGammaConversionModel.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"

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using namespace std;

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G4LivermoreGammaConversionModel::G4LivermoreGammaConversionModel(const G4ParticleDefinition*,
                                                                 const G4String& nam)
:G4VEmModel(nam),smallEnergy(2.*MeV),isInitialised(false),maxZ(99)
{
  fParticleChange = 0;

  lowEnergyLimit = 2.0*electron_mass_c2;
  data.resize(maxZ+1,0); 
         
  verboseLevel= 0;
  // Verbosity scale for debugging purposes:
  // 0 = nothing 
  // 1 = calculation of cross sections, file openings...
  // 2 = entering in methods

  if(verboseLevel > 0) 
  {
    G4cout << "G4LivermoreGammaConversionModel is constructed " << G4endl;
  }
}

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G4LivermoreGammaConversionModel::~G4LivermoreGammaConversionModel()
{  
  for(G4int i=0; i<=maxZ; ++i) { delete data[i]; }
}

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void 
G4LivermoreGammaConversionModel::Initialise(const G4ParticleDefinition* particle,
                                            const G4DataVector& cuts)
{
  if (verboseLevel > 1) 
  {
    G4cout << "Calling Initialise() of G4LivermoreGammaConversionModel." << G4endl
           << "Energy range: "
           << LowEnergyLimit() / MeV << " MeV - "
           << HighEnergyLimit() / GeV << " GeV"
           << G4endl;
  }

  // Initialise element selector
  
  InitialiseElementSelectors(particle, cuts);

  // Access to elements
  
  char* path = getenv("G4LEDATA");

  G4ProductionCutsTable* theCoupleTable =
    G4ProductionCutsTable::GetProductionCutsTable();
  G4int numOfCouples = theCoupleTable->GetTableSize();
  
  for(G4int i=0; i<numOfCouples; ++i) 
  {
    const G4Material* material = 
      theCoupleTable->GetMaterialCutsCouple(i)->GetMaterial();
    const G4ElementVector* theElementVector = material->GetElementVector();
    G4int nelm = material->GetNumberOfElements();
    
    for (G4int j=0; j<nelm; ++j) 
    {
        
      G4int Z = (G4int)(*theElementVector)[j]->GetZ();
      if(Z < 1)          { Z = 1; }
      else if(Z > maxZ)  { Z = maxZ; }
      if(!data[Z]) { ReadData(Z, path); }
    }
  }
  //
  
  if(isInitialised) { return; }
  fParticleChange = GetParticleChangeForGamma();
  isInitialised = true;
}

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void G4LivermoreGammaConversionModel::ReadData(size_t Z, const char* path)
{
  if (verboseLevel > 1) 
  {
    G4cout << "Calling ReadData() of G4LivermoreGammaConversionModel" 
           << G4endl;
  }

  if(data[Z]) { return; }
  
  const char* datadir = path;

  if(!datadir) 
  {
    datadir = getenv("G4LEDATA");
    if(!datadir) 
    {
      G4Exception("G4LivermoreGammaConversionModel::ReadData()",
                  "em0006",FatalException,
                  "Environment variable G4LEDATA not defined");
      return;
    }
  }

  //
  
  data[Z] = new G4LPhysicsFreeVector();
  
  // Activation of spline interpolation
  data[Z] ->SetSpline(true);
  //
  
  std::ostringstream ost;
  ost << datadir << "/livermore/pair/pp-cs-" << Z <<".dat";
  std::ifstream fin(ost.str().c_str());
  
  if( !fin.is_open()) 
  {
    G4ExceptionDescription ed;
    ed << "G4LivermoreGammaConversionModel data file <" << ost.str().c_str()
       << "> is not opened!" << G4endl;
    G4Exception("G4LivermoreGammaConversionModel::ReadData()",
                "em0003",FatalException,
                ed,"G4LEDATA version should be G4EMLOW6.27 or later.");
    return;
  } 
  
  else 
  {
    
    if(verboseLevel > 3) { G4cout << "File " << ost.str() 
             << " is opened by G4LivermoreGammaConversionModel" << G4endl;}
    
    data[Z]->Retrieve(fin, true);
  } 
  
  
}

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G4double 
G4LivermoreGammaConversionModel::ComputeCrossSectionPerAtom(const G4ParticleDefinition*,
                                                            G4double GammaEnergy,
                                                            G4double Z, G4double,
                                                            G4double, G4double)
{
  if (verboseLevel > 1) 
  {
    G4cout << "Calling ComputeCrossSectionPerAtom() of G4LivermoreGammaConversionModel" 
           << G4endl;
  }

  if (GammaEnergy < lowEnergyLimit) { return 0.0; } 

  G4double xs = 0.0;
  
  G4int intZ=G4int(Z);

  if(intZ < 1 || intZ > maxZ) { return xs; }

  G4LPhysicsFreeVector* pv = data[intZ];

  // element was not initialised
  if(!pv) 
  {
    char* path = getenv("G4LEDATA");
    ReadData(intZ, path);
    pv = data[intZ];
    if(!pv) { return xs; }
  }
  // x-section is taken from the table
  xs = pv->Value(GammaEnergy); 

  if(verboseLevel > 0)
  {
    G4int n = pv->GetVectorLength() - 1;
    G4cout  <<  "****** DEBUG: tcs value for Z=" << Z << " at energy (MeV)=" << GammaEnergy/MeV << G4endl;
    G4cout  <<  "  cs (Geant4 internal unit)=" << xs << G4endl;
    G4cout  <<  "    -> first cs value in EADL data file (iu) =" << (*pv)[0] << G4endl;
    G4cout  <<  "    -> last  cs value in EADL data file (iu) =" << (*pv)[n] << G4endl;
    G4cout  <<  "*********************************************************" << G4endl;
  }

  return xs;

}

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void G4LivermoreGammaConversionModel::SampleSecondaries(
                                 std::vector<G4DynamicParticle*>* fvect,
                                 const G4MaterialCutsCouple* couple,
                                 const G4DynamicParticle* aDynamicGamma,
                                 G4double, G4double)
{

// The energies of the e+ e- secondaries are sampled using the Bethe - Heitler
// cross sections with Coulomb correction. A modified version of the random
// number techniques of Butcher & Messel is used (Nuc Phys 20(1960),15).

// Note 1 : Effects due to the breakdown of the Born approximation at low
// energy are ignored.
// Note 2 : The differential cross section implicitly takes account of
// pair creation in both nuclear and atomic electron fields. However triplet
// prodution is not generated.

  if (verboseLevel > 1)
    G4cout << "Calling SampleSecondaries() of G4LivermoreGammaConversionModel" << G4endl;

  G4double photonEnergy = aDynamicGamma->GetKineticEnergy();
  G4ParticleMomentum photonDirection = aDynamicGamma->GetMomentumDirection();

  G4double epsilon ;
  G4double epsilon0Local = electron_mass_c2 / photonEnergy ;

  // Do it fast if photon energy < 2. MeV
  if (photonEnergy < smallEnergy )
  {
    epsilon = epsilon0Local + (0.5 - epsilon0Local) * G4UniformRand();
  }
  else
  {
    // Select randomly one element in the current material

    const G4ParticleDefinition* particle =  aDynamicGamma->GetDefinition();
    const G4Element* element = SelectRandomAtom(couple,particle,photonEnergy);

    if (element == 0)
      {
        G4cout << "G4LivermoreGammaConversionModel::SampleSecondaries - element = 0" 
               << G4endl;
        return;
      }
    G4IonisParamElm* ionisation = element->GetIonisation();
    if (ionisation == 0)
      {
        G4cout << "G4LivermoreGammaConversionModel::SampleSecondaries - ionisation = 0" 
               << G4endl;
        return;
      }

    // Extract Coulomb factor for this Element
    G4double fZ = 8. * (ionisation->GetlogZ3());
    if (photonEnergy > 50. * MeV) fZ += 8. * (element->GetfCoulomb());

    // Limits of the screening variable
    G4double screenFactor = 136. * epsilon0Local / (element->GetIonisation()->GetZ3()) ;
    G4double screenMax = std::exp ((42.24 - fZ)/8.368) - 0.952 ;
    G4double screenMin = std::min(4.*screenFactor,screenMax) ;

    // Limits of the energy sampling
    G4double epsilon1 = 0.5 - 0.5 * std::sqrt(1. - screenMin / screenMax) ;
    G4double epsilonMin = std::max(epsilon0Local,epsilon1);
    G4double epsilonRange = 0.5 - epsilonMin ;

    // Sample the energy rate of the created electron (or positron)
    G4double screen;
    G4double gReject ;

    G4double f10 = ScreenFunction1(screenMin) - fZ;
    G4double f20 = ScreenFunction2(screenMin) - fZ;
    G4double normF1 = std::max(f10 * epsilonRange * epsilonRange,0.);
    G4double normF2 = std::max(1.5 * f20,0.);

    do 
      {
        if (normF1 / (normF1 + normF2) > G4UniformRand() )
          {
            epsilon = 0.5 - epsilonRange * std::pow(G4UniformRand(), 0.333333) ;
            screen = screenFactor / (epsilon * (1. - epsilon));
            gReject = (ScreenFunction1(screen) - fZ) / f10 ;
          }
        else
          {
            epsilon = epsilonMin + epsilonRange * G4UniformRand();
            screen = screenFactor / (epsilon * (1 - epsilon));
            gReject = (ScreenFunction2(screen) - fZ) / f20 ;
          }
      } while ( gReject < G4UniformRand() );
    
  }   //  End of epsilon sampling

  // Fix charges randomly

  G4double electronTotEnergy;
  G4double positronTotEnergy;

  if (G4UniformRand() > 0.5)
    {
      electronTotEnergy = (1. - epsilon) * photonEnergy;
      positronTotEnergy = epsilon * photonEnergy;
    }
  else
    {
      positronTotEnergy = (1. - epsilon) * photonEnergy;
      electronTotEnergy = epsilon * photonEnergy;
    }

  // Scattered electron (positron) angles. ( Z - axis along the parent photon)
  // Universal distribution suggested by L. Urban (Geant3 manual (1993) Phys211),
  // derived from Tsai distribution (Rev. Mod. Phys. 49, 421 (1977)

  G4double u;
  const G4double a1 = 0.625;
  G4double a2 = 3. * a1;
  //  G4double d = 27. ;

  //  if (9. / (9. + d) > G4UniformRand())
  if (0.25 > G4UniformRand())
    {
      u = - std::log(G4UniformRand() * G4UniformRand()) / a1 ;
    }
  else
    {
      u = - std::log(G4UniformRand() * G4UniformRand()) / a2 ;
    }

  G4double thetaEle = u*electron_mass_c2/electronTotEnergy;
  G4double thetaPos = u*electron_mass_c2/positronTotEnergy;
  G4double phi  = twopi * G4UniformRand();

  G4double dxEle= std::sin(thetaEle)*std::cos(phi),dyEle= std::sin(thetaEle)*std::sin(phi),dzEle=std::cos(thetaEle);
  G4double dxPos=-std::sin(thetaPos)*std::cos(phi),dyPos=-std::sin(thetaPos)*std::sin(phi),dzPos=std::cos(thetaPos);
  
  
  // Kinematics of the created pair:
  // the electron and positron are assumed to have a symetric angular 
  // distribution with respect to the Z axis along the parent photon
  
  G4double electronKineEnergy = std::max(0.,electronTotEnergy - electron_mass_c2) ;
  
  G4ThreeVector electronDirection (dxEle, dyEle, dzEle);
  electronDirection.rotateUz(photonDirection);
      
  G4DynamicParticle* particle1 = new G4DynamicParticle (G4Electron::Electron(),
                                                        electronDirection,
                                                        electronKineEnergy);

  // The e+ is always created 
  G4double positronKineEnergy = std::max(0.,positronTotEnergy - electron_mass_c2) ;

  G4ThreeVector positronDirection (dxPos, dyPos, dzPos);
  positronDirection.rotateUz(photonDirection);   
  
  // Create G4DynamicParticle object for the particle2 
  G4DynamicParticle* particle2 = new G4DynamicParticle(G4Positron::Positron(),
                                                       positronDirection, 
                                                       positronKineEnergy);
  // Fill output vector
  fvect->push_back(particle1);
  fvect->push_back(particle2);

  // kill incident photon
  fParticleChange->SetProposedKineticEnergy(0.);
  fParticleChange->ProposeTrackStatus(fStopAndKill);   

}

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G4double 
G4LivermoreGammaConversionModel::ScreenFunction1(G4double screenVariable)
{
  // Compute the value of the screening function 3*phi1 - phi2

  G4double value;
  
  if (screenVariable > 1.)
    value = 42.24 - 8.368 * std::log(screenVariable + 0.952);
  else
    value = 42.392 - screenVariable * (7.796 - 1.961 * screenVariable);
  
  return value;
} 

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G4double 
G4LivermoreGammaConversionModel::ScreenFunction2(G4double screenVariable)
{
  // Compute the value of the screening function 1.5*phi1 - 0.5*phi2
  
  G4double value;
  
  if (screenVariable > 1.)
    value = 42.24 - 8.368 * std::log(screenVariable + 0.952);
  else
    value = 41.405 - screenVariable * (5.828 - 0.8945 * screenVariable);
  
  return value;
} 

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