G4ParticleHPPhotonDist.cc

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// neutron_hp -- source file
// J.P. Wellisch, Nov-1996
// A prototype of the low energy neutron transport model.
//
// 070523 Try to limit sum of secondary photon energy while keeping distribution shape 
//        in the of nDiscrete = 1 an nPartial = 1. Most case are satisfied. 
//        T. Koi
// 070606 Add Partial case by T. Koi 
// 070618 fix memory leaking by T. Koi
// 080801 fix memory leaking by T. Koi
// 080801 Correcting data disorder which happened when both InitPartial 
//        and InitAnglurar methods was called in a same instance by T. Koi
// 090514 Fix bug in IC electron emission case 
//        Contribution from Chao Zhang ([email protected]) and Dongming Mei([email protected])
//        But it looks like never cause real effect in G4NDL3.13 (at least Natural elements) TK
// 101111 Change warning message for "repFlag == 2 && isoFlag != 1" case 
//
// there is a lot of unused (and undebugged) code in this file. Kept for the moment just in case. @@
// P. Arce, June-2014 Conversion neutron_hp to particle_hp
//
#include <numeric>
 
#include "G4ParticleHPPhotonDist.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4ParticleHPLegendreStore.hh"
#include "G4Electron.hh"
#include "G4Poisson.hh"
 
G4bool G4ParticleHPPhotonDist::InitMean(std::istream & aDataFile)
{
  G4bool result = true;
  if(aDataFile >> repFlag)
  {
 
    aDataFile >> targetMass;
    if(repFlag==1)
    {
      // multiplicities
      aDataFile >> nDiscrete;
      disType = new G4int[nDiscrete];
      energy = new G4double[nDiscrete];
      //actualMult = new G4int[nDiscrete];
      theYield = new G4ParticleHPVector[nDiscrete];
      for (G4int i=0; i<nDiscrete; ++i)
      {
    aDataFile >> disType[i]>>energy[i];
    energy[i]*=eV;
    theYield[i].Init(aDataFile, eV);
      }
    }
    else if(repFlag == 2)
    {
       aDataFile >> theInternalConversionFlag;
       aDataFile >> theBaseEnergy;
       theBaseEnergy*=eV;
       aDataFile >> theInternalConversionFlag;
       aDataFile >> nGammaEnergies;
       theLevelEnergies = new G4double[nGammaEnergies];
       theTransitionProbabilities = new G4double[nGammaEnergies];
       if(theInternalConversionFlag == 2) thePhotonTransitionFraction = new G4double[nGammaEnergies];
       for(G4int  ii=0; ii<nGammaEnergies; ++ii)
       {
     if(theInternalConversionFlag == 1)
     {
           aDataFile >> theLevelEnergies[ii] >> theTransitionProbabilities[ii];
       theLevelEnergies[ii]*=eV;
     }
     else if(theInternalConversionFlag == 2)
     {
           aDataFile >> theLevelEnergies[ii] >> theTransitionProbabilities[ii] >> thePhotonTransitionFraction[ii];
       theLevelEnergies[ii]*=eV;
     }
     else
     {
           throw G4HadronicException(__FILE__, __LINE__, "G4ParticleHPPhotonDist: Unknown conversion flag");
     }
      }
    }
    else
    {
      G4cout << "Data representation in G4ParticleHPPhotonDist: "<<repFlag<<G4endl;
      throw G4HadronicException(__FILE__, __LINE__, "G4ParticleHPPhotonDist: This data representation is not implemented.");
    }
  }
  else
  {
    result = false;
  }
  return result;
}
 
void G4ParticleHPPhotonDist::InitAngular(std::istream & aDataFile)
{
  G4int i, ii;
  // angular distributions
  aDataFile >> isoFlag;
  if (isoFlag != 1)
  {
    if (repFlag == 2) G4cout << "G4ParticleHPPhotonDist: repFlag == 2 && isoFlag != 1 is unexpected! If you use G4ND3.x, then please report to Geant4 HyperNews. " << G4endl;
    aDataFile >> tabulationType >> nDiscrete2 >> nIso;
    if (theGammas != NULL && nDiscrete2 != nDiscrete) 
      G4cout << "080731c G4ParticleHPPhotonDist nDiscrete2 != nDiscrete, It looks like something wrong in your NDL files. Please update the latest. If you still have this messages after the update, then please report to Geant4 Hyper News." << G4endl;
 
    // The order of cross section (InitPartials) and distribution
    // (InitAngular here) data are different, we have to re-coordinate
    // consistent data order.
    std::vector < G4double > vct_gammas_par; 
    std::vector < G4double > vct_shells_par; 
    std::vector < G4int > vct_primary_par; 
    std::vector < G4int > vct_distype_par; 
    std::vector < G4ParticleHPVector* > vct_pXS_par;
    if ( theGammas != nullptr && theShells != nullptr ) 
    {
      //copy the cross section data 
      for ( i = 0 ; i < nDiscrete ; ++i )
      {
        vct_gammas_par.push_back( theGammas[ i ] );
        vct_shells_par.push_back( theShells[ i ] );
        vct_primary_par.push_back( isPrimary[ i ] );
        vct_distype_par.push_back( disType[ i ] );
        G4ParticleHPVector* hpv = new G4ParticleHPVector;
        *hpv = thePartialXsec[ i ];
        vct_pXS_par.push_back( hpv );
      }
    }
    if ( theGammas == nullptr ) theGammas = new G4double[nDiscrete2];
    if ( theShells == nullptr ) theShells = new G4double[nDiscrete2];
 
    for (i=0; i< nIso; ++i) // isotropic photons
    {
      aDataFile >> theGammas[i] >> theShells[i];
      theGammas[i]*=eV;
      theShells[i]*=eV;
    }
    nNeu = new G4int [nDiscrete2-nIso];
    if(tabulationType==1)theLegendre=new G4ParticleHPLegendreTable *[nDiscrete2-nIso];
    if(tabulationType==2)theAngular =new G4ParticleHPAngularP *[nDiscrete2-nIso];
    for(i=nIso; i< nDiscrete2; ++i)
    {
      if(tabulationType==1) 
      {
        aDataFile >> theGammas[i] >> theShells[i] >> nNeu[i-nIso];
        theGammas[i]*=eV;
        theShells[i]*=eV;
        theLegendre[i-nIso]=new G4ParticleHPLegendreTable[nNeu[i-nIso]];
        theLegendreManager.Init(aDataFile); 
        for (ii=0; ii<nNeu[i-nIso]; ++ii)
        {
          theLegendre[i-nIso][ii].Init(aDataFile);
        }
      }
      else if(tabulationType==2)
      {
        aDataFile >> theGammas[i] >> theShells[i] >> nNeu[i-nIso];
        theGammas[i]*=eV;
        theShells[i]*=eV;
        theAngular[i-nIso]=new G4ParticleHPAngularP[nNeu[i-nIso]];
        for (ii=0; ii<nNeu[i-nIso]; ++ii)
        {
          theAngular[i-nIso][ii].Init(aDataFile);
        }
      }
      else
      {
        G4cout << "tabulation type: tabulationType"<<G4endl;
        throw G4HadronicException(__FILE__, __LINE__, "cannot deal with this tabulation type for angular distributions.");
      }
    }
 
    if ( vct_gammas_par.size() > 0 ) 
    {
      // Reordering cross section data to corrsponding distribution data 
      for ( i = 0 ; i < nDiscrete ; ++i ) 
      {
        for ( G4int j = 0 ; j < nDiscrete ; ++j )  
        {
          // Checking gamma and shell to identification 
          if ( theGammas[ i ] == vct_gammas_par [ j ] && theShells [ i ] == vct_shells_par[ j ] )
          {
            isPrimary [ i ] = vct_primary_par [ j ];
            disType [ i ] = vct_distype_par [ j ];
            thePartialXsec[ i ] = ( *( vct_pXS_par[ j ] ) );
          }
        }
      }
      // Garbage collection 
      for ( auto it = vct_pXS_par.cbegin() ; it != vct_pXS_par.cend() ; ++it )
      {
        delete *it;
      }
    }
  }
}
 
void G4ParticleHPPhotonDist::InitEnergies(std::istream & aDataFile)
{
  G4int i, energyDistributionsNeeded = 0;
  for (i=0; i<nDiscrete; ++i)
  {
    if( disType[i]==1) energyDistributionsNeeded =1;
  }
  if(!energyDistributionsNeeded) return;
  aDataFile >>  nPartials;
  distribution = new G4int[nPartials];
  probs = new G4ParticleHPVector[nPartials];
  partials = new G4ParticleHPPartial * [nPartials];
  G4int nen;
  G4int dummy;
  for (i=0; i<nPartials; ++i)
  {
    aDataFile >> dummy;
    probs[i].Init(aDataFile, eV);
    aDataFile >> nen;
    partials[i] = new G4ParticleHPPartial(nen);
    partials[i]->InitInterpolation(aDataFile);
    partials[i]->Init(aDataFile);
  }
}
 
void G4ParticleHPPhotonDist::InitPartials(std::istream& aDataFile,
                                          G4ParticleHPVector* theXsec)
{
  if (theXsec) theReactionXsec = theXsec;
 
  aDataFile >> nDiscrete >> targetMass;
  if(nDiscrete != 1)
  {
    theTotalXsec.Init(aDataFile, eV);
  }
  G4int i;
  theGammas = new G4double[nDiscrete];
  theShells = new G4double[nDiscrete];
  isPrimary = new G4int[nDiscrete];
  disType = new G4int[nDiscrete];
  thePartialXsec = new G4ParticleHPVector[nDiscrete];
  for(i=0; i<nDiscrete; ++i)
  {
    aDataFile>>theGammas[i]>>theShells[i]>>isPrimary[i]>>disType[i];
    theGammas[i]*=eV;
    theShells[i]*=eV;
    thePartialXsec[i].Init(aDataFile, eV);
  }  
}
 
G4ReactionProductVector * G4ParticleHPPhotonDist::GetPhotons(G4double anEnergy)
{
  // the partial cross-section case is not all in this yet.
  if ( actualMult.Get() == nullptr ) {
     actualMult.Get() = new std::vector<G4int>( nDiscrete );
  }
  G4int i, ii, iii;
  G4int nSecondaries = 0;
  G4ReactionProductVector* thePhotons = new G4ReactionProductVector;
 
  if (repFlag==1) {
    G4double current=0;
    for (i = 0; i < nDiscrete; ++i) {
      current = theYield[i].GetY(anEnergy);
      actualMult.Get()->at(i) = (G4int)G4Poisson(current); // max cut-off still missing @@@
      if (nDiscrete == 1 && current < 1.0001) {
        actualMult.Get()->at(i) = static_cast<G4int>(current);
        if(current<1) 
        {
          actualMult.Get()->at(i) = 0;
          if(G4UniformRand()<current) actualMult.Get()->at(i) = 1;
        }
      }
      nSecondaries += actualMult.Get()->at(i);
    }
    for (i = 0; i < nSecondaries; ++i) {
      G4ReactionProduct * theOne = new G4ReactionProduct;
      theOne->SetDefinition(G4Gamma::Gamma());
      thePhotons->push_back(theOne);
    }
 
    G4int count = 0;
 
    if (nDiscrete == 1 && nPartials == 1) {
      if (actualMult.Get()->at(0) > 0) {
        if (disType[0] == 1) {
          // continuum
          G4ParticleHPVector* temp;
          temp = partials[ 0 ]->GetY(anEnergy); //@@@ look at, seems fishy
          G4double maximumE = temp->GetX( temp->GetVectorLength()-1 ); // This is an assumption.
 
          std::vector< G4double > photons_e_best( actualMult.Get()->at(0) , 0.0 );
          G4double best = DBL_MAX;
          G4int maxTry = 1000; 
          for (G4int j = 0; j < maxTry; ++j) {
            std::vector<G4double> photons_e(actualMult.Get()->at(0), 0.0);
            for (auto it = photons_e.begin(); it < photons_e.end(); ++it) {
              *it = temp->Sample();
            }
 
            if (std::accumulate(photons_e.cbegin(), photons_e.cend(), 0.0) > maximumE) {
              if (std::accumulate(photons_e.cbegin(), photons_e.cend(), 0.0) < best)
                photons_e_best = photons_e;
              continue;
 
            } else {
              G4int iphot = 0;
              for (auto it = photons_e.cbegin(); it < photons_e.cend(); ++it) {
                thePhotons->operator[](iphot)->SetKineticEnergy(*it);   // Replace index count, which was not incremented, 
                                                                        // with iphot, which is, as per Artem Zontikov,
                                                                        // bug report 2167
                ++iphot;
              }
 
              break;
            }
          }
          delete temp;
 
        } else {
          // discrete
          thePhotons->operator[](count)->SetKineticEnergy(energy[i]);
        }
        ++count;
    if (count > nSecondaries)
          throw G4HadronicException(__FILE__, __LINE__, "G4ParticleHPPhotonDist::GetPhotons inconsistency");
      }
         
    } else {  // nDiscrete != 1 or nPartials != 1
      for (i=0; i<nDiscrete; ++i) { 
        for (ii=0; ii< actualMult.Get()->at(i); ++ii) {   
          if (disType[i] == 1) {
            // continuum
            G4double  sum=0, run=0;
            for (iii = 0; iii < nPartials; ++iii)
              sum+=probs[iii].GetY(anEnergy);
            G4double random = G4UniformRand();
            G4int theP = 0;
            for (iii = 0; iii < nPartials; ++iii) {
              run+=probs[iii].GetY(anEnergy);
              theP = iii;
              if(random<run/sum) break;
            }
 
            if (theP == nPartials) theP=nPartials-1; // das sortiert J aus.
            sum = 0; 
            G4ParticleHPVector * temp;
            temp = partials[theP]->GetY(anEnergy); //@@@ look at, seems fishy
            G4double eGamm = temp->Sample();
            thePhotons->operator[](count)->SetKineticEnergy(eGamm);
            delete temp;
 
          } else { 
            // discrete
            thePhotons->operator[](count)->SetKineticEnergy(energy[i]);
      }
          ++count;
          if (count > nSecondaries)
            throw G4HadronicException(__FILE__, __LINE__, "G4ParticleHPPhotonDist::GetPhotons inconsistency");
        }
      }
    }
 
    // now do the angular distributions...
    if (isoFlag == 1) {
      for (i=0; i< nSecondaries; ++i)
      {
    G4double costheta = 2.*G4UniformRand()-1;
    G4double theta = std::acos(costheta);
    G4double phi = twopi*G4UniformRand();
    G4double sinth = std::sin(theta);
    G4double en = thePhotons->operator[](i)->GetTotalEnergy();
    G4ThreeVector temp(en*sinth*std::cos(phi), en*sinth*std::sin(phi), en*std::cos(theta) );
    thePhotons->operator[](i)->SetMomentum( temp ) ;
      }
    }
    else
    {
      for(i=0; i<nSecondaries; ++i)
      { 
    G4double currentEnergy = thePhotons->operator[](i)->GetTotalEnergy();
    for(ii=0; ii<nDiscrete2; ++ii) 
    {
          if (std::abs(currentEnergy-theGammas[ii])<0.1*keV) break;
    }
    if(ii==nDiscrete2) --ii; // fix for what seems an (file12 vs file 14) inconsistency found in the ENDF 7N14 data. @@
    if(ii<nIso)
    {
          // isotropic distribution
          //
          //Fix Bugzilla report #1745
          //G4double theta = pi*G4UniformRand();
      G4double costheta = 2.*G4UniformRand()-1;
      G4double theta = std::acos(costheta);
          G4double phi = twopi*G4UniformRand();
          G4double sinth = std::sin(theta);
          G4double en = thePhotons->operator[](i)->GetTotalEnergy();
          // DHW G4ThreeVector tempVector(en*sinth*std::cos(phi), en*sinth*std::sin(phi), en*std::cos(theta) );
          G4ThreeVector tempVector(en*sinth*std::cos(phi), en*sinth*std::sin(phi), en*costheta );
          thePhotons->operator[](i)->SetMomentum( tempVector ) ;
    }
    else if(tabulationType==1)
    {
          // legendre polynomials
          G4int it(0);
          for (iii=0; iii<nNeu[ii-nIso]; ++iii) // find the neutron energy
          {
            it = iii;
        if(theLegendre[ii-nIso][iii].GetEnergy()>anEnergy)
              break;
          }
          G4ParticleHPLegendreStore aStore(2);
          aStore.SetCoeff(1, &(theLegendre[ii-nIso][it]));  
          if ( it > 0 ) 
          {
             aStore.SetCoeff(0, &(theLegendre[ii-nIso][it-1])); 
          }
          else
          {
             aStore.SetCoeff(0, &(theLegendre[ii-nIso][it])); 
          }
          G4double cosTh = aStore.SampleMax(anEnergy);
          G4double theta = std::acos(cosTh);
          G4double phi = twopi*G4UniformRand();
          G4double sinth = std::sin(theta);
          G4double en = thePhotons->operator[](i)->GetTotalEnergy();
          G4ThreeVector tempVector(en*sinth*std::cos(phi), en*sinth*std::sin(phi), en*std::cos(theta) );
          thePhotons->operator[](i)->SetMomentum( tempVector ) ;
    }
    else
    {
          // tabulation of probabilities.
          G4int it(0);
          for (iii=0; iii<nNeu[ii-nIso]; ++iii) // find the neutron energy
          {
            it = iii;
        if(theAngular[ii-nIso][iii].GetEnergy()>anEnergy)
              break;
          }
          G4double costh = theAngular[ii-nIso][it].GetCosTh(); // no interpolation yet @@
          G4double theta = std::acos(costh);
          G4double phi = twopi*G4UniformRand();
          G4double sinth = std::sin(theta);
          G4double en = thePhotons->operator[](i)->GetTotalEnergy();
          G4ThreeVector tmpVector(en*sinth*std::cos(phi), en*sinth*std::sin(phi), en*costh );
          thePhotons->operator[](i)->SetMomentum( tmpVector ) ;
    }
      }  
    }
 
  } else if (repFlag == 2) {
    G4double * running = new G4double[nGammaEnergies];
    running[0]=theTransitionProbabilities[0];
    for(i=1; i<nGammaEnergies; ++i)
    {
      running[i]=running[i-1]+theTransitionProbabilities[i];
    }
    G4double random = G4UniformRand();
    G4int it=0;
    for(i=0; i<nGammaEnergies; ++i)
    {
      it = i;
      if(random < running[i]/running[nGammaEnergies-1]) break;
    }
    delete [] running;
    G4double totalEnergy = theBaseEnergy - theLevelEnergies[it];
    G4ReactionProduct * theOne = new G4ReactionProduct;
    theOne->SetDefinition(G4Gamma::Gamma());
    random = G4UniformRand();
    if(theInternalConversionFlag==2 && random>thePhotonTransitionFraction[it])
    {
      theOne->SetDefinition(G4Electron::Electron());
      //Bug reported Chao Zhang ([email protected]), Dongming Mei([email protected]) Feb. 25, 2009 
      //But never enter at least with G4NDL3.13
      totalEnergy += G4Electron::Electron()->GetPDGMass(); // proposed correction: add this line for electron
    }
    theOne->SetTotalEnergy(totalEnergy);
    if( isoFlag == 1 )
    {
      G4double costheta = 2.*G4UniformRand()-1;
      G4double theta = std::acos(costheta);
      G4double phi = twopi*G4UniformRand();
      G4double sinth = std::sin(theta);
      //Bug reported Chao Zhang ([email protected]), Dongming Mei([email protected]) Feb. 25, 2009 
      //G4double en = theOne->GetTotalEnergy();
      G4double en = theOne->GetTotalMomentum();
      //But never cause real effect at least with G4NDL3.13 TK
      G4ThreeVector temp(en*sinth*std::cos(phi), en*sinth*std::sin(phi), en*std::cos(theta) );
      theOne->SetMomentum( temp ) ;
    }
    else
    {
      G4double currentEnergy = theOne->GetTotalEnergy();
      for(ii=0; ii<nDiscrete2; ++ii) 
      {
        if (std::abs(currentEnergy-theGammas[ii])<0.1*keV) break;
      }
      if(ii==nDiscrete2) --ii; // fix for what seems an (file12 vs file 14) inconsistency found in the ENDF 7N14 data. @@
      if(ii<nIso)
      {
        //Bug reported Chao Zhang ([email protected]), Dongming Mei([email protected]) Feb. 25, 2009 
        // isotropic distribution
        //G4double theta = pi*G4UniformRand();
        G4double theta = std::acos(2.*G4UniformRand()-1.);
        //But this is alos never cause real effect at least with G4NDL3.13 TK  not repFlag == 2 AND isoFlag != 1
        G4double phi = twopi*G4UniformRand();
        G4double sinth = std::sin(theta);
        //Bug reported Chao Zhang ([email protected]), Dongming Mei([email protected]) Feb. 25, 2009 
        //G4double en = theOne->GetTotalEnergy();
        G4double en = theOne->GetTotalMomentum();
        //But never cause real effect at least with G4NDL3.13 TK
        G4ThreeVector tempVector(en*sinth*std::cos(phi), en*sinth*std::sin(phi), en*std::cos(theta) );
        theOne->SetMomentum( tempVector ) ;
      }
      else if(tabulationType==1)
      {
        // legendre polynomials
        G4int itt(0);
        for (iii=0; iii<nNeu[ii-nIso]; ++iii) // find the neutron energy
        {
          itt = iii;
      if(theLegendre[ii-nIso][iii].GetEnergy()>anEnergy)
            break;
        }
        G4ParticleHPLegendreStore aStore(2);
        aStore.SetCoeff(1, &(theLegendre[ii-nIso][itt]));  
        //aStore.SetCoeff(0, &(theLegendre[ii-nIso][it-1])); 
        //TKDB 110512
        if ( itt > 0 ) 
        {
           aStore.SetCoeff(0, &(theLegendre[ii-nIso][itt-1])); 
        }
        else
        {
           aStore.SetCoeff(0, &(theLegendre[ii-nIso][itt])); 
        }
        G4double cosTh = aStore.SampleMax(anEnergy);
        G4double theta = std::acos(cosTh);
        G4double phi = twopi*G4UniformRand();
        G4double sinth = std::sin(theta);
        //Bug reported Chao Zhang ([email protected]), Dongming Mei([email protected]) Feb. 25, 2009 
        //G4double en = theOne->GetTotalEnergy();
        G4double en = theOne->GetTotalMomentum();
        //But never cause real effect at least with G4NDL3.13 TK
        G4ThreeVector tempVector(en*sinth*std::cos(phi), en*sinth*std::sin(phi), en*std::cos(theta) );
        theOne->SetMomentum( tempVector ) ;
      }
      else
      {
        // tabulation of probabilities.
        G4int itt(0);
        for (iii=0; iii<nNeu[ii-nIso]; ++iii) // find the neutron energy
        {
          itt = iii;
      if(theAngular[ii-nIso][iii].GetEnergy()>anEnergy)
            break;
        }
        G4double costh = theAngular[ii-nIso][itt].GetCosTh(); // no interpolation yet @@
        G4double theta = std::acos(costh);
        G4double phi = twopi*G4UniformRand();
        G4double sinth = std::sin(theta);
        //Bug reported Chao Zhang ([email protected]), Dongming Mei([email protected]) Feb. 25, 2009 
        //G4double en = theOne->GetTotalEnergy();
        G4double en = theOne->GetTotalMomentum();
        //But never cause real effect at least with G4NDL3.13 TK
        G4ThreeVector tmpVector(en*sinth*std::cos(phi), en*sinth*std::sin(phi), en*costh );
        theOne->SetMomentum( tmpVector ) ;
      }
    }
    thePhotons->push_back(theOne);
  }
  else if( repFlag==0 )
  {
     if ( thePartialXsec == 0 ) 
     {
       return thePhotons;
     }
 
    // Partial Case 
 
      G4ReactionProduct * theOne = new G4ReactionProduct;
      theOne->SetDefinition( G4Gamma::Gamma() );
      thePhotons->push_back( theOne );
 
    // Energy 
 
      G4double sum = 0.0; 
      std::vector < G4double > dif( nDiscrete , 0.0 ); 
      for ( G4int j = 0 ; j < nDiscrete ; ++j ) 
      {
         G4double x = thePartialXsec[ j ].GetXsec( anEnergy );  // x in barn 
         if ( x > 0 ) 
         {
            sum += x;   
         } 
         dif [ j ] = sum; 
      }
      
      G4double rand = G4UniformRand();
 
      G4int iphoton = 0; 
      for ( G4int j = 0 ; j < nDiscrete ; ++j ) 
      {
         G4double y = rand*sum; 
         if ( dif [ j ] > y ) 
         {
            iphoton = j; 
            break;  
         } 
      }
 
      // Statistically suppress the photon according to reaction cross section  
      // Fix proposed by Artem Zontikov, Bug report #1824
      if (theReactionXsec) {
        if (thePartialXsec[iphoton].GetXsec(anEnergy)/theReactionXsec->GetXsec(anEnergy) < G4UniformRand() ) {
          delete thePhotons;
          thePhotons = nullptr;
          return thePhotons;
        }
      }
 
      // Angle 
      G4double cosTheta = 0.0; // mu
 
      if ( isoFlag == 1 )
      {
         // Isotropic Case
 
         cosTheta = 2.*G4UniformRand()-1;
      }
      else
      {
         if ( iphoton < nIso )
         {
            // still Isotropic 
 
            cosTheta = 2.*G4UniformRand()-1;
         }
         else
         {
            if ( tabulationType == 1 )
            {
               // Legendre polynomials
 
               G4int iangle = 0; 
               for ( G4int j = 0 ; j < nNeu [ iphoton - nIso ] ; ++j )
               {
                  iangle = j;
                  if ( theLegendre[ iphoton - nIso ][ j ].GetEnergy() > anEnergy ) break;
               }
 
               G4ParticleHPLegendreStore aStore( 2 );
               aStore.SetCoeff( 1 , &( theLegendre[ iphoton - nIso ][ iangle ] ) );  
               aStore.SetCoeff( 0 , &( theLegendre[ iphoton - nIso ][ iangle - 1 ] ) ); 
 
               cosTheta = aStore.SampleMax( anEnergy );
            }
            else if ( tabulationType == 2 )
            {
               // tabulation of probabilities.
 
               G4int iangle = 0; 
               for ( G4int j = 0 ; j < nNeu [ iphoton - nIso ] ; ++j )
               {
                  iangle = j;
                  if ( theAngular[ iphoton - nIso ][ j ].GetEnergy() > anEnergy ) break;
               }
               cosTheta = theAngular[iphoton-nIso][ iangle ].GetCosTh();
               // no interpolation yet @@
            }
         }
      }
      
      // Set 
      G4double phi = twopi*G4UniformRand();
      G4double theta = std::acos( cosTheta );
      G4double sinTheta = std::sin( theta );
 
      G4double photonE = theGammas[ iphoton ];
      G4ThreeVector direction ( sinTheta*std::cos( phi ) , sinTheta * std::sin( phi ) , cosTheta );
      G4ThreeVector photonP = photonE * direction;
      thePhotons->operator[]( 0 )->SetMomentum( photonP ) ;
  }
  else
  {
    delete thePhotons;
    thePhotons = nullptr; // no gamma data available; some work needed @@@@@@@
  }    
  return thePhotons;
}