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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 (Chao.Zhang@usd.edu) and Dongming Mei(Dongming.Mei@usd.edu)
//        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 "G4ParticleHPPhotonDist.hh"

#include "G4Electron.hh"
#include "G4ParticleHPLegendreStore.hh"
#include "G4PhysicalConstants.hh"
#include "G4Poisson.hh"
#include "G4SystemOfUnits.hh"

#include <numeric>

G4bool G4ParticleHPPhotonDist::InitMean(std::istream& aDataFile)
{
  G4bool result = true;
  if (aDataFile >> repFlag) {
    aDataFile >> targetMass;
    if (repFlag == 1) {
      // multiplicities
      aDataFile >> nDiscrete;
      const std::size_t msize = nDiscrete > 0 ? nDiscrete : 1;
      disType = new G4int[msize];
      energy = new G4double[msize];
      // actualMult = new G4int[msize];
      theYield = new G4ParticleHPVector[msize];
      for (std::size_t i = 0; i < msize; ++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;
      const std::size_t esize = nGammaEnergies > 0 ? nGammaEnergies : 1;
      theLevelEnergies = new G4double[esize];
      theTransitionProbabilities = new G4double[esize];
      if (theInternalConversionFlag == 2)
        thePhotonTransitionFraction = new G4double[esize];
      for (std::size_t ii = 0; ii < esize; ++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 != nullptr && 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]);
        auto hpv = new G4ParticleHPVector;
        *hpv = thePartialXsec[i];
        vct_pXS_par.push_back(hpv);
      }
    }
    const std::size_t psize = nDiscrete2 > 0 ? nDiscrete2 : 1;
    if (theGammas == nullptr) theGammas = new G4double[psize];
    if (theShells == nullptr) theShells = new G4double[psize];

    for (i = 0; i < nIso; ++i)  // isotropic photons
    {
      aDataFile >> theGammas[i] >> theShells[i];
      theGammas[i] *= eV;
      theShells[i] *= eV;
    }
    const std::size_t tsize = nDiscrete2 - nIso > 0 ? nDiscrete2 - nIso : 1;
    nNeu = new G4int[tsize];
    if (tabulationType == 1) theLegendre = new G4ParticleHPLegendreTable*[tsize];
    if (tabulationType == 2) theAngular = new G4ParticleHPAngularP*[tsize];
    for (i = nIso; i < nDiscrete2; ++i) {
      if (tabulationType == 1) {
        aDataFile >> theGammas[i] >> theShells[i] >> nNeu[i - nIso];
        theGammas[i] *= eV;
        theShells[i] *= eV;
        const std::size_t lsize = nNeu[i - nIso] > 0 ? nNeu[i - nIso] : 1;
        theLegendre[i - nIso] = new G4ParticleHPLegendreTable[lsize];
        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;
        const std::size_t asize = nNeu[i - nIso] > 0 ? nNeu[i - nIso] : 1;
        theAngular[i - nIso] = new G4ParticleHPAngularP[asize];
        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.empty()) {
      // 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 == 0) return;
  aDataFile >> nPartials;
  const std::size_t dsize = nPartials > 0 ? nPartials : 1;
  distribution = new G4int[dsize];
  probs = new G4ParticleHPVector[dsize];
  partials = new G4ParticleHPPartial*[dsize];
  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 != nullptr) theReactionXsec = theXsec;

  aDataFile >> nDiscrete >> targetMass;
  if (nDiscrete != 1) {
    theTotalXsec.Init(aDataFile, eV);
  }
  const std::size_t dsize = nDiscrete > 0 ? nDiscrete : 1;
  theGammas = new G4double[dsize];
  theShells = new G4double[dsize];
  isPrimary = new G4int[dsize];
  disType = new G4int[dsize];
  thePartialXsec = new G4ParticleHPVector[dsize];
  for (std::size_t i = 0; i < dsize; ++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;
  auto 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) {
      auto 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;
            }
            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) {
    auto 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];
    auto theOne = new G4ReactionProduct;
    theOne->SetDefinition(G4Gamma::Gamma());
    random = G4UniformRand();
    if (theInternalConversionFlag == 2 && random > thePhotonTransitionFraction[it]) {
      theOne->SetDefinition(G4Electron::Electron());
      // Bug reported Chao Zhang (Chao.Zhang@usd.edu), Dongming Mei(Dongming.Mei@usd.edu) 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 (Chao.Zhang@usd.edu), Dongming Mei(Dongming.Mei@usd.edu) 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 (Chao.Zhang@usd.edu), Dongming Mei(Dongming.Mei@usd.edu) 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 (Chao.Zhang@usd.edu), Dongming Mei(Dongming.Mei@usd.edu) 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 (Chao.Zhang@usd.edu), Dongming Mei(Dongming.Mei@usd.edu) 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 (Chao.Zhang@usd.edu), Dongming Mei(Dongming.Mei@usd.edu) 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 == nullptr) {
      return thePhotons;
    }

    // Partial Case

    auto 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 != nullptr) {
      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;
}