G4PenelopeBremsstrahlungFS.cc

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// $Id$
//
// Author: Luciano Pandola
//
// History:
// --------
// 23 Nov 2010   L Pandola    First complete implementation
// 02 May 2011   L.Pandola    Remove dependency on CLHEP::HepMatrix
// 24 May 2011   L. Pandola   Renamed (make v2008 as default Penelope)
//

//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
 
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4PenelopeBremsstrahlungFS.hh"
#include "G4PhysicsFreeVector.hh"
#include "G4PhysicsLogVector.hh" 
#include "G4PhysicsTable.hh"
#include "G4Material.hh"
#include "Randomize.hh"

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G4PenelopeBremsstrahlungFS::G4PenelopeBremsstrahlungFS() : 
  theReducedXSTable(0),theEffectiveZSq(0),theSamplingTable(0),
  thePBcut(0)
{
  G4double tempvector[nBinsX] = 
    {1.0e-12,0.025e0,0.05e0,0.075e0,0.1e0,0.15e0,0.2e0,0.25e0,
    0.3e0,0.35e0,0.4e0,0.45e0,0.5e0,0.55e0,0.6e0,0.65e0,0.7e0,
    0.75e0,0.8e0,0.85e0,0.9e0,0.925e0,0.95e0,0.97e0,0.99e0,
    0.995e0,0.999e0,0.9995e0,0.9999e0,0.99995e0,0.99999e0,1.0e0};

  for (size_t ix=0;ix<nBinsX;ix++)
    theXGrid[ix] = tempvector[ix];

  for (size_t i=0;i<nBinsE;i++)
    theEGrid[i] = 0.;

  theElementData = new std::map<G4int,G4DataVector*>;
  theTempVec = new G4PhysicsFreeVector(nBinsX);
}

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G4PenelopeBremsstrahlungFS::~G4PenelopeBremsstrahlungFS()
{
  ClearTables();

  if (theTempVec)
    delete theTempVec;

  //Clear manually theElementData
  std::map<G4int,G4DataVector*>::iterator i;
  if (theElementData)
    {
      for (i=theElementData->begin(); i != theElementData->end(); i++)        
    delete i->second;        
      delete theElementData;
      theElementData = 0;
    }

}

//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...


void G4PenelopeBremsstrahlungFS::ClearTables()
{  
  std::map< std::pair<const G4Material*,G4double> ,G4PhysicsTable*>::iterator j;

  if (theReducedXSTable)
    {
      for (j=theReducedXSTable->begin(); j != theReducedXSTable->end(); j++)
    {
      G4PhysicsTable* tab = j->second;
      tab->clearAndDestroy();
          delete tab;
    }
      delete theReducedXSTable;
      theReducedXSTable = 0;
    }

  if (theSamplingTable)
    {
      for (j=theSamplingTable->begin(); j != theSamplingTable->end(); j++)
    {
      G4PhysicsTable* tab = j->second;
      tab->clearAndDestroy();
          delete tab;
    }
      delete theSamplingTable;
      theSamplingTable = 0;
    }

  std::map< std::pair<const G4Material*,G4double> ,G4PhysicsFreeVector*>::iterator kk;
  if (thePBcut)
    {
      for (kk=thePBcut->begin(); kk != thePBcut->end(); kk++)   
    delete kk->second;
      delete thePBcut;
      thePBcut = 0;      
    }


  if (theEffectiveZSq)
    {
      delete theEffectiveZSq;
      theEffectiveZSq = 0;
    }
  
 return;
}

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G4double G4PenelopeBremsstrahlungFS::GetEffectiveZSquared(const G4Material* material)
{
  if (!theEffectiveZSq)
    {
      G4ExceptionDescription ed;
      ed << "The container for the <Z^2> values is not initialized" << G4endl;
      G4Exception("G4PenelopeBremsstrahlungFS::GetEffectiveZSquared()",
          "em2007",FatalException,ed);
      return 0;
    }
  //found in the table: return it 
  if (theEffectiveZSq->count(material))
    return theEffectiveZSq->find(material)->second;    
  else
    {
      G4ExceptionDescription ed;
      ed << "The value of  <Z^2> is not properly set for material " << 
    material->GetName() << G4endl;
      //requires running of BuildScaledXSTable()
      G4Exception("G4PenelopeBremsstrahlungFS::GetEffectiveZSquared()",
          "em2008",FatalException,ed);
    }
  return 0;
}

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void G4PenelopeBremsstrahlungFS::BuildScaledXSTable(const G4Material* material,
                            G4double cut)
{
  //Corresponds to subroutines EBRaW and EBRaR of PENELOPE
  /*
    This method generates the table of the scaled energy-loss cross section from 
    bremsstrahlung emission for the given material. Original data are read from 
    file. The table is normalized according to the Berger-Seltzer cross section.
  */

 //*********************************************************************
  //Determine the equivalent atomic number <Z^2>
  //*********************************************************************
  std::vector<G4double> *StechiometricFactors = new std::vector<G4double>;
  G4int nElements = material->GetNumberOfElements();
  const G4ElementVector* elementVector = material->GetElementVector();
  const G4double* fractionVector = material->GetFractionVector();
  for (G4int i=0;i<nElements;i++)
    {
      G4double fraction = fractionVector[i];
      G4double atomicWeigth = (*elementVector)[i]->GetA()/(g/mole);
      StechiometricFactors->push_back(fraction/atomicWeigth);
    }      
  //Find max
  G4double MaxStechiometricFactor = 0.;
  for (G4int i=0;i<nElements;i++)
    {
      if ((*StechiometricFactors)[i] > MaxStechiometricFactor)
        MaxStechiometricFactor = (*StechiometricFactors)[i];
    }
  //Normalize
  for (G4int i=0;i<nElements;i++)
    (*StechiometricFactors)[i] /=  MaxStechiometricFactor;
  
  G4double sumz2 = 0;
  G4double sums = 0;
  for (G4int i=0;i<nElements;i++)
    {
      G4double Z = (*elementVector)[i]->GetZ();
      sumz2 += (*StechiometricFactors)[i]*Z*Z;
      sums  += (*StechiometricFactors)[i];
    }
  G4double ZBR2 = sumz2/sums;
  
  theEffectiveZSq->insert(std::make_pair(material,ZBR2));
  

  //*********************************************************************
  // loop on elements and read data files
  //*********************************************************************
  G4DataVector* tempData = new G4DataVector(nBinsE); 
  G4DataVector* tempMatrix = new G4DataVector(nBinsE*nBinsX,0.);

  for (G4int iel=0;iel<nElements;iel++)
    {
      G4double Z = (*elementVector)[iel]->GetZ();
      G4int iZ = (G4int) Z;
      G4double wgt = (*StechiometricFactors)[iel]*Z*Z/ZBR2;
      //
      
      //the element is not already loaded
      if (!theElementData->count(iZ))
    {
      ReadDataFile(iZ);
      if (!theElementData->count(iZ))
        {
          G4ExceptionDescription ed;
          ed << "Error in G4PenelopeBremsstrahlungFS::BuildScaledXSTable" << G4endl;
          ed << "Unable to retrieve data for element " << iZ << G4endl;
          G4Exception("G4PenelopeBremsstrahlungFS::BuildScaledXSTable()",
              "em2009",FatalException,ed);
        }
    }

      G4DataVector* atomData = theElementData->find(iZ)->second;
      
      for (size_t ie=0;ie<nBinsE;ie++)
    {
      (*tempData)[ie] += wgt*(*atomData)[ie*(nBinsX+1)+nBinsX]; //last column contains total XS
      for (size_t ix=0;ix<nBinsX;ix++)
        (*tempMatrix)[ie*nBinsX+ix] += wgt*(*atomData)[ie*(nBinsX+1)+ix];    
    }
    }

  //*********************************************************************
  // the total energy loss spectrum is re-normalized to reproduce the total 
  // scaled cross section of Berger and Seltzer
  //*********************************************************************
  for (size_t ie=0;ie<nBinsE;ie++)
    {
      //for each energy, calculate integral of dSigma/dx over dx
      G4double* tempData2 = new G4double[nBinsX];
      for (size_t ix=0;ix<nBinsX;ix++)  
    tempData2[ix] = (*tempMatrix)[ie*nBinsX+ix]; 
      G4double rsum = GetMomentumIntegral(tempData2,1.0,0);
      delete[] tempData2; 
      G4double fact = millibarn*(theEGrid[ie]+electron_mass_c2)*(1./fine_structure_const)/
    (classic_electr_radius*classic_electr_radius*(theEGrid[ie]+2.0*electron_mass_c2));
      G4double fnorm = (*tempData)[ie]/(rsum*fact);
      G4double TST = 100.*std::fabs(fnorm-1.0);
      if (TST > 1.0)
    {
      G4ExceptionDescription ed;
      ed << "G4PenelopeBremsstrahlungFS. Corrupted data files?" << G4endl;
      G4cout << "TST= " << TST << "; fnorm = " << fnorm << G4endl;
      G4cout << "rsum = " << rsum << G4endl;
      G4cout << "fact = " << fact << G4endl;
      G4cout << ie << " " << theEGrid[ie]/keV << " " << (*tempData)[ie]/barn << G4endl;
      G4Exception("G4PenelopeBremsstrahlungFS::BuildScaledXSTable()",
              "em2010",FatalException,ed);
    }     
      for (size_t ix=0;ix<nBinsX;ix++)
    (*tempMatrix)[ie*nBinsX+ix] *= fnorm;                    
    }

  //*********************************************************************
  // create and fill the tables
  //********************************************************************* 
  G4PhysicsTable* thePhysicsTable = new G4PhysicsTable();
  // the table will contain 32 G4PhysicsFreeVectors with different 
  // values of x. Each of the G4PhysicsFreeVectors has a profile of 
  // log(XS) vs. log(E)
  
  //reserve space of the vectors. Everything is log-log
  //I add one extra "fake" point at low energy, since the Penelope
  //table starts at 1 keV
  for (size_t i=0;i<nBinsX;i++)
    thePhysicsTable->push_back(new G4PhysicsFreeVector(nBinsE+1));
  
  for (size_t ix=0;ix<nBinsX;ix++)
    {
      G4PhysicsFreeVector* theVec = 
    (G4PhysicsFreeVector*) ((*thePhysicsTable)[ix]);      
      for (size_t ie=0;ie<nBinsE;ie++)
    {
      G4double logene = std::log(theEGrid[ie]);
      G4double aValue = (*tempMatrix)[ie*nBinsX+ix];
      if (aValue < 1e-20*millibarn) //protection against log(0)
        aValue = 1e-20*millibarn;   
      theVec->PutValue(ie+1,logene,std::log(aValue));
    }
      //Add fake point at 1 eV using an extrapolation with the derivative 
      //at the first valid point (Penelope approach)
      G4double derivative = ((*theVec)[2]-(*theVec)[1])/(theVec->Energy(2) - theVec->Energy(1));
      G4double log1eV = std::log(1*eV);
      G4double val1eV = (*theVec)[1]+derivative*(log1eV-theVec->Energy(1));
      //fake point at very low energy
      theVec->PutValue(0,log1eV,val1eV);      
    }
  std::pair<const G4Material*,G4double> theKey = std::make_pair(material,cut);
  theReducedXSTable->insert(std::make_pair(theKey,thePhysicsTable));

  delete StechiometricFactors;
  delete tempData;
  delete tempMatrix;

  return;
}

//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....

void G4PenelopeBremsstrahlungFS::ReadDataFile(G4int Z)
{
 
  char* path = getenv("G4LEDATA");
  if (!path)
    {
      G4String excep = "G4PenelopeBremsstrahlungFS - G4LEDATA environment variable not set!";
      G4Exception("G4PenelopeBremsstrahlungFS::ReadDataFile()",
          "em0006",FatalException,excep);
      return;
    }
  /*
    Read the cross section file
  */
  std::ostringstream ost;
  if (Z>9)
    ost << path << "/penelope/bremsstrahlung/pdebr" << Z << ".p08";
  else
    ost << path << "/penelope/bremsstrahlung/pdebr0" << Z << ".p08";
  std::ifstream file(ost.str().c_str());
  if (!file.is_open())
    {
      G4String excep = "G4PenelopeBremsstrahlungFS - data file " + 
    G4String(ost.str()) + " not found!";
      G4Exception("G4PenelopeBremsstrahlungFS::ReadDataFile()",
          "em0003",FatalException,excep);
      return;
    }

  G4int readZ =0;
  file >> readZ;

  //check the right file is opened.
  if (readZ != Z)
    {
      G4ExceptionDescription ed;
      ed << "Corrupted data file for Z=" << Z << G4endl;
      G4Exception("G4PenelopeBremsstrahlungFS::ReadDataFile()",
          "em0005",FatalException,ed);
      return;
    }

  G4DataVector* theMatrix = new G4DataVector(nBinsE*(nBinsX+1),0.); //initialized with zeros

  for (size_t ie=0;ie<nBinsE;ie++)
    {
      G4double myDouble = 0;
      file >> myDouble; //energy (eV)
      if (!theEGrid[ie]) //fill only the first time
    theEGrid[ie] = myDouble*eV;
      //
      for (size_t ix=0;ix<nBinsX;ix++)
    {
      file >> myDouble;
      (*theMatrix)[ie*(nBinsX+1)+ix] = myDouble*millibarn;
    }
      file >> myDouble; //total cross section
      (*theMatrix)[ie*(nBinsX+1)+nBinsX] = myDouble*millibarn;
    }

  if (theElementData)
    theElementData->insert(std::make_pair(Z,theMatrix));
  else
    delete theMatrix;
  file.close();
  return;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....

G4double G4PenelopeBremsstrahlungFS::GetMomentumIntegral(G4double* y,
                               G4double xup,G4int momOrder)
//x is always the gridX
{
  //Corresponds to the function RLMOM of Penelope
  //This method performs the calculation of the integral of (x^momOrder)*y over the interval
  //from x[0] to xup, obtained by linear interpolation on a table of y. 
  //The independent variable is assumed to take positive values only.
  //
  size_t size = nBinsX;
  const G4double eps = 1e-35;

  //Check that the call is valid
  if (momOrder<-1 || size<2 || theXGrid[0]<0)
    {
      G4Exception("G4PenelopeBremsstrahlungFS::GetMomentumIntegral()",
          "em2011",FatalException,"Invalid call");
    }

  for (size_t i=1;i<size;i++)
    {
      if (theXGrid[i]<0 || theXGrid[i]<theXGrid[i-1])
    {
      G4ExceptionDescription ed;
      ed << "Invalid call for bin " << i << G4endl;
      G4Exception("G4PenelopeBremsstrahlungFS::GetMomentumIntegral()",
          "em2012",FatalException,ed);
    }
    }

  //Compute the integral
  G4double result = 0;
  if (xup < theXGrid[0])
    return result;
  bool loopAgain = true;
  G4double xt = std::min(xup,theXGrid[size-1]);
  G4double xtc = 0;
  for (size_t i=0;i<size-1;i++)
    {
      G4double x1 = std::max(theXGrid[i],eps);
      G4double y1 = y[i];
      G4double x2 = std::max(theXGrid[i+1],eps);
      G4double y2 = y[i+1];
      if (xt < x2)
    {
      xtc = xt;
      loopAgain = false;
    }
      else
    xtc = x2;
      G4double dx = x2-x1;
      G4double dy = y2-y1;
      G4double ds = 0;
      if (std::fabs(dx)>1e-14*std::fabs(dy))
    {
      G4double b=dy/dx;
      G4double a=y1-b*x1;    
      if (momOrder == -1)       
        ds = a*std::log(xtc/x1)+b*(xtc-x1);
      else if (momOrder == 0) //speed it up, not using pow()
        ds = a*(xtc-x1) + 0.5*b*(xtc*xtc-x1*x1);
      else
        ds = a*(std::pow(xtc,momOrder+1)-std::pow(x1,momOrder+1))/((G4double) (momOrder + 1))
          + b*(std::pow(xtc,momOrder+2)-std::pow(x1,momOrder+2))/((G4double) (momOrder + 2));       
    }
      else
    ds = 0.5*(y1+y2)*(xtc-x1)*std::pow(xtc,momOrder);
      result += ds;
      if (!loopAgain) 
    return result;
    }
  return result;
}

//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....

G4PhysicsTable* G4PenelopeBremsstrahlungFS::GetScaledXSTable(const G4Material* mat,
                                   G4double cut)
{
  //check if the container exists (if not, create it)
  if (!theReducedXSTable)
    theReducedXSTable = new std::map< std::pair<const G4Material*,G4double> ,
    G4PhysicsTable*>;
  if (!theEffectiveZSq)
    theEffectiveZSq = new std::map<const G4Material*,G4double>;

  //check if it already contains the entry
  std::pair<const G4Material*,G4double> theKey = std::make_pair(mat,cut);
  if (!(theReducedXSTable->count(theKey))) //not found
    BuildScaledXSTable(mat,cut);
  
  if (!(theReducedXSTable->count(theKey)))
    {
      G4Exception("G4PenelopeBremsstrahlungFS::GetScaledXSTable()",
          "em2013",FatalException,"Unable to retrieve the cross section table");
    }

  return theReducedXSTable->find(theKey)->second;
}

//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....

void G4PenelopeBremsstrahlungFS::InitializeEnergySampling(const G4Material* material,
                                G4double cut)
{  
  std::pair<const G4Material*,G4double> theKey = std::make_pair(material,cut);
 
  G4PhysicsTable* thePhysicsTable = new G4PhysicsTable();
  // the table will contain 57 G4PhysicsFreeVectors with different 
  // values of E.
  G4PhysicsFreeVector* thePBvec = new G4PhysicsFreeVector(nBinsE);

  //I reserve space of the vectors. 
  for (size_t i=0;i<nBinsE;i++)
    thePhysicsTable->push_back(new G4PhysicsFreeVector(nBinsX));

  //Retrieve existing table using the method GetScaledXSTable()
  //This will create the table ex-novo, if it does not exist for 
  //some reason 
  G4PhysicsTable* theTableReduced = GetScaledXSTable(material,cut);

  for (size_t ie=0;ie<nBinsE;ie++)
    {
      G4PhysicsFreeVector* theVec =     
    (G4PhysicsFreeVector*) ((*thePhysicsTable)[ie]);      
      //Fill the table
      G4double value = 0; //first value
      theVec->PutValue(0,theXGrid[0],value);
      for (size_t ix=1;ix<nBinsX;ix++)
    {
      //Here calculate the cumulative distribution
      // int_{0}^{x} dSigma(x',E)/dx' (1/x') dx'    
      G4PhysicsFreeVector* v1 = (G4PhysicsFreeVector*) (*theTableReduced)[ix-1];
      G4PhysicsFreeVector* v2 = (G4PhysicsFreeVector*) (*theTableReduced)[ix];

      G4double x1=std::max(theXGrid[ix-1],1.0e-35);   
      //Remember: the table theReducedXSTable has a fake first point in energy
      //so, it contains one more bin than nBinsE.
      G4double y1=std::exp((*v1)[ie+1]);
      G4double x2=std::max(theXGrid[ix],1.0e-35);
      G4double y2=std::exp((*v2)[ie+1]); 
      G4double B = (y2-y1)/(x2-x1);
      G4double A = y1-B*x1;
      G4double dS = A*std::log(x2/x1)+B*(x2-x1);
      value += dS;
      theVec->PutValue(ix,theXGrid[ix],value);
    }

      //fill the PB vector
      G4double xc = cut/theEGrid[ie];
      //Fill a temp data vector
      G4double* tempData = new G4double[nBinsX];
      for (size_t ix=0;ix<nBinsX;ix++)  
    {
      G4PhysicsFreeVector* vv = (G4PhysicsFreeVector*) (*theTableReduced)[ix];
      tempData[ix] = std::exp((*vv)[ie+1]);
    }
      G4double pbval = (xc<=1) ?
    GetMomentumIntegral(tempData,xc,-1) :
    GetMomentumIntegral(tempData,1.0,-1);   
      thePBvec->PutValue(ie,theEGrid[ie],pbval);
      delete[] tempData;
    }

  theSamplingTable->insert(std::make_pair(theKey,thePhysicsTable));
  thePBcut->insert(std::make_pair(theKey,thePBvec));
  return;
}

//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....

G4double G4PenelopeBremsstrahlungFS::SampleGammaEnergy(G4double energy,const G4Material* mat, 
                             G4double cut)
{
  if (!theSamplingTable)    
    theSamplingTable = 
      new std::map< std::pair<const G4Material*,G4double> , G4PhysicsTable*>;
  if (!thePBcut)
    thePBcut = 
      new std::map< std::pair<const G4Material*,G4double> , G4PhysicsFreeVector* >;

  std::pair<const G4Material*,G4double> theKey = std::make_pair(mat,cut);
  
  if (!(theSamplingTable->count(theKey)))
    {
      InitializeEnergySampling(mat,cut);
      if (!(theSamplingTable->count(theKey)) || !(thePBcut->count(theKey)))
    {
      G4ExceptionDescription ed;
      ed << "Unable to create the SamplingTable: " << 
        theSamplingTable->count(theKey) << " " << 
        thePBcut->count(theKey) << G4endl;
      G4Exception("G4PenelopeBremsstrahlungFS::SampleGammaEnergy()",
              "em2014",FatalException,ed);    
    }
    }

  G4PhysicsTable* theTableInte = theSamplingTable->find(theKey)->second;
  G4PhysicsTable* theTableRed = theReducedXSTable->find(theKey)->second;

  //Find the energy bin using bi-partition
  size_t eBin = 0;
  G4bool firstOrLastBin = false;

  if (energy < theEGrid[0]) //below first bin
    {
      eBin = 0;
      firstOrLastBin = true;
    }
  else if (energy > theEGrid[nBinsE-1]) //after last bin
    {
      eBin = nBinsE-1;
      firstOrLastBin = true;
    }
  else
    {
      size_t i=0;
      size_t j=nBinsE-1;
      while ((j-i)>1)
    {
      size_t k = (i+j)/2;
      if (energy > theEGrid[k])
        i = k;
      else
        j = k;   
    }
      eBin = i;
    }

  //Get the appropriate physics vector
  G4PhysicsFreeVector* theVec1 = (G4PhysicsFreeVector*) (*theTableInte)[eBin];

  //use a "temporary" vector which contains the linear interpolation of the x spectra 
  //in energy

  //theTempVect is allocated only once (member variable), but it is overwritten at 
  //every call of this method (because the interpolation factors change!)
  if (!firstOrLastBin)
    {  
      G4PhysicsFreeVector* theVec2 = (G4PhysicsFreeVector*) (*theTableInte)[eBin+1];
      for (size_t iloop=0;iloop<nBinsX;iloop++)
    {
      G4double val = (*theVec1)[iloop]+(((*theVec2)[iloop]-(*theVec1)[iloop]))*
        (energy-theEGrid[eBin])/(theEGrid[eBin+1]-theEGrid[eBin]);
      theTempVec->PutValue(iloop,theXGrid[iloop],val);
    }      
    }
  else //first or last bin, no interpolation
    {
      for (size_t iloop=0;iloop<nBinsX;iloop++) 
    theTempVec->PutValue(iloop,theXGrid[iloop],(*theVec1)[iloop]);  
    }

  //Start the game
  G4double pbcut = (*(thePBcut->find(theKey)->second))[eBin];
 
  if (!firstOrLastBin) //linear interpolation on pbcut as well
    {
      pbcut = (*(thePBcut->find(theKey)->second))[eBin] + 
    ((*(thePBcut->find(theKey)->second))[eBin+1]-(*(thePBcut->find(theKey)->second))[eBin])*
    (energy-theEGrid[eBin])/(theEGrid[eBin+1]-theEGrid[eBin]);
    }

  G4double pCumulative = (*theTempVec)[nBinsX-1]; //last value  
 
  G4double eGamma = 0;
  do
    {    
      G4double pt = pbcut + G4UniformRand()*(pCumulative - pbcut);

      //find where it is
      size_t ibin = 0;
      if (pt < (*theTempVec)[0])
    ibin = 0;
      else if (pt > (*theTempVec)[nBinsX-1])
    {
      //We observed problems due to numerical rounding here (STT). 
      //delta here is a tiny positive number
      G4double delta = pt-(*theTempVec)[nBinsX-1];
      if (delta < pt*1e-10) // very small! Numerical rounding only
        {
          ibin = nBinsX-2;
          G4ExceptionDescription ed;
          ed << "Found that (pt > (*theTempVec)[nBinsX-1]) with pt = " << pt << 
        " , (*theTempVec)[nBinsX-1] = " << (*theTempVec)[nBinsX-1] << " and delta = " << 
        (pt-(*theTempVec)[nBinsX-1]) << G4endl;
          ed << "Possible symptom of problem with numerical precision" << G4endl;
          G4Exception("G4PenelopeBremsstrahlungFS::SampleGammaEnergy()",
              "em2015",JustWarning,ed);
        }
      else //real problem
        {
          G4ExceptionDescription ed;
          ed << "Crash at (pt > (*theTempVec)[nBinsX-1]) with pt = " << pt << 
        " , (*theTempVec)[nBinsX-1]=" << (*theTempVec)[nBinsX-1] << " and nBinsX = " << 
        nBinsX << G4endl;
          ed << "Material: " << mat->GetName() << ", energy = " << energy/keV << " keV" << 
        G4endl;
          G4Exception("G4PenelopeBremsstrahlungFS::SampleGammaEnergy()",
              "em2015",FatalException,ed);    
        }
    }
      else
    {
      size_t i=0;
      size_t j=nBinsX-1;
      while ((j-i)>1)
        {
          size_t k = (i+j)/2;
          if (pt > (*theTempVec)[k])
        i = k;
          else
        j = k;
        }
      ibin = i;
    }
    
      G4double w1 = theXGrid[ibin];
      G4double w2 = theXGrid[ibin+1];            

      G4PhysicsFreeVector* v1 = (G4PhysicsFreeVector*) (*theTableRed)[ibin];
      G4PhysicsFreeVector* v2 = (G4PhysicsFreeVector*) (*theTableRed)[ibin+1];     
      //Remember: the table theReducedXSTable has a fake first point in energy
      //so, it contains one more bin than nBinsE.
      G4double pdf1 = std::exp((*v1)[eBin+1]);
      G4double pdf2 = std::exp((*v2)[eBin+1]);    
      G4double deltaW = w2-w1;
      G4double dpdfb = pdf2-pdf1;
      G4double B = dpdfb/deltaW;
      G4double A = pdf1-B*w1;
      //I already made an interpolation in energy, so I can use the actual value for the 
      //calculation of the wbcut, instead of the grid values (except for the last bin)
      G4double wbcut  = (cut < energy) ? cut/energy : 1.0;
      if (firstOrLastBin) //this is an particular case: no interpolation available
    wbcut  = (cut < theEGrid[eBin]) ? cut/theEGrid[eBin] : 1.0;
     
      if (w1 < wbcut)
    w1 = wbcut;
      if (w2 < w1)
    {
      G4cout << "Warning in G4PenelopeBremsstrahlungFS::SampleX()" << G4endl;
      G4cout << "Conflicting end-point values: w1=" << w1 << "; w2 = " << w2 << G4endl;
      G4cout << "wbcut = " << wbcut << " energy= " << energy/keV << " keV" << G4endl;
      G4cout << "cut = " << cut/keV << " keV" << G4endl;
      return w1*energy;
    }
  
      G4double pmax = std::max(A+B*w1,A+B*w2);
      G4bool loopAgain = false;    
      do
    {
      loopAgain = false;
      eGamma = w1* std::pow((w2/w1),G4UniformRand());
      if  (G4UniformRand()*pmax > (A+B*eGamma))
        loopAgain = true;   
    }while(loopAgain);     
      eGamma *= energy;
    }while(eGamma < cut); //repeat if sampled sub-cut!  

  return eGamma;
}