G4eeToHadronsModel.cc

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// $Id: G4eeToHadronsModel.cc 84488 2014-10-16 09:28:02Z gcosmo $
//
// -------------------------------------------------------------------
//
// GEANT4 Class header file
//
//
// File name:     G4eeToHadronsModel
//
// Author:        Vladimir Ivanchenko
//
// Creation date: 12.08.2003
//
// Modifications:
// 08-04-05 Major optimisation of internal interfaces (V.Ivantchenko)
// 18-05-05 Use optimized interfaces (V.Ivantchenko)
//
//
// -------------------------------------------------------------------
//


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#include "G4eeToHadronsModel.hh"
#include "Randomize.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4Electron.hh"
#include "G4Gamma.hh"
#include "G4Positron.hh"
#include "G4PionPlus.hh"
#include "Randomize.hh"
#include "G4Vee2hadrons.hh"
#include "G4PhysicsVector.hh"
#include "G4PhysicsLogVector.hh"

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using namespace std;

G4eeToHadronsModel::G4eeToHadronsModel(G4Vee2hadrons* mod, G4int ver,
                                       const G4String& nam)
  : G4VEmModel(nam),
    model(mod),
    crossPerElectron(0),
    crossBornPerElectron(0),
    isInitialised(false),
    nbins(100),
    verbose(ver)
{
  theGamma = G4Gamma::Gamma();
  highKinEnergy = HighEnergyLimit();
  lowKinEnergy  = LowEnergyLimit();
  emin = lowKinEnergy;
  emax = highKinEnergy;
  peakKinEnergy = highKinEnergy;
  epeak = emax;
}

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G4eeToHadronsModel::~G4eeToHadronsModel()
{
  delete model;
}

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void G4eeToHadronsModel::Initialise(const G4ParticleDefinition*,
                                    const G4DataVector&)
{
  if(isInitialised) { return; }
  isInitialised  = true;

  // CM system
  emin  = model->LowEnergy();
  emax  = model->HighEnergy();

  // peak energy
  epeak = std::min(model->PeakEnergy(), emax);
  
  if(verbose>0) {
    G4cout << "G4eeToHadronsModel::Initialise: " << G4endl;
    G4cout << "CM System: emin(MeV)= " << emin/MeV
           << " epeak(MeV)= " << epeak/MeV
           << " emax(MeV)= " << emax/MeV
           << G4endl;
  }

  crossBornPerElectron = model->PhysicsVector();
  crossPerElectron     = model->PhysicsVector(); 
  nbins = crossPerElectron->GetVectorLength();
  for(G4int i=0; i<nbins; i++) {
    G4double e  = crossPerElectron->Energy(i);
    G4double cs = model->ComputeCrossSection(e);
    crossBornPerElectron->PutValue(i, cs);
  }
  ComputeCMCrossSectionPerElectron();

  if(verbose>1) {
    G4cout << "G4eeToHadronsModel: Cross secsions per electron"
           << " nbins= " << nbins
           << " emin(MeV)= " << emin/MeV
           << " emax(MeV)= " << emax/MeV
           << G4endl;
    for(G4int i=0; i<nbins; i++) {
      G4double e  = crossPerElectron->Energy(i);
      G4double s1 = crossPerElectron->Value(e);
      G4double s2 = crossBornPerElectron->Value(e);
      G4cout << "E(MeV)= " << e/MeV
             << "  cross(nb)= " << s1/nanobarn
             << "  crossBorn(nb)= " << s2/nanobarn
             << G4endl;
    }
  }
}

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G4double G4eeToHadronsModel::CrossSectionPerVolume(
                                      const G4Material* mat,
                                      const G4ParticleDefinition* p,
                                      G4double kineticEnergy,
                                      G4double, G4double)
{
  return mat->GetElectronDensity()*
    ComputeCrossSectionPerElectron(p, kineticEnergy);
}

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G4double G4eeToHadronsModel::ComputeCrossSectionPerAtom(
                                      const G4ParticleDefinition* p,
                                      G4double kineticEnergy,
                                      G4double Z, G4double,
                                      G4double, G4double)
{
  return Z*ComputeCrossSectionPerElectron(p, kineticEnergy);
}

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G4double G4eeToHadronsModel::ComputeCrossSectionPerElectron(
                                          const G4ParticleDefinition*,
                                                G4double energy,
                                                G4double, G4double)
{
  G4double cross = 0.0;
  if(crossPerElectron) {
    cross = crossPerElectron->Value(energy);
  }
  return cross;
}

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void G4eeToHadronsModel::SampleSecondaries(std::vector<G4DynamicParticle*>* newp,
                                           const G4MaterialCutsCouple*,
                                           const G4DynamicParticle* dParticle,
                                           G4double,
                                           G4double)
{
  if(crossPerElectron) {
    G4double t = dParticle->GetKineticEnergy();
    G4double e = 2.0*electron_mass_c2*sqrt(1.0 + 0.5*t/electron_mass_c2);
    G4LorentzVector inlv = dParticle->Get4Momentum();
    G4ThreeVector inBoost = inlv.boostVector();
    if(e > emin) {
      G4DynamicParticle* gamma = GenerateCMPhoton(e);
      G4LorentzVector gLv = gamma->Get4Momentum();
      G4LorentzVector lv(0.0,0.0,0.0,e);
      lv -= gLv;
      G4double mass = lv.m();
      G4ThreeVector boost = lv.boostVector();
      const G4ThreeVector dir = gamma->GetMomentumDirection();
      model->SampleSecondaries(newp, mass, dir);
      G4int np = newp->size();
      for(G4int j=0; j<np; j++) {
        G4DynamicParticle* dp = (*newp)[j];
        G4LorentzVector v = dp->Get4Momentum();
        v.boost(boost);
        v.boost(inBoost);
        dp->Set4Momentum(v);
      }
      gLv.boost(inBoost);
      gamma->Set4Momentum(gLv);
      newp->push_back(gamma);
    }
  }
}

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void G4eeToHadronsModel::ComputeCMCrossSectionPerElectron()
{
  for(G4int i=0; i<nbins; i++) {
    G4double e  = crossPerElectron->GetLowEdgeEnergy(i);
    G4double cs = 0.0;
    if(i > 0) {
      G4double L   = 2.0*log(e/electron_mass_c2);
      G4double bt  = 2.0*fine_structure_const*(L - 1.0)/pi;
      G4double btm1= bt - 1.0;
      G4double del = 1. + fine_structure_const*(1.5*L + pi*pi/3. -2.)/pi;
      G4double s1  = crossBornPerElectron->Value(e);
      G4double e1  = crossPerElectron->GetLowEdgeEnergy(i-1);
      G4double x1  = 1. - e1/e;
      cs += s1*(del*pow(x1,bt) - bt*(x1 - 0.25*x1*x1));
      if(i > 1) {
        G4double e2  = e1;
        G4double x2  = x1;
        G4double s2  = crossBornPerElectron->Value(e2);
        G4double w2  = bt*(del*pow(x2,btm1) - 1.0 + 0.5*x2);
        G4double w1;      

        for(G4int j=i-2; j>=0; j--) {
          e1  = crossPerElectron->GetLowEdgeEnergy(j);
          x1  = 1. - e1/e;
          s1  = crossBornPerElectron->Value(e1);
          w1  = bt*(del*pow(x1,btm1) - 1.0 + 0.5*x1);
          cs += 0.5*(x1 - x2)*(w2*s2 + w1*s1);
          e2 = e1;
          x2 = x1;
          s2 = s1;
          w2 = w1;
        }
      }
    }
    crossPerElectron->PutValue(i, cs);
  }
}

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G4DynamicParticle* G4eeToHadronsModel::GenerateCMPhoton(G4double e)
{
  G4double x;
  G4DynamicParticle* gamma = 0;
  G4double L   = 2.0*log(e/electron_mass_c2);
  G4double bt  = 2.0*fine_structure_const*(L - 1.)/pi;
  G4double btm1= bt - 1.0;
  G4double del = 1. + fine_structure_const*(1.5*L + pi*pi/3. -2.)/pi;

  G4double s0 = crossBornPerElectron->Value(e);
  G4double de = (emax - emin)/(G4double)nbins;
  G4double x0 = min(de,e - emin)/e;
  G4double ds = crossBornPerElectron->Value(e)
              *(del*pow(x0,bt) - bt*(x0 - 0.25*x0*x0));
  G4double e1 = e*(1. - x0);

  if(e1 < emax && s0*G4UniformRand()<ds) { 
    x = x0*pow(G4UniformRand(),1./bt);
  } else {    

    x  = 1. - e1/e;
    G4double s1 = crossBornPerElectron->Value(e1);
    G4double w1 = bt*(del*pow(x,btm1) - 1.0 + 0.5*x);
    G4double grej = s1*w1;
    G4double f;
    //    G4cout << "e= " << e/GeV << " epeak= " << epeak/GeV 
    //       << " s1= " << s1 << " w1= " << w1 
    //       << " grej= " << grej << G4endl;
    // Above emax cross section is 0
    if(e1 > emax) {
      x  = 1. - emax/e;
      G4double s2 = crossBornPerElectron->Value(emax);
      G4double w2 = bt*(del*pow(x,btm1) - 1.0 + 0.5*x);
      grej = s2*w2;
      //  G4cout << "emax= " << emax << " s2= " << s2 << " w2= " << w2 
      //   << " grej= " << grej << G4endl;
    }

    if(e1 > epeak) {
      x  = 1. - epeak/e;
      G4double s2 = crossBornPerElectron->Value(epeak);
      G4double w2 = bt*(del*pow(x,btm1) - 1.0 + 0.5*x);
      grej = max(grej,s2*w2);
      //G4cout << "epeak= " << epeak << " s2= " << s2 << " w2= " << w2 
      //     << " grej= " << grej << G4endl;
    }
    G4double xmin = 1. - e1/e;
    if(e1 > emax) xmin = 1. - emax/e;
    G4double xmax = 1. - emin/e;
    do {
      x = xmin + G4UniformRand()*(xmax - xmin);
      G4double s2 = crossBornPerElectron->Value((1.0 - x)*e);
      G4double w2 = bt*(del*pow(x,btm1) - 1.0 + 0.5*x);
      //G4cout << "x= " << x << " xmin= " << xmin << " xmax= " << xmax
      //     << " s2= " << s2 << " w2= " << w2 
      //           << G4endl;
      f = s2*w2;
      if(f > grej) {
        G4cout << "G4DynamicParticle* G4eeToHadronsModel:WARNING "
               << f << " > " << grej << " majorant is`small!" 
               << G4endl; 
      }
    } while (f < grej*G4UniformRand());
  }

  G4ThreeVector dir(0.0,0.0,1.0);
  gamma = new G4DynamicParticle(theGamma,dir,x*e);
  return gamma;
}

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