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// $Id: G4eeToPGammaModel.cc,v 1.2 2009/02/20 16:38:33 vnivanch Exp $
// GEANT4 tag $Name: geant4-09-03 $
//
// -------------------------------------------------------------------
//
// GEANT4 Class header file
//
//
// File name:     G4eeToPGammaModel
//
// Author:        Vladimir Ivanchenko
//
// Creation date: 25.10.2003
//
// Modifications:
//
//
// -------------------------------------------------------------------
//


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#include "G4eeToPGammaModel.hh"
#include "Randomize.hh"
#include "G4PionZero.hh"
#include "G4Eta.hh"
#include "G4Gamma.hh"
#include "G4DynamicParticle.hh"
#include "G4PhysicsVector.hh"
#include "G4PhysicsLinearVector.hh"
#include "G4eeCrossSections.hh"

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using namespace std;

G4eeToPGammaModel::G4eeToPGammaModel(G4eeCrossSections* cr, const G4String& npart):
  cross(cr)
{
  pi0 = G4PionZero::PionZero();
  if(npart == "pi0") {
    massR = 782.62*MeV;
    particle = pi0;
  } else {
    massR = 1019.46*MeV;
    particle = G4Eta::Eta();
  }
  massP = particle->GetPDGMass();
}

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G4eeToPGammaModel::~G4eeToPGammaModel()
{}

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G4double G4eeToPGammaModel::ThresholdEnergy() const
{
  return LowEnergy();
}

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G4double G4eeToPGammaModel::PeakEnergy() const
{
  return massR;
}

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G4double G4eeToPGammaModel::ComputeCrossSection(G4double e) const
{
  G4double ee = std::min(HighEnergy(),e);
  G4double xs;
  if(particle == pi0) xs = cross->CrossSectionPi0G(ee);
  else                xs = cross->CrossSectionEtaG(ee);
  return xs;
}

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G4PhysicsVector* G4eeToPGammaModel::PhysicsVector(G4double emin, 
						  G4double emax) const
{
  G4double tmin = std::max(emin, ThresholdEnergy());
  G4double tmax = std::max(tmin, emax);
  G4int nbins = (G4int)((tmax - tmin)/(5.*MeV));
  G4PhysicsVector* v = new G4PhysicsLinearVector(emin,emax,nbins);
  v->SetSpline(true);
  return v;
}

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void G4eeToPGammaModel::SampleSecondaries(std::vector<G4DynamicParticle*>* newp,
	    G4double e, const G4ThreeVector& direction)
{
  G4double egam = 0.5*e*(1.0 - massP*massP/(massR*massR));
  G4double tkin = e - egam - massP;
  if(tkin < 0.0) tkin = 0.0;
  G4double cost;
  do {
    cost = 2.0*G4UniformRand() - 1.0;
  } while( 2.0*G4UniformRand() > 1.0 + cost*cost );

  G4double sint = sqrt(1.0 - cost*cost);
  G4double phi  = twopi * G4UniformRand();

  G4ThreeVector dir(sint*cos(phi),sint*sin(phi), cost);
  dir.rotateUz(direction);

  // create G4DynamicParticle objects
  G4DynamicParticle* p1 = 
     new G4DynamicParticle(particle,dir,tkin);
  G4DynamicParticle* p2 = 
     new G4DynamicParticle(G4Gamma::Gamma(),-dir,egam);
  newp->push_back(p1);
  newp->push_back(p2);
}

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