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#include "G4HETCAlpha.hh"

G4double G4HETCAlpha::K(const G4Fragment & aFragment)
{
  if (GetStage() != 1) return 1.0;
  // Number of protons in projectile
  G4double Pa = static_cast<G4int>(aFragment.GetParticleDefinition()->GetPDGCharge());
  // Number of neutrons in projectile 
  G4double Na = aFragment.GetParticleDefinition()->GetBaryonNumber();
  G4double TargetA = aFragment.GetA() - Na;
  G4double TargetZ = aFragment.GetZ() - Pa;
  Na -= Pa;
  G4double r = TargetZ/TargetA;

  
  G4double P = aFragment.GetNumberOfParticles();
  G4double H = aFragment.GetNumberOfHoles();

  G4double result = 0.0;
  if (P > 3)
    {
      result = 3.0/(P*(P-1.0)*(P-2.0)*(P-3.0)) * 
	(H*(H-1.0)*(H-2.0)*(H-3.0)*r*r*(r-1.0)*(r-1.0) +
	 2.0*H*(H-1.0)*(H-2.0)*(Pa*r*(1.0-r)*(1.0-r)+Na*r*r*(1.0-r)) +
	 H*(H-1.0)*(Pa*(Pa-1.0)*(1.0-r)*(1.0-r)+4.0*Na*Pa*r*(1.0-r)+Na*(Na-1.0)*r*r) +
	 2*H*(Pa*Na*(Na-1.0)*r+Pa*(Pa-1.0)*Na*(1.0-r)) +
	 Pa*(Pa-1.0)*Na*(Na-1.0));

      result /= 6.0*std::pow((TargetZ/TargetA)*((TargetA-TargetZ)/TargetA),2.0);
    }

  return std::max(0.0,result);

}