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// Implementation of formulas in analogy to NASA technical paper 3621 by Tripathi, et al.

#include "G4TripathiCrossSection.hh"
#include "G4ParticleTable.hh"
#include "G4IonTable.hh"
#include "G4HadTmpUtil.hh"

G4double G4TripathiCrossSection::
GetCrossSection(const G4DynamicParticle* aPart, 
                const G4Element*anEle, G4double )
{
  G4double result = 0;
  
  const G4double targetAtomicNumber = anEle->GetN();
  const G4double nTargetProtons = anEle->GetZ();
  
  const G4double kineticEnergy = aPart->GetKineticEnergy()/MeV;
  const G4double nProjProtons = aPart->GetDefinition()->GetPDGCharge();
  const G4double projectileAtomicNumber = aPart->GetDefinition()->GetBaryonNumber();

  const G4double nuleonRadius=1.1E-15;
  const G4double myNuleonRadius=1.36E-15;
  
  // needs target mass
  G4double targetMass = G4ParticleTable::GetParticleTable()
                                       ->GetIonTable()
				       ->GetIonMass(G4lrint(nTargetProtons), G4lrint(targetAtomicNumber));
  G4LorentzVector pTarget(0,0,0,targetMass); 
  G4LorentzVector pProjectile(aPart->Get4Momentum());
  pTarget = pTarget+pProjectile;
  G4double E_cm = (pTarget.mag()-targetMass-pProjectile.m())/MeV;
  
  // done
  G4double r_rms_p = 0.6 * myNuleonRadius * pow(projectileAtomicNumber, 1./3.);
  G4double r_rms_t = 0.6 * myNuleonRadius * pow(targetAtomicNumber, 1./3.);
  
  // done
  G4double r_p = 1.29*r_rms_p/nuleonRadius ;
  G4double r_t = 1.29*r_rms_t/nuleonRadius;
  
  // done
  G4double Radius = r_p + r_t + 
           1.2*(pow(targetAtomicNumber, 1./3.) + pow(projectileAtomicNumber, 1./3.))/
	   pow(E_cm, 1./3.);
  
  //done
  G4double B = 1.44*nProjProtons*nTargetProtons/Radius;
  
  // done
  G4double Energy = kineticEnergy/projectileAtomicNumber;

  // done
  //
  // Note that this correction to G4TripathiCrossSection is just to accurately
  // reflect Tripathi's algorithm.  However, if you're using alpha particles/protons
  // consider using the more accurate G4TripathiLightCrossSection, which
  // Tripathi developed specifically for light systems.
  //
  G4double D;
  if (nProjProtons==1 && projectileAtomicNumber==1)
  {
    D = 2.05;
  }
  else if (nProjProtons==2 && projectileAtomicNumber==4)
  {
    D = 2.77-(8.0E-3*targetAtomicNumber)+(1.8E-5*targetAtomicNumber*targetAtomicNumber)
                   - 0.8/(1+exp((250.-Energy)/75.));
  }
  else
  {
  //
  // This is the original value used in the G4TripathiCrossSection implementation,
  // and was used for all projectile/target conditions.  I'm not touching this, 
  // althoughJudging from Tripathi's paper, this is valid for cases where the
  // nucleon density changes little with A.
  // 
    D = 1.75;
  }
  // done
  G4double C_E = D * (1-exp(-Energy/40.)) - 0.292*exp(-Energy/792.)*cos(0.229*pow(Energy, 0.453));
  
  // done
  G4double S = pow(projectileAtomicNumber, 1./3.)*pow(targetAtomicNumber, 1./3.)/
               (pow(projectileAtomicNumber, 1./3.) + pow(targetAtomicNumber, 1./3.)); 
  
  // done
  G4double deltaE = 1.85*S + 0.16*S/pow(E_cm,1./3.) - C_E +
                    0.91*(targetAtomicNumber-2.*nTargetProtons)*nProjProtons/
		    (targetAtomicNumber*projectileAtomicNumber);
  
  // done 
  result = pi * nuleonRadius*nuleonRadius * 
           pow(( pow(targetAtomicNumber, 1./3.) + 
	         pow(projectileAtomicNumber, 1./3.) + deltaE),2.) * (1-B/E_cm);
  
  if(result < 0) result = 0;
  return result*m2;

}