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// $Id: G4HadronElastic.hh,v 1.4 2009-09-23 14:37:44 vnivanch Exp $
// GEANT4 tag $Name: not supported by cvs2svn $
//
// Geant4 Header : G4HadronElastic
//
// Author : V.Ivanchenko 29 June 2009 (redesign old elastic model)
//  
// Modified:
//
// Class Description
// Default model for elastic scattering; GHEISHA algorithm is used 
// Class Description - End

#ifndef G4HadronElastic_h
#define G4HadronElastic_h 1
 
#include "globals.hh"
#include "G4HadronicInteraction.hh"
#include "G4HadProjectile.hh"
#include "G4Nucleus.hh"
#include "G4NucleiProperties.hh"

class G4ParticleDefinition;

class G4HadronElastic : public G4HadronicInteraction
{
public:

  G4HadronElastic(const G4String& name = "hElasticLHEP");

  virtual ~G4HadronElastic();
 
  // implementation of the G4HadronicInteraction interface
  virtual G4HadFinalState * ApplyYourself(const G4HadProjectile & aTrack, 
					  G4Nucleus & targetNucleus);

  // sample momentum transfer using Lab. momentum
  virtual G4double SampleInvariantT(const G4ParticleDefinition* p, 
				    G4double plab,
				    G4int Z, G4int A);

  inline void SetLowestEnergyLimit(G4double value);

  inline G4double LowestEnergyLimit() const;

  inline G4double ComputeMomentumCMS(const G4ParticleDefinition* p, 
				     G4double plab, G4int Z, G4int A);
  
  virtual void Description() const;

private:

  G4ParticleDefinition* theProton;
  G4ParticleDefinition* theNeutron;
  G4ParticleDefinition* theDeuteron;
  G4ParticleDefinition* theAlpha;

  G4double lowestEnergyLimit;  

};

inline void G4HadronElastic::SetLowestEnergyLimit(G4double value)
{
  lowestEnergyLimit = value;
}

inline G4double G4HadronElastic::LowestEnergyLimit() const
{
  return lowestEnergyLimit;
}

inline G4double
G4HadronElastic::ComputeMomentumCMS(const G4ParticleDefinition* p, 
				     G4double plab, G4int Z, G4int A)
{
  G4double m1 = p->GetPDGMass();
  G4double m12= m1*m1;
  G4double m2 = G4NucleiProperties::GetNuclearMass(A, Z);
  return plab*m2/std::sqrt(m12 + m2*m2 + 2.*m2*std::sqrt(m12 + plab*plab));
}

#endif