G4WentzelVIRelXSection.hh

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// $Id: G4WentzelVIRelXSection.hh 96934 2016-05-18 09:10:41Z gcosmo $
//
// -------------------------------------------------------------------
//
//
// GEANT4 Class header file
//
//
// File name:     G4WentzelVIRelXSection
//
// Authors:       V.Ivanchenko  
//
// Creation date: 08.06.2012 from G4WentzelOKandVIxSection 
//
// Modifications:
//
//
// Class Description:
//
// Implementation of the computation of total and transport cross sections,
// sample scattering angle for the single scattering case.
// to be used by single and multiple scattering models. References:
// 1) G.Wentzel, Z. Phys. 40 (1927) 590.
// 2) J.M. Fernandez-Varea et al., NIM B73 (1993) 447.
//
// -------------------------------------------------------------------
//

#ifndef G4WentzelVIRelXSection_h
#define G4WentzelVIRelXSection_h 1

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#include "globals.hh"
#include "G4Material.hh"
#include "G4Element.hh"
#include "G4ElementVector.hh"
#include "G4NistManager.hh"
#include "G4ThreeVector.hh"
#include "G4Pow.hh"

class G4ParticleDefinition;

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class G4WentzelVIRelXSection 
{

public:

  explicit G4WentzelVIRelXSection(G4bool combined = true);

  virtual ~G4WentzelVIRelXSection();

  void Initialise(const G4ParticleDefinition*, G4double CosThetaLim);

  void SetupParticle(const G4ParticleDefinition*);

  // return cos(ThetaMax) for msc and cos(thetaMin) for single scattering
  // cut = DBL_MAX means no scattering off electrons 
  G4double SetupTarget(G4int Z, G4double cut);

  G4double ComputeTransportCrossSectionPerAtom(G4double CosThetaMax);
 
  G4ThreeVector& SampleSingleScattering(G4double CosThetaMin,
                    G4double CosThetaMax,
                    G4double elecRatio);

  inline G4double ComputeNuclearCrossSection(G4double CosThetaMin,
                         G4double CosThetaMax);
 
  inline G4double ComputeElectronCrossSection(G4double CosThetaMin,
                          G4double CosThetaMax);
 
  inline G4double SetupKinematic(G4double kinEnergy,
                 const G4Material* mat,
                 G4double cut,
                 G4double tmass);

  inline G4double GetMomentumSquare() const;

  inline G4double GetCosThetaNuc() const;

  inline G4double GetCosThetaElec() const;

private:

  void ComputeMaxElectronScattering(G4double cut);

  //  hide assignment operator
  G4WentzelVIRelXSection & operator=
  (const G4WentzelVIRelXSection &right) = delete;
  G4WentzelVIRelXSection(const  G4WentzelVIRelXSection&) = delete;

  const G4ParticleDefinition* theProton;
  const G4ParticleDefinition* theElectron;
  const G4ParticleDefinition* thePositron;
  const G4Material* currentMaterial;

  G4NistManager*  fNistManager;
  G4Pow*          fG4pow;

  G4ThreeVector   temp;

  G4double numlimit;

  // integer parameters
  G4int    nwarnings;
  G4int    nwarnlimit;

  G4bool   isCombined;

  // single scattering parameters
  G4double coeff;
  G4double cosTetMaxElec;
  G4double cosTetMaxNuc;
  G4double cosThetaMax;
  G4double alpha2;

  // projectile
  const G4ParticleDefinition* particle;

  G4double chargeSquare;
  G4double charge3;
  G4double spin;
  G4double mass;
  G4double tkin;
  G4double mom2;
  G4double momCM2;
  G4double invbeta2;
  G4double kinFactor;
  G4double etag;
  G4double ecut;
  G4double lowEnergyLimit;

  // target
  G4int    targetZ;
  G4double targetMass;
  G4double screenZ;
  G4double formfactA;
  G4double factorA2;
  G4double factB;
  G4double factB1;
  G4double factD;
  G4double gam0pcmp;
  G4double pcmp2;

  static G4double ScreenRSquare[100];
  static G4double FormFactor[100];
};

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inline G4double 
G4WentzelVIRelXSection::SetupKinematic(G4double kinEnergy,
                       const G4Material* mat,
                       G4double cut,
                       G4double tmass)
{
  if(kinEnergy != tkin || mat != currentMaterial ||
     ecut != cut || tmass != targetMass) { 

    currentMaterial = mat;
    ecut = cut;
    tkin  = kinEnergy;
    G4double momLab2  = tkin*(tkin + 2.0*mass);
    
    G4double etot = tkin + mass;
    G4double ptot = std::sqrt(momLab2);
    G4double m12  = mass*mass;

    targetMass = tmass;

    // relativistic reduced mass from publucation
    // A.P. Martynenko, R.N. Faustov, Teoret. mat. Fiz. 64 (1985) 179
        
    //incident particle & target nucleus
    G4double Ecm = std::sqrt(m12 + targetMass*targetMass + 2.0*etot*targetMass);
    G4double mu_rel = mass*targetMass/Ecm;
    G4double momCM  = ptot*targetMass/Ecm;
    // relative system
    mom2 = momCM*momCM;
    invbeta2 = 1.0 +  mu_rel*mu_rel/mom2;

    factB = spin/invbeta2;
    factD = std::sqrt(mom2)/tmass;
    if(isCombined) {
      G4double cost = 1.-factorA2*mat->GetIonisation()->GetInvA23()/mom2;
      if(cost > cosTetMaxNuc) { cosTetMaxNuc = cost; }
    }
  } 
  return cosTetMaxNuc;

}

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inline G4double G4WentzelVIRelXSection::GetMomentumSquare() const
{
  return mom2;
}

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inline G4double G4WentzelVIRelXSection::GetCosThetaNuc() const
{
  return cosTetMaxNuc;
}

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inline G4double G4WentzelVIRelXSection::GetCosThetaElec() const
{
  return cosTetMaxElec;
}

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inline G4double 
G4WentzelVIRelXSection::ComputeNuclearCrossSection(G4double cosTMin,
                           G4double cosTMax)
{
  G4double xsec = 0.0;
  if(cosTMax < cosTMin) {
    xsec = targetZ*kinFactor*(cosTMin - cosTMax)/
      ((1.0 - cosTMin + screenZ)*(1.0 - cosTMax + screenZ));
  }
  return xsec;
}

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inline G4double 
G4WentzelVIRelXSection::ComputeElectronCrossSection(G4double cosTMin,
                            G4double cosTMax)
{
  G4double xsec = 0.0;
  G4double cost1 = std::max(cosTMin,cosTetMaxElec);
  G4double cost2 = std::max(cosTMax,cosTetMaxElec);
  if(cost1 > cost2) {
    xsec = kinFactor*(cost1 - cost2)/
      ((1.0 - cost1 + screenZ)*(1.0 - cost2 + screenZ));
  }
  return xsec;
}
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#endif