G4IonFluctuations Class Reference

#include <G4IonFluctuations.hh>

Inheritance diagram for G4IonFluctuations:

Collaboration diagram for G4IonFluctuations:

Public Member Functions
	G4IonFluctuations (const G4String &nam="IonFluc")
virtual	~G4IonFluctuations ()
virtual G4double	SampleFluctuations (const G4MaterialCutsCouple *, const G4DynamicParticle *, G4double tmax, G4double length, G4double meanLoss) override
virtual G4double	Dispersion (const G4Material *, const G4DynamicParticle *, G4double tmax, G4double length) override
virtual void	InitialiseMe (const G4ParticleDefinition *) override
virtual void	SetParticleAndCharge (const G4ParticleDefinition *, G4double q2) override
Public Member Functions inherited from G4VEmFluctuationModel
	G4VEmFluctuationModel (const G4String &nam)
virtual	~G4VEmFluctuationModel ()
const G4String &	GetName () const

Detailed Description

Definition at line 61 of file G4IonFluctuations.hh.

Constructor & Destructor Documentation

G4IonFluctuations::G4IonFluctuations ( const G4String &  nam = "IonFluc" )

explicit

Definition at line 73 of file G4IonFluctuations.cc.

  : G4VEmFluctuationModel(nam),
    particle(0),
    particleMass(CLHEP::proton_mass_c2),
    charge(1.0),
    chargeSquare(1.0),
    effChargeSquare(1.0),
    parameter(10.0*CLHEP::MeV/CLHEP::proton_mass_c2),
    theBohrBeta2(50.0*keV/CLHEP::proton_mass_c2),
    minFraction(0.2),
    xmin(0.2),
    minLoss(0.001*CLHEP::eV)
{
  kineticEnergy = 0.0;
  beta2 = 0.0;
  g4calc = G4Pow::GetInstance();
}

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G4IonFluctuations::~G4IonFluctuations ( )

virtual

Definition at line 93 of file G4IonFluctuations.cc.

{}

Member Function Documentation

G4double G4IonFluctuations::Dispersion ( const G4Material *  material, const G4DynamicParticle *  dp, G4double  tmax, G4double  length  )

overridevirtual

Implements G4VEmFluctuationModel.

Definition at line 178 of file G4IonFluctuations.cc.

{
  kineticEnergy = dp->GetKineticEnergy();
  G4double etot = kineticEnergy + particleMass;
  beta2 = kineticEnergy*(kineticEnergy + 2.*particleMass)/(etot*etot);

  G4double electronDensity = material->GetElectronDensity();

  /*
  G4cout << "e= " <<  kineticEnergy << " m= " << particleMass
           << " tmax= " << tmax << " l= " << length 
           << " q^2= " << effChargeSquare << " beta2=" << beta2<< G4endl;
  */
  G4double siga = (1. - beta2*0.5)*tmax*length*electronDensity*
    twopi_mc2_rcl2*chargeSquare/beta2;

  // Low velocity - additional ion charge fluctuations according to
  // Q.Yang et al., NIM B61(1991)149-155.
  //G4cout << "sigE= " << sqrt(siga) << " charge= " << charge <<G4endl;

  G4double Z = material->GetIonisation()->GetZeffective();
 
  G4double fac = Factor(material, Z);

  // heavy ion correction
  //  G4double f1 = 1.065e-4*chargeSquare;
  //  if(beta2 > theBohrBeta2)  f1/= beta2;
  //  else                      f1/= theBohrBeta2;
  //  if(f1 > 2.5) f1 = 2.5;
  //  fac *= (1.0 + f1);

  // taking into account the cut
  G4double fac_cut = 1.0 + (fac - 1.0)*2.0*electron_mass_c2*beta2
    /(tmax*(1.0 - beta2));
  if(fac_cut > 0.01 && fac > 0.01) {
    siga *= fac_cut;
  }

  //G4cout << "siga(keV)= " << sqrt(siga)/keV << " fac= " << fac 
  //         << "  f1= " << f1 << G4endl;

  return siga;
}

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void G4IonFluctuations::InitialiseMe ( const G4ParticleDefinition *  part )

overridevirtual

Reimplemented from G4VEmFluctuationModel.

Definition at line 98 of file G4IonFluctuations.cc.

{
  particle       = part;
  particleMass   = part->GetPDGMass();
  charge         = part->GetPDGCharge()/eplus;
  chargeSquare   = charge*charge;
  effChargeSquare= chargeSquare;
  uniFluct.InitialiseMe(part);
}

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G4double G4IonFluctuations::SampleFluctuations ( const G4MaterialCutsCouple *  couple, const G4DynamicParticle *  dp, G4double  tmax, G4double  length, G4double  meanLoss  )

overridevirtual

Implements G4VEmFluctuationModel.

Definition at line 111 of file G4IonFluctuations.cc.

{
  //  G4cout << "### meanLoss= " << meanLoss << G4endl;
  if(meanLoss <= minLoss) return meanLoss;

  //G4cout << "G4IonFluctuations::SampleFluctuations E(MeV)= " 
  //     << dp->GetKineticEnergy()
  //         << "  Elim(MeV)= " << parameter*charge*particleMass << G4endl; 

  // Vavilov fluctuations
  if(dp->GetKineticEnergy() > parameter*charge*particleMass) {
    return uniFluct.SampleFluctuations(couple,dp,tmax,length,meanLoss);
  }

  const G4Material* material = couple->GetMaterial();
  G4double siga = Dispersion(material,dp,tmax,length);
  G4double loss = meanLoss;
  
  //G4cout << "### siga= " << sqrt(siga) << "  navr= " << navr << G4endl;

  // Gaussian fluctuation

  // Increase fluctuations for big fractional energy loss
  //G4cout << "siga= " << siga << G4endl;
  if ( meanLoss > minFraction*kineticEnergy ) {
    G4double gam = (kineticEnergy - meanLoss)/particleMass + 1.0;
    G4double b2  = 1.0 - 1.0/(gam*gam);
    if(b2 < xmin*beta2) b2 = xmin*beta2;
    G4double x   = b2/beta2;
    G4double x3  = 1.0/(x*x*x);
    siga *= 0.25*(1.0 + x)*(x3 + (1.0/b2 - 0.5)/(1.0/beta2 - 0.5) );
  }
  siga = sqrt(siga);
  G4double sn = meanLoss/siga;
  G4double twomeanLoss = meanLoss + meanLoss;
  //  G4cout << "siga= " << siga << "  sn= " << sn << G4endl;
  
  CLHEP::HepRandomEngine* rndmEngine = G4Random::getTheEngine();
  // thick target case  
  if (sn >= 2.0) {

    do {
      loss = G4RandGauss::shoot(rndmEngine,meanLoss,siga);
      // Loop checking, 03-Aug-2015, Vladimir Ivanchenko
    } while (0.0 > loss || twomeanLoss < loss);

    // Gamma distribution
  } else if(sn > 0.1) {

    G4double neff = sn*sn;
    loss = meanLoss*G4RandGamma::shoot(rndmEngine,neff,1.0)/neff;

    // uniform distribution for very small steps
  } else {
    loss = twomeanLoss*rndmEngine->flat();
  }

  //G4cout << "meanLoss= " << meanLoss << " loss= " << loss << G4endl;
  return loss;
}

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void G4IonFluctuations::SetParticleAndCharge ( const G4ParticleDefinition *  part, G4double  q2  )

overridevirtual

Reimplemented from G4VEmFluctuationModel.

Definition at line 442 of file G4IonFluctuations.cc.

{
  if(part != particle) {
    particle       = part;
    particleMass   = part->GetPDGMass();
    charge         = part->GetPDGCharge()/eplus;
    chargeSquare   = charge*charge;
  }
  effChargeSquare  = q2;
  uniFluct.SetParticleAndCharge(part, q2);
}

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The documentation for this class was generated from the following files:

• geant4.10.03.p01/source/processes/electromagnetic/standard/include/G4IonFluctuations.hh
• geant4.10.03.p01/source/processes/electromagnetic/standard/src/G4IonFluctuations.cc