G4UniversalFluctuation Class Reference

#include <G4UniversalFluctuation.hh>

Inheritance diagram for G4UniversalFluctuation:

Collaboration diagram for G4UniversalFluctuation:

Public Member Functions
	G4UniversalFluctuation (const G4String &nam="UniFluc")
virtual	~G4UniversalFluctuation ()
virtual G4double	SampleFluctuations (const G4MaterialCutsCouple *, const G4DynamicParticle *, G4double, G4double, G4double) override
virtual G4double	Dispersion (const G4Material *, const G4DynamicParticle *, G4double, G4double) override
virtual void	InitialiseMe (const G4ParticleDefinition *) final
virtual void	SetParticleAndCharge (const G4ParticleDefinition *, G4double q2) final
Public Member Functions inherited from G4VEmFluctuationModel
	G4VEmFluctuationModel (const G4String &nam)
virtual	~G4VEmFluctuationModel ()
const G4String &	GetName () const

Detailed Description

Definition at line 64 of file G4UniversalFluctuation.hh.

Constructor & Destructor Documentation

G4UniversalFluctuation::G4UniversalFluctuation ( const G4String &  nam = "UniFluc" )

explicit

Definition at line 86 of file G4UniversalFluctuation.cc.

 :G4VEmFluctuationModel(nam),
  particle(0),
  minNumberInteractionsBohr(10.0),
  minLoss(10.*eV),
  nmaxCont(16.),
  rate(0.55),
  fw(4.)
{
  lastMaterial = 0;

  particleMass = chargeSquare = ipotFluct = electronDensity = f1Fluct = f2Fluct 
    = e1Fluct = e2Fluct = e1LogFluct = e2LogFluct = ipotLogFluct = e0 = esmall 
    = e1 = e2 = 0;
  m_Inv_particleMass = m_massrate = DBL_MAX;
  sizearray = 30;
  rndmarray = new G4double[30];
}

G4UniversalFluctuation::~G4UniversalFluctuation ( )

virtual

Definition at line 107 of file G4UniversalFluctuation.cc.

{
  delete [] rndmarray;
}

Member Function Documentation

G4double G4UniversalFluctuation::Dispersion ( const G4Material *  material, const G4DynamicParticle *  dp, G4double  tmax, G4double  length  )

overridevirtual

Implements G4VEmFluctuationModel.

Definition at line 333 of file G4UniversalFluctuation.cc.

{
  if(dp->GetDefinition() != particle) { InitialiseMe(dp->GetDefinition()); }

  electronDensity = material->GetElectronDensity();

  G4double gam   = (dp->GetKineticEnergy())*m_Inv_particleMass + 1.0;
  G4double beta2 = 1.0 - 1.0/(gam*gam);

  G4double siga  = (1.0/beta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
                 * electronDensity * chargeSquare;

  return siga;
}

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void G4UniversalFluctuation::InitialiseMe ( const G4ParticleDefinition *  part )

finalvirtual

Reimplemented from G4VEmFluctuationModel.

Definition at line 114 of file G4UniversalFluctuation.cc.

{
  particle       = part;
  particleMass   = part->GetPDGMass();
  G4double q     = part->GetPDGCharge()/eplus;

  // Derived quantities
  m_Inv_particleMass = 1.0 / particleMass;
  m_massrate = electron_mass_c2 * m_Inv_particleMass ;
  chargeSquare   = q*q;
}

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G4double G4UniversalFluctuation::SampleFluctuations ( const G4MaterialCutsCouple *  couple, const G4DynamicParticle *  dp, G4double  tmax, G4double  length, G4double  averageLoss  )

overridevirtual

Implements G4VEmFluctuationModel.

Definition at line 129 of file G4UniversalFluctuation.cc.

{
  // Calculate actual loss from the mean loss.
  // The model used to get the fluctuations is essentially the same
  // as in Glandz in Geant3 (Cern program library W5013, phys332).
  // L. Urban et al. NIM A362, p.416 (1995) and Geant4 Physics Reference Manual

  // shortcut for very small loss or from a step nearly equal to the range
  // (out of validity of the model)
  //
  G4double meanLoss = averageLoss;
  G4double tkin  = dp->GetKineticEnergy();
  //G4cout<< "Emean= "<< meanLoss<< " tmax= "<< tmax<< " L= "<<length<<G4endl;
  if (meanLoss < minLoss) { return meanLoss; }

  if(dp->GetDefinition() != particle) { InitialiseMe(dp->GetDefinition()); }

  CLHEP::HepRandomEngine* rndmEngineF = G4Random::getTheEngine();
  
  G4double tau   = tkin * m_Inv_particleMass;            
  G4double gam   = tau + 1.0;
  G4double gam2  = gam*gam;
  G4double beta2 = tau*(tau + 2.0)/gam2;

  G4double loss(0.), siga(0.);

  const G4Material* material = couple->GetMaterial();
  
  // Gaussian regime
  // for heavy particles only and conditions
  // for Gauusian fluct. has been changed 
  //
  if ((particleMass > electron_mass_c2) &&
      (meanLoss >= minNumberInteractionsBohr*tmax))
  {
    G4double tmaxkine = 2.*electron_mass_c2*beta2*gam2/
                        (1.+m_massrate*(2.*gam+m_massrate)) ;
    if (tmaxkine <= 2.*tmax)   
    {
      electronDensity = material->GetElectronDensity();
      siga = sqrt((1.0/beta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
                  * electronDensity * chargeSquare);

      G4double sn = meanLoss/siga;
  
      // thick target case 
      if (sn >= 2.0) {

        G4double twomeanLoss = meanLoss + meanLoss;
        do {
          loss = G4RandGauss::shoot(rndmEngineF,meanLoss,siga);
          // Loop checking, 03-Aug-2015, Vladimir Ivanchenko
        } while  (0.0 > loss || twomeanLoss < loss);

        // Gamma distribution
      } else {

        G4double neff = sn*sn;
        loss = meanLoss*G4RandGamma::shoot(rndmEngineF,neff,1.0)/neff;
      }
      //G4cout << "Gauss: " << loss << G4endl;
      return loss;
    }
  }

  // Glandz regime : initialisation
  //
  if (material != lastMaterial) {
    f1Fluct      = material->GetIonisation()->GetF1fluct();
    f2Fluct      = material->GetIonisation()->GetF2fluct();
    e1Fluct      = material->GetIonisation()->GetEnergy1fluct();
    e2Fluct      = material->GetIonisation()->GetEnergy2fluct();
    e1LogFluct   = material->GetIonisation()->GetLogEnergy1fluct();
    e2LogFluct   = material->GetIonisation()->GetLogEnergy2fluct();
    ipotFluct    = material->GetIonisation()->GetMeanExcitationEnergy();
    ipotLogFluct = material->GetIonisation()->GetLogMeanExcEnergy();
    e0 = material->GetIonisation()->GetEnergy0fluct();
    esmall = 0.5*sqrt(e0*ipotFluct);  
    lastMaterial = material;   
  }

  // very small step or low-density material
  if(tmax <= e0) { return meanLoss; }

  G4double losstot = 0.;
  G4int    nstep = 1;
  if(meanLoss < 25.*ipotFluct)
    {
      if(rndmEngineF->flat()*ipotFluct< 0.04*meanLoss)          
        { nstep = 1; }
      else
        { 
          nstep = 2;
          meanLoss *= 0.5; 
        }
    }

  G4double a1, a2, a3;
  for (G4int istep=0; istep < nstep; ++istep) {
    
    loss = a1 = a2 = a3 = 0.;

    if(tmax > ipotFluct) {
      G4double w2 = G4Log(2.*electron_mass_c2*beta2*gam2)-beta2;

      if(w2 > ipotLogFluct)  {
        G4double C = meanLoss*(1.-rate)/(w2-ipotLogFluct);
        a1 = C*f1Fluct*(w2-e1LogFluct)/e1Fluct;
        if(w2 > e2LogFluct) {
          a2 = C*f2Fluct*(w2-e2LogFluct)/e2Fluct;
        }
        if(a1 < nmaxCont) { 
          //small energy loss
          G4double sa1 = sqrt(a1);
          if(rndmEngineF->flat() < G4Exp(-sa1))
            {
              e1 = esmall;
              a1 = meanLoss*(1.-rate)/e1;
              a2 = 0.;
              e2 = e2Fluct;
            } 
          else
            {
              a1 = sa1 ;    
              e1 = sa1*e1Fluct;
              e2 = e2Fluct;
            }

        } else {
          //not small energy loss
          //correction to get better fwhm value
          a1 /= fw;
          e1 = fw*e1Fluct;
          e2 = e2Fluct;
        }
      }   
    }

    G4double w1 = tmax/e0;
    if(tmax > e0) {
      a3 = rate*meanLoss*(tmax-e0)/(e0*tmax*G4Log(w1));
      if(a1+a2 <= 0.) { 
        a3 /= rate; 
      }
    }
    //'nearly' Gaussian fluctuation if a1>nmaxCont&&a2>nmaxCont&&a3>nmaxCont  
    G4double emean = 0.;
    G4double sig2e = 0.;
 
    // excitation of type 1
    AddExcitation(rndmEngineF, a1, e1, emean, loss, sig2e);

    // excitation of type 2
    AddExcitation(rndmEngineF, a2, e2, emean, loss, sig2e);

    if(emean > 0.0) { SampleGauss(rndmEngineF, emean, sig2e, loss); }

    // ionisation 
    if(a3 > 0.) {
      emean = 0.;
      sig2e = 0.;
      G4double p3 = a3;
      G4double alfa = 1.;
      if(a3 > nmaxCont)
        {
          alfa            = w1*(nmaxCont+a3)/(w1*nmaxCont+a3);
          G4double alfa1  = alfa*G4Log(alfa)/(alfa-1.);
          G4double namean = a3*w1*(alfa-1.)/((w1-1.)*alfa);
          emean          += namean*e0*alfa1;
          sig2e          += e0*e0*namean*(alfa-alfa1*alfa1);
          p3              = a3-namean;
        }

      G4double w2 = alfa*e0;
      G4double w  = (tmax-w2)/tmax;
      if(w > 0.0) {
        const G4int nb = G4Poisson(p3);
        if(nb > 0) {
          if(nb > sizearray) {
            sizearray = nb;
            delete [] rndmarray;
            rndmarray = new G4double[nb];
          }
          rndmEngineF->flatArray(nb, rndmarray);
          for (G4int k=0; k<nb; ++k) { loss += w2/(1.-w*rndmarray[k]); }
        }
      }
      if(emean > 0.0) { SampleGauss(rndmEngineF, emean, sig2e, loss); }
    }
    losstot += loss;
  }
  //G4cout << "Vavilov: " << losstot << "  Nstep= " << nstep << G4endl;

  return losstot;

}

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void G4UniversalFluctuation::SetParticleAndCharge ( const G4ParticleDefinition *  part, G4double  q2  )

finalvirtual

Reimplemented from G4VEmFluctuationModel.

Definition at line 355 of file G4UniversalFluctuation.cc.

{
  if(part != particle) {
    particle       = part;
    particleMass   = part->GetPDGMass();

    // Derived quantities
    if( particleMass != 0.0 ){
      m_Inv_particleMass = 1.0 / particleMass;
      m_massrate = electron_mass_c2 * m_Inv_particleMass ;
    }else{
      m_Inv_particleMass = DBL_MAX;
      m_massrate = DBL_MAX;
    }
  }
  chargeSquare = 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/G4UniversalFluctuation.hh
• geant4.10.03.p01/source/processes/electromagnetic/standard/src/G4UniversalFluctuation.cc