geant4/source/processes/electromagnetic/utils/include/G4MultipleScatteringx.icc

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// $Id: G4MultipleScatteringx.icc,v 1.2.2.2 2001/06/28 20:19:51 gunter Exp $
// GEANT4 tag $Name:  $
//
// $Id: 
// -------------------------------------------------------------
//    GEANT 4 class inlined methods file
//
//    History: based on object model of
//    2nd December 1995, G.Cosmo
//    ------- G4MultipleScatteringx physics process ------
//              by Laszlo Urban, March 2001
//---------------------------------------------------------------
//            New version of MSC model
//---------------------------------------------------------------
// Modified:
// 18/05/01 V.Ivanchenko Clean up againist Linux ANSI compilation 
//
//---------------------------------------------------------------


inline G4double G4MultipleScatteringx::AlongStepGetPhysicalInteractionLength(
                             const G4Track& track,
                             G4double previousStepSize,
                             G4double currentMinimumStep,
                             G4double& currentSafety,
                             G4GPILSelection* selection
                            )
{
  // get Step limit proposed by the process
  G4double steplength = 
     GetContinuousStepLimit(track,previousStepSize,currentMinimumStep, currentSafety);

  // set return value for G4GPILSelection
  *selection = valueGPILSelectionMSC;

  return  steplength ;
}


inline G4double G4MultipleScatteringx::GetContinuousStepLimit(
                                     const G4Track& track,                  
                                     G4double,
                                     G4double currentMinimumStep,
                                     G4double&)
{
  G4double zPathLength,tPathLength ;
  const G4DynamicParticle* aParticle ;
  G4Material* aMaterial ;
  G4double KineticEnergy,tau ;
  G4bool isOut ;

  static const G4double toler = 1.0e-6*mm ;
  static const G4double factlim = 0.10 ;
  G4double tlimit ;


  static G4double tausmall = 1.e-20 ;
  static G4double taulow   = 1.e-10 ;
  static G4double clim=1./3. ;
  G4double etau,beta2,cc,ccc,u  ;

  // this process is not a candidate for selection by default !!!!!!!!
  valueGPILSelectionMSC = NotCandidateForSelection;

  if(track.GetCurrentStepNumber() == 1)
    stepFlag = 0 ;

  tPathLength = currentMinimumStep ;

  aMaterial = track.GetMaterial() ;
  materialIndex = aMaterial->GetIndex() ;

  aParticle = track.GetDynamicParticle() ;
  KineticEnergy = aParticle->GetKineticEnergy() ;

  if((lastMaterial != aMaterial) || (lastKineticEnergy != KineticEnergy))
  {
    lastKineticEnergy = KineticEnergy ;
    materialIndex = aMaterial->GetIndex() ;

    if((lastMaterial != aMaterial)||(KineticEnergy >= Tlimit)||(stepFlag != 1))
    fTransportMeanFreePath = (*theTransportMeanFreePathTable)
                             (materialIndex)->GetValue(KineticEnergy,isOut);

    lastMaterial = aMaterial;

    if(KineticEnergy < Tlimit)
    {
      stepFlag = 1 ;
      range = G4EnergyLossTables::GetRange(aParticle->GetDefinition(),
                                       KineticEnergy,aMaterial) ;

      alpha1 = range/fTransportMeanFreePath+1 ;
    }
  }

  //  special treatment near boundaries ?
  if(boundary)   
  {                     
    // step limitation at boundary ?
    if(track.GetCurrentStepNumber() > 1)
    {
      if(track.GetStep()->GetPreStepPoint()->GetSafety() < toler)
      {
        tlimit = factlim*fTransportMeanFreePath ;
        if(tPathLength > tlimit)
        { 
          tPathLength = tlimit*G4UniformRand() ;
          valueGPILSelectionMSC = CandidateForSelection;
        }
      } 
    }    
  }               

  //  do the true -> geom transformation
  if( fTransportMeanFreePath > biglambda )
  {
    zPathLength = tPathLength ;
  }
  else if(stepFlag == 0)
  {
    tau = tPathLength/fTransportMeanFreePath ;
    if(tau < tausmall)
       zPathLength = tPathLength*(1.-0.5*tau)  ;
    else
    {
      // sample zPathLength
      etau = exp(-tau) ;
      if(scatteringparameter3 <= clim)
      {
        ccc = 1.-scatteringparameter3 ;
      }
      else
      {
        cc=0.5/scatteringparameter3-1.5 ;
        ccc=2.*scatteringparameter3*exp(cc) ;
      }
      if(tau < taulow)
        beta2 = (1.+scatteringparameter3)*(1.-2.*tau/3.)/tau ;
      else
        beta2 = 0.5*(1.+scatteringparameter3)*(1.-etau)/(tau-1+etau) ;
      do {
           u = -log(1.-G4UniformRand())/beta2 ;
         } while (G4UniformRand() > (1.-scatteringparameter3+
                   2.*scatteringparameter3*beta2*u)*exp(-beta2*u)/ccc ) ;
      zPathLength = tPathLength/(1.+u) ;
    }
  }
  else
  {
    tau = tPathLength/range ; 
    if(tau<perMillion)
      zPathLength = range*(1.-exp(-alpha1*tau))/alpha1 ;
    else if(tau<0.99) 
      zPathLength = range*(1.-exp(alpha1*log(1.-tau)))/alpha1 ;
    else
      zPathLength = range/alpha1 ;
  }  

  tLast = tPathLength ;
  zLast = zPathLength ; 

  return zPathLength ;
}

inline G4double G4MultipleScatteringx::GetMeanFreePath(
                                            const G4Track& track,
                                            G4double,
                                            G4ForceCondition* condition)

 //  it does not limit the Step size , but it sets condition to
 //   Forced , because the PostStepDoIt always has to be called

  {
    *condition = Forced ;

    return DBL_MAX ;
  }

inline G4VParticleChange* G4MultipleScatteringx::AlongStepDoIt(
                                       const G4Track& track,const G4Step& Step)          
 //   only a geom path->true path transformation is performed
{
  static const G4double tfacmx = 10. ;
  G4double tau,geomPathLength, truePathLength ;

  static G4double tausmall = 1.e-20 ;
  static G4double taulow   = 1.e-10 ;
  static G4double clim=1./3. ;
  G4double ltau,cc,ccc,beta2,u ;

  fParticleChange.Initialize(track);

  geomPathLength = track.GetStepLength() ;

  if(geomPathLength == zLast)
  { 
    truePathLength = tLast ;
  }
  else if( fTransportMeanFreePath > biglambda )
  {
    truePathLength = geomPathLength ;  
  }
  else if(stepFlag == 0)
  {
    tau = geomPathLength/fTransportMeanFreePath ;
    if(tau < tausmall)
      truePathLength = geomPathLength*(1.+0.5*tau) ;
    else if(tau < 1.)
    {
      // sample tPathLength
      ltau = -log(1.-tau) ;
      if(scatteringparameter3 <= clim)
      {
        ccc = 1.-scatteringparameter3 ;
      }
      else
      {
        cc=0.5/scatteringparameter3-1.5 ;
        ccc=2.*scatteringparameter3*exp(cc) ;
      }
      if(tau < taulow)
        beta2 = (1.+scatteringparameter3)*(1.-2.*tau/3.)/tau ;
      else
        beta2 = (1.+scatteringparameter3)*tau/(2.*(ltau-tau)) ;
      do {
           u = -log(1.-G4UniformRand())/beta2 ;
         } while (G4UniformRand() > (1.-scatteringparameter3+
                          2.*scatteringparameter3*beta2*u)*exp(-beta2*u)/ccc ) ;
      truePathLength = geomPathLength*(1.+u) ;
    }
    else
      truePathLength = tfacmx*fTransportMeanFreePath ;
  }
  else 
  {
    if(geomPathLength/range < perMillion)
      truePathLength = range*(1.-exp(-geomPathLength/range)) ;
    else
      truePathLength = range*(1.-exp(log(1.-alpha1*geomPathLength/range)/
                                     alpha1)) ;
  }

  fParticleChange.SetTrueStepLength(truePathLength) ;

  return &fParticleChange ;
  
}


inline G4bool G4MultipleScatteringx::IsApplicable(
                                    const G4ParticleDefinition& particle)
  {
   return(particle.GetPDGCharge() != 0.);
  }

inline G4double G4MultipleScatteringx::GetLambda(
                              G4double KineticEnergy,
                              G4Material* material)
{
  G4bool isOut;
  
  G4double lambda = (*theTransportMeanFreePathTable)
                    (material->GetIndex())->
                    GetValue(KineticEnergy,isOut);
  return lambda;
}