GB05BOptnSplitAndKillByCrossSection.cc

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// $Id$
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#include "Randomize.hh"
#include "GB05BOptnSplitAndKillByCrossSection.hh"

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GB05BOptnSplitAndKillByCrossSection::GB05BOptnSplitAndKillByCrossSection(G4String name)
: G4VBiasingOperation(name),
  fParticleChange(),
  fInteractionLength(-1.0)
{}

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GB05BOptnSplitAndKillByCrossSection::~GB05BOptnSplitAndKillByCrossSection()
{}

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G4double GB05BOptnSplitAndKillByCrossSection::
DistanceToApplyOperation( const G4Track*,
                          G4double,
                          G4ForceCondition* condition)
{
  *condition = NotForced;

  // -- Sample the exponential law using the total interaction length of processes
  // -- to couterbalance for:
  G4double proposedStepLength =  -std::log( G4UniformRand() ) * fInteractionLength;
  
  return proposedStepLength;
}

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G4VParticleChange* 
GB05BOptnSplitAndKillByCrossSection::GenerateBiasingFinalState( const G4Track* track,
                                                                const G4Step*       )
{
  
  // -- This method is called if we have limited the step.
  // -- We hence make the splitting or killing.

  // Get track weight:
  G4double initialWeight = track->GetWeight();
  
  // The "particle change" is the object to be used to communicate to
  // the tracking the update of the primary state and/or creation
  // secondary tracks.
  fParticleChange.Initialize(*track);

  // -- Splitting and killing factors.
  // -- They are taken the same, but the killing factor can be make bigger.
  G4double splittingFactor =  2.0;
  G4double   killingFactor =  2.0;


  if ( track->GetMomentumDirection().z() > 0 )
    {
      // -- We split if the track is moving forward:
      
      // Define the tracks weight:
      G4double weightOfTrack = initialWeight/splittingFactor;
      
      // Ask currect track weight to be changed to new value:
      fParticleChange.ProposeParentWeight( weightOfTrack );
      // Now make clones of this track (this is the actual splitting):
      // we will then have the primary and clone of it, hence the
      // splitting by a factor 2:
      G4Track* clone = new G4Track( *track );
      clone->SetWeight( weightOfTrack );
      fParticleChange.AddSecondary( clone );
      // -- Below's call added for safety & illustration : inform particle change to not
      // -- modify the clone (ie : daughter) weight to male it that of the
      // -- primary. Here call not mandatory and both tracks have same weights.
      fParticleChange.SetSecondaryWeightByProcess(true);
    }
  else
    {
      // -- We apply Russian roulette if the track is moving backward:
      
      // Shoot a random number (in ]0,1[ segment):
      G4double random = G4UniformRand();
      G4double killingProbability = 1.0 - 1.0/killingFactor;
      if ( random < killingProbability )
        {
          // We ask for the the track to be killed:
          fParticleChange.ProposeTrackStatus(fStopAndKill);
        }
      else
        {
          // In this case, the track survives. We change its weight
          // to conserve weight among killed and survival tracks:
          fParticleChange.ProposeParentWeight( initialWeight*killingFactor );
        }
    }
  
  return &fParticleChange;
  
}

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