G4eplusAnnihilation.cc

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// $Id: G4eplusAnnihilation.cc 68797 2013-04-05 13:27:11Z gcosmo $
//
// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:     G4eplusAnnihilation
//
// Author:        Vladimir Ivanchenko on base of Michel Maire code
//
// Creation date: 02.08.2004
//
// Modifications:
// 08-11-04 Migration to new interface of Store/Retrieve tables (V.Ivanchenko)
// 08-04-05 Major optimisation of internal interfaces (V.Ivanchenko)
// 03-05-05 suppress Integral option (mma)
// 04-05-05 Make class to be default (V.Ivanchenko)
// 25-01-06 remove cut dependance in AtRestDoIt (mma)
// 09-08-06 add SetModel(G4VEmModel*) (mma)
// 12-09-06, move SetModel(G4VEmModel*) in G4VEmProcess (mma)
// 30-05-12 propagate parent weight to secondaries (D. Sawkey)
//

//
// -------------------------------------------------------------------
//
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#include "G4eplusAnnihilation.hh"
#include "G4PhysicalConstants.hh"
#include "G4MaterialCutsCouple.hh"
#include "G4Gamma.hh"
#include "G4Positron.hh"
#include "G4eeToTwoGammaModel.hh"

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using namespace std;

G4eplusAnnihilation::G4eplusAnnihilation(const G4String& name)
  : G4VEmProcess(name), isInitialised(false)
{
  theGamma = G4Gamma::Gamma();
  SetIntegral(true);
  SetBuildTableFlag(false);
  SetStartFromNullFlag(false);
  SetSecondaryParticle(theGamma);
  SetProcessSubType(fAnnihilation);
  enableAtRestDoIt = true;
}

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G4eplusAnnihilation::~G4eplusAnnihilation()
{}

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G4bool G4eplusAnnihilation::IsApplicable(const G4ParticleDefinition& p)
{
  return (&p == G4Positron::Positron());
}

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G4double G4eplusAnnihilation::AtRestGetPhysicalInteractionLength(
                              const G4Track&, G4ForceCondition* condition)
{
  *condition = NotForced;
  return 0.0;
}

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void G4eplusAnnihilation::InitialiseProcess(const G4ParticleDefinition*)
{
  if(!isInitialised) {
    isInitialised = true;
    if(!EmModel(1)) { SetEmModel(new G4eeToTwoGammaModel(),1); }
    EmModel(1)->SetLowEnergyLimit(MinKinEnergy());
    EmModel(1)->SetHighEnergyLimit(MaxKinEnergy());
    AddEmModel(1, EmModel(1));
  }
}

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void G4eplusAnnihilation::PrintInfo()
{} 

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G4VParticleChange* G4eplusAnnihilation::AtRestDoIt(const G4Track& aTrack,
                                                   const G4Step& )
//
// Performs the e+ e- annihilation when both particles are assumed at rest.
// It generates two back to back photons with energy = electron_mass.
// The angular distribution is isotropic.
// GEANT4 internal units
//
// Note : Effects due to binding of atomic electrons are negliged.
{
  fParticleChange.InitializeForPostStep(aTrack);

  G4double cosTeta = 2.*G4UniformRand()-1.; 
  G4double sinTeta = sqrt((1.-cosTeta)*(1.0 + cosTeta));
  G4double phi     = twopi * G4UniformRand();
  G4ThreeVector dir(sinTeta*cos(phi), sinTeta*sin(phi), cosTeta);
  phi = twopi * G4UniformRand();
  G4ThreeVector pol(cos(phi), sin(phi), 0.0);
  pol.rotateUz(dir);
  
  // e+ parameters
  G4double weight = aTrack.GetWeight();
  G4double time   = aTrack.GetGlobalTime();

  // add gammas
  fParticleChange.SetNumberOfSecondaries(2);
  G4DynamicParticle* dp = 
    new G4DynamicParticle(theGamma, dir, electron_mass_c2);
  dp->SetPolarization(pol.x(),pol.y(),pol.z());
  G4Track* track = new G4Track(dp, time, aTrack.GetPosition());
  track->SetTouchableHandle(aTrack.GetTouchableHandle());
  track->SetWeight(weight); 
  pParticleChange->AddSecondary(track);

  dp = new G4DynamicParticle(theGamma,-dir, electron_mass_c2);
  dp->SetPolarization(-pol.x(),-pol.y(),-pol.z()); 
  track = new G4Track(dp, time, aTrack.GetPosition());
  track->SetTouchableHandle(aTrack.GetTouchableHandle());
  track->SetWeight(weight); 
  pParticleChange->AddSecondary(track);

  // Kill the incident positron
  //
  fParticleChange.ProposeTrackStatus(fStopAndKill);
  return &fParticleChange;
}

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