B2PrimaryGeneratorAction.cc

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#include "B2PrimaryGeneratorAction.hh"

#include "G4LogicalVolumeStore.hh"
#include "G4LogicalVolume.hh"
#include "G4Box.hh"
#include "G4Event.hh"
#include "G4ParticleGun.hh"
#include "G4ParticleTable.hh"
#include "G4ParticleDefinition.hh"
#include "G4SystemOfUnits.hh"

#include "Randomize.hh"

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B2PrimaryGeneratorAction::B2PrimaryGeneratorAction()
 : G4VUserPrimaryGeneratorAction()
{
  G4int nofParticles = 1;
  fParticleGun = new G4ParticleGun(nofParticles);

  // default particle kinematic

  G4ParticleDefinition* particleDefinition 
    = G4ParticleTable::GetParticleTable()->FindParticle("proton");

  fParticleGun->SetParticleDefinition(particleDefinition);
  fParticleGun->SetParticleMomentumDirection(G4ThreeVector(0.,0.,1.));
  fParticleGun->SetParticleEnergy(3.0*GeV);
}

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B2PrimaryGeneratorAction::~B2PrimaryGeneratorAction()
{
  delete fParticleGun;
}

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void B2PrimaryGeneratorAction::GeneratePrimaries(G4Event* anEvent)
{
  // This function is called at the begining of event

  // In order to avoid dependence of PrimaryGeneratorAction
  // on DetectorConstruction class we get world volume
  // from G4LogicalVolumeStore.

  G4double worldZHalfLength = 0;
  G4LogicalVolume* worldLV
    = G4LogicalVolumeStore::GetInstance()->GetVolume("World");
  G4Box* worldBox = NULL;
  if ( worldLV ) worldBox = dynamic_cast<G4Box*>(worldLV->GetSolid());
  if ( worldBox ) worldZHalfLength = worldBox->GetZHalfLength();
  else  {
    G4cerr << "World volume of box not found." << G4endl;
    G4cerr << "Perhaps you have changed geometry." << G4endl;
    G4cerr << "The gun will be place in the center." << G4endl;
  }

  // Note that this particular case of starting a primary particle on the world boundary
  // requires shooting in a direction towards inside the world.
  fParticleGun->SetParticlePosition(G4ThreeVector(0., 0., -worldZHalfLength));

  fParticleGun->GeneratePrimaryVertex(anEvent);
}

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