PrimaryGeneratorAction.cc

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#include "PrimaryGeneratorAction.hh"
#include "DetectorConstruction.hh"

#include "G4Event.hh"
#include "G4ParticleTable.hh"
#include "G4IonTable.hh"
#include "G4ParticleDefinition.hh"
#include "G4Geantino.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "Randomize.hh"

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PrimaryGeneratorAction::PrimaryGeneratorAction(DetectorConstruction* det)
: G4VUserPrimaryGeneratorAction(), fParticleGun(0), fDetector(det)
{
  G4int n_particle = 1;
  fParticleGun  = new G4ParticleGun(n_particle);

  fParticleGun->SetParticleEnergy(0*eV);
  fParticleGun->SetParticlePosition(G4ThreeVector(0.,0.,0.));
  fParticleGun->SetParticleMomentumDirection(G4ThreeVector(0.,0.,1.));  

}

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

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void PrimaryGeneratorAction::GeneratePrimaries(G4Event* anEvent)
{
  //particle type
  if (fParticleGun->GetParticleDefinition() == G4Geantino::Geantino()) {
    G4int Z = 95, A = 241;
    G4double ionCharge   = 0.*eplus;
    G4double excitEnergy = 0.*keV;

    G4ParticleDefinition* ion
       = G4IonTable::GetIonTable()->GetIon(Z,A,excitEnergy);
    fParticleGun->SetParticleDefinition(ion);
    fParticleGun->SetParticleCharge(ionCharge);
  }

  //vertex position uniform within the absorber
  //
  G4double Rmax = fDetector->GetAbsorRadius();
  G4double Rmax2 = Rmax*Rmax;
  G4double R2 = G4UniformRand()*Rmax2;
  G4double R  = std::sqrt(R2);
  
  G4double phi = twopi*G4UniformRand();
  G4double ux = R*std::cos(phi),
           uy = R*std::sin(phi);
  G4double uz = (fDetector->GetAbsorLength())*(G4UniformRand() - 0.5);
  
  fParticleGun->SetParticlePosition(G4ThreeVector(ux,uy,uz));

  //distribution uniform in solid angle
  //
  G4double cosTheta = 2*G4UniformRand() - 1.;
  G4double sinTheta = std::sqrt(1. - cosTheta*cosTheta);
  phi = twopi*G4UniformRand(); 
  G4double vx = sinTheta*std::cos(phi),
           vy = sinTheta*std::sin(phi),
           vz = cosTheta;

  fParticleGun->SetParticleMomentumDirection(G4ThreeVector(vx,vy,vz));
  
  fParticleGun->GeneratePrimaryVertex(anEvent);
}

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