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// $Id: PrimaryGeneratorAction.cc,v 1.3 2006/06/29 16:54:19 gunter Exp $
// GEANT4 tag $Name: geant4-09-03-cand-01 $
//
// 

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#include "PrimaryGeneratorAction.hh"

#include "G4Event.hh"
#include "G4ParticleGun.hh"
#include "G4ParticleTable.hh"
#include "G4ParticleDefinition.hh"
#include "Randomize.hh"

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PrimaryGeneratorAction::PrimaryGeneratorAction()
{
  G4int n_particle = 1;
  particleGun  = new G4ParticleGun(n_particle);
  
  // default particle kinematic

  G4ParticleDefinition* particle
           = G4ParticleTable::GetParticleTable()->FindParticle("gamma");
  particleGun->SetParticleDefinition(particle);
  particleGun->SetParticleMomentumDirection(G4ThreeVector(1.,0.,0.));
  particleGun->SetParticleEnergy(9*MeV);
  particleGun->SetParticlePosition(G4ThreeVector(0.*cm,0.*cm,0.*cm));

}

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

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void PrimaryGeneratorAction::GeneratePrimaries(G4Event* anEvent)
{
  //this function is called at the begining of event
  //
  //distribution uniform in solid angle
  //
  G4double cosTheta = 2*G4UniformRand() - 1., phi = twopi*G4UniformRand();
  G4double sinTheta = std::sqrt(1. - cosTheta*cosTheta);
  G4double ux = sinTheta*std::cos(phi),
           uy = sinTheta*std::sin(phi),
           uz = cosTheta;

  particleGun->SetParticleMomentumDirection(G4ThreeVector(ux,uy,uz));
  
  particleGun->GeneratePrimaryVertex(anEvent);
}

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