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//
/// \file PrimaryGeneratorAction.cc
/// \brief Implementation of the PrimaryGeneratorAction class
//
//
//
// 

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#include "PrimaryGeneratorAction.hh"

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

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PrimaryGeneratorAction::PrimaryGeneratorAction()
: G4VUserPrimaryGeneratorAction(),fParticleGun(0)
{
  G4int n_particle = 1;
  fParticleGun  = new G4ParticleGun(n_particle);
  
  // default particle kinematic

  G4ParticleDefinition* particle
           = G4ParticleTable::GetParticleTable()->FindParticle("neutron");
  fParticleGun->SetParticleDefinition(particle);
  fParticleGun->SetParticleMomentumDirection(G4ThreeVector(1.,0.,0.));
  fParticleGun->SetParticleEnergy(2*MeV);
  fParticleGun->SetParticlePosition(G4ThreeVector(0.*cm,0.*cm,0.*cm));

}

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

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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;

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

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