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// $Id: ExUCNPrimaryGeneratorAction.cc 75296 2013-10-30 09:34:21Z gcosmo $
//
/// \file exoticphysics/ucn/src/ExUCNPrimaryGeneratorAction.cc
/// \brief Implementation of the ExUCNPrimaryGeneratorAction class
//

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#include "ExUCNPrimaryGeneratorAction.hh"

#include "ExUCNDetectorConstruction.hh"

#include "G4Event.hh"
#include "G4ParticleGun.hh"
#include "G4ParticleTable.hh"
#include "G4ParticleDefinition.hh"
#include "Randomize.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"

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ExUCNPrimaryGeneratorAction::ExUCNPrimaryGeneratorAction(void)
{
  G4int n_particle = 1;
  fParticleGun  = new G4ParticleGun(n_particle);

  G4ParticleTable* particleTable = G4ParticleTable::GetParticleTable();

  G4ParticleDefinition* particle = particleTable->FindParticle("neutron");
  fParticleGun->SetParticleDefinition(particle);
}

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

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

  fParticleGun->SetParticlePosition(G4ThreeVector(0.0, 0.0, 0.0));
  fParticleGun->SetParticlePolarization(G4ThreeVector(0,1,0));

  G4double particleEnergy = 1e-9*eV + G4UniformRand()*(1e-7*eV-1e-9*eV);
  fParticleGun->SetParticleEnergy(particleEnergy);

  G4double theta = 2*pi*G4UniformRand();
  G4double phi = std::acos(1-2*G4UniformRand());
  if (phi > pi/2 && phi < pi) phi = pi-phi;

  G4double z = std::sin(phi)*std::cos(theta);
  G4double x = std::sin(phi)*std::sin(theta);
  G4double y = std::cos(phi);

  fParticleGun->SetParticleMomentumDirection(G4ThreeVector(x,y,z));

  fParticleGun->GeneratePrimaryVertex(anEvent);
}

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