PrimaryGeneratorAction.cc

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/// \file B5/src/PrimaryGeneratorAction.cc
/// \brief Implementation of the B5::PrimaryGeneratorAction class
 
#include "PrimaryGeneratorAction.hh"
 
#include "G4Event.hh"
#include "G4ParticleGun.hh"
#include "G4ParticleTable.hh"
#include "G4ParticleDefinition.hh"
#include "G4GenericMessenger.hh"
#include "G4SystemOfUnits.hh"
#include "Randomize.hh"
 
namespace B5
{
 
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PrimaryGeneratorAction::PrimaryGeneratorAction()
// : G4VUserPrimaryGeneratorAction(),
//   fParticleGun(nullptr), fMessenger(nullptr),
//   fPositron(nullptr), fMuon(nullptr), fPion(nullptr),
//   fKaon(nullptr), fProton(nullptr),
//   fMomentum(1000.*MeV),
//   fSigmaMomentum(50.*MeV),
//   fSigmaAngle(2.*deg),
//   fRandomizePrimary(true)
{
  G4int nofParticles = 1;
  fParticleGun  = new G4ParticleGun(nofParticles);
 
  auto particleTable = G4ParticleTable::GetParticleTable();
  fPositron = particleTable->FindParticle("e+");
  fMuon = particleTable->FindParticle("mu+");
  fPion = particleTable->FindParticle("pi+");
  fKaon = particleTable->FindParticle("kaon+");
  fProton = particleTable->FindParticle("proton");
 
  // default particle kinematics
  fParticleGun->SetParticlePosition(G4ThreeVector(0.,0.,-8.*m));
  fParticleGun->SetParticleDefinition(fPositron);
 
  // define commands for this class
  DefineCommands();
}
 
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PrimaryGeneratorAction::~PrimaryGeneratorAction()
{
  delete fParticleGun;
  delete fMessenger;
}
 
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void PrimaryGeneratorAction::GeneratePrimaries(G4Event* event)
{
  G4ParticleDefinition* particle;
  if (fRandomizePrimary) {
    auto i = (int)(5. * G4UniformRand());
    switch(i) {
      case 0:
          particle = fPositron;
          break;
      case 1:
          particle = fMuon;
          break;
      case 2:
          particle = fPion;
          break;
      case 3:
          particle = fKaon;
          break;
      default:
          particle = fProton;
          break;
    }
    fParticleGun->SetParticleDefinition(particle);
  }
  else {
    particle = fParticleGun->GetParticleDefinition();
  }
 
  auto pp = fMomentum + (G4UniformRand()-0.5)*fSigmaMomentum;
  auto mass = particle->GetPDGMass();
  auto ekin = std::sqrt(pp*pp+mass*mass)-mass;
  fParticleGun->SetParticleEnergy(ekin);
 
  auto angle = (G4UniformRand()-0.5)*fSigmaAngle;
  fParticleGun->SetParticleMomentumDirection(
                  G4ThreeVector(std::sin(angle),0.,std::cos(angle)));
 
  fParticleGun->GeneratePrimaryVertex(event);
}
 
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void PrimaryGeneratorAction::DefineCommands()
{
  // Define /B5/generator command directory using generic messenger class
  fMessenger
    = new G4GenericMessenger(this,
                             "/B5/generator/",
                             "Primary generator control");
 
  // momentum command
  auto& momentumCmd
    = fMessenger->DeclarePropertyWithUnit("momentum", "GeV", fMomentum,
        "Mean momentum of primaries.");
  momentumCmd.SetParameterName("p", true);
  momentumCmd.SetRange("p>=0.");
  momentumCmd.SetDefaultValue("1.");
  // ok
  //momentumCmd.SetParameterName("p", true);
  //momentumCmd.SetRange("p>=0.");
 
  // sigmaMomentum command
  auto& sigmaMomentumCmd
    = fMessenger->DeclarePropertyWithUnit("sigmaMomentum",
        "MeV", fSigmaMomentum, "Sigma momentum of primaries.");
  sigmaMomentumCmd.SetParameterName("sp", true);
  sigmaMomentumCmd.SetRange("sp>=0.");
  sigmaMomentumCmd.SetDefaultValue("50.");
 
  // sigmaAngle command
  auto& sigmaAngleCmd
    = fMessenger->DeclarePropertyWithUnit("sigmaAngle", "deg", fSigmaAngle,
        "Sigma angle divergence of primaries.");
  sigmaAngleCmd.SetParameterName("t", true);
  sigmaAngleCmd.SetRange("t>=0.");
  sigmaAngleCmd.SetDefaultValue("2.");
 
  // randomizePrimary command
  auto& randomCmd
    = fMessenger->DeclareProperty("randomizePrimary", fRandomizePrimary);
  G4String guidance
    = "Boolean flag for randomizing primary particle types.\n";
  guidance
    += "In case this flag is false, you can select the primary particle\n";
  guidance += "  with /gun/particle command.";
  randomCmd.SetGuidance(guidance);
  randomCmd.SetParameterName("flg", true);
  randomCmd.SetDefaultValue("true");
}
 
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}