PrimaryGeneratorGun2.cc

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//
// $Id: PrimaryGeneratorGun2.cc 68734 2013-04-05 09:47:02Z gcosmo $
// 
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#include "PrimaryGeneratorGun2.hh"

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

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PrimaryGeneratorGun2::PrimaryGeneratorGun2()
 : G4VUserPrimaryGeneratorAction(), fParticleGun(0)
{
  // default particle kinematic
  //
  G4int n_particle = 1;
  fParticleGun  = new G4ParticleGun(n_particle);
    
  G4ParticleDefinition* particle
           = G4ParticleTable::GetParticleTable()->FindParticle("geantino");
  fParticleGun->SetParticleDefinition(particle);
  fParticleGun->SetParticleEnergy(1*eV);
  
  // vertex 
  //  
  fRadius = 8.*mm;
  
  //opening angle
  //
  G4double alphaMin =  91.*deg;
  G4double alphaMax = 180.*deg;
  fCosAlphaMin = std::cos(alphaMin);
  fCosAlphaMax = std::cos(alphaMax);  
}

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PrimaryGeneratorGun2::~PrimaryGeneratorGun2()
{
  delete fParticleGun;  
}

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void PrimaryGeneratorGun2::GeneratePrimaries(G4Event* anEvent)
{
  //vertex position uniform in sphere
  //
  G4double cosTheta = 2*G4UniformRand() - 1;  //cosTheta uniform in [0, pi]
  G4double sinTheta = std::sqrt(1. - cosTheta*cosTheta);
  G4double phi      = twopi*G4UniformRand();  //phi uniform in [0, 2*pi]
  G4ThreeVector ur(sinTheta*std::cos(phi),sinTheta*std::sin(phi),cosTheta);

  fParticleGun->SetParticlePosition(fRadius*ur);

  //particle direction uniform around ur 
  //
  //1- in World frame
  //cosAlpha uniform in [cos(alphaMin), cos(alphaMax)]
  G4double cosAlpha = fCosAlphaMin-G4UniformRand()*(fCosAlphaMin-fCosAlphaMax);
  G4double sinAlpha = std::sqrt(1. - cosAlpha*cosAlpha);
  //psi uniform in (0,2*pi)
  G4double psi      = twopi*G4UniformRand();
  G4ThreeVector dir(sinAlpha*std::cos(psi),sinAlpha*std::sin(psi),cosAlpha);

  //2- rotate dir   (rotateUz transforms uz to ur)
  dir.rotateUz(ur);           

  fParticleGun->SetParticleMomentumDirection(dir);

  //create vertex
  //
  fParticleGun->GeneratePrimaryVertex(anEvent);
}

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