PrimaryGeneratorAction4.cc

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// $Id$
// 
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#include "PrimaryGeneratorAction4.hh"
#include "PrimaryGeneratorAction.hh"

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

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PrimaryGeneratorAction4::PrimaryGeneratorAction4(G4ParticleGun* gun)
: fParticleGun(gun)
{
  // vertex volume
  //  
  G4double Rmin = 2.*mm; 
  G4double Rmax = 8.*mm;
  fRmin3 = Rmin*Rmin*Rmin;
  fRmax3 = Rmax*Rmax*Rmax;
  
  //opening angle
  //
  G4double alphaMin =  0.*deg;
  G4double alphaMax = 10.*deg;
  fCosAlphaMin = std::cos(alphaMin);
  fCosAlphaMax = std::cos(alphaMax);  
}

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PrimaryGeneratorAction4::~PrimaryGeneratorAction4()
{ }

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void PrimaryGeneratorAction4::GeneratePrimaries(G4Event* anEvent)
{  
  //vertex position uniform in spherical shell
  //
  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);
  
  G4double R3 = fRmin3 + G4UniformRand()*(fRmax3 - fRmin3);
  G4double R  = std::pow(R3, 1./3);  
        
  fParticleGun->SetParticlePosition(R*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);
  G4double psi      = twopi*G4UniformRand();  //psi uniform in (0,2*pi)  
  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);
  
  //energy
  //  
  fParticleGun->SetParticleEnergy(1*MeV);
  
  //create vertex
  //   
  fParticleGun->GeneratePrimaryVertex(anEvent);
}
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