Editing How to Generate Primary Action (section)

===G4ParticleGun Generator===
G4ParticleGun is a generator provided by Geant4. This class generates primary particle(s) with a given momentum and position. It does not provide any sort of randomizing. The constructor of G4ParticleGun takes an integer which causes the generation of one or more primaries of exactly same kinematics. It is a rather frequent user requirement to generate a primary with randomized energy, momentum, and/or position.
G4ParticleGun is normally found in one of your constructors within your PrimaryGeneratorAction.
 fParticleGun = new G4ParticleGun(n_particle);
Next you must decribe the default Particle Kinematics:
 G4ParticleTable* particleTable = G4ParticleTable::GetParticleTable();
 G4String particleName = "nameofparticlehere";
 G4ParticleDefinition* particle = particleTable->FindParticle(particleName);
 fParticleGun->SetParticleDefinition(particle);