File Name: G4RayShooter.hh
the object of this class shoots a ray (actually geantino) primary particle    associated with a G4Event object. This slass must be used exclusively by    G4RayTracer.
void Shoot(G4Event* evt,G4ThreeVector vtx,G4ThreeVector direc); // This method generates a primary vertex and a primary particle at the // given vertex point and with the given direction. This method is invoked // by G4RayTracer and G4MaterialScanner.