On the Atomic Polarization of the Ground Level of Na I
  In a recent letter (Trujillo Bueno et al. 2002), we showed the remarkable result that the atomic alignment of the levels P$_{1/2}$ and S$_{1/2}$ of the D$_1$ line of Na I is practically destroyed in the presence of magnetic fields sensibly larger than 10 G, irrespectively of the field direction. In this paper, we demonstrate analytically that this property is a consequence of the decoupling of the electronic and nuclear angular momenta, J and I, in the excited state P$_{3/2}$, which is achieved when the Zeeman splitting from the local magnetic field becomes much larger than the typical hyperfine separation for that level. 
R. Casini, E. Landi Degl'Innocenti, M. Landolfi and J. Trujillo-Bueno