Polarization rate in percent. The atmospheric model is an optically thick slab with an unpolarized and uniform primary source and no incident radiation. Dashed lines: perturbation expansion. Solid lines: numerical results calculated with a PALI code based on Nagendra et al. (1999). From top to bottom, Chandrasekhar’s law, log₁₀ϵ = −4, −3, −2, −1. For log₁₀ϵ = −1, only the numerical solution is shown. The Chandrasekhar limit is graphically indistinguishable from the ϵ = 10⁻⁴ numerical results.