Partial redistribution in radiation transport

Abstract

Radiation diffusion in a slab of purely scattering atoms with only one transition is calculated using a Monte Carlo method. Partial redistribution because of the Doppler effect is included. The scattering is assumed to be isotropic and incoherent. Results are obtained for (1) the amount of diffuse reflection and transmission as a function of optical depth, and (2) the angular distribution and spectrum of the reflected component. The results are found to be similar to that obtained from a differential equation for radiation diffusion without redistribution. The light reflected is characterized by an albedo close to 1 at the line center when the optical depth is large compared to 1. The reflected intensity increases with the amount of scattering material corresponding to an increase in an effective line width. The total amount of diffusely transmitted radiation is insensitive to the amount of scattering material and has two spectral bands centered in the line wings where the optical depth is about 2. The angular distribution of reflected radiation is Lambertian.