Analytically Solvable Problems in Radiative Transfer. I

As is well known, the transfer of radiation in a medium is described by an integral equation, first given by Biberman and Holstein. They assumed that the emission coefficient is proportional to the absorption coefficient. After a discussion of the relation of this type of radiative transfer to Brownian motion, we solve the integral equation for a slab and for all line shapes of interest with and without hyperfine structure in the limit of high optical depth.