  Using a Monte Carlo method, we study Compton scattering and absorption of
X-rays and gamma-rays in cold media. We consider transmission of X/gamma-rays
through a shell of an arbitrary optical depth, for which we derive
energy-dependent Green's functions. Fitting the Green functions with simple
analytical formulae is in progress. We also present a simple treatment of the
effect of absorption on Green's functions for Compton scattering, which allow
to treat media with an arbitrary ionization state and chemical composition. Our
transmission Green's functions allow to treat Thomson-thick absorbers, e.g.
molecular tori of Seyfert 2s.
