The time-independent, transmission problem for a purely scattering, ho
mogeneous slab of finite thickness is considered. This problem corresp
onds to a planar beam of radiation impinging perpendicularly upon one
surface of a source-free slab. The scattering process is assumed suffi
ciently peaked in the forward direction so that the Fokker-Planck diff
erential scattering operator can be used. Further, the slab is assumed
sufficiently thin so that radiation backscattering is negligibly smal
l. Generally, this problem is approximated by the classic Fermi soluti
on. By using the recently reported solution for an obliquely incident
pencil beam, we show that the Fermi solution (or any other approximate
solution) can be improved via a variational formalism. Copyright (C)
1996 Elsevier Science Ltd