  The change in the decay rate of an excited atom that is brought about by
extinction and thermal-radiation effects in a nearby dielectric medium is
determined from a quantummechanical model. The medium is a collection of
randomly distributed thermally-excited spherical scatterers with absorptive
properties. The modification of the decay rate is described by a set of
correction functions for which analytical expressions are obtained as sums over
contributions from the multipole moments of the scatterers. The results for the
modified decay rate as a function of the distance between the excited atom and
the dielectric medium show the influence of absorption, scattering and
thermal-radiation processes. Some of these processes are found to be mutually
counteractive. The changes in the decay rate are compared to those following
from an effective-medium theory in which the discrete scatterers are replaced
by a continuum.
