Many real phenomena may be modelled as locally finite unions of
d-dimensional time dependent random closed sets in Rd, described
by birth-and-growth stochastic processes, so that their mean volume and surface
densities, as well as the so called mean \emph{extended} volume and surface
densities, may be studied in terms of relevant quantities characterizing the
process. We extend here known results in the Poissonian case to a wider class
of birth-and-growth stochastic processes, proving in particular the absolute
continuity of the random time of capture of a point x∈Rd by processes of
this class.Comment: 11 pages; revised version for publication: proof simplified, added
new resul