At the end of the pre-equilibrium stage, or a thermalizing
process, the residual nucleus is supposed to be left in an
equilibrium state, in which the excitation energy is shared by a
large number of nucleons. Such an equilibrated compound nucleus
is characterized by its mass, charge and excitation energy with
no further memory of the steps which led to its formation. If
the excitation energy is higher than the separation energy, it
can still eject nucleons and light fragments (d, t, He, ). These
constitute the low energy and most abundant part of the emitted
particles in the rest system of the residual nucleus. The
emission of particles by an excited compound nucleus has been
successfully described by comparing the nucleus with the
evaporation of molecules from a fluid . The first statistical
theory of compound nuclear decay is due to Weisskopf and Ewing.