The statistical decay of the compound nucleus is determined by the squared matrix element of the transition
to the continuum and by the density of final states. In the usual Hauser-Feshbach and WeisskopfEwing
evaporation models, the transition matrix element is expressed in terms of the transmission
coefficients or the cross section of the inverse formation process. In the Fermi breakup and statistical
multifragmentation models, the transition matrix element is taken to be equal for all decay channels.
In all cases the density of quasi-bound final fragment states plays an important role.
The density of quasi-bound states of a nucleus is the density of states in which all neutrons are
in bound single-particle states and all protons are in single particle states that are either bound or in
long-lived single particle states well below the Coulomb barrier. We associate these states with the
long-lived states of Bohr’s conception of the compound nucleus [1]. The excitation energy dependence
of the density of states was first estimated by Bethe [2] and has been the center of a great deal
of theoretical and experimental effort [3-5]. All of these calculations of the density of quasi-bound
states begin with a static set of single-particle states and analyze their occupation as a function of the
temperature. The Helmholtz free energy determined in this manner, F
∗
(T) is related to the density of
states ω(E
∗
) by a Laplace transform,