**Constraining
statistical-model
parameters for symmetric and asymmetric fission**,
D. Mancusi^{1},
R. J. Charity^{2}, and J. Cugnon^{3 }, [1] *CEA, Centre de Saclay, IRFU/Service de Physique
Nuclaire, F-91191
Gif-sur-Yvette, France*, [2] *Department
of Chemistry, Washington University, St. Louis, Missouri
63130, USA*, [3] *University
of Liège,
AGO Department, allée du 6 Août 17, bât.
B5, B-4000 Liège 1,Belgium* − The
de-excitation of compound nuclei has been successfully described
for several decades
by means of statistical models. However, it is not yet possible
to make
quantitatively accurate predictions without some fine-tuning of
the model
parameters. This is
partly due to the
vastness of the amount of nuclear data that must be fed into the
models, and
partly to the uncertainties in the fundamental ingredients of
de-excitation,
such as level densities and emission barriers. Even the choice of the
mathematical formalism
is not devoid of confusion.

The
degeneracy of the model
ingredients can be partially lifted by studying compound nuclei
with different
masses, charges, excitation energies and spins. Equivalently,
one can apply the
model to several entrance channels, which populate different
regions of the
parameter space of the compound nucleus. One should then be able
to identify the essential
physical ingredients for the description of the de-excitation.

Fusion
reactions play an important
role in this strategy because they fix three out of four of the
compound-nucleus parameters (mass, charge and excitation
energy). If the
incomplete-fusion component is negligible,
the only uncertainty on the compound nucleus comes from the spin
distribution.
Thus, fusion reactions minimize the uncertainty on the entrance
channel and
allow the formulation of global systematics. However, some de
excitation channels, such as
fission, are quite sensitive to spin. Other
entrance channels can then be used to discriminate between
equivalent parameter
sets.