1 - IAEA Nuclear Data Services

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been studied from the theoretical point o£ view, in order to
have a support for the hypothesis underlying the method of
spin assignment. A numerical simulation of the process has
been performed, exploiting existing experimental data on the
low-excitation levels and the theories for the level density
of higher excitation energy, and for transition probabilities
of the different multipolarities. Particular care has been
devoted to the influence of the limitations in the detecting
apparatus, such as the varying efficiency of Nal crystals as
a function of the energy, and the effect of the energy thresh­
olds which are artificially set to the gamma detection. In
this way the result of the comparison between computation and
experiment depends only on the consistency of the model used
with the real nuclear process. The calculation gives results
which are directly comparable with experiments related to the
Y-decay from neutron capture states. The experiment of spin
assignment involves some integral features of the y-decay,
such as mean multiplicity and the integral of the y-spectrum
above a given energy. In this respect the model works well,
the accordance with the experiment being satisfactory. A more
crucial test would be a systematic comparison with measurements
of the detailed shape of the y-energy spectra. The comparison
performed in the particular case of 1 77nf has shown a good
accordance, but has also indicated some deficiencies of the
model, when low-lying levels are involved. Such deficiencies
can be explained with the general uncertainties of the theory.
The results of the calculation can also be compared with other
possible experiments, such as absolute multiplicity of isomeric
cross section ratio measurements.