Pre-equilibrium emission and its possible relation to alpha-clustering in nuclei

The study of nuclear states built on clusters bound by valence neutrons
in their molecular configurations is a field of large interest. Clustering
becomes particularly important at the dripline, where weakly
bound systems prevail. For light nuclei, at an excitation energy close
to the particle separation value, there are experimental evidences of
such structure effects, but this is still not the case for heavier nuclear
systems. Several theoretical efforts have been done in the development
of pre-formation alpha-clustering models, but there is still a lack
of experimental data capable to give a direct feedback. The search
of alpha-cluster evidences in medium-mass systems is therefore a new
challenge which can give new hints in this field of research.
In the past we have studied the reactions 250, 192 and 130 MeV 16 O
+ 116 Sn, observing a significant increase in the fast emitted α -particle
yield. This effect was ascribed to the presence of pre-formed α -clusters
in the 16 O projectile nucleus. To further investigate these aspects in a
model independent way, a new experimental campaign has been performed
with the GARFIELD + RCo set up. Two different reaction
entrance channels (16 O and 19 F) at the same beam velocity (16AMeV)
have been measured, leading to the same 81 Rb* compound nucleus.
In this contribution we report on the preliminary light-charged particles
emission spectra obtained in coincidence with evaporation residues
and their comparison with the results obtained from a Hybrid Exciton
Model calculation.