Pre-equilibrium emission and 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, which is being renewed by the availability of exotic beams:
clustering is, in fact, predicted to become very important at the drip-line, where weakly bound
systems will prevail. Although for light nuclei at an excitation energy close to the particle separation
value there are experimental evidences of such structure effects, this is still not the case for heavier
nuclear systems. Many attempts have been done using preformation alpha clustering models, but
there is still a lack of experimental data capable to give a direct feedback. In particular, searching
for alpha clustering effects in medium mass systems is still a challenge, which can give new hints
in this subject. In the past we have studied the reactions 250, 192 and 130 MeV 16O + 116Sn,
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 16O projectile nucleus. In order to investigate these aspects,
in a model independent way, a new experimental campaign has been performed with the
GARFIELD + RCo set up, to compare results from two different reactions: a double magic α-cluster
(16O) and a non-magic α-cluster projectile (19F) at the same beam velocity (16AMeV) have been
chosen, impinging respectively on 65Cu and 62Ni targets, thus leading to the same 81Rb* compound
nucleus. The angular distributions and the light charged particles emission spectra in coincidence
with evaporation residues have been measured and analyzed. The preliminary results of the data
analysis and the main features of the theoretical model used for their interpretation are presented.