Collisions around the Coulomb barrier induced by halo and weakly bound nuclei:
recent experimental results at INFN-LNS Catania
P. Figuera 1*
1 INFN-Laboratori Nazionali del Sud
The study of collisions around the Coulomb barrier induced by halo and/or weakly bound nuclei has been object of many publications in the last years, since the peculiar structure of such nuclei may strongly affect elastic scattering and reaction mechanisms (see e.g.[1-3] and references therein). Recent results on the above topic, obtained by our group at INFN-LNS Catania, will be summarized in this presentation.
Results concerning different reaction channels for the collisions 11,10,9Be+64Zn at the same center of mass energy close to the Coulomb barrier will be presented. The analysis of elastic scattering shows a suppressed elastic angular distribution for the collision induced by the 11Be halo nucleus, when compared with the ones induced by 10,9Be. Correspondingly, the total reaction cross section extracted via optical model calculations for 11Be+ 64Zn is more than a factor two larger than for the other two systems. It will be shown that such an enhancement of the total reaction cross section with 11Be is mainly due to the presence of strong transfer/breakup channels. The present results with 11Be are similar to what observed by different authors in 6He induced reactions on different targets.
In the study of collisions induced by halo nuclei around the barrier, controversial conclusions, concerning the presence or not of possible enhancement effects on fusion cross sections, have been reached by different authors. We recently extended to lower energies our old study  of fusion excitation functions for the systems 6,4He+64Zn, and the new data will be presented. An enhancement of fusion cross section for the 6He induced collision when compared to the one induced by 4He is observed at the lowest measured energies and its possible origin will be discussed.
The study of collisions induced by weakly bound nuclei which do not have a halo structure has also a considerable interest and we recently measured elastic scattering angular distributions and fusion cross sections at different energies around the Coulomb Barrier for the systems 6,7Li+ 64Zn. From the analysis of the elastic scattering angular distributions within the optical model, the energy dependence of the optical potential around the Coulomb barrier has been studied. Absence of the usual threshold anomaly has been observed, as also found by other authors in collisions induced by weakly bound nuclei. The fusion excitation function for 6Li+64Zn, obtained with an activation technique, appears to be systematically larger than the one reported in the literature for the same system. This result might indicate the presence of experimental problems in the old 6Li+64Zn fusion data as already suggested in .
 L.F.Canto et al., Phys. Rep. 424, 1, (2006) .
 N.Keeley et al., Prog. Part. and Nucl. Phys. 59, 579, (2007).
 N.Keeley et al., Prog. Part. and Nucl. Phys. 63, 396, (2009).
 A.Di Pietro et al., Phys. Rev. C 69, 044613, (2004).
 P.R.S. Gomes et al., Phys.Rev. C 79, 027606, (2009).