The reaction entrance channel and isotopic composition of fragments in a dynamical and statistical multifragmentation regime.

From the study of the Ni+Ni,Ag 30 MeV/nucleon dissipative midperipheral collisions, it has been possible to detect events in which Intermediate Mass Fragments (IMF) are emitted by two different sources with different mechanisms. The sources are: a) a quasi-projectile (QP) (and a quasi-target (QT)), with an excitation energy that leads to multifragmentation totally described in terms of a statistical disassembly of a thermalized system (T <IMG SRC="/img/revistas/bjp/v34n3a/a59img01.gif">4. MeV, E*<IMG SRC="/img/revistas/bjp/v34n3a/a59img01.gif"> 4 MeV/nucleon); b) an intermediate source, emitting both light particles and IMF. In this second case, fragments are more neutron rich than the average matter of the overall system, and have a very different charge distribution, with respect to those statistically emitted from the QP. The above features can be considered as a signature of the dynamical origin of the midvelocity emission. The results of this analysis show that IMF can be produced via different mechanisms simultaneously present within the same collision. They also show that the probability of IMF production via dynamical reaction increase with the size of the target nucleus

Isospin transport in 84Kr+112-124Sn collisions at Fermi energies with the FAZIA detector

Isotopically resolved fragments up to Z 20 have been studied in a test experiment by the FAZIA Collaboration with a three-stage telescope. The reactions 84Kr+112Sn (n-poor) and 84Kr+124Sn (n-rich) at 35 MeV/nucleon were measured. The telescope was located near the grazing angle, so the detected fragments are mainly emitted from the phase-space region of the projectile. In the following, evidences for isospin diffusion and drift will be discussed

Emission of fragments in Ca+Ca reaction at 25 MeV/nucleon

We discuss experimental data concerning 40,48Ca+40,48Ca reactions at 25 MeV/nucleon; the 4π multi-detector Chimera has been used as detection device. Effects that can be attributed to the neutron to proton ratios (N/Z) degree of freedom have been investigated. From the analysis of experimental data it seems that the neutron richness of the interacting system plays an important role on the evolution of fusion-like sources formed in semi-central collisions. In particular, it is observed that the larger is the neutron content and the larger is the emission of heavy residues. Experimental data have been compared with CoMD-II model calculations; a moderately stiff symmetry energy should be used to reproduce satisfactorily the data. A thermodynamical analysis on fusion-like sources has been also performed. In semi-peripheral collisions, isospin diffusion signals have been found. They have been investigated by analyzing isobaric emission (7Li/7Be) of quasi-projectile sources. Experimental data indicate that an incomplete N/Z mixing is reached during the interaction phase