Search

It is known that the low-energy E1 strength, known as the Pygmy Dipole Resonance (PDR), can be excited by both isovector and isoscalar probes. In this work, we report on the results of an experiment, carried out at the LNS-INFN in Catania, with the aim to study the Pygmy Dipole Resonance induced in the 68Ni nucleus through the interaction with a 12C isoscalar target. The CHIMERA multidetector and the FARCOS array were used to detect, respectively, γ rays and charged particles. Details on the experimental set-up, data analysis and results are reported.

International audience; A comprehensive study of the evolution of the GDR properties from E∗ = 150 MeV to E∗ = 430 MeV has been undertaken in nuclei of mass A = 120 ÷ 132. The experimental investigation was performed using MEDEA detector. An onset of a quenching of the GDR gamma yield was found at E∗ = 270 MeV comparing the experimental gamma-ray spectrum with statistical model calculation. The quenching effect increases at E∗ = 330 MeV and is even more pronounced when the analysis is extended to higher excitation energies using data from previously performed experiments. The comparison with phenomenological models describing the quenching phenomenon gives a qualitative explanation for the effect but is not able to reproduce its detailed features as a function of excitation energy. A smooth cut-off approach describes reasonably well the progressive disappearance of the dipole strength, which occurs around 220–230 MeV excitation energy, and shows that the GDR quenching is a rather sharp effect.

We present preliminary results of barrier height distribution measurements for 24Mg+90 ; 92Zr systems. The experiment was performed at LNS INFN in Catania with the CHIMERA detector system and a 24Mg beam accelerated by Tandem MP. The measurements were done at the near-barrier beam energies of 68-88.5 MeV. A discrepancy between experimental results and the predictions of Coupled Channels (CC) calculations was observed. We suggest that this discrepancy may be due to a cumulative effect of many individual weak channels such as non-collective excitations of the target, which cannot be fully implemented in practical CC calculations of a standard form.

Isospin effects on dynamics of semi-central collisions involving 40Ca+ 40Ca, 40Ca+ 48Ca and 48Ca+ 48Ca reactions at 25 MeV/nucleon have been investigated. For the selected class of events, the balance between the emission of evaporation residues and the presence of binary-like phenomena seems to be influenced by the neutron to proton ratio (N/Z) of entrance channels. In particular, for neutron-rich systems, evaporation residue emission is enhanced. Experimental observations confirm the key role played by the N/Z degree of freedom on nuclear dynamics at 25 MeV/nucleon.