Search for the Dynamical Dipole in the mass region of 192Pb nucleus in fusion-evaporation and fission heavy-ion reactions at Elab = 11MeV/nucleon

The Dynamical Dipole mode is a pre-equilibrium collective dipole oscillation predicted to be excited in charge asymmetric heavy-ion collisions. It decays emitting prompt gamma–rays and gives important information on the reaction dynamics. Its study could allow us to probe the density dependence of the symmetry energy in the Equation of State at sub-saturation densities, where this oscillation is active. Furthermore, its prompt radiation could be of interest for the synthesis of super-heavy elements in hot fusion reactions as it cools down the formed nucleus on the fusion path through emission of prompt gamma–rays. We investigated the Dynamical Dipole in fusion-evaporation and fission reactions for a composite system in the mass region of lead, a mass region never studied before. For this research the reactions 40Ca + 152Sm and 48Ca + 144Sm have been performed at ELAB = 11 MeV/nucleon at the Laboratori Nazionali del Sud, (LNS, Italy). The gamma-rays and the light charged particles were detected by using the MEDEA apparatus, made of 180 BaF2 scintillators and 6 Parallel Plates Avalanche Counters for fission fragments and evaporation residues. Any difference in the gamma-ray multiplicity spectra and the gamma-ray angular distributions of the two investigated reactions constitutes the signature of a pre-equilibrium process, i.e. the Dynamical Dipole mode excitation and its subsequent decay. From the study of these observables in the two reactions it was shown, in a model independent way, that the Dynamical Dipole survives in such a heavy composite system with similar features in both evaporation and fission events. Our results were compared with theoretical calculations performed within a BNV transport model, based on a collective bremsstrahlung analysis of the entrance channel reaction dynamics

Reaction dynamics studies for the system 7Be + 208Pb at Coulomb barrier energies

The scattering process of the Radioactive Ion Beam 7Be from a 208Pb target was measured at three near-barrier energies. The quasi-elastic angular distributions were analyzed within the framework of the optical model to extract the reaction cross sections. The results are compared with those obtained for the reactions induced by the mirror projectile 7Li and by the lightest particle-stable lithium isotope 6Li on the same target. The angular distributions for the production of the two 7Be constituent clusters, namely 3He and 4He, were also measured. In agreement with what observed for the interaction of 7Be with lighter targets, the production of the heavier helium isotope resulted to be much more abundant than that of its lighter counterpart

Search for the Dynamical Dipole in the mass region of 192Pb nucleus in fusion-evaporation and fission heavy-ion reactions at Elab = 11MeV/nucleon

The Dynamical Dipole mode is a pre-equilibrium collective dipole oscillation predicted to be excited in charge asymmetric heavy-ion collisions. It decays emitting prompt gamma–rays and gives important information on the reaction dynamics. Its study could allow us to probe the density dependence of the symmetry energy in the Equation of State at sub-saturation densities, where this oscillation is active. Furthermore, its prompt radiation could be of interest for the synthesis of super-heavy elements in hot fusion reactions as it cools down the formed nucleus on the fusion path through emission of prompt gamma–rays. We investigated the Dynamical Dipole in fusion-evaporation and fission reactions for a composite system in the mass region of lead, a mass region never studied before. For this research the reactions 40Ca + 152Sm and 48Ca + 144Sm have been performed at ELAB = 11 MeV/nucleon at the Laboratori Nazionali del Sud, (LNS, Italy). The gamma-rays and the light charged particles were detected by using the MEDEA apparatus, made of 180 BaF2 scintillators and 6 Parallel Plates Avalanche Counters for fission fragments and evaporation residues. Any difference in the gamma-ray multiplicity spectra and the gamma-ray angular distributions of the two investigated reactions constitutes the signature of a pre-equilibrium process, i.e. the Dynamical Dipole mode excitation and its subsequent decay. From the study of these observables in the two reactions it was shown, in a model independent way, that the Dynamical Dipole survives in such a heavy composite system with similar features in both evaporation and fission events. Our results were compared with theoretical calculations performed within a BNV transport model, based on a collective bremsstrahlung analysis of the entrance channel reaction dynamics.Il Dipolo Dinamico è un’oscillazione dipolare collettiva di pre-equilibrio che si instaura in una reazione asimmetrica in carica fra ioni pesanti. Tale oscillazione decade emettendo raggi gamma dipolari di pre–equilibrio e può fornire importanti informazioni sulla dinamica delle reazioni. Il Dipolo Dinamico consente di avere informazioni sulla dipendenza dell’equazione di Stato della materia nucleare dalla densità, per densità al di sotto di quella di saturazione, dove questa oscillazione è attiva. Inoltre, la sua emissione “pronta” potrebbe essere utile per la formazione di nuclei superpesanti in processi di fusione “calda”, come possibile meccanismo di raffreddamento del sistema composito tramite l’emissione raggi di pre–equilibrio. Il Dipolo Dinamico è stato studiato nella regione di massa del Pb, una regione di massa mai investigata finora, sia in reazioni di fusione–evaporazione che di fissione. A tale scopo sono state realizzate le reazioni 40Ca + 152Sm e 48Ca + 144Sm ad un’energia incidente ELAB = 11 MeV/nucleone presso i Laboratori Nazionali del Sud, (LNS, Italy). I raggi gamma e le particelle leggere cariche sono state rivelate usando il setup sperimentale MEDEA, composto da 180 scintillatori BaF2 e 6 rivelatori Parallel Plates Avalanche Counters per i frammenti di fissione e i residui di evaporazione. Le differenze negli spettri di molteplicità e nelle distribuzioni angolari dei raggi gamma delle due reazioni studiate indicano la presenza di un processo di pre-equilibrio, ovvero del Dipolo Dinamico e del suo conseguente decadimento tramite raggi gamma. Dal confronto di queste osservabili nelle due reazioni è stato dimostrato, in maniera indipendente dai modelli, che il Dipolo Dinamico sopravvive in un sistema composto così pesante con caratteristiche simili sia in eventi di evaporazione che di fissione. Tali risultati sono stati confrontati con calcoli teorici effettuati nell’ambito di un modello di trasporto di tipo BNV, basato su un approccio di emissione bremsstrahlung collettivo della dinamica di reazione del canale d’ingresso

Direct processes for the systems 7Be, 8B + 208Pb at Coulomb barrier energies

The elastic scattering process for the nuclear reactions induced by the Radioactive Ion Beams 7Be and 8B on a 208Pb target was measured for the first time in the energy range around the Coulomb barrier. Extensive theoretical calculations within the framework of the optical model were performed. An excellent agreement between experimental data and theoretical predictions was achieved for the reaction 7Be + 208Pb, while a comprehensive understanding of the reaction dynamics induced by the more exotic projectile 8B is still far to be reached. Predictions of the cross section for the breakup for both systems will also be given.Polish National Science Centre 2014/14/M/ST2/00738Japan Society for the Promotion of Science 16K05369, 19K0388

7Be and 8B reaction dynamics at Coulomb barrier energies

We investigated the reaction dynamics induced by the 7Be,8B+208Pb collisions at energies around the Coulomb barrier. Charged particles originated by both the col- lisions were detected by means of 6 ΔE-Eres telescopes of a newly developed detector array. Experimental data were analysed within the framework of the Optical Model and the total reaction cross-sections were compared together and with the 6,7Li+208Pb colli-sion data. According to the preliminary results, 7Be nucleus reactivity is rather similar to the 7Li one whereas the 8B+208Pb total reaction cross section appears to be much larger than those measured for reactions induced by the other weakly-bound projectiles on the same target

Elastic scattering measurement for the system 17O + 58Ni at Coulomb barrier energies with silicon strip detectors exploiting ASIC electronics

The quasi elastic scattering of a 17O projectile from a 58Ni target has been studied at beam energies ranging from 42.5 to 55.0 MeV in 2.5 MeV steps. The total reaction cross sections were derived from the measured angular distributions by using an optical model fit within the coupled-channel code FRESCO. These cross sections are very similar to those measured for 17F (loosely bound by 0.6 MeV), mirror nucleus of 17O (tightly bound by 4.14 MeV). This outcome points out that, in this energy range, the small binding energy of the 17F valence proton has negligible influence onto the reactivity of such a loosely bound projectile, contrary to simple expectations, and to what observed for other loosely bound nuclei. The reaction dynamics seems to be influenced mainly by the Coulomb interaction which is similar for both mirror projectiles

Upgrade of the facility EXOTIC for the in-flight production of light Radioactive Ion Beams

The facility EXOTIC for the in-flight production of light weakly-bound Radioactive Ion Beams (RIBs) has been operating at INFN-LNL since 2004. RIBs are produced via two-body reactions induced by high intensity heavy-ion beams impinging on light gas targets and selected by means of a 30 -dipole bending magnet and a 1-m long Wien filter. The facility has been recently upgraded (i) by developing a cryogenic gas target, (ii) by replacing the power supplies of the middle lenses of the two quadrupole triplets, (iii) by installing two y-steerers and (iv) by placing two Parallel Plate Avalanche Counters upstream the secondary target to provide an event-by-event reconstruction of the position hit on the target. So far, RIBs of 7Be, 8B and 17F in the energy range 3-5 MeV/u have been produced with intensities about 3 7 105, 1.6 7 103 and 105 pps, respectively. Possible light RIBs (up to Z = 10) deliverable by the facility EXOTIC are also reviewed.\ua9 2013 Elsevier B.V. All rights reserved

The high granularity and large solid angle detection array EXPADES

The EXPADES (EXotic PArticle DEtection System) detector array consists of 16 Double Side Silicon Strip Detectors (DSSSD) with active areas of 64 7 64 mm2, arranged in 8 \u394E (40/50 \u3bcm)-E (300 \u3bcm) telescopes. All detector faces are segmented into 32 7 2-mm wide strips, ensuring a 2 7 2 mm2 pixel configuration. Eight ionization chambers can be alternatively used as \u394E stages or, if needed, as an additional third layer for more complex triple telescopes. The signals from silicon \u394E layers and from ionization chambers are read by standard electronics, while innovative 32-channel ASIC chips are employed for the readout of the E stages. The results of off-line tests with alpha sources and from the first in-beam experiment with a 17O beam are presented.\ua9 2013 Elsevier B.V. All rights reserved

Study of sub-barrier fusion of 36S+50Ti,51V systems

A detailed comparative study of the sub-barrier fusion of the two near-by systems 36S+50Ti,51V was performed at the National Laboratories of Legnaro (INFN). Aim of the experiment was the investigation of possible effects of the non-zero spin of the ground state of the 51V nucleus on the sub-barrier excitation function, and in particular on the shape of the barrier distribution. The results sh w that the two measured excitation functions are very similar down to the level of 20 - 30 μb. The same is observed for the two barrier distributions. Coupled-channels calculations have been performed and are in good agreement with the experimental data. This result indicates that the low-lying levels in 51V can be interpreted in the weak-coupling scheme, that is, 51V(I) = 50Ti(2+)⊗ p(1 f7/2)

Study of sub-barrier fusion of 36^{36}S+50^{50}Ti,51^{51}V systems

International audienceA detailed comparative study of the sub-barrier fusion of the two near-by systems 36S+50Ti,51V was performed at the National Laboratories of Legnaro (INFN). Aim of the experiment was the investigation of possible effects of the non-zero spin of the ground state of the 51V nucleus on the sub-barrier excitation function, and in particular on the shape of the barrier distribution. The results sh w that the two measured excitation functions are very similar down to the level of 20 - 30 μb. The same is observed for the two barrier distributions. Coupled-channels calculations have been performed and are in good agreement with the experimental data. This result indicates that the low-lying levels in 51V can be interpreted in the weak-coupling scheme, that is, 51V(I) = 50Ti(2+)⊗ p(1 f7/2)