M. La Commara

Decay competition in IMF production in the collisions 78 Kr+ 40 Ca and 86 Kr+ 48 Ca at 10 AMeV

De-excitation modes of compound systems 118 Ba and 134 Ba, produced respectively in the 78 Kr+ 40 Ca and 86 Kr+ 48 Ca collisions at 10 A.MeV, are investigated. In particular, the competition between the various disintegration decay paths of medium mass compound nuclei, formed by fusion processes and the isospin (related to N/Z) of the entrance channel influence on the decay process, are studied. Data were taken at the INFN-Laboratori Nazionali del Sud (LNS) in ISODEC experiment, by using the CHIMERA array. The experiment complements and improves the previous experiment performed at GANIL where the same mechanisms were studied at lower excitation energies. The results show the presence of a relaxed component in the reaction mechanism, evident staggering effects in the Z distributions, as well as different isotopic composition and neutron enrichment for the reaction products in the two systems.

Pre-equilibrium GDR in a heavy composite system

The excitation of the Dynamical Dipole mode along the fusion path was investigated for the first time in the formation of a heavy composite system in the A~190 mass region, in fusion-evaporation and fission events. The composite system was formed at identical conditions of excitation energy and spin from two reactions with different charge asymmetry: the charge asymmetric 40Ca + 152Sm and the nearly charge symmetric 48Ca + 144Sm at E lab =11 and 10.1 MeV/nucleon, respectively. In this paper, we report the results on fusion evaporation events and the preliminary analysis on fission channel.

N/Z effect on reaction mechanisms cross sections in the

Nuclear reactions between medium-mass nuclei at low energy are characterized by the competition between binary and evaporation process in the compound nucleus de-excitation. A study of the influence of the neutron richness of the entrance channel on the decay paths of the compound nuclei formed in the (78) Kr +(40) Ca and (86) Kr +(48) Ca at 10 MeV/A is presented. The experiment has been performed at Laboratori Nazionali del Sud by using the CHIMERA 4π multidetector for charged particles. The Kinematical characteristics of the two reactions support the conclusion of a production via long lived system. Besides the results relative to the n-poor system are compared to those obtained at GANIL, performed at 5.5 AMeV, in order to study the energy influence.

^{78}Kr+^{40}Ca

The dynamical dipole mode was investigated in the mass region of the 192Pb compound nucleus, by using the 40Ca + 152Sm and 48Ca + 144Sm reactions at Elab=11 and 10.1 MeV/nucleon, respectively. Both fusion-evaporation and fission events were studied simultaneously for the first time. Our results for evaporation and fission events (preliminary) show that the dynamical dipole mode survives in reactions involving heavier nuclei than those studied previously.

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C. PARASCANDOLO, D. PIERROUTSAKOU, C. AGODI, R. ALBA, V. BARAN, A. BOIANO, M. COLONNA, R. CONIGLIONE, E. DE FILIPPO, A. DEL ZOPPO, M. DI TORO, U. EMANUELE, F. FARINON, A. GUGLIELMETTI , M. LA COMMARA, C. MAIOLINO, B. MARTIN, M. MAZZOCCO, C. MAZZOCCHI , C. RIZZO, M. ROMOLI, D. SANTONOCITO, C. SIGNORINI, R. SILVESTRI, F. SORAMEL, E. STRANO, D. TORRESI, A. TRIFIRO AND M. TRIMARCHI a Dip. di Fisica e Astronomia, Universita di Padova and INFN, Sezione di Padova,

^{86}Kr+^{48}Ca

The de-excitation of medium mass nuclei 118,134 Ba produced in fusion process of 78,86 Kr on 40,48 Ca targets at 10 AMeV is studied, in order to investigate the isospin dependence of the decay modes; the neutron enrichment of the compound nuclei is in fact expected to play an important role on the emission mechanisms, providing crucial information on fundamental nuclear quantities such as level density, fission barrier, viscosity and symmetry energy. The experiment was performed at INFN-LNS with the 4π multidetector for charged particles CHIMERA, used for the first time in this low energy regime, thanks to a suitable Pulse Shape Discrimination method for charge identification applied to the silicon detectors. Preliminary results show a different isotopic composition and relative enrichment for the same Z in the two systems. The yields of the Intermediate Mass Fragments (IMF, 3<Z<12) exhibits a strong even-odd staggering, more pronounced for the n-poor system. The IMF energy spectra show some differences according to the entrance channel and to the charge and mass of the fragment.

collisions at 10 AMeV

The de-excitation of medium mass nuclei 118,134 Ba produced in fusion process of 78,86 Kr on 40,48 Ca targets at 10 AMeV is studied, in order to investigate the isospin dependence of the decay modes; the neutron enrichment of the compound nuclei is in fact expected to play an important role on the emission mechanisms, providing crucial information on fundamental nuclear quantities such as level density, fission barrier, viscosity and symmetry energy. The experiment was performed at INFN-LNS with the 4π multidetector for charged particles CHIMERA, used for the first time in this low energy regime, thanks to a suitable Pulse Shape Discrimination method for charge identification applied to the silicon detectors. Preliminary results show a different isotopic composition and relative enrichment for the same Z in the two systems. The yields of the Intermediate Mass Fragments (IMF, 3<Z<12) exhibits a strong even-odd staggering, more pronounced for the n-poor system. The IMF energy spectra show some differences according to the entrance channel and to the charge and mass of the fragment.

Dynamical Dipole mode in heavy-ion fusion reactions in the 192Pb mass region

The de-excitation of medium mass nuclei 118,134 Ba produced in fusion process of 78,86 Kr on 40,48 Ca targets at 10 AMeV is studied, in order to investigate the isospin dependence of the decay modes; the neutron enrichment of the compound nuclei is in fact expected to play an important role on the emission mechanisms, providing crucial information on fundamental nuclear quantities such as level density, fission barrier, viscosity and symmetry energy. The experiment was performed at INFN-LNS with the 4π multidetector for charged particles CHIMERA, used for the first time in this low energy regime, thanks to a suitable Pulse Shape Discrimination method for charge identification applied to the silicon detectors. Preliminary results show a different isotopic composition and relative enrichment for the same Z in the two systems. The yields of the Intermediate Mass Fragments (IMF, 3<Z<12) exhibits a strong even-odd staggering, more pronounced for the n-poor system. The IMF energy spectra show some differences according to the entrance channel and to the charge and mass of the fragment.

DYNAMICAL DIPOLE MODE IN FUSION HEAVY-ION REACTIONS IN THE MASS REGION OF A = 192

The existence of the dynamical dipole mode in the 192Pb composite system was investigated, through the study of its prompt γ decay, employing the 40Ca+152Sm and 48Ca+144Sm reactions at Elab=11 and 10.1 MeV/nucleon, respectively. The γ-rays and light charged particles were detected in coincidence with evaporation residues and fission fragments. First results of this experiment show that the dynamical dipole mode survives in collisions involving heavier mass reaction partners than those studied previously. As a fast cooling mechanism on the fusion path, the prompt dipole γ radiation could be of interest for the synthesis of super-heavy elements through hot fusion reactions. Furthermore, by using radioactive beams and the prompt γ radiation as a probe we could get information on the symmetry energy at sub-saturation densities.

Influence of neutron enrichment on compound system formation and decay in 78Kr+40Caand 86Kr+48Careactions at 10 AMeV

The prompt γ radiation originating from the dynamical dipole mode decay was investigated in the 192Pb composite system employing the 40Ca + 152Sm and 48Ca + 144Sm reactions at Elab=11 and 10.1 MeV/nucleon, respectively. The γ-ray energy spectra at various polar angles were obtained for fusion-evaporation and fission events by detecting the high energy γ rays with the MEDEA experimental apparatus in coincidence with evaporation residues and fission fragments. Preliminary results of this experiment show that the dynamical dipole mode survives in collisions involving heavier mass reaction partners than those studied previously. As a fast cooling mechanism on the fusion path, the prompt dipole γ radiation could be of interest for the synthesis of super-heavy elements through hot fusion reactions.