Search

The results of the analysis of the reactions 78,86Kr +40,48 Ca at 10 AMeV are presented. The experiment was performed at the INFN Laboratori Nazionali del Sud (LNS) in Catania by using the 4π multidetector CHIMERA, with beams delivered by the Superconductive Cyclotron. The competition among the various disintegration paths and in particular the isospin effects on the decay modes of the produced composite systems are investigated; this provides information about fundamental nuclear quantities such as level density, fission barrier and viscosity. Different isotopic composition and relative richness are observed among the reaction products of the two systems. An odd-even staggering effect is present in the charge distributions, in particular for the light fragments produced by the neutron-poor system. The kinematical characteristics of the IMF seem to indicate a high degree of the relaxation of the formed system. Besides, global features analysis seems to show some differences in the contribution arising from the various reaction mechanisms for the two reactions.

The study of the decay modes competition of the compound systems produced in the collisions 78Kr+40Ca and 86Kr+48Ca at 10AMeV is presented. In particular, the N/Z entrance channel influence on the decay paths of the compound systems, directly connected to the isospin influence, is investigated. The experiment was performed at the INFN Laboratori Nazionali del Sud (LNS) in Catania by using the 4π multi-detector CHIMERA. Charge, mass, angular distributions and kinematical features of the reaction products were studied. The analysis shows some differences in the contribution arising from the various reaction mechanisms for the neutron poor and neutron rich systems. Comparison with theoretical statistical and dynamical models are presented for the two systems. Besides a study of the influence of the energy on the entrance channel is performed for the 78Kr+40Ca reaction, by comparing the results of this experiment to those obtained for the same system at 5.5 AMeV with the INDRA device at GANIL.

The fragmentation of quasi-projectiles from the nuclear reaction 40Ca+12C at 25 MeV/nucleon was used to produce α-emission sources. From a careful selection of these sources provided by a complete detection and from comparisons with models of sequential and simultaneous decays, strong indications in favour of α-particle clustering in excited 16O, 20Ne and 24Mg are reported.

The present status and the perspectives of the FAZIA project are presented. The main achievements in terms of identification thresholds and isotopic resolution are discussed, together with the adopted technical solutions. The detector is particularly well suited for the investigation of isospin transport phenomena at intermediate beam energies; perspectives to reduce the identification thresholds to cope with lower energy ISOL beams are briefly introduced. Some experimental results concerning isospin transport effects obtained with a test telescope are presented. The study of isospin transport phenomena can give information on the symmetry energy term of the nuclear equation of state by comparing the experimental results on isospin related observables with the predictions of transport codes.

A completely exclusive experiment was performed by the INDRA collaboration to study the isospin dependence of the level density parameter. Over a large N/Z range, the fusion-evaporation charged products of 34,36,40Ar+58,60,64Ni reactions were measured and identified both in charge and mass by coupling INDRA and VAMOS spectrometer. Preliminary results obtained by combining data of both detectors are presented for the 36Ar+58Ni at 13.3 A MeV. The analysis method of relevant observables for such an ambitious investigation are discussed and the progress of the data analysis are reviewed.

A study of the identification properties and of the energy response of a Si-Si-CsI(Tl) ΔE-E telescope exploiting a partially depleted second Si stage has been performed. Five different bias voltages have been applied to the second stage of the telescope, one corresponding to full depletion, the others associated with a depleted layer ranging from 60% to 90% of the detector thickness. Fragment identification has been obtained using either the ΔE-E technique or the Pulse Shape Analysis (PSA). Charge collection efficiency has been evaluated. The ΔE-E performance is not affected by incomplete depletion. Isotopic separation capability improves at lower bias voltages with respect to full depletion, though charge identification thresholds increase.

Recent results of the INDRA collaboration are presented in this contribution. They concern the evolution of reaction dynamics from the first stage of the collision to the production of fragments. Different probes are used to evidence the stopping/transparency, collective flow and the symmetry energy term of the nuclear equation of state.

Decay modes of excited compound systems 118Ba and 134Ba, produced respectively in the 78Kr+40Ca and 86Kr+48Ca collisions at 10 A·MeV, are investigated. In particular, the competition between the various disintegration path of medium mass compound nuclei, formed by fusion processes, the production of the so referred Intermediate Mass Fragments (IMF), and the isospin dependence of the decay process are studied. Data were taken at the INFN-Laboratori Nazionali del Sud (LNS) by using the CHIMERA array. Data analysis is in progress; a first indication on the average-energy angular distributions suggests pre-equilibrium effects affecting the data and the presence of isotopical effects.

Preliminary outcome of ISODEC experiment, performed at INFNLNS with the CHIMERA array, are presented. Disintegration path dependence on the entrance-channel N/Z ratios (isospin asymmetries) for the reactions 78Kr+40Ca and 86Kr+48Ca at 10 A·MeV, which give origin to the intermediate systems 118Ba and 134Ba, is being investigated. Staggering effects seem to be present as it was the case of a complementary measurement performed at GANIL at lower energy, i.e. 78,82Kr+40Ca at 5.5 A·MeV.

The first results of the ISODEC experiment, performed at the INFN Laboratori Nazionali del Sud (LNS) by using the CHIMERA detector, are presented. The principal aim of this experiment is to explore the isospin dependence of the decay modes of medium mass compound nuclei formed by fusion processes, by studying the competition between the various disintegration modes of 118,134Ba nuclei produced in the reactions 78Kr+40Ca and 86Kr+48Ca at 10 AMeV. The studied systems allow in fact to produce compound nuclei with a large variation of N/Z, and such data will also provide new constraint on sophisticated models attempting to describe statistical and/or dynamical properties of excited nuclei. The experiment complements data already obtained at 5.5 AMeV for 78,82Kr+40Ca reactions, previously realized at GANIL by using the INDRA detector. First results show a strong staggering effects in the Z distributions, as well as different isotopic composition and enrichment for the reaction products in the two systems.

The cross section, kinetic energy distribution and angular distribution of fragments with atomic number 3 ≤ Z ≤ 28 emitted in the reaction 78Kr + 40Ca at the bombarding energy of 5.5 MeV/nucleon and coincidence between light charged particles and fragments were measured by means of the 4π-INDRA array to study the decay mechanism of medium mass excited nucleus. Global features indicate a high degree of relaxation and are compatible with a binary fission from compound nucleus. The mean value of the kinetic energy distributions of fragments indicates dominance of Coulomb interaction, while the width of the distribution signals large fluctuations. Inclusive cross-section distributions of fragments with charge 3 ≤ Z ≤ 28 are bell-shaped and a strong even-odd-staggering (o-es) is observed for 3 ≤ Z ≤ 12. Coincidence measurements suggest that the light partners in very asymmetric fission are emitted at excitation energies below the particle emission thresholds. Data were confronted to the predictions of statistical model describing the decay of compound nuclei by emission of light particles and fragments. Calculations assuming spherical fission fragments and finite-range liquid drop fission barriers are not able to explain the experimental features. Attempts have been made to improve the agreement with experimental data. The analysis indicates the strong influence of the shape parameterization of the potential energy surface in describing the fission process of intermediate mass compound nuclei.

We present the first results of the ISODEC experiment, performed at the INFN-LNS with the CHIMERA device, in order to study the competition between the various disintegration modes of 118,134Ba compound nuclei produced by bombarding 40,48Ca targets with beams of 78,86Kr at 10 AMeV. This work aims thus to explore the isospin dependence of the decay modes of medium mass compound nuclei formed by fusion processes. The experiment complements data already obtained at 5.5 MeV/A for 78,82Kr+40Ca reactions, studied by Ademard et al. with beams delivered by GANIL facility and by using the INDRA detector.

Decay modes of excited nuclei are studied in 78,82Kr + 40Ca reactions at 5.5 MeV/nucleon by means of light-charged particles measured in coincidence with intermediate mass fragments and fission-like fragments. Inclusive cross-section distributions of fragments with charge 3 ≤ Z ≤ 28 are bell-shaped and a strong oddeven-staggering (o-e-s) is observed for 3 ≤ Z ≤ 12. Coincidence measurements suggest that the light partners in very asymmetric fission are emitted at excitation energies below the particle emission thresholds. Data were confronted to the predictions of statistical models describing the decay of compound nuclei by emission of light particles and fragments. Comparison with models suggests that the o-e-s of the light-fragment yields is mainly due to the successive steps of compound nucleus disintegration.

The influence of the neutron richness on binary decays is investigated in 78,82Kr+ 40Ca reactions at 5.5 MeV/A incident energy. Kinetic energy distributions and angular distributions of fragments with atomic number 6 ≤ Z ≤ 28 were measured using the 4π-INDRA array. Global features are compatible with an emission from a long-lived system. The yields around the symmetric splitting are about 30The persistence of strong structural effects is evidenced from elemental cross-sections of the light fragments. The cross-sections for odd-Z fragments are higher for the neutron rich CN while cross-sections for even-Z fragments are higher for the neutron poor CN. Calculations assuming two different potential energy surfaces are presented.