Search

The production cross sections of neutron-rich fission residues produced in reactions induced by a 238U beam impinging onto Pb and Be targets were investigated at the Fragment Separator (FRS) at GSI using the inverse kinematic technique. These data allowed us to discuss the optimum energies in fission for producing the most neutron-rich residues.

Correlations between the energy, charge and the deflection angle of the projectile-like fragments were studied for the 136Xe + 209Bi reaction at E=A = 28 and 62 MeV. These correlations are seen to exhibit features characteristic of dissipative orbiting, commonly found at bombarding energies of a few MeV/nucleon above the interaction barrier, but also reported in the Fermi-energy domain. It was found, that in the studied bombarding energy range, the reaction cross section is still dominated by the dissipative binary reactions of well defined projectile- and target-like fragments. [ABSTRACT FROM AUTHOR]

Preliminary results of an analysis of experiments devoted to a study of the sensitivity of the 20Ne + 208Pb quasi-elastic angular distributions at two near-barrier energies and the previously measured corresponding barrier distribution to the value of the nuclear quadrupole deformation length of 20Ne are reported. [ABSTRACT FROM AUTHOR]

This paper presents the physical analysis results for the following reactions: 124Sn+64Ni, 124Sn+27Al, 124Sn+58Ni at 35MeV/A and 25 MeV/A. The main goal of this studies was to find observables sensitive to isospin effects and to present the similarities/differences between the systems characterised by various charge asymmetry factor, defined as I = (N - Z)/A. Theoretical simulations based on the Quantum Molecular Dynamics (QMD) model have been performed in order to compare them with the results of the analysis of experimental data. The first phase of the reaction was carried out with the code CHIMERA [1]. The sequential decay of hot fragments was simulated by the code COOLER [2]. The conclusions are as follows: there are observables sensitive to the isospin of the system, such as the Light Charged Particles (LCP) emission and their sensitivity is demonstrated more prominently in the analysis of central collisions at 35 MeV/A. The theoretical calculations do not reproduce these relations well. [ABSTRACT FROM AUTHOR]

A large set of experimental data was analyzed in terms of characteristic signatures of different interaction as well as product emission scenarios. The analysis confirms that the reaction cross-section appears still dominated by dissipative binary reactions involving the survival of well-defined projectile-and target-like fragments. Consistent with such a "gentle" collision scenario are the Galilei-invariant velocity distributions of charged products featuring statistical emission from two fully accelerated projectile- and target-like fragments. On the other hand, the Galilei-invariant velocity plots reveal the presence of a third effective emission source with velocity intermediate between the velocities of projectile- and target-like fragments. Fragments emitted from the intermediate-velocity source appear to be produced dynamically in the overlap zone of the projectile and target nuclei. The experimental multidimensional joint distributions of neutrons and charged reaction products were found to exhibit several different types of prominent correlation patterns. It makes them a useful tool for probing reactions scenarios, different from the traditional approach of interpreting inclusive yields of individual reaction products. [ABSTRACT FROM AUTHOR]

The fragmentation of neutron-rich Sn isotopes obtained from the fission of 238U projectiles at 950 MeV/u has been investigated at the FRagment Separator (FRS) at GSI. In order to study the feasibility of a two-step reaction scheme for the production of medium-mass neutron-rich nuclei, fragments with masses A ≈ 130 have been isotopically resolved in the first part of FRS and their fragmentation residues identified in the second part. [ABSTRACT FROM AUTHOR]

The transfer probabilities for 20Ne + 90Zr and 20Ne + 92Zr at energies near the Coulomb barrier were measured. This quantity turned out to be very similar for both Zr isotopes and does not explain the observed differences in the barrier height distributions for these systems. [ABSTRACT FROM AUTHOR]

Collisions of a very heavy nuclear system, 197Au + 197Au, were studied at the energy of 15 MeV/nucleon with the aim to identify and investigate main macroscopic modes of re-separation of such a heavy nuclear system. The experiment was performed at the INFN LNS laboratory in Catania by using the multidetector array CHIMERA. Along with binary strongly damped collisions, a strong component of a new re-separation mode: the "fast ternary fission" in characteristic nearly co-linear configuration was observed and the time scale of this process was determined. [ABSTRACT FROM AUTHOR]

197Au+197Au collisions at 15 MeV/nucleon were studied using the multidetector array CHIMERA and heavy ion beams from the superconducting cyclotron of LNS Catania. The experiment was aimed at studying the mechanism of energy dissipation in collisions of very heavy systems. In the present contribution we report on a part of our study concentrated on a subject of basically binary damped collisions, in which only two main fragments are formed prior to secondary deexcitation processes. Such "binary" events were selected by using complete information from the exclusive-type data (including all Z ≥ 3 fragments) obtained with the CHIMERA multidetector. Results are compared with predictions of a classical dynamical model of Blocki et al., in which both scenarios of energy dissipation, one-body or two-body dissipation mechanisms, are assumed. [ABSTRACT FROM AUTHOR]

Ternary events originating from the 197Au + 197Au reaction at 15 MeV/nucleon, studied by using the multidetector array CHIMERA at LNS Catania, have been collected in almost complete 2π range of the forward hemisphere of CHIMERA thus extending the angular range of our previously reported preliminary data. Energy- and time calibrations for heavy fragments at large angles were supplemented with an analysis of coincidence events of binary strongly damped reactions. Contrary to the previous preliminary results, the new complete data clearly show presence of sequential fission processes in which one of Au-like nuclei undergoes fission after re-separation of the primary binary system. Mechanism of these two types of reactions observed in our data, sequential fission reactions and prompt ternary processes, are presently studied using comparisons with predictions of the stochastic BNV model of Baran, Colonna and Di Toro and the QMD model of Łukasik. [ABSTRACT FROM AUTHOR]

The shape of the velocity distributions of charged particles projected on the beam direction can be explained if emissions from the hot projectile-like fragment and the target-like fragment are supplemented by an emission from an intermediate velocity source located between them. The creation of this source is predicted by a two-stage reaction model where, in the second stage, some of the nucleons identified in the first stage as participants form a group of clusters located in the region between the colliding nuclei. The cluster coalescence process is governed on the average by the maximum value of entropy, although its fluctuations are also significant. The properties of the intermediate velocity source are precisely described, including the isotopic composition of the emitted particles. [ABSTRACT FROM AUTHOR]

The creation of hot Ca-like fragments was investigated in the 40Ca + 40Ca reaction at 35 AMeV. Using the AMPHORA 4π detector system, the primary projectile-like fragment was reconstructed and its properties were determined. Both primary and secondary distributions are compared with the predictions of a Monte Carlo code describing a heavy-ion collision as a two-step process. Some of the nucleons which are identified as participants in the first step are transferred in the second step to these final states, which correspond on the average to the maximum value of entropy (thermodynamic probability). The model allows for competition between mean-field effects and nucleon-nucleon interactions in the overlap zone of the interacting nuclei. The analysis presented here suggests a thermalized source picture of the decay of the projectile-like fragment. The validity of the reconstruction procedure for projectile-like fragments is discussed. [ABSTRACT FROM AUTHOR]

The production cross sections of neutron-rich fission residues in reactions induced by 238U projectiles at 950A MeV impinging on Pb and Be targets are investigated at the Fragment Separator at GSI. These two targets allow us to investigate fission processes induced by two reaction mechanisms, Coulomb and nuclear excitations, and to study the role of these mechanisms in the neutron excess of the final fragments. [ABSTRACT FROM AUTHOR]

A new reaction mechanism of violent reseparation of a heavy nucleus-nucleus system, 197Au + 197Au, into three or four massive fragments in collisions at 15 MeV/nucleon has been observed. After reseparation, the fragments are almost exactly aligned, thus showing a very short time scale of the reseparation process, of about 70-80 fm/c.