CHIMERA Multidetector Research Articles

Isospin Against Size Effects In Projectile Dynamical Fission For 112,124Sn+58,64Ni and 124Xe+64Zn Reactions At 35 A.MeV

In past experiments, mass asymmetric projectile-target combinations124Sn+64Ni and 112Sn+58Ni were investigated at ELab(112'124Sn)=35 A.MeVbeam energybyusing the 4n multi-detector CHIMERA. From a quantitative comparison of cross sections associated to Statistical and Dynamical Fission of the Projectile-Like Fragments, it resulted that Dynamical Fission process is about two times more probable in the neutron rich 124Sn+64Ni system than in the 112 Sn +58 Ni neutron poor one. In contrast, no sizable difference was found for Statistical Fission mechanism. The observed difference in the strength of the Dynamical effects could arise from the difference in entrance channel Isospin (N/Z) content. In order to disentangle Isospin effects from effects due to the different masses of the two systems, a new experiment 124Xe+64Zn at 35 A.MeV beam energy has been recently carried out.

Entrance channel effects in medium mass nuclear systems at 25 MeV/nucleon

We discuss experimental data concerning 48Ca+48Ca and 42Ca+54Fe reactions at 25 MeV/nucleon obtained by using the 4π multi-detector Chimera. Effects due due to the different neutron to proton ratios (N/Z) of the two systems have been investigated. Charge distributions of forwardly emitted fragments show even-odd staggering whose amplitude is larger for the neutron poor system. Moreover, the neutron excess of the total system influence the evolution of fusion-like sources formed in semi-central collisions. In particular, for the neutron rich system, the relative emission yield of heavy residues is larger, while multi-fragmentation and binary-like events prevail in the neutron poor system.

Emission of fragments in Ca+Ca reactions at 25 MeV/nucleon

We discuss experimental data concerning 40,48Ca+40,48Ca reactions at 25 MeV/nucleon; the 4π multi-detector Chimera has been used as detection device. Effects that can be attributed to the neutron to proton ratios (N/Z) degree of freedom have been investigated. From the analysis of experimental data it seems that the neutron richness of the interacting system plays an important role on the evolution of fusion-like sources formed in semi-central collisions. In particular, it is observed that the larger is the neutron content and the larger is the emission of heavy residues. Experimental data have been compared with CoMD-II model calculations; a moderately stiff symmetry energy should be used to reproduce satisfactorily the data. A thermodynamical analysis on fusion-like sources has been also performed. In semi-peripheral collisions, isospin diffusion signals have been found. They have been investigated by analyzing isobaric emission (7Li/7Be) of quasi-projectile sources. Experimental data indicate that an incomplete N/Z mixing is reached during the interaction phase.

The N/Z key role on the dynamics of medium mass nuclear systems near fragmentation threshold

Effects related to the neutron to proton ratio (N/Z) degree of freedom in nuclear collisions 40Ca + 40Ca, 40Ca + 48Ca and 48Ca + 48Ca at 25 MeV per nucleon, analyzed by means of the Chimera multi-detector, have been investigated. Strong isotopic effects are found in mass distributions of light isotopes. Moreover, the competition between various reaction mechanisms at semi-central impact parameters seems to be influenced by the neutron richness of the total system formed.

Even-odd effects inZandNdistributions of fragments emitted at intermediate energies

Even-odd effects in Z and N distributions of light fragments emitted at forward angles in nuclear collisions 40Ca + 40Ca, 40Ca + 48Ca, and 48Ca + 48Ca at 25 MeV/nucleon and identified in charge and mass with the Chimera multidetector have been analyzed. The amplitude of even-odd staggering effects seems to be related to the neutron to proton ratio N/Z of the entrance channels. A qualitative explanation of this effect, taking into account the deexcitation phase of primary excited fragments, is discussed.Received 27 June 2011DOI:https://doi.org/10.1103/PhysRevC.84.024613©2011 American Physical Society

PRODUCTION OF α-PARTICLE CONDENSATE STATES IN HEAVY-ION COLLISIONS

The fragmentation of quasi-projectiles from the nuclear reaction 40Ca+12C at 25 MeV/nucleon was used to produce excited states candidates to α-particle condensation. The experiment was performed at LNS-Catania using the CHIMERA multidetector. Accepting the emission simultaneity and equality among the α-particle kinetic energies as experimental criteria for deciding in favor of the condensate nature of an excited state, we analyze the [Formula: see text] and [Formula: see text] states of 12 C and the [Formula: see text] state of 16 O . A sub-class of events corresponding to the direct 3-α decay of the Hoyle state is isolated.

Strong enhancement of dynamical emission of heavy fragments in the neutron-richSn124+Ni64reaction at35A MeV

A quantitative comparison is made between the absolute cross sections associated with statistical and dynamical emission of heavy fragments in the Sn124+Ni64 and Sn112+Ni58 collisions experimentally investigated at 35A MeV beam energy using the multidetector CHIMERA. The result shows that the dynamical process is about twice as probable in the neutron-rich Sn124+Ni64 system as in the Sn112+Ni58 neutron-poor one. This unexpected and significant difference indicates that the reaction mechanism is strongly dependent on the entrance-channel isospin (N/Z) content.Received 4 March 2010DOI:https://doi.org/10.1103/PhysRevC.81.064605©2010 American Physical Society

Isospin dependence of physical observables in Incomplete Fusion reactions at 25 MeV/nucleon

Isospin dependence of dynamical and thermodynamical physical quantities observed in the reactions 40 Ca + 40,48 Ca and 40 Ca + 46 Ti at 25 MeV/nucleon has been analyzed by means of the CHIMERA multi-detector.

SEARCH FOR HYPERHEAVY TOROIDAL NUCLEAR STRUCTURES FORMED IN AU + AU COLLISIONS

We study the feasibility of an experimental observation of toroidal breakup configurations in Au + Au collisions using the CHIMERA multidetector system. BUU simulations indicate that the threshold energy for toroidal configuration is around 23 MeV/nucleon. The simulations of decay process using the ETNA code indicate the sensitivity of some observables to different studied break-up geometries.

Isotope correlations as a probe for freeze-out characterization: centralSn+Ni,Sn+Ni collisions

124Sn+64Ni and112Sn+58Ni reactions at 35 AMeV incident energy were studied with the forward part of CHIMERA multi-detector. The most central collisions were selected by means of a multidimensional analysis. The characteristics of the source formed in the central collisions, as size, temperature and volume, were inspected. The measured isotopes of light fragments (3 ⩽Z ⩽ 8) were used to examine isotope yield ratios that provide information on the free neutron to proton densities.

Isotope correlations as a probe for freeze-out characterization: central 124Sn+ 64Ni, 112Sn+ 58Ni collisions

124Sn+ 64Ni and 112Sn+ 58Ni reactions at 35 AMeV incident energy were studied with the forward part of CHIMERA multi-detector. The most central collisions were selected by means of a multidimensional analysis. The characteristics of the source formed in the central collisions, as size, temperature and volume, were inspected. The measured isotopes of light fragments (3 ⩽ Z ⩽ 8) were used to examine isotope yield ratios that provide information on the free neutron to proton densities.

Isoscaling in central 124Sn+ 64Ni, 112Sn+ 58Ni collisions at 35 A MeV

124Sn+ 64Ni and 112Sn+ 58Ni reactions at 35 A MeV incident energy were studied by using the 688 Si–CsI telescopes of the forward part (1°⩽ θ lab⩽30°) of CHIMERA multi-detector. The most central part, 1% of the total measured cross section was selected by means of a multidimensional analysis of the experimental observables. The detected isotopes of light fragments (3⩽ Z⩽8) provided information on breakup temperatures of the emitting sources. The space–time structure of these sources was deduced from fragment correlations. An odd–even effect in the fragment production, enhanced by the isospin of the entrance channel, was observed. Freeze-out unbound neutron-to-proton relative densities for both studied reactions have been deduced, indicating for a possible isospin distillation mechanism related to a phenomenon of the liquid–gas phase transition in asymmetric systems.