217 research outputs found
Correlations between isospin dynamics and Intermediate Mass Fragments emission time scales: a probe for the symmetry energy in asymmetric nuclear matter
We show new data from the Ni+Sn and Ni+Sn
reactions studied in direct kinematics with the CHIMERA detector at INFN-LNS
and compared with the reverse kinematics reactions at the same incident beam
energy (35 A MeV). Analyzing the data with the method of relative velocity
correlations, fragments coming from statistical decay of an excited
projectile-like (PLF) or target-like (TLF) fragments are discriminated from the
ones coming from dynamical emission in the early stages of the reaction. By
comparing data of the reverse kinematics experiment with a stochastic mean
field (SMF) + GEMINI calculations our results show that observables from neck
fragmentation mechanism add valuable constraints on the density dependence of
symmetry energy. An indication is found for a moderately stiff symmetry energy
potential term of EOS.Comment: Talk given by E. De Filippo at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Evidence for a Novel Reaction Mechanism of a Prompt Shock-Induced Fission Following the Fusion of 78Kr and 40Ca Nuclei at E/A =10 MeV
An analysis of experimental data from the inverse-kinematics ISODEC
experiment on 78Kr+40Ca reaction at a bombarding energy of 10 AMeV has revealed
signatures of a hitherto unknown reaction mechanism, intermediate between the
classical damped binary collisions and fusion-fission, but also substantially
different from what is being termed in the literature as fast fission or quasi
fission. These signatures point to a scenario where the system fuses
transiently while virtually equilibrating mass asymmetry and energy and, yet,
keeping part of the energy stored in a collective shock-imparted and, possibly,
angular momentum bearing form of excitation. Subsequently the system fissions
dynamically along the collision or shock axis with the emerging fragments
featuring a broad mass spectrum centered around symmetric fission, relative
velocities somewhat higher along the fission axis than in transverse direction,
and virtually no intrinsic spin. The class of massasymmetric fission events
shows a distinct preference for the more massive fragments to proceed along the
beam direction, a characteristic reminiscent of that reported earlier for
dynamic fragmentation of projectile-like fragments alone and pointing to the
memory of the initial mass and velocity distribution.Comment: 5 PAGES, 6 FIGURE
Freeze-out configuration properties in the 197Au + 197Au reaction at 23 AMeV
Data from the experiment on the 197Au + 197Au reaction at 23 AMeV are
analyzed with an aim to find signatures of exotic nuclear configurations such
as toroid-shaped objects. The experimental data are compared with predictions
of the ETNA code dedicated to look for such configurations and with the QMD
model. A novel criterion of selecting events possibly resulting from the
formation of exotic freeze-out configurations, "the efficiency factor", is
tested. Comparison between experimental data and model predictions may indicate
for the formation of flat/toroidal nuclear systems
Dipolar degrees of freedom and Isospin equilibration processes in Heavy Ion collisions
Background: In heavy ion collision at the Fermi energies Isospin
equilibration processes occur- ring when nuclei with different charge/mass
asymmetries interacts have been investigated to get information on the
nucleon-nucleon Iso-vectorial effective interaction. Purpose: In this paper,
for the system 48Ca +27 Al at 40 MeV/nucleon, we investigate on this process by
means of an observable tightly linked to isospin equilibration processes and
sensitive in exclusive way to the dynamical stage of the collision. From the
comparison with dynamical model calculations we want also to obtain information
on the Iso-vectorial effective microscopic interaction. Method: The average
time derivative of the total dipole associated to the relative motion of all
emitted charged particles and fragments has been determined from the measured
charges and velocities by using the 4? multi-detector CHIMERA. The average has
been determined for semi- peripheral collisions and for different charges Zb of
the biggest produced fragment. Experimental evidences collected for the systems
27Al+48Ca and 27Al+40Ca at 40 MeV/nucleon used to support this novel method of
investigation are also discussed.Comment: Submitted for publication on Phys. Rev. C. 0n 24-oct-201
Projected Quasi-particle Perturbation theory
The BCS and/or HFB theories are extended by treating the effect of four
quasi-particle states perturbatively. The approach is tested on the pairing
hamiltonian, showing that it combines the advantage of standard perturbation
theory valid at low pairing strength and of non-perturbative approaches
breaking particle number valid at higher pairing strength. Including the
restoration of particle number, further improves the description of pairing
correlation. In the presented test, the agreement between the exact solution
and the combined perturbative + projection is almost perfect. The proposed
method scales friendly when the number of particles increases and provides a
simple alternative to other more complicated approaches
The ASY-EOS experiment at GSI: investigating the symmetry energy at supra-saturation densities
The elliptic-flow ratio of neutrons with respect to protons in reactions of
neutron rich heavy-ions systems at intermediate energies has been proposed as
an observable sensitive to the strength of the symmetry term in the nuclear
Equation Of State (EOS) at supra-saturation densities. The recent results
obtained from the existing FOPI/LAND data for Au+Au collisions
at 400 MeV/nucleon in comparison with the UrQMD model allowed a first estimate
of the symmetry term of the EOS but suffer from a considerable statistical
uncertainty. In order to obtain an improved data set for Au+Au collisions and
to extend the study to other systems, a new experiment was carried out at the
GSI laboratory by the ASY-EOS collaboration in May 2011.Comment: Talk given by P. Russotto at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
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.Comment: 4 pages, Contribution to 8th International Conference on
Nucleus-Nucleus Collisions, Moscow 200
Dynamics of "binary" 197Au+197 Au collisions as a test of energy dissipation mechanism
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 Błocki et al., in which both scenarios of energy dissipation, one-body or two-body dissipation mechanisms, are assumed
Impact of pulsed direct current on embryos, larvae, and young juveniles of Atlantic cod and its implications for electrotrawling of brown shrimp
The application of electrical pulses in fishing gear is considered a promising option to increase the sustainability of demersal trawl fisheries. In the electrotrawl fishery for brown shrimp Crangon crangon, an electrical field selectively induces a startle response in the shrimp. Other benthic organisms remain mainly on the seafloor and escape underneath a hovering trawl. Previous experiments have indicated that this pulse has no short-term major harmful effects on adult fish and invertebrates. However, the impact on young marine life stages is still unknown. Because brown shrimp are caught in shallow coastal zones and estuaries, which serve as important nurseries or spawning areas for a wide range of marine species, electrotrawling on these grounds could harm embryos, larvae, and juveniles. We carried out experiments with different developmental stages of Atlantic Cod Gadus morhua, which are considered vulnerable to electrical pulses. Three embryonic stages, four larval stages, and one juvenile stage of Atlantic Cod were exposed to a homogeneous electrical field of 150 V-peak/m for 5 s, mimicking a worst-case scenario. We detected no significant differences in embryo mortality rate between control and exposed groups. However, for the embryonic stage exposed at 18 d postfertilization, the initial hatching rate was lower. Larvae that were exposed at 2 and 26 d posthatch exhibited higher mortality rates than the corresponding nonexposed control groups. In the other larval and juvenile stages, no short-term impact of exposure on survival was observed. Morphometric analysis of larvae and juveniles revealed no differences in measurements or deformations of the yolk, notochord, eye, or head. Although exposure to a worst-case electrical field did not impact survival or development for six of the eight young life stages of Atlantic Cod, the observed delayed hatching rate and decreased survival for larvae might indicate an impact of electric pulses and warrant further research
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