178 research outputs found
Production of -particle condensate states in heavy-ion collisions
The fragmentation of quasi-projectiles from the nuclear reaction +
at 25 MeV/nucleon was used to produce excited states candidates to
-particle condensation. The experiment was performed at LNS-Catania
using the CHIMERA multidetector. Accepting the emission simultaneity and
equality among the -particle kinetic energies as experimental criteria
for deciding in favor of the condensate nature of an excited state, we analyze
the and states of C and the state of O. A
sub-class of events corresponding to the direct 3- decay of the Hoyle
state is isolated.Comment: contribution to the 2nd Workshop on "State of the Art in Nuclear
Cluster Physics" (SOTANCP2), Universite Libre de Bruxelles (Belgium), May
25-28, 2010, to be published in the International Journal of Modern Physics
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
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
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
Mapping the demise of collective motion in nuclei at high excitation energy
High energy gamma-rays from the 116Sn + 24Mg reaction at 23A MeV were measured using the MEDEA detector at LNS – INFN Catania. Combining this new data with previous measurements yields a detailed view of the quenching of the Giant Dipole Resonance as a function of excitation energy in nuclei of mass A in the range 120÷132. The transition towards the disappearance of the dipole strength, which occurs around 230 MeV excitation energy, appears to be remarkably sharp. Current phenomenological models give qualitative explanations for the quenching but cannot reproduce its detailed features. Keywords: Giant Dipole Resonance, Hot nuclei, Fusion reactions, Statistical Mode
Probing clustering in excited alpha-conjugate nuclei
15 pages, 6 figures, accepted in Physics Letters B; International audience; The fragmentation of quasi-projectiles from the nuclear reaction Ca+C at 25 MeV per nucleon bombarding energy was used to produce -emission sources. From a careful selection of these sources provided by a complete detection and from comparisons with models of sequential and simultaneous decays, evidence in favor of -particle clustering from excited , and is reported
Competition between dynamical and sequential reaction channels in ^{197}Au+^{197}Au collisions at a bombarding energy of 23A MeV
Competition between the two reaction channels: sequential breakup and neck fragmentation has been studied in peripheral and semi-peripheral collisions of the 197 Au+ 197 Au system at bombarding energy of 23A MeV. It was found that the emission of heavy (A < 50) neck-originating fragments occurs in about 22% of ternary breakup events, making this reaction channel highly competitive with the sequential breakup of the projectile- or target-like fragment (78% of events)
Determination of impact parameters in aligned breakup of projectile-like fragments in 197Au + 197Au collisions at 23AMeV
Symmetric and asymmetric aligned breakup of projectile-like fragments in 197Au + 197Au collisions at 23AMeV was studied. Independently of the asymmetry, the reaction yields have been found peaked at a common, very
narrow range of impact parameters
Isospin Diffusion and Equilibration for Sn+Sn collisions at E/A=35 MeV
Equilibration and equilibration rates have been measured by colliding Sn
nuclei with different isospin asymmetries at beam energies of E/A=35 MeV. Using
the yields of mirror nuclei of 7Li and 7Be, we have studied the diffusion of
isospin asymmetry by combining data from asymmetric 112Sn+124Sn and 124Sn+112Sn
collisions with that from symmetric 112Sn+112Sn and 124Sn+124Sn collisions. We
use these measurements to probe isospin equilibration in central collisions
where nucleon-nucleon collisions are strongly blocked by the Pauli exclusion
principal. The results are consistent with transport theoretical calculations
that predict a degree of transparency in these collisions, but inconsistent
with the emission of intermediate mass fragments by a single chemically
equilibrated source. Comparisons with ImQMD calculations are consistent with
results obtained at higher incident energies that provide constraints on the
density dependence of the symmetry energy.Comment: 13 pages, 3 figures, submitted to PRC Rapid Communication
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