311 research outputs found
Fission dynamics of intermediate-fissility systems: A study within a stochastic three-dimensional approach
Examination of isospin effects in multi-dimensional Langevin fission dynamics
Abstract One-dimensional and three-dimensional dynamical fission calculations based on Langevin equations are performed for the compound nuclei 194 Pb, 200 Pb, 206 Pb, 182 Hg, and 204 Hg to investigate the influence of the compound nucleus isospin on the prescission particle multiplicities and on the fission fragment mass–energy distribution. It is found that the prescission neutron, proton, and alpha particle multiplicities have approximately the same sensitivity to the dissipation strength for a given nucleus. This is at variance with conclusions of recent papers. The sensitivity of the calculated prescission particle multiplicities to the dissipation strength becomes higher with decreasing isospin of fissioning compound nucleus, and the increase of prescission particle multiplicities could reach 200%, when the reduction coefficient of one-body viscosity k s increases from 0.1 to 1, for the most neutron deficient nuclei considered. The variances of fission fragment mass and kinetic energy distributions are less sensitive to the change of dissipation strength than the prescission light particle multiplicities. A comparison to experimental data concerning 200 Pb nucleus is also presented
A new study of Mg(,n)Si angular distributions at = 3 - 5 MeV
The observation of Al gives us the proof of active nucleosynthesis in
the Milky Way. However the identification of the main producers of Al is
still a matter of debate. Many sites have been proposed, but our poor knowledge
of the nuclear processes involved introduces high uncertainties. In particular,
the limited accuracy on the Mg(,n)Si reaction cross
section has been identified as the main source of nuclear uncertainty in the
production of Al in C/Ne explosive burning in massive stars, which has
been suggested to be the main source of Al in the Galaxy. We studied
this reaction through neutron spectroscopy at the CN Van de Graaff accelerator
of the Legnaro National Laboratories. Thanks to this technique we are able to
discriminate the (,n) events from possible contamination arising from
parasitic reactions. In particular, we measured the neutron angular
distributions at 5 different beam energies (between 3 and 5 MeV) in the
\ang{17.5}-\ang{106} laboratory system angular range. The presented results
disagree with the assumptions introduced in the analysis of a previous
experiment.Comment: 9 pages, 9 figures - accepted by EPJ
Probing the statistical decay and alpha-clustering effects in 12c+12c and 14n+10b reactions
An experimental campaign has been undertaken at INFN Laboratori Nazionali di
Legnaro, Italy, in order to progress in our understanding of the statistical
properties of light nuclei at excitation energies above particle emission
threshold, by measuring exclusive data from fusion-evaporation reactions. A
first reaction 12C+12C at 7.9 AMeV beam energy has been measured, using the
GARFIELD+Ring Counter experimental setup. Fusion-evaporation events have been
exclusively selected. The comparison to a dedicated Hauser-Feshbach calculation
allows us to give constraints on the nuclear level density at high excitation
energy for light systems ranging from C up to Mg. Out-of-equilibrium emission
has been evidenced and attributed both to entrance channel effects favoured by
the cluster nature of reaction partners and, in more dissipative events, to the
persistence of cluster correlations well above the 24Mg threshold for 6 alphas
decay. The 24Mg compound nucleus has been studied with a new measurement 14N +
10B at 5.7 AMeV. The comparison between the two datasets would allow us to
further constrain the level density of light nuclei. Deviations from a
statistical behaviour can be analyzed to get information on nuclear clustering.Comment: 4 pages, 2 figures, Contribution to conference proceedings of the
25th International Nuclear Physics Conference (INPC 2013
Examination of isospin effects in multi-dimensional Langevin fission dynamics
One-dimensional and three-dimensional dynamical fission calculations based on Langevin equations are performed for the compound nuclei Pb-194, Pb-200, Pb-206, Hg-182, and Hg-204 to investigate the influence of the compound nucleus isospin on the prescission particle multiplicities and oil the fission fragment mass-energy distribution It is found that the prescission neutron, proton, and alpha particle multiplicities have approximately the same sensitivity to the dissipation strength for a given nucleus This is at variance with Conclusions of recent papers The sensitivity of the calculated prescission particle Multiplicities to the dissipation strength becomes higher with decreasing isospin of fissioning compound nucleus, and the increase of prescission particle multiplicities could reach 200%, when the reduction coefficient of one-body viscosity k(s) increases from 0 1 to 1, for the most neutron deficient nuclei considered The variances of fission fragment mass and kinetic energy distributions are less sensitive to the change of dissipation strength than the prescission light particle multiplicities A comparison to experimental data concerning Pb-200 nucleus is also presented
Clustering effects in 48Cr composite nuclei produced via 24Mg + 24Mg reaction
In the framework of studying clustering effects in N=Z light nuclei, an experiment was carried out to get information on the properties of the 48 Cr composite nuclei produced via the 24 Mg +24 Mg reaction. In particular, the study regards the 48 Cr at 60 MeV of excitation energy where a resonance with a narrow width (170 KeV) has been found by measuring the elastic and anelastic channels. To determine the deformation of this state, evaporative Light Charged Particles (LCP) are measured and compared to the Statistical Model (SM) predictions, which are very sensitive to nuclear deformation. The experiment was performed at LNL using the 8ĒLP apparatus to select LCPs and a Parallel Plate Avalanche Counter (PPAC) system to detect the Evaporation Residues (ER). Preliminary results on the measurements of ER – LCP and LCP – LCP angular correlations are presented which indicate the presence of a very large deformation.The analysis will proceed with the extraction of the LCP energy spectra and with the angular correlations for high multiplicity channels to determine the deformation
Fusion process studied with preequilibrium giant dipole resonance in time dependent Hartree-Fock theory
15 pages, 19 figures, revised versionInternational audienceThe equilibration of macroscopic degrees of freedom during the fusion of heavy nuclei, like the charge and the shape, are studied in the Time-Dependent Hartree-Fock theory. The pre-equilibrium Giant Dipole Resonance (GDR) is used to probe the fusion path. It is shown that such isovector collective state is excited in N/Z asymmetric fusion and to a less extent in mass asymmetric systems. The characteristics of this GDR are governed by the structure of the fused system in its preequilibrium phase, like its deformation, rotation and vibration. In particular, we show that a lowering of the pre-equilibrium GDR energy is expected as compared to the statistical one. Revisiting experimental data, we extract an evidence of this lowering for the first time. We also quantify the fusion-evaporation enhancement due to gamma-ray emission from the pre-equilibrium GDR. This cooling mechanism along the fusion path may be suitable to synthesize in the future super heavy elements using radioactive beams with strong N/Z asymmetries in the entrance channel
The Dynamical Dipole Mode in Dissipative Heavy Ion Collisions
We study the effect of a direct Giant Dipole Resonance () excitation in
intermediate dinuclear systems with exotic shape and charge distributions
formed in charge asymmetric fusion entrance channels. A related enhancement of
the gamma yield in the evaporation cascade of the fused nucleus is
expected. The dynamical origin of such extra strength will show up in a
characteristic anisotropy of the dipole gamma-emission. A fully microscopic
analysis of the fusion dynamics is performed with quantitative predictions of
the photon yield based on a dynamics- statistics coupling model. In
particular we focus our attention on the energy and mass dependence of the
effect.
We suggest a series of new experiments, in particular some optimal entrance
channel conditions. We stress the importance of using the new available
radioactive beams.Comment: 20 pages (Latex), 14 Postscript figure
High-energy gamma rays emission in coincidence with light charged particles from the32S +74Ge reaction at 210 MeV
High-energyγ-rays from the32S+74Ge reaction at 210 MeV bombarding energy were measured in coincidence with light charged particles detected in a large area hodoscope. Experimental results show that energeticγ-rays in coincidence with light charged particles are essentially emitted in the compound nucleus decay. The parameters of the giant dipole resonance (GDR) have been extracted from alineshape analysis of the experimentalγ-ray spectrum. The derived values of mean energyED, widthΓ and strengthS are in good agreement with results from previous experiments on Sn isotopes obtained by using different experimental techniques
Isospin transport in 84Kr + 112,124Sn collisions at Fermi energies
Isotopically resolved fragments with Z<=20 have been studied with high
resolution telescopes in a test run for the FAZIA collaboration. The fragments
were produced by the collision of a 84Kr beam at 35 MeV/nucleon with a n-rich
(124Sn) and a n-poor (112Sn) target. The fragments, detected close to the
grazing angle, are mainly emitted from the phase-space region of the
projectile. The fragment isotopic content clearly depends on the n-richness of
the target and it is a direct evidence of isospin diffusion between projectile
and target. The observed enhanced neutron richness of light fragments emitted
from the phase-space region close to the center of mass of the system can be
interpreted as an effect of isospin drift in the diluted neck region.Comment: 8 pages, 7 figure
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