417 research outputs found
Density profiles and collective excitations of a trapped two component Fermi vapour
We discuss the ground state and the small-amplitude excitations of a
degenerate vapour of fermionic atoms placed in two hyperfine states inside a
spherical harmonic trap. An equations-of-motion approach is set up to discuss
the hydrodynamic dissipation processes from the interactions between the two
components of the fluid beyond mean-field theory and to emphasize analogies
with spin dynamics and spin diffusion in a homogeneous Fermi liquid. The
conditions for the establishment of a collisional regime via scattering against
cold-atom impurities are analyzed. The equilibrium density profiles are then
calculated for a two-component vapour of 40K atoms: they are little modified by
the interactions for presently relevant values of the system parameters, but
spatial separation of the two components will spontaneously arise as the number
of atoms in the trap is increased. The eigenmodes of collective oscillation in
both the total particle number density and the concentration density are
evaluated analytically in the special case of a symmetric two-component vapour
in the collisional regime. The dispersion relation of the surface modes for the
total particle density reduces in this case to that of a one-component Fermi
vapour, whereas the frequencies of all other modes are shifted by the
interactions.Comment: 14 pages, 4 figure
Elastic Scattering and Total Reaction Cross Section for the 6He + 27Al System
The elastic scattering of the radioactive halo nucleus 6He on 27Al target was
measured at four energies close to the Coulomb barrier using the RIBRAS
(Radioactive Ion Beams in Brazil) facility. The Sao Paulo Potential(SPP) was
used and its diffuseness and imaginary strength were adjusted to fit the
elastic scattering angular distributions. Reaction cross-sections were
extracted from the optical model fits. The reduced reaction cross-sections of
6He on 27Al are similar to those for stable, weakly bound projectiles as
{6,7}Li, 9Be and larger than stable, tightly bound projectile as 16O on 27Al.Comment: 7 pages, 1 table, 3 figure
Reaction mechanisms in the 6Li+59Co system
The reactions induced by the weakly bound 6Li projectile interacting with the
intermediate mass target 59Co were investigated. Light charged particles
singles and - coincidence measurements were performed at the near
barrier energies E_lab = 17.4, 21.5, 25.5 and 29.6 MeV. The main contributions
of the different competing mechanisms are discussed. A statistical model
analysis, Continuum-Discretized Coupled-Channels calculations and two-body
kinematics were used as tools to provide information to disentangle the main
components of these mechanisms. A significant contribution of the direct
breakup was observed through the difference between the experimental sequential
breakup cross section and the CDCC prediction for the non-capture breakup cross
section.Comment: 30 pages, 8 figure
A clear signature of the breakup modes for 9Be on a proton target at 5.6 MeV/nucleon
The breakup of 9Be is studied via an inelastic scattering experiment on a proton
target at 5.6 A MeV in inverse kinematics. Two of the three cluster constituents (α and α)
as well as the proton target recoil were recorded in a triple coincidence mode allowing a full
kinematics approach analysis. In this respect relative α - α and α - n, Q-value and 9Be excitation
spectra, energy spectra for all fragments as well as the energy spectrum of the recoil proton
were reconstructed. A clear signature of the two breakup sequential modes (5He + 4He and
8Be + n) was identified via the recoiling proton reconstructed spectra together with the direct
breakup decay. A strong 5He + 4He mode was observed compatible with previous beta decay
experiments
Reaction mechanisms for weakly-bound, stable nuclei and unstable, halo nuclei on medium-mass targets
An experimental overview of reactions induced by the stable, but weakly-bound
nuclei 6Li, 7Li and 9Be, and by the exotic, halo nuclei 6He, 8B, 11Be and 17F
on medium-mass targets, such as 58Ni, 59Co or 64Zn, is presented. Existing data
on elastic scattering, total reaction cross sections, fusion processes, breakup
and transfer channels are discussed in the framework of a CDCC approach taking
into account the breakup degree of freedom.Comment: 7 pages, 6 figures, Invited Talk given by C. Beck to the 10th
International Conference on Nucleus-Nucleus Collisions, August 16-21, 2009
Beijing, China; Paper submitted to the NN2009 Proceedings, Nuclear Physics A
(to be published
Global study of 9 Be + p at 2.72 A MeV
Background: In our recent experiment,
9
Be
+
p
at
5.67
A
MeV, the breakup decay rates to the three configurations,
α
+
α
+
n
,
8
Be
∗
+
n
and
5
He
+
4
He
of
9
Be
, were observed and quantified in the proton recoil spectra, in a full kinematics approach. Unfolding step by step the accessibility to the above configurations, it will require similar experiments at lower or/and higher energies. It will also require the interpretation of the data in a theoretical framework. Three-body models for the structure of
9
Be
have been developed and applied to reactions with heavy targets. Further research on lighter targets is required for the best establishment of the model. Such models are relevant for the calculation of the corresponding radiative capture reaction rate,
α
(
α
,
γ
)
9
Be
followed by
9
Be
(
α
,
n
)
12
C
. The last is essential for the
r
-process abundance predictions.
Purpose: Investigate the breakup decay rate of
9
Be
+
p
at
2.72
A
MeV, where the direct configuration
α
+
α
+
n
is mainly accessible. Compare and interpret data at this low energy and at the higher energy of
5.67
A
MeV into a four-body continuum discretized coupled-channel formalism. Point out and discuss couplings to continuum.
Methods: Our experimental method includes an exclusive breakup measurement in a full kinematic approach of
9
Be
incident on a proton target at 24.5 MeV (
2.72
A
MeV). Complementary the elastic scattering is measured and other reaction channels are evaluated from previous measurements under the same experimental conditions. The interpretation of present data at
2.72
A
MeV and previous data at
5.67
A
MeV, are considered in a four-body continuum discretized coupled channel (CDCC) approach, using the transformed harmonic oscillator method for the three-body projectile.
Results: An elastic scattering angular distribution at
2.72
A
MeV is measured, which compares very well with CDCC calculations, indicating a strong coupling to continuum. At the same energy, the breakup and total reaction cross sections are measured as
σ
break
=
2.5
±
1
mb
and
σ
tot
=
510
±
L
90
mb
, in good agreement with the calculated values of 3.7 and 433 mb, respectively. Further on, into the same theoretical framework, the elastic scattering and breakup cross section data at
5.67
A
MeV are found in very good agreement with the CDCC calculations.
Conclusions: It was confirmed in a global experimental framework that four-body CDCC calculations can describe very well the data even at low energies. Coupling to continuum is very strong despite the small measured breakup cross section. Moreover, the present results support further our three-body model for the structure of
9
Be
, validating relevant radiative reaction rates obtained previously.Programa de investigación e innovación de la Unión Europea HORIZON2020 No. 654002-ENSAR2European Research Council (ERC) 714625Ministerio de Ciencia, Innovación y Universidades de España. PGC2018-095640-B-I00Ministerio de España de Economía y Competitividad y Fondo de Desarrollo de la Unión Europea (FEDER) FIS2017- 88410-PFondos SID 2019 (Università degli Studi di Padua, Italia) CASA_SID19_0
Sub- and above barrier fusion of loosely bound Li with Si
Fusion excitation functions are measured for the system Li+Si
using the characteristic -ray method, encompassing both the sub-barrier
and above barrier regions, viz., = 7-24 MeV. Two separate experiments
were performed, one for the above barrier region (= 11-24 MeV) and
another for the below barrier region (= 7-10 MeV). The results were
compared with our previously measured fusion cross section for the
Li+Si system. We observed enhancement of fusion cross section at
sub-barrier regions for both Li and Li, but yield was substantially
larger for Li. However, for well above barrier regions, similar type of
suppression was identified for both the systems.Comment: 8 pages, 6 figures, as accepted for publication in Eur.Phys.J.
Breakup of 6Li + p at near-barrier energies and the effect on elastic scattering
Exclusive breakup measurements have been performed for the Li6+p system in inverse kinematics at Li6 incident energies of 25 and 29 MeV. The results are considered in the Continuum Discretized Coupled-Channels framework, together with elastic scattering data at 16, 20, 25, and 29 MeV, obtained simultaneously in the same experiment and reported previously. Good agreement between data and theory is observed, interpreted as evidence for strong coupling to the continuum. The direct and sequential (via the Li631+ resonance) breakup cross sections are found to be equally large at the higher incident energies but the dominant effect on the elastic scattering is due to coupling to the sequential breakup. This effect remains dominant even at the lowest energy of 16 MeV, despite the negligible cross section for excitation of the resonance at this low incident energy.European Union 262010-ENSA
Elastic scattering for the system 6Li + p at near barrier energies with MAGNEX
Elastic scattering measurements have been performed for the 6Li+p system in inverse kinematics at the energies of 16, 20, 25 and 29 MeV. The heavy ejectile was detected by the large acceptance MAGNEX spectrometer at the Laboratori Nazionali del Sud (LNS) in Catania, in the angular range between ∼20 and 120 in the laboratory system, giving us the possibility to span almost a full angular range in the center of mass system. Results will be presented and discussed for one of the energies.European Union 262010-ENSA
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