92 research outputs found
Polarization of the nuclear surface in deformed nuclei
The density profiles of around 750 nuclei are analyzed using the Skyrme
energy density functional theory. Among them, more than 350 nuclei are found to
be deformed. In addition to rather standard properties of the density, we
report a non-trivial behavior of the nuclear diffuseness as the system becomes
more and more deformed. Besides the geometric effects expected in rigid body,
the diffuseness acquires a rather complex behavior leading to a reduction of
the diffuseness along the main axis of deformation simultaneously with an
increase of the diffuseness along the other axis. The possible isospin
dependence of this polarization is studied. This effect, that is systematically
seen in medium- and heavy-nuclei, can affect the nuclear dynamical properties.
A quantitative example is given with the fusion barrier in the Ca+
U reaction.Comment: 8 pages, 13 figure
Superfluid fission dynamics with microscopic approaches
Recent progresses in the description of the latter stage of nuclear fission
are reported. Dynamical effects during the descent of the potential towards
scission and in the formation of the fission fragments are studied with the
time-dependent Hartree-Fock approach with dynamical pairing correlations at the
BCS level. In particular, this approach is used to compute the final kinetic
energy of the fission fragments. Comparison with experimental data on the
fission of 258Fm are made.Comment: Proceeding of the "International Conference on Nuclear Structure and
Related Topics" (NSRT15
Neutron pair transfer in sub-barrier capture process
The sub-barrier capture reactions following the neutron pair transfer are
proposed to be used for the indirect study of neutron-neutron correlation in
the surface region of nucleus. The strong effect of the dineutron-like clusters
transfer stemming from the surface of magic and non-magic nuclei O,
Ca, Ni, Mo, Ru, Pd, and
Sn is demonstrated. The dominance of
two-neutron transfer channel at the vicinity of the Coulomb barrier is further
supported by time-dependent mean-field approaches.Comment: 17 pages, 7 figures, accepted in PR
Effet de l'appariement sur la dynamique nucléaire
Pairing correlations is an essential component for the description of the atomic nuclei. The effects of pairing on static property of nuclei are now well known. In this thesis, the effect of pairing on nuclear dynamics is investigated. Theories that includes pairing are benchmarked in a model case. The TDHF+BCS theory turns out to be a good compromise between the physics taken into account and the numerical cost. This TDHF+BCS theory was retained for realistic calculations. Nevertheless, the application of pairing in the BCS approximation may induce new problems due to (1) the particle number symmetry breaking, (2) the non-conservation of the continuity equation. These difficulties are analysed in detail and solutions are proposed. In this thesis, a 3 dimensional TDHF+BCS code is developed to simulate the nuclear dynamic. Applications to giant resonances show that pairing modify only the low lying peaks. The high lying collective components are only affected by the initial conditions. An exhaustive study of the giant quadrupole resonances with the TDHF+BCS theory is performed on more than 700 spherical or deformed nuclei. Is is shown that the TDHF+BCS theory reproduces well the collective energy of the resonance. After validation on the small amplitude limit problem, the approach was applied to study nucleon transfer in heavy ion reactions. A new method to extract transfer probabilities is introduced. It is demonstrated that pairing significantly increases the two-nucleon transfer probability.L'appariement est une composante indispensable à la description des noyaux atomiques. Ses effets sur les propriétés statiques du noyau sont à présent bien connus. Dans ce mémoire, l'effet de l'appariement sur la dynamique nucléaire est étudié. Différentes théories qui incluent l'appariement sont comparées dans un cas modèle. La théorie TDHF+BCS qui apparaît comme un bon compromis entre la richesse de la physique qu'elle contient et son coût numérique est retenue pour les applications aux noyaux. L'introduction de l'appariement dans cette approximation pose de nouveaux problémes liés à (1) la brisure de la symétrie associée au nombre de particules, (2) la non-conservation de l'équation de continuité. Ces difficultés sont analysées en détail et des solutions pratiques sont proposées. Dans cette thèse, un programme TDHF+BCS en 3 dimensions permettant de simuler la dynamique des noyaux a été d'eveloppé. L'application de cette théorie aux résonances géantes a montré que l'appariement n'affecte que les états excités de basse énergie. La composante collective de haute énergie n'étant modifiée que par les conditions initiales. Une étude complète des résonances géantes quadrupolaires a été réalisée pour plus de 700 noyaux sphériques ou déformés. Un bon accord est alors trouvé avec les données expérimentales pour l'énergie collective de la résonance. Cette théorie a ensuite été appliquée à l'étude des réactions de transfert de nucléons lors des collisions noyau-noyau. Une nouvelle méthode de détermination des probabilités de transfert est proposée. Il est montré que l'appariement augmente de manière significative les probabilités de transférer deux nucléons
Pairing dynamics in particle transport
We analyze the effect of pairing on particle transport in time-dependent
theories based on the Hartree-Fock-Bogoliubov (HFB) or BCS approximations. The
equations of motion for the HFB density matrices are unique and the theory
respects the usual conservation laws defined by commutators of the conserved
quantity with the Hamiltonian. In contrast, the theories based on the BCS
approximation are more problematic. In the usual formulation of TDHF+BCS, the
equation of continuity is violated and one sees unphysical oscillations in
particle densities. This can be ameliorated by freezing the occupation numbers
during the evolution in TDHF+BCS, but there are other problems with the BCS
that make it doubtful for reaction dynamics. We also compare different
numerical implementations of the time-dependent HFB equations. The equations of
motion for the and Bogoliubov transformations are not unique, but it
appears that the usual formulation is also the most efficient. Finally, we
compare the time-dependent HFB solutions with numerically exact solutions of
the two-particle Schrodinger equation. Depending on the treatment of the
initial state, the HFB dynamics produces a particle emission rate at short
times similar to that of the Schrodinger equation. At long times, the total
particle emission can be quite different, due to inherent mean-field
approximation of the HFB theory.Comment: 11 pages, 9 figure
The mass of odd-odd nuclei in microscopic mass models
Accurate estimates of the binding energy of nuclei far from stability that
cannot be produced in the laboratory are crucial to our understanding of
nuclear processes in astrophysical scenarios. Models based on energy density
functionals have shown that they are capable of reproducing all known masses
with root-mean-square error better than 800 keV, while retaining a firm
microscopic foundation. However, it was recently pointed out in [M. Hukkanen et
al., arXiv:2210.10674] that the recent BSkG1 model fails to account for a
contribution to the binding energy that is specific to odd-odd nuclei, and
which can be studied by using appropriate mass difference formulas. We analyse
here the (lacking) performance of three recent microscopic mass models with
respect to such formulas and examine possibilities to remedy this deficiency in
the future.Comment: 6 pages, 2 figures; Contribution to the proceedings of INPC 2022,
Cape Town, South Afric
Extracellular ATP-induced acidification leads to cytosolic calcium transient rise in single rat cardiac myocytes
Role of T-type calcium current in identified D-hair mechanoreceptor neurons studied in vitro
Different subsets of dorsal root ganglion (DRG) mechanoreceptors transduce low- and high-intensity mechanical stimuli. It was shown recently that, in vivo, neurotrophin-4 (NT-4)-dependent D-hair mechanoreceptors specifically express a voltage-activated T-type calcium channel (Ca(v)3.2) that may be required for their mechanoreceptive function. Here we show that D-hair mechanoreceptors can be identified in vitro by a rosette-like morphology in the presence of NT-4 and that these rosette neurons are almost all absent in DRG cultures taken from NT-4 knock-out mice. In vitro identification of the D-hair mechanoreceptor allowed us to explore the electrophysiological properties of these cells. We demonstrate that the T-type Ca(v)3.2 channel induced slow membrane depolarization that contributes to lower the voltage threshold for action potential generation and controls spike latency after stimulation of D-hair mechanoreceptors. Indeed, the properties of the T-type amplifier are particularly well suited to explain the high sensitivity of D-hair mechanoreceptors to slowly moving stimuli
Coupled-channels description of the 40Ca + 58,64Ni transfer and fusion reactions
Preliminary experimental data for nucleon transfer reactions of the 40Ca + 58Ni and 40Ca + 64Ni systems are analyzed with the coupled-channels approach. It is shown that a simple treatment for the transfer in the coupled-channels method cannot reproduce simultaneously the transfer probabilities and the subbarrier enhancement of fusion cross sections
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