arXiv subjects

C. Ducoin

Publications and source records attributed to C. Ducoin.

13 recordsLinked to original sources

arXiv2026

Studies of $\rm ^{144,148}Sm+\alpha$ potential for the $p$-process nucleosynthesis

Nucleosynthesis reaction networks leading to $p$-nuclei involve a combination of different types of photodisintegration and capture reactions, as well as $\beta^+$ decays or electron captures. Photodisintegration reactions involving $\alpha$ particles present a particular interest as they serve as branching points of the reaction networks. The cross sections of these reactions depend crucially on the $\alpha$-nucleus interaction. The $\alpha$ optical model potential (AOMP) is determined mostly by means of experimental differential elastic scattering distributions. Several previous studies have focused on the case of $\rm ^{144}Sm$, an intriguing $p$-nucleus that is semi-magic with 82 neutrons. This work presents new experimental data on $\alpha$ elastic and inelastic scattering on $\rm ^{148}Sm$, its closest stable isotope. Isotopic effects on the description of the AOMP are studied, as well as their consequences on the prediction of $\alpha$-induced reaction cross sections at astrophysical energies. It is shown that the isotopic ratio for $(\alpha,\gamma)$ cross sections can be multiplied up to a factor of two when these effects are included.

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arXiv2024

Bayesian uncertainty quantification on nuclear level density data and their impact on $(p,γ)$ reactions of astrophysical interest

The $p$ process nucleosynthesis is responsible for the synthesis of 35 neutron-deficient nuclei from $^{35}$Se to $^{196}$Hg. An important input that can affect the modeling of this process is the nuclear level density at the relevant excitation energies of the nuclei involved in the reaction network. The OSLO method has been extensively used for the measurement of level densities in excitation energies of several MeV. In this work, Bayesian optimization has been used in order to estimate the 95% high density intervals for the parameters of two level density models optimized on the OSLO data. These uncertainties are then propagated on the cross sections of $(p,γ)$ reactions leading to the compound nuclei $^{105,106}$Pd and $^{105,106}$Cd inside the astrophysically relevant energy range. Imposing constraints in this region of the isotopic chart is important for network calculations involving the nearby $p$ nuclei $^{102}$Pd and $^{106}$Cd. We discuss the reduction of the range of cross sections due to the uncertainties arising from the level density data compared to the range of the six default level density models available in TALYS and we highlight the need for level density data inside the astrophysically relevant energy ranges.

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arXiv2022

Structure of $^{83}$As, $^{85}$As and $^{87}$As: from semi-magicity to $γ$-softness

The structure of $^{83}$As, $^{85}$As and $^{87}$As have been studied in fusion-fission reaction $^{238}$U+$^9$Be. Fission fragments were identified in mass and atomic number using the VAMOS++ spectrometer and the coincident $γ$-rays were detected in the $γ$-ray tracking array AGATA. New transitions in $^{83}$As and $^{85}$As are reported and placed in the level schemes. A level scheme of the excited states in $^{87}$As is proposed for the first time. The data are interpreted in frame of Large-Scale Shell-Model calculations, SU3 symmetries and Beyond Mean-Field frameworks. A spherical regime at magic number $N$=50 is predicted and the location of the proton $g_{9/2}$ orbital is proposed for the first time. Development of collectivity in a prolate deformed, $γ$-soft regime in the open shell cases $^{85}$As and $^{87}$As, most neutron-rich isotopes beyond $N$=50, is concluded. Data and theoretical calculations give confidence to a relatively high extrapolated excitation energy about 4 MeV of the $9/2^+$ state in $^{79}$Cu, one proton above $^{78}$Ni.

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arXiv2019

Unified equations of state for cold non-accreting neutron stars with Brussels-Montreal functionals. I. Role of symmetry energy

The theory of the nuclear energy-density functional is used to provide a unified and thermodynamically consistent treatment of all regions of cold non-accreting neutron stars. In order to assess the impact of our lack of complete knowledge of the density dependence of the symmetry energy on the constitution and the global structure of neutron stars, we employ four different functionals. All of them were precision fitted to essentially all the nuclear-mass data with the Hartree-Fock-Bogoliubov method and two different neutron-matter equations of state based on realistic nuclear forces. For each functional, we calculate the composition, the pressure-density relation, and the chemical potentials throughout the star. We show that uncertainties in the symmetry energy can significantly affect the theoretical results for the composition and global structure of neutron stars. To facilitate astrophysical applications, we construct analytic fits to our numerical results.

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arXiv2019

Coupling between superfluid neutrons and superfluid protons in the elementary excitations of neutron star matter

Several phenomena occurring in neutron stars are affected by the elementary excitations that characterize the stellar matter. In particular, low-energy excitations can play a major role in the emission and propagation of neutrinos, neutron star cooling and transport processes. In this paper, we consider the elementary modes in the star region where both proton and neutron components are superfluid. We study the overall spectral functions of protons, neutrons and electrons on the basis of the Coulomb and nuclear interactions. This study is performed in the framework of the Random Phase Approximation, generalized to superfluid systems. The formalism we use ensures that the Generalized Ward's Identities are satisfied. We focus on the coupling between neutrons and protons. On one hand this coupling results in collective modes that involve simultaneously neutrons and protons, on the other hand it produces a damping of the excitations. Both effects are especially visible in the spectral functions of the different components of the matter. At high density while the neutrons and protons tend to develop independent excitations, as indicated by the spectral functions, the neutron-proton coupling still produces a strong damping of the modes.

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arXiv2016

Giant Pulsar Glitches and the Inertia of Neutron-Star Crusts

Giant pulsar frequency glitches as detected in the emblematic Vela pulsar have long been thought to be the manifestation of a neutron superfluid permeating the inner crust of a neutron star. However, this superfluid has been recently found to be entrained by the crust, and as a consequence it does not carry enough angular momentum to explain giant glitches. The extent to which pulsar-timing observations can be reconciled with the standard vortex-mediated glitch theory is studied considering the current uncertainties on dense-matter properties. To this end, the crustal moment of inertia of glitching pulsars is calculated employing a series of different unified dense-matter equations of state.

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arXiv2012

Inner crust of neutron stars with mass-fitted Skyrme functionals

The equation of state and composition of the inner crust of neutron stars at zero temperature are calculated, using the T = 0 version of the TETFSI (temperature-dependent extended Thomas-Fermi plus Strutinsky integral) method, for each of a family of three functionals based on Skyrme-type forces BSk19, BSk20 and BSk21, which are characterized by different degrees of symmetry-energy stiffness, and also for the SLy4 functional. We also solve the Tolman-Oppenheimer-Volkoff equations to calculate the distribution of mass within the inner crust. Qualitatively similar results are found for all four functionals, and in particular the number of protons per Wigner-Seitz cell is in all cases equal to 40 throughout the inner crust.

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arXiv2011

Spectroscopy of $^{18}$Na: Bridging the two-proton radioactivity of $^{19}$Mg

The unbound nucleus $^{18}$Na, the intermediate nucleus in the two-proton radioactivity of $^{19}$Mg, was studied by the measurement of the resonant elastic scattering reaction $^{17}$Ne(p,$^{17}$Ne)p performed at 4 A.MeV. Spectroscopic properties of the low-lying states were obtained in a R-matrix analysis of the excitation function. Using these new results, we show that the lifetime of the $^{19}$Mg radioactivity can be understood assuming a sequential emission of two protons via low energy tails of $^{18}$Na resonances.

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arXiv2008

Cluster formation in asymmetric nuclear matter: semi-classical and quantal approaches

The nuclear-matter liquid-gas phase transition induces instabilities against finite-size density fluctuations. This has implications for both heavy-ion-collision and compact-star physics. In this paper, we study the clusterization properties of nuclear matter in a scenario of spinodal decomposition, comparing three different approaches: the quantal RPA, its semi-classical limit (Vlasov method), and a hydrodynamical framework. The predictions related to clusterization are qualitatively in good agreement varying the approach and the nuclear interaction. Nevertheless, it is shown that i) the quantum effects reduce the instability zone, and disfavor short-wavelength fluctuations; ii) large differences appear bewteen the two semi-classical approaches, which correspond respectively to a collisionless (Vlasov) and local equilibrium description (hydrodynamics); iii) the isospin-distillation effect is stronger in the local equilibrium framework; iv) important variations between the predicted time-scales of cluster formation appear near the borders of the instability region.

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arXiv2007

Anomalous thermodynamics and phase transitions of neutron-star matter

In this letter we show that the presence of the long-range Coulomb force in dense stellar matter implies that the total charge cannot be associated with a chemical potential, even if it is a conserved quantity. As a further consequence, the analytical properties of the partition sum are modified, changing the order of the phase transitions and affecting the possible occurrence of critical behaviours. The peculiar thermodynamic properties of the system can be understood introducing a model hamiltonian in which each charge is independently neutralized by a uniform background of opposite charge.

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arXiv2006

Thermodynamics of compact-star matter within an ising approach

In the formation and evolution of compact stars, nuclear matter explores high thermal excursions and is the site of intense neutrino emission. Neutrino transport as well as structural properties of this matter depend on the presence of inhomogeneous phases (named "pasta" phases), which are the result of Coulomb frustration of the Liquid-Gas phase transition. We take into account charge fluctuations by employing a frustrated lattice-gas model to which we impose a neutrality constraint by the addition of an homogeneous background of charge, representing delocalised electrons. Within this schematic model we highlight a generaic feature of the phase-transition phenomenology: the temperature interval where pasta phases are formed is enhanced by Coulomb-frustration effects. This result is at variance with the behaviour of frustrated ferromagnetic systems as well as hot nuclei and mean-field approaches. Moreover, the region of phase coexistence is not found to end upon a critical point, indicating that no critical opalescence can occur in compact-star matter.

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arXiv2006

From multifragmentation to supernovae and neutron stars

The thermodynamics properties of globally neutral dense stellar matter are analyzed both in terms of mean field instabilities and structures beyond the mean field. The mean field response to finite wavelenght fluctuations is calculated with the realistic Sly230a effective interaction. A Monte Carlo simulation of a schematic lattice Hamiltonian shows the importance of calculations beyond the mean field to calculate the phase diagram of stellar matter. The analogies and differences respect to the thermodynamics of nuclear matter and finite nuclei are stressed.

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arXiv2006

Role of isospin in the nuclear liquid-gas phase transition

We study the thermodynamics of asymmetric nuclear matter using a mean field approximation with a Skyrme effective interaction, in order to establish its phase diagram and more particularly the influence of isospin on the order of the transition. A new statistical method is introduced to study the thermodynamics of a multifluid system, keeping only one density fixed the others being replaced by their intensive conjugated variables. In this ensemble phase coexistence reduces to a simple one dimensional Maxwell construction. For a fixed temperature under a critical value, a coexistence line is obtained in the plane of neutron and proton chemical potentials. Along this line the grand potential presents a discontinuous slope showing that the transition is first order except at the two ending points where it becomes second order. This result is not in contradiction with the already reported occurrence of a continuous transformation when a constant proton fraction is imposed. Indeed, the proton fraction being an order parameter in asymmetric matter, the constraint can only be fulfilled by gradual phase mixing along the first-order phase transition line leading to a continuous pressure.

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