arXiv subjects

M. Centelles

Publications and source records attributed to M. Centelles.

At least 37 records · Page 2Linked to original sources

arXiv2017

Deformation properties with a finite range simple effective interaction

Deformed and spherical even-even nuclei are studied using a finite range simple effective interaction within the Hartree-Fock-Bogoliubov mean field approach. Different parameter sets of the interaction, corresponding to different incompressibility, are constructed by varying the exponent gamma of the density in the traditional density-dependent term. Ten of the twelve parameters of these interactions are determined from properties of asymmetric nuclear matter and spin polarized pure neutron matter. The two remaining parameters are fitted to reproduce the experimental binding energies known in 620 even-even nuclei using several variants of the rotational energy correction. The rms deviations for the binding energy depend on the value of gamma and the way the rotational energy correction is treated but they can be as low as 1.56 MeV, a value competitive with other renowned effective interactions of Skyrme and Gogny type. Charge radii are compared to the experimental values of 313 even-even nuclei and the rms deviation is again comparable and even superior to the one of popular Skyrme and Gogny forces. Emphasis is given to the deformation properties predicted with these interactions by analyzing the Potential Energy Surfaces for several well deformed nuclei and the fission barriers of some nuclei. Comparison of the results with the experimental information, where available, as well as with the results of the Gogny D1S force shows satisfactory agreement.

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arXiv2016

Exact versus Taylor-expanded energy density in the study of the neutron star crust-core transition

The importance of the fourth and higher order terms in the Taylor series expansion of the energy of the isospin asymmetric nuclear matter in the study of the neutron star crust-core phase transition is investigated using the finite range simple effective interaction. Analytic expressions for the evaluation of the second and fourth order derivative terms in the Taylor series expansion for any general finite range interaction of Yukawa, exponential or Gaussian form have been obtained. The effect of the nuclear matter incompressibility, symmetry energy and slope parameters on the predictions for the crust-core transition density is examined. The crustal moment of inertia is calculated and the prediction for the radius of the Vela pulsar is analyzed using different equations of state.

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arXiv2016

Relativistic mean field interaction with density dependent meson-nucleon vertices based on microscopical calculations

Although ab-initio calculations of relativistic Brueckner theory lead to large scalar isovector fields in nuclear matter, at present, successful versions of covariant density functional theory neglect the interactions in this channel. A new high precision density functional DD-ME$δ$ is presented which includes four mesons $σ$, $ω$, $δ$, and $ρ$ with density dependent meson-nucleon couplings. It is based to a large extent on microscopic ab-initio calculations in nuclear matter. Only four of its parameters are determined by adjusting to binding energies and charge radii of finite nuclei. The other parameters, in particular the density dependence of the meson-nucleon vertices, are adjusted to non-relativistic and relativistic Brueckner calculations of symmetric and asymmetric nuclear matter. The isovector effective mass $m_{p}^{\ast}-m_{n}^{\ast}$ derived from relativistic Brueckner theory is used to determine the coupling strength of the $δ$-meson and its density dependence.

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arXiv2016

Model dependence of the neutron-skin thickness on the symmetry energy

The model dependence in the correlations of the neutron-skin thickness in heavy nuclei with various symmetry energy parameters is analyzed by using several families of systematically varied microscopic mean field models. Such correlations show a varying degree of model dependence once the results for all the different families are combined. Some mean field models associated with similar values of the symmetry energy slope parameter at saturation density $L$, and pertaining to different families, yield a greater-than-expected spread in the neutron-skin thickness of the $^{208}$Pb nucleus. The effective value of the symmetry energy slope parameter $L_{\rm eff}$, determined by using the nucleon density profiles of the finite nucleus and the density derivative $S^\prime(ρ)$ of the symmetry energy starting from about saturation density up to low densities typical of the surface of nuclei, seems to account for the spread in the neutron-skin thickness for the models with similar $L$. The differences in the values of $L_{\rm eff}$ are mainly due to the small differences in the nucleon density distributions of heavy nuclei in the surface region and the behavior of the symmetry energy at subsaturation densities.

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arXiv2015

The neutron skin thickness from the measured electric dipole polarizability in $^{68}$Ni, $^{120}$Sn, and $^{208}$Pb

The information on the symmetry energy and its density dependence is deduced by comparing the available data on the electric dipole polarizability $α_D$ of ${}^{68}$Ni, ${}^{120}$Sn, and ${}^{208}$Pb with the predictions of the Random Phase Approximation, using a representative set of nuclear energy density functionals. The calculated values of $α_D$ are used to validate different correlations involving $α_D$, the symmetry energy at the saturation density $J$, the corresponding slope parameter $L$ and the neutron skin thickness $Δr_{\!np}$, as suggested by the Droplet Model. A subset of models that reproduce simultaneously the measured polarizabilities in ${}^{68}$Ni, ${}^{120}$Sn, and ${}^{208}$Pb are employed to predict the values of the symmetry energy parameters at saturation density and $Δr_{\!np}$. The resulting intervals are: $J\!=\!30 \text{-}35$ MeV, $L\!=\!20 \text{-} 66$ MeV; and the values for $Δr_{\!np}$ in ${}^{68}$Ni, ${}^{120}$Sn, and ${}^{208}$Pb are in the ranges: 0.15\text{-}0.19 fm, 0.12\text{-}0.16 fm, and 0.13\text{-}0.19 fm, respectively. The strong correlation between the electric dipole polarizabilities of two nuclei is instrumental to predict the values of electric dipole polarizabilities in other nuclei.

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arXiv2015

Unified equation of state for neutron stars on a microscopic basis

We derive a new equation of state (EoS) for neutron stars (NS) from the outer crust to the core based on modern microscopic Brueckner-Hartree-Fock (BHF) calculations using the Argonne $v_{18}$ potential plus three-body forces computed with the Urbana model. To deal with the inhomogeneous structures of matter in the NS crust, we use the recent Barcelona-Catania-Paris-Madrid (BCPM) nuclear energy density functional that is directly based on the same microscopic BHF calculations, and which is able to reproduce the ground-state properties of nuclei along the periodic table. The EoS of the outer crust requires the masses of neutron-rich nuclei, which are obtained through Hartree-Fock-Bogoliubov calculations with the BCPM functional when they are unknown experimentally. To compute the inner crust, Thomas-Fermi calculations in Wigner-Seitz cells are performed with the same functional. Existence of nuclear pasta is predicted in a range of average baryon densities between $\simeq$0.067 fm$^{-3}$ and $\simeq$0.0825 fm$^{-3}$, where the transition to the core takes place. The NS core is computed from the nuclear EoS of the BHF calculation assuming non-exotic constituents (core of $npeμ$ matter). In each region of the star, we discuss the comparison of the new EoS with previous EoSes for the complete NS structure, in particular, with the Lattimer-Swesty EoS and with the Shen et al. EoS widely used in astrophysical calculations. The new microscopically derived EoS fulfills at the same time a NS maximum mass of 2~$M_\odot$ with a radius of 10 km, and a 1.5~$M_\odot$ NS with a radius of 11.7 km.

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arXiv2015

Study of spin polarized nuclear matter and finite nuclei with finite range simple effective interaction

The properties of spin polarized pure neutron matter and symmetric nuclear matter are studied using the finite range simple effective interaction, upon its parametrization revisited. Out of the total twelve parameters involved, we now determine ten of them from nuclear matter, against the nine parameters in our earlier calculation, as required in order to have predictions in both spin polarized nuclear matter and finite nuclei in unique manner being free from uncertainty found using the earlier parametrization. The information on the effective mass splitting in polarized neutron matter of the microscopic calculations is used to constrain the one more parameter, that was earlier determined from finite nucleus, and in doing so the quality of the description of finite nuclei is not compromised. The interaction with the new set of parameters is used to study the possibilities of ferromagnetic and antiferromagnetic transitions in completely polarized symmetric nuclear matter. Emphasis is given to analyze the results analytically, as far as possible, to elucidate the role of the interaction parameters involved in the predictions.

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arXiv2014

Influence of the single-particle structure on the nuclear surface and the neutron skin

We analyze the influence of the single-particle structure on the neutron density distribution and the neutron skin in Ca, Ni, Zr, Sn, and Pb isotopes. The nucleon density distributions are calculated in the Hartree-Fock+BCS approach with the SLy4 Skyrme force. A close correlation is found between the quantum numbers of the valence neutrons and the changes in the position and the diffuseness of the nuclear surface, which in turn affect the neutron skin thickness. Neutrons in the valence orbitals with low principal quantum number and high angular momentum mainly displace the position of the neutron surface outwards, while neutrons with high principal quantum number and low angular momentum basically increase the diffuseness of the neutron surface. The impact of the valence shell neutrons on the tail of the neutron density distribution is discussed.

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arXiv2014

From the crust to the core of Neutron Stars on a microscopic basis

Within a microscopic approach the structure of Neutron Stars is usually studied by modelling the homogeneous nuclear matter of the core by a suitable Equation of State, based on a many-body theory, and the crust by a functional based on a more phenomenological approach. We present the first calculation of Neutron Star overall structure by adopting for the core an Equation of State derived from the Brueckner-Hartree-Fock theory and for the crust, including the pasta phase, an Energy Density Functional based on the same Equation of State, and which is able to describe accurately the binding energy of nuclei throughout the mass table. Comparison with other approaches is discussed. The relevance of the crust Equation of state for the Neutron Star radius is particularly emphasised.

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arXiv2013

Symmetry energy of warm nuclear systems

The temperature dependence of the symmetry energy and symmetry free energy coefficients of infinite nuclear matter and of finite nuclei is investigated. For infinite matter, both these coefficients are found to have a weaker dependence on temperature at densities close to saturation; at low but homogeneous densities, the temperature dependence becomes stronger. For finite systems, different definitions of symmetry energy coefficients are encountered in the literature yielding different values. A resolution to this problem is suggested from a global liquid-drop-inspired fit of the energies and free energies of a host of nuclei covering the entire periodic table. The hot nucleus is modeled in a subtracted finite-temperature-Thomas-Fermi framework, with dynamical surface phonon coupling to nucleonic motion plugged in. Contrary to infinite nuclear matter, a substantial change in the symmetry energy coefficients is observed for finite nuclei with temperature.

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arXiv2013

Giant monopole energies from a constrained relativistic mean-field approach

Background: Average energies of nuclear collective modes may be efficiently and accurately computed using a non-relativistic constrained approach without reliance on a random phase approximation (RPA). Purpose: To extend the constrained approach to the relativistic domain and to establish its impact on the calibration of energy density functionals. Methods: Relativistic RPA calculations are compared against the predictions of the corresponding constrained approach using two accurately calibrated energy density functionals. Results: We find excellent agreement-at the 2% level or better-between the predictions of the relativistic RPA and the corresponding constrained approach for magic (or semi-magic) nuclei ranging from 16O to 208Pb. Conclusions: An efficient and accurate method is proposed for incorporating nuclear collective excitations into the calibration of future energy density functionals.

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arXiv2013

Electric Dipole Polarizability in ${}^{208}$Pb: insights from the Droplet Model

We study the electric dipole polarizability $α_D$ in ${}^{208}$Pb based on the predictions of a large and representative set of relativistic and non-relativistic nuclear mean field models. We adopt the droplet model as a guide to better understand the correlations between $α_D$ and other isovector observables. Insights from the droplet model suggest that the product of $α_D$ and the nuclear symmetry energy at saturation density $J$ is much better correlated with the neutron skin thickness $Δr_{np}$ of ${}^{208}$Pb than the polarizability alone. Correlations of $α_D J$ with $Δr_{np}$ and with the symmetry energy slope parameter $L$ suggest that $α_D J$ is a strong isovector indicator. Hence, we explore the possibility of constraining the isovector sector of thenuclear energy density functional by comparing our theoretical predictions against measurements of both $α_D$ and the parity-violating asymmetry in ${}^{208}$Pb. We find that the recent experimental determination of $α_D$ in ${}^{208}$Pb in combination with the range for the symmetry energy at saturation density $J=[31\pm (2)_{\rm est.}]$\,MeV suggests $Δr_{np}({}^{208}{\rm Pb}) = 0.165 \pm (0.009)_{\rm exp.} \pm (0.013)_{\rm theo.} \pm (0.021)_{\rm est.} {\rm fm}$ and $L= 43 \pm(6)_{\rm exp.} \pm (8)_{\rm theo.}\pm(12)_{\rm est.}$ MeV.

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arXiv2013

Density dependence of the symmetry energy from neutron skin thickness in finite nuclei

The density dependence of the symmetry energy around saturation density, characterized by the slope parameter L, is studied using information provided by the neutron skin thickness in finite nuclei. An estimate for L is obtained from experimental data on neutron skins extracted from antiprotonic atoms. We also discuss the ability of parity-violating elastic electron scattering to obtain information on the neutron skin thickness in 208Pb and to constrain the density dependence of the nuclear symmetry energy. The size and shape of the neutron density distribution of 208Pb predicted by mean-field models is briefly addressed. We conclude with a comparative overview of the L values predicted by several existing determinations.

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arXiv2013

Nuclear Symmetry Energy: constraints from Giant Quadrupole Resonances and Parity Violating Electron Scattering

Experimental and theoretical efforts are being devoted to the study of observables that can shed light on the properties of the nuclear symmetry energy. We present our new results on the excitation energy [X. Roca-Maza et al., Phys. Rev. C 87, 034301 (2013)] and polarizability of the Isovector Giant Quadrupole Resonance (IVGQR), which has been the object of new experimental investigation [S. S. Henshaw et al., Phys. Rev. Lett. 107, 222501 (2011)]. We also present our theoretical analysis on the parity violating asymmetry at the kinematics of the Lead Radius Experiment [S. Abrahamyan et al. (PREx Collaboration), Phys. Rev. Lett. 108, 112502 (2012)] and highlight its relation with the density dependence of the symmetry energy [X. Roca-Maza et al., Phys. Rev. Lett. 106, 252501 (2011)].

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arXiv2013

Electron scattering in isotonic chains as a probe of the proton shell structure of unstable nuclei

Electron scattering on unstable nuclei is planned in future facilities of the GSI and RIKEN upgrades. Motivated by this fact, we study theoretical predictions for elastic electron scattering in the N=82, N=50, and N=14 isotonic chains from very proton-deficient to very proton-rich isotones. We compute the scattering observables by performing Dirac partial-wave calculations. The charge density of the nucleus is obtained with a covariant nuclear mean-field model that accounts for the low-energy electromagnetic structure of the nucleon. For the discussion of the dependence of scattering observables at low-momentum transfer on the gross properties of the charge density, we fit Helm model distributions to the self-consistent mean-field densities. We find that the changes shown by the electric charge form factor along each isotonic chain are strongly correlated with the underlying proton shell structure of the isotones. We conclude that elastic electron scattering experiments in isotones can provide valuable information about the filling order and occupation of the single-particle levels of protons.

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arXiv2012

The effects of medium on nuclear properties in multifragmentation

In multifragmentation of hot nuclear matter, properties of fragments embedded in a soup of nucleonic gas and other fragments should be modified as compared with isolated nuclei. Such modifications are studied within a simple model where only nucleons and one kind of heavy nuclei are considered. The interaction between different species is described with a momentum-dependent two-body potential whose parameters are fitted to reproduce properties of cold isolated nuclei. The internal energy of heavy fragments is parametrized according to a liquid-drop model with density and temperature dependent parameters. Calculations are carried out for several subnuclear densities and moderate temperatures, for isospin-symmetric and asymmetric systems. We find that the fragments get stretched due to interactions with the medium and their binding energies decrease with increasing temperature and density of nuclear matter.

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arXiv2012

Microscopic-Macroscopic Approach for Binding Energies with the Wigner-Kirkwood Method - II

The binding energies of deformed even-even nuclei have been analysed within the framework of a recently proposed microscopic-macroscopic model. We have used the semiclassical Wigner - Kirkwood $\hbar$ expansion up to fourth - order, instead of the usual Strutinsky averaging scheme, to compute the shells corrections in a deformed Woods - Saxon potential including the spin-orbit contribution. For a large set of 561 even-even nuclei with $Z\ge 8$ and $N\ge 8$, we find an {\it rms} deviation from the experiment of 610 keV in binding energies, comparable to the one found for the same set of nuclei using the FRDM of Möller and Nix (656 keV). As applications of our model, we explore its predictive power near the proton and neutron drip lines as well as in the superheavy mass region. Next, we systematically explore the fourth - order Wigner - Kirkwood corrections to the smooth part of the energy. It is found that the ratio of the fourth - order to the second - order corrections behaves in a very regular manner as a function of the asymmetry parameter $I=(N-Z)/A$. This allows to absorb the fourth - order corrections into the second - order contributions to the binding energy, which enables to simplify and speed up the calculation of deformed nuclei.

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arXiv2012

Nuclear symmetry energy and neutron skin thickness

The relation between the slope of the nuclear symmetry energy at saturation density and the neutron skin thickness is investigated. Constraints on the slope of the symmetry energy are deduced from the neutron skin data obtained in experiments with antiprotonic atoms. Two types of neutron skin are distinguished: the "surface" and the "bulk". A combination of both types forms neutron skin in most of nuclei. A prescription to calculate neutron skin thickness and the slope of symmetry energy parameter $L$ from the parity violating asymmetry measured in the PREX experiment is proposed.

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