arXiv subjects

L. M. Robledo

Publications and source records attributed to L. M. Robledo.

At least 19 recordsLinked to original sources

arXiv2026

Impact of perturbative tensor interactions on the spontaneous fission half-lives of superheavy nuclei

The standard microscopic description of fission, based on the mean-field Hartree-Fock-Bogoliubov approximation and a semi-classical description of tunneling through the fission barrier, has been used to analyse the impact of introducing a (perturbative) tensor term along with the well known Gogny-D1S force in the spontaneous fission half-lives. Calculations in a series of even-even isotopes of superheavy nuclei ranging from nobelium to darmstatium have been carried out. The results show that the tensor term only impacts the height of the first fission barrier and leaves mostly unaffected the pairing properties and therefore the collective inertias. As a consequence of the reduction in the barrier height, the spontaneous fission lifetimes obtained by including the tensor term are significantly smaller than the ones without it bringing the theoretical predictions in closer agreement with experimental data.

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arXiv2026

Microscopic description of the fission process including intrinsic excitations. Part I: 240Pu adiabatic and asymmetric fission path within the Schrodinger Collective Intrinsic Model

This article is the first in a trilogy aimed at presenting the first practical implementation of the Schrodinger Collective-Intrinsic Model (SCIM) applied to nuclear fission. Within the SCIM framework, the many-body wave function explicitly couples collective motion to intrinsic excitations, necessitating sets of Hartree-Fock-Bogoliubov (HFB) configurations that remain continuous and regular across a broad deformation range, from the ground state to scission and beyond. This paper focuses on constructing adiabatic HFB paths suitable for subsequent SCIM dynamical calculations. Standard constrained adiabatic paths often suffer from discontinuities and irregularities, which prevent the direct application of the formalism. To address these challenges, we implement two recently proposed overlap-based protocols, the Link and Drop methods, and combine them into a new numerical procedure.A comparison with the exact Gaussian Overlap Approximation confirms that the resulting adiabatic kernels exhibit properties consistent with the assumptions of the SCIM formalism. The regularized path is then analyzed in the scission region. We identify characteristic structures in the proton and neutron chemical potentials, a pronounced neutron enrichment of the neck at scission, and fragment particle-number distributions displaying a strong odd-even staggering in the proton sector. Finally, using a microscopic fragment-separation procedure formulated in the canonical basis, we extract static scission properties including fragment deformation energies and both Coulomb and nuclear contributions to the fragment interaction energy. These results establish the adiabatic foundations required for future SCIM calculations with intrinsic excitations and provide a microscopic characterization of the scission region in 240Pu.

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arXiv2026

Microscopic description of the fission process including intrinsic excitations. Part II: 240Pu excited and asymmetric fission paths within the Schrodinger Collective

This second article of the trilogy presents the implementation of a third protocol, referred to as Continuous Deflation, designed to construct continuous and regular excited paths within the Schrodinger Collective-Intrinsic Model (SCIM), with applications to nuclear fission. We show that the use of standard 2QP excitations, even when combined with particle-number projection, prevents a consistent application of the SCIM framework. Motivated by the central role of pair breaking in low-energy fission, we explore how to construct intrinsic excited states that incorporate this mechanism while satisfying the continuity and regularity state requirements of the SCIM. To this end, we first analyze the Deflation procedure alone, which constructs excited states through orthogonality constraints. We then extend this construction along a deformation path by introducing an additional continuity constraint, thereby defining the Continuous Deflation method, which generates continuous paths based on excited states. In particular, we construct ten such continuous paths built on top of the adiabatic and asymmetric fission path of 240Pu. The resulting excited states are systematically analyzed in terms of their microscopic structure. We then investigate several fragment properties near scission, including neutron and proton chemical potentials, neutron necking as well as fragment particle-number distributions, and compare them with their adiabatic counterparts.

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arXiv2026

Microscopic description of the fission process including intrinsic excitations. Part III: 240Pu fission dynamics along 1D asymmetric paths within the Schrodinger Collective Intrinsic Model

This last article of the trilogy focuses on the dynamical equation of the Schrodinger Collective-Intrinsic Model (SCIM). First, we motivate and discuss the need to regularize the adiabatic and excited dynamical ingredients entering the collective-intrinsic Hamiltonian, namely the collective potential, the collective inertia tensor, and the collective dissipative tensor. In particular, we introduce a Savitzky-Golay low-pass filter to remove numerical fluctuations incompatible with the second-order truncation in the Symmetric Ordered Product of Operators used to derive the SCIM equations. The diagonal and off-diagonal properties of the three dynamical ingredients are then analyzed along the asymmetric fission path in 240Pu. This study highlights the dominant role of neutron and proton excitation channels, especially in the second well and scission regions, whereas proton-neutron couplings remain essentially negligible. Furthermore, in the adiabatic limit of the SCIM, we perform a comparison with the GOA which reveals very close predictions. Second, we discuss the construction of the initial wave packet and the numerical resolution of the collective-intrinsic Schrodinger equation. Using a continuity equation, we derive the probability fluxes associated with the different components of the wave function, which provide direct access to the contribution of the different excitations to the final observables for the fission problem. The excited states are found to account for more than 80% of the total flux at scission. Finally, we evaluate, the neutron and proton fragment distributions as well as the energy balance, including the total kinetic and excitation energies. The obtained results are found to be consistent with available experimental data and demonstrate the importance of explicitly including intrinsic excitations in the description of fission dynamics.

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arXiv2026

Impacts of hexadecapole correlations in actinide nuclei

The impact of hexadecapole correlations on the low-energy spectroscopic properties of Th, U, and Pu nuclei, within the mass range $232 \le A \le 240$, is studied systematically using the mapped $sdg$-IBM model. Fermionic input is obtained via the quadrupole-hexadecapole constrained Hartree-Fock-Bogoliubov approximation, based on the parametrization D1S of the Gogny energy density functional. The $sdg$-IBM Hamiltonian parameters are determined by mapping the quadrupole-hexadecapole fermionic mean-field potential energy surfaces onto the corresponding bosonic surfaces. The low-energy spectra and transition strengths, obtained via the diagonalization of the $sdg$-IBM Hamiltonian, compare well with the available experimental data. It is shown that the effects of hexadecapole collectivity can be observed in high-spin yrast states with spins $J^{\pi} \geqslant 10^{+}$. The mapped $sdg$-IBM improves the excitation energies of those states, as compared with the simpler $sd$-IBM model. The $sdg$-IBM also improves the description of the $E2$ transition strengths between high-spin yrast states and predicts strong $E4$ transitions from nonyrast $4^+$ states to the $0^+$ ground state.

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arXiv2026

Stability of intruder-driven quadrupole and hexadecapole deformation effects in Xenon, Barium, Cerium and Neodymium isotopes

Two-dimensional Generator Coordinate Method calculations for the axial quadrupole $\beta_{2}$ and hexadecapole $\beta_{4}$ collective deformations are carried out with the Gogny force in a series of Xe, Ba, Ce and Nd isotopes with neutron numbers covering both magic neutron shell closures N=82 and N=126. The underlying mean-field configurations are used to characterize the expected dynamic behavior of the system. Two regions of strong coupling between the quadrupole and hexadecapole degrees of freedom are found and characterized. Quantum fluctuations soften the mean-field ground state values of $\beta_{2}$ and $\beta_{4}$ in transitional regions. The ground state correlation energy coming from $\beta_{4}$ is comparable in size to the one coming from $\beta_{2}$, and both together amount to a sizable 1.5 MeV. Shape coexistence in some isotopes and its impact in the excitation energy of the first excited state is analysed. Finally, the role of a second intruder orbital in the explanation of the large deformation parameters of some nuclei in the region is discussed.

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arXiv2025

Microscopic pairing in fission dynamics

Nuclear fission can be modelled as a quantum tunneling process driven by the interplay between the nuclear binding energy and the collective inertia. Within the Wentzel-Kramers-Brillouin formalism, spontaneous fission half-lives can be obtained by minimizing the action integral in the multidimensional space of collective degrees of freedom. Hence, including the relevant collective variables is crucial for properly describing spontaneous fission probabilities. Pairing correlations play an essential role in this evaluation since the collective inertia decreases as the inverse of the square of the pairing gap, and, therefore, they should be considered as a relevant degree of freedom on the same footing as deformation parameters. In this work, we show that the spontaneous fission half-lives in fermium isotopes can be reproduced in a microscopic theory by considering the least-action fission path in a two-dimensional space with constraints on the quadrupole moment and pairing correlations. We consider two microscopic quantities as degrees of freedom associated with pairing: the pairing gap parameter $Δ$, and the particle number fluctuations $\langle ΔN^2 \rangle$. Least-action paths, computed using the Dijkstra algorithm, are compared with minimum-energy paths, highlighting the importance of pairing correlations as a dynamical degree of freedom.

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arXiv2025

Quadrupole-hexadecapole coupling in the rare earth region with beyond mean field correlations

The roles of static hexadecapole deformation and beyond-mean-field quadrupole-hexadecapole configuration mixing are studied for a selected set of Yb, Hf, W and Os isotopes within the mass range $170 \le A \le 202$, using the Hartree-Fock-Bogoliubov (HFB) and the two-dimensional Generator Coordinate Method (2D-GCM) approaches, based on the Gogny energy density functional. The 2D-GCM ground and excited states of the lighter isotopes are associated with diamond-like shapes while, for each isotopic chain, a region where those states correspond to square-like shapes has been found below the neutron shell closure $N=126$. It is shown, that for the studied nuclei the quadrupole and hexadecapole degrees of freedom are interwoven in the ground and excited states up to the mass number $A=184-188$. This structural evolution, encoded in the 2D-GCM collective wave functions, is accompanied by an enhanced prolate-oblate shape coexistence around the neutron number $N=116$. In agreement with previous studies, it is also shown that for the considered Yb, Hf, W and Os isotopes the inclusion of hexadecapole deformation in the ground state dynamics leads to a non trivial additional correlation energy comparable to the quadrupole correlation energy itself.

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arXiv2025

Pairing in fission: Mean-field and collective inertias study

Pairing plays a crucial role in the microscopic description of nuclear fission. Microscopic methods provide access to three quantities related to pairing, namely, the pairing gap ($Δ$), the particle number fluctuations ($ Δ\hat{N}^2 $), and the quenching factor (QF). The aim of this work is to analyse the impact of each of these quantities on the static description of the fission process.

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arXiv2025

Particle number projection on a spatial domain

The formalism of particle number on a spatial domain for mean field wave functions with pairing is revisited to account for the case where finite dimensional basis are used. The formulas differ from the ones previously used in the literature. It is shown that the present formalism has the right limit in the well known case of zero pairing whereas the other formalism do not satisfy this basic requirement. By using a simple one-dimensional model we illustrate the differences in the results for particle number distribution probability obtained with the two methods.

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arXiv2025

Pfaffian formulas for non equivalent bases

Pfaffian formulas used to compute overlaps necessary to carry out generator coordinate method calculations using a set of Hartree- Fock- Bogoliubov wave functions, is generalized to the case where each of the HFB states are expanded in different arbitrary bases spanning different sub-space of the Hilbert space. The formula obtained is compared with previous results proving to be completely equivalent to them. A discussion of equivalent formulas obtained in the literature is carried out.

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arXiv2025

Quadrupole-hexadecapole correlations in neutron-rich samarium and gadolinium isotopes

We present an extensive study of quadrupole-hexadecapole correlation effects in even-even Sm and Gd isotopes with neutron number $N=88-106$. The calculations are performed in the framework of the Gogny energy density functional (EDF) with the D1S parametrization and the $sdg$ interacting boson model (IBM). The quadrupole-hexadecapole constrained self-consistent mean-field potential energy surface is mapped onto the expectation value of the $sdg$-boson Hamiltonian. This procedure determines the parameters of the $sdg$-IBM Hamiltonian microscopically. Calculated excitation energies and transition strengths are compared to the ones obtained with a simpler $sd$-IBM, as well as with the experimental data. The Gogny-EDF mapped $sdg$-IBM reproduces spectroscopic properties of the studied nuclei as reasonably as in the case of the previous $sdg$-boson mapping calculations that were based on the relativistic EDF, indicating that the axial quadrupole-hexadecapole method is sound regardless of whether relativistic or nonrelativistic EDF is employed. The mapped $sdg$-IBM improves some of the results in lighter Sm and Gd isotopes compared to the mapped $sd$-IBM, implying the existence of significant hexadecapole correlations in those nuclei. For those nuclei with $N \geq 94$, hexadecapole effects are minor, and the only significant difference between the two boson models can be found in the description of $E0$ monopole transitions.

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arXiv2025

Microscopic description of quadrupole-hexadecapole coupling in radium, thorium, uranium and plutonium isotopes with the Gogny energy density functional

The emergence and stability of static hexadecapole deformations as well as the impact in the development of dynamic deformation due to collective motion considering quadrupole-hexadecapole coupling are studied for a selected set of radium, thorium, uranium and plutonium isotopes, using the Gogny Hartree-Fock-Bogoliubov and Generator Coordinate Method frameworks. Sizable hexadecapole deformations are found to play a significant role in the ground and excited states of nuclei in the neighborhood of $^{238}$U. For each of the studied isotopic chains, it is shown that a region with small negative hexadecapole deformation, just below the neutron magic number $N =184$, remains stable once zero-point quadrupole-hexadecapole fluctuations are taken into account. A transition is predicted, with increasing mass number, from a regime in which the quadrupole and hexadecapole degrees of freedom are interwoven to a regime in which they are decoupled, accompanied by an enhanced shape coexistence in the more neutron-rich sectors of the isotopic chains. It is also shown, that quadrupole-hexadecapole configuration mixing brings a nontrivial additional correlation energy gain comparable to the quadrupole correlation energy itself.

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arXiv2024

Microscopic description of spontaneous fission based on a Gogny energy density functional including tensor contributions

This paper extends previous studies on the impact of tensor forces in fission dynamics of neutron-deficient Thorium isotopes to other isotopic chains of heavy actinides and low-mass super-heavy nuclei. Calculations are carried out within a mean-field framework based on the Gogny-D1S parametrization supplemented with the D1ST2a perturbative tensor term as driving force. Fission barrier heights and spontaneous fission half-lives are used as benchmarks to analyze the impact of the tensor term. A significant reduction of fission barrier heights and half-lives is associated to the tensor component of the force.

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arXiv2024

Odd nuclei and quasiparticle excitations within the Barcelona Catania Paris Madrid energy density functional

An extension of the Barcelona Catania Paris Madrid (BCPM) energy density functional is proposed to deal with odd-mass systems as well as multiquasiparticle excitations. The extension is based on the assumption that the equal filling approximation (EFA) is a valid alternative to the traditional full blocking procedure of the Hartree-Fock-Bogoliubov method. The assumption is supported by the excellent agreement between full blocking and EFA calculations obtained with different parametrizations of the Gogny interaction. The EFA augmented BCPM functional is used to compute low energy excitation spectra of selected nuclei in different regions of the nuclear chart, and high-$K$ isomers in $^{178}$Hf. We show that BCPM predictions are in good agreement with Gogny D1M results and experimental data.

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arXiv2023

Structure of single $Λ$-hypernuclei with Gogny-type $Λ$-nucleon forces

We study the structure of single $Λ$-hypernuclei using the Hartree--Fock--Bogoliubov method. Finite range Gogny-type forces are used to describe the nucleon-nucleon and $Λ$-nucleon interactions. Three different $Λ$-nucleon Gogny forces are built. The unknown parameters of these forces are obtained by fitting the experimental binding energies of the $1s$ $Λ$ single-particle state in various hypernuclei using the ``Simulated Annealing Method''. These forces are then used to calculate the binding energies of the other ($1p, 1d, 1f, 1g$) $Λ$ single-particle states in the different hypernuclei. The predicted values are found to be in good agreement with the experimental data for the three forces constructed. In addition, we calculate also the root-mean-square radii of ground state $Λ$ orbital, as well as several global properties of the hypernuclei considered such as their ground-state Hartree--Fock--Bogoliubov energy, their pairing energy and their quadrupole moment.

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arXiv2023

High-$K$ isomers in a self-consistent mean-field approach with the Gogny force

High-$K$ isomeric states in even-even and odd-mass nuclei are described within a mean-field framework with full blocking and using the finite range Gogny force. Theoretical calculations of low energy spectra of several nuclei across the nuclear chart are compared with equal filling approximation results and experimental data. Despite the global character of the employed interactions, a good agreement between the different many-body methods and experimental data is found.

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arXiv2023

Beyond-mean-field description of octupolarity in dysprosium isotopes with the Gogny-D1M energy density functional

The emergence and stability of (static) octupole deformation effects in Dy isotopes from dripline to dripline ($72 \le N \le 142$) is analyzed in this paper using mean-field and beyond-mean-field techniques often used for this purpose. We find static octupole deformations at the Hartree-Fock-Bogoliubov (HFB) level with the Gogny D1M force for $N \approx 134$ isotopes, while nuclei with $N \approx 88$ exhibit reflection-symmetric ground states. It is shown that, given the softness found in the mean-field and parity-projected potential energy surfaces along the octupole direction, neither of these two levels of approximation is suficcient to extract conclusions about the (permanent and/or vibrational) nature of octupole dynamic in Dy isotopes. From the analysis of the collective wave functions as well as the excitation energies of the first negative-parity states and $B(E3)$ strengths, obtained within the framework of a two-dimensional symmetry-conserving generator coordinate method (2D-GCM), it is concluded that the increased octupole collectivity in Dy isotopes with $N \approx 88$ and $N \approx 134$ is a vibrational-like effect that is not directly related to permanent mean-field octupole deformation in the considered nuclei. A pronounced suppression of the $B(E1)$ strengths is predicted for isotopes with $N \approx 82$ and $N \approx 126$. The comparison of results obtained with other parametrizations, show the robustness of the predicted trends with respect to the underlying Gogny energy density functional.

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