arXiv subjects

P. Sarriguren

Publications and source records attributed to P. Sarriguren.

At least 19 recordsLinked to original sources

arXiv2024

Isospin breaking in the $^{71}$Kr and $^{71}$Br mirror system

Isospin symmetry is a fundamental concept in nuclear physics. Even though isospin symmetry is partially broken, it holds approximately for most nuclear systems, which makes exceptions very interesting from the nuclear structure perspective. In this framework, it is expected that the spins and parities of the ground states of mirror nuclei should be the same, in particular for the simplest systems where a proton is exchanged with a neutron or vice versa. In this work, we present evidence that this assumption is broken in the mirror pair $^{71}$Br and $^{71}$Kr system. Our conclusions are based on a high-statistics $\beta$ decay study of $^{71}$Kr and on state-of-the-art shell model calculations. In our work, we also found evidence of a new state in $^{70}$Se, populated in the $\beta$-delayed proton emission process which can be interpreted as the long sought coexisting 0$^+$ state.

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arXiv2023

133In: A Rosetta Stone for decays of r-process nuclei

The $β$ decays from both the ground state and a long-lived isomer of $^{133}$In were studied at the ISOLDE Decay Station (IDS). With a hybrid detection system sensitive to $β$, $γ$, and neutron spectroscopy, the comparative partial half-lives (logft) have been measured for all their dominant $β$-decay channels for the first time, including a low-energy Gamow-Teller transition and several First-Forbidden (FF) transitions. Uniquely for such a heavy neutron-rich nucleus, their $β$ decays selectively populate only a few isolated neutron unbound states in $^{133}$Sn. Precise energy and branching-ratio measurements of those resonances allow us to benchmark $β$-decay theories at an unprecedented level in this region of the nuclear chart. The results show good agreement with the newly developed large-scale shell model (LSSM) calculations. The experimental findings establish an archetype for the $β$ decay of neutron-rich nuclei southeast of $^{132}$Sn and will serve as a guide for future theoretical development aiming to describe accurately the key $β$ decays in the rapid-neutron capture (r-) process.

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arXiv2023

Beta-delayed neutron spectroscopy of $^{133}$In

The decay properties of $^{133}$In were studied in detail at the ISOLDE Decay Station (IDS). The implementation of the Resonance Ionization Laser Ion Source (RILIS) allowed separate measurements of its $9/2^+$ ground state ($^{133g}$In) and $1/2^-$ isomer ($^{133m}$In). With the use of $β$-delayed neutron and $γ$ spectroscopy, the decay strengths above the neutron separation energy were quantified in this neutron-rich nucleus for the first time. The allowed Gamow-Teller transition $9/2^+\rightarrow7/2^+$ was located at 5.92 MeV in the $^{133g}$In decay with a logft = 4.7(1). In addition, several neutron-unbound states were populated at lower excitation energies by the First-Forbidden decays of $^{133g,m}$In. We assigned spins and parities to those neutron-unbound states based on the $β$-decay selection rules, the logft values, and systematics.

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arXiv2022

Bulk and decay properties of neutron-deficient odd-mass Hg isotopes around A = 185

Ground and isomeric states of the neutron-deficient odd-$A$ isotopes $^{183}$Hg, $^{185}$Hg, and $^{187}$Hg are described from a microscopic calculation based on a self-consistent, axially-deformed Hartree-Fock mean field with the Skyrme functional and pairing within BCS approximation. For each equilibrium shape and different odd-neutron states, results on mean square charge radii and magnetic dipole moments are given and analyzed in the context of their sensitivity to the nuclear deformation and to the spin and parity. Spin-isospin correlations within proton-neutron quasiparticle random phase approximation are then introduced in the nuclear states to obtain the distributions of Gamow-Teller strength and the $β^+/EC$ half-lives of these isotopes, whose measurements are planned at ISOLDE-CERN using total absorption gamma-ray spectroscopy techniques.

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arXiv2021

Nuclear symmetry energy components and their ratio: A new approach within the coherent density fluctuation model

A new alternative approach to calculate the ratio of the surface to volume components of the nuclear symmetry energy is proposed in the framework of the coherent density fluctuation model (CDFM). A new expression (scheme II) for the ratio is derived consistently within the model. This expression appears in a form more direct and physically motivated than the expression (scheme I) that was used in our previous works within the CDFM and avoids preliminary assumptions and mathematical ambiguities in scheme I. The calculations are based on the Skyrme and Brueckner energy-density functionals for nuclear matter and on nonrelativistic Brueckner-Hartree-Fock method with realistic Bonn B and Bonn CD nucleon-nucleon potentials. The approach is applied to isotopic chains of Ni, Sn, and Pb nuclei using nuclear densities obtained in self-consistent Hartree-Fock+BCS calculations with SLy4 Skyrme effective interaction. The applicability of both schemes within the CDFM is demonstrated by a comparison of the results with the available empirical data and with results of other theoretical studies of the considered quantities. Although in some instances the results obtained for the studied ratio and the symmetry energy components are rather close in both schemes, the new scheme II leads to more realistic values that agree better with the empirical data and exhibits conceptual and operational advantages.

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arXiv2021

Systematic trends of neutron skin thickness versus relative neutron excess

Available experimental neutron skin thicknesses of even-even stable Ca, Ni, Sn, Pb, and Cd isotopes are evaluated, and separate trends of neutron skin thickness versus relative neutron excess $δ=(N-Z)/A$ are firstly observed for different isotopic chains. This phenomenon is quantitatively reproduced by the deformed Skyrme Hartree-Fock $+$ BCS model with SLy4 force.

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arXiv2020

On the $β$-decay of $^{186}$Hg

The Gamow-Teller strength distribution of the decay of $^{186}$Hg into $^{186}$Au has been determined for the first time using the total absorption gamma spectroscopy technique and has been compared with theoretical QRPA calculations using the SLy4 Skyrme force. The measured Gamow-Teller strength distribution and the half-life are described by mixing oblate and prolate configurations independently in the parent and daughter nuclei. The best description of the experimental beta strength is obtained with dominantly prolate components for both parent $^{186}$Hg and daughter $^{186}$Au. The approach also allowed us to determine an upper limit of the oblate component in the parent state. The complexity of the analysis required the development of a new approach in the analysis of the X-ray gated total absorption spectrum.

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arXiv2020

Nuclear shape transitions and elastic magnetic electron scattering

Backward elastic electron scattering from odd-A nuclear targets is characterized by magnetic form factors containing precise information on the nuclear structure. We study the sensitivity of the magnetic form factors to structural effects related to the evolution and shape transitions in both isotopic and isotonic chains. Calculations of magnetic form factors are performed in the plane-wave Born approximation. The nuclear structure is obtained from a deformed self-consistent mean-field calculation based on a Skyrme HF+BCS formalism. Collective effects are included in the cranking approximation, whereas nucleon-nucleon correlations are taken into account in the coherent density fluctuation model. The evolution of the magnetic form factors is found to exhibit signatures of shape transitions that show up in selected isotopic and isotonic chains involving both stable and unstable nuclei. Several cases are identified as suitable candidates for showing such fingerprints of shape transitions. A new generation of electron scattering experiments involving electron-radioactive beam colliders will be available in the near future, leading to a renewed interest in this field.

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arXiv2020

Proton and neutron skins and symmetry energy of mirror nuclei

The neutron skin of nuclei is an important fundamental property, but its accurate measurement faces many challenges. Inspired by charge symmetry of nuclear forces, the neutron skin of a neutron-rich nucleus is related to the difference between the charge radii of the corresponding mirror nuclei. We investigate this relation within the framework of the Hartree-Fock-Bogoliubov method with Skyrme interactions. Predictions for proton skins are also made for several mirror pairs in the middle mass range. For the first time the correlation between the thickness of the neutron skin and the characteristics related with the density dependence of the nuclear symmetry energy is investigated simultaneously for nuclei and their corresponding mirror partners. As an example, the Ni isotopic chain with mass number $A=48-60$ is considered. These quantities are calculated within the coherent density fluctuation model using Brueckner and Skyrme energy-density functionals for isospin asymmetric nuclear matter with two Skyrme-type effective interactions, SkM* and SLy4. Results are also presented for the symmetry energy as a function of $A$ for a family of mirror pairs from selected chains of nuclei with $Z=20$, $N=14$, and $N=50$. The evolution curves show a similar behavior crossing at the $N=Z$ nucleus in each chain and a smooth growing deviation when $N\neq Z$ starts. Comparison of our results for the radii and skins with those from the calculations based on high-precision chiral forces is made.

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arXiv2020

Symmetry energy properties of neutron-rich nuclei from the coherent density fluctuation model applied to nuclear matter calculations with Bonn potentials

We derive the values of nuclear symmetry energy, its components, as well as pressure in finite nuclei at saturation density from their corresponding values in nuclear matter obtained in non-relativistic Brueckner-Hartree-Fock calculations with the realistic Bonn B and Bonn CD potentials using the coherent density fluctuation model in the framework of a self-consistent Skyrme-Hartree-Fock plus BCS method. We focus on three isotopic chains of spherical nuclei (Ni, Sn, and Pb) and compare our results with those obtained with an effective Brueckner density-dependent potential. The role of the three-body forces on the considered quantities is also studied and discussed.

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arXiv2019

Mean-field calculations of charge radii in ground and isomeric states of Cd isotopes

Quadrupole moments and charge radii in cadmium isotopes are studied from a microscopic perspective. The results obtained from self-consistent deformed Hartree-Fock+BCS calculations with Skyrme forces are compared with isomer and isotope shifts measured from high resolution laser spectroscopy experiments. The microscopic calculations reproduce fairly well the main features observed in those isotopes that include the linear increase with the neutron number of the quadrupole moments of the 11/2- isomers, as well as the parabolic behavior of the mean-square charge radii difference between isomers and ground states.

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arXiv2019

Microscopic calculations of weak decays in superheavy nuclei

Half-lives of beta+ decay and electron capture are studied in some selected superheavy nuclei produced in hot fusion reactions, namely, 290Fl, 293Mc, 294Lv, and 295Ts. The nuclear structure is described microscopically from deformed self-consistent Skyrme Hartree-Fock mean-field calculations that include pairing correlations. The sensitivity of the half-lives to deformation and to the QEC energies, which are still not determined experimentally, are studied. The results are compared with phenomenological alpha-decay half-lives, showing that the latter decay mode is dominant in this mass region.

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arXiv2019

Total absorption $γ$-ray spectroscopy of niobium isomers

The $β$ intensity distributions of the decays of $^{100\text{gs},100\text{m}}$Nb and $^{102\text{gs},102\text{m}}$Nb have been determined using the Total Absorption $γ$-Ray Spectroscopy technique. The JYFLTRAP double Penning trap system was employed to disentangle the isomeric states involved, lying very close in energy, in a campaign of challenging measurements performed with the Decay Total Absorption $γ$-ray Spectrometer at the Ion Guide Isotope Separator On-Line facility in Jyväskylä. The low-spin isomeric state of each niobium case was populated through the decay of the zirconium parent, that was treated as a contaminant. We have applied a method to extract this contamination, and additionally we have obtained $β$ intensity distributions for these zirconium decays. The $β$-strength distributions evaluated with these results were compared with calculations in quasiparticle random-phase approximation, suggesting a prolate configuration for the ground states of $^{100,102}$Zr. The footprint of the Pandemonium effect was found when comparing our results for the analyses of the niobium isotopes with previous decay data. The $β$-intensities of the decay of $^{102\text{m}}$Nb were obtained for the first time. A careful evaluation of the uncertainties was carried out, and the consistency of our results was validated taking advantage of the segmentation of our spectrometer. The final results were used as input in reactor summation calculations. A large impact on antineutrino spectrum calculations was already reported and here we detail the significant impact on decay heat calculations.

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arXiv2019

Elastic magnetic electron scattering from deformed nuclei

Magnetic form factors corresponding to elastic electron scattering from odd-A nuclei are presented. The calculations are carried out in plane-wave Born approximation. The one-body properties are obtained in a deformed self-consistent mean-field calculation based on a Skyrme HF+BCS method. Collective effects are also included in the cranking approximation. Results on several stable nuclei are compared with the available experimental information. It is shown that a deformed formalism improves the agreement with experiment in deformed nuclei, while reproducing equally well spherical nuclei by taking properly the spherical limit of the deformed model and the effect of nucleon-nucleon correlations. Thus, the capability of the model to describe magnetic form factors is demonstrated. This opens the door to explore also unstable nuclei of particular interest that could be measured in future experiments on electron-radioactive beam colliders.

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arXiv2018

Temperature dependence of the volume and surface contributions to the nuclear symmetry energy within the coherent density fluctuation model

The temperature dependence of the volume and surface components of the nuclear symmetry energy (NSE) and their ratio is investigated in the framework of the local density approximation (LDA). The results of these quantities for finite nuclei are obtained within the coherent density fluctuation model (CDFM). The CDFM weight function is obtained using the temperature-dependent proton and neutron densities calculated through the HFBTHO code that solves the nuclear Skyrme-Hartree-Fock-Bogoliubov problem by using the cylindrical transformed deformed harmonic-oscillator basis. We present and discuss the values of the volume and surface contributions to the NSE and their ratio obtained for the Ni, Sn, and Pb isotopic chains around double-magic $^{78}$Ni, $^{132}$Sn, and $^{208}$Pb nuclei. The results for the $T$-dependence of the considered quantities are compared with estimations made previously for zero temperature showing the behavior of the NSE components and their ratio, as well as with the available experimental data. The sensitivity of the results on various forms of the density dependence of the symmetry energy is studied. We confirm the existence of `kinks' of these quantities as functions of the mass number at $T=0$ MeV for the double closed-shell nuclei $^{78}$Ni and $^{132}$Sn and the lack of `kinks' for the Pb isotopes, as well as the disappearance of these kinks as the temperature increases.

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arXiv2018

Beta-decay properties of neutron-rich Ca, Ti, and Cr isotopes

Beta-decay properties of neutron-rich Ca, Ti, and Cr isotopes are studied within a deformed proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme Hartree-Fock calculations with pairing correlations. Residual spin-isospin interactions in the particle-hole and particle-particle channels are also included in the formalism. The energy distributions of the Gamow-Teller strength, the beta-decay feedings, the beta-decay half-lives, and the beta-delayed neutron emission probabilities are discussed and compared with other theoretical results, as well as with the available experimental information. The evolution of these nuclear beta-decay properties is investigated in isotopic chains in a search for structural changes. A reliable estimate of the beta-decay properties in this mass region is a valuable information for evaluating decay rates in astrophysical scenarios.

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arXiv2018

Combined few-body and mean-field model for nuclei

The challenging nuclear many-body problem is discussed along with classifications and qualitative descriptions of existing methods and models. We present detailed derivations of a new method where cluster correlations co-exist with an underlying mean-field described core-structure. The variation of an antisymmetrized product of cluster and core wave functions and a given nuclear interaction, provide sets of self-consistent equations of motion. After the applications on dripline nuclei we discuss perspectives with improvements and applications. In the conclusion we summarize while emphasizing the merits of consistently treating both short- and large-distance properties, few- and many-body correlations, ordinary nuclear structure, and concepts of halos and Efimov states.

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arXiv2017

Two-proton capture on the $^{68}$Se nucleus with a new self-consistent cluster model

We investigate the two-proton capture reaction of the prominent rapid proton capture waiting point nucleus, $^{68}$Se, that produces the borromean nucleus $^{70}$Kr ($^{68}$Se$+p+p$). We apply a recently formulated general model where the core nucleus, $^{68}$Se, is treated in the mean-field approximation and the three-body problem of the two valence protons and the core is solved exactly. The same Skyrme interaction is used to find core-nucleon and core valence-proton interactions. We calculate $E2$ electromagnetic two-proton dissociation and capture cross sections, and derive the temperature dependent capture rates. We vary the unknown $2^+$ resonance energy without changing any of the structures computed self-consistently for both core and valence particles. We find rates increasing quickly with temperature below $2-4$~GK after which we find rates varying by less than a factor of two independent of $2^+$ resonance energy. The capture mechanism is sequential through the $f_{5/2}$ proton-core resonance, but the continuum background contributes significantly.

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