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Esperanza Maya-Barbecho

Publications and source records attributed to Esperanza Maya-Barbecho.

4 recordsLinked to original sources
arXiv2026

Nuclear shapes of Nb isotopes

The study of the structure of odd-mass nuclei in regions characterized by the interplay of multiple particle-hole configurations represents a major challenge in nuclear structure physics. The odd-mass niobium isotopes ($Z = 41$), located near the $N = 60$ region, are of particular interest due to shape coexistence and quantum phase transitions. This work investigates the structure of the $^{93-103}$Nb isotopes using the intrinsic-frame formalism of the interacting boson-fermion model with configuration mixing (IBFM-CM), aiming to determine nuclear shapes and explore shape coexistence, configuration crossing, and quantum phase transitions. We employ the intrinsic formalism of the IBFM-CM, including both 0p-0h (regular) and 2p-2h (intruder) configurations interacting with the unpaired nucleon, providing a self-consistent framework to study energy surfaces, shape coexistence, and intruder bands for both positive- and negative-parity states. A realistic Hamiltonian for niobium, determined in previous studies, is adopted. The formalism is applied to the $^{93-103}$Nb isotopes for both positive- and negative-parity bands. A detailed analysis of the mean-field energy surfaces has been performed, including axial energy curves, triaxial energy surfaces in the $β-γ$ plane, and the corresponding equilibrium deformation parameters. The results reveal clear evidence of configuration coexistence and crossing along the isotopic chain. The existence of crossing configurations is demonstrated around $N = 60$, corresponding to a quantum phase transition previously identified in the Sr and Zr isotopic chains. Furthermore, the presence of an unpaired nucleon in Nb influences the abruptness of the quantum phase transition, underscoring the sensitivity of the structural evolution to single-particle degrees of freedom.

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arXiv2023

At the edge of shape coexistence in the Z=40 region

In this contribution, the shape coexistence phenomenon near the proton sub-shell closure at Z=40 is analyzed. Particular emphasis is placed on extracting the nuclear deformation values by examining experimental B(E2) transition rates and observing how the kinematic moment of inertia evolves in these nuclei. Based on the analysis of these two observables, we arrive at the conclusion that the notable effects of shape coexistence at approximately Z=40 are largely diminished in Mo isotopes and are scarcely detectable in Ru isotopes.

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arXiv2022

Shape coexistence in Sr isotopes

Sr isotopes are located in the mass region $A\approx 100$, where a very quick onset of nuclear deformation exists, being other notable examples of this area Yb, Zr, and Nb nuclei. The presence of the proton subshell closure $Z=40$ allows the existence of particle-hole excitations that produces low-lying intruder bands. Purpose: The goal of this work is the study of the nuclear structure of the even-even $^{92-102}$Sr isotopes through the accurate description of excitation energies, $B(E2)$ transition rates, nuclear radii and two-neutron separation energies. Method: The interacting boson model with configuration mixing will be the framework to calculate all the observables of the Sr isotopes. Only two types of configurations will be considered, namely, 0particle-0hole and 2particle-2hole excitations. The parameters of the model are determined using a least-squares procedure for the excitation energies and the $B(E2)$ transition rates. Results: For the whole chain of isotopes, the value of excitation energies, $B(E2)$'s, two-neutron separation energies, nuclear radii, and isotope shifts have been obtained, with a good agreement between theory and experiment. Also, a detailed analysis of the wave functions have been performed and, finally, the mean-field energy surfaces and the value of the nuclear deformation, $β$, have been obtained. Conclusions: The presence of low-lying intruder states in even-even Sr isotopes have been confirmed and its connection with the onset of deformation has been clarified. Lightest Sr isotopes present a spherical structure while the heaviest ones are clearly deformed. The rapid onset of deformation at neutron number $60$ is due to the crossing of the regular and intruder configurations and, moreover, both families of states present an increase of deformation with the neutron number.

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