Disentangling the nuclear shape coexistence in even-even Hg isotopes using the interacting boson model

We intend to provide a consistent description of the even-even Hg isotopes, 172-200Hg, using the interacting boson model including configuration mixing. We pay special attention to the description of the shape of the nuclei and to its connection with the shape coexistence phenomenon.Comment: To appear in CGS15 conference proceedings (EPJ Web of Conferences

Quantum Phase Transitions in the Interacting Boson Model: Integrability, level repulsion and level crossing

We study the quantum phase transition mechanisms that arise in the Interacting Boson Model. We show that the second-order nature of the phase transition from U(5) to O(6) may be attributed to quantum integrability, whereas all the first-order phase transitions of the model are due to level repulsion with one singular point of level crossing. We propose a model Hamiltonian with a true first-order phase transition for finite systems due to level crossings.Comment: Accepted in PR

Phase diagram of an extended Agassi model

Background: The Agassi model is an extension of the Lipkin-Meshkov-Glick model that incorporates the pairing interaction. It is a schematic model that describes the interplay between particle-hole and pair correlations. It was proposed in the 1960's by D. Agassi as a model to simulate the properties of the quadrupole plus pairing model. Purpose: The aim of this work is to extend a previous study by Davis and Heiss generalizing the Agassi model and analyze in detail the phase diagram of the model as well as the different regions with coexistence of several phases. Method: We solve the model Hamiltonian through the Hartree-Fock-Bogoliubov (HFB) approximation, introducing two variational parameters that play the role of order parameters. We also compare the HFB calculations with the exact ones. Results: We obtain the phase diagram of the model and classify the order of the different quantum phase transitions appearing in the diagram. The phase diagram presents broad regions where several phases, up to three, coexist. Moreover, there is also a line and a point where four and five phases are degenerated, respectively. Conclusions: The phase diagram of the extended Agassi model presents a rich variety of phases. Phase coexistence is present in extended areas of the parameter space. The model could be an important tool for benchmarking novel many-body approximations.Comment: Accepted for publication in PR

An extended Agassi model: algebraic structure, phase diagram, and large size limit

The Agassi model is a schematic two-level model that involves pairing and monopole-monopole interactions. It is, therefore, an extension of the well known Lipkin-Meshkov-Glick (LMG) model. In this paper we review the algebraic formulation of an extension of the Agassi model as well as its bosonic realization through the Schwinger representation. Moreover, a mean-field approximation for the model is presented and its phase diagram discussed. Finally, a $1/j$ analysis, with $j$ proportional to the degeneracy of each level, is worked out to obtain the thermodynamic limit of the ground state energy and some order parameters from the exact Hamiltonian diagonalization for finite$-j$.Comment: Accepted in Physica Scripta. Focus on SSNET 201

On the nature of the shape coexistence and the quantum phase transition phenomena: lead region and Zr isotopes

The goal of this contribution is to analyze the connection between shape coexistence and quantum phase transition, two seemingly unrelated phenomena that share common aspects, namely, the rapid change in the ground state structure along an isotope chain or the presence of several minima at the mean-field level. To illustrate the similarities and differences between both phenomena, we will focus in the Pb region, in particular in Pt and Hg isotopes, as well as in Zr isotopes.Comment: To be published in the CGS16 (Shanghai, China) conference proceeding

Scaling Properties of the Lipkin Model at the Critical Point

The influence of Franco Iachello in Physics during the last 50 years and, in particular, in the use of algebraic methods applied to very different physical problems has been broad, extense and have permeated most branches of Physics, from Nuclear and Molecular to Particle and Condensed Matter physics. Apart of many other contributions, at the beginning of the 2000's he introduced the concept of critical point symmetry and triggered the study of the many faces of quantum phase transitions in nuclei and other mesoscopic systems. In this contribution, we present the analysis of the scaling properties of the Lipkin model spectrum at the phase transition point and we focus on the differences between first and second order quantum phase transitions. Moreover, we explain how the obtained results can be also of application for the interacting boson model.Comment: Contribution to the proceedings of the meeting Symmetries and Order: Algebraic Methods in Many Body Systems, in honor of Prof. Francesco Iachell

Shape coexistence in Sr isotopes

We are very grateful to K. Heyde for the careful reading of this manuscript. This work was supported by the Grant No. PID2019-104002GB-C21 funded by MCIN/AEI/10.13039/501100011033 and FEDER “A way of making Europe,” the Consejería de Economía, Innovación, Ciencia y Empleo de la Junta de Andalucía (Spain) under Group FQM-370, and by FEDER SOMM17/6105/UGR. Resources supporting this work were provided by the CEAFMC and the Universidad de Huelva High Performance Computer (HPC@UHU) funded by ERDF/MINECO Project No. UNHU-15CE-2848.Background: Sr isotopes are located in the mass region A ≈ 100, where a very quick onset of nuclear deformation exists; other notable examples of this area are Yb, Zr, and Nb nuclei. The presence of the proton subshell closure Z = 40 allows the existence of particle-hole excitations that produce low-lying intruder bands. Purpose: The goal of this work is the study of the nuclear structure of the even-even 92–102Sr 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, 0-particle–0-hole and 2-particle–2-hole 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 has been confirmed and its connection with the onset of deformation has been clarified. The 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.CEAFMCFEDER SOMM17/6105/UGRUniversidad de Huelva High Performance ComputerConsejería de Economía, Innovación, Ciencia y Empleo, Junta de Andalucía FQM-370Ministerio de Economía y Competitividad UNHU-15CE-2848European Regional Development Fun

THROES: a caTalogue of HeRschel Observations of Evolved Stars. I. PACS range spectroscopy

This is the first of a series of papers presenting the THROES (A caTalogue of HeRschel Observations of Evolved Stars) project, intended to provide a comprehensive overview of the spectroscopic results obtained in the far-infrared (55-670 microns) with the Her- schel space observatory on low-to-intermediate mass evolved stars in our Galaxy. Here we introduce the catalogue of interactively reprocessed PACS (Photoconductor Array Camera and Spectrometer) spectra covering the 55-200 microns range for 114 stars in this category for which PACS range spectroscopic data is available in the Herschel Science Archive (HSA). Our sample includes objects spanning a range of evolutionary stages, from the asymptotic giant branch to the planetary nebula phase, displaying a wide variety of chemical and physical properties. The THROES/PACS catalogue is accessible via a dedicated web-based inter- face (https://throes.cab.inta-csic.es/) and includes not only the science-ready Herschel spectroscopic data for each source, but also complementary photometric and spectroscopic data from other infrared observatories, namely IRAS (Infrared Astronomical Satellite), ISO (Infrared Space Observatory) or AKARI, at overlapping wavelengths. Our goal is to create a legacy-value Herschel dataset that can be used by the scientific community in the future to deepen our knowledge and understanding of these latest stages of the evolution of low-to-intermediate mass stars.Comment: 38 page

Two-neutron transfer reactions as a tool to study the interplay between shape coexistence and quantum phase transitions

The goal of this study is to find an observable that could distinguish between both phenomena, shape coexistence and quantum phase transitions. The selected observable to be analyzed is the two-neutron transfer intensity between the 0+ states in the parent and daughter nuclei. The framework in which the study is done is the Interacting Boson Model (IBM), including its version with configuration mixing (IBM-CM). In order to generate the wave functions of the isotope chains of interest, needed for calculating transfer intensities, previous systematic studies with IBM and IBM-CM are taken without changing the parameters. Results for two-neutron transfer intensities are presented for Zr, Hg and Pt isotopic chains using IBM-CM and, moreover, the same is done for Zr, Pt and Sm isotopic chains using IBM with just a single configuration, i.e., without using configuration mixing. In the case of Zr, the two-neutron transfer intensities between the ground states provide a clear observable indicating that normal and intruder configurations coexist in the low-lying spectrum and that they cross at A=98->100, and this could allow to disentangle whether or not shape coexistence is inducing a given QPT. In the case of Pt, where shape coexistence is present and the regular and the intruder configurations cross for the ground state, there is almost no influence in the value of the two-neutron transfer, neither in the case of Hg where the ground state always has regular nature. For the Sm isotope chain that is one of the quantum phase transition paradigms, the value of the two-neutron transfer is strongly affected.Comment: To be published in the Chinese Physics

Manual for inspection of sprayers in use and PRITEAF, dedicated software for inspection of sprayers: success tools developed for the inspector’s training process in Spain

Software dedicated to inspection of sprayers in use has been developed with the aim to facilitate the accomplishment of the mandatory requirements from EU Directive for a Sustainable Use of Pesticides, specifically those concerning the inspection of sprayers in use. The software- PRITEAF- has been developed according to the European standards EN 13790 concerning mandatory inspection of sprayers in use and it is ready to be used not only for inspectors among all the EU members but also for training purposes all over the world. The software is ready to be on line –after minor arrangements - with the recently approved new international inspection standards ISO 16122, and its main features are: to facilitate the sprayer’s inspection procedure, to manage, storage and transfer all the information to the official bodies in charge of the procedure, and to be used as a support tool to improve the training activities during the process, according the European Directive 2009/128/CE for a Sustainable Use of Pesticides. For this purpose, PRITEAF has been designed for three different types of users: inspection teams, inspection workshops and regional authorities. PRITEAF has been developed using the File Maker Pro package and it is composed of three databases – inspections activities, database on sprayers already inspected, and owners or official responsible for the agricultural activity. The software is completed with specific modules for data acquisition and for generating official reports, files and communications. For its implementation, PRITEAF uses specific hardware (a PC server, a tablet and local Wi-Fi) necessary to ensure proper data collection in the field. After data collection, the software generates an official inspection report and an inspection certificate, as required by law. Using PRITEAF reduces inspection time by 33% compared to traditional sprayer inspection systems. Following its validation, PRITEAF has been made available to regional authorities and inspection workshops across Spain, and is also being used to train all inspection teams in the country. More than 800 inspectors have been officially trained using the developed software, resulting in an interesting tool to improve the daily activities to be executed in all the inspection’s workshops in Europe