arXiv subjects

F. Arias de Saavedra

Publications and source records attributed to F. Arias de Saavedra.

18 recordsLinked to original sources

arXiv2022

Anisotropic multicluster model in light nuclei

Multicluster models consider that the nucleons can be moving around different centers in the nuclei. These models have been widely used to describe light nuclei but always considering that the mean field is composed of isotropic harmonic oscillators with different centers. In this work, we propose an extension of these models by using anisotropic harmonic oscillators. The strenghts of these oscillators, the distance among the different centers and the disposition of the nucleons inside every cluster are free parameters which have been fixed using the variational criterion. We have used a hamiltonian with the kinetic energy terms and a phenomenological two-body potential like Volkov V2 potential. All the one-body and two-body matrix elements have been analytically calculated. Only a numerical integration on the Euler angles, it is needed to carry out the projection on the values of the total spin of the state and its third component. We have studied the ground state and the first excited states of 8 Be, 12 C and 10 Be getting good results for the energies. The disposition of the nucleons in the different clusters have been also analyzed by using projection on the different cartesian planes getting much more information than when the radial one-body density is used.

nucl-th↗

arXiv2021

Production of 177Lu with deuterons at IFMIF-DONES facility

The International Fusion Materials Irradiation Facility - Demo Oriented NEutron Source (IFMIF-DONES) is a single-sited novel Research Infrastructure for testing, validation and qualification of the materials to be used in a fusion reactor. The main purpose of IFMIF-DONES is related to fusion technology and neutron irradiation of the materials to be used in the future fusion power plants. However, there is an important effort to take advantage of the outstanding characteristics of the facility in terms of neutrons and deuterons. One of the applications could be radioisotopes production with deuterons and neutrons. We discuss here the possible production of radioisotopes with deuterons at DONES. In this work, we have focused on the production of 177Lu with deuterons. The study has been carried out through the design and simulation of a device as cooling system for the sample producing the radioisotope. The results show the viability of using DONES for such production. In addition, the study suggests that new nuclear energy data above 20 MeV for deuterons is mandatory for an accurate study in this field.

physics.ins-det↗

arXiv2012

Ferromagnetic transition of a two-component Fermi gas of Hard Spheres

We use microscopic many-body theory to analyze the problem of itinerant ferromagnetism in a repulsive atomic Fermi gas of Hard Spheres. Using simple arguments, we show that the available theoretical predictions for the onset of the ferromagnetic transition predict a transition point at a density ($k_F a \sim 1$) that is too large to be compatible with the universal low-density expansion of the energy. We present new variational calculations for the hard-sphere Fermi gas, in the framework of Fermi hypperneted chain theory, that shift the transition to higher densities ($k_F a \sim 1.8$). Backflow correlations, which are mainly active in the unpolarized system, are essential for this shift.

cond-mat.quant-gas↗

arXiv2007

Renormalized Fermi hypernetted chain approach in medium-heavy nuclei

The application of the Correlated basis function theory and of the Fermi hypernetted chain technique, to the description of the ground state of medium-heavy nuclei is reviewed. We discuss how the formalism, originally developed for symmetric nuclear matter, should be changed in order to describe finite nuclear systems, with different number of protons and neutrons. This approach allows us to describe doubly closed shell nuclei by using microscopic nucleon-nucleon interactions. We presents results of numerical calculations done with two-nucleon interactions of Argonne type,implemented with three-body forces of Urbana type. Our results regard ground-state energies, matter, charge and momentum distributions, natural orbits, occupation numbers, quasi-hole wave functions and spectroscopic factors of 12C, 16O, 40Ca, 48Ca and 208Pb nuclei.

nucl-th↗

arXiv2007

Momentum distributions and spectroscopic factors of doubly-closed shell nuclei in correlated basis function theory

The momentum distributions, natural orbits, spectroscopic factors and quasi-hole wave functions of the C12, O16, Ca40, Ca48, and Pb208 doubly closed shell nuclei, have been calculated in the framework of the Correlated Basis Function theory, by using the Fermi hypernetted chain resummation techniques. The calculations have been done by using the realistic Argonne v8' nucleon-nucleon potential, together with the Urbana IX three-body interaction. Operator dependent correlations, which consider channels up to the tensor ones, have been used. We found noticeable effects produced by the correlations. For high momentum values, the momentum distributions show large enhancements with respect to the independent particle model results. Natural orbits occupation numbers are depleted by about the 10\% with respect to the independent particle model values. The effects of the correlations on the spectroscopic factors are larger on the more deeply bound states.

nucl-th↗

arXiv2006

New Results in the CBF theory for medium-heavy nuclei

Momentum distributions, spectroscopic factors and quasi-hole wave functions of medium-heavy doubly closed shell nuclei have been calculated in the framework of the Correlated Basis Function theory, by using the Fermi hypernetted chain resummation techniques. The calculations have been done by using microscopic two-body nucleon-nucleon potentials of Argonne type, together with three-body interactions. Operator dependent correlations, up to the tensor channels, have been used.

nucl-th↗

arXiv2006

Ground state of medium-heavy doubly-closed shell nuclei in correlated basis function theory

The correlated basis function theory is applied to the study of medium-heavy doubly closed shell nuclei with different wave functions for protons and neutrons and in the jj coupling scheme. State dependent correlations including tensor correlations are used. Realistic two-body interactions of Argonne and Urbana type, together with three-body interactions have been used to calculate ground state energies and density distributions of the 12C, 16O, 40Ca, 48Ca and 208Pb nuclei.

nucl-th↗

arXiv2004

Recent results in CBF theory for medium-heavy nuclei

We extend the correlated basis functions theory (CBF) for nuclei with different number of protons and neutrons and in j-j coupling scheme. By means of the Fermi hypernetted chain integral equations, in conjunction with the single operator chain approximation (FHNC/SOC), we evaluate the ground state and the one-body densities for 40Ca, 48Ca and 208Pb nuclei. The realistic Argonne V8' two-nucleon potentials has been used. We compare the ground-state properties of these nuclei calculated by using correlation functions with and without tensor components.

nucl-th↗

arXiv2001

Effects of Short-Range Correlations in (e,e'p) reactions and nuclear overlap functions

A study of the effects of short-range correlations over the (e,e'p) reaction for low missing energy in closed shell nuclei is presented. We use correlated, quasi-hole overlap functions extracted from the asymptotic behavior of the one-body density matrix, containing central correlations of Jastrow type, up to first-order in a cluster expansion, and computed in the very high asymptotic region, up to 100 fm. The method to extract the overlap functions is checked in a simple shell model, where the exact results are known. We find that the single-particle wave functions of the valence shells are shifted to the right due to the short-range repulsion by the nuclear core. The corresponding spectroscopic factors are reduced only a few percent with respect to the shell model. However, the (e,e'p) response functions and cross sections are enhanced in the region of the maximum of the missing momentum distribution due to short-range correlations.

nucl-th↗

arXiv2001

A correlated model for lambda-hypernuclei

We study the properties of hypernuclei containing one lambda hyperon in the framework of the correlated basis function theory with Jastrow correlations. Fermi hypernetted chain integral equations are derived and used to evaluate energies and one-body densities of lambda hypernuclei having a doubly closed shell nucleonic core in the jj coupling scheme, from Carbon to Lead. We also study hypernuclei having the least bound neutron substituted by the lambda particle. The semi-realistic Afnan and Tang nucleon-nucleon potential and Bodmer and Usmani lambda-nucleon potential are adopted. The effect of many-body forces are considered by means either of a three body lambda-nucleon-nucleon potential of the Argonne type or of a density dependent modification of the lambda-nucleon interaction, fitted to reproduce the lambda binding energy in nuclear matter. While Jastrow correlations underestimate the attractive contribution of the three body $\la$ interaction, the density dependent potential provides a good description of the lambda binding energies over all the nuclear masses range, in spite of the relative simplicity of the model.

nucl-th↗

arXiv2000

Ground State Correlations in 16O and 40Ca

We study the ground state properties of doubly closed shell nuclei $^{16}$O and $^{40}$Ca in the framework of Correlated Basis Function theory using state dependent correlations, with central and tensor components. The realistic Argonne $v_{14}$ and $v'_{8}$ two-nucleon potentials and three-nucleon potentials of the Urbana class have been adopted. By means of the Fermi Hypernetted Chain integral equations, in conjunction with the Single Operator Chain approximation, we evaluate the ground state energy, one- and two-body densities and electromagnetic and spin static responses for both nuclei. In $^{16}$O we compare our results with the available Monte Carlo and Coupled Cluster ones and find a satisfying agreement. As in the nuclear matter case with similar interactions and wave functions, the nuclei result under-bound by 2--3 MeV/A.

nucl-th↗

arXiv1999

Correlations and realistic interactions in doubly closed shell nuclei

We review the latest variational calculations of the ground state properties of doubly closed shell nuclei, from $^{12}$C to $^{208}$Pb, with semirealistic and realistic two- and three-nucleon interactions. The studies are carried on within the framework of the correlated basis function theory and integral equations technique, with state dependent correlations having central and tensor components. We report results for the ground state energy, one- and two-body densities and static structure functions. For $^{16}$O and $^{40}$Ca we use modern interactions and find that the accuracy of the method is comparable to that attained in nuclear matter with similar hamiltonians, giving nuclei underbound by $\sim$2 MeV/A. The computed Coulomb sums are in complete agreement with the latest analysis of the experimental data.

nucl-th↗

arXiv1999

Electron scattering with a short-range correlation model

The inclusive electromagnetic responses in the quasi-elastic region are calculated with a model which considers the terms of the cluster expansion containinga single correlation line. The validity of this model is studied by comparing, in nuclear matter, its results with those of a complete calculation. Results in finite nuclei for both one-and two-nucleon emission are presented.

nucl-th↗

arXiv1997

Ground state of N=Z doubly closed shell nuclei in CBF theory

The ground state properties of N=Z doubly closed shell nuclei are studied within correlated basis function theory. A truncated version of the Urbana v14 realistic potential, with spin, isospin and tensor components, is adopted, together with state dependent correlations. Fermi hypernetted chain integral equation and single operator chain approximation are used to evaluate density, distribution function and ground state energy of 16O and 40Ca. The results favourably compare with the available, variational MonteCarlo estimates and provide a first substantial check of the accuracy of the cluster summation method for state dependent correlations. We achieve in finite nuclei at least the same level of accuracy in the treatment of non central interactions and correlations as in nuclear matter. This opens the way for a microscopic study of medium heavy nuclei ground state using present days realistic hamiltonians.

nucl-th↗

arXiv1996

Effects of state dependent correlations on nucleon density and momentum distributions

The proton momentum and density distributions of closed shell nuclei are calculated within a model treating short--range correlations up to first order in the cluster expansion. The validity of the model is verified by comparing the results obtained with purely scalar correlations with those produced by finite nuclei Fermi Hypernetted Chain calculations. State dependent correlations are used to calculate momentum and density distributions of 12C, 16O, 40Ca, and 48Ca, and the effects of their tensor components are studied.

nucl-th↗

arXiv1996

Model calculations of doubly closed shell nuclei in CBF theory III. j-j coupling and isospin dependence

Correlated Basis Function theory and Fermi Hypernetted Chain technique are extended to study medium-heavy, doubly closed shell nuclei in j-j coupling scheme, with different single particle wave functions for protons and neutrons and isospin dependent two-body correlations. Central semirealistic interactions are used. Ground state energies, one-body densities, distribution functions and momentum distributions are calculated for 12C, 16O, 40Ca, 48Ca and 208Pb nuclei. The values of the ground state energies provided by isospin dependent correlations are lower than those obtained with isospin independent correlations. In finite nuclear systems, the two--body Euler equations provide correlation functions variationally more effective than those obtained with the same technique in infinite nuclear matter.

nucl-th↗

arXiv1995

Short-range Correlations in a CBF description of closed-shell nuclei

The Correlated Basis Function theory (CBF) provides a theoretical framework to treat on the same ground mean-field and short-range correlations. We present, in this report, some recent results obtained using the CBF to describe the ground state properties of finite nuclear systems. Furthermore we show some results for the excited state obtained with a simplified model based on the CBF theory.

nucl-th↗

arXiv1994

Effective Mass of One 4he Atom in Liquid 3he

A microscopic calculation of the effective mass of one $^4$He impurity in homogeneous liquid $^3$He at zero temperature is performed for an extended Jastrow--Slater wave function, including two-- and three--body dynamical correlations and also backflow correlations between the $^4$He atom and the particles in the medium. The effective mass at saturation density, $m_4^*/m_4=1.21$, is in very good agreement with the recent experimental determination by Edwards {\it et al}. The three-- particle correlations appear to give a small contribution to the effective mass and different approximations for the three--particle distribution function give almost identical results for $m_4^*/m_4$.

cond-mat↗