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M. Anguiano

Publications and source records attributed to M. Anguiano.

At least 37 records · Page 2Linked to original sources
arXiv2012

Nuclear proton and neutron distributions in the detection of weak interacting massive particles

In the evaluation of weak interacting massive particles (WIMPs) detection rates, the WIMP-nucleus cross section is commonly described by using form factors extracted from charge distributions. In this work, we use different proton and neutron distributions taken from Hartree-Fock calculations. We study the effects of this choice on the total detection rates for six nuclei with different neutron excess, and taken from different regions of the nuclear chart. The use of different distributions for protons and neutrons becomes more important if isospin-dependent WIMP-nucleon interactions are considered. The need of distinct descriptions of proton and neutron densities reduces with the lowering of the detection energy thresholds.

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arXiv2012

Magnetic excitations in nuclei with neutron excess

The excitation of the $1^+$, $2^-$ and $3^+$ modes in $^{16}$O, $^{22}$O, $^{24}$O, $^{28}$O, $^{40}$Ca, $^{48}$Ca, $^{52}$Ca and $^{60}$Ca nuclei is studied with self-consistent random phase approximation calculations. Finite-range interactions of Gogny type, containing also tensor-isospin terms, are used. We analyze the evolution of the magnetic resonances with the increasing number of neutrons, the relevance of collective effects, the need of a correct treatment of the continuum and the role of the tensor force.

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arXiv2012

Mean-field calculations of exotic nuclei ground states

We study the predictions of three mean-field theoretical approaches in the description of the ground state properties of some spherical nuclei far from the stability line. We compare binding energies, single particle spectra, density distributions, charge and neutron radii obtained with non-relativistic Hartree-Fock calculations carried out with both zero and finite-range interactions, and with a relativistic Hartree approach which uses a finite-range interaction. The agreement between the results obtained with the three different approaches indicates that these results are more related to the basic hypotheses of the mean-field approach rather than to its implementation in actual calculations.

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arXiv2011

Self-consistent continuum random phase approximation calculations of $^4$He electromagnetic responses

We study the electromagnetic responses of $^4$He within the framework of the self-consistent continuum random phase approximation theory. In this approach the ground state properties are described by a Hartree-Fock calculation. The single particle basis constructed in this manner is used in the calculations of the continuum responses of the system. Finite-range interactions are considered in the calculations. We compare our results with photon absorption cross sections and electron scattering quasi-elastic data. From this comparison, and also from the comparison with the results of microscopic calculations, we deduce that our approach describes well the continuum excitation.

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arXiv2011

Tensor effective interaction in self-consistent Random Phase Approximation calculations

We present a study of the effects of the tensor-isospin term of the effective interaction in Hartree-Fock and Random Phase Approximation calculations. We used finite-range forces of Gogny type, and we added to them a tensor-isospin term which behaves, at large internucleonic distances, as the analogous term of the microscopic interactions. The strength of this tensor force has been chosen to reproduce the experimental energy of the lowest 0$^-$ excited state in $^{16}$O, which shows large sensitivity to this term of the interaction. With these finite-range interactions, we have studied the effects of the tensor-isospin force in ground and excited states of carbon, oxygen, calcium, nickel, zirconium, tin and lead isotopes. Our results show that the tensor force affects mainly the nucleon single particle energies. However, we found some interesting cases where also bulk nuclear properties are sensitive to the tensor interaction.

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arXiv2011

Self-consistent Continuum Random Phase Approximation calculations with finite-range interactions

We present a technique which allows us to solve the Random Phase Approximation equations with finite-range interactions and treats the continuum part of the excitation spectrum without approximations. The interaction used in the Hartree-Fock calculations to generate the single particle basis is also used in the Continuum Random Phase Approximation calculations. We present results for the electric dipole and quadrupole excitations in the $^{16}$O, $^{22}$O, $^{24}$O, $^{40}$Ca, $^{48}$Ca and $^{52}$Ca nuclei. We compare our results with those of the traditional discrete Random Phase Approximation, with the continuum mean-field results and with the results obtained by a phenomenological approach. We study the relevance of the continuum, of the residual interaction and of the self-consistency. We also compare our results with the available total photoabsorption cross section data. We compare our photoabsorption cross section in $^4$He with that obtained by a calculation which uses a microscopic interaction.

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arXiv2010

Effective tensor forces and neutron rich nuclei

We study the effects of the tensor term of the effective nucleon-nucleon interaction on nuclear excited states. Our investigation has been conducted by using a self-consistent Random Phase Approximation approach. We investigate various nuclei in different regions of the isotopes chart. Results for a set of calcium isotopes are shown.

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arXiv2009

Evolution of the pygmy dipole resonance in nuclei with neutron excess

The electric dipole excitation of various nuclei is calculated with a Random Phase Approximation phenomenological approach. The evolution of the strength distribution in various groups of isotopes, oxygen, calcium, zirconium and tin, is studied. The neutron excess produces $E1$ strength in the low energy region. Indexes to measure the collectivity of the excitation are defined. We studied the behavior of proton and neutron transition densities to determine the isoscalar or isovector nature of the excitation. We observed that in medium-heavy nuclei the low-energy $E1$ excitation has characteristics rather different that those exhibited by the giant dipole resonance. This new type of excitation can be identified as pygmy dipole resonance.

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arXiv2009

Low-lying magnetic excitations of doubly-closed-shell nuclei and nucleon-nucleon effective interactions

We have studied the low lying magnetic spectra of 12C, 16O, 40Ca, 48Ca and 208Pb nuclei within the Random Phase Approximation (RPA) theory, finding that the description of low-lying magnetic states of doubly-closed-shell nuclei imposes severe constraints on the spin and tensor terms of the nucleon-nucleon effective interaction. We have first made an investigation by using four phenomenological effective interactions and we have obtained good agreement with the experimental magnetic spectra, and, to a lesser extent, with the electron scattering responses. Then we have made self-consistent RPA calculations to test the validity of the finite-range D1 Gogny interaction. For all the nuclei under study we have found that this interaction inverts the energies of all the magnetic states forming isospin doublets.

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arXiv2007

Superscaling in electroweak excitation of nuclei

Superscaling properties of 12C, 16O and 40Ca nuclear responses, induced by electron and neutrino scattering, are studied for momentum transfer values between 300 and 700 MeV/c. We have defined two indexes to have quantitative estimates of the scaling quality. We have analyzed experimental responses to get the empirical values of the two indexes. We have then investigated the effects of finite dimensions, collective excitations, meson exchange currents, short-range correlations and final state interactions. These effects strongly modify the relativistic Fermi gas scaling functions, but they conserve the scaling properties. We used the scaling functions to predict electron and neutrino cross sections and we tested their validity by comparing them with the cross sections obtained with a full calculation. For electron scattering we also made a comparison with data. We have calculated the total charge-exchange neutrino cross sections for neutrino energies up to 300 MeV.

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arXiv2006

Testing superscaling predictions in electroweak excitations of nuclei

Superscaling analysis of electroweak nuclear response functions is done for momentum transfer values from 300 to 700 MeV/c. Some effects, absent in the Relativistic Fermi Gas model, where the superscaling holds by construction, are considered. From the responses calculated for the 12C, 16O and 40Ca nuclei, we have extracted a theoretical universal superscaling function similar to that obtained from the experimental responses. Theoretical and empirical universal scaling functions have been used to calculate electron and neutrino cross sections. These cross sections have been compared with those obtained with a complete calculation and, for the electron scattering case, with the experimental data.

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arXiv2006

Monte Carlo simulation of the electron transport through thin slabs: A comparative study of PENELOPE, GEANT3, GEANT4, EGSnrc and MCNPX

The Monte Carlo simulation of the electron transport through thin slabs is studied with five general purpose codes: PENELOPE, GEANT3, GEANT4, EGSnrc and MCNPX. The different material foils analyzed in the old experiments of Kulchitsky and Latyshev [Phys. Rev. 61 (1942) 254-266] and Hanson et al. [Phys. Rev. 84 (1951) 634-637] are used to perform the comparison between the Monte Carlo codes. Non-negligible differences are observed in the angular distributions of the transmitted electrons obtained with the some of the codes. The experimental data are reasonably well described by EGSnrc, PENELOPE (v. 2005) and GEANT4. A general good agreement is found for EGSnrc and GEANT4 in all the cases analyzed.

physics.med-ph↗
arXiv2006

Dose distribution in water for monoenergetic photon point sources in the energy range of interest in brachytherapy: Monte Carlo simulations with PENELOPE and GEANT4

Monte Carlo calculations using the codes PENELOPE and GEANT4 have been performed to characterize the dosimetric properties of monoenergetic photon point sources in water. The dose rate in water has been calculated for energies of interest in brachytherapy, ranging between 10 keV and 2 MeV. A comparison of the results obtained using the two codes with the available data calculated with other Monte Carlo codes is carried out. A chi2-like statistical test is proposed for these comparisons. PENELOPE and GEANT4 show a reasonable agreement for all energies analyzed and distances to the source larger than 1 cm. Significant differences are found at distances from the source up to 1 cm. A similar situation occurs between PENELOPE and EGS4.

physics.med-ph↗
arXiv2006

Proton emission induced by polarized photons

The proton emission induced by polarized photons is studied in the energy range above the giant resonance region and below the pion emission threshold. Results for the 12C, 16O and 40Ca nuclei are presented. The sensitivity of various observables to final state interaction, meson exchange currents and short range correlations is analyzed. We found relevant effects due to the virtual excitation of the $Δ$ resonance.

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arXiv2002

Mean-field Based Approaches to Pairing Correlations in Atomic Nuclei

The evolution of the pairing correlations from closed shell to middle shell nuclei is analyzed with a Finite Range Density Dependent interaction in the Sn isotopes. As theoretical approaches we use the Hartree-Fock-Bogoliubov, the Lipkin-Nogami, their particle number projected counterparts and the full variation after particle number projection method. We find that whereas all approaches succeed rather well in the description of the total energy they differ significantly in the pairing correlation content of the wave functions. The description of the evolution from the weak to the strong pairing regime is also approach dependent, specially at shell closure.

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arXiv2002

Short-range correlations and meson exchange currents in photonucleon emission

One-nucleon emission processes induced by photon absorption are studied by considering short-range correlations effects. At energies above the giant resonance region the validity of the direct knock-out model has been tested by comparison with continuum Random Phase Approximation results. Nucleon re-scattering effects have been considered by using an optical potential. The role of the electromagnetic convection, magnetization and meson exchange currents has been investigated as a function of both excitation energy and momentum transfer. The short-range correlation effects have been studied by using various correlation functions. We found that the nucleon photo-emission cross section is rather sensitive to the presence of short-range correlations at large values of nucleon emission angle. In this region, however, the effects of meson exchange currents are even larger than those produced by short-range correlations.

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arXiv2001

Short-range correlations in semi-exclusive electron scattering experiments

One-nucleon emission electron scattering experiments are studied with a model that considers short--range correlations up to the first order in the number of correlation lines. The proper normalization of the many-body wave functions requires the evaluation of two- and three-point diagrams, the last ones usually neglected in the literature. When all these diagrams are included the effects of the short-range correlations are rather small. The results of our calculations are compared with experimental data taken on $^{16}$O.

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