Navegando por Autor "Malheiro, M."

Agora exibindo 1 - 4 de 4

Dirac-Hartree-Bogoliubov calculation for spherical and deformed hot nuclei: Temperature dependence of the pairing energy and gaps, nuclear deformation, nuclear radii, excitation energy, and entropy
(American Physical Society, 2016-02-25) Lisboa, Ronai Machado; Malheiro, M.; Carlson, B. V.
Background: Unbound single-particle states become important in determining the properties of a hot nucleus as its temperature increases. We present relativistic mean field (RMF) for hot nuclei considering not only the self-consistent temperature and density dependence of the self-consistent relativistic mean fields but also the vapor phase that takes into account the unbound nucleon states. Purpose: The temperature dependence of the pairing gaps, nuclear deformation, radii, binding energies, entropy, and caloric curves of spherical and deformed nuclei are obtained in self-consistent RMF calculations up to the limit of existence of the nucleus. Method: We perform Dirac-Hartree-Bogoliubov (DHB) calculations for hot nuclei using a zero-range approximation to the relativistic pairing interaction to calculate proton-proton and neutron-neutron pairing energies and gaps. A vapor subtraction procedure is used to account for unbound states and to remove long range Coulomb repulsion between the hot nucleus and the gas as well as the contribution of the external nucleon gas. Results: We show that p-p and n-n pairing gaps in the 1 S0 channel vanish for low critical temperatures in the range Tcp ≈ 0.6–1.1 MeV for spherical nuclei such as 90Zr, 124Sn, and 140Ce and for both deformed nuclei 150Sm and 168Er. We found that superconducting phase transition occurs at Tcp = 1.03pp(0) for 90Zr, Tcp = 1.16pp(0) for 140Ce, Tcp = 0.92pp(0) for 150Sm, and Tcp = 0.97pp(0) for 168Er. The superfluidity phase transition occurs at Tcp = 0.72nn(0) for 124Sn, Tcp = 1.22nn(0) for 150Sm, and Tcp = 1.13nn(0) for 168Er. Thus, the nuclear superfluidity phase—at least for this channel—can only survive at very low nuclear temperatures and this phase transition (when the neutron gap vanishes) always occurs before the superconducting one, where the proton gap is zero. For deformed nuclei the nuclear deformation disappear at temperatures of about Tcs = 2.0–4.0 MeV, well above the critical temperatures for pairing, Tcp . If we associate the melting of hot nuclei into the surrounding vapor with the liquid-gas phase transition our results indicate that it occurs at temperatures around T = 8.0–10.0 MeV, somewhat higher than observed in many experimental results. Conclusions: The change of the pairing fields with the temperature is important and must be taken into account in order to define the superfluidity and superconducting phase transitions. We obtain a Hamiltonian form of the pairing field calibrated by an overall constant cpair to compensate for deficiencies of the interaction parameters and of the numerical calculation. When the pairing is not zero, the states close to the Fermi energy make the principal contribution to the anomalous density that appears in the pairing field. By including temperature through the use of the Matsubara formalism, the normal and anomalous densities are multiplied by a Fermi occupation factor. This leads to a reduction in the anomalous density and in the pairing as the temperature increases. When the temperature increases (T 4 MeV), the effects of the vapor phase that take into account the unbound nucleon states become important, allowing the study of nuclear properties of finite nuclei from zero to high temperatures
Relativistic pseudospin and spin symmetries in physical systems – recent results
(IOP Publishing, 2014-03-11) Lisboa, Ronai Machado; Alberto, Pedro; Castro, A.; Fiolhais, M.; Malheiro, M.
In this paper we revise the main features of pseudospin and spin symmetries of the Dirac equation with scalar and vector potentials and mention several of its applications to physical systems. These symmetries have been extensively researched in the last 15 years, especially pseudospin symmetry, mainly in its application in understanding certain nuclear structure features of heavy nuclei. The realization of both symmetries has also been studied using several mean-field scalar and vector potentials. For many classes of potentials, these symmetries allow to have analytical solutions of the Dirac equation which otherwise would not have been possible. We report here some recent results related to anti-fermions, Coulomb and confining potentials
Spin and pseudospin symmetries in the antinucleon spectrum of nuclei
(American Physical Society, 2010-06-28) Lisboa, Ronai Machado; Malheiro, M.; Alberto, P.; Fiolhais, M.; Castro, A. S.
Spin and pseudospin symmetries in the spectra of nucleons and antinucleons are studied in a relativistic mean-field theory with scalar and vector Woods-Saxon potentials, in which the strength of the latter is allowed to change. We observe that, for nucleons and antinucleons, the spin symmetry is of perturbative nature and it is almost an exact symmetry in the physical region for antinucleons. The opposite situation is found in the pseudospin symmetry case, which is better realized for nucleons than for antinucleons, but is of dynamical nature and cannot be viewed in a perturbative way for either nucleons or antinucleons. This is shown by computation of the spin-orbit and pseudospin-orbit couplings for selected spin and pseudospin partners in both spectra
Temperature effects on nuclear pseudospin symmetry in the Dirac-Hartree-Bogoliubov formalism
(American Physical Society, 2017) Lisboa, Ronai Machado; Alberto, P.; Carlson, B. V.; Malheiro, M.
We present finite-temperature Dirac-Hartree-Bogoliubov (FTDHB) calculations for the tin isotope chain to study the dependence of pseudospin on the nuclear temperature. In the FTDHB calculation, the density dependence of the self-consistent relativistic mean fields, the pairing, and the vapor phase that takes into account the unbound nucleon states are considered self-consistently. The mean-field potentials obtained in the FTDHB calculations are fit by Woods-Saxon (WS) potentials to examine how the WS parameters are related to the energy splitting of the pseudospin pairs as the temperature increases. We find that the nuclear potential surface diffuseness is the main driver for the pseudospin splittings and that it increases as the temperature grows. We conclude that pseudospin symmetry is better realized when the nuclear temperature increases. The results confirm the findings of previous works using relativistic mean field theory at T = 0, namely that the correlation between the pseudospin splitting and the parameters of the Woods-Saxon potentials implies that pseudospin symmetry is a dynamical symmetry in nuclei. We show that the dynamical nature of the pseudospin symmetry remains when the temperature is considered in a realistic calculation of the tin isotopes, such as that of the Dirac-Hartree-Bogoliubov formalism

SIGAA

Navegando por Autor "Malheiro, M."