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The scope of the paper is to apply a state-of-the-art beyond mean-field model to the description of the Gamow-Teller response in atomic nuclei. This topic recently attracted considerable renewed interest, due, in particular, to the possibility of performing experiments in unstable nuclei. We study the cases of 48Ca,78Ni,132Sn, and 208Pb. Our model is based on a fully self-consistent Skyrme Hartree-Fock plus random phase approximation. The same Skyrme interaction is used to calculate the coupling between particles and vibrations, which leads to the mixing of the Gamow-Teller resonance with a set of doorway states and to its fragmentation. We compare our results with available experimental data. The microscopic coupling mechanism is also discussed in some detail. [ABSTRACT FROM AUTHOR]

The properties of single-particle states in the magic nuclei 40Ca and 208Pb, in particular the energies, spectroscopic factors, and the effective mass, have been studied in a fully self-consistent particle-vibration coupling (PVC) approach within the framework of Skyrme energy density functional theory. All selected phonons are obtained by the random phase approximation, and the same Skyrme interaction is also used in the PVC vertex. We focus on the effect of the noncentral two-body spin-orbit and tensor interactions on the single-particle properties. It has been found that the contributions of those terms are important to improve the results for 208Pb. The calculated single-particle energies and spectroscopic factors are compared to available experimental data. The single-particle level density around the Fermi surface is significantly increased due to the effect of PVC. [ABSTRACT FROM AUTHOR]

Although many random-phase approximation (RPA) calculations of the Gamow-Teller (GT) response exist, this is not the case for calculations going beyond the mean-field approximation. We apply a consistent model, that includes the coupling of the GT resonance to low-lying vibrations, to nuclei of the fp shell. Among other motivations, our goal is to see if the particle-vibration coupling can redistribute the low-lying GT+ strength that is relevant for electron-capture processes in core-collapse supernova. We conclude that the lowering and fragmentation of that strength are consistent with the experimental findings and validate our model. However, the particle-vibration coupling cannot account for the quenching of the total value of the low-lying strength. [ABSTRACT FROM AUTHOR]

We investigate the impact of the neutron-skin thickness ΔRnp on the energy difference between the anti-analog giant dipole resonance (AGDR), EAGDR, and the isobaric analog state (IAS), EIAS, in a heavy nucleus such as 208Pb. For guidance, we first develop a simple and analytic, yet physical, approach based on the Droplet Model that linearly connects the energy difference EAGDR-EIAS with ΔRnp. To test this correlation on more fundamental grounds, we employ a family of systematically varied Skyrme energy density functionals where variations on the value of the symmetry energy at saturation density J are explored. The calculations have been performed within the fully self consistent Hartree-Fock (HF) plus charge-exchange random phase approximation (RPA) framework. We confirm the linear correlation within our microscopic apporach and, by comparing our results with available experimental data in 208Pb, we find that our analysis is consistent with ΔRnp = 0.204±0.009 fm, J = 31.4±0.5 MeV and a slope parameter of the symmetry energy at saturation of L = 76.4±5.4 MeV - the attached errors correspond to a lower-limit estimate of the systematic plus experimental uncertainties. These results are in agreement with those extracted from different experimental data albeit, L and ΔRnp are somewhat large when compared to previous estimations based on giant resonance studies. Possible hints whether model dependence can explain this difference are provided. [ABSTRACT FROM AUTHOR]

The Gamow-Teller (GT) strength distributions and isobaric analog resonance (IAR) states of several N = Z + 2 nuclei with mass number A = 42 - 58 are studied by using a self-consistent Skyrme Hartree-Fock-Bogoliubov method plus quasiparticle random phase approximation (HFB+QRPA) formalism. The isoscalar spin-triplet pairing interaction is included in QRPA on top of the isovector spin-singlet one in the HFB method. It is found that the isoscalar pairing correlations mix largely the (νj> → πj<) configurations into the low-energy states, and this mixing plays an important role in the formation and in the collectivity of these low-energy states. Furthermore, the observed excitation energy of the low-energy GT state with respect to the IAR can be well reproduced when the strength of isoscalar pairing is about 1.0-1.05 times that of the isovector pairing, irrespective of the adopted Skyrme interactions. In N = Z + 2 nuclei in the middle of the pf-shell, a mutual cooperative effect of isoscalar pairing and tensor interaction is found; namely, the tensor force reduces the spin-orbit splittings and enhances the effect of the isoscalar pairing. [ABSTRACT FROM AUTHOR]

We study the electric dipole polarizability αD in 208Pb based on the predictions of a large and representative set of relativistic and nonrelativistic nuclear mean-field models. We adopt the droplet model as a guide to better understand the correlations between αD and other isovector observables. Insights from the droplet model suggest that the product of αD and the nuclear symmetry energy at saturation density J is much better correlated with the neutron skin thickness Δrnp of 208Pb than the polarizability alone. Correlations of αDJ with &#Δrnp and with the symmetry energy slope parameter L suggest that αDJ is a strong isovector indicator. Hence, we explore the possibility of constraining the isovector sector of the nuclear energy density functional by comparing our theoretical predictions against measurements of both αD and the parity-violating asymmetry in 208Pb. We find that the recent experimental determination of αD in 208Pb in combination with the range for the symmetry energy at saturation density J = [31 ± (2)est] MeV suggests Δrnp(208Pb) = 0.165 ± (0.009)expt ± (0.013)theor ± (0.021)est fm and L = 43 ± (6)expt ± (8)theor ± (12)est MeV. [ABSTRACT FROM AUTHOR]

The isoscalar giant monopole resonance (ISGMR) in Cd, Sn, and Pb isotopes has been studied within the self-consistent Skyrme Hartree-Fock + BCS and quasiparticle random phase approximation (QRPA). Three Skyrme parameter sets are used in the calculations (i.e., SLy5, SkM*, and SkP) since they are characterized by different values of the compression modulus in symmetric nuclear matter; namely, K∞ = 230,217, and 202 MeV, respectively. We also investigate the effect of different types of pairing forces on the ISGMR in Cd, Sn, and Pb isotopes. The various calculated energies and the strength distributions of the ISGMR are compared with available experimental data. We find that SkP underestimates the various energies for all isotopes due to its low value of the nuclear matter incompressibility; namely, K∞ = 202 MeV. However, it can give a better description on the constrained energies for Cd isotopes and a reasonable peak energy for some nuclei. On the other hand, the SLy5 parameter set, supplemented by an appropriate pairing interaction, gives a reasonable description of the scaling energies in Cd and Sn isotopes and a good centroid energy in Pb isotopes. A better description of ISGMR in Cd and Sn isotopes is achieved by the SkM* interaction, which has a somewhat softer value of the nuclear incompressibility. [ABSTRACT FROM AUTHOR]

The recent high-resolution measurement of the electric dipole (El) polarizability aD in 208Pb [A. Tamii et al., Phys. Rev. Lett. 107, 062502 (2011)] provides a unique constraint on the neutron-skin thickness of this nucleus. The neutron-skin thickness rskin of 208Pb is a quantity of critical importance for our understanding of a variety of nuclear and astrophysical phenomena. To assess the model dependence of the correlation between αD and rskin, we carry out systematic calculations for 208Pb, 132Sn, and 48Ca based on the nuclear density functional theory using both nonrelativistic and relativistic energy density functionals. Our analysis indicates that whereas individual models exhibit a linear dependence between αD and rskjn, this correlation is not universal when one combines predictions from a host of different models. By averaging over these model predictions, we provide estimates with associated systematic errors for rskin and αD for the nuclei under consideration. We conclude that precise measurements of rskin in both 48Ca and 208Pb--combined with the recent measurement of αD--should significantly constrain the isovector sector of the nuclear energy density functional. [ABSTRACT FROM AUTHOR]

The multipole dependent effects induced by tensor correlations on the charge-exchange spin-dipole (SD) modes of the light nucleus 16O are studied within a Hartree-Fock (HF) plus self-consistent random-phase approximation (RPA), using Skyrme-type interactions. The role played by the triplet-even and triplet-odd tensor terms are examined separately to explain either the softening or hardening of the excitation energies of SD modes. The unperturbed and RPA summed strengths, calculated with and without the tensor force, are discussed and compared with the results of shell-model calculations. [ABSTRACT FROM AUTHOR]

We present a systematic analysis of the effects induced by tensor correlations on low-lying collective states of magic nuclei, by using the fully self-consistent random phase approximation (RPA) model with Skyrme interactions. The role of the tensor correlations is analyzed in detail in the case of quadrupole (2+) and octupole (3-) low-lying collective states in 208Pb. The example of 40Ca is also discussed, as well as the case of magnetic dipole states (1+). [ABSTRACT FROM AUTHOR]

The information on the symmetry energy and its density dependence is deduced by comparing the available data on the electric dipole polarizability αD of 68Ni, l20Sn, and 208Pb with the predictions of the random-phase approximation, using a representative set of nuclear energy density functionals. The calculated values of αD are used to validate different correlations involving αD, the symmetry energy at the saturation density J, the corresponding slope parameter L, and the neutron skin thickness Δrnp, as suggested by the droplet model. A subset of models that reproduce simultaneously the measured polarizabilities in 68Ni, l20Sn, and 208Pb are employed to predict the values of the symmetry energy parameters at saturation density and Δrnp. The resulting intervals are 7 = 30-35 MeV, L = 20-66 MeV; and the values for Δrnp in 68Ni, l20Sn, and 208Pb are in the ranges 0.15-0.19, 0.12-0.16, and 0.13-0.19 fm, respectively. The strong correlation between the electric dipole polarizabilities of two nuclei is instrumental to predict the values of electric dipole polarizabilities in other nuclei. [ABSTRACT FROM AUTHOR]

The outer-crust structure and composition of a cold, non-accreting magnetar are studied. We model the outer crust to be made of fully equilibrated matter where ionized nuclei form a Coulomb crystal embedded in an electron gas. The main effects of the strong magnetic field are those of quantizing the electron motion in Landau levels and of modifying the nuclear single-particle levels producing, on average, an increased binding of nucleons in nuclei present in the Coulomb lattice. The effect of a homogeneous and constant magnetic field on nuclear masses has been predicted by using a covariant density functional in which induced currents and axial deformation due to the presence of a magnetic field that breaks time-reversal symmetry have been included self-consistently in the nucleon and meson equations of motion. Although not yet observed, for B ≳ 1016 G both effects contribute to produce different compositions--odd-mass nuclei are frequently predicted--and to increase the neutron-drip pressure as compared to a typical neutron star. Specifically, in such a regime, the magnetic-field effects on nuclei favor the appearance of heavier nuclei at low pressures. As B increases, such heavier nuclei are also preferred up to larger pressures. For the most extreme magnetic field considered, B = 1018 G, and for the models studied, almost the whole outer crust is made of 9240Zr52. [ABSTRACT FROM AUTHOR]

Isoscalar giant resonances have been measured in the unstable 68Ni nucleus using inelastic alpha and deuteron scattering at 50A MeV in inverse kinematics with the active target MAYA at GANIL. Using alpha scattering, the extracted isoscalar giant monopole resonance (1SGMR) centroid was determined to be 21.1 ± 1.9 MeV and the isoscalar giant quadrupole resonance (ISGQR) to be 15.9 ± 1.3 MeV. Indications for soft isoscalar monopole and dipole modes are provided. Results obtained with both (α, α') and (d, d') probes are compatible. The evolution of isoscalar giant resonances along the Ni isotopic chain from 56Ni to 68Ni is discussed [ABSTRACT FROM AUTHOR]

To study the Gamow-Teller (GT) transitions from the Tz = +1 nucleus 42Ca to the Tz = 0 nucleus 42Sc, where Tz is the z component of isospin T, we performed a (p,n)-type (³He,t) charge-exchange reaction at 140 MeV/nucleon and scattering angles around 0°. With an energy resolution of 29 keV, states excited by GT transitions (GT states) could be studied accurately. The reduced GT transition strengths B(GT) were derived up to the excitation energy of 13 MeV, assuming the proportionality between the cross sections at 0° and B(GT) values. The main part of the observed GT transition strength is concentrated in the lowest 0.611-MeV, Jπ = 1+ GT state. All the other states at higher energies are weakly excited. Shell-model calculations could reproduce the gross feature of the experimental B(GT) distribution, and random-phase-approximation calculations including an attractive isoscalar interaction showed that the 0.611-MeV state has a collective nature. It was found that this state has all of the properties of a "low-energy super-Gamow-Teller state." It is expected that low-lying Jπ = 1+ GT states have T = 0 in the Tz = 0 nucleus 42Sc. However, T = 1 states are situated in a higher energy region. Assuming an isospin-analogous structure in A = 42 isobars, analogous T = 1, 1+ states are also expected in 42Ca. Comparing the 42Ca(³He,t) 42Sc and 42Ca(p,p') spectra measured at 0°, candidates for T = 1 GT states could be found in the 10-12-MeV region of 42Sc. They were all weakly excited. The mass dependence of the GT strength distributions in Sc isotopes is also discussed. [ABSTRACT FROM AUTHOR]

From empirically determined values of some of the characteristic constants associated with homogeneous nuclear matter at saturation and subsaturation densities, within the framework of a Skyrme-inspired energy density functional, we construct an equation of state (EoS) of nuclear matter. This EoS is then used to predict values of density slope parameters of symmetry energy L(ρ), isoscalar incompressibility K(ρ), and a few related quantities. The close consonance of our predicted values with the currently available ones for the density dependence of symmetry energy and incompressibility gleaned from diverse approaches offers the possibility that our method may help in settling their values in tighter bounds. Extrapolation of our EoS at supranormal densities shows that it is in good harmony with the one extracted from experimental data. [ABSTRACT FROM AUTHOR]

The 65Cu nucleus was populated by the 64Ni(7Li,α2n)65Cu reaction and the lifetime of the 9/2+ state at 2.5 MeV was measured by electronic fast-timing technique, providing the value τ = 37(3) ps. The reduced transition probability B(E3) = 8.82(165) W.u. is deduced and compared to theoretical predictions in the framework of a particle-vibration (weak) coupling model. The results indicate that the 9/2+ state is a member of the 3-⊗πp3/2 multiplet, built by coupling the octupole 3- phonon of 64Ni to an unpaired proton in the p3/2 level, confirming the robustness of core excitations in the medium mass nucleus 64Ni. [ABSTRACT FROM AUTHOR]

Empirically determined values of the nuclear volume and surface symmetry energy coefficients from nuclear masses are expressed in terms of density distributions of nucléons in heavy nuclei in the local density approximation. This is then used to extract the value of the symmetry energy slope parameter L. The density distributions in both spherical and well deformed nuclei calculated within microscopic framework with different energy density functionals give L = 59.0 ± 13.0 MeV. Application of the method also helps in a precision determination of the neutron skin thickness of nuclei that are difficult to measure accurately. [ABSTRACT FROM AUTHOR]

Recent improvements in the experimental determination of properties of the isovector giant quadrupole resonance (IVGQR), as demonstrated in the A=208 mass region, may be instrumental for characterizing the isovector channel of the effective nuclear interaction. We analyze properties of the IVGQR in 208Pb, using both macroscopic and microscopic approaches. The microscopic method is based on families of nonrelativistic and covariant energy density functionals (EDF), characterized by a systematic variation of isoscalar and isovector properties of the corresponding nuclear matter equations of state. The macroscopic approach yields an explicit dependence of the nuclear symmetry energy at some subsaturation density, for instance S(ρ=0.1 fm-3), or the neutron skin thickness Δrnp of a heavy nucleus, on the excitation energies of isoscalar and isovector GQRs. Using available data it is found that S(ρ=0.1 fm-3)=23.3±0.6 MeV. Results obtained with the microscopic framework confirm the correlation of the Δrnp to the isoscalar and isovector GQR energies, as predicted by the macroscopic model. By exploiting this correlation together with the experimental values for the isoscalar and isovector GQR energies, we estimate Δrnp=0.14±0.03 fm for 208Pb, and the slope parameter of the symmetry energy: L=37±18 MeV. [ABSTRACT FROM AUTHOR]

In a quantum Fermi system the energy per particle calculated at the second order beyond the mean-field approximation diverges if a zero-range interaction is employed. We have previously analyzed this problem in symmetric nuclear matter by using a simplified nuclear Skyrme interaction, and proposed a strategy to treat such a divergence. In the present work, we extend the same strategy to the case of the full nuclear Skyrme interaction. Moreover we show that, in spite of the strong divergence (∼Λ5, where Λ is the momentum cutoff) related to the velocity-dependent terms of the interaction, the adopted cutoff regularization can be always simultaneously performed for both symmetric and nuclear matter with different neutron-to-proton ratios. This paves the way for applications to finite nuclei. [ABSTRACT FROM AUTHOR]

The γ decays of neutron-rich Ca isotopes around 48Ca were measured at Legnaro National Laboratory with the PRISMA-CLARA setup, using the heavy-ion transfer reactions 48Ca on MNi and 48Ca on 208Pb at &ap;6 MeV/A. The work shows the feasibility to perform full in-beam y spectroscopy with heavy-ion transfer reactions (in terms of angular distributions, polarizations, and lifetimes analysis), providing a method that can be further exploited in the future with heavy targets and radioactive beams. For the one-neutron transfer channels, 49Ca and 47Ca, shell-model and particle-vibration coupling calculations are used to understand the nature of the states. In particular, in both nuclei evidence is found for particle-vibration coupled states based on the 3- phonon of 48Ca. In the two-neutron transfer channels, 46Ca and 50Ca, the experimental data are in global agreement with predictions based on full fp shell-model calculations. [ABSTRACT FROM AUTHOR]

Multinucleon transfer cross sections in the 96Zr+40Ca system have been measured, in inverse kinematics, at bombarding energies ranging from the Coulomb barrier to ~25% below. Targetlike recoils have been identified in A, Z and velocity with the large solid angle magnetic spectrometer PRISMA. The experimental data for one- and two-neutron transfer channels have been compared with semiclassical microscopic calculations. For the two-neutron transfer channels the relevance of the transitions to the ground state and to the 0+ excited states of 42Ca are discussed by employing, for the reaction mechanism, the successive approximation. It is found that the transition to the 0+ state at ~6 MeV, whose wave function is dominated by the two neutrons in the 2p3/2 shell, is much larger than the ground state one. The comparison with the inclusive data reveals that transitions to states with high multipolarity and non-natural parity are important. This suggests that more complex two-particle correlations have to be incorporated in the treatment of the transfer process. [ABSTRACT FROM AUTHOR]

Gamow-Teller (GT) and charge-exchange spin-dipole (SD) excitation energies in 90Zr and 208Pb are systematically studied to determine the appropriate magnitude of the tensor terms of the Skyrme interactions. We have found that the centroid energies of GT and SD excitations are sensitive to the adopted strengths of the triplet-even and triplet-odd tensor interactions. Especially, the 1- SD state plays a crucial role in constraining the triplet-even part while the triplet-odd part is related rather to the GT peaks. Among the 36 TIJ parameter sets that include nonperturbatively the tensor terms, the four sets, T21, T32, T43, and T54, give reasonable results for the centroid energies in comparison with the experimental data. The sign and magnitude of the tensor terms are also discussed when these terms are added to the existing Skyrme interactions SGII and SLy5. The triplet-even strength can be constrained in a narrow range by using the available experimental data while further empirical data are needed to set a constraint on the triplet-odd term. [ABSTRACT FROM AUTHOR]