Proton electric pygmy dipole resonance

The evolution of the low-lying E1 strength in proton-rich nuclei is analyzed in the framework of the self-consistent relativistic Hartree-Bogoliubov model and the relativistic quasiparticle random-phase approximation (RQRPA). Model calculations are performed for a series of N=20 isotones and Z=18 isotopes. For nuclei close to the proton drip line, the occurrence of pronounced dipole peaks is predicted in the low-energy region below 10 MeV excitation energy. From the analysis of the proton and neutron transition densities and the structure of the RQRPA amplitudes, it is shown that these states correspond to the proton pygmy dipole resonance.     

Soft Giant Dipole Modes in Ca Isotopes in the Relativistic RPA

The isovector giant dipole resonance in Ca isotopes is investigated in the framework of the fully consistent relativistic random phase approximation.The calculations are performed in an effective Lagrangian with a parameter set NL3,which was proposed for satisfactorily describing nuclear ground state properties.It is found that a soft isovector dipole mode for Ca isotopes near drip lines exists at energy around 6-7MeV.The soft dipole states are mainly due to the excitation of the weakly bound and pure neutron (proton)states near Fermi surface as well as the correlation of isoscalar and isovector operators.For nuclei with the extreme value of N/Z,the contributions of isoscalar mesons in the isovector mode play a non-negligible role.     

Role of Tensor Force in Light Nuclei with Tensor-Optimized Shell Model

We propose a new theoretical approach to describe nucleus using bare nuclear interaction, in which the tensor and short-range correlations are described with the tensor-optimized shell model (TOSM) and the unitary correlation operator method (UCOM), respectively. We use a bare nucleon–nucleon interaction AV8′ and show the spectroscopic results of the He and Li isotopes with TOSM+UCOM, such as the importance of the pn pair correlated by the tensor force and the corresponding high momentum components.     

Spin-isospin resonances: a self-consistent covariant description

For the first time a fully self-consistent charge-exchange relativistic RPA based on the relativistic Hartree-Fock (RHF) approach is established. The self-consistency is verified by the so-called isobaric analog state (IAS) check. The excitation properties and the nonenergy weighted sum rules of two important charge-exchange excitation modes, the Gamow-Teller resonance (GTR) and the spin-dipole resonance (SDR), are well reproduced in the doubly magic nuclei 48Ca, 90Zr and 208Pb without readjustment of the particle-hole residual interaction. The dominant contribution of the exchange diagrams is demonstrated.     

Nuclear chart in covariant density functional theory with dynamic correlations: From oxygen to tin

Nuclear masses of even-even nuclei with the proton number 8≤Z≤50(O to Sn isotopes)from the proton drip line to neutron drip line are investigated using the triaxial relativistic Hartree-Bogoliubov theory with the relativistic density functional PC-PK1.Further,the dynamical correlation energies(DCEs)associated with the rotational motion and quadrupole-shaped vibrational motion are taken into account by the five-dimensional collective Hamiltonian(5DCH)method.The root-mean-square deviation with respect to the experimental masses reduces from 2.50 to 1.59 MeV after the consideration of DCEs.The inclusion of DCEs has little influence on the position of drip lines,and the predicted numbers of bound even-even nuclei between proton and neutron drip lines from O to Sn isotopes are 569 and 564 with and without DCEs,respectively.     

Charge transition densities for the excitation and nucleon decay of the giant dipole resonance in16O

Predictions on charge transition densities in¹⁶O for the excitation of the giant dipole resonance are given within a continuum self-consistent RPA-SK3 theory. The nuclear states are allowed to decay with proton or neutron ejection. The discussion is focused on the analysis of the radial behaviour of transition densities in terms of their microscopic structure. The rôle of RPA ground state correlations is clarified. The surface properties of resonant nuclear states extracted from photonuclear and (e, e′ x) reactions at low momentum transfer are confronted with the full radial dependence of the resonant structure shown in charge transition densities.     

Role of Tensor Force in He and Li Isotopes with Tensor Optimized Shell Model

We propose a new theoretical approach to describe nucleus using bare nuclear interaction, in which the tensor and short-range correlations are described with the tensor optimized shell model (TOSM) and the unitary correlation operator method (UCOM), respectively. We show the obtained results of He and Li isotopes using TOSM + UCOM, such as the importance of the pn-pair correlated by the tensor force, and the structure differences in the 3/2^? and 1/2^? states of ⁵He.     

Excitation of pygmy dipole resonance in neutron-rich nuclei via Coulomb and nuclear fields

We study the nature of the low-lying dipole strength in neutron-rich nuclei, often associated with the pygmy dipole resonance. The states are described within the Hartree-Fock plus RPA formalism, using different parametrizations of the Skyrme interaction. We show how the information from combined reaction processes involving the Coulomb and different mixtures of isoscalar and isovector nuclear interactions can provide a clue to reveal the characteristic features of these states.     

Ferromagnetic resonance investigation of collective phenomena in two-dimensional periodic arrays of Co particles

The ferromagnetic resonance (FMR) method is used to study the collective phenomena in two-dimensional periodic arrays of disk-shaped Co particles. A study of geometrically similar structures with different periods reveals a broadening of the FMR resonance lines due to the excitation of additional size-dependent non-uniform spin waves. It is shown that these collective spin-wave modes are based on dipole–dipole interactions between the ferromagnetic particles in the array. Qualitative and quantitative data on magnetic interparticle interactions can thus be obtained from FMR spectra for two-dimensional periodic arrays of ferromagnetic particles. PACS 73.21.-b, 75.75.+a, 76.50.+g     

Fine structure of the isoscalar giant quadrupole resonance in Ca due to Landau damping?

The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in ⁴⁰Ca has been investigated in high energy-resolution experiments using proton inelastic scattering at Ep=200 MeV$E_{\mathrm{p}}=200\text{MeV}$. Fine structure is observed in the region of the ISGQR and its characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The experimental scales are well described by Random Phase Approximation (RPA) and second-RPA calculations with an effective interaction derived from a realistic nucleon–nucleon interaction by the Unitary Correlation Operator Method (UCOM). In these results characteristic scales are already present at the mean-field level pointing to their origination in Landau damping, in contrast to the findings in heavier nuclei and also to SRPA calculations for ⁴⁰Ca based on phenomenological effective interactions, where fine structure is explained by the coupling to two-particle–two-hole (2p–2h) states.     

Microscopic description of giant resonances in highly excited nuclei

Giant resonances of general multipolarity in highly excited nuclei, which are produced in compound nuclear and deep inelastic heavy ion reactions, are described microscopically in the finite temperature linear response formalism. The linear response function is calculated in the finite temperature (FT) quasi-particle RPA approximation (FT-HFB-RPA) and is based on the corresponding self-consistent quasi-particle basis (FT-HFB). The theory is derived from the small amplitude limit of FT-TDHFB. The inclusion of cranking constraints allows the investigation of giant resonances in nuclei with large intrinsic excitation energy and high spin. A schematic model for the FT-HFB-RPA is developed and applied to the isovector giant dipole resonance in hot spherical nuclei. It is shown that the energy of the resonance depends only weakly on temperature in these systems. The experimentally observed lowering of the giant mode in highly excited nuclei is to be attributed to different effects. The descritpion of resonance damping lies beyond the scope of the random phase approximation. Possible extensions in this direction and qualitative features of the width of giant resonances at finite temperature are discussed.     

A microscopic study of the dipole giant resonance in fissioning nuclei

Microscopic calculations of the dipole giant resonance in fissioning nuclei give a splitting of the dipole strength into three collective branches, contrary to two branches as predicted by the hydrodynamical model. These collective phenomena have been studied with simplifying separable interactions and sum-rule approaches, and found to be fairly independent of mass number and shell structure. The detailed dependence of excitation energies, dipole strengths and transition densities on the fission coordinate could give rise to interesting phenomena, particularly in electrofission experiments.     

The compression modes in atomic nuclei and their relevance for the nuclear equation of state

Accurate assessment of the value of the incompressibility coefficient, K _∞, of symmetric nuclear matter, which is directly related to the curvature of the equation of state (EOS), is needed to extend our knowledge of the EOS in the vicinity of the saturation point. We review the current status of K _∞ as determined from experimental data on isoscalar giant monopole and dipole resonances (compression modes) in nuclei by employing the microscopic theory based on the Random Phase Approximation (RPA). The importance of full self-consistent calculations is emphasized. In recent years, a comparision between RPA calculations based on either non-relativistic effective interactions or relativistic Lagrangians has been pursued in great detail. It has been pointed out that these two types of models embed different ansatz for the density dependence of the symmetry energy. This fact has consequences on the extraction of the nuclear incompressibility, as it is discussed. The comparison with other ways of extracting K _∞ from experimental data is highlighted. The text was submitted by the author in English.     

Mass Predictions from Mean-Field Calculations

Several methods based on effective interactions or Lagrangians are available today. Although different in many respects (use of zero range or finite range interactions, relativistic or non relativistic framework, different treatments of pairing correlations), their applications to nuclei far from stability have shown converging results which still have to be incorporated in macroscopic approaches. Many efforts are also actually devoted to the improvements of the effective interactions, especially of the pairing force. Finally, developments are performed to include in a microscopic framework correlations beyond a mean-field (in particular, the correlations generated by rotation and vibration in the deformed nuclear potential). I shall review some key aspects of these developments and show how they affect the determination of nuclear masses in particular at the limits of stability. This revised version was published online in July 2006 with corrections to the Cover Date.