1,721,082 research outputs found
Correlation energy contribution to nuclear masses
No full textDuring the last few years, much effort has been made to develop a microscopic description of the nuclear masses based on mean field theory. The accuracy achieved, when phenomenological parameters are added to take specific effects into account (Wigner term, cut-off in pairing space, etc.), leads to a rms of 0.6–0.7 MeV [S. Goriely, F. Tondeur, J.M. Pearson, Atom Data Nucl. Data Tables 77 (2001) 311] (see also [M. Bender, P.H. Heenen, P.G. Reinhard, Rev. Modern Phys. 75 (2003) 121]). We present evidence that further progress can be made by taking into account medium polarization effects associated with surface and pairing vibrations [S. Baroni, M. Armati, F. Barranco, R.A. Broglia, G. Colò, G. Gori, E. Vigezzi, J. Phys. G: Nucl. Part. Phys. 30 (2004) 1353; S. Baroni, F. Barranco, P.F. Bortignon, R.A. Broglia, G. Colò, E. Vigezzi, Phys. Rev. C 74 (2006) 024305] (see also [M. Bender, G.F. Bertsch, P.-H. Heenen, Phys. Rev. C 73 (2006) 034322])
Continuum particle-vibration coupling method in coordinate-space representation for finite nuclei
Full text linkIn this paper we present a new formalism to implement the nuclear particle-vibration coupling (PVC) model. The key issue is the proper treatment of the continuum that is allowed by the coordinate space representation. Our formalism, based on the use of zero-range interactions such as the Skyrme forces, is microscopic and fully self-consistent. We apply it to the case of neutron single-particle states in Ca-40, Pb-208, and O-24. The first two cases are meant to illustrate the comparison with the usual (i.e., discrete) PVC model. However, we stress that the present approach allows one to calculate properly the effect of PVC on resonant states. We compare our results with those from experiments in which the particle transfer in the continuum region has been attempted. The latter case, namely O-24, is chosen as an example of a weakly-bound system. Such a nucleus, being double magic and not displaying collective low-lying vibrational excitations, is characterized by quite pure neutron single-particle states around the Fermi surface
Gamow-Teller response and its spreading mechanism in double magic nuclei
Full text linkThe 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 Ca48,Ni78,Sn132, and Pb208. 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
The giant dipole resonance as a quantitative constraint on the symmetry energy
No full textThe possible constraints on the poorly determined symmetry part of the effective nuclear Hamiltonians or effective energy functionals, i.e., the so-called symmetry energy S(rho), are very much under debate. In the present work, we show that the value of the symmetry energy associated with Skyrme functionals, at densities rho around 0.1 fm(-3), is strongly correlated with the value of the centroid of the Giant Dipole Resonance (GDR) in spherical nuclei. Consequently, the experimental value of the GDR in, e.g., Pb-208 can be used as a constraint on the symmetry energy, leading to 23.3 MeV < S(rho=0.1 fm(-3)) < 24.9 MeV
Gamow-Teller Response Calculated in Quasiparticle Random Phase Approximation Plus Quasiparticle Vibration Coupling Model
No full textThe self-consistent quasiparticle random phase approximation (QRPA) plus quasiparticle-vibration coupling (QPVC) with Skyrme interactions is used to describe the Gamow-Teller (GT) response in open-shell nuclei. The effect of superfluidity, including both the isoscalar spin-triplet and the isovector spin-singlet pairing interactions, is taken into account in both the ground state and the excited states. Zero-range pairing forces of volumetype and surface-type are both used in our investigation. The phonon properties and GT strength distributions obtained with either type of force are compared, by taking the superfluid nucleus 120Sn as an example. In both cases, a spreading width is developed, and the agreement with experimental data of the strength distribution in 120Sn is improved with the inclusion of QPVC effect
Pairing correlations in nuclei : bare, induced and effective interactions
No full textThe bare nucleon–nucleon interaction is essential for the production of pair correlations in nuclei, but the induced interaction due to phonon exchange also contributes. In this paper, we shall present examples of the interplay between these two sources of pairing interaction in the case of finite nuclei and of the inner crust of neutron stars
Microscopic quantal calculation of the vortex-nucleus interaction in the inner crust of neutron stars
No full textIn this article we study the interaction between vortices and nuclei present in the
inner crust of neutron stars, performing microscopic calculations based on quantum mean
field theory. We find that the properties of the vortex are strongly influenced by finite
size effects, leading to qualitative differences respect to results based on semiclassical
approximations
On the structure of vortices in the inner crust of neutron stars
No full textWe study the structure of vortices and their interaction with nuclei in the inner crust of neutron stars. Vortices carry most of the angular momentum of the crust and according to some models are expected to play a key role in the phenomenon of glitches. The quantities of interest (the energy, the pairing gap, the density and the velocity field) are calculated in the framework of the Hartree-Fock-Bogoliubov (HFB) quantum mean field theory. We solve the HFB equations testing four different Skyrme functionals in the particle hole-channel and using a density-dependent contact interaction in the particle-particle channel. We find that the structure of a vortex is strongly affected by the presence of the nucleus, a fact which reflects itself in the density dependence of the pinning energy we calculate
Parity inversion and breakdown of shell closure in Be isotopes
Full text linkThe coupling of single-particle motion and of vibrations in 411Be produces dressed neutrons which spend only a fraction of the time in pure single-particle states, and which weighing differently from the bare neutrons lead to parity inversion. The interaction of the two least bound neutrons in the ground state of 412Be mediated by the v14 Argonne nucleon-nucleon potential and by the exchange of surface vibrations of the core 10Be gives rise to a strongly correlated state, where the two valence neutrons are distributed over s2,p2, and d2 configurations, resulting in the breaking of the N=8 shell closure
Particle-vibration coupling in halo nuclei
No full textIn halo nuclei like 11Li and 12Be, polarization effects based on the particle-vibration coupling mechanism leads to a density dependent pairing interaction which provides most of the observed correlation energy which stabilizes the least two bound neutrons. The same mechanism is at the basis of the parity inversion phenomenon observed in 10Li and 11Be
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