1,721,028 research outputs found
Dipole states in stable and unstable nuclei
No full textA nuclear structure model based on linear response theory (i.e., random phase approximation) and which includes pairing
correlations and anharmonicities (coupling with collective vibrations), has been implemented in such a way that it can be applied
on the same footing to magic as well as open-shell nuclei. As applications, we have chosen to study the dipole excitations both
in well known, stable isotopes like 208Pb and 120Sn as well as in the neutron-rich, unstable 132Sn nucleus, by addressing in the
latter case the question about the nature of the low-lying strength. Our results suggest that the model is reliable and predicts in
all cases low-lying strength of non collective nature
Microscopic study of the isoscalar giant monopole resonance in Cd, Sn, and Pb isotopes
Full text linkThe 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-infinity = 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-infinity = 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
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
Covariance analysis for energy density functionals and instabilities
Full text linkWe present the covariance analysis of two successful nuclear energy density functionals (EDFs), (i) a non-relativistic Skyrme functional built from a zero-range effective interaction, and (ii) a relativistic nuclear EDF based on density dependent meson–nucleon couplings. The covariance analysis is a useful tool for understanding the limitations of a model, the correlations between observables and the statistical errors. We show, for our selected test nucleus Pb, that when the constraint on a property A included in the fit is relaxed, correlations with other observables B become larger; on the other hand, when a strong constraint is imposed on A, the correlations with other properties become very small. We also provide a brief review, partly connected with the covariance analysis, of some instabilities displayed by several EDFs currently used in nuclear physics
Gamma decay of giant resonances by using Skyrme functionals
Full text linkA microscopic model, entirely based on Skyrme energy density lunctionals, has been developed to study the γ -decay ol giant resonances. In particular, it treats the ground-state decay within the fully self-consistent Random Phase Approximation (RPA) and the decay to low-lying states at the lowest order beyond RPA. This model is applied to 208 Pb and the results are compared with experimental data and with previous theoretical results obtained, in the past decades, using phenomenological models
Regularization of zero-range effective interactions in finite nuclei
No full textThe problem of the divergences which arise in beyond mean-field calculations, when a zero-range effective interaction is employed, has not been much considered so far. Some of us have proposed, quite recently, a scheme to regularize a zero-range Skyrme-type force when it is employed to calculate the total energy, at second-order perturbation theory level, in uniform matter. Although this scheme looked promising, the extension for finite nuclei is not straightforward. We introduce such a procedure in the current paper, by proposing a regularization procedure that is similar, in spirit, to the one employed to extract the so-called Vlow-k from the bare force. Although this has been suggested already by B. G. Carlsson and collaborators, the novelty of our work consists of setting on equal footing uniform matter and finite nuclei; in particular, we show how the interactions that have been regularized in uniform matter behave when they are used in a finite nucleus with the corresponding cutoff. We also address the problem of the validity of the perturbative approach in finite nuclei for the total energy
Deducing the nuclear-matter incompressibilty coefficient from data on isoscalar compression modes
No full textAccurate 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)
Hybrid configuration mixing model for odd nuclei
Full text linkIn this work, we introduce a new approach which is meant to be a first step towards complete self-consistent low-lying spectroscopy of odd nuclei. So far, we essentially limit ourselves to the description of a double-magic core plus an extra nucleon. The model does not contain any free adjustable parameter and is instead based on a Hartree-Fock (HF) description of the particle states in the core, together with self-consistent random-phase approximation (RPA) calculations for the core excitations. We include both collective and noncollective excitations, with proper care of the corrections due to the overlap between them (i.e., due to the nonorthonormality of the basis). As a consequence, with respect to traditional particle-vibration coupling calculations in which one can only address single-nucleon states and particle-vibration multiplets, we can also describe states of shell-model types like 2 particle-1 hole. We will report results for Ca49 and Sb133 and discuss future perspectives
Microscopic study of the isoscalar giant resonances in 208Pb induced by inelastic alpha scattering
No full textThe energetic beam of (spin and isospin zero) α-particles remains a very efficient probe for the nuclear isoscalar giant resonances. In the present work, a microscopic folding model study of the isoscalar giant resonances in 208Pb induced by inelastic View the MathML source scattering at Elab=240 and 386 MeV has been performed using the (complex) CDM3Y6 interaction and nuclear transition densities given by both the collective model and Random Phase Approximation (RPA) approach. The fractions of energy weighted sum rule around the main peaks of the isoscalar monopole, dipole and quadrupole giant resonances were probed in the Distorted Wave Born Approximation analysis of inelastic View the MathML source scattering using the double-folded form factors given by different choices of the nuclear transition densities. The energy distribution of the E0, E1 and E2 strengths given by the multipole decomposition analyses of the (α,α′) data under study are compared with those predicted by the RPA calculation
The hybrid configuration mixing model and the spectroscopy of odd nuclei
No full textWe introduce a new approach which is meant to be a step towards complete low-lying spectroscopy of odd nuclei. In the first applications, we limit ourselves to a magic core plus an extra neutron or proton. The model does not contain any free adjustable parameter, but is based on a Hartree-Fock (HF) description of particle states and Random Phase Approximation (RPA) calculations for core excitations. With respect to traditional particle-vibration coupling calculations, in which one can only address single-nucleon states and particle-vibration multiplets, we can also describe states of shell-model type like 2 particle-1 hole. The underlying spirit is, of course, related to filling the gap between shell-model-like approaches for low-lying spectroscopy, and the traditional HF+RPA approach to high-lying states like giant resonances
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