5,085 research outputs found
Microscopic Models for the Particle-Vibration Coupling in Exotic Nuclei
Recent results obtained, often in fruitful collaboration with Japanese
colleagues in the study of the interplay between single-particle and collective
degrees of freedom are reviewed.Comment: 8 pages. Proceedings of the Italy-Japan Meeting On Heavy Ion Physics
200
Nuclear single-particle states: dynamical shell model and energy density functional methods
We discuss different approaches to the problem of reproducing the observed
features of nuclear single-particle (s.p.) spectra. In particular, we analyze
the dominant energy peaks, and the single-particle strength fragmentation,
using the example of neutron states in 208Pb. Our main emphasis is the
interpretation of that fragmentation as due to particle-vibration coupling
(PVC). We compare with recent Energy Density Functional (EDF) approaches, and
try to present a critical perspective.Comment: 7 pages. Contribution to the "Focus issue on Open Problems in Nuclear
Structure", Journal of Physics
Dipole states in stable and unstable nuclei
A 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 Pb and Sn as well as in the
neutron-rich, unstable Sn 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.Comment: 16 pages, 6 figures; submitted for publicatio
Self-consistent description of multipole strength: systematic calculations
We use the quasiparticle random phase approximation with a few Skyrme density
functionals to calculate strength functions in the Jpi = 0+, 1-, and 2+
channels for even Ca, Ni, and Sn isotopes, from the proton drip line to the
neutron drip line. We show where and how low-lying strength begins to appear as
N increases. We also exhibit partial energy-weighted sums of the transition
strength as functions of N for all nuclei calculated, and transition densities
for many of the interesting peaks. We find that low-energy strength increases
with N in all multipoles, but with distinctive features in each. The low-lying
0+ strength near the neutron at large N barely involves protons at all, with
the strength coming primarily from a single two-quasineutron configuration with
very large spatial extent. The low-lying 1- strength is different, with protons
contributing to the transition density in the nuclear interior together with
neutrons at large radii. The low-lying 2+ transition strength goes largely to
more localized states. The three Skyrme interactions we test produce similar
results, differing most significantly in their predictions for the location of
the neutron drip line, the boundaries of deformed regions, energies of and
transition strengths to the lowest 2+ states between closed shells, and
isovector energy-weighted sum rules.Comment: 43 pages, 48 figures, 1 tabl
Sum Rules of the Multiple Giant Dipole States
Various sum rules for multiple giant dipole resonance states are derived. For
the triple giant dipole resonance states, the energy-weighted sum of the
transition strengths requires a model to be related to those of the single and
double giant dipole resonance states. It is also shown that the non-diagonal
matrix elements of the double commutator between the dipole operator and the
nuclear Hamiltonian give useful identities for the excitation energy and
transition strength of each excited state. Using those identities, the
relationship between width of the single dipole state and those of the multiple
ones is qualitatively discussed.Comment: 8 pages, 1 figure, using PTPTeX styl
Neutrino Capture Cross Sections for Ar-40 and beta-decay of Ti-40
Shell-model calculations of solar neutrino absorption cross sections for
Ar, the proposed component of the ICARUS detector, are presented. It is
found that low-lying Gamow-Teller transitions lead to a significant enhancement
of the absorption rate over that expected from the Fermi transition between the
isobaric analog states, leading to an overall absorption rate of 6.7 SNU. We
also note that the pertinent Gamow-Teller transitions in ^{\sss 40}Ar are
experimentally accessible from the -decay of the mirror nucleus ^{\sss
40}Ti. Predictions for the branching ratios to states in ^{\sss 40}Sc are
presented, and the theoretical halflife of 53~ms is found to be in good
agreement with the experimental value of ~ms.Comment: 12 pages including references and table. NTGMI-94-
Compression modes in nuclei: microscopic models with Skyrme interactions
The isoscalar giant monopole resonances (ISGMR) and giant dipole resonances
(ISGDR) in medium-heavy nuclei are investigated in the framework of HF+RPA and
HF-BCS+QRPA with Skyrme effective interactions. It is found that pairing has
little effect on these modes. It is also found that the coupling of the RPA
states to 2p-2h configurations results in about (or less than) 1 MeV shifts of
the resonance energies and at the same time gives the correct total widths. For
the ISGMR, comparison with recent data leads to a value of nuclear matter
compression modulus close to 215 MeV. However, a discrepancy between calculated
and measured energies of the ISGDR in Pb is found and remains an open
problem.Comment: To appear in: ``RIKEN Symposium and Workshop on Selected Topics in
Nuclear Collective Excitations'', proceedings of the meeting, RIKEN, Wako
city (Japan), March 20--24, 199
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