32 research outputs found
Coulomb exchange and pairing contributions in nuclear Hartree-Fock-Bogoliubov calculations with the Gogny force
We present exact Hartree-Fock-Bogoliubov calculations with the finite range
density dependent Gogny force using a triaxial basis. For the first time, all
contributions to the Pairing and Fock Fields arising from the Gogny and Coulomb
interactions as well as the two-body correction of the kinetic energy have been
calculated in this basis. We analyze the relevance of these terms in different
regions of the periodic table at zero and high angular momentum. The validity
of commonly used approximations that neglect different terms in the variational
equations is also checked. We find a decrease of the proton pairing energies
mainly due to a Coulomb antipairing effect.Comment: 32 pages, 12 figures. In press in Nucl. Physics
Simultaneous description of four positive and four negative parity bands
The extended coherent state model is further extended in order to describe
two dipole bands of different parities. The formalism provides a consistent
description of eight rotational bands. A unified description for spherical,
transitional and deformed nuclei is possible. Projecting out the angular
momentum and parity from a sole state, the band acquires a
magnetic character, while the electric properties prevail for the other band.
Signatures for a static octupole deformation in some states of the dipole bands
are pointed out. Some properties which distinguish between the dipole band
states and states of the same parity but belonging to other bands are
mentioned. Interesting features concerning the decay properties of the two
bands are found. Numerical applications are made for Gd, Yb,
Th, Ra, U and Pu, and the results are
compared with the available data.Comment: 36 pages, 13 figures, 12 table
Momentum distribution in heavy deformed nuclei: role of effective mass
The impact of nuclear deformation on the momentum distributions (MD) of
occupied proton states in U is studied with a phenomenological
Woods-Saxon (WS) shell model and the self-consistent Skyrme-Hartree-Fock (SHF)
scheme. Four Skyrme parameterizations (SkT6, SkM*, SLy6, SkI3) with different
effective masses are used. The calculations reveal significant deformation
effects in the low-momentum domain of states, mainly of
those lying near the Fermi surface. For other states, the deformation effect on
MD is rather small and may be neglected. The most remarkable result is that the
very different Skyrme parameterizations and the WS potential give about
identical MD. This means that the value of effective mass, being crucial for
the description of the spectra, is not important for the spatial shape of the
wave functions and thus for the MD. In general, it seems that, for the
description of MD at MeV/c, one may use any single-particle
scheme (phenomenological or self-consistent) fitted properly to the global
ground state properties.Comment: 14 pages, 6 figure
High-spin states in boson models with applications to actinide nuclei
We use the 1/ expansion formalism in a systematic study of high-spin
states in the and boson models with emphasis on spin dependence of
moment of inertia and E2 transitions. The results are applied to the high-spin
states in the actinide nuclei Th, U, where the need for
bosons is especially acute but until now, no realistic calculation existed. We
find that the -boson energy plays a crucial role in description of the
high-spin data.Comment: 11 pages Latex, 4 figures available upon request (to appear in Phys.
Lett. B
Particle number projection with effective forces
The particle number projection method is formulated for density dependent
forces and in particular for the finite range Gogny force. Detailed formula for
the projected energy and its gradient are provided. The problems arising from
the neglection of any exchange term, which may lead to divergences, are
throughly discussed and the possible inaccuracies estimated. Numericala results
for the projection after variation method are shown for the nucleus 164Er and
for the projection before variation approach for the nuclei 48-50Cr. We also
confirm the Coulomb antipairing effect found in mean field theories.Comment: 33 pages, 8 figures. Submit to Nuc. Phys.
Anharmonic double-phonon excitations in the interacting boson model
Double- vibrations in deformed nuclei are analyzed in the context of
the interacting boson model. A simple extension of the original version of the
model towards higher-order interactions is required to explain the observed
anharmonicities of nuclear vibrations. The influence of three- and four-body
interactions on the moments of inertia of ground- and -bands, and on
the relative position of single- and double- bands is studied
in detail. As an example of a realistic calculation, spectra and transitions of
the highly -anharmonic nuclei Dy, Er, and Er
are interpreted in this approach.Comment: 38 pages, TeX (ReVTeX). 15 ps figures. Submitted to Phys. Rev.
Gamow-Teller Strengths of the Inverse-Beta Transition 176Yb --> 176Lu for Spectroscopy of Proton-Proton and other sub-MeV Solar Neutrinos
Discrete Gamow-Teller (GT) transitions, 176Yb-->176Lu at low excitation
energies have been measured via the (3He,t) reaction at 450 MeV and at 0
degrees. For 176Yb, two low-lying states are observed, setting low thresholds
Q(neutrino)=301 and 445 keV for neutrino capture. Capture rates estimated from
the measured GT strengths, the simple two-state excitation structure, and the
low Q(neutrino) in Yb--Lu indicate that Yb-based neutrino-detectors are well
suited for a direct measurement of the complete sub-MeV solar electron-neutrino
spectrum (including pp neutrinos) where definitive effects of flavor conversion
are expected
Ground- band coupling in heavy deformed nuclei and SU(3) contraction limit
We derive analytic expressions for the energies and -transition
probabilities in the states of the ground and bands of heavy deformed
nuclei within a collective Vector-Boson Model with SU(3) dynamical symmetry. On
this basis we examine the analytic behavior of the SU(3) energy splitting and
the B(E2) interband transition ratios in the SU(3) contraction limits of the
model. The theoretical analyses outline physically reasonable ways in which the
ground- band coupling vanishes. The experimental data on the lowest
collective states of even-even rare earth nuclei and actinides strongly support
the theoretical results. They suggest that a transition from the
ground- band coupling scheme to a scheme in which the ground band is
situated in a separate irreducible representation of SU(3) should be realized
towards the midshell regions. We propose that generally the SU(3) group
contraction process should play an important role for such a kind of
transitions in any collective band coupling scheme in heavy deformed nuclei.Comment: 24 pages (LaTeX), 7 figures (12 postscript files
Analytical description of the Coherent State Model for near vibrational and well deformed nuclei
Analytical formulas for the excitation energies as well as for the electric
quadrupole reduced transition probabilities in the ground, beta and gamma bands
were derived within the coherent state model for the near vibrational and well
deformed nuclei. Numerical calculations were performed for 42 nuclei exhibiting
various symmetries and therefore with specific properties. Comparison of the
calculation results with the corresponding experimental data shows a good
agreement. The parameters involved in the proposed model satisfy evident
regularities being interpolated by smooth curves. Few of them, which fall out
of the curves, are interpreted as signatures for a critical point in a specific
phase transition. This is actually supported also by the figures showing the
excitation energy dependence on the angular momentum. The formulas provided for
energies and B(E2) values are very simple, being written in a compact form, and
therefore easy to be handled to explain the new experimental data.Comment: 9 figures, 50 page