185 research outputs found
1/N expansion formalism for high-spin states
The 1/ expansion solutions for the interacting boson model are extended to
higher orders using computer algebra. The analytic results are compared with
those obtained from an exact diagonalization of the Hamiltonian and are shown
to be very accurate. The extended formulas for level energies and E2
transitions will be useful in the analysis of high-spin states in both normal
and superdeformed nuclei.Comment: 11 pages, Latex, 3 figures available upon reques
Tests and applications of self-consistent cranking in the interacting boson model
The self-consistent cranking method is tested by comparing the cranking
calculations in the interacting boson model with the exact results obtained
from the SU(3) and O(6) dynamical symmetries and from numerical
diagonalization. The method is used to study the spin dependence of shape
variables in the and boson models. When realistic sets of parameters
are used, both models lead to similar results: axial shape is retained with
increasing cranking frequency while fluctuations in the shape variable
are slightly reduced.Comment: 9 pages, 3 ps figures, Revte
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
Description of Nuclear Structure Effects in Subbarrier Fusion by the Interacting Boson Model
Recent theoretical developments in using the Interacting Boson Model to
describe nuclear structure effects in fusion reactions below the Coulomb
barrier are reviewed. Methods dealing with linear and all orders coupling
between the nuclear excitations and the translational motion are discussed, and
the latter is found to lead to a better description of the barrier distribution
data. A systematic study of the available data (cross sections, barrier and
spin distributions) in rare-earth nuclei is presented.Comment: 9 pages + 2 Figures (in eps form). To be published in the Proceedings
of the FUSION97 Conference, South Durras, Australia, March 1997 (J. Phys. G).
Full text and figures are also available at
http://nucth.physics.wisc.edu/preprints/mad-nt-97-01.abs.htm
Anharmonic phonon excitations in subbarrier fusion reactions
Recently measured high precision data of fusion excitation function have
enabled a detailed study on the effects of nuclear collective excitations on
fusion reactions. Using such highly accurate data of the O +
Sm reactions, we discuss the anharmonic properties of collective
phonon excitations in Sm nuclei. It is shown that subbarrier fusion
reactions are strongly affected by the anharmonic effects and thus offer an
alternative method to extract the static quadrupole moments of phonon states in
a spherical nucleus.Comment: 10 pages, To be published in the Proceedings of the Tours Symposium
on Nuclear Physics III, Tours, France, September 1997 (American Institute of
Physics
Description of superdeformed nuclei in the interacting boson model
The interacting boson model is extended to describe the spectroscopy of
superdeformed bands. Microscopic structure of the model in the second minimum
is discussed and superdeformed bosons are introduced as the new building
blocks. Solutions of a quadrupole Hamiltonian are implemented through the
expansion method. Effects of the quadrupole parameters on dynamic moment of
inertia and electric quadrupole transition rates are discussed and the results
are used in a description of superdeformed bands in the Hg-Pb and Gd-Dy
regions.Comment: 18 pages revtex, 9 figures available upon reques
Effects of nuclear structure on average angular momentum in subbarrier fusion
We investigate the effects of nuclear quadrupole and hexadecapole couplings
on the average angular momentum in sub-barrier fusion reactions. This quantity
could provide a probe for nuclear shapes, distinguishing between prolate vs.
oblate quadrupole and positive vs. negative hexadecapole couplings. We describe
the data in the O + Sm system and discuss heavier systems where shape effects
become more pronounced.Comment: Latex (uses the epsf macro), 10 pages of text, 3 postscript figures
included. Full postscript version available by anonymous ftp from
wisnuf.physics.wisc.edu:/pub/preprints. MAD-NT-94-0
Generator Coordinate Truncations
We investigate the accuracy of several schemes to calculate ground-state
correlation energies using the generator coordinate technique. Our test-bed for
the study is the interacting boson model, equivalent to a 6-level
Lipkin-type model. We find that the simplified projection of a triaxial
generator coordinate state using the subgroup of the rotation group is
not very accurate in the parameter space of the Hamiltonian of interest. On the
other hand, a full rotational projection of an axial generator coordinate state
gives remarkable accuracy. We also discuss the validity of the simplified
treatment using the extended Gaussian overlap approximation (top-GOA), and show
that it works reasonably well when the number of boson is four or larger.Comment: 19 pages, 6 eps figure
Role of Anharmonicities of Nuclear Vibrations in Fusion Reactions at Sub-barrier Energies
We discuss the effects of double octupole and quadrupole phonon excitations in Sm on fusion reactions between O and Sm at subbarrier energies. The effects of anharmonicities of the vibrational states are taken into account by using the -interacting boson model. We compare the results with those in the harmonic limit to show that anharmonicities play an essential role in reproducing the experimental fusion barrier distribution. From the analysis of the high quality fusion data available for this system, we deduce negative static quadrupole moments for both the first 2 and 3 states in Sm. This is the first time that the sign of static quadrupole moments of phonon states in a spherical nucleus is determined from the data of subbarrier fusion reactions
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