405 research outputs found
Triaxiality and the determination of the cubic shape parameter K3 from five observables
The absolute and the relative quadrupole shape invariants q3 and K3 provide a
model independent measure of triaxiality for beta-rigid nuclei. We will show
that one can obtain q3 and K3 from a small number of observables. The
approximations which are made will be shown to hold within a few percent both
in the rigid triaxial rotor model and the interacting boson model. The shape
parameter K3 is given for an exemplary set of nuclei and is translated into
effective values of the geometrical deformation parameters beta and gamma.Comment: 16 pages, 4 figure
Alternative Interpretation of Sharply Rising E0 Strengths in Transitional Regions
It is shown that strong 0+2 -> 0+1 E0 transitions provide a clear signature
of phase transitional behavior in finite nuclei. Calculations using the IBA
show that these transition strengths exhibit a dramatic and robust increase in
spherical-deformed shape transition regions, that this rise matches well the
existing data, that the predictions of these E0 transitions remain large in
deformed nuclei, and that these properties are intrinsic to the way that
collectivity and deformation develop through the phase transitional region in
the model, arising from the specific d-boson coherence in the wave functions,
and that they do not necessarily require the explicit mixing of normal and
intruder configurations from different IBA spaces.Comment: 6 pages, 3 figure
49Cr: Towards full spectroscopy up to 4 MeV
The nucleus 49Cr has been studied analysing gamma-gamma coincidences in the
reaction 46Ti(alpha,n)49Cr at the bombarding energy of 12 MeV. The level scheme
has been greatly extended at low excitation energy and several new lifetimes
have been determined by means of the Doppler Shift Attenuation Method.
Shell model calculations in the full pf configuration space reproduce well
negative-parity levels. Satisfactory agreement is obtained for positive parity
levels by extending the configuration space to include a nucleon-hole either in
the 1d3/2 or in the 2s1/2 orbitals.
A nearly one-to-one correspondence is found between experimental and
theoretical levels up to an excitation energy of 4 MeV.
Experimental data and shell model calculations are interpreted in terms of
the Nilsson diagram and the particle-rotor model, showing the strongly coupled
nature of the bands in this prolate nucleus. Nine values of K(pi) are proposed
for the levels observed in this experiment.
As a by-result it is shown that the values of the experimental magnetic
moments in 1f7/2 nuclei are well reproduced without quenching the nucleon
g-factors.Comment: 13 pages, 8 figure
Spectral Decorrelation of Nuclear Levels in the Presence of Continuum Decay
The fluctuation properties of nuclear giant resonance spectra are studied in
the presence of continuum decay. The subspace of quasi-bound states is
specified by one-particle one-hole and two-particle two-hole excitations and
the continuum coupling is generated by a scattering ensemble. It is found that,
with increasing number of open channels, the real parts of the complex
eigenvalues quickly decorrelate. This appears to be related to the transition
from power-law to exponential time behavior of the survival probability of an
initially non-stationary state.Comment: 10 Pages, REVTEX, 4 PostScript figure
Otimização da avaliação da atividade ciliar em traquéias como parâmetro para determinar a eficácia de vacinas vivas de bronquite infecciosa.
Projeto: 03.09.00.018
Interfering Doorway States and Giant Resonances. I: Resonance Spectrum and Multipole Strengths
A phenomenological schematic model of multipole giant resonances (GR) is
considered which treats the external interaction via common decay channels on
the same footing as the coherent part of the internal residual interaction. The
damping due to the coupling to the sea of complicated states is neglected. As a
result, the formation of GR is governed by the interplay and competition of two
kinds of collectivity, the internal and the external one. The mixing of the
doorway components of a GR due to the external interaction influences
significantly their multipole strengths, widths and positions in energy. In
particular, a narrow resonance state with an appreciable multipole strength is
formed when the doorway components strongly overlap.Comment: 20 pages, LaTeX, 3 ps-figures, to appear in PRC (July 1997
Quadrupole shape invariants in the interacting boson model
In terms of the Interacting Boson Model, shape invariants for the ground
state, formed by quadrupole moments up to sixth order, are studied in the
dynamical symmetry limits and, for the first time, over the whole structural
range of the IBM-1. The results are related to the effective deformation
parameters and their fluctuations in the geometrical model. New signatures that
can distinguish vibrator and gamma-soft rotor structures, and one that is
related to shape coexistence, are identified.Comment: 10 pages, ReVTeX, epsf, 2 Postscript figures include
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