658 research outputs found
Double electron capture in 156Dy, 162Er and 168Yb
The double electron capture half-lives of 156Dy, 162Er and 168Yb are
evaluated using the pseudo SU(3) model, which describes ground and excited
bands as well as their B(E2) and B(M1) transition strengths in remarkable
agreement with experiment. The best candidate for experimental detection is the
decay 156Dy -> 156Gd, with tau{1/2} (0+{gs} --> 0+{gs}) = 2.74 E22 yrs and
tau{1/2} (0+{gs} --> 0+{1}) = 8.31 E24 yrs.Comment: 7 pages, 1 figure. Physics Letters B, in pres
Microscopic description of the scissors mode in odd-mass heavy deformed nuclei
Pseudo-SU(3) shell-model results are reported for M1 excitation strengths in
157-Gd, 163-Dy and 169-Tm in the energy range between 2 and 4 MeV. Non-zero
pseudo-spin couplings between the configurations play a very important role in
determining the M1 strength distribution, especially its rapidly changing
fragmentation pattern which differs significantly from what has been found in
neighboring even-even systems. The results suggest one should examine
contributions from intruder levels.Comment: 5 pages, 3 figure
Pseudo + quasi SU(3): Towards a shell-model description of heavy deformed nuclei
The pseudo-SU(3) model has been extensively used to study normal parity bands
in even-even and odd-mass heavy deformed nuclei. The use of a realistic
Hamiltonian that mixes many SU(3) irreps has allowed for a successful
description of energy spectra and electromagnetic transition strengths. While
this model is powerful, there are situations in which the intruder states must
be taken into account explicitly. The quasi-SU(3) symmetry is expected to
complement the model, allowing for a description of nucleons occupying normal
and intruder parity orbitals using a unified formalism.Comment: 9 pages, 2 figures, invited talk at Computational and Group
Theoretical Methods in Nuclear Physics, Playa del Carmen, Mexico, February
18-21, 200
Nuclear masses, deformations and shell effects
We show that the Liquid Drop Model is best suited to describe the masses of
prolate deformed nuclei than of spherical nuclei. To this end three Liquid Drop
Mass formulas are employed to describe nuclear masses of eight sets of nuclei
with similar quadrupole deformations. It is shown that they are able to fit the
measured masses of prolate deformed nuclei with an RMS smaller than 750 keV,
while for the spherical nuclei the RMS is, in the three cases, larger than 2000
keV. The RMS of the best fit of the masses of semi-magic nuclei is also larger
than 2000 keV. The parameters of the three models are studied, showing that the
surface symmetry term is the one which varies the most from one group of nuclei
to another. In one model, isospin dependent terms are also found to exhibit
strong changes. The inclusion of shell effects allows for better fits, which
continue to be better in the prolate deformed nuclei regionComment: 10 pages, 8 tables, Proc. of the XXXIV Nuclear Physics Symposium,
January 4-7 2011, Cocoyoc, Morelos, Mexico. IOP Journal of Physics:
Conference Series (in press
Microscopic mass estimations
The quest to build a mass formula which have in it the most relevant
microscopic contributions is analyzed. Inspired in the successful Duflo-Zuker
mass description, the challenges to describe the shell closures in a more
transparent but equally powerful formalism are discussed.Comment: 14 pages, 6 figures, submitted to Journal of Physics G, Focus issue
on Open Problems in Nuclear Structure Theor
Excited bands in odd-mass rare-earth nuclei
Normal parity bands in [Formula Presented] and [Formula Presented] are studied using the pseudo-SU(3) shell model. Energies and [Formula Presented] transition strengths of states belonging to six low-lying, same-parity rotational bands in each nuclei are considered. The pseudo-SU(3) basis includes states with pseudospin 0 and 1, and [Formula Presented] and [Formula Presented] for even and odd nucleon numbers, respectively. States with pseudospin 1 and [Formula Presented] must be included for a proper description of some excited bands. © 2002 The American Physical Society
Nuclear masses set bounds on quantum chaos
It has been suggested that chaotic motion inside the nucleus may
significantly limit the accuracy with which nuclear masses can be calculated.
Using a power spectrum analysis we show that the inclusion of additional
physical contributions in mass calculations, through many-body interactions or
local information, removes the chaotic signal in the discrepancies between
calculated and measured masses. Furthermore, a systematic application of global
mass formulas and of a set of relationships among neighboring nuclei to more
than 2000 nuclear masses allows to set an unambiguous upper bound for the
average errors in calculated masses which turn out to be almost an order of
magnitude smaller than estimated chaotic components.Comment: 4 pages, Accepted for publication in Physical Review Letter
Coherent State Description of the Ground State in the Tavis-Cummings Model and its Quantum Phase Transitions
Quantum phase transitions and observables of interest of the ground state in
the Tavis-Cummings model are analyzed, for any number of atoms, by using a
tensorial product of coherent states. It is found that this "trial" state
constitutes a very good approximation to the exact quantum solution, in that it
globally reproduces the expectation values of the matter and field observables.
These include the population and dipole moments of the two-level atoms and the
squeezing parameter. Agreement in the field-matter entanglement and in the
fidelity measures, of interest in quantum information theory, is also found.The
analysis is carried out in all three regions defined by the separatrix which
gives rise to the quantum phase transitions. It is argued that this agreement
is due to the gaussian structure of the probability distributions of the
constant of motion and the number of photons. The expectation values of the
ground state observables are given in analytic form, and the change of the
ground state structure of the system when the separatrix is crossed is also
studied.Comment: 38 pages, 16 figure
Residual correlations in liquid drop mass calculations
A systematic study of correlations in the chart of calculated masses of
Moller and Nix is presented. It is shown that the differences between the
masses calculated by Moller at al and the measured ones have a well defined
oscillatory component as function of N and Z, which can be removed with an
appropriate fit, reducing significantly the error width, and concentrating the
error distribution on a single peak around zero. The residual correlations can
have important consequences in the errors as signaling the presence of chaos,
as was recently proposed.Comment: 23 pages, 18 figures. A more focused article with imporved figure
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