233 research outputs found
Structure of the doublet bands in doubly odd nuclei: The case of
The structure of the doublet bands in is
investigated within the framework of the Interacting Vector Boson Fermion Model
(IVBFM). A new, purely collective interpretation of these bands is given on the
basis of the used boson-fermion dynamical symmetry of the model. The energy
levels of the doublet bands as well as the absolute and
transition probabilities between the states of both yrast and yrare bands are
described quite well. The observed odd-even staggering of both and
values is reproduced by the introduction of an appropriate interaction
term of quadrupole type, which produces such a staggering effect in the
transition strengths. The calculations show that the appearance of doublet
bands in certain odd-odd nuclei could be a consequence of the realization of a
larger dynamical symmetry based on the non-compact supersymmetry group
.Comment: 12 pages, 8 figure
Phase Transitions in Finite Nuclei and the Integer Nucleon Number Problem
The study of spherical-deformed ground--state phase transitions in finite
nuclei as a function of N and Z is hindered by the discrete values of the
nucleon number. A resolution of the integer nucleon number problem, and
evidence relating to phase transitions in finite nuclei, are discussed from the
experimental point of view and interpreted within the framework of the
interacting boson model.Comment: 8 pages Latex + 8 figs (postscript). In Phys Rev Lett, June 199
Enhanced Production of Neutron-Rich Rare Isotopes in Peripheral Collisions at Fermi Energies
A large enhancement in the production of neutron-rich projectile residues is
observed in the reactions of a 25 MeV/nucleon 86Kr beam with the neutron rich
124Sn and 64Ni targets relative to the predictions of the EPAX parametrization
of high-energy fragmentation, as well as relative to the reaction with the less
neutron-rich 112Sn target. The data demonstrate the significant effect of the
target neutron-to-proton ratio (N/Z) in peripheral collisions at Fermi
energies. A hybrid model based on a deep-inelastic transfer code (DIT) followed
by a statistical de-excitation code appears to account for part of the observed
large cross sections. The DIT simulation indicates that the production of the
neutron-rich nuclides in these reactions is associated with peripheral nucleon
exchange. In such peripheral encounters, the neutron skins of the neutron-rich
124Sn and 64Ni target nuclei may play an important role. From a practical
viewpoint, such reactions between massive neutron-rich nuclei offer a novel and
attractive synthetic avenue to access extremely neutron-rich rare isotopes
towards the neutron-drip line.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Regularities and symmetries of subsets of collective 0+ states
The energies of subsets of excited 0+ states in geometric collective models
are investigated and found to exhibit intriguing regularities. In models with
an infinite square well potential, it is found that a single formula, dependent
on only the number of dimensions, describes a subset of 0+ states. The same
behavior of a subset of 0+ states is seen in the large boson number limit of
the Interacting Boson Approximation (IBA) model near the critical point of a
first order phase transition, in contrast to the fact that these 0+ state
energies exhibit a harmonic behavior in all three limiting symmetries of the
IBA. Finally, the observed regularities in 0+ energies are analyzed in terms of
the underlying group theoretical framework of the different models.Comment: 9 pages, 3 figures, added reference [38
Spectral properties of a tractable collective Hamiltonian
The spectral properties of a tractable collective model Hamiltonian are
studied. The potential energy is truncated up to quartic terms in the
quadrupole deformation variables, incorporating vibrational,
-independent rotational and axially deformed rotational structures.
These physically significant limits are analysed in detail and confronted with
well-established approximation schemes. Furthermore, transitional Hamiltonians
in between the limits are presented and discussed. All results are obtained
within a recently presented Cartan-Weyl based framework to calculate
embedded quadrupole collective observables.Comment: submitted to PR
Triaxial projected shell model study of gamma-vibrational bands in even-even Er isotopes
We expand the triaxial projected shell model basis to include
triaxially-deformed multi-quasiparticle states. This allows us to study the
yrast and gamma-vibrational bands up to high spins for both gamma-soft and
well-deformed nuclei. As the first application, a systematic study of the
high-spin states in Er-isotopes is performed. The calculated yrast and
gamma-bands are compared with the known experimental data, and it is shown that
the agreement between theory and experiment is quite satisfactory. The
calculation leads to predictions for bands based on one- and two-gamma phonon
where current data are still sparse. It is observed that gamma-bands for
neutron-deficient isotopes of 156Er and 158Er are close to the yrast band, and
further these bands are predicted to be nearly degenerate for high-spin states.Comment: 6 pages, 9 figure
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.
Lifetime determination of excited states in Cd-106
Two separate experiments using the Differential Decay Curve Method have been performed to extract mean lifetimes of excited states in 106 Cd. The inedium-spin states of interest were populated by the Mo-98(C-12, 4n) Cd-106 reaction performed at the Wright Nuclear Structure Lab., Yale University. From this experiment, two isomeric state mean lifetimes have been deduced. The low-lying states were populated by the Mo-96(C-13, 3n)Cd-106 reaction performed at the Institut fur Kernphysik, Universitat zu Koln. The mean lifetime of the I-pi = 2(1)(+) state was deduced, tentatively, as 16.4(9) ps. This value differs from the previously accepted literature value from Coulomb excitation of 10.43(9) ps
Scenarios of domain pattern formation in a reaction-diffusion system
We performed an extensive numerical study of a two-dimensional
reaction-diffusion system of the activator-inhibitor type in which domain
patterns can form. We showed that both multidomain and labyrinthine patterns
may form spontaneously as a result of Turing instability. In the stable
homogeneous system with the fast inhibitor one can excite both localized and
extended patterns by applying a localized stimulus. Depending on the parameters
and the excitation level of the system stripes, spots, wriggled stripes, or
labyrinthine patterns form. The labyrinthine patterns may be both connected and
disconnected. In the the stable homogeneous system with the slow inhibitor one
can excite self-replicating spots, breathing patterns, autowaves and
turbulence. The parameter regions in which different types of patterns are
realized are explained on the basis of the asymptotic theory of instabilities
for patterns with sharp interfaces developed by us in Phys. Rev. E. 53, 3101
(1996). The dynamics of the patterns observed in our simulations is very
similar to that of the patterns forming in the ferrocyanide-iodate-sulfite
reaction.Comment: 15 pages (REVTeX), 15 figures (postscript and gif), submitted to
Phys. Rev.
Quadrupole Collective States in a Large Single-J Shell
We discuss the ability of the generator coordinate method (GCM) to select
collective states in microscopic calculations. The model studied is a
single- shell with hamiltonian containing the quadrupole-quadrupole
interaction. Quadrupole collective excitations are constructed by means of the
quadrupole single-particle operator. Lowest collective bands for =31/2 and
particle numbers =4,6,8,10,12, and are found. For lower values of ,
exact solutions are obtained and compared with the GCM results.Comment: submitted for publication in Phys. Rev. C, revtex, 28 pages, 15
PostScript figures available on request from [email protected], preprint
No. IFT/17/9
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