730 research outputs found
Disentangling the nuclear shape coexistence in even-even Hg isotopes using the interacting boson model
We intend to provide a consistent description of the even-even Hg isotopes,
172-200Hg, using the interacting boson model including configuration mixing. We
pay special attention to the description of the shape of the nuclei and to its
connection with the shape coexistence phenomenon.Comment: To appear in CGS15 conference proceedings (EPJ Web of Conferences
The influence of intruder states in even-even Po isotopes
We study the role of intruder states and shape coexistence in the even-even
Po isotopes, through an interacting boson model with configuration
mixing calculation. We analyzed the results in the light of known systematics
on various observable in the Pb region, paying special attention to the
unperturbed energy systematics and quadrupole deformation. We find that shape
coexistence in the Po isotopes behaves in very much the same way as in the Pt
isotopes, i.e., it is somehow hidden, contrary to the situation in the Pb and
the Hg isotopes.Comment: Contribution to the Nuclear Structure and Dynamics 2015 (Portorose,
Slovenia) proceeding
Nuclear shape coexistence in Po isotopes: An interacting boson model study
Background: The lead region, Po, Pb, Hg, and Pt, shows up the presence of
coexisting structures having different deformation and corresponding to
different particle-hole configurations in the Shell Model language.
Purpose: We intend to study the importance of configuration mixing in the
understanding of the nuclear structure of even-even Po isotopes, where the
shape coexistence phenomena are not clear enough.
Method: We study in detail a long chain of polonium isotopes, 190-208Po,
using the interacting boson model with configuration mixing (IBM-CM). We fix
the parameters of the Hamiltonians through a least-squares fit to the known
energies and absolute B(E2) transition rates of states up to 3 MeV.
Results: We obtained the IBM-CM Hamiltonians and we calculate excitation
energies, B(E2)'s, electric quadrupole moments, nuclear radii and isotopic
shifts, quadrupole shape invariants, wave functions, and deformations.
Conclusions: We obtain a good agreement with the experimental data for all
the studied observables and we conclude that shape coexistence phenomenon is
hidden in Po isotopes, very much as in the case of the Pt isotopes.Comment: To be published in Physical Review C. arXiv admin note: text overlap
with arXiv:1312.459
Shape evolution and shape coexistence in Pt isotopes: comparing interacting boson model configuration mixing and Gogny mean-field energy surfaces
The evolution of the total energy surface and the nuclear shape in the
isotopic chain Pt are studied in the framework of the interacting
boson model, including configuration mixing. The results are compared with a
self-consistent Hartree-Fock-Bogoliubov calculation using the Gogny-D1S
interaction and a good agreement between both approaches shows up. The
evolution of the deformation parameters points towards the presence of two
different coexisting configurations in the region 176 A 186.Comment: Submitted to PR
A theoretical description of energy spectra and two-neutron separation energies for neutron-rich zirconium isotopes
Very recently the atomic masses of neutron-rich Zr isotopes, from Zr
to Zr, have been measured with high precision. Using a schematic
Interacting Boson Model (IBM) Hamiltonian, the evolution from spherical to
deformed shapes along the chain of Zr isotopes, describing at the same time the
excitation energies as well as the two-neutron separation energies, can be
rather well reproduced. The interplay between phase transitions and
configuration mixing of intruder excitations in this mass region is succinctly
addressed.Comment: Accepted in European Journal of Physics
On the nature of the shape coexistence and the quantum phase transition phenomena: lead region and Zr isotopes
The goal of this contribution is to analyze the connection between shape
coexistence and quantum phase transition, two seemingly unrelated phenomena
that share common aspects, namely, the rapid change in the ground state
structure along an isotope chain or the presence of several minima at the
mean-field level. To illustrate the similarities and differences between both
phenomena, we will focus in the Pb region, in particular in Pt and Hg isotopes,
as well as in Zr isotopes.Comment: To be published in the CGS16 (Shanghai, China) conference proceeding
Nuclear binding energies: Global collective structure and local shell-model correlations
Nuclear binding energies and two-neutron separation energies are analyzed
starting from the liquid-drop model and the nuclear shell model in order to
describe the global trends of the above observables. We subsequently
concentrate on the Interacting Boson Model (IBM) and discuss a new method in
order to provide a consistent description of both, ground-state and
excited-state properties. We address the artefacts that appear when crossing
mid-shell using the IBM formulation and perform detailed numerical calculations
for nuclei situated in the 50-82 shell. We also concentrate on local deviations
from the above global trends in binding energy and two-neutron separation
energies that appear in the neutron-deficient Pb region. We address possible
effects on the binding energy, caused by mixing of low-lying intruder
states into the ground state, using configuration mixing in the IBM framework.
We also study ground-state properties using a deformed mean-field approach.
Detailed comparisons with recent experimental data in the Pb region are amply
discussed.Comment: 69 pages, TeX (ReVTeX). 23 eps figures. 1 table. Modified version.
Accepted in Nucl. Phys.
Effects of T=0 two body matrix elements on M1 and Gamow-Teller transitions: isospin decomposition
We perform calculations for M1 transitions and allowed Gamow Teller (GT)
transitions in the even-even Titanium isotopes - Ti, Ti, and
Ti. We first do calculations with the FPD6 interaction. Then to study
the effect of T=0 matrix elements on the M1 and GT rates we introduce a second
interaction in which all the T=0 matrix elements are set equal to zero and a
third in which all the T=0 matrix elements are set to a constant. For the
latter two interactions the T=1 matrix elements are the same as for FPD6. We
are thus able to study the effects of the fluctuating T=0 matrix elements on M1
and GT rates
Proton-neutron quadrupole interactions: an effective contribution to the pairing field
We point out that the proton-neutron energy contribution, for low multipoles
(in particular for the quadrupole component), effectively renormalizes the
strength of the pairing interaction acting amongst identical nucleons filling
up a single-j or a set of degenerate many-j shells. We carry out the
calculation in lowest-order perturbation theory. We perform a study of this
correction in various mass regions. These results may have implications for the
use of pairing theory in medium-heavy nuclei and for the study of pairing
energy corrections to the liquid drop model when studying nuclear masses.Comment: 19 pages, TeX, 3 tables, 2 figures. Accepted in PR
Some results and problems for anisotropic random walks on the plane
This is an expository paper on the asymptotic results concerning path
behaviour of the anisotropic random walk on the two-dimensional square lattice
Z^2. In recent years Mikl\'os and the authors of the present paper investigated
the properties of this random walk concerning strong approximations, local
times and range. We give a survey of these results together with some further
problems.Comment: 20 page
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