174 research outputs found
Shell stabilization of super- and hyperheavy nuclei without magic gaps
Quantum stabilization of superheavy elements is quantified in terms of the
shell-correction energy. We compute the shell correction using self-consistent
nuclear models: the non-relativistic Skyrme-Hartree-Fock approach and the
relativistic mean-field model, for a number of parametrizations. All the forces
applied predict a broad valley of shell stabilization around Z=120 and
N=172-184. We also predict two broad regions of shell stabilization in
hyperheavy elements with N approx 258 and N approx 308. Due to the large
single-particle level density, shell corrections in the superheavy elements
differ markedly from those in lighter nuclei. With increasing proton and
neutron numbers, the regions of nuclei stabilized by shell effects become
poorly localized in particle number, and the familiar pattern of shells
separated by magic gaps is basically gone.Comment: 6 pages REVTEX, 4 eps figures, submitted to Phys. Lett.
Skyrme mean-field study of rotational bands in transfermium isotopes
Self-consistent mean field calculations with the SLy4 interaction and a
density-dependent pairing force are presented for nuclei in the Nobelium mass
region. Predicted quasi-particle spectra are compared with experiment for the
heaviest known odd N and odd Z nuclei. Spectra and rotational bands are
presented for nuclei around No252,4 for which experiments are either planned or
already running.Comment: 13 pages LATEX, elsart style, 6 embedded eps figure
Comment on ``Structure of exotic nuclei and superheavy elements in a relativistic shell model''
A recent paper [M. Rashdan, Phys. Rev. C 63, 044303 (2001)] introduces the
new parameterization NL-RA1 of the relativistic mean-field model which is
claimed to give a better description of nuclear properties than earlier ones.
Using this model ^{298}114 is predicted to be a doubly-magic nucleus. As will
be shown in this comment these findings are to be doubted as they are obtained
with an unrealistic parameterization of the pairing interaction and neglecting
ground-state deformation.Comment: 2 pages REVTEX, 3 figures, submitted to comment section of Phys. Rev.
C. shortened and revised versio
Shell Corrections of Superheavy Nuclei in Self-Consistent Calculations
Shell corrections to the nuclear binding energy as a measure of shell effects
in superheavy nuclei are studied within the self-consistent Skyrme-Hartree-Fock
and Relativistic Mean-Field theories. Due to the presence of low-lying proton
continuum resulting in a free particle gas, special attention is paid to the
treatment of single-particle level density. To cure the pathological behavior
of shell correction around the particle threshold, the method based on the
Green's function approach has been adopted. It is demonstrated that for the
vast majority of Skyrme interactions commonly employed in nuclear structure
calculations, the strongest shell stabilization appears for Z=124, and 126, and
for N=184. On the other hand, in the relativistic approaches the strongest
spherical shell effect appears systematically for Z=120 and N=172. This
difference has probably its roots in the spin-orbit potential. We have also
shown that, in contrast to shell corrections which are fairly independent on
the force, macroscopic energies extracted from self-consistent calculations
strongly depend on the actual force parametrisation used. That is, the A and Z
dependence of mass surface when extrapolating to unknown superheavy nuclei is
prone to significant theoretical uncertainties.Comment: 14 pages REVTeX, 8 eps figures, submitted to Phys. Rev.
Enhanced Stability of Superheavy Nuclei due to High-Spin Isomerism
Configuration-constrained calculations of potential-energy surfaces in
even-even superheavy nuclei reveal systematically the existence at low
excitation energies of multi-quasiparticle states with deformed axially
symmetric shapes and large angular momenta. These results indicate the
prevalence of long-lived, multi-quasiparticle isomers. In a quantal system, the
ground state is usually more stable than the excited states. In contrast, in
superheavy nuclei the multi-qausiparticle excitations decrease the probability
for both fission and decay, implying enhanced stability. Hence, the
systematic occurrence of multi-qausiparticle isomers may become crucial for
future production and study of even heavier nuclei. The energies of
multi-quasiparticle states and their decays are calculated and
compared to available data.Comment: 4 pages, 5 figures, accepted for publication in PR
Semiempirical Shell Model Masses with Magic Number Z = 126 for Superheavy Elements
A semiempirical shell model mass equation applicable to superheavy elements
up to Z = 126 is presented and shown to have a high predictive power. The
equation is applied to the recently discovered superheavy nuclei Z = 118, A =
293 and Z = 114, A = 289 and their decay products.Comment: 7 pages, including 2 figures and 2 table
Potential energy surfaces of superheavy nuclei
We investigate the structure of the potential energy surfaces of the
superheavy nuclei 258Fm, 264Hs, (Z=112,N=166), (Z=114,N=184), and (Z=120,N=172)
within the framework of self-consistent nuclear models, i.e. the
Skyrme-Hartree-Fock approach and the relativistic mean-field model. We compare
results obtained with one representative parametrisation of each model which is
successful in describing superheavy nuclei. We find systematic changes as
compared to the potential energy surfaces of heavy nuclei in the uranium
region: there is no sufficiently stable fission isomer any more, the importance
of triaxial configurations to lower the first barrier fades away, and
asymmetric fission paths compete down to rather small deformation. Comparing
the two models, it turns out that the relativistic mean-field model gives
generally smaller fission barriers.Comment: 8 pages RevTeX, 6 figure
New results from an extensive aging test on bakelite Resistive Plate Chambers
We present recent results of an extensive aging test, performed at the CERN
Gamma Irradiation Facility on two single--gap RPC prototypes, developed for the
LHCb Muon System. With a method based on a model describing the behaviour of an
RPC under high particle flux conditions, we have periodically measured the
electrode resistance R of the two RPC prototypes over three years: we observe a
large spontaneous increase of R with time, from the initial value of about 2
MOhm to more than 250 MOhm. A corresponding degradation of the RPC rate
capabilities, from more than 3 kHz/cm2 to less than 0.15 kHz/cm2 is also found.Comment: 6 pages, 7 figures, presented at Siena 2002, 8th Topical Seminar on
Innovative Particle and Radiation Detectors 21-24 October 2002, Siena, Ital
Beyond mean-field description of the low-lying spectrum of 16O
Starting from constrained Skyrme-mean-field calculations, the low-energy
excitation spectrum of 16O is calculated by configuration mixing of
particle-number and angular-momentum projected mean-field states in the
framework of the Generator Coordinate Method. Without any adjustable
parameters, this approach gives a very good description of those states and
their transition moments that can be described with our restriction to axially
and reflection-symmetric shapes. The structure of low-lying 0+ states is
analyzed in terms of self-consistent 0p-0h, 2p-2h, and 4p-4h Hartree-Fock
states.Comment: 15 pages LATEX, 6 figures, 3 tables, revision of sections 4 and
Anomalous Behavior of 2+ Excitations around 132Sn
In certain neutron-rich Te isotopes, a decrease in the energy of the first
excited 2+ state is accompanied by a decrease in the E2 strength to that state
from the ground state, contradicting simple systematics and general intuition
about quadrupole collectivity. We use a separable quadrupole-plus-pairing
Hamiltonian and the quasiparticle random phase approximation to calculate
energies, B(E2,0+ -> 2+) strengths, and g factors for the lowest 2+ states near
132Sn (Z >= 50). We trace the anomalous behavior in the Te isotopes to a
reduced neutron pairing above the N = 82 magic gap.Comment: 1 figure added. to be published in Phys. Rev.
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