1,897 research outputs found
Closed shells at drip-line nuclei
The shell structure of magic nuclei far from stability is discussed in terms
of the self-consistent spherical Hartree-Fock-Bogoliubov theory. In particular,
the sensitivity of the shell-gap sizes and the two-neutron separation energies
to the choice of particle-hole and particle-particle components of the
effective interaction is investigated.Comment: 19 pages, LaTeX, 8 uuencoded figures available upon reques
On three topical aspects of the N=28 isotonic chain
The evolution of single-particle orbits along the N=28 isotonic chain is
studied within the framework of a relativistic mean-field approximation. We
focus on three topical aspects of the N=28 chain: (a) the emergence of a new
magic number at Z=14; (b) the possible erosion of the N=28 shell; and (c) the
weakening of the spin-orbit splitting among low-j neutron orbits. The present
model supports the emergence of a robust Z=14 subshell gap in 48Ca, that
persists as one reaches the neutron-rich isotone 42Si. Yet the proton removal
from 48Ca results in a significant erosion of the N=28 shell in 42Si. Finally,
the removal of s1/2 protons from 48Ca causes a ~50% reduction of the spin-orbit
splitting among neutron p-orbitals in 42Si.Comment: 12 pages with 5 color figure
The additional-mode garden of RR Lyrae stars
Space-based photometric missions revealed a surprising abundance of
millimagnitude-level additional modes in RR Lyrae stars. The modes that appear
in the modulated fundamental-mode (RRab) stars can be ordered into four major
categories. Here we present the distribution of these groups in the Petersen
diagram, and discuss their characteristics and connections to additional modes
observed in other RR Lyrae stars.Comment: 4 pages, 4 figures, proceedings of the Joint
TASC2-KASC9-SPACEINN-HELAS8 Conference "Seismology of the Sun and the Distant
Stars 2016", to be published in EPJ Wo
A K=3 two-quasiparticle isomer in Sr
The decay of on-line mass-separated
98
Rb
to
98
Sr
is studied by
Îł
spectroscopy. The revised decay scheme adds further evidence of the coexistence of very different shapes in
98
Sr
.
A set of levels is proposed to originate from particle-hole pair excitations across the
Z
=
40
spherical gap in analogy with
96
Sr
.
A deformed
K
=
3
band with probable even parity is built on a 7.1-ns isomer at 1838 keV. It is interpreted as a two-quasineutron excitation in accordance with a quantum Monte Carlo pairing calculation based on a deformed shell model. Configurations of the calculated lowest-lying two-quasiparticle levels confirm the importance of the [404]9/2 neutron orbital at the largest deformations in the neutron-rich
A
â
100
region
Dependence of direct neutron capture on nuclear-structure models
The prediction of cross sections for nuclei far off stability is crucial in
the field of nuclear astrophysics. We calculate direct neutron capture on the
even-even isotopes Sn and Pb with energy levels,
masses, and nuclear density distributions taken from different
nuclear-structure models. The utilized structure models are a
Hartree-Fock-Bogoliubov model, a relativistic mean field theory, and a
macroscopic-microscopic model based on the finite-range droplet model and a
folded-Yukawa single-particle potential. Due to the differences in the
resulting neutron separation and level energies, the investigated models yield
capture cross sections sometimes differing by orders of magnitude. This may
also lead to differences in the predicted astrophysical r-process paths.
Astrophysical implications are discussed.Comment: 25 pages including 12 figures, RevTeX, to appear in Phys. Rev.
First decay study of the very neutron-rich isotope Br-93
The decay of the mass-separated, very neutron-rich isotope Br-93 has been
studied by gamma-spectroscopy. A level scheme of its daughter Kr-93 has been
constructed. Level energies, gamma-ray branching ratios and multipolarities
suggest spins and parities which are in accord with a smooth systematics of the
N=57 isotones for Z less-equal 40, suggesting the N=56 shell closure still to
be effective in Kr isotopes. So far, there is no indication of a progressive
onset of deformation in neutron-rich Kr isotopes.Comment: 17 pages, 3 figures, Phys. Rev. C, in prin
The possible existence of Hs in nature from a geochemical point of view
A hypothesis of the existence of a long-lived isotope 271Hs in natural
molybdenites and osmirides is considered from a geochemical point of view. It
is shown that the presence of Hs in these minerals can be explained only by
making an additional ad hoc assumption on the existence of an isobaric pair of
271Bh-271Hs. This assumption could be tested by mass-spectrometric measurements
of U, Pb, Kr, Xe, and Zr isotopic shifts.Comment: 5 pages, no figures. Physics of Particles and Nuclei Letters, 2006,
Vol. 3, No. 3, pp. 165-168 in pres
Nucleosynthesis in the Early Galaxy
Recent observations of r-process-enriched metal-poor star abundances reveal a
non-uniform abundance pattern for elements . Based on non-correlation
trends between elemental abundances as a function of Eu-richness in a large
sample of metal-poor stars, it is shown that the mixing of a consistent and
robust light element primary process (LEPP) and the r-process pattern found in
r-II metal-poor stars explains such apparent non-uniformity. Furthermore, we
derive the abundance pattern of the LEPP from observation and show that it is
consistent with a missing component in the solar abundances when using a recent
s-process model. As the astrophysical site of the LEPP is not known, we explore
the possibility of a neutron capture process within a site-independent
approach. It is suggested that scenarios with neutron densities
or in the range best
explain the observations.Comment: 28 pages, 7 Postscript figures. To be published in The Astrophysical
Journa
Neutron Drops and Skyrme Energy-Density Functionals
The J=0 ground state of a drop of 8 neutrons and the lowest
1/2 and 3/2 states of 7-neutron drops, all in an external well, are
computed accurately with variational and Green's function Monte Carlo methods
for a Hamiltonian containing the Argonne two-nucleon and Urbana IX
three-nucleon potentials. These states are also calculated using Skyrme-type
energy-density functionals. Commonly used functionals overestimate the central
density of these drops and the spin-orbit splitting of 7-neutron drops.
Improvements in the functionals are suggested
Beta-decay half-lives and beta-delayed neutron emission probabilities of nuclei in the region below A=110, relevant for the r-process
Measurements of the beta-decay properties of r-process nuclei below A=110
have been completed at the National Superconducting Cyclotron Laboratory, at
Michigan State University. Beta-decay half-lives for Y-105, Zr-106,107 and
Mo-111, along with beta-delayed neutron emission probabilities of Y-104,
Mo-109,110 and upper limits for Y-105, Zr-103,104,105,106,107 and Mo-108,111
have been measured for the first time. Studies on the basis of the quasi-random
phase approximation are used to analyze the ground-state deformation of these
nuclei.Comment: 21 pages, 10 figures, article accepted for publication in Physical
Review
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