293 research outputs found
Empirical Abundance Scaling Laws and Implications for the Gamma-Process in Core-Collapse Supernovae
Analyzing the solar system abundances, we have found two empirical abundance
scaling laws concerning the p- and s-nuclei with the same atomic number. The
first scaling is s/p ratios are almost constant over a wide range of the atomic
number, where the p-nculei are lighter than the s-nuclei by two or four
neutrons. The second scaling is p/p ratios are almost constant, where the
second -nuclei are lighter than the first p-nucleus by two neutrons. These
scalings are a piece of evidence that most p-nuclei are dominantly synthesized
by the gamma-process in supernova explosions. The scalings lead to a novel
concept of "universality of gamma-process" that the s/p and p/p ratios of
nuclei produced by individual gamma-processes are almost constant,
respectively. We have calculated the ratios by gamma-process based on
core-collapse supernova explosion models under various astrophysical conditions
and found that the scalings hold for materials produced by individual
gamma-processes independent of the astrophysical conditions assumed. The
universality originates from three mechanisms: the shifts of the gamma-process
layers to keep their peak temperature, the weak s-process in pre-supernovae,
and the independence of the s/p ratios of the nuclear reactions. The results
further suggest an extended universality that the s/p ratios in the
gamma-process layers are not only constant but also centered on a specific
value of 3. With this specific value and the first scaling, we estimate that
the ratios of -process abundance contributions from the AGB stars to the
massive stars are almost 6.7 for the -nuclei of A > 90. We find that large
enhancements of s/p ratios for Ce, Er, and W are a piece of evidence that the
weak s-process actually occurred before SNe.Comment: 35 pages, 15 figure
Second Backbend in the Mass A ~ 180 Region
Within the framework of selfconsistent cranked Hartree-Fock- Bogoliubov
theory(one-dimensional) we predict second backbend in the yrast line of Os-182
at , which is even sharper than the first one observed
experimentally at .
Around such a high spin the structure becomes multi-quasiparticle type, but
the main source of this strong discontinuity is a sudden large alignment of
i_13/2 proton orbitals along the rotation axis followed soon by the alignment
of j_15/2 neutron orbitals. This leads to drastic structural changes at such
high spins. When experimentally confirmed, this will be observed for the first
time in this mass region, and will be at the highest spin so far.Comment: 13 pages, 4 ps figure
RPA calculations with Gaussian expansion method
The Gaussian expansion method (GEM) is extensively applied to the
calculations in the random-phase approximation (RPA). We adopt the
mass-independent basis-set that has been tested in the mean-field calculations.
By comparing the RPA results with those obtained by several other available
methods for Ca isotopes, using a density-dependent contact interaction and the
Woods-Saxon single-particle states, we confirm that energies, transition
strengths and widths of their distribution are described by the GEM bases to
good precision, for the , and collective states. The GEM is
then applied to the self-consistent RPA calculations with the finite-range
Gogny D1S interaction. The spurious center-of-mass motion is well separated
from the physical states in the response, and the energy-weighted sum
rules for the isoscalar transitions are fulfilled reasonably well. Properties
of low-energy transitions in Ca are argued in some detail.Comment: 30 pages including 12 figure
Photo-disintegration cross section measurements on W, Re and Os: Implications for the Re-Os cosmochronology
Cross sections of the W, Re, Os() reactions
were measured using quasi-monochromatic photon beams from laser Compton
scattering (LCS) with average energies from 7.3 to 10.9 MeV. The results are
compared with the predictions of Hauser-Feshbach statistical calculations using
four different sets of input parameters. In addition, the inverse neutron
capture cross sections were evaluated by constraining the model parameters,
especially the strength function, on the basis of the experimental data.
The present experiment helps to further constrain the correction factor
for the neutron capture on the 9.75 keV state in Os.
Implications of to the Re-Os cosmochronology are discussed with a
focus on the uncertainty in the estimate of the age of the Galaxy.Comment: 11 page
Superdeformation in Asymmetric NZ Nucleus Ar
A rotational band with five -ray transitions ranging from 2 to
12 states was identified in Ar. This band is linked through
transitions from the excited 2, 4 and 6 levels to
the low-lying states; this determines the excitation energy and the spin-parity
of the band. The deduced transition quadrupole moment of 1.45 indicates that the band has a superdeformed shape. The nature of the band
is revealed by cranked Hartree--Fock--Bogoliubov calculations and a
multiparticle--multihole configuration is assigned to the band
Experimental apparatus at KUR-ISOL to identify isomeric transitions from fission products, and decay spectroscopy of 151Ce
Decay studies on 151Ce have been performed using the on-line isotope separator connected to the Kyoto University Reactor. In addition to conventional γ and conversion electron spectroscopy, β-gated measurements were carried out on mass-separated 151Ce to identify an isomeric transition. From the analysis of the obtained data, the half-life of the isotope was ascertained to be 1.76(6) s and a decay scheme containing six excited levels was constructed for the first time. The excited level at 35.1 keV in 151Pr was found to be a long-lived state (a half-life of approximately 10us or longer)
Direct determination of photodisintegration cross sections and the p-process
Photon-induced reactions play a key role in the nucleosynthesis of heavy
neutron-deficient nuclei, the so-called p-nuclei. In this paper we review the
present status of experiments on photon-induced reactions at energies of
astrophysical importance and their relevance to p-process modeling.Comment: Nucl. Phys. A, in pres
Nuclear structure of 30S and its implications for nucleosynthesis in classical novae
The uncertainty in the 29P(p,gamma)30S reaction rate over the temperature
range of 0.1 - 1.3 GK was previously determined to span ~4 orders of magnitude
due to the uncertain location of two previously unobserved 3+ and 2+ resonances
in the 4.7 - 4.8 MeV excitation region in 30S. Therefore, the abundances of
silicon isotopes synthesized in novae, which are relevant for the
identification of presolar grains of putative nova origin, were uncertain by a
factor of 3. To investigate the level structure of 30S above the proton
threshold (4394.9(7) keV), a charged-particle spectroscopy and an in-beam
gamma-ray spectroscopy experiments were performed. Differential cross sections
of the 32S(p,t)30S reaction were measured at 34.5 MeV. Distorted wave Born
approximation calculations were performed to constrain the spin-parity
assignments of the observed levels. An energy level scheme was deduced from
gamma-gamma coincidence measurements using the 28Si(3He,n-gamma)30S reaction.
Spin-parity assignments based on measurements of gamma-ray angular
distributions and gamma-gamma directional correlation from oriented nuclei were
made for most of the observed levels of 30S. As a result, the resonance
energies corresponding to the excited states in 4.5 MeV - 6 MeV region,
including the two astrophysically important states predicted previously, are
measured with significantly better precision than before. The uncertainty in
the rate of the 29P(p,gamma)30S reaction is substantially reduced over the
temperature range of interest. Finally, the influence of this rate on the
abundance ratios of silicon isotopes synthesized in novae are obtained via 1D
hydrodynamic nova simulations.Comment: 22 pages, 12 figure
Discovery of Yttrium, Zirconium, Niobium, Technetium, and Ruthenium Isotopes
Currently, thirty-four yttrium, thirty-five zirconium, thirty-four niobium,
thirty-five technetium, and thirty-eight ruthenium isotopes have been observed
and the discovery of these isotopes is discussed here. For each isotope a brief
synopsis of the first refereed publication, including the production and
identification method, is presented.Comment: To be published in Atomic Data and Nuclear Data Table
Collective and broken pair states of 65,67Ga
Excited states of 65Ga and 67Ga nuclei were populated through the 12C(58Ni,αp) and 12C(58Ni,3p) reactions, respectively, and investigated by in-beam γ-ray spectroscopic methods. The NORDBALL array equipped with a charged particle ball and 11 neutron detectors was used to detect the evaporated particles and γ rays. The level schemes of 65,67Ga were constructed on the basis of γγ-coincidence relations up to 8.6 and 10 MeV excitation energy, and Iπ=27/2 and 33/2+ spin and parity, respectively. The structure of 65,67Ga nuclei was described in the interacting boson-fermion plus broken pair model, including quasiproton, quasiproton-two-quasineutron, and three-quasiproton fermion configurations in the boson-fermion basis states. Most of the states were assigned to quasiparticle + phonon and three quasiparticle configurations on the basis of their electromagnetic decay properties
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