12,691 research outputs found
Self-consistent relativistic quasiparticle random-phase approximation and its applications to charge-exchange excitations and -decay half-lives
The self-consistent quasiparticle random-phase approximation (QRPA) approach
is formulated in the canonical single-nucleon basis of the relativistic
Hatree-Fock-Bogoliubov (RHFB) theory. This approach is applied to study the
isobaric analog states (IAS) and Gamov-Teller resonances (GTR) by taking Sn
isotopes as examples. It is found that self-consistent treatment of the
particle-particle residual interaction is essential to concentrate the IAS in a
single peak for open-shell nuclei and the Coulomb exchange term is very
important to predict the IAS energies. For the GTR, the isovector pairing can
increase the calculated GTR energy, while the isoscalar pairing has an
important influence on the low-lying tail of the GT transition. Furthermore,
the QRPA approach is employed to predict nuclear -decay half-lives. With
an isospin-dependent pairing interaction in the isoscalar channel, the
RHFB+QRPA approach almost completely reproduces the experimental -decay
half-lives for nuclei up to the Sn isotopes with half-lives smaller than one
second. Large discrepancies are found for the Ni, Zn, and Ge isotopes with
neutron number smaller than , as well as the Sn isotopes with neutron
number smaller than . The potential reasons for these discrepancies are
discussed in detail.Comment: 34 pages, 14 figure
Test of quantum chemistry in vibrationally-hot hydrogen molecules
Precision measurements are performed on highly excited vibrational quantum
states of molecular hydrogen. The rovibrational levels of H
(), lying only cm below the first dissociation
limit, were populated by photodissociation of HS and their level energies
were accurately determined by two-photon Doppler-free spectroscopy. A
comparison between the experimental results on level energies with the
best \textit{ab initio} calculations shows good agreement, where the present
experimental accuracy of cm is more precise than
theory, hence providing a gateway to further test theoretical advances in this
benchmark quantum system.Comment: 5 pages, 4 figures, and 2 table
High-speed measurement of rotational anisotropy nonlinear optical harmonic generation using position sensitive detection
We present a method of performing high-speed rotational anisotropy nonlinear
optical harmonic generation experiments at rotational frequencies of several
hertz by projecting the harmonic light reflected at different angles from a
sample onto a stationary position sensitive detector. The high rotational speed
of the technique, to times larger than existing methods, permits
precise measurements of the crystallographic and electronic symmetries of
samples by averaging over low frequency laser power, beam pointing, and pulse
width fluctuations. We demonstrate the sensitivity of our technique by
resolving the bulk four-fold rotational symmetry of GaAs about its [001] axis
using second harmonic generation
High-precision laser spectroscopy of the CO A - X (2,0), (3,0) and (4,0) bands
High-precision two-photon Doppler-free frequency measurements have been
performed on the CO A - X fourth-positive system (2,0),
(3,0), and (4,0) bands. Absolute frequencies of forty-three transitions, for
rotational quantum numbers up to , have been determined at an accuracy
of cm, using advanced techniques of two-color 2+1'
resonance-enhanced multi-photon ionization, Sagnac interferometry,
frequency-chirp analysis on the laser pulses, and correction for AC-Stark
shifts. The accurate transition frequencies of the CO A - X
system are of relevance for comparison with astronomical data in the search for
possible drifts of fundamental constants in the early universe. The present
accuracies in laboratory wavelengths of may be considered exact for the purpose of such comparisons.Comment: 13 pages, 6 figures, The Journal of Chemical Physics (2015) accepte
Possible discovery of the r-process characteristics in the abundances of metal-rich barium stars
We study the abundance distributions of a sample of metal-rich barium stars
provided by Pereira et al. (2011) to investigate the s- and r-process
nucleosynthesis in the metal-rich environment. We compared the theoretical
results predicted by a parametric model with the observed abundances of the
metal-rich barium stars. We found that six barium stars have a significant
r-process characteristic, and we divided the barium stars into two groups: the
r-rich barium stars (, [La/Nd]\,) and normal barium stars. The
behavior of the r-rich barium stars seems more like that of the metal-poor
r-rich and CEMP-r/s stars. We suggest that the most possible formation
mechanism for these stars is the s-process pollution, although their abundance
patterns can be fitted very well when the pre-enrichment hypothesis is
included. The fact that we can not explain them well using the s-process
nucleosynthesis alone may be due to our incomplete knowledge on the production
of Nd, Eu, and other relevant elements by the s-process in metal-rich and super
metal-rich environments (see details in Pereira et al. 2011).Comment: 5 pages, 5 figures, accepted for publication in A&
-decay half-lives of neutron-rich nuclei and matter flow in the -process
The -decay half-lives of neutron-rich nuclei with are systematically investigated using the newly developed fully
self-consistent proton-neutron quasiparticle random phase approximation (QRPA),
based on the spherical relativistic Hartree-Fock-Bogoliubov (RHFB) framework.
Available data are reproduced by including an isospin-dependent proton-neutron
pairing interaction in the isoscalar channel of the RHFB+QRPA model. With the
calculated -decay half-lives of neutron-rich nuclei a remarkable
speeding up of -matter flow is predicted. This leads to enhanced -process
abundances of elements with , an important result for the
understanding of the origin of heavy elements in the universe.Comment: 14 pages, 4 figure
The CO A-X System for Constraining Cosmological Drift of the Proton-Electron Mass Ratio
The band system of carbon monoxide,
which has been detected in six highly redshifted galaxies (), is
identified as a novel probe method to search for possible variations of the
proton-electron mass ratio () on cosmological time scales. Laboratory
wavelengths of the spectral lines of the A-X (,0) bands for have
been determined at an accuracy of
through VUV Fourier-transform absorption spectroscopy, providing a
comprehensive and accurate zero-redshift data set. For the (0,0) and (1,0)
bands, two-photon Doppler-free laser spectroscopy has been applied at the accuracy level, verifying the absorption data. Sensitivity
coefficients for a varying have been calculated for the CO A-X
bands, so that an operational method results to search for -variation.Comment: 7 pages (main article), 3 figures, includes supplementary materia
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