275 research outputs found
Lifetime Measurement of the 6s Level of Rubidium
We present a lifetime measurements of the 6s level of rubidium. We use a
time-correlated single-photon counting technique on two different samples of
rubidium atoms. A vapor cell with variable rubidium density and a sample of
atoms confined and cooled in a magneto-optical trap. The 5P_{1/2} level serves
as the resonant intermediate step for the two step excitation to the 6s level.
We detect the decay of the 6s level through the cascade fluorescence of the
5P_{3/2} level at 780 nm. The two samples have different systematic effects,
but we obtain consistent results that averaged give a lifetime of 45.57 +- 0.17
ns.Comment: 10 pages, 9 figure
Polarization and relaxation of radon
Investigations of the polarization and relaxation of Rn by spin
exchange with laser optically pumped rubidium are reported. On the order of one
million atoms per shot were collected in coated and uncoated glass cells.
Gamma-ray anisotropies were measured as a signal of the alignment (second order
moment of the polarization) resulting from the combination of polarization and
quadrupole relaxation at the cell walls. The temperature dependence over the
range 130C to 220C shows the anisotropies increasing with
increasing temperature as the ratio of the spin exchange polarization rate to
the wall relaxation rate increases faster than the rubidium polarization
decreases. Polarization relaxation rates for coated and uncoated cells are
presented. In addition, improved limits on the multipole mixing ratios of some
of the main gamma-ray transitions have been extracted. These results are
promising for electric dipole moment measurements of octupole-deformed
Rn and other isotopes, provided sufficient quantities of the rare
isotopes can be produced.Comment: 4 pages, 4 figure
Executive Summary of the Topical Program: Nuclear Isomers in the Era of FRIB
We report on the Facility for Rare Isotope Beams (FRIB) Theory Alliance
topical program "Nuclear Isomers in the Era of FRIB". We outline the many ways
isomers influence and contribute to nuclear science and technology, especially
in the four FRIB pillars: properties of rare isotopes, nuclear astrophysics,
fundamental symmetries, and applications for the nation and society. We
conclude with a resolution stating our recommendation that the nuclear physics
community actively pursue isomer research. A white paper is forthcoming.Comment: 4 pages including reference
First application of mass measurement with the Rare-RI Ring reveals the solar r-process abundance trend at A=122 and A=123
The Rare-RI Ring (R3) is a recently commissioned cyclotron-like storage ring
mass spectrometer dedicated to mass measurements of exotic nuclei far from
stability at Radioactive Isotope Beam Factory (RIBF) in RIKEN. The first
application of mass measurement using the R3 mass spectrometer at RIBF is
reported. Rare isotopes produced at RIBF, Sn, In, Cd,
Ag, Pd, were injected in R3. Masses of In, Cd,
and Pd were measured whereby the mass uncertainty of Pd was
improved. This is the first reported measurement with a new storage ring mass
spectrometery technique realized at a heavy-ion cyclotron and employing
individual injection of the pre-identified rare nuclei. The latter is essential
for the future mass measurements of the rarest isotopes produced at RIBF. The
impact of the new Pd result on the solar -process abundances in a
neutron star merger event is investigated by performing reaction network
calculations of 20 trajectories with varying electron fraction . It is
found that the neutron capture cross section on Pd increases by a
factor of 2.2 and -delayed neutron emission probability,
, of Rh increases by 14\%. The neutron capture cross
section on Pd decreases by a factor of 2.6 leading to pileup of
material at , thus reproducing the trend of the solar -process
abundances. The trend of the two-neutron separation energies (S)
was investigated for the Pd isotopic chain. The new mass measurement with
improved uncertainty excludes large changes of the S value at
. Such large increase of the S values before was
proposed as an alternative to the quenching of the shell gap to
reproduce -process abundances in the mass region of
Endotoxin-induced changes in expression of cyclooxygenase isoforms in the lamellar tissue of extracorporeally haemoperfused equine limbs
Potency of extracts from selected Egyptian plants as inducers of the Nrf2-dependent chemopreventive enzyme NQO1
Horizons: nuclear astrophysics in the 2020s and beyond
Nuclear astrophysics is a field at the intersection of nuclear physics and astrophysics, which seeks to understand the nuclear engines of astronomical objects and the origin of the chemical elements. This white paper summarizes progress and status of the field, the new open questions that have emerged, and the tremendous scientific opportunities that have opened up with major advances in capabilities across an ever growing number of disciplines and subfields that need to be integrated. We take a holistic view of the field discussing the unique challenges and opportunities in nuclear astrophysics in regards to science, diversity, education, and the interdisciplinarity and breadth of the field. Clearly nuclear astrophysics is a dynamic field with a bright future that is entering a new era of discovery opportunities
Horizons: Nuclear Astrophysics in the 2020s and Beyond
Nuclear Astrophysics is a field at the intersection of nuclear physics and
astrophysics, which seeks to understand the nuclear engines of astronomical
objects and the origin of the chemical elements. This white paper summarizes
progress and status of the field, the new open questions that have emerged, and
the tremendous scientific opportunities that have opened up with major advances
in capabilities across an ever growing number of disciplines and subfields that
need to be integrated. We take a holistic view of the field discussing the
unique challenges and opportunities in nuclear astrophysics in regards to
science, diversity, education, and the interdisciplinarity and breadth of the
field. Clearly nuclear astrophysics is a dynamic field with a bright future
that is entering a new era of discovery opportunities.Comment: 96 pages. Submitted to Journal of Physics
A complete set of nascent transcription rates for yeast genes
The amount of mRNA in a cell is the result of two opposite reactions: transcription and mRNA degradation. These reactions are governed by kinetics laws, and the most regulated step for many genes is the transcription rate. The transcription rate, which is assumed to be exercised mainly at the RNA polymerase recruitment level, can be calculated using the RNA polymerase densities determined either by run-on or immunoprecipitation using specific antibodies. The yeast Saccharomyces cerevisiae is the ideal model organism to generate a complete set of nascent transcription rates that will prove useful for many gene regulation studies. By combining genomic data from both the GRO (Genomic Run-on) and the RNA pol ChIP-on-chip methods we generated a new, more accurate nascent transcription rate dataset. By comparing this dataset with the indirect ones obtained from the mRNA stabilities and mRNA amount datasets, we are able to obtain biological information about posttranscriptional regulation processes and a genomic snapshot of the location of the active transcriptional machinery. We have obtained nascent transcription rates for 4,670 yeast genes. The median RNA polymerase II density in the genes is 0.078 molecules/kb, which corresponds to an average of 0.096 molecules/gene. Most genes have transcription rates of between 2 and 30 mRNAs/hour and less than 1% of yeast genes have >1 RNA polymerase molecule/gene. Histone and ribosomal protein genes are the highest transcribed groups of genes and other than these exceptions the transcription of genes is an infrequent phenomenon in a yeast cell
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