323 research outputs found
The Demand for Savings Bonds in the United States--With Emphasis on the Significance of Interest Rates in the Postwar Period.
Precision Measurement of the 29Si, 33S, and 36Cl Binding Energies
The binding energies of 29Si, 33S, and 36Cl have been measured with a
relative uncertainty using a flat-crystal spectrometer.
The unique features of these measurements are 1) nearly perfect crystals whose
lattice spacing is known in meters, 2) a highly precise angle scale that is
derived from first principles, and 3) a gamma-ray measurement facility that is
coupled to a high flux reactor with near-core source capability. The binding
energy is obtained by measuring all gamma-rays in a cascade scheme connecting
the capture and ground states. The measurements require the extension of
precision flat-crystal diffraction techniques to the 5 to 6 MeV energy region,
a significant precision measurement challenge. The binding energies determined
from these gamma-ray measurements are consistent with recent highly accurate
atomic mass measurements within a relative uncertainty of .
The gamma-ray measurement uncertainties are the dominant contributors to the
uncertainty of this consistency test. The measured gamma-ray energies are in
agreement with earlier precision gamma-ray measurements.Comment: 13 pages, 4 figure
Cauchois and S\'en\'emaud Tables of wavelengths of X-ray emission lines and absorption edges
We present the Cauchois and S\'en\'emaud Tables of X-ray emission lines and
absorption edges. They are written both in French and English. They were
published in 1978 by Pergamon Press and are insufficiently known. However they
are of large interest because of their completeness. They comprise the energies
of all the K, L, M, N and O emission lines of natural elements from lithium up
to uranium as well as the energies of satellite emissions and absorption
discontinuities. The more intense lines of radio-elements up to fermium (Z =
100) are also given. The Tables range from the hard X-rays (122 keV, 0.01 nm)
to the extreme ultra-violet (12 eV, 102 nm). For each transition, the
wavelength ({\AA} and uX) and energy (eV and Ry) are given and references are
indicated. The transitions are grouped by increasing wavelength (decreasing
photon energy) and also by element and spectral series. We present, as an
example, the use of the Tables to identify the emissions of the molybdenum L
spectrum. We decided to scan the Cauchois and S\'en\'emaud Tables and make them
available for the scientific community. They are now available at the Website
of our laboratory, http://www.lcpmr.upmc.fr/.Comment: The Cauchois and S\'en\'emaud Tables are now available at the
following address : http://www.lcpmr.upmc.fr/themes-A2f.php The definitive
version of the paper is available at www3.interscience.wiley.com X-Ray
Spectrom. 2011, 40, 12-1
Polarized X-ray-emission Studies of Methyl Chloride and the Chlorofluoromethanes
A new technique sensitive to molecular orientation and geometry, and based on measuring the polarization of x-ray emission, has been applied to the Cl-containing molecules methyl chloride (CH3Cl) and the chlorofluoromethanes (CF3Cl, CF2Cl2, and CFCl3) in the gas phase. Upon selective excitation using monochromatic synchrotron radiation in the Cl K-edge (Cl 1s) near-threshold region, polarization-selective x-ray emission studies reveal highly polarized molecular valence x-ray fluorescence for all four molecules. The degree and the orientation of the polarized emission are observed to be sensitive to the incident excitation energy near the Cl Kedge. In some cases, the polarization direction for x-ray emission reverses for small changes in incident excitation energy (a few eV). It is shown that the polarized x-ray emission technique can be used to infer, directly from experiment, symmetries of occupied and unoccupied valence molecular orbitals, an- isotropies in absorption and emission, and orientational and geometrical information. It is suggested that the x-ray polarized-fluorescence phenomenon, reported here for simple molecules, can be used as a new approach to study more complicated systems in a variety of environments
Molecular-orbital Studies Via Satellite-free X-ray Fluorescence: Cl-K Absorption and K–Valence-level Emission Spectra of Chlorofluoromethanes
X-ray absorption and emission measurements in the vicinity of the chlorine K edge of the three chlorofluoromethanes have been made using monochromatic synchrotron radiation as the source of excitation. By selectively tuning the incident radiation to just above the Cl 1s single-electron ionization threshold for each molecule, less complex x-ray-emission spectra are obtained. This reduction in complexity is attributed to the elimination of multielectron transitions in the Cl K shell, which commonly produce satellite features in x-ray emission. The resulting satellite-free x-ray-emission spectra exhibit peaks due only to electrons in valence molecular orbitals filling a single Cl 1s vacancy. These simplified emission spectra and the associated x-ray absorption spectra are modeled using straightforward procedures and compared with semiempirical ground-state molecular-orbital calculations. Good agreement is observed between the present experimental and theoretical results for valence-orbital energies and those obtained from ultraviolet photoemission, and between relative radiative yields determined both experimentally and theoretically in this work
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Resonant inelastic x-ray scattering from molecules and atoms
X-ray fluorescence spectroscopy is one of the most powerful methods for the understanding of the electronic structure of matter. We report here on fluorescence experiments in the 2 to 6 keV photon energy range using tunable synchrotron radiation and the resulting experimental programs on resonant inelastic scattering in atoms and on polarization measurements in resonant molecular excitations
Calculation of quasi-degenerate energy levels of two-electron ions
Accurate QED calculations of the interelectron interaction corrections for
the , two-electron configurations for ions
with nuclear charge numbers are performed within the line
profile approach. Total energies of these configurations are evaluated.
Employing the fully relativistic treatment based on the {--} coupling
scheme these energy levels become quasi-degenerate in the region . To
treat such states within the framework of QED we utilize the line profile
approach. The calculations are performed within the Coulomb gauge.Comment: 22 pages, 11 figure
Lamb Shift in Muonic Hydrogen. II. Analysis of the Discrepancy of Theory and Experiment
Currently, both the g factor measurement of the muon as well as the Lamb
shift 2S-2P measurement in muonic hydrogen are in disagreement with theory.
Here, we investigate possible theoretical explanations, including proton
structure effects and small modifications of the vacuum polarization potential.
In particular, we investigate a conceivable small modification of the spectral
function of vacuum polarization in between the electron and muon energy scales
due to a virtual millicharged particle and due to an unstable vector boson
originating from a hidden sector of an extended standard model. We find that a
virtual millicharged particle which could explain the muonic Lamb shift
discrepancy alters theoretical predictions for the muon anomalous magnetic
moment by many standard deviations and therefore is in conflict with
experiment. Also, we find no parameterizations of an unstable virtual vector
boson which could simultaneously explain both "muonic" discrepancies without
significantly altering theoretical predictions for electronic hydrogen, where
theory and experiment currently are in excellent agreement. A process-dependent
correction involving electron screening is evaluated to have the right sign and
order-of-magnitude to explain the observed effect in muonic hydrogen.
Additional experimental evidence from light muonic atoms and ions is needed in
order to reach further clarification.Comment: 19 pages; LaTeX; literature references have been updated at the time
of submission to a scientific journa
Three-Phase Segmentation of Solid Oxide Fuel Cell Anode Materials Using Lab Based X-ray Nano-Computed Tomography
Triple-phase boundaries are an important microstructural metric to assess the performance and durability of solid oxide fuel cell electrodes and are known to significantly influence the performance at cell level. In recent years many advancements have been made in the quantification of TPBs including the use of focused ion beam scanning electron microscopes and synchrotron X-ray tomography, although neither technique comes without limitation; the former being destructive and the latter having limited availability. This work demonstrates the first example of the application of lab-based X-ray nano-CT for non-destructive, microstructural characterization of a SOFC electrode, where three-phase segmentation has been achieved. A SOFC anode cermet consisting of nickel and yttria-stabilized zirconia was imaged under X-ray using two fields of view: 64 µm × 64 µm and 16 µm × 16 µm, with compositional data displayed for several samples at the two resolutions. This work highlights the possibility of three-phase segmentation using lab-based equipment allowing non-destructive quantification and mapping of triple-phase boundaries without the need for synchrotron radiation
Nanoparticles as multimodal photon transducers of ionizing radiation
In biomedical imaging, nanoparticles combined with radionuclides that generate Cerenkov luminescence are used in diagnostic imaging, photon-induced therapies, and as activatable probes. In these applications, the nanoparticle is often viewed as a carrier inert to ionizing radiation from the radionuclide. However, certain phenomena such as enhanced nanoparticle luminescence and generation of reactive oxygen species cannot be explained by only Cerenkov luminescence interactions with nanoparticles. Herein, we report methods to examine the mechanisms of nanoparticle excitation by radionuclides, including interactions with Cerenkov luminescence, β particles, and γ radiation. We demonstrate that β scintillation contributes appreciably to excitation and reactivity in certain nanoparticle systems and that excitation of nanoparticles composed of large atomic number atoms by radionuclides generates X-rays, enabling multiplexed imaging through single photon emission computed tomography. These findings demonstrate practical optical imaging and therapy using radionuclides with emission energies below the Cerenkov threshold, thereby expanding the list of applicable radionuclides
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