384 Matching Results

Search Results

Advanced search parameters have been applied.

Observed Differences in the Arc Spectra of U²³⁵ and U²³⁸

Description: Abstract: "It has been found that the two principal uranium isotopes exhibit slightly different arc spectra. Certain U-235 lines have been found to be displaced from corresponding U-238 lines by about one reciprocal centimeter. The intensity ratio, IU235/IU238, has been shown to be a steadily increasing function of the U-235 concentration. These data indicate the possibility of developing a method for the determination of isotopic concentration by means of emission spectra."
Date: January 15, 1947
Creator: Long, D. R. & Smith, D. D.
Partner: UNT Libraries Government Documents Department

Laboratory measurements of resonant contributions to Fe XXIV line emission

Description: A number of X-ray astronomy satellites are scheduled for launch in the next few years. The Advanced X-ray Astrophysics Facility (AXAF) is scheduled for launch in 1998, and the X-Ray Multi-mirror Mission (XMM) and Astro-E in 1999. These satellites will carry spectrometers with resolving powers in the Fe L-shell emission region over an order of magnitude greater than the spectrometers aboard A CA. Interpreting AXAF, XMM, Astro-E spectra will require atomic data at an accuracy significantly greater than the data presently used in the standard emission codes. To address some of the existing and upcoming needs of X-ray astrophysics, we have continued our studies of Fe XXIV line emission. In this work, we measured Fe XXIV 3{yields}2 line emission at energies around threshold, using EBIT to examine the resonance contributions to the line emissivity. Here we present relative cross sections, at electron energies between 700 and 1500 eV, for producing line emission at wavelength A = 11.18 of the Fe XXIV 3d{sub 5/2}{yields}2P{sub 3} transition. Various processes can contribute to line emission observed from a collisional plasma. Direct excitation (DE) is the most important one at energies above the EIE threshold. Below threshold, Dielectronic recombination (DR) produces high n satellites which cannot be resolved from the EIE line. Resonant excitation (RE) can populate the same levels as DE via dielectronic capture followed by autoionization to the level of interest.
Date: October 27, 1997
Creator: Gu, M.F.; Beiersdorfer, P.; Brown, G.V.; Kahn, S.M.; Liedahl, D.A.; Reed, K.J. et al.
Partner: UNT Libraries Government Documents Department

Atomic and molecular supernovae

Description: Atomic and molecular physics of supernovae is discussed with an emphasis on the importance of detailed treatments of the critical atomic and molecular processes with the best available atomic and molecular data. The observations of molecules in SN 1987A are interpreted through a combination of spectral and chemical modelings, leading to strong constraints on the mixing and nucleosynthesis of the supernova. The non-equilibrium chemistry is used to argue that carbon dust can form in the oxygen-rich clumps where the efficient molecular cooling makes the nucleation of dust grains possible. For Type Ia supernovae, the analyses of their nebular spectra lead to strong constraints on the supernova explosion models.
Date: December 1, 1997
Creator: Liu, W.
Partner: UNT Libraries Government Documents Department

Spectra of rare earth ions and hydrogen molecules. Final report, November 1, 1952--October 31, 1971

Description: Research on the experimental spectrum analysis of the isotopic hydrogen molecules, experimental level analysis of rare earth ions in crystals, and the development of the theory of atomic structure of complex atoms is summarized. This research covers the spectra of molecular hydrogen and its isotopes, rare earth crystal spectra, theoretical spectroscopy, and rare earth and uranium free ion spectra. A list of publications is included. (JFP)
Date: January 1, 1971
Creator: Crosswhite, H. M.
Partner: UNT Libraries Government Documents Department

Electronic structure effects in liquid water studied by photoelectron spectroscopy and density functional theory

Description: We present valence photoelectron emission spectra of liquid water in comparison with gas-phase water, ice close to the melting point, low temperature amorphous and crystalline ice. All aggregation states have major electronic structure changes relative to the free molecule, with rehybridization and development of bonding and anti-bonding states accompanying the hydrogen bond formation. Sensitivity to the local structural order, most prominent in the shape and splitting of the occupied 3a{sub 1} orbital, is understood from the electronic structure averaging over various geometrical structures, and reflects the local nature of the orbital interaction.
Date: April 29, 2008
Creator: Nordlund, Dennis; Odelius, Michael; Bluhm, Hendrik; Ogasawara, Hirohito; Pettersson, Lars G.M. & Nilsson, Anders
Partner: UNT Libraries Government Documents Department

Comment on ?Spin crossover in (Mg,Fe)O: A M?ssbauer effect study with an alternative interpretation of x-ray emission spectroscopy data?

Description: Electronic spin-pairing transition of iron in magnesiow{umlt u}stite-(Mg,Fe)O has been recently studied with X-ray emission and M{umlt o}ssbauer spectroscopies under high pressures. While these studies reported a high-spin to low-spin transition of iron to occur at pressures above approximately 50 GPa, the width of the observed transition varies significantly. In particular, Kantor et al. reported that the transition in (Mg0.8,Fe0.2)O occurs over a pressure range of approximately 50 GPa in high-pressure M{umlt o}ssbauer measurements. To account for the discrepancy in the transition pressure, Kantor et al. reanalyzed the X-ray emission spectra by Lin et al. using a simple spectral decomposition method and claimed that X-ray emission measurements are also consistent with a spin crossover of iron at high pressures. Here we show that the proposed fitting method is inadequate to describe the X-ray emission spectrum of the low-spin FeS2 and would give an erroneous satellite peak (K{sub beta}') intensity, leading to an artificial high-spin component and, consequently, to invalid conclusions regarding the width of the pressure-induced transition in magnesiow{umlt u}stite. Furthermore, we compare Kantor's M{umlt o}ssbauer data with other recent high-pressure M{umlt o}ssbauer studies and show that the width of the transition can be simply explained by different experimental conditions (sample thickness, diameter, and hydrostaticity).
Date: May 23, 2006
Creator: Lin, J.; Struzhkin, V. V. & Garriliuk, A.
Partner: UNT Libraries Government Documents Department

Complexation of Lanthanides with Nitrate at Variable Temperatures: Thermodynamics and Coordination Modes

Description: Complexation of neodymium(III) with nitrate was studied at variable temperatures (25, 40, 55 and 70 C) by spectrophotometry and microcalorimetry. The NdNO{sub 3}{sup 2+} complex is weak and becomes slightly stronger as the temperature is increased. The enthalpy of complexation at 25 C was determined by microcalorimetry to be small and positive, (1.5 {+-} 0.2) kJ {center_dot} mol{sup -1}, in good agreement with the trend of the stability constant at variable temperatures. Luminescence emission spectra and lifetime of Eu(III) in nitrate solutions suggest that inner-sphere and bidentate complexes form between trivalent lanthanides (Nd{sup 3+} and Eu{sup 3+}) and nitrate in aqueous solutions. Specific Ion Interaction approach (SIT) was used to obtain the stability constants of NdNO{sub 3}{sup 2+} at infinite dilution and variable temperatures.
Date: December 10, 2008
Creator: Rao, Linfeng & Tian, Guoxin
Partner: UNT Libraries Government Documents Department

Water-Soluble 2-Hydroxyisophthalamides for Sensitization of Lanthanide Luminescence

Description: A series of octadentate ligands featuring the 2-hydroxyisophthalamide (IAM) antenna chromophore (to sensitize Tb(III) and Eu(III) luminescence) has been prepared and characterized. The length of the alkyl amine scaffold that links the four IAM moieties has been varied in order to investigate the effect of the ligand backbone on the stability and photophysical properties of the Ln(III) complexes. The amine backbones utilized in this study are N,N,N{prime},N{prime}-tetrakis-(2-aminoethyl)-ethane-1,2-diamine [H(2,2)-], N,N,N{prime},N{prime}-tetrakis-(2-aminoethyl)-propane-1,3-diamine [H(3,2)-] and N,N,N{prime},N{prime}-tetrakis-(2-aminoethyl)-butane-1,4-diamine [H(4,2)-]. These ligands also incorporate methoxyethylene [MOE] groups on each of the IAM chromophores to increase their water solubility. The aqueous ligand protonation constants and Tb(III) and Eu(III) formation constants were determined from solution thermodynamic studies. The resulting values indicate that at physiological pH, the Eu(III) and Tb(III) complexes of H(2,2)-IAM-MOE and H(4,2)-IAM-MOE are sufficiently stable to prevent dissociation at nanomolar concentrations. The photophysical measurements for the Tb(III) complexes gave overall quantum yield values of 0.56, 0.39, and 0.52 respectively for the complexes with H(2,2)-IAM-MOE, H(3,2)-IAM-MOE and H(4,2)-IAM-MOE, while the corresponding Eu(III) complexes displayed significantly weaker luminescence, with quantum yield values of 0.0014, 0.0015, and 0.0058, respectively. Analysis of the steady state Eu(III) emission spectra provides insight into the solution symmetries of the complexes. The combined solubility, stability and photophysical performance of the Tb(III) complexes in particular make them well suited to serve as the luminescent reporter group in high sensitivity time-resolved fluoroimmunoassays.
Date: February 20, 2008
Creator: Samuel, Amanda P. S.; Moore, Evan G.; Melchior, Marco; Xu, Jide & Raymond, Kenneth N.
Partner: UNT Libraries Government Documents Department

Measurements of NaI(Tl) electron response: comparison of different samples

Description: This paper measures the sample to sample variation in the light yield proportionality of NaI(Tl), and so explores whether this is an invariant characteristic of the material or whether it depends on the chemical and physical properties of the tested samples. We report on the electron response of nine crystals of NaI(Tl), differing in shape, volume, age, manufacturer and quality. The proportionality has been measured at the SLYNCI facility in the energy range between 3.5 to 460 keV. We observe that while samples produced by the same manufacturer at approximately the same time have virtually identical electron response curves, there are significant sample to sample variations among crystals produced by different manufacturers or at different times. In an effort to correlate changes in the electron response with details of the scintillation mechanism, we characterized other scintillation properties, including the gamma response and the x-ray excited emission spectra and decay times, for the nine crystals. While sample to sample differences in these crystals were observed, we have been unable to identify the underlying fundamental mechanisms that are responsible for these differences.
Date: December 10, 2008
Creator: Hull, Giulia; Choong, Woon-Seng; Moses, William W.; Bizarri, Gregory; Valentine, John D.; Payne, Stephen A. et al.
Partner: UNT Libraries Government Documents Department

ICPES analyses using full image spectra and astronomical data fitting algorithms to provide diagnostic and result information

Description: ICP emission analyses are prone to errors due to changes in power level, nebulization rate, plasma temperature, and sample matrix. As a result, accurate analyses of complex samples often require frequent bracketing with matrix matched standards. Information needed to track and correct the matrix errors is contained in the emission spectrum. But most commercial software packages use only the analyte line emission to determine concentrations. Changes in plasma temperature and the nebulization rate are reflected by changes in the hydrogen line widths, the oxygen emission, and neutral ion line ratios. Argon and off-line emissions provide a measure to correct the power level and the background scattering occurring in the polychromator. The authors` studies indicated that changes in the intensity of the Ar 404.4 nm line readily flag most matrix and plasma condition modifications. Carbon lines can be used to monitor the impact of organics on the analyses and calcium and argon lines can be used to correct for spectral drift and alignment. Spectra of contaminated groundwater and simulated defense waste glasses were obtained using a Thermo Jarrell Ash ICP that has an echelle CID detector system covering the 190-850 nm range. The echelle images were translated to the FITS data format, which astronomers recommend for data storage. Data reduction packages such as those in the ESO-MIDAS/ECHELLE and DAOPHOT programs were tried with limited success. The radial point spread function was evaluated as a possible improved peak intensity measurement instead of the common pixel averaging approach used in the commercial ICP software. Several algorithms were evaluated to align and automatically scale the background and reference spectra. A new data reduction approach that utilizes standard reference images, successive subtractions, and residual analyses has been evaluated to correct for matrix effects.
Date: October 1, 1997
Creator: Spencer, W.A. & Goode, S.R.
Partner: UNT Libraries Government Documents Department

Gamma-Ray Bursts: Relativistic shells or central engines?

Description: In many models of Gamma-Ray Bursts (GRBs) relativistic shells are responsible for the overall envelope of emission. The authors use kinematics and symmetry to calculate the time history and spectral evolution expected from a relativistic shell including effects from intrinsic variations in the shell`s intensity and spectra. They find that the decay phase of an envelope is produced by photons delayed by the shell`s curvature. These delayed photons are produced by regions that are off-axis such that the spectra evolve according to a universal function ({proportional_to} T{sup {minus}1}) regardless of intrinsic variations in the rest frame of the shell. They compare these predictions to the overall envelope of emission of GRBs. The observed spectra evolve faster ({approximately} T{sup {minus}3}). Intrinsic variations cannot make the spectra evolve that fast, which adds strength to the shell symmetry problem: models, in particular, the external shock model, that involve relativistic shells must either confine the material to narrow pencil beams, be very inefficient, or break the local spherical symmetry so that the shell acts like a parallel slab. In the case of the internal shock models involving winds (i.e., central engines), it will probably be easier to break the local spherical symmetry, but the none must postulate nearly continuous energy generation at 10{sup 51} erg s{sup {minus}1} lasting up to hundreds of seconds at the central site.
Date: August 1, 1997
Creator: Fenimore, E.E. & Summer, M.C.
Partner: UNT Libraries Government Documents Department

Laser-driven inner-shell excitation in high-Z atoms: A shell-selective impact ionization mechanism

Description: A highly selective, coherent impact ionization mechanism is proposed for the efficient generation of inner-shell population inversion in laser-driven plasmas. The theoretical analysis is consistent with observed L-shell (2p{l_arrow}3d) emission spectra from laser-excited Xe clusters.
Date: June 7, 2000
Partner: UNT Libraries Government Documents Department

Laser Induced Material Modification in the Bulk KDP Crystals

Description: Laser induced material modifications in the bulk and on the surface of KDP (KH{sub 2}PO{sub 4}) and DKDP (70-80% deuterated KDP) are studied using fluorescence imaging and spectroscopy. Photoluminescence is observed at damaged regions following above threshold exposure with an emission peak centered at 550-nm. In addition, surfaces exposed to >100 high power, 355-nm laser pulses reveal a reduced surface finishing quality as evidenced by an associated emission under UV photoexcitation. The emission spectra from the laser-induced damage sites and the laser degraded surfaces are similar suggesting the generation of similar defect species.
Date: December 16, 1999
Creator: Radousky, H.B.; Staggs, M.; Runkel, M. & Burnham, A.
Partner: UNT Libraries Government Documents Department

An efficient, selective collisional ejection mechanism for inner-shell population inversion in laser-driven plasmas

Description: A theoretical analysis of laser-driven collisional ejection of inner-shell electrons is presented to explain the previously observed anomalous kilovolt L-shell x-ray emission spectra from atomic Xe cluster targets excited by intense sub-picosecond 248nrn ultraviolet radiation. For incident ponderomotively-driven electrons photoionized by strong above threshold ionization, the collisional ejection mechanism is shown to be highly l-state and significantly n-state (i.e. radially) selective for time periods shorter than the collisional dephasing time of the photoionized electronic wavefunction. The resulting preference for the collisional ejection of 2p electrons by an ionized 4p state produces the measured anomalous Xe(L) emission which contains direct evidence for (i) the generation of Xe{sup 27+}(2p{sup 5}3d{sup 10}) and Xe{sup 28+}(2p{sup 5}3d{sup 9}) ions exhibiting inner-shell population inversion and (ii) a coherent correlated electron state collision responsible for the production of double 2p vacancies. For longer time periods, the selectivity of this coherent impact ionization mechanism is rapidly reduced by the combined effects of intrinsic quantum mechanical spreading and dephasing--in agreement with the experimentally observed and extremely strong {minus}{lambda}{sup {minus}6} pump-laser wavelength dependence of the efficiency of inner-shell (2p) vacancy production in Xe clusters excited in underdense plasmas.
Date: June 7, 2000
Partner: UNT Libraries Government Documents Department

3D Simulations of line emission from ICF capsules

Description: Line emission from ICF implosions can be used to diagnose the temperature of the DT fuel and provides an indication of the distortion in the fuel-pusher interface. 2D simulations have provided valuable insights into the usefulness of argon and titanium dopants as diagnostics of instabilities. Characterizing the effects of drive asymmetries requires 3D modeling with large demands for computer time and memory, necessitating the use of parallel computers. We present the results of some 3D simulations achieved with a code utilizing both shared memory and distributed parallelism. We discuss the code structure and related performance issues.
Date: October 1, 1998
Creator: Langer, S; Marinak, M M & Scott, H
Partner: UNT Libraries Government Documents Department

A laser spectroscopic study of Nd-doped Zirconia

Description: High-surface-area rare-earth (RE) modified zirconia powders prepared by solution methods can be used as catalytic support of noble metals and as electrolyte oxygen sensors in automobile exhaust-emission- control systems. Previous neutron-scattering study showed that substituting Zr with trivalent RE ions not only stabilizes the cubic and tetrgonal phases over a wide range of temperatures but also creates oxygen vacancies in the RE-Zr oxide solid solution. This work focuses on Nd fluorescence in Nd{sub 0.1}Zr{sub 0.9}O{sub 1.95} powders under laser excitation of the Nd{sup 3+} ground state to the {sup 4}G{sub 7.2} states. Distinct features were found at 8K in the {sup 4}I{sub 9/2}{r_arrow}{sup 4}G{sub 7/2} excitation and {sup 4}F{sub 3.2}{r_arrow}{sup 4}I{sub 9/2} emission spectra using two sets of incident and emission frequencies, respectively. Results are discussed in terms of site-sensitive local structures surrounding the Nd ions in the two-phased oxide structure.
Date: June 1, 1996
Creator: Loong, C.-K.; Liu, G.K.; Ozawa, M. & Suzuki, S.
Partner: UNT Libraries Government Documents Department

Near-field single molecule spectroscopy

Description: The high spatial resolution and sensitivity of near-field fluorescence microscopy allows one to study spectroscopic and dynamical properties of individual molecules at room temperature. Time-resolved experiments which probe the dynamical behavior of single molecules are discussed. Ground rules for applying near-field spectroscopy and the effect of the aluminum coated near-field probe on spectroscopic measurements are presented.
Date: February 1, 1995
Creator: Xie, X.S. & Dunn, R.C.
Partner: UNT Libraries Government Documents Department

Advanced laser diodes for sensing applications

Description: The authors have developed diode lasers for short pulse duration and high peak pulse power in the 0.01--100.0 m pulsewidth regime. A primary goal of the program was producing up to 10 W while maintaining good far-field beam quality and ease of manufacturability for low cost. High peak power, 17 W, picosecond pulses have been achieved by gain switching of flared geometry waveguide lasers and amplifiers. Such high powers area world record for this type of diode laser. The light emission pattern from diode lasers is of critical importance for sensing systems such as range finding and chemical detection. They have developed a new integrated optical beam transformer producing rib-waveguide diode lasers with a symmetric, low divergence, output beam and increased upper power limits for irreversible facet damage.
Date: January 1, 2000
Partner: UNT Libraries Government Documents Department