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Methane coupling by membrane reactor. Quarterly technical progress report, September 25--December 24, 1996

Description: A new catalyst, 1.9%(wt) Mn-5%(wt) Na{sub 2}WO{sub 4}/SiO{sub 2} was synthesized by the incipient wetness impregnation method. X-ray diffraction studies of the catalyst calcined at 800 C showed that cristobalite, Na{sub 2}WO{sub 4}, and Mn{sub 2}O{sub 3} were the three phases that coexisted in the catalyst. Calcination at 1,000 C resulted in the formation of a new SiO{sub 2} phase (tridymite). The new catalyst was characterized by running the methane oxidative coupling reactions in a conventional packed bed reactor. The highest C{sub 2} yield obtained was 25%. The Mn-W-Na/SiO{sub 2} catalyst was coated on the inside wall of the SrFeCo{sub 0.5}O{sub 3{minus}x} dense membrane tube. A methane oxidative coupling experiment was conducted with the new catalyst in a dense membrane reactor. The oxygen permeance of the dense membrane tube coated with the catalyst was about 0.05 cc/min/cm{sup 2} at 850 C. By co-feeding methane and oxygen to the tube side of the reactor, C{sub 2} yields up to 7% were observed in these runs. To prepare the membrane tube for the radial flow reactor, silica was deposited on a lanthanum stabilized gamma alumina membrane tube and gas permeances were measured after the membrane tube was calcined at different temperatures. The pressure drop across the membrane was high enough for the membrane to be used in the radial flow reactor.
Date: March 10, 1997
Creator: Ma, Y.H.
Partner: UNT Libraries Government Documents Department

Photo- and cathodoluminescence of hydrothermally synthesized Y{sub 3}Al{sub 5}O{sub 12}:Tb and NaY(WO{sub 4}){sub 2}:Tb

Description: Cathodoluminescent (CL) phosphors with improved low-voltage characteristics are needed for use in emissive flat panel displays. Conventional high-temperature methods for phosphor synthesis yield large polycrystalline grains that must be pulverized prior to screen deposition. Grinding has been implicated in reducing phosphor efficiency by causing surface contamination and defects. Hydrothermal synthesis has been used to improve the quality of ceramic powders by producing fine, well-formed crystallites without grinding. Two green-emitting phosphors, Y{sub 3}Al{sub 5}O{sub 12}:Tb (YAG:Tb) and NaY(WO{sub 4}){sub 2}:Tb, were used to test the effects of hydrothermal. synthesis on grain size and morphology, and on low-voltage CL properties. YAG:Th prepared hydrothermally consisted of submicron crystallites with a typical garnet habit. The CL efficiency of hydrothermally synthesized YAG:Tb (3 lm/W at 800 V) was comparable to that of equivalent YAG:Tb compositions prepared via high-temperature solid state reaction. In comparison, CL intensities of Gd{sub 3}Ga{sub 5}O{sub l2}:Tb were slightly better (3.5 lm/W at 800 V), while those of NaY(WO{sub 4}){sub 2}:Tb were approximately 1/100th that of YAG:Tb. Both CL and photoluminescence data show that the difference in the cathodoluminescence of YAG and NaY(WO{sub 4}){sub 2} can be understood in terms of differences in the mechanism of activation.
Date: October 1, 1995
Creator: Phillips, M.L.F. & Potter, B.G. Jr.
Partner: UNT Libraries Government Documents Department

Implications of the unusual redox behavior exhibited by the heteropolyanion [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12{minus}}

Description: Materials containing more than one electroactive species may exhibit a variety of unusual properties, including mixed or intermediate valence, and their related phenomena. Intermediate valence arises when localized orbitals, notably valence f-states, interact in a bonding fashion with delocalized, molecular orbitals in the same material. Electrons are viewed to be rapidly hopping between these two very different kinds of orbitals, and it is their relative residence times that are interpreted as a non-integral valence. Whereas there has been considerable efforts expended to understand this unusual behavior, these efforts have not proven successful, largely because the problem is many-bodied and is usually studied on infinite band states, often in chemically complex systems. The authors report here on the novel electrochemical behavior of the heteropolyanion [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12}, and examine the valence of Eu in both the oxidized and reduced form of the anion, as determined from Eu L{sub 3}-edge X-ray absorption near edge structure (XANES). The results demonstrate that, with careful electrochemical control, Eu in this ion may become intermediate valent. Such a result would provide an entirely new and unique approach to longstanding questions related to the phenomenon of intermediate valence.
Date: August 1, 1997
Creator: Antonio, M.R. & Soderholm, L.
Partner: UNT Libraries Government Documents Department

A photon calorimeter using lead tungstate crystals for the CEBAF HAll A Compton polarimeter

Description: A new Compton polarimeter is built on the CEBAF Hall A electron beam line. Performances of 10% resolution and 1% calibration are required for the photon calorimeter of this polarimeter. This calorimeter is built with lead tungstate scintillators coming from the CMS electromagnetic calorimeter R&D. Beam tests of this detector have been made using the tagged photon beam line at MAMI, Mainz, and a resolution of 1.76%+2.75%/v+0.41%/E has been measured.
Date: May 1, 2000
Creator: Neyret, D.; Pussieux, T.; Auger, T.; Baylac, M.; Burtin, E.; Cavata, C. et al.
Partner: UNT Libraries Government Documents Department

Redox behavior of europium in the Preyssler heteropolyanion [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12-}

Description: In aqueous, mineral-acid electrolytes, the cyclic voltammetry of the europium- exchanged Preyssler heteropolyanion, [Eu{sup III}P{sub 5}W{sub 30}O{sub 110}]{sup 12-}, is unique among all the other trivalent-lanthanide-exchanged anions, [Ln{sup III}P{sub 5}W{sub 30}O{sub 110}]{sup 12-} for Ln {triple_bond} Ce-Lu. All [LnP{sub 5}W{sub 30}O{sub 110}]{sup 12-}, including Eu, form heteropoly blues upon reduction. In order to obtain insights about this issue, we conducted in situ Eu L{sub 3}-edge XANES (X-ray absorption near edge structure) spectroelectrochemical experiments on an aqueous solution of [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12-} (5.5 mM) in a supporting electrolyte of 1 M H{sub 2}SO{sub 4} at two extreme potentials. The results demonstrate that the Eu{sup III} ion in the colorless Preyssler anion solution at open circuit potential (+0.21 V vs Ag/AgCl) is electroactive and is reduced to Eu{sup II} in the resulting dark blue solution from constant-potential bulk electrolysis at -0.55 V vs Ag/AgCl. This unusual redox behavior of [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12-} may be of technological importance in the area of oxidation catalysis.
Date: August 1, 1997
Creator: Antonio, M.R. & Soderholm, L.
Partner: UNT Libraries Government Documents Department

BTeV - A dedicated B experiment at the Tevatron

Description: BTeV is a dedicated b-physics experiment that is expected to begin operation at the Fermilab Tevatron in 2008. BTeV is designed to take full advantage of the large production cross section of b particles (including B{sub S}) in high energy hadron collisions. A quick description of the BTeV spectrometer is given in this paper. Two unique aspects of BTeV, the pixel-based trigger and the high quality lead tungstate electromagnetic calorimeter, are described in slightly greater detail.
Date: December 17, 2002
Creator: Christian, David C.
Partner: UNT Libraries Government Documents Department

High range gamma radiation meter

Description: A low power meter has been constructed and tested to measure gamma fields from .1 R/hr to 1500 R/hr over the energy range of 60 keV to 1.2 MeV. The portable, battery-powered meter consists of a local display unit and remote probe. The display unit indicates gamma intensities via a 4-1/2 digit liquid crystal display (LCD) and a 50-segment bargraph LCD.
Date: January 1, 1985
Creator: Baird, W.; Bjarke, G.O. & Eisen, Y.
Partner: UNT Libraries Government Documents Department

Polishing procedure and surface characterization lead tungstate crystal scintillator Road No. 723 and No. 754

Description: Step by step procedures are given for polishing the scintillator rods. A Strasbaugh spindle polishing machine was used along with visual inspection and hand polishing. Extensive data is given on pre-polish surface characterization, profilometry, microphotography, and interferometry.
Date: May 1, 1996
Creator: Kellam, M
Partner: UNT Libraries Government Documents Department

Hadron calorimeter performance with a PbWO4 EM compartment

Description: The CMS detector[1] at the LHC has chosen PbWO4 in order to achieve the superior photon energy resolution which is crucial in searching for the 2 photon decay of low mass Higgs bosons. The hadronic compartment is thought to be Cu absorber, since one is immersed in a 4 T magnetic field, read out by scintillator tiles coupled to wavelength shifter (WLS) fibers. The combined performance of this calorimeter is of interest in the study of jets and missing transverse energy (neutrino, SUSY signatures). For this reason, a test was made of the electromagnetic (EM) compartment combined with a reasonable approximation to the baseline HCAL ``barrel`` calorimeter. Data was taken in the H4 CERN beamline. The EM compartment was a 7 {times} 7 square array of PbWO4 crystals, which for the purposes of this study are considered as a single readout in depth (or ``compartment``) [2]. The HCAL module consisted of large scintillator plates with 24 individual longitudinal readout channels. The EM compartment was followed by 10 Cu plates each 3 cm thick, followed by 9 Cu plates each 6 cm thick. This set of absorber plates represented the HCAL compartments inside the coil. The coil itself [1] was approximated as Al and Fe plates, of a total thickness of about 1.4 absorption lengths. The coil mockup was sampled and then followed by 4 plates of 8 cm thick Cu, each with an individual readout which represented a test of the ``Tailcatcher`` concept.
Date: January 1996
Creator: Green, D.
Partner: UNT Libraries Government Documents Department

CdWO4-Boron FY 2000 Task 4 Completion Report

Description: The fabrication of boron-covered crystal scintillation detectors is described. Bulk boron-loaded epoxy material was cast and cut into 0.5 mm-thick wafers that were mounted on CdWO{sub 4} and CsI(Tl) crystals. The crystals were mounted on miniature photomultiplier tubes and gamma spectra were obtained with the detectors. The ability of these small detectors to produce spectra that can be analyzed to provide isotopic identification has been demonstrated. In addition, the detector can produce a signature indicating the presence of neutrons. The same miniature size of these detectors that makes them attractive for hand-held portable use, may be a limiting factor in their efficiency. The small size of the scintillation crystals makes them not as efficient as larger NaI(Tl) crystals simply by virtue of significantly decreased sensitive volume and surface area. It may be worthwhile to consider slightly larger crystals (approximately 15 mm cubic CdWO{sub 4}) mounted on rectangular photomultipliers in a detecting head connected to the electronics package by a signal cable.
Date: February 1, 2001
Creator: Bell, Z. W. & Moyer, M. W.
Partner: UNT Libraries Government Documents Department

Radionuclide separations using pillared layered materials

Description: This is the final report of a two-year Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Pillared Layered Materials (PLMs) are layered inorganic ion exchangers propped apart by metal oxide pillars. PLMs have been synthesized to sorb strontium from liquid nuclear wastes. A study that compared over 60 sorbers for their ability to sorb strontium from Hanford simulants showed that PLMs were the best sorbers; strontium distribution coefficients ({sup Sr}K{sub d}) > 20000 mL/g were obtained. In addition, PLMs showed a high degree of selectivity for strontium over cesium, transition metals, lanthanides and actinides. The sorption of strontium is, however, inhibited by complexants (EDTA); {sup Sr}K{sub d} values drop to <20 mL/g when they are present. The most promising PLMs were the Cr, Ti, Zr, and Si pillared tantalum tungstate. The K{sub d} values for Sr{sup 2+} and Ba{sup 2+} show a strong pH dependence; K{sub d} values increase to >10{sup 4} above pH 12. The general surface complexation mechanism explains the sorption of these cations on PLMs.
Date: December 31, 1998
Creator: Schroeder, N.C.; Wade, K.L. & Morgan, D.M.
Partner: UNT Libraries Government Documents Department

Neutron diffraction and scattering study on M/sub x/WO/sub 3/ (M=Rb and K)

Description: To study the relationship between the lattice instability and the superconductivity of nonstoichiometric hexagonal tungsten bronze, M/sub x/WO/sub 3/, neutron diffraction and scattering studies were made. Two types of the structural phase transitions were observed. One is associated with the distortion of the corner linked WO/sub 6/ octahedra. The other is associated with the ordering of the M atoms which partially fill the sites in the WO/sub 3/ cage. A long period modulation of the structure appears for some values of x at low temperature. The discussion on the x dependence of the superconducting transition temperature is presented.
Date: January 1, 1982
Creator: Sato, M.; Fujishita, H.; Moodenbaugh, A.R.; Hoshino, S. & Grier, B.H.
Partner: UNT Libraries Government Documents Department

Synthesis and properties of lanthanide-exchanged Preyssler`s heteropolyanions

Description: Na{sup +} in the Preyssler heteropolytungstate anion [NaP{sub 5}W{sub 30}O{sub 110}]{sup 14{minus}} can be exchanged for a trivalent lanthanide ion. The potential significance of this new class of lanthanide heteropolyanions relates to their applications in catalysis science. This view follows from the fact that Keggin heteropolyanions and their free acids are used as heterogeneous solid catalysts and homogeneous solution catalysts. The authors describe synthetic conditions that lead to the incorporation of Ce{sup 3+} and Pr{sup 3+} within the Preyssler anion, and the coprecipitation of Ce{sup 3+} and the Preyssler anion. Initial studies indicate that the latter, coprecipitated, material deserves study for bifunctional catalytic activity.
Date: December 1994
Creator: Antonio, M. R.; Malinsky, J. & Soderholm, L.
Partner: UNT Libraries Government Documents Department

Uranyl fluoride luminescence in acidic aqueous solutions

Description: Luminescence emission spectra and decay rates are reported for uranyl species in acidic aqueous solutions containing HF or added NaF. The longest luminescence lifetime, 0.269 {+-} 0.006 ms, was observed from uranyl in 1 M HF + 1 M HClO{sub 4} at 296 K and decreased with increasing temperature. Based on a luminescence dynamics model that assumes equilibrium among electronically excited uranyl fluoride species and free fluoride ion, this long lived uranyl luminescence in aqueous solution is attributed primarily to UO{sub 2}F{sub 2}. Studies on the effect of added LiNO{sub 3} or Na{sub 2}WO{sub 4}{center_dot}2H{sub 2}O showed relatively weak quenching of uranyl fluoride luminescence which suggests that high sensitivity determination of the UF{sub 6} content of WF{sub 6} gas should be feasible via uranyl luminescence analysis of hydrolyzed gas samples of impure WF{sub 6}.
Date: August 1, 1996
Creator: Beitz, J.V. & Williams, C.W.
Partner: UNT Libraries Government Documents Department

A study of the optical and radiation damage properties of lead tungstate crystals

Description: Lead tungstate (PbWO{sub 4}) is a new scintillating material which is of great interest for use in high energy electromagnetic calorimeters. It has a very high density, short radiation length and small Moliere radius and has a scintillation light output which peaks between 450--550 nm with a decay time in the range from 5--15 ns. It is presently being considered for use in two large, high resolution electromagnetic calorimeters, one for the CMS experiment and the other for the ALICE experiment, at the Large Hadron Collider at CERN. In order to meet the stringent demands of these two experiments, the crystals are required to be of high purity, produced uniform light output, and, in the case of CMS, be resistant to radiation damage up to several megarads. Here, a study has been made of the optical and radiation damage properties of undoped and niobium doped lead tungstate crystals. Data were obtained on the optical absorbance, the intensity and decay time of the scintillation light output, and the radioluminescence and photoluminescence emission spectra. Radiation damage was studied in several undoped and niobium doped samples using {sup 60}Co gamma ray irradiation. The change in optical absorption and observed scintillation light output was measured as a function of dose up to total cumulative doses on the order of 800 krad. The radiation induced phosphorescence and thermoluminescence was also measured, as well as recovery from damage by optical bleaching and thermal annealing. An investigation was also made to determine trace element impurities in several samples.
Date: December 31, 1995
Creator: Woody, C.L.; Kierstead, J.A.; Stoll, S.P.; Zhu, R.Y.; Ma, D.A. & Newman, H.B.
Partner: UNT Libraries Government Documents Department

Final Report: Acidic Properties of Doped Aerogels, April 19, 1993 - June 30, 1998

Description: Over this grant period we have studied extensively zirconia and alumina aerogels doped with a wide variety of dopants including silica, sulfate, phosphate, tungstate and combinations thereof. These results have deepened our understanding of the effects of dopants on acidic properties, which is the main goal of the project, and in particular led to the development of a hierarchy with which the Broensted acid strength of different samples can be meaningfully compared. We provide a more detailed description of several specific systems.
Date: June 30, 1998
Creator: Boyse, Raymond
Partner: UNT Libraries Government Documents Department

Current trends in scintillator detectors and materials

Description: The last decade has seen a renaissance in inorganic scintillator development for gamma ray detection. Lead tungstate (PbWO4) has been developed for high energy physics experiments, and possesses exceptionally high density and radiation hardness, albeit with low luminous efficiency. Lutetium orthosilicate or LSO (Lu2SiO5:Ce) possesses a unique combination of high luminous efficiency, high density, and reasonably short decay time, and is now incorporated in commercial positron emission tomography (PET) cameras. There have been advances in understanding the fundamental mechanisms that limit energy resolution, and several recently discovered materials (such as LaBr3:Ce) possess energy resolution that approaches that of direct solid state detectors. Finally, there are indications that a neglected class of scintillator materials that exhibit near band-edge fluorescence could provide scintillators with sub-nanosecond decay times and high luminescent efficiency.
Date: October 23, 2001
Creator: Moses, William W.
Partner: UNT Libraries Government Documents Department

A study of the optical band gap of lithium tungsten trioxide thin films

Description: The insertion of lithium (lithiation) into tungsten trioxide results in the formation of the tungsten bronze Li{sub x}WO{sub 3}. Polycrystalline, rf sputter deposited thin films of Li{sub x}WO{sub 3} were investigated for their application in Smart Window Devices. The optical band gap studies of these films revealed the narrowing of the intrinsic band gap as a consequence of lithium insertion. The results suggest that the rigid band model, which is generally adopted in interpreting the electronic structure of the tungsten bronzes may not be applicable in Li{sub x}WO{sub 3}. 14 refs., 2 tabs.
Date: January 1, 1990
Creator: Berera, G.; Goldner, R.B.; Arntz, F.O.; Wong, K.K.; Ciaccia, A.; Welch, M. et al.
Partner: UNT Libraries Government Documents Department

Hybrid Calorimeter Algorithm Development for Primex Experiment

Description: The PrimEx Collaboration seeks to measure the lifetime of the 0 meson (neutral pion) at high precision. The decay rate of the pion is considered to be the most fundamental prediction of low-energy quantum chromodynamics (QCD). Pions will be produced by the Primakoff Effect: a few GeV photon interacts with the coulomb field of a nucleus to produce a pion. The pion then decays almost immediately ({approx}10-16 seconds) into two photons. The decay photons will be detected by an electromagnetic hybrid calorimeter (HYCAL), an array of lead tungstate and lead glass crystals. An algorithm is needed to calculate the angular separation of the two decay photons (and thus the invariant mass of the pion) from the energies deposited in HYCAL. A GEANT Monte Carlo simulation of the experiment is used to test and develop the algorithm to achieve the best angular resolution. The development of the algorithm is essential to the PrimEx project.
Date: January 1, 2002
Creator: Motoyama, E.; Gasparian, A. & Bernstein, A.
Partner: UNT Libraries Government Documents Department

Fast neutron radiography research at ANL-W

Description: Thirty-seven different elements were tested for their suitability as converter screens for direct and indirect fast neutron radiography. The use of commercial X-ray scintillator screens containing YTaO{sub 4}, LaOBr:Tm, YTaO{sub 4}:Nb, YTaO{sub 4}:Tm, CaWO{sub 4}, BaSO{sub 4}:Sr, and GdO{sub 2}S:Tb was also explored for direct fast neutron radiography. For the indirect radiographic process, only one element, holmium, was found to be better than copper. Iron was also found to work as well as copper. All other elements that were tested were inferior to copper for indirect fast neutron radiography. For direct fast neutron radiography, the results were markedly different. Copper was found to be a poor material to sue, as thirty-two of the elements performed better than the copper. Tantalum was found to be the best material to use. Several other materials that also performed remarkably well include, in order of decreasing utility, gold, lutetium, germanium, dysprosium, and thulium. Several interesting results were obtained for the commercial X-ray scintillator screens. Most notably, useful radiographs were produced with all of the various scintillation screens. However, the screens containing YTaO{sub 4}:Nb offered the greatest film densities for the shortest exposure times. Screens using GdSO{sub 4}:Tb provided the best resolution and clearest images at the sacrifice of exposure time. Also, as previous researchers found, scintillator screens offered significantly shorter exposure times than activation foils.
Date: June 1, 1996
Creator: Klann, R.T. & Natale, M.D.
Partner: UNT Libraries Government Documents Department

Integrated readout electronics for the PbWO{sub 4} photon spectrometer

Description: The PbWO{sub 4} calorimeter of the ALICE detector is designed to detect the prompt photons to provide direct information on the partonic, early phases of the heavy-ion interaction. The goal is to measure all the photons over a large enough solid angle to reconstruct both {pi}{sup 0}`s and {eta}`s. A proposed readout system for the ALICE PbWO{sub 4} photon spectrometer is presented. In one proposed implementation, light will be detected from each end of the crystals by PIN photodiodes and this signal will be amplified by charge-sensitive amplifiers. The 73,728 channel readout system will accept the preamplifier signals and deliver digitized data to the data collection modules. A readout board will consist of 8-channel, custom front-end chips which form energy and timing signals, and board-level control and communication circuits. Many of the subcircuits proposed for this spectrometer have been developed for use in other applications. The performance of these circuits is shown.
Date: December 31, 1995
Creator: Simpson, M.L.; Alley, G.T. & Awes, T.
Partner: UNT Libraries Government Documents Department