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A study of stability of tungstophosphoric acid, H{sub 3}PW{sub 12}O{sub 40}, using synchrotron XPS, XANES, Hexane cracking, XRD and IR spectroscopy

Description: Tungstophosphoric Acid (HPW) has been investigated using different spectroscopic and chemical techniques. Bulk sensitive techniques such as x-ray diffract ion (XRD) and infrared (IR) spectroscopy indicate that the acid is stable at temperatures as high as 300 degrees C or higher. However, our work suggests that HPW starts loosing stability at temperature as low as 200 degrees C. For instance, P 2p peak was not detected in the XPS spectrum of HPW preheated at 100 degrees C, but was clearly observed after preheating the acid at 200 degrees C and 400 degrees C. This suggests the destruction of the molecules of the surface leading to the enrichment of surface with phosphorus. These results may explain why HPW deactivates very fast, e.g., 8 min at 200 degrees C, in hexane cracking experiments. This could limit the use of HPW in surface reactions that even require moderate temperatures. Detailed infrared spectroscopic investigation of the HPW as a function of temperature showed a gradual in crease in absorbance of the W-O-W corner shared vibration relative to the absorbance of the other bands. This indicates that the symmetry, and hence the stability, of the molecule was decreased upon heating.
Date: June 7, 2002
Creator: Jalil, Pasl A.; Faiz, M.; Tabet, N.; Hamdan, N.M. & Hussain, Z.
Partner: UNT Libraries Government Documents Department

High resolution XPS study of oxide layers grown on Ge substrates

Description: High resolution X-ray Photoelectron Spectroscopy (XPS) was used to analyze thin layers of germanium oxide grown on germanium substrates under various conditions. The results reveal the presence of high density of electron states located at the oxide/germanium interface that lead to the energy band bending. The surface of native oxide layers and that of thin oxide layer grown under dry oxygen correspond to GeO2 composition. Under Ar etching, lower oxidation states were revealed. Short in-situ heat treatment at T=400 degrees C under ultra high vacuum leads to the removal of the oxide layer. In addition, the analysis of the layer grown at T=380 degrees C under dry oxygen suggest that carbides form at the oxide/substrate interface.
Date: July 29, 2002
Creator: Tabet, N.; Faiz, M.; Hamdan, N.M. & Hussain, Z.
Partner: UNT Libraries Government Documents Department

A space bourne crystal diffraction telescope for the energy range of nuclear transitions

Description: Recent experimental work of the Toulouse-Argonne collaboration has opened for perspective of a focusing gamma-ray telescope operating in the energy range of nuclear transitions, featuring unprecedented sensitivity, angular and energy resolution. The instrument consists of a tunable crystal diffraction lens situated on a stabilized spacecraft, focusing gamma-rays onto a small array of Germanium detectors perched on an extendible boom. While the weight of such an instrument is less than 500 kg, it features an angular resolution of 15 in., an energy resolution of 2 keV and a 3 {sigma} narrow line sensitivity of a few times 10{sup {minus}7} photons s{sup {minus}1} cm{sup {minus}2} (10{sup 6} sec observation). This instrumental concept permits observation of any identified source at any selected line-energy in a range of typically 200 keV to 1300 keV. The resulting ``sequential`` operation mode makes sites of explosive nucleosynthesis natural scientific objectives for such a telescope: the nuclear lines of extragalactic supernovae ({sup 56}Ni, {sup 44}Ti, {sup 60}Fe) and galactic novae (p{sup {minus}}p{sup +} line, {sup 7}Be) are accessible to observation, one at a time, due to the erratic appearance and the sequence of half-lifes of these events. Other scientific objectives, include the narrow 511 keV line from galactic broad class annihilators (such as 1E1740-29, nova musca) and possible redshifted annihilation lines from AGN`s.
Date: October 1, 1995
Creator: von Ballmoos, P.; Naya, J.E.; Albernhe, F.; Vedrenne, G.; Smither, R.K.; Faiz, M. et al.
Partner: UNT Libraries Government Documents Department

Crystal diffraction lens telescope for focusing nuclear gamma rays

Description: A crystal diffraction lens was constructed at Argonne National Laboratory for use as a telescope to focus nuclear gamma rays. It consisted of 600 single crystals of germanium arranged in 8 concentric rings. The mounted angle of each crystal was adjusted to intercept and diffract the incoming gamma rays with an accuracy of a few arc sec. The performance of the lens was tested in two ways. In one case, the gamma rays were focused on a single medium size germanium detector. In the second case, the gamma rays were focused on the central germanium detector of a 3 x 3 matrix of small germanium detectors. The efficiency, image concentration and image quality, and shape were measured. The tests performed with the 3 x 3 matrix detector system were particularly interesting. The wanted radiation was concentrated in the central detector. The 8 other detectors were used to detect the Compton scattered radiation, and their energy was summed with coincident events in the central detector. This resulted in a detector with the efficiency of a large detector (all 9 elements) and the background of a small detector (only the central element). The use of the 3 x 3 detector matrix makes it possible to tell if the source is off axis and, if so, to tell in which direction. The crystal lens acts very much like a simple convex lens for visible light. Thus if the source is off to the left then the image will focus off to the right illuminating the detector on the right side: telling one in which direction to point the telescope. Possible applications of this type of crystal lens to balloon and satellite experiments will be discussed.
Date: August 1, 1996
Creator: Smither, R.K.; Fernandez, P.B.; Graber, T.; Ballmoos, P. von; Naya, J.; Albernhe, F. et al.
Partner: UNT Libraries Government Documents Department

Experimental results obtained with the positron-annihilation- radiation telescope of the Toulouse-Argonne collaboration

Description: We present laboratory measurements obtained with a ground-based prototype of a focusing positron-annihilation-radiation telescope developed by the Toulouse-Argonne collaboration. This balloon-borne telescope has been designed to collect 511-keV photons with an extremely low instrumental background. The telescope features a Laue diffraction lens and a detector module containing a small array of germanium detectors. It will provide a combination of high spatial and energy resolution (15 arc sec and 2 keV, respectively) with a sensitivity of {approximately}3{times}10{sup {minus}5} photons cm{sup {minus}2}s{sup {minus}1}. These features will allow us to resolve a possible narrow 511-keV line both energetically and spatially within a Galactic center ``microquasar`` or in other broad-class annihilators. The ground-based prototype consists of a crystal lens holding small cubes of diffracting germanium crystals and a 3{times}3 germanium array that detects the concentrated beam in the focal plane. Measured performances of the instrument at different line energies (511 keV and 662 keV) are presented and compared with Monte-Carlo simulations. The advantages of a 3{times}3 Ge-detector array with respect to a standard-monoblock detector have been confirmed. The results obtained in the laboratory have strengthened interest in a crystal-diffraction telescope, offering new perspectives for die future of experimental gamma-ray astronomy.
Date: October 1, 1995
Creator: Naya, J.E.; von Ballmoos, P.; Albernhe, F.; Vedrenne, G.; Smither, R.K.; Faiz, M. et al.
Partner: UNT Libraries Government Documents Department

Review of crystal diffraction and its application to focusing energetic gamma rays

Description: The basic features of crystal diffraction and their application to the construction of a crystal diffraction lens for focusing energetic gamma rays are described using examples from the work preformed at the Argonne National Laboratory. Both on-axis and off-axis performance are discussed. The review includes of normal crystals, bent crystals, and crystals with variable crystal-plane spacings to develop both condenser-type lenses and point-to-point imaging lenses.
Date: October 1, 1995
Creator: Smither, R.K.; Fernandez, P.B.; Graber, T.; von Ballmoos, P.; Naya, J.; Albernhe, F. et al.
Partner: UNT Libraries Government Documents Department

A space crystal diffraction telescope for the energy range of nuclear transitions

Description: This paper contains literature from American Power Conference Air Toxics Being Measured Accurately, Controlled Effectively NO{sub x} and SO{sub 2} Emissions Reduced; Surface Condensers Improve Heat Rate; Usable Fuel from Municipal Solid Waste; Cofiring Technology Reduces Gas Turbine Emissions; Trainable, Rugged Microsensor Identifies of Gases; High-Tc Superconductors Fabricated; High-Temperature Superconducting Current Leads; Vitrification of Low-Level Radioactive and Mixed Wastes; Characterization, Demolition, and Disposal of Contaminated Structures; On-Line Plant Diagnostics and Management; Sulfide Ceramic Materials for Improved Batteries; Flywheel Provides Efficient Energy Storage; Battery Systems for Electric Vehicles; Polymer-Electrolyte Fuel Cells for Transportation; Solid-Oxide Fuel Cells for Transportation; Surface Acoustic Wave Sensor Monitors Emissions in Real-Time; Advance Alternative-Fueled Automotive Technologies; Thermal & Mechanical Process; Flow-Induced Vibration & Flow Distribution in Shell-and-Tube Heat Exchangers; Ice Slurries for District Cooling; Advanced Fluids; Compact Evaporator and Condenser Technology; and Analysis of Failed Nuclear Power Station Components.
Date: April 1, 1995
Creator: von Ballmoos, P.; Naya, J.E.; Albernhe, F.; Vedrenne, G.; Smither, R.K.; Faiz, M. et al.
Partner: UNT Libraries Government Documents Department