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Rf phase measurement at PHERMEX (Pulsed High Energy Radiographic Machine Emitting X-Rays) using time-to-digital converters

Description: Recent advances in time-to-digital converters (TDCs) have made 50-MHz rf phase measurement possible without the use of double-balanced mixers. These advances allow zero crossing discriminators to be used in conjunction with fast CAMAC TDCs to make amplitude-independent phase measurements. This method uses a time interval proportional to the phase angle, thus eliminating any of the calculations and calibration required with double-balanced mixers. 4 refs., 1 fig., 1 tab.
Date: January 1, 1989
Creator: Watson, S.A.; Jennings, G.R. & Moir, D.C.
Partner: UNT Libraries Government Documents Department

Why cryogenically cooled, thin crystals handle extremely high power densities

Description: Recently, a new type of cryogenically cooled high heat load monochromator was proposed and, developed at Argonne National Laboratory and tested at European Synchrotron Radiation Facility (ESRF.) These tests showed that powers of 153 W and power densities of 450 W/mm{sup 2} cause only negligible strain. These powers and power densities are larger than will be absorbed by the first crystal on an undulator beamline at the Advanced Photon Source (APS). In our earlier work we suggested that the crystal might show strain at much lower values of the powers and power densities. We now can explain the ESRF results in terms of the unique role the negative thermal expansion coefficient of Si plays in minimizing strain.
Date: September 1, 1995
Creator: Knapp, G.S.; Jennings, G. & Beno, M.A.
Partner: UNT Libraries Government Documents Department

Synchrotron and laboratory studies utilizing a new powder diffraction technique

Description: We have developed a new type of powder diffractometer that is much more efficient than existing methods. The diffractometer has the potential of both high count rates and very high resolution when used at a synchrotron source. The laboratory based instrument has an order of magnitude improvement in count rate over existing methods. The method uses a focusing diffracted beam monochromator in combination with a multichannel detector. The incident x-rays fall on a flat plate or capillary sample and are intercepted by a bent focusing monochromator which has the focus of the bend at the sample surface. The powder diffraction lines emerging from the bent crystal monochromator are detected by a linear or 2-dimensional detector. This allows us to eliminate the background from fluorescence or other scattering and to take data over a range of 3{degrees} to 4{degrees} instead of one angle at a time thereby providing a large improvement over conventional diffractometers. Results are presented for fluorapatite Fe{sub 2}O{sub 3}, and a high-TC superconductor.
Date: October 1, 1992
Creator: Knapp, G. S.; Beno, M. A.; Jennings, G.; Engbretson, M. & Ramanathan, M.
Partner: UNT Libraries Government Documents Department

Synchrotron and laboratory studies utilizing a new powder diffraction technique

Description: We have developed a new type of powder diffractometer that is much more efficient than existing methods. The diffractometer has the potential of both high count rates and very high resolution when used at a synchrotron source. The laboratory based instrument has an order of magnitude improvement in count rate over existing methods. The method uses a focusing diffracted beam monochromator in combination with a multichannel detector. The incident x-rays fall on a flat plate or capillary sample and are intercepted by a bent focusing monochromator which has the focus of the bend at the sample surface. The powder diffraction lines emerging from the bent crystal monochromator are detected by a linear or 2-dimensional detector. This allows us to eliminate the background from fluorescence or other scattering and to take data over a range of 3[degrees] to 4[degrees] instead of one angle at a time thereby providing a large improvement over conventional diffractometers. Results are presented for fluorapatite Fe[sub 2]O[sub 3], and a high-TC superconductor.
Date: October 1, 1992
Creator: Knapp, G.S.; Beno, M.A.; Jennings, G.; Engbretson, M. & Ramanathan, M.
Partner: UNT Libraries Government Documents Department

Magnetic x-ray measurements using the elliptical multipole wiggler

Description: The EMW at the BESSRC beam lines at the APS provides high photon flux at high energies with the capability of producing circular polarization on axis. The authors observe a high degree of circularly polarized x-rays at such energies. The polarization and frequency tunability of the elliptical multipole wiggler (EMW) is an ideal source for many magnetic measurements from X-ray Magnetic Circular Dichroism (XMCD) to Compton scattering experiments. They performed Compton scattering measurements to determine the polarization and photon flux at the sample as a function of the deflection parameters K{sub y} and K{sub x}. They used for their measurements a Si (220) Laue monochromator providing simultaneous photon energies at 50 keV, 100 keV and 150 keV. Magnetic Compton Profiles were determined by either switching the magnet polarity or the photon helicity. The results obtained using Fe(110) single crystals were very similar.
Date: October 26, 1999
Creator: Montano, P. A.; Li, Y.; Beno, M. A.; Jennings, G. & Kimball, C. W.
Partner: UNT Libraries Government Documents Department

Cryogenic monochromator as a solution to undulator heat loads at third generation synchrotron sources

Description: We have developed a new design for a cryogenically cooled monochromator employing a thin-crystal strategy which is capable of handling the central-cone power of the Advanced Photon Source`s Undulator A at closed gap and at the full design current of 300 mA. We have designed and fabricated a Si (111) crystal which has a thin section where the x-rays hit and has internal cooling channels. A invar manifold has also been designed and it will be attached to the Si via In gaskets. We have done detailed modeling, both with approximate analytical and with finite element calculations. The results shown that our design has negligible thermal strain even for closed gap operation.
Date: October 1, 1994
Creator: Knapp, G. S.; Rogers, C. S.; Beno, M. A.; Jennings, G. & Cowan, P. L.
Partner: UNT Libraries Government Documents Department

An object-oriented implementation of a graphical-programming system

Description: Object-oriented (OO) analysis, design, and programming is a powerful paradigm for creating software that is easily understood, modified, and maintained. In this paper the authors demonstrate how the OO concepts of abstraction, inheritance, encapsulation, polymorphism, and dynamic binding have aided in the design of a graphical-programming tool. The tool that they have developed allows a user to build radiographic system models for computing simulated radiographic data. It will eventually be used to perform Bayesian reconstructions of objects given radiographic data. The models are built by connecting icons that represent physical transformations, such as line integrals, exponentiation, and convolution, on a canvas. They will also briefly discuss ParcPlace`s application development environment, VisualWorks, which they have found to be as helpful as the OO paradigm.
Date: April 1, 1994
Creator: Cunningham, G. S.; Hanson, K. M.; Jennings, G. R. Jr. & Wolf, D. R.
Partner: UNT Libraries Government Documents Department

Coordination and valence of europium in [Eu({alpha}-2-As{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup 17{minus}} and [Eu(W{sub 5}O{sub 18}){sub 2}]{sup 9{minus}}

Description: Europium L{sub 3}-edge X-ray absorption fine structure (XAFS) spectroelectrochemistry was used to determine the valence of europium in [Eu({alpha}-2-As{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup 17{minus}} and [Eu(w{sub 5}O{sub 18}){sub 2}]{sup 9{minus}}. Dilute solutions of these anions in aqueous supporting electrolytes were examined at ambient temperature and at extreme potentials. In situ XANES (X-ray absorption near edge structure) data revealed that Eu is trivalent in both [Eu({alpha}-2-As{sub 2}W{sub 17}O{sub 61}){sub 2}]{sup 17{minus}} and [Eu(W{sub 5}O{sub 18}){sub 2}]{sup 9{minus}} at rest potential. Furthermore, it was not reduced to Eu{sup 2+} by constant-potential bulk electrolysis at significantly reducing potentials under the electrochemical conditions used herein. These results stand in obvious contrast to the redox behavior of [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12{minus}}, in which Eu{sup 3+} is reduced to Eu{sup 2+} under similar electrochemical conditions.
Date: September 1, 1997
Creator: Antonio, M.R.; Soderholm, L.; Jennings, G.; Francesconi, L.C.; Dankova, M. & Bartis, J.
Partner: UNT Libraries Government Documents Department

An x-ray fluorescence study of lake sediments from ancient Turkey using synchrotron radiation.

Description: Sediments from relic Lake Golbasi were analyzed by X-ray fluorescence with synchrotrons radiation to determine changes in element concentrations over time with selected elements serving as proxies for environmental change. Increases in Ca and Sr suggest soil formation during a dry period, from ca. 4500 BC to ca. 200 AD at which point K, Rb, Zr, Ti, and Y increase, indicating the return of a wet environment. Soil erosion, represented by Cr and Ni, increases ca. 7000 BC, probably as a consequence of environmental change, prior to suggested exploitation of natural resources by the newly urbanized society of the third millennium BC.
Date: March 10, 1999
Creator: Alatas, A.; Alp, E. E.; Friedman, E. S.; Jennings, G.; Johnson, C. E.; Lai, B. et al.
Partner: UNT Libraries Government Documents Department