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Second crystal cooling on cryogenically cooled undulator and wiggler double crystal monochromators.

Description: Simple methods for the cooling of the second crystals of cryogenically cooled undulator and wiggler double crystal monochromators are described. Copper braids between the first and second crystals are used to cool the second crystals of the double crystal monochromators. The method has proved successful for an undulator monochromator and we describe a design for a wiggler monochromator.
Date: August 3, 1998
Creator: Knapp, G. S.
Partner: UNT Libraries Government Documents Department

Exploratory heat transfer studies on critical elements of a proposed 6 GeV synchrotron

Description: Certain types of insertion devices for angiography, can produce extraordinarily large heat fluxes on critical components of a synchrotron beam line and its optics. The shutters, beam splitters, filters, and the first-stage monochromators all are subjected to large fluxes of radiation. The cooling requirements of such beam line components are approached in a comprehensive manner to identify the governing parameters from first principles. Analytical techniques have been used to study various methods of handling the heat loads using both liquid metal and water coolants for various potential heated geometries. It is found that when properly designed, liquid metal cooling can be much more efficient. In addition, composites and low Z surfaces have been considered. Also investigated are the heat transfer problems of the optical stages and rotating monochromators.
Date: November 1, 1985
Creator: Kuzay, T.M. & Knapp, G.S.
Partner: UNT Libraries Government Documents Department

High resolution monochromator systems using thermal gradient induced variable Bragg spacing

Description: The vertical divergences of bending magnet and wiggler synchrotron sources are generally considerably larger than the acceptance angles of typical monochromator systems. This is particularly true at high energies (E greater than or equal to 14 keV) where the Darwin widths of perfect crystals are of the order 10/sup -6/ radians. By imposing a thermal gradient on the crystal, an efficient, wide acceptance angle monochromator can be obtained. The necessary condition being that the resulting d . sin theta is a constant across the beam. Gains in intensity of 3 to 100 can be realized relative to standard flat crystal systems. A number of possible designs are presented for both two and four crystal monochromator systems. The use of Si, Ge, and quartz monochromators are discussed.
Date: July 1, 1985
Creator: Knapp, G.S. & Smither, R.K.
Partner: UNT Libraries Government Documents Department

Extended x-ray absorption fine structure (EXAFS) studies of the actinides

Description: The basic EXAFS parameters of the backscattering amplitude and phase shift have been computed as a function of k for the neutral atoms of Th, U, Np and Pu. It is found that an anomalous variation of the backscattering phase shift with respect to k occurs for the actinide elements at approximately k = 7 A/sup -1/. However, this variation is monotonic, unlike those for Pb and a few other lighter elements. It is also found that the detailed behavior of the parameters is sensitive to the distribution of electrons in the 5f open shell. Comparison with experiments on uranium arsenide and selenide emphasizes the need for careful modeling of the 5f electronic configuration.
Date: July 1, 1984
Creator: Chan, S.K. & Knapp, G.S.
Partner: UNT Libraries Government Documents Department

Calorimetric study of the intermetallic compounds UAl$sub 2$ and PuAl$sub 2$

Description: Results of low temperature specific heat measurements are presented on the strongly paramagnetic intermetallic compounds UAl$sub 2$ and PuAl$sub 2$ in the temperature intervals 0.9 to 20$sup 0$K, respectively. These compounds are characterized by very narrow 5f bands near the Fermi energy. The low-temperature properties of UAl$sub 2$ and PuAl$sub 2$ are dominated by long lived spin fluctuations within these narrow bands. In UAl$sub 2$ a nearly field-independent T$sup 3$logT contribution dominates the specific heat below 10$sup 0$K, consistent with the predictions of ferromagnetic spin-fluctuation theory. The specific heat, static susceptibility, and electrical resistivity are mutually consistent with T/sub sf/ = 25 +- 10$sup 0$K, where T/sub sf/ is the characteristic spin-fluctuation temperature of the system. Below 20$sup 0$K, the specific heat of PuAl$sub 2$ contains a very large linear term, C greater than or approximately equal to 260T (mJ/mole-$sup 0$K), which is approximately four times the magnitude of the measured susceptibility, when both quantities are expressed in the same units. The specific heat of PuAl$sub 2$ exhibits no anomalous behavior below 10$sup 0$K, where a resistivity anomaly has been previously observed. The properties of PuAl$sub 2$ are qualitatively discussed in terms of antiferromagnetic spin fluctuations. (auth)
Date: January 1, 1975
Creator: Trainor, R. J.; Brodsky, M. B. & Knapp, G. S.
Partner: UNT Libraries Government Documents Department

Mode softening and high superconducting transition temperature in some A-15 compounds

Description: The electronic density of states at the Fermi level, N(E/sub F/), and the geometric mean phonon frequencies, $omega$/sub g/, were determined from heat- capacity data for a number of A-15 superconductors. Although $omega$/sub g/ is an appropriate average phonon parameter for evaluating McMillan's expression for lambda, it was found that the T/sub c/ values cannot be reliably estimated using $omega$/sub g/. There are, however, strong correlations between lambda, N(E/sub F/), and the temperature dependence of $omega$/sub g/, dln$omega$/sub g//dT. The high-T/sub c/, high-N(E/sub F/) materials V$sub 3$Si and V$sub 3$Ga show the largest phonon-mode softening on cooling. It is proposed that, for the higher- N(E/sub F/) materials, particular phonon-modes strongly couple to the electronic system and enhance T/sub c/ to a greater extent than average phonon properties would indicate. (auth)
Date: January 1, 1975
Creator: Knapp, G. S.; Bader, S. D. & Fisk, Z.
Partner: UNT Libraries Government Documents Department

Length of beamlines and width of the experimental hall at a 6-GeV synchrotron facility

Description: The width of the experimental hall at a 6-GeV facility is closely related to the length of the beamlines. This note addresses this aspect in some detail. In general, no two beamlines will have identical lengths or the placement of various optical elements. Hence fixing the beamline lengths prior to their assignment to specific experiments is difficult. In spite of this fact, a few general conclusions can be made. 1. At least 25 m of all the beamlines will be behind the shielding wall. Within this length many beamline components can be accommodated. 2. For most beamlines on bending magnets, the first optical element will be at 30 m. For a 3:1 aspect ratio for the optics, the hutch will be at about 40-50 m. This will cover most of the general applications like absorption spectroscopy, diffraction, etc. 3. The undulator beamlines will have to be somewhat longer with the experimental hutch located at about 70-80 m for most investigations. This demands the width of the hall to be about 32 m measured from the beamline to the ring road.
Date: November 10, 1985
Creator: Shenoy, G.K. & Knapp, G.S.
Partner: UNT Libraries Government Documents Department

Liquid-metal-cooled, curved-crystal monochromator for Advanced Photon Source bending-magnet beamline 1-BM

Description: The authors describe a horizontally focusing curved-crystal monochromator that invokes a 4-point bending scheme and a liquid-metal cooling bath. The device has been designed for dispersive diffraction and spectroscopy in the 5--20 keV range, with a predicted focal spot size of {le} 100 {micro}m. To minimize thermal distortions and thermal equilibration time, the 355 x 32 x 0.8 mm crystal will be nearly half submerged in a bath of Ga-In-Sn-Zn alloy. The liquid metal thermally couples the crystal to the water-cooled Cu frame, while permitting the required crystal bending. Calculated thermal profiles and anticipated focusing properties are discussed.
Date: June 1, 1996
Creator: Brauer, S.; Rodricks, B.; Assoufid, L.; Beno, M.A. & Knapp, G.S.
Partner: UNT Libraries Government Documents Department

On the use of electronic tilt sensors as angle encoders for synchrotron applications

Description: The authors have tested several electrolytic tilt sensors produced by Applied Geomechanics Inc. A pair of sensors were tested by mounting them on the Chi circle of a Huber 4 circle diffractometer. The angles were scanned in 1{degrees} intervals over a range of {+-}35{degrees}. In these tests the resolution was about {+-}5 {mu}rad but the repeatability depended on angle and varied from 70 {mu}rad (one standard deviation) at large angles to 7 {mu}rad at small angles. This type of tilt sensor may be too slow (2-10 second settling time) as a primary angle encoder for a monochromator or diffractometer, but for a system run by stepping motors, they would prove quite useful as secondary angle encoders. Other models which have a narrower angular range would be useful in setting and tuning focusing mirrors.
Date: September 1, 1994
Creator: Knapp, G.S.; You, H. & Holzhausen, G.R.
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

Development of a monochromator system for the APS X-ray BESSRC beamlines

Description: The authors have designed a double crystal, fixed exit monochromator which allows windowless operation of the APS beamlines. The crystals are mounted on a turntable with the first crystal at the center of rotation. A mechanical linkage is used to correctly position the second crystal and maintain a constant offset. The monochromator is designed with two adjacent vacuum chambers, one containing the drive mechanism, a vacuum compatible Huber goniometer, and another chamber containing a turntable on which the monochromator linkage and crystals are mounted. The small annular opening around a hollow stainless steel shaft which connects the Huber goniometer to the turntable is the only passage between the two adjacent chambers. The design of the monochromator is such that it can accommodate water, liquid nitrogen or galium cooling for the crystal optics. The basic design for the monochromator linkage mechanism is presented along with details of the monochromator chamber. The results of initial optical tests of the monochromator system using tilt sensors and a precision autocollimator will also be given.
Date: March 1, 1997
Creator: Beno, M.A.; Knapp, G.S. & Ramanathan, M.
Partner: UNT Libraries Government Documents Department

High heat load crystal cooling strategies for an APS wiggler beamline

Description: High energy wigglers produce extremely high total powers. For example, the insertion device for one beamline of the Basic Energy Sciences Synchrotron Research Center (BESSRC) is an elliptical multipole wiggler (EMPW) which can generate circularly polarized X-rays on axis and produces a total power of {approximately}8 kW. This insertion device will be used to simultaneously provide x-rays to three branch lines, a branch equipped with a normal double crystal monochromator feeding a scattering and spectroscopy station, and two branches with single-bounce horizontally deflecting monochromators for Compton scattering and High Energy Diffraction. The crystal optics for this type of device require substantially different heat load solutions than those used for undulator beamlines. We will discuss how the beam is split and shared among the beamline branch lines and present the crystal cooling strategies employed for both the double-crystal monochromator and horizontally deflecting single-bounce monochromators.
Date: July 1, 1997
Creator: Beno, M.A.; Knapp, G.S. & Engbretson, M.
Partner: UNT Libraries Government Documents Department

High resolution bragg focusing optics for synchrotron monochromators and analyzers

Description: A number of different applications for high resolution Bragg Focusing Optics are reviewed. Applications include Sagittal Focusing, Energy Dispersive optics for x-ray absorption and diffraction, a curved analyzer-multichannel detector method for efficient acquisition of powder and small angle scattering data, the use of Backscattering Analyzers for very high resolution inelastic scattering, and curved crystals for high energy applications.
Date: July 1, 1997
Creator: Knapp, G.S.; Beno, M.A. & Gofron, K.J.
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

Bonding of metal oxides in sodium silicate glass

Description: X-ray photoelectron spectroscopy (XPS) and extended x-ray absorption fine structure (EXAFS) studies have been undertaken on sodium disilicate glasses containing varying amounts of Fe/sub 2/O/sub 3/ and UO/sub 2/. The XPS results enable one to distinguish the different bonding characteristics of iron and uranium in these glasses. A three dimensional model for the iron coordination in the sodium disilicate glass is inferred from the combined XPS and EXAFS results.
Date: January 1, 1978
Creator: Lam, D.J.; Veal, B.W.; Chen, H. & Knapp, G.S.
Partner: UNT Libraries Government Documents Department

EXAFS studies of sodium silicate glasses containing dissolved actinides

Description: Sodium silicate glasses containing dissolved Th, U, Np, and Pu have been studied using the EXAFS technique. Th/sup 4 +/, U/sup 4 +/, Np/sup 4 +/, and Pu/sup 4 +/ ions in the silicate glasses are 8-fold coordinated to oxygen neighbors. The higher valent U/sup 6 +/ and Np/sup 5 +/ ions have complex local symmetries. The U/sup 6 +/ ions appear in a uranyl configuration with 2 oxygen atoms at 1.85A and 4 at 2.25A from the U ion. The Np/sup 5 +/ local symmetry is more complex and difficult to determine uniquely. The U/sup 6 +/ glasses show substantial clustering of the uranium atoms. A structural model, with nearly planar uranyl sheets sandwiched between alkali and silica layers, is used to explain the U/sup 6 +/ EXAFS data. This model allows us to understand why U/sup 6 +/ ions are much more soluble in the glasses than the actinide 4/sup +/ ions. 4 references, 2 figures.
Date: July 1, 1984
Creator: Knapp, G.S.; Veal, B.W.; Paulikas, A.P.; Mitchell, A.W.; Lam, D.J. & Klippert, T.E.
Partner: UNT Libraries Government Documents Department

Further tests on liquid-nitrogen-cooled, thin silicon-crystal monochromators using a focused wiggler synchrotron beam

Description: A newly designed cryogenically cooled, thin Si crystal monochromator was tested at the European Synchrotrons Radiation Facility (ESRF) beamline BL3. It exhibited less than 1 arcsec of thermal strain up to a maximum incident power of 186 W and average power density of 521 W/mm{sup 2}. Data were collected for the thin (0.7 mm) portion of the crystal and for the thick (>25 mm) part. Rocking curves were measured as a function of incident power. With a low power beam, the Si(333) rocking curve at 30 keV for the thin and thick sections was < 1 arcsec FWHM at room temperature. The rocking curve of the thin section increased to 2.0 arcsec when cooled to 78 K, while the thick part was unaffected by the reduction in temperature. The rocking curve of the this section broadened to 2.5 arcsec FWHM and that of the thick section broadened to 1.7 arcsec at the highest incident power. The proven range of performance for this monochromator has been extended to the power density, but not the absorbed power, expected for the Advanced Photon Source (APS) undulator A in closed-gap operation (first harmonic at 3.27 kev) at a storage-ring current of 300 mA.
Date: May 9, 2000
Creator: Rogers, C. S.; Mills, D. M.; Fernandez, P. B.; Knapp, G. S.; Wulff, M.; Hanfland, M. et al.
Partner: UNT Libraries Government Documents Department

A shutter design for time domain studies using synchrotron radiation at the advanced photon source

Description: In general a variable repetition rate of the x-ray bunches is needed to explore time domain problems using x-ray radiation. In some instances the results of several hundreds or thousands of x-ray pulses must be averaged requiring the sample to be in the same time dependent state each time the monitoring pulse strikes. In the most advanced and most detailed version of this type experiment an intense laser pulse would be used to create an excited state from a relaxed ground state. An additional probe-pulse'' that follows the laser pump-pulse'' would examine the sample. The important point is that before a second x-ray pulse hits the sample, the system must return to its initial relaxed ground state prior to another laser pulse in order to prepare the same excited state again. Otherwise the second x-ray probes a different condition of the system than the previous x-ray bunch such that any data averaging scheme would be invalid. Our system is primarily designed for the Advanced Photon source (APS) at Argonne National Laboratory. In the 20-bunch mode of APS an x-ray pulse will occur every 177 nanoseconds, requiring each edge of a conventional two-blade shutter'' to travel at least 0.25 mm in {approximately}177 nanoseconds. Our key design principle employs a subsonic, rotating mirror whose period is slaved to the synchrotron intra-pulse period. The synchrotron x-ray bunches will be reflected a distance of about two meters to a narrow 0.5 mm slit just in front of the sample. The time that the reflected synchrotron spends striking the slit is given by 1/(4{pi}rf) where r is the radius from the center of the spindle to the slit, and f is the frequency of rotation of the spindle. A mirror rotating at a low 7,500 rpm (125 Hz) is sufficient to select a single synchrotron ...
Date: September 1, 1991
Creator: Norris, J.R.; Bowman, M.K.; Chen, L.; Tang, J.; Thurnauer, M.C.; Knapp, G.S. et al.
Partner: UNT Libraries Government Documents Department

In situ x-ray diffraction study of CoSi{sub 2} formation during annealing of a Co/Ti bilayer on Si*(100)

Description: X-ray diffraction (XRD) was performed in situ during annealing of a Co/Ti/Si(001) multilayer, which produced an epitaxial CoSi{sub 2} layer. The results indicate that the Ti layer did. not stay intact during the reaction, and thus could not act like a membrane, moderating Co/Si interdiffusion. A strongly textured metastable phase (M) formed prior to CoSi{sub 2} nucleation. This intermediary reaction product was unobservable upon completion of the anneal. We report that nucleation and growth of CoSi{sub 2} on Si(100) took place in the presence of M, a new Co-Ti-Si-(O) phase, located at the metal/Si interface. M might play an important role in the perfection of the silicide. Ti and Co metals intermix already below 300{degrees}C, and there was evidence that metallic Ti precipitated at the surface, commencing at 550{degrees}C.
Date: June 1, 1995
Creator: Selinder, T.I.; Roberts, T.A.; Miller, D.J.; Beno, M.A.; Knapp, G.S.; Gray, K.E. et al.
Partner: UNT Libraries Government Documents Department