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Preparation of high-purity beryllium foils

Description: A technique is described for the preparation of beryllium foils by vapor deposition. The high-purity, pinhole-free foils are vacuum tight and suitable for many x-ray analysis applications. The beryllium is evaporated from an electron beam heated crucible source onto a heated substrated. Substrate temperatures of 450 to 700/sup 0/C are necessary to obtain the desired mechanical properties of the foils. At these temperatures, contamination of the foils by diffusion of the substrate material into the beryllium can be a significant problem, as impurity levels of more than several hundred ppM are detrimental to the x-ray transparency of the windows. This problem is minimized by careful selection and preparation of the substrate. A clean deposition system and pure source material are necessary to preserve elemental integrity of the vapor-deposited foils.
Date: January 1, 1980
Creator: Taylor, R.D.
Partner: UNT Libraries Government Documents Department

Moessbauer effect in Eu and EuO to pressures of 31 GPa

Description: We report /sup 151/Eu Moessbauer Effect measurements on Eu metal in the range 4 < T < 300 K and P < 12.5 GPa and on EuO for P < 31 GPa. Hydrostatic pressures using argon as the pressurizing medium were obtained in a simple Merrill-Bassett-type diamond anvil cell. Pressures were measured by the ruby fluorescence method. The 160-mCi /sup 151/SmF/sub 3/ source and the absorbers were held at the same temperature. The small sample size (about 8 ..mu..g) and rather large source diameter necessitated counting times of about one day per datum. Raw f-values of about 15% near 100 K reflected the efficient collimation of the 90 Ta 10 W gasket used/1/. 7 refs., 4 figs.
Date: January 1, 1988
Creator: Taylor, R.D.
Partner: UNT Libraries Government Documents Department

Rapid visual scanning

Description: A description is given of improvements in equipment and inspection techniques for visual inspection of electronic component assemblies. Comparison devices for enhancing differences between a master and test parts are evaluated. Illumination methods and television inspection developments were investigated. Indexing devices were evaluated and improved optical systems and methods were developed. An effective low-cost television comparison system was built; this system uses techniques such as blinking and subtraction for detecting differences in printed circuit boards. A glare-free illumination system called omnidirectional illumination was also developed and tested. This system reduces eyestrain, and performs very well on all types of surfaces and especially well on highly polished substrates. A low-cost manual indexing system called the Pantograph was designed and tested for quick, precise positioning of small circuit boards. The ultimate inspection system is one in which the inspector is an equipment operator instead of a decision maker. This is the reason for development of an automated comparison system. In this system, a PDP-11 computer controls a digital scanner and software was developed to monitor subtraction, hole location and size, path width, texture analysis, missing components, and feature analysis.
Date: August 1, 1976
Creator: Taylor, R. D.
Partner: UNT Libraries Government Documents Department

Energy-conserving and passive-solar construction details

Description: Diagrams are presented which show construction details for insulating foundations, walls, joists, roofs, and other components of energy-conserving residential and light commercial buildings; glazing systems; installing thermal mass; rock beds; and a passive hot air collector. The emphasis is on using commercially available building materials in new applications to minimize costs and maximize thermal design. The costs are given which are typical of what builders have incurred in different parts of the country. The thermal performance figures and comments are included. (LEW)
Date: April 1, 1981
Creator: Taylor, R D
Partner: UNT Libraries Government Documents Department

Diamond anvil cells: a new tool for high pressure studies

Description: Literally hundreds of papers have appeared in the last few years covering a myriad of uses of the diamond anvil cells. The crescendo shows no signs of abating. Static pressures as high as 1.8 megabar have been reported. Still higher pressures appear possible. Measurements have been made at dilution refrigerator temperatures (less than 50 millikelvins) and to temperatures over 1000 C in special sample ovens. Obviously these methods cannot be applied to every physics problem, but the limitations of the DAC are being challenged daily.
Date: January 1, 1985
Creator: Taylor, R.D.
Partner: UNT Libraries Government Documents Department

Mossbauer effect studies at pressures to 300 kbar

Description: In a recent experiment carried out at Los Alamos National Laboratory in collaboration with Prof. Moshe Paz Pasternak of Tel Aviv University, we have used the diamond anvil cell for a Mossbauer effect absorber experiment. A high-atomic-weight gasket material was developed; it served both to contain the pressure and to collimate the 27.8-keV Mossbauer effect gamma rays and nearby K x-rays emitted from the source. Elemental iodine is known to transform with pressure becoming metallic near 160 kbar. Furthermore, it has been reported that I/sub 2/ becomes monatomic at about 215 kbar. The Mossbauer effect of iodine-129 was employed to check this latter supposition. The Mossbauer effect ''fingerprint'' of I/sub 2/ was found to change slowly with pressure up to about 160 kbar whereupon a new high pressure phase or site began to appear. At 300 kbar the Mossbauer spectrum shows about half of the low temperature phase (I/sub 2/) is still present. This contradiction with x-ray results and or their interpretation is still under investigation.
Date: January 1, 1985
Creator: Taylor, R.D.
Partner: UNT Libraries Government Documents Department

Moessbauer Effect applications using intense radioactive ion beams

Description: The Moessbauer Effect is reviewed as a promising tool for a number of new solid state studies when used in combination with radioactive beam/implantation facilities. The usual Moessbauer Effect involves long-lived radioactive parents (days to years) that populate low-lying nuclear excited states that subsequently decay to the ground state. Resonant emission/absorption of recoil-free gamma rays from these states provide information on a number of properties of the host materials. Radioactive ion beams (RIB) produced on-line allow new Moessbauer nuclei to be studied where there is no suitable parent. The technique allows useful sources to be made having extremely low local concentrations. The ability to separate the beams in both Z and A should provide high specific activity conventional'' sources, a feature important in some applications such as Moessbauer studies in diamond anvil high pressure cells. Exotic chemistry is proposed using RIB and certain Krypton and Xenon Moessbauer isotopes.
Date: January 1, 1990
Creator: Taylor, R.D.
Partner: UNT Libraries Government Documents Department

Magnetic behavior at the iron sites in Pd Fe Mn alloys

Description: Moessbauer Effect hyperfine measurements of (Pd/sub 0/ /sub 9965/Fe/sub 0/ /sub 0035/)/sub 1-x/Mn/sub x/ have been obtained for 1.1 < T < 30 K and 0 < H < 6T for x = 0.01, 0.05, 0.06, and 0.065. Ferromagnetic ordering is clear for x = 0.01 and is suggested for x = 0.05 at 4 K. At 1.1 K ordering at the iron sites in all samples, except x = 0.01, is consistent with a spin-glass or antiferromagnetic phase.
Date: January 1, 1979
Creator: Taylor, R.D. & Willis, J.O.
Partner: UNT Libraries Government Documents Department

Moessbauer effect of europium metal under pressure

Description: The pressure dependence of the magnetic hyperfine field and of the isomer shift of /sup 151/Eu in europium metal has been studied in a diamond anvil pressure cell at low temperatures. In the pressure range 0-12 GPa at 44/sup 0/K (T/sub N/ = 90/sup 0/K), the magnetic hyperfine field changes from -22 T to -8 T while the isomer shift increases from -7.3 to -3.8 mm s/sup -1/ relative to a SmF/sub 3/ source. The changes are interpreted as indicative of a pressure-driven intermediate valence state causing a reduced magnetic moment in Eu. Intermediate valence and magnetic order coexist over the range of pressures studied.
Date: September 1, 1986
Creator: Taylor, R.D. & Farrell, J.N.
Partner: UNT Libraries Government Documents Department

Giant moments in Pd(Mn,Co) alloys

Description: Near T/sub M/, the large effective moment on Fe in the Pd(Co,Mn) alloys provides a high sensitivity ME magnetic field probe. For the Pd/sub 0/ /sub 99/Mn/sub 0/ /sub 01/ alloy, peak sensitivity occurs in the 6.5 to 10/sup 0/K range, but T/sub M/, and therefore the region of high field sensitivity, can easily be shifted by changing the Co or Mn concentration. These probes represent an order of magnitude improvement in sensitivity over the Pd ME probes previously used, and they should be quite useful in magnetic field profiling at cryogenic temperatures.
Date: January 1, 1979
Creator: Taylor, R.D. & Willis, J.O.
Partner: UNT Libraries Government Documents Department

Microprobe field measurements in ErRh/sub 4/B/sub 4/

Description: A small hyperfine field at Fe impurity sites in ErRh/sub 4/B/sub 4/ at 0.38 K was observed. The magnitude of the field at the nonmagnetic impurity sites was 0.5 T. This hyperfine field reflects spin order at the Er sites but the sensitivity of the probe technique employed turned out to be marginal for investigating quantitatively the shape of the ordering curve with temperature near and below T/sub c2/.
Date: January 1, 1979
Creator: Taylor, R.D. & Willis, J.O.
Partner: UNT Libraries Government Documents Department

High pressure /sup 129/I Moessbauer studies of GeI/sub 4/ molecular crystals

Description: The Moessbauer effect in /sup 129/I in conjunction with Diamond-Anvil-Cell high pressure techniques was applied to investigate the high pressure phase(s) of the molecular crystal GeI/sub 4/. The /sup 129/I Quadrupole Interaction was the main probe for characterizing the intermolecular structural transformation with pressure. With increasing pressure, at about 15 GPAa, the onset of a partial molecular-association phase (HP1) is first observed. In HP1 two out of the four iodines strongly overlap to form linear chains of GeI/sub 4/. The HP1 phase coexists with the low pressure (LP) molecular phase, but its population increases with increasing pressure. At P /approx/20 GPa a second high pressure phase (HP2) is identified where all four iodines strongly overlap to form a three dimensional, fully molecular-associated structure. With increasing pressure and at P > 20 GPa, HP2 is the only phase up to P = 34 GPa, the highest pressure used. A significant hysteresis of the relative abundances with pressure is observed. The isomer shift of the HP2 and HP1 structures is considerably larger than that of the LP one. 11 refs., 3 figs.
Date: January 1, 1989
Creator: Pasternak, M.P. & Taylor, R.D.
Partner: UNT Libraries Government Documents Department

Very high pressure Moessbauer spectroscopy using diamond anvil cells

Description: The technique of generating very high pressure by means of Diamond Anvil Cells (DAC) for Mossbauer Effect applications is outlined. A comprehensive description is presented of the principles of DAC, modification for the use in M/umlt o/ssbauer Spectroscopy (MS), the Merrill--Bassett and Bassett cells, of pressure measurements, of gasketing and collimation, and of hydrostatic media. Examples of /sup 151/Eu, /sup 119/Sn and /sup 129/I are given showing the feasibility of DAC applications in MS. Other isotopes with potential use for high pressure MS using DAC are suggested. 27 refs., 9 figs.
Date: January 1, 1988
Creator: Pasternak, M.P. & Taylor, R.D.
Partner: UNT Libraries Government Documents Department

Committee on Atomic, Molecular, and Optical Sciences (CAMOS). Technical progress report & continuation proposal, February 1, 1993--January 31, 1994

Description: The Committee on Atomic, Molecular and Optical Sciences (CAMOS) of the National Research Council (NRC) is charged with monitoring the health of the field of atomic, molecular, and optical (AMO) science in the United States. Accordingly, the Committee identifies and examines both broad and specific issues affecting the field. Regular meetings, teleconferences, briefings from agencies and the scientific community, the formation of study panels to prepare reports, and special symposia are among the mechanisms used by the CAMOS to meet its charge. This progress report presents a review of CAMOS activities from February 1, 1993 to January 31, 1994. The details of prior activities are discussed in earlier progress reports. This report also includes the status of activities associated with the CAMOS study on the field that is being conducted by the Panel on the Future of Atomic, Molecular, and Optical Sciences (FAMOS). During the above period, CAMOS has continued to track and participate in, when requested, discussions on the health of the field. Much of the perspective of CAMOS has been presented in the recently-published report Research Briefing on Selected Opportunities in Atomic, Molecular, and Optical Sciences. That report has served as the basis for briefings to representatives of the federal government as well as the community-at-large. In keeping with its charge to monitor the health of the field, CAMOS launched a study designed to highlight future directions of the field.
Date: October 1, 1997
Creator: Taylor, R.D.
Partner: UNT Libraries Government Documents Department

Internal magnetic fields in hcp-iron

Description: The magnetic behavior of hcp-Fe (epsilon iron) has been investigated by the Moessbauer Effect over a wide range of temperature T, pressure P, and applied magnetic field H/sub 0/. The internal field H/sub i/ of the induced moment is given by H/sub i/ = 0.20 +- .01 H/sub 0/ and is independent of T and P. Enhanced paramagnetism is suggested as the most likely origin for a contribution of this magnitude to H/sub i/.
Date: January 1, 1982
Creator: Taylor, R.D.; Cort, G. & Willis, J.O.
Partner: UNT Libraries Government Documents Department

Search for magnetism in hcp epsilon-Fe

Description: The results of recent experimental investigation which extends the search for magnetic ordering in the high-pressure, hcp phase of iron (epsilon-phase) to a temperature of 0.030 K are reported. Moessbauer effect measurements were performed in the pressure range from atmospheric pressure to 21.5 GPa on a foil of natural iron (doped with /sup 57/Co). Measurements were made of the properties of both the ..cap alpha..- and epsilon-phase constituents of the sample. No measurable magnetic hyperfine field was observed in the epsilon-phase from any of the spectra at pressures as high as 21.5 GPa and temperatures as low as 0.030 K.
Date: January 1, 1981
Creator: Cort, G.; Taylor, R.D. & Willis, J.O.
Partner: UNT Libraries Government Documents Department

The Moessbauer effect of SnI/sub 4/ at high pressures

Description: Tetravalent tin iodide is a molecular crystal composed of SnI/sub 4/ tetrahedra loosely packed into a cubic configuration. Under pressure SnI/sub 4/ becomes metallic at about 15 GPa. We report a Moessbauer effect study of /sup 119/Sn and /sup 129/I in SnI/sub 4/ to pressures of 26 GPa. The spectra exhibit dramatic changes with pressure starting at about 10 GPa and show large pressure hysteresis effects upon reducing the pressure from 26 GPa. In the intermediate region tin exists in both Sn/sup 4 +/ and Sn/sup 2 +/ states, and iodine exists in two nonequivalent sites characterized by a different symmetry and different sign and magnitude of the electric field gradient. 11 refs., 6 figs.
Date: January 1, 1987
Creator: Taylor, R.D.; Pasternak, M. & Farrell, J.N.
Partner: UNT Libraries Government Documents Department

/sup 57/Fe impurity atom lattice dynamics and systematics in group V and VI host metals

Description: The Moessbauer recoil-free fraction f and thermal shift have been measured for very dilute /sup 57/Fe impurities in body-centered cubic V, Nb, Mo, Ta, and W host metals in the range 4 to 860/sup 0/K. These experimental quantities have been interpreted in terms of an impurity-atom lattice-dynamical model of Mannheim where the important parameter ..gamma../sub ih//..gamma../sub hh/ is a measure of the coupling of the impurity atom to the host lattice relative to the corresponding coupling in the pure host lattice. Values of ..gamma../sub ih//..gamma../sub hh/ for each host from the f-value data were obtained and, independently, from the shift data, and for each host rather good agreement is obtained. The general trend of the data shows that for neighboring hosts of the same row of the periodic table, the relative /sup 57/Fe impurity binding is stronger for the Group V host than for the Group VI host. The results also support a previous conjecture that the nearest-neighbor binding between the impurity and the host should be proportional to a geometric mean of the nearest-neighbor couplings for a lattice consisting entirely of impurity atoms and for a lattice of host atoms only.
Date: January 1, 1976
Creator: Taylor, R. D.; Kitchens, T. A. Jr. & Erickson, D. J.
Partner: UNT Libraries Government Documents Department