Water adsorption, solvation and deliquescence of alkali halide thin films on SiO2 studied by ambient pressure X-ray photoelectron spectroscopy (open access)

Water adsorption, solvation and deliquescence of alkali halide thin films on SiO2 studied by ambient pressure X-ray photoelectron spectroscopy

The adsorption of water on KBr thin films evaporated onto SiO2 was investigated as a function of relative humidity (RH) by ambient pressure X-ray photoelectron spectroscopy. At 30percent RH adsorbed water reaches a coverage of approximately one monolayer. As the humidity continues to increase, the coverage of water remains constant or increases very slowly until 60percent RH, followed by a rapid increase up to 100percent RH. At low RH a significant number of the Br atoms are lost due to irradiation damage. With increasing humidity solvation increases ion mobility and gives rise to a partial recovery of the Br/K ratio. Above 60percent RH the increase of the Br/K ratio accelerates. Above the deliquescence point (85percent RH), the thickness of the water layer continues to increase and reaches more than three layers near saturation. The enhancement of the Br/K ratio at this stage is roughly a factor 2.3 on a 0.5 nm KBr film, indicating a strong preferential segregation of Br ions to the surface of the thin saline solution on SiO2.
Date: March 31, 2010
Creator: Arima, Kenta; Jiang, Peng; Deng, Xingyi; Bluhm, Henrik & Salmeron, Miquel
System: The UNT Digital Library
Stability of modulation transfer function calibration of surface profilometers using binary pseudo-random gratings and arrays with nonideal groove shapes (open access)

Stability of modulation transfer function calibration of surface profilometers using binary pseudo-random gratings and arrays with nonideal groove shapes

The major problem of measurement of a power spectral density (PSD) distribution of surface heights with surface profilometers arises due to the unknown Modulation Transfer Function (MTF) of the instruments, which tends to distort the PSD at higher spatial frequencies. The special mathematical properties of binary pseudo-random patterns make them an ideal basis for developing MTF calibration test surfaces. Two-dimensional binary pseudo-random arrays (BPRAs) have been fabricated and used for the MTF calibration of the MicroMap{trademark}-570 interferometric microscope with all available objectives. An investigation into the effects of fabrication imperfections on the quality of the MTF calibration and a procedure for accounting for such imperfections are presented.
Date: March 31, 2010
Creator: Barber, Samuel K.; Anderson, Erik H.; Cambie, Rossana; Marchesini, Stefano; McKinney, Wayne R.; Takacs, Peter Z. et al.
System: The UNT Digital Library
Towards laboratory-produced relativistic electron-positron pair-plasmas (open access)

Towards laboratory-produced relativistic electron-positron pair-plasmas

Relativistic pair-plasmas and jets are believed to exist in many astrophysical objects and are often invoked to explain energetic phenomena related to Gamma Ray Bursts and Black Holes. On earth, positrons from radioactive isotopes or accelerators are used extensively at low energies (sub-MeV) in areas related to surface science positron emission tomography and basic antimatter science. Experimental platforms capable of producing the high-temperature pair-plasma and high-flux jets required to simulate astrophysical positron conditions have so far been absent. In the last few years, we performed extensive experiments generating positrons with intense lasers where we found that relativistic electron and positron jets are produced by irradiating a solid gold target with an intense picosecond laser pulse. The positron temperatures in directions parallel and transverse to the beam both exceeded 0.5 MeV, and the density of electrons and positrons in these jets are of order 10{sup 16} cm{sup -3} and 10{sup 13} cm{sup -3}, respectively. With the advent of high-energy ultra-short laser pulses, we expect that a charge-neutral, relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter. This talk will present some details of the laser-produced pair-plasma experiments.
Date: August 31, 2010
Creator: Chen, H.; Wilks, S. C.; Meyerhofer, D. D.; Beiersdorfer, P.; Cauble, R.; Dollar, F. et al.
System: The UNT Digital Library
Transparent Ceramic Scintillators for Gamma Spectroscopy and Radiography (open access)

Transparent Ceramic Scintillators for Gamma Spectroscopy and Radiography

None
Date: August 31, 2010
Creator: Cherepy, N. J.; Kuntz, J. D.; Seeley, Z. M.; Fisher, S. E.; Drury, O. B.; Sturm, B. W. et al.
System: The UNT Digital Library
Isotopic Tracking of Hanford 300 Area Derived Uranium in the Columbia River (open access)

Isotopic Tracking of Hanford 300 Area Derived Uranium in the Columbia River

Our objectives in this study are to quantify the discharge rate of uranium (U) to the Columbia River from the Hanford Site's 300 Area, and to follow that U down river to constrain its fate. Uranium from the Hanford Site has variable isotopic composition due to nuclear industrial processes carried out at the site. This characteristic makes it possible to use high-precision isotopic measurements of U in environmental samples to identify even trace levels of contaminant U, determine its sources, and estimate discharge rates. Our data on river water samples indicate that as much as 3.2 kg/day can enter the Columbia River from the 300 Area, which is only a small fraction of the total load of dissolved natural background U carried by the Columbia River. This very low-level of Hanford derived U can be discerned, despite dilution to < 1 percent of natural background U, 350 km downstream from the Hanford Site. These results indicate that isotopic methods can allow the amounts of U from the 300 Area of the Hanford Site entering the Columbia River to be measured accurately to ascertain whether they are an environmental concern, or are insignificant relative to natural uranium background in the Columbia …
Date: October 31, 2010
Creator: Christensen, John N.; Dresel, P. Evan; Conrad, Mark E.; Patton, Gregory W. & DePaolo, Donald J.
System: The UNT Digital Library
REMOVAL OF CESIUM FROM SAVANNAH RIVER SITE WASTE WITH SPHERICAL RESORCINOL FORMALDEHYDE ION EXCHANGE RESIN EXPERIMENTAL TESTS (open access)

REMOVAL OF CESIUM FROM SAVANNAH RIVER SITE WASTE WITH SPHERICAL RESORCINOL FORMALDEHYDE ION EXCHANGE RESIN EXPERIMENTAL TESTS

A principal goal at the Savannah River Site (SRS) is to safely dispose of the large volume of liquid nuclear waste held in many storage tanks. In-tank ion exchange (IX) columns are being considered for cesium removal. The spherical form of resorcinol formaldehyde ion exchange resin (sRF) is being evaluated for decontamination of dissolved saltcake waste at SRS, which is generally lower in potassium and organic components than Hanford waste. The sRF performance with SRS waste was evaluated in two phases: resin batch contacts and IX column testing with both simulated and actual dissolved salt waste. The tests, equipment, and results are discussed.
Date: March 31, 2010
Creator: Duignan, M. & Nash, C.
System: The UNT Digital Library
Wavelength-specific reflections: A decade of EUV actinic mask inspection research (open access)

Wavelength-specific reflections: A decade of EUV actinic mask inspection research

Mask inspection is essential for the success of any pattern-transfer lithography technology, and EUV Lithography in particular faces unique challenges. EUV masks resonant-reflective multilayer coatings have a narrow, wavelength-specific response that dramatically affects the way that defects appear, or disappear, at various illuminating wavelengths. Furthermore, the ever-shrinking size of 'critical' defects limits the potential effectiveness of DUV inspection techniques over time. Researchers pursuing numerous ways of finding and characterizing defects on EUV masks and have met with varying degrees of success. Their lessons inform the current, urgent exploration to select the most effective techniques for high-volume manufacturing. Ranging from basic research and demonstration experiments to commercial inspection tool prototypes, we survey the recent history of work in this area, including sixteen projects in Europe, Asia, and America. Solutions range from scanning beams to microscopy, dark field imaging to pattern transfer.
Date: December 31, 2010
Creator: Goldberg, Kenneth & Mochi, Iacopo
System: The UNT Digital Library
Tcap Hydrogen Isotope Separation Using Palladium and Inverse Columns (open access)

Tcap Hydrogen Isotope Separation Using Palladium and Inverse Columns

The Thermal Cycling Absorption Process (TCAP) was further studied with a new configuration. Previous configuration used a palladium packed column and a plug flow reverser (PFR). This new configuration uses an inverse column to replace the PFR. The goal was to further improve performance. Both configurations were experimentally tested. The results showed that the new configuration increased the throughput by a factor of more than 2.
Date: August 31, 2010
Creator: Heung, L.; Sessions, H. & Xiao, S.
System: The UNT Digital Library
Phasing beams with different dispersions and application to the Petawatt-class beamline at the National Ignition Facility (open access)

Phasing beams with different dispersions and application to the Petawatt-class beamline at the National Ignition Facility

None
Date: August 31, 2010
Creator: Homoelle, D; Crane, J K; Shverdin, M; Haefner, C L & Siders, C W
System: The UNT Digital Library
Ion acceleration and cooling in gasless self-sputtering (open access)

Ion acceleration and cooling in gasless self-sputtering

Copper plasma with hyperthermal directed velocity (8.8 eV) but very low temperature (0.6 eV) has been obtained using self-sputtering far above the runaway threshold. Ion energy distribution functions (IEDFs) were simultaneously measured at 34 locations. The IEDFs show the tail of the Thompson distribution near the magnetron target. They transform to shifted Maxwellians with the ions being accelerated and cooled. We deduce the existence of a highly asymmetric, pressure-driven potential hump which acts as a controlling"watershed" between the ion return flux and the expanding plasma.
Date: October 31, 2010
Creator: Horwat, David & Anders, Andre
System: The UNT Digital Library
In situ soft X-ray absorption spectroscopy investigation of electrochemical corrosion of copper in aqueous NaHCO3 solution (open access)

In situ soft X-ray absorption spectroscopy investigation of electrochemical corrosion of copper in aqueous NaHCO3 solution

A novel electrochemical setup has been developed for soft x-ray absorption studies of the electronic structure of electrode materials during electrochemical cycling. In this communication we illustrate the operation of the cell with a study of the corrosion behavior of copper in aqueous NaHCO3 solution via the electrochemically induced changes of its electronic structure. This development opens the way for in situ investigations of electrochemical processes, photovoltaics, batteries, fuel cells, water splitting, corrosion, electrodeposition, and a variety of important biological processes.
Date: March 31, 2010
Creator: Jiang, Peng; Chen, Jeng-Lung; Borondics, Ferenc; Glans, Per-Anders; West, Mark W.; Chang, Ching-Lin et al.
System: The UNT Digital Library
A new Scanning Transmission X-ray Microscope at the ALS for operation up to 2500eV (open access)

A new Scanning Transmission X-ray Microscope at the ALS for operation up to 2500eV

We report on the design and construction of a higher energy Scanning Transmission X-ray Microscope on a new bend magnet beam line at the Advanced Light Source. Previously we have operated such an instrument on a bend magnet for C, N and O 1s NEXAFS spectroscopy. The new instrument will have similar performance at higher energies up to and including the S 1s edge at 2472eV. A new microscope configuration is planned. A more open geometry will allow a fluorescence detector to count emitted photons from the front surface of the sample. There will be a capability for zone plate scanning in addition to the more conventional sample scanning mode. This will add the capability for imaging a massive sample at high resolution over a limited field of view, so that heavy reaction cells may be used to study processes in-situ, exploiting the longer photon attenuation length and the longer zone plate working distances available at higher photon energy. The energy range will extend down to include the C1s edge at 300eV, to allow high energy NEXAFS microscopic studies to correlate with the imaging of organics in the same sample region of interest.
Date: January 31, 2010
Creator: Kilcoyne, David; Ade, Harald; Attwood, David; Hitchcock, Adam; McKean, Pat; Mitchell, Gary et al.
System: The UNT Digital Library
3-D Mapping Technologies for High Level Waste Tanks (open access)

3-D Mapping Technologies for High Level Waste Tanks

This research investigated four techniques that could be applicable for mapping of solids remaining in radioactive waste tanks at the Savannah River Site: stereo vision, LIDAR, flash LIDAR, and Structure from Motion (SfM). Stereo vision is the least appropriate technique for the solids mapping application. Although the equipment cost is low and repackaging would be fairly simple, the algorithms to create a 3D image from stereo vision would require significant further development and may not even be applicable since stereo vision works by finding disparity in feature point locations from the images taken by the cameras. When minimal variation in visual texture exists for an area of interest, it becomes difficult for the software to detect correspondences for that object. SfM appears to be appropriate for solids mapping in waste tanks. However, equipment development would be required for positioning and movement of the camera in the tank space to enable capturing a sequence of images of the scene. Since SfM requires the identification of distinctive features and associates those features to their corresponding instantiations in the other image frames, mockup testing would be required to determine the applicability of SfM technology for mapping of waste in tanks. There may be …
Date: August 31, 2010
Creator: Marzolf, A. & Folsom, M.
System: The UNT Digital Library
The QCD Phase Diagram: Large Nc, Quarkyonic Matter and the Triple Point (open access)

The QCD Phase Diagram: Large Nc, Quarkyonic Matter and the Triple Point

I discuss the phase diagram of QCD in the large N_c limit. Quarkyonic Matter is described. The properties of QCD matter as measured in the abundance of produced particles are shown to be consistent with this phase diagram. A possible triple point of Hadronic Mater, Deconfined Matter and Quarkyonic matter is shown to explain various behaviors of ratios of particles abundances seen in CERN fixed target experiments.
Date: January 31, 2010
Creator: McLerran, L.
System: The UNT Digital Library
ScalaTrace: Tracing, Analysis and Modeling of HPC Codes at Scale (open access)

ScalaTrace: Tracing, Analysis and Modeling of HPC Codes at Scale

Characterizing the communication behavior of large-scale applications is a difficult and costly task due to code/system complexity and their long execution times. An alternative to running actual codes is to gather their communication traces and then replay them, which facilitates application tuning and future procurements. While past approaches lacked lossless scalable trace collection, we contribute an approach that provides orders of magnitude smaller, if not near constant-size, communication traces regardless of the number of nodes while preserving structural information. We introduce intra- and inter-node compression techniques of MPI events, we develop a scheme to preserve time and causality of communication events, and we present results of our implementation for BlueGene/L. Given this novel capability, we discuss its impact on communication tuning and on trace extrapolation. To the best of our knowledge, such a concise representation of MPI traces in a scalable manner combined with time-preserving deterministic MPI call replay are without any precedence.
Date: March 31, 2010
Creator: Mueller, F; Wu, X; Schulz, M; de Supinski, B & Gamblin, T
System: The UNT Digital Library
New Features of the Mercury Monte Carlo Particle Transport Code (open access)

New Features of the Mercury Monte Carlo Particle Transport Code

None
Date: August 31, 2010
Creator: Procassini, R J; Brantley, P S; Dawson, S A; Greenman, G M; McKinley, M S; O'Brien, M J et al.
System: The UNT Digital Library
Modern Calculations of Pulsed-Sphere Time-of-Flight Experiments Using the Mercury Monte Carlo Transport Code (open access)

Modern Calculations of Pulsed-Sphere Time-of-Flight Experiments Using the Mercury Monte Carlo Transport Code

None
Date: August 31, 2010
Creator: Procassini, R. J. & McKinley, M. S.
System: The UNT Digital Library
Transmission Nuclear Resonance Fluorescence Measurements of 238U in Thick Targets (open access)

Transmission Nuclear Resonance Fluorescence Measurements of 238U in Thick Targets

Transmission nuclear resonance fluorescence measurements were made on targets consisting of Pb and depleted U with total areal densities near 86 g/cm2. The 238U content n the targets varied from 0 to 8.5percent (atom fraction). The experiment demonstrates the capability of using transmission measurements as a non-destructive technique to identify and quantify the presence of an isotope in samples with thicknesses comparable to he average thickness of a nuclear fuel assembly. The experimental data also appear to demonstrate the process of notch refilling with a predictable intensity. Comparison of measured spectra to previous backscatter 238U measurements indicates general agreement in observed excited states. Two new 238U excited states and possibly a third state have also been observed.
Date: August 31, 2010
Creator: Quiter, Brian J.; Ludewigt, Bernhard A.; Mozin, Vladimir V.; Wilson, Cody & Korbly, Steve
System: The UNT Digital Library
Developing the Next Generation of International Safeguards and Nonproliferation Experts: Highlights of Select Activities at the National Laboratories (open access)

Developing the Next Generation of International Safeguards and Nonproliferation Experts: Highlights of Select Activities at the National Laboratories

With many safeguards experts in the United States at or near retirement age, and with the growing and evolving mission of international safeguards, attracting and educating a new generation of safeguards experts is an important element of maintaining a credible and capable international safeguards system. The United States National Laboratories, with their rich experience in addressing the technical and policy challenges of international safeguards, are an important resource for attracting, educating, and training future safeguards experts. This presentation highlights some of the safeguards education and professional development activities underway at the National Laboratories. These include university outreach, summer courses, internships, mid-career transition, knowledge retention, and other projects. The presentation concludes with thoughts on the challenge of interdisciplinary education and the recruitment of individuals with the right balance of skills and backgrounds are recruited to meet tomorrow's needs.
Date: March 31, 2010
Creator: Reed, J.; Mathews, C.; Kirk, B.; Lynch, P.; Doyle, J.; Meek, E. et al.
System: The UNT Digital Library
Successful Completion of the Top-off Upgrade of the Advanced Light Source (open access)

Successful Completion of the Top-off Upgrade of the Advanced Light Source

An upgrade of the Advanced Light Source to enable top-off operation has been completed during the last four years. The final work centered around radiation safety aspects, culminating in a systematic proof that top-off operation is equally safe as decaying beam operation. Commissioning and transition to full user operations happened in late 2008 and early 2009. Top-off operation at the ALS provides a very large increase in time-averaged brightness (by about a factor of 10) as well as improvements in beam stability. The following sections provide an overview of the radiation safety rationale, commissioning results, as well as experience in user operations.
Date: January 31, 2010
Creator: Steier, C.; Bailey, B.; Baptiste, K.; Barry, W.; Biocca, A.; Byrne, W. et al.
System: The UNT Digital Library
Generalized Energy-Dependent Q Values for Fission (open access)

Generalized Energy-Dependent Q Values for Fission

We extend Madland's parameterization of the energy release in fission to obtain the dependence of the fission Q value for major and minor actinides on the incident neutron energies in the range 0 {le} E{sub n} {le} 20 MeV. Our parameterization is based on the actinide evaluations recommended for the ENDF/B-VII.1 release. This paper describes the calculation of energydependent fission Q values based on the calculation of the prompt energy release in fission by Madland. This calculation was adopted for use in the LLNL ENDL database and then generalized to obtain the prompt fission energy release for all actinides. Here the calculation is further generalized to the total energy release in fission. There are several stages in a fission event, depending on the time scale. Neutrons and gammas may be emitted at any time during the fission event.While our discussion here is focussed on compound nucleus creation by an incident neutron, similar parameterizations could be obtained for incident gammas or spontaneous fission.
Date: March 31, 2010
Creator: Vogt, R
System: The UNT Digital Library
Calculation of 239Pu fission observables in an event-by-event simulation (open access)

Calculation of 239Pu fission observables in an event-by-event simulation

The increased interest in more exclusive fission observables has demanded more detailed models. We describe a new computational model, FREYA, that aims to meet this need by producing large samples of complete fission events from which any observable of interest can then be extracted consistently, including any interesting correlations. The various model assumptions are described and the potential utility of the model is illustrated. As a concrete example, we use formal statistical methods, experimental data on neutron production in neutron-induced fission of {sup 239}Pu, along with FREYA, to develop quantitative insights into the relation between reaction observables and detailed microscopic aspects of fission. Current measurements of the mean number of prompt neutrons emitted in fission taken together with less accurate current measurements for the prompt post-fission neutron energy spectrum, up to the threshold for multi-chance fission, place remarkably fine constraints on microscopic theories.
Date: March 31, 2010
Creator: Vogt, R; Randrup, J; Pruet, J & Younes, W
System: The UNT Digital Library
A Soft X-ray Spectrometer using a Highly Dispersive Multilayer Grating (open access)

A Soft X-ray Spectrometer using a Highly Dispersive Multilayer Grating

There is a need for higher resolution spectrometers as a tool for inelastic x-ray scattering. Currently, resolving power around R = 10,000 is advertised. Measured RIXS spectra are often limited by this instrumental resolution and higher resolution spectrometers using conventional gratings would be prohibitively large. We are engaged in a development program to build blazed multilayer grating structures for diffracting soft x-rays in high order. This leads to spectrometers with dispersion much higher than is possible using metal coated-gratings. The higher dispersion then provides higher resolution and the multilayer gratings are capable of operating away from grazing incidence as required. A spectrometer design is presented with a total length 3.8m and capable of 10{sup 5} resolving power.
Date: January 31, 2010
Creator: Warwick, Tony; Padmore, Howard; Voronov, Dmitriy & Yashchuk, Valeriy
System: The UNT Digital Library
Elliptically Bent X-ray Mirrors with Active Temperature Stabilization (open access)

Elliptically Bent X-ray Mirrors with Active Temperature Stabilization

We present details of design of elliptically bent Kirkpatrick-Baez mirrors developed and successfully used at the Advanced Light Source for submicron focusing. A distinctive feature of the mirror design is an active temperature stabilization based on a Peltier element attached directly to the mirror body. The design and materials have been carefully optimized to provide high heat conductance between the mirror body and substrate. We describe the experimental procedures used when assembling and precisely shaping the mirrors, with special attention paid to laboratory testing of the mirror-temperature stabilization. For this purpose, the temperature dependence of the surface slope profile of a specially fabricated test mirror placed inside a temperature-controlled container was measured. We demonstrate that with active mirror-temperature stabilization, a change of the surrounding temperature by more than 3K does not noticeably affect the mirror figure. Without temperature stabilization, the surface slope changes by approximately 1.5 ?mu rad rms (primarily defocus) under the same conditions.
Date: January 31, 2010
Creator: Yuan, Sheng; Church, Matthew; Yashchuk, Valeriy V.; Goldberg, Kenneth A.; Celestre, Rich; McKinney, Wayne R. et al.
System: The UNT Digital Library