bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of the Corrosion Behavior of Tank 51 Sludge-Based
Glass and a Nonradioactive Homologue Glass
Authors: Nuñez L. , Ebert W. L. , Wolf S. F. , Bates J. K. 
Published: September 2012

ABSTRACTWe are characterizing the corrosion behavior of the radioactive glass that
was made with sludge from Tank 51 at the Defense Waste Processing Facility
(DWPF) and a nonradioactive glass having the same composition, except for
the absence of radionuclides. Static dissolution tests are being conducted
in a tuff groundwater solution at glass surface area/solution volume ratios
(S/V) of 2000 and 20,000 m−1. These tests are being conducted to
assess the relationship between the behavior of this glass in a 7-day
Product Consistency Test and in long-term tests, to assess the effects of
radionuclides on the glass corrosion behavior, and to measure the
disposition of radionuclides that are released as the radioactive glass
corrodes. The radioactive glass reacts slower than the nonradioactive glass
through the longest test durations completed to date, which are 140 days for
tests at 2000 m−1 and about 400 days for tests at 20,000
m−1. This is probably because radiolysis results in lower
solution pH values being maintained in tests with the radioactive glass.
Rate-affecting alteration phases that had formed within one year in tests
with other glasses having compositions similar to the Tank 51 glass have not
yet formed in tests with either glass.
An Electrodeless Melter for Vitrification of Nuclear
Waste
Authors: Freidberg J. P. , Shajii A. J. , Wenzel K. W. , Lierzer J. R. 
Published: September 2012

ABSTRACTThis paper describes a new concept for a high-temperature, electrodeless
melter for vitrifying radioactive wastes. Based on the principles of
induction heating, it circumvents a number of difficulties associated with
existing technology. The melter can operate at higher temperatures
(1500–2000°C vs 1150°C), allowing for a higher quality, more durable glass
which reduces the long-term leaching rate. Higher processing temperatures
also enable conversion from borosilicate to high-silica glass which can
accommodate 2 to 3 times as much radioactive waste, potentially halving the
ultimate required long-term disposal space. Finally, with high temperatures,
conversion of nuclear waste into ceramics can also be considered. This too
leads to higher waste loading and the reduction of repository space. The
melter is toroidal, linked by an iron core transformer that allows efficient
electrical operation even at 60 Hz. One-dimensional electrical and thermal
analyses are presented.
The Incorporation of Cerium in Zirconolite
Authors: Begg B. D. , Vance E. R. 
Published: September 2012

ABSTRACTZirconolite (CaZrTi2O7) is the primary
actinide-bearing Synroc phase for the immobilisation of high-level nuclear
waste. Using X-ray absorption spectroscopy and microanalysis we have
investigated the incorporation of cerium, as a simulant for plutonium, on
both zirconolite's Ca and Zr sites under a range of redox conditions. The Ce
valence state was found to vary between Ce3+ and Ce4+
depending on the both the sintering atmosphere and temperature. The
existence of alternative charge compensation schemes, predominantly cation
vacancies, in addition to those used in the sample design was inferred in
many of the zirconolites and will be discussed in detail.
Spent Fuel Reaction: the Behavior of the ε-Phase Over 3.1
Years
Authors: Finn P. A. , Hoh J. C. , Wolf S. F. , Surchik M. T. , Buck E. C. , Bates J. K. 
Published: September 2012

ABSTRACTThe release fractions of the five elements in the ε-phase (99Tc,
97Mo, Ru, Rh, and Pd) as well as that of 238U are
reported for the reaction of two oxide fuels (ATM-103 and ATM-106) in
unsaturated tests under oxidizing conditions. The 99Tc release
fractions provide a lower limit for the magnitude of the spent fuel
reaction. The 99Tc release fractions indicate that a surface
reaction might be the rate controlling mechanism for fuel reaction under
unsaturated conditions and the oxidant is possibly
H2O2, a product of alpha radiolysis of water.
Dissolution of Unirradiated UO2 Fuel Under Oxidizing
Conditions: Evaluation of Solubility (Steady State) Limiting Factors
(EQ3/6)
Authors: Ollila K. 
Published: September 2012

ABSTRACTThe solubility behavior of unirradiated UO2 pellets was studied
under oxic, air-saturated conditions in deionized water, in
NaHCO3 solutions and in two types of synthetic groundwater
(25°C). The Allard groundwater represents natural fresh groundwater
conditions at great depths in granite bedrock and bentonite groundwater
simulates the effects of bentonite on granitic fresh groundwater. The
release of uranium was measured during static batch dissolution experiments
of long duration (6 years). A comparison was made with the theoretical
solubility data calculated with the geochemical code, EQ3/6, in order to
evaluate solubility (steady state) limiting factors. Various hypotheses for
redox control (redox potential of the bulk solution or redox potential at
the surface) were tested in the modeling calculations.The measured concentrations for uranium at steady-state in deionized water
were equal to the solubility of schoepite (PO2 = 0.2 atm). In
NaHCO3 solutions with lower carbonate concentrations (0.98 –
1.96 mmol/1) and in Allard groundwater they were close to the calculated
solubilities of U at the U3O7/U3O8 redox potential. In bentonite
groundwater, the results suggest the formation of a secondary phase with a
lower solubility. Only uranium oxide with a crystal structure of uraninite
(UO2 - U3O7) was identified in all
waters, when analyzing particulate material in the solutions after contact
with UO2 pellets.
The Kinetics of Spinel Crystallization from a High-Level Waste
Glass
Authors: Reynolds J. G. , Hrma P. 
Published: September 2012

ABSTRACTThe kinetics of spinel crystallization from a molten high-iron simulated
high-level nuclear waste glass was studied using isothermal heat treatments.
Optical microscopy with image analysis was used to measure volume fraction
of spinel as a function of heat treatment time and temperature. The
Johnson-Mehl-Avrami equation was fitted to data to determine kinetic
coefficients for spinel crystallization. The liquidus temperature and Avrami
number are TL = 1337K and n = 1.5.
Solubility of Sn(IV) Oxide in Dilute NaClO4 Solution
at Ambient Temperature
Authors: Amaya Takayuki , Chiba Tamotsu , Suzuki Kazunori , Oda Chie , Yoshikawa Hideki , Yui Mikazu 
Published: September 2012

ABSTRACTThe solubility of Sn(IV) oxide was determined in a dilute NaClO4
solution with pH 2 through 12 at ambient temperature. Both oversaturation
and undersaturation experiments were carried out in an inert gas glovebox
where the concentration of the oxygen and carbon dioxide were less than 1
ppm. The solubility of Sn(IV) oxide was 3×10-8 mol/1 at neutral
pH, and increased at pH >7.5. Equilibrium constants of soluble reactions
were calculated from the experimental data, using curve fitting method.The study suggests that the solubility of Sn(IV) oxide would be higher than
that provisionally used in current safety assessments of HLW disposal
sites.
Plutonium Solubility and Speciation to be Applied to the Separation of Hydrothermal Waste Treatment Effluent
Authors: Neu M. P. , Reilly S. D. , Runde W. H. 
Published: September 2012

ABSTRACTOne of the most complex problems concerning nuclear waste management and the restoration of plutonium production sites is the treatment and disposition of mixed and TRU wastes. Hydrothermal oxidation, which has been shown to be effective in oxidizing a wide variety of organic material to CO2, water, salts and other nonhazardous oxides, is a promising new technology for the treatment and volume reduction of actinide-containing waste. Information on the speciation and solubility of plutonium under process effluent conditions will facilitate the development of separation techniques for removing it from the treated solutions. Such a strongly oxidizing environment will generate plutonium(VT); and upon the destruction of organics, hydrothermal reactor solutions will contain carbonate. We are investigating the solubility and speciation of the plutonium(VI) carbonate system as a function of ionic strength (0.1 to 5.0 M). Formation constants for the tris- and biscarbonato complexes of plutonium(IV) were determined to be, log β130= 17.7 and log β120= 13.6, respectively, by spectrophotometry. These formation constants indicate that PuO2CO3(aq)is the plutonium (VI) carbonate solution species with the largest relevant stability range. We prepared and characterized the corresponding solid using XRD, EXAFS, and diffuse reflectance, and initiated solubility experiments in 0.1, 0.2, 0.5, 1,2, and 5 M NaCl at 22±1°C under 100% CO2. Data collected thus far yield the solubility products, log Kspmol2/kg2= -12.9 (0.1 m NaCl), -12.4 (0.2 m NaCl), -12.5 (0.5 m NaCl), -12.3 (1 m NaCl), -12.2 (2 m NaCl), -12.3 (5 m NaCl).
Chlorine-36 Investigations of Groundwater Infiltration in the
Exploratory Studies Facility at Yucca Mountain, Nevada
Authors: Levy Schön S. , Fabryka-Martin June T. , Dixon Paul R. , Liu Beiling , Turin H. J. , Wolfsberg Andrew V. 
Published: September 2012

ABSTRACTChlorine-36, including the natural cosmogenic component and the component
produced during atmospheric nuclear testing in the 1950's and 1960's (bomb
pulse), is being used as an isotopie tracer for groundwater infiltration
studies at Yucca Mountain, a potential nuclear waste repository. Rock
samples have been collected systematically in the Exploratory Studies
Facility (ESF), and samples were also collected from fractures, faults, and
breccia zones. Isotopie ratios indicative of bomb-pulse components in the
water (36Cl/Cl values > 1250 × 10-15), signifying
less than 40-yr travel times from the surface, have been detected at a few
locations within the Topopah Spring Tuff, the candidate host rock for the
repository. The specific features associated with the high
36Cl/Cl values are predominantly cooling joints and syngenetic
breccias, but most of the sites are in the general vicinity of faults. The
non-bomb pulse samples have 36Cl/Cl values interpreted to
indicate groundwater travel times of at least a few thousand to possibly
several hundred thousand years. Preliminary numerical solute-travel
experiments using the FEHM (Finite Element Heat and Mass transfer) code
demonstrate consistency between these interpreted ages and the observed
36Cl/Cl values but do not validate the interpretations.
Immobilization and Recovery of Thorium, A Neptunium Surrogate,
using Phase-Separated Glasses
Authors: Meaker T. F. , Karraker D. , Tosten M. , Pareizs J. M. , Ramsey W. G. 
Published: September 2012

ABSTRACTThe Savannah River Site has the majority of the United States' supply of
neptunium currently stored in an acid solution in one of their canyon
facilities. A program is being developed that could be utilized to ship this
material, as glass, to Oak Ridge National Laboratory where the Np could be
leached from the glass, purified by ion exchange and made into target
material for the production of Pu-238. Ion exchange purification dictates no
material be in the leachate making the isolation of the Np difficult. We
have developed a process using thorium as a surrogate for Np that could
immobilize the Np into a soda borosilicate glass for shipment. To achieve
recovery of the Np, the glass can be phase separated prior to leaching with
nitric acid. Phase separation would produces a Np-rich sodium-borate phase
and a Si-rich phase similar to a Vycor® glass. The nitric acid selectively
attacks the sodium-borate phase allowing high Np recovery in a solution that
contains only sodium and boron. These can be easily separated from Np by ion
exchange. Essentially all of the silicon which would interfere with ion
exchange by precipitation is retained in the Vycor®-type phase. This
technology may also be applied to other actinides stored in relatively pure
solutions.This paper will report the optimization of variables for maximizing Th (a Np
surrogate) recovery while minimizing Si release. Th solubility in glass,
heat treatment conditions and leaching parameters will be discussed.
Transmission Electron Microscopy (TEM) with energy dispersive spectroscopy
(EDS) data will be included to show phase separation after heat
treatment.
High-Temperature Optical Properties of Thin-Film Vanadium Oxides – VO2 and V2O3
Authors: Thomas Michael S. , DeNatale Jeff F. , Hood Patrick J. 
Published: September 2012

AbstractThin-film vanadium dioxide (VO2) and vanadium sesquioxide (V2O3) undergo shear phase transformations at 340K and 120K, respectively. The electrical and infrared optical properties of these materials are dramatically impacted by this phase transformation. Below the phase transition temperature, both VO2 and V2O3 are “poor” electrical insulators and have minimal absorption in the infrared spectral region. Above the phase transition temperature, both VO2 and V2O3 are poor conductors and are opaque in the infrared. The infrared thermochromic properties of these materials make them interesting candidates for several optical applications.Utilization of either VO2 or V2O3 necessitates an accurate knowledge of the optical properties both above and below the phase transition temperature. This paper reports on some recent infrared ellipsometric measurements on the optical properties of these materials above the transition temperature. These measurements found that both are strongly dispersive through the 3–12 micron spectral region. In addition, the temperature dependence of the optical properties of VO2 above the transition temperature can be related to the film morphology and stoichiometry.
Numerical Modeling of Nonlinear Beam Propagation Phenomena
Authors: Swartzlander G. A. , Deykoon A. M. , Jackson D. W. , Law C. T. 
Published: September 2012

AbstractA user-friendly beam propagation program has been developed for use over the worldwide- web to aid the optical limiting community in modeling the transmission of light through nonlinear refractive and absorptive media having local intensity-dependent or nonlocal fluencedependent mechanisms.
Non-Linear Light Scattering in a Two Component Medium Optical Limiting Application
Authors: Joudrier V. , Fabre J C. , Bourdon P. , Hache F. , Flytzanis C 
Published: September 2012

AbstractThe first experimental investigation of an optical limiting device based on a suspension of spherical particles in a surrounding liquid is presented. The expected property is the non-linear light scattering based on a refractive index mismatch between the two components that appears at high intensity. Several experiments performed at 532 nm with nanosecond laser pulses provide good indication that such non-linear scattering is observed.
Modeling the Effects of Solvation on the Structure and Properties of Optical Limiting Materials Using Ab Initio Quantum Chemistry
Authors: Day P. N. , Wang Z. , Pachter R. 
Published: September 2012

Abstracthe Effective Fragment Potential (EFP) model of solvation can now be extended beyond aqueous systems due to the development of transferable exchange repulsion potentials. EFPs for methanol and chloroform have been developed, and calculations with these new EFPs agree well with full ab initio calculations. Ab initio calculations have been carried out on zinc tetraphenyl-octobromyl-porphyrin both with and without the EFP solvation model. While the aqueous calculation, which had its geometry optimized, gave good results, the single-point calculations carried out with the two new solvent models indicate the need for geometry optimization.
Effect of AlGaN/GaN Strained Layer Superlattice Period on InGaN MQW Laser Diodes
Authors: Hansen Monica , Abare Amber C. , Kozodoy Peter , Katona Thomas M. , Craven Michael D. , Speck Jim S. , Mishra Umesh K. , Coldren Larry A. , DenBaars Steven P. 
Published: September 2012

AbstractAlGaN/GaN strained layer superlattices have been employed in the cladding layers of InGaN multi-quantum well laser diodes grown by metalorganic chemical vapor deposition (MOCVD). Superlattices have been investigated for strain relief of the cladding layer, as well as an enhanced hole concentration, which is more than ten times the value obtained for bulk AlGaN films. Laser diodes with strained layer superlattices as cladding layers were shown to have superior structural and electrical properties compared to laser diodes with bulk AlGaN cladding layers. As the period of the strained layer superlattices is decreased, the threshold voltage, as well as the threshold current density, is decreased. The resistance to vertical conduction through p-type superlattices with increasing superlattice period is not offset by the increase in hole concentration for increasing superlattice spacing, resulting in higher voltages.
New Materials-Theory-Based Model for Output Characteristics of AlGaN/GaN Heterostructure Field Effect Transistors
Authors: Albrecht J.D. , Ruden P.P. , Ancona M.G. 
Published: September 2012

AbstractA new model is used to examine the DC output characteristics of AlGaN/GaN heterostructure field effect transistors. The model is based on the charge-control/gradualchannel approximation and takes into account the non-linear current vs. voltage characteristics of the ungated AlGaN/GaN heterostructure channel regions. The model also includes thermal effects associated with device self-heating. For the power dissipation levels considered for many applications, the thermal degradation of the carrier drift velocity is shown to cause a negative output conductance in saturation. The temperature is incorporated self-consistently into the model through the field and temperature dependent mobility obtained from Monte Carlo transport simulations for electron transport in GaN. Calculated results presented for the DC output characteristics of several AlGaN/GaN field effect transistors show a strong dependence on the thermal properties of the substrate material. The substrate materials considered in this work are sapphire, SiC, AlN, and GaN.
Optical Spectroscopy and Composition of InGaN
Authors: O'Donnell K.P. , Martin R.W. , White M.E. , Jacobs K. , Van der Stricht W. , Demeester P. , Vantomme A. , Wu M.F. , Mosselmans J.F.W. 
Published: September 2012

AbstractCommercial light emitting devices (LEDs) containing InGaN layers offer unrivalled performance in the violet (∼400 nm), blue (∼450 nm) and green (∼520 nm) spectral regions. Nichia Chemicals Company has also produced amber InGaN LEDs with peak output near 590 nm. Here, we predict, on purely theoretical grounds, a surprisingly high limiting value of 1020 nm (peak) for InGaN intrinsic emission. We partly confirm this prediction by spectroscopic measurements of samples with photoluminescence (PL) peaks between 370 nm and 980 nm. In addition, we have measured the indium content of a range of light-emitting layers, using Rutherford Backscattering Spectrometry (RBS), Extended X-Ray Absorption Fine Structure (EXAFS) and Energy Dispersive X-Ray Analysis (EDX). The PL peak energy is found to depend linearly on the indium fraction: violet-emitting layers have an indium content of ∼8%, blue layers ∼16% and green layers ∼25%. A linear extrapolation to the limit set by the Stokes' shift prediction, mentioned earlier, yields a limiting indium concentration of only ∼52%. The profound impact of these results on future extensions of nitride technology and current theoretical models of InGaN is briefly discussed.
Carrier Dynamics Studies of Thick GaN Grown by HVPE
Authors: Bunea G.E. , Ünlü M.S. , Goldberg B.B. 
Published: September 2012

AbstractWe present a comparison between optical properties of two samples grown by hydride vapor phase epitaxy, one directly on Sapphire substrate (non-ELO) and one epitaxial lateral overgrown (ELO) on SiO2 patterned Sapphire substrate. The ELO material shows an improvement of the UV emission and slight decrease of the yellow emission. The band edge emission is red shifted due to the relaxation of the compressive strain. In spite of the increase in the UV emission, the lifetime of the excitons in the ELO material is more than twice lower than non-ELO material. We attribute this to screening effects of the background electron concentration.
Deep Level Related Yellow Luminescence in P-Type GaN Grown by MBE on (0001) Sapphire
Authors: Salviati Giancarlo , Armani Nicola , Zanotti-Fregonara Carlo , Gombia Enos , Albrecht Martin , Strunk Horst P. , Mayer Markus , Kamp Markus , Gasparotto Andrea 
Published: September 2012

AbstractYellow luminescence (YL) has been studied in GaN:Mg doped with Mg concentrations ranging from 1019 to 1021 cm−3 by spectral CL (T=5K) and TEM and explained by suggesting that a different mechanism could be responsible for the YL in p-type GaN with respect to that acting in n-type GaN.Transitions at 2.2, 2.8, 3.27, 3.21, and 3.44 eV were found. In addition to the wurtzite phase, TEM showed a different amount of the cubic phase in the samples. Nano tubes with a density of 3×109 cm−2 were also observed by approaching the layer/substrate interface. Besides this, coherent inclusions were found with a diameter in the nm range and a volume fraction of about 1%.The 2.8 eV transition was correlated to a deep level at 600 meV below the conduction band (CB) due to MgGa-VN complexes. The 3.27 eV emission was ascribed to a shallow acceptor at about 170-190 meV above the valence band (VB) due to MgGa.The 2.2 eV yellow band, not present in low doped samples, increased by increasing the Mg concentration. It was ascribed to a transition between a deep donor level at 0.8-1.1 eV below the CB edge due to NGa and the shallow acceptor due to MgGa. This assumption was checked by studying the role of C in Mg compensation. CL spectra from a sample with high C content showed transitions between a C-related 200 meV shallow donor and a deep donor level at about 0.9- 1.1 eV below the CB due to a NGa-VN complex. In our hypothesis this should induce a decrease of the integrated intensity in both the 2.2 and 2.8 eV bands, as actually shown by CL investigations.
The Effect of Nitrogen Ion Damage on the Optical and Electrical Properties of MBE GaN Grown on MOCVD GaN/Sapphire Templates
Authors: Young Alexander P. , Brillson Leonard J. , Naoi Yoshiki , Tu Charles W. 
Published: September 2012

AbstractWe have established a correlation between localized states responsible for mid-gap optical emission and film mobility of GaN grown under different nitrogen conditions. By imposing a deflector voltage at the tip of the plasma source, we varied the ion/neutral flux ratio to determine how N ions affect mid-gap luminescence and electrical mobility. Low energy electron-excited nanometer scale luminescence (LEEN) spectroscopy in ultrahigh vacuum (UHV) showed mid-gap emission intensities in the bulk that decreased in the ratio, 50 : 1.3 : 1 with increasing deflector voltage. Hall measurements indicated over a factor of two increase in mobility, and a factor of 8 decrease in residual charge density with increasing deflector voltage. The correlation of optical and electrical properties with a reduction in N ion flux suggests the primary role of native defects, such as N or Ga vacancies, in the mid-gap emissions.
Processing and Device Performance of GaN Power Rectifiers
Authors: Zhang A.P. , Dang G.T. , Cao X.A. , Cho H. , Ren F. , Han J. , Chyi J.-I. , Lee C.-M. , Nee T.-E. , Chuoa C.-C. , Chi G.-C. , Chu S.N.G. , Wilson R.G. , Pearton S.J. 
Published: September 2012

AbstractMesa and planar geometry GaN Schottky rectifiers were fabricated on 3-12µm thick epitaxial layers. In planar diodes utilizing resistive GaN, a reverse breakdown voltage of 3.1 kV was achieved in structures containing p-guard rings and employing extension of the Schottky contact edge over an oxide layer. In devices without edge termination, the reverse breakdown voltage was 2.3 kV. Mesa diodes fabricated on conducting GaN had breakdown voltages in the range 200-400 V, with on-state resistances as low as 6m Ωcm−2.