bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct Imaging of Atomic Rearrangements on Extended Gold Surfaces
Authors: Smith David J. , Marks L. D.
Published: March 2011

Rearrangements of atomic columns on extended gold surfaces have been imaged directly using a 500kV high resolution electron microscope. The (100), (110) and (111) surface profiles were all found to be highly mobile and microscopically rough, with (111) in particular developing a characteristic hill-and-valley morphology. The presence of surface steps had a marked influence on the direction of surface diffusion only for the (100) surface. The observations establish that high-resolution profile imaging can provide unique information about surface self-diffusion which is unobtainable by other techniques.
Analysis of Domain-Size Distributions in Epitaxial Growth Using Leed Angular Profiles
Authors: Saloner D. , Lagally M. G.
Published: March 2011

Angular profiles of diffracted beams in surface-sensitive diffraction techniques can be used to establish the degree of order at the surface of crystals. Results are presented showing the sensitivity of such profiles to the growth mode of overlayer islands. A method is presented to incorporate the two-dimensional nature of the problem into the analysis and to extract finite-size effects from fundamental and superlattice beams.
Grain Boundary Structural Transformations Induced by Solute Segregation
Authors: Sickafus K. , Sass S. L.
Published: March 2011

The problem of solute segregation came to prominence with relation to studies of the temper embrittlement of low alloy steels. McLean and Northcott1(1948) first suggested that segregation of various elements to the grain boundaries was primarily responsible for the intergranular fracture observed in steels susceptible to this embrittlement. Direct evidence for segregation came much later with the development of surface sensitive analytical techniques, especially Auger electron spectroscopy (AES). Using AES, it was determined that impurity elements such as P, Sb and Sn, as well as alloying elements such as Ni and Cr, were highly concentrated at the fracture surfaces in embrittled steels2. It is not clear, however, why solute segregation changes the mechanical strength of the grain boundaries in these materials. Based on recent calculations, Messmer and Briant3proposed that certain solute species at a grain boundary change the chemical bonding at the interface. However, other more dramatic structural rearrangements may be possible upon segregation. Such structural changes were first suggested by the observation of facetted fracture surfaces in tellurium-doped iron alloys4. In the study presented here, it is shown that low concentrations of solute can cause changes in grain boundary structure. In particular, small concentrations of Au solute were found to cause a major change in the dislocation structure of low angle [001] Fe twist boundaries. Preliminary observations on the str ucture of a Fe-0.18 at.% Au* twist boundary were presented elsewhere5. Additional results will be presented here on the effect of changes in solute concentration and misorientation angle, θ, on this structural transformation. It is believed that these observations are evidence for the occurrence of a two-dimensional phase transformation in the grain boundary, similar to that predicted by Hart6
In Situ Hvem Studies of Electron-Beam-Driven Composition Changes in Thin Film Alloys: Displacement-Rate Gradient Effects
Authors: Okamoto P. R. , Lam N. Q.
Published: March 2011

In situ high-voltage electron microscopy (HVEM) observations have shown that the highly-focused electron beams normally employed for HVEM irradiation experiments can cause large chemical composition changes in the irradiated zone of thin film alloys during elevated temperature irradiations. The driving force for the process comes primarily from the radial gradients in displacement rates generated by the beam. Hence, the rate of change in composition exhibits a strong dependence not only on the temperature and beam intensity, but also on the spatial characteristics of the beam profile. This dependence on beam shape and size poses previously unrecognized problems, particularly for HVEM studies of the effects of dose-rate on radiation-induced phenomena that are sensitive to alloy composition. Moreover, composition changes driven by radial gradients in the displacement- rate occur at increasingly rapid rates as the beam diameter is reduced. Hence, at higher voltages, beam-induced composition changes occurring during analysis may become a serious problem, even at relatively low temperatures, for microchemical analysis techniques, such as EDX and EELS, which employ far smaller diameter electron beams than those used for irradiation purposes in the HVEM.
Structural Changes of a σ = 51 Tilt Boundary in Germanium During High Temperature Creep
Authors: Skrotski W. , Wendt H. , Carter C. B. , Kohlstedt D. L.
Published: March 2011

The incorporation of lattice dislocations into a 16° [011] tilt bound-ary in Ge bicrystals has been analyzed with high-resolution and conventional transmission electron microscopy techniques. Dislocations in subgrain boundaries produced during high-temperature creep, knit into the high-angle grain boundary. As these lattice dislocations are absorbed, the structure changes along the grain boundary from one subgrain to the next. Analysis of the boundary structure by lattice-fringe imaging demonstrates that the secon-dary dislocations which accomodate the deviation from the coincidence orien-tation do not have primitive DSC Burgers vectors.
Exafs Studies of Ion Implanted Bismuth
Authors: Kunoff E. M. , Dresselhaus M. S. , Kao Y. H.
Published: March 2011

Magnetorefiection and preliminary Rutherford Backscattering channeling experiments indicate that point defects induced in the bismuth lattice by ion implantation are largely annealed out during the implantation process due to its low melting temperature of 271.3°C. These experiments also show that the implanted ions cause long range strains in the crystal. Single crystal bismuth samples have been implanted at low temperatures (from 273°K down to 77°K) with 75 As to a total fluence of 5 × 1016/cm2 at energies ranging from 50 keV to 200 keV to yield an approximately constant arsenic profile from the sample surface to a depth of 625 Å. To study the local environment of the implanted As ions, EXAFS measurements have been made at the Cornell High Energy Synchrotron Source (CHESS). From these data, we obtain a comparison of the As nearest neighbor distances in samples implanted at different temperatures. We discuss the effect of sample temperature during implantation on these properties. This work represents the first use of EXAFS to characterize annealing of implantation-induced lattice defects during the process of ion implantation.
Rutherford Backscattering and Channeling Studies of Laser Annealed, Nitrogen Implanted and Non-Implanted Single Crystal Austenitic Stainless Steel.
Authors: Whitton J. L. , Laursen T. , Nilson J. A. , Nip Wing , Mitchell I. V. , Plattner H. H. , Swanson M. L.
Published: March 2011

Ion backscattering and channeling of 2.0 MeV He+ has been used to observe the effects of excimer laser annealing on unimplanted and nitrogen implanted single crystal austenitic stainless steel. The laser annealing was done either in air or in flowing helium. In general, laser annealing resulted in a significant increase in lattice disorder of both unimplanted and implanted specimens. Laser annealing in helium atmosphere caused a near-surface decrease of disorder in the implanted specimens with, however, a higher dechanneling rate at greater depths. Channeling with nuclear reaction analysis shows that the as - implanted nitrogen occupies octahedral interstitial sites as evidenced by flux peaking along the <110> axis and a decreased signal along the <100> axis. A similar effect is observed after laser annealing in a helium atmosphere.
Tin-Doping Induced Defects in GaAs Films Grown by Molecular Beam Epitaxy
Authors: Chen S. H. , Enquist P. , Carter C. B.
Published: March 2011

Heavily Sn-doped GaAs films have been grown by molecular-beam epitaxy and found to contain single-crystal Sn particles situated in the near-surface region of the epilayer GaAs. The morphology and chemical composition of the particles have been examined by using cross-section transmission electron microscopy combined with energy-dispersive x-ray spectroscopy. Different growth conditions were used to study the Sn-particle formation and high-resolution transmission electron microscopy was used to investigate microstructures. The observations are discussed in terms of several models previously proposed for these phenomena.
Characterization of Emitter-Collector Shorts by Anodization, Voltage Contrast Sem, and Tem
Authors: Carim A. H. , Sinclair R. , Stacy W. T.
Published: March 2011

Chemical anodization and voltage contrast scanning electron microscopy (VC-SEM) have been used to identify electrically faulty structures in a bipolar test array. Direct comparison of these techniques was achieved by examining the same emitters with each method. VC-SEM is shown to be a useful technique for delineating E-C shorts because of its nondestructive and purely electrical nature. Further investigations by transmission electron microscopy revealed dislocations in many short-circuited emitters and occasionally in unshorted devices. This confirmed prior observations that crystallographic defects in silicon devices may sometimes be, but are not always, electrically active.
Positron Annihilation Studies of Vacancy Formation in Tungsten, Chromium, and Niobium
Authors: Smedskjaer L. C. , Loper G. D. , Chason M. K. , Siegel R. W.
Published: March 2011

Vacancy formation was studied in the refractory bcc metals, tungsten, chromium, and niobium, using the positron annihilation spectroscopy Doppler broadening technique, between room temperature and the respective melting temperatures, under ultra-high vacuum conditions. Temperatures were measured by optical and infrared pyrometry, a W(Rh) thermocouple, and the power delivered to the sample, with calibrations against known melting temperatures. For W, a trapping-model analysis of the data from the temperature range 300–3633 K yielded a vacancy formation enthalpy of 3.76 ± 0.39 eV. For Cr, a similar fit to the data from 296–2049 K yielded a vacancy formation enthalpy of 2.0 ± 0.2 eV. The results are discussed in relation to previous vacancy formation and self-diffusion studies. Measurements on Nb as a function of temperature and oxygen content are also presented.
Small Angle X-Ray Scattering (Saxs) Study of Coarsening Kinetics in an Aluminum-Lithium Alloy
Authors: Spooner Stephen
Published: March 2011

Coarsening kinetics was studied in a A190. 6 Li9. 4 alloy aged at 100°C, 128°C, 165°C, 178 ° C, and 209 °C. The time-dependent behavior of the average precipitate radius followed t1/3 behavior. The precipitate/ matrix interfacial energy obtained from analysis of the kinetic constant was 0.015 J/M2 and was largely independent of temperature. The scattering curves exhibit interparticle interference which prevents us from calculating a particle size distribution.
Influence of Aggregates on the Strength and Elastic Modulus of High Strength Mortars Containing Microsilica
Authors: Dingsøyr E. , Mosberg T. , Young J. F.
Published: March 2011

The strength development of mortars made with a high strength paste containing microsilica was investigated as a function of aggregate type and
content. Strength could be modelled using composite theory; the predicted strengths of the paste and aggregate component reflected the influence of
the cement-aggregate bond. Scanning electron microscopic examinations gave a qualitative idea of the extent of bond failure, which correlated satisfactorily with the predicted behavior. The modulus of elasticity for SiC mortars could be predicted well by Hirsch's model or the aggregate model.
Optimized High Strength Mortars: Effects of Chemistry, Particle Packing, and Interface Bonding
Authors: Roy Della M. , Nakagawa Zenbe-E , Scheetz Barry E. , White Elizabeth L.
Published: March 2011

High strength mortars have been prepared utilizing optimized particle packing, reactive substituents to modify the chemistry- and addition of superplasticizers. Otherwise the processing techniques were conventional. The compressive strengths of one prototype material after curing at temperatures from 38 C to 250 C were above 70 MPa. The strengths were particularly high at 175 C (195 MPa) where excellent bonding had developed; one chemically modified material reached 245 MPa. The specimens cured at 175 and 250 C (after a lower temperature precure) developed their strengths rapidly, having reached essentially full strength by 7 days. At lower curing temperatures the strength increased with time, apparently still increasing at 56 days (106 MPa) for the materials cured at 38 C. Modified mixtures were prepared using different proportions of silica fume, MgO, different ratios of sand to fine components, and different sand mineralogy and other admixture proportions for rheological optimization. Microhardness, dynamic Young's modulus, density, and permeability were measured in addition to strength. Matrix chemistry and sand mineralogy and proportions affected the strength. Matrix-aggregate bond was very important. The above types of cementitious materials have potential importance for applications where they may be exposed to extreme conditions and to temperature cycling.
High Strength Autoclaved Mortars
Authors: Baggott R. , Sarandily A.
Published: March 2011

Autoclaved cement-silica mortars having flexural strengths of up to 57 MPa were prepared by pressing and casting methods of fabrication. It was found that the Griffith dependence of strength upon the size of the largest flaw, the modulus of elasticity and the surface energy was applicable. The relative contributions of these three parameters were evaluated and it was established that although the maximum flaw was the dominant factor in a specific material, surface energy changes were responsible for major strength differences associated with water-solid ratios or variations in the preparation method. Preliminary studies identified the various microstructural features that operated as Griffith's flaws.
A Contribution to the Modelling of the Corrosion Process for HLW Glasses
Authors: Conradt R. , Roggendorf H. , Scholze H.
Published: March 2011

An evaluation of a broad set of HLWg lass corrosion data implies that adequate corrosion models must also take into account kinetics slower than √t. Solubility limits may not give a sufficient explanation for these cases. Before all, the long term leach rates are not infinitely small. A proposal is made how “slow” kinetics can be included in a model.
The Effect of Groundwater Flow on Release Rate Behavior of Borosilicate Glass
Authors: Apted M. J. , Adiga R.
Published: March 2011

A simple open-system model is used to evaluate the effect of groundwater flow on borosilicate glass dissolution. With appropriate assumptions, the mass balance equation is: dc/dt=R-kfc;R=k(ceq-c)

where c is the concentration of dissolved species i, t is time, kf is the flushing frequency (i.e., volumetric flow rate divided by fixed pore volume), and R is the normalized rate of dissolution. A first-order dependence of R on departure of c from the equilibrium saturation concentration, Ceq, is also assumed. Results from steady-state (dc/dt = 0; c = css = constant) static and dynamic flow tests on a borosilicate glass at 90°C were used to calculate R and the dissolution rate constant, k, as a function of flow rate. The calculated results of the model are in good agreement with independent measurements.

There are three important conclusions. First, even the slowest flow rate used (0.1 ml/hr) corresponds to a high flow rate with respect to the intrinsic dissolution rate of the glass and expected repository flow conditions. Second, previous release models that scale radionuclide release rate directly to solubility concentration may overestimate release at high flow rates. This is because previous models fail to account for the pronounced decrease in steady-state solution concentration at the solid interface with increasing flow rate. Third, increased flow rate accelerates the glass dissolution rate without changing the reaction mechanism. This effect is attributable to constant replenishment of undersaturated solution at the glass surface and an apparent increase in the dissolution rate constant with increasing flow rate.
Surface Film Characterization of Corroded HLW Glass Specimens
Authors: Bart Gerhard , Aerne Ernst T. , Grauer Rolf , Linder Hanspeter , Z'berg Doris , Zwicky Hans U.
Published: March 2011

In a joint Japanese, Swedish, Swiss HLW glass characterization programme, interactions of real waste glass specimens with possible burial system components are studied. The report describes the glass surface analytical work performed at the Swiss Federal Institute for Reactor Research (EIR) during the first completed phase of the programme.
Wipp Waste Package Testing on Simulated DHLW: Emplacement
Authors: Molecke Martin A.
Published: March 2011

Several series of simulated (nonradioactive) defense high-level waste (DHLW) package tests have recently been emplaced in the WIPP, a research and development facility authorized to demonstrate the safe disposal of defense-related wastes. The primary purpose of these 3-to-7 year duration tests is to evaluate the in situ materials performance of waste package barriers (canisters, overpacks, backfills, and nonradioactive DHLW glass waste form) for possible future application to a licensed waste repository in salt. This paper describes all test materials, instrumentation, and emplacement and testing techniques, and discusses progress of the various tests.

These tests are intended to provide information on materials behavior (i.e., corrosion, metallurgical and geochemical alterations, waste form durability, surface interactions, etc.), as well as comparison between several waste package designs, fabrications details, and actual costs.These experiments involve 18 full-size simulated DHLW packages (approximately 3.0 m x 0.6 m diameter) emplaced in vertical boreholes in the salt drift floor. Six of the test packages contain internal electrical heaters (470 W/canister), and were emplaced under approximately reference DHLW repository conditions. Twelve other simulated DHLW packages were emplaced tinder accelerated-aging or overtest conditions, including the artificial introduction of brine, and a thermal loading approximately three to four times higher than reference. Eight of these 12 test packages contain 1500 W/canister electrical heaters; the other four are filled with DHLW glass.
Corrosion of Candidate Iron-Base Waste Package Structural Barrier Materials in Moist Salt Environments
Authors: Westerman R. E. , Pitman S. G.
Published: March 2011

Mild steels are considered to be strong candidates for waste package structural barrier (e.g., overpack) applications in salt repositories. Corrosion rates of these materials determined in autoclave tests utilizing a simulated intrusion brine based on Permian Basin core samples are low, generally μm (1 mil) per year. When the steels are exposed to moist salts containing simulated inclusion brines, the corrosion rates are found to increase significantly. The magnesium in the inclusion brine component of the environment is believed to be responsible for the increased corrosion rates.
Technetium and Neptunium Reactions in Basalt/Groundwater Systems
Authors: Meyer R. E. , Arnold W. D. , Kelmers A. D. , Kessler J. H. , Clark R. J. , Johnson J. S. , Young G. C. , Case F. I. , Westmoreland C. G.
Published: March 2011

Sorption isotherms and apparent concentration limits for Tc(VII) and Np(V) for a variety of groundwater/basalt systems were determined using Grande Ronde basalt samples representative of the Hanford Site candidate high-level waste repository. Under oxic redox conditions (air present), little or no sorption of technetium was observed; neptunium exhibited low to moderate sorption ratios. Under anoxic redox conditions (oxygen-free), low to moderate sorption of technetium was often observed, but the extent of sorption was highly dependent upon the groundwater composition and the method of pretreatment (if any) of the basalt. Sorption isotherms for technetium under reducing redox conditions (hydrazine added) indicate an apparent concentration limit of approximately 10−6mol/L Tc. No apparent concentration limit was found for neptunium for concentrations in groundwater up to.∼10−6mol/L and 8 × 10−7mol/L under oxic and reducing (hydrazine added) redox conditions, respectively.

Valence control and valence analysis experiments suggest that the sorption or precipitation of Tc and Np from groundwater in the presence of basalt may result from a heterogeneous reaction occurring on the surface of the basalt. One of the critical factors of this reduction reaction appears to be the accessibility of the reactive ferrous iron component of the basalt. The laboratory simulation of groundwater redox conditions representative of the repository environment through the use of solution phase redox reagents is of questionable validity, and information obtained by such experimental methods may not be defensible for site performance assessment calculations. Anoxic experiments conducted in an argon-filled glove box appear better suited for the laboratory simulation ofin situredox conditions.
Diffusion of Plutonium in Compacted, Brine-Saturated Bentonite
Authors: Nowak E. J.
Published: March 2011

Diffusivities were measured for plutonium in brine-saturated compacted Wyoming bentonite. Complexities of the solution chemistry and retardation of transuranics necessitate diffusion studies under conditions that are specific for repository host rock types in this case salt. Diffusivity values in the range of 10−15 to 10−14 m2/s were obtained for bentonite at a packing density of 1800 kg/m3. That density was obtained by compaction at 15 i0Pa, a typical lithostatic pressure in a repository in salt at 650 m depth. Even a 0.05 m (2 inch) thick bentonite-containing engineered barrier could decrease radionuclide release rates by approximately 4 orders-of-magnitude if the diffusivity for that radionuclide were in the observed range of 10−15 to 10−14 m2/s. These results confirm the effectiveness of uncompacted bentonite-containing materials as engineered barriers for radioactive waste isolation.
Spent UO2-fuel Dissolution. Tentative Modelling of Experimental Apparent Solubilities
Authors: Bruno J , Forsyth R S , Werme L O
Published: March 2011

Experimentally measured concentrations in spent UO2-fuel leachates are reported for uranium and plutonium for contact times ranging from 14 days to 2 years at different pH. The experimental results for uranium clearly indicated saturation. This interpretation was supported by comparison with theoretical solubilities, calculated using a modified SOLGASWATER program. The calculated solubilities were found to agree well with the experimentally determined concentrations.
Conceptual Model for Deriving the Repository Source Term
Authors: Alexander D. H. , Apted M. J. , Liebetrau A. M. , Luik A. E. Van , Williford R. E. , Doctor P. G.
Published: March 2011

Part of a strategy for evaluating the compliance of geologic repositories with Federal regulations is a modeling approach that would provide realistic release estimates for a particular configuration of the engineered-barrier system. The objective is to avoid worst-case bounding assumptions that are physically impossible or excessively conservative and to obtain probabilitistic estimates of (1) the penetration time for metal barriers and (2) radionuclide-release rates for individually simulated waste packages after penetration has occurred. The conceptual model described in this paper will assume that release rates are explicitly related to such time-dependent processes as mass transfer, dissolution and precipitation, radionuclide decay, and variations in the geochemical environment. The conceptual model will take into account the reduction in the rates of waste-form dissolution and metal corrosion due to a buildup of chemical reaction products. The sorptive properties of the metal-barrier corrosion products in proximity to the waste form surface will also be included. Cumulative releases from the engineered-barrier system will be calculated by summing the releases from a probabilistically generated population of individual waste packages.
Hydrothermal Waste Package Interactions With Methane-Containing Basalt Groundwater
Authors: McGrail B. P.
Published: March 2011

Hydrothermal waste package interaction tests were conducted with a mixture of crushed glass, basalt, and steel in methane-containing synthetic basalt groundwater. In the absence of gamma radiolysis, methane was found to have little influence on the corrosion behavior of the waste package constituents. Under gamma radiolysis, methane was found to significantly lower the solution oxidation potential when compared to identical tests without methane. In addition, colloidal hydrocarbon polymers that have been produced under the irradiation conditions of these experiments were not formed. The presence of the waste package constituents apparently inhibited the formation of the polymers. However, the mechanism which prevented their formation was not determined.
Probabilistic Analysis of Human Intrusion in a High Level Nuclear Waste Repository in Salt Using Draft EPA Assumptions
Authors: Harper William V. , Raines Gilbert E.
Published: March 2011

The Office of Nuclear Waste Isolation (ONWI) has planned performance assessments that will quantify various performance measures for the eventual licensing of a repository in salt. In addition to studying “expected” conditions, selected discrete event scenarios must be analyzed. This paper presents a probabilistic analysis of a human intrusion scenario in which boreholes may be drilled into the repository, contact nuclear waste, and release the radionuclides to the environment. A stochastic analysis using draft EPA limiting factors regarding probability of drilling and quantities of water flow is compared to the proposed EPA 10,000 year limits. The years in which boreholes penetrate the repository are probabilistically determined in each iteration of the analysis. For each borehole, the probability of contacting radioactivity is an increasing function of time. When a borehole does make contact with radioactivity, the curie release of a given nuclide is a function of solubility limits and current inventory. Prediction intervals and complementary cumulative probability distribution functions are developed for the curie release as a fraction of the EPA limits. Radionuclide releases are small fractions of the EPA limits. This study shows that there is a high expectation that the EPA requirements would be met with a repository in salt.
Effects of Radiation-Induced Stress on the Chemical Durability of Nuclear Waste Glasses
Authors: Ougouag Abderrafi M. , Machiels Albert J.
Published: March 2011

The growth of stresses in irradiated glasses is modeled, and the resulting effects on chemical durability are evaluated. It is shown that in actinide-doped glasses, maximum stresses are small when compared to those that act on a plane parallel to the ion tracks of an implanted glass, at equivalent fluences. The theory also offers an explanation for the apparent change in the dissolution enhancement factor with fluence in ion-implantation experiments.
A Generalized Model for the Analysis of Groundwater Radiolysis
Authors: Nicolosi Stephen L.
Published: March 2011

A generalized groundwater radiolysis model which is under development at Battelle-Columbus is described. This model uses a 55 reaction basis set for the radiolysis of the solvent. The basis set of reactions was chosen from the literature after comparing several descriptions against experimental data. This basis set has been augmented with 17 additional reactions to allow the description of the radiolysis of groundwater containing iron. The development of this mechanism is described, and comparisons with experimental data are shown.
Functions of the Materials Review Board
Authors: Steindler M. J. , Seefeldt W. B.
Published: March 2011

Some nuclear waste is destined for disposal in deep geological formations. The disposal system for wastes from commercial nuclear activities, and perhaps also for high-level wastes from defense-related activities, is to be designed and operated by the Department of Energy (DOE) and licensed by the Nuclear Regulatory Commission (NRC). The Nuclear Waste Policy Act [1] outlines some of the procedures and schedules that are to be followed by DOE in carrying out its assignment in the disposal of high-level nuclear waste (HLW). The regulations of the NRC that deal with HLW [2] are only partly in place, and amendments (e.g., related to the unsaturated zone) are yet to be approved and issued. The Environmental Protection Agency (EPA) has issued only draft versions of the regulations pertaining to HLW disposal [3], but key features of these drafts are at present in adequate agreement with NRC documents. On the basis of the trends that have become evident in the last few years, the DOE will be required to substantiate performance predictions for all pertinent aspects of a repository, especially the performance of the engineered waste package. The basis for demonstrating that the waste package performance in the repository will be in concert with the requirements is data on the waste package materials. These key materials data must clearly be highly reliable, and DOE will be required to assure this reliability. This paper addresses the organization and functions that have been assembled to aid in establishing the quality of materials data that are important in the licensing of a waste repository.
Test Methods to Predict Long-Term Corrosion of Container Materials in Repositories
Authors: Merz Martin D. , Wang Rong
Published: March 2011

MCC test methods in support of basalt, salt and tuff repositories are described. The methods consist of three general corrosion tests for basalt, two general corrosion tests and three stress corrosion tests for salt, and two general corrosion tests for tuff. The tests encompass the various conditions that are expected in the different repositories. A summary is provided of experimental activities of the MCC, and detailed results of MCC 105.1 Test Method for Long Term General Corrosion in a Basalt Repository (Static System) for standardized, benchmark conditions are presented. A summary of the statistical treatment of data is provided with examples of confidence intervals and the dependence on number of test vessels. The total relative standard deviation for the mean corrosion penetration rate was 11.4% for a mean corrosion penetration rate of 0.0244 mm/yr for 120 d tests at 100°C.
The Chemical Environment in Cements
Authors: Glasser F. P. , Angus M. J. , McCulloch C. E. , Macphee D. , Rahman A. A.
Published: March 2011

The alkalinity of Portland cements is responsible for precipitation and low solubility of many radwaste species. The sources of alkalinity are evaluated and two chemical models, based on experimental and theoretical data presented enabling the effect of blending agents (PFA, silica fume, etc.) to be evaluated and the alkalinity of the system at longer ages predicted. The data take the form of a solubility model which is applicable to non-heat generating wastes.
Physical Properties of Saltstone: Physical Properties of Saltstone: A Savannah River Plant Waste Form
Authors: Langton Christine A.
Published: March 2011

A cement-based waste form, “saltstone,” has been designed for disposal of Savannah River Plant low-level radioactive salt waste. Laboratory and field tests indicate that this stabilization process greatly reduces the mobility of all of the waste constituents in the surface and near-surface environment. Bulk properties of this material have been tailored with respect to salt leach rate, permeability, and compressive strength. Microstructure and mineralogy were characterized by SEM and x-ray diffraction analyses.

Compressive strength was found to increase as the water to cement ratio decreased. Porosity and mean pore size increased with increasing water to cement ratios. Bulk diffusivities of the various ions dissolved in the pore solutions were also found to increase as water to cement ratios increased.
Leachability of Cement Encapsulated West Valley Radwaste Streams
Authors: Grant D. C. , Smeltzer E. E. , Skriba M. C. , Cwynar J. C. , Eisenstatt L. R.
Published: March 2011

Low-level radwaste streams to be generated during the cleanup of the nuclear fuel reprocessing plant at West Valley, New York will require disposal in an environmentally acceptable manner. A study was conducted to determine if presently identified waste streams could be encapsulated in cement to produce a waste form which complies with present NRC guidelines for the disposal of.low-level radwaste streams. One waste stability guideline is leachability which was examined in this study. The leach testing was performed in accordance with the ANS 16.1 procedure. This static, deionized water test examined the leach rate of contaminants from radioactively spiked (Cs-137) samples of each waste type. The data obtained from this method were used to generate from diffusion calculations a parameter called a leachability index (L) which is related to the leaching characteristics of the solidified waste. All waste forms exceeded an L value of 6, which is the minimum suggested by the NRC “Branch Technical Position on Waste Form” for the disposal of Class B and Class C radioactive wastes.
Stability of NZP Waste Forms and their Application To ICCP Waste
Authors: Scheetz B. E. , Komarneni S. , Fajun W. , Yang L. J. , Ollinen M. , Roy R.
Published: March 2011

The crystal structure of NaZr2(PO4)3, (NZP), contains three distinct crystallographic sites which between them can readily accommodate the majority of elements that are present in high level nuclear waste. The applicability of this host phase to the immobilization of mixed zirconia/alumina waste from the Idaho Chemical Processing Plant (ICPP) was demonstrated. A waste form consisting of CaF2, a number of NZP phases and F-apatite was prepared and the results of leach testing reported. Detailed stability studies of the host sodium zirconium phosphate phase were also conducted as a function of temperature, pH and time.
Tuff-Cement or Concrete Interactions in the Repository Environment
Authors: Komarneni Sridhar , Roy Della M. , Kumar Amitabha
Published: March 2011

Hydrothermal interactions of tuff or tuff minerals with cement or concrete were investigated at 200 0C under a confining pressure of 8 or 30 MPa for I to 20 weeks. These chemical interactions produced crystalline hydrous calcium silicates such as Al-substituted tobermorite, xonotlite and gyrolite. Tobermorite was the most common interaction product of cement and tuff or tuff minerals because of pozzolanic reaction. The extent of cement hydration and the quantity of cement in the cement mix affected the abundance of tobermorite as expected. The reaction of concrete with tuff resulted in the formation of smectite in addition to tobermorite due to the generation of slight acidic conditions in this reaction mixture under the present hydrothermal conditions. The formation of tobermorite by the interaction of tuff with cement or concrete has positive implications to the physical (bonding) and chemical (sorption) properties in the repository sealing system because tobermorite (Al-substituted) acts both as a binding agent and as a cation exchanger.
Geochemical Performance Evaluation and Characterization of a Potential Cementitious Repository Sealing Material for Application in the Topopah Spring Tuff Nnwsi Investigations
Authors: Scheetz Barry E. , Roy Della M.
Published: March 2011

Preliminary geochemical evaluations of some portland cement based materials have been made in Nevada Nuclear Waste Storage Investigations (NNWSI), for possible nuclear waste repository sealing applications in welded tuff focused in the Yucca Mountain area. Portland cement based sealing materials have been evaluated in the NNWSI for possible sealing applications in a nuclear waste repository in the Topopah Spring tuff member. Cementitious sealing materials developed for long-term stability should be as nearly as possible in thermodynamic equilibrium with the host rock, or any disequilibrium should not have negative impact upon the integrity of the host rock. A primary step in achieving this equilibrium condition is to minimize the chemical potential between the sealant and the host rock. Two different approaches were evaluated to achieve this compatibility. The one approach utilized indigenous materials for the formulation of the concrete and the other utilized reactive admixtures to adjust the bulk chemical composition of the concrete formulation to approximate the local rock bulk chemistry. Testing of both formulations at conditions that represented the maximum credible temperature and pressure conditions of a repository were completed and show that the use of an indigenous tuff in the formulation without adjusting the matrix chemistry caused alterations which might compromise the performance of the concrete. In contrast, the chemically adjusted cementitious formulation exhibited minimal alteration in the J-13 groundwater of the designed test.
Heavy Phosphorus Implantation of Ge0.83Si0.17 Epitaxial Layers
Authors: Bean J.C. , Fiory A.T. , Hopkins L.C.
Published: March 2011

Epitaxial Ge-Si alloy films were grown on Si(100) by molecular beam epitaxy, subsequently given a shallow P implant, and subjected to rapid thermal processing. Heat treatment causes solid-phase epitaxial regrowth of the amorphized implanted layer similar to the case of pure Ge. Phosphorus redistribution, loss, and trapping at the Ge-Si/Si interface are also observed. Anomalous electrical activation is observed for P concentrations below 1 at.%, where the-carriers are either trapped or compensated at room temperature, but not below 100K. Analyses were carried out by Rutherford backscattering and channeling, secondary ion mass spectrometry, and temperature-dependent electrical transport.
Positive-Tone Polymer Images by Surface Modification in Ion Beam Exposures
Authors: Hiraoka Hiroyuki
Published: March 2011

Under exposures of high energy radiation in vacuum, decarboxylation takes place efficiently on polymer surfaces having carboxylic acid groups. Low energy electron and ion beams are particularly efficient in these chemical reactions on the surfaces because their energy deposition is limited to very shallow depths. The surface areas exposed to the radiation have properties similar to hydrocarbons after decarboxylation, resulting in non-reactions in gas phase silylation, while unexposed areas undergo silylation readily due to the presence of reactive acid groups. The non-silylated areas etch faster in oxygen reactive ion etchings, giving rise to positive tone polymer images. Polymers like poly(methacrylic acid), poly(acrylic acid), and their copolymers have been used. Other polymers like poly(styrene), poly(chloromethylstyrene), and Novolac resins can also be used, because these polymers readily undergo photo-oxidation under uv-irradiation in air, generating carboxylic acid groups on their surfaces.
Outgassing of Photoresist During Ion Implantation
Authors: Roche D. , Michaud J.F. , Bruel M.
Published: March 2011

Outgassing of HUNT HPR 204 photoresist during ion implantation has been characterized by means of quadrupole mass analysis. The influence of the various parameters (implantation eneray, beam current, ion species) has been studied in order to point out the evolutions, in terms of time or implanted dose, of the target chamber pressure and the peaks at masses 26 and 28, characteristic of the photoresist outqassing. The pressure integral in the target chamber which is easily related to the integrated outgassing flux, has been found essentially dependent on the total energy deposited in the photoresist layer and on the ion penetration depth.
A Study of Ion Beam Induced Adhesion Effects in Some Metal/Insulator Systems
Authors: Sood D. K. , Skinner W. M. , Gazecki J. , Williams J. S. , Baglin J. E. E.
Published: March 2011

Cooper and platinum films were deposited by evaporation and sputtering techniques onto prepared substrates of alumina, sapphire (cut along an a or c axis) and yttria stabilized zirconia. The films are then bombarded with ions of H, He, Ne and Kr at energies within and outside the ion beam mixing regime. Ion beam induced modification in adhesion and its thermal stability were measured by three techniques - a scratch test, a pull test and a peel test. Adhesive energies of these solid-solid systems were determined by contact angle measurements using scanning electron microscopy. The resistance of the films to chemical attack is modified by ion bombardment and will be shown to correlate with adhesion alterations.
Buried SiC Layers in (100) Bulk Silicon and Silicon-on-Sapphire Produced by Carbon Ion Implantation
Authors: Kroko L. , Golecki I. , GLASS H.L.
Published: March 2011

We demonstrate the formation of buried layers of SiC in (100) single-crystal bulk Si and silicon-on-sapphire by ion implantation of 125-180 keV, (0.56-1.00)×1018 C/cm2 at 30-40 μA/cm2 into samples held at 450-650¼C. The as-implanted and 950°C annealed samples are characterized by differential infra-red absorbance and reflectance, Rutherford backscattering and channeling spectrometry, X-ray diffraction, four-point probe, Dektak profilometry, I-V measurements, spreading resistance and secondary ion mass spectrometry.
Furnace and Rapid Thermal Annealing of P–Implanted Silicon for Solar Cell Fabrication
Authors: Harrison H.B. , Lee Y.H. , Pogany A. , Kenny M.J.
Published: March 2011

Single crystal silicon has been implanted with low energy (20 keV) phosphorus ions and a comparison made of furnace annealing (which produces excellent solar cells) and rapid annealing using a radiant incoherent light source. The light source is used to anneal and activate implanted layers in the isothermal mode on a time scale of the order of seconds compared with the much longer furnace annealing times of several hours.

Initial results using the incoherent light source show a high dark current and inferior photoresponse. However a subsequent thermal treatment at 600°C for 10–15 minutes shows that the resultant photoresponse can approach that of the longer time furnace anneal. Transmission electron microscopy shows the formation of large voids (20–100 nm) after the initial annealing phase. These reduce in size after furnace annealing. This photoresponse may be related to this void formation.
Structural Characterization of Dynamic Annealing Effects of P+ Implanted SI
Authors: Berti Marina , Drigo A.V. , Gabilli E. , Lotti R. , Lulli G. , Merli P.G. , Antisari M. Vittori
Published: March 2011

Some renarks about the mechanism for dynamic annealing during high dose rate P implantation of Si are reported. TEM observations and RBS channeling measurements show that the ion bombardment enhances the amorphous to crystalline transformation in the temperature range 200 ≤ T ≤ 600°C. It is found that the ratio between the observed recrystalli-zation velocity and the thermal SPE velocity decreases with increasing temperature. This indicates that a transition temperature must exist between the ion-assisted recrystallization regime and the ?lermal SPE regime. For the energy (100 keV) and the dose rate (60,uA/cm2) used in our experiments the transition temperature is about 700°C.
Electronic and Magnetic Properties of Interstitial 3d Impurities in Silicon
Authors: Katayama-Yoshida H. , Zunger Alex
Published: March 2011

Self-consistent spin-unrestricted all-electron Green's function calculations are reported for the first time for a series of interstitial 3d impurities in silicon. The calculations, performed within the selfinteraction- corrected local-spin-density fromalism show: (i) not all 3d impurities follow Hund's rule: Tio, Ti−, Vo, V+ and Co2+ have a low-spin ground state, (ii) the angular momentum part gL of g-value is quenched due to p-d hybridization effects, (iii) covalency explains also the chemical trends in the central hyperfine coupling constants, (iii) chemical trends in donor andacceptor transitions are reproduced and are consistent with a high-spin to lowspin transition at the low-Z end and high-Z end of the 3d series, (iv) A number of predictions are offered.
Identification of Chalcogen Defects in Silicon
Authors: Beeler Franz , Scheffler Matthias , Jepsen Ove , Gunnarsson Olle
Published: March 2011

We show how self-consistent total-energy calculations can be used to identify the position of defects in semiconductors. Despite intensive experimental research on S, Se and Te point defects in Si, it has remained unclear whether these impurities occupy substitutional or Td-interstitial sites. Our Green-function total-energy calculations show that the substitutional site is favored by several eV and therefore the stable defect position is identified as substitutional. We further consider the formation energies of distant defect pairs consisting of a substitutional chalcogen and a Si self-interstitial and we study the reaction where the two constituents change places.
Microscopic Identification of Defects in Semiconductors by Electron-Spin-Resonance and Related Techniques
Authors: Schneider Jorgen
Published: March 2011

This talk will review and compare very basic intrinsic and extrinsic paramagnetic defect structures which are characteristic for group IIB-VI, III-V and elemental semiconductors. The case of cation vacancy related defects in ZnS and ZnSe, that of antisite defects in GaP and GaAs and that of deep impurity donors in IIB-VI semiconductors and silicon will be treated as representative examples, thus illustrating the possibilities (and limitations) of the ESR technique.
Distant Pair Interactions Involving Antisites in GaAs
Authors: Cavenett B.C. , Deiri M.
Published: March 2011

An investigation of the photoquenching behaviour in semi-insulating GaAs at low temperature shows that the ASGa antisite MCD-ODMR is persistently quenched while a broad vacancy-like resonance near g=2, which shows a variation of g-factor with absorption energy, broadens and becomes energy independent. The results are discussed in terms of interacting antisite and vacancy centres in analogy with the distant pair model for donor-acceptor pair recombination and the advantages of the triplet model for the EL2 metastahle state are reviewed.
Characterization of Semiconductors and Semiconducting Superlattices Using High-Resolution Photoluminescence Spectroscopy
Authors: Reynolds D. C. , Bajaj K. K. , Litton C. W.
Published: March 2011

High resolution photoluminescence for the identification of impurities and defects in semiconductors has emerged as a powerful technique. We review the technique with emphasis on GaAs realizing that it is applicable to many different semiconductor materials. The binding energies of thle ground state and of several low-lying excited states of the impurity centers are determined by studying the radiative transitions associated with excitons bound to neutral donors or acceptors. Recent developments in the studies of GaAs-AlGaAs multi-quantum-well (MQW) structures using high resolution photoluminescence are also reported. Variations of the energies of the various transitions in MQW structures as a function of well size are presented. Estimates of the interfacial quality in these heterostructures are made from line shape analysis.