bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of Cesium and Strontium Migration Through Sodium Bentonite Altered by Cation Exchange with Groundwater Components
Authors: Jacobsen J. S. , Carnahan C. L. 
Published: March 2011

ABSTRACTNumerical simulations have been used to investigate how spatial and temporal changes in the ion exchange properties of bentonite affect the migration of cationic fission products from high-level waste. Simulations in which fission products compete for exchange sites with ions present in groundwater diffusing into the bentonite are compared to simulations in which the exchange properties of bentonite are constant.
The Speciation of Uranium and Thorium at the Broubster Natural Analogue Site, Caithness, Scotland
Authors: Read D. , Hooker P. J. 
Published: March 2011

ABSTRACTAnomalously high concentrations of uranium, thorium and the rare earth elements (REE) are associated with peat-rich soils near Broubster, northern Scotland. The source of the anomaly has been traced to a hydrocarbon-containing mineralised zone within a uraniferous, calcareous Devonian sedimentary sequence. From there, the elements have been transported approximately 100 metres downslope and fixed within waterlogged peat deposits. The degree of concentration and fractionation accompanying actinide transport is extreme. This paper describes the results of a theoretical modelling exercise and complementary experimental study carried out to determine the chemical speciation of actinides at the Broubster site. Efforts made to identify mobilisation and retention mechanisms for uranium and thorium have led to the development of a simple model for actinide behaviour in the peat soils. The work, which forms part of an on-going programme of research into natural radionuclide migration, is primarily aimed at improving confidence in predictive models used for radiological assessment.
Modeling Flow and Transport in Fractured Crystalline Rock using the Discrete Fracture Network Concept
Authors: Dverstorp Björn , Nordqvist Wille , Andersson Johan 
Published: March 2011

ABSTRACTThe conductive properties of fractured crystalline rock vary considerably in space, which implies that the flow is very unevenly distributed in space. The large variability raises doubts on modeling the flow with a large scale continuum model. Modeling flow in fractured crystalline rock in a network of discrete fractures provides an increased understanding of the character of the rock heterogeneity. Compared to a continuum model discrete models introduce new parameters such as statistical distributions for fracture orientation, radii, density and transmissivity that need to be estimated. By analyzing the migration experiment in the Stripa research mine in Sweden it is demonstrated how to calibrate and eventually validate a discrete model on field data. The flow analysis shows that the flow distribution on the drift roof and in two out of three vertical boreholes can be modelled with the same discrete model. The properties of the third borehole differ substantially. Initial attempts of analyzing the tracer experiment are also described.
The Migration Behaviour of Transuranium Elements in Gorleben Aquifer Systems: Colloid Generation and Retention Process
Authors: Kim J. I. , Buckau G. , Rommel H. , Sohnius B. 
Published: March 2011

ABSTRACTThe colloid generation as a part of the migration process of trans-uranic ions has been studied in the Gorlben aquifer system. From the migration study for the Gorleben repository site, typical examples are selected to demonstrate the influence of colloids. The quantification of colloid generation and its influence on the dissolution and geochemical sorption of transuranium elements are discussed.
Testing Safety Assessment Models Using Natural Analogues in High Natural-Series Groundwaters. The Second Year of the Pocos De Caldas Project.
Authors: Smellie John , Chapman Neil , McKinley Ian , Franca Eduardo Penna , Shea Michael 
Published: March 2011

ABSTRACTProgress in the second year of the project is outlined in terms of four analogue objectives. Results of modelling of the preliminary data sets on groundwater chemical speciation of radionuclides, colloids, redox processes, and hydrothermal fluid transport are presented.
The Solubility and Sorption of Radium and Tin in a Cementitious Near-Field Environment
Authors: Bayliss S , Ewart F. T. , Howse R. M. , Lane S. A. , Pilkington N. J. , Smith-Briggs J. L. , Williams S. J. 
Published: March 2011

ABSTRACTThe solubility and sorption of radium and tin have been studied for a cementitious near-field environment.The solubility of radium was observed to be greater than 10−7M, even with the addition of IM sulphate to the cement equilibrated water. The values of Rn for radium varied from 102 to 103 ml g−1 for the cement types and initial radium concentrations studied.The solubility of tin was observed to be about 10−4M for a range of cement equilibrated waters above tin oxides and metallic tin. The solubility of tin was observed to increase with pH. Tin solubilities were not affected by the redox conditions. Tin was present in a range of particle sizes in the sorption studies. A value of RD of 104 ml g−1 was observed for tin species less than 0.45μm.
Geochemical Analogue Study in the Krunkelbach Mine, Menzenschwand, Southern Germany: Geology and Water-Rock Interaction
Authors: Hofmann Beda A. 
Published: March 2011

ABSTRACTThe mineralogy, geochemistry and hydrochemistry of water-bearing zones in the Krunkelbach vein-type U deposit, Southern Germany, have been investigated. The U ore body is aligned parallel and a few metres apart from a major waterbearing structure. Oxidation of pitchblende and of iron sulfides has been extensive down to a depth of at least 240 m. U retardation is due to neoformation of U(VI)-phases and to fixation on iron hydroxides, gorceixite and clay minerals. Under the prevailing conditions, Ra is fixed in baryte, but Ba and probably Ra were more mobile during earlier stages of the oxidation event, probably due to the presence of intermediate valence sulphur species as a product of pyrite oxidation.
U - Th - REE Mobility and Diffusion in Granitic Environments During Alteration of Accessory Minerals and U - Ores: A Geochemical Analogue to Radioactive Waste Disposal
Authors: Cathelineau M. , Vergneaud M. 
Published: March 2011

ABSTRACTU, Th and REE concentrations and distributions have been studied in granitic rocks, using a multidisciplinary approach involving fission-track micromapping of cracks in oriented samples, together with mineralogical and geochemical studies of the different U-Th-REE bearing phases. The behaviour of U, Th and Nd, considered as chemical analogue elements of the radiotoxic nuclides, was investigated either in the vicinity of microsites (accessory mineral environment) or along plurimetric sections around U-ore bodies. The different granite minerals, especially the accessory minerals (uraninite, monazite, thorite, apatite, xenotime), as well as U-ores, present different initial concentrations of U, Th and REE. Limitations to the analogy between these U-Th-REE concentrations and the radwastes is discussed as a function of their mineralogical features, chemical composition, size and solubilities. These primary concentrations present different behaviour when subjected to hydrothermal alteration, such as propylitization, phyllite type alteration, or clay alteration. Results show that in reduced media, in the temperature range 80–200°C, the rate of mobilization of U, Th, REE is relatively moderate. However, fluids enriched in fluorides, phosphates or carbonates may significantly solubilize and transport U and REE under specific conditions. In addition, the degree of opening of the microcracks and faults, as well as the oxidation-reduction processes, are critical parameters for the efficiency of the granitic geological barrier.
Effect of Environmental Materials on Aqueous Corrosion of R7T7 Glass
Authors: Godon N. , Vernaz E. , Thomassin J. H. , Touray J. C. 
Published: March 2011

ABSTRACTR7T7 glass behavior was investigated in contact with eleven different materials including smectites, bentonites, illites, granite and sand. The experiments were conducted at 90°C under atmospheric pressure with a 4 cm−1 SA/V ratio using two grams of material in double distilled water under static leaching conditions without renewal of the leachate. For each material a control test was conducted under the same conditions but without the glass specimen, as well as a series of tests on glass alone, without the environmental material. Kinetics studies lasting up to 364 days were performed on four selected materials.The test results (mass loss, ICP analysis of the leachates, SEM and TEM observations) showed relatively slight glass alteration in contact with sand, granite and one bentonite (i.e. the same order of magnitude as glass alone in deionized water), but greater alteration of glass in contact with all the other clays.The significant differences in glass behavior in contact with environmental materials can be accounted for by the behavior of the latter in solution: activated bentonite releases very large amounts of silicon and sodium into solution while smectite seems to remove silicon from solution.
Cluster Size Measurements in an Ionized Cluster Beam System
Authors: Turner D. E. , Lakin K. M. , Shanks H. R. 
Published: March 2011

ABSTRACTIonized Cluster Beam (ICB) deposition has received considerable attention in recent years because of its potential application to low temperature semiconductor and metal film growth. To better understand this deposition process, however, it is necessary to determine the properties of the cluster source and the cluster size distribution obtained. This paper discusses the design of a time-of-flight mass spectrometer with single atom resolution for the measurement of cluster size in a conventional ICB deposition system. Results have been obtained for silver and germanium deposition. In both cases most of the clusters have been found to consist of less than 35 atoms. With the high resolution spectrometer it has been possible to show that certain cluster sizes are more stable than others.
Precipitation of Ar, Kr and Xe in Ni at Room Temperaturey
Authors: Liu A. S. , Birtcher R. C. 
Published: March 2011

ABSTRACTTransmission electron microscopy (TEM) has been used to study the precipitation of inert gases (Ar, Kr and Xe) injected into Ni at room temperature. The nucleation and size distribution of precipitates were found to be insensitive to the type of inert gas atom but dependent on gas concentration (ion fluence). The precipitate density decreases and the sizes increases with increasing gas concentration. In all cases, the inert gases precipitate as solid fcc crystals with their axes aligned with those of the host Ni lattice. For the same inert gas concentration, the lattice parameter is larger for the higher atomic mass in accord with bulk results. The lattice parameter of each type of inert gas precipitate increases with increasing gas concentration owing to the pressure relaxation that accompanies precipitate growth. This results in melting of large precipitates in accord with the behavior of bulk quantities of the gases at low temperatures.
The Effects of Ar-Bombardment on the Dissolution and Reprecipitation of Carbonitrides Implanted Into Low Carbon Steel
Authors: Ramos Stella M. M. , Amaral L. , Behar M. , Vasquez A. , Zawislak F. C. 
Published: March 2011

ABSTRACTThe effects of Ar post-bombardment on the dissolution and reprecipitation of carbonitrides present in implanted 1020 low carbon steel are investigated using conversion electron Mössbauer spectroscopy (CEMS). The results are compared with similar experiments where samples of the same steel were post-bombarded with He. The experimental data show that the Ar is more efficient in the dissolution of precipitates and also more efficient in the precipitate retention at 450 °C, for the same peak concentration.
Temperature and Orientation Effects in Iron Nitride Crystal Formation
Authors: Lowder L. J. , Franzen W. , Culbertson R. J. 
Published: March 2011

ABSTRACTPure rolled iron foils 0.025 mm thick have been implanted at two different angles of incidence and at several different temperatures. The implantation dose in each case was 5×1017 atoms/cm2. Both implanted and unimplanted foils were analyzed by transmission x-ray diffraction. Foils implanted at 320 ± 5°C exhibit peaks that correspond to the formation of several different phases of iron-nitride crystals, as observed by other investigators.[ 1,2] No such formation takes place at an implantation temperature of-20°C. We have evidence that the orientation of the iron nitride crystals is correlated with the orientation of the iron crystals.
Microstructural Characterization of Al2O3 Following Simultaneous Triple Ion Bombardment
Authors: Zinkle S. J. 
Published: March 2011

ABSTRACTThe through-range microstructure of polycrystalline alumina has been examined by cross-section TEM following simultaneous implantation of 2.0 MeV Al+, 1.44 MeV O+, and 0.2 to 0.4 MeV He+ ions at room temperature to a dose of 3.1 keV/atom. The specimen remained crystalline following the irradiation, and four distinct radiation-induced defect features were observed: Network dislocations, dislocation loops, small cavities, and oblong clusters that may be aluminum colloids. The microstructure near the implanted ion region was qualitatively similar to that observed in irradiated regions far from the implanted zone.
Evaluation of Multilayers for Soft X-Ray Fabricated by Ion Beam Sputtering.
Authors: Kataoka I. , Yamada I. , Eto K. , Ito K. 
Published: March 2011

ABSTRACTMultilayer structures of Li20 and Ni were deposited onto polished fused quartz by the dual ion beam sputtering method. Optical and physical properties of the multilayer structure were evaluated. Reflectivity of multilayer mirrors at an incident angle of 79.6 deg. was 17% for 44Å(C-K line). There was good agreement with the calculated value considering the interface roughness and residual oxygen contamination in the Ni layer from the background of Li2O deposition.
Ion-Beam-Induced Epitaxy and Solute Segregation at the Si Crystal-Amorphous Interface
Authors: Poate J. M. , Jacobson D. C. , Priolo F. , Thompson Michael O. 
Published: March 2011

ABSTRACTSegregation and diffusion of impurities in amorphous Si during furnace and ion-beam-induced epitaxy will be discussed. The use of ion beams to enhance the crystal growth process has resulted in novel behavior for fast diffusers such as Au. Diffusion is enhanced in the temperature range 300–700 K with activation energies ∼0.3 eV. Segregation and trapping are analogous to behavior at liquid-solid interfaces
Study of Enhanced Solid Phase Epitaxy of Amorphous Silicon with Low Concentrations of Implanted Phosphorous
Authors: Jeon Young- Jin , Park Won Woo , Becker M. F. , Walser Rodger. M. 
Published: March 2011

ABSTRACTIn this work we measured the functional dependence of the solid phase epitaxial (SPE) regrowth of amorphous silicon on the implanted phosphorous concentration, Np. The growth rates of self-ion amorphized layers in silicon wafers with (100) substrate orientation were measured by in situ, high precision, isothermal cw laser interferometry for temperatures from 460°C to 590°C, and concentrations in the range 2x1017 cm-3<Np<4x1020 cm-3. For low impurity concentrations, the fractional increase in the intrinsic SPE growth velocity ΔV/Vi depended linearly on Np as previously established for boron. For a given impurity concentration, the relative change V/Vi decreased with increasing annealing temperature.
Ion-Assisted Regrowth of Deposited Si Layers Mechanisms and Morphology
Authors: Priolo F. , Spinella C. , Ferla A. La , Battaglia A. , Rimini E. , Ferla G. , Carnera A. , Gasparotto A. 
Published: March 2011

ABSTRACTIon-assisted regrowth of chemical vapor deposited amorphous Si layers was investigated for different cleaning procedures. The process was directly monitored by transient reflectivity measurements. The c-a interface stops at the deposited layer/substrate interface for doses depending on the effectiveness of the cleaning procedure in removing the native oxide. Small concentrations of twins are found in the regrown layer. Their amount is also correlated to the cleaning procedure. In oxygen implanted bare Si samples the ion-induced growth rate is reduced to 0.3 of the normal value at a peak O concentration of 1 X 1021/cm3. The results on the ion-induced regrowth of deposited layers are explained in terms of oxygen profile broadening during irradiation and retardation of the growth for the presence of dissolved O.
Ion Beam Self Annealing in Thin Silicon Films
Authors: Rubio J. D. , Vijay R. P. , Hart R. R. , Pearce J. D. 
Published: March 2011

ABSTRACTResidual lattice disorder in lμm-thick silicon films as a function of the dose rate of 120 keV Ar+ ion implantations has been investigated. At a fluence of l×1 014 ions/cm2, low dose rates produced a highly damaged surface layer as expected; however, at a dose rate sufficient to locally heat the implanted film to a temperature of approximately 700°K, essentially complete annealing of the lattice disorder was observed. This temperature is significantly less than that normally required for post-implant thermal annealing. Measurements of lattice disorder were based on medium energy Rutherford backscattering and channeling analyses.
Furnace Anneal of A–Axis Sapphire Amorphised by Indium Ion Implantation
Authors: Sood D. K. , Cao D. X. 
Published: March 2011

ABSTRACTIndium implantation at 77°K into a–axis sapphire to peak concentrations of 6–45 mol % In produces amorphous surface layers. Isothermal annealing in Ar at temperatures between 600–900°C shows effects strongly dependent on ion dose. At lower doses <2×1016 In/cm2, the amorphous layer undergoes epitaxial regrowth as the amorphous to crystalline interface advances out towards the surface. Regrowth velocity is high in about the first half hour of the anneal. Regrowth obeys Arrhenius behaviour with an activation energy of 0.7eV for initial faster growth and 1.28eV for further anneal times. The amorphous phase transforms directly to ⊥-A12O3 without any evidence of an intermediary γ-phase. At higher doses, epitaxial regrowth is substantially retarded and rapid diffusion of In within the amorphous phase dominates.
Radiation Damage of SiO2/Si By Energetic Neutral Beam and Vjuv Photons
Authors: Mizutani Tatsumi , Nishimatsu Shigeru , Yunogami Takashi 
Published: March 2011

ABSTRACTTo clarify the generation mechanism of radiation damage induced in SiO2/Si by plasma processes, effects of three different beams, i.e., ions, neutrals and vacuum ultraviolet (VUV) photons have been evaluated independently. The radiation damage caused by these energetic bombardments has been measured by capacitance-voltage (C-V) measurements. These reveal that bombardments with a 250 eV Neo neutral beam generate + far less flat-band voltage shifts ( ΔVFB) than those with a Ne+ ion beam of equal kinetic energy. This c n be interpreted in terms of the differences in charge build-up and in hole production upon the incidence of these particles. VUV photons produced in the plasma are also responsible for large ΔVFB.
Interband Optical Properties of the Microcrystalline Component within the Damage Layer of Be+ - Implanted GaAs
Authors: Feng G. F. , Zallen R. 
Published: March 2011

ABSTRACTThe damage layer in unannealed Be+-implanted GaAs samples (45-keV Be+ ions, 1013 to 5 × 1014 ions/cm2) consists of a fine-grain mixture of amorphous GaAs and GaAs microcrystals, with the characteristic microcrystal size L of the microcrystalline component decreasing with increasing fluence. We have carried out reflectivity measurements on these samples for photon energies from 2.0 to 5.6 eV, in the electronic interband regime. Using Lorentz oscillator analysis and the effective medium approximation, we have extracted the dielectric function of the microcrystalline component (μ-GaAs) within the damage layer. The optical properties of μ-GaAs deviate appreciably from those of the bulk crystal near the interband absorption peaks. The linevidths of these peaks are found to increase over the bulk-crystal value by an amount proportional to (l/L), the increase being about 0.2 eV when L =100 Å. These finite-size effects can be understood in terms of a lifetime reduction caused by the short time it takes for electrons to reach the microcrystal boundaries.
Characteristics of Si-Implanted (211) Versus (100) GaAs
Authors: Epp J. , Dillard J. G. , Siochi A. , Zallen R. , Cole E. D. , Sen S. , Vaseashta A. , Burton L. C. 
Published: March 2011

ABSTRACTTransport, Raman and XPS measurements were made on SI-implanted (1.7×1013cm−2, 50keV) and rapid-thermal annealed (100) and (211) GaAs substrates In an effort to distinguish differences between the two orientations. With these techniques, no significant differences were found. The implant-damage depth was about 1200Å for both orientations, with slightly higher near-surface damage (and lower mobility) apparent for (211). No unusual features in the (211) carrier concentration profile, as was previously reported, were evident.
Ion Implantation and Ion Beam Analysis of Lithium Niobate
Authors: Arnold G. W. 
Published: March 2011

ABSTRACTImplantations of He and Ti were made into LiNbO3 and the H and Li profiles determined by elastic recoil detection (ERD) techniques. The loss of Li and gain of H depends upon the supply of surface H (surface contaminants or ambient atmosphere). For 50 keV He implants into LiNbO3 through a 200 Å Al film, the small Li loss is governed by the interface H. This is also the case for He implants into uncoated LiNbO3 in a beam line with low hydrocarbon surface contamination; similar implants under conditions of greater hydrocarbon deposition result in proportionally larger Li loss and H gain in the implant damage region. The exchange is possible only for those He energies, i.e., 50 keV, where the damage profile intersects the surface. For Ti implants Li is lost with little H gain. For this case the Li loss is believed to result from radiation-enhanced diffusion. Where He implantation is used to establish waveguiding in LiNbO3, the presence or absence of H in the implanted region is crucial with regard to refractive index stability, due to the replacement of H by Li from the bulk.
Ion Implantation of KnbO3 and LiNbO3 at Elevated Temperatures
Authors: Buchal C H. , Irmscher R. , Günter P. 
Published: March 2011

ABSTRACTIon implantation, annealing and channeling of single crystalline samples of KnbO3 and LiNbO3 have been studied. Raising the substrate temperature above 600 K, greatly increases the tolerance of the crystals for high-dose implantation. In LiNbO3 dynamic recrystallization has been observed for the first time.