bluuebunny/crossref_metadata_2025_split huggingface dataset:
Van De Graaff ion Beams as a Useful Instrument of Scintillation Study of Crystals
Authors: Egorov V.K. , Zuev A.P. 
Published: April 2011

ABSTRACTThe search of new efficient scintillators can be simplified by the application of ion beams. The beam flux density of the order magnitude 1012–1014 ions/cm2sec can be easily achieved. The light yield visualization takes place even for weak scintillators as PbF2 under excitation by such beams. The light response of crystals for ion beams with E0 = 1–2 MeV is not connected with the Cherenkov's radiation. Ion excitation enables one to find the crystals with surface scintillation. Measurement were performed by means of 0.15–2.0 MeV H+, D+ and 4He+ ions with current 0.1–10 nA. Quantitative values of the light yield for the cubic phase of monocrystal PbF2 in random and channeling were obtained. Restrictions of the technique applicability are discussed.
Computer Modeling of the Optical Properties of Transition-Metal Ions in Solids
Authors: Bartram Ralph H. 
Published: April 2011

ABSTRACTComputational methods for modeling the optical properties of substitutional transition-metal impurities in insulating solids, potentially applicable to some scintillator and phosphor materials, are reviewed. Methods considered include crystal-field and semi-empirical ligand-field models; SCF-Xα-SW, SCF-RHF-LCAO, SCF-UHF-LCAO and CI ab initio methods: and ICECAP and HADESR embedded cluster methods with lattice relaxation. A detailed example of the application of the HADESR method to crystal-field spectra of Cr3+ in halide elpasolites is described. In this method, ab initio molecular-orbital calculations with effective core potentials are performed for selected ionic configurations. Simultaneous relaxation of the cluster and surrounding lattice, with mutual pair. potential interactions, is accomplished by a modified lattice statics program. Calculated properties include pressure-dependent optical transition energies, vibration frequencies and radiationless transition rates.
Calculation of Energy Levels of Cerium in Inorganic Scintillator Crystals
Authors: Andriessen J. , Dorenbos P. , van Eijk C.W.E. 
Published: April 2011

ABSTRACTFully relativistic ab initio calculations have been performed on energy levels of cerium in BaF2, LaF3, YAP and YAG. Also nonrelativistic calculations were done on cerium in LSO. The results are in fair agreement with experiment. Both the splitting of the 4f and 5d levels and the 4f–5d energy gap can be explained in the high symmetry crystal BaF2 as well as in the low symmetry crystals LaF3, YAP, YAG and LSO.
Charge-State Stability and Optical Transitions of Oxygen Impurities in Barium Fluoride Crystal
Authors: Wang L. M. , Chen L. Y. , Wu X. 
Published: April 2011

ABSTRACTThe linear combination of atomic orbital-molecular orbital embedded-cluster is used to investigate the electronic structure and binding energies of small oxygen impurity clustersin the local density theory. Binding energies for substitutional oxygen ions in BaF2 crystal are studied for its 2–, 1–, and 0 charge states. These are used to assess charge-state stability. The energy eigenvalue spectra and optical transitions are obtained by transition state calculations for the oxygen impurities. These results of optical transition calculations obtained are very good and provide a useful interpretation of the ultraviolet-absorption experiments.
Charge-Transfer Transitions of RE3+ —O2– Associates in BaF2 Crystal
Authors: Wang L. M. , Chen L. Y. , Wu X. 
Published: April 2011

ABSTRACTLocal-density-functional calculations have been performed to study the electronic structure and charge-transfer transitions of RE3+ —O2–(RE=Eu and Tm) associates in barium fluoride crystal. These systemsare simulated by small clusters which are surrounded by over 2000 point charges. It is found that the presence of oxygen in the lattice strongly influences the optical propertiesof RE3+ ions. The charge transfer transitions of RE3+O2– and RE ions with ligand F— ions derived from the embedded cluster are equal to 5.1 eV and 6.2 eV. The energy gap derived from the HFS model with REOBa2F6 clusters embedded in the crystal is 9.8 eV,which is near the experimental results.
Low Dose Rate Tests of Plastic Scintillator Plates and Wavelength Shifting Fibers
Authors: Zorn C. , Burkert V. , Kross B. , Majewski S. , Weisenberger A. , Wojcik R. , Asryan G. , Amaryan M. , Demirchyan R. , Egiyan K. , Sharabyan Yu. , Stepanyan S. 
Published: April 2011

ABSTRACTA low dose rate evaluation of several scintillators and wavelength shifters of interest to the CEBAF program was performed with a 60Co line source to a total dose of 160 Gray at a rate of 0.5 Gy/hr in a slowly flowing oxygen atmosphere. The samples included the following: (1) a 2 meter piece of Bicron BC412 scintillator being extensively used in the CEBAF Large Acceptance Spectrometer, (2) a 1 meter long piece of green scintillator doped with a uniquely fast green fluor (G2), (3) wavelength shifting fiber dopedalso with G2, and (4) grooved acrylic-based scintillator that is readout with the WLS fiber. The data indicates that the BC412 shows no loss in intrinsic light output, but does have an attenuation loss amounting to 10% at 1 meter and 16% at 2 meters. The fast green scintillator (and fibers) showed no damage. When read out by WLS fibers, the acrylic scintillator displayed a loss in intrinsic light output, but no change in attenuation.
Barium Fluoride Crystals for Future Hadron Colliders
Authors: Zhu Ren-yuan , Ma Da-an , Newman Harvey 
Published: April 2011

ABSTRACTThis report summarizes the radiation resistance of the current production BaF2crystals. An approach to implement optical bleachingin situis also presented. By using optical bleaching current production quality BaF2crystals could serve as an excellent candidate to construct a precision electromagnetic calorimeter at future hadron colliders.
Strength of Single Crystal Al2O3 Fibers in Ni-Based Intermetallic and Superalloy Composites
Authors: Bowman Randy R. , Locci Ivan E. , Draper Susan L. , Misra Ajay K. 
Published: April 2011

AbstractStrength degradation of single crystal Al2O3 fibers due to the effect of fiber/matrix interaction and processing of NiAl and superalloy matrix composites, was investigated. Strength loss was quantified by tensile testing fibers that were exposed to the matrix alloy using two different methods. In one method, the fibers were incorporated into a composite by either the Powder Cloth (P-C) or binderless powder technique. The fibers were then extracted from the composite by chemical dissolution of the matrix and subsequently tensile tested and examined by scanning electron microscopy. In the other method, fibers were sputter-coated with a similar matrix composition and heat-treated to simulate conditions similar to those experienced during composite powder fabrication methods. In the sputter coating method, the contribution of fiber-matrix reaction on fiber strength loss was isolated from the effects of the various mechanical loads which are present during powder fabrication. For all matrices studied, significant strength loss was observed both in fibers extracted from composites and in fibers sputter-coated and annealed. Although surface ridges and pores were observed on the degraded fibers, it remains uncertain whether these features were responsible for the strength loss.
Powder Metallurgy Processing of Intermetallic Matrix Composites
Authors: German Randall M. , Iacocca Ronald G. 
Published: April 2011

AbstractIntermetallic compounds are similar to ceramics because they are stoichiometric, with limited compositional ranges and brittle behavior. The limited ductility forces a reliance on powder techniques for shaping and consolidation. The high temperature character of intermetallics is beneficial to high temperature service, but this same attribute contributes to difficulty in processing. This paper reviews the several powder approaches to forming intermetallic structures. Examples are given on powders, consolidation options, and properties. Densification maps are introduced for estimation of consolidation cycles. Unfortunately, many of the composites exhibit little strengthening benefit from incorporation of reinforcing phases.
Pest Resistant and Low CTE MoSi2-Matrix for High Temperature Structural Applications
Authors: Hebsur M. G. 
Published: April 2011

AbstractThe objective of this investigation was to identify a pest resistant MoSi2-base matrix composition having properties suitable for SiC reinforcement. A 30 vol.% addition of fine Si3N4 particulates to MoSi2 significantly improved the low temperature accelerated oxidation resistance and thereby eliminated pest failure. Addition of Si3N4 also improved the high temperature oxidation resistance, strength and more importantly lowered the CTE of MoSi2 such that cracking was eliminated in a hybrid composite consisting of 30 vol.% Si3N4 and 30 vol. % SCS-6 fibers.
Processing Map and Flow Localization of a TiAl/TiB2 XD Composite
Authors: Zhao D. , Chaudhury P. K. , Thirukkonda M. , Valencia J. J. 
Published: April 2011

AbstractIsothermal compression tests were conducted on a particulate reinforced Ti-44Al–3V+7.5v/o TiB2 composite produced by the XD® process over wide ranges of temperatures and strain rates, 1050 to 1300 C and 0.001 to 1.0 s-1, respectively. Flow localization parameter analysis was performed to analyze the flow behavior of the composite under various processing conditions, and the results were compared to those by dynamic material modeling. Microstructural characterization was also conducted to correlate the flow behavior with post-deformation microstructures. With combined information on flow behavior and microstructures, the processing condition for relatively stable flow and uniform microstructure was determined to be 1300 C and 0.01 to 0.1 s-1.
Synthesis and Processing of Nanograined Fe - (Fe, Mo)6C Composite Powders
Authors: Sadangi R. K. , Kear B. H. , McCandlish L. E. 
Published: April 2011

ABSTRACTSpray Conversion Processing was used to synthesize high volume fractions (0.52 - 0.74) of nanograined (Fe, Mo)6C carbide dispersions in iron, starting from water soluble precursors. The essential features of the process are, (1) preparation of a chemically homogeneous precursor powder, and (2) thermochemical conversion of the precursor powder to the desired nanostructured composite powder through controlled gas-solid reactions. The thermodynamic and kinetic features of the gas-solid reactions, and the influence of various processing parameters on the structures developed, are discussed. The powders were consolidated to near theoretical density by pressureless sintering and hot pressing. All the consolidated samples had bicontinuous structures. Compared to M2 high speed tool steels, these high volume fraction carbide strengthened iron alloys display superior hardness values up to 500°C.
Preparation of Polypeptide-Dye Multilayers by an Electrostatic Assembly Process
Authors: Cooper Thomas M. , Angela L. Campbell , Noffsinger Carol , Gunther-Greer Janelle , Crane Robert L. , Adams W. Wade 
Published: April 2011

ABSTRACTTo develop novel optical thin films, we have prepared self-assembled polypeptide films by an electrostatic process. The films were placed on a glass slide previously silanized by an amino silane and given a positive charge by immersion in aqueous acid. Subsequent immersion of the slide in aqueous anionic solutions of either poly(L-glutamic acid), congo red, copper phthalocyanine tetrasulfonic acid orp-nitroaniline-modified poly(L-glutamic acid) resulted in deposition of the anions on the surface. Following anionic immersion, the slides were dipped into a cationic poly(L-lysine) solution. Alternate dipping into anionic and cationic solutions yielded multilayers. The thin films were characterized by optical absorption and circular dichroism. The optical density increased with dipping cycles. Circular dichroism measurements of the thin films showed induced dichroism of the congo red and phthalocyanine-containing films, suggesting formation of a locally ordered dye-polypeptide complex. Solution circular dichroism measurements of the polypeptides indicated a coil conformation, while poly(Lglutamic acid)/poly(L-lysine) complexes showed circular dichroism spectrum characteristic of a β-sheet.
Exfoliation of MoS2 Catalysts: Structural and Catalytic Changes
Authors: Valle M. Del , Avalos-Borja M. , Cruz J. , Fuentes S. 
Published: April 2011

ABSTRACTA study of the microstructural differences between exfoliated and non-exfoliated MoS2-based materials is presented, relating them to differences in their catalytic activity. Both commercial (crystalline) MoS2 and molybdenum sulfide catalysts prepared by thiosalt decomposition are subjected to chemical exfoliation reported to separate MoS2 monolayers from the original structure. Electron microscopy results show that the chemical treatment yields non-typical MoS2 nanostructures. Average surface area is also modified by exfoliation. The thiophene HDS activity of commercial MoS2 increases after exfoliation, while it decreases after exfoliation in the case of MoS2 catalysts.
Structure and Properties of Strained Crystalline Multilayers
Authors: Hoekstra J. , Yan H. , Kalonji G. , Jonsson H. 
Published: April 2011

ABSTRACTWe present a computer simulation study of thin crystalline multilayers constructed from two FCC solids with differing lattice constants and binding energies. Both materials are described by Lennard-Jones interatomic potentials and initially have the same orientation and coherent interfaces. We have studied systems in which interfaces are perpendicular to the common [100] and [111] directions, respectively. A novel technique for analyzing local atomic ordering, Common Neighbor Analysis, is used to identify structural characteristics in these systems. We have found several structural changes in the layers of smaller atoms, including an FCC to HCP transition. In a system with (111) texture, a coherent interface to incoherent interface transformation is observed. Calculations of elastic constants of these multilayer structures show that elastic anomalies are associated with the structural variations.
Chemical Vapor Synthesis of Nanostructured Ceramics
Authors: Chang W. , Skandan G. , Hahn H. , Danforth S. C. , Kear B. 
Published: April 2011

ABSTRACTA modification of the conventional inert gas condensation apparatus for making nanostructured powders, wherein as evaporative source is replaced by a chemical source, is described. The new chemical synthetic process, called chemical vapor condensation(CVC), combines rapid thermal decomposition and expansion of a precursor/carrier gas stream in a hot tubular reactor with rapid condensation of the product particle species on a cold substrate under a reduced inert gas pressure of 1-50 mbar. The process has been used to synthesize loosely agglomerated nanoparticles (6 to 10 nm) of n-SiCxNy, starting from hexamethyldisilazane (HMDS) as precursor compound. The phase, morphology, and composition of n-SiCxNy powders can be modified by heat treatment. β-SiC particles with grain size less than 10 nm form after annealing at 1300°C in flowing Ar. In a 1:1 NH3/H2 mixture n-SiCxNy powders transform into α-Si3N4 whiskers, with [100] growth direction.
FT-IR Characterization and Ab Initio Study of the Surface Species of a Nanosized SiC Powder
Authors: Baraton Marie-Isabelle , Besnaïnou Sylvette , Merhari Lhadi 
Published: April 2011

ABSTRACTThe v(SiH) stretching absorption band is known to be sensitive to the local environment of the silicon atom. The presence of SiH groups on silicon carbide surface can be taken advantage of to evaluate the oxidation degree of this ceramic powder.The surface analysis of a SiC nanosized powder was performed by FT-IR spectrometry. The evolution of the v(SiH) absorption band, followed in situ under controlled temperatures and oxygen pressures, consists in a frequency shift toward higher wavenumbers when oxidation proceeds. The resolution of the Sill absorption range into four subbands corresponding to the HSiOxC3−x possible surface groups showed the relative evolution of the different species. Ab initio SCF MO calculations on molecular models gave evidence of the charge transfer to the more electronegative oxygen atom, making the silicon atom more positive and seemingly strengthening the SiH bond and thus inducing an upward shift of the v(SiH) frequency.
Self-Assembly of Inorganic/Organic Multilayer Films
Authors: Zeppenfeld Astrid C. , Page Catherine J. 
Published: April 2011

ABSTRACTIn order to investigate the influence of substrate functionalization on the subsequent selfassembly of multilayer films, multilayers composed of alternating hafnium and 1,10-decanediylbis(phosphonic) acid (DBPA) have been grown on three different substrates. Substrates studied include gold wafers functionalized with 4-mercaptobutylphosphonic acid, silicon wafers functionalized using a hafnium oxychloride solution, and silicon wafers coated with an octadecylphosphonate LB-template layer. The nature of these films is probed using ellipsometry and grazing angle x-ray diffraction. These studies indicate that the overall order and the individual layer thickness can vary substantially from sample to sample and depend strongly on the initial surface functionalization prior to multilayer growth.
Layered Silicate/Polystyrene Nanocomposite
Authors: Moet A. , Akelah A. , Hiltner A. , Baer E. 
Published: April 2011

ABSTRACTNano-composites have been prepared from Na+ and Ca++ montmorillonite (MMT) in a polystyrene matrix via chemical intercalation. Vinyl monomer-g-MMT was prepared by exchanging the mineral cation by vinylbenzyl trimethylammonium chloride, thus rendering the mineral organophilic and forming polymerizable moieties directly bonded to the lamellar surface of the mineral. Styrene was added and polymerized by free radical in selected solvents. The ratio of mineral to the bound polymer ranged from 0.3 to 1.25 (by weight) depending on the initial mineral concentration in the feed and on the solvent used. The mineral domains in the composite, measured from suspension cast film fall in the range of 150 nm to 400 nm. Measured from compression molded samples, the domains were ca. 50 nm which is much smaller than the mineral aggregate and comparable to that of the primary particle of the mineral. WAXD disclosed that the d (001) spacing of MMT in the composite ranged from 1.7 to 2.5 nm suggesting that the mineral aggregates (ca. 10 μm) were dissociated into individual layers then reassembled into lamellar nanoclusters.
The Effect of Na-Bearing Thermal Solutions on Ca-Mg-Bentonite Sorption of Sr and Cs
Authors: Mukhamet-Galeyev Alexander P. , Kudrin Alexey V. , Nikonov Boris S. , Shikina Nadezhda D. 
Published: April 2011

AbstractThe sorption of Sr and Cs has been investigated on Ca-Mg-bentonite preliminary treated by 0.1–1.0 m NaCl solutions at 25, 170–250°C during 0.5–7 months. The bentonite remained stable in these conditions. Moreover, hydrothermal treatment has raised the sorption activity of the bentonite. The treated bentonite has shown a strong selectivity for Sr and less pronounced one for Cs. The sorption of the elements increased with temperature and decreased with NaCl content more significant for Sr, than for Cs. The distribution ratio Rd was nearly independent on ion loading for Cs and strongly increased up to 104.5 mL/g in 10−2.0−10−0.5 meq/g ion loading interval for Sr, dropping sharply at more concentrations.
Modeling Relations Between the Composition and Properties of French Light Water Reactor Waste Containment Glass
Authors: Ghaleb D. , Dussossoy J. L. , Fillet C. , Pacaud F. , Jacquet-Francillon N. 
Published: April 2011

AbstractModels have been developed to calculate the density, molten-state viscosity and initial corrosion rate according to the chemical composition of glass formulations used to vitrify high-level fission product solutions from reprocessed light water reactor fuel. Developed from other published work, these models have been adapted to allow for the effects of platinoid (Ru, Pd, Rh) inclusions on the molten glass rheology.
Sorption Aspects for in Situ Matrix Diffusion Modelling at Palmottu Natural Analogue Site, Sw Finland
Authors: Rasilainen Kari , Suksi Juhani , Hakanen Martti , Olin Markus 
Published: April 2011

AbstractConcentration profiles in rock matrix around water-carrying fissures were measured at Palmottu U deposit. The profiles were interpreted by the classical matrix diffusion concept. Site-specific sorption studies were performed for U using standard batch experiments and surface complexation modelling; the response of sorption isotherms was also tested. Sitespecific matrix properties as well as initial and boundary conditions were used in simulations. Our results indicate that matrix diffusion alone cannot explain the observed enrichment of U and its daughters in the rock matrix.
Principles and Practice of Reactive Transport Modeling
Authors: Lichtner Peter C 
Published: April 2011

AbstractThis paper presents a review of the principles underlying a continuum formulation of reactive transport in a porous medium. Partial differential equations representing conservation of mass are derived for transport by advection, diffusion, and electrochemical migration combined with chemical reaction of aqueous species and solids. Several examples are presented to illustrate the general theory. These include weathering along a narrow crevice, electrochemical migration in a dilute NaCl solution, secondary pyrite formation mediated through intermediate sulfur oxidation states, and a description of a uranium roll-front deposit. Numerical techniques which take advantage of the quasi-stationary state approximation, based on the much longer time scale involved in mineral alteration compared to that characterizing changes in the aqueous phase, permit solving the reactive transport equations over geologic time scales.
Mobility of Uranium, Thorium and Lanthanides Around the Bangombe Natural Reactor (Gabon)
Authors: Bros R. , Gauthier-Lafaye F. , Larque P. , Samuel J. , Stille P. 
Published: April 2011

AbstractNew mineralogical and isotopic studies were carried out on samples from the Bangombé natural nuclear reactor. This reactor is located at shallow depth in the weathering profile and has been subjected to severe supergene alteration. Textural evidence indicates partial dissolution of uraninite in the Bangombé ore related to precipitation of Fe-Ti oxi-hydroxides and clay minerals (kaolinite and metahalloysite). As a consequence of the alteration of the uraninite, uranium and f issiogenic rare earth elements were released in the clayey border of the reactor, whereas radiogenic232Th remained confined in the close vicinity of the core. A retention effect is also evidenced, under reducing conditions, in the black shales located above the reactor.
Modelling Study on Uranium Migration in Rocks Under Weathering Condition
Authors: Ohnuki Toshihiko , Murakami Takashi , Isobe Hiroshi , Sato Tsutomu , Yanase Nobuyuki 
Published: April 2011

AbstractA modelling study has been completed to understand the effect of rock alteration on uranium migration at the Koongarra ore deposit, Australia. The model considers the weathering process, the mechanism and rate of chlorite alteration, a major mineral of the host rock, and assumes the presence of reversible sorption sites of chlorite and the presence of reversible and irreversible sorption sites of the weathering products. One- and two-dimensional, calculated uranium concentrations were compared with those observed. Good agreement between the calculated and observed uranium concentration profiles was obtained only when an appropriate fraction of uranium is fixed to the irreversible sorption sites of Fe-minerals produced during weathering of chlorite. On the other hand, the conventional Kd model failed to estimate an adequate uranium concentration profile. The results suggest that the fixation of uranium to Fe-minerals has dominated the migration of uranium in the vicinity of the Koongarra ore deposit.