bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phase Transformation and Densification Behavior of Microwave Sintered γ-A12O3
Authors: Freim John , McKittrick Joanna , Katz Joel , Sickafus Kurt 
Published: April 2011

ABSTRACTThe phase transformation and densification behavior of gas condensation synthesized γA12O3 sintered with microwave radiation has been studied. Nucleation and growth phase transformations, which produce α-A12O3 occurred as the material was heated through the temperature range of 800–1300°C. These phase transformations resulted in anomalous grain growth with a distinct change in particle morphology, crystallite size and surface area. A12O3 derived from a chemically synthesized boehmite precursor has been shown to exhibit the same nucleation and growth phase transformation behavior when conventionally heated. It is concluded that nanocrystalline γ or β alumina will not be a viable starting material for the production of dense bodies with grain sizes of less than 100 nm.
Microwave Sintering of Nanocrystalline ZrO2 Powders
Authors: Jinsong Zhang , Yongjin Yang , Lihua Cao , Shengqi Chen , Xiaoping Shong , Fei Xia 
Published: April 2011

ABSTRACTNanociystalline Z1O2 powders, prepared by plasma-chemical method, were sintered by microwave heating. The experimental results indicated that the thermal runaway and hot spot are two important obstacles to successful microwave sintering of nanocrystalline ZrO2. By controlling ratio of dielectric loss between sintered ZrO2 compact and adjacent thermal insulator, the ZrO2 compact with diameter larger than 30 mm could be microwave-heated rapidly and uniformly from room temperature to 1600 °C in 80 minutes, the mean grain size of ZrCh ( 96% T.D. sintered at 1500°C for 5 minutes) is lower than 20 nm determined by means of quantitative XRD and TEM. The change of ZrO2 grain size may be related to phase transformation (t→m).
Microwave Induced Polymerization of Monomer Impregnated Hardened Cement
Authors: Hetz Joseph , Chang John , Brodwin Morris 
Published: April 2011

ABSTRACTIt is well known that when pores of hardened cement are filled with a suitable polymer, desirable properties are greatly enhanced. With microwave induced polymerization, significant increases in compressive strength are observed.Mortar samples with a sand cement ratio of 2.5 and water cement ratios, 0.3, 0.4, and 0.5, were molded and hardened. After sufficient hydration, they were evacuated, filled with MMA and pressurized. The samples were then processed in a dynamic multimode applicator. Temperature was monitored and they were processed until the temperature exceeded 85°C.The principal result is the increase in compressive strength as compared to an untreated sample. For a W/C=0.5, and a sample hydrated for one day, the strength increased by a factor of6.0. In addition, the highly porous 1 day polymerized samples exhibited significantly greater strength than 28 day unpolymerized material.
Experimental Study of Loss Mechanisms in Polymer-Metal Composites at Microwave Frequencies
Authors: Ludman John P. , Stern Curtis H. 
Published: April 2011

ABSTRACTThe microwave heatability of a low loss polymer (polypropylene) was enhanced by the addition of a conductive powder (iron). The effects of the amount (5–40% iron by volume) and size of the conductive particles on the microwave heatability were studied. The complex permittivity and complex permeability at microwave frequencies and the dc resistivity were measured. Samples were also heated in a multimode microwave cavity. Results show that microwave heating increased with increasing iron concentration. However, the penetration depth of the microwaves decreased with increasing iron content, and dramatically decreased when the polypropylene-iron composites became electrically conductive at the percolation threshold.
Processing of Thermoset Prepreg Laminates Via Exposure to Microwave Radiation
Authors: Paulauskas Felix L. , Mee Thomas T. 
Published: April 2011

ABSTRACTStudies of microwave-assisted curing of neat resins (epoxy) and unidirectional glass and carbon fiber laminates have shown that a substantial reduction in the curing time was obtained [1]. This may be explained by the penetration of microwave energy directly and throughout the laminate with enhancement of the kinetics of the chemical reaction.Results of this work indicate that the microwave assisted curing of glass fiber laminates also shows a substantial reduction of the required curing time.Microwave radiation of 2.45 GHz has been demonstrated to be an acceptable method to cure unidirectional carbon fiber laminates. Also, effective curing of crossply (0/90) laminates through this method was observed when proper rotation of the parts accompanied the curing process. This is in accordance with previous work [2,3].Multidirectional carbon fiber/epoxy laminates demonstrate a lack of coupling during the curing process. A direct curing of these laminates was not possible by microwave radiation with the experimental approach used, in agreement with previous work [4[. Nevertheless, a moderate reduction in the curing time of these thin laminates was observed due to hybrid curing.
Critical Assessment of Microwave-Enhanced Diffusion
Authors: Rothman Steven J. 
Published: April 2011

ABSTRACTThe use of microwave heating or microwave plasmas in the sintering of ceramics has often been observed to result in more rapid sintering than the same heating schedule in a conventional furnace; the increased sintering rate has sometimes been ascribed to the enhancement of diffusion by microwave heating/plasma. Some experiments on diffusion measurements under microwave heating have also been carried out in order to check this hypothesis. In this paper, we evaluate the experimental evidence for microwave enhanced diffusion, discuss the various models that have been proposed for the enhanced diffusion, and suggest some further experiments aimed at understanding these phenomena.
High Power Gyrotrons
Authors: Temkin R. J. , Kreischer K. E. 
Published: April 2011

ABSTRACTHigh power gyrotrons have been developed for application to plasma heating in the program of magnetically confined nuclear fusion research. Gyrotron power levels of up to 1 MW in long pulse operation (>ls) and up to 200 kW in true continuous operation (CW) have been demonstrated at frequencies in the 8 to 140 GHz range. The status of high power gyrotron development is reviewed. One current goal of the worldwide gyrotron effort is the development of 1 MW,CW gyrotrons at a frequency of about 170 GHz for heating the proposed international tokamak ITER to ignition. Gyrotrons are also now being used in a variety of other applications including materials processing. Improved gyrotrons with features such as wide range tuning could be developed for industrial applications.
The Klystrode® Iot a New, Compact, High Efficiency Electron Tube
Authors: Peters R. Donald , Haase Andrew , Johnson Chris , Tornoe Robert N. 
Published: April 2011

ABSTRACTThe Klystrode® (IOT) is a new high power electron tube which combines the features of Klystron and the Tetrode. During the past six years it has virtually taken over the UHF-TV market and has demonstrated its capabilities in high power research applications. This paper describes the principles of Klystrode IOT operation and the power and frequency ranges where it is most useful. Field experience with over fifty (50) transmitters in UHF TV service is reported as well as test results from high power scientific devices operated at 267 MHz, 250 kW (CW) and 425 MHz, 500 kW (pulse). Finally, future improvements in the Klystrode IOT to reduce cost, improve efficiency and optimize the tube for industrial applications.
Cerium-Activated Lanthanum Beryllate as A Gamma Detector Material
Authors: Czirr J. Bart , Berrondo Manuel 
Published: April 2011

AbtractWe have tested a single crystal of Ce-activated lanthanum beryllate BEL(Ce) as a potential gamma detector material. The density (6.1 g.cm−3) and decay time (50 ns) are competitive with other recently developed materials. The scintillation efficiency is 57- to -95% that of BGO. For an excitation wavelength of 340 nm, the emission spectrum is a broad peak centered at 450 nm. The H2 annealed sample is transparent for wavelengths greater than 400 nm. We are continuing a program to improve the scintillation efficiency by varying the crystal growth conditions.The crystal was prepared by M. Long and E.W. O'Dell of AlliedSignal, Inc., using the Czochralski technique.
Structure Characteristics of Cubic and Orthorhombic Phases of High Density Scintillator Pbf2 from 4.2–300 K
Authors: Shmyt'ko Ivan , Savchenko I.B. , Klassen N.V. , Bagautdinov B.Sh. , Emel'chenko G.A. , Sinitzin V.V. 
Published: April 2011

ABSTRACTAn anomaly of the temperature dependence of the unit cell parameter has been observed for β–PbF2 single crystals at 200 K that is interpreted as a phase transition to a pseudocubic lattice. Such a pseudocubic phase is observable at room temperature after uniaxial plastic deformation of the bulk single crystals. The structural aspects of the β→α transition have been established. The as-grown crystals of α–PbF2 phase are shown to undergo a phase transition at 100 K.
Photoluminescence and Scintillation Properties of Pb2+ Based Quantum Dots in CsCI Host Crystal
Authors: Nikl M. , Nitsch K. , Dafinei I. , Lecoq P. , Pazzi G.P. , Fabeni P. , Gurioli M. 
Published: April 2011

ABSTRACTThe spectral and kinetic properties of photoluminescence of Pb2+ aggregated phase in CsC1 host, together with scintillation characteristics of CsCI:Pb crystals, are reported in the 10 - 300 K temperature range. Absorption, steady-state excitation and emission spectra of Pb2+ phase in CsCI host are similar to those of CsPbCl3 bulk crystal (emission peak at 419 nm at 10 K). The decay of the 421 nm luminescence of the Pb2+ phase in CsCl shows single exponential behavior with extremely short decay time of 40 ps at 421 nm and 10 K,which is considerably shorter than the decay times found in the decay of CsPbCl3 bulk emission (0.45, 2.8 and 12 ns at 418 nm and 10 K). In the scintillation decay of CsCI:Pb, two components with 0.95-1 ns and 2-3 ns decay times were found and no slower component is present at room temperature.
New Fluors for Radiation Tolerant Scintillators
Authors: Gao F. , Dharia J.R. , Mcgowan W.M. , Hilinski E.F. , Johnson K.F. , Schlenoff J.B. 
Published: April 2011

ABSTRACTThe new generation of high energy accelerators - LHC, CEBAF, RHIC - have encouraged the development of more robust plastic scintillators. Monitors and detectors for these machines will require plastic scintillator with greater radiation tolerance. Although the major cause of radiation damage in plastic scintillator is the creation of color centers in the base plastic, the most successful approach to date has been to utilize fluors which circumvent, rather than solve, the radiation damage problem. Two techniques have been found to be useful. First, increase the concentration of fluors so that the optical density of the fluors for absorption of the scintillation photons remains much higher than the optical density of the radiation induced color centers. Second, use fluors which emit at longer wavelengths than traditional fluors, thus avoiding radiation induced color centers. The present work attempts to meet these requirements by modifying the structure of the 3-HF molecule.
Elastic Scintillation Materials Based on Polyorganosiloxane
Authors: Grine B.V. , Andryushchenko L.A. , Shershukov V.M. , Ulanenko K.B. , Minakova R.A. , Sevastjanova I.V. 
Published: April 2011

SummaryThe developed elastic scintillators based on polymethylphenylsiloxane rubber are characterized by an elevated light output and a low toxicity. The increase of their light output is achieved by raising the content of phenyl chains, varying the chemical structure of luminescent additions and using isopropylnaphthalene. This high-boiling solvent introduced into the scintillation siloxane compositions is confined within siloxane matrix after the hardening of the rubber.
Relationship Between Microstructure and Efficiency of Scintillating Glasses
Authors: Bliss M. , Craig R. A. , Reeder P. L. , Sunberg D. S. , Weber M. J. 
Published: April 2011

ABSTRACTPrior work has shown that there is a correlation between trap densities and scintillation efficiency of cerium-activated, lithium-aluminosilicate glasses. Raman spectroscopy has strongly suggested that phase separation may be playing an important role in governing the scintillation efficiency. In this study, we relate the thermoluminescence glow-curve data and microstructural analysis for a compositional series. The thermoluminescence data provide information about the traps in the neighborhood of the activator (Ce3+). The microscopy and crystallization of the glasses provide direct evidence of activator partitioning.
On the Temperature Stability of NaI(T1) Scintillators
Authors: Gektin A.V. , Brinev B.V. , Serebrayannyi V.Ya. , Vinograd E.L. 
Published: April 2011

ABSTRACTThe temperature stability of NaI(T1) scintillators is studied for crystals with various Tl+ impurity content. It is shown that supersaturation of the T1+ ions and regulation of solid solution decomposition increase the light output at elevated temperatures. An explanation of this phenomenon is proposed.
Energy Localization and Decay in Highly Ionic Crystals
Authors: Williams R. T. , Thoma E. D. , Bunton P. H. 
Published: April 2011

ABSTRACTLuminescence from localized states in pure wide-gap crystals is examined from the perspective of modern fast scintillator requirements. Recent advances in the understanding of self-trapped excitons are summarized with regard to excited-state configurations, spectra, and luminescence efficiency. As an example, the fast luminescence of partially quenched type I STEs in RbI offers tuneable-lifetime subnanosecond pulses which could be useful for timing applications. The possible role of hole localization in cross luminescence is discussed. Stokes-shifted luminescence in some pure rare-earth fluoride crystals probably originates from self-trapped excitons of forms to be discussed.
Cluster Models of Doped Ionic Crystal Scintillators. Quantum Calculations+
Authors: Berrondo M. , Rivas-Silva J.F. , Czirr J.B. 
Published: April 2011

ABSTRACTWe have performed quantum electronic ab initio calculations of clusters of alkali halides, both pure and doped. In order to estimate the pure crystal energy gap and the dopant excitation, we have considered a central cation and four shells of ions surrounding it. We have studied KC1, Nal, NaCl and KI, both pure and with a Tl+ ion replacing thecentral alkali cation. Encouraging results are presented for absorption and emission.
Creation of Electron-Hole Pairs in Inorganic Scintillators
Authors: Rodnyi Piotr A. , Dorenbos Pieter , Van Euk Carel W.E. 
Published: April 2011

ABSTRACTModels are discussed of the first stage of the scintillation mechanism in an inorganic scintillator: the primary interaction and the thermalization process. The model predictionsare compared with experimental results, an extension of the theory is made and conclusions are drawn concerning the best description of the first stage.
Radiation Damage Mechanisms In Scintillator Materials: Applications to BaF2 and CeF3
Authors: Halliburton L. E. , Edwards G. J. 
Published: April 2011

ABSTRACTResults from recent radiation damage studies in high quality BaF2 and CeF3 crystals are presented. Optical absorption and electron paramagnetic resonance (EPR) techniques are used to identify specific radiation damage mechanisms. Specific attention is given to the role of oxygen and hydrogen in the room temperature damage of BaF2. Also, Mn2+ ions are shown to change valence state in BaF2during room temperature irradiation. Numerous optical absorption bands are created in CeF3 during irradiations at low temperature. These bands are associated with electron traps (either F centers or Ce2+ ions) and they thermal anneal below room temperature. An EPR spectrum, assigned to F centers, is observed in low-temperature irradiated CeF3.
The Radiation Effect Mechanism of Some Rare Earth Doped BaF2 Crystal
Authors: Mu Gu , Lingyan Chen , Jie Du , Kaihua Xiang , Gang Chen , Shaoxia Ren , Fengyin Zhang 
Published: April 2011

ABSTRACTIn this paper, we used the Discrete Variational Xα, (DV-Xα) method to calculate the energy level of some rare earth doped BaF2 crystals and indicated that the Eu, Dy and Yb elements will change their valence from +3 to +2 under irradiation and thus change the optical properties of the crystals.The results show that this radiation effect model presented agree well with experiments.
An Investigation of Radiation Damage Induced by Hydroxyl and Oxygen Impurities In BaF2 Crystal
Authors: Lingyan Chen , Mu Gu , Liming Wang , Kaiiiua Xiang 
Published: April 2011

ABSTRACTThe radiation effect in hydrolyzed BaF2 was investigated through tile changes in their optical absorption and EPR spectra before and after γ-irradiation. The resulti demonstrated that hydroxyl and oxygen can be easily introduced into BaF2by means of a hydrolysis, the most likely modes are OH— ions substituting for fluorine and O2– ions substituting for fluorine associated with charge-compensating fluorine vacancies O2– — F+. Combining with the Hartree-Fock-Slater local-density discrete variational (HFS-Xα-DV) cluster calculation on some possible defects related to hydrogen and oxygen impurities, we propose that the radiation damage observed in hydrolyzedBaF2 can be explained in terms of OH— and O2– — F+ dissociation through a radiolysis.
Growth of Halide Scintillators with a Modified Heat Exchange Method
Authors: Berthold T.G. , Grabmaier B.C. 
Published: April 2011

ABSTRACTTo test the potential of the heat exchange method for growing scintillator crystals, ingots of mono-, bi- and trivalent halides were prepared. Except for monovalent halides, the removal of oxygen compounds is indispensable. In the case of CaF2 and BaF2, the purification by reaction with NH4F and a superheating of the melt could be included in the crystal growth process. Clear, monocrystalline ingots of these substances were grown in 4f-heated glassy carbon crucibles without seed crystals. Oxygen-free starting material had to be prepared for the growth of inclusion free CeF3 crystals.
Enhanced Luminescence From Rare Earth Doped Thin Films
Authors: Olmsted B. L. , Jones M. L. 
Published: April 2011

ABSTRACTResults of a study of the luminescence of rare earth ions in crystalline thin films grown on reflective substrates will be presented. As an example, the luminescence of Sm2+:CaF2 films has been calculated as a function of the separation between the active layer and a silicon substrate. These calculations involve coupling the narrow resonance of the rare earth ions to the electromagnetic modes of the film. Results including the optimum thickness for enhanced luminescence will be presented. Experimental work on Sm2+:CaF2 films grown on Si by molecular beam epitaxy will also be discussed.
Precision Machining And Polishing Of Scintillating Crystals For Large Calorimeters And Hodoscopes
Authors: Wuest Craig R. , Fuchs Baruch A. , Holdener Fred R. , Heck Joaquim L. 
Published: April 2011

ABSTRACTNew machining and polishing techniques have been developed for large scintillating crystal arrays such as the Barium Fluoride Electromagnetic Calorimeter for the GEM Detector at SSCL, the Crystal Clear Collaboration's cerium fluoride or lead tungstenate calorimeter at the proposed LHC at CERN, the PHENIX Detector at RHIC (barium fluoride), and the cesium iodide Calorimeter for the BaBar Detector at PEP-I B Factory at SLAC. The machining and polishing methods to be presented in this paper provide crystalline surfaces without sub-surface damage or deformation as verified by Rutherford Back-scattering (RBS) analysis. Surface roughness of about 10-20 angstroms and sub-micron mechanical tolerances have been demonstrated on large barium fluoride crystal samples. Mass production techniques have also been developed for machining the proper angled surfaces and polishing up to five 50 cm long crystals at one time. These techniques utilize kinematic mount technology developed at LLNL to allow precision machining and polishing of complex surfaces. We will present this technology along with detailed surface studies of barium fluoride and cerium fluoride crystals polished with this technique.
Lead Tungstate For High Energy Calorimetry
Authors: Dafinei I. , Auffray E. , Lecoq P. , Schneegans M. 
Published: April 2011

ABSTRACTThe very large volumes needed to build a crystal calorimeter for High Energy Physics experiments bring cost considerations at the front of the stage. A reasonable compromise between cost and performances must be reached. One possible solution is to look at very dense materials like PbWO4, which will reduce the detector volume, even if the relatively low light yield will impose some limitations to the energy resolution. A review of the different results obtained by the Crystal Clear collaboration will be given for this crystal, including spectroscopic data and radiation damage measurements.
Fiber Coating Performance in TiAl
Authors: McCullough C. , Kieschke R. R. 
Published: April 2011

AbstractThe interfacial chemical behavior of two candidate coating systems for use on fine diameter (∼10 μm) Al2O3 in TiAl is presented. The performance of the Nb/Y2O3 system appears to be related to the transport rate of Ti through the Y2O3 layer. Interfacial reaction is then observed at points where the Y2O3 thickness is less than about 1 μm. The main reaction product formed appears to be an oxygen saturated TiAl phase. An alternative system, C/TiN/Y2O3 is then presented as a solution to the Ti transport problem and may offer more desirable interfacial mechanical properties.
Effects of Processing on Fiber/Matrix Interfaces in Ni3Al/Sapphire Single Crystal Composites
Authors: Ringer D. , White C. L. 
Published: April 2011

AbstractComposites consisting of Ni3Al modified with Zr, Fe, and B (IC-50) reinforced with continuous sapphire single crystal fibers have been prepared by vacuum hot pressing foil/fiber multilayers. Previous research detected formation of Zr-rich precipitates and sulfur segregation at fiber/matrix interfaces in these materials subsequent to fabrication. In this work, fiber bonding to the Ni3Al matrix has been characterized using fiber push-out tests. Segregation and precipitation at fiber/matrix interfaces has been examined using scanning Auger electron spectroscopy and scanning electron microscopy. For comparison, composites have also been prepared from Ni, Ni-Al, and Ni-Al-Zr solid solution matrices, to evaluate the effects of matrix strength and reactivity on processing and fiber/matrix reactions.
The Contribution of Matrix Plasticity to the “Frictional” Sliding of Debonded Fibers in Sapphire-Reinforced TiAl Matrix Composites
Authors: Galbraith J. M. , Koss D. A. , Hellmann J. R. 
Published: April 2011

AbstractLarge-scale fiber displacement behavior, usually characterized by a “frictional” sliding stress (τslide), has been studied in two sapphire-reinforced TiAl systems. Experimental results from fiber pushout and reverse push-back tests indicate that the large-scale sliding behavior of debonded fibers leads to an average τslide-value which progressively decreases during fiber displacements. Previous studies of SCS-6 (SiC) fiber-reinforced glass and metal matrix composites have attributed decreases in τslide to the fracture and wear of fiber asperities. However, given a matrix in which fiber asperities do not easily wear (e.g., a TiAl alloy), SEM examination of the fiber/matrix interface indicates that matrix plasticity plays a dominant role in the decrease of τslide with fiber displacement. Experimental evidence suggests that the observed decrease in τslide can be attributed to (1) a decrease in fiber roughness perceived by the matrix due to matrix grooving and (2) a relaxation of radial clamping as a result of material removal from the interface.