Sample records for alkali halide photocathodes

  1. On the surface morphology of thin alkali halide photocathode "lms

    E-print Network

    On the surface morphology of thin alkali halide photocathode "lms T. Boutboul *, A. Breskin , R-91128 Palaiseau Cedex, France Abstract Thin alkali halide "lms are currently used as transmissive UV, such thin evaporated alkali halide "lms, CsI, NaI or CsBr, are currently employed as protective layers

  2. Fabrication of alkali halide UV photocathodes by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Brendel', V. M.; Bukin, V. V.; Garnov, Sergei V.; Bagdasarov, V. Kh; Denisov, N. N.; Garanin, Sergey G.; Terekhin, V. A.; Trutnev, Yurii A.

    2012-12-01

    A technique has been proposed for the fabrication of atmospheric corrosion resistant alkali halide UV photocathodes by pulsed laser deposition. We produced photocathodes with a highly homogeneous photoemissive layer well-adherent to the substrate. The photocathodes were mounted in a vacuum photodiode, and a tungsten grid was used as an anode. Using pulsed UV lasers, we carried out experiments aimed at evaluating the quantum efficiency of the photocathodes. With a dc voltage applied between the photocathode and anode grid, we measured a shunt signal proportional to the total charge emitted by the cathode exposed to UV laser light. The proposed deposition technique enables one to produce photocathodes with photoemissive layers highly uniform in quantum efficiency, which is its main advantage over thin film growth by resistive evaporation.

  3. Quantum efficiencies of imaging detectors with alkali halide photocathodes. 1: Microchannel plates with separate and integral Csl photocathodes.

    PubMed

    Carruthers, G R

    1987-07-15

    We have measured and compared the quantum efficiencies of microchannel plate (MCP) detectors in the far- UV (below 2000-A) wavelength range using CsI photocathodes (a) deposited on the front surfaces of microchannel plates and (b) deposited on solid substrates as opaque photocathodes with the resulting photoelectrons input to microchannel plates. The efficiencies were measured in both pulse-counting and photodiode modes of operation. Typical efficiencies are ~15% at 1216 A for a CsI-coated MCP compared with 65% for an opaque CsI photocathode MCP detector. Special processing has yielded an efficiency as high as 20% for a CsI-coated MCP. This may possibly be further improved by optimization of the tilt angle of the MCP channels relative to the front face of the MCP and incident radiation. However, at present there still remains a factor of at least 3 quantum efficiency advantage in the separate opaque CsI photocathode configuration. PMID:20489984

  4. Quantum efficiencies of imaging detectors with alkali halide photocathodes. I - Microchannel plates with separate and integral CsI photocathodes

    NASA Technical Reports Server (NTRS)

    Carruthers, George R.

    1987-01-01

    Measurements and comparisons have been made of the quantum efficiencies of microchannel plate (MCP) detectors in the far-UV (below 2000-A) wavelength range using CsI photocathodes (a) deposited on the front surfaces of microchannel plates and (b) deposited on solid substrates as opaque photocathodes with the resulting photoelectrons input to microchannel plates. The efficiences were measured in both pulse-counting and photodiode modes of operation. Typical efficiencies are about 15 percent at 1216 A for a CsI-coated MCP compared with 65 percent for an opaque CsI photocathode MCP detector. Special processing has yielded an efficiency as high as 20 percent for a CsI-coated MCP. This may possibly be further improved by optimization of the tilt angle of the MCP channels relative to the front face of the MCP and incident radiation. However, at present there still remains a factor of at least 3 quantum efficiency advantage in the separate opaque CsI photocathode configuration.

  5. Quantum efficiencies of imaging detectors with alkali halide photocathodes. I - Microchannel plates with separate and integral CsI photocathodes

    NASA Astrophysics Data System (ADS)

    Carruthers, George R.

    1987-07-01

    Measurements and comparisons have been made of the quantum efficiencies of microchannel plate (MCP) detectors in the far-UV (below 2000-A) wavelength range using CsI photocathodes (a) deposited on the front surfaces of microchannel plates and (b) deposited on solid substrates as opaque photocathodes with the resulting photoelectrons input to microchannel plates. The efficiences were measured in both pulse-counting and photodiode modes of operation. Typical efficiencies are about 15 percent at 1216 A for a CsI-coated MCP compared with 65 percent for an opaque CsI photocathode MCP detector. Special processing has yielded an efficiency as high as 20 percent for a CsI-coated MCP. This may possibly be further improved by optimization of the tilt angle of the MCP channels relative to the front face of the MCP and incident radiation. However, at present there still remains a factor of at least 3 quantum efficiency advantage in the separate opaque CsI photocathode configuration.

  6. Positronium in Alkali Halides

    Microsoft Academic Search

    Jun-ichi Kasai; Toshio Hyodo; Kunio Fujiwara

    1988-01-01

    Momentum distribution of annihilation gamma rays from several alkali halide crystals has been measured using high resolution 1D angular correlation apparatuses. Formation of Bloch-type positronium (Ps) in NaBr and RbCl has been newly confirmed, while no evidence for it has been seen in LiF, KF, and CsI. Effective mass of the Ps in the Bloch state has been determined by

  7. TRANSMISSION ELECTRON MICROSCOPY OF WEAKLY DEFORMED ALKALI HALIDE CRYSTALS

    E-print Network

    Boyer, Edmond

    377 TRANSMISSION ELECTRON MICROSCOPY OF WEAKLY DEFORMED ALKALI HALIDE CRYSTALS H. STRUNK Max) is applied to the investigation of the dis- location arrangement of [001]-orientated alkali halide crystals

  8. Ionic alkali halide XUV laser feasibility study

    Microsoft Academic Search

    T. T. Yang; V. T. Gylys; R. D. Bower; D. G. Harris; J. A. Blauer; C. E. Turner; R. N. Hindy

    1989-01-01

    The objective of this work is to assess the feasibility of a select set of ionic alkali halide XUV laser concepts by obtaining the relevant kinetic and spectroscopic parameters required for a proof-of-principle and conceptual design. The proposed lasers operate in the 80--200 nm spectral region and do not require input from outside radiation sources for their operation. Frequency up-conversion

  9. Ionic alkali halide XUV laser feasibility study

    SciTech Connect

    Yang, T.T.; Gylys, V.T.; Bower, R.D.; Harris, D.G.; Blauer, J.A.; Turner, C.E.; Hindy, R.N.

    1989-11-10

    The objective of this work is to assess the feasibility of a select set of ionic alkali halide XUV laser concepts by obtaining the relevant kinetic and spectroscopic parameters required for a proof-of-principle and conceptual design. The proposed lasers operate in the 80--200 nm spectral region and do not require input from outside radiation sources for their operation. Frequency up-conversion and frequency mixing techniques and therefore not considered in the work to be described. An experimental and theoretical study of a new type of laser operating in the extreme ultraviolet wavelength region has been conducted. The lasing species are singly ionized alkali halide molecules such as Rb{sup 2+}F{sub {minus}}, Rb{sup 2+}Br{sup {minus}} and Cs{sup 2+}F{sup {minus}}. These species are similar in electronic structure to the rare gas halide excimers, such as XeF and Krf, except that the ionic molecules emit at wavelengths of 80--200 nm, much shorter than the conventional rare-gas halide excimer laser. The radiative lifetime of these molecules are typically near 1 ns, which is about an order of magnitude shorter than that for rare-gas halide systems. The values of the cross section for stimulated emission are on the order of 1 {times} 10{sup {minus}16}cm{sup 2}. Because of the fundamental similarity to existing UV lasers, these systems show promise as a high power, efficient XUV lasers. 55 refs., 50 figs., 5 tabs.

  10. Enhanced quantum efficiency from hybrid cesium halide/copper photocathodes

    NASA Astrophysics Data System (ADS)

    Kong, Lingmei; Joly, Alan G.; Droubay, Timothy C.; Gong, Yu; Hess, Wayne P.

    2014-04-01

    The quantum efficiency (QE) of Cu is found to increase dramatically when coated by a CsI film and then irradiated by a UV laser. Over three orders of magnitude quantum efficiency enhancement at 266 nm is observed in CsI/Cu(100), indicating potential application in future photocathode devices. Upon laser irradiation, a large work function reduction to a value less than 2 eV is also observed, significantly greater than for similarly treated CsBr/Cu(100). The initial QE enhancement, prior to laser irradiation, is attributed to interface interaction and the intrinsic properties of the Cs halide film. Further QE enhancement following activation is attributed to formation of inter-band states and Cs metal accumulation at the interface induced by laser irradiation.

  11. Development of high performance bi-alkali photocathodes for next-generation sensors

    NASA Astrophysics Data System (ADS)

    Xie, Junqi; Byrum, Karen; Demarteau, Marcel; Wagner, Robert; Walters, Dean; Wang, Jingbo; Xia, Lei; Zhao, Huyue

    2015-04-01

    Next generation sensors such as microchannel plate based photomultiplier tubes call for robust, low-cost photocathodes with high quantum efficiency and low dark current. Traditional alkali photocathodes grown through a diffusion growth process encounter material challenge and are being investigated using X-ray scattering to optimize their performance. Photocathodes with peak quantum efficiency over 30% at ~ 400 nm wavelength were grown via a newly proposed growth method. A new photocathode growth chamber was built and incorporated into the Argonne photodetector fabrication facility to obtain robust, highly efficiencient bi-alkali photocathodes. The progress on the photocathode study, growth design and experimental results will be reported and discussed.

  12. Relation between the electroforming voltage in alkali halide-polymer diodes and the bandgap of the alkali halide

    NASA Astrophysics Data System (ADS)

    Bory, Benjamin F.; Wang, Jingxin; Gomes, Henrique L.; Janssen, René A. J.; De Leeuw, Dago M.; Meskers, Stefan C. J.

    2014-12-01

    Electroforming of indium-tin-oxide/alkali halide/poly(spirofluorene)/Ba/Al diodes has been investigated by bias dependent reflectivity measurements. The threshold voltages for electrocoloration and electroforming are independent of layer thickness and correlate with the bandgap of the alkali halide. We argue that the origin is voltage induced defect formation. Frenkel defect pairs are formed by electron-hole recombination in the alkali halide. This self-accelerating process mitigates injection barriers. The dynamic junction formation is compared to that of a light emitting electrochemical cell. A critical defect density for electroforming is 1025/m3. The electroformed alkali halide layer can be considered as a highly doped semiconductor with metallic transport characteristics.

  13. Structured alkali halides for medical applications

    NASA Astrophysics Data System (ADS)

    Schmitt, B.; Fuchs, M.; Hell, E.; Knüpfer, W.; Hackenschmied, P.; Winnacker, A.

    2002-05-01

    Image plates based on storage phosphors are a major application of radiation defects in insulators. Storage phosphors absorb X-ray quanta creating trapped electron-hole pairs in the material. Optical stimulation of the electron causes recombination leading to light emission. Application of image plates requires an optimal compromise between resolution (represented by the modulation transfer function (MTF)) and sensitivity. In our paper we present a new solution of the problem of combining a high MTF with a high sensitivity by structuring the image plates in form of thin needles acting as light guides. This suppresses the lateral spread of light which is detrimental to resolution. As doped CsBr, e.g. CsBr:Ga [Physica Medica XV (1999) 301], can pose a good storage phosphor evaporated layers are of interest in computed radiography. Needle structured CsI:Tl is used as scintillator in direct radiography [IEEE Trans. Nucl. Sci. 45 (3) (1998)]. CsBr layers have been produced by evaporation in vacuum and in inert gas atmosphere varying pressure and temperature. The resulting structures are of fibrous or columnar nature being in good agreement with the zone model of Thornton [Ann. Rev. Mater. Sci. 7 (1977) 239]. A zone model for CsBr has been developed. Measurements on doped alkali halide image plates having needle structure show good MTF at high sensitivity making a significant progress in image plate technology.

  14. Configurational coordinates model in the alkali-halide exciton laser

    Microsoft Academic Search

    JOSE M. GUERRA; JOSB LUIS ESCUDERO; JESUS SANCHO

    1974-01-01

    A configurational coordinates model in the fully quantum theoretical treatment of the alkali-halide exciton laser is used. The theory predicts a correlation between threshold pumping power and the Stokes shift. The predictions of the theory are compared with the observed characteristics of laser action on the first exciton peak of KBr. The observed spectral narrowing is in good agreement with

  15. Measurement of the Electric Dipole Polarizabilities of Alkali Halide Dimers

    Microsoft Academic Search

    Robert Louis Kremens Jr.

    1981-01-01

    An electric field deflection method has been used to measure the space average polarizabilities of the dimers of the alkali halide salts of rubidium, cesium, potassium, and chlorine, flourine, bromine and iodine. The experimental procedure consisted of passing an effusive thermal beam of molecules through a region of inhomogeneous electric field and studying the deflection pattern obtained at the detector.

  16. Cohesive Energy-Lattice Constant and Bulk Modulus-Lattice Constant Relationships: Alkali Halides, Ag Halides, Tl Halides

    NASA Technical Reports Server (NTRS)

    Schlosser, Herbert

    1992-01-01

    In this note we present two expressions relating the cohesive energy, E(sub coh), and the zero pressure isothermal bulk modulus, B(sub 0), of the alkali halides. Ag halides and TI halides, with the nearest neighbor distances, d(sub nn). First, we show that the product E(sub coh)d(sub 0) within families of halide crystals with common crystal structure is to a good approximation constant, with maximum rms deviation of plus or minus 2%. Secondly, we demonstrate that within families of halide crystals with a common cation and common crystal structure the product B(sub 0)d(sup 3.5)(sub nn) is a good approximation constant, with maximum rms deviation of plus or minus 1.36%.

  17. COLOUR CENTRES IN NON-ALKALI HALIDES. F CENTERS IN IONIC CRYSTALS : ANALYSIS

    E-print Network

    Paris-Sud XI, Université de

    COLOUR CENTRES IN NON-ALKALI HALIDES. F CENTERS IN IONIC CRYSTALS : ANALYSIS BY ABSORPTION SPECTRUM energy and mean charge density seen by the electron. This method can be applied to the cases of alkali by the electron. This procedure can be used to study the ground state of the F center in alkali halides [1

  18. Photoelectron Spectroscopy of Alkali Halide Clusters with Excess Electrons

    Microsoft Academic Search

    Ping Xia; Ping

    1993-01-01

    We have studied excess electrons in alkali halide clusters, using a combination of a laser vaporization source, time-of-flight mass spectrometer, and magnetic bottle photoelectron electron spectrometer. We have obtained photoelectron spectra of (NaCl)_{rm n} ^-, (NaCl)_{rm n}Na^-, (NaCl) _{rm n}Na_ {rm m}^- and (KI) _3K_{rm m} ^- cluster anions with visible and ultraviolet photon energies. These cluster anions contain either

  19. Optical Absorption Spectra of the Alkali Halides at 10°K

    Microsoft Academic Search

    K. Teegarden; G. Baldini

    1967-01-01

    The absorption spectra of all the alkali halides except LiF and LiI, measured in the range 5.0 to 12.0 eV at 10°K, are presented. These data complement earlier measurements made at 80°K. Identification of excition lines involving d-like electrons is made by a comparison of the crystal absorption and the absorption spectra of rare-gas atoms. From the positions of exciton

  20. Evidence for the direct ejection of clusters from alkali-halides during laser vaporization

    Microsoft Academic Search

    L. A. Bloomfield; Y. A. Yang; P. Xia

    1991-01-01

    We have studied the formation of clusters of alkali halides during laser vaporization. Measurements of the abundances of cluster ions produced by several different source configurations indicate that clusters are ejected directly from the source sample and do not necessarily grow from an atomic or molecular vapor. Using samples consisting of mixed alkali halide powders, we have found that unalloyed

  1. Structural and Dynamic Properties of Concentrated Alkali Halide Solutions:  A Molecular Dynamics Simulation Study

    Microsoft Academic Search

    Hao Du; Jayendran C. Rasaiah; Jan D. Miller

    2007-01-01

    The physicochemical properties of alkali halide solutions have long been attributed to the collective interactions between ions and water molecules in the solution, yet the structure of water in these systems and its effect on the equilibrium and dynamic properties of these systems are not clearly understood. Here, we present a systematic view of water structure in concentrated alkali halide

  2. JOURNAL DE PHYSIQUE Colloque C4, suppliment au no 5, Tome 35, Mai 1974, page C4-377 THE ELECTRICAL CONDUCTIVITY OF ALKALI METAL-ALKALI HALIDE

    E-print Network

    Paris-Sud XI, Université de

    CONDUCTIVITY OF ALKALI METAL-ALKALI HALIDE SOLUTIONS R. GILBERT and G. J. MORGAN The Physics Department to liquid alkali metals electrons are removed from the conduction band until the insulating salt is formed. When something like 30 % of the alkali metal ions are replaced by halide ions the Landau limit

  3. A new polarizable force field for alkali and halide ions

    NASA Astrophysics Data System (ADS)

    Kiss, Péter T.; Baranyai, András

    2014-09-01

    We developed transferable potentials for alkali and halide ions which are consistent with our recent model of water [P. T. Kiss and A. Baranyai, J. Chem. Phys. 138, 204507 (2013)]. Following the approach used for the water potential, we applied Gaussian charge distributions, exponential repulsion, and r-6 attraction. One of the two charges of the ions is fixed to the center of the particle, while the other is connected to this charge by a harmonic spring to express polarization. Polarizability is taken from quantum chemical calculations. The repulsion between different species is expressed by the combining rule of Kong [J. Chem. Phys. 59, 2464 (1972)]. Our primary target was the hydration free energy of ions which is correct within the error of calculations. We calculated water-ion clusters up to 6 water molecules, and, as a crosscheck, we determined the density and internal energy of alkali-halide crystals at ambient conditions with acceptable accuracy. The structure of hydrated ions was also discussed.

  4. A new polarizable force field for alkali and halide ions

    SciTech Connect

    Kiss, Péter T.; Baranyai, András [Institute of Chemistry, Eötvös University, 1518 Budapest 112, PO BOX 32 (Hungary)

    2014-09-21

    We developed transferable potentials for alkali and halide ions which are consistent with our recent model of water [P. T. Kiss and A. Baranyai, J. Chem. Phys. 138, 204507 (2013)]. Following the approach used for the water potential, we applied Gaussian charge distributions, exponential repulsion, and r{sup ?6} attraction. One of the two charges of the ions is fixed to the center of the particle, while the other is connected to this charge by a harmonic spring to express polarization. Polarizability is taken from quantum chemical calculations. The repulsion between different species is expressed by the combining rule of Kong [J. Chem. Phys. 59, 2464 (1972)]. Our primary target was the hydration free energy of ions which is correct within the error of calculations. We calculated water-ion clusters up to 6 water molecules, and, as a crosscheck, we determined the density and internal energy of alkali-halide crystals at ambient conditions with acceptable accuracy. The structure of hydrated ions was also discussed.

  5. A COMPARISON OF THE MIGRATION ENTROPY FOR THE CATION AND THE ANION VACANCY MOTION IN ALKALI HALIDES

    E-print Network

    Boyer, Edmond

    L-171 A COMPARISON OF THE MIGRATION ENTROPY FOR THE CATION AND THE ANION VACANCY MOTION IN ALKALI vacancy in alkali halides has been calculated through macroscopic parameters (such as bulk modulus.390 The entropy values Sm and Srn for cation and anion vacancy motion respectively in alkali halides are obtained

  6. Efficient destruction of CF4 through in situ generation of alkali metals from heated alkali halide reducing mixtures.

    PubMed

    Lee, Myung Churl; Choi, Wonyong

    2002-03-15

    Perfluorocarbons (PFCs) are the most potent green house gases that are very recalcitrant at destruction. An effective way of converting PFCs using hot solid reagents into safe products has been recently introduced. By investigating the thermal reductive destruction of tetrafluoromethane (CF4) we provided new insight and more physicochemical consideration on this novel process. The complete destruction of CF4was successfully achieved by flowing the gas through a heated reagent bed (400-950 degrees C) that contained powder mixtures of alkali halides, CaO, and Si. The silicon acted as a reducing agent of alkali halides for the in-situ production of alkali metals, and the calcium oxide played the role of a halide ion acceptor. The absence of any single component in this ternary mixture drastically reduced the destruction efficiency of CF4. The CF4 destruction efficiencies with the solid reagent containing the alkali halide, MX, increased in the order of Li approximately Na < K < Cs for alkali cations and I < Br < Cl < F for halide anions. This trend agreed with the endothermicity of the alkali metal generation reaction: the higher the endothermicity, the lower the destruction efficiency. Alkali metal generation was indirectly detected by monitoring H2 production from its reaction with water. The production of alkali metals increased with NaF, KF, and CsF in this order. The CsF/CaO/Si system exhibited the complete destruction of CF4 at as low as 600 degrees C. The solid product analysis by X-ray diffraction (XRD) showed the formation of CaF2 and the depletion of Si with black carbon particles formed in the solid reagent residue. No CO/CO2 and toxic HF and SiF4 formation were detected in the exhaust gas. PMID:11944694

  7. Strong Turbulence in Alkali Halide Negative Ion Plasmas

    NASA Astrophysics Data System (ADS)

    Sheehan, Daniel

    1999-11-01

    Negative ion plasmas (NIPs) are charge-neutral plasmas in which the negative charge is dominated by negative ions rather than electrons. They are found in laser discharges, combustion products, semiconductor manufacturing processes, stellar atmospheres, pulsar magnetospheres, and the Earth's ionosphere, both naturally and man-made. They often display signatures of strong turbulence^1. Development of a novel, compact, unmagnetized alkali halide (MX) NIP source will be discussed, it incorporating a ohmically-heated incandescent (2500K) tantulum solenoid (3cm dia, 15 cm long) with heat shields. The solenoid ionizes the MX vapor and confines contaminant electrons, allowing a very dry (electron-free) source. Plasma densities of 10^10 cm-3 and positive to negative ion mass ratios of 1 <= fracm_+m- <= 20 are achievable. The source will allow tests of strong turbulence theory^2. 1 Sheehan, D.P., et al., Phys. Fluids B5, 1593 (1993). 2 Tsytovich, V. and Wharton, C.W., Comm. Plasma Phys. Cont. Fusion 4, 91 (1978).

  8. Nanocrystal growth in alkali halides observed by exciton spectroscopy

    NASA Astrophysics Data System (ADS)

    Haselhoff, M.; Weber, H.-J.

    1998-08-01

    We have developed a method to study the growth of CuCl and CuBr nanocrystals in alkali halides by in situ absorption spectroscopy. Exciton lines are used as a signature of crystallinity and a broad absorption peak measures the number of Cu+ ions. The mean radius R and the concentration xcr of nanocrystals are determined simultaneously, which in turn enables the determination of the particle density N of crystals as a function of time. Neither the size-distribution function nor R(t) follow the prediction of the classical growth theory. xcr(t) reveals two different growth mechanisms, one for high and one for low growth temperatures. N(t) demonstrates that the growth of big crystals at the expense of small crystals happens from the beginning of the growth process. This result contradicts the traditional view of Ostwald ripening as a final stage of precipitation and stresses the dynamical character of cluster growth. The experimental data are described by a set of empirical parameters that can be used as a guide for controlled growth of CuCl nanocrystals in NaCl. The smallest nanocrystals detected by exciton spectroscopy consist of 50 unit cells. The kinetic properties of KCl and NaBr crystals doped with CuCl and CuBr are very similar to those observed in NaCl doped with CuCl.

  9. Dissipative tunneling, breathers, and anomalous delay in doped alkali halides

    NASA Astrophysics Data System (ADS)

    Fabeni, Pasquale; Mugnai, Daniela; Pazzi, Gian P.; Ranfagni, Anedio; Susini, Carlo; Vannini, Matteo; Cacciari, Ilaria; Vitali, Maria A.; Schulman, Lawrence S.

    2007-09-01

    In studying the decay kinetics of the excited states in alkali halides doped with heavy impurities, anomalous behaviour in the slow emission, consisting of several decay components, was found. New efforts were made to interpret this behaviour by invoking delicate and sophisticated mechanisms which transcend the systems considered. The evolution of the lattice reaction time is fundamental to this purpose, and requires Jahn-Teller models able to interpret the slow complex decay of the emission in the A-band. One model is based on the formation and confinement of discrete breathers, as a result of the Jahn-Teller cluster distortion, whose temporal stability is of the same order as the luminescence decay time (ms). Another model is based on a dissipative tunneling process, the duration of which strongly depends on the consistency of the barrier and presents a very large variation of the decay time (from ns to ms). An attempt is here made for a unification of the two mechanisms.

  10. Comparison of CsBr and KBr coated Cu photocathodes: Effects of laser irradiation and work function changes

    SciTech Connect

    He, Weidong; VilayurGanapathy, Subramanian; Joly, Alan G.; Droubay, Timothy C.; Chambers, Scott A.; Maldonado, Juan R.; Hess, Wayne P.

    2013-02-20

    Thin films (7 nm layers) of CsBr and KBr were deposited on Cu(100) to investigate photoemission properties of these potential photocathode materials. After thin film deposition and prolonged laser ultraviolet (UV) irradiation (266 nm picosecond laser) photoemission quantum efficiency increases by factors of 26 and 77 for KBr/Cu(100) and CsBr/Cu(100) photocathodes, respectively. Immediately following thin film deposition, a decrease in work function is observed, compared to bare Cu, in both cases. Quantum efficiency enhancements are attributed to the decrease in photocathode work function, due to the deposition of alkali halide thin films, and photo-induced processes, that introduce defect states into the alkali halide bandgap, induced by UV laser irradiation. It is possible that alkali metal formation occurs during UV irradiation and that this further contributes to photoemission enhancement. Our results suggest that KBr, a relatively stable alkali-halide, has potential for photocathode applications.

  11. JOURNAL DE PHYSIQUE Colloque Cl, supplment au n 12, Tome 37, Dcembre 1976, page C7-101 POSITRON ANNIHILATION STUDIES IN ALKALI HALIDES

    E-print Network

    Paris-Sud XI, Université de

    ANNIHILATION STUDIES IN ALKALI HALIDES G. W. DEAN, S. DANNEFAER, B. V. SOBOLEV (*), D. P. KERR and B. G. HOGG employée pour étudier seize alkali halides. Les cristaux étaient irradiés par les rayons y. Un composant in a series of 16 alkali halides has been studied using the techniques of both lifetime and Doppler broadening

  12. Lattice-Vibration Effects Due to Impurities in an Alkali Halide

    Microsoft Academic Search

    Leon Gunther

    1965-01-01

    The Green's-function approach to the study of impurity effects on lattice vibrations is applied to alkali halides. Due to the strong phonon-photon interaction, some care must be taken in the application of the results for the pure crystal. A simplified approach for obtaining the impurity contribution to the lattice thermal conductivity is presented which leads to a phonon lifetime having

  13. Polarization of the Electroluminescence of Alkali-Halide Crystals Inactivated and Activated with Europium

    Microsoft Academic Search

    A. P. Druzhinin; S. G. Ekhanin; N. S. Nesmelov; I. V. Sveshnikov

    2004-01-01

    Among works devoted to the electroluminescence (EL) of alkali-halide crystals (AHCs), there are no works devoted to an analysis of the polarization characteristics, though the polarization is an important luminescence characteristic. A comprehensive analysis of this problem can give new information not only on the structure of the luminescence centers but also on the mechanism of luminescence excitation. From the

  14. Activation Energy for the Diffusion of Coupled Pairs of Vacancies in Alkali Halide Crystals

    Microsoft Academic Search

    G. J. Dienes

    1948-01-01

    The theoretical activation energy for the diffusion of neutral combined pairs of positive- and negative-ion vacancies in alkali halides has been determined. Changes in Coulombic, repulsive, and polarization energies were taken into account with appropriate corrections for second-order effects. Calculations for the rigid and distorted lattice showed that distortion effects during diffusion are of appreciable magnitude. This energy contribution has

  15. Optical Dielectric Strength of Alkali-Halide Crystals Obtained by Laser-Induced Breakdown

    Microsoft Academic Search

    Eli Yablonovitch

    1971-01-01

    CO2 laser-induced breakdown was studied in ten of the alkali halides. The bulk intrinsic breakdown thresholds are intimately related to the corresponding dc dielectric strengths. It is therefore concluded that the same mechanism is operative in both types of experiment. A method is proposed for designing more damage-resistant materials. In addition, the question of inclusions is dealt with.

  16. Electron-and photon-stimulated desorption of atomic hydrogen from radiation-modified alkali halide surfaces

    E-print Network

    Tolk, Norman H.

    Electron- and photon-stimulated desorption of atomic hydrogen from radiation-modified alkali halide containing an excess of alkali metal. A desorption mechanism is presented in which incident electrons or photons induce a valence excitation to a neutral, antibonding state of the surface alkali hydride molecule

  17. JOURNAL DE PHYSIQUE Colloque C6, suppkment au no 7, Tome 41, Juillet 1980,page C6-109 COLOUR CENTRES IN ALKALI HALIDES (2).

    E-print Network

    Boyer, Edmond

    CENTRES IN ALKALI HALIDES (2). Defects induced in NaMgF, crystals by X- and VUV-irradiation N attention was given to the study of alkali- halides and relatively few works dealt with radiation defects aggregate centers [5]. Some of these interpre- tations were drawn on knowledge gained from alkali

  18. JOURNAL DE PHYSIQUE Colloque C7, suppliment au no 12, Tome 37, Dkcembre 1976,page C7-541 SPUTTERING OF ALKALI HALIDES

    E-print Network

    Boyer, Edmond

    OF ALKALI HALIDES BY 70 TO 300 keV H, He, Ar IONS J. P. BIERSACK and E. SANTNER HahnVH+,He+,and Arf ions impingingon KCl, and KI. The alkali halide samples are prepared as polycristallinelayers of the upper and lower limit for the thermal activation energy of the jumps of the STE in alkali fluoride

  19. Refined potentials for rare gas atom adsorption on rare gas and alkali-halide surfaces

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Heinbockel, J. H.; Outlaw, R. A.

    1985-01-01

    The utilization of models of interatomic potential for physical interaction to estimate the long range attractive potential for rare gases and ions is discussed. The long range attractive force is calculated in terms of the atomic dispersion properties. A data base of atomic dispersion parameters for rare gas atoms, alkali ion, and halogen ions is applied to the study of the repulsive core; the procedure for evaluating the repulsive core of ion interactions is described. The interaction of rare gas atoms on ideal rare gas solid and alkali-halide surfaces is analyzed; zero coverage absorption potentials are derived.

  20. Reactions between cold methyl halide molecules and alkali-metal atoms

    SciTech Connect

    Lutz, Jesse J.; Hutson, Jeremy M. [Joint Quantum Centre (JQC) Durham-Newcastle, Department of Chemistry, Durham University, South Road, Durham DH1 3LE (United Kingdom)] [Joint Quantum Centre (JQC) Durham-Newcastle, Department of Chemistry, Durham University, South Road, Durham DH1 3LE (United Kingdom)

    2014-01-07

    We investigate the potential energy surfaces and activation energies for reactions between methyl halide molecules CH{sub 3}X (X = F, Cl, Br, I) and alkali-metal atoms A (A = Li, Na, K, Rb) using high-level ab initio calculations. We examine the anisotropy of each intermolecular potential energy surface (PES) and the mechanism and energetics of the only available exothermic reaction pathway, CH{sub 3}X + A ? CH{sub 3} + AX. The region of the transition state is explored using two-dimensional PES cuts and estimates of the activation energies are inferred. Nearly all combinations of methyl halide and alkali-metal atom have positive barrier heights, indicating that reactions at low temperatures will be slow.

  1. Physics and nanofriction of alkali halide solid surfaces at the melting point

    Microsoft Academic Search

    T. Zykova-Timan; D. Ceresoli; U. Tartaglino; E. Tosatti

    2006-01-01

    Alkali halide (100) surfaces are anomalously poorly wetted by their own melt at the triple point. We carried out simulations for NaCl(100) within a simple (BMHFT) model potential. Calculations of the solid–vapor, solid–liquid and liquid–vapor free energies showed that solid NaCl(100) is a nonmelting surface, and that the incomplete wetting can be traced to the conspiracy of three factors: surface

  2. IR spectroscopy of aqueous alkali halide solutions: Pure salt-solvated water spectra and hydration numbers

    Microsoft Academic Search

    Jean-Joseph Max; Camille Chapados

    2001-01-01

    Extrapolation techniques were used to obtain pure salt-solvated water spectra from the attenuated total reflection infrared spectra (ATR-IR) of aqueous solutions of the nine alkali halide salts LiCl, NaCl, KCl, CsCl, NaBr, KBr, NaI, KI, and CsI and the alkaline-earth chloride salt MgCl2. These salts ionize completely in water. The ions by themselves do not absorb in the IR, but

  3. Second, third-, and fourth-order elastic constants of mixed alkali-halide crystals

    Microsoft Academic Search

    J. Shanker; G. D. Jain

    1983-01-01

    The second-order elastic constants (SOEC), third-order elastic constants (TOEC), and fourth-order elastic constants (FOEC) of mixed alkali-halide crystals are calculated using a phenomenological potential model which takes into account the effect of Lundqvist's three-body forces along with other relevant interactions in ionic solids. Values of three SOEC, six TOEC, eleven FOEC, and pressure derivatives of SOEC have been calculated for

  4. Subpicosecond spectroscopy of hole and exciton self-trapping in alkali-halide crystals

    NASA Astrophysics Data System (ADS)

    Thoma, E. D.; Yochum, H. M.; Williams, R. T.

    1997-10-01

    Subpicosecond and picosecond optical absorption spectra following band-gap excitation of alkali-halide crystals have been measured and analyzed. It is found that a simple rule relates the low-energy edge of the ``N band'' previously attributed to the one-center (Landau-type) hole polaron, the photon energy of the (two-photon) excitation pulse, and the band gap. This rule describes important features of all subpicosecond absorption spectra of excited alkali halides compiled from the present work and other published works, within the framework of two-photon cross-correlated absorption of the excitation and probe pulses as well as pulse dispersion in the optics and in the sample. It is concluded that the one-center self-trapped hole in alkali halides has not yet been identified by absorption spectroscopy in the visible-uv spectral range. The self-trapped hole and/or associated self-trapped exciton is observed in the two-center configuration. We also report studies using the fourth harmonic of an amplified Ti:sapphire laser to excite insulators with band gaps as large as 11.6 eV by two-photon absorption and observe the subsequent development of defect spectra.

  5. Operation GREENHOUSE. Scientific Director's report. Annex 5. 1 - Annex a. Alkali halide and phosphate glass radiological casualty dosimeters

    Microsoft Academic Search

    R. S. Alger; J. P. Dyson; R. A. Levy; D. W. McQuilling

    1951-01-01

    Photochemical reactions induced by ionizing radiations can produce color centers in alkali halide crystals and fluorescent centers in silver-bearing phosphate glasses. These reactions are being investigated as a basis for casualty-badge radiation dosimeters. Potassium bromide and potassium chloride crystals were satisfactorily sensitized by heating in a combined atmosphere of alkali vapor and hydrogen. Doses of 25 r of cobalt 60

  6. Calculation of the melting point of alkali halides by means of computer simulations

    NASA Astrophysics Data System (ADS)

    Aragones, J. L.; Sanz, E.; Valeriani, C.; Vega, C.

    2012-09-01

    In this paper, we study the liquid-solid coexistence of NaCl-type alkali halides, described by interaction potentials such as Tosi-Fumi (TF), Smith-Dang (SD), and Joung-Cheatham (JC), and compute their melting temperature (Tm) at 1 bar via three independent routes: (1) liquid/solid direct coexistence, (2) free-energy calculations, and (3) Hamiltonian Gibbs-Duhem integration. The melting points obtained by the three routes are consistent with each other. The calculated Tm of the Tosi-Fumi model of NaCl is in good agreement with the experimental value as well as with other numerical calculations. However, the other two models considered for NaCl, SD and JC, overestimate the melting temperature of NaCl by more than 200 K. We have also computed the melting temperature of other alkali halides using the Tosi-Fumi interaction potential and observed that the predictions are not always as close to the experimental values as they are for NaCl. It seems that there is still room for improvement in the area of force-fields for alkaline halides, given that so far most models are still unable to describe a simple yet important property such as the melting point.

  7. Optical Constants and Excitons of Alkali Cuprous Halide Crystals

    NASA Astrophysics Data System (ADS)

    Edamatsu, Keiichi; Nanba, Takao; Ikezawa, Mikihiko

    1989-01-01

    The anisotropic reflection spectra of K2AgI3, Rb2AgI3 and Rb2AgBr3 have been measured in the range from 4 to 26 eV using synchrotron radiation. The optical constants have been obtained through the Kramers-Kronig analysis. The characters of the band edge excitons of K2AgI3 and Rb2AgI3 are very similar to those of the alkali iodides. However, the perturbation calculation has indicated that the spin-orbit interaction scarcely affect the outline of the valence band structure of Rb2AgI3 and that no spin-orbit doublet appears in the absorption spectra. The anisotropic absorption due to the core excitons of K+ or Rb+ have been found around 20 or 17 eV, respectively. The prominent structures due to plasmons of valence electrons have been found at 10-12 eV in the energy loss spectra.

  8. Analysis of the Interrelationship Between Melting and Fracturing of Alkali Halides

    NASA Astrophysics Data System (ADS)

    Zou, Yong; Huang, Hulin; Cui, Guang Lei

    2015-05-01

    On the basis of the lattice potential energy with two forms proposed by Born-Mie and Born-Mayer, respectively, the critical interionic separations {{ r}}i where the lattice is fractured due to tensile force have been evaluated for alkali metal halides. The theoretical results are analyzed together with the interionic separations {{ r}}m determined by the melting temperature and the help of the isobaric equation of state. A new and simple interrelationship between {{ r}}m and {{ r}}i is obtained, and the crystal melting behavior can be accordingly predicted for NaCl-structure ionic crystals.

  9. JOURNAL DE PHYSIQUE Co//oqueC9, supp/dmetlt au no 11-12, Tome 34, Novembl.e-Ddcembre 1973,page C9-11 ATOMIC TRANSPORT IN ALKALI HALIDES DOPED BY DIVALENT ANIONS

    E-print Network

    Paris-Sud XI, Université de

    -11 ATOMIC TRANSPORT IN ALKALI HALIDES DOPED BY DIVALENT ANIONS AND CATIONS M. CHEMLA and F. BENIERE in alkali halides are reviewed, especially those concerning single crystals doped by divalent anions. We of the lattice defects. In these works, alkali halides hold a predominating place for three chief reasons. First

  10. Alkali Halide Interfacial Behavior in a Sequence of Charged Slit Pores

    SciTech Connect

    Wander, Matthew C [ORNL; Shuford, Kevin L [ORNL

    2011-01-01

    In this paper, a variety of alkali halide, aqueous electrolyte solutions in contact with charged, planar-graphite slit-pores are simulated using classical molecular dynamics. Size trends in structure and transport properties are examined by varying the choice of ions among the alkali metal and halide series. As with the uncharged pores, system dynamics are driven by changes in water hydration behavior and specifically by variations in the number of hydrogen bonds per water molecule. Overall, the larger ions diffuse more rapidly under high surface charge conditions than the smaller ions. In particular, for the 1 nmslit, ion diffusivity increased by a factor of 4 compared to the uncharged case. Finally, a quantitative fit to the interfacial charge structure is presented, which confirms the presence of two distinct types of layers in an aqueous interface. This model indicates that the chemistry of the interface is able to create a small interfacial potential, and it shows how water molecules can rotate to increase charge separation in response to a surface potential.

  11. Molecular dispersion energy parameters for alkali and halide ions in aqueous solution

    NASA Astrophysics Data System (ADS)

    Reiser, S.; Deublein, S.; Vrabec, J.; Hasse, H.

    2014-01-01

    Thermodynamic properties of aqueous solutions containing alkali and halide ions are determined by molecular simulation. The following ions are studied: Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I-. The employed ion force fields consist of one Lennard-Jones (LJ) site and one concentric point charge with a magnitude of ±1 e. The SPC/E model is used for water. The LJ size parameter of the ion models is taken from Deublein et al. [J. Chem. Phys. 136, 084501 (2012)], while the LJ energy parameter is determined in the present study based on experimental self-diffusion coefficient data of the alkali cations and the halide anions in aqueous solutions as well as the position of the first maximum of the radial distribution function of water around the ions. On the basis of these force field parameters, the electric conductivity, the hydration dynamics of water molecules around the ions, and the enthalpy of hydration is predicted. Considering a wide range of salinity, this study is conducted at temperatures of 293.15 and 298.15 K and a pressure of 1 bar.

  12. ture peculiar to each compound. The advantage of alkali halide salts in this respect is that they are readily available

    E-print Network

    Zare, Richard N.

    ture peculiar to each compound. The advantage of alkali halide salts in this respect RECEIVEDfor review December 17, 1974. Accepted Febru- ary 18,1975. Laser Fluorescence Analysis-resolved and wavelength- resolved laser-induced fluorescence. We have detected as low as 0.2 ng of aflatoxin B1 and we

  13. Lattice model calculation of hugoniot curves and the grüneisen parameter at high pressure for the alkali halides

    Microsoft Academic Search

    H. H. Demarest

    1974-01-01

    A seven parameter shell model of the interatomic forces in the NaCl lattice is used to make a detailed lattice dynamics calculation at arbitrary volume, for fourteen alkali halides. The calculated normal mode spectrum gives an explicit vibrational contribution to the pressure and the elastic constants in the quasiharmonic approximation. The seven parameters are chosen to fit low pressure ultrasonic

  14. Quantum efficiency enhancement in CsI/metal photocathodes

    NASA Astrophysics Data System (ADS)

    Kong, Lingmei; Joly, Alan G.; Droubay, Timothy C.; Hess, Wayne P.

    2015-02-01

    High quantum efficiency enhancement is found for hybrid metal-insulator photocathodes consisting of thin films of CsI deposited on Cu(1 0 0), Ag(1 0 0), Au(1 1 1) and Au films irradiated by 266 nm laser pulses. Low work functions (near or below 2 eV) are observed following ultraviolet laser activation. Work functions are reduced by roughly 3 eV from that of clean metal surfaces. We discuss various mechanisms of quantum efficiency enhancement for alkali halide/metal photocathode systems and conclude that the large change in work function, due to Cs accumulation of Cs metal at the metal-alkali halide interface, is the dominant mechanism for quantum efficiency enhancement.

  15. Measurements of the electric dipole polarizabilities of the alkali halide dimers

    SciTech Connect

    Kremens, R.; Bederson, B.; Jaduszliwer, B.; Stockdale, J.; Tino, A.

    1984-08-15

    We report the first measurements of the average electric dipole polarizabilities of five alkali halide dimers. A combined monomer-dimer molecular beam deflection pattern in an inhomogeneous electric field is subject to an appropriate computational analysis to extract the polarizabilities. A simple combination of bond and effective ionic models to estimate the polarizabilities gives reasonably good agreement with the measured values. The values are, in units of 10/sup -24/ cm/sup 2/, (KF)/sub 2/:25.3 +- 3.2; (KCl)/sub 2/:28.6 +- 3.0; (RbCl)/sub 2/:43.4 +- 4.2; (CsCl)/sub 2/:36.6 +- 5.0; (CsF)/sub 2/:21.2 +- 2.6.

  16. Measurements of the electric dipole polarizabilities of the alkali halide dimers

    SciTech Connect

    Kremens, R.; Bederson, B.; Jaduszliwer, B.; Stockdale, J.; Tino, A.

    1984-04-15

    We report the first measurements of the average electric dipole polarizabilities of five alkali halide dimers. A combined monomer--dimer molecular beam deflection pattern in an inhomogeneous electric field is subject to an appropriate computational analysis to extract the polarizabilities. A simple combination of bond and effective ionic models to estimate the polarizabilities gives reasonably good agreement with the measured values. The values are, in units of 10/sup -24/ cm/sup 2/, (DF(/sub 2/: 25.3 +- 3.2; (KDl)/sub 2/: 28.6 +- 3.0; (RbCl)/sub 2/:43.4 +- 4.2; (CsCl)/sub 2/:36.6 +- 5.0; (CsF)/sub 2/:21.2 +- 2.6.

  17. Silicon Halide-alkali Metal Flames as a Source of Solar Grade Silicon

    NASA Technical Reports Server (NTRS)

    Olson, D. B.; Gould, R. K.

    1979-01-01

    A program is presented which was aimed at determining the feasibility of using high temperature reactions of alkali metals and silicon halides to produce low cost solar-grade silicon. Experiments are being conducted to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, and determine the effects of the reactants and/or products on materials of reactor construction. During the current reporting period, the results of heat release experiments were used to design and construct a new type of thick-wall graphite reactor to produce larger quantities of silicon. A reactor test facility was constructed. Material compatibility tests were performed for Na in contact with graphite and several coated graphites. All samples were rapidly degraded at T = 1200K, while samples retained structural strength at 1700K. Pyrolytic graphite coatings cracked and separated from substances in all cases.

  18. Second-, third-, and fourth-order elastic constants of mixed alkali-halide crystals

    NASA Astrophysics Data System (ADS)

    Shanker, J.; Jain, G. D.

    1983-02-01

    The second-order elastic constants (SOEC), third-order elastic constants (TOEC), and fourth-order elastic constants (FOEC) of mixed alkali-halide crystals are calculated using a phenomenological potential model which takes into account the effect of Lundqvist's three-body forces along with other relevant interactions in ionic solids. Values of three SOEC, six TOEC, eleven FOEC, and pressure derivatives of SOEC have been calculated for NaCl-NaBr, KCl-KBr, and KBr-KI mixed crystals for the entire range of compositions. The results are compared with available experimental values. The applicability of knowledge of TOEC and FOEC has been discussed for predicting the conductivity and thermal expansion coefficient of mixed crystals.

  19. Silicon halide-alkali metal flames as a source of solar grade silicon

    NASA Technical Reports Server (NTRS)

    Olsen, D. B.; Miller, W. J.

    1979-01-01

    The feasibility of using alkali metal-silicon halide diffusion flames to produce solar-grade silicon in large quantities and at low cost is demonstrated. Prior work shows that these flames are stable and that relatively high purity silicon can be produced using Na + SiCl4 flames. Silicon of similar purity is obtained from Na + SiF4 flames although yields are lower and product separation and collection are less thermochemically favored. Continuous separation of silicon from the byproduct alkali salt was demonstrated in a heated graphite reactor. The process was scaled up to reduce heat losses and to produce larger samples of silicon. Reagent delivery systems, scaled by a factor of 25, were built and operated at a production rate of 0.5 kg Si/h. Very rapid reactor heating rates are observed with wall temperatures reaching greater than 2000 K. Heat release parameters were measured using a cooled stainless steel reactor tube. A new reactor was designed.

  20. Silicon halide-alkali metal flames as a source of solar grade silicon. Final report

    SciTech Connect

    Olson, D.B.; Miller, W.J.; Gould, R.K.

    1980-01-01

    The object of this program was to determine the feasibility of using continuous high-temperature reactions of alkali metals and silicon halides to produce silicon in large quantities and of suitable purity for use in the production of photovoltaic solar cells. Equilibrium calculations showed that a range of conditions were available where silicon was produced as a condensed phase but the byproduct alkali metal salt was a vapor. A process was proposed using the vapor phase reaction of Na with SiCl/sub 4/. Low pressure experiments were performed demonstrating that free silicon was produced and providing experience with the construction of reactant vapor generators. Further experiments at higher reagent flow rates were performed in a low temperature flow tube configuration with co-axial injection of reagents. Relatively pure silicon was produced in these experiments. A high temperature graphite flow tube was built and continuous separation of Si from NaCl was demonstrated. A larger-scaled well-stirred reactor was built. Experiments were performed to investigate the compatibility of graphite-based reactor materials of construction with sodium. At 1100 to 1200 K none of these materials were found to be suitable. At 1700 K the graphites performed well with little damage except to coatings of pyrolytic graphite and silicon carbide which were damaged.

  1. Chemistry of alkali cation exchanged faujasite and mesoporous NaX using alkyl halides and phosphates

    NASA Astrophysics Data System (ADS)

    Lee, Min-Hong

    The purpose of this work was to increase the reactivity of Faujasite X (NaX) zeolite toward the reactive decontamination of materials subject to nucleophilic attack by means of zeolite cation optimization and by means of the synthesis of mesoporous Faujasite X. Primary alkyl halides and trialkyl phosphates have been the test materials on which the cation-optimized and mesoporous zeolites have been tested. In the alkali cation optimization work, reactions of methyl iodide and 1-chloropropane with alkali metal cation exchanged Faujasite zeolite X were investigated at room temperature. The reactivity of the framework and the product formation were shown to depend on zeolite framework counter-cation. A quantitative study of zeolite product formation has been carried out, primarily using solid-state NMR spectroscopy. Large alkali cations showed preference toward substitution chemistry. In contrast, alkyl halide exposed LiX and NaX zeolites underwent both substitution and elimination. Subsequently introduced water molecules led to hydrolysis of framework species that was sensitive to framework counter-cation. The mesoporous NaX zeolites work undertakes to test whether an improvement in surface chemical reactivity can be achieved by introducing mesopores into the already reactive nucleophilic microporous NaX zeolite. Incorporation of the polydiallyl dimethyl ammonium chloride (PDADMAC) template and the formation of mesopores in Faujasite X zeolite (NaX) were successful and well-characterized. The mesopores are proposed to have occurred from incorporation of the cationic PDADMAC polymer into the zeolite by compensating zeolite framework charge. Subsequent sodium cation exchange of calcined mesoporous NaX was shown to restore the chemical reactivity characteristic of as-synthesized NaX. Trialkyl organophosphorous compounds underwent substitution reactions. The reactivity of both microporous and mesoporous Faujasite zeolite X and the product formation was shown to depend on the length of the alkyl chain. Although introduced mesopores alleviated the limited reagent diffusion to reactive sites due to the microporosity of the NaX zeolites, no marked improvement in the product yields was achieved with either the 1-chloroalkanes or the trialkyl phosphates test compounds, regardless of alkyl chain length. The disappointing results have been attributed to lack of substantial net increase in the numbers of zeolite nucleophilic sites accompanying mesopore introduction.

  2. Abstract. --A survey is given of the various ways in which interstitial halogen atoms produced by ionising radiation can be trapped in alkali halides. First, the fundamental interstitial halogen

    E-print Network

    Paris-Sud XI, Université de

    by ionising radiation can be trapped in alkali halides. First, the fundamental interstitial halogen atom : foreign halogen ions, foreign alkali ions or pairs of both. The discussion is limited to a des- cription. -- Because the alkali halides are it is likely that a number of parallels exist between the prototypes

  3. Physics of solid and liquid alkali halide surfaces near the melting point

    NASA Astrophysics Data System (ADS)

    Zykova-Timan, T.; Ceresoli, D.; Tartaglino, U.; Tosatti, E.

    2005-10-01

    This paper presents a broad theoretical and simulation study of the high-temperature behavior of crystalline alkali halide surfaces typified by NaCl(100), of the liquid NaCl surface near freezing, and of the very unusual partial wetting of the solid surface by the melt. Simulations are conducted using two-body rigid-ion Born-Mayer-Huggins-Fumi-Tosi (BMHFT) potentials, with full treatment of long-range Coulomb forces. After a preliminary check of the description of bulk NaCl provided by these potentials, which seems generally good even at the melting point, we carry out a new investigation of solid and liquid surfaces. Solid NaCl(100) is found in this model to be very anharmonic and yet exceptionally stable when hot. It is predicted by a thermodynamic integration calculation of the surface free energy that NaCl(100) should be a well-ordered, nonmelting surface, metastable even well above the melting point. By contrast, the simulated liquid NaCl surface is found to exhibit large thermal fluctuations and no layering order. In spite of that, it is shown to possess a relatively large surface free energy. The latter is traced to a surface entropy deficit, reflecting some kind of surface short-range order. We show that the surface short-range order is most likely caused by the continuous transition of the bulk ionic melt into the vapor, made of NaCl molecules and dimers rather than of single ions. Finally, the solid-liquid interface free energy is derived through Young's equation from direct simulation of partial wetting of NaCl(100) by a liquid droplet. The resulting interface free energy is large, in line with the conspicuous solid-liquid 27% density difference. A partial wetting angle near 50° close to the experimental value of 48° is obtained in the process. It is concluded that three elements, namely, the exceptional anharmonic stability of the solid (100) surface, the molecular short-range order at the liquid surface, and the costly solid-liquid interface, all conspire to cause the anomalously poor wetting of the (100) surface by its own melt in the BMHFT model of NaCl—and most likely also in real alkali halide surfaces.

  4. JOURNALDE PHYSIQUE ColloqueCl,suppl&mentau n O 1, Tome41,janvier 1980,page C1-451 C W OF 5 7 ~ eIMPLANTS I N ALKALI HALIDES

    E-print Network

    Boyer, Edmond

    IMPLANTS I N ALKALI HALIDES J. Kowalski, J. dtanek, B.D. sawickax, J.A. Sawicki and M. ~rwiega* Institute compounds, Seve- r a l polycrystalline alkali-halides having the NaCl structure were implanted with 70 keV 5 that iron implants i n alkali halides exist mainly i n the form of ~ e ~ +ions, This is i n drastic

  5. Silicon halide-alkali metal flames as a source of solar grade silicon

    NASA Technical Reports Server (NTRS)

    Olson, D. B.; Miller, W. J.; Gould, R. K.

    1980-01-01

    The feasibility of using continuous high-temperature reactions of alkali metals and silicon halides to produce silicon in large quantities and of suitable purity for use in the production of photovoltaic solar cells was demonstrated. Low pressure experiments were performed demonstrating the production of free silicon and providing experience with the construction of reactant vapor generators. Further experiments at higher reagent flow rates were performed in a low temperature flow tube configuration with co-axial injection of reagents and relatively pure silicon was produced. A high temperature graphite flow tube was built and continuous separation of Si from NaCl was demonstrated. A larger scaled well stirred reactor was built. Experiments were performed to investigate the compatability of graphite based reactor materials of construction with sodium. At 1100 to 1200 K none of these materials were found to be suitable. At 1700 K the graphites performed well with little damage except to coatings of pyrolytic graphite and silicon carbide which were damaged.

  6. Building alkali-metal-halide layers within a perovskite host by sequential intercalation: (A(2)Cl)LaNb(2)O(7) (A = Rb, Cs).

    PubMed

    Choi, Jonglak; Zhang, Xiao; Wiley, John B

    2009-06-01

    Alkali-metal-halide layers were constructed within Dion-Jacobson (DJ) layered perovskites by a two-step sequential intercalation method. Reductive intercalation with an alkali metal, followed by oxidative intercalation with chlorine gas, leads to the formation of the compounds, (A(2)Cl)LaNb(2)O(7) (A = Rb, Cs). Rietveld refinement of X-ray powder diffraction data shows that an alkali-metal-halide layer is formed between the perovskite blocks. The alkali-metal cation is eight-coordinate with four oxygens from the perovskite layer and four chlorides from the new halide layer; this environment is similar to cesium in the CsCl structure (B2). Thermal analysis indicates that these are low-temperature phases where decomposition begins by 400 degrees C. Details on the synthesis and characterization of this set of compounds are presented, and the general utility of this approach discussed. PMID:19466802

  7. Lower consolute boundaries of the nonionic surfactant C8E5 in aqueous alkali halide solutions: an approach to reproduce the effects of alkali halides on the cloud-point temperature.

    PubMed

    Weckström, Kristian; Papageorgiou, Anastassios C

    2007-06-01

    In the temperature-composition phase diagram of the nonionic surfactant n-octyl-hydroxypenta(oxyethylene), C(8)E(5), there are three principal curves; the one for the critical micelle concentration (cmc), the one delineating the existence of the hexagonal phase, and then the lower consolute boundary (lcb). In this work it is clarified how the presence of the alkali halides NaF, LiCl, NaCl, NaBr and NaI in the aqueous solutions, up to high molalities, change the lcb temperature-position and shape. The lcbs are obtained from measurements of cloud-point temperatures. Rather marked anion-controlled shifts are observed in the boundary temperature-position, and the order of the anions is in accordance with the prediction of the Hofmeister series. Also the shape of the boundary is affected in an anion-specific way, so that the largest changes are found with the strongest salting-out agent. The separation point varies in distinctly non-linear manners with the molality of the studied alkali halides. An approach is presented that can reproduce the effects of the alkali halides on the cloud-point temperature of C(8)E(5) and a poly(ethylene oxide) polymer, at low amounts of the macroentities. In this approach use is made of the known behaviour of the electrolytes at the air/water surface and the virial expansion, to account for the initial salting-out/-in effect and the variation of the effect with electrolyte molality. PMID:17306288

  8. Experimental studies of photon-surface interaction dynamics in the alkali halides

    SciTech Connect

    Haglund, R.F. Jr.; Tolk, N.H.

    1986-01-01

    We describe recent measurements which have provided, in unprecedented detail, insights into the electronic mechanisms through which energy carried into a material by photon irradiation is absorbed, localized and rechanneled to produce desorption, surface modification, erosion and damage. The specific object of these studies has been desorption induced by electronic transition in alkali halide crystals, with particular emphasis on the dynamics of changes in the surface and near-surface regions. In our experiments, the irradiating ultraviolet photons are provided by a synchrotron storage ring, and the dynamical information about desorption products is obtained from optical measurements of the quantum states, yields and velocity distributions of neutral ground-state and excited-state atoms ejected from the surface of the irradiating material. These studies have shown that the dominant exit channels in photon-induced particle emission are those producing ground-state and excited-state neutral atoms. Using dynamical information about these desorbing neutral species, obtained, for example, by laser-induced fluorescence and laser Doppler spectroscopy, we are generating an increasingly comprehensive picture of the dynamics of electronic energy flow into and out of pure crystalline surfaces in these prototypical dielectrics. We are also beginning to be able to relate desorption dynamics to specific materials properties, and to discriminate between pure surface and near-surface effects in these materials. Applications of these techniques to the problem of photon-induced surface damage and to analysis of surface dynamics in dielectric materials are discussed, and the relationships between these nearly ideal model materials and the non-crystalline, covalently bonded materials more typical of real optical elements are pointed out. 19 refs., 13 figs.

  9. Optical properties of alkali halide crystals from all-electron hybrid TD-DFT calculations

    NASA Astrophysics Data System (ADS)

    Webster, R.; Bernasconi, L.; Harrison, N. M.

    2015-06-01

    We present a study of the electronic and optical properties of a series of alkali halide crystals AX, with A = Li, Na, K, Rb and X = F, Cl, Br based on a recent implementation of hybrid-exchange time-dependent density functional theory (TD-DFT) (TD-B3LYP) in the all-electron Gaussian basis set code CRYSTAL. We examine, in particular, the impact of basis set size and quality on the prediction of the optical gap and exciton binding energy. The formation of bound excitons by photoexcitation is observed in all the studied systems and this is shown to be correlated to specific features of the Hartree-Fock exchange component of the TD-DFT response kernel. All computed optical gaps and exciton binding energies are however markedly below estimated experimental and, where available, 2-particle Green's function (GW-Bethe-Salpeter equation, GW-BSE) values. We attribute this reduced exciton binding to the incorrect asymptotics of the B3LYP exchange correlation ground state functional and of the TD-B3LYP response kernel, which lead to a large underestimation of the Coulomb interaction between the excited electron and hole wavefunctions. Considering LiF as an example, we correlate the asymptotic behaviour of the TD-B3LYP kernel to the fraction of Fock exchange admixed in the ground state functional cHF and show that there exists one value of cHF (˜0.32) that reproduces at least semi-quantitatively the optical gap of this material.

  10. Simple electrolyte solutions: Comparison of DRISM and molecular dynamics results for alkali halide solutions

    PubMed Central

    Joung, In Suk; Luchko, Tyler; Case, David A.

    2013-01-01

    Using the dielectrically consistent reference interaction site model (DRISM) of molecular solvation, we have calculated structural and thermodynamic information of alkali-halide salts in aqueous solution, as a function of salt concentration. The impact of varying the closure relation used with DRISM is investigated using the partial series expansion of order-n (PSE-n) family of closures, which includes the commonly used hypernetted-chain equation (HNC) and Kovalenko-Hirata closures. Results are compared to explicit molecular dynamics (MD) simulations, using the same force fields, and to experiment. The mean activity coefficients of ions predicted by DRISM agree well with experimental values at concentrations below 0.5 m, especially when using the HNC closure. As individual ion activities (and the corresponding solvation free energies) are not known from experiment, only DRISM and MD results are directly compared and found to have reasonably good agreement. The activity of water directly estimated from DRISM is nearly consistent with values derived from the DRISM ion activities and the Gibbs-Duhem equation, but the changes in the computed pressure as a function of salt concentration dominate these comparisons. Good agreement with experiment is obtained if these pressure changes are ignored. Radial distribution functions of NaCl solution at three concentrations were compared between DRISM and MD simulations. DRISM shows comparable water distribution around the cation, but water structures around the anion deviate from the MD results; this may also be related to the high pressure of the system. Despite some problems, DRISM-PSE-n is an effective tool for investigating thermodynamic properties of simple electrolytes. PMID:23387564

  11. Simple electrolyte solutions: Comparison of DRISM and molecular dynamics results for alkali halide solutions

    NASA Astrophysics Data System (ADS)

    Joung, In Suk; Luchko, Tyler; Case, David A.

    2013-01-01

    Using the dielectrically consistent reference interaction site model (DRISM) of molecular solvation, we have calculated structural and thermodynamic information of alkali-halide salts in aqueous solution, as a function of salt concentration. The impact of varying the closure relation used with DRISM is investigated using the partial series expansion of order-n (PSE-n) family of closures, which includes the commonly used hypernetted-chain equation (HNC) and Kovalenko-Hirata closures. Results are compared to explicit molecular dynamics (MD) simulations, using the same force fields, and to experiment. The mean activity coefficients of ions predicted by DRISM agree well with experimental values at concentrations below 0.5 m, especially when using the HNC closure. As individual ion activities (and the corresponding solvation free energies) are not known from experiment, only DRISM and MD results are directly compared and found to have reasonably good agreement. The activity of water directly estimated from DRISM is nearly consistent with values derived from the DRISM ion activities and the Gibbs-Duhem equation, but the changes in the computed pressure as a function of salt concentration dominate these comparisons. Good agreement with experiment is obtained if these pressure changes are ignored. Radial distribution functions of NaCl solution at three concentrations were compared between DRISM and MD simulations. DRISM shows comparable water distribution around the cation, but water structures around the anion deviate from the MD results; this may also be related to the high pressure of the system. Despite some problems, DRISM-PSE-n is an effective tool for investigating thermodynamic properties of simple electrolytes.

  12. Analysis of the off-center effect of Cu+ in alkali halides using crystal-field theory

    Microsoft Academic Search

    Stephen A. Payne

    1987-01-01

    We have found that the relative intensity of the 1A1g-->1Eg and 1A1g-->1T2g crystal-field components of the 3d10-->3d94s transition of Cu+ in alkali halide hosts provides a measure of the Cu+ ground-state off-center displacement along the [111] axis. This is shown by deriving the crystal- field potential that describes the off-center effect of Cu+, and then calculating the transition moments to

  13. Analysis of the off-center effect of Cu\\/sup +\\/ in alkali halides using crystal-field theory

    Microsoft Academic Search

    Stephen Payne

    1987-01-01

    We have found that the relative intensity of the ¹A\\/sub 1g\\/..-->..¹E\\/sub g\\/ and ¹A\\/sub 1g\\/..-->..¹T\\/sub 2g\\/ crystal-field components of the 3d¹°..-->..3d⁹4s transition of Cu\\/sup +\\/ in alkali halide hosts provides a measure of the Cu\\/sup +\\/ ground-state off-center displacement along the (111) axis. This is shown by deriving the crystal- field potential that describes the off-center effect of Cu\\/sup +\\/,

  14. Low-Energy Grazing Ion-Scattering From Alkali-Halide Surfaces: A Novel Approach To C-14 Detection

    NASA Astrophysics Data System (ADS)

    Meyer, F. W.; Galutschek, E.; Hotchkis, M.

    2009-03-01

    Carbon-14 labeled compounds are widely used in the pharmaceutical industry, e.g., as tracers to determine the fate of these compounds in vivo. Conventional accelerator mass spectrometry (AMS) is one approach that offers sufficiently high sensitivity to avoid radiological waste and contamination issues in such studies, but requires large, expensive facilities that are usually not solely dedicated to this task. At the ORNL Multicharged Ion Research Facility (MIRF) we are exploring a small size, low cost alternative to AMS for biomedical 14C tracer studies that utilizes ECR-ion-source-generated keV-energy-range multicharged C beams grazingly incident on an alkali halide target, where efficient negative ion production by multiple electron capture takes place. By using C ion charge states of +3 or higher, the molecular isobar interference at mass 14, e.g. 12CH2 and 13CH, is eliminated. The negatively charged ions in the beam scattered from the alkali halide surface are separated from other scattered charge states by two large acceptance (˜15 msr) stages of electrostatic analysis. The N-14 isobar interference is thus removed, since N does not support a stable negative ion. Initial results for C-14 detection obtained using C-14 enriched CO2 from ANSTO will be described.

  15. Low-Energy Grazing Ion-Scattering From Alkali-Halide Surfaces: A Novel Approach To C-14 Detection

    SciTech Connect

    Meyer, F. W.; Galutschek, E. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6372 (United States); Hotchkis, M. [Australian Nuclear Science and Technology Organization, PMB1, Menai, NSW 2234 (Australia)

    2009-03-10

    Carbon-14 labeled compounds are widely used in the pharmaceutical industry, e.g., as tracers to determine the fate of these compounds in vivo. Conventional accelerator mass spectrometry (AMS) is one approach that offers sufficiently high sensitivity to avoid radiological waste and contamination issues in such studies, but requires large, expensive facilities that are usually not solely dedicated to this task. At the ORNL Multicharged Ion Research Facility (MIRF) we are exploring a small size, low cost alternative to AMS for biomedical {sup 14}C tracer studies that utilizes ECR-ion-source-generated keV-energy-range multicharged C beams grazingly incident on an alkali halide target, where efficient negative ion production by multiple electron capture takes place. By using C ion charge states of +3 or higher, the molecular isobar interference at mass 14, e.g. {sup 12}CH{sub 2} and {sup 13}CH, is eliminated. The negatively charged ions in the beam scattered from the alkali halide surface are separated from other scattered charge states by two large acceptance ({approx}15 msr) stages of electrostatic analysis. The N-14 isobar interference is thus removed, since N does not support a stable negative ion. Initial results for C-14 detection obtained using C-14 enriched CO{sub 2} from ANSTO will be described.

  16. JOURNAL DE PHYSIQUE Colloque C4, supplment au n 4, Tome 40, avril 1979, page C4-207 Alkali metal actinide complex halides: thermochemical and structural

    E-print Network

    Boyer, Edmond

    actinide complex halides: thermochemical and structural considerations J. Fuger Institute of Radiochemistry on the thermodynamics of the actinide halogeno-complexes with alkali metal ions is reviewed, with special emphasis on chloro- and bromo-derivatives. Where enough thermodynamic and structural data are available, attempts

  17. Treating I anion as a zero-electron system : the Li I and CsI alkali halides anions Vincent ROBERT , 1, 2 Fernand SPIEGELMAN, 1 and Marie-Bernadette LEPETIT 1

    E-print Network

    Treating I anion as a zero-electron system : the Li I and CsI alkali halides anions Vincent ROBERT in alkali rare- gas molecules. The early studies suggested empirical or l-independent MP 's 5,8,10 . More treatments since quasi-spectroscopic accu- racy has been reached on alkali rare-gas and rare-earth rare

  18. 1. Introduction. --It is well known to the physi-Mixed crystals hyperoxide-halide have not been pro-cists working in the field of color centers that the duced so far. The alkali hyperoxides can be considered

    E-print Network

    Paris-Sud XI, Université de

    pro- cists working in the field of color centers that the duced so far. The alkali hyperoxides can anion 0 2 . alkali halides. The O^ center has been of considerable They are among the rare candidates]. of orthorhombic symmetry, and it is amenable to a It turns out that the magnetic behaviour of the alkali detailed

  19. Sensitivity of alkali halide scintillating calorimeters with particle identification to investigate the DAMA dark matter detection claim

    NASA Astrophysics Data System (ADS)

    Nadeau, P.; Clark, M.; Di Stefano, P. C. F.; Lanfranchi, J.-C.; Roth, S.; von Sivers, M.; Yavin, I.

    2015-07-01

    Scintillating calorimeters are cryogenic detectors combining a measurement of scintillation with one of phonons to provide particle identification. In view of developing alkali halide devices of this type able to check the DAMA/LIBRA claim for the observation of dark matter, we have simulated detector performances to determine their sensitivity by two methods with little model-dependence. We conclude that if performance of the phonon channel can be brought in line with those of other materials, an exposure of 10 kg-days would suffice to check the DAMA/LIBRA claim in standard astrophysical scenarios. Additionally, a fairly modest array of 5 kg with background rejection would be able to directly check the DAMA/LIBRA modulation result in 2 years.

  20. Development of processes for the production of solar grade silicon from halides and alkali metals, phase 1 and phase 2

    NASA Technical Reports Server (NTRS)

    Dickson, C. R.; Gould, R. K.; Felder, W.

    1981-01-01

    High temperature reactions of silicon halides with alkali metals for the production of solar grade silicon are described. Product separation and collection processes were evaluated, measure heat release parameters for scaling purposes and effects of reactants and/or products on materials of reactor construction were determined, and preliminary engineering and economic analysis of a scaled up process were made. The feasibility of the basic process to make and collect silicon was demonstrated. The jet impaction/separation process was demonstrated to be a purification process. The rate at which gas phase species from silicon particle precursors, the time required for silane decomposition to produce particles, and the competing rate of growth of silicon seed particles injected into a decomposing silane environment were determined. The extent of silane decomposition as a function of residence time, temperature, and pressure was measured by infrared absorption spectroscopy. A simplistic model is presented to explain the growth of silicon in a decomposing silane enviroment.

  1. Size distributions and geometries of alkali halide nanoclusters probed using ESI FT-ICR mass spectrometry and quantum chemistry

    NASA Astrophysics Data System (ADS)

    Lemke, K.; Sadjadi, S.; Seward, T.

    2010-12-01

    The structures and energetic properties of ionic alkali metal halide clusters play a significant role in our understanding of aqueous geochemical processes such as salt dissolution, precipitation and neutralization reactions. Mass spectrometric and quantum chemical studies of such systems offer new opportunities to study the size-dependent evolution of cluster structures, the occurrence of magic number species as well as their fundamental properties. The work here presents new results for the stability, abundance and structure of pure [Na(NaClm)]+ , [K(KCl)m]+ and mixed [Na(NaCl)p(KCl)q]+ metal halide clusters with m<23 and p+q<14, respectively, using ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS) in combination with the Gn and CBS-x multistep ab initio methods. Ion-cluster experiments were conducted on a modified 7T Bruker FT-ICR/MS equipped with electrospray ionization (ESI) sources and a custom-designed solvent gas inlet interface. In ESI FT-ICR/MS experiments performed with solutions containing NaCl and KCl salts (1mM; 80/20 CH3CN/H2O), singly and doubly charged salt clusters were generated up to a cluster size of [Na(NaCl)22]+, [K(KCl)17]+ and [K2(KCl)21,23]2+, respectively, including “magic number” clusters that correspond to the completed cluster cuboids with the dimensions 3x3x1 (m=4), 3x3x2+3 (m=10) 3x3x3 (m=13) and 3x3x5 (m=22) (see Figure). On the other hand, no pure clusters except [K(KCl)1-3]+ were generated when alkali halides were electrosprayed from 1mM NaCl/KCl solutions. Instead, mixed [Na(NaCl)p(KCl)q]+ clusters are generated up to p+q=14, which are the largest mixed alkali halide clusters yet generated in mass spectrometric experiments, including a suite of ionic species that are generated via CH3CN fragmentation and charge transfer in [Na(CH3CN)n]+ to yield the clusters [Na(NaCN)(CH3CN)n-1]+. We describe our ESI FT-ICR/MS experiments and discuss ion cluster abundances and extent of clustering in terms of variation of the solvent, desolvation temperature, ESI capillary and cone voltage as well as solution concentration. We also report and compare local minima geometries and relative energies for a number of representative [Na(NaCl)m]+ and [K(KCl)m]+ clusters using the composite CBS-QB3 and G4 methods and comment on the onset of the doubly charged cluster series. FT-ICR mass spectra for [Na(NaCl)n]+ clusters generated from 1mM NaCl in 20%H2O 80% acetonitrile in positive ion mode.

  2. Boosting the photocurrent density of p-type solar cells based on organometal halide perovskite-sensitized mesoporous NiO photocathodes.

    PubMed

    Wang, Huan; Zeng, Xianwei; Huang, Zhanfeng; Zhang, Wenjun; Qiao, Xianfeng; Hu, Bin; Zou, Xiaoping; Wang, Mingkui; Cheng, Yi-Bing; Chen, Wei

    2014-08-13

    The p-n tandem design of a sensitized solar cell is a novel concept holding the potential to overcome the efficiency limitation of conventional single-junction sensitized solar cells. Significant improvement of the photocurrent density (Jsc) of the p-type half-cell is a prerequisite for the realization of a highly efficient p-n tandem cell in the future. This study has demonstrated effective photocathodes based on novel organometal halide perovskite-sensitized mesoporous NiO in liquid-electrolyte-based p-type solar cells. An acceptably high Jsc up to 9.47 mA cm(-2) and efficiency up to 0.71% have been achieved on the basis of the CH3NH3PbI3/NiO solar cell at 100 mW cm(-2) light intensity, which are significantly higher than those of any previously reported liquid-electrolyte-based p-type solar cells based on sensitizers of organic dyes or inorganic quantum dots. The dense blocking layer made by spray pyrolysis of nickel acetylacetonate holds the key to determining the current flow direction of the solar cells. High hole injection efficiency at the perovskite/NiO interface and high hole collection efficiency through the mesoporous NiO network have been proved by time-resolved photoluminescence and transient photocurrent/photovoltage decay measurements. The limitation of these p-type solar cells primarily rests with the adverse light absorption by the NiO mesoporous film; the secondary limitation arises from the highly viscous ethyl acetate-based electrolyte, which is helpful for the solar cell stability but hinders fluent diffusion into the pore channels, giving rise to a nonlinear dependence of Jsc on the light intensity. PMID:24972278

  3. Quantum yield of photocathodes in far and extreme ultraviolet wavelength area

    NASA Astrophysics Data System (ADS)

    Haas, Christoph

    1989-03-01

    A microchannel plate detector is developed for a spectrograph working in far ultraviolet light. The choice of the photocathode materials is investigated. In this wavelength area, alkali halides are employed because they are generally hygroscopic. A model for the quantum yield is developed which takes into account the angle of incidence of the radiation, the layer reflectivity, the linear absorption coefficient and the number of emitted photoelectrons and their output probability. For the photocathode, hydrogen was chosen, because of the three lines of the Lyman spectrum. The tests show a good reproductibility of the photocathode and a weak increase of the quantum yield under vacuum conditions. This study forms a part of the Orpheus telescope project.

  4. An Investigation of Ion-Pairing of Alkali Metal Halides in Aqueous Solutions Using the Electrical Conductivity and the Monte Carlo Computer Simulation Methods

    PubMed Central

    Gujt, Jure; Bešter-Roga?, Marija; Hribar-Lee, Barbara

    2013-01-01

    The ion pairing is, in very dilute aqueous solutions, of rather small importance for solutions’ properties, which renders its precise quantification quite a laborious task. Here we studied the ion pairing of alkali halides in water by using the precise electric conductivity measurements in dilute solutions, and in a wide temperature range. The low-concentration chemical model was used to analyze the results, and to estimate the association constant of different alkali halide salts. It has been shown that the association constant is related to the solubility of salts in water and produces a ’volcano relationship’, when plotted against the difference between the free energy of hydration of the corresponding individual ions. The computer simulation, using the simple MB+dipole water model, were used to interprete the results, to find a microscopic basis for Collins’ law of matching water affinities. PMID:24526801

  5. Lattice model calculation of elastic and thermodynamic properties at high pressure and temperature. [for alkali halides in NaCl lattice

    NASA Technical Reports Server (NTRS)

    Demarest, H. H., Jr.

    1972-01-01

    The elastic constants and the entire frequency spectrum were calculated up to high pressure for the alkali halides in the NaCl lattice, based on an assumed functional form of the inter-atomic potential. The quasiharmonic approximation is used to calculate the vibrational contribution to the pressure and the elastic constants at arbitrary temperature. By explicitly accounting for the effect of thermal and zero point motion, the adjustable parameters in the potential are determined to a high degree of accuracy from the elastic constants and their pressure derivatives measured at zero pressure. The calculated Gruneisen parameter, the elastic constants and their pressure derivatives are in good agreement with experimental results up to about 600 K. The model predicts that for some alkali halides the Grunesen parameter may decrease monotonically with pressure, while for others it may increase with pressure, after an initial decrease.

  6. Multi-alkali photocathode thermal performance analysis of image intensifier based on low-high temperature environment testing conditions

    Microsoft Academic Search

    Youtang Gao; Si Tian; Benkang Chang; Yafeng Qiu; Jianliang Qiao

    2008-01-01

    Low-level-light (LLL) weapon sight measurement technologies based on Low-high temperature environments testing conditions are always concerned by military equipments manufacturers. Because low-high temperature environment, etc. are under loaded function, the electric performance parameter change to make LLL weapon sight, causing the LLL weapon sight can't be worked and used normally while taking aim. Generally believed that many photocathode is n-type

  7. Alkali and halide-resistant catalysis by the multipotent oxidase from Marinomonas mediterranea.

    PubMed

    Jimenez-Juarez, Nuria; Roman-Miranda, Rosa; Baeza, Alejandro; Sánchez-Amat, Antonio; Vazquez-Duhalt, Rafael; Valderrama, Brenda

    2005-04-20

    The incorporation of fungal laccases into novel applications has been delayed mainly due to their intrinsic sensitivity towards halides and alkaline conditions. In order to explore new sources of enzymes we evaluated the multipotent polyphenol oxidase PPO1 from the marine bacterium Marinomonas mediterranea. Here we report that, in contrast to its fungal counterparts, PPO1 remained functional above neutral pH presenting high specificity for phenolic compounds, in particular for methoxyl-substituted mono-phenols and catechols. These properties, in addition to its tolerance towards chloride (up to 1 M) and its elevated redox potential at neutral pH (0.9 V), suggest this enzyme may be an interesting candidate for specific applications such as the Amperometric determination of phenolic compounds and bio-fuel cells. PMID:15831249

  8. Interaction of wide band gap single crystals with 248 nm excimer laser radiation. XII. The emission of negative atomic ions from alkali halides

    SciTech Connect

    Kimura, Kenichi; Langford, S. C.; Dickinson, J. T. [Research Institute, National Printing Bureau of Japan, Odawara, Kanagawa 256-0816 (Japan); Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2814 (United States)

    2007-12-01

    Many wide band gap materials yield charged and neutral emissions when exposed to sub-band-gap laser radiation at power densities below the threshold for optical breakdown and plume formation. In this work, we report the observation of negative alkali ions from several alkali halides under comparable conditions. We observe no evidence for negative halogen ions, in spite of the high electron affinities of the halogens. Significantly, the positive and negative alkali ions show a high degree of spatial and temporal overlap. A detailed study of all the relevant particle emissions from potassium chloride (KCl) suggests that K{sup -} is formed by the sequential attachment of two electrons to K{sup +}.

  9. Alkali halide decomposition and desorption by photons—the role of excited point defects and surface topographies

    NASA Astrophysics Data System (ADS)

    Szymonski, Marek; Droba, Anna; Goryl, Maria; Kolodziej, Jacek J.; Krok, Franciszek

    2006-08-01

    Our recent work on photon-stimulated desorption of alkali halide surfaces has been reviewed. Most of the experimental data are presented for the first time. This new material is supplemented with two examples of our work published previously (see Szymonski et al 1996 Surf. Sci. 363 229 2002 Acta Phys. Pol. 33 2237). The results are discussed and compared with relevant experimental and theoretical work by other authors. In particular, we focus on two aspects of the studies: high resolution AFM imaging of desorbed surfaces, and measurements of mass selected fluxes of the desorbing atoms. It is found that, at initial stages of the UV-photon stimulated desorption, the process is occurring in a 'layer-by-layer' mode as a result of growth and linking of monatomic pits on the surface. This results in periodic changes of surface topography from atomically flat to rough with a period equal to the time needed for desorption of 1 ML. Such periodic changes of the surface topography affect the efficiency of the desorption and result in oscillatory dependence of the emitted particle yields versus photon fluence. Careful analysis of the yields reveals that during irradiation there is a substantial number of stable ground state F-centres accumulated under the surface. The number of accumulated defects is changing periodically with the photon fluence in anti-correlation with the desorption yields. Based on the mentioned results, we argue that the production of F-centres and their interaction with the surface are, in fact, the limiting factor for PSD. To test the validity of this statement a series of desorption experiments for the crystal co-irradiated with visible light (with a wavelength corresponding to the F-centre absorption band) and UV photons have been performed. A dramatic increase in the desorption yield, as well as pronounced changes in the surface erosion process, have been found.

  10. Thermal diffusivity of alkali and silver halide crystals as a function of temperature

    NASA Astrophysics Data System (ADS)

    Yu, Xueyang; Hofmeister, Anne M.

    2011-02-01

    The phonon component of thermal diffusivity (D) for ten synthetic single-crystals (LiF, NaCl, NaI, NaI:Tl, KCl, KBr, CsI, CsI:Tl, AgCl, and AgBr) with the B1 and B2 structures was measured from ambient temperature (T) up to ˜1093 K using contact-free, laser-flash analysis, from which effects of ballistic radiative transfer were removed. We investigated optical flats from different manufacturers as well as pellets made from compressed powders of most of the above chemical compositions plus LiI, NaBr, KI, RbCl, RbBr, RbI, CsCl, CsBr, and AgI. Impurities were characterized using various spectroscopic methods. With increasing T ,D decreases such that near melting the derivatives ?D/?T are low, -0.0006±0.0004 mm2 s-1 K-1. Our results are ˜16% lower than D298 previously obtained with contact methods, which are elevated by ballistic radiative transfer for these infrared (IR) windows, and are well described by either D-1 following a low order polynomial in T, or by D-1?T+n, where n ranges from 1.0294 to 1.9429. Inverse correlations were found between D298 and both density and thermal expansivity (?). Primitive lattice constant times compressional velocity correlates directly with D but changes much more slowly with temperature. Instead, D(T ) is proportional to (T?L)-1 from ˜0 K up to the limit of measurements, in accord with these physical properties being anharmonic. On average, the damped harmonic oscillator-phonon gas model reproduces D298 based on two physical properties: compressional velocity and the damping coefficient (? ) from analysis of IR reflectivity data. Given large uncertainties in ?(T ), D-1(T) is reproduced for LiF, NaCl, MgO, and the silver halides, for which IR reflectivity data are available. Our correlations show that optical phonons largely govern heat transport of insulators, and permit prediction of D and thus thermal conductivity for simple, diatomic solids.

  11. Evidence for New Excess Electron Localization Sites in Na{sub {ital n}}F{sub {ital n}{minus}1 } Alkali-Halide Clusters

    SciTech Connect

    Durand, G.; Spiegelmann, F. [Laboratoire de physique quantique (UMR 5626 CNRS-UPS), IRSAMC, Universite Paul Sabatier, 118 Route de Narbonne, F31062 Toulouse Cedex 4 (France)] [Laboratoire de physique quantique (UMR 5626 CNRS-UPS), IRSAMC, Universite Paul Sabatier, 118 Route de Narbonne, F31062 Toulouse Cedex 4 (France); Labastie, P.; LHermite, J.; Poncharal, P. [Laboratoire CAR (UMR 5589 CNRS-UPS), IRSAMC, Universite Paul Sabatier, 118 Route de Narbonne, F31062 Toulouse cedex 4 (France)] [Laboratoire CAR (UMR 5589 CNRS-UPS), IRSAMC, Universite Paul Sabatier, 118 Route de Narbonne, F31062 Toulouse cedex 4 (France)

    1997-07-01

    This Letter examines new types of localization sites for an excess electron in finite alkali-halide clusters resulting from defects on cuboidal structures, namely {open_quotes}edge states,{close_quotes} R center, and other surface defects. We present theoretical calculations on Na{sub n}F {sub n{minus}1} clusters with one excess electron. Comparisons with experimental results are presented for different cluster sizes (n=17 , 23, 28, and 29). Structures with edge or surface defects are relevant for n=23 , 28, and 29. {copyright} {ital 1997} {ital The American Physical Society}

  12. On the generalized stacking energy, core structure and Peierls stress of the 1/2 < {110} > {110} dislocations in alkali halide

    NASA Astrophysics Data System (ADS)

    Liu, L.; Wu, X. Z.; Wang, R.; Feng, H. F.; Wu, S.

    2012-02-01

    Using the improved P-N theory in which the lattice discrete effect is taken into account, the core width and Peierls stress of the 1/2 \\mlab 110\\mrab {110} dislocations in NaCl structure alkali halide have been investigated with the generalized stacking fault energy calculated by the ab initio calculation. The anisotropic of elasticity are taken into account while calculation the lattice discrete correction coefficient and the energy coefficient for dislocations. The discrete effect leads to a wider dislocation core in the improved P-N theory than that in the P-N theory. The obtained Peierls stress are in agreement with the existing experimental results. The predicted Peierls stress for edge dislocations in LiF and NaCl are 0.13 × 10-3? and 0.46 × 10-3?, respectively. The corresponding experimental values are 0.16 × 10-3? and 0.50 × 10-3?. It is also found that the Peierls stress and the anisotropic factor decrease with the increasing radius of the positive ion for the same negative ion in alkali halide.

  13. Measurement of the Electric Dipole Polarizabilities of Alkali Halide Dimers, and DOUBLET-P(1/2) Indium and Thallium.

    NASA Astrophysics Data System (ADS)

    Guella, Thomas Paul

    1985-12-01

    An electric field deflection technique has been used to obtain the average dimer polarizabilities of all the alkali halides, and the scalar ('2)P(, 1/2) polarizabilities of indium and thallium. The experimental procedure consisted of passing a well collimated effusive beam through a region of inhomogeneous electric field and analyzing the deflected beam pattern, with respect to the undeflected beam shape, at the detector. The beam deflections were analyzed in two ways. One method consisted of normalizing the deflections by comparing the experi- mental deflections to those obtained from atomic lithium, whose polarizability is known to within 2%. The normalization reduces the polarizability determination to the ratio of measured line slopes. This procedure lessens systematic errors resulting from a lack of detailed information concerning field variations along the beam path within the interaction region. A second method, employing a C.D.C. Cyber 360 computer, comprizes a quantitative analysis of the monomer and dimer deflections in which part of the actual deflected beam shape is used. Our results are compared with the polarizability values obtained from a simple 'mass-spring' model for the dimer which employs calculated (and experimental) vibrational frequencies and effective ionic polarizabilities from various dimer models. In addition to an electric deflection measurement, and E-H gradient balance technique was also employed for the indium and thallium ('2)P(, 1/2) measurements. This method consisted of balancing the magnetic dipole force for negative magnetic substates against the induced electric dipole force in a region where simultaneous and congruent inhomogeneous electric and magnetic fields are estab- lished. These measurements were normalized to an m = -3 substate of Cs whose polarizability is known to within (.5%). The results of our electric deflection and E-H gradient balance measurements for these atomic systems were (UNFORMATTED TABLE FOLLOWS). In Tl. 10.18 (+OR-) 1.2 (ANGSTROM)('3)) 7.6 (+OR-) 0.8 (ANGSTROM)('3). (TABLE ENDS). These values compare extremely well with the recent calculation for Tl of Flambaum and Sushkov (7.11 (ANGSTROM)('3)) and that of Liberman and Zangwill for In (9.66 (ANGSTROM)('3)) and Tl (7.74 (ANGSTROM)('3)).

  14. Ion partitioning at the liquid/vapor interface of a multicomponent alkali halide solution: a model for aqueous sea salt aerosols.

    PubMed

    Ghosal, Sutapa; Brown, Matthew A; Bluhm, Hendrik; Krisch, Maria J; Salmeron, Miquel; Jungwirth, Pavel; Hemminger, John C

    2008-12-01

    The chemistry of Br species associated with sea salt ice and aerosols has been implicated in the episodes of ozone depletion reported at Arctic sunrise. However, Br(-) is only a minor component in sea salt, which has a Br(-)/Cl(-) molar ratio of approximately 0.0015. Sea salt is a complex mixture of many different species, with NaCl as the primary component. In recent years experimental and theoretical studies have reported enhancement of the large, more polarizable halide ion at the liquid/vapor interface of corresponding aqueous alkali halide solutions. The proposed enhancement is likely to influence the availability of sea salt Br(-) for heterogeneous reactions such as those involved in the ozone depletion episodes. We report here ambient pressure X-ray photoelectron spectroscopy studies and molecular dynamics simulations showing direct evidence of Br(-) enhancement at the interface of an aqueous NaCl solution doped with bromide. The experiments were carried out on samples with Br(-)/Cl(-) ratios in the range 0.1% to 10%, the latter being also the ratio for which simulations were carried out. This is the first direct measurement of interfacial enhancement of Br(-) in a multicomponent solution with particular relevance to sea salt chemistry. PMID:19006284

  15. A different view of structure-making and structure-breaking in alkali halide aqueous solutions through x-ray absorption spectroscopy.

    PubMed

    Waluyo, Iradwikanari; Nordlund, Dennis; Bergmann, Uwe; Schlesinger, Daniel; Pettersson, Lars G M; Nilsson, Anders

    2014-06-28

    X-ray absorption spectroscopy measured in transmission mode was used to study the effect of alkali and halide ions on the hydrogen-bonding (H-bonding) network of water. Cl(-) and Br(-) are shown to have insignificant effect on the structure of water while I(-) locally weakens the H-bonding, as indicated by a sharp increase of the main-edge feature in the x-ray absorption spectra. All alkali cations act as structure-breakers in water, weakening the H-bonding network. The spectral changes are similar to spectra of high density ices where the 2nd shell has collapsed due to a break-down of the tetrahedral structures, although here, around the ions, the breakdown of the local tetrahedrality is rather due to non-directional H-bonding to the larger anions. In addition, results from temperature-dependent x-ray Raman scattering measurements of NaCl solution confirm the H-bond breaking effect of Na(+) and the effect on the liquid as similar to an increase in temperature. PMID:24985653

  16. Lithium-selective phosphine oxide-based ditopic receptors show enhanced halide binding upon alkali metal ion coordination†

    PubMed Central

    Gavette, Jesse V.; Lara, Juven; Reling, Linda L.; Haley, Michael M.; Johnson, Darren W.

    2012-01-01

    Previous work on a ditopic receptor based on a tripodal phosphine oxide core demonstrated preferential enhancement of bromide binding over chloride or iodide in the presence of lithium cation. Current studies on an elongated receptor provide evidence that preferential bromide binding enhancement in the presence of lithium cation is common to this receptor class in general, and that lengthening of the receptor results in an overall increase in halide association. Furthermore, the extended receptor shows a strong preference for Li+ binding in solution. PMID:23505609

  17. Correlated studies of electric properties of ionic molecules: alkali and alkaline-earth hydrides, halides and chalcogenides

    NASA Astrophysics Data System (ADS)

    Fowler, P. W.; Sadlej, A. J.

    Electric polarizabilities, dipole and quadrupole moments of the molecules LiH, LiF, LiCl, NaH, NaF, NaCl, BeO, BeS, MgO, MgS, BeH, BeF, BeCl, MgH, MgF, MgCl, LiO, LiS, NaO and NaS are computed in a uniform basis at the correlated level of theory. The results are rationalized in terms of the properties of ion pairs, and the stability of the isolated anions: the hydrides, oxides and sulphides show large and positive correlation corrections to the polarizability in CASSCF, and erratic convergence of the MBPT series. The open-shell alkaline-earth hydrides and halides in the series all exhibit negative polarizability anisotropy.

  18. Band-structure calculations of noble-gas and alkali halide solids using accurate Kohn-Sham potentials with self-interaction correction

    SciTech Connect

    Li, Y.; Krieger, J.B. (Department of Physics, Brooklyn College, City University of New York, Brooklyn, New York 11210 (United States)); Norman, M.R. (Material Sciences Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)); Iafrate, G.J. (U.S. Army Research Office, Research Triangle Park, North Carolina 27709-2211 (United States))

    1991-11-15

    The optimized-effective-potential (OEP) method and a method developed recently by Krieger, Li, and Iafrate (KLI) are applied to the band-structure calculations of noble-gas and alkali halide solids employing the self-interaction-corrected (SIC) local-spin-density (LSD) approximation for the exchange-correlation energy functional. The resulting band gaps from both calculations are found to be in fair agreement with the experimental values. The discrepancies are typically within a few percent with results that are nearly the same as those of previously published orbital-dependent multipotential SIC calculations, whereas the LSD results underestimate the band gaps by as much as 40%. As in the LSD---and it is believed to be the case even for the exact Kohn-Sham potential---both the OEP and KLI predict valence-band widths which are narrower than those of experiment. In all cases, the KLI method yields essentially the same results as the OEP.

  19. Correlation of CsK2Sb photocathode lifetime with antimony thickness

    NASA Astrophysics Data System (ADS)

    Mamun, M. A.; Hernandez-Garcia, C.; Poelker, M.; Elmustafa, A. A.

    2015-06-01

    CsK2Sb photocathodes with quantum efficiency on the order of 10% at 532 nm, and lifetime greater than 90 days at low voltage, were successfully manufactured via co-deposition of alkali species emanating from an effusion source. Photocathodes were characterized as a function of antimony layer thickness and alkali consumption, inside a vacuum chamber that was initially baked, but frequently vented without re-baking. Photocathode lifetime measured at low voltage is correlated with the antimony layer thickness. Photocathodes manufactured with comparatively thick antimony layers exhibited the best lifetime. We speculate that the antimony layer serves as a reservoir, or sponge, for the alkali.

  20. Characterization of an Alkali- and Halide-Resistant Laccase Expressed in E. coli: CotA from Bacillus clausii

    PubMed Central

    Brander, Søren; Mikkelsen, Jørn D.; Kepp, Kasper P.

    2014-01-01

    The limitations of fungal laccases at higher pH and salt concentrations have intensified the search for new extremophilic bacterial laccases. We report the cloning, expression, and characterization of the bacterial cotA from Bacillus clausii, a supposed alkalophilic ortholog of cotA from B. subtilis. Both laccases were expressed in E. coli strain BL21(DE3) and characterized fully in parallel for strict benchmarking. We report activity on ABTS, SGZ, DMP, caffeic acid, promazine, phenyl hydrazine, tannic acid, and bilirubin at variable pH. Whereas ABTS, promazine, and phenyl hydrazine activities vs. pH were similar, the activity of B. clausii cotA was shifted upwards by ?0.5–2 pH units for the simple phenolic substrates DMP, SGZ, and caffeic acid. This shift is not due to substrate affinity (KM) but to pH dependence of catalytic turnover: The kcat of B. clausii cotA was 1 s?1 at pH 6 and 5 s?1 at pH 8 in contrast to 6 s?1 at pH 6 and 2 s?1 at pH 8 for of B. subtilis cotA. Overall, kcat/KM was 10-fold higher for B. subtilis cotA at pHopt. While both proteins were heat activated, activation increased with pH and was larger in cotA from B. clausii. NaCl inhibited activity at acidic pH, but not up to 500–700 mM NaCl in alkaline pH, a further advantage of the alkali regime in laccase applications. The B. clausii cotA had ?20 minutes half-life at 80°C, less than the ?50 minutes at 80°C for cotA from B. subtilis. While cotA from B. subtilis had optimal stability at pH?8, the cotA from B. clausii displayed higher combined salt- and alkali-resistance. This resistance is possibly caused by two substitutions (S427Q and V110E) that could repel anions to reduce anion-copper interactions at the expense of catalytic proficiency, a trade-off of potential relevance to laccase optimization. PMID:24915287

  1. Simulation of Coherent Dissociation of the Self-Trapped Exciton in Alkali Andreas Markmann,1

    E-print Network

    Markmann, Andreas

    Simulation of Coherent Dissociation of the Self-Trapped Exciton in Alkali Halides Andreas Markmann crystals is the self-trapped exciton in alkali halides. We have used existing theoretical and experimental studied crystalline defects are the Frenkel defects in alkali halides, most promi- nently the self

  2. Masked Photocathode for Photoinjector

    SciTech Connect

    Qiang, Ji

    2010-01-21

    In this research note, we propose a scheme to insert a photocathode inside a photoinjector for generating high brightness electron beam. Instead of mounting the photocathode onto the electrode, a masked electrode with small hole is used to shield the photocathode from the accelerating vacuum chamber. Using such a masked photocathode will make the replacement of photocathode material very simple by rotating the photocathode behind the mask into the hole. This will significantly increase the usage lifetime of a photocathode. Furthermore, this also helps reduce the dark current or secondary electron emission from the photocathode. The hole on the mask also provides a transverse cut-off to the Gaussian laser profile which can be beneficial from the beam dynamics point of view.

  3. A Masked Photocathode in Photoinjector

    E-print Network

    Qiang, Ji

    2011-01-01

    In this paper, we propose a masked photocathode inside the photoinjector for generating high brightness electron beam. Instead of mounting the photocathode onto an electrode, an electrode with small hole is used as a mask to shield the photocathode from the accelerating vacuum chamber. Using such a masked photocathode will make the replacement of photocathode material easy by rotating the photocathode behind the electrode into the hole. Furthermore, this helps reduce the dark current or secondary electron emission from the photocathode material. The masked photocathode also provides transverse cut-off to a Gaussian laser beam that reduces electron beam emittance growth from nonlinear space-charge effects.

  4. A Masked Photocathode in Photoinjector

    SciTech Connect

    Qiang, Ji

    2010-12-14

    In this paper, we propose a masked photocathode inside the photoinjector for generating high brightness election beam. Instead of mounting the photocathode onto an electrode, an electrode with small hole is used as a mask to shield the photocathode from the accelerating vacuum chamber. Using such a masked photocathode will make the replacement of photocathode material easy by rotating the photocathode behind the electrode into the hole. Furthermore, this helps reduce the dark current or secondary electron emission from the photocathode material. The masked photocathode also provides transverse cut-off to a Gaussian laser beam that reduces electron beam emittance growth from nonlinear space-charge effects.

  5. Cerium doped elpasolite halide scintillators.

    SciTech Connect

    Doty, F. Patrick (Sandia National Laboratories, Livermore, CA); Shah, Kanai Subodhbhai (Radiation Monitoring Devices, Watertown, MA); Noda, Frank T.; Yang, Pin; Zhou, Xiao Wang (Sandia National Laboratories, Livermore, CA)

    2010-05-01

    Low-cost, high-performance gamma-ray spectrometers are urgently needed for proliferation detection and homeland security. The cost and availability of large scintillators used in the spectrometer generally hinge on their mechanical property and crystal symmetry. Low symmetry, intrinsically brittle crystals, such as these emerging lanthanide halide scintillators, are particularly difficult to grow in large sizes due to the development of large anisotropic thermomechanical stresses during solidification process. Isotropic cubic scintillators, such as alkali halides, while affordable and can be produced in large sizes, are poor spectrometers due to severe nonproportional response and modest light yield. This work investigates and compares four new elpasolite based lanthanide halides, including Cs2LiLaBr6, Cs2NaLaBr6, Cs2LiLaI6, and Cs2NaLaI6, in terms of their crystal symmetry, characteristics of photoluminescence and optical quantum efficiency. The mechanical property and thermal expansion behavior of the cubic Cs2LiLaBr6 will be reported. The isotropic nature of this material has potential for scaled-up crystal growth, as well as the possibility of low-cost polycrystalline ceramic processing. In addition, the proportional response with gamma-ray energy of directionally solidified Cs2LiLaBr6 will be compared with workhorse alkali halide scintillators. The processing challenges associated with hot forged polycrystalline elpasolite based lanthanide halides will also be discussed.

  6. Molecular compressibility of some halides in alcohols

    NASA Technical Reports Server (NTRS)

    Serban, C.; Auslaender, D.

    1974-01-01

    After measuring ultrasonic velocity and density, the molecular compressibility values from Wada's formula were calculated, for alkali metal halide solutions in methyl, ethyl, butyl, and glycol alcohol. The temperature and concentration dependence were studied, finding deviations due to the hydrogen bonds of the solvent.

  7. Gaseous photodetectors with solid photocathodes

    Microsoft Academic Search

    A. F. Buzulutskov

    2008-01-01

    Remarkable properties of gas photodetectors make them attractive for application in high energy physics, astrophysics, and\\u000a medical imaging. This review presents the results of research and development of gaseous photodetectors with solid photocathodes\\u000a (GPDs). In particular, efficient photocathodes for the ultraviolet (mainly CsI) and the visible ranges, including photocathodes\\u000a with protective dielectric nanofilms, are described. Some problems of the physics

  8. Piezoelectrically enhanced photocathode

    NASA Technical Reports Server (NTRS)

    Beach, Robert A. (Inventor); Nikzad, Shouleh (Inventor); Strittmatter, Robert P. (Inventor); Bell, Lloyd Douglas (Inventor)

    2009-01-01

    A photocathode, for generating electrons in response to incident photons in a photodetector, includes a base layer having a first lattice structure and an active layer having a second lattice structure and epitaxially formed on the base layer, the first and second lattice structures being sufficiently different to create a strain in the active layer with a corresponding piezoelectrically induced polarization field in the active layer, the active layer having a band gap energy corresponding to a desired photon energy.

  9. Computation of methodology-independent single-ion solvation properties from molecular simulations. IV. Optimized Lennard-Jones interaction parameter sets for the alkali and halide ions in water

    SciTech Connect

    Reif, Maria M.; Huenenberger, Philippe H. [Laboratory of Physical Chemistry, ETH Zuerich, CH-8093 Zuerich (Switzerland)

    2011-04-14

    The raw single-ion solvation free energies computed from atomistic (explicit-solvent) simulations are extremely sensitive to the boundary conditions and treatment of electrostatic interactions used during these simulations. However, as shown recently [M. A. Kastenholz and P. H. Huenenberger, J. Chem. Phys. 124, 224501 (2006); M. M. Reif and P. H. Huenenberger, J. Chem. Phys. 134, 144103 (2010)], the application of appropriate correction terms permits to obtain methodology-independent results. The corrected values are then exclusively characteristic of the underlying molecular model including in particular the ion-solvent van der Waals interaction parameters, determining the effective ion size and the magnitude of its dispersion interactions. In the present study, the comparison of calculated (corrected) hydration free energies with experimental data (along with the consideration of ionic polarizabilities) is used to calibrate new sets of ion-solvent van der Waals (Lennard-Jones) interaction parameters for the alkali (Li{sup +}, Na{sup +}, K{sup +}, Rb{sup +}, Cs{sup +}) and halide (F{sup -}, Cl{sup -}, Br{sup -}, I{sup -}) ions along with either the SPC or the SPC/E water models. The experimental dataset is defined by conventional single-ion hydration free energies [Tissandier et al., J. Phys. Chem. A 102, 7787 (1998); Fawcett, J. Phys. Chem. B 103, 11181] along with three plausible choices for the (experimentally elusive) value of the absolute (intrinsic) hydration free energy of the proton, namely, {Delta}G{sub hyd} {sup O-minus} [H{sup +}]=-1100, -1075 or -1050 kJ mol{sup -1}, resulting in three sets L, M, and H for the SPC water model and three sets L{sub E}, M{sub E}, and H{sub E} for the SPC/E water model (alternative sets can easily be interpolated to intermediate {Delta}G{sub hyd} {sup O-minus} [H{sup +}] values). The residual sensitivity of the calculated (corrected) hydration free energies on the volume-pressure boundary conditions and on the effective ionic radius entering into the calculation of the correction terms is also evaluated and found to be very limited. Ultimately, it is expected that comparison with other experimental ionic properties (e.g., derivative single-ion solvation properties, as well as data concerning ionic crystals, melts, solutions at finite concentrations, or nonaqueous solutions) will permit to validate one specific set and thus, the associated {Delta}G{sub hyd} {sup O-minus} [H{sup +}] value (atomistic consistency assumption). Preliminary results (first-peak positions in the ion-water radial distribution functions, partial molar volumes of ionic salts in water, and structural properties of ionic crystals) support a value of {Delta}G{sub hyd} {sup O-minus} [H{sup +}] close to -1100 kJ{center_dot}mol{sup -1}.

  10. Ionic structure and physicochemical properties of molten halides

    SciTech Connect

    Smirnov, M.V.; Stepanov, V.P.; Khokhlov, V.A.

    1988-05-01

    A large body of experimental data on different physicochemical (thermodynamic, transport, surface) properties of molten halides is summarized. Trends in their variation during transition from typical ionic liquids, which are molten halides of alkali metals, to mixed ionic-covalent liquids, which contain halides of polyvalent metals, are demonstrated. It is concluded that for qualitative explanation and quantitative description of the temperature and concentration dependences of the physicochemical properties of molten halides, it is necessary to consider their actual ionic compositions, i.e., the existence also of clustered particles (clusters, groups of ions) besides the elemental ions. Such an approach allows us to accurately predict the physicochemical properties of molten halides of given chemical compositions.

  11. Robust activation method for negative electron affinity photocathodes

    DOEpatents

    Mulhollan, Gregory A. (Dripping Springs, TX); Bierman, John C. (Austin, TX)

    2011-09-13

    A method by which photocathodes(201), single crystal, amorphous, or otherwise ordered, can be surface modified to a robust state of lowered and in best cases negative, electron affinity has been discovered. Conventional methods employ the use of Cs(203) and an oxidizing agent(207), typically carried by diatomic oxygen or by more complex molecules, for example nitrogen trifluoride, to achieve a lowered electron affinity(404). In the improved activation method, a second alkali, other than Cs(205), is introduced onto the surface during the activation process, either by co-deposition, yo-yo, or sporadic or intermittent application. Best effect for GaAs photocathodes has been found through the use of Li(402) as the second alkali, though nearly the same effect can be found by employing Na(406). Suitable photocathodes are those which are grown, cut from boules, implanted, rolled, deposited or otherwise fabricated in a fashion and shape desired for test or manufacture independently supported or atop a support structure or within a framework or otherwise affixed or suspended in the place and position required for use.

  12. Final Report, Photocathodes for High Repetition Rate Light Sources

    SciTech Connect

    Ben-Zvi, Ilan [Stony Brook University

    2014-04-20

    This proposal brought together teams at Brookhaven National Laboratory (BNL), Lawrence Berkeley National Laboratory (LBNL) and Stony Brook University (SBU) to study photocathodes for high repetition rate light sources such as Free Electron Lasers (FEL) and Energy Recovery Linacs (ERL). The work done under this grant comprises a comprehensive program on critical aspects of the production of the electron beams needed for future user facilities. Our program pioneered in situ and in operando diagnostics for alkali antimonide growth. The focus is on development of photocathodes for high repetition rate Free Electron Lasers (FELs) and Energy Recovery Linacs (ERLs), including testing SRF photoguns, both normal-conducting and superconducting. Teams from BNL, LBNL and Stony Brook University (SBU) led this research, and coordinated their work over a range of topics. The work leveraged a robust infrastructure of existing facilities and the support was used for carrying out the research at these facilities. The program concentrated in three areas: a) Physics and chemistry of alkali-antimonide cathodes b) Development and testing of a diamond amplifier for photocathodes c) Tests of both cathodes in superconducting RF photoguns and copper RF photoguns

  13. Photocathodes in accelerator applications

    SciTech Connect

    Fraser, J.S.; Sheffield, R.L.; Gray, E.R.; Giles, P.M.; Springer, R.W.; Loebs, V.A.

    1987-01-01

    Some electron accelerator applications require bursts of short pulses at high microscopic repetition rates and high peak brightness. A photocathode, illuminated by a mode-locked laser, is well suited to filling this need. The intrinsic brightness of a photoemitter beam is high; experiments are under way at Los Alamos to study the brightness of short bunches with high space charge after acceleration. A laser-illuminated Cs/sub 3/Sb photoemitter is located in the first rf cavity of an injector linac. Diagnostics include a pepper-pot emittance analyzer, a magnetic spectrometer, and a streak camera.

  14. TOTAL ORGANIC HALIDE MEASUREMENTS

    EPA Science Inventory

    Currently, the most popular method of analyzing total dissolved halide in water involves carbon adsorption, oxidative combustion, and measurement of the hydrogen halide by microcoulometry. Total dissolved organic halide can be used as an indicator of water quality, providing a di...

  15. Study of strain optical constants of mixed lithium halides

    Microsoft Academic Search

    Narender Singh; R. P. Goyal; S. C. Goyal

    1993-01-01

    The theory of photo-elasticity of mixed alkali halides has been used to analyse the strain optical constants and volume derivative of the electronic dielectric constant of the mixed crystal, LiF0.5Cl0.5.

  16. Metal-halide mixtures for latent heat energy storage

    NASA Technical Reports Server (NTRS)

    Chen, K.; Manvi, R.

    1981-01-01

    Alkali metal and alkali halide mixtures are identified which may be suitable for thermal energy storage at temperatures above 600 C. The use of metal-halides is appropriate because of their tendency to form two immiscible melts with a density difference, which reduces scale formation and solidification on heat transfer surfaces. Also, the accumulation of phase change material along the melt interface is avoided by the self-dispersing characteristic of some metal-halides, in particular Sr-SrCl2, Ba-BaCl2, and Ba-BaBr2 mixtures. Further advantages lie in their high thermal conductivities, ability to cope with thermal shock, corrosion inhibition, and possibly higher energy densities.

  17. Cs based photocathodes for gaseous detectors

    SciTech Connect

    Borovick-Romanov, A. [Inst. for Physical Problems (Russian Federation); Peskov, V. [Fermi National Accelerator Lab., Batavia, IL (United States)

    1993-08-01

    We demonstrated that some standard photocathodes SbCs, GaAs(Cs), Au(Cs) can easily be manufactured for use inside gaseous detectors. When filed with clean quenched gases such detectors have a quantum efficiency of a few percent in the visible region of the spectra and can operate at a gain >10{sup 3}. We tried to make these photocathodes more air stable by protecting their surfaces with a thin layer of CsI or liquid TMAE. The most air stable were photocathodes with a CsI protective layer. A wavelengths {le}185 nm such photocathodes have the highest quantum efficiency among all known air stable photocathodes, including CsI. Gaseous detectors with such photocathodes can operate at a gain of 10{sup 5}. Results of first tests of doped CsI photocathode are also presented. Possible fields of application of new photocathodes are discussed.

  18. Halogens and Halides (GCMP)

    NSDL National Science Digital Library

    Halogens and Halides: this is a resource in the collection "General Chemistry Multimedia Problems". In this problem we will study the oxidation-reduction reactions between the halogens and the halide ions. The halogens and halides will be dissolved in water and hexane. General Chemistry Multimedia Problems ask students questions about experiments they see presented using videos and images. The questions asked apply concepts from different parts of an introductory course, encouraging students to decompartmentalize the material.

  19. Prevention of electron field emission from molybdenum substrates for photocathodes by the native oxide layer

    NASA Astrophysics Data System (ADS)

    Lagotzky, Stefan; Barday, Roman; Jankowiak, Andreas; Kamps, Thorsten; Klimm, Carola; Knobloch, Jens; Müller, Günter; Senkovskiy, Boris; Siewert, Frank

    2015-05-01

    Comprehensive investigations of the electron field emission (FE) properties of annealed single crystal and polycrystalline molybdenum plugs, which are used as substrates for actual alkali-based photocathodes were performed with a FE scanning microscope. Well-polished and dry-ice cleaned Mo samples with native oxide did not show parasitic FE up to a field level of 50 MV/m required for photoinjector cavities. In situ heat treatments (HT) above 400 °C, which are usual before photocathode deposition, activated field emission at lower field strength. Oxygen loading into the Mo surface, however, partially weakened these emitters. X-ray photoelectron spectroscopy of comparable Mo samples showed the dissolution of the native oxide during such heat treatments. These results reveal the suppression of field emission by native Mo oxides. Possible improvements for the photocathode preparation will be discussed.

  20. Pressure Dependence of the NMR Chemical Shifts in Cesium and Rubidium Halides

    Microsoft Academic Search

    Robert Baron

    1963-01-01

    The chemical shifts, line shapes, linewidths, and line intensities have been measured as a function of pressure and crystal structure from 1 to 104 kg\\/cm2 at room temperature for both metal and halide nuclei in alkali halide pressed powder pellets. Measurements were made on Rb87, Cs133, Cl35, Br81, and I127 in RbCl, RbBr, RbI, CsBr, and CsI. The chemical shifts

  1. Purification of silicon halides

    SciTech Connect

    Kray, W.D.; Razzano, J.S.

    1988-07-05

    A method is described for purifying silicon halides comprising: (A) adding to a solution of silicon halide contaminated with small amounts of Lewis acid impurities a stoichiometric excess, based on the concentration of the impurities, of an organosiloxane selected from the group consisting of cyclic siloxane monomers, polydimethylsiloxane fluids and dimethyl (methyl hydrogen) siloxane copolymers; (B) reacting the impurities in solution with the organosiloxane at a temperature of from about 100/sup 0/C to 200/sup 0/C until substantially all the impurities form non-volatile products; and thereafter (C) removing purified silicon halide by distillation.

  2. Metal-halide mixtures for latent heat energy storage

    NASA Technical Reports Server (NTRS)

    Chen, K.; Manvi, R.

    1981-01-01

    Some candidates for alkali metal and alkali halide mixtures suitable for thermal energy storage at temperatures 600 C are identified. A solar thermal system application which offer advantages such as precipitation of salt crystals away from heat transfer surfaces, increased thermal conductivity of phase change materials, corrosion inhibition, and a constant monotectic temperature, independent of mixture concentrations. By using the lighters, metal rich phase as a heat transfer medium and the denser, salt rich phase as a phase change material for latent heat storage, undesirable solidification on the heat transfer surface may be prevented, is presented.

  3. CsI and some new photocathodes

    SciTech Connect

    Anderson, D.F.; Kwan, S.; Peskov, V.

    1993-06-01

    A discussion of the possible sources of discrepancies in the measurements of the quantum efficiency of CsI photocathodes is presented. We propose that the major causes for disagreements in QE are due to the QE dependence on the current density extracted from the photocathode, on the electric field, and on the temperature of the photocathode. Preliminary results on TMAE enhanced GaAs and Si, plus TMAE protected CsTe and SbCs photocathodes, operated in gas, are also presented.

  4. JOURNAL DE PHYSI?UE CoZZoque C8, suppZ6ment au n08, Tome 41, aoiit 1980, page C8-555 THERMODYNAMIC PROPERTIES OF LIQUID CESIUM-CESIUM HALIDE MIXTURES AT 9 2 5 K

    E-print Network

    Paris-Sud XI, Université de

    . Introduction 5 0 The thermodynamic properties of the liquid mix- tures of the alkali metals with their halides of the thermodynamic freezing point depression. A small correction for properties of the liquid cesium-cesium halide PROPERTIES OF LIQUID CESIUM-CESIUM HALIDE MIXTURES AT 9 2 5 K H. yokokawaf and O.J. Kleppa The James Frunck

  5. Depolarizers for lithium halide batteries

    SciTech Connect

    Harney, M.J.

    1981-06-30

    The present invention relates to a depolarizer for use in a lithium halide battery which comprises a halogen and a charge transfer complex consisting of the halogen and an organic component of (A) quaternary amine halide selected from the group consisting of (I) polyvinylalkylpyridinium halide or polyvinylalkylquinolinium halide and (II) poly (N,n'-dialkyl 1,2 bis (4-pyridinium halide)) ethylene or poly (N-alkyl 1,2 bis (4pyridinium halide) ethylene) and (B) phenyl methane dyes wherein said halogen is present in an amount of from about 3 to 50 parts by weight for each part of organic component.

  6. Bio-conventional bleaching of kadam kraft-AQ pulp by thermo-alkali-tolerant xylanases from two strains of Coprinellus disseminatus for extenuating adsorbable organic halides and improving strength with optical properties and energy conservation.

    PubMed

    Lal, Mohan; Dutt, Dharm; Tyagi, C H

    2012-04-01

    Two novel thermo-alkali-tolerant crude xylanases namely MLK-01 (enzyme-A) and MLK-07 (enzyme-B) from Coprinellus disseminatus mitigated kappa numbers of Anthocephalus cadamba kraft-AQ pulps by 32.5 and 34.38%, improved brightness by 1.5 and 1.6% and viscosity by 5.75 and 6.47% after (A)XE(1) and (B)XE(1)-stages, respectively. The release of reducing sugars and chromophores was the highest during prebleaching of A. cadamba kraft-AQ pulp at enzyme doses of 5 and 10 IU/g, reaction times 90 and 120 min, reaction temperatures 75 and 65°C and consistency 10% for MLK-01 and MLK-07, respectively. MLK-07 was more efficient than MLK01 in terms of producing pulp brightness, improving mechanical strength properties and reducing pollution load. MLK-01 and MLK-07 reduced AOX by 19.51 and 42.77%, respectively at 4% chlorine demands with an increase in COD and colour due to removal of lignin carbohydrates complexes. A. cadamba kraft-AQ pulps treated with xylanases from MLK-01 to MLK-07 and followed by CEHH bleaching at half chlorine demand (2%) showed a drastic reduction in brightness with slight improvement in mechanical strength properties compared to pulp bleached at 4% chlorine demand. MLK-01 reduced AOX, COD and colour by 43.83, 39.03 and 27.71% and MLK-07 by 38.34, 40.48 and 30.77%, respectively at half chlorine demand compared to full chlorine demand (4%). pH variation during prebleaching of A. cadamba kraft-AQ pulps with strains MLK-01 and MLK-07 followed by CEHH bleaching sequences showed a decrease in pulp brightness, AOX, COD and colour with an increase in mechanical strength properties, pulp viscosity and PFI revolutions to get a beating level of 35 ± 1 °SR at full chlorine demand. PMID:22805918

  7. Pulsed copper halide vapor lasers

    NASA Astrophysics Data System (ADS)

    Kazarian, M. A.; Petrash, G. G.; Trofimov, A. N.

    The theory and the performance characteristics of copper halide lasers are examined with reference to recent theoretical and experimental research in the field of metal vapor lasers. The discussion covers gas discharge tubes, comparative characteristics of copper halide lasers, determination of the metastable level decomposition rates in copper chloride and copper bromide lasers, and spectroscopic measurements of the discharge plasma in copper halide lasers. Attention is also given to the kinetics of copper atoms formation in copper halide lasers and calculation of the kinetic characteristics of copper halide lasers.

  8. PHOTOCATHODES FOR THE ENERGY RECOVERY LINACS.

    SciTech Connect

    RAO, T.; BURRILL, A.; CHANG, X.Y.; SMEDLEY, J.; ET AL.

    2005-03-19

    This paper presents an overview of existing and emerging technologies on electron sources that can service various Energy Recovering Linacs under consideration. Photocathodes that can deliver average currents from 1 mA to 1 A, the pros and cons associated with these cathodes are addressed. Status of emerging technologies such as secondary emitters, cesiated dispenser cathodes, field and photon assisted field emitters and super lattice photocathodes are also reviewed.

  9. Photocathodes for the energy recovery linacs

    SciTech Connect

    T. Rao; A. Burrill; X.Y. Chang; J. Smedley; T. Nishitani; C. Hernandez Garcia; M. Poelker; E. Seddon; F.E. Hannon; C.K. Sinclair; J. Lewellen; D. Feldman

    2005-03-19

    This paper presents an overview of existing and emerging technologies on electron sources that can service various Energy Recovering Linacs under consideration. Photocathodes that can deliver average currents from 1 mA to 1 A, the pros and cons associated with these cathodes are addressed. Status of emerging technologies such as secondary emitters, cesiated dispenser cathodes, field and photon assisted field emitters and super lattice photocathodes are also reviewed.

  10. Gallium nitride photocathodes for imaging photon counters

    NASA Astrophysics Data System (ADS)

    Siegmund, Oswald H. W.; Hull, Jeffrey S.; Tremsin, Anton S.; McPhate, Jason B.; Dabiran, Amir M.

    2010-07-01

    Gallium nitride opaque and semitransparent photocathodes provide high ultraviolet quantum efficiencies from 100 nm to a long wavelength cutoff at ~380 nm. P (Mg) doped GaN photocathode layers ~100 nm thick with a barrier layer of AlN (22 nm) on sapphire substrates also have low out of band response, and are highly robust. Opaque GaN photocathodes are relatively easy to optimize, and consistently provide high quantum efficiency (70% at 120 nm) provided the surface cleaning and activation (Cs) processes are well established. We have used two dimensional photon counting imaging microchannel plate detectors, with an active area of 25 mm diameter, to investigate the imaging characteristics of semitransparent GaN photocathodes. These can be produced with high (20%) efficiency, but the thickness and conductivity of the GaN must be carefully optimized. High spatial resolution of ~50 ?m with low intrinsic background (~7 events sec-1 cm-2) and good image uniformity have been achieved. Selectively patterned deposited GaN photocathodes have also been used to allow quick diagnostics of optimization parameters. GaN photocathodes of both types show great promise for future detector applications in ultraviolet Astrophysical instruments.

  11. Rotational relaxation of hydrogen halides

    SciTech Connect

    Koura, K.

    1980-03-15

    The comment of Levine on the rotational relaxation of hydrogen halides are answered. In particular the information theoretic predictions for the rotational transitions rate constant are considered. (AIP)

  12. Stability enhanced halide lasers

    SciTech Connect

    Brown, R.T.; Nighan, W.L.

    1982-05-25

    The onset of electric discharge instability in electron beam enhanced electric discharge lasers employing halides, such as rare-gas monohalides (E.G., krf*) and mercury vapor halide (E.G., hgbr*), is delayed by limiting the production of secondary electrons during laser pulse generation, to account for critical loss of halogen or halide fuel. Secondary electron production is controlled, in order to extend the pulse duration before the onset of discharge instability, by temporal tailoring of the primary electron concentration in the electric discharge region across the temporal expanse of possible laser action; the population of primary electrons can be temporally restrained by temporal decrease of the current density of the electron gun output, as a function, for instance, of gun driving voltage, or by temporal defocusing of the electron beam so as to provide reduced densities within the electric discharge region. Secondary electron production is also controlled by tailoring the production of rare-gas metastables. The production of metastables is controlled, in turn, by temporal tailoring of the electric field so as to provide a decreasing electric field to neutral particle density ratio across the temporal expanse of the laser pulse.

  13. RF Gun Photocathode Research at SLAC

    SciTech Connect

    Jongewaard, E.; Akre, R.; Brachmann, A.; Corbett, J.; Gilevich, S.; Grouev, K.; Hering, P.; P.Krejcik,; Lewandowski, J.; Loos, H.; Montagne, T.; Sheppard, J.C.; Stefan, P.; Vlieks, A.; Weathersby, S.; Zhou, F.; /SLAC

    2012-05-16

    LCLS is presently operating with a third copper photocathode in the original rf gun, with a quantum efficiency (QE) of {approx}1 x 10{sup -4} and projected emittance {gamma}{var_epsilon}{sub x,y} = 0.45 {micro}m at 250 pC bunch charge. The spare LCLS gun is installed in the SLAC Accelerator Structure Test Area (ASTA), fully processed to high rf power. As part of a wider photocathode R and D program, a UV laser system and additional gun diagnostics are being installed at ASTA to measure QE, QE lifetime, and electron beam emittance under a variety of operating conditions. The near-term goals are to test and verify the spare photocathode production/installation sequence, including transfer from the final holding chamber to the rf gun. Mid- and longer-term goals include development of a rigorous understanding of plasma and laser-assisted surface conditioning and investigation of new, high-QE photocathode materials. In parallel, an x-ray photoemission spectroscopy station is nearing completion, to analyze Cu photocathode surface chemistry. In this paper we review the status and anticipated operating parameters of ASTA and the spectroscopy test chamber.

  14. Cold ablation driven by localized forces in alkali halides.

    PubMed

    Hada, Masaki; Zhang, Dongfang; Pichugin, Kostyantyn; Hirscht, Julian; Kochman, Micha? A; Hayes, Stuart A; Manz, Stephanie; Gengler, Regis Y N; Wann, Derek A; Seki, Toshio; Moriena, Gustavo; Morrison, Carole A; Matsuo, Jiro; Sciaini, Germán; Miller, R J Dwayne

    2014-01-01

    Laser ablation has been widely used for a variety of applications. Since the mechanisms for ablation are strongly dependent on the photoexcitation level, so called cold material processing has relied on the use of high-peak-power laser fluences for which nonthermal processes become dominant; often reaching the universal threshold for plasma formation of ~1 J cm(-2) in most solids. Here we show single-shot time-resolved femtosecond electron diffraction, femtosecond optical reflectivity and ion detection experiments to study the evolution of the ablation process that follows femtosecond 400 nm laser excitation in crystalline sodium chloride, caesium iodide and potassium iodide. The phenomenon in this class of materials occurs well below the threshold for plasma formation and even below the melting point. The results reveal fast electronic and localized structural changes that lead to the ejection of particulates and the formation of micron-deep craters, reflecting the very nature of the strong repulsive forces at play. PMID:24835317

  15. Cold ablation driven by localized forces in alkali halides

    NASA Astrophysics Data System (ADS)

    Hada, Masaki; Zhang, Dongfang; Pichugin, Kostyantyn; Hirscht, Julian; Kochman, Micha? A.; Hayes, Stuart A.; Manz, Stephanie; Gengler, Regis Y. N.; Wann, Derek A.; Seki, Toshio; Moriena, Gustavo; Morrison, Carole A.; Matsuo, Jiro; Sciaini, Germán; Miller, R. J. Dwayne

    2014-05-01

    Laser ablation has been widely used for a variety of applications. Since the mechanisms for ablation are strongly dependent on the photoexcitation level, so called cold material processing has relied on the use of high-peak-power laser fluences for which nonthermal processes become dominant; often reaching the universal threshold for plasma formation of ~1?J?cm-2 in most solids. Here we show single-shot time-resolved femtosecond electron diffraction, femtosecond optical reflectivity and ion detection experiments to study the evolution of the ablation process that follows femtosecond 400?nm laser excitation in crystalline sodium chloride, caesium iodide and potassium iodide. The phenomenon in this class of materials occurs well below the threshold for plasma formation and even below the melting point. The results reveal fast electronic and localized structural changes that lead to the ejection of particulates and the formation of micron-deep craters, reflecting the very nature of the strong repulsive forces at play.

  16. Formation of tungsten monocarbide from a molten tungstate-halide phase by gas sparging

    SciTech Connect

    Gomes, J.M.; Raddatz, A.E.; Baglin, E.G.

    1988-02-23

    A process for preparation of tungsten monocarbide is described comprising: (a) providing a molten composition comprising an alkali metal halide and an oxygen compound of tungsten; (b) sparging the composition with a gas comprising a gaseous hydrocarbon which is selected from the group consisting of natural gas, methane, ethane, acetylene, propane, butane, mixtures thereof, and admixtures of these gases with H/sub 2/ or CO, at a temperature of about 900/sup 0/ to 1100/sup 0/C for a sufficient time for the tungsten compound to be substantially converted to tungsten carbide; and (c) decanting the molten halide from the tungsten carbide product.

  17. Halide laser glasses

    SciTech Connect

    Weber, M.J.

    1982-01-14

    Energy storage and energy extraction are of prime importance for efficient laser action and are affected by the line strengths and linewidths of optical transitions, excited-state lifetimes, nonradiative decay processes, spectroscopic inhomogeneities, nonlinear refractive index, and damage threshold. These properties are all host dependent. To illustrate this, the spectroscopic properties of Nd/sup 3 +/ have been measured in numerous oxide, oxyhalide, and halide glasses. A table summarizes the reported ranges of stimulated emission cross sections, peak wavelengths, linewidths, and radiative lifetimes associated with the /sup 4/F/sub 3/2/ ..-->.. /sup 4/I/sub 11/2/ lasing transition.

  18. Nonradiative electronic capture rates by a halide vacancy in alkali halides

    Microsoft Academic Search

    S. Fraser

    1974-01-01

    We treat non-radiative electronic capture rates induced by the non-adiabatic perturbation operator with corresponding transition probabilities. Therefore a dynamical electronic wavefunction is evaluated. By coupling the electron to “dressed phonon” modes, which connect the “local” optical mode to the acoustic phonons, exact energy balance in the transition probabilities is possible. The Franck-Condon-Integrals arising there are thermal averaged analytically. The method

  19. Photoionization in alkali lasers.

    PubMed

    Knize, R J; Zhdanov, B V; Shaffer, M K

    2011-04-11

    We have calculated photoionization rates in alkali lasers. The photoionization of alkali atoms in the gain medium of alkali lasers can significantly degrade the laser performance by reducing the neutral alkali density and with it the gain. For a ten atmosphere Rb laser and a Cs exciplex laser, the photoionization induced alkali atom loss rates are greater than 10(5) sec(-1). These high loss rates will quickly deplete the neutral alkali density, reducing gain, and may require fast, possibly, supersonic flow rates to sufficiently replenish the neutral medium for CW operation. PMID:21503101

  20. Alkali metal nitrate purification

    DOEpatents

    Fiorucci, Louis C. (Hamden, CT); Morgan, Michael J. (Guilford, CT)

    1986-02-04

    A process is disclosed for removing contaminants from impure alkali metal nitrates containing them. The process comprises heating the impure alkali metal nitrates in solution form or molten form at a temperature and for a time sufficient to effect precipitation of solid impurities and separating the solid impurities from the resulting purified alkali metal nitrates. The resulting purified alkali metal nitrates in solution form may be heated to evaporate water therefrom to produce purified molten alkali metal nitrates suitable for use as a heat transfer medium. If desired, the purified molten form may be granulated and cooled to form discrete solid particles of purified alkali metal nitrates.

  1. Wire ageing with the TEA photocathode

    SciTech Connect

    Va`vra, J.

    1996-06-01

    Recently several RICH protypes successfully tested a gaseous TEA photocathode. However, its wire ageing behavior is unknown. In principle, TEA is a more strongly bonded molecule than TMAE, and, as a result, one would expect better wire ageing behavior. This paper explores this question.

  2. High polarization photocathode R D at SLAC

    SciTech Connect

    Maruyama, Takashi; Garwin, E.L. (Stanford Linear Accelerator Center, Menlo Park, CA (United States)); Prepost, R.; Zaplac, G.H. (Wisconsin Univ., Madison, WI (United States). Dept. of Physics)

    1993-01-01

    This paper describes recent progress on the development of high polarization photocathodes for polarized electron sources. A strained InGaAs cathode has achieved a maximum electron-spin polarization of 71% and has demonstrated the strain enhancement of polarization for the first time. Strained GaAs cathodes have yielded polarizations as high as 90% with much higher quantum efficiency.

  3. The search for rugged, efficient photocathode materials

    Microsoft Academic Search

    Douglas J. Bamford; Mira H. Bakshi; David A. G. Deacon

    1992-01-01

    The ideal photocathode material for advanced accelerators and FELS would have high emission efficiency (for drive laser cost containment) and high ruggedness (for operating lifetime extension). In practice, these goals are somewhat contradictory; the most efficient materials (such as CsK2Sb) have short lifetimes due to poisoning, while the most rugged materials (metals) have low quantum efficiencies. To complement the work

  4. Dye-Sensitized Cuprrous Iodide Photocathode

    NASA Astrophysics Data System (ADS)

    Tennakone, K.; Fernando, C. A. N.; Dewasurendra, M.; Kariappert, M. S.

    1987-04-01

    Copper plates coated with cuprous iodide (p-type semiconductor) are found to adsorb iodides of cationic dyes extremely well. Photocurrent efficiency and stability of dye-sensitized CuI photocathodes in aqueous KI+I2 are studied. Deposition of trace quantities of platinum on top of the dye layer is found to increase the stability and the photocurrent quantum efficiency.

  5. Diode pumped alkali lasers

    Microsoft Academic Search

    B. V. Zhdanov; R. J. Knize

    2011-01-01

    Diode pumped alkali lasers attract growing attention during the past several years because they have demonstrated potential to compete and, possibly, replace the best existing high power laser systems. In spite of the fact that an optically pumped alkali (potassium) vapor laser was first proposed by A.L. Schawlow and C.H. Townes in 1958, the intensive research and development of alkali

  6. A Summary of the 2010 Photocathode Physics for Photoinjectors Workshop

    SciTech Connect

    Bazarov, I [Cornell University; Dowell, D [SLAC National Accelerator Laboratory; Hannon, Fay [Thomas Jefferson National Accelerator Facility; Harkay, K [Argonne National Laboratory; Garcia, C H [Thomas Jefferson National Accelerator Facility; Padmore, H [Lawrence Berkeley National Laboratory; Rao, T [Brookhaven National Laboratory; Smedley, J [Brookhaven National Laboratory

    2010-10-01

    This contribution contains a summary and some highlights from the Photocathode Physics for Photoinjectors (P3) Workshop [1]. This workshop, held at Brookhaven National Laboratory in Ocotber of 2010, was aimed at bringing the photocathode community together to discuss and explore the current state of the art in accelerator photocathodes, from both a theoretical and a materials science perspective. All types of photocathode materials were discussed, including metals, NEA and PEA semiconductors, and "designer" photocathodes with bespoke properties. Topics of the workshop included: Current status of photocathodes for accelerator applications Current fabrication methods Applications of modern materials science to the growth and analysis of cathodes Photoemission spectroscopy as a diagnostic of cathode performance Utilization of modern user facilities Photoemission theory Novel ideas in cathode development Discussion forum on future collaboration for cathode growth, analysis and testing

  7. Methyl Halide Production by Fungi

    NASA Astrophysics Data System (ADS)

    Dailey, G. D.; Varner, R. K.; Blanchard, R. O.; Sive, B. C.; Crill, P. M.

    2005-12-01

    Methyl chloride (CH3Cl), methyl bromide (CH3Br) and methyl iodide (CH3I) are methyl halide gases that contribute significant amounts of halogen radicals to the atmosphere. In an effort to better understand the global budget of methyl halides and their impact on the atmosphere, we need to identify the natural sources in addition to the known anthropogenic sources of these compounds. We are investigating the role of fungi in the production of methyl halides in the soils and wetlands in southern New Hampshire, USA. Previous research has shown that wood decay fungi and ectomycorrhizal fungi, which are within a group of fungi called basidiomycetes, emit methyl halides. In our study, measurements of headspace gas extracted from flasks containing fungi grown in culture demonstrate that a variety of fungi, including basidiomycetes and non-basidiomycetes, emit methyl halides. Our research sites include four ecosystems: an agricultural field, a temperate forest, a fresh water wetland, and coastal salt marshes. We have collected and isolated fungi at each site by culturing tissue samples of fruiting bodies and plant material, by using wood baits, and from the direct culture of soil. We compared the rates of methyl halide emissions from the fungi in the four ecosystems. In addition, we measured emissions from previously assayed fungal isolates after reintroducing them to sterilized soils that were collected from their original environments. Fungal biomass was determined by substrate-induced respiration (SIR). The emission rate by the fungus was determined by a linear regression of the concentration of methyl halide in the sample headspace over time divided by the fungal biomass.

  8. PROGRESS ON LEAD PHOTOCATHODES FOR SUPERCONDUCTING INJECTORS.

    SciTech Connect

    SMEDLEY, J.; RAO, T.; SEKUTOWICZ, J.; KNEISEL, P.; LANGNER, J.; STRZYZEWSKI, P.; LEFFERTS, R.; LIPSKI, A.

    2005-05-16

    We present the results of our investigation of bulk lead, along with various types of lead films, as suitable photocathode materials for superconducting RF injectors. The quantum efficiency of each sample is presented as a function of the photon energy of the incident light, from 3.9 eV to 6.5 eV. Quantum efficiencies of 0.5% have been obtained. Production of a niobium cavity with a lead-plated cathode is underway.

  9. Progress on lead photocathodes for superconducting injectors

    SciTech Connect

    John Smedley; Triveni Rao; Jacek Sekutowicz; Peter Kneisel; J. Langner; P. Strzyzewski; Richard Lefferts; Andrzej Lipski

    2005-05-16

    We present the results of our investigation of bulk lead, along with various types of lead films, as suitable photocathode materials for superconducting RF injectors. The quantum efficiency of each sample is presented as a function of the photon energy of the incident light, from 3.9 eV to 6.5 eV. Quantum efficiencies of 0.5% have been obtained. Production of a niobium cavity with a lead plated cathode is underway.

  10. High-Yield Metal Materials for Photocathode RF Gun

    Microsoft Academic Search

    X. J. Wang; I. Ben-Zvi; J. Smedley; T. Srinivasan-Rao; M. Woodle; D. T. Palmer; R. H. Miller

    1997-01-01

    Significant progress has been made in both improving the quantum efficiency and understanding the physics process of photoemission of metal photocathode materials under high electric field. Metal material, copper and magnesium were installed on the photocathode RF gun, and experimentally investigated using frequency quadrupled Nd:Yag laser (266 nm). A systemic procedure was developed for preparing cathode; this involves diamond polishing,

  11. Photoemission Spectroscopic Study of Cesium Telluride Thin Film Photocathode

    SciTech Connect

    Sugiyama, Harue; Ogawa, Koji; Azuma, Junpei; Takahashi, Kazutoshi; Kamada, Masao [Synchrotron Light Application Center, Saga University, 1 Honjo, Saga 840-8502 (Japan)

    2009-08-04

    The photoemission spectroscopy using synchrotron radiation has been carried out to study the high quantum efficiency and long working lifetime of cesium telluride (Cs{sub x}Te{sub y}) thin film photocathode. The electron affinity derived from the observed energy-distribution curves provides an important hint for long persistency of the photocathode.

  12. Development of Polarized Photocathodes for the Linear Collider

    SciTech Connect

    Richard Prepost

    2009-12-22

    In prior years a Wisconsin-SLAC collaboration developed polarized photocathodes which were used for the SLAC SLD and fixed target programs. Currently, the R&D program goal is the development of a polarized electron source (PES) which meets the ILC requirements for polarization, charge, lifetime, and pulse structure. There are two parts to this program. One part is the continued improvement of photocathode structures with higher polarization. The second part is the design and development of the laser system used to drive the photocathode. The long pulse train for the ILC introduces new challenges for the PES. More reliable and stable operation of the PES may be achievable if appropriate R&D is carried out for higher voltage operation and for a simpler photocathode load-lock system. The collaboration with SLAC is through the Polarized Photocathode Research Collaboration (PPRC). Senior SLAC personnel include T. Maruyama, J. Clendenin, R. Kirby, and A. Brachmann.

  13. Advances in DC photocathode electron guns

    SciTech Connect

    Bruce M. Dunham; P. Heartmann; Reza Kazimi; Hongxiu Liu; B. M. Poelker; J. S. Price; P. M. Rutt; W. J. Schneider; Charles K. Sinclair

    1998-07-01

    At Jefferson Lab, a DC photoemission gun using GaAs and GaAs-like cathodes provides a source of polarized electrons for the main accelerator. The gun is required to produce high average current with long operational lifetimes and high system throughout. Recent work has shown that careful control of the parameters affecting cathode lifetime lead to dramatic improvements in source operation. These conditions include vacuum and the related effect of ion backbombardment, and precise control of all of the electrons emitted from the cathode. In this paper, the authors will review recent results and discuss implications for future photocathode guns.

  14. Simulations of the laser photocathode injector

    SciTech Connect

    Herrmannsfeldt, W.; Miller, R.; Hanerfeld, H.

    1988-06-01

    New, fully electromagnetic simulations of the beam optics in a laser-photocathode injector have been make using the PIC Code MASK. The recent studies are for the two-cavity design now undergoing tests by R. Sheffield, LANL. Pulses up to 10 nC are simulated, using cavities operating at 1300 MHz with above 1 MeV energy gain per cavity. The work is guided by previous simulation results which show that to achieve good agreement with the best experimental results, it is necessary to use very high RF fields near the cathode and to maintain small beam cross sections, corresponding to very high emission density.

  15. Optically pumped alkali lasers

    Microsoft Academic Search

    Boris V. Zhdanov; Thomas Ehrenreich; Randall J. Knize

    2007-01-01

    Optically pumped alkali vapor lasers have been developed during last several years. Efficient operation of Cesium, Rubidium and Potassium vapor lasers has been demonstrated. Laser slope efficiencies higher than 80% have been achieved. In this paper we present the latest achievements in this field, discuss the main directions and problems in high power alkali lasers development and possible solutions of

  16. DEVELOPMENT AND EVALUATION OF METHODS FOR TOTAL ORGANIC HALIDE AND PURGEABLE ORGANIC HALIDE IN WASTEWATER

    EPA Science Inventory

    This report describes a series of studies involving the use of 'surrogate' methods for the determination of total organic halides (TOX), purgeable organic halides (POX), and solvent extractable organic halides (EOX), in wastewater and solid wastes. A pyrolysis/microcoulometric sy...

  17. Milk-alkali syndrome

    MedlinePLUS

    ... the dynamics of calcium homeostasis. Clin J Am Soc Nephrol . 1006;1:641– 654. Grubb M, Gaurav ... Welcome to the calcium-alkali syndrome. J Am Soc Nephrol. 2010;21:1440-1443. Yoshizawa H, Morishita ...

  18. The QE numerical simulation of PEA semiconductor photocathode

    E-print Network

    Li, Xudong; Zhang, Meng; Zhao, Minghua

    2011-01-01

    Several kinds of models have already been proposed for explaining the photoemission process. The exact photoemission theory of semiconductor photocathode was not well established after decades of research. In this paper an integral equation of quantum efficiency (QE) is constructed to describe the photoemission of positive electron affinity (PEA) semiconductor photocathode based on three-step photoemission model. The influences of forbidden gap, electron affinity, photon energy, incident angle, degree of polarization, refractive index, extinction coefficient, initial/final electron energy, relaxation time and external electric field on the QE of PEA semiconductor photocathode are taken into account. In addition, a computer code is also programmed to calculate the QE of K2CsSb photocathode theoretically at 532nm wavelength, the result is in line with the experimental value by and large. What are the reasons caused to the distinction between the experimental measuring and theoretical QE are discussed.

  19. High gradient rf gun studies of CsBr photocathodes

    NASA Astrophysics Data System (ADS)

    Vecchione, Theodore; Maldonado, Juan R.; Gierman, Stephen; Corbett, Jeff; Hartmann, Nick; Pianetta, Piero A.; Hesselink, Lambertus; Schmerge, John F.

    2015-04-01

    CsBr photocathodes have 10 times higher quantum efficiency with only 3 times larger intrinsic transverse emittance than copper. They are robust and can withstand 80 MV /m fields without breaking down or emitting dark current. They can operate in 2 ×10-9 torr vacuum and survive exposure to air. They are well suited for generating high pulse charge in rf guns without a photocathode transfer system.

  20. Advanced 3D Photocathode Modeling and Simulations Final Report

    SciTech Connect

    Dimitre A Dimitrov; David L Bruhwiler

    2005-06-06

    High brightness electron beams required by the proposed Next Linear Collider demand strong advances in photocathode electron gun performance. Significant improvement in the production of such beams with rf photocathode electron guns is hampered by the lack high-fidelity simulations. The critical missing piece in existing gun codes is a physics-based, detailed treatment of the very complex and highly nonlinear photoemission process.

  1. Freeze Enhanced Halate Halide Reactions

    NASA Astrophysics Data System (ADS)

    Newberg, J. T.; Weaver, K.; Broderick, A.

    2014-12-01

    Relatively little is known about halate ion species (XO3-; X = I, Br, Cl) in atmospheric condensed phases. It was initial thought that iodate was a terminal stable species upon iodide oxidation. However, it is becoming increasingly recognized that reactions involving iodate can lead to reactive iodine, and this chemistry is accelerated under acidic conditions. The environmental concentrations and chemistry of bromate and chlorate are largely unexplored in environmental ices. We present results from a series of aqueous phase halate ion reactions with halides under acidic conditions, showing that the kinetics are strongly enhanced upon freezing. The products of these reactions are reactive halogens, which have important implications to marine boundary layer chemistry.

  2. Fluorination of the cyanogen halides 

    E-print Network

    Ward, Raymond Anthony

    1960-01-01

    with the gas. The hydrolyeats ms then washed out of the bulb and diluted to a known volume. Yields vers usually based on the number of molee of silver halide formed from the moles of sliver fluoride reactant. Harshew specification 101 off ver fluoride... was warmed t, o room temperature, a gas seemed to be bubbling out. The solution was heated and the gas evolved waa trapped at liquid nitrogen temperature after it had passed through a calcium chloride dryland tube. The white precipitate was filtered off...

  3. Progress on diamond amplified photo-cathode

    SciTech Connect

    Wang, E.; Ben-Zvi, I.; Burrill, A.; Kewisch, J.; Chang, X.; Rao, T.; Smedley, J.; Wu, Q.; Muller, E.; Xin, T.

    2011-03-28

    Two years ago, we obtained an emission gain of 40 from the Diamond Amplifier Cathode (DAC) in our test system. In our current systematic study of hydrogenation, the highest gain we registered in emission scanning was 178. We proved that our treatments for improving the diamond amplifiers are reproducible. Upcoming tests planned include testing DAC in a RF cavity. Already, we have designed a system for these tests using our 112 MHz superconducting cavity, wherein we will measure DAC parameters, such as the limit, if any, on emission current density, the bunch charge, and the bunch length. The diamond-amplified photocathode, that promises to support a high average current, low emittance, and a highly stable electron beam with a long lifetime, is under development for an electron source. The diamond, functioning as a secondary emitter amplifies the primary current, with a few KeV energy, that comes from the traditional cathode. Earlier, our group recorded a maximum gain of 40 in the secondary electron emission from a diamond amplifier. In this article, we detail our optimization of the hydrogenation process for a diamond amplifier that resulted in a stable emission gain of 140. We proved that these characteristics are reproducible. We now are designing a system to test the diamond amplifier cathode using an 112MHz SRF gun to measure the limits of the emission current's density, and on the bunch charge and bunch length.

  4. Proceedings of the workshop on photocathodes for polarized electron sources for accelerators. Revision

    SciTech Connect

    Chatwell, M.; Clendenin, J.; Maruyama, T.; Schultz, D. [eds.

    1994-04-01

    Application of the GaAs polarized electron source to studies of surface magnetism; thermal stability of Cs on NES III-V-Photocathodes and its effect on quantum efficiency; AFEL accelerator; production and detection of SPIN polarized electrons; emittance measurements on a 100-keV beam from a GaAs photocathode electron gun; modern theory of photoemission and its applications to practical photocathodes; experimental studies of the charge limit phenomenon in GaAs photocathodes; new material for photoemission electron source; semiconductor alloy InGaAsP grown on GaAs substrate; NEA photocathode surface preparation; technology and physics; metalorganic chemical vapor deposition of GaAs-GaAsP spin-polarized photocathodes; development of photocathodes injectors for JLC-ATF; effect of radiation trapping on polarization of photoelectrons from semiconductors; and energy analysis of electrons emitted by a semiconductor photocathode.

  5. Photocathode Optimization for a Dynamic Transmission Electron Microscope: Final Report

    SciTech Connect

    Ellis, P; Flom, Z; Heinselman, K; Nguyen, T; Tung, S; Haskell, R; Reed, B W; LaGrange, T

    2011-08-04

    The Dynamic Transmission Electron Microscope (DTEM) team at Harvey Mudd College has been sponsored by LLNL to design and build a test setup for optimizing the performance of the DTEM's electron source. Unlike a traditional TEM, the DTEM achieves much faster exposure times by using photoemission from a photocathode to produce electrons for imaging. The DTEM team's work is motivated by the need to improve the coherence and current density of the electron cloud produced by the electron gun in order to increase the image resolution and contrast achievable by DTEM. The photoemission test setup is nearly complete and the team will soon complete baseline tests of electron gun performance. The photoemission laser and high voltage power supply have been repaired; the optics path for relaying the laser to the photocathode has been finalized, assembled, and aligned; the internal setup of the vacuum chamber has been finalized and mostly implemented; and system control, synchronization, and data acquisition has been implemented in LabVIEW. Immediate future work includes determining a consistent alignment procedure to place the laser waist on the photocathode, and taking baseline performance measurements of the tantalum photocathode. Future research will examine the performance of the electron gun as a function of the photoemission laser profile, the photocathode material, and the geometry and voltages of the accelerating and focusing components in the electron gun. This report presents the team's progress and outlines the work that remains.

  6. Optimization of photomultiplier spectral sensitivity with a graded thickness photocathode

    NASA Astrophysics Data System (ADS)

    Townsend, P. D.; Valberg, L.; Momchilov, N.; Harmer, S. W.; Downey, R.; Cormack, A. J.

    2008-09-01

    The efficiency of S20 multialkali photocathodes is a function of thickness, wavelength, polarization and angle of incidence of light into the cathode. Therefore no single set of conditions can maximize performance over the entire spectral range. Consequently, two prototype photocathodes have been made with a gradation in thickness so that during monochromatic analysis the optical beam can be addressed to different thickness regions at preferred angles of incidence. This potentially enables a spectrum to be recorded under optimal conditions at a single interaction event. Relative to normal commercial S20 photomultipliers the quantum efficiency (QE) has been significantly raised across the entire spectral range. The current data were primarily obtained between 450 and 800 nm and at 450 nm it resulted in values of at least 65% QE, which is the highest value ever cited at this wavelength. Signals at longer wavelengths, for example at 750 and 800 nm, were recorded with up to 20 and 10% QE, respectively. Once again these are new record values that match performance from multiple interactions in waveguide cathodes. The data from this new design of photocathode underline the potential for improvements in efficiency for non-normal incidence in graded thickness photocathodes and indicate that current S20 technology could be significantly enhanced. Alternative enhancement methods are mentioned, particularly for spectrally dispersed signals. The enhancements are compared with data for a standard high quality S20 photocathode.

  7. RF phase stabilization for RF photocathode gun through electro-optical monitoring

    SciTech Connect

    Leung, K.P.; Yu, L.H.; Ben-Zvi, I.

    1993-08-01

    An electro-optical technique is being developed at the Brookhaven National Laboratory (BNL) Accelerator Test Facility (ATF) to monitor and control the phase of the photocathode laser beam with respect to the RF drive field for the RF photocathode gun. This technique utilizes the RF field induced birefringence which is probed by the photocathode laser beam. A proof-of-principle experiment is described which has been performed using the ATF RF photocathode gun injection system for the linac.

  8. Sealed GEM photomultiplier with a CsI photocathode: ion feedback and ageing

    E-print Network

    1 Sealed GEM photomultiplier with a CsI photocathode: ion feedback and ageing A. Breskin a , A, 630090 Novosibirsk, Russia. Abstract We present the performance of a sealed gaseous photomultiplierI photocathode, in Ar/CH4 (95/5). A few-month stability study of the photocathode in a sealed mode is presented

  9. Significantly improved charge-collection efficiencies result from a general chemical approach to synthesizing photocathodes.

    E-print Network

    as photocathodes for p-type semiconductor-sensitized solar cells. Compared to dye-sensitized NiO photocathodes for photoelectrochemical solar cells. Key Result Compared to dye-sensitized NiO photocathodes, the CdS-sensitized Ni coupled to a dye-sensitized photoanode, could significantly increase overall solar conversion efficiency

  10. Transfer of aryl halide to alkyl halide: reductive elimination of alkylhalide from alkylpalladium halides containing syn-?-hydrogen atoms.

    PubMed

    Hao, Wei; Wei, Junnian; Geng, Weizhi; Zhang, Wen-Xiong; Xi, Zhenfeng

    2014-12-22

    ?-Hydride abstraction is a well-accepted elementary step for catalytic cycles in organometallic chemistry. It is usually anticipated that alkylpalladium halides containing syn-?-hydrogen atoms will undergo ?-hydride abstraction to afford the Heck-type products. However, this study discloses that the above general knowledge is only conditionally correct. Our experimental results demonstrate that the reductive elimination of alkylhalides from alkylpalladium halides containing syn-?-hydrogen atoms may surpass the ?-hydride abstraction or even become exclusive in certain cases. PMID:25367776

  11. Alkali-vapor lasers

    Microsoft Academic Search

    J. Zweiback; A. Komashko; W. F. Krupke

    2010-01-01

    We report on the results from several of our alkali laser systems. We show highly efficient performance from an alexandrite-pumped rubidium laser. Using a laser diode stack as a pump source, we demonstrate up to 145 W of average power from a CW system. We present a design for a transversely pumped demonstration system that will show all of the

  12. FEMTO SECOND ELECTRON BEAM DIFFRACTION USING A PHOTOCATHODE RF GUN.

    SciTech Connect

    WANG,X.J.WU,Z.IHEE,H.

    2003-05-12

    One of the 21st century scientific frontiers is to explore the molecule structure transition on the femtosecond time scale. X-ray free electron laser (XFEL) is one of the tools now under development for investigating femto-second structure transition. We are proposing an alternative technique--femto-second electron diffraction based on a photocathode RF gun. We will present a design of a kHz femto-seconds electron diffraction system based on a photocathode RF gun. Our simulation shows that, the photocathode RF gun can produce 100 fs (FWHM) electron bunch with millions electrons at about 2 MeV. This is at least one order of magnitude reduction in bunch length, and two orders of magnitude increase in number of electrons comparing to present time-resolved electron diffraction system. We will also discuss various issues and limitations related to MeV electron diffraction.

  13. Intrinsic Emittance Reduction of an Electron Beam from Metal Photocathodes

    SciTech Connect

    Hauri, C. P.; Ganter, R.; Le Pimpec, F.; Trisorio, A.; Ruchert, C.; Braun, H. H. [Paul Scherrer Institute, 5232 Villigen (Switzerland)

    2010-06-11

    Electron beams in modern linear accelerators are now becoming limited in brightness by the intrinsic emittance of the photocathode electron source. Therefore it becomes important for large scale facilities such as free electron lasers to reduce this fundamental limit. In this Letter we present measurements of the intrinsic emittance for different laser wavelength (from 261 to 282 nm) and for different photocathode materials such as Mo, Nb, Al, Cu. Values as low as 0.41{+-}0.03 mm{center_dot}mrad/mm laser spot size (rms) were measured for a copper photocathode illuminated with a 282 nm laser wavelength. The key element for emittance reduction is a uv laser system which allows adjustment of the laser photon energy to match the effective work function of the cathode material and to emit photoelectrons with a lower initial kinetic energy. The quantum efficiency over the explored wavelength range varies by less than a factor of 3.

  14. Hydrothermal alkali metal recovery process

    DOEpatents

    Wolfs, Denise Y. (Houston, TX); Clavenna, Le Roy R. (Baytown, TX); Eakman, James M. (Houston, TX); Kalina, Theodore (Morris Plains, NJ)

    1980-01-01

    In a coal gasification operation or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein solid particles containing alkali metal residues are produced, alkali metal constituents are recovered from the particles by treating them with a calcium or magnesium-containing compound in the presence of water at a temperature between about 250.degree. F. and about 700.degree. F. and in the presence of an added base to establish a pH during the treatment step that is higher than would otherwise be possible without the addition of the base. During the treating process the relatively high pH facilitates the conversion of water-insoluble alkali metal compounds in the alkali metal residues into water-soluble alkali metal constituents. The resultant aqueous solution containing water-soluble alkali metal constituents is then separated from the residue solids, which consist of the treated particles and any insoluble materials formed during the treatment step, and recycled to the gasification process where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst. Preferably, the base that is added during the treatment step is an alkali metal hydroxide obtained by water washing the residue solids produced during the treatment step.

  15. Emission properties of body-centered cubic elemental metal photocathodes

    NASA Astrophysics Data System (ADS)

    Li, Tuo; Rickman, Benjamin L.; Schroeder, W. Andreas

    2015-04-01

    A first principles analysis of photoemission is developed to explain the lower than expected rms transverse electron momentum measured using the solenoid scan technique for the body-centered cubic Group Vb (V, Nb, and Ta) and Group VIb (Cr, Mo, and W) metallic photocathodes. The density functional theory based analysis elucidates the fundamental role that the electronic band structure (and its dispersion) plays in determining the emission properties of solid-state photocathodes and includes evaluation of work function anisotropy using a thin-slab method.

  16. Reflection silver-halide gelatin holograms

    NASA Astrophysics Data System (ADS)

    Usanov, Yuri E.; Vavilova, Ye. A.; Kosobokova, N. L.; Shevtsov, Michail K.

    1991-02-01

    A new principle of reflection silverhalide gelatin (SHG) holograms generation is presented. The formation mechanism of the micro-cavity structure of holographic gratings is investigated. Based on the principle discussed here three methods of processing are suggested for making highly efficient SHG reflection holograms in the blue the green and the red regions of spectra with properties similar to those of conventional dichromated gelatin (DCG) holograms. 2. SHG HOLOGRAMS AND ANALYSIS OF THE PRINCIPAL OF THEIR FABRICATION Optical properties of DCG holograms and high light sensitivity of silver halide materials in the whole visible spectrum range can be combined in SHG holograms in which light field interference pattern recording is realized on silver halide grains while the light diffraction during the reconstruction takes place on a gelatin layer similar to DCG layer having a refractive index modulation. There exist a number of methods for transforming a ''silver'' structure into refracted index modulation structure. They are based on selective hardening of silver-halide layer gelatin. According to Pennington et. al. [1] selective hardening takes place as a result of the effect of laser or UV light on a silver halide developed fixed bleached and ammonium dichromate sensitized. A gelatin in isophase grating planes is hardened to a less degree that between planes due to high adsorption of a halide silver. After the removal of halide silver from the layer during the next fixing process

  17. C-AD electron-cooling Photocathode and Laser

    E-print Network

    availability ­ Modifications needed · Diamond amplifier ­ Theoretical analysis ­ Gain measurements ­ RF testing ­ Capsule fabrication · Brazing · Metallization #12;C-AD electron-cooling Overview Photocathode Requirements-cooling 9.4 MHz 532 nm, 355 nm 10 ps pulse length Synchronized to master RF clock Adjustable output power

  18. Metal-Insulator Photocathode Heterojunction for Directed Electron Emission

    SciTech Connect

    Droubay, Timothy C.; Chambers, Scott A.; Joly, Alan G.; Hess, Wayne P.; Nemeth, Karoly; Harkay, Katherine C.; Spentzouris, Linda

    2014-02-14

    New photocathode materials capable of producing intense and directed electron pulses are needed for development of next generation light sources and dynamic transmission electron microscopy. Ideal photocathodes should have high photoemission quantum efficiency (QE) and be capable of delivering collimated and well-shaped pulses of consistent charge under high-field operating conditions. High-brightness and low-intrinsic emittance electron pulses have been predicted for hybrid metal-insulator photocathode designs constructed from three to four monolayer MgO films on atomically flat silver. Here we use angle-resolved photoelectron spectroscopy to confirm directional photoemission and a large increase in QE under ultraviolet laser excitation of an ultrathin MgO film on Ag(001). We observe new low-binding energy photoemission, not seen for Ag(001), and greater electron emission in the normal direction. Under 4.66 eV laser excitation, the photoemission quantum efficiency of the MgO/Ag(001) hybrid photocathode is a factor of seven greater than that for clean Ag(001).

  19. High gradient acceleration in a 17 GHz photocathode RF gun

    Microsoft Academic Search

    S. C. Chen; J. Gonichon; L. C.-L. Lin; R. J. Temkin; S. Trotz; B. G. Danly; J. S. Wurtele

    1993-01-01

    The physics and technological issues involved in high gradient particle acceleration at high microwave (RF) frequencies are under study at MIT. The 17 GHz photocathode RF gun has a 1½ cell room temperature copper cavity with a peak accelerating gradient of about 250 MV\\/m. The anticipated beam parameters, when operating with a photoemission cathode, are: energy 2 MeV, normalized emittance

  20. MBE-grown InGaAs photocathodes

    Microsoft Academic Search

    Loig E. Bourree; David R. Chasse; P. L. Stephan Thamban; Robert Glosser

    2003-01-01

    The material constitution of modern photocathodes (i.e. third generation) has remained a constant for almost two decades. The active GaAs layer is grown by metal organic chemical vapor deposition (MOCVD) and processed to create a negative electron affinity (NEA) surface for photoemission. Thus, these types of cathodes are limited in their spectral response by the band gap energy of the

  1. Dimming of metal halide lamps

    NASA Technical Reports Server (NTRS)

    Schurer, Kees

    1994-01-01

    We ran some tests on the effect of dimming of metal halide (MH) lamps upon the stability and the spectral quality of the light output. Lamps used were a new Philips lamp HPI-T 250W, a similar Philips lamp with a few thousand burning hours and a new Osram lamp HQI-T 250W/D. The ballast was a BBC type DJ 250/2KS, the starter a BAS TORGI type MZN 250 SE and the dimmer an Elstrom Control System type ERHQ-T 250. Power was derived from a Philips stabilizer, type PE 1602. Lamp output was monitored with a PAR meter. Spectra were taken at 100% and at 50% output as measured with the PAR meter. Lamps were allowed to stabilize at any setting for 30 minutes before measurements were made. Lamp manufacturers advise against dimming for fear of poor stability and intolerable changes of the spectrum. However, none of the lamps showed a decrease in stability, no flicker or wandering of the discharge, and the changes of the spectrum were not negligible, but certainly not dramatic. Lamps of either manufacture retain their white color, relative peak heights of spectral lines did shift, but no gaps in the spectrum occurred. Spectra taken at 50% with 30 minutes intervals coincided. Differences between the new and the older Philips lamp were noticeable, but not really significant.

  2. Structural effects in molecular metal halides.

    PubMed

    Hargittai, Magdolna

    2009-03-17

    Metal halides are a relatively large class of inorganic compounds that participate in many industrial processes, from halogen metallurgy to the production of semiconductors. Because most metal halides are ionic crystals at ambient conditions, the term "molecular metal halides" usually refers to vapor-phase species. These gas-phase molecules have a special place in basic research because they exhibit the widest range of chemical bonding from the purely ionic to mostly covalent bonding through to weakly interacting systems. Although our focus is basic research, knowledge of the structural and thermodynamic properties of gas-phase metal halides is also important in industrial processes. In this Account, we review our most recent work on metal halide molecular structures. Our studies are based on electron diffraction and vibrational spectroscopy, and increasingly, we have augmented our experimental work with quantum chemical computations. Using both experimental and computational techniques has enabled us to determine intriguing structural effects with better accuracy than using either technique alone. We loosely group our discussion based on structural effects including "floppiness", relativistic effects, vibronic interactions, and finally, undiscovered molecules with computational thermodynamic stability. Floppiness, or serious "nonrigidity", is a typical characteristic of metal halides and makes their study challenging for both experimentalists and theoreticians. Relativistic effects are mostly responsible for the unique structure of gold and mercury halides. These molecules have shorter-than-expected bonds and often have unusual geometrical configurations. The gold monohalide and mercury dihalide dimers and the molecular-type crystal structure of HgCl(2) are examples. We also examined spin-orbit coupling and the possible effect of the 4f electrons on the structure of lanthanide trihalides. Unexpectedly, we found that the geometry of their dimers depends on the f electron configuration. Metal halides are unique in exhibiting strong vibronic interactions such as the Jahn-Teller effect and the related Renner-Teller effect. Some metal trihalide molecules have an almost T-shape due to static Jahn-Teller distortions. The nonlinear structure with a 150 degree bond angle of the chromium dichloride molecule demonstrates the Renner-Teller effect. Finally, we present a few examples of unknown structures that appear to be thermodynamically stable, including gold and silver triiodides and all silver subhalides. The combination of experimental and computational techniques has brought new insights to the structural chemistry of metal halides. We expect that the continuing progress in computational chemistry will shed further light on the intricate details of these and other molecular structures. PMID:19170522

  3. Quantitative evaluation of the nucleophilicity of some ethers and metal halides in radical exchange between phenyllithium and bromobenzene

    SciTech Connect

    Batalov, A.P.

    1987-05-01

    The authors discuss the results of a study of the effect of alkali metal and tetramethylammonium halides (MX) on the rate of radical exchange between phenyllithium and bromobenzene in diethyl ether. The phenyllithium was synthesized by an exchange reaction, from ethyllithium and triphenylantimony. The MX concentration (0.15 mole/liter) in all cases was an excess as compared with the phenyllithium concentration (0.1 mole/liter). In the present work, /sup 14/C-bromobenzene was used. The rate of exchange was followed from the rise in radioactivity of the benzoic acid isolated after carbonation of the reaction mixture.

  4. Alkali metal-sulfur cells

    SciTech Connect

    Auborn, J.J.; Granstaff, S.M.

    1982-11-02

    An alkali metal, such as sodium, sulfur cell having an alkali metal anode, a solid ionic electrolyte, such as sodium beta alumina, and a liquid catholyte formed by sulfur, a halosulfane, such as sulfur monochloride and a haloacid, such as aluminum chloride, is described.

  5. Purification of alkali metal nitrates

    DOEpatents

    Fiorucci, Louis C. (Hamden, CT); Gregory, Kevin M. (Woodridge, IL)

    1985-05-14

    A process is disclosed for removing heavy metal contaminants from impure alkali metal nitrates containing them. The process comprises mixing the impure nitrates with sufficient water to form a concentrated aqueous solution of the impure nitrates, adjusting the pH of the resulting solution to within the range of between about 2 and about 7, adding sufficient reducing agent to react with heavy metal contaminants within said solution, adjusting the pH of the solution containing reducing agent to effect precipitation of heavy metal impurities and separating the solid impurities from the resulting purified aqueous solution of alkali metal nitrates. The resulting purified solution of alkali metal nitrates may be heated to evaporate water therefrom to produce purified molten alkali metal nitrate suitable for use as a heat transfer medium. If desired, the purified molten form may be granulated and cooled to form discrete solid particles of alkali metal nitrates.

  6. The effect of surface cleaning on quantum efficiency in AlGaN photocathode

    NASA Astrophysics Data System (ADS)

    Hao, Guanghui; Zhang, Yijun; Jin, Muchun; Feng, Cheng; Chen, Xinlong; Chang, Benkang

    2015-01-01

    To improve the quantum efficiency of AlGaN photocathode, various surfaces cleaning techniques for the removal of alumina and carbon from AlGaN photocathode surface were investigated. The atomic compositions of AlGaN photocathode structure and surface were measured by the X-ray photoelectron spectroscopy and Ar+ ion sputtering. It is found that the boiling KOH solution and the mixture of sulfuric acid and hydrogen peroxide, coupled with the thermal cleaning at 850 °C can effectively remove the alumina and carbon from the AlGaN photocathode surface. The quantum efficiency of AlGaN photocathode is improved to 35.1% at 240 nm, an increase of 50% over the AlGaN photocathode chemically cleaned by only the mixed solution of sulfuric acid and hydrogen peroxide and thermally cleaned at 710 °C.

  7. Photocathode performance measurements for the SLC polarized electron gun

    SciTech Connect

    Garden, C.L.; Hoyt, E.W.; Schultz, D.C.; Tang, H.

    1993-04-01

    A low-voltage test system is used to qualify various III-V semiconductor materials as photocathodes for the SLC. The system features a load lock to introduce samples, high pumping speed, a sensitive residual gas analyzer, and an infrared temperature detector. Heat cleaning, cesiation, and oxidation procedures have been studied to optimize cathode activation for achieving an optimum NEA surface. VGF GaAs, MBE-grown AlGaAs, MBE GaAs layered on AlGaAs, and MOCVD GaAsP cathodes with different active layer thicknesses and doping concentrations have been tested for quantum efficiency and lifetime. New higher-polarization strained-layer GaAs on GaAsP photocathodes have also been tested. Results and operational experience are discussed.

  8. Femtosecond response time measurements of a Cs2Te photocathode

    E-print Network

    Aryshev, A; Honda, Y; Terunuma, N; Urakawa, J

    2015-01-01

    We present the response time measurements of a Cs2Te photocathode illuminated with two 100 fs duration, variable time separation laser pulses at 266 nm wavelength. The response time was confirmed in dispersive region downstream of a 12-cell standing wave S-band acceleration structure using a well-known RF zero-crossing technique. At the same time it was also measured by changing mechanical path-length difference between two micro-bunches. Both methods agree that Cs2Te photocathode time response is of the order of 250 fs and thereby it is possible to generate and control a THz sequence of relativistic electron bunches by a conventional S-band RF gun. This result further opens a possibility to construct wide-range tunable THz FEL.

  9. Magnetron Driven L Band RF Gun using a Photocathode Emitter

    Microsoft Academic Search

    Kirk Evans; Amnon Fisher; Moshe Friedman

    1996-01-01

    Magnetron Driven L Band RF Gun using a Photocathode Emitter A tunable 5 megawatt L-Band injection locked magnetron amplifier is used to drive a 1-1\\/2 cell RF cavity gun, to produce a 2.5 megavolt electron beam. A tunable RF source relaxes the precision of the cavity gun construction, and therefore simplifies the design and reduces the overall cost. The design

  10. Thermal emittance measurements of a cesium potassium antimonide photocathode

    NASA Astrophysics Data System (ADS)

    Bazarov, Ivan; Cultrera, Luca; Bartnik, Adam; Dunham, Bruce; Karkare, Siddharth; Li, Yulin; Liu, Xianghong; Maxson, Jared; Roussel, William

    2011-05-01

    Thermal emittance measurements of a CsK2Sb photocathode at several laser wavelengths are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. The thermal emittance is 0.56±0.03 mm mrad/mm(rms) at 532 nm wavelength. The results are compared with a simple photoemission model and found to be in a good agreement.

  11. MBE-grown InGaAs photocathodes

    NASA Astrophysics Data System (ADS)

    Bourree, Loig E.; Chasse, David R.; Thamban, P. L. Stephan; Glosser, Robert

    2003-02-01

    The material constitution of modern photocathodes (i.e. third generation) has remained a constant for almost two decades. The active GaAs layer is grown by metal organic chemical vapor deposition (MOCVD) and processed to create a negative electron affinity (NEA) surface for photoemission. Thus, these types of cathodes are limited in their spectral response by the band gap energy of the GaAs. There is interest in extending this range past 1000nm while preserving a high quantum efficiency (QE). This would allow taking advantage of an increased luminescence of night sky in the infrared. MOCVD grown InGaAs photocathodes have a photoresponse (PR) in the near infrared. Still, a major drawback to date has been its low QE. We believe that the use of molecular beam epitaxy (MBE) to grow this alloy will permit the fabrication of a higher quality device beyond today's standards, with improved equivalent background illumination and higher QE over a 700nm to 1100nm spectral range. To demonstrate this concept two reflection mode InGaAs photocathode were grown. These cathodes were NEA activated with Cs:O in situ in the MBE reactor after their growth and their PR recorded. Following the activation, optical characterization techniques (i.e. photoluminescence, Raman spectroscopy) were employed to probe electron and phonon energy to relate fundamental material parameters to the observed PR. The collected information is being used to correct and enhance growth characteristics to increase spectral response and QE.

  12. Comparison of resolution characteristics between exponential-doping and uniform-doping GaN photocathodes

    NASA Astrophysics Data System (ADS)

    Wang, Hong-gang; Qian, Yun-sheng; Lu, Liu-bing; Cheng, Hong-chang; Chang, Ben-kang

    2013-08-01

    The studies of quantum efficiency, electronic energy distribution and stability are highly concerned in the application of Negative electron affinity (NEA) gallium nitride (GaN) photocathodes while the resolution of photocathodes are concerned rarely. The resolutions of some image intensifiers are smaller than computational value partly because of ignoring the resolution of photocathodes. To a certain extent, the resolutions of image intensifiers are influenced by photocathodes. Electronic transverse diffusion is the main cause of decreasing the resolution of photocathodes whereas the exponential-doping structure can reduce its influence. In this paper, the resolution characteristics of photocathodes have been studied by using the modulation transfer function (MTF) method. The MTF expressions of transmission-mode exponential-doping photocathodes have been obtained by solving the two-dimensional continuity equations. According to the MTF expressions, the resolution characteristics between exponential-doping and uniform-doping GaN photocathodes are calculated theoretically and analyzed comparatively. At the same time, the relationships between resolution and thickness of the emission layer Te, electron diffusion length LD are researched in detail. The calculated results show that, compared with the uniform-doping photocathode, the exponential-doping structure can increase the resolution of photocathode evidently. The resolution of exponential-doping GaN photocathode is improved distinctly when the spatial frequency varies from 400 to 800 lp/mm. The MTF characteristics approach gradually when f increases or decreases. Let f =600 lp/mm, the resolution increases by 20%-48% approximately. The constant built-in electric field for exponential-doping GaN photocathode can increase the resolution of photocathode. The improvement of resolution is different from decreasing Te, LD or increasing the recombination velocity of back-interface which are at the cost of reducing the quantum efficiency of photocathode. Therefore, the MTF expressions of transmission-mode exponential-doping photocathode play a positive role in improving the resolution of ultraviolet detector and optimizing the structural design of GaN photocathode.

  13. Optical gaps of alkali borate and alkali fluoroborate glasses

    NASA Astrophysics Data System (ADS)

    Suzuki, Takenobu; Hirano, Masahiro; Hosono, Hideo

    2002-04-01

    The optical gaps of B2O3 alkali borate, and alkali fluoroborate glasses were determined by using blown films. The gap of B2O3 glass was 8.0 eV and the value decreased monotonically with decreasing the B2O3 content in both fluoroborate and borate glasses. When compared at a constant B2O3 content, the gap is in the order Li>Na>K and fluoroborate>borate. Ab initio molecular orbital calculation on the model clusters of the glasses revealed that the lowest excitations in B2O3 and alkali (fluoro) borate glasses are the transitions from nonbonding 2p orbitals of oxygen atoms in boroxol rings to vacant nonbonding 2p orbitals of boron atoms on "loose" BO3 triangles and from nonbonding 2p orbitals of oxygen atoms bonded with borons in tetrahedral coordination to the vacant ns orbitals of neighboring alkali ions, respectively. The vacant ns orbitals of the alkali ions neighboring oxygen atoms attached to tetrahedral borons primarily contribute to the lowest unoccupied molecular orbital (LUMO) levels. On the other hand, fluorine indirectly contributes to lowering the highest occupied molecular orbital (HOMO) levels via inductive effect (polarization of B-F ?-bond). It was therefore concluded that the effect of alkali addition on lowering LUMO levels is larger than that of fluorine addition on lowering the HOMO level.

  14. Accessing a low-lying bound electronic state of the alkali oxides, LiO and NaO, using laser induced fluorescence

    Microsoft Academic Search

    J. V. Pugh; K. K. Shen; C. B. Winstead; J. L. Gole

    1996-01-01

    The first laser based probe for the sodium and lithium monoxides is established. The Li(Na)+N2O reactions studied in a multiple collision entrainment mode produce the LiO and NaO ground X2? and low-lying monoxide excited states. In contrast to the alkali halides, laser induced excitation spectroscopy confirms that the LiO and NaO B 2? states, counter to recent predictions, are located

  15. Tunable alkali metallic vapor laser

    Microsoft Academic Search

    I. Itzkan; R. T. V. Kung

    1979-01-01

    A tunable alkali metallic vapor laser system is disclosed. Stimulated Raman scattering (SRS) in a low pressure atomic alkali metallic vapor of potassium or cesium is utilized wherein the atomic vapor is provided and then primed to populate an intermediate level such as the 4Pââ level for potassium and the 6Pââ level for cesium from which the desired upper laser

  16. Alkali-isomerized linoleic acid

    Microsoft Academic Search

    D. E. Terry; D. H. Wheeler

    1946-01-01

    Summary  Alkali-isomerized linoleic acid and its methyl ester have been found to have boiling points higher than the corresponding\\u000a normal C18 acids and esters.\\u000a \\u000a By careful fractional distillation of methyl esters of alkali-isomerized C18 cottonseed acids, methyl linoleate of 95% or more purity is obtained consisting of 75% conjugated methyl linoleate and some\\u000a 20% of methyl ester of an altered linoleic

  17. Theoretical characterization of dihydrogen adducts with halide anions

    NASA Astrophysics Data System (ADS)

    Vitillo, Jenny G.; Damin, Alessandro; Zecchina, Adriano; Ricchiardi, Gabriele

    2006-06-01

    The interaction between a hydrogen molecule and the halide anions F-, Cl-, Br-, and I- has been studied at different levels of theory and with different basis sets. The most stable configurations of the complexes have a linear geometry, while the t-shaped complexes are saddle points on the potential energy surface, opposite to what is observed for alkali cations. An electrostatic analysis conducted on the resulting adducts has highlighted the predominance of the electrostatic term in the complexation energy and, in particular, of the quadrupole- and dipole-polarizability dependent contributions. Another striking difference with respect to the positive ions, is the fact that although the binding energies have similar values (ranging between 25 and 3kJ/mol for F- and I-, respectively), the vibrational shift of the ?˜H-H and in general the perturbation of the hydrogen molecule in complexes are much greater in the complexes with anions (??˜H-H ranges between -720 and -65cm-1). Another difference with respect to the interaction with cations is a larger charge transfer from the anion to the hydrogen molecule. The ??˜ is the result of the cooperative role of the electrostatics and of the charge transfer in the interaction. The correlation between binding energies and vibrational shift is far from linear, contrary to what is observed for cation complexes, in accordance with the higher polarizability and dynamic polarizability of the molecule along the molecular axis. The observed correlation may be valuable in the interpretation of spectra and thermodynamic properties of adsorbed H2 in storage materials.

  18. 40 CFR 721.10181 - Halide salt of an alkylamine (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...2011-07-01 2011-07-01 false Halide salt of an alkylamine (generic). 721...Chemical Substances § 721.10181 Halide salt of an alkylamine (generic). (a...substance identified generically as halide salt of an alkylamine (PMN...

  19. 40 CFR 721.10181 - Halide salt of an alkylamine (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...2012-07-01 2012-07-01 false Halide salt of an alkylamine (generic). 721...Chemical Substances § 721.10181 Halide salt of an alkylamine (generic). (a...substance identified generically as halide salt of an alkylamine (PMN...

  20. 40 CFR 721.10181 - Halide salt of an alkylamine (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...2010-07-01 2010-07-01 false Halide salt of an alkylamine (generic). 721...Chemical Substances § 721.10181 Halide salt of an alkylamine (generic). (a...substance identified generically as halide salt of an alkylamine (PMN...

  1. EVALUATION OF METHODS FOR THE DETERMINATION OF TOTAL ORGANIC HALIDE IN WATER AND WASTE

    EPA Science Inventory

    Various methods for the determination of total organic halides (TOX) in groundwater and in waste oil samples have been evaluated. Of three inorganic halide species generation approaches and three inorganic halide determinative techniques evaluated for groundwater analyses, one co...

  2. OPTIMAL PARAMETERS OF THE PHOTOCATHODE GUN SPACE CHARGE TO IMPROVE BEAM QUALITY

    E-print Network

    Brookhaven National Laboratory

    OPTIMAL PARAMETERS OF THE PHOTOCATHODE GUN SPACE CHARGE TO IMPROVE BEAM QUALITY M. Fedurin# , C National Laboratory (BNL ATF) operates with 5 MeV photocathode gun and 70 MeV linac for different range to the electron bunch in the gun with space charge affecting on the own bunch length and transverse profile

  3. Studies of TTF RF Photocathode Gun using acoustic sensors J. Nelson and M. Ross

    E-print Network

    1 Studies of TTF RF Photocathode Gun using acoustic sensors J. Nelson and M. Ross SLAC November 27 RF high voltage breakdown locations in the photocathode gun system. It is not known if the acoustic gun [4] to locate its breakdown events during operation with a pulse length of 300µs and a pulse

  4. Experiments on 2D Vortex Patterns in a Malmberg-Penning Trap with a Photocathode

    E-print Network

    Fajans, Joel

    Experiments on 2D Vortex Patterns in a Malmberg-Penning Trap with a Photocathode by Daniel Richard Fall 1998 #12;Experiments on 2D Vortex Patterns in a Malmberg-Penning Trap with a Photocathode Copyright Fall 1998 by Daniel Richard Durkin #12;1 Abstract Experiments on 2D Vortex Patterns in a Malmberg

  5. Technical memo on new results on CsI photocathodes: Enhancement and aging

    SciTech Connect

    Anderson, D.F.; Kwan, S. (Fermi National Accelerator Lab., Batavia, IL (United States)); Hoeneisen, B. (Universidad San Francisco de Quito (Ecuador)); Peskov, V. (European Organization for Nuclear Research, Geneva (Switzerland). World Lab.)

    1991-09-01

    It appears that there are 4 processes involved in the enhancement and aging of a CsI or CsI-TMAE photocathode: water absorption, charging up of the photocathode, a self annealing aging, and a permanent aging. The evidence for these processes are presented. 9 refs., 6 figs.

  6. Development and Characterization of Diamond Film and Compound Metal Surface High Current Photocathodes

    Microsoft Academic Search

    R. P. Shurter; D. C. Moir

    1997-01-01

    High current photocathodes operating in vacuum environments as high as 10-5 torr are being developed at Los Alamos for use in a new generation of linear induction accelerators. We report high quantum efficiencies and high current densities in wide bandgap semiconductor and compound metal surface thermally augmented photocathode materials illuminated by ultraviolet laser radiation.

  7. Research on mechanical vibration impacts of GaAs photocathode photoemission performance

    NASA Astrophysics Data System (ADS)

    Shi, Feng; Cheng, Hong-chang; Bai, Xiao-feng; Yan, Lei

    2015-04-01

    The GaAs photocathode has widely been used in optoelectronic devices such as image intensifiers, photomultiplier tubes, but these devices is inevitable to withstand a variety of mechanical vibration. In order to study the mechanical vibration impact on the photoemission performance of GaAs photocathode, GaAs photocathode image intensifier is researched in this paper. The spectral response of the GaAs photocathode before and after 5~55Hz scan frequency, 14Hz, 33Hz, 52Hz stay frequency, 5?60Hz scan frequency mechanical vibration respectively was tested, then the parameter of photocathode was calculated by MATLAB software according to quantum efficiency formula, the quantum efficiency curve were fitted. The results show that surface escape probability is increased after photocathode is subjected to mechanical vibration, so that its photoemission performance will be improved. We think this phenomenon is due to the GaAs photocathode surface Cs-O reconstruction. This finding provided a new method to enhance the photoemission performance of photocathode.

  8. A pulsed electron injector using a metal photocathode irradiated by an excimer laser

    SciTech Connect

    Kauppila, T.J.; Builta, L.A.; Crutcher, J.K.; Elliott, J.C.; Moir, D.C.

    1987-01-01

    The hot cathode of an electron gun is replaced by a metallic photocathode driven by an excimer laser. The current, current density, and emittance of the 500-kV electron beam produced by the photoelectron source are presented. In addition, the temperature of the photocathode is varied to study the possibility of a hybrid source.

  9. Process and composition for drying of gaseous hydrogen halides

    DOEpatents

    Tom, Glenn M. (New Milford, CT); Brown, Duncan W. (Wilton, CT)

    1989-08-01

    A process for drying a gaseous hydrogen halide of the formula HX, wherein X is selected from the group consisting of bromine, chlorine, fluorine, and iodine, to remove water impurity therefrom, comprising: contacting the water impurity-containing gaseous hydrogen halide with a scavenger including a support having associated therewith one or more members of the group consisting of: (a) an active scavenging moiety selected from one or more members of the group consisting of: (i) metal halide compounds dispersed in the support, of the formula MX.sub.y ; and (ii) metal halide pendant functional groups of the formula -MX.sub.y-1 covalently bonded to the support, wherein M is a y-valent metal, and y is an integer whose value is from 1 to 3; (b) corresponding partially or fully alkylated compounds and/or pendant functional groups, of the metal halide compounds and/or pendant functional groups of (a); wherein the alkylated compounds and/or pendant functional groups, when present, are reactive with the gaseous hydrogen halide to form the corresponding halide compounds and/or pendant functional groups of (a); and M being selected such that the heat of formation, .DELTA.H.sub.f of its hydrated halide, MX.sub.y.(H.sub.2 O).sub.n, is governed by the relationship: .DELTA.H.sub.f .gtoreq.n.times.10.1 kilocalories/mole of such hydrated halide compound wherein n is the number of water molecules bound to the metal halide in the metal halide hydrate. Also disclosed is an appertaining scavenger composition and a contacting apparatus wherein the scavenger is deployed in a bed for contacting with the water impurity-containing gaseous hydrogen halide.

  10. Effects of atomic hydrogen and deuterium exposure on high polarization GaAs photocathodes

    SciTech Connect

    M. Baylac; P. Adderley; J. Brittian; J. Clark; T. Day; J. Grames; J. Hansknecht; M. Poelker; M. Stutzman; A. T. Wu; A. S. Terekhov

    2005-12-01

    Strained-layer GaAs and strained-superlattice GaAs photocathodes are used at Jefferson Laboratory to create high average current beams of highly spin-polarized electrons. High electron yield, or quantum efficiency (QE), is obtained only when the photocathode surface is atomically clean. For years, exposure to atomic hydrogen or deuterium has been the photocathode cleaning technique employed at Jefferson Laboratory. This work demonstrates that atomic hydrogen cleaning is not necessary when precautions are taken to ensure that clean photocathode material from the vendor is not inadvertently dirtied while samples are prepared for installation inside photoemission guns. Moreover, this work demonstrates that QE and beam polarization can be significantly reduced when clean high-polarization photocathode material is exposed to atomic hydrogen from an rf dissociator-style atomic hydrogen source. Surface analysis provides some insight into the mechanisms that degrade QE and polarization due to atomic hydrogen cleaning.

  11. COLOUR CENTRES IN DOPED ALKALI HALIDES. THE ROLE OF OXYGEN AND TITANIUM

    E-print Network

    Paris-Sud XI, Université de

    LiF : Mg : Ti, utilisé dans les dosimètres commerciaux, la concen- tration des impuretés est choisie fonction du défaut complexe [Ti4+, 3 02-]. Abstract. -- In commercial dosimeter material LiF : Mg : Ti ~ 0.02 nm from a normal lattice site. Previously, the degree to which oxygen occurs in LiF : Mg : Ti

  12. The aluminum electrode in AlCl3-alkali-halide melts.

    NASA Technical Reports Server (NTRS)

    Holleck, G. L.; Giner, J.

    1972-01-01

    Passivation phenomena have been observed upon cathodic and anodic polarization of the Al electrode in AlCl3-KCl-NaCl melts between 100 and 160 C. They are caused by formation of a solid salt layer at the electrode surface resulting from concentration changes upon current flow. The anodic limiting currents increased with temperature and with decreasing AlCl3 content of the melt. Current voltage curves obtained on a rotating aluminum disk showed a linear relationship between the anodic limiting current and omega to the minus 1/2 power. Upon cathodic polarization, dendrite formation occurs at the Al electrode. The activation overvoltage in AlCl3-KCl-NaCl was determined by galvanostatic current step methods. An apparent exchange current density of 270 mA/sq cm at 130 C and a double layer capacity of 40 plus or minus 10 microfarad/sq cm were measured.

  13. Elastic properties of alpha quartz and the alkali halides based on an interatomic force model.

    NASA Technical Reports Server (NTRS)

    Weidner, D. J.; Simmons, G.

    1972-01-01

    A two-body central-force atomic model can be used to describe accurately the elastic properties of alpha quartz if the nontetrahedral O:O forces are included. The strength of the Si:O interaction has little effect on the bulk modulus. The technique is sufficiently general to allow calculations of the elastic properties of a specified structure under arbitrary pressure from a complete description of the interatomic forces. The elastic constants for the NaCl structure and the CsCl structure are examined. Our model includes two-body, central, anion-anion, anion-cation, and electrostatic interactions.

  14. Effects of ion beam polishing on alkali halide laser window materials

    Microsoft Academic Search

    J. A. Bruce; J. J. Comer; C. V. Collins; H. G. Lipson

    1975-01-01

    Samples of single crystal KCl, KCl-KBr, and polycrystalline pressure-induced recrystallized KCl were polished using an argon ion beam. The specimens were rotated at a constant rate during bombardment. The angle-of-incidence of the ion beam, the ion current, and the time of sample exposure were varied. After polishing the surfaces of the samples were examined by X-ray topography, scanning electron microscopy,

  15. Shear viscosity of molten alkali halides from equilibrium and nonequilibrium molecular-dynamics simulations.

    PubMed

    Galamba, N; de Castro, C A Nieto; Ely, James F

    2005-06-01

    The shear viscosity of molten NaCl and KCl was calculated through equilibrium (EMD) and nonequilibrium molecular-dynamics (NEMD) simulations in the canonical (N,V,T) ensemble. Two rigid-ion potentials were investigated, namely, the Born-Mayer-Huggins-Tosi-Fumi potential and the Michielsen-Woerlee-Graaf-Ketelaar potential with the parameters proposed by Ladd. The NEMD simulations were performed using the SLLOD equations of motion [D. J. Evans and G. P. Morriss, Phys. Rev. A 30, 1528 (1984)] with a Gaussian isokinetic thermostat and the results are compared with those obtained from Green-Kubo EMD (N,V,T) simulations and experimental shear viscosity data. The NEMD zero strain rate shear viscosity, eta(0), was obtained by fitting a simplified Carreau-type equation and by application of mode-coupling theory, i.e., a eta-gamma(1/2) linear relationship. The values obtained from the first method are found to be significantly lower than those predicted by the second. The agreement between the EMD and NEMD results with experimental data is satisfactory for the two potentials investigated. The ion-ion radial distribution functions obtained with the two rigid-ion potentials for both molten salts are discussed in terms of the differences between the two models. PMID:15974685

  16. Zeeman Effect of the A Absorption Bands in Tl and Pb-Doped Alkali Halides

    Microsoft Academic Search

    Ryumyo Onaka; Teruhiko Mabuchi; Akira Yoshikawa

    1967-01-01

    Zeeman effects of the A absorption bands in KBr:Tl, KI:Tl, KCl:Pb and KBr:Pb are studied by means of circular dichroism, and g-factors of the excited states relevant to these absorption bands are found to be 0.6˜0.8.

  17. Is surface layering of aqueous alkali halides determined by ion pairing in the bulk solution?

    NASA Astrophysics Data System (ADS)

    Brandes, Eva; Stage, Christiane; Motschmann, Hubert; Rieder, Julian; Buchner, Richard

    2014-11-01

    This contribution aims to elucidate the connection between ion-ion-solvent interactions in the bulk of aqueous electrolyte solutions and the properties of their liquid-air interface. In particular, we were interested in the conditions under which ion pairs form at the surface and whether this is linked to ion pairing in the bulk. For this reason different combinations of hard (Cl-, Li+) and soft ions (I-, Cs+) were investigated. Ion hydration and possible ion association in the bulk was probed with dielectric relaxation spectroscopy. This technique monitors the cooperative reorientation of the dipolar solvent molecules and detects all ion-pair species possibly present in the solution. At the interface, the formation of contact ion pairs was investigated by infrared-visible-sum frequency spectroscopy (SFG). This nonlinear optical technique possesses an inherent surface specificity and can be used for the characterization of interfacial water. The intensity of the SFG-active vibrational stretching modes depends on the number of oriented water molecules. The electric field at the surface of a charged aqueous interface aligns the water dipoles, which in turn increases the SFG response. Hence, the enhancement of the oscillator strengths of the water vibrational modes can be used to draw some conclusions on the strengths and geometrical extension of the electric field. The formation of ion pairs at the interface reduces the intensity of the band associated with hydrogen-bonded water. The underlying theory is presented. The combined data show that there are no contact ion pairs in the bulk of the fluid and—at best—only small amounts of solvent shared ion pairs. On the other hand, the combination of hard/hard or soft/soft ions leads to the formation of ion pairs at the liquid-air interface.

  18. IR and visible wavelength obscuration by pyrotechnically generated alkali-halide smokes

    NASA Astrophysics Data System (ADS)

    Hanley, J. T.; Kile, J. N.; Wattle, B. J.; Mack, E. J.

    1983-01-01

    In pursuit of an effective IR wavelength screen and an increased understanding of the particle formation mechanisms and resultant size distribution, this year's efforts focused on two primary objectives: (1) Through a series of chamber tests, assess the visible and IR wavelength extinction characteristics of four recently developed NWC pyrotechnics: LiC1 1, LM9, LM11 and LM12 and (2) Through a series of chamber tests conducted by Calspan with participants from NRL and NWC, investigate the smoke particle size distribution as functions of pyrotechnic and associated burn parameters.

  19. Thermal conductivity of molten alkali halides from equilibrium molecular dynamics simulations.

    PubMed

    Galamba, N; Nieto de Castro, C A; Ely, J F

    2004-05-01

    The thermal conductivity of molten sodium chloride and potassium chloride has been computed through equilibrium molecular dynamics Green-Kubo simulations in the microcanonical ensemble (N,V,E). In order to access the temperature dependence of the thermal conductivity coefficient of these materials, the simulations were performed at five different state points. The form of the microscopic energy flux for ionic systems whose Coulombic interactions are calculated through the Ewald method is discussed in detail and an efficient formula is used by analogy with the methods used to evaluate the stress tensor in Coulombic systems. The results show that the Born-Mayer-Huggins-Tosi-Fumi potential predicts a weak negative temperature dependence for the thermal conductivity of NaCl and KCl. The simulation results are in agreement with part of the experimental data available in the literature with simulation values generally overpredicting the thermal conductivity by 10%-20%. PMID:15267797

  20. First-principles study of the rocksalt-cesium chloride relative phase stability in alkali halides

    NASA Astrophysics Data System (ADS)

    Flórez, M.; Recio, J. M.; Francisco, E.; Blanco, M. A.; Pendás, A. Martín

    2002-10-01

    We present a detailed investigation of observable properties associated with the relative stability of the rocksalt (B1) and cesium chloride (B2) phases in the AX (A=Li, Na, K, Rb, Cs; X=F, Cl, Br, I) crystal family. Thermodynamic B1-->B2 transition pressures and ?Y=Y(B2)-Y(B1) differences in total energies, volumes, and bulk moduli at zero and transition pressures are computed following a localized Hartree-Fock method. The arrangement of the data in clear trends is shown to be mainly dominated by the cation atomic number. This behavior is well interpreted in terms of a variety of microscopic arguments that emerge from (i) the evaluation of the energy Hessian at the B1 and B2 points and (ii) the decomposition of the energy and pressure in anionic and cationic classical and quantum-mechanical contributions.

  1. Solvation thermodynamics of alkali and halide ions in ionic liquids through integral equations

    NASA Astrophysics Data System (ADS)

    Bruzzone, Samantha; Malvaldi, Marco; Chiappe, Cinzia

    2008-08-01

    In this work, we study the solvation thermodynamics and other solvation properties of small ions in two room-temperature ionic liquids, dimethyl imidazolium hexafluorophosphate [mmim] [pf6] and dimethyl imidazolium chloride [mmim][cl] with the reference interaction site model (RISM). The nature of the charge affects several aspects of solvation, from electrostriction to the mutual disposition of cations around the solute; nevertheless, the long-range screening behavior of the liquid appears to be insensitive to both charge and dimensions of the solute. The ion solvation is energy driven, as expected for the nature of the solvent, and displays a marked asymmetry between cation and anion solvation chemical potential. Such asymmetry is dependent, even qualitatively, on the ionic liquid chosen as solvent. Partial molar volumes of ions in solution are found to follow the nature of ion-solvent interaction.

  2. Non-melting and self-wetting of alkali halide surfaces at high temperatures

    NASA Astrophysics Data System (ADS)

    Ceresoli, Davide; Zykova-Timan, Tania; Tartaglino, Ugo; Sekkal, Wassila; Jagla, Edoardo; Tosatti, Erio

    2004-03-01

    We investigated theoretically the high temperature thermodynamic properties and the (lack of) self-wetting of ionic crystal surfaces, with NaCl(100) as a prototype case. We found by classical molecular dynamics simulations that NaCl(100) is a non-melting crystal surface and can be overheated to a spinodal temperature TS 150 K above the bulk melting temperature (T_M). While surface non-melting is in itself well known, and is observed on semiconductors as well as on close packed metal surfaces, the basic mechanism for NaCl appears to be different from either of them. Moreover, there appear to be two distinct metastability regimes of solid NaCl(100) above T_M. The first regime TM < T < T_1, (T1 - TM = 60 K) the metastable solid surface is strongly protected by a nucleation barrier of large thickness. This thickness decreases with temperature, until it drops to a lattice spacing a at T_1. In the second regime T1 < T < TS is characterized by a ``fragile'' metastability, with a nucleation barrier one lattice spacing thick. Here, the smallest seed is able to cause melting, i.e., it is enough to melt the first monolayer for the liquid to break through and melt the whole system. A basic explanation of these facts and of the two regimes is given, based on a short-range oscillatory interaction between the solid-liquid and the liquid-vapor interfaces. In addition, we also simulated a liquid NaCl nanodroplet, deposited on a solid NaCl surface in the vicinity of the bulk melting point. The anomalously large contact angle measured long ago by Mutaftschiev [1] is well reproduced by this realistic molecular dynamics droplet simulation. Based on these results, and on independent determinations of the liquid-vapor (?_LV) and the solid-vapor interface free energy (?_SV) an estimate of the solid-liquid interface free energy (?_SL) is extracted. The solid-vapor surface free energy turns out to be anomalously small and similar to the liquid-vapor one, providing a direct thermodynamic explanation of the reduced wetting ability of the ionic melt. G. Grange and B. Mutaftschiev, Surf. Sci. 47, 723 (1975).

  3. Second Order Elastic Constants and Some Thermoelastic Properties of Alkali Halides Using WOODCOCK Potential

    NASA Astrophysics Data System (ADS)

    Yazar, Harun Reþýt; Aðan, Sedat; Çolakoðlu, Kemal

    2001-07-01

    Second Order Elastic Constants (S.O.E.C) of NaCl-type crystals have been calculated using the Woodcock potential. Short-range repulsive interactions have been included up to second-nearest neighbors. This potential form represents the composite form of the inverse power dependence and exponential dependence of the repulsive energy on interionic distance. Some thermoelastic and thermodynamic properties such as Anderson-Grüneisen parameters d T, and d S, Volume thermal expansion coefficient b and Grüneisen gama g G have been calculated in terms of calculated values of S.O.E.C and Third Order Elastic Constant ( T.O.E.C).

  4. A structural study of saturated aqueous solutions of some alkali halides by X-ray diffraction

    Microsoft Academic Search

    Hitoshi Ohtaki; Nobuhiro Fukushima

    1992-01-01

    The structure of nearly saturated or supersaturated aqueous solutions of NaCI [6.18 mol (kg H2O)-1], KCI [4.56 mol (kg H2O)-1], KF [16.15 mol (kg H2O)-1] and CsF [31.96 mol (kg H2O)-1] has been investigated by means of solution X-ray diffraction at 25°C. In the NaCI and KCI solutions about 30% and 60%, respectively, of the ions form ion pairs and

  5. External field enhanced photoemission in silver-cesium-oxygen photocathodes.

    PubMed

    Burroughs, E G

    1969-02-01

    Reduction in the surface barrier of silver-cesium-oxygen photocathodes by the application of high external electric fields has been demonstrated by the extension of the photoelectric threshold. Photocurrent for selected wavelengths as a function of field strength have been fitted to Schottky plots; however, the observed shifts in photoelectric threshold are not consistent with this theory. Photoyield increases near threshold of five times have been observed for fields of 10(4) V/cm. In addition, data of thermionic emission as a function of photoelectric threshold and cathode temperature are presented along with a discussion of these parameters and their effect on optimum signal-to-noise ratio. PMID:20072211

  6. Characterization of quantum well structures using a photocathode electron microscope

    NASA Technical Reports Server (NTRS)

    Spencer, Michael G.; Scott, Craig J.

    1989-01-01

    Present day integrated circuits pose a challenge to conventional electronic and mechanical test methods. Feature sizes in the submicron and nanometric regime require radical approaches in order to facilitate electrical contact to circuits and devices being tested. In addition, microwave operating frequencies require careful attention to distributed effects when considering the electrical signal paths within and external to the device under test. An alternative testing approach which combines the best of electrical and optical time domain testing is presented, namely photocathode electron microscope quantitative voltage contrast (PEMQVC).

  7. Laser Development for Future Photocathode Research at SLAC

    SciTech Connect

    Brachmann, A.; Cone, K.; Clendenin, J.E.; Garwin, E.L.; Kirby, R.E.; Luh, D.-A.; Maruyama, T.; Prepost, R.; Prescott, C.Y.; /SLAC

    2005-07-27

    This report summarizes results of recent upgrades to SLAC's polarized source drive laser system. A Q-switching system has been incorporated into the flashlamp-pumped Ti:Sapphire laser system. The Q-switched laser provides energies up to 5 mJ for a 200 ns long pulse. Slow Q-switching provides control over length and shape of the laser pulse. A peak current of > 5.5 A has been demonstrated using a GaAs photocathode illuminated by this laser system.

  8. Thermal emittance and response time of a cesium antimonide photocathode

    NASA Astrophysics Data System (ADS)

    Cultrera, Luca; Bazarov, Ivan; Bartnik, Adam; Dunham, Bruce; Karkare, Siddharth; Merluzzi, Richard; Nichols, Matthew

    2011-10-01

    Measurements of the intrinsic emittance and response time of a Cs3Sb photocathode are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. Photoemission response time is evaluated using a RF deflecting cavity synchronized to a picosecond laser pulse train. We find that Cs3Sb has both small mean transverse energy, 160 ± 10 meV at 532 nm laser wavelength, and a prompt response time (below the resolution of our measurement) making it a suitable material for high brightness electron photoinjectors.

  9. A new chemical analysis system using a photocathode RF gun

    NASA Astrophysics Data System (ADS)

    Aoki, Yasushi; Yang, Jinfeng; Hirose, Masafumi; Sakai, Fumio; Tsunemi, Akira; Yorozu, Masafumi; Okada, Yasuhiro; Endo, Akira; Wang, Xijie; Ben-Zvi, Ilan

    2000-11-01

    A compact chemical analysis (pulse radiolysis) apparatus using a BNL-type s-band photocathode RF gun (GUN-IV) is now under development at Sumitomo Heavy Industries (SHI). Using the apparatus, fast chemical reactions induced by 3.5 ps pulse of electron beam can be analyzed by means of time-resolved photo-absorption spectroscopy with 10 ps laser pulses in the wavelength range of 210-2000 nm. The high-precision control of RF phase makes 10 ps of time-resolution possible for the analysis.

  10. Polarization and charge limit studies of strained GaAs photocathodes

    SciTech Connect

    Saez, P.J.

    1997-03-01

    This thesis presents studies on the polarization and charge limit behavior of electron beams produced by strained GaAs photocathodes. These photocathodes are the source of high-intensity, high-polarization electron beams used for a variety of high-energy physics experiments at the Stanford Linear Accelerator Center. Recent developments on P-type, biaxially-strained GaAs photocathodes have produced longitudinal polarization in excess of 80% while yielding beam intensities of {approximately} 2.5 A/cm{sup 2} at an operating voltage of 120 kV. The SLAC Gun Test Laboratory, which has a replica of the SLAC injector, was upgraded with a Mott polarimeter to study the polarization properties of photocathodes operating in a high-voltage DC gun. Both the maximum beam polarization and the maximum charge obtainable from these photocathodes have shown a strong dependence on the wavelength of illumination, on the doping concentration, and on the negative electron affinity levels. The experiments performed for this thesis included studying the effects of temperature, cesiation, quantum efficiency, and laser intensity on the polarization of high-intensity beams. It was found that, although low temperatures have been shown to reduce the spin relaxation rate in bulk semiconductors, they don`t have a large impact on the polarization of thin photocathodes. It seems that the short active region in thin photocathodes does not allow spin relaxation mechanisms enough time to cause depolarization. Previous observations that lower QE areas on the photocathode yield higher polarization beams were confirmed. In addition, high-intensity, small-area laser pulses were shown to produce lower polarization beams. Based on these results, together with some findings in the existing literature, a new proposal for a high-intensity, high-polarization photocathode is given. It is hoped that the results of this thesis will promote further investigation on the properties of GaAs photocathodes.

  11. Characteristic of photocurrent decline of transmission-mode equally doped GaAs photocathode

    NASA Astrophysics Data System (ADS)

    Zhang, Dong Lian; Shi, Feng; Gao, Xiang; Cheng, Hong-Chang; Miao, Zhuang; Niu, Sen; Wang, Long; Chen, Chang

    2014-09-01

    Photocurrent of GaAs photocathode activated with Cs and O was tested by auto-activation monitor, the fitting curves of photocurrent showed that the photocurrent of the photocathode after the first activation declines exponentially, and then declines linearly with very small slope |k1|; the photocurrent after the second activation rises exponentially, and then declines linearly with a slope|k2| which is a bit larger than |k1|.Based on the mechanism difference between twice annealing of the photocathode, the degeneration behavior of the photocathode was analyzed by three-dipoles model and XPS test after the first activation and succedent thermal cleaning. It is indicated that Cs2O dipoles on the surface are saturated after the photocathode was activated for the first time, the remained Cs and Cs2O in the ultra-high vacuum chamber which deposited on the photocathode surface will prevent the emission of photoelectrons. The photocathode surface with Cs and O reconstructed when it was annealing for the second time, a lot of Cs2O dipoles changed into more stable GaAs-O-Cs dipoles, and this phenomenon would happened immediately as soon as the photocathode was activating for the second time. After the residual Cs and Cs2O dipoles depleted, the neutral gas CO2, H2O, O2, damaging the surface dipoles layer, are the main factors resulted in the decline of photocurrent. Due to the instable Cs2O dipoles on the surface of photocathode have greater chances of converting into stable GaAs-O-Cs dipoles when photocathode was activated for the first time, the photocurrent declines more slowly compared with the second activation. The discussion for the phenomenon is of great significance for exploring the photoemission mechanism of ?-? semiconductors.

  12. Alkali metal cluster theory

    SciTech Connect

    Chen, J.

    1990-01-01

    The tight-binding Hubbard model has been applied to alkali metal clusters with Hartree-Fock self-consistent methods and perturbation methods for the numerical calculations. The relaxation has been studied between the equilibrium structures and the range of the hopping matrix elements in the Hubbard Hamiltonian. The structures are not sensitive to the interaction range but are determined by the number of valence electrons each atom has. Inertia tensors are used to analyze the symmetries of the clusters. The principal axes of the clusters are determined to be the axes of rotational symmetries of clusters if the clusters have any. The eigenvalues of inertia tensors are compared between this model and the ellipsoidal jellium model. The agreement is good for large clusters. At a finite temperature, the thermal motion fluctuates the structures. A fluctuation function has been defined with the distance matrix of a cluster. The fluctuation has been studied with the Monte Carlo simulation method. Energy levels of clusters are calculated from the Hubbard model. Ionization potentials and magic numbers are also obtained from these energy levels. The results confirm that the Hubbard model is a good approximation for a small cluster. The excitation energy is presented by the difference between the original level and excited level, and the electron-hole interactions. The author also studied cooling of clusters between the nozzle and detector in molecular beam apparatus with three cooling mechanisms, adiabatic expansion, photon emission and cluster decay. The adiabatic expansion and the photon emission do not affect mass abundances of clusters. The studies show that cluster decay cooling produces a shift in the mass spectra. The shift is dependent on the temperature of the beam and increases as the temperature increases.

  13. Large charge extraction from metallic multifilamentary Nb3Sn photocathode.

    PubMed

    Anghel, A; Ardana-Lamas, F; Le Pimpec, F; Hauri, C P

    2012-05-11

    The current density limit for photoemission from metals was measured in an rf photogun to be below 10(9)??A/m2. We have achieved 1.6×10(11)??A/m2 by photofield emission from a new type of photocathode made from a metallic-composite, multifilamentary Nb3Sn wire driven by a 266 nm picosecond laser pulse and a 2 ns, 50 kV accelerating voltage. This cathode has a micrometer arrayed structure with tens of thousands of Nb/Nb3Sn filaments embedded in a bronze matrix. Our measurements revealed the existence of a new electron emission regime at high laser fluence (100??mJ/cm2). We have extracted stably, and without any surface ablation, up to 4800 pC of charge. This corresponds to 0.9% quantum efficiency, 100 times larger than what is measured from conventional metallic photocathodes. The unexpected large and stable charge extraction cannot be explained by the 3-step model. Thanks to the small emitting area, the measured emittance (0.6??mm·mrad) is low in spite of the high current density and space charge effects. This cathode will be of benefit for many applications based on short and bright electron bunches. PMID:23003048

  14. AlGaN/InGaN Photocathode Development

    NASA Astrophysics Data System (ADS)

    Buckley, J. H.; Leopold, D. J.

    2008-12-01

    An increase in quantum efficiency in photodetectors could result in a proportional reduction in the area of atmospheric Cherenkov telescopes and an even larger reduction in cost. We report on the development of high quantum efficiency, high gain, UV/blue photon-counting detectors based on AlGaN/InGaN photocathode heterostructures grown by molecular beam epitaxy. This research could eventually result in nearly ideal light detectors with a number of distinct advantages over existing technologies for numerous applications in high-energy physics and particle astrophysics. Potential advantages include much lower noise detection, better stability and radiation resistance than other cathode structures, high VUV sensitivity and very low radioactive background levels for deep underground experiments, and high detection efficiency for the detection of individual VUV-visible photons. We are also developing photocathodes with intrinsic gain, initially improving the detection efficiency of hybrid semiconductor-vacuum tube devices and eventually leading to a new type of all-solid-state photomultiplier device.

  15. Surface Science Analysis of GaAs Photocathodes Following Sustained Electron Beam Delivery

    SciTech Connect

    Shutthanandan, V.; Zhu, Zihua; Stutzman, Marcy L.; Hannon, Fay; Hernandez-Garcia, Carlos; Nandasiri, Manjula I.; Kuchibhatla, Satyanarayana V N T; Thevuthasan, Suntharampillai; Hess, Wayne P.

    2012-06-12

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Several photocathode degradation processes are suspected, including defect formation by ion back bombardment, photochemistry of surface adsorbed species and irradiation-induced surface defect formation. To better understand the mechanisms of photocathode degradation, we have conducted surface and bulk analysis studies of two GaAs photocathodes removed from the FEL photoinjector after delivering electron beam for a few years. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, strained super-lattice GaAs photocathode samples, removed from the CEBAF photoinjector were analyzed using Transmission Electron Microscopy (TEM) and SIMS. This analysis of photocathode degradation during nominal photoinjector operating conditions represents first steps towards developing robust new photocathode designs necessary for generating sub-micron emittance electron beams required for both fourth generation light sources and intense polarized CW electron beams for nuclear and high energy physics facilities.

  16. Electrolytic method to make alkali alcoholates using ion conducting alkali electrolyte/separator

    DOEpatents

    Joshi, Ashok V. (Salt Lake City, UT); Balagopal, Shekar (Sandy, UT); Pendelton, Justin (Salt Lake City, UT)

    2011-12-13

    Alkali alcoholates, also called alkali alkoxides, are produced from alkali metal salt solutions and alcohol using a three-compartment electrolytic cell. The electrolytic cell includes an anolyte compartment configured with an anode, a buffer compartment, and a catholyte compartment configured with a cathode. An alkali ion conducting solid electrolyte configured to selectively transport alkali ions is positioned between the anolyte compartment and the buffer compartment. An alkali ion permeable separator is positioned between the buffer compartment and the catholyte compartment. The catholyte solution may include an alkali alcoholate and alcohol. The anolyte solution may include at least one alkali salt. The buffer compartment solution may include a soluble alkali salt and an alkali alcoholate in alcohol.

  17. Developments in Alkali-Metal Atomic Magnetometry

    E-print Network

    Romalis, Mike

    Developments in Alkali-Metal Atomic Magnetometry Scott Jeffrey Seltzer A DISSERTATION PRESENTED by Scott Jeffrey Seltzer. All rights reserved. #12;Abstract Alkali-metal magnetometers use the coherent physics research. In this thesis we discuss several developments in alkali-metal atomic magnetometry

  18. Modified model of alkali-silica reaction

    Microsoft Academic Search

    Tsuneki Ichikawa; Masazumi Miura

    2007-01-01

    Experimental studies have been carried out for understanding why soft and fluid hydrated alkali silicate generated by the alkali–silica reaction (ASR) of aggregate with alkaline pore solution accumulates the expansive pressure for cracking the aggregate and the surrounding concrete. The elemental analysis of aggregate (andesite) embedded in a cement paste has revealed that the alkali silicate has no ability of

  19. Photocathode non-uniformity contribution to the energy resolution of scintillators.

    PubMed

    Mottaghian, M; Koohi-Fayegh, R; Ghal-Eh, N; Etaati, G R

    2010-06-01

    This paper introduces the basics of the light transport simulation in scintillators and the wavelength-dependencies in the process. The non-uniformity measurement of the photocathode surface is undertaken, showing that for the photocathode used in this study the quantum efficiency falls to about 4 % of its maximum value, especially in areas far from the centre. The wavelength- and position-dependent quantum efficiency is implemented in the Monte Carlo light transport code, showing that, the contribution of the photocathode non-uniformity to the energy resolution is estimated to be around 18 %, when all position- and wavelength-dependencies are included. PMID:20167795

  20. Properties of CsI and CsI-TMAE photocathodes

    SciTech Connect

    Anderson, D.F.; Kwan, S.; Peskov, V. [Fermi National Accelerator Lab., Batavia, IL (United States); Hoeneisen, B. [Universidad San Francisco de Quito (Ecuador)

    1992-06-01

    The importance of heating the CsI or CsI-TMAE photocathodes during preparation, as well as the importance of the gas environment on the quantum efficiency is presented. The dependence of the aging characteristics of these photocathodes on the operating temperature, on the presence of gas, and on the charge amplification of the chamber is also discussed. For CsI photocathodes charges in excess of 2{times}10{sup 14} e{sup {minus}}/mm{sup 2} can be collected with little degradation of performance. A timing resolution of 0.55 ns is also achieved for single photoelectrons suggesting a possible time-of-flight detector.

  1. The effects of electromagnetic space-charge fields in RF photocathode guns

    NASA Astrophysics Data System (ADS)

    Park, C. S.; Hess, M.

    2010-04-01

    In high-brightness rf photocathode guns, the effects of space-charge are important for electron bunches with high bunch charge. In an effort to accurately simulate the effects of these space-charge fields without the presence of numerical grid dispersion, a Green's function based code called IRPSS (Indiana Rf Photocathode Source Simulator) was developed. In this paper, we show the results of numerical simulations of the Argonne Wakefield Accelerator photocathode gun using IRPSS, and compare them with the results of an electrostatic Green's function version of IRPSS.

  2. A novel system for measurement of the transverse electron momentum distribution from photocathodes.

    PubMed

    Feng, J; Nasiatka, J; Wan, W; Vecchione, T; Padmore, H A

    2015-01-01

    The transverse momentum of electrons produced by a photocathode contributes significantly to the performance of several different types of accelerator-based light sources, such as Free Electron Lasers, as well as systems designed for ultrafast electron diffraction and dynamic transmission electron microscopy. Minimization of the transverse emittance from photocathodes is the subject of intensive research, and therefore measurement of this parameter is of great importance. Here, we describe a simple system that offers real time measurements of transverse emittance and can be easily integrated into the photocathode fabrication process. PMID:25638118

  3. N-Alkylation of Unsymmetrical 1,6Dihydro1,2,4,5-tetrazine Under Alkali Condition

    Microsoft Academic Search

    Feng Xu; Zhen-Zhen Yang; Shi-Jie Zhang; Wei-Xiao Hu

    2011-01-01

    6-Methyl-3-phenyl-1,6-dihydro-1,2,4,5-tetrazine was stable in alkali solution at room temperature and decomposed gradually to form 1,2-dibenzylidenehydrazine. The plausible mechanism of the reaction is discussed. Because it was stable for a period of time, a convenient and effective method for synthesis of 1-alkyl-1,6-dihydro-1,2,4,5-tetrazines has been developed. The starting 1,6-dihydro-1,2,4,5-tetrazine can be alkylated with alkyl halides in methanol and lithium hydroxide monohydrate as

  4. Halide ion-mediated growth of single crystalline Fe nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhang, Sen; Jiang, Guangming; Filsinger, Gabriel T.; Wu, Liheng; Zhu, Huiyuan; Lee, Jonghun; Wu, Zhongbiao; Sun, Shouheng

    2014-04-01

    We report a facile halide ion (Cl- or Br-) mediated synthesis of Fe nanoparticles (NPs) by thermal decomposition of Fe(CO)5. The NP structure is controlled to be either amorphous (in the absence of halide ions) or single crystalline bcc (in the presence of halide ions). Through systematic investigation on the synthetic conditions, we have confirmed that the formation of bcc-Fe NPs is facilitated by the strong interactions between halide ions and Fe, which favor thermodynamic growth of Fe over the existing Fe NPs. Compared with the amorphous Fe NPs, the bcc-Fe NPs exhibit much enhanced magnetization values and chemical stability. This halide ion mediated growth may become a general strategy to control the growth of metallic NPs, especially first-row transition metal NPs, in a thermodynamically more stable way, producing single crystalline NPs with much controlled physical and chemical properties for magnetic and catalytic applications.We report a facile halide ion (Cl- or Br-) mediated synthesis of Fe nanoparticles (NPs) by thermal decomposition of Fe(CO)5. The NP structure is controlled to be either amorphous (in the absence of halide ions) or single crystalline bcc (in the presence of halide ions). Through systematic investigation on the synthetic conditions, we have confirmed that the formation of bcc-Fe NPs is facilitated by the strong interactions between halide ions and Fe, which favor thermodynamic growth of Fe over the existing Fe NPs. Compared with the amorphous Fe NPs, the bcc-Fe NPs exhibit much enhanced magnetization values and chemical stability. This halide ion mediated growth may become a general strategy to control the growth of metallic NPs, especially first-row transition metal NPs, in a thermodynamically more stable way, producing single crystalline NPs with much controlled physical and chemical properties for magnetic and catalytic applications. Electronic supplementary information (ESI) available: Table S1 and Fig. S1-3. See DOI: 10.1039/c4nr00193a

  5. Improved processing for silver halide pulse holography

    NASA Astrophysics Data System (ADS)

    Mikhailov, Viktor N.; Son, Jung-Young; Grinevitskaya, Olga V.; Lee, Hyuk-Soo; Choi, Yong-Jin

    1996-04-01

    Using of an improved developer with optical latensification allowed to significantly increase exposure sensitivity of currently in use silver halide materials. Transmission large-scale holograms (30 X 40 cm2) of diffused objects have been recorded under pulse exposure of about 6.5 X 10-6 J/cm2 for VRP and of about 2 X 10-6 J/cm2 for Agfa-Gavaert 8E56HD, in both cases without appreciable contrast deterioration. Results of the first experiments on pulse reflection holography are also discussed.

  6. The Vapor Pressure of Plutonium Halides

    Microsoft Academic Search

    T. E. Phipps; G. W. Sears; R. L. Seifert; O. C. Simpson

    1950-01-01

    Vapor pressure measurements have been made with three halides of plutonium by a modification of the Knudsen effusion method. Measurements with solid plutonium trifluoride from 1200°K to 1440°K give the vapor pressure-temperature relation log10pmm=12.468–21,120\\/T. Measurements with liquid plutonium trifluoride from 1440°K to 1770°K give log10pmm=11.273–19,400\\/T. Measurements with solid plutonium trichloride from 850°K to 1007°K give log10pmm=12.726–15,910\\/T; with liquid trichloride from

  7. Self-activity in lanthanum halides

    Microsoft Academic Search

    W. J. Kernan

    2006-01-01

    Scintillators fabricated from lanthanum halides, specifically cerium-activated lanthanum bromide (LaBr3 [Ce]) and lanthanum chloride (LaCl3 [Ce]), have been shown to exhibit energy resolution far superior to that for thallium-activated sodium iodide. The high resolution, high Z, and high density (LaBr3 5.29 g\\/cm3 and LaCl3 3.79 g\\/cm3) of these materials hold out the prospect of use for building superior room-temperature, hand-held

  8. Alkali-activated fly ashes

    Microsoft Academic Search

    A. Palomo; M. W. Grutzeck; M. T. Blanco

    1999-01-01

    The alkali activation of waste materials (especially those coming from industrial and mining activities) has become an important area of research in many laboratories because it is possible to use these materials to synthesize inexpensive and ecologically sound cementlike construction materials. In the present paper, the mechanism of activation of a fly ash (no other solid material was used) with

  9. Progress in alkali lasers development

    Microsoft Academic Search

    B. V. Zhdanov; R. J. Knize

    2008-01-01

    Diode pumped alkali vapor lasers developed during the last several years have the potential to achieve high power. Efficient operation of Rubidium, Cesium and Potassium lasers has been demonstrated. Laser slope efficiencies higher than 80% have been achieved. A diode laser pumping can provide high overall efficiency of these devices. A diode pumped continuous wave 10 W Cs laser and

  10. Atomic hydrogen cleaning of GaAS Photocathodes

    SciTech Connect

    M. Poelker; J. Price; C. Sinclair

    1997-01-01

    It is well known that surface contaminants on semiconductors can be removed when samples are exposed to atomic hydrogen. Atomic H reacts with oxides and carbides on the surface, forming compounds that are liberated and subsequently pumped away. Experiments at Jefferson lab with bulk GaAs in a low-voltage ultra-high vacuum H cleaning chamber have resulted in the production of photocathodes with high photoelectron yield (i.e., quantum efficiency) and long lifetime. A small, portable H cleaning apparatus also has been constructed to successfully clean GaAs samples that are later removed from the vacuum apparatus, transported through air and installed in a high-voltage laser-driven spin-polarized electron source. These results indicate that this method is a versatile and robust alternative to conventional wet chemical etching procedures usually employed to clean bulk GaAs.

  11. Silicon based tandem cells: novel photocathodes for hydrogen production.

    PubMed

    Calvet, W; Murugasen, E; Klett, J; Kaiser, B; Jaegermann, W; Finger, F; Hoch, S; Blug, M; Busse, J

    2014-06-28

    A photovoltaic tandem cell made of amorphous silicon (a-Si) and microcrystalline silicon (?c-Si) was investigated as a photocathode for hydrogen evolution in a photoelectrochemical device. The electronic and electrochemical properties of the samples were characterized using X-ray photoemission spectroscopy (XPS) and cyclic voltammetry (CV), whereas the morphology of the surface in contact with the electrolyte was investigated by scanning electron microscopy (SEM). The electric efficiency of the tandem cell was determined to be 5.2% in a photoelectrochemical (PEC) setup in acidic solution which is only about half of the photovoltaic efficiency of the tandem cell. A significant improvement in efficiency was achieved with platinum as a catalyst which was deposited by physical vapour deposition (PVD) under ultra-high vacuum (UHV) conditions. PMID:24710175

  12. Evaluation of chemical cleaning for Ga1-xAlxAs photocathode by spectral response

    NASA Astrophysics Data System (ADS)

    Chen, Xinlong; Chang, Benkang; Zhao, Jing; Hao, Guanghui; Jin, Muchun; Xu, Yuan

    2013-11-01

    The spectral response has been used to evaluate the chemical cleaning for Ga1-xAlxAs photocathode by an on-line spectral response measurement system. The spectral response curves of Ga1-xAlxAs photocathodes treated by different chemical cleaning methods are measured and analyzed in detail. We use the quantum efficiency formulas to fit the experimental curves transforming from the spectral response curves, and obtain the related performance parameters such as the surface electron escape probability, the back-interface recombination velocity, the electron diffusion length, and the thickness of the etching GaAs layer. The results show that the GaAs photocathode cleaned by the HF solution could obtain a good photoemission effect, while the Ga0.37Al0.63As photocathode could be well cleaned by the solution of sulfuric acid and hydrogen peroxide.

  13. Progress in the production of CsI and diamond thin film photocathodes

    Microsoft Academic Search

    M. A. Nitti; E. Nappi; A. Valentini; F. Bénédic; P. Bruno; G. Cicala

    2005-01-01

    The comparison between the quantum efficiency of photocathodes coated with thin CsI films obtained by thermal evaporation and, for the first time, by Ar ion-beam sputtering is reported. The sensitivity of photocathodes has been found to be strongly dependent on the morphology and roughness of the evaporated and sputtered CsI films. The effect of surface roughness on four different substrates

  14. Study of the THGEM detector with a reflective CsI photocathode

    NASA Astrophysics Data System (ADS)

    Liu, Hong-Bang; Zheng, Yang-Heng; Xie, Yi-Gang; Lu, Jun-Guang; Zhou, Li; Yu, Bo-Xiang; Zhang, Ai-Wu; An, Zheng-Hua; Xie, Yu-Guang; Zhang, Dong; Zheng, Zhi-Peng

    2011-04-01

    The THGEM detector without and with a CsI has been tested successfully. The optimal parameters of THGEM have been determined from eight samples. The UV photoelectric effect of the CsI photocathode is observed. The changing tendency related to the extraction efficiency (?extr) versus the extraction electric field is measured, and several electric fields influencing the anode current are adjusted to adapt to the THGEM detector with a reflective CsI photocathode.

  15. High Performance AlInGaAs/AlGaAs Photocathode

    SciTech Connect

    Mamaev, Yu. A.; Gerchikov, L. G.; Yashin, Yu. P.; Vasiliev, D. A.; Kuzmichev, V. V. [State Polytechnic University, 195251, St. Petersburg (Russian Federation); Ustinov, V. M.; Zhukov, A. E. [St. Petersburg Scientific-Educational Center RAS, 195251, St. Petersburg (Russian Federation); Mikhrin, V. S. [Ioffe Physico-Technical Institute, RAS, 194021, St. Petersburg (Russian Federation)

    2008-02-06

    New photocathode for highly polarized electron emission has been developed, fabricated and studied. Polarized electron source is based on short-period strained AlInGaAs/AlGaAs superlattice grown by MBE method. Deformation of AlInGaAs quantum well results in 85 meV energy splitting between heavy hole and light hole minibands. Electron emission from the developed photocathode demonstrates maximal polarization of 92% with quantum efficiency of 0.85%.

  16. Alkali and alkali-earth ions in 4He systems

    NASA Astrophysics Data System (ADS)

    Rossi, M.; Verona, M.; Galli, D. E.; Reatto, L.

    2004-06-01

    We study with variational Monte Carlo simulations a single ion impurity in nanodroplets and in liquid 4He . Within the shadow wave function (SWF) approach we have studied alkali-earth ion doped 4He systems ( Be+ and Mg+ ) and we have also improved our previous variational results for alkali ion impurities ( Na+ , K+ , and Cs+ ). The new SWF allows for anisotropic correlations between 4He atoms and the ion. The first shell of 4He atoms around the ions has always a well defined solidlike structure, which is remarkably different for each ion but it does not depend on the 4He system (bulk liquid or cluster). We also give results for the chemical potential, the single particle excitation spectrum, and the effective mass of the ions in the bulk.

  17. Optical Design Considerations Relevant to Reflective UV Launch Gratings for Photocathode Irradiation

    SciTech Connect

    Bolton, Paul

    2010-12-07

    The characteristics of photoelectron microbunches emitted from a photocathode in response to laser irradiation determine many of the incident laser pulse requirements. RF photocathode designs based on grazing incidence of the irradiation benefit from the removal of launch optics from the electron beamline and enhanced absorption at Brewster angles. However, this also introduces two well known complexities in the laser pulse 'launch' requirements: (i) a transverse spatial anamorphism to guarantee that the projected transverse spatial profile of the irradiation is circular (in the plane of the photocathode) and (ii) a 'time slew' or tilted amplitude front on the laser pulse that is incident on the photocathode to guarantee that the temporal (longitudinal) profiles are synchronous across the entire transverse irradiation profile in the photocathode plane. A single diffraction grating can be used to fulfill these combined requirements. This reported work focuses on grating behavior only. It does not address imaging requirements associated with relayed optical transport from the grating to the photocathode. Because the grating is a highly dispersive optical element by design, the dispersive aspects of all launch requirements are important.

  18. Stereoselective glycosylations using benzoylated glucosyl halides with inexpensive promoters.

    PubMed

    Murakami, Teiichi; Sato, Yukari; Shibakami, Motonari

    2008-06-01

    Reactions of O-benzoylated glucopyranosyl halide (I, Br), isolated or generated in situ from per-benzoylated glucose (8a) and trimethylsilyl halide, with various alcohols were efficiently promoted by zinc halide (Cl, Br) or N-bromosuccinimide with a catalytic ZnI(2) to give the corresponding 1,2-trans-beta-glucosides in good to high yields. When the anomeric halogenation of 8a was carried out in the presence of reactive alcohols, 1,2-cis-alpha-glucosides were selectively formed. PMID:18406402

  19. Adsorption of ions on semiconductor surfaces. I. Silver and halide ions on silver halides

    NASA Astrophysics Data System (ADS)

    Zeiri, Y.; Tenne, R.; Shapiro, Moshe

    1984-05-01

    Interaction potentials of silver and halide ions adsorbed on the surfaces of silver halides crystals are calculated. The adsorption of such ions leads to a redistribution of charges at the interface between the semiconductor and an electrolyte (emulsion) containing such ions. This has important implications for such processes as photography and liquid-junction solar cells. We find that the adsorption of silver and halide ions occurs all over the crystal surface [(100) plane], with a pronounced tendency of Ag+ to be adsorbed onto X- sites, the X- onto Ag+ sites, and both to be adsorbed onto the midpoint site. The adsorption of Ag+ ions is found to be weaker than that of the X- ions, in accordance with experiments. The adsorption of ions when interstitial Ag+ ion and Ag+ vacancy (Frenkel defect) are present close to the surface is also considered. We find that adsorbed X- ions enrich the space-charge layer of the AgX crystal with extra positive charge, shifting the band edges towards a more cathodic potential. The reverse trend is found when Ag+ ions are adsorbed. In a forthcoming publication, we extend the present model to include model of charge transfer processes at these interfaces. From these calculations we obtain some guidelines for the construction of systems with high charge transfer probability. Surprisingly, these guidelines are satisfied by most photoelectrochemical cells as well as by other systems.

  20. Directly observed reductive elimination of aryl halides from monomeric arylpalladium(II) halide complexes.

    PubMed

    Roy, Amy H; Hartwig, John F

    2003-11-19

    Monomeric, three-coordinate arylpalladium(II) halide complexes undergo reductive elimination of aryl halide to form free haloarene and Pd(0). Reductive elimination of aryl chlorides, bromides, and iodides were observed upon the addition of P(t-Bu)3 to Pd[P(t-Bu)3](Ar)(X) (X = Cl, Br, I). Conditions to observe the equilibrium between reductive elimination and oxidative addition were established with five haloarenes. Reductive elimination of aryl chloride was most favored thermodynamically, and elimination of aryl iodide was the least favored. However, reductive elimination from the aryl chloride complex was the slowest, and reductive elimination from the aryl bromide complex was the fastest. These data show that the electronic properties of the halide, not the thermodynamic driving force for the addition of elimination reaction, control the rates for addition and elimination of haloarenes. Mechanistic data suggest that reversible reductive elimination of aryl bromide to form Pd[P(t-Bu)3] and free aryl bromide is followed by rate-limiting coordination of P(t-Bu)3 to form Pd[P(t-Bu)3]2. PMID:14611215

  1. Positron-alkali atom scattering

    NASA Technical Reports Server (NTRS)

    Mceachran, R. P.; Horbatsch, M.; Stauffer, A. D.; Ward, S. J.

    1990-01-01

    Positron-alkali atom scattering was recently investigated both theoretically and experimentally in the energy range from a few eV up to 100 eV. On the theoretical side calculations of the integrated elastic and excitation cross sections as well as total cross sections for Li, Na and K were based upon either the close-coupling method or the modified Glauber approximation. These theoretical results are in good agreement with experimental measurements of the total cross section for both Na and K. Resonance structures were also found in the L = 0, 1 and 2 partial waves for positron scattering from the alkalis. The structure of these resonances appears to be quite complex and, as expected, they occur in conjunction with the atomic excitation thresholds. Currently both theoretical and experimental work is in progress on positron-Rb scattering in the same energy range.

  2. Rubidium and potassium alkali lasers

    Microsoft Academic Search

    J. Zweiback; B. Krupke

    2009-01-01

    We report on the results of our diode pumped alkali laser experiments. Using volume bragg gratings, we have produced a 1.28 kW diode stack with a 0.35 nm bandwidth and ~70% of the power contained in the peak. We use two of these stacks to pump a 23 mm rubidium cell. We achieve 29 W of average output power at

  3. Alkali-activated cementitious materials: Mechanisms, microstructure and properties

    Microsoft Academic Search

    Weimin Jiang

    1997-01-01

    The goal of this study was to examine the activation reaction, microstructure, properties, identify the mechanisms of activation, and achieve an enhanced understanding of activation processes occurring during the synthesis of alkali activated cementitious materials (AAC). The discussions classify the following categories. (1) alkali activated slag cement; (2) alkali activated portland-slag cement; (3) alkali activated fly ash-slag cement; (4) alkali

  4. The Surface Activation Layer of GaAs Negative Electron Affinity Photocathode Activated by Cs, Li and NF3

    SciTech Connect

    Sun, Yun; /SLAC, SSRL; Kirby, R.E.; /Saxet Surface Sci.; Maruyama, T.; /SLAC; Mulhollan, G.A.; Bierman, J.C.; /Saxet Surface Sci.; Pianetta, P.; /SLAC, SSRL

    2009-12-11

    The lifetime of GaAs photocathodes can be greatly improved by introducing Li in the Cs+NF{sub 3} activation process. The surface activation layer of such photocathodes is studied by synchrotron radiation photoemission and is compared with GaAs photocathodes activated without Li. The charge distributions of N, F and Cs experience significant changes when Li is added in the activation. In addition, the presence of Li causes NF{sub x} molecules to take an orientation with F atoms on top. All these changes induced by Li hold the key for the lifetime improvement of GaAs photocathodes.

  5. Defects in the silver halide photographic process

    NASA Astrophysics Data System (ADS)

    Pawlik, T. D.; Eachus, R. S.; Baetzold, R. C.; McDugle, W. G.; Olm, M. T.

    The imaging efficiency of today's photographic film and paper is influenced in a variety of ways. Among them, the incorporation of dopants is widely used to increase efficiency, control contrast or improve imaging deficiencies such as reciprocity law failure. Transition metal-organic ligand dopants are attractive because the organic ligand influences the photographic properties. Experimental studies have shown that many of these dopants incorporate well into the silver halide microcrystal even with large organic ligands. In this paper, experimental and computational results are presented on a variety of Ir-OL dopants in AgCl where OL is a small nitrogen and/or sulfur-containing heterocycle. Electron paramagnetic resonance methods provide information about the electronic structure, electron trapping properties and the stability of the electron trap state. These results are complemented by ab initio studies that give information about the optimum structure, charge compensation and the possibility of electron and hole trapping.

  6. Diode pumped alkali vapor fiber laser

    Microsoft Academic Search

    Stephen A. Payne; Raymond J. Beach; Jay W. Dawson; William F. Krupke

    2007-01-01

    A method and apparatus is provided for producing near-diffraction-limited laser light, or amplifying near-diffraction-limited light, in diode pumped alkali vapor photonic-band-gap fiber lasers or amplifiers. Laser light is both substantially generated and propagated in an alkali gas instead of a solid, allowing the nonlinear and damage limitations of conventional solid core fibers to be circumvented. Alkali vapor is introduced into

  7. Diode pumped alkali vapor fiber laser

    Microsoft Academic Search

    Stephen A. Payne; Raymond J. Beach; Jay W. Dawson; William F. Krupke

    2006-01-01

    A method and apparatus is provided for producing near-diffraction-limited laser light, or amplifying near-diffraction-limited light, in diode pumped alkali vapor photonic-band-gap fiber lasers or amplifiers. Laser light is both substantially generated and propagated in an alkali gas instead of a solid, allowing the nonlinear and damage limitations of conventional solid core fibers to be circumvented. Alkali vapor is introduced into

  8. Regenerable activated bauxite adsorbent alkali monitor probe

    DOEpatents

    Lee, Sheldon H. D. (Willowbrook, IL)

    1992-01-01

    A regenerable activated bauxite adsorber alkali monitor probe for field applications to provide reliable measurement of alkali-vapor concentration in combustion gas with special emphasis on pressurized fluidized-bed combustion (PFBC) off-gas. More particularly, the invention relates to the development of a easily regenerable bauxite adsorbent for use in a method to accurately determine the alkali-vapor content of PFBC exhaust gases.

  9. An accelerator for alkali metal plasmas

    Microsoft Academic Search

    A. K. Chakraborty; Ajai Kumar; S. K. Mattoo

    1994-01-01

    A washer plasma gun for alkali-metal plasma is developed. This gun is suitable as a source for experiments on alkali-metal plasmas, plasma diagnostics, and in various applications such as ion-beam sputter deposition. The gun uses an injector of alkali-metal vapor based on the principles of laser ablation. Acceleration is performed by a large electrical field provided across eight washers. The

  10. Purification and Characterization of an Extracellular, Thermo-Alkali-Stable, Metal Tolerant Laccase from Bacillus tequilensis SN4

    PubMed Central

    Sondhi, Sonica; Sharma, Prince; Saini, Shilpa; Puri, Neena; Gupta, Naveen

    2014-01-01

    A novel extracellular thermo-alkali-stable laccase from Bacillus tequilensis SN4 (SN4LAC) was purified to homogeneity. The laccase was a monomeric protein of molecular weight 32 KDa. UV-visible spectrum and peptide mass fingerprinting results showed that SN4LAC is a multicopper oxidase. Laccase was active in broad range of phenolic and non-phenolic substrates. Catalytic efficiency (kcat/Km) showed that 2, 6-dimethoxyphenol was most efficiently oxidized by the enzyme. The enzyme was inhibited by conventional inhibitors of laccase like sodium azide, cysteine, dithiothreitol and ?-mercaptoethanol. SN4LAC was found to be highly thermostable, having temperature optimum at 85°C and could retain more than 80% activity at 70°C for 24 h. The optimum pH of activity for 2, 6-dimethoxyphenol, 2, 2?-azino bis[3-ethylbenzthiazoline-6-sulfonate], syringaldazine and guaiacol was 8.0, 5.5, 6.5 and 8.0 respectively. Enzyme was alkali-stable as it retained more than 75% activity at pH 9.0 for 24 h. Activity of the enzyme was significantly enhanced by Cu2+, Co2+, SDS and CTAB, while it was stable in the presence of halides, most of the other metal ions and surfactants. The extracellular nature and stability of SN4LAC in extreme conditions such as high temperature, pH, heavy metals, halides and detergents makes it a highly suitable candidate for biotechnological and industrial applications. PMID:24871763

  11. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    SciTech Connect

    Carlos Hernandez-Garcia, Fay Hannon, Marcy Stutzman, V. Shutthanandan, Z. Zhu, M. Nandasri, S. V. Kuchibhatla, S. Thevuthasan, W. P. Hess

    2012-06-01

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Photocathode quantum efficiency (QE) degradation is due to residual gasses in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the Continuous Electron Beam Accelerator Facility (CEBAF) photoinjector and one unused, were also analyzed using Transmission Electron Microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but shows evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  12. Available alkalis in fly ash and their effects on alkali-aggregate reaction

    Microsoft Academic Search

    1986-01-01

    The available alkalis of four Class C and two Class F fly ashes were evaluated according to ASTM C 311. The effects of alkalis in three Class C fly ashes on expansion of mortar bars with high and low-alkali cements were studied using the procedures described in ASTM C 441. This research studied: (1) the significance of the standard available

  13. Search for improved-performance scintillator candidates among the electronic structures of mixed halides

    NASA Astrophysics Data System (ADS)

    Li, Qi; Williams, Richard T.; Burger, Arnold; Adhikari, Rajendra; Biswas, Koushik

    2014-09-01

    The application of advanced theory and modeling techniques has become an essential component to understand material properties and hasten the design and discovery of new ones. This is true for diverse applications. Therefore, current efforts aimed towards finding new scintillator materials are also aligned with this general predictive approach. The need for large scale deployment of efficient radiation detectors requires discovery and development of high-performance, yet low-cost, scintillators. While Tl-doped NaI and CsI are still some of the widely used scintillators, there are promising new developments, for example, Eu-doped SrI2 and Ce-doped LaBr3. The newer candidates have excellent light yield and good energy resolution, but challenges persist in the growth of large single crystals. We will discuss a theoretical basis for anticipating improved proportionality as well as light yield in solid solutions of certain systems, particularly alkali iodides, based on considerations of hot-electron group velocity and thermalization. Solid solutions based on NaI and similar alkali halides are attractive to consider in more detail because the end point compositions are inexpensive and easy to grow. If some of this quality can be preserved while reaping improved light yield and possibly improved proportionality of the mixture, the goal of better performance at the low price of NaI:Tl might be attainable by such a route. Within this context, we will discuss a density functional theory (DFT) based study of two prototype systems: mixed anion NaIxBr1-x and mixed cation NaxK1-xI. Results obtained from these two prototype candidates will lead to further targeted theoretical and experimental search and discovery of new scintillator hosts.

  14. 40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...Substituted halogenated pyridinol, alkali salt. 721.8900 Section 721.8900 ...Substituted halogenated pyridinol, alkali salt. (a) Chemical substances and significant...substituted halogenated pyridinols, alkali salts (PMNs P-88-1271 and...

  15. 40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...Substituted naphthalenesulfonic acid, alkali salt. 721.5278 Section 721.5278 ...Substituted naphthalenesulfonic acid, alkali salt. (a) Chemical substance and significant...substituted naphthalenesulfonic acid, alkali salt (PMN P-95-85) is subject to...

  16. 40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...Substituted naphthalenesulfonic acid, alkali salt. 721.5278 Section 721.5278 ...Substituted naphthalenesulfonic acid, alkali salt. (a) Chemical substance and significant...substituted naphthalenesulfonic acid, alkali salt (PMN P-95-85) is subject to...

  17. 40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...Substituted halogenated pyridinol, alkali salt. 721.8900 Section 721.8900 ...Substituted halogenated pyridinol, alkali salt. (a) Chemical substances and significant...substituted halogenated pyridinols, alkali salts (PMNs P-88-1271 and...

  18. High Pressure Electrochemistry: Application to silver halides

    NASA Astrophysics Data System (ADS)

    Havens, K.; Kavner, A.

    2007-12-01

    Electron and ion charge transfer processes help govern electrical conductivity and diffusive mass and heat transport properties in deep Earth minerals. In an attempt to understand how pressure influences charge transfer behavior, the halide silver bromide (AgBr) was studied under the influence of an electric potential difference applied across two electrodes in a diamond anvil cell. This study follows our previous work on AgI, which was found to dissociate to molecular iodine and silver metal due to pressure and voltage influences. We performed two sets of experiments on AgBr at high pressure in a diamond anvil cell: electrochemical dissociation and electrical resistance measurements. In our study, we were able to electrochemically dissociate AgBr at pressures of 0.25-1.6 GPa by applying a voltage across the electrodes in the diamond cell sample chamber. Ag metal grew visibly on the negatively-charged electrode when voltages varying from 0.1 V to 5 V were applied. Additionally, a dark blue color appeared in low pressure areas of the diamond cell and grew darker from both voltage application and light exposure, indicating photochemical effects. We found that the reaction area and growth rate of both metal and dark blue color strongly increased as voltage increased, but tended to decrease with greater pressure. The resistance across the cell was observed to be influenced by both pressure and light exposure. As the AgBr sample was exposed to visible light, the resistance dropped instantaneously, and after the light was turned off, the resistance increased on a timescale of 10's of seconds to minutes. Notably, at higher pressures, the AgBr showed less photosensitivity. Exploration of these metal halide systems has many potential applications. First, these experiments explore the pressure-dependence of photochemical and photovoltaic processes, and may spur development of pressure-tuned microscale electronic devices. Second, these experimental results can be used to constrain thermodynamic models of pressure-dependent electrochemical behavior of materials, which may then be applied to the high temperature, high pressure mineral phases of the deep Earth and planets.

  19. A Hybrid Laser-driven E-beam Injector Using Photo-cathode Electron Gun and superconducting Cavity*

    E-print Network

    Geng, Rong-Li

    A Hybrid Laser-driven E-beam Injector Using Photo-cathode Electron Gun and superconducting Cavity, Beijing 100871, China * Work supported by NNSF of China Abstract A laser-driven photo-cathode electron gun constructed and tested. As the next step, a hybrid photo-injector, using a DC laser-driven electron gun

  20. Photoemission of Pd-Ag-O-Cs and Sb-Na?KCs photocathodes under the illumination of clear star radiation

    Microsoft Academic Search

    Tao Zhaomin

    1987-01-01

    The photoemission of Pd-Ag-O-Cz and Sb-Na-K-Cs photocathodes under the illumination of clear star radiation are calculated and compared. From the calculated\\u000a results, it gives a prospect that the Pd?Ag?O?Cs photocathode may be used in image intensifier as passive night vision instruments.

  1. Method of handling radioactive alkali metal waste

    DOEpatents

    Wolson, Raymond D. (Lockport, IL); McPheeters, Charles C. (Plainfield, IL)

    1980-01-01

    Radioactive alkali metal is mixed with particulate silica in a rotary drum reactor in which the alkali metal is converted to the monoxide during rotation of the reactor to produce particulate silica coated with the alkali metal monoxide suitable as a feed material to make a glass for storing radioactive material. Silica particles, the majority of which pass through a 95 mesh screen or preferably through a 200 mesh screen, are employed in this process, and the preferred weight ratio of silica to alkali metal is 7 to 1 in order to produce a feed material for the final glass product having a silica to alkali metal monoxide ratio of about 5 to 1.

  2. High quantum efficiency photocathode simulation for the investigation of novel structured designsa)

    NASA Astrophysics Data System (ADS)

    Opachich, Y. P.; Ross, P. W.; MacPhee, A. G.; Hilsabeck, T. J.; Nagel, S. R.; Huffman, E.; Bell, P. M.; Bradley, D. K.; Koch, J. A.; Landen, O. L.

    2014-11-01

    A computer model in CST Studio Suite has been developed to evaluate several novel geometrically enhanced photocathode designs. This work was aimed at identifying a structure that would increase the total electron yield by a factor of two or greater in the 1-30 keV range. The modeling software was used to simulate the electric field and generate particle tracking for several potential structures. The final photocathode structure has been tailored to meet a set of detector performance requirements, namely, a spatial resolution of <40 ?m and a temporal spread of 1-10 ps. We present the details of the geometrically enhanced photocathode model and resulting static field and electron emission characteristics.

  3. Dye-controlled interfacial electron transfer for high-current indium tin oxide photocathodes.

    PubMed

    Huang, Zhongjie; He, Mingfu; Yu, Mingzhe; Click, Kevin; Beauchamp, Damian; Wu, Yiying

    2015-06-01

    Efficient sensitized photocathodes are highly desired for solar fuels and tandem solar cells, yet the development is hindered by the scarcity of suitable p-type semiconductors. The generation of high cathodic photocurrents by sensitizing a degenerate n-type semiconductor (tin-doped indium oxide; ITO) is reported. The sensitized mesoporous ITO electrodes deliver cathodic photocurrents of up to 5.96±0.19?mA?cm(-2) , which are close to the highest record in conventional p-type sensitized photocathodes. This is realized by the rational selection of dyes with appropriate energy alignments with ITO. The energy level alignment between the highest occupied molecular orbital of the sensitizer and the conduction band of ITO is crucial for efficient hole injection. Transient absorption spectroscopy studies demonstrate that the cathodic photocurrent results from reduction of the photoexcited sensitizer by free electrons in ITO. Our results reveal a new perspective toward the selection of electrode materials for sensitized photocathodes. PMID:25907357

  4. Surface activation behavior of negative-electron-affinity exponential-doping GaAs photocathodes

    NASA Astrophysics Data System (ADS)

    Zhang, Yijun; Niu, Jun; Zou, Jijun; Chen, Xinlong; Xu, Yuan; Chang, Benkang; Shi, Feng

    2014-06-01

    In view of the effect of doping structure on the surface activation behavior, the Cs-O activation experiments under the same preparation condition were performed on the exponential-doping and uniform-doping GaAs photocathodes. The activation results show that, compared with the uniform-doping photocathode, the exponential-doping photocathode presents a lower photocurrent peak after the initial Cs activation and a higher photocurrent peak after the Cs-O alternate activation. Based on the double dipole model, the parameters of surface potential barrier are obtained from the calculation of longitudinal energy distribution of emitted electrons according to the ratio of photocurrent peak after Cs-O activation to that after Cs activation. The discrepancy in the photocurrent evolution during the entire activation process is related to the different variations in surface potential barrier profile.

  5. Experimental studies of the charge limit phenomenon in GaAs photocathodes

    SciTech Connect

    Tang, H.; Alley, R.; Aoyagi, H.; Clendenin, J.; Saez, P.; Schultz, D.; Turner, J.

    1993-10-01

    GaAs photocathodes have been in use for generating high intensity polarized electron beams (up to a peak current of 6 A in 2 ns pulses) for the SLC high energy physics program. If the quantum efficiency (measured at low light intensities) of a GaAs photocathode is below a certain level, the maximum photoemitted charge is found to be limited by the intrinsic properties of the cathode instead of by the space charge limit. We have studied this charge limit phenomenon in a variety of GaAs photocathodes. The effects of the quantum efficiency, excitation laser wavelength, and extraction electric field on the charge limit have been examined. The temporal behavior of the charge limit as manifested in both intrapulse and interpulse effects has also been studied. These results will be discussed in light of possible mechanisms.

  6. Photoemission Study of Cs-NF3 Activated GaAs(100) Negative Electron Affinity Photocathodes

    SciTech Connect

    Liu, Z.; Sun, Y.; Peterson, S.; Pianetta, P.

    2008-05-28

    GaAs based negative electron affinity photocathodes activated with Cs and NF{sub 3} are used as polarized electron sources for linear accelerators. It is generally believed that the activation layer consists of CsF. The activation layers of Cs-NF{sub 3} on GaAs photocathodes are herein investigated using synchrotron radiation photoelectron spectroscopy (SR-PES). F1s, N1s and other core levels are recorded at photon energies ranging from 70eV to 820eV. Surprisingly, a significant amount of nitrogen is observed in the activation layers. Two distinct species of nitrogen are observed, one of which decreases along with the Fluorine signal as the yield of the photocathode decays with time.

  7. Color silver halide hologram production and mastering

    NASA Astrophysics Data System (ADS)

    Bjelkhagen, Hans I.; Huang, Qiang

    1997-04-01

    Color reflection holograms recorded with the Denisyuk geometry have been demonstrated by the recently formed HOLOS Corporation in New Hampshire. The Slavich red-green-blue (RGB) sensitized ultra-high resolution silver halide emulsion was used for the hologram recording. The employed laser wavelengths were 647 nm, 532 nm, and 476 nm, generated by an argon ion, a frequency doubled Nd:YAG, and a krypton ion laser, respectively. A beam combination mechanism with dichroic filters enabled a simultaneous RGB exposure, which made the color balance and overall exposure energy easy to control as well as simplifying the recording procedure. HOLOS has been producing limited edition color holograms in various sizes from 4' X 5' to 12' X 16'. A 30 foot long optical table and high power lasers will enable HOLOS to record color holograms up to the size of one meter square in the near future. Various approaches have been investigated in generating color hologram masters which have sufficiently high diffraction efficiency to contact copy the color images onto photopolymer materials. A specially designed test object including the 1931 CIE chromaticity diagram, a rainbow ribbon cable, pure yellow dots, and a cloisonne elephant was used for color recording experiments. In addition, the Macbeth Color Checker chart was used. Both colorimetric evaluation and scattering noise measurements were performed using the PR-650 Photo Research SpectraScan SpectraCalorimeter.

  8. High-brightness electron beam evolution following laser-based cleaning of a photocathode

    NASA Astrophysics Data System (ADS)

    Zhou, F.; Brachmann, A.; Decker, F.-J.; Emma, P.; Gilevich, S.; Iverson, R.; Stefan, P.; Turner, J.

    2012-09-01

    Laser-based techniques have been widely used for cleaning metal photocathodes to increase quantum efficiency (QE). However, the impact of laser cleaning on cathode uniformity and thereby on electron beam quality are less understood. We are evaluating whether this technique can be applied to revive photocathodes used for high-brightness electron sources in advanced x-ray free-electron laser (FEL) facilities, such as the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory. The laser-based cleaning was applied to two separate areas of the current LCLS photocathode on July 4 and July 26, 2011, respectively. The QE was increased by 8-10 times upon the laser cleaning. Since the cleaning, routine operation has exhibited a slow evolution of the QE improvement and comparatively rapid improvement of transverse emittance, with a factor of 3 QE enhancement over five months, and a significant emittance improvement over the initial 2-3 weeks following the cleaning. Currently, the QE of the LCLS photocathode is holding constant at about 1.2×10-4, with a normalized injector emittance of about 0.3?m for a 150-pC bunch charge. With the proper procedures, the laser-cleaning technique appears to be a viable tool to revive the LCLS photocathode. We present observations and analyses for the QE and emittance evolution in time following the laser-based cleaning of the LCLS photocathode, and comparison to the previous studies, the measured thermal emittance versus the QE and comparison to the theoretical model.

  9. SRRC/ANL high current l-band single cell photocathode rf gun.

    SciTech Connect

    Ho, C. H.

    1998-07-16

    A high current L-band photocathode rf gun is under development at SRRC (Synchrotron Radiation Research Center, Taiwan) in collaboration with ANL (Argonne National Laboratory, USA). The goal is to produce up to 100 nC charge with the surface field gradient of over 90 MV/m at the center of the photocathode. In this report, they present the detailed design and initial test results. If successful, this gun will be used as the future AWA (Argonne Wakefield Accelerator)[1] high current gun.

  10. Quantum efficiency of technical metal photocathodes under laser irradiation of various wavelength

    E-print Network

    Pimpec, F Le; Milne, C

    2012-01-01

    Quantum efficiency studies for various wavelength and various technical metal surfaces were carried out in a dedicated unbaked vacuum chamber. Copper, magnesium, aluminium and aluminium-lithium photocathodes were irradiated by two different high power, high repetition rate, laser systems. We have observed an emission of electrons for photon energy below the work function of the material. This is explained by multiple photon absorption at the photocathode. We have not observed any degradation of the QE for those materials, but an improvement when irradiating them over a long period of time. This is contrary to observations made in RF photoguns.

  11. Zintl cluster chemistry in the alkali-metal-gallium systems

    SciTech Connect

    Henning, R.

    1998-03-27

    Previous research into the alkali-metal-gallium systems has revealed a large variety of networked gallium deltahedra. The clusters are analogues to borane clusters and follow the same electronic requirements of 2n+2 skeletal electrons for closo-deltahedra. This work has focused on compounds that do not follow the typical electron counting rules. The first isolated gallium cluster was found in Cs{sub 8}Ga{sub 11}. The geometry of the Ga{sub 11}{sup 7{minus}} unit is not deltahedral but can be described as a penta-capped trigonal prism. The reduction of the charge from a closo-Ga{sub 11}{sup 13{minus}} to Ga{sub 11}{sup 7{minus}} is believed to be the driving force of the distortion. The compound is paramagnetic because of an extra electron but incorporation of a halide atom into the structure captures the unpaired electron and forms a diamagnetic compound. A second isolated cluster has been found in Na{sub 10}Ga{sub 10}Ni where the tetra-capped trigonal prismatic gallium is centered by nickel. Stabilization of the cluster occurs through Ni-Ga bonding. A simple two-dimensional network occurs in the binary K{sub 2}Ga{sub 3} Octahedra are connected through four waist atoms to form a layered structure with the potassium atoms sitting between the layers. Na{sub 30.5}Ga{sub 60{minus}x}Ag{sub x} is nonstoichiometric and needs only a small amount of silver to form (x {approximately} 2--6). The structure is composed of three different clusters which are interconnected to form a three-dimensional structure. The RbGa{sub 3{minus}x}Au{sub x} system is also nonstoichiometric with a three-dimensional structure composed of Ga{sub 8} dodecahedra and four-bonded gallium atoms. Unlike Na{sub 30.5}Ga{sub 60{minus}x}Ag{sub x}, the RbGa{sub 3} binary is also stable. The binary is formally a Zintl phase but the ternary is not. Some chemistry in the alkali-metal-indium system also has been explored. A new potassium-indium binary is discussed but the structure has not been completely characterized.

  12. Analysis of the physical atomic forces between noble gas atoms, alkali ions and halogen ions

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Heinbockel, J. H.; Outlaw, R. A.

    1986-01-01

    The physical forces between atoms and molecules are important in a number of processes of practical importance, including line broadening in radiative processes, gas and crystal properties, adhesion, and thin films. The components of the physical forces between noble gas atoms, alkali ions, and halogen ions are analyzed and a data base for the dispersion forces is developed from the literature based on evaluations with the harmonic oscillator dispersion model for higher order coefficients. The Zener model of the repulsive core is used in the context of the recent asymptotic wave functions of Handler and Smith; and an effective ionization potential within the Handler and Smith wave functions is defined to analyze the two body potential data of Waldman and Gordon, the alkali-halide molecular data, and the noble gas crystal and salt crystal data. A satisfactory global fit to this molecular and crystal data is then reproduced by the model to within several percent. Surface potentials are evaluated for noble gas atoms on noble gas and salt crystal surfaces with surface tension neglected. Within this context, the noble gas surface potentials on noble gas and salt crystals are considered to be accurate to within several percent.

  13. Thermodynamic reactivity, growth and characterization of mercurous halide crystals

    NASA Technical Reports Server (NTRS)

    Singh, N. B.; Gottlieb, M.; Henningsen, T.; Hopkins, R. H.; Mazelsky, R.; Singh, M.; Glicksman, M. E.; Paradies, C.

    1992-01-01

    Thermodynamic calculations were carried out for the Hg-X-O system (X = Cl, Br, I) to identify the potential sources of contamination and relative stability of oxides and oxy-halide phases. The effect of excess mercury vapor pressure on the optical quality of mercurous halide crystal was studied by growing several mercurous chloride crystals from mercury-rich composition. The optical quality of crystals was examined by birefringence interferometry and laser scattering studies. Crystals grown in slightly mercury-rich composition showed improved optical quality relative to stoichiometric crystals.

  14. Charge Lifetime Study of K2CsSb Photocathode Inside a JLAB DC High Voltage Gun

    SciTech Connect

    Mammei, R.; Rao, T.; Suleiman, R.; Poelker, M.; Smedley, J.; McCarter, J.L.

    2011-10-01

    Two photocathodes are frequently considered for generating high average current electron beams and/or beams with high brightness for current and future accelerator applications: GaAs:Cs and K2CsSb. Each photocathode has advantages and disadvantages, and need to demonstrate performance at 'production' accelerator facilities. To this end a K2CsSb photocathode was manufactured at Brookhaven National Lab and delivered to Jefferson Lab within a compact vacuum apparatus at pressure {approx} 5 x 10{sup -11} Torr. This photocathode was installed inside a dc high voltage photogun biased at voltages up to 200 kV, and illuminated with laser light at 440 or 532 nm, to generate beams up to 20 mA. Photocathode charge lifetime measurements indicate that under some conditions this cathode has exceptionally high charge lifetime, without measurable QE decay, even from the center of the photocathode where operation using GaAs photocathodes is precluded due to ion bombardment. These studies also suggest a complex QE decay mechanism likely related to chemistry and localized heating via the laser beam.

  15. Studies in Laser Photo-cathode RF Guns A Dissertation Presented

    E-print Network

    Studies in Laser Photo-cathode RF Guns A Dissertation Presented by Xiangyun Chang to The Graduate-cathode RF Guns by Xiangyun Chang Doctor of Philosophy in Physics Stony Brook University 2005 The emittance compensation mechanics of a "non-magnetized" (the magnetic field on cathode is zero) beam in a compact RF gun

  16. NREL Improves Hole Transport in Sensitized CdS-NiO Nanoparticle Photocathodes (Fact Sheet)

    SciTech Connect

    Not Available

    2012-01-01

    Significantly improved charge-collection efficiencies result from a general chemical approach to synthesizing photocathodes. It has been reported that a dye-sensitized nickel oxide (NiO) photocathode, when coupled to a dye-sensitized photoanode, could significantly increase overall solar conversion efficiency. However, the conversion efficiencies of these cells are still low. There has been much effort to improve the conversion efficiency by fabricating films with improved properties and developing more effective sensitizing dyes for p-type NiO. One of the factors limiting the use of NiO for solar cell application is the low hole conductivity in p-NiO. A team of researchers from the National Renewable Energy Laboratory (NREL) developed a general chemical approach to synthesize NiO-cadmium sulfide (CdS) core-shell nanoparticle films as photocathodes for p-type semiconductor-sensitized solar cells. Compared to dye-sensitized NiO photocathodes, the CdS-sensitized NiO cathodes exhibited two orders of magnitude faster hole transport (attributable to the passivation of surface traps by the CdS) and almost 100% charge-collection efficiencies.

  17. The influences of vacuum pressure and gas components on the stability of GaAs photocathode

    NASA Astrophysics Data System (ADS)

    Wang, Long; Shi, Feng; Cheng, Hongchang; Niu, Sen; Shi, Hongli; Yan, Lei; Cheng, Xing; Yuan, Yuan

    2015-04-01

    The photocurrent attenuation of GaAs photocathode within one hour after activation under three different vacuum pressure (5×10-9Pa, 5×10-8Pa, 5×10-7Pa) were recorded by automatically activated monitor. The results show that: the photocurrent quickly descend in the beginning and then descend linearly at a low slope; the amplitude of the quickly descending area were 10%, 14.74% and 36%separately, with the respective slope of the linear descending area were -0.00653, -0.01132and -0.02. Three samples' gas components of H2, CH4, CO, H2O, O2, CO2 etc under the same vacuum pressure (5×10-8Pa)during photocurrent attenuation were collected by quadrupole mass spectrometer. By comparing the gas components content and the attenuation law of the photocurrent, it has been found that H2O and H2 had a greater impact on the stability of GaAs photocathode in the ultra-high vacuum environment and H2O was the predominant effect. This paper has important guiding significance and reference value in studying the stability of GaAs photocathode and the improvement of semiconductor photocathode process.

  18. Diamond Amplified Photocathode Ilan Ben-Zvi, Andrew Burrill, Xiangyun Chang, Peter D.

    E-print Network

    Diamond Amplified Photocathode R&D Plans Ilan Ben-Zvi, Andrew Burrill, Xiangyun Chang, Peter D;The basic idea Photon in Primary electrons Secondary electrons CsK2Sb Diamond #12;Motivation · Capable& assembly · Low thermal emittance · Prompt emission #12;Schematic Arrangement of the System #12;· Diamond

  19. Development of Large Area CsI Photocathodes for the ALICE\\/HMPID RICH Detector

    Microsoft Academic Search

    H Hoedlmoser; Christian Wolfgang Fabjan; E Schyns

    2005-01-01

    The work carried out within the framework of this PhD deals with the measurement of the photoelectric properties of large area thin film Cesium Iodide (CsI) photocathodes (PCs) which are to be used as a photon converter in a proximity focusing RICH detector for High Momentum Particle Identification (HMPID) in the ALICE experiment at the LHC. The objective was to

  20. Highlights on photocathodes based on thin films prepared by pulsed laser deposition

    Microsoft Academic Search

    A. Lorusso; F. Gontad; A. Perrone; N. Stankova

    2011-01-01

    We review the current status of metallic photocathodes based on thin films prepared by pulsed laser deposition (PLD) and we explore ways to improve the performance of these devices. PLD seems to be a very efficient and suitable technique for producing adherent and uniform thin films. Time-resolved mass spectrometric investigations definitively suggest that the deposition of high-purity metallic thin films

  1. Highlights on photocathodes based on thin films prepared by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Lorusso, A.; Gontad, F.; Perrone, A.; Stankova, N.

    2011-09-01

    We review the current status of metallic photocathodes based on thin films prepared by pulsed laser deposition (PLD) and we explore ways to improve the performance of these devices. PLD seems to be a very efficient and suitable technique for producing adherent and uniform thin films. Time-resolved mass spectrometric investigations definitively suggest that the deposition of high-purity metallic thin films should be carried out in ultrahigh vacuum systems and after a deep and careful laser cleaning of the target surface. Moreover, the laser cleaning of the target surface is highly recommended not only to remove the first contaminated layers but also to improve the quality of the vacuum by reducing the partial pressure of reactive chemical species as H2O, H2, and O2 molecules. The challenge to realize high-purity Mg and Y thin films is very interesting for the photocathode R&D due to the good photoemission properties of these metals. Photocathodes based on Mg and Y thin films have been characterized by scanning electron microscopy and x-ray diffraction techniques to derive the morphological and structural features, respectively. They were also tested in a photodiode cell to deduce the photoelectron properties. The quantum efficiency of such photocathodes was systematically improved by in situ laser cleaning treatments of the surface in order to remove the contaminated layers reaching, in this way, the quantum efficiency of the corresponding bulk materials.

  2. Comparison of the optical characteristics of GaAs photocathodes grown using MBE and MOCVD

    Microsoft Academic Search

    Loig E. Bourree; David R. Chasse; P. L. Stephan Thamban; Robert Glosser

    2003-01-01

    Modern image tube intensifier photocathodes rely on a GaAs active layer, which has traditionally been grown using metallorganic chemical vapor deposition (MOCVD) due to its high throughput and lower cost of operation. Molecular beam epitaxy (MBE) processes have not been thoroughly investigated in that context. The latter technique demonstrates greater structural interface control as well as an improved growth quality

  3. The degradation of quantum efficiency in negative electron affinity GaAs photocathodes under gas exposure

    NASA Astrophysics Data System (ADS)

    Chanlek, N.; Herbert, J. D.; Jones, R. M.; Jones, L. B.; Middleman, K. J.; Militsyn, B. L.

    2014-02-01

    The influence of O2, CO2, CO, N2, H2 and CH4 on the stability of the quantum efficiency (QE) of a negative electron affinity gallium arsenide (GaAs) photocathode activated with caesium (Cs) and oxygen (O) has been demonstrated for the first time under an extremely high vacuum condition, a base pressure of 1.5 × 10-11 mbar, where the influence of the background gas is minimized. It was found that exposure of a GaAs photocathode to N2, H2 and CH4 does not affect the QE, whereas exposure to O2, CO2 and CO leads to a substantial reduction in photocathode QE. It was also found that the QE of photocathodes which have been degraded under O2 exposure can be recovered to 95% of their initial QE level by the re-caesiation process, while those which have been degraded under exposure to CO and CO2 can only be partly restored to 60-70% of their initial QE levels.

  4. Negative ion production rates in rare gas-halide lasers

    Microsoft Academic Search

    KAARE J. NYGAARD; HOWARD L. BROOKS; SCOTT R. HUNTER

    1979-01-01

    This paper reports on dissociative electron attachment in F2, NF3, Cl2, and I2. The principle of the method is to produce a short burst of photoelectrons from a photocathode by means of light from an argon-fluoride laser. Subsequently, by studying the motion of electrons and negative ions in a constant electric field (E) region, information is obtained about drift velocities

  5. Microwave and infrared spectra of deuterium-substituted germyl halides and the structures of the germyl halides

    NASA Astrophysics Data System (ADS)

    Cradock, Stephen; McKean, Donald C.; MacKenzie, Moray W.

    1981-07-01

    We have obtained microwave spectra of fully and partially deuterated germyl halides GeD 3X and GeHD 2X (X = F, Cl, Br, I) and analysed the infrared spectra in the GeH stretching region of the asymmetric species. The resulting Ao and Bo values have been combined with existing data on GeH 3X to give improved structures for the germyl halides. The values of the HGeX angles obtained show a correlation with GeH stretching frequencies, as in methyl compounds, but there appears to be no such correlation between stretching frequencies and GeH bond lengths.

  6. Superconductivity in alkali-doped C60

    NASA Astrophysics Data System (ADS)

    Ramirez, Arthur P.

    2015-07-01

    Superconductivity in alkali-doped C60 (A3C60, A = an alkali atom) is well described by an s-wave state produced by phonon mediated pairing. Moderate coupling of electrons to high-frequency shape-changing intra-molecular vibrational modes produces transition temperatures (Tc) up to 33 K in single-phase material. The good understanding of pairing in A3C60 offers a paradigm for the development of new superconducting materials.

  7. Fate of alkalis in coal combustion

    SciTech Connect

    Stewart, G.W. (Aerodyne Research, Inc., Bedford, MA); Stinespring, C.D.; Davidovits, P.

    1982-01-01

    The results of these measurements and experiments provide a plausible way to begin an explanation for the distribution of alkali in the ash particulates. To summarize: (1) under typical coal combustion conditions in an atmosphere rich in CO/sub 2/ and/or SO/sub 2/, the alkalis in the organic fraction do not vaporize but remain bound in the ash as stable carbonates or sulfates; (2) the alkalis in the inorganic fraction diffuse to the surface producing enrichment by a factor of about 13 to a depth of about 100A. The results, however, do not provide conclusive evidence about the fate of the alkalis. The effect of water vapor in the combustion stream has not yet been studied. Clearly, water could have an important effect on the vaporization process. Furthermore, the reasoning we have followed to explain the absence of alkali enrichment in the submicron particles requires that the volatilization of the alkalis in both the organic and inorganic fraction not be significant (say less than 20%).

  8. Structural Characterization of Methanol Substituted Lanthanum Halides.

    PubMed

    Boyle, Timothy J; Ottley, Leigh Anna M; Alam, Todd M; Rodriguez, Mark A; Yang, Pin; McIntyre, Sarah K

    2010-05-10

    The first study into the alcohol solvation of lanthanum halide [LaX(3)] derivatives as a means to lower the processing temperature for the production of the LaBr(3) scintillators was undertaken using methanol (MeOH). Initially the de-hydration of {[La(micro-Br)(H(2)O)(7)](Br)(2)}(2) (1) was investigated through the simple room temperature dissolution of 1 in MeOH. The mixed solvate monomeric [La(H(2)O)(7)(MeOH)(2)](Br)(3) (2) compound was isolated where the La metal center retains its original 9-coordination through the binding of two additional MeOH solvents but necessitates the transfer of the innersphere Br to the outersphere. In an attempt to in situ dry the reaction mixture of 1 in MeOH over CaH(2), crystals of [Ca(MeOH)(6)](Br)(2) (3) were isolated. Compound 1 dissolved in MeOH at reflux temperatures led to the isolation of an unusual arrangement identified as the salt derivative {[LaBr(2.75)*5.25(MeOH)](+0.25) [LaBr(3.25)*4.75(MeOH)](-0.25)} (4). The fully substituted species was ultimately isolated through the dissolution of dried LaBr(3) in MeOH forming the 8-coordinated [LaBr(3)(MeOH)(5)] (5) complex. It was determined that the concentration of the crystallization solution directed the structure isolated (4 concentrated; 5 dilute) The other LaX(3) derivatives were isolated as [(MeOH)(4)(Cl)(2)La(micro-Cl)](2) (6) and [La(MeOH)(9)](I)(3)*MeOH (7). Beryllium Dome XRD analysis indicated that the bulk material for 5 appear to have multiple solvated species, 6 is consistent with the single crystal, and 7 was too broad to elucidate structural aspects. Multinuclear NMR ((139)La) indicated that these compounds do not retain their structure in MeOD. TGA/DTA data revealed that the de-solvation temperatures of the MeOH derivatives 4 - 6 were slightly higher in comparison to their hydrated counterparts. PMID:20514349

  9. Halide adsorption on single-crystal silver substrates: dynamic

    E-print Network

    Rikvold, Per Arne

    · Investigated validity of lattice-gas approach * Justified for well-localized adsorption sites · Tested MarkovHalide adsorption on single-crystal silver substrates: dynamic simulations and ab initio density State University Supported by US NSF #12;How good is lattice-gas approximation? Using 2D corrugation

  10. Structure and optical properties of high light output halide scintillators

    SciTech Connect

    Singh, David J [ORNL

    2010-01-01

    Structural and optical properties of several high light output halide scintillators and closely related materials are presented based on first-principles calculations. The optical properties are based on the Engel-Vosko generalized gradient approximation and the recently developed density functional of Tran and Blaha. The materials investigated are BaBr{sub 2}, BaIBr, BaCl{sub 2}, BaF{sub 2}, BaI{sub 2}, BiI{sub 3}, CaI{sub 2}, Cs{sub 2}LiYCl{sub 6}, CsBa{sub 2}Br{sub 5}, CsBa{sub 2}I{sub 5}, K{sub 2}LaBr{sub 5}, K{sub 2}LaCl{sub 5}, K{sub 2}LaI{sub 5}, LaBr{sub 3}, LaCl{sub 3}, SrBr{sub 2}, and YI{sub 3}. For comparison results are presented for the oxide CdWO{sub 4}. We find that the Tran Blaha functional gives greatly improved band gaps and optical properties in this class of materials. Furthermore, we find that unlike CdWO{sub 4}, most of these halides are highly isotropic from an optical point of view even though in many cases the crystal structures and other properties are not. This general result is rationalized in terms of halide chemistry. Implications for the development of ceramic halide scintillators are discussed.

  11. Metal halide lamps in the international space station ISS

    Microsoft Academic Search

    T. Nimalasuriya; A. J. Flikweert; M. Haverlag; P. C. M. Kemps; G. M. W. Kroesen; W. W. Stoffels; J. J. A. M. van der Mullen

    2006-01-01

    Optical emission spectroscopy was performed on a metal-halide lamp under micro-gravity conditions of the international space station. Several transitions of atomic and ionic Dy and atomic Hg have been measured at different lateral positions from which we obtained atomic and ionic Dy and atomic Hg intensity profiles. After Abel inversion, the calibrated radial intensity profile of Hg was used to

  12. Medical applications of infrared transmitting silver halide fibers

    Microsoft Academic Search

    F. Moser; D. Bunimovich; A. DeRowe; O. Eyal; A. German; Y. Gotshal; A. Levite; L. Nagli; A. Ravid; V. Scharf; S. Shalem; D. Shemesh; R. Simchi; I. Vasserman; A. Katzir

    1996-01-01

    It is clear that infrared transmitting fibers of high quality, with many uses in IR optical systems, can be fabricated from silver halide crystals. The process requires ultrapure starting material and control of extrusion parameters such as temperature and pressure. Under laboratory conditions, fibers have been produced that are usefully transparent from 2-25 ?m and have a loss coefficient of

  13. Calcium Phosphate: A potential host for halide contaminated plutonium wastes

    Microsoft Academic Search

    Brian L. Metcalfe; Ian W. Donald; Shirley K. Fong; Lee A. Gerrard; Denis M. Strachan

    The presence of significant quantities of fluoride and chloride in four types of legacy wastes from plutonium pyrochemical reprocessing required the development of a new wasteform which could adequately immobilize the halides in addition to the Pu and Am. Using a simulant chloride-based waste (Type I waste) and Sm as the surrogate for the Pu 3+ and Am 3+ present

  14. Semiempirical and DFT Investigations of the Dissociation of Alkyl Halides

    ERIC Educational Resources Information Center

    Waas, Jack R.

    2006-01-01

    Enthalpy changes corresponding to the gas phase heats of dissociation of 12 organic halides were calculated using two semiempirical methods, the Hartree-Fock method, and two DFT methods. These calculated values were compared to experimental values where possible. All five methods agreed generally with the expected empirically known trends in the…

  15. Reorientation of Impurity-Vacancy Dipoles in Cesium Halides

    Microsoft Academic Search

    S. Radhakrishna; K. P. Pande; R. Narayanan

    1972-01-01

    Dielectric loss measurements of lead and cadmium doped cesium halides have been reported in the temperature range 90-180°C. One loss peak which is attributed to the jump of vacancy in the six equivalent nn positions, has been observed in the plot of \\\\tandelta versus frequency isothermals. The plot of log fm (fm being the peak frequency) against 1\\/T gives a

  16. On the Boiling Points of the Alkyl Halides.

    ERIC Educational Resources Information Center

    Correia, John

    1988-01-01

    Discusses the variety of explanations in organic chemistry textbooks of a physical property of organic compounds. Focuses on those concepts explaining attractive forces between molecules. Concludes that induction interactions play a major role in alkyl halides and other polar organic molecules and should be given wider exposure in chemistry texts.…

  17. Alkali metal crystalline polymer electrolytes.

    PubMed

    Zhang, Chuhong; Gamble, Stephen; Ainsworth, David; Slawin, Alexandra M Z; Andreev, Yuri G; Bruce, Peter G

    2009-07-01

    Polymer electrolytes have been studied extensively because uniquely they combine ionic conductivity with solid yet flexible mechanical properties, rendering them important for all-solid-state devices including batteries, electrochromic displays and smart windows. For some 30 years, ionic conductivity in polymers was considered to occur only in the amorphous state above Tg. Crystalline polymers were believed to be insulators. This changed with the discovery of Li(+) conductivity in crystalline poly(ethylene oxide)(6):LiAsF(6). However, new crystalline polymer electrolytes have proved elusive, questioning whether the 6:1 complex has particular structural features making it a unique exception to the rule that only amorphous polymers conduct. Here, we demonstrate that ionic conductivity in crystalline polymers is not unique to the 6:1 complex by reporting several new crystalline polymer electrolytes containing different alkali metal salts (Na(+), K(+) and Rb(+)), including the best conductor poly(ethylene oxide)(8):NaAsF(6) discovered so far, with a conductivity 1.5 orders of magnitude higher than poly(ethylene oxide)(6):LiAsF(6). These are the first crystalline polymer electrolytes with a different composition and structures to that of the 6:1 Li(+) complex. PMID:19543313

  18. Alkali metal crystalline polymer electrolytes

    NASA Astrophysics Data System (ADS)

    Zhang, Chuhong; Gamble, Stephen; Ainsworth, David; Slawin, Alexandra M. Z.; Andreev, Yuri G.; Bruce, Peter G.

    2009-07-01

    Polymer electrolytes have been studied extensively because uniquely they combine ionic conductivity with solid yet flexible mechanical properties, rendering them important for all-solid-state devices including batteries, electrochromic displays and smart windows. For some 30 years, ionic conductivity in polymers was considered to occur only in the amorphous state above Tg. Crystalline polymers were believed to be insulators. This changed with the discovery of Li+ conductivity in crystalline poly(ethylene oxide)6:LiAsF6 (refs 4, 5). However, new crystalline polymer electrolytes have proved elusive, questioning whether the 6:1 complex has particular structural features making it a unique exception to the rule that only amorphous polymers conduct. Here, we demonstrate that ionic conductivity in crystalline polymers is not unique to the 6:1 complex by reporting several new crystalline polymer electrolytes containing different alkali metal salts (Na+, K+ and Rb+), including the best conductor poly(ethylene oxide)8:NaAsF6 discovered so far, with a conductivity 1.5 orders of magnitude higher than poly(ethylene oxide)6:LiAsF6. These are the first crystalline polymer electrolytes with a different composition and structures to that of the 6:1 Li+ complex.

  19. Resolution characteristics of graded doping and graded composition transmission-mode AlGaAs/GaAs photocathodes.

    PubMed

    Deng, Wenjuan; Zou, Jijun; Peng, Xincun; Feng, Lin; Zhu, Zhifu; Wang, Weilu; Zhang, Yijun; Chang, Benkang

    2015-02-20

    The resolution model of a graded doping and graded composition transmission-mode AlGaAs/GaAs photocathode is solved numerically from the two-dimensional continuity equations. According to the model, we calculate the theoretical modulation transfer function (MTF) of different graded doping and graded composition structures. The simulation results show that both graded composition and graded doping structures can increase the resolution of the photocathode. The exponentially doping and linear composition photocathode has the maximum resolution among the possible graded doping and graded composition photocathodes. The resolution improvement is attributed to the built-in electric field induced by a graded composition or graded doping structure. The simulation results also show that the MTFs of AlGaAs/GaAs cathodes increase as the AlGaAs layer thickness decreases, or the incident light wavelength increases. PMID:25968207

  20. A low emittance and high efficiency visible light photocathode for high brightness accelerator-based X-ray light sources

    SciTech Connect

    Vecchione, T.; Ben-Zvi, I.; Dowell, D.H.; Feng, J.; Rao, T.; Smedley, J.; Wan, W.; Padmore, H.A.

    2011-07-21

    Free-electron lasers and energy recovery linacs represent a new generation of ultra-high brightness electron accelerator based x-ray sources. Photocathodes are a critical performance-limiting component of these systems. Here, we describe the development of photocathodes based on potassium-cesium-antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light, and low transverse emittance.

  1. Simulations of the BNL\\/SLAC\\/UCLA 1.6 Cell Emittance Compensated Photocathode RF Gun Low Energy Beam Line

    Microsoft Academic Search

    D. T. PALMER; R. H. M ILLER; H. WINICK; X. J. WANG; K. B ATCHELOR; M. W OODLE; I. BEN-ZVI

    1996-01-01

    A dedicated low energy (2 to 10 MeV) experimental beam line is now under construction at Brookhaven National Laboratories Accelerator Test Facility (BNL\\/ATF) for photocathode RF gun testing and photoemission experiments. The design of the exper- imental line, using the 1.6 cell photocathode RF gun developed by the BNL\\/SLAC\\/UCLA RF gun collaboration is presented. Detailed beam dynamics simulations were performed

  2. Optical properties of strongly coupled Yb2+ and CN ions in alkali halide crystals: Electronic absorption and emission

    Microsoft Academic Search

    C. P. An; Volkmar Dierolf; Fritz Luty

    2000-01-01

    We have studied absorption and emission spectra of the 4f144f135d electronic transitions of Yb2+:(CN-)n defect complexes in NaCl, KCl, RbCl, and KBr host crystals under concentration variation of both dopants Yb2+ and CN-. Due to strong coupling between Yb2+ and (CN-)n, the Yb2+ electronic transitions shift drastically towards lower energies (from near uv to near ir) as the n value

  3. Cocrystallization of certain 4f and 5f elements in the bivalent state with alkali metal halides

    SciTech Connect

    Mikheev, N.B.; Kamenskaya, A.M.; Veleshko, I.E.; Kulyukhin, S.A.

    1987-01-01

    The cocrystallization of Fm/sup 2 +/, Es/sup 2 +/, Cf/sup 2 +/, Am/sup 2 +/, Yb/sup 2 +/, Eu/sup 2 +/ and Sr/sup 2 +/ with NaCl, KCl and KBr in tetrahydrofuran (THF), hexamethylphosphorotriamide (HMPA), and ethanol has been studied. It is shown that in water-ethanol medium An/sup 2 +/ cocrystallize with KCl by the formation of anomalous mixed crystals and Ln/sup 2 +/ do not cocrystallize. In HMPA neither Ln/sup 2 +/ nor An/sup 2 +/ are observed to transfer into the KBr solid phase, while in THF both Ln/sup 2 +/ and An/sup 2 +/ cocrystallize with NaCl. The change in the behavior on Ln/sup 2 +/ and An/sup 2 +/ cocrystallize with a change from one solvent to another is caused by the difference in the effective ionic radii of these elements, which arises from the large nephelauxetic effect for An/sup 2 +/ as well as by the different solvating power of these solvents.

  4. Additional evidence for the interconnection of the conductivity activation energy with bulk properties in multiphased alkali halide mixed crystals

    NASA Astrophysics Data System (ADS)

    Katsika-Tsigourakou, Vassiliki; Symeonidis, Chrysoleon

    2009-05-01

    The preparation of mixed crystals of NaBr and KBr from melt as well as their physical characterization have recently been reported. Electrical measurements were carried out at various temperatures, which showed that their conductivity increases with the increase in temperature and varies nonlinearly with bulk composition. We find that for most of the compositions studied, the activation energy deduced from the temperature variation of their conductivity obeys a thermodynamical model that interrelates the defect Gibbs energy with the bulk elastic and expansivity data. The present finding is similar to the one recently obtained in the mixed crystals of NaBr and KCl (V. Katsika-Tsigourakou, A. Vassilikou-Dova, Physica B, 403 (2008) 3809).

  5. Charge Lifetime Measurements at High Average Current Using a K{sub 2}CsSb Photocathode inside a DC High Voltage Photogun

    SciTech Connect

    Mammei, Russell; Feingold, Joshua; Adderley, Philip; Clark, James; Covert, Steven; Grames, Joseph; Hansknecht, John; Machie, Danny; Poelker, Benard; Rao, Triveni; Smedley, John; Walsh, John; McCarter, James

    2013-03-01

    Two K{sub 2}CsSb photocathodes were manufactured at Brookhaven National Lab and delivered to Jefferson Lab within a compact vacuum apparatus at pressure ~ 10{sup -11} Torr. These photocathodes were evaluated using a dc high voltage photogun biased at voltages up to 200 kV, and illuminated with laser light at wavelengths 440 or 532 nm, to generate dc electron beams at currents up to 20 mA. Some conditions produced exceptionally large photocathode charge lifetimes, without measurable quantum efficiency (QE) decay, even from the center of the photocathode where operation using GaAs photocathodes is precluded due to ion bombardment. Under other conditions the charge lifetime was poor, suggesting a complex QE decay mechanism likely related to chemistry and localized heating via the laser beam. Following beam delivery, the photocathodes were evaluated using a scanning electron microscope with energy dispersive x-ray spectroscopy capability, to determine surface morphology and chemical composition.

  6. Methods and Mechanisms for Cross-Electrophile Coupling of Csp(2) Halides with Alkyl Electrophiles.

    PubMed

    Weix, Daniel J

    2015-06-16

    Cross-electrophile coupling, the cross-coupling of two different electrophiles, avoids the need for preformed carbon nucleophiles, but development of general methods has lagged behind cross-coupling and C-H functionalization. A central reason for this slow development is the challenge of selectively coupling two substrates that are alike in reactivity. This Account describes the discovery of generally cross-selective reactions of aryl halides and acyl halides with alkyl halides, the mechanistic studies that illuminated the underlying principles of these reactions, and the use of these fundamental principles in the rational design of new cross-electrophile coupling reactions. Although the coupling of two different electrophiles under reducing conditions often leads primarily to symmetric dimers, the subtle differences in reactivity of aryl halides and alkyl halides with nickel catalysts allowed for generally cross-selective coupling reactions. These conditions could also be extended to the coupling of acyl halides with alkyl halides. These reactions are exceptionally functional group tolerant and can be assembled on the benchtop. A combination of stoichiometric and catalytic studies on the mechanism of these reactions revealed an unusual radical-chain mechanism and suggests that selectivity arises from (1) the preference of nickel(0) for oxidative addition to aryl halides and acyl halides over alkyl halides and (2) the greater propensity of alkyl halides to form free radicals. Bipyridine-ligated arylnickel intermediates react with alkyl radicals to efficiently form, after reductive elimination, new C-C bonds. Finally, the resulting nickel(I) species is proposed to regenerate an alkyl radical to carry the chain. Examples of new reactions designed using these principles include carbonylative coupling of aryl halides with alkyl halides to form ketones, arylation of epoxides to form ?-aryl alcohols, and coupling of benzyl sulfonate esters with aryl halides to form diarylmethanes. Arylnickel(II) intermediates can insert carbon monoxide to form acylnickel(II) intermediates that react with alkyl halides to form ketones, demonstrating the connection between the mechanisms of reactions of aryl halides and acid chlorides with alkyl halides. The low reactivity of epoxides with nickel can be overcome by the use of either titanium or iodide cocatalysis to facilitate radical generation and this can also be extended to enantioselective arylation of meso-epoxides. The high reactivity of benzyl bromide with nickel, which leads to the formation of bibenzyl in attempted reactions with bromobenzene, can be overcome by using a benzyl mesylate along with cobalt phthalocyanine cocatalysis to convert the mesylate into an alkyl radical. PMID:26011466

  7. Robust CsBr/Cu photocathodes for the linac coherent light source

    NASA Astrophysics Data System (ADS)

    Maldonado, Juan R.; Liu, Zhi; Dowell, D. H.; Kirby, Robert E.; Sun, Yun; Pianetta, Piero; Pease, Fabian

    2008-06-01

    The linac coherent light source (LCLS), an x-ray free-electron laser project presently under construction at SLAC, uses a 2.856 GHz rf photocathode gun with a copper cathode for its electron source. While the copper cathode is performing well for the LCLS project, a cathode material with higher quantum efficiency would reduce the drive laser requirements and allow a greater range of operating conditions. Therefore a robust CsBr/Cu photocathode with greater than 50 times the quantum yield at 257 nm relative to the present LCLS copper cathode has been investigated. Preliminary experiments using a dedicated electron source development test stand at SLAC/SSRL are encouraging and are presented in this paper.

  8. Magnetic emittance suppression using a bucking coil for a dc photocathode electron gun.

    PubMed

    Nagai, Ryoji; Hajima, Ryoichi; Nishimori, Nobuyuki

    2012-12-01

    Magnetic emittance suppression was demonstrated using a bucking coil for a dc photocathode electron gun. The magnetic emittance is derived from a leakage magnetic field on the cathode surface originating from a solenoid lens, and is important for realizing a high brightness dc photocathode electron gun. In order to solve this problem, a bucking coil integrated solenoid lens has been developed. The solenoid lens consists of a main coil, a bucking coil, and a pure iron yoke. The bucking coil and the main coil are integrated in the same yoke in order to prevent distortion of the magnetic field due to misalignment of the two coils. The emittance was measured and calculated as a function of the exciting current of the bucking coil and as a function of the electron beam size on the cathode. PMID:23277978

  9. Magnetic emittance suppression using a bucking coil for a dc photocathode electron gun

    NASA Astrophysics Data System (ADS)

    Nagai, Ryoji; Hajima, Ryoichi; Nishimori, Nobuyuki

    2012-12-01

    Magnetic emittance suppression was demonstrated using a bucking coil for a dc photocathode electron gun. The magnetic emittance is derived from a leakage magnetic field on the cathode surface originating from a solenoid lens, and is important for realizing a high brightness dc photocathode electron gun. In order to solve this problem, a bucking coil integrated solenoid lens has been developed. The solenoid lens consists of a main coil, a bucking coil, and a pure iron yoke. The bucking coil and the main coil are integrated in the same yoke in order to prevent distortion of the magnetic field due to misalignment of the two coils. The emittance was measured and calculated as a function of the exciting current of the bucking coil and as a function of the electron beam size on the cathode.

  10. Activation processes on GaAs photocathode by different currents of oxygen source

    NASA Astrophysics Data System (ADS)

    Miao, Zhuang; Shi, Feng; Cheng, Hongchang; Wang, Shufei; Zhang, Xiaohui; Yuan, Yuan; Chen, Chang

    2015-04-01

    In order to know the influence of activation processes on GaAs photocathodes, three GaAs samples were activated by a fixed current of cesium source and different currents of oxygen source. The current of caesium source is same during activation to ensure initial adsorption of caesium quantum is similar, which is the base to show the difference during alternation activation of caesium and oxygen. Analysed with the activation data, it is indicated that Cs-to-O current ratio of 1.07 is the optimum ratio to obtain higher sensitivity and better stability. According to double dipole model, stable and uniform double dipole layers of GaAs-O-Cs:Cs-O-Cs are formed and negative electron affinity is achieved on GaAs surface by activation with cesium and oxygen. The analytical result is just coincident with the model. Thus there is an efficient technological method to improve sensitivity and stability of GaAs photocathode.

  11. Experimental studies of the charge limit phenomenon in NEA GaAs photocathodes

    SciTech Connect

    Tang, H.; Alley, R.K.; Aoyagi, H.; Clendenin, J.E.; Frisch, J.C.; Mulhollan, G.A.; Saez, P.J.; Schultz, D.C.; Turner, J.L.

    1994-06-01

    Negative electron affinity GaAs photocathodes have been in continuous use at SLAC for generating polarized electron beams since early 1992. If the quantum efficiency of a GaAs cathode is below a critical value, the maximum photoemitted charge with photons of energies close to the band gap in a 2-ns pulse is found to be limited by the intrinsic properties of the cathode instead of by the space charge limit. We have studied this novel charge limit phenomenon in a variety of GaAs photocathodes of different structures and doping densities. We find that the charge limit is strongly dependent on the cathode`s quantum efficiency and the extraction electric field, and to a lesser degree on the excitation laser wavelength. In addition, we show that the temporal behavior of the charge limit depends critically on the doping density.

  12. Silicon photocathode behavior in acidic V(II)-V(III) solutions

    SciTech Connect

    Heller, A.; Lewerenz, H.J.; Miller, B.

    1981-01-01

    The photoelectrochemical cell: p-Si/VCl/sub 3/-VCl/sub 2/-HCl/C shows a 2.87% light-to-electrical conversion efficiency at 101 mW/cm/sup 2/ of natural sunlight. Over a 0.5 V range, the photovoltage follows the redox potential of the solution. Pinning of the p-Si surface Fermi level, previously proposed for this system, is ruled out. The advantages of photocathode-based semi-conductor-liquid junction solar cells (over photoanode-based systems) are demonstrated and discussed and comparisons made with the previously described p-InP photocathode (9.47% light-to-electrical conversion efficiency). Current-voltage characteristics of the cell are given at 101 mW/cm/sup 2/ sunlight. It is shown that the stability and efficiency of this cell is the best of any Si-based photoelectrochemical cell studied so far. (MJJ)

  13. Engineering Design and Fabrication of an Ampere-Class Superconducting Photocathode Electron Gun

    SciTech Connect

    Ben-Zvi,I.

    2008-11-17

    Over the past three years, Advanced Energy Systems and Brookhaven National Laboratory (BNL) have been collaborating on the design of an Ampere- class superconducting photocathode electron gun. BNL performed the physics design of the overall system and RF cavity under prior programs. Advanced Energy Systems (AES) is currently responsible for the engineering design and fabrication of the electron gun under contract to BNL. We will report on the engineering design and fabrication status of the superconducting photocathode electron gun. The overall configuration of the cryomodule will be reviewed. The layout of the hermitic string, space frame, shielding package, and cold mass will be discussed. The engineering design of the gun cavity and removable cathode will be presented in detail and areas of technical risk will be highlighted. Finally, the fabrication sequence and fabrication status of the gun cavity will be discussed.

  14. Photo-cathode preparation system of the A0 photo-injector

    SciTech Connect

    Moyses Kuchnir et al.

    2002-08-23

    The A0 Photo-Injector is an electron accelerator located in the AZero high bay area of Fermilab. A pulsed laser system generates electron bunches by the photo-electric effect when hitting a photo-cathode in a 1.5-cell, 1.3 GHz RF gun. A 9-cell, 1.3 GHz superconducting resonant cavity then accelerates the electrons to 15 MeV. The 10 ps time resolved waveform of the laser pulses is transferred to the electron bunches. This report is focused on the first hardware component of this accelerator, the Photo-cathode Preparation System. The reason for its existence is in the nature of the photo-electric material film used: Cs{sub 2}Te (Cesium Telluride), a very reactive compound that once coated on the cathode requires that it be transported and used in ultra high vacuum (UHV), i.e. < 10{sup -9} Torr.

  15. Large area polycrystalline diamond films as high current photocathodes for linear induction accelerators

    SciTech Connect

    Shurter, R.P.; Moir, D.C.; Devlin, D.J.; Springer, R.W.

    1997-08-01

    Investigations are underway at Los Alamos to develop a new generation of high current, low source temperature photo cathodes able to operate in vacuum environments with pressures above 10e-6 torr without poisoning or degradation of emission properties. Polycrystalline diamond films are emerging as the ideal material for these photocathodes. Robustness, high quantum efficiency and high thermal conductivity are fundamental necessary attributes that are found in diamond. The high electron/hole mobility in the boron doped diamond lattice and the ability to create a negative electron affinity surface through downward band bending allow for high current density emission with quantum efficiencies of 0.5% when illuminated by a ArF laser. We report the results to date toward the development of a four kiloampere photocathode with a source temperature below 5eV for the DARHT linear induction Accelerator

  16. Photoemission Studies of Metallic Photocathodes Prepared by Pulsed Laser Ablation Deposition Technique

    SciTech Connect

    Fasano, V.; Lorusso, A.; Perrone, A. [National Institute of Nuclear Physics and Physics Department, University of Salento, Via Arnesano, 73100-Lecce (Italy); De Rosa, H. [Laboratorio de Metalografia, Dpto. Ingenieria Mecanica y Naval, Facultad de Ingenieria, Universidad de Buenos Aires (Argentina); Cultrera, L. [National Institute of Nuclear Physics, National Laboratories, Frascati (Italy)

    2010-11-10

    We present the results of our investigation on metallic films as suitable photocathodes for the production of intense electron beams in RF photoinjector guns. Pulsed laser ablation deposition technique was used for growing Mg and Y thin films onto Si and Cu substrates in high vacuum and at room temperature.Different diagnostic methods were used to characterize the thin films deposited on Si with the aim to optimize the deposition process. Photoelectron performances were investigated on samples deposited on Cu substrate in an ultra high vacuum photodiode chamber at 10{sup -7} Pa. Relatively high quantum efficiencies have been obtained for the deposited films, comparable to those of corresponding bulks. Samples could stay for several months in humid open air before being tested in a photodiode cell. The deposition process and the role of the photocathode surface contamination and its influence on the photoelectron performances are presented and discussed.

  17. Numerical modeling of alkali vapor lasers.

    PubMed

    Shu, Hong; Chen, Ying; Bass, Michael; Monjardin, J Fernando; Deile, Jochen

    2011-10-10

    Detailed numerical analyses are presented of a continuous wave (cw), single spatial mode alkali vapor laser pumped by a diffraction-limited Ti: Sapphire laser. These analyses provide insight into the operation of alkali vapor lasers to aid in the development of high power, diode laser pumped alkali vapor lasers. It is demonstrated that in the laser considered the laser spatial pattern is significantly changed after each pass through the gain medium, and the laser spatial pattern in steady state operation is also very different from that of the passive cavity mode. According to the calculation, lasing significantly improves the pump absorption efficiency and changes the absorbed pump distribution. The effect of varying the transverse size of the pumped region is also analyzed and an optimum pump beam waist radius is demonstrated. In addition, the shift of the pump beam waist location is also studied. The computation method and its convergence behavior are also described in detail. PMID:21996995

  18. SAFE Alkali Metal Heat Pipe Reliability

    NASA Astrophysics Data System (ADS)

    Reid, Robert S.

    2003-01-01

    Alkali metal heat pipes are among the best understood and tested of components for first generation space fission reactors. A flight reactor will require production of a hundred or more heat pipes with assured reliability over a number of years. To date, alkali metal heat pipes have been built mostly in low budget development environments with little formal quality assurance. Despite this, heat pipe test samples suggest that high reliability can be achieved with the care justified for space flight qualification. Fabrication procedures have been established that, if consistently applied, ensure long-term trouble-free heat pipe operation. Alkali metal heat pipes have been successfully flight tested in micro gravity and also have been shown capable of multi-year operation with no evidence of sensitivity to fast neutron fluence up to 1023 n/cm2. This represents 50 times the fluence of the proposed Safe Affordable Fission Engine (SAFE-100) heat pipe reactor core.

  19. Quantum efficiency measurements of a copper photocathode in an RF electron gun

    Microsoft Academic Search

    P. Davis; G. Hairapetian; C. Clayton; C. Joshi; S. Hartman; C. Pellegrini; J. Rosenzweig

    1993-01-01

    A 4.5 MeV photocathode RF gun has been commissioned at UCLA. A photo-injector drive laser produces sub 2 ps pulses of UV (?=266 nm) light with up to 200 ?J\\/pulse, and illuminates a copper cathode. The photoelectrons are accelerated to an energy of 3.5 MeV within the gun. The electron beam charge is measured as a function of laser energy

  20. Quantum efficiency measurements of photocathode candidates for back-lighted thyratrons

    Microsoft Academic Search

    Esin B. Sozer; Chunqi Jiang; Martin A. Gundersen; Ryan J. Umstattd

    2009-01-01

    Light-activated pseudospark switches, also called back-lighted thyratrons (BLTs), are low pressure, high voltage (typ. 10-50 kV), high current (typ. 1-100 kA) glow-mode switches. It is of interest to develop BLTs with reliable and practical optical triggering systems for applications of compact pulsed power. This paper reports the results of research into photocathode materials for BLTs to enhance switching performance and

  1. Results from Cs activated GaN photocathode development for MCP detector systems at NASA GSFC

    Microsoft Academic Search

    Timothy J. Norton; Bruce E. Woodgate; Joseph Stock; George Hilton; Melville P. Ulmer; Shahid Aslam; R. D. Vispute

    2003-01-01

    We describe the development of high quantum efficiency UV photocathodes for use in large area two dimensional microchannel plated based, detector arrays to enable new UV space astronomy missions. Future UV missions will require improvements in detector sensitivity, which has the most leverage for cost-effective improvements in overall telescope\\/instrument sensitivity. We use new materials such as p-doped GaN, AlGaN, ZnMgO,

  2. The Argonne Wakefield Accelerator high current photocathode gun and drive linac

    Microsoft Academic Search

    P. Schoessow; E. Chojnacki; G. Cox; W. Gai; C. Ho; R. Konecny; J. Power; M. Rosing; J. Simpson; N. Barov; M. Conde

    1995-01-01

    The Argonne Wakefield Accelerator (AWA) is a new facility for advanced accelerator research. A major component of the AWA is its drive linac, consisting of a unique high current short pulse L-band photocathode based gun and special standing wave preaccelerator designed to produce 100 nC, 30 ps electron bunches at 20 MeV. Commissioning on the drive linac is now underway.

  3. The Argonne Wakefield Accelerator high current photocathode, gun and drive linac

    SciTech Connect

    Schoessow, P.; Chojnacki, E.; Cox, G. [and others

    1995-06-01

    The Argonne Wakefield Accelerator (AWA) is a new facility for advanced accelerator research. A major component of the AWA is its drive linac, consisting of a unique high current short pulse L-Band photocathode based gun and special standing wave preaccelerator designed to produce 100 nC, 30 ps electron bunches at 20 MeV. Commissioning on the drive linac is now underway. We report on our initial operating experience with this novel machine, including bunch length and emittance measurements.

  4. Band filling with free charge carriers in organometal halide perovskites

    NASA Astrophysics Data System (ADS)

    Manser, Joseph S.; Kamat, Prashant V.

    2014-09-01

    The unique and promising properties of semiconducting organometal halide perovskites have brought these materials to the forefront of solar energy research. Here, we present new insights into the excited-state properties of CH3NH3PbI3 thin films through femtosecond transient absorption spectroscopy measurements. The photoinduced bleach recovery at 760?nm reveals that band-edge recombination follows second-order kinetics, indicating that the dominant relaxation pathway is via recombination of free electrons and holes. Additionally, charge accumulation in the perovskite films leads to an increase in the intrinsic bandgap that follows the Burstein-Moss band filling model. Both the recombination mechanism and the band-edge shift are studied as a function of the photogenerated carrier density and serve to elucidate the behaviour of charge carriers in hybrid perovskites. These results offer insights into the intrinsic photophysics of semiconducting organometal halide perovskites with direct implications for photovoltaic and optoelectronic applications.

  5. Membrane Cells in Chlor Alkali Application

    E-print Network

    Lesker, K.

    MEMBRANE CELLS IN COLOR ALKALI APPLICATION Dr. K. Lesker, UHDE GmbH ABSTRACT The worldwide chlorine/caustic soda production has reached approximately 40 million tpy. Despite the stagnation of the chlorine demand in thc wcstcrn world, e... lias t:spl:cially proVt:1I ils vt:rsalilily in oruer lo tultill all reqUirements tor the conversion of an existing chlor alkali plant. The worldwide chlorine/causlic soda production has reached approximately 40 milhon tpv. The United States...

  6. Metal on metal oxide nanowire Co-catalyzed Si photocathode for solar water splitting

    NASA Astrophysics Data System (ADS)

    Sun, Ke; Madsen, Kristian; Andersen, Pål; Bao, Weining; Sun, Zhelin; Wang, Deli

    2012-05-01

    We report a systematic study of Si|ZnO and Si|ZnO| metal photocathodes for effective photoelectrochemical cells and hydrogen generation. Both ZnO nanocrystalline thin films and vertical nanowire arrays were studied. Si|ZnO electrodes showed increased cathodic photocurrents due to improved charge separation by the formation of a p/n junction, and Si|ZnO:Al (n+-ZnO) and Si|ZnO(N2) (thin films prepared in N2/Ar gas) lead to a further increase in cathodic photocurrents. Si|ZnONW (nanowire array) photocathodes dramatically increased the photocurrents and thus photoelectrochemical conversion efficiency due to the enhanced light absorption and enlarged surface area. The ZnO film thickness and ZnO nanowire length were important to the enhancements. A thin metal coating on ZnO showed increased photocurrent due to a catalyzed hydrogen evolution reaction and Ni metal showed comparable catalytic activities to those of Pt and Pd. Moreover, photoelectrochemical instability of Si|ZnO electrodes was minimized by metal co-catalysts. Our results indicate that the metal and ZnO on p-type Si serve as co-catalysts for photoelectrochemical water splitting, which can provide a possible low-cost and scalable method to fabricate high efficiency photocathodes for practical applications in clean solar energy harvesting.

  7. Modeling Photoemission of Spin-Polarized Electrons from NEA GaAs Photocathodes

    NASA Astrophysics Data System (ADS)

    Chubenko, Oksana; Afanasev, Andrei

    2015-04-01

    At present, photoemission from strained GaAs activated to negative electron affinity (NEA) is a main source of polarized electrons for modern nuclear-physics and particle-physics facilities. Future experiments at advanced electron colliders will require high-current polarized electron beams, which could provide high polarization and luminosity. This sets new requirements for photocathodes in terms of high quantum efficiency (QE) (>>1%) and spin polarization (~85%). Detailed simulation and modeling of physics processes in photocathodes is important for optimization of their design in order to achieve high QE and reduce depolarization mechanisms. The purpose of the present work was to develop a semi-phenomenological model, which could predict photoemission and electron spin polarization from NEA GaAs photocathodes. Effect of the presence of nanostructures was also studied. Simulation results were compared to the experimental results obtained by the polarized electron source group at Thomas Jefferson National Accelerator Facility. Work supported by Thomas Jefferson Accelerator Facility and George Washington University.

  8. Comparison of the optical characteristics of GaAs photocathodes grown using MBE and MOCVD

    NASA Astrophysics Data System (ADS)

    Bourree, Loig E.; Chasse, David R.; Thamban, P. L. Stephan; Glosser, Robert

    2003-02-01

    Modern image tube intensifier photocathodes rely on a GaAs active layer, which has traditionally been grown using metallorganic chemical vapor deposition (MOCVD) due to its high throughput and lower cost of operation. Molecular beam epitaxy (MBE) processes have not been thoroughly investigated in that context. The latter technique demonstrates greater structural interface control as well as an improved growth quality for a multitude of applications. Still, at this point it is uncertain, considering actual fabrication techniques for image intensifiers, that the higher growth quality will result in an improvement of devices. Studies are being carried out to compare fundamental optical parameters between GaAs photocathodes grown by both MOCVD and MBE following the same growth and fabrication guidelines. These experiments involve using photoluminescence and Raman spectroscopy to obtain electron and phonon energy information on the materials. An atomic force microscope (AFM) is employed to compare the surface roughness of both methods. In addition, the white light responses of the photocathodes are also evaluated during the creation of a negative electron affinity (NEA) surface to observe any differences between the two growth techniques.

  9. Nonlinear response of the photocathode of an x-ray streak camera to UV light

    SciTech Connect

    Kyrala, G.A.; Oro, D.M.; Studebaker, J.K.; Wood, W.M.; Schappert, G.T.; Watts, S.; Fulton, R.D.

    1994-09-01

    We have found that a potassium-iodide photocathode of an x-ray streak camera responds to UV light at {lambda}=308 nm. The photocathode surface work function, 6.5 eV, is larger than the 4 eV energy of the UV photon, hence the source of the response is interesting. We will present results on the response of a transmission type potassium-iodide photocathode to the UV light from a {lambda}308 nm, subpicosecond XeCl laser and from a {lambda}=326 nm HeCd laser. We will test for the nonlinearity of the yield to measure of the number of photons that are needed to be absorbed before a signal is recorded. We will present data on the effect of the UV irradiance on the yield, as well as on the temporal width of the recorded signal. We will give an explanation of the observation and its effect on the dynamic-range response of the streak-camera. We will show that the response is linear with the incident irradiance, up to an incident irradiance of 10{sup 8} W/cm{sup 2} and we will explain the observation.

  10. Rare gas recovery systems for rare gas halide lasers

    SciTech Connect

    Kutschke, K.O.; Hackett, P.A.; Willis, C.

    1981-11-01

    A system is described for the recovery of xenon from XeCl lasers and variants for other rare gas halide (RGH) combinations are presented. The batch recovery systems discussed are simple and cost effective and lead to no degradation of laser performance. The added cost associated with continuous gas processing seems difficult to justify at the present time for a system of this size.

  11. Organometal halide perovskites as useful materials in sensitized solar cells.

    PubMed

    Singh, Surya Prakash; Nagarjuna, P

    2014-04-14

    Organometal halide perovskites offer dual potential properties as a light harvester and at the same time as a hole conductor in inorganic-organic hybrid heterojunction solar cells. The sequential deposition route provides a power conversion efficiency of 15% under standard AM1.5G test conditions. In this perspective, we will briefly summarize the development of perovskite-sensitized solar cells from their first report up to the present. PMID:24577264

  12. Improved spatial frequency response in silver halide sensitized gelatin holograms

    Microsoft Academic Search

    A. Beléndez; C. Neipp; I. Pascual

    1998-01-01

    We report what we believe to be the best results obtained to date with regard to the spatial frequency response of silver halide sensitized gelatin (SHSG) holograms. A very high diffraction efficiency, as high as 91% (after allowing for reflection), and an almost flat spatial frequency response between 800 lines\\/mm and 2800 lines\\/mm have been achieved using the new BB-640

  13. Silver Halide Photonic Crystal Fibers for the Middle Infrared

    Microsoft Academic Search

    Eran Rave; Pinhas Ephrat; Mati Goldberg; Efi Kedmi; Abraham Katzir

    2004-01-01

    Photonic crystal fibers are normally holey silica fibers, which are opaque in the mid- and far-infrared. We have fabricated novel fibers by multiple extrusions of silver halide crystalline materials, which are highly transparent in the mid-infrared. These fibers are composed of two solid materials; The core consists of pure AgBr, and the cladding includes AgCl fiberoptic elements arranged in two

  14. Methyl halide emissions from savanna fires in southern Africa

    Microsoft Academic Search

    M. O. Andreae; E. Atlas; G. W. Harris; G. Helas; A. de Kock; R. Koppmann; W. Maenhaut; S. Manø; W. H. Pollock; J. Rudolph; D. Scharffe; G. Schebeske; M. Welling

    1996-01-01

    The methyl halides, methyl chloride (CH3Cl), methyl bromide (CH3Br), and methyl iodide (CH3I), were measured in regional air samples and smoke from savanna fires in southern Africa during the Southern Africa Fire-Atmosphere Research Initiative-92 (SAFARI-92) experiment (August-October 1992). All three species were significantly enhanced in the smoke plumes relative to the regional background. Good correlations were found between the methyl

  15. Kinetics of halide chemical vapor deposition of silicon carbide film

    Microsoft Academic Search

    Rong Wang; Ronghui Ma

    2007-01-01

    Halide chemical vapor deposition (HCVD) emerges as a promising method for growing thick silicon carbide (SiC) epilayers, due to its ability to deposit SiC film at a high growth rate. In this paper, we develop a comprehensive model for HCVD of SiC film using silicon tetrachloride and propane as precursors. The model includes gas flow, heat and mass transfer, gas-phase

  16. Diode Pumped Alkali Lasers: History, current state and perspectives

    Microsoft Academic Search

    B. V. Zhdanov; M. K. Shaffer; R. J. Knize

    2011-01-01

    emission. However, the real interest to alkali vapor lasers appeared after the first demonstration in 2003 [2] of a really efficient lasing in Rb vapor optically pumped by Ti:Sapphire laser. This interest was stimulated by a possibility of using efficient diode lasers for pumping of alkali vapors that promised a very high total wall plug efficiency Diode Pumped Alkali Laser

  17. Ultrafast Electron Dynamics at Alkali/Ice Structures

    E-print Network

    Wolf, Martin

    Ultrafast Electron Dynamics at Alkali/Ice Structures Adsorbed on a Metal Surface Im Fachbereich or indirectly via the hydrogen bonded water molecules. In both cases the presence of the alkali influences, which can mediate chemical reactions by dissociative electron attachment (DEA). The influence of alkali

  18. Spin-Exchange Optical Pumping with Alkali-Metal Vapors

    E-print Network

    Walker, Thad G.

    Spin-Exchange Optical Pumping with Alkali-Metal Vapors by Earl D. Babcock A dissertation submitted the values of the rate coef- ficients for spin-exchange, many aspects of the alkali-metal polarization measurements of spin-exchange rate coefficients and efficiencies. A method to extend SEOP to multiple alkali

  19. Microscopic surface structure of liquid alkali metals H. Tostmann

    E-print Network

    Pershan, Peter S.

    Microscopic surface structure of liquid alkali metals H. Tostmann Division of Applied Sciences study of the microscopic structure of the surface of a liquid alkali metal. The bulk liquid structure of an elemental liquid alkali metal. Analysis of off-specular diffuse scattering and specular x-ray reflectivity

  20. Core repulsion e ects in alkali trimers R. Gu erout

    E-print Network

    Recanati, Catherine

    Core repulsion e#11;ects in alkali trimers R. Gu#19;erout Laboratoire Aim#19;e Cotton, CNRS, B was entitled "Electronic structure properties of alkali dimers and trimers. Prospects for alignment separation, involved when the potential energy surfaces of alkali trimers are calculated with a quantum

  1. Spin relaxation in alkali-metal 1 S. Kadlecek,1

    E-print Network

    Walker, Thad G.

    Spin relaxation in alkali-metal 1 g ¿ dimers S. Kadlecek,1 L. W. Anderson,1 C. J. Erickson,2 and T May 2001; published 15 October 2001 We discuss the relaxation of a spin-polarized alkali-metal vapor spin-exchange collisions with an electron-spin-polarized alkali-metal vapor. Since the efficiency

  2. Geneticprogrammingapproachforelectron-alkali-metalatomcollisions SalahYaseenEl-Bakry1

    E-print Network

    Fernandez, Thomas

    1 Geneticprogrammingapproachforelectron-alkali-metalatomcollisions SalahYaseenEl-Bakry1 andAmrRadi2 the total collisional cross sections of the scattering of electrons by alkali atoms. The experimental match to the experimental data. Keywords: Genetic Programming, electron scattering, alkali atoms, total

  3. Depth profile of halide anions under highly charged biological membrane

    NASA Astrophysics Data System (ADS)

    Sung, Woongmo; Wang, Wenjie; Lee, Jonggwan; Vaknin, David; Kim, Doseok

    2015-03-01

    Halide ion (Cl- and I-) distribution under a cationic Langmuir monolayer consisting of 1,2-dipalmitoyl-3 trimethylammonium-propane (DPTAP) molecules was investigated by vibrational sum-frequency generation (VSFG) and X-ray spectroscopy. From VSFG spectra, it was observed that large halide anions (I-) screen surface charge more efficiently so that interfacial water alignment becomes more randomized. On the other hand, number density of ions directly measured by X-ray fluorescence spectroscopy at grazing incidence angle reveals that the ion densities within 6 ~ 8 nm are the same for both I- and Cl-. Since the observed ion densities in both cases are almost equal to the charge density of the DPTAP monolayer, we propose that larger halide anions are attracted closer to the surface making direct binding with the charged headgroups of the molecules in the monolayer, accomplishing charge neutrality in short distance. This direct adsorption of anions also disturbs the monolayer structure both in terms of the conformation of alkyl chains and the vertical configuration of the monolayer, with iodine having the stronger effect. Our study shows that the length scale that ions neutralize a charged interface varies significantly and specifically even between monovalent ions.

  4. Colloidal nanocrystals with inorganic halide, pseudohalide, and halometallate ligands.

    PubMed

    Zhang, Hao; Jang, Jaeyoung; Liu, Wenyong; Talapin, Dmitri V

    2014-07-22

    We investigate simple halides and pseudohalides as an important class of inorganic ligands for nanocrystals (NCs) in solution phase ligand exchange. These short, robust, and easy to model ligands bind to the NC surface and provide electrostatic stabilization of NC dispersions in N-methylformamide. The replacement of organic ligands on NCs with compact halide and pseudohalide ligands greatly facilitates electronic communication between NCs. For example, a high electron mobility of ? ? 12 cm(2) V(-1) s(-1) has been observed in thin films made of I(-)-capped CdSe NCs. We also studied charge transport properties of thin films based on the pseudohalide N3(-)-capped InAs NCs, suggesting the possibility of obtaining "all III-V" NC solids. In addition, we extend the surface chemistry of halometallates (e.g., CH3NH3PbI3), which can stabilize colloidal solutions of lead chalcogenide NCs. These halide, pseudohalide, and halometallate ligands enrich the current family of inorganic ligands and can open up more opportunities for applications of NCs in the fields of electronics, optoelectronics, and thermoelectrics. PMID:24988140

  5. Physical and electrochemical study of halide-modified activated carbons

    NASA Astrophysics Data System (ADS)

    Barpanda, Prabeer

    The current thesis aims to improve the electrochemical capacity of activated carbon electrodes, which enjoy prominent position in commercial electrochemical capacitors. Our approach was to develop electrochemical capacity by developing faradaic pseudocapacitance in carbon through a novel mechanochemical modification using iodine and bromine. Various commercial carbons were mechanochemically modified via solid-state iodation and vapour phase iodine-incorporation. The halidation-induced changes in the structure, composition, morphology, electrical and electrochemical properties of carbon materials were studied using different characterization techniques encompassing XRD, XRF, XPS, Raman spectroscopy, BET study, TEM, SAXS and electrochemical testing followed by an intensive battery of physical and electrochemical characterization. The introduction of iodine into carbon system led to the formation of polyiodide species that were preferentially reacted within the micropore voids within the carbon leading to the development of a faradaic reaction at 3.1V. In spite of the lower surface area of modified carbon, we observed manyfold increase in its electrochemical capacity. Parallel inception of non-faradaic development and faradaic pseudocapacitive reaction led to promising gravimetric, surface area normalized and volumetric capacity in iodated carbons. With promising electrochemical improvement post halidation process, the chemical halidation method was extended to different class of carbons and halides. Carbons ranging from amorphous (activated) carbons to crystalline carbons (graphites, fluorographites) were iodine-modified to gain further insight on the local graphite-iodine chemical interaction. In addition, the effect of pore size distribution on chemical iodation process was studied by using in-house fabricated microporous carbon. A comparative study of commercial mesoporous carbons and in-house fabricated microporous carbons showed higher iodine-uptake ability and larger volumetric capacity development in case of microporous carbons. For halides, bromine was also tested in activated carbons, which showed similar set of physical and electrochemical modification, but to a smaller degree. Carbon-polyhalide nanocomposites form a very interesting system both for fundamental research and as new electrode systems for asymmetric hybrid capacitor and low-voltage high power battery type applications.

  6. Lasing in alkali atoms pumped by the dissociation of alkali-rare gas exciplexes (excimers)

    Microsoft Academic Search

    J. D. Readle; C. J. Wagner; J. T. Verdeyen; D. L. Carroll; J. G. Eden

    2009-01-01

    Lasing on the 62P1\\/2-->62S1\\/2(D1) resonance transition of atomic Cs at 894.3 nm has been demonstrated in mixtures of Ar, ethane, and Cs vapor by the photoexcitation of ground state Cs-Ar collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (exciplexes or excimers). The blue satellites of the alkali D2 lines provide a pathway for optically pumping atomic alkali lasers

  7. ALKALI-ACTIVATED FLY ASH CONCRETE

    Microsoft Academic Search

    Smith Songpiriyakij

    Fly ash concrete was produced without Portland cement incorporated in this work. Sodium hydroxide and sodium silicate solution were used as alkali activated in 7 different ratios to substitute calcium hydroxide from hydration process. Water was added to adjust their slump to about 200 + 25 mm. Cube samples 100 x 100 x 100 mm were cast to perform compressive

  8. Advanced diode-pumped alkali lasers

    Microsoft Academic Search

    B. V. Zhdanov; R. J. Knize

    2008-01-01

    In this review we present the analysis of optically pumped alkali lasers research and development from their first proposal in 1958 to the current state. Main achievements and problems existing in this field of research are discussed and possible solutions of the problems are proposed. Detailed description of the most important experiments and their results are presented. We have tried

  9. Terahertz radiation in alkali vapor plasmas

    SciTech Connect

    Sun, Xuan; Zhang, X.-C., E-mail: Xi-Cheng.Zhang@rochester.edu [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States)

    2014-05-12

    By taking advantage of low ionization potentials of alkali atoms, we demonstrate terahertz wave generation from cesium and rubidium vapor plasmas with an amplitude nearly one order of magnitude larger than that from nitrogen gas at low pressure (0.02–0.5?Torr). The observed phenomena are explained by the numerical modeling based upon electron tunneling ionization.

  10. Involvement of S-adenosylmethionine-dependent halide\\/thiol methyltransferase (HTMT) in methyl halide emissions from agricultural plants: isolation and characterization of an HTMT-coding gene from Raphanus sativus (daikon radish)

    Microsoft Academic Search

    Nobuya Itoh; Hiroshi Toda; Michiko Matsuda; Takashi Negishi; Tomokazu Taniguchi; Noboru Ohsawa

    2009-01-01

    BACKGROUND: Biogenic emissions of methyl halides (CH3Cl, CH3Br and CH3I) are the major source of these compounds in the atmosphere; however, there are few reports about the halide profiles and strengths of these emissions. Halide ion methyltransferase (HMT) and halide\\/thiol methyltransferase (HTMT) enzymes concerning these emissions have been purified and characterized from several organisms including marine algae, fungi, and higher

  11. Physics and chemistry of alkali-silica reactions

    SciTech Connect

    Diamond, S.; Barneyback, R.S. Jr.; Struble, L.J.

    1981-01-01

    The philosophy underlying recent research on alkali-silica reactions is reviewed and illustrations of recent results are provided. It has been possible to follow the kinetics of the chemical reaction between dissolved alkalis and opal in mortars by monitoring the rate at which alkalis are removed from the pore solutions of reacting mortars. Studies of the expansion behavior of synthetic alkali silica gels under controlled conditions were carried out and show no obvious correlation to chemical composition. The alkali reaction in mortars was found to produce changes in the appearance of opal grains documentable by the use of a scanning electron microscope.

  12. Development and evaluation of methods for total organic halide and purgeable organic halide in wastewater. Report for September 1980-October 1981

    SciTech Connect

    Riggin, R.M.; Lucas, S.V.; Lathouse, J.; Jungclaus, G.A.; Wensky, A.K.

    1984-01-01

    This report describes a series of studies involving the use of 'surrogate' methods for the determination of total organic halides (TOX), purgeable organic halides (POX), and solvent extractable organic halides (EOX), in wastewater and solid wastes. A pyrolysis/microcoulometric system was used as the analytical detection device for all studies. Method performance data are presented for the various surrogate methods. The results obtained using the surrogate methods were compared to those obtained using compound-specific methods based on gas chromatography (GC) or combined gas chromatography-mass spectrometry (gc/MS). The advantages and limitations of using the surrogate methods in place of more sophisticated procedures are discussed.

  13. Alkali metal recovery from carbonaceous material conversion process

    DOEpatents

    Sharp, David W. (Seabrook, TX); Clavenna, LeRoy R. (Baytown, TX); Gorbaty, Martin L. (Fanwood, NJ); Tsou, Joe M. (Galveston, TX)

    1980-01-01

    In a coal gasification operation or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein solid particles containing alkali metal residues are produced in the gasifier or similar reaction zone, alkali metal constitutents are recovered from the particles by withdrawing and passing the particles from the reaction zone to an alkali metal recovery zone in the substantial absence of molecular oxygen and treating the particles in the recovery zone with water or an aqueous solution in the substantial absence of molecular oxygen. The solution formed by treating the particles in the recovery zone will contain water-soluble alkali metal constituents and is recycled to the conversion process where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst. Preventing contact of the particles with oxygen as they are withdrawn from the reaction zone and during treatment in the recovery zone avoids the formation of undesirable alkali metal constituents in the aqueous solution produced in the recovery zone and insures maximum recovery of water-soluble alkali metal constituents from the alkali metal residues.

  14. Vibrational Spectroscopy of Aqueous Sodium Halide Solutions and Air-Liquid Interfaces: Observation of Increased Interfacial Depth

    E-print Network

    ; In Final Form: December 9, 2003 Air-aqueous sodium halide solution interfaces are examined using-selective spectroscopy, is used to investigate the interfacial water structure of several aqueous sodium halide airVibrational Spectroscopy of Aqueous Sodium Halide Solutions and Air-Liquid Interfaces: Observation

  15. Homogeneous and Heterogeneous Crystallization in Nanometer-Sized Regions of the Copper Halide Phase in Photochromic Glasses

    Microsoft Academic Search

    I. Zh. Bus'ko; V. V. Golubkov; M. I. Vasil'ev; V. V. Pshenitsina; V. A. Tsekhomskii

    2002-01-01

    The halide phase in copper halide photochromic glasses is studied by the small-angle X-ray scattering (SAXS) technique. The dependences of the volume and composition of the halide phase on the temperature of primary heat treatment are determined. The temperature of the formation of a vacuum pore upon cooling from the temperature of primary heat treatment and the temperature of pore

  16. Thermodynamic analysis of halide binding to haloalkane dehalogenase suggests the occurrence of large conformational changes.

    PubMed Central

    Krooshof, G. H.; Floris, R.; Tepper, A. W.; Janssen, D. B.

    1999-01-01

    Haloalkane dehalogenase (DhlA) hydrolyzes short-chain haloalkanes to produce the corresponding alcohols and halide ions. Release of the halide ion from the active-site cavity can proceed via a two-step and a three-step route, which both contain slow enzyme isomerization steps. Thermodynamic analysis of bromide binding and release showed that the slow unimolecular isomerization steps in the three-step bromide export route have considerably larger transition state enthalpies and entropies than those in the other route. This suggests that the three-step route involves different and perhaps larger conformational changes than the two-step export route. We propose that the three-step halide export route starts with conformational changes that result in a more open configuration of the active site from which the halide ion can readily escape. In addition, we suggest that the two-step route for halide release involves the transfer of the halide ion from the halide-binding site in the cavity to a binding site somewhere at the protein surface, where a so-called collision complex is formed in which the halide ion is only weakly bound. No large structural rearrangements are necessary for this latter process. PMID:10048328

  17. THE DETERMINATION OF TOTAL ORGANIC HALIDE IN WATER: AN INTERLABORATORY COMPARATIVE STUDY OF TWO METHODS

    EPA Science Inventory

    Total organic halide (TOX) analyzers are commonly used to measure the amount of dissolved halogenated organic byproducts in disinfected waters. Because of the lack of information on the identity of disinfection byproducts, rigorous testing of the dissolved organic halide (DOX) pr...

  18. THE DETERMINATION OF TOTAL ORGANIC HALIDE IN WATER: A COMPARATIVE STUDY OF TWO INSTRUMENTS

    EPA Science Inventory

    Total organic halide (TOX) analyzers are commonly used to measure the amount of dissolved halogenated organic byproducts in disinfected waters. ecause of the lack of information on the identity of disinfection byproducts, rigorous testing of the dissolved organic halide (DOX) pro...

  19. Cyclic carbonate formation from carbon dioxide and oxiranes in tetrabutylammonium halides as solvents and catalysts.

    PubMed

    Caló, Vincenzo; Nacci, Angelo; Monopoli, Antonio; Fanizzi, Antonello

    2002-07-25

    [reaction: see text] Epoxides dissolved in molten tetralkylammonium salts bearing halides as counterions are converted into cyclic carbonates under atmospheric pressure of carbon dioxide. The reaction rate depends on the nucleophilicity of the halide ion as well as the structure of the cation. PMID:12123376

  20. The Effects of Dissolved Halide Anions on Hydrogen Bonding in Liquid Water

    E-print Network

    Cohen, Ronald C.

    The Effects of Dissolved Halide Anions on Hydrogen Bonding in Liquid Water Jared D. Smith,, Richard halides in liquid water result instead from the actions of ions' electric fields on adjacent water. Introduction The physical and chemical properties of ions in aqueous solution are centrally important for many

  1. An efficient transformation of primary halides into nitriles through palladium-catalyzed hydrogen transfer reaction.

    PubMed

    Zou, Tao; Yu, Xiaoqiang; Feng, Xiujuan; Bao, Ming

    2015-07-01

    Two-step one-pot transformation of primary halides into corresponding nitriles is successfully achieved. Nucleophilic substitution of primary halides with sodium azide and subsequent palladium-catalyzed hydrogen transfer proceeds smoothly in the presence of sterically bulky ligand dicyclohexyl(2',4',6'-triisopropylbiphenyl-2-yl)phosphine (XPhos) in acetone to produce nitriles in satisfactory to good yields. PMID:26050994

  2. Solar Hydrogen Production by Amorphous Silicon Photocathodes Coated with a Magnetron Sputter Deposited Mo2C Catalyst.

    PubMed

    Morales-Guio, Carlos G; Thorwarth, Kerstin; Niesen, Bjoern; Liardet, Laurent; Patscheider, Jörg; Ballif, Christophe; Hu, Xile

    2015-06-10

    Coupling of Earth-abundant hydrogen evolution catalysts to photoabsorbers is crucial for the production of hydrogen fuel using sunlight. In this work, we demonstrate the use of magnetron sputtering to deposit Mo2C as an efficient hydrogen evolution reaction catalyst onto surface-protected amorphous silicon (a-Si) photoabsorbers. The a-Si/Mo2C photocathode evolves hydrogen under simulated solar illumination in strongly acidic and alkaline electrolytes. Onsets of photocurrents are observed at potentials as positive as 0.85 V vs RHE. Under AM 1.5G (1 sun) illumination, the photocathodes reach current densities of -11.2 mA cm(-2) at the reversible hydrogen potential in 0.1 M H2SO4 and 1.0 M KOH. The high photovoltage and low-cost of the Mo2C/a-Si assembly make it a promising photocathode for solar hydrogen production. PMID:26005904

  3. A H2-evolving photocathode based on direct sensitization of MoS3 with an organic photovoltaic cell

    PubMed Central

    Bourgeteau, Tiphaine; Tondelier, Denis; Geffroy, Bernard; Brisse, Romain; Laberty-Robert, Christel; Campidelli, Stéphane; de Bettignies, Rémi; Artero, Vincent; Palacin, Serge; Jousselme, Bruno

    2013-01-01

    An organic solar cell based on a poly-3-hexylthiophene (P3HT): phenyl-C61-butyric acid (PCBM) bulk hetero-junction was directly coupled with molybdenum sulfide resulting in the design of a new type of photocathode for the production of hydrogen. Both the light-harvesting system and the catalyst were deposited by low-cost solution-processed methods, i.e. spin coating and spray coating respectively. Spray-coated MoS3 films are catalytically active in strongly acidic aqueous solutions with the best efficiencies for thicknesses of 40 to 90 nm. The photocathodes display photocurrents higher than reference samples, without catalyst or without coupling with a solar cell. Analysis by gas chromatography confirms the light-induced hydrogen evolution. The addition of titanium dioxide in the MoS3 film enhances electron transport and collection within thick films and therefore the performance of the photocathode. PMID:24404434

  4. Thermal conductivity of halide solid solutions: measurement and prediction.

    PubMed

    Gheribi, Aïmen E; Poncsák, Sándor; St-Pierre, Rémi; Kiss, László I; Chartrand, Patrice

    2014-09-14

    The composition dependence of the lattice thermal conductivity in NaCl-KCl solid solutions has been measured as a function of composition and temperature. Samples with systematically varied compositions were prepared and the laser flash technique was used to determine the thermal diffusivity from 373 K to 823 K. A theoretical model, based on the Debye approximation of phonon density of state (which contains no adjustable parameters) was used to predict the thermal conductivity of both stoichiometric compounds and fully disordered solid solutions. The predictions obtained with the model agree very well with our measurement. A general method for predicting the thermal conductivity of different halide systems is discussed. PMID:25217938

  5. Chemistry and superconductivity of intercalated metal nitride halides

    NASA Astrophysics Data System (ADS)

    Fuertes, Amparo

    2014-06-01

    Titanium, zirconium and hafnium nitride halides show layered structures based on double slabs with compositions [X-M-N-N-M-X] (X = Cl, Br or I; M = Ti, Zr or Hf) that are separated by van der Waals gaps. Intercalation of electron donor species between the double layers induces superconductivity with critical temperatures up to 25.5 K. This review discusses the synthesis and structural chemistry of the hosts and intercalation compounds in this group of materials, as well as the influence of the structural and chemical features of the intercalates on the superconducting properties.

  6. New applications of silver halide photo-materials

    NASA Astrophysics Data System (ADS)

    Gudaitis, Giedrius A.; Zacharovas, Stanislovas J.; Ratcliffe, David B.; Sazonov, Jurij A.

    2006-05-01

    A review of the high-resolution VRP Silver Halide photo-materials (available through the Geola international distribution network) is presented. In addition to traditional holographic applications, the behaviour of current VRP materials is discussed in relation to embossed mastering origination, masks for microelectronics and X-ray tomography. Properties and applications of the fine grain, blue-green sensitive VRP plates are compared with previously available materials from other manufacturers. Recommended chemistries that may be employed with the VRP emulsion in different applications are reviewed.

  7. NIST-JANAF Thermochemical Tables. III. Diatomic Hydrogen Halide Gases

    NASA Astrophysics Data System (ADS)

    Shenyavskaya, Elena A.; Yungman, Vladimir S.

    2004-09-01

    The spectroscopic and thermodynamic properties of the four diatomic hydrogen halide molecules—HX(g), where X=F, Cl, Br, and I—have been reviewed. Four revised thermochemical tables result from this critical review. The revisions involved the consideration of new spectroscopic information and the use of a direct summation over states for the generation of the thermochemical tables. Compared to previous calculations, the entropies at 298.15 K are unchanged, but the high temperature values (T>4000 K) are significantly different.

  8. A novel scaling law relating the geometrical dimensions of a photocathode radio frequency gun to its radio frequency properties.

    PubMed

    Lal, Shankar; Pant, K K; Krishnagopal, S

    2011-12-01

    Developing a photocathode RF gun with the desired RF properties of the ?-mode, such as field balance (e(b)) ~1, resonant frequency f(?) = 2856 MHz, and waveguide-to-cavity coupling coefficient ?(?) ~1, requires precise tuning of the resonant frequencies of the independent full- and half-cells (f(f) and f(h)), and of the waveguide-to-full-cell coupling coefficient (?(f)). While contemporary electromagnetic codes and precision machining capability have made it possible to design and tune independent cells of a photocathode RF gun for desired RF properties, thereby eliminating the need for tuning, access to such computational resources and quality of machining is not very widespread. Therefore, many such structures require tuning after machining by employing conventional tuning techniques that are iterative in nature. Any procedure that improves understanding of the tuning process and consequently reduces the number of iterations and the associated risks in tuning a photocathode gun would, therefore, be useful. In this paper, we discuss a method devised by us to tune a photocathode RF gun for desired RF properties under operating conditions. We develop and employ a simple scaling law that accounts for inter-dependence between frequency of independent cells and waveguide-to-cavity coupling coefficient, and the effect of brazing clearance for joining of the two cells. The method has been employed to successfully develop multiple 1.6 cell BNL?SLAC/UCLA type S-band photocathode RF guns with the desired RF properties, without the need to tune them by a tiresome cut-and-measure process. Our analysis also provides a physical insight into how the geometrical dimensions affect the RF properties of the photo-cathode RF gun. PMID:22225212

  9. Geopolymers and Related Alkali-Activated Materials

    NASA Astrophysics Data System (ADS)

    Provis, John L.; Bernal, Susan A.

    2014-07-01

    The development of new, sustainable, low-CO2 construction materials is essential if the global construction industry is to reduce the environmental footprint of its activities, which is incurred particularly through the production of Portland cement. One type of non-Portland cement that is attracting particular attention is based on alkali-aluminosilicate chemistry, including the class of binders that have become known as geopolymers. These materials offer technical properties comparable to those of Portland cement, but with a much lower CO2 footprint and with the potential for performance advantages over traditional cements in certain niche applications. This review discusses the synthesis of alkali-activated binders from blast furnace slag, calcined clay (metakaolin), and fly ash, including analysis of the chemical reaction mechanisms and binder phase assemblages that control the early-age and hardened properties of these materials, in particular initial setting and long-term durability. Perspectives for future research developments are also explored.

  10. Removal of Retired Alkali Metal Test Systems

    SciTech Connect

    Brehm, W. F.; Church, W. R.; Biglin, J. W.

    2003-02-26

    This paper describes the successful effort to remove alkali metals, alkali metal residues, and piping and structures from retired non-radioactive test systems on the Hanford Site. These test systems were used between 1965 and 1982 to support the Fast Flux Test Facility and the Liquid Metal Fast Breeder Reactor Program. A considerable volume of sodium and sodium-potassium alloy (NaK) was successfully recycled to the commercial sector; structural material and electrical material such as wiring was also recycled. Innovative techniques were used to safely remove NaK and its residues from a test system that could not be gravity-drained. The work was done safely, with no environmental issues or significant schedule delays.

  11. Pulsed 4-MeV electron injector with an excimer laser driven photocathode

    SciTech Connect

    Kauppila, T.J.; Builta, L.A.; Carlson, R.L.; Moir, D.C.; Ridlon, R.N.

    1989-01-01

    The Relativistic Electron-Beam Experiment injector at the Los Alamos National Laboratory is used to generate a 4-MV pulse across an anode-cathode gap. A simple metal photocathode is illuminated by a pulsed excimer laser. Time-resolved measurements of current, voltage, and current density are made. The resulting quantum efficiencies are being used to obtain the required laser power for a multikiloampere, high-brightness electron gun to be used as an injector for a linear induction accelerator. 3 refs., 5 figs.

  12. Quantum Efficiency and Topography of Heated and Plasma-Cleaned Copper Photocathode Surfaces

    SciTech Connect

    Palmer, Dennis T.; /Titan PSD; Kirby, R.E.; King, F.K.; /SLAC

    2005-08-04

    We present measurements of photoemission quantum efficiency (QE) for copper photocathodes heated and cleaned by low energy argon and hydrogen ion plasma. The QE and surface roughness parameters were measured before and after processing and surface chemical composition was tracked in-situ with x-ray photoelectron spectroscopy (XPS). Thermal annealing at 230 C was sufficient to improve the QE by 3-4 orders of magnitude, depending on the initial QE. Exposure to residual gas slowly reduced the QE but it was easily restored by argon ion cleaning for a few minutes. XPS showed that the annealing or ion bombardment removed surface water and hydrocarbons.

  13. Thermal emittance and response time measurements of a GaN photocathode

    NASA Astrophysics Data System (ADS)

    Bazarov, Ivan V.; Dunham, Bruce M.; Liu, Xianghong; Virgo, Matt; Dabiran, Amir M.; Hannon, Fay; Sayed, Hisham

    2009-04-01

    We present the measurements of thermal emittance and response time for a GaN photocathode illuminated with 5 ps pulses at 260 nm wavelength. The thermal emittance was measured downstream of a 100 kV dc gun using a solenoid scan with a wire scanner and a beam viewscreen and was found to be 1.35±0.11 mm mrad normalized rms emittance per 1 mm rms of illuminated spot size. The response time of the photoemitted electrons was evaluated using a deflecting mode rf cavity synchronized to the laser pulses and was found to be prompt within the time resolution capability of our setup.

  14. Slice emittance measurement for photocathode RF gun with solenoid scanning and RF deflecting cavity

    NASA Astrophysics Data System (ADS)

    Li, Chen; Huang, WenHui; Du, YingChao; Yan, LiXin; Tang, ChuanXiang

    2011-12-01

    The radiation of high-gain short-wavelength free-electron laser depends on the slice transverse emittance of the electron bunch. This essay introduces the method of slice emittance measurement, and shows the brief setup of this experiment using the solenoid scanning and RF deflecting cavity at Tsinghua University. The preliminary experimental results show that the slice rms emittance of the electron bunch generated by photocathode RF gun has considerable variations along the bunch and is typically less than 0.55 mm mrad for the laser rms radius of 0.4 mm.

  15. Alkali metal protective garment and composite material

    SciTech Connect

    Ballif, J.L.; Yuan, W.W.

    1980-09-16

    A protective garment and composite material providing satisfactory heat resistance and physical protection for articles and personnel exposed to hot molten alkali metals, such as sodium are described. Physical protection is provided by a continuous layer of nickel foil. Heat resistance is provided by an underlying backing layer of thermal insulation. Overlying outer layers of fireproof woven ceramic fibers are used to protect the foil during storage and handling.

  16. Alkali Metal Heat Pipe Life Issues

    NASA Technical Reports Server (NTRS)

    Reid, Robert S.

    2004-01-01

    One approach to space fission power system design is predicated on the use of alkali metal heat pipes, either as radiator elements, thermal management components, or as part of the core primary heat-transfer system. This synopsis characterizes long-life core heat pipes. References are included where more detailed information can be found. Specifics shown here are for demonstrational purposes and do not necessarily reflect current Project Prometheus point designs.

  17. Alkali lasers for magnetic resonance imaging

    Microsoft Academic Search

    Boris V. Zhdanov; Randall J. Knize

    2010-01-01

    Spin-polarized nuclei of such gases as 3He and 129Xe are successfully used for magnetic resonance imaging of lungs and other organs of human body. To produce large numbers\\u000a of spin-polarized nuclei required for this medical application, a high power narrowband tunable laser source is required.\\u000a Diode pumped alkali lasers, developed during last several years can be an ideal source for

  18. Alkali solution treatment on sandstone cores 

    E-print Network

    Lee, Suk Jin

    1978-01-01

    by the injection of an alkali solution. This work should provide the first step in developing a technique that can be used in the stimulation of oil and gas wells. A series of tests was conducted in which sodium hydroxide solutions with concentrations ranging... reduction in the permeability of the sandstone cores before the injection of sodium hydroxide solution and in other cases the samples were not damaged by the injection of distilled water before the sodium hydroxide solution treatment. It was found...

  19. Selection of non-adsorbing alkali components

    Microsoft Academic Search

    S. H. D. Lee; K. Natesan; W. M. Swift

    1992-01-01

    This project consists of three phases of laboratory experimental study. In phase I (screening), eight candidate materials, 304SS (serves as a base material for comparison), Hastelloy C-276, Hastelloy X, Haynes No. 188, Allonized 304SS, Pt-coated 304SS, and ceramic-coated 304SS, will be subjected to atmospheric TGA study under the simulated PFBC (oxidizing) environment with and without alkali vapor doping. Each candidate

  20. Chemospecific and ligand free CuI catalysed heterogeneous N-arylation of amines with diheteroaryl halides at room temperature.

    PubMed

    Verma, Sanjeev K; Acharya, B N; Kaushik, M P

    2011-03-01

    A ligand free, copper-catalyzed N-arylation reaction of amines with diheteroaryl halides in heterogeneous medium at room temperature has been developed. The protocol is very effective for low boiling amines and useful for amines available in aqueous solution. The reaction gives chemospecific arylation of amines with diheteroaryl halides in the mixture monoheteroaryl halides, diheteroaryl halides and carbocyclic aryl halides. The reaction is also chemospecific with respect to arylation of aliphatic amines. Monoarylated piperazines were also synthesized at room temperature following this protocol. PMID:21218234

  1. MAMA detector systems - A status report

    NASA Technical Reports Server (NTRS)

    Timothy, J. Gethyn; Morgan, Jeffrey S.; Slater, David C.; Kasle, David B.; Bybee, Richard L.

    1989-01-01

    Third-generation, 224 x 960 and 360 x 1024-pixel multianode microchannel (MAMA) detectors are under development for satellite-borne FUV and EUV observations, using pixel dimensions of 25 x 25 microns. An account is presently given of the configurations, modes of operation, and recent performance data of these systems. At UV and visible wavelengths, these MAMAs employ a semitransparent, proximity-focused photocathode structure. At FUV and EUV wavelengths below about 1500 A, opaque alkali-halide photocathodes deposited directly on the front surface of the MCP furnish the best detective quantum efficiencies.

  2. Oxide Film Aging on Alloy 22 in Halide Containing Solutions

    SciTech Connect

    Rodriguez, Martin A.; Carranza, Ricardo M. [Dept. Materiales, Comision Nacional de Energia Atomica, Av. Gral. Paz 1499, Villa Maipu, 1650 (Argentina); Rebak, Raul B. [Lawrence Livermore National Laboratory, 7000 East Ave, L-631, Livermore, CA, 94550-9698 (United States)

    2007-07-01

    Passive and corrosion behaviors of Alloy 22 in chloride and fluoride containing solutions, changing the heat treatment of the alloy, the halide concentration and the pH of the solutions at 90 deg. C, was investigated. The study was implemented using electrochemical techniques, which included open circuit potential monitoring over time, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements carried out at open circuit and at passivity potentials. Corrosion rates obtained by EIS measurements after 24 h immersion in naturally aerated solutions were below 0.5 {mu}m/year. The corrosion rates were practically independent of solution pH, alloy heat treatment and halide ion nature and concentration. EIS low frequency resistance values increased with applied potential in the passive domain and with polarization time in pH 6 - 1 M NaCl at 90 deg. C. This effect was attributed to an increase in the oxide film thickness and oxide film aging. High frequency capacitance measurements indicated that passive oxide on Alloy 22 presented a double n-type/p-type semiconductor behavior in the passive potential range. (authors)

  3. Fragmentation mechanism and energetics of some alkyl halide ions

    SciTech Connect

    Rosenstock, H.M.; Buff, R.; Ferreira, M.A.; Lias, S.G.; Parr, A.C.; Stockbauer, R.L.; Holmes, J.L.

    1982-05-05

    Halogen loss from iodoethane, 1-bromopropane, 2-bromopropane, 1-iodopropane, and 2-iodopropane has been studied by means of electron-ion coincidence techniques and by observation of metastable transition. Analysis of the breakdown curves and the study of residence times gave the zero-kelvin thresholds for halogen loss and indicated the size of the kinetic shift. The fragmentation onset for iodoethane was located in a Franck-Condon gap. The zero-kelvin thresholds for the propyl halides were found to lie at or just above the upper spin-orbit level of the parent ion. All of the propyl halides exhibited a unimolecular metastable transition. At fragmentation onset the 2-halopropane ions have negligible fragment kinetic energy while the 1-halopropane produce secondary propyl ions wih 100-200 meV of kinetic energy. It was established that a potential barrier must be surmounted in this fragmentation-isomerization process and analysis suggests a dynamic mechanism other than conventional QET, for example, weak couplings of vibrational modes. Analysis of the 2-halopropane fragmentation thresholds leads to an accurate, absolute value for the proton affinity of propylene, 751.4 +/- 2.9 kJ/mol at room temperature. This value reconciles some differences inherent in the proton affinity scale based on various relative measurements.

  4. Exciplex pumped alkali laser (XPAL) modeling and theory

    Microsoft Academic Search

    Andrew D. Palla; Joseph T. Verdeyen; David L. Carroll

    2010-01-01

    The exciplex pumped alkali laser (XPAL) system has been demonstrated in mixtures of Cs vapor, Ar, with and without ethane, by pumping Cs-Ar atomic collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (exciplexes or excimers). The blue satellites of the alkali D2 lines provide an advantageous pathway for optically pumping atomic alkali lasers on the principal series (resonance)

  5. Photoinduced plasmon excitations in alkali-metal overlayers

    NASA Astrophysics Data System (ADS)

    Barman, S. R.; Horn, K.; Häberle, P.; Ishida, H.; Liebsch, A.

    1998-03-01

    Collective surface excitations in alkali-metal overlayers are observed using photoyield spectroscopy. Spectra for Na and K on Al(111) reveal a multipole surface plasmon and bulklike overlayer plasmon. In contrast, Li on Al exhibits only the multipole mode. In the submonolayer regime, all three alkali metals provide evidence for the threshold excitation. Time-dependent density-functional calculations for realistic alkali-metal overlayers agree well with these observations.

  6. Performance of Gaasp/gaas Superlattice Photocathodes in High Energy Experiments Using Polarized Electrons

    NASA Astrophysics Data System (ADS)

    Brachmann, A.; Clendenin, J. E.; Maruyama, T.; Garwin, E. L.; Ioakeimidi, K.; Prescott, C. Y.; Turner, J. L.; Prepost, R.

    2007-04-01

    The GaAsP/GaAs strained superlattice photocathode structure has proven to be a significant advance for polarized electron sources operating with high peak currents per microbunch and relatively low duty factor. This is the characteristic type of operation for SLAC and is also planned for the ILC. This superlattice structure was studied at SLAC [1], and an optimum variation was chosen for the final stage of E-158, a high-energy parity violating experiment at SLAC. Following E-158, the polarized source was maintained on standby with the cathode being re-cesiated about once a week while a thermionic gun, which is installed in parallel with the polarized gun, supplied the linac electron beams. However, in the summer of 2005, while the thermionic gun was disabled, the polarized electron source was again used to provide electron beams for the linac. The performance of the photocathode 24 months after its only activation is described and factors making this possible are discussed.

  7. Use of non evaporable getter pumps to ensure long term performances of high quantum efficiency photocathodes

    SciTech Connect

    Sertore, Daniele, E-mail: daniele.sertore@mi.infn.it; Michelato, Paolo; Monaco, Laura [Istituto Nazionale di Fisica Nucleare Sez. Milano – LASA, Via Fratelli Cervi 201, I-20090 Segrate (Italy); Manini, Paolo; Siviero, Fabrizio [SAES Getters S.p.A., Viale Italia 77, 20020 Lainate (Italy)

    2014-05-15

    High quantum efficiency photocathodes are routinely used as laser triggered emitters in the advanced high brightness electron sources based on radio frequency guns. The sensitivity of “semiconductor” type photocathodes to vacuum levels and gas composition requires special care during preparation and handling. This paper will discuss the results obtained using a novel pumping approach based on coupling a 20?l s{sup ?1} sputter ion getter pump with a CapaciTorr® D100 non evaporable getter (NEG) pump. A pressure of 8?10{sup ?8}?Pa was achieved using only a sputter ion pump after a 6?day bake-out. With the addition of a NEG pump, a pressure of 2?10{sup ?9}?Pa was achieved after a 2?day bake-out. These pressure values were maintained without power due to the ability of the NEG to pump gases by chemical reaction. Long term monitoring of cathodes quantum efficiencies was also carried out at different photon wavelengths for more than two years, showing no degradation of the photoemissive film properties.

  8. Heat load of a P-doped GaAs photocathode in SRF electron gun

    SciTech Connect

    Wang, E.; Ben-Zvi, I.; Kewisch, J.; Burrill, A.; Rao, T.; Wu, Q.; Jain, A.; Gupta, R.; Holmes, D.

    2010-05-23

    Many efforts were made over the last decades to develop a better polarized electron source for the high energy physics. Several laboratories operate DC guns with the Gallium-Arsenide photo-cathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved using a Superconducting RF electron gun, which delivers beams of higher brightness than DC guns does, because the field gradient at the cathode is higher. SRF guns with metal cathodes and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since the cathode will be normal conducting, the problem about the heat load stemming from the cathode arises. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and the verification by measuring the quality factor of the gun with and without cathode.

  9. Energy-conversion properties of vapor-liquid-solid-grown silicon wire-array photocathodes.

    PubMed

    Boettcher, Shannon W; Spurgeon, Joshua M; Putnam, Morgan C; Warren, Emily L; Turner-Evans, Daniel B; Kelzenberg, Michael D; Maiolo, James R; Atwater, Harry A; Lewis, Nathan S

    2010-01-01

    Silicon wire arrays, though attractive materials for use in photovoltaics and as photocathodes for hydrogen generation, have to date exhibited poor performance. Using a copper-catalyzed, vapor-liquid-solid-growth process, SiCl4 and BCl3 were used to grow ordered arrays of crystalline p-type silicon (p-Si) microwires on p+-Si(111) substrates. When these wire arrays were used as photocathodes in contact with an aqueous methyl viologen(2+/+) electrolyte, energy-conversion efficiencies of up to 3% were observed for monochromatic 808-nanometer light at fluxes comparable to solar illumination, despite an external quantum yield at short circuit of only 0.2. Internal quantum yields were at least 0.7, demonstrating that the measured photocurrents were limited by light absorption in the wire arrays, which filled only 4% of the incident optical plane in our test devices. The inherent performance of these wires thus conceptually allows the development of efficient photovoltaic and photoelectrochemical energy-conversion devices based on a radial junction platform. PMID:20056886

  10. Transmission photocathodes based on stainless steel mesh coated with deuterated diamond like carbon films

    NASA Astrophysics Data System (ADS)

    Huran, J.; Balalykin, N. I.; Feshchenko, A. A.; Kobzev, A. P.; Kleinová, A.; Sasinková, V.; Hrub?ín, L.

    2014-07-01

    In this study we report on the dependence of electron emission properties on the transmission photocathodes DC gun based on stainless steel mesh coated with diamond like carbon films prepared at various technological conditions. Diamond like carbon films were deposited on the stainless steel mesh and silicon substrate by plasma enhanced chemical vapor deposition from gas mixtures CH4+D2+Ar, CH4+H2+Ar and reactive magnetron sputtering using a carbon target and gas mixtures Ar+D2, Ar+H2. The concentration of elements in films was determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analytical methods simultaneously. Chemical compositions were analyzed by Fourier transform infrared spectroscopy (FT-IR). Raman spectroscopy at visible excitation wavelength was used for the intensity ratio determination of Gaussian fit D-peak and G-peak of Raman spectra. The quantum efficiency was calculated from the measured laser energy and the measured cathode charge. The quantum efficiency of a prepared transmission photocathode was increased with increasing intensity ratio of D-peak and G-peak, which was increased by adding deuterium to the gas mixture and using technology reactive magnetron sputtering.

  11. Performance Study of K2CsSb Photocathode Inside a DC High Voltage Gun

    SciTech Connect

    McCarter J. L.; Rao T.; Smedley, J.; Grames, J.; Mammei, R.; Poelker, M.; Suleiman, R.

    2011-09-01

    In the past decade, there has been considerable interest in the generation of tens of mA average current in a photoinjector. Until recently, GaAs:Cs cathodes and K{sub 2}CsSb cathodes have been tested successfully in DC and RF injectors respectively for this application. Our goal is to test the K{sub 2}CsSb photocathode inside a DC gun. Since the multialkali cathode is a compound with constant characteristics over its entire thickness, we anticipate that the lifetime issues seen in GaAs:Cs due to surface damage by ion bombardment would be minimized. Hence successful operation of the K{sub 2}CsSb cathode in a DC gun could lead to a relatively robust electron source capable of delivering ampere level currents. In order to test the performance of a K{sub 2}CsSb cathode in a DC gun, we have designed and built a load lock system that allows the fabrication of the cathode at Brookhaven National Lab (BNL) and its testing at Jefferson Lab (JLab). In this paper, we will present the performance of the K{sub 2}CsSb photocathode in the preparation chamber and in the DC gun.

  12. High temperature alkali corrosion of ceramics in coal gas

    SciTech Connect

    Pickrell, G.R.; Sun, T.; Brown, J.J.

    1992-05-27

    High temperature alkali corrosion has been known to cause premature failure of ceramic components used in advanced high temperature coal combustion systems such as coal gasification and clean-up, coal fired gas turbines, and high efficiency heat engines. The objective of this research is to systematically evaluate the alkali corrosion resistance of the most commonly used structural ceramics including silicon carbide, silicon nitride, cordierite, mullite, alumina, aluminum titanate, zirconia, and fireclay glass. The study consists of identification of the alkali reaction products (phase equilibria) and the kinetics of the alkali reactions as a function of temperature and time.

  13. High temperature alkali corrosion of ceramics in coal gas

    SciTech Connect

    Pickrell, G.R.; Sun, T.; Brown, J.J.

    1991-11-30

    High temperature alkali corrosion has been known to cause premature failure of ceramic components used in advanced high temperature coal combustion systems such as coal gasification and clean-up, coal fired gas turbines, and high efficiency heat engines. The objective of this program is to systematically evaluate the alkali corrosion resistance of the most commonly used structural ceramics including silicon carbide, silicon nitride, cordierite, mullite, alumina, aluminum titanate, zirconia, and fireclay glass. The study consists of identification of the alkali reaction products (phase equilibria) and the kinetics of the alkali reactions as a function of temperature and time.

  14. Small-signal gain modeling for optical pumping of the alkali-xenon and alkali dimer laser transitions

    Microsoft Academic Search

    A. J. Palmer

    1976-01-01

    A kinetics model for broadband optical pumping of the alkali–rare-gas and alkali dimer A-to-X laser transitions is developed and is used to compute the small-signal gain coefficient as a function of wavelength for the excimer and dimer bands of all of the alkali-xenon systems. Net gain coefficients of ?10?3–10?2 cm?1 are predicted on the excimer and dimer bands of all

  15. Small-signal gain modeling for optical pumping of the alkali-xenon and alkali dimer laser transitions

    Microsoft Academic Search

    A. J. Palmer

    1976-01-01

    A kinetics model for broadband optical pumping of the alkali-rare-gas and alkali dimer A-to-X laser transitions is developed and is used to compute the small-signal gain coefficient as a function of wavelength for the excimer and dimer bands of all of the alkali-xenon systems. Net gain coefficients of ~10-3-10-2 cm-1 are predicted on the excimer and dimer bands of all

  16. 40 CFR 721.5452 - Alkali metal salt of halogenated organoborate (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 2013-07-01 false Alkali metal salt of halogenated organoborate (generic...Substances § 721.5452 Alkali metal salt of halogenated organoborate (generic...substances identified generically as alkali metal salt of halogenated organoborate (PMN...

  17. 40 CFR 721.10098 - Disubstituted benzoic acid, alkali metal salt (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...Disubstituted benzoic acid, alkali metal salt (generic). 721.10098 Section 721...Disubstituted benzoic acid, alkali metal salt (generic). (a) Chemical substance...disubstituted benzoic acid, alkali metal salt (PMN P-03-643) is subject to...

  18. 40 CFR 721.10098 - Disubstituted benzoic acid, alkali metal salt (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...Disubstituted benzoic acid, alkali metal salt (generic). 721.10098 Section 721...Disubstituted benzoic acid, alkali metal salt (generic). (a) Chemical substance...disubstituted benzoic acid, alkali metal salt (PMN P-03-643) is subject to...

  19. 40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

  20. 40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

  1. 40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

  2. 40 CFR 721.5985 - Fatty alkyl phosphate, alkali metal salt (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... Fatty alkyl phosphate, alkali metal salt (generic). 721.5985 Section 721... Fatty alkyl phosphate, alkali metal salt (generic). (a) Chemical substance...as a fatty alkyl phosphate, alkali metal salt (PMN P-99-0385) is subject to...

  3. 40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

  4. 40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

  5. ALKALI AGGREGATE REACTION AND DELAYED ETTRINGITE FORMATION: COMMON FEATURES AND DIFFERENCES

    E-print Network

    Paris-Sud XI, Université de

    ALKALI AGGREGATE REACTION AND DELAYED ETTRINGITE FORMATION: COMMON FEATURES AND DIFFERENCES Renaud Department, Paris, France Abstract Alkali-Aggregate Reaction (AAR) and Delayed Ettringite Formation (DEF effects 1 INTRODUCTION Alkali Aggregate Reaction (AAR) and Delayed Ettringite Formation (DEF) are internal

  6. THE OPERATION OF THE BNL/ATF GUN-IV PHOTOCATHODE RF GUN AT THE ADVANCED PHOTON SOURCE

    E-print Network

    Brookhaven National Laboratory

    THE OPERATION OF THE BNL/ATF GUN-IV PHOTOCATHODE RF GUN AT THE ADVANCED PHOTON SOURCE * S (SASE) process is nearing completion. Recently, an rf photoinjector gun system was made available, and integration of this gun with the APS will be discussed. 1 INTRODUCTION The Advanced Photon Source (APS

  7. Hydrogen-evolution characteristics of NiMo-coated, radial junction, p-silicon microwire array photocathodes

    E-print Network

    Atwater, Harry

    as photocathodes in regenerative electrochemical cells.2,3 Solid-state photovoltaic devices made from n+ p radial on the basis of thermodynamic energy-conversion efficiency as well as solar cell figures of merit. The Ni photosynthetic system, capable of directly converting solar energy to chemical fuel, remains a challenge

  8. Silicon nanowire arrays coupled with cobalt phosphide spheres as low-cost photocathodes for efficient solar hydrogen evolution.

    PubMed

    Bao, Xiao-Qing; Fatima Cerqueira, M; Alpuim, Pedro; Liu, Lifeng

    2015-06-18

    We demonstrate the first example of silicon nanowire array photocathodes coupled with hollow spheres of the emerging earth-abundant cobalt phosphide catalysts. Compared to bare silicon nanowire arrays, the hybrid electrodes exhibit significantly improved photoelectrochemical performance toward the solar-driven H2 evolution reaction. PMID:26050844

  9. (abstract) Fundamental Mechanisms of Electrode Kinetics and Alkali Metal Atom Transport at the Alkali Beta'-Alumina/Porous Electrode/Alkali Metal Vapor Three Phase Boundary

    NASA Technical Reports Server (NTRS)

    Williams, R. M.; Jeffries-Nakamura, B.; Ryan, M. A.; Underwood, M. L.; O'Connor, D.; Kisor, A.; Kikkert, S. K.

    1993-01-01

    The mechanisms of electrode kinetics and mass transport of alkali metal oxidation and alkali metal cation reduction at the solid electrolyte/porous electrode boundary as well as alkali metal transport through porous metal electrodes has important applications in optimizing device performance in alkali metal thermal to electric converter (AMTEC) cells which are high temperature, high current density electrochemical cells. Basic studies of these processes also affords the opportunity to investigate a very basic electrochemical reaction over a wide range of conditions; and a variety of mass transport modes at high temperatures via electrochemical techniques. The temperature range of these investigations covers 700K to 1240K; the alkali metal vapor pressures range from about 10(sup -2) to 10(sup 2) Pa; and electrodes studied have included Mo, W, Mo/Na(sub 2)MoO(sub 4), W/Na(sub 2)WO(sub 4), WPt(sub x), and WRh(sub x) (1.0 < x < 6.0 ) with Na at Na-beta'-alumina, and Mo with K at K-beta'-alumina. Both liquid metal/solid electrolyte/alkali metal vapor and alkali metal vapor/solid electrolyte/vapor cells have been used to characterize the reaction and transport processes. We have previously reported evidence of ionic, free molecular flow, and surface transport of sodium in several types of AMTEC electrodes.

  10. Canadian Micro-Mineral Association: ALKALI - NUTS

    NSDL National Science Digital Library

    This website, created by the Canadian Micro-Mineral Association, furnishes information on the minerals and environments near Mont Saint-Hilaire (MSH) in Quebec, Canada. Students and educators can discover the physical characteristics, fluorescence, and the distribution and rarity of the hundreds of species of minerals found around MSH. Each description includes helpful images of the amazing minerals and environments. Users can learn about the two classification systems: Dana and Strunz. The site presents MSH-related current news, articles, and announcements. Users can also discover the meaning and origin of the term, ALKALI-NUTS.

  11. Monte Carlo simulations of electron thermalization in alkali iodide and alkaline-earth fluoride scintillators

    SciTech Connect

    Wang, Zhiguo; Xie, YuLong; Campbell, Luke W.; Gao, Fei; Kerisit, Sebastien N.

    2012-07-01

    A Monte Carlo model of electron thermalization in inorganic scintillators, which was developed and applied to CsI in a previous publication [Wang et al., J. Appl. Phys. 110, 064903 (2011)], is extended to another material of the alkali halide class, NaI, and to two materials from the alkaline-earth halide class, CaF2 and BaF2. This model includes electron scattering with both longitudinal optical (LO) and acoustic phonons as well as the effects of internal electric fields. For the four pure materials, a significant fraction of the electrons recombine with self-trapped holes and the thermalization distance distributions of the electrons that do not recombine peak between approximately 25 and 50 {per_thousand}nm and extend up to a few hundreds of nanometers. The thermalization time distributions of CaF2, BaF2, NaI, and CsI extend to approximately 0.5, 1, 2, and 7 ps, respectively. The simulations show that the LO phonon energy is a key factor that affects the electron thermalization process. Indeed, the higher the LO phonon energy is, the shorter the thermalization time and distance are. The thermalization time and distance distributions show no dependence on the incident {gamma}-ray energy. The four materials also show different extents of electron-hole pair recombination due mostly to differences in their electron mean free paths (MFPs), LO phonon energies, initial densities of electron-hole pairs, and static dielectric constants. The effect of thallium doping is also investigated for CsI and NaI as these materials are often doped with activators. Comparison between CsI and NaI shows that both the larger size of Cs+ relative to Na+, i.e., the greater atomic density of NaI, and the longer electron mean free path in NaI compared to CsI contribute to an increased probability for electron trapping at Tl sites in NaI versus CsI.

  12. Monte Carlo simulations of electron thermalization in alkali iodide and alkaline-earth fluoride scintillators

    SciTech Connect

    Wang Zhiguo; Gao Fei; Kerisit, Sebastien [Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Xie Yulong [Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Campbell, Luke W. [National Security Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)

    2012-07-01

    A Monte Carlo model of electron thermalization in inorganic scintillators, which was developed and applied to CsI in a previous publication [Wang et al., J. Appl. Phys. 110, 064903 (2011)], is extended to another material of the alkali halide class, NaI, and to two materials from the alkaline-earth halide class, CaF{sub 2} and BaF{sub 2}. This model includes electron scattering with both longitudinal optical (LO) and acoustic phonons as well as the effects of internal electric fields. For the four pure materials, a significant fraction of the electrons recombine with self-trapped holes and the thermalization distance distributions of the electrons that do not recombine peak between approximately 25 and 50 nm and extend up to a few hundreds of nanometers. The thermalization time distributions of CaF{sub 2}, BaF{sub 2}, NaI, and CsI extend to approximately 0.5, 1, 2, and 7 ps, respectively. The simulations show that the LO phonon energy is a key factor that affects the electron thermalization process. Indeed, the higher the LO phonon energy is, the shorter the thermalization time and distance are. The thermalization time and distance distributions show no dependence on the incident {gamma}-ray energy. The four materials also show different extents of electron-hole pair recombination due mostly to differences in their electron mean free paths (MFPs), LO phonon energies, initial densities of electron-hole pairs, and static dielectric constants. The effect of thallium doping is also investigated for CsI and NaI as these materials are often doped with activators. Comparison between CsI and NaI shows that both the larger size of Cs{sup +} relative to Na{sup +}, i.e., the greater atomic density of NaI, and the longer electron mean free path in NaI compared to CsI contribute to an increased probability for electron trapping at Tl sites in NaI versus CsI.

  13. Monte Carlo simulations of electron thermalization in alkali iodide and alkaline-earth fluoride scintillators

    NASA Astrophysics Data System (ADS)

    Wang, Zhiguo; Xie, YuLong; Campbell, Luke W.; Gao, Fei; Kerisit, Sebastien

    2012-07-01

    A Monte Carlo model of electron thermalization in inorganic scintillators, which was developed and applied to CsI in a previous publication [Wang et al., J. Appl. Phys. 110, 064903 (2011)], is extended to another material of the alkali halide class, NaI, and to two materials from the alkaline-earth halide class, CaF2 and BaF2. This model includes electron scattering with both longitudinal optical (LO) and acoustic phonons as well as the effects of internal electric fields. For the four pure materials, a significant fraction of the electrons recombine with self-trapped holes and the thermalization distance distributions of the electrons that do not recombine peak between approximately 25 and 50 nm and extend up to a few hundreds of nanometers. The thermalization time distributions of CaF2, BaF2, NaI, and CsI extend to approximately 0.5, 1, 2, and 7 ps, respectively. The simulations show that the LO phonon energy is a key factor that affects the electron thermalization process. Indeed, the higher the LO phonon energy is, the shorter the thermalization time and distance are. The thermalization time and distance distributions show no dependence on the incident ?-ray energy. The four materials also show different extents of electron-hole pair recombination due mostly to differences in their electron mean free paths (MFPs), LO phonon energies, initial densities of electron-hole pairs, and static dielectric constants. The effect of thallium doping is also investigated for CsI and NaI as these materials are often doped with activators. Comparison between CsI and NaI shows that both the larger size of Cs+ relative to Na+, i.e., the greater atomic density of NaI, and the longer electron mean free path in NaI compared to CsI contribute to an increased probability for electron trapping at Tl sites in NaI versus CsI.

  14. Recent progress in efficient hybrid lead halide perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Cui, Jin; Yuan, Huailiang; Li, Junpeng; Xu, Xiaobao; Shen, Yan; Lin, Hong; Wang, Mingkui

    2015-06-01

    The efficiency of perovskite solar cells (PSCs) has been improved from 9.7 to 19.3%, with the highest value of 20.1% achieved in 2014. Such a high photovoltaic performance can be attributed to optically high absorption characteristics and balanced charge transport properties with long diffusion lengths of the hybrid lead halide perovskite materials. In this review, some fundamental details of hybrid lead iodide perovskite materials, various fabrication techniques and device structures are described, aiming for a better understanding of these materials and thus highly efficient PSC devices. In addition, some advantages and open issues are discussed here to outline the prospects and challenges of using perovskites in commercial photovoltaic devices.

  15. Electron spectroscopy of agueous solution interfaces revealssurface enhancement of halides

    SciTech Connect

    Ghosal, Sutapa; Hemminger, John C.; Bluhm, Hendrik; Mun, BongjinSimon; Hebenstreit, Eleonore L.D.; Ketteler, Guido; Ogletree, D. Frank; Requejo, Felix; Salmeron, Miquel

    2004-10-18

    It has been suggested that enhanced anion concentrations at the liquid/vapor interface of airborne saline droplets are important to aerosol reactions in the atmosphere. We report ionic concentrations in the surface of such solutions. Using x-ray photoelectron spectroscopy operating at near ambient pressure, we have measured the composition of the liquid/vapor interface for deliquesced samples of potassium bromide and potassium iodide. In both cases, the surface composition of the saturated solution is enhanced in the halide anion compared with the bulk of the solution. The enhancement of anion concentration is more dramatic for the larger, more polarizable iodide anion. By varying photoelectron kinetic energies, we have obtained depth profiles of the liquid/vapor interface. Our results are in good qualitative agreement with classical molecular dynamics simulations. Quantitative comparison between the experiments and the simulations indicates that the experimental results exhibit more interface enhancement than predicted theoretically.

  16. Direct current ballast circuit for metal halide lamp

    NASA Technical Reports Server (NTRS)

    Lutus, P. (inventor)

    1981-01-01

    A direct current ballast circuit for a two electrode metal halide lamp is described. Said direct current ballast circuit includes a low voltage DC input and a high frequency power amplifier and power transformer for developing a high voltage output. The output voltage is rectified by diodes and filtered by inductor and capacitor to provide a regulated DC output through commutating diodes to one terminal of the lamp at the output terminal. A feedback path from the output of the filter capacitor through the bias resistor to power the high frequency circuit which includes the power amplifier and the power transformer for sustaining circuit operations during low voltage transients on the input DC supply is described. A current sensor connected to the output of the lamp through terminal for stabilizing lamp current following breakdown of the lamp is described.

  17. Emission spectroscopy for characterizing metal-halide lamps

    NASA Astrophysics Data System (ADS)

    Flikweert, A. J.; Nimalasuriya, T.; Kroesen, G. M. W.; Haverlag, M.; Stoffels, W. W.

    2008-10-01

    The metal-halide (MH) lamp shows an unwanted axial non-uniform distribution of the metal additives when burning in vertical position, which is caused by the interplay between convection and diffusion. Various MH lamps are investigated by means of emission spectroscopy under varying gravity conditions (1-10g) in a centrifuge. The method yields spectra, axial inhomogeneity parameters and axially integrated intensities. The method is easier than methods used before on the same type of lamp. Measurements on lamps with DyI3 as salt filling are used as a calibration of the setup. After comparison with the earlier measurements, we conclude that the new emission spectroscopy is valid for characterization of MH lamps. Next, we apply the method on commercial lamps (Philips MASTER CosmoWhite). For these lamps, in addition NaI densities at the wall and axial temperature profiles are obtained by using self-reversed lines of Na and Hg, respectively.

  18. Venus: Halide cloud condensation and volatile element inventories

    NASA Technical Reports Server (NTRS)

    Lewis, J. S.; Fegley, B., Jr.

    1982-01-01

    Several Venus cloud condensates, including A12C16 as well as halides, oxides and sulfides of arsenic and antimony, are assessed for their thermodynamic and geochemical plausibility. Aluminum chloride can confidently be ruled out, and condensation of arsenic sulfides on the surface will cause arsenic compounds to be too rare to produce the observed clouds. Antimony may conceivably be sufficiently volatile, but the expected molecular form is gaseous SbS, not the chloride. Arsenic and antimony compounds in the atmosphere will be regulated at very low levels by sulfide precipitation, irrespective of the planetary inventory of As and Sb. Thus the arguments for a volatile-deficient origin for Venus based on the depletion of water and mercury (relative to Earth) cannot be tested by a search for atmospheric arsenic or antimony.

  19. Alkali–aggregate reaction in activated fly ash systems

    Microsoft Academic Search

    I. García-Lodeiro; A. Palomo; A. Fernández-Jiménez

    2007-01-01

    Certain aspects of the durability of a new cementitious material, alkali activated fly ash, are addressed in this article; specifically, a series of findings relating to the alkali-silica reaction are reported. The approach adopted in the study was to compare the new cementitious systems to analogous Portland cement mortars using aggregates of differing reactivity and a procedure based on the

  20. Alkali Activated Geopolymeric Binder Using Tungsten Mine Waste: Preliminary Investigation

    Microsoft Academic Search

    F. Pacheco-Torgal; J. P. Castro-Gomes; S. Jalali

    This paper reports preliminary results of a PhD research project related to the development of an alkali- activated geopolymeric binder using mineral waste mud from the Portuguese tungsten mine Panasqueira which is still operating. Mineralogical analysis indicates that the waste mud is compose mainly of muscovite and quartz with a high content of iron and alkali metals. Results of the

  1. ORIGINAL ARTICLE Mitigation of autogenous shrinkage in alkali activated slag

    E-print Network

    Bentz, Dale P.

    , produced from alkaline blast furnace slags with high Al2O3 contents, calcium sulfate, and an alkalineORIGINAL ARTICLE Mitigation of autogenous shrinkage in alkali activated slag mortars by internal online: 29 November 2012 Ó RILEM 2012 Abstract Alkali activated slag shows considerable promise

  2. Diatomic Cesium in a Diode-Pumped Alkali Laser System

    Microsoft Academic Search

    Jamey Christy; Eric Martinez; Tanner Oakes; Jake Smith; Kendrick Walter

    2008-01-01

    Abstract Diode Pumped Alkali Laser (DPAL) systems combine the positive characteristics of chemical and diode lasers. These systems create a laser that is compact and ecient, while working well at high temperatures and high powers. In conjunction with the Air Force Research Laboratory (AFRL), an attempt was made to improve DPAL technology by using a diatomic alkali metal as a

  3. Modeling laser performance of scalable side pumped alkali laser

    Microsoft Academic Search

    Aleksey M. Komashko; Jason Zweiback

    2010-01-01

    Diode pumped alkali lasers (DPAL) offer the potential for high power and efficient operation. The extremely low quantum defect of the alkali system minimizes thermal management requirements. At the same time DPALs keep advantages of gas lasers (no thermal stresses, high intrinsic beam quality). Side pumped geometry simplifies system design, separating laser and pump light and providing physical space for

  4. Method of assembling and sealing an alkali metal battery

    Microsoft Academic Search

    P. E. Elkins; J. E. Bell; R. A. Harlow; G. G. Chase

    1983-01-01

    A method of initially assembling and then subsequently hermetically sealing a container portion of an alkali metal battery to a ceramic portion of such a battery is disclosed. Sealing surfaces are formed respectively on a container portion and a ceramic portion of an alkali metal battery. These sealing surfaces are brought into juxtaposition and a material is interposed there between.

  5. Self-discharge in bimetallic cells containing alkali metal

    NASA Technical Reports Server (NTRS)

    Foster, M. S.; Hesson, J. C.; Shimotake, H.

    1969-01-01

    Theoretical analysis of thermally regenerative bimetallic cells with alkali metal anodes shows a relation between the current drawn and the rate of discharge under open-circuit conditions. The self-discharge rate of the cell is due to the dissolution and ionization of alkali metal atoms in the fused-salt electrolyte

  6. Recovery of alkali metal constituents from catalytic coal conversion residues

    DOEpatents

    Soung, Wen Y. (Houston, TX)

    1984-01-01

    In a coal gasification operation (32) or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein particles containing alkali metal residues are produced, alkali metal constituents are recovered from the particles by contacting them (46, 53, 61, 69) with water or an aqueous solution to remove water-soluble alkali metal constituents and produce an aqueous solution enriched in said constituents. The aqueous solution thus produced is then contacted with carbon dioxide (63) to precipitate silicon constituents, the pH of the resultant solution is increased (81), preferably to a value in the range between about 12.5 and about 15.0, and the solution of increased pH is evaporated (84) to increase the alkali metal concentration. The concentrated aqueous solution is then recycled to the conversion process (86, 18, 17) where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst.

  7. ALKALI-ACTIVATED BINDERS AND POZZOLAN CEMENT BINDERS - COMPETE BINDER REACTION OR TWO SIDES OF THE SAME STORY?

    Microsoft Academic Search

    A. Buchwald; Ch. Kaps; M. Hohmann

    Increasingly attention has been paid in the last years on alkali-activated binders such as alkali- activated fly ash and slag. Related binders are known as geopolymers which are at least alkali- activated metakaolin binders. In all cases the activation of the solid is made with different alkaline solutions containing alkali hydroxides, alkali silicates and\\/or alkali carbonates. It could be shown

  8. Reactivity of halide and pseudohalide ligands in transition-metal complexes

    SciTech Connect

    Kukushkin, Yu.N.; Kukushkin, V.Yu.

    1985-10-01

    The experimental material on the reactions of coordinated halide ligands, as well as cyanide, azido, thiocyanato, and cyanato ligands, in transition-metal complexes has been generalized in this review.

  9. Hydrogen peroxide oxidation of benzylic alcohols to benzaldehydes and benzoic acids under halide-free conditions

    Microsoft Academic Search

    Kazuhiko Sato; Junko Takagi; Masao Aoki; Ryoji Noyori

    1998-01-01

    A series of benzaldehyde and benzoic acid derivatives can be obtained from benzylic alcohols by tungsten-catalyzed oxidation with aqueous hydrogen peroxide under halide-free, aqueous\\/organic biphasic conditions.

  10. The Crystallography of Metal Halides formed within Single Walled Carbon Nanotubes J. Sloan1,2

    E-print Network

    Dunin-Borkowski, Rafal E.

    The Crystallography of Metal Halides formed within Single Walled Carbon Nanotubes J. Sloan1,2 , G Street, Cambridge, CB2 3QZ, U.K. ABSTRACT The crystal growth behaviour and crystallography of a variety

  11. Methods for synthesizing alane without the formation of adducts and free of halides

    DOEpatents

    Zidan, Ragaiy; Knight, Douglas A; Dinh, Long V

    2013-02-19

    A process is provided to synthesize an alane without the formation of alane adducts as a precursor. The resulting product is a crystallized .alpha.-alane and is a highly stable product and is free of halides.

  12. Halide and nitrite recognizing hexanuclear metallacycle copper(II) pyrazolates.

    PubMed

    Mohamed, Ahmed A; Ricci, Simone; Burini, Alfredo; Galassi, Rossana; Santini, Carlo; Chiarella, Gina M; Melgarejo, Doris Y; Fackler, John P

    2011-02-01

    Halide-centered hexanuclear, anionic copper(II) pyrazolate complexes [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)X](-), X = Cl, Br, I are isolated in a good yield from the redox reaction of the trinuclear copper(I) pyrazolate complex [?-Cu(3)((3,5-CF(3))(2)pz)(3)] with a halide source such as PPh(3)AuCl or [Bu(4)N]X, X = Cl, Br, or I, in air. X-ray structures of the anion-centered hexanuclear complexes show that the six copper atoms are bridged by bis(3,5-trifluoromethyl)pyrazolate and hydroxyl ligands above and below the six copper atom plane. The anions are located at the center of the cavity and weakly bound to the six copper atoms in a ?(6)-arrangement, Cu-X = ~3.1 Å. A nitrite-centered hexanuclear copper(II) pyrazolate complex [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))](-) was obtained when a solution of [PPN]NO(2) in CH(3)CN was added dropwise to the trinuclear copper(I) pyrazolate complex [?-Cu(3)((3,5-CF(3))(2)pz)(3)] dissolved in CH(3)CN, in air. Blue crystals are produced by slow evaporation of the acetonitrile solvent. The X-ray structure of [PPN][trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))] complex shows the nitrite anion sits in the hexanuclear cavity and is perpendicular to the copper plane with a O-N-O angle of 118.3(7)°. The (19)F and (1)H NMR of the pyrazolate ring atoms are sensitive to the anion present in the ring. Anion exchange of the NO(2)(-) by Cl(-) can be observed easily by (1)H NMR. PMID:21190383

  13. A combined metal-halide/metal flux synthetic route towards type-I clathrates: crystal structures and thermoelectric properties of A8Al8Si38 (A = K, Rb, and Cs).

    PubMed

    Baran, Volodymyr; Senyshyn, Anatoliy; Karttunen, Antti J; Fischer, Andreas; Scherer, Wolfgang; Raudaschl-Sieber, Gabriele; Fässler, Thomas F

    2014-11-10

    Single-phase samples of the compounds K8Al8Si38 (1), Rb8Al8Si38 (2), and Cs7.9Al7.9Si38.1 (3) were obtained with high crystallinity and in good quantities by using a novel flux method with two different flux materials, such as Al and the respective alkali-metal halide salt (KBr, RbCl, and CsCl). This approach facilitates the removal of the product mixture from the container and also allows convenient extraction of the flux media due to the good solubility of the halide salts in water. The products were analyzed by means of single-crystal X-ray structure determination, powder X-ray and neutron diffraction experiments, (27)Al-MAS NMR spectroscopy measurements, quantum chemical calculations, as well as magnetic and transport measurements (thermal conductivity, electrical resistivity, and Seebeck coefficient). Due to the excellent quality of the neutron diffraction data, the difference between the nuclear scattering factors of silicon and aluminum atoms was sufficient to refine their mixed occupancy at specific sites. The role of variable-range hopping for the interpretation of the resistivity and the Seebeck coefficient is discussed. PMID:25267571

  14. Electrical conductivity and relaxation in mixed alkali tellurite glasses.

    PubMed

    Ghosh, S; Ghosh, A

    2007-05-14

    The authors have reported the electrical conductivity and the conductivity relaxation in mixed alkali tellurite glasses of compositions of 70TeO2-xNa2O-(30-x)Li2O in the frequency range from 10 Hz to 2 MHz and in the temperature range from room temperature to just below the glass transition temperature. They have analyzed the relaxation data in the framework of different models. They have observed the mixed alkali effect in the dc and ac conductivities, the crossover frequency, and the conductivity relaxation frequency as well as in their respective activation energies in these glasses. They have also observed the mixed alkali effect in the decoupling index. The scaling property of the modulus spectra of these mixed alkali glasses shows that the conductivity relaxation in the mixed alkali tellurite glasses is independent of temperature but depends on the glass compositions. PMID:17508813

  15. Dynamics of reactive ultracold alkali polar molecules

    NASA Astrophysics Data System (ADS)

    Quéméner, Goulven; Bohn, John; Petrov, Alexander; Kotochigova, Svetlana

    2011-05-01

    Recently, ultracold polar molecules of KRb have been created. These molecules are chemically reactive and their lifetime in a trap is limited. However, their lifetime increases when they are loaded into a 1D optical lattice in the presence of an electric field. These results naturally raise the question of manipulating ultracold collisions of other species of alkali dimer molecules, with an eye toward both novel stereochemistry, as well as suppressing unwanted reactions, to enable condensed matter applications. In this talk, we report on a comparative study between the bi-alkali polar molecules of LiNa, LiK, LiRb, LiCs which have been predicted to be reactive. We compute the isotropic C6 coefficients of these systems and we predict the elastic and reactive rate coefficients when an electric field is applied in a 1D optical lattice. We will discuss the efficacy of evaporative cooling for each species. This work was supported by a MURI-AFOSR grant.

  16. Decalcification resistance of alkali-activated slag.

    PubMed

    Komljenovi?, Miroslav M; Baš?arevi?, Zvezdana; Marjanovi?, Nataša; Nikoli?, Violeta

    2012-09-30

    This paper analyses the effects of decalcification in concentrated 6M NH(4)NO(3) solution on mechanical and microstructural properties of alkali-activated slag (AAS). Portland-slag cement (CEM II/A-S 42.5 N) was used as a benchmark material. Decalcification process led to a decrease in strength, both in AAS and in CEM II, and this effect was more pronounced in CEM II. The decrease in strength was explicitly related to the decrease in Ca/Si atomic ratio of C-S-H gel. A very low ratio of Ca/Si ~0.3 in AAS was the consequence of coexistence of C-S-H(I) gel and silica gel. During decalcification of AAS almost complete leaching of sodium and tetrahedral aluminum from C-S-H(I) gel also took place. AAS showed significantly higher resistance to decalcification in relation to the benchmark CEM II due to the absence of portlandite, high level of polymerization of silicate chains, low level of aluminum for silicon substitution in the structure of C-S-H(I), and the formation of protective layer of polymerized silica gel during decalcification process. In stabilization/solidification processes alkali-activated slag represents a more promising solution than Portland-slag cement due to significantly higher resistance to decalcification. PMID:22818592

  17. Unconventional Superconductivity of Alkali-doped Fullerenes

    NASA Astrophysics Data System (ADS)

    Potocnik, Anton; Krajnc, Andraz; Jeglic, Peter; Prassides, Kosmas; Rosseinsky, Matthew J.; Arcon, Denis

    2014-03-01

    The superconductivity of the alkali-doped fullerenes (A3C60, A = alkali metal) has been so far discussed within the standard theory of superconductivity developed by Bardeen, Cooper and Shrieffer (BCS), even thought, they exhibit relatively high critical temperatures (up to Tc = 32 K). However, after our recent high-pressure measurements on Cs3C60 such description became questionable. We have shown that the superconducting phase of A3C60, in fact, borders the antiferromagnetic insulating phase (AFI), commonly observed for high-temperature superconductors like cuprates or pnictides. In addition, we also increased the maximal Tc to 38 K. To investigate this peculiar superconductivity close to the border with AFI state we employed nuclear magnetic resonance technique on Cs3-xRbxC60 and on Cs3C60 at various high pressures. Our results could not be correctly explained either by the standard BCS or the extended BCS that includes electron-electron repulsion interaction - the Migdal-Eliashberg theory. Far better agreement is obtained by the Dynamical Mean Field Theory. Due to similarity with other unconventional superconductors these results could also be relevant to other unconventional high-temperature superconductors.

  18. Participation of the myeloperoxidase-H2O2-halide system in immune complex nephritis

    Microsoft Academic Search

    Richard J Johnson; Seymour J Klebanoff; Rex F Ochi; Stephen Adler; Patricia Baker; Louise Sparks; William G Couser

    1987-01-01

    Participation of the myeloperoxidase-H2o2-halide system in immune complex nephritis. Neutrophils (PMNs) mediate injury in experimental glomerulonephritis (GN) in part via the release of reactive oxygen species, particularly hydrogen peroxide (H2O2). Recent kidney perfusion studies demonstrate that H2O2 can cause glomerular injury by reaction with halides in the presence of the PMN cationic enzyme myeloperoxidase (MPO) to form oxidants which can

  19. Unique properties of halide perovskites as possible origins of the superior solar cell performance.

    PubMed

    Yin, Wan-Jian; Shi, Tingting; Yan, Yanfa

    2014-07-16

    Halide perovskites solar cells have the potential to exhibit higher energy conversion efficiencies with ultrathin films than conventional thin-film solar cells based on CdTe, CuInSe2 , and Cu2 ZnSnSe4 . The superior solar-cell performance of halide perovskites may originate from its high optical absorption, comparable electron and hole effective mass, and electrically clean defect properties, including point defects and grain boundaries. PMID:24827122

  20. New ligands that promote cross-coupling reactions between aryl halides and unactivated arenes.

    PubMed

    Qiu, Yatao; Liu, Yanghan; Yang, Kai; Hong, Wenkun; Li, Zheng; Wang, Zhaoyang; Yao, Zhiyi; Jiang, Sheng

    2011-07-15

    Several ligands were designed to promote transition-metal-free cross-coupling reactions of aryl halides with benzene derivatives. Among the systems probed, quinoline-1-amino-2-carboxylic acid was found to serve as an excellent catalyst for cross-coupling between aryl halides and unactivated benzene. Reactions using this inexpensive catalytic system displayed a high functional group tolerance as well as excellent chemoselectivities. PMID:21688855

  1. Rare-gas-halide laser performance by the use of two halogen donors

    SciTech Connect

    Chantry, P.J.; Denes, L.J.; Kline, L.E.

    1987-06-02

    A method is described of operating a self-sustained discharge pumped rare gas-halide laser employing a rare gas selected from the group consisting of helium, neon, argon, krypton, xenon, and radon. A single strongly attaching halogen donor, XHn functions in the discharge and laser kinetics to simultaneously affect laser performance in achieving high energy deposition at low concentration values of XHn and high excited rare gas-halide production efficiency at high concentration values of XH/sub n/.

  2. Diversity and mechanisms of alkali tolerance in lactobacilli.

    PubMed

    Sawatari, Yuki; Yokota, Atsushi

    2007-06-01

    We determined the maximum pH that allows growth (pHmax) for 34 strains of lactobacilli. High alkali tolerance was exhibited by strains of Lactobacillus casei, L. paracasei subsp. tolerans, L. paracasei subsp. paracasei, L. curvatus, L. pentosus, and L. plantarum that originated from plant material, with pHmax values between 8.5 and 8.9. Among these, L. casei NRIC 1917 and L. paracasei subsp. tolerans NRIC 1940 showed the highest pHmax, at 8.9. Digestive tract isolates of L. gasseri, L. johnsonii, L. reuteri, L. salivarius subsp. salicinius, and L. salivarius subsp. salivarius exhibited moderate alkali tolerance, with pHmax values between 8.1 and 8.5. Dairy isolates of L. delbrueckii subsp. bulgaricus, L. delbrueckii subsp. lactis, and L. helveticus exhibited no alkali tolerance, with pHmax values between 6.7 and 7.1. Measurement of the internal pH of representative strains revealed the formation of transmembrane proton gradients (DeltapH) in a reversed direction (i.e., acidic interior) at alkaline external-pH ranges, regardless of their degrees of alkali tolerance. Thus, the reversed DeltapH did not determine alkali tolerance diversity. However, the DeltapH contributed to alkali tolerance, as the pHmax values of several strains decreased with the addition of nigericin, which dissipates DeltapH. Although neutral external-pH values resulted in the highest glycolysis activity in the presence of nigericin regardless of alkali tolerance, substantial glucose utilization was still detected in the alkali-tolerant strains, even in a pH range of between 8.0 and 8.5, at which the remaining strains lost most activity. Therefore, the alkali tolerance of glycolysis reactions contributes greatly to the determination of alkali tolerance diversity. PMID:17449704

  3. Investigation of quantum efficiencies in multilayered photocathodes for microchannel plate applications

    SciTech Connect

    Ze, F.; Landen, O.L.; Bell, P.M.; Turner, R.E.; Tutt, T.; Alvarez, S.S.; Costa, R.L. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)] [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

    1999-01-01

    Microchannel plates (MCPs) are used in many diagnostic systems to study laser-plasma interactions. Typically the front surface of a MCP is coated with some photocathode (PC) material to convert x ray to electron. This is followed by electron multiplication along the microchannels. Materials such as CsI, Al, and Au have been identified as good PC materials, but the overall quantum efficiencies of these materials are low, so that electron multiplication along the channel has been the only path to signal amplification. This approach is known to have some problems (J. D. Wiedwald, University of California UCRL-JC-110906, August 1992). We investigated the effect of pairing transmission PC to standard MC{close_quote}s and found that CsI and Au foils used in multilayered configuration, significantly enhance the overall quantum efficiency of the combination. The findings could lead to better MCP design and fabrication.

  4. Generation of Low Emtttance Beams Using Iii-V Semiconductor Photocathodes in AN RF Gun

    NASA Astrophysics Data System (ADS)

    Clendenin, J. E.; Kotseroglou, T.; Mulhollan, G. A.; Palmer, D. T.; Schmerge, J. F.

    2000-12-01

    Normalized rms emittances well below 10-6 m (with thermal emittance ignored) are now predicted for a 1-nC, 10-ps, flattop beam wing an S-band if gun. The expected thermal emittance of a Cu cathode excited at 263 nm is shown to be ~0.3 × 10-6 m, which is potentially a serious limit on the overall minimum emittance. For GaAs, the photoelectron energy parallel to the emitting surface is now known as a function of the perpendicular energy. By adjusting the vacuum level for the semiconductor, it appears that the thermal emittance can be reduced (compared to Cu) by a factor of 2--even more if the cathode is cooled. The prospects for operating an rf gun with a III-V semiconductor photocathode such as GaAs is summarized.

  5. Optical and structural properties of CsI thin film photocathode

    NASA Astrophysics Data System (ADS)

    Triloki; Rai, R.; Singh, B. K.

    2015-06-01

    In the present work, the performance of a cesium iodide thin film photocathode is studied in detail. The optical absorbance of cesium iodide films has been analyzed in the spectral range from 190 nm to 900 nm. The optical band gap energy of 500 nm thick cesium iodide film is calculated from the absorbance data using a Tauc plot. The refractive index is estimated from the envelope plot of transmittance data using Swanepoel's method. The absolute quantum efficiency measurement has been carried out in the wavelength range from 150 nm to 200 nm. The crystallographic nature and surface morphology are investigated by X-ray diffraction and transmission electron microscopy techniques. In addition, the elemental composition result obtained by energy dispersive X-ray analysis is also reported in the present work.

  6. Measurements of intrinsic emittance dependence on rf field for copper photocathodes

    NASA Astrophysics Data System (ADS)

    Prat, Eduard; Bettoni, Simona; Braun, Hans-Heinrich; Divall, Marta Csatari; Schietinger, Thomas

    2015-06-01

    Radio-frequency (rf) photoinjectors are used to generate high-brightness electron beams for a wide range of applications. Because of their outstanding beam quality, they are particularly well-suited as sources for X-ray free-electron lasers (FELs). The beam emittance, which is significantly influenced by the intrinsic emittance of the cathode, is fundamental for FELs, since it has a strong impact on the lasing performance and it defines the length and cost of the facility. In this paper we present measurements of the intrinsic emittance as a function of the rf field for a copper photocathode. Our measurements match with the theoretical expectations, showing that the intrinsic emittance can be reduced by decreasing the rf field at the cathode. We obtained normalized intrinsic emittances down to 350 nm /mm , the lowest values ever measured in a rf photoinjector.

  7. High Performance Polarized Electron Photocathodes Based on InGaAlAs/AlGaAs Superlattices

    SciTech Connect

    Mamaev, Yu.

    2004-12-10

    Highly efficient emitters of polarized electrons based on the InAlGaAs/AlGaAs superlattice give an optimistic prognosis to explorations of such structures as the sources for accelerators. A new set of these SL structures with minimized conduction band offset was designed and recently tested. A new technology of surface protection in MBE growth leads to a significantly reduced heat-cleaning temperature. At these lowered cleaning temperatures, the thermal degradation of the working structure parameters is avoided. As a result a polarization P of up to 91% at corresponding quantum efficiency (QE) of 0.3% was achieved at room temperature. A 50% increase in the photocathode lifetime has been achieved with Sb coverage.

  8. Highly segmented large-area hybrid photodiodes with bialkali photocathodes and enclosed VLSI readout electronics

    NASA Astrophysics Data System (ADS)

    Braem, A.; Chesi, E.; Dulinski, W.; Filthaut, F.; Go, A.; Joram, C.; Séguinot, J.; Weilhammer, P.; Wenzel, H.; Wicht, P.; Ypsilantis, T.

    2000-03-01

    We report on the principles, design, fabrication, and operation of a highly segmented, large-area hybrid photodiode, which is being developed in the framework of the LHCb RICH project. The device consists of a cylindrical, 127 mm diameter vacuum envelope capped with a spherical borosilicate UV-glass entrance window, with an active-to-total-area fraction of 81%. A fountain-focusing electron optics is used to demagnify the image onto a 50 mm diameter silicon sensor, containing 2048 pads of size 1×1 mm2. The sensor pads are read out by 16 analogue multiplexed readout chips enclosed in the vacuum envelope. A large ultra-high vacuum plant for the evaporation of visible-light transmittive bialkali (K2CsSb) photocathodes and subsequent tube encapsulation has been built and successfully operated. The characteristics and performance of the first HPDs have been measured to be in full agreement with expectations.

  9. Measurements of the Argonne Wakefield Accelerator's low charge, 4 MeV RF photocathode witness beam

    NASA Astrophysics Data System (ADS)

    Power, J.; Chojnacki, E.; Conde, M.; Gai, W.; Konecny, R.; Schoessow, P.; Simpson, J.

    1997-03-01

    The Argonne Wakefield Accelerator's (AWA) witness RF photocathode gun produced its first electron beam in April of 1996. We have characterized the charge, energy, emittance and bunch length of the witness beam over the last several months. The emittance was measured by both a quad scan that fitted for space charge using an in house developed Mathematica routine and a pepper pot technique. The bunch length was measured by imaging Cherenkov light from a quartz plate to a Hamamatsu streak camera with 2 psec resolution. A beam energy of 3.9 MeV was measured with a 6 inch round pole spectrometer while a beam charge was measured with both an ICT and a Faraday Cup. Although the gun will normally be run at 100 pC it has produced charges from 10 pC to 4 nC. All results of the measurements to date are presented here.

  10. Determination of halide impurities in ionic liquids by total reflection X-ray fluorescence spectrometry.

    PubMed

    Vander Hoogerstraete, Tom; Jamar, Steven; Wellens, Sil; Binnemans, Koen

    2014-04-15

    The determination and quantification of halide impurities in ionic liquids is highly important because halide ions can significantly influence the chemical and physical properties of ionic liquids. The use of impure ionic liquids in fundamental studies on solvent extraction or catalytic reactions can lead to incorrect experimental data. The detection of halide ions in solution by total reflection X-ray fluorescence (TXRF) has been problematic because volatile hydrogen halide (HX) compounds are formed when the sample is mixed with the acidic metal standard solution. The loss of HX during the drying step of the sample preparation procedure gives imprecise and inaccurate results. A new method based on an alkaline copper standard Cu(NH3)4(NO3)2 is presented for the determination of chloride, bromide, and iodide impurities in ionic liquids. The 1-butyl-3-methylimidazolium ([C4mim]) ionic liquids with the anions acetate ([C4mim][OAc]), nitrate ([C4mim][NO3]), trifluoromethanesulfonate ([C4mim][OTf]), and bis(trifluoromethylsulfonyl)imide ([C4mim][Tf2N]) were synthesized via a halide-free route and contaminated on purpose with known amounts of [C4mim]Cl, [C4mim]Br, [C4mim]I, or potassium halide salts in order to validate the new method and standard. PMID:24628670

  11. Measurements of photocathode operational lifetime at beam currents up to 10-mA using an improved DC high voltage GaAs photogun

    SciTech Connect

    J. Grames; M. Poelker; P. Adderley; J. Brittian; J. Clark; J. Hansknecht; D. Machie; M.L. Stutzman; K. Surles-Law

    2007-06-01

    This work extends past research at Jefferson Lab aimed at better appreciating the mechanisms that limit photocathode operational lifetime at high current (> 1 mA). Specifically, the performance of an improved 100 kV DC high voltage load locked photogun will be described. Although difficult to measure directly, we believe the new gun has better vacuum conditions compared to the original gun, as indicated by enhanced photocathode lifetimes exceeding 2000 C using a 1.55 mm diameter drive laser spot at the photocathode. In addition, the dependence of the lifetime on the laser spot size at the photocathode was measured and a charge density lifetime exceeding 10^6 C/cm^2 was measured with a 0.32 mm laser spot diameter.

  12. Observation of vapor pressure enhancement of rare-earth metal-halide salts in the temperature range relevant to metal-halide lamps

    SciTech Connect

    Curry, J. J.; Henins, A.; Hardis, J. E. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Estupinan, E. G. [Osram Sylvania Inc., Beverly, Massachusetts 01915 (United States); Lapatovich, W. P. [Independent Consultant, 51 Pye Brook Lane, Boxford, Massachusetts 01921 (United States); Shastri, S. D. [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

    2012-02-20

    Total vapor-phase densities of Dy in equilibrium with a DyI{sub 3}/InI condensate and Tm in equilibrium with a TmI{sub 3}/TlI condensate have been measured for temperatures between 900 K and 1400 K. The measurements show strong enhancements in rare-earth vapor densities compared to vapors in equilibrium with the pure rare-earth metal-halides. The measurements were made with x-ray induced fluorescence on the sector 1-ID beam line at the Advanced Photon Source. The temperature range and salt mixtures are relevant to the operation of metal-halide high-intensity discharge lamps.

  13. Stable High-Brightness Electron Beam System with a Photocathode RF Gun for Short Pulse X-Ray Generation by Thomson Scattering

    Microsoft Academic Search

    Fumio Sakai; Jinfeng Yang; Masafumi Yorozu; Yasuhiro Okada; Tatsuya Yanagida; Akira Endo

    2002-01-01

    A high-brightness electron accelerator system with a photocathode RF gun and an all-solid stable laser for the photocathode was installed, and a commissioning test was performed to generate short-pulse X-ray beams by the Thomson scattering method. Electron energy was boosted by a linear accelerator (linac) up to 14 MeV. Energy dispersion of the electron beams was measured to be 0.7%

  14. Dimethyl selenide complexes of copper, gallium and indium halides as potential precursors for selenium-containing chalcopyrite semiconducting materials

    Microsoft Academic Search

    Shashank Mishra; Erwann Jeanneau; Stéphane Daniele

    2010-01-01

    The coordination chemistry of copper, gallium and indium halides with the simplest possible selenoether i.e. Me2Se was investigated with the aim to use the resulting complexes as precursors for selenium-containing chalcopyrite semiconducting materials. An optimized general procedure for the high yield synthesis is described and the influence of a halide ion on the structure and solubility of these metal halide

  15. Elastic properties of alkali-feldspars

    NASA Astrophysics Data System (ADS)

    Waeselmann, N.; Brown, J.; Angel, R. J.; Ross, N.; Kaminsky, W.

    2013-12-01

    New measurements of single crystal elastic moduli for a suite of the alkali feldspars are reported. In order to interpret Earth's seismic structure, knowledge of the elastic properties of constituent minerals is essential. The elasticity of feldspar minerals, despite being the most abundant phase in Earth's crust (estimated to be more than 60%), were previously poorly characterized. All prior seismic and petrologic studies have utilized 50-year-old results, of questionable quality, based on 1-bar measurements on pseudo-single crystals. Alkali-feldspars present a large experimental challenge associated with their structural complexity. In the K-end member (KAlSi3O8) the symmetry is governed by Al/Si ordering, in the Na-end member (NaAlSi3O8) the symmetry is governed by whether or not there is a displacive collapse of the framework independent of the Al/Si ordering. K-feldspars exhibit monoclinic (C2/m) symmetry (necessitating determination of 13 elastic moduli) if disordered and triclinic (C-1) symmetry (21 elastic moduli) if ordered. Exsolution of Na-rich and K-rich phases is ubiquitous in natural samples, making it difficult to find suitable single phase and untwinned samples for study. The small single domain samples selected for this study were previously characterized by x-ray diffraction and microprobe analysis to ensure adequate sample quality. Surface wave velocities were measured on oriented surfaces of natural and synthetic single crystals using impulsively stimulated light scattering. A surface corrugation with a spacing of about 2 microns was impulsively created by the overlap of 100 ps infrared light pulses. The time evolution of the stimulated standing elastic waves was detected by measuring the intensity of diffraction from the surface corrugation of a variably delayed probe pulse. This method allows accurate (better than 0.2%) determination of velocities on samples smaller than 100 microns. The combination of measured surface wave velocities and separately determined compressibilities, based on high-pressure x-ray studies, allowed determination of the full elastic tensor for alkali-feldspars as a function of composition and structure.

  16. Charge Transfer during Alkali-Surface Collisions

    NASA Astrophysics Data System (ADS)

    Weare, Christopher Bruce

    The transfer of electrons between atoms and solid surfaces is the driving force behind ionic bond formation in adsorption and determines the final charge state in particle-surface collisions. Despite its importance, however, many aspects of charge transfer are not completely understood. The experiments presented in this dissertation use the scattering of ^7Li ^+ ions from surfaces to study several aspects of charge transfer. Primarily, the effects of alkali adsorption on the surface local electrostatic potential (LEP) are investigated via resonant charge transfer. In addition, the effects of charge promotion on the final charge state distributions of scattered ^7Li ^+ ions are determined. On metal surfaces, large differences in the final charge state distributions of ^7Li ^+ ions scattered from substrate and adsorbate sites are observed at low alkali coverages, which disappear at high coverages. The final charge state distribution of ^7Li^+ ions is determined primarily by resonant charge transfer, which is dependent on the LEP. Thus, there is a transition in the LEP from inhomogeneous to nearly homogeneous as the adsorbate coverage increases. The LEP is modeled as a collection of isolated dipoles positioned at the adsorbate sites. Calculations of the final charge state distributions of ions scattered from such model surfaces do an excellent job of reproducing the measured charge state distributions. From these calculations, it is shown that the inhomogeneous to homogeneous transition in the LEP is due to a coverage dependent depolarization of the adsorbate dipoles. For the alkali-covered Si(111)-7 x 7 surface, the final charge state distribution is independent of scattering site. This behavior is not attributed to a homogeneous LEP, rather, it is due to the dangling bonds of the Si(111) -7 x 7 surface, which allow resonant charge transfer to take place well above the surface. As a consequence, variations in the LEP near the adsorbate sites are not detected. During the Li-Al charge promotion process, a Li 1s hole is created, which later decays by electron emission. Because of this, the charge state distributions of promoted ions differ significantly from those of non-promoted ions. From a combination of charge state distributions and secondary electron spectra, it is shown that the lifetime of the hole is on the order of the ion-surface interaction time, i.e., 10 fs.

  17. Lasing in alkali atoms pumped by the dissociation of alkali-rare gas exciplexes (excimers)

    Microsoft Academic Search

    J. D. Readle; C. J. Wagner; J. G. Eden

    Lasing on the 62P1\\/2?6 2 S1\\/2 (D1) resonance transition of atomic Cs at 894.3 nm has been demonstrated in mixtures of Ar, ethane, and Cs vapor by the photoexcitation of ground state Cs-Ar collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (exciplexes or excimers). The blue satellites of the alkali D2 lines provide a pathway for optically pumping

  18. Alkali-activated cementitious materials: Mechanisms, microstructure and properties

    NASA Astrophysics Data System (ADS)

    Jiang, Weimin

    The goal of this study was to examine the activation reaction, microstructure, properties, identify the mechanisms of activation, and achieve an enhanced understanding of activation processes occurring during the synthesis of alkali activated cementitious materials (AAC). The discussions classify the following categories. (1) alkali activated slag cement; (2) alkali activated portland-slag cement; (3) alkali activated fly ash-slag cement; (4) alkali activated pozzolana-lime cement; (5) alkali activated pozzolana cement. The activators involved are NaOH, KOH; Nasb2SOsb4;\\ Nasb2COsb3;\\ CaSOsb4, and soluble silicate of sodium and potassium. The effect of alkali activation on the microstructure of these materials were analyzed at the micro-nanometer scale by SEM, EDS, ESEM, and TEM. Also sp{29}Si and sp{27}Al MAS-NMR, IR, Raman, TGA, and DTA were performed to characterize the phase in these systems. Slag, fly ash, silica fume, as well as blended cements containing mixtures of these and other components were characterized. A set of ordinary portland cement paste samples served as a control. This study confirmed that AAC materials have great potential because they could generate very early high strength, greater durability and high performance. Among the benefits to be derived from this research is a better understanding of the factors that control concrete properties when using AAC materials, and by controlling the chemistry and processing to produce desired microstructures and properties, as well as their durability.

  19. Ultrasonic coal washing to leach alkali elements from coals.

    PubMed

    Balakrishnan, S; Reddy, V Midhun; Nagarajan, R

    2015-11-01

    Deposition of fly ash particles onto heat-transfer surfaces is often one of the reasons for unscheduled shut-downs of coal-fired boilers. Fouling deposits encountered in convective sections of a boiler are characterized by arrival of ash particles in solidified (solid) state. Fouling is most frequently caused by condensation and chemical reaction of alkali vapors with the deposited ash particles creating a wet surface conducive to collect impacting ash particles. Hence, the amount of alkali elements present in coals, which, in turn, is available in the flue gas as condensable vapors, determines the formation and growth of fouling deposits. In this context, removal of alkali elements becomes vital when inferior coals having high-ash content are utilized for power generation. With the concept of reducing alkali elements present in a coal entering the combustor, whereby the fouling deposits can either be minimized or be weakened due to absence of alkali gluing effect, the ultrasonic leaching of alkali elements from coals is investigated in this study. Ultrasonic water-washing and chemical-washing, in comparison with agitation, are studied in order to estimate the intensification of the alkali removal process by sonication. PMID:26186840

  20. Controlled in-situ dissolution of an alkali metal

    DOEpatents

    Jones, Jeffrey Donald; Dooley, Kirk John; Tolman, David Donald

    2012-09-11

    A method for the controllable dissolution of one or more alkali metals from a vessel containing a one or more alkali metals and/or one or more partially passivated alkali metals. The vessel preferably comprising a sodium, NaK or other alkali metal-cooled nuclear reactor that has been used. The alkali metal, preferably sodium, potassium or a combination thereof, in the vessel is exposed to a treatment liquid, preferably an acidic liquid, more preferably citric acid. Preferably, the treatment liquid is maintained in continuous motion relative to any surface of unreacted alkali metal with which the treatment liquid is in contact. The treatment liquid is preferably pumped into the vessel containing the one or more alkali metals and the resulting fluid is extracted and optionally further processed. Preferably, the resulting off-gases are processed by an off-gas treatment system and the resulting liquids are processed by a liquid disposal system. In one preferred embodiment, an inert gas is pumped into the vessel along with the treatment liquid.

  1. Comparative alkali washing of simulated radioactive sludge

    SciTech Connect

    Fugate, G.A.; Ensor, D.D. [Tennessee Technological Univ., Cookeville, TN (United States); Egan, B.Z. [Oak Ridge National Lab., TN (United States)

    1996-10-01

    The treatment of large volumes of radioactive sludge generated from uranium and plutonium recovery processes is a pressing problem in the environmental restoration currently planned at various U.S. Department of Energy sites. This sludge, commonly stored in underground tanks, is mainly in the form of metal oxides or precipitated metal hydroxides and the bulk of this material is nonradioactive. One method being developed to pretreat this waste takes advantage of the amphoteric character of aluminum and other nonradioactive elements. Previous studies have reported on the dissolution of eleven elements from simulated sludge using NaOH solutions up to 6M. This work provides a comparative study using KOH. The effectiveness of the alkali washing as a treatment method to reduce the bulk of radioactive sludge requiring long term isolation will be discussed.

  2. Twist Mode in Spherical Alkali Metal Clusters

    E-print Network

    V. O. Nesterenko; J. R. Marinelli; F. F. de Souza Cruz; W. Kleinig; P. -G. Reinhard

    2000-10-02

    A remarkable orbital quadrupole magnetic resonance, so-called twist mode, is predicted in alkali metal clusters where it is represented by $I^{\\pi}=2^-$ low-energy excitations of valence electrons with strong M2 transitions to the ground state. We treat the twist by both macroscopic and microscopic ways. In the latter case, the shell structure of clusters is fully exploited, which is crucial for the considered size region ($8\\le N_e\\le 1314$). The energy-weighted sum rule is derived for the pseudo-Hamiltonian. In medium and heavy spherical clusters the twist dominates over its spin-dipole counterpart and becomes the most strong multipole magnetic mode.

  3. Alkali-Activity Correlations in Open Clusters Jeremy R. King and Simon C. Schuler

    E-print Network

    King, Jeremy

    Alkali-Activity Correlations in Open Clusters Jeremy R. King and Simon C. Schuler Department a census of correlations between activity measures and neutral resonance lines of the alkali elements Li I of a few ×106 to 4×107 years. Alkali- alkali and/or -activity correlations are newly noted within IC 2391

  4. Raman spectroscopic studies on mixed alkali borotungsten glasses

    NASA Astrophysics Data System (ADS)

    Edukondalu, A.; Srinivasu, CH.; Rahman, Syed; Sathe, V.; Kumar, K. Siva

    2014-04-01

    Mixed alkali borate glasses of composition xLi2O-(30-x)K2O-10WO3-60B2O3 (0 ? x ? 30 mol%) were prepared by melt quench technique. The structure of present glass system was investigated by Raman spectroscopy. The characteristic bands of these glasses due to the stretching and bending vibrations were identified and analyzed by the increasing of alkali content. This fact allowed us to identify the specific structural units which appear in these glasses and thus to point out the network modifier role of alkali oxide for low concentrations and its former role at high concentrations.

  5. Electrochemical cell utilizing molten alkali metal electrode-reactant

    DOEpatents

    Virkar, Anil V. (Sandy, UT); Miller, Gerald R. (Salt Lake City, UT)

    1983-11-04

    An improved electrochemical cell comprising an additive-modified molten alkali metal electrode-reactant and/or electrolyte is disclosed. Various electrochemical cells employing a molten alkali metal, e.g., sodium, electrode in contact with a cationically conductive ceramic membrane experience a lower resistance and a lower temperature coefficient of resistance whenever small amounts of selenium are present at the interface of the electrolyte and the molten alkali metal. Further, cells having small amounts of selenium present at the electrolyte-molten metal interface exhibit less degradation of the electrolyte under long term cycling conditions.

  6. Insight into the photoelectron angular dependent energy distribution of negative-electron-affinity InP photocathodes

    NASA Astrophysics Data System (ADS)

    Chen, Zhanghui; Jiang, Xiangwei; Dong, Shan; Li, Jingbo; Li, Shushen; Wang, Linwang

    2014-01-01

    Energy distribution and angular distribution of the photoelectrons from InP photocathodes are investigated using a precise Monte Carlo model. It is found that ?-valley electrons contribute to the first peak of the energy distribution curve, but the second peak is contributed by both ?-valley and L-valley electrons rather than only L-valley electrons. L valley electrons are shown to have a smaller angular spread than ?-valley electrons, which is attributed to the much higher potential energy of L-valley minimum. The further simulation indicates that the performance of InP photocathodes can be improved by increasing the hole concentration or decreasing the temperature, but the activation layer thickness variation only has very slight influence on either energy or angular distribution.

  7. Insight into the photoelectron angular dependent energy distribution of negative-electron-affinity InP photocathodes

    SciTech Connect

    Chen, Zhanghui; Jiang, Xiangwei; Dong, Shan; Li, Jingbo, E-mail: jbli@semi.ac.cn; Li, Shushen [State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Wang, Linwang [Materials Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Mail Stop 50F, Berkeley, California 94720 (United States)

    2014-01-13

    Energy distribution and angular distribution of the photoelectrons from InP photocathodes are investigated using a precise Monte Carlo model. It is found that ?-valley electrons contribute to the first peak of the energy distribution curve, but the second peak is contributed by both ?-valley and L-valley electrons rather than only L-valley electrons. L valley electrons are shown to have a smaller angular spread than ?-valley electrons, which is attributed to the much higher potential energy of L-valley minimum. The further simulation indicates that the performance of InP photocathodes can be improved by increasing the hole concentration or decreasing the temperature, but the activation layer thickness variation only has very slight influence on either energy or angular distribution.

  8. Theoretical Design of High-Brightness Photocathodes Based on Ultrathin Surface Layers on Metals and on Nanostructures

    NASA Astrophysics Data System (ADS)

    Németh, Károly; Harkay, Katherine C.; van Veenendaal, Michel; Spentzouris, Linda; White, Marion; Attenkofer, Klaus; Srajer, George

    2010-11-01

    We demonstrate by means of electronic structure calculations, how ultrathin MgO films on Ag(001) surfaces can be used to control the emittance properties of photocathodes. In addition to substantially reducing the work-function of the metal surface, the MgO layers also favorably influence the shape of the surface bands resulting in the generation of well collimated high-brightness electron beams in which the transverse momenta of the electrons are extremely small compared to the longitudinal ones. As the number of MgO surface layers varies from 0 to 3, the emitted electron beam becomes gradually brighter, reducing its transverse emittance to the extremely small value of 0.06 mm-mrad. We suggest the use of such photocathodes for the development of free-electron x-ray lasers and energy-recovery linac x-ray sources. A practical implementation and further tunability through nanophotonics means is also discussed.

  9. VUV-induced radiation ageing processes in CsI photocathodes studied by microscopy and spectroscopy techniques

    NASA Astrophysics Data System (ADS)

    Singh, B. K.; Triloki; Garg, P.; Prakash, A.; Di Santo, G.; Nappi, E.; Nitti, M. A.; Valentini, A.; Zanoni, R.

    2009-10-01

    CsI thin film photocathodes of 600 nm thickness deposited on polished Al surfaces by resistive evaporation technique were studied by angle-resolved X-ray photoelectron spectroscopy (ARXPS), before and after UV-irradiation under vacuum. It is shown that the "UV-irradiated" sample keeps the stoichiometric ratio Cs:I unchanged (1:1) while it shows a higher concentration of carbon in comparison with "as-deposited" samples. The morphology of the "as-deposited" sample is strongly affected after VUV-irradiation. The consequence of such effects on the physical and chemical properties of the "as-deposited" and "UV-irradiated" CsI thin film photocathodes is discussed.

  10. Measurement of the tradeoff between intrinsic emittance and quantum efficiency from a NaKSb photocathode near threshold

    NASA Astrophysics Data System (ADS)

    Maxson, Jared; Cultrera, Luca; Gulliford, Colwyn; Bazarov, Ivan

    2015-06-01

    We measure the tradeoff between the quantum efficiency and intrinsic emittance from a NaKSb photocathode at three increasing wavelengths (635, 650, and 690 nm) at or below the energy of the bandgap plus the electron affinity, h ??Eg+Ea . These measurements were performed using a high voltage dc gun for varied photocathode surface fields of 1.4 -4.4 MV/m. Measurements of intrinsic emittance are performed using two different methods and were found to agree. At the longest wavelength available, 690 nm, the intrinsic emittance was 0.26 ?m/mm-rms with a quantum efficiency of ˜10-4 . The suitability of NaKSb emitting at threshold for various low emittance applications is discussed.

  11. Simulations of the BNL/SLAC/UCLA 1.6 cell emittance compensated photocathode RF gun low energy beam line

    SciTech Connect

    Palmer, D.T.; Miller, R.H.; Winick, H. [Stanford Univ., CA (United States). Stanford Linear Accelerator Center; Wang, X.J.; Batchelor, K.; Woodle, M.; Ben-Zvi, I. [Brookhaven National Lab., Upton, NY (United States)

    1995-06-01

    A dedicated low energy (2 to 10 MeV) experimental beam line is now under construction at Brookhaven National Laboratories Accelerator Test Facility (BNL/ATF) for photocathode RF gun testing and photoemission experiments. The design of the experimental line, using the 1.6 cell photocathode RF gun developed by the BNL/SLAC/UCLA RF gun collaboration is presented. Detailed beam dynamics simulations were performed for the 1.6 cell RF gun injector using a solenoidal emittance compensation technique. An experimental program for testing the 1.6 cell RF gun is presented. This program includes beam loading caused by dark current, higher order mode field measurements, integrated and slice emittance measurements using a pepper-pot and RF kicker cavity.

  12. Growth mechanisms of silver halide clusters from the molecule to the colloidal particle

    SciTech Connect

    Hayes, D.; Schmidt, K.H.; Meisel, D. (Argonne National Lab., IL (USA))

    1989-08-10

    Studies of growing silver halide clusters, from the molecular level to colloidal-size particles, have been undertaken and correlations between particle size and physical properties have been investigated. The production of halide ions by dissociative electron attachment following pulse radiolysis of methylene halide solutions was utilized to instantaneously produce homogeneous, supersaturated solutions of halide and silver ions. The growth of silver halide particles in these solutions has been examined by conductance, absorption spectroscopy, and light scattering measurements. Conductivity measurements show that the initial reaction between the ions occurs at a diffusion-controlled rate and allow determination of the stability constants of molecular silver halide species. In solutions containing excess silver ions, particle growth of silver iodide and silver bromide occurs via a diffusion-controlled aggregation mechanism during the first seconds. The growth rate is reduced significantly, due to electrostatic repulsion between particles, when the concentration of halide ions is almost equal to or greater than the stoichiometric concentration of silver ions. The absorbance of silver iodide suspensions produced in this manner has also been measured. The initial absorbance, due to AgI molecules, occurs at wavelengths of 280 nm and below. The lowest energy exciton band appears {approximately} 50 {mu}s after initiation of the reaction. This band initially peaks at around 320 nm and shifts toward 425 nm (the wavelength of exciton absorption in bulk silver iodide). The surface potential at the interface evolves at about the same rate as the bulk properties of the material. For the mostly dissociated AgCl molecules growth by addition of ions to a small number of particles of critical size was observed.

  13. A Si Photocathode Protected and Activated with a Catalytic Ti and Ni Composite Film for Solar Hydrogen Production in Water

    E-print Network

    Lai, Yi-Hsuan; Park, Hyun S.; Zhang, Jenny Z.; Matthews, Peter D.; Wright, Dominic S.; Reisner, Erwin

    2015-02-04

    for several hours, and serves as a benchmark non-noble photocathode for solar H2 evolution that operates efficiently under neutral–alka- line conditions. Photoelectrochemical (PEC) water splitting is an attractive strategy to generate the renewable energy... for profitable solar H2 generation of 15–20%. [3] However, the implementation of PEC water splitting can only be accomplished when such semiconductors are not only efficient, but also stable and scal- able. Crystalline silicon (Si) displays excellent light...

  14. First demonstration of a free-electron laser driven by electrons from a laser-irradiated photocathode

    Microsoft Academic Search

    Mark Curtin; Glenn Bennett; Robert Burke; Anup Bhowmik; Phillip Metty; Stephen Benson; J. M. J. Madey

    1990-01-01

    We report the results from the first operation of a free electron laser (FEL) driven by an electron beam from a laser-irradiated photocathode. The Rocketdyne\\/Stanford FEL achieved sustained oscillations, lasting in excess of three hours, driven by photoelectrons accelerated by the Stanford Mark III radiofrequency linac. A LaB6 cathode, irradiated by a tripled Nd: Yag mode-locked drive laser was the

  15. First Demonstration Of A Free-electron Laser Driven By Electrons From A Laser-Irradiated Photocathode

    Microsoft Academic Search

    Mark Curtin; Glenn Bennett; Robert Burke; A. Bhowmik; P. Metty; S. Benson; J. M. J. Madey

    1989-01-01

    Results are reported from the first observation of a free-electron laser (FEL) driven by an electron beam from a laser-irradiated photocathode. The Rocketdyne\\/Stanford FEL achieved sustained oscillations lasting over three hours and driven by photoelectrons accelerated by the Stanford Mark III radio-frequency linac. A LaB6 cathode, irradiated by a tripled Nd:YAG mode-locked drive laser, is the source of the photoelectrons.

  16. Production of picosecond square-shaped ultraviolet pulses for low-emittance electron bunch generation from an RF photocathode

    Microsoft Academic Search

    Akira Yada; Kazuya Takasago; Shinji Ito; Tatsuya Yanagida; Jinfeng Yang; Masakazu Washio; Kenji Torizuka; Akira Endo

    2002-01-01

    We demonstrated generation of square-shaped ultraviolet pulses and that they reduces the emittance of electron beams from laser-photocathode RF-gun. Some frequency components of femtosecond pulses from a Ti:sapphire oscillator are modulated with a pulse shaper that consists of a lens pair, gratings, and a liquid crystal spatial light modulator (LC-SLM) to generate square-shaped pulses. The shaped pulses were amplified up

  17. Development of the emittance measurement system of a high intensity pulsed electron beam from NEA-GaAs type photocathode

    Microsoft Academic Search

    Masahiro Yamamoto; Naoto Yamamoto; Taro Konomi; Yasuhide Nakagawa; Hikaru Saito; Shoji Okumi; Tsutomu Nakanishi; Masatoshi Tanioku; Xiuguang Jin; Toru Ujihara; Yoshikazu Takeda

    The generation of low emittans beam of 10mA or more in the average current and normalized emittance of 0.5 ?.mm.mrad or less is indispensable to ERL electron source. A high gradient DC-gun that uses the NEA-GaAs type photocathode is the prime candidate of the ERL gun. We have developed of a 200keV DC-gun designed for ILC electron source and reconstructed

  18. Calcium Phosphate: A potential host for halide contaminated plutonium wastes.

    SciTech Connect

    Metcalfe, Brian L.; Donald, Ian W.; Fong, Shirley K.; Gerrard, Lee A.; Strachan, Denis M.; Scheele, Randall D.

    2009-07-06

    The presence of significant quantities of fluoride and chloride in four types of legacy wastes from plutonium pyrochemical reprocessing required the development of a new wasteform which could adequately immobilize the halides in addition to the Pu and Am. Using a simulant chloride-based waste (Type I waste) and Sm as the surrogate for the Pu3+ and Am3+ present in the waste, AWE developed a process which utilised Ca3(PO4)2 as the host material. The waste was successfully incorporated into two crystalline phases, chlorapatite, [Ca5(PO4)3Cl], and spodiosite, [Ca2(PO4)Cl]. Radioactive studies performed at PNNL with 239Pu and 241Am confirmed the process. A slightly modified version of the process in which CaHPO4 was used as the host was successful in immobilizing a more complex multi-cation oxide–based waste (Type II) which contained significant concentrations of Cl and F in addition to 239Pu and 241Am. This waste resulted in the formation of cation-doped whitlockite, Ca3-xMgx(PO4)2, ?-calcium phosphate, ?-Ca2P2O7 and chlor-fluorapatite rather than the chlorapatite and spodiosite formed with Type I waste.

  19. TRPM7 is regulated by halides through its kinase domain

    PubMed Central

    Yu, Haijie; Zhang, Zheng; Lis, Annette; Penner, Reinhold; Fleig, Andrea

    2013-01-01

    Transient receptor potential melastatin 7 (TRPM7) is a divalent-selective cation channel fused to an atypical ?-kinase. TRPM7 is a key regulator of cell growth and proliferation, processes accompanied by mandatory cell volume changes. Osmolarity-induced cell volume alterations regulate TRPM7 through molecular crowding of solutes that affect channel activity, including magnesium (Mg2+), Mg-nucleotides and a further unidentified factor. Here, we assess whether chloride and related halides can act as negative feedback regulators of TRPM7. We find that chloride and bromide inhibit heterologously expressed TRPM7 in synergy with intracellular Mg2+ ([Mg2+]i) and this is facilitated through the ATP-binding site of the channel’s kinase domain. The synergistic block of TRPM7 by chloride and Mg2+ is not reversed during divalent-free or acidic conditions, indicating a change in protein conformation that leads to channel inactivation. Iodide has the strongest inhibitory effect on TRPM7 at physiological [Mg2+]i. Iodide also inhibits endogenous TRPM7-like currents as assessed in MCF-7 breast cancer cells, where upregulation of SLC5A5 sodium-iodide symporter enhances iodide uptake and inhibits cell proliferation. These results indicate that chloride could be an important factor in modulating TRPM7 during osmotic stress and implicate TRPM7 as a possible molecular mechanism contributing to the anti-proliferative characteristics of intracellular iodide accumulation in cancer cells. PMID:23471296

  20. Imaging of hydrogen halides photochemistry on argon and ice nanoparticles

    NASA Astrophysics Data System (ADS)

    Poterya, V.; Lengyel, J.; Pysanenko, A.; Svr?ková, P.; Fárník, M.

    2014-08-01

    The photodissociation dynamics of HX (X = Cl, Br) molecules deposited on large ArN and (H2O)N, bar{N}? 102-103, clusters is investigated at 193 nm using velocity map imaging of H and Cl photofragments. In addition, time-of-flight mass spectrometry after electron ionization complemented by pickup cross section measurements provide information about the composition and structure of the clusters. The hydrogen halides coagulate efficiently to generate smaller (HX)n clusters on ArN upon multiple pickup conditions. This implies a high mobility of HX molecules on argon. On the other hand, the molecules remain isolated on (H2O)N. The photodissociation on ArN leads to strong H-fragment caging manifested by the fragment intensity peaking sharply at zero kinetic energy. Some of the Cl-fragments from HCl photodissociation on ArN are also caged, while some of the fragments escape the cluster directly without losing their kinetic energy. The images of H-fragments from HX on (H2O)N also exhibit a strong central intensity, however, with a different kinetic energy distribution which originates from different processes: the HX acidic dissociation followed by H3O neutral hydronium radical formation after the UV excitation, and the slow H-fragments stem from subsequent decay of the H3O. The corresponding Cl-cofragment from the photoexcitation of the HCl.(H2O)N is trapped in the ice nanoparticle.