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1

Fabrication of alkali halide UV photocathodes by pulsed laser deposition  

SciTech Connect

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. (laser technologies)

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

2012-12-31

2

Alkali Halides  

Microsoft Academic Search

\\u000a Surfaces of alkali halide crystals have properties which make them interesting model surfaces for the surface science of insulators:\\u000a they perfectly terminate ionic crystals, they are chemically inert, and they have no free electrons. Structural and point\\u000a defects are well described. Some model systems for film growth like Au on NaCl have been extensively studied for decades.\\u000a With the invention

Roland Bennewitz; Martin Bammerlin; Ernst Meyer

3

Stability of quantum efficiency and visible light rejection of alkali halide photocathodes  

NASA Astrophysics Data System (ADS)

We have studied the UV sensitivity degradation of CsI and KBr thin films under UV illumination and the stability of their visible light rejection for CsI and KBr opaque photocathodes evaporated on microchannel plates. For both materials the greatest degradation of the relative quantum detection efficiency was observed near the photocathode sensitivity cut off, while there was almost no change in their EUV response. The aging of the photocathodes is likely to be independent of the angle of radiation incidence. Of the two materials the CsI films appeared to be more solar blind and less subject to visible sensitivity activation by UV exposure.

Tremsin, Anton S.; Siegmund, Oswald H.

2000-07-01

4

Synthetic Alkali Halides  

NSDL National Science Digital Library

This complex experimental investigation uses alkali halides (NaCl, KCl, and mixtures of both) to simulate the melting of alkali feldspars which melt at too high of temperatures to work with in lab. Three hypotheses are tested: It is possible to crystallize alkali-chloride salts from a magma with any composition between NaCl and KCl. Because K+ and Na+ do not have the same ionic size, the atomic spacing in alkali chlorides will vary systematically with composition. Alkali chlorides are equally stable at high (just below liquidus) and low (subsolidus)temperatures. This project takes more than one class period, depending on how many students are in the class, because there will be lines at the scales, oven, and XRD. It is advisable to introduce the lab in class and have students complete various parts on their own time. There are three main parts. Part one: Synthesize all alkali halide compositions at high temperature (hopefully above the solvus. Part two: Put grown crystals back in an oven at lower temperature to see if they will unmix. Part three: Write a report evaluating and interpreting all results, relevant graphs, and the above three hypothesis.

Perkins, Dexter

5

Positronium in Alkali Halides  

Microsoft Academic Search

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

Jun-ichi Kasai; Toshio Hyodo; Kunio Fujiwara

1988-01-01

6

Shell model calculations for alkali halide molecules  

Microsoft Academic Search

This work applies the shell model to study the behaviour of the internuclear interactions of diatomic alkali halide molecules\\u000a from data given by the dynamical models for alkali halide crystals. Our interest is to test the breathing shell model when\\u000a core holes have been introduced. This will provide another source of information on the nature of the interaction potential\\u000a between

S. Y. Yousif; A. N. Imtani

1992-01-01

7

The Additive Coloration of Alkali Halides  

ERIC Educational Resources Information Center

Describes the construction and use of an inexpensive, vacuum furnace designed to produce F-centers in alkali halide crystals by additive coloration. The method described avoids corrosion or contamination during the coloration process. Examination of the resultant crystals is discussed and several experiments using additively colored crystals are…

Jirgal, G. H.; and others

1969-01-01

8

The Additive Coloration of Alkali Halides  

ERIC Educational Resources Information Center

|Describes the construction and use of an inexpensive, vacuum furnace designed to produce F-centers in alkali halide crystals by additive coloration. The method described avoids corrosion or contamination during the coloration process. Examination of the resultant crystals is discussed and several experiments using additively colored crystals are…

Jirgal, G. H.; and others

1969-01-01

9

Self-assembled films of alkyl halides on alkali halides  

SciTech Connect

Monolayer films of four different alkyl halides were prepared by exposing freshly cleaved alkali halide (001) surfaces via immersion for at least 48 h to dilute benzene solutions of these compounds. The thickness and orientation of each film were inferred from the variation with take-off angle of the characteristic atomic peak heights in x-ray photoelectron spectroscopy spectra. For each of these compounds on each alkali halide surface, the spectra indicate that the halogen end of the molecule lies at the substrate interface and the other end points away from the interface. Films of BrCH{sub 2}(CH{sub 2}){sub 4}CH{sub 3} were formed by deposition in vacuum on a cleaved KBr(001) target at {approximately}140 K. The growth and evolution with thermal cycling of the film up to its desorption temperature at {approximately}180 K were followed by monitoring the specular reflection of a helium atomic beam from the surface. Films heated above {approximately}170 K appear to anneal to a more ordered structure; helium diffractive scattering from the deposited film taken at {approximately}50 K without annealing yielded {ital broad} diffraction peaks at the KBr positions, while similar measurements taken after annealing produced {ital sharp} diffraction peaks at these angles and at half-order angles as well. Consistent with helium diffraction measurements over a range of azimuths, the structure of this annealed film could be interpreted as one of mixed (1{times}2) and (2{times}1) domains. Specular intensity measurements as a function of surface temperature yielded a Debye temperature of the annealed film {approximately}95 K. {copyright} {ital 1996 American Vacuum Society}

Hernandez, J.J.; Li, J.A.; Baker, J.; Safron, S.A.; Skofronick, J.G. [Departments of Physics and Chemistry, and the Center for Materials Research and Technology (MARTECH), Florida State University, Tallahassee, Florida 32306 (United States)

1996-05-01

10

Polysiloxane depolymerization with dimethyl carbonate using alkali metal halide catalysts  

Microsoft Academic Search

Polydimethylsiloxane terminated by a methyl group was almost completely depolymerized in the mixture of dimethyl carbonate (DMC) and methanol using alkali metal halide catalysts to form dimethoxydimethylsilane (DMDMS) and methoxytrimethylsilane (MTMS) monomers. The various alkali metal halides tested as catalysts gave the same monomer yield. The depolymerization rate depended on the kind of alcohol but not on dialkyl carbonate. The

Masaki Okamoto; Sumiko Suzuki; Eiichi Suzuki

2004-01-01

11

Curve Crossing in Collisional Dissociation of Alkali Halide Molecules  

Microsoft Academic Search

The primary dissociation step for alkali halide diatomics in argon has been studied in order to determine whether collisional dissociation produces ions, atoms, or a mixture of both types of products. The method is based on time-resolved absorption spectroscopy of shock-heated vapors. Results show that the cesium halides, and the rubidium and potassium halides, with the exception of the two

J. J. Ewing; Richard Milstein; R. Stephen Berry

1971-01-01

12

Thermoluminescence of alkali halides and its implications  

NASA Astrophysics Data System (ADS)

Trapping levels present in some alkali halides namely NaCl, KCl, KBr, and KI are determined by deconvolution of the thermoluminescence (TL) curves. Unlike most of the studies undertaken over the last few decades, we have presented a comprehensive picture of the phenomenon of TL as an analytical technique capable of revealing the position of the trapping levels present in the materials.We show that for all practical purposes, TL can be described involving only the three key trapping parameters, namely, the activation energy (E), the frequency factor (s), and the order of kinetics (b) even for complex glow curves having a number of TL peaks.Finally, based on these, we logically infer the importance of TL in development and characterization of materials used in dosimetry, dating and scintillation.

Gartia, R. K.; Rey, L.; Tejkumar Singh, Th.; Basanta Singh, Th.

2012-03-01

13

Surface Segregation in Mixed Alkali Halide Solutions  

NASA Astrophysics Data System (ADS)

Bromine compounds in the marine troposphere have been of great interest since the observation that tropospheric ozone depletion events in the arctic are correlated with gas phase bromine chemistry. Reactions with sea salt aerosols, particles and ice appears to be the source of these bromine compounds. In previous experiments we have shown that bromine segregates to the surface of sodium chloride crystals that are uniformly doped with low levels of bromide. We describe here experiments in which we have used high pressure photoelectron spectroscopy (HPPES) at the Advanced Light Source (ALS) to measure the ion concentrations at the surface of mixed alkali halide solutions. The experiments start with single crystals of sodium chloride that are uniformly doped with bromide at 7% and 0.1% level. The x-ray photoelectron spectra of the sample surface are obtained as a function of water vapor up to and at sample deliquescence. The concentrations of bromide and chloride ions at the liquid/vapor interface for the saturated solution that is produced upon deliquescence are obtained. For both samples, after deliquescence the bromide concentration at the surface of the saturated solution is greatly enhanced. The results will be compared with molecular dynamics simulations of a mixed bromide/chloride solution.

Ghosal, Sutapa; Bluhm, Hendrik

2005-03-01

14

Infrared absorption by methane adsorbed on alkali halide films  

Microsoft Academic Search

Summary  The infrared absorption by methane physically adsorbed on alkali halide films at?206°C was measured during the whole course\\u000a of the adsorption and desorption experiments. The alkali halide films—NaCl, NaBr, NaJ, KCl, KBr, KJ—were prepared in the IR\\u000a cell by condensation on KBr disks.\\u000a \\u000a All observed bands of the adsorbed molecules are shifted compared to the bands in the gas spectrum.

S. Zehme; J. Heidberg; H. Hartmann

1971-01-01

15

Curve Crossing in Collisional Dissociation of Alkali Halide Molecules.  

National Technical Information Service (NTIS)

The primary dissociation step for alkali halide diatomics in argon has been studied in order to determine whether collisional dissociation produces ions, atoms, or a mixture of both types of products. The method is based on time-resolved absorption spectr...

J. J. Ewing R. Milstein R. S. Berry

1970-01-01

16

Device Engineering of Large Area, High Performance Bi-Alkali Photocathodes for Fast-Timing Applications  

NASA Astrophysics Data System (ADS)

The photo-cathodes are devices that convert a photon into free electrons, used in vacuum tubes for detecting photons. With its extremely low dark current and ultra-fast time response, alkali photo-cathodes have been widely used in high energy physics and astrophysics. However, until recently, fundamental understanding of the physics behind the variation of the photo-cathode performance was still limited, which prevents reliable and reproducible production of high performance photo-cathodes. This talk will discuss the development of large area bi-alkali photo-cathode for pico-second detector project. With thorough and careful investigation of several mature growth recipes, critical parameters which may affect the cathode performance were identified and subsequently studied. Optical and electrical measurements clearly reveal the affection of Sb thickness to the overall photo-cathode performance. Based on these studies, large area photo-cathode with high uniformity was achieved. The study also makes it possible for high performance photo-detector development.

Xie, Junqi; Demarteau, Marcel; Frisch, Henry; May, Edward; Paramonov, Alexander; Wagner, Robert; Walters, Dean

2013-04-01

17

Precision Measurements of Crystals of the Alkali Halides  

Microsoft Academic Search

Crystal structure and dimensions for all the alkali halides.-The Hull powder method of obtaining x-ray diffraction patterns was used. By comparing each diffraction pattern directly with the pattern of NaCl simultaneously recorded on the other half of the film, the grating space of each crystal powder was measured in terms of the side of the unit cube of NaCl, assumed

Wheeler P. Davey

1923-01-01

18

Nature of Melting and Superionicity in Alkali and Alkaline-Earth Halides  

Microsoft Academic Search

A parameter-free theory is shown to provide an explanation for both melting in alkali halides, and superionicity in alkaline-earth halides, in terms of different types of instabilities of the perfect lattice.

L. L. Boyer

1980-01-01

19

Charge-Charge Liquid Structure Factor and the Freezing of Alkali Halides  

Microsoft Academic Search

The peak height of the charge-charge liquid structure factor SQQ in molten alkali halides is proposed as a criterion for freezing. Available data on molten alkali chlorides, when extrapolated to the freezing point suggests SQQ ? 5.

N. H. March; M. P. Tosi

1980-01-01

20

Stimulation of the Salt Receptor of the Blowfly: III. The alkali halides  

Microsoft Academic Search

Application of solutions of each of the alkali halides to the tip of a labellar sensillum of the blowfly elicited a repetitive neural discharge from the salt receptor. The records were qualitatively similar to those for NaCl. For each of the alkali chlorides and sodium halides, the shapes of the curves of the response of the salt receptor as a

HOWARD L. GILLARY

1966-01-01

21

Low-energy electron transport in alkali halides  

NASA Astrophysics Data System (ADS)

A model of electron transport in alkali halides, below 10 eV, is described. It is based on theoretically calculated microscopic cross sections of electron interactions with lattice phonons. Both acoustic and optical scatterings are taken into account, the former being also treated as a quasielastic process that randomizes the electron motion. Monte Carlo calculations based on the model simulate the UV-induced photoelectron emission from CsI. The calculated quantum efficiency and energy spectra are in good agreement with experimental data, in the photon energy range of 6.3 - 8.6 eV. The probability for an electron to escape from CsI, NaCl, and KCl is provided as a function of its energy and creation depth. A comparison is made between our approach and other phenomenological models.

Akkerman, A.; Boutboul, T.; Breskin, A.; Chechik, R.; Gibrekhterman, A.

1994-10-01

22

Alkali halide clusters produced by fast ion impact  

PubMed Central

The most abundant geometries and relative stabilities of alkali halide clusters with a (XY)no configuration (e.g., LiF, NaCl, KBr) are described. Five main series were obtained: linear, cyclic, cubic, arc strips and nanotubes. The stability analysis shows that higher members are likely to be formed from the lower member of the same series and/or from two building blocks (n = 1, 2). The energy analysis (D-plot) indicates that the most compact ones (e.g., cubic and nanotubes) present higher stability when compared to the linear, cyclic and arc strip structures; moreover, relative stability between the cubic and nanotube series varies with the cluster size.

Fernandez-Lima, Francisco Alberto; Nascimento, Marco Antonio Chaer; da Silveira, Enio Frota

2011-01-01

23

Ion pairing in molecular simulations of aqueous alkali halide solutions.  

PubMed

Using classical molecular dynamics simulations, we study ion-ion interactions in water. We study the potentials of mean force (PMF) for the full set of alkali halide ion pairs, and in each case, we test different parameter sets for modeling both the water and the ions. Altogether, we compared 300 different PMFs. We also calculate association equilibrium constants (KA) and compare them to two types of experiments. Of additional interest here was the proposition of Collins called the "law of matching water affinities", where the relative affinity of ions in solution depends on the matching of cation and anion sizes. From observations on the relative depths of the free energies of the contact ion pair (CIP) and the solvent-shared ion pair (SIP), along with related solvent structure analyses, we find a good correlation with this proposition: small-small and large-large should associate in water, and small-large should be more dissociated. PMID:19206510

Fennell, Christopher J; Bizjak, Alan; Vlachy, Vojko; Dill, Ken A

2009-05-14

24

Interpretation of three-photon spectra in alkali halides  

NASA Astrophysics Data System (ADS)

A symmetry analysis is presented which determines the selection rules of three-photon absorption processes. In the case of photons of equal energy, in addition to the dipole and the polarization selection rules an additional selection rule arises due to the symmetrization of the interaction operator. Contrary to the case of two-photon transitions the polarization dependence can now contain undetermined dynamical parameters. These considerations are applied to the case of an Oh point group in order to interpret recent experiments on alkali halides. The effect of a magnetic field in different directions is also studied. The theory accounts for the observed transitions and their polarization properties. Moreover, the presence of a new line in the absorption spectrum of CsI is predicted, and possible configurations in which this line could be detected are discussed.

Pasquarello, Alfredo; Andreani, Lucio Claudio

1990-06-01

25

Ion pairing in molecular simulations of aqueous alkali halide solutions  

PubMed Central

Using classical molecular dynamics simulations, we study ion-ion interactions in water. We study the potentials of mean force (PMF) for the full set of alkali halide ion pairs, and in each case, we test different parameter sets for modeling both the water and the ions. Altogether, we compared 300 different PMFs. We also calculate association equilibrium constants (KA) and compare them to two types of experiments. Of additional interest here was the proposition of Collins called the ‘law of matching water affinities’, where the relative affinity of ions in solution depends on the matching of cation and anion sizes. From observations on the relative depths of the free energies of the contact ion pair (CIP) and the solvent-shared ion pair (SIP), along with related solvent structure analyses, we find a good correlation with this proposition: small-small and large-large should associate in water and small-large should be more dissociated.

Fennell, Christopher J.; Bizjak, Alan; Vlachy, Vojko; Dill, Ken A.

2009-01-01

26

Perturbative Treatment of Quasi-Resonant Proton Neutralization at Alkali-Halide Surfaces.  

National Technical Information Service (NTIS)

A theoretical investigation of proton neutralization by proton scattering from several alkali-halide surfaces is presented. These systems ae suitable for a perturbative treatment since no hydrogenic atomic shell is embedded in the valence band of the soli...

F. Battaglia T. F. George A. Lanaro

1985-01-01

27

Enthalpies of dissolution of alkali halides in mixtures of dimethyl sulfoxide with water or heavy water  

Microsoft Academic Search

The enthalpies of dissolution of cesium fluoride, lithium and sodium chlorides, potassium bormide, sodium and cesium iodides, and tetrabutylammonium bromide were measured by means of calorimetry, and the standard enthalpies of dissolution of all alkali halides (except rubidium halides) in mixtures of dimethyl sulfoxide with water or heavy water at 298.15 K were calculated from the differences of the enthalpies

Egorov

1995-01-01

28

Strong Turbulence in Alkali Halide Negative Ion Plasmas  

NASA Astrophysics Data System (ADS)

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).

Sheehan, Daniel

1999-11-01

29

Surface charge of alkali halide particles as determined by laser-Doppler electrophoresis  

SciTech Connect

Nonequilibrium electrophoretic-mobility measurements by laser-Doppler electrophoresis are reported for alkali halide particles. These measurements have been made for the first time and allow for the sign of the surface charge to be predicted for alkali halides in their saturated brines. In general, the results can be explained from the simplified lattice ion hydration theory; however, potassium chloride is, at least, one noteworthy exception. On the basis of this analysis, particle dispersion/aggregation behavior in saturated brines can be explained. Further, the nature of collector (surfactant) adsorption and the flotation behavior of the alkali halide salts from their saturated brines can now be described more accurately. 20 refs., 7 figs., 3 tabs.

Miller, J.D.; Yalamanchili, M.R. (Univ. of Utah, Salt Lake City, UT (United States)); Kellar, J.J. (South Dakota School of Mines and Technology, Rapid City, SD (United States))

1992-05-01

30

Optical amplification and induced absorption in activated alkali-halide crystals under lamp pumping  

SciTech Connect

Competing optical amplification and induced absorption are discovered under broadband pulsed excitation with 10/sup 3/--10/sup 5/ W/cm/sup 2/ absorbed power density in alkali-halide crystals, activated by mercurylike ions. The kinetics of these processes is studied in the micro- and millisecond ranges. It is shown that induced absorption is due to stepwise ionization of the impurity centers. The results obtained are discussed in connection with the prospective use for building lasers based on impurity centers and for the purpose of active coloring of activated alkali-halide crystals.

Aseev, G. I.; Gorin, G. B.

1988-09-01

31

Interaction of soft x-ray photons with free alkali-halide molecular clusters  

NASA Astrophysics Data System (ADS)

Alkali-halide molecular clusters were formed from the vaporized molecules in collisions with an intense beam of argon clusters. Photoionization of the alkali-halide clusters as the result of interaction with x-ray radiation has been utilized in a photoelectron spectroscopy study of cluster bonding mechanisms. The changes in the energy structure due to the transformation from molecules to the solid salt were observed both in the inner and outer shells of constituent elements (metal and halogen) and were used to deduce the geometric structure of the clusters in question.

Zhang, Chaofan; Andersson, Tomas; Huttula, Marko; Mikkelä, Mikko-Heikki; Anin, Dmitri; Tchaplyguine, Maxim; Öhrwall, Gunnar; Svensson, Svante; Björneholm, Olle

2012-11-01

32

Apparatus for the coloration of laser-quality alkali halide crystals.  

PubMed

A heat-pipe apparatus allowing for the additive coloration of laser-quality alkali halide crystals is described. It has the following features: (1) Prepolished crystals emerge ready for direct installation in the laser; (2) F-center densities are directly proportional to the buffer gas pressure; (3) An air lock allows the same charge of alkali metal to be used many times over. PMID:18699199

Mollenauer, L F

1978-06-01

33

Manifestation of the Urbach rule in the fundamental electronic absorption spectra of halide salt melts: I. Tails of the absorption edge of alkali metal halide melts  

Microsoft Academic Search

The long-wavelength tails of the fundamental electronic absorption spectra of alkali metal halide melts have been investigated.\\u000a The obtained values of the absorption characteristics of the alkali metal halide melts have confirmed the assumption that,\\u000a over a wide temperature range (600–900°C), the exponential tail of the absorption coefficient of these disordered systems\\u000a is associated with the presence of the spectrum

V. S. Naumov

2011-01-01

34

A simple melting theory applied to alkali halide, alkaline-earth chalcogenide, and alkali chalco-genide compounds  

NASA Astrophysics Data System (ADS)

A useful and simple method for studying the melting temperature T-m of ion compounds has been developed by using analyses originally due to diffusional force theory, incorporating Pandey's formulation and Harrison's potential function. The calculated values of T-m for a wide range of compounds of types IA-VII (alkali halide), IIA-VI (alkaline-earth chalcogenide), and IA-VI (alkali chalcogenide) are found to agree fairly well with experimental values for T-m and to be superior to results from previous approaches involving similar methods.

Liu, Q.; Chen, L. R.

2005-06-01

35

Lattice Dynamics and Specific-Heat Data for Rocksalt-Structure Alkali Halides  

Microsoft Academic Search

Vibrational distribution functions are derived for a number of rocksalt-structure alkali halides using a more refined treatment of the interionic forces than that provided by regarding them as rigid point charges. The dipole moment at any given ion site is calculated taking into account the contribution from the deformation of the electron distribution resulting from both polarization and overlap repulsion

Arnold Karo; John R. Hardy

1963-01-01

36

Silicon halide--alkali metal flames as a source of solar grade silicon. First quarterly report  

Microsoft Academic Search

This program is designed to test the feasibility of utilizing continuous, high temperature, diffusion flames of gaseous alkali metals and silicon halides as an economical source of high purity silicon. Thermochemical analyses of these systems indicate that high temperatures are attained and that silicon is the only condensed-phase material in the equilibrium product distribution. The reactions are self-initiating and their

1977-01-01

37

Effects of Moisture and High Electric Fields on Conductivity in Alkali-Halide-Doped Cellulose Acetate  

Microsoft Academic Search

Several problems associated with ionic conduction in amorphous hydrophilic polymers have been investigated from a theoretical point of view and then discussed in the light of experiments with alkali-halide-doped cellulose 2.5 acetate. The main ideas emphasized are: (1) The major effects of moisture on conductivity ? in this class of polymers are to increase the dielectric constant &egr;? and therefore

R. E. Barker; Charles R. Thomas

1964-01-01

38

Ultrasonic Speed as a Guide of the Concentration of Alkali-Halides Ions in Water.  

National Technical Information Service (NTIS)

The speed of an ultrasonic wave has been examined in many alkali-halides water solutions at 35 deg. C and different concentrations. The speed seems to be subject to substantial changes with changing the mass of the negative ions rather than the positive i...

M. H. Hanna M. K. Luqman M. S. Hussain

1988-01-01

39

A re-investigation of the quadratic electrostriction of alkali halides of rocksalt type  

Microsoft Academic Search

In order to clarify the reasons for the contradictory results regarding quadratic electrostriction in alkali halides reported by various authors, we developed an improved capacitive dilatometer. Employing the frequency-modulation technique, the resolution of the experimental set-up reaches icons\\/Journals\\/Common\\/Delta\\

J. Schreuer; S. Haussühl

1999-01-01

40

THE ELECTRICAL CONDUCTIVITY OF SOLUTIONS OF ALKALI METALS IN THEIR MOLTEN HALIDES  

Microsoft Academic Search

The electrical conductivity of alkali metal solutions in their molten ; halides has been measured by means of a synthetic sapphire conductance cell. The ; specific conductance increases with increasing metal concentration. The ; equivalent conductance of K, A K, in both KCl and KBr also increases, namely, ; from 2800 ohm⁻¹ cm² (K--KCl, 820 deg ), 6100 (K--KBr, 760

H. R. Bronstein; M. A. Bredig

1958-01-01

41

A mass-spectrometric determination of the work function of alkali metal halide crystals  

NASA Astrophysics Data System (ADS)

Thermochemical cycles including experimentally measured enthalpies of sublimation of alkali metal halides in the form of M2X+ and MX{2/?} ionic clusters and MX molecules were used to calculate work functions for NaCl, NaBr, NaI, KCl, KBr, KI, RbCl, and RbI.

Kudin, L. S.; Dunaev, A. M.; Butman, M. F.; Kryuchkov, A. S.

2011-02-01

42

The role of halide ions on the electrochemical behaviour of iron in alkali solutions  

NASA Astrophysics Data System (ADS)

Active dissolution and passivation of transition metals in alkali solutions is of technological importance in batteries. The performance of alkaline batteries is decided by the presence of halides as they influence passivation. Cyclic voltammetric studies were carried out on iron in different sodium hydroxide solutions in presence of halides. In alkali solutions iron formed hydroxo complexes and their polymers in the interfacial diffusion layer. With progress of time they formed a cation selective layer. The diffusion layer turned into bipolar ion selective layer consisted of halides, a selective inner sublayer to the metal side and cation selective outer layer to the solution side. At very high anodic potentials, dehydration and deprotonation led to the conversion of salt layer into an oxide.

Begum, S. Nathira; Muralidharan, V. S.; Basha, C. Ahmed

43

Luminescencs of Alkali Halide Crystals Induced by UV-Light at Low Temperature  

Microsoft Academic Search

The luminescence of pure alkali halide crystals induced by the excitation with UV-light in the fundamental absorption region at low temperature is observed in NaCl, KCl, RbCl, NaBr, KBr, RbBr and KI. In KCl, RbCl and NaBr one emission band, in NaCl, KBr and RbBr two emission bands and in KI three emission bands are induced at 11°K. All of

Mikihiko Ikezawa; Tadanobu Kojima

1969-01-01

44

Gamma-ray and electron response in doped alkali halide scintillators  

Microsoft Academic Search

The wide angle Compton coincidence technique was used to study non-proportionality of light yield and intrinsic resolution of doped alkali halides. The tested scintillators were 1 inch × 1 inch cylindrical crystals of NaI:Tl, CsI:Na and CsI:Tl. The experimental setup comprised a High Purity Germanium detector and the tested samples coupled to a photomultiplier. The results obtained for Compton electrons

L. Swiderski; M. Moszynski; W. Czarnacki; M. Szawlowski; T. Szczesniak; G. Pausch; C. Plettner; K. Roemer; P. Schotanus

2011-01-01

45

The Systematic Variation of Optical Properties of Alkali Halides: an Ab Initio Study  

Microsoft Academic Search

In this paper we study a correlation between the optical properties, electronic structure and anion-cation electronegativity difierence in three groups of alkali halides MX (M = Li, Na, K; X = F, Cl, Br, I). The elec- tronic structure was calculated by flrst-principle, density-functional theory based full-potential linear augmented plane wave method. Then the complex dielectric function was computed, allowing

G. C. Gon; M. V. Lali; O. L. Malta

2007-01-01

46

Electron-beam production of colour centres on alkali halide crystals and films  

Microsoft Academic Search

In this article we analyze the production of localized colour centres on the surface of alkali halide crystals and films produced by electron beam radiations in the 10-30 keV range. It was found that the colour centre production is restricted to electron penetration (3-10 mum depending on the material and electron energy) with a very intense local optical density (above

Raul A. Nunes; Hypolito J. Kalinowski; Sidnei Paciornik; Astor M. de Souza; Luiz C. Scavarda Do Carmo

1988-01-01

47

Electrical Conductance, Density, and Viscosity in Mixtures of Alkali-Metal Halides and Glycerol  

Microsoft Academic Search

This paper presents the results of density, viscosity, and electrical conductivity measurements for glycerol solutions of some alkali-metal halides at 25°C. The apparent and partial molar volumes (VF and V1) in mixtures of KCl, NaCl, KBr, KI, and glycerol were calculated from the density data. The Debye–Hückel limiting law was assumed to be valid at low concentrations, and values of

A. Hammadi

2004-01-01

48

Atomic force microscopy studies of alkali halide surfaces nanostructured by DIET  

Microsoft Academic Search

We report on surface topography modification of single crystal alkali halides due to creation of the excitonic states by keV electron irradiation. The DIET—structured surfaces have been studied with nanometer scale resolution by means of a dynamic (non-contact) atomic force microscopy (DFM) in UHV. The force microscopy studies reveal that randomly spread rectangular pits of monolayer depth in the topmost

M. Goryl; B. Such; F. Krok; K. Meisel; J. J. Kolodziej; M. Szymonski

2005-01-01

49

Effects of alkali cations and halide anions on the DOPC lipid membrane.  

PubMed

By means of molecular dynamics simulations with an all-atom force field, we investigated the affinities of alkali cations and halide anions for the dioleoylphosphatidylcholine lipid membrane in aqueous salt solutions. In addition, changes in phospholipid lateral diffusion and in headgroup mobility upon adding NaCl were observed using fluorescence spectroscopy. The simulations revealed that sodium is attracted to the headgroup region with its concentration being maximal in the vicinity of the phosphate groups. Potassium and cesium, however, do not preferentially adsorb to the membrane. Similarly, halide anions do not exhibit a strong affinity for the lipid headgroups but merely compensate for the positive charge of the sodium countercations. Nevertheless, larger halides such as bromide and iodide penetrate deeper into the headgroup region toward the boundary with the hydrophobic alkyl chain, this effect being likely underestimated within the present nonpolarizable force field. Addition of alkali halide salts modifies physical properties of the bilayer including the electronic density profiles, the electrostatic potential, and the area per lipid headgroup. PMID:19290591

Vácha, Robert; Siu, Shirley W I; Petrov, Michal; Böckmann, Rainer A; Barucha-Kraszewska, Justyna; Jurkiewicz, Piotr; Hof, Martin; Berkowitz, Max L; Jungwirth, Pavel

2009-07-01

50

Alkali metal/halide thermal energy storage systems performance evaluation  

NASA Astrophysics Data System (ADS)

A pseudoheat-pipe heat transfer mechanism has been demonstrated effective in terms of both total heat removal efficiency and rate, on the one hand, and system isothermal characteristics, on the other, for solar thermal energy storage systems of the kind being contemplated for spacecraft. The selection of appropriate salt and alkali metal substances for the system renders it applicable to a wide temperature range. The rapid heat transfer rate obtainable makes possible the placing of the thermal energy storage system around the solar receiver canister, and the immersing of heat transfer fluid tubes in the phase change salt to obtain an isothermal heat source.

Phillips, W. M.; Stearns, J. W.

51

MULTI-ALKALI PHOTOCATHODE DEVELOPMENT AT BROOKHAVEN NATIONAL LAB FOR APPLICATION IN SUPERCONDUCTING PHOTOINJECTORS. KICKERS.  

SciTech Connect

The development of a suitable photocathode for use in a high average current photoinjector at temperatures ranging from 273 K down to 2 K is a subject of considerable interest, and active research. The choice of photocathode material is often a trade-off made based on the quantum efficiency of the cathode material, the tolerance to adverse vacuum conditions, and the laser wavelength needed to produce photoelectrons. In this paper an overview of the BNL work to date on CsK{sub 2}Sb photocathodes on a variety of substrates, irradiated at multiple wavelengths, and at temperatures down to 170 K will be discussed. The application of this photocathode material into a SRF photoinjector will also be discussed.

BURRILL, A.; BEN-ZVI, I.; RAO, T.; PATE, D.; SEGALOV, Z.

2005-05-16

52

Multi-Alkali Photocathode Development at Brookhaven National Lab for Application in Superconducting Photoinjectors  

SciTech Connect

The development of a suitable photocathode for use in a high average current photoinjector at temperatures ranging from 273 K down to 2 K is a subject of considerable interest, and active research. The choice of photocathode material is often a trade-off made based on the quantum efficiency of the cathode material, the tolerance to adverse vacuum conditions, and the laser wavelength needed to produce photoelectrons. In this paper an overview of the BNL work to date on CsK{sub 2}Sb photocathodes on a variety of substrates, irradiated at multiple wavelengths, and at temperatures down to 170 K will be discussed. The application of this photocathode material into a SRF photoinjector will also be discussed.

Burrill, A.; Ben-Zvi, I.; Pate, D.; Rao, T.; Segalov, Z.; /Brookhaven; Dowell, D.; /SLAC

2006-02-15

53

Resolution of the Conductivity Dilemma in Liquid Solutions of Alkali Metals in Alkali Halides  

NASA Astrophysics Data System (ADS)

Nuclear magnetic resonance measurements are reported for liquid Na-NaBr, Cs-CsCl, and Cs-CsI solutions containing less than 10 mole% metal. Correlation of the resonance shifts, relaxation rates, and de electrical conductivity shows that the electronic mobility is independent of concentration in Na-NaBr, in sharp contrast with the cesium solutions. The results provide an explanation for the apparently anomalous electronic conductivity observed in liquid-sodium-sodium-halide solutions.

Warren, W. W., Jr.; Sotier, S.; Brennert, G. F.

1983-05-01

54

Use of alkali halide crystals with Z color centers for passive mode locking of a YAG:Nd laser  

NASA Astrophysics Data System (ADS)

The use of alkali halide crystals containing Z color centers for passive mode locking of a YAG:Nd laser is demonstrated experimentally. A passive shutter made of alkali-halide crystals was placed in a cell with an immersion fluid in a YAG:Nd laser resonator. Trains of ultrashort pulses were detected with a photocell, and the length of a single pulse from the train was measured with a calorimeter. The average length of the ultrashort pulses was 45 ps, and the energy was 0.2 mJ. The most stable mode locking was observed when RbBr-Ba crystals were added to the original alkali-halide samples.

Demchuk, M. I.; Mikhailov, V. P.; Sobolev, L. M.; Penzina, E. E.; Parfianovich, I. A.; Makushev, K. A.; Gilev, A. K.; Briukvin, V. V.

1984-03-01

55

Intrinsic Multiple-Shot Laser-Induced Bulk Damage in Alkali Halides at 532 NM.  

NASA Astrophysics Data System (ADS)

When an alkali halide crystal is subjected to a series of laser pulses well below the established single shot damage threshold, it, nevertheless, eventually succumbs to catastrophic damage. The damage event is best described as the accumulation of laser-induced microscopic changes in the crystal lattice. For very pure crystals F centers form the predominant stable product of bandgap excitations. The role played by the accumulation of F centers in multishot laser-induced bulk damage is investigated, and model is developed which successfully describes the experimentally observed behavior for the two material studied (KBr and KI). The multishot damage model is built upon the established multiphoton absorption theory for single pulse laser-induced damage in alkali halides, and the known F center formation is suggested to play a major role in the cumulative damage process. The accumulation of F centers is accompanied by a lattice expansion and the buildup of stresses within the interaction volume of the laser beam. The model assumes that, when the defect-induced stress together with the thermal stress exceed the yield stress of the material, the crystal will fail. The model results are compared with experimental data for KBr and KI for several initial temperatures ranging from 55 K to 300 K and using 70 psec laser pulses of 22-52 GW cm^{-2} at 532 nm. It is shown that the proposed multishot damage mechanism adequately describes the observed behavior.

Casper, Richard Thomas

1990-01-01

56

Reverse Osmosis Transport of Alkali Halides and Nickel Salts through Cellulose Triacetate Membranes. Performance Prediction from NaCl Experiments  

Microsoft Academic Search

The separation of alkali metal halides, nickel chloride, and nickel sulfate was determined for cellulose triacetate reverse osmosis (CTA RO) membranes. From transport analysis, the relative free energy parameters for transport of these salts through CTA membranes were determined. From these relative free energy parameters of salts, the solute separation by CTA membranes could be predicted from RO experiment with

J. D. Nirmal; V. P. Pandya; N. V. Desai; R. Rangarajan

1992-01-01

57

Ion Segregation and Deliquescence of Alkali Halide Nanocrystals on SiO2  

SciTech Connect

The adsorption of water on alkali halide (KBr, KCl, KF, NaCl) nanocrystals on SiO{sub 2} and their deliquescence was investigated as a function of relative humidity (RH) from 8% to near saturation by scanning polarization force microscopy. At low humidity, water adsorption solvates ions at the surface of the crystals and increases their mobility. This results in a large increase in the dielectric constant, which is manifested in an increase in the electrostatic force and in an increase in the apparent height of the nanocrystals. Above 58% RH, the diffusion of ions leads to Ostwald ripening, where larger nanocrystals grow at the expense of the smaller ones. At the deliquescence point, droplets were formed. For KBr, KCl, and NaCl, the droplets exhibit a negative surface potential relative to the surrounding region, which is indicative of the preferential segregation of anions to the air/solution interface.

Arima, Kenta; Jiang, Peng; Lin, Deng-Sung; Verdaguer, Albert; Salmeron, Miquel

2009-08-11

58

Strong hysteresis near solidification points of alkali halides with high ionic-radii ratios  

NASA Astrophysics Data System (ADS)

A series of conductance measurements of alkali halides NaCl, NaBr, and NaI was performed in a range of 600-1100 K including liquid and solid states for both cooling and heating regimes. The hysteresis phenomenon is observed to be more pronounced for salts with higher ionic-radii ratio (200 K for NaI) with relaxation time exceeding hundreds of hours. At the cooling regime the conductivity drops slowly from a high value typical for liquids at the freezing point to a solid-salt value defined by a Na+ migration energy at the end of the hysteresis interval instead of an abrupt jump expected at the usual first-order transition. A sort of glassification is assumed to be present at the solidification interval of the salts with high ionic-radii ratios.

Voronel, A.; Shasha, E.; Linsky, D.; Feldberg, S.

1993-07-01

59

Structural disorder within computer-simulated crystalline clusters of alkali halides  

NASA Astrophysics Data System (ADS)

The method of molecular-dynamics (MD) simulation of alkali halides and computer code cluster were developed. The method was applied to calculate structural and kinetic characteristics of small clusters of RbBr, NaBr, NaI, NaCl, KI, and KCl from 10 K to their assumed melting points (Tm). The temperature dependence of relative mean-square vibrational amplitudes has a universal character and satisfies the Lindemann criterion of melting in the vicinity of Tm. In spite of the size effect the values of Tm for all the salts except NaI agree within the error bars of about 100 K with the bulk melting temperatures. The anomalous behavior of NaI at about 200 K below its experimental melting point is interpreted in terms of enhanced mobility of Na+ ions linked to the anomalous enhancement of conductivity observed previously for this salt.

Frenkel, A.; Shasha, E.; Gorodetsky, O.; Voronel, A.

1993-07-01

60

Optical properties of ? hole centres in alkali halides: I. Investigation with optical detection of paramagnetic resonance  

NASA Astrophysics Data System (ADS)

The spectra of the magnetic circular dichroism of the absorption (MCDA) and of optically detected electron paramagnetic resonance (ODEPR) of 0953-8984/10/29/007/img9 hole centres have been investigated in a number of alkali halides. Several new absorption bands were found using excitation spectra of the 0953-8984/10/29/007/img9 ODEPR lines. The number of the MCDA transitions of 0953-8984/10/29/007/img9 in the bromides and especially in the iodides is larger than predicted by the molecular orbital picture discussed so far in the literature. An explanation will be given in part II by Cabria et al on the basis of 0953-8984/10/29/007/img12 calculations including the spin-orbit effects of the ligands.

Rogulis, U.; Spaeth, J.-M.; Cabria, I.; Moreno, M.; Aramburu, J. A.; Barriuso, M. T.

1998-07-01

61

Studies of non-proportionality in alkali halide and strontium iodide scintillators using SLYNCI  

SciTech Connect

Recently a collaboration of LLNL and LBNL has constructed a second generation Compton coincidence instrument to study the non-proportionality of scintillators. This device, known as SLYNCI (Scintillator Light-Yield Non-proportionality Characterization Instrument), has can completely characterize a sample with less than 24 hours of running time. Thus, SLYNCI enables a number of systematic studies of scintillators since many samples can be processed in a reasonable length of time. These studies include differences in nonproportionality between different types of scintillators, different members of the same family of scintillators, and impact of different doping levels. The results of such recent studies are presented here, including a study of various alkali halides, and the impact of europium doping level in strontium iodide. Directions of future work area also discussed.

Ahle, Larry; Bizarri, Gregory; Boatner, Lynn; Cherepy, Nerine J.; Choong, Woon-Seng; Moses, William W.; Payne, Stephen A.; Shah, Kanai; Sheets, Steven; Sturm, Benjamin, W.

2010-10-14

62

Studies of Non-Proportionality in Alkali Halide and Strontium Iodide Scintillators Using SLYNCI  

SciTech Connect

Recently a collaboration of LLNL and LBNL has constructed a second generation Compton coincidence instrument to study the non-proportionality of scintillators [1-3]. This device, known as SLYNCI (Scintillator Light-Yield Non-proportionality Characterization Instrument), has can completely characterize a sample with less than 24 hours of running time. Thus, SLYNCI enables a number of systematic studies of scintillators since many samples can be processed in a reasonable length of time. These studies include differences in nonproportionality between different types of scintillators, different members of the same family of scintillators, and impact of different doping levels. The results of such recent studies are presented here, including a study of various alkali halides, and the impact of europium doping level in strontium iodide. Directions of future work area also discussed.

Ahle, L; Bizarri, G; Boatner, L; Cherepy, N J; Choong, W; Moses, W W; Payne, S A; Shah, K; Sheets, S; Sturm, B W

2009-05-05

63

Dynamics of the defect-mediated desorption of alkali halide surfaces  

NASA Astrophysics Data System (ADS)

Dynamic processes leading to desorption of Rb and I atoms from the RbI (100) surface co-irradiated with 1 keV electrons and visible light (with a wavelength corresponding to the F-center absorption band) have been studied by means of mass-selected time-of-flight (TOF) spectroscopy. Depending on the sample temperature, substantial enhancement of the desorption yield as well as pronounced changes in the TOF spectra of the emitted atoms have been found. The TOF spectra of halogen atoms consist of two components: the thermal (which can be fitted with Maxwellian distribution) and the non-thermal one. The non-thermal peak is temperature-independent. There is no non-thermal component for alkali atoms. The comparison of TOF spectra for I atoms emitted from electron bombarded sample with and without simultaneous light irradiation indicates that the yield increase is caused by thermally desorbed atoms, while the non-thermal peak remains unchanged. Presented results confirm well the predictions of the theoretical model of desorption proposed earlier, known as the defect-mediated (F and H center) desorption of alkali halide.

Szymonski, M.; Droba, A.; Struski, P.; Krok, F.

2012-08-01

64

Dependence of the density of solutions of alkali metal halides on the composition of methylpyrrolidone-water mixed solvents  

NASA Astrophysics Data System (ADS)

The densities of solutions of alkali metal halides in methylpyrrolidone (MP)-water mixtures were measured at 298.15 K over the entire range of mixed solvent compositions. The standard partial molar volumes of the electrolytes overline {V_2^ circ } were calculated. The overline {V_2^ circ } values of alkali metal halides in MP-H2O mixtures were related linearly to the overline {V_2^ circ } values in aqueous solutions. These dependences were used to determine the standard partial molar volumes of ions overline {V_i^ circ } in the mixtures studied. The standard partial molar volumes of transfer of the ions from water into MP-water mixtures were calculated.

Novikov, A. N.; Lenina, O. F.; Vasilev, V. A.

2008-07-01

65

X- (X = O, S) ions in alkali halide lattices through density functional calculations. 1. Substitutional defect models.  

PubMed

Monoatomic X- (X = O, S) chalcogen centers in MZ (M = Na, K, Rb and Z = Cl, Br, I) alkali halide lattices are investigated within the framework of density functional theory with the principal aim to establish defect models. In electron paramagnetic resonance (EPR) experiments, X- defects with tetragonal, orthorhombic, and monoclinic g-tensor symmetry have been observed. In this paper, models in which X- replaces a single halide ion, with a next nearest neighbor and a nearest neighbor halide vacancy, are validated for the X- centers with tetragonal and orthorhombic symmetry, respectively. As such defect models are extended, the ability to reproduce experimental data is a stringent test for various computational approaches. Cluster in vacuo and embedded cluster schemes are used to calculate energy and EPR parameters for the two vacancy configurations. The final assignment of a defect structure is based on the qualitative and quantitative reproduction of experimental g and (super)hyperfine tensors. PMID:16623497

Stevens, F; Vrielinck, H; Van Speybroeck, V; Pauwels, E; Callens, F; Waroquier, M

2006-04-27

66

Reverse osmosis transport of alkali halides and nickel salts through cellulose triacetate membranes. Performance prediction from NaCl experiments  

SciTech Connect

The separation of alkali metal halides, nickel chloride, and nickel sulfate was determined for cellulose triacetate reverse osmosis (CTA RO) membranes. From transport analysis, the relative free energy parameters for transport of these salts through CTA membranes were determined. From these relative free energy parameters of salts, the solute separation by CTA membranes could be predicted from RO experiment with NaCl solution. The transport analysis and an illustration of how the concept is useful are presented in this paper.

Nirmal, J.D.; Pandya, V.P.; Desai, N.V.; Rangarajan, R. (Central Salt and Marine Chemicals Research Inst., Bhavnagar (India))

1992-10-01

67

Integrating 2-D position sensitive X-ray detectors with low-density alkali halide storage targets  

Microsoft Academic Search

For the use in scattering experiments with synchrotron radiation, integrating position sensitive X-ray detectors are discussed. These detectors store the photon number equivalent charge (PNEC) in low-density alkali halide targets. Performance tests are given for a detector which uses a Gd2O2S fluorescence screen for X-ray detection and the low-density KCl storage target of a television SEC vidicon tube for photon

H.-G. Haubold; W. Hoheisel; P. Hiller

1986-01-01

68

Molecular Modeling and Monte Carlo Simulation of Concentrated Aqueous Alkali Halide Solutions at 25 C.  

NASA Astrophysics Data System (ADS)

A study of concentrated aqueous alkali halide solutions is made at the molecular level, through modeling and computer simulation of their structural and thermodynamic properties. It is found that the HNC approximation is the best integral equation theory to predict such properties within the framework of the primitive model (PM). The intrinsic limitations of the PM in describing ionic association and hydration effects are addressed and discussed in order to emphasize the need for explicitly including the water molecules in the treatment of aqueous electrolyte solutions by means of a civilized model (CM). As a step toward developing a CM as simple as possible, it is shown that a modified version of the SPC model of liquid water in which the Lennard-Jones interaction between intermolecular oxygen sites is replaced by a hard core interaction, is still successful enough to predict the degree of hydrogen bonding of real water. A simple civilized model (SCM) (in which the ions are treated as hard spheres interacting through Coulombic potentials and the water molecules are simulated using the simplified SPC model) is introduced in order to study the changes in the structural features of various aqueous alkali halide solutions upon varying both the concentration and the size of the ions. Both cations and anions are found to be solvated by the water molecules at expense of a breakdown in the hydrogen-bonded water network. Hydration numbers are reported for the first time for NaBr and KBr, and the first simulation -based estimates for LiBr, NaI and KI are also obtained. In several cases, values of the hydration numbers based on the SCM are found to be in excellent agreement with available experimental results obtained from x-ray diffraction measurements. Finally, it is shown that a neoprimitive model (NPM) can be developed by incorporating some of the structural features seen in the SCM into the short-range part of the PM interionic potential via a shielded square well whose width and depth's temperature coefficient can be determined from a fit of experimental data for the osmotic coefficient and heat of dilution, respectively.

Llano-Restrepo, Mario Andres

69

Angular dependence of static and kinetic friction on alkali halide surfaces  

NASA Astrophysics Data System (ADS)

The angular dependence of the lateral forces acting on an atomically sharp tip slowly pulled by an elastic spring along a crystal surface with square symmetry is investigated in the framework of a separable two-dimensional tip-surface interaction potential. In the stick-slip regime kinetic friction is proportional to (cos?+|sin?|) , ? being the angle between the scan direction and a particular symmetry axis. For a high enough normal force, static friction is proportional to 1/cos? , whereas for intermediate loads it shows a ? -dependent spread of possible values. Continuous sliding with ultralow friction sets in below a load-dependent corrugation amplitude. Numerical simulations help interpret those analytic results in terms of the zigzag motion of a friction force microscope tip sliding on the (001) surface of a rocksalt crystal. The influence of the offset between the start of a scan and the center of the corresponding unit cell, in particular, for scans along ?100? directions is also elucidated. The predicted ratio of kinetic friction along the ?100? and ?110? directions agrees best with values measured on alkali halides with similar cation and anion radii. This ratio, as well as the angular dependence of the static friction may be used to determine fine details of the lateral tip-sample interaction.

Steiner, Pascal; Roth, Raphael; Gnecco, Enrico; Baratoff, Alexis; Meyer, Ernst

2010-11-01

70

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

NASA Astrophysics Data System (ADS)

A two-body central-force atomic model can be used to describe accurately the elastic properties of ? 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. An anion-anion force term for the halogens is found as a function of separation from values of c12 and c44 for the B1 structure and (c11 - c12) and (c11 - c44) for the B2 structure. This anion-anion force term consistently describes these elastic constants for the alkali halides as the pressure, structure, and cation species are varied. Knowledge of this force term as a function of anion separation allows the calculation of these moduli as a function of pressure.

Weidner, Donald J.; Simmons, Gene

1972-02-01

71

Surface Spectroscopy Studies of the Reactive Uptake of Ozone on Alkali Halides  

NASA Astrophysics Data System (ADS)

Heterogeneous reactions in the atmosphere have attracted a lot of attention. In particular, reactions involving sea-salt in the form of aerosol droplets, particles, and/or sea-ice have been implicated to significantly affect the chemistry and composition of the marine boundary layer. For example, highly reactive chlorine and bromine atoms resulting from the oxidation of sea-salt halides (Cl- and Br-) have been implicated in tropospheric ozone depletion in the arctic and in lower latitude marine regions, as well as the deposition of mercury. While the heterogeneous processing of sea-salt has been studied extensively in laboratory, field and model studies, the mechanistic details behind the release of gas-phase halogens remains unclear and has sparked some interests. Recently there has been attention focused on the interaction of important atmospheric oxidants (e.g., OH and O3) with halides that reside at the air-particle interface of sea-salt. Such chemical interactions at the surface of particles may lead to unique chemical transformations that can alter current views of known chemical processing of sea-salt particles. There are several laboratory investigations which have investigated the surface reactivity of salts by measuring the reactive loss and/or formation of gas-phase species, indicating that reactions at the interface likely play an important role in aerosol chemistry. The efficacy of such surface-phase chemistry has yet to be elucidated with surface spectroscopy studies. X-ray photoelectron spectroscopy (XPS) is a surface spectroscopy technique with submonolayer resolution. Using XPS, we have investigated changes in the surface chemistry of various alkali halide salts upon exposure to ozone in an ultra-high vacuum (UHV) instrument. Salt samples were either freshly cleaved single crystals which were prepared from a melt, or purified salt crystals/powders pressed into pellets. Upon exposure to ozone, oxygen on the salt surfaces was monitored by measuring the O(1s) photoelectron peak. Initial XPS spectra of salts in the vacuum chamber prior to ozone exposure indicated that the salts were either devoid of oxygen, or contained a small amount of oxygen from strongly adsorbed water under ultra-high vacuum. In all cases, in-vacuo exposure of the salts to ozone lead to an increase in O(1s) photoelectron signal. For NaCl this was surprising since previous studies have been interpreted to indicate that ozone is essentially unreactive towards solid NaCl. The initial uptake of oxygen on the surface gave a broad O(1s) peak, indicating that there are several types of oxygen species on the surface. Reference spectra were obtained for NaClO2, NaClO3, and NaClO4 salts. The O(1s) binding energies in these reference spectra increased in series with NaClO2 < NaClO3 < NaClO4. Based on these results, it is suggested that the reaction of ozone with pure NaCl initially leads to the formation of NaClO2 and NaClO3, with the formation of NaClO4 at higher ozone doses. The oxygen uptake upon ozone exposure to alkali bromide and iodide salts were also investigated and compared to reference salts. Future work will incorporate the influence of adsorbed water and subsequent ozone exposures on the surface chemistry of salts.

Newberg, J. T.; Hemminger, J. C.

2003-12-01

72

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

PubMed

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

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

2013-01-28

73

Crystal lattice properties fully determine short-range interaction parameters for alkali and halide ions  

NASA Astrophysics Data System (ADS)

Accurate models of alkali and halide ions in aqueous solution are necessary for computer simulations of a broad variety of systems. Previous efforts to develop ion force fields have generally focused on reproducing experimental measurements of aqueous solution properties such as hydration free energies and ion-water distribution functions. This dependency limits transferability of the resulting parameters because of the variety and known limitations of water models. We present a solvent-independent approach to calibrating ion parameters based exclusively on crystal lattice properties. Our procedure relies on minimization of lattice sums to calculate lattice energies and interionic distances instead of equilibrium ensemble simulations of dense fluids. The gain in computational efficiency enables simultaneous optimization of all parameters for Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I- subject to constraints that enforce consistency with periodic table trends. We demonstrate the method by presenting lattice-derived parameters for the primitive model and the Lennard-Jones model with Lorentz-Berthelot mixing rules. The resulting parameters successfully reproduce the lattice properties used to derive them and are free from the influence of any water model. To assess the transferability of the Lennard-Jones parameters to aqueous systems, we used them to estimate hydration free energies and found that the results were in quantitative agreement with experimentally measured values. These lattice-derived parameters are applicable in simulations where coupling of ion parameters to a particular solvent model is undesirable. The simplicity and low computational demands of the calibration procedure make it suitable for parametrization of crystallizable ions in a variety of force fields.

Mao, Albert H.; Pappu, Rohit V.

2012-08-01

74

Crystal lattice properties fully determine short-range interaction parameters for alkali and halide ions.  

PubMed

Accurate models of alkali and halide ions in aqueous solution are necessary for computer simulations of a broad variety of systems. Previous efforts to develop ion force fields have generally focused on reproducing experimental measurements of aqueous solution properties such as hydration free energies and ion-water distribution functions. This dependency limits transferability of the resulting parameters because of the variety and known limitations of water models. We present a solvent-independent approach to calibrating ion parameters based exclusively on crystal lattice properties. Our procedure relies on minimization of lattice sums to calculate lattice energies and interionic distances instead of equilibrium ensemble simulations of dense fluids. The gain in computational efficiency enables simultaneous optimization of all parameters for Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I- subject to constraints that enforce consistency with periodic table trends. We demonstrate the method by presenting lattice-derived parameters for the primitive model and the Lennard-Jones model with Lorentz-Berthelot mixing rules. The resulting parameters successfully reproduce the lattice properties used to derive them and are free from the influence of any water model. To assess the transferability of the Lennard-Jones parameters to aqueous systems, we used them to estimate hydration free energies and found that the results were in quantitative agreement with experimentally measured values. These lattice-derived parameters are applicable in simulations where coupling of ion parameters to a particular solvent model is undesirable. The simplicity and low computational demands of the calibration procedure make it suitable for parametrization of crystallizable ions in a variety of force fields. PMID:22897252

Mao, Albert H; Pappu, Rohit V

2012-08-14

75

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

NASA Astrophysics Data System (ADS)

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.

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

2013-01-01

76

Cell having an alkali metal anode, a fluorinated carbon cathode and an electrolyte which includes an alkali metal halide salt and a solvent system consisting of an ether solvent and a cyclic carbonate cosolvent  

SciTech Connect

A novel electrochemical cell is disclosed utilizing an alkali metal anode, a fluorinated carbon cathode, and an electrolyte which includes an alkali metal halide salt and a mixed solvent system consisting of an ether and a cyclic carbonate. Preferred are the cells wherein the anode is lithium, the cathode is C/sub 2/F, and the electrolyte contains essentially of LiCl and a solvent system of dimethoxyethane and propylene carbonate.

Malachesky, P. A.

1981-02-03

77

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

NASA Astrophysics Data System (ADS)

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- is formed by the sequential attachment of two electrons to K+.

Kimura, Kenichi; Langford, S. C.; Dickinson, J. T.

2007-12-01

78

Optical constants of as-deposited and treated alkali halides and their VUV quantum efficiency  

NASA Astrophysics Data System (ADS)

The optical constants of thin films of CsI, KI, and KBr in the spectral range of 53.6-174.4 nm were obtained from the measurements of reflectivity as a function of the incidence angle. The effect of film heating to 420 K and exposure to UV radiation on the optical constants of the three materials was also investigated. The quantum efficiencies of the planar photocathodes made with the three alkalihalides, as well as the changes in these QEs after the photocathode treatment similar to that applied to the thin films was measured. KBr was found to be the most stable to heating and irradiation. KI appeared to be close to temperature-stable, while UV exposure affected its optical constants. CsI optical constants were changed after 420-K heating, as well as after UV exposure. The changes in the optical constants were related to the QE changes and the correlation between these variations was determined.

Larruquert, Juan I.; Mendez, Jose A.; Aznarez, Jose A.; Tremsin, Anton S.; Siegmund, Oswald H.

1999-10-01

79

Integrating 2-D position sensitive X-ray detectors with low-density alkali halide storage targets  

NASA Astrophysics Data System (ADS)

For the use in scattering experiments with synchrotron radiation, integrating position sensitive X-ray detectors are discussed. These detectors store the photon number equivalent charge (PNEC) in low-density alkali halide targets. Performance tests are given for a detector which uses a Gd2O2S fluorescence screen for X-ray detection and the low-density KCl storage target of a television SEC vidicon tube for photon integration. Rather than directly by X-rays, this target is charged by 6 keV electrons from the image intensifier section of the vidicon. Its excellent storage capability allows measurements of extremely high-contrast, high-flux X-ray patterns with the same accuracy as achieved with any single photon detection system if the discussed readout techniques are applied.

Haubold, H.-G.; Hoheisel, W.; Hiller, P.

1986-05-01

80

Studies of Non-Proportionality in Alkali Halide and Strontium Iodide Scintillators Using SLYNCI 6-16-2009  

SciTech Connect

Recently a collaboration of LLNL and LBNL has constructed a second generation Compton coincidence instrument to study the non-proportionality of scintillators. This device, known as SLYNCI (Scintillator Light-Yield Non-proportionality Characterization Instrument), has can completely characterize a sample with less than 24 hours of running time. Thus, SLYNCI enables a number of systematic studies of scintillators since many samples can be processed in a reasonable length of time. These studies include differences in non-proportionality between different types of scintillators, different members of the same family of scintillators, and impact of different doping levels. The results of such recent studies are presented here, including a study of various alkali halides, and the impact of europium doping level in strontium iodide. Directions of future work area also discussed.

Ahle, Larry [Lawrence Livermore National Laboratory (LLNL); Bizarri, Gregory [Lawrence Berkeley National Laboratory (LBNL); Boatner, Lynn A [ORNL; Cherepy, Nerine [Lawrence Livermore National Laboratory (LLNL); Choong, Woon-Seng [Lawrence Berkeley National Laboratory (LBNL); Moses, W. W. [Lawrence Berkeley National Laboratory (LBNL); Payne, Stephen A. [Lawrence Livermore National Laboratory (LLNL); Shah, Kanai [Radiation Monitoring Devices, Watertown, MA; Sheets, Steven [Lawrence Livermore National Laboratory (LLNL); Sturm, Benjamin [Lawrence Livermore National Laboratory (LLNL)

2009-01-01

81

ESCA Studies of Ion Complexes Between a Crown-ether and Alkali Halides  

Microsoft Academic Search

ESCA has been used to study the complexation of the alkali cations Na+, K+ and Rb+ by the crown-ether, dibenzo-18-crown-6. The binding energies of cations as well as the counter ions (Cl-, Br- and I-), oxygens and carbons have been measured. The results reveal strong backbonding effects. A comparison of the electron binding energies for the complexed and uncomplexed alkali

Ove Bohman; Per Ahlberg; Nils Mårtensson; Kai Siegbahn

1977-01-01

82

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

NASA Astrophysics Data System (ADS)

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.

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

2010-12-01

83

Dependences of molar volumes in solids, partial molal and hydrated ionic volumes of alkali halides on covalent and ionic radii and the golden ratio  

Microsoft Academic Search

New linear dependences are presented here for the volumes of alkali halides in crystals and in aqueous solutions: (1) the molar volumes in solids (VBo) and the partial molal volumes (?Vo) in aqueous solutions on the sums of crystal ionic volumes, V(M+,X?)cr, (2) ?Vo on VBo, (3) ?Vo on the sum of aqueous ionic volumes, V(M+,X?)aq and (4) ?Vo, VBo,

Raji Heyrovska

2007-01-01

84

A contribution to test the theories of interdiffusion: experimental studies of alkali halide interdiffusion with a common anion (AY-BY)  

Microsoft Academic Search

Two sets of experimental data about the Kirkendall effect and interdiffusion coefficients in alkali halides with a common ion are presented as a contribution to test the present theory of interdiffusion in ionic crystals. It is proved that a measurable Kirkendall shift can be observed in these materials (e.g. NaCl-KCl interdiffusion at 903K), i.e. that the common anions are able

L. Bonpunt; N.-B. Chanh; Y. Haget

1985-01-01

85

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

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 +}.

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

86

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

NASA Astrophysics Data System (ADS)

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.

Yu, Xueyang; Hofmeister, Anne M.

2011-02-01

87

Molecular simulation of aqueous electrolyte solubility. 3. Alkali-halide salts and their mixtures in water and in hydrochloric acid.  

PubMed

We extend the osmotic ensemble Monte Carlo (OEMC) molecular simulation method (Mou?ka et al. J. Phys Chem. B 2011, 115, 7849-7861) for directly calculating the aqueous solubility of electrolytes and for calculating their chemical potentials as functions of concentration to cases involving electrolyte hydrates and mixed electrolytes, including invariant points involving simultaneous precipitation of several solutes. The method utilizes a particular semigrand canonical ensemble, which performs simulations of the solution at a fixed number of solvent molecules, pressure, temperature, and specified overall electrolyte chemical potential. It avoids calculations for the solid phase, incorporating available solid chemical potential data from thermochemical tables, which are based on well-defined reference states, or from other sources. We apply the method to a range of alkali halides in water and to selected examples involving LiCl monohydrate, mixed electrolyte solutions involving water and hydrochloric acid, and invariant points in these solvents. The method uses several existing force-field models from the literature, and the results are compared with experiment. The calculated results agree qualitatively well with the experimental trends and are of reasonable accuracy. The accuracy of the calculated solubility is highly dependent on the solid chemical potential value and also on the force-field model used. Our results indicate that pairwise additive effective force-field models developed for the solution phase are unlikely to also be good models for the corresponding crystalline solid. We find that, in our OEMC simulations, each ionic force-field model is characterized by a limiting value of the total solution chemical potential and a corresponding aqueous concentration. For higher values of the imposed chemical potential, the solid phase in the simulation grows in size without limit. PMID:22475081

Mou?ka, Filip; Lísal, Martin; Smith, William R

2012-05-01

88

Photocathode aging in MCP PMT  

NASA Astrophysics Data System (ADS)

We study aging of alkali-antimonide photocathodes in the microchannel plate photomultiplier tubes (MCP PMT) manufactured in Novosibirsk by ``Ekran FEP'' company. Such PMTs are used in the particle identification systems of KEDR, SND and CMD-3 experiments carried out at e+e- colliders VEPP-4M and VEPP-2000 in the Budker Institute of Nuclear Physics. The quantum efficiency (QE) degradation of a PMT equipped with MCP Chevron has been measured at different photon counting rates from 4?107 to 6?1010 s-1cm-2. It is found that the QE decrease is proportional to the charge extracted from the MCP nearest to the photocathode rather than to the output charge. The comparison of different types of alkali-antimonide photocathodes has shown that the treatment of photocathode with vapors of cesium and antimony can dramatically reduce the photocathode aging rate. The photocathode lifetime of the best MCP PMT sample has been measured at the photon counting rate of 107 cm-2s-1 and the initial gain of 106. The peak quantum efficiency degraded by 20% after accumulation of 3.3 C/cm2 anode charge.

Barnyakov, M. Yu; Mironov, A. V.

2011-12-01

89

Enthalpies of Dilution of N,N?-hexamethylenebisacetamide in Pure Water and Aqueous Solutions of Alkali Halide at 298.15 K  

Microsoft Academic Search

Enthalpies of dilution of N,N?-hexamethylenebisacetamide in water and aqueous alkali halide solutions at the concentration\\u000a of 0.150 mol?kg?1 (approximately the concentration of physiological saline) have been determined by isothermal titration microcalorimetry at\\u000a 298.15 K. The enthalpic interaction coefficients in the solutions have been calculated according to the excess enthalpy concept\\u000a based on the calorimetric data. The values of enthalpic pair-wise interaction coefficients

Hui Li; Min Liu; Jifeng Liu; Linwei Li; Dezhi Sun

2010-01-01

90

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Optical surface breakdown of alkali halide crystals by microsecond pulses from a wide-aperture CO2 laser  

NASA Astrophysics Data System (ADS)

A study was made of the dynamics of temporal and spatial changes in the spectral characteristics of plasmas. A three-stage mechanism of the damage to surfaces of alkali halide crystals by microsecond pulses from a TEA CO2 laser was proposed: breakdown initiation (at a distance of 3-5 mm from the surface with a time delay up to 1 ?s relative to the leading edge of a laser pulse), evaporation (after a further delay of 3-5 ?s), and interaction of the adsorbates with a plasma jet and with the laser radiation, as well as heating and cracking of a crystal by the UV plasma radiation.

Kazantsev, S. G.

1998-04-01

91

Dynamics of the Optical-Pumping Cycle of F Centers in Alkali Halides-Theory and Application to Detection of Electron-Spin and Electron-Nuclear-Double-Spin Resonance in the Relaxed-Excited State  

Microsoft Academic Search

The dynamics of the optical-pumping cycle of F centers in alkali halides are governed by two prime factors: the large magnetic circular dichroism exhibited by the F band and a large electron-spin memory over the entire cycle. A model of the pump cycle and associated rate equations are given. The most general solutions are given, and important special cases are

L. F. Mollenauer; S. Pan

1972-01-01

92

Origin of the characteristic electron density distribution in silver halides  

Microsoft Academic Search

The pointed contour lines of the electron density distribution in silver halides, as contrasted with the flat contour lines in alkali halides, are commonly regarded as indicators of partially covalent bonding. On the other hand, orbital moments and interaction potentials indicate that very strong van der Waals forces, rather than partial covalency, distinguish the silver halides from alkali halides. Based

Manfred Bucher

1987-01-01

93

SUPERCONDUCTING PHOTOCATHODES.  

SciTech Connect

We present the results of our investigation of lead and niobium as suitable photocathode materials for superconducting RF injectors. Quantum efficiencies (QE) have been measured for a range of incident photon energies and a variety of cathode preparation methods, including various lead plating techniques on a niobium substrate. The effects of operating at ambient and cryogenic temperatures and different vacuum levels on the cathode QE have also been studied.

SMEDLEY, J.; RAO, T.; WARREN, J.; SEKUTOWICZ, LANGNER, J.; STRZYZEWSKI, P.; LEFFERS, R.; LIPSKI, A.

2005-10-09

94

A multi-frequency EPR and ENDOR study of Rh and Ir complexes in alkali and silver halides  

NASA Astrophysics Data System (ADS)

Aliovalent Rh and Ir cations have been frequently used to influence the photographic properties of silver halide emulsions. The doping introduces several types of related defects with distinct trapping and recombination properties. EPR and ENDOR are, in principle, ideally suited for the determination of the microscopic structure of the individual centres but it will be demonstrated that well-chosen, sometimes sophisticated multi-frequency experiments are necessary in order to (partially) reach this goal. Model studies on single crystals of AgCl and NaCl also appeared indispensable for the unravelling of the spectra. In the review of Rh-centres in NaCl and AgCl special attention is paid to methods that allow to detect cation vacancies near Rh2+ complexes. An alternative explanation for the high temperature behaviour of the [RhCl6](4-) complexes in AgCl is presented.

Callens, F.; Vrielinck, H.; Matthys, P.

2003-01-01

95

Development of processes for the production of solar grade silicon from halides and alkali metals. First quarterly report, October 3-December 31, 1979  

SciTech Connect

This program is directed toward the development of processes involving high temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost. Experiments are being performed to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, determine the effects of reactants and/or products on materials of reactor construction, and make preliminary engineering and economic analyses of a scaled-up process. Samples of the silicon product will be delivered to JPL for evaluation of solar cell performance. During this reporting period the silicon reactor test apparatus reached operational capabilities after a shutdown for two months. Several design improvements were made while returning it to an operational stage. During the initial series of experiments complete product separation of the silicon from the salt was achieved and small samples (approx. = 3 to 40 g) of fused silicon were collected. The test apparatus is now being operated on a routine basis for periods of about twenty minutes. Finally, the initial work began on the engineering and economic analysis for scale-up of the silicon production process.

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

1980-02-01

96

Development of processes for the production of solar grade silicon from halides and alkali metals. Third quarterly report, April 1-June 30, 1980  

SciTech Connect

This program is directed toward the development of processes involving high temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost. Experiments are performed to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, determine the effects of reactants and/or products on materials of reactor construction, and make preliminary engineering and economic analyses of a scaled-up process. During this report period work concentrated on preparing samples of silicon for purity analyses. The results of six such analyses are given. In general, they indicate that the process is capable of producing very pure silicon. A number of impurity elements appear in 0.1 to 10 ppMa concentrations in one or another of the samples in unpredictable patterns. This would be expected for the one hour runs performed since atmospheric dust has easy access to collection surfaces during assembly and laboratory conditions do not allow clean assembly procedures to be followed. Particularly encouraging is the observation that sodium levels are below 10 ppMa in most runs.

Gould, R.K.

1980-09-01

97

Thermochemistry of Charge-Unsymmetrical Binary Fused Halide Systems. Ii. Mixtures of Magnesium Chloride with the Alkali Chlorides and with Silver Chloride.  

National Technical Information Service (NTIS)

The integral enthalpies of mixing of the liquid mixtures of magnesium chloride with the alkali chlorides and with silver chloride were determined calorimetrically. The magnesium chloride-silver chloride system is slightly endothermic, while the alkali chl...

O. J. Kleppa F. G. McCarty

1965-01-01

98

The Effect of Halide Impurities on the Mass Production of Metal Whiskers by Reduction  

Microsoft Academic Search

Thin whisker crystals of nickel, cobalt and silver can be mass-produced by the reduction of a molten mixture consisting of a starting halide and a secondary halide which are permeated in an absorbent powder. Many halides such as alkali halides can be used as the secondary halide. Carbonaceous powder can be used as the absorbent, but in the case of

Kiyoshi Kishi

1973-01-01

99

A Masked Photocathode in Photoinjector  

SciTech Connect

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.

Qiang, Ji

2010-12-14

100

Silver alkali halide glasses and a vitreous analog of the RbAg/sub 4/I/sub 5/ superionic conductor  

SciTech Connect

We report the existence of silver halide-rich glasses of a type not previously recognized. These contain only monovalent halides and represent perhaps the simplest ionic glasses yet realized. Despite the lack of the usual oxyanion matrix the new glasses show room temperature conductances which equal or exceed those of the best Ag/sup +/ glasses yet reported. Cu/sup +/ analogues have also been prepared. At the high conducting extreme apparently lies a vitreous state analog of the well-known crystalline conductor RbAg/sub 4/I/sub 5/. A crystalline analog of the latter FIC, CsAg/sub 4/(I /SUB 0.45/ C1 /SUB 0.55/ )/sub 5/ forms metastably on careful devitrification of the glass. Like its prototype, it has a very high conductivity and exhibits a sharp C /SUB p/ anomaly at low temperatures, -77/sup 0/C, in the vicinity of which the activation energy for conductance changes abruptly.

Liu, C.; Angell, C.A.; Sundar, H.G.K.

1985-05-01

101

Report of high quantum efficiency photocathode at Milano  

SciTech Connect

R D activity on high quantum efficiency alkali antimonide photocathode is in progress at Milano, in the context of the ARES program. Inside a preliminary preparation chamber, Cs[sub 3]Sb layers with qunatum efficiency up to 9% (at [lambda]=543.5 nm) and lifetime of some days has been recently produced on copper, stainless steel and niobium, using a reproducible deposition procedure adapted to the material of the different substrata.

Michelato, P. (INFN and University of Milano, Lab. LASA, Via F.lli Cervi 201, 2009, Segrate (Georgia))

1992-07-01

102

Recognition of alkali metal halide contact ion pairs by uranyl-salophen receptors bearing aromatic sidearms. The role of cation-pi interactions.  

PubMed

Hard anions have long been known to bind strongly to the uranium of uranyl-salophen complexes. Upon functionalization of the salophen framework with one or two benzyloxy substituents, efficient ditopic receptors for alkali metal ions are obtained. The solid-state structures of complexes formed by the two-armed receptor 1 with CsF and with the chlorides of K+, Rb+, and Cs+ reported here reveal the existence of dimeric supramolecular assemblies in which two receptor units assemble into capsules fully enclosing (MX)2 ion quartets. In addition to the strong coordinative binding of the anion to the uranyl center and to electrostatic cation-anion interactions, stabilizing interactions arise from coordination of each cation to six oxygens, three from each receptor, and most importantly, to two aromatic sidearms belonging to different receptors. There are marked differences in organization at the supramolecular level in the CsCl complex of the one-armed receptor 3, in that four uranyl-salophen units instead of two are assembled in a capsule-like arrangement housing a (CsCl)2 ion quartet. However, both receptors achieve the common goal of having each metal cation in close contact with carbon atoms of two aromatic rings. 1H NMR data provide strong evidence that cation-pi(arene) interactions with the sidearms participate in binding also in solution. PMID:15771518

Cametti, Massimo; Nissinen, Maija; Dalla Cort, Antonella; Mandolini, Luigi; Rissanen, Kari

2005-03-23

103

Photocathodes in accelerator applications  

SciTech Connect

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.

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

1987-01-01

104

DIAMOND AMPLIFIED PHOTOCATHODES.  

SciTech Connect

High-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while protecting the cathode from the accelerator. The amplifier is a thin diamond wafer which converts energetic (few keV) primary electrons into hundreds of electron-hole pairs via secondary electron emission. The electrons drift through the diamond under an external bias and are emitted into vacuum via a hydrogen-terminated surface with negative electron affinity (NEA). Secondary emission gain of over 200 has been achieved. Two methods of patterning diamond, laser ablation and reactive-ion etching (RIE), are being developed to produce the required geometry. A variety of diagnostic techniques, including FTIR, SEM and AFM, have been used to characterize the diamonds.

SMEDLEY,J.; BEN-ZVI, I.; BOHON, J.; CHANG, X.; GROVER, R.; ISAKOVIC, A.; RAO, T.; WU, Q.

2007-11-26

105

Infrared-sensitive photocathode  

DOEpatents

A single-crystal, multi-layer device is described incorporating an IR absorbing layer that is compositionally different from the Ga{sub x}Al{sub 1{minus}x}Sb layer which acts as the electron emitter. Many different IR absorbing layers can be envisioned for use in this embodiment, limited only by the ability to grow quality material on a chosen substrate. A non-exclusive list of possible IR absorbing layers would include GaSb, InAs and InAs/Ga{sub w}In{sub y}Al{sub 1{minus}y{minus}w}Sb superlattices. The absorption of the IR photon excites an electron into the conduction band of the IR absorber. An externally applied electric field then transports electrons from the conduction band of the absorber into the conduction band of the Ga{sub x}Al{sub 1{minus}x}Sb, from which they are ejected into vacuum. Because the band alignments of Ga{sub x}Al{sub 1{minus}x}Sb can be made the same as that of GaAs, emitting efficiencies comparable to GaAs photocathodes are obtainable. The present invention provides a photocathode that is responsive to wavelengths within the range of 0.9 {mu}m to at least 10 {mu}m. 9 figures.

Mariella, R.P. Jr.; Cooper, G.A.

1995-04-04

106

High Temperature Thermal Expansion of Alkali Halides.  

National Technical Information Service (NTIS)

Thermal expansion data for 11 sodium chloride structure-type solids have been evaluated with an empirical modified quasi-harmonic model for thermal expansion. Earlier it was shown for Group 4 elements and 10 Grimm-Sommerfeld compounds that an empirical qu...

K. Wang R. R. Reeber

1995-01-01

107

Debye-Waller factors of alkali halides  

SciTech Connect

Using very-high-intensity ({approximately}70 Ci) {sup 183}Ta M{umlt o}ssbauer sources, we have measured the Debye-Waller factors (DWF{close_quote}s) of sodium chloride, potassium chloride, and potassium bromide single crystals for several of the (h00) and (nnn) Bragg reflections. We have used an approach which properly accounts for thermal expansion over the temperature range of our experiment, from 90 K to 900 K, about 100 K below the melting point of our crystals. We have found that a procedure used to analyze data by earlier workers leads to incorrect parameters in the Debye-Waller factor exponent, and our procedure does not require empirical parameters to account for the effects of thermal expansion. Additionally, we find three items of significance. Contrary to earlier results, we observe that the cations and the anions have identical DWF{close_quote}s in NaCl and also in KBr. We observe terms in the expansion of the DWF exponential which are quartic in the scattering wave vector {rvec Q} in NaCl and KCl, with some evidence for a Q{sup 4} term in KBr. The size of the Q{sup 4} contribution is reported and varies with the direction of momentum transfer. We also observe that the Debye temperature and the coefficient of the anharmonic Q{sup 2} term also vary with the direction of momentum transfer. We believe our data are the definitive evidence for a nonspherical thermal cloud in a cubic crystal; the ions have a larger amplitude of oscillation in the [h00] direction than in the [nnn] direction, contrary to the commonly held view of crystallographers that the most general form of the mean-square thermal motion is of an ellipsoid shape. {copyright} {ital 1998} {ital The American Physical Society}

Shepard, C.K.; Mullen, J.G. [Purdue University, West Lafayette, Indiana 47907-1396 (United States); Schupp, G. [University of Missouri Research Reactor, Columbia, Missouri 65211 (United States)

1998-01-01

108

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

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}.

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

2011-04-14

109

Cs based photocathodes for gaseous detectors  

SciTech Connect

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.

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

1993-08-01

110

Recent Progress toward Robust Photocathodes  

SciTech Connect

RF photoinjectors for next generation spin-polarized electron accelerators require photo-cathodes capable of surviving RF gun operation. Free electron laser photoinjectors can benefit from more robust visible light excited photoemitters. A negative electron affinity gallium arsenide activation recipe has been found that diminishes its background gas susceptibility without any loss of near bandgap photoyield. The highest degree of immunity to carbon dioxide exposure was achieved with a combination of cesium and lithium. Activated amorphous silicon photocathodes evince advantageous properties for high current photoinjectors including low cost, substrate flexibility, visible light excitation and greatly reduced gas reactivity compared to gallium arsenide.

Mulhollan, G. A.; Bierman, J. C. [Saxet Surface Science, Austin, TX 78744 (United States)

2009-08-04

111

COHESIVE ENERGY OF THE ALKALI HALICE CRYSTALS  

Microsoft Academic Search

BS>It is shown that the Born repulsive energy in the alkali halides at ; atmospheric pressure is represented better by a single exponential form than by ; the inverse power form. The role of the van der Waals energy and proper ; treatment of the equation of state in the determination of the parameters ; entering the Born model expression

M TOSI

1963-01-01

112

Coordination trends in alkali metal crown ether uranyl halide complexes: the series [A(crown)]2[UO(2)X(4)] where A=Li, Na, K and X=Cl, Br.  

PubMed

UO(2)(C(2)H(3)O(2))(2).2H(2)O reacts with AX or A(C(2)H(3)O(2) or ClO(4)) (where A = Li, Na, K; X = Cl, Br) and crown ethers in HCl or HBr aqueous solutions to give the sandwich-type compounds [K(18-crown-6)](2)[UO(2)Cl(4)] (1), [K(18-crown-6)](2)[UO(2)Br(4)] (2), [Na(15-crown-5)](2)[UO(2)Cl(4)] (3), [Na(15-crown-5)](2)[UO(2)Br(4)] (4), [Li(12-crown-4)](2)[UO(2)Cl(4)] (5), and [Li(12-crown-4)](2)[UO(2)Br(4)] (6). The compounds have been characterized by single-crystal X-ray diffraction, powder diffraction, elemental analysis, IR, and Raman spectroscopy. The [UO(2)X(4)](2-) ions coordinate to two [A(crown)](+) cations through the four halides only (2), through two halides only (3), through the two uranyl oxygens and two halides (3, 4), or through the two uranyl oxygen atoms only (5, 6). Raman spectra reveal nu(U-O) values that correlate with expected trends. The structural trends are discussed within the context of classical principles of hard-soft acid-base theory. PMID:11421684

Danis, J A; Lin, M R; Scott, B L; Eichhorn, B W; Runde, W H

2001-07-01

113

Advanced photocathode simulation and theory  

Microsoft Academic Search

A low work function dispenser type photocathode that is self-annealing or repairing would have a substantial impact on Free Electron Lasers (FELs). On such a cathode, the emitting surface is constantly renewed by replenishment of low-work-function material. A photo-dispenser cathode should operate at a relatively low temperature compared to a conventional dispenser cathode and is anticipated to be robust and

K. L. Jensen; D. W. Feldman; P. G. O’Shea

2003-01-01

114

ERL R and D: Photocathode Deposition and Transport System.  

National Technical Information Service (NTIS)

The purpose of the photocathode deposition and transport system is to (1) produce a robust, high yield multialkali photocathode and (2) have a method of transporting the multialkali photocathode for insertion into a super conducting RF electron gun. This ...

A. Burrill D. Pate I. Ben-Zvi J. Smedley R. Todd T. Rao

2010-01-01

115

S-20 photocathode research activity. Part I  

SciTech Connect

The goal of this activity has been to develop and implement S-20 photocathode processing techniques at Lawrence Livermore National Laboratory (LLNL) in order to study the physical properties of the photocathode films. The present work is the initial phase of a planned activity in understanding cathode fabrication techniques and the optical/electrical characterization of these films.

Gex, F.; Huen, T.; Kalibjian, R.

1983-11-22

116

Stability of Bi2Sr2CaCu2O8 superconductor in molten halide salts  

NASA Astrophysics Data System (ADS)

Stability of preformed Bi2Sr2CaCu2O8 phase in molten halide salts is described here. Salt systems containing Li+ and other halides except chlorides are negative in their ability to stabilize the Bi-2212 phase. Among all the salt systems evaluated, only some of the alkali chloride salt systems proved positive in stabilizing the Bi-2212 phase.

Gopalakrishnan, Sudhakar; Schulze, Walter A.

1994-08-01

117

Studies on the melts of alkali metal acetates.  

PubMed

The density, viscosity, and electrical conductivity of alkali metal acetates were measured over the temperature interval between melting and decomposition. The apparent activation energies of the equivalent conductivities and viscosities were calculated. It has been concluded from the results that alkali metal acetates, similarly to alkali metal benzenesulphonates studied earlier, exhibit properties quite unlike those of alkali metal halides. In the dependence of equivalent conductivity on the nature of the cation, the anomalous behaviour of lithium salts appears to be due to association prevailing in the melt phase. PMID:18960850

Halmos, Z; Meisel, T; Seybold, K; Erdey, L

1970-12-01

118

Purification of silicon halides  

SciTech Connect

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.

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

1988-07-05

119

Performance of the Brookhaven photocathode rf gun  

Microsoft Academic Search

The Brookhaven Accelerator Test Facility (ATF) uses a photocathode rf gun to provide a high-brightness electron beam intended for FEL and laser acceleration experiments. The rf gun consists of 11\\/2 cells driven at 2856 MHz in pi-mode with a maximum cathode field of 100 MV\\/m. To achieve long lifetimes, our photocathode development concentrates on robust metals such as copper, yttrium

K. Batchelor; I. Ben-Zvi; R. C. Fernow; J. Fischer; A. S. Fisher; J. Gallardo; G. Ingold; H. G. Kirk; K. P. Leung; R. Malone; I. Pogorelsky; T. Srinivasan-Rao; J. Rogers; T. Tsang; J. Sheehan; S. Ulc; M. Woodle; J. Xie; R. S. Zhang; L. Y. Lin; K. T. McDonald; D. P. Russell; C. M. Hung; X. J. Wang

1992-01-01

120

Performance of the Brookhaven photocathode RF gun  

Microsoft Academic Search

The Brookhaven Accelerator Test Facility (ATF) uses a photocathode RF gun to provide a high brightness electron beam intended for FEL and laser acceleration experiments. The RF gun consists of 1(1\\/2) cells driven at 2856 MHz in pi-mode with a maximum cathode field of 100 MV\\/m. To achieve long lifetimes, the photocathode development concentrates on robust metals such as copper,

K. Batchelor; I. Ben-Zvi; R. C. Fernow; J. Fischer; A. S. Fisher; J. Gallardo; G. Ingold; H. G. Kirk; K. P. Leung; R. Malone; I. Pogorelsky; T. Srinivasan-Rao; J. Rogers; T. Tsang; J. Sheehan; S. Ulc; M. Woodle; J. Xie; R. S. Zhang; L. Y. Lin; K. T. McDonald; D. P. Russell; C. M. Hung; X. J. Wang

1991-01-01

121

PHOTOCATHODES FOR THE ENERGY RECOVERY LINACS.  

SciTech Connect

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.

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

2005-03-19

122

Highly polarized electrons from superlattice photocathodes  

SciTech Connect

Our collaboration group have continued the research to develop the high performance photocathode and the guns to produce the highly polarized electron beam for high energy accelerator physics. In this report, the experimental results obtained from the photocathodes with superlattice structures, such as, AlGaAs-GaAs, InGaAs-GaAs and InGaAs-AlGaAs are described.

Nakanishi, T.; Okumi, S.; Togawa, K.; Takahashi, C.; Suzuki, C.; Furuta, F.; Ida, T.; Wada, K. [Dept. of Physics, Nagoya University, Chikusa-ku, Nagoya-464 (Japan); Omori, T.; Kurihara, Y.; Tawada, M.; Yoshioka, M. [High Energy Accelerator Research Organization, Tsukuba-305 (Japan); Horinaka, H.; Wada, K.; Matsuyama, T. [College of Engineering, University of Osaka Prefecture, Sakai-593 (Japan); Baba, T.; Mizuta, M. [Fundamental Research Laboratory, NEC Corporation, Tsukuba-305 (Japan)

1998-01-20

123

Oxidation of hydrogen halides to elemental halogens with catalytic molten salt mixtures  

DOEpatents

A process for oxidizing hydrogen halides by means of a catalytically active molten salt is disclosed. The subject hydrogen halide is contacted with a molten salt containing an oxygen compound of vanadium and alkali metal sulfates and pyrosulfates to produce an effluent gas stream rich in the elemental halogen. The reduced vanadium which remains after this contacting is regenerated to the active higher valence state by contacting the spent molten salt with a stream of oxygen-bearing gas.

Rohrmann, Charles A. (Kennewick, WA)

1978-01-01

124

Electron Propagator Theory of Aqueous Halide Photoelectron Spectra  

NASA Astrophysics Data System (ADS)

Electron binding energies and corresponding Dyson orbitals of solvated anions have been examined with ab initio electron propagator calculations on clusters that are embedded in a model electrostatic potential. Spectral predictions represent averages over solvent configurations that are generated by Monte--Carlo simulations with classical potentials. Predicted photoelectron spectra of aqueous alkali halide solutions are stable with respect to cluster size, basis set and self--energy approximations, and the sampling of solvent configurations. Dyson orbitals reveal a fundamental difference in electronic structure between fluoride and other halide solutions. Strong hydrogen bonding in the former case is responsible for delocalization of Dyson orbitals over many solvent molecules near the ionization threshold and for the dispersion of the fluoride contribution to the density of states over the inner--valence region of the spectrum. For other halides, Dyson orbitals near the ionization threshold are more localized on the anionic center.

Ortiz, J. V.

2012-06-01

125

RF Gun Photocathode Research at SLAC  

SciTech Connect

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.

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

126

Chemistry of Halide Window Growth.  

National Technical Information Service (NTIS)

The chemistry of reactive atmosphere processing (RAP) for the growth of crystals of chlorides, bromides, and halides was studied. The purity and freedom from extrinsic absorption obtained by RAP are important in the application of halides as optical eleme...

R. C. Pastor H. V. Winston

1976-01-01

127

The Thz Spectrum of Lanthanide and Transition Metal Halides - Effects on the Water Spectrum  

NASA Astrophysics Data System (ADS)

Recently, we were able to show that aqueous solutions of alkali and earth-alkali halides show strong resonances in the THz range that may be attributed to movements of individual ions in their surrounding water cage. Here, we extend this study to bromides and chlorides of selected lanthanides and transition metals. The effects of these strong ions on the water network as well as the detectability of contact ion complexes will be discussed.

Schwaab, G.; Sharma, Vinay; Havenith, Martina

2012-06-01

128

Photocathode RF gun using cartridge-type electric tubes  

Microsoft Academic Search

This report describes an S-band photoinjector with replaceable Cs2Te photocathodes. The photoinjector is equipped with a cathode-module, which is composed of four cartridge-type electric tubes with Cs2Te photocathodes. The photocathodes can be inserted into a single cell pillbox-type RF cavity. The maximum electric field strength on the photocathode surface, 90MV\\/m, has been achieved for the pillbox-type cavity in only 2h

Jun Sasabe; Hirofumi Hanaki; Takao Asaka; Hideki Dewa; Toshiaki Kobayashi; Akihiko Mizuno; Shinsuke Suzuki; Tsutomu Taniuchi; Hiromitsu Tomizawa; Kenichi Yanagida; Mitsuru Uesaka

2004-01-01

129

R&D ERL: Photocathode Deposition and Transport System  

Microsoft Academic Search

The purpose of the photocathode deposition and transport system is to (1) produce a robust, high yield multialkali photocathode and (2) have a method of transporting the multialkali photocathode for insertion into a super conducting RF electron gun. This process is only successful if a sufficient quantum efficiency lifetime of the cathode, which is inserted in the SRF electron gun,

D. Pate; I. Ben-Zvi; T. Rao; R. Burrill; R. Todd; J. Smedley; D. Holmes

2010-01-01

130

High-rep rate photocathode injector for LCLS  

Microsoft Academic Search

A preliminary design of the photocathode RF gun injection system for LCLS 120 Hz operation will be presented in this report. The injection system includes a photocathode RF gun, an emittance compensation solenoid magnet, an Mg cathode, a laser and laser beam delivery system and electron beam diagnostics. The photocathode RF gun for 120 Hz LCLS operation is based on

X. J. Wang; M. Babzien; I. Ben-Zvi; X. Y. Chang; S. Pjerov; M. Woodle

2001-01-01

131

CsI photocathode QE and a simple production technique  

NASA Astrophysics Data System (ADS)

The importance on quantum efficiency of a CsI photocathode of the starting material used, the deposition procedure, and electric field on the photocathode is discussed. A simple, non vacuum-deposition technique for making CsI photocathodes is also presented.

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

1993-03-01

132

Process for oxidation of hydrogen halides to elemental halogens  

DOEpatents

An improved process for generating an elemental halogen selected from chlorine, bromine or iodine, from a corresponding hydrogen halide by absorbing a molten salt mixture, which includes sulfur, alkali metals and oxygen with a sulfur to metal molar ratio between 0.9 and 1.1 and includes a dissolved oxygen compound capable of reacting with hydrogen halide to produce elemental halogen, into a porous, relatively inert substrate to produce a substrate-supported salt mixture. Thereafter, the substrate-supported salt mixture is contacted (stage 1) with a hydrogen halide while maintaining the substrate-supported salt mixture during the contacting at an elevated temperature sufficient to sustain a reaction between the oxygen compound and the hydrogen halide to produce a gaseous elemental halogen product. This is followed by purging the substrate-supported salt mixture with steam (stage 2) thereby recovering any unreacted hydrogen halide and additional elemental halogen for recycle to stage 1. The dissolved oxygen compound is regenerated in a high temperature (stage 3) and an optical intermediate temperature stage (stage 4) by contacting the substrate-supported salt mixture with a gas containing oxygen whereby the dissolved oxygen compound in the substrate-supported salt mixture is regenerated by being oxidized to a higher valence state.

Lyke, Stephen E. (Middleton, WI)

1992-01-01

133

Results from the average power laser experiment photocathode injector test  

NASA Astrophysics Data System (ADS)

Tests of the electron beam injector for the Boeing/Los Alamos Average Power Laser Experiment (APLE) have demonstrated first time operation of a photocathode RF gun accelerator at 25% duty factor. This exceeds previous photocathode operation by three orders of magnitude. The success of these tests was dependent upon the development of reliable and efficient photocathode preparation and processing. This paper describes the fabrication details for photocathodes with quantum efficiencies up to 12% which were used during electron beam operation. Measurements of photocathode lifetime as it depends upon the presence of water vapor are also presented. Observations of photocathode quantum efficiency rejuvenation and extended lifetime in the RF cavities are described. The importance of these effects upon photocathode lifetime during high average power operation are discussed.

Dowell, D. H.; Bethel, S. Z.; Friddell, K. D.

1995-02-01

134

Photocathode Preparation System for the ALICE Photoinjector  

NASA Astrophysics Data System (ADS)

ALICE-Accelerators and Lasers in Combined Experiments-is a relatively new accelerator built at Daresbury Laboratory that will demonstrate the process of energy recovery by the end of 2008. The project is a research facility to develop the technology required to build a New Light Source (NLS) in the UK. This paper details the current ALICE photoinjector design and highlights the limitations before focusing on a photoinjector upgrade. The key component of the upgrade is a three-stage extreme high vacuum load-lock system that will be incorporated into the ALICE photoinjector in 2010. The load-lock system has de facto become a standard component of a type III-V semiconductor photocathode injector and comprises: 1) loading chamber to allow new photocathodes to be introduced, 2) cleaning chamber for atomic hydrogen cleaning of the photocathodes and, 3) a preparation and activation chamber where the photocathodes will be activated to the NEA state ready for use on the ALICE accelerator. Once commissioned the load-lock system will allow rapid transfer of photocathodes between the load-lock system and the ALICE photoinjector whilst maintaining the integrity of the vacuum system and providing many other benefits. The new load-lock system will not only remove the problems with the existing set-up, it will also permit a new vacuum chamber to be designed for the gun itself. This new design will also aim to improve vacuum performance by addressing some of the major vacuum associated problems ALICE has encountered in the past 2 years.

Middleman, Keith J.; Burrows, I.; Cash, R.; Fell, B.; Jones, L. B.; McKenzie, J.; Militsyn, B.; Terekhov, A. S.

2009-08-01

135

Photocathode Preparation System for the ALICE Photoinjector  

SciTech Connect

ALICE--Accelerators and Lasers in Combined Experiments--is a relatively new accelerator built at Daresbury Laboratory that will demonstrate the process of energy recovery by the end of 2008. The project is a research facility to develop the technology required to build a New Light Source (NLS) in the UK. This paper details the current ALICE photoinjector design and highlights the limitations before focusing on a photoinjector upgrade. The key component of the upgrade is a three-stage extreme high vacuum load-lock system that will be incorporated into the ALICE photoinjector in 2010. The load-lock system has de facto become a standard component of a type III-V semiconductor photocathode injector and comprises: 1) loading chamber to allow new photocathodes to be introduced, 2) cleaning chamber for atomic hydrogen cleaning of the photocathodes and, 3) a preparation and activation chamber where the photocathodes will be activated to the NEA state ready for use on the ALICE accelerator. Once commissioned the load-lock system will allow rapid transfer of photocathodes between the load-lock system and the ALICE photoinjector whilst maintaining the integrity of the vacuum system and providing many other benefits. The new load-lock system will not only remove the problems with the existing set-up, it will also permit a new vacuum chamber to be designed for the gun itself. This new design will also aim to improve vacuum performance by addressing some of the major vacuum associated problems ALICE has encountered in the past 2 years.

Middleman, Keith J.; Burrows, I.; Cash, R.; Jones, L. B.; McKenzie, J.; Militsyn, B. [STFC Daresbury Laboratory, Keckwick Lane, Warrington, Cheshire, UK, WA4 4AD (United Kingdom); Terekhov, A. S. [Institute of Semiconductor Physics, Novosibirsk, 630090 (Russian Federation); Fell, B

2009-08-04

136

SWIFT HEAVY ION IRRADIATION EFFECTS ON DOPED ALKALI HALIDES  

Microsoft Academic Search

The effects produced by heavy ion irradiation in KBr:Ag and KCl:Ag crystals are investigated using optical spectroscopy. For KCl, the results are compared with the effects obtained in the pure crystals. After irradiation with heavy ions up to 11.2 MeV\\/u specific energy, the absorption bands suffer a series of changes, related to the structure of defects and also to their

M. Enculescu

137

Ionic Thermocurrents in Alkali Halide Crystals Containing Substitutional Beryllium Ions  

Microsoft Academic Search

The dielectric relaxations of NaCl and KCl single crystals containing beryllium ions have been studied using the technique of the ionic thermocurrents (ITC) in the range of temperatures between 1.2 and 300°K. The ITC spectra are characterized by three types of relaxations in both host crystals. The analysis of such relaxations and the observed temperature dependence of their relaxation times

Cesare Bucci

1967-01-01

138

Thermally populated intrinsic localized modes in pure alkali halide crystals  

NASA Astrophysics Data System (ADS)

The possibility of thermal excitation of intrinsic localized modes (ILMs) arising from anharmonicity in ionic perfect crystals is studied numerically for realistic model systems in one and three dimensions. Implications are discussed for an interesting high-temperature feature seen in earlier inelastic neutron scattering experiments on single crystal NaI. The general conclusion is that ILM formation energies are far too large for thermal excitation of ILMs to account for the observed feature in a pure crystal.

Sievers, A. J.; Sato, M.; Page, J. B.; Rössler, T.

2013-09-01

139

Three-photon magnetoabsorption of excitons in alkali halides  

Microsoft Academic Search

Three-photon magnetoabsorption measurements in fields up to 9 T are presented for the first time. A narrow exciton line of Gamma-5 symmetry is resolved in CsI at 5.8076 eV. A g value of 1.17 is deduced from the Zeeman splitting of this exciton. At high magnetic fields an exciton of Gamma-3 symmetry is detected. The analysis of the field-dependent mixing

F. Beerwerth; D. Fröhlich

1986-01-01

140

Three-photon magnetoabsorption of excitons in alkali halides  

NASA Astrophysics Data System (ADS)

Three-photon magnetoabsorption measurements in fields up to 9 T are presented for the first time. A narrow exciton line of ?-5 symmetry is resolved in CsI at 5.8076 eV. A g value of 1.17 is deduced from the Zeeman splitting of this exciton. At high magnetic fields an exciton of ?-3 symmetry is detected. The analysis of the field-dependent mixing of the ?-3 and ?-5 excitons yields a zero-field shift of the ?-3 exciton to lower energies of 0.54 meV and an effective g value for the admixture of 1.20.

Beerwerth, F.; Fröhlich, D.

1986-09-01

141

Magnetic Properties of Lattice Imperfections in Alkali Halide Single Crystals  

Microsoft Academic Search

Using a torque magnetometer, experimental results are reported on some new magnetic properties in high-purity, optical-quality single crystals of lithium fluoride, potassium chloride, and sodium chloride. Since the torque observations are not produced by the gross diamagnetism of these salts, the magnetic centers may be along dislocations because the magnetic susceptibility is observed to possess uniaxial anisotropy. Soft x irradiation

T. W. Adair; E. J. Sharp; C. F. Squire

1966-01-01

142

Making Solid Solutions with Alkali Halides (and Breaking Them)  

NSDL National Science Digital Library

In this exercise, the class will grow a variety of crystals of the same mineral, but with different chemical compositions. These crystals will be made from mixtures of halite (NaCl)and sylvite (KCl) that are melted and cooled. Because K+1 is significantly larger than Na+1,the unit cell is larger in sylvite than in halite. Intermediate compositions have intermediate unit cell sizes. Thus, a measurement of the lattice spacing of the crystalline products of your experiments can be used to determine their chemical composition. The principle goal of these experiments is to demonstrate that solid solutions do occur and that their physical properties vary with their chemical composition. Additional goals include studying the effect of composition on melting, exploring the process of exsolution as a function of temperature, and seeing the effect of fluids and deformation on crystallization kinetics.

Brady, John

143

Progress on lead photocathodes for superconducting injectors  

SciTech Connect

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.

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

2005-05-16

144

PROGRESS ON LEAD PHOTOCATHODES FOR SUPERCONDUCTING INJECTORS.  

SciTech Connect

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.

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

2005-05-16

145

PREPARATION OF HALIDES OF PLUTONIUM  

DOEpatents

A dry chemical method is described for preparing plutonium halides, which consists in contacting plutonyl nitrate with dry gaseous HCl or HF at an elevated temperature. The addition to the reaction gas of a small quantity of an oxidizing gas or a reducing gas will cause formation of the tetra- or tri-halide of plutonium as desired.

Garner, C.S.; Johns, I.B.

1958-09-01

146

Casting of halide and flouride alloys for laser windows  

NASA Astrophysics Data System (ADS)

The problem of residual strain in castings of alkali halides (KCl and SrCl2 doped KCl) and alkaline earth fluorides (CaF2) has been overcome by the development of proper annealing and slow cooling procedures. Large castings (5-1/2 in. diameter) of CaF2 and small castings (3 in. diameter) of SrF2 have been produced with low optical absorption coefficients at 5.25 micrometers. High quality CaF2 castings have been obtained by using as starting material either high purity single crystal chips or reagent grade powder that has been subjected to reactive atmosphere processing (RAP) in Teflon vapors.

Newberg, R. T.; Pappis, J.

1974-10-01

147

Photoemission Spectroscopic Study of Cesium Telluride Thin Film Photocathode  

SciTech Connect

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.

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

148

Alkali Doping Heterogeneous Catalysts.  

National Technical Information Service (NTIS)

Alkali doping mechanisms were considered: catalytic action of the alkali; creation of basic centers; neutralization of acid centers; alteration of the electronic properties of the catalyst surface; remedies for catalyst preparation; influencing the physic...

W. D. Mross

1983-01-01

149

Silver nanorod arrays for photocathode applications  

NASA Astrophysics Data System (ADS)

We explore the use of plasmonic Ag nanorod arrays featuring enhanced photoemission as high-brightness photocathode material. Silver nanorod arrays are synthesized by the direct current electrodeposition method and their dimensionality, uniformity, crystallinity, and oxide/impurity content are characterized. The yielded arrays exhibit greatly enhanced two-photon photoemission under 400 nm femtosecond pulsed laser excitation. Plasmonic field enhancement in the array produces photoemission hot spots that are mapped using photoemission electron microscopy. The relative photoemission enhancement of nanorod hot spots relative to that of a flat Ag thin film is found to range between 102 and 3 × 103.

Vilayurganapathy, Subramanian; Nandasiri, Manjula I.; Joly, Alan G.; El-Khoury, Patrick Z.; Varga, Tamas; Coffey, Greg; Schwenzer, Birgit; Pandey, Archana; Kayani, Asghar; Hess, Wayne P.; Thevuthasan, Suntharampillai

2013-10-01

150

STATUS OF DIAMOND SECONDARY EMISSION ENHANCED PHOTOCATHODE  

SciTech Connect

The diamond secondary emission enhanced photocathode (SEEP) provides an attractive alternative for simple photo cathodes in high average current electron injectors. It reduces the laser power required to drive the cathode, simultaneously isolating the cathode and the FW cavity from each other, thereby protecting them from contamination and increasing their life time. In this paper, we present the latest results on the secondary electron yield using pulsed thermionic and photo cathodes as primary electron sources, shaping the diamond using laser ablation and reactive ion etching as well as the theoretical underpinning of secondary electron generation and preliminary results of modeling.

RAO,T.; BEN-ZVI, I.; CHANG, X.; GRIMES, J.; GROVER, R.; ISAKOVIC, A.; SMEDLEY, J.; TODD, R.; WARREN, J.; WU, Q.

2007-05-25

151

Diode pumped alkali lasers  

Microsoft Academic Search

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

B. V. Zhdanov; R. J. Knize

2011-01-01

152

Actinide halide complexes  

DOEpatents

A compound of the formula MX{sub n}L{sub m} wherein M = Th, Pu, Np,or Am thorium, X = a halide atom, n = 3 or 4, L is a coordinating ligand selected from the group consisting of aprotic Lewis bases having an oxygen-, nitrogen-, sulfur-, or phosphorus-donor, and m is 3 or 4 for monodentate ligands or is 2 for bidentate ligands, where n + m = 7 or 8 for monodentate ligands or 5 or 6 for bidentate ligands, a compound of the formula MX{sub n} wherein M, X, and n are as previously defined, and a process of preparing such actinide metal compounds including admixing the actinide metal in an aprotic Lewis base as a coordinating solvent in the presence of a halogen-containing oxidant, are provided.

Avens, L.R.; Zwick, B.D.; Sattelberger, A.P.; Clark, D.L.; Watkin, J.G.

1991-02-07

153

Solubilities of various alkali metal and alkaline earth metal compounds in methanol  

Microsoft Academic Search

Solubilities of the halides, nitrates, carbonates, sulfates, and some perchlorates of all the alkali metals and alkaline earth metals in methanol at room temperature have been determined. Data on some, such as cesium and rubidium fluoride, nitrate, carbonate, and sulfate, appear to be reported for the first time. Comparison with earlier results from the literature reveals a number of discrepancies.

Vernon A. Stenger

1996-01-01

154

METHOD OF PREPARING METAL HALIDES  

DOEpatents

The conversion of plutonium halides from plutonium peroxide can be done by washing the peroxide with hydrogen peroxide, drying the peroxide, passing a dry gaseous hydrohalide over the surface of the peroxide at a temperature of about lOO icient laborato C until the reaction rate has stabillzed, and then ralsing the reaction temperature to between 400 and 600 icient laborato C until the conversion to plutonium halide is substantially complete.

Hendrickson, A.V.

1958-11-18

155

Methyl Halide Production by Fungi  

NASA Astrophysics Data System (ADS)

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.

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

2005-12-01

156

Actinide halide complexes  

DOEpatents

A compound is described of the formula MX[sub n]L[sub m] wherein M is a metal atom selected from the group consisting of thorium, plutonium, neptunium or americium, X is a halide atom, n is an integer selected from the group of three or four, L is a coordinating ligand selected from the group consisting of aprotic Lewis bases having an oxygen-, nitrogen-, sulfur-, or phosphorus-donor, and m is an integer selected from the group of three or four for monodentate ligands or is the integer two for bidentate ligands, where the sum of n+m equals seven or eight for monodentate ligands or five or six for bidentate ligands. A compound of the formula MX[sub n] wherein M, X, and n are as previously defined, and a process of preparing such actinide metal compounds are described including admixing the actinide metal in an aprotic Lewis base as a coordinating solvent in the presence of a halogen-containing oxidant.

Avens, L.R.; Zwick, B.D.; Sattelberger, A.P.; Clark, D.L.; Watkin, J.G.

1992-11-24

157

Actinide halide complexes  

DOEpatents

A compound of the formula MX.sub.n L.sub.m wherein M is a metal atom selected from the group consisting of thorium, plutonium, neptunium or americium, X is a halide atom, n is an integer selected from the group of three or four, L is a coordinating ligand selected from the group consisting of aprotic Lewis bases having an oxygen-, nitrogen-, sulfur-, or phosphorus-donor, and m is an integer selected from the group of three or four for monodentate ligands or is the integer two for bidentate ligands, where the sum of n+m equals seven or eight for monodentate ligands or five or six for bidentate ligands, a compound of the formula MX.sub.n wherein M, X, and n are as previously defined, and a process of preparing such actinide metal compounds including admixing the actinide metal in an aprotic Lewis base as a coordinating solvent in the presence of a halogen-containing oxidant, are provided.

Avens, Larry R. (Los Alamos, NM); Zwick, Bill D. (Santa Fe, NM); Sattelberger, Alfred P. (Los Alamos, NM); Clark, David L. (Los Alamos, NM); Watkin, John G. (Los Alamos, NM)

1992-01-01

158

High energy photocathodes for laser fusion diagnostics  

SciTech Connect

Laser fusion experiments at the National Ignition Facility require time-resolved x-ray images of the ignition target self-emission. The photon energies are expected to be greater than 10 keV. Photoemission quantum yield measurement data and photoelectron energy spectrum data are presently unavailable in this photon energy range, but are essential in the design of x-ray imaging diagnostics. We developed an apparatus to measure the quantum efficiency of primary and secondary photoelectron emission and to estimate the energy spectrum of the secondary photoelectrons. The apparatus has been tested using photon energies less than 10 keV to allow comparisons with prior work. A method for preparing photocathodes with geometrically enhanced photoefficiency has been developed.

Halvorson, C.; Houck, T.; Macphee, A.; Opachich, Y. P.; Lahowe, D.; Copsey, B. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)

2010-10-15

159

High energy photocathodes for laser fusion diagnostics.  

PubMed

Laser fusion experiments at the National Ignition Facility require time-resolved x-ray images of the ignition target self-emission. The photon energies are expected to be greater than 10 keV. Photoemission quantum yield measurement data and photoelectron energy spectrum data are presently unavailable in this photon energy range, but are essential in the design of x-ray imaging diagnostics. We developed an apparatus to measure the quantum efficiency of primary and secondary photoelectron emission and to estimate the energy spectrum of the secondary photoelectrons. The apparatus has been tested using photon energies less than 10 keV to allow comparisons with prior work. A method for preparing photocathodes with geometrically enhanced photoefficiency has been developed. PMID:21034008

Halvorson, C; Houck, T; Macphee, A; Opachich, Y P; Lahowe, D; Copsey, B

2010-10-01

160

High energy photocathodes for laser fusion diagnostics  

NASA Astrophysics Data System (ADS)

Laser fusion experiments at the National Ignition Facility require time-resolved x-ray images of the ignition target self-emission. The photon energies are expected to be greater than 10 keV. Photoemission quantum yield measurement data and photoelectron energy spectrum data are presently unavailable in this photon energy range, but are essential in the design of x-ray imaging diagnostics. We developed an apparatus to measure the quantum efficiency of primary and secondary photoelectron emission and to estimate the energy spectrum of the secondary photoelectrons. The apparatus has been tested using photon energies less than 10 keV to allow comparisons with prior work. A method for preparing photocathodes with geometrically enhanced photoefficiency has been developed.

Halvorson, C.; Houck, T.; Macphee, A.; Opachich, Y. P.; Lahowe, D.; Copsey, B.

2010-10-01

161

A Two-Frequency RF Photocathode Gun  

SciTech Connect

In this paper we resurrect an idea originally proposed by Serafini[1] in 1992 for an RF photocathode gun capable of operating simultaneously at the fundamental frequency and a higher frequency harmonic. Driving the gun at two frequencies with the proper field ratio and relative phase produces a beam with essentially no rf emittance and a linear longitudinal phase space distribution. Such a gun allows a completely new range of operating parameters for controlling space charge emittance growth. In addition, the linear longitudinal phase space distribution aids in bunch compression. This paper will compare results of simulations for the two-frequency gun with the standard rf gun, and the unique properties of the two-frequency gun will be discussed.

Dowell, D.

2004-11-05

162

Development of femtosecond photocathode RF gun  

NASA Astrophysics Data System (ADS)

Femtosecond electron bunches are essential for the observation of ultrafast reactions and phenomena in materials. To improve the time resolution of pulse radiolysis and ultrafast electron diffraction (UED), which involve the use of ultrashort electron bunches and ultrashort light, a femtosecond photocathode RF gun driven by a femtosecond laser was investigated experimentally. Bunch charge generated in the RF gun was studied based on the Schottky effect. Thermal emittance was estimated as 0.26 mm mrad at an rms laser spot size of 0.21 mm. Bunch length and longitudinal emittance were obtained as 180 fs and 0.87 deg keV, respectively, at a bunch charge of 3.5 pC and rms laser spot size of 0.38 mm.

Kan, K.; Yang, J.; Kondoh, T.; Yoshida, Y.

2011-12-01

163

Advanced 3D Photocathode Modeling and Simulations Final Report  

SciTech Connect

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.

Dimitre A Dimitrov; David L Bruhwiler

2005-06-06

164

Sealed gaseous photomultiplier with CsI photocathode  

Microsoft Academic Search

A sealed gaseous photomultiplier tube (PMT) with a CsI photocathode has been developed using a micropattern gas detector (MPGD) made of Pyrex glass. A microblasting technique (MB) was employed for the production of a new hole-type MPGD. We investigated gaseous PMTs with a semi-transparent CsI photocathode for two different gas mixtures of Ne(90%)+i-C4H10 (10%) and Ne (90%)+CF4 (10%) at a

Fuyuki Tokanai; Takayuki Sumiyoshi; Hiroyuki Sugiyama; Teruyuki Okada; Noboru Ohishi; Hirohisa Sakurai; Shuichi Gunji; Shunji Kishimoto

2011-01-01

165

R&D ERL: Photocathode Deposition and Transport System  

SciTech Connect

The purpose of the photocathode deposition and transport system is to (1) produce a robust, high yield multialkali photocathode and (2) have a method of transporting the multialkali photocathode for insertion into a super conducting RF electron gun. This process is only successful if a sufficient quantum efficiency lifetime of the cathode, which is inserted in the SRF electron gun, is maintained. One important element in producing a multialkali photocathode is the strict vacuum requirements of 10{sup -11} torr to assure success in the production of longlived photocathodes that will not have their QE or lifetime depleted due to residual gas poisoning in a poor vacuum. A cutaway view of our third generation deposition system is shown in figure 1. There are certain design criteria and principles required. One must be able to install, remove, rejuvenate and replace a cathode without exposing the source or cathode to atmosphere. The system must allow one to deposit Cs, K, and Sb on a cathode tip surface at pressures in the 10{sup -10} to 10{sup -9} torr range. The cathode needs to be heated to as high as 850 C for cleaning and maintained at 130 C to 150 C during deposition. There should also be the capability for in-situ QE measurements. In addition the preparation of dispenser photocathodes must be accounted for, thus requiring an ion source for cathode cleaning. Finally the transport cart must be mobile and be able to negotiate the ERL facility labyrinth.

Pate, D.; Ben-Zvi, I.; Rao, T.; Burrill, R.; Todd, R.; Smedley, J.; Holmes, D.

2010-01-01

166

Optically pumped alkali lasers  

Microsoft Academic Search

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

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

2007-01-01

167

Optically pumped alkali lasers  

NASA Astrophysics Data System (ADS)

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 these problems.

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

2007-06-01

168

Development of a plasma pinch photocathode  

NASA Astrophysics Data System (ADS)

The need in advanced Linacs is for a high-performance (emittance, current, and life) cathode that will not poison in the only moderately good vacuums of such systems. Our approach embodies the durability of an unsensitized metal photocathode that is illuminated by a high-Z, high-density plasma pinch formed from a liquid-jet source in vacuum. The principal advantage of this pinch over a laser is both its simplicity and its ability to efficiently produce high-power vacuum ultraviolet radiation. The laser-guided gas-embedded pinch vacuum-ultraviolet source has been converted to a liquid-jet configuration in vacuum. This was undertaken for several reasons. First, the necessity of interposed high-density background gas is avoided. Second, a channel-forming guide laser beam is no longer needed. Finally, a wide variety of high-Z low cost substances are available in liquid form. For these reasons the liquid-jet approach makes sense for a rep-rate version of the pinch illuminator. Background gas absorption of hard UV is lessened. A large gas-transport system is not needed. Radiation output may be optimized through selection of the liquid's vapor pressure, surface tension, density, and composition.

Asmus, John F.

169

Progress on diamond amplified photo-cathode  

SciTech Connect

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.

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

2011-03-28

170

Diode pumped alkali lasers  

NASA Astrophysics Data System (ADS)

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 vapor started only in 2003, when really efficient lasing in Rb and Cs vapors was demonstrated. The interest to this research was stimulated by the possibility of using efficient diode lasers for optical pumping of the alkali gain medium that promises high overall efficiency of the device. A variety of experiments on alkali lasers, including the demonstration of efficient Rb, Cs and K vapor lasers, power scaling experiments with multiple diode laser pumping sources and experiments on diode pumped alkali vapor amplifiers were performed during the past several years. In this paper we present a review of the most important achievements in high power alkali lasers research and development, discuss some problems existing in this field and future perspectives in DPAL development.

Zhdanov, B. V.; Knize, R. J.

2011-10-01

171

Polarization Possibilities of Small Spin-Orbit Interaction in Strained-Superlattice Photocathodes  

SciTech Connect

Strained-superlattice photocathodes based on InGaP/GaAs were investigated. The photocathode performance is found highly dependent on the superlattice parameters. The electron confinement energy in superlattice appears important.

Maruyama, T.; Brachmann, A.; Clendenin, J.E.; Garwin, E.L.; Ioakeimidi, K.; Kirby, R.E.; /SLAC; Prepost, R.; /Wisconsin U., Madison; Moy, A.M.; /SVT Assoc., Eden Prairie

2006-12-12

172

Photocathode Optimization for a Dynamic Transmission Electron Microscope: Final Report  

SciTech Connect

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.

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

2011-08-04

173

Recent Pes Photocathode R&d at Nagoya University  

NASA Astrophysics Data System (ADS)

The strained-layer superlattice structures have been exhibiting the most promising performance as a photocathode for the polarized electron source (PES). In our experiments, the GaAs-GaAsP photocathode achieved maximum polarization of 92±6% with quantum efficiency of 0.5%, while the InGaAs-AlGaAs photocathode provided higher quantum efficiency (0.7%) with lower polarization (77±5%). Criteria for achieving high spin polarization and high quantum efficiency using superlattice photocathodes were clarified by employing the spin-resolved quantum efficiency spectra. However, it seems that major problems still remained for the PES R&D are to improve (1) beam emittance and (2) NEA lifetime under gun operations for high peak current and high average current, respectively. In order to overcome these problems simultaneously, we started a development of a new type photocathode using field emission mechanism. First, we tried to use a pyramidal shape GaAs (tip-GaAs). Using the tip-GaAs, electrons can be emitted from a small area at the top of pyramid, and thus the beam emittance is expected to be small. This emission mechanism also enables to extract electrons from the poor NEA or small PEA surface into vacuum, and it helps to relax the NEA lifetime problem. Preliminary results were already obtained.

Kuwahara, M.; Nakanishi, T.; Okumi, S.; Yamamoto, M.; Furuta, F.; Miyamoto, M.; Yamamoto, N.; Naniwa, K.; Yasui, K.; Nishitani, T.; Watanabe, O.; Takeda, Y.; Kobayakawa, H.; Takashima, Y.; Togawa, K.

2005-08-01

174

Spin relaxation in alkali vapors  

NASA Astrophysics Data System (ADS)

In this dissertation, I describe a series of experimental and theoretical studies directed toward the understanding of spin-relaxation mechanisms in an alkali vapor. I present a large volume of new data that allows prediction of spin-relaxation rates under a wider variety of circumstances than was possible before. These results can be described by a model consisting of four relaxation mechanisms: relaxation on the vessel walls, in collisions with a buffer gas, in alkali singlet dimers, and what I refer to as alkali-alkali relaxation. The latter half of this work is devoted to a search for a theoretical model of alkali-alkali relaxation. I show that the previously held belief that alkali-alkali relaxation occurs during binary alkali collisions cannot be reconciled with the data presented here, and discuss possible alternate theories. Finally, I suggest that relaxation in metastable alkali trimer complexes may be the microscopic mechanism best able to explain these new results.

Kadlecek, Stephen John

1999-11-01

175

Theoretical and Experimental Studies of a 17 GHZ Photocathode RF Gun  

Microsoft Academic Search

Photocathode RF guns are a promising source of high-brightness electron beams. While the operating frequencies of existing systems are all at or below 3 GHz, the primary emphasis of this thesis is to study a 17 GHz photocathode RF gun. Many important issues regarding photocathode RF guns are theoretically addressed for the first time. First, a frequency scaling law based

Chia-Liang Lin

1995-01-01

176

Characterization of diamond film and bare metal photocathodes as a function of temperature and surface preparation  

SciTech Connect

High current photocathodes using bare metal and polycrystalline diamond films illuminated by ultraviolet lasers are being developed at Los Alamos for use in a new generation of linear induction accelerators. These photocathodes must be able to produce multiple 60 ns pulses separated by several to tens of nanoseconds. The vacuum environment in which the photocathodes must operate is 10{sup -5} torr.

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

1996-07-01

177

A polarization study of strained GaAs photocathode structures  

SciTech Connect

The polarized electron source at SLAC has performed extremely well during recent years supplying electrons having a spin polarization of 78% (85%) for high (low) current operation with beam current limited primarily by experimental requirements. However, there is room for improvement in the electron polarization. The less-than-ideal polarizations are a result of both imperfections and depolarizing mechanisms within the photocathode. The structure of the photocathode used at SLAC in the polarized electron source is a single-strained emitting layer structure grown atop a GaAs substrate. Here, the properties of several types of strained GaAs and GaAsP photocathodes have been studied using x-ray diffraction and photoemission.

Mulhollan, G.; Garwin, E.L.; Maruyama, T.; Tang, H. [Stanford Linear Accelerator Center, Menlo Park, CA (United States); Mair, R.; Prepost, R. [Univ. of Wisconsin, Madison, WI (United States)

1996-10-01

178

L-band Photocathode RF gun at KEK-STF  

NASA Astrophysics Data System (ADS)

The superconducting RF test facility (STF) in KEK is a facility to promote R&D of the International Linear Collider (ILC) cavities and cryomodule. L-band photocathode RF gun has been developed at KEK-STF as an electron beam source for cryomodule test scheduled in autumn of 2011. The RF cavity of the gun will be operated with a 1.3 GHz RF frequency, 1 msec RF pulse width, 5 Hz repetition rate at normal conductivity. The cavity was prepared by collaborative work with DESY and FNAL, and fabricated by FNAL. The RF conditioning of the cavity has been started since April 2010. A cesium telluride thin film as a photocathode material has been adopted, and the preparation equipment for cesium telluride has been newly designed and constructed. By using this new system, a fabrication and a performance estimation of the cesium telluride thin film as a photocathode are the next step of the research.

Sugiyama, H.; Takahashi, Y.; Hayano, H.; Urakawa, J.; Kashiwagi, S.; Isoyama, G.; Kato, R.; Sugimoto, N.; Kuriki, M.

2011-05-01

179

Intrinsic Emittance Reduction of an Electron Beam from Metal Photocathodes  

SciTech Connect

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.

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

2010-06-11

180

Alkali metal ionization detector  

DOEpatents

Variations in the conventional filament and collector electrodes of an alkali metal ionization detector, including the substitution of helical electrode configurations for either the conventional wire filament or flat plate collector; or, the substitution of a plurality of discrete filament electrodes providing an in situ capability for transferring from an operationally defective filament electrode to a previously unused filament electrode without removing the alkali metal ionization detector from the monitored environment. In particular, the helical collector arrangement which is coaxially disposed about the filament electrode, i.e. the thermal ionizer, provides an improved collection of positive ions developed by the filament electrode. The helical filament design, on the other hand, provides the advantage of an increased surface area for ionization of alkali metal-bearing species in a monitored gas environment as well as providing a relatively strong electric field for collecting the ions at the collector electrode about which the helical filament electrode is coaxially positioned. Alternatively, both the filament and collector electrodes can be helical. Furthermore, the operation of the conventional alkali metal ionization detector as a leak detector can be simplified as to cost and complexity, by operating the detector at a reduced collector potential while maintaining the sensitivity of the alkali metal ionization detector adequate for the relatively low concentration of alkali vapor and aerosol typically encountered in leak detection applications.

Bauerle, James E. (Plum Borough, PA); Reed, William H. (Monroeville, PA); Berkey, Edgar (Murrysville, PA)

1978-01-01

181

Analysis of Slice Transverse Emittance Evolution ina Photocathode RF Gun  

SciTech Connect

The slice transverse emittance of an electron beam is of critical significance for an x-ray FEL. In a photocathode RF gun, the slice transverse emittance is not only determined by the emission process, but also influenced strongly by the non-linear space charge effect. In this paper, we study the slice transverse emittance evolution in a photocathode RF gun using a simple model that includes effects of RF acceleration, focusing, and space charge force. The results are compared with IMPACT-T space charge simulations and may be used to understand the development of the slice emittance in an RF gun.

Huang, Z.; Ding, Y.; /SLAC; Qiang, J.; /LBL, Berkeley

2007-10-17

182

Rare-gas halide lasers  

Microsoft Academic Search

Lasers driven by rare-gas monohalides have the capability of providing overall electrical efficiency as high as 10%. Operating in the ultraviolet and vacuum UV spectra, the lasers are apparently scalable to high single-pulse energies greater than 100 J\\/pulse. Applications include photochemical separation. Physical properties of rare-gas halides are reviewed with attention to a spectral analysis of their radiative properties. Excitation

James J. Ewing

1978-01-01

183

Covalency of noble metal halides  

Microsoft Academic Search

The covalency is calculated for several compounds with diamond structure, zinc blend structure and rock salt structure using the DV-X? cluster method. The covalency of noble metal halides is in the border between that of the four-fold coordinated compounds and that of the six-fold coordinated compounds. These calculation results on the covalency support the tendency of the Phillips's ionicity. The

S. Ono; M. Kobayashi; T. Tomoyose

2005-01-01

184

Halide sensing using the SPQ molecule  

Microsoft Academic Search

The fluorescent and halide sensitive 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) molecule has been synthesised and incorporated into a hydrophilic copolymer to produce a halide sensor film. The sensor film typically swells in aqueous media allowing dye fluorescence to be quenched by the diffusion of aqueous halide ions at high pH. The steady-state Stern–Volmer constants, KSV, for the sensor film towards chloride, bromide and

Chris D. Geddes

2001-01-01

185

TRANSURANIC METAL HALIDES AND A PROCESS FOR THE PRODUCTION THEREOF  

DOEpatents

Halides of transuranic elements are prepared by contacting with aluminum and a halogen, or with an aluminum halide, a transuranic metal oxide, oxyhalide, halide, or mixture thereof at an elevated temperature.

Fried, S.

1951-03-20

186

A new estimation of the lattice energies of the ammonium halides and the proton affinity of gaseous ammonia  

Microsoft Academic Search

A linear relationship between the viscosity B-coefficient of the Jones-Dole equation for aqueous solutions of certain alkali metal salts and the enthalpy of hydration of the gaseous monatomic constituent ions has been established. The assumption that a similar rectilinear law applies to ammonium halides appears justified and the enthalpies of solution of NH4 (g)+X(g) have been estimated and used to

H. D. B. Jenkins; D. F. C. Morris

1976-01-01

187

Polarized Light Sources for photocathode electron guns at SLAC  

SciTech Connect

We describe current and future Polarized Light Sources at SLAC for use with photocathode electron guns to produce polarized electron beams. The SLAC experiments SLD and E142 are considered, and are used to define the required parameters for the Polarized Light Sources.

Woods, M.; Frisch, J.; Witte, K.; Zolotorev, M.

1992-12-01

188

MBE-grown InGaAs photocathodes  

Microsoft Academic Search

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

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

2003-01-01

189

Highly active oxide photocathode for photoelectrochemical water reduction  

Microsoft Academic Search

A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor\\/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H2 production, consisting of

Adriana Paracchino; Vincent Laporte; Kevin Sivula; Michael Grätzel; Elijah Thimsen

2011-01-01

190

The QE numerical simulation of PEA semiconductor photocathode  

NASA Astrophysics Data System (ADS)

Several kinds of models have already been proposed to explain the photoemission process. The exact photoemission theory of the 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) of the semiconductor photocathode based on the three-step photoemission model. Various factors (e.g., forbidden band gap, electron affinity, photon energy, incident angle, degree of polarization, refractive index, extinction coefficient, initial and final electron energy, relaxation time, external electric field and so on) have an impact on the QE of the PEA semiconductor photocathode, which are entirely expressed in the QE equation. In addition, a simulation code is also programmed to calculate the QE of the K2CsSb photocathode theoretically at 532 nm wavelength. By and large, the result is in line with the expected experimental value. The reasons leading to the distinction between the experimental and theoretical QE are discussed.

Li, Xu-Dong; Gu, Qiang; Zhang, Meng; Zhao, Ming-Hua

2012-06-01

191

Breakdown processes in metal halide lamps  

Microsoft Academic Search

Metal halide lamps typically have cold fills of tens to a few hundred Torr of a rare gas and the vapour from the dosing of a metal halide solid and mercury. Breakdown and starting of the lamp occurs following application of multi-kV pulses across electrodes separated by a few centimetres. Restarting of warm lamps is often problematic as the available

Brian Lay; Richard S Moss; Shahid Rauf; Mark J Kushner

2003-01-01

192

Ideas about Acids and Alkalis.  

ERIC Educational Resources Information Center

|Investigates students' ideas, conceptions, and misconceptions about acids and alkalis before and after a teaching sequence in a small-scale research project. Concludes that student understanding of acids and alkalis is lacking. (DDR)|

Toplis, Rob

1998-01-01

193

Dissociation pathways of carbonyl halides  

SciTech Connect

Reaction pathways for the decomposition of carbonyl halides, F{sub 2}CO, Cl{sub 2}CO, and FClCO, have been studied by using ab initio methods. Equilibrium geometries and transition structures have been fully optimized at the UHF/3-21G, UHF/6-31G*, and UMP2/6-31G* levels. Heats of reaction and barrier heights have been computed by using the Moeller-Plesset perturbation theory with and without annihilation of spin contaminants for molecular and free radical dissociation pathways. The most favorable reaction path to dissociation is the extrusion of halogen atoms to yield XCO radicals.

Francisco, J.S.; Li, Z. (Wayne State Univ., Detroit, MI (USA))

1989-11-30

194

Milk-Alkali Syndrome  

PubMed Central

Milk-alkali syndrome (MAS) consists of hypercalcemia, various degrees of renal failure, and metabolic alkalosis due to ingestion of large amounts of calcium and absorbable alkali. This syndrome was first identified after medical treatment of peptic ulcer disease with milk and alkali was widely adopted at the beginning of the 20th century. With the introduction of histamine2 blockers and proton pump inhibitors, the occurrence of MAS became rare; however, a resurgence of MAS has been witnessed because of the wide availability and increasing use of calcium carbonate, mostly for osteoporosis prevention. The aim of this review was to determine the incidence, pathogenesis, histologic findings, diagnosis, and clinical course of MAS. A MEDLINE search was performed with the keyword milk-alkali syndrome using the PubMed search engine. All relevant English language articles were reviewed. The exact pathomechanism of MAS remains uncertain, but a unique interplay between hypercalcemia and alkalosis in the kidneys seems to lead to a self-reinforcing cycle, resulting in the clinical picture of MAS. Treatment is supportive and involves hydration and withdrawal of the offending agents. Physicians and the public need to be aware of the potential adverse effects of ingesting excessive amounts of calcium carbonate.

Medarov, Boris I.

2009-01-01

195

Chlor-Alkali Technology.  

ERIC Educational Resources Information Center

|Chlor-alkali technology is one of the largest electrochemical industries in the world, the main products being chlorine and caustic soda (sodium hydroxide) generated simultaneously by the electrolysis of sodium chloride. This technology is reviewed in terms of electrochemical principles and manufacturing processes involved. (Author/JN)|

Venkatesh, S.; Tilak, B. V.

1983-01-01

196

Alkali-vapor lasers  

Microsoft Academic Search

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

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

2010-01-01

197

Thermodynamics of Aqueous Mixtures of Electrolytes and Nonelectrolytes. I. Ethyl Acetate and Eight 1-1 Alkali Metal Salts at 25C.  

National Technical Information Service (NTIS)

Partial molal enthalpies of transfer of ethyl acetate from water to eight aqueous 1 m alkali halides and nitrates were determined via calorimetry at 25. The enthalpies of transfer range from 204 to -66 cal/mole and were combined with free energies calcula...

J. H. Stern A. Hermann

1966-01-01

198

Hydrothermal alkali metal recovery process  

SciTech Connect

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/sup 0/F and about 700/sup 0/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 watersoluble 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.

Clavenna, L.R.; Eakman, J.M.; Kalina, T.; Wolfs, D.Y.

1980-08-26

199

High-Yield Metal Materials for Photocathode RF Gun  

SciTech Connect

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, ultrasonic cleaning and high temperature vacuum bake out. Using laser cleaning and explosive electron emission cleaning, the highest quantum efficiency measured for copper and magnesium are 0.02% and 0.3%, respectively. The Schottky effect was experimental investigated, the quantum efficiency of the Cu is dominated by the Schottky effect since the work function of the copper is almost equal to the photon energy used (4.66 eV). The quantum efficiency of the magnesium is significant enhanced by the Schottky effect.

Wang, X.J.; Ben-Zvi, I.; Smedley, J.; Srinivasan-Rao, T.; Woodle, M. [Brookhaven National Lab., Upton, NY (United States); Palmer, D.T.; Miller, R.H. [Stanford Linear Accelerator Center, Menlo Park, CA (United States)

1997-11-01

200

Quantum efficiency and thermal emittance of metal photocathodes  

NASA Astrophysics Data System (ADS)

Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths with major advances occurring since the invention of the photocathode gun and the realization of emittance compensation. These state-of-the-art electron beams are now becoming limited by the intrinsic thermal emittance of the cathode. In both dc and rf photocathode guns details of the cathode emission physics strongly influence the quantum efficiency and the thermal emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal emittance. This paper investigates the relationship between the quantum efficiency and the thermal emittance for metal cathodes using the Fermi-Dirac model for the electron distribution. We use a consistent theory to derive the quantum efficiency and thermal emittance, and compare our results to those of others.

Dowell, David H.; Schmerge, John F.

2009-07-01

201

Preliminary Results from a superconducting photocathode sample cavity  

SciTech Connect

Pure niobium has been proposed as a photocathode material to extract directly photo-currents from the surface of a RF-gun cavity [1]. However, the quantum efficiency of niobium is {approx}3 {center_dot} 10{sup -4}, whereas electro- or vacuum deposited lead has an {approx} 10 times higher quantum efficiency. We have designed and tested a photo-injector niobium cavity, which can be used to insert photo-cathodes made of different materials in the high electric field region of the cavity. Experiments have been conducted with niobium and lead, which show that neither the Q- values of the cavity nor the obtainable surface fields are significantly lowered. This paper reports about the results from these tests.

Peter Kneisel; Jacek Sekutowicz; R. Lefferts; A. Lipski

2005-05-01

202

Sealed gaseous photomultiplier with CsI photocathode  

NASA Astrophysics Data System (ADS)

A sealed gaseous photomultiplier tube (PMT) with a CsI photocathode has been developed using a micropattern gas detector (MPGD) made of Pyrex glass. A microblasting technique (MB) was employed for the production of a new hole-type MPGD. We investigated gaseous PMTs with a semi-transparent CsI photocathode for two different gas mixtures of Ne(90%)+i-C4H10 (10%) and Ne (90%)+CF4 (10%) at a gas pressure of 700 torr. Gains of up to 105 were attained with the microblasted glass plate (MB-GP) for both neon gas mixtures. Quantum efficiencies of up to 0.5% were obtained for UV light at the wavelength of 170 nm. The results of the aging test and the characteristics in a high magnetic-field environment are described for the gaseous PMT filled with neon gas mixture.

Tokanai, Fuyuki; Sumiyoshi, Takayuki; Sugiyama, Hiroyuki; Okada, Teruyuki; Ohishi, Noboru; Sakurai, Hirohisa; Gunji, Shuichi; Kishimoto, Shunji

2011-02-01

203

Pulse selection control for the IR FEL photocathode drive laser  

SciTech Connect

The method for current control of a photocathode source is described. This system allows for full remote control of a photocathode drive laser for resulting electron beam currents ranging from less than one microamp to a full current ranging from less than one microamp to a full current of five milliamps. All current modes are obtained by gating the drive laser with a series of electro-optical cells. The system remotely generates this control signal by assuming a mode of operation with the following properties selectable: Current mode as continuous or gated, micropulse density, macropulse gate width from single shot to 1ms duration, macropulse synchronization to A/C line voltage (60 Hz) or an external trigger, 60 Hz phase and slewing through 60 Hz when applicable. All selections are derived from programmable logic devices operating from a master-oscillator resulting in a discrete, phase stable, pulse control for the drive laser.

Jordan, K.; Evans, R.; Garza, O. [and others

1997-08-01

204

The Quantum Efficiency and Thermal Emittance of Metal Photocathodes  

SciTech Connect

Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths, with the principle improvements occurring since the invention of the photocathode gun. The state-of-the-art normalized emittance electron beams are now becoming limited by the thermal emittance of the cathode. In both DC and RF photocathode guns, details of the cathode emission physics strongly influence the quantum efficiency and the thermal emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal emittance. This paper investigates the relationship between the quantum efficiency and the thermal emittance of metal cathodes using the Fermi-Dirac model for the electron distribution. We derive the thermal emittance and its relationship to the quantum efficiency, and compare our results to those of others.

Dowell, David H.; Schmerge, John F.; /SLAC

2009-03-04

205

S-11 and S-20 photocathode research activity. Rev. 1  

SciTech Connect

The S-1 semi-transparent photocathode is the only one that can be used to study the 1.06 ..mu..m neodynium laser pulses of less than 10 ps duration. We first reviewed the recent results obtained at the Paris Observatory (research sponsored by the CEA), and then we tried to determine the role of the main constituents and their contributions in photoemission.

Gex, F.; Huen, T.; Kalibjian, R.

1984-08-27

206

Thermal emittance measurements of a cesium potassium antimonide photocathode  

NASA Astrophysics Data System (ADS)

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.

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

2011-05-01

207

A new chemical analysis system using a photocathode RF gun  

Microsoft Academic Search

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 3.5ps pulse of electron beam can be analyzed by means of time-resolved photo-absorption spectroscopy with 10ps laser pulses in the wavelength range of 210–2000nm. The high-precision control of

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

2000-01-01

208

Performance of Au transmission photocathode on a microchannel plate detector  

SciTech Connect

X-ray framing cameras, employing microchannel plates (MCPs) for detection and signal amplification, play a key role in research in high-energy-density physics. These instruments convert radiographic x-rays into electrons produced by plasma during such experiments into electrons that are amplified in the channels and then detected by a phosphor material. The separation of detection from signal amplification offers potential improvements in sensitivity and noise properties. We have implemented a suspended Au transmission photocathode (160 A thick) on a MCP and are evaluating it using a 1.5 keV Al K{alpha} x-ray source. We find an approximately twofold increase in the ratio of detected events to incident photons when the photocathode-to-MCP voltage difference is sufficiently large. Our calculations indicate that this increase is probably caused by a combination of signal produced by the photocathode and an increase in the efficiency of detection of x-rays that reach the MCP surface through modification of the local electric field.

Lowenstern, M. E.; Harding, E. C.; Huntington, C. M.; Visco, A. J.; Rathore, G.; Drake, R. P. [University of Michigan, 2455 Hayward Street, Ann Arbor, Michigan 48109 (United States)

2008-10-15

209

Comparative research on activation technique for GaAs photocathodes  

NASA Astrophysics Data System (ADS)

The properties of GaAs photocathodes mainly depend on the material design and activation technique. In early researches, high-low temperature two-step activation has been proved to get more quantum efficiency than high-temperature single-step activation. But the variations of surface barriers for two activation techniques have not been well studied, thus the best activation temperature, best Cs-O ratio and best activation time for two-step activation technique have not been well found. Because the surface photovoltage spectroscopy (SPS) before activation is only in connection with the body parameters for GaAs photocathode such as electron diffusion length and the spectral response current (SRC) after activation is in connection with not only body parameters but also surface barriers, thus the surface escape probability (SEP) can be well fitted through the comparative research between SPS before activation and SEP after activation. Through deduction for the tunneling process of surface barriers by Schrödinger equation, the width and height for surface barrier I and II can be well fitted through the curves of SEP. The fitting results were well proved and analyzed by quantitative analysis of angle-dependent X-ray photoelectron spectroscopy (ADXPS) which can also study the surface chemical compositions, atomic concentration percentage and layer thickness for GaAs photocathodes. This comparative research method for fitting parameters of surface barriers through SPS before activation and SRC after activation shows a better real-time in system method for the researches of activation techniques.

Chen, Liang; Qian, Yunsheng; Chang, Benkang; Chen, Xinlong; Yang, Rui

2012-03-01

210

Some Thermodynamic Aspects of Molten Salts: Halides of Uranium, Zirconium, Thorium, and Cerium in Alkali Halide Eutectics  

Microsoft Academic Search

The technique of thermodynamic studies by means of galvanic cells and ; the processes occurring at working electrodes is described. Measurement of the ; dependence of the reversible, or stationary, electrode upon concentration, ; temperature, current density, and time are described for the systems U\\/UClâ; ; Zr\\/ZrClâ; Th\\/ThClâ; and Ce\\/ CeClâ. (W.L.H.);

D. Inman; G. J. Hills; L. Young; J. O'm. Bockris

1960-01-01

211

Chemistry of halide window growth  

NASA Astrophysics Data System (ADS)

The chemistry of reactive atmosphere processing (RAP) for the growth of crystals of chlorides, bromides, and halides was studied. The purity and freedom from extrinsic absorption obtained by RAP are important in the application of halides as optical elements in high power lasers. The prototype of RAP is CCl4 in the growth of KCl; it reacts directly with water to scavenge out all traces of this contaminant and pyrolyzes with the formation of nascent halogen to react rapidly with hydroxide ions in the melt. The approach with the bromides and fluorides has been to seek RAP agents which simulate the behavior of CCl4 with KCl. On the basis of its hydrolysis behavior, CH2 Br2/He was used as the RAP agent for KBr. This has consistently yielded material with a 10.6 micrometer bulk absorption coefficient of 1/.0002 cm, an order of magnitude below that of non-RAP KBr. Further improvement is possible. In addition, it was found that the minimum-melting solid solution of NaBr and KBr prepared under RAP conditions does not retain phase homogeneity below the melting point, making it impossible to grow single crystals of this material. Work on KCl toward problems associated with the scale up of RAP to produce KCl crystals of greater than 10-cm diameter. Hydrogen fluoride, previously used alone as a RAP agent for fluoride crystal growth, is fast acting but does not achieve a low RAP index, P(H2O)/P(HF). Supplementing it with a fluorocarbon an improved transparency with CF4 admixtures was achieved.

Pastor, R. C.; Winston, H. V.

1976-02-01

212

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

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

213

GaAsP photocathode with 40% QE at 550 nm  

NASA Astrophysics Data System (ADS)

We have fabricated 18 mm format vacuum photodiodes incorporating GaAsP/AlGaAsP photocathodes (Eg approximately equals 1.8 eV) with P-20 phosphor screens. The photocathode response peaks at approximately 550 nm. The quantum efficiency at 550 nm is in excess of 55% (electrons per incident photon). The photocathode dark current for these tubes is less than 10-14 Amps/cm2 at room temperature. We have compared this cathode with the GaAs/AlGaAs photocathode.

Edgecumbe, John P.; Aebi, Verle W.; Davis, Gary A.

1992-06-01

214

Alkali-vapor lasers  

NASA Astrophysics Data System (ADS)

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 required laser physics for a high power system.

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

2010-02-01

215

Reactive scattering of electronically excited alkali atoms with molecules  

SciTech Connect

Representative families of excited alkali atom reactions have been studied using a crossed beam apparatus. For those alkali-molecule systems in which reactions are also known for ground state alkali and involve an early electron transfer step, no large differences are observed in the reactivity as Na is excited. More interesting are the reactions with hydrogen halides (HCl): it was found that adding electronic energy into Na changes the reaction mechanism. Early electron transfer is responsible of Na(5S, 4D) reactions, but not of Na(3P) reactions. Moreover, the NaCl product scattering is dominated by the HCl/sup -/ repulsion in Na(5S, 4D) reactions, and by the NaCl-H repulsion in the case of Na(3P). The reaction of Na with O/sub 2/ is of particular interest since it was found to be state specific. Only Na(4D) reacts, and the reaction requires restrictive constraints on the impact parameter and the reactants' relative orientation. The reaction with NO/sub 2/ is even more complex since Na(4D) leads to the formation of NaO by two different pathways. It must be mentioned however, that the identification of NaO as product in these reactions has yet to be confirmed.

Mestdagh, J.M.; Balko, B.A.; Covinsky, M.H.; Weiss, P.S.; Vernon, M.F.; Schmidt, H.; Lee, Y.T.

1987-06-01

216

Halide binding by the purified halorhodopsin chromoprotein. I. Effects on the chromophore.  

PubMed

The halorhodopsin chromoprotein, a retinal-protein complex with an apparent molecular mass of 20 kilo-daltons, exhibits all of the halide-dependent effects found for the chromophore of functional halorhodopsin in cell envelope vesicles. With increasing halide concentration (a) an alkali-dependent 580/410 nm chromophore equilibrium (attributed to reversible deprotonation of the retinal Schiff's base) is shifted toward the 580-nm chromophore and (b) the flash-induced photocycle proceeds increasingly via P520, rather than via P660. The halide-binding site(s) responsible for these effects must reside, therefore, in the chromoprotein. Chloride and bromide are about equivalent, but iodide is much less effective in these effects and in being transported. Several other anions, i.e. thiocyanate, nitrate, phosphate, and acetate, affect the absorption maximum of the chromophore but do not allow the production of P520 upon flash illumination and are not transported. However, these ions appear to compete with chloride in the flash experiments. These observations suggest that binding of anions to a relatively nonspecific site affects the protonation state of the Schiff's base in the chromophore. Either this site directly or a more specific site, connected to the first one by a sequential pathway, is involved with the photocycle intermediates and with chloride transport by halorhodopsin. PMID:6698961

Steiner, M; Oesterhelt, D; Ariki, M; Lanyi, J K

1984-02-25

217

Model of the physical properties of halides with complete graph-based indices  

NASA Astrophysics Data System (ADS)

Complete graph-based molecular connectivity indices are used to model different theoretical and experimental properties of a class of 20 alkali halides, as well as a theoretical quantum property of a class of fluorides and chlorides. The experimental properties are the lattice enthalpy, the binding enthalpy, and the polarizability in three different media of the alkali halides. The experimental lattice and binding enthalpy are used as training set to evaluate the other sets of theoretical energies, with which the two enthalpies have, finally, been "reconstructed." The theoretical energies are Coulomb energy, polarization energy, van der Waals energy, repulsion energy, and zero-point energy. The lattice enthalpy descriptors are rather good descriptors of its constituent energies: Coulomb, van der Waals, repulsion, and zero-point. The descriptors of the binding enthalpies, instead, fail to model some of its constituent energies: Coulomb, polarization, van der Waals, and repulsion energies. All types of energies are described by basis molecular connectivity indices based on odd complete graph algorithms, which allow an optimal description of the "reconstructed" calculated enthalpies. A common description of the experimental lattice and binding enthalpies with a descriptor trained on the binding enthalpies alone has also been possible. The model of three sets of polarization values of the metal halides with a descriptor trained with one set of polarization values compares positively with a previous study on the polarization of organic compounds. The model of this property requires molecular connectivity basis indices based on a sequential complete graph algorithm. The model of the quantum theoretical property, the electron density at the bond critical point of a class of fluorides and chlorides, allows an interesting comparison with density functional theory calculations.

Pogliani, Lionello

218

Development and characterization of diamond film and compound metal surface high current photocathodes  

SciTech Connect

High current photocathodes operating in vacuum environments as high as 8xE-5 torr are being developed at Los Alamos for use in a new generation of linear induction accelerators. We report quantum efficiencies in wide bandgap semiconductors, pure metals, and compound metal surfaces photocathode materials illuminated by ultraviolet laser radiation.

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

1997-09-01

219

Research on mechanical shock impact of GaAs photocathode photoemission performance  

NASA Astrophysics Data System (ADS)

The GaAs photocathode has been widely used in optoelectronic devices such as image intensifiers and photomultiplier tubes, but it is inevitable for these devices to withstand a variety of mechanical shock. In order to study the impact on the GaAs photocathode's photoemission performance caused by mechanical shock, GaAs photocathode image intensifier is researched in this paper . The spectral response of the GaAs photocathode was tested respectively before and after several value of mechanical shock?the value of mechanical shock:55g?65g?75g?85g and 95g?.The parameter of the GaAs photocathode can be calculated and the quantum efficiency curve can be fitted as well using the MATLAB software. The results show that surface escape probability is increased after photocathode is subjected to mechanical shock, 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.

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

2013-08-01

220

Dark Current and Multipacting in the Photocathode RF Guns at PITZ  

Microsoft Academic Search

For photocathode rf guns, the amount of dark current depends on the cavity surface as well as on the photocathodes. Smooth conditioning reduces the amount of dark current. Multipacting in the gun cavity changes the surface status of the cathodes and sometimes obstructs the gun operation because of vacuum interlocks. In this paper, dark current and multipacting features of an

J. H. Han; J. Bahr; H.-J. Grabosch; M. Krasilnikov; V. Miltchev; A. Oppelt; B. Petrosyan; S. Riemann; L. Staykov; F. Stephan; M. V. Hartrott; K. Flottmann; S. Schreiber; J. Ronsch; P. Michelato; L. Monaco; D. Sertore

2005-01-01

221

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

SciTech Connect

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.

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

222

Halide Ion Enhancement of Nitrate Ion Photolysis  

NASA Astrophysics Data System (ADS)

Nitrate ion photochemistry is an important source of NOx in the polar regions. It is uncertain whether coexisting ions such as halides play a role in nitrate photochemistry. The effect of halides on NO3 photolysis was investigated using photolysis experiments in 230 L Teflon chambers that contain deliquesced aerosols of NaBr:NaNO3, KBr:KNO3 and ternary mixtures of NaCl:NaBr:NaNO3. Gas phase NO2 and gaseous halogen products were measured as a function of photolysis time using long path FTIR, NOx chemiluminescence and API-MS (atmospheric pressure ionization mass spectrometry). Experiments were conducted with NO3- held at a constant 0.5 M and with the amount of total halide concentration varying from 0.25 M to 4 M. Studies on NaBr:NaNO3 mixtures suggest that as the bromide ion to nitrate ion ratio increases, there is an enhancement in the rate of production of NO2 in the nitrate-bromide mixtures over that formed in the photolysis of NaNO3. Molecular dynamic (MD) simulations provide molecular level insight into the ions near the air-water interface in the aqueous halide-nitrate mixtures. These studies suggest that the presence of sodium halides at the air-water interface may encourage some nitrate ions to approach the top layers of water, allowing for more efficient escape of photoproducts than is seen in the absence of halides. Experiments on mixtures of KBr:KNO3 are being conducted to determine potential cation effects. In addition, ternary mixtures of NaCl:NaBr:NaNO3 are being examined to determine the effects of mixtures of halides on production of NO2 and gaseous halogen products. The implications of this photochemistry for tropospheric chemistry will be discussed.

Richards, N. K.; Wingen, L. M.; Callahan, K. M.; Tobias, D. J.; Finlayson-Pitts, B. J.

2009-12-01

223

Novel lithium halide battery structure  

SciTech Connect

The present invention relates to a lithium halide battery structure comprising an outer metal envelope and top portion which is hermetically sealed to the envelope. The top portion includes an insulator conforming to and positioned thereon to the base configuration of the top portion and a support means having a base configuration substantially the same as the insulator. The support means also includes a flange depending from the support base and a pair of spaced apart post holders integral with said flange. First and second posts are positioned in the post holders with a metal anode collector screen positioned between and attached to said posts. The first post extends through the support means, insulator and top portion to define the anode terminal. The second post terminates in the associated post holder. A first and second pair of lithium anodes are pressure bonded together to sandwich therebetween the support means and anode collector screen. First and second depolarizer pellets are positioned between and in coextensive contact with the first and second anodes and the inner surface of the envelope.

Harney, M.J.; Icore, B.; O'Boyle, M.

1980-12-30

224

Quantum efficiency of cesium iodide photocathodes at soft x-ray and extreme ultraviolet wavelengths  

SciTech Connect

We have measured the quantum efficiency for normal incidence radiation of microchannel plate detectors which use opaque or semitransparent photocathodes made of fluffy CsI, solid CsI, or both. At wavelengths below --44 A-circle, detectors with fluffy CsI semitransparant photocathodes are more efficient than those with opaque photocathodes of silid CsI, but the opposite is true at longer wavelengths. Fluffy CsI semitransparent photocathodes with surface densities between 150 and 400 ..mu..m/cm/sup 2/ are optimum at soft x-ray wavelengths, and we have obtained efficiencies of 35 and 41% at 8 and 44A-circle, respectively, for a single-layer photocathode. The measured peak efficiency for an opaque layer of solid CsI, deposited at O/sup 0/ coating angle and 5000 A-circle (226 ..-->..g/cm/sub 2/) in thickness, is 56% at 110 A-circle.

Kowalski, M.P.; Fritz, G.G.; Cruddace, R.G.; Unzicker, A.E.; Swanson, N.

1986-07-15

225

Kelvin probe studies of cesium telluride photocathode for the AWA photoinjector  

NASA Astrophysics Data System (ADS)

Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (> 1%), is robust in a photoinjector, and long lifetime. This photocathode is fabricated in-house for a new Argonne Wakefield Accelerator (AWA) beamline to produce high charge per bunch (~50 nC) in a long bunch train. We present some results from a study of the work function of cesium telluride photocathode using the Kelvin Probe technique. The study includes an investigation of the correlation between the quantum efficiency and the work function, the effect of photocathode aging, the effect of UV light exposure on the work function, and the evolution of the work function during and after photocathode rejuvenation via heating.

Velazquez, D.; Wisniewski, E. E.; Yusof, Z.; Harkay, K.; Spentzouris, L.; Terry, J.

2012-12-01

226

Calculation of integral photoluminescence for the GaAs photocathode bonding assembly  

NASA Astrophysics Data System (ADS)

The ideal status of the GaAs photocathode bonding assembly is as fellows: the GaAs photocathode should not have additional stress; the crystal lattice should keep integrity after deposited Si3N4 reflection reducing coating and bonging process that GaAs epitaxial material on a glass window. In order to estimating the bonding quality of the GaAs photocathode bonding assembly, integral photoluminescence intensity was calculated on the ideal bonding condition. Assuming the energy of incident light was absorbed by GaAs active layer except reflection, according to the optical character of the GaAs photocathode bonding assembly, the value was calculated. This value could be the standard to assess the quality of the GaAs photocathode bonding assembly and improve the bonding technology that the GaAs epitaxial material is bonded to a glass window.

Feng, Chi; Jiao, Gangcheng; Cheng, Wei; Peng, Chaxia; Miao, Zhuang

2013-08-01

227

Enhanced photoelectrochemical hydrogen production from silicon nanowire array photocathode.  

PubMed

Herein we report that silicon nanowires (SiNWs) fabricated via metal-catalyzed electroless etching yielded a photoelectrochemical hydrogen generation performance superior to that of a planar Si, which is attributed to a lower kinetic overpotential due to a higher surface roughness, favorable shift in the flat-band potential, and light-trapping effects of the SiNW surface. The SiNW photocathode yielded a photovoltage of 0.42 V, one of the highest values ever reported for hydrogen generation on p-type Si/electrolyte interfaces. PMID:22142272

Oh, Ilwhan; Kye, Joohong; Hwang, Seongpil

2011-12-13

228

A new chemical analysis system using a photocathode RF gun  

NASA Astrophysics Data System (ADS)

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 3.5ps pulse of electron beam can be analyzed by means of time-resolved photo-absorption spectroscopy with 10ps laser pulses in the wavelength range of 210-2000nm. The high-precision control of RF phase makes 10ps of time-resolution possible for the analysis.

Aoki, Y.; Yang, J.; Hirose, M.; Sakai, F.; Tsunemi, A.; Yorozu, M.; Okada, Y.; Endo, A.; Wang, X.; Ben-Zvi, I.

2000-11-01

229

Photocathode device using diamondoid and cesium bromide films  

NASA Astrophysics Data System (ADS)

A photocathode structure is presented that shows promise for use in high brightness electron sources. The structure consists of a metal substrate, a monolayer of a diamondoid derivative, and a thin film of cesium bromide. Diamondoid monolayers reduce the energy spread of electron emitters, while cesium bromide increases the yield and stability of cathodes. We demonstrate that the combined structure retains these properties, producing an emitter with lower energy spread than the corresponding cesium bromide emitter (1.06 eV versus 1.45 eV) and higher yield and stability than un-coated diamondoid emitters.

Clay, William A.; Maldonado, Juan R.; Pianetta, Piero; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Schreiner, Peter R.; Fokin, Andrey A.; Tkachenko, Boryslav A.; Melosh, Nicholas A.; Shen, Zhi-Xun

2012-12-01

230

Nanosecond length electron pulses from a laser-excited photocathode  

SciTech Connect

A photocathode made from polycrystalline lanthanum hexaboride (LaB{sub 6}) has produced nanosecond length electron pulses when excited by an excimer laser at 308nm. Peak currents in excess of 1A have been observed, with quantum yields of 4 {times} 10{sup {minus}5} being measured. A method for extracting the electrons from an emission-limited cathode, plasma extraction, has been demonstrated. This technique uses a low power continuous discharge to provide the electric field needed to extract the photoelectrons. This technique may be useful in producing high repetition rate short pulse ion sources. 10 refs., 4 figs.

Young, A.T.; D'Etat, B.; Stutzin, G.C.; Leung, K.N.; Kunkel, W.B.

1989-06-01

231

Modeling the quantum efficiency of controlled porosity dispenser photocathodes  

NASA Astrophysics Data System (ADS)

A theoretical model of diffusion, evaporation, and rejuvenation of cesium on the surface of a controlled porosity dispenser photocathode is developed. The model applies a novel hexagonal meshgrid for increased numerical accuracy. For activation temperatures within the range of 400 K-1000 K, simulation found differences of less than 5% between the quantum efficiency (QE) maximum and minimum over ideal homogenous surfaces. Simulations suggest more variation for real cases to include real surface non uniformity. Changes in the QE map across the surface suggest that the emittance can change depending on temperature. Extensions to the model as well as connections to experiment are discussed.

Pan, Z.; Jensen, K.; O'Shea, P.

2012-01-01

232

Auger spectra of tetrahedral halides and hydrides  

SciTech Connect

Auger electron spectra are presented for the gas-phase molecular species CF/sub 4/, SiF/sub 4/, CCl/sub 4/, and SiCl/sub 4/ and discussed in terms of the effect of the interaction of the two final-state holes on the spectral line shapes. The highly polar character of the bonding for this series leads to systematic behavior with respect to this hole--hole interaction, showing rare gas-like localized halide spectra for SiF/sub 4/ and a delocalized component of increasing intensity as we proceed through the series to SiCl/sub 4/, CF/sub 4/, and CCl/sub 4/. The central atom spectra show a composite line shape resulting from the sum of two versions of the same one-electron final states but with different values of U (the hole--hole interaction energy). The Auger process occurs as a result of the electron density available at the central atom site but, since the one-electron orbitals are highly polarized towards the halide, the two holes principally appear around the halide sites. With both holes on the same halide site a rather large U results, but with the two holes on separate halide sites one obtains a reduced value of U. The relative intensity of the smaller U component appears to increase as we proceed through the series SiF/sub 4/, SiCl/sub 4/, CF/sub 4/, and CCl/sub 4/. This tendency in both the halide spectra and in the central atom spectra depends on the strength of the intersite interaction. The molecular parameter which seems most reasonable to predict this division between localized and delocalized behavior is the ratio of the halide--halide distance to the halide radius. In addition, we demonstrate that for a rather extended series of molecular species the trends in the value of U can be predicted surprisingly well on the basis of an experimental value of U for Ne and the known atomic and molecular dimensions. The implications of this simple predictive capability to other molecular systems is discussed.

Rye, R.R.; Houston, J.E.

1983-04-01

233

The Remarkable Reactivity of Aryl Halides with Nucleophiles  

ERIC Educational Resources Information Center

|Discusses the reactivity of aryl halides with nucleophilic or basic reagents, including nucleophilic attacks on carbon, hydrogen, halogen, and arynes. Suggestions are made concerning revisions of the sections on aryl halide chemistry courses and the corresponding chapters in textbooks. (CC)|

Bunnett, Joseph F.

1974-01-01

234

AlGaN/InGaN Photocathode Development  

SciTech Connect

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.

Buckley, J. H.; Leopold, D. J. [Department of Physics and McDonnell Center for the Space Sciences, Washington University, St. Louis, MO 63130 (United States)

2008-12-24

235

Highly active oxide photocathode for photoelectrochemical water reduction  

NASA Astrophysics Data System (ADS)

A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H2 production, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electrodeposited Pt nanoparticles. The roles of the different surface protection components were investigated, and in the best case electrodes showed photocurrents of up to -7.6?mA?cm-2 at a potential of 0?V versus the reversible hydrogen electrode at mild pH. The electrodes remained active after 1?h of testing, cuprous oxide was found to be stable during the water reduction reaction and the Faradaic efficiency was estimated to be close to 100%.

Paracchino, Adriana; Laporte, Vincent; Sivula, Kevin; Grätzel, Michael; Thimsen, Elijah

2011-06-01

236

Influence of air exposure on CsI photocathodes  

NASA Astrophysics Data System (ADS)

We investigate the influence of air exposure on the quantum efficiency (QE) and surface morphology of CsI photocathodes (PCs), at relative humidities (RH) higher than 80% down to nearly 3% (both at room temperature) and a 60 °C baking condition. By atomic force microscopy (AFM) surface analysis, it is clearly seen that RH >60% speeds up water film formation and CsI dissolution on the surface of the photocathode at the minute scale, while both grain size and QE change slowly at RH <30% at the hour scale. In the baking environment, the peak QE decreases less than 1.5% (absolute) within one week, and a stainless steel substrate and electron beam evaporation technique tend to effectively weaken the influence of air. With an Au-coated FR-4 substrate, the QE degradation is found to strongly depend on wavelength in the range of 120-210 nm. According to spectra of X-ray photoelectron spectroscopy (XPS), an excess of cesium was observed and the chemical reaction between water and CsI when exposed to humid air is proved. It is found that carbon, and not H2O or O2, is the main pollutant in the baking condition.

Xie, Yuguang; Zhang, Aiwu; Liu, Yingbiao; Liu, Hongbang; Hu, Tao; Zhou, Li; Cai, Xiao; Fang, Jian; Yu, Boxiang; Ge, Yongshuai; Lü, Qiwen; Sun, Xilei; Sun, Lijun; Xue, Zheng; Xie, Yigang; Zheng, Yangheng; Lü, Junguang

2012-10-01

237

Silver halide emulsion and silver halide photographic light-sensitive material containing the same  

US Patent & Trademark Office Database

In a silver halide emulsion, a sum of projected areas of tabular silver halide grains, in which an outer shell region which is 40% in volume from a grain surface contains 5 mol % to 20 mol % of iodide ions with respect to a silver halide in the outer shell region, and which have a projected area diameter of 0.08 .mu.m to 0.5 .mu.m and an aspect ratio of 2 to 30, accounts for 80% or more of the total projected area of all grains.

2001-12-11

238

Opaque gallium nitride photocathodes in UV imaging detectors with microchannel plates  

NASA Astrophysics Data System (ADS)

The optimization and performance of opaque Galium Nitride (GaN) photocathodes deposited directly on novel Microchannel Plates (MCPs) are presented in this paper. The novel borosilicate glass MCPs, which are manufactured with the help of Atomic Layer Deposition, can withstand higher temperatures enabling direct deposition of GaN films on their surfaces. The quantum efficiency of MBE-grown GaN photocathodes of various thickness and buffer layers was studied in the spectral range of ~200-400 nm for the films grown on different surface layers (such as Al2O3 or buffer AlN layer) in order to determine the optimal opaque photocathode configuration. The MCPs with the GaN photocathodes were activated with surface cesiation in order to achieve the negative Electron Affinity for the efficient photon detection. The opaque photocathodes enable substantial broadening of the spectral sensitivity range compared to the semitransparent configuration when the photocathodes are deposited on the input window. The design of currently processed sealed tube event counting detector with an opaque GaN photocathode are also described in this paper. Our experiments demonstrate that although there is still development work required the detection quantum efficiencies exceeding 20% level should be achievable in 200-400 nm range and <50% in 100-200 nm range for the event counting MCP detectors with high spatial resolution (better than 50 ?m) and timing resolution of <100 ps and very low background levels of only few events cm-2 s-1.

Tremsin, Anton S.; Hull, Jeffrey S.; Siegmund, Oswald H. W.; McPhate, Jason B.; Vallerga, John V.; Dabiran, Amir M.; Mane, Anil; Elam, Jeff

2013-09-01

239

Molten salt synthesis of alkali niobate powders  

SciTech Connect

A mixture of niobium pentoxide, an oxide of an alkali selected from the group consisting of sodium, potassium, lithium and mixtures thereof, and an alkali chloride salt solvent is heated to melt the chloride salt solvent in which the niobium oxide and alkali oxide dissolve and react precipitating the alkali niobate.

Arendt, R.H.; Rosolowski, J.H.

1980-11-18

240

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

PubMed

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

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

2010-02-18

241

Photocathode-Uniformity Tests of the Hamamatsu R5912 Photomultiplier Tubes Used in the Milagro Experiment  

NASA Astrophysics Data System (ADS)

The Milagro experiment observes the extensive air showers produced by very high energy gamma-rays impacting the Earth’s atmosphere. Milagro uses 898 Hamamatsu R5912 Photomultiplier Tubes. To complete our Monte Carlo simulations, we tested the photocathode uniformity of our PMTs. The main finding was that the PMT gain and detection efficiency are a function of the distance from the center of the photocathode. Both quantities become considerably smaller as the illumination position nears the edge of the photocathode. Inclusion of the measured quantities in our MC simulations greatly increased the agreement between the simulations and the experiment.

Vasileiou, V.; Ellsworth, R. W.; Smith, A.

242

Ion back-bombardment of GaAs photocathodes inside dc high voltage electron guns  

SciTech Connect

DC high voltage GaAs photoguns are key components at accelerator facilities worldwide. New experiments and new accelerator facilities demand improved performance from these guns, in particular higher current operation and longer photocathode operating lifetime. This conference submission explores bulk GaAs photocathode lifetime as a function of beam current, active photocathode area, laser spot size and the vacuum of the gun and beam line. Lifetime measurements were made at 100 microamps, a beam current relevant for accelerators like CEBAF, and at beam currents of 1 milliamps and 5 milliamps, a regime that is interesting for high current Free Electron Laser (FEL) and Energy Recovery Linac (ERL) operation.

Joseph Grames; Philip Adderley; Joshua Brittian; Daniel Charles; James Clark; John Hansknecht; Benard Poelker; Marcy Stutzman; Kenneth Surles-law

2005-05-01

243

Properties of CsI and CsI-TMAE photocathodes  

SciTech Connect

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.

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

244

Experimental study of a 17 GHz high gradient photocathode injector  

NASA Astrophysics Data System (ADS)

This thesis describes experimental research on a 17 GHz photocathode RF gun. This work represents the first operation of a photocathode electron gun at a frequency above 3 GHz. Photocathode RF guns have the potential for achieving record high values of electron beam quality. The 1[1/over 2] cell, ?-mode, copper cavity was tested with 5-10 MW, 100 ns, 17 GHz pulses from a 24 MW Haimson Research Corp. klystron amplifier. Klystron power is stable to within ±5% up to 8 MW. The klystron output was made stable by the implementation of a Bragg filter as a replacement for a short as the termination to the RF gun coupling waveguide. The output of the klystron amplifier is phase locked to the input to within ±8o from shot-to-shot and less than ±4o on a single-shot basis. Conditioning of the RF gun structure with high power microwaves resulted in a minimum surface field of 250 MV/m, corresponding to an average on-axis gradient of 150 MV/m. Field emission or 'dark' current of 0.5 mA was observed at 175 MV/m, consistent with Fowler-Nordheim field emission theory if a field enhancement factor of about 100 is assumed. Electron bunches were generated by a regenerative laser amplifier that produces 1.9 ps, 1.9 mJ pulses at 800 nm with ±10% energy stability. These pulses were frequency tripled to 46 ?J of UV with an efficiency of approximately 12%. Shot-to-shot ultraviolet pulse energy stability was 20%. Faraday cup beam measurements indicate that 0.12 nC bunches were produced with a kinetic energy of about 1 MeV. The electron bunches are approximately 0.3 mm long and 1 mm in diameter. This corresponds to a peak current of about 120 A, and a density at the cathode of 8.8 kA/cm2. Phase scans of laser induced emission reveal an overall phase stability of better than ±20o corresponding to synchronization of the laser pulses to the microwave field with an error of less than ±3 ps. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-153- 1690.)

Trotz, Seth Reuben

245

Plasma chemical vapor deposition of halide glasses  

Microsoft Academic Search

The present invention described herein relates to the field of preparing preforms which are used to make optical fibers. More specifically, the invention relates to making preforms for halide glass fibers. The invention especially relates to making preforms for fluoride glass fibers. Simple chemical vapor deposition processes are well known in the manufacture of silica fibers. More specifically, simple chemical

Lynda E. Busse; Ishwar D. Aggarwal

1991-01-01

246

Computer simulation of alkaline earth halides  

Microsoft Academic Search

Monte Carlo calculations have been carried out for model systems consisting of 324 ions (108 cations and 216 anions). The aims were: (a) to study the thermodynamic and structural properties of liquid and solid alkaline earth halides; (b) to test the rigid ion model.Although the general agreement between experimental and predicted properties is less satisfactory than in the case of

Simon W. de Leeuw

1978-01-01

247

Computer simulation of alkaline earth halides  

Microsoft Academic Search

Monte Carlo calculations have been carried out for model systems consisting of 324 ions (108 cations and 216 anions). The aims were: (a) to study the thermodynamic and structural properties of liquid and solid alkaline earth halides; (b) to test the rigid ion model. Although the general agreement between experimental and predicted properties is less satisfactory than in the case

Simon W. de Leeuw

1978-01-01

248

Rare-gas halide avalanche discharge lasers  

Microsoft Academic Search

This paper summarizes a series of studies aimed at understanding rare-gas halide lasers excited by UV preionized avalanche discharges. Discussions include steady-state rate equation calculations of the kinetics, parametric variations and optimizations of discharge characteristics, and gas mixture optimizations for high-energy lasing.

R. Sze

1979-01-01

249

An Improved Electrically Excited Mercury Halide Laser.  

National Technical Information Service (NTIS)

An improved electric-discharge-excited, mercury halide dissociation laser is operable on the (B-X) transitions in HgCl, HgBr, and HgI at 558, 502, and 443 nm respectively. The laser discharge cell is elongated and made from temperature-resistant silicon-g...

R. L. Burnham

1978-01-01

250

Electrical Resistivity of Alkali Elements.  

National Technical Information Service (NTIS)

This technical report presents and discusses the available data and information on the electrical resistivity of alkali elements (lithium, sodium, potassium, rubidium, cesium, and francium) and contains recommended reference values (or provisional or typi...

T. C. Chi

1976-01-01

251

Tunable alkali metallic vapor laser  

Microsoft Academic Search

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

I. Itzkan; R. T. V. Kung

1979-01-01

252

Reproducible, rugged, and inexpensive photocathode x-ray diode  

SciTech Connect

The photoemissive cathode type of x-ray diode (XRD) is popular for measuring time and spectrally resolved output of pulsed power experiments. Vitreous carbon XRDs currently used on the Sandia National Laboratories Z-machine were designed in the early 1980s and use materials and processes no longer available. Additionally cathodes used in the high x-ray flux and dirty vacuum environment of a machine such as Z suffer from response changes requiring recalibration. In searching for a suitable replacement cathode, we discovered very high purity vitreous-carbon planchets are commercially available for use as biological substrates in scanning electron microscope (SEM) work. After simplifying the photocathode mounting to use commercially available components, we constructed a set of 20 XRDs using SEM planchets that were then calibrated at the National Synchrotron Light Source at Brookhaven National Laboratory. We present comparisons of the reproducibility and absolute calibrations between the current vitreous-carbon XRDs and our new design.

Idzorek, G. C.; Tierney, T. E.; Lockard, T. E. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Moy, K. J. [NSTec, Las Vegas, Nevada 89193 (United States); Keister, J. W. [SFA, Inc. Brookhaven National Laboratory, Upton, New York 11973 (United States)

2008-10-15

253

New configuration of metallic photocathodes prepared by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

We propose a new photocathode configuration which presents the quantum efficiency and work function of yttrium (Y) and at the same time preserves all of the advantages of copper (Cu) when inserted into a radio-frequency gun. The configuration consists of a disk of Y covered by a coating of Cu deposited using the pulsed laser ablation technique, while masking the central part of the Y disk by a shield making the photoemission directly from the Y bulk possible. The new device was characterised by scanning electron microscopy to deduce the morphology and by X-ray diffraction to obtain structure information on both Cu film and Y substrate. The electrical resistivity of the Cu film was also measured obtaining a value slightly greater than that of bulk high purity Cu.

Lorusso, A.; Cola, A.; Gontad, F.; Koutselas, I.; Panareo, M.; Vainos, N. A.; Perrone, A.

2013-10-01

254

Enhanced lifetime hybrid-diffuser cesium reservoir photocathode  

NASA Astrophysics Data System (ADS)

A novel self-healing hybrid-diffuser cesium reservoir photocathode is demonstrated. The model-driven design optimizes operating temperature to match diffusion and evaporation rates and maximize quantum efficiency of the cesiated tungsten surface. A sintered-wire tungsten emitter promotes surface uniformity. Cesium loss is less than 0.023 µg/cm2/hr at 125ºC, and conservatively extrapolated reservoir lifetime exceeds 30,000 hours. Contamination robustness to a direct atmospheric leak with room-temperature contamination by over 200 Langmuirs of oxidizing gases is excellent, with 90% of maximum QE repeatedly restored via in situ self-healing recesiation under gentle 90ºC heating.

Montgomery, Eric J.; Pan, Zhigang; Riddick, Blake C.; O'Shea, Patrick G.; Feldman, Donald W.; Jensen, Kevin L.; Ives, R. Lawrence; Falce, Louis R.

2013-01-01

255

Design and construction of the photocathode electron gun cavity  

SciTech Connect

A 1300-MHz, two-cell rf accelerator cavity has been constructed for the high-brightness photocathode electron source program. Each cell has an rf drive. Cell one has a replacement photocathode plug on the back wall and has a shape designed for linear radial fields. Cell two has a more standard high-shunt-impedance shape. SUPERFISH values for shunt impedances are, respectively, 29.5 and 45.8 M/Omega//m. Peak surface field maximums are 58.9 and 32.1 MV/m for an electron acceleration of 0.9 and 1.0 MeV. Drive coupling is matched for 55 and 86% beam loading at 1-A average current. The system has vacuum pumping ports, into both cells and is baked at 300/degree/C. Typical operating pressures are in low 10/sup /minus/10//-torr range. Cell frequencies are fine tuned by a combination of operating temperature and cell nose pulling. Cell-to-cell coupling was intended to be low (K = 0.0002); however, because of the high Qs (13,300 and 20,000), substantial coupling effects are seen. Cutting the vacuum-port slots shifted the frequencies by 1.5 MHz and gave an apparent 10% increase in the cavity Qs. Construction of the cavity required a series of four brazes with several annealing cycles. All joints are flat, and the sequence is such that each joint is brazed horizontally; as a result, all joints were successfully brazed on the first attempt. The latest experiment measurements are given in another paper at this conference. 2 refs., 3 figs.

Gray, E.R.; Fraser, J.S.

1988-01-01

256

High-Brightness Electron Beam Evolution Following the Laser-Based Cleaning of a Photocathode.  

National Technical Information Service (NTIS)

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 whet...

F. Zhou

2012-01-01

257

Towards a Robust, Efficient Dispenser Photocathode: the Effect of Recesiation on Quantum Efficiency  

SciTech Connect

Future electron accelerators and Free Electron Lasers (FELs) require high brightness electron sources; photocathodes for such devices are challenged to maintain long life and high electron emission efficiency (high quantum efficiency, or QE). The UMD dispenser photocathode design addresses this tradeoff of robustness and QE. In such a dispenser, a cesium-based surface layer is deposited on a porous substrate. The surface layer can be replenished from a subsurface cesium reservoir under gentle heating, allowing cesium to diffuse controllably to the surface and providing demonstrably more robust photocathodes. In support of the premise that recesiation is able to restore contaminated photocathodes, we here report controlled contamination of cesium-based surface layers with subsequent recesiation and the resulting effect on QE. Contaminant gases investigated include examples known from the vacuum environment of typical electron guns.

Montgomery, Eric J.; Pan Zhigang; Leung, Jessica; Feldman, Donald W.; O'Shea, Patrick G. [Institute for Research in Electronics and Applied Physics, University of MD, College Park, MD 20742 (United States); Jensen, Kevin L. [Code 6843, ESTD, Naval Research Laboratory, Washington D.C. 20375-5347 (United States)

2009-01-22

258

A statistically-designed experiment for assessing cesium-potassium-antimonide photocathode fabrication parameters  

NASA Astrophysics Data System (ADS)

A vapor-phase deposition process for fabricating cesium-potassium-antimonide photocathodes is investigated. A 3×24-1 fractional factorial statistical experimental design was created to simultaneously determine the effects of five processing variables on photocathode performance based on quantum efficiency (QE) measurements of nascent photocathodes. The five processing variables are antimony thickness, potassium thickness, source temperature, cesium temperature rampdown, and substrate temperature. Thirty-five combinations of the five variables were performed (resulting in 35 cathodes): 24 combinations were unique and 11 were replicates. A twelve-run complementary phase followed the amin experiment, for a total of 47 photocathodes. This statistical approach enables independent estimation of the main effects and interaction effects of the five variables. Statistically significant effects are separated from nonsignificant effects. The fabrication process will be used on the Average Power Laser Experiment (APLE) conducted at Boeing.

Ternes, R. L.; Bethel, S. Z.; Janky, D. G.

1992-07-01

259

Quantum Efficiency and Topography of Heated and Plasma Cleaned Copper Photocathode Surfaces.  

National Technical Information Service (NTIS)

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 chemica...

D. T. Palmer R. E. Kirby F. K. King

2005-01-01

260

Induction of crystal growth in alkali-halide aggregates by means of internal seeding  

NASA Astrophysics Data System (ADS)

Following our previous work, new results for seed induced nucleation and crystal growth in nano droplets are presented. A new method that allows to place the seed inside the droplet is presented. The new results show a considerable independence of the processes of nucleation and crystal growth regarding the size of the host droplet. The crystal growth model also previously reported was applied giving good predictions. It supports more insights into the growth trends for different seed placements. Based on its deviation from the ideal condition considered in the crystal growth model development, a reinterpretation for the outside seeding behavior is presented. Additionally, the present results strongly sustain a non-self-wetting behavior for ionic salts aggregates.

Rodrigues, P. C. R.; Silva Fernandes, F. M. S.

2012-06-01

261

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

NASA Astrophysics Data System (ADS)

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).

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

2004-03-01

262

Optical responses of alkali-halide matrix (NaCl)-doped silver  

Microsoft Academic Search

In this work, we investigated the optical properties and the evolution of AgCl semiconductor aggregates dispersed in an ionic crystalline matrix, NaCl. These aggregates were obtained by doping the NaCl matrix with a silver powder (Ag). Microcrystals of AgCl of various sizes were consequently obtained with a mean size of 30A?. A thermal annealing, whose principal effect is the variation

Madani Samah; Hocine Khelfane; Madjid Bouguerra; Abdelhamid Chergui; Mohamed Akli Belkhir; Sofiane Mahtout

2004-01-01

263

An overlap model for exchange-induction: application to alkali halides  

Microsoft Academic Search

An existing method for estimating intermolecular exchange energies in weak Van der Waals interactions, based on the overlap between their ground-state charge densities, is extended to ionic interactions using the overlap between the polarised charge density of a negative ion and the ground-state charge density of surrounding positive ions. This enables the exchange-induction energy to be included in the model.

Richard J. Wheatley

1998-01-01

264

Branching transport model of sodium iodide(thalium) alkali-halide scintillator  

NASA Astrophysics Data System (ADS)

The experimental data presented in this study demonstrate that the light pulses of NaI(Tl) scintillator consist of two dominant nonexponential light components with strong temperature redistribution. The measured time-dependence, at different temperatures, shows that the amplitude ratio of these two components has Arrhenius temperature dependence. The slow component occupies up to 40% of the total light at -20°C. The nonlinear rate equations model, presented in this work, shows that the temperature-dependent behavior of the NaI(Tl) scintillators is based on two dominant transport pathways for reaching the Tl activator levels in the scintillator. The two effective components correspond to these two pathways. The first of them is the hopping transport of Self-Trapped Excitons (STEs) to the Tl activator sites, and the second is multiphonon-assisted dissociation of the STEs followed by the binary diffusion of separated holes and electrons to the Tl sites. The experimental data presented, show a linear dependence of the total light output over a wide temperature range. These experimental results, obtained by a recently patented method and device, confirmed that the nonlinear temperature behavior, observed in the past, is an artificial effect of the commonly used shaping electronics. The temperature nonlinearity arises because of a convolution between the temperature-dependent redistribution between the fast and slow channels of the light output, and the pulse response of the shaping circuitry. The temperature dependence of the nonlinear rate equations led to a prediction that the nonproportionality of the NaI(Tl) light output is also temperature and shaper dependent. In this study, the presented experimental data show the existence of a measurable dependency of the nonproportionality from temperature and shaping. In the dissertation, experimental data are presented from a study of temperature stability of a state-of-the-art monitoring systems based on NaI(Tl) detectors used in uranium enrichment monitoring. A custom-designed detector preamplifier that stabilizes the shape of the light pulses from the detector, over the working temperature range, is presented.

Alexandrov, Boian S.

265

On the Question of Spinodal Decomposition in Alkali Halide Mixed Crystals.  

National Technical Information Service (NTIS)

In the solid-solution system NaCl-KCl there is a mismatch of the lattice parameters of the end members of greater than 10%. The strain energy which is generated by this mismatch depresses the maximum spinodal temperature to well below ambient temperature....

C. Jantzen H. Herman

1973-01-01

266

Differential Calorimeter and Temperature Controller for Stored Energy Measurements in Irradiated Alkali halides.  

National Technical Information Service (NTIS)

The design and performance of a simple temperature-controlled differential calorimeter are presented. This system measures radiation-induced stored energy in insulators, above room temperature with a differential thermal analysis method. With platelets of...

L. Delgado Martinez

1977-01-01

267

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

Microsoft Academic Search

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

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

2004-01-01

268

Theory of negative-ion conversion of neutral atoms in grazing scattering from alkali halide surfaces  

NASA Astrophysics Data System (ADS)

The theoretical approach proposed by Borisov et al. [Phys. Rev. Lett. 77, 1893 (1996)] to treat negative-ion conversion of neutral atoms at ionic crystal surfaces is described in detail. Due to the localization of the valence-band electrons at the anionic sites of the crystal, the conversion process is viewed as a result of successive binary collisions between the projectile and the negatively charged sites at the surface. Parameter-free calculations of F- formation in grazing scattering from LiF(100) and KI(100) are performed using a model in which all sites of the crystal lattice but one, the active site, are represented by eventually polarizable point charges. Parallel velocity thresholds for negative-ion formation, relative efficiency of the negative-ion formation for LiF and KI crystals, and dependences of this efficiency on the scattering angle correspond well to the experimental results.

Borisov, A. G.; Sidis, V.

1997-10-01

269

Building foundations for molecular electronics: Growth of organic molecules on alkali halides as prototypical insulating substrates  

NASA Astrophysics Data System (ADS)

The epitaxy and growth of a series of organic molecules deposited on insulating surfaces were investigated by noncontact atomic force microscopy (nc-AFM). The molecules studied, C60, 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), 3,4,9,10-perylene tetracarboxlylic diimide (PTCDI), and copper (II) phthalocyanine (CuPc), were selected to investigate the effect of different molecular geometries, charge distributions and intermolecular interactions and as interesting candidates in molecular electronic applications. As it is known that the properties of molecules are influenced by their structural arrangements, an understanding of the interactions of molecules with substrates of interest as well as the dominant processes involved in growth are of great interest. Model insulating substrates KBr and NaCl were used for growth studies, due to the necessity of insulators in electrically isolating device regions. Dewetting processes were observed in several of these systems: C 60 on KBr and NaCl, PTCDA on NaCl and PTCDI on NaCl. The specific influences of de- wetting are discussed for each system, in particular the morphological impact of dewetting and the driving of dewetting by strained metastable monolayers. For C60 deposits, interesting branched structures are formed in the process of dewetting which are remarkably stable once formed, yet do not represent the equilibrium growth morphology. A determination of the large cell coincident epitaxy reveals a small, yet significant discrepancy between the observed overlayer and calculated stable adsorption sites indicating a dominance of the intermolecular interaction over the molecule---substrate interaction. For both PTCDA and PTCDI on NaCl, strained metastable monolayer epitaxies were observed giving rise to a transition in both interface structure and morphology: a dewetting transition. A comparison of the observed molecular scale structures and growth modalities is made in order to build a framework for understanding the prevalence of dewetting for molecules on ionic surfaces. Finally, in order to better understand the connection between molecular scale structures and interesting opto-electronic properties, the application of a hybrid-electrostatic characterization technique by nc-AFM is discussed. Using this technique, the opto-electrostatic response of three different PTCDA arrangements on a nanotemplated NaCl surface are shown to differ according to the degree of intermolecular interaction permitted by the structure.

Burke, Sarah A.

270

Holding onto electrons in alkali metal halide clusters: decreasing polarizability with increasing coordination.  

PubMed

The connection between the electronic polarizability and the decrease of the system size from macroscopic solid to nanoscale clusters has been addressed in a combined experimental and model-calculation study. A beam of free neutral potassium chloride clusters has been probed using synchrotron-radiation-based photoelectron spectroscopy. The introduction of "effective" polarizability for chlorine, lower than that in molecules and dimers and decreasing with increasing coordination, has allowed us to significantly improve the agreement between the experimental electron binding energies and the electrostatic model predictions. Using the calculated site-specific binding energies, we have been able to assign the spectral details of the cluster response to the ionizing X-ray radiation, and to explain its change with cluster size. From our assignments we find that the higher-coordination face-atom responses in the K 3p spectra increase significantly with increasing cluster size relative to that of the edge atoms. The reasons behind the decrease of polarizability predicted earlier by ab initio calculations are discussed in terms of the limited mobility of the electron clouds caused by the interaction with the neighboring ions. PMID:23157589

Zhang, Chaofan; Andersson, Tomas; Svensson, Svante; Björneholm, Olle; Huttula, Marko; Mikkelä, Mikko-Heikki; Anin, Dmitri; Tchaplyguine, Maxim; Öhrwall, Gunnar

2012-11-28

271

A study of ion-photon emission in alkali-halide crystals  

Microsoft Academic Search

Optical emission under bombardment of the NaCl, NaI, CsCl, and CsI crystals by Ar+ ions with an energy of 25 keV was studied, and the emission quantum yield of the sputtered alkaline-metal atoms is found to be higher for chlorides than for iodides. At the same time, the crystal luminescence reveals an inverse dependence. The assumption is made that population

T. S. Kiyan; Yu. E. Logachev

1994-01-01

272

Excited states of F centres in alkali halides resonant with the conduction band  

NASA Astrophysics Data System (ADS)

With magnetic circular dichroism of the optical absorption (MCDA) and MCDA-detected electron paramagnetic resonance (MCDA-EPR) it is possible to unambiguously identify the higher absorption bands (L1-L3) of F centres. In CsBr, similarly as found earlier for example KCI, there are several transitions beyond the K band to states resonant in the conduction band up to about 1.5 eV. It is observed that the peak-to-peak separation of the MCDA increases with increasing transition energy indicating the dominant role played by lifetime effects additionally to the spin-orbit coupling in the resonance states. In RbBr similar bands and features have been observed. However, the phase of the derivative-like MCDA-L band structures is opposite to that in CsBr. A preliminary theoretical approach to explain the resonance states is presented.

Assmann, S.; Schweizer, S.; Overhof, H.; Spaeth, J. M.

273

Optical properties of ? hole centres in alkali halides: II. MS-X? calculations  

NASA Astrophysics Data System (ADS)

0953-8984/10/29/008/img9 calculations at different values of the metal-ligand distance, R, have been performed for 0953-8984/10/29/008/img10 units (0953-8984/10/29/008/img11, Br, I) subjected to the electrostatic potential of KX lattices. The results confirm that the optical absorption bands peaked at 3.4 and 4.2 eV in KCl:0953-8984/10/29/008/img12 can be associated with the 0953-8984/10/29/008/img13 and 0953-8984/10/29/008/img14 charge transfer (CT) transitions respectively of the 0953-8984/10/29/008/img15 complex. Also, the systematic red shift experienced by such transitions on passing from KX to RbX is related to the increase of R induced by the host lattice change. The spin-orbit coupling in 0953-8984/10/29/008/img16 and 0953-8984/10/29/008/img17 levels determines the sign of the magnetic circular dichroism of the optical absorption (MCDA) and it is shown that for bromides and iodides the two CT transitions can exhibit a different pattern as is experimentally observed. Also the non-existence of MCDA signal in the 0953-8984/10/29/008/img14 region of KCl:0953-8984/10/29/008/img12 is related to a practically zero value of the spin-orbit splitting. The existence of five CT peaks for iodides is explained through the 0953-8984/10/29/008/img20 component of the 0953-8984/10/29/008/img21 CT transition, whose oscillator strength increases following the ligand spin-orbit coefficient. As 0953-8984/10/29/008/img22 is always found to be located about 0.15 eV below 0953-8984/10/29/008/img16, this new component can also explain the asymmetry observed in the MCDA spectra of chlorides and bromides in the high energy side of the 0953-8984/10/29/008/img13 transition. In all these 0953-8984/10/29/008/img10 units, the unpaired electron is found to be located mainly on the X ligands, the charge on them increasing along the 0953-8984/10/29/008/img26 series. This is related to the corresponding decrease of the hyperfine constant for whose core polarization effects are calculated to be negligible. From the present results, the equilibrium 0953-8984/10/29/008/img27 distance would be close to 2.80 Å thus implying a 10% inwards relaxation with respect to the host lattice. To our knowledge these are the first calculations reported on heavy 0953-8984/10/29/008/img28 impurities.

Cabria, I.; Moreno, M.; Aramburu, J. A.; Barriuso, M. T.; Rogulis, U.; Spaeth, J.-M.

1998-07-01

274

Local and gap modes due to a substitutional impurity in alkali halides: One dimensional treatment  

Microsoft Academic Search

Local modes for substitutional impurity H in NaCl, NaBr and KCl have been calculated. Isotope shift for 35Cl and 37Cl substituted in KI has also been calculated. Good agreement with the experimental data has been obtained.

Shashi Bala; A. K. Ghatak; D. P. S. Malik

1972-01-01

275

Thermoluminescent dosimetric characteristics of irradiated ternary alkali halides doped with lanthanum  

NASA Astrophysics Data System (ADS)

In the present study thermoluminesce properties of Lanthanum doped KCl0.2NaClxNaBr0.8-x ternary crystals with ? - irradiation has been carried out. The crystals were grown by slow evaporation and doped with rare earth Lanthanum ion. The grown crystals were irradiated with ? - radiation for dosages of 25 kGy, 50 kGy and 100 kGy. The results show that TL intensity as well as the peak position of the glow curves change with time of exposure. In few compositions, there is no change in intensity with time whereas; in few other compositions there is a small fading of intensity with time. Study reveals that these crystals have high capacity to store optical energy.

Maruthi, G.; Chandramani, R.

2013-02-01

276

Alkali Halide Opacity in Brown Dwarf and Cool Stellar Atmospheres: A Study of Lithium Chloride  

NASA Astrophysics Data System (ADS)

Recent thermochemical equilibrium calculations have revealed the important role played by lithium chloride in the lithium chemistry of cool dwarf atmospheres (K. Lodders 1999, ApJ 519, 793). Indeed, LiCl appears to be the dominant Li-bearing gas over an extended domain of the (P,T) diagram, typically for temperatures below 1500 K. LiCl has a large dipole moment in its ground electronic state which can give rise to intense rovibrational line spectra. In addition, LiCl can make dipole transitions to several low-lying unbound excited states, causing dissociation of the molecule. For these reasons, LiCl may be a significant source of line and continuum opacity in brown dwarf and cool stellar atmospheres. In this work, we report calculations of complete lists of line oscillator strengths and photodissociation cross sections for the low-lying electronic states of LiCl. We have performed single- and double-excitation configuration interaction calculations using the ALCHEMY ab initio package (Mc Lean et al. 1991, MOTECC 91, Elsevier, Leiden) and obtained the potential curves and the corresponding dipole transition moment functions between the X 1? ^+ ground state and the B 1? ^+ and A 1? excited states. The resulting line oscillator strengths and molecular photodissociation cross sections have been included in the PHOENIX stellar atmosphere code (Hauschildt & Baron 1999, J. Comput. App. Math. 102, 41). The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state (EOS). This work was supported in part by NSF grants AST-9720704 and AST-0086246, NASA grants NAG5-8425, NAG5-9222, and NAG5-10551 as well as NASA/JPL grant 961582.

Kirby, K.; Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt, P. H.

2003-12-01

277

Growth and hardening of alkali halides for use in infrared laser windows  

NASA Astrophysics Data System (ADS)

KCl crystals pulled from pretreated melts under an Ti gettered inert atmosphere have been shown to have as low an absorption as crystals grown by the RAP Bridgman method. A simple optical method has been developed to analyze KCl:Eu for Eu content. Radiation damage significantly increases the 10.6 micrometers absorption of both KCl and NaCl. The absorption increase is caused by the F-aggregate centers. This result probably rules out the use of radiation strengthened KCl for high power laser window applications. The flow stress of KCl:Eu was found to increase linearly with Eu content. The flow stresses of KBr(x)Cl(1-x) crystals have the same temperature dependence as the flow stress of pure KCl.

Martin, J. J.; Butler, C. T.; Sibley, W. A.

1975-07-01

278

Optical responses of alkali-halide matrix (NaCl)-doped silver  

NASA Astrophysics Data System (ADS)

In this work, we investigated the optical properties and the evolution of AgCl semiconductor aggregates dispersed in an ionic crystalline matrix, NaCl. These aggregates were obtained by doping the NaCl matrix with a silver powder (Ag). Microcrystals of AgCl of various sizes were consequently obtained with a mean size of 30Å. A thermal annealing, whose principal effect is the variation of crystallite sizes, was then carried out. The study was undertaken in a systematic way by PL, CL measurements and X-ray diffraction (XRD). PL spectrum exhibits a response leading to the formation of AgCl aggregates within NaCl host confirmed by DRX patterns. Also photoluminescence showed the presence of the silver chloride aggregates and their photosensitivity was revealed by the formation of silver clusters.

Samah, Madani; Khelfane, Hocine; Bouguerra, Madjid; Chergui, Abdelhamid; Akli Belkhir, Mohamed; Mahtout, Sofiane

2004-06-01

279

Casting of halide and fluoride alloys for laser windows. Semiannual technical report No. 1  

SciTech Connect

The problem of residual strain in castings of alkali halides (KCl and SrCl/sub 2/-doped KCl) and alkaline earth fluorides (CaF/sub 2/) has been overcome by the development of proper annealing and slow cooling procedures. Large castings (5/sup 1///sub 2/ in. dia) of CaF/sub 2/ and small castings (3 in. dia) of SrF/sub 2/ have been produced with low optical absorption coefficients at 5.25 ..mu..m. High quality CaF/sub 2/ castings have been obtained by using as starting material either high purity single crystal chips or ''reagent'' grade powder that has been subjected to reactive atmosphere processing (RAP) in teflon vapors.

Newberg, R.T.; Pappis, J.

1974-10-15

280

GaAs photocathode cleaning by atomic hydrogen from a plasma source  

Microsoft Academic Search

A clean GaAs surface is required in order to fabricate negative-electron-affinity photocathodes. Surface preparation is routinely performed by chemical cleaning and heating in ultra-high vacuum. These processes could damage the surface and produce photocathodes with low quantum efficiencies. Here an alternative technique which overcomes these problems, namely chemical cleaning and heating in ultra-high vacuum, is used. A helical resonator discharge

K. A. Elamrawi; H. E. Elsayed-Ali

1999-01-01

281

High-surface-area microporous carbon as the efficient photocathode of dye-sensitized solar cells  

Microsoft Academic Search

This paper reports on the application of cornstalks-derived high-surface-area microporous carbon (MC) as the efficient photocathode of dye-sensitized solar cells (DSCs). The photocathode, which contains MC active material, Vulcan XC–72 carbon black conductive agent, and TiO2 binder, was obtained by a doctor blade method. Electronic impedance spectroscopy (EIS) of the MC film uniformly coated on fluorine doped SnO2 (FTO) glass

Shengjie Peng; Fangyi Cheng; Jifu Shi; Jing Liang; Zhanliang Tao; Jun Chen

2009-01-01

282

Study of the THGEM detector with a reflective CsI photocathode  

NASA Astrophysics Data System (ADS)

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.

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

283

Progress in the production of CsI and diamond thin film photocathodes  

Microsoft Academic Search

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

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

2005-01-01

284

Halide electroadsorption on single crystal surfaces  

SciTech Connect

The structure and phase behavior of halides have been investigated on single crystals of Ag and Au using synchrotron x-ray scattering techniques. The adlayer coverages are potential dependent. For all halides studied the authors found that with increasing potential, at a critical potential, a disordered adlayer transforms into an ordered structure. Often these ordered phases are incommensurate and exhibit potential-dependent lateral separations (electrocompression). The authors have analyzed the electrocompression in terms of a model which includes lateral interactions and partial charge. A continuous compression is not observed for Br on Ag(100). Rather, they find that the adsorption is site-specific (lattice gas) in both the ordered and disordered phases. The coverage increases with increasing potential and at a critical potential the disordered phase transforms to a well-ordered commensurate structure.

Ocko, B.M. [Brookhaven National Lab., Upton, NY (United States). Dept. of Physics; Wandlowski, T. [Univ. of Ulm (Germany). Dept. of Electrochemistry

1997-07-01

285

Interaction of boron halides with carbon preparations  

SciTech Connect

The authors investigated the interaction of boron trichloride and boron tribromide vapor with hydroxyl functional groups of the surfaces of diamond and technical carbon at vapor pressures in the range 0.33-3.52 kPa and at temperatures in the range 32-200/sup 0/C. The interaction of boron halides with the surfaces of preparations of diamond and technical carbon at temperatures of 32-300/sup 0/C and pressures of 0.33-3.52 kPa goes irreversibly. The rate of adsorption of boron halides is described by a kinetic equation for a homogeneous surface. The activation energies of chemisorption and the rate constants were found.

Gavrilin, A.V.; Luk'yanov, I.M.; Smirnov, E.P.; Aleskovskii, V.B.

1987-12-10

286

Relative halide-concentration dependence of the F-centre optical absorption properties in KClxBr(1-x): Eu2+ crystals: influence of Eu2+-cation vacancy dipoles  

NASA Astrophysics Data System (ADS)

The influence of Eu2+-cation vacancy (I-V) dipoles on the relative halide-concentration dependence of the F-centre optical absorption properties in KClxBr(1-x): Eu2+ crystals has been investigated. These crystals are made of a single mixed face-centred cubic (FCC)-phase whose unit-cell size a(0) obeys the Vegard's rule, and their optical absorption spectrum consists of a single F-band whose spectral width depends on x, reaching 0.414 +/- 0.006 eV at x = 0.5, and whose spectral frequency nu(m) and equivalent energy epsilon(m) satisfy the equations nu(m)a(o) 2.24 +/- 0.09 = 26 +/- 2 and epsilon(m) ( eV) = (0.06 +/- 0.01) x(2) + (0.16 +/- 0.01) x + ( 1.98 +/- 0.01). Comparison with the F-centre optical absorption properties reported elsewhere for pure FCC alkali-halide and KClxBr(1-x) crystals showed that in KClxBr(1-x): Eu2+ crystals, the alkali and halide ion sizes drive mainly the F-band spectral position, and also that this position is more sensitive to changes in a(0) in KClxBr(1-x): Eu2+ crystals than in pure FCC alkali-halides. This is due to the crystalline electric field distortion caused locally at the F-centre by the mixed halide surroundings. This distortion affected the F-band spectral position in KClxBr(1-x): Eu2+ crystals to a lesser extent than it did in KClxBr(1-x) crystals. This might be due to the presence of I - V dipoles.

Cordero-Borboa, A. E.; Flores, C. J.; Hernandez, J. A.; Aguilar, G. S.; Murrieta, H.

2005-03-01

287

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides  

PubMed Central

Summary Iridium-catalyzed intramolecular [4 + 2] cycloadditions of diene-tethered alkynyl halides were investigated by using [IrCl(cod)]2 as catalyst, and dppe was found to be the most suitable phosphine ligand for the reaction. No oxidative insertion of the iridium into the carbon–halide bond was observed, and the reactions proceeded to provide the halogenated cycloadducts in good yield (75–94%). These results are the first examples of cycloadditions of alkynyl halides using an iridium catalyst.

Tigchelaar, Andrew

2012-01-01

288

Indium phosphide negative electron affinity photocathodes: Surface cleaning and activation  

NASA Astrophysics Data System (ADS)

InP(100) is a very important semi-conductor for many applications. When activated by Cs and oxygen, the InP surface achieves the state of Negative Electron Affinity (NEA) making the Cs+O/InP system a very efficient electron source. Despite many years of study, the chemical cleaning and activation of InP are still not well understood. In our work, we have established an understanding of the basic physics and chemistry for the chemical cleaning and activation of the InP(100) surface. Synchrotron Radiation Photoelectron Spectroscopy is the main technique used in this study because of its high surface sensitivity and ability to identify chemical species present on the surface at each stage of our process. A clean, stoichiometric InP(100) surface is crucial for obtaining high performance of NEA photocathodes. Therefore, the first part of our study focused on the chemical cleaning of InP(100). We found that hydrogen peroxide based solutions alone, originally developed to clean GaAs(100) surfaces and widely used for InP(100), do not result in clean InP(I00) surfaces because oxide is left on the surface. A second cleaning step, which uses acid solutions like HCl or H2SO4, can remove all the oxide and leave a 0.4 ML protective layer of elemental phosphorous on the surface. The elemental phosphorous can be removed by annealing at 330°C and a clean InP(100) surface can be obtained. Cs deposition on InP(100) surface shows clear charge transfer from the Cs ad-atoms to the substrate. When the Cs/InP(100) surface is dosed with oxygen, the charge transfer from the Cs to substrate is reduced and substrate is oxidized. The activation of InP as a NEA photocathode is carried out by an alternating series of steps consisting of Cs deposition and Cs+O co-deposition. Two types of oxygen are found after activation. The first is dissociated oxygen and the other is a di-oxygen species (peroxide or superoxide). The decay of quantum-yield with time and with annealing is studied and changes in both the Cs oxide and oxidation of substrate are observed, which we conclude are the causes for the decrease of the quantum yield.

Sun, Yun

289

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...

290

10 CFR 431.322 - Definitions concerning metal halide lamp ballasts and fixtures.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Definitions concerning metal halide lamp ballasts and fixtures...COMMERCIAL AND INDUSTRIAL EQUIPMENT Metal Halide Lamp Ballasts and Fixtures § 431.322 Definitions concerning metal halide lamp ballasts and fixtures....

2010-01-01

291

Progress in alkali lasers development  

NASA Astrophysics Data System (ADS)

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 continuous wave 17 W Rb laser were demonstrated. In this paper we review the main results and recent achievements in high power alkali lasers development, discuss some problems existing in this field and ways to solve them.

Zhdanov, B. V.; Knize, R. J.

2008-02-01

292

Crystallographic and Kinetic Evidence of a Collision Complex Formed during Halide Import in Haloalkane Dehalogenase  

Microsoft Academic Search

Haloalkane dehalogenase (DhlA) converts haloalkanes to their corresponding alcohols and halide ions. The rate-limiting step in the reaction of DhlA is the release of the halide ion. The kinetics of halide release have been analyzed by measuring halide binding with stopped-flow fluorescence experiments. At high halide concentrations, halide import occurs predominantly via the rapid formation of a weak initial collision

Henriëtte J. Rozeboom; Ivo S. Ridder; Mariël G. Pikkemaat; Kor H. Kalk; Bauke W. Dijkstra; Dick B. Janssen

1999-01-01

293

Surface science analysis of GaAs photocathodes following sustained electron beam delivery  

SciTech Connect

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.

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

2012-06-01

294

InGaAs/InP photocathode grown by solid-source MBE  

NASA Astrophysics Data System (ADS)

As an III-V semiconductor material, InxGa1-xAs can response from 0.87?m (GaAs) to 3.5?m (InAs) by tuning the relative amount of Gallium in the alloy. In order to get better the response of the photocathode in near infrared radiation region (1~1.7?m), InGaAs/InP heterostructure is widely used for photocathode material. The only composition of In0.53Ga0.47As is lattice matched to the InP substrate and their spectral response is from 0.9?m to 1.6?m. thus In0.53Ga0.47As/InP heterostructure is selected for near infrared response photocathode. The In0.53Ga0.47As layer has been grown on InP substrate used for photocathode by solid source molecular beam epitaxiy (SS-MBE). The photocathode samples were grown to optimize the growth temperature, III/V ratio and growth rate. The In0.53Ga0.47As layer crystalline quality and component were performed by applying high resolution X-ray diffractometer, surface roughness investigations were performed by applying atomic force microscopy. The Be doping characteristic was checked by the electrochemical capacitance-voltage?ECV?. The optical performance of the photocathode is measured by the spectral meter. The collected information is being used to correct and enhance growth characteristics and optimize InGaAs/InP photocathode structure to increase spectral response and quantum efficiency.

Jiao, Gang-cheng; Xu, Xiao-bing; Zhang, Lian-dong; Wang, Shu-fei; Peng, Cha-xia; Cheng, Wei; Hu, Cang-lu; Zhou, Yu-jian; Feng, Chi

2013-08-01

295

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

DOEpatents

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.

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

2011-12-13

296

Alkali metal sources for OLED devices  

Microsoft Academic Search

In OLED organic layers electron injection is improved by using alkali metals as cathodes, to lower work function or, as dopants of organic layer at cathode interface. The creation of an alkali metal layer can be accomplished through conventional physical vapor deposition from a heated dispenser. However alkali metals are very reactive and must be handled in inert atmosphere all

Lorena Cattaneo; Giorgio Longoni; Antonio Bonucci; Stefano Tominetti

2005-01-01

297

Advanced metal alloy systems for massive high-current photocathodes  

NASA Astrophysics Data System (ADS)

The physical principles of precise alloying are formulated with the aim of increasing the low quantum efficiency (QE) of suitable simple metals (Mg, Al, Cu) as well as of decreasing their electron work function ( e ?) in the UV spectral range. The new approach provides valuable information for elucidating the origin of photoemission enhancement in bulk metal-based alloy systems. Bulk in-situ nanoclustering promises to be the most effective way of producing a much higher QE and a lower e ? in simple metals. In this article we show that the quantum efficiency of the metal-based alloys Mg-Ba, Al-Li, and Cu-BaO is considerably higher than the simple metals Mg, Al, and Cu, respectively. The spectral characteristics of the Mg-Ba, Al-Li and Cu-BaO systems obey the well-known Fowler square law for a near-free-electron model. The advanced metal alloys systems are promising photocathode materials usable for generation of high brightness electron beams.

Tkachenko, V. G.; Kondrashev, A. I.; Maksimchuk, I. N.

2010-03-01

298

Beyond injection: Trojan horse underdense photocathode plasma wakefield acceleration  

SciTech Connect

An overview on the underlying principles of the hybrid plasma wakefield acceleration scheme dubbed 'Trojan Horse' acceleration is given. The concept is based on laser-controlled release of electrons directly into a particle-beam-driven plasma blowout, paving the way for controlled, shapeable electron bunches with ultralow emittance and ultrahigh brightness. Combining the virtues of a low-ionization-threshold underdense photocathode with the GV/m-scale electric fields of a practically dephasing-free beam-driven plasma blowout, this constitutes a 4th generation electron acceleration scheme. It is applicable as a beam brightness transformer for electron bunches from LWFA and PWFA systems alike. At FACET, the proof-of-concept experiment 'E-210: Trojan Horse Plasma Wakefield Acceleration' has recently been approved and is in preparation. At the same time, various LWFA facilities are currently considered to host experiments aiming at stabilizing and boosting the electron bunch output quality via a trojan horse afterburner stage. Since normalized emittance and brightness can be improved by many orders of magnitude, the scheme is an ideal candidate for light sources such as free-electron-lasers and those based on Thomson scattering and betatron radiation alike.

Hidding, B.; Rosenzweig, J. B.; Xi, Y.; O'Shea, B.; Andonian, G.; Schiller, D.; Barber, S.; Williams, O.; Pretzler, G.; Koenigstein, T.; Kleeschulte, F.; Hogan, M. J.; Litos, M.; Corde, S.; White, W. W.; Muggli, P.; Bruhwiler, D. L.; Lotov, K. [Institut fuer Laser- und Plasmaphysik, Heinrich-Heine-Universitaet Duesseldorf 40225 Duesseldorf (Germany) and Particle Beam Physics Laboratory, Department for Physics and Astronomy, UCLA (United States); Particle Beam Physics Laboratory, Department for Physics and Astronomy, UCLA (United States); Institut fuer Laser- und Plasmaphysik, Heinrich-Heine-Universitaet Duesseldorf 40225 Duesseldorf (Germany); Stanford Linear Accelerator Center (United States); Max-Planck-Institut fuer Physik, Muenchen (Germany); Tech-X Corporation, Boulder, Colorado (United States) and 1348 Redwood Ave., Boulder, Colorado 80304 (United States); Budker Institute of Nuclear Physics SB RAS, 630090, Novosibirsk (Russian Federation) and Novosibirsk State University, 630090, Novosibirsk (Russian Federation)

2012-12-21

299

High brightness photocathode injector for BNL Accelerator Test Facility  

SciTech Connect

An analysis of the BNL photocathode (1-1/2 cell) Gun'' operating at 2856 MHZ, is presented. The beam parameters including beam energy, and emittance are calculated. A review of the Gun parameters and full input and output of our analysis with program PARMELA, is given in Section 2, some of our results, are tabulated. The phase plots and the beam parameters, at downstream ends of the elements, from cathode through the cavity, first cell is labeled as element 2; and second cell is labeled as element to the exit of the GUN. The analysis was made for 3 cases, using three different initial values (EO) for the average accelerating gradient (MV/m), for comparison with previous works. For illustration, the field obtained with program SUPERFISH is given, and conclusion including shunt impedances obtained for the cells and the cavity are given in Section 6. PARMELA is used as a standard design program at ATF. At the request of some of the users of program PARMELA, this request of some of the users of program PARMELA, this report include and illustrates some of our data, in the input and output format of the program PARMELA. 5 refs., 7 figs., 3 tabs.

Parsa, Z.; Young, L.

1990-01-01

300

The influence of halide and pseudo-halide antioxidants in Fenton-like reaction systems containing copper(II) ions  

Microsoft Academic Search

Application of the N,N?-(5-nitro-1,3-phenylene)bisglutaramide (NPG) hydroxylation assay for spectrophotometric determination of the rate of generation of oxidizing species in systems containing copper(II) ions\\/phosphate buffer\\/H2O2 in the presence of halide and pseudo-halide antioxidants was evaluated. A satisfactory correlation was demonstrated between the kinetics of NPG hydroxylation, determined both spectrophotometrically and chromatographically.Employing the assay, efficiency of various halide and pseudo-halide antioxidants was

Jasna Maleši?; Matija Strli?; Jana Kolar; Slovenko Polanc

2005-01-01

301

Lifetime test of photoemission from Cs3Sb photocathode coated with W or Cr film  

NASA Astrophysics Data System (ADS)

Cs3Sb photocathodes were fabricated at 8-16 °C with sandwiched layers of Sb, Cs, and Sb deposited onto the fine tips of three cathodes at 15 °C. After examining the influence of the cathode tip temperature on the changes in the quantum efficiencies of the Cs3Sb photocathodes during and after additional Cs depositions, we performed lifetime tests of the three Cs3Sb photocathodes using a 405-nm semiconductor laser and 488-nm Ar ion laser. The decrease in the photocurrent with time was more rapid with the 488-nm laser irradiation than with the 405-nm laser irradiation, and continuous laser irradiation caused a much more rapid decrease in photoelectrons with time than intermittent laser irradiation did. We deposited a 0.32-0.64-nm-thick W film or a 0.43-nm-thick Cr film onto the Cs3Sb photocathode during the lifetime test at 0.9-1.0 × 10-7 Pa. We found that the passive WO3 or Cr2O3 film, which was formed at a reduced vacuum level of 1.6 × 10-7 Pa or during the continuous 405-nm laser irradiation, increased the lifetime of the Cs3Sb photocathode by effectively protecting its surface against oxidation and evaporation of Cs. This protection effect was most effective at approximately 90 °C.

Kimoto, Takayoshi; Arai, Yoshihiro; Ren, Xiaobing

2013-11-01

302

Design of quantum efficiency measurement system for variable doping GaAs photocathode  

NASA Astrophysics Data System (ADS)

To achieve high quantum efficiency and good stability has been a main direction to develop GaAs photocathode recently. Through early research, we proved that variable doping structure is executable and practical, and has great potential. In order to optimize variable doping GaAs photocathode preparation techniques and study the variable doping theory deeply, a real-time quantum efficiency measurement system for GaAs Photocathode has been designed. The system uses FPGA (Field-programmable gate array) device, and high speed A/D converter to design a high signal noise ratio and high speed data acquisition card. ARM (Advanced RISC Machines) core processor s3c2410 and real-time embedded system are used to obtain and show measurement results. The measurement precision of photocurrent could reach 1nA, and measurement range of spectral response curve is within 400~1000nm. GaAs photocathode preparation process can be real-time monitored by using this system. This system could easily be added other functions to show the physic variation of photocathode during the preparation process more roundly in the future.

Chen, Liang; Yang, Kai; Liu, HongLin; Chang, Benkang

2008-03-01

303

Vibrational Spectroscopy of Sodium Halide and Hydrogen Halide Aqueous Solutions: Application to Atmospheric Aerosol Chemistry  

Microsoft Academic Search

Heterogeneous reactions on the surfaces of atmospheric aerosols play an important role in atmospheric chemistry. These reactions are capable of converting alkyl and hydrogen halides (common constituents of marine boundary aerosols) into active halogen compounds. Fundamental questions still remain concerning surface species and reaction mechanisms pertaining to marine boundary aerosols. The first step in beginning to understand these heterogeneous reactions

L. M. Levering; D. Liu; H. C. Allen

2003-01-01

304

Synthesis of lithium cobaltate in halide melts  

NASA Astrophysics Data System (ADS)

A new method for the synthesis of lithium cobaltate LiCoo2 in salt melts is proposed and tested. The method is based on the oxidation of halide ions with molecular oxygen in Li X-CoCl2 mixtures ( X = Cl, Br, I). The chemical and phase compositions of the prepared powders and the crystal structure of the synthesized compound are studied by Fourier transform infrared spectroscopy and X-ray diffraction analysis. The average size of LiCoO2 crystallites is estimated from the X-ray diffraction data.

Modenov, D. V.; Dokutovich, V. N.; Khokhlov, V. A.; Antonov, B. D.; Kochedykov, V. A.; Zakir'yanova, I. D.

2013-02-01

305

Photoemission characteristics of (Cs, O) activation exponential-doping Ga0.37Al0.63As photocathodes  

NASA Astrophysics Data System (ADS)

Based on the studies of the GaAs photocathode, the surface model of the Ga0.37Al0.63As photocathode is investigated and the energy distributions of electrons reaching the surface charge region, reaching the surface and emitting into vacuum are calculated. The (Cs, O) adsorption and photoemission characteristics of the Ga0.37Al0.63As photocathode are studied according to the experiments. We use the quantum efficiency formula to fit the experimental curve, and obtain the performance parameters of the photocathode and the surface barrier parameters. The results show that the surface barrier of the Ga0.37Al0.63As photocathode is similar to that of the GaAs photocathode. The prepared reflection-mode Ga0.37Al0.63As photocathode responds to the blue-green light, while the transmission-mode Ga0.37Al0.63As photocathode is sensitive to the 532 nm light.

Chen, Xinlong; Zhao, Jing; Chang, Benkang; Yu, Xiaohua; Hao, Guanghui; Xu, Yuan; Cheng, Hongchang

2013-06-01

306

Development of a high-sensitivity UV photocathode using GaN film that works in transmission mode  

NASA Astrophysics Data System (ADS)

We developed a high-sensitivity GaN photocathode that works in transmission mode. It has 40.9 % quantum efficiency at 310 nm wavelength. Conventional GaN photocathodes, both transmission mode and reflection mode, are made on a sapphire substrate using metal-organic vapor phase epitaxy (MOVPE). In reflection mode, a GaN photocathode has very high quantum efficiency (QE) of over 50 %. However, in transmission mode, the quantum efficiency of a GaN photocathode was about 25 % at 240 nm with this technique. Therefore, we developed a new GaN photocathode using a glass-bonding technique, where a GaN thin film was bonded to a glass face plate. We found out that constituting an Al- GaN layer on the light incidence side of the photocathode surface provided higher QE than a sole GaN layer type for transmission mode. We focused on the band bending of the photocathode, and analyzed QE for both transmission mode and reflection mode. We then verified the effectiveness of the AlGaN layer using the results from the analysis. The high-sensitivity UV photocathode will be used for flame detection, corona discharge observation, and other UV imaging.

Ishigami, Yoshihiro; Akiyama, Keisuke; Nagata, Takaaki; Kato, Kazumasa; Ihara, Tsuneo; Nakamura, Kimitsugu; Mizuno, Itaru; Matsuo, Tetsuji; Chino, Emiko; Kyushima, Hiroyuki

2012-05-01

307

Higher quantum efficiency GaAs photocathode material with exponential-doping structure  

NASA Astrophysics Data System (ADS)

To improve the performance of GaAs NEA photocathodes, an exponential-doping structure GaAs material has been put forward, in which from the GaAs bulk-to-surface doping concentration is distributed exponentially from high to low. We apply this exponential-doping GaAs structure to the transmission-mode GaAs photocathodes. This sample was grown on the high quality p-type Be-doped GaAs (100) substrate by MBE. We have calculated the band-bending energy in exponential-doping GaAs emission-layer, and the total band-bending energy is 59 meV which helps to improve the photoexcited electrons movement towards surface for the thin epilayer. The integrated sensitivity of the exponential-doping GaAs photocathode samples reaches 1547uA/lm.

Chen, Huailin; Yang, Wenzheng; Tang, Weidong; Fu, Xiaoqian; Du, Yujie; Zhang, Junju

308

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

SciTech Connect

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.

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

2008-05-28

309

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

NASA Astrophysics Data System (ADS)

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.

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

2012-09-01

310

Quantum efficiency of technical metal photocathodes under laser irradiation of various wavelengths  

NASA Astrophysics Data System (ADS)

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

Le Pimpec, F.; Milne, C. J.; Hauri, C. P.; Ardana-Lamas, F.

2013-09-01

311

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

SciTech Connect

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.

Ho, C. H.

1998-07-16

312

Alkali metal/sulfur battery  

DOEpatents

Alkali metal/sulfur batteries in which the electrolyte-separator is a relatively fragile membrane are improved by providing means for separating the molten sulfur/sulfide catholyte from contact with the membrane prior to cooling the cell to temperatures at which the catholyte will solidify. If the catholyte is permitted to solidify while in contact with the membrane, the latter may be damaged. The improvement permits such batteries to be prefilled with catholyte and shipped, at ordinary temperatures.

Anand, Joginder N. (Clayton, CA)

1978-01-01

313

A compact optical flow cell for use in aqueous halide determination  

Microsoft Academic Search

A compact optical flow cell for use in aqueous halide determination has been developed. The performance of the cell and optical set-up has been tested by studying the halide quenching of fluorescence from thin polymeric films containing a halide-sensitive fluorophore. Aqueous halide is injected into the flow cell and the quenched fluorescence emission observed orthogonal to the plane of excitation

Chris D Geddes; Peter Douglas; Christopher P Moore; Trevor J Wear; Peter L Egerton

1999-01-01

314

DESIGN NOTE: A compact optical flow cell for use in aqueous halide determination  

Microsoft Academic Search

A compact optical flow cell for use in aqueous halide determination has been developed. The performance of the cell and optical set-up has been tested by studying the halide quenching of fluorescence from thin polymeric films containing a halide-sensitive fluorophore. Aqueous halide is injected into the flow cell and the quenched fluorescence emission observed orthogonal to the plane of excitation

Chris D. Geddes; Peter Douglas; Christopher P. Moore; Trevor J. Wear; Peter L. Egerton

1999-01-01

315

Diode pumped alkali vapor fiber laser  

Microsoft Academic Search

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

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

2007-01-01

316

Diode pumped alkali vapor fiber laser  

Microsoft Academic Search

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

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

2006-01-01

317

Regenerable activated bauxite adsorbent alkali monitor probe  

DOEpatents

This invention relates to a regenerable activated bauxite adsorber alkali monitor probe for field applications to provide reliable measurement of alkali-vapor 5 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 10 exhaust gases.

Lee, S.H.D.

1991-01-22

318

Straightforward synthesis of thiazoline-incorporated chalconoids from phenacyl halides.  

PubMed

A series of thiazoline-incorporated chalconoids, designed based on natural product scaffold, were efficiently synthesized via the reaction of 3-methyl-4-arylthiazole-2(3H)-thiones and appropriate phenacyl halides, and subsequent desulfurization. The starting 3-methyl-4- arylthiazole-2(3H)-thiones were also prepared from phenacyl halides. The structural aspects and (Z)-geometry of compounds were confirmed by IR and (1)H NMR spectral data. This chemistry provides a new library of compounds basically originated from phenacyl halides as building blocks, with potential activity for biomedical screening. PMID:23314739

Ayati, Adile; Emami, Saeed

2013-01-12

319

Palladium-catalyzed amination of aryl halides on solid support.  

PubMed

[reaction: see text] The first examples of the Pd(0)-catalyzed amination of aryl halides using Rink-resins as nitrogen source are described. Pd(2)dba(3)/BINAP/NaO-t-Bu was found to be the most efficient catalyst/base system, while a solvent mixture of dioxane and tert-butyl alcohol was shown to enhance the selectivity toward the desired monoarylation. Moderate to good yields and excellent purities of the amination products were found with electron-poor aryl halides, while electon-rich aryl halides failed to react under these conditions. PMID:12489962

Weigand, Klaus; Pelka, Sylvie

2002-12-26

320

Transfer of atomic alignment in alkali systems  

NASA Astrophysics Data System (ADS)

The well-known phenomenon of ``spin exchange'' has been thoroughly characterized in alkali-alkali collisions, and atomic orientation is easily transferred between different alkali isotopes. Nevertheless, collisional transfer of higher-order polarization moments (such as atomic alignment) has received little attention in the literature. Such alignment transfer should be forbidden in sudden binary collisions of alkali atoms, but it is reasonable to question at what level. Here we discuss recent experiments to place limits on this alignment-exchange rate between isotopes of rubidium and cesium in a room-temperature vapor cell.

Patton, B.; Neitzke, O.; Rochester, S.; Bahr, E.; Guttikonda, S.; Kimball, D. F. Jackson; Coste, B.; Novikova, I.; Budker, D.

2012-06-01

321

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

SciTech Connect

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.

Not Available

2012-01-01

322

Photocathodic behavior of ferroelectric Pb(Zr,Ti)O(3) films decorated with silver nanoparticles.  

PubMed

ITO/Pb(Zr,Ti)O(3) contacts and Ag nanoparticles were used to construct a novel ferroelectric film photocathode exhibiting a stable short-circuit photocurrent of 110 ?A cm(-2) and an open-circuit voltage of 0.76 V under 100 mW cm(-2) Xe-lamp illumination and zero-bias versus SCE. PMID:23535610

Wang, Chunyan; Cao, Dawei; Zheng, Fengang; Dong, Wen; Fang, Liang; Su, Xiaodong; Shen, Mingrong

2013-03-28

323

Simulation study of sub-femtosecond electron bunch generation using photocathode RF gun linac  

Microsoft Academic Search

Pulse radiolysis, a stroboscopic method involving the use of an ultrashort electron bunch and ultrashort light, is essential for the observation of ultrafast reactions. The time resolution of pulse radiolysis depends on the electron bunch length. At Osaka University, a 98-fs electron bunch was generated using a photocathode RF gun linac for the development of femtosecond pulse radiolysis. In order

K. Kan; J. Yang; T. Kondoh; K. Norizawa; A. Ogata; T. Kozawa; Y. Yoshida

2010-01-01

324

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

Microsoft Academic Search

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

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

2003-01-01

325

Single-side electron multipacting at the photocathode in rf guns  

Microsoft Academic Search

Multiple electron impacting (multipacting) can take place in rf fields when the rf components are composed of materials with a secondary electron yield greater than one. In rf gun cavities, multipacting may change the properties of the vacuum components or even damage them. First systematic measurements of the multipacting occurring in a photocathode rf gun were made at the Fermilab\\/NICADD

Jang-Hui Han; Klaus Flöttmann; Walter Hartung

2008-01-01

326

Test of the photocathode cooling system of the 3 1 2 cell SRF gun  

Microsoft Academic Search

This paper presents results of the photocathode cooling system test of the 312 cell SRF gun at the Forschungszentrum Rossendorf. The SRF gun will produce short electron pulses with high bunch charges and low transverse emittance. The requirement for the superconducting electron linear accelerator in Rossendorf (ELBE) is to provide a low emittance electron beam up to 1mA current and

F. Staufenbiel; H. Bttig; P. Evtushenko; D. Janssen; U. Lehnert; P. Michel; K. Möller; Ch. Schneider; R. Schurig; J. Teichert; R. Xiang; J. Stephan; W.-D. Lehmann; T. Kamps; D. Lipka; I. Will; V. Volkov

2006-01-01

327

Operation principles and properties of the multi-GEM gaseous photomultiplier with reflective photocathode  

Microsoft Academic Search

Gas Electron Multipliers with a reflective photocathode deposited on the surface of the first multiplying element are very attractive devices for photon detection and imaging over large area at moderate cost. They combine production and operation simplicity, high sensitivity to single photons, fast time response and accurate localization. In this work we present in detail the mechanisms governing the operation

D. Mörmann; A. Breskin; R. Chechik; C. Shalem

2004-01-01

328

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

Microsoft Academic Search

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

H Hoedlmoser; Christian Wolfgang Fabjan; E Schyns

2005-01-01

329

Variable doping narrow-band response GaAlAs photocathode the preparation method of the research  

NASA Astrophysics Data System (ADS)

In order to avoid the low sensitivity common problem of 532nm sensitive narrow-band response photocathode, variable doping narrow-band response GaAlAs photocathode structure is designed. The photocathode is composed of GaAs substrates, Ga1-x1Alx1As buffer layer, Ga1-x2Alx2As doping concentration gradient emissive layer and GaAs protection layer from bottom to top. Among them, exponential doping method is applied to Ga1-x2Alx2As unit layer from the bottom to the top. And a preparation methods of GaAlAs photocathode is developed. For the GaAlAs photocathode components which grow well, chemical cleaning, heating purification and (Cs, O) activation are operated, and ultimately Cs / O activation layer is formed on the surface of Ga1-x2Alx2As doping concentration gradient emissive layer. The highest sensitivity of the photocathode peak response is at 532nm, and the photocathode quantum efficiency in 532nm peaks at 36%.

Xu, Yuan; Chen, XinLong; Zhao, Jing; Wang, Honggang; Chang, BenKang

2012-11-01

330

Defects in the silver halide photographic process  

NASA Astrophysics Data System (ADS)

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.

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

331

Tellurium halide IR fibers for remote spectroscopy  

NASA Astrophysics Data System (ADS)

The new family of IR transmitting glasses, the TeX glasses, based on the association of tellurium and halide (Cl, Br, or I) are characterized by a wide optical window extending from 2 to 18 micrometers and a strong stability towards devitrification. Optical fibers drawn from these glasses exhibit low losses in the 7 - 10 micrometers range (less than 1 dB/m for single index fibers, 1 - 2 dB/m for fibers having a core-clad structure). The TeX glass fibers have been used in a remote analysis set-up which is mainly composed of a FTIR spectrometer coupled with a HgCdTe detector. This prototype system permits qualitative and quantitative analysis in a wide wavelength region lying from 3 to 13 micrometers , covering the fundamental absorption of more organic species. The evolution of a lactic and an alcoholic fermentation has been monitored by means of this set-up.

Zhang, Xhang H.; Ma, Hong-Li; Blanchetiere, Chantal; Le Foulgoc, K.; Lucas, Jacques; Heuze, Jean; Colardelle, P.; Froissard, P.; Picque, D.; Corrieu, G.

1994-07-01

332

40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.  

Code of Federal Regulations, 2013 CFR

...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...

2013-07-01

333

40 CFR 721.1878 - Alkali metal alkyl borohydride (generic).  

Code of Federal Regulations, 2013 CFR

...2013-07-01 2013-07-01 false Alkali metal alkyl borohydride (generic). 721...Chemical Substances § 721.1878 Alkali metal alkyl borohydride (generic). (a...substance identified generically as alkali metal alkyl borohydride (PMN...

2013-07-01

334

40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.  

Code of Federal Regulations, 2010 CFR

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

2010-07-01

335

40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.  

Code of Federal Regulations, 2013 CFR

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

2013-07-01

336

40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.  

Code of Federal Regulations, 2010 CFR

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

2009-07-01

337

Development status of High-QE HPDs with 18-mm GaAsP photocathode for IACTs  

NASA Astrophysics Data System (ADS)

A new type of Hybrid PhotoDetectors (HPDs) with an 18-mm-diameter GaAsP photocathode was developed in order to lower the energy threshold of the MAGIC-II Project. The Quantum Efficiency (QE) reaches more than 50% at around 500 nm and is enhanced in the UV region by the wavelength shifting technique. The total light conversion efficiency could be practically improved by about a factor 2 compared to the conventional PhotoMultiplier Tubes (PMT). Photocathode ageing measurements indicate that GaAsP photocathode have a sufficiently long lifetime for being used in the MAGIC telescope imaging camera.

Hayashida, M.; Ninkovic, J.; Hose, J.; Hsu, C. C.; Mirzoyan, R.; Teshima, M.

2007-03-01

338

Palladium-catalyzed carboxylative coupling of allylstannanes and allyl halides  

SciTech Connect

A three-component carboxylative coupling between allyl halides, allylstannanes, and CO{sub 2} to produce allyl esters is catalyzed by Pd and Pt phosphine complexes. Tentative mechanistic pathways for the catalytic reaction are proposed.

Franks, R.J.; Nicholas, K.M.

2000-04-17

339

Halide compound mass spectrometry method and mass spectrometry apparatus  

US Patent & Trademark Office Database

A mass spectrometry apparatus is provided with an emitter for emitting metal ions, a reaction chamber where the detected gas is introduced and ionized by the metal ions, an aperture for guiding molecules of the ionized detected gas, and a mass spectrometer for measuring the guided molecules. The metal ions emitted from the emitter are caused to fly to the reaction chamber to ionize said detected gas. The detected gas is a halide compound. Further provision is made of a sample gas source for feeding a halide compound to the reaction chamber and an N.sub.2 gas source for feeding to the reaction chamber a gas (N.sub.2 etc.) to which the metal ions attach less easily than to the halide compound. It is therefore made possible to apply cation attachment of the Fujii system to mass spectrometry of a halide compound and enable precise measurement of fluoride compounds etc. having a large impact on global warming.

2003-01-14

340

Crystallographic and fluorescence studies of the interaction of haloalkane dehalogenase with halide ions. Studies with halide compounds reveal a halide binding site in the active site.  

PubMed

Haloalkane dehalogenase from Xanthobacter autotrophicus GJ10 catalyzes the conversion of 1,2-dichloroethane to 2-chloroethanol and chloride without use of oxygen or cofactors. The active site is situated in an internal cavity, which is accessible from the solvent, even in the crystal. Crystal structures of the dehalogenase enzyme complexed with iodoacetamide, chloroacetamide, iodide, and chloride at pH 6.2 and 8.2 revealed a halide binding site between the ring NH's of two tryptophan residues, Trp-125 and Trp-175, located in the active site. The halide ion lies on the intersection of the planes of the rings of the tryptophans. The binding of iodide and chloride to haloalkane dehalogenase caused a strong decrease in protein fluorescence. The decrease could be fitted to a modified form of the Stern-Volmer equation, indicating the presence of fluorophors of different accessibilities. Halide binding was much stronger at pH 6.0 than at pH 8.2. Assuming ligand binding to Trp-125 and Trp-175 as the sole cause of fluorescence quenching, dissociation constants at pH 6.0 with chloride and iodide were calculated to be 0.49 +/- 0.04 and 0.074 +/- 0.007 mM, respectively. Detailed structural investigation showed that the halide binding site probably stabilizes the halide product as well as the negatively charged transition state occurring during the formation of the covalent intermediate. PMID:8369276

Verschueren, K H; Kingma, J; Rozeboom, H J; Kalk, K H; Janssen, D B; Dijkstra, B W

1993-09-01

341

Binding and Selectivity of Halides with Macrocyclic polyamines  

PubMed Central

This review covers the binding and selectivity aspects of halide anions in positively charged polyammonium hosts including monocyclic, bicyclic and tricyclic systems. The binding affinity and selectivity of host molecules for halides are largely depended on the shape, charges, and ring size of the host molecules. In general, a monocycle that has a flexible cavity binds an anion from both side, however a bicyclic or tricyclic molecule tends to bind a single anion in its cavity.

Hossain, Md. Alamgir; Saeed, Musabbir A.

2010-01-01

342

Evaluation of the removal of aqueous halides by Octolig®  

Microsoft Academic Search

Evaluation of the removal of aqueous halides by Octolig®. C.H. McCANE and D.F. MARTIN. Institute for Environmental Studies, Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620. There are good and cogent reasons for the removal of halide ions from natural water systems. This study was concerned with evaluating the ease or possibility of removing

Cheryl H McCane; Dean F Martin

2011-01-01

343

Halide concentrations in camel plasma in various states of hydration  

Microsoft Academic Search

Instrumental epithermal neutron activation analysis was used in determining the halide concentration of camel serum. The halides\\u000a determined were sodium, chloride, bromide, and iodide. Serum was examined when the camels had free access to drinking water,\\u000a following 10 d of water restriction and 2 h following rapid rehydration. When the camels were dehydrated there was a “serum\\u000a storage” of iodide.

Z. Etzion; Z. Alfassi; N. Lavi; R. Yagil

1987-01-01

344

Synthesis of methyl halides from biomass using engineered microbes.  

PubMed

Methyl halides are used as agricultural fumigants and are precursor molecules that can be catalytically converted to chemicals and fuels. Plants and microorganisms naturally produce methyl halides, but these organisms produce very low yields or are not amenable to industrial production. A single methyl halide transferase (MHT) enzyme transfers the methyl group from the ubiquitous metabolite S-adenoyl methionine (SAM) to a halide ion. Using a synthetic metagenomic approach, we chemically synthesized all 89 putative MHT genes from plants, fungi, bacteria, and unidentified organisms present in the NCBI sequence database. The set was screened in Escherichia coli to identify the rates of CH(3)Cl, CH(3)Br, and CH(3)I production, with 56% of the library active on chloride, 85% on bromide, and 69% on iodide. Expression of the highest activity MHT and subsequent engineering in Saccharomyces cerevisiae results in productivity of 190 mg/L-h from glucose and sucrose. Using a symbiotic co-culture of the engineered yeast and the cellulolytic bacterium Actinotalea fermentans, we are able to achieve methyl halide production from unprocessed switchgrass (Panicum virgatum), corn stover, sugar cane bagasse, and poplar (Populus sp.). These results demonstrate the potential of producing methyl halides from non-food agricultural resources. PMID:19378995

Bayer, Travis S; Widmaier, Daniel M; Temme, Karsten; Mirsky, Ethan A; Santi, Daniel V; Voigt, Christopher A

2009-05-13

345

Halide and proton binding kinetics of yellow fluorescent protein variants.  

PubMed

A T203Y substitution in green fluorescent protein causes a red shift in emission to yield a class of mutants known as yellow fluorescent protein (YFP). Many of these YFP mutants bind halides with affinities in the millimolar range, which often results in the chromophore pK values being shifted into the physiological range. While such sensitivities may be exploited for halide and pH sensors, it is desirable to reduce such environmental sensitivities in other studies, such as in Förster resonance energy transfer probes to measure conformational changes within fusion proteins. Venus and Citrine are two such variants that have been developed with much reduced halide sensitivities. Here we compare the kinetics of halide binding, and the coupled protonation reaction, for several YFP variants and detect slow kinetics (dissociation rate constants in the range of 0.1-1 s(-1)), indicative of binding to an internal site, in all cases. The effective halide affinity for Venus and Citrine is much reduced compared with that of the original YFP 10C construct, primarily through a reduced association rate constant. Nuclear magnetic resonance studies of YFP 10C confirm halide binding occurs on a slow time scale (<4 s(-1)) and that perturbations in the chemical shift occur throughout the sequence and structure. PMID:23514090

Seward, Harriet E; Basran, Jaswir; Denton, Roanne; Pfuhl, Mark; Muskett, Frederick W; Bagshaw, Clive R

2013-04-02

346

Evidence for a halide-binding site in halorhodopsin.  

PubMed

In attempting to describe a halide-binding site in halorhodopsin (P580), a light-driven chloride pump in halobacterial membranes, we have investigated the effects of chloride and bromide on flash-induced absorption changes in this pigment, and studied the effects of a diuretic drug, MK-473, on the photochemistry and the transport. We find that at high sulfate or phosphate concentrations, but in the absence of halide, the principal photointermediate is P660, whose half-life is about 1.5 ms. When chloride or bromide are added, the production of P660 is depressed and its half-life becomes longer (up to approximately 10 ms). With increasing halide concentration, the cycle proceeds more and more via the alternative photointermediate, P520, whose half-life varies with the halide concentration in a fashion similar to that of P660. Transport activity, measured during sustained illumination, increases in a manner parallel to the accumulation of P520 up to about 400 mM halide, but declines at concentrations above this value. The transport is inhibited by MK-473 with competitive kinetics, and the effects of this inhibitor on the photocycle are also consistent with displacement of halide ions from their binding site. The observations reported here suggest that chloride and bromide bind to P580, P660, and P520, and that this binding is to a distinct site on the protein. PMID:6654911

Schobert, B; Lanyi, J K; Cragoe, E J

1983-12-25

347

The Five Alkali Metals under High Pressure  

Microsoft Academic Search

Effect of high pressure on the melting constants, electrical resistance and volume of the alkali metals.-(1) New data for Rb and Cs, presented in detail elsewhere, are given in three tables. Then, since similar data have previously been obtained for Li, Na and K, the results of a comparative study of all five alkali metals under pressure are given and

P. W. Bridgman

1926-01-01

348

Toward hot and dense monoatomic alkali vapor  

Microsoft Academic Search

Superheating and specific laser excitation can severely reduce alkali molecule density enabling the study of collision induced spectral phenomena in pure atomic cloud. These features may serve in finding new ways for the formation and the detection of ultracold molecules from ultracold atoms on one hand, and may help in plasma diagnostic of high pressure alkali discharge lamps. We shall

Goran Pichler; Ticijana Ban; Damir Aumiler; Viktor Zivcec

2002-01-01

349

Solubility of Neon in Liquid Alkali Metals  

Microsoft Academic Search

We have previously [1] reviewed the published experimental data on the solubility of inert gases in molten alkali metals. The critical analysis carried out in that review paper revealed that the earlier investigations mainly involved the measurements of the solubility of helium and argon in liquid lithium and sodium, while other “inert gas?alkali metal melt” systems were studied either incompletely

E. E. Shpil'rain; S. N. Skovorod'ko; A. G. Mozgovoi

2002-01-01

350

In situ characterization of halide adsorption and Ag-halide growth on Ag(111) electrodes using atomic force microscopy  

Microsoft Academic Search

The structure and growth of halide adlayers and bulk Ag-halide deposits on Ag(111) has been studied by in situ atomic force microscopy as a function of electrode potential. For solutions containing F? and Cl?, only the underlying Ag(111) structure is observed at all potentials. However, for Br? and I?-containing solutions ordered overlayers are present on the surface. In the Br?

Douglas D. Sneddon; Andrew A. Gewirth

1995-01-01

351

Complex formation in the systems uranium halide--alkali metal halide. Enthalpy of formation of RbâUBrâ and CsâUBrâ  

Microsoft Academic Search

Standard enthalpies of formation of RbâUBrâ and CsâUBr\\/; sub 6\\/ at 25 deg C were determined. The determination was made by measuring the ; enthalpy of solution of the compounds studied in 0.5% FeClâ solution in 2% ; HCl. The enthalpy of formation of the hexabromouranate (IV) ion and the energy ; of the U-Br bond remain constant with a

V. M. Vdovenko; I. G. Suglobova; D. E. Chirkst

1973-01-01

352

Optical detection of alkali compounds  

SciTech Connect

Experiments to evaluate the photofragment fluorescence diagnostic technique for NaCl, KCl, and NaOH in terms of discrimination potential, sensitivity, and quantitative behavior have been completed. All results so far make this technique look very promising for potential applications in post-combustion coal gas streams. Based on the success of the investigations to date, we are continuing to expand the application of the photofragment technique to other gas-phase alkali compounds of importance in fossil fuel combustion. In particular, work is now in progress to investigate potassium hydroxide, KOH. Ongoing experiments are to determine (1) the optimum wavelength for K* production, (2) whether KOH can be measured in the presence of KCl, (3) if the signals linearly track the KOH monomer density, and (4) the absolute sensitivity of the technique for KOH in high-temperature environments.

Oldenborg, R.C.; Baughcum, S.L.

1986-01-01

353

Alkali metal diffuse band lasers  

NASA Astrophysics Data System (ADS)

Progress is described on study of a new class of potential excimer lasers based on diffuse bands of the alkali metal vapors. In particular, the violet diffuse bands of sodium vapor and the yellow diffuse bands of potassium vapor have been shown by detailed modeling of single vibrational-rotational level emission to be each composed of overlapping singlet and triplet excimer emission continua of the diatomic molecule. The gain and low absorption loss previously found in the violet and yellow with laser optical pumping of sodium vapor and potassium vapor, respectively, have been quantitatively examined. Prospects for laser oscillation appear to be good at low pressures where quenching is not dominant. Free-bound-free spectra (which include only the triplet portion of the diffuse bands) have been produced and analyzed in sodium, potassium, rubidium and cesium.

Stwalley, William C.

1987-08-01

354

Melt synthesis of inorganic nitrides and halides  

NASA Astrophysics Data System (ADS)

Novel halide chlorides Sr7Cl2H12, Sr 7Br2H12, and Ba2ClH3 were formed from sodium chloride and strontium metal in sodium metal melts at 900°C. Sr7Br2H12 crystallizes in the anti-Fe 12Zr2P7 structure type, and Sr7Cl 2H12 crystallizes in a slightly distorted variant of this structure. Ba2ClH3 crystallizes in a structure containing infinite two-dimensional sheets of edge-sharing Ba6Cl chlorine-centered octahedra. Single crystals of gallium nitride can be obtained by reaction of gallium metal and dinitrogen gas at 750°C. Small amounts of alkaline earth metals added to the reaction mixture promote the formation of large crystals. Polycrystalline GaN nucleates rapidly under these conditions on the surface of a stainless steel autoclave; nucleation is far less pronounced on tungsten surfaces. Trace concentrations of hydrogen greatly enhance GaN nucleation. Melts of magnesium metal with cerium, gadolinium, and lanthanum were exposed to ammonia and nitrogen gas at temperatures from 700°C to 900°C. Binary rare earth and magnesium nitrides and hydrides are formed, but no ternary compounds are seen. The absence of ternary compounds is discussed in the light of a thermodynamic model predicting ternary formation in these systems.

Molstad, Jay Clark

355

Measurement of alkali in PFBC exhaust  

SciTech Connect

This project supports the DOE/METC Fossil Energy Program for the development of PFBC technology. Based on the analytical activated-bauxite sorber-bed technique, we are developing the RABSAM as an altemative to the on-line alkali analyzer for field application. As shown in Fig. 1, the RABSAM is a sampling probe containing a regenerable activated-bauxite adsorbent (RABA). It can be inserted directly into the PFBC exhaust duct and requires no HTHP sampling line. Alkali vapors are captured by the adsorbent purely through physical adsorption. The adsorbent is regenerated by a simple water-leaching process, which also recovers the adsorbed alkalis. The alkali analysis of the leachate by atomic absorption (AA) provides a basis for calculating the time-averaged alkali-vapor concentration in the PFBC exhaust. If the RABA is to use commercial grade activated bauxite, the clay impurities in activated bauxite can react with alkali vapors and, therefore, need to be either removed or deactivated. In earlier work, a 6M-LiCl-solution impregnation technique was shown to deactivate these impurities in fresh activated bauxite [8]. During this year, RABA prepared by this technique was tested in a pressurized alkali-vapor sorption test unit to determine its NaCl-vapor capture efficiency and the regenerability of the sorbent by water extraction. Results of this study are presented and discussed.

Lee, S.H.D.; Swift, W.M.

1992-11-01

356

Measurement of alkali in PFBC exhaust  

SciTech Connect

This project supports the DOE/METC Fossil Energy Program for the development of PFBC technology. Based on the analytical activated-bauxite sorber-bed technique, we are developing the RABSAM as an altemative to the on-line alkali analyzer for field application. As shown in Fig. 1, the RABSAM is a sampling probe containing a regenerable activated-bauxite adsorbent (RABA). It can be inserted directly into the PFBC exhaust duct and requires no HTHP sampling line. Alkali vapors are captured by the adsorbent purely through physical adsorption. The adsorbent is regenerated by a simple water-leaching process, which also recovers the adsorbed alkalis. The alkali analysis of the leachate by atomic absorption (AA) provides a basis for calculating the time-averaged alkali-vapor concentration in the PFBC exhaust. If the RABA is to use commercial grade activated bauxite, the clay impurities in activated bauxite can react with alkali vapors and, therefore, need to be either removed or deactivated. In earlier work, a 6M-LiCl-solution impregnation technique was shown to deactivate these impurities in fresh activated bauxite [8]. During this year, RABA prepared by this technique was tested in a pressurized alkali-vapor sorption test unit to determine its NaCl-vapor capture efficiency and the regenerability of the sorbent by water extraction. Results of this study are presented and discussed.

Lee, S.H.D.; Swift, W.M.

1992-01-01

357

Method for resurrecting negative electron affinity photocathodes after exposure to an oxidizing gas  

DOEpatents

A method by which negative electron affinity photocathodes (201), single crystal, amorphous, or otherwise ordered, can be made to recover their quantum yield following exposure to an oxidizing gas has been discovered. Conventional recovery methods employ the use of cesium as a positive acting agent (104). In the improved recovery method, an electron beam (205), sufficiently energetic to generate a secondary electron cloud (207), is applied to the photocathode in need of recovery. The energetic beam, through the high secondary electron yield of the negative electron affinity surface (203), creates sufficient numbers of low energy electrons which act on the reduced-yield surface so as to negate the effects of absorbed oxidizing atoms thereby recovering the quantum yield to a pre-decay value.

Mulhollan, Gregory A; Bierman, John C

2012-10-30

358

Thermal emittance and response time measurements of negative electron affinity photocathodes  

NASA Astrophysics Data System (ADS)

The thermal emittance and temporal response of a photocathode set an upper limit on the maximum achievable electron beam brightness from a photoemission electron source, or photoinjector. We present measurements of these parameters over a broad range of laser wavelength for two different negative electron affinity (NEA) photocathodes. The thermal emittance of NEA GaAs and GaAsP has been measured by two techniques-a measurement of the beam size downstream from a solenoid, whose strength was varied, and a double slit transmission measurement-for different laser spot sizes and shapes. The effect of space charge on the beam spot size allows a good estimation of the photoemission response time from these cathodes. Both cathodes show a subpicosecond response for laser wavelengths shorter than 520 nm.

Bazarov, Ivan V.; Dunham, Bruce M.; Li, Yulin; Liu, Xianghong; Ouzounov, Dimitre G.; Sinclair, Charles K.; Hannon, Fay; Miyajima, Tsukasa

2008-03-01

359

Simulation study of sub-femtosecond electron bunch generation using photocathode RF gun linac  

NASA Astrophysics Data System (ADS)

Pulse radiolysis, a stroboscopic method involving the use of an ultrashort electron bunch and ultrashort light, is essential for the observation of ultrafast reactions. The time resolution of pulse radiolysis depends on the electron bunch length. At Osaka University, a 98-fs electron bunch was generated using a photocathode RF gun linac for the development of femtosecond pulse radiolysis. In order to improve the time resolution of pulse radiolysis, the feasibility of sub-femtosecond electron bunch generation using a photocathode RF gun linac and a magnetic bunch compressor was studied in a simulation. Increase in bunch length due to higher-order effects and bunch charge was investigated using the simulation codes PARMELA and ELEGANT.

Kan, K.; Yang, J.; Kondoh, T.; Norizawa, K.; Ogata, A.; Kozawa, T.; Yoshida, Y.

2010-10-01

360

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

SciTech Connect

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.

Ben-Zvi,I.

2008-11-17

361

The optimal thickness of a transmission-mode GaN photocathode  

NASA Astrophysics Data System (ADS)

A 150-nm-thick GaN photocathode with a Mg doping concentration of 1.6 × 1017 cm-3 is activated by Cs/O in an ultrahigh vacuum chamber, and a quantum efficiency (QE) curve of the negative electron affinity transmission-mode (t-mode) of the GaN photocathode is obtained. The maximum QE reaches 13.0% at 290 nm. According to the t-mode QE equation solved from the diffusion equation, the QE curve is fitted. From the fitting results, the electron escape probability is 0.32, the back-interface recombination velocity is 5 × 104 cm·s-1, and the electron diffusion length is 116 nm. Based on these parameters, the influence of GaN thickness on t-mode QE is simulated. The simulation shows that the optimal thickness of GaN is 90 nm, which is better than the 150-nm GaN.

Wang, Xiao-Hui; Shi, Feng; Guo, Hui; Hu, Cang-Lu; Cheng, Hong-Chang; Chang, Ben-Kang; Ren, Ling; Du, Yu-Jie; Zhang, Jun-Ju

2012-08-01

362

Characterization and control of the electronic properties of a NiO based dye sensitized photocathode.  

PubMed

One compartment tandem DSSCs are based on two photoactive electrodes which are mediated by a redox electrolyte. Electron accumulation in the photoanode (n-type DSSC) alongside hole accumulation in the photocathode (p-type DSSC) should generate high photovoltage using different parts of the solar spectrum. While impressive efficiencies are reported for n-type DSSCs, the performance of the p-type analogue is very low due to insufficient understanding and a lack of materials. Electrochemical impedance spectroscopy of the p-type DSSC reveals that hole transport within the NiO mesoporous photocathode is the performance limiting factor. Modification of the NiO electrode with molecular dipoles significantly increases the cell photovoltage but has no significant effect on the photocurrent of the p-DSSC. Consequently, the development of better hole conducting materials in conjunction with surface dipole modification can lead to high photovoltage, high photocurrent p-DSSCs and thus to efficient tandem DSSCs. PMID:23518797

Hod, Idan; Tachan, Zion; Shalom, Menny; Zaban, Arie

2013-05-01

363

First operation of a photocathode radio frequency gun injector at high duty factor  

SciTech Connect

Tests of the electron beam injector for the Boeing/Los Alamos Average Power Laser Experiment have demonstrated first time operation of a photocathode radio frequency gun accelerator at 25% duty factor, exceeding previous photocathode operating parameters by three orders of magnitude. The macropulse format was 30 Hz and 8.3 ms with a micropulse frequency of 27 MHz. Average beam currents of up to 32 mA have been accelerated to 5 MeV for an average beam power of 160 kW. The macropulse peak current was 128 mA. The 32 mA average beam current exceeds previous cathode performance by a factor of 1000. Emittance measurements demonstrate excellent electron beam quality.

Dowell, D.H.; Davis, K.J.; Friddell, K.D.; Tyson, E.L.; Lancaster, C.A.; Milliman, L.; Rodenburg, R.E.; Aas, T.; Bemes, M.; Bethel, S.Z.; Johnson, P.E.; Murphy, K.; Whelen, C. (Boeing Defense Space Group, Seattle, Washington 98124-2499 (United States)); Busch, G.E.; Remelius, D.K. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States))

1993-10-11

364

High-voltage testing of a 500-kV dc photocathode electron gun  

NASA Astrophysics Data System (ADS)

A high-voltage dc photocathode electron gun was successfully conditioned up to a voltage of 550 kV and a long-time holding test for 8 h was demonstrated at an acceleration voltage of 500 kV. The dc photocathode electron gun is designed for future light sources based on energy-recovery linac and consists of a Cockcroft-Walton generator, a segmented cylindrical ceramic insulator, guard-ring electrodes, a support-rod electrode, a vacuum chamber, and a pressurized insulating gas tank. The segmented cylindrical ceramic insulator and the guard-ring electrodes were utilized to prevent any damage to the insulator from electrons emitted by the support-rod electrode.

Nagai, Ryoji; Hajima, Ryoichi; Nishimori, Nobuyuki; Muto, Toshiya; Yamamoto, Masahiro; Honda, Yosuke; Miyajima, Tsukasa; Iijima, Hokuto; Kuriki, Masao; Kuwahara, Makoto; Okumi, Shoji; Nakanishi, Tsutomu

2010-03-01

365

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

SciTech Connect

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

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

1997-08-01

366

Photo-cathode preparation system of the A0 photo-injector  

SciTech Connect

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.

Moyses Kuchnir et al.

2002-08-23

367

Very high QE HPDs with a GaAsP photocathode for the MAGIC telescope project  

NASA Astrophysics Data System (ADS)

Hybrid photon detectors are one of the few low light level sensors that can provide an excellent single and multiple photoelectron amplitude resolution. The recently developed hybrid photon detectors for the Major Atmospheric Gamma-Imaging Cherenkov (MAGIC) telescope project with an 18-mm-diameter GaAsP photocathode (the Hamamatsu R9792U-40) have a peak quantum efficiency of more than 50% and a pulse width of ˜2.3ns. In addition, the afterpulsing rate of these tubes is ˜300 times lower compared to that of conventional photomultiplier tubes. Photocathode aging measurements showed lifetimes of more than 10 years under standard operating conditions of Cherenkov Telescopes. The temperature dependence of the avalanche gain can be reduced to the same level of a photomultiplier by a simple compensation circuit. Here we report on the recent progress with the above-mentioned hybrid photon detectors.

Saito, T. Y.; Bernardini, E.; Bose, D.; Fonseca, M. V.; Lorenz, E.; Mannheim, K.; Mirzoyan, R.; Orito, R.; Schweizer, T.; Shayduk, M.; Teshima, M.

2009-10-01

368

A High-Gradient CW R Photo-Cathode Electron Gun for High Current Injectors  

SciTech Connect

The paper describes the analysis and preliminary design of a high-gradient photo-cathode RF gun optimized for high current CW operation. The gun cell shape is optimized to provide maximum acceleration for the newly emitted beam while minimizing wall losses in the structure. The design is intended for use in future high-current high-power CW FELs but the shape optimization for low wall losses may be advantageous for other applications such as XFELs or Linear Colliders using high peak power low duty factor guns where pulse heating is a limitation. The concept allows for DC bias on the photocathode in order to repel ions and improve cathode lifetime.

Robert Rimmer

2005-05-01

369

Zintl cluster chemistry in the alkali-metal-gallium systems  

SciTech Connect

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.

Henning, R.

1998-03-27

370

UV radiation resistance and solar blindness of CsI and KBr photocathodes  

Microsoft Academic Search

A detailed study of the stability of CsI and KBr photocathodes under UV irradiation is presented. UV quantum efficiency degradation was found to be more pronounced at lower illumination intensity for the same accumulated dose and illumination wavelength. For an equal number of extracted photoelectrons in-band UV exposure led to a larger sensitivity decay as compared to out-of-band illumination. The

A. S. Tremsin; O. H. W. Siegmund

2001-01-01

371

Magnetic field effects on the photocathode uniformity of Hamamatsu R7081 photomultiplier tubes  

NASA Astrophysics Data System (ADS)

We tested the effects of magnetic fields on a photomultiplier tube (PMT), namely, Hamamatsu R7081, with a large surface area photocathode. The output signals of the PMT were affected in such a way that the magnetic fields deflected photoelectrons to the first dynode. We measured the effects produced by the orientation of the PMT relative to the magnetic fields and the variations in the output signals with respect to the incident light positions in the magnetic fields.

Jeon, E. J.; Kim, J. Y.; Kim, Y. D.; Ma, K. J.; Nam, J. T.

2013-01-01

372

Development of photocathode and device of near-shortwave infrared extension  

NASA Astrophysics Data System (ADS)

HgCdTe and InGaAs material are able to detect near-shortwave infrared extension. The progress of HgCdTe and InGaAs material and their performances have been discussed. This article mainly presented three aspects of InGaAs negative electron affinity (NEA) photocathode and image intensifier which are widely used in near-shortwave infrared devices: the research status, the possible application prospects and the trend.

Luo, Mei-na; Bai, Ting-zhu; Guo, Hui

2013-08-01

373

Photocathode quantum efficiency mapping at high resolution using a digital micromirror device  

NASA Astrophysics Data System (ADS)

An electron beam’s quality is fundamentally limited by its attributes at the cathode. The emission from photocathodes can be bright, but not necessarily uniform. Quantum efficiency (QE) maps generated by selectively illuminating the cathode surface reveal this nonuniformity. In this paper a proof-of-principle experiment is described in which a high resolution map of the QE is generated using a digital micromirror device. We show a substantial improvement over the best results reported for laser raster scanning.

Riddick, B. C.; Montgomery, E. J.; Fiorito, R. B.; Zhang, H. D.; Shkvarunets, A. G.; Pan, Z.; Khan, S. A.

2013-06-01

374

Growth and characterization of rugged sodium potassium antimonide photocathodes for high brilliance photoinjector  

NASA Astrophysics Data System (ADS)

Sodium potassium antimonide photocathodes with Quantum Efficiency (QE) in the range of few percent have been grown, and their photoemission properties are measured. We report the intrinsic emittance and response time of electron bunches extracted from this material. It is possible to recover the QE of an overheated cathode by simple potassium addition, and the cathode is rugged enough to deliver tens of mA of average current with no or minimal degradation.

Cultrera, L.; Karkare, S.; Lillard, B.; Bartnik, A.; Bazarov, I.; Dunham, B.; Schaff, W.; Smolenski, K.

2013-09-01

375

The Argonne Wakefield Accelerator high current photocathode gun and drive linac  

Microsoft Academic Search

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.

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

376

Experimental verification of laser photocathode RF gun as an injector for a laser plasma accelerator  

Microsoft Academic Search

The feasibility of the laser photocathode RF gun, BNL\\/GUN-IV, as an injector for a laser plasma accelerator was investigated at the subpicosecond S-band twin linac system of the Nuclear Engineering Research Laboratory, University of Tokyo. Electron beam energy of 16 MeV, emittance of 6? mm mrad, bunch length of 240 fs (FWHM), and charge per bunch of 350 pC were

Mitsuru Uesaka; Kenichi Kinoshita; Takahiro Watanabe; Jun Sugahara; Toru Ueda; Koji Yoshii; Tetsuya Kobayashi; Nasr Hafz; Kazuhisa Nakajima; Fumio Sakai; Masaki Kando; Hideki Dewa; Hideyuki Kotaki; Shuji Kondo

2000-01-01

377

Alkali Metal for Ultraviolet Band-Pass Filter.  

National Technical Information Service (NTIS)

An alkali metal filter having a layer of metallic bismuth deposited onto the alkali metal is provided. The metallic bismuth acts to stabilize the surface of the alkali metal to prevent substantial surface migration from occurring on the alkali metal, whic...

N. Mardesich G. A. Fraschetti T. Mccann S. D. Mayall D. E. Dunn

1992-01-01

378

Hemibonding of hydroxyl radical and halide anion in aqueous solution.  

PubMed

Molecular geometries and properties of the possible reaction products between the hydroxyl radical and the halide anions in aqueous solution were investigated. The formation of two-center three-electron bonding (hemibonding) between the hydroxyl radical and halide anions (Cl, Br, I) was examined by density functional theory (DFT) calculation with a range-separated hybrid (RSH) exchange-correlation functional. The long-range corrected hybrid functional (LC-?PBE), which have given quantitatively satisfactory results for odd electron systems and excited states, was examined by test calculations for dihalogen radical anions (X(2)(-); X = Cl, Br, I) and hydroxyl radical-water clusters. Equilibrium geometries with hemibonding between the hydroxyl radical and halide anions were located by including four hydrogen-bonded water molecules. Excitation energies and oscillator strengths of ?-?* transitions calculated by the time-dependent DFT method showed good agreement with observed values. Calculated values of the free energy of reaction on the formation of hydroxyl halide radical anion from the hydroxyl radical and halide anion were endothermic for chloride but exothermic for bromide and iodide, which is consistent with experimental values of equilibrium constants. PMID:22136588

Yamaguchi, Makoto

2011-12-05

379

Uptake of haloacetyl and carbonyl halides by water surfaces  

SciTech Connect

Gas-liquid uptake studies have been completed for the carbonyl halides CCl{sub 2}O and CF{sub 2}O and the haloacetyl halides CCl{sub 3}CCIO, CF{sub 3}CFO, and CF{sub 3}CCIO, which are intermediate products from gas phase oxidation of volatile halogen-containing species in the atmosphere. The fluorine-containing species result from the degradation of hydrochlorofluorocarbons (HCFCs) (proposed substitutes for chlorofluorocarbons, CFCs). The tropospheric lifetime of the halides depends on their dissolution in the aqueous phase, determined by Henry`s law solubility (H) and hydrolysis rate (k{sub hyd}). Using a bubble column apparatus, time-resolved gas-liquid interaction experiments measured the product Hk{sub hyd}{1/2}. Studies were performed at 278 K and pH = 1-13; for CCl{sub 3}CClO and CCl{sub 2}O, temperature was varied from 278 to 298 K. From this work and results from other laboratories, limits on values of the product Hk{sub hyd} were established and used to estimate a `global` cloud processing rate of these halides. A approximately 30-day upper limit to their tropospheric lifetime implies that tropospheric removal of the halide degradation products is fast enough not to contribute to the ozone depletion potential of the parent HCFCs. 39 refs., 6 figs., 1 tab.

De Bruyn, W.J.; Shorter, J.A.; Davidovits, P. [Boston College, Chestnut Hill, MA (United States); Worsnop, D.R.; Zahniser, M.S.; Kolb, C.E. [Aerodyne Research, Inc., Billerica, MA (United States)

1995-05-01

380

Modeling the resupply, diffusion, and evaporation of cesium on the surface of controlled porosity dispenser photocathodes  

NASA Astrophysics Data System (ADS)

A controlled porosity dispenser (CPD) photocathode is currently being explored and developed to replace the Cs during operation and increase photocathode lifetime. Experimental results from cesium (Cs) emission of a sintered-wire tungsten CPD are presented and are used to inform a theoretical model of Cs resupply, diffusion, and evaporation on the surface of the photocathode. The evaporation of Cs from a tungsten surface is modeled using an effective one-dimensional potential well representation of the binding energy. The model accounts for both local and global interactions of Cs with the surface metal as well as with other Cs atoms. It is found that for typical activation temperatures within the range of 500 K-750 K, differences of less than 5% between the quantum efficiency (QE) maximum and minimum over ideal homogenous surfaces occur, even when variations to mimic surface non-uniformity due to pore blockage are included. The theoretical evaporation rates of sub-monolayer surface coverage of Cs compare well to the data of Taylor and Langmuir [I. Langmuir and J. B. Taylor, Phys. Rev. 40, 463-464 (1932)] and reproduce the nonlinear behavior of evaporation with varying coverage and temperature.

Pan, Zhigang; Jensen, Kevin L.; Montgomery, Eric J.

2013-09-01

381

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

PubMed

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(N(2)) (thin films prepared in N(2)/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. PMID:22539234

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

2012-04-27

382

Alkali mass balance during the accelerated concrete prism test for alkali–aggregate reactivity  

Microsoft Academic Search

The alkali mass balance was calculated in concrete specimens submitted to the storage conditions of the Canadian standard CSA A23.2-14A concrete prism test for expansion due to alkali–aggregate reaction (AAR). The alkali concentration of both the concrete pore solution expressed under high pressure and the water below specimens in storage pails (bottom water) was measured. Measurements were conducted over a

Patrice Rivard; Marc-André Bérubé; Jean-Pierre Ollivier; Gérard Ballivy

2003-01-01

383

Solid state cell with alkali metal halo-alkali thiocyanate electrolyte  

Microsoft Academic Search

A novel electrochemical cell is disclosed utilizing: (A) an anode which contains an alkali metal as an anode-active material; (B) a cathode and (C) an electrolyte comprising an electrolytically effective amount of one or more compounds having the formula: (Ax)ma'scn wherein a is an alkali metal, X is a halogen, a' is an alkali metal and 0.1 < or =

B. M. Rao; B. G. Silbernagel

1980-01-01

384

Thermodynamic quantities of surface formation of aqueous electrolyte solutions VII. Aqueous solution of alkali metal nitrates LiNO3, NaNO3, and KNO3.  

PubMed

To compare the effect of nitrate anions on the surface tension increments of aqueous solutions with that of halide anions, the surface tension of aqueous solutions of lithium nitrate, sodium nitrate, and potassium nitrate was measured as a function of temperature and concentration. It is shown that the surface tension of aqueous alkali metal nitrate solutions is determined primarily by the kinds of anions, since the surface tension increments of these nitrates were of the same magnitude. The importance of the electrical double layer at the surface is discussed in relation to these surface tension increments. PMID:17707855

Matubayasi, Norihiro; Yoshikawa, Ryuji

2007-08-20

385

Structure and properties of lanthanide halides  

NASA Astrophysics Data System (ADS)

Lanthanum and cerium bromides and chlorides form isomorphous alloy systems with the UCl3 type structure. These scintillating alloys exhibit high luminosity and proportional response, making them the first scintillators comparable to room temperature semiconductors for gamma spectroscopy; Ce(III) activated lanthanum bromide has recently enabled scintillating gamma ray spectrometers with < 3% FWHM energy resolutions at 662 keV. However brittle fracture of these materials impedes development of large volume crystals. Low fracture stress and perfect cleavage along prismatic planes cause material cracking during and after crystal growth. These and other properties pose challenges for material production and post processing; therefore, understanding mechanical behavior is key to fabricating large single crystals, and engineering of robust detectors and systems. Recent progress on basic structure and properties of the lanthanide halides is reported here, including thermomechanical and thermogravimetric analyses, hygroscopicity, yield strength, and fracture toughness. Observations including reversible hydrate formation under atmospheric pressure, loss of stoichiometry at high temperature, anisotropic thermal expansion, reactivity towards common crucible materials, and crack initiation and propagation under applied loads are reported. The fundamental physical and chemical properties of this system introduce challenges for material processing, scale-up, and detector fabrication. Analysis of the symmetry and crystal structure of this system suggests possible mechanisms for deformation and crack initiation under stress. The low c/a ratio and low symmetry relative to traditional scintillators indicate limited and highly anisotropic plasticity cause redistribution of residual process stress to cleavage planes, initiating fracture. This proposed failure mechanism and its implications for scale up to large diameter crystal growth are also discussed.

Doty, F. P.; McGregor, Douglas; Harrison, Mark; Findley, Kip; Polichar, Raulf

2007-10-01

386

Langmuir Probe Curves for Alkali Metal Magnetoplasmas.  

National Technical Information Service (NTIS)

Langmuir probe curves for a cesium plasma are given for selected values of density, temperature and probe size. A computer program is supplied which can be used to plot curves for other alkali metal plasmas. (Author)

J. C. Corbin J. P. Oss

1969-01-01

387

Atmospheric Emissions from Chlor-Alkali Manufacture.  

National Technical Information Service (NTIS)

The manufacture of chlorine and related products is generally known as the chlor-alkali industry. A description is given of the electrolytic process. Process information includes the discussion of normal process variables that affect the range and quantit...

1971-01-01

388

Operating techniques for high-temperature mercury halide lasers  

NASA Astrophysics Data System (ADS)

A comparative analysis of the existing static gas fill techniques and the proposed flowing gas techniques for producing three-component mixtures of a rare gas, nitrogen, and mercury halide vapor within a heated mercury halide laser discharge tube is presented. The technique developed involves passing flow-mixed nitrogen and rare gas through an evaporator consisting of a Pyrex tube with tightly packed glass wool impregnated with finely divided mercury halide powder. The technique allows higher accuracy of the gas-vapor mixture introduction into the discharge tube to be achieved and provides high-temperature gas purging, thereby eliminating the need for high-vacuum processing. Finally, the system is noted to be capable of rapid flow direction reversal and recirculation of the buffer gas.

Baker, H. J.; Seddon, N.

1985-04-01

389

HOEs recorded in silver halide sensitized gelatin emulsions  

NASA Astrophysics Data System (ADS)

Silver halide sensitized gelatin (SHSG) holograms are similar to holograms recorded in dichromated gelatin (DCG), the main recording material for holographic optical elements (HOEs). The drawbacks of DCG is its low sensitivity and limited spectral response. Silver halide materials can be processed in such a way that the final hologram will have properties like a DCG hologram. Recently, this technique has become more interesting after the introduction of the new ultra-high-resolution silver halide emulsions. An optimized processing technique for transmission HOEs recorded in these materials is reported. Diffraction efficiencies over 90% can be obtained for transmissive diffraction gratings. Understanding the importance of the selective hardening process has made it possible to obtain results similar to conventional DCG processing. The main advantage of the SHSG process is that high sensitivity recording can be performed employing laser wavelengths anywhere within the visible spectrum. This simplifies the manufacturing of high-quality, large-format HOEs.

Kim, Jong Man; Bjelkhagen, Hans I.; Phillips, Nicholas J.

2000-03-01

390

Refractories for high-alkali environments  

Microsoft Academic Search

There are two reliable and cost-effective tests for evaluating refractory materials. They are used to determine which refractory products allow greater variance in fuel type with respect to alkali environment for coal-fired applications. Preselection of a particular refractory is important because of down-time cost for premature failure. One test is a variation of the standard alkali cup test. The second

A. W. Rau; F. Cloer

1996-01-01

391

"On water" sp3-sp2 cross-couplings between benzylic and alkenyl halides†  

PubMed Central

Organic-solvent-free cross-couplings between benzylic and alkenyl halides have been developed. Various alkenyl halides can be effciently benzylated by combining the precursor halides in the presence of Zn dust and a Pd catalyst at room temperature, in water as the only medium.

Krasovskaya, Valeria; Krasovskiy, Arkady; Bhattacharjya, Anish; Lipshutz, Bruce H.

2011-01-01

392

Annual Methyl Halides Fluxes and Isotopic Signatures of Methyl Chloride from Irish Soil Ecosystems  

Microsoft Academic Search

Methyl halides (CH3X, where X = Cl, Br or I) provide a significant portion of reactive halide radicals to the atmosphere, where the radicals are responsible for ozone catalysis within the stratosphere and decreasing the oxidative capacity of the troposphere. One of the least understood reservoirs within the methyl halide budgets is the soil, or subsurface, ecosystem. Here we present

K. R. Redeker; D. Harper; J. T. Hamilton; C. McRoberts; R. M. Kalin

2004-01-01

393

"On water" sp3-sp2 cross-couplings between benzylic and alkenyl halides.  

PubMed

Organic-solvent-free cross-couplings between benzylic and alkenyl halides have been developed. Various alkenyl halides can be efficiently benzylated by combining the precursor halides in the presence of Zn dust and a Pd catalyst at room temperature, in water as the only medium. PMID:21487612

Krasovskaya, Valeria; Krasovskiy, Arkady; Bhattacharjya, Anish; Lipshutz, Bruce H

2011-04-12

394

First-order correction for bond energy applied to polar molecules: Alkali halides, alkali cyanides, LiCH3, and CH3F  

NASA Astrophysics Data System (ADS)

The ionic bond in molecules containing an electropositive moiety and an electronegative moiety originates from a coupling between the ionic and the covalent contributions. Some representative cases in the example of LiF, LiCl, NaF, NaCl, KF, KCl, LiCH3, CH3F, LiCN, NaCN and KCN are calculated by ab initio and density functional methods. The resulting bond energy can be improved a posteriori by a recently proposed first-order method using the dipole moment or the effective charge. For the ab initio calculations, this method brings about a systematic improvement of the bond energy with respect to the experimental value. While the density functional method gives qualitatively mixed results, application of this first-order method generally improves the bond energy.

Lee, Dong-Ki; Lee, Yoon Sup; Hagebaum-Reignier, D.; Jeung, Gwang-Hi

2006-09-01

395

Reaction of hydrogen chloride with halides of quaternary ammonium salts  

Microsoft Academic Search

1.The solubility of (n-C4H9)4NCl and (n-C4H9)4NBr in benzene was determined at 25°.2.The interaction of gaseous HCl with tetra-substituted ammonium halides was investigated. A decrease in the dimensions of the anion and an increase in the dimensions of the cation promote interaction.3.The behavior of the reaction products of HCl with tetra-substituted ammonium halides in benzene was investigated. In the case of

N. M. Aplatova; Yu. M. Kessler; A. I. Gorbanev

1964-01-01

396

Copper(I)-catalyzed boryl substitution of unactivated alkyl halides.  

PubMed

Borylation of alkyl halides with diboron proceeded in the presence of a copper(I)/Xantphos catalyst and a stoichiometric amount of K(O-t-Bu) base. The boryl substitution proceeded with normal and secondary alkyl chlorides, bromides, and iodides, but alkyl sulfonates did not react. Menthyl halides afforded the corresponding borylation product with excellent diastereoselectivity, whereas (R)-2-bromo-5-phenylpentane gave a racemic product. Reaction with cyclopropylmethyl bromide resulted in ring-opening products, suggesting the reaction involves a radical pathway. PMID:22260229

Ito, Hajime; Kubota, Koji

2012-01-19

397

Solar pumped, alkali vapor laser  

NASA Astrophysics Data System (ADS)

High power lasers based in space have been considered as sources for power transmission, laser propulsion, materials processing and space defense. The feasibility of such systems is based on the cost per unit power delivered, with detailed studies indicating that light weight has a greater impact on cost than laser efficiency. Solar radiation is a natural source of power for these devices and two methods for conversion of solar radiation to laser radiation can be considered. An indirectly solar pumped laser would first convert the solar radiation to electricity or longer wavelength blackbody radiation which is then used to power the laser. A directly longer wavelength blackbody radiation which is then used to power the laser. A directly pumped solar laser would utilize a portion of te solar spectrum to directly pump the laser medium, eliminating the intervening step and substantially reducing the systems weight and complexity. Detailed comparisons showed a directly pumped laser with an overall efficiency of only 1.5 percent can compete with an indirectly energized solar laser with an overall efficiency of ten percent. With this in mind, a concept for a directly solar pumped laser was developed based on an alkali vapor (sodium) as the laser medium.

Ham, David; Defaccio, Mark A.

1987-09-01

398

40 CFR 721.10098 - Disubstituted benzoic acid, alkali metal salt (generic).  

Code of Federal Regulations, 2010 CFR

... false Disubstituted benzoic acid, alkali metal salt (generic). 721...10098 Disubstituted benzoic acid, alkali metal salt (generic). ...generically as disubstituted benzoic acid, alkali metal salt (PMN...

2010-07-01

399

40 CFR 721.10097 - Disubstituted benzenesulfonic acid, alkali metal salt (generic).  

Code of Federal Regulations, 2010 CFR

... Disubstituted benzenesulfonic acid, alkali metal salt (generic). 721... Disubstituted benzenesulfonic acid, alkali metal salt (generic). ...disubstituted benzenesulfonic acid, alkali metal salt (PMN...

2010-07-01

400

40 CFR 721.10097 - Disubstituted benzenesulfonic acid, alkali metal salt (generic).  

Code of Federal Regulations, 2010 CFR

... Disubstituted benzenesulfonic acid, alkali metal salt (generic). 721... Disubstituted benzenesulfonic acid, alkali metal salt (generic). ...disubstituted benzenesulfonic acid, alkali metal salt (PMN...

2009-07-01

401

40 CFR 721.10097 - Disubstituted benzenesulfonic acid, alkali metal salt (generic).  

Code of Federal Regulations, 2013 CFR

... Disubstituted benzenesulfonic acid, alkali metal salt (generic). 721... Disubstituted benzenesulfonic acid, alkali metal salt (generic). ...disubstituted benzenesulfonic acid, alkali metal salt (PMN...

2013-07-01

402

40 CFR 721.10098 - Disubstituted benzoic acid, alkali metal salt (generic).  

Code of Federal Regulations, 2010 CFR

... false Disubstituted benzoic acid, alkali metal salt (generic). 721...10098 Disubstituted benzoic acid, alkali metal salt (generic). ...generically as disubstituted benzoic acid, alkali metal salt (PMN...

2009-07-01

403

Structural Characterization of Methanol Substituted Lanthanum Halides  

PubMed Central

The first study into the alcohol solvation of lanthanum halide [LaX3] derivatives as a means to lower the processing temperature for the production of the LaBr3 scintillators was undertaken using methanol (MeOH). Initially the de-hydration of {[La(µ-Br)(H2O)7](Br)2}2 (1) was investigated through the simple room temperature dissolution of 1 in MeOH. The mixed solvate monomeric [La(H2O)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 CaH2, 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 {[LaBr2.75•5.25(MeOH)]+0.25 [LaBr3.25•4.75(MeOH)]?0.25} (4). The fully substituted species was ultimately isolated through the dissolution of dried LaBr3 in MeOH forming the 8-coordinated [LaBr3(MeOH)5] (5) complex. It was determined that the concentration of the crystallization solution directed the structure isolated (4 concentrated; 5 dilute) The other LaX3 derivatives were isolated as [(MeOH)4(Cl)2La(µ-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 (139La) 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.

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

2010-01-01

404

Cooled Transmission-Mode NEA-Photocathode with a Band-Graded Active Layer for High Brightness Electron Source  

SciTech Connect

A Free-Electron Laser (FEL) places many exacting demands on a Negative Electron Affinity (NEA) photocathode, such as the need for an ultra-fast response time, low energy spread for emitted electrons, high quantum efficiency (Q.E.) and a high average photocurrent. However, these key requirements are conflicting, and cannot be fulfilled by conventional photocathode design. For example, to achieve {approx}10 ps response time, the photocathode active layer should be thinned to {approx}100-150 nm, but this thickness is insufficient to provide near-complete absorption of light with hv{approx_equal}{epsilon}{sub g} so high Q.E. cannot be achieved. Complete optical absorption and high Q.E. can be obtained using a thin active layer at higher photon energies, but this generates photoelectrons with excess kinetic energy within the semiconductor. These photoelectrons do not thermalise in a thin active layer, so yield a broad energy distribution in the emitted electrons. Moreover, cooling of the conventional semiconductor photocathode structure is ineffective due to its fragility, so it cannot be pressed firmly to a heat sink to attain good thermal contact. Consequently, the maximum CW photocurrent is limited to a few miiliamps. The goal of our work is to develop a new design of NEA-photocathode which is optimised for FEL applications.

Jones, L. B.; Militsyn, B. L.; Smith, S. L. [STFC Daresbury Laboratory, Warrington, WA4 4AD (United Kingdom); Rozhkov, S. A. [Novosibirsk State University, Novosibirsk, 630090 (Russian Federation); Bakin, V. V.; Kosolobov, S. N.; Scheibler, H. E. [Institute of Semiconductor Physics, Novosibirsk, 630090 (Russian Federation); Terekhov, A. S. [Novosibirsk State University, Novosibirsk, 630090 (Russian Federation); Institute of Semiconductor Physics, Novosibirsk, 630090 (Russian Federation)

2009-08-04

405

Casting of Halide and Fluoride Alloys for Laser Windows.  

National Technical Information Service (NTIS)

During the first quarter of this program several important goals were accomplished. The problem of residual strain in castings of halides (KCl and SrCl2 doped KCl) and fluorides (pure CaFs) has been largely overcome by using proper annealing and cooling p...

R. T. Newberg D. W. Readey H. A. Newborn

1974-01-01

406

Structure and optical properties of high light output halide scintillators  

NASA Astrophysics Data System (ADS)

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 BaBr2 , BaIBr, BaCl2 , BaF2 , BaI2 , BiI3 , CaI2 , Cs2LiYCl6 , CsBa2Br5 , CsBa2I5 , K2LaBr5 , K2LaCl5 , K2LaI5 , LaBr3 , LaCl3 , SrBr2 , and YI3 . For comparison results are presented for the oxide CdWO4 . 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 CdWO4 , 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.

Singh, David J.

2010-10-01

407

Test of interaction potentials for rare gas-halide systems  

Microsoft Academic Search

Ab initio, model and empirical potentials for the interaction of rare gas atoms and halide ions are tested by their ability to reproduce gaseous ion transport data. The ab initio potentials are in poor agreement with the data. The model potentials give good agreement with experiment for some systems, moderate agreement for others, and very poor agreement for Br? in

Larry A. Viehland; Charles C. Kirkpatrick

1996-01-01

408

Method for calcining nuclear waste solutions containing zirconium and halides  

DOEpatents

A reduction in the quantity of gelatinous solids which are formed in aqueous zirconium-fluoride nuclear reprocessing waste solutions by calcium nitrate added to suppress halide volatility during calcination of the solution while further suppressing chloride volatility is achieved by increasing the aluminum to fluoride mole ratio in the waste solution prior to adding the calcium nitrate.

Newby, Billie J. (Idaho Falls, ID)

1979-01-01

409

Theory of Self-Trapped Exciton Luminescence in Halide Crystals  

Microsoft Academic Search

A detailed phenomenological theory of the triplet luminescence from self-trapped excitons in halide crystals is developed. Energy levels and wave functions are obtained by constructing and diagonalizing a Hamiltonian matrix. Coupled rate equations for the decay of the three lowest triplet levels are solved for the general case in which the levels are not in thermal equilibrium, and circular polarizations,

W. Beall Fowler; M. J. Marrone; M. N. Kabler

1973-01-01

410

Mechanism of Interaction of the Magnesium Atom with Alkyl Halides  

Microsoft Academic Search

The reaction of insertion of the magnesium atom into the Alk?Hal or Ar?Hal bond is well known and is often used in organic synthesis. This reaction is obliged for its renown to Grignard, who was the first to observe the formation of ethylmagnesium halides (the Grignard reagent) in dry diethyl ether in the presence of freshly prepared magnesium chips. The

A. V. Tulub; V. V. Porsev; A. A. Tulub

2004-01-01

411

Methyl halide emissions from savanna fires in southern Africa  

NASA Astrophysics Data System (ADS)

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 halides and carbon monoxide, suggesting that emission was predominantly associated with the smoldering phase of the fires. About 90% of the halogen content of the fuel burned was released to the atmosphere, mostly as halide species, but a significant fraction (3-38%) was emitted in methylated form. On the basis of comparison with the composition of the regional background atmosphere, emission ratios to carbon dioxide and carbon monoxide were determined for the methyl halide species. The emission ratios decreased in the sequence CH3Cl > CH3Br > CH3I. Extrapolation of these results in combination with data from other types of biomass burning, e.g. forest fires, suggests that vegetation fires make a significant contribution to the atmospheric budget of CH3Cl and CH3Br. For tropospheric CH3I, on the other hand, fires appear to be a minor source. Our results suggest that pyrogenic emissions of CH3Cl and CH3Br need to be considered as significant contributors to stratospheric ozone destruction.

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

1996-10-01

412

Nature of the superionic transition in Ag+ and Cu+ halides  

Microsoft Academic Search

Silver and copper halides generally display an abrupt (first-order) transition to the superionic state. However, powder diffraction studies and molecular dynamics (MD) simulations of AgI under hydrostatic pressure both indicate that a continuous superionic transition occurs on heating. The gradual onset of the highly conducting state is accompanied by an increasing fraction of dynamic Frenkel defects, a peak in the

D. A. Keen; S. Hull; A. C. Barnes; P. Berastegui; W. A. Crichton; P. A. Madden; M. G. Tucker; M. Wilson

2003-01-01

413

Erratum: The Structure of Alkali Halide Dimers: A Critical Test of Ionic Models and New Ab Initio Results  

Microsoft Academic Search

It has come to our attention that some of the ab initio results presented are incorrect due to errors in the Cs and C1 basis sets, and a small error in the binding energy of Rb2F2. The corrected results are presented below for the species that were affected, modifying the results in Table III of the original paper. Only those

Robert J. Cave

2006-01-01

414

The structure of alkali halide dimers: A critical test of ionic models and new ab initio results  

Microsoft Academic Search

In semiempirical ionic models a number of adjustable parameters have to be fitted to experimental data of either monomer molecules or crystals. This leads to strong correlations between these constants and prevents a unique test and a clear physical interpretation of the fit parameters. Moreover, it is not clear whether these constants remain unchanged when the model is applied to

T. Törring; S. Biermann; J. Hoeft; R. Mawhorter; R. J. Cave; C. Szemenyei

1996-01-01

415

The role of an alkali halide flux in the growth of YBa2Cu3O7-? single crystals  

NASA Astrophysics Data System (ADS)

In order to understand the precise role of a NaCl-KCl flux in controlling the crystal growth process of YBa2Cu3O7-?, the microstructure of pellets prepared with various amounts of flux were studied by means of optical microscopy. Quenching experiments indicate significant flux loss during the growth cycle and DTA reveals liquid phase formation below the peritectic decomposition. The observations suggest a complex liquid phase-promoted growth mechanism.

Abell, J. S.; Gencer, F.

1991-12-01

416

Application of laser microspectral analysis for the determination of activating additives in alkali-halide single crystals  

Microsoft Academic Search

We applied microspectral analysis with the direct excitation of the spectra by laser radiation, as shown in [13, 14], to the determination of the content of activators -- thallium and sodium -- in single crystals of sodium and cesium iodide. We focused the radiation from a neodymium-activated yttrium aluminum garnet laser (LTIPCh-7 apparatus), operating in the pulsed Q-switched mode, on

É. S. Zolotovitskaya; V. K. Shevchenko

1985-01-01

417

Interaction of alkali halides with metal and semiconductor surfaces studied by low-energy D[sup +] scattering  

SciTech Connect

The bond nature and the growth mode of KF and KI on Si(100) and W(110) surfaces are studied using low-energy (50--200 eV) D[sup +] ion scattering. It is found that dissociative adsorption occurs in a low-coverage regime ([lt]0.5 monolayer); the resultant K and halogen adatoms are covalently adsorbed on W(110) while, on Si(100), halogen atoms preferentially react with the dangling bond and K is left ionized on the surface. The saturation of the Si dangling bond due to hydrogenation leads to film growth without formation of a reactive interface.

Souda, R.; Hayami, W.; Aizawa, T.; Otani, S.; Ishizawa, Y. (National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba, Ibaraki 305 (Japan))

1993-02-15

418

Optical properties of TI2 hole centres in alkali halides investigated with optical detection of paramagnetic resonance  

NASA Astrophysics Data System (ADS)

The optical absorption band of Tl2+ hole centres has been investigated by measuring the magnetic circular dichroism of the absorption bands (MCDA) as well as MCDA-detected electron paramagnetic resonance (MCDA-EPR). Several new absorption bands were found using the excitation spectra of the MCDA-EPR lines of TI2+. In the iodides there is a total of 7 MCDA bands, more than predicted by the molecular orbital picture discussed so far in the literature.

Spaeth, J.-M.; Rogulis, U.

419

Simulation of H-centre migration along dislocation lines applied to UV-induced afterglow in Eu doped alkali halides  

NASA Astrophysics Data System (ADS)

In this work we have simulated the migration of H centres along dislocation lines and their recombination with F-z centres after a pulse irradiation. The variable parameter in our simulations was the probability p of recombination between H and F-z centres when they meet. The results of the simulation for p =1 were in good agreement with a previous derived approximation and with the experimental data. We found that the function I = I 0 n -alpha could be fitted very well to the afterglow decay for all p values. The afterglow yield, defined as the total amount of afterglow, divided by the total amount of generated precursors of the H-F-z pairs was found to decrease with increasing p . The exponent alpha however was found to be remarkably stable at 1.49 over a range of p from 1 to 0.2 below which it decreases to 0.5.

Piters, T. M.; Alvarez-Garcia, S.

420

30-kV spin-polarized transmission electron microscope with GaAs-GaAsP strained superlattice photocathode  

NASA Astrophysics Data System (ADS)

A spin-polarized electron beam has been used as the probe beam in a transmission electron microscope by using a photocathode electron gun with a photocathode made of a GaAs-GaAsP strained superlattice semiconductor with a negative electron affinity (NEA) surface. This system had a spatial resolution of the order of 1 nm for at 30 keV and it can generate an electron beam with an energy width of 0.24 eV without employing monochromators. This narrow width suggests that a NEA photocathode can realize a high energy resolution in electron energy-loss spectroscopy and a longitudinal coherence of 3 × 10-7 m.

Kuwahara, M.; Kusunoki, S.; Jin, X. G.; Nakanishi, T.; Takeda, Y.; Saitoh, K.; Ujihara, T.; Asano, H.; Tanaka, N.

2012-07-01

421

Formation of cesium peroxide and cesium superoxide on InP photocathode activated by cesium and oxygen  

SciTech Connect

Activation of p-type III-V semiconductors with cesium and oxygen has been widely used to prepare negative electron affinity (NEA) photocathodes. However, the nature of the chemical species on the surface after the activation is not well understood. In this study, InP NEA photocathodes activated with cesium and oxygen are studied using synchrotron radiation photoelectron spectroscopy, also called photoemission. Based on the O 1s core level as well as the valence band spectra, Cs peroxide and Cs superoxide are identified on the InP surface. Transformation from Cs peroxide to Cs superoxide is observed after the activation, and is probably the major reason for the decay of the quantum yield of the photocathode. The oxidation of the InP substrate is also observed with elapse of time, adding to the decay of the quantum yield.

Sun Yun; Liu Zhi; Pianetta, Piero; Lee, Dong-Ick [Stanford Synchrotron Radiation Laboratory, Menlo Park, California 94025 (United States); Department of Material Science and Engineering, Stanford University, California 94305 (United States)

2007-10-01

422

A polarized photoluminescence study of strained layer GaAs photocathodes  

SciTech Connect

Photoluminescence measurements have been made on a set of epitaxially grown strained GaAs photocathode structures. The photocathodes are designed to exhibit a strain-induced enhancement of the electron spin polarization obtainable by optical pumping with circularly polarized radiation of near band gap energy. For the case of non-strained GaAs, the degree of spin polarization is limited to 50% by crystal symmetry. Under an appropriate uniaxial compression or tension, however, the valence band structure near the gap minimum is modified such that a spin polarization of 100% is theoretically possible. A total of nine samples with biaxial compressive strains ranging from zero to {approximately}0.8% are studied. X-ray diffraction analysis, utilizing Bragg reflections, is used to determine the crystal lattice structure of the samples. Luminescence spectra and luminescence circular polarization data are obtained at room temperature, {approx}78 K and {approx}12 K. The degree of luminescence circular polarization is used as a relative measure of the photo-excited electron spin polarization. The room temperature luminescence circular polarization data is compared with the measured electron spin polarization when the samples are used as electron photo-emitters with a negative electron affinity surface preparation. The luminescence data is also analyzed in conjunction with the crystal structure data with the goal of understanding the strain dependent valence band structure, optical pumping characteristics and spin depolarization mechanisms of the photocathode structures. A simple model is used to describe the luminescence data, obtained for the set of samples. Within the assumptions of the model, the deformation potentials a, b and d for GaAs are determined. The measured values are a = -10.16{+-}.21 eV, b = -2.00{+-}.05 eV and d = -4.87{+-}.29 eV. Good agreement with published values of the deformation potentials provides support for the model used to describe the data.

Mair, R.A.

1996-07-01

423

Measurements and studies of secondary electron emission of diamond amplified photocathode  

NASA Astrophysics Data System (ADS)

The Diamond Amplifier Photocathode (DAP) provides a very promising new approach to provide high-average-current, high-brightness electron source for accelerators. High purity Chemical Vapor Deposition diamond films are used as the amplifier of the electron beam. Primary electrons are provided by a traditional photocathode and are bombarded onto tens of nanometer thick metal coating and into the diamond sample. Within 1 micron travel in the diamond, the primary electrons generate secondary electrons by collision on the order of two magnitudes increase in number. Secondary electrons are accelerated through the diamond and will emit into vacuum through surface with hydrogen termination. The electrons emitted should have very low thermal emittance, for the electrons are constrained to the bottom of the conduction band. The entire sample preparing process includes severe chemical etching, metallization coating, and hydrogenation. Measurements are done with specific equipments, and the quality of preparation is controlled by the Atomic Force Microscope and electron or photon spectroscopy. This thesis covers all aspects of this project, and will focus on the physics of electron transfer within and out of the diamond sample. The measurements of the gain are taken and compared under different conditions for obtaining the highest amplification. The experiments have already demonstrated the secondary electron gain of over 200 in the diamond and over 70 for emission into the vacuum. The diamond will also act as a vacuum barrier, protecting the photocathode from contamination by the accelerator vacuum. The emittance measurement is carefully designed to reach the precision of 0.1eV. Theoretical calculations and computational simulation are developed to fit with our experimental results.

Wu, Qiong

424

Quantum Efficiency and Topography of Heated and Plasma-Cleaned Copper Photocathode Surfaces  

SciTech Connect

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.

Palmer, Dennis T.; /Titan PSD; Kirby, R.E.; King, F.K.; /SLAC

2005-08-04

425

Thermal emittance and response time measurements of a GaN photocathode  

NASA Astrophysics Data System (ADS)

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.

Bazarov, Ivan V.; Dunham, Bruce M.; Liu, Xianghong; Virgo, Matt; Dabiran, Amir M.; Hannon, Fay; Sayed, Hisham

2009-04-01

426

Slice emittance measurement for photocathode RF gun with solenoid scanning and RF deflecting cavity  

NASA Astrophysics Data System (ADS)

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.

Li, Chen; Huang, WenHui; Du, YingChao; Yan, LiXin; Tang, ChuanXiang

2011-12-01

427

Thermal emittance and response time measurements of a GaN photocathode.  

SciTech Connect

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.

Bazarov, I. V.; Dunham, B. M.; Liu, X.; Virgo, M.; Dabiran, A. M.; Hannon, F.; Sayed, H. (High Energy Physics); ( SUF-USR); (Cornell Univ.); (SVT Associates); (Thomas Jefferson National Accelerator Facility)

2009-04-01

428

A high-charge high-brightness L-band photocathode RF gun  

SciTech Connect

The Argonne Wakefield Accelerator has been successfully commissioned and used for conducting wakefield experiments in dielectric loaded structures and plasmas. Although the initial wakefield experiments were successful, higher drive beam quality would substantially improve the wakefield accelerating gradients. In this paper the authors present a new 1-1/2 cell L-band photocathode RF gun design. This gun will produce 10--100 nC beam with 2--5 ps ms pulse length and normalized emittance less than 100 mm mrad. The final gun design and numerical simulations of the beam dynamics are presented.

Conde, M. E.; Gai, W.; Konecny, R.; Power, J. G.; Schoessow, P.; Sun, X.

2000-02-25

429

Development of hybrid photodetectors using single-crystal III-V photocathodes  

NASA Astrophysics Data System (ADS)

Improved performance photodetectors are required for a variety of applications in Biomedical, Astronomy and High-Energy Physics research. The combination of high Quantum efficiencies, III-V photocathodes and Avalanche PhotoDiodes (APDs) can provide enhancements applicable to these research areas. This is particularly true in the photon counting regime. Preliminary development of a Winston-cone-based Hybrid device (ReFerence) and an APD-based imaging Hybrid Photomultiplier Tube are presented. These devices take advantage of the high-performance cathodes and mechanically robust structures used in state of the art night vision imagining systems. Theoretical and observed performance are described.

Smith, Bill; Passmore, Keith; Smith, Arlynn; Lundberg, Randy; Thomas, Nils; Bell, Nick; Lively, Chris; Sillmon, Roger; Benz, Rudy; Karplus, Eric; Abraham, Jim; Farrell, Richard; Ferenc, Daniel

2003-05-01

430

Development of an accelerator-ready photocathode drive laser at CEBAF  

SciTech Connect

Many injector designs for free-electron lasers and linear colliders use photocathode sources in lieu of a thermionic cathode. These designs require mode-locked lasers with very tight phase and amplitude jitter specifications to achieve the electron beam quality needed for these applications. We have characterized the long term stability of a mode-locked laser for use in the injector test stand at CEBAF. The sources of drift and instabilities were studied and characterized. Initial results indicate that the most important source of drift is a change in the effective cavity length. A possible design for automatically optimizing the length is presented. 8 refs., 5 figs.

Benson, S.; Shinn, M.

1996-10-01

431

Quantum yield measurements of photocathodes illuminated by pulsed ultraviolet laser radiation  

SciTech Connect

The electron quantum yields from polycrystalline lanthanum hexaboride and barium irradiated by near ultraviolet laser excitation have been determined. These measurements show that the quantum yields from these materials are dependent on the processing and previous history of the photocathode material. For lanthanum hexaboride, a yield of 7 {times} 10{sup {minus}6} with 337 nm irradiation has been achieved. For barium, a yield of 1 {times} 10{sup {minus}6} has been measured with excitation at 308 nm. These results are discussed and future plans are outlined. 4 refs., 4 figs.

Young, A.T.; Chen, P.; Kunkel, W.B.; Leung, K.N.; Li, C.Y. (Lawrence Berkeley Lab., CA (United States)); Watson, J.M. (Superconducting Super Collider Lab., Dallas, TX (United States))

1991-05-01

432

A novel scaling law relating the geometrical dimensions of a photocathode radio frequency gun to its radio frequency properties.  

PubMed

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

Lal, Shankar; Pant, K K; Krishnagopal, S

2011-12-01

433

Preventing the accelerated low-temperature oxidation of MoSi{sub 2} (pesting) by the application of superficial alkali-salt layers  

SciTech Connect

Previous work showed that MoSi{sub 2} diffusion coatings formed by a NaF-activated pack cementation process did not pest. A Na-Al-oxide by-product layer resulting from the NaF activator formed a Na-silicate layer to passivate MoSi{sub 2}. Superficial NaF layers were then used to prevent the pesting of MoSi{sub 2} diffusion coatings that were otherwise susceptible to pest disintegration. In this study, the use of superficial alkali-salt layers to prevent the accelerated oxidation of bulk MoSi{sub 2} at 500{degrees}C is investigated more broadly. The application of Na-halide, KF, LiF, Na{sub 2}B{sub 4}O{sub 7}, or Na-silicate layers prior to oxidation prevented accelerated oxidation and pesting for at least 2000 hr at 500{degrees}C in air. The formation of a fast-growing, Na-silicate layer passivates MoSi{sub 2}. The MoO{sub 3} that forms during oxidation absorbs sodium by intercalation to form stable Na-molybdate precipitates. Na{sub 2}B{sub 4}O{sub 7}, Na-silicate, LiF, and KF prevented accelerated oxidation at 500{degrees}C by a similar mechanism. The application of alkali-halide salts is a simple, effective solution to prevent the accelerated oxidation and pesting of MoSi{sub 2}.

Cockeram, B.V.; Wang, G.; Rapp, R.A. [Ohio State Univ., Colombus, OH (United States)

1996-02-01

434

Polarized Electrons from Photoionization of Polarized Alkali Atoms.  

National Technical Information Service (NTIS)

The process of photoionization of polarized alkali atoms in an atomic beam has been studied for potassium and lithium. Depolarization processes associated with photoionization of alkali molecules and optically excited atoms were discovered. After eliminat...

M. Posner M. S. Lubell R. L. Long V. W. Hughes W. Raith

1971-01-01

435

Absorption chamber for alkali-helium magnetometer  

SciTech Connect

This paper presents an improved design of an absorption chamber for an alkali-helium magnetometer that ensures reliable firing and maintenance of gas discharge and has a long service life. Use of the improved absorption chamber reduces the HF power of the discharge generator required for firing and maintenance of stable discharge. In addition, owing to introduction into the chamber of an excess amount of alkali metal, whose shielding effect on the discharge is practically eliminated, substantially increases the life of the absorption chamber. Photographs of both the improved and original absorption chambers are provided in the paper.

Blinov, E.V.; Dmitriev, S.P.; Kuleshov, P.P.

1985-12-01

436

Spectroscopic effects of disorder and vibrational localization in mixed-halide metal-halide chain solids  

SciTech Connect

Resonance Raman techniques, together with lattice-dynamics and Peierls-Hubbard modelling, are used to explore the electronic and vibrational dynamics of the quasi-one-dimensional metal-halogen chain solids [Pt(en){sub 2}][R(en){sub 2}X{sub 2}](ClO{sub 4}){sub 4}, (en = C{sub 2}H{sub 8}N{sub 2} and X=Cl, Br), abbreviated ``PLX.`` The mixed-halide materials PtCl{sub 1-x}Br{sub x} and PtCl{sub 1-x}I{sub x} consist of long mixed chains with heterojunctions between segments of the two constituent materials. Thus, in addition to providing mesoscale modulation of the chain electronic states, they serve as prototypes for elucidating the properties to be expected for macroscopic heterojunctions of these highly nonlinear materials. Once a detailed understanding of the various local vibrational modes occurring in these disordered solids is developed, the electronic structure of the chain segments and junctions can be probed by tuning the Raman excitation through their various electronic resonances.

Love, S.P.; Scott, B.; Worl, L.A.; Huckett, S.C.; Saxena, A.; Huang, X.Z.; Bishop, A.R.; Swanson, B.I.

1993-02-01

437

Rheological characterization of corn starch isolated by alkali method  

Microsoft Academic Search

The pasting properties of alkali-isolated corn starches obtained from corn grits, as well as the rheological behaviour of their 8% gels were investigated. The alkali isolation was performed using different conditions concerning alkali concentration (0.15% and 0.30%), steeping time (30 min and 90 min) and temperature (25 °C and 50 °C).Alkali-isolated starches exhibited lower pasting temperatures and higher peak viscosities than the wet-milled starch.

Ljubica Doki?; Tamara Dap?evi?; Veljko Krstonoši?; Petar Doki?; Miroslav Hadna?ev

2010-01-01

438

Alkali measurement in advanced coal-fueled systems  

Microsoft Academic Search

The measurement of alkali in advanced coal-fueled systems, such as pressurized fluidized-bed combustion (PFBC), direct coal-fueled turbine (DCFT), and integrated gasification combined-cycle (IGCC) systems, is reported. The systems in which the alkali is measured are described. The location of the alkali monitoring in the systems is also discussed. The status of developing alkali monitoring techniques, such as the fiber optic

D. C. Cicero; M. C. Williams

1990-01-01

439

Salts of alkali metal anions and process of preparing same  

DOEpatents

Compounds of alkali metal anion salts of alkali metal cations in bicyclic polyoxadiamines are disclosed. The salts are prepared by contacting an excess of alkali metal with an alkali metal dissolving solution consisting of a bicyclic polyoxadiamine in a suitable solvent, and recovered by precipitation. The salts have a gold-color crystalline appearance and are stable in a vacuum at -10.degree. C. and below.

Dye, James L. (East Lansing, MI); Ceraso, Joseph M. (Lansing, MI); Tehan, Frederick J. (Utica, NY); Lok, Mei Tak (Urbana, IL)

1978-01-01

440

Got Calcium? Welcome to the Calcium-Alkali Syndrome  

Microsoft Academic Search

We recommend changing the name of the milk-alkali syndrome to the calcium- alkali syndrome, because the new terminology better reflects the shifting epide- miology and understanding of this disorder. The calcium-alkali syndrome is now the third most common cause of hospital admission for hypercalcemia, and those at greatest risk are postmenopausal or pregnant women. The incidence of the cal- cium-alkali

Ami M. Patel; Stanley Goldfarb

2010-01-01

441

Coprecipitation of alkali metal ions with calcium carbonate  

Microsoft Academic Search

The coprecipitation of alkali metal ions (Li + , Na + , K + and Rb + ) with calcium carbonate has been studied experimentally and the following results have been obtained: 1. (1) Alkali metal ions are more easily coprecipitated with aragonite than with calcite. 2. (2) The relationship between the amounts of alkali metal ions coprecipitated with aragonite

Minoru Okumura; Yasushi Kitano

1986-01-01

442

Diode Pumped Alkali Lasers: History, current state and perspectives  

Microsoft Academic Search

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

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

2011-01-01

443

Using TiO2 as a conductive protective layer for photocathodic H2 evolution.  

PubMed

Surface passivation is a general issue for Si-based photoelectrodes because it progressively hinders electron conduction at the semiconductor/electrolyte interface. In this work, we show that a sputtered 100 nm TiO(2) layer on top of a thin Ti metal layer may be used to protect an n(+)p Si photocathode during photocatalytic H(2) evolution. Although TiO(2) is a semiconductor, we show that it behaves like a metallic conductor would under photocathodic H(2) evolution conditions. This behavior is due to the fortunate alignment of the TiO(2) conduction band with respect to the hydrogen evolution potential, which allows it to conduct electrons from the Si while simultaneously protecting the Si from surface passivation. By using a Pt catalyst the electrode achieves an H(2) evolution onset of 520 mV vs NHE and a Tafel slope of 30 mV when illuminated by the red part (? > 635 nm) of the AM 1.5 spectrum. The saturation photocurrent (H(2) evolution) was also significantly enhanced by the antireflective properties of the TiO(2) layer. It was shown that with proper annealing conditions these electrodes could run 72 h without significant degradation. An Fe(2+)/Fe(3+) redox couple was used to help elucidate details of the band diagram. PMID:23289745

Seger, Brian; Pedersen, Thomas; Laursen, Anders B; Vesborg, Peter C K; Hansen, Ole; Chorkendorff, Ib

2013-01-11

444

Wet etching of AlGaN/GaN photocathode grown by MOCVD  

NASA Astrophysics Data System (ADS)

The AlGaN/GaN with thin GaN surface was grown by metalorganic chemical vapor deposition (MOCVD). And one of two AlGaN/GaN photocathode samples was etched by molten KOH about 40s, and its reflectivity and transmittance are tested. The thickness of AlGaN and GaN layers are fitted by the matrix formula for thin film optics, and the GaN thickness of them are 7nm and 2.5nm respectively. And etch speed of GaN are got in molten KOH at about 400°C. Then the etched and original AlGaN/GaN photocathode samples are activated by Cs/O in the same way. The spectral response and the result of simulation show that the cut-off wavelength of the etched AlGaN/GaN deviate to the short-wave. And the quantum efficiency decline with the GaN thickness decrease.

Hao, Guanghui; Chang, Benkang; Cheng, Hongchang

2013-08-01

445

Graphene incorporated nanocrystalline TiO2 films for the photocathodic protection of 304 stainless steel  

NASA Astrophysics Data System (ADS)

Composite films of TiO2 and graphene (GR) were prepared on 304 stainless steel (304SS) by the sol–gel method and heat treatment. The morphology, crystalline phase, and composition of the GR/TiO2 films were characterized systematically by X-ray diffraction, Raman spectroscopy and scanning electron microscopy, respectively. The photocathodic protection performances of the composite film under illumination and dark conditions in 3.0% NaCl solution were evaluated through the electrochemical measurements. It is indicated that the incorporation of GR in TiO2 film can improve effectively the photocathodic protection effect for 304SS under the UV illumination. Compared to 350 mV of pure TiO2 film, the electrode potentials can be negatively shifted to about ?600 mV under UV light irradiation by incorporating GR into TiO2 films. At the same time, a 14-fold photocurrent density can be obtained for the GR/TiO2 film. This indicates that GR can play an excellent enhancing effect on the photogenerated cathodic protection of TiO2 films.

Guo, Xiangqin; Liu, Wei; Cao, Lixin; Su, Ge; Xu, Hongmei; Liu, Binhao

2013-10-01

446

Performance Study of K2CsSb Photocathode Inside a DC High Voltage Gun  

SciTech Connect

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.

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

2011-09-01

447

Raman spectra of ionic liquids: a simulation study of LaCl3 and its mixtures with alkali chlorides.  

PubMed

Theoretical Raman spectra of the elpasolite-structured crystal Cs2NaLaCl6 and of molten mixtures of LaCl6 with NaCl and CsCl have been obtained from computer simulations in order to examine how the Raman spectra reflect the coordination structure around the La3+ ions. This system is a model for many other trivalent metal halides and for examining how the network structure of the pure melts is broken down by the addition of alkali halides with different structure-breaking powers. The results suggest a way of reconciling the conclusions of Raman studies about the structures of the melts with those of neutron and x-ray-diffraction studies, which have already been examined with the same simulation methods. The Raman spectra, both polarized and depolarized, are calculated from a model for the dependence of the polarizability of the system on the ionic coordinates which was inspired by electronic structure calculations of the polarizabilities of ions in a condensed phase environment. Some results on the lifetimes of the coordination complexes responsible for the appearance of the discrete Raman bands are discussed. PMID:15473798

Glover, William J; Madden, Paul A

2004-10-15

448

Raman spectra of ionic liquids: A simulation study of LaCl3 and its mixtures with alkali chlorides  

NASA Astrophysics Data System (ADS)

Theoretical Raman spectra of the elpasolite-structured crystal Cs2NaLaCl6 and of molten mixtures of LaCl6 with NaCl and CsCl have been obtained from computer simulations in order to examine how the Raman spectra reflect the coordination structure around the La3+ ions. This system is a model for many other trivalent metal halides and for examining how the network structure of the pure melts is broken down by the addition of alkali halides with different structure-breaking powers. The results suggest a way of reconciling the conclusions of Raman studies about the structures of the melts with those of neutron and x-ray-diffraction studies, which have already been examined with the same simulation methods. The Raman spectra, both polarized and depolarized, are calculated from a model for the dependence of the polarizability of the system on the ionic coordinates which was inspired by electronic structure calculations of the polarizabilities of ions in a condensed phase environment. Some results on the lifetimes of the coordination complexes responsible for the appearance of the discrete Raman bands are discussed.

Glover, William J.; Madden, Paul A.

2004-10-01

449

Ingestion of caustic alkali farm products.  

PubMed

Since the Poison Prevention Packaging Act took effect, the number of ingestions of caustic alkali from household products has been significantly reduced. Commercial caustic alkalis used on farms, however, were not included in this legislation. Fourteen children over a 5 year period were seen after ingestion of commercial caustic alkalis used on farms. Seven of the children had ingested liquid pipeline cleaners and seven had ingested solid agents used for a variety of reasons. Six of seven children ingesting liquid agents did so from nonoriginal containers into which the caustic had been transferred for convenience. All seven children ingesting solid agents did so from the original container. Eight of the 14 children were found to have second-degree or worse esophageal involvement. Both solid and liquid caustic agents used commercially on farms can cause significant morbidity. Development of a child-resistant container for daily transfer of liquid pipeline agents could be helpful in preventing injuries from liquid pipeline cleaners. Pediatric gastroenterologists as well as primary care physicians in rural areas should be familiar with this type of injury and should take an active role in instructing parents of children living on farms to prevent such injuries. Extension of the Poison Prevention Packaging Act to caustic alkalis used on farms needs to be considered. PMID:8433244

Neidich, G

1993-01-01

450

Ion exchange of mixed-alkali glasses  

NASA Astrophysics Data System (ADS)

The effect of mixed-alkali composition on ion-exchange strengthening of glasses was studied. The partial substitution of potassium for sodium in a soda-lime-silicate host glass was found to increase the potassium penetration depth during ion exchange in molten potassium nitrate. A host glass with an alkali ratio of K:Na = 0.27 showed a 13% increase in potassium penetration depth for an eight-hour exchange at 510°C, as compared to the base soda-lime-silicate glass. However, the substitution of potassium caused a decrease in the strain point which resulted in appreciable stress relaxation during ion-exchange strengthening. Hence less compressive stress developed. This decrease was addressed by a partial substitution of alumina for silica in the host glass. The substitution of 3 mol% alumina increased the strain point ? 12°C and resulted in a decrease in the stress relaxation of the host glass. For high-temperature ion-exchange treatments, the addition of alumina was found to increase the potassium penetration depth of the mixed-alkali glasses. As a result of the increased potassium penetration depth and the decreased stress relaxation, the mixed-alkali glasses were found to have an increased resistance to abrasion by SiC, as measured by breaking strength.

Mattos, Louis, Jr.

1999-11-01

451

Photoionization of Alkali-Doped Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

Superfluid helium droplets (He_N) provide a cold, weakly-interacting environment for the investigation of weakly bound molecules. Whereas the host-dopant interaction is weak for neutral molecules, ion impurities may be surrounded by frozen shells of polarized helium atoms. An extreme example of the different behavior is given by alkali metal impurities that stay at the surface of the droplet as neutrals but immerse into the droplet as cations releasing a considerable amount of binding energy. We report measurements of the photoionization efficiency for the rubidium-He_N and cesium-He_N systems and find that the ionization threshold is lowered compared with the free atoms and is in good agreement with Rydberg state spectroscopy of these systems. The corresponding energy shift increases when going from heavy to light alkali metals and from small to large helium droplets. Both effects can be explained by the difference in polarization energies associated with submerged alkali metal cations. The findings agree qualitatively well with recent calculations of helium snowball formation around alkali metal cations. M. Theisen, F. Lackner, G. Krois, and W. E. Ernst, J. Phys. Chem. Lett. 2, 2778 (2011). F. Lackner, G. Krois, M. Theisen, M. Koch, and W. E. Ernst, Phys. Chem. Chem. Phys. 13, 18781 (2011). D. E. Galli, D. M. Ceperley, and L. Reatto, J. Phys. Chem. A 115, 7300 (2011).

Theisen, Moritz; Lackner, Florian; Krois, Günter; Koch, Markus; Ernst, Wolfgang E.

2012-06-01

452

Zur Neutralisationstherapie bei Alkali und Säurevergiftung  

Microsoft Academic Search

After poisoning with acid or alkali the most important therapeutic procedure, according to our observations, is the immediate intake of large quantities of water (the fluid must not contain carbonic acid) in order to dilute the poison. It is particularly important that this should be done quickly. No time should be lost in looking for milk or lemons. After poisoning

C. Gloxhuber

1967-01-01

453

Alkali activation of Australian slag cements  

Microsoft Academic Search

Investigation of alkali activation of Australian slag (AAS) was carried out using sodium silicate, sodium hydroxide, sodium carbonate, sodium phosphate, and combinations of these activators. Compressive strengths in the range from 20 to 40 MPa were achieved for the pastes. The most effective activator was liquid sodium silicate. With this activator, the effect of curing at 60 °C, modulus (Ms)

Tatiana Bakharev; Jay Gnananandan Sanjayan; Yi-Bing Cheng

1999-01-01

454

Diode-Pumped Alkali Atom Lasers.  

National Technical Information Service (NTIS)

The recent work at LLNL on alkali-atom lasers has been remarkably successful and productive. Three main phases (so far) can be identified. First, the concept and demonstration of red lasers using (Ti:sapphire pumping) took place; during this time, Rubidiu...

R. H. Page R. J. Beach

2005-01-01

455

Alkali metal thermal to electric conversion  

Microsoft Academic Search

With potential efficiencies of up to 40%, AMTEC technology offers reliability and fuel flexibility for aerospace and ground power applications. Alkali Metal Thermal to Electric Conversion (AMTEC), a direct power-conversion technology, is emerging from the laboratory for use in a number of applications that require lightweight, long-running, efficient power systems. AMTEC is compatible with many heat and fuel sources, and

R. K. Sievers; J. F. Ivanenok; T. K. Hunt

1995-01-01

456

Developments in alkali-metal atomic magnetometry  

Microsoft Academic Search

Alkali-metal magnetometers use the coherent precession of polarized atomic spins to detect and measure magnetic fields. Recent advances have enabled magnetometers to become competitive with SQUIDs as the most sensitive magnetic field detectors, and they now find use in a variety of areas ranging from medicine and NMR to explosives detection and fundamental physics research. In this thesis we discuss

Scott Jeffrey Seltzer

2008-01-01

457

Tropospheric heterogeneous chemistry of haloacetyl and carbonyl halides  

NASA Astrophysics Data System (ADS)

A series of uptake studies for the gas phase carbonyl halides CCl2O and CF2O and the haloacetyl halides CCl3CClO, CF3CFO, and CF3CClO are reported. The measured uptake coefficients for these molecules are less than the experimental detection limit of 5 x 10 exp -4 for pH 7 droplets at 300 K. Using the experimental data the uptake coefficients are estimated to be between 10 exp -6 and 10 exp -4. The lower limit is sufficiently large so that the tropospheric removal rate of the species is not expected to affect the ozone depletion potential values of the HCFC parent species for CF2O, CF3CFO, and CF3CClO.

de Bruyn, W. J.; Duan, S. X.; Shi, X. Q.; Davidovits, P.; Worsnop, D. R.; Zahniser, M. S.; Kolb, C. E.

1992-10-01

458

Enhanced Born charge and proximity to ferroelectricity in thallium halides  

NASA Astrophysics Data System (ADS)

Electronic-structure and lattice-dynamics calculations on thallium halides show that the Born effective charges in these compounds are more than twice larger than the nominal ionic charges. This is a result of cross-band-gap hybridization between Tlp and halogen- p states. The large Born charges cause giant splitting between longitudinal and transverse-optic phonon modes, bringing the lattice close to ferroelectric instability. Our calculations indeed show that cubic TlBr develops ferroelectric instabilities upon lattice expansion starting at 2%. It is remarkable that the apparently ionic thallium halides with a simple cubic CsCl structure and large differences in electronegativity between cations and anions can be very close to ferroelectricity. This can lead to effective screening of defects and impurities that would otherwise be strong carrier traps and may therefore contribute to the relatively good carrier transport properties in TlBr radiation detectors.

Du, Mao-Hua; Singh, David J.

2010-04-01

459

Magnesium halide hydrates and polymerization catalysts prepared therefrom  

SciTech Connect

The patent describes a process for the polymerization of an alpha olefin. It comprises contacting the alpha olefin under polymerization conditions with a catalyst prepared by reacting a hydrous magnesium dihalide composition with reactants comprising a benzoic acid ester and an alkoxytitanium compound to form a first catalyst component, then reacting the first catalyst component with an organoaluminum halide to form a solid product, then reacting the sold product with a halogenating agent comprising a titanium halide, wherein the molar ratio of water to magnesium dihalide in the hydrous magnesium dihalide composition is in the range of about 0.5/1 to 2/1 and the hydrous magnesium dihalide composition is prepared by comminuting a mixture of an anhydrous magnesium dihalide and a hydrous magnesium dihalide at least until the amount of the most highly hydrated magnesium dihalide species in the comminuted product has become substantially stabilized.

Inkrott, K.E.; Hawley, G.R.

1989-08-01

460

A binary Al\\/Li alloy as a new material for the realization of high-intensity pulsed photocathodes  

Microsoft Academic Search

We propose a new material for the fabrication of high-current photocathodes: a binary Al\\/Li alloy acting as a lithium dispenser cathode. This material would have the great advantage to allow regeneration of the Li layer after poisoning or air exposure, by a simple heating process. In a first experiment, we have measured the photoemission energy threshold, WPhi, of a piece

A. Septier; F. Sabary; J. C. Dudek; H. Bergeret; B. Leblond

1991-01-01

461

UV laser-induced cleaning of native-oxide-covered W photocathodes: the effect of recontamination at various pressures  

Microsoft Academic Search

The fifth harmonic (213 nm) of a picosecond Nd3+ :YAG laser was used to remove small fractions of the covering oxide overlayer from polycrystalline metallic photocathodes. The evolution of the photoemitted charge (high-density electron pulses) was followed along with the surface reflectivity change, and they were interpreted in terms of the work function change of the surface. The careful choice

C. Beleznai; D. Vouagner; J. P. Girardeau-Montaut

1998-01-01

462

The effect of CsO activation temperature on the surface escape probability of NEA (In,Ga)As photocathodes  

Microsoft Academic Search

It has been found that the temperature TAat which Cs and O are applied to (In,Ga)As negative electron affinity photocathodes has a strong influence on the surface escape probability B. Over the temperature range investigated, 25-100°C, B changes by a factor of approximately 30.

D. G. Fisher

1974-01-01

463

Palladium- (and nickel-) catalyzed vinylation of aryl halides†  

PubMed Central

Functionalized styrenes are extremely useful building blocks for organic synthesis and for functional polymers. One of the most general syntheses of styrenes involves the combination of an aryl halide with a vinyl organometallic reagent under catalysis by palladium or nickel complexes. This Feature Article provides the first comprehensive summary of the vinylation methods currently available along with a critical comparison of the efficiency, cost and scope of the methods.

Denmark, Scott E.; Butler, Christopher R.

2009-01-01

464

Vibrational population distributions from rare gas halide spectra  

Microsoft Academic Search

An inversion technique, based on multiple linear regression, has been developed to extract vibrational population distributions from bound-free transitions in rare gas halide spectra. Some simple tests of the method are described and the technique is then applied to some experimental XeI B(½)-->X(½) spectra taken from the literature. For the systems Xe(3P2)\\/CF3I and Xe(3P2)\\/CH2I2 the vibrational distributions obtained in this

Keith Johnson; Agust Kvaran; J. P. Simons

1983-01-01

465

Interaction of halide ions with copper: the DFT approach  

Microsoft Academic Search

The applicability of density functional theory to the adsorbate-adsorbent interaction has been tested with the final goal of defining an appropriate combination of the DFT method with basis sets for metal cluster-halide ions studies. The Cu-X? (X = F, Cl, Br, I) systems have been taken as tests cases to probe the different DFT methods (SVWN, BP86 and B3LYP) together

Anna Ignaczak; José A. N. F. Gomes

1996-01-01

466

Production of copper(I) halide emission spectra by MECA  

Microsoft Academic Search

THE introduction of copper (II) salts into most commonly used flames gives a green emission. Copper halides give a particularly intense emission, which is used in the well-known Beilstein test for halogens. The spectra from all copper salts, however, are very similar, and consist mainly of diffuse CuOH bands in the region 535-555 nm, a CuH band centred around 429

R. Belcher; S. L. Bogdanski; S. A. Ghonaim; A. Townshend

1974-01-01

467

Physical and electrochemical study of halide-modified activated carbons  

Microsoft Academic Search

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

Prabeer Barpanda

2009-01-01

468

X-ray preionization of rare-gas-halide lasers  

Microsoft Academic Search

The preionization characteristics of X-rays for self-sustained discharge rare-gas-halide lasers are summarized. The X-rays showed features superior to UV for preionization of large volume high-pressure discharge lasers, which was experimentally confirmed. Furthermore, the effect of preionization on laser output was found to depend on the spatial distribution of preionization electron density and discharge electric field. When a uniform-electric-field area was

K. Midorikawa; M. Obara; T. Fujioka

1984-01-01

469

Carbon tetrachloride free benzylic brominations of methyl aryl halides  

Microsoft Academic Search

A series of mono- and dimethyl aryl halides was alpha-brominated with NBS using either light-induction or microwave-assistance. Instead of the commonly used CCl4 or other chlorinated solvents, MeOAc was used as an environmentally more benign solvent for these side-chain bromination reactions. Moreover, in MeOAc the use of initiator was not required, while the product yields were comparable. With microwave-assistance various

G. van Koten; C. H. M. Amijs; G. P. M. van Klink

2003-01-01

470

X-ray preionisation of the mercury halide lasers  

Microsoft Academic Search

X-rays have been used to preionize all three mercury halide lasers (HgX: X = Cl, Br, I) for the first time. This paper describes the design of the laser head, the discharge circuitry, and the X-ray preionization source used. The minimum X-ray source strength required to saturate the laser energy dependence on the preionization electron density has been determined; this

Michael D. L. Stonefield; Terence A. King

1989-01-01

471

Ionic alkylation of tertiary alkyl halides with tetraalkysilanes  

SciTech Connect

In the reaction of tertiary alkyl halides with tetraethyl-, tetrapropyl-, tetrabutyl-, and tetraamylsilane in the presence of AlX/sub 3/ the halogen atom is substituted by the alkyl group with the formation of the corresponding saturated hydrocarbons containing a quaternary carbon atom. As a result of the hydride mobility of the ..beta..-hydrogen atom in the tetraalkylsilane ionic hydrogenolysis of the substrate occurs in addition to alkylation, and the degree of hydrogenolysis depends on the alkyl substituent in the silane.

Bolestova, G.I.; Parnes, Z.N.

1987-06-10

472

Infrared Study of the Intercalation of Potassium Halides in Kaolinite  

Microsoft Academic Search

Abstraet--KCl-, KBr-, and KI-kaolinite intercalation complexes were synthesized by gradually heating potassium-halide discs of the dimethylsulfoxide (DMSO)-kaolinite intermediate at temperatures to 330~ Two types of complexes were identified by infrared spectroscopy: almost non-hydrous, obtained during thermal treatment of the DMSO complex; and hydrated, produced by regrinding the disc in air. The former showed basal spacings with integral series of 00l

S. Yariv; I. LAPIDES; A. NASSER; N. LAHAV; I. BRODSKY; K. H. MICHAELIAN

2000-01-01

473

Alkylation of adamantane with alkyl halides catalyzed by ruthenium complexes  

Microsoft Academic Search

The feasibility of catalytic alkylation of adamantane and 1-bromoadamantane with alkyl halides in the presence of ruthenium-containing\\u000a catalysts was revealed. The optimum molar ratios between the catalyst components and the reactants, as well as the reaction\\u000a conditions for the selective synthesis of mono-and dialkylsubstituted adamantane derivatives with a 70–98% yield, were determined.

R. I. Khusnutdinov; N. A. Schchadneva; A. I. Malikov; U. M. Dzhemilev

2006-01-01

474

Kinetics of halide chemical vapor deposition of silicon carbide film  

Microsoft Academic Search

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

Rong Wang; Ronghui Ma

2007-01-01

475

Will Lanthanum Halide Scintillators Make NaI(Tl) Obsolete?  

NASA Astrophysics Data System (ADS)

The commercial availability of lanthanum halide scintillators (LaCl3:Ce and LaBr3:Ce) has been much anticipated due to their significantly better resolution (3-4% at 662 keV) relative to NaI(Tl). Unfortunately, our initial investigation of these scintillators revealed significant alpha contamination quite apparent in background spectra. Using measurements of the detector in coincidence with a HPGe detector, we identified the alpha-contaminant as Ac-227. Since this time, the alpha contamination has been substantially reduced so that a second contaminant, La-138 (a beta, gamma, and x-ray source) has become the dominant contaminant in the material. Commercially-available sizes of lanthanum halide scintillators have now reached sizes suitable for handheld Radioactive Isotope Identification Devices (RIIDs). To study the potential of this new material for RIIDs we performed a series of measurements comparing a 1.5'' x 1.5'' LaBr3 detector with an Exploranium GR-135 RIID, which contains a 1.5'' x 2.2'' NaI(Tl) detector. Measurements were taken for short timeframes of seconds to minutes, as typifies RIID usage. Measurements included examples of naturally occurring radioactive material (NORM) typically found in cargo. Of particular interest was the extent to which interference between the La-138 contaminant and K-40, a radioisotope commonly found in NORM, compromise the lanthanum halide performance. Example spectra, detector comparisons and results will be shown.

Milbrath, Brian

2006-05-01

476

Extensive and Highly Accurate Line Lists for Hydrogen Halides  

NASA Astrophysics Data System (ADS)

New dipole moment functions (DMF) for the ground X 1?+ electronic states of the hydrogen halides (HF, HCl, HBr, HI) have been obtained using a direct fit approach that fits the best available and appropriately weighted experimental line intensity data for individual ro-vibrational transitions. Combining the newly developed (taking into account the most recent experiments) empirical potential energy functions and the DMFs, line positions and line intensities of the hydrogen halides and their isotopologues have been calculated numerically using program LEVEL. In addition, new semi-empirical algorithms for assigning line-shape parameters for these species have been developed. Using these improvements, new line lists for hydrogen halides were created to update the HITRAN spectroscopic database. These new lists are more accurate and significantly more extensive than those included in the current version of the database (HITRAN2008). R.J. Le Roy, ``LEVEL 8.0, 2007'', University of Waterloo Chemical Physics Research Report CP-663 (2007); see http://leroy.uwaterloo.ca/programs/. L.S. Rothman, I.E. Gordon, A. Barbe, D.C. Benner, P.F. Bernath, et al., ``The HITRAN 2008 Molecular Spectroscopic Database,'' JQSRT 110, 532-572 (2009).

Li, G.; Bernath, P. F.; Gordon, I. E.; Rothman, L. S.; Richard, C.; Le Roy, R. J.; Coxon, J. A.; Hajigeorgiou, P.

2011-06-01

477

Effects of Halides on Plasmid-Mediated Silver Resistance in Escherichia coli  

PubMed Central

Silver resistance of sensitive Escherichia coli J53 and resistance plasmid-containing J53(pMG101) was affected by halides in the growth medium. The effects of halides on Ag+ resistance were measured with AgNO3 and silver sulfadiazine, both on agar and in liquid. Low concentrations of chloride made the differences in MICs between sensitive and resistant strains larger. High concentrations of halides increased the sensitivities of both strains to Ag+.

Gupta, Amit; Maynes, Maria; Silver, Simon

1998-01-01

478

Effects of halides on plasmid-mediated silver resistance in Escherichia coli.  

PubMed

Silver resistance of sensitive Escherichia coli J53 and resistance plasmid-containing J53(pMG101) was affected by halides in the growth medium. The effects of halides on Ag+ resistance were measured with AgNO3 and silver sulfadiazine, both on agar and in liquid. Low concentrations of chloride made the differences in MICs between sensitive and resistant strains larger. High concentrations of halides increased the sensitivities of both strains to Ag+. PMID:9835606

Gupta, A; Maynes, M; Silver, S

1998-12-01

479

Method for producing hydrocarbon fuels from heavy polynuclear hydrocarbons by use of molten metal halide catalyst  

DOEpatents

In a process for hydrocracking heavy polynuclear carbonaceous feedstocks to produce lighter hydrocarbon fuels by contacting the heavy feedstocks with hydrogen in the presence of a molten metal halide catalyst, thereafter separating at least a substantial portion of the carbonaceous material associated with the reaction mixture from the spent molten metal halide and thereafter regenerating the metal halide catalyst, an improvement comprising contacting the spent molten metal halide catalyst after removal of a major portion of the carbonaceous material therefrom with an additional quantity of hydrogen is disclosed.

Gorin, Everett (San Rafael, CA)

1979-01-01

480

USING A 100 KV DC LOAD LOCK PHOTOGUN TO MEASURE PHOTOCATHODE LIFETIME OF HIGH POLARIZATION STRAINED SUPERLATTICE GAAS/GAASP AT BEAM INTENSITY >1 MILLIAMP  

SciTech Connect

A new GaAs DC high voltage load lock photogun has been constructed at Jefferson Laboratory (JLab), with improved vacuum and photocathode preparation capabilities. As reported previously, this gun was used to study photocathode lifetime with bulk GaAs at DC beam currents between 1 and 10 mA. In this submission, lifetime measurements were performed using high polarization strained-superlattice GaAs photocathode material at beam currents up to 1 mA, with near bandgap light from a fiber based drive laser having picosecond optical pulses and RF time structure.

Joseph Grames; Benard Poelker; Philip Adderley; Joshua Brittian; James Clark; John Hansknecht; Danny Machie; Marcy Stutzman; Kenneth Surles-law; Riad Suleiman

2007-07-02