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1

Extreme ultraviolet quantum efficiency of opaque alkali halide photocathodes on microchannel plates  

NASA Technical Reports Server (NTRS)

Comprehensive measurements are presented for the quantum detection efficiency (QDE) of the microchannel plate materials CsI, KBr, KCl, and MgF2, over the 44-1800 A wavelength range. QDEs in excess of 40 percent are achieved by several materials in specific wavelength regions of the EUV. Structure is noted in the wavelength dependence of the QDE that is directly related to the valence-band/conduction-band gap energy and the onset of atomic-like resonant transitions. A simple photocathode model allows interpretation of these features, together with the QDE efficiency variation, as a function of illumination angle.

Siegmund, O. H. W.; Everman, E.; Vallerga, J. V.; Lampton, M.

1988-01-01

2

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.

Dexter Perkins

3

Alkali halide FLIR lens development  

Microsoft Academic Search

This report describes development of materials and processes for environmental protection of alkali halide lenses. The alkali halide lenses are fabricated by direct hot forging, which yields a finished lens without need for polishing. These lenses are intended for potential application in FLIR thermal imaging systems. The lenses require coatings to protect them against water vapor in the atmosphere. The

R. H. Anderson; R. J. Stokes; T. J. Moravec; J. W. Lin; F. M. Schmit; J. F. Ready; D. K. Greenlaw; D. Stoltzmann

1981-01-01

4

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

5

Solvation at nanoscale: Alkali-halides in water clusters  

SciTech Connect

The solvation of alkali-halides in water clusters at nanoscale is studied by photoelectron spectroscopy using synchrotron radiation. The Na 2p, K 3p, Cl 2p, Br 3d, and I 4d core level binding energies have been measured for salt-containing water clusters. The results have been compared to those of alkali halide clusters and the dilute aqueous salt solutions. It is found that the alkali halides dissolve in small water clusters as ions.

Partanen, Leena [Department of Physics, Tampere University of Technology, Box 692, 33101 Tampere (Finland); Mikkelae, Mikko-Heikki; Huttula, Marko [Department of Physics, University of Oulu, Box 3000, 90014 University of Oulu (Finland); Tchaplyguine, Maxim [MAX-lab, Lund University, Box 118, 22100 Lund (Sweden); Zhang Chaofan; Andersson, Tomas; Bjoerneholm, Olle [Department of Physics and Astronomy, University of Uppsala, Box 516, 75120 Uppsala (Sweden)

2013-01-28

6

Ionic alkali halide XUV laser feasibility study  

SciTech Connect

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

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

1989-11-10

7

Enhanced Quantum Efficiency From Hybrid Cesium Halide/Copper Photocathode  

SciTech Connect

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

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

2014-04-28

8

The alkali halide disk technique in infra-red spectrometry Anomalous behaviour of some samples dispersed in alkali halide disks  

Microsoft Academic Search

Some difficulties encountered in the application of the alkali halide disk technique in infra-red spectrometry are discussed. Complications due to interaction of the sample with the alkali halide have been studied experimentally. It was found that the anomalous behaviour of benzoic acid, succinic acid, adipic acid and suocinimide in KBr and KCl disks must be ascribed to adsorption of the

A. Tolk

1961-01-01

9

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

10

Magnetic polarizations of electrons at dislocations in alkali halides  

E-print Network

interval. 25 NAGNETIC POLARIZATIONS OF ELECTRONS AT DISLOCATIONS IN ALKALI HALIDES 1. INTRODUCTION. The new magnetic effects observed in our laboratory on a number of single crystals of alkali halides are thought to be caused by electrons trapped... on d1slocations. The magnet1c properties are perhaps more interesting as a bas1c contribution to the sc1ence of magnetism than to a knowledge of d. islocations 1n these very pure, optically clear, s1ngle crystals of alkal1 halides. The gross magnet...

McClurg, Gene Roark

1969-01-01

11

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

12

Halide vacancies created by the heterogeneous reaction of OH with alkali halide single crystals.  

PubMed

The heterogeneous surface reaction of OH with dry KI(100) results in iodide vacancies in the surface lattice sites that are filled with OH to generate a stable layer of KOH. Under high-vacuum conditions, in which surface ions are not mobile, the reaction is self-passivating and generates two molecular layers of potassium hydroxide, releasing 1.6 x 10(16) iodide ions per cm(2) of surface area. Reaction rates are identical with those of NaI(100). A similar surface reaction occurs with alkali bromides (KBr(100)), albeit at a much slower rate to generate approximately one-tenth of a monolayer of KOH, whereas no observable reaction occurs with KCl(100) under the conditions of this experiment. The heterogeneous reaction of OH with alkali halides is found to be dependent solely on the identity of the halide anion and independent of the alkali metal cation with the relative reaction rates following the anion ordering, I(-) > Br(-) > Cl(-). The release of halide-containing species is expected to impact the chemistry of the marine boundary layer. PMID:19296711

Brown, Matthew A; McIntire, Theresa M; Johánek, Viktor; Hemminger, John C

2009-03-26

13

A new polarizable force field for alkali and halide ions  

NASA Astrophysics Data System (ADS)

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

Kiss, Péter T.; Baranyai, András

2014-09-01

14

A new polarizable force field for alkali and halide ions  

SciTech Connect

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

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

2014-09-21

15

Coloration of the Alkali Halides by X-rays  

Microsoft Academic Search

Coloration of alkali halides and other salts by x-rays.-(1) Hues produced. CsF, RbF, CaF2, CsCl, RbCl, KCl, NaCl, LiCl, AgCl, BaCl, BeCl, CaCl2, CsBr, RbBr, KBr, KI, NaI, CdI, HgI and K2SiO3 were colored, whereas KF, NaF, LiF, NaBr, RbI, ZnCl, NH4Cl and about 20 other salts showed no coloration with 5 hours exposure to intense radiation. (2) Spectral absorption

P. L. Bayley

1924-01-01

16

The influence of defects and defect clusters on alkali atom desorption stimulated by low energy electron bombardment of alkali halides  

NASA Astrophysics Data System (ADS)

An important challenge in studies of electronically induced desorption on alkali halides is to determine the degree to which the desorption rate of alkali atoms as a function of dose and temperature is influenced by alkali island formation on the surface, alkali colloid formation in the bulk, and individual defect diffusion from the bulk to the surface. To address this problem, we report measurements of transmission optical absorption which gives direct information on defect, cluster and surface island concentrations, and of electron bombardment induced alkali desorption yields performed simultaneously on NaCl, NaF, and LiF at temperatures between 27 and 400°C. These experiments provide insight into the formation of surface and bulk agglomerates which in turn act as sources of desorbing alkali atoms. Our data support a physical picture where bombardment induced F-centers lead to the formation of F-center aggregates in the bulk and alkali metal clusters on the surface at temperatures around room temperature. At higher temperatures alkali metal desorption during electron bombardment is dominated by the emission of weakly bound single alkali atoms, and alkali atoms from alkali metal clusters on the surface of the crystals. After the cessation of the electron beam, the desorption yield is controlled by the thermal stability of metallic colloids which have been formed in the bulk during electron bombardment due to the temperature dependent higher mobility of the F-centers.

Seifert, N.; Ye, H.; Tolk, N.; Husinsky, W.; Betz, G.

1994-01-01

17

Real time evolution of antimony deposition for high performance alkali photocathode development  

NASA Astrophysics Data System (ADS)

The development of X-ray techniques opens new opportunities for real-time in-situ study of photocathode growth process in details. The initial ultra thin Sb films during photocathode process were investigated on multiple substrates based on different applications. The real-time X-ray scattering and post-growth X-ray reflectivity and diffraction measurement were performed and analyzed. Experiment results indicate that Sb deposition performs a phase change from amorphous to crystalline, the critical thicknesses are different on B33 float glass, Si and Mo. Two methods were applied for film thickness calculation from X-ray scattering data, and they agree well with thickness monitor result. Sb films deposited on different substrates show similar final film roughnesses. The real time x-ray study indicates that the initial Sb layer deposition process on different substrate has different structure during deposition, the optimized thickness of the initial Sb layer may varies depends on the substrate. This study also paved the road for further study of the more complex alkali metal vapor diffusion process in photocathode growth.

Xie, Junqi; Demarteau, Marcel; Wagner, Robert; May, Edward; Zhang, Jiang; Ruiz-Oses, Miguel; Liang, Xue; Ben-Zvi, Ilan; Attenkofer, Klaus; Schubert, Susan; Smedley, John; Wong, Jared; Padmore, Howard

2013-09-01

18

Model of self-trapped excitons in alkali halides  

NASA Astrophysics Data System (ADS)

We have carried out an ab initio many-electron variational calculation of the adiabatic potential-energy surface (APES) for the lowest triplet state of the self-trapped exciton (STE) in LiCl, NaCl, and KCl. Calculations of the H center in these crystals show that the <111> orientation is favored, in agreement with experimental results for NaCl but not for KCl, in which it is oriented along a <110> direction (no measurement exists for LiCl), and hence most detailed calculations for STE's are carried out for NaCl. It is found that the APES minimum for each crystal occurs when the Cl-2 molecular ion is displaced along its molecular axis from its symmetrical position (D2h) nearly halfway to the nearest halogen lattice point. The calculated transition energies for the optical absorption and luminescence at this configuration agree with the experimental values for the triplet STE, although the calculated stretching vibration frequency of the Cl-2 molecular ion in NaCl is much smaller than that for the H center, contradictory to recent resonant Raman studies. Other minima are found at the nearest F-H pair configuration, in which the Cl-2 molecular ion is reoriented by 90° from the initial orientation and next-nearest F-H pair. Extremely small luminescence energy at these configurations excludes the possibility that they are the candidates for the luminescent state of the STE. It is found that, after the displacement of the Cl-2 molecular ion beyond the first minimum of the APES towards the nearest F-H pair configuration, the total energy is lowered by reorientation, inducing an anomaly on the APES. The results of a recent experimental investigation, including existence of several types of relaxed configuration of the STE in alkali halides, the stretching vibration frequency, and the femtosecond oscillation on APES, are discussed on the basis of the results of the calculation.

Puchin, V. E.; Shluger, A. L.; Tanimura, K.; Itoh, N.

1993-03-01

19

New AIG Method of Growing Alkali Halide Crystals and Potential Application to CZT  

NASA Astrophysics Data System (ADS)

The new AIG (Advance Interface Growth) method has been successfully applied to alkali halide scintillation crystals at PhotoPeak, Inc. for the last four years. It produces single, stress-free crystals having a low level of defects and has resulted in increasing the yield of usable CsI(Tl) crystals to 75-85%. Essentially it is a low gradient method but has the capability to adapt the gradient to that needed by an individual crystal for the most successful growth. High quality crystals have been supplied to national laboratories and the nuclear medicine market. For example, a blank CsI(Tl) crystal 2 in diameter and 2 in length was produced having a measured energy resolution of 6.5% at 662 keV on a 2 -diameter PMT having a standard blue bialkali photocathode. This far exceeds the best resolution, 8.5-9.5%, obtained for CsI(Tl) crystals grown by the conventional Bridgman method. It is expected that this method can be successfully applied to grow high quality CZT crystals with substantially higher yield, 25-35%, than the presently existing 5-10%. The reasons for the expected improved yield of CZT crystals are that the phase diagram of CZT material has a narrow range of stability and CZT crystals should benefit from growth in a low gradient environment. Since the AIG method does not involve any moving parts, the temperature control and stability are much higher than for the conventional Bridgman method. The experience with CsI crystals indicates that imperfections like twinning, sparks, and multiplicities can be substantially reduced or even eliminated in CZT crystals. The expected higher yield and improved spectroscopic quality of CZT should allow many commercial applications to become a reality.

Gleyzer, A.; Rhodes, E.

2002-10-01

20

Alkali Metal Photocathodes Claire Stortstrom, Patrick O'Shea, Eric J. Montgomery, Noah SennettClaire Stortstrom, Patrick O Shea, Eric J. Montgomery, Noah Sennett  

E-print Network

beams for Free Electron Lasers through use of alkali metal Experiment ·An ultra high vacuum chamber through argon ion bombardment using an ion gun. Potassium, and Sodium alkali metals will be deposited ontoAlkali Metal Photocathodes Claire Stortstrom, Patrick O'Shea, Eric J. Montgomery, Noah Sennett

Anlage, Steven

21

Ordering of alkali halide salts dissolved in bacteriophage Pf1 solutions: A nuclear magnetic resonance study  

E-print Network

Ordering of alkali halide salts dissolved in bacteriophage Pf1 solutions: A nuclear magnetic into filamentous bacteriophage Pf1 solutions display line splittings and shifts consistent with an interaction phospholipid bicelles1 and filamen- tous virus2 and bacteriophage3 particles partially restores an- isotropic

Augustine, Mathew P.

22

SURFACE AND SPACE CHARGES. Electrostatic charge effects on surface defects in alkali halide crystals  

E-print Network

SURFACE AND SPACE CHARGES. Electrostatic charge effects on surface defects in alkali halide crystals Abstract. -- The presence of a surface charge and a compensating Debye-Hiickel layer of charged point defects in ionic crystals was suggested by Lehovec [1]. The surface charge was later associated [2

Paris-Sud XI, Université de

23

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

E-print Network

COLOUR CENTRES IN DOPED ALKALI HALIDES. THE ROLE OF OXYGEN AND TITANIUM IN THE LUMINESCENCE OF Li that the luminescence occurs by hole capture at a titanium defect site. However electron spin resonance has shown that the titanium is incorporated in the crystal as Ti3+ and Ti4+ ions with the possibility of charge compensa- tion

Paris-Sud XI, Université de

24

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

25

CRYOSCOPY OF THE LiCl-KCl EUTECTIC MELT CONTAINING ALKALI HALIDES AND ALKALI TITANIUM FLUORIDES AS SOLUTES  

Microsoft Academic Search

The cryoscopic behavior of NaCl, LiF, NaF, KF, LiâTiFâ, Na\\/; sub 2\\/TiFâ, and KâTiFâ in the LiCl--KC l eutectic melt is ; reported. In the regions of dilute concentrations. the behavior of the alkali ; halides is in accord with complete dissociation, the deviations from ; thermodynamic ideality being attributed to solid solution formation, and for LiF, ; in addition,

G. J. Janz; C. Solomons; H. J. Gardner; J. Goodkin; C. T. Brown

1958-01-01

26

Low temperature multi-alkali photocathode processing technique for sealed intensified CCD tubes  

NASA Technical Reports Server (NTRS)

A low temperature photocathode process has been used to fabricate an intensified CCD visual photocathode image tube, by incorporating a thinned, backside-illumined CCD as the target anode of a digicon tube of Hubble Space Telescope (HST) design. The CCD digicon tube employs the HST's sodium bialkali photocathode and MgF2 substrate, thereby allowing a direct photocathode quantum efficiency comparison between photocathodes produced by the presently employed low temperature process and those of the conventional high temperature process. Attention is given to the processing chamber used, as well as the details of gas desorption and photocathode processing.

Doliber, D. L.; Dozier, E. E.; Wenzel, H.; Beaver, E. A.; Hier, R. G.

1989-01-01

27

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

28

Hot-carrier transport processes in stimulated desorption of alkali halides  

NASA Astrophysics Data System (ADS)

Electron- and photon-stimulated desorption of epitaxial thin films and bulk single crystals of alkali halides has been investigated. It has been found that the widely accepted model based on self-trapped exiton decay and thermally activated defect diffusion cannot account for a number of experimental observations. In particular, it cannot explain the stability of the very thin alkali-halide films against the electron beam, and it fails to interpret correctly the yield dependence of the halogen atoms emitted with nonthermal energies on the film thickness and sample temperature. It is shown that for satisfactory interpretation of those data one has to take into account early stages of crystal excitation, i.e., hot carrier formation and transport processes occurring prior to self-trapped exciton phase. Consequently, a comprehensive description of the observed desorption features is presented.

Kolodziej, J. J.; Szymonski, M.

1998-11-01

29

Theory of metal atom-water interactions and alkali halide dimers  

NASA Technical Reports Server (NTRS)

Theoretical studies of the interactions of metal atoms with water and some of its isoelectronic analogs, and of the properties of alkali halides and their aggregates are discussed. Results are presented of ab initio calculations of the heats of reaction of the metal-water adducts and hydroxyhydrides of Li, Be, B, Na, Mg, and Al, and of the bond lengths and angles an; the heats of reaction for the insertion of Al into HF, H2O, NH3, H2S and CH3OH, and Be and Mg into H2O. Calculations of the electron affinities and dipole moments and polarizabilities of selected gas phase alkali halide monomers and dimers are discussed, with particular attention given to results of calculations of the polarizability of LiF taking into account electron correlation effects, and the polarizability of the dimer (LiF)2.

Jordan, K. D.; Kurtz, H. A.

1982-01-01

30

Correlations for calculating the surface tension and enthalpies of sublimation of alkali halides  

NASA Astrophysics Data System (ADS)

The capability of a new model on predicting the surface tension of molten alkali halides is described. A relationship, with a simple form of calculation, exists between the surface tension (?) at the melting point, molar volume (V), inter-nuclear distance (D) and the enthalpy of sublimation (Es). The basic idea results from the assumption that all the parameters are constants that are usually easy to acquire. Moreover, two previous models (Furth and Schytil equations) were also checked and applied for calculating surface tension of molten salts. The three formulas have been examined for 20 salts and showed remarkable agreement between calculated and experimental data with a difference of less than 10% for most of the salts studied. The heats of sublimation of alkali halides were, theoretically, calculated and compared to literature values.

Aqra, Fathi

2014-05-01

31

Alkali metal\\/halide thermal energy storage systems performance evaluation  

Microsoft Academic Search

Materials compatibility and durability of advanced salt\\/alkali metal slurry thermal energy storage systems has been demonstrated. Applications are being evaluated for both space and terrestrial solar thermal power conversion. High energy density of these thermal storage systems is achieved by colocation of heat input and extraction within the slurry mixture which is overwhelmingly phase-change salt. This paper addresses performance testing

W. M. Phillips; J. W. Stearns

1987-01-01

32

Alkali metal\\/halide thermal energy storage systems performance evaluation  

Microsoft Academic Search

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

W. M. Phillips; J. W. Stearns

1986-01-01

33

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

Microsoft Academic Search

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

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

2006-01-01

34

Development of processes for the production of solar grade silicon from halides and alkali metals  

NASA Technical Reports Server (NTRS)

High temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost were studied. Experiments were 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.

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

1980-01-01

35

Electron distributions and ionic binding in series of alkali halide molecules  

Microsoft Academic Search

Electron density maps for series of diatomic alkali halide molecules are determined from near-Hartree-Fock wavefunctions. The charge distributions in these molecules are analyzed in terms of the total-molecular density and density-difference maps. The outermost orbital is found to play a dominant role in the ionic bonding. Finally, the changes in the distributions at various internuclear separations and the relation of

L. A. Curtiss; C. W. Kern; R. L. Matcha

1975-01-01

36

Alkali metal/halide thermal energy storage systems performance evaluation  

NASA Technical Reports Server (NTRS)

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.

1986-01-01

37

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

38

Optical Constants and Excitons of Alkali Cuprous Halide Crystals  

NASA Astrophysics Data System (ADS)

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

Edamatsu, Keiichi; Nanba, Takao; Ikezawa, Mikihiko

1989-01-01

39

Response of alkali halide scintillators to neutrons from 5 to 100 MeV  

SciTech Connect

The response of three alkali halide scintillators to neutrons in the range 5 to 100 MeV was investigated with the spallation neutron source at LAMPF/WNR. Scintillating crystals were NaI(Tl), KI(Tl) and CsI(Tl), each 2.5 cm in diameter and 1.2 cm thick. Pulse shapes that depend on particle type were observed for NaI(Tl) and CsI(Tl) but not for KI(Tl). Pulse height spectra for are reported as a function of neutron energy, and, where pulse shape discrimination was observed, for individual charged-particle groups.

Bartle, C.M. [Institute of Geophysical and Nuclear Sciences, Lower Hutt (New Zealand); Haight, R.C. [Los Alamos National Lab., NM (United States)

1994-12-31

40

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

41

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

42

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

43

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

PubMed

Thermodynamic properties of aqueous solutions containing alkali and halide ions are determined by molecular simulation. The following ions are studied: Li(+), Na(+), K(+), Rb(+), Cs(+), F(-), Cl(-), Br(-), and I(-). The employed ion force fields consist of one Lennard-Jones (LJ) site and one concentric point charge with a magnitude of ±1 e. The SPC/E model is used for water. The LJ size parameter of the ion models is taken from Deublein et al. [J. Chem. Phys. 136, 084501 (2012)], while the LJ energy parameter is determined in the present study based on experimental self-diffusion coefficient data of the alkali cations and the halide anions in aqueous solutions as well as the position of the first maximum of the radial distribution function of water around the ions. On the basis of these force field parameters, the electric conductivity, the hydration dynamics of water molecules around the ions, and the enthalpy of hydration is predicted. Considering a wide range of salinity, this study is conducted at temperatures of 293.15 and 298.15 K and a pressure of 1 bar. PMID:25669552

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

2014-01-28

44

Alkali Halide Interfacial Behavior in a Sequence of Charged Slit Pores  

SciTech Connect

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

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

2011-01-01

45

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

SciTech Connect

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

Reiser, S.; Deublein, S.; Hasse, H., E-mail: hans.hasse@mv.uni-kl.de [Laboratory of Engineering Thermodynamics, University of Kaiserslautern, 67663 Kaiserslautern (Germany); Vrabec, J. [Thermodynamics and Energy Technology, University of Paderborn, 33098 Paderborn (Germany)] [Thermodynamics and Energy Technology, University of Paderborn, 33098 Paderborn (Germany)

2014-01-28

46

Role of water in alkali halide heterogeneous chemistry relevant to the atmosphere: A surface science study  

NASA Astrophysics Data System (ADS)

Water is a ubiquitous atmospheric constituent. The interaction of water in its various forms (vapor, liquid, ice) with other atmospheric constituents has a significant impact on the chemistry of the atmosphere. Another class of compounds that are of considerable importance in atmospheric chemistry are alkali halide salts such as sea salt particles. Heterogeneous reactions of alkali halides with gas phase pollutants are believed to be an important source of halogens in the troposphere. There is an increasing amount of evidence that the presence of water plays an important role in the heterogeneous chemistry of alkali halide particles. It is the goal of this dissertation to contribute to the understanding of the interaction of water with alkali halide surfaces and its atmospheric implications. Surface processes are of fundamental importance in heterogeneous atmospheric chemistry, but they are often difficult to study because of their inherent complexity. As this dissertation shows, the use of modern surface science techniques offer valuable insights into these complex processes and as such offer complementary alternatives to the traditional atmospheric chemistry experiments. The surface science techniques used in this dissertation are X-ray photoelectron spectroscopy (XPS), scanning polarization force microscopy (SPFM) and scanning electron microscopy (SEM). Presented here are the results of the XPS and SEM studies undertaken to determine the nature and content of surface adsorbed water on NaCl as a function of surface defects. The details of HNO3 uptake on NaCl and the effect of surface adsorbed water on this uptake are also discussed. Our results show that the amount of ``strongly adsorbed water'' (SAW) on the surface of NaCl particles depends on the particle size and hence, on the concentration of surface defects. Unlike the (100) single crystal the more defective surfaces show dissociative water uptake at room temperature upon exposure to water vapor well below the deliquescence point of NaCl. The binding energy and temperature dependence characteristics of the SAW related oxygen signal on the NaCl particles are consistent with OH- like species. We also show that the dissociative adsorption of HNO3(g) on NaCl to form NaNO3(s) and HCl(g) follows single-site Langmuir adsorption behavior. The dissociative adsorption accompanied by water-induced recrystallization of the NaNO3 product on the NaCl surface gives rise to the experimentally observed HNO3 pressure dependence of the reactive sticking coefficient for reaction under steady-state reaction conditions. Surface segregation of bromine in bromide doped NaCl single crystals has been studied using XPS, SEM and SPFM. Our results show, for the first time, that substantial segregation of Br- to the surface of NaCl samples with low level Br- dopant concentrations occurs under conditions of water vapor exposure. The segregation phenomenon is likely to play an important role in atmospheric phenomena involving surface reactions of sea salt particles and aerosols.

Ghosal, Sutapa

2001-05-01

47

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

48

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

49

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

50

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

51

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

52

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

NASA Astrophysics Data System (ADS)

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

Lee, Min-Hong

53

Determination of Alkali and Halide Monovalent Ion Parameters for Use in Explicitly Solvated Biomolecular Simulations  

PubMed Central

Alkali (Li+, Na+, K+, Rb+, and Cs+) and halide (F?, Cl?, Br?, and I?) ions play an important role in many biological phenomena, roles that range from stabilization of biomolecular structure, to influence on biomolecular dynamics, to key physiological influence on homeostasis and signaling. To properly model ionic interaction and stability in atomistic simulations of biomolecular structure, dynamics, folding, catalysis, and function, an accurate model or representation of the monovalent ions is critically necessary. A good model needs to simultaneously reproduce many properties of ions, including their structure, dynamics, solvation, and moreover both the interactions of these ions with each other in the crystal and in solution and the interactions of ions with other molecules. At present, the best force fields for biomolecules employ a simple additive, nonpolarizable, and pairwise potential for atomic interaction. In this work, we describe our efforts to build better models of the monovalent ions within the pairwise Coulombic and 6-12 Lennard-Jones framework, where the models are tuned to balance crystal and solution properties in Ewald simulations with specific choices of well-known water models. Although it has been clearly demonstrated that truly accurate treatments of ions will require inclusion of nonadditivity and polarizability (particularly with the anions) and ultimately even a quantum mechanical treatment, our goal was to simply push the limits of the additive treatments to see if a balanced model could be created. The applied methodology is general and can be extended to other ions and to polarizable force-field models. Our starting point centered on observations from long simulations of biomolecules in salt solution with the AMBER force fields where salt crystals formed well below their solubility limit. The likely cause of the artifact in the AMBER parameters relates to the naive mixing of the Smith and Dang chloride parameters with AMBER-adapted Åqvist cation parameters. To provide a more appropriate balance, we reoptimized the parameters of the Lennard-Jones potential for the ions and specific choices of water models. To validate and optimize the parameters, we calculated hydration free energies of the solvated ions and also lattice energies (LE) and lattice constants (LC) of alkali halide salt crystals. This is the first effort that systematically scans across the Lennard-Jones space (well depth and radius) while balancing ion properties like LE and LC across all pair combinations of the alkali ions and halide ions. The optimization across the entire monovalent series avoids systematic deviations. The ion parameters developed, optimized, and characterized were targeted for use with some of the most commonly used rigid and nonpolarizable water models, specifically TIP3P, TIP4PEW, and SPC/E. In addition to well reproducing the solution and crystal properties, the new ion parameters well reproduce binding energies of the ions to water and the radii of the first hydration shells. PMID:18593145

2008-01-01

54

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

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

55

Stable geometries of the self-trapped exciton in alkali halide crystals  

NASA Astrophysics Data System (ADS)

According to recent works, the self-trapped excitons (STE) in alkali halides are grouped in three different types. In some (e.g. RbI), a population transfer is observed among coexisting types as temperature is raised. In others (NaBr and NaI) extra type emission bands have been observed under dilational strain. We studied the adiabatic potential energy surface (APES) of the STE under the effect of expanded or compressed lattices, and of rotation of the V k core in several directions, based on both extended-ion and ab initio Hartree-Fock methods. A critical study of the zero field splitting parameter D of the spin Hamiltonian is made in assessing the effect of rotation. It is shown that: (a) the potential barrier separating the adjacent local minima on the APES becomes smaller as the lattice is dilated; (b) the APES associated with rotation of the halogen molecule-ion axis from [110] toward [001], upto about 30°, is flat; Rotations in other directions are stiff, however; (c) the observed anomaly of the D parameter in NaCl is compatible with the rotation described in (b) above. The geometries of the three types are discussed on the basis of this study.

Song, K. S.; Baetzold, R. C.; Kong, F.

1994-06-01

56

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

PubMed

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

Weckström, Kristian; Papageorgiou, Anastassios C

2007-06-01

57

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

PubMed Central

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.

2013-01-01

58

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

SciTech Connect

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

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

1986-01-01

59

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

60

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

SciTech Connect

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

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

2009-03-10

61

Theoretical Compton profile anisotropies in molecules and solids. VII. Zero point Compton profile anisotropies and bond polarities in alkali halide diatomic molecules  

Microsoft Academic Search

A correlation between bond polarities and zero point Compton profile anisotropies is shown for alkali halide molecules. The correlation derives from the fact that both quantities are determined by molecular binding and antibinding forces and are thus functionally related to nuclear charge ratios.

Robert L. Matcha; Bernard M. Pettitt

1980-01-01

62

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

63

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

Microsoft Academic Search

The incorporation of fungal laccases into novel applications has been delayed mainly due to their intrinsic sensitivity towards halides and alkaline conditions. In order to explore new sources of enzymes we evaluated the multipotent polyphenol oxidase PPO1 from the marine bacterium Marinomonas mediterranea. Here we report that, in contrast to its fungal counterparts, PPO1 remained functional above neutral pH presenting

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

2005-01-01

64

THE SPECIFIC HEATS OF THE ALKALI HALIDES AND THEIR SPECTROSCOPIC BEHAVIOUR. PART X. THE LITHIUM SALTS  

Microsoft Academic Search

The great disparity between the atomic weights of the constituent metal ; and halogen atoms has a notable influence on the character of the vibration ; spectra as also on the thermal behavior of the lithium halides. The atomic heat ; rises rather steeply in the lower ranges of temperature and this is followed by a ; relatively slow increase

1962-01-01

65

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

NASA Astrophysics Data System (ADS)

Low-level-light (LLL) weapon sight measurement technologies based on Low-high temperature environments testing conditions are always concerned by military equipments manufacturers. Because low-high temperature environment, etc. are under loaded function, the electric performance parameter change to make LLL weapon sight, causing the LLL weapon sight can't be worked and used normally while taking aim. Generally believed that many photocathode is n-type and p-type doping of the inner surface layer comprising more photocathode not light sensitive, but also sensitive to temperature. To image intensifier is non-working state at the temperature 70°C +/-2°C test boxes and thermostats time one hour, five minutes to image intensifier into -50°C+/-2°C Test Box temperature one hour, then five minutes again placed 70°C +/-2°C high temperature test box for three cycle question image intensifier restore normal temperature after the test. The experiments show that, when the temperature rises, the heat semiconductor photocathode current density, thermal current rise in the temperature range 0 to 70°C, 4°C temperature is increased, almost twice its current heat. Of course, image intensifier imported the equivalent background illumination will also increase, resulting in night vision systems observed at the scene image contrast and differential rates were lowered, target detection system performance last night caused the decline. A study of the reasons is the photo-cathode materials and fabrication of thermal electron emission standards restricting the ability.

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

2008-03-01

66

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

PubMed

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

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

2014-08-13

67

The specific heats of the alkali halides and their spectroscopic behaviour  

Microsoft Academic Search

Summary  The great disparity between the atomic weights of the constituent metal and halogen atoms has a notable influence on the character\\u000a of the vibration spectra as also on the thermal behaviour of the lithium halides. The atomic heat rises rather steeply in\\u000a the lower ranges of temperature and this is followed by a relatively slow increase towards the limiting value

C. V. Raman

1962-01-01

68

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

PubMed Central

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

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

2013-01-01

69

Ca-Fe and Alkali-Halide Alteration of an Allende Type B CAI: Aqueous Alteration in Nebular or Asteroidal Settings  

NASA Technical Reports Server (NTRS)

Ca-Fe and alkali-halide alteration of CAIs is often attributed to aqueous alteration by fluids circulating on asteroidal parent bodies after the various chondritic components have been assembled, although debate continues about the roles of asteroidal vs. nebular modification processes [1-7]. Here we report de-tailed observations of alteration products in a large Type B2 CAI, TS4 from Allende, one of the oxidized subgroup of CV3s, and propose a speculative model for aqueous alteration of CAIs in a nebular setting. Ca-Fe alteration in this CAI consists predominantly of end-member hedenbergite, end-member andradite, and compositionally variable, magnesian high-Ca pyroxene. These phases are strongly concentrated in an unusual "nodule" enclosed within the interior of the CAI (Fig. 1). The Ca, Fe-rich nodule superficially resembles a clast that pre-dated and was engulfed by the CAI, but closer inspection shows that relic spinel grains are enclosed in the nodule, and corroded CAI primary phases interfinger with the Fe-rich phases at the nodule s margins. This CAI also contains abundant sodalite and nepheline (alkali-halide) alteration that occurs around the rims of the CAI, but also penetrates more deeply into the CAI. The two types of alteration (Ca-Fe and alkali-halide) are adjacent, and very fine-grained Fe-rich phases are associated with sodalite-rich regions. Both types of alteration appear to be replacive; if that is true, it would require substantial introduction of Fe, and transport of elements (Ti, Al and Mg) out of the nodule, and introduction of Na and Cl into alkali-halide rich zones. Parts of the CAI have been extensively metasomatized.

Ross, D. K.; Simon, J. I.; Simon, S. B.; Grossman, L.

2012-01-01

70

Mechanism of the influence of ultrasonic and electric fields on the vibrational motion of dislocations in the ultrasonic vibration of alkali-halide crystals  

Microsoft Academic Search

The influence of electric and ultrasonic fields on the vibrational motion of disolocations in alkali-halide crystals was investigated by the method of current-voltage characteristics I(V) and the measurement of the amplitude dependence of the damping Q-1(?0) and the defect of the modulus DeltaM\\/M(?0) in a composite piezoelectric oscillator. An abrupt decrease of I(t) is observed at amplitudes of the relative

É. P. Belozerova

1987-01-01

71

Mechanism of the influence of ultrasonic and electric fields on the vibrational motion of dislocations in the ultrasonic vibration of alkali-halide crystals  

Microsoft Academic Search

The influence of electric and ultrasonic fields on the vibrational motion of disolocations in alkali-halide crystals was investigated by the method of current-voltage characteristics I(V) and the measurement of the amplitude dependence of the damping Q-1(e0) and the defect of the modulus ?M\\/M(e0) in a composite piezoelectric oscillator. An abrupt decrease of I(t) is observed at amplitudes of the relative

É. P. Belozerova

1987-01-01

72

Universal scaling of potential energy functions describing intermolecular interactions. II. The halide-water and alkali metal-water interactions  

SciTech Connect

The scaled forms of the newly introduced generalized potential energy functions (PEFs) describing intermolecular interactions [J. Chem. Phys. xx, yyyyy (2011)] have been used to fit the ab-initio minimum energy paths (MEPs) for the halide- and alkali metal-water systems X-(H2O), X=F, Cl, Br, I, and M+(H2O), M=Li, Na, K, Rb, Cs. These generalized forms produce fits to the ab-initio data that are between one and two orders of magnitude better in the ?2 than the original forms of the PEFs. They were found to describe both the long-range, minimum and repulsive wall of the potential energy surface quite well. Overall the 4-parameter extended Morse (eM) and generalized Buckingham exponential-6 (gB-e6) potentials were found to best fit the ab-initio data. Furthermore, a single set of parameters of the reduced form was found to describe all candidates within each class of interactions. The fact that in reduced coordinates a whole class of interactions can be represented by a single PEF, yields the simple relationship between the molecular parameters associated with energy (well depth, ?), structure (equilibrium distance, rm) and spectroscopy (anharmonic frequency, ?):€? = A? (? /?)1/ 2 /rm + B?? /rm 3 , where A and B are constants depending on the underlying PEF. This more general case of Badger’s rule has been validated using the experimentally measured frequencies of the hydrogen bonded OH stretching vibrations in the halide-water series.

Werhahn, Jasper C.; Akase, Dai; Xantheas, Sotiris S.

2014-08-14

73

Salting out of alcohols by alkali halides at the freezing temperature  

Microsoft Academic Search

The freezing-point depression of the ternary systems water-alkali halidesalcohols was measured with a precision Advanced Instrument osmometer. From the corresponding freezing-point depression of the binary systems the salting-out constantsks were calculated. The effect of ionic size was investigated withtert-butanol, and the effect of alcohol chain length with NaCl. The trends ofks with ionic size are similar to those of typical

Jacques E. Desnoyers; Michel Billon; Sylvain Léger; Gérald Perron; Jean-Pierre Morel

1976-01-01

74

Characterization of alkali halides doped 1-(2-methoxy benzyloxy)-8- hydroxy-9,10-anthraquinone films for photovoltaic applications  

NASA Astrophysics Data System (ADS)

Thin films of 1-(2-methoxy benzyloxy)-8-hydroxy-9, 10-anthraquinone (AQ) have been prepared by hot wall technique onto glass substrates kept at 348 K in a vacuum of 10-5 Torr. Chemical modifications of films have been performed by their treatment with different alkali halides. The films so obtained are systematically studied for their electrical and optical properties. The electrical conductivities of the resulting films exhibited semiconductor-like temperature dependence in the experimental range studied. LiCl and LiBr doped films exhibit almost three orders of magnitude higher conductivity, than untreated films, whereas NaCl, NaBr and KBr do not show any remarkable change in the conductivity. Analysis of optical absorption measurements indicate that the interband transition energies of films lie in the range of 2.57-2.66 eV. Keeping in view the electrical and optical properties of films, ITO/AQ/Al solar cells have been fabricated and characterized. The J-V characteristics of these devices are found to be in good agreement with standard diode equation. Power conversion efficiency of Li doped AQ based devices are found to increase by an order of two as compared to undoped AQ based devices.

Mahajan, Aman; Singh, Mandeep; Gupta, Himani; Bedi, R. K.; Kumar, S.; Aswal, D. K.

2012-06-01

75

Thermodynamics of small alkali metal halide cluster ions: comparison of classical molecular simulations with experiment and quantum chemistry.  

PubMed

We evaluate the ability of selected classical molecular models to describe the thermodynamic and structural aspects of gas-phase hydration of alkali metal halide ions and the formation of small water clusters. To understand the effect of many-body interactions (polarization) and charge penetration effects on the accuracy of a force field, we perform Monte Carlo simulations with three rigid water models using different functional forms to account for these effects: (i) point charge nonpolarizable SPC/E, (ii) Drude point charge polarizable SWM4-DP, and (iii) Drude Gaussian charge polarizable BK3. Model predictions are compared with experimental Gibbs free energies and enthalpies of ion hydration, and with microscopic structural properties obtained from quantum DFT calculations. We find that all three models provide comparable predictions for pure water clusters and cation hydration but differ significantly in their description of anion hydration. None of the investigated classical force fields can consistently and quantitatively reproduce the experimental gas-phase hydration thermodynamics. The outcome of this study highlights the relation between the functional form that describes the effective intermolecular interactions and the accuracy of the resulting ion hydration properties. PMID:25513841

Vlcek, Lukas; Uhlik, Filip; Moucka, Filip; Nezbeda, Ivo; Chialvo, Ariel A

2015-01-22

76

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

77

Photocathodes for RF photoinjectors  

NASA Astrophysics Data System (ADS)

Over the past ten years photocathodes have been extensively used as high-brightness electron sources in RF guns. In this paper, I present a general review of the alkali-based high quantum efficiency (QE) photoemitters (e.g. Cs 3Sb, K 2CsSb and Cs 2Te), together with a comparative analysis of the different preparation procedures and the results obtained, both in the preparation chambers and in RF guns. The need to increase the photocathode reliability has provided the impetus to get an R&D activity to go over the alchemy of photocathode preparation procedure. In this paper, I will discuss the results so far obtained in different laboratories, both by using traditional investigation strategy (e.g. QE and RF behavior) and by means of surface science techniques as Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS). Alkali antimonides have been used at first in the RF gun due to the high QE response to the green light of the Nd:YLF second-harmonic radiation. Measurements have confirmed the high reactivity of the alkali antimonide photocathodes to the residual gases: this fact makes their use in RF guns not practical, mainly for short lifetimes. Further investigations have shown that the choice of the substratum preparation procedure and chemical composition plays a fundamental role in the photocathode performance, both from the point of view of the QE and the operative lifetime and ruggedness to gas exposition. Cesium telluride (Cs 2Te) prepared on a molybdenum substratum seems to be, nowadays, the best compromise, in terms of preparation procedure reliability and ruggedness, that now the characteristics and drawbacks of this material are well understood (e.g. the need of an UV laser source). Future possible developments will be discussed. In particular, the measurement and the control of the thermal emittance and the time response could be an important task.

Michelato, P.

1997-02-01

78

Molecular Dynamics Simulations of the Dynamic and Energetic Properties of Alkali and Halide Ions Using Water-Model-Specific Ion Parameters  

PubMed Central

The dynamic and energetic properties of the alkali and halide ions were calculated using molecular dynamics (MD) and free energy simulations with various different water and ion force fields including our recently developed water-model-specific ion parameters. The properties calculated were activity coefficients, diffusion coefficients, residence times of atomic pairs, association constants, and solubility. Through calculation of these properties, we can assess the validity and range of applicability of the simple pair potential models and better understand their limitations. Due to extreme computational demands, the activity coefficients were only calculated for a subset of the models. The results qualitatively agree with experiment. Calculated diffusion coefficients and residence times between cation?anion, water?cation, and water?anion showed differences depending on the choice of water and ion force field used. The calculated solubilities of the alkali?halide salts were generally lower than the true solubility of the salts. However, for both the TIP4PEW and SPC/E water-model-specific ion parameters, solubility was reasonably well-reproduced. Finally, the correlations among the various properties led to the following conclusions: (1) The reliability of the ion force fields is significantly affected by the specific choice of water model. (2) Ion?ion interactions are very important to accurately simulate the properties, especially solubility. (3) The SPC/E and TIP4PEW water-model-specific ion force fields are preferred for simulation in high salt environments compared to the other ion force fields. PMID:19757835

2009-01-01

79

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

PubMed

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

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

2008-12-01

80

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

81

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

E-print Network

compounds, Seve- r a l polycrystalline alkali-halides having the NaCl structure were implanted with 70 keV 5- plantation i n metals and semiconductors /e.g. i n ref. 2 and 3/ also can be useful t o study ionic crystals) or unresolved broad structures (Hal?, Kl?) with the isomer s h i f t values typical for a f e r r i c iron

Boyer, Edmond

82

Free energies of transfer of alkali metal halides in isodielectric acetonitrile and ethylene glycol mixtures at 25°C  

Microsoft Academic Search

Standard free energies of transfer (?Gto) of alkali metal chlorides MCl (M=Li, Na, K, Rb, Cs) and of potassium bromide and iodide from ethylene glycol to its isodielectric mixtures containing 20, 40, and 60 wt. % acetonitrile have been determined from emf measurements at 25°C. The standard potentials of the M\\/M+, the Ag-AgBr, and the Ag-AgI electrodes have been calculated

Kurnardev Bose; Kiron K. Kundu

1979-01-01

83

Alkali reduction of graphene oxide in molten halide salts: production of corrugated graphene derivatives for high-performance supercapacitors.  

PubMed

Herein we present a green and facile approach to the successful reduction of graphene oxide (GO) materials using molten halide flux at 370 °C. GO materials have been synthesized using a modified Hummers method and subsequently reduced for periods of up to 8 h. Reduced GO (rGO) flakes have been characterized using X-ray-diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR), all indicating a significantly reduced amount of oxygen-containing functionalities on the rGO materials. Furthermore, impressive electrical conductivities and electrochemical capacitances have been measured for the rGO flakes, which, along with the morphology determined from scanning electron microscopy, highlight the role of surface corrugation in these rGO materials. PMID:25337832

Abdelkader, Amr M; Vallés, Cristina; Cooper, Adam J; Kinloch, Ian A; Dryfe, Robert A W

2014-11-25

84

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

SciTech Connect

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

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

1991-11-15

85

[Sources of error in the European Pharmacopoeia assay of halide salts of organic bases by titration with alkali].  

PubMed

A short overview has been given by the authors on the titrimetric assay methods of halide salts of organic bases in the pharmacopoeias of greatest importance. The alternative procedures introduced by the European Pharmacopoeia Commission some years ago to replace the non-aqueous titration with perchloric acid in the presence of mercuric acetate have also been presented and evaluated. The authors investigated the limits of applicability and the sources of systematic errors (bias) of the strongly preferred titration with sodium hydroxide in an alcoholic medium. To assess the bias due to the differences between the results calculated from the two inflexion points of the titration curves and the two real endpoints corresponding to the strong and weak acids, respectively, the mathematical analysis of the titration curve function was carried out. This bias, generally negligible when the pH change near the endpoint of the titration is more than 1 unit, is the function of the concentration, the apparent pK of the analyte and the ionic product of water (ethanol) in the alcohol-water mixtures. Using the validation data gained for the method with the titration of ephedrine hydrochloride the authors analysed the impact of carbon dioxide in the titration medium on the additive and proportional systematic errors of the method. The newly introduced standardisation procedure of the European Pharmacopoeia for the sodium hydroxide titrant to decrease the systematic errors caused by carbon dioxide has also been evaluated. PMID:11379027

Kószeginé, S H; Ráfliné, R Z; Paál, T; Török, I

2000-01-01

86

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

87

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

PubMed Central

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

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

2014-01-01

88

Masked Photocathode for Photoinjector  

SciTech Connect

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

Qiang, Ji

2010-01-21

89

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

90

Piezoelectrically Enhanced Photocathodes  

NASA Technical Reports Server (NTRS)

Doping of photocathodes with materials that have large piezoelectric coefficients has been proposed as an alternative means of increasing the desired photoemission of electrons. Treating cathode materials to increase emission of electrons is called "activation" in the art. It has been common practice to activate photocathodes by depositing thin layers of suitable metals (usually, cesium). Because cesium is unstable in air, fabrication of cesiated photocathodes and devices that contain them must be performed in sealed tubes under vacuum. It is difficult and costly to perform fabrication processes in enclosed, evacuated spaces. The proposed piezoelectrically enhanced photocathodes would have electron-emission properties similar to those of cesiated photocathodes but would be stable in air, and therefore could be fabricated more easily and at lower cost. Candidate photocathodes include nitrides of elements in column III of the periodic table . especially compounds of the general formula Al(x)Ga(1.x)N (where 0< or = x < or =.1). These compounds have high piezoelectric coefficients and are suitable for obtaining response to ultraviolet light. Fabrication of a photocathode according to the proposal would include inducement of strain in cathode layers during growth of the layers on a substrate. The strain would be induced by exploiting structural mismatches among the various constituent materials of the cathode. Because of the piezoelectric effect in this material, the strain would give rise to strong electric fields that, in turn, would give rise to a high concentration of charge near the surface. Examples of devices in which piezoelectrically enhanced photocathodes could be used include microchannel plates, electron- bombarded charge-coupled devices, image tubes, and night-vision goggles. Piezoelectrically enhanced photocathode materials could also be used in making highly efficient monolithic photodetectors. Highly efficient and stable piezoelectrically enhanced, ultraviolet-sensitive photocathodes and photodetectors could be fabricated by use of novel techniques for growing piezoelectrically enhanced layers, in conjunction with thinning and dopant-selective etching techniques.

Beach, Robert A.; Nikzad, Shouleh; Bell, Lloyd Douglas; Strittmatter, Robert

2011-01-01

91

Acicular photomultiplier photocathode structure  

DOEpatents

A method and apparatus for increasing the quantum efficiency of a photomultiplier tube by providing a photocathode with an increased surface-to-volume ratio. The photocathode includes a transparent substrate, upon one major side of which is formed one or more large aspect-ratio structures, such as needles, cones, fibers, prisms, or pyramids. The large aspect-ratio structures are at least partially composed of a photoelectron emitting material, i.e., a material that emits a photoelectron upon absorption of an optical photon. The large aspect-ratio structures may be substantially composed of the photoelectron emitting material (i.e., formed as such upon the surface of a relatively flat substrate) or be only partially composed of a photoelectron emitting material (i.e., the photoelectron emitting material is coated over large aspect-ratio structures formed from the substrate material itself.) The large aspect-ratio nature of the photocathode surface allows for an effective increase in the thickness of the photocathode relative the absorption of optical photons, thereby increasing the absorption rate of incident photons, without substantially increasing the effective thickness of the photocathode relative the escape incidence of the photoelectrons.

Craig, Richard A.; Bliss, Mary

2003-09-30

92

Molecular compressibility of some halides in alcohols  

NASA Technical Reports Server (NTRS)

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

Serban, C.; Auslaender, D.

1974-01-01

93

Low-workfunction photocathodes based on acetylide compounds  

DOEpatents

A low-workfunction photocathode includes a photoemissive material employed as a coating on the photocathode. The photoemissive material includes A.sub.nMC.sub.2, where A is a first metal element, the first element is an alkali metal, an alkali-earth element or the element Al; n is an integer that is 0, 1, 2, 3 or 4; M is a second metal element, the second metal element is a transition metal or a metal stand-in; and C.sub.2 is the acetylide ion C.sub.2.sup.2-. The photoemissive material includes a crystalline structure or non-crystalline structure of rod-like or curvy 1-dimensional polymeric substructures with MC.sub.2 repeating units embedded in a matrix of A.

Terdik, Joseph Z; Spentzouris, Linda; Terry, Jr., Jeffrey H; Harkay, Katherine C; Nemeth, Karoly; Srajer, George

2014-05-20

94

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  

NASA Astrophysics Data System (ADS)

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. Hünenberger, J. Chem. Phys. 124, 224501 (2006), 10.1529/biophysj.106.083667; M. M. Reif and P. H. Hünenberger, 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+, Na+, K+, Rb+, Cs+) and halide (F-, Cl-, Br-, I-) 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), 10.1021/jp982638r; 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, ? G_hyd^{ominus }[H+] = -1100, -1075 or -1050 kJ mol-1, resulting in three sets L, M, and H for the SPC water model and three sets LE, ME, and HE for the SPC/E water model (alternative sets can easily be interpolated to intermediate ? G_hyd^{ominus }[H+] 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 ? G_hyd^{ominus }[H+] 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 ? G_hyd^{ominus }[H+] close to -1100 kJ.mol-1.

Reif, Maria M.; Hünenberger, Philippe H.

2011-04-01

95

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.  

PubMed

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. Hu?nenberger, J. Chem. Phys. 124, 224501 (2006); M. M. Reif and P. H. Hu?nenberger, 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(+), Na(+), K(+), Rb(+), Cs(+)) and halide (F(-), Cl(-), Br(-), I(-)) 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, ?G(hyd)(?)[H(+)] = -1100, -1075 or -1050 kJ mol(-1), resulting in three sets L, M, and H for the SPC water model and three sets L(E), M(E), and H(E) for the SPC/E water model (alternative sets can easily be interpolated to intermediate ?G(hyd)(?)[H(+)] 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 ?G(hyd)(?)[H(+)] 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 ?G(hyd)(?)[H(+)] close to -1100 kJ·mol(-1). PMID:21495739

Reif, Maria M; Hünenberger, Philippe H

2011-04-14

96

Gaseous photodetectors with solid photocathodes  

Microsoft Academic Search

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

A. F. Buzulutskov

2008-01-01

97

Piezoelectrically enhanced photocathode  

NASA Technical Reports Server (NTRS)

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

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

2009-01-01

98

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

99

Final Report, Photocathodes for High Repetition Rate Light Sources  

SciTech Connect

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

Ben-Zvi, Ilan [Stony Brook University

2014-04-20

100

Spectroscopic predictions for alkali-atom-alkali-halide reaction intermediates  

NASA Astrophysics Data System (ADS)

The semi-empirical Roach-Child model is used to predict ionisation potentials, rotational constants, vibrational frequencies and the first three electronic absorption bands for the reaction intermediates Na 2Cl, K 2Cl and NaKCl, which are known to be isolatable by supersonic beam techniques.

Thompson, J. W.; Child, M. S.

1989-05-01

101

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

102

Infrared-sensitive photocathode  

DOEpatents

A single-crystal, multi-layer device incorporating an IR absorbing layer that is compositionally different from the Ga.sub.x Al.sub.1-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-y-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-x Sb, from which they are ejected into vacuum. Because the band alignments of Ga.sub.x Al.sub.1-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.

Mariella, Jr., Raymond P. (Danville, CA); Cooper, Gregory A. (Pleasant Hill, CA)

1995-01-01

103

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

104

Optical and Modeling Studies of Sodium/Halide Reactions for the Formation of Titanium and Boron  

E-print Network

diffusion flame reactor. After the Cl is stripped from the metal chloride by the Na vapor, nanosize Ti or B flame model show that formation of TiB2 likely occurs by gas-phase clustering reactions involving both or K with metal halides to yield the metal and an alkali halide salt. Such reactions15,16 have been

Zachariah, Michael R.

105

Lightweight, High-Yield Photocathode  

NASA Technical Reports Server (NTRS)

Layer of Astroquartz (or equivalent) cloth woven from quartz thread multiplies electron current emitted by aluminum photocathode sensitive to ultraviolet light when placed in external steady-state electric field. Desirable in applications where low power consumption required.

Leung, Philip L.; Gabriel, Stephen B.; Wuerker, Ralph F.

1992-01-01

106

Increasing Photocathode Charge Output  

SciTech Connect

A fundamental concern in the operation of electron accelerators is the generation of intense beams with high polarization. The time structure of the electron beam determines whether the limiting factor in emission is laser power or surface charge buildup. The presence of excess surface charge comes about due to the photon absorption that excites electrons from the valence to the conduction band. Some fraction of the electrons can be trapped near the surface which induces a rise in the electron affinity through the increased electrostatic potential. The higher affinity causes a lower emission probability and thus less emitted charge at later times. The electron affinity can recover to the zero charge limit after electron-hole recombination. As an example, the Next Linear Collider requires 95 micropulses having 2 x 10{sup 10} electrons per pulse in 0.7 ns with an interpulse spacing of 2.8 ns. Experience at SLAC has shown it is possible to generate 16 x 10{sup 10} electrons in 2 ns pulses with the requisite polarization. However, subsequent pulses may experience strong intensity damping. Several parameters can be varied to enhance the net charge output of the later pulses. Among these are increasing either the electric field at the photocathode surface or the surface charge dissipation rate by raising the carrier concentration or shunting the trapped charge. We present a series of measurements and a phenomenological model to characterize the range of these influences.

Mulhollan, Gregory A

1999-10-19

107

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

108

Metal-halide mixtures for latent heat energy storage  

NASA Technical Reports Server (NTRS)

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

Chen, K.; Manvi, R.

1981-01-01

109

Halogens and Halides (GCMP)  

NSDL National Science Digital Library

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

110

Alkali Metal/Salt Thermal-Energy-Storage Systems  

NASA Technical Reports Server (NTRS)

Proposed thermal-energy-storage system based on mixture of alkali metal and one of its halide salts; metal and salt form slurry of two immiscible melts. Use of slurry expected to prevent incrustations of solidified salts on heat-transfer surfaces that occur where salts alone used. Since incrustations impede heat transfer, system performance improved. In system, charging heat-exchanger surface immersed in lower liquid, rich in halide-salt, phase-charge material. Discharging heat exchanger surface immersed in upper liquid, rich in alkali metal.

Phillips, Wayne W.; Stearns, John W.

1987-01-01

111

CsI and some new photocathodes  

SciTech Connect

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

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

1993-06-01

112

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

113

Binary technetium halides  

NASA Astrophysics Data System (ADS)

In this work, the synthetic and coordination chemistry as well as the physico-chemical properties of binary technetium (Tc) chlorides, bromides, and iodides were investigated. Resulting from these studies was the discovery of five new binary Tc halide phases: alpha/beta-TcCl3, alpha/beta-TcCl 2, and TcI3, and the reinvestigation of the chemistries of TcBr3 and TcX4 (X = Cl, Br). Prior to 2009, the chemistry of binary Tc halides was poorly studied and defined by only three compounds, i.e., TcF6, TcF5, and TcCl4. Today, ten phases are known (i.e., TcF6, TcF5, TcCl4, TcBr 4, TcBr3, TcI3, alpha/beta-TcCl3 and alpha/beta-TcCl2) making the binary halide system of Tc comparable to those of its neighboring elements. Technetium binary halides were synthesized using three methods: reactions of the elements in sealed tubes, reactions of flowing HX(g) (X = Cl, Br, and I) with Tc2(O2CCH3)4Cl2, and thermal decompositions of TcX4 (X = Cl, Br) and alpha-TcCl 3 in sealed tubes under vacuum. Binary Tc halides can be found in various dimensionalities such as molecular solids (TcF6), extended chains (TcF5, TcCl4, alpha/beta-TcCl2, TcBr 3, TcI3), infinite layers (beta-TcCl3), and bidimensional networks of clusters (alpha-TcCl3); eight structure-types with varying degrees of metal-metal interactions are now known. The coordination chemistry of Tc binary halides can resemble that of the adjacent elements: molybdenum and ruthenium (beta-TcCl3, TcBr3, TcI 3), rhenium (TcF5, alpha-TcCl3), platinum (TcCl 4, TcBr4), or can be unique (alpha-TcCl2 and beta-TcCl 2) in respect to other known transition metal binary halides. Technetium binary halides display a range of interesting physical properties that are manifested from their electronic and structural configurations. The thermochemistry of binary Tc halides is extensive. These compounds can selectively volatilize, decompose, disproportionate, or convert to other phases. Ultimately, binary Tc halides may find application in the nuclear fuel cycle and as precursors in inorganic and organometallic chemistry.

Johnstone, Erik Vaughan

114

Alkali Bee  

Technology Transfer Automated Retrieval System (TEKTRAN)

The alkali bee, Nomia melanderi, is native to deserts and semi-arid desert basins of the western United States. It is a very effective and manageable pollinator for the production of seed in alfalfa (=lucerne) and some other crops, such as onion. It is the world’s only intensively managed ground-n...

115

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

116

Vitrification of IFR and MSBR halide salt reprocessing wastes  

SciTech Connect

Both of the genuinely sustainable (breeder) nuclear fuel cycles (IFR - Integral Fast Reactor - and MSBR - Molten Salt Breeder Reactor -) studied by the USA's national laboratories would generate high level reprocessing waste (HLRW) streams consisting of a relatively small amount ( about 4 mole %) of fission product halide (chloride or fluoride) salts in a matrix comprised primarily (about 95 mole %) of non radioactive alkali metal halide salts. Because leach resistant glasses cannot accommodate much of any of the halides, most of the treatment scenarios previously envisioned for such HLRW have assumed a monolithic waste form comprised of a synthetic analog of an insoluble crystalline halide mineral. In practice, this translates to making a 'substituted' sodalite ('Ceramic Waste Form') of the IFR's chloride salt-based wastes and fluoroapatite of the MSBR's fluoride salt-based wastes. This paper discusses my experimental studies of an alternative waste management scenario for both fuel cycles that would separate/recycle the waste's halide and immobilize everything else in iron phosphate (Fe-P) glass. It will describe both how the work was done and what its results indicate about how a treatment process for both of those wastes should be implemented (fluoride and chloride behave differently). In either case, this scenario's primary advantages include much higher waste loadings, much lower overall cost, and the generation of a product (glass) that is more consistent with current waste management practices. (author)

Siemer, D.D. [Idaho National Laboratory, 12N 3167E, Idaho Falls, ID 83402 (United States)

2013-07-01

117

Photocathodes: Mapping, controlled porosity, cesium, and gold  

NASA Astrophysics Data System (ADS)

Photocathodes play a critical role in a large variety of applications, from detectors in medical imaging to electron beam sources for fundamental science. Via the photoelectric effect, photocathodes emit electrons in response to light of sufficient energy. Three important characteristics of photocathodes are quantum efficiency (the fraction of incident photons that generates emitted electrons), lifetime (how long the cathodes are operational), and emission uniformity. Coating a photocathode with an atomic layer of cesium dramatically improves quantum efficiency, but the inherent fragility of this layer worsens lifetime. The design and testing of a cesium rejuvenation system which prolongs lifetime will be presented, and a controlled porosity design which could improve emission uniformity will be discussed. A new method of mapping quantum efficiency will be presented. The initial results of testing cesium auride will be discussed, as they show the cathodes have surprisingly high quantum efficiency and the potential for very long lifetime.

Riddick, Blake C.

118

Ultraviolet response of semitransparent multialkali photocathodes  

NASA Technical Reports Server (NTRS)

The UV spectral sensitivity of two semitransparent visible sensitive photocathodes for spaceborne applications, a trialkali, Cs-Na2KSB, and a bialkali, K2CsSb, both on MgF2 substrates. Results show that for extended wavelength coverage, the bialkali photocathode affords increased quantum yield as compared with the trialkali type, and that the latter has a more variable responsivity with wavelength.

Sobieski, S.

1976-01-01

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 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

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 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

121

Efficient esterification of carboxylic acids with alkyl halides catalyzed by fluoride ions in ionic liquids  

Microsoft Academic Search

Ionic liquids based on 1,3-dialkylimidazolinium methanesulfonate have been used as efficient reusable reaction media in the esterification of several carboxylic acids with alkyl halides catalyzed by fluoride ions. The method has wide applicability, and it is mild and green; it is useful for the protection of acids, via ester formation, for alkali labile molecules.

L Brinchi; R Germani; G Savelli

2003-01-01

122

Far infrared photoelectric thresholds of extrinsic semiconductor photocathodes  

E-print Network

to the photoelectric effect at a metal (photocathode)-vacuum in- terface. At lower doping levels normally usedFar infrared photoelectric thresholds of extrinsic semiconductor photocathodes A. G. U. Perera, FL

Perera, A. G. Unil

123

High Efficiency Visible Photocathode Development  

SciTech Connect

The alkali antimonides are of significant interest to the accelerator community, as they have a high quantum efficiency (QE) under illumination by green light. These cathodes are attractive for high-average-current photoinjector applications and understanding their fundamental properties are critical to the production of long lived, reliable cathodes. We report on ongoing work to characterize cathode formation during growth. In-situ X-ray Diffraction (XRD) has been used to compare grain size and texture in antimony layers, and X-ray Photoelectron Spectroscopy (XPS) has been used to investigate the solid-state chemistry of cathode formation.

Smedley J.; Rao T.; Mueller, K.; Ben-Zvi, I.; Ruiz-Oses, M.; Liang, X.; Muller, E.M.; Lee, S.; Attenkofer, K.; Padmore, H.; Vecchione, T.

2011-09-30

124

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

125

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.

John Brady

126

Skylab experiments on semiconductors and alkali halides. [single crystal growth  

NASA Technical Reports Server (NTRS)

The space processing experiments performed during the Skylab missions included one on single crystal growth of germanium selenide and telluride, one on pure and doped germanium crystals, two on pure and doped indium antimonide, one on gallium-indium-antimony systems, and one on a sodium chloride-sodium fluoride eutectic. In each experiment, three ampoules of sample were processed in the multipurpose electric furnace within the Skylab Materials Processing Facility. All were successful in varying degrees and gave important information about crystal growth removed from the effects of earth surface gravity.

Lundquist, C. A.

1974-01-01

127

FA(Li) centers in mixed crystals of alkali halides  

NASA Astrophysics Data System (ADS)

The emission and absorption of FA(Li) centers in mixed crystals of KCl and KBr have been studied from 1.6 to 100 K at atmospheric and high pressures. While only one pair, FA1 and FA2, of absorption bands is observed, two types of emission bands, type I and type II, are obtained. The relative intensities of the type-I and type-II emissions depend both on the composition of the solid solution and on temperature. A possible formation mechanism of two relaxed excited states in a complete solid solution is discussed. The energy separation and intensity of the FA absorption band (FA1 and FA2) in the KCl1-xBrx:Li system are observed under various pressures. Information about the off-center behavior in the mixed crystals is obtained from the pressure dependence of the separation between FA1 and FA2 absorption. The pressure variation of intensity in type-I and type-II emissions is also measured. These results show a different pressure effect on the relaxation processes of the two types of emission: the type-II emission is scarcely affected by the applied pressure contrary to a considerable pressure-induced nonradiative transition in the type-I emission. This situation leads us to investigate the relaxation process of the type-II emission under hydrostatic pressure.

Asami, Kumiko; Ishiguro, Masakazu

1986-09-01

128

Linkage Isomerism of CO Adsorbed on Alkali Halides.  

PubMed

Variable-temperature FTIR spectra of CO adsorbed on NaCl and KBr films are shown to reveal linkage isomerism, that is, formation of C- and O-bonded adsorption complexes with the same cationic sites. Not all of the sites can be involved in that, only the three- or four-coordinated cations located on kinks, edges, or steps of microcrystals. For NaCl, these adsorption complexes account for the high-frequency (HF) C-O stretching bands at 2175 and 2160 cm(-1). Coresponding LF bands of O-bonded CO were found at 2115 and 2124 cm(-1). In the spectrum of KBr, the HF band is poorly resolved, and only one LF band can be clearly seen, near 2124 cm(-1). The value of the isomerization enthalpy for complexes that account for the bands at 2160 and 2124 cm(-1) of CO adsorbed on NaCl, estimated from the experiment, is 4.0 ± 0.2 kJ/mol. Quantum mechanical calculations by DFT methods applied to NaCl model clusters interacting with the CO molecule confirm the existence of two potential wells with adsorption and isomerization energies close to the experimentally measured values, and enable us to estimate the height of the potential barrier between the two adsorption states. PMID:25222795

Belykh, Roman; Maevskaya, Maria; Krauklis, Irina; Tsyganenko, Alexey

2015-03-19

129

Performance of the Brookhaven photocathode rf gun  

SciTech Connect

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, yttrium and samarium. We illuminate these cathodes with a 10-ps, frequency-quadrupled Nd:YAG laser. We describe the initial operation of the gun, including measurements of transverse and longitudinal emittance, quantum efficiencies, and peak current. The results are compared to models.

Batchelor, K.; Ben-Zvi, I.; Fernow, R.C.; Fischer, J.; Fisher, A.S.; Gallardo, J.; Ingold, G.; Kirk, H.G.; Leung, K.P.; Malone, R.; Pogorelsky, I.; Srinivasan-Rao, T.; Rogers, J.; Tsang, T.; Sheehan, J.; Ulc, S.; Woodle, M.; Xie, J.; Zhang, R.S. (Brookhaven National Lab., Upton, NY (United States)); Lin, L.Y. (Columbia Univ., New York, NY (United States). Dept. of Applied Physics); McDonald, K.T.; Russell, D.P. (Pr

1991-01-01

130

Performance of the Brookhaven photocathode rf gun  

SciTech Connect

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, yttrium and samarium. We illuminate these cathodes with a 10-ps, frequency-quadrupled Nd:YAG laser. We describe the initial operation of the gun, including measurements of transverse and longitudinal emittance, quantum efficiencies, and peak current. The results are compared to models.

Batchelor, K.; Ben-Zvi, I.; Fernow, R.C.; Fischer, J.; Fisher, A.S.; Gallardo, J.; Ingold, G.; Kirk, H.G.; Leung, K.P.; Malone, R.; Pogorelsky, I.; Srinivasan-Rao, T.; Rogers, J.; Tsang, T.; Sheehan, J.; Ulc, S.; Woodle, M.; Xie, J.; Zhang, R.S. [Brookhaven National Lab., Upton, NY (United States); Lin, L.Y. [Columbia Univ., New York, NY (United States). Dept. of Applied Physics; McDonald, K.T.; Russell, D.P. [Princeton Univ., NJ (United States). Dept. of Physics; Hung, C.M. [State Univ. of New York, Stony Brook, NY (United States). Dept. of Physics; Wang, X.J. [California Univ., Los Angeles, CA (United States). Dept. of Physics

1991-12-31

131

Large photocathode area picosecond streak tube  

NASA Astrophysics Data System (ADS)

The paper reports on the development of a new streak image tube with accelerating mesh and large (18 mm) photocathode work area. The tube's temporal resolution is close to one picosecond. To govern photoelectronic images the tube possesses shutter and deflector plates. Its geometric design allows uniform spatial resolution (more than 25 lp/mm) along the entire photocathode work area at 1.3 electron-optical magnification and negligibly small distortion. Being a continuation of the well-known PV and PIF - type streak image tubes developed in due time in GPI, the tube represents a promising tool for taking pictures of ultrafast processes in wide radiation spectrum range.

Andreev, S. V.; Belolipetski, V. S.; Ivanova, S. R.; Kulechenkova, T. P.; Levina, G. P.; Makushina, V. A.; Monastyrskiy, M. A.; Polykarkina, N. D.; Schelev, M. Ya.; Semichastnova, Z. M.; Sokolov, V. E.

2008-11-01

132

Graphene shield enhanced photocathodes and methods for making the same  

DOEpatents

Disclosed are graphene shield enhanced photocathodes, such as high QE photocathodes. In certain embodiments, a monolayer graphene shield membrane ruggedizes a high quantum efficiency photoemission electron source by protecting a photosensitive film of the photocathode, extending operational lifetime and simplifying its integration in practical electron sources. In certain embodiments of the disclosed graphene shield enhanced photocathodes, the graphene serves as a transparent shield that does not inhibit photon or electron transmission but isolates the photosensitive film of the photocathode from reactive gas species, preventing contamination and yielding longer lifetime.

Moody, Nathan Andrew

2014-09-02

133

Halide laser glasses  

SciTech Connect

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

Weber, M.J.

1982-01-14

134

Wire ageing with the TEA photocathode  

SciTech Connect

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

Va`vra, J.

1996-06-01

135

Optically triggered pseudospark switches with metal photocathodes  

Microsoft Academic Search

Pseudospark switches have been successfully employed in a variety of pulsed power applications including high power electron beam sources, high power microwaves, and transient plasma ignition for pulsed detonation engines [1–3]. Investigation of magnesium, copper and molybdenum photocathode candidates for optically triggered pseudospark switches, also called back-lighted thyratrons (BLTs), has shown that magnesium has a higher quantum efficiency (up to

Esin B Sozer; Chunqi Jiang; Martin A. Gundersen

2011-01-01

136

Diamond Amplified Photocathodes John Smedley1  

E-print Network

Diamond Amplified Photocathodes John Smedley1 , Ilan Ben-Zvi1 , Jen Bohon2 , Xiangyun Chang1 protecting the cathode from the accelerator. The amplifier is a thin diamond wafer which converts energetic. The electrons drift through the diamond under an external bias and are emitted into vacuum via a hydrogen

137

Alkali metal nitrate purification  

DOEpatents

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

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

1986-02-04

138

A Summary of the 2010 Photocathode Physics for Photoinjectors Workshop  

SciTech Connect

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

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

2010-10-01

139

The semiconductor field-emission photocathode  

Microsoft Academic Search

The recently developed large-area field-emission photocathode is described. It consists of a finely spaced array of point emitters fabricated by etching of p-type silicon or other semiconductor. Uniform emission over areas of 6-7 cm2have been obtained. For Si, the spectral response extends from 0.4 to 1.1 µm. Quantum yields of 25 percent at 0.86 µm have been measured, which is

DIETER K. SCHRODER; R. NOEL THOMAS; JAMES VINE; H. C. Nathanson

1974-01-01

140

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

141

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

142

Thermal ionization ion mobility spectrometry of alkali salts.  

PubMed

Positive and negative thermal ionization ion mobility spectra (TI-IMS) of some sodium and potassium halides are reported here. The data provide the first measurement of the thermal ionization ion mobility spectrometry of inorganic compounds. A thin Nichrome filament was used as a thermionic ionization source. Sample was directly deposited on the filament, where it was heated and ionized. Each salt produced a different ion mobility pattern, but all sodium salts spectra were common in their first peak. This peak differs from the common peak observed in the spectra of potassium salts. The drift time of the second peak in all spectra was found to be linearly dependent on the size of the counteranion of the salt. Negative thermal ionization ion mobility spectra of alkali halides were also observed. An alkali halide salt (MX), in general, produced its own anion as well as some heavier ions that are thought to be hydrated X- (MX)n species. The capability of the method in quantitative analysis was demonstrated by measuring potassium impurity in sodium bromide. A detection limit of 0.01% K+ in NaBr and a linear rage of 3 orders of magnitude were obtained. The results from this study suggest that TI-IMS has potential as a field technique for the detection of some elements in samples. PMID:12964757

Tabrizchi, Mahmoud

2003-07-01

143

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

144

Exchange experiments of C60 and halides on a Au(1 1 1) surface  

NASA Astrophysics Data System (ADS)

The influence of halides (I-, Br-, Cl-) on the stability of C60 adlayers on Au(1 1 1) was studied by scanning tunneling microscopy (STM) in air at room temperature. The C60 layers on gold were immersed into alkali halides solutions of several concentrations for different time intervals. The results show that C60 can be removed from the gold surface by iodide when the halide concentration is high and time of immersion is long. A rotated hexagonal structure of iodide is formed on some surface areas although with distortion. Bromide and chloride do not remove C60 completely from the gold surface. Nevertheless, they are able to penetrate the C60 layer. The result is that bromide and chloride adsorb on top of the gold and C60 sits on the halide adlayer. This condition enables the growth of well organized domains of C60. It is possible to identify the formation of multilayers of the fullerene on some areas. Intramolecular resolution for C60 was attained in the STM images when the halides were present on the surface.

Pinheiro, Lucidalva dos Santos; Filho, Josué Mendes

2013-09-01

145

Development of Polarized Photocathodes for the Linear Collider  

SciTech Connect

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

Richard Prepost

2009-12-22

146

Performance of photocathode rf gun electron accelerators  

SciTech Connect

In Photo-Injectors (PI) electron guns, electrons are emitted from a photocathode by a short laser pulse and then accelerated by intense rf fields in a resonant cavity. The best known advantage of this technique is the high peak current with a good emittance (high brightness). This is important for short wavelength Free-Electron Lasers and linear colliders. PIs are in operation in many electron accelerator facilities and a large number of new guns are under construction. Some applications have emerged, providing, for example, very high pulse charges. PIs have been operated over a wide range of frequencies, from 144 to 3000 MHz (a 17 GHz gun is being developed). An exciting new possibility is the development of superconducting PIs. A significant body of experimental and theoretical work exists by now, indicating the criticality of the accelerator elements that follow the gun for the preservation of the PI's performance as well as possible avenues of improvements in brightness. Considerable research is being done on the laser and photocathode material of the PI, and improvement is expected in this area.

Ben-Zvi, I.

1993-01-01

147

Performance of photocathode rf gun electron accelerators  

SciTech Connect

In Photo-Injectors (PI) electron guns, electrons are emitted from a photocathode by a short laser pulse and then accelerated by intense rf fields in a resonant cavity. The best known advantage of this technique is the high peak current with a good emittance (high brightness). This is important for short wavelength Free-Electron Lasers and linear colliders. PIs are in operation in many electron accelerator facilities and a large number of new guns are under construction. Some applications have emerged, providing, for example, very high pulse charges. PIs have been operated over a wide range of frequencies, from 144 to 3000 MHz (a 17 GHz gun is being developed). An exciting new possibility is the development of superconducting PIs. A significant body of experimental and theoretical work exists by now, indicating the criticality of the accelerator elements that follow the gun for the preservation of the PI`s performance as well as possible avenues of improvements in brightness. Considerable research is being done on the laser and photocathode material of the PI, and improvement is expected in this area.

Ben-Zvi, I.

1993-07-01

148

Development of Halide and Oxy-Halides for Isotopic Separations  

SciTech Connect

The goal of this project was to synthesize a volatile form of Np for introduction into mass spectrometers at INL. Volatile solids of the 5f elements are typically those of the halides (e.g. UF6), however fluorine is highly corrosive to the sensitive internal components of the mass separator, and the other volatile halides exist as several different stable isotopes in nature. However, iodide is both mono-isotopic and volatile, and as such presents an avenue for creation of a form of Np suitable for introduction into the mass separator. To accomplish this goal, the technical work in the project sought to establish a novel synthetic route for the conversion NpO2+ (dissolved in nitric acid) to NpI3 and NpI4.

Leigh R. Martin; Aaron T. Johnson; Jana Pfeiffer; Martha R. Finck

2014-10-01

149

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

150

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

EPA Science Inventory

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

151

Alkali and Halogen Chemistry in Volcanic Gases on Io  

E-print Network

We use chemical equilibrium calculations to model the speciation of alkalis and halogens in volcanic gases emitted on Io. The calculations cover wide temperature (500-2000 K) and pressure (10^-6 to 10^+1 bars) ranges, which overlap the nominal conditions at Pele (T = 1760 K, P = 0.01 bars). About 230 compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are considered. We predict the major alkali and halogen species in a Pele-like volcanic gas and the major alklai and halogen condensates. We also model disequilibrium chemistry of the alkalis and halogens in the volcanic plume. Based on this work and our prior modeling for Na, K, and Cl in a volcanic plume, we predict the major loss processes for the alkali halide gases are photolysis and/or condensation onto grains. On the basis of elemental abundances and photochemical lifetimes, we recommend searching for gaseous KCl, NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during eruptions. Based on abundance considerations and observations of brown dwarfs, we also recommend a search of Io's extended atmosphere and the Io plasma torus for neutral and ionized Li, Cs, Rb, and F.

Laura Schaefer; Bruce Fegley Jr

2004-09-20

152

Fabrication and measurement of regenerable low work function dispenser photocathodes  

NASA Astrophysics Data System (ADS)

Laser-switched photoemitters are a source of electrons for high current applications such as free electron lasers. Laser-modulated photoemission permits rapid switching of the electron beam, far surpassing what can be achieved using electric-field gated emission. Photoinjector systems consist of a drive laser producing short bunches of photons and an efficient photocathode, which converts photon bunches into electron beam pulses. Development of both technologies is required, but the scope of this project is restricted to improvement of the photocathode. Most high-efficiency photocathodes employ cesium-based surface coatings to reduce work function and enable efficient electron emission in the visible range. Lifetime is severely limited by the loss of this delicate coating, which degrades rapidly in practical vacuum environments. More robust photocathodes exist, but have much lower efficiency, and place unrealistic demands on drive laser power and stability. This research proposes a novel dispenser concept that dramatically extends the lifetime of high efficiency cesium-based cathodes by continuously or periodically restoring the cesium surface monolayer during an in situ rejuvenation process. Sintered tungsten provides an interface between a cesium reservoir and the photoemitting surface. During temperature-controlled rejuvenation, cesium diffuses through and across the sintered tungsten to create and sustain a low-work function photocathode. The prototype dispenser cathode was fabricated and tested for two modes of operation: continuous and periodic near-room temperature rejuvenation. The data are compared with a photoemission model of partially covered surfaces under design for integration with existing beam simulations. Overall performance suggests that this cesium-delivery mechanism can significantly enhance the efficiency and operational lifetime of a wide variety of present and future cesium-based photocathodes. Also reported are surface characterization, ion beam cleaning, and fabrication techniques used to optimize performance of the dispenser photocathode.

Moody, Nathan A.

153

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

154

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

155

Halide transport in Xenopus oocytes.  

PubMed Central

1. Radioisotopes and intracellular microelectrodes were used to characterize the permeability of Xenopus oocytes to chloride and other halides. 2. Uptake of 36Cl had a half-time for equilibration of approximately 3 h, with an initial rate of Cl- entry corresponding to a permeability coefficient of 3.9 x 10(-7) cm/s, and an equilibrium uptake of 36Cl of 33 mM. 3. Replacement of bathing Na+ by K+ depolarized the oocytes from -46 to -7 mV and stimulated influx approximately 3-fold. 4. Influx was linearly dependent on bathing [Cl-] and was temperature dependent with an activation energy of 46 kJ/mol. Influx of 125I of 36Cl was not affected by the presence of equal concentrations of other halides or thiocyanate. These results are consistent with a channel-mediated entry mechanism. 5. Diphenylamine-2-carboxylate (DPAC) and 9-anthracene carboxylate (9-AC), blockers of Cl- channels in other cells, inhibited Cl- entry with dissociation constants (Kds) of approximately 5 x 10(-4) and approximately 10(-3) M, respectively. Inhibitors of Cl(-)-HCO3- exchange or Na(+)-K(+)-2Cl- co-transport did not affect Cl- influx. 6. Attempts to lower or raise intracellular Ca2+ with BAPTA or A23187, respectively, were also without effect on Cl- influx. 7. The halide selectivity sequence determined with isotopes was I- (3.2) greater than Br- (1.3) greater than Cl- (1.0). However, DPAC inhibited almost all of the 36Cl influx but only a small fraction of 125I influx. 8. Replacement of bathing Cl- by I- or Br-resulted in hyperpolarizations, from which the same selectivity sequence was determined. 9. Replacement of bathing Cl- by gluconate caused a marked depolarization, which was inhibited by DPAC and, less potently, by 9-AC. Images Fig. 9 PMID:1822540

Katayama, Y; Widdicombe, J H

1991-01-01

156

Activation and evaluation of GaN photocathodes  

NASA Astrophysics Data System (ADS)

Gallium Nitride (GaN) photocathodes are potentially attractive as UV detective materials and electron sources. Based on the activation and evaluation system for GaAs photocathode, which consists of ultra-high vacuum (UHV) activation chamber, multi-information measurement system, X-ray photoelectron spectroscopy (XPS), and ultraviolet ray photoelectron spectroscopy (UPS), the control and measurement system for the activation of UV photocathodes was developed. The developed system, which consists of Xenon lamp, monochromator with scanner, signal-processing module, power control unit of Cs and O source, A/D adapter, digital I/O card, computer and software, can control the activation of GaN photocathodes and measure on-line the spectral response curves of GaN photocathodes. GaN materials on sapphire substrate were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) with p-type Mg doping. The GaN materials were activated by Cs-O. The spectral response and quantum efficiency (QE) were measured and calculated. The experiment results are discussed.

Qian, Yunsheng; Chang, Benkang; Qiao, Jiangliang; Zhang, Yijun; Fu, Rongguo; Qiu, Yafeng

2009-09-01

157

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

158

Fullerenes Doped with Metal Halides  

NASA Astrophysics Data System (ADS)

The cage-like structure of fullerenes is a challenge to every experimentalist to put something inside—to dope the fullerenes. In fact, the research team that first identified C60 as a football-like molecule quickly succeeded in trapping metal atoms inside and in shrinking the cage around this atom by photofragmentation. In this paper we report the results of “shrink-wrapping” the fullerenes around metal halide molecules. Of special interest is the critical size (the minimum number of carbon atoms) that can still enclose the dopant. A rough model for the space available inside a carbon cage gives good agreement with the measured shrinking limits.

Martin, T. P.; Heinebrodt, M.; Näher, U.; Göhlich, H.; Lange, T.; Schaber, H.

159

Hygroscopicity Evaluation of Halide Scintillators  

SciTech Connect

A collaborative study of relative hygroscopicity of anhydrous halide scintillators grown at various laboratories is presented. We have developed a technique to evaluate moisture sensitivity of both raw materials and grown crystals, in which the moisture absorption rate is measured using a gravimetric analysis. Degradation of the scintillation performance was investigated by recording gamma-ray spectra and monitoring the photopeak position, count rate and energy resolution. The accompanying physical degradation of the samples exposed to ambient atmosphere was photographically recorded as well. The results were compared with ben

Zhuravleva, M [The University of Tennessee] [The University of Tennessee; Stand, L [The University of Tennessee] [The University of Tennessee; Wei, H [The University of Tennessee] [The University of Tennessee; Hobbs, C. L. [University of Tennessee, Knoxville (UTK)] [University of Tennessee, Knoxville (UTK); Boatner, Lynn A [ORNL] [ORNL; Ramey, Joanne Oxendine [ORNL] [ORNL; Burger, Arnold [Fisk University, Nashville] [Fisk University, Nashville; Rowe, E [Fisk University, Nashville] [Fisk University, Nashville; Bhattacharya, P. [Fisk University, Nashville] [Fisk University, Nashville; Tupitsyn, E [Fisk University, Nashville] [Fisk University, Nashville; Melcher, Charles L [University of Tennessee, Knoxville (UTK)] [University of Tennessee, Knoxville (UTK)

2014-01-01

160

Alkali Soils, Irrigation Waters.  

E-print Network

for sev- eral Tears been collecting data in regard to the occurrence, and nature of alkali soils in Texas. It appears time for us to gi ~ort of pro'gresq containing informntion concerning alkali. Alks imp0 r- tant matter in some portions of the State... of cjt? of Pecus. Grass grows where irrigated; otherwise, almost bzre, 5 inches. RTater d~es not penetrate this soil, but flows off on other soils and injures them. 1799-Soil from near Pecos and partly washed from ap hills and !lot regarded as good...

Fraps, G. S. (George Stronach)

1910-01-01

161

Methods of recovering alkali metals  

DOEpatents

Approaches for alkali metal extraction, sequestration and recovery are described. For example, a method of recovering alkali metals includes providing a CST or CST-like (e.g., small pore zeolite) material. The alkali metal species is scavenged from the liquid mixture by the CST or CST-like material. The alkali metal species is extracted from the CST or CST-like material.

Krumhansl, James L; Rigali, Mark J

2014-03-04

162

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

163

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

164

Chlorine from the mantle: Magmatic halides in the Udachnaya-East kimberlite, Siberia  

NASA Astrophysics Data System (ADS)

The Devonian Udachnaya-East pipe (Siberia) presents a rare example of exceptionally fresh kimberlite rocks, containing a rich assemblage of alkali carbonate, chloride and sulphate minerals in its groundmass. Accordingly, bulk groundmass compositions have unusually high concentrations of sodium and chlorine (up to 6 wt.% each), while water contents are very low. High Na 2O and low H 2O are inconsistent with currently accepted model kimberlite magma compositions; and high Na and Cl contents in the Udachnaya-East pipe have been ignored by the geoscience community, because of possibility of contamination from sedimentary crustal rocks. New textural evidence suggests that the chloride and alkali carbonate minerals in this kimberlite are co-magmatic with perovskite. Radiogenic isotope ratios for the perovskite ( 87Sr/ 86Sr ~ 0.7031, ?Nd + 5, ?Hf + 5.3, obtained by solution-mode and laser-ablation methods) are very primitive and provide no support for a crustal contaminant. The new perovskite data confirm previously published Sr-Nd-Pb isotopic evidence for the chlorides and alkali carbonates themselves, but are considered more reliable because of possible open system behaviour and analytical problems with unstable halide and carbonate minerals. Similar isotope ratios ( 87Sr/ 86Sr = 0.70292, ?Nd = + 5, ?Hf = + 6.5) are recorded in a clinopyroxene macrocryst, which contains chlorides and alkali carbonates within melt inclusions, implying a similarly primitive isotopic signature for the host kimberlite. We infer that assimilation of evaporitic sediments is unlikely and that abundant chlorine and sodium in the kimberlite originated in the upper mantle. Our results and published experimental data on mantle chloride melts and presence of a chloride component in diamond-hosted fluid inclusions suggest a previously unrecognised role for mantle-derived halide melts in the genesis, composition and rheological properties of kimberlite primary melts.

Kamenetsky, Vadim S.; Maas, Roland; Kamenetsky, Maya B.; Paton, Chad; Phillips, David; Golovin, Alexander V.; Gornova, Marina A.

2009-07-01

165

Shallow halogen vacancies in halide optoelectronic materials  

NASA Astrophysics Data System (ADS)

Halogen vacancies (VH ) are usually deep color centers (F centers) in halides and can act as major electron traps or recombination centers. The deep VH contributes to the typically poor carrier transport properties in halides. However, several halides have recently emerged as excellent optoelectronic materials, e.g., C H3N H3Pb I3 and TlBr. Both C H3N H3Pb I3 and TlBr have been found to have shallow VH , in contrast to commonly seen deep VH in halides. In this paper, several halide optoelectronic materials, i.e., C H3N H3Pb I3 , C H3N H3Sn I3 (photovoltaic materials), TlBr, and CsPbB r3 (gamma-ray detection materials) are studied to understand the material chemistry and structure that determine whether VH is a shallow or deep defect in a halide material. It is found that crystal structure and chemistry of n s2 ions both play important roles in creating shallow VH in halides such as C H3N H3Pb I3 , C H3N H3Sn I3 , and TlBr. The key to identifying halides with shallow VH is to find the right crystal structures and compounds that suppress cation orbital hybridization at VH , such as those with large cation-cation distances and low anion coordination numbers and those with crystal symmetry that prevents strong hybridization of cation dangling bond orbitals at VH . The results of this paper provide insight and guidance to identifying halides with shallow VH as good electronic and optoelectronic materials.

Shi, Hongliang; Du, Mao-Hua

2014-11-01

166

Hydrothermal alkali metal recovery process  

DOEpatents

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

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

1980-01-01

167

Equilibrium coverage of halides on metal electrodes  

NASA Astrophysics Data System (ADS)

The adsorption of halides on Cu(111) and Pt(111) has been studied using periodic density functional theory calculations. The equilibrium coverage of the halides as a function of the electrode potential was determined using a thermodynamic approach in which the electrochemical environment is not explicitly taken into account. For all considered systems, halide coverages between 1/3 and 3/8 should be stable over a wide potential range. Although some quantitative discrepancies with experiment are obtained, the qualitative trends derived from the calculations are consistent with experimental observations. The reasons for the remaining discrepancies with the experiment are discussed.

Gossenberger, Florian; Roman, Tanglaw; Groß, Axel

2015-01-01

168

SUPPRESSION OF AFTERPULSING IN PHOTOMULTIPLIERS BY GATING THE PHOTOCATHODE  

EPA Science Inventory

A number of gating schemes to minimize the long-term afterpulse signal in photomultipliers have been evaluated. Blocking the excitation pulse by gating the photocathode was found to reduce the gate-on afterpulse background by a factor of 230 over that for nongated operation. Thi...

169

PROGRESS TOWARD AN ALL NIOBIUM SUPERCONDUCTING RF PHOTOCATHODE ELECTRON GUN*  

E-print Network

PROGRESS TOWARD AN ALL NIOBIUM SUPERCONDUCTING RF PHOTOCATHODE ELECTRON GUN* M. Cole, H. Bluem, J and understand the QE of the niobium cathode we have designed a replacement cathode plate for the BNL ATF a brazed niobium slug as the cathode. The method for fabrication calls for nickel plating the tapered

Brookhaven National Laboratory

170

Axial RF Power Input into Photocathode Electron Guns  

Microsoft Academic Search

The RF power input into an accelerating cavity is usually performed with special couplers that deliver the power in an asymmetric manner. Further, for superconducting cavities, the delivery point is typically into the beam tube beyond the cavity cells. In photocathode electron guns, where the cathode is isolated from the surrounding cavity by a coaxial vacuum gap, another power coupling

D. Janssen; V. Volkov; H. P. Bluem; A. M. M. Todd

2005-01-01

171

Metal-Insulator Photocathode Heterojunction for Directed Electron Emission  

SciTech Connect

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

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

2014-02-14

172

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

173

Reflection silver-halide gelatin holograms  

NASA Astrophysics Data System (ADS)

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

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

1991-02-01

174

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

175

The effect of surface cleaning on quantum efficiency in AlGaN photocathode  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

176

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

177

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

178

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 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

179

Preparation of graphene/polymer composite photocathode for QDSSC  

NASA Astrophysics Data System (ADS)

Graphene (rGO) was fabricated by modified Hummers method and a reducing process. Conductive polymer/graphene films were obtained by scalpel technology and used as photocathode in CdS quantum dot-sensitized solar cell (QDSSC). Polymers used in this paper were ethyl cellulose (EC), polyphenyl vinyl (PPV) and polyvinyl butyral (PVB), respectively. The obtained composite films were investigated by X-ray diffraction, Raman spectroscopy technology and scanning electron microscope (SEM). The photoelectric properties of QDSSCs were tested under AM 1.5 irradiation. Test results show that the film performance of the EC/rGO and PPV/rGO photocathode have been improved effectively. Power conversion efficiency (PCE) of the relative QDSSCs under AM 1.5 irradiation were 0.81% and 0.86%, respectively.

Wang, Qiandi; Shen, Yue; Tan, Jie; Xu, Kai; Shen, Tan; Cao, Meng; Gu, Feng; Wang, Linjun

2013-12-01

180

Purification of alkali metal nitrates  

DOEpatents

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

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

1985-05-14

181

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

E-print Network

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.

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

2007-11-13

182

Fourfold Increase in Quantum Efficiency in Highly Spin-Polarized Transmission-Type Photocathode  

NASA Astrophysics Data System (ADS)

We developed a new transmission-type GaAs/GaAsP strained superlattice photocathode with an AlGaAs transparent inter-layer and Si3N4 anti-reflection coating. The electrons emitted from this photocathode demonstrate a high spin-polarization of 90% with quantum efficiency as high as 0.4% that is a fourfold increase at room temperature compared with our previous photocathode.

Jin, Xiuguang; Ichihashi, Fumiaki; Mano, Atsushi; Yamamoto, Naoto; Takeda, Yoshikazu

2012-10-01

183

Synchronizable high voltage pulser with laser-photocathode trigger  

Microsoft Academic Search

High gradient pulsed electron guns have been studied to suppress the space-charge induced transverse emittance growth of the electron beam in the injection stage. Synchronizable high-voltage (HV) pulsers are needed to power up high-gradient guns. In this article, we propose to build a HV pulser with a new switching technique that exploits a special trigger, a laser-photocathode subsystem. With this

P. Chen; M. Lundquist; R. Yi; D. Yu

2007-01-01

184

Magnesium based photocathode for back-lighted thyratron  

Microsoft Academic Search

Optically triggered pseudospark switches, also called back­ lighted thyratrons (BLTs), are high voltage (>37 kV), high current (> 17 kA), glow-mode plasma switches, in which breakdown is initiated by photoemission from the switch cathode l-4 • Investigation of metal photocathodes under BLT­ relevant conditions showed that magnesium is a promising cathode candidate for BLT with its relatively high quantum efficiency

Esin B Sozer; Chunqi Jiang; Martin A. Gundersen

2011-01-01

185

Magnesium-Based Photocathodes for Back-Lighted Thyratrons  

Microsoft Academic Search

Pseudospark switches have been successfully employed in a variety of pulsed power applications including high-power electron beam sources, high-power microwaves, and transient plasma ignition for pulsed detonation engines. For applications such as these, advances that improve and simplify triggering are important. Here, magnesium was investigated as a photocathode candidate for optically triggered pseudospark switches, also called back-lighted thyratrons (BLTs). A

Esin B. Sozer; Martin A. Gundersen; Chunqi Jiang

2012-01-01

186

Applications of Laser and Synchrotron Based ARPES to Photocathode Research  

SciTech Connect

Laser angle resolved photoelectron spectroscopy (ARPES) provides unique information about angle and energy distribution of photoelectrons. Laser ARPES gives unique insight into how NEA materials work. ARPES combined with some ancillary measurements gives a very complete picture of system electronic physics. For H:C[100] there is now a clear program for engineering as well as development analogous systems. ARPES well suited for identifying 'ideal' photocathodes with intrinsically low emittance and high QE.

Rameau J.; Smedley J.; Muller, E.; Kidd, T.; Johnson, P.; Allen, P.; Carr, L.; Valla, T.

2010-10-12

187

Recent advances in technetium halide chemistry.  

PubMed

Transition metal binary halides are fundamental compounds, and the study of their structure, bonding, and other properties gives chemists a better understanding of physicochemical trends across the periodic table. One transition metal whose halide chemistry is underdeveloped is technetium, the lightest radioelement. For half a century, the halide chemistry of technetium has been defined by three compounds: TcF6, TcF5, and TcCl4. The absence of Tc binary bromides and iodides in the literature was surprising considering the existence of such compounds for all of the elements surrounding technetium. The common synthetic routes that scientists use to obtain binary halides of the neighboring elements, such as sealed tube reactions between elements and flowing gas reactions between a molecular complex and HX gas (X = Cl, Br, or I), had not been reported for technetium. In this Account, we discuss how we used these routes to revisit the halide chemistry of technetium. We report seven new phases: TcBr4, TcBr3, ?/?-TcCl3, ?/?-TcCl2, and TcI3. Technetium tetrachloride and tetrabromide are isostructural to PtX4 (X = Cl or Br) and consist of infinite chains of edge-sharing TcX6 octahedra. Trivalent technetium halides are isostructural to ruthenium and molybdenum (?-TcCl3, TcBr3, and TcI3) and to rhenium (?-TcCl3). Technetium tribromide and triiodide exhibit the TiI3 structure-type and consist of infinite chains of face-sharing TcX6 (X = Br or I) octahedra. Concerning the trichlorides, ?-TcCl3 crystallizes with the AlCl3 structure-type and consists of infinite layers of edge-sharing TcCl6 octahedra, while ?-TcCl3 consists of infinite layers of Tc3Cl9 units. Both phases of technetium dichloride exhibit new structure-types that consist of infinite chains of [Tc2Cl8] units. For the technetium binary halides, we studied the metal-metal interaction by theoretical methods and magnetic measurements. The change of the electronic configuration of the metal atom from d(3) (Tc(IV)) to d(5) (Tc(II)) is accompanied by the formation of metal-metal bonds in the coordination polyhedra. There is no metal-metal interaction in TcX4, a Tc?Tc double bond is present in ?/?-TcCl3, and a Tc?Tc triple bond is present in ?/?-TcCl2. We investigated the thermal behavior of these binary halides in sealed tubes under vacuum at elevated temperature. Technetium tetrachloride decomposes stepwise to ?-TcCl3 and ?-TcCl2 at 450 °C, while ?-TcCl3 converts to ?-TcCl3 at 280 °C. The technetium dichlorides disproportionate to Tc metal and TcCl4 above ?600 °C. At 450 °C in a sealed Pyrex tube, TcBr3 decomposes to Na{[Tc6Br12]2Br}, while TcI3 decomposes to Tc metal. We have used technetium tribromide in the preparation of new divalent complexes; we expect that the other halides will also serve as starting materials for the synthesis of new compounds (e.g., complexes with a Tc3(9+) core, divalent iodide complexes, binary carbides, nitrides, and phosphides, etc.). Technetium halides may also find applications in the nuclear fuel cycle; their thermal properties could be utilized in separation processes using halide volatility. In summary, we hope that these new insights on technetium binary halides will contribute to a better understanding of the chemistry of this fascinating element. PMID:24393028

Poineau, Frederic; Johnstone, Erik V; Czerwinski, Kenneth R; Sattelberger, Alfred P

2014-02-18

188

Dialkylzinc-mediated cross-coupling reactions of perfluoroalkyl and perfluoroaryl halides with aryl halides.  

PubMed

A highly chemoselective perfluoroalkylation reaction of aromatic halides is reported. Thermally stable perfluoroalkylzinc reagents, generated by a rapid halogen-zinc exchange reaction between diorganozinc and perfluoroalkyl halide species, couple with a wide range of aryl halides in the presence of a copper catalyst, in moderate to high yields. Good stability of the perfluoroalkylzinc species was indicated by DFT calculation and the reagents were storable for at least three months under argon without loss of activity. This method is applicable to gram-scale synthesis, and its functional group tolerance compares favorably with reported protocols. PMID:25630706

Kato, Hisano; Hirano, Keiichi; Kurauchi, Daisuke; Toriumi, Naoyuki; Uchiyama, Masanobu

2015-03-01

189

Influence of Al fraction on photoemission performance of AlGaN photocathode.  

PubMed

To research the photoemission performance of a transmission-mode Al(1-x)Ga(x)N photocathode, Al0.24Ga0.76N and GaN photocathodes with the same structure were activated, their spectral responses were measured using a multi-information measurement system at room temperature, and the photocathode parameters were obtained by fitting quantum efficiency curves. The results showed that both the reflective-mode and transmission-mode spectral responses of the AlGaN photocathode were lower than those of the GaN photocathode. Compared with the GaN photocathode, the short-wavelength spectral response of the Al0.24Ga0.76N photocathode was less seriously affected by lattice defects between the buffer and emission layers. The Al atom at the AlGaN photocathode surface could affect the optimal Cs adsorption position, which mainly affects the surface electron escape probability of the photocathode. PMID:24921126

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

2014-06-10

190

Transport of Soil Halides through Rice Paddies: A Viable Mechanism for Rapid Dispersion of the Soil Halide Reservoir  

Microsoft Academic Search

On short time scales (1-10 years) soil halide concentrations have been assumed to be primarily driven by leaching and deposition processes. Recent results however, have shown that terrestrial plants volatilize soil halides in the form of methyl halides. Emissions of methyl chloride, methyl bromide and methyl iodide represent major pathways for delivery of inorganic halogen radicals to the atmosphere. Inorganic

K. R. Redeker; S. Manley; N. Wang; R. Cicerone

2002-01-01

191

Gas-Phase Identity SN2 Reactions of Halide Anions and Methyl Halides with Retention of Configuration  

E-print Network

Gas-Phase Identity SN2 Reactions of Halide Anions and Methyl Halides with Retention at the G2(+) level of theory have been carried out on the identity front-side nucleophilic substitution and appear to represent an unlikely mechanistic pathway for identity halide exchange. Introduction

Schlegel, H. Bernhard

192

Breakdown processes in metal halide lamps  

NASA Astrophysics Data System (ADS)

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 voltage is insufficient to break down the higher pressure (>many atm) of metal halide vapour. In this paper, fundamental processes during breakdown in cold and warm, idealized metal halide lamps in mixtures of Ar and Hg are investigated using a two-dimensional fluid model for plasma transport. We find that the capacitances of the walls of the discharge tube and adjacent ground planes are important in determining the breakdown voltage and avalanche characteristics. The prompt capacitance represented by, for example, external trigger wires provides a larger E/N to sustain ionization early in the avalanche. This effect is lost as the walls charge and shield the plasma from the ground planes. More rapid breakdown occurs in slightly warm lamps having small vapour pressures of Hg due to the resulting Penning mixture. Warmer lamps, having larger mole fractions of Hg, have less efficient breakdown as the increase in momentum transfer of the electrons is not offset by the additional ionization sources of the Penning mixture.

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

2003-02-01

193

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

194

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

E-print Network

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

Brookhaven National Laboratory

195

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

E-print Network

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

196

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

197

Upgrading platform using alkali metals  

DOEpatents

A process for removing sulfur, nitrogen or metals from an oil feedstock (such as heavy oil, bitumen, shale oil, etc.) The method involves reacting the oil feedstock with an alkali metal and a radical capping substance. The alkali metal reacts with the metal, sulfur or nitrogen content to form one or more inorganic products and the radical capping substance reacts with the carbon and hydrogen content to form a hydrocarbon phase. The inorganic products may then be separated out from the hydrocarbon phase.

Gordon, John Howard

2014-09-09

198

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

SciTech Connect

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

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

2005-12-01

199

Amorphous Si thin film based photocathodes with high photovoltage for efficient hydrogen production.  

PubMed

An amorphous Si thin film with TiO2 encapsulation layer is demonstrated as a highly promising and stable photocathode for solar hydrogen production. With platinum as prototypical cocatalyst, a photocurrent onset potential of 0.93 V vs RHE and saturation photocurrent of 11.6 mA/cm(2) are measured. Importantly, the a-Si photocathodes exhibit impressive photocurrent of ~6.1 mA/cm(2) at a large positive bias of 0.8 V vs RHE, which is the highest for all reported photocathodes at such positive potential. Ni-Mo alloy is demonstrated as an alternative low-cost catalyst with onset potential and saturation current similar to those obtained with platinum. This low-cost photocathode with high photovoltage and current is a highly promising photocathode for solar hydrogen production. PMID:24079390

Lin, Yongjing; Battaglia, Corsin; Boccard, Mathieu; Hettick, Mark; Yu, Zhibin; Ballif, Christophe; Ager, Joel W; Javey, Ali

2013-01-01

200

Mean transverse energy and response time measurements of GaInP based photocathodes  

SciTech Connect

GaInP, which has a wider band gap than GaAs, is introduced as a photocathode for energy recovery linac (ERL). The wide band gap of material is expected to reduce the heating effect in the thermal relaxation process after high energy excitation. GaInP photocathodes exhibited higher quantum efficiency than GaAs and low thermal emittance as the same as GaAs photocathodes under green laser light irradiation. A short picosecond electron pulse was also achieved with the GaInP photocathode under 532?nm pulse laser irradiation. These experimental results demonstrate that the GaInP photocathode is an important candidate for ERL.

Jin, Xiuguang [Institute for Advanced Research, Nagoya University, Nagoya 464-8603 (Japan); Yamamoto, Masahiro; Miyajima, Tsukasa; Honda, Yosuke; Uchiyama, Takashi [High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801 (Japan); Tabuchi, Masao [Nagoya University Synchrotron Radiation Research Center, Nagoya 464-8603 (Japan); Takeda, Yoshikazu [Nagoya Industrial Science Research Institute, Nagoya 464-0819 (Japan); Aichi Synchrotron Radiation Center, Aichi Science and Technology Foundation, Seto 489-0965 (Japan)

2014-08-14

201

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

202

High voltage switch triggered by a laser-photocathode subsystem  

DOEpatents

A spark gap switch for controlling the output of a high voltage pulse from a high voltage source, for example, a capacitor bank or a pulse forming network, to an external load such as a high gradient electron gun, laser, pulsed power accelerator or wide band radar. The combination of a UV laser and a high vacuum quartz cell, in which a photocathode and an anode are installed, is utilized as triggering devices to switch the spark gap from a non-conducting state to a conducting state with low delay and low jitter.

Chen, Ping; Lundquist, Martin L.; Yu, David U. L.

2013-01-08

203

Polarization and charge limit studies of strained GaAs photocathodes  

SciTech Connect

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

Saez, P.J.

1997-03-01

204

Study of the effective Debye temperature in alkali metals and their halides  

Microsoft Academic Search

The reported study makes use of two approaches described by de Launay (1954, 1956, 1959) and by Betts et al. (1956). The results obtained for the effective Debye temperature by both methods agree within 1% in all cases. The obtained data support the notion that the frequency of a solid depends on the relative masses and the ratio of the

N. D. Tripathi; S. K. Pandey

1976-01-01

205

THERMAL GRADIENT MIGRATION OF BRINE INCLUSIONS IN SYNTHETIC ALKALI HALIDE SINGLE CRYSTALS  

SciTech Connect

An apparatus consisting of an optical microscope with a hot stage attachment capable of simultaneously non-uniformly heating and mechanically loading small single crystals of salt was used to measure the velocities of all-liquid inclusions in NaCl and KCl specimens under various conditions of temperature, temperature gradient, and uniaxial stress. The rate-controlling elementary step in the migration of the inclusions was found to be associated with interfacial processes, probably dissolution of the hot face. Dislocations are required for this step to take place. The small number of dislocation intersections with small inclusions in nearly perfect crystals causes substantial variations in the velocity, a sensitivity of the velocity to mechanical loading of the crystal, and a velocity which varies approximately as the square of the temperature gradient.

Olander, D.R.; Machiels, A.J.; Balooch, M.; Yagnik, S.

1981-01-01

206

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

207

The aluminum electrode in AlCl3-alkali-halide melts  

NASA Technical Reports Server (NTRS)

Passivation phenomena were observed upon cathodic and anodic polarization of the Al electrode in AlCl3-KCl-NaCl melts between 100 and 160 C. They are caused by formation of a solid salt layer at the electrode surface resulting from concentration changes upon current flow. The anodic limiting currents increased with temperature and with decreasing AlCl3 content of the melt. Current voltage curves obtained on a rotating aluminum disk showed a linear relationship between the anodic limiting current and 1/sq root of 2 pi (rps). Upon cathodic polarization dentrite formation occurs at the Al electrode. The activation overvoltage in AlCl3-KCl-NaCl (57.5-12.5-20 mol%) was determined by galvanostatic current step methods. An apparent exchange current density of 270 mA/cm2 at 130 C and a double layer capacity of 40 plus or minus 10 microfarad/cm2 were measured.

Holleck, G. L.; Giner, J.

1972-01-01

208

Structure of adsorbates on alkali halides (theory). I. HBr on LiF(001)  

NASA Astrophysics Data System (ADS)

We report a first computation of the geometry of HBr adsorbed on a LiF(001) substrate. The interaction energy of 200 HBr molecules with periodic boundary conditions was determined with respect to adsorbate-substrate and adsorbate-adsorbate electrostatic interaction (point charges in HBr simulated its dipole and multipoles) as well as a short-range ``core'' potential (comprising dispersion forces and repulsive overlap). The monolayer heat of adsorption at T=100 K according to this model was 0. 27 eV, which was also the experimental value [E. B. D. Bourdon, et al., J. Chem. Phys. (submitted)]. The major contribution to this energy came from electrostatic binding. The preferred HBr location at all surface coverages (0.25, 0.50, and 1.0 ML) in the temperature range T=70-130 K was with Br over Li+ and H almost eclipsing one of the four neighboring F-. In this configuration, Br-H is tilted down by 23 ° from the crystal plane in an arrangement resembling a Br-H- -F- hydrogen bond. This computed geometry agrees well with recent experimental findings for HBr/LiF(001) using polarized infrared spectroscopy [P. M. Blass et al.; J. Chem. Phys. (submitted)], and is also in qualitative accord with the observed angular distribution of fast H from the photolysis of HBr adsorbed on LiF(001). At the separations dictated by the LiF(001) lattice, the net adsorbate-adsorbate interaction is attractive, leading to a tentative prediction of island formation at lower coverages under equilibrium conditions.

Polanyi, J. C.; Williams, R. J.; O'Shea, S. F.

1991-01-01

209

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

PubMed

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

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

2004-05-01

210

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

NASA Technical Reports Server (NTRS)

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

Weidner, D. J.; Simmons, G.

1972-01-01

211

Spectroscopic studies of Sb3 + color centers in alkali halide single crystals  

NASA Astrophysics Data System (ADS)

The emission from KCl: Sb3+ and KI: Sb3+ excited in the A-absorption band was measured as a function of exciting photon energy and temperature. The A-band excitation produced two emission bands for KCl: Sb3+ and a single band for KI: Sb3+. The definitive assignment of these bands is presented in terms of the adiabatic potential energy surface (APES), in which the effect of the spin-orbit interaction (SO) on the Jahn-Teller (JT) interaction coupling to the Eg mode is taken into account. The polarization spectrum and the angular dependence of polarization ratio of the A-band emission were also studied to determine the symmetry axes of the Sb3+ -vacancies complex. The results indicate that the anisotropy is associated with the relaxed excited state (RES) of Sb3+. It is also found that the JT interaction coupling to the T2g mode and the vacancies, situated in the next-nearest-neighbor (nnn) and the nearest-neighbor (nn) positions to the Sb3+ ion, give rise to an additive perturbation.

Choi, K. O.; Lee, S. W.; Bae, H. K.; Jung, S. H.; Chang, C. K.; Kang, J. G.

1991-05-01

212

Two types of self-trapped excitons in alkali halide crystals  

NASA Astrophysics Data System (ADS)

We have carried out ab initio many-electron variational calculations of the adiabatic potential-energy surface (APES) for the lowest triplet state of the self-trapped exciton (STE) in KCl and LiCl. For KCl, it is found that at the APES minimum, the Cl-2 molecular ion comprising the STE hole is displaced along the <110> axis by about 0.90 Å from its symmetrical position. The STE electron and hole are shifted in the direction opposite to that of the Cl-2 displacement. The calculated optical-transition energies due to electron and hole excitations of the STE at the APES minimum, and the luminescence energy due to the transition to the crystal ground state agree well with the experimental results. It is found that the <110> displacement of the Cl-2 molecular ion at the APES minimum from its symmetrical position for LiCl is 0.07 Å, much smaller than that in KCl, and that the direction of the shift of the electron and hole is opposite to that for KCl; the electron and hole are localized near one of the Cl-2 ions located closer to the lattice site. It is shown that, for a small shift of the Cl-2 molecular ion from its symmetrical position, the states in which electron and hole are shifted to opposite directions appear in both LiCl and KCl crystals within energy intervals less than 0.8 eV. It is pointed out that the configuration interaction between the two states with the electron and hole shifted in opposite directions should be included for more precise APES calculations at small off-center displacements, and that the electron-hole correlation is important to determine the electronic structure of the STE.

Shluger, A. L.; Itoh, N.; Puchin, V. E.; Heifets, E. N.

1991-07-01

213

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

Microsoft Academic Search

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

Ryumyo Onaka; Teruhiko Mabuchi; Akira Yoshikawa

1967-01-01

214

Transport and Deposition of Halide in Alkali Metal-Stainless Steel Systems, (IV)  

Microsoft Academic Search

Solubility of sodium iodide in sodium is measured separately (a) with concentrations of major constituents leached from stainless steel in sodium and (b) with controlled concentration of oxide in sodium by the use of stainless steel capsule. The capsules loaded with 20 g sodium and 0.1–0.3 g powder of additives are heated at their upper part in a furnace and

Suguru TASHIRO; Norihiko SAGAWA

2000-01-01

215

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

Code of Federal Regulations, 2010 CFR

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

2010-07-01

216

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

Code of Federal Regulations, 2011 CFR

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

2011-07-01

217

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

Code of Federal Regulations, 2012 CFR

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

2012-07-01

218

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...

219

Lanthanide-halide based humidity indicators  

DOEpatents

The present invention discloses a lanthanide-halide based humidity indicator and method of producing such indicator. The color of the present invention indicates the humidity of an atmosphere to which it is exposed. For example, impregnating an adsorbent support such as silica gel with an aqueous solution of the europium-containing reagent solution described herein, and dehydrating the support to dryness forms a substance with a yellow color. When this substance is exposed to a humid atmosphere the water vapor from the air is adsorbed into the coating on the pore surface of the silica gel. As the water content of the coating increases, the visual color of the coated silica gel changes from yellow to white. The color change is due to the water combining with the lanthanide-halide complex on the pores of the gel.

Beitz, James V. (Hinsdale, IL); Williams, Clayton W. (Chicago, IL)

2008-01-01

220

Magnesium-based photocathodes for triggering back-lighted thyratrons  

NASA Astrophysics Data System (ADS)

This dissertation presents experimental studies of application of magnesium-based photocathodes to optically triggered pseudospark switches, called back-lighted thyratrons (BLTs). Magnesium was chosen as a low work function metal photocathode for its potential to increase triggering performance of the switch with a higher photoemission performance than traditional BLT cathodes. Improvement in triggering performance of plasma switches is of interest for device development of compact pulsed power systems where the size of switching units can limit the overall size and the mobility of the system. Experiments were conducted on photoemission performance of photocathode candidates under BLT-relevant conditions; and delay and jitter performance of a BLT with photocathode candidates with changing helium pressure and switch voltages. A review of photocathode literature showed that Mg and Cu are the most promising candidates for increasing the photoemission during the triggering of BLTs. As a commonly used BLT cathode in the switch literature, Mo was chosen together with Mg and Cu to be tested under BLT-relevant pressure and field conditions. Quantum efficiency measurements of high-purity foils of Mg, Cu and Mo showed a superior performance of Mg and Cu over Mo. Mg had the highest quantum efficiency of 1.5 x 10-5 among all three materials. After photoemission measurements in a test bed were concluded, testing of these cathodes for their switching performance was done in two stages. First, an unfocused UV laser beam (8.5 x 106 W/cm 2) with a wavelength of 266 nm was used for delay measurements of a BLT with Mg, Cu and Mo-based cathodes. Mg-based cathodes showed at least a thirty-fold reduction in delay and jitter compared to Cu-based and at least an eighty-fold reduction in delay and jitter compared to Mo-based cathodes at any given helium pressure and switch voltage pair. Subsequently, a partial focusing of the same light source was utilized (7.4 x 107W/cm 2) for delay measurements of a BLT with copper electrodes at constant switch voltage and changing helium pressure before and after integration of a Mg foil. These measurements showed an order of magnitude shorter delay and jitter throughout the pressure range when the high-purity Mg-foil was present at the switch cathode. Theoretical estimations of electron emission from the cathode during the triggering suggested that the main mechanism responsible for the observed change in delay and jitter was the increased photoemission due to the lower work function of the Mg cathode and that the effect of temperature on triggering is negligible. SEM images of the high-purity Mg foil integrated at the BLT cathode for 106 shots showed signs of melting around the bore hole. No degradation of the switch performance was observed for the duration of 10 6 shots. In conclusion, magnesium-based cathodes for BLTs showed an important potential for small triggering units for optical triggering, especially when the intensity of the optical source is limited. A future work involving plasma simulations is suggested for assessing potential of different cathode/optical source pairs for triggering BLTs.

Sozer, Esin B.

221

Process and composition for drying of gaseous hydrogen halides  

DOEpatents

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

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

1989-08-01

222

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

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

2012-06-12

223

Photoemission behaviors of transmission-mode InGaAs photocathode  

NASA Astrophysics Data System (ADS)

Based on the studies of the GaAs photocathode, the surface model of the InGaAs photocathode is investigated and the energy distributions of electrons reaching the band bending region, reaching the surface and emitting into vacuum are calculated. We use the quantum efficiency formula to fit the experimental curves, and obtain the performance parameters of the photocathode and the surface barrier parameters. The results show that the electron escape probability is seriously influenced by energy distribution and plays an important role in the research of high quantum efficiency as well. After the theoretical calculation, the energy range of electrons crossing the BBR broaden, the peak of the electron energy distribution shifts forward to low energy, the number of low energy electrons increases obviously; The surface barriers of the InGaAs photocathode is similar to that of the GaAs photocathode. The height of barrier II not only decreases the number of electrons, but also makes the width of electron energy distribution narrow. The prepared transmission-mode InGaAs photocathode contains 20% InAs and 80% GaAs. This combination of InGaAs photocathodes is widely used in the weak light detection field, such as night vision technology, forest fire prevention and harsh climate monitoring.

Jin, Muchun; Chang, Benkang; Chen, Xinlong; Zhang, Yijun; Cheng, Hongchang

2014-10-01

224

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

225

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

PubMed

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

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

2015-01-01

226

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

227

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

228

Environmental controls over methyl halide emissions from rice paddies  

Microsoft Academic Search

This paper examines primary controlling factors that affect methyl halide emissions from rice paddy ecosystems. Observations of four cultivars under multiple growth conditions during studies in commercial fields and the University of California, Irvine, greenhouse lead to the conclusion that daily emissions of methyl halides are primarily determined by the growth stage of the rice plant, with the exception that

K. R. Redeker; R. J. Cicerone

2004-01-01

229

Emissions of Methyl Halides and Methane from Rice Paddies  

Microsoft Academic Search

Methyl halide gases are important sources of atmospheric inorganic halogen compounds, which in turn are central reactants in many stratospheric and tropospheric chemical processes. By observing emissions of methyl chloride, methyl bromide, and methyl iodide from flooded California rice fields, we estimate the impact of rice agriculture on the atmospheric budgets of these gases. Factors influencing methyl halide emissions are

K. R. Redeker; N.-Y. Wang; J. C. Low; A. McMillan; S. C. Tyler; R. J. Cicerone

2000-01-01

230

Attenuation performance of reflection-mode AlGaN photocathode under different preparation methods.  

PubMed

To research the attenuation performance of the AlGaN photocathode, three samples with the same structures grown by metalorganic chemical vapor deposition were activated with three different activation methods, which are called Cs-only, Cs-O, and Cs-O-Cs activation, respectively. The spectral responses and attenuated photocurrents of the three AlGaN photocathodes were measured. The results show that the Cs-O activated AlGaN photocathode exhibits the lowest attenuation speed in the first few hours, and the attenuation speed of the Cs-only activated one is fastest. After attenuating for 90 min, the attenuation photocurrent curve of the Cs-O-Cs activated sample is coincident with that of the Cs-O activated one. The main factor affecting the photocurrent attenuation is related to Cs atoms desorbed from the photocathode surface. PMID:23938417

Hao, Guanghui; Yang, Mingzhu; Chang, Benkang; Chen, Xinlong; Zhang, Junju; Fu, Xiaoqian

2013-08-10

231

Blue-green reflection-mode GaAlAs photocathodes  

NASA Astrophysics Data System (ADS)

In order to obtain the suitable photocathode which could be applicable for the field of ocean exploration, the p-type zinc (Zn)-doped reflection-mode GaAlAs photocathode sample using exponential-doping technique is grown by metal organic chemical vapor deposition, the Al component of GaAlAs emission layer is designed to be 0.63. After the chemical etching, the photocathode samples are heated in vacuum at high-temperature of 650°C and 600°C respectively, the vacuum variation curves during the heat cleaning are measured, which correspond to the desorption of oxides in the surface of GaAlAs emission layer. The (Cs, O) activation for the photocathodes is executed after heat cleaning. Different proportion of Cs and O is performed on the different photocathode samples. The activation photocurrent curves of two samples with different heat cleaning temperature show that the GaAlAs surface treated by higher heat cleaning temperature is more sensitive to the Cs-O adsorption. The photocathode activated with the larger Cs current has a shorter time to reach the first photocurrent peak, and also obtains a bigger final photocurrent peak. According to the measured spectral response curves, it could be found that a suitable heat cleaning temperature and a moderate Cs/O current ratio are very important to prepare high performance GaAlAs photocathode. The prepared reflection-mode GaAlAs photocathodes are response to the blue-green light, and the cut-off wavelength is at about 580 nm.

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

2012-11-01

232

Photoemission studies with barium and LaB6 photocathodes and polarized laser light  

NASA Astrophysics Data System (ADS)

In this paper, presented is a work on the optimization of the performance of barium photocathodes. Studies on the dependence of the quantum yield on the polarization and angle of incidence of the laser beam are conducted. Moreover, studies on single crystal LaB6 photocathodes are reported. This material possesses a lower quantum yield than barium, but chemically it is much less reactive and have a very good thermionic emission characteristics.

Conde, M. E.; Kwon, S. I.; Young, A. T.; Leung, K. N.; Kim, K.-J.

1994-11-01

233

The Vapor Pressure of Plutonium Halides  

Microsoft Academic Search

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

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

1950-01-01

234

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

SciTech Connect

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

Bolton, Paul

2010-12-07

235

RADIOLYSIS OF ALKYL HALIDE-HYDROCARBON SOLUTIONS AND SZILARD-CHALMERS CHEMISTRY OF ALKYL HALIDE-HYDROCARBON SOLUTIONS  

Microsoft Academic Search

Work was carried out to obtain a better understanding of the ; interactions occurring between solvent and solute during irradiations of alkyl ; halide-hydrocarbon solutions. This was done by investigating the chemical fate ; of several alkyl halide solutes which were labeled with either I¹³¹ or C\\/; sup 14\\/ and whose concentration in pentane solutions was varied. Using optical ;

Geissler

1962-01-01

236

Positron-alkali atom scattering  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

237

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

SciTech Connect

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

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

2009-12-11

238

Nickel-Catalyzed Borylation of Halides and Pseudo-Halides with Tetrahydroxydiboron [B2(OH)4  

PubMed Central

Arylboronic acids are gaining increased importance as reagents and target structures in a variety of useful applications. Recently, the palladium-catalyzed synthesis of arylboronic acids employing the atom economical tetrahydroxydiboron (BBA) reagent has been reported. The high cost associated with palladium, combined with several limitations of both palladium and copper-catalyzed processes, prompted us to develop an alternative method. Thus, the nickel-catalyzed borylation of aryl and heteroaryl halides and pseudo-halides using tetrahydroxydiboron (BBA) has been formulated. The reaction proved to be widely functional group tolerant and applicable to a number of heterocyclic systems. To the best of our knowledge, the examples presented here represent the only effective Ni-catalyzed Miyaura borylations conducted at room temperature. PMID:23777538

Molander, Gary A.; Cavalcanti, Livia N.; García-García, Carolina

2013-01-01

239

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

240

Regenerable activated bauxite adsorbent alkali monitor probe  

DOEpatents

A regenerable activated bauxite adsorber alkali monitor probe for field applications to provide reliable measurement of alkali-vapor concentration in combustion gas with special emphasis on pressurized fluidized-bed combustion (PFBC) off-gas. More particularly, the invention relates to the development of a easily regenerable bauxite adsorbent for use in a method to accurately determine the alkali-vapor content of PFBC exhaust gases. 6 figs.

Lee, S.H.D.

1992-12-22

241

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

242

A cesium bromide photocathode excited by 405?nm radiation  

SciTech Connect

In several applications, such as electron beam lithography and X-ray differential phase contrast imaging, there is a need for a free electron source with a current density at least 10?A/cm{sup 2} yet can be shaped with a resolution down to 20?nm and pulsed. Additional requirements are that the source must operate in a practical demountable vacuum (>1e-9?Torr) and be reasonably compact. In prior work, a photocathode comprising a film of CsBr on metal film on a sapphire substrate met the requirements except it was bulky because it required a beam (>10?W/cm{sup 2}) of 257?nm radiation. Here, we describe an approach using a 405?nm laser which is far less bulky. The 405?nm laser, however, is not energetic enough to create color centers in CsBr films. The key to our approach is to bombard the CsBr film with a flood beam of about 1?keV electrons prior to operation. Photoelectron efficiencies in the range of 100–1000?nA/mW were demonstrated with lifetimes exceeding 50?h between electron bombardments. We suspect that the electron bombardment creates intraband color centers whence electrons can be excited by the 405?nm photons into the conduction band and thence into the vacuum.

Maldonado, J. R.; Cheng, Y. T.; Pease, Fabian W.; Hesselink, L. [Electrical Engineering Department, Stanford University, Stanford, California 94305 (United States); Pianetta, P. [SLAC National Accelerator Center, Menlo Park, CA 94025 (United States)

2014-07-14

243

Hybrid modeling of relativistic underdense plasma photocathode injectors  

NASA Astrophysics Data System (ADS)

The dynamics of laser ionization-based electron injection in the recently introduced plasma photocathode concept is analyzed analytically and with particle-in-cell simulations. The influence of the initial few-cycle laser pulse that liberates electrons through background gas ionization in a plasma wakefield accelerator on the final electron phase space is described through the use of Ammosov-Deloine-Krainov theory as well as nonadiabatic Yudin-Ivanov (YI) ionization theory and subsequent downstream dynamics in the combined laser and plasma wave fields. The photoelectrons are tracked by solving their relativistic equations of motion. They experience the analytically described transient laser field and the simulation-derived plasma wakefields. It is shown that the minimum normalized emittance of fs-scale electron bunches released in mulit-GV/m-scale plasma wakefields is of the order of 10-2mmmrad. Such unprecedented values, combined with the dramatically increased controllability of electron bunch production, pave the way for highly compact yet ultrahigh quality plasma-based electron accelerators and light source applications.

Xi, Y.; Hidding, B.; Bruhwiler, D.; Pretzler, G.; Rosenzweig, J. B.

2013-03-01

244

Impact of the spatial laser distribution on photocathode gun operation  

DOE PAGESBeta

It is widely believed that a drive laser with uniform temporal and spatial laser profiles is required to generate the lowest emittance beam at the photoinjector. However, for a given 3 ps smooth-Gaussian laser temporal profile, our recent simulations indicate that a truncated-Gaussian laser spatial profile produces an electron beam with smaller emittance. The simulation results are qualitatively confirmed by later analytical calculation, and also confirmed by measurements: emittance reduction of ?25% was observed at the linac coherent light source (LCLS) injector with a truncated-Gaussian laser spatial profile at the nominal operating bunch charge of 150 pC. There was a significant secondary benefit—laser transmission through the iris for the truncated-Gaussian profile was about twice that compared to the nearly uniform distribution, which significantly loosens the laser power and quantum efficiency requirements for drive laser system and photocathode. Since February 9, 2012, the drive laser with the truncated-Gaussian spatial distribution has been used for LCLS routine user operations and the corresponding free electron laser power is at least the same as the one when using the nearly uniform spatial profile.

Zhou, Feng; Brachmann, Axel; Emma, Paul; Gilevich, Sasha; Huang, Zhirong

2012-09-01

245

A cesium bromide photocathode excited by 405 nm radiation  

NASA Astrophysics Data System (ADS)

In several applications, such as electron beam lithography and X-ray differential phase contrast imaging, there is a need for a free electron source with a current density at least 10 A/cm2 yet can be shaped with a resolution down to 20 nm and pulsed. Additional requirements are that the source must operate in a practical demountable vacuum (>1e-9 Torr) and be reasonably compact. In prior work, a photocathode comprising a film of CsBr on metal film on a sapphire substrate met the requirements except it was bulky because it required a beam (>10 W/cm2) of 257 nm radiation. Here, we describe an approach using a 405 nm laser which is far less bulky. The 405 nm laser, however, is not energetic enough to create color centers in CsBr films. The key to our approach is to bombard the CsBr film with a flood beam of about 1 keV electrons prior to operation. Photoelectron efficiencies in the range of 100-1000 nA/mW were demonstrated with lifetimes exceeding 50 h between electron bombardments. We suspect that the electron bombardment creates intraband color centers whence electrons can be excited by the 405 nm photons into the conduction band and thence into the vacuum.

Maldonado, J. R.; Cheng, Y. T.; Pianetta, P.; Pease, Fabian W.; Hesselink, L.

2014-07-01

246

Passive particle dosimetry. [silver halide crystal growth  

NASA Technical Reports Server (NTRS)

Present methods of dosimetry are reviewed with emphasis on the processes using silver chloride crystals for ionizing particle dosimetry. Differences between the ability of various crystals to record ionizing particle paths are directly related to impurities in the range of a few ppm (parts per million). To understand the roles of these impurities in the process, a method for consistent production of high purity silver chloride, and silver bromide was developed which yields silver halides with detectable impurity content less than 1 ppm. This high purity silver chloride was used in growing crystals with controlled doping. Crystals were grown by both the Czochalski method and the Bridgman method, and the Bridgman grown crystals were used for the experiments discussed. The distribution coefficients of ten divalent cations were determined for the Bridgman crystals. The best dosimeters were made with silver chloride crystals containing 5 to 10 ppm of lead; other impurities tested did not produce proper dosimeters.

Childs, C. B.

1977-01-01

247

Formation of structured nanophases in halide crystals.  

PubMed

When halide crystals KCl and NaCl are slightly doped by PbCl(2), (in orders of 10(-4)?mol/mol) the structurally stable nanophases ("quantum dots") are formed via nucleation within the bulks of their matrices. Using lattice modeling we have found in KCl-Pb system natural nucleation pathway from single impurity-vacancy complex to Suzuki phase, not demonstrated in previous analyses; further transition to PbCl(2) is difficult due to high stability of this phase. In the case of NaCl-Pb, no stable "end point" of aggregation was observed and our calculations suggest nucleation may readily proceed to large PbCl(2) clusters when initially formed platelike cluster reaches a certain critical thickness. These results coincide with our experimental data. PMID:21495761

Kulveit, J; Demo, P; Polák, K; Sveshnikov, A M; Kožíšek, Z

2011-04-14

248

Formation of structured nanophases in halide crystals  

NASA Astrophysics Data System (ADS)

When halide crystals KCl and NaCl are slightly doped by PbCl_2, (in orders of 10^{-4} mol/mol) the structurally stable nanophases ("quantum dots") are formed via nucleation within the bulks of their matrices. Using lattice modeling we have found in KCl-Pb system natural nucleation pathway from single impurity-vacancy complex to Suzuki phase, not demonstrated in previous analyses; further transition to PbCl_2 is difficult due to high stability of this phase. In the case of NaCl-Pb, no stable "end point" of aggregation was observed and our calculations suggest nucleation may readily proceed to large PbCl_2 clusters when initially formed platelike cluster reaches a certain critical thickness. These results coincide with our experimental data.

Kulveit, J.; Demo, P.; Polák, K.; Sveshnikov, A. M.; Kožíšek, Z.

2011-04-01

249

Direct deposition of GaN-based photocathodes on microchannel plates  

NASA Astrophysics Data System (ADS)

Epitaxial growth of p-type GaN-based UV photocathode by RF plasma assisted molecular beam epitaxy (MBE) on sapphire, fused silica, and alumina substrates was investigated. The electrical measurements indicted the growth of highly p-type GaN films as thin as 0.1 ?m on c-plane sapphire with a thin AlN nucleation layer. Polycrystalline p-type GaN was obtained for growth on fused silica and alumina. Negative electron affinity (NEA) photocathodes were fabricated by cesium activation of the p-type GaN films in vacuum. Quantum efficiency for UV detection on different substrates was then characterized. To study the integration of UV photocathodes with MCPs, direct deposition of p-type GaN films on glass MCPs were done at low growth temperatures by MBE. The detection efficiency of polycrystalline p- GaN photocathodes in reflection mode was much less than the high quality p-type GaN films on sapphire, however, it was comparable to the detection efficiency of the latter measured in the semitransparent mode. This indicates the potential for fabrication of improved photocathodes with higher gain and better spatial and temporal resolutions.

Dabiran, Amir M.; Wowchak, Andrew M.; Chow, Peter P.; Siegmund, Oswald H. W.; Hull, Jeffrey S.; Malloy, James; Tremsin, Anton S.

2009-02-01

250

FUV quantum efficiency degradation of cesium iodide photocathodes caused by exposure to thermal atomic oxygen  

NASA Astrophysics Data System (ADS)

The color dependence of the measured decline of the on-orbit sensitivity of the FUV channel of the HST Cosmic Origins Spectrograph (HST-COS) indicated the principal loss mechanism to be degradation of the cesium iodide (CsI) photocathode of the open-faced FUV detector. A possible cause of this degradation is contamination by atomic oxygen (AO), prompting an investigation of the interaction of AO with CsI. To address this question, opaque CsI photocathodes were deposited on stainless steel substrates employing the same deposition techniques and parameters used for the photocathodes of the HST-COS FUV detector. The as-deposited FUV quantum efficiency of these photocathodes was measured in the 117-174 nm range. Several of the photocathodes were exposed to varying levels of thermalized, atomic oxygen (AO) fluence (produced via an RF plasma). The post AO exposure QE's were measured and the degradation of sensitivity versus wavelength and AO fluence are presented.

McPhate, Jason; Anne, Joshi; Bacinski, John; Banks, Bruce; Cates, Carey; Christensen, Paul; Cruden, Brett; Dunham, Larry; Graham, Eric; Hughes, David; Kimble, Randy; Lupie, Olivia; Niedner, Malcolm; Osterman, Steven; Penton, Steven; Proffitt, Charles; Pugel, Diane; Siegmund, Oswald; Wheeler, Thomas

2011-09-01

251

Cross-coupling reactions of unactivated alkyl halides  

E-print Network

My graduate research at MIT has been focused on the development of palladium- or nickel-catalyzed cross-coupling reactions using unactivated alkyl electrophiles (e.g., halides and sulfonates). Although aryl and alkenyl ...

Zhou, Jianrong (Jianrong Steve)

2005-01-01

252

Study of methyl halide fluxes in temperate and tropical ecosystems   

E-print Network

CH3Br and CH3Cl (methyl halides) are the most abundant natural vectors of bromine and chlorine into the stratosphere and play an important role in stratospheric ozone destruction. The current knowledge of their respective ...

Blei, Emanuel

2010-01-01

253

Spectroscopy on Metal-Halide Lamps under Varying Gravity Conditions  

E-print Network

. Subject headings : plasma physics / gas discharges / metal-halide lamps / light sources / plasma.1 Incandescent lamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Gas discharges.4.2 The centrifuge . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.5 Diagnostics

Eindhoven, Technische Universiteit

254

Tellurite glass as a waste form for mixed alkali-chloride waste streams: Candidate materials selection and initial testing  

NASA Astrophysics Data System (ADS)

Tellurite glasses have historically been shown to host large concentrations of halides. They are here considered for the first time as a waste form for immobilizing chloride wastes, such as may be generated in the proposed molten alkali salt electrochemical separations step in nuclear fuel reprocessing. Key properties of several tellurite glasses are determined to assess acceptability as a chloride waste form. TeO2 glasses with other oxides (PbO, Al2O3 + B2O3, WO3, P2O5, or ZnO) were fabricated with and without 10 mass% of a simulated (non-radioactive) mixed alkali, alkaline-earth, and rare earth chloride waste. Measured chemical durability is compared for the glasses, as determined by the product consistency test (PCT), a common standardized chemical durability test often used to validate borosilicate glass waste forms. The glass with the most promise as a waste form is the TeO2-PbO system, as it offers good halide retention, a low sodium release (by PCT) comparable with high-level waste silicate glass waste forms, and a high storage density.

Riley, Brian J.; Rieck, Bennett T.; McCloy, John S.; Crum, Jarrod V.; Sundaram, S. K.; Vienna, John D.

2012-05-01

255

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

PubMed Central

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

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

2014-01-01

256

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

Code of Federal Regulations, 2011 CFR

...2011-07-01 2011-07-01 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...

2011-07-01

257

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

258

40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.  

Code of Federal Regulations, 2011 CFR

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

2011-07-01

259

40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.  

Code of Federal Regulations, 2010 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...

2010-07-01

260

40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.  

Code of Federal Regulations, 2014 CFR

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

2014-07-01

261

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

262

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

E-print Network

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

Geng, Rong-Li

263

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

264

Genetic control of methyl halide production in Arabidopsis.  

PubMed

Methyl chloride (CH(3)Cl) and methyl bromide (CH(3)Br) are the primary carriers of natural chlorine and bromine, respectively, to the stratosphere, where they catalyze the destruction of ozone, whereas methyl iodide (CH(3)I) influences aerosol formation and ozone loss in the boundary layer. CH(3)Br is also an agricultural pesticide whose use is regulated by international agreement. Despite the economic and environmental importance of these methyl halides, their natural sources and biological production mechanisms are poorly understood. Besides CH(3)Br fumigation, important sources include oceans, biomass burning, tropical plants, salt marshes, and certain crops and fungi. Here, we demonstrate that the model plant Arabidopsis thaliana produces and emits methyl halides and that the enzyme primarily responsible for the production is encoded by the HARMLESS TO OZONE LAYER (HOL) gene. The encoded protein belongs to a group of methyltransferases capable of catalyzing the S-adenosyl-L-methionine (SAM)-dependent methylation of chloride (Cl(-)), bromide (Br(-)), and iodide (I(-)) to produce methyl halides. In mutant plants with the HOL gene disrupted, methyl halide production is largely eliminated. A phylogenetic analysis with the HOL gene suggests that the ability to produce methyl halides is widespread among vascular plants. This approach provides a genetic basis for understanding and predicting patterns of methyl halide production by plants. PMID:14561407

Rhew, Robert C; Østergaard, Lars; Saltzman, Eric S; Yanofsky, Martin F

2003-10-14

265

Comparative research on indium seal process for transmission-mode GaAs photocathodes  

NASA Astrophysics Data System (ADS)

For night vision devices and other applications, the transmission-mode photocathodes must be sealed to tube by indium seal process (ISP) in practical application. But in early research, the integral sensitivity has large drop to about 30% amplitude after ISP process than after activation process. In order to well study the influence of ISP on surface barriers of activated GaAs photocathodes, we used the comparative research method by surface photovoltage spectroscopy (SPS) and spectral response current (SRC). Through fitting calculation, we can find that the impurity gas sources by micro channel plate and fluorescent screen have deep influence on the amplitude and width of surface barriers which lead to the large drop on SRC curves before and after ISP process. This on-line comparative research method can help to optimize ISP technique and vacuum degree optimization for transmission-mode GaAs photocathodes in the future.

Chen, Liang; Zhang, Shuqin; Jin, Shangzhong; Xu, Sunan; Jiao, Gangcheng

2013-01-01

266

High quantum efficiency photocathode simulation for the investigation of novel structured designs  

SciTech Connect

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

Opachich, Y. P., E-mail: opachiyp@nv.doe.gov; Ross, P. W.; Huffman, E.; Koch, J. A. [National Security Technologies LLC, Livermore, California 94550 (United States); MacPhee, A. G.; Nagel, S. R.; Bell, P. M.; Bradley, D. K.; Landen, O. L. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); Hilsabeck, T. J. [General Atomics, San Diego, California 92121 (United States)

2014-11-15

267

High quantum efficiency photocathode simulation for the investigation of novel structured designs.  

PubMed

A computer model in CST Studio Suite has been developed to evaluate several novel geometrically enhanced photocathode designs. This work was aimed at identifying a structure that would increase the total electron yield by a factor of two or greater in the 1-30 keV range. The modeling software was used to simulate the electric field and generate particle tracking for several potential structures. The final photocathode structure has been tailored to meet a set of detector performance requirements, namely, a spatial resolution of <40 ?m and a temporal spread of 1-10 ps. We present the details of the geometrically enhanced photocathode model and resulting static field and electron emission characteristics. PMID:25430201

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

2014-11-01

268

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

269

10 CFR 431.324 - Uniform test method for the measurement of energy efficiency of metal halide ballasts.  

Code of Federal Regulations, 2010 CFR

...the measurement of energy efficiency of metal halide ballasts. 431.324 Section...CERTAIN COMMERCIAL AND INDUSTRIAL EQUIPMENT Metal Halide Lamp Ballasts and Fixtures Test...the measurement of energy efficiency of metal halide ballasts. (a) Scope....

2010-01-01

270

Photoelectrochemical water splitting: silicon photocathodes for hydrogen evolution  

NASA Astrophysics Data System (ADS)

The development of low cost, scalable, renewable energy technologies is one of today's most pressing scientific challenges. We report on progress towards the development of a photoelectrochemical water-splitting system that will use sunlight and water as the inputs to produce renewable hydrogen with oxygen as a by-product. This system is based on the design principle of incorporating two separate, photosensitive inorganic semiconductor/liquid junctions to collectively generate the 1.7-1.9 V at open circuit needed to support both the oxidation of H2O (or OH-) and the reduction of H+ (or H2O). Si microwire arrays are a promising photocathode material because the high aspect-ratio electrode architecture allows for the use of low cost, earth-abundant materials without sacrificing energy-conversion efficiency, due to the orthogonalization of light absorption and charge-carrier collection. Additionally, the high surfacearea design of the rod-based semiconductor array inherently lowers the flux of charge carriers over the rod array surface relative to the projected geometric surface of the photoelectrode, thus lowering the photocurrent density at the solid/liquid junction and thereby relaxing the demands on the activity (and cost) of any electrocatalysts. Arrays of Si microwires grown using the Vapor Liquid Solid (VLS) mechanism have been shown to have desirable electronic light absorption properties. We have demonstrated that these arrays can be coated with earth-abundant metallic catalysts and used for photoelectrochemical production of hydrogen. This development is a step towards the demonstration of a complete artificial photosynthetic system, composed of only inexpensive, earth-abundant materials, that is simultaneously efficient, durable, and scalable.

Warren, Emily L.; Boettcher, Shannon W.; McKone, James R.; Lewis, Nathan S.

2010-08-01

271

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

DOE PAGESBeta

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

272

Amorphous Si Thin Film Based Photocathodes with High Photovoltage for Efficient Hydrogen Production  

E-print Network

generation such as p- Si,10,11 p-InP,12-14 p-WSe2,15 Cu2O with ZnO/Al and TiO2,16 p-GaP,17 and CdS-coated pAmorphous Si Thin Film Based Photocathodes with High Photovoltage for Efficient Hydrogen Production-Si photocathodes exhibit impressive photo- current of 6.1 mA/cm2 at a large positive bias of 0.8 V vs RHE, which

Javey, Ali

273

Compact narrow-band THz radiation source based on photocathode rf gun  

NASA Astrophysics Data System (ADS)

Narrow-band THz coherent Cherenkov radiation can be driven by a subpicosecond electron bunch traveling along the axis of a hollow cylindrical dielectric-lined waveguide. We present a scheme of compact THz radiation source based on the photocathode rf gun. On the basis of our analytic result, the subpicosecond electron bunch with high charge (800 pC) can be generated directly in the photocathode rf gun. According to the analytical and simulated results, a narrow emission spectrum peaked at 0.24 THz with 2 megawatt (MW) peak power is expected to gain in the proposed scheme (the length of the facility is about 1.2 m).

Li, Wei-Wei; He, Zhi-Gang; Jia, Qi-Ka

2014-04-01

274

III-V photocathode with nitrogen doping for increased quantum efficiency  

NASA Technical Reports Server (NTRS)

An increase in the quantum efficiency of a 3-5 photocathode is achieved by doping its semiconductor material with an acceptor and nitrogen, a column-5 isoelectronic element, that introduces a spatially localized energy level just below the conduction band similar to a donor level to which optical transitions can occur. This increases the absorption coefficient, alpha without compensation of the acceptor dopant. A layer of a suitable 1-5, 1-6 or 1-7 compound is included as an activation layer on the electron emission side to lower the work function of the photocathode.

James, L. W. (inventor)

1976-01-01

275

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

276

Identification of gas phase alkali species released during biomass combustion  

SciTech Connect

Direct sampling, molecular beam, mass spectrometry has been used to monitor alkali metal-containing vapors released during the combustion of a wide variety of biomass feedstocks that have potential use for power generation. Interpretation of the mass spectral data has revealed correlations between alkali metal release and feedstock composition. Alkali chlorides are the primary form of alkali metal vapor released during the combustion of grasses and straws. Alkali hydroxides are the most abundant alkali species released during the combustion of feedstocks with high alkali metal and low chlorine. Primary alkali metal release during the combustion of relatively low alkali metal woody feedstocks is from alkali sulfates. The chlorine content of biomass has been identified as an important parameter that facilitates alkali metal release. These results will ultimately be used to develop a predictive model that relates feedstock composition to fouling and slagging behavior in power generating facilities.

Dayton, D.C.; French, R.J.; Milne, T.A. [National Renewable Energy Lab., Golden, CO (United States)

1994-12-31

277

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

278

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

279

Genetic Control of Methyl Halide Production in Arabidopsis  

NASA Astrophysics Data System (ADS)

Methyl chloride and methyl bromide are the primary carriers of natural chlorine and bromine to the stratosphere where they catalyze the destruction of ozone, whereas methyl iodide influences aerosol formation and ozone loss in the troposphere. Methyl bromide is also an agricultural fumigant whose use is scheduled to be phased out by international agreement. Despite the economic and environmental importance of these methyl halides, their natural sources and biological production mechanisms are poorly understood. Currently identified sources include oceans, biomass burning, industrial and agricultural use, fuel combustion, salt marshes, wetlands, rice paddies, certain terrestrial plants and fungi, and abiotic processes. We demonstrate that the model plant Arabidopsis thaliana produces and emits methyl halides and that the enzyme primarily responsible for the production is encoded by the HARMLESS TO OZONE LAYER (HOL) gene located on chromosome II. In mutant plants that have a disruption of the HOL gene, methyl halide production is largely eliminated. A phylogenetic analysis using the HOL gene suggests that the ability to produce methyl halides is widespread among vascular plants. This approach provides a genetic basis for understanding and predicting patterns of methyl halide production by plants.

Rhew, R. C.; Ostergaard, L.; Saltzman, E. S.; Yanofsky, M. F.

2003-12-01

280

Quantum efficiency study of the sensitive to blue-green light transmission-mode GaAlAs photocathode  

NASA Astrophysics Data System (ADS)

The quantum efficiency of the blue-green transmission-mode GaAlAs photocathode has been studied. Two transmission-mode GaAlAs photocathodes with different structures are prepared, and the quantum efficiency curves are measured. We use the quantum efficiency formula to fit the experimental curves, and obtain the performance parameters of photocathodes such as the electron diffusion length, the back interface recombination velocity, and the surface electron escape probability. The effects of the Al compositions, the thickness of emission layer, and the electron diffusion length on quantum efficiency are investigated. The results show that both of transmission-mode GaAlAs photocathodes are sensitive to the blue-green light. The peak quantum efficiency of one photocathode appears at about 565 nm, while that of another photocathode appears at about 535 nm. The Al composition of emission layer plays a major role on the peak position of quantum efficiency of transmission-mode GaAlAs photocathode. Besides, the thickness of emission layer and the Al composition of window layer also have a large influence on the quantum efficiency.

Chen, Xinlong; Jin, Muchun; Xu, Yuan; Chang, Benkang; Shi, Feng; Cheng, Hongchang

2015-01-01

281

Alkali Silicate Vehicle Forms Durable, Fireproof Paint  

NASA Technical Reports Server (NTRS)

The problem: To develop a paint for use on satellites or space vehicles that exhibits high resistance to cracking, peeling, or flaking when subjected to a wide range of temperatures. Organic coatings will partially meet the required specifications but have the inherent disadvantage of combustibility. Alkali-silicate binders, used in some industrial coatings and adhesives, show evidence of forming a fireproof paint, but the problem of high surface-tension, a characteristic of alkali silicates, has not been resolved. The solution: Use of a suitable non-ionic wetting agent combined with a paint incorporating alkali silicate as the binder.

Schutt, John B.; Seindenberg, Benjamin

1964-01-01

282

Reactions of ultracold alkali-metal dimers  

SciTech Connect

We investigate the energetics of reactions involving pairs of alkali-metal dimers. Atom exchange reactions to form homonuclear dimers are energetically allowed for some but not all of the heteronuclear dimers. We carry out high-level electronic structure calculations on the potential energy surfaces of all the heteronuclear alkali-metal trimers and show that trimer formation reactions are always energetically forbidden for low-lying singlet states of the dimers. The results have important implications for the stability of quantum gases of alkali-metal dimers.

Zuchowski, Piotr S.; Hutson, Jeremy M. [Department of Chemistry, Durham University, South Road, Durham, DH1 3LE (United Kingdom)

2010-06-15

283

Diode pumped alkali vapor fiber laser  

DOEpatents

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 the center hole of a photonic-band-gap fiber, which can then be pumped with light from a pump laser and operated as an oscillator with a seed beam, or can be configured as an amplifier.

Payne, Stephen A. (Castro Valley, CA); Beach, Raymond J. (Livermore, CA); Dawson, Jay W. (Livermore, CA); Krupke, William F. (Pleasanton, CA)

2006-07-26

284

Diode pumped alkali vapor fiber laser  

DOEpatents

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 the center hole of a photonic-band-gap fiber, which can then be pumped with light from a pump laser and operated as an oscillator with a seed beam, or can be configured as an amplifier.

Payne, Stephen A. (Castro Valley, CA); Beach, Raymond J. (Livermore, CA); Dawson, Jay W. (Livermore, CA); Krupke, William F. (Pleasanton, CA)

2007-10-23

285

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

286

Low emittance electron beam production and characterization with a 17 GHz photocathode RF gun  

E-print Network

This thesis presents theoretical and experimental results of the production of very high brightness electron beams using a 17 GHz photocathode RF gun. A beam brightness of up to 8x 1013 A/([pi]m rad)2 was measured for a 1 ...

Brown, Winthrop Joseph

2001-01-01

287

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

E-print Network

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

288

STATUS OF SPRING8 PHOTOCATHODE RF GUN FOR FUTURE LIGHT SOURCES  

Microsoft Academic Search

Since 1996, we have been researching a photocathode single-cell pillbox rf gun for future light sources, and to date have achieved a maximum field gradient of 187 MV\\/m with a chemical etching processed cavity. For the last three years, we have been focusing on the development of a stable and highly qualified UV laser source for the rf gun. The

H. Tomizawa; H. Dewa; T. Taniuchi; A. Mizuno; T. Asaka; K. Yanagida; S. Suzuki; T. Kobayashi; H. Hanaki; F. Matsui

2005-01-01

289

Arsenic volatilization of GaAs photocathode at low temperature during thermal cleaning  

NASA Astrophysics Data System (ADS)

The gallium arsenide (GaAs) photocathode was generally cleaned by radiant heating, direct heating, ion bombardment annealing, and so on. In this paper, the radiant heating method, namely thermal cleaning method, was adopted for GaAs photocathode surface purification. Using this method could obtain an atomic clean surface, ensure the integrity of the GaAs surface lattice, and guarantee the uniformity of surface cleaning effect at the same time. But because the accurate measurement of the GaAs photocathode surface temperature in the vacuum system was very difficult, the residual gas analyzer (RGA) was used in this experiment to monitor the residual gas composition in ultrahigh vacuum during the thermal cleaning process and determine the thermal cleaning temperature by the partial pressure curves of As and Ga. It was found that the first peaks of As and Ga elements both appeared after heating about one hour, accompanied with H2O, N2/CO, CO2 and other common gas. According to partial pressure curves of H2O, N2/CO, CO2 and the heating time, it could be judged that the temperature at that time was not high, which should be under 150°C.After thermal cleaning experiment of three GaAs photocathodes, it was found that the peak value of As partial pressure at low temperature was generally within 10-11mbar~10-10mbar, and the peak value was at 10-10mbar at high temperature. Sometimes it was appeared that the peak value of As partial pressure at low temperature was even higher than the peak value at high temperature. The As volatilization phenomenon occurred at low temperature indicated that the elemental As exist on the GaAs photocathode surface or near surface after the chemical etching process, and the As could volatilize from GaAs photocathode at low temperature in the beginning of thermal cleaning. This research has guiding significance for further understanding the thermal cleaning mechanism of GaAs photocathode and improving the thermal cleaning technology.

Liu, Hui; Shi, Feng; Miao, Zhuang; Gao, Xiang; Cheng, Hong-chang; Niu, Sen; Wang, Long; Chen, Chang

2014-09-01

290

10 CFR 429.54 - Metal halide lamp ballasts and fixtures.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 2013-01-01 false Metal halide lamp ballasts and fixtures. 429...EQUIPMENT Certification § 429.54 Metal halide lamp ballasts and fixtures. ...requirements of § 429.11 are applicable to metal halide lamp ballasts; and (2)...

2013-01-01

291

10 CFR 429.54 - Metal halide lamp ballasts and fixtures.  

Code of Federal Regulations, 2014 CFR

...2014-01-01 2014-01-01 false Metal halide lamp ballasts and fixtures. 429...EQUIPMENT Certification § 429.54 Metal halide lamp ballasts and fixtures. ...requirements of § 429.11 are applicable to metal halide lamp ballasts; and (2)...

2014-01-01

292

10 CFR 429.54 - Metal halide lamp ballasts and fixtures.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 2012-01-01 false Metal halide lamp ballasts and fixtures. 429...EQUIPMENT Certification § 429.54 Metal halide lamp ballasts and fixtures. ...requirements of § 429.11 are applicable to metal halide lamp ballasts; and (2)...

2012-01-01

293

Alkali Metal Handling Practices at NASA MSFC  

NASA Technical Reports Server (NTRS)

NASA Marshall Space Flight Center (MSFC) is NASA s principle propulsion development center. Research and development is coordinated and carried out on not only the existing transportation systems, but also those that may be flown in the near future. Heat pipe cooled fast fission cores are among several concepts being considered for the Nuclear Systems Initiative. Marshall Space Flight Center has developed a capability to handle high-purity alkali metals for use in heat pipes or liquid metal heat transfer loops. This capability is a low budget prototype of an alkali metal handling system that would allow the production of flight qualified heat pipe modules or alkali metal loops. The processing approach used to introduce pure alkali metal into heat pipe modules and other test articles are described in this paper.

Salvail, Patrick G.; Carter, Robert R.

2002-01-01

294

Desulfurizing Coal With an Alkali Treatment  

NASA Technical Reports Server (NTRS)

Experimental coal-desulfurization process uses alkalies and steam in fluidized-bed reactor. With highly volatile, high-sulfur bituminous coal, process removed 98 percent of pyritic sulfur and 47 percent of organic sulfur. Used in coal liquefaction and in production of clean solid fuels and synthetic liquid fuels. Nitrogen or steam flows through bed of coal in reactor. Alkalies react with sulfur, removing it from coal. Nitrogen flow fluidizes bed while heating or cooling; steam is fluidizing medium during reaction.

Ravindram, M.; Kalvinskas, J. J.

1987-01-01

295

Thermodynamic reactivity, growth and characterization of mercurous halide crystals  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

296

Negative ion production rates in rare gas-halide lasers  

Microsoft Academic Search

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

K. J. Nygaard; H. L. Brooks; S. R. Hunter

1979-01-01

297

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

SciTech Connect

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

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

2011-07-21

298

Alkali metal and alkali metal hydroxide intercalates of the layered transition metal disulfides  

NASA Astrophysics Data System (ADS)

The intercalation reaction of some layered transition metal disulfides with alkali metals, alkali metal hydroxides, and tetraalkylammonium hydroxides were investigated. The alkali metal intercalates were prepared in the respective metal-hexamethylphosphoric triamide solutions in vacuo, and the hydroxide intercalates in aqueous hydroxide solutions. According to the intercalation reaction, the c-lattice parameter was increased, and the increase indicated the expansion of the interlayer distance. In the case of alkali metal intercalates, the expansion of the interlayer distance increased continuously, corresponding to the atomic radius of the alkali metal. On the other hand, the hydroxide intercalates showed discrete expansion corresponding to the effective ionic radius of the intercalated cation. All intercalates of TaS 2 and NbS 2 were superconductors. The expansion of the interlayer distance tended to increase the superconducting transition temperature in the intercalates of TaS 2 and vice versa in those of NbS 2.

Kanzaki, Y.; Konuma, M.; Matsumoto, O.

1981-05-01

299

On the Boiling Points of the Alkyl Halides.  

ERIC Educational Resources Information Center

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

Correia, John

1988-01-01

300

Assessing Global Terrestrial Sources of Methyl Halides - Ozone Regulating Gases   

E-print Network

Methyl bromide (CH3Br) and methyl chloride (CH3Cl) play significant roles in the depletion of the stratospheric ozone layer. The vast portion of methyl halide sources and sinks sources and sinks are natural in origin. The sources are poorly...

Gancarczyk, Maciej

2010-11-24

301

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

302

Kinetic Studies of the Solvolysis of Two Organic Halides  

ERIC Educational Resources Information Center

Describes an undergraduate organic chemistry laboratory experiment which utilizes the solvolysis of organic halides to demonstrate first and second order reaction kinetics. The experiment also investigates the effect of a change of solvent polarity on reaction rate, common-ion and noncommon-ion salt effects, and the activation parameters of a…

Duncan, J. A.; Pasto, D. J.

1975-01-01

303

Chemical form effects on the surface ionization of lithium halides  

Microsoft Academic Search

The surface ionization of lithium halides, i.e. fluoride, chloride, bromide and iodide, was studied using a mass spectrometer. In the measurements of ionization using rhenium filaments, it was found that the ionization efficiencies depend on the chemical forms of the samples. To analyze the mechanism of ionization, direct ionization by dissociative ionization is introduced in the present work. The ionization

Tatsuya Suzuki; Hideki Iwabuchi; Kazuko Takahashi; Masao Nomura; Makoto Okamoto; Yasuhiko Fujii

1995-01-01

304

Analysis and design of metal halide lamp igniter  

Microsoft Academic Search

This paper describes the operation principle, effects of design parameters and critical design issues related to igniters used for the ignition of metal halide lamps. Mathematical modeling for the circuit is also given. A prototype with two step-up transformers has been built, and the test results have verified the theoretical analysis. The test results show that the prototype has. produced

Yue-Quan Hu; Jun Zhang; Wei Chen; Chau-chun Wen

2001-01-01

305

Catalytic Enantioselective Negishi Reactions of Racemic Secondary Benzylic Halides  

E-print Network

Catalytic Enantioselective Negishi Reactions of Racemic Secondary Benzylic Halides Forrest O. Arp with excellent enantioselectivity (eqs 3 and 4). Table 1. Catalytic Enantioselective Negishi Reactions of Racemic in developing nickel-catalyzed cross-coupling reactions of secondary alkyl electrophiles.1 To fully exploit

Fu, Gregory C.

306

Metal halide lamps in the international space station ISS  

Microsoft Academic Search

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

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

2006-01-01

307

Semiempirical and DFT Investigations of the Dissociation of Alkyl Halides  

ERIC Educational Resources Information Center

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

Waas, Jack R.

2006-01-01

308

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

SciTech Connect

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

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

2013-03-01

309

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

310

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

311

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

312

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

313

Use of MgF2 and LiF photocathodes in the extreme ultraviolet.  

NASA Technical Reports Server (NTRS)

The photoelectric yields of 2000-A thick samples of MgF2 and LiF have been measured at wavelengths in the range from 1216 to 461 A. Peak values of 43 and 34%, respectively, were obtained at wavelengths around 550 A at 45 deg incidence. Coating the cathode of a channel electron multiplier with 3000 A of MgF2 produced no significant deterioration in the electrical properties and increased the sensitivity by factors of 1.62, 2.76, and 2.60 at wavelengths of 742, 584, and 461 A, respectively. Since the stability of response of the MgF2 photocathodes appears to be equal to that of conventional metallic and semiconducting cathodes, it is concluded that MgF2 would be a practical, high-efficiency photocathode for use in the extreme ultraviolet.

Lapson, L. B.; Timothy, J. G.

1973-01-01

314

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

SciTech Connect

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

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

2010-11-10

315

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

NASA Astrophysics Data System (ADS)

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

Nagai, Ryoji; Hajima, Ryoichi; Nishimori, Nobuyuki

2012-12-01

316

Ultraviolet quantum detection efficiency of potassium bromide as an opaque photocathode applied to microchannel plates  

NASA Technical Reports Server (NTRS)

The quantum detection efficiency (QDE) of potassium bromide as a photocathode applied directly to the surface of a microchannel plate over the 250-1600 A wavelength range has been measured. The contributions of the photocathode material in the channels and on the interchannel web to the QDE have been determined. Two broad peaks in the QDE centered at about 450 and about 1050 A are apparent, the former with about 50 percent peak QDE and the latter with about 40 percent peak QDE. The photoelectric threshold is observed at about 1600 A, and there is a narrow QDE minimum at about 750 A which correlates with 2X the band gap energy for KBr. The angular variation of the QDE from 0 to 40 deg to the channnel axis has also been examined. The stability of Kbr with time is shown to be good with no significant degradation of QDE at wavelengths below 1216 A over a 15-day period in air.

Siegmund, Oswald H. W.; Everman, E.; Vallerga, J. V.; Sokolowski, J.; Lampton, M.

1987-01-01

317

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

318

Quantum efficiency measurements of photocathode candidates for back-lighted thyratrons  

Microsoft Academic Search

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

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

2009-01-01

319

Reflective UV photocathodes with gas-phase electron extraction: solid, liquid, and adsorbed thin films  

Microsoft Academic Search

The photoemission quantum efficiency of reflective photocathodes in methane gas has been investigated in the spectral range between 140 and 250 nm. The spectral response of solid metals and CsI, as well as of liquid and solid TMAE film, have been measured. The high quantum efficiency of CsI (35% at 170 nm) makes it attractive for BaF2 or xenon scintillation

Jacques Séguinot; Georges Charpak; Y. Giomataris; Vladimir Peskov; Johann Tischhauser; Thomas Ypsilantis

1990-01-01

320

POWWER TESTS OF A PLD FILM MG PHOTOCATHODE IN A RF GUN  

Microsoft Academic Search

Metallic film photo-cathodes are rugged, have a fast response and good emission uniformity. Mg has also a relevant Quantum Efficiency (QE) in the near UV. A cathode suitable for a 1.5 cells S-band RF gun has been produced by depositing an Mg film on Cu by Pulsed Laser Deposition (PLD) technique. After different optimizations, stable good results have been reached

G. Gatti; L. Cultrera; F. Tazzioli; A. Perrone INFN-Lecce; P. Musumeci; J. Moody

321

Power tests of a PLD film MG photocathode in a RF gun  

Microsoft Academic Search

Metallic film photo-cathodes are rugged, have a fast response and good emission uniformity. Mg has also a relevant Quantum Efficiency (QE) in the near UV. A cathode suitable for a 1.5 cells S-band RF gun has been produced by depositing an Mg film on Cu by Pulsed Laser Deposition (PLD) technique. After different optimizations, stable good results have been reached

G. Gatti; L. Cultrera; F. Tazzioli; A. Perrone; P. Musumeci; J. Moody

2007-01-01

322

ELECTRICAL CONDUCTANCE OF THE LiCl-KCl EUTECTIC MELT CONTAINING HALIDES AND ALKALI TITANIUM FLUORIDES AS SOLUTES  

Microsoft Academic Search

The electrical conductances over the temperature range 350 to 400 of ; the LiCl-KCl eutectic melt and solutions of NaCl, LiF, NaF, KF, LiâTiF\\/sub ; 6\\/, NaâTiFâ, and KâTiFâ in this melt are reported for the ; region of dilute concentrations of the solutes. A reduced total specific ; conductance is found on the addition of fluorides to the chloride

George J. Janz; C. T. Brown; H. J. Gardner; C. Solomons

1958-01-01

323

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

E-print Network

appreciate the helpful advice of Barry Smith at the beginning of this work. LITERATURE CITED (1) E. M (1973). (3) P. G. Seybold, R. K. Sorrell, and R. A. Schuffert, Presentedat the 165th American Chemical Paul G.Seybold Wayne White (1973). Department of Chemistry Wright State University Dayton, OH 45431

Zare, Richard N.

324

Selective Recognition of an Alkali Halide Contact Joseph M. Mahoney, Alicia M. Beatty, and Bradley D. Smith*  

E-print Network

- association constant by slightly less than ten.5 An X-ray crystal structure showed that receptor 1 binds NaCl as a solvent separated ion-pair. We felt that the binding cooperativity would be improved if the salt were- in DMSO-d6.8 The 2/Cl- association constant is hardly affected by the presence of Na+, but it is increased

Smith, Bradley D.

325

Cs-Te photocathode RF electron gun for applied research at the Waseda University  

NASA Astrophysics Data System (ADS)

A compact electron accelerator based on photo-cathode RF electron gun is under development for applied research at the Waseda University. Higher charge and higher energy are key issues for applications such as pulse radiolysis experiment and laser-Compton X-ray generation. The new RF-gun cavity with cesium telluride (Cs-Te) photo-cathode which has higher quantum efficiency (Q.E.) compared with metal cathodes has been installed. The evaluation of Q.E. of the photo-cathode has been performed and the value obtained is more than 5% at the preparation stage. For understanding the Cs-Te cathode properties and the higher Q.E. operation, fundamental studies by single bunch beam operation have been performed resulting in more than 6 nC bunch charge with a high Q.E. of 2.9%. Additionally, the new RF-gun cavity was improved for obtaining a higher Q value. Higher beam energy, i.e. shunt impedance compared with old type cavity, was observed. The shunt impedance increased by about 20%. These successful results will considerably contribute to the applied research.

Sakaue, Kazuyuki; Hayano, Hitoshi; Kashiwagi, Shigeru; Kuroda, Ryunosuke; Masuda, Akihiko; Suzuki, Tatsuya; Takatomi, Toshikazu; Terunuma, Nobuhiro; Urakawa, Junji; Washio, Masakazu

2011-12-01

326

Channel electron multipliers - Detection efficiencies with opaque MgF2 photocathodes at XUV wavelengths  

NASA Technical Reports Server (NTRS)

Detection efficiencies of channel electron multipliers (CEM) with opaque MgF2 photocathodes obtained in the extreme ultraviolet (XUV), 44 A to 990 A, are reported. A stable highly efficient response is reported for that interval, with no adverse effects on CEM performance. Efficiencies twice those of uncoated CEMs are obtained for 50 A to 350 A. The Mullard B419BL and Galileo 4510WL single-stage cone-cathode CEMs were used in the experiments. A rare-gas double ionization chamber was employed as absolute standard detector for 406 A to 990 A, and a flow Geiger counter filled with 96% argon and 4% isobutane for 44 A to 256 A. Absolute detection efficiencies are 10% higher from 67 A to 990 A when photocathodes are illuminated at an angle of incidence 45 deg. The photocathodes suffered no loss of response in storage (in vacuum or air) after an initial aging period. Effects of scattered UV radiation are greatly reduced when MgF2-coated CEMs are used in the XUV.

Lapson, L. B.; Timothy, J. G.

1976-01-01

327

Dilute phosphide nitride materials as photocathodes for electrochemical solar energy conversion  

NASA Astrophysics Data System (ADS)

Dilute nitride materials have been used in a variety of III-V photonic devices, but have not been significantly explored in photoelectrochemical applications. This work focuses on using dilute phosphide nitride materials of the form (Al,In)P1-xNx as photocathodes for the generation of hydrogen fuel from solar energy. Heteroepitaxial MOCVD growth of AlPN thin films on GaP yields high quality material with a direct bandgap energy of 2.218 eV. Aligned epitaxial growth of InP and GaP nanowires on InP and Si substrates, respectively, provides a template for designing nanostructured photocathodes over a large area. Electrochemical testing of a AlPN/GaP heterostructure electrode yields up to a sixfold increase in photocurrent enhancement under blue light illumination as compared to a GaP electrode. Additionally, the AlPN/GaP electrodes exhibit no degradation in performance after galvanostatic biasing over time. These results show that (Al,In)P1-xNx is a promising materials system for use in nanoscale photocathode structures.

Parameshwaran, Vijay; Xu, Xiaoqing; Kang, Yangsen; Harris, James; Wong, H.-S. Philip; Clemens, Bruce

2013-03-01

328

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. The strained-superlattice structure based on GaAsP/GaAs, with a maximum polarization as high as 90% and more than 1% quantum efficiency, is presently the prime candidate for the ILC polarized electron photocathodes. A recent systematic study shows, however, that the peak polarization seems saturated even though the heavy-hole (HH) and light-hole (LH) band splitting is increased significantly, indicating that there is a material specific spin relaxation mechanism. It is widely accepted that the D'yakonov-Perel mechanism is the dominant spin relaxation mechanism in the III-V compound superlattice structures with a low p-doping ({le} 10{sup 17} cm{sup -3}), and that the spin relaxation may be reduced by choosing a material with a smaller spin-orbit interaction. As the spin-orbit interaction in phosphides is much smaller than in arsenides, strained-superlattice structure based on InGaP/GaAs were investigated. The computer code SPECCODE developed by Subashiev and Gerchikov has been used for calculating the band structures in superlattice.

Not Available

2010-08-25

329

Refractories for high-alkali environments  

SciTech Connect

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 involves reacting test specimens with the contaminant, followed by physical properties testing to determine degree of degradation and properties affected. The alkali cup test rates products using a relative numerical scale based upon visual appearance. This test indicates the presence and relative degree of chemical attack to the refractory. The physical properties test determines the specific properties affected by the given contaminant.

Rau, A.W. [Ahlstrom Pyropower Customer Services Inc., Houston, TX (United States); Cloer, F. [Resco Products Inc., Greensboro, NC (United States)

1996-01-01

330

Alkali ion exchange in ?-irradiated glasses  

NASA Astrophysics Data System (ADS)

The alkali ion exchange of ?-irradiated glasses was investigated using the structural energy barrier model for ion exchange of glasses. It is shown that rates of alkali ion exchange have a non-Arrhenius behaviour depending both on irradiation dose and dose rate. For this reason some effects cannot be simulated by external irradiation and require in situ measurements. Higher doses and dose rates of ?-radiation lead to increased ion exchange rates. Significant changes occur in the activation energies demonstrating a many times decrease depending on glass composition. Radiation-induced changes are higher at relatively low temperatures being diminished by increased glass temperature. Numerical estimations show that changes in alkali ion exchange kinetics occur below the glass network damaging doses.

Ojovan, Michael I.; Lee, William E.

2004-12-01

331

Alkali metal vapors - Laser spectroscopy and applications  

NASA Technical Reports Server (NTRS)

The paper examines the rapidly expanding use of lasers for spectroscopic studies of alkali metal vapors. Since the alkali metals (lithium, sodium, potassium, rubidium and cesium) are theoretically simple ('visible hydrogen'), readily ionized, and strongly interacting with laser light, they represent ideal systems for quantitative understanding of microscopic interconversion mechanisms between photon (e.g., solar or laser), chemical, electrical and thermal energy. The possible implications of such understanding for a wide variety of practical applications (sodium lamps, thermionic converters, magnetohydrodynamic devices, new lasers, 'lithium waterfall' inertial confinement fusion reactors, etc.) are also discussed.

Stwalley, W. C.; Koch, M. E.

1980-01-01

332

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

333

Matrix isolation infrared spectra of hydrogen halide and halogen complexes with nitrosyl halides  

NASA Technical Reports Server (NTRS)

Matrix isolation infrared spectra of nitrosyl halide (XNO) complexes with HX and X2 (X = Cl, Br) are presented. The relative frequency shifts of the HX mode are modest (ClNO H-Cl, delta-nu/nu = -0.045; BrNO H-Br, delta-nu/nu = -0.026), indicating weak hydrogen bonds 1-3 kcal/mol. These shifts are accompanied by significant shifts to higher frequencies in the XN-O stretching mode (CIN-O HCl, delta-nu/nu = +0.016; BrN-O HBr, delta-nu/nu = +0.011). Similar shifts were observed for the XN-O X2 complexes (ClN-O Cl2, delta-nu/nu = +0.009; BrN-O-Br2, delta-nu/nu = +0.013). In all four complexes, the X-NO stretching mode relative shift is opposite in sign and about 1.6 times that of the NO stretching mode. These four complexes are considered to be similar in structure and charge distribution. The XN-O frequency shift suggests that complex formation is accompanied by charge withdrawal from the NO bond ranging from about .04 to .07 electron charges. The HX and X2 molecules act as electron acceptors, drawing electrons out of the antibonding orbital of NO and strengthening the XN-O bond. The implications of the pattern of vibrational shifts concerning the structure of the complexes are discussed.

Allamandola, Louis J.; Lucas, Donald; Pimentel, George C.

1982-01-01

334

ORIGINAL ARTICLE Mitigation of autogenous shrinkage in alkali activated slag  

E-print Network

ORIGINAL ARTICLE Mitigation of autogenous shrinkage in alkali activated slag mortars by internal online: 29 November 2012 Ó RILEM 2012 Abstract Alkali activated slag shows considerable promise of alkali activated slags, however, is not well understood, and is a hurdle to widespread adoption. The use

Bentz, Dale P.

335

Alkali resistant optical coatings for alkali lasers and methods of production thereof  

DOEpatents

In one embodiment, a multilayer dielectric coating for use in an alkali laser includes two or more alternating layers of high and low refractive index materials, wherein an innermost layer includes a thicker, >500 nm, and dense, >97% of theoretical, layer of at least one of: alumina, zirconia, and hafnia for protecting subsequent layers of the two or more alternating layers of high and low index dielectric materials from alkali attack. In another embodiment, a method for forming an alkali resistant coating includes forming a first oxide material above a substrate and forming a second oxide material above the first oxide material to form a multilayer dielectric coating, wherein the second oxide material is on a side of the multilayer dielectric coating for contacting an alkali.

Soules, Thomas F; Beach, Raymond J; Mitchell, Scott C

2014-11-18

336

Band filling with free charge carriers in organometal halide perovskites  

NASA Astrophysics Data System (ADS)

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

Manser, Joseph S.; Kamat, Prashant V.

2014-09-01

337

Enhanced Born Charge and Proximity to Ferroelectricity in Thallium Halides  

SciTech Connect

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 Tl-p 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 spontaneous lattice polarization 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 [ORNL; Singh, David J [ORNL

2010-01-01

338

Large methyl halide emissions from south Texas salt marshes  

NASA Astrophysics Data System (ADS)

Coastal salt marshes are natural sources of methyl chloride (CH3Cl) and methyl bromide (CH3Br) to the atmosphere, but measured emission rates vary widely by geography. Here we report large methyl halide fluxes from subtropical salt marshes of south Texas. Sites with the halophytic plant, Batis maritima, emitted methyl halides at rates that are orders of magnitude greater than sites containing other vascular plants or macroalgae. B. maritima emissions were generally highest at midday; however, diurnal variability was more pronounced for CH3Br than CH3Cl, and surprisingly high nighttime CH3Cl fluxes were observed in July. Seasonal and intra-site variability were large, even taking into account biomass differences. Overall, these subtropical salt marsh sites show much higher emission rates than temperate salt marshes at similar times of the year, supporting the contention that low-latitude salt marshes are significant sources of CH3Cl and CH3Br.

Rhew, R. C.; Whelan, M. E.; Min, D.-H.

2014-06-01

339

Large methyl halide emissions from south Texas salt marshes  

NASA Astrophysics Data System (ADS)

Coastal salt marshes are natural sources of methyl chloride (CH3Cl) and methyl bromide (CH3Br) to the atmosphere, but measured emission rates vary widely by geography. Here we report large methyl halide fluxes from subtropical salt marshes of south Texas. Sites with the halophytic plant, Batis maritima, emitted methyl halides at rates that are orders of magnitude greater than sites containing other vascular plants or macroalgae. B. maritima emissions were generally highest at midday; however, diurnal variability was more pronounced for CH3Br than CH3Cl, and surprisingly high nighttime CH3Cl fluxes were observed in July. Seasonal and intra-site variability were large, even taking into account biomass differences. Overall, these subtropical salt marsh sites show much higher emission rates than temperate salt marshes at similar times of the year, supporting the contention that low-latitude salt marshes are significant sources of CH3Cl and CH3Br.

Rhew, R. C.; Whelan, M. E.; Min, D.-H.

2014-11-01

340

Duration of nucleation process in supercooled halide melts  

NASA Astrophysics Data System (ADS)

We present a model allowing to estimate the so-called time lag of nucleating halide melts using electrical conductivity measurements. Due to the complex-forming nature of molten halide salts we suppose two basic types of charge carriers in the melt: complexes (playing the role of monomers—building units) and clusters of a newly forming solid phase. Within context of the nonstationary nucleation theory we determined a formula expressing the time dependency of electrical conductivity of such a system and compared this result with the experimental data obtained for the melts of PbBr2, PbCl2, and KPb2Cl5. In terms of this formula the time lag of nucleation may be estimated. This important quantity characterizing the moment from which the nucleated clusters only grow to the macroscopic sizes has been found to be approximately 75% of the total duration of the nucleation process itself.

Demo, P.; Sveshnikov, A. M.; Nitsch, K.; Rodová, M.; Kožíšek, Z.

2005-08-01

341

Process for preparing alkali metal phosphate  

Microsoft Academic Search

A continuous method for producing alkali metal phosphates from wet process phosphoric acid is described comprising the steps: (a) contacting crude aqueous phosphoric acid with a solvent consisting of normally liquid trialkyl phosphate in the presence of sulfuric acid in at least one countercurrent flow extraction unit to form a solvent solution of phosphoric acid and an aqueous raffinate phase,

R. E. Hall; D. P. Brochu

1988-01-01

342

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

343

Treatment of a severe alkali burn  

Microsoft Academic Search

The case history of a 20-year-old male patient who sustained an 85 per cent total body surface area alkali burn to his skin, after falling into a caustic lime pit, is reported. Considerable problems regarding the correct estimate of burn wound depth, predominant location of the deepest burn on the posterior half of the body, appropriate wound coverage, and lack

D. Erdmann; J. Hussmann; J. O. Kucan

1996-01-01

344

Terahertz radiation in alkali vapor plasmas  

SciTech Connect

By taking advantage of low ionization potentials of alkali atoms, we demonstrate terahertz wave generation from cesium and rubidium vapor plasmas with an amplitude nearly one order of magnitude larger than that from nitrogen gas at low pressure (0.02–0.5?Torr). The observed phenomena are explained by the numerical modeling based upon electron tunneling ionization.

Sun, Xuan; Zhang, X.-C., E-mail: Xi-Cheng.Zhang@rochester.edu [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States)

2014-05-12

345

SO2 REMOVAL BY LIMESTONE DUAL ALKALI  

EPA Science Inventory

The article gives results of testing (between February 1982 and March 1983) on a pilot-scale, limestone, dual-alkali, flue gas desulfurization (FGD) system at IERL-RTP, where testing started in 1979. These results that significant improvement in soda ash consumption and filter ca...

346

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

347

Solvent extraction studies on thorium sulphate and halides  

Microsoft Academic Search

The effect of water-miscible alcohols, acetone and haloacids in the aqueous phase of sulphuric acid solutions has been studied\\u000a on the extraction of thorium sulphate and halides by bis(2-ethylhexyl) phosphoric acid (HDEHP) and tri-n-butyl phosphate (TBP).\\u000a The partition coefficient (E) is greatly affected by these additives, and this gives useful separations from many other elements.\\u000a Besides, the log-log relationship between

A. Haggag; S. A. El-Fekey; M. El-Mamoon Yehia; W. Sanad

1976-01-01

348

High-pressure low-symmetry phases of cesium halides  

Microsoft Academic Search

The relative stability of different high-pressure phases of various cesium halides is studied from first principles and analyzed using the Landau theory of phase transitions. We present results for CsI, CsBr, and CsCl up to pressures of ~=100 GPa. A cubic-to-orthorhombic transition, driven by the softening of an acoustic phonon at the M point of the Brillouin zone, is competing

Marco Buongiorno Nardelli; Stefano Baroni; Paolo Giannozzi

1995-01-01

349

Methyl halide emissions from savanna fires in southern Africa  

Microsoft Academic Search

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

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

1996-01-01

350

Halide-bridged binuclear HX-splitting catalysts.  

PubMed

Two-electron mixed-valence compounds promote the rearrangement of the two-electron bond photochemically. Such complexes are especially effective at managing the activation of hydrohalic acids (HX). Closed HX-splitting cycles require proton reduction to H2 and halide oxidation to X2 to be both accomplished, the latter of which is thermodynamically and kinetically demanding. Phosphazane-bridged Rh2 catalysts have been especially effective at activating HX via photogenerated ligand-bridged intermediates; such intermediates are analogues of the classical ligand-bridged intermediates proposed in binuclear elimination reactions. Herein, a new family of phosphazane-bridged Rh2 photocatalysts has been developed where the halide-bridged geometry is designed into the ground state. The targeted geometries were accessed by replacing previously used alkyl isocyanides with aryl isocyanide ligands, which provided access to families of Rh2L1 complexes. H2 evolution with Rh2 catalysts typically proceeds via two-electron photoreduction, protonation to afford Rh hydrides, and photochemical H2 evolution. Herein, we have directly observed each of these steps in stoichiometric reactions. Reactivity differences between Rh2 chloride and bromide complexes have been delineated. H2 evolution from both HCl and HBr proceeds with a halide-bridged Rh2 hydride photoresting state. The H2-evolution efficiency of the new family of halide-bridged catalysts is compared to a related catalyst in which ligand-bridged geometries are not stabilized in the molecular ground state, and the new complexes are found to more efficiently facilitate H2 evolution. PMID:25137532

Powers, David C; Hwang, Seung Jun; Zheng, Shao-Liang; Nocera, Daniel G

2014-09-01

351

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. PMID:19081992

Denmark, Scott E.; Butler, Christopher R.

2009-01-01

352

Bright Light-Emitting Diodes based on Organometal Halide Perovskite  

E-print Network

Luminescence as Solar Cells Approach the Shockley-Queisser Limit. Photovoltaics, IEEE Journal of 2, 303-311 (2012). Acknowledgements We thank EPSRC (UK) for financial support. Z.K.T. thanks the Singapore National Research Foundation (Energy Innovation... of materials into efficient and color tunable light emitters for low-cost display, lighting and optical communication applications. Recent reports on earth-abundant organometal halide based perovskite for high efficiency photovoltaics have demonstrated...

Tan, Zhi-Kuang; Moghaddam, Reza Saberi; Lai, May Ling; Docampo, Pablo; Higler, Ruben; Deschler, Felix; Price, Michael; Sadhanala, Aditya; Pazos, Luis M.; Credgington, Dan; Hanusch, Fabian; Bein, Thomas; Snaith, Henry J.; Friend, Richard H.

2014-08-03

353

Development of High Quantum Efficiency UV/Blue Photocathode Epitaxial Semiconductor Heterostructures for Scintillation and Cherenkov Radiation Detection  

NASA Technical Reports Server (NTRS)

The primary goal of this research project was to further extend the use of advanced heteroepitaxial-semiconductor crystal growth techniques such as molecular beam epitaxy (MBE) and to demonstrate significant gains in UV/blue photonic detection by designing and fabricating atomically-tailored heteroepitaxial GaAlN/GaInN photocathode device structures. This NASA Explorer technology research program has focused on the development of photocathodes for Cherenkov and scintillation radiation detection. Support from the program allowed us to enhance our MBE system to include a nitrogen plasma source and a magnetic bearing turbomolecular pump for delivery and removal of high purity atomic nitrogen during GaAlN/GaInN film growth. Under this program we have also designed, built and incorporated a cesium activation stage. In addition, a connected UHV chamber with photocathode transfer/positioner components as well as a hybrid phototube stage was designed and built to make in-situ quantum efficiency measurements without ever having to remove the photocathodes from UHV conditions. Thus we have constructed a system with the capability to couple atomically-tailored MBE-grown photocathode heterostructures with real high gain readout devices for single photon detection evaluation.

Leopold, Daniel J.

2002-01-01

354

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

NASA Astrophysics Data System (ADS)

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 ˜10 ps response time, the photocathode active layer should be thinned to ˜100-150 nm, but this thickness is insufficient to provide near-complete absorption of light with hv??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.; Rozhkov, S. A.; Bakin, V. V.; Kosolobov, S. N.; Militsyn, B. L.; Scheibler, H. E.; Smith, S. L.; Terekhov, A. S.

2009-08-01

355

Long term operation of high quantum efficiency GaAs(Cs,O) photocathodes using multiple recleaning by atomic hydrogen  

NASA Astrophysics Data System (ADS)

Atomic hydrogen, produced by thermal dissociation of H2 molecules inside a hot tungsten capillary, is shown to be an efficient tool for multiple recleaning of degraded surfaces of high quantum efficiency transmission-mode GaAs photocathodes within an ultrahigh vacuum (UHV) multichamber photoelectron gun. Ultraviolet quantum yield photoemission spectroscopy has been used to study the removal of surface pollutants and the degraded (Cs,O)-activation layer during the cleaning procedure. For photocathodes grown by the liquid-phase epitaxy technique, the quantum efficiency is found to be stable at about 20% over a large number of atomic hydrogen cleaning cycles. A slow degradation of the quantum efficiency is observed for photocathodes grown by metal-organic chemical vapor deposition, although they reached a higher initial quantum efficiency of about 30%-35%. Study of the spatial distributions of photoluminescence intensity on these photocathodes proved that this overall degradation is likely due to insertion of a dislocation network into the mechanically strained photocathode heterostructures during multiple heating cycles and is not due to the atomic hydrogen treatment itself.

Orlov, D. A.; Krantz, C.; Wolf, A.; Jaroshevich, A. S.; Kosolobov, S. N.; Scheibler, H. E.; Terekhov, A. S.

2009-09-01

356

Comparative studies of dissociative electron attachment to methyl halides  

NASA Astrophysics Data System (ADS)

The dissociative electron attachment cross sections for the methyl halides vary in an enormous range from the virtually unmeasurable 10-23 cm2 for CH3Cl at room temperature to 10-14 cm2 for CH3I. In this paper we supplement our previous studies by calculations of dissociative electron attachment to CH3Br and compare results for all methyl halides studied so far. The rate as a function of temperature for CH3Cl and CH3Br exhibits an exponential dependence on 1/T (Arrhenius law) with the activation energy lower for CH3Br. CH3I does not obey the Arrhenius law since the crossing point of the neutral and anion potential curves occurs near the lowest vibrational levels. The cross section as a function of electron energy for all of the methyl halides studied here exhibits structure at the vibrational excitation thresholds that is associated with a vibrational Feshbach resonance like that observed recently in CH3I by Schramm et al (Schramm A, Fabrikant I I, Weber J M, Leber E, Ruf M-W and Hotop H 1999 J. Phys. B: At. Mol. Opt. Phys. 32 2153).

Wilde, R. S.; Gallup, G. A.; Fabrikant, I. I.

2000-12-01

357

Comparative studies of dissociative electron attachment to methyl halides  

NASA Astrophysics Data System (ADS)

Methyl halides belong to the class of polyatomic molecules for which nuclear dynamics relevant to low-energy electron scattering can be treated relatively simply by assuming that only one vibrational mode is influenced by collisions. At the same time dissociative attachment cross sections for these compounds vary in enormous range from the virtually unmeasurable 10-23 cm^2 for methyl chloride at room temperature to the much larger 10-14 cm^2 for methyl iodide. In the present work we supplement our previous studies by calculations of dissociative attachment to methyl bromide and compare results for all methyl halides studied so far. The rate as a function of temperature for all methyl halides exhibit the exponential dependence on 1/T (Arrhenius law) with the activation energy lowest for methyl iodide and largest for methyl chloride. The cross section as a function of electron energy exhibits structure at vibrational excitation thresholds associated with vibrational Feshbach resonances observed previously for methyl iodide (A. Schramm, I. I. Fabrikant, J. M. Weber, E. Leber, M. -W. Ruf, H. Hotop, J. Phys. B, to be published.).

Wilde, R. S.; Gallup, G. A.; Fabrikant, I. I.

1999-10-01

358

Saline-alkali soils of Russia  

NASA Astrophysics Data System (ADS)

Diagnostics, methods of evaluation, and geography of saline-alkali (soda) soils are discussed. The saline-alkali soils include soils of different genetic types with the following chemical properties: the pH of the water suspensions equal to or higher than 8.5; the total alkalinity exceeding 1.4 meq/100 g of soil and the sum of water-soluble calcium and magnesium; and the presence of soluble “alkaline” salts in the soil profiles, the hydrolysis of which results in the alkaline reaction of the soils. The chemical properties of the saline-alkali soils are largely related to the presence of soda (Na2CO3, NaHCO3) in the soils. According to their morphological properties, saline-alkali soils are divided into two groups: alkaline soils with an undiferentiated profile and without a morphologically pronounced solonetzic (natric) horizon, and alkaline soils with a pronounced natric horizon (solonetzes). Solonetzes, in turn, are divided into (a) alkaline solonetzes (with soda or with soda and neutral salts), (b) solonetzes salinized with neutral salts (saline soils) with increased alkalinity in the solonetzic and lower lying horizons, (c) saline solonetzes throughout the profile, and (d) leached solonetzes containing no soluble salts in the profile and almost no exchangeable sodium in the soil exchange complex (SEC) (“dead” solonetzes). The latter two groups of solonetzes cannot be ranked among the alkaline soils. The alkalinity of the saline-alkali soils under study is due to carbonate and bicarbonate ions (carbonate alkalinity), organic acid anions (organic alkalinity), and borate ions (borate alkalinity). The carbonate alkalinity is due to both soda (Na2CO3, NaHCO3) and CaCO3.

Vorob'eva, L. A.; Pankova, E. I.

2008-05-01

359

Alkali metal recovery from carbonaceous material conversion process  

DOEpatents

In a coal gasification operation or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein solid particles containing alkali metal residues are produced in the gasifier or similar reaction zone, alkali metal constitutents are recovered from the particles by withdrawing and passing the particles from the reaction zone to an alkali metal recovery zone in the substantial absence of molecular oxygen and treating the particles in the recovery zone with water or an aqueous solution in the substantial absence of molecular oxygen. The solution formed by treating the particles in the recovery zone will contain water-soluble alkali metal constituents and is recycled to the conversion process where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst. Preventing contact of the particles with oxygen as they are withdrawn from the reaction zone and during treatment in the recovery zone avoids the formation of undesirable alkali metal constituents in the aqueous solution produced in the recovery zone and insures maximum recovery of water-soluble alkali metal constituents from the alkali metal residues.

Sharp, David W. (Seabrook, TX); Clavenna, LeRoy R. (Baytown, TX); Gorbaty, Martin L. (Fanwood, NJ); Tsou, Joe M. (Galveston, TX)

1980-01-01

360

Alkali element background reduction in laser ICP-MS  

NASA Astrophysics Data System (ADS)

Alkali backgrounds in laser ablation ICP-MS analyses can be enhanced by electron-induced ionisation of alkali contamination on the skimmer cone, reducing effective detection limits for these elements. Traditionally, this problem is addressed by isolating analyses of high-alkali materials onto a designated cone set, or by operating the ICP-MS in a "soft extraction" mode, which reduces the energy of electrons repelled into the potentially contaminated sampling cone by the extraction field. Here we present a novel approach, where we replace the traditional alkali glass tuning standards with synthetic low-alkali glass reference materials. Using this vitreous tuning solution, we find that this approach reduces the amount of alkali contamination produced, halving backgrounds for the heavy alkali elements without any change to analytical procedures. Using segregated cones is still the most effective method for reducing lithium backgrounds, but since the procedures are complimentary, both can easily be applied to the routine operations of an analytical lab.

Magee, C. W., Jr.; Norris, C. A.

2015-03-01

361

Abiotic Formation of Methyl Halides in the Terrestrial Environment  

NASA Astrophysics Data System (ADS)

Methyl chloride and methyl bromide are the most abundant chlorine and bromine containing organic compounds in the atmosphere. Since both compounds have relatively long tropospheric lifetimes they can effectively transport halogen atoms from the Earth's surface, where they are released, to the stratosphere and following photolytic oxidation form reactive halogen gases that lead to the chemical destruction of ozone. Methyl chloride and methyl bromide account for more than 20% of the ozone-depleting halogens delivered to the stratosphere and are predicted to grow in importance as the chlorine contribution to the stratosphere from anthropogenic CFCs decline. Today methyl chloride and methyl bromide originate mainly from natural sources with only a minor fraction considered to be of anthropogenic origin. However, until as recently as 2000 most of the methyl chloride and methyl bromide input to the atmosphere was considered to originate from the oceans, but investigations in recent years have clearly demonstrated that terrestrial sources such as biomass burning, wood-rotting fungi, coastal salt marshes, tropical vegetation and organic matter degradation must dominate the atmospheric budgets of these trace gases. However, many uncertainties still exist regarding strengths of both sources and sinks, as well as the mechanisms of formation of these naturally occurring halogenated gases. A better understanding of the atmospheric budget of both methyl chloride and methyl bromide is therefore required for reliable prediction of future ozone depletion. Biotic and abiotic methylation processes of chloride and bromide ion are considered to be the dominant pathways of formation of these methyl halides in nature. In this presentation I will focus on abiotic formation processes in the terrestrial environment and the potential parameters that control their emissions. Recent advances in our understanding of the abiotic formation pathway of methyl halides will be discussed. This will include a consideration on how stable isotope studies assisted advancements in this subject area. For example, it has been shown that the methoxyl groups of lignin and pectin which together constitute the bulk of the C1 plant pool have a carbon isotope signature significantly depleted in 13C. Plant-derived C1 volatile organic compounds (VOCs) are also highly depleted in 13C compared with Cn+1 VOCs. These observations suggest that the plant methoxyl pool is the predominant source of methyl halides released from senescent and dead plant litter. The distinct 13C depletion of plant methoxyl groups and naturally produced methyl halides may provide a helpful tool in constraining complex environmental processes and therefore improve our understanding of the global cycles of atmospheric methyl halides.

Keppler, F.

2011-12-01

362

A H2-evolving photocathode based on direct sensitization of MoS3 with an organic photovoltaic cell.  

PubMed

An organic solar cell based on a poly-3-hexylthiophene (P3HT): phenyl-C61-butyric acid (PCBM) bulk hetero-junction was directly coupled with molybdenum sulfide resulting in the design of a new type of photocathode for the production of hydrogen. Both the light-harvesting system and the catalyst were deposited by low-cost solution-processed methods, i.e. spin coating and spray coating respectively. Spray-coated MoS3 films are catalytically active in strongly acidic aqueous solutions with the best efficiencies for thicknesses of 40 to 90 nm. The photocathodes display photocurrents higher than reference samples, without catalyst or without coupling with a solar cell. Analysis by gas chromatography confirms the light-induced hydrogen evolution. The addition of titanium dioxide in the MoS3 film enhances electron transport and collection within thick films and therefore the performance of the photocathode. PMID:24404434

Bourgeteau, Tiphaine; Tondelier, Denis; Geffroy, Bernard; Brisse, Romain; Laberty-Robert, Christel; Campidelli, Stéphane; de Bettignies, Rémi; Artero, Vincent; Palacin, Serge; Jousselme, Bruno

2013-01-01

363

A H2-evolving photocathode based on direct sensitization of MoS3 with an organic photovoltaic cell  

PubMed Central

An organic solar cell based on a poly-3-hexylthiophene (P3HT): phenyl-C61-butyric acid (PCBM) bulk hetero-junction was directly coupled with molybdenum sulfide resulting in the design of a new type of photocathode for the production of hydrogen. Both the light-harvesting system and the catalyst were deposited by low-cost solution-processed methods, i.e. spin coating and spray coating respectively. Spray-coated MoS3 films are catalytically active in strongly acidic aqueous solutions with the best efficiencies for thicknesses of 40 to 90 nm. The photocathodes display photocurrents higher than reference samples, without catalyst or without coupling with a solar cell. Analysis by gas chromatography confirms the light-induced hydrogen evolution. The addition of titanium dioxide in the MoS3 film enhances electron transport and collection within thick films and therefore the performance of the photocathode. PMID:24404434

Bourgeteau, Tiphaine; Tondelier, Denis; Geffroy, Bernard; Brisse, Romain; Laberty-Robert, Christel; Campidelli, Stéphane; de Bettignies, Rémi; Artero, Vincent; Palacin, Serge; Jousselme, Bruno

2013-01-01

364

Experience at Fermilab with high quantum efficiency photo-cathodes for rf electron guns  

SciTech Connect

As part of the A0 Photo-injector collaboration at Fermi-lab [1, 2] and the TeSLA collaboration [3], a high bright-ness, low emittance electron source has been developed. In the process, a system was constructed for coating molybde-num cathodes with a layer of cæsium telluride (Cs2 Te), a photo-emissive material of high quantum efficiency (QE). The use of Cs2 Te was first investigated at CERN [4] and LANL [5]. The development of the systems for the TeSLA Test Facility Linac and the Fermilab Photo-injector was done in Milano [6]. The system at Fermilab incorporates manipulator arms to transfer a cathode from the preparation chamber into a 1.3 GHz photo-electron RF gun while it re-mains in an ultra-high vacuum (UHV) environment, in or-der to avoid the deleterious effects of residual gases on the QE. A first prototype electron gun has been operated with a photo-cathode for several months [1]. This paper describes preliminary results obtained with the first 2 photo-cathodes and the first gun. Some of the desired parameters for the TeSLA Test Fa-cility beam are given in Table 1. The desired characteristics for the photo-cathodes include (i) high QE, (ii) high current density (>500 A/cm{sup 2} ), (iii) long lifetime, and (iv) low field emission. The choice of Cs2 Te is a compromise between long lifetime, rugged metal cathodes with low QE (typi-cally between 10{sup -6} and 10{sup -4} and semiconductor cathodes with high QE (>10%), which generally have a short life-time because of their sensitivity to contamination.

A. Fry, E. Hahn, W. Hartung, M. Kuchnir, P. Michelato and D. Sertore

1998-10-01

365

Development of UV-photocathodes using GaN film on Si substrate  

Microsoft Academic Search

We developed GaN photocathodes for detecting ultraviolet radiation by using Mg-doped GaN. Crack-free, 200 nm thick GaN:Mg layers were grown by metal organic chemical vapor phase epitaxy (MOVPE) on a GaN template having a structure of undoped GaN\\/(AlN\\/GaN) multilayers on Si (111) substrate. The Mg concentration was varied in the range from 7×1018 to 7×1019 cm-3. The grown film was

S. Fuke; M. Sumiya; T. Nihashi; M. Hagino; M. Matsumoto; Y. Kamo; M. Sato; K. Ohtsuka

2008-01-01

366

Design of a high charge CW photocathode injector test stand at CEBAF  

SciTech Connect

A 10 MeV high-charge CW electron injector test stand has been designed for the CEBAF UV FEL driver accelerator. It consists of a 500 kV DC photocathode gun, a 1500 MHz room-temperature buncher, a modified CEBAF cryounit (quarter cryomodule) with an SRF accelerating gradient of {approximately}10 MV/m, two solenoids in the 500 kV region and an achromatic, non-isochronous injection transport line delivering 10 MeV beam to the driver accelerator. Experimental work is in progress toward establishing design system performance. 21 refs. , 2 figs., 3 tabs.

Lliu, H.; Kehne, D.; Benson, S. [and others

1996-08-01

367

Influence of the p-type doping concentration on reflection-mode GaN photocathode  

NASA Astrophysics Data System (ADS)

Four different p-type doping GaN photocathodes are activated by Cs/O, and the quantum efficiency (QE) curves are obtained. According to the QE equation, the curves are fitted. Both the QE curves and the fitting results show that the optimal p-type doping concentration is at 1017 cm-3. The electron diffusion length and surface-electron escape probability can be balanced well at 1017 cm-3. To a certain degree, thick emission layer is conducive to improving the QE, which is more obvious with the long wavelength.

Wang, Xiaohui; Chang, Benkang; Ren, Ling; Gao, Pin

2011-02-01

368

Removal of Retired Alkali Metal Test Systems  

SciTech Connect

This paper describes the successful effort to remove alkali metals, alkali metal residues, and piping and structures from retired non-radioactive test systems on the Hanford Site. These test systems were used between 1965 and 1982 to support the Fast Flux Test Facility and the Liquid Metal Fast Breeder Reactor Program. A considerable volume of sodium and sodium-potassium alloy (NaK) was successfully recycled to the commercial sector; structural material and electrical material such as wiring was also recycled. Innovative techniques were used to safely remove NaK and its residues from a test system that could not be gravity-drained. The work was done safely, with no environmental issues or significant schedule delays.

Brehm, W. F.; Church, W. R.; Biglin, J. W.

2003-02-26

369

Geopolymers and Related Alkali-Activated Materials  

NASA Astrophysics Data System (ADS)

The development of new, sustainable, low-CO2 construction materials is essential if the global construction industry is to reduce the environmental footprint of its activities, which is incurred particularly through the production of Portland cement. One type of non-Portland cement that is attracting particular attention is based on alkali-aluminosilicate chemistry, including the class of binders that have become known as geopolymers. These materials offer technical properties comparable to those of Portland cement, but with a much lower CO2 footprint and with the potential for performance advantages over traditional cements in certain niche applications. This review discusses the synthesis of alkali-activated binders from blast furnace slag, calcined clay (metakaolin), and fly ash, including analysis of the chemical reaction mechanisms and binder phase assemblages that control the early-age and hardened properties of these materials, in particular initial setting and long-term durability. Perspectives for future research developments are also explored.

Provis, John L.; Bernal, Susan A.

2014-07-01

370

Alkali-activated cements Opportunities and challenges  

Microsoft Academic Search

Alkali-activated cements as discussed here are those with compositions falling in the Me2O-MeO-Me2O3-SiO2-H2O system. This paper reviews their history of development and discusses their present status. Currently, there are major opportunities for such cements based upon (a) substantial knowledge of properties and mechanisms; (b) good track record of field performance in various applications and; (c) future orientation as environmentally friendly

Della M Roy

1999-01-01

371

Membrane Cells in Chlor Alkali Application  

E-print Network

MEMBRANE CELLS IN COLOR ALKALI APPLICATION Dr. K. Lesker, UHDE GmbH ABSTRACT The worldwide chlorine/caustic soda production has reached approximately 40 million tpy. Despite the stagnation of the chlorine demand in thc wcstcrn world, e... of the per fluorinated ion exchange membrane 1968-72 Development of the membrane process 1Membranes for > 30% of NaOH IY81 first conversion of a diaphragm plant In a membrane chloralkali...

Lesker, K.

372

Alkali Metal Heat Pipe Life Issues  

NASA Technical Reports Server (NTRS)

One approach to space fission power system design is predicated on the use of alkali metal heat pipes, either as radiator elements, thermal management components, or as part of the core primary heat-transfer system. This synopsis characterizes long-life core heat pipes. References are included where more detailed information can be found. Specifics shown here are for demonstrational purposes and do not necessarily reflect current Project Prometheus point designs.

Reid, Robert S.

2004-01-01

373

Alkali metal protective garment and composite material  

DOEpatents

A protective garment and composite material providing satisfactory heat resistance and physical protection for articles and personnel exposed to hot molten alkali metals, such as sodium. Physical protection is provided by a continuous layer of nickel foil. Heat resistance is provided by an underlying backing layer of thermal insulation. Overlying outer layers of fireproof woven ceramic fibers are used to protect the foil during storage and handling.

Ballif, III, John L. (Salt Lake City, UT); Yuan, Wei W. (Seattle, WA)

1980-01-01

374

Drift Instability in Collisionless Alkali Metal Plasmas  

Microsoft Academic Search

Measurements of low-frequency (?≪?i) oscillations in collisionless, low-?, alkali metal Q-device plasmas are reported. These oscillations are conclusively identified as density-gradient-driven drift waves by the agreement between experiment and the predictions of the linear theory with regard to frequency, wave-number, and stabilization by ion Landau damping. The linear theory of collisionless drift waves is modified to take into account effects

Peter A. Politzer

1971-01-01

375

Interfield and intrafield variability of methyl halide emissions from rice paddies  

Microsoft Academic Search

Methyl halide gases are important sources of atmospheric inorganic halogen radicals. We measured methyl halide emissions from three rice fields over two full growing seasons. Rice paddy emissions of methyl chloride, methyl bromide and methyl iodide are insignificant until field flooding. Rice growth stage determines methyl bromide and methyl iodide emissions while methyl chloride emissions are comparable between planted and

K. R. Redeker; J. Andrews; F. Fisher; R. Sass; R. J. Cicerone

2002-01-01

376

Halide Peroxidase in Tissues That Interact With Bacteria in the Host Squid Euprymna scolopes  

E-print Network

Halide Peroxidase in Tissues That Interact With Bacteria in the Host Squid Euprymna scolopes Andrea peroxidase in mammalian neutrophils, occurs abundantly in the light organ tissue of Euprymna scolopes independent assays typically applied to the analysis of halide peroxidase enzymes, we directly compared

McFall-Ngai, Margaret

377

THE DETERMINATION OF TOTAL ORGANIC HALIDE IN WATER: AN INTERLABORATORY COMPARATIVE STUDY OF TWO METHODS  

EPA Science Inventory

Total organic halide (TOX) analyzers are commonly used to measure the amount of dissolved halogenated organic byproducts in disinfected waters. Because of the lack of information on the identity of disinfection byproducts, rigorous testing of the dissolved organic halide (DOX) pr...

378

THE DETERMINATION OF TOTAL ORGANIC HALIDE IN WATER: A COMPARATIVE STUDY OF TWO INSTRUMENTS  

EPA Science Inventory

Total organic halide (TOX) analyzers are commonly used to measure the amount of dissolved halogenated organic byproducts in disinfected waters. ecause of the lack of information on the identity of disinfection byproducts, rigorous testing of the dissolved organic halide (DOX) pro...

379

Conceptual design of an angular multiplexed rare gas halide laser fusion driver  

Microsoft Academic Search

A conceptual definition for angular multiplexed rare gas halide drivers was formulated and several design examples analyzed. Angular multiplexed rare gas halide lasers can be designed to meet inertial confinement fusion requirements. These lasers are scalable, emit at short wavelengths (KiF 250 nm), and through the use of optical angular multiplexing, produce the required high energy (approx. 1 to 5

J. H. Parks

1980-01-01

380

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

Code of Federal Regulations, 2010 CFR

...probe-start metal halide lamp that contains a third starting electrode (probe) in the arc tube, and does not generally contain an igniter but instead starts lamps with high ballast open circuit voltage. Pulse-start metal halide ballast means an...

2010-01-01

381

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

Code of Federal Regulations, 2014 CFR

...probe-start metal halide lamp that contains a third starting electrode (probe) in the arc tube, and does not generally contain an igniter but instead starts lamps with high ballast open circuit voltage. Pulse-start metal halide ballast means an...

2014-01-01

382

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

Code of Federal Regulations, 2011 CFR

...probe-start metal halide lamp that contains a third starting electrode (probe) in the arc tube, and does not generally contain an igniter but instead starts lamps with high ballast open circuit voltage. Pulse-start metal halide ballast means an...

2011-01-01

383

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

Code of Federal Regulations, 2012 CFR

...probe-start metal halide lamp that contains a third starting electrode (probe) in the arc tube, and does not generally contain an igniter but instead starts lamps with high ballast open circuit voltage. Pulse-start metal halide ballast means an...

2012-01-01

384

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

Code of Federal Regulations, 2013 CFR

...probe-start metal halide lamp that contains a third starting electrode (probe) in the arc tube, and does not generally contain an igniter but instead starts lamps with high ballast open circuit voltage. Pulse-start metal halide ballast means an...

2013-01-01

385

10 CFR Appendix B to Subpart S to... - Certification Report for Metal Halide Lamp Ballasts  

Code of Federal Regulations, 2011 CFR

...Metal Halide Lamp Ballasts B Appendix B to Subpart S to Part 431 Energy DEPARTMENT OF ENERGY ENERGY...Halide Lamp Ballasts and Fixtures Pt. 431, Subpt. S, App. B Appendix B to Subpart S to Part 431—Certification Report for Metal...

2011-01-01

386

10 CFR Appendix A to Subpart S of... - Compliance Statement for Metal Halide Lamp Ballasts  

Code of Federal Regulations, 2011 CFR

...Metal Halide Lamp Ballasts A Appendix A to Subpart S of Part 431 Energy DEPARTMENT OF ENERGY ENERGY...Halide Lamp Ballasts and Fixtures Pt. 431, Subpt. S, App. A Appendix A to Subpart S of Part 431—Compliance Statement for Metal...

2011-01-01

387

EPA (ENVIRONMENTAL PROTECTION AGENCY) METHOD STUDY 32: METHOD 450.1 - TOTAL ORGANIC HALIDES (TOX)  

EPA Science Inventory

The report describes the interlaboratory method study that was performed to evaluate interim Method 450.1 for total organic halides (TOX). In the method, a measured volume of water is passed through two columns in series each containing 40 mg of activated charcoal. Organic halide...

388

Impact of the organic halide salt on final perovskite composition for photovoltaic applications  

SciTech Connect

The methylammonium lead halide perovskites have shown significant promise as a low-cost, second generation, photovoltaic material. Despite recent advances, however, there are still a number of fundamental aspects of their formation as well as their physical and electronic behavior that are not well understood. In this letter we explore the mechanism by which these materials crystallize by testing the outcome of each of the reagent halide salts. We find that components of both salts, lead halide and methylammonium halide, are relatively mobile and can be readily exchanged during the crystallization process when the reaction is carried out in solution or in the solid state. We exploit this fact by showing that the perovskite structure is formed even when the lead salt's anion is a non-halide, leading to lower annealing temperature and time requirements for film formation. Studies into these behaviors may ultimately lead to improved processing conditions for photovoltaic films.

Moore, David T.; Sai, Hiroaki; Wee Tan, Kwan; Estroff, Lara A.; Wiesner, Ulrich, E-mail: ubw1@cornell.edu [Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853 (United States)

2014-08-01

389

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

390

Heat load of a P-doped GaAs photocathode in SRF electron gun  

SciTech Connect

Many efforts were made over the last decades to develop a better polarized electron source for the high energy physics. Several laboratories operate DC guns with the Gallium-Arsenide photo-cathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved using a Superconducting RF electron gun, which delivers beams of higher brightness than DC guns does, because the field gradient at the cathode is higher. SRF guns with metal cathodes and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since the cathode will be normal conducting, the problem about the heat load stemming from the cathode arises. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and the verification by measuring the quality factor of the gun with and without cathode.

Wang, E.; Ben-Zvi, I.; Kewisch, J.; Burrill, A.; Rao, T.; Wu, Q.; Jain, A.; Gupta, R.; Holmes, D.

2010-05-23

391

Cold Photocathode Electron Sources and Perspectives for Low-Energy Magnetically Guided Electron Beams  

SciTech Connect

Cold electron beams from a cryogenic GaAs photocathode source, developed for the electron target of the Heidelberg TSR, will serve as a major tool to cool the ions and to study electron-ion interactions at the low-energy electrostatic Cryogenic Storage Ring which will be built in the institute. The photocathode source delivers electrons within emission energy spreads of about 10 meV allowing to reach low longitudinal and transverse temperatures of magnetized electron beams of eV energies and finally to improve cooling rates and the energy resolution in merged beam experiments. We propose a new electron-ion merging scheme for a low-energy cooler which improves magnetic field homogeneity in the beam merging area and, in contrast to standard schemes, does not deteriorate the dynamics of the low-energy ions in the ring through non-linear coupling. Even for 20 keV protons, magnetic guiding fields of about 50 G, as is required to suppress electron temperature heating, can be used this way. The electric and magnetic fields of the individual elements of the ring and cooler were calculated with the TOSCA code and models of the entire ring were simulated by particle tracking.

Orlov, D. A.; Fadil, H.; Grieser, M.; Wolf, A. [Max-Planck-Institut fuer Kernphysik, 69117 Heidelberg (Germany)

2006-10-18

392

Use of non evaporable getter pumps to ensure long term performances of high quantum efficiency photocathodes  

SciTech Connect

High quantum efficiency photocathodes are routinely used as laser triggered emitters in the advanced high brightness electron sources based on radio frequency guns. The sensitivity of “semiconductor” type photocathodes to vacuum levels and gas composition requires special care during preparation and handling. This paper will discuss the results obtained using a novel pumping approach based on coupling a 20?l s{sup ?1} sputter ion getter pump with a CapaciTorr® D100 non evaporable getter (NEG) pump. A pressure of 8?10{sup ?8}?Pa was achieved using only a sputter ion pump after a 6?day bake-out. With the addition of a NEG pump, a pressure of 2?10{sup ?9}?Pa was achieved after a 2?day bake-out. These pressure values were maintained without power due to the ability of the NEG to pump gases by chemical reaction. Long term monitoring of cathodes quantum efficiencies was also carried out at different photon wavelengths for more than two years, showing no degradation of the photoemissive film properties.

Sertore, Daniele, E-mail: daniele.sertore@mi.infn.it; Michelato, Paolo; Monaco, Laura [Istituto Nazionale di Fisica Nucleare Sez. Milano – LASA, Via Fratelli Cervi 201, I-20090 Segrate (Italy); Manini, Paolo; Siviero, Fabrizio [SAES Getters S.p.A., Viale Italia 77, 20020 Lainate (Italy)

2014-05-15

393

Hydrogen evolution from a copper(I) oxide photocathode coated with an amorphous molybdenum sulphide catalyst  

NASA Astrophysics Data System (ADS)

Concerns over climate change resulting from accumulation of anthropogenic carbon dioxide in the atmosphere and the uncertainty in the amount of recoverable fossil fuel reserves are driving forces for the development of renewable, carbon-neutral energy technologies. A promising clean solution is photoelectrochemical water splitting to produce hydrogen using abundant solar energy. Here we present a simple and scalable technique for the deposition of amorphous molybdenum sulphide films as hydrogen evolution catalyst onto protected copper(I) oxide films. The efficient extraction of excited electrons by the conformal catalyst film leads to photocurrents of up to -5.7mAcm-2 at 0V versus the reversible hydrogen electrode (pH 1.0) under simulated AM 1.5 solar illumination. Furthermore, the photocathode exhibits enhanced stability under acidic environments, whereas photocathodes with platinum nanoparticles as catalyst deactivate more rapidly under identical conditions. The work demonstrates the potential of earth-abundant light-harvesting material and catalysts for solar hydrogen production.

Morales-Guio, Carlos G.; Tilley, S. David; Vrubel, Heron; Grätzel, Michael; Hu, Xile

2014-01-01

394

Transmission photocathodes based on stainless steel mesh coated with deuterated diamond like carbon films  

NASA Astrophysics Data System (ADS)

In this study we report on the dependence of electron emission properties on the transmission photocathodes DC gun based on stainless steel mesh coated with diamond like carbon films prepared at various technological conditions. Diamond like carbon films were deposited on the stainless steel mesh and silicon substrate by plasma enhanced chemical vapor deposition from gas mixtures CH4+D2+Ar, CH4+H2+Ar and reactive magnetron sputtering using a carbon target and gas mixtures Ar+D2, Ar+H2. The concentration of elements in films was determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analytical methods simultaneously. Chemical compositions were analyzed by Fourier transform infrared spectroscopy (FT-IR). Raman spectroscopy at visible excitation wavelength was used for the intensity ratio determination of Gaussian fit D-peak and G-peak of Raman spectra. The quantum efficiency was calculated from the measured laser energy and the measured cathode charge. The quantum efficiency of a prepared transmission photocathode was increased with increasing intensity ratio of D-peak and G-peak, which was increased by adding deuterium to the gas mixture and using technology reactive magnetron sputtering.

Huran, J.; Balalykin, N. I.; Feshchenko, A. A.; Kobzev, A. P.; Kleinová, A.; Sasinková, V.; Hrub?ín, L.

2014-07-01

395

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

396

Improved Ion Resistance for III-V Photocathodes in High Current Guns  

SciTech Connect

The two photocathode test systems were modified, baked and recommissioned. The first system was dedicated to ion studies and the second to electron stimulated recovery (ESR) work. The demonstration system for the electron beam rejuvenation was set up, tested and demonstrated to one of the SSRL team (Dr. Kirby) during a site visit. The requisite subsystems were transferred to SSRL, installed and photoemission studies conducted on activated surfaces following electron beam exposure. Little surface chemistry change was detected in the photoemission spectra following the ESR process. The yield mapping system for the ion (and later, the electron beam rejuvenation) studies was implemented and use made routine. Ion species and flux measurements were performed for H, He, Ne, Ar, Kr and Xe ions at energies of 0.5, 1.0 and 2.0 kV. Gas induced photoyield measurements followed each ion exposure measurement. These data permit the extraction of photoyield induced change per ion (by species) at the measured energies. Electron beam induced rejuvenation was first demonstrated in the second chamber with primary electron beam energy and dependency investigations following. A Hiden quadrupole mass spectrometer for the electron stimulated desorption (ESD) measurements was procured. The UHV test systems needed for subsequent measurements were configured, baked, commissioned and utilized for their intended purposes. Measurements characterizing the desorption products from the ESD process and secondary electron (SE) yield at the surfaces of negative electron affinity GaAs photocathodes have been performed. One US Utility Patent was granted covering the ESR process.

Mulhollan, Gregory, A.

2012-11-16

397

Optical catheters based on silver halide infrared fibers  

NASA Astrophysics Data System (ADS)

Laser power transmission, luminescence, mechanical behavior and effects of various thermal treatments have been investigated on mixed sliver halide crystals. This knowledge may suggest ways of optimizing the fabrication of optical fibers from such crystals. Anti-reflection coating for high-power 10.6 micrometer light transmission was studied both on crystals and fibers. Laser power transmission and mechanical properties of the fibers also have been investigated. On the basis of these experiments the prototype of the medical catheter was produced and surgery experiments with this catheter have been performed.

Nagli, Lev; German, Alla; Katzir, Abraham; Tschepe, Johannes; Prapavat, Viravuth; Eberle, Hans-Georg; Mueller, Gerhard J.

1995-01-01

398

Selective Cross-Coupling of Organic Halides with Allylic Acetates  

PubMed Central

A general protocol for the coupling of haloarenes with a variety of allylic acetates is presented. Strengths of the method are a tolerance for electrophilic (ketone, aldehyde) and acidic (sulfonamide, trifluoroacetamide) substrates and the ability to couple with a variety of substituted allylic acetates. Secondary alkyl bromides can also be allylated under slightly modified conditions, demonstrating the generality of the approach. Finally, the coupling of a reactive vinyl halide could be achieved by the use of a very hindered ligand and more reactive, branched allylic acetates. PMID:23095043

Anka-Lufford, Lukiana L.; Prinsell, Michael R.

2012-01-01

399

MAMA detector systems - A status report  

NASA Technical Reports Server (NTRS)

Third-generation, 224 x 960 and 360 x 1024-pixel multianode microchannel (MAMA) detectors are under development for satellite-borne FUV and EUV observations, using pixel dimensions of 25 x 25 microns. An account is presently given of the configurations, modes of operation, and recent performance data of these systems. At UV and visible wavelengths, these MAMAs employ a semitransparent, proximity-focused photocathode structure. At FUV and EUV wavelengths below about 1500 A, opaque alkali-halide photocathodes deposited directly on the front surface of the MCP furnish the best detective quantum efficiencies.

Timothy, J. Gethyn; Morgan, Jeffrey S.; Slater, David C.; Kasle, David B.; Bybee, Richard L.

1989-01-01

400

The Properties of Alkali Metal and Alkali-Coadsorbate Overlayers on Metal Surfaces  

Microsoft Academic Search

I have investigated properties of alkalis on metal surfaces and coadsorbate-alkali interactions. The systems in this investigation are Na\\/Cu(111) Na\\/Ni(111), Cs\\/Ni(111), Na\\/Cu(110), O_{2}\\/Cu(110),O _{2}\\/Na\\/Cu(110), O _{2}\\/Na\\/Ni(111), CO\\/Na\\/Ni(111), and O_{2}\\/Na\\/Cu(111). The experiments were all performed in ultra high vacuum. Thermal Desorption Spectroscopy, Low Energy Electron Diffraction, and work function change measurements have been carried out to study the adsorption of sodium

Daixing Tang

1993-01-01

401

Determination of the common and rare alkalies in mineral analysis  

USGS Publications Warehouse

Methods are described which afford a determination of each member of the alkali group and are successful in dealing with the quantities of the rare alkalies found in rocks and minerals. The procedures are relatively rapid and based chiefly on the use of chloroplatinic acid, absolute alcohol and ether, and ammonium sulfate. The percentages of all the alkalies found in a number of minerals are given.

Wells, R.C.; Stevens, R.E.

1934-01-01

402

Soft X-ray and extreme utraviolet quantum detection efficiency of potassium chloride photocathode layers on microchannel plates  

NASA Technical Reports Server (NTRS)

The quantum detection efficiency (QDE) of KCl photocathodes in the 44-1460 A range was investigated. An opaque layer of KCl, about 15,000-A-thick, was evaporated and applied the surface of a microchannel plate (MCP), and the contribution of the photocathode material in the channels (and on the interchannel web) to the QDE was measured using a Z stack MCP detector. It is shown that KCl is a relatively stable photocathode material, with the QDE equal to 30-40 percent in the EUV. At wavelengths above 200 A, the QDE is slightly better than the QDE of CsI, as reported by Siegmund et al. (1986). While the shape of the QDE curve as a function of wavelength is similar to those reported for CsI and KBr, KCl was found to lack the high QDE peak found in the curves of CsI and KBr at about 100 A. A simple QDE model is described, the predictions of which were found to agree with the measurements on the KCl photocathode.

Siegmund, Oswald H. W.; Everman, Elaine; Hull, Jeff; Vallerga, John V.; Lampton, Michael

1988-01-01

403

Electrochemical devices utilizing molten alkali metal electrode-reactant  

DOEpatents

Electrochemical cells are provided with a reactive metal to reduce the oxide of the alkali metal electrode-reactant. Cells employing a molten alkali metal electrode, e.g., sodium, in contact with a ceramic electrolyte, which is a conductor of the ions of the alkali metal forming the electrode, exhibit a lower resistance when a reactive metal, e.g., vanadium, is allowed to react with and reduce the alkali metal oxide. Such cells exhibit less degradation of the electrolyte and of the glass seals often used to joining the electrolyte to the other components of the cell under cycling conditions.

Hitchcock, D.C.; Mailhe, C.C.; De Jonghe, L.C.

1985-07-10

404

Electrochemical devices utilizing molten alkali metal electrode-reactant  

DOEpatents

Electrochemical cells are provided with a reactive metal to reduce the oxide of the alkali metal electrode-reactant. Cells employing a molten alkali metal electrode, e.g., sodium, in contact with a ceramic electrolyte, which is a conductor of the ions of the alkali metal forming the electrode, exhibit a lower resistance when a reactive metal, e.g., vanadium, is allowed to react with and reduce the alkali metal oxide. Such cells exhibit less degradation of the electrolyte and of the glass seals often used to joining the electrolyte to the other components of the cell under cycling conditions.

Hitchcock, David C. (Omaha, NE); Mailhe, Catherine C. (Berkeley, CA); De Jonghe, Lutgard C. (Oakland, CA)

1986-01-01

405

High temperature alkali corrosion of ceramics in coal gas  

SciTech Connect

High temperature alkali corrosion has been known to cause premature failure of ceramic components used in advanced high temperature coal combustion systems such as coal gasification and clean-up, coal fired gas turbines, and high efficiency heat engines. The objective of this research is to systematically evaluate the alkali corrosion resistance of the most commonly used structural ceramics including silicon carbide, silicon nitride, cordierite, mullite, alumina, aluminum titanate, zirconia, and fireclay glass. The study consists of identification of the alkali reaction products (phase equilibria) and the kinetics of the alkali reactions as a function of temperature and time.

Pickrell, G.R.; Sun, T.; Brown, J.J.

1992-05-27

406

Oxide Film Aging on Alloy 22 in Halide Containing Solutions  

SciTech Connect

Passive and corrosion behaviors of Alloy 22 in chloride and fluoride containing solutions, changing the heat treatment of the alloy, the halide concentration and the pH of the solutions at 90 deg. C, was investigated. The study was implemented using electrochemical techniques, which included open circuit potential monitoring over time, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements carried out at open circuit and at passivity potentials. Corrosion rates obtained by EIS measurements after 24 h immersion in naturally aerated solutions were below 0.5 {mu}m/year. The corrosion rates were practically independent of solution pH, alloy heat treatment and halide ion nature and concentration. EIS low frequency resistance values increased with applied potential in the passive domain and with polarization time in pH 6 - 1 M NaCl at 90 deg. C. This effect was attributed to an increase in the oxide film thickness and oxide film aging. High frequency capacitance measurements indicated that passive oxide on Alloy 22 presented a double n-type/p-type semiconductor behavior in the passive potential range. (authors)

Rodriguez, Martin A.; Carranza, Ricardo M. [Dept. Materiales, Comision Nacional de Energia Atomica, Av. Gral. Paz 1499, Villa Maipu, 1650 (Argentina); Rebak, Raul B. [Lawrence Livermore National Laboratory, 7000 East Ave, L-631, Livermore, CA, 94550-9698 (United States)

2007-07-01

407

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

408

Influence of ageing processing on GaAs photocathode of 3rd generation low-light-level image intensifier  

NASA Astrophysics Data System (ADS)

The 3rd generation low-light-level image intensifiers should be aged for 100 hours before its normal use. In order to know the influence of ageing processing on GaAs photocathodes, five 3rd generation low-light-level image intensifiers were aged with the life testing instrument of low-light-level image intensifier in an experiment. With the spectral response testing instrument, the intensifiers were measured for totally 8 times to get their spectral response respectively before they were aged and in a half year after aged, and to calculate the integral sensitivity according to the spectral response curves. Based on the fluctuating spectral response curves and the varying integral sensitivity, it was indicated that the aged intensifiers up to standard had more stable photocathode sensitivity, smaller decrease in their spectral response curves, while those not up to standard had more obvious decline as a whole in their spectral response curves. Additionally, the threshold wavelength of all intensifiers was moving toward shortwave. The degeneration of GaAs photocathode resulted from the instability of the Cs-O layer on GaAs photocathode surface. During the ageing processing, the lack of a longtime light radiation on Cs-O layer, the widening surface barrier and the decreasing escape probability led to less photoelectronic emission and lower sensitivity. Moreover, the destruction of dipole layer resulted in smaller bending of surface band and higher vacuum level, so that the electrons in impurity level could not escape and the threshold wavelength moved toward shortwave. Thus the ageing processing played a role of picking out the 3rd generation low-light-level image intensifiers to get rid of the products not up to standard and to put the photocathodes of products up to standard into a relatively stable random failure period.

Feng, Liu; Shi, Feng; Yin, Lei; Miao, Zhuang; Cheng, Hong-chang; Wang, Long; Niu, Sen; Zhang, Xiao-hui

2014-09-01

409

40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.  

Code of Federal Regulations, 2014 CFR

...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

2014-07-01

410

40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.  

Code of Federal Regulations, 2012 CFR

...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

2012-07-01

411

40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.  

Code of Federal Regulations, 2011 CFR

...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

2011-07-01

412

40 CFR 721.5985 - Fatty alkyl phosphate, alkali metal salt (generic).  

Code of Federal Regulations, 2012 CFR

... Fatty alkyl phosphate, alkali metal salt (generic). 721.5985 Section 721... Fatty alkyl phosphate, alkali metal salt (generic). (a) Chemical substance...as a fatty alkyl phosphate, alkali metal salt (PMN P-99-0385) is subject to...

2012-07-01

413

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

Code of Federal Regulations, 2013 CFR

...Disubstituted benzoic acid, alkali metal salt (generic). 721.10098 Section 721...Disubstituted benzoic acid, alkali metal salt (generic). (a) Chemical substance...disubstituted benzoic acid, alkali metal salt (PMN P-03-643) is subject to...

2013-07-01

414

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

Code of Federal Regulations, 2011 CFR

...Disubstituted benzoic acid, alkali metal salt (generic). 721.10098 Section 721...Disubstituted benzoic acid, alkali metal salt (generic). (a) Chemical substance...disubstituted benzoic acid, alkali metal salt (PMN P-03-643) is subject to...

2011-07-01

415

40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.  

Code of Federal Regulations, 2010 CFR

...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

2010-07-01

416

40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.  

Code of Federal Regulations, 2013 CFR

...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

2013-07-01

417

40 CFR 721.10630 - Amino acid, carboxyalkyl, alkylsulfonate, alkali salt (generic).  

Code of Federal Regulations, 2013 CFR

...carboxyalkyl, alkylsulfonate, alkali salt (generic). 721.10630 Section 721...carboxyalkyl, alkylsulfonate, alkali salt (generic). (a) Chemical substances...carboxyalkyl, alkylsulfonate, alkali salts (PMNs P-11-619 and...

2013-07-01

418

40 CFR 721.5452 - Alkali metal salt of halogenated organoborate (generic).  

Code of Federal Regulations, 2013 CFR

... 2013-07-01 false Alkali metal salt of halogenated organoborate (generic...Substances § 721.5452 Alkali metal salt of halogenated organoborate (generic...substances identified generically as alkali metal salt of halogenated organoborate (PMN...

2013-07-01

419

40 CFR 721.5452 - Alkali metal salt of halogenated organoborate (generic).  

Code of Federal Regulations, 2010 CFR

... 2010-07-01 false Alkali metal salt of halogenated organoborate (generic...Substances § 721.5452 Alkali metal salt of halogenated organoborate (generic...substances identified generically as alkali metal salt of halogenated organoborate (PMN...

2010-07-01

420

40 CFR 721.5985 - Fatty alkyl phosphate, alkali metal salt (generic).  

Code of Federal Regulations, 2011 CFR

... 2011-07-01 false Fatty alkyl phosphate, alkali metal salt (generic). 721...Substances § 721.5985 Fatty alkyl phosphate, alkali metal salt (generic). ...identified generically as a fatty alkyl phosphate, alkali metal salt (PMN...

2011-07-01

421

40 CFR 721.5985 - Fatty alkyl phosphate, alkali metal salt (generic).  

Code of Federal Regulations, 2010 CFR

... 2010-07-01 false Fatty alkyl phosphate, alkali metal salt (generic). 721...Substances § 721.5985 Fatty alkyl phosphate, alkali metal salt (generic). ...identified generically as a fatty alkyl phosphate, alkali metal salt (PMN...

2010-07-01

422

40 CFR 721.5985 - Fatty alkyl phosphate, alkali metal salt (generic).  

Code of Federal Regulations, 2014 CFR

... 2014-07-01 false Fatty alkyl phosphate, alkali metal salt (generic). 721...Substances § 721.5985 Fatty alkyl phosphate, alkali metal salt (generic). ...identified generically as a fatty alkyl phosphate, alkali metal salt (PMN...

2014-07-01

423

40 CFR 721.5985 - Fatty alkyl phosphate, alkali metal salt (generic).  

Code of Federal Regulations, 2013 CFR

... 2013-07-01 false Fatty alkyl phosphate, alkali metal salt (generic). 721...Substances § 721.5985 Fatty alkyl phosphate, alkali metal salt (generic). ...identified generically as a fatty alkyl phosphate, alkali metal salt (PMN...

2013-07-01

424

(abstract) Fundamental Mechanisms of Electrode Kinetics and Alkali Metal Atom Transport at the Alkali Beta'-Alumina/Porous Electrode/Alkali Metal Vapor Three Phase Boundary  

NASA Technical Reports Server (NTRS)

The mechanisms of electrode kinetics and mass transport of alkali metal oxidation and alkali metal cation reduction at the solid electrolyte/porous electrode boundary as well as alkali metal transport through porous metal electrodes has important applications in optimizing device performance in alkali metal thermal to electric converter (AMTEC) cells which are high temperature, high current density electrochemical cells. Basic studies of these processes also affords the opportunity to investigate a very basic electrochemical reaction over a wide range of conditions; and a variety of mass transport modes at high temperatures via electrochemical techniques. The temperature range of these investigations covers 700K to 1240K; the alkali metal vapor pressures range from about 10(sup -2) to 10(sup 2) Pa; and electrodes studied have included Mo, W, Mo/Na(sub 2)MoO(sub 4), W/Na(sub 2)WO(sub 4), WPt(sub x), and WRh(sub x) (1.0 < x < 6.0 ) with Na at Na-beta'-alumina, and Mo with K at K-beta'-alumina. Both liquid metal/solid electrolyte/alkali metal vapor and alkali metal vapor/solid electrolyte/vapor cells have been used to characterize the reaction and transport processes. We have previously reported evidence of ionic, free molecular flow, and surface transport of sodium in several types of AMTEC electrodes.

Williams, R. M.; Jeffries-Nakamura, B.; Ryan, M. A.; Underwood, M. L.; O'Connor, D.; Kisor, A.; Kikkert, S. K.

1993-01-01

425

Canadian Micro-Mineral Association: ALKALI - NUTS  

NSDL National Science Digital Library

This website, created by the Canadian Micro-Mineral Association, furnishes information on the minerals and environments near Mont Saint-Hilaire (MSH) in Quebec, Canada. Students and educators can discover the physical characteristics, fluorescence, and the distribution and rarity of the hundreds of species of minerals found around MSH. Each description includes helpful images of the amazing minerals and environments. Users can learn about the two classification systems: Dana and Strunz. The site presents MSH-related current news, articles, and announcements. Users can also discover the meaning and origin of the term, ALKALI-NUTS.

426

High power diode pumped alkali vapor lasers  

NASA Astrophysics Data System (ADS)

Diode pumped alkali lasers have developed rapidly since their first demonstration. These lasers offer a path to convert highly efficient, but relatively low brightness, laser diodes into a single high power, high brightness beam. General Atomics has been engaged in the development of DPALs with scalable architectures. We have examined different species and pump characteristics. We show that high absorption can be achieved even when the pump source bandwidth is several times the absorption bandwidth. In addition, we present experimental results for both potassium and rubidium systems pumped with a 0.2 nm bandwidth alexandrite laser. These data show slope efficiencies of 67% and 72% respectively.

Zweiback, J.; Krupke, B.

2008-05-01

427

Systematic hardness measurements on mixed and doped crystals of rubidium halides  

Microsoft Academic Search

Efforts are made to improve the hardness of rubidium halide crystals by (i) solid solution hardening and (ii) impurity hardening.\\u000a Systematic microhardness measurements have been made on rubidium halide mixed crystals (RbBr-RbI and KI-RbI) and rubidium\\u000a halide crystals doped with Sr2+ ions. The composition dependence of the hardness of mixed crystals follows the law ?H\\u000a \\u000a v\\u000a =K x\\u000a (1? x),where

D. B. Sirdeshmukh; T. Kumara Swamy; P. Geeta Krishna; K. G. Subhadra

2003-01-01

428

Mild palladium-catalyzed cyanation of (hetero)aryl halides and triflates in aqueous media.  

PubMed

A mild, efficient, and low-temperature palladium-catalyzed cyanation of (hetero)aryl halides and triflates is reported. Previous palladium-catalyzed cyanations of (hetero)aryl halides have required higher temperatures to achieve good catalytic activity. This current reaction allows the cyanation of a general scope of (hetero)aryl halides and triflates at 2-5 mol % catalyst loadings with temperatures ranging from rt to 40 °C. This mild method was applied to the synthesis of lersivirine, a reverse transcriptase inhibitor. PMID:25555140

Cohen, Daniel T; Buchwald, Stephen L

2015-01-16

429

A photocathode rf gun design for a mm-wave linac-based FEL  

SciTech Connect

In recent years, advances in the rf gun technology have made it possible to produce small beam emittances suitable for short period microundulators which take advantage of the low emittance beam to reduce the wavelength of FELs. At the Advanced Photon Source, we are studying the design of a compact 50-MeV superconducting mm-wave linac-based FEL for the production of short wavelengths ({approximately}300 nm) to carry out FEL demonstration experiments. The electron source considered for the linac is a 30- GHz, 3 1/2-cell {pi}-mode photocathode rf gun. For cold model rf measurements a 15-GHz prototype structure was fabricated. Here we report on the design, numerical modelling and the initial cold-model rf measurement results on the 15-GHz prototype structure.

Nassiri, A.; Berenc, T,; Foster, J.; Waldschmidt, G.; Zhou, J.

1995-07-01

430

Measurements of the Argonne Wakefield Accelerator's low charge, 4 MeV RF photocathode witness beam.  

SciTech Connect

The Argonne Wakefield Accelerator's (AWA) witness RF photocathode gun produced its first electron beam in April of 1996. We have characterized the charge, energy, emittance and bunch length of the witness beam over the last several months. The emittance Was measured by both a quad scan that fitted for space charge using an in house developed Mathematica routine and a pepper pot technique. The bunch length was measured by imaging Cherenkov light from a quartz plate to a Hamamatsu streak camera with 2 psec resolution. A beam energy of 3.9 Mev was measured with a 6 inch round pole spectrometer while a beam charge was measured with both an ICT and a Faraday Cup. Although the gun will normally be run at 100 pC it has produced charges from 10 pC to 4 nc. All results of the measurements to date are presented here.

Power, J.

1998-04-01

431

Biopolymer-Activated Graphitic Carbon Nitride towards a Sustainable Photocathode Material  

PubMed Central

Photoelectrochemical (PEC) conversion of solar light into chemical fuels is one of the most promising solutions to the challenge of sustainable energy. Graphitic carbon (IV) nitride polymer (g-CN) is an interesting sustainable photocathode material due to low-cost, visible-light sensitivity, and chemical stability up to 500°C in air. However, grain boundary effects and limited active sites greatly hamper g-CN activity. Here, we demonstrate biopolymer-activation of g-CN through simultaneous soft-templating of a sponge-like structure and incorporation of active carbon-dopant sites. This facile approach results in an almost 300% increase in the cathodic PEC activity of g-CN under simulated solar-irradiation. PMID:23831846

Zhang, Yuanjian; Schnepp, Zoë; Cao, Junyu; Ouyang, Shuxin; Li, Ying; Ye, Jinhua; Liu, Songqin

2013-01-01

432

Nanoporous photocathode and photoanode made by multilayer assembly of quantum dots.  

PubMed

We perform in this paper a kinetic study of the photoelectrochemical responses of nanoporous thin photoactive films. The films were fabricated by by a layer-by-layer assembly of positively charged polyelectrolytes (poly-l-Lysine, pLys) and negatively charged semiconductor nanoparticles (NPs) on a carboxylic acid terminated alkanethiol-modified gold electrode. Two types of NPs were used to build uniform films: cadmium selenide (CdSe) and cadmium selenide/cadmium sulfide core/shell (CdSe@CdS). Large photocathodic and photoanodic currents were recorded for CdSe and CdSe@CdS sensitized films, respectively. A theoretical model of the photocurrent responses was developed to analyze the kinetics of photoinduced processes and coupled reactions, showing that the multilayer films behave as homogeneous nanoporous semiconducting photoelectrodes. PMID:19206496

Hojeij, Mohamad; Su, Bin; Tan, Shuxin; Mériguet, Guillaume; Girault, Hubert H

2008-05-01

433

High Performance Polarized Electron Photocathodes Based on InGaAlAs/AlGaAs Superlattices  

NASA Astrophysics Data System (ADS)

Highly efficient emitters of polarized electrons based on the InAlGaAs/AlGaAs superlattice give an optimistic prognosis to explorations of such structures as the sources for accelerators. A new set of these SL structures with minimized conduction band offset was designed and recently tested. A new technology of surface protection in MBE growth leads to a significantly reduced heat-cleaning temperature. At these lowered cleaning temperatures, the thermal degradation of the working structure parameters is avoided. As a result a polarization P of up to 91% at corresponding quantum efficiency (QE) of 0.3% was achieved at room temperature. A 50% increase in the photocathode lifetime has been achieved with Sb coverage.

Mamaev, Y. A.; Subashiev, A. V.; Yashin, Y. P.; Gerchikov, L. G.; Luh, D.; Maruyama, T.; Clendenin, J. E.; Ustinov, V. M.; Zhukov, A. E.

2005-08-01

434

Recovery of alkali metal constituents from catalytic coal conversion residues  

DOEpatents

In a coal gasification operation (32) or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein particles containing alkali metal residues are produced, alkali metal constituents are recovered from the particles by contacting them (46, 53, 61, 69) with water or an aqueous solution to remove water-soluble alkali metal constituents and produce an aqueous solution enriched in said constituents. The aqueous solution thus produced is then contacted with carbon dioxide (63) to precipitate silicon constituents, the pH of the resultant solution is increased (81), preferably to a value in the range between about 12.5 and about 15.0, and the solution of increased pH is evaporated (84) to increase the alkali metal concentration. The concentrated aqueous solution is then recycled to the conversion process (86, 18, 17) where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst.

Soung, Wen Y. (Houston, TX)

1984-01-01

435

Environmental mercury contamination around a chlor-alkali plant  

Microsoft Academic Search

The chlor-alkali industry is one of the most important emitters of mercury. This metal is effectively spread from chlor-alkali plants into the atmosphere and it has been reported that only a few percent of the mercury emissions are deposited locally the major part spreading over very large areas. The purpose of this investigation was to study the spreading of mercury

Martin Lodenius; Esa Tulisalo

1984-01-01

436

Preliminary study on combined-alkali–slag paste materials  

Microsoft Academic Search

This article mainly describes a study on combined-alkali-activated slag paste materials. Without any coarse and fine aggregates, the effect of several factors, such as the kind of alkali, additives, as well as curing conditions on the strength and other properties of the paste materials, has been investigated. The activation of sodium hydroxide shows a better early strength developing than sodium

Yongde Li; Yao Sun

2000-01-01

437

Ion Partitioning at the liquid/vapor interface of a multi-component alkali halidesolution: A model for aqueous sea salt aerosols  

SciTech Connect

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

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

2008-12-22

438

Dynamics of reactive ultracold alkali polar molecules  

NASA Astrophysics Data System (ADS)

Recently, ultracold polar molecules of KRb have been created. These molecules are chemically reactive and their lifetime in a trap is limited [1]. However, their lifetime increases when they are loaded into a 1D optical lattice in the presence of an electric field [2]. These results naturally raise the question of manipulating ultracold collisions of other species of alkali dimer molecules, with an eye toward both novel stereochemistry, as well as suppressing unwanted reactions, to enable condensed matter applications. In this talk, we report on a comparative study between the bi-alkali polar molecules of LiNa, LiK, LiRb, LiCs which have been predicted to be reactive [3]. We compute the isotropic C6 coefficients of these systems and we predict the elastic and reactive rate coefficients when an electric field is applied in a 1D optical lattice. We will discuss the efficacy of evaporative cooling for each species.[4pt] [1] Ni et al., Science 322, 231 (2008); Ospelkaus et al., Science 327, 853 (2010); Ni et al., Nature 464, 1324 (2010). [2] Qu'em'ener et al., Phys. Rev. A 81, 060701(R) (2010) ; Qu'em'ener et al., Phys. Rev. A 83, 012705 (2011); de Miranda et al., arXiv:1010.3731, to appear in Nature Physics. [3] Zuchowski et al., Phys. Rev. A 81, 060703(R) (2010).

Quéméner, Goulven; Bohn, John; Petrov, Alexander; Kotochigova, Svetlana

2011-06-01

439

ALKALI-ACTIVATED BINDERS AND POZZOLAN CEMENT BINDERS - COMPETE BINDER REACTION OR TWO SIDES OF THE SAME STORY?  

Microsoft Academic Search

Increasingly attention has been paid in the last years on alkali-activated binders such as alkali- activated fly ash and slag. Related binders are known as geopolymers which are at least alkali- activated metakaolin binders. In all cases the activation of the solid is made with different alkaline solutions containing alkali hydroxides, alkali silicates and\\/or alkali carbonates. It could be shown

A. Buchwald; Ch. Kaps; M. Hohmann

440

Electrical conductivity and relaxation in mixed alkali tellurite glasses.  

PubMed

The authors have reported the electrical conductivity and the conductivity relaxation in mixed alkali tellurite glasses of compositions of 70TeO2-xNa2O-(30-x)Li2O in the frequency range from 10 Hz to 2 MHz and in the temperature range from room temperature to just below the glass transition temperature. They have analyzed the relaxation data in the framework of different models. They have observed the mixed alkali effect in the dc and ac conductivities, the crossover frequency, and the conductivity relaxation frequency as well as in their respective activation energies in these glasses. They have also observed the mixed alkali effect in the decoupling index. The scaling property of the modulus spectra of these mixed alkali glasses shows that the conductivity relaxation in the mixed alkali tellurite glasses is independent of temperature but depends on the glass compositions. PMID:17508813

Ghosh, S; Ghosh, A

2007-05-14

441

Mechanisms of alkali metal release during biomass combustion  

SciTech Connect

A limiting factor in using solid biomass fuels for electricity production is the accelerated fouling and slagging caused by alkali metal release during biomass combustion. A detailed understanding of alkali release mechanisms during biomass combustion as well as identification of these alkali metal species will provide insights as to how these vapors enhance deposit formation in power generating facilities. A molecular beam mass spectrometer (MBMS) system, in conjunction with a variable-temperature quartz tube reactor, was used to directly sample the hot gases liberated from the combustion of small (20-60-mg) biomass samples. The results of these laboratory studies indicate that initial feedstock composition has the most pronounced effect on the amount and form of the alkali metal released during biomass combustion. Four alkali metal release mechanisms have been identified based on the various biomass feedstocks investigated.

Dayton, D.C.; Milne, T.A. [National Renewable Energy Lab., Golden, CO (United States)

1995-12-31

442

Measurements of photocathode operational lifetime at beam currents up to 10-mA using an improved DC high voltage GaAs photogun  

SciTech Connect

This work extends past research at Jefferson Lab aimed at better appreciating the mechanisms that limit photocathode operational lifetime at high current (> 1 mA). Specifically, the performance of an improved 100 kV DC high voltage load locked photogun will be described. Although difficult to measure directly, we believe the new gun has better vacuum conditions compared to the original gun, as indicated by enhanced photocathode lifetimes exceeding 2000 C using a 1.55 mm diameter drive laser spot at the photocathode. In addition, the dependence of the lifetime on the laser spot size at the photocathode was measured and a charge density lifetime exceeding 10^6 C/cm^2 was measured with a 0.32 mm laser spot diameter.

J. Grames; M. Poelker; P. Adderley; J. Brittian; J. Clark; J. Hansknecht; D. Machie; M.L. Stutzman; K. Surles-Law

2007-06-01

443

Dehalogenation of aromatic halides using metallic calcium in ethanol.  

PubMed

The scope and limitations of the dehalogenation of aromatic halides 1 and 4a-p using metallic calcium in ethanol at room temperature were revealed. The cleavage of the carbon-chlorine bond on the aromatic ring bearing electron-donating group was difficult compared to the one bearing electron-withdrawing group. Moreover, we applied this method to the dechlorination of polychlorinated biphenyls (PCBs) in transformer oil. It was also found that the dechlorination took place easily under mild conditions. The existence of PCBs residue in the reaction at room temperature was less than 0.04% according to the GC-MS analysis. The chlorine was identified as calcium chloride. PMID:11686379

Mitoma, Y; Nagashima, S; Simion, C; Simion, A M; Yamada, T; Mimura, K; Ishimoto, K; Tashiro, M

2001-10-15

444

The Oxidation State of Europium in Halide Glasses  

PubMed Central

The luminescent properties of divalent europium ions can be exploited to produce storage phosphors for x-ray imaging applications. The relatively high cost and limited availability of divalent europium halides makes it desirable to synthesize them from the readily available trivalent salts. In this work, samples of pure EuCl3 and fluoride glass melts doped with EuCl3 were processed at 700-800 °C in an inert atmosphere furnace. The Eu oxidation state in the resulting materials was determined using fluorescence and Mössbauer spectroscopy. Heat treatment of pure EuCl3 for 10 minutes at 710 °C resulted in a material comprising approximately equal amounts of Eu2+ and Eu3+. Glasses made using mixtures of EuCl2 and EuCl3 in the starting material contained both oxidation states. This paper describes the sample preparation and analysis and discusses the results in the context of chemical equilibria in the melts. PMID:22101252

Weber, J.K.R.; Vu, M.; Paßlick, C.; Schweizer, S.; Brown, D.E.; Johnson, C.E.; Johnson, J.A.

2012-01-01

445

The oxidation state of europium in halide glasses  

NASA Astrophysics Data System (ADS)

The luminescent properties of divalent europium ions can be exploited to produce storage phosphors for x-ray imaging applications. The relatively high cost and limited availability of divalent europium halides makes it desirable to synthesize them from the readily available trivalent salts. In this work, samples of pure EuCl3 and fluoride glass melts doped with EuCl3 were processed at 700-800?°C in an inert atmosphere furnace. The Eu oxidation state in the resulting materials was determined using fluorescence and Mössbauer spectroscopy. Heat treatment of pure EuCl3 for 10 min at 710?°C resulted in a material comprising approximately equal amounts of Eu2+ and Eu3+. Glasses made using mixtures of EuCl2 and EuCl3 in the starting material contained both oxidation states. This paper describes the sample preparation and analysis and discusses the results in the context of chemical equilibria in the melts.

Weber, J. K. R.; Vu, M.; Paßlick, C.; Schweizer, S.; Brown, D. E.; Johnson, C. E.; Johnson, J. A.

2011-12-01

446

Venus: Halide cloud condensation and volatile element inventories  

NASA Technical Reports Server (NTRS)

Several Venus cloud condensates, including A12C16 as well as halides, oxides and sulfides of arsenic and antimony, are assessed for their thermodynamic and geochemical plausibility. Aluminum chloride can confidently be ruled out, and condensation of arsenic sulfides on the surface will cause arsenic compounds to be too rare to produce the observed clouds. Antimony may conceivably be sufficiently volatile, but the expected molecular form is gaseous SbS, not the chloride. Arsenic and antimony compounds in the atmosphere will be regulated at very low levels by sulfide precipitation, irrespective of the planetary inventory of As and Sb. Thus the arguments for a volatile-deficient origin for Venus based on the depletion of water and mercury (relative to Earth) cannot be tested by a search for atmospheric arsenic or antimony.

Lewis, J. S.; Fegley, B., Jr.

1982-01-01

447

Direct current ballast circuit for metal halide lamp  

NASA Technical Reports Server (NTRS)

A direct current ballast circuit for a two electrode metal halide lamp is described. Said direct current ballast circuit includes a low voltage DC input and a high frequency power amplifier and power transformer for developing a high voltage output. The output voltage is rectified by diodes and filtered by inductor and capacitor to provide a regulated DC output through commutating diodes to one terminal of the lamp at the output terminal. A feedback path from the output of the filter capacitor through the bias resistor to power the high frequency circuit which includes the power amplifier and the power transformer for sustaining circuit operations during low voltage transients on the input DC supply is described. A current sensor connected to the output of the lamp through terminal for stabilizing lamp current following breakdown of the lamp is described.

Lutus, P. (inventor)

1981-01-01

448

Theoretical study of the scandium and yttrium halides  

NASA Technical Reports Server (NTRS)

The X1Sigma(+) ground states and a3Delta excited states of the diatomic halides of Sc and Y are characterized theoretically, using the SDCI coupled-pair functional method and the state-averaged CASSCF method to determine the spectroscopic constants and related properties. The techniques employed are discussed, and the results are presented in extensive tables. The dissociation energies are given as D0 = 6.00 eV for ScF, 4.55 eV for ScCl, 3.90 eV for ScBr, 6.72 eV for YF, 5.36 eV for YCl, and 4.74 eV for YBr.

Langhoff, Stephen R.; Bauschlicher, Charles W., Jr.; Partridge, Harry

1988-01-01

449

Bright light-emitting diodes based on organometal halide perovskite.  

PubMed

Solid-state light-emitting devices based on direct-bandgap semiconductors have, over the past two decades, been utilized as energy-efficient sources of lighting. However, fabrication of these devices typically relies on expensive high-temperature and high-vacuum processes, rendering them uneconomical for use in large-area displays. Here, we report high-brightness light-emitting diodes based on solution-processed organometal halide perovskites. We demonstrate electroluminescence in the near-infrared, green and red by tuning the halide compositions in the perovskite. In our infrared device, a thin 15?nm layer of CH3NH3PbI(3-x)Cl(x) perovskite emitter is sandwiched between larger-bandgap titanium dioxide (TiO2) and poly(9,9'-dioctylfluorene) (F8) layers, effectively confining electrons and holes in the perovskite layer for radiative recombination. We report an infrared radiance of 13.2?W?sr(-1)?m(-2) at a current density of 363?mA?cm(-2), with highest external and internal quantum efficiencies of 0.76% and 3.4%, respectively. In our green light-emitting device with an ITO/PEDOT:PSS/CH3NH3PbBr3/F8/Ca/Ag structure, we achieved a luminance of 364?cd?m(-2) at a current density of 123?mA?cm(-2), giving external and internal quantum efficiencies of 0.1% and 0.4%, respectively. We show, using photoluminescence studies, that radiative bimolecular recombination is dominant at higher excitation densities. Hence, the quantum efficiencies of the perovskite light-emitting diodes increase at higher current densities. This demonstration of effective perovskite electroluminescence offers scope for developing this unique class of materials into efficient and colour-tunable light emitters for low-cost display, lighting and optical communication applications. PMID:25086602

Tan, Zhi-Kuang; Moghaddam, Reza Saberi; Lai, May Ling; Docampo, Pablo; Higler, Ruben; Deschler, Felix; Price, Michael; Sadhanala, Aditya; Pazos, Luis M; Credgington, Dan; Hanusch, Fabian; Bein, Thomas; Snaith, Henry J; Friend, Richard H

2014-09-01

450

Bright light-emitting diodes based on organometal halide perovskite  

NASA Astrophysics Data System (ADS)

Solid-state light-emitting devices based on direct-bandgap semiconductors have, over the past two decades, been utilized as energy-efficient sources of lighting. However, fabrication of these devices typically relies on expensive high-temperature and high-vacuum processes, rendering them uneconomical for use in large-area displays. Here, we report high-brightness light-emitting diodes based on solution-processed organometal halide perovskites. We demonstrate electroluminescence in the near-infrared, green and red by tuning the halide compositions in the perovskite. In our infrared device, a thin 15?nm layer of CH3NH3PbI3-xClx perovskite emitter is sandwiched between larger-bandgap titanium dioxide (TiO2) and poly(9,9?-dioctylfluorene) (F8) layers, effectively confining electrons and holes in the perovskite layer for radiative recombination. We report an infrared radiance of 13.2?W?sr-1?m-2 at a current density of 363?mA?cm-2, with highest external and internal quantum efficiencies of 0.76% and 3.4%, respectively. In our green light-emitting device with an ITO/PEDOT:PSS/CH3NH3PbBr3/F8/Ca/Ag structure, we achieved a luminance of 364?cd?m-2 at a current density of 123?mA?cm-2, giving external and internal quantum efficiencies of 0.1% and 0.4%, respectively. We show, using photoluminescence studies, that radiative bimolecular recombination is dominant at higher excitation densities. Hence, the quantum efficiencies of the perovskite light-emitting diodes increase at higher current densities. This demonstration of effective perovskite electroluminescence offers scope for developing this unique class of materials into efficient and colour-tunable light emitters for low-cost display, lighting and optical communication applications.

Tan, Zhi-Kuang; Moghaddam, Reza Saberi; Lai, May Ling; Docampo, Pablo; Higler, Ruben; Deschler, Felix; Price, Michael; Sadhanala, Aditya; Pazos, Luis M.; Credgington, Dan; Hanusch, Fabian; Bein, Thomas; Snaith, Henry J.; Friend, Richard H.

2014-09-01

451

p-Si/W2C and p-Si/W2C/Pt photocathodes for the hydrogen evolution reaction.  

PubMed

p-Si/W2C photocathodes are synthesized by evaporating tungsten metal in an ambient of ethylene gas to form tungsten semicarbide (W2C) thin films on top of p-type silicon (p-Si) substrates. As deposited the thin films contain crystalline W2C with a bulk W:C atomic ratio of approximately 2:1. The W2C films demonstrate catalytic activity for the hydrogen evolution reaction (HER), and p-Si/W2C photocathodes produce cathodic photocurrent at potentials more positive than 0.0 V vs RHE while bare p-Si photocathodes do not. The W2C films are an effective support for Pt nanoparticles allowing for a considerable reduction in Pt loading. p-Si/W2C/Pt photocathodes with Pt nanoparticles achieve photocurrent onset potentials and limiting photocurrent densities that are comparable to p-Si/Pt photocathodes with Pt loading nine times higher. This makes W2C an earth abundant alternative to pure Pt for use as an electrocatalyst on photocathodes for the HER. PMID:24393053

Berglund, Sean P; He, Huichao; Chemelewski, William D; Celio, Hugo; Dolocan, Andrei; Mullins, C Buddie

2014-01-29

452

A combined metal-halide/metal flux synthetic route towards type-I clathrates: crystal structures and thermoelectric properties of A8Al8Si38 (A = K, Rb, and Cs).  

PubMed

Single-phase samples of the compounds K8Al8Si38 (1), Rb8Al8Si38 (2), and Cs7.9Al7.9Si38.1 (3) were obtained with high crystallinity and in good quantities by using a novel flux method with two different flux materials, such as Al and the respective alkali-metal halide salt (KBr, RbCl, and CsCl). This approach facilitates the removal of the product mixture from the container and also allows convenient extraction of the flux media due to the good solubility of the halide salts in water. The products were analyzed by means of single-crystal X-ray structure determination, powder X-ray and neutron diffraction experiments, (27)Al-MAS NMR spectroscopy measurements, quantum chemical calculations, as well as magnetic and transport measurements (thermal conductivity, electrical resistivity, and Seebeck coefficient). Due to the excellent quality of the neutron diffraction data, the difference between the nuclear scattering factors of silicon and aluminum atoms was sufficient to refine their mixed occupancy at specific sites. The role of variable-range hopping for the interpretation of the resistivity and the Seebeck coefficient is discussed. PMID:25267571

Baran, Volodymyr; Senyshyn, Anatoliy; Karttunen, Antti J; Fischer, Andreas; Scherer, Wolfgang; Raudaschl-Sieber, Gabriele; Fässler, Thomas F

2014-11-10

453

Absorption of NO and NO2 in Caprolactam Tetrabutyl Ammonium Halide Ionic Liquids  

Microsoft Academic Search

To explore environmentally benign solvents for the absorption of NO and NO2, a series of caprolactam tetrabutyl ammonium halide ionic liquids were synthesized. The solubility of NO and NO2 was measured at temperatures ranging from 298.2 to 363.2 K and atmospheric pressure, and the following trend in the solubility of NO and NO2 in ionic liquids with various halide anions

Erhong Duan; Bin Guo; Dandan Zhang; Long Shi; Hua Sun; Yanan Wang

2011-01-01

454

Copper-Catalyzed trans-Carbohalogenation of Terminal Alkynes with Functionalized Tertiary Alkyl Halides.  

PubMed

A highly trans-selective Cu-catalyzed carbohalogenation including carbobromination, carboiodination, and carbochlorination of terminal alkynes with activated tertiary alkyl halides has been realized, providing quaternary-carbon-containing alkenyl halides in good yields with excellent regio- and stereoselectivity. Meanwhile, an unprecedented alkyne trans-carboalkynylation process has been achieved via the tandem trans-carbohalogenation/Sonogashira coupling reaction, which furnishes highly functionalized 1,3-enynes in a single chemical transformation. PMID:25742315

Che, Chao; Zheng, Hanliang; Zhu, Gangguo

2015-03-20

455

Alkali oxide-tantalum oxide and alkali oxide-niobium oxide ionic conductors  

NASA Technical Reports Server (NTRS)

A search was made for new cationic conducting phases in alkali-tantalate and niobate systems. The phase equilibrium diagrams were constructed for the six binary systems Nb2O5-LiNbO3, Nb2O5-NaNbO3, Nb2O5-KNbO3, Ta2O5-NaTaO3, Ta2O5-LiTaO3, and Ta2O5-KTaO3. Various other binary and ternary systems were also examined. Pellets of nineteen phases were evaluated (by the sponsoring agency) by dielectric loss measurements. Attempts were made to grow large crystals of eight different phases. The system Ta2O5-KTaO3 contains at least three phases which showed peaks in dielectric loss vs. temperature. All three contain structures related to the tungsten bronzes with alkali ions in non-stoichiometric crystallographic positions.

Roth, R. S.; Parker, H. S.; Brower, W. S.; Minor, D.

1974-01-01

456

The effect of low solubility organic acids on the hygroscopicity of sodium halide aerosols  

NASA Astrophysics Data System (ADS)

In order to accurately assess the influence of fatty acids on the hygroscopic and other physicochemical properties of sea salt aerosols, hexanoic, octanoic or lauric acid together with sodium halide salts (NaCl, NaBr and NaI) have been chosen to be investigated in this study. The hygroscopic properties of sodium halide sub-micrometre particles covered with organic acids have been examined by Fourier-transform infrared spectroscopy in an aerosol flow cell. Covered particles were generated by flowing atomized sodium halide particles (either dry or aqueous) through a heated oven containing the gaseous acid. The obtained results indicate that gaseous organic acids easily nucleate onto dry and aqueous sodium halide particles. On the other hand, scanning electron microscopy (SEM) images indicate that lauric acid coating on NaCl particles makes them to aggregate in small clusters. The hygroscopic behaviour of covered sodium halide particles in deliquescence mode shows different features with the exchange of the halide ion, whereas the organic surfactant has little effect in NaBr particles, NaCl and NaI covered particles experience appreciable shifts in their deliquescence relative humidities, with different trends observed for each of the acids studied. In efflorescence mode, the overall effect of the organic covering is to retard the loss of water in the particles. It has been observed that the presence of gaseous water in heterogeneously nucleated particles tends to displace the cover of hexanoic acid to energetically stabilize the system.

Miñambres, L.; Méndez, E.; Sánchez, M. N.; Castaño, F.; Basterretxea, F. J.

2014-10-01

457

The effect of low solublility organic acids on the hygroscopicity of sodium halide aerosols  

NASA Astrophysics Data System (ADS)

In order to accurately assess the influence of fatty acids on the hygroscopic and other physicochemical properties of sea salt aerosols, hexanoic, octanoic or lauric acid together with sodium halide salts (NaCl, NaBr and NaI) have been chosen to be performed in this study. The hygroscopic properties of sodium halide submicrometer particles covered with organic acids have been examined by Fourier-transform infrared spectroscopy in an aerosol flow cell. Covered particles were generated by flowing atomized sodium halide particles (either dry or aqueous) through a heated oven containing the gaseous acid. The obtained results indicate that gaseous organic acids easily nucleate onto dry and aqueous sodium halide particles. On the other hand, Scanning Electron Microscopy (SEM) images indicate that lauric acid coating on NaCl particles makes them to aggregate in small clusters. The hygroscopic behaviour of covered sodium halide particles in deliquescence mode shows different features with the exchange of the halide ion: whereas the organic covering has little effect in NaBr particles, NaCl and NaI covered particles change their deliquescence relative humidities, with different trends observed for each of the acids studied. In efflorescence mode, the overall effect of the organic covering is to retard the loss of water in the particles. It has been observed that the presence of gaseous water in heterogeneously nucleated particles tends to displace the cover of hexanoic acid to energetically stabilize the system.

Miñambres, L.; Méndez, E.; Sánchez, M. N.; Castaño, F.; Basterretxea, F. J.

2014-02-01

458

Fluorescence-based bacterial bioreporter for specific detection of methyl halide emissions in the environment.  

PubMed

Methyl halides are volatile one-carbon compounds responsible for substantial depletion of stratospheric ozone. Among them, chloromethane (CH3Cl) is the most abundant halogenated hydrocarbon in the atmosphere. Global budgets of methyl halides in the environment are still poorly understood due to uncertainties in their natural sources, mainly from vegetation, and their sinks, which include chloromethane-degrading bacteria. A bacterial bioreporter for the detection of methyl halides was developed on the basis of detailed knowledge of the physiology and genetics of Methylobacterium extorquens CM4, an aerobic alphaproteobacterium which utilizes chloromethane as the sole source of carbon and energy. A plasmid construct with the promoter region of the chloromethane dehalogenase gene cmuA fused to a promotorless yellow fluorescent protein gene cassette resulted in specific methyl halide-dependent fluorescence when introduced into M. extorquens CM4. The bacterial whole-cell bioreporter allowed detection of methyl halides at femtomolar levels and quantification at concentrations above 10 pM (approximately 240 ppt). As shown for the model chloromethane-producing plant Arabidopsis thaliana in particular, the bioreporter may provide an attractive alternative to analytical chemical methods to screen for natural sources of methyl halide emissions. PMID:23956392

Farhan Ul Haque, Muhammad; Nadalig, Thierry; Bringel, Françoise; Schaller, Hubert; Vuilleumier, Stéphane

2013-11-01

459

Fluorescence-Based Bacterial Bioreporter for Specific Detection of Methyl Halide Emissions in the Environment  

PubMed Central

Methyl halides are volatile one-carbon compounds responsible for substantial depletion of stratospheric ozone. Among them, chloromethane (CH3Cl) is the most abundant halogenated hydrocarbon in the atmosphere. Global budgets of methyl halides in the environment are still poorly understood due to uncertainties in their natural sources, mainly from vegetation, and their sinks, which include chloromethane-degrading bacteria. A bacterial bioreporter for the detection of methyl halides was developed on the basis of detailed knowledge of the physiology and genetics of Methylobacterium extorquens CM4, an aerobic alphaproteobacterium which utilizes chloromethane as the sole source of carbon and energy. A plasmid construct with the promoter region of the chloromethane dehalogenase gene cmuA fused to a promotorless yellow fluorescent protein gene cassette resulted in specific methyl halide-dependent fluorescence when introduced into M. extorquens CM4. The bacterial whole-cell bioreporter allowed detection of methyl halides at femtomolar levels and quantification at concentrations above 10 pM (approximately 240 ppt). As shown for the model chloromethane-producing plant Arabidopsis thaliana in particular, the bioreporter may provide an attractive alternative to analytical chemical methods to screen for natural sources of methyl halide emissions. PMID:23956392

Farhan Ul Haque, Muhammad; Nadalig, Thierry; Bringel, Françoise; Schaller, Hubert

2013-01-01

460

Zn-doped p-type gallium phosphide nanowire photocathodes from a surfactant-free solution synthesis.  

PubMed

Gallium phosphide (GaP) nanowire photocathodes synthesized using a surfactant-free solution-liquid-solid (SLS) method were investigated for their photoelectrochemical evolution of hydrogen. Zinc as a p-type dopant was introduced into the nanowires during synthesis to optimize the photocathode's response. Investigation of the electrical properties of Zn-doped GaP nanowires confirmed their p-type conductivity. After optimization of the nanowire diameter and Zn doping concentration, higher absorbed photon-to-current efficiency (APCE) over the spectrum was achieved. The versatility of the SLS synthesis and the capability to control the electrical properties suggest that our approach could be generalized to other III-V and II-VI semiconductors. PMID:23025657

Liu, Chong; Sun, Jianwei; Tang, Jinyao; Yang, Peidong

2012-10-10

461

Alkali differentiation in LL-chondrites  

NASA Astrophysics Data System (ADS)

The Kraehenberg and Bhola LL-group chondrites are heterogeneous agglomerates which contain a variety of lithic fragments and chondrules as well as crystal fragments. Both meteorites contain large, cm-sized fragments with high K enrichments. The K-rich inclusions are fragments of larger rock bodies which crystallized from melts of chondritic parent material that had previously been enriched in K and in heavier alkalies,while also being depleted in Na and metal. It is suggested that the K enrichment occurred as an exchange for Na in feldspars via a vapor phase, whose presence on the chondrite parent body (or bodies) is supported by the recent finding of fluid inclusions in chondritic silicates. Cooling rate considerations indicate that the K-rich rock units could not have been very large, implying that the K-rich materials were locally molten by, for example, impact.

Wlotzka, F.; Palme, H.; Spettel, B.; Wanke, H.; Fredriksson, K.; Noonan, A. F.

1983-04-01

462

Heat pipes containing alkali metal working fluid  

NASA Technical Reports Server (NTRS)

A technique for improving high temperature evaporation-condensation heat-transfer devices which have important and unique advantage in terrestrial and space energy processing is described. The device is in the form of a heat pipe comprising a sealed container or envelope which contains a capillary wick. The temperature of one end of the heat pipe is raised by the input of heat from an external heat source which is extremely hot and corrosive. A working fluid of a corrosive alkali metal, such as lithium, sodium, or potassium transfers this heat to a heat receiver remote from the heat source. The container and wick are fabricated from a superalloy containing a small percentage of a corrosion inhibiting or gettering element. Lanthanum, scandium, yttrium, thorium, and hafnium are utilized as the alloying metal.

Morris, J. F. (inventor)

1981-01-01

463

Comparative alkali washing of simulated radioactive sludge  

SciTech Connect

The treatment of large volumes of radioactive sludge generated from uranium and plutonium recovery processes is a pressing problem in the environmental restoration currently planned at various U.S. Department of Energy sites. This sludge, commonly stored in underground tanks, is mainly in the form of metal oxides or precipitated metal hydroxides and the bulk of this material is nonradioactive. One method being developed to pretreat this waste takes advantage of the amphoteric character of aluminum and other nonradioactive elements. Previous studies have reported on the dissolution of eleven elements from simulated sludge using NaOH solutions up to 6M. This work provides a comparative study using KOH. The effectiveness of the alkali washing as a treatment method to reduce the bulk of radioactive sludge requiring long term isolation will be discussed.

Fugate, G.A.; Ensor, D.D. [Tennessee Technological Univ., Cookeville, TN (United States); Egan, B.Z. [Oak Ridge National Lab., TN (United States)

1996-10-01

464

Controlled in-situ dissolution of an alkali metal  

DOEpatents

A method for the controllable dissolution of one or more alkali metals from a vessel containing a one or more alkali metals and/or one or more partially passivated alkali metals. The vessel preferably comprising a sodium, NaK or other alkali metal-cooled nuclear reactor that has been used. The alkali metal, preferably sodium, potassium or a combination thereof, in the vessel is exposed to a treatment liquid, preferably an acidic liquid, more preferably citric acid. Preferably, the treatment liquid is maintained in continuous motion relative to any surface of unreacted alkali metal with which the treatment liquid is in contact. The treatment liquid is preferably pumped into the vessel containing the one or more alkali metals and the resulting fluid is extracted and optionally further processed. Preferably, the resulting off-gases are processed by an off-gas treatment system and the resulting liquids are processed by a liquid disposal system. In one preferred embodiment, an inert gas is pumped into the vessel along with the treatment liquid.

Jones, Jeffrey Donald; Dooley, Kirk John; Tolman, David Donald

2012-09-11

465

Alkali elemental and potassium isotopic compositions of Semarkona chondrules  

USGS Publications Warehouse

We report measurements of K isotope ratios in 28 Semarkona chondrules with a wide range of petrologic types and bulk compositions as well as the compositions of CPX-mesostasis pairs in 17 type I Semarkona chondrules, including two chondrules with radial alkali zonation and 19 type II chondrules. Despite the wide range in K/Al ratios, no systematic variations in K isotopic compositions were found. Semarkona chondrules do not record a simple history of Rayleigh-type loss of K. Experimentally determined evaporation rates suggest that considerable alkali evaporation would have occurred during chondrule formation. Nevertheless, based on Na CPX-mesostasis distribution coefficients, the alkali contents of the cores of most chondrules in Semarkona were probably established at the time of final crystallization. However, Na CPX-mesostasis distribution coefficients also show that alkali zonation in type I Semarkona chondrules was produced by entry of alkalis after solidification, probably during parent body alteration. This alkali metasomatism may have gone to completion in some chondrules. Our preferred explanation for the lack of systematic isotopic enrichments, even in alkali depleted type I chondrule cores, is that they exchanged with the ambient gas as they cooled. ?? The Meteoritical Society, 2005.

Alexander, C.M. O'D.; Grossman, J.N.

2005-01-01

466

First Demonstration Of A Free-electron Laser Driven By Electrons From A Laser-Irradiated Photocathode  

Microsoft Academic Search

Results are reported from the first observation of a free-electron laser (FEL) driven by an electron beam from a laser-irradiated photocathode. The Rocketdyne\\/Stanford FEL achieved sustained oscillations lasting over three hours and driven by photoelectrons accelerated by the Stanford Mark III radio-frequency linac. A LaB6 cathode, irradiated by a tripled Nd:YAG mode-locked drive laser, is the source of the photoelectrons.

Mark Curtin; Glenn Bennett; Robert Burke; A. Bhowmik; P. Metty; S. Benson; J. M. J. Madey

1989-01-01

467

First demonstration of a free-electron laser driven by electrons from a laser-irradiated photocathode  

Microsoft Academic Search

We report the results from the first operation of a free electron laser (FEL) driven by an electron beam from a laser-irradiated photocathode. The Rocketdyne\\/Stanford FEL achieved sustained oscillations, lasting in excess of three hours, driven by photoelectrons accelerated by the Stanford Mark III radiofrequency linac. A LaB6 cathode, irradiated by a tripled Nd: Yag mode-locked drive laser was the

Mark Curtin; Glenn Bennett; Robert Burke; Anup Bhowmik; Phillip Metty; Stephen Benson; J. M. J. Madey

1990-01-01

468

Microbial reverse-electrodialysis chemical-production cell for acid and alkali production  

E-print Network

.14 mmol of alkali. The acid- and alkali-production efficiencies based on generated current were 58 ± 3Microbial reverse-electrodialysis chemical-production cell for acid and alkali production Xiuping-production cell (MRCC), was developed to produce acid and alkali using energy derived from organic matter (acetate

469

Electrochemical cell utilizing molten alkali metal electrode-reactant  

SciTech Connect

An improved electrochemical cell comprising an additive-modified molten alkali metal electrode-reactant and/or electrolyte is disclosed. Various electrochemical cells employing a molten alkali metal, e.g., sodium, electrode in contact with a cationically conductive ceramic membrane experience a lower resistance and a lower temperature coefficient of resistance whenever small amounts of selenium are present at the interface of the electrolyte and the molten alkali metal. Further, cells having small amounts of selenium present at the electrolyte-molten metal interface exhibit less degradation of the electrolyte under long term cycling conditions.

Virkar, A.V.; Miller, G.R.

1983-10-04

470

Planting six tree species on soda-saline-alkali soil  

Microsoft Academic Search

Populus simonigra, Salix matsudana, Ulmus pumila, Populus nigra, Acer negundo, Fraxinus mandshurica. Tamarix chinensis, Hippophae\\u000a rhammoldes, Syriga onlata were planted on the soda-saline-alkali. The soil had pH 8.5–9.6, salinity 0.1%–0.3%, sodiumionized\\u000a ratio 16%–51% and normality ratio of saline base Na+\\/(Ca+++Mg++)>4. Populus simonigra grows very well on the all kinds of soda-saline-alkali soils except on the alkali sport with the worst

Zhang Yujiang; Liu Peng; Yang Dewei; Ma Chenghui; Liu Gang

1998-01-01

471

Electrochemical cell utilizing molten alkali metal electrode-reactant  

DOEpatents

An improved electrochemical cell comprising an additive-modified molten alkali metal electrode-reactant and/or electrolyte is disclosed. Various electrochemical cells employing a molten alkali metal, e.g., sodium, electrode in contact with a cationically conductive ceramic membrane experience a lower resistance and a lower temperature coefficient of resistance whenever small amounts of selenium are present at the interface of the electrolyte and the molten alkali metal. Further, cells having small amounts of selenium present at the electrolyte-molten metal interface exhibit less degradation of the electrolyte under long term cycling conditions.

Virkar, Anil V. (Sandy, UT); Miller, Gerald R. (Salt Lake City, UT)

1983-11-04

472

High temperature alkali corrosion of ceramics in coal gas  

SciTech Connect

The high temperature alkali corrosion kinetics of SiC have been systematically investigated from 950 to 1100[degrees]C at 0.63 vol % alkali vapor concentration. The corrosion rate in the presence of alkaliis approximately 10[sup 4] to 10[sup 5] times faster than the oxidation rate of SiC in air. The activation energy associated with the alkali corrosion is 406 kJ/mol, indicating a highly temperature-dependent reaction rate. The rate-controlling step of the overall reaction is likely to be the dissolution of silica in the sodium silicate liquid, based on the oxygen diffusivity data.

Pickrell, G.R.; Sun, T.; Brown, J.J.

1992-02-24

473

A si photocathode protected and activated with a ti and ni composite film for solar hydrogen production.  

PubMed

An efficient, stable and scalable hybrid photoelectrode for visible-light-driven H2 generation in an aqueous pH?9.2 electrolyte solution is reported. The photocathode consists of a p-type Si substrate layered with a Ti and Ni-containing composite film, which acts as both a protection and electrocatalyst layer on the Si substrate. The film is prepared by the simple drop casting of the molecular single-source precursor, [{Ti2 (OEt)9 (NiCl)}2 ] (TiNipre ), onto the p-Si surface at room temperature, followed by cathodic in?situ activation to form the catalytically active TiNi film (TiNicat ). The p-Si|TiNicat photocathode exhibits prolonged hydrogen generation with a stable photocurrent of approximately -5?mA?cm(-2) at 0?V vs. RHE in an aqueous pH?9.2 borate solution for several hours, and serves as a benchmark non-noble photocathode for solar H2 evolution that operates efficiently under neutral-alkaline conditions. PMID:25650832

Lai, Yi-Hsuan; Park, Hyun S; Zhang, Jenny Z; Matthews, Peter D; Wright, Dominic S; Reisner, Erwin

2015-03-01

474

A Si Photocathode Protected and Activated with a Ti and Ni Composite Film for Solar Hydrogen Production  

PubMed Central

An efficient, stable and scalable hybrid photoelectrode for visible-light-driven H2 generation in an aqueous pH?9.2 electrolyte solution is reported. The photocathode consists of a p-type Si substrate layered with a Ti and Ni-containing composite film, which acts as both a protection and electrocatalyst layer on the Si substrate. The film is prepared by the simple drop casting of the molecular single-source precursor, [{Ti2(OEt)9(NiCl)}2] (TiNipre), onto the p-Si surface at room temperature, followed by cathodic in?situ activation to form the catalytically active TiNi film (TiNicat). The p-Si|TiNicat photocathode exhibits prolonged hydrogen generation with a stable photocurrent of approximately ?5?mA?cm?2 at 0?V vs. RHE in an aqueous pH?9.2 borate solution for several hours, and serves as a benchmark non-noble photocathode for solar H2 evolution that operates efficiently under neutral–alkaline conditions. PMID:25650832

Lai, Yi-Hsuan; Park, Hyun S; Zhang, Jenny Z; Matthews, Peter D; Wright, Dominic S; Reisner, Erwin

2015-01-01

475

Spectroscopic study of the interactions of alkali fluorides with D-xylose  

NASA Astrophysics Data System (ADS)

The interactions of alkali fluorides with D-xylose have been studied by X-ray diffraction (XRD), infrared spectroscopy (IR), nuclear magnetic resonance (NMR, 1H and 13C) and atomic absorption spectrophotometry. KF and CsF form complexes with D-xylose in a 1:1 molar ratio. These complexes can be obtained by solid state milling the reactants in an agate mortar or from methanolic solutions of the sugar and the salt. LiF and NaF do not form complex with D-xylose. IR and XRD prove the identical nature of the complexes obtained by milling and from solution. IR spectra indicate strong perturbation of the OH stretching vibrations with considerable shifts to lower frequencies, which must be caused by strong hydrogen bond formation to the fluorine anion. The perturbations of C?O bond are weak, indicating that cation binding to the oxygen atoms is not the main interaction responsible for the complex formation. 1H NMR spectra of the D-xylose-KF complex dissolved in deuterium oxide is equal to that of pure D-xylose, indicating the destruction of the complex in solution. The complex is stable in DMSO, and 13C spectra of the complex in DMSO-d 6 and in solid state (CPMAS) spectra are in accordance with the observed interactions in the IR spectra. As far as we know, this is the first report of a sugar-halide salt complex in which the anion instead of the cation provides the binding forces.

Fernández-Bertrán, Jose; Reguera, Edilso; Ortiz, Pedro

2001-11-01

476

Crossed-Beam Reactions of Barium with Hydrogen Halides Measurement of Internal State Distributions by Laser-Induced Fluorescence  

E-print Network

optical detection system. MOLECULAR BEAM SYSTEM Thebeam apparatus ishoused inside a cylindrical stainless PHOTOCATHODE- TUBE ,I b k L N 2 DEWARI I k L N 2 DEWAR i /-LASE'R BEAM */-BEAM TRAP SECONDARY BEAM SOURCE

Zare, Richard N.

477

Structure and Chemistry in Halide Lead-Tellurite Glasses  

SciTech Connect

A series of TeO2-PbO glasses were fabricated with increasing fractions of mixed alkali, alkaline earth, and lanthanide chlorides. The glass and crystal structure was studied with Raman spectroscopy, nuclear magnetic resonance (NMR), X-ray diffraction, and electron microscopy. As the chloride fraction increased, the medium-range order in the glass decreased up to a critical point (~14 mass% of mixed chlorides), above which the glasses became phase-separated. Resulting phases are a TeO2/PbO-rich phase and a crystalline phase rich in alkali chlorides. The 125Te NMR indicates, contrary to previous studies, that Te site distribution did not change with increased concentrations of M+, M2+, and M3+ cations, but rather is controlled by the Te/Pb molar ratio. The 207Pb NMR shows that two Pb species exist and their relative concentration changes nearly linearly with addition of the mixed chlorides, indicating that the additives to the TeO2-PbO glass are accommodated by changing the Pb species. The 23Na and 35Cl NMR indicate that Na and Cl are distributed in the single-phase glass phase up to the critical point, and at higher concentrations partition to crystalline phases. Transmission electron microscopy shows that the sampl