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1

Fabrication of alkali halide UV photocathodes by pulsed laser deposition  

SciTech Connect

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

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

2012-12-31

2

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

3

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

4

Bi-alkali antimonide photocathodes for high brightness accelerators  

NASA Astrophysics Data System (ADS)

Alkali-antimonide photocathodes were grown on Si(100) and studied by means of XPS and UHV-AFM to validate the growth procedure and morphology of this material. The elements were evaporated sequentially at elevated substrate temperatures (first Sb, second K, third Cs). The generated intermediate K-Sb compound itself is a photocathode and the composition of K2.4Sb is close to the favored K3Sb stoichiometry. After cesium deposition, the surface layer is cesium enriched. The determined rms roughness of 25 nm results in a roughness domination of the emittance in the photoinjector already above 3 MV/m.

Schubert, S.; Ruiz-Osés, M.; Ben-Zvi, I.; Kamps, T.; Liang, X.; Muller, E.; Müller, K.; Padmore, H.; Rao, T.; Tong, X.; Vecchione, T.; Smedley, J.

2013-09-01

5

Alkali Halide Nanotubes: Structure and Stability  

PubMed Central

Accurate density functional theory (DFT) and coupled-cluster (CCSD) calculations on a series of (LiF)n=2,36 neutral clusters suggest that nanotube structures with hexagonal and octagonal transversal cross sections show stability equal to or greater than that of the typical cubic form of large LiF crystals. The nanotube stability was further corroborated by quantum dynamic calculations at room temperature. The fact that stable nanotube structures were also found for other alkali halides (e.g., NaCl and KBr) suggests that this geometry may be widely implemented in material sciences. PMID:24376901

Fernandez-Lima, Francisco A.; Henkes, Aline Veronica; da Silveira, Enio F.; Nascimento, Marco Antonio Chaer

2013-01-01

6

TRANSMISSION ELECTRON MICROSCOPY OF WEAKLY DEFORMED ALKALI HALIDE CRYSTALS  

E-print Network

377 TRANSMISSION ELECTRON MICROSCOPY OF WEAKLY DEFORMED ALKALI HALIDE CRYSTALS H. STRUNK Max) is applied to the investigation of the dis- location arrangement of [001]-orientated alkali halide crystals mainly to NaCl-(0.1-1) mole-% NaBr crystals, because these exhibit a relatively long stage I. The time

Boyer, Edmond

7

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

2012-06-07

8

STUDY OF THE EXCESS CONDUCTIVITY IN PLASTICALLY DEFORMED ALKALI HALIDES  

Microsoft Academic Search

The results of measurements on the excess ionic conductivity of ; plastically deformed alkali halides are given. The recovery of conductivity ; after deformation was investigated at various temperatures in KCl, KBr, NaCl, and ; LiF, with the aim to reach some knowledge on the nature of the defects ; responsible for enhanced conduction. It was found that the excess

P. Camagni; G. Chiarotti; A. Manara

1962-01-01

9

Correlated annealing of radiation defects in alkali halide crystals  

Microsoft Academic Search

The kinetics of the correlated annealing of pairs of neutral (F-H) and charged ( alpha -I) Frenkel defects in alkali halides is treated theoretically, taking into account defect diffusion, annihilation at short distances, and elastic or Coulomb interactions. It is shown that elastic interactions considerably affect the annealing kinetics and survival probability even for defect pairs that are third or

E. A. Kotomin; A. I. Popov; R. I. Eglitis

1992-01-01

10

Momentum Distributions of Photons from Positrons Annihilating in Alkali Halides  

Microsoft Academic Search

The angular correlation of photons from the two-gamma decay of positrons in all sodium halides and all alkali chlorides has been measured. The data yields the momentum distribution of the two gamma rays which is also the momentum distribution of the annihilating electron-positron pairs. It is seen that the positive ion has very little influence on the momentum distribution in

A. T. Stewart; N. K. Pope

1960-01-01

11

On the surface morphology of thin alkali halide photocathode "lms  

E-print Network

microscope (SEM) and atomic force microscope (AFM) of 10}20 nm thick CsI and NaI "lms, evap- orated on Ca "lm were successively deposited by resistive evap- oration onto an optically polished CaF substrate

12

Structure and bonding in small neutral alkali halide clusters  

NASA Astrophysics Data System (ADS)

The structural and bonding properties of small neutral alkali halide clusters, (AX)n with n<=10, A=Li+,Na+,K+,Rb+, and X=F-,Cl-,Br-,I-, are studied using the ab initio perturbed ion (PI) model and a restricted structural relaxation criterion. A trend of competition between rocksalt and hexagonal ringlike isomers is found and discussed in terms of the relative ionic sizes. The main conclusion is that an approximate value of rC/rA=0.5 (where rC and rA are the cationic and anionic radii) separates the hexagonal from the rocksalt structures. The classical electrostatic part of the total energy at the equilibrium geometry is enough to explain these trends. The magic numbers in the size range studied are n=4, 6, and 9, and these are universal since they occur for all alkali halides and do not depend on the specific ground-state geometry. Instead those numbers allow for the formation of compact clusters. Full geometrical relaxations are considered for (LiF)n (n=3-7) and (AX)3 clusters, and the effect of Coulomb correlation is studied in a few selected cases. These two effects preserve the general conclusions achieved thus far.

Aguado, Andrés; Ayuela, Andrés; López, José M.; Alonso, Julio A.

1997-12-01

13

Ion pairing in molecular simulations of aqueous alkali halide solutions  

PubMed Central

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

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

2009-01-01

14

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

PubMed

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

Lee, Myung Churl; Choi, Wonyong

2002-03-15

15

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

16

Study of bi-alkali photocathode growth on glass by X-ray techniques for fast timing response photomultipliers  

NASA Astrophysics Data System (ADS)

Bi-alkali antimonide photocathode is an essential component in fast timing response photomultipliers. Real-time in-situ grazing incidence x-ray diffraction and post-growth x-ray reflectivity measurement were performed to study the photocathode deposition process on glass substrate. Grazing incidence x-ray diffraction patterns show the formation of Sb crystalline, dissolution of crystalline phase Sb by the application of K vapor and reformation of refined crystal textures. XRR result exhibits that the film thickness increases ~ 4.5 times after K diffusion and almost have no change after Cs diffusion. Further investigation is expected to understand the photocathode growth process and provide guidelines for photocathode development.

Xie, Junqi; Demarteau, Marcel; Wagner, Robert; Ruiz-Oses, Miguel; Liang, Xue; Ben-Zvi, Ilan; Attenkofer, Klaus; Schubert, Susanne; Smedley, John; Wong, Jared; Padmore, Howard; Woll, Arthur

2014-03-01

17

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

SciTech Connect

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

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

2013-02-20

18

Band-bending in organic semiconductors: the role of alkali-halide interlayers.  

PubMed

Band-bending in organic semiconductors, occurring at metal/alkali-halide cathodes in organic-electronic devices, is experimentally revealed and electrostatically modeled. Metal-to-organic charge transfer through the insulator, rather than doping of the organic by alkali-metal ions, is identified as the origin of the observed band-bending, which is in contrast to the localized interface dipole occurring without the insulating buffer layer. PMID:24338797

Wang, Haibo; Amsalem, Patrick; Heimel, Georg; Salzmann, Ingo; Koch, Norbert; Oehzelt, Martin

2014-02-12

19

Electrical conductivity, self-diffusion, and volume expansion of alkali halides at the melting point  

Microsoft Academic Search

In an earlier paper, Heisenberg's uncertainty principle was invoked at the melting point T m of crystalline solids to provide fundamental justification for Lindemann's melting law and to compute diffusion coefficients of several alkali halides. The uncertainty principle defines breakdown of Debye zone boundary (ZB) phonons as valid collective excitations when phonon energies and line widths due to anharmonicity become

B. H. Armstrong

1988-01-01

20

Electrical conductivity, self-diffusion, and volume expansion of alkali halides at the melting point  

Microsoft Academic Search

In an earlier paper, Heisenberg's uncertainty principle was invoked at the melting point Tm of crystalline solids to provide fundamental justification for Lindemann's melting law and to compute diffusion coefficients of several alkali halides. The uncertainty principle defines breakdown of Debye zone boundary (ZB) phonons as valid collective excitations when phonon energies and line widths due to anharmonicity become comparable

B. H. Armstrong

1988-01-01

21

Excited States of Alkali-Halide Cluster Anions with Excess Electrons  

Microsoft Academic Search

We have used photoelectron spectroscopy to probe the electronically excited states of alkali-halide cluster anions with excess electrons. These excess electrons are pumped up to their excited states by one laser pulse before being driven into the continuum by a second laser pulse. By studying the energy spectra of the continuum electrons as functions of the pump laser wavelength, we

Louis Bloomfield; Fredrik Fatemi; Andy Dally

1998-01-01

22

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

23

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

24

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

PubMed

We investigate the potential energy surfaces and activation energies for reactions between methyl halide molecules CH3X (X = F, Cl, Br, I) and alkali-metal atoms A (A = Li, Na, K, Rb) using high-level ab initio calculations. We examine the anisotropy of each intermolecular potential energy surface (PES) and the mechanism and energetics of the only available exothermic reaction pathway, CH3X + A ? CH3 + AX. The region of the transition state is explored using two-dimensional PES cuts and estimates of the activation energies are inferred. Nearly all combinations of methyl halide and alkali-metal atom have positive barrier heights, indicating that reactions at low temperatures will be slow. PMID:24410225

Lutz, Jesse J; Hutson, Jeremy M

2014-01-01

25

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

26

Amplitude dependence of the internal friction of alkali-halide crystals in an electric field  

NASA Astrophysics Data System (ADS)

The influence of an electrical field on the internal friction of an alkali-halide crystal (AHC) was investigated for relative deformation amplitudes corresponding to separation of dislocations from fastening centers, and for higher amplitudes when plastic deformation of the specimen occurs in an ultrasonic wave field. The influence of the electrical field in the deformation domain under consideration reduces to direct action on charged dislocations, re-orientation of dipole fastening centers, and activation of sources in block boundaries.

Belozerova, É. P.

1989-08-01

27

Long wavelength optical mode frequencies and the Anderson-Gruneisen parameter for alkali halide crystals  

Microsoft Academic Search

The relation between long wavelength optical mode frequencies and the Anderson-Gruneisen parameter delta for alkali halides studied by Madan suffers from a mathematical error which is rectified in the present communication. A theoretical analysis of delta is presented adopting six potential functions for the short range repulsion energy. Values of delta and gammaTO calculated from the Varshni-Shukla potential are found

A. P. Gupta; Jai Shanker

1980-01-01

28

High-pressure optical studies of doped alkali halides. II. Jahn-Teller effects  

Microsoft Academic Search

The emission spectra of heavy-metal-doped alkali halides exhibit a doublet in some temperature ranges at 1 atm. This splitting results from the Jahn-Teller effect which gives excited-state minima corresponding to a tetragonal (AT) and a rhombic (AX) distortion. The latter lies lower in energy. The effect of pressure has been studied on the shifts of the emission peaks and the

W. D. Drotning; H. G. Drickamer

1976-01-01

29

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

30

Mass and orientation effects in dissociative collisions between rare gas atoms and alkali halide molecules  

SciTech Connect

The collision induced dissociation of alkali halide molecules to ion pairs upon impact with hyperthermal rare gas atoms has been investigated using the crossed molecular beam method. Relative total cross sections for the dissociation of CsI, CsBr, RbI, and KI to ion pairs upon collision with xenon and krypton have been measured over a relative collision energy range from threshold to 10 and 8 eV, respectively. In addition, complete angular and energy distributions of both dissociated ions from Xe+CsI, CsBr, and RbI collisions and from Kr+CsI and CsBr collisions have been obtained at several collision energies within the above energy range. Mass, collision orientation, and energy dependence effects observed throughout this work define two limiting case dissociation mechanisms for the Xe(Kr)+MX..-->..Xe(Kr)+M/sup +/+X/sup -/ processes. The dominant dissociation configuration consists of the rare gas atom incident on the light atom end of the alkali halide molecule in a near collinear collision. The less preferred dissociation mechanism results when the rare gas atom is incident in a near collinear configuration on the heavy atom end of the alkali halide molecule. Experimental measurements of the percentage of energy transfer from the relative kinetic energy between Xe(Kr) and MX to the relative motion of M/sup +/--X/sup -/ range as high as 95%; these percentage energy transfers correlate well with the predictions of an impulsive collision model. Three-dimensional classical trajectory calculations using realistic interaction potentials have been performed and they verify the dynamical interpretation suggested by the experiments.

Tully, F.P.; Cheung, N.H.; Haberland, H.; Lee, Y.T.

1980-11-01

31

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

32

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

33

Molecular Simulation of Aqueous Electrolyte Solubility. 3. Alkali-Halide Salts and Their Mixtures in Water and in Hydrochloric Acid  

E-print Network

Molecular Simulation of Aqueous Electrolyte Solubility. 3. Alkali- Halide Salts and Their Mixtures. Phys Chem. B 2011, 115, 7849-7861) for directly calculating the aqueous solubility of electrolytes and are of reasonable accuracy. The accuracy of the calculated solubility is highly dependent on the solid chemical

Lisal, Martin

34

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

35

A Kirkwood-Buff Derived Force Field for Aqueous Alkali Halides  

PubMed Central

A classical nonpolarizable force field is presented for the simulation of aqueous alkali halide solutions (MX), where M = Li+, Na+, K+, Rb+, Cs+ and X = F?, Cl?, Br?, I?, and their interactions with biomolecules. The models are specifically designed to reproduce the experimental Kirkwood-Buff integrals, and thereby the solution salt activities, as a function of salt concentration. Additionally, we demonstrate that these models reasonably reproduce other experimental properties including ion diffusion constants, dielectric decrements, and the excess heats of mixing. The parameters are developed by considering the properties of aqueous NaX and MCl solutions using a previously established model for NaCl. Transferability of the parameters to other salts is then established by the successful simulation of additional aqueous salt solutions, KI and CsBr, not originally included in the parameterization procedure. PMID:21789033

Gee, Moon Bae; Cox, Nicholas R.; Jiao, Yuanfang; Bentenitis, Nikolaos; Weeerasinghe, Samantha; Smith, Paul E.

2011-01-01

36

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

37

Oxidizing agents produced by radiolysis of alkali-metal halide melts  

SciTech Connect

The principal short-lived products from the radiolysis of alkali-metal halide melts are solvated electrons (e/sub s//sup -/), which are particles with the F-center type structure, and molecular anion-radicals of the halogen (GAMMA/sub 2//sup -/); these are formed in the reactions: (1)GAMMA/sup -/ ..-->.. GAMMA/sup 0/ + e/sup -/; (2) e/sup -/ ..-->.. e/sub s//sup -/; (3) GAMMA/sup 0/ + GAMMA/sup -/ ..-->.. GAMMA/sub 2//sup -/. Solvated electrons are strong reducing agents, and they disappear almost completely in rections with the metal cations. Here we are presenting results from a study of the properties of the oxidizer products GAMMA/sub 2//sup -/, by means of a pulse radiolysis method. The optical spectra of the oxidizer components of radiolysis of alkali-metal halide melts, the molecular anion-radicals GAMMA/sub 2//sup -/, are similar to the spectra of the corresponding species in aqueous solutions. Rate constants have been measured for the disappearance of GAMMA/sub 2//sup -/, which goes forward mainly in the reaction of GAMMA/sub 2//sup -/ with the reduced form of the cation. In the presence of alkaline-earth metal cations, owing to the fast disproportionation of their reduced form, there is a greater contribution from the relatively slow reaction of disproportionation of GAMMA/sub 2//sup -/, leading to an observed retardation of the rate of GAMMA/sub 2//sup -/ disappearance and an increase in the yield of molecular halogen.

Makarov, I.E.; Zhukova, T.N.; Pikaev, A.K.; Spitsyn, V.I.

1982-04-01

38

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

39

Dynamics of the defect-mediated desorption of alkali halide surfaces  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

40

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

41

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

SciTech Connect

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

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

1992-10-01

42

6.5: Electron emission from alkali-coated metal photocathodes  

Microsoft Academic Search

Quantum efficiency (QE) of a photoemissive surface is lowered via a sub-monolayer coating of adsorbed alkali metal: we here measure QE of cesium, potassium, and sodium on tungsten and refine theoretical predictions using a hard-sphere model to compare to experiment. We identify variation of the percent-monolayer coverage corresponding to peak QE as affected by adsorbate covalent diameter and substrate lattice

Eric J. Montgomery; D. W. Feldman; P. G. O'Shea; P. Z. Pan; N. Sennett; K. L. Jensen

2010-01-01

43

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

PubMed

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

Mao, Albert H; Pappu, Rohit V

2012-08-14

44

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

45

Alkali halide solutions under thermal gradients: soret coefficients and heat transfer mechanisms.  

PubMed

We report an extensive analysis of the non-equilibrium response of alkali halide aqueous solutions (Na(+)/K(+)-Cl(-)) to thermal gradients using state of the art non-equilibrium molecular dynamics simulations and thermal diffusion forced Rayleigh scattering experiments. The coupling between the thermal gradient and the resulting ionic salt mass flux is quantified through the Soret coefficient. We find the Soret coefficient is of the order of 10(-3) K(-1) for a wide range of concentrations. These relatively simple solutions feature a very rich behavior. The Soret coefficient decreases with concentration at high temperatures (higher than T ? 315 K), whereas it increases at lower temperatures. In agreement with previous experiments, we find evidence for sign inversion in the Soret coefficient of NaCl and KCl solutions. We use an atomistic non-equilibrium molecular dynamics approach to compute the Soret coefficients in a wide range of conditions and to attain further microscopic insight on the heat transport mechanism and the behavior of the Soret coefficient in aqueous solutions. The models employed in this work reproduce the magnitude of the Soret coefficient, and the general dependence of this coefficient with temperature and salt concentration. We use the computer simulations as a microscopic approach to establish a correlation between the sign and magnitude of the Soret coefficients and ionic solvation and hydrogen bond structure of the solutions. Finally, we report an analysis of heat transport in ionic solution by quantifying the solution thermal conductivity as a function of concentration. The simulations accurately reproduce the decrease of the thermal conductivity with increasing salt concentration that is observed in experiments. An explanation of this behavior is provided. PMID:23758489

Römer, Frank; Wang, Zilin; Wiegand, Simone; Bresme, Fernando

2013-07-11

46

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

PubMed

The scaled versions of the newly introduced [S. S. Xantheas and J. C. Werhahn, J. Chem. Phys. 141, 064117 (2014)] generalized forms of some popular potential energy functions (PEFs) describing intermolecular interactions--Mie, Lennard-Jones, Morse, and Buckingham exponential-6--have been used to fit the ab initio relaxed approach paths and fixed approach paths for the halide-water, X(-)(H2O), X = F, Cl, Br, I, and alkali metal-water, M(+)(H2O), M = Li, Na, K, Rb, Cs, interactions. The generalized forms of those PEFs have an additional parameter with respect to the original forms and produce fits to the ab initio data that are between one and two orders of magnitude better in the ?(2) than the original PEFs. They were found to describe both the long-range, minimum and repulsive wall of the respective potential energy surfaces quite accurately. Overall the 4-parameter extended Morse (eM) and generalized Buckingham exponential-6 (gBe-6) potentials were found to best fit the ab initio data for these two classes of ion-water interactions. The fitted values of the parameter of the (eM) and (gBe-6) PEFs that control the repulsive wall of the potential correlate remarkably well with the ionic radii of the halide and alkali metal ions. PMID:25134562

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

2014-08-14

47

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

48

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

E-print Network

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

Nadeau, Patrick; Di Stefano, P C F; Lanfranchi, J -C; Roth, S; von Sivers, M; Yavin, Itay

2014-01-01

49

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

E-print Network

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

Patrick Nadeau; Michael Clark; P. C. F. Di Stefano; J. -C. Lanfranchi; S. Roth; M. von Sivers; Itay Yavin

2014-10-06

50

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

51

Effect of radiation-induced emission of Schottky defects on the formation of colloids in alkali halides  

NASA Astrophysics Data System (ADS)

Formation of vacancy clusters in irradiated crystals is considered taking into account radiation-induced Schottky defect emission (RSDE) from extended defects. RSDE acts in the opposite direction compared with Frenkel pair production, and it results in the radiation-induced recovery processes. In the case of alkali halides, Schottky defects can be produced as a result of the interaction of extended defects with excitons , as has been suggested by Seitz in 1954. We consider a model that takes into account excitonic mechanisms for the creation of both Frenkel and Schottky defects, and which shows that although the contribution of the latter mechanism to the production of primary defects may be small, its role in the radiation-induced evolution of microstructure can be very significant. The model is applied to describe the evolution of sodium colloids and the formation of voids in NaCl, which is followed by a sudden fracture of the material, presenting a potential problem in rock salt-based nuclear waste repositories. The temperature, dose rate and dose dependence of colloid growth in NaCl doped with different types of impurities is analyzed. We have found that colloid growth may become negative below a threshold temperature (or above a threshold dose rate), or below a certain impurity concentration , which is determined by the RSDE, that depends strongly on the type and concentration of the impurities. The results obtained with the model are compared with experimental observations.

Dubinko, V. I.; Vainshtein, D. I.; den Hartog, H. W.

2003-10-01

52

Aqueous alkali halide solutions: can osmotic coefficients be explained on the basis of the ionic sizes alone?  

PubMed Central

We use the AMSA, associative mean spherical theory of associative fluids, to study ion–ion interactions in explicit water. We model water molecules as hard spheres with four off-center square-well sites and ions as charged hard spheres with sticky sites that bind to water molecules or other ions. We consider alkali halide salts. The choice of model parameters is based on two premises: (i) The strength of the interaction between a monovalent ion and a water molecule is inversely proportional to the ionic (crystal) diameter ?i. Smaller ions bind to water more strongly than larger ions do, taking into account the asymmetry of the cation–water and anion–water interactions. (ii) The number of contacts an ion can make is proportional to ?i2. In short, small ions bind waters strongly, but only a few of them. Large ions bind waters weakly, but many of them. When both a monovalent cation and anion are large, it yields a small osmotic coefficient of the salt, since the water molecules avoid the space in between large ions. On the other hand, salts formed from one small and one large ion remain hydrated and their osmotic coefficient is high. The osmotic coefficients, calculated using this model in combination with the integral equation theory developed for associative fluids, follow the experimental trends, including the unusual behavior of caesium salts. PMID:20405084

Kalyuzhnyi, Yu V.; Vlachy, Vojko; Dill, Ken A.

2014-01-01

53

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

54

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

55

Photocathode aging in MCP PMT  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

56

Effects of Alkali Metal Halide Salts on the Hydrogen Bond Network of Liquid Water Christopher D. Cappa, Jared D. Smith, Kevin R. Wilson, Benjamin M. Messer, Mary K. Gilles,  

E-print Network

Form: February 7, 2005 Measurements of the oxygen K-edge X-ray absorption spectrum (XAS) of aqueousEffects of Alkali Metal Halide Salts on the Hydrogen Bond Network of Liquid Water Christopher D network beyond the first solvation shell. This contrasts the temperature-dependent spectral variations

Cohen, Ronald C.

57

JOURNAL DE PHYSIQUE Colloque C 4, Supplkment au no 8-9, tome 28, Aozit-Septembre 1967,pages C 4-120 OH-DIPOLE CENTERS IN ALKALI HALIDES (*)  

E-print Network

- dipoles and charged point defects (Frenkel pairs) were quantitatively studied, using the electro (paires de Frenkel). Abstract. - Alkali halides containing substitutional OH- ions have become prominent and phonons. Interaction effects among concentrated OH - dipole systems and among systems of diluted OH

Paris-Sud XI, Université de

58

Development of processes for the production of solar grade silicon from halides and alkali metals, Phase 1 and Phase 2. Final report, October 1979 - February 1981  

SciTech Connect

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.

1981-03-01

59

Time-dependent quantum calculations of negative ion formation in scattering of atoms from alkali-halide surfaces  

E-print Network

-halide surfaces G.R. Darling a,*, R. Kosloff b , Y. Zeiri c a Surface Science Research Centre, Department-151-794-3888; fax: +44- 151-708-0662. E-mail address: darling@liv.ac.uk (G.R. Darling). 0039-6028/02/$ - see front

Zeiri, Yehuda

60

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

61

Preparation of negative electron affinity gallium nitride photocathode  

NASA Astrophysics Data System (ADS)

Negative electron affinity (NEA) Gallium Nitride (GaN) photocathode is an ideal new kind of UV photocathode. NEA GaN photocathode is widely used in such fields as high-performance ultraviolet photoelectric detector, electron beam lithography etc. The preparation of negative electron affinity gallium nitride photocathode relates to the growth technology, the cleaning method, the activation method and the evaluation of photocathode. The mainstream growth technology of GaN photocathode such as metal organic chemistry vapor phase deposits technology, molecule beam epitaxial technology and halide vapor phase epitaxial technology were discussed. The chemical cleaning method and the heat cleaning method for GaN photocathode were given in detail. After the chemical cleaning, the atom clean surface was gotten by a 700 °C heat about 20 minutes in the vacuum system. The activation of GaN photocathode can be realized with only Cs or with Cs/O alternately. Using the activation and evaluation system for NEA photocathode, the photocurrent curve during Cs activation process for GaN photocathode was gotten. The evaluation of photocathode can be done by measuring the quantum efficiency. Employing the UV spectral response measurement instrument, the spectral response and quantum efficiency of NEA GaN photocathode were measured. The measured quantum efficiency of reflection-mode NEA GaN photocathode reached up to 37% at 230 nm.

Qiao, Jianliang; Chang, Benkang; Qian, Yunsheng; Du, Xiaoqing; Zhang, Yijun; Wang, Xiaohui

2010-10-01

62

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

63

Biological photocathodes.  

PubMed Central

Biological surfaces emit electrons when subjected to UV light. This emission is increased greatly after exposure to cesium vapor. Increases from 2 to 3 orders of magnitude are observed, depending on the biochemicals present. Heme and chlorophyll exhibit unusually high photoemission currents, which are increased further after cesiation. Photoemission from proteins and lipids is much less but also is increased by exposure to cesium. The formation of photocathodes with cesium greatly increases the practical magnifications attainable in photoelectron microscopy of organic and biological specimens. Photoelectron micrographs taken at magnifications greater than or equal to X 100,000 of chlorophyll-rich thylakoid membranes and of colloidal gold-labeled cytoskeleton preparations of cultured epithelial cells demonstrate the improvement in magnification. The selectivity and stability of the photocathodes suggest the possibility of detecting chromophore binding proteins in membranes and the design of photoelectron labels for tagging specific sites on biological surfaces. Images PMID:2928305

Griffith, O H; Habliston, D L; Birrell, G B; Skoczylas, W P; Hedberg, K K

1989-01-01

64

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

65

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

66

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

67

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

68

Electrorefining of zirconium metal in alkali chloride and alkali fluoride fused electrolytes  

Microsoft Academic Search

The electrorefining of zirconium metal in alkali halide melts has been investigated. Variables affecting the electrodeposition process such as the composition of the electrolyte, the current density, and the configuration of the electrodes were studied. Two types of electrolytes were used: the alkali chloride-rich and the alkali fluoride-rich electrolytes. The various electrolytes are considered in terms of their ability to

S. N. Flengas; G. J. Kipouros

1985-01-01

69

Optical and Spectral Studies on beta Alanine Metal Halide Hybrid Crystals  

Microsoft Academic Search

We have synthesized and grown beta alanine metal halide hybrid crystals viz. beta alanine cadmium chloride (BACC), an amino acid transition metal halide complex crystal and beta alanine potassium chloride (BAPC), an amino acid alkali metal halide complex crystal by slow evaporation method. The grown crystals were found to be transparent and have well defined morphology. The optical characteristics of

M. Daniel Sweetlin; P. Selvarajan; S. Perumal; S. Ramalingom

2011-01-01

70

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

71

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

72

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

73

Debye-Waller factors of alkali halides  

SciTech Connect

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

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

1998-01-01

74

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

75

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

76

Robust activation method for negative electron affinity photocathodes  

DOEpatents

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

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

2011-09-13

77

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

SciTech Connect

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

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

2011-04-14

78

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

79

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

80

Photocathodes for free electron lasers  

SciTech Connect

Many different photocathodes have been used as electron sources for FELs and other electron accelerator systems. In choosing one, a compromise between lifetime and quantum efficiency have been unavoidable. High quantum efficiency photocathodes such as CsK{sub 2}Sb, Cs{sub 3}Sb, and cesiated GaAs have short operational lifetimes and require an ultrahigh-vacuum environment. Long lifetime photocathodes such as LaB{sub 6}, Cu, and Y have relatively low quantum efficiencies. However, recently, cesium telluride was found to be an exception. Initial results from CERN and now at Los Alamos have shown that Cs{sub 2}Te is reasonably rugged with a high quantum efficiency below 270 nm. Further studies were carried out at Los Alamos in determining its performance as an electron source for the Los Alamos Advanced FEL. The Los Alamos Advanced FEL was successfully operated at 5-6 microns with a Cs{sub 2}Te photocathode driven by a frequency quadrupled Nd:YLF laser as the electron source. Cs{sub 2}Te photocathodes with quantum efficiencies of 12-18% at 254 mn were fabricated in an ultrahigh-vacuum chamber and transferred under high vacuum to the FEL. The authors estimated that the operational lifetime of Cs{sub 2}Te photocathodes to be at least 20 times that for K{sub 2}CsSb photocathodes. Furthermore, experiments in the fabrication chamber have shown that heating to 150-200{degrees}C photocathodes exposed for one hour at 2{times}10{sup {minus}4} torr of air was sufficient to revive the quantum efficiency from below 1% to about 10%. The electron beam for the FEL extracted from a cesium telluride target was also characterized. The emittance, response time, saturation level and dark current of cesium telluride photocathodes was determined to be sufficient for FEL applications.

Kong, S.H.; Kinross-Wright, J.; Nuguyen, D.C.; Sheffield, R.L.

1994-09-01

81

Combustion synthesis of nano-sized tungsten carbide powder and effects of sodium halides  

Microsoft Academic Search

The synthesis of nano-size tungsten carbide powder has been investigated with a WO3 + Mg + C + carbonate system using alkali halides. The effects of different types of alkali halides on combustion temperature\\u000a and tungsten carbide formation were discussed. Sodium fluoride had a notable effect on the particle size of the product and\\u000a the degree of transformation from the initial mixture. A small amount

H. I. Won; H. H. Nersisyan; C. W. Won

2010-01-01

82

Optical and Spectral Studies on ? Alanine Metal Halide Hybrid Crystals  

NASA Astrophysics Data System (ADS)

We have synthesized and grown ? alanine metal halide hybrid crystals viz. ? alanine cadmium chloride (BACC), an amino acid transition metal halide complex crystal and ? alanine potassium chloride (BAPC), an amino acid alkali metal halide complex crystal by slow evaporation method. The grown crystals were found to be transparent and have well defined morphology. The optical characteristics of the grown crystals were carried out with the help of UV-Vis Spectroscopy. The optical transmittances of the spectrums show that BAPC is more transparent than BACC. The Photoluminescence of the materials were determined by the Photoluminescent Spectroscopy

Sweetlin, M. Daniel; Selvarajan, P.; Perumal, S.; Ramalingom, S.

2011-10-01

83

Recent Progress toward Robust Photocathodes  

SciTech Connect

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

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

2009-08-04

84

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

85

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.

86

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

87

Metal-halide mixtures for latent heat energy storage  

NASA Technical Reports Server (NTRS)

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

Chen, K.; Manvi, R.

1981-01-01

88

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

89

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

90

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

91

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

92

Third-Order Elastic Constants of Alkali Halide Crystals  

Microsoft Academic Search

Third-order elastic constants of NaCl-type and CsCl-type crystals have been calculated using the Born model of ionic solids. Short-range repulsive interactions have been included up to second-nearest neighbors. Assuming that the temperature variation of these constants is linear, we have calculated the temperature coefficients aalphabetagamma in the high-temperature limit. In the case of NaCl-type crystals, C111, C112, and C166 are

P. B. Ghate

1965-01-01

93

Ionic Thermocurrents in Alkali Halide Crystals Containing Substitutional Beryllium Ions  

Microsoft Academic Search

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

Cesare Bucci

1967-01-01

94

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

95

Photocathodes for the energy recovery linacs  

Microsoft Academic Search

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

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

2006-01-01

96

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

97

Photocathode Preparation System for the ALICE Photoinjector  

NASA Astrophysics Data System (ADS)

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

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

2009-08-01

98

Photocathode Preparation System for the ALICE Photoinjector  

SciTech Connect

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

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

2009-08-04

99

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

100

Transport Mechanisms in Polarized Semiconductor Photocathodes  

SciTech Connect

We investigated the effect of an accelerating field on the spin polarization of photogenerated electrons in a 100nm thick GaAs based photocathode active region. By decreasing the transport time of the electrons and the number of scattering events that cause depolarization, we expected to increase the polarization as was indicated by Monte Carlo simulations of the scattering and transport time statistics of the electrons. A tungsten (W) grid was deposited on the cathode surface to provide a uniform voltage distribution across the cathode surface. The metal grid formed a Schottky contact with the semiconductor surface. The bias voltage was primarily dropped at the metal semiconductor interface region, which is the cathode active region. For positive surface bias, the accelerating voltage not only increased the polarization, but it also enhanced the quantum efficiency of the photocathode. Preliminary results verify the bias effect on both quantum efficiency and polarization by a factor of 1.8 and 1% respectively.

Ioakeimidi, K.; Brachmann, A.; Clendenin, J.E.; Garwin, E.L.; Kirby, R.E.; Maruyama, T.; Prescott, C.Y.; /SLAC; Prepost, R.; /Wisconsin U., Madison

2006-12-18

101

Progress on lead photocathodes for superconducting injectors  

SciTech Connect

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

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

2005-05-16

102

PROGRESS ON LEAD PHOTOCATHODES FOR SUPERCONDUCTING INJECTORS.  

SciTech Connect

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

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

2005-05-16

103

Negative affinity X-ray photocathodes  

NASA Technical Reports Server (NTRS)

A new X-ray image intensifier is described. The device should eventually have a quantum efficiency which is an order of magnitude greater than that of presently available high spatial resolution X-ray detectors, such as microchannel plates. The new intesifier is based upon a GaAs crystal photocathode which is activated to achieve negative electron affinity. Details concerning the detector concept are discussed together with the theoretical relations involved, X-ray data, and optical data.

Vanspeybroeck, L.; Kellogg, E.; Murray, S.; Duckett, S.

1974-01-01

104

Microwave-assisted hydrothermal hydrolysis of cellobiose and effects of additions of halide salts.  

PubMed

Microwave irradiation was compared with induction heating for hydrothermal hydrolysis of cellobiose. Microwave heating improved glucose selectivity and resulted in a pH of the hydrolyzates that was ?0.57 units lower than those from conventional heating, which suggests that fewer side-reactions occurred. Halide salts of alkali and alkali earth metals improved microwave-assisted hydrothermal saccharification of cellobiose at lower reaction severity by around 0.3 of logR(0). NaCl addition of ?10mM reduced the required microwave output to 58.6-66.2% as compared to conventional microwave-hydrothermal hydrolysis without halide salts. Kinetic analyses revealed that the addition of salt increased the hydrolysis rate by increasing the frequency factor of the reaction. The results showed that microwave irradiation in the presence of microwave-absorbing salts is effective for hydrothermal hydrolysis of carbohydrates. PMID:22939594

Tsubaki, Shuntaro; Oono, Kiriyo; Onda, Ayumu; Yanagisawa, Kazumichi; Azuma, Jun-Ichi

2012-11-01

105

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

106

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

107

Enhancement of photoemission from and postprocessing of K2CsSb photocathode using excimer laser  

NASA Astrophysics Data System (ADS)

The high quantum efficiency at visible wavelengths of alkali-antimonide photoemissive materials, such as K2CsSb, makes them excellent potential photocathodes for high-current applications. We have developed a technique of using an ultraviolet laser to clean the cathode's substrate and thus enhance the photoyield of a K2CsSb photocathode subsequently deposited on the substrate. We have shown that the quantum efficiency of the cathode from the laser-exposed substrate can be at least 50% higher than that of an unexposed surface. We have also formulated a nonthermal technique for completely removing the cathode from the substrate while preserving an ultrahigh vacuum to assure the regrowth of the cathode. The bialkali cathode is dissociated and then removed completely upon 10 s exposure to a 248 nm laser beam with 3.5 mJ/mm2 of energy density at a 30 Hz repetition frequency. Here, we discuss these experimental results and their potential applications. We also describe applications of this technique to reduce the beam's halo and its emittance.

Wang, Erdong; Rao, Triveni; Ben-zvi, Ilan

2014-02-01

108

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

109

Radiochemical synthesis of pure anhydrous metal halides  

NASA Technical Reports Server (NTRS)

Method uses radiation chemistry as practical tool for inorganic preparations and in particular deposition of metals by irradiation of their aqueous metal salt solutions with high energy electrons. Higher valence metal halide is dissolved in organic liquid and exposed to high energy electrons. This causes metal halide to be reduced to a lower valence metal halide.

Philipp, W. H.; Marsik, S. J.; May, C. E.

1973-01-01

110

Modern theory and applications of photocathodes  

SciTech Connect

Over the last thirty years, the Spicer Three-Step model has provided a very useful description of the process of photoemission for both fundamental and practical applications. By treating photoemission in terms of three successive steps-optical absorption, electron transport, and escape across the surface this theory allows photoemission to be related to parameters of the emitter, such as the optical absorption coefficient, electron scattering mechanisms, and the height of the potential barrier at the surface. Using simple equations and established parameters, the Three-Step model predicts the performance of cathodes and provides detailed understanding of the unexpected phenomena that appear when photocathodes are pushed into new practical domains. As an example, time responses are estimated for existing cathodes, and are found to cover a range of six orders of magnitude. Further, the time response is found to be directly related to the sensitivity (i.e., quantum efficiency) of the cathode. The quantum yield systematically decreases with the time response. Thus, metals are predicted to have the shortest time response (as little as 10{sup {minus}15} sec) and the smallest quantum efficiency (as little as 10{sup {minus}4} electrons per photon), whereas the negative affinity photocathodes have high yield (as high as 0.6 electrons per photon) but long response times (as long as 10{sup {minus}9} sec). Other applications of the Three-Step model are discussed.

Spicer, W.E.; Herrera-Gomez, A.

1993-08-01

111

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

112

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

113

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

114

Observation of a charge limit for semiconductor photocathodes  

SciTech Connect

The Stanford Linear Accelerator Center is currently operating with a photocathode electron gun (PEG) to produce polarized electrons for its experimental program. Bunch intensities of up to 10[sup 11] electrons within 2 ns (8 A) are required from the electron gun. Operation of PEG has demonstrated a charge limit phenomenon, whereby the charge that can be extracted from the gun with an intense laser beam saturates at significantly less than 10[sup 11] electrons (the expected space-charge-limited charge) when the photocathode quantum efficiency is low. Studies of this charge limit phenomenon observed with a GaAs photocathode are reported.

Woods, M.; Clendenin, J.; Frisch, J.; Kulikov, A.; Saez, P.; Schultz, D.; Turner, J.; Witte, K.; Zolotorev, M. (Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309 (United States))

1993-06-15

115

Observation of a charge limit for photocathode electron guns  

SciTech Connect

The Photocathode Electron Gun (PEG) at SLAC is required to produce bunch intensities of up to 10{sup 11} electrons within 2 ns (8 Amps). Operation of PEG has demonstrated a `Charge Limit` phenomenon, whereby the charge that can be extracted from the gun with an intense laser beam saturates at significantly less than 10{sup 11} electrons (the expected `Space Charge Limited` charge) when the photocathode Quantum Efficiency is low. We report studies of this Charge Limit phenomenon observed with a GaAs photocathode.

Woods, M.; Clendenin, J.; Frisch, J.; Kulikov, A.; Saez, P.; Schultz, D.; Turner, J.; Witte, K.; Zolotorev, M.

1992-12-01

116

Observation of a charge limit for photocathode electron guns  

SciTech Connect

The Photocathode Electron Gun (PEG) at SLAC is required to produce bunch intensities of up to 10[sup 11] electrons within 2 ns (8 Amps). Operation of PEG has demonstrated a 'Charge Limit' phenomenon, whereby the charge that can be extracted from the gun with an intense laser beam saturates at significantly less than 10[sup 11] electrons (the expected Space Charge Limited' charge) when the photocathode Quantum Efficiency is low. We report studies of this Charge Limit phenomenon observed with a GaAs photocathode.

Woods, M.; Clendenin, J.; Frisch, J.; Kulikov, A.; Saez, P.; Schultz, D.; Turner, J.; Witte, K.; Zolotorev, M.

1992-12-01

117

Jefferson Lab IR demo FEL photocathode quantum efficiency scanner  

SciTech Connect

Jefferson Laboratory's Free Electron Laser (FEL) incorporates a cesiated gallium arsenide (GaAs) DC photocathode gun as its electron source. By using a setof scanning mirrors, the surface of the GaAs wafer is illuminated with a 543.5nm helium-neon laser. Measuring the current flow across the biased photocathodegenerates a quantum efficiency (QE) map of the 1-in. diameter wafer surface. The resulting QE map provides a very detailed picture of the efficiency of thewafer surface. By generating a QE map in a matter of minutes, the photocathode scanner has proven to be an exceptional tool in quickly determining sensitivityand availability of the photocathode for operation.

Grippo, Albert; Gubeli, Joseph; Jordan, Kevin; Michelle D. Shinn; Evans, Richard

2001-12-01

118

Alkali Soils, Irrigation Waters.  

E-print Network

, or it may be carried away to accumulate in another field. JVhen water comes in contact with the soil, it dissolves the soluble constituents as far as it penetrates. If afterwards it rises and evap- orates, it leaves there all the alkali which it held... Vetch .................................. The Bureau cf Soils of the United States Department of Agriculture divides soils into six grades, according to their average of soluble calts to a depth of six feet. - Percentage Black of Total Salts Alkali...

Fraps, G. S. (George Stronach)

1910-01-01

119

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

120

Design study of a L-band photocathode RF injector  

NASA Astrophysics Data System (ADS)

In the proposal of the Beijing Advanced Light Source, a compact combination of XERL and XFEL using a common SC linac is being considered. In the meantime, an ERL-FEL test facility is being proposed and will be used for THz radiation. In this test facility, a L-band photocathode RF injector is needed. In this paper, we give the physical design of the L-band photocathode RF injector for the test facility.

Zhu, Xiong-Wei; Wang, Shu-Hong; Chen, Sen-Yu

2010-02-01

121

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

122

Milk-alkali syndrome.  

PubMed

Milk-alkali syndrome (MAS) consists of hypercalcemia, various degrees of renal failure, and metabolic alkalosis due to ingestion of large amounts of calcium and absorbable alkali. This syndrome was first identified after medical treatment of peptic ulcer disease with milk and alkali was widely adopted at the beginning of the 20th century. With the introduction of histamine2 blockers and proton pump inhibitors, the occurrence of MAS became rare; however, a resurgence of MAS has been witnessed because of the wide availability and increasing use of calcium carbonate, mostly for osteoporosis prevention. The aim of this review was to determine the incidence, pathogenesis, histologic findings, diagnosis, and clinical course of MAS. A MEDLINE search was performed with the keyword milk-alkali syndrome using the PubMed search engine. All relevant English language articles were reviewed. The exact pathomechanism of MAS remains uncertain, but a unique interplay between hypercalcemia and alkalosis in the kidneys seems to lead to a self-reinforcing cycle, resulting in the clinical picture of MAS. Treatment is supportive and involves hydration and withdrawal of the offending agents. Physicians and the public need to be aware of the potential adverse effects of ingesting excessive amounts of calcium carbonate. PMID:19252114

Medarov, Boris I

2009-03-01

123

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

124

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

125

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

126

rf phase stabilization for rf photocathode gun through electro-optical monitoring  

NASA Astrophysics Data System (ADS)

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

Leung, King P.; Yu, Li-Hua; Ben-Zvi, Ilan

1993-11-01

127

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

SciTech Connect

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

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

1993-08-01

128

Thermoelectric Power of Silver Halides  

Microsoft Academic Search

Thermoelectric power measurements have been made on the systems AgCl+CdCl2, AgBr+Ag2S, and AgBr+CdS, as well as the pure silver halides, in the temperature range from 100° to 400°C. Silver metal electrodes were used. The behavior of AgCl and CdCl2 is similar to the previously investigated AgBr+CdBr2 system, except that the effect of the impurity is more pronounced in AgCl. The

R. W. Christy

1961-01-01

129

New layered manganese oxide halides.  

PubMed

The first layered manganese(III) oxide chlorides, Sr2MnO3Cl and Sr4Mn3O8-yCl2, have been synthesised; Sr2MnO3Cl adopts a K2NiF4 type structure with sheets of MnO5 square based pyramids linked through oxygen and separated by SrCl layers; it is the end member of a new family of Ruddlesden-Popper type manganese oxide halides which includes the three-layer member Sr4Mn3O8-yCl2 also reported herein. PMID:12120392

Knee, Christopher S; Weller, Mark T

2002-02-01

130

Polarized Photocathode R and D for Future Linear Colliders  

SciTech Connect

It is a challenge to generate full charge electrons from the electron sources without compromising polarization for the proposed ILC and CLIC. It is essential to advance polarized photocathodes to meet the requirements. SLAC has worldwide unique dedicated test facilities, Cathode Test System and dc-Gun Test Laboratory, to fully characterize polarized photocathodes. Recent systematic measurements on a strained-well InAlGaAs/AlGaAs cathode at the facilities show that 87% polarization and 0.3% QE are achieved. The QE can be increased to approx1.0% with atomic hydrogen cleaning. The surface charge limit at a very low current intensity and the clear dependence of the polarization on the surface charge limit are observed for the first time. Ongoing programs to develop photocathodes for the ILC and CLIC are briefly introduced.

Zhou, F.; Brachmann, A.; Maruyama, T.; Sheppard, J. C. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States)

2009-08-04

131

FEMTO SECOND ELECTRON BEAM DIFFRACTION USING A PHOTOCATHODE RF GUN.  

SciTech Connect

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

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

2003-05-12

132

Intrinsic Emittance Reduction of an Electron Beam from Metal Photocathodes  

SciTech Connect

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

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

2010-06-11

133

A polarization study of strained GaAs photocathode structures  

SciTech Connect

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

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

1996-10-01

134

Analysis of Slice Transverse Emittance Evolution ina Photocathode RF Gun  

SciTech Connect

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

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

2007-10-17

135

SLAC rf photocathode gun test facility  

NASA Astrophysics Data System (ADS)

A high brightness electron injector is a necessary component for x-ray FELs. A dedicated rf gun test facility is being developed at SLAC to measure the phase space distribution from a photocathode rf gun generated electron beam. This Gun Test Facility will allow optimization of the beam brightness by independently adjusting parameters such as accelerating field, laser pulse shape and total charge. The test facility is comprised of a single S-band klystron, 3 m SLAC linac section, analyzing magnet, diagnostic section, a cathode drive laser and the gun under test. The laser is comprised of a Nd:YLF oscillator and a Nd:glass regenerative amplifier. The light incident on the cathode is capable of both normal and near grazing incidence and is currently frequency quadrupled into the UV. In the near future a Nd:glass oscillator will be installed which will be capable of generating pulses as short as 200 fs. This oscillator will be used to make emittance measurements as a function of the laser pulse width and shape. Both oscillators will be phase-locked to the 24th sub-harmonic of the linac frequency. Emittance measurements will be made downstream of the linac at an electron beam energy of approximately 30 - 50 MeV using a quad scan with a beam profile screen and/or a wire scanner to measure the spot size. A current transformer and a Faraday cup will be used to measure the charge while a streak camera or a transition radiator can be used to measure the micropulse width. The first gun to undergo testing will be the BNL/SLAC/UCLA 1.6 cell symmetrized cavity gun with a copper cathode. With field gradients in the gun as high as 150 MV/m, using solenoidal emittance compensation and spatial and temporal flat top laser pulses, PARMELA simulations predict normalized emittances of less than 1.5 pi mm-mrad with 10 ps long pulses and 1 nC of charge after acceleration in a 3 meter linac section to about 30 MeV. Appropriate additional acceleration can further reduce the emittance below 1 pi mm-mrad.

Schmerge, John F.; Reis, David A.; Hernandez, Mike; Meyerhofer, David D.; Miller, Roger H.; Palmer, Dennis T.; Weaver, Jim N.; Winick, Herman; Yeremian, A. D.

1997-05-01

136

Polarized Light Sources for photocathode electron guns at SLAC  

SciTech Connect

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

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

1992-12-01

137

High gradient acceleration in a 17 GHz photocathode RF gun  

Microsoft Academic Search

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

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

1993-01-01

138

Scope channel Photo-cathode UV laser light  

E-print Network

1 Scope channel Anode Photo-cathode UV laser light 2mm grid spacer 4.45mm grid spacer Top MCP atmospheric pressure (when pumped) Demountable (typical vacuum gauge reading ~ 1e-6 torr) Stack compression: cross bars screwed onto the tray 8" chamber (typical vacuum gauge reading ~ 1e-8 torr) Test Setups #12

139

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...

140

Reactions of Organic Halides in Solution  

Microsoft Academic Search

REACTIONS of organic halides in solution which involve substitution by a nucleophilic reagent at a saturated carbon atom have been extensively studied by Hughes, Ingold and co-workers1. These authors conclude that reactions of this type may occur by two possible mechanisms, a unimolecular mechanism SN1 or a bimolecular mechanism SN2. The increase in the unimolecular SN1 reaction-rate of the halide

Alwyn G. Evans

1946-01-01

141

Preparation of alkali metal dispersions  

NASA Technical Reports Server (NTRS)

A method is described for producing alkali metal dispersions of high purity. The dispersions are prepared by varying the equilibrium solubility of the alkali metal in a suitable organic solvent in the presence of aromatic hydrocarbons. The equilibrium variation is produced by temperature change. The size of the particles is controlled by controlling the rate of temperature change.

Rembaum, A.; Landel, R. F. (inventors)

1968-01-01

142

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

143

UV pulse shaping for the photocathode RF gun  

NASA Astrophysics Data System (ADS)

Recently, manipulation with the drive laser plays a significant role in high brightness electron beam production by the photocathode RF gun. The article takes efforts on the temporal shaping of the driving laser for the photocathode RF gun. Method based on pulse stacking by birefringent crystal of ?-BBO serials was tried to directly shape ultraviolet laser pulse. Using four pieces of ?-BBO crystals to separate an input UV pulse with appropriate duration into 16 sub-pulses can form a ps-spaced pulse train suitable for coherent THz production. The group delay dispersion induced by the crystals was also carefully considered. To avoid beam deterioration by long path propagation, imaging relay of the shaped pulse was applied.

Yan, Lixin; Du, Qiang; Du, Yingchao; Hua, Jianfei; Huang, Wenhui; Tang, Chuanxiang

2011-05-01

144

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

145

Extreme ultraviolet quantum detection efficiency of rubidium bromide opaque photocathodes  

NASA Technical Reports Server (NTRS)

Measurements are presented of the quantum detection efficiency (QDE) of three samples of RbBr photocathode layers over the 44-150-A wavelength range. The QDE of RbBr-coated microchannel plate (MCP) was measured using a back-to-back Z-stack MCP configuration in a detector with a wedge and strip position-sensitive anode, of the type described by Siegmund et al. (1984). To assess the stability of RbBr layer, the RbBr photocathode was exposed to air at about 30 percent humidity for 20 hr. It was found that the QDE values for the aged cathode were within the QDE measurement errors of the original values. A simple QDE model was developed, and it was found that its predictions are in accord with the QDE measurements.

Siegmund, Oswald H. W.; Gaines, Geoffrey A.

1990-01-01

146

Sealed gaseous photomultiplier with CsI photocathode  

NASA Astrophysics Data System (ADS)

A sealed gaseous photomultiplier tube (PMT) with a CsI photocathode has been developed using a micropattern gas detector (MPGD) made of Pyrex glass. A microblasting technique (MB) was employed for the production of a new hole-type MPGD. We investigated gaseous PMTs with a semi-transparent CsI photocathode for two different gas mixtures of Ne(90%)+i-C 4H 10 (10%) and Ne (90%)+CF 4 (10%) at a gas pressure of 700 torr. Gains of up to 10 5 were attained with the microblasted glass plate (MB-GP) for both neon gas mixtures. Quantum efficiencies of up to 0.5% were obtained for UV light at the wavelength of 170 nm. The results of the aging test and the characteristics in a high magnetic-field environment are described for the gaseous PMT filled with neon gas mixture.

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

2011-02-01

147

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

148

The upgraded photocathode laser of the TESLA Test Facility  

NASA Astrophysics Data System (ADS)

This paper describes the photocathode laser of the TESLA Test Facility (TTF). The laser system generates trains of ultraviolet picosecond pulses with 262 nm wavelength. Special measures were required to allow for stable and reliable generation of these pulse trains that are up to 800 ?s long and can contain up to 800 micropulses at 1 MHz repetition rate, alternatively, up to 2400 micropulses at 3 MHz repetition rate within the train. The duration of the individual micropulses is 11 ps FWHM ( ?˜4.5 ps). In the 1 MHz mode the micropulse energy at 262 nm wavelength reaches 54 ?J. Laser pulses are generated synchronously to the RF system of the TTF-2 linear accelerators (linac) with synchronization accuracy better than 1 ps. The laser is able to run at 10 Hz repetition rate with full remote control. It illuminates the photocathode of an RF gun to generate the electron bunches which are subsequently accelerated in the TTF linac.

Will, I.; Koss, G.; Templin, I.

2005-04-01

149

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

SciTech Connect

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

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

1984-08-27

150

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

151

Comparison of cesium iodide and gold photocathodes for x-ray streak cameras  

Microsoft Academic Search

X-ray streak cameras at Lawrence Livermore Laboratory use gold transmission photocathodes for x-ray detection. Other photocathode materials which might provide improved sensitivity without loss of temporal resolution are of interest. Of particular interest are dielectrics such as cesium iodide. Simultaneous measurements of the sensitivity to 500 eV x-rays of both gold and cesium iodide photocathodes in the LLL Soft X-ray

G. L. Stradling; H. Medecki; D. T. Attwood; R. L. Kauffman; B. L. Henke

1979-01-01

152

Advanced Laser Technologies for High-brightness Photocathode Electron Gun  

NASA Astrophysics Data System (ADS)

A laser-excited photocathode RF gun is one of the most reliable high-brightness electron beam sources for XFELs. Several 3D laser shaping methods have been developed as ideal photocathode illumination sources at SPring-8 since 2001. To suppress the emittance growth caused by nonlinear space-charge forces, the 3D cylindrical UV-pulse was optimized spatially as a flattop and temporally as squarely stacked chirped pulses. This shaping system is a serial combination of a deformable mirror that adaptively shapes the spatial profile with a genetic algorithm and a UV-pulse stacker that consists of four birefringent ?-BBO crystal rods for temporal shaping. Using this 3D-shaped pulse, a normalized emittance of 1.4 ? mm mrad was obtained in 2006. Utilizing laser's Z-polarization, Schottky-effect-gated photocathode gun was proposed in 2006. The cathode work functions are reduced by a laser-induced Schottky effect. As a result of focusing a radially polarized laser pulse with a hollow lens in vacuum, the Z-field (Z-polarization) is generated at the cathode.

Tomizawa, Hiromitsu

153

Performance of Au transmission photocathode on a microchannel plate detectora)  

NASA Astrophysics Data System (ADS)

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

Lowenstern, M. E.; Harding, E. C.; Huntington, C. M.; Visco, A. J.; Rathore, G.; Drake, R. P.

2008-10-01

154

MBE-grown InGaAs photocathodes  

NASA Astrophysics Data System (ADS)

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

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

2003-02-01

155

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

156

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

SciTech Connect

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

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

1997-09-01

157

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

158

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

159

Vibration-Resistant Support for Halide Lamps  

NASA Technical Reports Server (NTRS)

Lamp envelope protected against breakage. Old and new mounts for halide arc lamp sealed in housing with parabolic refector and quartz window. New version supports lamp with compliant garters instead of rigid brazed joint at top and dimensionally unstable finger stock at bottom.

Kiss, J.

1987-01-01

160

Unraveling halide hydration: A high dilution approach  

NASA Astrophysics Data System (ADS)

The hydration properties of halide aqua ions have been investigated combining classical Molecular Dynamics (MD) with Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Three halide-water interaction potentials recently developed [M. M. Reif and P. H. Hünenberger, J. Chem. Phys. 134, 144104 (2011)], along with three plausible choices for the value of the absolute hydration free energy of the proton (? G^{ominus }_{hyd}[H^+]), have been checked for their capability to properly describe the structural properties of halide aqueous solutions, by comparing the MD structural results with EXAFS experimental data. A very good agreement between theory and experiment has been obtained with one parameter set, namely LE, thus strengthening preliminary evidences for a ? G^{ominus }_{hyd}[H^+] value of -1100 kJ mol-1 [M. M. Reif and P. H. Hünenberger, J. Chem. Phys. 134, 144104 (2011)]. The Cl-, Br-, and I- ions have been found to form an unstructured and disordered first hydration shell in aqueous solution, with a broad distribution of instantaneous coordination numbers. Conversely, the F- ion shows more ordered and defined first solvation shell, with only two statistically relevant coordination geometries (six and sevenfold complexes). Our thorough investigation on the effect of halide ions on the microscopic structure of water highlights that the perturbation induced by the Cl-, Br-, and I- ions does not extend beyond the ion first hydration shell, and the structure of water in the F- second shell is also substantially unaffected by the ion.

Migliorati, Valentina; Sessa, Francesco; Aquilanti, Giuliana; D'Angelo, Paola

2014-07-01

161

An Improved Electrically Excited Mercury Halide Laser.  

National Technical Information Service (NTIS)

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

R. L. Burnham

1978-01-01

162

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

163

Mean transverse energy and response time measurements of GaInP based photocathodes  

NASA Astrophysics Data System (ADS)

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; Yamamoto, Masahiro; Miyajima, Tsukasa; Honda, Yosuke; Uchiyama, Takashi; Tabuchi, Masao; Takeda, Yoshikazu

2014-08-01

164

Calculation of integral photoluminescence for the GaAs photocathode bonding assembly  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

165

Interaction of the model alkyltrimethylammonium ions with alkali halide salts: an explicit water molecular dynamics study  

E-print Network

We present an explicit water molecular dynamics simulation of dilute solutions of model alkyltrimethylammonium surfactant ions (number of methylene groups in the tail is 3, 5, 8, 10, and 12) in mixture with NaF, NaCl, NaBr, and NaI salts, respectively. The SPC/E model is used to describe water molecules. Results of the simulation at 298 K are presented in the form of radial distribution functions between nitrogen and carbon atoms of CH$_2$ groups on the alkyltrimethylammonium ion, and the counterion species in the solution. The running coordination numbers between carbon atoms of surfactants and counterions are also calculated. We show that I$^-$ counterion exhibits the highest, and F$^-$ the lowest affinity to "bind" to the model surfactants. The results are discussed in view of the available experimental and simulation data for this and similar solutions.

M. Druchok; ?. Podlipnik; V. Vlachy

2013-12-16

166

The aluminum electrode in AlCl3-alkali-halide melts.  

NASA Technical Reports Server (NTRS)

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

Holleck, G. L.; Giner, J.

1972-01-01

167

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

168

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

PubMed

This contribution aims to elucidate the connection between ion-ion-solvent interactions in the bulk of aqueous electrolyte solutions and the properties of their liquid-air interface. In particular, we were interested in the conditions under which ion pairs form at the surface and whether this is linked to ion pairing in the bulk. For this reason different combinations of hard (Cl(-), Li(+)) and soft ions (I(-), Cs(+)) were investigated. Ion hydration and possible ion association in the bulk was probed with dielectric relaxation spectroscopy. This technique monitors the cooperative reorientation of the dipolar solvent molecules and detects all ion-pair species possibly present in the solution. At the interface, the formation of contact ion pairs was investigated by infrared-visible-sum frequency spectroscopy (SFG). This nonlinear optical technique possesses an inherent surface specificity and can be used for the characterization of interfacial water. The intensity of the SFG-active vibrational stretching modes depends on the number of oriented water molecules. The electric field at the surface of a charged aqueous interface aligns the water dipoles, which in turn increases the SFG response. Hence, the enhancement of the oscillator strengths of the water vibrational modes can be used to draw some conclusions on the strengths and geometrical extension of the electric field. The formation of ion pairs at the interface reduces the intensity of the band associated with hydrogen-bonded water. The underlying theory is presented. The combined data show that there are no contact ion pairs in the bulk of the fluid and-at best-only small amounts of solvent shared ion pairs. On the other hand, the combination of hard/hard or soft/soft ions leads to the formation of ion pairs at the liquid-air interface. PMID:25399174

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

2014-11-14

169

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

170

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

171

Long-lived submicrometric bubbles in very diluted alkali halide water solutions  

E-print Network

Solutions of LiCl and of NaCl in ultrapure water were studied through Rayleigh/Brillouin scattering as a function of the concentration (molarity, M) of dissolved salt from 0.2M to extremely low concentration (2.10^-17 M ). The Landau-Placzek ratio, R/B, of the Rayleigh scattering intensity over the total Brillouin, was measured thanks to the dynamically controlled stability of the used Fabry-Perot interferometer. It was observed that the R/B ratio follows two stages as a function of increasing dilution rate: after a strong decrease between 0.2M and 2.10^-5 M, it increases to reach a maximum between 10^-9 M and 10^-16 M. The first stage corresponds to the decrease of the Rayleigh scattering by the ion concentration fluctuations with the decrease of salt concentration. The second stage, at lower concentrations, is consistent with the increase of the Rayleigh scattering by long-lived sub-microscopic bubbles with the decrease of ion concentration. The origin of these sub-microscopic bubbles is the shaking of the solutions which was carried out after each centesimal dilution. The very long lifetime of the sub-microscopic bubbles and the effects of aging originate in the electric charge of bubbles. The increase of R/B with the decrease of the low salt concentration corresponds to the increase of the sub-microscopic bubble size with the decrease of concentration, that is imposed by the bubble stability due to the covering of the surface bubble by negative ions.

Eugene Duval; Sergey Adichtchev; Sergey Sirotkin; Alain Mermet

2012-01-20

172

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

173

Transport of Alkali Halides through a Liquid Organic Membrane Containing a Ditopic Salt-Binding Receptor  

E-print Network

, K.; Stephan, H.; Grotjahn, M. Chem. Eng. Technol. 2003, 26, 1107-1117. (3) Phase Transfer Catalysis on an industrial scale.1 The principle of using phase-transfer agents to selectively complex a target ion has been as tetraalkylammonium or tetra- arylborate salts) are often used as phase-transfer agents that operate by ion

Smith, Bradley D.

174

Kinetics of correlated annealing of radiation defects in alkali halide crystals  

Microsoft Academic Search

Kinetics of the correlated annealing of pairs of neutral (F-H) Frenkel defects in the KBr crystal is treated theoretically, taking into account defect diffusion, and annihilation at short distances stimulated by an elastic interaction. It is shown that an elastic interaction affects the annealing kinetics and the survival probability of close geminate detects considerably. The widespread description of the correlated

E. A. Kotomin; R. I. Eglitis; A. I. Popov

1992-01-01

175

Effect of impurities on the hardness of alkali halide single crystals  

NASA Astrophysics Data System (ADS)

Micro hardness number of KCl, KBr and KCl-Br grown by Czocharlski technique, in the presence of homovalent and aliovalent ions of different ionic radii were measured in the indentation load range from 5 to 80*10-3 N. The measured data showed that there is an indentation size effect and classical Meyer's law was used for the characterization of crystal hardness of these crystals. The Meyer's index was also found to be smaller than 2 indicating brittle material characteristic. The P.R.S. model was used for the determination of the load independent micro hardness value. Result can be explained on the basis of interaction between created dislocation and point defect. It was found that hardness of these crystals is depending on the type of impurity.

Verma, Ashok K.; Ojha, Chaturbhuj; Shrivastava, A. K.

2014-04-01

176

Hellmann potential extended to next-nearest neighbors for alkali halide crystals  

Microsoft Academic Search

The short-range Hellmann potential function exhibiting the characteristics of both the Born-Lande and the Born-Mayer potential functions has been extended to include the contributions of next-nearest neighbors and van der Waals interactions. It is further employed to calculate the isothermal bulk modulus (BT) and its first- and second-order pressure derivatives (dBT\\/dP, d2BT\\/dP2), coefficient of volume expansion (beta), adiabatic and isothermal

S. K. Sipani; V. P. Gupta

1991-01-01

177

Formation of the self-trapped exciton via thermally induced defect reactions in alkali halides  

NASA Astrophysics Data System (ADS)

Low-temperature thermoluminescence has been studied in KBr, NaCl, and KI by means of emission-spectrum measurements of glow peaks and of detailed analysis as to the quantitative correlation between emission intensities and the amount of reacted defects. It is found that the luminescence center is the self-trapped exciton which results in both ? and ? emissions in these salts below 100 K and that the self-trapped exciton is produced at the temperature where the annihilation of the F center takes place. It is, however, shown that the recombination between F and H centers can excite only the lowest triplet exciton in KBr. The quantum yield of the exciton formation by F-H recombination is estimated less than 0.03. The energetic correlation between the exciton and the F-H pair state in the defect-annihilation process in KBr is discussed.

Tanimura, K.; Okada, T.

1980-02-01

178

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

NASA Astrophysics Data System (ADS)

The nuclear magnetic resonance (NMR) spectra of the I=3/2 monovalent ions 23Na, 35Cl, 39K, and 79Br for NaCl and KBr dissolved into filamentous bacteriophage Pf1 solutions display line splittings and shifts consistent with an interaction between the nuclear spin and the electric field gradient produced by the Pf1 particles. The average electric field gradient and thus the spectral splitting for ions in the void space between magnetically aligned Pf1 particles is modeled using a numerical solution to the Poisson-Boltzmann equation. An NMR titration experiment in a 57 mg/mL Pf1 solution is used to determine the background Na+ ion concentration in solution as 32 mM which compares well with the 31.1 mM negative surface charge on Pf1.

Vyas, S.; Hernandez, C. J.; Augustine, M. P.

2002-04-01

179

Atomic hydrogen cleaning of polarized GaAs photocathodes  

SciTech Connect

Atomic hydrogen cleaning followed by heat cleaning at 450 C was used to prepare negative-electron-affinity GaAs photocathodes. When hydrogen ions were eliminated, quantum efficiencies of 15% were obtained for bulk GaAs cathodes, higher than the results obtained using conventional 600 C heat cleaning. The low-temperature cleaning technique was successfully applied to thin, strained GaAs cathodes used for producing highly polarized electrons. No depolarization was observed even when the optimum cleaning time of about 30 seconds was extended by a factor of 100.

Maruyama, Takashi

2003-04-03

180

Laser Development for Future Photocathode Research at SLAC  

NASA Astrophysics Data System (ADS)

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

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

2005-08-01

181

Characterization of quantum well structures using a photocathode electron microscope  

NASA Technical Reports Server (NTRS)

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

Spencer, Michael G.; Scott, Craig J.

1989-01-01

182

Nanosecond length electron pulses from a laser-excited photocathode  

SciTech Connect

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

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

1989-06-01

183

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

184

Interactions of polar alkali dimers  

NASA Astrophysics Data System (ADS)

The effects of external electric static fields on the interactions of polar alkali diatoms for the purposes of alignment is investigated for a variety of trapping geometries and external field strengths. We also present new results for the dispersion and induction van der Waals coefficients calculated using the sum over states method of time dependent density functional transition moments. Additionally the static electric moments and polarizabilities for each heteronuclear alkali diatom have been calculated. These new results are used to accurately model the interactions between polar alkali molecules in the long range by a van der Waals expansion up to R-8. We find that strong alignment of specific heteronuclear diatoms is possible with strong but physically realizable external electric fields.

Byrd, Jason; Montgomery, John, Jr.; Cøté, Robin

2011-06-01

185

Theoretical characterization of dihydrogen adducts with halide anions.  

PubMed

The interaction between a hydrogen molecule and the halide anions F(-), Cl(-), Br(-), and I(-) has been studied at different levels of theory and with different basis sets. The most stable configurations of the complexes have a linear geometry, while the t-shaped complexes are saddle points on the potential energy surface, opposite to what is observed for alkali cations. An electrostatic analysis conducted on the resulting adducts has highlighted the predominance of the electrostatic term in the complexation energy and, in particular, of the quadrupole- and dipole-polarizability dependent contributions. Another striking difference with respect to the positive ions, is the fact that although the binding energies have similar values (ranging between 25 and 3 kJ /mol for F(-) and I(-), respectively), the vibrational shift of the nu(H-H) and in general the perturbation of the hydrogen molecule in complexes are much greater in the complexes with anions (Delta nu(H-H) ranges between -720 and -65 cm(-1)). Another difference with respect to the interaction with cations is a larger charge transfer from the anion to the hydrogen molecule. The Delta nu is the result of the cooperative role of the electrostatics and of the charge transfer in the interaction. The correlation between binding energies and vibrational shift is far from linear, contrary to what is observed for cation complexes, in accordance with the higher polarizability and dynamic polarizability of the molecule along the molecular axis. The observed correlation may be valuable in the interpretation of spectra and thermodynamic properties of adsorbed H(2) in storage materials. PMID:16784275

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

2006-06-14

186

Highly active oxide photocathode for photoelectrochemical water reduction  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

187

Very high quantum efficiency PMTs with bialkali photo-cathode  

NASA Astrophysics Data System (ADS)

Since the mid-1960s and until today the classical PMTs with semitransparent bialkali photo-cathode provide peak Quantum Efficiency (QE) of ˜25%. About 2 years ago we started a program with the PMT manufacturers Hamamatsu, Photonis and Electron Tubes for boosting up the QE of bialkali PMTs. In the mean time we have obtained several batches of experimental PMTs from the above-mentioned manufacturers and measured few samples with QE values as high as 32-36% in the peak. Also, we want to report on the modest (5-7) % increase of the QE of the PMTs with flat input window after sandblasting. Earlier we have reported that by coating the hemi-spherical input window of bialkali PMTs with a milky layer we could enhance their QE by ˜10-20% for wavelengths ˜320 nm. Assuming that the industry can reliably produce PMTs with 32-35% QE in the peak, by applying the milky layer coating technique to the PMTs with hemi-spherical input window one shall be able to achieve peak QE values of ˜35-40%. Being by an order of magnitude cheaper and providing a matching level of QE such PMTs will become strong competitors for hybrid photo-diodes (HPD) with GaAsP photo-cathode.

Mirzoyan, R.; Laatiaoui, M.; Teshima, M.

2006-11-01

188

Opaque gallium nitride photocathodes in UV imaging detectors with microchannel plates  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

189

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

190

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

NASA Astrophysics Data System (ADS)

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 halogen radicals destroy ozone in the stratosphere and modify the oxidative capacity of the lower atmosphere. We have previously shown that rice paddies emit methyl halides and that emissions depend on growth stage of the rice plant as well as field water management. We show here that rice grown in a greenhouse at UCI is capable of volatilizing and/or storing up to 30%, 5%, and 10% of the available chloride, bromide and iodide within the top meter of soil. The percent of plant tissue halide volatilized as methyl halide over the course of the season is calculated to be 0.05%, 0.25% and 85.0% for chloride, bromide and iodide. We compare our greenhouse soil halide concentrations to other commercial rice fields around the world and estimate the e-folding time for soil halides within each region. We suggest that rice agriculture is the driving removal mechanism for halides within rice paddies and that terrestrial plants play a larger role in global cycling of halides than previously estimated.

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

2002-05-01

191

Halide electroadsorption on single crystal surfaces  

SciTech Connect

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

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

1997-07-01

192

Decomposition of Halide Compounds by Nonequilibrium Discharge  

NASA Astrophysics Data System (ADS)

A narrow-gap silent discharge has been successfully applied to the resolution of halide compounds (CCl2F2 and CF4) diluted in mixed gases of H2O, O2, N2 and Ar with a varied composition at an atmospheric pressure. The optimum composition of the discharge gas is discussed in terms of an effective decomposition energy Ed defined as the energy necessary for e-1-fold reduction of the halide concentration. Efficient decomposition of CF4 gas is realized with the use of Ar gas as the dilution gas; the minimum value of Ed approaches 760 eV/CF4-molecule, which must be compared with the value of 18 keV/CF4 obtained when N2 is used as the dilution gas.

Gotou, Toyokazu; Wada, Noboru; Kurahashi, Masato; Kuzumoto, Masaki; Kitamura, Akira

2005-11-01

193

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

194

Unraveling halide hydration: A high dilution approach.  

PubMed

The hydration properties of halide aqua ions have been investigated combining classical Molecular Dynamics (MD) with Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Three halide-water interaction potentials recently developed [M. M. Reif and P. H. Hünenberger, J. Chem. Phys. 134, 144104 (2011)], along with three plausible choices for the value of the absolute hydration free energy of the proton (?G [minus sign in circle symbol]hyd[H+]), have been checked for their capability to properly describe the structural properties of halide aqueous solutions, by comparing the MD structural results with EXAFS experimental data. A very good agreement between theory and experiment has been obtained with one parameter set, namely LE, thus strengthening preliminary evidences for a ?G [minus sign in circle symbol]hyd[H] value of -1100 kJ mol(-1) [M. M. Reif and P. H. Hünenberger, J. Chem. Phys. 134, 144104 (2011)]. The Cl(-), Br(-), and I(-) ions have been found to form an unstructured and disordered first hydration shell in aqueous solution, with a broad distribution of instantaneous coordination numbers. Conversely, the F(-) ion shows more ordered and defined first solvation shell, with only two statistically relevant coordination geometries (six and sevenfold complexes). Our thorough investigation on the effect of halide ions on the microscopic structure of water highlights that the perturbation induced by the Cl(-), Br(-), and I(-) ions does not extend beyond the ion first hydration shell, and the structure of water in the F(-) second shell is also substantially unaffected by the ion. PMID:25084928

Migliorati, Valentina; Sessa, Francesco; Aquilanti, Giuliana; D'Angelo, Paola

2014-07-28

195

Physics of silver halides and their applications  

Microsoft Academic Search

Silver halides are notable for exhibiting both ionic and electronic conductivity which is responsible for their widespread\\u000a use in photography. Due to differences in ionicity and bonding, their properties vary from the highly ionic silver fluoride\\u000a to the more covalent silver iodide. These fundamental properties such as defect formation energies, carrier mobilities and\\u000a band-structures, particularly of silver iodide, have only

D N Bose; P A Govindacharyulu

1980-01-01

196

Flame inhibition by hydrogen halides - Some spectroscopic measurements  

NASA Technical Reports Server (NTRS)

The far-ultraviolet absorption spectrum of an air-propane diffusion flame inhibited with hydrogen halides has been studied. Plots of the absorption of light by hydrogen halides as a function of position in the flame and also as a function of the amount of hydrogen halide added to the flame have been obtained. The hydrogen halides are shown to be more stable on the fuel side of the reaction zone than they are on the air side. Thermal diffusion is seen to be important in determining the concentration distribution of the heavier hydrogen halides in diffusion flames. The relationship between the concentration distribution of the hydrogen halides in the flame and the flame inhibition mechanism is discussed.

Lerner, N. R.; Cagliostro, D. E.

1973-01-01

197

Alkali-activated fly ashes  

Microsoft Academic Search

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

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

1999-01-01

198

Reactions of trichlorogermane with alkyl, alkenyl, and alkynyl halides  

Microsoft Academic Search

1.The condensation of trichlorogermane with allyl-type halides, which consists in the replacement of halogen in the latter by the trichlorogermyl group, can be extended to tertiary saturated halides. Secondary and primary alkyl halides do not undergo this reaction.2.3-Chloro- and 3-bromo-propynes also condense with trichlorogermane, but the reaction is accompanied by an addition reaction.3.The possibility of condensation occurring is probably determined

V. F. Mironov; T. K. Gar

1965-01-01

199

Experimental study of a 17 GHz high gradient photocathode injector  

NASA Astrophysics Data System (ADS)

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

Trotz, Seth Reuben

200

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...

201

High-power fiber lasers for photocathode electron injectors  

NASA Astrophysics Data System (ADS)

Many new applications for electron accelerators require high-brightness, high-average power beams, and most rely on photocathode-based electron injectors as a source of electrons. To achieve such a photoinjector, one requires both a high-power laser system to produce the high average current beam, and also a system at reduced repetition rate for electron beam diagnostics to verify high beam brightness. Here we report on two fiber laser systems designed to meet these specific needs, at 50 MHz and 1.3 GHz repetition rate, together with pulse pickers, second harmonic generation, spatiotemporal beam shaping, intensity feedback, and laser beam transport. The performance and flexibility of these laser systems have allowed us to demonstrate electron beam with both low emittance and high average current for the Cornell energy recovery linac.

Zhao, Zhi; Bartnik, Adam; Wise, Frank W.; Bazarov, Ivan V.; Dunham, Bruce M.

2014-05-01

202

Mechanism and Selectivity in Nickel-Catalyzed Cross-Electrophile Coupling of Aryl Halides with Alkyl Halides  

PubMed Central

The direct cross-coupling of two different electrophiles, such as an aryl halide with an alkyl halide, offers many advantages over conventional cross-coupling methods that require a carbon nucleophile. Despite its promise as a versatile synthetic strategy, a limited understanding of the mechanism and origin of cross selectivity has hindered progress in reaction development and design. Herein, we shed light on the mechanism for the nickel-catalyzed cross-electrophile coupling of aryl halides with alkyl halides and demonstrate that the selectivity arises from an unusual catalytic cycle that combines both polar and radical steps to form the new C-C bond. PMID:23952217

Biswas, Soumik; Weix, Daniel J.

2013-01-01

203

Superlattice Photocathode with High Brightness and Long NEA-Surface Lifetime  

SciTech Connect

We have suggested that a small momentum spread of photoelectrons and high quantum efficiency can be obtained concurrently by a photocathode using a semiconductor with a superlattice instead of a bulk. We have begun to search for the suitable semiconductor material of a superlattice photocathode for maintaining the surface with a negative electron affinity state for a long time. We measured quantum efficiency degradation of photocathodes using GaAs and AlGaAs semiconductors with various electron affinities. The AlGaAs semiconductor had a quantum efficiency lifetime of 10 times long compared with the GaAs semiconductor. We found that the AlGaAs semiconductor was the suitable material for the superlattice photocathode with the surface maintaining a negative electron affinity state for a long time.

Nishitani, Tomohiro; Meguro, Takashi [Beam Application Team, RIKEN, Wako, Saitama, 351-0198 (Japan); Tabuchi, Masao [Venture Business Laboratory, Nagoya University, Nagoya, 464-8601 (Japan); Takeda, Yoshikazu; Suzuki, Yuji; Motoki, Kazuya [Department of Crystalline Materials Science, Nagoya University, Nagoya, 464-8601 (Japan)

2009-08-04

204

Experimental data on the reflection and transmission spectral response of photocathodes  

NASA Astrophysics Data System (ADS)

The spectral transmission and electron emissivity responses, measured for a series of typical photocathodes, are presented and analysed. Specifically, samples of S1, S20, S25, Bialkali and two types of solar-blind telluride photocathodes were investigated in both transmission and reflection modes of operation. The transmission mode is more convenient for imaging, night vision and for scintillation counting applications such as CT scanners and is more commonly used than the reflection mode. However, more recent work has focussed on the reflection photocathode as a source of electrons with low energy spread used for electron guns for microscopy and lithographic free electron lasers [1]. Our analysis provides a determination of the reflectivity of the substrate/cathode and cathode/vacuum interface, enabling the refractive index to be deduced. The high apparent quantum efficiency (QE) of some conventional photocathodes is shown to be due to the conversion of each photon to two or more electrons.

Brooks, R. J.; Howorth, J. R.; McGarry, K.; Powell, J. R.; Joseph, C. L.

2007-09-01

205

Characterization of a superconducting Pb photocathode in a superconducting rf photoinjector cavity  

NASA Astrophysics Data System (ADS)

Photocathodes are a limiting factor for the next generation of ultrahigh brightness photoinjectors. We studied the behavior of a superconducting Pb cathode in the cryogenic environment of a superconducting rf gun cavity to measure the quantum efficiency, its spatial distribution, and the work function. We will also discuss how the cathode surface contaminants modify the performance of the photocathode as well as the gun cavity and we discuss the possibilities to remove these contaminants.

Barday, R.; Burrill, A.; Jankowiak, A.; Kamps, T.; Knobloch, J.; Kugeler, O.; Matveenko, A.; Neumann, A.; Schmeißer, M.; Völker, J.; Kneisel, P.; Nietubyc, R.; Schubert, S.; Smedley, J.; Sekutowicz, J.; Will, I.

2013-12-01

206

Position-Sensitive Detector with GaAs photocathode and high time resolution  

NASA Astrophysics Data System (ADS)

The Position-Sensitive Detector (PSD) on base of GaAs photocathode and microchannel plate set has been developed. PSD consists of thick semi-conductor photocathode with quantum efficiency about 48% in the range of 4000-7500 A, two micro-channel plates, and 16-electrode collector. The detector has spatial resolution of 20-40 microns for about 5.102 pixels, time resolution of 1 ?s and effective sensitivity up to 35%.

de-Bur, Vjacheslav; Terekhov, Alexander; Kosolobov, Sergey; Sheibler, Heinrich; Beskin, Grigory; Karpov, Sergey; Plokhotnichenko, Vladimir

2008-02-01

207

Position-Sensitive Detector with GaAs photocathode and high time resolution  

SciTech Connect

The Position-Sensitive Detector (PSD) on base of GaAs photocathode and microchannel plate set has been developed. PSD consists of thick semi-conductor photocathode with quantum efficiency about 48% in the range of 4000-7500 A, two micro-channel plates, and 16-electrode collector. The detector has spatial resolution of 20-40 microns for about 5{center_dot}10{sup 2} pixels, time resolution of 1 {mu}s and effective sensitivity up to 35%.

De-Bur, Vjacheslav; Beskin, Grigory; Karpov, Sergey; Plokhotnichenko, Vladimir [Special Astropysical Observatory, Nizhnij Arkhyz, 369167 (Russian Federation); Terekhov, Alexander; Kosolobov, Sergey; Sheibler, Heinrich [Institute of Semiconductor Physics, Novosibirsk, 630090 (Russian Federation)

2008-02-22

208

Single-electron characteristics of FEU-83 with local photocathode illumination  

SciTech Connect

The amplitude distributions of single-electron pulses (ADSEP) are measured for FEU-83 photomultipliers with local photocathode illumination. It is found that the ADSEP varies as the point of illumination is moved along the diameter of the photocathode perpendicular to the direction of the louver and that an ADSEP with a single-electron peak can be obtained. These variations are related to the flight of photoelectrons past the first dynode.

Bagduev, R.I.; Zhuravlev, K.S.; Terekhov, A.S.

1987-02-01

209

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

Microsoft Academic Search

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

C. S. Park; M. Hess

2010-01-01

210

Quantum efficiency and ageing studies for bulk and porous CsI photocathodes in a MWPC  

Microsoft Academic Search

The quantum efficiency of CsI photocathodes operating in a proportional gas chamber is measured in the wavelength range 185-220 nm. The tests are carried out with methane gas at atmospheric pressure using a pulsed UV lamp. Two different techniques are used to produce the photocathodes. The CsI is either evaporated under high vacuum or under low pressure of argon. The

R. Aleksan; P. Besson; Ph. Bourgeois; P. Garganne; J. P. Robert

1994-01-01

211

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

212

Study on photoemission surface of varied doping GaN photocathode  

NASA Astrophysics Data System (ADS)

For varied doping GaN photocathode, from bulk to surface the doping concentrations are distributed from high to low. The varied doping GaN photocathode may produce directional inside electric field within the material, so the higher quantum efficiency can be obtained. The photoemission surface of varied doping GaN photocathode is very important to the high quantum efficiency, but the forming process of the surface state after Cs activation or Cs/O activation has been not known completely. Encircling the photoemission mechanism of varied GaN photocathode, considering the experiment phenomena during the activation and the successful activation results, the varied GaN photocathode surface model [GaN(Mg):Cs]:O-Cs after activation with cesium and oxygen was given. According to GaN photocathode activation process and the change of electronic affinity, the comparatively ideal NEA property can be achieved by Cs or Cs/O activation, and higher quantum efficiency can be obtained. The results show: The effective NEA characteristic of GaN can be gotten only by Cs. [GaN(Mg):Cs] dipoles form the first dipole layer, the positive end is toward the vacuum side. In the activation processing with Cs/O, the second dipole layer is formed by O-Cs dipoles, A O-Cs dipole includes one oxygen atom and two Cs atoms, and the positive end is also toward the vacuum side thus the escape of electrons can be promoted.

Qiao, Jianliang; Du, Ruijuan; Ding, Huan; Gao, Youtang; Chang, Benkang

2014-09-01

213

Catalytic Enantioselective Negishi Reactions of Racemic Secondary Benzylic Halides  

E-print Network

Catalytic Enantioselective Negishi Reactions of Racemic Secondary Benzylic Halides Forrest O. Arp of reaction partners, racemic secondary benzylic halides, can be coupled with organozinc reagents in very good (a benzylic bromide). Fourth, the process is stereoconvergent; both enantiomers of the racemic

Fu, Gregory C.

214

Melt synthesis of inorganic nitrides and halides  

Microsoft Academic Search

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

Jay Clark Molstad

1999-01-01

215

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

E-print Network

of configuration has been found in nucleophilic substitution reactions at saturated silicon,13 early reportsGas-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

Schlegel, H. Bernhard

216

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.

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

1992-01-01

217

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

218

Methyl halide production associated with kelp  

NASA Technical Reports Server (NTRS)

Methyl halides (MeX) are important trace constituents of the atmosphere because they, mostly MeCl, have a major impact on the atmospheric ozone layer. Also, MeCl may account for 5 pct. of the total Cl budget and MeI may have a central role in the biogeochemical cycling of iodine. High MeI concentrations were found in seawater from kelp beds and it has been suggested that MeI is produced by kelps and that MeI and MeBr along with numerous other halocarbons were released by non-kelp marine macroalgae. The objective was to determine if kelps (and other seaweeds) are sources of MeX and to assess their contribution to the estimated global source strength (EGSS) of MeX. Although the production of MeX appears to be associated with kelp, microbes involved with kelp degradation also produce MeX. Microbial MeX production may be of global significance. The microbial MeX production potential, assuming annual kelp production equals kelp degradation and 100 pct. conversion of kelp halides to MeX, is approx. 2 x the EGSS. This is not achieved but indicates that microbial production of MeX may be of global significance.

Dastoor, Minoo N.; Manley, Steven L.

1985-01-01

219

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

220

Surface science analysis of GaAs photocathodes following sustained electron beam delivery  

SciTech Connect

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

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

2012-06-01

221

Surface science analysis of GaAs photocathodes following sustained electron beam delivery  

NASA Astrophysics Data System (ADS)

Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power free electron lasers (FEL). Photocathode quantum efficiency degradation is due to residual gases in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include helium ion microscopy, Rutherford backscattering spectrometry (RBS), atomic force microscopy, and secondary ion mass spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the continuous electron beam accelerator facility (CEBAF) photoinjector and one unused, were also analyzed using transmission electron microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but show evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements, the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

Shutthanandan, V.; Zhu, Z.; Stutzman, M. L.; Hannon, F. E.; Hernandez-Garcia, C.; Nandasiri, M. I.; Kuchibhatla, S. V. N. T.; Thevuthasan, S.; Hess, W. P.

2012-06-01

222

Performance of cesium telluride photocathodes as an electron source for the Los Alamos FEL  

SciTech Connect

The Los Alamos Advanced FEL was successfully operated with a Cs{sub 2}Te photocathode driven by a frequency quadrupled Nd:YLF laser as the electron source. Lasing was achieved at 5-6 microns. Cs{sub 2}Te photocathodes with quantum efficiencies of 12-18% at 254 nm were fabricated in an ultrahigh-vacuum chamber and transferred under high vacuum to the FEL. 263 mn light from the drive laser was focused to an 8 mm spot on the center of the photocathode. The authors estimated the operational life time of Cs{sub 2}Te photocathodes to be at least 20 times that for K{sub 2}CsSb photocathodes. The measured dark current of 0.3 mA in an electric field of 22-24 MV/m is well within the acceptable level. The maximum amount of charge extracted was observed to be limited by space charge to about 3.5 nC per micropulse. The emittance of the beam was estimated by fitting the data from a quadrupole scan. The authors measured an emittance that is comparable with the emittance measured with a K{sub 2}CsSb photocathode in their system. A pulse length of 9.3 {+-} 2 ps for 1.3 {+-} 0.2 nC electron micropulses and a pulse length of 7.1 {+-} 0.7 ps for the laser pulses were measured with a streak camera. Therefore, the response of the Cs{sub 2}Te photocathode to the laser pulse is sufficiently fast for FEL applications.

Kong, S.H.; Kinross-Wright, J.; Nuguyen, D.C.; Sheffield, R.L.; Weber, M.E.

1994-09-01

223

Physiological and biochemical controls over methyl halide emissions from rice plants  

Microsoft Academic Search

This paper investigates physiological and biochemical aspects of methyl halide production in rice plants over two growing seasons. Multiple separate mechanisms appear to be responsible for production of methyl halides in rice plant tissues. Evidence for multiple mechanisms is found in timing of peak emissions of methyl halides from rice, inconsistent effects of competitive inhibitors on methyl halide emissions, and

K. R. Redeker; S. L. Manley; M. Walser; R. J. Cicerone

2004-01-01

224

Impact of the spatial laser distribution on photocathode gun operation  

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

225

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

226

Advanced metal alloy systems for massive high-current photocathodes  

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

227

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

228

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

229

Laser driver for a photocathode of an electron linear accelerator  

SciTech Connect

A laser system is designed for operation with a photocathode electron gun for a linear accelerator with the following parameters of radiation at a wavelength of 262 nm (the fourth harmonic of a Nd:YLF laser). The pulse trains (macropulses) with a repetition rate of 5 Hz and a duration of 900 {mu}s consist of 8-ps micropulses with an energy of 1.4 {mu}J and a repetition rate of 2.708 MHz. This repetition rate is variable within {+-}32 kHz and is stabilised by an external signal with an accuracy of 10 Hz. Due to the use of a feedback-controlled acousto-optic modulator, the root-mean-square deviation of the micropulse energy in the first and second harmonics is 2.5% and 3.6%, respectively. Using the decaying branch of the dependence of the second-to-fourth harmonic conversion efficiency on the second harmonic intensity, we decreased the root-mean-square deviation of the energy of the fourth-harmonic micropulses to 2.3% at the first-to-fourth harmonic conversion efficiency of 27%. (lasers and amplifiers)

Potemkin, A K; Gacheva, E I; Zelenogorskii, V V; Katin, E V; Kozhevatov, I E; Lozhkarev, V V; Luchinin, G A; Silin, D E; Khazanov, Efim A [Institute of Applied Physics, Russian Academy of Sciences, Nizhnii Novgorod (Russian Federation); Trubnikov, D V; Shirkov, G D [Joint Institute for Nuclear Research, Dubna, Moscow region (Russian Federation); Kuriki, M [Hiroshima University, Higashi-Hiroshima, Hiroshima (Japan); Urakava, J [High Energy Accelerator Research Organisation, KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)

2011-01-24

230

40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.  

Code of Federal Regulations, 2012 CFR

...halogenated pyridinol, alkali salt. 721.8900 Section 721...halogenated pyridinol, alkali salt. (a) Chemical substances...halogenated pyridinols, alkali salts (PMNs P-88-1271 and...adsorption. (iv) Release to water. Requirements as...

2012-07-01

231

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

NASA Astrophysics Data System (ADS)

Heterogeneous reactions on the surfaces of atmospheric aerosols play an important role in atmospheric chemistry. These reactions are capable of converting alkyl and hydrogen halides (common constituents of marine boundary aerosols) into active halogen compounds. Fundamental questions still remain concerning surface species and reaction mechanisms pertaining to marine boundary aerosols. The first step in beginning to understand these heterogeneous reactions is to determine how ions in solution affect the structure of water at the interface. Vibrational sum frequency generation spectroscopy is used to examine the air-liquid interface of sodium halide and hydrogen halide (i.e. strong acid) solutions. In addition, comparison of the bulk water structure to that of the interface is accomplished using Raman spectroscopy. The hydrogen-bonding environment at the surface of NaCl is found to be similar to that of the air-water interface. In contrast, the interfacial water structure of NaBr, HCl, and HBr solutions is significantly altered from that of neat water. In the bulk, NaCl, NaBr, HCl, and HBr solutions disturb the hydrogen-bonding network of neat water. A comparison between the corresponding salts and acids show that the salts produce greater disorder (i.e. less coupling of the water symmetric stretching modes) in the bulk water structure.

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

2003-12-01

232

Diurnal variation in methyl halide emission rates from tropical ferns  

NASA Astrophysics Data System (ADS)

We measured foliar emission rates of methyl chloride (CH 3Cl) and methyl bromide (CH 3Br) from tropical ferns. The diurnal variation in methyl halide emission rates was quite different between tropical ferns of the same genus: Cyathea podophylla showed diurnal cycles with a midday maximum, whereas Cyathea lepifera showed a midday decline in emission rates. It is likely that the efficiency of methylation of halide ions in the leaves is affected positively or negatively by environmental factors such as temperature and solar radiation, depending on the species. These unique diurnal variations in methyl halide emission rates could be important keys to our understanding of the production of these compounds.

Saito, Takuya; Yokouchi, Yoko

233

Raman spectroscopy of rare earth doped silver halide crystals  

NASA Astrophysics Data System (ADS)

The phonon energy of rare earth doped silver halide crystals was investigated using Raman spectroscopy. An additional phonon vibrational mode was observed and attributed to localized defect vibrational modes. Good agreement was found between the measured and the predicted frequencies of the local modes. These additional low energy (65-80 cm-1) vibrational modes do not increase the thermal quenching of mid-IR luminescence of the rare earth ions in silver halide crystals. The rare earth doped silver halide crystals are suitable for the fabrication of mid-IR solid state lasers and fiber lasers due to their extremely low phonon energies.

Shafir, I.; Nagli, L.; Katzir, A.

2009-06-01

234

Spectral response variation of a negative-electron-affinity photocathode in the preparation process  

NASA Astrophysics Data System (ADS)

In order to research the spectral response variation of a negative electron affinity (NEA) photocathode in the preparation process, we have done two experiments on a transmission-type GaAs photocathode. First, an automatic spectral response recording system is described, which is used to take spectral response curves during the activation procedure of the photocathode. By this system, the spectral response curves of a GaAs:Cs-O photocathode measured in situ are presented. Then, after the cathode is sealed with a microchannel plate and a fluorescence screen into the image tube, we measure the spectral response of the tube by another measurement instrument. By way of comparing and analyzing these curves, we can find the typical variation in spectral-responses. The reasons for the variation are discussed. Based on these curves, spectral matching factors of a GaAs cathode for green vegetation and rough concrete are calculated. The visual ranges of night-vision goggles under specific circumstances are estimated. The results show that the spectral response of the NEA photocathode degraded in the sealing process, especially at long wavelengths. The variation has also influenced the whole performance of the intensifier tube.

Liu, Lei; Du, Yujie; Chang, Benkang; Yunsheng, Qian

2006-08-01

235

Spectral response variation of a negative-electron-affinity photocathode in the preparation process.  

PubMed

In order to research the spectral response variation of a negative electron affinity (NEA) photocathode in the preparation process, we have done two experiments on a transmission-type GaAs photocathode. First, an automatic spectral response recording system is described, which is used to take spectral response curves during the activation procedure of the photocathode. By this system, the spectral response curves of a GaAs:Cs-O photocathode measured in situ are presented. Then, after the cathode is sealed with a microchannel plate and a fluorescence screen into the image tube, we measure the spectral response of the tube by another measurement instrument. By way of comparing and analyzing these curves, we can find the typical variation in spectral-responses. The reasons for the variation are discussed. Based on these curves, spectral matching factors of a GaAs cathode for green vegetation and rough concrete are calculated. The visual ranges of night-vision goggles under specific circumstances are estimated. The results show that the spectral response of the NEA photocathode degraded in the sealing process, especially at long wavelengths. The variation has also influenced the whole performance of the intensifier tube. PMID:16892108

Liu, Lei; Du, Yujie; Chang, Benkang; Yunsheng, Qian

2006-08-20

236

A T-shaped selenenyl halide.  

PubMed

The title selenenyl halide complex, 3-iodo-2-phenyl-3H-3-selenaindazole, C(12)H(9)IN(2)Se, has an almost planar conformation and a nearly ideal T-shape for the Se(INC) moiety [Se-I 2.8122 (12), Se-C 1.881 (7) and Se-N2 2.051 (6) A; C-Se-N 79.6 (3), C-Se-I 96.8 (2) and N-Se-I 176.17 (17) degrees ]. This arrangement, together with the two selenium lone pairs, leads to a distorted trigonal-bipyrimidal geometry about the Se atom. Intermolecular interactions are largely limited to stacking forces. PMID:15263218

Majeed, Z; McWhinnie, W R; Lowe, P R

2000-03-15

237

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

238

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

239

Schedule visualization and analysis for halide image processing language  

E-print Network

Image processing applications require high performance software implementations in order to satisfy large input data and run on smaller mobile devices that require high efficiency. Halide is a language and compiler for ...

Kneževi?, Jovana

2013-01-01

240

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

241

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

242

Polarization studies of strained GaAs photocathodes at the SLAC Gun Test Laboratory  

SciTech Connect

The SLAC Gun Test Laboratory apparatus, the first two meters of which is a replica of the SLAC injector, is used to study the production of intense, highly-polarized electron beams required for the Stanford Linear Collider and future linear colliders. The facility has been upgraded with a Mott polarimeter in order to characterize the electron polarization from photocathodes operating in a DC gun. In particular, SLAC utilizes p-type, biaxially strained GaAs photocathodes which have produced longitudinal electron polarizations greater than 80% while yielding pulses of 5 A/sq cm at an operating voltage of 120 kV. Among the experiments performed include studying the influences of the active layer thickness, temperature, quantum efficiency and cessation on the polarization. The results might help to develop strained photocathodes with higher polarization.

Saez, P.; Alley, R.; Clendenin, J.; Frisch, J.; Kirby, R.; Mair, R.; Maruyama, T.; Miller, R.; Mulhollan, G.; Prescott, C. [and others

1995-08-01

243

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

244

First operation of cesium telluride photocathodes in the TTF injector RF gun  

NASA Astrophysics Data System (ADS)

During the run 1998/1999 a new injector based on a laser-driven RF gun was brought in operation at the TESLA Test Facility (TTF) linac at DESY, in order to produce the beam structure and quality required either by TeV collider and SASE FEL experiments. High quantum efficiency cesium telluride photocathodes, prepared at Milano and transferred to DESY, have been successfully operated in the RF gun. A bunch charge of 50 nC, only limited by space charge effects, was achieved. The photocathodes have shown an operative lifetime of several months. A new cathode surface finishing has showed a promising decrease of the photocathode dark current. Measurements of dark current, quantum efficiency and lifetime are reported.

Sertore, D.; Schreiber, S.; Floettmann, K.; Stephan, F.; Zapfe, K.; Michelato, P.

2000-05-01

245

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

SciTech Connect

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

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

2008-05-28

246

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

247

Reactions of nitrogen heterocycle-organolithium intermediates with lead halides  

E-print Network

REACTIONS OF NITROGEN HETEROCYCLE- ORGANOLITHIUM INTERMEDIATES WITH LEAD HALIDES A Thesis by JERRY HEAL KINNEY Submitted to the Graduate College of Texas ALM University In partial fulfillment of the requirement for the degree ot MASTER...) (Mem er) December 1970 ABSTRACT Reactions of Nitrogen Heterocycle-Organollthium intermediates With Lead Halides. (December l970) Jerry Neal Kinney, B. S. , Texas AE, M University Directed by: Dr. Choo-Seng Giam Reactions of nitrogen heterocycle...

Kinney, Jerry Neal

2012-06-07

248

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

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

249

Copper(I)-catalyzed synthesis of 1,3-enynes via coupling between vinyl halides and alkynes or domino coupling of vinyl halides.  

PubMed

1,3-Enynes were easily prepared from coupling between vinyl halides and alkynes or domino coupling of vinyl halides in the presence of copper iodide. It is noteworthy that the double-bond geometry of the vinyl halides was retained during the reaction. This ligand-free protocol is potentially useful and practical. PMID:21915420

Zhu, Yan; Li, Tingyi; Qu, Xiaoming; Sun, Peng; Yang, Hailong; Mao, Jincheng

2011-11-01

250

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

251

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

252

Temporal Profile of the LCLS Photocathode Ultraviolet Drive Laser Tolerated by the Microbunching Instability  

SciTech Connect

The high quality LCLS electron beam generated in the photoinjector is subject to many instabilities in the downstream acceleration and compression. The instability can be initiated by any density modulation of the electron beam generated at the photocathode. In this paper, we prescribe the tolerance on the initial electron beam density modulation possibly introduced by the ultraviolet (uv) laser at the cathode. Our study shows that with a matched Landau damping laser-heater, the initial rms density modulation of the electron beam at the photocathode must be less than 5% to ensure the FEL lasing and saturation.

Wu, J

2004-06-15

253

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

254

Color silver halide hologram production and mastering  

NASA Astrophysics Data System (ADS)

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

Bjelkhagen, Hans I.; Huang, Qiang

1997-04-01

255

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

256

Charge transfer states in alkali metals  

Microsoft Academic Search

The excitation spectra of halogen impurities in alkali metals was investigated throughout the photon energy range from 5 eV to 12 eV. The charge transfer configurations adopted by a variety of impurities in alkali metals were further investigated by measurements of the composition and temperature dependence of the electrical resistivity. Charge transfer effects observed to cause metal-to-insulator transitions at specific

R. Avci

1978-01-01

257

Comparison of module structure of wideband response GaAs photocathode grown by MBE and MOCVD  

NASA Astrophysics Data System (ADS)

In order to compare the structures of GaAs photocathodes grown by molecular beam epitaxy (MBE) and metal-organic chemical vapour deposition (MOCVD), four wideband response exponential doping photocathodes were prepared. Their reflectivity and transmittivity were measured by the spectrophotometer, and three thin layer thicknesses were fitted based on the matrix theory in Thin-film Optics. The comparison of the results indicated that for the GaAs photocathode grown by MBE, only one amendatory layer with the low Al component should be added between the Ga1-xAlxAs window layer and the GaAs active layer in order to the higher fitting accuracy. Opposite occurs for the MOCVD samples. In the case of accurately controlling the layered doping concentration, the material grown by MBE is the optimal, while that grown by MOCVD is suit for the exponential doping situation. These results are available for the material growth and the module preparation of the varied doping transmission-mode GaAs photocathodes.

Zhao, Jing; Shen, Weikang; Chang, Benkang; Zhang, Yijun; Zhang, Jian; Qin, Cui

2014-10-01

258

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

259

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

260

Gallium Arsenide preparation and QE Lifetime Studies using the ALICE Photocathode Preparation Facility  

E-print Network

In recent years, Gallium Arsenide (GaAs) type photocathodes have become widely used as electron sources in modern Energy Recovery Linac based light sources such as the Accelerators and Lasers in Combined Experiments (ALICE) at Daresbury Laboratory and as polarised electron source for the proposed International Linear Collider (ILC). Once activated to a Low Electron Affinity (LEA) state and illuminated by a laser, these materials can be used as a high-brightness source of both polarised and un-polarised electrons. This paper presents an effective multi-stage preparation procedure including heat cleaning, atomic hydrogen cleaning and the activation process for a GaAs photocathode. The stability of quantum efficiency (QE) and lifetime of activated to LEA state GaAs photocathode have been studied in the ALICE load-lock photocathode preparation facility which has a base pressure in the order of 10^-11 mbar. These studies are supported by further experimental evidence from surface science techniques such as X-ray P...

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

2010-01-01

261

Spectral response variation of a negative-electron-affinity photocathode in the preparation process  

SciTech Connect

In order to research the spectral response variation of a negative electron affinity (NEA) photocathode in the preparation process, we have done two experiments on a transmission-type GaAs photocathode.First, an automatic spectral response recording system is described, which is used to take spectral response curves during the activation procedure of the photocathode. By this system, the spectral response curves of a GaAs:Cs-Ophotocathode measured in situ are presented. Then, after the cathode is sealed with a microchannel plate and a fluorescence screen into the image tube, we measure the spectral response of the tube by another measurement instrument. By way of comparing and analyzing these curves, we can find the typical variation in spectral-responses.The reasons for the variation are discussed. Based on these curves, spectral matching factors of a GaAs cathode for green vegetation and rough concrete are calculated. The visual ranges of night-vision goggles under specific circumstances are estimated. The results show that the spectral response of the NEA photocathode degraded in the sealing process, especially at long wavelengths. The variation has also influenced the whole performance of the intensifier tube.

Liu Lei; Du Yujie; Chang Benkang; Yunsheng Qian

2006-08-20

262

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

E-print Network

-Si photocathodes exhibit impressive photo- current of 6.1 mA/cm2 at a large positive bias of 0.8 V vs RHE, which of solar water splitting produces hydrogen, a storable clean fuel. To be competitive with fossil fuels requires large external bias to perform water splitting and therefore limits the solar to hydrogen

Javey, Ali

263

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

264

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

PubMed Central

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

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

2011-01-01

265

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

PubMed

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

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

2011-05-28

266

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

267

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.; Feng, J.; Wan, W.; Padmore, H. A. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Ben-Zvi, I. [Brookhaven National Laboratory, Upton, New York 11973 (United States); Stony Brook University, Stony Brook, New York 11794 (United States); Dowell, D. H. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Rao, T.; Smedley, J. [Brookhaven National Laboratory, Upton, New York 11973 (United States)

2011-07-18

268

Dynamic optical modulation of an electron beam on a photocathode RF gun: Toward intensity-modulated radiation therapy (IMRT)  

NASA Astrophysics Data System (ADS)

In intensity-modulated radiation therapy (IMRT), the aim is to deliver reduced doses of radiation to normal tissue. As a step toward IMRT, we examined dynamic optical modulation of an electron beam produced by a photocathode RF gun. Images on photomasks were transferred onto a photocathode by relay imaging. The resulting beam was controlled by a remote mirror. The modulated electron beam maintained its shape on acceleration, had a fine spatial resolution, and could be moved dynamically by optical methods.

Kondoh, Takafumi; Kashima, Hiroaki; Yang, Jinfeng; Yoshida, Yoichi; Tagawa, Seiichi

2008-10-01

269

Structural Characterization of Methanol Substituted Lanthanum Halides  

PubMed Central

The first study into the alcohol solvation of lanthanum halide [LaX3] derivatives as a means to lower the processing temperature for the production of the LaBr3 scintillators was undertaken using methanol (MeOH). Initially the de-hydration of {[La(µ-Br)(H2O)7](Br)2}2 (1) was investigated through the simple room temperature dissolution of 1 in MeOH. The mixed solvate monomeric [La(H2O)7(MeOH)2](Br)3 (2) compound was isolated where the La metal center retains its original 9-coordination through the binding of two additional MeOH solvents but necessitates the transfer of the innersphere Br to the outersphere. In an attempt to in situ dry the reaction mixture of 1 in MeOH over CaH2, crystals of [Ca(MeOH)6](Br)2 (3) were isolated. Compound 1 dissolved in MeOH at reflux temperatures led to the isolation of an unusual arrangement identified as the salt derivative {[LaBr2.75•5.25(MeOH)]+0.25 [LaBr3.25•4.75(MeOH)]?0.25} (4). The fully substituted species was ultimately isolated through the dissolution of dried LaBr3 in MeOH forming the 8-coordinated [LaBr3(MeOH)5] (5) complex. It was determined that the concentration of the crystallization solution directed the structure isolated (4 concentrated; 5 dilute) The other LaX3 derivatives were isolated as [(MeOH)4(Cl)2La(µ-Cl)]2 (6) and [La(MeOH)9](I)3•MeOH (7). Beryllium Dome XRD analysis indicated that the bulk material for 5 appear to have multiple solvated species, 6 is consistent with the single crystal, and 7 was too broad to elucidate structural aspects. Multinuclear NMR (139La) indicated that these compounds do not retain their structure in MeOD. TGA/DTA data revealed that the de-solvation temperatures of the MeOH derivatives 4 – 6 were slightly higher in comparison to their hydrated counterparts. PMID:20514349

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

2010-01-01

270

The effects of halide anions on the dielectric response of potassium halide solutions in visible, UV and far UV region  

NASA Astrophysics Data System (ADS)

Based on the experimentally measured dispersion of refractive indices, we studied the effects of halide anions on the dielectric response of potassium halide solutions in the visible, UV and far UV regions. It was shown that a specific ion effect according to the Hofmeister series is clearly demonstrated for the visible range of spectra. For the near-, mid-, and far UV ranges of spectra, the specific ion effect essentially depends on solution concentration and temperature. The influence of ions on the behavior of dynamic dielectric permittivity of a solution is discussed on the basis of ion/water and ion/ion electrostatic and electrodynamic interactions and hydration shell structure.

Shagieva, F. M.; Boinovich, L. B.

2013-06-01

271

SAFE Alkali Metal Heat Pipe Reliability  

NASA Astrophysics Data System (ADS)

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

Reid, Robert S.

2003-01-01

272

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

E-print Network

of Chromatograms: Sub-Nanogram Detection of Aflatoxins Sir: The presence of carcinogenic mold metabolites, par- ticularly aflatoxins, in food and feed products has become increasingly recognized as a serious health

Zare, Richard N.

273

Monolayer films of liquid crystal 12CB grown by molecular beam deposition on cleaved surfaces of alkali halides  

Microsoft Academic Search

Ultrathin films of liquid crystal 12CB with monolayer-order thickness were grown on cleaved (001) surfaces of NaCl, KCl and KBr substrates by molecular beam deposition. The molecular arrangement and the morphology of the films were analyzed by high sensitivity reflection high energy electron diffraction and atomic force microscopy (AFM), respectively. Epitaxial films were formed on KCl and KBr, whereas only

T. Shimada; M. Nagahori; A. Koma

1999-01-01

274

Selection of non-adsorbing alkali components  

SciTech Connect

This project consists of three phases of laboratory experimental study. In phase I (screening), eight candidate materials, 304SS (serves as a base material for comparison), Hastelloy C-276, Hastelloy X, Haynes No. 188, Allonized 304SS, Pt-coated 304SS, and ceramic-coated 304SS, will be subjected to atmospheric TGA study under the simulated PFBC (oxidizing) environment with and without alkali vapor doping. Each candidate material will be evaluated for its resistance toward alkali-vapor capture. In addition, a post-test metallographic characterization of the sample will be performed to obtain a better understanding of the alkali capture mechanism and material behavior. The material(s) with little or no alkali-vapor adsorption will be selected as the promising material(s) for the Phase II study. In Phase II, the promising material(s) will be further tested in the TGA under elevated pressure to simulate the PFBC environment (in terms of temperature, pressure, and gas composition). The effect of pressure on the extent of alkali-vapor adsorption will be evaluated, and the test samples will be metallographically characterized. The most promising candidate material(s) will be identified and recommended for further tesfing in the actual PFBC environment. In Phase III, four materials will be selected from the eight candidate materials screened in the PFBC environment and will be evaluated for their alkali-vapor capture by atmospheric TGA under the coal gasification fuel gas (reducing) environment. The tested samples will also be metallographically characterized. The most promising material(s) will be identified and recommended for further testing in the actual coal gasification environment.

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

1992-11-01

275

Selection of non-adsorbing alkali components  

SciTech Connect

This project consists of three phases of laboratory experimental study. In phase I (screening), eight candidate materials, 304SS (serves as a base material for comparison), Hastelloy C-276, Hastelloy X, Haynes No. 188, Allonized 304SS, Pt-coated 304SS, and ceramic-coated 304SS, will be subjected to atmospheric TGA study under the simulated PFBC (oxidizing) environment with and without alkali vapor doping. Each candidate material will be evaluated for its resistance toward alkali-vapor capture. In addition, a post-test metallographic characterization of the sample will be performed to obtain a better understanding of the alkali capture mechanism and material behavior. The material(s) with little or no alkali-vapor adsorption will be selected as the promising material(s) for the Phase II study. In Phase II, the promising material(s) will be further tested in the TGA under elevated pressure to simulate the PFBC environment (in terms of temperature, pressure, and gas composition). The effect of pressure on the extent of alkali-vapor adsorption will be evaluated, and the test samples will be metallographically characterized. The most promising candidate material(s) will be identified and recommended for further tesfing in the actual PFBC environment. In Phase III, four materials will be selected from the eight candidate materials screened in the PFBC environment and will be evaluated for their alkali-vapor capture by atmospheric TGA under the coal gasification fuel gas (reducing) environment. The tested samples will also be metallographically characterized. The most promising material(s) will be identified and recommended for further testing in the actual coal gasification environment.

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

1992-01-01

276

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

277

Charge lifetime measurements at high average current using a K2CsSb photocathode inside a dc high voltage photogun  

NASA Astrophysics Data System (ADS)

Two K2CsSb photocathodes were manufactured at Brookhaven National Lab and delivered to Jefferson Lab within a compact vacuum apparatus at pressure ˜10-11Torr. 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 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 due to extensive ion bombardment under severely degraded vacuum conditions, and as a result of localized heating via the laser beam. Following beam delivery, the photocathodes were evaluated using a scanning electron microscope to determine surface morphology.

Mammei, R. R.; Suleiman, R.; Feingold, J.; Adderley, P. A.; Clark, J.; Covert, S.; Grames, J.; Hansknecht, J.; Machie, D.; Poelker, M.; Rao, T.; Smedley, J.; Walsh, J.; McCarter, J. L.; Ruiz-Osés, M.

2013-03-01

278

Photoelectron energy spectra of opaque photocathodes in the extreme and far ultraviolet  

NASA Technical Reports Server (NTRS)

Measurements of the EUV quantum detection efficiency (QDE) of opaque RbBr, CsBr, and KBr photocathodes are described and investigations of their photoemission characteristics over the 44-1560 A wavelength range are reported. The results show that high QDEs can be obtained in the EUV. Narrow QDE peaks at soft X-ray wavelengths occur at slightly different wavelengths for each of the materials studied. The long-wavelength thresholds vary according to the material band gap. Data on the photoemission from the photocathode layer on the microchannel plate interchannel web area are used to determine the number and energy distribution of the emitted photoelelectrons as a function of wavelength.

Siegmund, Oswald H. W.; Gaines, Geoffrey A.

1990-01-01

279

Change of the surface potential barrier of GaAs photocathode during two-step activation  

NASA Astrophysics Data System (ADS)

High and low temperature activation experiments were carried out for a transmission-mode GaAs photocathode sample, and the activation photocurrent curves were recorded. The variety of the activation photocurrent curves between high and low temperatures was studied. By using fitting calculation, the surface potential barrier parameters of NEA photocathode after high and low temperature activations were obtained, respectively, and the change of the surface potential barriers between high and low -temperature activations is indicated. Besides, The NEA cathode surface after high-temperature activation and low temperature activation were analyzed respectively by using angle-dependent X-ray photoelectron spectroscopy (XPS). Above investigation results indicate that, with contrast to high-temperature activation, the thickness of surface potential barriers after low-temperature activation become thin and the vacuum level is reduced further. As a result, the cathode spectral sensitivity is improved remarkably.

Niu, Jun; Gao, Youtang; Qian, Yunsheng; Chang, Benkang

2014-09-01

280

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

PubMed

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

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

2013-05-01

281

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

282

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

PubMed

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

Nagai, Ryoji; Hajima, Ryoichi; Nishimori, Nobuyuki

2012-12-01

283

Effect of humid air exposure on photoemissive and structural properties of KBr thin film photocathode  

E-print Network

We have investigated the influence of water molecule absorption on photoemissive and structural properties of potassium bromide (KBr) thin film photocathode under humid air exposure at relative humidity (RH) 65%. It is evident from photoemission measurement that the photoelectron yield of KBr photocathode is degraded exponentially with humid air exposed time. Structural studies of the "as-deposited" and "humid air aged" films reveal that there is no effect of RH on film's crystalline face centered cubic (fcc) structure. However, the average crystallite size of "humid air exposed film" KBr film has been increased as compared to "as-deposited". In addition, topographical properties of KBr film are also examined by means of scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) and it is observed that granular characteristic of film has been altered, even for short exposure to humid air.

Rai, R; Ghosh, N; Singh, B K

2014-01-01

284

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

285

Direct Current Ballast Circuit for Metal Halide Lamp.  

National Technical Information Service (NTIS)

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 o...

P. Lutus

1981-01-01

286

Process for treatment of wells with acid halides  

Microsoft Academic Search

Methods are provided for acidization of wells which are useful in deep high-temperature oil and gas wells. The methods include injection of an acid halide which upon reaction with water in situ in the subterranean formation surrounding the well forms 2 acids, one of which is a halogen acid. The method entails first drying the borehole, and then injecting into

1976-01-01

287

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

288

Silver catalyzed zinc Barbier reaction of benzylic halides in water  

Microsoft Academic Search

Benzylic chlorides react in aqueous dibasic potassium phosphate under silver catalysis with aromatic aldehydes in the presence of zinc dust to give 1,2-diaryl alcohols in moderate to good yields. Dimerization to bibenzyls and reduction of the halide are important side reactions. A wide range of substituted aromatic and heteroaromatic aldehydes and of substituted benzylic chlorides can be used. Aliphatic aldehydes

Lothar W. Bieber; Elisabeth C. Storch; Ivani Malvestiti; Margarete F. da Silva

1998-01-01

289

Methyl halide emissions from greenhouse-grown mangroves  

Microsoft Academic Search

Two mangrove species, Avicennia germinans and Rhizophora mangle, were greenhouse grown for nearly 1.5 years from saplings. A single individual of each species was monitored for the emission of methyl halides from aerial tissue. During the first 240 days, salinity was incrementally increased with the addition of seawater, and was maintained between 18 and 28‰ for the duration of the

Steven L. Manley; Nun-Yii Wang; Maggie L. Walser; Ralph J. Cicerone

2007-01-01

290

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

291

A Very High Charge, High Polarization Gradient-Doped Strained GaAs Photocathode  

SciTech Connect

A high-gradient-doping technique is applied to strained polarized photocathodes. The electron spin-polarization increases significantly as the highly-doped layer thickness is reduced. A 5.0-7.5 nm p-type surface layer doped to 5 x 10{sup 19} cm{sup -3} is found sufficient to overcome the surface charge limit. It is shown that the charge requirements of the Next Linear Collider can be met with a polarization approaching 80%.

Maruyama, Takashi

2002-03-25

292

Porous copper zinc tin sulfide thin film as photocathode for double junction photoelectrochemical solar cells.  

PubMed

Porous copper zinc tin sulfide (CZTS) thin film was prepared via a solvothermal approach. Compared with conventional dye-sensitized solar cells (DSSCs), double junction photoelectrochemical cells using dye-sensitized n-type TiO(2) (DS-TiO(2)) as the photoanode and porous p-type CZTS film as the photocathode shows an increased short circuit current, external quantum efficiency and power conversion efficiency. PMID:22322239

Dai, Pengcheng; Zhang, Guan; Chen, Yuncheng; Jiang, Hechun; Feng, Zhenyu; Lin, Zhaojun; Zhan, Jinhua

2012-03-21

293

The capability comparison of high-performance GaAs photocathodes  

NASA Astrophysics Data System (ADS)

High-performance reflection-mode GaAs photocathode (named cathode 1 for short) with the integral sensitivity of 2140?A/lm is prepared by adopting "high-low temperature" two-step activation and using heavily p-type Be-doped GaAs materials, which is grown by molecular beam epitaxy (MBE) technique. Moreover, spectral response characteristic and cathodes performance parameters of two cathodes are obtained by spectral response database we compiled, one is the reflection-mode photocathode (named cathode 2 for short) with the integral sensitivity of 1800?A/lm reported by G. H. Olsen in the 70s; the other is the transmission-mode photocathode (named cathode 3 for short) with the integral sensitivity 3070?A/lm reported by O. H. W. Siegmund in 2003. A transmission-mode cathode (named cathode 4 for short) is acquired by computer simulation on the basis of cathode 1, and its integral sensitivity is 1907?A/lm, then we compare the reflection-mode cathodes (cathode 1 and cathode 2) and the transmission-mode cathodes (cathode 3 and cathode 4), respectively, and analyze the cause for performance difference among these cathodes, the results show that the surface escape probability of cathode 1 reach to 0.62, which is lower slightly that of cathode 2, so preparation technique of cathode 1 has gotten higher the surface escape probability, but the electron diffusion length of cathode 1 and the back interface recombination velocity of cathode 4 is not better compared to cathode 2 or cathode 3. Which shows preparation technique of cathode 1 obtains better surface barrier, it need to be optimized all the same for achieving higher performance GaAs photocathodes.

Wang, Hui; Chang, Benkang; Zou, Jijun; Li, Ming; Du, Xiaoqing; Yang, Zhi

2006-09-01

294

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

SciTech Connect

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

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

1994-09-01

295

Longitudinal Emittance Compensation In a Photocathode RF gun Injector - Analysis and Experiments  

NASA Astrophysics Data System (ADS)

The concept of longitudinal emittance compensation in a photocathode RF gun injector is introduced first. The analysis shows that the arrangements of the transverse emittance compensation photocathode RF gun injector is well suited for longitudinal emittance compensation. By setting the laser phase relative to the RF field close to the zero crossing, the photoelectron beam produced at the gun exit will have short bunchlength and large energy spread, this beam was further compressed in the drift space followed the RF gun and solenoid. The linac after the drift space will preserve the short bunch and reduce the energy spread through acceleration. The solenoid magnet plays an important role in the bunch compression in the drift space to reduce the bunch lengthening caused by the beam divergence. Experiments performed at the Brookhaven Accelerator Test Facility (ATF) has produced a 370 fs electron beam with 40 pC using a 15 ps laser, more than a facto of 30 bunch compression. We will also discussed various effects may reduce the longitudinal emittance compensation in the photocathode RF gun injector.

Wang, X. J.

1997-05-01

296

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

297

40 CFR 721.4660 - Alcohol, alkali metal salt.  

Code of Federal Regulations, 2011 CFR

...false Alcohol, alkali metal salt. 721.4660 Section 721...4660 Alcohol, alkali metal salt. (a) Chemical substance...identified as alcohol, alkali metal salt (PMN P-91-151) is subject...uses are: (i) Release to water. Requirements as...

2011-07-01

298

40 CFR 721.4660 - Alcohol, alkali metal salt.  

Code of Federal Regulations, 2013 CFR

...false Alcohol, alkali metal salt. 721.4660 Section 721...4660 Alcohol, alkali metal salt. (a) Chemical substance...identified as alcohol, alkali metal salt (PMN P-91-151) is subject...uses are: (i) Release to water. Requirements as...

2013-07-01

299

40 CFR 721.4660 - Alcohol, alkali metal salt.  

Code of Federal Regulations, 2012 CFR

...false Alcohol, alkali metal salt. 721.4660 Section 721...4660 Alcohol, alkali metal salt. (a) Chemical substance...identified as alcohol, alkali metal salt (PMN P-91-151) is subject...uses are: (i) Release to water. Requirements as...

2012-07-01

300

40 CFR 721.4660 - Alcohol, alkali metal salt.  

Code of Federal Regulations, 2010 CFR

...false Alcohol, alkali metal salt. 721.4660 Section 721...4660 Alcohol, alkali metal salt. (a) Chemical substance...identified as alcohol, alkali metal salt (PMN P-91-151) is subject...uses are: (i) Release to water. Requirements as...

2010-07-01

301

Photoabsorption Spectra of Hydrogen and Alkali Atoms in Electric Fields  

Microsoft Academic Search

A systematic study of the photoabsorption spectra of highly excited hydrogen and alkali atoms in electric fields is presented, based on the semiclassical closed -orbit theory. In most respects, hydrogen and alkali atoms behave similarly, because the excited alkali atoms have a single electron outside of a small ionic core, and the core only produces small shifts of energy levels

Jing Gao

1994-01-01

302

Detection of soft X-rays with NEA III-V photocathodes. [Negative Electron Affinity X-ray detector for astronomy  

NASA Technical Reports Server (NTRS)

A description is presented of the results of tests on an X-ray photomultiplier containing a negative electron affinity (NEA) photocathode. This device makes it possible to investigate the response of the NEA photocathode to X-rays of various energies. The obtained data provide a basis for the determination of the photoelectron yield and energy resolution of the considered photocathode as a function of energy in the range from 0.8 to 3 keV. The investigation demonstrates the feasibility of using an NEA III-V photocathode for the detection of soft X-rays.

Bardas, D.; Kellogg, E.; Murray, S.; Enck, R., Jr.

1978-01-01

303

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

304

Kraft continuous digester effective alkali control  

Microsoft Academic Search

Optimal control of a continuous pulp digester is a difficult problem. The objective is to achieve maximum pulp production at a specified Kappa number with a minimum of chemicals and energy input. Existing Kappa number control strategies focus on H factor control. These strategies attempt to model the relationship between Kappa number, H factor, sulphidity, and effective alkali. Reducing the

B. Gough; JOHN T. KAY

1996-01-01

305

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

306

Calcium-alkali syndrome in the modern era.  

PubMed

The ingestion of calcium, along with alkali, results in a well-described triad of hypercalcemia, metabolic alkalosis, and renal insufficiency. Over time, the epidemiology and root cause of the syndrome have shifted, such that the disorder, originally called the milk-alkali syndrome, is now better described as the calcium-alkali syndrome. The calcium-alkali syndrome is an important cause of morbidity that may be on the rise, an unintended consequence of shifts in calcium and vitamin D intake in segments of the population. We review the pathophysiology of the calcium-alkali syndrome. PMID:24288027

Patel, Ami M; Adeseun, Gbemisola A; Goldfarb, Stanley

2013-12-01

307

Calcium-Alkali Syndrome in the Modern Era  

PubMed Central

The ingestion of calcium, along with alkali, results in a well-described triad of hypercalcemia, metabolic alkalosis, and renal insufficiency. Over time, the epidemiology and root cause of the syndrome have shifted, such that the disorder, originally called the milk-alkali syndrome, is now better described as the calcium-alkali syndrome. The calcium-alkali syndrome is an important cause of morbidity that may be on the rise, an unintended consequence of shifts in calcium and vitamin D intake in segments of the population. We review the pathophysiology of the calcium-alkali syndrome. PMID:24288027

Patel, Ami M.; Adeseun, Gbemisola A.; Goldfarb, Stanley

2013-01-01

308

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

309

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

SciTech Connect

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

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

2009-08-04

310

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

311

Developments in alkali-metal atomic magnetometry  

NASA Astrophysics Data System (ADS)

Alkali-metal magnetometers use the coherent precession of polarized atomic spins to detect and measure magnetic fields. Recent advances have enabled magnetometers to become competitive with SQUIDs as the most sensitive magnetic field detectors, and they now find use in a variety of areas ranging from medicine and NMR to explosives detection and fundamental physics research. In this thesis we discuss several developments in alkali-metal atomic magnetometry for both practical and fundamental applications. We present a new method of polarizing the alkali atoms by modulating the optical pumping rate at both the linear and quadratic Zeeman resonance frequencies. We demonstrate experimentally that this method enhances the sensitivity of a potassium magnetometer operating in the Earth's field by a factor of 4, and we calculate that it can reduce the orientation-dependent heading error to less than 0.1 nT. We discuss a radio-frequency magnetometer for detection of oscillating magnetic fields with sensitivity better than 0.2 fT/ Hz , which we apply to the observation of nuclear magnetic resonance (NMR) signals from polarized water, as well as nuclear quadrupole resonance (NQR) signals from ammonium nitrate. We demonstrate that a spin-exchange relaxation-free (SERF) magnetometer can measure all three vector components of the magnetic field in an unshielded environment with comparable sensitivity to other devices. We find that octadecyltrichlorosilane (OTS) acts as an anti-relaxation coating for alkali atoms at temperatures below 170°C, allowing them to collide with a glass surface up to 2,000 times before depolarizing, and we present the first demonstration of high-temperature magnetometry with a coated cell. We also describe a reusable alkali vapor cell intended for the study of interactions between alkali atoms and surface coatings. Finally, we explore the use of a cesium-xenon SERF comagnetometer for a proposed measurement of the permanent electric dipole moments (EDMs) of the electron and the 129Xe atom, with projected sensitivity of deltade=9x10 -30 e-cm and deltadXe=4x10 -31 e-cm after 100 days of integration; both bounds are more than two orders of magnitude better than the existing experimental limits on the EDMs of the electron and of any diamagnetic atom.

Seltzer, Scott Jeffrey

312

Effects of potassium alkalis and sodium alkalis on the dechlorination of o-chlorophenol in supercritical water.  

PubMed

Effects of potassium alkalis and sodium alkalis on the dechlorination of o-chlorophenol (o-CP) in supercritical water (SCW) were studied in this paper under the conditions of 450 degrees C and 25 MPa. Experimental results indicated that the dechlorination of o-CP can be accelerated significantly by all alkalis investigated. The dechlorination of o-CP proceeded mainly via two pathways: hydrodechlorination and hydrolysis. Both of the two pathways can be promoted by alkalis, and the dechlorination of o-CP can be accelerated by both the cations and hydroxide ion dissociated from alkalis. The overall dechlorination of o-CP can be accelerated by cations via promoting the hydrodechlorination pathway, while, hydroxide ion via promoting the hydrolysis pathway. In addition, the hydrodechlorination can be accelerated faster by sodium alkalis than that by potassium ones, while, the hydrolysis can be promoted faster by potassium alkalis. This difference may be caused by the different charge density between potassium ion and sodium ion, and the different solubility and dissociation constant between potassium alkalis and sodium alkalis in SCW. Dechlorination of o-CP with addition of alkalis prior to supercritical water oxidation (SCWO) process not only can avoid the reactor corrosion caused by the generated hydrochloric acid in direct SCWO of o-CP, but also can reduce the formation of toxic chlorinated byproducts compared with direct SCWO process or SCWO of o-CP with addition of alkali. PMID:17005235

Sun, Zhirong; Takahashi, Fumitake; Odaka, Yu; Fukushi, Kensuke; Oshima, Yoshito; Yamamoto, Kazuo

2007-01-01

313

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

314

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

315

Organometal halide perovskites as useful materials in sensitized solar cells.  

PubMed

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

Singh, Surya Prakash; Nagarjuna, P

2014-04-14

316

Experiments and modeling of optically-pumped hydrogen halide lasers  

Microsoft Academic Search

Experiments on an optically-pumped hydrogen fluoride laser are discussed. Rotation-vibration transitions are pumped on overtone bands and lasing is observed on delta v = I transitions at wavelengths near 2.7 microns. Kinetic modeling of short-pulsed optically-pumped hydrogen halide lasers has been carried out. The model utilizes sealing laws to obtain rate constants describing the energy transfer reactions. A truncated version

Nicholas P. Machara; Harold C. Miller; Dan T. Radzykewycz Jr.; Gordon D. Hager

1993-01-01

317

Thermal isomerization in isolated cesium–halide cluster anions  

Microsoft Academic Search

We have used photoelectron spectroscopy to observe thermal isomerization in cesium–halide cluster anions. In many of the (CsX)nCsm? (X=Cl, Br, I; n=2–7; m=0, 1) systems we have studied, small changes in the source nozzle temperature produce dramatic changes in the distributions of cluster isomers. There is also evidence that the isomer distributions are in dynamic equilibrium, with their temperatures controlling

F. K. Fatemi; D. J. Fatemi; L. A. Bloomfield

1999-01-01

318

Thermal Isomerization in Isolated Cesium-Halide Clusters  

Microsoft Academic Search

We have used photoelectron spectroscopy to observe thermal isomerization in cesium-halide cluster anions. In many of the (CsX)_nCs_m^- (X = Cl, Br, I; n = 2-7; m = 0, 1) systems we have studied, small changes in the source nozzle temperature produce dramatic changes in the distribution of cluster isomers. When specific isomers are selectively photodepleted, isomer interconversion quickly reestablishes

Louis Bloomfield; Fredrik Fatemi; Darius Fatemi

1996-01-01

319

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

320

Colloidal nanocrystals with inorganic halide, pseudohalide, and halometallate ligands.  

PubMed

We investigate simple halides and pseudohalides as an important class of inorganic ligands for nanocrystals (NCs) in solution phase ligand exchange. These short, robust, and easy to model ligands bind to the NC surface and provide electrostatic stabilization of NC dispersions in N-methylformamide. The replacement of organic ligands on NCs with compact halide and pseudohalide ligands greatly facilitates electronic communication between NCs. For example, a high electron mobility of ? ? 12 cm(2) V(-1) s(-1) has been observed in thin films made of I(-)-capped CdSe NCs. We also studied charge transport properties of thin films based on the pseudohalide N3(-)-capped InAs NCs, suggesting the possibility of obtaining "all III-V" NC solids. In addition, we extend the surface chemistry of halometallates (e.g., CH3NH3PbI3), which can stabilize colloidal solutions of lead chalcogenide NCs. These halide, pseudohalide, and halometallate ligands enrich the current family of inorganic ligands and can open up more opportunities for applications of NCs in the fields of electronics, optoelectronics, and thermoelectrics. PMID:24988140

Zhang, Hao; Jang, Jaeyoung; Liu, Wenyong; Talapin, Dmitri V

2014-07-22

321

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

322

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

323

Hydrogen-exchange reaction of alkyl halides with formic and acetic acids  

Microsoft Academic Search

1.An investigation was made of the hydrogen exchange of alkyl halides in media differing in dielectric constant, namely formic and acetic acids.2.Tertiary halides (chloride, bromides, and iodides) undergo hydrogen exchange with formic acid-d, whereas secondary alkyl halides do not undergo hydrogen exchange under the same conditions. Tertiary chlorides do not undergo hydrogen exchange with acetic acid-d, whereas under the same

D. N. Kursanov; E. V. Bykova; V. N. Setkina

1959-01-01

324

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

325

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

326

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, Stephane; de Bettignies, Remi; Artero, Vincent; Palacin, Serge; Jousselme, Bruno

2013-01-01

327

High time resolution beam-based measurement of the rf-to-laser jitter in a photocathode rf gun  

NASA Astrophysics Data System (ADS)

Characterizing the rf-to-laser jitter in the photocathode rf gun and its possible origins is important for improving the synchronization and beam quality of the linac based on the photocathode rf gun. A new method based on the rf compression effect in the photocathode rf gun is proposed to measure the rf-to-laser jitter in the gun. By taking advantage of the correlation between the rf compression and the laser injection phase, the error caused by the jitter of the accelerating field in the gun is minimized and thus 10fs time resolution is expected. Experimental demonstration at the Tsinghua Thomson scattering x-ray source with a time resolution better than 35 fs is reported in this paper. The experimental results are successfully used to obtain information on the possible cause of the jitter and the accompanying drifts.

Zhang, Zhen; Du, Yingchao; Yan, Lixin; Du, Qiang; Hua, Jianfei; Shi, Jiaru; Yang, Jin; Wang, Dan; Huang, Wenhui; Chen, Huaibi; Tang, Chuanxiang

2014-03-01

328

Chemically induced fracturing in alkali feldspar  

NASA Astrophysics Data System (ADS)

Fracturing in alkali feldspar during Na+-K+ cation exchange with a NaCl-KCl salt melt was studied experimentally. Due to a marked composition dependence of the lattice parameters of alkali feldspar, any composition gradient arising from cation exchange causes coherency stress. If this stress exceeds a critical level fracturing occurs. Experiments were performed on potassium-rich gem-quality alkali feldspars with polished (010) and (001) surfaces. When the feldspar was shifted toward more sodium-rich compositions over more than about 10 mole %, a system of parallel cracks with regular crack spacing formed. The cracks have a general (h0l) orientation and do not correspond to any of the feldspar cleavages. The cracks are rather oriented (sub)-perpendicular to the direction of maximum tensile stress. The critical stress needed to initiate fracturing is about 325 MPa. The critical stress intensity factor for the propagation of mode I cracks, K Ic, is estimated as 2.30-2.72 MPa m1/2 (73-86 MPa mm1/2) from a systematic relation between characteristic crack spacing and coherency stress. An orientation mismatch of 18° between the crack normal and the direction of maximum tensile stress is ascribed to the anisotropy of the longitudinal elastic stiffness which has pronounced maxima in the crack plane and a minimum in the direction of the crack normal.

Scheidl, K. S.; Schaeffer, A.-K.; Petrishcheva, E.; Habler, G.; Fischer, F. D.; Schreuer, J.; Abart, R.

2014-01-01

329

Microscopic surface structure of liquid alkali metals  

SciTech Connect

We report an x-ray scattering study of the microscopic structure of the surface of a liquid alkali metal. The bulk liquid structure factor of the eutectic K{sub 67}Na{sub 33} alloy is characteristic of an ideal mixture, and so shares the properties of an elemental liquid alkali metal. Analysis of off-specular diffuse scattering and specular x-ray reflectivity shows that the surface roughness of the K-Na alloy follows simple capillary wave behavior with a surface structure factor indicative of surface-induced layering. Comparison of the low-angle tail of the K{sub 67}Na{sub 33} surface structure factor with the one measured for liquid Ga and In previously suggests that layering is less pronounced in alkali metals. Controlled exposure of the liquid to H{sub 2} and O{sub 2} gas does not affect the surface structure, indicating that oxide and hydride are not stable at the liquid surface under these experimental conditions. (c) 2000 The American Physical Society.

Tostmann, H. [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States)] [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); DiMasi, E. [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States)] [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States); Pershan, P. S. [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States)] [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Ocko, B. M. [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States)] [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States); Shpyrko, O. G. [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States)] [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Deutsch, M. [Department of Physics, Bar-Ilan University, Ramat-Gan 52100, (Israel)] [Department of Physics, Bar-Ilan University, Ramat-Gan 52100, (Israel)

2000-03-15

330

A polarized photoluminescence study of strained layer GaAs photocathodes  

SciTech Connect

Photoluminescence measurements have been made on a set of epitaxially grown strained GaAs photocathode structures. The photocathodes are designed to exhibit a strain-induced enhancement of the electron spin polarization obtainable by optical pumping with circularly polarized radiation of near band gap energy. For the case of non-strained GaAs, the degree of spin polarization is limited to 50% by crystal symmetry. Under an appropriate uniaxial compression or tension, however, the valence band structure near the gap minimum is modified such that a spin polarization of 100% is theoretically possible. A total of nine samples with biaxial compressive strains ranging from zero to {approximately}0.8% are studied. X-ray diffraction analysis, utilizing Bragg reflections, is used to determine the crystal lattice structure of the samples. Luminescence spectra and luminescence circular polarization data are obtained at room temperature, {approx}78 K and {approx}12 K. The degree of luminescence circular polarization is used as a relative measure of the photo-excited electron spin polarization. The room temperature luminescence circular polarization data is compared with the measured electron spin polarization when the samples are used as electron photo-emitters with a negative electron affinity surface preparation. The luminescence data is also analyzed in conjunction with the crystal structure data with the goal of understanding the strain dependent valence band structure, optical pumping characteristics and spin depolarization mechanisms of the photocathode structures. A simple model is used to describe the luminescence data, obtained for the set of samples. Within the assumptions of the model, the deformation potentials a, b and d for GaAs are determined. The measured values are a = -10.16{+-}.21 eV, b = -2.00{+-}.05 eV and d = -4.87{+-}.29 eV. Good agreement with published values of the deformation potentials provides support for the model used to describe the data.

Mair, R.A.

1996-07-01

331

40 CFR 63.2465 - What requirements must I meet for process vents that emit hydrogen halide and halogen HAP or HAP...  

Code of Federal Regulations, 2010 CFR

...that emit hydrogen halide and halogen HAP or HAP metals? 63.2465 Section...Pollutants: Miscellaneous Organic Chemical Manufacturing...that emit hydrogen halide and halogen HAP or HAP metals? (a) You...process emit hydrogen halide and halogen...

2010-07-01

332

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

333

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

334

Large Photocathode Photodetectors Using Photon Amplification and Phase-Space Compression  

E-print Network

We describe a simple technique to both amplify incident photons and compress their angular x area phase space. These Optical Compressor Amplifier Tubes (OCA Tube) use techniques analogous to image intensifiers, using vacuum photocathodes to detect photons as converted to photoelectrons, amplify the photons via photoelectron bombardment of fast scintillators, and compress the optical phase space onto optical fibers, so that small, high gain photodetectors, like miniature PMT or SiPM, can be used to detect photons from large areas, at comparatively low cost. The properties of and benefits of OCA tubes are described.

Carrio, Alex; Greener, Kevin; McGuiness, Sean; Podrasky, Victor; Sullivan, John; Winn, David R; Bilki, Burak; Onel, Yasar

2014-01-01

335

Generation and measurement of sub-picosecond electron bunch in photocathode rf gun  

E-print Network

We consider a scheme to generate sub-picosecond electron bunch in the photocathode rf gun by improving the acceleration gradient in the gun, suitably tuning the bunch charge, the laser spot size and the acceleration phase, and reducing the growth of transverse emittance by laser shaping. A nondestructive technique is also reported to measure the electron bunch length, by measuring the high-frequency spectrum of wakefield radiation which is caused by the passage of a relativistic electron bunch through a channel surrounded by a dielectric.

Li, Weiwei; Jia, Qika

2013-01-01

336

A high-charge high-brightness L-band photocathode RF gun  

SciTech Connect

The Argonne Wakefield Accelerator has been successfully commissioned and used for conducting wakefield experiments in dielectric loaded structures and plasmas. Although the initial wakefield experiments were successful, higher drive beam quality would substantially improve the wakefield accelerating gradients. In this paper the authors present a new 1-1/2 cell L-band photocathode RF gun design. This gun will produce 10--100 nC beam with 2--5 ps ms pulse length and normalized emittance less than 100 mm mrad. The final gun design and numerical simulations of the beam dynamics are presented.

Conde, M. E.; Gai, W.; Konecny, R.; Power, J. G.; Schoessow, P.; Sun, X.

2000-02-25

337

Intrinsic electron beam emittance from metal photocathodes: the effect of the electron effective mass.  

PubMed

A theoretical development of prior analyses, together with our solenoid scan measurements on eight planar metal photocathodes (Ag, Be, Cr, Cu, Mo, Sn, Ta, and W) and previous data on Mg [X.?J. Wang, M. Babzien, R. Malone, and Z. Wu, in Proceedings of LINAC2002, Gyeongju, Korea, 2002 (Pohang Accelerator Laboratory, Pohang, Korea, 2002), pp. 142-144.] indicate that the transverse momentum (and hence intrinsic emittance) of an electron beam is fundamentally dependent on the electron effective mass in the metal. PMID:24476300

Rickman, B L; Berger, Joel A; Nicholls, A W; Schroeder, W Andreas

2013-12-01

338

Impact of transverse irregularities at the photocathode on the production of high-charge electron bunches  

SciTech Connect

The properties of electron beams produced in a photoinjector are strongly dependent on the initial conditions, i.e. the photocathode drive laser shape and its uniformity. We explore the impact of well-defined transverse laser perturbations on the evolution of the electron beam both in configuration and velocity spaces and especially investigate how certain types of perturbations evolve as the beam propagates in the Argonne Wakefield Accelerator facility. Numerical simulations performed with IMPACT-T are presented. Finally preliminary experimental results aimed at validating our simulations are discussed.

Rihaoui, M.; Bohn, C.L.; /Northern Illinois U.; Piot, P.; /Northern Illinois U. /Fermilab; Power, J.G.; /Argonne

2007-06-01

339

Generation and measurement of sub-picosecond electron bunch in photocathode rf gun  

NASA Astrophysics Data System (ADS)

We consider a scheme to generate a sub-picosecond electron bunch in the photocathode rf gun by improving the acceleration gradient in the gun, suitably tuning the bunch charge, the laser spot size and the acceleration phase, and reducing the growth of transverse emittance by laser shaping. A nondestructive technique is also reported to measure the electron bunch length, by measuring the high-frequency spectrum of wakefield radiation which is caused by the passage of a relativistic electron bunch through a channel surrounded by a dielectric.

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

2013-12-01

340

Selective substitution of alkali cations in mixed alkali glass by solid-state electrochemistry  

NASA Astrophysics Data System (ADS)

Electrosubstitution of alkali cations in mixed-alkali glass containing both Na 2O and K 2O for other monovalent metal cations ( M+=Li +, Ag +, and Cs +) was investigated using a solid-state electrochemical method. The fundamental electrolysis system consists of anode/ M+-conducting microelectrode/glass/Na- ??-Al 2O 3/cathode, where M+ is substituted for the alkali metal ions in the glass under an applied electric field. Li + ions attacked only Na + sites, and Ag + ions replaced Na + sites more readily than K +. In contrast, Cs + ions simultaneously substituted for both Na + and K + sites. The substitution behavior appears to depend on the difference in ionic conductivity between K + and Na + and the radius of the dopant. This mechanism was discussed qualitatively.

Kamada, Kai; Tsutsumi, Yuko; Yamashita, Shuichi; Matsumoto, Yasumichi

2004-01-01

341

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

342

Mixed alkali effect in the ac conductivity of glasses  

Microsoft Academic Search

The ac electrical conductivity of mixed alkali LiF-KF-Al(PO3)3 glasses has been investigated using the complex conductivity formalism. For the first time, a mixed alkali effect has been detected in the ac conductivity of glasses which also exhibit the classical mixed alkali effect in the dc conductivity. The observed conductivity relaxations have been analyzed using three and four parameter functions. Jonscher’s

A. R Kulkarni; P Lunkenheimer; A Loidl

2000-01-01

343

Alkali cation specific adsorption onto fcc(111) transition metal electrodes.  

PubMed

The presence of alkali cations in electrolyte solutions is known to impact the rate of electrocatalytic reactions, though the mechanism of such impact is not conclusively determined. We use density functional theory (DFT) to examine the specific adsorption of alkali cations to fcc(111) electrode surfaces, as specific adsorption may block catalyst sites or otherwise impact surface catalytic chemistry. Solvation of the cation-metal surface structure was investigated using explicit water models. Computed equilibrium potentials for alkali cation adsorption suggest that alkali and alkaline earth cations will specifically adsorb onto Pt(111) and Pd(111) surfaces in the potential range of hydrogen oxidation and hydrogen evolution catalysis in alkaline solutions. PMID:24722828

Mills, J N; McCrum, I T; Janik, M J

2014-07-21

344

New EBCCD with transferred electron photocathode for range-gated active imaging system  

NASA Astrophysics Data System (ADS)

A detailed comparison between conventional image intensifiers and electron bombarded CCD (EBCCD) is conducted. These sensors' advantages and drawbacks are analyzed. EBCCD with transferred electron (TE) photocathode and its application in Laser Illuminated Viewing and Ranging (LIVAR) system are shown in details. The TE Photocathode (TEP) developed by Intevac in 1996 has a demonstrated quantum efficiency of 20% or higher over the spectral range between 0.95 and 1.7 ?m. The TEP is coupled directly with a CCD chip in an electron bombarded CCD (EBCCD) configuration. The overall noise figure of the EBCCD camera is close to one, approximately half that of a standard Generation-III image intensifier. The EBCCD eliminates the micro-channel plate (MCP), phosphor screen, and fiber optics, and as a result both improved image quality and increased sensitivity can be obtained in a smaller sized camera. Because of the reduction in the number of image conversions and the significantly greater signal-to-noise performance, an EBCCD has higher contrast and resolution than an ICCD. These characteristics make the EBCCD a good candidate for military, helmet-mounted night-vision systems as well as for covert surveillance applications.

Xu, Xiaowen; Guo, Jin

2002-09-01

345

Performance of GAASP/GAAS Superlattice Photocathodes in High Energy Experiments using Polarized Electrons  

SciTech Connect

The GaAsP/GaAs strained superlattice photocathode structure has proven to be a significant advance for polarized electron sources operating with high peak currents per microbunch and relatively low duty factor. This is the characteristic type of operation for SLAC and is also planned for the ILC. This superlattice structure was studied at SLAC [1], and an optimum variation was chosen for the final stage of E-158, a high-energy parity violating experiment at SLAC. Following E-158, the polarized source was maintained on standby with the cathode being re-cesiated about once a week while a thermionic gun, which is installed in parallel with the polarized gun, supplied the linac electron beams. However, in the summer of 2005, while the thermionic gun was disabled, the polarized electron source was again used to provide electron beams for the linac. The performance of the photocathode 24 months after its only activation is described and factors making this possible are discussed.

Brachmann, A.; Clendenin, J.E.; Maruyama, T.; Garwin, E.L.; Ioakemidi, K.; Prescott, C.Y.; Turner, J.L.; /SLAC; Prepost, R.; /Wisconsin U., Madison

2006-02-27

346

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

347

The Boeing photocathode accelerator magnetic pulse compression and energy recovery experiment  

NASA Astrophysics Data System (ADS)

An 18 MeV photocathode accelerator, consisting of a two-cell RF photocathode injector (previously operated at 27 MHz micropulse repetition frequency, 5 nC micropulse charge, and 25% duty factor [D.H. Dowell et al., Appl. Phys. Lett. 63 (1993) 2035]) followed by four new multicell cavities, all operating at 433 MHz, is currently being tested for FEL applications. In the present experiment, the inclusion of a third harmonic RF linearizer (operating at 1300 MHz) will allow tailoring of flat-topped micropulse shapes with high peak current. This pulse shaping leads to optimal FEL efficiency and is discussed in another contribution to this conference [J.L. Adamski et al.]. The 1300 MHz structure can also be used in a simple experiment to investigate energy recovery for high power and high efficiency FELs. In this case, proper RF phasing of the drive laser micropulses will allow the 1300 MHz accelerator section to simultaneously accelerate and decelerate alternate micropulses. Longitudinal phase space preparation for both experimental modes is discussed.

Dowell, D. H.; Adamski, J. L.; Hayward, T. D.; Parazzoli, C. G.; Vetter, A. M.

1996-02-01

348

Optical spectroscopy of alkali and alkali-like ions in superfluid 4He  

Microsoft Academic Search

Recent experimental work by the authors on optical microprobes in superfluid 4He is extended to the recombination of snowball structured ions (alkali ions) and electron-bubbles. First results for Li, Na and K are indicating radiationless transitions for these ions, while in the case of the transition elements Cu, Ag and Au with similar valence electron configuration, several recombination bands have

H. Bauer; M. Beau; J. Fischer; H. J. Reyher; J. Rosenkranz; K. Venter

1990-01-01

349

Synthesis of Styrene Carbonate from Carbon Dioxide and Styrene Oxide with Various Zinc Halide-Based Ionic Liquids  

Microsoft Academic Search

\\u000a Abstract  Various zinc halide-based ionic liquids were prepared from zinc halides and onium halides as catalysts for the synthesis of\\u000a styrene carbonate (SC) from styrene oxide and carbon dioxide. The effects of the ionic liquid catalyst composition (types\\u000a of onium cation and halide, onium cation\\/zinc ratio) and CO2 pressure on the reaction were investigated. The effectiveness of the onium cation as

Shin-ichiro Fujita; Masahiro Nishiura; Masahiko Arai

2010-01-01

350

(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

351

Determining Addition Rates for the Growth of Uniform Silver Halide Crystals  

E-print Network

Determining Addition Rates for the Growth of Uniform Silver Halide Crystals David M. Ambrose is determined by the mean crystal size and the dispersity of sizes of the silver halide crystals in the film. A large crystal size provides a film with a fast speed, but the advantage of speed carries

352

Halide peroxidase in tissues that interact with bacteria in the host squidEuprymna scolopes  

Microsoft Academic Search

An enzyme with similarities to myeloperoxidase, the antimicrobial halide peroxidase in mammalian neutrophils, occurs abundantly in the light organ tissue of Euprymna scolopes, a squid that maintains a beneficial association with the luminous bacterium Vibrio fischeri. Using three independent assays typically applied to the analysis of halide peroxidase enzymes, we directly compared the activity of the squid enzyme with that

Andrea L. Small

1999-01-01

353

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...

354

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...

355

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...

356

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.

357

Electrodes For Alkali-Metal Thermoelectric Converters  

NASA Technical Reports Server (NTRS)

Combination of thin, porous electrode and overlying collector grid reduces internal resistance of alkali-metal thermoelectric converter cell. Low resistance of new electrode and grid boosts power density nearly to 1 W/cm2 of electrode area at typical operating temperatures of 1,000 to 1,300 K. Conductive grid encircles electrode film on alumina tube. Bus wire runs along tube to collect electrical current from grid. Such converters used to transform solar, nuclear, and waste heat into electric power.

Williams, Roger M.; Wheeler, Bob L.; Jeffries-Nakamura, Barbara; Lamb, James L.; Bankston, C. Perry; Cole, Terry

1989-01-01

358

Volatile species in halide-activated-diffusion coating packs  

NASA Technical Reports Server (NTRS)

An atmospheric pressure sampling mass spectrometer was used to identify the vapor species generated in a halide-activated cementation pack. Pack powder mixtures containing a Cr-Al binary masteralloy powder, an NH4Cl activator salt, and either ZrO2 or Y2O3 (or neither) were analyzed at 1000 C. Both the equilibrium calculations for the pack and mass spectrometer results indicated that volatile AlCl(x) and CrCl(y) species were generated by the pack powder mixture; in packs containing the reactive element oxide, volatile ZrCl(z) and YCl(w) species were formed by the conversion of their oxide sources.

Bianco, Robert; Rapp, Robert A.; Jacobson, Nathan S.

1992-01-01

359

Heavy ion passive dosimetry with silver halide single crystals  

NASA Technical Reports Server (NTRS)

A method of detecting radiation damage tracks due to heavy particles in large single crystals of the silver halides is described. The tracks, when made visible with a simple electrical apparatus, appear similar to tracks in emulsions. The properties of the crystals, the technique of printing out the tracks, and evidence concerning the threshold energy for registering particles indicates that this method may find application in heavy ion dosimetry. The method has been found to be sensitive to stopping He nuclei and relativistic M group cosmic rays. Some impurities strongly influence the printout of the tracks, and the effects of these impurities are discussed.

Childs, C. B.; Parnell, T. A.

1972-01-01

360

Bright Light-Emitting Diodes based on Organometal Halide Perovskite  

E-print Network

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... . All electroluminescence and device characteristics were measured in air at room temperature. In our infrared PeLED, we use a simple 3-layered structure of TiO2/CH3NH3PbI3-xClx/F8 (Fig. 1a), which is sandwiched between indium tin oxide (ITO) and MoO3...

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

361

New route for the synthesis of tricyclopentadienyluranium halides  

SciTech Connect

A facile synthetic route for UCp/sub 4/, UCp/sub 3/, U(COT)/sub 2/, and other related organoactinides has been achieved by the direct reaction of a fresh reactive uranium powder from electrolytic amalgamation with respective organic substrates. In this work we further demonstrate the applicability of the uranium powder method to the simple synthesis of UCp/sub 3/X, where X = Cl, Br, and I, respectively. The uranium powder was reacted with cyclopentadiene and alkyl halides simultaneously under a mild condition to obtain the respective complexes.

Sung-Yu, N.K.; Hsu, F.F.; Chang, C.C.; Her, G.R.; Chang, C.T.

1981-08-01

362

Thermal conductivity of halide solid solutions: Measurement and prediction.  

PubMed

The composition dependence of the lattice thermal conductivity in NaCl-KCl solid solutions has been measured as a function of composition and temperature. Samples with systematically varied compositions were prepared and the laser flash technique was used to determine the thermal diffusivity from 373 K to 823 K. A theoretical model, based on the Debye approximation of phonon density of state (which contains no adjustable parameters) was used to predict the thermal conductivity of both stoichiometric compounds and fully disordered solid solutions. The predictions obtained with the model agree very well with our measurement. A general method for predicting the thermal conductivity of different halide systems is discussed. PMID:25217938

Gheribi, Aïmen E; Poncsák, Sándor; St-Pierre, Rémi; Kiss, László I; Chartrand, Patrice

2014-09-14

363

Temperature dependence of third order elastic constants of ammonium halides  

Microsoft Academic Search

The third order elastic constants of ammonium halides have been evaluated for the first time using Lundqvist three body potential\\u000a incorporating the effect of thermal contributions. Theoretical investigations have been carried out above ?-temperature where\\u000a both NH4Cl and NH4Br have cubic CsCl structure. Analysis has been extended to mixed NH4Cl1?x\\u000a Br\\u000a x\\u000a . The repulsive potential which is assumed significant

S. S. Bedi; Jaspal Singh

1997-01-01

364

New applications of silver halide photo-materials  

NASA Astrophysics Data System (ADS)

A review of the high-resolution VRP Silver Halide photo-materials (available through the Geola international distribution network) is presented. In addition to traditional holographic applications, the behaviour of current VRP materials is discussed in relation to embossed mastering origination, masks for microelectronics and X-ray tomography. Properties and applications of the fine grain, blue-green sensitive VRP plates are compared with previously available materials from other manufacturers. Recommended chemistries that may be employed with the VRP emulsion in different applications are reviewed.

Gudaitis, Giedrius A.; Zacharovas, Stanislovas J.; Ratcliffe, David B.; Sazonov, Jurij A.

2006-05-01

365

p-d hybridization of noble metal halides  

NASA Astrophysics Data System (ADS)

The electronic band calculations of noble metal halides are studied to make the high ionic conducting origin of silver and cupper ions clear using the tight-binding method. The d bands of Ag ions are much more weakly coupled with the p bands of halogen ions, while those of Cu ions are much more strongly coupled with the p bands. The strength of p-d hybridization is discussed to connect with the activation energy for the ionic conduction. It is shown that the high ionic conductivity of AgX primary stems from combination of the deformability of the d shell and the weakness of the p-d hybridization.

Kobayashi, M.; Iyetomi, H.; Ono, S.; Tomoyose, T.

366

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

Code of Federal Regulations, 2011 CFR

...2011-07-01 false Alkali metal salt of halogenated organoborate... § 721.5452 Alkali metal salt of halogenated organoborate...generically as alkali metal salt of halogenated organoborate...uses are: (i) Release to water. Requirements as...

2011-07-01

367

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

Code of Federal Regulations, 2012 CFR

...2012-07-01 false Alkali metal salt of halogenated organoborate... § 721.5452 Alkali metal salt of halogenated organoborate...generically as alkali metal salt of halogenated organoborate...uses are: (i) Release to water. Requirements as...

2012-07-01

368

THE OPERATION OF THE BNL/ATF GUN-IV PHOTOCATHODE RF GUN AT THE ADVANCED PHOTON SOURCE  

E-print Network

THE OPERATION OF THE BNL/ATF GUN-IV PHOTOCATHODE RF GUN AT THE ADVANCED PHOTON SOURCE * S (SASE) process is nearing completion. Recently, an rf photoinjector gun system was made available, and integration of this gun with the APS will be discussed. 1 INTRODUCTION The Advanced Photon Source (APS

Brookhaven National Laboratory

369

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

370

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

371

Induced Spin-Currents in Alkali-Films  

E-print Network

In sandwiches of FeK and FeCs the conduction electrons in the alkali metals have a large mean free path. The experiments suggest that the specular reflection for spin up and down electrons is different at the interface yielding a spin current in the alkali film. The spin current is detected by the anomalous Hall effect of Pb surface impurities.

Gerd Bergmann; Funing Song; Doug Garrett

2004-03-01

372

Binding of chloride and alkalis in Portland cement systems  

Microsoft Academic Search

A thermodynamic model for describing the binding of chloride and alkalis in hydrated Portland cement pastes has been developed. The model is based on the phase rule, which for cement pastes in aggressive marine environment predicts multivariant conditions, even at constant temperature and pressure. The effect of the chloride and alkalis has been quantified by experiments on cement pastes prepared

Erik P. Nielsen; Duncan Herfort; Mette R. Geiker

2005-01-01

373

Self-discharge in bimetallic cells containing alkali metal  

NASA Technical Reports Server (NTRS)

Theoretical analysis of thermally regenerative bimetallic cells with alkali metal anodes shows a relation between the current drawn and the rate of discharge under open-circuit conditions. The self-discharge rate of the cell is due to the dissolution and ionization of alkali metal atoms in the fused-salt electrolyte

Foster, M. S.; Hesson, J. C.; Shimotake, H.

1969-01-01

374

Photocrystallographic observation of halide-bridged intermediates in halogen photoeliminations.  

PubMed

Polynuclear transition metal complexes, which frequently constitute the active sites of both biological and chemical catalysts, provide access to unique chemical transformations that are derived from metal-metal cooperation. Reductive elimination via ligand-bridged binuclear intermediates from bimetallic cores is one mechanism by which metals may cooperate during catalysis. We have established families of Rh2 complexes that participate in HX-splitting photocatalysis in which metal-metal cooperation is credited with the ability to achieve multielectron photochemical reactions in preference to single-electron transformations. Nanosecond-resolved transient absorption spectroscopy, steady-state photocrystallography, and computational modeling have allowed direct observation and characterization of Cl-bridged intermediates (intramolecular analogues of classical ligand-bridged intermediates in binuclear eliminations) in halogen elimination reactions. On the basis of these observations, a new class of Rh2 complexes, supported by CO ligands, has been prepared, allowing for the isolation and independent characterization of the proposed halide-bridged intermediates. Direct observation of halide-bridged structures establishes binuclear reductive elimination as a viable mechanism for photogenerating energetic bonds. PMID:25264809

Powers, David C; Anderson, Bryce L; Hwang, Seung Jun; Powers, Tamara M; Pérez, Lisa M; Hall, Michael B; Zheng, Shao-Liang; Chen, Yu-Sheng; Nocera, Daniel G

2014-10-29

375

X-ray preionisation of the mercury halide lasers  

NASA Astrophysics Data System (ADS)

X-rays have been used to preionize all three mercury halide lasers (HgX: X = Cl, Br, I) for the first time. This paper describes the design of the laser head, the discharge circuitry, and the X-ray preionization source used. The minimum X-ray source strength required to saturate the laser energy dependence on the preionization electron density has been determined; this corresponds to a dose of about 4 mR in a 70 ns FWHM pulse for the optimum mercury bromide laser gas mixture. Typical maximum energies and efficiencies obtained with the three mercury halides in N2/Ne/HgX2 gas mixtures were: 93 mJ (0.27 percent) for HgCl2, 100 mJ (0.34 percent) for HgBr2, and 22 mJ (0.08 percent) for HgI2. The possibility of scaling the mercury chloride and mercury iodide laser energies and efficiencies to levels comparable to the known best results for mercury bromide is discussed.

Stonefield, Michael D. L.; King, Terence A.

1989-06-01

376

Pd-catalyzed cross-coupling reactions of alkyl halides.  

PubMed

Cross-coupling reactions have become indispensable tools for creating carbon-carbon (or heteroatom) bonds in organic synthesis. Like in other important transition metal catalyzed reactions, such as metathesis, addition, and polymerization, unsaturated compounds are usually employed as substrates for cross-coupling reactions. However during the past decade, a great deal of effort has been devoted to the use of alkyl halides as saturated compounds in cross-coupling reactions, which has resulted in significant progress in this undeveloped area by introducing new effective ligands. Many useful catalytic systems are now available for synthetic transformations based on C(sp(3))-C(sp(3)), C(sp(3))-C(sp(2)) and C(sp(3))-C(sp) bond formation as complementary methods to conventional C(sp(2))-C(sp(2)), C(sp(2))-C(sp) and C(sp)-C(sp) coupling. This tutorial review summarizes recent advances in cross-coupling reactions of alkyl halides and pseudohalides catalyzed by a palladium complex. PMID:21785791

Kambe, Nobuaki; Iwasaki, Takanori; Terao, Jun

2011-10-01

377

Biological Photocathodes  

Microsoft Academic Search

Biological surfaces emit electrons when subjected to UV light. This emission is increased greatly after exposure to cesium vapor. Increases from 2 to 3 orders of magnitude are observed, depending on the biochemicals present. Heme and chlorophyll exhibit unusually high photoemission currents, which are increased further after cesiation. Photoemission from proteins and lipids is much less but also is increased

O. Hayes Griffith; Douglas L. Habliston; G. Bruce Birrell; Walter P. Skoczylas; Karen K. Hedberg

1989-01-01

378

Electrical conductivity and relaxation in mixed alkali tellurite glasses  

NASA Astrophysics Data System (ADS)

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 10Hzto2MHz 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.

Ghosh, S.; Ghosh, A.

2007-05-01

379

HELSINKI UNIVERSITY OF TECHNOLOGY ENE-47.153 Trace elements and alkaliTrace elements and alkali  

E-print Network

HELSINKI UNIVERSITY OF TECHNOLOGY ENE-47.153 Trace elements and alkaliTrace elements and alkali ·· Trace elements in fuels and wastesTrace elements in fuels and wastes ·· Emission standards for trace elementsEmission standards for trace elements ·· Trace elements (excluding mercury) emission control

Zevenhoven, Ron

380

P552 X-Ray Streak Tube With Removable Photocathode, Improved Spatial Resolution And Temporal Fiducial  

NASA Astrophysics Data System (ADS)

We present here the P552 soft X-ray streak tube which is derived from the P500-P550 X-ray tube from RTC 1. To meet the requirements of X-ray diagnostics in high power laser interaction experiments performed at Centre d' Etudes de Limeil-Valenton some modifications were carried out to allow an easier control of the photocathode and the insertion of an optical fiducial of the laser pulse. We describe the main features of the whole device. This tube associated with a Thomson 2 TSN 505 camera has been used in laser plasma experiments and we present here some results obtained on the PHFBUS laser facility at CEL-V.

de Mascureau, J.; Bourgade, J.-L.; Mens, A.; Sauneif, R.; Rebuffie, J.-C.; Roux, J.-P.

1989-02-01

381

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

382

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, Zoe; Cao, Junyu; Ouyang, Shuxin; Li, Ying; Ye, Jinhua; Liu, Songqin

2013-01-01

383

Evaluation of high efficiency Csl and Cul photocathodes for soft x-ray diagnostics.  

PubMed

The photoefficiency of CsI and CuI photocathodes was measured for photons in the 22-240-eV (50-560-A) energy range. The within-batch and batch-to-batch variation in photoefficiency were studied as was the sensitivity of the samples to storage under dry nitrogen. The effect of exposure to air was investigated. The shape of the photoefficiency curves was found to agree quite well with that expected from the photoabsorption cross sections of the materials. CsI in particular appears useful as a detector in soft x-ray diagnostics, especially as a narrowband detector in the 100-eV photon energy range where peak measured efficiencies can exceed 300%. PMID:20220926

Saloman, E B; Pearlman, J S; Henke, B L

1980-03-01

384

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

385

Photoemission and optical constant measurements of Cesium Iodide thin film photocathode  

E-print Network

Performance of cesium iodide (CsI) as a reflective photocathode is presented. Absolute quantum efficiency (QE) measurement of 500 nm thick CsI film has been carried out in the wavelength range of 150 nm to 200 nm. Optical absorbance of 500 nm thick CsI film in the spectral range of 190 nm to 900 nm is analyzed and optical energy band gap is calculated using Tauc plot. To see the dispersive behavior of CsI film, refractive index has been determined by envelop plot of transmittance data, using Swanepoel method. Additional information on morphological and elemental composition results of CsI film, gained by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively are also reported in present work.

Triloki,; Gupta, Nikita; Jammal, Nabeel F A; Singh, B K

2014-01-01

386

An Approximate Analytic Expression for the Flux Density of Scintillation Light at the Photocathode  

SciTech Connect

The flux density of light exiting scintillator crystals is an important factor affecting the performance of radiation detectors, and is of particular importance for position sensitive instruments. Recent work by T. Woldemichael developed an analytic expression for the shape of the light spot at the bottom of a single crystal [1]. However, the results are of limited utility because there is generally a light pipe and photomultiplier entrance window between the bottom of the crystal and the photocathode. In this study, we expand Woldemichael s theory to include materials each with different indices of refraction and compare the adjusted light spot shape theory to GEANT 4 simulations [2]. Additionally, light reflection losses from index of refraction changes were also taken into account. We found that the simulations closely agree with the adjusted theory.

Braverman, Joshua B [ORNL; Harrison, Mark J [ORNL; Ziock, Klaus-Peter [ORNL

2012-01-01

387

Elastic properties of alkali-feldspars  

NASA Astrophysics Data System (ADS)

New measurements of single crystal elastic moduli for a suite of the alkali feldspars are reported. In order to interpret Earth's seismic structure, knowledge of the elastic properties of constituent minerals is essential. The elasticity of feldspar minerals, despite being the most abundant phase in Earth's crust (estimated to be more than 60%), were previously poorly characterized. All prior seismic and petrologic studies have utilized 50-year-old results, of questionable quality, based on 1-bar measurements on pseudo-single crystals. Alkali-feldspars present a large experimental challenge associated with their structural complexity. In the K-end member (KAlSi3O8) the symmetry is governed by Al/Si ordering, in the Na-end member (NaAlSi3O8) the symmetry is governed by whether or not there is a displacive collapse of the framework independent of the Al/Si ordering. K-feldspars exhibit monoclinic (C2/m) symmetry (necessitating determination of 13 elastic moduli) if disordered and triclinic (C-1) symmetry (21 elastic moduli) if ordered. Exsolution of Na-rich and K-rich phases is ubiquitous in natural samples, making it difficult to find suitable single phase and untwinned samples for study. The small single domain samples selected for this study were previously characterized by x-ray diffraction and microprobe analysis to ensure adequate sample quality. Surface wave velocities were measured on oriented surfaces of natural and synthetic single crystals using impulsively stimulated light scattering. A surface corrugation with a spacing of about 2 microns was impulsively created by the overlap of 100 ps infrared light pulses. The time evolution of the stimulated standing elastic waves was detected by measuring the intensity of diffraction from the surface corrugation of a variably delayed probe pulse. This method allows accurate (better than 0.2%) determination of velocities on samples smaller than 100 microns. The combination of measured surface wave velocities and separately determined compressibilities, based on high-pressure x-ray studies, allowed determination of the full elastic tensor for alkali-feldspars as a function of composition and structure.

Waeselmann, N.; Brown, J.; Angel, R. J.; Ross, N.; Kaminsky, W.

2013-12-01

388

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

389

Monte Carlo simulations of electron thermalization in alkali iodide and alkaline-earth fluoride scintillators  

NASA Astrophysics Data System (ADS)

A Monte Carlo model of electron thermalization in inorganic scintillators, which was developed and applied to CsI in a previous publication [Wang et al., J. Appl. Phys. 110, 064903 (2011)], is extended to another material of the alkali halide class, NaI, and to two materials from the alkaline-earth halide class, CaF2 and BaF2. This model includes electron scattering with both longitudinal optical (LO) and acoustic phonons as well as the effects of internal electric fields. For the four pure materials, a significant fraction of the electrons recombine with self-trapped holes and the thermalization distance distributions of the electrons that do not recombine peak between approximately 25 and 50 nm and extend up to a few hundreds of nanometers. The thermalization time distributions of CaF2, BaF2, NaI, and CsI extend to approximately 0.5, 1, 2, and 7 ps, respectively. The simulations show that the LO phonon energy is a key factor that affects the electron thermalization process. Indeed, the higher the LO phonon energy is, the shorter the thermalization time and distance are. The thermalization time and distance distributions show no dependence on the incident ?-ray energy. The four materials also show different extents of electron-hole pair recombination due mostly to differences in their electron mean free paths (MFPs), LO phonon energies, initial densities of electron-hole pairs, and static dielectric constants. The effect of thallium doping is also investigated for CsI and NaI as these materials are often doped with activators. Comparison between CsI and NaI shows that both the larger size of Cs+ relative to Na+, i.e., the greater atomic density of NaI, and the longer electron mean free path in NaI compared to CsI contribute to an increased probability for electron trapping at Tl sites in NaI versus CsI.

Wang, Zhiguo; Xie, YuLong; Campbell, Luke W.; Gao, Fei; Kerisit, Sebastien

2012-07-01

390

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

391

First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands  

SciTech Connect

Two new organic-inorganic compounds based on polyoxometalates, metal halide clusters and organic ligands: [BW{sub 12}O{sub 40}]{sub 2}[Cu{sub 2}(Phen){sub 4}Cl](H{sub 2}4, 4 Prime -bpy){sub 4}{center_dot}H{sub 3}O{center_dot}5H{sub 2}O (1) and [HPW{sub 12}O{sub 40}][Cd{sub 2}(Phen){sub 4}Cl{sub 2}](4, 4 Prime -bpy) (2) (Phen=1, 10-phenanthroline, bpy=bipyridine), have been prepared and characterized by IR, UV-vis, XPS, XRD and single crystal X-ray diffraction analyses. Crystal structure analyses reveal that compound 1 is constructed from [BW{sub 12}O{sub 40}]{sup 5-}, metal halide clusters [Cu{sub 2}(Phen){sub 4}Cl]{sup +}and 4, 4 Prime -bpy ligands, while compound 2 is constructed from [PW{sub 12}O{sub 40}]{sup 3-}, metal halide cluster [Cd{sub 2}(Phen){sub 4}Cl{sub 2}]{sup 2+} and 4, 4 Prime -bpy ligands. Compound 1 and compound 2 are not common hybrids based on polyoxometalates and metal halide clusters, they also contain dissociated organic ligands, therefore, compound 1 and 2 are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. - Graphical Abstract: Two new compounds have been synthesized and characterized. Structure analyses revealed that the two compounds are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. Highlights: Black-Right-Pointing-Pointer First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. Black-Right-Pointing-Pointer Two different kinds of metal halide clusters. Black-Right-Pointing-Pointer Supramolecular structures based on polyoxometalates, metal halide clusters and organic ligands. Black-Right-Pointing-Pointer Hybridization of three different of building blocks.

Wang Lamei; Fan Yong; Wang Yan; Xiao Lina; Hu Yangyang; Peng Yu; Wang Tiegang; Gao Zhongmin; Zheng Dafang [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China); Cui Xiaobing, E-mail: cuixb@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China); Xu Jiqing, E-mail: xjq@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China)

2012-07-15

392

Fundamental study on alkali metal thermoelectric converter  

NASA Astrophysics Data System (ADS)

The alkali metal thermoelectric converter (AMTEC), which utilizes the sodium ion conducting beta-double prime-alumina, is a device for directly converting heat energy to electric energy. It is characterized by high conversion efficiencies of 20 to 40 percent, high power densities of 1 W/sq cm, no moving parts, low maintenance requirements, high durability, and efficiency independent of size. Because of these merits, AMTEC is one of the most promising candidates for dispersed small-scale power stations, remote power stations, and aerospace power systems. In this paper, the results of theoretical and experimental studies on AMTEC power generating characteristics, internal electrical resistances of single cells, and system analysis of AMTEC power-generating systems are reported.

Masuda, Toshihisa

1989-11-01

393

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

394

Heat pipes containing alkali metal working fluid  

NASA Astrophysics Data System (ADS)

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.

1981-03-01

395

Coherent control of alkali cluster fragmentation dynamics  

NASA Astrophysics Data System (ADS)

Metal clusters exhibit extraordinary chemical and catalytic properties, which sensitively depend upon their size. This behavior makes them interesting candidates for the real-time analysis of ultrafast photo-induced processes—ultimately leading to coherent control scenarii. We have performed transient multi-photon ionization experiments on small alkali clusters of different size in order to probe their wave packet dynamics, structural reorientations, charge transfers and dissociative events in different vibrationally excited electronic states including their ground state. The observed processes were highly dependent on the irradiated pulse parameters, like its phase, amplitude and duration; an emphasis to employ a feedback control system for generating the optimum pulse shapes. Their spectral and temporal behavior reflects interesting properties about the investigated system and the irradiated photochemical process. We present first the vibrational dynamics of bound, dissociated, and pre-dissociated electronically excited states of alkali dimers and trimers. The scheme for observing the wave packet dynamics in the electronic ground state using stimulated Raman-pumping is shown. Since the employed pulse parameters significantly influence the efficiency of the irradiated dynamic pathways photo-induced fragmentation experiments on bifurcating reaction channels were carried out. In these experiments different branching ionization and fragmentation pathways of electronically excited Na 2K were investigated. By employing an evolutionary algorithm for optimizing the phase and amplitude of the applied laser field, the yield of the resulting parent or fragment ions could significantly be influenced and interesting features could be concluded from the obtained optimum pulse shapes revealing the characteristic molecular oscillation period. Moreover, the influence on the optimal pulse shape due to fragmentation from larger clusters into NaK is obtained. The substructure of the optimal pulse shape thereby offers new insight into the fragmentation channel during the control process. Characteristic motions of the involved wave packets are proposed, in order to explain the optimized dynamic dissociation pathways.

Lindinger, Albrecht; Lupulescu, Cosmin; Bartelt, Andreas; Vajda, Štefan; Wöste, Ludger

2003-06-01

396

Alkali-activated cementitious materials: Mechanisms, microstructure and properties  

NASA Astrophysics Data System (ADS)

The goal of this study was to examine the activation reaction, microstructure, properties, identify the mechanisms of activation, and achieve an enhanced understanding of activation processes occurring during the synthesis of alkali activated cementitious materials (AAC). The discussions classify the following categories. (1) alkali activated slag cement; (2) alkali activated portland-slag cement; (3) alkali activated fly ash-slag cement; (4) alkali activated pozzolana-lime cement; (5) alkali activated pozzolana cement. The activators involved are NaOH, KOH; Nasb2SOsb4;\\ Nasb2COsb3;\\ CaSOsb4, and soluble silicate of sodium and potassium. The effect of alkali activation on the microstructure of these materials were analyzed at the micro-nanometer scale by SEM, EDS, ESEM, and TEM. Also sp{29}Si and sp{27}Al MAS-NMR, IR, Raman, TGA, and DTA were performed to characterize the phase in these systems. Slag, fly ash, silica fume, as well as blended cements containing mixtures of these and other components were characterized. A set of ordinary portland cement paste samples served as a control. This study confirmed that AAC materials have great potential because they could generate very early high strength, greater durability and high performance. Among the benefits to be derived from this research is a better understanding of the factors that control concrete properties when using AAC materials, and by controlling the chemistry and processing to produce desired microstructures and properties, as well as their durability.

Jiang, Weimin

397

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

398

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

399

Generation of ultrashort electromagnetic radiation pulses with a repetition rate of ˜100 MHz by a vacuum photoemission element with an antimony cesium photocathode  

NASA Astrophysics Data System (ADS)

We studied the generation of ultrashort electromagnetic radiation pulses with the maximal repetition rate by a vacuum photoemission element with an antimony cesium photocathode. Photoelectrons are emitted as a result of supplying four nanosecond initiating laser radiation pulses with a wavelength of 527 nm and an interval from 3.65 to 6.7 ns between the pulses. The voltage between the anode and the photocathode (from 5 to 60 kV) is measured in experiments.

Zavolokov, E. V.; Zamuraev, D. O.; Kondrat'ev, A. A.; Kupyrin, N. V.; Potapov, A. V.; Romanov, Yu. O.; Sorokin, I. A.; Tishchenko, A. S.; Khavronin, N. N.; Shamraev, A. L.

2014-08-01

400

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

401

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

402

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

403

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

404

Halide adsorption on close-packed metal electrodes.  

PubMed

Two mechanisms have been cited as the reason for unexpected work function decrease upon adsorption of electronegative adatoms: electron spillout depletion [Michaelides et al., Phys. Rev. Lett., 2003, 90, 246103] and polarization of the adatom [Roman et al., Phys. Rev. Lett., 2013, 110, 156804]. We attempt to bridge the two pictures in this work. Work function changes due to the adsorption of halides on (111) surfaces of fcc metals (Ca, Sr, Ni, Pd, Pt, Cu, Ag, Au, Al and Pb) were studied using periodic density functional theory. The two mechanisms were found to be clearly independent of each other because of the opposite factors that lead to the work function decrease, and are therefore easy to distinguish. A more general picture of interpreting bond ionicity based on observed work function changes is discussed. PMID:24643669

Roman, Tanglaw; Gossenberger, Florian; Forster-Tonigold, Katrin; Groß, Axel

2014-07-21

405

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

406

Increasing Class C fly ash reduces alkali silica reactivity  

SciTech Connect

Contrary to earlier studies, it has been found that incremental additions of Class C fly ash do reduce alkali silica reactivity (ASR), in highly reactive, high alkali concrete mixes. AST can be further reduced by substituting 5% metakaolin or silica fume for the aggregate in concrete mixes with high (more than 30%) Class C fly ash substitution. The paper reports results of studies using Class C fly ash from the Labadie Station plant in Missouri which typically has between 1.3 and 1.45% available alkalis by ASTM C311. 7 figs.

Hicks, J.K. [Mineral Resources Technologies, Inc. (United States)

2007-07-01

407

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

408

IR analysis of polyvinylidene fluoride doped with transition metal halides  

NASA Astrophysics Data System (ADS)

Pure and doped polyvinylidene fluoride (PVDF) films were prepared by casting. Films with various concentrations of transition metal halides TMHs (AlCl3, ZnCl2, and CoCl2) were prepared. The microstructure and physical properties of these films were studied by IR analysis. The two factors affecting the interaction between the PVDF and MHs are (i) the dopant weight fraction (Hc) (0.05% -30%) by weght, and (ii) precasting time (tpc) which is the time during which the PVDF pellets are maintained solved with the halides added before casting. From the IR quantitative analysis, it is evident that the addition of the three MH to the undoped PVDF film makes ?-phase as the dominant crystalline structures in the doped films without the need for mechanical drawing treatment. The precasting time plays a role for new crystalline structures to appear which becomes strong for CoCl2 doping, moderate in ZnCl2 doping and weak in AlCl3 doping. This phase is maximum for the relatively low doping levels < 5%. The stability of these structures in the samples doped with CoCl2 is high compared to the doping with ZnCl2 and AlCl3. This result is extremely important hence the ?-phase is that one which is electrically active compared with the other two phases and it is needed in all the samples used in the useful applications of the PVF2 films. Remembering, that ?-phase is obtained in the crystallization from melt samples by the uneasy mechanical stress and elevated temperature, it becomes evident the importance of the present result.

El Hefnawy, Somia M.; Aboelkher, Mervet M.; Abdelkader, H.

2009-05-01

409

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

410

A reactor system for studying the interactions between alkali vapors and ceramic compounds  

Microsoft Academic Search

The kinetics and mechanism of interaction between alkali vapors and several ceramic compounds are studied. A unique micro-gravimetric reactor is designed and utilized for this study. Bauxite and kaolin are very good adsorbents for alkali chlorides and are potentially good additives for control of alkali during coal combustion and gasification. The experimental data shows that the alkali capturing process is

F. Shadman; W. A. Punjak

1987-01-01

411

Fe(III) doped and grafted PbTiO3 film photocathode with enhanced photoactivity for hydrogen production  

NASA Astrophysics Data System (ADS)

The photoelectrochemical activity of the PbTiO3 film photocathode deposited on indium tin oxide-coated quartz substrate was significantly improved through modifying the film surface by both the Fe(III) doping and grafting. Doping the PbTiO3 with Fe(III) ions narrows its band gap thus increases the visible light utilization, while the surface-grafted Fe(III) ions on the doped PbTiO3 surface are helpful to improve the charge transfer on the photocathode/electrolyte interface. Consequently, the photocurrent was increased from 38 ?A/cm2 to 220 ?A/cm2 under the irradiation of 100 mW/cm2 Xe lamp by using 0.1M Na2SO4 as an electrolyte and zero-potential versus saturated calomel as a reference electrode. The corresponding increase in open circuit voltage was 0.95-1.11 V.

Hu, Yuxiang; Dong, Wen; Zheng, Fengang; Fang, Liang; Shen, Mingrong

2014-08-01

412

Nickel catalysed electrosynthesis of ketones from organic halides and iron pentacarbonyl. Part 2: Unsymmetrical ketones  

Microsoft Academic Search

Unsymmetrical aryl–benzyl or aryl–alkyl ketones are obtained by electrolysing in an undivided cell a DMF solution containing two organic halides, iron pentacarbonyl and a catalytic amount of a nickel-2,2?-bipyridine complex.

Eric Dolhem; Rachid Barhdadi; Jean Claude Folest; Jean Yves Nédelec; Michel Troupel

2001-01-01

413

A palladium-catalyzed reaction of aryl halides, potassium metabisulfite, and hydrazines.  

PubMed

Aryl N-aminosulfonamides could be easily produced via a palladium-catalyzed coupling of aryl halides, potassium metabisulfite, and hydrazines. Potassium metabisulfite is an excellent equivalent of sulfur dioxide in the reaction of palladium-catalyzed aminosulfonylation. PMID:22945283

Ye, Shengqing; Wu, Jie

2012-10-14

414

40 CFR 721.4740 - Alkali metal nitrites.  

Code of Federal Regulations, 2013 CFR

...of chemical substances which are nitrites of the alkali metals (Group IA in the periodic classification of chemical elements) lithium, sodium, potassium, rubidium, cesium, and francium, is subject to reporting under this section for the significant...

2013-07-01

415

40 CFR 721.4740 - Alkali metal nitrites.  

Code of Federal Regulations, 2012 CFR

...of chemical substances which are nitrites of the alkali metals (Group IA in the periodic classification of chemical elements) lithium, sodium, potassium, rubidium, cesium, and francium, is subject to reporting under this section for the significant...

2012-07-01

416

40 CFR 721.4740 - Alkali metal nitrites.  

Code of Federal Regulations, 2011 CFR

...of chemical substances which are nitrites of the alkali metals (Group IA in the periodic classification of chemical elements) lithium, sodium, potassium, rubidium, cesium, and francium, is subject to reporting under this section for the significant...

2011-07-01

417

40 CFR 721.4740 - Alkali metal nitrites.  

Code of Federal Regulations, 2010 CFR

...nitrites of the alkali metals (Group IA in the periodic classification of chemical elements) lithium, sodium, potassium, rubidium, cesium, and francium, is subject to reporting under this section for the significant new use described in paragraph...

2010-07-01

418

Spectral response variation of exponential-doping transmission-mode GaAs photocathodes in the preparation process  

NASA Astrophysics Data System (ADS)

The exponential-doping structure was applied to prepare the transmission-mode GaAs photocathode, and spectral response curves after high-temperature activation, low-temperature activation and the indium sealing process were respectively measured by use of the on-line spectral response measurement system, to research into the practical effect of the exponential-doping structure on cathode performance. The results show that a high photosensitivity ranging from 560 nm to 880 nm with an ascending trend can be obtained after the high-low temperature activation. In the region of longwave threshold, there is a distinct inflexion indicating a better photoemission capability than the former uniform-doping photocathodes. Besides, the spectral response curve in the whole response waveband, especially the long-wave region obviously decreases after indium seal. Compared with the fitted surface electron escape probability after Cs-O activation, it decreases after indium seal according to the quantum efficiency formula of exponential-doping transmission-mode GaAs photocathodes. Based on the double dipole model, the reasons for the variation of spectral response shape are explained on account of the relation between surface escape probability and the evolution of surface potential barrier profile.

Zhang, Yijun; Niu, Jun; Chang, Benkang; Xiong, Yajuan; Yang, Zhi; Du, Yujie

2010-10-01

419

Detection of fast BaF[sub 2] scintillations with a CsI photocathode coupled to a MWPC  

SciTech Connect

CsI photocathodes coupled to wire chambers offer the position sensitive detection of UV photons with very good timing resolution. Such photocathodes have been considered as a possibility for detection of the fast components of BaF[sub 2] scintillations in calorimeters at the future high energy colliders. The authors have investigated the efficiency of a CsI photocathode in a MWPC for detection of the fast BaF[sub 2] scintillation component, the variation of this efficiency over a period of two months and it's behavior under an elevated radiation level. They find an extrapolated initial yield of 13 photoelectrons per MeV of energy deposited in the scintillator. This yield decreased exponentially with two decay constants. During the first three weeks the decay constant amounted to 5% daily and then it reduced to 1% per day. No noticeable change in the photoelectron yield or it's rate of decrease was observed after a 3 day irradiation amounting to a collected charge of 0.3 mC/cm[sup 2].

Staric, M. (Jozef Stefan Inst., Ljubljana (Slovenia) Univ. of Ljubljana (Slovenia)); Stanovnik, A. (Univ. of Ljubljana (Slovenia). Faculty for Electrical Engineering); Korpar, S. (Univ. of Maribor (Slovenia). Technical Faculty)

1994-08-01

420

Spectroscopic study of the interactions of alkali fluorides with D-xylose.  

PubMed

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-d6 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. PMID:11765788

Fernandez-Bertrán, J; Reguera, E; Ortiz, P

2001-11-01

421

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 sample at the critical point contains ~10 nm seed nuclei that increase in size and concentration with exposure to the electron beam.

McCloy, John S.; Riley, Brian J.; Lipton, Andrew S.; Windisch, Charles F.; Washton, Nancy M.; Olszta, Matthew J.; Rodriguez, Carmen P.

2013-02-11

422

Summary of Substitution and Elimination Reactions of Alkyl Halides Polar protic solvent  

E-print Network

­X E2, SN2, E1/SN1 First, you need to know which products to expect from each mechanism. Second, you will come from E2 and/or SN2, or there will be no reaction, depending upon the structure of the alkyl halide products from SN2. 3° halides will give mostly SN1 and E1. III) If there is no good nucleophile

Walba, David

423

A closed-cycle gas recirculating system for rare-gas halide excimer lasers  

Microsoft Academic Search

A closed-cycle recirculating system is described which enables prolonged operation of a rare-gas halide excimer laser on a single charge of rare-gas mixture. The flowing gas is continuously purified in a high-temperature titanium gettering furnace, following removal of the halogen by reaction to form a volatile, but condensable, metal halide. The halogen is reintroduced after the rare-gas purification, being consumed

P. M. Johnson; N. Keller; R. E. Turner

1978-01-01

424

Thermodynamic analysis of halide binding to haloalkane dehalogenase suggests the occurrence of large conformational changes  

Microsoft Academic Search

Haloalkane dehalogenase ~DhlA! hydrolyzes short-chain haloalkanes to produce the corresponding alcohols and halide ions. Release of the halide ion from the active-site cavity can proceed via a two-step and a three-step route, which both contain slow enzyme isomerization steps. Thermodynamic analysis of bromide binding and release showed that the slow unimolecular isomerization steps in the three-step bromide export route have

GEJA H. KROOSHOF; RENÉ FLORIS; ARMAND W. J. W. TEPPER; DICK B. JANSSEN

2006-01-01

425

Halide anion recognition by calix[4]pyrrole: a quantum chemical study  

Microsoft Academic Search

The spherical recognition of halide anions by the calix[4]pyrrole molecule has been investigated with the aid of Hartree–Fock, hybrid DFT (B3LYP), and semi-empirical (PM3) quantum chemical methods. The free calix[4]pyrrole molecule adopts the 1,3-alternate conformation, as confirmed by an earlier X-ray crystal structure analysis, whereas a transition to a cone-like conformation occurs upon capture of a single halide anion. The

Fabio Pichierri

2002-01-01

426

Unique properties of halide perovskites as possible origins of the superior solar cell performance.  

PubMed

Halide perovskites solar cells have the potential to exhibit higher energy conversion efficiencies with ultrathin films than conventional thin-film solar cells based on CdTe, CuInSe2 , and Cu2 ZnSnSe4 . The superior solar-cell performance of halide perovskites may originate from its high optical absorption, comparable electron and hole effective mass, and electrically clean defect properties, including point defects and grain boundaries. PMID:24827122

Yin, Wan-Jian; Shi, Tingting; Yan, Yanfa

2014-07-16

427

Cationic Interracial Polymerization of p-Methoxystyrene by Means of Triphenylmethylium Halide-Aerosil Initiation  

Microsoft Academic Search

Cationic polymerizations of p-methoxystyrene initiated by triphenylmethylium halides in conjunction with silica surfaces proceed via ion pair intermediates. The polymerization yields both aerosil-polymer composites and soluble polymers. The triphenylmethylium halides are active only on the surface of the solid, which is demonstrated by means of adsorption and zeta-potential measurements in 1,2-dichloroethane. The influence of the overall monomer concentration and initiator

Stefan Spange; Günther Heublein; Frank Simon

1991-01-01

428

Holographic 4 x 4 star coupler in silver-halide sensitized gelatin  

NASA Astrophysics Data System (ADS)

This paper describes a modified processing technique for silver-halide sensitized gelatin (SHSG) derived from Agfa-Geveart holographic plates having diffraction efficiency up to 80%, and a frequency response that is spatially flat. Results from fabrication of a 4 x 4 holographic star coupler in SHGS are discussed. Techniques for eliminating the reciprocity law failure in silver halide emulsions are described. Application of the star coupler to fiber-based LANs is discussed.

Simova, Eli S.; Kavehard, Mohsen

1993-09-01

429

Soft scorpionate coordination at alkali metals.  

PubMed

Reported here are the single-crystal X-ray structure analyses of bis-?-methanol-?(4)O:O-bis{[hydrotris(3-phenyl-2-sulfanylidene-2,3-dihydro-1H-1,3-imidazol-1-yl)borato-?(3)H,S,S'](methanol-?O)sodium(I)}, [Na2(C27H22BN6S3)2(CH4O)4] (NaTm(Ph)), bis-?-methanol-?(4)O:O-bis{[hydrotris(3-isopropyl-2-sulfanylidene-2,3-dihydro-1H-1,3-imidazol-1-yl)borato-?(3)H,S,S'](methanol-?O)sodium(I)}-diethyl ether-methanol (1/0.3333/0.0833), [Na2(C18H28BN6S3)2(CH4O)4]·0.3333C4H10O·0.0833CH3OH (NaTm(iPr)), and a novel anhydrous form of sodium hydrotris(methylthioimidazolyl)borate, poly[[?-hydrotris(3-methyl-2-sulfanylidene-2,3-dihydro-1H-1,3-imidazol-1-yl)borato]sodium(I)], [Na(C12H16BN6S3)] ([NaTm(Me)]n). NaTm(iPr) and NaTm(Ph) have similar dimeric molecular structures with ?(3)H,S,S'-bonding, but they differ in that NaTm(Ph) is crystallographically centrosymmetric (Z' = 0.5) while NaTm(iPr) contains one crystallographically centrosymmetric dimer and one dimer positioned on a general position (Z' = 1.5). [NaTm(Me)]n is a one-dimensional coordination polymer that extends along the a direction and which contains a hitherto unseen side-on ?(2)-C=S-to-Na bond type. An overview of the structural preferences of alkali metal soft scorpionate complexes is presented. This analysis suggests that these thione-based ligands will continue to be a rich source of interesting alkali metal motifs worthy of isolation and characterization. PMID:24816005

Rajesekharan-Nair, Rajeev; Lutta, Samuel T; Kennedy, Alan R; Reglinski, John; Spicer, Mark D

2014-05-01

430

Electrochemical cell having an alkali-metal-nitrate electrode  

DOEpatents

A power-producing secondary electrochemical cell includes a molten alkali metal as the negative-electrode material and a molten-nitrate salt as the positive-electrode material. The molten material in the respective electrodes are separated by a solid barrier of alkali-metal-ion conducting material. A typical cell includes active materials of molten sodium separated from molten sodium nitrate and other nitrates in mixture by a layer of sodium ..beta..'' alumina.

Roche, M.F.; Preto, S.K.

1982-06-04

431

Alkali absorption and citrate excretion in calcium nephrolithiasis  

NASA Technical Reports Server (NTRS)

The role of net gastrointestinal (GI) alkali absorption in the development of hypocitraturia was investigated. The net GI absorption of alkali was estimated from the difference between simple urinary cations (Ca, Mg, Na, and K) and anions (Cl and P). In 131 normal subjects, the 24 h urinary citrate was positively correlated with the net GI absorption of alkali (r = 0.49, p < 0.001). In 11 patients with distal renal tubular acidosis (RTA), urinary citrate excretion was subnormal relative to net GI alkali absorption, with data from most patients residing outside the 95% confidence ellipse described for normal subjects. However, the normal relationship between urinary citrate and net absorbed alkali was maintained in 11 patients with chronic diarrheal syndrome (CDS) and in 124 stone-forming patients devoid of RTA or CDS, half of whom had "idiopathic" hypocitraturia. The 18 stone-forming patients without RTA or CDS received potassium citrate (30-60 mEq/day). Both urinary citrate and net GI alkali absorption increased, yielding a significantly positive correlation (r = 0.62, p < 0.0001), with the slope indistinguishable from that of normal subjects. Thus, urinary citrate was normally dependent on the net GI absorption of alkali. This dependence was less marked in RTA, confirming the renal origin of hypocitraturia. However, the normal dependence was maintained in CDS and in idiopathic hypocitraturia, suggesting that reduced citrate excretion was largely dietary in origin as a result of low net alkali absorption (from a probable relative deficiency of vegetables and fruits or a relative excess of animal proteins).

Sakhaee, K.; Williams, R. H.; Oh, M. S.; Padalino, P.; Adams-Huet, B.; Whitson, P.; Pak, C. Y.

1993-01-01

432

Floristic characterisation of alkali soils in northwestern India  

Microsoft Academic Search

Summary  Floristic composition studied in a 40 hectares representative site of alkali soils in the Indo-gangetic plains of Northwestern\\u000a India revealed a remarkably restricted spectrum of natural vegetation. Soil analysis of specific niches, occupied by aggregations\\u000a of different species, was employed to identify alkali halophytes. Response functions of eight prominent species to increasing\\u000a levels of soil alkalinity, studied in pot culture,

R. S. Rana; V. Parkash

1987-01-01

433

Hypercalcemia in Pregnancy: A Case of Milk-Alkali Syndrome  

Microsoft Academic Search

Milk-alkali syndrome is a rare cause of hypercalcemia characterized by the triad of hypercalcemia, renal insufficiency, and\\u000a metabolic alkalosis that results from the overconsumption of calcium containing products. In the setting of pregnancy where\\u000a there is a physiologic increase in calcium absorption, milk-alkali syndrome can be potentially life threatening. We report\\u000a a case of a 26-year-old woman in her second

Leanne Kolnick; Bryan D. Harris; David P. Choma; Neesha N. Choma

434

A Combined Metal-Halide/Metal Flux Synthetic Route towards Type-I Clathrates: Crystal Structures and Thermoelectric Properties of A8 Al8 Si38 (A=K, Rb, and Cs).  

PubMed

Single-phase samples of the compounds K8 Al8 Si38 (1), Rb8 Al8 Si38 (2), and Cs7.9 Al7.9 Si38.1 (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

435

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

436

Determination of halide impurities in ionic liquids by total reflection X-ray fluorescence spectrometry.  

PubMed

The determination and quantification of halide impurities in ionic liquids is highly important because halide ions can significantly influence the chemical and physical properties of ionic liquids. The use of impure ionic liquids in fundamental studies on solvent extraction or catalytic reactions can lead to incorrect experimental data. The detection of halide ions in solution by total reflection X-ray fluorescence (TXRF) has been problematic because volatile hydrogen halide (HX) compounds are formed when the sample is mixed with the acidic metal standard solution. The loss of HX during the drying step of the sample preparation procedure gives imprecise and inaccurate results. A new method based on an alkaline copper standard Cu(NH3)4(NO3)2 is presented for the determination of chloride, bromide, and iodide impurities in ionic liquids. The 1-butyl-3-methylimidazolium ([C4mim]) ionic liquids with the anions acetate ([C4mim][OAc]), nitrate ([C4mim][NO3]), trifluoromethanesulfonate ([C4mim][OTf]), and bis(trifluoromethylsulfonyl)imide ([C4mim][Tf2N]) were synthesized via a halide-free route and contaminated on purpose with known amounts of [C4mim]Cl, [C4mim]Br, [C4mim]I, or potassium halide salts in order to validate the new method and standard. PMID:24628670

Vander Hoogerstraete, Tom; Jamar, Steven; Wellens, Sil; Binnemans, Koen

2014-04-15

437

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, Francoise; Schaller, Hubert

2013-01-01

438

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

439

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

440

Two-phase alkali-metal experiments in reduced gravity  

SciTech Connect

Future space missions envision the use of large nuclear reactors utilizing either a single or a two-phase alkali-metal working fluid. The design and analysis of such reactors require state-of-the-art computer codes that can properly treat alkali-metal flow and heat transfer in a reduced-gravity environment. A literature search of relevant experiments in reduced gravity is reported on here, and reveals a paucity of data for such correlations. The few ongoing experiments in reduced gravity are noted. General plans are put forth for the reduced-gravity experiments which will have to be performed, at NASA facilities, with benign fluids. A similar situation exists regarding two-phase alkali-metal flow and heat transfer, even in normal gravity. Existing data are conflicting and indequate for the task of modeling a space reactor using a two-phase alkali-metal coolant. The major features of past experiments are described here. Data from the reduced-gravity experiments with innocuous fluids are to be combined with normal gravity data from the two-phase alkali-metal experiments. Analyses undertaken here give every expectation that the correlations developed from this data base will provide a valid representation of alkali-metal heat transfer and pressure drop in reduced gravity.

Antoniak, Z.I.

1986-06-01

441

Alkali-metal azides interacting with metal-organic frameworks.  

PubMed

Interactions between alkali-metal azides and metal-organic framework (MOF) derivatives, namely, the first and third members of the isoreticular MOF (IRMOF) family, IRMOF-1 and IRMOF-3, are studied within the density functional theory (DFT) paradigm. The investigations take into account different models of the selected IRMOFs. The mutual influence between the alkali-metal azides and the ? rings or Zn centers of the involved MOF derivatives are studied by considering the interactions both of the alkali-metal cations with model aromatic centers and of the alkali-metal azides with distinct sites of differently sized models of IRMOF-1 and IRMOF-3. Several exchange and correlation functionals are employed to calculate the corresponding interaction energies. Remarkably, it is found that, with increasing alkali-metal atom size, the latter decrease for cations interacting with the ?-ring systems and increase for the azides interacting with the MOF fragments. The opposite behavior is explained by stabilization effects on the azide moieties and determined by the Zn atoms, which constitute the inorganic vertices of the IRMOF species. Larger cations can, in fact, coordinate more efficiently to both the aromatic center and the azide anion, and thus stabilizing bridging arrangements of the azide between one alkali-metal and two Zn atoms in an ?(2) coordination mode are more favored. PMID:23161861

Armata, Nerina; Cortese, Remedios; Duca, Dario; Triolo, Roberto

2013-01-14

442

Absorption spectra of alkali-C60 nanoclusters.  

PubMed

We investigate the absorption spectra of alkali-doped C60 nanoclusters, namely C60Nan, C60Kn, and C60Lin, with n = 1, 2, 6, 12, in the framework of the time-dependent density-functional theory (TDDFT). We study the dependence of the absorption spectra on the nature of the alkali. We show that in few cases the absorption spectra depend on the arrangement of the alkali atoms over the fullerene, though sometimes the absorption spectra do not allow us to distinguish between different configurations. When only one or two alkali atoms are adsorbed on the fullerene, the optical response of alkali-doped C60 is similar to that of the anion C60(-) with a strong response in the UV domain. In contrast, for higher concentration of alkali, a strong optical response is predicted in the visible range, particularly when metal-metal bonds are formed. The weak optical response of the Ih-symmetry C60Li12 is proposed to be used as a signature of its structure. PMID:25223347

Rabilloud, Franck

2014-10-28

443

Results From Cs Activated GaN Photocathode Development for MCP Detector Systems at GSFC  

NASA Technical Reports Server (NTRS)

We describe the development of high quantum efficiency W photocathodes for use in large area two dimensional microchannel plate based detector arrays to enable new W space astronomy missions. Future W missions will require improvements in detector sensitivity, which has the most leverage for cost-effective improvements in overall telescope/instrument sensitivity. We use new materials such as p-doped GaN, AIGaN, ZnMgO, Sic and diamond. We have currently obtained QE values > 40 % at 185 nm with Cesiated GaN, and hope to demonstrate higher values in the future. By using controlled internal fields and nano-structuring of the surfaces, we plan to provide field emission assistance for photoelectrons while maintaining their energy distinction from dark noise electrons. We will transfer these methods from GaN to ZnMgO, a new family of wide band-gap materials more compatible with microchannel plates. We also are exploring technical parameters such as doping profiles, internal and external field strengths, angle of incidence, field emission assistance, surface preparation, etc.

Norton, Tim; Woodgate, Bruce; Stock, Joe; Hilton, George; Ulmer, Mel; Aslam, Shahid; Vispute, R. D.

2003-01-01

444

Software Tools for the Analysis of the Photocathode Response of Photomultiplier Vacuum Tubes  

E-print Network

The central institute of electronics (ZEA-2) in the Forschungszentrum Juelich (FZJ) has developed a system to scan the response of the photocathode of photomultiplier tubes (PMT). The PMT sits tight on a supporting structure, while a blue light emitting diode is moved along its surface by two stepper motors, spanning both the x and y coordinates. All the system is located in a light-tight box made by wood. A graphical software was developed in-situ to perform the scan operations under different configurations (e.g., the step size of the scan and the number of measurements per point). During each point measurement the current output generated in the vacuum photomultiplier is processed in sequence by a pre-amplifier (mainly to convert the current signal into a voltage signal), an amplifier, and by an ADC module (typically a CAEN N957). The information of the measurement is saved in files at the end of the scan. Recently, software based on the CERN ROOT and on the Qt libraries was developed to help the user anal...

Fabbri, R

2013-01-01

445

Characterization of photocathode dark current vs. temperature in image intensifier tube modules and intensified televisions  

NASA Astrophysics Data System (ADS)

Image intensifiers (I2) have gained wide acceptance throughout the Army as the premier nighttime mobility sensor for the individual soldier, with over 200,000 fielded systems. There is increasing need, however, for such a sensor with a video output, so that it can be utilized in remote vehicle platforms, and/or can be electronically fused with other sensors. The image-intensified television (I2TV), typically consisting of an image intensifier tube coupled via fiber optic to a solid-state imaging array, has been the primary solution to this need. I2TV platforms in vehicles, however, can generate high internal heat loads and must operate in high-temperature environments. Intensifier tube dark current, called "Equivalent Background Input" or "EBI", is not a significant factor at room temperature, but can seriously degrade image contrast and intra-scene dynamic range at such high temperatures. Cooling of the intensifier's photocathode is the only practical solution to this problem. The US Army RDECOM CERDEC Night Vision & Electronic Sensors Directorate (NVESD) and Ball Aerospace have collaborated in the reported effort to more rigorously characterize intensifier EBI versus temperature. NVESD performed non-imaging EBI measurements of Generation 2 and 3 tube modules over a large range of ambient temperature, while Ball performed an imaging evaluation of Generation 3 I2TVs over a similar temperature range. The findings and conclusions of this effort are presented.

Bender, Edward J.; Wood, Michael V.; Hart, Steve; Heim, Gerald B.; Torgerson, John A.

2004-10-01

446

Plasmon-enhanced photocathode for high brightness and high repetition rate x-ray sources  

SciTech Connect

High brightness electron sources are at the heart of anew generation of x-ray sources based on the Free ElectronLaser (FEL) as well as in Energy Recovery Linac (ERL) and Inverse Compton Scattering (ICS) sources.The source of electrons consists of a photoinjector, comprised of a laser-driven photocathode in a high gradient electric field produced by an rf cavity. The function of the rf cavity is to provide a field sufficient for acceleration of electrons to relativistic velocity over a small distance, thus minimizing effects of the space-charge. Even so, the dense electron beam required for high brightness suffers from a space charge field that chirps and reshapes the electron pulse increasing beam emittance and thus reducing the overall brightness. This emittance growth can be avoided if the initial distribution of electrons is pancake shaped, with a semicircular transverse intensity profile. In this case, the electron distribution develops under its space charge field from a pancake into a uniformly filled ellipsoidal beam. This condition, referred to as the blowout regime, requires ultrashort pulses less than 100 fs long and has been successfully demonstrated recently in a high gradient photoinjector.

Polyakov, Aleksandr; Senft, Christoph; Thompson, K. F.; Feng, J.; Cabrini, S.; Schuck, P. J.; Padmore, Howard; Peppernick, Samuel J.; Hess, Wayne P.

2013-02-11

447

A low-voltage retarding-field Mott polarimeter for photocathode characterization  

E-print Network

Nuclear physics experiments at Thomas Jefferson National Accelerator Facility's CEBAF rely on high polarization electron beams. We describe a recently commissioned system for prequalifying and studying photocathodes for CEBAF with a load-locked, low-voltage polarized electron source coupled to a compact retarding-field Mott polarimeter. The polarimeter uses simplified electrode structures and operates from 5 to 30 kV. The effective Sherman function for this device has been calibrated by comparison with the CEBAF 5 MeV Mott polarimeter. For elastic scattering from a thick gold target at 20 keV, the effective Sherman function is 0.201(5). Its maximum efficiency at 20 keV, defined as the detected count rate divided by the incident particle current, is 5.4(2) x 10-4, yielding a figure-of-merit, or analyzing power squared times efficiency, of 1.0(1) x 10-5. The operating parameters of this new polarimeter design are compared to previously published data for other compact Mott polarimeters of the retarding-field type.

James L. McCarter; Marcy L. Stutzman; Kenneth W. Trantham; Tyler G. Anderson; April M. Cook; Timothy J. Gay

2010-03-29

448

Preliminary Study for an RF photocathode based electron injector for awake project  

E-print Network

AWAKE project, a proton driven plasma wakefield acceleration (PDPWA) experiment is approved by CERN. The PDPWA scheme consists of a seeding laser, a drive beam to establish the accelerating wakefields within the plasma cell; and a witness beam to be accelerated. The drive beam protons will be provided by the CERN's Super Proton Synchrotron (SPS). The plasma ionisation will be performed by a seeding laser and the drive beam protons to produce the accelerating wakefields. After establishing the wakefields, witness beam, namely, electron beam from a dedicated source should be injected into the plasma cell. The primary goal of this experiment is to demonstrate acceleration of a 5-15$\\,$MeV single bunch electron beam up to 1$\\,$GeV in a 10$\\,$m of plasma. This paper explores the possibility of an RF photocathode as the electron source for this PDPWA scheme based on the existing PHIN photo-injector at CERN. The modifications to the existing design, preliminary beam dynamics simulations in order to provide the requi...

Mete, Oznur; Burt, Graeme; Chattopadhyay, Swapan

2014-01-01

449

The reaction dynamics of alkali dimer molecules and electronically excited alkali atoms with simple molecules  

SciTech Connect

This dissertation presents the results from the crossed molecular beam studies on the dynamics of bimolecular collisions in the gas phase. The primary subjects include the interactions of alkali dimer molecules with simple molecules, and the inelastic scattering of electronically excited alkali atoms with O{sub 2}. The reaction of the sodium dimers with oxygen molecules is described in Chapter 2. Two reaction pathways were observed for this four-center molecule-molecule reaction, i.e. the formations of NaO{sub 2} + Na and NaO + NaO. NaO{sub 2} products exhibit a very anisotropic angular distribution, indicating a direct spectator stripping mechanism for this reaction channel. The NaO formation follows the bond breaking of O{sub 2}, which is likely a result of a charge transfer from Na{sub 2} to the excited state orbital of O{sub 2}{sup {minus}}. The scattering of sodium dimers from ammonium and methanol produced novel molecules, NaNH{sub 3} and Na(CH{sub 3}OH), respectively. These experimental observations, as well as the discussions on the reaction dynamics and the chemical bonding within these molecules, will be presented in Chapter 3. The lower limits for the bond dissociation energies of these molecules are also obtained. Finally, Chapter 4 describes the energy transfer between oxygen molecules and electronically excited sodium atoms.

Hou, H. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley National Lab., CA (United States). Chemical Sciences Div.

1995-12-01

450

Electrical conductivity anisotropy in alkali feldspar at high pressure  

NASA Astrophysics Data System (ADS)

Magnetotelluric studies have shown that electrical conductivity in the crust is highly anisotropic. Knowledge of the anisotropy of crustal minerals, such as feldspar and quartz, is essential to interpreting this phenomenon. Feldspars are the most abundant minerals in the earth's crust, and thus, the electrical conductivity of feldspars may help in understanding of the bulk conductivity of the crust. The electrical conductivities of single-crystal and polycrystalline feldspars have been previously studied, but few studies have considered the electrical conductivity of single alkali feldspars. In this study, we investigated the electrical conductivity of alkali feldspars at different orientations under high temperatures and pressures through several heating and cooling cycles. The starting materials were natural alkali feldspar minerals collected from Beijing, China. The samples contain 65 % potassium-rich host (microcline) and 30 % sodium-rich exsolution lamellae (albite), as well as ~5% minor phases. The impedance spectrum measurements were carried out in a high-pressure cubic-anvil apparatus.All complex impedance measurements were performed at 1 GPa using a Solartron 1260 impedance phase analyzer. Impedance arcs representing crystal conductivity occur in the frequency range of ~10^3-10^6 Hz. The electrical conductivity of alkali feldspars increased with increasing temperature. The highest electrical conductivities in alkali feldspars were measured along the a-axis, with somewhat lower conductivities along the b-axis and the lowest conductivities along the c-axis, suggesting minor anisotropy. The activation enthalpies ranged from 100 to 110 kJ/mol. The electrical conductivity of alkali feldspar is mildly anisotropic, with an anisotropy factor of approximately 2. The minor anisotropy in conductivity for alkali feldspar may not account for the anisotropy of the crust. This work is supported by the Important Field Knowledge Innovation Program (KZCX2-YW-QN608), National Natural Science Foundation of China (No. 40774036)

Wang, D.; Yu, Y.

2013-12-01

451

Water Content of Lunar Alkali Fedlspar  

NASA Technical Reports Server (NTRS)

Detection of indigenous hydrogen in a diversity of lunar materials, including volcanic glass, melt inclusions, apatite, and plagioclase suggests water may have played a role in the chemical differentiation of the Moon. Spectroscopic data from the Moon indicate a positive correlation between water and Th. Modeling of lunar magma ocean crystallization predicts a similar chemical differentiation with the highest levels of water in the K- and Th-rich melt residuum of the magma ocean (i.e. urKREEP). Until now, the only sample-based estimates of water content of KREEP-rich magmas come from measurements of OH, F, and Cl in lunar apatites, which suggest a water concentration of < 1 ppm in urKREEP. Using these data, predict that the bulk water content of the magma ocean would have <10 ppm. In contrast, estimate water contents of 320 ppm for the bulk Moon and 1.4 wt % for urKREEP from plagioclase in ferroan anorthosites. Results and interpretation: NanoSIMS data from granitic clasts from Apollo sample 15405,78 show that alkali feldspar, a common mineral in K-enriched rocks, can have approx. 20 ppm of water, which implies magmatic water contents of approx. 1 wt % in the high-silica magmas. This estimate is 2 to 3 orders of magnitude higher than that estimated from apatite in similar rocks. However, the Cl and F contents of apatite in chemically similar rocks suggest that these melts also had high Cl/F ratios, which leads to spuriously low water estimates from the apatite. We can only estimate the minimum water content of urKREEP (+ bulk Moon) from our alkali feldspar data because of the unknown amount of degassing that led to the formation of the granites. Assuming a reasonable 10 to 100 times enrichment of water from urKREEP into the granites produces an estimate of 100-1000 ppm of water for the urKREEP reservoir. Using the modeling of and the 100-1000 ppm of water in urKREEP suggests a minimum bulk silicate Moon water content between 2 and 20 ppm. However, hydrogen loss was likely very significant in the evolution of the lunar mantle. Conclusions: Lunar granites crystallized between 4.3-3.8 Ga from relatively wet melts that degassed upon crystallization. The formation of these granites likely removed significant amounts of water from some mantle source regions, e.g. later mare basalts predicting derivation from a mantle with <10 ppm water. However, this would have been a heterogeneous pro-cess based on K distribution. Thus some, if not most of the mantle may not have been devolatilized by this process; as seen by water in volcanic glasses and melt inclusions.

Mills, R. D.; Simon, J. I.; Wang, J.; Alexander, C. M. O'D.; Hauri, E. H.

2016-01-01

452

Imaging of hydrogen halides photochemistry on argon and ice nanoparticles  

NASA Astrophysics Data System (ADS)

The photodissociation dynamics of HX (X = Cl, Br) molecules deposited on large ArN and (H2O)N, bar{N}? 102-103, clusters is investigated at 193 nm using velocity map imaging of H and Cl photofragments. In addition, time-of-flight mass spectrometry after electron ionization complemented by pickup cross section measurements provide information about the composition and structure of the clusters. The hydrogen halides coagulate efficiently to generate smaller (HX)n clusters on ArN upon multiple pickup conditions. This implies a high mobility of HX molecules on argon. On the other hand, the molecules remain isolated on (H2O)N. The photodissociation on ArN leads to strong H-fragment caging manifested by the fragment intensity peaking sharply at zero kinetic energy. Some of the Cl-fragments from HCl photodissociation on ArN are also caged, while some of the fragments escape the cluster directly without losing their kinetic energy. The images of H-fragments from HX on (H2O)N also exhibit a strong central intensity, however, with a different kinetic energy distribution which originates from different processes: the HX acidic dissociation followed by H3O neutral hydronium radical formation after the UV excitation, and the slow H-fragments stem from subsequent decay of the H3O. The corresponding Cl-cofragment from the photoexcitation of the HCl.(H2O)N is trapped in the ice nanoparticle.

Poterya, V.; Lengyel, J.; Pysanenko, A.; Svr?ková, P.; Fárník, M.

2014-08-01

453

Mixing the spacers in azacryptands: effects on halide recognition.  

PubMed

In this work, we report on two new asymmetric dicopper cryptates, characterized by alternate furanyl and p-xylyl spacers. The results of the potentiometric, UV-vis and X-ray diffraction studies are discussed. In particular, for one of the cages in the octaprotonated form, the crystal structure of the complex with nitrate is described. From the point of view of the anion binding in water, the new dicopper cryptates display stronger similarities to each other than to the symmetric analogues (i.e. p-xylyl and furan cryptates). The substitution of even only one spacer modifies the distance between the metal ions. This prevents the development of the CT band, typically accompanying the binding of halides by the furan cryptate, and favors the formation of complexes of different stoichiometry with the linear azide anion, not observed for the symmetric cryptates. The obtained results may be very helpful in the design of new molecular receptors based on dimetallic cryptates, in particular for the tuning of the sensitivity towards specific anionic substrates. PMID:24926852

Bergamaschi, Greta; Boiocchi, Massimo; Perrone, Maria Lucia; Poggi, Antonio; Viviani, Ivan; Amendola, Valeria

2014-08-01