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1

Fabrication of alkali halide UV photocathodes by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

2

On the surface morphology of thin alkali halide photocathode films  

NASA Astrophysics Data System (ADS)

Thin alkali halide films are currently used as transmissive UV-photocathodes and as protecting layers for visible photocathodes. The surface morphology of 20 and 75 nm thick evaporated CsI, NaI and CsBr films was investigated by means of a scanning electron microscope, to which the samples were transferred, under vacuum, with practically no contact with air. It is shown that the film continuity, in particular that of NaI, is strongly affected by short exposure to moisture. CsI, which is the less hygroscopic material among the three, exhibits the most continuous structure.

Boutboul, T.; Breskin, A.; Chechik, R.; Klein, E.; Braem, A.; Lion, G.; Miné, P.

1999-12-01

3

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

NASA Astrophysics Data System (ADS)

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

Carruthers, George R.

1987-07-01

4

Dependence of quantum efficiency of alkali halide photocathodes on the radiation incidence angle  

NASA Astrophysics Data System (ADS)

We studied variation efficiencies of CsI, KBr and KI- evaporated reflective planar phototcathodes with the angle of radiation incidence in the spectral range of 25-115 nm. The photocurrent increases with the photon incidence angle for short wavelengths, while it changes only approximately 5 percent at wavelengths approximately 90-115 nm. The theoretical calculations of the photocathode angular response based on the absorption length of the photons and the escape length of the photoelectronics are in a relatively good agreement with the measured data. A detailed study of the detection efficiency angular variation for the microchannel plates with CsI, KI and KBr photocathodes in the spectral range of 25-191 nm is also presented. Heat annealing of the planar photocathodes did not result in any significant variation in their angular response.

Tremsin, Anton S.; Siegmund, Oswald H.

1999-10-01

5

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

NASA Astrophysics Data System (ADS)

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

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

6

Infrared Refractive Indices of Alkali Halides.  

National Technical Information Service (NTIS)

The authors developed mathematical relationships of alkali halide refractive indices called the cogenerational formulas. The best constants of these expressions are established by least-squares fitting.

H. I. Heaton

1970-01-01

7

Core Exciton of Alkali and Alkali-Earth Halides  

NASA Astrophysics Data System (ADS)

Low energy electron loss spectra (LEELS) of alkali halides LiF, NaCl, KCl, KBr, KI, RbBr and CsCl, and alkali-earth halides CaF2 and CaCl2 are measured for primary energies 30 to 900 eV. For K and Ca-halides, there are four loss peaks in the core exciton regions, some of which have not been observed in optical measurements and high energy electron loss spectra. The intensities of these loss peaks are primary energy dependent and decrease with the increase of incident energy. The primary energy dependency is largest for K and Ca-halides and decreases for Rb and Cs, and is almost not observed for Li and Na-halides. These loss peaks are thought to be caused by intra-atomic transitions between localized p-core and d-conduction bands in metal ions.

Mabuchi, Teruhiko; Toda, Hidemichi; Yamanaka, Hideo

1993-01-01

8

Removable organic protective coating for alkali-antimonide photocathodes  

NASA Astrophysics Data System (ADS)

We describe a technique for protecting alkali-antimonide visible light photocathodes against deterioration by exposure to impurities, during handling or storage in poor vacuum or gas. The photocathodes are coated with a ˜1 ?m vacuum-deposited hexatriacontane film, which can be subsequently removed by low-temperature sublimation. We show that Cs 3Sb coated photocathodes can be exposed for several minutes to considerable amounts of oxygen, without deterioration. Their initial photoemission properties are almost fully recovered after film removal.

Breskin, A.; Buzulutskov, A.; Shefer, E.; Chechik, R.; Prager, M.

9

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

10

Solvation at nanoscale: Alkali-halides in water clusters  

NASA Astrophysics Data System (ADS)

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; Mikkelä, Mikko-Heikki; Huttula, Marko; Tchaplyguine, Maxim; Zhang, Chaofan; Andersson, Tomas; Björneholm, Olle

2013-01-01

11

Ionic alkali halide XUV laser feasibility study  

SciTech Connect

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

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

1989-11-10

12

Enhanced quantum efficiency from hybrid cesium halide/copper photocathodes  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

13

Preparation and Investigation of Multi-alkali Photocathode  

NASA Astrophysics Data System (ADS)

Multialikali antimonide photocathodes exhibit high quantum efficiency in visible light range, so this kind of cathodes is attractive for use in high average current photoinjectors to generate high quality electron beams. We have grown multi-alkali photocathodes on silicon (100) substrates, simultaneously acquiring in-situ X-ray reflection (XRR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) data throughout the growth process. Correlations between cathode structure and growth parameters and the resulting quantum efficiency (QE) have been explored.

Liang, Xue

14

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.

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

2013-01-01

15

Crystal mechanics of some alkali halides  

NASA Astrophysics Data System (ADS)

A three-body-force shell model (TSM) has been employed for a comprehensive and unified calculation of the crystal mechanics of some alkali halides. This includes the description of phonon dispersion, two-phonon Raman and infrared spectra, specific heats, cohesive energy, relative stability, phase-transition pressure and volume, dielectric constants, quasi- harmonic elastic and photoelastic properties of lithium fluoride, potassiumchloride and rubidium chloride. These predictions are reasonably good and have led to the conclusion that TSM is an appropriate model for lattice mechanical descriptions of ionic crystals.

Nirwal, V. V. S.; Singh, R. K.

1981-02-01

16

Curve Crossing in Collisional Dissociation of Alkali Halide Molecules  

Microsoft Academic Search

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

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

1971-01-01

17

Thermoluminescence of alkali halides and its implications  

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

18

Femtosecond Real-Time Probing of Reactions. 4. The Reactions of Alkali Halides.  

National Technical Information Service (NTIS)

The photodissociation dynamics of some alkali halides are explored via the method of femtosecond transition-state spectroscopy (FTS). The alkali halide dissociation reaction is influenced by the interaction between the covalent and the ground state ionic ...

T. S. Rose M. J. Rosker A. H. Zewail

1989-01-01

19

Photocathode transfer and storage techniques using alkali vapor feedback control  

SciTech Connect

Photocathodes of quantum efficiency above 1% at the doubled YAG frequency of 532 nM are very sensitive to the local vacuum environment. These cathodes must have a band gap of less than 2.3 eV, and a work function that is also on the order of {approximately}2 volts or less. As such, these surfaces are very reactive as they provide many surface states for the residual gases that have positive electron affinities such as oxygen and omnipotent water. Attendant to this problem is that the optimal operating point for some of these cesium based cathodes is unstable. Three of the cesium series were tried, the Cs-Ag-Bi-O, the Cs{sub 3}Sb and the K{sub 2}CsSb. The most stable material found is the K{sub 2}CsSb. The vacuum conditions can be met by a variety of pumping schemes. The vacuum is achieved by using sputter ion diode pumps, and baking at 250{degrees}C or less for whatever time is required to reduce the pump currents to below 1 uA at room temperature. To obtain the required partial pressure of cesium, a simple very sensitive diagnostic gauge has been developed that can discriminate between free alkali and other gases present. This Pressure Alkali Monitor (PAM) can be used cesium sources to provide a low partial pressure using standard feedback techniques. Photocathodes of arbitrary composition have been transferred to a separate vacuum system and preserved for over 10 days with less than a 25% loss to the QE at 543.5 nM.

Springer, R.W.; Cameron, B.J.

1991-12-20

20

Calculation of the Energies of Gaseous Alkali Halide Dimer Molecules  

Microsoft Academic Search

The energies of formation of gaseous alkali halide dimer molecules from the monomers have been calculated with a model suggested by Pauling. The dimers were found to be from 40 to 60 kcal more stable, energetically, than their separated monomers. These results are in agreement with the experimental data available. The free energies of dimerization were estimated and used to

Thomas A. Milne; Daniel Cubicciotti

1958-01-01

21

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

NASA Technical Reports Server (NTRS)

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

Schlosser, Herbert

1992-01-01

22

Gradient-Elastic Tensor of Alkali Halide Crystals  

Microsoft Academic Search

Origin of electric field gradient due to strains in alkali halide crystals is unravelled from the experimental determination of gradient-elastic tensors. Tensors for 23Na, 35Cl, 81Br and 127I in a series of crystals are determined from the quadrupolar broadening of resonance lines due to solute ions, using lattice distortion derived from lattice parameter changes. Results are interpreted by the theory

Yuh Fukai

1964-01-01

23

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

24

Volcanic Origin of Alkali Halides on Io  

NASA Technical Reports Server (NTRS)

The recent observation of NaCl (gas) on Io confirms our earlier prediction that NaCl is produced volcanically. Here we extend our calculations by modeling thermochemical equilibrium of O, S, Li, Na, K, Rb, Cs, F, Cl, Br, and I as a function of temperature and pressure in a Pele-like volcanic gas with O/S/Na/Cl/K = 1.518/1/0.05/0.04/0.005 and CI chondritic ratios of the other (as yet unobserved) alkalis and halogens. For reference, the nominal temperature and pressure for Pele is 1760 plus or minus 210 K and 0.01 bars based on Galileo data and modeling.

Schaefer, L.; Fegley, B., Jr.

2003-01-01

25

Electronic excitation in bulk and nanocrystalline alkali halides  

NASA Astrophysics Data System (ADS)

The lowest energy excitations in bulk alkali halides are investigated by considering five different excited state descriptions. It is concluded that excitation transfers one outermost halide electron in the fully ionic ground state to the lowest energy vacant s orbital of one closest cation neighbour to produce the excited state termed dipolar. The excitation energies of seven salts were computed using shell model description of the lattice polarization produced by the effective dipole moment of the excited state neutral halogen-neutral metal pair. Ab initio uncorrelated short-range inter-ionic interactions computed from anion wavefunctions adapted to the in-crystal environment were augmented by short-range electron correlation contributions derived from uniform electron-gas density functional theory. Dispersive attractions including wavefunction overlap damping were introduced using reliable semi-empirical dispersion coefficients. The good agreement between the predicted excitation energies and experiment provides strong evidence that the excited state is dipolar. In alkali halide nanocrystals in which each ionic plane contains only four ions, the Madelung energies are significantly reduced compared with the bulk. This predicts that the corresponding intra-crystal excitation energies in the nanocrystals, where there are two excited states depending on whether the halide electron is transferred to a cation in the same or in the neighbouring plane, will be reduced by almost 2 eV. For such an encapsulated KI crystal, it has been shown that the greater polarization in the excited state of the bulk crystal causes these reductions to be lowered to a 1.1 eV-1.5 eV range for the case of charge transfer to a neighbouring plane. For intra-plane charge transfer the magnitude of the polarization energy is further reduced thus causing the excitation in these encapsulated materials to be only 0.2 eV less than in the bulk crystal.

Bichoutskaia, Elena; Pyper, Nicholas C.

2012-11-01

26

Molten Alkali Halides: Straightforward Prediction of Surface Tension  

NASA Astrophysics Data System (ADS)

This article provides a new model for predicting the surface tension of molten alkali halides, because the subject is worthy of investigation. A relationship exists between the surface tension ( ?) at the melting point ( T m ), molar volume ( V), internuclear distance ( D), and radius ratio The basic idea results from the assumption that all of the parameters are constants. The relation depends on the reliability and accuracy of all the constants on which it is based. The formula was examined and showed remarkable agreement between the calculated surface tension and experimental data within a difference of less than 10 pct for most of the salts studied.

Aqra, Fathi

2014-05-01

27

A new mechanism for radiation damage processes in alkali halides  

NASA Astrophysics Data System (ADS)

We present a theory of radiation damage formation in alkali halides based on a new mechanism of dislocation climb, which involves the production of VF centers (self-trapped hole neighboring a cation vacancy) as a result of the absorption of H centers of dislocation lines. We consider the evolution of all experimentally observed extended defects: metal colloids, gas bubbles, and vacancy voids. Voids are shown to arise and grow large due to the reaction between F and VF centers at the surface of halogen bubbles. Voids can ignite a back reaction between the radiolytic products resulting in decomposition of the irradiated material.

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

1999-12-01

28

Femtosecond real-time probing of reactions. IV. The reactions of alkali halides  

Microsoft Academic Search

The photodissociation dynamics of some alkali halides are explored via the method of femtosecond transition-state spectroscopy (FTS). The alkali halide dissociation reaction is influenced by the interaction between the covalent and the ground state ionic potential energy surfaces (PES), which cross at a certain internuclear separation. Depending upon the adiabaticity of the PES, the dissociating fragments may be trapped in

Todd S. Rose; Mark J. Rosker; Ahmed H. Zewail

1989-01-01

29

Silver halide micro- and nanocrystals embedded in an alkali halide matrix: suppression of the Jahn-Teller effect in nanoparticles  

Microsoft Academic Search

Self-organized microcrystals and nanocrystals (quantum dots) of AgCl and AgBr embedded in KCl and KBr crystalline matrices and retaining the orientation of the host lattice were studied by optically detected magnetic resonance. It was unambiguously shown that self-organized microcrystalline silver halides can be grown inside alkali halide crystals with the properties of bulk crystals since the optically detected magnetic resonance

P. G. Baranov; N. G. Romanov; V. A. Khramtsov; V. S. Vikhnin

2001-01-01

30

Lattice Energies of the Alkali Halides and the Electron Affinities of the Halogens  

Microsoft Academic Search

The overlap repulsion parameters that occur in the Born-Mayer treatment of lattice energies have been re-evaluated for the alkali halides from recent compressibility data. With these parameters the lattice energies of the alkali halides were calculated. The lattice energies were combined with thermochemical data to calculate the electron affinities of the halogens. The values obtained were: F 80.2; Cl 85.0;

Daniel Cubicciotti

1959-01-01

31

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

32

Strong Turbulence in Alkali Halide Negative Ion Plasmas  

NASA Astrophysics Data System (ADS)

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

Sheehan, Daniel

1999-11-01

33

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

34

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

35

Defects production in UV alkali halides doped with europium  

NASA Astrophysics Data System (ADS)

The defect production in alkali halide with doped divalent impurities and exposed to ionizing radiation can be explained by means of the creation of self-trapped excitons (STE), which are formed by either the excitation of halogen ion or trapped electrons in VK centers coming from prior halogen ion ionization. Radiative recombination of self-trapped exciton produces a characteristic excitonic luminescence and no radiative recombination causes Frenkel defects (F-H centers). In the present work we provide experimental evidence that indicates that same crystals when exposed to a non ionizing radiation, such as UV near to 230 nm, similar Frenkel defects are generated. This situation is remarkable since 230 nm photons (5.3 eV) cannot directly produce excitons because their energy is below of the creation excitons energy around 7.7 eV. Thermoluminescence and optically stimulated luminescence techniques were used for investigating comparatively the effects of both ionizing and no ionizing radiations. We found that for ionizing and non ionizing radiation the luminescence signal was composed by two bands; the main part of the luminescence response was a broad band centered at 420 nm, which is ascribed to the well known energy transition 4f^65d(t_2g)-4f^7(^8S_7/2) of Eu_2+ ion and other additional band near to 460 nm which it has perhaps an intrinsic origin. In addition, we addressed the participation of the F and FZ centers in the TL and OSL processes. In this way, we found that TL signal are strongly correlated with F centers (470 K TL peak in KCl:Eu_2+) and FZ centers (370 K TL peak). Furthermore, through a selective photostimulation process, we also obtained evidence that the F center is involved in the OSL process. The present results point the existence of a common mechanism for the formation of Frenkel defects under ionizing and no ionizing radiation, by means of a possible excitonic mechanism.

Barboza-Flores, M.; Castañeda, B.; Pedroza-Montero, M.; Meléndrez, R.

2003-03-01

36

Magneto-optical properties of the UV absorption bands of VK centres in alkali halides  

Microsoft Academic Search

A new UV absorption band below the original UV band has been discovered through the magnetic circular dichroism of the VK centre absorption (MCDA) in seven alkali halide crystals. This new band is attributed to the transition Sigma u to Pi u, which becomes dipole allowed as a result of a loss of inversion symmetry. We attribute this lowered symmetry

U. Rogulis; K. S. Song; J.-M. Spaeth

1995-01-01

37

Theory of L bands in face-centred cubic alkali halides  

Microsoft Academic Search

The L band absorption spectra observed in alkali halides is considered to arise from transitions from the ground state of the F centre to localized excited states arising from conduction band wave functions of higher energy. These localized states are linear combinations of Wannier functions for the conduction bands centred on the cell containing the F centre and adjacent cells,

P. G. Dawber; I. M. Parker

1970-01-01

38

Cluster-Bethe Lattice Treatment for the F-Center in Alkali Halides.  

National Technical Information Service (NTIS)

The electronic structure of the F-center in alkali halides with the NaCl structure has been studied using the cluster-Bethe lattice method. The central cluster has been taken as constituted by the vacancy and the nearest and second- neighbors to it, respe...

S. L. A. de Queiroz B. Koiller B. Maffeo H. S. Brandi

1977-01-01

39

Basic Mechanisms of Color Centres Production by Excitons in Activated Alkali Halides.  

National Technical Information Service (NTIS)

The paper deals with some peculiarities of colour centers formation which are caused by introduction of the activator in alkali halide crystals. The crystals of KBr and KI activated with Tl exp + , In exp + , Sn exp ++ in concentrations 10 exp 17 -10 exp ...

G. Vale

1981-01-01

40

Proton Nuclear Magnetic Resonance Solvent Shifts in Aqueous Solutions of Alkali Halides  

Microsoft Academic Search

Aqueous proton NMR chemical shifts induced by molal alkali halides have been re-examined and separated into two categories. The first, an upfield shift, has been quantitatively related to the change in hydrogen-bond fraction of the solvent as determined by others. The residue, a downfield shift, is anion dependent, cation independent, and directly proportional to effects induced in organic solutes present

R. E. Glick; W. E. Stewart; K. C. Tewari

1966-01-01

41

Drift model of photoinduced processes in alkali-halide crystals during volume hologram recording  

NASA Astrophysics Data System (ADS)

Investigations of photoinduced processes, which occur in alkali-halide crystals during volume hologram recording, are performed with the help of new holographic method. New diffusion-drift model of the charge carriers and defects migration in high gradient interference light field during hologram recording is offered.

Popov, Andrey Y.; Belous, W. M.; Mandel, Vladimir E.; Shugailo, Yu. B.; Tyurin, Alexander V.

1999-11-01

42

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

43

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

44

CO/sub 2/ laser absorption and saturation studies of molecular impurities in alkali halide crystals  

SciTech Connect

The objective of this research program has been to explore the equilibrium and non-equilibrium dynamical properties of ReO/sub 4//sup -/ molecules embedded in alkali halide lattices using electromagnetic radiation. Both incoherent sources and CO/sub 2/ laser radiation have been used to explore the full dynamic range of the molecular vibrational modes. To achieve this objective stable molecular dopant - alkali halide combinations have been fabricated which have vibrational modes near the CO/sub 2/ laser frequencies. In order to uncouple the molecular modes from the lattice modes, to simplify the analysis as much as possible, low temperature spectroscopic measurements were required. In general, it was found that the molecular vibrational modes in the low temperature quiescent lattice had extremely narrow linewidths (less than 0.1 cm/sup -1/) so that most of the coincidences with the CO/sub 2/ laser lines were eliminated.

Sievers, A.J.

1980-12-01

45

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

46

Sample Preparation and Photoluminescence of ZnO Particles Embedded in Thin Alkali Halide Crystals  

NASA Astrophysics Data System (ADS)

We have prepared samples of ZnO particles embedded in thin alkali halide crystals by a melt growth method and have measured photoluminescence spectra at various temperatures. In the spectra measured at 8.5 K, free exciton (FE) and bound exciton (BE) emission lines are clearly recognized, while the well-known green band is hardly observed. The FE line appears at temperatures between 8.5 K and 300 K. The widths of both lines are very sharp and almost equal to that of ZnO epitaxial layers grown by a molecular beam epitaxy method. These results strongly suggest that high-quality ZnO particles can be well embedded in thin alkali halide crystals.

Harada, Yoshiyuki; Kondo, Hisao; Ichimura, Nobuko; Hashimoto, Satoshi

1999-11-01

47

Effective dielectric functions of samples obtained by evaporation of alkali halides  

Microsoft Academic Search

This paper investigates the dielectric properties of inhomogeneous samples consisting of small alkali halide particles (NaCl, KBr) on gold-coated substrates. Our reflection measurements in the far infrared can be simulated as a thin layer of the powder with an effective dielectric function on a perfectly reflecting substrate. Scanning electron micrographs provide useful information about sample topology. Several mixing formulas (e.g.

J. Sturm; P. Grosse; W. Theiß

1991-01-01

48

Water structure in aqueous solutions of alkali halide salts: FTIR spectroscopy of the OD stretching band  

Microsoft Academic Search

Water structure making\\/breaking studies in solutions of five alkali halide salts (KF, KI, NaI, CsF and CsCl) in 4 wt% D2O in H2O mixtures have been performed by FTIR analysis of the OD stretching band in the full solubility range. The proposed method gives a microscopic picture of the water structure making\\/breaking character of the salts in terms of the

Z. S. Nickolov; J. D. Miller

2005-01-01

49

Demulsifying petroleum emulsions with aryl sulfonates-oxyalkylated phenolformaldehyde resins and alkali metal halides  

Microsoft Academic Search

A process for recovering oil from oil-in-water petroleum emulsions stabilized with clay and\\/or other solids by subjecting them to the action of an optimum amount of non-ionic, water soluble, aryl sulfonates-oxyalkylated phenol formaldehyde resins at a ph of 7.0 to 8.0 and then adding a saturated aqueous alkali metal halide solution to the resulting mixture. The process is carried out

1981-01-01

50

The change of the electronic structure of alkali halide films on W(110) under electron bombardment  

NASA Astrophysics Data System (ADS)

NaCl and Csl films of up to four layers were deposited onto W(110) surfaces and investigated by metastable impact electron spectroscopy (MIES), UPS and AES. The electronic structure of the films under electron bombardment was then studied by MIES/UPS. The results are compared with the corresponding ones obtained by thermal desorption spectroscopy (TDS). An interpretation of the results is attempted on the basis of existing theories for desorption induced by electronic transitions (DIET) of alkali halides.

Dieckhoff, S.; Maus-Friedrichs, W.; Kempter, V.

1992-03-01

51

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

Microsoft Academic Search

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

Jean-Joseph Max; Camille Chapados

2001-01-01

52

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

NASA Technical Reports Server (NTRS)

High temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost were studied. Experiments were performed to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, determine the effects of reactants and/or products on materials of reactor construction, and make preliminary engineering and economic analyses of a scaled-up process.

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

1980-01-01

53

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

Microsoft Academic Search

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

J. Shanker; G. D. Jain

1983-01-01

54

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

Microsoft Academic Search

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

A. Hammadi

2004-01-01

55

A Monte Carlo model of alkali halides under low energy electron irradiation  

Microsoft Academic Search

A Monte Carlo random walk model was used to study the creation and dynamics of F- and H-centers induced by electron irradiation in alkali-halide single crystals. The purpose of the study was to observe the effects of depth dependent electron energy deposition near the surface region using beam energies of 500 eV or less and relatively low currents (< 100

M. Portillo; M. V. Ascherl; D. P. Russell

1998-01-01

56

The Structure of the Mixed Alkali Halide Dimer LiNaF_2  

Microsoft Academic Search

The structure and dipole moment of the mixed alkali halide dimer LiNaF2 has been determined by two microwave spectroscopy experiments in Berlin as well as one at NIST footnote A joint publication of both the Berlin and NIST data is in preparation. A large number of both ^7LiNaF2 and ^6LiNaF2 lines have been observed and assigned to an asymmetric top

R. J. Mawhorter; T. Toerring; S. Biermann; J. Hoeft; F. J. Lovas; R. D. Suenram; Y. Kawashima; E. Hirota

1996-01-01

57

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

PubMed

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

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

2009-07-01

58

Formamide adsorption and habit changes of alkali halide crystals grown from solutions  

NASA Astrophysics Data System (ADS)

The possibility to obtain {1 1 1} surfaces on NaCl crystals grown from pure water solutions was investigated in order to verify some early observations. Repeating the same experiments as reported by Kern in 1953 (Bull. Soc. Fr. Mineral Cristallogr. 76 (1953) 391) followed by detailed examination using optical microscopy and optical goniometry revealed that, independent of supersaturation, {1 0 0} is the only stable form. We also studied the morphology of the alkali halide crystals obtained from formamide solutions. We noticed that the appearance of the octahedral form is strictly related to unit cell size. Octahedrons appear starting from NaF crystals with unit cell size 0.462 nm up to KCl with a unit cell of 0.628 nm. All the alkali halide crystals with dimensions outside this range are cubes. In addition to rocksalt structure crystals, a new, non-cubic pseudo-polymorph was obtained for several alkali halide crystals grown from formamide solution. For sodium iodide this new compound was identified as NaI-1(formamide). In addition (to this and our recent paper (Surf. Sci. 523 (2003) 307)), we tried to obtain NaCl crystals with {1 1 1} faces using pyridine, aniline and glycine. In the case of pyridine and anyline we only observed cubes, whereas from aqueous solutions containing glycine we obtained crystals with well-developed faces with an average {1 1 0} orientation.

Radenovi?, Neda; van Enckevort, Willem; Vlieg, Elias

2004-03-01

59

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

Microsoft Academic Search

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

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

1951-01-01

60

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

PubMed

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 (T(m)) 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 T(m) 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. PMID:22979874

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

2012-09-14

61

Alkali-halide cluster ions produced by laser vaporization of solids  

Microsoft Academic Search

The mass spectra of alkali-halide cluster ions M(MX)+n and X(MX)-n, produced by laser vaporization of a solid sample, were measured by tilted-plate time-of-flight mass spectrometry. The measured abundances of sodium chloride clusters (n=1-200), sodium iodide clusters (n=1-125), cesium chloride clusters (n=1-125), and cesium iodide clusters (n=1-100) confirm that surface terraces are the most stable additions to a cuboid base lattice.

Y. J. Twu; C. W. S. Conover; Y. A. Yang; L. A. Bloomfield

1990-01-01

62

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

SciTech Connect

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

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

2006-02-15

63

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

64

Protection of cesium-antimony photocathodes  

NASA Astrophysics Data System (ADS)

In order to operate gaseous photomultipliers in the visible range it was suggested to protect sensitive photocathodes against contact to air and counting gases by their coating with a thin solid dielectric film. We present data on coating of cesium-antimony photocathodes with alkali-halide (NaI, CsI, CsF, NaF), oxide (SiO) and organic (hexatriacontane, calcium stearate) films. The photoelectron transmission through these films and their protection capability have been studied in detail. Cesium-antinomy photocathodes are shown to withstand exposure to considerable doses of oxygen and dry air when coated with NaI films. This opens ways to their operation in gas media.

Buzulutskov, A.; Breskin, A.; Chechik, R.; Prager, M.; Shefer, E.

1997-02-01

65

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

Microsoft Academic Search

An electric field deflection technique has been used to obtain the average dimer polarizabilities of all the alkali halides, and the scalar ('2)P(, 1\\/2) polarizabilities of indium and thallium. The experimental procedure consisted of passing a well collimated effusive beam through a region of inhomogeneous electric field and analyzing the deflected beam pattern, with respect to the undeflected beam shape,

Thomas Paul Guella

1985-01-01

66

Colorazione di alogenuri alcalini mediante irraggiamento con elettroni. (Generation of colour centers in alkali halides by electron radiation).  

National Technical Information Service (NTIS)

Point defects in alkali halides can be produced by using chemical or physical methods. The defects created by the first method are usually more stable than those created by the second one, but a few defects can be produced only with physical methods. For ...

G. Baldacchini, G. Messina, R. M. Montereali, E. Ciaramella

1992-01-01

67

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

SciTech Connect

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

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

2010-10-14

68

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

69

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

NASA Astrophysics Data System (ADS)

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

Shanker, J.; Jain, G. D.

1983-02-01

70

Reaction-rate approach to the dipolar relaxation in alkali halides  

NASA Astrophysics Data System (ADS)

An alternative reaction-rate approach is suggested for dealing with the relaxation times of dipolar defects in alkali halides. It rests on an occurrence-probability definition of the transition rate, accounting for both classical and quantal effects. A simple model Hamiltonian is postulated to describe the reorientational motion of a dipole within the framework of the adiabatic approximation. Two infamous examples are considered from this point of view. In one of these, the OH- dipole is assumed to couple only electronically to the neighboring cations, while all its remaining reorientational characteristics are, to a first approximation, independent of the host lattice. Assuming further that a single local oscillator drives the reorientational motion, this model agrees well with the experimental temperature dependence of the OH- relaxation time in four host halides up to 10 K, as measured by Kapphan and Lüty. The other example is the off-center Ag+ ion in RbBr and RbCl where a formal application of the reaction-rate method has been found to fit closely, over the entire range, the experimental temperature dependence of the relaxation time for 90° reorientation, measured by the same authors.

Georgiev, M.; Gochev, A.

1985-04-01

71

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

72

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

73

Synergistic effect of alkali halide and Lewis base on the catalytic synthesis of cyclic carbonate from CO 2 and epoxide  

NASA Astrophysics Data System (ADS)

The synthesis of cyclic carbonates from CO 2 and epoxides catalyzed by alkali metal halides (MX) in combination with a Lewis base (LB) is reported here. The unique synergistic effect between MX and LB has been observed at an optimum mole ratio of 1:1. High turnover frequency (TOF, h -1) indicates that an increase in the reaction efficiency of up to 40 times is obtained by comparison with the reaction carried out using only MX. The activity of MX primarily falls in the order of alkali metal ion's Lewis acidity. The optimum conditions for this solventless reaction were 130 °C and 2 MPa of CO 2 pressure.

Ramidi, Punnamchandar; Munshi, Pradip; Gartia, Yashraj; Pulla, Sharon; Biris, Alexandru S.; Paul, Amit; Ghosh, Anindya

2011-08-01

74

Effect of plastic deformation on spectral characteristics of alkali halide crystals doped with indium or nickel ions  

NASA Astrophysics Data System (ADS)

The opportunity of investigation of impurity defect properties in alkali halide crystals by study of the spectral characteristics of the strongly deformed crystals is shown. The spectral characteristics of KCl-In and NaCl-Ni crystals before and after deformation, and also after X- irradiation, are given. The effect of methods of impurity doping of a host crystal on spectral properties of powdered specimens under study was examined.

Kochubey, Vyacheslav I.; Sedova, Yuliya G.

2000-03-01

75

Spectral Property and Stability of Color Centers in Alkali Halide Crystals Induced by He+ Ion Implantation at Room Temperature  

Microsoft Academic Search

Thin colored layers with high density defect centers could be produced on alkali halide crystals implanted by 300-400 keV He+ ions at room temperature. Besides well known absorption bands, several new absorption bands and colloid absorption band are observed in the crystals, such as 520 and 842 nm absorption bands in the implanted LiF crystals, 840 nm absorption band in

Hongen Gu; Zhifang Chen; Zhijuan Li

1993-01-01

76

Off-centre effects in the triplet relaxed excited state of impurity ns2 ions in alkali halides  

Microsoft Academic Search

An off-centre displacement of an excited ns2 ion from a crystal lattice site is studied for Ga+, In+ and TI+ centres in alkali halides at 0.09-5 K by the time-resolved polarization spectroscopy method. A theory is developed, which considers the off-centre effects as a result of the mixing of the impurity 3nsnp and 3npnp excited states by T1u vibrations.

V. Hizhnyakov; K. Kalder; V. Korrovits; V. Nagirnyi; A. Stolovich; S. Zazubovich

1995-01-01

77

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

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

78

Possible mechanism of energy storage in optically stimulable materials: doped alkali halides  

NASA Astrophysics Data System (ADS)

Radiation-induced effects in doped alkali halides, mainly in KBr:In, are studied by the luminescence technique. The activator luminescence during a 10 s under UV-light or electron irradiation and, after it, the pulsed photostimulated luminescence on a phosphorescence background were investigated. The obtained results allow us to conclude that the main host lattice excitation relevant to both the luminescence processes mentioned above is a very mobile excitonic excitation including a photon phase and the self- trapped exciton in its composition. The photon phase, as we suppose, represents a free exciton luminescence at room temperature. In this phase, via multiple reabsorption in the low-energy exciton absorption band, the excitonic excitation can overcome large distances. In the phase of the self- trapped exciton, the induced decay within a perturbed region around the activator hole center takes place. As a result, the pairs of F-type electron and activator hole centers, contributing to the photostimulated luminescence under stimulation with light in the F absorption band, are formed. The above-mentioned defect formation process is dominant over the excitation of activator ion at low activator concentration. At high activator concentration, when strong competition between reabsorption in the exciton absorption band and absorption in the local center band connected with the activator takes place, the activator luminescence prevails. The activator luminescence spectrum is found to be sensitive to the F or F-aggregate centers formation in the region near the activator hole center.

Plavina, Irena; Popov, Anatoli I.; Tale, Aija; Kalnins, A.

1997-02-01

79

Vibrational entropy of polyatomic solids: Metal carbides, metal borides, and alkali halides  

NASA Astrophysics Data System (ADS)

It is shown that in the high temperature vibrational entropy of polyatomic solids, the influence of the atomic masses is described by an effective mass M_e = M_1^{C_1 } M_1^{C_2 } .{text{ }}.{text{ }}.{text{ }}M_j^{C_j } , where c i is the concentration of mass M i . This mass effect explains almost all of the differences between TiC, ZrC, and HfC in the recommended entropy data of Hultgren et al. (1973). Analogous results are found for VC, NbC, and TaC and for TiB2, ZrB2, and HfB2. Mass differences also explain a major part of the measured entropy differences between alkali halides AB, with A=Li, Na, or K and B=F, Cl, Br, or I. Finally, we discuss different methods, including one used in the JANAF Thermochemical Tables, to estimate standard entropies from data on chemically related compounds.

Grimvall, G.; Rosén, J.

1983-06-01

80

Off-center self-trapped excitons and creation of lattice defects in alkali halide crystals  

NASA Astrophysics Data System (ADS)

Self-consistent calculations and experimental evidence indicating that self-trapped excitons in alkali halides relax spontaneously to an off-center configuration are examined in relation to radiation-induced lattice defect formation. The theoretical results show that the shift of the diatomic halogen core in relaxation of the self-trapped exciton (STE) from D2h to C2v point-group symmetry is quite large (e.g., about 4 a.u. in KCl). The clear implication is that the STE triplet state which is responsible for the well-known ?-polarized recombination luminescence is effectively a nearest-neighbor F-H pair, analogous in many ways to the F-H pair configuration which is known to constitute the STE luminescent state in alkaline-earth-metal fluorides. From this new perspective, in which conversion of an STE to an F-H pair reduces to conversion of a nearest-neighbor F-H pair to a more distant F-H pair, a number of formerly puzzling aspects of photochemical F-center generation can be rationalized quite simply.

Williams, R. T.; Song, K. S.; Faust, W. L.; Leung, C. H.

1986-05-01

81

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

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

82

Performance of a multi-anode photomultiplier employing an ultra bi-alkali photo-cathode and rugged dynodes  

NASA Astrophysics Data System (ADS)

We report on the performance testing of a multi-anode photomultiplier (MAPMT), the R8900-200-M16MOD-UBA, newly developed by Hamamatsu Photonics K.K. Although the R8900 series offers the great advantage of a highly sensitive surface ( ?80% of physical area), the quantum efficiency (Q.E.) was relatively low (at up to 20%). This paper describes two substantial changes we have made to the R8900-200-M16MOD-UBA: (1) improving the Q.E. to the 40% level by employing an ultra bi-alkali (UBA) photo-cathode and (2) constructing a rugged dynode that can withstand vibration for future use in space. We measured each pixel signal at the single photoelectron level and the signals of scintillation photons by using a 16-pixel plastic scintillator array. Thanks to high Q.E., good energy resolution of 29.9% (FWHM) was obtained for 59.5 keV ?-rays. We also demonstrated tolerance to vibration up to 17 Grms in possible launching vehicles.

Toizumi, T.; Inagawa, S.; Nakamori, T.; Kataoka, J.; Tsubuku, Y.; Yatsu, Y.; Shimokawabe, T.; Kawai, N.; Okada, T.; Ohtsu, I.

2009-06-01

83

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

PubMed

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

Weckström, Kristian; Papageorgiou, Anastassios C

2007-06-01

84

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

85

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

PubMed

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

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

2013-01-28

86

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

NASA Astrophysics Data System (ADS)

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

Mao, Albert H.; Pappu, Rohit V.

2012-08-01

87

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

88

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

89

A Study of the intensities of the impurity vibrational spectra at different concentrations of NO 2 ? and NO 3 ? ions in alkali halide matrices  

Microsoft Academic Search

The infrared absorption spectra of NO 2 and NO~ ions introduced into various alkali halide crystals have been very intensively studied in recent years. A detailed interpretation has been carried out for the bands due to the fundamental vibrations and for some frequencies involving two vibrational quanta, both in lattices with the sodium chloride structure [1-3] and in lattices with

V. N. Gnatovskaya; P. F. Ol'khovich; I. N. Khalimonova

1974-01-01

90

RAMAN SCATTERING IN RESONANCE WITH THE ABSORPTION BAND OF THE F CENTRE IN ALKALI HALIDES : BREAKDOWN OF THE SCATTERING SELECTION RULES DUE OF THE SPIN ORBIT INTERACTION  

Microsoft Academic Search

We present the theory and the theoretical evaluations for the cross sections of the polarized Raman scattering in resonance with the F absorption bands of the F centres in alkali halides, characterized by a spin orbit interaction coupling coefficient A different from zero in the excited electronic states. We show that for all the polarizations of the incident and scattered

E. MULAZZI; M. F. BISHOP

1976-01-01

91

Design and construction of systems for the single-crystals growth of ternary silver halides, alkali halides, and alkaline earth fluorides, and the dielectric investigation of silver halide  

NASA Astrophysics Data System (ADS)

Large single crystals of several congruently melting and incongruently melting compounds are produced for optics applications. The state diagrams of the quasi-binary silver halide system, are described and verified. The methods for the growth of single crystals from the melt, and from melting solutions, are outlined. The different developed crystal growth apparatus are described. Large single crystals of the congruently melting compounds NaCl, KBr, CsI, MgF2, CaF2, and the incongruently melting compounds RbAg4I5, Rb2AgBr3, AgPb2Br5, Ag3PbI5 are produced. The ionic conductivity of these synthetic ternary silver compounds is measured using a dielectric spectrometer.

Hueben-Riechert, Werner

92

Growth by Molecular Beam Epitaxy of Vanadyl Phthalocyanine on Alkali-Substituted Alkali-Halide Mixed Crystal Substrates  

NASA Astrophysics Data System (ADS)

The epitaxial growth of vanadyl phthalocyanine (VOPc) onKBr NaBr mixed-crystal substrates was examined. The experimentalresults indicate that the orientation and morphology of the film areprimarily affected by the lattice constants of the substrates, but notby differences in the substituted components, e.g., alkali orhalogen. The VOPc island crystal domains grew even on large-mismfitNaBr substrates. Their characteristic shape and the possible growthprocess are also discussed.

Gomyou, Makoto; Nakao, Satoru; Hoshi, Hajime; Ishikawa, Ken; Takezoe, Hideo

1999-11-01

93

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

NASA Astrophysics Data System (ADS)

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

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

1999-10-01

94

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

SciTech Connect

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

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

2009-01-01

95

Effect of a magnetic field on the luminescent lifetime of Cu/sup +/ in alkali halide host crystals  

SciTech Connect

We have measured the change in the triplet emission lifetime of the Cu/sup +/ impurity in various alkali halide hosts at 4.2 K as a function of applied magnetic field. Pedrini (Phys. Status Solidi B 87, 273 (1978)) has proposed that the /sup 3/E/sub g/ emitting state is split into T/sub 1g/ and T/sub 2g/ spin-orbit components and has found that the emission lifetime depends sensitively on the splitting. We have utilized an external magnetic field to mix these spin-orbit levels. This produced a measurable decrease in the emission lifetime which we explained with Pedrini's model. We also diagonalized the d/sup 9/s excited-state matrix to calculate independently the T/sub 1g/,T/sub 2g/ spin-orbit splitting and obtained reasonable agreement with our experimental results.

Payne, S.A.; Austin, R.H.; McClure, D.S.

1984-01-01

96

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

NASA Astrophysics Data System (ADS)

For the use in scattering experiments with synchrotron radiation, integrating position sensitive X-ray detectors are discussed. These detectors store the photon number equivalent charge (PNEC) in low-density alkali halide targets. Performance tests are given for a detector which uses a Gd 2O 2S fluorescence screen for X-ray detection and the low-density KCl storage target of a television SEC vidicon tube for photon integration. Rather than directly by X-rays, this target is charged by 6 keV electrons from the image intensifier section of the vidicon. Its excellent storage capability allows measurements of extremely high-contrast, high-flux X-ray patterns with the same accuracy as achieved with any single photon detection system if the discussed readout techniques are applied.

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

1986-05-01

97

Structure and energetics of LiF chains as a model for low dimensional alkali halide nanocrystals  

NASA Astrophysics Data System (ADS)

Nanocrystals of inorganic salts constrained in geometry by encapsulation in single walled carbon nanotubes have been shown by recent high-resolution transmission electron microscopy experiments to exhibit specific distortions of their structure in comparison with the ideal bulk. These structural distortions of low dimensional crystallites are analyzed within the Hartree-Fock approximation and density functional theory based on the simplest alkali halide chains, LiF. The observed patterns of distortions in the structure of nanocrystals are the results of low dimensionality and the axial strain (end effects). The structural trends calculated ab initio for LiF are compared with analytical predictions based on the traditional Born theory of bulk crystals and experiments. The energetics of the LiF crystallites is discussed.

Bichoutskaia, Elena; Pyper, Nicholas C.

2006-05-01

98

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

99

Studies on Ag Centers in Alkali Halides. III. Polarization and Decay-Time of Luminescence  

Microsoft Academic Search

Polarized emissions from Ag- centers and radiative lifetimes of Ag- and Ag-(Na) centers were measured for several kinds of potassium halides. Polarization diagrams for the C emission of Ag- centers were obtained as a function of excitation wavelength and temperature. The decay time of the A emission was measured against varying temperature. The experiments demonstrate that emissions occur from trigonally

Kazuko Kojima; Shigetaka Shimanuki; Tadanobu Kojima

1972-01-01

100

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

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

101

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

102

Thermal conductivity under pressure and through phase transitions in solid alkali halides. II. Theory  

Microsoft Academic Search

For pt.I see ibid., vol.18, p.3943 (1985). The results in the preceding paper concerning the variation of the thermal conductivity, lambda , of six potassium and rubidium halides with temperature and pressure are analysed using a Leibfried-Schlomann formulation for the phonon-phonon scattering. The concept of a reference thermal conductivity is introduced which demonstrates how lambda varies with both the mass

G. A. Slack; R. G. Ross

1985-01-01

103

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

NASA Technical Reports Server (NTRS)

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

Demarest, H. H., Jr.

1972-01-01

104

Implementation of Kunz-Klein Localization in Icecap and AN Application to the Problem of Off-Center Isovalent Substitutional Impurities in Alkali Halides  

Microsoft Academic Search

Theoretical models of off-center isovalent substitutional impurities in alkali halides are examined. Calculations have been performed on Li('+) in KCl, a representative system known experimentally to exhibit off-center behavior. The potential seen by the Li('+) ion in the lattice has been calculated within the shell model using the computer program HADES and by means of an Unrestricted Hartree-Fock (UHF) cluster

Phillip Brooks Keegstra

1986-01-01

105

Ruthenium(II) tris-(2,2'-bipyridine) -specific extrinsic lyoluminescences of x-ray irradiation colored and electrolytically colored alkali halides  

Microsoft Academic Search

Short-lived solid\\/solution interfaces, which are sufficiently energetic to initiate the radiative 3MLCT-based transition of rutheniumdl) tris-(2,2'-bipyridine) chelate, can be produced by dissolving x-ray irradiation colored or electrolytically colored alkali halides in water. This study discusses in detail the mechanisms of these ruthenium(II) tris-(2,2'-bipyridine)-specific extrinsic lyoluminescences of x-ray irradiated sodium chloride and electrolytically colored potassium chloride and, in addition, points out

S. Kulmala; A. Hakanen; P. Raerinne; A. Kulmala; K. Haapakka

1995-01-01

106

Model for F-center production in alkali halides doped with divalent cation impurities that change their valence state by irradiation  

Microsoft Academic Search

A model for the radiation-induced F-center coloring in alkali halides doped with doubly valent metal impurity ions (M2+) that can change their valence state by irradiation is proposed in the present paper. The primary event is assumed to be the creation of F centers and interstitial halogen (H) pairs. The thermal- and radiation-induced processes associated with the dynamics of H

S. Ramos B; J. Hernández A; H. Murrieta S; J. Rubio O; F. Jaque

1985-01-01

107

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

Microsoft Academic Search

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

Raji Heyrovska

2007-01-01

108

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

109

Density difference representation of the charge clouds of the monatomic ions of the alkali halides  

NASA Astrophysics Data System (ADS)

Density difference functions, defined in terms of the radial density function of an ion and the corresponding neutral atom, reveal the changes in the charge cloud which occur when an electron is removed from an alkali metal atom or added to a halogen atom. The changes are not restricted to the valence region. Removal of an electron from a Group IA element leads to a reduction of the valence-shell electron density, whereas adding an electron to a halogen increases the electron density in the valence region. For both types of ions, substantial increases and decreases in the electron density are observed in the inner shells. Explicit calculations are presented for the Li +, Na +, K +, Rb +, F -, Cl -, Br - and I - ions at the Hartree-Fock level.

Boyd, Russell J.; Choi, Sai-Cheng

110

Electron paramagnetic resonance, optical transmission spectra and DC conductivity studies of vanadyl-doped alkali halide borate glasses  

NASA Astrophysics Data System (ADS)

Electron paramagnetic resonance, optical transmission spectra and DC conductivity of the glasses 2 xMX·(0.30- x) M2O ·0.70B 2O 3 ( M=Na or K; X=Cl or Br) (0.01? x?0.10) containing 2.0 mol% of V 2O 5 have been studied. The spin-Hamiltonian parameters (SHP) of the VO 2+ ions, the dipolar hyperfine parameter, P, the Fermi contact interaction parameter, K, and the molecular orbital coefficients ( ?2 and ?2) have been calculated. It is observed that in K X·K 2O ·B 2O 3 ( X=Cl or Br) glasses, the tetragonal nature of V 4+O 6 complex decreases with KBr for x?0.05. An increase in the 2K X:K 2O ratio ( x?0.05) also results in the contraction of 3dxy orbit of the unpaired electron in the vanadyl ion, whereas in case of Na X·Na 2O ·B 2O 3 ( X=Cl or Br) glasses, the SHP are independent of change in 2Na X: M2O ratio. It is observed that the SHP in these alkali halide borate glasses are independent of the theoretical optical basicity, ?th. It is also observed that the DC conductivity increases with increase in temperature. The order of conductivity is 10 -6 ? -1 m -1 at low temperatures and 10 -4 ? -1 m -1 at high temperatures. In MCl ·M2O ·B 2O 3 ( M=Na or K) glasses, the conductivity increases and the activation energy decreases with an increase in mol% of the NaCl or KCl content whereas, in MBr ·M2O ·B 2O 3 ( M=Na or K) glasses, the conductivity first increases and then decreases with mol% of the MBr content.

Khasa, S.; Seth, V. P.; Gahlot, P. S.; Agarwal, A.; Krishna, R. M.; Gupta, S. K.

2003-07-01

111

Photocathodes for RF photoinjectors  

NASA Astrophysics Data System (ADS)

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

Michelato, P.

1997-02-01

112

Spin-orbit coupling, spin-lattice relaxation, and spin-memory studies of F -center-molecular-ion pairs in alkali halides  

Microsoft Academic Search

Summary  The spin-orbit parameter ?, spin-lattice relaxation timeT\\u000a 1, and spin-mixing parameter ? ofF\\u000a H(OH?) andF\\u000a H(CN?) centers in several alkali halides have been studied with magnetic circular dichroism at ?2 K. A close comparison of the\\u000a experimental results before and after optically induced association of theF center with the molecular ion has been made. In crystals of NaCl structure the

G. Baldacchini; S. Botti; U. M. Grassano; F. Luty

1993-01-01

113

PES of high-temperature vapors. IV. The cesium halides. Effect of spin-orbit interaction on the photoelectron and mass spectra of the alkali halides  

Microsoft Academic Search

The He(I) photoelectron spectra of the cesium halides are presented. They exhibit two well-separated sets of peaks, one deriving from orbitals formed from halogen p -type orbitals and the other from the cesium p orbitals. Each set of bands is analyzed by taking into account spin-orbit interaction within the degenerate ? states and subsequently between the ?(1?2) and ?(1?2) states.

J. Berkowitz; J. L. Dehmer; T. E. H. Walker

1973-01-01

114

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

115

Excitonic absorption edge in alkali halides and the Urbach-Martienssen rule studied by three-photon difference-frequency generation  

NASA Astrophysics Data System (ADS)

Three-photon difference-frequency generation (TP-DFG) is used to excite resonances on the lower exciton-polariton branch in alkali halides. The line shape of the resonances is investigated in KI and RbI for temperatures between 1.5 and 800 K. A drastic variation of the linewidth ranging from 0.2 to about 50 meV is observed as a function of temperature and polariton energy. The experimental results are interpreted in the framework of polariton response theory, which links the shape of the TP-DFG resonance to the complex dielectric function. From the measured positions and widths of the resonance peaks, accurate data on dispersion and absorption are obtained for the region of the exponential tail of the excitonic absorption edge. The method allows us to determine the parameters of the Urbach-Martienssen rule by measurements on large single crystals.

Fröhlich, D.; Köhler, P.; Nieswand, W.; Rappen, T.; Mohler, E.

1991-05-01

116

Study on influence of growth conditions on position and shape of crystal/melt interface of alkali lead halide crystals at Bridgman growth  

NASA Astrophysics Data System (ADS)

Suitable conditions for growth of high quality single crystals of ternary alkali lead halides prepared by a Bridgman method were explored using direct observation of a crystal/melt interface when pulling an ampoule out of a furnace, deliberated striations' induction and measurement of a temperature field in the filled ampoule in the vertical Bridgman arrangement, as model compounds lead chloride and ternary rubidium lead bromide were used. By direct observation only position of the crystal/melt interface was markedly determined, while by induced striations both the position and the shape of the interface were visualized but their contrast had to be intensified by adding admixtures. Performed temperature measurements in the filled ampoule brought both a view of temperature field in the 3D radial symmetry and basic data for comparison of a real temperature field with those obtained by projected modeling.

Král, Robert

2012-12-01

117

Optical properties and stable, broadly tunable cw laser operation of new F A-type centers in Tl +-doped alkali halides  

NASA Astrophysics Data System (ADS)

A new group of complex color centers with F A-type properties, involving simple center production and high thermal and optical stabilities, has been found in six Tl +-doped alkali halides: NaCl, KCl, RbCl, KBr, RbBr and RbI. In its first tested examples, KCl and KBr, broadly tunable cw laser operation over the 1.4 to 1.7 ?m range has been obtained, with output powers in the 100 mW range. In contrast to already existing F +2 and F +2-like centers, operating in the same wavelength range, the new F A(Tl +) lasers are optically stable and do not show any bleaching effects under laser operation.

Gellermann, W.; L?y, F.; Pollock, C. R.

1981-11-01

118

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

Microsoft Academic Search

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

Kurnardev Bose; Kiron K. Kundu

1979-01-01

119

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

NASA Astrophysics Data System (ADS)

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

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

2003-01-01

120

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

SciTech Connect

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

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

1991-11-15

121

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

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

1989-01-01

122

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

123

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

PubMed Central

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

Brander, S?ren; Mikkelsen, J?rn D.; Kepp, Kasper P.

2014-01-01

124

Solidphase oxidation of 2,4Di tert -butylphenol and 3,6Di tert -butylpyrocatechol in the presence of alkali and alkaline earth metal halides under elastic deformation  

Microsoft Academic Search

Solid-phase oxidation of 2,4-di-tert-butylphenol to give 2,2?,4,4?-tert-butyl-6,6?-bisphenol and of 3,6-di-tert-butylpyrocatechol to afford 3,6-di-tert-butyl-l,2-benzoquinone was performed in the presence of alkali and alkaline earth metals halides under conditions of modified\\u000a extrusion. The formation of the corresponding metal 3,6-di-tert-butylsemiquinolates was registered by ESR method. The different behavior of chlorides, bromides, and iodides was observed\\u000a and rationalized basing on the dissimilar complexing ability

V. B. Vol’eva; A. I. Prokof’ev; I. S. Belostotskaya; A. Yu. Karmilov; N. L. Komissarova; T. I. Prokof’eva; V. V. Ershov

2000-01-01

125

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

National Technical Information Service (NTIS)

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

O. J. Kleppa F. G. McCarty

1965-01-01

126

Effects of Dynamic Lattice Distortions on the Structure of the F Band in the Cesium Halides  

Microsoft Academic Search

The smooth, nearly Gaussian, optical absorption band of F centers in most alkali halides contrasts with that observed at low temperatures in the cesium halides, where two or sometimes three components are partially resolved. A strong spin-orbit coupling could account for two components, but the third has remained a mystery because of the cubic symmetry of the alkali-halide lattice. The

P. R. Moran

1965-01-01

127

Cerium doped elpasolite halide scintillators.  

SciTech Connect

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

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

2010-05-01

128

Basic properties of the F-type centers in halides, oxides and perovskites  

NASA Astrophysics Data System (ADS)

We present a short survey of the optical properties of primary radiation-induced point defects in alkali halides, simple oxides and some ABO 3 perovskites. We discuss in details the optical properties of single electron F and F+ centers in rock-salt (f.c.c.) alkali halides and oxides and show that the Mollwo-Ivey law well-known for the F-type centers in alkali halides may be extended for other rock-salt structure insulators. We also discuss the major differences in point defect production mechanisms in halides and oxides. We show that the Rabin-Klick diagram may be generalized for a whole family of alkali halides. The F-type center migration and aggregation into metal colloids in alkali halides and oxides is also discussed.

Popov, A. I.; Kotomin, E. A.; Maier, J.

2010-10-01

129

Resolving all atoms of an alkali halide via nanomodulation of the thin NaCl film surface using the Au(111) reconstruction  

NASA Astrophysics Data System (ADS)

We investigated the local influence of the Au(111) herringbone reconstruction on the properties of thin adsorbed NaCl films using cryogenic scanning tunneling microscopy (STM) and spectroscopy. Depending on the local hcp versus fcc character of the reconstruction, NaCl adsorption gives rise to a different shift of the Au(111) surface state toward the Fermi level, in agreement with ab initio calculations. Such lateral modulation may allow for tunable nanostructuring of thin insulating films, which opens up new perspectives for molecular electronics applications. Furthermore, we demonstrate the simultaneous visualization of both the alkali and the halogen atoms in hcp regions of the NaCl/Au(111) surface using a functionalized STM tip. Ab initio calculations relate this simultaneous visualization to the larger electron density in the hcp regions.

Lauwaet, K.; Schouteden, K.; Janssens, E.; Van Haesendonck, C.; Lievens, P.; Trioni, M. I.; Giordano, L.; Pacchioni, G.

2012-06-01

130

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

NASA Astrophysics Data System (ADS)

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

Reif, Maria M.; Hünenberger, Philippe H.

2011-04-01

131

High Temperature Thermal Expansion of Alkali Halides.  

National Technical Information Service (NTIS)

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

K. Wang R. R. Reeber

1995-01-01

132

Interface electronic structure of alkali halide contacts  

NASA Astrophysics Data System (ADS)

The electronic structure of contacts of different ionic crystals was calculated for LiCl, NaCl and KCL using the LCAO method within the next-nearest-neighbour approximation. No localized states (interface states) were found which leads to the conclusion that the experimentally observed influence of such contacts on photoelectron spectra is mainly due to the changed position of the bottom of conduction band in the interface region. Calculated values are compared with measured shifts of photoelectron spectra and a reasonable qualitative agreement is obtained. We suggest that the contact of two ionic crystals can be treated as a classical Schottky barrier.

Kisiel, W.; Stankiewicz, B.; St??licka, Maria

1988-07-01

133

SELF-DIFFUSION IN MOLTEN ALKALI HALIDES  

Microsoft Academic Search

A new method for the measurement of self-diffusion coefficients in ; molten salts is described. Determinations of D\\/sub i\\/ for i = Na\\/sup +\\/ and Cl\\/; sup -\\/ in NaCl; Rb\\/sup +\\/ and Cl⁻ in RbC l; Cs\\/sup +\\/ and Cl⁻ in ; CsCl; and Na\\/sup +\\/ and I⁻ in NaI as a function of temperature, are ; reported. The

J. O. M. Bockris; G. W. Hooper

1962-01-01

134

DIAMOND AMPLIFIED PHOTOCATHODES.  

SciTech Connect

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

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

2007-11-26

135

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

136

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

137

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

138

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

139

Color Centers in Cesium Halide Single Crystals  

Microsoft Academic Search

Color centers have been investigated in the CsCl-type alkali halides. Cesium chloride, bromide, and iodide single crystals were grown from the melt and CsCl crystals also from solution. Coloration was produced by 130-kv x rays, 3.0-Mev electrons, and by electrolysis. In CsI coloration resulted from electrolysis only. The absorption of uncolored and colored crystals has been measured from 0.175 to

Peter Avakian; A. Smakula

1960-01-01

140

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

141

Binding Energies of Gaseous Alkali Hydrides  

Microsoft Academic Search

2)r=req = P (force constant). The application of these equations to the entire group of alkali metal halides gave generally good agreement between calculated binding energies and the so-called experimental binding energies given by -W=D+I-E, where D is the dissociation energy of the ionic molecule into neutral atoms, I is the first ionization potential of the alkali atom, and E

William A. Klemperer; John L. Margrave

1952-01-01

142

The Silver Halides  

ERIC Educational Resources Information Center

Illustrates the type of fractional bonding for solid silver halides. Treats the silver halides as electron excess compounds, and develops a model of a localized bonding unit that may be iterated in three dimensions to describe the bulk phase. (MLH)

Sahyun, M. R. V.

1977-01-01

143

Cs2Te PHOTOCATHODES ROBUSTNESS STUDIES  

Microsoft Academic Search

Cs2Te photocathodes are used as laser driven electron sources at FLASH and PITZ. Besides many aspects of their performances, their robustness to gas exposition and the effect of pollutants on photocathode properties, and indirectly on the photoemitted electrons, are a field still unexplored. In this article we present the results of controlled exposition of Cs2Te photocathodes to gases typical present

P. Michelato; L. Monaco; C. Pagani; D. Sertore; S. Lederer; S. Schreiber

144

Investigating and Supplying Halid Flux-Grown KTP Crystals.  

National Technical Information Service (NTIS)

The original purpose of this contract was to supply KTiOPO(4) (KTP) crystals grown by Cristal Laser S.A. by flux of alkali metal halide. Therefore, the experiments were performed on crystals from Cristal Laser S.A. The main tests provided for in the contr...

D. Lupinski

1995-01-01

145

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

146

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

147

Metal-halide mixtures for latent heat energy storage  

NASA Astrophysics Data System (ADS)

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.

148

CsI and some new photocathodes  

NASA Astrophysics Data System (ADS)

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

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

1993-06-01

149

Electromagnetic Simulation Studies of Photocathode Sources  

Microsoft Academic Search

We present the results of electromagnetic simulation studies on space-charge dominated electron beams produced by photocathode sources. In particular, we demonstrate the computational requirements on the Green's function based simulation code IRPSS (Indiana Rf Photocathode Source Simulator) for obtaining relative space-charge electromagnetic field errors of at most 1%, and show how these fields compare with electrostatic based field solver methods.

Mark Hess; Chong Shik Park

2007-01-01

150

Gated Cesium Iodide Photocathode for Particle Detectors  

Microsoft Academic Search

A key feature of many noble gas based particle detectors is the detection of scintillation. The efficiency for detection of VUV radiation from noble gasses can be greatly enhanced by placing an internal photocathode in the detector. Furthermore, a gating circuit on the photocathode is required to alleviate runaway ionization conditions. Motivation, electronics, and concepts will be discussed.

J. Miller; R. Blessitt; J. Gao; J. Maxin; G. Salinas; J. Seifert; J. T. White

2004-01-01

151

Gated Cesium Iodide Photocathode for Particle Detectors  

NASA Astrophysics Data System (ADS)

A key feature of many noble gas based particle detectors is the detection of scintillation. The efficiency for detection of VUV radiation from noble gasses can be greatly enhanced by placing an internal photocathode in the detector. Furthermore, a gating circuit on the photocathode is required to alleviate runaway ionization conditions. Motivation, electronics, and concepts will be discussed.

Miller, J.; Blessitt, R.; Gao, J.; Maxin, J.; Salinas, G.; Seifert, J.; White, J. T.

2004-10-01

152

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

153

High QE photocathodes performance during operation at FLASH \\/ PITZ photoinjectors  

Microsoft Academic Search

Since 1998, the DESY photoinjectors at FLASH and PITZ routinely use high quantum efficiency (QE) photocathodes produced at LASA (INFN-Milano). To further understand the photocathode behavior during beam operation, photocathode QE measurements have been performed at different operating conditions in both photoinjectors. The analysis of these measurements will be used to improve the photocathode preparation procedures and deepen our understanding

L. Monaco; P. Michelato; C. Pagani; D. Sertore; J. H. Han; Siegfried Schreiber

2007-01-01

154

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

PubMed

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

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

2012-04-01

155

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

156

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

157

Photosensor with a photocathode in reflective mode  

US Patent & Trademark Office Database

A hybrid photon detector with a photocathode in reflective mode where the same vacuum tube components acts both as a perfect incoming light concentrator and as a perfect focusing electron lens and the photoelectrons are electrostatically focused by the same CPC-shape in the opposite direction (i.e., from the small light collection surface towards a point-like region in the middle of the large-area entrance aperture). The CPC is electrically conductive and split into two electrodes by a narrow nonconductive interval positioned in a particular place along the CPC. The photocathode covers the light collection area of the CPC, and the photocathode is operated in the reflective mode such that photoelectrons emerge from the same surface through which the photons enter. Photoelectrons emerging from the entire photocathode are accelerated and focused onto a small electronic sensor placed in the middle of the entrance aperture of the CPC.

2004-01-06

158

Substrate studies of cesium-iodide photocathodes  

Microsoft Academic Search

We report on the quantum efficiency (QE) of cesium-iodide (CsI) photocathodes vacuum deposited on various substrates. The substrates, Ni, Au, solder, and Al were vacuum deposited on copper-clad FR4 and ceramic printed circuit boards. The results were obtained in a low-pressure, parallel-plate, pad-chamber with a solid CsI photocathode operated with ethane and isobutane gas. We present QE measurements for each

W. Kononenko; N. S Lockyer

1996-01-01

159

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

160

Atomic hydrogen cleaning of semiconductor photocathodes  

SciTech Connect

Negative Electron Affinity (NEA) semiconductor photocathodes are widely used for the production of polarized electron beams, and are also useful for the production of high brightness electron beams which can be modulated at very high frequencies. Preparation of an atomically clean semiconductor surface is an essential step in the fabrication of a NEA photocathode. This cleaning step is difficult for certain semiconductors, such as the very thin materials which produce the highest beam polarization, and those which have tightly bound oxides and carbides. Using a small RF dissociation atomic hydrogen source, the authors have reproducibly cleaned GaAs wafers which have been only degreased prior to installation in vacuum. They have consistently prepared very high quantum efficiency photocathodes following atomic hydrogen cleaning. Details of their apparatus and most recent results are presented.

Sinclair, C.K.; Poelker, B.M.; Price, J.S. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)

1997-06-01

161

A study for the characterization of high QE photocathodes  

Microsoft Academic Search

Based on our experience on photocathode production, we present in this paper the results of the application of different optical diagnostic techniques on fresh and used photocathodes. These techniques allow studying effects like non uniformity, cathode aging, etc. In particular, photocathode optical parameters and QE characterization, both done at different wavelengths, give fundamentals information for the construction of a model

Daniele Sertore; Paolo Michelato; Laura Monaco; Carlo Pagani

2007-01-01

162

CsI photocathode QE and a simple production technique  

Microsoft Academic Search

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

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

1993-01-01

163

Mean Residence Times of Alkali Ions on Polycrystalline Wolfram Surfaces as Studied with a Pulsed-Molecular-Beam Mass Spectrometer  

Microsoft Academic Search

The mean residence time i of alkali ions on both atomically clean and strongly gas-covered surfaces of polycrystalline wolfram has been studied with a recently developed technique of combining modulated atomic and\\/or molecular beams from vapors of alkali metals and alkali halides with phase-sensitive mass-spectrometic detection. The experimental arrangement allows the direct determination of the mean residence time i of

Manfred Kaminsky

1966-01-01

164

Copper doped alkali halides for computed radiography and digital imaging.  

PubMed

We report here the results of our x-ray fluorescence, photostimulated luminescence, and time resolved laser spectroscopy studies in KCI:Cu. This material seems to possess some desirable properties for being used as an imaging plate in computed radiography. This is a US government work. There are no restrictions on its use. PMID:9735463

Chakrabarti, K; Bandyopadhyay, P K; Barkyoumb, J H

1998-08-01

165

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

NASA Technical Reports Server (NTRS)

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

Lundquist, C. A.

1974-01-01

166

Cold ablation driven by localized forces in alkali halides.  

PubMed

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

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

2014-01-01

167

Electron stimulated desorption of positive ions from alkali halide surfaces  

NASA Astrophysics Data System (ADS)

Electron stimulated desorption (ESD) of positive ions from LiF, LiBr and RbF is observed in the incident electron energy region below 800 eV. In ESD from LiF, the experimental results are mostly explained in terms of the Knotek-Feibelman (KF) mechanism. On the other hand the KF mechanism is not satisfactory to understand the desorption yield spectra from LiBr, because the threshold energy of desorption was not necessarily observed at binding energies of core levels of LiBr. Since the yield spectrum of Li + ions showed quite different profile from that of Br + ions in ESD from LiBr, it is possible that the desorption mechanism for cations is not the same as that for anions. In the case of ESD from RbF the enhancement of the desorption yields was observed at about 80 eV of the incident energy, which does not agree with any interband transition or ionization energy. We observed the desorption of Rb 2+ ions besides that of Rb + and F + ions, which are always associated with the desorption of H 2O + ions. The role of H 2O + ions is also discussed.

Yasue, Tsuneo; Ichimiya, Ayahiko; Ohtani, Shunsuke

1987-07-01

168

Extinction Characteristics of Pyrotechnically-Generated Alkali-Halide Smokes.  

National Technical Information Service (NTIS)

The major findings realized from this year's effort are: (1) At approx. 40% RH, the NWC 90 and NWC 164 pyrotechnics appear to provide greater extinction at IR wavelengths longer than approx. 7 micron relative to the other pyrotechnics. This performance ma...

J. T. Hanley B. J. Wattle E. J. Mack

1981-01-01

169

Cs based photocathodes for gaseous detectors.  

National Technical Information Service (NTIS)

We demonstrated that some standard photocathodes SbCs, GaAs(Cs), Au(Cs) can easily be manufactured for use inside gaseous detectors. When filed with clean quenched gases such detectors have a quantum efficiency of a few percent in the visible region of th...

A. Borovick-Romanov V. Peskov

1993-01-01

170

CsI and some new photocathodes.  

National Technical Information Service (NTIS)

A discussion of the possible sources of discrepancies in the measurements of the quantum efficiency of CsI photocathodes is presented. We propose that the major causes for disagreements in QE are due to the QE dependence on the current density extracted f...

D. F. Anderson S. Kwan V. Peskov

1993-01-01

171

Organic UV photocathodes for gaseous particle detectors  

NASA Astrophysics Data System (ADS)

We report on the result of search for organic photocathodes, to be used in multiplicative particle detectors, as alternatives to TMAE. We review the measurements we performed in recent years, in the wavelength range of 150-220 nm. The quantum efficiencies are given relative to TMAE and CsI. Some ferrocene derivatives exhibit relatively high quantum efficiency.

Miné, Ph.; Malamud, G.; Vartsky, D.; Vasileiadis, G.

1997-02-01

172

Protection of cesium-antimony photocathodes.  

National Technical Information Service (NTIS)

In order to operate gaseous photomultipliers in the visible range it was suggested to protect sensitive photocathodes against contact to air and counting gases by their coating with a thin solid dielectric film. We present data on coating of cesium- antim...

A. Buzulutskov A. Breskin R. Chechik M. Prager E. Shefer

1996-01-01

173

Development and Evaluation of Methods for Total Organic Halide and Purgeable Organic Halide in Wastewater.  

National Technical Information Service (NTIS)

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

R. M. Riggin S. V. Lucas J. Lathouse G. A. Jungclaus A. K. Wensky

1984-01-01

174

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

175

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

176

Alkali-hydrogen reactions  

Microsoft Academic Search

Highly endoergic alkali-hydrogen reactions are usually initiated by electronic excitation of the alkali atom. This implies that non-adiabatic couplings take place along the reaction path, the collision mechanism being dominated by the electron transfer jump that occurs between the alkali atom and the hydrogen molecule. Since electronic excitation can be selectively achieved over many atomic states, these reactions constitute good

King-Chuen Lin; Raymond Vetter

2002-01-01

177

Diode pumped alkali lasers  

Microsoft Academic Search

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

B. V. Zhdanov; R. J. Knize

2011-01-01

178

Infrared absorption and rotational dynamics of OH and OD defects in cesium halides  

Microsoft Academic Search

The rotational degrees of freedom of substitutional OH- and OD- defects in CsCl, CsBr, and CsI have been studied between 2 and 300 K using infrared absorption in the range of the 2.7 and 3.7-mum stretching absorption. In CsCl the first direct evidence for quasi-free-rotational behavior of OH- in alkali-metal halides is found in the form of a vibration-rotation spectrum

Matthias Krantz; Fritz Lüty

1988-01-01

179

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

1992-01-01

180

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

181

Methyl Halide Production by Fungi  

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

182

Coacervation of Aqueous Solutions of Tetraalkylammonium Halides.  

National Technical Information Service (NTIS)

The coacervation of aqueous solutions of tatraalkylammonium halides in the presence of not of inorganic halides and acids has been studied, considering thermodynamic and spectroscopic aspects. The importance of dispersion forces as well as forces resultin...

A. Mugnier de Trobriand

1979-01-01

183

STATUS OF DIAMOND SECONDARY EMISSION ENHANCED PHOTOCATHODE  

SciTech Connect

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

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

2007-05-25

184

Silver nanorod arrays for photocathode applications  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

185

Simulations of the laser photocathode injector  

NASA Astrophysics Data System (ADS)

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

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

1988-06-01

186

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

187

Kelvin probe studies of cesium telluride photocathode for AWA photoinjector  

NASA Astrophysics Data System (ADS)

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

Wisniewski, Eric E.; Velazquez, Daniel; Yusof, Zikri; Spentzouris, Linda; Terry, Jeff; Sarkar, Tapash J.; Harkay, Katherine

2013-05-01

188

Suppression of afterpulsing in photomultipliers by gating the photocathode.  

PubMed

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. This afterpulse or signal-induced background (SIB), which is particularly troublesome in stratospheric lidar measurements, appears as a weak exponentially decaying signal extending into the millisecond region after the photomultiplier tube (PMT) is exposed to an intense submicrosecond optical pulse. Photocathode gating is not feasible in PMTs with semitransparent bialkali photocathodes because of their slow gate response time, but is easily implemented in PMTs with opaque bialkali or semitransparent multialkali (S-20) photocathodes that can be gated with nanosecond response. In those PMTs with semitransparent bialkali photocathodes, a gated (adjacent) focus grid (if available) also produces a significant reduction in the SIB. PMID:12206204

Bristow, Michael P

2002-08-20

189

Suppression of afterpulsing in photomultipliers by gating the photocathode  

NASA Astrophysics Data System (ADS)

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. This afterpulse or signal-induced background (SIB), which is particularly troublesome in stratospheric lidar measurements, appears as a weak exponentially decaying signal extending into the millisecond region after the photomultiplier tube (PMT) is exposed to an intense submicrosecond optical pulse. Photocathode gating is not feasible in PMTs with semitransparent bialkali photocathodes because of their slow gate response time, but is easily implemented in PMTs with opaque bialkali or semitransparent multialkali (S-20) photocathodes that can be gated with nanosecond response. In those PMTs with semitransparent bialkali photocathodes, a gated (adjacent) focus grid (if available) also produces a significant reduction in the SIB.

Bristow, Michael P.

2002-08-01

190

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

191

Preparation of cerium halide solvate complexes  

DOEpatents

Crystals of a solvated cerium(III) halide solvate complex resulted from a process of forming a paste of a cerium(III) halide in an ionic liquid, adding a solvent to the paste, removing any undissolved solid, and then cooling the liquid phase. Diffusing a solvent vapor into the liquid phase also resulted in crystals of a solvated cerium(III) halide complex.

Vasudevan, Kalyan V; Smith, Nickolaus A; Gordon, John C; McKigney, Edward A; Muenchaussen, Ross E

2013-08-06

192

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

193

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

194

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

195

A Two-Frequency RF Photocathode Gun  

SciTech Connect

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

Dowell, D.

2004-11-05

196

Development of a Novel Superconducting RF Photocathode Electron Gun.  

National Technical Information Service (NTIS)

Over the past year Advanced Energy Systems Inc, and Brookhaven National Laboratory have undertaken a program to develop a Superconducting Photocathode Electron Gun utilizing a unique cathode concept. The cathode concept is much simpler than many other app...

M. Cole H. Bluem J. Rathke J. Schultheiss I. Ben-Zvi T. Srinivasan-Rao

2000-01-01

197

DEVELOPMENT OF A MULTI-BUNCH PHOTOCATHODE RF GUN SYSTEM  

Microsoft Academic Search

A multibunch photo-cathode RF gun system has been developed as an electron source for the production of quasi-monochromatic X-rays based on inverse Compton scattering. This system consists of a photocathode RF gun, a cathode system, a laser system, a beam diagnostic section, and a control system. The gun produces 100 bunches with a 2.8 ns bunch spacing and 5 nC

K. Hirano; M. Nomura; M. Fukuda; M. Takano; Y. Yamazaki; T. Muto; S. Araki; N. Terunuma; M. Kuriki; M. Akemoto; H. Hayano; J. Urakawa

2004-01-01

198

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

199

THERMAL SIMULATIONS OF A PHOTOCATHODE R.F. GUN  

Microsoft Academic Search

We are developing a photocathode linac, which uses a 2856 MHz r.f. gun, with a copper cathode driven by a 102 MHz, 266 nm laser at inclined incidence. The laser photocathode r.f. gun is a 1.6 cell BNL\\/SLAC\\/UCLA type III r.f. gun. In this paper we present the dynamic thermal cooling simulations to calculate the structural deformations and consequent frequency

B. Biswas; Shankar Lal; K. K. Pant; Arvind Kumar; S. Krishnagopal; Raja Ramanna

2007-01-01

200

Re-evaluation of the temporal response of Csl photocathodes  

SciTech Connect

The optimization of photocathodes for ultra-fast x-ray detectors is an area of active interest in the x-ray diagnostic community. New evaluations of CsI and Au transmission photocathodes in side-by-side in situ streak camera measurements are discussed here. Temporal response of the two materials and sensitivity comparisons over a wide range of thicknesses are presented. 11 references.

Stradling, G.L.; Attwood, D.T.; Kauffman, R.L.

1982-01-01

201

Preparation and surface studies of negative electron affinity semiconductors photocathodes  

NASA Astrophysics Data System (ADS)

Fabrication of high quantum efficiency, long lifetime negative electron affinity photocathodes is important for applications such as photomultipliers, image intensifiers, electron beam lithography, electron microscopy, and polarized electron sources. The surface cleanliness of the III-V semiconductor photocathode is crucial in obtaining high photosensitivity. GaAs(100) and InP(100) photocathodes are prepared by atomic hydrogen cleaning. The cleaning effect on the photocathode performance is discussed. The surface degradation mechanisms which reduce the photocathode lifetime are presented. The photocathode surface cleanliness, structure, and morphology are studied using reflection high-energy electron diffraction (RHEED). Quantum efficiencies of ˜14% and 8% are obtained for GaAs and InP, respectively, in response to 632.8 nm light after atomic hydrogen cleaning. Longer photoemission time is obtained under low accelerating voltage, low light and photocurrent intensities, and continuous cesiation. RHEED patterns after atomic hydrogen cleaning show reconstructed, group V terminated surfaces suitable for negative electron affinity activation. The out-of-phase diffraction patterns after atomic hydrogen cleaning or reviving have higher intensities than those obtained after heat cleaning, indicating that the surfaces have less defects and contaminants.

Elamrawi, Khaled Abdelrahman

202

Diode pumped alkali lasers  

NASA Astrophysics Data System (ADS)

Diode pumped alkali lasers attract growing attention during the past several years because they have demonstrated potential to compete and, possibly, replace the best existing high power laser systems. In spite of the fact that an optically pumped alkali (potassium) vapor laser was first proposed by A.L. Schawlow and C.H. Townes in 1958, the intensive research and development of alkali vapor started only in 2003, when really efficient lasing in Rb and Cs vapors was demonstrated. The interest to this research was stimulated by the possibility of using efficient diode lasers for optical pumping of the alkali gain medium that promises high overall efficiency of the device. A variety of experiments on alkali lasers, including the demonstration of efficient Rb, Cs and K vapor lasers, power scaling experiments with multiple diode laser pumping sources and experiments on diode pumped alkali vapor amplifiers were performed during the past several years. In this paper we present a review of the most important achievements in high power alkali lasers research and development, discuss some problems existing in this field and future perspectives in DPAL development.

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

2011-10-01

203

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

EPA Science Inventory

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

204

Spin relaxation in alkali vapors  

NASA Astrophysics Data System (ADS)

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

Kadlecek, Stephen John

1999-11-01

205

Stability diagrams for fourfold coordination of polyvalent metal ions in molten mixtures of halide salts  

SciTech Connect

The stability of local fourfold coordination for divalent and trivalent metal ions in liquid mixtures of polyvalent metal halides and alkali halides is classified by means of structural coordinates obtained from properties of the elements. In parallel with earlier classifications of compound crystal structures and molecular shapes, the elemental properties are taken from first-principles calculations of valence electron orbitals in atoms, in the form of (i) the nodal radii of Andreoni, Baldereschi and Guizzetti or (ii) the pseudopotential radii or Zunger and Cohen. As a third alternative a classification based on Pettifor's phenomenological chemical scale of the elements is also considered. The alternative structural classification schemes that are developed from these elemental properties are generally successfully in distinguishing molten mixtures in which the available experimental evidence indicates long-lived fourfold coordination of polyvalent metal ions. In addition, Pettifor's chemical scale scheme is useful in sorting out finer details of local coordination in the liquid state. 3 figs., 71 refs.

Akdeniz, Z. (International Centre for Theoretical Physics, Trieste (Italy) Istanbul Univ. (Turkey). Dept. of Physics); Tosi, M.P. (Trieste Univ. (Italy). Dipt. di Fisica Teorica Argonne National Lab., IL (USA))

1988-11-01

206

Fabrication and measurement of regenerable low work function dispenser photocathodes  

NASA Astrophysics Data System (ADS)

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

Moody, Nathan A.

207

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

208

Synthesis of aryl halides via organoborane chemistry  

SciTech Connect

A method for the rapid synthesis of a variety of substituted aryl halides by the reaction of organoboranes with halide ions in the presence of chloramine-T is described in detail. The products were purified by column chromatography on silica gel using a mixture of petroleum ether-ethyl acetate as eluent.

Kabalka, G.W.; Sastry, K.A.R.; Sastry, U.; Somayaji, V.

1982-01-01

209

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

210

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

211

Negative Electron Affinity Photocathodes as High-Performance Electron Sources. Part 2. Energy Spectrum Measurements.  

National Technical Information Service (NTIS)

The energy spectra of electrons emitted from transmission-mode negative electron affinity photocathodes have been measured at high resolution using a parallel-plate retarding technique. The spectra from GaAs photocathodes have a basic structure that varie...

A. W. Baum W. E. Spicer R. F. Pease K. A. Costello V. W. Aebi

1995-01-01

212

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

213

Apparatus enables accurate determination of alkali oxides in alkali metals  

NASA Technical Reports Server (NTRS)

Evacuated apparatus determines the alkali oxide content of an alkali metal by separating the metal from the oxide by amalgamation with mercury. The apparatus prevents oxygen and moisture from inadvertently entering the system during the sampling and analytical procedure.

Dupraw, W. A.; Gahn, R. F.; Graab, J. W.; Maple, W. E.; Rosenblum, L.

1966-01-01

214

The stability of cesium iodide X-ray photocathodes  

NASA Astrophysics Data System (ADS)

For pulsed X-ray measurements as applied, for example, in high temperature plasma diagnostics, it has been established that the cesium iodide photocathode is very efficient for X-ray diode and streak camera applications. Its quantum yield (electrons/incident photon) is ten to one-hundred times higher than that for the gold photocathode in the 100-10 000 eV region. The width of its secondary electron energy distribution is appreciably less than that for gold, allowing time resolved, streak camera measurements to be extended into the picosecond region. In this note an experimental study is described which demonstrates that the cesium iodide photocathode quantum yield and secondary electron energy distribution can be stable under practical conditions of preparation, handling, storage and short period exposures to the atmosphere.

Premaratne, K.; Dietz, E. R.; Henke, B. L.

1983-04-01

215

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

216

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

SciTech Connect

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

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

1996-07-01

217

Ideas about Acids and Alkalis.  

ERIC Educational Resources Information Center

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

Toplis, Rob

1998-01-01

218

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

219

Alkali metal ionization detector  

Microsoft Academic Search

Variations in the conventional filament and collector electrodes of an alkali metal ionization detector, including the substitution of helical electrode configurations for either the conventional wire filament or flat plate collector; or, the substitution of a plurality of discrete filament electrodes providing an in situ capability for transferring from an operationally defective filament electrode to a previously unused filament electrode

James E. Bauerle; William H. Reed; Edgar Berkey

1978-01-01

220

Milk-Alkali Syndrome  

PubMed Central

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

Medarov, Boris I.

2009-01-01

221

Nanosecond Length Electron Pulses from a Laser-Excited Photocathode.  

National Technical Information Service (NTIS)

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 ...

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

1989-01-01

222

Photocathodes for use in an electron image projector  

Microsoft Academic Search

In this paper factors influencing the choice of photocathode for an image projector are discussed. First of all, a description is given of the principles of operation of an image projector. It is shown that ionic insulators are likely to be the best materials, and the most likely ones are considered. Of these, cesium iodide is the best. In the

J. P. Scott

1975-01-01

223

Investigation of Improved Framing Camera Efficiency by Photocathode Heating  

NASA Astrophysics Data System (ADS)

With the upcoming activation of NIF there has been a growing interest in the quest to increase the efficiency and spatial resolution of x-ray framing cameras, particularly in energy ranges of 1-100 keV. The efficiency of a framing camera depends primarily on the quantum efficiency (Q.E.) of the photocathode material used to coat the pores of the micro-channel plate. Due to experimental considerations it is desirable that the Q.E. of the photocathode exceed 10We report the results of an investigation of the effects of temperature variation on the quantum efficiency of photocathode materials. The poster will present our review of current literature and our analysis of the potential to increase the Q.E. of various photocathode materials through heating. Work at U. of M. supported by the U.S. Naval Research Laboratory and by U.S. DoE under grants DE-FG03-99DP00284, DE-FG03-00SF22021 and other grants and contracts, with technical contributions from Lawrence Livermore National Laboratory.

Harding, E. C.; Drake, R. P.; Bell, P. M.

2003-10-01

224

Solar-driven microbial photoelectrochemical cells with a nanowire photocathode.  

PubMed

We report a self-biased, solar-driven microbial photoelectrochemical cell (solar MPC) that can produce sustainable energy through coupling the microbial catalysis of biodegradable organic matter with solar energy conversion. The solar MPC consists of a p-type cuprous oxide nanowire-arrayed photocathode and an electricigen (Shewanella oneidensis MR-1)-colonizing anode, which can harvest solar energy and bioenergy, respectively. The photocathode and bioanode are interfaced by matching the redox potentials of bacterial cells and the electronic bands of semiconductor nanowires. We successfully demonstrated substantial current generation of 200 ?A from the MPC device based on the synergistic effect of the bioanode (projected area of 20 cm2) and photocathode (projected area of 4 cm2) at zero bias under white light illumination of 20 mW/cm2. We identified the transition of rate-limiting step from the photocathode to the bioanode with increasing light intensities. The solar MPC showed self-sustained operation for more than 50 h in batch-fed mode under continuous light illumination. The ability to tune the synergistic effect between microbial cells and semiconductor nanowire systems could open up new opportunities for microbial/nanoelectronic hybrid devices with unique applications in energy conversion, environmental protection, and biomedical research. PMID:20939571

Qian, Fang; Wang, Gongming; Li, Yat

2010-11-10

225

Development of Advanced Models for 3D Photocathode PIC Simulations  

Microsoft Academic Search

Codes for simulating photocathode electron guns invariably assume the emission of an idealized electron distribution from the cathode, regardless of the particular particle emission model that is implemented. The output of such simulations, a relatively clean and smooth distribution with very little variation as a function of the azimuthal angle, is inconsistent with the highly irregular and asymmetric electron bunches

D. A. Dimitrov; D. L. Bruhwiler; J. R. Cary; P. Messmer; P. Stoltz; Kevin L. Jensen; Donald W. Feldman; P. G. O'Shea

2005-01-01

226

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

227

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...

228

Electrochemical and Spectroscopic Studies of Molten Halides.  

National Technical Information Service (NTIS)

This program deals with the chemistry and electrochemistry of molten halides, media which are used in the production of several important elements, such as aluminum, magnesium and fluorine, in some high energy battery systems, as well as in other applicat...

G. Mamantov

1993-01-01

229

Hybrid excitations in layered iron halides  

Microsoft Academic Search

Layered iron halides (FeCl2, FeBr2) are known to exhibit several unusual features, especially in comparison with those of the first- and more commonly investigated-member of the halide series, FeF2. In contrast with the latter, the crystal-field excitations are dominated by spin-orbit effects and the magnon dispersion approaches that of a two-dimensional ferromagnet. For FeCl2, hybridization effects between magnons and acoustic

U. Balucani; A. Stasch

1985-01-01

230

Hydrothermal alkali metal recovery process  

DOEpatents

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

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

1980-01-01

231

Reflection silver-halide gelatin holograms  

NASA Astrophysics Data System (ADS)

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

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

1991-02-01

232

Reactive scattering of electronically excited alkali atoms with molecules  

SciTech Connect

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

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

1987-06-01

233

Dimming of metal halide lamps  

NASA Technical Reports Server (NTRS)

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

Schurer, Kees

1994-01-01

234

The silver halide photographic process  

NASA Astrophysics Data System (ADS)

The light-sensitive elements of conventional photographic materials are crystallites principally of the bromide or chloride salts of silver. Certain chemical modifications employing sulphur and gold compounds are used to maximize the response, and organic dyes are adsorbed to provide sensitivity throughout the visible spectrum. Absorption of a few photons results in the reductive formation of one or more clusters of silver or gold atoms on the surface. These clusters act as catalysts to promote further reduction of the host crystallites during photographic development. The success of the system depends upon the particular physical properties of the silver halides, such as their bonding and electron structure, the dielectric properties, the point defect structure, and the electronic transport characteristics. These are all reviewed, and the ways in which they interact to lead to the favourable photodecomposition are followed in some detail. A nucleation-and-growth mechanism operates to provide several of the favourable features of the process, and the chemical treatments used optimize the competition between these desirable steps and the unwanted recombination of electronic carriers.

Hamilton, J. F.

1988-07-01

235

Mass spectroscopic and matrix isolation studies on the ternary metal halides CsMCl{sub 3} (M = Pb, Cd, Co)  

SciTech Connect

Mass spectrometric and matrix isolation infrared studies have been carried out on the vapor species present in the high temperature ternary halide systems Cs/Pb/Cl, Cs/Cd/cl, and Cs/Co/Cl, and for all three systems, both binary and ternary halide molecules are identified. In particular, the ternary species present in the Cs/Pb/Cl system is identified as molecular CsPbCl{sub 3}, and on the basis of IR band intensities nd isotopic data, a C{sub 3v} structure is proposed for this species. The high temperature vapors above the Cs/Cd/Cl and Cs/Co/Cl systems also contain ternary CsMCl{sub 3} species, but for these molecules, the vibrational data indicate planar C{sub 2v} geometries involving bidentate coordination at the alkali metal.

Gregory, P.D.; Ogden, J.S. [Univ. of Southampton (United Kingdom). Dept. of Chemistry

1995-01-01

236

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

237

Preparation of graphene/polymer composite photocathode for QDSSC  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

238

Emittance of a photocathode: Effects of temperature and field  

NASA Astrophysics Data System (ADS)

The emittance of a photocathode is evaluated using a distribution function (“Moments”) approach to calculate the moments of the momentum. The effects of temperature and field, which affect the electron distribution and transmission probability, respectively, of electrons incident on the surface barrier, are found. The resulting formulations of emittance are compared to the asymptotic limit found by D. H. Dowell and J. F. Schmerge [Phys. Rev. ST Accel. Beams 12, 074201 (2009)PRABFM1098-440210.1103/PhysRevSTAB.12.074201], and their formulation is shown to be more generally applicable than the approximations within it would indicate for metals. The methodology is extended to develop an asymptotic emittance estimate for semiconductor photocathodes.

Jensen, Kevin L.; O'Shea, P. G.; Feldman, D. W.

2010-08-01

239

The Remarkable Reactivity of Aryl Halides with Nucleophiles  

ERIC Educational Resources Information Center

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

Bunnett, Joseph F.

1974-01-01

240

Thermal emittance measurements of a cesium potassium antimonide photocathode  

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

241

Suppression of afterpulsing in photomultipliers by gating the photocathode  

Microsoft Academic Search

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. This afterpulse or signal-induced background (SIB), which is particularly troublesome in stratospheric lidar measurements, appears as a weak

Michael P. Bristow

2002-01-01

242

CsI UV photocathodes: history and mystery  

Microsoft Academic Search

CsI films are known to be efficient photoconvertors, intensively investigated for UV-photon imaging devices. The article reviews the production and characterization techniques of CsI photocathodes and their photoemission properties in vacuum and gas media, in charge collection and multiplication modes. The important roles of surface phenomena, gas and electric fields are described. The stability of the films is discussed.

A. Breskin

1996-01-01

243

Highly efficient photocathodes for dye-sensitized tandem solar cells.  

PubMed

Thin-film dye-sensitized solar cells (DSCs) based on mesoporous semiconductor electrodes are low-cost alternatives to conventional silicon devices. High-efficiency DSCs typically operate as photoanodes (n-DSCs), where photocurrents result from dye-sensitized electron injection into n-type semiconductors. Dye-sensitized photocathodes (p-DSCs) operate in an inverse mode, where dye-excitation is followed by rapid electron transfer from a p-type semiconductor to the dye (dye-sensitized hole injection). Such p-DSCs and n-DSCs can be combined to construct tandem solar cells (pn-DSCs) with a theoretical efficiency limitation well beyond that of single-junction DSCs (ref. 4). Nevertheless, the efficiencies of such tandem pn-DSCs have so far been hampered by the poor performance of the available p-DSCs (refs 3, 5-15). Here we show for the first time that p-DSCs can convert absorbed photons to electrons with yields of up to 96%, resulting in a sevenfold increase in energy conversion efficiency compared with previously reported photocathodes. The donor-acceptor dyes, studied as photocathodic sensitizers, comprise a variable-length oligothiophene bridge, which provides control over the spatial separation of the photogenerated charge carriers. As a result, charge recombination is decelerated by several orders of magnitude and tandem pn-DSCs can be constructed that exceed the efficiency of their individual components. PMID:19946281

Nattestad, A; Mozer, A J; Fischer, M K R; Cheng, Y-B; Mishra, A; Bäuerle, P; Bach, U

2010-01-01

244

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

245

Some studies of the applications of CsI photocathodes in gaseous detectors  

Microsoft Academic Search

Cesium-iodide photocathodes have been investigated in combination with gaseous detectors. The quantum efficiency of a semi-transparent CsI photocathode has been measured in the UV range and found to be 10% at 140 nm. We report experimental results obtained with such photocathodes coupled to BaF2 and KMgF3 scintillators and read out by parallel-plate gaseous detectors.

G. Charpak; I. Gaudean; Y. Giomataris; V. Peskov; D. Scigocki; F. Sauli; D. Stuart

1993-01-01

246

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

Microsoft Academic Search

The quantum efficiency is measured for normal incidence radiation of microchannel plate detectors which use opaque or semitransparent photocathodes made of fluffy CsI, solid CsI, or both. At wavelengths below 44 A, detectors with fluffy CsI semitransparent photocathodes are more efficient than those with opaque photocathodes of solid CsI, but the opposite is true at longer wavelengths. Fluffy CsI semitransparent

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

1986-01-01

247

Some studies of the applications of CsI photocathodes in gaseous detectors  

NASA Astrophysics Data System (ADS)

Cesium-iodide photocathodes have been investigated in combination with gaseous detectors. The quantum efficiency of a semi-transparent CsI photocathode has been measured in the UV range and found to be 10% at 140 nm. We report experimental results obtained with such photocathodes coupled to BaF 2 and KMgF 3 scintillators and read out by parallel-plate gaseous detectors.

Charpak, G.; Gaudean, I.; Giomataris, Y.; Peskov, V.; Scigocki, D.; Sauli, F.; Stuart, D.

1993-09-01

248

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

Microsoft Academic Search

We have measured the quantum efficiency for normal incidence radiation of microchannel plate detectors which use opaque or semitransparent photocathodes made of fluffy CsI, solid CsI, or both. At wavelengths below --44 A-circle, detectors with fluffy CsI semitransparant photocathodes are more efficient than those with opaque photocathodes of silid CsI, but the opposite is true at longer wavelengths. Fluffy CsI

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

1986-01-01

249

Activation of glycosyl halides by halogen bonding.  

PubMed

Halogen bonding is the formation of a non-covalent interaction between an electrophilic halogen substituent and a Lewis base, for instance, a halide. These kinds of relatively weak interactions have found applications in crystal engineering and initial applications in solution-phase chemistry are starting to appear. We report on the exploration of bis(iodoimidazolium) compounds as halogen-based Lewis acids in the activation of glycosyl halides. We show that these dicationic halogen-bond donors can be used to activate glycosyl halides if the carbohydrate core is sufficiently reactive enough. Furthermore, we provide comparison experiments which indicate that the mode of activation is indeed based on halogen bonding. This represents the first glycosylation reaction mediated by a (carbon-backbone-based) halogen-bond donor. PMID:24962953

Castelli, Riccardo; Schindler, Severin; Walter, Sebastian M; Kniep, Florian; Overkleeft, Herman S; Van der Marel, Gijsbert A; Huber, Stefan M; Codée, Jeroen D C

2014-08-01

250

Silver halide light-sensitive element  

US Patent & Trademark Office Database

A silver halide light sensitive photographic element comprising a support bearing on one side thereof at least one light-sensitive silver halide emulsion layer, wherein the emulsion layer or a separate hydrophilic colloid layer of the element comprises a soluble absorber dye of the following formula (I): ##STR1## wherein each M is H or a counterion; each R.sup.1 and R.sup.2 independently represents H or a photographically acceptable substituent; m+p equals from 1 to 4; n+q equals from 1 to 4; and each of r and t represents from 0 to 3. In preferred embodiments of the invention, the element comprises at least one red-sensitive silver halide emulsion layer, and a dye of formula (I) is coated on the same side of the support as the red-sensitive emulsion layer. In particularly preferred embodiments, the element comprises a support bearing on the same side at least one blue-sensitive silver halide emulsion yellow-image forming layer, at least one red-sensitive silver halide emulsion cyan-image forming layer, at least one green-sensitive silver halide emulsion magenta-image forming layer, and a dye of the formula (I) is coated in at least one of the emulsion layers or a separate hydrophilic colloid layer on the same side of the support. Dyes of formula (I) typically provide substantial absorption at short red wavelengths below about 630 nm, and photographic elements in accordance with the invention accordingly exhibit effective safelight performance for commonly used safelights emitting in the range of 560-630 nm, such as those using a Kodak Safelight Filter No. 8.

1997-11-04

251

Alkali silica reactions — Some paradoxes  

Microsoft Academic Search

This paper provides an exposition of several special chemically-related areas of ASR that have been actively investigated in the past few years. It was found that: (a) the addition of alkali hydroxide to cement to simulate cement of higher alkali contents in laboratory studies has unexpected consequences that may jeopardize the validity of interpretations made; (b) partial drying of concrete

Sidney Diamond

1997-01-01

252

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

253

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

254

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

255

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

256

Breakdown characteristics of metal halide plasma lamps  

Microsoft Academic Search

Nowadays, metal halide plasma lamps are compact and efficient light sources. The dynamics of their breakdown stage are of actual research interest for improving reliable lamp ignition at comparatively low voltages. In order to study the influence of additives on the lamps' breakdown phase at high pressure, a simplified lamp geometry was used, containing 5 bar Xenon and some milligrams

S. Peters; M. Kettlitz; M. Wendt; A. Moss

2008-01-01

257

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

National Technical Information Service (NTIS)

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

D. F. Anderson S. Kwan B. Hoeneisen V. Peskov

1991-01-01

258

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

259

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

260

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

SciTech Connect

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

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

1991-09-01

261

Use of replaceable dynode electron multiplier for comparative measurements of opaque cesium iodid photocathodes in the ultraviolet  

Microsoft Academic Search

A simple means of performing comparative assessment of opaque cesium iodide ultraviolet photocathodes was developed in order to study sensitivity variation with means of deposition. A replaceable dynode electron multiplier was modified to accept a removable metal plate on which was deposited an ultraviolet photocathode. This allowed a large number of photocathode samples to be rapidly compared in a low-cost

Ed Roberts; D. L. Hanson; M. A. Palmer; M. K. Matzen; T. W. Hus

1990-01-01

262

Laser Development for Future Photocathode Research at SLAC  

SciTech Connect

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.-A.; Maruyama, T.; Prepost, R.; Prescott, C.Y.; /SLAC

2005-07-27

263

Thermal emittance and response time of a cesium antimonide photocathode  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

264

Metal-insulator photocathode heterojunction for directed electron emission.  

PubMed

We use angle-resolved photoemission under ultraviolet laser excitation to demonstrate that the electron emission properties of Ag(001) can be markedly enhanced and redirected along the surface normal by the deposition of a few monolayers of epitaxial MgO. We observe new low-binding energy states with small spreads in their surface parallel momenta as a result of MgO/Ag(001) interface formation. Under 4.66 eV laser excitation, the quantum efficiency of MgO/Ag(001) is a factor of 7 greater than that of clean Ag(001), revealing the utility of such heterojunctions as advanced photocathodes. PMID:24580707

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

2014-02-14

265

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

266

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

SciTech Connect

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

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

1986-07-15

267

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

NASA Astrophysics Data System (ADS)

The quantum efficiency is measured for normal incidence radiation of microchannel plate detectors which use opaque or semitransparent photocathodes made of fluffy CsI, solid CsI, or both. At wavelengths below 44 A, detectors with fluffy CsI semitransparent photocathodes are more efficient than those with opaque photocathodes of solid CsI, but the opposite is true at longer wavelengths. Fluffy CsI semitransparent photocathodes with surface densities between 150 and 400 micrograms/sq cm are optimum at soft X-ray wavelengths, and efficiencies of 35 and 41 percent at 8 and 44 A, respectively, were obtained for a single-layer photocathode. The measured peak efficiency for an opaque layer or solid CsI, deposited at 0 deg coating angle and 5000 A (226 micrograms/sq cm) in thickness, is 56 percent at 110 A.

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

1986-07-01

268

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

269

Characterization of x-ray photocathode in transmission mode for imaging application  

SciTech Connect

The performance of an Al x-ray transmission photocathode was experimentally characterized by measuring the total electron yield from backsurface photocathodes of varying thickness. It was demonstrated that the backsurface electron yield is proportional to the x-ray photocurrent transmitted through the photocathode for thicknesses thicker than the optimum thickness. The optimum photocathode thickness with the highest conversion efficiency was found to be approximately 70 nm at 2.963 keV. An escape depth of the secondary electrons was determined to be approximately 13 nm from the yield-versus-thickness data fitted with a semiempirical equation. Using this parameter, the dependence of the optimum photocathode thickness on the x-ray energy was calculated for the 30-10000 eV range. As one example of imaging applications, different photoemission images in the transmission and reflection modes are also presented.

Ikeura-Sekiguchi, Hiromi; Sekiguchi, Tetsuhiro; Koike, Masaki; Yagi-Watanabe, Kazutoshi [National Institute of Advanced Industrial Science and Technology (AIST), Central 2-5, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); Japan Atomic Energy Agency (JAEA), Naka, Tokai, Ibaraki 319-1195 (Japan); National Institute of Advanced Industrial Science and Technology (AIST), Central 2-5, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); National Institute of Advanced Industrial Science and Technology (AIST), Central 2-5, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)

2009-09-15

270

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

271

Kelvin probe studies of cesium telluride photocathode for the AWA photoinjector  

SciTech Connect

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

Velazquez, D.; Wisniewski, E. E.; Yusof, Z.; Harkay, K.; Spentzouris, L.; Terry, J. [Physics Department at Illinois Institute of Technology, Chicago, IL 60616 and High Energy Physics Division at Argonne National Laboratory, Lemont, IL 60439 (United States); High Energy Physics Division at Argonne National Laboratory, Lemont, IL 60439 (United States); Accelerator Science Division at Argonne National Laboratory, Lemont, IL 60439 (United States); Physics Department at Illinois Institute of Technology, Chicago, IL 60616 (United States)

2012-12-21

272

Polarization and charge limit studies of strained GaAs photocathodes  

SciTech Connect

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

Saez, P.J.

1997-03-01

273

Mechanical filter for alkali atoms  

Microsoft Academic Search

The recent past has shown a significant progress in the spin exchange optical pumping technology. Spin-exchange optical pumping is a process whereby photon angular momentum is transferred to target nuclei through spin-exchange collisions with polarized alkali-metal atoms. In spite of their small numbers, alkali-metal atoms could significantly dilute the nucleon polarization in the target, because of there are a large

Dmitrij Toporkov; Bogdan Wojtsekhowski

1998-01-01

274

Influence of air exposure on CsI photocathodes  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

275

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

276

Highly active oxide photocathode for photoelectrochemical water reduction.  

PubMed

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 H(2) 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%. PMID:21552270

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

2011-06-01

277

Magnetron Driven L Band RF Gun using a Photocathode Emitter  

NASA Astrophysics Data System (ADS)

Magnetron Driven L Band RF Gun using a Photocathode Emitter A tunable 5 megawatt L-Band injection locked magnetron amplifier is used to drive a 1-1/2 cell RF cavity gun, to produce a 2.5 megavolt electron beam. A tunable RF source relaxes the precision of the cavity gun construction, and therefore simplifies the design and reduces the overall cost. The design of the L-Band ( 1.3 GHz) RF cavity linear accelerator is presented, along with Superfish, SOS computer simulations, and calculations of beam energy and temporal qualities. Measurements of a few robust photocathode materials as well as measurements of the beam qualities of the final accelerator are presented. Future work will utilize new semiconductor laser diodes that can be electrically driven in the gigahertz range. This makes possible an electron gun system which can run at the RF frequency used to accelerate the electron beam. Such a system produces a "lock to clock" and synchronized RF and electron beam source which can be run single shot or any rep rate up to the RF frequency.

Evans, Kirk; Fisher, Amnon; Friedman, Moshe

1996-11-01

278

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

279

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

Microsoft Academic Search

Solubility of sodium iodide in liquid sodium was determined over a temperature range of 350~650°C by using capsules of two different kinds.Stainless steel capsule of short type loaded with 2~3.5g sodium and fragments of sodium iodide crystal was put in a pair of holders and heated under an uniform temperature distribution in a vertical electric furnace. Stainless steel capsule of

Norihiko SAGAWA; Shinya MIYAHARA

1992-01-01

280

Formamide adsorption and habit changes of alkali halide crystals grown from solutions  

Microsoft Academic Search

The possibility to obtain {111} surfaces on NaCl crystals grown from pure water solutions was investigated in order to verify some early observations. Repeating the same experiments as reported by Kern in 1953 (Bull. Soc. Fr. Mineral Cristallogr. 76 (1953) 391) followed by detailed examination using optical microscopy and optical goniometry revealed that, independent of supersaturation, {100} is the only

Neda Radenovi?; Willem van Enckevort; Elias Vlieg

2004-01-01

281

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

NASA Astrophysics Data System (ADS)

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

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

1983-01-01

282

Epitaxial growth of pentacene on alkali halide surfaces studied by Kelvin probe force microscopy.  

PubMed

In the field of molecular electronics, thin films of molecules adsorbed on insulating surfaces are used as the functional building blocks of electronic devices. Control of the structural and electronic properties of the thin films is required for reliably operating devices. Here, noncontact atomic force and Kelvin probe force microscopies have been used to investigate the growth and electrostatic landscape of pentacene on KBr(001) and KCl(001) surfaces. We have found that, together with molecular islands of upright standing pentacene, a new phase of tilted molecules appears near step edges on KBr. Local contact potential differences (LCPD) have been studied with both Kelvin experiments and density functional theory calculations. Our images reveal that differently oriented molecules display different LCPD and that their value is independent of the number of molecular layers. These results point to the formation of an interface dipole, which may be explained by a partial charge transfer from the pentacene to the surface. Moreover, the monitoring of the evolution of the pentacene islands shows that they are strongly affected by dewetting: Multilayers build up at the expense of monolayers, and in the Kelvin images, previously unknown line defects appear, which reveal the epitaxial growth of pentacene crystals. PMID:24601525

Neff, Julia L; Milde, Peter; León, Carmen Pérez; Kundrat, Matthew D; Eng, Lukas M; Jacob, Christoph R; Hoffmann-Vogel, Regina

2014-04-22

283

Formation of defect triplets by synchrotron radiation in alkali halide crystals at 8K  

Microsoft Academic Search

The formation of spatially correlated defects (F-VK-I) and (F-VK-H triplets) was revealed in KBr crystals irradiated by 6-25 eV photons under the conditions of multiplication of electronic excitationsE The efficiency of F-VK-I creation nu is high when one exciting photon forms two electron-hole pairs. The value of nu for F-VK-H triplets is high at the decay of cation excitons.

A. Lushchik; M. Kirm; Ch. Lushchik; I. Martinson; V. Nagirnyi; E. Vasil'Chenko

1999-01-01

284

Theory of Spin-Orbit Effects in the F Band in Alkali Halides  

Microsoft Academic Search

A calculation of the spin-orbit splitting of the first optically excited state of the F center is reported. It is based on a tight-binding, static lattice model of the crystal and assumes a vacancy-centered electronic wave function for the F center. To satisfy the Pauli principle, the F-center state must be orthogonalized to the occupied states of the crystal. This

David Young Smith

1965-01-01

285

Photostimulated luminescence in alkali halides induced by excitation with ionizing radiation  

NASA Astrophysics Data System (ADS)

The photostimulated luminescence (PSL) phenomenon induced in copper-doped sodium chloride (NaCl:Cu) and europiumdoped potassium chloride (KCl:Eu) phosphor crystals by excitation with ionizing radiation such as X-rays is studied. The emission mechanism of the PSL in both phosphor crystals is discussed in terms of the recombination of electrons optically stimulated from the radiation-induced F centers with the luminescence centers such as Cu 2+ in NaCl and Eu 3+ ions in KCl. The potentiality of both phosphor crystals as a material for two-dimensional X-ray imaging sensors utilizing the PSL phenomenon is also discussed.

Nanto, H.; Endo, F.; Hirai, Y.; Murayama, K.; Nasu, S.; Taniguchi, S.; Nakamura, S.; Inabe, K.; Takeuchi, N.

1994-06-01

286

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

287

Growth of pure single crystals of alkali halides and alkaline earth fluorides  

NASA Astrophysics Data System (ADS)

The final report covers the design of ion selective filters and development of an ion exchange purification system for potassium bromide. The system consists of an ion selective filter for passage of potassium ions and a bromide anion exchange system for reduction of anionic impurities. Because of the high ionic strength of the solutions used and particularly their ability to hydrolyze amide and ester bonds, limitations are imposed on the materials that can be used for construction of those parts of the systems that contact these solutions. Certain addition polymers are more promising for construction of the components of such a system than others, these are discussed in the body of the report. A special group of components have been designed and assembled to provide the fittings, valves, electrode chambers, sampling valves, columns and filters necessary for a closed purification system. The preparation of the resins for use in such a system required that their conversion to the forms required for purification of KBr, require that the reactions for this conversion go almost to completion. The extent of conversion of the resins affect the operational characteristics of the system and are discussed in this report. The product of the initial purification is a strongly acid KBr solution and the techniques were developed to minimize external contamination during reduction of the purified salt solution to a solid. The final purification step made during the growth of the crystal is treatment with a reactive gas. A greaseless reactive gas manifold was constructed and several reactive gas treatments were used in an attempt to purify the KBr.

Fredericks, W. J.

1981-05-01

288

Thermodynamical computations for removal of alkali halides and lead compounds from electric arc furnace dust  

Microsoft Academic Search

Thermodynamical aspects of a separation process, proposed by the authors for the removal of volatile species from EAF dust, have been studied. Computations have been performed using FACT (Facility for Analysis of Chemical Thermodynamics) software. Different conditions have been considered through calculations of equilibrium state. Effects of different additives, temperature and atmosphere at different total pressure were investigated. It has

Ahad Zabett; Wei-Kao Lu

2008-01-01

289

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

290

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

291

ir absorption of CN defects in cesium halides rotationally aligned by alkali-metal-ion impurities  

Microsoft Academic Search

Substitutional CN- defects in CsCl, CsBr, and CsI show under increasing temperature strong broadening of their ir stretching absorption line nu0 into unresolved vibrational-rotational spectra characteristic of a quasifree rotor. Additional K+ or Rb+ impurities in these hosts produce two extra CN- absorption lines nu1 and nu2 (at lower energy than nu0), which remain sharp and resolved to high temperatures.

Wolf von der Osten; Fritz Lüty

1987-01-01

292

Thermoluminescent dosimetric characteristics of irradiated ternary alkali halides doped with lanthanum  

NASA Astrophysics Data System (ADS)

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

Maruthi, G.; Chandramani, R.

2013-02-01

293

New formulation of the modeling of radiation-induced microstructure evolution in alkali halides  

Microsoft Academic Search

Recent experimental results on heavily irradiated natural and synthetic NaCl crystals give a strong evidence for the formation of large vacancy voids, which cannot be explained by the Jain-Lidiard model used up to date for description of metal colloids and dislocation loops formed during earlier stages of irradiation. We propose a new mechanism of dislocation climb, which involves production of

V. I. Dubinko; A. A. Turkin; D. I. Vainshtein; H. W. Den Hartog

1999-01-01

294

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

NASA Astrophysics Data System (ADS)

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

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

2001-07-01

295

New aspects on the dielectric properties of the alkali halides with divalent impurities  

Microsoft Academic Search

Dielectric losses were measured in the following crystals NaCl+ (Mg2+, Co2+, Ni2+, Sr2+, Ca2+, Mn2+, Zn2+, Cd2+, Ba2+, Pb2+), KCl + (Ca2+, Sr2+, Ba2+, 2+, Pb2+) and KBr + (Sr2+, Ba2+) in the frequency region 5 500 kHz. It was found that when the divalent cation impurity has an electronic configuration similar to the inert gases (1) no observable deviation

P. Varotsos; D. Miliotis

1974-01-01

296

Electronic line-up in light-emitting diodes with alkali-halide\\/metal cathodes  

Microsoft Academic Search

The electronic nature of metal-semiconductor contacts is a fundamental issue in the understanding of semiconductor device physics, because such contacts control charge injection, and therefore play a major role in determining the electron\\/hole population in the semiconductor itself. This role is particularly important for organic semiconductors as they are generally used in their pristine, undoped form. Here, we review our

T. M. Brown; R. H. Friend; I. S. Millard; D. J. Lacey; T. Butler; J. H. Burroughes; F. Cacialli

2003-01-01

297

Rotational Degrees of Freedom of Molecules in Solids. I. The Cyanide Ion in Alkali Halides  

Microsoft Academic Search

By means of infrared-absorption, thermal-conductivity, and specific-heat measurements at low temperatures, the problem of rotational motion of molecules in solids has been studied using CN- ions substituted for the halogen in KCl, KBr, KI, RbCl, NaCl, and NaBr. Energy levels associated with the ion performing free rotation, hindered rotation, oscillation, and tunneling motion were observed. It was found that a

W. D. Seward; V. Narayanamurti

1966-01-01

298

Dynamics of Radiation Damage in Face-Centered-Cubic Alkali Halides  

Microsoft Academic Search

Computer simulations of ionic motion in 3-dimensional potassium chloride and sodium chloride crystallites have been undertaken to investigate the effect of the regular lattice in influencing the energy spread in the crystal from a primary event such as might be caused by an incident energetic charged particle. Focusing of energy has been found to occur in several low-index crystallographic directions,

Ian Mcc. Torrens; Lewis T. Chadderton

1967-01-01

299

FTS infrared measurements of alkali halides in the gas phase: Rubidium fluoride and cesium fluoride  

NASA Astrophysics Data System (ADS)

High-resolution Fourier transform spectroscopy measurements have been made on rubidium fluoride and cesium fluoride vapor in the region of the fundamental vibrational bands between 290 and 360 cm -1. The measurements were made at temperatures between 1020 and 1180 K. Vibrational transitions covering the range from v = 1-0 to v = 9-8 were observed. Dunham potential and rovibrational constants were determined for CsF and for 85RbF and 87RbF.

Maki, Arthur G.; Olson, Wm. Bruce

1990-03-01

300

Growth and Hardening of Alkali Halides for Use in Infrared Laser Windows.  

National Technical Information Service (NTIS)

KCl crystals pulled from pretreated melts under an Ti gettered inert atmosphere have been shown to have as low an absorption as crystals grown by the RAP Bridgman method. A simple optical method has been developed to analyze KCl:Eu for Eu content. Radiati...

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

1975-01-01

301

Growth and Hardening of Alkali Halides for Use in Infrared Laser Windows.  

National Technical Information Service (NTIS)

Several KCl crystals have been pulled from melts of reagent grade KCl, RAP treated reagent grade KCl, and HCl/Cl2 treated KCl. The OH(-) concentrations and the 10.6 micrometers optical absorption of these crystals were evaluated. The results indicate that...

W. A. Sibley C. T. Butler J. R. Hopkins J. J. Martin

1974-01-01

302

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

Microsoft Academic Search

We report a first computation of the geometry of HBr adsorbed on a LiF(001) substrate. The interaction energy of 200 HBr molecules with periodic boundary conditions was determined with respect to adsorbate–substrate and adsorbate–adsorbate electrostatic interaction (point charges in HBr simulated its dipole and multipoles) as well as a short-range ‘‘core’’ potential (comprising dispersion forces and repulsive overlap). The monolayer

J. C. Polanyi; R. J. Williams; S. F. O’Shea

1991-01-01

303

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

NASA Astrophysics Data System (ADS)

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

Burke, Sarah A.

304

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

SciTech Connect

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

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

1981-01-01

305

Energies and Vibrational Frequencies of Gaseous Alkali Halide M2X+ Ions  

Microsoft Academic Search

A potential function describing the interaction between the ions of M2X+ molecules has been developed using a model suggested by Pauling. From this potential the energies and vibrational frequencies have been calculated for these molecules. The harmonic contributions to the bending frequencies are shown to be far from negligible based on this purely ionic model. The entropy and free energy

Thomas A. Milne; Daniel Cubicciotti

1959-01-01

306

F' and M' Traps in Alkali Halides Studied by Means of Photostimulated Thermoluminescence.  

National Technical Information Service (NTIS)

The nature of some traps in NaCl, KCl, KBr is investigated by means of correlated experiments on photostimulated thermoluminescence and optical absorption. The glow peaks centered at 149K in KBr and at 340K in NaCl are due to the thermal release of F' ele...

P. Scaramelli

1966-01-01

307

Heteroepitaxial strain in alkali halide thin films: KCl on NaCl  

NASA Astrophysics Data System (ADS)

We have performed Monte Carlo simulations of the properties of a NaCl (001) surface covered by full or partial layers of KCl, for coverages up to 5 monolayers (ML). A wide variety of structures of the film is found. For integer ML coverages we find the continuous, so-called floating mode rumple structure, as was previously found in the KBr/NaCl system. However, for a coverage of ~2.1 ML, we find a discrete structure of periodicity 3:4 of small regularly spaced KCl pyramids. It has the same scattering characteristics as the structure observed by Henzler et al. [Phys. Rev. B 52, 17 060 (1995)], but it is two-dimensional modulated, rather than the rowlike stacking fault structure proposed by Henzler et al. Also, at a coverage of ~0.8 ML there is a stable 3:4 structure. Other structures are found at intermediate coverages, corresponding to regular arrays of dislocation lines with periodicity 9:10. A further growth from such structures would give rise to growth of a ~5° miscut KCl crystal relative to the NaCl lattice. The reciprocal space patterns corresponding to the continuous and the discrete film deformations are also calculated.

Baker, Jeff; Lindgård, Per-Anker

1999-12-01

308

Interface structure of alkali-halide heteroepitaxial films studied by x-ray-absorption fine structure  

NASA Astrophysics Data System (ADS)

We have investigated the interface structures of KCl and NaCl thin films grown on NaBr(100) by means of Cl K-edge x-ray-absorption fine structure. The x-ray-absorption near-edge structure of 1-ML-thick KCl on NaBr indicates that the mixed crystal does not form at the interface. Through the analysis of extended x-ray-absorption fine structure, it was revealed that with a decrease in film thickness, the K-Cl bond distance is slightly shortened in KCl/NaBr(100), while the Na-Cl bond is elongated in NaCl/NaBr(100). The 1-ML-thick film does not, however, form coherent bonds with the substrate. This implies that the in-plane bond distance of the film does not coincide with that of the substrate but is close to the bond distance of the bulk material. For further understanding of the bond character between the film and substrate, Monte Carlo calculations have been carried out for the KCl/KBr system which gave a similar conclusion in our previous study. The calculated results were found to agree with the experimental results reasonably. These findings are contradictory with the previous diffraction results that have suggested the formation of coherent bonding at the interface. Such a discrepancy implies that the short-range order (bond distance) does not always reflect the long-range order (lattice constant).

Kiguchi, Manabu; Yokoyama, Toshihiko; Matsumura, Daiju; Kondoh, Hiroshi; Ohta, Toshiaki; Kitajima, Yoshinori

1999-12-01

309

Structures of vinylidene fluoride oligomer thin films on alkali halide substrate  

NASA Astrophysics Data System (ADS)

Structures and crystal transformation of the newly synthesized vinylidene fluoride (VDF) oligomer with large electric dipoles evaporated on KCl (001) at various substrate temperatures have been investigated by an energy dispersive-grazing incidence x-ray diffraction system, Fourier transform infrared spectroscopy, and atomic force microscope (AFM). It was revealed that the molecules grow epitaxially and are influenced greatly by forces of the crystal surface field in terms of van der Waals or electrostatic potentials, and found that the phase transformation from form II (? phase) to form I (? phase) is induced by raising the temperature of the substrate from 50 to 80 °C, accompanying the alternation in the crystal axes on the substrate from the a axis of form II to the polar b axis of the form I crystal. This fact suggests that the molecular chain of VDF oligomers aligns their c axes along the <110> row of K+ or Cl- with the aid of electrostatic interaction under enough thermal movement. Moreover, in the transformation process, a pair of ``rod-like'' crystals, suggesting ferroelectric activity, were observed by AFM.

Noda, Kei; Ishida, Kenji; Horiuchi, Toshihisa; Matsushige, Kazumi; Kubono, Atsushi

1999-10-01

310

Dynamical Jahn-Teller Effect in Alkali Halide Phosphors Containing Heavy Metal Ions  

Microsoft Academic Search

Possible patterns of vibration-induced splitting in the absorption band of localized electrons in solid are investigated within the Condon approximation. The modes of lattice vibrations around the imperfection which give rise to the level splitting of degenerate excited states are classified into active and potentially active modes according as they cause the absorption band to split or not. The result

Yutaka Toyozawa; Masaharu Inoue

1966-01-01

311

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

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

312

Optical properties of halide and oxide scintillators  

SciTech Connect

Knowledge of optical properties of scintillators is important both for the optimization of scintillator systems and the development of new materials particularly ceramic scintillators. Recent theoretical developments, especially new density functionals that enable accurate prediction of band gaps, have made it possible to perform quantitative calculations of the optical properties of scintillator materials. We used these techniques to obtain optical properties of a large number of high light output halide scintillators. These calculations showed that many halide scintillators have remarkably little optical anisotropy and may be good candidates for development as ceramic scintillators. These include materials such as CaI{sub 2}:Eu{sup 2+} that have very high light output and other favorable properties but are difficult to develop due to crystal growth issues. We review some of our recent results and present new results for CeCl{sub 3}.

Singh, David J [ORNL

2011-01-01

313

Ultraviolet photoelectron spectra of cesium halides  

Microsoft Academic Search

Energy distributions of photoelectrons from evaporated films of cesium halides were measured at photon energies of 11-23 eV. The photoelectron spectra show structures that can be identified as relatively high densities of states in the Cs+ 5p core as well as in the valence and conduction bands. Doublet core states due to spin-orbit splitting are observed for all the cesium

Jerel A. Smith; W. Pong

1975-01-01

314

Electron phonon interactions in optical transitions of silver halides  

Microsoft Academic Search

Recent experimental results on low temperature optical studies of silver halides are summarized. Various structures in absorption edge spectra and many narrow emission bands are observed in pure silver halides and silver halides containing isoelectronic impurities below 4.2°K. Various aspects of electron-phonon interactions, especially exciton-phonon interactions, are discussed for optical transitions corresponding to creation and radiative decay of both free

Hiroshi Kanzaki

1970-01-01

315

Process and composition for drying of gaseous hydrogen halides  

DOEpatents

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

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

1989-08-01

316

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

317

79 FR 7745 - Energy Conservation Program: Energy Conservation Standards for Metal Halide Lamp Fixtures  

Federal Register 2010, 2011, 2012, 2013

...Program: Energy Conservation Standards for Metal Halide Lamp Fixtures; Final Rule Federal...Program: Energy Conservation Standards for Metal Halide Lamp Fixtures AGENCY: Office of...commercial and industrial equipment, including metal halide lamp fixtures (MHLFs). EPCA...

2014-02-10

318

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...

319

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

Code of Federal Regulations, 2010 CFR

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

2010-01-01

320

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

Code of Federal Regulations, 2011 CFR

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

2011-07-01

321

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

Code of Federal Regulations, 2010 CFR

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

2010-07-01

322

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

Code of Federal Regulations, 2012 CFR

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

2012-07-01

323

Short-arc metal halide lamp suitable for projector application  

NASA Astrophysics Data System (ADS)

Recently, progress has been made in the development of projectors used for large screen displays. Projection systems employing high luminous efficiency Metal Halide Lamps as a light source demonstrate unique and desirable features. For example, compared to conventional lamps, a Metal Halide Lamp has longer life, higher luminous efficiency, the shortest arc length possible, and higher color-rendering characteristics, resulting in an overall superior performance. Several lamps, including Metal Halide, Xenon, and Halogen lamps, are used in HDTV (High Definition Television). Recently, Metal Halide Lamps have become accepted as the light source of choice. The reason for this is the high brightness, color balance, and long life of the Metal Halide Lamp. The fundamental operating principal for Metal Halide Lamps is almost the same as that of Mercury lamps. A Metal Halide Lamp has very different characteristics in that, the spectrum of illumination can be varied by varying the mixture of Metal Halide generated in the lamp. For these lamps, we have improved the electrode, the chemical composition of the Metal Halide, and the glass envelope. We have achieved a longer average life (greater than 2500 hours) for a compact, single-bulb, projection-type lamp.

Kawai, Kouji; Matsumoto, Masayuki

1995-04-01

324

Properties of CsI and CsI-TMAE photocathodes  

SciTech Connect

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

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

1992-06-01

325

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

PubMed

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

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

2010-06-01

326

Enhanced lifetime hybrid-diffuser cesium reservoir photocathode  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

327

Silicon based tandem cells: novel photocathodes for hydrogen production.  

PubMed

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

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

2014-05-28

328

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

329

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

National Technical Information Service (NTIS)

We present measurements of photoemission quantum efficiency (QE) for copper photocathodes heated and cleaned by low energy argon and hydrogen ion plasma. The QE and surface roughness parameters were measured before and after processing and surface chemica...

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

2005-01-01

330

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

National Technical Information Service (NTIS)

Laser-based techniques have been widely used for cleaning metal photocathodes to increase quantum efficiency (QE). However, the impact of laser cleaning on cathode uniformity and thereby on electron beam quality are less understood. We are evaluating whet...

F. Zhou

2012-01-01

331

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

SciTech Connect

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

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

2009-01-22

332

Evaluation of chemical cleaning for Ga1?xAlxAs photocathode by spectral response  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

333

Integration of Transients in Axisymmetrical Cavities for Accelerators: Formulation and applications to BNL Photocathode Gun  

SciTech Connect

This note provides a sketch of the formalism used for the Integration of Transients in Axisymmetrical Cavities for Accelerators, (ITACA). Application to study the BNL Photocathode Gun via the code ITACA is also included.

Parsa, Z. [Brookhaven National Lab., Upton, NY (United States); Serafini, L. [Istituto Nazionale di Fisica Nucleare, Milan (Italy)]|[Milan Univ. (Italy)

1992-04-01

334

Controlling Metal-Halide Vapor Density in Lasers  

NASA Technical Reports Server (NTRS)

Streams of buffer gas convect and dilute metal-halide vapor. Technique uses flow of buffer gas through reservoir, which contains heated metal halide, to convect vapors into discharge tube. Second stream of buffer gas dilutes vapor. Final vapor density in laser tube controlled and changed by adjusting either one or both of buffer gas flow rates.

Pivirotto, T. J.

1984-01-01

335

Chemiluminescent emission spectra of tin mono- and di-halides  

Microsoft Academic Search

Chemiluminescent emission from flames of tin halides burning at low pressure in potassium vapor is found to include vibronic bands of mono- and di-halides. The emitters are, quite certainly, electrically neutral species. Bands from SnCl2 are analyzed with the aid of a Deslandres scheme and some vibrational constants are assigned to the upper and lower states.

David Naegeli; Howard B. Palmer

1966-01-01

336

Comparison between gradient-doping GaAs photocathode and uniform-doping GaAs photocathode.  

PubMed

We compared two reflection-mode negative electron affinity (NEA) GaAs photocathode samples that are grown by molecular beam epitaxy with p-type beryllium doping. One sample is uniform doping, and another is gradient doping. Experimental curves of spectral response sensitivity and quantum efficiency are obtained. The thicknesses of the two cathodes are both 2.6 microm. The integrated sensitivity of the uniform doping one is 1966 microA/lm, and that of the gradient-doping one is 2421 microA/lm. The escape probability and diffusion length are fitted from the spectral response curves. For the uniform-doping sample, the escape probability is 0.45 and the diffusion length is 5 microm. For the gradient-doping sample, the escape probability is 0.55 and the diffusion length is 5.5 microm. PMID:17906733

Yang, Zhi; Chang, Benkang; Zou, Jijun; Qiao, Jianliang; Gao, Pin; Zeng, Yiping; Li, Hui

2007-10-01

337

Improved processing for silver halide pulse holography  

NASA Astrophysics Data System (ADS)

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

Mikhailov, Viktor N.; Son, Jung-Young; Grinevitskaya, Olga V.; Lee, Hyuk-Su; Choi, Y.-J.

1996-04-01

338

Synthesis of lithium cobaltate in halide melts  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

339

Hole transport in sensitized CdS-NiO nanoparticle photocathodes.  

PubMed

A general chemical approach was used to synthesise NiO-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. PMID:21858333

Kang, Soon Hyung; Zhu, Kai; Neale, Nathan R; Frank, Arthur J

2011-10-01

340

Design and beam dynamics simulations of an S-band photocathode rf gun  

Microsoft Academic Search

We are building an S-band photocathode rf gun as an injector to a 30MeV electron linac for FEL applications. Here we discuss details of design simulations performed using superfish and gdfidl and compare with results of cold tests performed on prototype cells of the photocathode rf gun. We also discuss beam dynamics simulations performed using parmela and report results from

Arvind Kumar; K. K. Pant; S. Krishnagopal

2002-01-01

341

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

342

Modified model of alkali-silica reaction  

Microsoft Academic Search

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

Tsuneki Ichikawa; Masazumi Miura

2007-01-01

343

Alkali-Silica Reactivity Field Identification Handbook.  

National Technical Information Service (NTIS)

Two types of alkali-aggregate reaction (AAR) are currently recognized depending on the nature of the reactive mineral; these are alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). Both types of reaction can result in expansion and cracking ...

B. Fournier K. I. Folliard M. D. A. Thomas Y. A. Resendez

2011-01-01

344

Process for preparing dispersions of alkali metals  

NASA Technical Reports Server (NTRS)

Finely divided particles of alkali metals are produced by combining alkali metals with certain aromatic compounds in selected solvents to form low-temperature soluble complexes from which the pure alkali metals precipitate quantitatively when the solutions are warmed. All operations must be carried out in an inert gas atmosphere.

Landel, R. F.; Rembaum, A.

1966-01-01

345

Halide ion-mediated growth of single crystalline Fe nanoparticles.  

PubMed

We report a facile halide ion (Cl(-) or Br(-)) mediated synthesis of Fe nanoparticles (NPs) by thermal decomposition of Fe(CO)5. The NP structure is controlled to be either amorphous (in the absence of halide ions) or single crystalline bcc (in the presence of halide ions). Through systematic investigation on the synthetic conditions, we have confirmed that the formation of bcc-Fe NPs is facilitated by the strong interactions between halide ions and Fe, which favor thermodynamic growth of Fe over the existing Fe NPs. Compared with the amorphous Fe NPs, the bcc-Fe NPs exhibit much enhanced magnetization values and chemical stability. This halide ion mediated growth may become a general strategy to control the growth of metallic NPs, especially first-row transition metal NPs, in a thermodynamically more stable way, producing single crystalline NPs with much controlled physical and chemical properties for magnetic and catalytic applications. PMID:24667889

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

2014-05-01

346

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

SciTech Connect

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

Bolton, Paul

2010-12-07

347

Microfabricated alkali atom vapor cells  

Microsoft Academic Search

We describe the fabrication of chip-sized alkali atom vapor cells using silicon micromachining and anodic bonding technology. Such cells may find use in highly miniaturized atomic frequency references or magnetometers. The cells consist of cavities etched in silicon, with internal volumes as small as 1 mm3. Two techniques for introducing cesium and a buffer gas into the cells are described:

Li-Anne Liew; Svenja Knappe; John Moreland; Hugh Robinson; Leo Hollberg; John Kitching

2004-01-01

348

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

349

Electrocatalytic potentialities of silver as a cathode for organic halide reductions  

Microsoft Academic Search

The peculiar halide affinity for silver results in an extraordinary electrocatalytic activity for the reduction of halides (either glycosyl halides or, more generally, aryl and alkyl halides). The most striking features are: (a) a reduction potential shift in the positive direction of about 1000 mV with respect to glassy carbon and 500 mV with respect to mercury; (b) a cage

Sandra B. Rondinini; Patrizia R. Mussini; Federico Crippa; Guido Sello

2000-01-01

350

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

351

The surface activation layer of GaAs negative electron affinity photocathode activated by Cs, Li, and NF3  

NASA Astrophysics Data System (ADS)

The lifetime of GaAs photocathodes can be greatly improved by introducing Li in the Cs+NF3 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 NFx 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, Y.; Kirby, R. E.; Maruyama, T.; Mulhollan, G. A.; Bierman, J. C.; Pianetta, P.

2009-10-01

352

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

PubMed Central

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

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

2013-01-01

353

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

354

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

355

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

356

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

357

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

358

The III-V photocathode - A major detector development.  

NASA Technical Reports Server (NTRS)

Description of new (III-V) photocathodes which show improvements in sensitivity of as much as ten to a hundred times over conventional cathodes in the near infrared and useful improvements at shorter wavelengths. The development stems from a combination of basic knowledge of the photoemission process, gained in the 1950s, and the advancing understanding of the technology of III-V materials, in the 1960s. The superior performance of these cathodes is due to the fact that the vacuum level at the surface lies below the bottom of the conduction band in the bulk of the material. Consequently, the threshold of response is set by the III-V bandgap. The bandgap (and the threshold of response) can be varied by alloying different III-V materials together. A reduction in thermionic emission is realized with these cathodes. At present no semitransparent III-V cathodes with comparably interesting performance are available. The problems hindering further improvements, as well as the problems of placing these cathodes in practical multipliers and image tubes, are discussed briefly.

Spicer, W. E.; Bell, R. L.

1972-01-01

359

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

360

Defects in the silver halide photographic process  

NASA Astrophysics Data System (ADS)

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

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

361

The alkali-silica reaction  

Microsoft Academic Search

Electrical double-layer theory has been used successfully to explain the expansion caused by the alkali-silica reaction. The net proton surface charge density of the reactive aggregate is a critical parameter for this approach. However, little work has been done to measure the surface charge density of silica as a function of pH at background electrolyte concentrations that are relevant to

Flávio A. Rodrigues; Paulo J. M. Monteiro; Garrison Sposito

1999-01-01

362

The alkali–silica reaction  

Microsoft Academic Search

The degree of expansion of alkali–silica reaction (ASR) gel is dependent on the valence and relative concentrations of cations present in the ASR gel. The electrical double-layer (EDL) model can predict which gel will be more expansive. If double-layer models are applied in a complex system, as in concrete, it is necessary to characterize the surface charge density of amorphous

Flávio A. Rodrigues; Paulo J. M. Monteiro; Garrison Sposito

2001-01-01

363

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

364

Silver halide reflection noise gratings recorded in dichromated gelatin  

Microsoft Academic Search

It is shown that reflection noise gratings may be copied from silver halide emulsion to dichromated gelatin. These have been found to display lower angular selectivity and diffraction efficiency than transmission noise gratings recorded under the same conditions.

L. T. Blair; L. Solymar

1990-01-01

365

Photo-injection of hydrogen in Ag and Cu halides  

Microsoft Academic Search

For the first time photo-initiated injection of hydrogen was carried out into Ag- and Cu-halides (AgCl, AgJ, Ag4RbI5, CuCl) -- the materials which are very important for investigations of the photographic process. To carry out the photoinjection of hydrogen into the halides a double-layer structure was used. Onto a quartz substrate two thin films were evaporated one after the other:

Alexander Gavrilyuk

1997-01-01

366

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

367

Diode pumped alkali vapor fiber laser  

Microsoft Academic Search

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

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

2007-01-01

368

Diode pumped alkali vapor fiber laser  

Microsoft Academic Search

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

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

2006-01-01

369

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

370

Photoelectron extraction efficiency from cesium iodide photocathodes in a pressurized atmosphere of argon and xenon up to 10 bar  

Microsoft Academic Search

Photoelectron extraction efficiency is a key parameter in gaseous detectors design requiring CsI photocathodes, particularly in pressurized applications for rare event experiments. Within this work we report on our measurements of the photoelectron extraction efficiency from a CsI photocathode into argon and xenon up to 10 atm. It is demonstrated that the photoelectron extraction efficiency is independent from pressure when

D. S. Covita; C. D. R. Azevedo; C. C. Caldas; J. F. C. A. Veloso

2011-01-01

371

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

372

A nitride based polarization-engineered photocathode for water splitting without a p-type semiconductor.  

PubMed

Photoelectrochemical water splitting is a promising way for hydrogen production with low environmental burden. Although III-nitride semiconductors have potentially favorable properties as water splitting photoelectrodes, they have several limitations for practical use currently. In this study, the concept of a polarization-engineered nitride photocathode for water splitting is proposed to overcome this problem. We observed that the proposed GaN/AlN/GaN structure worked as a photocathode even though it consisted of only n-type III-nitride semiconductors. This polarization-engineered photocathode showed a remarkably stable and relatively high photocurrent since it can avoid the causes of problems from which both n-type and p-type conventional GaN photoelectrodes suffer. PMID:24942671

Nakamura, Akihiro; Fujii, Katsushi; Sugiyama, Masakazu; Nakano, Yoshiaki

2014-08-01

373

GL140L Photocathode Granularity Test for High S/n Stability  

NASA Astrophysics Data System (ADS)

CYCLE 5 calibration of photocathode granularity for domains covered by G140L in SSA and LSA. The signal-to-noise attainable with GHRS in standard ACCUM modes will normally be limited to a few percent by uncalibrated sensitivity variations on the photocathodes. With prior calibration this limitation can be alleviated. This proposal covers only D1 for which the granularity is to be a severe limitation. A test of high S/N calibration stability is made in ECH-A at 1478 A in SSA , a region where independent GTO/OS observations will obtain high S/N (about 500) in a separate star. Region of photocathode ind. meas. for G140M

Schultz, Alfred

1995-07-01

374

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

375

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

376

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

Code of Federal Regulations, 2013 CFR

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

2013-07-01

377

40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.  

Code of Federal Regulations, 2011 CFR

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

2011-07-01

378

40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.  

Code of Federal Regulations, 2010 CFR

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

2009-07-01

379

40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.  

Code of Federal Regulations, 2010 CFR

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

2010-07-01

380

Density functional studies on hydrogen-bonded clusters of hydrogen halides and the interaction on halide anions  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) calculations have been performed to study the structures and stability of X-·(HX)n=2-5 clusters where X = F, Cl, Br at B3LYP/6-311++G** level of theory. The presence of halide ions in these clusters disintegrates the hydrogen halide clusters. All the hydrogen halides are then hydrogen bonded to the centrally placed halide ions, thereby forming multiple hydrogen bonds. The interaction energies have been corrected for the basis set superposition error (BSSE) using Boy's counterpoise correction method. Evidence for the destruction of hydrogen bonds in hydrogen halide clusters due to the presence of halide ions is further obtained from topological analysis and natural bond orbital analysis. The chemical hardness and chemical potential have been calculated for all the anion clusters. The above analysis reveals that hydrogen bonding in these systems is not an essentially electrostatic interaction. The nature of the stabilization interactions operative in these multiple hydrogen-bonded clusters has been explained in terms of many-body contribution to interaction energies. From these studies, an attempt has been made to understand the nature of the molecular properties resulting from different electronegativities of the halogens.

Nirmala, V.; Kolandaivel, P.

381

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

382

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

383

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

384

Studies of a gas-filled ultraviolet detector with a semitransparent photocathode  

NASA Astrophysics Data System (ADS)

A "pumpable tube" has been built in which a semitransparent gold photocathode was exposed to ultraviolet light. It was filled with various pressures of methane, argon and neon, and configured as a triode, a tetrode or a pentode. Detailed results were obtained on photocathode and grid performance at different pressures and voltages. Used as an ultraviolet-sensitive photomultiplier it has reached an overall gas gain of 9.5 × 10 4. This work is part of a progmme to developed a gas-filled photomuliplier which will ampify scintillation pulses in the high magnetic fields of particle physics experiments at colliders.

Edmends, John Stuart; Miller, David John; Barlow, Fred

1987-08-01

385

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

386

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

PubMed

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

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

2014-01-01

387

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

PubMed Central

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

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

2014-01-01

388

Alkali Attack of Coal Gasifier Refractor Linings.  

National Technical Information Service (NTIS)

This investigation examines the alkali-refractory corrosion in non-slagging coal gasifiers and in the non-slagging portions of slagging gasifiers. The alkali species in a typical gasifier atmosphere were calculated using the SOLGASMIX-PV computer program....

J. J. Brown

1988-01-01

389

Alkali–silica reactivity of Japanese rocks  

Microsoft Academic Search

Since 1982, problems relating to the alkali–silica reaction of concrete structures have been occurring in Japan. To identify the aggregates causing the reaction, the reactivity of Japanese rocks and the distribution of reactive rocks in Japan have been studied. Observations of aggregates in concrete structures affected by the alkali–silica reaction, reaction experiments (chemical method: ASTM C 289, mortar bar method:

Yasuhiko Wakizaka

2000-01-01

390

Alkali-silica reactions and silica fume  

Microsoft Academic Search

In Iceland, silica fume has been blended with all Icelandic cement since 1979. Icelandic cement is unique in many ways. Common raw material for cement production is not found; therefore, less appropriate material is utilised for production. As a result, the alkali content of the cement clinker is relatively high. Because alkali-silica reactive aggregates are relatively common and favourable environmental

Gisli Gudmundsson; Hakon Olafsson

1999-01-01

391

Lead halide perovskites and other metal halide complexes as inorganic capping ligands for colloidal nanocrystals.  

PubMed

Lead halide perovskites (CH3NH3PbX3, where X = I, Br) and other metal halide complexes (MXn, where M = Pb, Cd, In, Zn, Fe, Bi, Sb) have been studied as inorganic capping ligands for colloidal nanocrystals. We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV-VI, II-VI, and III-V semiconductor nanocrystals. In particular, we show that the Lewis acid-base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability. High luminescence quantum efficiencies of 20-30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50-65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface. PMID:24746226

Dirin, Dmitry N; Dreyfuss, Sébastien; Bodnarchuk, Maryna I; Nedelcu, Georgian; Papagiorgis, Paris; Itskos, Grigorios; Kovalenko, Maksym V

2014-05-01

392

Optical properties of halide and oxide compounds including the excitonic effects  

NASA Astrophysics Data System (ADS)

We have studied the optical properties of alkali halide and alkaline-earth oxide compounds including the excitonic effects by using the newly developed bootstrap kernel approximation for the exchange-correlation kernel of the Time-Dependent Density Functional Theory (TD-DFT) implemented in Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method in the elk code. The bootstrap calculations are computationally less expensive and give results the same quality as the Bethe-Salpeter equation. We found improved results when compared to normal Density Functional Theory calculations, and observed results are comparable with the experiments. The lower energy peak of imaginary part of dielectric spectra shifts to lower energy regions as we move from MgO to BaO indicating the decrease in the band gap of these compounds from MgO to BaO. In all the studied compounds, the lower energy peak of the imaginary part of dielectric function is due to the transition from halogen p or oxide p states to metal derived s/d states.

Shwetha, G.; Kanchana, V.

2014-04-01

393

Photo-injection of hydrogen in Ag and Cu halides  

NASA Astrophysics Data System (ADS)

For the first time photo-initiated injection of hydrogen was carried out into Ag- and Cu-halides (AgCl, AgJ, Ag4RbI5, CuCl) -- the materials which are very important for investigations of the photographic process. To carry out the photoinjection of hydrogen into the halides a double-layer structure was used. Onto a quartz substrate two thin films were evaporated one after the other: the first one -- a silver or copper halide film, and the second one -- an amorphous WO3 thin film. The film double-layer structure was illuminated by UV-light from the side of the WO3 film. The role of a hydrogen source was played by specially selected organic molecules previously adsorbed on the WO3 surface. Hydrogen atoms detached from the adsorbed molecules under light illumination, diffused first into the WO3 film and then, afterwards, migrated into the halide layer. Hence, illumination of the halide surface was accompanied by injection of hydrogen atoms released from the organic molecules adsorbed on the WO3 surface.

Gavrilyuk, Alexander

1997-02-01

394

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

395

Electromagnetic simulations of photocathode sources using green~s function methods  

Microsoft Academic Search

Summary form only given. The inclusion of space-charge fields into beam simulations of photocathode sources can be challenging since the beam is typically tightly bunched (implying rapid spatial and time variations of the fields) and fields are reflected by surrounding conducting structures, i.e. cathode, cavity walls, and irises. Since a Green's function by definition is generated by a Delta function

M. Hess; Chong Shik Park; Ling Zhu

2006-01-01

396

Effects of Variations in the Photocathode Voltages of Electronic Streak Cameras.  

National Technical Information Service (NTIS)

Electronic streak cameras are used to record subnanosecond data at the Nevada Test Site. It has been found that externally induced variations in the photocathode voltage of the streak tube can produce both temporal and spatial errors on the output image. ...

M. W. Bowers G. L. Biggs J. J. Ronchetto A. T. Teruya

1988-01-01

397

Electric field effects on the quantum efficiency of Cesium-iodide photocathodes in gas media.  

National Technical Information Service (NTIS)

We have measured the quantum efficiency (QE) of Cesium iodide photocathodes as a function of the electric field strength in a parallel-plate geometry, in CH(sub 4), C(sub 2)H(sub 6) AND i-C(sub 4)H(sub 10) both in charge collection and multiplication mode...

A. Breskin R. Chechik A. Buzulutskov D. Vartsky G. Malamud

1993-01-01

398

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

Microsoft Academic Search

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

H Hoedlmoser; Christian Wolfgang Fabjan; E Schyns

2005-01-01

399

Review of the development of cesium iodide photocathodes for application to large RICH detectors  

Microsoft Academic Search

CsI photocathodes were studied in order to evaluate their potential use as large photoconverters in RICH detectors for the PID system at ALICE (LHC in heavy ion collider mode). It has been demonstrated that a quantum efficiency comparable to the reference value obtained on small samples can be obtained on CsI layers evaporated on large pad electrodes operated in a

J. Almeida; A. Amadon; P. Besson; P. Bourgeois; André Braem; Amos Breskin; A F Buzulutskov; R. Chechik; C. Coluzza; A. Di Mauro; J. Friese; J. Homolka; F. Iacovella; A. Ljubicic Jr.; G. Margaritondo; Ph. Mine; E. Nappi; T. dell'Orto; G. Paic; F. Piuz; F. Posa; J. C. Santiard; P. Sartori; S. Sgobba; G. Vasileiadis; T. D. Williams

1995-01-01

400

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

401

TUNING OF THE WAVEGUIDE TO CAVITY COUPLING COEFFICIENT FOR A PWT LINAC AND A PHOTOCATHODE GUN  

Microsoft Academic Search

The waveguide to cavity coupling coefficient ? for two types of accelerating structures: a Plane Wave Transformer (PWT) linac and a 1.6 cell photocathode gun have been tuned to obtain critical coupling in both. Analytical calculations of the dimensions of the slot required for critical coupling have been done using Gao's formulation based on the Bethe's theory for hole coupling.

S. Krishnagopal; Shankar Lal; K. K. Pant; Umesh Kale

402

The role of the adsorbed gases on the photoelectron performance of Mg-based photocathodes  

Microsoft Academic Search

The influence of the adsorbed gases on the photoelectron performance of Mg thin film-based photocathodes was investigated. Mg thin films were deposited on Silicon and Copper substrates by pulsed laser ablation technique. The samples deposited on Silicon substrate were used to deduce the morphology, the structure and the thickness by using different diagnostic techniques. On the contrary, the samples deposited

L. Cultrera; G. Gatti; P. Miglietta; F. Tazzioli; A. Perrone

2008-01-01

403

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

404

Enhanced Raman scattering from cesium suboxides on silver particles and the structure of S-1 photocathodes  

NASA Technical Reports Server (NTRS)

An explanation is given for the results of recent enhanced Raman scattering studies of photomultiplier tubes with S-1 photocathode surfaces which indicated the presence of Cs11O3 but not Cs2O. The reason for the discrepancy between the currently accepted model of the S-1 and this recent result is discussed.

Bates, C. W., Jr.

1984-01-01

405

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

SciTech Connect

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

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

2011-10-01

406

Structure and properties of lanthanide halides  

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

407

Methyl halide emissions from greenhouse-grown mangroves  

NASA Astrophysics Data System (ADS)

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 study. Exponential growth occurred after 180 days. Methyl halide emissions normalized to leaf area were measured throughout the study and varied dramatically. Emission rates normalized to land area (mg m-2 y-1), assuming a LAI = 5, yielded 82 and 29 for CH3Cl, 10 and 1.6 for CH3Br, and 26 and 11 for CH3I, for A. germinans and R. mangle, respectively. From these preliminary determinations, only CH3I emissions emerge as being of possible global atmospheric significance. This study emphasizes the need for field studies of methyl halide emissions from mangrove forests.

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

2007-01-01

408

HOEs recorded in silver halide sensitized gelatin emulsions  

NASA Astrophysics Data System (ADS)

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

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

2000-03-01

409

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

410

Zintl cluster chemistry in the alkali-metal-gallium systems  

SciTech Connect

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

Henning, R.

1998-03-27

411

Alkali-Silica Reactivity: An Overview of Research.  

National Technical Information Service (NTIS)

Part I of this report is a synthesis of our knowledge of mechanisms of damage to concrete by alkali-silica reactivity. Alkali-silica reaction gels are composed of two-component mixtures of alkali-calcium-silicate hydrate and alkali-silica sols of nearly f...

R. Helmuth D. Stark S. Diamond M. Morganville-Regourd

1993-01-01

412

Electrochemical reduction of benzyl halides at a silver electrode  

Microsoft Academic Search

The electrochemical reduction of benzyl halides PhCH2X (X=Cl, Br and I) has been investigated at Ag and glassy carbon (GC) electrodes in CH3CN+0.1M Et4NClO4. At both electrodes reduction of PhCH2X involves irreversible electron transfer concerted with breaking of the carbon–halogen bond. All three halides exhibit a single 2e? reduction peak at GC, whereas up to three peaks can be observed

Abdirisak A. Isse; Alessio De Giusti; Armando Gennaro; Luigi Falciola; Patrizia R. Mussini

2006-01-01

413

Alkali Silicate Vehicle Forms Durable, Fireproof Paint  

NASA Technical Reports Server (NTRS)

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

Schutt, John B.; Seindenberg, Benjamin

1964-01-01

414

Diode pumped alkali vapor fiber laser  

DOEpatents

A method and apparatus is provided for producing near-diffraction-limited laser light, or amplifying near-diffraction-limited light, in diode pumped alkali vapor photonic-band-gap fiber lasers or amplifiers. Laser light is both substantially generated and propagated in an alkali gas instead of a solid, allowing the nonlinear and damage limitations of conventional solid core fibers to be circumvented. Alkali vapor is introduced into the center hole of a photonic-band-gap fiber, which can then be pumped with light from a pump laser and operated as an oscillator with a seed beam, or can be configured as an amplifier.

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

2006-07-26

415

Diode pumped alkali vapor fiber laser  

DOEpatents

A method and apparatus is provided for producing near-diffraction-limited laser light, or amplifying near-diffraction-limited light, in diode pumped alkali vapor photonic-band-gap fiber lasers or amplifiers. Laser light is both substantially generated and propagated in an alkali gas instead of a solid, allowing the nonlinear and damage limitations of conventional solid core fibers to be circumvented. Alkali vapor is introduced into the center hole of a photonic-band-gap fiber, which can then be pumped with light from a pump laser and operated as an oscillator with a seed beam, or can be configured as an amplifier.

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

2007-10-23

416

Alkali metal for ultraviolet band-pass filter  

NASA Technical Reports Server (NTRS)

An alkali metal filter having a layer of metallic bismuth deposited onto the alkali metal is provided. The metallic bismuth acts to stabilize the surface of the alkali metal to prevent substantial surface migration from occurring on the alkali metal, which may degrade optical characteristics of the filter. To this end, a layer of metallic bismuth is deposited by vapor deposition over the alkali metal to a depth of approximately 5 to 10 A. A complete alkali metal filter is described along with a method for fabricating the alkali metal filter.

Mardesich, Nick (inventor); Fraschetti, George A. (inventor); Mccann, Timothy A. (inventor); Mayall, Sherwood D. (inventor); Dunn, Donald E. (inventor); Trauger, John T. (inventor)

1993-01-01

417

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

418

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

419

Spectral sensitivity calibration of Au and CsI photocathodes of high speed x-ray scanning camera  

NASA Astrophysics Data System (ADS)

High speed X-ray scanning camera (XSC) is an extra precision temporal and spatial diagnostic instrument in the inertial confinement fusion (ICF) experiment. In order to quantitatively analyze the measurement results, the spectral sensitivity of XSC, which depends on the response of the transmission photocathode, is necessary to be absolutely calibrated. A method of measuring the spectral response of Au and CsI transmission photocathodes of XSC is described. Based on Beijing Synchrotron Radiation Facility (BSRF), Au and CsI transmission photocathodes with slits are calibrated in the photon energy range of 60 eV-1500 eV and 2.1 keV-5.5 keV. Utilizing the quantum efficiency of the standard detector AXUV-100, the calibrated quantum efficiency of Au and CsI photocathodes are derived. The calibration data agree well with the photoelectric emission theory of Henke.

Yuan, Zheng; Zeng, Peng; Deng, Bo; Chen, Tao; Cao, Zhurong; Liu, Shenye; Yuan, Yongteng

2012-10-01

420

The characterization of X-ray photocathodes in the 0.1-10-keV photon energy region  

NASA Astrophysics Data System (ADS)

A method and an instrument are described for the measurement of the absolute quantum yield for front-surface and transmission photocathodes in the 0.1-10-keV photon energy region. Total and secondary electron photoemission yields have been measured for Al, Au, CuI, and CsI photocathodes for the absolute calibration of the X-ray diode detectors and for the X-ray streak cameras. The relative secondary electron yields have also been measured for the same photocathodes by high resolution electron spectroscopy of the secondary electron energy distributions. Cs I is shown to be an effective photocathode for sensitive, time-resolved spectroscopy into the picosecond region. A simple model for X-ray photoemission is described which leads to semiempirical equations for front and back surface secondary electron photoemission; model predictions are consistent with the experiment.

Henke, B. L.; Knauer, J. P.; Premaratne, K.

1981-03-01

421

Milk Alkali and Hydrochlorothiazide: A Case Report  

PubMed Central

Hypercalcemia is a relatively common clinical problem in both outpatient and inpatient settings. Primary pathophysiology is the entry of calcium that exceeds its excretion into urine or deposition in bone into circulation. Among a wide array of causes of hypercalcemia, hyperparathyroidism and malignancy are the most common, accounting for greater than 90 percent of cases. Concordantly, there has been a resurgence of milk-alkali syndrome associated with the ingestion of large amounts of calcium and absorbable alkali, making it the third leading cause of hypercalcemia (Beall and Scofield, 1995 and Picolos et al., 2005). This paper centers on a case of over-the-counter calcium and alkali ingestion for acid reflux leading to milk alkali with concordant use of thiazide diuretic for hypertension.

Parvez, Babar; Emuwa, Chinenye; Faulkner, Marquetta L.; Murray, John J.

2011-01-01

422

Alkali Metal Handling Practices at NASA MSFC  

NASA Technical Reports Server (NTRS)

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

Salvail, Patrick G.; Carter, Robert R.

2002-01-01

423

Improved alkali-metal/silicate binders  

NASA Technical Reports Server (NTRS)

Family of inorganic binders utilizes potassium or sodium oxide/silicate dispersion and employs high mole ratio of silicon dioxide to alkali-metal binder. Binders are stable, inexpensive, extremely water resistant, and easy to apply.

Schutt, J.

1978-01-01

424

Eliminating or Minimizing Alkali-Silica Reactivity.  

National Technical Information Service (NTIS)

This report describes investigations into various aspects of alkali silica reactivity (ASR) as it affects performance of highway structures. Emphasis was placed on practical needs of the concrete engineer, primarily with respect to improving means to eval...

B. Morgan D. Stark P. Okamoto S. Diamond

1993-01-01

425

Alkali-Silica Reaction in Concrete.  

National Technical Information Service (NTIS)

Reaction in concrete between alkalies from the cement and reactive silica in the aggregate may cause expansion and cracking, and occasionally may cause significant weakening of the structure. The objective of this program is to determine whether there is ...

L. J. Struble

1985-01-01

426

Experimental Study on Alkali Metal Thermoelectric Converter.  

National Technical Information Service (NTIS)

The alkali metal thermoelectric converter (AMTEC) utilizing the sodium ion conducting beta-alumina is a device to convert heat energy to electric energy directly. It is characterized by high conversion efficiencies, high power densities, no moving parts a...

T. Masuda K. Tanaka T. Honda A. Negishi

1989-01-01

427

Gaseous Ternary Compounds of the Alkali Metals.  

National Technical Information Service (NTIS)

An extensive summary is given of the existing information on gaseous ternary salts of the alkali metals. Three groups of compounds are considered: (1) salts of monobasic acids or pseudohalides (e.g., hydroxides, metaborates, nitrates, perrhenates); (2) sa...

A. Buchler J. Berkowitz-Mattuck

1967-01-01

428

Alkali-metal intercalation in carbon nanotubes  

NASA Astrophysics Data System (ADS)

We report on successful intercalation of multiwall (MWNT) and single wall (SWNT) carbon nanotubes with alkali metals by electrochemical and vapor phase reactions. A LiC10 compound was produced by full electrochemical reduction of MWNT. KC8 and CsC8-MWNT first stage derivatives were synthesized in conditions of alkali vapor saturation. Their identity periods and the 2×2 R 0° alkali superlattice are comparable to their parent graphite compounds. The dysonian shape of KC8 EPR line and the temperature-independent Pauli susceptibility are both characteristic of a metallic behavior, which was confirmed by 13C NMR anisotropic shifts. Exposure of SWNT bundles to alkali vapor led to an increase of the pristine triangular lattice from 1.67 nm to 1.85 nm and 1.87 nm for potassium and rubidium, respectively.

Béguin, F.; Duclaux, L.; Méténier, K.; Frackowiak, E.; Salvetat, J. P.; Conard, J.; Bonnamy, S.; Lauginie, P.

1999-09-01

429

Performance of dual phase XeTPC with CsI photocathode and PMTs readout for the scintillation light  

Microsoft Academic Search

We have tested a dual phase xenon time projection chamber (TPC) consisting of a reflective cesium iodide photocathode and an array of seven PMTs for scintillation light readout. Present results show that 19% quantum efficiency (QE) of CsI photocathode can be achieved at 3 kV\\/cm. The dependence of quantum efficiency as a function of different electric field was measured and

E. Aprile; K. L. Giboni; S. Kamat; P. Majewski; K. Ni; B. K. Singh; M. Yamashita

2005-01-01

430

Photoelectron extraction efficiency from cesium iodide photocathodes in a pressurized atmosphere of argon and xenon up to 10 bar  

NASA Astrophysics Data System (ADS)

Photoelectron extraction efficiency is a key parameter in gaseous detectors design requiring CsI photocathodes, particularly in pressurized applications for rare event experiments. Within this work we report on our measurements of the photoelectron extraction efficiency from a CsI photocathode into argon and xenon up to 10 atm. It is demonstrated that the photoelectron extraction efficiency is independent from pressure when scaling the electric field accordingly. This measurement provides experimental validation to the Monte Carlo predictions.

Covita, D. S.; Azevedo, C. D. R.; Caldas, C. C.; Veloso, J. F. C. A.

2011-07-01

431

Observation of Cherenkov rings using a low-pressure parallel-plate chamber and a solid cesium-iodide photocathode  

Microsoft Academic Search

We have observed Cherenkov rings from minimum-ionizing particles using a low-pressure, parallel-plate pad-chamber with a cesium-iodide solid photocathode. This detector is blind to minimum-ionizing particles, and sensitive to Cherenkov photons of wavelengths 170-210 nm. An average of 5 photoelectrons per Cherenkov ring were detected using a 2-cm-thick radiator of liquid C6F14. This paper reports on the chamber construction, photocathode preparation

N. S. Lockyer; J. E. Millan; C. Lu; K. T. McDonald; A. Lopez

1993-01-01

432

Observation of Cherenkov rings using a low-pressure parallel-plate chamber and a solid cesium-iodide photocathode  

NASA Astrophysics Data System (ADS)

We have observed Cherenkov rings from minimum-ionizing particles using a low-pressure, parallel-plate pad-chamber with a cesium-iodide solid photocathode. This detector is blind to minimum-ionizing particles, and sensitive to Cherenkov photons of wavelengths 170-210 nm. An average of 5 photoelectrons per Cherenkov ring were detected using a 2-cm-thick radiator of liquid C 6F 14. This paper reports on the chamber construction, photocathode preparation and testbeam results.

Lockyer, N. S.; Millan, J. E.; Lu, C.; McDonald, K. T.; Lopez, A.

1993-07-01

433

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

434

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

435

Alkali metal intercalates of molybdenum disulfide.  

NASA Technical Reports Server (NTRS)

Study of some of the physicochemical properties of compounds obtained by subjecting natural molybdenite and single crystals of molybdenum disulfide grown by chemical vapor transport to intercalation with the alkali group of metals (Li, Na, K, Rb, and Cs) by means of the liquid ammonia technique. Reported data and results include: (1) the intercalation of the entire alkali metal group, (2) stoichiometries and X-ray data on all of the compounds, and (3) superconductivity data for all the intercalation compounds.

Somoano, R. B.; Hadek, V.; Rembaum, A.

1973-01-01

436

CO2 electrochemical reduction via adsorbed halide anions  

NASA Astrophysics Data System (ADS)

The electrochemical reduction of CO2 was studied utilizing halide ions as electrolytes, specifically, aqueous solutions of KCl, KBr, KI. Electrochemical experiments were carried out in a laboratory-made, divided H-type cell. The working electrode was a copper mesh, while the counter and reference electrodes were a Pt wire and an Ag/AgCl electrode, respectively. The results of our work suggest a reaction mechanism for the electrochemical reduction of CO2 where the presence of Cu-X as the catalytic layer facilitates the electron transfer from the electrode to CO2. Electron-transfer to CO2 may occur via the X- ad(Br-, Cl-, I-)-C bond, which is formed by the electron flow from the specifically adsorbed halide anion to the vacant orbital of CO2. The stronger the adsorption of the halide anion to the electrode, the more strongly CO2 is restrained, resulting in higher CO2 reduction current. Furthermore, it is suggested that specifically adsorbed halide anions could suppress the adsorption of protons; leading to a higher hydrogen overvoltage. These effects may synergistically mitigate the over potential necessary for CO2 reduction, and thus increase the rate of electrochemical CO2 reduction.

Ogura, Kotaro; Salazar-Villalpando, Maria D.

2011-01-01

437

Electroluminescence from polymeric halides subjected to an AC voltage  

Microsoft Academic Search

Electroluminescence (EL) from polymeric halides and hydrocarbons has been investigated under voltages to clarify the effect of halogens in the polymers on the EL. We used polymer films with semi-transparent gold electrodes, namely, polytetrafluoroethylene (PTFE), polyvinylchloride (PVC), low-density polyethylene (LDPE), and polypropylene (PP). The light emission from PVC and PTFE started from lower fields and had a larger light intensity

T. Mizuno; Y. S. Liu; W. Shionoya; H. Miyata; A. Yokoyama; K. Yasuoka; S. Ishii

1996-01-01

438

Students' understanding of alkyl halide reactions in undergraduate organic chemistry  

NASA Astrophysics Data System (ADS)

Organic chemistry is an essential subject for many undergraduate students completing degrees in science, engineering, and pre-professional programs. However, students often struggle with the concepts and skills required to successfully solve organic chemistry exercises. Since alkyl halides are traditionally the first functional group that is studied in undergraduate organic chemistry courses, establishing a robust understanding of the concepts and reactions related to them can be beneficial in assuring students' success in organic chemistry courses. Therefore, the purpose of this study was to elucidate and describe students' understanding of alkyl halide reactions in an undergraduate organic chemistry course. Participants were interviewed using a think-aloud protocol in which they were given a set of exercises dealing with reactions and mechanisms of alkyl halide molecules in order to shed light on the students' understanding of these reactions and elucidate any gaps in understanding and incorrect warrants that may be present. These interviews were transcribed and analyzed using qualitative inquiry approaches. In general, the findings from this study show that the students exhibited gaps in understanding and incorrect warrants dealing with: (1) classifying substances as bases and/or nucleophiles, (2) assessing the basic or nucleophilic strength of substances, (3) accurately describing the electron movement of the steps that take place during alkyl halide reaction mechanisms, and (4) assessing the viability of their proposed reactive intermediates and breakage of covalent bonds. In addition, implications for teaching and future research are proposed.

Cruz-Ramirez de Arellano, Daniel

439

Applications of AMS to electronic and silver halide imaging research  

Microsoft Academic Search

A collaborative program is underway between the University of Rochester's Nuclear Structure Research Laboratory (NSRL) and the Eastman Kodak Company to apply AMS to the detection of trace elements in silver halides and in silicon semiconductor devices. In the manufacture of both it is important to understand the role played by dopants and impurities under various processing conditions. For example,

H. E. Gove; P. W. Kubik; P. Sharma; S. Datar; U. Fehn; T. Z. Hossain; J. Koffer; J. P. Lavine; S.-T. Lee; D. Elmore

1990-01-01

440

Metal halide lamp with improved red rendition and CRI  

US Patent & Trademark Office Database

A ceramic metal halide arc tube is surrounded by a protective neodymium sleeve supported by a metal frame. As a result of the neodymium sleeve, the lamp is observed to have improved transmission of red color and to exhibit a CRI of at least about 90.

2005-10-25

441

Structure and optical properties of high light output halide scintillators  

SciTech Connect

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

Singh, David J [ORNL

2010-01-01

442

Studies of some reactions between uranyl halides and hydrocarbyl anions.  

National Technical Information Service (NTIS)

Reactions of uranyl halides (UO sub 2 X sub 2) with hydrocarbyl anions of the type (R=Ar sup - or Ar sub n H sub 3 sub - sub n C sup -), result in the formation of thermally unstable intermediates ((UO sub 2 R sub 2 X sub 2) sup - sup 2) which undergo the...

A. Alarouri

1987-01-01

443

On the Boiling Points of the Alkyl Halides.  

ERIC Educational Resources Information Center

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

Correia, John

1988-01-01

444

Metal halide lamps in the international space station ISS  

Microsoft Academic Search

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

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

2006-01-01

445

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

446

Iron-catalyzed Suzuki-Miyaura coupling of alkyl halides.  

PubMed

In the presence of novel iron(II) chloride-diphosphine complexes and magnesium bromide, lithium arylborates react with primary and secondary alkyl halides to give the corresponding coupling products in good to excellent yields. High functional group compatibility is also demonstrated in the reactions of substrates possessing reactive substituents, such as alkoxycarbonyl, cyano, and carbonyl groups. PMID:20681696

Hatakeyama, Takuji; Hashimoto, Toru; Kondo, Yoshiyuki; Fujiwara, Yuichi; Seike, Hirofumi; Takaya, Hikaru; Tamada, Yoshinori; Ono, Teruo; Nakamura, Masaharu

2010-08-11

447

Silver halide noise gratings recorded in dichromated gelatin  

Microsoft Academic Search

It is shown that high efficiency noise gratings may be recorded in dichromated gelatin when a single beam traverses a silver halide plate held in contact with a dichromated gelatin plate. A replay beam, in the same direction as the recording beam, will then reconstruct the noise radiation and will itself be depleted. Owing to swelling of the dichromated gelatin

L. Solymar; J. C. W. Newell

1989-01-01

448

Non linear recording in silver halide planar volume holograms  

Microsoft Academic Search

A series of bromine-vapour bleached, planar, volume holograms were formed in silver halide emulsion. The holograms were characterised by measuring the variation in intensity of the transmitted replaying beam with angles at several wavelengths. The results were investigated using coupled-wave theory, allowing for the existence of grating harmonics and higher diffraction orders. The effects of first, second and third grating

C. W. Slinger; R. R. A. Syms; L. Solymar

1985-01-01

449

Analysis and design of metal halide lamp igniter  

Microsoft Academic Search

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

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

2001-01-01

450

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

Code of Federal Regulations, 2010 CFR

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

2009-07-01

451

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

Code of Federal Regulations, 2010 CFR

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

2009-07-01

452

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

Code of Federal Regulations, 2013 CFR

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

2013-07-01

453

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

Code of Federal Regulations, 2010 CFR

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

2010-07-01

454

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

Code of Federal Regulations, 2010 CFR

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

2010-07-01

455

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

PubMed

A high-voltage dc photocathode electron gun was successfully conditioned up to a voltage of 550 kV and a long-time holding test for 8 h was demonstrated at an acceleration voltage of 500 kV. The dc photocathode electron gun is designed for future light sources based on energy-recovery linac and consists of a Cockcroft-Walton generator, a segmented cylindrical ceramic insulator, guard-ring electrodes, a support-rod electrode, a vacuum chamber, and a pressurized insulating gas tank. The segmented cylindrical ceramic insulator and the guard-ring electrodes were utilized to prevent any damage to the insulator from electrons emitted by the support-rod electrode. PMID:20370167

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

2010-03-01

456

Electric field effects on the quantum efficiency of Cesium-iodide photocathodes in gas media  

NASA Astrophysics Data System (ADS)

We have measured the quantum efficiency (QE) of Cesium iodide photocathodes as a function of the electric field strength in a parallel-plate geometry, in CH4, C2H6, and i-C4H10 both in charge collection and multiplication modes. It was found that in the collection mode the QE value in gases is lower compared to that of vacuum and is independent on the field; in gas media the QE starts to increase at the transition between collection and multiplication modes and reaches the vacuum value at high gas gain. We explain this effect by a decrease of the electron-molecule elastic backscattering while entering the multiplication mode. We conclude that the electric field effects observed here would also apply for other photocathodes and gas mixtures. An enhancement of the QE after micro discharges was observed and is discussed in detail.

Breskin, A.; Buzulutskov, A.; Chechik, R.; Vartsky, D.; Malamud, G.; Mine, P.

1993-12-01

457

Fast RICH detector with a cesium iodide photocathode at atmospheric pressure  

NASA Astrophysics Data System (ADS)

CsI photocathodes of 30 × 30 cm 2 size have been operated in a fast RICH detector composed of a NaF radiator and a multiwire proportional chamber with a cathode pad readout. Results are presented from tests with a 3 {GeV}/{c} proton beam. A Cherenkov angular resolution of 8 mrad is obtained by detecting a mean of 8 photoelectrons per ring. Methods are described for counting the Cherenkov photons and evaluating the differential quantum efficiency of the CsI photocathode. The results obtained with photons impinging at a large angle on the CsI layer are presented and discussed in comparison with higher quantum efficiencies observed under different experimental conditions.

Braem, A.; DiMauro, A.; Nappi, E.; Ljubicic, A.; Paic, G.; Piuz, F.; Posa, F.; Ribeiro, R. S.; Scognetti, T.; Williams, T. D.

1994-04-01

458

Use of MgF2 and LiF photocathodes in the extreme ultraviolet.  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

459

Thermal emittance and response time measurements of negative electron affinity photocathodes  

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

460

The optimal thickness of a transmission-mode GaN photocathode  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

461

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

NASA Astrophysics Data System (ADS)

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

Nagai, Ryoji; Hajima, Ryoichi; Nishimori, Nobuyuki

2012-12-01

462

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

463

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

464

Photo-cathode preparation system of the A0 photo-injector  

SciTech Connect

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

Moyses Kuchnir et al.

2002-08-23

465

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

SciTech Connect

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

Ben-Zvi,I.

2008-11-17

466

Robust CsBr/Cu Photocathodes for the Linac Coherent Light Source  

SciTech Connect

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

Maldonado, Juan R.; /Stanford U., Phys. Dept.; Liu, Zhi; Dowell, D.H.; Kirby, Robert E.; Sun, Yun; Pianetta, Piero; /SLAC; Pease, Fabian; /Stanford U., Phys. Dept.

2011-06-21

467

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

468

Intrinsic Electron Beam Emittance from Metal Photocathodes: The Effect of the Electron Effective Mass  

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

469

Electric field effects on the quantum efficiency of Cesium-iodide photocathodes in gas media  

Microsoft Academic Search

We have measured the quantum efficiency (QE) of Cesium iodide photocathodes as a function of the electric field strength in a parallel-plate geometry, in CH4, C2H6, and i-C4H10 both in charge collection and multiplication modes. It was found that in the collection mode the QE value in gases is lower compared to that of vacuum and is independent on the

A. Breskin; A. Buzulutskov; R. Chechik; D. Vartsky; G. Malamud; P. Mine

1993-01-01

470

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

Microsoft Academic Search

The color dependence of the measured decline of the on-orbit sensitivity of the FUV channel of the HST Cosmic Origins Spectrograph (HST-COS) indicated the principal loss mechanism to be degradation of the cesium iodide (CsI) photocathode of the open-faced FUV detector. A possible cause of this degradation is contamination by atomic oxygen (AO), prompting an investigation of the interaction of

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

2011-01-01

471

Fast RICH detector with a cesium iodide photocathode at atmospheric pressure  

Microsoft Academic Search

CsI photocathodes of 30 × 30 cm2 size have been operated in a fast RICH detector composed of a NaF radiator and a multiwire proportional chamber with a cathode pad readout. Results are presented from tests with a 3 GeV\\/c proton beam. A Cherenkov angular resolution of 8 mrad is obtained by detecting a mean of 8 photoelectrons per ring.

André Braem; A. Dimauro; E. Nappi; A LJUBICICJR; G. Paic; François Piuz; F. Posa; R. S. Ribeiro; T. Scognetti; T. D. Williams

1994-01-01

472

Influence of humidity on the photoemission properties and surface morphology of cesium iodide photocathode  

Microsoft Academic Search

We report on the photoemission properties of 500nm thick CsI films photocathodes. The surface morphology and electron diffraction pattern of 500nm thick “as-deposited” CsI and further “aged” CsI by exposing it to the humid air were investigated by means of transmission electron microscopy. It is observed that photoemission properties are degraded after long term exposure in humid air however there

Triloki; B. Dutta; B. K. Singh

473

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

Microsoft Academic Search

Hybrid photon detectors are one of the few low light level sensors that can provide an excellent single and multiple photoelectron amplitude resolution. The recently developed hybrid photon detectors for the Major Atmospheric Gamma-Imaging Cherenkov (MAGIC) telescope project with an 18-mm-diameter GaAsP photocathode (the Hamamatsu R9792U-40) have a peak quantum efficiency of more than 50% and a pulse width of

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

2009-01-01

474

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

475

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

476

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

Microsoft Academic Search

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

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

2000-01-01

477

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

478

CHARACTARIZATION OF ELECTRON BEAM FROM A Mg PHOTOCATHODE RF GUN SYSTEM  

Microsoft Academic Search

Characterization of a photo-electron beam generated from a magnesium photo-cathode rf gun system at Waseda University has been developed. The vertical emittance of the electron beam was measured using slit scan technique. As a result, the vertical emittance was measured to vary from 9 mm mrad to 15 mm mrad at the bunch charge of 0.75 nC as the solenoid

R. Kuroda; Y. Ham; S. Kasahiwagi; H. Kawai; F. Nagasawa

479

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

Microsoft Academic Search

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 ~10 MV\\/m, two solenoids in the 500 kV region and an achromatic, non-isochronous injection transport

H. Liu; D. Kehne; S. Benson; J. Bisognano; L. Cardman; F. Dylla; D. Engwall; J. Fugitt; K. Jordan; G. Neil; D. Neuffer; C. Sinclair; M. Wiseman; B. Yunn

1995-01-01

480

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

Microsoft Academic Search

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 Oâ. The reaction of the sodium dimers with oxygen molecules is described in Chapter 2. Two

Hou

1995-01-01

481

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