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Sample records for metastable argon atoms

  1. Low energy collisions of spin-polarized metastable argon atoms with ground state argon atoms

    Science.gov (United States)

    Taillandier-Loize, T.; Perales, F.; Baudon, J.; Hamamda, M.; Bocvarski, V.; Ducloy, M.; Correia, F.; Fabre, N.; Dutier, G.

    2018-04-01

    The collision between a spin-polarized metastable argon atom in Ar* (3p54s, 3P2, M = +2) state slightly decelerated by the Zeeman slower-laser technique and a co-propagating thermal ground state argon atom Ar (3p6, 1S0), both merged from the same supersonic beam, but coming through adjacent slots of a rotating disk, is investigated at the center of mass energies ranging from 1 to 10 meV. The duration of the laser pulse synchronised with the disk allows the tuning of the relative velocity and thus the collision energy. At these sub-thermal energies, the ‘resonant metastability transfer’ signal is too small to be evidenced. The explored energy range requires using indiscernibility amplitudes for identical isotopes to have a correct interpretation of the experimental results. Nevertheless, excitation transfers are expected to increase significantly at much lower energies as suggested by previous theoretical predictions of potentials 2g(3P2) and 2u(3P2). Limits at ultra-low collisional energies of the order of 1 mK (0.086 μeV) or less, where gigantic elastic cross sections are expected, will also be discussed. The experimental method is versatile and could be applied using different isotopes of Argon like 36Ar combined with 40Ar, as well as other rare gases among which Krypton should be of great interest thanks to the available numerous isotopes present in a natural gas mixture.

  2. The measurement of argon metastable atoms in the barrier discharge plasma

    Science.gov (United States)

    Ghildina, Anna R.; Mikheyev, Pavel Anatolyevich; Chernyshov, Aleksandr Konstantinovich; Lunev, Nikolai Nikolaevich; Azyazov, Valeriy Nikolaevich

    2018-04-01

    The mandatory condition for efficient operation of an optically-pumped all-rare-gas laser (OPRGL) is the presence of rare gas metastable atoms in the discharge plasma with number density of the order of 1012-1013 cm-3. This requirement mainly depends on the choice of a discharge system. In this study the number density values of argon metastable atoms were obtained in the condition of the dielectric-barrier discharge (DBD) at an atmospheric pressure.

  3. Role of metastable atoms in argon-diluted silane Rf plasmas

    International Nuclear Information System (INIS)

    Sansonnens, L.; Howling, A.A.; Hollenstein, C.; Dorier, J.L.; Kroll, U.

    1994-01-01

    The evolution of the argon metastable density has been studied by absorption spectroscopy in power-modulated plasmas of argon and a mixture of 4% silane in argon. A small concentration of silane suppresses the argon metastable density by molecular quenching. This molecular quenching adds to the electronic collisional dissociation to increase the silane dissociation rate as compared with pure silane plasmas. Using time-resolved emission spectroscopy, the role of metastables in excitation to the argon 2P 2 state has been determined in comparison with production from the ground state. In silane plasmas, emission from SiH* is due essentially to electron impact dissociation of silane, whereas in 4% silane-in-argon plasmas, emission from SiH* seems to be due to electron impact excitation of the SiH ground state. These studies demonstrate that argon is not simply a buffer gas but has an influence on the dissociation rate in the plasma-assisted deposition of amorphous silicon using argon-diluted silane plasmas. (author) 7 figs., 30 refs

  4. Metastable argon atom density in complex argon/acetylene plasmas determined by means of optical absorption and emission spectroscopy

    International Nuclear Information System (INIS)

    Sushkov, Vladimir; Herrendorf, Ann-Pierra; Hippler, Rainer

    2016-01-01

    Optical emission and absorption spectroscopy has been utilized to investigate the instability of acetylene-containing dusty plasmas induced by growing nano-particles. The density of Ar(1s 5 ) metastable atoms was derived by two methods: tunable diode laser absorption spectroscopy and with the help of the branching ratio method of emitted spectral lines. Results of the two techniques agree well with each other. The density of Ar(1s 3 ) metastable atoms was also measured by means of optical emission spectroscopy. The observed growth instability leads to pronounced temporal variations of the metastable and other excited state densities. An analysis of optical line ratios provides evidence for a depletion of free electrons during the growth cycle but no indication for electron temperature variations. (paper)

  5. Trapping cold ground state argon atoms.

    Science.gov (United States)

    Edmunds, P D; Barker, P F

    2014-10-31

    We trap cold, ground state argon atoms in a deep optical dipole trap produced by a buildup cavity. The atoms, which are a general source for the sympathetic cooling of molecules, are loaded in the trap by quenching them from a cloud of laser-cooled metastable argon atoms. Although the ground state atoms cannot be directly probed, we detect them by observing the collisional loss of cotrapped metastable argon atoms and determine an elastic cross section. Using a type of parametric loss spectroscopy we also determine the polarizability of the metastable 4s[3/2](2) state to be (7.3±1.1)×10(-39)  C m(2)/V. Finally, Penning and associative losses of metastable atoms in the absence of light assisted collisions, are determined to be (3.3±0.8)×10(-10)  cm(3) s(-1).

  6. Kinetics of Ar+*(2G9/2) metastable ions and transport of argon ions in ICP reactor

    NARCIS (Netherlands)

    Sadeghi, N.; Derouard, J.; Grift, van de M.; Kroesen, G.M.W.; Hoog, de F.J.; Tachibana, K.; Watanabe, Y.

    1997-01-01

    The decay time of the argon Ar~~(2G912) metastable ions was measured in the afterglow of a low pressure pulsed helicon reactor. From the argon pressure and electron density dependence of this decay time, rate coefficients for quenching of these ions by argon atoms and by plasma electrons have been

  7. Atom diffraction with a 'natural' metastable atom nozzle beam

    International Nuclear Information System (INIS)

    Karam, J-C; Wipf, N; Grucker, J; Perales, F; Boustimi, M; Vassilev, G; Bocvarski, V; Mainos, C; Baudon, J; Robert, J

    2005-01-01

    The resonant metastability-exchange process is used to obtain a metastable atom beam with intrinsic properties close to those of a ground-state atom nozzle beam (small angular aperture, narrow velocity distribution). The estimated effective source diameter (15 μm) is small enough to provide at a distance of 597 mm a transverse coherence radius of about 873 nm for argon, 1236 nm for neon and 1660 nm for helium. It is demonstrated both by experiment and numerical calculations with He*, Ne* and Ar* metastable atoms, that this beam gives rise to diffraction effects on the transmitted angular pattern of a silicon-nitride nano-slit grating (period 100 nm). Observed patterns are in good agreement with previous measurements with He* and Ne* metastable atoms. For argon, a calculation taking into account the angular aperture of the beam (0.35 mrad) and the effect of the van der Waals interaction-the van der Waals constant C 3 1.83 +0.1 -0.15 au being derived from spectroscopic data-leads to a good agreement with experiment

  8. Trapping cold ground state argon atoms for sympathetic cooling of molecules

    OpenAIRE

    Edmunds, P. D.; Barker, P. F.

    2014-01-01

    We trap cold, ground-state, argon atoms in a deep optical dipole trap produced by a build-up cavity. The atoms, which are a general source for the sympathetic cooling of molecules, are loaded in the trap by quenching them from a cloud of laser-cooled metastable argon atoms. Although the ground state atoms cannot be directly probed, we detect them by observing the collisional loss of co-trapped metastable argon atoms using a new type of parametric loss spectroscopy. Using this technique we als...

  9. Localization of metastable atom beams with optical standing waves: nanolithography at the heisenberg limit

    Science.gov (United States)

    Johnson; Thywissen; Dekker; Berggren; Chu; Younkin; Prentiss

    1998-06-05

    The spatially dependent de-excitation of a beam of metastable argon atoms, traveling through an optical standing wave, produced a periodic array of localized metastable atoms with position and momentum spreads approaching the limit stated by the Heisenberg uncertainty principle. Silicon and silicon dioxide substrates placed in the path of the atom beam were patterned by the metastable atoms. The de-excitation of metastable atoms upon collision with the surface promoted the deposition of a carbonaceous film from a vapor-phase hydrocarbon precursor. The resulting patterns were imaged both directly and after chemical etching. Thus, quantum-mechanical steady-state atom distributions can be used for sub-0.1-micrometer lithography.

  10. Coherent and non coherent atom optics experiment with an ultra-narrow beam of metastable rare gas atoms

    International Nuclear Information System (INIS)

    Grucker, J.

    2007-12-01

    In this thesis, we present a new type of atomic source: an ultra-narrow beam of metastable atoms produced by resonant metastability exchange inside a supersonic beam of rare gas atoms. We used the coherence properties of this beam to observe the diffraction of metastable helium, argon and neon atoms by a nano-transmission grating and by micro-reflection-gratings. Then, we evidenced transitions between Zeeman sublevels of neon metastable 3 P 2 state due to the quadrupolar part of Van der Waals potential. After we showed experimental proofs of the observation of this phenomenon, we calculated the transition probabilities in the Landau - Zener model. We discussed the interest of Van der Waals - Zeeman transitions for atom interferometry. Last, we described the Zeeman cooling of the supersonic metastable argon beam ( 3 P 2 ). We have succeeded in slowing down atoms to speeds below 100 m/s. We gave experimental details and showed the first time-of-flight measurements of slowed atoms

  11. Collisional interaction between metastable neon atoms

    Energy Technology Data Exchange (ETDEWEB)

    Drunen, Wouter Johannes van

    2008-07-07

    In this thesis, the study of cold gases of neon atoms in different metastable states is described. It contains measurements of the collisional parameters for both the 3s[3/2]{sub 2} and the 3s'[1/2]{sub 0} metastable state and the dependence of the inelastic loss on external fields. Furthermore, the investigation of frequency dependent laser-induced collisions, and the possibility to excite photoassociation resonances is presented. For the measurements described here, neon atoms have been confined in a magnetooptical trap, in a magnetostatic trap, or in an optical dipole trap, respectively. By laser cooling inside the magnetic trap, atomic samples with more than 95 percent occupation of the magnetic substate m{sub J} = +2 could be prepared. They have a typical temperature of 0.5 mK, central densities up to 10{sup 11} cm{sup -3}, and a central phase-space density of up to 2.2.10{sup -7}. After loading the optical dipole trap from the magnetic trap, 2.5.10{sup 6} atoms with typical temperatures of 0.1 mK, and central densities up to 5.10{sup 10} cm{sup -3} were trapped. By evaporative cooling of the atoms in the magnetic trap we could increase the phase-space density by a factor of 200 to 5.10{sup -5}. Investigating the frequency dependence of laser-induced collisions did not reveal an experimental signature for the excitation of photoassociation resonances. For the {sup 3}D{sub 3} line a frequency dependence of laser enhanced Penning ionization was observed. Measurement of the two-body loss coefficient as function of the magnetic field showed a field dependence of the inelastic loss. These losses increase towards both small and large offset fields. The implementation of an optical dipole trap allowed us to trap the {sup 3}P{sub 0} metastable state. From the trap loss measurements we determined the two-body loss coefficient of the {sup 3}P{sub 0} metastable state for both bosonic isotopes {sup 20}Ne and {sup 22}Ne. For {sup 20}Ne we obtained {beta}=6{sup +5}{sub

  12. Collisional interaction between metastable neon atoms

    International Nuclear Information System (INIS)

    Drunen, Wouter Johannes van

    2008-01-01

    In this thesis, the study of cold gases of neon atoms in different metastable states is described. It contains measurements of the collisional parameters for both the 3s[3/2] 2 and the 3s'[1/2] 0 metastable state and the dependence of the inelastic loss on external fields. Furthermore, the investigation of frequency dependent laser-induced collisions, and the possibility to excite photoassociation resonances is presented. For the measurements described here, neon atoms have been confined in a magnetooptical trap, in a magnetostatic trap, or in an optical dipole trap, respectively. By laser cooling inside the magnetic trap, atomic samples with more than 95 percent occupation of the magnetic substate m J = +2 could be prepared. They have a typical temperature of 0.5 mK, central densities up to 10 11 cm -3 , and a central phase-space density of up to 2.2.10 -7 . After loading the optical dipole trap from the magnetic trap, 2.5.10 6 atoms with typical temperatures of 0.1 mK, and central densities up to 5.10 10 cm -3 were trapped. By evaporative cooling of the atoms in the magnetic trap we could increase the phase-space density by a factor of 200 to 5.10 -5 . Investigating the frequency dependence of laser-induced collisions did not reveal an experimental signature for the excitation of photoassociation resonances. For the 3 D 3 line a frequency dependence of laser enhanced Penning ionization was observed. Measurement of the two-body loss coefficient as function of the magnetic field showed a field dependence of the inelastic loss. These losses increase towards both small and large offset fields. The implementation of an optical dipole trap allowed us to trap the 3 P 0 metastable state. From the trap loss measurements we determined the two-body loss coefficient of the 3 P 0 metastable state for both bosonic isotopes 20 Ne and 22 Ne. For 20 Ne we obtained β=6 +5 -4 .10 -10 cm 3 /s and for 22 Ne β = 11 +7 -6 .10 -10 cm 3 /s. (orig.)

  13. Coherent and non coherent atom optics experiment with an ultra-narrow beam of metastable rare gas atoms; Experiences d'optique atomique coherente ou non avec un jet superfin d'atomes metastables de gaz rares

    Energy Technology Data Exchange (ETDEWEB)

    Grucker, J

    2007-12-15

    In this thesis, we present a new type of atomic source: an ultra-narrow beam of metastable atoms produced by resonant metastability exchange inside a supersonic beam of rare gas atoms. We used the coherence properties of this beam to observe the diffraction of metastable helium, argon and neon atoms by a nano-transmission grating and by micro-reflection-gratings. Then, we evidenced transitions between Zeeman sublevels of neon metastable {sup 3}P{sub 2} state due to the quadrupolar part of Van der Waals potential. After we showed experimental proofs of the observation of this phenomenon, we calculated the transition probabilities in the Landau - Zener model. We discussed the interest of Van der Waals - Zeeman transitions for atom interferometry. Last, we described the Zeeman cooling of the supersonic metastable argon beam ({sup 3}P{sub 2}). We have succeeded in slowing down atoms to speeds below 100 m/s. We gave experimental details and showed the first time-of-flight measurements of slowed atoms.

  14. Interaction of rare gas metastable atoms

    International Nuclear Information System (INIS)

    Wang, A.Z.F.

    1977-11-01

    The physical and chemical properties of metastable rare gas atoms are discussed and summarized. This is followed by a detailed examination of the various possible pathways whereby the metastable's excess electronic energy can be dissipated. The phenomenon of chemi-ionization is given special emphasis, and a theoretical treatment based on the use of complex (optical) potential is presented. This is followed by a discussion on the unique advantages offered by elastic differential cross section measurements in the apprehension of the fundamental forces governing the ionization process. The methodology generally adopted to extract information about the interaction potential for scattering data is also systematically outlined. Two widely studied chemi-ionization systems are then closely examined in the light of accurate differential cross section measurements obtained in this work. The first system is He(2 3 S) + Ar for which one can obtain an interaction potential which is in good harmony with the experimental results of other investigators. The validity of using the first-order semiclassical approximation for the phase shifts calculation in the presence of significant opacities is also discussed. The second reaction studied is He*+D 2 for which measurements were made on both spin states of the metastable helium. A self-consistent interaction potential is obtained for the triplet system, and reasons are given for not being able to do likewise for the singlet system. The anomalous hump proposed by a number of laboratories is analyzed. Total elastic and ionization cross sections as well as rate constants are calculated for the triplet case. Good agreement with experimental data is found. Finally, the construction and operation of a high power repetitively pulsed nitrogen laser pumped dye laser system is described in great details. Details for the construction and operation of a flashlamp pumped dye laser are likewise given

  15. Investigation of systematic errors of metastable "atomic pair" number

    CERN Document Server

    Yazkov, V

    2015-01-01

    Sources of systematic errors in analysis of data, collected in 2012, are analysed. Esti- mations of systematic errors in a number of “atomic pairs” fr om metastable π + π − atoms are presented.

  16. Theory of hollow cathode arc discharges. II. Metastable state balance inside the cathode. Application to argon

    International Nuclear Information System (INIS)

    Ferreira, C.M.; Delcroix, J.L.

    1975-01-01

    In the hollow cathode the metastable species are created by fast electrons, which are emitted by the cathode wall and injected in the plasma across a space-charge sheath, and destroyed by Maxwellian electrons. A detailed analysis of the different electronic destruction mechanisms in argon shows that the re-excitation up to 3p 5 4p states plays a very important role. Solutions of the metastable balance equation were obtained in a wide range of variation of the discharge parameters displaying the best conditions of operation to obtain high concentrations [fr

  17. Chemi-ionization in the metastable neon--metastable argon system

    International Nuclear Information System (INIS)

    Neynaber, R.N.; Tang, S.Y.

    1980-01-01

    Studies were made by a merging-beams technique of the associative ionization (AI) reaction (1) Ne/sup asterisk/+Ar/sup asterisk/→NeAr + +e and the Penning ionization (PI) reactions (2) Ne/sup asterisk/+Ar/sup asterisk/→Ne+Ar + +e and (3) Ne/sup asterisk/+Ar/sup asterisk/→Ne + +Ar+e. The relative kinetic energy of the reactants was varied from 0.01 to 10 eV. The Ne/sup asterisk/ and Ar/sup asterisk/ each represents a composite of the metastable 0 P/sub 2,0/ states. There is a complication in the present investigation which arises because AI and PI occur in collisions of Ne/sup asterisk/ with ground-state Ar. Since the reactant beams consist of metastable as well as ground-state species, the measurements are composites of chemi-ionization in both the Ne/sup asterisk/--Ar/sup asterisk/ and Ne/sup asterisk/--Ar systems. Information on AI and PI for the Ne/sup asterisk/--Ar/sup asterisk/ system is obtained by subtracting from these composite measurements known contributions of the Ne/sup asterisk/--Ar system. From such information it appears that the molecular states of the reactants are different for reactions (2) and

  18. Energetic Metastable Oxygen and Nitrogen Atoms in the Terrestrial Atmosphere

    Science.gov (United States)

    Kharchenko, Vasili; Dalgarno, A.

    2005-01-01

    This report summarizes our research performed under NASA Grant NAG5-11857. The three-year grant have been supported by the Geospace Sciences SR&T program. We have investigated the energetic metastable oxygen and nitrogen atoms in the terrestrial stratosphere, mesosphere and thermosphere. Hot atoms in the atmosphere are produced by solar radiation, the solar wind and various ionic reactions. Nascent hot atoms arise in ground and excited electronic states, and their translational energies are larger by two - three orders of magnitude than the thermal energies of the ambient gas. The relaxation kinetics of hot atoms determines the rate of atmospheric heating, the intensities of aeronomic reactions, and the rate of atom escape from the planet. Modeling of the non-Maxwellian energy distributions of metastable oxygen and nitrogen atoms have been focused on the determination of their impact on the energetics and chemistry of the terrestrial atmosphere between 25 and 250 km . At this altitudes, we have calculated the energy distribution functions of metastable O and N atoms and computed non-equilibrium rates of important aeronomic reactions, such as destruction of the water molecules by O(1D) atoms and production of highly excited nitric oxide molecules. In the upper atmosphere, the metastable O(lD) and N(2D) play important role in formation of the upward atomic fluxes. We have computed the upward fluxes of the metastable and ground state oxygen atoms in the upper atmosphere above 250 km. The accurate distributions of the metastable atoms have been evaluated for the day and night-time conditions.

  19. A metastable helium trap for atomic collision physics

    International Nuclear Information System (INIS)

    Colla, M.; Gulley, R.; Uhlmann, L.; Hoogerland, M.D.; Baldwin, K.G.H.; Buckman, S.J.

    1999-01-01

    Full text: Metastable helium in the 2 3 S state is an important species for atom optics and atomic collision physics. Because of its large internal energy (20eV), long lifetime (∼8000s) and large collision cross section for a range of processes, metastable helium plays an important role in atmospheric physics, plasma discharges and gas laser physics. We have embarked on a program of studies on atom-atom and electron-atom collision processes involving cold metastable helium. We confine metastable helium atoms in a magneto-optic trap (MOT), which is loaded by a transversely collimated, slowed and 2-D focussed atomic beam. We employ diode laser tuned to the 1083 nm (2 3 S 1 - 2 3 P2 1 ) transition to generate laser cooling forces in both the loading beam and the trap. Approximately 10 million helium atoms are trapped at temperatures of ∼ 1mK. We use phase modulation spectroscopy to measure the trapped atomic density. The cold, trapped atoms can collide to produce either atomic He + or molecular He 2 + ions by Penning Ionisation (PI) or Associative Ionisation (AI). The rate of formation of these ions is dependant upon the detuning of the trapping laser from resonance. A further laser can be used to connect the 2 3 S 1 state to another higher lying excited state, and variation of the probe laser detuning used to measure interatomic collision potential. Electron-atom collision processes are studied using a monochromatic electron beam with a well defined spatial current distribution. The total trap loss due to electron collisions is measured as a function of electron energy. Results will be presented for these atomic collision physics measurements involving cold, trapped metastable helium atoms. Copyright (1999) Australian Optical Society

  20. Decay of atomic metastable states in a plasma

    International Nuclear Information System (INIS)

    Kleiman, E.B.

    1985-01-01

    This paper discusses the influence of polarization plasma effects on the lifetime of metastable atomic levels. It is shown that plasma effects can also be important in the case when the distance between the metastable level and the closest emitting level exceeds the Langmuir frequency. The lifetime of the 2S level of a hydrogen atom in a rarefied plasma connected with the action of a longitudinal fluctuation field on the atom is estimated. It is found that this mechanism can determine the lifetime of the 2S level in a rarefied cosmic plasma

  1. Fast metastable hydrogen atoms from H2 molecules: twin atoms

    Directory of Open Access Journals (Sweden)

    Trimèche A.

    2015-01-01

    Full Text Available It is a difficult task to obtain “twin atoms”, i.e. pairs of massive particles such that one can perform experiments in the same fashion that is routinely done with “twin photons”. One possible route to obtain such pairs is by dissociating homonuclear diatomic molecules. We address this possibility by investigating the production of metastable H(2s atoms coming from the dissociation of cold H2 molecules produced in a Campargue nozzle beam crossing an electron beam from a high intensity pulsed electron gun. Dissociation by electron impact was chosen to avoid limitations of target molecular excited states due to selection rules. Detectors placed several centimeters away from the collision center, and aligned with respect to possible common molecular dissociation channel, analyze the neutral fragments as a function of their time-of-flight (TOF through Lyman-α detection. Evidence for the first time observed coincidence of pairs of H(2s atoms obtained this way is presented.

  2. Photoassociation of cold metastable helium atoms

    NARCIS (Netherlands)

    Woestenenk, G.R.

    2001-01-01

    During the last decades the study of cold atoms has grown in a great measure. Research in this field has been made possible due to the development of laser cooling and trapping techniques. We use laser cooling to cool helium atoms down to a temperature of 1 mK and we are able to

  3. Measurement of cross-sections for step-bystep excitation of inert gas atoms from metastable states by electron collisions

    International Nuclear Information System (INIS)

    Mityureva, A.A.; Penkin, N.P.; Smirnov, V.V.

    1989-01-01

    Excitation of argon atoms by electron collisions from metastable (MS) to high-lying states of inert gases (the so-called step-by-step excitation) is investigated. Formation of MS atoms m and their further step-by-step excitation up to k level is carried out by an electron beam with energy from 1 up to 40 eV. Time distribution of forming metastable and step-by-step electron collisions is used. The method used permits to measure the functions of step-by-step excitation and the absolute values of cross sections. Absolute values of cross-sections and functions of step-by-step excitation of some lines and argon levels are obtained

  4. Scattering of electrons from argon atoms

    International Nuclear Information System (INIS)

    Dasgupta, A.; Bhatia, A.K.

    1985-01-01

    The scattering of electrons from argon atoms is studied by the method of polarized orbitals. The 3p→d perturbed orbital calculated using the Sternheimer approximation gives the polarizability 14.29a 0 3 . The perturbation of the orbitals 1s, 2s, 2p, and 3s is taken into account by renormalizing the 3p→d orbitals to give the experimental value 11.06a 0 3 . Using only the modified orbital in the total wave function, phase shifts for various partial waves have been calculated in the exchange, exchange-adiabatic, and polarized-orbital approximations. They are compared with the results of the previous calculations. The calculated total elastic, differential, and momentum-transfer cross sections are compared with the experimental results. The elastic total cross sections obtained in the polarized-orbital approximation agree very closely with the recently measured cross sections by Jost et al. and Nickel et al. The critical point (the value of k 2 and theta at which the differential cross section is minimum) is at 0.306 eV and 80 0 , in good agreement with the measurements of Weyhreter et al

  5. Behavior of Excited Argon Atoms in Inductively Driven Plasmas

    International Nuclear Information System (INIS)

    HEBNER, GREGORY A.; MILLER, PAUL A.

    1999-01-01

    Laser induced fluorescence has been used to measure the spatial distribution of the two lowest energy argon excited states, 1s 5 and 1s 4 , in inductively driven plasmas containing argon, chlorine and boron trichloride. The behavior of the two energy levels with plasma conditions was significantly different, probably because the 1s 5 level is metastable and the 1s 4 level is radiatively coupled to the ground state but is radiation trapped. The argon data is compared with a global model to identify the relative importance of processes such as electron collisional mixing and radiation trapping. The trends in the data suggest that both processes play a major role in determining the excited state density. At lower rfpower and pressure, excited state spatial distributions in pure argon were peaked in the center of the discharge, with an approximately Gaussian profile. However, for the highest rfpowers and pressures investigated, the spatial distributions tended to flatten in the center of the discharge while the density at the edge of the discharge was unaffected. The spatially resolved excited state density measurements were combined with previous line integrated measurements in the same discharge geometry to derive spatially resolved, absolute densities of the 1s 5 and 1s 4 argon excited states and gas temperature spatial distributions. Fluorescence lifetime was a strong fi.mction of the rf power, pressure, argon fraction and spatial location. Increasing the power or pressure resulted in a factor of two decrease in the fluorescence lifetime while adding Cl 2 or BCl 3 increased the fluorescence lifetime. Excited state quenching rates are derived from the data. When Cl 2 or BCl 3 was added to the plasma, the maximum argon metastable density depended on the gas and ratio. When chlorine was added to the argon plasma, the spatial density profiles were independent of chlorine fraction. While it is energetically possible for argon excited states to dissociate some of the

  6. An investigation of Ar metastable state density in low pressure dual-frequency capacitively coupled argon and argon-diluted plasmas

    International Nuclear Information System (INIS)

    Liu, Wen-Yao; Xu, Yong; Peng, Fei; Guo, Qian; Li, Xiao-Song; Zhu, Ai-Min; Liu, Yong-Xin; Wang, You-Nian

    2015-01-01

    An tunable diode laser absorption spectroscopy has been used to determine the Ar*( 3 P 2 ) and Ar*( 3 P 0 ) metastable atoms densities in dual-frequency capacitively coupled plasmas. The effects of different control parameters, such as high-frequency power, gas pressure and content of Ar, on the densities of two metastable atoms and electron density were discussed in single-frequency and dual-frequency Ar discharges, respectively. Particularly, the effects of the pressure on the axial profile of the electron and Ar metastable state densities were also discussed. Furthermore, a simple rate model was employed and its results were compared with experiments to analyze the main production and loss processes of Ar metastable states. It is found that Ar metastable state is mainly produced by electron impact excitation from the ground state, and decayed by diffusion and collision quenching with electrons and neutral molecules. Besides, the addition of CF 4 was found to significantly increase the metastable destruction rate by the CF 4 quenching, especially for large CF 4 content and high pressure, it becomes the dominant depopulation process

  7. Enhanced atom mobility on the surface of a metastable film.

    Science.gov (United States)

    Picone, A; Riva, M; Fratesi, G; Brambilla, A; Bussetti, G; Finazzi, M; Duò, L; Ciccacci, F

    2014-07-25

    A remarkable enhancement of atomic diffusion is highlighted by scanning tunneling microscopy performed on ultrathin metastable body-centered tetragonal Co films grown on Fe(001). The films follow a nearly perfect layer-by-layer growth mode with a saturation island density strongly dependent on the layer on which the nucleation occurs, indicating a lowering of the diffusion barrier. Density functional theory calculations reveal that this phenomenon is driven by the increasing capability of the film to accommodate large deformations as the thickness approaches the limit at which a structural transition occurs. These results disclose the possibility of tuning surface diffusion dynamics and controlling cluster nucleation and self-organization.

  8. Behavior of Excited Argon Atoms in Inductively Driven Plasmas

    CERN Document Server

    Hebner, G A

    1999-01-01

    Laser induced fluorescence has been used to measure the spatial distribution of the two lowest energy argon excited states, 1s sub 5 and 1s sub 4 , in inductively driven plasmas containing argon, chlorine and boron trichloride. The behavior of the two energy levels with plasma conditions was significantly different, probably because the 1s sub 5 level is metastable and the 1s sub 4 level is radiatively coupled to the ground state but is radiation trapped. The argon data is compared with a global model to identify the relative importance of processes such as electron collisional mixing and radiation trapping. The trends in the data suggest that both processes play a major role in determining the excited state density. At lower rfpower and pressure, excited state spatial distributions in pure argon were peaked in the center of the discharge, with an approximately Gaussian profile. However, for the highest rfpowers and pressures investigated, the spatial distributions tended to flatten in the center of the disch...

  9. Charge transfer cross-sections of argon ions colliding on argon atoms

    International Nuclear Information System (INIS)

    Aubert, J.; Bliman, S.; Chan-Tung, N.; Geller, R.; Jacquot, B.; Van Houtte, D.

    1980-04-01

    A device has been built to measure charge changing cross-sections of Argon ions colliding on argon atoms. It consists of an E.C.R. ion source (Micromafios) that delivers argon ions up to charge + 13. The ion source potential may be varied from 1 up to 10 kVolts. A first magnet is used to charge analyze the extracted beam. For a given separated charge state, the ion beam is passed in a collision cell whose pressure may be varied. The ions undergoing collisions on the target are analyzed by a second magnet and collected. The pressure is varied in the collision cell in order to check that the single collision condition is satisfied. It is shown that the ions do two types of collisions: charge exchange and stripping whose cross-sections are measured. Interpretation of charge exchange is proposed along yet classic theoretical approaches. As to stripping no available theory allows interpretation

  10. Two-photon polarization Fourier spectroscopy of metastable atomic hydrogen

    International Nuclear Information System (INIS)

    Duncan, A.J.; Beyer, H.-J.; Kleinpoppen, H.; Sheikh, Z.A,; B-Z Univ., Multan

    1997-01-01

    A novel Fourier-transform spectroscopic method using two-photon polarization to determine the spectral distribution of the two photons emitted in the spontaneous decay of metastable atomic hydrogen is described. The method uses birefringent retardation plates and takes advantage of the subtle interplay between the spectral properties and the entangled polarization properties of the radiation emitted in the decay. Assuming the validity of the theoretical spectral distribution, it is shown that the experimental results agree well with theory. On the other hand, success in solving the inverse problem of determining the spectral distribution from the experimental results is limited by the small number of experimental points. However, making reasonable assumptions it is deduced that the observed spectrum is characterized by a broadband signal of width (0.43 ± 0.06) x 10 16 rad s -1 and centre angular frequency (0.77 ± 0.03) x 10 16 rad s -1 in good agreement with the predictions of 0.489 x 10 16 rad s -1 and 0.775 x 10 16 rad s -1 , respectively, obtained from the theoretical spectral distribution modified to take account of the absorption of the two-photon radiation in air. The values of 1.5 fs for the coherence time and 440 nm for the coherence length for single photons of the two-photon pair which are obtained from the measured bandwidth imply that, in the ideal case, these values are determined by the essentially zero lifetime of the virtual intermediate state of the decay process rather than the long lifetime of the metastable state which, it is suggested, determines the coherence time and coherence length appropriate to certain types of fourth-order interference experiments. (Author)

  11. Experiments on state selection and Penning ionisation with fast metastable rare gas atoms

    International Nuclear Information System (INIS)

    Kroon, J.P.C.

    1985-01-01

    This thesis describes experiments with metastable He/Ne atoms. The experiments are performed in a crossed beam machine. Two different sources are used for the production of metastable atoms: a source for the production of metastable atoms in the thermal energy range and a hollow cathode arc for the production of metastable atoms in the superthermal energy range (1-7 eV). The progress made in the use of the hollow cathode arc is described as well as the experimental set-up. The rare gas energy-level diagram is characterized by two metastable levels. By optical pumping it is possible to select a single metastable level, both for He and Ne. For the case of He this is done by a recently built He quenchlamp which selectively quenches the metastable 2 1 S level population. In the thermal energy range the quenching is complete; in the superthermal energy range the 2 1 S level population is only partly quenched. For the optical pumping of Ne* atoms a cw dye laser is used. New experiments have been started on the measurement, in a crossed beam machine, of the fluorescence caused by inelastic collisions where metastable atoms are involved. The He* + Ne system is used as a pilot study for these experiments. The He-Ne laser is based on this collision system. (Auth.)

  12. Metal-atom fluorescence from the quenching of metastable rare gases by metal carbonyls

    International Nuclear Information System (INIS)

    Hollingsworth, W.E.

    1982-11-01

    A flowing afterglow apparatus was used to study the metal fluorescence resulting from the quenching of metastable rare-gas states by metal carbonyls. The data from the quenching or argon, neon, and helium by iron and nickel carbonyl agreed well with a restricted degree of freedom model indicating a concerted bond-breaking dissociation

  13. Behavior of 23S metastable state He atoms in low-temperature recombining plasmas

    Science.gov (United States)

    Kajita, Shin; Tsujihara, Tadashi; Aramaki, Mitsutoshi; van der Meiden, Hennie; Oshima, Hiroshi; Ohno, Noriyasu; Tanaka, Hirohiko; Yasuhara, Ryo; Akiyama, Tsuyoshi; Fujii, Keisuke; Shikama, Taiichi

    2017-07-01

    We measured the electron density and temperature using laser Thomson scattering and metastable state (23S) of He atoms by laser absorption spectroscopy in the detached recombining plasmas in the divertor simulator NAGDIS-II. Using the measured electron density and temperature combined with the particle trajectory trace simulation, we discussed the behavior of the metastable state He atoms based on comparisons with the experimental results. It is shown that the metastable state atoms are mainly produced in the peripheral region of the plasma column, where the temperature is lower than the central part, and diffused in the vacuum vessel. It was shown that the 0D model is not valid and the transport of the metastable states is to be taken into account for the population distribution of He atoms in the detached plasmas.

  14. Primary populations of metastable antiprotonic $^{4}He$ and $^{3}He$ atoms

    CERN Document Server

    Hori, Masaki; Hayano, R S; Ishikawa, T; Sakuguchi, J; Tasaki, T; Widmann, E; Yamaguchi, H; Torii, H A; Juhász, B; Horváth, D; Yamazaki, T

    2002-01-01

    Initial population distributions of metastable antiprotonic **4He and **3He atoms over principal and angular momentum quantum numbers were investigated using laser spectroscopy. The total fractions of antiprotons captured into the metastable states of the atoms were deduced. Cascade calculations were performed using the measure populations to reproduce the delayed annihilation time spectrum. Results showed agreement between the simulated and measured spectra. (Edited abstract) 30 Refs.

  15. Resonant excitation of uranium atoms by an argon ion laser

    Energy Technology Data Exchange (ETDEWEB)

    Maeyama, H; Morikawa, M; Aihara, Y; Mochizuki, T; Yamanaka, C [Osaka Univ. (Japan)

    1979-03-01

    Photoionization of uranium atoms by UV lines, 3511 A and 3345 A, of an argon ion laser was observed and attributed due to resonant two-photon ionization. The dependence of the photoion currents on laser power was measured in focusing and non-focusing modes of laser beam, which has enabled us to obtain an absorption cross section and an ionization cross section independently. The orders of magnitude of these cross sections averaged over the fine structure were determined to be 10/sup -14/ cm/sup 2/ and 10/sup -17/ cm/sup 2/ respectively from a rate equation model. Resonance between 3511-A laser line and the absorption line of uranium isotopes was also confirmed by the ionization spectra obtained by near-single-frequency operation of the ion laser, which allowed the isotopic selective excitation of the uranium atoms. The maximum value of the enrichment of /sup 235/U was about 14%. The isotope separation of uranium atoms by this resonant excitation has been discussed.

  16. Beam experiments with state selected Ne (3P0, 3P2) metastable atoms

    International Nuclear Information System (INIS)

    Verheijen, M.J.

    1984-01-01

    Metastable rare gas atoms play an important role in all types of plasmas and gas discharges, e.g. in fluorescent lamps and in laser discharges (helium-neon laser or excimer lasers). In this thesis, the metastable states of NeI are studied. First, the theory of excited neon atoms and diatomic molecules is introduced, as well as Penning ionisation. Next, some experimental facilities are described (e.g. the dye laser system). With these instruments, natural lifetime measurements of the 2p fine structure states of NeI are carried out. Results are reported. Finally, total Penning ionisation cross sections are calculated using the optical potential model. (Auth.)

  17. Metastable states in antiprotonic helium atoms an island stability in a sea of continuum

    CERN Document Server

    Korobov, V I

    2002-01-01

    In this contribution we consider a phenomenon of metastable states in antiprotonic helium atoms, precise spectroscopy of these states and a present-day study of the electromagnetic properties of antiprotons. Calculation of nonrelativistic energies, relativistic and QED corrections as well as the fine and hyperfine structure and the magnetic moment of an antiproton are the main parts of this study. Refs. 22 (nevyjel)

  18. Tensorial analysis of the long-range interaction between metastable alkaline-earth-metal atoms

    International Nuclear Information System (INIS)

    Santra, Robin; Greene, Chris H.

    2003-01-01

    Alkaline-earth-metal atoms in their lowest (nsnp) 3 P 2 state are exceptionally long lived and can be trapped magnetically. The nonspherical atomic structure leads to anisotropic long-range interactions between two metastable alkaline-earth-metal atoms. The anisotropy affects the rotational motion of the diatomic system and couples states of different rotational quantum numbers. This paper develops a tensorial decomposition of the most important long-range interaction operators, and a systematic inclusion of molecular rotations, in the presence of an external magnetic field. This analysis illuminates the nature of the coupling between the various degrees of freedom. The consequences are illustrated by application to a system of practical interest: metastable 88 Sr. Using atomic parameters determined in a nearly ab initio calculation, we compute adiabatic potential-energy curves. The anisotropic interatomic interaction, in combination with the applied magnetic field, is demonstrated to induce the formation of a long-range molecular potential well. This curve correlates to two fully polarized, low-field seeking atoms in a rotational s-wave state. The coupling among molecular rotational states controls the existence of the potential well, and its properties vary as a function of magnetic-field strength, thus allowing the scattering length in this state to be tuned. The scattering length of metastable 88 Sr displays a resonance at a field of 339 G

  19. An investigation into the role of metastable states on excited populations of weakly ionized argon plasmas, with applications for optical diagnostics

    Science.gov (United States)

    Arnold, Nicholas; Loch, Stuart; Ballance, Connor; Thomas, Ed

    2017-10-01

    Low temperature plasmas (Te ADAS) code suite to calculate a level-resolved, generalized collisional-radiative (GCR) model for line emission in low temperature argon plasmas. By combining our theoretical model with experimental electron temperature, density, and spectral measurements from the Auburn Linear eXperiment for Instability Studies (ALEXIS), we have developed diagnostic techniques to measure metastable fraction, electron temperature, and electron density. In the future we hope to refine our methods, and extend our model to plasmas other than ALEXIS. Supported by the U.S. Department of Energy. Grant Number: DE-FG02-00ER54476.

  20. Collisional effects on metastable atom population in vapour generated by electron beam heating

    International Nuclear Information System (INIS)

    Dikshit, B; Majumder, A; Bhatia, M S; Mago, V K

    2008-01-01

    The metastable atom population distribution in a free expanding uranium vapour generated by electron beam (e-beam) heating is expected to depart from its original value near the source due to atom-atom collisions and interaction with electrons of the e-beam generated plasma co-expanding with the vapour. To investigate the dynamics of the electron-atom and atom-atom interactions at different e-beam powers (or source temperatures), probing of the atomic population in ground (0 cm -1 ) and 620 cm -1 metastable states of uranium was carried out by the absorption technique using a hollow cathode discharge lamp. The excitation temperature of vapour at a distance ∼30 cm from the source was calculated on the basis of the measured ratio of populations in 620 to 0 cm -1 states and it was found to be much lower than both the source temperature and estimated translational temperature of the vapour that is cooled by adiabatic free expansion. This indicated relaxation of the metastable atoms by collisions with low energy plasma electrons was so significant that it brings the excitation temperature below the translational temperature of the vapour. So, with increase in e-beam power and hence atom density, frequent atom-atom collisions are expected to establish equilibrium between the excitation and translational temperatures, resulting in an increase in the excitation temperature (i.e. heating of vapour). This has been confirmed by analysing the experimentally observed growth pattern of the curve for excitation temperature with e-beam power. From the observed excitation temperature at low e-beam power when atom-atom collisions can be neglected, the total de-excitation cross section for relaxation of the 620 cm -1 state by interaction with low energy electrons was estimated and was found to be ∼10 -14 cm 2 . Finally using this value of cross section, the extent of excitational cooling and heating by electron-atom and atom-atom collisions are described at higher e-beam powers

  1. Properties of the triplet metastable states of the alkaline-earth-metal atoms

    International Nuclear Information System (INIS)

    Mitroy, J.; Bromley, M.W.J.

    2004-01-01

    The static and dynamic properties of the alkaline-earth-metal atoms in their metastable state are computed in a configuration interaction approach with a semiempirical model potential for the core. Among the properties determined are the scalar and tensor polarizabilities, the quadrupole moment, some of the oscillator strengths, and the dispersion coefficients of the van der Waals interaction. A simple method for including the effect of the core on the dispersion parameters is described

  2. Three-Dimensional Atomic Structure of Metastable Nanoclusters in Doped Semiconductors

    Science.gov (United States)

    Couillard, Martin; Radtke, Guillaume; Knights, Andrew P.; Botton, Gianluigi A.

    2011-10-01

    Aberration-corrected scanning transmission electron microscopy is used to determine the atomic structure of nanoclusters of cerium dopant atoms embedded in silicon. By channeling electrons along two crystallographic orientations, we identify a characteristic zinc-blende chemical ordering within CeSi clusters coherent with the silicon host matrix. Strain energy limits the size of these ordered arrangements to just above 1 nm. With the local order identified, we then determine the atomic configuration of an individual subnanometer cluster by quantifying the scattering intensity under weak channeling condition in terms of the number of atoms. Analysis based on single-atom visualization also evidences the presence of split-vacancy impurity complexes, which supports the hypothesis of a vacancy-assisted formation of these metastable CeSi nanophases.

  3. A calculation of internal kinetic energy and polarizability of compressed argon from the statistical atom model

    NARCIS (Netherlands)

    Seldam, C.A. ten; Groot, S.R. de

    1952-01-01

    From Jensen's and Gombás' modification of the statistical Thomas-Fermi atom model, a theory for compressed atoms is developed by changing the boundary conditions. Internal kinetic energy and polarizability of argon are calculated as functions of pressure. At 1000 atm. an internal kinetic energy of

  4. First observation of laser-induced resonant annihilation in metastable antiprotonic helium atoms

    International Nuclear Information System (INIS)

    Morita, N.; Kumakura, M.; Yamazaki, T.

    1993-11-01

    We have observed the first laser-induced resonant transitions in antiprotonic helium atoms. These occur between metastable states and Auger dominated short lived states, and show that the anomalous longevity of antiprotons previously observed in helium media results from the formation of high-n high-l atomic states of p-barHe + . The observed transition with vacuum wavelength 597.259 ± 0.002 nm and lower-state lifetime 15 ± 1 ns is tentatively assigned to (n,l) = (39,35) → (38,34). (author)

  5. Rabi oscillations in extreme ultraviolet ionization of atomic argon

    Science.gov (United States)

    Flögel, Martin; Durá, Judith; Schütte, Bernd; Ivanov, Misha; Rouzée, Arnaud; Vrakking, Marc J. J.

    2017-02-01

    We demonstrate Rabi oscillations in nonlinear ionization of argon by an intense femtosecond extreme ultraviolet (XUV) laser field produced by high-harmonic generation. We monitor the formation of A r2 + as a function of the time delay between the XUV pulse and an additional near-infrared (NIR) femtosecond laser pulse, and show that the population of an A r+* intermediate resonance exhibits strong modulations both due to an NIR laser-induced Stark shift and XUV-induced Rabi cycling between the ground state of A r+ and the A r+* excited state. Our experiment represents a direct experimental observation of a Rabi-cycling process in the XUV regime.

  6. Anomalous evolution of Ar metastable density with electron density in high density Ar discharge

    International Nuclear Information System (INIS)

    Park, Min; Chang, Hong-Young; You, Shin-Jae; Kim, Jung-Hyung; Shin, Yong-Hyeon

    2011-01-01

    Recently, an anomalous evolution of argon metastable density with plasma discharge power (electron density) was reported [A. M. Daltrini, S. A. Moshkalev, T. J. Morgan, R. B. Piejak, and W. G. Graham, Appl. Phys. Lett. 92, 061504 (2008)]. Although the importance of the metastable atom and its density has been reported in a lot of literature, however, a basic physics behind the anomalous evolution of metastable density has not been clearly understood yet. In this study, we investigated a simple global model to elucidate the underlying physics of the anomalous evolution of argon metastable density with the electron density. On the basis of the proposed simple model, we reproduced the anomalous evolution of the metastable density and disclosed the detailed physics for the anomalous result. Drastic changes of dominant mechanisms for the population and depopulation processes of Ar metastable atoms with electron density, which take place even in relatively low electron density regime, is the clue to understand the result.

  7. Energy transfers between N_2(A"3Σ) nitrogen metastable molecules and oxygen atoms and molecules

    International Nuclear Information System (INIS)

    De Souza, Antonio Rogerio

    1985-01-01

    This research thesis aims at determining reaction coefficients for energy transfers between nitrogen in its metastable status and oxygen atoms and molecules, the variation of these coefficients with respect to temperature (mainly in the 200-400 K range), products formed and more particularly branching rates of O("1S) oxygen and of NO_2. Reaction coefficients are experimentally determined by using the technique of post-discharge in flow. The experimental set-up is described and the study of the best operating conditions is reported. In the next part, the author reports the study of the energy transfer between nitrogen in its metastable status N_2(A) and oxygen molecules. Reaction coefficients are determined for the first three vibrational levels. The author then reports the study of the transfer of N_2(A) molecules on oxygen atoms in their fundamental status. Reactions coefficients and their variations are determined for the three first vibrational levels. The author describes the dissociation method and the method of detection of atomic oxygen. A kinetic model is proposed for the analysis of formed products during a post-discharge in flow, and the branching rate for the formation of O("1S) oxygen between 190 and 365 K is determined. The author finally discusses publications on the role of these reactions in the interpretation of some atmospheric phenomena

  8. X-ray laser implementation by means of a strong source of high-spin metastable atoms

    International Nuclear Information System (INIS)

    Helman, J.S.; Rau, C.; Bunge, C.F.

    1983-01-01

    High-spin metastable atomic beams of high density and extremely small divergence can be produced by electron capture during grazing-angle scattering of ion beams at ferromagnetic surfaces. This can be used to generate a long-lived reservoir of Li 1s2s2p 4 P/sub 5/2//sup ts0/ with enough density of metastables so that after laser-induced transfer to Li 1s2p/sup ts2/P strong lasing at 207 A should occur. This novel technique can also be used to produce a variety of other metastables known as potential candidates for lasing at shorter wavelengths

  9. Behaviour of tunnelling transition rate of argon atom exposed to ...

    Indian Academy of Sciences (India)

    in the strong laser field ionization of atoms and molecules. ... state in the discrete spectrum and the final state in the continuum of a quantum system in ... In this paper we used the ADK model to describe the tunnel ionization of atoms and.

  10. Collisional energy dependence of molecular ionization by metastable rare gas atoms

    International Nuclear Information System (INIS)

    Martin, R.M.; Parr, T.P.

    1979-01-01

    The collisional energy dependence of several molecular total ionization cross sections by metastable rare gas atoms was studied over the thermal energy region using the crossed molecular beam time-of-flight method. Results are reported for the collision systems He, Ne, and Ar ionizing the geometric isomers cis- and trans-dichloroethylene and ortho- and para-dichlorobenzene. The He ionization cross sections oscillate about an energy dependence of E/sup -1/2/ over the energy range 0.004--1.0 eV, and the Ar*+para-dichlorobenzene cross section oscillates about an energy dependence of E/sup -2/5/ over the energy range 0.011--0.64 eV. The remaining systems are characterized by ''bent'' E/sup -m/ dependences with m values of 0.56--0.70 at low energies changing to 0.07--0.29 at higher energies. Comparison with the slopes of the He* systems and the Ar*+para-dichlorobenzene system shows that the ''bent'' and ''oscillating'' energy dependences are similar except for the form of the cross section functions at the lowest energies. No systematic differences are found between the cross section energy dependences for ionization of different geometric isomers or for ionization by the different metastable rare gas atoms

  11. Laser absorption spectroscopy for measurement of He metastable atoms of a microhollow cathode plasma

    Science.gov (United States)

    Ueno, Keisuke; Kamebuchi, Kenta; Kakutani, Jiro; Matsuoka, Leo; Namba, Shinichi; Fujii, Keisuke; Shikama, Taiichi; Hasuo, Masahiro

    2018-01-01

    We generated a 0.3-mm-diameter DC, hollow-cathode helium discharge in a gas pressure range of 10-80 kPa. In discharge plasmas, we measured position-dependent laser absorption spectra for helium 23S1-23P0 transition with a spatial resolution of 55 µm. From the results of the analysis of the measured spectra using Voigt functions and including both the Doppler and collision broadening, we produced two-dimensional maps of the metastable 23S1 atomic densities and gas temperatures of the plasmas. We found that, at all pressures, the gas temperatures were approximately uniform in space with values in the range of 400-1500 K and the 23S1 atomic densities were ˜1019 m-3. We also found that the two-dimensional density distribution profiles became ring-shaped at high gas pressures, which is qualitatively consistent with the two-dimensional fluid simulation results.

  12. The Decay of Optically Thick Helium Plasmas, Taking into Account Ionizing Collisions between Metastable Atoms or Molecules

    Energy Technology Data Exchange (ETDEWEB)

    Stevefelt, J

    1970-11-15

    The effective recombination rate of a helium afterglow plasma, which is optically thick towards the resonance lines, is calculated from the coupled rate equations for the number densities of free electrons and of metastable atoms or molecules. The model employed is a neutral plasma, consisting of one kind of ions and one kind of metastables. The ions are lost by electron-ion recombination only, with subsequent formation of metastables, which are then deactivated in collisions with free electrons or with other metastables: in the latter case one electron is regained to the free state. When the rate constants for these various processes are time-independent, it is found that after a certain transition time a transient equilibrium between the number densities of electrons and metastables is attained. In a dense afterglow plasma, where the recombination coefficient may be large, the transient equilibrium density of metastables may become significantly higher than the qua si-equilibrium value obtained by equating the time derivative of the metastable density to zero, and the effective recombination coefficient may be reduced by much more than a factor of two

  13. The Decay of Optically Thick Helium Plasmas, Taking into Account Ionizing Collisions between Metastable Atoms or Molecules

    International Nuclear Information System (INIS)

    Stevefelt, J.

    1970-11-01

    The effective recombination rate of a helium afterglow plasma, which is optically thick towards the resonance lines, is calculated from the coupled rate equations for the number densities of free electrons and of metastable atoms or molecules. The model employed is a neutral plasma, consisting of one kind of ions and one kind of metastables. The ions are lost by electron-ion recombination only, with subsequent formation of metastables, which are then deactivated in collisions with free electrons or with other metastables: in the latter case one electron is regained to the free state. When the rate constants for these various processes are time-independent, it is found that after a certain transition time a transient equilibrium between the number densities of electrons and metastables is attained. In a dense afterglow plasma, where the recombination coefficient may be large, the transient equilibrium density of metastables may become significantly higher than the qua si-equilibrium value obtained by equating the time derivative of the metastable density to zero, and the effective recombination coefficient may be reduced by much more than a factor of two

  14. Results on the role of metastable Ar atoms in a 9-MHz high-power atmospheric ICP by using emission/absorption spectrometry

    International Nuclear Information System (INIS)

    Gunter, W.; Zeeman, P.B.; Visser, K.

    1984-01-01

    An investigation into the role of overpopulations of metastable argon levels as agents for causing non-local thermal equilibrium (LTE) in an inductively coupled plasma source (ICP), was carried out. Four argon transitions in the near infrared region were monitored through absorption measurements at two different observation heights in a 9-MHz high-power ICP. The lower states of the four transitions consist of two metastable (11.55 and 11.72 eV) and two radiating (11.62 and 11.83 eV) levels. Comparison of measured metastable level to radiating level absorbance ratios with calculated population ratios gave an indication whether overpopulations of certain levels existed. Results indicate no overpopulation of metastable states with respect to radiating states, arguing against their role as non-LTE mechanism agents. This conclusion is, however, preliminary, since the calculation of absolute population densities from absorbance measurements must still be carried out

  15. Atomic physics

    International Nuclear Information System (INIS)

    Anon.

    1976-01-01

    Research activities in atomic physics at Lawrence Berkeley Laboratory during 1976 are described. Topics covered include: experiments on stored ions; test for parity violation in neutral weak currents; energy conservation and astrophysics; atomic absorption spectroscopy, atomic and molecular detectors; theoretical studies of quantum electrodynamics and high-z ions; atomic beam magnetic resonance; radiative decay from the 2 3 Po, 2 levels of helium-like argon; quenching of the metastable 2S/sub 1/2/ state of hydrogen-like argon in an external electric field; and lifetime of the 2 3 Po level of helium-like krypton

  16. Plasma effects on the metastable H0(2s) atom

    International Nuclear Information System (INIS)

    Benage, J.F. Jr.

    1986-01-01

    Atomic radiative processes that occur in plasmas have long been of interest of plasma physicists. The process investigated here is atomic dipole transitions, specifically transitions from the metastable 2s to the 2p in hydrogen, which are induced by processes that occur in the plasma. An experiment was done to measure the rate of transitions from 2s to 2p in hydrogen. This experiment was divided into two sections. The first was to measure the transition rate in a near equilibrium plasma. The second section measured the transition rate when RF oscillations were imposed on the plasma. Results of the first part show that microscopic fluctuating electric fields produced by the motions of the charged particles induce transitions from 2s to 2p in hydrogen. The magnitude of this effect is compared to predicted transition rates due to collisions with electrons and ions and to rates predicted for an equilibrium plasma. In the second part, the plasma was shown to act as a filter, preventing transitions from being caused by the RF unless the RF was in the range where plasma waves could be launched. The interpretation given for this effect is that, when the oscillations are inducing transitions, it is because plasma waves are being launched in the plasma and it is these waves that are inducing the transitions

  17. Study of the metastable singlet of molecular nitrogen and of oxygen atoms in discharges and post-discharges

    International Nuclear Information System (INIS)

    Magne, Lionel

    1991-01-01

    Whereas discharges in nitrogen, in oxygen and in their mixtures are used in many different industrial processes (surface treatment, nitridation, oxidation, and so on), in order to get a better knowledge on nitrogen electronic states, this research thesis reports the study of the metastable singlet state of molecular nitrogen, and of oxygen atoms in their fundamental state. The molecular metastable has been observed by far-UV optical emission spectroscopy, in the positive column of a continuous discharge and in time post-discharge. As far as continuous discharge is concerned, the author measured the vibrational distribution of this state. A kinetic model has been developed, and calculated vibrational distributions are in good agreement with measurements. The density of oxygen atoms in fundamental state in time post-discharge has been measured by far-UV absorption optical spectroscopy. The probability of atom re-association of glass walls is deduced from the obtained results [fr

  18. X-ray fluorescence/Auger-electron coincidence spectroscopy of vacancy cascades in atomic argon

    International Nuclear Information System (INIS)

    Arp, U.

    1996-01-01

    Argon L 2.3 -M 2.3 M 2.3 Auger-electron spectra were measured in coincidence with Kα fluorescent x-rays in studies of Ar K-shell vacancy decays at several photon energies above the K-threshold and on the 1s-4p resonance in atomic argon. The complex spectra recorded by conventional electron spectroscopy are greatly simplified when recorded in coincidence with fluorescent x-rays, allowing a more detailed analysis of the vacancy cascade process. The resulting coincidence spectra are compared with Hartree-Fock calculations which include shake-up transitions in the resonant case. Small energy shifts of the coincidence electron spectra are attributed to post-collision interaction with 1s photoelectrons

  19. Spectral Analysis and Metastable Absorption Measurements of High Pressure Capacitively and Inductively Coupled Radio-Frequency Argon-Helium Discharges

    Science.gov (United States)

    2013-06-01

    absorbance. 8 Flow Rates The flow rate of the gas through the cell can be calculated using the incompressible Bernoulli equation as it relates to...Kinetics Racah and Paschen Notation Angular momentum coupling schemes are used to describe and organize the energy level spacings of an atom. For most...momenta of the electron, ~l and their spins ~s are combined sepa- rately. The two are then summed to give a total angular momentum , ~L+ ~S = ~J . For

  20. Metastable hydrogen

    International Nuclear Information System (INIS)

    Dose, V.

    1982-01-01

    This paper deals with the basic physical properties of the metastable 2 2 sub(1/2) state of atomic hydrogen. Applications relying on its special properties, including measurement of the Lamb shift, production of spin-polarized protons and the measurement of molecular electric moments, are discussed. (author)

  1. Atomic and ionic spectrum lines below 2000A: hydrogen through argon

    International Nuclear Information System (INIS)

    Kelly, R.L.

    1982-10-01

    A critical tabulation of observed spectral lines below 2000 angstroms has been prepared from the published literature up to July 1978. It is intended principally as an aid to those physicists and astronomers who deal with the spectra of highly stripped atoms. This report includes the first 18 elements, from hydrogen (including deuterium) through argon. The tabulation is divided into two main sections: the spectrum lines by spectrum, and a finding list. The entries for each element give the ionization species, ground state term, and ionization potential, as well as the best values of vacuum wavelength, intensity, and classification. A list of the pertinent references is appended at the end

  2. Experimental study of the electron-atom Bremsstrahlung emission in an argon plasma jet

    International Nuclear Information System (INIS)

    Ranson, P.; Vallee, O.; Chapelle, J.

    1977-01-01

    Electron-neutral atom bremsstrahlung is studied between 0.4 μm and 5 μm in a decaying argon plasma jet; in visible and infra-red range, some discrepancies appear between experimental results and theoretical calculations of different authors (Geltman, Stallcop). In the infra-red, the discrepancy can be partly explained because theoretical elastic cross sections are higher than experimental values in the vicinity of the Ramsauer minimum. In the visible range, a very small amount of fast electrons due to superelastic and recombination collisions explain the observed discrepancy [fr

  3. Determination of Ar metastable atom densities in Ar and Ar/H2 inductively coupled low-temperature plasmas

    International Nuclear Information System (INIS)

    Fox-Lyon, N; Knoll, A J; Oehrlein, G S; Franek, J; Demidov, V; Koepke, M; Godyak, V

    2013-01-01

    Ar metastable atoms are important energy carriers and surface interacting species in low-temperature plasmas that are difficult to quantify. Ar metastable atom densities (N Ar,m ) in inductively coupled Ar and Ar/H 2 plasmas were obtained using a model combining electrical probe measurements of electron density (N e ) and temperature (T e ), with analysis of spectrally resolved Ar plasma optical emission based on 3p → 1s optical emission ratios of the 419.8 nm line to the 420.1 nm line. We present the variation of N Ar,m as the Ar pressure and the addition of H 2 to Ar are changed comparatively to recent adsorption spectroscopy measurements. (paper)

  4. Electronic relaxation dynamics of a metal atom deposited on argon cluster

    International Nuclear Information System (INIS)

    Awali, Slim

    2014-01-01

    This thesis is a study on the interaction between electronically excited atomic states and a non-reactive environment. We have theoretically and experimentally studied situations where a metal atom (Ba or K) is placed in a finite size environment (argon cluster). The presence of the medium affects the electronic levels of the atom. On the other side, the excitation of the atom induces a relaxation dynamics of the electronic energy through the deformation of the cluster. The experimental part of this work focuses on two aspects: the spectroscopy and the dynamics. In both cases a first laser electronically excites the metal atom and the second ionizes the excited system. The observable is the photoelectron spectrum recorded after photoionization and possibly information on the photoion which are also produced. This pump/probe technique, with also two lasers, provide the ultrafast dynamic when the lasers pulses used are of ultrashort (60 fs). The use of nanosecond lasers leads to resonance spectroscopic measurement, unresolved temporally, which give information on the position of the energy levels of the studied system. From a theoretical point-of-view, the excited states of M-Ar n were calculated at the ab initio level, using large core pseudo-potential to limit the active electrons of the metal to valence electrons. The study of alkali metals (potassium) is especially well adapted to this method since only one electron is active. The ab-initio calculation and a Monte-Carlo simulation where coupled to optimize the geometry of the KAr n (n = 1-10) cluster when K is in the ground state of the neutral and the ion, or excited in the 4p or 5s state. Calculations were also conducted in collaboration with B. Gervais (CIMAP, Caen) on KAr n clusters having several tens of argon atoms. Absorption spectra were also calculated. From an experimental point-of-view, we were able to characterize the excited states of potassium and barium perturbed by the clusters. In both cases a

  5. Atomic approaches in metastable antiprotonic helium atoms. REPLY to 'analysis of the lifetimes and fractions of antiprotons trapped in metastable antiprotonic-helium states' by I. Shimamura and M. Kimura

    International Nuclear Information System (INIS)

    Yamazaki, Toshimitsu; Ohtsuki, Kazumasa.

    1994-08-01

    In the present note the authors clarify the purpose of YO and complement its essential points, thus showing that the criticisms of SK are inappropriate. The paper YO [1] was aimed at discussing some new aspects related to the metastability of hadronic helium atoms which had been discovered when negative kaons [2], negative pions [3] and antiprotons [4] were stopped in liquid helium. The delayed fraction, time spectrum shape and lifetimes were the observables. Further experimental studies are in progress [5], and as of today there is no successful explanation for these interesting phenomena. So, YO tried to give brief and rather qualitative estimates for the observations in an intuitive way, considering only the leading terms. The following problems are discussed in as simple a manner as possible, starting from the exotic-atom viewpoints of Condo [6] and Russell [7]: i)the atomic core polarization effect, ii)the structure and radiative lifetimes, iii)the non-statistical distribution of the angular momentum and an estimate of the delayed fraction, and iv)the isotope effect, though the title represents only i). To respond to the comments of SK, it is important to consider the correspondence between the atomic approach and the molecular approach for the metastable antiprotonic helium atom of Condo-Russell. We therefore begin this note with a discussion of this aspect. (author)

  6. Fragmented metastable states exist in an attractive bose-einstein condensate for atom numbers well above the critical number of the Gross-Pitaevskii theory.

    Science.gov (United States)

    Cederbaum, Lorenz S; Streltsov, Alexej I; Alon, Ofir E

    2008-02-01

    It is well known that attractive condensates do not posses a stable ground state in three dimensions. The widely used Gross-Pitaevskii theory predicts the existence of metastable states up to some critical number N(cr)(GP) of atoms. It is demonstrated here that fragmented metastable states exist for atom numbers well above N(cr)(GP). The fragments are strongly overlapping in space. The results are obtained and analyzed analytically as well as numerically. The implications are discussed.

  7. Argon line broadening by neutral atoms and application to the measurement of oscillator strengths of AI resonance lines

    International Nuclear Information System (INIS)

    Vallee, O.; Ranson, P.; Chapelle, J.

    1977-01-01

    AI line broadening was studied from collisions between neutral argon atoms (3p 5 4p-3p 5 4s transitions) in a weakly ionised plasma jet (neutral atoms temperature T 0 approximately 4000K, electrons temperature Tsub(e) approximately 6000K, electronic density Nsub(e) 15 cm -3 , ionisation rate α -4 , and pressure range from 1 to 3 kg/cm 2 ). A satisfactory description of Van der Waals broadened lines is obtained by means of a Lennard-Jones potential. Measurement of line widths whose corresponding transitions occur on resonant levels, gives with relatively good accuracy the oscillator strength of the argon resonance lines [fr

  8. Some metals determination in beers by atomic emission spectrometry of induced argon plasma

    International Nuclear Information System (INIS)

    Matsushige, I.

    1990-01-01

    It was made the identification and determination of metals in brazilian bottled and canned beer, using atomic emission spectrometry with d.c. are and argon coupled plasma excitation sources. The elements Co, Cr, Cu, Fe, Pb and Zn were determined in beer samples, after treatment with HNO sub(3) conc. /H sub(2) O sub(2) (30%). In the determination of Co, Cr, Cu, Pb and Zn and alternative method using HNO sub(3) conc. /O sub(3) was proved be useful. The results obtained for Co, Cr, Cu, Fe, Pb and Zn were below the limits established by brazilian legislation, showing the good quality of the beer concerning the metals. The results of this work were requested by the previous Ministerio do Meio Ambiente e Urbanismo in order to contribute to review the brazilian legislation in foods and beverages about metals contents. (author)

  9. ENDOR/ESR of Mn atoms and MnH molecules in solid argon

    Science.gov (United States)

    van Zee, R. J.; Garland, D. A.; Weltner, W., Jr.

    1986-09-01

    Mn atoms and MnH molecules, the latter formed by reaction between metal and hydrogen atoms, were trapped in solid argon and their ESR/ENDOR spectra measured at 4 K. At each pumping magnetic field two ENDOR lines were observed for 55Mn(I=5/2) atoms, corresponding to hyperfine transitions within the MS =±1/2 levels. Values of the hyperfine interaction constant and nuclear moment of 55Mn were derived from the six sets of data. For MnH, three sets of signals were detected: a proton ``matrix ENDOR'' line, transitions in the MS =0,±1 levels involving MI (55Mn)=1/2, 3/2, 5/2 levels, and proton transitions corresponding to νH and νH±aH. Analysis yielded the hyperfine constant aH =6.8(1) MHz and the nuclear quadrupole coupling constant Q'(55Mn)=-11.81(2) MHz. The latter compared favorably with a theoretical value derived earlier by Bagus and Schaefer. A higher term in the spin Hamiltonian appeared to be necessary to fit the proton hyperfine data.

  10. An ultracold, optically trapped mixture of 87Rb and metastable 4He atoms

    NARCIS (Netherlands)

    Flores, A.S.; Mishra, H.P.; Vassen, Wim; Knoop, S.

    2017-01-01

    We report on the realization of an ultracold (<25 μK) mixture of rubidium (87Rb) and metastable triplet helium (4He) in an optical dipole trap. Our scheme involves laser cooling in a dual-species magneto-optical trap, simultaneous MW- and RF-induced forced evaporative cooling in a quadrupole

  11. Negative atomic halogens incident on argon and molecular nitrogen: electron detachment studies

    International Nuclear Information System (INIS)

    Jalbert, G; Medina, A; Magalhaes, S D; Wolff, W; Barros, A L F de; Carrilho, P; Rocha, A B; Faria, N V de Castro

    2007-01-01

    During the last years we have measured total detachment cross sections of atomic and cluster anions colliding with gases in the velocity range of 0.2 to 1.8 a.u. In particular, we measured negative atomic halogens incident on argon and molecular nitrogen. These last data are for the first time analyzed using the simple semi-classical model that we have developed. For that purpose, the values of elastic plus inelastic cross sections for impact of free electrons on Ar and N 2 , the latter showing a shape resonance, convoluted with the anion's outermost electron momentum distribution yielded the overall shape of the anion cross sections. Inclusion of a velocity independent additive term, interpreted as an effective area of the collision region, led to accurate absolute cross section values. The high affinity of the halogens and the existence of a not well described resonance in the e-N 2 collision, are characteristics that may be used to delimit the scope and validity of the model

  12. Inactivation of Bacillus atrophaeus and of Aspergillus niger using beams of argon ions, of oxygen molecules and of oxygen atoms

    Energy Technology Data Exchange (ETDEWEB)

    Raballand, V; Benedikt, J; Keudell, A von [Research Group Reactive Plasmas, Ruhr-Universitaet Bochum, 44780 Bochum (Germany); Wunderlich, J [Fraunhofer Institut for Process Engineering and Packaging, Giggenhauser Strasse 35, 85354 Freising (Germany)], E-mail: Achim.vonKeudell@rub.de

    2008-06-07

    The inactivation of spores of Bacillus atrophaeus and of Aspergillus niger using beams of argon ions, of oxygen molecules and of oxygen atoms is studied. Thereby, the conditions occurring in oxygen containing low pressure plasmas are mimicked and fundamental inactivation mechanisms can be revealed. It is shown that the impact of O atoms has no effect on the viability of the spores and that no etching of the spore coat occurs up to an O atom fluence of 3.5 x 10{sup 19} cm{sup -2}. The impact of argon ions with an energy of 200 eV does not cause significant erosion for fluences up to 1.15 x 10{sup 18} cm{sup -2}. However, the combined impact of argon ions and oxygen molecules or atoms causes significant etching of the spores and significant inactivation. This is explained by the process of chemical sputtering, where an ion-induced defect at the surface of the spore reacts with either the incident bi-radical O{sub 2} or with an incident O atom. This leads to the formation of CO, CO{sub 2} and H{sub 2}O and thus to erosion.

  13. Photoionization from metastable (1s2s) 1Se and 3Se states of the He atom for energies between the N=2 and 3 thresholds of He+

    International Nuclear Information System (INIS)

    Zhou, B.; Lin, C.D.

    1994-01-01

    Photoionization cross sections from the metastable state (1s2s) 1 Se of the He atom for photon energies between the He + (N=2) and (N=3) thresholds are calculated using the hyperspherical close-coupling method. The calculated spectra are convoluted with an energy resolution of 5.4 meV and are compared with the spectra for photoionization from the ground state. It is found that among the four possible outgoing channels, the 1sεp channel, which is the dominant channel for photoionization from the ground state, makes negligible contributions to the total cross sections for photoionization from the metastable state. As a result, the propensity rule derived from the ground-state photoionization no longer applies and more series of the doubly excited states are populated with significant spectral intensity in photoionization from the metastable state. Photoionization cross sections from the metastable (1s2s) 3 Se state are also calculated and analyzed

  14. Trapping of negative kaons by metastable states during the atomic cascade in liquid helium

    International Nuclear Information System (INIS)

    Yamazaki, T.; Aoki, M.; Iwasaki, M.; Hayano, R.S.; Ishikawa, T.; Outa, H.; Takada, E.; Tamura, H.; Sakaguchi, A.

    1989-06-01

    We observed two distinct peaks, 205 MeV/cπ - and 235 MeV/cμ - , associated with K π2 - and K μ2 - decays at rest, respectively, from negative kaons stopped in liquid helium. These peaks were found to be delayed with respect to the stopping K - , showing that stopped K - mesons of about 2% fraction are trapped in metastable states with an overall lifetime of about 40 nsec. This observation provides a direct evidence for Condo's trapping hypothesis for the at-rest decay components of K - and π - in liquid helium. (author)

  15. Excitation into 3p55p levels from the metastable levels of Ar

    International Nuclear Information System (INIS)

    Jung, R. O.; Boffard, John B.; Anderson, L. W.; Lin, Chun C.

    2007-01-01

    Measurements of cross sections for electron-impact excitation out of the J=0 and J=2 3p 5 4s metastable levels of argon into nine of the ten levels of the 3p 5 5p manifold are presented in the energy range from threshold to 10 eV. A mixed target of atoms in both metastable levels was created by a hollow cathode discharge. Laser quenching was used to depopulate either one of the metastable levels, allowing separate measurements of the cross sections from each of the two metastable levels. Unlike the metastable excitation cross sections into 3p 5 4p levels, the cross sections into the 3p 5 5p levels are not found to be proportional to optical oscillator strengths

  16. Bibliography of electron and photon cross sections with atoms and molecules published in the 20th century. Argon

    Energy Technology Data Exchange (ETDEWEB)

    Hayashi, Makoto [Gaseous Electronics Institute, Nagoya, Aichi (Japan)

    2003-01-01

    A bibliography of original and review reports of experiments or theories of electron and photon cross sections and also electron swarm data are presented for atomic or molecular species with specified targets. These works covered 17 atoms and 51 molecules. The present bibliography is only for argon (Ar). About 1,960 papers were compiled. A comprehensive author index is included. The bibliography covers the period 1921 through 2000 for Ar. Finally, author's recommended Ar electron collision cross section set is given in numerical tables. (author)

  17. Bibliography of electron and photon cross sections with atoms and molecules published in the 20th century. Argon

    International Nuclear Information System (INIS)

    Hayashi, Makoto

    2003-01-01

    A bibliography of original and review reports of experiments or theories of electron and photon cross sections and also electron swarm data are presented for atomic or molecular species with specified targets. These works covered 17 atoms and 51 molecules. The present bibliography is only for argon (Ar). About 1,960 papers were compiled. A comprehensive author index is included. The bibliography covers the period 1921 through 2000 for Ar. Finally, author's recommended Ar electron collision cross section set is given in numerical tables. (author)

  18. Simulation of charged and excited particle transport in the low-current discharge in argon-mercury mixture

    International Nuclear Information System (INIS)

    Bondarenko, G G; Fisher, M R; Kristya, V I

    2012-01-01

    Simulation of the electron, ion and metastable excited atom transport in the argon-mercury mixture low-current discharge is fulfilled. Distributions of the particle densities along the discharge gap under different mixture temperatures are obtained and it is demonstrated that the principal mechanism of mercury ion generation is the Penning ionization of mercury atoms by argon metastables, which contribution grows sharply with the mixture temperature due to mercury density increase. Calculations show that the mercury and argon ion flow densities near the cathode are of the same order already under the relative mercury content of about 10 −4 corresponding at the argon pressure 10 3 Pa to the mixture temperature 30 C. Therefore, at the room temperature the electrodes of mercury illuminating lamps at the stage of their ignition are sputtered predominantly by mercury ions.

  19. Microscopic modeling of gas-surface scattering: II. Application to argon atom adsorption on a platinum (111) surface

    Science.gov (United States)

    Filinov, A.; Bonitz, M.; Loffhagen, D.

    2018-06-01

    A new combination of first principle molecular dynamics (MD) simulations with a rate equation model presented in the preceding paper (paper I) is applied to analyze in detail the scattering of argon atoms from a platinum (111) surface. The combined model is based on a classification of all atom trajectories according to their energies into trapped, quasi-trapped and scattering states. The number of particles in each of the three classes obeys coupled rate equations. The coefficients in the rate equations are the transition probabilities between these states which are obtained from MD simulations. While these rates are generally time-dependent, after a characteristic time scale t E of several tens of picoseconds they become stationary allowing for a rather simple analysis. Here, we investigate this time scale by analyzing in detail the temporal evolution of the energy distribution functions of the adsorbate atoms. We separately study the energy loss distribution function of the atoms and the distribution function of in-plane and perpendicular energy components. Further, we compute the sticking probability of argon atoms as a function of incident energy, angle and lattice temperature. Our model is important for plasma-surface modeling as it allows to extend accurate simulations to longer time scales.

  20. Time-resolved study of the electron temperature and number density of argon metastable atoms in argon-based dielectric barrier discharges

    Science.gov (United States)

    Desjardins, E.; Laurent, M.; Durocher-Jean, A.; Laroche, G.; Gherardi, N.; Naudé, N.; Stafford, L.

    2018-01-01

    A combination of optical emission spectroscopy and collisional-radiative modelling is used to determine the time-resolved electron temperature (assuming Maxwellian electron energy distribution function) and number density of Ar 1s states in atmospheric pressure Ar-based dielectric barrier discharges in presence of either NH3 or ethyl lactate. In both cases, T e values were higher early in the discharge cycle (around 0.8 eV), decreased down to about 0.35 eV with the rise of the discharge current, and then remained fairly constant during discharge extinction. The opposite behaviour was observed for Ar 1s states, with cycle-averaged values in the 1017 m-3 range. Based on these findings, a link was established between the discharge ionization kinetics (and thus the electron temperature) and the number density of Ar 1s state.

  1. Studies on production of metastable core-excited atoms by laser-produced x-rays. Final report, 1 October 1984-30 September 1985

    International Nuclear Information System (INIS)

    Harris, S.E.; Young, J.F.

    1986-04-01

    The overall objective of the work on this program was to study methods for production of core-excited metastable atoms by laser-generated x-rays. We are interested in the spectroscopy of these levels, their autoionizing and radiative rates, and their metastability in the presence of hot electrons and ions. The concept of using x-rays emitted from a laser-produced plasma to excite large densities of energetic excited levels in atoms and ions has been thoroughly experimentally investigated using modest, 100 mJ, plasma-producing lasers. One of the objectives of this work was to verify that these techniques could be scaled up to higher energies, such as 20 J. Thus a major effort this year has been devoted to the design and construction of the high energy (20 J) 1064 nm plasma-forming laser system and the tunable probe/transfer laser

  2. Ionization of small molecules by state-selected neon (3P0, 3P2) metastable atoms in the 0.06

    NARCIS (Netherlands)

    Berg, van den F.T.M.; Schonenberg, J.H.M.; Beijerinck, H.C.W.

    1987-01-01

    The velocity dependence and absolute values of the total ionisation cross section for the molecules H2, N2, O2, NO, CO, N2O, CO2, and CH4 by metastable Ne* (3P0) and Ne* (3P2) atoms at collision energies ranging from 0.06 to 6.0 eV have been measured in a crossed beam experiment. State selection of

  3. Importance of polarization effects in electron impact single ionization of argon atom

    Energy Technology Data Exchange (ETDEWEB)

    Purohit, G., E-mail: g_vpurohit@yahoo.co [Department of Basic Sciences, School of Engineering, Sir Padampat Singhania University, Bhatewar, Udaipur 313 601 (India); Patidar, Vinod; Sud, K.K. [Department of Basic Sciences, School of Engineering, Sir Padampat Singhania University, Bhatewar, Udaipur 313 601 (India)

    2009-12-15

    We report the results of our calculations of triple differential cross section (TDCS) for electron impact single ionization (i.e. (e, 2e) processes) from the 3s shell of argon using a modified distorted wave Born approximation formalism by including correlation-polarization potential, which accounts for both correlation and polarization effects. We observe that DWBA formalism including polarization potential is able to reproduce most of the trends of experimental data and hence provide a future direction for further investigation of ionization process from the 3s shell of argon. We also compare our results with the available theoretical and experimental results. The present calculations significantly improve the agreement with the experimental results but still there are certain discrepancies, which is a matter of further investigation.

  4. Time-resolved tunable diode laser absorption spectroscopy of excited argon and ground-state titanium atoms in pulsed magnetron discharges

    Czech Academy of Sciences Publication Activity Database

    Sushkov, V.; Do, H.T.; Čada, Martin; Hubička, Zdeněk; Hippler, R.

    2013-01-01

    Roč. 22, č. 1 (2013), 1-10 ISSN 0963-0252 R&D Projects: GA ČR(CZ) GAP205/11/0386; GA ČR GAP108/12/2104 Institutional research plan: CEZ:AV0Z10100522 Keywords : absorption spectroscopy * diode laser * magnetron * argon metastable * HiPIMS * titanium * time-resolved Subject RIV: BH - Optics, Masers, Lasers Impact factor: 3.056, year: 2013 http://iopscience.iop.org/0963-0252/22/1/015002/

  5. Metastable atomic species in the N{sub 2} flowing afterglow

    Energy Technology Data Exchange (ETDEWEB)

    Levaton, J. [Laboratorio Nacional de Ciencia e Tecnologia do Bioetanol - CTBE/CNPEM, Caixa Postal 6170, 13083-970 Campinas, Sao Paulo (Brazil); Amorim, J., E-mail: jayr.amorim@bioetanol.org.br [Laboratorio Nacional de Ciencia e Tecnologia do Bioetanol - CTBE/CNPEM, Caixa Postal 6170, 13083-970 Campinas, Sao Paulo (Brazil)

    2012-03-13

    Graphical abstract: Calculated N({sup 4}S), N({sup 2}D) and N({sup 2}P) absolute densities as a function of the afterglow time. Highlights: Black-Right-Pointing-Pointer Nitrogen flowing post-discharge. Black-Right-Pointing-Pointer N({sup 4}S) and N({sup 2}D) densities. Black-Right-Pointing-Pointer Kinetic numerical model of the nitrogen afterglow. - Abstract: We have studied by optical emission spectroscopy the post-discharge of a pure N{sub 2} DC flowing discharge in such experimental conditions that the pink afterglow and the Lewis-Rayleigh afterglow occur. The emission profiles originated from the N{sub 2}(B{sup 3}{Pi}{sub g}), N{sub 2}(C{sup 3}{Pi}{sub u}) and N{sub 2}{sup +}(B{sup 2}{Sigma}{sub u}{sup +}) states and the N{sub 2}(B{sup 3}{Pi}{sub g},6{<=}v{<=}12) and N{sub 2}(C{sup 3}{Pi}{sub u},0{<=}v{<=}4) vibrational distributions were obtained in the post-discharge region. With basis on the works of Bockel et al. [S. Bockel, A.M. Diamy, A. Ricard, Surf. Coat. Tech. 74 (1995) 474] and Amorim and Kiohara [J. Amorim, V. Kiohara, Chem. Phys. Lett. 385 (2004) 268], we have obtained the experimental N({sup 4}S) and N({sup 2}D) relative densities along the post-discharge. A numerical model, previously developed to describe the neutral atomic, molecular and ionic species in the afterglow, was improved to include the kinetics of N({sup 2}D) and N({sup 2}P) states. Several kinetic mechanisms leading to the production of N({sup 2}D) in the post-discharge have been studied in order to explain the experimental data. We have determined that the dominant one is the reaction N{sub 2}(X{sup 1}{Sigma}{sub g}{sup +},v>8)+N({sup 4}S){yields}N{sub 2}(X{sup 1}{Sigma}{sub g}{sup +})+N({sup 2}D) with an estimated rate constant of 7 Multiplication-Sign 10{sup -14} cm{sup 3} s{sup -1}. Also, the fit of the numerical density profiles of N{sub 2}(C{sup 3}{Pi}{sub u}) and N{sub 2}{sup +}(B{sup 2}{Sigma}{sub u}{sup +}) to the experimental ones has provided the rate constant for reaction

  6. Spin-polarized 3He nuclear targets and metastable 4He atoms by optical pumping with a tunable, Nd:YAP laser

    International Nuclear Information System (INIS)

    Bohler, C.L.; Schearer, L.D.; Leduc, M.; Nacher, P.J.; Zachorowski, L.; Milner, R.G.; McKeown, R.D.; Woodward, C.E.

    1988-01-01

    Several Nd:YAP lasers were constructed which could be broadly tuned in the 1083-nm region which includes the helium 2 3 S-2 3 P transition, using a Lyot filter and thin, uncoated etalons within the laser cavity. 1 W of power could be extracted at 1083 nm through a 1% transmitting output coupler. This laser beam was used to optically pump metastable 4 He and 3 He 2 3 S helium atoms in a weak discharge cell, spin polarizing the metastable ensemble. In a 3 He cell the polarization is transferred to the nuclear spin system. A 3 He target cell at 0.3 Torr was polarized to 52% in a few minutes. We describe the application of this system to the design of polarized targets for experiments in nuclear physics

  7. Immobilization of single argon atoms in nano-cages of two-dimensional zeolite model systems.

    Science.gov (United States)

    Zhong, Jian-Qiang; Wang, Mengen; Akter, Nusnin; Kestell, John D; Boscoboinik, Alejandro M; Kim, Taejin; Stacchiola, Dario J; Lu, Deyu; Boscoboinik, J Anibal

    2017-07-17

    The confinement of noble gases on nanostructured surfaces, in contrast to bulk materials, at non-cryogenic temperatures represents a formidable challenge. In this work, individual Ar atoms are trapped at 300 K in nano-cages consisting of (alumino)silicate hexagonal prisms forming a two-dimensional array on a planar surface. The trapping of Ar atoms is detected in situ using synchrotron-based ambient pressure X-ray photoelectron spectroscopy. The atoms remain in the cages upon heating to 400 K. The trapping and release of Ar is studied combining surface science methods and density functional theory calculations. While the frameworks stay intact with the inclusion of Ar atoms, the permeability of gasses (for example, CO) through them is significantly affected, making these structures also interesting candidates for tunable atomic and molecular sieves. These findings enable the study of individually confined noble gas atoms using surface science methods, opening up new opportunities for fundamental research.

  8. Zinc, lead and copper in human teeth measured by induced coupled argon plasma atomic emission spectroscopy (ICP-AES)

    Energy Technology Data Exchange (ETDEWEB)

    Chew, L.T.; Bradley, D.A. E-mail: D.A.Bradley@exeter.ac.uk; Mohd, Y.; Jamil, M

    2000-11-15

    Inductively Coupled Argon Plasma Atomic Emission Spectroscopy (ICP-AES) has been used to determine Pb, Zn and Cu levels in 47 exfoliated human teeth (all of which required extraction for orthodontic reasons). Lead concentrations for the group were 1.7 {mu}g (g tooth mass){sup -1} to 40.5 {mu}g (g tooth mass){sup -1}, with a median of 9.8 {mu}g (g tooth mass){sup -1}. A median lead level in excess of the group value was found for the teeth of six lorry drivers who were included in the study. A more significant enhancement was found for the seven subjects whose age was in excess of 60 years. The median values for Zn and Cu were 123.0 and 0.6 {mu}g (g tooth mass){sup -1} respectively. Present values for tooth-Zn are lower than published data for other ethnic groups.

  9. Study of total ionization by {alpha} particles, in pure gases and gaseous mixtures containing metastable atoms, as a function of temperature; Etude de l'ionisation totale par les paricules {alpha}, dans les gaz purs et les melanges gazeux contenant des atomes metastables, en fonction de la temperature

    Energy Technology Data Exchange (ETDEWEB)

    Bristeau, P [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1969-07-01

    Experiments have been carried out on the total ionization by alpha particles, in pure gases and gaseous mixtures containing metastable atoms, as a function of temperature. Using a different experimental method, the results for the mean ionization energy at 300 K given by Jesse in 1953 have been confirmed to within 1 per cent. It is established that in pure gases the mean energy W required to form a pair of ions remains constant as the temperature varies from 77 to 300 K. It is shown that there is a temperature effect for W in binary gas mixtures of the type A-B containing meta-stable atoms A{sup *} and an 'impurity' B. A systematic study is made of the change {delta}W in W as a function of the temperature and of the B 'impurity' concentration in the mixtures Ne - Ar, Ne - Kr, Ne - H{sub 2}, Ne - N{sub 2}, Ne - CH{sub 4} and He - Ar. Experiments have been carried out on a ternary gas mixture of the type A - B - C, where C is a second ionizable 'impurity' added to the binary mixture A - B; they show the existence of excited atoms B{sup *} formed from the 'impurity' B. Finally, it is shown that the amount of metastable atoms formed in a pure gas must be very close to the number N{sub 0} of ion pairs, and that there must exist a correlation between the number N{sub 0} of ion pairs and the number {approx_equal} N{sub 0} of metastable atoms created in the pure rare gases. (author) [French] On realise des experiences sur l'ionisation totale par les particules alpha, dans les gaz purs et les melanges gazeux contenant des atomes metastables, en fonction de la temperature. Avec une methode experimentale differente, on retrouve a mieux que 1 pour cent pres les valeurs de l'energie moyenne d'ionisation que JESSE a obtenues en 1953 et a 300 K. On etablit que dans les gaz purs, l'energie moyenne W pour creer une paire d'ions demeure constante, quand la temperature varie entre 77 et 300 K. On met en evidence un effet de temperature sur W, dans les melanges gazeux binaires du type

  10. Inductively coupled plasma--atomic emission spectroscopy: an evaluation of the use of nitrogen--argon admixtures as plasma discharge atmospheres

    International Nuclear Information System (INIS)

    Zalewski, J.C.

    1979-01-01

    The effects of the use of nitrogen in either the plasma coolant or aerosol carrier gas flows on the physical and spectrochemical properties of the inductively coupled plasma (ICP) were examined. While the plasma operated with nitrogen in the coolant flow exhibited a stability comparable to that of the argon plasma, the use of nitrogen in the aerosol carrier gas flow resulted in a plasma that was less stable. The detection limits obtained for the three plasmas exhibited a similar trend. In addition, the use of nitrogen--argon admixtures in the plasma coolant gas flow yielded an increase in both the net analyte and the background emission intensities when the corresponding argon and nitrogen--argon plasmas were operated under various conditions. Furthermore, the effect of aluminum on the Ca II (393.4 nm) spectral line was reported for the 1000/1 Al/Ca molar ratio. At an observation height of 15 mm, the signal depressions were 4 and 14% for the nitrogen--argon and the argon plasmas, respectively. The above experimental evidence suggested that the operation of the ICP with an Ar--N 2 coolant gas might be hotter than the argon plasma currently in use in this laboratory. The demountable plasma torch designed in collaboration with K. Olson yielded detection limits for 15 elements and 19 spectral lines that were approximately within a factor of two of those obtained with the torch of fused quartz design. The design also appeared to offer a more readily initiated plasma discharge. The experimental evidence presented supports the utilization of nitrogen--argon admixtures in the plasma coolant gas flow as alternate discharge atmospheres for inductively coupled plasma--atomic emission spectroscopy. In contrast, the experimental evidence shows that there is a deterioration in both physical and spectrochemical properties of plasmas operated with a nitrogen aerosol carrier gas

  11. Monitoring of atomic metastable state lifetimes by the laser-enhanced ionization technique--A new method for probing local stoichiometric combustive conditions

    International Nuclear Information System (INIS)

    Ljungberg, Peter; Malmsten, Yvonne; Axner, Ove

    1995-01-01

    The lifetimes of atomic metastable states in an acetylene/air flame have been investigated using the laser-enhanced ionization technique. The lifetimes were found to be several orders of magnitude less than the natural ones, which clearly shows that they are fully determined by the surrounding environment. The lifetime of a specific state has been investigated as a function of flame conditions. It was found that the lifetime is strongly dependent on the local flame composition, with a distinct maximum for stoichiometric conditions. For fuel-lean local conditions, the excess of O2 acts as an effective quencher of the metastable state, while for fuel-rich conditions the quenching is dominated by unburned fuel components. An acetylene/air flame has been probed both as a function of height in the flame, as well as a function of fuel/air composition fed to the burner. The experiments show clearly for which heights and fuel/air compositions that lean, stoichiometric or rich conditions prevail. This makes a monitoring of metastable state lifetimes a useful technique for combustion analysis

  12. Observation of double resonant laser induced transitions in the $v = n - l - 1 = 2$ metastable cascade of antiprotonic helium-4 atoms

    CERN Document Server

    Hayano, R S; Tamura, H; Torii, H A; Hori, Masaki; Maas, F E; Morita, N; Kumakura, M; Sugai, I; Hartmann, F J; Daniel, H; Von Egidy, T; Ketzer, B; Pohl, R; Horváth, D; Eades, John; Widmann, E; Yamazaki, T

    1997-01-01

    A new laser-induced resonant transition in the $v=n-l-1=2$ metastable cascade of antiprotonic $^4$He atoms has been found by using a double resonance technique. This was done by setting the first laser to the already known 470.724 nm resonance ($(n,l)=(37,34)\\rightarrow (36,33)$), while the $(38,35)\\rightarrow (37,34)$ transition was searched for with the second laser. The resonant transition was found at wavelength of 529.622$\\pm$0.003 nm, showing excellent agreement with a recent prediction of Korobov.

  13. Production of H(2s) fast metastable atoms (0.25-3 keV) on a Cs target. Detection of the α Lyman radiation induced by Stark effect: polarisation. Destruction of H(2s) atoms on an IH target

    International Nuclear Information System (INIS)

    Valance, Antoine.

    1974-01-01

    The production, detection and destruction of the 2S1/2 metastable state of the hydrogen atom were studied. The quasi-resonant charge exchange processes between fast protons and cesium target, in the total cross sections for production of metastable H(2s) atoms and radiative H(2p) atoms showed structures hitherto unobserved. The theoretical study is based on calculation of the adiabatic molecular potential terms of the ionic quasi-molecule (CsH) + , taking a Helmann type pseudopotential to describe the electron with respect to the core of the cesium ion. The probabilities of transition towards the output channels are calculated using a stationary state perturbation method. From the data obtained the interferece phenomena of excited quasi-molecular states can be interpreted coherently in slow collision. The probability of transition along the inelastic output channels displays characteristics of a harmonic oscillatory function inversely proportional to the speed of approach of the particles. The frequency of these oscillations depends very slightly on the impact parameter. The theory proposed involves three Σ states. During detection of the metastable ions the Lyman-α radiation induced in the de-excitation electric field by Stark effect present anisotropic features. The degree of polarization measured as a function of the field strength oscillates around a slow decay toward a limit-1 at strong electric field. A theory not accounting for the hyperfine structure of states mixed by Stark effect showed a double oscillatory structure containing the two frequencies correlated to the 2P1/2 and 2P3/2 states from the 2S1/2 state. Finally the results on the electron detachment reaction between fast metastable atoms and hydroiodic acid target have contributed towards research on polarized proton sources [fr

  14. Scattering of hyperthermal argon atoms from clean and D-covered Ru surfaces

    NARCIS (Netherlands)

    Ueta, H.; Gleeson, M.A.; Kleyn, A.W.

    2011-01-01

    Hyperthermal Ar atoms were scattered from a Ru(0001) surface held at temperatures of 180, 400 and 600 K, and from a Ru(0001)-(1×1)D surface held at 114 and 180 K. The resultant angular intensity and energy distributions are complex. The in-plane angular distributions have narrow (FWHM ≤ 10°)

  15. Effects of oxygen concentration on atmospheric pressure dielectric barrier discharge in Argon-Oxygen Mixture

    Science.gov (United States)

    Li, Xuechun; Li, Dian; Wang, Younian

    2016-09-01

    A dielectric barrier discharge (DBD) can generate a low-temperature plasma easily at atmospheric pressure and has been investigated for applications in trials in cancer therapy, sterilization, air pollution control, etc. It has been confirmed that reactive oxygen species (ROS) play a key role in the processes. In this work, we use a fluid model to simulate the plasma characteristics for DBD in argon-oxygen mixture. The effects of oxygen concentration on the plasma characteristics have been discussed. The evolution mechanism of ROS has been systematically analyzed. It was found that the ground state oxygen atoms and oxygen molecular ions are the dominated oxygen species under the considered oxygen concentrations. With the oxygen concentration increasing, the densities of electrons, argon atomic ions, resonance state argon atoms, metastable state argon atoms and excited state argon atoms all show a trend of decline. The oxygen molecular ions density is high and little influenced by the oxygen concentration. Ground state oxygen atoms density tends to increase before falling. The ozone density increases significantly. Increasing the oxygen concentration, the discharge mode begins to change gradually from the glow discharge mode to Townsend discharge mode. Project supported by the National Natural Science Foundation of China (Grant No. 11175034).

  16. Non-resonant two and three-photon ionization of the singlet and triplet metastable helium atoms of an atomic jet

    International Nuclear Information System (INIS)

    Mathieu, Bernard.

    1978-01-01

    The three-photon ionization cross-section of the helium metastables He(2 1 S) and He(2 3 S) is determined by means of the linearly polarized radiation of a pulsed ruby laser with an emission wavelength equal to 6946.4 A at 19 0 C. Two-photon ionization, obtained by doubling the laser beam frequency, is also studied [fr

  17. Density of atoms in Ar*(3p5 4s) states and gas temperatures in an argon surfatron plasma measured by tunable laser spectroscopy

    NARCIS (Netherlands)

    Hübner, S.; Sadeghi, N.; Carbone, E.A.D.; Mullen, van der J.J.A.M.

    2013-01-01

    This study presents the absolute argon 1 s (in Paschens’s notation) densities and the gas temperature, Tg, obtained in a surfatron plasma in the pressure range 0:65

    atoms in 1s3, 1s4,and 1s5 states, were

  18. Room-temperature atomic layer deposition of ZrO{sub 2} using tetrakis(ethylmethylamino)zirconium and plasma-excited humidified argon

    Energy Technology Data Exchange (ETDEWEB)

    Kanomata, K. [Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa 992-8510 (Japan); Japan Society for the Promotion of Science, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo 102-0083 (Japan); Tokoro, K.; Imai, T.; Pansila, P.; Miura, M.; Ahmmad, B.; Kubota, S.; Hirahara, K. [Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa 992-8510 (Japan); Hirose, F., E-mail: fhirose@yz.yamagata-u.ac.jp [Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa 992-8510 (Japan)

    2016-11-30

    Highlights: • RT-ALD of ZrO{sub 2} is developed using TEMAZ and plasma-excited humidified argon. • The plasma-excited humidified argon is effective in oxidizing the TEMAZ saturated ZrO{sub 2}. • We discuss the reaction mechanism of the RT-ZrO{sub 2} ALD. - Abstract: Room-temperature atomic layer deposition (ALD) of ZrO{sub 2} is developed with tetrakis(ethylmethylamino)zirconium (TEMAZ) and a plasma-excited humidified argon. A growth per cycle of 0.17 nm/cycle at room temperature is confirmed, and the TEMAZ adsorption and its oxidization on ZrO{sub 2} are characterized by IR absorption spectroscopy with a multiple internal reflection mode. TEMAZ is saturated on a ZrO{sub 2} surface with exposures exceeding ∼2.0 × 10{sup 5} Langmuir (1 Langmuir = 1.0 × 10{sup −6} Torr s) at room temperature, and the plasma-excited humidified argon is effective in oxidizing the TEMAZ-adsorbed ZrO{sub 2} surface. The IR absorption spectroscopy suggests that Zr-OH works as an adsorption site for TEMAZ. The reaction mechanism of room-temperature ZrO{sub 2} ALD is discussed in this paper.

  19. Calculation of the Ionization Coefficient in the Townsend Discharge in the Mixture of Argon and Mercury Vapors with Temperature-Dependent Composition

    Science.gov (United States)

    Bondarenko, G. G.; Dubinina, M. S.; Fisher, M. R.; Kristya, V. I.

    2018-04-01

    For a hybrid model of the low-current discharge considering, along with direct ionization of the mixture components by electrons, the Penning ionization of mercury atoms by metastable argon atoms, the ionization coefficient in the argon-mercury mixture used in illuminating lamps is calculated. The analytical approximation formula describing the dependence of the ionization coefficient of the mixture on the reduced electric field strength and temperature is obtained for sufficiently wide ranges of their variations, and its accuracy is estimated. It is demonstrated that the discharge ignition voltage calculated using this formula is in agreement with the results of simulation and the available experimental data.

  20. Electron impact with argon excitation out of the e-Ar(3p54s,J = 2)

    International Nuclear Information System (INIS)

    Jin Shiqi; Xu Zhizhan

    1998-01-01

    It is shown that the electron impact with argon excitation out of the metastable to the 3p 5 4p levels is very important for spectrum, laser physics and plasma processing. Analysis of the cross sections of 3p 5 4p, J = 3 level in manifolds of 3p 5 4p is valuable. It also provides the atomic character of emission harmonics in intense laser field

  1. Influences of the propyl group on the van der Waals structures of 4-propylaniline complexes with one and two argon atoms studied by electronic and cationic spectroscopy

    International Nuclear Information System (INIS)

    Yang, Zhijun; Gu, Quanli; Trindle, Carl O.; Knee, J. L.

    2015-01-01

    4-propylaniline complexes with one and two argon atoms formed in the molecular beam were studied in the first excited electronic state, S 1 , using resonance enhanced two-photon ionization spectroscopy and in the cation ground state, D 0 , using mass analyzed threshold ionization spectroscopy. The combination of electronic and cationic spectra of the clusters allows two conformations to be identified in both aniline-Ar 1 and aniline-Ar 2 , which are assigned to either the gauche configuration or anti-configuration of 4-propylaniline. The gauche isomer exhibits complex bands shifted 29 cm −1 and 89 cm −1 from the S 1 origin bands and 83 cm −1 and 148 cm −1 from the ionization potential assigned to the Ar 1 and Ar 2 complexes, respectively. For the anti-rotamer, the corresponding shifts actually become nearly additive, 53 cm −1 and 109 cm −1 for the S 1 origin bands, and 61 cm −1 and 125 cm −1 for the ionization potentials. Ab initio calculations provide insights into the influences of the propyl and amino groups on the positions of the argon atoms within the clusters. In addition, the binding energy of one argon with the gauche isomer of 4-propylaniline has been measured to be 550 ± 5 cm −1 in the D 0 state, 496 ± 5 cm −1 in the S 1 state, and 467 ± 5 cm −1 in the neutral ground state, S 0

  2. Orientation of Ar(3P2) atoms by laser optical pumping

    International Nuclear Information System (INIS)

    Giberson, K.W.; Hart, M.W.; Hammond, M.S.; Dunning, F.B.; Walters, G.K.

    1984-01-01

    A beam of argon metastable atoms with a high degree of electron-spin polarization has been produced by optical pumping using an Oxazine 750 dye laser. The beam is suitable for the study of electron spin and orbital orientation dependences in a variety of collision processes

  3. Comparison in the analytical performance between krypton and argon glow discharge plasmas as the excitation source for atomic emission spectrometry.

    Science.gov (United States)

    Wagatsuma, Kazuaki

    2009-04-01

    The emission characteristics of ionic lines of nickel, cobalt, and vanadium were investigated when argon or krypton was employed as the plasma gas in glow discharge optical emission spectrometry. A dc Grimm-style lamp was employed as the excitation source. Detection limits of the ionic lines in each iron-matrix alloy sample were compared between the krypton and the argon plasmas. Particular intense ionic lines were observed in the emission spectra as a function of the discharge gas (krypton or argon), such as the Co II 258.033 nm for krypton and the Co II 231.707 nm for argon. The explanation for this is that collisions with the plasma gases dominantly populate particular excited levels of cobalt ion, which can receive the internal energy from each gas ion selectively, for example, the 3d(7)4p (3)G(5) (6.0201 eV) for krypton and the 3d(7)4p (3)G(4) (8.0779 eV) for argon. In the determination of nickel as well as cobalt in iron-matrix samples, more sensitive ionic lines could be found in the krypton plasma rather than the argon plasma. Detection limits in the krypton plasma were 0.0039 mass% Ni for the Ni II 230.299-nm line and 0.002 mass% Co for the Co II 258.033-nm line. However, in the determination of vanadium, the argon plasma had better analytical performance, giving a detection limit of 0.0023 mass% V for the V II 309.310-nm line.

  4. Influence of ion-to-atom ratio on the microstructure of evaporated molybdenum thin films grown using low energy argon ions

    Energy Technology Data Exchange (ETDEWEB)

    Yadav, Praveen Kumar, E-mail: praveenyadav@rrcat.gov.in; Nayak, Maheswar; Rai, Sanjay Kumar; Lodha, Gyanendra Singh [X-ray Optics Section, Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Sant, Tushar; Sharma, Surinder Mohan [High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Mukherjee, Chandrachur [Mechanical and Optical Support Section, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)

    2014-03-15

    The authors report the effect of argon ion to molybdenum atom ratio (r) on the microstructure of low energy (70 eV) argon ion assisted electron beam evaporated Mo thin films. Surface roughness, morphology, and crystallinity of Mo films are found to strongly depend on “r.” Increase of “r” from 0 to 100 induces gradual loss in crystallinity, reduction in surface roughness and systematic increase in density of the film. For “r” ∼ 100, average atomic density of the film approaches the bulk value (97%) with lowest surface roughness. Further, increasing “r” up to 170 reduces the atomic density, increases roughness, and increase in crystallinity induced by low energy Ar ion beam. The observed surface roughness and grain size determined by x-ray reflectivity and glancing incidence x-ray diffraction correlate well with atomic force microscopy measurements. This study demonstrates that for r = 100 one gets lowest roughness Mo film with highest density and nearly amorphous microstructure. The growth model is discussed by structural zone model.

  5. Energy of the Isolated Metastable Iron-Nickel FCC Nanocluster with a Carbon Atom in the Tetragonal Interstice.

    Science.gov (United States)

    Bondarenko, Natalya V; Nedolya, Anatoliy V

    2017-12-01

    The energy of the isolated iron-nickel nanocluster was calculated by molecular mechanics method using Lennard-Jones potential. The cluster included a carbon atom that drifted from an inside octahedral interstice to a tetrahedral interstice in [Formula: see text] direction and after that in direction to the surface. In addition, one of 14 iron atoms was replaced by a nickel atom, the position of which was changing during simulation.The energy of the nanocluster was estimated at the different interatomic distances. As a result of simulation, the optimal interatomic distances of Fe-Ni-C nanocluster was chosen for the simulation, in which height of the potential barrier was maximal and face-centered cubic (FCC) nanocluster was the most stable.It is shown that there were three main positions of a nickel atom that significantly affected nanocluster's energy.The calculation results indicated that position of the carbon atom in the octahedral interstice was more energetically favorable than tetrahedral interstice in the case of FCC nanocluster. On the other side, the potential barrier was smaller in the direction [Formula: see text] than in the direction .This indicates that there are two ways for carbon atom to drift to the surface of the nanocluster.

  6. Spatial profiles of electron and metastable atom densities in positive polarity fast ionization waves sustained in helium

    International Nuclear Information System (INIS)

    Weatherford, Brandon R.; Barnat, E. V.; Xiong, Zhongmin; Kushner, Mark J.

    2014-01-01

    Fast ionization waves (FIWs), often generated with high voltage pulses over nanosecond timescales, are able to produce large volumes of ions and excited states at moderate pressures. The mechanisms of FIW propagation were experimentally and computationally investigated to provide insights into the manner in which these large volumes are excited. The two-dimensional structure of electron and metastable densities produced by short-pulse FIWs sustained in helium were measured using laser-induced fluorescence and laser collision-induced fluorescence diagnostics for times of 100–120 ns after the pulse, as the pressure was varied from 1 to 20 Torr. A trend of center-peaked to volume-filling to wall-peaked electron density profiles was observed as the pressure was increased. Instantaneous FIW velocities, obtained from plasma-induced emission, ranged from 0.1 to 3 × 10 9  cm s −1 , depending on distance from the high voltage electrode and pressure. Predictions from two-dimensional modeling of the propagation of a single FIW correlated well with the experimental trends in electron density profiles and wave velocity. Results from the model show that the maximum ionization rate occurs in the wavefront, and the discharge continues to propagate forward after the removal of high voltage from the powered electrode due to the potential energy stored in the space charge. As the pressure is varied, the radial distribution of the ionization rate is shaped by changes in the electron mean free path, and subsequent localized electric field enhancement at the walls or on the centerline of the discharge.

  7. Using the van der Waals broadening of the spectral atomic lines to measure the gas temperature of an argon microwave plasma at atmospheric pressure

    International Nuclear Information System (INIS)

    Yubero, C.; Dimitrijevic, M.S.; Garcia, M.C.; Calzada, M.D.

    2007-01-01

    The ro-vibrational emission spectra of the molecular species are usually used to measure the gas temperature of a discharge at atmospheric pressure. However, under some experimental conditions, it is difficult to detect them. In order to overcome this difficulty and obtain the temperature, there are methods based on the relation between the gas temperature and the van der Waals broadening of argon atomic spectral lines with a Stark contribution negligible. In this work, we propose a method based on this relation but for lines with a Stark broadening comparable with the van der Waals one

  8. High-performance liquid chromatographic separation of biologically important arsenic species utilizing on-line inductively coupled argon plasma atomic emission spectrometric detection

    Energy Technology Data Exchange (ETDEWEB)

    Spall, W.D.; Lynn, J.G.; Andersen, J.L.; Valdez, J.G.; Gurley, L.R.

    1986-06-01

    An anion exchange, high-performance liquid chromatography technique using a 15-min linear gradient from water to 0.5 M ammonium carbonate to separate arsenite, arsenate, methylarsonic acid, and dimethylarsinic acid from neutral arsenic containing compounds was developed for application to a study of arsenic metabolism in cultured cell suspensions. Arsenic detection was accomplished by the direct coupling of the column effluent to an inductively coupled argon plasma atomic emission spectrometer (ICAP-AES) set to monitor the arsenic emission line at 197.19 nm. The analysis requires 20 min and is sensitive to as low as 60 ng of arsenic injected to the column.

  9. Influences of the propyl group on the van der Waals structures of 4-propylaniline complexes with one and two argon atoms studied by electronic and cationic spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Zhijun [School of Basic Medical Sciences, Xinxiang Medical University, Xinxiang, Henan 453003 (China); Gu, Quanli [School of Basic Medical Sciences, Xinxiang Medical University, Xinxiang, Henan 453003 (China); Department of Chemistry, University of Oklahoma, Norman, Oklahoma 73019 (United States); Trindle, Carl O., E-mail: cot@virginia.edu [Chemistry Department, University of Virginia, Charlottesville, Virginia 22904 (United States); Knee, J. L., E-mail: jknee@wesleyan.edu [Chemistry Department, Wesleyan University, Middletown, Connecticut 06459 (United States)

    2015-07-21

    4-propylaniline complexes with one and two argon atoms formed in the molecular beam were studied in the first excited electronic state, S{sub 1}, using resonance enhanced two-photon ionization spectroscopy and in the cation ground state, D{sub 0}, using mass analyzed threshold ionization spectroscopy. The combination of electronic and cationic spectra of the clusters allows two conformations to be identified in both aniline-Ar{sub 1} and aniline-Ar{sub 2}, which are assigned to either the gauche configuration or anti-configuration of 4-propylaniline. The gauche isomer exhibits complex bands shifted 29 cm{sup −1} and 89 cm{sup −1} from the S{sub 1} origin bands and 83 cm{sup −1} and 148 cm{sup −1} from the ionization potential assigned to the Ar{sub 1} and Ar{sub 2} complexes, respectively. For the anti-rotamer, the corresponding shifts actually become nearly additive, 53 cm{sup −1} and 109 cm{sup −1} for the S{sub 1} origin bands, and 61 cm{sup −1} and 125 cm{sup −1} for the ionization potentials. Ab initio calculations provide insights into the influences of the propyl and amino groups on the positions of the argon atoms within the clusters. In addition, the binding energy of one argon with the gauche isomer of 4-propylaniline has been measured to be 550 ± 5 cm{sup −1} in the D{sub 0} state, 496 ± 5 cm{sup −1} in the S{sub 1} state, and 467 ± 5 cm{sup −1} in the neutral ground state, S{sub 0}.

  10. Electron-impact excitation of atomic-argon 3p54s-3p55p spectral transitions

    International Nuclear Information System (INIS)

    Bogdanova, I.P.; Yurgenson, S.V.

    1990-01-01

    Cross sections of excitation of some spectral lines of argon corresponding to transitions from 3p 5 5p-levels are measured using a pulsed electron beam. Cross sections of level excitation are estimated. It is shown that in transition from 3p 5 4p-levels to 3p 5 5p-levels, the cross section of levels by means of the electron impact decreases 20 times

  11. Laboratory studies on the excitation and collisional deactivation of metastable atoms and molecules in the aurora and airglow

    International Nuclear Information System (INIS)

    Zipf, E.C.

    1974-02-01

    The aeronomy group at the University of Pittsburgh is actively engaged in a series of coordinated satellite, sounding rocket, and laboratory studies designed to expand and clarify knowledge of the physics and chemistry of planetary atmospheres. Three major discoveries have been made that will lead ultimately to a complete and dramatic revision of our ideas on the ionospheres of Mars, Venus, and the Earth and on the origin of their vacuum ultraviolet airglows. The results have already suggested a new generation of ionosphere studies which probably can be carried out best by laser heterodyning techniques. Laboratory studies have also identified, for the first time, the physical mechanism responsible for the remarkable nitric oxide buildup observed in some auroral arcs. This development is an important break-through in auroral physics, and has military ramifications of considerable interest to the Department of Defense. This work may also shed some light on related NO and atomic nitrogen problems in the mesosphere. (U.S.)

  12. Ionization of H2O molecules through second order collisions in an argon-filled flow ionization chamber

    International Nuclear Information System (INIS)

    Leonhardt, J.

    1976-01-01

    In an argon-filled ionization chamber with a constant radionuclide radiation source, the ionization of H 2 O through second order collisions with 3sub(p) 2 states of argon excited by field-accelerated electrons is considered within the range of discharge caused by external potentials under atmospheric pressure. It is found that the logarithm of the change of ionization current is proportional to power 3/2 of the electric field strength. Possible formation mechanisms are discussed. Most probable is the ionization of H 2 O through collision with Ar 2 argon dimers originating from excited metastable atoms as a result of triple collision. The production cross section for H 2 O + has been estimated to be sigmasub(H 2 O) approximately 5x10 -15 . (author)

  13. Deviation from Boltzmann distribution in excited energy levels of singly-ionized iron in an argon glow discharge plasma for atomic emission spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Lei; Kashiwakura, Shunsuke; Wagatsuma, Kazuaki, E-mail: wagatuma@imr.tohoku.ac.jp

    2012-01-15

    A Boltzmann plot for many iron ionic lines having excitation energies of 4.7-9.1 eV was investigated in an argon glow discharge plasma when the discharge parameters, such as the voltage/current and the gas pressure, were varied. A Grimm-style radiation source was employed in a DC voltage range of 400-800 V at argon pressures of 400-930 Pa. The plot did not follow a linear relationship over a wide range of the excitation energy, but it yielded a normal Boltzmann distribution in the range of 4.7-5.8 eV and a large overpopulation in higher-lying excitation levels of iron ion. A probable reason for this phenomenon is that excitations for higher excited energy levels of iron ion would be predominantly caused by non-thermal collisions with argon species, the internal energy of which is received by iron atoms for the ionization. Particular intense ionic lines, which gave a maximum peak of the Boltzmann plot, were observed at an excitation energy of ca. 7.7 eV. They were the Fe II 257.297-nm and the Fe II 258.111-nm lines, derived from the 3d{sup 5}4s4p {sup 6}P excited levels. The 3d{sup 5}4s4p {sup 6}P excited levels can be highly populated through a resonance charge transfer from the ground state of argon ion, because of good matching in the excitation energy as well as the conservation of the total spin before and after the collision. An enhancement factor of the emission intensity for various Fe II lines could be obtained from a deviation from the normal Boltzmann plot, which comprised the emission lines of 4.7-5.8 eV. It would roughly correspond to a contribution of the charge transfer excitation to the excited levels of iron ion, suggesting that the charge-transfer collision could elevate the number density of the corresponding excited levels by a factor of ca.10{sup 4}. The Boltzmann plots give important information on the reason why a variety of iron ionic lines can be emitted from glow discharge plasmas.

  14. Isentropic Compression of Argon

    International Nuclear Information System (INIS)

    Oona, H.; Solem, J.C.; Veeser, L.R.; Ekdahl, C.A.; Rodriquez, P.J.; Younger, S.M.; Lewis, W.; Turley, W.D.

    1997-01-01

    We are studying the transition of argon from an insulator to a conductor by compressing the frozen gas isentropically to pressures at which neighboring atomic orbitals overlap sufficiently to allow some electron motion between atoms. Argon and the other rare gases have closed electron shells and therefore remain montomic, even when they solidify. Their simple structure makes it likely that any measured change in conductivity is due to changes in the atomic structure, not in molecular configuration. As the crystal is compressed the band gap closes, allowing increased conductivity. We have begun research to determine the conductivity at high pressures, and it is our intention to determine the compression at which the crystal becomes a metal

  15. Elastic electron differential cross sections for argon atom in the intermediate energy range from 40 eV to 300 eV

    Science.gov (United States)

    Ranković, Miloš Lj.; Maljković, Jelena B.; Tökési, Károly; Marinković, Bratislav P.

    2018-02-01

    Measurements and calculations for electron elastic differential cross sections (DCS) of argon atom in the energy range from 40 to 300 eV are presented. DCS have been measured in the crossed beam arrangement of the electron spectrometer with an energy resolution of 0.5 eV and angular resolution of 1.5∘ in the range of scattering angles from 20∘ to 126∘. Both angular behaviour and energy dependence of DCS are obtained in a separate sets of experiments, while the absolute scale is achieved via relative flow method, using helium as a reference gas. All data is corrected for the energy transmission function, changes of primary electron beam current and target pressure, and effective path length (volume correction). DCSs are calculated in relativistic framework by expressing the Mott's cross sections in partial wave expansion. Our results are compared with other available data.

  16. Electron-capture cross sections for low-energy highly charged neon and argon ions from molecular and atomic hydrogen

    International Nuclear Information System (INIS)

    Can, C.; Gray, T.J.; Varghese, S.L.; Hall, J.M.; Tunnell, L.N.

    1985-01-01

    Electron-capture cross sections for low-velocity (10 6 --10 7 cm/s) highly charged Ne/sup q/+ (2< or =q< or =7) and Ar/sup q/+ (2< or =q< or =10)= projectiles incident on molecular- and atomic-hydrogen targets have been measured. A recoil-ion source that used the collisions of fast heavy ions (1 MeV/amu) with target gas atoms was utilized to produce slow highly charged ions. Atomic hydrogen was produced by dissociating hydrogen molecules in a high-temperature oven. Measurements and analysis of the data for molecular- and atomic-hydrogen targets are discussed in detail. The measured absolute cross sections are compared with published data and predictions of theoretical models

  17. Atomic hydrogen and argon ground state density determination in a recombining plasma using visible light absorption spectroscopy

    NARCIS (Netherlands)

    Otorbaev, D.K.; Buuron, A.J.M.; Sanden, van de M.C.M.; Meulenbroeks, R.F.G.; Schram, D.C.

    1995-01-01

    The atomic radical density in the first excited state, obtained by the technique of optical absorption spectroscopy, and a simple kinetic model are used to determine the radical ground state density in a recombining expanding plasma. The kinetic model used does not require knowledge of the shape of

  18. Metastable and bistable defects in silicon

    International Nuclear Information System (INIS)

    Mukashev, Bulat N; Abdullin, Kh A; Gorelkinskii, Yurii V

    2000-01-01

    Existing data on the properties and structure of metastable and bistable defects in silicon are analyzed. Primary radiation-induced defects (vacancies, self-interstitial atoms, and Frenkel pairs), complexes of oxygen, carbon, hydrogen, and other impurity atoms and defects with negative correlation energy are considered. (reviews of topical problems)

  19. Boltzmann statistical consideration on the excitation mechanism of iron atomic lines emitted from glow discharge plasmas

    International Nuclear Information System (INIS)

    Zhang Lei; Kashiwakura, Shunsuke; Wagatsuma, Kazuaki

    2011-01-01

    A Boltzmann plot for many iron atomic lines having excitation energies of 3.3–6.9 eV was investigated in glow discharge plasmas when argon or neon was employed as the plasma gas. The plot did not show a linear relationship over a wide range of the excitation energy, but showed that the emission lines having higher excitation energies largely deviated from a normal Boltzmann distribution whereas those having low excitation energies (3.3–4.3 eV) well followed it. This result would be derived from an overpopulation among the corresponding energy levels. A probable reason for this is that excitations for the high-lying excited levels would be caused predominantly through a Penning-type collision with the metastable atom of argon or neon, followed by recombination with an electron and then stepwise de-excitations which can populate the excited energy levels just below the ionization limit of iron atom. The non-thermal excitation occurred more actively in the argon plasma rather than the neon plasma, because of a difference in the number density between the argon and the neon metastables. The Boltzmann plots yields important information on the reason why lots of Fe I lines assigned to high-lying excited levels can be emitted from glow discharge plasmas. - Highlights: ► This paper shows the excitation mechanism of Fe I lines from a glow discharge plasma. ► A Boltzmann distribution is studied among iron lines of various excitation levels. ► We find an overpopulation of the high-lying energy levels from the normal distribution. ► It is caused through Penning-type collision of iron atom with argon metastable atom.

  20. Boltzmann statistical consideration on the excitation mechanism of iron atomic lines emitted from glow discharge plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Lei; Kashiwakura, Shunsuke; Wagatsuma, Kazuaki, E-mail: wagatuma@imr.tohoku.ac.jp

    2011-11-15

    A Boltzmann plot for many iron atomic lines having excitation energies of 3.3-6.9 eV was investigated in glow discharge plasmas when argon or neon was employed as the plasma gas. The plot did not show a linear relationship over a wide range of the excitation energy, but showed that the emission lines having higher excitation energies largely deviated from a normal Boltzmann distribution whereas those having low excitation energies (3.3-4.3 eV) well followed it. This result would be derived from an overpopulation among the corresponding energy levels. A probable reason for this is that excitations for the high-lying excited levels would be caused predominantly through a Penning-type collision with the metastable atom of argon or neon, followed by recombination with an electron and then stepwise de-excitations which can populate the excited energy levels just below the ionization limit of iron atom. The non-thermal excitation occurred more actively in the argon plasma rather than the neon plasma, because of a difference in the number density between the argon and the neon metastables. The Boltzmann plots yields important information on the reason why lots of Fe I lines assigned to high-lying excited levels can be emitted from glow discharge plasmas. - Highlights: Black-Right-Pointing-Pointer This paper shows the excitation mechanism of Fe I lines from a glow discharge plasma. Black-Right-Pointing-Pointer A Boltzmann distribution is studied among iron lines of various excitation levels. Black-Right-Pointing-Pointer We find an overpopulation of the high-lying energy levels from the normal distribution. Black-Right-Pointing-Pointer It is caused through Penning-type collision of iron atom with argon metastable atom.

  1. Analysis of Indium Tin Oxide Film Using Argon Fluroide (ArF) Laser-Excited Atomic Fluorescence of Ablated Plumes.

    Science.gov (United States)

    Ho, Sut Kam; Garcia, Dario Machado

    2017-04-01

    A two-pulse laser-excited atomic fluorescence (LEAF) technique at 193 nm wavelength was applied to the analysis of indium tin oxide (ITO) layer on polyethylene terephthalate (PET) film. Fluorescence emissions from analytes were induced from plumes generated by first laser pulse. Using this approach, non-selective LEAF can be accomplished for simultaneous multi-element analysis and it overcomes the handicap of strict requirement for laser excitation wavelength. In this study, experimental conditions including laser fluences, times for gating and time delay between pulses were optimized to reveal high sensitivity with minimal sample destruction and penetration. With weak laser fluences of 100 and 125 mJ/cm 2 for 355 and 193 nm pulses, detection limits were estimated to be 0.10% and 0.43% for Sn and In, respectively. In addition, the relation between fluorescence emissions and number of laser shots was investigated; reproducible results were obtained for Sn and In. It shows the feasibility of depth profiling by this technique. Morphologies of samples were characterized at various laser fluences and number of shots to examine the accurate penetration. Images of craters were also investigated using scanning electron microscopy (SEM). The results demonstrate the imperceptible destructiveness of film after laser shot. With such weak laser fluences and minimal destructiveness, this LEAF technique is suitable for thin-film analysis.

  2. Spectral Diagnosis on Contribution of Metastable Atoms to Ionization in Hall Effect Thruster%亚稳态原子对霍尔推力器电离影响的光谱诊断

    Institute of Scientific and Technical Information of China (English)

    颜世林; 宁中喜; 于达仁

    2013-01-01

    In order to quantitatively evaluate the contribution of metastable atoms in the ionization process in Hall thrusters (HET),and to improve the accuracy of ionization simulation models,we adopted the emissive-spectrum-intensity-ratio method to obtain the Krypton effective ionization-rate in the channel of HET.The experimental results revealed that,by taking the effect of metastable atoms into consideration,compared with that of base atoms,the Krypton effective ionization-rate increased by about 11 % and the increase is most within the electron temperature range of 15~20 eV.Hence,it is concluded that Krypton atoms in HET channel have a relatively high effective ionization rate,and the metastable contribution should be considered in HET ionization models.%霍尔推力器(HET)是一种先进的电推进装置,在航天领域有着广泛应用.为了衡量亚稳态原子对于推力器电离过程的影响,提高相应电离计算模拟模型的准确性,应用发射光谱线强度比计算方法来确定HET通道中包含亚稳态原子贡献的氪原子有效电离速率.实验发现,考虑亚稳态院子的贡献后,氪原子有效电离速率相对于未考虑亚稳态贡献的基态原子电离速率高,在15~20 eV的电子温度范围内增加最多,大约11%.计算结果说明亚稳态原子的存在使得HET通道内氪原子具有较高的有效电离速率,所以在HET电离模型中必须引入亚稳态的贡献项.

  3. Preferential site occupancy observed in coexpanded argon-krypton clusters

    International Nuclear Information System (INIS)

    Lundwall, M.; Bergersen, H.; Lindblad, A.; Oehrwall, G.; Svensson, S.; Bjoerneholm, O.; Tchaplyguine, M.

    2006-01-01

    Free heterogeneous argon-krypton clusters have been produced by coexpansion and investigated by means of x-ray photoelectron spectroscopy. By examining cluster surface and bulk binding energy shifts, relative intensities, and peak widths, we show that in the mixed argon-krypton clusters the krypton atoms favor the bulk and argon atoms are pushed to the surface. Furthermore, we show that krypton atoms in the surface layer occupy high-coordination sites and that heterogeneous argon-krypton clusters produced by coexpansion show the same surface structure as argon host clusters doped with krypton. These observations are supported by site-dependent calculations of chemical shifts

  4. The argon excimer laser

    International Nuclear Information System (INIS)

    Wrobel, W.G.

    1981-02-01

    The electron-beam-pumped argon eximer laser is investigated and tuned for the first time. The electron beam is generated by means of an improved coaxial field emmision diode in which argon gas is excited with power densities of 0.3 GW/cm 3 for 18 ns. The processes in the excited gas of 20 to 65 bar are described in the context of a kinetic model as a sequence of stationary states. Investigations of the amplified spontaneous emission (superfluorescence) confirm the predictions of this model. Only the absorption due to the excited Ar atoms is anomalously high. Reproducible operation of the argon eximer laser was achieved in a wide pressure range with various resonator arrangements. The wavelength of this shortest wavelength of this shortest wavelength excimer laser is 126 nm, the laser line width approx. 1.7 nm, the pulse length 7 to 13 ns, and the laser power 250 kW. The laser emission is tuned from 123.2 nm to 128.4 nm by two different methods (diffraction grating and prism). This tunable laser is thus the one with the shortest wavelength at present. Its line width is 0.25 to 0.4 nm, and the power ue 1.7 kW. (orig.)

  5. Inelastic collision rates of trapped metastable hydrogen

    NARCIS (Netherlands)

    Landhuis, D; Matos, L; Moss, SC; Steinberger, JK; Vant, K; Willmann, L; Greytak, TJ; Kleppner, D

    We report the first detailed decay studies of trapped metastable (2S) hydrogen. By two-photon excitation of ultracold H samples, we have produced clouds of at least 5x10(7) magnetically trapped 2S atoms at densities greater than 4x10(10) cm(-3) and temperatures below 100 muK. At these densities and

  6. Chemi-ionization in collisions of metastable argon with sodium

    International Nuclear Information System (INIS)

    Neynaber, R.H.; Magnuson, G.D.

    1977-01-01

    Absolute and relative cross sections were obtained for the Penning-ionization (PI) reaction Ar*+Na→Ar+Na + +e and the associative-ionization (AI) reaction Ar*+Na→ArNa + +e. The studies were made by a merging-beams technique for a relative kinetic energy W of the reactants from nominally 0.01 to 10 eV for PI and 0.01 to 0.4 eV for AI. The Ar* represents a composite of Ar(4s 3 P 2 ) and Ar(4s 3 P 0 ). The PI is directed and occurs predominantly when the difference between the relative kinetic energy of the heavy products and the reactants is approximately 0.1 eV. Cross sections for AI are roughly proportional to W -1 . Cross sections for total ionization (AI plus PI) vary as W -1 / 3 for the lower W

  7. Mechanism of selenium hydride atomization, fate of free atoms and temperature distribution in an argon shielded, highly fuel-rich, hydrogen-oxygen diffusion micro-flame studied by atomic absorption spectrometry

    Czech Academy of Sciences Publication Activity Database

    D'Ulivo, A.; Dědina, Jiří; Lampugnani, L.; Matoušek, Tomáš

    2002-01-01

    Roč. 17, č. 3 (2002), s. 253-257 ISSN 0267-9477 R&D Projects: GA ČR GA203/01/0453; GA ČR GA203/98/0754 Institutional research plan: CEZ:AV0Z4031919 Keywords : hydride atomization * hydride generation * atomic absorption spectrometry Subject RIV: CB - Analytical Chemistry, Separation Impact factor: 4.250, year: 2002

  8. Study of a contracted glow in low-frequency plasma-jet discharges operating with argon

    Energy Technology Data Exchange (ETDEWEB)

    Minotti, F.; Giuliani, L.; Xaubet, M.; Grondona, D. [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, C1428EHA, Buenos Aires, Argentina and Instituto de Física del Plasma (INFIP), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad de Buenos Aires - UBA, C1428EHA, Buenos Aires (Argentina)

    2015-11-15

    In this work, we present an experimental and theoretical study of a low frequency, atmospheric plasma-jet discharge in argon. The discharge has the characteristics of a contracted glow with a current channel of submillimeter diameter and a relatively high voltage cathode layer. In order to interpret the measurements, we consider the separate modeling of each region of the discharge: main channel and cathode layer, which must then be properly matched together. The main current channel was modeled, extending a previous work, as similar to an arc in which joule heating is balanced by lateral heat conduction, without thermal equilibrium between electrons and heavy species. The cathode layer model, on the other hand, includes the emission of secondary electrons by ion impact and by additional mechanisms, of which we considered emission due to collision of atoms excited at metastable levels, and field-enhanced thermionic emission (Schottky effect). The comparison of model and experiment indicates that the discharge can be effectively sustained in its contracted form by the secondary electrons emitted by collision of excited argon atoms, whereas thermionic emission is by far insufficient to provide the necessary electrons.

  9. Observations of acoustic-wave-induced superluminescence in an argon plasma

    International Nuclear Information System (INIS)

    Aramyan, A.R.

    2003-01-01

    It is shown that in an argon discharge plasma it is possible to obtain overpopulation of certain electronic levels of atomic argon under the influence of acoustic waves. When the specified threshold is exceeded, then a superluminescence (in the form of light flashes) from the overpopulated electronic levels of atomic argon is observed

  10. Detonation of Meta-stable Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Kuhl, Allen; Kuhl, Allen L.; Fried, Laurence E.; Howard, W. Michael; Seizew, Michael R.; Bell, John B.; Beckner, Vincent; Grcar, Joseph F.

    2008-05-31

    We consider the energy accumulation in meta-stable clusters. This energy can be much larger than the typical chemical bond energy (~;;1 ev/atom). For example, polymeric nitrogen can accumulate 4 ev/atom in the N8 (fcc) structure, while helium can accumulate 9 ev/atom in the excited triplet state He2* . They release their energy by cluster fission: N8 -> 4N2 and He2* -> 2He. We study the locus of states in thermodynamic state space for the detonation of such meta-stable clusters. In particular, the equilibrium isentrope, starting at the Chapman-Jouguet state, and expanding down to 1 atmosphere was calculated with the Cheetah code. Large detonation pressures (3 and 16 Mbar), temperatures (12 and 34 kilo-K) and velocities (20 and 43 km/s) are a consequence of the large heats of detonation (6.6 and 50 kilo-cal/g) for nitrogen and helium clusters respectively. If such meta-stable clusters could be synthesized, they offer the potential for large increases in the energy density of materials.

  11. Extension of equilibrium formation criteria to metastable microalloys

    International Nuclear Information System (INIS)

    Kaufmann, E.N.; Vianden, R.; Chelikowsky, J.R.; Phillips, J.C.

    1977-01-01

    Metastable microalloys of 25 metallic elements with beryllium have been prepared by ion implantation. The injected atoms have been found to occupy one of three sites available in the solvent lattice. A modified Laudau-Ginsburg expansion using bulk alloy variables proposed by Miedema is completely successful in predicting the observed metastable-site preferences and indicates a broader applicability of these variables than was heretofore anticipated

  12. Metastable superconducting alloys

    International Nuclear Information System (INIS)

    Johnson, W.L.

    1978-07-01

    The study of metastable metals and alloys has become one of the principal activities of specialists working in the field of superconducting materials. Metastable crystalline superconductors such as the A15-type materials have been given much attention. Non-crystalline superconductors were first studied over twenty years ago by Buckel and Hilsch using the technique of thin film evaporation on a cryogenic substrate. More recently, melt-quenching, sputtering, and ion implantation techniques have been employed to produce a variety of amorphous superconductors. The present article presents a brief review of experimental results and a survey of current work on these materials. The systematics of superconductivity in non-crystalline metals and alloys are described along with an analysis of the microscopic parameters which underlie the observed trends. The unique properties of these superconductors which arise from the high degree of structural disorder in the amorphous state are emphasized

  13. Magneto-optical trap for metastable helium at 389 nm

    NARCIS (Netherlands)

    Koelemeij, J.C.J.; Stas, R.J.W.; Hogervorst, W.; Vassen, W.

    2003-01-01

    We have constructed a magneto-optical trap (MOT) for metastable triplet helium atoms utilizing the 2 S-3(1)-->3 P-3(2) line at 389 nm as the trapping and cooling transition. The far-red-detuned MOT (detuning Delta=-41 MHz) typically contains few times 10(7) atoms at a relatively high (similar

  14. Metastable dark energy

    Directory of Open Access Journals (Sweden)

    Ricardo G. Landim

    2017-01-01

    Full Text Available We build a model of metastable dark energy, in which the observed vacuum energy is the value of the scalar potential at the false vacuum. The scalar potential is given by a sum of even self-interactions up to order six. The deviation from the Minkowski vacuum is due to a term suppressed by the Planck scale. The decay time of the metastable vacuum can easily accommodate a mean life time compatible with the age of the universe. The metastable dark energy is also embedded into a model with SU(2R symmetry. The dark energy doublet and the dark matter doublet naturally interact with each other. A three-body decay of the dark energy particle into (cold and warm dark matter can be as long as large fraction of the age of the universe, if the mediator is massive enough, the lower bound being at intermediate energy level some orders below the grand unification scale. Such a decay shows a different form of interaction between dark matter and dark energy, and the model opens a new window to investigate the dark sector from the point-of-view of particle physics.

  15. Spectroscopic Investigation of the Argon Metastable State Through Optical Emission From Pulsed Argon Discharge

    Science.gov (United States)

    2010-07-01

    supply to energize the discharge was connected in series with an ohmite L225J high power 150 Ω resistor and the hollow electrode anode. A stainless...input analog voltage signal to control a piezo -electric actuator within the diode laser head. The general beam path of the diode laser involved an initial

  16. Separation of seven arsenic compounds by high performance liquid chromatography with on-line detection by hydrogen-argon flame atomic absorption spectrometry and inductively coupled plasma mass spectrometry

    DEFF Research Database (Denmark)

    Hansen, S. H.; Larsen, Erik Huusfeldt; Pritzl, G.

    1992-01-01

    -to-noise ratio of the on-line AAS detector was optimized. This involved the use of the hydrogen-argon-entrained air flame, a slotted tube atom trap in the flame for signal enhancement, electronic noise damping and a high-intensity light source. The detection limits in mu-g cm-3, using 100 mm3 injections...... of mixtures of arsenic standards into the HPLC system were: arsenite, As(III) 1.1; arsenate, As(V) 1.4; MMA 1.4; DMA 0.7; AsB 0.3; AsC 0.5; and the TMAs 0.4. The HPLC-AAS system was used for the analysis of arsenic species in aqueous extracts of soil samples from a polluted land site. Only arsenate was found...

  17. Shape of argon spectral lines emitted from an electric arc (P=760 Torr). Study and application of pressure broadening

    International Nuclear Information System (INIS)

    Kretzas, Dimitrios.

    1978-01-01

    We have studied the broadening and shift of argon spectral lines corresponding to 3p 5 5p-3p 5 4s and 3p 5 4p-3p 5 4s transitions emitted from an electric arc burning under atmospheric pressure. We have revealed the broadening due to neutral atoms pressure effect, distinguishing the transitions whose lower level is a metastable one (1s 3 and 1s 5 ) or a level of strong (1s 2 ) or feeble resonance (1s 4 ). In this study we have employed a mixture of argon (98%) and hydrogen (2%); hydrogen's feeble proportion does not perturb much the discharge and is very suitable for the measure of the electronic density. The important departure of L.T.E. has guided us to imagine and apply an original method to measure the temperature and the overpopulation of the neutral atoms in the fondamental state. Our method which is independent of the existence of L.T.E. is based on the different behavior of the spectral lines which are under the influence of the resonance or Van der Waals broadening. The measure of the broadening constants which in the resonance case are independent of the temperature and vary as Tsup(0,3) for V.d.W's broadening, give us a suitable tool to measure the density and the temperature of the neutral atoms [fr

  18. Topodynamics of metastable brains

    Science.gov (United States)

    Tozzi, Arturo; Peters, James F.; Fingelkurts, Andrew A.; Fingelkurts, Alexander A.; Marijuán, Pedro C.

    2017-07-01

    The brain displays both the anatomical features of a vast amount of interconnected topological mappings as well as the functional features of a nonlinear, metastable system at the edge of chaos, equipped with a phase space where mental random walks tend towards lower energetic basins. Nevertheless, with the exception of some advanced neuro-anatomic descriptions and present-day connectomic research, very few studies have been addressing the topological path of a brain embedded or embodied in its external and internal environment. Herein, by using new formal tools derived from algebraic topology, we provide an account of the metastable brain, based on the neuro-scientific model of Operational Architectonics of brain-mind functioning. We introduce a ;topodynamic; description that shows how the relationships among the countless intertwined spatio-temporal levels of brain functioning can be assessed in terms of projections and mappings that take place on abstract structures, equipped with different dimensions, curvatures and energetic constraints. Such a topodynamical approach, apart from providing a biologically plausible model of brain function that can be operationalized, is also able to tackle the issue of a long-standing dichotomy: it throws indeed a bridge between the subjective, immediate datum of the naïve complex of sensations and mentations and the objective, quantitative, data extracted from experimental neuro-scientific procedures. Importantly, it opens the door to a series of new predictions and future directions of advancement for neuroscientific research.

  19. Desensitization of metastable intermolecular composites

    Science.gov (United States)

    Busse, James R [South Fork, CO; Dye, Robert C [Los Alamos, NM; Foley, Timothy J [Los Alamos, NM; Higa, Kelvin T [Ridgecrest, CA; Jorgensen, Betty S [Jemez Springs, NM; Sanders, Victor E [White Rock, NM; Son, Steven F [Los Alamos, NM

    2011-04-26

    A method to substantially desensitize a metastable intermolecular composite material to electrostatic discharge and friction comprising mixing the composite material with an organic diluent and removing enough organic diluent from the mixture to form a mixture with a substantially putty-like consistency, as well as a concomitant method of recovering the metastable intermolecular composite material.

  20. Fast production of Bose-Einstein condensates of metastable helium

    Science.gov (United States)

    Bouton, Q.; Chang, R.; Hoendervanger, A. L.; Nogrette, F.; Aspect, A.; Westbrook, C. I.; Clément, D.

    2015-06-01

    We report on the Bose-Einstein condensation of metastable 4He atoms using a hybrid approach, consisting of a magnetic quadrupole and an optical dipole trap. In our setup we cross the phase transition with 2 ×106 atoms, and we obtain pure condensates of 5 ×105 atoms in the optical trap. This approach to cooling 4He provides enhanced cycle stability, large optical access to the atoms and results in the production of a condensate every 6 s—a factor 2 faster than the state of the art. This speed-up will significantly reduce the data acquisition time needed for the measurement of many particle correlations, made possible by the ability of metastable helium atoms to be detected individually.

  1. Complexity, Metastability and Nonextensivity

    Science.gov (United States)

    Beck, C.; Benedek, G.; Rapisarda, A.; Tsallis, C.

    Work and heat fluctuations in systems with deterministic and stochastic forces / E. G. D. Cohen and R. Van Zon -- Is the entropy S[symbol] extensive or nonextensive? / C. Tsallis -- Superstatistics: recent developments and applications / C. Beck -- Two stories outside Boltzmann-Gibbs statistics: Mori's Q-phase transitions and glassy dynamics at the onset of chaos / A. Robledo, F. Baldovin and E. Mayoral -- Time-averages and the heat theorem / A. Carati -- Fundamental formulae and numerical evidences for the central limit theorem in Tsallis statistics / H. Suyari -- Generalizing the Planck distribution / A. M. C. Soma and C. Tsallis -- The physical roots of complexity: renewal or modulation? / P. Grigolini -- Nonequivalent ensembles and metastability / H. Touchette and R. S. Ellis -- Statistical physics for cosmic structures / L. Pietronero and F. Sylos Labini -- Metastability and anomalous behavior in the HMF model: connections to nonextensive thermodynamics and glassy dynamics / A. Pluchino, A. Rapisarda and V. Latora -- Vlasov analysis of relaxation and meta-equilibrium / C. Anteneodo and R. O. Vallejos -- Weak chaos in large conservative systems - infinite-range coupled standard maps / L. G. Moyano, A. P. Majtey and C. Tsallis -- Deterministc aging / E. Barkai -- Edge of chaos of the classical kicked top map: sensitivity to initial conditions / S. M. Duarte Queirós and C. Tsallis -- What entropy at the edge of chaos? / M. Lissia, M. Coraddu and R. Tonelli -- Fractal growth of carbon schwarzites / G. Benedek ... [et al.] -- Clustering and interface propagation in interacting particle dynamics / A. Provata and V. K. Noussiou -- Resonant activation and noise enhanced stability in Josephson junctions / A. L. Pankratov and B. Spagnolo -- Symmetry breaking induced directed motions / C.-H. Chang and T. Y. Tsong -- General theory of Galilean-invariant entropic lattic Boltzmann models / B. M. Boghosian -- Unifying approach to the jamming transition in granular media and

  2. Photodetachment of metastable He-

    International Nuclear Information System (INIS)

    Thompson, J.S.; Dellwo, J.; Compton, R.N.

    1990-01-01

    A crossed-beams apparatus has been used to measure angular distributions and cross sections for photoelectron detachment from metastable He - . Energy- and angle-resolved electron spectroscopy was used to investigate the spectral dependences of the angular distribution of the photoelectrons. The angular distributions along with photoelectron yield measurements were used to determine the cross sections for photodetachment of He - (2 4 P) via the energy resolved He(2 3 P) and He(2 3 S) exit channels. The precision of the cross section measurements was enhanced by exploiting the kinematic effects associated with detachment from a fast beam source. Calculated cross sections for the photodetachment of H - were used to establish an absolute scale for the He - cross section measurements

  3. On Metastability in FPU

    CERN Document Server

    Bambusi, D

    2005-01-01

    We present an analytical study of the Fermi--Pasta--Ulam (FPU) $\\alpha$--model with periodic boundary conditions. We analyze the dynamics corresponding to initial data with some low frequency Fourier modes excited. We show that, correspondignly, a pair of KdV equations constitute the resonant normal form of the system. We also use such a normal form in order to prove the existence of a metastability phenomenon. More precisely, we show that the time average of the modal energy spectrum rapidly attains a well defined distribution corresponding to a packet of low frequencies modes. Subsequently, the distribution remains unchanged up to the time scales of validity of our approximation. The phenomenon is controlled by the specific energy.

  4. Argon analytical procedures for potassium-argon dating

    International Nuclear Information System (INIS)

    Gabites, J.E.; Adams, C.J.

    1981-01-01

    A manual for the argon analytical methods involved in potassium-argon geochronology, including: i) operating procedures for the ultra-high vacuum argon extraction/purification equipment for the analysis of nanolitre quantities of radiogenic argon in rocks, minerals and gases; ii) operating procedures for the AEI-MS10 gas source mass spectrometer

  5. Using the van der Waals broadening of spectral atomic lines to measure the gas temperature of an argon-helium microwave plasma at atmospheric pressure

    International Nuclear Information System (INIS)

    Munoz, J.; Dimitrijevic, M.S.; Yubero, C.; Calzada, M.D.

    2009-01-01

    The applications of plasmas generated with gas mixtures have become increasingly common in different scientific and technological fields. In order to understand the advantages of these discharges, for instance in chemical analysis, it is necessary to know the gas temperature (T g , kinetic energy of the heavy particles) since it has a great influence on the atomization reactions of the molecules located in the discharge, along with the dependence of the reaction rate on this parameter. The ro-vibrational emission spectra of the molecular species are usually used to measure the gas temperature of a discharge at atmospheric pressure although under some experimental conditions, these are difficult to detect. In such cases, the gas temperature can be determined from the van der Waals broadening of the emitted atomic spectral lines related to this parameter. The method proposed is based on the van der Waals broadening taking into account two perturbers

  6. Metastable gravity on classical defects

    International Nuclear Information System (INIS)

    Ringeval, Christophe; Rombouts, Jan-Willem

    2005-01-01

    We discuss the realization of metastable gravity on classical defects in infinite-volume extra dimensions. In dilatonic Einstein gravity, it is found that the existence of metastable gravity on the defect core requires violation of the dominant energy condition for codimension N c =2 defects. This is illustrated with a detailed analysis of a six-dimensional hyperstring minimally coupled to dilaton gravity. We present the general conditions under which a codimension N c >2 defect admits metastable modes, and find that they differ from lower codimensional models in that, under certain conditions, they do not require violation of energy conditions to support quasilocalized gravity

  7. Potassium-argon technology

    International Nuclear Information System (INIS)

    Cassignol, Charles; Cornette, Yves; David, Benjamin; Gillot, P.-Y.

    1978-04-01

    The main features of the method of processing rocks and minerals and measuring the extracted argon, for the purpose of potassium-argon dating are described. It differs in several respects from the conventional one, as described, f.i., in Dalrymple and Lanphere's monography. Principally it was established that the continual purification of the gases in the mass spectrometer cell during the measurement, stops the peaks of current drift, and renders them representative of the introduced argon. This allows on the one hand to improve the reliability and accuracy of measurements, on the other hand to get rid of the isotopic dilution method, with 38 A as a spike. Moreover the reliability of the radiogenic argon is improved by taking into account the mislinearness of the M.S. response. All this results in a higher performance of the K/Ar dating method, especially in the recent ages range. The technological side of the problem was only dealt with [fr

  8. Atoms

    International Nuclear Information System (INIS)

    Fuchs, Alain; Villani, Cedric; Guthleben, Denis; Leduc, Michele; Brenner, Anastasios; Pouthas, Joel; Perrin, Jean

    2014-01-01

    Completed by recent contributions on various topics (atoms and the Brownian motion, the career of Jean Perrin, the evolution of atomic physics since Jean Perrin, relationship between scientific atomism and philosophical atomism), this book is a reprint of a book published at the beginning of the twentieth century in which the author addressed the relationship between atomic theory and chemistry (molecules, atoms, the Avogadro hypothesis, molecule structures, solutes, upper limits of molecular quantities), molecular agitation (molecule velocity, molecule rotation or vibration, molecular free range), the Brownian motion and emulsions (history and general features, statistical equilibrium of emulsions), the laws of the Brownian motion (Einstein's theory, experimental control), fluctuations (the theory of Smoluchowski), light and quanta (black body, extension of quantum theory), the electricity atom, the atom genesis and destruction (transmutations, atom counting)

  9. Effect of oxygen atoms dissociated by non-equilibrium plasma on flame of methane oxygen and argon pre-mixture gas

    Science.gov (United States)

    Akashi, Haruaki; Yoshinaga, Tomokazu; Sasaki, Koichi

    2014-10-01

    For more efficient way of combustion, plasma-assisted combustion has been investigated by many researchers. But it is very difficult to clarify the effect of plasma even on the flame of methane. Because there are many complex chemical reactions in combustion system. Sasaki et al. has reported that the flame length of methane and air premixed burner shortened by irradiating microwave power. They also measured emission from Second Positive Band System of nitrogen during the irradiation. The emission indicates existence of high energy electrons which are accelerated by the microwave. The high energy electrons also dissociate oxygen molecules easily and oxygen atom would have some effects on the flame. But the dissociation ratio of oxygen molecules by the non-equilibrium plasma is significantly low, compared to that in the combustion reaction. To clarify the effect of dissociated oxygen atoms on the flame, dependence of dissociation ratio of oxygen on the flame has been examined using CHEMKIN. It is found that in the case of low dissociation ratio of 10-6, the ignition of the flame becomes slightly earlier. It is also found that in the case of high dissociation ratio of 10-3, the ignition time becomes significantly earlier by almost half. This work was supported by KAKENHI (22340170).

  10. Hydrogen–argon plasma pre-treatment for improving the anti-corrosion properties of thin Al2O3 films deposited using atomic layer deposition on steel

    International Nuclear Information System (INIS)

    Härkönen, Emma; Potts, Stephen E.; Kessels, Wilhelmus M.M.; Díaz, Belén; Seyeux, Antoine; Światowska, Jolanta; Maurice, Vincent; Marcus, Philippe; Radnóczi, György; Tóth, Lajos; Kariniemi, Maarit; Niinistö, Jaakko; Ritala, Mikko

    2013-01-01

    The effect of H 2 –Ar plasma pre-treatment prior to thermal atomic layer deposition (ALD) and plasma-enhanced atomic layer deposition (PEALD) of Al 2 O 3 films on steel for corrosion protection was investigated. Time-of-flight secondary ion mass spectrometry and transmission electron microscopy were used to observe the changes in the interface. The electrochemical properties of the samples were studied with polarization measurements, and the coating porosities were calculated from the polarization results for easier comparison of the coatings. Prior to thermal ALD the plasma pre-treatment was observed to reduce the amount of impurities at the interface and coating porosity by 1–3 orders of magnitude. The anti-corrosion properties of the PEALD coatings could also be improved by the pre-treatment. However, exposure of the pre-treatment plasma activated steel surface to oxygen plasma species in PEALD led to facile oxide layer formation in the interface. The oxide layer formed this way was thicker than the native oxide layer and appeared to be detrimental to the protective properties of the coating. The best performance for PEALD Al 2 O 3 coatings was achieved when, after the plasma pre-treatment, the surface was given time to regrow a thin protective interfacial oxide prior to exposure to the oxygen plasma. The different effects that thermal and plasma-enhanced ALD have on the substrate-coating interface were compared. The reactivity of the oxygen precursor was shown to have a significant influence on substrate surface in the early stages of film growth and thereafter also on the overall quality of the protective film. - Highlights: • Influence of H 2 –Ar plasma pre-treatment to ALD coatings on steel was studied. • The pre-treatment modified the coating–substrate interface composition and thickness. • The pre-treatment improved the barrier properties of the coatings

  11. Metastable enhancement of C+ and O+ capture reactions

    International Nuclear Information System (INIS)

    Thomas, E.W.; Moran, T.F.

    1990-09-01

    Single electron capture by 10- to 500-eV singly charged C and O ions traversing targets of H 2 and H was studied with emphasis on comparing cross sections for metastable species with those for the ground state. For an H 2 target cross sections are of the order 10 Angstrom and 20 to 30 times larger than for ground state species. Electron impact ion sources typically produce 5 to 30% of their output in the metastable state. Previous published work has largely ignored (or failed to detect) the presence of metastables and is incorrect by as much as an order of magnitude. Discrepancies between data sets have been resolved, and a reliable data set is provided for energies from 10 to 10 5 eV. Similar experiments for an atomic H target are underway. It is proposed to extend the program to similar studies with multiply charged projectile species

  12. SLD liquid argon calorimeter

    International Nuclear Information System (INIS)

    Vella, E.

    1992-10-01

    The liquid argon calorimeter (LAC) of the SLD detector is a parallel plate -- liquid argon sampling calorimeter, used to measure particle energies in Z 0 decays at the Stanford Linear Collider. The LAC module design is based on a unique projective tower structure, in which lead plates and segmented lead tiles serve both as absorbers and electrodes. The LAC front end electronics incorporates several novel features, including extensive multiplexing and optical fiber readout, which take advantage of the low SLC beam crossing frequency. The operational performance of the LAC during the recently completed SLD physics run (which recorded over 10,000 Z 0 events) is discussed

  13. Atom

    International Nuclear Information System (INIS)

    Auffray, J.P.

    1997-01-01

    The atom through centuries, has been imagined, described, explored, then accelerated, combined...But what happens truly inside the atom? And what are mechanisms who allow its stability? Physicist and historian of sciences, Jean-Paul Auffray explains that these questions are to the heart of the modern physics and it brings them a new lighting. (N.C.)

  14. Cross sections of electron excitation out of metastable helium levels with a fast metastable target product produced via charge exchange

    International Nuclear Information System (INIS)

    Lagus, M.E.; Boffard, J.B.; Anderson, L.W.; Lin, C.C.

    1996-01-01

    Absolute direct cross sections for electron excitation out of the 2 3 S level and into the 3 3 D, 4 3 D, and 3 3 S levels of the helium atom from threshold to 500 eV and into the 3 3 P level over a more limited energy range have been measured using a fast metastable atomic beam target. We produce the metastable atoms via near-resonant charge exchange between a 1.6-keV He + ion beam and Cs vapor. Because this reaction is highly nonresonant with the ground state of helium, the charge-transfer process yields a primarily metastable beam. We use a thermal detector which we calibrate with ions to measure absolutely the neutral beam flux. The atomic beam is crossed by an electron beam, and we collect the resulting fluorescence at right angles to both the electron and atomic beams. We obtain the cross sections for excitation out of the 2 3 S level into the various excited levels by monitoring the emission out of the excited level of interest. copyright 1996 The American Physical Society

  15. Argon in action

    CERN Multimedia

    Corinne Pralavorio

    2015-01-01

    Over the past few days, the SPS has been accelerating argon ions, which have started to be sent to the NA61/SHINE experiment. This operating mode, using a new type of ion, required a number of modifications to the accelerator.   Picture 1: a “super-cycle” of the SPS, featuring a proton cycle for the LHC, followed by an argon ion cycle for the North Area. Today, the accelerators are once again juggling particles and even performing completely new tricks. The SPS is supplying beams of argon ions for the first time, at energies never before achieved for this type of beam. They are destined for the NA61/SHINE experiment (see box) located in the North Area, which began receiving the beams on 11 February. Argon ions have a relatively large mass, as they consist of 40 nucleons, so they can be used in a similar way to lead ions. The main difficulty in accelerating them lies in the SPS, where the variation in acceleration frequency is limited. “The SPS was designed for a...

  16. Role of carbon atoms in the remote plasma deposition of hydrogenated amorphous carbon

    International Nuclear Information System (INIS)

    Benedikt, J.; Wisse, M.; Woen, R.V.; Engeln, R.; Sanden, M.C.M. van de

    2003-01-01

    The aim of this article is to determine the role of carbon atoms in the growth of hydrogenated amorphous carbon (a-C:H) films by means of an argon/acetylene expanding thermal plasma. Cavity ring down absorption spectroscopy is used to detect metastable carbon atoms by probing the 1s 2 2s 2 2p 3s 1 P 1 2 2s 2 2p 2 1 S 0 electronic transition. In addition to absorption measurements, the emission of the same transition is monitored by means of optical emission spectroscopy. These two measurements provide information about the local production of the C atoms and about their reactivity in the gas phase. It will be shown that under growth conditions in an Ar/C 2 H 2 expanding thermal plasma, the metastable carbon density is also representative for the ground state carbon density. From obtained results it is concluded that the carbon atoms react rapidly with acetylene in the gas phase and therefore their contribution to the growth of hard diamond-like a-C:H films can be neglected. Only at low acetylene flows, the condition when soft polymer-like films are deposited, carbon atoms are detected close to the substrate and can possibly contribute to the film growth

  17. Features of copper etching in chlorine-argon plasma

    International Nuclear Information System (INIS)

    Efremov, A.M.; Svettsov, V.I.

    1995-01-01

    Chlorine mixtures with inert gases including argon exhibit promise as plasma feed gases for etching metals and semiconductors in the microelectronics industry. It was shown that even strong dilution of reactive gas with an inert gas (up to 80-90% of the latter) has virtually no effect in decreasing the rate of plasma etching of materials such as silicon and gallium arsenide, compared to etching in pure chlorine. The principal reactive species responsible for etching these substrates are chlorine atoms therefore, a possible explanation of the effect is an increase in the rate of bulk generation of chlorine atoms in the presence of argon. In this work the authors studied the influence of argon on the rate of copper etching in chlorine, because copper, unlike the above substrates, reacts effectively not only with the atoms but with the ground-state molecules of chlorine

  18. ATLAS Liquid Argon Calorimeter Module Zero

    CERN Multimedia

    1993-01-01

    This module was built and tested with beam to validate the ATLAS electromagnetic calorimeter design. One original design feature is the folding. 10 000 lead plates and electrodes are folded into an accordion shape and immersed in liquid argon. As they cross the folds, particles are slowed down by the lead. As they collide with the lead atoms, electrons and photons are ejected. There is a knock-on effect and as they continue on into the argon, a whole shower is produced. The electrodes collect up all the electrons and this signal gives a measurement of the energy of the initial particle. The M0 was fabricated by French institutes (LAL, LAPP, Saclay, Jussieu) in the years 1993-1994. It was tested in the H6/H8 beam lines in 1994, leading to the Technical Design Report in 1996.

  19. Metastable states in magnetic nanorings

    DEFF Research Database (Denmark)

    Castaño, F. J.; Ross, C. A.; Frandsen, Cathrine

    2003-01-01

    Magnetization states and hysteresis behavior of small ferromagnetic rings, of diameters 180-520 nm, have been investigated using magnetic force microscopy. In addition to the expected bi-domain ("onion") and flux-closed ("vortex") magnetization states, a metastable state has been found. This "twi......Magnetization states and hysteresis behavior of small ferromagnetic rings, of diameters 180-520 nm, have been investigated using magnetic force microscopy. In addition to the expected bi-domain ("onion") and flux-closed ("vortex") magnetization states, a metastable state has been found....... This "twisted" state contains a 360degrees domain wall which can exist over a wide range of applied fields. Four possible configurations of the twisted state are possible. Micromagnetic modeling shows that the twisted state is stabilised in small diameter, narrow rings. Additionally, more complex configurations...

  20. Instability of colliding metastable strings

    Energy Technology Data Exchange (ETDEWEB)

    Hiramatsu, Takashi [Kyoto Univ. (Japan). Yukawa Inst. for Theoretical Physics; Eto, Minoru [Yamagata Univ. (Japan). Dept. of Physics; Kamada, Kohei [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Kobayashi, Tatsuo [Kyoto Univ. (Japan). Dept. of Physics; Ookouchi, Yutaka [Kyoto Univ. (Japan). Dept. of Physics; Kyoto Univ. (Japan). The Hakubi Center for Advanced Research

    2013-04-15

    We investigate the collision dynamics of two metastable strings which can be viewed as tube-like domain walls with winding numbers interpolating a false vacuum and a true vacuum. We find that depending on the relative angle and speed of two strings, instability of strings increases and the false vacuum is filled out by rapid expansion of the strings or of a remnant of the collision.

  1. Instability of colliding metastable strings

    International Nuclear Information System (INIS)

    Hiramatsu, Takashi; Kobayashi, Tatsuo; Ookouchi, Yutaka; Kyoto Univ.

    2013-04-01

    We investigate the collision dynamics of two metastable strings which can be viewed as tube-like domain walls with winding numbers interpolating a false vacuum and a true vacuum. We find that depending on the relative angle and speed of two strings, instability of strings increases and the false vacuum is filled out by rapid expansion of the strings or of a remnant of the collision.

  2. Superfluorescence with cold trapped neon atoms

    International Nuclear Information System (INIS)

    Zachorowski, Jerzy

    2003-01-01

    A method for observation of superfluorescence in a cloud of cold metastable Ne atoms is proposed. Means of achieving a cold sample of trapped metastable atoms are discussed. The feasibility of obtaining conditions for a superfluorescence pulse is studied. The paper also discusses the prospects for obtaining intense pulses of extreme ultraviolet radiation

  3. The Argon Geochronology Experiment (AGE)

    Science.gov (United States)

    Swindle, T. D.; Bode, R.; Fennema, A.; Chutjian, A.; MacAskill, J. A.; Darrach, M. R.; Clegg, S. M.; Wiens, R. C.; Cremers, D.

    2006-01-01

    This viewgraph presentation reviews the Argon Geochronology Experiment (AGE). Potassium-Argon dating is shown along with cosmic ray dating exposure. The contents include a flow diagram of the Argon Geochronology Experiment, and schematic diagrams of the mass spectrometer vacuum system, sample manipulation mechanism, mineral heater oven, and the quadrupole ion trap mass spectrometer. The Laser-Induced Breakdown Spectroscopy (LIBS) Operation with elemental abundances is also described.

  4. Liquid-argon calorimetry

    International Nuclear Information System (INIS)

    Fabjan, C.W.

    1989-01-01

    In this paper the viability of liquid-argon calorimetric techniques in the experimental environment of the Superconducting Super Collider (SSC) is briefly analyzed. The authors compare the required and achievable energy resolution with benchmark figures obtained using practical instruments. Comments on the desirable (i.e. required) temporal performance are made and compared with the state of the art. Some of the major engineering challenges are listed, for which solutions will have to be developed if such instruments are to find a place in an SSC experimental area

  5. Ionization relaxation in shock-heated krypton-argon mixtures

    International Nuclear Information System (INIS)

    Ezumi, Hiromichi; Kawamura, Masahiko; Yokota, Toshiaki.

    1977-01-01

    The ionization relaxation processes behind shock waves in pure krypton and krypton-argon mixtures have been investigated using a Mach-Zehnder interferometer technique. The incident shock velocity was fixed in the neighborhood of Us=2800 m/sec, and the initial pressure was fixed at 0.95 Torr. The experimental results were compared with theoretical values based on the two-step collisional ionization model taking into account of the wall boundary-layer effect. The slope constants of excitation cross section against relative kinetic energy between krypton atom-atom collisions, krypton atom-electron collisions, and krypton-argon atom-atom collisions were determined to be 4.2 x 10 -19 cm 2 /eV, 1.2 x 10 -17 cm 2 /eV, and 4.2 x 10 -19 cm 2 /eV, respectively. (auth.)

  6. Argon solubility in liquid steel

    NARCIS (Netherlands)

    Boom, R; Dankert, O; Van Veen, A; Kamperman, AA

    2000-01-01

    Experiments have been performed to establish the solubility of argon in liquid interstitial-free steel. The solubility appears to be lower than 0.1 at ppb, The results are in line with argon solubilities reported in the literature on liquid iron. Semiempirical theories and calculations based on the

  7. Vacuum metastability with black holes

    Energy Technology Data Exchange (ETDEWEB)

    Burda, Philipp [Centre for Particle Theory, Durham University,South Road, Durham, DH1 3LE (United Kingdom); Gregory, Ruth [Centre for Particle Theory, Durham University,South Road, Durham, DH1 3LE (United Kingdom); Perimeter Institute, 31 Caroline Street North,Waterloo, ON, N2L 2Y5 (Canada); Moss, Ian G. annd [School of Mathematics and Statistics, Newcastle University,Newcastle Upon Tyne, NE1 7RU (United Kingdom)

    2015-08-24

    We consider the possibility that small black holes can act as nucleation seeds for the decay of a metastable vacuum, focussing particularly on the Higgs potential. Using a thin-wall bubble approximation for the nucleation process, which is possible when generic quantum gravity corrections are added to the Higgs potential, we show that primordial black holes can stimulate vacuum decay. We demonstrate that for suitable parameter ranges, the vacuum decay process dominates over the Hawking evaporation process. Finally, we comment on the application of these results to vacuum decay seeded by black holes produced in particle collisions.

  8. Vacuum metastability with black holes

    International Nuclear Information System (INIS)

    Burda, Philipp; Gregory, Ruth; Moss, Ian G. annd

    2015-01-01

    We consider the possibility that small black holes can act as nucleation seeds for the decay of a metastable vacuum, focussing particularly on the Higgs potential. Using a thin-wall bubble approximation for the nucleation process, which is possible when generic quantum gravity corrections are added to the Higgs potential, we show that primordial black holes can stimulate vacuum decay. We demonstrate that for suitable parameter ranges, the vacuum decay process dominates over the Hawking evaporation process. Finally, we comment on the application of these results to vacuum decay seeded by black holes produced in particle collisions.

  9. Geometrically induced metastability and holography

    Energy Technology Data Exchange (ETDEWEB)

    Aganagic, Mina; Aganagic, Mina; Beem, Christopher; Seo, Jihye; Vafa, Cumrun

    2006-10-23

    We construct metastable configurations of branes and anti-branes wrapping 2-spheres inside local Calabi-Yau manifolds and study their large N duals. These duals are Calabi-Yau manifolds in which the wrapped 2-spheres have been replaced by 3-spheres with flux through them, and supersymmetry is spontaneously broken. The geometry of the non-supersymmetric vacuum is exactly calculable to all orders of the't Hooft parameter, and to the leading order in 1/N. The computation utilizes the same matrix model techniques that were used in the supersymmetric context. This provides a novel mechanism for breaking supersymmetry in the context of flux compactifications.

  10. Grain Formation Processes in Oxygen-Rich Circumstellar Outflows: Testing the Metastable Eutectic Condensation Hypothesis and Measuring Atom-Grain & Grain-Grain Sticking Coefficients (A Sub-orbital Investigation)

    Science.gov (United States)

    Nuth, Joseph

    An experimentally-based model of grain formation in oxygen-rich circumstellar outflows that includes vapor-solid nucleation, grain growth, thermal annealing and grain aggregation in sufficient detail to predict the spectral energy distribution (SED) of the shells for comparison with observations of a wide range of stellar sources still lacks critical data. In order to gather this data we propose to conduct a series of laboratory experiments using our proven experimental system and microgravity condensation, growth and grain aggregation experiments on sounding rockets with a flight-proven payload provided by Dr. Yuki Kimura of Hokkaido University. We have proposed that solids from a hydrogen-rich, supersaturated, Fe-Mg-SiO vapor condense at metastable eutectic points in this ternary phase diagram. Because the FeOMgO system is totally miscible (has no eutectic or metastable eutectic compositions), this predicts that condensates will be pure Mg-silicate or Fe-silicate grains and that no primary condensate will be a mixed Fe-Mg-silicate. We have shown that this observation leads to a logical explanation as to why pure magnesium olivine and enstatite minerals are detected in circumstellar winds rather than the mixed Mg-Fe-silicate grains that might otherwise be expected (Rietmeijer, Nuth & Karner, 1999). This simplifying hypothesis has been built into our models of circumstellar condensation and growth. However, these experimental results require confirmation and testing since they should apply to other, quite similar condensable systems. We propose to test this hypothesis by condensing solids from the Fe-Mg-AlO ternary vapor system. Since FeO-MgO miscibility also applies to this system, the primary condensates from such a vapor should consist of pure amorphous Fe-aluminates and Mg-aluminates. No mixed Fe-Mg-spinels should be detected as primary condensates if this hypothesis is correct, just as none were detected for the FeO-MgO-SiO system. Confirmation of this

  11. Electrically induced metastability in SI-GaAs studied by positron lifetime spectroscopy

    International Nuclear Information System (INIS)

    Luo, Y.L.; Beling, C.D.; Fung, S.; Ling, C.C.; Lui, M.K.; Mui, W.K.

    2001-01-01

    Recently, a room temperature electrically induced metastability in semi-insulating (SI)-GaAs has been reported in which the normally high resistance state of SI-GaAs converts into a low resistance state when breakdown electric fields are applied to the metal/Si-GaAs/metal system. The low resistance state persists when the electric field is lowered below the breakdown bias and as such may thus be considered as metastable state of the material. To clarify whether the high field breakdown has its origins in some atomic configurational change induced through high energy electron collisions we have employed positron lifetime spectroscopy. Lifetime spectra that have been taken at the same bias in both the high current and low current phases show that the positron lifetime in the metastable state has no change within the experimental error from that of the normal state, thus suggesting that the metastability is most likely of purely electronic origin. (orig.)

  12. Enhanced high-order harmonic generation from Argon-clusters

    NARCIS (Netherlands)

    Tao, Yin; Hagmeijer, Rob; Bastiaens, Hubertus M.J.; Goh, S.J.; van der Slot, P.J.M.; Biedron, S.; Milton, S.; Boller, Klaus J.

    2017-01-01

    High-order harmonic generation (HHG) in clusters is of high promise because clusters appear to offer an increased optical nonlinearity. We experimentally investigate HHG from Argon clusters in a supersonic gas jet that can generate monomer-cluster mixtures with varying atomic number density and

  13. Field Induced Magnetic Moments in a Metastable Iron-Mercury Alloy

    DEFF Research Database (Denmark)

    Pedersen, M.S.; Mørup, Steen; Linderoth, Søren

    1996-01-01

    The magnetic properties of a metastable iron-mercury alloy have been investigated in the temperature range from 5 to 200 K by Mossbauer spectroscopy and magnetization measurements. At low temperature the magnetic moment per iron atom is larger than af alpha-Fe. The effective spontaneous magnetic ....... It was found that the field-induced increase of the magnetic moment in the metastable iron-mecury alloy was about 0.06 Bohr magnetons per iron atom in the temperature range from 5 to 200 K for a field change from 6 to 12 T....

  14. Smoothing an isolated interface of cobalt-copper under irradiation by low-energy argon ions

    International Nuclear Information System (INIS)

    Stognij, A.I.; Novitskij, N.N.; Stukalov, O.M.

    2003-01-01

    Multilayer film structures, i.e. gold layer-copper-cobalt, are considered. It is shown that the structure, where cobalt surface prior to copper layer deposition was subjected to additional irradiation by a flow of argon ions, features the smoothest surface. The conclusion is made about smoothing out of cobalt-copper interface as a result of multiple collisions of argon slow ions and cobalt atoms during braking within two or three upper atomic rows of the cobalt layer [ru

  15. Study of argon-oxygen flowing afterglow

    Science.gov (United States)

    Mazánková, V.; Trunec, D.; Navrátil, Z.; Raud, J.; Krčma, F.

    2016-06-01

    The reaction kinetics in argon-oxygen flowing afterglow (post-discharge) was studied using NO titration and optical emission spectroscopy. The flowing DC post-discharge in argon-oxygen mixture was created in a quartz tube at the total gas pressure of 1000 Pa and discharge power of 90 W. The O(3P) atom concentration was determined by NO titration at different places along the flow tube. The optical emission spectra were also measured along the flow tube. Argon spectral lines, oxygen lines at 777 nm and 844.6 nm and atmospheric A-band of {{\\text{O}}2} were identified in the spectra. Rotational temperature of {{\\text{O}}2} was determined from the oxygen atmospheric A-band and also the outer wall temperature of the flow tube was measured by a thermocouple and by an IR thermometer. A zero-dimensional kinetic model for the reactions in the afterglow was developed. This model allows the time dependencies of particle concentrations and of gas temperature to be calculated. The wall recombination probability for O(3P) atoms {γ\\text{O≤ft(\\text{P}\\right)}}=≤ft(1.63+/- 0.06\\right)× {{10}-3} and wall deactivation probability for {{\\text{O}}2} (b {{}1}Σ\\text{g}+ ) molecules {γ{{\\text{O}2}≤ft(\\text{b}\\right)}}=≤ft(1.7+/- 0.1\\right)× {{10}-3} were determined from the fit of model results to experimental data. Sensitivity analysis was applied for the analysis of kinetic model in order to reveal the most important reactions in the model. The calculated gas temperature increases in the afterglow and then decreases at later afterglow times after reaching the maximum. This behavior is in good agreement with the spatial rotational temperature dependence. A similar trend was also observed at outer wall temperature measurement.

  16. Metastable Supersymmetry Breaking in a Cooling Universe

    International Nuclear Information System (INIS)

    Kaplunovsky, Vadim S.

    2007-01-01

    I put metastable supersymmetry breaking in a cosmological context. I argue that under reasonable assumptions, the cooling down early Universe favors metastable SUSY-breaking vacua over the stable supersymmetric vacua. To illustrate the general argument, I analyze the early-Universe history of the Intriligator-Seiberg-Shih model

  17. Desensitization and recovery of metastable intermolecular composites

    Science.gov (United States)

    Busse, James R [South Fork, CO; Dye, Robert C [Los Alamos, NM; Foley, Timothy J [Los Alamos, NM; Higa, Kelvin T [Ridgecrest, CA; Jorgensen, Betty S [Jemez Springs, NM; Sanders, Victor E [White Rock, NM; Son, Steven F [Los Alamos, NM

    2010-09-07

    A method to substantially desensitize a metastable intermolecular composite material to electrostatic discharge and friction comprising mixing the composite material with an organic diluent and removing enough organic diluent from the mixture to form a mixture with a substantially putty-like consistency, as well as a concomitant method of recovering the metastable intermolecular composite material.

  18. The Argon Dark Matter Experiment

    CERN Document Server

    AUTHOR|(CDS)2071720

    2009-01-01

    The ArDM experiment, a 1 ton liquid argon TPC/Calorimeter, is designed for the detection of dark matter particles which can scatter off the spinless argon nucleus, producing nuclear recoils. These events will be discerned by their light to charge ratio, as well as the time structure of the scintillation light. The experiment is presently under construction and commissioning on surface at CERN. Cryogenic operation and light detection performance was recently confirmed in a test run of the full 1 ton liquid argon target under purely calorimetric operation and with a prototype light readout system. This note describes the experimental concept, the main detector components and presents some first results.

  19. Optical spectroscopy of high-L Rydberg states of argon

    International Nuclear Information System (INIS)

    Wright, L. E.; Snow, E. L.; Lundeen, S. R.; Sturrus, W. G.

    2007-01-01

    High-L fine structure patterns in n=9 and n=17 Rydberg levels of argon have been studied using a Doppler-tuned CO 2 laser and a fast beam of argon atoms. Analysis of the measured pattern using the polarization model yields the scalar dipole polarizability and quadrupole moment of the 2 P 3 at ∼sol∼ at 2 Ar + ion. The results are α S =6.83(8)a 0 3 and Q=-0.5177(15)ea 0 2 . Within the precision of this study, no vector component of the structure was observed

  20. Data relative to (e, argon) and (e, ethane) interactions necessary for strong field transport calculations

    International Nuclear Information System (INIS)

    Florent, J.J.

    1988-01-01

    Collisions between electrons and argon atoms and ethane molecules are studied in order to better understand phenomena occurring at each stage of detection in gas detectors used in nuclear and high energy physics. Elastic collisions between an electron and argon, those producing an electronic excitation of the atom, and those leading to its ionisation are reviewed. For the ethane collisions, vibrational excitation is considered. Photoionisation of argon and ethane is also examined. Total or partial cross sections, and differential cross sections are presented [fr

  1. The Liquid Argon Purity Demonstrator

    Energy Technology Data Exchange (ETDEWEB)

    Adamowski, M.; Carls, B.; Dvorak, E.; Hahn, A.; Jaskierny, W.; Johnson, C.; Jostlein, H.; Kendziora, C.; Lockwitz, S.; Pahlka, B.; Plunkett, R.; Pordes, S.; Rebel, B.; Schmitt, R.; Stancari, M.; Tope, T.; Voirin, E.; Yang, T.

    2014-07-01

    The Liquid Argon Purity Demonstrator was an R&D test stand designed to determine if electron drift lifetimes adequate for large neutrino detectors could be achieved without first evacuating the cryostat. We describe here the cryogenic system, its operations, and the apparatus used to determine the contaminant levels in the argon and to measure the electron drift lifetime. The liquid purity obtained by this system was facilitated by a gaseous argon purge. Additionally, gaseous impurities from the ullage were prevented from entering the liquid at the gas-liquid interface by condensing the gas and filtering the resulting liquid before returning to the cryostat. The measured electron drift lifetime in this test was greater than 6 ms, sustained over several periods of many weeks. Measurements of the temperature profile in the argon, to assess convective flow and boiling, were also made and are compared to simulation.

  2. Metal clusters on supported argon layers; Metallcluster auf dielektrischen Substraten

    Energy Technology Data Exchange (ETDEWEB)

    Faber, Bernhard

    2011-10-21

    The deposition of small sodium clusters on supported Ar(001)-surfaces is simulated. Theoretical description is achieved by a hierarchical model consisting of time-dependent DFT and molecular dynamics. The valence electrons of the sodium atoms are considered by Kohn-Sham-Scheme with self interaction correction. The interaction of argon atoms and sodium ions is described by atom-atom potentials whereas the coupling to the QM electrons is done by local pseudo-potentials. A decisive part of the model is the dynamical polarizability of the rare-gas atoms. The optional metal support is considered by the method of image charges. The influence of the forces caused by image charges and the influence of the number of argon monolayers on structure, optical response and deposition dynamics of Na{sub 6} and Na{sub 8} is investigated. There is very little influence on cluster structure and only a small shift of the cluster perpendicular to the surface. Concerning optical response the position of the Mie plasmon peak stays robust whereas the details of spectral fragmentation react very sensitively to changes. The forces caused by image charges of the metal support play only a little role with the dynamics of deposition while the thickness of the argon surface strongly influences the dissipation. (orig.)

  3. High-power frequency-stabilized laser for laser cooling of metastable helium at 389 nm

    NARCIS (Netherlands)

    Koelemeij, J.C.J.; Hogervorst, W.; Vassen, W.

    2005-01-01

    A high-power, frequency-stabilized laser for cooling of metastable helium atoms using the 2 S13 →3 P23 transition at 389 nm has been developed. The 389 nm light is generated by frequency doubling of a titanium:sapphire laser in an external enhancement cavity containing a lithium-triborate nonlinear

  4. Electron spin polarization effects in low-energy electron diffraction, ion neutralization, and metastable-atom deexcitation at solid surfaces. Progress report No. 3, January 1-December 31, 1983

    International Nuclear Information System (INIS)

    Walters, G.K.; Dunning, F.B.

    1983-01-01

    The importance of electron spin polarization (ESP) effects in the various spectroscopies used to study solid surfaces has become increasingly apparent in recent years. Recent low energy electron diffraction (LEED) investigations in this laboratory and elsewhere have shown that a great deal of new information contributing to the understanding of the geometrical arrangements of atoms at a surface can be obtained if the polarization of the various LEED beams is measured, or if the incident electron beam is polarized. Polarized LEED studies have shown large polarization features that are very sensitive to the presence of adsorbed layers, surface reconstruction, etc. In addition, theory suggests that polarization measurements can provide a more sensitive test of many of the parameters used in a surface model than can conventional LEED intensity measurements alone. Polarized LEED has also been applied to the study of surface magnetism. In the present contract year, polarized LEED has been used, together with Auger analysis and LEED intensity measurements, as a diagnostic to characterize Ni(001) surfaces produced by laser annealing

  5. Constitutive modeling of metastable austenitic stainless steel

    NARCIS (Netherlands)

    Perdahcioglu, Emin Semih; Geijselaers, Hubertus J.M.; Huetink, Han; Khan, A.

    2010-01-01

    A physically based, macroscale constitutive model has been developed that can describe the complex mechanical behavior of metastable austenitic stainless steels. In the developed model a generalized model for the mechanically induced martensitic transformation is introduced. Mechanical tests have

  6. Consitutive modeling of metastable austenitic stainless steel

    NARCIS (Netherlands)

    Perdahcioglu, Emin Semih; Perdahcioglu, Emin Semih

    2008-01-01

    Metastable austenitic stainless steels combine high formability and high strength, which are generally opposing properties in materials. This property is a consequence of the martensitic phase transformation that takes place during deformation. This transformation is purely mechanically induced

  7. On a metastable vacuum burning phenomenon

    International Nuclear Information System (INIS)

    Berezin, V.A.; Tkachev, I.I.; Kuzmin, V.A.; AN SSSR, Moscow. Inst. Yadernykh Issledovanij)

    1983-02-01

    Equations of motion of an interface between two phases with arbitrary equations of state are obtained. It is found that there may take place a process of metastable vacuum burning. It is shown that under some conditions the process of the new phase bubble expansion is described by the detonation wave equations. Possible cosmological consequences of the metastable phase burning effect are briefly discussed. (author)

  8. Metastability and Rydberg states of triatomic hydrogen

    International Nuclear Information System (INIS)

    Helm, H.

    1991-01-01

    The np,nd and nf Rydberg series of H 3 have been studied by one- or two-photon excitation from the lowest metastable state of H 3 :B2p 2 A 2 ''. The lifetime of the metastable state has been measured and the influence of an external electric field on the Rydberg states has been studied under both aspects of dynamics (field-ionization and field-induced predissociation) and structure (Strak effect)

  9. The role of the Pauli principle in metastability exchange collisions

    International Nuclear Information System (INIS)

    Pinard, M.; Laloe, F.

    1980-01-01

    In optical pumping experiments, metastability exchange collisions are used to transfer orientation, alignment, ... between different atomic levels. This article studies the effect of such collisions on the atom internal variables density operator by a method used in a previous publication for spin exchange collisions. The calculations are valid when the nuclei of the two atoms are distinguishable as well as when they are identical particles, wich allows a detailed discussion of nuclear identity effects (apparent magnetic field, etc...). Two cases are successively studied: no depolarization of the electronic angular momentum (He*-He collisions) and partial depolarization (Ne*-Ne collisions for example). The nuclear identity effects should be observable in low temperature optical pumping experiments with noble gases. In an Appendix, another particle identity effect is studied, which can be observed in atomic beam experiments: during the collision of two 3 He atoms, both in the ground state, the spin state of the atoms scattered in a particular direction can be changed by nuclear indistinguishability effects

  10. First measurement of the ionization yield of nuclear recoils in liquid argon

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, T. [Univ. of California, Berkeley, CA (United States). Dept. of Nuclear Engineering; Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Sangiorgio, Samuele [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Bernstein, A. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Foxe, Michael P. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Pennsylvania State Univ., University Park, PA (United States). Dept. of Mechanical and Nuclear Engineering; Hagmann, Chris [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Jovanovic, Igor [Pennsylvania State Univ., University Park, PA (United States). Dept. of Mechanical and Nuclear Engineering; Kazkaz, K. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Mozin, Vladimir V. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Norman, E. B. [Univ. of California, Berkeley, CA (United States). Dept. of Nuclear Engineering; Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Pereverzev, S. V. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Rebassoo, Finn O. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Sorensen, Peter F. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

    2014-05-01

    Liquid phase argon has long been used as a target medium for particle detection via scintillation light. Recently there has been considerable interest in direct detection of both hypothetical darkmatter particles and coherent elastic neutrino nucleus scattering. These as-yet unobserved neutral particle interactions are expected to result in a recoiling argon atom O(keV), generally referred to in the literature as a nuclear recoil. This prompts the question of the available electromagnetic signal in a liquid argon detector. In this Letter we report the first measurement of the ionization yield (Qy), detected electrons per unit energy, resulting from nuclear recoils in liquid argon, measured at 6.7 keV. This is also the lowest energy measurement of nuclear recoils in liquid argon.

  11. Growth kinetics of metastable (331) nanofacet on Au and Pt(110) surfaces

    International Nuclear Information System (INIS)

    Ndongmouo, U.T.; Houngninou, E.; Hontinfinde, F.

    2006-12-01

    A theoretical epitaxial growth model with realistic barriers for surface diffusion is investigated by means of kinetic Monte Carlo simulations to study the growth modes of metastable (331) nanofacets on Au and Pt(110) surfaces. The results show that under experimental atomic fluxes, the (331) nanofacets grow by 2D nucleation at low temperature in the submonolayer regime. A metastable growth phase diagram that can be useful to experimentalists is presented and looks similar to the one found for the stationary growth of the bcc(001) surface in the kinetic 6-vertex model. (author)

  12. Metastable He (n=2) - Ne potential interaction calculation

    International Nuclear Information System (INIS)

    Rahal, H.

    1983-10-01

    Diabatic potential terms corresponding to He (2 1 S)-Ne and He (2 3 S)-Ne interactions are calculated. These potentials reproduce the experimental results thermal metastable atom elastic scattering on Ne target. A model which reduces the interaction to a one-electron problem is proposed: the He excited electron. Its interaction with the He + center is reproduced by a ''l'' dependent potential model with a 1/2 behaviour at short range. The electron interaction facing the Ne is described by a l-dependent pseudopotential reproducing with accuracy the electron elastic scattering on a Ne atom. The importance of the corrective term related to the Ne polarizations by the electron and the He + ion is showed in this work. In the modelling problems, the accuracy cannot be better than 0.1 MeV [fr

  13. Modelling electroluminescence in liquid argon

    International Nuclear Information System (INIS)

    Stewart, D Y; Barker, G J; Bennieston, A J; Harrison, P F; McConkey, N; Morgan, B; Ramachers, Y A; Lightfoot, P K; Robinson, M; Spooner, N J C; Thompson, L

    2010-01-01

    We present Monte-Carlo simulations of electron transport through liquid argon motivated by our recent observation of electroluminescence light emanating from a thick gaseous electron multiplier (THGEM) in a liquid argon volume. All known elastic and inelastic reaction cross-sections have been accounted for, providing electroluminescence light yield predictions for arbitrary electrostatic fields. This study concludes that the large field gradients needed to produce electroluminescence cannot be accounted for by straightforward electrostatic field calculations based on ideal THGEM holes, suggesting that further experimental investigations are required.

  14. Fast neutron spectroscopy with tensioned metastable fluid detectors

    Energy Technology Data Exchange (ETDEWEB)

    Grimes, T.F.; Taleyarkhan, R.P., E-mail: rusi@purdue.edu

    2016-09-11

    This paper describes research into development of a rapid-turnaround, neutron-spectroscopy capable (gamma-beta blind), high intrinsic efficiency sensor system utilizing the tensioned metastable fluid detector (TMFD) architecture. The inability of prevailing theoretical models (developed successfully for the classical bubble chamber) to adequately predict detection thresholds for tensioned metastable fluid conditions is described. Techniques are presented to overcome these inherent shortcomings, leading thereafter, to allow successful neutron spectroscopy using TMFDs – via the newly developed Single Atom Spectroscopy (SAS) approach. SAS also allows for a unique means for rapidly determining neutron energy thresholds with TMFDs. This is accomplished by simplifying the problem of determining Cavitation Detection Events (CDEs) arising from neutron interactions with one in which several recoiling atom species contribute to CDEs, to one in which only one dominant recoil atom need be considered. The chosen fluid is Heptane (C{sub 7}H{sub 16}) for which only recoiling C atoms contribute to CDEs. Using the SAS approach, the threshold curve for Heptane was derived using isotope neutron source data, and then validated against experiments with mono-energetic (2.45/14 MeV) neutrons from D-D and D-T accelerators. Thereafter the threshold curves were used to produce the response matrix for various geometries. The response matrices were in turn combined with experimental data to recover the continuous spectra of fission (Cf-252) and (α,n) Pu–Be isotopic neutron sources via an unfolding algorithm. A generalized algorithm is also presented for performing neutron spectroscopy using any other TMFD fluid that meets the SAS approach assumptions.

  15. Primary retention following nuclear recoil in β-decay: Proposed synthesis of a metastable rare gas oxide ((38)ArO4) from ((38)ClO4(-)) and the evolution of chemical bonding over the nuclear transmutation reaction path.

    Science.gov (United States)

    Timm, Matthew J; Matta, Chérif F

    2014-12-01

    Argon tetroxide (ArO4) is the last member of the N=50 e(-) isoelectronic and isosteric series of ions: SiO4(4-), PO4(3-), SO4(2-), and ClO4(-). A high level computational study demonstrated that while ArO4 is kinetically stable it has a considerable positive enthalpy of formation (of ~298kcal/mol) (Lindh et al., 1999. J. Phys. Chem. A 103, pp. 8295-8302) confirming earlier predictions by Pyykkö (1990. Phys. Scr. 33, pp. 52-53). ArO4 can be expected to be difficult to synthesize by traditional chemistry due to its metastability and has not yet been synthesized at the time of writing. A computational investigation of the changes in the chemical bonding of chlorate (ClO4(-)) when the central chlorine atom undergoes a nuclear transmutation from the unstable artificial chlorine isotope (38)Cl to the stable rare argon isotope (38)Ar through β-decay, hence potentially leading to the formation of ArO4, is reported. A mathematical model is presented that allows for the prediction of yields following the recoil of a nucleus upon ejecting a β-electron. It is demonstrated that below a critical angle between the ejected β-electron and that of the accompanying antineutrino their respective linear momentums can cancel to such an extent as imparting a recoil to the daughter atom insufficient for breaking the Ar-O bond. As a result, a primary retention yield of ~1% of ArO4 is predicted following the nuclear disintegration. The study is conducted at the quadratic configuration interaction with single and double excitations [QCISD/6-311+G(3df)] level of theory followed by an analysis of the electron density by the quantum theory of atoms in molecules (QTAIM). Crossed potential energy surfaces (PES) were used to construct a PES from the metastable ArO4 ground singlet state to the Ar-O bond dissociation product ArO3+O((3)P) from which the predicted barrier to dissociation is ca. 22kcal/mol and the exothermic reaction energy is ca. 28kcal/mol [(U)MP2/6-311+G(d)]. Copyright © 2014

  16. Geminate recombination in liquid argon

    International Nuclear Information System (INIS)

    Freeman, G.R.

    1984-01-01

    The extended Onsager model for geminate neutralization is supported by the field dependence of the ionization yield in liquid argon irradiated by high energy electrons or x rays. Attempts to employ the model fail unless the distribution of initial separation distances between the thermalized electrons and their sibling ions (secondary electron thermalization ranges) is included. Data of Scalettar and co-workers are reanalyzed

  17. Entropy-driven metastable defects in silicon

    International Nuclear Information System (INIS)

    Hamilton, B.; Peaker, A.R.; Pantelides, S.T.

    1989-01-01

    The known metastable defects are usually describable by a configuration coordinate diagram in which two energy minima are separated by a barrier. This diagram does not change with temperature and each configuration is stable over some temperature range. Here we report the observation of a novel metastability: A configuration change occurs spontaneously and abruptly at a critical temperature, giving rise to a discontinuous DLTS (deep level transient spectroscopy) spectrum. We propose that this phenomenon is a manifestation of entropy variations in the configurational space. (author) 12 refs., 4 figs

  18. Chalcogenides Metastability and Phase Change Phenomena

    CERN Document Server

    Kolobov, Alexander V

    2012-01-01

    A state-of-the-art description of metastability observed in chalcogenide alloys is presented with the accent on the underlying physics. A comparison is made between sulphur(selenium)-based chalcogenide glasses, where numerous photo-induced phenomena take place entirely within the amorphous phase, and tellurides where a reversible crystal-to-amorphous phase-change transformation is a major effect. Applications of metastability in devices¿optical memories and nonvolatile electronic phase-change random-access memories among others are discussed, including the latest trends. Background material essential for understanding current research in the field is also provided.

  19. Time resolved laser induced fluorescence on argon intermediate pressure microwave discharges: Measuring the depopulation rates of the 4p and 5p excited levels as induced by electron and atom collisions

    Energy Technology Data Exchange (ETDEWEB)

    Palomares, J.M., E-mail: j.m.palomares-linares@tue.nl; Graef, W.A.A.D.; Hübner, S.; Mullen, J.J.A.M. van der, E-mail: jjamvandermullen@gmail.com

    2013-10-01

    The reaction kinetics in the excitation space of Ar is explored by means of Laser Induced Fluorescence (LIF) experiments using the combination of high rep-rate YAG–Dye laser systems with a well defined and easily controllable surfatron induced plasma setup. The high rep-rate favors the photon statistics while the low energy per pulse avoids intrusive plasma laser interactions. An analysis shows that, despite the low energy per pulse, saturation can still be achieved even when the geometrical overlap and spectral overlap are optimal. Out of the various studies that can be performed with this setup we confine the current paper to the study of the direct responses to the laser pump action of three 4p and one 5p levels of the Ar system. By changing the plasma in a controlled way one gets for these levels the rates of electron and atom quenching and therewith the total destruction rates of electron and atom collisions. Comparison with literature shows that the classical hard sphere collision rate derived for hydrogen gives a good description for the observed electron quenching (e-quenching) in Ar whereas for heavy particle quenching (a-quenching) this agreement was only found for the 5p level. An important parameter in the study of electron excitation kinetics is the location of the boundary in the atomic system for which the number of electron collisions per radiative life time equals unity. It is observed that for the Ar system this boundary is positioned lower than what is expected on grounds of H-like formulas. - Highlights: • Time resolved laser induced fluorescence at high repetition rate • Decay times as function of pressure, electron density and temperature • Measurement of total electron atom depopulation rates • Reasonable agreement of electron total rates with hard sphere approximations.

  20. Liquid Argon Barrel Cryostat Arrived

    CERN Multimedia

    Pailler, P

    Last week the first of three cryostats for the ATLAS liquid argon calorimeter arrived at CERN. It had travelled for 46 days over several thousand kilometers from Japan to CERN. During three years it has been fabricated by Kawasaki Heavy Industries Ltd. at Harima, close to Kobe, under contract from Brookhaven National Laboratory (BNL) of the U.S.. This cryostat consists of two concentric cylinders made of aluminium: the outer vacuum vessel with a diameter of 5.5 m and a length of 7 m, and the inner cold vessel which will contain the electromagnetic barrel calorimeter immersed in liquid argon. The total weight will be 270 tons including the detectors and the liquid argon. The cryostat is now located in building 180 where it will be equipped with 64 feed-throughs which serve for the passage of 122,880 electrical lines which will carry the signals of the calorimeter. After integration of the calorimeter, the solenoidal magnet of ATLAS will be integrated in the vacuum vessel. A final cold test of the cryostat inc...

  1. Energy and charge transfer in ionized argon coated water clusters

    International Nuclear Information System (INIS)

    Kočišek, J.; Lengyel, J.; Fárník, M.; Slavíček, P.

    2013-01-01

    We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H 2 O) n clusters resulting in the ionization threshold above ≈15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar + and water occurs above the threshold; at higher electron energies above ∼28 eV, an excitonic transfer process between Ar + * and water opens leading to new products Ar n H + and (H 2 O) n H + . On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H 2 O) n H 2 2+ and (H 2 O) n 2+ ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent

  2. Formation and annealing of metastable (interstitial oxygen)-(interstitial carbon) complexes in n- and p-type silicon

    CERN Document Server

    Makarenko, L F; Lastovskii, S B; Murin, L I; Moll, M; Pintilie, I

    2014-01-01

    It is shown experimentally that, in contrast to the stable configuration of (interstitial carbon)-(interstitial oxygen) complexes (CiOi), the corresponding metastable configuration (CiOi{*}) cannot be found in n-Si based structures by the method of capacitance spectroscopy. The rates of transformation CiOi{*} -> CiOi are practically the same for both n- and p-Si with a concentration of charge carriers of no higher than 10(13) cm(-3). It is established that the probabilities of the simultaneous formation of stable and metastable configurations of the complex under study in the case of the addition of an atom of interstitial carbon to an atom of interstitial oxygen is close to 50\\%. This is caused by the orientation dependence of the interaction potential of an atom of interstitial oxygen with an interstitial carbon atom, which diffuses to this oxygen atom.

  3. Modelling the material behaviour of metastable stainless

    NARCIS (Netherlands)

    Datta, K.; Geijselaers, Hubertus J.M.; Post, J.; Beyer, J.; Huetink, Han; Cesar de Sa, Jose M.A.; Santos, Abel D.

    2007-01-01

    Metastable austenitic stainless steels are designed to be thermodynamically unstable such that deformation even at room temperatures can bring about a change in the phase of face centred cubic austenite to either hexagonal close packed martensite and/or to body centred cubic martensite. This solid

  4. Inflating metastable quark-gluon plasma universe

    International Nuclear Information System (INIS)

    Jenkovszky, L.L.; Kaempfer, B.; Sysoev, V.M.

    1990-01-01

    We show within the Friedmann model with the equation of state p(T)=aT 4 -AT that our universe has expanded exponentially when it was in a metastable quark-gluon plasma state. The scale factor during that epoch increased by many orders of magnitude. 13 refs.; 5 figs

  5. Radiation-sustained nanocluster metastability in oxide dispersion strengthened materials

    Science.gov (United States)

    Ribis, J.; Bordas, E.; Trocellier, P.; Serruys, Y.; de Carlan, Y.; Legris, A.

    2015-12-01

    ODS materials constitute a new promising class of structural materials for advanced fission and fusion energy application. These Fe-Cr based ferritic steels contain ultra-high density of dispersion-strengthening nanoclusters conferring excellent mechanical properties to the alloy. Hence, guarantee the nanocluster stability under irradiation remain a critical issue. Nanoclusters are non-equilibrium multicomponent compounds (YTiCrO) forming through a complex nucleation pathway during the elaboration process. In this paper, it is proposed to observe the response of these nanoclusters when the system is placed far from equilibrium by means of ion beam. The results indicate that the Y, Ti, O and Cr atoms self-organized so that nanoclusters coarsened but maintain their non-equilibrium chemical composition. It is discussed that the radiation-sustained nanocluster metastability emerges from cooperative effects: radiation-induced Ostwald ripening, permanent creation of vacancies in the clusters, and fast Cr diffusion mediated by interstitials.

  6. Metastable and unstable cellular solidification of colloidal suspensions

    Science.gov (United States)

    Deville, Sylvain; Maire, Eric; Bernard-Granger, Guillaume; Lasalle, Audrey; Bogner, Agnès; Gauthier, Catherine; Leloup, Jérôme; Guizard, Christian

    2009-12-01

    Colloidal particles are often seen as big atoms that can be directly observed in real space. They are therefore becoming increasingly important as model systems to study processes of interest in condensed-matter physics such as melting, freezing and glass transitions. The solidification of colloidal suspensions has long been a puzzling phenomenon with many unexplained features. Here, we demonstrate and rationalize the existence of instability and metastability domains in cellular solidification of colloidal suspensions, by direct in situ high-resolution X-ray radiography and tomography observations. We explain such interface instabilities by a partial Brownian diffusion of the particles leading to constitutional supercooling situations. Processing under unstable conditions leads to localized and global kinetic instabilities of the solid/liquid interface, affecting the crystal morphology and particle redistribution behaviour.

  7. Radiation-sustained nanocluster metastability in oxide dispersion strengthened materials

    International Nuclear Information System (INIS)

    Ribis, J.; Bordas, E.; Trocellier, P.; Serruys, Y.; Carlan, Y. de; Legris, A.

    2015-01-01

    ODS materials constitute a new promising class of structural materials for advanced fission and fusion energy application. These Fe–Cr based ferritic steels contain ultra-high density of dispersion-strengthening nanoclusters conferring excellent mechanical properties to the alloy. Hence, guarantee the nanocluster stability under irradiation remain a critical issue. Nanoclusters are non-equilibrium multicomponent compounds (YTiCrO) forming through a complex nucleation pathway during the elaboration process. In this paper, it is proposed to observe the response of these nanoclusters when the system is placed far from equilibrium by means of ion beam. The results indicate that the Y, Ti, O and Cr atoms self-organized so that nanoclusters coarsened but maintain their non-equilibrium chemical composition. It is discussed that the radiation-sustained nanocluster metastability emerges from cooperative effects: radiation-induced Ostwald ripening, permanent creation of vacancies in the clusters, and fast Cr diffusion mediated by interstitials.

  8. Time resolved laser induced fluorescence on argon intermediate pressure microwave discharges: Measuring the depopulation rates of the 4p and 5p excited levels as induced by electron and atom collisions

    Science.gov (United States)

    Palomares, J. M.; Graef, W. A. A. D.; Hübner, S.; van der Mullen, J. J. A. M.

    2013-10-01

    The reaction kinetics in the excitation space of Ar is explored by means of Laser Induced Fluorescence (LIF) experiments using the combination of high rep-rate YAG-Dye laser systems with a well defined and easily controllable surfatron induced plasma setup. The high rep-rate favors the photon statistics while the low energy per pulse avoids intrusive plasma laser interactions. An analysis shows that, despite the low energy per pulse, saturation can still be achieved even when the geometrical overlap and spectral overlap are optimal. Out of the various studies that can be performed with this setup we confine the current paper to the study of the direct responses to the laser pump action of three 4p and one 5p levels of the Ar system. By changing the plasma in a controlled way one gets for these levels the rates of electron and atom quenching and therewith the total destruction rates of electron and atom collisions. Comparison with literature shows that the classical hard sphere collision rate derived for hydrogen gives a good description for the observed electron quenching (e-quenching) in Ar whereas for heavy particle quenching (a-quenching) this agreement was only found for the 5p level. An important parameter in the study of electron excitation kinetics is the location of the boundary in the atomic system for which the number of electron collisions per radiative life time equals unity. It is observed that for the Ar system this boundary is positioned lower than what is expected on grounds of H-like formulas.

  9. Opacity measurements in shock-generated argon plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Erskine, D.

    1993-07-01

    Dense plasmas having uniform and constant density and temperature are generated by passage of a planar shock wave through gas. The opacity of the plasma is accurately measured versus wavelength by recording the risetime of emitted light. This technique is applicable to a wide variety of species and plasma conditions. Initial experiments in argon have produced plasmas with 2 eV temperatures, 0.004--0.04 g/cm{sup 3} densities, and coupling parameters {Gamma} {approximately}0.3--0.7. Measurements in visible light are compared with calculations using the HOPE code. An interesting peak in the capacity at 400 nm is observed for the first time and is identified with the 4s-5p transition in excited neutral argon atoms.

  10. Melting in Two-Dimensional Lennard-Jones Systems: Observation of a Metastable Hexatic Phase

    International Nuclear Information System (INIS)

    Chen, K.; Kaplan, T.; Mostoller, M.

    1995-01-01

    Large scale molecular dynamics simulations of two-dimensional melting have been carried out using a recently revised Parrinello-Rahman scheme on massively parallel supercomputers. A metastable state is observed between the solid and liquid phases in Lennard-Jones systems of 36 864 and 102 400 atoms. This intermediate state shows the characteristics of the hexatic phase predicted by the theory of Kosterlitz, Thouless, Halperin, Nelson, and Young

  11. Rotational spectrum of 1,1-difluoroethane-argon: influence of the interaction with the Ar atom on the V 3 barrier to internal rotation of the methyl group

    Science.gov (United States)

    Velino, Biagio; Melandri, Sonia; Favero, Paolo G.; Dell'Erba, Adele; Caminati, Walther

    2000-01-01

    The free-jet millimeter-wave absorption spectrum of 1,1-difluoroethane-Ar is reported. Most of the measured lines are split due to internal rotation of the methyl group and the tunnelling motion of Ar connecting two equivalent potential energy minima. The Ar atom, close to the CHF 2 group, eclipses one of the methylic hydrogens in the symmetryless geometry of the complex, reducing in this way the barrier to the internal rotation of the methyl group with respect to isolated 1,1-difluoroethane. For high J levels the distance of Ar from the molecule increases, however, due to the centrifugal distortion, and the barrier increases towards the value for 1,1-difluoroethane.

  12. Prospects for photosensitive dopants in liquid argon

    International Nuclear Information System (INIS)

    Anderson, D.F.

    1990-12-01

    Evidence is presented that the addition of a few ppM of a photosensitive dopant to a U/liquid argon or Pb/liquid argon calorimeter will make a substantial reduction in the e/π ratio. Previous results indicating high voltage problems and no change in the e/π ratio in tests of photosensitive dopants with the Fermilab D0 experiment's U/liquid argon tests calorimeter are also explained. 13 refs., 3 figs

  13. Shear response of grain boundaries with metastable structures by molecular dynamics simulations

    Science.gov (United States)

    Zhang, Liang; Lu, Cheng; Shibuta, Yasushi

    2018-04-01

    Grain boundaries (GBs) can play a role as the favored locations to annihilate point defects, such as interstitial atoms and vacancies. It is thus highly probable that different boundary structures can be simultaneously present in equilibrium with each other in the same GB, and thus the GB achieves a metastable state. However, the structural transition and deformation mechanism of such GBs are currently not well understood. In this work, molecular dynamics simulations were carried out to study the multiple structures of a Σ5(310)/[001] GB in bicrystal Al and to investigate the effect of structural multiplicity on the mechanical and kinetic properties of such a GB. Different GB structures were obtained by changing the starting atomic configuration of the bicrystal model, and the GB structures had significantly different atomic density. For the Σ5(310) GB with metastable structures, GB sliding was the dominant mechanism at a low temperature (T = 10 K) under shear stress. The sliding mechanism resulted from the uncoordinated transformation of the inhomogeneous structural units. The nucleation of voids was observed during GB sliding at the low temperature, and the voids subsequently evolved to a nanocrack at the boundary plane. Increasing the temperature can induce the structural transition of local GB structures and can change their overall kinetic properties. GB migration with occasional GB sliding dominated the deformation mechanism at elevated temperatures (T = 300 and 600 K), and the migration process of the metastable GB structures is closely related to the thermally assisted diffusion mechanism.

  14. High densities and optical collisions in a two-colour magneto-optical trap for metastable helium

    NARCIS (Netherlands)

    Koelemeij, J.C.J.; Tychkov, A.; Jeltes, T.; Hogervorst, W.; Vassen, W.

    2004-01-01

    We have studied a cloud of cold metastable helium (He*) atoms interacting with near-resonant light at 1083 nm and 389 nm. The 1083 nm light allows for efficient loading of a large magneto-optical trap (MOT) and the 389 nm light is subsequently used to increase the density and reduce the temperature

  15. Dynamics of imploding argon plasmas

    International Nuclear Information System (INIS)

    Clark, W.; Richardson, R.; Brannon, J.; Wilkinson, M.; Katzenstein, J.

    1982-01-01

    The BLACKJACK 5 pulse generator has been used to implode annular argon plasmas to form dense Z pinches. Visible streak photography, framing photography, and laser shadowgraphy were used to observe the radial position and velocity of the plasmas as they imploded. The measured position and velocity of the imploding plasmas have been compared with the results of calculations based on a one-dimensional snowplow model. Good agreement is obtained between the snowplow calculations and the optical measurements. Empirically determined optimum implosion parameters are also found to agree with those predicted by the model

  16. Populations and lifetimes in the $v=n-l-1=2$ and 3 metastable cascades of $\\overline{p} He^{+}$ measured by pulsed and continuous antiproton beams

    CERN Document Server

    Hori, Masaki; Widmann, E; Yamazaki, T; Hayano, R S; Ishikawa, T; Torie, H A; Von Egidy, T; Hartmann, F; Ketzer, B; Maierl, C; Pohl, R; Kumakura, M; Morita, N; Horváth, D; Sugai, I

    2004-01-01

    Using the laser spectroscopy, the time evolution of the state population in the v equivalent n-l=2 and 3 metastable cascades of antiprotonic helium atoms were studied. The effects of the collision between antiprotonic helium and the ordinary helium atoms on the atomic cascade were also analyzed. The measurements were done using the pulsed and continuous types of antiproton beams supplied by the Low Energy Antiproton Ring. The studies revealed five phases in the life history of the metastable antiprotonic helium. (Edited abstract) 71 Refs.

  17. Metastability-exchange optical pumping of 3He for neutron polarizers

    International Nuclear Information System (INIS)

    Gentile, T.R.; Thompson, A.K.; Snow, W.M.

    1995-01-01

    Research is underway at NIST and IU to develop neutron polarizers that are based on polarized 3 He. Such polarizers rely on the strong spin dependence of the cross section for neutron capture by polarized 3 He. Two methods can produce the high density of polarized 3 He gas (10 19 -10 20 cm -3 ) required for an effective neutron polarizer: spin-exchange optical pumping, which is performed directly at high pressure (1-10 bar), and metastability-exchange optical pumping, in which the gas is polarized at low pressure (1 mbar) and then compressed. While we are pursuing both methods, progress in the metastable method will be discussed. The features of the metastable method are the high rate at which the gas can be polarized and the inherent separation of the optical pumping and target cells. In a landmark achievement, researchers at the Univ. of Mainz have developed a piston compressor that can fill a 130 cm 3 cell to a pressure of 7 bar of 45% polarized 3 He gas in 2 hours. We plan to develop a compressor and test it at the NIST Cold Neutron Research Facility. We have constructed a metastable-pumping apparatus at NIST and have obtained 76% polarization with a pumping rate of 1.2 x 10 18 atoms/sec in a 0.4 mbar, 270 cm 3 cell

  18. Experimental and modelling investigations of a dielectric barrier discharge in low-pressure argon

    International Nuclear Information System (INIS)

    Wagenaars, E; Brandenburg, R; Brok, W J M; Bowden, M D; Wagner, H-E

    2006-01-01

    The discharge behaviour of a dielectric barrier discharge (DBD) in low-pressure argon gas was investigated by experiments and modelling. The electrical characteristics and light emission dynamics of the discharge were measured and compared with the results of a two-dimensional fluid model. Our investigations showed that the discharge consisted of a single, diffuse discharge per voltage half-cycle. The breakdown phase of the low-pressure DBD (LPDBD) was investigated to be similar to the ignition phase of a low-pressure glow discharge without dielectrics, described by Townsend breakdown theory. The stable discharge phase of the LPDBD also showed a plasma structure with features similar to those of a classical glow discharge. The presence of the dielectric in the discharge gap led to the discharge quenching and thus the decay of the plasma. Additionally, the argon metastable density was monitored by measuring light emission from nitrogen impurities. A metastable density of about 5 x 10 17 m -3 was present during the entire voltage cycle, with only a small (∼10%) increase during the discharge. Finally, a reduction of the applied voltage to the minimum required to sustain the discharge led to a further reduction of the role of the dielectric. The discharge was no longer quenched by the dielectrics only but also by a reduction of the applied voltage

  19. Electron capture, electron loss, and deexcitation of fast H(2 2S) and H(1 2S) atoms in collisions with molecular hydrogen and inert gases

    International Nuclear Information System (INIS)

    Roussel, F.; Pradel, P.; Spiess, G.

    1977-01-01

    Collisions of ground-state (1 2 S) and metastable (2 2 S) hydrogen atoms with rare gases and molecular hydrogen have been studied in the energy range 0.5--3.0 keV. For an acceptance angle of 55 mrad, the electron loss and the electron-capture cross sections of both H(1 2 S) and H(2 2 S) have been measured and compared with previous experimental values. The deexcitation cross section for H(2 2 S) has been deduced with the help of previously measured total-quenching cross sections for H(2 2 S). The ratio of the electron-capture cross sections for H(2 2 S) relative to H(1 2 S) is found to be very large for argon at low energies. The effects of large-angle scattering and of highly excited states of H are discussed

  20. Continuum radiation of argon plasma

    International Nuclear Information System (INIS)

    D'Yachkov, L.G.

    1995-01-01

    A simple completely analytical method of the calculation of radiative continuum of plasmas is derived and an analysis of experimental data on continuum radiation of argon plasma is made. The method is based on the semiclassical quantum defect theory. To calculate radial matrix elements of dipole transitions the asymptotic expansion in powers of E c /ω 2/3 , with an accuracy to the linear term, where E, is the arithmetic mean of the initial and final energies of the transition, is used. This expansion has the same form for free-free, free-bound and bound-bound transitions. If the quantum defects are also approximated by a linear function of energy, the integration over the electron energy (the Maxwell-Boltzmann distribution is assumed) can be performed in analytical form. For Rydberg states the sum of photoionization continua can be replaced by an integral. We have calculated the absorption coefficient pf argon plasma. The photoionization cross section is calculated for all the states of 4s, 5s, 6s, 4p, 5p, 3d, 4d, 4s', 5s', 6s', 4p', 5p', 3d' and 4d' configurations taking into account P-coupling and multiplet splitting (56 states). Other excited states are allowed for by the integral formula together with free-free transitions

  1. Electron-ion recombination study in argon at atmospheric pressure

    International Nuclear Information System (INIS)

    Kafrouni, Hanna.

    1979-01-01

    This study deals with a wall-stabilized arc burning in argon at atmospheric pressure. A transient mode is obtained using a fast thyristor connected to the electrodes, which short-circuits the discharge. By means of two wavelengths laser interferometry and spectroscopy measurements we have determined the temporal changes of the electron density, ground state atom density and excited atom density. We have shown that, when the electric field is suppressed, the electron temperature rapidly decreases to the gas temperature before changing electron and atom densities. This phenomenon is applied to determine the gas temperature and to evaluate the role played by ionization in electron density balance. The coefficients of ambipolar diffusion, ionization and recombination and an apparent recombination coefficient are determined versus electron temperature and compared with theoretical values [fr

  2. Metastable states in amorphous chalcogenide semiconductors

    CERN Document Server

    Mikla, Victor I

    2009-01-01

    This book addresses an interesting and technologically important class of materials, the amorphous chalcogenide semiconductors. Experimental results on the structural and electronic metastable states in Se-rich chalcogenides are presented. Special attention is paid to the states in the mobility gap and their sensitivity to various factors such as irradiation, annealing and composition. Photoinduced changes of structure and physical properties are also considered and structural transformation at photocrystallization is studied in detail. Finally, the authors discuss potential applications of th

  3. A Note on Scenarios of Metastable Water

    Czech Academy of Sciences Publication Activity Database

    Jirsák, Jan; Nezbeda, Ivo

    2010-01-01

    Roč. 75, č. 5 (2010), s. 593-605 ISSN 0010-0765 R&D Projects: GA AV ČR IAA400720802; GA AV ČR IAA200760905; GA AV ČR IAA400720710 Institutional research plan: CEZ:AV0Z40720504 Keywords : metastable water * spinodal * scenarios Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 0.853, year: 2010

  4. Metastability in Field Theory and Statistical Mechanics

    International Nuclear Information System (INIS)

    Carvalho, C.A. de.

    1984-01-01

    After a phase transition analysis which can occur in the framework of a scalar field theory, at finite temperature and in presence of a external field, possibles metastable situations are studied and also how is their relationship with the transitions. In both cases it is used a semiclassical approximation to the theory which, in Statistical Mechanics, corresponds to the droplet-bubble model. (L.C.) [pt

  5. Investigation of metastable ions by mass spectrometry

    International Nuclear Information System (INIS)

    Szilagyi, Z.

    1998-01-01

    Metastable decompositions of ions was studied by various methods. The results are summarized in three chapters in this thesis. The development of a method can be used for evaluation of experimental data is described in the first chapter; the second one presents an example for the application of the developed method; and the laser power dependence of MALDI-TOF PSD (matrix-assisted laser desorption/ionization time-of-flight post-source decay) spectra is discussed in chapter three. (author)

  6. Metastability of Queuing Networks with Mobile Servers

    Science.gov (United States)

    Baccelli, F.; Rybko, A.; Shlosman, S.; Vladimirov, A.

    2018-04-01

    We study symmetric queuing networks with moving servers and FIFO service discipline. The mean-field limit dynamics demonstrates unexpected behavior which we attribute to the metastability phenomenon. Large enough finite symmetric networks on regular graphs are proved to be transient for arbitrarily small inflow rates. However, the limiting non-linear Markov process possesses at least two stationary solutions. The proof of transience is based on martingale techniques.

  7. Atomic collisions research with excited atomic species

    International Nuclear Information System (INIS)

    Hoogerland, M.D.; Gulley, R.J.; Colla, M.; Lu, W.; Milic, D.; Baldwin, K.G.H.; Buckman, S.J.

    1999-01-01

    Measurements and calculations of fundamental atomic collision and spectroscopic properties such as collision cross sections, reaction rates, transition probabilities etc. underpin the understanding and operation of many plasma and gas-discharge-based devices and phenomena, for example plasma processing and deposition. In almost all cases the complex series of reactions which sustains the discharge or plasma, or produces the reactive species of interest, has a precursor electron impact excitation, attachment, dissociation or ionisation event. These processes have been extensively studied in a wide range of atomic and molecular species and an impressive data base of collision cross sections and reaction rates now exists. However, most of these measurements are for collisions with stable atomic or molecular species which are initially in their ground electronic state. Relatively little information is available for scattering from excited states or for scattering from unstable molecular radicals. Examples of such species would be metastable excited rare gases, which are often used as buffer gases, or CF 2 radicals formed by electron impact dissociation in a CF 4 plasma processing discharge. We are interested in developing experimental techniques which will enable the quantitative study of such exotic atomic and molecular species. In this talk I would like to outline one such facility which is being used for studies of collisions with metastable He(2 3 S) atoms

  8. Rotational study on the van der Waals complex 1-chloro-1,1-difluoroethane-argon

    Science.gov (United States)

    Wang, Juan; Chen, Junhua; Feng, Gang; Xia, Zhining; Gou, Qian

    2018-03-01

    The rotational spectrum of the van der Waals complex formed between 1-chloro-1,1-difluoroethane and argon has been investigated by using a pulsed jet Fourier transform microwave spectrometer. Only one set of rotational transitions belonging to the lowest energy conformer has been observed and assigned, although theoretical calculations suggest six stable conformers that might be observed. The observed conformer, according to the experimental evidence from two isotopologues (35Cl and 37Cl), adopts a configuration in which the argon atom is located, close to the sbnd CF2Cl top, between the CCF and CCCl planes (the dihedral angle ∠ ArCCCl is 65.2°). The distance between argon atom and the center of mass of CH3CF2Cl is 3.949(2) Å. The dissociation energy, with pseudo diatomic approximation, is evaluated to be 2.4 kJ mol- 1.

  9. Study of argon-based Penning gas mixtures for use in proportional counters

    International Nuclear Information System (INIS)

    Agrawal, P.C.; Ramsey, B.D.; Weisskopf, M.C.

    1989-01-01

    Results from an experimental investigation of three Penning gas mixtures, namely argon-acetylene (Ar-C 2 H 2 ), argon-xenon (Ar-Xe) and argon-xenon-trimethylamine (Ar-Xe-TMA), are reported. The measurements, carried out in cylindrical geometry as well as parallel plate geometry detectors, demonstrate that the Ar-C 2 H 2 mixtures show a significant Penning effect even at an acetylene concentration of 10% and provide the best energy resolution among all the argon-based gas mixtures (≤13% FWHM at 5.9 keV and 6.7% at 22.2 keV). In the parallel plate detector the Ar-C 2 H 2 fillings provide a resolution of ≅7% FWHM at 22.2 keV up to a gas gain of at least ≅10 4 . The nonmetastable Penning mixture Ar-Xe provides the highest gas gain among all the argon-based gas mixtures and is well suited for use in long-duration space-based experiments. Best results are obtained with 5% and 20% Xe in Ar, the energy resolution being ≅7% FWHM at 22.2 keV and ≅4.5% at 59.6 keV for gas gain 3 . Addition of ≥1% TMA to an 80% Ar-20% Xe mixture produces a dramatic increase in gas gain but the energy resolution remains unaffected (≅7% FWHM at 22.2 keV). This increase in gas gain is attributed to the occurrence of a Penning effect between Xe and TMA, the ionization potential of TMA being 8.3 eV, just below the xenon metastable potential of 8.39 eV. (orig.)

  10. Rate coefficients for collisional population transfer between 3p54p argon levels at 300 0K

    International Nuclear Information System (INIS)

    Nguyen, T.D.; Sadeghi, N.

    1978-01-01

    The population transfer between excited 3p 5 4p argon levels induced by the collisional process Ar* (3p 5 4p)/sub i/ + Ar( 1 S 0 ) arrow-right-left Ar* (3p 5 4p)/sub j/ + Ar( 1 S 0 ) + ΔE was studied in the afterglow of an argon pulsed discharge, at the pressure range of 0.2--1 Torr. Selective population of one particular argon 3p 5 4p level was achieved by laser excitation from one metastable state by use of a tunable cw dye laser. The populations of the laser-excited level and of the collisional excited levels were determined by intensity measurements of the fluorescence line and of the sensitized fluorescence lines. The time-dependence study of the populations of the metastable state, of the laser-excited state, and of the collisional excited states was carried out to ascertain the product channel and to determine the collisional transfer rate coefficients

  11. Experimental confirmation of photon-induced spin-flip transitions in helium via triplet metastable yield spectra

    International Nuclear Information System (INIS)

    Rubensson, Jan-Erik; Moise, Angelica; Richter, Robert; Mihelic, Andrej; Bucar, Klemen; Zitnik, Matjaz

    2010-01-01

    Doubly excited states below the N=2 ionization threshold are populated by exciting helium atoms in a supersonic beam with monochromatized synchrotron radiation. The fluorescence decay of these states triggers a radiative cascade back to the ground state with large probability to populate long lived singlet and triplet helium metastable states. The yield of metastables is measured using a multichannel plate detector after the beam has passed a singlet-quenching discharge lamp. The variation of the yield observed with the lamp switched on or off is related to the triplet-singlet mixing of the doubly excited states.

  12. Liquid argon calorimetry for the SSC

    International Nuclear Information System (INIS)

    Gordon, H.A.

    1990-01-01

    Liquid argon calorimetry is a mature technique. However, adapting it to the challenging environment of the SSC requires a large amount of R ampersand D. The advantages of the liquid argon approach are summarized and the issues being addressed by the R ampersand D program are described. 18 refs

  13. Diffraction experiments of argon or helium on polluted surfaces

    International Nuclear Information System (INIS)

    Berthier, J.P.; Constans, A.; Daury, G.; Lostis, P.

    1975-01-01

    Scattering patterns of molecular beams of argon or helium from metal surfaces (bulk metal or thin films) are reported. The pressure in the scattering chamber is about 10 -6 torr. So, the surfaces are polluted. Diffraction peaks are observed which can be interpreted very well by assuming that nitrogen, oxygen or carbon atoms are adsorbed of the surface. On the other hand, diffraction peaks from a silicon crystal have been observed which can be reproduced very well by using silicon crystal lattice. These experiments are not interpreted accurately, but show that molecular reflection can be used for some surface studies [fr

  14. Spatio-temporal dynamics of a pulsed microwave argon plasma: ignition and afterglow

    International Nuclear Information System (INIS)

    Carbone, Emile; Sadeghi, Nader; Vos, Erik; Hübner, Simon; Van Veldhuizen, Eddie; Van Dijk, Jan; Nijdam, Sander; Kroesen, Gerrit

    2015-01-01

    In this paper, a detailed investigation of the spatio-temporal dynamics of a pulsed microwave plasma is presented. The plasma is ignited inside a dielectric tube in a repetitively pulsed regime at pressures ranging from 1 up to 100 mbar with pulse repetition frequencies from 200 Hz up to 500 kHz. Various diagnostic techniques are employed to obtain the main plasma parameters both spatially and with high temporal resolution. Thomson scattering is used to obtain the electron density and mean electron energy at fixed positions in the dielectric tube. The temporal evolution of the two resonant and two metastable argon 4s states are measured by laser diode absorption spectroscopy. Nanosecond time-resolved imaging of the discharge allows us to follow the spatio-temporal evolution of the discharge with high temporal and spatial resolution. Finally, the temporal evolution of argon 4p and higher states is measured by optical emission spectroscopy. The combination of these various diagnostics techniques gives deeper insight on the plasma dynamics during pulsed microwave plasma operation from low to high pressure regimes. The effects of the pulse repetition frequency on the plasma ignition dynamics are discussed and the plasma-off time is found to be the relevant parameter for the observed ignition modes. Depending on the delay between two plasma pulses, the dynamics of the ionization front are found to be changing dramatically. This is also reflected in the dynamics of the electron density and temperature and argon line emission from the plasma. On the other hand, the (quasi) steady state properties of the plasma are found to depend only weakly on the pulse repetition frequency and the afterglow kinetics present an uniform spatio-temporal behavior. However, compared to continuous operation, the time-averaged metastable and resonant state 4s densities are found to be significantly larger around a few kHz pulsing frequency. (paper)

  15. Vascular anastomosis by Argon Laser

    International Nuclear Information System (INIS)

    Gomes, O.M.; Macruz, R.; Armelin, E.; Brum, J.M.G.; Ribeiro, M.P.; Mnitentog, J.; Verginelli, G.; Pileggi, F.; Zerbini, E.J.

    1982-01-01

    Twenty four mongrel dogs, wheighing 13 to 24 kilograms were studied. After anesthesia, intubation and controlled ventilation, they were submitted to three types of vascular anastomosis: Group I - eight dogs with saphenous vein inter-carotid arteries by-pass: Group II - eight dogs with left mammary artery - left anterior descending coronary artery by-pass; Group III - eight dogs with venovenous anastomosis. In all groups 0.8 to 15 watts of Argon Laser power was applied to a total time of 90 to 300 seconds. The lower power for venovenous anastomosis and the greater for the arterial ones. The mean valves of resistence of the Laser anastomosis to pressure induced rupture was 730 mmHg in the immediate post operative study, and superior to 2.500 mmHg 30 days after. No signs of occlusion was demonstrated at the anastomosis sites by the angiographic and anathomo-patological study performed. (Author) [pt

  16. Lifetime of the metastable 23S1 state in stored Li+ ions

    International Nuclear Information System (INIS)

    Knight, R.D.

    1979-04-01

    A laser-induced fluorescence technique combined with the observation of spontaneous magnetic dipole photons from the highly metastable 2 3 S 1 state of Li + was used to measure the radiative lifetime of this state. The ions are created by electron impact on a lithium atomic beam and are subsequently stored for periods of many seconds in an RF-quadrupole ion trap. A tunable dye laser excites the 2 3 S--2 3 P, transition at 5485A, and the intercombination electric dipole transition 2 3 P 1 --1 1 S 0 at 202A is observed. This process depletes the metastable population in a time tau/sub d/ 3 S 1 / and provides a measure of the total number of metastables. Comparison with the rate of 210A spontaneously emitted photons yields a measured value for the 2 3 S 1 radiative lifetime of tau/sub rad/ = 58.6 +- 12.9 sec, where the quoted error represents 95% confidence levels. The theoretical lifetime is tau/sub theory/ = 49.0 sec. The measured value includes data taken with both 6 Li + and 7 Li + isotopes and was corrected for the slightly different detector efficiencies at 202A and 210A. A careful study of nonradiative quenching of the metastable state was necessary to understand observed differences between tau/sub rad/ and tau/sub 3 S 1 /, the total metastable lifetime. Spatial density profiles of the ions within the trap, useful for determining the ion temperature, were obtained by scanning the laser beam horizontally across the ion trap while storing 2 3 P 1 -- 1 S 0 photon counts as a function of the laser beam's position. Agreement with a simple equilibrium model, including space charge effects, is satisfactory. A study of the optical pumping process is necessary to understand the laser-ion interaction, and observational and theoretical data are presented. 47 references

  17. INTERSTELLAR METASTABLE HELIUM ABSORPTION AS A PROBE OF THE COSMIC-RAY IONIZATION RATE

    International Nuclear Information System (INIS)

    Indriolo, Nick; McCall, Benjamin J.; Hobbs, L. M.; Hinkle, K. H.

    2009-01-01

    The ionization rate of interstellar material by cosmic rays has been a major source of controversy, with different estimates varying by three orders of magnitude. Observational constraints of this rate have all depended on analyzing the chemistry of various molecules that are produced following cosmic-ray ionization, and in many cases these analyses contain significant uncertainties. Even in the simplest case (H + 3 ), the derived ionization rate depends on an (uncertain) estimate of the absorption path length. In this paper, we examine the feasibility of inferring the cosmic-ray ionization rate using the 10830 A absorption line of metastable helium. Observations through the diffuse clouds toward HD 183143 are presented, but yield only an upper limit on the metastable helium column density. A thorough investigation of He + chemistry reveals that only a small fraction of He + will recombine into the triplet state and populate the metastable level. In addition, excitation to the triplet manifold of helium by secondary electrons must be accounted for as it is the dominant mechanism which produces He* in some environments. Incorporating these various formation and destruction pathways, we derive new equations for the steady state abundance of metastable helium. Using these equations in concert with our observations, we find ζ He -15 s -1 , an upper limit about 5 times larger than the ionization rate previously inferred for this sight line using H + 3 . While observations of interstellar He* are extremely difficult at present, and the background chemistry is not nearly as simple as previously thought, potential future observations of metastable helium would provide an independent check on the cosmic-ray ionization rate derived from H + 3 in diffuse molecular clouds, and, perhaps more importantly, allow the first direct measurements of the ionization rate in diffuse atomic clouds.

  18. Atomic collisions related to atomic laser isotope separation

    International Nuclear Information System (INIS)

    Shibata, Takemasa

    1995-01-01

    Atomic collisions are important in various places in atomic vapor laser isotope separation (AVLIS). At a vaporization zone, many atomic collisions due to high density have influence on the atomic beam characteristics such as velocity distribution and metastable states' populations at a separation zone. In the separation zone, a symmetric charge transfer between the produced ions and the neutral atoms may degrade selectivity. We have measured atomic excitation temperatures of atomic beams and symmetric charge transfer cross sections for gadolinium and neodymium. Gadolinium and neodymium are both lanthanides. Nevertheless, results for gadolinium and neodymium are very different. The gadolinium atom has one 5d electron and neodymium atom has no 5d electron. It is considered that the differences are due to existence of 5d electron. (author)

  19. Laser Spectroscopy of Antiprotonic Helium Atoms

    CERN Multimedia

    2002-01-01

    %PS205 %title\\\\ \\\\Following the discovery of metastable antiprotonic helium atoms ($\\overline{p}He^{+} $) at KEK in 1991, systematic studies of their properties were made at LEAR from 1991 to 1996. In the first two years the lifetime of $\\overline{p}He^{+}$ in liquid and gaseous helium at various temperatures and pressures was measured and the effect of foreign gases on the lifetime of these atoms was investigated. Effects were also discovered which gave the antiproton a 14\\% longer lifetime in $^4$He than in $^3$He, and resulted in important differences in the shape of the annihilation time spectra in the two isotopes.\\\\ \\\\Since 1993 laser spectroscopy of the metastable $\\overline{p}He^{+}$ atoms became the main focus of PS205. Transitions were stimulated between metastable and non-metastable states of the $\\overline{p}He^{+}$ atom by firing a pulsed dye laser beam into the helium target every time an identified metastable atom was present (Figure 1). If the laser frequency matched the transition energy, the...

  20. Peculiarities of spectroscopic determination of the isotopic hydrogen composition in a mixture with neon and argon

    International Nuclear Information System (INIS)

    Nemets, V.M.; Petrov, A.A.; Solov'ev, A.A.

    1987-01-01

    The dependence of the relative intensity of atomic lines of hydrogen isotopes in the mixture with neon and argon during excitation in a high-frequency discharge under medium and high pressures is investigated. A physical model is suggested for processes determining the isotopic effects in the atomic hydrogen spectrum due to isotopic differences in velocity constants of dissociation-association, transfer and ionic-molecular reactions in a gas discharge plasma

  1. Transient cognitive dynamics, metastability, and decision making.

    Directory of Open Access Journals (Sweden)

    Mikhail I Rabinovich

    2008-05-01

    Full Text Available The idea that cognitive activity can be understood using nonlinear dynamics has been intensively discussed at length for the last 15 years. One of the popular points of view is that metastable states play a key role in the execution of cognitive functions. Experimental and modeling studies suggest that most of these functions are the result of transient activity of large-scale brain networks in the presence of noise. Such transients may consist of a sequential switching between different metastable cognitive states. The main problem faced when using dynamical theory to describe transient cognitive processes is the fundamental contradiction between reproducibility and flexibility of transient behavior. In this paper, we propose a theoretical description of transient cognitive dynamics based on the interaction of functionally dependent metastable cognitive states. The mathematical image of such transient activity is a stable heteroclinic channel, i.e., a set of trajectories in the vicinity of a heteroclinic skeleton that consists of saddles and unstable separatrices that connect their surroundings. We suggest a basic mathematical model, a strongly dissipative dynamical system, and formulate the conditions for the robustness and reproducibility of cognitive transients that satisfy the competing requirements for stability and flexibility. Based on this approach, we describe here an effective solution for the problem of sequential decision making, represented as a fixed time game: a player takes sequential actions in a changing noisy environment so as to maximize a cumulative reward. As we predict and verify in computer simulations, noise plays an important role in optimizing the gain.

  2. Emissive spectra of shock-heated argon

    International Nuclear Information System (INIS)

    Tang Jingyou; Gu Yan; Peng Qixian; Bai Yulin; Li Ping

    2003-01-01

    To study the radiant properties of argon under weak shock compression, an aluminum target filled with gaseous argon at ambient states was impacted by a tungsten alloy projectile which was launched from a two-stage light gun to 2.00 km/s. The radiant signals of single shock-compressed argon were recorded by a six-channel pyrometer and oscilloscopes, which varied with time linearly for the five channels from 405 nm to 700 nm and exponentially for the channel 800 nm, and the corresponding velocity of shock wave was determined to be 4.10 ± 0.09 km/s. By the present experiment, it has been shown that the absorbability of the shock-heated argon is low for visual light and the optical depths of argon gas turn from thin to thick as wavelengths gradually increase. The time-resolved spectra in the rising-front of the radiant signal in the re-shocked argon were recorded by means of an OMA, and strong emissive spectrum bands near 450 nm light-wave length but no linear spectrum were found. The emissive spectrum properties of shock-compression argon were qualitatively explained by the state parameters and ionization degree

  3. Metastable structure formation during high velocity grinding

    International Nuclear Information System (INIS)

    Samarin, A.N.; Klyuev, M.M.

    1984-01-01

    Metastable structures in surface layers of samples are; investigated during force high-velocity abrasive grinding. Samples of martensitic (40Kh13), austenitic (12Kh18N10T), ferritic (05Kh23Yu5) steels and some alloys, in particular KhN77TYuR (EhI437B), were grinded for one pass at treatment depth from 0.17 up to 2.6 mm. It is established that processes of homogenizing, recrystallization and coagulation are; developed during force high-velocity grinding along with polymorphic transformations in the zone of thermomechanical effect, that leads to changes of physical and mechanical properties of the surface

  4. Bitopic Ligands and Metastable Binding Sites

    DEFF Research Database (Denmark)

    Fronik, Philipp; Gaiser, Birgit I; Sejer Pedersen, Daniel

    2017-01-01

    of orthosteric binding sites. Bitopic ligands have been employed to address the selectivity problem by combining (linking) an orthosteric ligand with an allosteric modulator, theoretically leading to high-affinity subtype selective ligands. However, it remains a challenge to identify suitable allosteric binding...... that have been reported to date, this type of bitopic ligands would be composed of two identical pharmacophores. Herein, we outline the concept of bitopic ligands, review metastable binding sites, and discuss their potential as a new source of allosteric binding sites....

  5. Argon cover gas purity control on LMFBR

    Energy Technology Data Exchange (ETDEWEB)

    Maeda, Hiroshi; Kobayashi, Takayoshi [PNC (Japan); Ishiyama, Satoshi [Toshiba (Japan); Motonaga, Tetsuji [Hitachi (Japan)

    1987-07-01

    Various control methods on chemical impurities and radioactive materials (fission products) in the primary argon gas of LMFBRs' have been studied based on experiences in Joyo and results of research and development. These results are reflected on MONJU design. On-line gas chromatographs are installed both in the Primary and in the Secondary Argon Gas Systems in JOYO. Also, chemical analysis has been done by batch sampling in JOYO. Though the rise of impurity concentration had been measured after periodical fuel exchange operation, impurity concentration has been controlled sufficiently under target control limits. In MONJU detailed design, the Rare Gas Removal and Recovery System which consisted of cryogenic distillation equipment had been eliminated and the capacity of Charcoal Beds in the Primary Argon Gas System has been improved to keep the concentration of radioactive materials sufficient low levels. The necessity to control the impurities in fresh argon gas which is supplied to the Primary Argon Gas System is now considered to keep the concentration of Kr and Xe isotopes in specified level, because their isotopes may make background rise for the Tagging Gas Failed Fuel Detection and Location System. Based on various investigations performed on sodium vapor trapping to obtain its detailed characteristics, design specifications and operating conditions of MONJU's Vapor Traps have been decided. To keep the level of radioactivity in gaseous effluents to the environment as low as reasonably achievable, the following means are now adopted in MONJU: the Primary Argon Gas System is composed of a closed recirculating path, but the exhaust gas discharged has different path after the Charcoal Beds; fresh argon gas is blown down to prevent Primary Argon Gas from releasing to the circumference during opening of the primary argon gas boundary, such as fuel exchange operations. (author)

  6. Virial Coefficients for the Liquid Argon

    Science.gov (United States)

    Korth, Micheal; Kim, Saesun

    2014-03-01

    We begin with a geometric model of hard colliding spheres and calculate probability densities in an iterative sequence of calculations that lead to the pair correlation function. The model is based on a kinetic theory approach developed by Shinomoto, to which we added an interatomic potential for argon based on the model from Aziz. From values of the pair correlation function at various values of density, we were able to find viral coefficients of liquid argon. The low order coefficients are in good agreement with theoretical hard sphere coefficients, but appropriate data for argon to which these results might be compared is difficult to find.

  7. Using the Pairs of Lines Broadened by Collisions with Neutral and Charged Particles for Gas Temperature Determination of Argon Non-Thermal Plasmas at Atmospheric Pressure

    Directory of Open Access Journals (Sweden)

    Cristina Yubero

    2017-10-01

    Full Text Available The spectroscopic method for gas temperature determination in argon non-thermal plasmas sustained at atmospheric pressure proposed recently by Spectrochimica Acta Part B 129 14 (2017—based on collisional broadening measurements of selected pairs of argon atomic lines, has been applied to other pairs of argon atomic lines, and the discrepancies found in some of these results have been analyzed. For validation purposes, the values of the gas temperature obtained using the different pairs of lines have been compared with the rotational temperatures derived from the OH ro-vibrational bands, using the Boltzmann-plot technique.

  8. Excited argon 1s5 production in micro-hollow cathode discharges for use as potential rare gas laser sources

    Science.gov (United States)

    Peterson, Richard D.; Eshel, Ben; Rice, Christopher A.; Perram, Glen P.

    2018-02-01

    The diode-pumped rare gas laser (DPRGL) has been suggested as a potential high-gain, high-energy laser which requires densities on the order of 1013 cm-3 at pressures around 1 atmosphere for efficient operation. Argon 1s5 number densities have been measured in micro-hollow cathode discharges with electrode gaps of 127 and 254 μm and hole diameters from 100-400 μm. The dependency of the metastable argon (1s5) density on total gas pressure, electrode gap distance and hole diameter were explored. The measured densities were all in the range of 0.5 - 2 × 1013 cm-3 with the 400 μm hole diameters being the lowest.

  9. A study on metastable superconducting magnets

    International Nuclear Information System (INIS)

    Koyama, Kenichi

    1976-01-01

    It is important to construct superconducting magnets as cheap as possible. One of the methods to achieve such a purpose is to save the superconducting material and operate the magnets at a high current density. Therefore it is useful to investigate the requirements for the operation of metastable superconducting magnets which can work at a current higher than the recovery current. Using the theory of flux jump, we introduce a ''stable current'' below which no flux jump can occur. On a rough approximation, it is given by I sub(s) =√A P sub(i) H sub(e) T sub(o) f(x)/rho where A : cross-section of the composite conductor. P sub(i) : total perimeter of all the superconducting cores. h sub(e) : effective heat transfer coefficient to the liquid helium through the stabilizer. T sub(o) : a characteristic temperature of the superconducting cores. f(x) : a characteristic function for the relative core radius x. rho : effective resistivity of the composite. Then it is shown that superconducting magnets can operate without unexpected normal transitions in the region enclosed by the two curves of I sub(s) and I sub(c). Next, we discuss the characteristics of our saddle shaped superconducting magnet for an one-KW MHD generator. We found that, 1) the magnet does safely operate in the metastable state; 2) the characteristics of the magnet are consistent with our theoretical results. (auth.)

  10. Metastable beta limit in DIII-D

    International Nuclear Information System (INIS)

    La Haye, R.J.; Callen, J.D.; Gianakon, T.A.

    1997-06-01

    The long-pulse, slowly evolving single-null divertor (SND) discharges in DIII-D with H-mode, ELMs, and sawteeth are found to be limited significantly below (factor of 2) the predicted ideal limit β N = 4l i by the onset of tearing modes. The tearing modes are metastable in that they are explained by the neoclassical bootstrap current (high β θ ) destabilization of a seed island which occurs even if Δ' θ , there is a region of the modified Rutherford equation such that dw/dt > 0 for w larger than a threshold value; the plasma is metastable, awaiting the critical perturbation which is then amplified to the much larger saturated island. Experimental results from a large number of tokamaks indicate that the high beta operational envelope of the tokamak is well defined by ideal magnetohydrodynamic (MHD) theory. The highest beta values achieved have historically been obtained in fairly short pulse discharges, often <1-2 sawteeth periods and < 1-2 energy replacement times. The maximum operational beta in single-null divertor (SND), long-pulse discharges in DIII-D with a cross-sectional shape similar to the proposed ITER tokamak is found to be limited significantly below the threshold for ideal instabilities by the onset of resistive MHD instabilities

  11. Broadband Ftmw Spectroscopy of the Urea-Argon and Thiourea-Argon Complexes

    Science.gov (United States)

    Medcraft, Chris; Bittner, Dror M.; Cooper, Graham A.; Mullaney, John C.; Walker, Nick

    2017-06-01

    The rotational spectra complexes of argon-urea, argon-thiourea and water-thiourea have been measured by chirped-pulse Fourier transform microwave spectroscopy from 2-18.5 GHz. The sample was produced via laser vaporisation of a rod containing copper and the organic sample as a stream of argon was passed over the surface and subsequently expanded into the vacuum chamber cooling the sample. Argon was found to bind to π system of the carbonyl bond for both the urea and thiourea complexes.

  12. Negative corona current pulses in argon and in mixture argon with SF6

    International Nuclear Information System (INIS)

    Zahoranova, A.; Zahoran, M.; Bucek, A.; Cernak, M.; Bosko, J.

    2004-01-01

    Waveforms of the first negative current pulses in a short negative point-to plane gap in pure argon and argon with SF 6 admixture have been investigated with a nanosecond time resolution at a gas pressure 50 kPa as a function of applied gap voltage and content of SF 6 in the mixture. We have made an attempt to explain the differences in the discharge development in pure argon and in argon with admixture of SF 6 based on the observed changes of the pulse shape. The experimental results obtained will be discussed in context with existing computer simulation models (Authors)

  13. Methane from benzene in argon dielectric barrier discharge

    International Nuclear Information System (INIS)

    Das, Tomi Nath; Dey, G.R.

    2013-01-01

    Highlights: ► Efficient on-line conversion of benzene to methane at room temperature. ► Absence of other H-atom donor suggests new type of chemistry. ► For parent loss > 90%, methane yield was ∼40% of limit due to H-atom availability. ► Surface moisture contributed ·OH radical for trace phenolic products’ formation. ► This method may emerge as an exploitable tactic for pollutants’ usable alterations. -- Abstract: A first-time account of direct, on-line, instantaneous and efficient chemical conversion of gas phase benzene to methane in argon Dielectric Barrier Discharge (DBD) is presented. In the absence of another overt hydrogen-donating source, potency of analogous parents toward methane generation is found to follow the order: benzene > toluene > p-xylene. Simultaneous production of trace amounts of phenolic surface deposits suggest (a) prompt decomposition of the parent molecules, including a large fraction yielding atomic transients (H-atom), (b) continuous and appropriate recombination of such parts, and (c) trace moisture in parent contributing ·OH radicals and additional H-atoms, which suitably react with the unreacted fraction of the parent, and also other intermediates. Results highlight Ar DBD to be a simple and exploitable technology for transforming undesirable hazardous aromatics to usable/useful low molecular weight open-chain products following the principles of green chemistry and engineering

  14. Melting of “non-magic” argon clusters and extrapolation to the bulk limit

    International Nuclear Information System (INIS)

    Senn, Florian; Wiebke, Jonas; Schumann, Ole; Gohr, Sebastian; Schwerdtfeger, Peter; Pahl, Elke

    2014-01-01

    The melting of argon clusters Ar N is investigated by applying a parallel-tempering Monte Carlo algorithm for all cluster sizes in the range from 55 to 309 atoms. Extrapolation to the bulk gives a melting temperature of 85.9 K in good agreement with the previous value of 88.9 K using only Mackay icosahedral clusters for the extrapolation [E. Pahl, F. Calvo, L. Koči, and P. Schwerdtfeger, “Accurate melting temperatures for neon and argon from ab initio Monte Carlo simulations,” Angew. Chem., Int. Ed. 47, 8207 (2008)]. Our results for argon demonstrate that for the extrapolation to the bulk one does not have to restrict to magic number cluster sizes in order to obtain good estimates for the bulk melting temperature. However, the extrapolation to the bulk remains a problem, especially for the systematic selection of suitable cluster sizes

  15. Mass spectrometry of solid samples in open air using combined laser ionization and ambient metastable ionization

    International Nuclear Information System (INIS)

    He, X.N.; Xie, Z.Q.; Gao, Y.; Hu, W.; Guo, L.B.; Jiang, L.; Lu, Y.F.

    2012-01-01

    Mass spectrometry of solid samples in open air was carried out using combined laser ionization and metastable ionization time-of-flight mass spectrometry (LI-MI-TOFMS) in ambient environment for qualitative and semiquantitative (relative analyte information, not absolute information) analysis. Ambient metastable ionization using a direct analysis in realtime (DART) ion source was combined with laser ionization time-of-flight mass spectrometry (LI-TOFMS) to study the effects of combining metastable and laser ionization. A series of metallic samples from the National Institute of Standards and Technology (NIST 494, 495, 498, 499, and 500) and a pure carbon target were characterized using LI-TOFMS in open air. LI-MI-TOFMS was found to be superior to laser-induced breakdown spectroscopy (LIBS). Laser pulse energies between 10 and 200 mJ at the second harmonic (532 nm) of an Nd:YAG laser were applied in the experiment to obtain a high degree of ionization in plasmas. Higher laser pulse energy improves signal intensities of trace elements (such as Fe, Cr, Mn, Ni, Ca, Al, and Ag). Data were analyzed by numerically calculating relative sensitivity coefficients (RSCs) and limit of detections (LODs) from mass spectrometry (MS) and LIBS spectra. Different parameters, such as boiling point, ionization potential, RSC, LOD, and atomic weight, were shown to analyze the ionization and MS detection processes in open air.

  16. From materials control to astrophysics: metastable superconductors

    International Nuclear Information System (INIS)

    Waysand, G.

    1984-01-01

    The basic properties of metastable superconducting materials are reviewed: superheated domain, size of the granules, reading of the change of state. In the case of superheating, the phase transition can occur following two paths: a) increase of temperature (thermal nucleation) which allows an analysis of the calorimetric behavior for particle detection; b) increase of the applied magnetic field which allows the evaluation of surface defects promoting the nucleation of the normal state, and, more generally, the study of the superheated material as a disordered system. The thermal nucleation is useful for X-ray detection in non-destructive control as well as for the solar neutrino detection in real time. The magnetic nucleation is the basis for a proposal of detection of magnetic monopoles by induction [fr

  17. Metastable electroweak vacuum. Implications for inflation

    Energy Technology Data Exchange (ETDEWEB)

    Lebedev, Oleg; Westphal, Alexander [DESY Theory Group, Hamburg (Germany)

    2012-10-15

    Within the Standard Model, the current Higgs and top quark data favor metastability of the electroweak vacuum, although the uncertainties are still significant. The true vacuum is many orders of magnitude deeper than ours and the barrier separating the two is tiny compared to the depth of the well. This raises a cosmological question: how did the Higgs field get trapped in the shallow minimum and why did it stay there during inflation? The Higgs initial conditions before inflation must be fine-tuned to about one part in 10{sup 8} in order for the Higgs field to end up in the right vacuum. In this note, we show that these problems can be resolved if there is a small positive coupling between the Higgs and the inflaton.

  18. Transition Manifolds of Complex Metastable Systems

    Science.gov (United States)

    Bittracher, Andreas; Koltai, Péter; Klus, Stefan; Banisch, Ralf; Dellnitz, Michael; Schütte, Christof

    2018-04-01

    We consider complex dynamical systems showing metastable behavior, but no local separation of fast and slow time scales. The article raises the question of whether such systems exhibit a low-dimensional manifold supporting its effective dynamics. For answering this question, we aim at finding nonlinear coordinates, called reaction coordinates, such that the projection of the dynamics onto these coordinates preserves the dominant time scales of the dynamics. We show that, based on a specific reducibility property, the existence of good low-dimensional reaction coordinates preserving the dominant time scales is guaranteed. Based on this theoretical framework, we develop and test a novel numerical approach for computing good reaction coordinates. The proposed algorithmic approach is fully local and thus not prone to the curse of dimension with respect to the state space of the dynamics. Hence, it is a promising method for data-based model reduction of complex dynamical systems such as molecular dynamics.

  19. Metastable cosmic strings in realistic models

    International Nuclear Information System (INIS)

    Holman, R.

    1992-01-01

    The stability of the electroweak Z-string is investigated at high temperatures. The results show that, while finite temperature corrections can improve the stability of the Z-string, their effect is not strong enough to stabilize the Z-string in the standard electroweak model. Consequently, the Z-string will be unstable even under the conditions present during the electroweak phase transition. Phenomenologically viable models based on the gauge group SU(2) L x SU(2) R x U(1) B-L are then considered, and it is shown that metastable strings exist and are stable to small perturbations for a large region of the parameter space for these models. It is also shown that these strings are superconducting with bosonic charge carriers. The string superconductivity may be able to stabilize segments and loops against dynamical contraction. Possible implications of these strings for cosmology are discussed

  20. Metastable electroweak vacuum. Implications for inflation

    International Nuclear Information System (INIS)

    Lebedev, Oleg; Westphal, Alexander

    2012-10-01

    Within the Standard Model, the current Higgs and top quark data favor metastability of the electroweak vacuum, although the uncertainties are still significant. The true vacuum is many orders of magnitude deeper than ours and the barrier separating the two is tiny compared to the depth of the well. This raises a cosmological question: how did the Higgs field get trapped in the shallow minimum and why did it stay there during inflation? The Higgs initial conditions before inflation must be fine-tuned to about one part in 10 8 in order for the Higgs field to end up in the right vacuum. In this note, we show that these problems can be resolved if there is a small positive coupling between the Higgs and the inflaton.

  1. Metastability and reliability of CdTe solar cells

    Science.gov (United States)

    Guo, Da; Brinkman, Daniel; Shaik, Abdul R.; Ringhofer, Christian; Vasileska, Dragica

    2018-04-01

    Thin-film modules of all technologies often suffer from performance degradation over time. Some of the performance changes are reversible and some are not, which makes deployment, testing, and energy-yield prediction more challenging. Manufacturers devote significant empirical efforts to study these phenomena and to improve semiconductor device stability. Still, understanding the underlying reasons of these instabilities remains clouded due to the lack of ability to characterize materials at atomistic levels and the lack of interpretation from the most fundamental material science. The most commonly alleged causes of metastability in CdTe devices, such as ‘migration of Cu’, have been investigated rigorously over the past fifteen years. Still, the discussion often ended prematurely with stating observed correlations between stress conditions and changes in atomic profiles of impurities or CV doping concentration. Multiple hypotheses suggesting degradation of CdTe solar cell devices due to interaction and evolution of point defects and complexes were proposed, and none of them received strong theoretical or experimental confirmation. It should be noted that atomic impurity profiles in CdTe provide very little intelligence on active doping concentrations. The same elements could form different energy states, which could be either donors or acceptors, depending on their position in crystalline lattice. Defects interact with other extrinsic and intrinsic defects; for example, changing the state of an impurity from an interstitial donor to a substitutional acceptor often is accompanied by generation of a compensating intrinsic interstitial donor defect. Moreover, all defects, intrinsic and extrinsic, interact with the electrical potential and free carriers so that charged defects may drift in the electric field and the local electrical potential affects the formation energy of the point defects. Such complexity of interactions in CdTe makes understanding of temporal

  2. Metastable Magnesium fluorescence spectroscopy using a frequency-stabilized 517 nm laser

    DEFF Research Database (Denmark)

    He, Ming; Jensen, Brian B; Therkildsen, Kasper T

    2009-01-01

    We present a laser operating at 517 nm for our Magnesium laser-cooling and atomic clock project. A two-stage Yb-doped fiber amplifier (YDFA) system generates more than 1.5 W of 1034 nm light when seeded with a 15 mW diode laser. Using a periodically poled lithium niobate (PPLN) waveguide, we obta...... obtained more than 40 mW of 517 nm output power by single pass frequency doubling. In addition, fluorescence spectroscopy of metastable magnesium atoms could be used to stabilize the 517 nm laser to an absolute frequency within 1 MHz.......We present a laser operating at 517 nm for our Magnesium laser-cooling and atomic clock project. A two-stage Yb-doped fiber amplifier (YDFA) system generates more than 1.5 W of 1034 nm light when seeded with a 15 mW diode laser. Using a periodically poled lithium niobate (PPLN) waveguide, we...

  3. Metastable State Diamond Growth and its Applications to Electronic Devices.

    Science.gov (United States)

    Jeng, David Guang-Kai

    Diamond which consists of a dense array of carbon atoms joined by strong covalent bonds and formed into a tetrahedral crystal structure has remarkable mechanical, thermal, optical and electrical properties suitable for many industrial applications. With a proper type of doping, diamond is also an ideal semiconductor for high performance electronic devices. Unfortunately, natural diamond is rare and limited by its size and cost, it is not surprising that people continuously look for a synthetic replacement. It was believed for long time that graphite, another form of carbon, may be converted into diamond under high pressure and temperature. However, the exact condition of conversion was not clear. In 1939, O. I. Leipunsky developed an equilibrium phase diagram between graphite and diamond based on thermodynamic considerations. In the phase diagram, there is a low temperature (below 1000^ circC) and low pressure (below 1 atm) region in which diamond is metastable and graphite is stable, therefore establishes the conditions for the coexistence of the two species. Leipunsky's pioneer work opened the door for diamond synthesis. In 1955, the General Electric company (GE) was able to produce artificial diamond at 55k atm pressure and a temperature of 2000^ circC. Contrary to GE, B. Derjaguin and B. V. Spitzyn in Soviet Union, developed a method of growing diamonds at 1000^circC and at a much lower pressure in 1956. Since then, researchers, particularly in Soviet Union, are continuously looking for methods to grow diamond and diamond film at lower temperatures and pressures with slow but steady progress. It was only in the early 80's that the importance of growing diamond films had attracted the attentions of researchers in the Western world and in Japan. Recent progress in plasma physics and chemical vapor deposition techniques in integrated electronics technology have pushed the diamond growth in its metastable states into a new era. In this research, a microwave plasma

  4. Calculation of Photonic decay width for meta-stable muonic symmetric ion in adiabatic representation method

    International Nuclear Information System (INIS)

    Gheisari, R.; Eskandari, M. R.

    2006-01-01

    Meta-stable symmetric ions ppμ * and ddμ * are formed in the collisions of the excited muonic atoms with the hydrogen isotopes. By dissociation of them, the muon transfers from 2s to 1s via the new channels. Considering the quantum electrodynamics field and employing the new wave functions, the matrix elements are simply integrated. In this method using the adiabatic representations, the photo-decay widths for the some of ppμ * and ddμ * states are variationally calculated. The decay rates for X-ray productions of the similar states are approximately same.

  5. Non-local thermodynamic equilibrium effects on isentropic coefficient in argon and helium thermal plasmas

    International Nuclear Information System (INIS)

    Sharma, Rohit; Singh, Kuldip

    2014-01-01

    In the present work, two cases of thermal plasma have been considered; the ground state plasma in which all the atoms and ions are assumed to be in the ground state and the excited state plasma in which atoms and ions are distributed over various possible excited states. The variation of Zγ, frozen isentropic coefficient and the isentropic coefficient with degree of ionization and non-equilibrium parameter θ(= T e /T h ) has been investigated for the ground and excited state helium and argon plasmas at pressures 1 atm, 10 atm, and 100 atm in the temperature range from 6000 K to 60 000 K. For a given value of non-equilibrium parameter, the relationship of Zγ with degree of ionization does not show any dependence on electronically excited states in helium plasma whereas in case of argon plasma this dependence is not appreciable till degree of ionization approaches 2. The minima of frozen isentropic coefficient shifts toward lower temperature with increase of non-equilibrium parameter for both the helium and argon plasmas. The lowering of non-equilibrium parameter decreases the frozen isentropic coefficient more emphatically in helium plasma at high pressures in comparison to argon plasma. The increase of pressure slightly reduces the ionization range over which isentropic coefficient almost remains constant and it does not affect appreciably the dependence of isentropic coefficient on non-equilibrium parameter

  6. Liquid--vapor isotope fractionation factors in argon--krypton binary mixtures

    International Nuclear Information System (INIS)

    Lee, M.W.; Neufeld, P.; Bigeleisen, J.

    1977-01-01

    An equilibrium isotope effect has been studied as a continuous function of the potential field acting on the atom undergoing isotopic exchange. This has been accomplished through a study of the liquid vapor isotope fractionation factors for both, 36 Ar/ 40 Ar and 80 Kr/ 84 Kr in a series of binary mixtures which span the range between the pure components at 117.5 0 K. The 36 Ar/ 40 Ar fractionation factor increases (linearly) from (lnα)2.49 x 10 -3 in pure liquid argon to 2.91 x 10 -3 in an infinitely dilute solution in liquid krypton. Conversely, the 80 Kr/ 84 Kr fractionation factor decreases (linearly) from (lnα)0.98 x 10 -3 in pure liquid krypton to 0.64 x 10 -3 in an infinetely dilute solution in pure liquid argon. The mean force constants 2 U>/sub c/ on both argon and krypton atoms in the mixtures are derived from the respective isotope fractionation factors.The mean force constants for argon and krypton as a function of composition have been calculated by a modified corresponding states theory which uses the pure liquids as input parameters. The discrepancy is 8 percent at X/sub Ar/ + O. A systematic set of calculations has been made of 2 U> (Ar) and 2 U> (Kr) as a function of composition using radial distribution functions generated by the Weeks--Chandler--Anderson perturbation theory

  7. Computer simulation of cooling properties of UF5 hot-clusters in argon

    International Nuclear Information System (INIS)

    Okamoto, Tsuyoshi; Ohno, Fubito

    1999-01-01

    Brownian collision-coalescence models have been proposed by many researchers to describe a cluster or a particle growth process. In these mathematical models, the effect of a cluster temperature on a sticking probability is not included, although the cluster temperature is one of the most important factors which determines the particle growth rate at the incipient stage of coagulation. A hot-cluster consisting of 30 UF 5 molecules is formed in a computer and is bombarded with argon atoms. Measuring a kinetic energy of argon atom scattered from the hot-cluster, the cluster temperature can be estimated by molecular dynamics simulations. It is concluded that the hot-cluster is rapidly cooled under the conditions of molecular laser isotope separation (MLIS) process, so that the cluster-argon system can reach its thermal equilibrium state. Therefore, in the analysis of the dynamics of clustering process, the temperature of UF 5 molecular cluster may be set equal to that of argon gas. (author)

  8. Using ion production to monitor the birth and death of a metastable helium Bose-Einstein condensate

    International Nuclear Information System (INIS)

    Seidelin, S; Sirjean, O; Gomes, J Viana; Boiron, D; Westbrook, C I; Aspect, A

    2003-01-01

    We discuss observations of the ion flux from a cloud of trapped 2 3 S 1 metastable helium atoms. Both Bose-Einstein condensates (BEC) and thermal clouds were investigated. The ion flux is compared with time-of-flight observations of the expanded cloud. We show data concerning BEC formation and decay, as well as measurements of two-and three-body ionization rate constants. We also discuss possible improvements and extensions of our results

  9. Design and performance of a high intensity copper atom beam source nozzle for use in inelastic atom--atom collision experiments

    International Nuclear Information System (INIS)

    Santavicca, D.A.

    1975-01-01

    The research was aimed at developing a neutral copper atom beam source which could be used to study the collision cross sections for electronic excitation of neutral copper atoms in collision with neutral argon atoms. Of particular interest is the excitation from the ground state to the two upper laser levels at 3.80 and 3.82 electron volts

  10. Compilation of electron collision excitation cross sections for neutral argon

    International Nuclear Information System (INIS)

    Blanco, F.

    1993-01-01

    The present work presents a compilation and critical analysis of the available data on electron collision excitation cross sections for neutral Argon levels. This study includes: 1.- A detailed description in intermediate coupling for all the levels belonging the 20 configurations 3p5 ns (n=4to 12), np(n=4to8) and nd(n=3to8)of neutral Argon. 2.- Calculation of the electron collision excitation cross sections in Born and Born-Oppenheimer-Ochkur approximations for all the levels in the 14 configurations 3p5 ns (n=4 to 7), np (n=4 to 7) and nd (n=3 to 8). 3.- comparison and discussion of the compiled data. These are the experimental and theoretical values available from the literature, and those from this work. 4.- Analysis of the regularities and systematic behaviors in order to determine which values can be considered more reliable. It is show that the concept of one electron cross section results quite useful for this purpose. In some cases it has been possible to obtain in this way approximate analytical expressions interpolating the experimental data. 5.- All the experimental and theoretical values studied are graphically presented and compared. 6.- The last part of the work includes a listing of several general purpose programs for Atomic Physics calculations developed for this work. (Author) 35 refs

  11. Compilation of electron collision excitation cross sections for neutro argon

    International Nuclear Information System (INIS)

    Blanco Ramos, F.

    1993-01-01

    The present work presents a compilation and critical analysis of the available data on electron collision excitation cross sections for neutral Argon levels. This study includes: 1.- A detailed description in intermediate coupling for all the levels belonging the 20 configurations 3p''5 ns(n=4 to 12), np(n=4 to 8) and nd(n=3 to 8) of neutral Argon. 2.- Calculation of the electron collision excitation cross sections in Born and Born-Oppenheimer-Ochkur approximations for all the levels in the 14 configurations 3p''5 ns(n=4 to 7), np(n=4 to 7) and nd(n=3 to 8). 3.- Comparison and discussion of the compiled data. These are the experimental and theoretical values available from the literature, and those from this work. 4.- Analysis of the regularities and systematic behaviors in order to determine which values can be considered more reliable. It is show that the concept of one electron cross section results quite useful for this purpose. In some cases it has been possible to obtain in this way approximate analytical expressions interpolating the experimental data. 5.- All the experimental and theoretical values studied are graphically presented and compared. 6.- The last part of the work includes a listing of several general purpose programs for Atomic Physics calculations developed for this work. (Author)

  12. Characterization of argon direct-current glow discharge with a longitudinal electric field applied at ambient air

    Science.gov (United States)

    Jiang, Weiman; Tang, Jie; Wang, Yishan; Zhao, Wei; Duan, Yixiang

    2014-09-01

    A direct-current-driven plasma jet is developed by applying a longitudinal electric field on the flowing argon at ambient air. This plasma shows a torch shape with its cross-section increased from the anode to the cathode. Comparison with its counterparts indicates that the gas flow plays a key role in variation of the plasma structure and contributes much to enlarging the plasma volume. It is also found that the circular hollow metal base promotes generation of plasma with a high-power volume density in a limited space. The optical emission spectroscopy (OES) diagnosis indicates that the plasma comprises many reactive species, such as OH, O, excited N2, and Ar metastables. Examination of the rotational and vibrational temperature indicates that the plasma is under nonequilibrium condition and the excited species OH(A 2Σ+), O(5P), and N2(C 3Πu) are partly generated by energy transfer from argon metastables. The spatially resolved OES of plasma reveals that the negative glow, Faraday dark space, and positive column are distributed across the gas gap. The absence of the anode glow is attributed to the fact that many electrons in the vicinity of the anode follow ions into the positive column due to the ambipolar diffusion in the flowing gas.

  13. The liquid metastable miscibility gap in Cu-based systems

    DEFF Research Database (Denmark)

    Curiotto, S.; Greco, R.; Pryds, Nini

    2007-01-01

    Some Cu-based alloys, like Cu–Co, Cu–Fe and Cu–Co–Fe, display a liquid metastable miscibility gap. When the melt is undercooled below a certain temperature depending on the alloy composition, they present a separation in two liquid phases, followed by coagulation before dendritic solidification....... In order to predict the phase equilibria and the mechanisms of microstructure formation, a determination of the metastable monotectics in the phase diagrams is essential. This paper focuses on the up-to-date findings on the Cu–Co, Cu–Fe and Cu–Co–Fe metastable miscibility gap in the liquid phase...

  14. Sodium evaporation into a forced argon flow

    International Nuclear Information System (INIS)

    Kumada, Toshiaki; Kasahara, Fumio; Ishiguro, Ryoji

    1975-01-01

    Evaporation from a rectangular sodium free surface into an argon flow was measured. Tests were carried out with varying sodium temperature, argon velocity and argon temperature respectively under conditions of fog formation being possible. In order to clarify the enhancement of evaporation by fog formation, convection heat transfer from a plate of the same geometry into an air flow was also measured. The evaporation rate and Sherwood number were compared with those predicted by both the heat transfer experiment and the theory proposed by Hill and Szekely, and also a comparison was run with the previously reported experimental results of sodium evaporation. As a result it was shown that the sodium evaporation rate in this experiment is at least four times as large as that predicted by the heat transfer experiment and varies almost linearly with the heat transfer rate and the sodium vapour pressure. (auth.)

  15. Waves in periodic medium. Atomic matter waves in light crystals

    International Nuclear Information System (INIS)

    Oberthaler, M. K.

    1997-07-01

    This work deals with the propagation of matter waves inside a periodic potential. In analogy to photon optics a potential can be described by a refractive index for matter waves. A real potential leads to a refractive spatial structure while an imaginary potential leads to an absorptive structure. A general theoretical description is given in the framework of Floquet theory. The equivalent approach of dynamical diffraction theory will be treated in detail. The analytic solution for weak potentials are given in a general form so that they are applicable for every kind of wave and medium. For our experiments an open two level atom (metastable Argon) propagating inside a standing light wave was used. Detuning the frequency of the light wave from the atomic resonance leads to a real (refractive) periodic potential. Tuning the laser exact on resonance gives rise to a pure imaginary (absorptive) periodic potential. In analogy to solid state crystals in X-ray and neutron optics we call a standing light wave a light crystal. Tuning the standing light field on resonance we demonstrated experimentally the Borrmann effect. This effect describes the increase of the total transmission through a crystal for Bragg incidence. Furthermore, we confirmed that this effect is coherent and that a sinusoidal wave field is formed inside the crystal. The nodes of the wave field were found to coincide with the maxima of absorption. For a detuned standing light field a refractive crystal was realized, for which the expected Pendelloesung effect was demonstrated. In this case the maximum of the wave field inside the crystal was found at the steepest gradient of the potential as predicted by dynamical diffraction theory. Superposing an absorptive and a refractive light crystal a complex light crystal was realized. With such a crystal the violation of Friedel's law was demonstrated in a very clear way. (author)

  16. Atomic absorption spectrometry using tungsten and molybdenum tubes as metal atomizer

    International Nuclear Information System (INIS)

    Kaneco, Satoshi; Katsumata, Hideyuki; Ohta, Kiyohisa; Suzuki, Tohru

    2007-01-01

    We have developed a metal tube atomizer for the electrothermal atomization atomic absorption spectrometry (ETA-AAS). Tungsten, molybdenum, platinum tube atomizers were used as the metal atomizer for ETA-AAS. The atomization characteristics of various metals using these metal tube atomizers were investigated. The effects of heating rate of atomizer, atomization temperature, pyrolysis temperature, argon purge gas flow rate and hydrogen addition on the atomic absorption signal were investigated for the evaluation of atomization characteristics. Moreover, ETA-AAS with metal tube atomizer has been combined with the slurry-sampling techniques. Ultrasonic slurry-sampling ETA-AAS with metal tube atomizer were effective for the determination of trace metal elements in biological materials, calcium drug samples, herbal medicine samples, vegetable samples and fish samples. Furthermore, a preconcentration method of trace metals involving adsorption on a metal wire has been applied to ETA-AAS with metal tube atomizer. (author)

  17. Two-photon excitation of argon

    International Nuclear Information System (INIS)

    Pindzola, P.S.; Payne, M.C.

    1982-01-01

    The authors calculate two photon excitation parameters for various excited states of argon assuming the absorption of near resonance broad-bandwidth laser radiation. Results are given for the case of two photons absorbed for the same laser beam as well as the case of absorbing photons of different frequency from each of two laser beams. The authors use multiconfiguration Hartree-Fock wave functions to evaluate the second-order sums over matrix elements. Various experimental laser schemes are suggested for the efficient excitation and subsequent ionization of argon

  18. Argon isotopes as recorders of magmatic processes

    Science.gov (United States)

    Layer, P. W.; Gardner, J. E.; Mora Chaparro, J. C.; Arce, J. L.

    2003-12-01

    Argon isotopic ratios vary enough between different reservoirs (atmosphere, crust, mantle) and diffuse fast enough through most minerals at magmatic temperatures (700-1200 C) to make them ideal for looking at magma chamber dynamics. Indeed, diffusion is sufficiently fast to allow short time scales to be deciphered, setting argon apart from many other isotopic methods. A mineral's ability to retain "excess" argon (40Ar/36Ar ratios greater than the atmospheric value and apparent ages older than the known eruption age) during post-eruption cooling is key to Ar studies. Previous work shows that both phenocrysts (crystallizing in the magma chamber; e.g. Mt St. Helens; Layer and Gardner, 2001) and xenocrysts (introduced into the magma chamber; e.g Toba; Gardner et al., 2002) preserve excess argon, which enables magma chamber processes to be deciphered through the variable diffusion rates between crystal phases. Single crystal 40Ar/39Ar step-heating of biotite from the 10.5 ka eruption of Nevado de Toluca volcano, Mexico indicates that they are xenocrystic and resided for only a short (< 1 year) time in the magma before it erupted. The biotite has reaction rims of hornblende, orthopyroxene and plagioclase, and failed to grow experimentally at pressure-temperature conditions of the magma, confirming the xenocrystic nature of this phase. Single-step fusion of plagioclase phenocrysts from eruptions of El Chichon volcano, Mexico, shows evidence of excess (mantle) argon, whereas hornblende from the same eruptions contains little or none. In this case, faster diffusion of Ar in plagioclase than in hornblende allow plagioclase to incorporate excess argon during magma recharge; hornblende does not. Combining such results with other isotopic systems may in fact better determine magma chamber processes. At El Chichon, Sr isotopes suggest magma recharges ocurred (Tepley et al., 2000), whereas the argon isotopes suggest such pulses occurred just before each eruption. The fast and

  19. Observation of Ω mode electron heating in dusty argon radio frequency discharges

    Energy Technology Data Exchange (ETDEWEB)

    Killer, Carsten; Bandelow, Gunnar; Schneider, Ralf; Melzer, André [Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald, 17489 Greifswald (Germany); Matyash, Konstantin [Universitätsrechenzentrum, Ernst-Moritz-Arndt-Universität Greifswald, 17489 Greifswald (Germany)

    2013-08-15

    The time-resolved emission of argon atoms in a dusty plasma has been measured with phase-resolved optical emission spectroscopy using an intensified charge-coupled device camera. For that purpose, three-dimensional dust clouds have been confined in a capacitively coupled rf argon discharge with the help of thermophoretic levitation. While electrons are exclusively heated by the expanding sheath (α mode) in the dust-free case, electron heating takes place in the entire plasma bulk when the discharge volume is filled with dust particles. Such a behavior is known as Ω mode, first observed in electronegative plasmas. Furthermore, particle-in-cell simulations have been carried out, which reproduce the trends of the experimental findings. These simulations support previous numerical models showing that the enhanced atomic emission in the plasma can be attributed to a bulk electric field, which is mainly caused by the reduced electrical conductivity due to electron depletion.

  20. Quantum mechanical metastability: When and why?

    International Nuclear Information System (INIS)

    Boyanovsky, D.; Willey, R.; Holman, R.

    1992-01-01

    We study quantum mechanical metastability with an eye towards false vacuum decay. We point out some technical and conceptual problems with the familiar bounce treatment of this process. We illustrate with simple quantum mechanical examples that the bounce formalism fails to account for the correct boundary conditions. It is also shown, that the bounce approach overestimates the time scales for tunneling of localized packets in typical (slightly) biased double well potentials. We present a thorough WKB analysis with particular attention to semiclassical trajectories corresponding to complex saddle points. We point out that the boundary conditions determine the proper choice of saddle points and the bounce approach fails to account for semiclassical trajectories in many physically relevant cases. We recognize that these saddle points account for the matching conditions of the WKB wave functions beyond the barriers and restore unitarity and reality of eigenvalues for self-adjoint boundary conditions. We provide a novel approach to the semiclassical analysis of out of equilibrium decay in real time in quantum statistical mechanics. (orig.)

  1. Constitutive modeling of metastable austenitic stainless steel (CD-rom)

    NARCIS (Netherlands)

    Perdahcioglu, Emin Semih; Geijselaers, Hubertus J.M.; Huetink, Han; Boisse, P.

    2008-01-01

    A stress-update algorithm is developed for austenitic metastable steels which undergo phase evolution during deformation. The material initially comprises only the soft and ductile austenite phase which due to the phenomenon of mechanically induced martensitic transformation, transforms completely

  2. Modeling of metastable phase formation diagrams for sputtered thin films.

    Science.gov (United States)

    Chang, Keke; Music, Denis; To Baben, Moritz; Lange, Dennis; Bolvardi, Hamid; Schneider, Jochen M

    2016-01-01

    A method to model the metastable phase formation in the Cu-W system based on the critical surface diffusion distance has been developed. The driver for the formation of a second phase is the critical diffusion distance which is dependent on the solubility of W in Cu and on the solubility of Cu in W. Based on comparative theoretical and experimental data, we can describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation. Metastable phase formation diagrams for Cu-W and Cu-V thin films are predicted and validated by combinatorial magnetron sputtering experiments. The correlative experimental and theoretical research strategy adopted here enables us to efficiently describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation during magnetron sputtering.

  3. The role of metastables in the formation of an argon discharge in a two-pin geometry

    NARCIS (Netherlands)

    Sobota, A.; Manders, F.; Veldhuizen, van E.M.; Dijk, van J.; Haverlag, M.

    2010-01-01

    The breakdown process in gases is a versatile research topic. Numerous processes play more or less important roles in discharge formation, strongly depending on the gas mixture, the electrode configuration, the applied electric field, the size of the geometry, and even on the structures surrounding

  4. Spectroscopy of highly ionized atoms

    International Nuclear Information System (INIS)

    Livingston, A.E.

    1987-01-01

    The atomic structure and decay characteristics of excited states in multiply ionized atoms represent a fertile testing ground for atomic calculations ranging from accurate ab initio theory for few-electron systems to practical semi-empirical approaches for many-electron species. Excitation of fast ions by thin foils generally produces the highest ionization stages for heavy ions in laboratory sources. The associated characteristics of spectroscopic purity and high time resolution provide unique capabilities for studying the atomic properties of highly-ionized atoms. This report is limited to a brief discussion of three classes of atomic systems that are experiencing current theoretical and experimental interest: precision structure of helium-like ions, fine structure of doubly-excited states, and lifetimes of metastable states. Specific measurements in each of these types of systems are mentioned, with emphasis on the relation to studies involving slow, highly-charged ions

  5. High Cycle Fatigue of Metastable Austenitic Stainless Steels

    OpenAIRE

    Fargas Ribas, Gemma; Zapata Dederle, Ana Cristina; Anglada Gomila, Marcos Juan; Mateo García, Antonio Manuel

    2009-01-01

    Metastable austenitic stainless steels are currently used in applications where severe forming operations are required, such as automotive bodies, due to its excellent ductility. They are also gaining interest for its combination of high strength and formability after forming. The biggest disadvantage is the difficulty to predict the mechanical response, which depends heavily on the amount of martensite formed. The martensitic transformation in metastable stainless steels can b...

  6. Electrical conductivity and charge carrier screening in weakly non-ideal argon plasmas

    International Nuclear Information System (INIS)

    Guenther, K.; Lang, S.; Radtke, R.

    1983-01-01

    A pulsed argon discharge as a stable source of weakly non-ideal plasmas is described in connection with the diagnostic necessities for conductivity measurements. The parameters overlap the range for stationary arcs and allow comparison with measurements in cascade arcs. The measured conductivities are explained using the binary collision model considering collisions with neutrals, excited atoms, and ions. A relation between the screening parameter and non-ideality is proposed which should be valid for all elements. (author)

  7. Electrical conductivity and charge carrier screening in weakly non-ideal argon plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Guenther, K; Lang, S; Radtke, R [Akademie der Wissenschaften der DDR, Jena. Zentralinstitut fuer Elektronenphysik

    1983-07-14

    A pulsed argon discharge as a stable source of weakly non-ideal plasmas is described in connection with the diagnostic necessities for conductivity measurements. The parameters overlap the range for stationary arcs and allow comparison with measurements in cascade arcs. The measured conductivities are explained using the binary collision model considering collisions with neutrals, excited atoms, and ions. A relation between the screening parameter and non-ideality is proposed which should be valid for all elements.

  8. Rayleigh light scattering in fullerene covered by a spherical argon film - a molecular dynamics study

    CERN Document Server

    Dawid, A

    2003-01-01

    We have calculated (by a molecular dynamics method) the interaction-induced polarizability correlation functions and spectra of the depolarized light scattering from fullerene C sub 6 sub 0 molecules surrounded by an argon 'atmosphere' (layer). The calculated correlation functions and spectra of (C sub 6 sub 0)Ar sub n (n = 32, 40, 46) clusters show a substantial dependence on the number n of atoms in the layer.

  9. Contraction ionization waves in the argon contracted discharge

    International Nuclear Information System (INIS)

    Golubovskij, Yu.B.; Kulikov, V.V.; Nekutchaev, V.O.

    1985-01-01

    An investigation of ionization waves in the argon contracted discharge and a definition of their arising propagation mechanism accounting for the specificity of elementary pocesses characteristic of argon are presented. (author)

  10. Co thin film with metastable bcc structure formed on GaAs(111 substrate

    Directory of Open Access Journals (Sweden)

    Minakawa Shigeyuki

    2014-07-01

    Full Text Available Co thin films are prepared on GaAs(111 substrates at temperatures ranging from room temperature to 600 ºC by radio-frequency magnetron sputtering. The growth behavior and the detailed resulting film structure are investigated by in-situ reflection high-energy electron diffraction and X-ray diffraction. In early stages of film growth at temperatures lower than 200 ºC, Co crystals with metastable A2 (bcc structure are formed, where the crystal structure is stabilized through hetero-epitaxial growth. With increasing the film thickness beyond 2 nm, the metastable structure starts to transform into more stable A1 (fcc structure through atomic displacements parallel to the A2{110} close-packed planes. The crystallographic orientation relationship between the A2 and the transformed A1 crystals is A1{111} || A2{110}. When the substrate temperature is higher than 400 ºC, Ga atoms of substrate diffuse into the Co films and a Co-Ga alloy with bcc-based ordered structure of B2 is formed.

  11. A G/NARRLI Effort. Measuring the Ionization Yield of Low-Energy Nuclear Recoils in Liquid Argon

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, Tenzing Henry Yatish [Univ. of California, Berkeley, CA (United States)

    2014-01-01

    Liquid argon has long been used for particle detection due to its attractive drift properties, ample abundance, and reasonable density. The response of liquid argon to lowenergy O(102 -1044 eV) interactions is, however, largely unexplored. Weakly interacting massive particles such as neutrinos and hypothetical dark-matter particles (WIMPs) are predicted to coherently scatter on atomic nuclei, leaving only an isolated low-energy nuclear recoil as evidence. The response of liquid argon to low-energy nuclear recoils must be studied to determine the sensitivity of liquid argon based detectors to these unobserved interactions. Detectors sensitive to coherent neutrino-nucleus scattering may be used to monitor nuclear reactors from a distance, to detect neutrinos from supernova, and to test the predicted behavior of neutrinos. Additionally, direct detection of hypothetical weakly interacting dark matter would be a large step toward understanding the substance that accounts for nearly 27% of the universe. In this dissertation I discuss a small dual-phase (liquid-gas) argon proportional scintillation counter built to study the low-energy regime and several novel calibration and characterization techniques developed to study the response of liquid argon to low-energy O(102 -104 eV) interactions.

  12. Metastable enhancement of C+ and O+ capture reactions

    International Nuclear Information System (INIS)

    Thomas, E.W.

    1992-01-01

    The project is devoted to the study of charge transfer neutralization of Carbon and oxygen ions in H and H 2 gases at energies from 10 to 500 eV. A major motivation was to provide cross section data to support analysis of edge plasmas in Tokamak Fusion devices. The first objective was to measure cross sections for metastable excited singly charged ions separately from the cross sections for ground state ions. Previously published values are confusing because the beams used included unknown fractions of metastables and these metastables have cross sections greatly different from the ground states. The program was fully accomplished, metastable cross sections were found to be over an order of magnitude greater than ones for the ground state and existing discrepancies in the literature were resolved. Considerable effort was devoted to the design and operation of ion source configurations were the metastable content of the ion beam was known. Subsequently study progressed to the neutralization of multiply charged C and 0 ions in the same targets. First there has been a need to develop ion sources which can produce useful beams of multiply charged species. This has now been accomplished. The intent is to use these sources for the measurement of cross sections with again an attempt to differentiate between the behavior of ground and metastably excited species

  13. Argon-ion contamination of the plasmasphere

    International Nuclear Information System (INIS)

    Chiu, Y.T.; Cornwall, J.M.; Luhmann, J.G.; Schulz, M.

    1979-01-01

    This paper applies present observational and analytic knowledge on effects of plasma beam interaction wth the magnetosphere to the plasmasphere contamination problem of the argon ion engine exhaust expected to be deposited in the magnetosphere during the construction phase of the Satellite Power System. Effects of plasmasphere, ionosphere, and radiation belt modifications are discussed

  14. Silicon compounds of neon and argon

    Czech Academy of Sciences Publication Activity Database

    Roithová, J.; Schröder, Detlef

    -, č. 46 (2009), s. 8788-8790 ISSN 1433-7851 R&D Projects: GA ČR GA203/09/1223 Grant - others: ERC (XE) Adg HORIZOMS Institutional research plan: CEZ:AV0Z40550506 Keywords : argon * bond formation * dications * neon Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 11.829, year: 2009

  15. Performance of a uranium liquid argon calorimeter

    International Nuclear Information System (INIS)

    Tuts, P.M.

    1987-01-01

    The author presents results on the performance of a uranium and liquid argon colorimeter in the NW test beam at Fermilab. This study describes the calorimeter, and discusses its performance with electrons, pions and muons from 10 GeV to 150 GeV. The performance parameters measure response, linearity, resolution, compensation, and e/π separation

  16. SLD liquid argon calorimeter prototype test results

    International Nuclear Information System (INIS)

    Dubois, R.; Eigen, G.; Au, Y.

    1985-10-01

    The results of the SLD test beam program for the selection of a calorimeter radiator composition within a liquid argon system are described, with emphasis on the study of the use of uranium to obtain equalization of pion and electron responses

  17. Commissioning of the ATLAS Liquid Argon Calorimeters

    CERN Document Server

    Cooke, Mark S

    2009-01-01

    A selection of ATLAS liquid argon (LAr) calorimeter commissioning studies are presented. These include a coherent noise study, a measurement of the quality of the physics pulse shape prediction, and energy and time reconstruction analyses with cosmic and single beam signals.

  18. Thermal decomposition of barium valerate in argon

    DEFF Research Database (Denmark)

    Torres, P.; Norby, Poul; Grivel, Jean-Claude

    2015-01-01

    The thermal decomposition of barium valerate (Ba(C4H9CO2)(2)/Ba-pentanoate) was studied in argon by means of thermogravimetry, differential thermal analysis, IR-spectroscopy, X-ray diffraction and hot-stage optical microscopy. Melting takes place in two different steps, at 200 degrees C and 280...

  19. Long lived quantum memory with nuclear atomic spins

    International Nuclear Information System (INIS)

    Sinatra, A.; Reinaudi, G.; Dantan, A.; Giacobino, E.; Pinard, M.

    2005-01-01

    We propose store non-classical states of light into the macroscopic collective nuclear spin (10 18 atoms) of a 3 He vapor, using metastability exchange collisions. We show that these collisions currently used to transfer orientation from the metastable state 2 3 S 1 to the ground state state of 3 He, may conserve quantum correlations and give a possible experimental scheme to perfectly map a squeezed vacuum field state onto a nuclear spin state, which should allow for extremely long storage times (hours). In addition to the apparent interest for quantum information, the scheme offers the intriguing possibility to create a long-lived non classical state for spins. During a metastability exchange collision an atom in the ground state state and an atom in the metastable triplet state 2 3 S exchange their electronic spin variables. The ground state atom is then brought into the metastable state and vice-versa. A laser transition is accessible from the metastable state so that the metastable atoms are coupled with light. This, together with metastability exchange collisions, provides an effective coupling between ground state atoms and light. In our scheme, a coherent field and a squeezed vacuum field excite a Raman transition between Zeeman sublevels of the metastable state, after the system is prepared in the fully polarized state by preliminary optical pumping. According to the intensity of the coherent field, which acts as a control parameter, the squeezing of the field can be selectively transferred either to metastable or to ground state atoms. Once it is encoded in the purely nuclear spin of the ground state of 3 He, which is 20 eV apart from the nearest excited state and interacts very little with the environment, the quantum state can survive for times as long as several hours. By lighting up only the coherent field in the same configuration as for the 'writing' phase, the nuclear spin memory can be 'read' after a long delay, the squeezing being transferred

  20. Excitation mechanism for nickel and argon lines emitted by radio-frequency glow discharge plasma associated with bias current introduction

    International Nuclear Information System (INIS)

    Kodama, Kenji; Wagatsuma, Kazuaki

    2004-01-01

    The introduction of d.c. bias current to an r.f. glow discharge plasma led to enhancement in the intensity of particular emission lines. In order to investigate the excitation mechanism, a large number of nickel emission lines was measured with and without the bias-current introduction. Emission intensities of nickel atomic lines were predominantly elevated by conducting bias current, especially when the emission lines have an excitation energy of approximately 5 eV. This phenomenon could be explained from the additional excitation through collisions with the introduced electrons having kinetic energies favorable for the excitation of such nickel atomic lines. However, this additional excitation mechanism was less effective for excited states of nickel ion, argon atom and argon ion, because their excitation energies were fairly high compared with the excitation energies of Ni atomic lines

  1. Lifetime measurements in Crsub(I) by laser excitation from the metastable states

    International Nuclear Information System (INIS)

    Kwiatkowski, M.; Micali, G.; Werner, K.; Zimmermann, P.

    1981-01-01

    A combination of collisional and laser excitation was used to measure radiative lifetimes in Cr I. By a discharge an atomic beam of metastable atoms in the 3d 5 4sa 5 S, a 5 G, b 5 D, a 3 I, b 1 I and 3d 4 4s 2 a 5 D terms was produced. Spatially separated from the place of collisional excitation laser radiation selectively populated levels belonging to the 3d 5 4p z 5 P, y 5 P, u 5 F, u 5 D, x 3 I, y 1 I, 3d 5 5pz 5 G and 3d 4 4s4px 5 G terms. Time-resolved observation of the reemitted resonance fluorescence yielded the lifetimes of 28 levels. The values are compared with other experimental and theoretical results. (orig.)

  2. Observation of a barium xenon exciplex within a large argon cluster.

    Science.gov (United States)

    Briant, M; Gaveau, M-A; Mestdagh, J-M

    2010-07-21

    Spectroscopic measurements provide fluorescence and excitation spectra of a single barium atom codeposited with xenon atoms on argon clusters of average size approximately 2000. The spectra are studied as a function of the number of xenon atoms per cluster. The excitation spectrum with approximately 10 xenon atoms per cluster is qualitatively similar to that observed when no xenon atom is present on the cluster. It consists of two bands located on each side of the 6s6p (1)P-6s(2) (1)S resonance line of the free barium. In contrast, the fluorescence spectrum differs qualitatively since a barium-xenon exciplex is observed, which has no counterpart in xenon free clusters. In particular an emission is observed, which is redshifted by 729 cm(-1) with respect to the Ba(6s6p (1)P-6s(2) (1)S) resonance line.

  3. Effect of low-temperature argon matrices on IR spectra and structure of flexible N-acetylglycine molecules

    International Nuclear Information System (INIS)

    Stepan'yan, S.G.; Ivanov, A.Yu.; Adamowicz, L.

    2016-01-01

    The influence of the matrix environment on structure and IR spectra of the N-acetylglycine conformers was studied. Based on the FTIR spectra of N-acetyl-glycine isolated in low temperature argon matrices we determined its conformational composition. The spectra bands of main and two minor conformers of N-acetylglycine were identified in the FTIR spectra. The structure of the observed conformers was stabilized by different intramolecular hydrogen bonds. The Gibbs free energies of the conformers (CCSD(T)/CBS method) were performed and population of the con-formers at 360 K were determined. They were 85.3% for the main conformer and 9.6 and 5.1% for the mi-nor N-acetylglycine conformers. We also determined size and shape of the cavities which were formed by embedding of the N-acetylglycine conformers in argon matrices during deposition. It was found that for the planar main conformer the most energetically preferred cavity was formed by substituting of 7 argon atoms. At the same time, bulky minor conformers were embedded in a cavity formed by substituting of 8 argon atoms. Complexation energies as well as the deformation energies of the argon crystal and conformers of N-acetylglycine were calculated. Also we determined values of the matrix shifts of vibrational frequencies of N-acetylglycine conformers.

  4. 46 CFR 151.50-36 - Argon or nitrogen.

    Science.gov (United States)

    2010-10-01

    ... 46 Shipping 5 2010-10-01 2010-10-01 false Argon or nitrogen. 151.50-36 Section 151.50-36 Shipping... BULK LIQUID HAZARDOUS MATERIAL CARGOES Special Requirements § 151.50-36 Argon or nitrogen. (a) A cargo tank that contains argon or nitrogen and that has a maximum allowable working pressure of 172 kPa (25...

  5. Examination of the metastable and stable pitting corrosion of aluminum modified with carbon by ion beam techniques

    International Nuclear Information System (INIS)

    Lensch, O.; Enders, B.; Knecht, J.; Ensinger, W.

    2001-01-01

    It is well known that aluminum and aluminum alloys are sensitive to pitting corrosion when exposed to aqueous solutions containing aggressive anions like halides. The destructive nature of pitting is due to its high local dissolution rates at electrode potentials above the so-called pitting potential U p . Recently, it has been realized that also at potentials below U p , in the passive and cathodic regions and around the free corrosion potential, anodic current transients appear which have been attributed to metastable pitting events. For the purpose of full characterization of the pitting behavior, a program routine has been developed where the occurrence frequency, lifetime and rate of metastable pitting events are extracted from potentiostatic current/time-measurements depending on the electrode potential. The routine has been applied to measurements of carbon modified pure aluminum. Carbon modifications were done with carbon evaporation and carbon sputtering under concurrent argon ion bombardment. The results are discussed in terms of the applied modification technique, their parameters and their effects on the corrosion protection ability of aluminum modified by carbon

  6. The effect of ethanol gas impurity on the discharge mode and discharge products of argon plasma jet at atmospheric pressure

    Science.gov (United States)

    Xia, Wenjie; Liu, Dingxin; Xu, Han; Wang, Xiaohua; Liu, Zhijie; Rong, Mingzhe; Kong, Michael G.

    2018-05-01

    Argon is a widely used working gas of plasmas, which is much cheaper than helium but on the other hand much more difficult to generate diffuse discharge at atmospheric pressure. In order to meet the application requirements, plenty of researches have been reported to facilitate the diffuse discharge happening for argon plasmas, and in this paper an approach of using ethanol gas (EtOH) impurity is investigated. The discharge characteristics of Ar + EtOH plasma jet are studied as a function of the applied voltage and the concentration of EtOH, from which the concentration of EtOH between ∼200 and ∼3300 parts per million (ppm) is determined necessary for the generation of diffuse discharge. Compared with the helium plasma jet in literature, it is deduced that the diffuse discharge is probably caused by the Penning ionization happening between the metastable argon and EtOH. The discharge products of Ar + EtOH (672 ppm) plasma jet are measured and the corresponding chemistry pathways are analyzed. About 20% of EtOH is decomposed via complex chemical reactions to form more than a dozen of neutral species, such as CH3CHO, CH3COOH, CO, H2O, and C n H2n+2 (n ≥ 3), and various kinds of ionic species, including C+, CH+, ArH+, {{{{O}}}2}-, CH3CH2O‑, etc.

  7. Velocity dependence of the Penning ionization of D atoms by He(21S) and H2(23S) atoms

    International Nuclear Information System (INIS)

    Fort, J.; Laucagne, J.J.; Pesnelle, A.; Watel, G.

    1975-01-01

    A time-of-flight technique has been developed for the study of the velocity dependence of the cross section for Penning ionization of D atoms by metastable He atoms: He(2 1 S)+D→He(1 1 S)+D + +e - , He(2 3 S)+D→He(1 1 S)+D + e - [fr

  8. Using Quantum Defect Theory in the (e,2e) ionization of argon

    International Nuclear Information System (INIS)

    Mazevet, S.; Fakhreddine, K.; Vien, G. Nguyen; Tweed, R.J.; Langlois, J.

    2002-01-01

    Quantum Defect theory is a well established theoretical concept in modern spectroscopy that was found particularly powerful in the study of Rydberg states and photoionization of various atomic and molecular species. We show that this approach can also be useful in electron impact ionization problems where state of the art theoretical methods are presently restricted mostly to simple atomic targets. We found that this approach leads to significant improvements over previous calculations for the well documented case of the ionization of argon in equal energy sharing geometry

  9. Photon energy dependent intensity variations observed in Auger spectra of free argon clusters

    International Nuclear Information System (INIS)

    Lundwall, M; Lindblad, A; Bergersen, H; Rander, T; Oehrwall, G; Tchaplyguine, M; Peredkov, S; Svensson, S; Bjoerneholm, O

    2006-01-01

    Photon energy dependent intensity variations are experimentally observed in the L 2,3 M 2,3 M 2,3 Auger spectra of argon clusters. Two cluster sizes are examined in the present study. Extrinsic scattering effects, both elastic and inelastic, involving the photoelectron are discussed and suggested as the explanation of the variations in the Auger signal. The atoms in the first few coordination shells surrounding the core-ionized atom are proposed to be the main targets for the scattering processes

  10. Extended Neural Metastability in an Embodied Model of Sensorimotor Coupling

    Directory of Open Access Journals (Sweden)

    Miguel Aguilera

    2016-09-01

    Full Text Available The hypothesis that brain organization is based on mechanisms of metastable synchronization in neural assemblies has been popularized during the last decades of neuroscientific research. Nevertheless, the role of body and environment for understanding the functioning of metastable assemblies is frequently dismissed. The main goal of this paper is to investigate the contribution of sensorimotor coupling to neural and behavioural metastability using a minimal computational model of plastic neural ensembles embedded in a robotic agent in a behavioural preference task. Our hypothesis is that, under some conditions, the metastability of the system is not restricted to the brain but extends to the system composed by the interaction of brain, body and environment. We test this idea, comparing an agent in continuous interaction with its environment in a task demanding behavioural flexibility with an equivalent model from the point of view of 'internalist neuroscience'. A statistical characterization of our model and tools from information theory allows us to show how (1 the bidirectional coupling between agent and environment brings the system closer to a regime of criticality and triggers the emergence of additional metastable states which are not found in the brain in isolation but extended to the whole system of sensorimotor interaction, (2 the synaptic plasticity of the agent is fundamental to sustain open structures in the neural controller of the agent flexibly engaging and disengaging different behavioural patterns that sustain sensorimotor metastable states, and (3 these extended metastable states emerge when the agent generates an asymmetrical circular loop of causal interaction with its environment, in which the agent responds to variability of the environment at fast timescales while acting over the environment at slow timescales, suggesting the constitution of the agent as an autonomous entity actively modulating its sensorimotor coupling

  11. Extended Neural Metastability in an Embodied Model of Sensorimotor Coupling.

    Science.gov (United States)

    Aguilera, Miguel; Bedia, Manuel G; Barandiaran, Xabier E

    2016-01-01

    The hypothesis that brain organization is based on mechanisms of metastable synchronization in neural assemblies has been popularized during the last decades of neuroscientific research. Nevertheless, the role of body and environment for understanding the functioning of metastable assemblies is frequently dismissed. The main goal of this paper is to investigate the contribution of sensorimotor coupling to neural and behavioral metastability using a minimal computational model of plastic neural ensembles embedded in a robotic agent in a behavioral preference task. Our hypothesis is that, under some conditions, the metastability of the system is not restricted to the brain but extends to the system composed by the interaction of brain, body and environment. We test this idea, comparing an agent in continuous interaction with its environment in a task demanding behavioral flexibility with an equivalent model from the point of view of "internalist neuroscience." A statistical characterization of our model and tools from information theory allow us to show how (1) the bidirectional coupling between agent and environment brings the system closer to a regime of criticality and triggers the emergence of additional metastable states which are not found in the brain in isolation but extended to the whole system of sensorimotor interaction, (2) the synaptic plasticity of the agent is fundamental to sustain open structures in the neural controller of the agent flexibly engaging and disengaging different behavioral patterns that sustain sensorimotor metastable states, and (3) these extended metastable states emerge when the agent generates an asymmetrical circular loop of causal interaction with its environment, in which the agent responds to variability of the environment at fast timescales while acting over the environment at slow timescales, suggesting the constitution of the agent as an autonomous entity actively modulating its sensorimotor coupling with the world. We

  12. Structural Properties and Thermodynamic Stability of Metastable Phases in the Zr-Nb and Ti-V Systems

    International Nuclear Information System (INIS)

    Aurelio, Gabriela

    2003-01-01

    The structural properties and relative stability of metastable phases have been studied in the Zr-Nb and Ti-V systems.The first part of this Thesis is connected to a previous work performed in our Group (G. Grad, PhD Thesis, Instituto Balseiro, Argentina, 1999).It presents a phenomenological analysis of the systematics of interatomic distances in the omega (Ω ) and bcc (β) phases of the transition metals, which concerns a parameter entering into Pauling's resonating-valence- bond-theory and the structural and bonding properties of the Ω and β phases.Neutron diffraction experiments in Zr-Nb and Ti-V alloys are reported, aimed at studying possible atomic ordering in the Ω phase and the composition dependence of its interatomic distances.An extensive neutron diffraction study was performed on a series of Zr-Nb and Ti-V alloys quenched from high temperatures, where β is the stable phase.Upon quenching, three metastable structures are formed, viz., the hcp (∝ q ) phase, the Ω q phase, and the untransformed β q phase.The structural properties of these metastable phases were determined as a function of the Nb and V contents to generate a reliable experimental database.With such data, a series of issues are discussed related to the structure, relative stability, and phase relations in the alloys and its constitutive elements.The effect of composition upon the lattice parameters of the metastable β q and Ω q phases was combined in a consistent way with a critical analysis of structural and thermophysical data on the metastable phases of Ti and Zr.The relative stability of the metastable ∝ q , Ω q and β q phases in Zr-Nb alloys, and its evolution towards thermodynamic equilibrium, were studied combining neutron thermodiffraction and analytical electron microscopy techniques.During isothermal heat treatments performed at high temperature, the structural properties of the alloys were determined as a function of temperature, time and composition.A method of

  13. Directional emission of single photons from small atomic samples

    DEFF Research Database (Denmark)

    Miroshnychenko, Yevhen; V. Poulsen, Uffe; Mølmer, Klaus

    2013-01-01

    We provide a formalism to describe deterministic emission of single photons with tailored spatial and temporal profiles from a regular array of multi-level atoms. We assume that a single collective excitation is initially shared by all the atoms in a metastable atomic state, and that this state i...... is coupled by a classical laser field to an optically excited state which rapidly decays to the ground atomic state. Our model accounts for the different field polarization components via re-absorption and emission of light by the Zeeman manifold of optically excited states.......We provide a formalism to describe deterministic emission of single photons with tailored spatial and temporal profiles from a regular array of multi-level atoms. We assume that a single collective excitation is initially shared by all the atoms in a metastable atomic state, and that this state...

  14. Demonstration of a CW diode-pumped Ar metastable laser operating at 4  W.

    Science.gov (United States)

    Han, J; Heaven, M C; Moran, P J; Pitz, G A; Guild, E M; Sanderson, C R; Hokr, B

    2017-11-15

    Optically pumped rare gas lasers are being investigated as potential high-energy, high beam quality systems. The lasing medium consists of rare gas atoms (Rg=Ne, Ar, Kr, or Xe) that have been electric discharge excited to the metastable np 5 (n+1)s P3 2 state. Following optical excitation, helium (He) at pressures of 200-1000 Torr is used as the energy transfer agent to create a population inversion. The primary technical difficulty for this scheme is the discharge production of sufficient Rg* metastables in the presence of >200  Torr of He. In this Letter, we describe a pulsed discharge that yields >10 13   cm -3 Ar* in the presence of He at total pressures up to 750 Torr. Using this discharge, a diode-pumped Ar* laser providing 4.1 W has been demonstrated.

  15. A few proofs for nonexistence of the metastable states

    International Nuclear Information System (INIS)

    Blazjevski, Atanas

    2007-01-01

    This paper is the bigger part of one until now unpublished author's work, whose title is 'A few proofs for nonexistence of the metastable states'. Because of a big volume of the work, the problems of supersaturated (metastable) steam which appears at the following of slightly, superheated, saturated or wet steam in the convergent and Laval nozzles will be discussed in the main. This steam is mentioned in the literature as one between of the strongest proofs for existence of metastable states in the substances. In this work the steam is not one -phase gaseous metastable steam, as it was thought until now, but yat it is nonequilibrium wet steam in which during the expanding process in the nozzles extreme small particles condensate, consisted of two, three or only few agglomerated molecules are formed which stay in heat, mechanical and internal nonequilibrium with the rest of the expanding gaseous phase of the steam. It means, that this steam, which is called a supersaturated or metastable steam, in fact does not exist in reality because it is nothing else but only nonequilibrium wet steam consisted of tho phases: the expanding gaseous phase of the steam in the nozzle and the mentioned small and nonequilibrium particles condensate which are formed there...

  16. A metastable liquid melted from a crystalline solid under decompression

    Science.gov (United States)

    Lin, Chuanlong; Smith, Jesse S.; Sinogeikin, Stanislav V.; Kono, Yoshio; Park, Changyong; Kenney-Benson, Curtis; Shen, Guoyin

    2017-01-01

    A metastable liquid may exist under supercooling, sustaining the liquid below the melting point such as supercooled water and silicon. It may also exist as a transient state in solid-solid transitions, as demonstrated in recent studies of colloidal particles and glass-forming metallic systems. One important question is whether a crystalline solid may directly melt into a sustainable metastable liquid. By thermal heating, a crystalline solid will always melt into a liquid above the melting point. Here we report that a high-pressure crystalline phase of bismuth can melt into a metastable liquid below the melting line through a decompression process. The decompression-induced metastable liquid can be maintained for hours in static conditions, and transform to crystalline phases when external perturbations, such as heating and cooling, are applied. It occurs in the pressure-temperature region similar to where the supercooled liquid Bi is observed. Akin to supercooled liquid, the pressure-induced metastable liquid may be more ubiquitous than we thought.

  17. Diffusion of lithium ions in argon

    International Nuclear Information System (INIS)

    Stefansson, T.

    1983-01-01

    Published measurements of transport coefficients for Li + ions in argon seem to be limited to the mobility and the longitudinal diffusion coefficient in the field-to-density ratio range at and below 200 Td 1-5 . In this paper results are presented from measurements of the transverse diffusion coefficient to mobility ratio (Dsub(T)/μ) for Li + ions in argon in the field-to-density ratio range 10 < E/n < 800 Td. The measurements were made with a drift tube mass spectrometer at a gas temperature of 295 +- 1 K using the modified Townsend method of Skullerud. The experimental curve is compared to a calculation by H.R. Skullerud in the same proceedings. (G.Q.)

  18. Argon laser irradiation of the otolithic organ

    Energy Technology Data Exchange (ETDEWEB)

    Okuno, T.; Nomura, Y.; Young, Y.H.; Hara, M. (Univ. of Tokyo (Japan))

    1990-12-01

    An argon laser was used to irradiate the otolithic organs of guinea pigs and cynomolgus monkeys. After stapedectomy, the argon laser (1.5 W x 0.5 sec/shot) irradiated the utricle or saccule without touching the sensory organs. The stapes was replaced over the oval window after irradiation. The animals used for acute observation were killed immediately for morphologic studies; those used for long-term observation were kept alive for 2, 4, or 10 weeks. Acute observation revealed that sensory and supporting cells were elevated from the basement membrane only in the irradiated area. No rupture of the membranous labyrinth was observed. Long-term observation revealed that the otolith of the macula utriculi had disappeared in 2-week specimens. The entire macula utricili had disappeared in 10-week specimens. No morphologic changes were observed in cochlea, semicircular canals, or membranous labyrinth. The saccule showed similar changes.

  19. Reflection-type hologram for atoms

    International Nuclear Information System (INIS)

    Shimizu, Fujio; Fujita, Jun-ichi

    2002-01-01

    A cold metastable neon atomic beam was manipulated with a reflective amplitude hologram that was encoded on a silicon surface. A black-and-white pattern of atoms was reconstructed on a microchannel plate detector. The hologram used the enhanced quantum reflection developed by authors and was made of a two-dimensional array of rectangular low and high reflective cells. The surface of the high reflective cell was composed of regularly spaced roof-shaped ridges, while the low reflective cell was simply a flat surface. The hologram was the first demonstration of reflective atom-optical elements that used universal interaction between a neutral atom and solid surface

  20. Quenching of the OH and nitrogen molecular emission by methane addition in an Ar capacitively coupled plasma to remove spectral interference in lead determination by atomic fluorescence spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Frentiu, T., E-mail: ftibi@chem.ubbcluj.r [Faculty of Chemistry and Chemical Engineering, Babes-Bolyai University, Arany Janos 11, 400028 Cluj-Napoca (Romania); Ponta, M., E-mail: mponta@chem.ubbcluj.r [Faculty of Chemistry and Chemical Engineering, Babes-Bolyai University, Arany Janos 11, 400028 Cluj-Napoca (Romania); Mihaltan, A.I., E-mail: alinblaj2005@yahoo.co [National Institute for Research and Development of Optoelectronics Bucharest - Research Institute for Analytical Instrumentation, Donath 67, 400293 Cluj-Napoca (Romania); Darvasi, E., E-mail: edarvasi@chem.ubbcluj.r [Faculty of Chemistry and Chemical Engineering, Babes-Bolyai University, Arany Janos 11, 400028 Cluj-Napoca (Romania); Frentiu, M., E-mail: frentiu.maria@yahoo.co [National Institute for Research and Development of Optoelectronics Bucharest - Research Institute for Analytical Instrumentation, Donath 67, 400293 Cluj-Napoca (Romania); Cordos, E., E-mail: emilcordos@gmail.co [National Institute for Research and Development of Optoelectronics Bucharest - Research Institute for Analytical Instrumentation, Donath 67, 400293 Cluj-Napoca (Romania)

    2010-07-15

    A new method is proposed to remove the spectral interference on elements in atomic fluorescence spectrometry by quenching of the molecular emission of the OH radical (A{sup 2{Sigma}+} {yields} X{sup 2{Pi}}) and N{sub 2} second positive system (C{sup 3{Pi}}{sub u} {yields} B{sup 3{Sigma}}{sub g}) in the background spectrum of medium power Ar plasmas. The experiments were carried out in a radiofrequency capacitively coupled plasma (275 W, 27.12 MHz) by CH{sub 4} addition. The quenching is the result of the high affinity of OH radical for a hydrogen atom from the CH{sub 4} molecule and the collisions of the second kind between nitrogen excited molecules and CH{sub 4}, respectively. The decrease of the emission of N{sub 2} second positive system in the presence of CH{sub 4} is also the result of the deactivation of the metastable argon atoms that could excite the nitrogen molecules. For flow rates of 0.7 l min{sup -1} Ar with addition of 7.5 ml min{sup -1} CH{sub 4}, the molecular emission of OH and N{sub 2} was completely removed from the plasma jet spectrum at viewing heights above 60 mm. The molecular emission associated to CH and CH{sub 2} species was not observed in the emission spectrum of Ar/CH{sub 4} plasma in the ultraviolet range. The method was experimented for the determination of Pb at 283.31 nm by atomic fluorescence spectrometry with electrodeless discharge lamp and a multichannel microspectrometer. The detection limit was 35 ng ml{sup -1}, 2-3 times better than in atomic emission spectrometry using the same plasma source, and similar to that in hollow cathode lamp microwave plasma torch atomic fluorescence spectrometry.

  1. Metastability and avalanche dynamics in strongly correlated gases with long-range interactions

    Science.gov (United States)

    Hruby, Lorenz; Dogra, Nishant; Landini, Manuele; Donner, Tobias; Esslinger, Tilman

    2018-03-01

    We experimentally study the stability of a bosonic Mott insulator against the formation of a density wave induced by long-range interactions and characterize the intrinsic dynamics between these two states. The Mott insulator is created in a quantum degenerate gas of 87-Rubidium atoms, trapped in a 3D optical lattice. The gas is located inside and globally coupled to an optical cavity. This causes interactions of global range, mediated by photons dispersively scattered between a transverse lattice and the cavity. The scattering comes with an atomic density modulation, which is measured by the photon flux leaking from the cavity. We initialize the system in a Mott-insulating state and then rapidly increase the global coupling strength. We observe that the system falls into either of two distinct final states. One is characterized by a low photon flux, signaling a Mott insulator, and the other is characterized by a high photon flux, which we associate with a density wave. Ramping the global coupling slowly, we observe a hysteresis loop between the two states—a further signature of metastability. A comparison with a theoretical model confirms that the metastability originates in the competition between short- and global-range interactions. From the increasing photon flux monitored during the switching process, we find that several thousand atoms tunnel to a neighboring site on the timescale of the single-particle dynamics. We argue that a density modulation, initially forming in the compressible surface of the trapped gas, triggers an avalanche tunneling process in the Mott-insulating region.

  2. Simple and efficient method of spin-polarizing a metastable helium beam by diode laser optical pumping

    International Nuclear Information System (INIS)

    Granitza, B.; Salvietti, M.; Torello, E.; Mattera, L.; Sasso, A.

    1995-01-01

    Diode laser optical pumping to produce a highly spin-polarized metastable He beam to be used in a spin-polarized metastable atom deexcitation spectroscopy experiment on magnetized surfaces is described. Efficient pumping of the beam is performed by means of an SDL-6702 distributed Bragg reflector diode laser which yields 50 mW of output power in a single longitudinal mode at 1083 nm, the resonance wavelength for the 2 3 S→2 3 P 0,1,2 (D 0 , D 1 , and D 2 ) transitions of He*. The light is circularly polarized by a quarter-wave plate, allowing easy change of the sense of atomic polarization. The laser frequency can be locked to the atomic transition for several hours by phase-sensitive detection of the saturated absorption signal in a He discharge cell. Any of the three transitions of the triplet system can be pumped with the laser but the maximum level of atomic polarization of 98.5% is found pumping the D 2 line. copyright 1995 American Institute of Physics

  3. Investigation on the effect of nonlinear processes on similarity law in high-pressure argon discharges

    Science.gov (United States)

    Fu, Yangyang; Parsey, Guy M.; Verboncoeur, John P.; Christlieb, Andrew J.

    2017-11-01

    In this paper, the effect of nonlinear processes (such as three-body collisions and stepwise ionizations) on the similarity law in high-pressure argon discharges has been studied by the use of the Kinetic Global Model framework. In the discharge model, the ground state argon atoms (Ar), electrons (e), atom ions (Ar+), molecular ions (Ar2+), and fourteen argon excited levels Ar*(4s and 4p) are considered. The steady-state electron and ion densities are obtained with nonlinear processes included and excluded in the designed models, respectively. It is found that in similar gas gaps, keeping the product of gas pressure and linear dimension unchanged, with the nonlinear processes included, the normalized density relations deviate from the similarity relations gradually as the scale-up factor decreases. Without the nonlinear processes, the parameter relations are in good agreement with the similarity law predictions. Furthermore, the pressure and the dimension effects are also investigated separately with and without the nonlinear processes. It is shown that the gas pressure effect on the results is less obvious than the dimension effect. Without the nonlinear processes, the pressure and the dimension effects could be estimated from one to the other based on the similarity relations.

  4. Classification of knotted tori in 2-metastable dimension

    KAUST Repository

    Cencelj, Matija

    2012-11-30

    This paper is devoted to the classical Knotting Problem: for a given manifold N and number m describe the set of isotopy classes of embeddings N → Sm. We study the specific case of knotted tori, that is, the embeddings Sp × Sq → Sm. The classification of knotted tori up to isotopy in the metastable dimension range m > p + 3 2 q + 2, p 6 q, was given by Haefliger, Zeeman and A. Skopenkov. We consider the dimensions below the metastable range and give an explicit criterion for the finiteness of this set of isotopy classes in the 2-metastable dimension: Theorem. Assume that p+ 4 3 q +2 < mp+ 3 2 q +2 and m > 2p+q +2. Then the set of isotopy classes of smooth embeddings Sp × Sq → Sm is infinite if and only if either q + 1 or p + q + 1 is divisible by 4. © 2012 RAS(DoM) and LMS.

  5. Classification of knotted tori in 2-metastable dimension

    KAUST Repository

    Cencelj, Matija; Repovš, Dušan; Skopenkov, Mikhail

    2012-01-01

    This paper is devoted to the classical Knotting Problem: for a given manifold N and number m describe the set of isotopy classes of embeddings N → Sm. We study the specific case of knotted tori, that is, the embeddings Sp × Sq → Sm. The classification of knotted tori up to isotopy in the metastable dimension range m > p + 3 2 q + 2, p 6 q, was given by Haefliger, Zeeman and A. Skopenkov. We consider the dimensions below the metastable range and give an explicit criterion for the finiteness of this set of isotopy classes in the 2-metastable dimension: Theorem. Assume that p+ 4 3 q +2 < mp+ 3 2 q +2 and m > 2p+q +2. Then the set of isotopy classes of smooth embeddings Sp × Sq → Sm is infinite if and only if either q + 1 or p + q + 1 is divisible by 4. © 2012 RAS(DoM) and LMS.

  6. Dynamical SUSY breaking in meta-stable vacua

    International Nuclear Information System (INIS)

    Intriligator, Kenneth; Seiberg, Nathan; Shih, David

    2006-01-01

    Dynamical supersymmetry breaking in a long-lived meta-stable vacuum is a phenomenologically viable possibility. This relatively unexplored avenue leads to many new models of dynamical supersymmetry breaking. Here, we present a surprisingly simple class of models with meta-stable dynamical supersymmetry breaking: N = 1 supersymmetric QCD, with massive flavors. Though these theories are strongly coupled, we definitively demonstrate the existence of meta-stable vacua by using the free-magnetic dual. Model building challenges, such as large flavor symmetries and the absence of an R-symmetry, are easily accommodated in these theories. Their simplicity also suggests that broken supersymmetry is generic in supersymmetric field theory and in the landscape of string vacua

  7. Sequences by Metastable Attractors: Interweaving Dynamical Systems and Experimental Data

    Directory of Open Access Journals (Sweden)

    Axel Hutt

    2017-05-01

    Full Text Available Metastable attractors and heteroclinic orbits are present in the dynamics of various complex systems. Although their occurrence is well-known, their identification and modeling is a challenging task. The present work reviews briefly the literature and proposes a novel combination of their identification in experimental data and their modeling by dynamical systems. This combination applies recurrence structure analysis permitting the derivation of an optimal symbolic representation of metastable states and their dynamical transitions. To derive heteroclinic sequences of metastable attractors in various experimental conditions, the work introduces a Hausdorff clustering algorithm for symbolic dynamics. The application to brain signals (event-related potentials utilizing neural field models illustrates the methodology.

  8. Metastability at the Yield-Stress Transition in Soft Glasses

    Science.gov (United States)

    Lulli, Matteo; Benzi, Roberto; Sbragaglia, Mauro

    2018-04-01

    We study the solid-to-liquid transition in a two-dimensional fully periodic soft-glassy model with an imposed spatially heterogeneous stress. The model we consider consists of droplets of a dispersed phase jammed together in a continuous phase. When the peak value of the stress gets close to the yield stress of the material, we find that the whole system intermittently tunnels to a metastable "fluidized" state, which relaxes back to a metastable "solid" state by means of an elastic-wave dissipation. This macroscopic scenario is studied through the microscopic displacement field of the droplets, whose time statistics displays a remarkable bimodality. Metastability is rooted in the existence, in a given stress range, of two distinct stable rheological branches, as well as long-range correlations (e.g., large dynamic heterogeneity) developed in the system. Finally, we show that a similar behavior holds for a pressure-driven flow, thus suggesting possible experimental tests.

  9. Metastable Structures in Cluster Catalysis from First-Principles: Structural Ensemble in Reaction Conditions and Metastability Triggered Reactivity.

    Science.gov (United States)

    Sun, Geng; Sautet, Philippe

    2018-02-28

    Reactivity studies on catalytic transition metal clusters are usually performed on a single global minimum structure. With the example of a Pt 13 cluster under a pressure of hydrogen, we show from first-principle calculations that low energy metastable structures of the cluster can play a major role for catalytic reactivity and that hence consideration of the global minimum structure alone can severely underestimate the activity. The catalyst is fluxional with an ensemble of metastable structures energetically accessible at reaction conditions. A modified genetic algorithm is proposed to comprehensively search for the low energy metastable ensemble (LEME) structures instead of merely the global minimum structure. In order to reduce the computational cost of density functional calculations, a high dimensional neural network potential is employed to accelerate the exploration. The presence and influence of LEME structures during catalysis is discussed by the example of H covered Pt 13 clusters for two reactions of major importance: hydrogen evolution reaction and methane activation. The results demonstrate that although the number of accessible metastable structures is reduced under reaction condition for Pt 13 clusters, these metastable structures can exhibit high activity and dominate the observed activity due to their unique electronic or structural properties. This underlines the necessity of thoroughly exploring the LEME structures in catalysis simulations. The approach enables one to systematically address the impact of isomers in catalysis studies, taking into account the high adsorbate coverage induced by reaction conditions.

  10. Antibody-Unfolding and Metastable-State Binding in Force Spectroscopy and Recognition Imaging

    Science.gov (United States)

    Kaur, Parminder; Qiang-Fu; Fuhrmann, Alexander; Ros, Robert; Kutner, Linda Obenauer; Schneeweis, Lumelle A.; Navoa, Ryman; Steger, Kirby; Xie, Lei; Yonan, Christopher; Abraham, Ralph; Grace, Michael J.; Lindsay, Stuart

    2011-01-01

    Force spectroscopy and recognition imaging are important techniques for characterizing and mapping molecular interactions. In both cases, an antibody is pulled away from its target in times that are much less than the normal residence time of the antibody on its target. The distribution of pulling lengths in force spectroscopy shows the development of additional peaks at high loading rates, indicating that part of the antibody frequently unfolds. This propensity to unfold is reversible, indicating that exposure to high loading rates induces a structural transition to a metastable state. Weakened interactions of the antibody in this metastable state could account for reduced specificity in recognition imaging where the loading rates are always high. The much weaker interaction between the partially unfolded antibody and target, while still specific (as shown by control experiments), results in unbinding on millisecond timescales, giving rise to rapid switching noise in the recognition images. At the lower loading rates used in force spectroscopy, we still find discrepancies between the binding kinetics determined by force spectroscopy and those determined by surface plasmon resonance—possibly a consequence of the short tethers used in recognition imaging. Recognition imaging is nonetheless a powerful tool for interpreting complex atomic force microscopy images, so long as specificity is calibrated in situ, and not inferred from equilibrium binding kinetics. PMID:21190677

  11. Stabilization of metastable tetragonal zirconia nanocrystallites by surface modification

    DEFF Research Database (Denmark)

    Nielsen, Mette Skovgaard; Almdal, Kristoffer; Lelieveld, A. van

    2011-01-01

    Metastable tetragonal zirconia nanocrystallites were studied in humid air and in water at room temperature (RT). A stabilizing effect of different surfactants on the tetragonal phase was observed. Furthermore, the phase stability of silanized metastable tetragonal zirconia nanocrystallites was te...... exposure to humidity. Only silanes and phosphate esters of these were able to stabilize the tetragonal phase in water. Even as small amounts of silanes as 0.25 silane molecule per nm2 are able to stabilize the tetragonal phase in water at RT. Aminopropyl trimethoxy silane and γ...

  12. Metastable states of plasma particles close to a charged surface

    Energy Technology Data Exchange (ETDEWEB)

    Shavlov, A. V., E-mail: shavlov@ikz.ru [The Institute of the Earth Cryosphere, RAS Siberian branch, 625000, P.O. 1230, Tyumen (Russian Federation); Tyumen State Oil and Gas University, 38, Volodarskogo St., 625000, Tyumen (Russian Federation); Dzhumandzhi, V. A. [The Institute of the Earth Cryosphere, RAS Siberian branch, 625000, P.O. 1230, Tyumen (Russian Federation)

    2015-09-15

    The free energy of the plasma particles and the charged surface that form an electroneutral system is calculated on the basis of the Poisson-Boltzmann equation. It is shown that, owing to correlation of light plasma particles near the charged surface and close to heavy particles of high charge, there can be metastable states in plasma. The corresponding phase charts of metastable states of the separate components of plasma, and plasma as a whole, are constructed. These charts depend on temperature, the charge magnitude, the size of the particles, and the share of the charge of the light carriers out of the total charge of the plasma particles.

  13. Photochemistry of the ozone-water complex in cryogenic neon, argon, and krypton matrixes.

    Science.gov (United States)

    Tsuge, Masashi; Tsuji, Kazuhide; Kawai, Akio; Shibuya, Kazuhiko

    2013-12-12

    The photochemistry of ozone-water complexes and the wavelength dependence of the reactions were studied by matrix isolation FTIR spectrometry in neon, argon, and krypton matrixes. Hydrogen peroxide was formed upon the irradiation of UV light below 355 nm. Quantitative analyses of the reactant and product were performed to evaluate the matrix cage effect of the photoreaction. In argon and krypton matrixes, a bimolecular O((1)D) + H2O → H2O2 reaction was found to occur to form hydrogen peroxide, where the O((1)D) atom generated by the photolysis of ozone diffused in the cryogenic solids to encounter water. In a neon matrix, hydrogen peroxide was generated through intracage photoreaction of the ozone-water complex, indicating that a neon matrix medium is most appropriate to study the photochemistry of the ozone-water complex.

  14. Pre-breakdown light emission phenomena in low-pressure argon between parabolic electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Wagenaars, E [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Perriens, N W B [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Brok, W J M [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Bowden, M D [Department of Physics and Astronomy, The Open University, Milton Keynes, MK7 6AA (United Kingdom); Veldhuizen, E M van [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Kroesen, G M W [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands)

    2006-09-07

    An experimental study on pre-breakdown light emission in low-pressure argon gas was performed. In a pulsed discharge, pre-breakdown phenomena were observed for repetition rates between 100 and 2000 Hz and pulse duration of 100 {mu}s. These phenomena were studied with time-resolved emission imaging using an intensified charge coupled device camera. The origin of the pre-breakdown emission was identified as diffusion of volume charges left over from previous discharges. These charges were accelerated towards the anode in small electron avalanches causing excitation of argon atoms. Different spatial distributions of the pre-breakdown light emission for different times between discharges were measured and the effects of the pre-breakdown phenomena on the main breakdown phase were studied using a double voltage pulse. The observed effects were attributed to the distribution of volume charges, left over from previous discharges, in the discharge gap during the pre-breakdown phase.

  15. Controlling interactions between highly magnetic atoms with Feshbach resonances.

    Science.gov (United States)

    Kotochigova, Svetlana

    2014-09-01

    This paper reviews current experimental and theoretical progress in the study of dipolar quantum gases of ground and meta-stable atoms with a large magnetic moment. We emphasize the anisotropic nature of Feshbach resonances due to coupling to fast-rotating resonant molecular states in ultracold s-wave collisions between magnetic atoms in external magnetic fields. The dramatic differences in the distribution of resonances of magnetic (7)S3 chromium and magnetic lanthanide atoms with a submerged 4f shell and non-zero electron angular momentum is analyzed. We focus on dysprosium and erbium as important experimental advances have been recently made to cool and create quantum-degenerate gases for these atoms. Finally, we describe progress in locating resonances in collisions of meta-stable magnetic atoms in electronic P-states with ground-state atoms, where an interplay between collisional anisotropies and spin-orbit coupling exists.

  16. Glassy and Metastable Crystalline BaTi2O5 by Containerless Processing

    Science.gov (United States)

    Yoda, Shinichi; Kentei Yu, Yu; Kumar, Vijaya; Kameko, Masashi

    Many efforts have been devoted to forming bulk glass from the melt of ferroelectric crystalline materials without adding any network-forming oxides such as SiO2 due to the potential for producing transparent glass ceramics with high dielectric constant and enhanced piezoelectric, pyroelectric and electro-optic use. The containerless processing is an attractive synthesis tech-nique as it can prevent melt contamination, minimize heterogeneous nucleation, and allow melt to achieve deep undercooling for forming metastable and glassy materials. We have fabricated a new ferroelectric materiel BaTi2 O5 [1] as bulk glass from melt by us-ing containerless processing and studied the phase relationship between microstructure and ferroelectric properties of BaTi2 O5 [2]. The structures of glassy and metastable crystalline BaTi2 O5 fabricated by the containerless pro-cessing were comprehensively investigated by combined X-ray and neutron diffractions, XANES analyses and computer simulations [3]. The 3-dimensional atomic structure of glassy BaTi2 O5 (g-BaTi2 O5 ), simulated by Reverse Monte Carlo (RMC) modelling on diffraction data, shows that extremely distorted TiO5 polyhedra interconnected with both corner-and edge-shared oxy-gen, formed a higher packing density structure than that of conventional silicate glass linked with only corner-sharing of SiO4 polyhedra. In addition, XANES measurement reveales that five-coordinated TiO5 polyhedra were formable in the crystallized metastable a-and b-BaTi2 O5 phases. The structure of metastable b-BaTi2 O5 was solved by ab initio calculation, and refined by Rietveld refinement as group Pnma with unit lattices a = 10.23784 ˚, b = 3.92715 ˚, c A A = 10.92757 A ˚. Our results show that the glass-forming ability enhanced by containerless pro-cessing, not by `strong glass former', fabricated new bulk oxide glasses with peculiar structures and properties. The intermediate-range structure of g-BaTi2 O5 and the crystalline structure of

  17. Combining density functional theory (DFT) and pair distribution function (PDF) analysis to solve the structure of metastable materials: the case of metakaolin.

    Science.gov (United States)

    White, Claire E; Provis, John L; Proffen, Thomas; Riley, Daniel P; van Deventer, Jannie S J

    2010-04-07

    Understanding the atomic structure of complex metastable (including glassy) materials is of great importance in research and industry, however, such materials resist solution by most standard techniques. Here, a novel technique combining thermodynamics and local structure is presented to solve the structure of the metastable aluminosilicate material metakaolin (calcined kaolinite) without the use of chemical constraints. The structure is elucidated by iterating between least-squares real-space refinement using neutron pair distribution function data, and geometry optimisation using density functional modelling. The resulting structural representation is both energetically feasible and in excellent agreement with experimental data. This accurate structural representation of metakaolin provides new insight into the local environment of the aluminium atoms, with evidence of the existence of tri-coordinated aluminium. By the availability of this detailed chemically feasible atomic description, without the need to artificially impose constraints during the refinement process, there exists the opportunity to tailor chemical and mechanical processes involving metakaolin and other complex metastable materials at the atomic level to obtain optimal performance at the macro-scale.

  18. Development of a low-cost inductively coupled argon plasma

    International Nuclear Information System (INIS)

    Ripson, P.A.M.

    1983-01-01

    The aim of this investigation is to drastically reduce running costs of an inductively coupled plasma. This is done by reducing the argon consumption from 20 l/min to about 1 l/min. First, a sample introduction system operating on 0.1 l/min of carrier argon is described. This system ensures a high ratio of plasma argon and carrier argon even at the low total argon consumptions intended. Next, the developed low consumption plasma is presented. In the proposed design, air is blown perpendicularly against the outside of the torch. A different coil has been developed to make air-cooling efficient. Preliminary data on coupling efficiency for the air-cooled plasma are presented. A similarly low argon consumption has been achieved with water as an external coolant medium. It is concluded that a cheaper alternative to the current ICP has become available. (Auth.)

  19. Characterization of Cr-rich Cr-Sb multilayer films: Syntheses of a new metastable phase using modulated elemental reactants

    International Nuclear Information System (INIS)

    Regus, Matthias; Mankovsky, Sergiy; Polesya, Svitlana; Kuhn, Gerhard; Ditto, Jeffrey; Schürmann, Ulrich; Jacquot, Alexandre; Bartholomé, Kilian; Näther, Christian; Winkler, Markus; König, Jan D.; Böttner, Harald; Kienle, Lorenz; Johnson, David C.; Ebert, Hubert; Bensch, Wolfgang

    2015-01-01

    The new metastable compound Cr 1+x Sb with x up to 0.6 has been prepared via a thin film approach using modulated elemental reactants and investigated by in-situ X-ray reflectivity, X-ray diffraction, differential scanning calorimetry, energy dispersive X-ray analysis as well as transmission electron microscopy and atomic force microscopy. The new Cr-rich antimonide crystallizes in a structure related to the Ni 2 In-type structure, where the crystallographic position (1/3, 2/3, 3/4) is partially occupied by excess Cr. The elemental layers of the pristine material interdiffused significantly before Cr 1+x Sb crystallized. A change in the activation energy was observed for the diffusion process when crystal growth starts. First-principles electronic structure calculations provide insight into the structural stability, magnetic properties and resistivity of Cr 1+x Sb. - Graphical abstract: 1 amorphous multilayered film 2 interdiffused amorphous film 3 metastable crystalline phase 4 thermodynamic stable phase (and by-product). - Highlights: • Interdiffusion of amorphous Cr and Sb occurs before crystallization. • Crystallization of a new metastable phase Cr 1.6 Sb in Ni 2 In-type structure. • The new Cr-rich phase shows half-metallic behavior

  20. Two new Np--Ga phases: α-NpGa2 and metastable m-NpGa2

    International Nuclear Information System (INIS)

    Giessen, B.C.; Elliott, R.O.

    1976-01-01

    Following an earlier study of metastable Np-rich Np--Ga alloys, rapidly quenched Np--Ga alloys with 63 to 80 at. pct. Ga were prepared and studied. Two new NpGa 2 phases, both with an AlB 2 type structure, were found: α-NpGa 2 , with a = 4.246A, c = 4.060A, c/a = 0.956, and m-NpGa 2 , with a = 4.412A, c = 3.642A, c/a = 0.825. While m-NpGa 2 was observed only in very fast quenched (splat cooled) samples and appears to be metastable, α-NpGa 2 is probably an equilibrium phase. In a splat cooled alloy with 75 at. pct. Ga, another, unidentified, metastable phase was observed. Crystal chemical discussions of atomic volumes, interatomic distances and axial ratios are given; the volume difference between the two forms of NpGa 2 is correlated with a valence change of Np

  1. Argon spill in the hall of the ATLAS experiment

    CERN Document Server

    Peón-Hernández, G

    1998-01-01

    A hazard analysis is in progress to determine the operation mode of the ventilation system in the ATLAS hall in case of an Argon spill. Two risk scenarios have been investigated so far. In the first, the behaviour of an Argon gas pool is calculated for different ventilation strategies. In the second, the behaviour of Argon gas leaking from the bottom part of the detector is studied for different flows. The description of the study, results and conclusions are presented.

  2. Metastable defect response in CZTSSe from admittance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Koeper, Mark J.; Hages, Charles J.; Li, Jian V.; Levi, Dean; Agrawal, Rakesh

    2017-10-02

    Admittance spectroscopy is a useful tool used to study defects in semiconductor materials. However, metastable defect responses in non-ideal semiconductors can greatly impact the measurement and therefore the interpretation of results. Here, admittance spectroscopy was performed on Cu2ZnSn(S,Se)4 where metastable defect response is illustrated due to the trapping of injected carriers into a deep defect state. To investigate the metastable response, admittance measurements were performed under electrically and optically relaxed conditions in comparison to a device following a low level carrier-injection pretreatment. The relaxed measurement demonstrates a single capacitance signature while two capacitance signatures are observed for the device measured following carrier-injection. The deeper level signature, typically reported for kesterites, is activated by charge trapping following carrier injection. Both signatures are attributed to bulk level defects. The significant metastable response observed on kesterites due to charge trapping obscures accurate interpretation of defect levels from admittance spectroscopy and indicates that great care must be taken when performing and interpreting this measurement on non-ideal devices.

  3. Metastable Behavior in Uniaxial Ferroelectrics TGS and TGSe near TC

    NARCIS (Netherlands)

    Fernández del Castillo, J.R.; Przeslawski, J.; Iglesias, T.; Noheda, B.; Gonzalo, J.A.

    1998-01-01

    High resolution hysteresis loops measurements in triglycine sulfate (ordinary critical point) and in triglycine selenate (tricritical point) allow the approximate characterization of the behavior in the metastable region (E < 0, P > 0, or vice versa) at T ≤ TC. The coercive field may be assumed to

  4. Metastability of Reversible Random Walks in Potential Fields

    Science.gov (United States)

    Landim, C.; Misturini, R.; Tsunoda, K.

    2015-09-01

    Let be an open and bounded subset of , and let be a twice continuously differentiable function. Denote by the discretization of , , and denote by the continuous-time, nearest-neighbor, random walk on which jumps from to at rate . We examine in this article the metastable behavior of among the wells of the potential F.

  5. Cyclic cosmology, conformal symmetry and the metastability of the Higgs

    Energy Technology Data Exchange (ETDEWEB)

    Bars, Itzhak [Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089-0484 (United States); Steinhardt, Paul J., E-mail: steinh@princeton.edu [California Institute of Technology, Pasadena, CA 91125 (United States); Department of Physics and Princeton Center for Theoretical Physics, Princeton University, Princeton, NJ 08544 (United States); Turok, Neil [Perimeter Institute for Theoretical Physics, Waterloo, ON N2L 2Y5 (Canada)

    2013-10-07

    Recent measurements at the LHC suggest that the current Higgs vacuum could be metastable with a modest barrier (height (10{sup 10–12} GeV){sup 4}) separating it from a ground state with negative vacuum density of order the Planck scale. We note that metastability is problematic for standard bang cosmology but is essential for cyclic cosmology in order to end one cycle, bounce, and begin the next. In this Letter, motivated by the approximate scaling symmetry of the standard model of particle physics and the primordial large-scale structure of the universe, we use our recent formulation of the Weyl-invariant version of the standard model coupled to gravity to track the evolution of the Higgs in a regularly bouncing cosmology. We find a band of solutions in which the Higgs field escapes from the metastable phase during each big crunch, passes through the bang into an expanding phase, and returns to the metastable vacuum, cycle after cycle after cycle. We show that, due to the effect of the Higgs, the infinitely cycling universe is geodesically complete, in contrast to inflation.

  6. Cyclic cosmology, conformal symmetry and the metastability of the Higgs

    Science.gov (United States)

    Bars, Itzhak; Steinhardt, Paul J.; Turok, Neil

    2013-10-01

    Recent measurements at the LHC suggest that the current Higgs vacuum could be metastable with a modest barrier (height ( GeV)4) separating it from a ground state with negative vacuum density of order the Planck scale. We note that metastability is problematic for standard bang cosmology but is essential for cyclic cosmology in order to end one cycle, bounce, and begin the next. In this Letter, motivated by the approximate scaling symmetry of the standard model of particle physics and the primordial large-scale structure of the universe, we use our recent formulation of the Weyl-invariant version of the standard model coupled to gravity to track the evolution of the Higgs in a regularly bouncing cosmology. We find a band of solutions in which the Higgs field escapes from the metastable phase during each big crunch, passes through the bang into an expanding phase, and returns to the metastable vacuum, cycle after cycle after cycle. We show that, due to the effect of the Higgs, the infinitely cycling universe is geodesically complete, in contrast to inflation.

  7. Cyclic cosmology, conformal symmetry and the metastability of the Higgs

    International Nuclear Information System (INIS)

    Bars, Itzhak; Steinhardt, Paul J.; Turok, Neil

    2013-01-01

    Recent measurements at the LHC suggest that the current Higgs vacuum could be metastable with a modest barrier (height (10 10–12 GeV) 4 ) separating it from a ground state with negative vacuum density of order the Planck scale. We note that metastability is problematic for standard bang cosmology but is essential for cyclic cosmology in order to end one cycle, bounce, and begin the next. In this Letter, motivated by the approximate scaling symmetry of the standard model of particle physics and the primordial large-scale structure of the universe, we use our recent formulation of the Weyl-invariant version of the standard model coupled to gravity to track the evolution of the Higgs in a regularly bouncing cosmology. We find a band of solutions in which the Higgs field escapes from the metastable phase during each big crunch, passes through the bang into an expanding phase, and returns to the metastable vacuum, cycle after cycle after cycle. We show that, due to the effect of the Higgs, the infinitely cycling universe is geodesically complete, in contrast to inflation

  8. Tumor ocular metastásico Metastatic ocular tumor

    Directory of Open Access Journals (Sweden)

    Martha G Domínguez Expósito

    2004-06-01

    Full Text Available El carcinoma metastásico del ojo es considerado la neoplasia maligna que más frecuente se encuentra de forma intraocular. Solo cerca del 10 % de las personas que tienen una o más lesiones metastásicas intraoculares son detectadas clínicamente antes de la muerte. A menudo, el carcinoma metastásico ocular es diagnosticado por el oftalmólogo ante la presencia de síntomas oculares. Las lesiones están localizadas con preferencia en coroides. Nos motivo a realizar la presentación de este caso la presencia de lesiones intraoculares múltiples tumorales metastásicos en un paciente cuyo síntoma de presentación fue la disminución de la agudeza visualThe eye metastatic carcinoma is considered the most frequently found intraocular malignant neoplasia. Only 10 % of the persons with one or more metastatic intraocular injuries are clinically detected before death. The metastatic ocular carcinoma is often diagnosed by the ophthalmologist in the presence of ocular symptoms. The injuries are preferably located in the choroid. The appearance of multiple metastatic intraaocular tumoral injuries in a patient whose chief complaint was the reduction of visual acuity motivated us to presente this case

  9. Colour chemistry - a study of metastable multiquark molecules

    International Nuclear Information System (INIS)

    Chan, H.-M.; Fukugita, M.; Hansson, T.H.; Hoffman, H.J.; Konishi, K.; Hoegaasen, H.; Tsou, S.T.

    1978-03-01

    A framework is proposed for treating metastable multiquark states in general, borrowing some of the chemist's concepts and terminology. Lists of 'ions' and 'bonds' are are compiled which allow one in principle to construct models of complex 'molecules' and to predict their masses and decays. (author)

  10. 235U isotope enrichment in the metastable levels of UI

    International Nuclear Information System (INIS)

    Gagne, J.M.; Demers, Y.; Dreze, C.; Pianarosa, P.

    1983-01-01

    We have used optical pumping to produce a substantial 235 U enrichment in the metastable levels of UI in the discharge afterglow of a hollow-cathode vapor generator. The measured isotope-enrichment factor for the level at 3800 cm -1 is approximately 20

  11. Metastability Thresholds for Anisotropic Bootstrap Percolation in Three Dimensions

    NARCIS (Netherlands)

    Enter, Aernout C.D. van; Fey, Anne

    In this paper we analyze several anisotropic bootstrap percolation models in three dimensions. We present the order of magnitude for the metastability thresholds for a fairly general class of models. In our proofs, we use an adaptation of the technique of dimensional reduction. We find that the

  12. Argon laser treatment of central serous chorioretinopathy

    Directory of Open Access Journals (Sweden)

    Ting- Bing Fang

    2013-04-01

    Full Text Available AIM: To observe the efficacy of the argon laser photocoagulation treatment of central serous chorioretinopathy(CSC. METHODS: The treatment groups: 18 patients(18 eyes, argon laser photocoagulation and oral jolethin, vitamin B1, inosine and venoruton tablets. Control group: 18 patients(18 eyes, oral lecithin complex iodine, vitamin B1, inosine, venoruton tablets. Foveal thickness and neuroepithelial layer detachment range were measured by optical coherence tomography(OCTbefore treatment, after 1 month and 3 months post-operation to compare the decline in value of foveal thickness and neuroepithelial layer detachment range of the two groups. RESULTS: After 1 month of treatment, the decline in value of the center foveal thickness: the value of treatment group was 256±72μm; the value of the control group was 82±57μm, and the difference of the two groups, P <0.05; the decline in value of neuroepithelial layer detachment range: the value of the treatment group was 3 548±168μm, the value of the control group was 1 520±143μm, And the difference of the two groups, P<0.05. After three months of treatment, the decline in value of the center foveal thickness: the value of treatment group was 383±75μm, the value of the control group was 312±67 μm, and the difference of the two groups, P<0.05; decline in value of neuroepithelial layer detachment range: the value of the treatment group was 4 908±172μm, the value of the control group was 4 211±153μm, and the difference of the two groups, P <0.05. The differences were statistically significant between the treatment and the control groups(two independent samples t-test. CONCLUSION:Argon laser photocoagulation treatment of CSC is an effective treatment method and can significantly shorten the course.

  13. Mass spectrometric probes of metal cluster distributions and metastable ion decay

    International Nuclear Information System (INIS)

    Parks, E.K.; Liu, K.; Cole, S.K.; Riley, S.J.

    1988-01-01

    The study of metal clusters has provided both an opportunity and a challenge to the application of mass spectrometry. These days the most often-used technique for cluster generation - laser vaporization - leads to extensive distributions of cluster sizes, from one to perhaps thousands of atoms, and most studies reported to date use excimer laser ionization and time-of-flight mass spectrometry for cluster detection. Our apparatus is a simple one-stage TOF design employing Wiley-McLauren spatial focusing and a one-meter drift tube. In a second apparatus employing a pulsed valve in the cluster source, we see asymmetric broadening of niobium cluster mass peaks under multiphoton ionization conditions, indicating metastable decay of parent cluster ions. Other studies of niobium clusters have shown no such asymmetric peaks. 2 figs

  14. Near-infrared scintillation of liquid argon

    Energy Technology Data Exchange (ETDEWEB)

    Alexander, T. [Fermilab; Escobar, C. O. [Campinas State U.; Lippincott, W. H. [Fermilab; Rubinov, P. [Fermilab

    2016-03-03

    Since the 1970s it has been known that noble gases scintillate in the near infrared (NIR) region of the spectrum (0.7 $\\mu$m < $\\lambda$; < 1.5$\\mu$m). More controversial has been the question of the NIR light yield for condensed noble gases. We first present the motivation for using the NIR scintillation in liquid argon detectors, then briefly review early as well as more recent efforts and finally show encouraging preliminary results of a test performed at Fermilab.

  15. Gasdynamic structure of free argon plasma jet

    International Nuclear Information System (INIS)

    Dunder, J.

    1973-01-01

    The paper deals with the experimental results of research conducted on the argon plasma jet. Special miniaturized water cooled Pitot probes (1.45 and 2.5 mm. dia.) were used for the measurement of the total head. The results correlate the length of the arc chamber and other main parameters of the plasma generator with the length of the core and maximum values of the total pressure and velocity in the core of the jet. For the plasma generator used for the experiments the axial and radial distributions of the pressure as well as the generalized volt-ampere dependence were obtained. (author)

  16. Sterile searches with Liquid Argon at FNAL

    CERN Document Server

    Raselli, Gian Luca

    2017-01-01

    A new Short Baseline Neutrino (SBN) experiment is in preparation at FNAL to definitely prove or exclude the existence of non-standard neutrino oscillations into sterile states. The program foresees the deployment along the Booster Neutrino Beam (BNB) of three detectors, all based on the liquid-argon time projection chamber technique. This technology has been taken to full maturity with ICARUS T600, which will act as far detector after the completion of the overhauling at CERN and its transportation to FNAL. The program foresees the data taking for three years.

  17. Energy resolution in liquid argon doped with allene

    International Nuclear Information System (INIS)

    Ichinose, H.; Doke, T.; Masuda, K.; Shibamura, E.

    1989-01-01

    Studies have been made on liquid argon as detection medium with large volume and good energy and position resolution. It is advantageous to dope liquid argon with molecules with an ionization potential lower than the energy of scintillation light. In the present work, the energy resolution for 5.305MeV alpha particles is examined, and the effect of allene added to liquid argon is investigated. Some preliminary results for 976 KeV electrons are also presented. Allene is purified by two methods: (a) small-quantity purification and (b) mass purification. Three methods are tried for mixing allene with argon. Results concerning the allene purification methods, effect of allene concentration, and allene-argon mixing methods are presented. Discussion is made of the collected charge and energy resolution. It is concluded that the addition of allene to liquid argon greatly improves the energy resolution of 5.305 MeV alpha particles. The best intrinsic resolution is 1.4 percent FWHM obtained for 4 ppm allene doped liquid argon. In the case of 976 KeV electron radiation, energy resolution is not improved by adding allene to liquid argon. The best resolution is 31 KeV FWHM obtaiend for 65ppm allene doped liquid argon. (N.K.)

  18. Bose-Einstein condensation of atomic gases

    International Nuclear Information System (INIS)

    Anglin, J. R.; Ketterle, W.

    2003-01-01

    The early experiments on Bose-Einstein condensation in dilute atomic gases accomplished three longstanding goals. First, cooling of neutral atoms into their motional state, thus subjecting them to ultimate control, limited only by Heisenberg uncertainty relation. Second, creation of a coherent sample of atoms, in which all occupy the same quantum states, and the realization of atom lasers - devices that output coherent matter waves. And third, creation of gaseous quantum fluid, with properties that are different from the quantum liquids helium-3 and helium-4. The field of Bose-Einstein condensation of atomic gases has continued to progress rapidly, driven by the combination of new experimental techniques and theoretical advances. The family of quantum degenerate gases has grown, and now includes metastable and fermionic atoms. condensates have become an ultralow-temperature laboratory for atom optics, collisional physics and many-body physics, encompassing phonons, superfluidity, quantized vortices, Josephson junctions and quantum phase transitions. (author)

  19. Formation of carbon nanostructures using acetylene, argon-acetylene and argon-hydrogen-acetylene plasmas

    International Nuclear Information System (INIS)

    Marcinauskas, L.; Grigonis, A.; Minialga, V.; Marcinauskas, L.; Valincius, V.

    2013-01-01

    The films prepared in argon-acetylene plasma are attributed to graphite-like carbon films. Addition of the hydrogen decreases growth rate and the surface roughness of the films and lead to the formation of nanocrystalline graphite. The carbon nanotubes were formed at low (≤ 450°C; p = 40 Pa) temperature in pure acetylene plasma. (authors)

  20. Hot oxygen atoms: Their generation and chemistry

    International Nuclear Information System (INIS)

    Ferrieri, R.A.; Chu, Yung Y.; Wolf, A.P.

    1987-01-01

    Oxygen atoms with energies between 1 and 10 eV have been produced through ion beam sputtering from metal oxide targets. Argon ion beams were used on Ta 2 O 5 and V 2 O 5 . Results show that some control may be exerted over the atom's kinetic energy by changing the target. Reactions of the hot O( 3 P) with cis- and trans-butenes were investigated

  1. Nucleation of metastable aragonite CaCO3 in seawater.

    Science.gov (United States)

    Sun, Wenhao; Jayaraman, Saivenkataraman; Chen, Wei; Persson, Kristin A; Ceder, Gerbrand

    2015-03-17

    Predicting the conditions in which a compound adopts a metastable structure when it crystallizes out of solution is an unsolved and fundamental problem in materials synthesis, and one which, if understood and harnessed, could enable the rational design of synthesis pathways toward or away from metastable structures. Crystallization of metastable phases is particularly accessible via low-temperature solution-based routes, such as chimie douce and hydrothermal synthesis, but although the chemistry of the solution plays a crucial role in governing which polymorph forms, how it does so is poorly understood. Here, we demonstrate an ab initio technique to quantify thermodynamic parameters of surfaces and bulks in equilibrium with an aqueous environment, enabling the calculation of nucleation barriers of competing polymorphs as a function of solution chemistry, thereby predicting the solution conditions governing polymorph selection. We apply this approach to resolve the long-standing "calcite-aragonite problem"--the observation that calcium carbonate precipitates as the metastable aragonite polymorph in marine environments, rather than the stable phase calcite--which is of tremendous relevance to biomineralization, carbon sequestration, paleogeochemistry, and the vulnerability of marine life to ocean acidification. We identify a direct relationship between the calcite surface energy and solution Mg:Ca [corrected] ion concentrations, showing that the calcite nucleation barrier surpasses that of metastable aragonite in solutions with Mg:Ca ratios consistent with modern seawater, allowing aragonite to dominate the kinetics of nucleation. Our ability to quantify how solution parameters distinguish between polymorphs marks an important step toward the ab initio prediction of materials synthesis pathways in solution.

  2. Electron scattering and transport in liquid argon

    International Nuclear Information System (INIS)

    Boyle, G. J.; Cocks, D. G.; White, R. D.; McEachran, R. P.

    2015-01-01

    The transport of excess electrons in liquid argon driven out of equilibrium by an applied electric field is revisited using a multi-term solution of Boltzmann’s equation together with ab initio liquid phase cross-sections calculated using the Dirac-Fock scattering equations. The calculation of liquid phase cross-sections extends previous treatments to consider multipole polarisabilities and a non-local treatment of exchange, while the accuracy of the electron-argon potential is validated through comparison of the calculated gas phase cross-sections with experiment. The results presented highlight the inadequacy of local treatments of exchange that are commonly used in liquid and cluster phase cross-section calculations. The multi-term Boltzmann equation framework accounting for coherent scattering enables the inclusion of the full anisotropy in the differential cross-section arising from the interaction and the structure factor, without an a priori assumption of quasi-isotropy in the velocity distribution function. The model, which contains no free parameters and accounts for both coherent scattering and liquid phase screening effects, was found to reproduce well the experimental drift velocities and characteristic energies

  3. The H1 liquid argon calorimeter system

    International Nuclear Information System (INIS)

    Andrieu, B.; Babayev, A.; Ban, J.

    1993-06-01

    The liquid argon calorimeter of the H1 detector presently taking data at the HERA ep - collider at DESY, Hamburg, is described here. The main physics requirements and the most salient design features relevant to this calorimeter are given. The aim to have smooth and hermetic calorimetric coverage over the polar angular range 4 ≤ θ ≤ 154 is achieved by a single liquid argon cryostat containing calorimeter stacks structured in wheels and octants for easy handling. The absorber materials used are lead in the electromagnetic part and stainless steel in the hadronic part. The read-out system is pipelined to reduce the dead time induced by the high trigger rate expected at the HERA collider where consecutive bunches are separated in time by 96 ns. The main elements of the calorimeter, such as the cryostat, with its associated cryogenics, the stack modules, the read-out, calibration and trigger electronics as well as the data acquisition system are described. Performance results from data taken in calibration runs with full size H1 calorimeter stacks at a CERN test beam, as well as results from data collected with the complete H1 detector using cosmic rays during the initial phase of ep operations are presented. The observed energy resolutions and linearities are well in agreement with the requirements. (orig.)

  4. Electron scattering and transport in liquid argon

    Energy Technology Data Exchange (ETDEWEB)

    Boyle, G. J.; Cocks, D. G.; White, R. D. [College of Science, Technology and Engineering, James Cook University, Townsville 4810 (Australia); McEachran, R. P. [Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200 (Australia)

    2015-04-21

    The transport of excess electrons in liquid argon driven out of equilibrium by an applied electric field is revisited using a multi-term solution of Boltzmann’s equation together with ab initio liquid phase cross-sections calculated using the Dirac-Fock scattering equations. The calculation of liquid phase cross-sections extends previous treatments to consider multipole polarisabilities and a non-local treatment of exchange, while the accuracy of the electron-argon potential is validated through comparison of the calculated gas phase cross-sections with experiment. The results presented highlight the inadequacy of local treatments of exchange that are commonly used in liquid and cluster phase cross-section calculations. The multi-term Boltzmann equation framework accounting for coherent scattering enables the inclusion of the full anisotropy in the differential cross-section arising from the interaction and the structure factor, without an a priori assumption of quasi-isotropy in the velocity distribution function. The model, which contains no free parameters and accounts for both coherent scattering and liquid phase screening effects, was found to reproduce well the experimental drift velocities and characteristic energies.

  5. NBS measurement system for natural argon-37

    International Nuclear Information System (INIS)

    Currie, L.A.; Lindstrom, R.M.

    1973-01-01

    A project to determine the cosmic-ray production rate and the natural levels of 35-day half-life 37 Ar in the atmosphere has been underway at the National Bureau of Standards for about the past year. The prime objective of this project is to determine the spatial dependence of 37 Ar production in the atmosphere, and the spatial distribution of the naturally-produced 37 Ar (observed concentrations). The results of this study are to be used, in cooperation with L. Machta (National Oceanographic and Atmospheric Administration), to derive information about atmospheric mixing. The purpose of this communication, however, is to present a general description of the various components of the measurement system. As the lowest concentrations of interest are but approximately equal to 10 -3 dpm ( 37 Ar)/l-Ar, very high sensitivity measurement techniques are required. Among the techniques which we have adopted are: quantitative separation of the noble gases from about 1 m 3 of air, using a CaC 2 reactor; gas chromatographic separation of the argon fraction; isotopic enrichment (by a factor of approximately equal to 100) of purified argon; use of specially selected low-level gas proportional counters together with massive shielding and anticoincidence meson cancellation; and the application of pulse discrimination based upon both amplitude (energy) and pulse shape. Finally, on-line computer techniques are being applied for data acquisition and system control

  6. Scaling-resistance of ruthenium- and ruthenium phosphides powders in argon and air

    International Nuclear Information System (INIS)

    Chernogorebko, V.B.; Semenov-Kobzar', A.A.; Kulik, L.Ya.

    1976-01-01

    The thermal stability of ruthenium phosphides in air diminishes as the content of phosphorus in the compound increases. The temperatures at which active oxidation of the powders starts are as follows: Ru-600, Ru 2 P-590, RuP-390, and RuP 2 -270 0 C. The oxidation of phosphorus in the phosphides proceeds in steps. The atoms of phosphorus which are most accessible to oxygen are first oxidated. Phosphorus atoms in the octahedral spaces are oxidated less easily, simultaneously with the oxidation of the ruthenium atoms. When heated in argon, Ru 2 P and RuP fuse congruently at 1,500 and 1,555 0 C respectively, while RuP 2 dissociates at 950 0 C. (author)

  7. Numerical simulation of nonequilibrium effects in an argon plasma jet

    International Nuclear Information System (INIS)

    Chang, C.H.; Ramshaw, J.D.

    1994-01-01

    Departures from thermal (translational), ionization, and excitation equilibrium in an axisymmetric argon plasma jet have been studied by two-dimensional numerical simulations. Electrons, ions, and excited and ground states of neutral atoms are represented as separate chemical species in the mixture. Transitions between excited states, as well as ionization/recombination reactions due to both collisional and radiative processes, are treated as separate chemical reactions. Resonance radiation transport is represented using Holstein escape factors to simulate both the optically thin and optically thick limits. The optically thin calculation showed significant underpopulation of excited species in the upstream part of the jet core, whereas in the optically thick calculation this region remains close to local thermodynamic equilibrium, consistent with previous experimental observations. Resonance radiation absorption is therefore an important effect. The optically thick calculation results also show overpopulations (relative to equilibrium) of excited species and electron densities in the fringes and downstream part of the jet core. In these regions, however, the electrons and ions are essentially in partial local thermodynamic equilibrium with the excited state at the electron temperature, even though the ionized and excited states are no longer in equilibrium with the ground state. Departures from partial local thermodynamic equilibrium are observed in the outer fringes and far downstream part of the jet. These results are interpreted in terms of the local relative time scales for the various physical and chemical processes occurring in the plasma

  8. Argon defect complexes in low energy Ar irradiated molybdenum

    International Nuclear Information System (INIS)

    Veen, A. van; Buters, W.T.M.; Kolk, G.J. van der; Caspers, L.M.; Armstrong, T.R.

    1982-01-01

    Thermal desorption spectrometry has been used to study the defects created in Mo irradiated along the direction with Ar ions ranging in energy from 0.1 to 2 keV. In addition to monitoring the release of the implanted Ar, additional information has been obtained by decoration of the defects with low energy helium and subsequent monitoring of the helium release. The studies show evidence that the Ar can be trapped in both substitutional sites and in a configuration in which the Ar is associated with vacancies (ArVsub(n), n >= 2). Most of the Ar implanted at high energy is released at approx. equal to 1500 K by thermal vacancy assisted diffusion. Argon trapped closer to the surface is released at lower temperatures via at least three different surface related release mechanisms. Additional results are presented on the interaction of self interstitial atoms (introduced by 100 eV Xe bombardment) with the Ar defects. Substitutional Ar is found to convert to interstitial Ar which seems to be mobile at room temperature. The Ar-vacancy complexes are found to be reduced to substitutional Ar. The results of atomistic calculations of the release mechanisms will also be presented. (orig.)

  9. About the EDF formation in a capacitively coupled argon plasma

    International Nuclear Information System (INIS)

    Tatanova, M; Thieme, G; Basner, R; Hannemann, M; Golubovskii, Yu B; Kersten, H

    2006-01-01

    The formation of the electron distribution function (EDF) in the bulk plasma of a capacitively coupled radio-frequency (rf) discharge in argon generated in the plasma-chemical reactor PULVA-INP is investigated experimentally and theoretically. Measurements of the EDF and internal plasma parameters were performed by means of a Langmuir probe at pressures of 0.5-100 Pa and discharge powers of 5-100 W. The observed EDFs have revealed a two-temperature behaviour at low pressures and evolved into a Maxwellian distribution at high gas pressures and large discharge powers. Theoretical determination of the EDF is based on the numerical solution of the Boltzmann kinetic equation in the local and non-local approaches under experimental conditions. The model includes elastic and inelastic electron-atom collisions and electron-electron interactions. Low electron temperatures and relatively high ionization degrees are the features of the PULVA-INP rf discharge. This leads to significant influence of the electron-electron collisions on the EDF formation. The modelled and measured distributions show good agreement in a wide range of discharge parameters, except for a range of low gas pressures, where the stochastic electron heating is intense. Additionally, mechanisms of the EDF formation in the dc and rf discharge were compared under similar discharge conditions

  10. About the EDF formation in a capacitively coupled argon plasma

    Energy Technology Data Exchange (ETDEWEB)

    Tatanova, M [Institute of Physics, Saint-Petersburg State University, ul. Ulianovskaja 1, 198504 Saint-Petersburg (Russian Federation); Thieme, G [Institut fur Niedertemperatur-Plasmaphysik, Friedrich-Ludwig-Jahn-Str 19, D-17489 Greifswald (Germany); Basner, R [Institut fur Niedertemperatur-Plasmaphysik, Friedrich-Ludwig-Jahn-Str 19, D-17489 Greifswald (Germany); Hannemann, M [Institut fur Niedertemperatur-Plasmaphysik, Friedrich-Ludwig-Jahn-Str 19, D-17489 Greifswald (Germany); Golubovskii, Yu B [Institute of Physics, Saint-Petersburg State University, ul. Ulianovskaja 1, 198504 Saint-Petersburg (Russian Federation); Kersten, H [Institut fur Niedertemperatur-Plasmaphysik, Friedrich-Ludwig-Jahn-Str 19, D-17489 Greifswald (Germany)

    2006-08-01

    The formation of the electron distribution function (EDF) in the bulk plasma of a capacitively coupled radio-frequency (rf) discharge in argon generated in the plasma-chemical reactor PULVA-INP is investigated experimentally and theoretically. Measurements of the EDF and internal plasma parameters were performed by means of a Langmuir probe at pressures of 0.5-100 Pa and discharge powers of 5-100 W. The observed EDFs have revealed a two-temperature behaviour at low pressures and evolved into a Maxwellian distribution at high gas pressures and large discharge powers. Theoretical determination of the EDF is based on the numerical solution of the Boltzmann kinetic equation in the local and non-local approaches under experimental conditions. The model includes elastic and inelastic electron-atom collisions and electron-electron interactions. Low electron temperatures and relatively high ionization degrees are the features of the PULVA-INP rf discharge. This leads to significant influence of the electron-electron collisions on the EDF formation. The modelled and measured distributions show good agreement in a wide range of discharge parameters, except for a range of low gas pressures, where the stochastic electron heating is intense. Additionally, mechanisms of the EDF formation in the dc and rf discharge were compared under similar discharge conditions.

  11. Aluminium Morphological Modification by Nitrogen-Argon Mixture PIII

    International Nuclear Information System (INIS)

    Munnoz-Castro, A.E.; Valencia Alvarado, R.; Penna-Eguiluz, R.; Mercado-Cabrera, A.; Barocio, S.R.; Rodriguez-Mendez, B.G.; Lopez-Callejas, R.; Piedad-Beneitez, A. de la

    2011-01-01

    With incident fluences of ∼ 10 12 atoms/cm 2 aluminium samples have been plasma immersion ion implanted with either pure nitrogen or argon/nitrogen mixtures at temperatures around 450 o C. X-ray diffraction studies have validated the formation of the cubic phase of AlN, in samples treated with both the gas mixtures and pure nitrogen. Likewise, the presence of the hexagonal phase of AlN has been detected when either pure nitrogen or a 70% N/30% Ar mixture have been used. The signature peak of AlN has also been confirmed by the Raman spectroscopy. The maximal microhardness values were found in samples treated with the mixture. The maximal roughness was achieved with the equal part mixture in all cases, although increasing with the implantation pulse width up to a 300 nm peak at 150 μs. The latter critical value remains invariant under the pure nitrogen plasma treatment, provided that implantation periods in the order of 4.5 h are carried out. (author)

  12. Argon-ion charge distributions following near-threshold ionization

    International Nuclear Information System (INIS)

    Levin, J.C.

    1990-01-01

    When an atom is photoionized in an inner shell, there are two mechanisms by which the remaining electron cortege relaxes to fill the vacancy: x-ray emission and radiationless Auger and Coster-Kronig transitions. In the former, the inner-shell hole moves to a less tightly bound orbital without increasing the number of atomic vacancies. In Auger processes, however, the energy liberated by transfer of a less-tightly-bound electron to the inner-shell vacancy is transferred to another electron which is ejected into the continuum. In this case, the charge on the residual ion increases by one. Through a series of radiative and non-radiative processes, the initial vacancy bubbles up until all vacancies arrive at the outermost shell. Due to the many possible routes by which this may occur, there can be a broad distribution of residual ion charge states characteristic of the decay of a single inner-shell vacancy. Because so many processes can contribute to each charge state, it is difficult to determine the effect of each by examining the total ion charge distribution; the total-ion charge distribution represents an average over many effects. To overcome this limitation, the author has recently measured argon-ion production as a function of both photon energy and Auger decay channel following photoionization of K-shell electrons with highly monochromatic synchrotron radiation. When measured differential in decay channel, the ion charge distributions are greatly simplified. Analysis, in progress, of these simplified distributions will permit extraction of information about relative decay rates and shakeoff effects that is obscured in the single spectra

  13. Investigation of argon ion sputtering on the secondary electron emission from gold samples

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Jing; Cui, Wanzhao, E-mail: cuiwanzhao@126.com; Li, Yun; Xie, Guibai; Zhang, Na; Wang, Rui; Hu, Tiancun; Zhang, Hongtai

    2016-09-30

    Highlights: • An “equivalent work function” is presented in this thesis to establish the relationship between SE yield and surface properties. • After sputtering, A decrease of δmax and an increase of E1 were observed with increasing Eion. • Further sputtering at higher energies broaden the SE spectra, and the equivalent work function, ϕ, increase considerably to 12.6 eV. - Abstract: Secondary electron (SE) yield, δ, is a very sensitive surface property. The values of δ often are not consistent for even identical materials. The influence of surface changes on the SE yield was investigated experimentally in this article. Argon ion sputtering was used to remove the contamination from the surface. Surface composition was monitored by X-ray photoelectron spectroscopy (XPS) and surface topography was scanned by scanning electron microscope (SEM) and atomic force microscope (AFM) before and after every sputtering. It was found that argon sputtering can remove contamination and roughen the surface. An “equivalent work function” is presented in this thesis to establish the relationship between SE yield and surface properties. Argon ion sputtering of 1.5keV leads to a significant increase of so called “work function” (from 3.7 eV to 6.0 eV), and a decrease of SE yield (from 2.01 to 1.54). These results provided a new insight into the influence of surface changes on the SE emission.

  14. Impact of Argon gas on optical and electrical properties of Carbon thin films

    Energy Technology Data Exchange (ETDEWEB)

    Usman, Arslan, E-mail: arslan.usman@gmail.com [Department of Physics, COMSATS Institute of Information Technology, Lahore (Pakistan); Rafique, M.S. [Department of Physics, University of Engineering & Technology, Lahore 54890 (Pakistan); Shaukat, S.F. [Department of Physics, COMSATS Institute of Information Technology, Lahore (Pakistan); Siraj, Khurram [Department of Physics, University of Engineering & Technology, Lahore 54890 (Pakistan); Ashfaq, Afshan [Institute of Nuclear Medicine and Oncology Lahore (INMOL), 54000 Pakistan (Pakistan); Anjum, Safia [Department of Physics, Lahore College for Women University (Pakistan); Imran, Muhammad; Sattar, Abdul [Department of Physics, COMSATS Institute of Information Technology, Lahore (Pakistan)

    2016-12-15

    Nanostructured thin films of carbon were synthesized and investigated for their electrical, optical, structural and surface properties. Pulsed Laser Deposition (PLD) technique was used for the preparation of these films under Argon gas environment. A KrF Laser (λ=248 nm) was used as source of ablation and plasma formation. It was observed that the carbon ions and the background gas environment has deep impact on the morphology as well as on the microstructure of the films. Time of Flight (TOF) method was used to determine the energies of the ablated carbon ions. The morphology of film surfaces deposited at various argon pressure was analysed using an atomic force microscope. The Raman spectroscopic measurement reveal that there is shift in phase from sp{sup 3} to sp{sup 2} and a decrease in FWHM of G band, which is a clear indication of enhanced graphitic clusters. The electrical resistivity was also reduced from 85.3×10{sup −1} to 2.57×10{sup −1} Ω-cm. There is an exponential decrease in band gap E{sub g} of the deposited films from 1.99 to 1.37 eV as a function of argon gas pressure.

  15. The effects of argon ion bombardment on the corrosion resistance of tantalum

    Science.gov (United States)

    Ramezani, A. H.; Sari, A. H.; Shokouhy, A.

    2017-02-01

    Application of ion beam has been widely used as a surface modification method to improve surface properties. This paper investigates the effect of argon ion implantation on surface structure as well as resistance against tantalum corrosion. In this experiment, argon ions with energy of 30 keV and in doses of 1 × 1017-10 × 1017 ions/cm2 were used. The surface bombardment with inert gases mainly produces modified topography and morphology of the surface. Atomic Force Microscopy was also used to patterned the roughness variations prior to and after the implantation phase. Additionally, the corrosion investigation apparatus wear was applied to compare resistance against tantalum corrosion both before and after ion implantation. The results show that argon ion implantation has a substantial impact on increasing resistance against tantalum corrosion. After the corrosion test, scanning electron microscopy (SEM) analyzed the samples' surface morphologies. In addition, the elemental composition is characterized by energy-dispersive X-ray (EDX) analysis. The purpose of this paper was to obtain the perfect condition for the formation of tantalum corrosion resistance. In order to evaluate the effect of the ion implantation on the corrosion behavior, potentiodynamic tests were performed. The results show that the corrosion resistance of the samples strongly depends on the implantation doses.

  16. Investigation of argon ion sputtering on the secondary electron emission from gold samples

    International Nuclear Information System (INIS)

    Yang, Jing; Cui, Wanzhao; Li, Yun; Xie, Guibai; Zhang, Na; Wang, Rui; Hu, Tiancun; Zhang, Hongtai

    2016-01-01

    Highlights: • An “equivalent work function” is presented in this thesis to establish the relationship between SE yield and surface properties. • After sputtering, A decrease of δmax and an increase of E1 were observed with increasing Eion. • Further sputtering at higher energies broaden the SE spectra, and the equivalent work function, ϕ, increase considerably to 12.6 eV. - Abstract: Secondary electron (SE) yield, δ, is a very sensitive surface property. The values of δ often are not consistent for even identical materials. The influence of surface changes on the SE yield was investigated experimentally in this article. Argon ion sputtering was used to remove the contamination from the surface. Surface composition was monitored by X-ray photoelectron spectroscopy (XPS) and surface topography was scanned by scanning electron microscope (SEM) and atomic force microscope (AFM) before and after every sputtering. It was found that argon sputtering can remove contamination and roughen the surface. An “equivalent work function” is presented in this thesis to establish the relationship between SE yield and surface properties. Argon ion sputtering of 1.5keV leads to a significant increase of so called “work function” (from 3.7 eV to 6.0 eV), and a decrease of SE yield (from 2.01 to 1.54). These results provided a new insight into the influence of surface changes on the SE emission.

  17. Investigation of argon ion sputtering on the secondary electron emission from gold samples

    Science.gov (United States)

    Yang, Jing; Cui, Wanzhao; Li, Yun; Xie, Guibai; Zhang, Na; Wang, Rui; Hu, Tiancun; Zhang, Hongtai

    2016-09-01

    Secondary electron (SE) yield, δ, is a very sensitive surface property. The values of δ often are not consistent for even identical materials. The influence of surface changes on the SE yield was investigated experimentally in this article. Argon ion sputtering was used to remove the contamination from the surface. Surface composition was monitored by X-ray photoelectron spectroscopy (XPS) and surface topography was scanned by scanning electron microscope (SEM) and atomic force microscope (AFM) before and after every sputtering. It was found that argon sputtering can remove contamination and roughen the surface. An ;equivalent work function; is presented in this thesis to establish the relationship between SE yield and surface properties. Argon ion sputtering of 1.5keV leads to a significant increase of so called ;work function; (from 3.7 eV to 6.0 eV), and a decrease of SE yield (from 2.01 to 1.54). These results provided a new insight into the influence of surface changes on the SE emission.

  18. Optically thick model for radiative and collisional effects in nonequilibrium argon plasma flows in a circular tube

    International Nuclear Information System (INIS)

    Shirai, Hiroyuki; Tabei, Katsuine; Koaizawa, Hisashi.

    1984-01-01

    Experimental and theoretical studies were made to gain a deeper understanding of the radiative properties of nonequilibrium argon plasma flows in a circular tube. The self-absorption effects were taken into account as rigorously as possible. Experimentally, the radial profiles of the population densities of argon atoms at the excited 4s, 4p, 5p, and 5d levels were obtained from the lateral distributions of the absolute intensities of ArI spectral lines originating from these levels. On the other hand, theoretical profiles of the population densities for the same levels were calculated based on the optically thick model for collisional and radiative processes proposed by Bates et al. and experimentally measured atom temperature, electron temperature, electron density and gas pressure. Comparison of the experimental and theoretical results showed a reasonably good agreement and the importance of the self-absorption effects. (author)

  19. Fast sampling calorimetry with solid argon ionization chambers

    International Nuclear Information System (INIS)

    Clark, E.; Linn, S.; Piekarz, H.; Wahl, H.; Womersley, J.; Hansen, S.; Hurh, P.; Rivetta, C.; Sanders, R.; Schmitt, R.; Stanek, R.; Stefanik, A.

    1992-01-01

    A proposal for the fast sampling calorimetry with solid argon as active medium and the preliminary results from the solid argon test cell are presented. The proposed test calorimeter module structure, the signal routing and the mechanical and cryogenic arrangements are also discussed

  20. Luminescence decay in condensed argon under high energy excitation

    International Nuclear Information System (INIS)

    Carvalho, M.J.; Klein, G.

    1978-01-01

    α and β particles were used to study the luminescence of condensed argon. The scintillation decay has always two components independently of the phase and the kind of the exciting particles. Decay time constants are given for solid, liquid and also gaseous argon. Changes in the relative intensity values of the two components are discussed in terms of track effects

  1. Thermal conductivity in an argon arc at atmospheric pressure

    NARCIS (Netherlands)

    Bol, L.; Timmermans, C.J.; Schram, D.C.

    1984-01-01

    The thermal conductivity of an argon plasma has been determined in a phi 5 mm wall stabilized atmospheric argon arc in the temperature range from 10000 to 16000 K. The calculations are based on the energy balance, and include non-LTE effects like ambipolar diffusion and overpopulation of the ground

  2. WARP: a double phase argon programme for dark matter detection

    International Nuclear Information System (INIS)

    Ferrari, N

    2006-01-01

    WARP (Wimp ARgon Programme) is a double phase Argon detector for Dark Matter search under construction at Laboratori Nazionali del Gran Sasso. We present recent results obtained operating a prototype with a sensitive mass of 2.3 litres deep underground

  3. Stopping Power of Solid Argon for Helium Ions

    DEFF Research Database (Denmark)

    Besenbacher, F.; Bøttiger, Jørgen; Grauersen, O.

    1981-01-01

    By means of the Rutherford-backscattering method, the stopping cross section of solid argon has been measured for 0.5–3 MeV helium ions to an accuracy of not, vert, similar3%. The results agree within the experimental accuracies with our earlier measurements for gaseous argon over the energy region...

  4. Numerical simulations of a nonequilibrium argon plasma in a shock-tube experiment

    Science.gov (United States)

    Cambier, Jean-Luc

    1991-01-01

    A code developed for the numerical modeling of nonequilibrium radiative plasmas is applied to the simulation of the propagation of strong ionizing shock waves in argon gas. The simulations attempt to reproduce a series of shock-tube experiments which will be used to validate the numerical models and procedures. The ability to perform unsteady simulations makes it possible to observe some fluctuations in the shock propagation, coupled to the kinetic processes. A coupling mechanism by pressure waves, reminiscent of oscillation mechanisms observed in detonation waves, is described. The effect of upper atomic levels is also briefly discussed.

  5. Impact of keV-energy argon clusters on diamond and graphite

    DEFF Research Database (Denmark)

    Popok, Vladimir; Samela, Juha; Nordlund, Kai

    2012-01-01

    Impact of keV-energy size-selected Arn (n = 16, 27, 41) cluster ions on diamond and graphite is studied both experimentally and by molecular dynamics simulations. For the case of diamond, relatively high cluster kinetic energies (above certain threshold) are required to produce severe radiation...... the graphene planes, significant radiation damage is already introduced by impact of clusters with low kinetic energies (a few tens of eV/atom). However, collisions of the argon clusters cause very elastic response of the graphene planes that leads to efficient closure of the craters which could be formed...

  6. Alternatives to argon for gas stopping volumes in the B194 neutron imager

    Energy Technology Data Exchange (ETDEWEB)

    Bleuel, D. L. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Anderson, S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Caggiano, J. A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Hall, J. M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Johnson, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Ratkiewicz, A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Rusnak, B. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2017-05-17

    In a recent experiment at Lawrence Berkeley National Laboratory, the 40Ar(d,p)41Ar excitation function between 3-7 MeV was measured, confirming a previous estimation that there may be an intolerable radiation dose from 41Ar production by slowing to rest 6.74 MeV deuterons in the gas cell of the neutron imaging facility being constructed in B194. Gas alternatives to argon are considered, including helium, nitrogen (N2), neon, sulfur hexafluoride (SF6), krypton, and xenon, as well as high atomic number solid backings such as tantalum.

  7. Cleaning of diffusion bonding surface by argon ion bombardment treatment

    International Nuclear Information System (INIS)

    Wang, Airu; Ohashi, Osamu; Yamaguchi, Norio; Aoki, Masanori; Higashi, Yasuo; Hitomi, Nobuteru

    2003-01-01

    The specimens of oxygen-free high conductivity copper, SUS304L stainless steel and pure iron were treated by argon ion bombardment and then were bonded by diffusion bonding method. The effects of argon ion bombardment treatment on faying surface morphology, tensile strength of bonding joints and inclusions at the fracture surface were investigated. The results showed that argon ion bombardment treatment was effective to remove the oxide film and contamination at the faying surface and improve the quality of joints. The tensile strength of the bonded joints was improved, and minimum bonding temperature to make the metallic bonding at the interface was lowered by argon ion bombardment treatment. At the joints with argon ion bombardment treatment, ductile fractured surface was seen and the amount of inclusions was obviously decreased

  8. Effect of argon addition into oxygen atmosphere on YBCO thin films deposition

    International Nuclear Information System (INIS)

    Mozhaev, P. B.; Borisenko, I. V.; Ovsyannikov, G. A.; Kuehle, A.; Bindslev-Hansen, J.; Johannes, L.; Skov, J. L.

    2002-01-01

    Multicomponent nature of the YBa 2 Cu 3 O x (YBCO) high-temperature superconductor makes difficult fabrication of smooth thin films: every local deviation from stoichiometry can result in seeding of a non-superconducting oxide particle. High density of such particles on typical YBCO thin film surface, however, presumes overall non-stoichiometry of the film. Such an effect can result from (i) non-uniform material transport from target to substrate, and (ii) re-evaporation or re-sputtering from the growing film surface. The first reason is more usual for laser ablation deposition technique, the second is typical for long sputtering deposition processes. Substitution of oxygen with argon in the deposition atmosphere improves surface quality of YBCO thin films deposited both by laser ablation and DC-sputtering at high pressure techniques. In the first case, the ablated species are scattered different ways in the oxygen atmosphere. Addition of argon decreases the inelastic scattering of barium; the proper part of Ar in the deposition atmosphere makes scattering and, hence, transport of all atoms uniform. The YBCO films deposited by DC-sputtering at high pressure technique are Ba-deficient also, but the reason is re-sputtering of Ba from the growing film as a result of negative oxygen ions bombardment. Such bombardment can lead also to chemical interaction of the deposited material with the substrate, as in the case of deposition of YBCO thin film on the CeO 2 buffer layer on sapphire. Substitution of oxygen with argon not only suppresses ion bombardment of the film, but also increases discharge stability due to presence of positive Ar + ions. The limiting factor of argon substitution is sufficient oxygenation of the growing oxide film. When oxygen partial pressure is too small, the superconducting quality of the YBCO thin film decreases and such a decrease cannot be overcome by prolonged oxygenation after deposition. (Authors)

  9. Metastable Amyloid Phases and their Conversion to Mature Fibrils

    Science.gov (United States)

    Muschol, Martin; Miti, Tatiana; Mulaj, Mentor; Schmit, Jeremy

    Self-assembly of proteins into amyloid fibrils plays a key role in both functional biological responses and pathogenic disorders which include Alzheimer's disease and type II diabetes. Amyloid fibril assembly frequently generates compact oligomeric and curvilinear polymeric intermediates which are implicated to be toxic to cells. Yet, the relation between these early-stage oligomeric aggregates and late-stage rigid fibrils, which are the hallmark structure of amyloid plaques, has remained unclear. Our measurements indicate that lysozyme amyloid oligomers and their curvilinear fibrils only form after crossing a salt and protein concentration dependent threshold. These oligomeric aggregates are structurally distinct from rigid fibrils and are metastable against nucleation and growth of rigid fibrils. Our experimental transition boundaries match well with colloidal model predictions accounting for salt-modulated charge repulsion. We also report our preliminary findings on the mechanism by which these metastable oligomeric phases are converted into stable amyloid fibrils.

  10. Metastability in spin polarised Fermi gases and quasiparticle decays

    DEFF Research Database (Denmark)

    Sadeghzadeh, Kayvan; Bruun, Georg; Lobo, Carlos

    2011-01-01

    We investigate the metastability associated with the first order transition from normal to superfluid phases in the phase diagram of two-component polarised Fermi gases.We begin by detailing the dominant decay processes of single quasiparticles.Having determined the momentum thresholds of each...... the interaction strength at which a polarised phase of molecules becomes the groundstate, to the one at which the single quasiparticle groundstate changes character from polaronic to molecular. Our argument in terms of a Fermi sea of polarons naturally suggests their use as an experimental probe. We propose...... experiments to observe the threshold of the predicted region of metastability, the interaction strength at which the quasiparticle groundstate changes character, and the decay rate of polarons....

  11. Stabilizing effect of driving and dissipation on quantum metastable states

    Science.gov (United States)

    Valenti, Davide; Carollo, Angelo; Spagnolo, Bernardo

    2018-04-01

    We investigate how the combined effects of strong Ohmic dissipation and monochromatic driving affect the stability of a quantum system with a metastable state. We find that, by increasing the coupling with the environment, the escape time makes a transition from a regime in which it is substantially controlled by the driving, displaying resonant peaks and dips, to a regime of frequency-independent escape time with a peak followed by a steep falloff. The escape time from the metastable state has a nonmonotonic behavior as a function of the thermal-bath coupling, the temperature, and the frequency of the driving. The quantum noise-enhanced stability phenomenon is observed in the investigated system.

  12. Cooperative photoinduced metastable phase control in strained manganite films

    Science.gov (United States)

    Zhang, Jingdi; Tan, Xuelian; Liu, Mengkun; Teitelbaum, S. W.; Post, K. W.; Jin, Feng; Nelson, K. A.; Basov, D. N.; Wu, Wenbin; Averitt, R. D.

    2016-09-01

    A major challenge in condensed-matter physics is active control of quantum phases. Dynamic control with pulsed electromagnetic fields can overcome energetic barriers, enabling access to transient or metastable states that are not thermally accessible. Here we demonstrate strain-engineered tuning of La2/3Ca1/3MnO3 into an emergent charge-ordered insulating phase with extreme photo-susceptibility, where even a single optical pulse can initiate a transition to a long-lived metastable hidden metallic phase. Comprehensive single-shot pulsed excitation measurements demonstrate that the transition is cooperative and ultrafast, requiring a critical absorbed photon density to activate local charge excitations that mediate magnetic-lattice coupling that, in turn, stabilize the metallic phase. These results reveal that strain engineering can tune emergent functionality towards proximal macroscopic states to enable dynamic ultrafast optical phase switching and control.

  13. Dependence of stability of metastable superconductors on copper fraction

    International Nuclear Information System (INIS)

    Elrod, S.A.; Lue, J.W.; Miller, J.R.; Dresner, L.

    1980-12-01

    The stability of composite superconductors operating in the metastable regime depends upon such factors as matrix resistivity, cooled surface dimensions, fraction of critical current, and volume fraction of stabilizer. By assuming constant thermophysical properties, we developed analytic expressions for the energy and voltage of the minimum propagating zone (MPZ). With other factors held constant, these expressions have been used to predict composite superconductor stability as a function of copper fraction: lower copper fractions lead to higher MPZ energies. MPZ voltages have been measured for three NbTi/Cu composites having different copper fractions and different critical current densities for several magnetic fields and transport currents. Experimental MPZ voltages have been used to calculate an effective heat transfer coefficient, which is subsequently used to calculate the MPZ energy. The experimental MPZ energies support the theoretical expectation that lower copper fractions lead to higher stability in the metastable regime

  14. Planktic foraminifera form their shells via metastable carbonate phases.

    Science.gov (United States)

    Jacob, D E; Wirth, R; Agbaje, O B A; Branson, O; Eggins, S M

    2017-11-02

    The calcium carbonate shells of planktic foraminifera provide our most valuable geochemical archive of ocean surface conditions and climate spanning the last 100 million years, and play an important role in the ocean carbon cycle. These shells are preserved in marine sediments as calcite, the stable polymorph of calcium carbonate. Here, we show that shells of living planktic foraminifers Orbulina universa and Neogloboquadrina dutertrei originally form from the unstable calcium carbonate polymorph vaterite, implying a non-classical crystallisation pathway involving metastable phases that transform ultimately to calcite. The current understanding of how planktic foraminifer shells record climate, and how they will fare in a future high-CO 2 world is underpinned by analogy to the precipitation and dissolution of inorganic calcite. Our findings require a re-evaluation of this paradigm to consider the formation and transformation of metastable phases, which could exert an influence on the geochemistry and solubility of the biomineral calcite.

  15. Argon activation analysis, application to dating by the potassium-argon method; Analyse par activation de l'argon. Application a la datation par la methode potassium-argon

    Energy Technology Data Exchange (ETDEWEB)

    Dumesnil, P. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1967-07-01

    Activation analysis using radiogenic argon-40 has been applied to rock-dating by the K-Ar method. The argon is extracted from the sample, purified, activated to saturation in a flux of 2 X 10{sup 13} neutrons/cm{sup 2} sec{sup -1} and measured by gamma spectroscopy. The sensitivity obtained is such that it is possible to measure amounts of argon corresponding to age of a few thousand years only. However since it has not been possible to measure the amount of pollution of radiogenic argon by atmospheric argon with any accuracy, the measurable age limit is in fact of the order of MY. The method has been applied to basalts from the Mont-Dore region. The results obtained are in fairly good agreement with geological, stratigraphic and paleomagnetic data. (author) [French] L'analyse par activation de l'argon 40 radiogenique a ete appliquee a la datation des roches par la methode K-Ar. L'argon est extrait de l'echantillon, purifie, active a saturation dans un flux de 2.10{sup 13} neutrons.cm{sup -2}.s{sup -1} et mesure en spectrometrie gamma. La sensibilite obtenue est telle qu'il est possible de mesurer des quantites d'argon correspondant a des ages de quelques milliers d'annees seulement. Cependant la correction de pollution de l'argon radiogenique par l'argon atmospherique n'ayant pu etre etablie avec precision, la limite d'age mesurable pratique est de l'ordre de 1 Ma. La methode a ete appliquee aux basaltes de la region du Mont-Dore. Les ages obtenus sont en assez bon accord avec les donnees geologiques, stratigraphiques et paleomagnetiques. (auteur)

  16. Effect of Emergency Argon on FCF Operational Incidents

    International Nuclear Information System (INIS)

    Solbrig, Charles

    2011-01-01

    The following report presents analyses of operational incidents which are considered in the safety analysis of the FCF argon cell and the effect that the operability of the emergency argon system has on the course of these incidents. The purpose of this study is to determine if the emergency argon system makes a significant difference in ameliorating the course of these incidents. Six incidents were considered. The following three incidents were analyzed. These are: 1. Cooling failing on 2. Vacuum Pump Failing on 3. Argon Supplies Failing on. In the remaining three incidents, the emergency argon supply would have no effect on the course of these transients since it would not come on during these incidents. The transients are 1. Loss of Cooling 2. Loss of power (Differs from above by startup delay till the Diesel Generators come on.) 3. Cell rupture due to an earthquake or other cause. The analyses of the first three incidents are reported on in the next three sections. This report is issued realizing the control parameters used may not be optimum, and additional modeling must be done to model the inertia of refrigeration system, but the major conclusion concerning the need for the emergency argon system is still valid. The timing of some events may change with a more accurate model but the differences between the transients with and without emergency argon will remain the same. Some of the parameters assumed in the analyses are Makeup argon supply, 18 cfm, initiates when pressure is = -6 iwg., shuts off when pressure is = -3.1 iwg. 170,000 ft3 supply. Min 1/7th always available, can be cross connected to HFEF argon supply dewar. Emergency argon supply, 900 cfm, initiates when pressure is = -8 iwg. shuts off when pressure is =-4 iwg. reservoir 220 ft3, refilled when tank farm pressure reduces to 1050 psi which is about 110 ft3.

  17. Argon activation analysis, application to dating by the potassium-argon method; Analyse par activation de l'argon. Application a la datation par la methode potassium-argon

    Energy Technology Data Exchange (ETDEWEB)

    Dumesnil, P [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1967-07-01

    Activation analysis using radiogenic argon-40 has been applied to rock-dating by the K-Ar method. The argon is extracted from the sample, purified, activated to saturation in a flux of 2 X 10{sup 13} neutrons/cm{sup 2} sec{sup -1} and measured by gamma spectroscopy. The sensitivity obtained is such that it is possible to measure amounts of argon corresponding to age of a few thousand years only. However since it has not been possible to measure the amount of pollution of radiogenic argon by atmospheric argon with any accuracy, the measurable age limit is in fact of the order of MY. The method has been applied to basalts from the Mont-Dore region. The results obtained are in fairly good agreement with geological, stratigraphic and paleomagnetic data. (author) [French] L'analyse par activation de l'argon 40 radiogenique a ete appliquee a la datation des roches par la methode K-Ar. L'argon est extrait de l'echantillon, purifie, active a saturation dans un flux de 2.10{sup 13} neutrons.cm{sup -2}.s{sup -1} et mesure en spectrometrie gamma. La sensibilite obtenue est telle qu'il est possible de mesurer des quantites d'argon correspondant a des ages de quelques milliers d'annees seulement. Cependant la correction de pollution de l'argon radiogenique par l'argon atmospherique n'ayant pu etre etablie avec precision, la limite d'age mesurable pratique est de l'ordre de 1 Ma. La methode a ete appliquee aux basaltes de la region du Mont-Dore. Les ages obtenus sont en assez bon accord avec les donnees geologiques, stratigraphiques et paleomagnetiques. (auteur)

  18. Argon Diffusion Measured in Rhyolite Melt at 100 MPa

    Science.gov (United States)

    Weldon, N.; Edwards, P. M.; Watkins, J. M.; Lesher, C. E.

    2016-12-01

    Argon diffusivity (D_{Ar} ) controls the rate and length scale of argon exchange between melt and gas phases and is used as a parameter to model noble gas fractionation during magma degassing. D_{Ar} may also be useful in geochronology to estimate the distribution of excess (non-radiogenic) atmospheric argon in lavas. Our measurements of D_{Ar} in molten anhydrous rhyolite near 1000 °C and 100 MPa add to the existing dataset. Using a rapid-quench cold seal pressure apparatus we exposed cylindrical charges drilled from a Miocene rhyolite flow near Buck Mtn., CA to a pure argon atmosphere resulting in a gradually lengthening argon concentration gradient between the saturated surface and the argon poor interior. Argon concentration was measured by electron microprobe along radial transects from the center to the surface of bisected samples. D_{Ar} was calculated for each transect by fitting relative argon concentration (as a function of distance from the surface) to Green's function (given each experiment's specific temperature, pressure and runtime). Variability (σ = 1.202{μm }^{2} /s) was smaller than in previous studies, but still greater than what is likely due to analytical or experimental uncertainty. We observed a symmetric geometric bias in the distribution of argon in our samples, possibly related to advective redistribution of argon accompanying the deformation of cylindrical charges into spheroids driven by surface tension. Average diffusivity, D_{Ar} = 4.791{μm }^{2} /s, is close to the predicted value, D_{Ar} = {μm }^{2} /s ( σ_{ \\bar{x} } = 1.576 {μm }^{2} /s), suggesting that Behrens and Zhang's (2001) empirical model is valid for anhydrous rhyolite melts to relatively higher temperatures and lower pressures. Behrens, H. and Y. Zhang (2001). "Ar diffusion in hydrous silicic melts: implications for volatile diffusion mechanisms and fractionation." Earth and Planetary Science Letters 192: 363-376.

  19. The (e,2e) spectrum of argon

    International Nuclear Information System (INIS)

    Mitroy, J.; Amos, K.; Morrison, I.

    1983-01-01

    The Plane Wave Impulse Approximation is used to analyse the experimental cross-section for the Argon (e,2e) reaction (using the non-coplanar symmetric geometry). A series of Configuration Interaction calculations for the structure of Ar I and Ar II are reported demonstrating that correlation effects have only a minor effect on the momentum distributions (which are well described by the Target Hartree-Fock Approximation). Fair agreement between the theoretical and experimental spectroscopic factors for the separation energy spectrum is obtained, and in particular the distribution of strength amongst the 3s 2 3p 4 nd 2 S/sup e/ satellite states specified by the largest calculations is in better agreement with data than that obtained with simple structure models

  20. Paschen like behavior in argon RF discharge

    International Nuclear Information System (INIS)

    Al-Jwaady, Y. I.

    2011-01-01

    A 13.56 MHz radio frequency inductively coupled discharge system is used in this work to study the relation between Argon gas pressure in the discharge chamber and the threshold breakdown RF power needed to create the discharge. Experimental results indicated that although the data involve some features related to the traditional Paschen relation used in Dc discharge, this relation cannot provide a quantitative description of experimental data. For such reason, a modified from Paschen relation is suggested. The modified relation provides good agreement with experimental data. Furthermore, it seems that the Paschen relation will have significant reflections on the behavior of the transit process from capacitive to inductive discharge. This is demonstrated by studying the transit region. (author)

  1. Neutron Inelastic Scattering Study of Liquid Argon

    Energy Technology Data Exchange (ETDEWEB)

    Skoeld, K; Rowe, J M; Ostrowski, G [Solid State Science Div., Argonne National Laboratory, Argonne, Illinois (US); Randolph, P D [Nuclear Technology Div., Idaho Nuclear Corporation, Idaho Falls, Idaho (US)

    1972-02-15

    The inelastic scattering functions for liquid argon have been measured at 85.2 K. The coherent scattering function was obtained from a measurement on pure A-36 and the incoherent function was derived from the result obtained from the A-36 sample and the result obtained from a mixture of A-36 and A-40 for which the scattering is predominantly incoherent. The data, which are presented as smooth scattering functions at constant values of the wave vector transfer in the range 10 - 44/nm, are corrected for multiple scattering contributions and for resolution effects. Such corrections are shown to be essential in the derivation of reliable scattering functions from neutron scattering data. The incoherent data are compared to recent molecular dynamics results and the mean square displacement as a function of time is derived. The coherent data are compared to molecular dynamics results and also, briefly, to some recent theoretical models

  2. Potassium-argon dating in archaeology

    Energy Technology Data Exchange (ETDEWEB)

    McDougall, I. (Australian National Univ., Canberra (Australia). Research School of Earth Sciences)

    1990-01-01

    The potassium-argon (K-Ar) isotopic dating method can provide precise and accurate numerical ages on suitable rocks, especially igneous rocks, over a wide range of age from less than 100,000 years old, with no older limit. Together with its variants, the {sup 40}Ar/{sup 39}Ar technique, the K-Ar method is very useful for the numerical age calibration of stratigraphic sequences, including those containing archaeological or fossil material, in cases where appropriate rocks for dating are present. This brief review of the basis of the K-Ar dating method and the underlying assumptions, concludes with an example of its application to the Plio-Pleistocene stratigraphic sequence in the Turkana Basin, northern Kenya. By dating alkali feldspars separated from pumice blocks in tuffaceous beds, excellent age control has been obtained for the wealth of vertebrate fossils, including hominids, as well as archaeological materials that has been found in the sequence. (author).

  3. Decadal variability and metastability in the Southern Hemisphere

    Science.gov (United States)

    O'Kane, Terence; Risbey, James; Franzke, Christian; Horenko, Illia; Monselesan, Didier

    2014-05-01

    An examination of systematic changes in the metastability of the southern hemisphere 500hPa circulation is performed using both cluster analysis techniques and split flow blocking indices. The cluster methodology is a purely data-driven approach for parametrisation whereby a multi-scale approximation to non-stationary dynamical processes is achieved through optimal sequences of locally stationary fast Vector Auto-Regressive Factor (VARX) processes and some slow (or persistent) hidden process switching between them. Comparison is made with blocking indices commonly used in weather forecasting and climate analysis to identify dynamically relevant metastable regimes in the 500hPa circulation in both reanalysis and AMIP model data sets. Our analysis characterises the metastable regime in both reanalysis and model data sets prior to 1978 as positive and negative phases of a hemispheric mid-latitude blocking state with the Southern Annular Mode (SAM) associated with a transition state. Post 1978, SAM emerges as a true metastable state replacing the negative phase of the hemispheric blocking pattern. The hidden state frequency of occurrences exhibits strong trends. The blocking pattern dominates in the early 1980s then gradually decreases. There is a corresponding increase in the SAM frequency of occurrence. This trend is largely evident in the reanalysis summer and spring but was not evident in the AMIP data set. Non-stationary cluster analysis was then further used to identify the Southern Oceans response to the systematic changes in the mid-latitude atmospheric circulation and identify dynamical regimes associated with subsurface thermocline anomalies which were found to teleconnect the Pacific and Atlantic regions of the Antarctic Circumpolar Current (ACC).

  4. flu, a metastable gene controlling surface properties of Escherichia coli.

    OpenAIRE

    Diderichsen, B

    1980-01-01

    flu, a gene of Escherichia coli K-12, was discovered and mapped between his and shiA. It is shown that flu is a metastable gene that changes frequently between the flu+ and flu states. flu+ variants give stable homogeneous suspensions, are piliated, and form glossy colonies. flu variants aggregate, fluff and sediment from suspensions, are nonpiliated, and form frizzy colonies. flu+ and flu variants can be isolated from most strains. Implications of these observations are discussed, and it is ...

  5. Automatic acquisition and shape analysis of metastable peaks

    International Nuclear Information System (INIS)

    Maendli, H.; Robbiani, R.; Kuster, Th.; Seibl, J.

    1979-01-01

    A method for automatic acquisition and evaluation of metastable peaks due to transitions in the first field-free region of a double focussing mass spectrometer is presented. The data are acquired by computer-controlled repetitive scanning of the accelerating voltage and concomitant accumulation, the evaluation made by a mathematical derivatization of the resulting curve. Examples for application of the method are given. (Auth.)

  6. Stark--Zeeman effect of metastable hydrogen molecules

    International Nuclear Information System (INIS)

    Kagann, R.H.

    1975-01-01

    The Stark effect of the N = 1 rotational level of orthohydrogen and the N = 2 rotational level of parahydrogen in the metastable c 3 PI/sub u/ electronic state has been measured using the molecular beam magnetic resonance method. The Stark effect of the metastable state is 10,000 times larger than that of the ground electronic state. The Stark effect of parahydrogen was found to be weakly dependent on static magnetic field strength, whereas the Stark effect of orthohydrogen was found to be more strongly dependent on the magnetic field strength. The Stark effect of orthohydrogen has been calculated using second-order perturbation theory with a pure Stark effect perturbation. The magnetic field dependence of the Stark effect was calculated using third-order perturbation theory with a mixed Stark--Zeeman effect double perturbation. A comparison of the experimental and theoretical values of α/sub perpendicular/ provides information on the electronic transition moment connecting the c 3 PI/sub u/ state to the a 3 Σ + /sub g/ state. The transition moment is needed to calculate the radiative lifetimes of the various vibrational levels of the c 3 PI/sub u/ state. The transition moment also enters the calculation of the quenching of this metastable state by an external electric field. There is a disagreement between theoretical predictions and the results of an experiment on the electric field quenching of the metastables. A test of the electronic transition moment may help shed light on this question. The experimental determination of the values of the transition moments allows one to test theory by comparing these values to those obtained by calculations employing ab initio wavefunctions

  7. Laboratory Infrared Spectra of Polycyclic Aromatic Nitrogen Heterocycles: Quinoline, and Phenanthridine in Solid Argon and H2O

    Science.gov (United States)

    Bernstein, M. P.; Mattioda, A. L.; Sandford, S. A.; Hudgins, D. M.

    2004-01-01

    Polycyclic aromatic hydrocarbons (PAHs) are common throughout the universe. Their detection and identification are based on telescopic infrared (IR) spectra compared with laboratory data. Polycyclic Aromatic Nitrogen Heterocycles (PANHs) are heterocyclic aromatics i.e., PAHs with carbon atoms replaced by a nitrogen atom. These molecules should be present in the interstellar medium, but have received relatively little attention. We present mid-IR spectra of two PANHs, quinoline (C9H7N), and phenanthridine (C13H9N) isolated in solid argon and frozen in solid H2O at 12 K, conditions yielding data directly comparable to astronomical observations. In contrast to simple PAHs, that do not interact strongly with solid H2O, the nitrogen atoms in PANHs are potentially capable of hydrogen bonding with H2O. Whereas the IR spectrum of phenanthridine in H2O is similar to that of the same compound isolated in an argon matrix, quinoline absorptions shift up to 16 cm(sup -1) (0.072 mm) between argon and H2O. Thus, astronomers will not always be able to rely on IR band positions of matrix isolated PANHs to correctly interpret the absorptions of PANHs frozen in H2O ice grains. Furthermore, our data suggest that relative band areas also vary, so determining column densities to better than a factor of 3 will require knowledge of the matrix in which the PANH is embedded and laboratory studies of relevant samples.

  8. Metastable growth of pure wurtzite InGaAs microstructures.

    Science.gov (United States)

    Ng, Kar Wei; Ko, Wai Son; Lu, Fanglu; Chang-Hasnain, Connie J

    2014-08-13

    III-V compound semiconductors can exist in two major crystal phases, namely, zincblende (ZB) and wurtzite (WZ). While ZB is thermodynamically favorable in conventional III-V epitaxy, the pure WZ phase can be stable in nanowires with diameters smaller than certain critical values. However, thin nanowires are more vulnerable to surface recombination, and this can ultimately limit their performances as practical devices. In this work, we study a metastable growth mechanism that can yield purely WZ-phased InGaAs microstructures on silicon. InGaAs nucleates as sharp nanoneedles and expand along both axial and radial directions simultaneously in a core-shell fashion. While the base can scale from tens of nanometers to over a micron, the tip can remain sharp over the entire growth. The sharpness maintains a high local surface-to-volume ratio, favoring hexagonal lattice to grow axially. These unique features lead to the formation of microsized pure WZ InGaAs structures on silicon. To verify that the WZ microstructures are truly metastable, we demonstrate, for the first time, the in situ transformation from WZ to the energy-favorable ZB phase inside a transmission electron microscope. This unconventional core-shell growth mechanism can potentially be applied to other III-V materials systems, enabling the effective utilization of the extraordinary properties of the metastable wurtzite crystals.

  9. Stable, metastable, and kinetically trapped amyloid aggregate phases.

    Science.gov (United States)

    Miti, Tatiana; Mulaj, Mentor; Schmit, Jeremy D; Muschol, Martin

    2015-01-12

    Self-assembly of proteins into amyloid fibrils plays a key role in a multitude of human disorders that range from Alzheimer's disease to type II diabetes. Compact oligomeric species, observed early during amyloid formation, are reported as the molecular entities responsible for the toxic effects of amyloid self-assembly. However, the relation between early-stage oligomeric aggregates and late-stage rigid fibrils, which are the hallmark structure of amyloid plaques, has remained unclear. We show that these different structures occupy well-defined regions in a peculiar phase diagram. Lysozyme amyloid oligomers and their curvilinear fibrils only form after they cross a salt and protein concentration-dependent threshold. We also determine a boundary for the onset of amyloid oligomer precipitation. The oligomeric aggregates are structurally distinct from rigid fibrils and are metastable against nucleation and growth of rigid fibrils. These experimentally determined boundaries match well with colloidal model predictions that account for salt-modulated charge repulsion. The model also incorporates the metastable and kinetic character of oligomer phases. Similarities and differences of amyloid oligomer assembly to metastable liquid-liquid phase separation of proteins and to surfactant aggregation are discussed.

  10. Metastability at the Yield-Stress Transition in Soft Glasses

    Directory of Open Access Journals (Sweden)

    Matteo Lulli

    2018-05-01

    Full Text Available We study the solid-to-liquid transition in a two-dimensional fully periodic soft-glassy model with an imposed spatially heterogeneous stress. The model we consider consists of droplets of a dispersed phase jammed together in a continuous phase. When the peak value of the stress gets close to the yield stress of the material, we find that the whole system intermittently tunnels to a metastable “fluidized” state, which relaxes back to a metastable “solid” state by means of an elastic-wave dissipation. This macroscopic scenario is studied through the microscopic displacement field of the droplets, whose time statistics displays a remarkable bimodality. Metastability is rooted in the existence, in a given stress range, of two distinct stable rheological branches, as well as long-range correlations (e.g., large dynamic heterogeneity developed in the system. Finally, we show that a similar behavior holds for a pressure-driven flow, thus suggesting possible experimental tests.

  11. ArgonCube: a Modular Approach for Liquid Argon TPC Neutrino Detectors for Near Detector Environments

    CERN Document Server

    Auger, M; Sinclair, JR

    2017-01-01

    Liquid Argon Time Projection Chambers (LAr TPCs) are an ideal detector candidate for future neutrino oscillation physics experiments, underground neutrino observatories and proton decay searches. A large international project based on this technology is currently under consideration at the future LBNF/DUNE facility in the United States. That particular endeavor would be on the very large mass scale of 40~kt. Following diverse and long standing R\\&D work conducted over several years, with contributions from international collaborators, we propose a novel LAr TPC based on a fully-modular, innovative design, ArgonCube. ArgonCube will demonstrate that LAr TPCs are a viable detector technology for high-energy and high-multiplicity environments, such as the DUNE near detector. Necessary R\\&D work is proceeding along two main pathways; the first, aimed at the demonstration of modular detector design and the second, at the exploration of new signal readout methods. This two-pronged approach has provided a hig...

  12. The drift velocity of excess electrons in fluid methane, argon and mixtures of methane and argon

    International Nuclear Information System (INIS)

    Engels, J.M.L.

    1979-01-01

    A description is given of an experimental investigation of the drift velocity of excess electrons in fluid methane at temperatures between 91K and 215K, and at pressures up to 65X10 5 Pa. These measurements that have become possible especially due to the improved purification techniques of the liquids under investigation. The purification prevents the electron from being captured too soon by an electron-impurity. From the results of the measurements in methane it appeared that in some respects the behaviour of excess electrons in methane is qualitatively similar to that in argon. For this reason a number of measurements of the electron drift velocity have been carried out in argon and in mixtures of methane and argon as well. A detailed description of the experimental set-up is presented. The excess electrons are generated with a high-voltage electron gun, which produces a pulse of highly energetic electrons. A fraction of these electrons enters the liquid sample by passing through a thin metal foil which separates the liquid sample and the vacuum present in the electron gun. At the same time the foil is used as one of two plane-parallel electrodes of the measuring capacitor in which the drift velocity of the excess electrons is to be measured. (Auth.)

  13. Atomic quasi-Bragg-diffraction in a magnetic field

    NARCIS (Netherlands)

    Domen, K.F.E.M.; Jansen, M.A.H.M.; Dijk, van W.; Leeuwen, van K.A.H.

    2009-01-01

    We report on a technique to split an at. beam coherently with an easily adjustable splitting angle. In our expt. metastable helium atoms in the |{1s2s}3S1 M=1 state diffract from a polarization gradient light field formed by counterpropagating .sigma.+ and .sigma.- polarized laser beams in the

  14. Laser techniques for spectroscopy of core-excited atomic levels

    Science.gov (United States)

    Harris, S. E.; Young, J. F.; Falcone, R. W.; Rothenberg, J. E.; Willison, J. R.

    1982-01-01

    We discuss three techniques which allow the use of tunable lasers for high resolution and picosecond time scale spectroscopy of core-excited atomic levels. These are: anti-Stokes absorption spectroscopy, laser induced emission from metastable levels, and laser designation of selected core-excited levels.

  15. On the dependence of structural and sensing properties of sputtered MoO{sub 3} thin films on argon gas flow

    Energy Technology Data Exchange (ETDEWEB)

    Khojier, K., E-mail: k_khojier@yahoo.com [Department of Physics, Chalous Branch, Islamic Azad University, Chalous (Iran, Islamic Republic of); Savaloni, H. [Department of Physics, University of Tehran, North Kargar Street, Tehran (Iran, Islamic Republic of); Zolghadr, S. [Department of Physics, Faculty of Science, Central Tehran Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of)

    2014-11-30

    Highlights: • MoO{sub 3} thin films are sputter coated and their structure are analyzed. • Effect of argon gas flow on the structural and some properties is studied. • CO sensing ability of MoO{sub 3} increases with argon gas flow. • MoO{sub 3} nano-strain decreases with argon gas flow. - Abstract: Nitrogen and carbon oxides (CO, NO and NO{sub 2}), released from combustion facilities and automobiles, are known to be extremely harmful to the human body and also are the main cause of air pollution. Therefore, effective methods to monitor and suppress the carbon and nitrogen oxides have been highly demanded for atmospheric environmental measurements and controls. It is known that molybdenum oxide (MoO{sub 3}) can be a good semiconductor material for use as a gas sensor in monitoring CO, NO and NO{sub 2}. In this paper we report the structural characteristics and sensing properties of the sputtered MoO{sub 3} thin films as a function of argon gas flow. MoO{sub 3} thin films were deposited by DC reactive magnetron sputtering technique on glass substrates at different argon gas flows in the range of 5–20 sccm. X-ray diffraction (XRD) analysis was used for studying crystallographic structure. XRD results showed that all of our films were of polycrystalline structure and of α-MoO{sub 3} stable orthorhombic phase. Results also showed that crystallite size increases while compressive nano-strain in the structure of the films decreases with increasing the argon gas flow. Atomic force microscope and the field emission scanning electron microscope studies showed granular structures for all samples, which increased in size consistent with the XRD results, with argon gas flow, while the surface roughness of the films also increased with argon gas flow. Chemical composition study showed optimum reaction between oxygen and molybdenum atoms for films produced at 15 sccm flow of argon gas. The electrical response of samples was measured in the vacuum and the CO

  16. Kinetic analysis of rare gas metastable production and optically pumped Xe lasers

    Science.gov (United States)

    Demyanov, A. V.; Kochetov, I. V.; Mikheyev, P. A.; Azyazov, V. N.; Heaven, M. C.

    2018-01-01

    Optically pumped all-rare-gas lasers use metastable rare gas atoms as the lasing species in mixtures with He or Ar buffer gas. The metastables are generated in a glow discharge, and we report model calculations for the optimal production of Ne*, Ar*, Kr* and Xe*. Discharge efficiency was estimated by solving the Boltzmann equation. Laser efficiency, gain and output power of the CW optically pumped Xe laser were assessed as functions of heavier rare gas content, pressure, optical pump intensity and the optical path length. It was found that, for efficient operation the heavier rare gas content has to be of the order of one percent or less, and the total pressure—in the range 0.3-1.5 atm. Output power and specific discharge power increase approximately linearly with pump intensity over the output range from 300-500 W cm-2. Ternary mixtures Xe:Ar:He were found to be the most promising. Total laser efficiency was found to be nearly the same for pumping the 2p8 or 2p9 state, reaching 61%-70% for a pump intensity of ~720 W cm-2 when the Xe fraction was in the range 0.001 ÷ 0.01 and Ar fraction—0.1 ÷ 0.5. However, when the 2p8 state was pumped, the maximum total efficiency occurred at larger pressures than for pumping of the 2p9 state. The discharge power density required to sustain a sufficient Xe* number density was in the range of tens of watts per cubic centimeter for 50% Ar in the mixture.

  17. Limited mobility of argon in a metamorphic terrain

    Energy Technology Data Exchange (ETDEWEB)

    Foland, K A [Pennsylvania Univ., Philadelphia (USA). Dept. of Geology

    1979-06-01

    Excess /sup 40/Ar in biotite from some relatively anhydrous charnockitic rocks in the Appalachian Piedmont indicates limited mobility or argon. Biotite from the Arden pluton of the granulite-facies Wilmington Complex apparently formed as a retrograde product at the expense of pyroxene and K-feldspar Rb-Sr ages of biotite from all rocks are approximately 365 Myr. The same micas have apparent K-Ar ages which range from about 365-590 Mye, six of which clearly exceed the Sr isotope whole-rock date of 500 Myr. They contain variable amounts of excess /sup 40/Ar incorporated during crystallization or recrystallization of biotite at about 365 Myr ago. None of the other minerals appears to contain significant amounts of excess argon. The K-Ar apparent ages show strong, positive correlation with whole-rock K concentrations. These relations yield a correlation between excess argon in the biotite phase and rock potassium. This suggests that excess /sup 40/Ar in biotite is of local derivation and is due to an imprint of the local argon activity. If the amount incorporated is roughly proportional to the prevailing argon partial pressure then substantial differences in psub(Ar) existed. Argon did not have a uniform chemical potential over large rock volumes. Analysis of closely spaced samples suggests different argon activity over the scale of less than 10 m. This implies restricted transport of Ar and is probably due to very low effective permeability of the anhydrous assemblages.

  18. Argon laser induced changes to the carbonate content of enamel

    International Nuclear Information System (INIS)

    Ziglo, M.J.; Nelson, A.E.; Heo, G.; Major, P.W.

    2009-01-01

    Argon laser irradiation can be used to cure orthodontic brackets onto teeth in significantly less time than conventional curing lights. In addition, it has been shown that the argon laser seems to impart a demineralization resistance to the enamel. The purpose of this study was to use surface science techniques to ascertain if this demineralization resistance is possibly a result of a decrease in the carbonate content of enamel. Eleven mandibular third molars previously scheduled for extraction were collected and used in the present study. The teeth were sectioned in two and randomly assigned to either the argon laser (457-502 nm; 250 mW cm -2 ) or the control (no treatment) group. The sections assigned to the argon laser group were cured for 10 s and analyzed. To exaggerate any potential changes the experimental sections were then exposed to a further 110 s of argon laser irradiation. Surface analysis was performed using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results showed no statistically significant change in the carbonate content of enamel after argon laser irradiation (p > 0.05). Thus, it is suggested that any demineralization resistance imparted to the enamel surface by argon laser irradiation is not due to alterations in carbonate content.

  19. Argon laser induced changes to the carbonate content of enamel

    Energy Technology Data Exchange (ETDEWEB)

    Ziglo, M.J. [Orthodontic Graduate Program, Faculty of Medicine and Dentistry, University of Alberta, Private Practice, Regina, Saskatchewan (Canada); Nelson, A.E., E-mail: aenelson@dow.com [Department of Chemical and Materials Engineering, Faculty of Engineering, University of Alberta (Canada); Heo, G.; Major, P.W. [Orthodontic Graduate Program, Faculty of Medicine and Dentistry, University of Alberta (Canada)

    2009-05-15

    Argon laser irradiation can be used to cure orthodontic brackets onto teeth in significantly less time than conventional curing lights. In addition, it has been shown that the argon laser seems to impart a demineralization resistance to the enamel. The purpose of this study was to use surface science techniques to ascertain if this demineralization resistance is possibly a result of a decrease in the carbonate content of enamel. Eleven mandibular third molars previously scheduled for extraction were collected and used in the present study. The teeth were sectioned in two and randomly assigned to either the argon laser (457-502 nm; 250 mW cm{sup -2}) or the control (no treatment) group. The sections assigned to the argon laser group were cured for 10 s and analyzed. To exaggerate any potential changes the experimental sections were then exposed to a further 110 s of argon laser irradiation. Surface analysis was performed using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results showed no statistically significant change in the carbonate content of enamel after argon laser irradiation (p > 0.05). Thus, it is suggested that any demineralization resistance imparted to the enamel surface by argon laser irradiation is not due to alterations in carbonate content.

  20. Argon laser induced changes to the carbonate content of enamel

    Science.gov (United States)

    Ziglo, M. J.; Nelson, A. E.; Heo, G.; Major, P. W.

    2009-05-01

    Argon laser irradiation can be used to cure orthodontic brackets onto teeth in significantly less time than conventional curing lights. In addition, it has been shown that the argon laser seems to impart a demineralization resistance to the enamel. The purpose of this study was to use surface science techniques to ascertain if this demineralization resistance is possibly a result of a decrease in the carbonate content of enamel. Eleven mandibular third molars previously scheduled for extraction were collected and used in the present study. The teeth were sectioned in two and randomly assigned to either the argon laser (457-502 nm; 250 mW cm -2) or the control (no treatment) group. The sections assigned to the argon laser group were cured for 10 s and analyzed. To exaggerate any potential changes the experimental sections were then exposed to a further 110 s of argon laser irradiation. Surface analysis was performed using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results showed no statistically significant change in the carbonate content of enamel after argon laser irradiation ( p > 0.05). Thus, it is suggested that any demineralization resistance imparted to the enamel surface by argon laser irradiation is not due to alterations in carbonate content.

  1. Ghost imaging with atoms

    Science.gov (United States)

    Khakimov, R. I.; Henson, B. M.; Shin, D. K.; Hodgman, S. S.; Dall, R. G.; Baldwin, K. G. H.; Truscott, A. G.

    2016-12-01

    Ghost imaging is a counter-intuitive phenomenon—first realized in quantum optics—that enables the image of a two-dimensional object (mask) to be reconstructed using the spatio-temporal properties of a beam of particles with which it never interacts. Typically, two beams of correlated photons are used: one passes through the mask to a single-pixel (bucket) detector while the spatial profile of the other is measured by a high-resolution (multi-pixel) detector. The second beam never interacts with the mask. Neither detector can reconstruct the mask independently, but temporal cross-correlation between the two beams can be used to recover a ‘ghost’ image. Here we report the realization of ghost imaging using massive particles instead of photons. In our experiment, the two beams are formed by correlated pairs of ultracold, metastable helium atoms, which originate from s-wave scattering of two colliding Bose-Einstein condensates. We use higher-order Kapitza-Dirac scattering to generate a large number of correlated atom pairs, enabling the creation of a clear ghost image with submillimetre resolution. Future extensions of our technique could lead to the realization of ghost interference, and enable tests of Einstein-Podolsky-Rosen entanglement and Bell’s inequalities with atoms.

  2. A popular metastable omega phase in body-centered cubic steels

    Energy Technology Data Exchange (ETDEWEB)

    Ping, D.H., E-mail: ping.de-hai@nims.go.jp [National Institute for Materials Science, Sengen 1-2-1, Tsukuba 305-0047 (Japan); Geng, W.T., E-mail: geng@ustb.edu.cn [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China)

    2013-05-15

    Steel remains to be one of the most common structural materials in the world as human civilization advances from the Iron Age to the ongoing Silicon Age. Our knowledge of its microstructure evolution and structure–performance relationship is nevertheless still incomplete. We report the observation and characterization of a long ignored metastable phase formed in steels with body-centered cubic (bcc) structure using both transmission electron microscopy and density functional theory calculations. This ω phase has a hexagonal structure and coherent interface with the matrix: a{sub ω} = √2 × a{sub bcc} and c{sub ω} = √3/2 × a{sub bcc}. It is 3.6% smaller in volume and 0.18 eV higher in energy than bcc-Fe, with atoms in alternating close- and loose-packed layers couple anti-ferromagnetically. Carbon plays a crucial role in promoting bcc to ω transformation. At a concentration higher than 4 at.% they tend to segregate from the bcc matrix to the ω-phase; at about 14 at.%, they can induce bcc to ω transformation; and finally at 25 at.%, they stabilize the ω phase as ω-Fe{sub 3}C. The ω phase in bcc Fe can serve as sinks for vacancies, H, and He atoms, leading to improved resistance of martensitic steels to irradiation damage. - Highlights: ► A long-ignored metastable ω phase in body-centered cubic (bcc) steel. ► The ω phase has hexagonal structure with lattice parameters a{sub ω} = √2 × a{sub bcc} and c{sub ω} = √3/2 × a{sub bcc}. ► Carbon enrichment is found to play a crucial role on the bcc-to-ω phase transformation. ► The ω phase is strongly related to the martensitic transformation and twinning structure. ► The ω phase in bcc Fe can serve as sinks for vacancies, H, and He atoms.

  3. Ionizing collisions: a new diagnostic for Bose-Einstein condensates of metastable helium

    International Nuclear Information System (INIS)

    Sirjean, O.

    2003-06-01

    At this writing, metastable helium (23S1) is the only example of Bose-Einstein condensation of an atom in an excited electronic state. The corresponding internal energy permits efficient and fast electronic detection of the atoms using a micro-channel plate detector (MCP). Moreover, this energy is responsible for ionizing collisions inside the magnetically trapped cloud (Penning ionization). These ions are also easily detected by the MCP. This thesis begins by describing the characteristics of the MCP detector. Next, the experimental procedure to achieve Bose-Einstein condensation is presented. These preliminaries are followed by a description of the experiments performed in order to determine the origin of the ions produced and by a presentation of some of the new experimental possibilities provided by the ion signal. For clouds with a low enough density, ions are mainly produced by collisions with the residual gas, and the signal is proportional to the number of trapped atoms. For clouds with a sufficiently high density, for example close to the condensation threshold, ions are mainly produced by 2- and 3-body collisions. In this case, the ion signal is also related to the density of the cloud. Depending on the density, the signal gives a real-time and 'non-destructive' measurement of these different characteristics. In particular, we have shown it is a valuable indicator of the onset of condensation, because it signals the sudden increase of density which then occurs. By studying the ion rate versus the density and the number of atoms for pure condensates and for thermal clouds at critical temperature, we have measured the collision rate constants for these ionizing processes. Our results are in agreement with theoretical predictions. (author)

  4. Nuclear dynamics in the metastable phase of the solid acid caesium hydrogen sulfate.

    Science.gov (United States)

    Krzystyniak, Maciej; Drużbicki, Kacper; Fernandez-Alonso, Felix

    2015-12-14

    High-resolution spectroscopic measurements using thermal and epithermal neutrons and first-principles calculations within the framework of density-functional theory are used to investigate the nuclear dynamics of light and heavy species in the metastable phase of caesium hydrogen sulfate. Within the generalised-gradient approximation, extensive calculations show that both 'standard' and 'hard' formulations of the Perdew-Burke-Ernzerhof functional supplemented by Tkatchenko-Scheffler dispersion corrections provide an excellent description of the known structure, underlying vibrational density of states, and nuclear momentum distributions measured at 10 and 300 K. Encouraged by the agreement between experiment and computational predictions, we provide a quantitative appraisal of the quantum contributions to nuclear motions in this solid acid. From this analysis, we find that only the heavier caesium atoms reach the classical limit at room temperature. Contrary to naïve expectation, sulfur exhibits a more pronounced quantum character relative to classical predictions than the lighter oxygen atom. We interpret this hitherto unexplored nuclear quantum effect as arising from the tighter binding environment of this species in this technologically relevant material.

  5. Energy barriers between metastable states in first-order quantum phase transitions

    Science.gov (United States)

    Wald, Sascha; Timpanaro, André M.; Cormick, Cecilia; Landi, Gabriel T.

    2018-02-01

    A system of neutral atoms trapped in an optical lattice and dispersively coupled to the field of an optical cavity can realize a variation of the Bose-Hubbard model with infinite-range interactions. This model exhibits a first-order quantum phase transition between a Mott insulator and a charge density wave, with spontaneous symmetry breaking between even and odd sites, as was recently observed experimentally [Landig et al., Nature (London) 532, 476 (2016), 10.1038/nature17409]. In the present paper, we approach the analysis of this transition using a variational model which allows us to establish the notion of an energy barrier separating the two phases. Using a discrete WKB method, we then show that the local tunneling of atoms between adjacent sites lowers this energy barrier and hence facilitates the transition. Within our simplified description, we are thus able to augment the phase diagram of the model with information concerning the height of the barrier separating the metastable minima from the global minimum in each phase, which is an essential aspect for the understanding of the reconfiguration dynamics induced by a quench across a quantum critical point.

  6. Adsorption on metal oxides Studies with the metastable impact electron spectroscopy

    CERN Document Server

    Krischok, S; Kempter, V

    2002-01-01

    An overview is given on the application of metastable impact electron spectroscopy, in combination with UPS, to the study of clean magnesia and titania surfaces and their interaction with metal atoms and small molecules. The mechanisms for metal adsorption on reducible (titania) and non-reducible (magnesia) substrates are different: while on titania the metal atom often bonds by electron transfer to Ti3d states, it is hybridization of the adsorbate and anion wavefunctions which accounts for the bonding on MgO. In the case of H sub 2 O, molecular adsorption takes place both on MgO and TiO sub 2; on the other hand, water-alkali coadsorption leads to hydroxide formation. In the case of CO sub 2 , chemisorption takes place in form of carbonate (CO sub 3) species. These originate from the CO sub 2 interaction with O sup 2 sup - surface anions. While for CaO chemisorption takes place at regular oxygen sites, for MgO this occurs at low-coordinated oxygen ions only; for TiO sub 2 chemisorption requires alkali coadsor...

  7. Adsorption on metal oxides: Studies with the metastable impact electron spectroscopy

    International Nuclear Information System (INIS)

    Krischok, S.; Hoefft, O.; Kempter, V.

    2002-01-01

    An overview is given on the application of metastable impact electron spectroscopy, in combination with UPS, to the study of clean magnesia and titania surfaces and their interaction with metal atoms and small molecules. The mechanisms for metal adsorption on reducible (titania) and non-reducible (magnesia) substrates are different: while on titania the metal atom often bonds by electron transfer to Ti3d states, it is hybridization of the adsorbate and anion wavefunctions which accounts for the bonding on MgO. In the case of H 2 O, molecular adsorption takes place both on MgO and TiO 2 ; on the other hand, water-alkali coadsorption leads to hydroxide formation. In the case of CO 2 , chemisorption takes place in form of carbonate (CO 3 ) species. These originate from the CO 2 interaction with O 2- surface anions. While for CaO chemisorption takes place at regular oxygen sites, for MgO this occurs at low-coordinated oxygen ions only; for TiO 2 chemisorption requires alkali coadsorption

  8. Shear viscosity of liquid argon and liquid rubidium

    International Nuclear Information System (INIS)

    Chiakwelu, O.

    1978-01-01

    A direct evaluation of the shear viscosity coefficient for models of liquid rubidium and liquid argon is presented by neglecting the cross-terms in the autocorrelation function of the transverse component of the momentum stress tensor. The time dependence of the shear viscosity for liquid argon is found to display a long decaying tail in qualitative agreement with a computer calculation of Levesque et al. However, the numerical values of the shear viscosity coefficients are smaller than the experimentally determined values of about 45% for liquid rubidium and 35% for liquid argon

  9. Properties of excited xenon atoms in a plasma display panel

    International Nuclear Information System (INIS)

    Uhm, Han S.; Hong, Byoung H.; Oh, Phil Y.; Choi, Eun H.

    2009-01-01

    The luminance efficiency of a plasma display panel is directly related to the vacuum ultraviolet (VUV) light that is emitted from excited xenon (Xe) atoms and molecules. It is therefore necessary to investigate the properties of excited xenon atoms. This study presents experimental data associated with the behavior of excited xenon atoms in a PDP discharge cell and compares the data with the theoretical results obtained using an analytical model. The properties of excited xenon atoms in the discharge cells of a plasma display panel are investigated by measuring the excited atom density through the use of laser absorption spectroscopy. The density of the excited xenon atoms increases from zero, reaches its peak, and decreases with time in the discharge cells. The profile of the excited xenon atoms is also studied in terms of the xenon mole fraction. The typical density of the excited xenon atoms in the metastable state is on the order of 10 13 atoms per cubic cm.

  10. Cryosorption of helium on argon frost in Tokamak Fusion Test Reactor neutral beamlines

    International Nuclear Information System (INIS)

    Kamperschroer, J.H.; Cropper, M.B.; Dylla, H.F.; Garzotto, V.; Dudek, L.E.; Grisham, L.R.; Martin, G.D.; O'Connor, T.E.; Stevenson, T.N.; von Halle, A.; Williams, M.D.; Kim, J.

    1990-01-01

    Helium pumping on argon frost has been investigated on Tokamak Fusion Test Reactor (TFTR) neutral beam injectors and shown to be viable for limited helium beam operation. Maximum pumping speeds are ∼25% less than those measured for pumping of deuterium. Helium pumping efficiency is low, >20 argon atoms are required to pump each helium atom. Adsorption isotherms are exponential and exhibit a twofold increase in adsorption capacity as the cryopanel temperature is reduced from 4.3 K to 3.7 K. Pumping speed was found to be independent of cryopanel temperature over the temperature range studied. After pumping a total of 2000 Torr l of helium, the beamline base pressure rose to 2x10 -5 Torr from an initial value of 10 -8 Torr. Accompanying this three order of magnitude increase in pressure was a modest 40% decrease in pumping speed. The introduction of 168 Torr l of deuterium prior to helium injection reduced the pumping speed by a factor of two with no decrease in adsorption capacity

  11. Cryosorption of helium on argon frost TFTR [Tokamak Fusion Test Reactor] neutral beamlines

    International Nuclear Information System (INIS)

    Kamperschroer, J.H.; Cropper, M.B.; Dylla, H.F.

    1989-11-01

    Helium pumping on argon frost has been investigated on TFTR neutral beam injectors and shown to be viable for limited helium beam operation. Maximum pumping speeds are ∼ 25% less than those measured for pumping of deuterium. Helium pumping efficiency is low, > 20 argon atoms are required to pump each helium atom. Adsorption isotherms are exponential and exhibit a two-fold increase in adsorption capacity as the cryopanel temperature is reduced from 4.3 K to 3.7 K. Pumping speed was found to be independent of cryopanel temperature over the temperature range studied. After pumping a total of 2000 torr-l of helium, the beamline base pressure rose to 2x10 -5 torr from an initial value of 10 -8 torr. Accompanying this three order of magnitude increase in pressure was a modest 40% decrease in pumping speed. The introduction of 168 torr-l of deuterium prior to helium injection reduced the pumping speed by a factor of two with no decrease in adsorption capacity. 29 refs., 7 figs

  12. Compilation of electron collision excitation cross sections for neutral argon; Compilacion de resultados de secciones eficaces de excitacion para niveles del Argon neutro

    Energy Technology Data Exchange (ETDEWEB)

    Blanco, F

    1993-07-01

    The present work presents a compilation and critical analysis of the available data on electron collision excitation cross sections for neutral Argon levels. This study includes: 1.- A detailed description in intermediate coupling for all the levels belonging the 20 configurations 3p5 ns (n=4to 12), np(n=4to8) and nd(n=3to8)of neutral Argon. 2.- Calculation of the electron collision excitation cross sections in Born and Born-Oppenheimer-Ochkur approximations for all the levels in the 14 configurations 3p5 ns (n=4 to 7), np (n=4 to 7) and nd (n=3 to 8). 3.- comparison and discussion of the compiled data. These are the experimental and theoretical values available from the literature, and those from this work. 4.- Analysis of the regularities and systematic behaviors in order to determine which values can be considered more reliable. It is show that the concept of one electron cross section results quite useful for this purpose. In some cases it has been possible to obtain in this way approximate analytical expressions interpolating the experimental data. 5.- All the experimental and theoretical values studied are graphically presented and compared. 6.- The last part of the work includes a listing of several general purpose programs for Atomic Physics calculations developed for this work. (Author) 35 refs.

  13. Effect of argon gas flow rate on properties of film electrodes prepared by thermal vacuum evaporation from synthesized Cu{sub 2}SnSe{sub 3} source

    Energy Technology Data Exchange (ETDEWEB)

    Sabli, Nordin; Talib, Zainal Abidin; Yunus, Wan Mahmood Mat [Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang (Malaysia); Zainal, Zulkarnain [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang (Malaysia); Hilal, Hikmat S. [SSERL, Department of Chemistry An-Najah N. University, PO Box 7, Nablus, West Bank (Country Unknown); Fujii, Masatoshi [Department of Molecular Science, School of Medicine, Shimane University, Izumo, Shimane, 693-8501 (Japan)

    2014-03-05

    This work describes a new technique to enhance photoresponse of metal chalcogenide-based semiconductor film electrodes deposited by thermal vacuum evaporation under argon gas flow from synthesized Cu{sub 2}SnSe{sub 3} sources. SnSe formation with Cu-doped was obtained under higher argon gas flow rate (V{sub A} = 25 cm{sup 3}/min). Higher value of photoresponse was observed for films deposited under V{sub A} = 25 cm{sup 3}/min which was 9.1%. This finding indicates that Cu atoms inside the SnSe film were important to increase carrier concentrations that promote higher photoresponse.

  14. Determination of the effective radiative lifetimes of the 6 3P1 atomic mercury level in low-pressure mercury discharges

    International Nuclear Information System (INIS)

    van de Weijer, P.; Cremers, R.M.M.

    1984-01-01

    Experiments are described in which low-pressure mercury, mercury-argon and mercury-krypton discharges were irradiated with a dye laser pulse at 365.5 nm, thus exciting mercury atoms from the metastable 6 3 P 2 level to the 6 3 D 2 level. The 6 3 D 2 level decays radiatively to the 6 P levels. By recording the time dependence of the overpopulation in the 6 3 P 1 and the 6 1 P 1 level at the fluorescence signals at 254 nm and 185 nm, respectively, the effective radiative lifetime of these levels were determined. The effective radiative lifetime of the 6 3 P 1 level was measured in the k 0 R regime 0.1-500. The 6 1 P 1 lifetime was determined for the following discharge conditions: tube diameter 10-36 mm, mercury density 7.10 18 -2.10 21 m -3 , and noble gas pressure 0, 130, 400 Pa

  15. Liquid Argon Calorimeter performance at High Rates

    CERN Document Server

    Seifert, F; The ATLAS collaboration

    2013-01-01

    The expected increase of luminosity at HL-LHC by a factor of ten with respect to LHC luminosities has serious consequences for the signal reconstruction, radiation hardness requirements and operations of the ATLAS liquid argon calorimeters in the endcap, respectively forward region. Small modules of each type of calorimeter have been built and exposed to a high intensity proton beam of 50 GeV at IHEP/Protvino. The beam is extracted via the bent crystal technique, offering the unique opportunity to cover intensities ranging from $10^6$ p/s up to $3\\cdot10^{11}$ p/s. This exceeds the deposited energy per time expected at HL-LHC by more than a factor of 100. The correlation between beam intensity and the read-out signal has been studied. The data show clear indications of pulse shape distortion due to the high ionization build-up, in agreement with MC expectations. This is also confirmed from the dependence of the HV currents on beam intensity.

  16. Collisional destruction of fast hydrogen Rydberg atoms

    International Nuclear Information System (INIS)

    King, M.R.

    1984-01-01

    A new modulated electric field technique was developed to study Rydberg atom destruction processes in a fast beam. The process of destruction of a band of Rydberg atom destruction of a band of Rydberg atoms through the combined processes of ionization, excitation, and deexcitation was studied for collisions with gas targets. Rydberg atoms of hydrogen were formed by electron capture, and detected by field ionization. The modulated field technique described proved to be an effective technique for producing a large signal for accurate cross section measurements. The independent particle model for Rydberg atom destruction processes was found to hold well for collisions with molecular nitrogen, argon, and carbon dioxide. The resonances in the cross sections for the free electron scattering with these targets were found to also occur in Rydberg destruction. Suggestions for future investigations of Rydberg atom collision processes in the fast beam regime are given

  17. Combined transmission electron microscope and ion channeling study of metastable metal alloys formed by ion implantation

    International Nuclear Information System (INIS)

    Cullis, A.G.; Borders, J.A.; Hirvonen, J.K.; Poate, J.M.

    1977-01-01

    Recently, ion implantation has been used to produce metastable alloy layers with a range of structures from crystalline substitutional solid solutions to amorphous. The technique offers the possibility of producing metastable metal layers with unique physical properties. Its application in the formation of alloys exhibiting different although complementary types of metastability is described. The metal combinations chosen (Ag-Cu and Ta-Cu) show little mutual solubility under equilibrium conditions

  18. Neutrino Event Reconstruction in a Liquid Argon TPC

    Energy Technology Data Exchange (ETDEWEB)

    Barker, Gary, E-mail: G.J.Barker@Warwick.ac.uk [Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL (United Kingdom)

    2011-07-25

    We present some preliminary findings and results from activities in Europe and the USA working towards an automated, algorithmic, reconstruction of particle interactions in liquid argon time projection chambers.

  19. Improvement of helium characteristics using argon in cylindrical ion source

    International Nuclear Information System (INIS)

    Abdel salam, F.W.; El-Khabeary, H.; Abdel reheem, A.M.; Kassem, N.E.; Ahmed, M.M.

    2004-01-01

    the discharge characteristics of pure helium gas were measured at different pressures in the range of 10 -4 torr. in order o improve its characteristics, argon gas was added . different percentages of argon gas ,1%,2%,3%,4%,5%,10% and 20% were used at constant values of pressures . Measurements of the efficiency of the cylindrical ion source in case of adding different percentages of argon gas to pure helium gas were made . an optimum value of the output ion beam current was obtained when 2% argon gas was added to pure helium gas . an output ion beam current of 105 μA was obtained at a pressure of 7X10 -4 torr inside the vacuum chamber and discharge current of 0.6 m A

  20. Phenomenological modeling of argon Z-pinch implosions

    International Nuclear Information System (INIS)

    Whitney, K.G.; Thornhill, J.W.; Deeney, C.; LePell, P.D.; Coulter, M.C.

    1992-01-01

    The authors investigate some of the effects of plasma turbulence on the K-shell emission dynamics of argon gas puff Z-pinch implosions. The increases that turbulence produces in the plasma viscosity, heat conductivity, and electrical resistivity are modeled phenomenologically using multipliers for these quantities in the MHD calculations. The choice of multipliers was made by benchmarking a 1-D MHD simulation of a Physics International Inc. argon gas puff experiment against the inferred densities and temperatures achieved in the experiment. These multipliers were then used to study the parametric dependence of the K-shell emission on the energy input to the argon plasma for a fixed mass loading. Comparisons between turbulent and non-turbulent argon implosions are made

  1. Characterization of DC argon plasma jet at atmospheric pressure

    International Nuclear Information System (INIS)

    Yan Jianhua; Ma Zengyi; Pan Xinchao; Cen Kefa; Bruno, C

    2006-01-01

    An original DC double anode plasma torch operating with argon at atmospheric pressure which provides a long time and highly stable plasma jet is analyzed through its electrical and optical signals. Effects of gas flow rate and current intensity on the arc dynamics behaviour are studied using standard diagnostic tools such as FFT and correlation function. An increasing current-voltage characteristic is reported for different argon flow rates. It is noted that the takeover mode is characteristic for argon plasma jet and arc fluctuations in our case are mainly induced by the undulation of torch power supply. Furthermore, the excitation temperatures and electron densities of the plasma jet inside and outside the arc chamber have been determined by means of optical emission spectroscopy (OES). The criteria for the existence of local thermodynamic equilibrium (LTE) in plasma is then discussed. The results show that argon plasma jet at atmospheric pressure under our experimental conditions is close to LTE. (authors)

  2. Dependences of the van der Waals atom-wall interaction on atomic and material properties

    International Nuclear Information System (INIS)

    Caride, A.O.; Klimchitskaya, G.L.; Mostepanenko, V.M.; Zanette, S.I.

    2005-01-01

    The 1%-accurate calculations of the van der Waals interaction between an atom and a cavity wall are performed in the separation region from 3 nm to 150 nm. The cases of metastable He * and Na atoms near metal, semiconductor, and dielectric walls are considered. Different approximations to the description of wall material and atomic dynamic polarizability are carefully compared. The smooth transition to the Casimir-Polder interaction is verified. It is shown that to obtain accurate results for the atom-wall van der Waals interaction at short separations with an error less than 1% one should use the complete optical-tabulated data for the complex refractive index of the wall material and the accurate dynamic polarizability of an atom. The obtained results may be useful for the theoretical interpretation of recent experiments on quantum reflection and Bose-Einstein condensation of ultracold atoms on or near surfaces of different kinds

  3. Electronic and atomic impacts on large clusters

    International Nuclear Information System (INIS)

    Gspann, J.

    1982-01-01

    Describing first the generation and properties of molecular beams of large Van der Waals clusters such as speed distribution, cluster size distribution, and internal temperature of the clusters, the review then features the results of electronic impacts on large clusters: metastable electronic cluster excitations, ejection of positive cluster ions of less than 100 atoms from much larger parent clusters, and ionization of the large clusters. Atomic impacts at thermal energies are treated with respect to the scattering cross section of the clusters, their drag coefficient in free molecular flow, and the peculiarities of impacts on helium clusters of either isotope. (Auth.)

  4. Metastable Features of Economic Networks and Responses to Exogenous Shocks.

    Directory of Open Access Journals (Sweden)

    Ali Hosseiny

    Full Text Available It is well known that a network structure plays an important role in addressing a collective behavior. In this paper we study a network of firms and corporations for addressing metastable features in an Ising based model. In our model we observe that if in a recession the government imposes a demand shock to stimulate the network, metastable features shape its response. Actually we find that there exists a minimum bound where any demand shock with a size below it is unable to trigger the market out of recession. We then investigate the impact of network characteristics on this minimum bound. We surprisingly observe that in a Watts-Strogatz network, although the minimum bound depends on the average of the degrees, when translated into the language of economics, such a bound is independent of the average degrees. This bound is about 0.44ΔGDP, where ΔGDP is the gap of GDP between recession and expansion. We examine our suggestions for the cases of the United States and the European Union in the recent recession, and compare them with the imposed stimulations. While the stimulation in the US has been above our threshold, in the EU it has been far below our threshold. Beside providing a minimum bound for a successful stimulation, our study on the metastable features suggests that in the time of crisis there is a "golden time passage" in which the minimum bound for successful stimulation can be much lower. Hence, our study strongly suggests stimulations to arise within this time passage.

  5. A statistical physics of stationary and metastable states

    International Nuclear Information System (INIS)

    Cabo, A; González, A; Curilef, S; Cabo-Bizet, N G; Vera, C A

    2011-01-01

    We present a generalization of Gibbs statistical mechanics designed to describe a general class of stationary and metastable equilibrium states. It is assumed that the physical system maximizes the entropy functional S subject to the standard conditions plus an extra conserved constraint function F, imposed to force the system to remain in the metastable configuration. After requiring additivity for two quasi-independent subsystems, and the commutation of the new constraint with the density matrix ρ, it is argued that F should be a homogeneous function of ρ, at least for systems in which the spectrum is sufficiently dense to be considered as continuous. Therefore, surprisingly, the analytic form of F turns out to be of the kind F(p i ) = p i q , where the p i are the eigenvalues of the density matrix and q is a real number to be determined. Thus, the discussion identifies the physical relevance of Lagrange multiplier constraints of the Tsallis kind and their q parameter, as enforced by the additivity of the constraint F which fixes the metastable state. An approximate analytic solution for the probability density is found for q close to unity. The procedure is applied to describe the results from the plasma experiment of Huang and Driscoll. For small and medium values of the radial distance, the measured density is predicted with a precision similar to that achieved by minimal enstrophy and Tsallis procedures. Also, the particle density is predicted at all the radial positions. Thus, the discussion gives a solution to the conceptual difficulties of the two above mentioned approaches as applied to this problem, which both predict a non-analytic abrupt vanishing of the density above a critical radial distance

  6. Stimulated transitions in resonant atom Majorana mixing

    Science.gov (United States)

    Bernabéu, José; Segarra, Alejandro

    2018-02-01

    Massive neutrinos demand to ask whether they are Dirac or Majorana particles. Majorana neutrinos are an irrefutable proof of physics beyond the Standard Model. Neutrinoless double electron capture is not a process but a virtual Δ L = 2 mixing between a parent A Z atom and a daughter A ( Z - 2) excited atom with two electron holes. As a mixing between two neutral atoms and the observable signal in terms of emitted two-hole X-rays, the strategy, experimental signature and background are different from neutrinoless double beta decay. The mixing is resonantly enhanced for almost degeneracy and, under these conditions, there is no irreducible background from the standard two-neutrino channel. We reconstruct the natural time history of a nominally stable parent atom since its production either by nature or in the laboratory. After the time periods of atom oscillations and the decay of the short-lived daughter atom, at observable times the relevant "stationary" states are the mixed metastable long-lived state and the non-orthogonal short-lived excited state, as well as the ground state of the daughter atom. We find that they have a natural population inversion which is most appropriate for exploiting the bosonic nature of the observed atomic transitions radiation. Among different observables of the atom Majorana mixing, we include the enhanced rate of stimulated X-ray emission from the long-lived metastable state by a high-intensity X-ray beam: a gain factor of 100 can be envisaged at current XFEL facilities. On the other hand, the historical population of the daughter atom ground state can be probed by exciting it with a current pulsed optical laser, showing the characteristic absorption lines: the whole population can be excited in a shorter time than typical pulse duration.

  7. Sputtering of copper (110) by 3 keV argon - a computer simulation

    International Nuclear Information System (INIS)

    Weygandt, A.; King, B.V.

    1998-01-01

    The aims of this study are to investigate the angular distribution of atoms sputtered from {110} surface of a copper monocrystal due to normal incidence 3 keV Argon impact as well as to examine the change of sputtering behaviour with temperature from 0 K to 670 K. We have used the Molecular Dynamics (MD) code SPUT93 to study sputtering. In MD codes Newton's equations of motion are solved simultanously for all atoms of a crystal. The forces acting on a particle are found from derivatives of a model potential function. For the present study an embedded atom method (EAM) potential was used. It was found that the total sputter yield for the warm crystal (670K) of 3.13 ± 0.03 is in agreement with experimental results and indicate that the temperature of the target has generally no direct influence on the sputtering yield. It was estimated that heating the crystal only causes more uniform emission. It was also found that ejection due to the collisions between atoms in the top layers along closed-packed directions become important. The mechanisms which determine the angular distributions of atoms sputtered from a copper crystal were identified

  8. Studies on EOS of shock-generated argon plasmas

    International Nuclear Information System (INIS)

    Wang Fanhou; Jing Fuqian

    2001-01-01

    The equation of state for argon plasma, covering the thermodynamic states of 10000-30000 K in temperature and 0.0133-0.166 GPa in pressure, is computed using the Saha model and Debye-Huckel correction. Comparisons of the measured EOS with the calculated ones demonstrate the Saha model and Debye-Huckel correction can be used to well describe the essential behavior of argon plasma under the thermodynamic condition above-mentioned

  9. Resonances in the potential scattering and decay of metastable states

    International Nuclear Information System (INIS)

    Batsch, J.

    1975-04-01

    The analytic properties of the S-matrix in the complex energy plane are reviewed for potential scattering with particular attention to resonance scattering and decay of metastable states. For a one dimensional model potential with a potential barrier and a repulsive core exact formulas are derived for the energy and width of a resonance in terms of the scattering amplitudes of the barrier and the repulsive core alone. For narrow resonances simple and intuitive results are obtained, which are applied to semiclassical cases where the WKB approximation is valid. (orig.) [de

  10. Investigating the Metastability of Clathrate Hydrates for Energy Storage

    Energy Technology Data Exchange (ETDEWEB)

    Koh, Carolyn Ann [Colorado School of Mines, Golden, CO (United States)

    2014-11-18

    Important breakthrough discoveries have been achieved from the DOE award on the key processes controlling the synthesis and structure-property relations of clathrate hydrates, which are critical to the development of clathrate hydrates as energy storage materials. Key achievements include: (i) the discovery of key clathrate hydrate building blocks (stable and metastable) leading to clathrate hydrate nucleation and growth; (ii) development of a rapid clathrate hydrate synthesis route via a seeding mechanism; (iii) synthesis-structure relations of H2 + CH4/CO2 binary hydrates to control thermodynamic requirements for energy storage and sequestration applications; (iv) discovery of a new metastable phase present during clathrate hydrate structural transitions. The success of our research to-date is demonstrated by the significant papers we have published in high impact journals, including Science, Angewandte Chemie, J. Am. Chem. Soc. Intellectual Merits of Project Accomplishments: The intellectual merits of the project accomplishments are significant and transformative, in which the fundamental coupled computational and experimental program has provided new and critical understanding on the key processes controlling the nucleation, growth, and thermodynamics of clathrate hydrates containing hydrogen, methane, carbon dioxide, and other guest molecules for energy storage. Key examples of the intellectual merits of the accomplishments include: the first discovery of the nucleation pathways and dominant stable and metastable structures leading to clathrate hydrate formation; the discovery and experimental confirmation of new metastable clathrate hydrate structures; the development of new synthesis methods for controlling clathrate hydrate formation and enclathration of molecular hydrogen. Broader Impacts of Project Accomplishments: The molecular investigations performed in this project on the synthesis (nucleation & growth)-structure-stability relations of clathrate

  11. Metastable carbon in two chondritic porous interplanetary dust particles

    International Nuclear Information System (INIS)

    Rietmeijer, F.J.M.; Mackinnon, I.D.R.

    1987-01-01

    An analytical electron microscope study is presented on carbonaceous material in two chondritic porous aggregates, W7029* A and W7010* A2, from the Johnson Space Center Cosmic Dust Collection. The finding of well-ordered carbon-2H (lonsdaleite) in the two aggregates suggests that a record of hydrocarbon carbonization may be preserved in these materials. This carbon is a metastable phase resulting from hydrous pyrolysis below 300-350 0 C and may be a precursor to poorly graphitized carbons in primitive extra terrestrial materials. (UK)

  12. Light-induced metastable structural changes in hydrogenated amorphous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Fritzsche, H. [Univ. of Chicago, IL (United States)

    1996-09-01

    Light-induced defects (LID) in hydrogenated amorphous silicon (a-Si:H) and its alloys limit the ultimate efficiency of solar panels made with these materials. This paper reviews a variety of attempts to find the origin of and to eliminate the processes that give rise to LIDs. These attempts include novel deposition processes and the reduction of impurities. Material improvements achieved over the past decade are associated more with the material`s microstructure than with eliminating LIDs. We conclude that metastable LIDs are a natural by-product of structural changes which are generally associated with non-radiative electron-hole recombination in amorphous semiconductors.

  13. Simple model for the dynamics towards metastable states

    International Nuclear Information System (INIS)

    Meijer, P.H.E.; Keskin, M.; Bodegom, E.

    1986-01-01

    Circumstances under which a quenched system will freeze in a metastable state are studied in simple systems with long-range order. The model used is the time-dependent pair approximation, based on the most probable path (MPP) method. The time dependence of the solution is shown by means of flow diagrams. The fixed points and other features of the differential equations in time are independent of the choice of the rate constants. It is explained qualitatively how the system behaves under varying descending temperatures: the role of the initial conditions, the dependence on the quenching rate, and the response to precooling

  14. Spin dynamics in tunneling decay of a metastable state

    OpenAIRE

    Ban, Yue; Sherman, E. Ya.

    2012-01-01

    We analyze spin dynamics in the tunneling decay of a metastable localized state in the presence of spin-orbit coupling. We find that the spin polarization at short time scales is affected by the initial state while at long time scales both the probability- and the spin density exhibit diffraction-in-time phenomenon. We find that in addition to the tunneling time the tunneling in general can be characterized by a new parameter, the tunneling length. Although the tunneling length is independent...

  15. Direct gauge mediation of uplifted metastable supersymmetry breaking in supergravity

    International Nuclear Information System (INIS)

    Maru, Nobuhito

    2010-01-01

    We propose a direct gauge mediation model based on an uplifted metastable supersymmetry (SUSY) breaking coupled to supergravity. A constant superpotential plays an essential role to fix the moduli as well as breaking SUSY and R symmetry and the cancellation of the cosmological constant. Gaugino masses are generated at leading order of SUSY breaking scale, and comparable to the sfermion masses as in the ordinary gauge mediation. The Landau pole problem for QCD coupling can be easily solved since more than half of messengers become superheavy, which are heavier than the grand unified theory (GUT) scale.

  16. Transport of excess electrons in dense dielectric fluids. Phenomenological interpretation and application to a one-dimensional argon fluid

    International Nuclear Information System (INIS)

    Leycuras, A.; Larour, J.

    1978-01-01

    The main results about the drift velocities of excess electrons in dense argon are summarized. The weaknesses of the available theories are mainly due to poor information concerning the electron-atom potential during an atom-atom collision. The drift velocities, as a function of the applied electric field present the following features at high fields: the drift velocity reaches a limit that is at most one order of magnitude larger than the sound velocity at the same density. These remarks and the attractive nature of the electron-atom potential suggest a transport model, the collisional transfer model analog to the one applied to the determination of the sound velocity. Drift velocities obtained with this model applied to a one-dimensional molecular dynamics simulation are presented [fr

  17. Dielectric barrier discharge plasma atomizer for hydride generation atomic absorption spectrometry—Performance evaluation for selenium

    Energy Technology Data Exchange (ETDEWEB)

    Duben, Ondřej [Institute of Analytical Chemistry of the CAS, v.v.i., Veveří 97, CZ-602 00 Brno (Czech Republic); Faculty of Science, Department of Analytical Chemistry, Charles University in Prague, Hlavova 8, Prague, CZ 128 43 Czech Republic (Czech Republic); Boušek, Jaroslav [Faculty of Electrical Engineering and Communications, Brno University of Technology, Technická 1058/10, 61600 Brno (Czech Republic); Dědina, Jiří [Institute of Analytical Chemistry of the CAS, v.v.i., Veveří 97, CZ-602 00 Brno (Czech Republic); Kratzer, Jan, E-mail: jkratzer@biomed.cas.cz [Institute of Analytical Chemistry of the CAS, v.v.i., Veveří 97, CZ-602 00 Brno (Czech Republic)

    2015-09-01

    Atomization of selenium hydride in a quartz dielectric barrier discharge (DBD) atomizer was optimized and its performance was compared to that of the externally heated quartz multiatomizer. Argon was found as the best DBD discharge gas employing a flow rate of 75 ml min{sup −1} Ar while the DBD power was optimized at 14 W. The detection limits reached 0.24 ng ml{sup −1} Se in the DBD and 0.15 ng ml{sup −1} Se in the multiatomizer. The tolerance of DBD to interferences is even better than with the multiatomizer. - Highlights: • SeH{sub 2} atomization in a dielectric barrier discharge (DBD) was optimized for AAS. • Atomizer performance was compared for DBD and externally heated quartz atomizer. • Detection limits were quantified and interferences were studied in both atomizers. • Atomization efficiency in the DBD was estimated.

  18. Electron densities and energies of a guided argon streamer in argon and air environments

    International Nuclear Information System (INIS)

    Hübner, S; Hofmann, S; Van Veldhuizen, E M; Bruggeman, P J

    2013-01-01

    In this study we report the temporally and spatially resolved electron densities and mean energies of a guided argon streamer in ambient argon and air obtained by Thomson laser scattering. The plasma is driven by a positive monopolar 3.5 kV pulse, with a pulse width of 500 ns and a frequency of 5 kHz which is synchronized with the high repetition rate laser system. This configuration enables us to use the spatial and temporal stability of the guided streamer to accumulate a multitude of laser/plasma shots by a triple grating spectrometer equipped with an ICCD camera and to determine the electron parameters. We found a strong initial n e -overshoot with a maximum of 7 × 10 19  m −3 and a mean electron energy of 4.5 eV. This maximum is followed by a fast decay toward the streamer channel. Moreover, a 2D distribution of the electron density is obtained which exhibits a peculiar mushroom-like shape of the streamer head with a diameter significantly larger than that of the emission profile. A correlation of the width of the streamer head with the expected pre-ionization channel is found. (paper)

  19. Surface modification of argon/oxygen plasma treated vulcanized ethylene propylene diene polymethylene surfaces for improved adhesion with natural rubber

    International Nuclear Information System (INIS)

    Basak, Ganesh C.; Bandyopadhyay, Abhijit; Neogi, Sudarsan; Bhowmick, Anil K.

    2011-01-01

    Vulcanized ethylene propylene diene polymethylene (EPDM) rubber surface was treated in a radio frequency capacitatively coupled low pressure argon/oxygen plasma to improve adhesion with compounded natural rubber (NR) during co-vulcanization. The plasma modified surfaces were analyzed by means of contact angle measurement, surface energy, attenuated total reflection-infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray sulfur mapping and atomic force microscopy. Several experimental variables such as plasma power, length of exposure time and composition of the argon-oxygen gas mixture were considered. It was delineated that plasma treatment changed both surface composition and roughness, and consequently increased peel strength. The change in surface composition was mainly ascribed to the formation of C-O and -C=O functional groups on the vulcanized surfaces. A maximum of 98% improvement in peel strength was observed after plasma treatment.

  20. Surface modification of argon/oxygen plasma treated vulcanized ethylene propylene diene polymethylene surfaces for improved adhesion with natural rubber

    Energy Technology Data Exchange (ETDEWEB)

    Basak, Ganesh C. [Rubber Technology Centre, Indian Institute of Technology, Kharagpur 721302 (India); Bandyopadhyay, Abhijit [Department of Polymer Science and Technology, University of Calcutta, Calcutta 700 009 (India); Neogi, Sudarsan [Department of Chemical Engineering, Indian Institute of Technology, Kharagpur 721302 (India); Bhowmick, Anil K., E-mail: anilkb@rtc.iitkgp.ernet.in [Rubber Technology Centre, Indian Institute of Technology, Kharagpur 721302 (India)

    2011-01-15

    Vulcanized ethylene propylene diene polymethylene (EPDM) rubber surface was treated in a radio frequency capacitatively coupled low pressure argon/oxygen plasma to improve adhesion with compounded natural rubber (NR) during co-vulcanization. The plasma modified surfaces were analyzed by means of contact angle measurement, surface energy, attenuated total reflection-infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray sulfur mapping and atomic force microscopy. Several experimental variables such as plasma power, length of exposure time and composition of the argon-oxygen gas mixture were considered. It was delineated that plasma treatment changed both surface composition and roughness, and consequently increased peel strength. The change in surface composition was mainly ascribed to the formation of C-O and -C=O functional groups on the vulcanized surfaces. A maximum of 98% improvement in peel strength was observed after plasma treatment.

  1. Surface wet-ability modification of thin PECVD silicon nitride layers by 40 keV argon ion treatments

    Science.gov (United States)

    Caridi, F.; Picciotto, A.; Vanzetti, L.; Iacob, E.; Scolaro, C.

    2015-10-01

    Measurements of wet-ability of liquid drops have been performed on a 30 nm silicon nitride (Si3N4) film deposited by a PECVD reactor on a silicon wafer and implanted by 40 keV argon ions at different doses. Surface treatments by using Ar ion beams have been employed to modify the wet-ability. The chemical composition of the first Si3N4 monolayer was investigated by means of X-ray Photoelectron Spectroscopy (XPS). The surface morphology was tested by Atomic Force Microscopy (AFM). Results put in evidence the best implantation conditions for silicon nitride to increase or to reduce the wet-ability of the biological liquid. This permits to improve the biocompatibility and functionality of Si3N4. In particular experimental results show that argon ion bombardment increases the contact angle, enhances the oxygen content and increases the surface roughness.

  2. Novel criterion for formation of metastable phase from undercooled melt

    International Nuclear Information System (INIS)

    Kuribayashi, Kazuhiko; Nagashio, Kosuke; Niwata, Kenji; Kumar, M.S. Vijaya; Hibiya, Taketoshi

    2007-01-01

    Undercooling a melt facilitates the preferential nucleation of a metastable phase. In the present study, the formation of metastable phases from undercooled melts was considered from the viewpoint of the competitive nucleation criterion. The classical nucleation theory shows us that the most critical factor for forming a critical nucleus is the interface free energy σ. Furthermore, Spaepen's negentropic model on σ generated the role of the scaling factor α that depends on the polyhedral order in the liquid and solid phases prominent in simple liquids such as the melt of monoatomic metals. In ionic materials such as oxides, however, in which oxygen polyhedrons including a cation at their center are the structural units both in the solid and liquid phases, the entropy of fusion, rather than α, can be expected to become dominant in the determination of σ. In accordance with this idea, using REFeO 3 as the model material (where RE denotes rare-earth elements) the entropy-undercooling regime criterion was proposed and verified

  3. Negative pion trapping by metastable state in liquid helium

    International Nuclear Information System (INIS)

    Nakamura, S.N.; Iwasaki, M.; Outa, H.

    1991-11-01

    We found long-lived metastable states of stopped π - 's in liquid helium by measuring time spectra of two different delayed products: 1) protons emitted after π - absorption by 4 He nuclei and 2) 70-MeV electrons originating from free π - → e - (ν e )-bar decay. The lifetime and fraction of delayed π - absorption obtained by emitted protons are 7.26±0.12 nsec and 1.66±0.05%, respectively. The free-decay fraction was calculated to be 0.64±0.03% from this result, which is consistent with the observed free-decay fraction of π e2 decay. These results imply that 2.30±0.07% of stopped π - are trapped in metastable states which have an overall lifetime of 10.1±0.2 nsec. The same experiment and analysis were performed for stopped π - in liquid neon. No evidence for trapping was found in liquid neon. (author)

  4. Isothermal α″ formation in β metastable titanium alloys

    International Nuclear Information System (INIS)

    Aeby-Gautier, E.; Settefrati, A.; Bruneseaux, F.; Appolaire, B.; Denand, B.; Dehmas, M.; Geandier, G.; Boulet, P.

    2013-01-01

    Highlights: ► Isothermal kinetics of orthorhombic α″ formation is characterized by HEXRD. ► Cell parameters of parent and product phases are obtained. ► Partitioning of solutes during the transformation and the ageing is discussed. -- Abstract: Thanks to time resolved high energy X-ray diffraction, isothermal decomposition of β metastable phase was studied, directly after solution treatment in the β temperature range, for temperatures ranging from 300 to 450 °C for two beta metastable alloys (Ti 17 and Ti 5553). The formation of an orthorhombic α″ phase is clearly identified at the beginning of the transformation whatever the alloy studied. If transformation occurs at the higher temperature an evolution of α″ is observed toward the hexagonal α phase. The phase amounts and the mean cell parameters of each phase were quantified by the Rietveld refinement method. The obtained cell parameters evolutions and the orthorhombicity of α″ are discussed. Moreover, the orthorhombicity of α″ compared to that obtained for stress induced martensite may indicate a slight partitioning of solutes in isothermal α″

  5. Isothermal α″ formation in β metastable titanium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Aeby-Gautier, E., E-mail: Elisabeth.Gautier@mines.inpl-nancy.fr [Institut Jean Lamour, UMR CNRS Nancy Université, UPVM 7198, Nancy (France); Settefrati, A. [Institut Jean Lamour, UMR CNRS Nancy Université, UPVM 7198, Nancy (France); Airbus Operations, Materials and Processes, Toulouse (France); Bruneseaux, F. [Institut Jean Lamour, UMR CNRS Nancy Université, UPVM 7198, Nancy (France); Appolaire, B. [Laboratoire d’Etudes des Microstructures ONERA – CNRS Chatillon (France); Denand, B.; Dehmas, M.; Geandier, G.; Boulet, P. [Institut Jean Lamour, UMR CNRS Nancy Université, UPVM 7198, Nancy (France)

    2013-11-15

    Highlights: ► Isothermal kinetics of orthorhombic α″ formation is characterized by HEXRD. ► Cell parameters of parent and product phases are obtained. ► Partitioning of solutes during the transformation and the ageing is discussed. -- Abstract: Thanks to time resolved high energy X-ray diffraction, isothermal decomposition of β metastable phase was studied, directly after solution treatment in the β temperature range, for temperatures ranging from 300 to 450 °C for two beta metastable alloys (Ti 17 and Ti 5553). The formation of an orthorhombic α″ phase is clearly identified at the beginning of the transformation whatever the alloy studied. If transformation occurs at the higher temperature an evolution of α″ is observed toward the hexagonal α phase. The phase amounts and the mean cell parameters of each phase were quantified by the Rietveld refinement method. The obtained cell parameters evolutions and the orthorhombicity of α″ are discussed. Moreover, the orthorhombicity of α″ compared to that obtained for stress induced martensite may indicate a slight partitioning of solutes in isothermal α″.

  6. Fluxes, hierarchies, and metastable vacua in supersymmetric field theories

    International Nuclear Information System (INIS)

    Bruemmer, F.

    2008-01-01

    This thesis concerns topics both in low-energy effective field theories from type IIB superstring flux compactifications and in four-dimensional, rigidly supersymmetric gauge theories. We introduce flux compactifications with so-called ''warped throat'' regions, which lead to large hierarchies of scales in the effective four-dimensional theory. The correspondence between a particular such throat and a five-dimensional Randall-Sundrum-like model is established. We shown how certain string-theoretic features of the compactification, such as moduli stabilization by fluxes or the presence of an unstabilized Kaehler modulus, are incorporated in the five-dimensional picture. The KKLT construction for metastable de Sitter vacua is reviewed, as well as some possible modifications involving spontaneous F-term supersymmetry breaking. For KKLT-like models with their hidden sector localized inside a throat, the mediation of supersymmetry breaking to the visible sector is investigated. We review the mechanism of mixed modulus-anomaly mediation, and show that there can be additional equally important gravity-mediated contributions. We finally turn to the ISS model of metastable dynamical supersymmetry breaking in four dimensions, and present a renormalizable extension which generates a large hierarchy naturally. We also recapitulate how the ISS model may be obtained from a type IIB superstring model. (orig.)

  7. Fluxes, hierarchies, and metastable vacua in supersymmetric field theories

    Energy Technology Data Exchange (ETDEWEB)

    Bruemmer, F.

    2008-02-06

    This thesis concerns topics both in low-energy effective field theories from type IIB superstring flux compactifications and in four-dimensional, rigidly supersymmetric gauge theories. We introduce flux compactifications with so-called ''warped throat'' regions, which lead to large hierarchies of scales in the effective four-dimensional theory. The correspondence between a particular such throat and a five-dimensional Randall-Sundrum-like model is established. We shown how certain string-theoretic features of the compactification, such as moduli stabilization by fluxes or the presence of an unstabilized Kaehler modulus, are incorporated in the five-dimensional picture. The KKLT construction for metastable de Sitter vacua is reviewed, as well as some possible modifications involving spontaneous F-term supersymmetry breaking. For KKLT-like models with their hidden sector localized inside a throat, the mediation of supersymmetry breaking to the visible sector is investigated. We review the mechanism of mixed modulus-anomaly mediation, and show that there can be additional equally important gravity-mediated contributions. We finally turn to the ISS model of metastable dynamical supersymmetry breaking in four dimensions, and present a renormalizable extension which generates a large hierarchy naturally. We also recapitulate how the ISS model may be obtained from a type IIB superstring model. (orig.)

  8. Preparation and characterization of thick metastable sputter deposits

    International Nuclear Information System (INIS)

    Allen, R.P.; Dahlgren, S.D.; Merz, M.D.

    1975-01-01

    High-rate dc supported-discharge sputtering techniques were developed and used to prepare 0.1 mm to 5.0 mm-thick deposits of a variety of metastable materials including amorphous alloys representing more than 15 different rare-earth-transition metal systems and a wide range of compositions and deposition conditions. The ability to prepare thick, homogeneous deposits has made it possible for the first time to investigate the structure, properties, and annealing behavior of these unique sputtered alloys using neutron diffraction, ultrasonic, and other experimental techniques that are difficult or impractical for thin films. More importantly, these characterization studies show that the structure and properties of the massive sputter deposits are independent of thickness and can be reproduced from deposit to deposit. Other advantages and applications of this metastable materials preparation technique include the possibility of varying structure and properties by control of the deposition parameters and the ability to deposit even reactive alloys with a very low impurity content

  9. Laser-induced fluorescence measurements of argon ion velocities near the sheath boundary of an argon-xenon plasma

    International Nuclear Information System (INIS)

    Lee, Dongsoo; Severn, Greg; Oksuz, Lutfi; Hershkowitz, Noah

    2006-01-01

    The Bohm sheath criterion in single- and two-ion species plasma is studied with laser-induced fluorescence using a diode laser. Xenon is added to a low pressure unmagnetized dc hot filament argon discharge confined by surface multidipole magnetic fields. The Ar II transition at 668.614 nm is adopted for optical pumping to detect the fluorescence from the plasma and to measure the argon ion velocity distribution functions with respect to positions relative to a negatively biased boundary plate. The structures of the plasma sheath and presheath are measured by an emissive probe. The ion concentrations of the two-species in the bulk plasma are calculated from ion acoustic wave experiments. Results are compared with previous experiments of Ar-He plasmas in which the argon ions were the heavier ion species. Unlike the previous results, the argon speed is slower than its own Bohm velocity near the sheath-presheath boundary in the Ar-Xe plasma where argon ions are the lighter ion species. We argue that this result is consistent with the behaviour of the helium ion required by the generalized Bohm criterion in the previous experiments with Ar-He plasmas. Further, our results suggest that the measured argon ion speed approaches the ion sound speed of the system

  10. New argon-argon (40Ar/39Ar) radiometric age dates from selected subsurface basalt flows at the Idaho National Laboratory, Idaho

    Science.gov (United States)

    Hodges, Mary K. V.; Turrin, Brent D.; Champion, Duane E.; Swisher, Carl C.

    2015-01-01

    In 2011, the U.S. Geological Survey, in cooperation with the U.S. Department of Energy, collected samples for 12 new argon-argon radiometric ages from eastern Snake River Plain olivine tholeiite basalt flows in the subsurface at the Idaho National Laboratory. The core samples were collected from flows that had previously published paleomagnetic data. Samples were sent to Rutgers University for argon-argon radiometric dating analyses.

  11. Metastability of atomic ordering in lead-strontium nitrate solid solutions

    International Nuclear Information System (INIS)

    Shtukenberg, A.G.

    2005-01-01

    A decrease in the anomalous birefringence of ostensibly cubic crystals of (Pb,Sr)(NO 3 ) 2 during annealing between 280-450 deg. C shows first-order reaction kinetics with Arrhenius-like temperature dependence. The activation energies associated with this process were 111(5) and 359(17) kJ/mol below 370 deg. C and above 400 deg. C, respectively. Such behavior agrees with theoretical predictions and confirms that the ordering of cations is the primary cause of the anomalous birefringence

  12. Polydiagnostic calibration performed on a low pressure surface wave sustained argon plasma

    International Nuclear Information System (INIS)

    Vries, N de; Iordanova, E I; Van Veldhuizen, E M; Mullen, J J A M van der; Palomares, J M

    2008-01-01

    The electron density and electron temperature of a low pressure surface wave sustained argon plasma have been determined using passive and active (laser) spectroscopic methods simultaneously. In this way the validity of the various techniques is established while the plasma properties are determined more precisely. The electron density, n e , is determined with Thomson scattering (TS), absolute continuum measurements, Stark broadening and an extrapolation of the atomic state distribution function (ASDF). The electron temperature, T e , is obtained using TS and absolute line intensity (ALI) measurements combined with a collisional-radiative (CR) model for argon. At an argon pressure of 15 mbar, the n e values obtained with TS and Stark broadening agree with each other within the error bars and are equal to (4 ± 0.5) x 10 19 m -3 , whereas the n e value (2 ± 0.5) x 10 19 m -3 obtained from the continuum is about 30% lower. This suggests that the used formula and cross-section values for the continuum method have to be reconsidered. The electron density determined by means of extrapolation of the ASDF to the continuum is too high (∼10 20 m -3 ). This is most probably related to the fact that the plasma is strongly ionizing so that the extrapolation method is not justified. At 15 mbar, the T e values obtained with TS are equal to 13 400 ± 1100 K while the ALI/CR-model yields an electron temperature that is about 10% lower. It can be concluded that the passive results are in good or fair agreement with the active results. Therefore, the calibrated passive methods can be applied to other plasmas in a similar regime for which active diagnostic techniques cannot be used.

  13. Polydiagnostic calibration performed on a low pressure surface wave sustained argon plasma

    Energy Technology Data Exchange (ETDEWEB)

    Vries, N de; Iordanova, E I; Van Veldhuizen, E M; Mullen, J J A M van der [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Palomares, J M [Departamento de Fisica, Universidad de Cordoba, Campus de Rabanales, ed. C-2, 14071 Cordoba (Spain)], E-mail: j.j.a.m.v.d.Mullen@tue.nl

    2008-10-21

    The electron density and electron temperature of a low pressure surface wave sustained argon plasma have been determined using passive and active (laser) spectroscopic methods simultaneously. In this way the validity of the various techniques is established while the plasma properties are determined more precisely. The electron density, n{sub e}, is determined with Thomson scattering (TS), absolute continuum measurements, Stark broadening and an extrapolation of the atomic state distribution function (ASDF). The electron temperature, T{sub e}, is obtained using TS and absolute line intensity (ALI) measurements combined with a collisional-radiative (CR) model for argon. At an argon pressure of 15 mbar, the n{sub e} values obtained with TS and Stark broadening agree with each other within the error bars and are equal to (4 {+-} 0.5) x 10{sup 19} m{sup -3}, whereas the n{sub e} value (2 {+-} 0.5) x 10{sup 19} m{sup -3} obtained from the continuum is about 30% lower. This suggests that the used formula and cross-section values for the continuum method have to be reconsidered. The electron density determined by means of extrapolation of the ASDF to the continuum is too high ({approx}10{sup 20} m{sup -3}). This is most probably related to the fact that the plasma is strongly ionizing so that the extrapolation method is not justified. At 15 mbar, the T{sub e} values obtained with TS are equal to 13 400 {+-} 1100 K while the ALI/CR-model yields an electron temperature that is about 10% lower. It can be concluded that the passive results are in good or fair agreement with the active results. Therefore, the calibrated passive methods can be applied to other plasmas in a similar regime for which active diagnostic techniques cannot be used.

  14. Polarization transfer between oriented metastable helium atoms and neon atoms. A comparison of even and odd isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Pepper, D M; Wang, H T.M.

    1983-11-01

    Collision-induced polarization transfer from optically pumped helium to excited states of neon is studied using various combinations of even and odd isotopes. It is found that, within our experimental accuracy of 10%, the resultant polarization is independent of the isotopic composition of the binary mixture. Possible applications using this mechanism are discussed.

  15. On the fermion pair production in the process of metastable vacuum decay

    International Nuclear Information System (INIS)

    Lavrelashvili, G.V.; Rubakov, V.A.; Tinyakov, P.G.

    1985-01-01

    Production of fermion pairs during the tunneling process leading to the decay of metastable vacuum is considered. The technique based on non-unitary Bogolyubov transformations is developed and formulae for fermionic spectrum are obtained. As an example, the spectrum of fermionic pairs produced during the homogeneous decay of metastable vacuum is evaluated

  16. Isotope separation by laser deflection of an atomic beam

    International Nuclear Information System (INIS)

    Bernhardt, A.F.

    1975-02-01

    Separation of isotopes of barium was accomplished by laser deflection of a single isotopic component of an atomic beam. With a tunable narrow linewidth dye laser, small differences in absorption frequency of different barium isotopes on the 6s 2 1 S 0 --6s6p 1 P 1 5536A resonance were exploited to deflect atoms of a single isotopic component of an atomic beam through an angle large enough to physically separate them from the atomic beam. It is shown that the principal limitation on separation efficiency, the fraction of the desired isotopic component which can be separated, is determined by the branching ratio from the excited state into metastable states. The isotopic purity of the separated atoms was measured to be in excess of 0.9, limited only by instrumental uncertainty. To improve the efficiency of separation, a second dye laser was employed to excite atoms which had decayed to the 6s5d metastable state into the 6p5d 1 P 1 state from which they could decay to the ground state and continue to be deflected on the 5535A transition. With the addition of the second laser, separation efficiency of greater than 83 percent was achieved, limited by metastable state accumulation in the 5d 2 1 D 2 state which is accessible from the 6p5d 1 P 1 level. It was found that the decay rate from the 6p5d state into the 5d 2 metastable state was fully 2/3 the decay rate to the ground state, corresponding to an oscillator strength of 0.58. (U.S.)

  17. Atom optics

    International Nuclear Information System (INIS)

    Balykin, V. I.; Jhe, W.

    1999-01-01

    Atom optics, in analogy to neutron and electron optics, deals with the realization of as a traditional elements, such as lenes, mirrors, beam splitters and atom interferometers, as well as a new 'dissipative' elements such as a slower and a cooler, which have no analogy in an another types of optics. Atom optics made the development of atom interferometer with high sensitivity for measurement of acceleration and rotational possible. The practical interest in atom optics lies in the opportunities to create atom microprobe with atom-size resolution and minimum damage of investigated objects. (Cho, G. S.)

  18. Searching for high magnetization density in bulk Fe: the new metastable Fe-6 phase

    Energy Technology Data Exchange (ETDEWEB)

    Umemoto, K; Himmetoglu, B; Wang, JP; Wentzcovitch, RM; Cococcioni, M

    2014-11-26

    We report the discovery of a new allotrope of iron by first principles calculations. This phase has Pmn2(1) symmetry, a six-atom unit cell (hence the name Fe-6), and the highest magnetization density (M-s) among all the known crystalline phases of iron. Obtained from the structural optimizations of the Fe3C-cementite crystal upon carbon removal, Pmn2(1) Fe-6 is shown to result from the stabilization of a ferromagnetic FCC phase, further strained along the Bain path. Although metastable from 0 to 50 GPa, the new phase is more stable at low pressures than the other well-known HCP and FCC allotropes and smoothly transforms into the FCC phase under compression. If stabilized to room temperature, for example, by interstitial impurities, Fe-6 could become the basis material for high M-s rare-earth-free permament magnets and high-impact applications such as light-weight electric engine rotors or high-density recording media. The new phase could also be key to explaining the enigmatic high M-s of Fe16N2, which is currently attracting intense research activity.

  19. Metastability, spectrum, and eigencurrents of the Lennard-Jones-38 network

    International Nuclear Information System (INIS)

    Cameron, Maria K.

    2014-01-01

    We develop computational tools for spectral analysis of stochastic networks representing energy landscapes of atomic and molecular clusters. Physical meaning and some properties of eigenvalues, left and right eigenvectors, and eigencurrents are discussed. We propose an approach to compute a collection of eigenpairs and corresponding eigencurrents describing the most important relaxation processes taking place in the system on its way to the equilibrium. It is suitable for large and complex stochastic networks where pairwise transition rates, given by the Arrhenius law, vary by orders of magnitude. The proposed methodology is applied to the network representing the Lennard-Jones-38 cluster created by Wales's group. Its energy landscape has a double funnel structure with a deep and narrow face-centered cubic funnel and a shallower and wider icosahedral funnel. However, the complete spectrum of the generator matrix of the Lennard-Jones-38 network has no appreciable spectral gap separating the eigenvalue corresponding to the escape from the icosahedral funnel. We provide a detailed description of the escape process from the icosahedral funnel using the eigencurrent and demonstrate a superexponential growth of the corresponding eigenvalue. The proposed spectral approach is compared to the methodology of the Transition Path Theory. Finally, we discuss whether the Lennard-Jones-38 cluster is metastable from the points of view of a mathematician and a chemical physicist, and make a connection with experimental works

  20. Deformation mechanisms induced under high cycle fatigue tests in a metastable austenitic stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Roa, J.J., E-mail: joan.josep.roa@upc.edu [CIEFMA-Departament de Ciència dels Materials i Enginyeria Metallúrgica, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain); CRnE, Campus Diagonal Sud, Edificio C’, Universitat Politècnica de Catalunya, C/ Pascual i Vila 15, 08028 Barcelona (Spain); Fargas, G. [CIEFMA-Departament de Ciència dels Materials i Enginyeria Metallúrgica, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain); Jiménez-Piqué, E. [CIEFMA-Departament de Ciència dels Materials i Enginyeria Metallúrgica, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain); CRnE, Campus Diagonal Sud, Edificio C’, Universitat Politècnica de Catalunya, C/ Pascual i Vila 15, 08028 Barcelona (Spain); Mateo, A. [CIEFMA-Departament de Ciència dels Materials i Enginyeria Metallúrgica, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona (Spain)

    2014-03-01

    Advanced techniques were used to study the deformation mechanisms induced by fatigue tests in a metastable austenitic stainless steel AISI 301LN. Observations by Atomic Force Microscopy were carried out to study the evolution of a pre-existing martensite platelet at increasing number of cycles. The sub-superficial deformation mechanisms of the austenitic grains were studied considering the cross-section microstructure obtained by Focused Ion Beam and analysed by Scanning Electron Microscopy and Transmission Electron Microscopy. The results revealed no deformation surrounding the pre-existing martensitic platelet during fatigue tests, only the growth on height was observed. Martensite formation was associated with shear bands on austenite, mainly in the {111} plane, and with the activation of the other intersecting austenite {111}〈110〉 slip system. Furthermore, transmission electron microscopy results showed that the nucleation of ε-martensite follows a two stages phase transformation (γ{sub fcc}→ε{sub hcp}→α'{sub bcc})

  1. Metastable honeycomb SrTiO_3/SrIrO_3 heterostructures

    International Nuclear Information System (INIS)

    Anderson, T. J.; Ryu, S.; Podkaminer, J. P.; Ma, Y.; Eom, C. B.; Zhou, H.; Xie, L.; Irwin, J.; Rzchowski, M. S.; Pan, X. Q.

    2016-01-01

    Recent theory predictions of exotic band topologies in (111) honeycomb perovskite SrIrO_3 layers sandwiched between SrTiO_3 have garnered much attention in the condensed matter physics and materials communities. However, perovskite SrIrO_3 film growth in the (111) direction remains unreported, as efforts to synthesize pure SrIrO_3 on (111) perovskite substrates have yielded films with monoclinic symmetry rather than the perovskite structure required by theory predictions. In this study, we report the synthesis of ultra-thin metastable perovskite SrIrO_3 films capped with SrTiO_3 grown on (111) SrTiO_3 substrates by pulsed laser deposition. The atomic structure of the ultra-thin films was examined with scanning transmission electron microscopy (STEM), which suggests a perovskite layering distinct from the bulk SrIrO_3 monoclinic phase. In-plane 3-fold symmetry for the entire heterostructure was confirmed using synchrotron surface X-ray diffraction to measure symmetry equivalent crystal truncation rods. Our findings demonstrate the ability to stabilize (111) honeycomb perovskite SrIrO_3, which provides an experimental avenue to probe the phenomena predicted for this material system.

  2. Effect of argon ion beam voltages on the microstructure of aluminum nitride films prepared at room temperature by a dual ion beam sputtering system

    International Nuclear Information System (INIS)

    Chen, H.-Y.; Han Sheng; Cheng, C.-H.; Shih, H.C.

    2004-01-01

    Aluminum nitride (AlN) films were successfully deposited at room temperature onto p-type (1 0 0) silicon wafers by manipulating argon ion beam voltages in a dual ion beam sputtering (DIBS). X-ray diffraction spectra showed that aluminum nitride films could be synthesized above 800 V. The (0 0 2) orientation was dominant at 800 V, above which the orientation was random. The atomic force microscope (AFM) images displayed a relatively smooth surface with the root-mean-square roughness of 2-3 nm, where this roughness decreased with argon ion beam voltage. The Al 2p 3/2 and N 1s spectra indicated that both the aluminum-aluminum bond and aluminum-nitrogen bond appeared at 600 V, above which only the aluminum-nitrogen bond was detected. Moreover, the atomic concentration in aluminum nitride films was concentrated in aluminum-rich phases in all cases. Nevertheless, the aluminum concentration markedly increased with argon ion beam voltages below 1000 V, above which the concentration decreased slightly. The correlation between the microstructure of aluminum nitride films and argon ion beam voltages is also discussed

  3. Metastable modular metastructures for on-demand reconfiguration of band structures and nonreciprocal wave propagation

    Science.gov (United States)

    Wu, Z.; Zheng, Y.; Wang, K. W.

    2018-02-01

    We present an approach to achieve adaptable band structures and nonreciprocal wave propagation by exploring and exploiting the concept of metastable modular metastructures. Through studying the dynamics of wave propagation in a chain composed of finite metastable modules, we provide experimental and analytical results on nonreciprocal wave propagation and unveil the underlying mechanisms that facilitate such unidirectional energy transmission. In addition, we demonstrate that via transitioning among the numerous metastable states, the proposed metastructure is endowed with a large number of bandgap reconfiguration possibilities. As a result, we illustrate that unprecedented adaptable nonreciprocal wave propagation can be realized using the metastable modular metastructure. Overall, this research elucidates the rich dynamics attainable through the combinations of periodicity, nonlinearity, spatial asymmetry, and metastability and creates a class of adaptive structural and material systems capable of realizing tunable bandgaps and nonreciprocal wave transmissions.

  4. Characterisation of GERDA Phase-I detectors in liquid argon

    Energy Technology Data Exchange (ETDEWEB)

    Barnabe Heider, Marik; Schoenert, Stefan [Max-Planck-Institut fuer Kernphysik (Germany); Gusev, Konstantin [Russian Research Center, Kurchatov Institute (Russian Federation); Joint Institute for Nuclear Research (Russian Federation)

    2009-07-01

    GERDA will search for neutrinoless double beta decay in {sup 76}Ge by submerging bare enriched HPGe detectors in liquid argon. In GERDA Phase-I, reprocessed enriched-Ge detectors, which were previously operated by the Heidelberg-Moscow and IGEX collaborations, and reprocessed natural-Ge detectors from Genius-TF, will be redeployed. We have tested the operation and performance of bare HPGe detectors in liquid nitrogen and in liquid argon over more than three years with three non-enriched p-type prototype detectors. The detector handling and mounting procedures have been defined and the Phase-I detector technology, the low-mass assembly and the long-term stability in liquid argon have been tested successfully. The Phase-I detectors were reprocessed by Canberra Semiconductor NV, Olen, according to their standard technology but without the evaporation of a passivation layer. After their reprocessing, the detectors have been mounted in their low-mass holders and their characterisation in liquid argon performed. The leakage current, the counting characteristics and the efficiency of the detectors have been measured. The testing of the detectors was carried out in the liquid argon test stand of the GERDA underground Detector Laboratory (GDL) at LNGS. The detectors are now stored underground under vacuum until their operation in GERDA.

  5. Charge changing collision cross sections of atomic ions

    International Nuclear Information System (INIS)

    Bliman, S.; Dousson, S.; Geller, R.; Jacquot, B.; Van Houtte, D.

    1980-05-01

    A device has been built to measure charge changing cross sections of atomic ions. It consists of an E.C.R. ion source (Micromafios) that delivers oxygen ions up to charge + 8, argon ions up to charge + 13. The ion source potential may be varied from 1 up to 10 kVolts. A first magnet is used to charge analyze the extracted beam. For a given charge state, the ion beam is passed in a collision cell whose pressure may be varied. The ions undergoing collisions on the target are analyzed by a second magnet and collected. The single collision condition is checked. Different collisions are considered: 1- Charge exchange collisions of argon ions with charge 2<=Z<=12 on argon. Cross sections for capture of 1, 2 and 3 electrons are given. 2- Stripping of argon ions (1<=Z<=4) on argon atoms. 3- Charge exchange of oxygen ions (2<=Z<=8) colliding on deuterium. One and two electron capture cross sections are presented

  6. Small sample analysis using sputter atomization/resonance ionization mass spectrometry

    International Nuclear Information System (INIS)

    Christie, W.H.; Goeringer, D.E.

    1986-01-01

    We have used secondary ion mass spectrometry (SIMS) to investigate the emission of ions via argon sputtering from U metal, UO 2 , and U 3 O 8 samples. We have also used laser resonance ionization techniques to study argon-sputtered neutral atoms and molecules emitted from these same samples. For the case of U metal, a significant enhancement in detection sensitivity for U is obtained via SA/RIMS. For U in the fully oxidized form (U 3 O 8 ), SA/RIMS offers no improvement in U detection sensitivity over conventional SIMS when sputtering with argon. 9 refs., 1 fig., 2 tabs

  7. First principles study of inert-gas (helium, neon, and argon) interactions with hydrogen in tungsten

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Xiang-Shan [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P. O. Box 1129, Hefei 230031 (China); Hou, Jie [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P. O. Box 1129, Hefei 230031 (China); University of Science and Technology of China, Hefei 230026 (China); Li, Xiang-Yan [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P. O. Box 1129, Hefei 230031 (China); Wu, Xuebang, E-mail: xbwu@issp.ac.cn [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P. O. Box 1129, Hefei 230031 (China); Liu, C.S., E-mail: csliu@issp.ac.cn [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P. O. Box 1129, Hefei 230031 (China); Chen, Jun-Ling; Luo, G.-N. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)

    2017-04-15

    We have systematically evaluated binding energies of hydrogen with inert-gas (helium, neon, and argon) defects, including interstitial clusters and vacancy-inert-gas complexes, and their stable configurations using first-principles calculations. Our calculations show that these inert-gas defects have large positive binding energies with hydrogen, 0.4–1.1 eV, 0.7–1.0 eV, and 0.6–0.8 eV for helium, neon, and argon, respectively. This indicates that these inert-gas defects can act as traps for hydrogen in tungsten, and impede or interrupt the diffusion of hydrogen in tungsten, which supports the discussion on the influence of inert-gas on hydrogen retention in recent experimental literature. The interaction between these inert-gas defects and hydrogen can be understood by the attractive interaction due to the distortion of the lattice structure induced by inert-gas defects, the intrinsic repulsive interaction between inert-gas atoms and hydrogen, and the hydrogen-hydrogen repelling in tungsten lattice.

  8. Design considerations for teleoperation systems operating in gas-tight argon cells

    Directory of Open Access Journals (Sweden)

    Seungnam Yu

    2017-12-01

    Full Text Available In the nuclear industry, mechanical engineers spend a significant portion of their time designing equipment such as manipulators, bogies, mechanical grippers, and so on. Some customized designs can be considered as standard mechanical equipment in this area, although it is not unusual to find that an existing design cannot simply be copied from one project to another. Varied performance requirements can dictate that redesign, often quite extensive redesign, is required. However, if something similar has been done before, engineers could use that as a starting point for the new project. In this regard, this study presents several guidelines inspired by previous design knowledge for similar development cases. Moreover, this study presents more detailed suggestions such as design guidelines for an argon-based hot cell atmosphere and design experience for a large-scale practical hot cell facility. Design considerations and case studies dealt with in this study are dedicated to teleoperation manipulators that are used at a large-scale argon cell facility for pyroprocess integrated inactive demonstration (PRIDE, at the Korea Atomic Energy Research Institute. In particular, for case studies to support the suggested recommendations, a fabricated telemanipulator system for PRIDE is introduced, and several kinds of experimental results associated with it are presented.

  9. Dual beam organic depth profiling using large argon cluster ion beams

    Science.gov (United States)

    Holzweber, M; Shard, AG; Jungnickel, H; Luch, A; Unger, WES

    2014-01-01

    Argon cluster sputtering of an organic multilayer reference material consisting of two organic components, 4,4′-bis[N-(1-naphthyl-1-)-N-phenyl- amino]-biphenyl (NPB) and aluminium tris-(8-hydroxyquinolate) (Alq3), materials commonly used in organic light-emitting diodes industry, was carried out using time-of-flight SIMS in dual beam mode. The sample used in this study consists of a ∽400-nm-thick NPB matrix with 3-nm marker layers of Alq3 at depth of ∽50, 100, 200 and 300 nm. Argon cluster sputtering provides a constant sputter yield throughout the depth profiles, and the sputter yield volumes and depth resolution are presented for Ar-cluster sizes of 630, 820, 1000, 1250 and 1660 atoms at a kinetic energy of 2.5 keV. The effect of cluster size in this material and over this range is shown to be negligible. © 2014 The Authors. Surface and Interface Analysis published by John Wiley & Sons Ltd. PMID:25892830

  10. Metastable decay of photoionized niobium clusters: Evaporation vs fission fragmentation

    International Nuclear Information System (INIS)

    Cole, S.K.; Liu, K.; Riley, S.J.

    1986-01-01

    The metastable decay of photoionized niobium clusters (Nb/sub n/ + ) has been observed in a newly constructed cluster beam machine. The decay manifests itself in the time-of-flight (TOF) mass spectrum as an asymmetric broadening of daughter ion peaks. Pulsed ion extraction has been used to measure the decay rate constants and to establish the mechanism of the fragmentation, evaporation and/or fission of the photoionized clusters. It is found that within the experimental time window evaporation dominates for the smaller clusters (n 6 sec -1 . The average kinetic energy release is also determined and is found to be on the order of 5 MeV. 8 refs., 3 figs., 1 tab

  11. Fundamentals of metastability exchange optical pumping in helium

    International Nuclear Information System (INIS)

    Batz, M; Nacher, P-J; Tastevin, G

    2011-01-01

    Advances in metastability exchange optical pumping (MEOP) at high laser powers, but also at high gas pressures and high magnetic field strengths, has provided strong motivation for revisiting the understanding of the limitations of this powerful technique. A comprehensive model has been developed for improved description of the combined effects of OP, ME, and relaxation, and of detailed MEOP features observed over the broad range of operating conditions. A brief description is provided, with illustrative comparisons of computed and experimental results. This improved tool is used to explain the excellent photon efficiency of OP obtained at all field strengths. It is combined with an angular momentum budget approach to quantitatively investigate the newly discovered strong OP-enhanced polarisation losses that currently limits MEOP performance.

  12. Fundamentals of metastability exchange optical pumping in helium

    Science.gov (United States)

    Batz, M.; Nacher, P.-J.; Tastevin, G.

    2011-06-01

    Advances in metastability exchange optical pumping (MEOP) at high laser powers, but also at high gas pressures and high magnetic field strengths, has provided strong motivation for revisiting the understanding of the limitations of this powerful technique. A comprehensive model has been developed for improved description of the combined effects of OP, ME, and relaxation, and of detailed MEOP features observed over the broad range of operating conditions. A brief description is provided, with illustrative comparisons of computed and experimental results. This improved tool is used to explain the excellent photon efficiency of OP obtained at all field strengths. It is combined with an angular momentum budget approach to quantitatively investigate the newly discovered strong OP-enhanced polarisation losses that currently limits MEOP performance.

  13. Raman studies of methane-ethane hydrate metastability.

    Science.gov (United States)

    Ohno, Hiroshi; Strobel, Timothy A; Dec, Steven F; Sloan, E Dendy; Koh, Carolyn A

    2009-03-05

    The interconversion of methane-ethane hydrate from metastable to stable structures was studied using Raman spectroscopy. sI and sII hydrates were synthesized from methane-ethane gas mixtures of 65% or 93% methane in ethane and water, both with and without the kinetic hydrate inhibitor, poly(N-vinylcaprolactam). The observed faster structural conversion rate in the higher methane concentration atmosphere can be explained in terms of the differences in driving force (difference in chemical potential of water in sI and sII hydrates) and kinetics (mass transfer of gas and water rearrangement). The kinetic hydrate inhibitor increased the conversion rate at 65% methane in ethane (sI is thermodynamically stable) but retards the rate at 93% methane in ethane (sII is thermodynamically stable), implying there is a complex interaction between the polymer, water, and hydrate guests at crystal surfaces.

  14. The easy way to metastability tunnelling time and critical configurations

    CERN Document Server

    Manzo, F; Olivieri, E; Scoppola, E

    2003-01-01

    for given energy function $H$ and symmetric Markov kernel $q$. We propose a simple approach to determine the asymptotic behavior, for large $\\beta$, of the first hitting time to the ground state starting from a particular class of local minima for $H$ called metastable states. We separate the asymptotic behavior of the transition time from the determination of the tube of typical paths realizing the transition. This approach turns out to be useful when the determination of the tube of typical paths is too difficult, as for instance in the case of conservative dynamics. We analyze the structure of the saddles introducing the notion of ``essentiality" and describing essential saddles in terms of ``gates". As an example we discuss the case of the 2D Ising Model in the degenerate case of integer $2J\\over h$.

  15. Supersymmetry breaking metastable vacua in runaway quiver gauge theories

    CERN Document Server

    Garcia-Etxebarria, Inaki; Uranga, Angel M

    2007-01-01

    In this paper we consider quiver gauge theories with fractional branes whose infrared dynamics removes the classical supersymmetric vacua (DSB branes). We show that addition of flavors to these theories (via additional non-compact branes) leads to local meta-stable supersymmetry breaking minima, closely related to those of SQCD with massive flavors. We simplify the study of the one-loop lifting of the accidental classical flat directions by direct computation of the pseudomoduli masses via Feynman diagrams. This new approach allows to obtain analytic results for all these theories. This work extends the results for the $dP_1$ theory in hep-th/0607218. The new approach allows to generalize the computation to general examples of DSB branes, and for arbitrary values of the superpotential couplings.

  16. Metastable self-trapping of positrons in MgO

    Science.gov (United States)

    Monge, M. A.; Pareja, R.; González, R.; Chen, Y.

    1997-01-01

    Low-temperature positron annihilation measurements have been performed on MgO single crystals containing either cation or anion vacancies. The temperature dependence of the S parameter is explained in terms of metastable self-trapped positrons which thermally hop through the crystal lattice. The experimental results are analyzed using a three-state trapping model assuming transitions from both delocalized and self-trapped states to deep trapped states at vacancies. The energy level of the self-trapped state was determined to be (62+/-5) meV above the delocalized state. The activation enthalpy for the hopping process of self-trapped positrons appears to depend on the kind of defect present in the crystals.

  17. Metastability and thermophysical properties of metallic bulk glass forming alloys

    International Nuclear Information System (INIS)

    Wunderlich, R.K.; Fecht, H.J.

    1998-01-01

    The absence of crystallization over a wide time/temperature window can be used to produce bulk metallic glass by relatively slow cooling of the melt. For a number of alloys, including several multicomponent Zr-based alloys, the relevant thermodynamic and thermomechanical properties of the metastable glassy and undercooled liquid states have been measured below and above the glass transition temperature. These measurements include specific heat, viscosity, volume, and elastic properties as a function of temperature. As a result, it becomes obvious that the maximum undercooling for these alloys is given by an isentropic condition before an enthalpic or isochoric instability is reached. Alternatively, these glasses can also be produced by mechanical alloying, thus replacing the thermal disorder by static disorder and resulting in the same thermodynamic glass state. During heating through the undercooled liquid, a nanoscale phase separation occurs for most glasses as a precursor of crystallization

  18. International bulletin on atomic and molecular data for fusion. No. 18

    International Nuclear Information System (INIS)

    Katsonis, K.

    1982-02-01

    This bulletin deals with atomic and molecular data for fusion. A bibliography for the most recent data presented in the document is provided. Work in progress is briefly reported (electron impact excitation of hydrogen-like argon ions, excitation and charge transfer in collisions of Li atoms with alpha particles)

  19. Chlorine-induced modifications in the electronic structure of Ag surfaces: a metastable deexcitation spectroscopy and photoemission comparative study

    CERN Document Server

    Pasquali, L; Canepa, M; Staicu-Casagrande, E M; Esaulov, V A

    2003-01-01

    Surface-sensitive spectroscopic techniques, namely metastable deexcitation spectroscopy (MDS) and ultraviolet photoemission (UPS), have been applied to investigate the effects of chlorine chemisorption on the electronic properties (surface density of states and charge density) of Ag(100), Ag(110) and Ag(111) surfaces. Initial stages of chemisorption, up to the formation of a saturated Cl overlayer, have been examined. In particular, MDS permitted us to observe at low Cl gas exposure a progressive depletion of the Ag (5s) charge due to transfer and bonding with Cl atoms. From both MDS and UPS it was possible to observe the development of Cl (3p) bonding and anti-bonding states, the amount of their splitting increasing with coverage. Differences between chemisorption at the three surfaces have been noticed and they have been justified in terms of the different adatom packing and possible formation of small AgCl clusters (especially for the Ag(111) surface).

  20. Metastable phase transformation and hcp-ω transformation pathways in Ti and Zr under high hydrostatic pressures

    International Nuclear Information System (INIS)

    Gao, Lei; Ding, Xiangdong; Sun, Jun; Lookman, Turab; Salje, E. K. H.

    2016-01-01

    The energy landscape of Zr at high hydrostatic pressure suggests that its transformation behavior is strongly pressure dependent. This is in contrast to the known transition mechanism in Ti, which is essentially independent of hydrostatic pressure. Generalized solid-state nudged elastic band calculations at constant pressure shows that α-Zr transforms like Ti only at the lowest pressure inside the stability field of ω-phase. Different pathways apply at higher pressures where the energy landscape contains several high barriers so that metastable states are expected, including the appearance of a transient bcc phase at ca. 23 GPa. The global driving force for the hcp-ω transition increases strongly with increasing pressure and reaches 23.7 meV/atom at 23 GPa. Much of this energy relates to the excess volume of the hcp phase compared with its ω phase.