Sample records for helium atom scattering

  1. Feasibility of measuring surface electron spin dynamics by inelastic scattering of metastable helium atoms

    E-print Network

    Kais, Sabre

    helium atoms M. El-Batanouny, G. Murthy, and C. R. Willis Department of Physics, Boston University atoms (He*) from surfaces of magnetic insulators to study the dynamical properties of surface electron a metastable He atom and the surface electron spins are determined by a configuration interaction calculation

  2. The Scattering of Thermal Energy Helium Atoms from the Disordered Surface of Potassium Cyanide and Lattice Dynamics of Epitaxial Growth

    NASA Astrophysics Data System (ADS)

    Gillman, Edward S.

    High resolution helium atom scattering (HAS) experiments were performed on the disordered surface of KCN(001) in the rhombohedral phase and on expitaxial grown layers of KBr on RbCl(001). The experiments on KCN used the time -of-flight (TOF) method to measure multiphonon interactions of the incident helium atoms with the crystal surface as a function of incident energy and crystal temperature. These measurements were used to model a cutoff factor (Q _{c} = 4.5{A}^ {-1}) for parallel momentum transfer, a range parameter (beta = 4.5A ^{-1}) of an exponential potential V~ exp(-beta z ), and a surface Debye temperature (Theta _{S} = 195K). The experiments with RbCl involved the deposition of one to three monolayers of KBr onto the RbCl(001) surface, which was monitored in situ by attenuation of the atomic helium beam. Inelastic scattering experiments were performed on each atomic layer to determine the surface phonon dispersion curves as a function of coverage. This experiment was performed to validate and also, to provide additional results that will extend the shell model for ionic insulators. Measurements were made in both the {overline{ Gamma M}} and {overline {Gamma X}} high symmetry directions for coverages of one, two, and three monolayers. The KBr/RbCl system which is nearly perfectly lattice matched is compared to the KBr/NaCl system which has lattice registry of 6 KBr to 7 NaCl.

  3. Inelastic x-ray scattering study of the state-resolved differential cross section of Compton excitations in helium atoms

    SciTech Connect

    Xie, B. P.; Yang, K.; Zhou, B.; Feng, D. L. [Department of Physics, Surface Physics Laboratory (National Key Laboratory), and Advanced Materials Laboratory, Fudan University, Shanghai 200433 (China); Zhu, L. F.; Wang, E. L. [Hefei National Laboratory for Physical Sciences at Microscale, Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Hiraoka, N.; Cai, Y. Q. [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Yao, Y.; Wu, C. Q. [Department of Physics, Fudan University, Shanghai 200433 (China)

    2010-09-15

    The state-resolved differential cross sections for both the 1s{sup 2} {sup 1}S{sub 0}{yields}1s2s {sup 1}S{sub 0} monopolar transition and the 1s{sup 2} {sup 1}S{sub 0}{yields}1s2p {sup 1}P{sub 1} dipolar transition of atomic helium had been measured over a large momentum transfer region by high-resolution inelastic x-ray scattering (IXS). The almost-perfect match of the present measurement with the theoretical calculations gives a stringent test of the theoretical method and the calculated wave functions. Our results demonstrate that high-resolution IXS is a powerful tool for studying the excitations in atoms and molecules.

  4. Investigations of the dynamics and growth of insulator films by high resolution helium atom scattering. Final report, May 1, 1985--April 30, 1997

    SciTech Connect

    Safron, S.A.; Skofronick, J.G.

    1997-07-01

    Over the twelve years of this grant from the U.S. Department of Energy, DE-FG05-85ER45208, the over-reaching aims of this work have been to explore and to attempt to understand the fundamental physics and chemistry of surfaces and interfaces. The instrument we have employed m in this work is high-resolution helium atom scattering (HAS) which we have become even more convinced is an exceptionally powerful and useful tool for surface science. One can follow the evolution of the development and progress of the experiments that we have carried out by the evolution of the proposal titles for each of the four three-year periods. At first, m in 1985-1988, the main objective of this grant was to construct the HAS instrument so that we could begin work on the surface vibrational dynamics of crystalline materials; the title was {open_quotes}Helium Atom-Surface Scattering Apparatus for Studies of Crystalline Surface Dynamics{close_quotes}. Then, as we became more interested m in the growth of films and interfaces the title m in 1988-1991 became {open_quotes}Helium Atom Surface Spectroscopy: Surface Lattice Dynamics of Insulators, Metal and Metal Overlayers{close_quotes}. In 1991-1994, we headed even more m in this direction, and also recognized that we should focus more on insulator materials as very few techniques other than helium atom scattering could be applied to insulators without causing surface damage. Thus, the proposal title became {open_quotes}Helium Atom-Surface Scattering: Surface Dynamics of Insulators, Overlayers and Crystal Growth{close_quotes}. M in the final period of this grant the title ended up {open_quotes}Investigations of the Dynamics and Growth of Insulator Films by High Resolution Helium Atom Scattering{close_quotes} m in 1994-1997. The list of accomplishments briefly discussed in this report are: tests of the shell model; multiphoton scattering; physisorbed monolayer films; other surface phase transitions; and surface magnetic effects.

  5. Atom lithography with metastable helium

    SciTech Connect

    Allred, Claire S.; Reeves, Jason; Corder, Christopher; Metcalf, Harold [Physics and Astronomy, Stony Brook University, Stony Brook. New York 11794-3800 (United States)

    2010-02-15

    A bright metastable helium (He*) beam is collimated sequentially with the bichromatic force and three optical molasses velocity compression stages. Each He* atom in the beam has 20 eV of internal energy that can destroy a molecular resist assembled on a gold coated silicon wafer. Patterns in the resist are imprinted onto the gold layer with a standard selective etch. Patterning of the wafer with the He{sup *} was demonstrated with two methods. First, a mesh was used to protect parts of the wafer making an array of grid lines. Second, a standing wave of {lambda}=1083 nm light was used to channel and focus the He* atoms into lines separated by {lambda}/2. The patterns were measured with an atomic force microscope establishing an edge resolution of 80 nm. Our results are reliable and repeatable.

  6. Atom lithography with metastable helium

    NASA Astrophysics Data System (ADS)

    Allred, Claire S.; Reeves, Jason; Corder, Christopher; Metcalf, Harold

    2010-02-01

    A bright metastable helium (He?) beam is collimated sequentially with the bichromatic force and three optical molasses velocity compression stages. Each He? atom in the beam has 20 eV of internal energy that can destroy a molecular resist assembled on a gold coated silicon wafer. Patterns in the resist are imprinted onto the gold layer with a standard selective etch. Patterning of the wafer with the He? was demonstrated with two methods. First, a mesh was used to protect parts of the wafer making an array of grid lines. Second, a standing wave of ? =1083 nm light was used to channel and focus the He? atoms into lines separated by ? /2. The patterns were measured with an atomic force microscope establishing an edge resolution of 80 nm. Our results are reliable and repeatable.

  7. Differential scattering cross sections for collisions of 0.5-, 1.5-, and 5.0-keV helium atoms with He, H2, N2, and O2. [for atmospheric processes modeling

    NASA Technical Reports Server (NTRS)

    Newman, J. H.; Smith, K. A.; Stebbings, R. F.; Chen, Y. S.

    1985-01-01

    This paper reports the first results of an experimental program established to provide cross section data for use in modeling various atmospheric processes. Absolute cross sections, differential in the scattering angle, have been measured for collisions of 0.5-, 1.5-, and 5.0-keV helium atoms with He, H2, N2, and O2 at laboratory scattering angles between 0.1 deg and 5 deg. The results are the sums of cross sections for elastic and inelastic scattering of helium atoms; charged collision products are not detected. Integration of the differential cross section data yields integral cross sections consistent with measurements by other workers. The apparatus employs a position-sensitive detector for both primary and scattered particles and uses a short target cell with a large exit aperture to ensure a simple and well-defined apparatus geometry.

  8. The Structure of the Helium Atom

    Microsoft Academic Search

    Irving Langmuir

    1921-01-01

    Models for the Helium Atom.-(1) Bohr's model is unsatisfactory because it gives too great a value for the ionizing potential and is not in accord with the optical and magnetic properties of helium. Now the chemical evidence suggests that each electron in an atom has its own separate orbit, and that these orbits are closely interrelated. Accordingly two new models

  9. Atomic Scattering Factors

    NSDL National Science Digital Library

    From the Lawrence Berkeley Laboratory's Center for X-Ray Optics, these "atomic scattering factors are based upon photoabsorption measurements of elements in their elemental state." These easy-to-use tables allow users to search out atomic scattering factor data by element and look up the x-ray properties of elements, the index of refraction for a compound material, the x-ray attenuation length of a solid, the x-ray transmission of a solid or a gas, and more. Most of the tables are accessed by way of an online query form with variables such as material, density, and photon energy range entered by the user. Most outputs come in plot form for quick viewing, or results may be retrieved as a text or postscript file for use with a personal plotting software.

  10. Searching for dark matter with helium atom

    E-print Network

    Imre Ferenc Barna

    2006-08-10

    With the help of the boost operator we can model the interaction between a weakly interacting particle(WIMP) of dark matter(DAMA) and an atomic nuclei. Via this "kick" we calculate the total electronic excitation cross section of the helium atom. The bound spectrum of He is calculated through a diagonalization process with a configuration interaction (CI) wavefunction built up from Slater orbitals. All together 19 singly- and doubly-excited atomic sates were taken with total angular momenta of L=0,1 and 2. Our calculation may give a rude estimation about the magnitude of the total excitation cross section which could be measured in later scintillator experiments. The upper limit of the excitation cross section is $9.7\\cdot 10^{-8}$ barn.

  11. Asymptotic wavefunctions for helium-like atoms

    NASA Astrophysics Data System (ADS)

    Lieber, Michael

    2002-05-01

    From the earliest days of quantum mechanics, study of the helium atom has been a major challenge. Because the three-Coulomb problem cannot be solved exactly, approximate numerical techniques are required. In recent years use variational trial wavefunctions, in the form of large basis sets extracted from complete sets of functions, have resulted in exquisitely precise computations of the energy levels [e.g. by Gordon Drake and coworkers]. Yet the form of the corresponding eigenstate wavefunctions is only imperfectly known and has been controversial. Variational wavefunctions which give accurate values for the energy may not be accurate in themselves. Recently, Hubert Klar [J. Phys. B34, 2725 (2001)] has found, to lowest order, the form of the wavefunction in the asymptotic region where all three interparticle distances are large. The present work will elaborate and extend the results of Klar. The author wishes to thank Hubert Klar and the University of Freiburg, where this work was initiated, for their kind hospitality.

  12. Classical Helium Atom with Radiation Reaction

    E-print Network

    G. Camelio; A. Carati; L. Galgani

    2011-11-24

    We study a classical model of Helium atom in which, in addition to the Coulomb forces, the radiation reaction forces are taken into account. This modification brings in the model a new qualitative feature of a global character. Indeed, as pointed out by Dirac, in any model of classical electrodynamics of point particles involving radiation reaction one has to eliminate, from the a priori conceivable solutions of the problem, those corresponding to the emission of an infinite amount of energy. We show that the Dirac prescription solves a problem of inconsistency plaguing all available models which neglect radiation reaction, namely, the fact that in all such models most initial data lead to a spontaneous breakdown of the atom. A further modification is that the system thus acquires a peculiar form of dissipation. In particular, this makes attractive an invariant manifold of special physical interest, the zero--dipole manifold, that corresponds to motions in which no energy is radiated away (in the dipole approximation). We finally study numerically the invariant measure naturally induced by the time--evolution on such a manifold, and this corresponds to studying the formation process of the atom. Indications are given that such a measure may be singular with respect to that of Lebesgue.

  13. ENERGY RELAXATION OF HELIUM ATOMS IN ASTROPHYSICAL GASES

    SciTech Connect

    Lewkow, N. R.; Kharchenko, V. [Department of Physics, University of Connecticut, Storrs, CT 06269 (United States); Zhang, P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2012-09-01

    We report accurate parameters describing energy relaxation of He atoms in atomic gases, important for astrophysics and atmospheric science. Collisional energy exchange between helium atoms and atomic constituents of the interstellar gas, heliosphere, and upper planetary atmosphere has been investigated. Energy transfer rates, number of collisions required for thermalization, energy distributions of recoil atoms, and other major parameters of energy relaxation for fast He atoms in thermal H, He, and O gases have been computed in a broad interval of energies from 10 meV to 10 keV. This energy interval is important for astrophysical applications involving the energy deposition of energetic atoms and ions into atmospheres of planets and exoplanets, atmospheric evolution, and analysis of non-equilibrium processes in the interstellar gas and heliosphere. Angular- and energy-dependent cross sections, required for an accurate description of the momentum-energy transfer, are obtained using ab initio interaction potentials and quantum mechanical calculations for scattering processes. Calculation methods used include partial wave analysis for collisional energies below 2 keV and the eikonal approximation at energies higher than 100 eV, keeping a significant energy region of overlap, 0.1-2 keV, between these two methods for their mutual verification. The partial wave method and the eikonal approximation excellently match results obtained with each other as well as experimental data, providing reliable cross sections in the astrophysically important interval of energies from 10 meV to 10 keV. Analytical formulae, interpolating obtained energy- and angular-dependent cross sections, are presented to simplify potential applications of the reported database. Thermalization of fast He atoms in the interstellar gas and energy relaxation of hot He and O atoms in the upper atmosphere of Mars are considered as illustrative examples of potential applications of the new database.

  14. Helium nanobubble release from Pd surface: An atomic simulation

    SciTech Connect

    Wang, Liang; Hu, Wangyu; Deng, Huiqiu; Xiao, Shifang; Yang, Jianyu; Gao, Fei; Heinisch, Howard L.; Hu, Shilin

    2011-02-14

    Molecular dynamic simulations of helium atoms escaping from a helium-filled nano-bubble near the surface of crystalline palladium reveal unexpected behavior. Significant deformation and cracking near the helium bubble occur initially, and then a channel forms between the bubble and the surface, providing a pathway for helium atoms to propagate towards the surface. The helium atoms erupt from the bubble in an instantaneous and volcano-like process, which leads to surface deformation consisting of cavity formation on the surface, along with modification and atomic rearrangement at the periphery of the cavity. The present simulation results show that, near the palladium surface, there is a helium-bubble-free zone, or denuded zone, with a typical thickness of about 3.0 nm. Combined with experimental measurements and continuum-scale evolutionary model predictions, the present atomic simulations demonstrate that the thickness of the denuded zone, which contains a low concentration of helium atoms, is somewhat larger than the diameter of the helium bubbles in the metal tritide. Furthermore, a relationship between the tensile strength and thickness of metal film is also determined.

  15. Atomic beam scattering from single crystal surfaces

    NASA Astrophysics Data System (ADS)

    Frankl, Daniel R.

    Application of atom-scattering to a variety of surface problems is expanding rapidly, owing in large part to the extreme surface- sensitivity of this probe. Helium is particularly useful because of its low mass and chemical inertness. Beams with velocity spreads of less than one percent and wavelength of the order of one Angstrom can be formed by nozzle expansion. The scattered flux from a clean, well-ordered crystal surface contains elastic and inelastic, coherent and incoherent, components. The coherent elastic component (i.e., the specular and diffracted beams) contains information about the crystallographic structure of the outer- most atomic layer of the crystal and about the interaction potential between the crystal and the scattered particle. The latter manifests itself in the form of resonances between the incoming free-particle state, and the two-dimensional Bloch states bound in the potential well at the surface. Elastic scattering theory has reached the point where the resonance signatures in the various diffracted beams can be predicted accurately. Crystallographic information resides in the diffracted beam intensities. Theoretical interpretation is less well advanced, though some progress has been made with “hard-wall” models. Experimental studies of reconstructed surfaces and chemisorbed overlayers appear very promising. In inelastic scattering, energy resolution has been achieved by both time-of-flight and diffraction methods. High-resolution studies on alkali halide surfaces have led to experimental determination of Rayleighwave dispersion relations over the full Brillouin zone. Preliminary results have also been obtained on some metals.

  16. Gas-Surface Energy Exchange in Collisions of Helium Atoms with Aligned Single-Walled Carbon

    E-print Network

    Maruyama, Shigeo

    1 Gas-Surface Energy Exchange in Collisions of Helium Atoms with Aligned Single-Walled Carbon #12;2 ABSTRACT Since gas flows in micro/nano devices are dominated by the interaction of gas molecules accommodation of gas molecules on surfaces. The scattering of gas molecules on quartz surfaces covered with VA

  17. Atomic origins of solid helium bubbles in tungsten

    NASA Astrophysics Data System (ADS)

    Xia, Min; Guo, Hong-Yan; Dai, Yong; Yan, Qing-Zhi; Guo, Li-Ping; Li, Tie-Cheng; Qiao, Yi; Ge, Chang-Chun

    2014-12-01

    Solid helium bubbles were directly observed in the helium ion implanted tungsten (W), by different transmission electron microscopy (TEM) techniques at room temperature. The diameters of these solid helium bubbles range from 1 nm to 8 nm in diameter with the mean bubble size about 3 nm. The selected area electron diffraction (SAED) and fast Fourier transform (FFT) images revealed that solid helium bubbles possess body-centered cubic (bcc) structure with a lattice constant of 0.447 nm. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images further confirmed the existence of helium bubble in tungsten. The present findings provide an atomic level view of the microstructure evolution of helium in the materials, and revealed the existence of solid helium bubbles in materials.

  18. REFLECTION OF METASTABLE HELIUM ATOMS ON A MOLYBDENUM /110/ SURFACE

    E-print Network

    Paris-Sud XI, Université de

    571 REFLECTION OF METASTABLE HELIUM ATOMS ON A MOLYBDENUM /110/ SURFACE EFFECT OF OXYGEN ADSORPTION kinetic energy by a monocrystalline surface of molybdenum / 110/, as a function ofangle ofincidence in the reflection coefficient of metastable helium from a molybdenum /110/ target, as a function of angle

  19. Neutron scattering study of elementary excitations in liquid helium-3

    Microsoft Academic Search

    K. Skold; C. A. Pelizzari; R. Kleb; G. E. Ostrowski

    1976-01-01

    The neutron inelastic scattering function of liquid helium-3 at 0.015 K has been measured for wave vectors in the range 0.8 A⁻¹< or =q< or =2.2 A⁻¹. For q<1.4 A⁻¹, the scattering function contains two peaks. The peak at lower energy is due to spin-fluctuation scattering in the particle-hole region while the peak at higher energy is identified to be

  20. Muonic helium atom as a classical three-body problem

    NASA Astrophysics Data System (ADS)

    Stuchi, T. J.; Antunes, A. C. B.; Andreu, M. A.

    2000-12-01

    We study the classical problem of the muonic helium atom, a helium atom with one of its electrons replaced by a muon. First, we establish the connection of the model with the one-dimensional frozen planetary approximation of the helium atom and find that there is classically stable motion for the configuration ?-particle-electron-muon, and no stable motion for the ?-particle-muon-electron configuration. After that, we introduce the restricted muonic helium problem, a model for the movement of an electron in the potential of the ? particle/muon pair moving in a circular orbit. In this model, the equilibrium points, their associated Lyapunov families of periodic orbits, and their stability parameters were studied. The most interesting feature is the stability of the halo orbits, for a range of energy values. The vicinity of the ? particle is also studied, examining Poincaré sections for increasing energy values showing an increase of the chaotic motion.

  1. Total Cross Sections for Inelastic Scattering of Charged Particles by Atoms and Molecules. III. Accurate Bethe Cross Section for Ionization of Helium

    Microsoft Academic Search

    Mitio Inokuti; Young-Ki Kim

    1969-01-01

    The Bethe cross section sigmai for ionization of He by fast charged particles is accurately evaluated by a subtraction sigmai=sigmatot-sigmaex, where sigmatot is the total inelastic scattering cross section and sigmaex is the sum of all discrete-excitation cross sections. Our earlier work has given a highly precise value of sigmatot, and recent results on discrete excitations enables one to determine

  2. Positron-alkali atom scattering

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  3. Spectroscopy of barium atoms in liquid and solid helium matrices

    SciTech Connect

    Lebedev, V.; Moroshkin, P.; Weis, A. [Departement de Physique, Universite de Fribourg, Chemin du Musee 3, CH-1700 Fribourg (Switzerland)

    2011-08-15

    We present an exhaustive overview of optical absorption and laser-induced fluorescence lines of Ba atoms in liquid and solid helium matrices in visible and near-infrared spectral ranges. Due to the increased density of isolated atoms, we have found a large number of spectral lines that were not observed in condensed helium matrices before. We have also measured the lifetimes of metastable states. The lowest {sup 3}D{sub 1} metastable state has lifetime of 2.6 s and can be used as an intermediate state in two-step excitations of high-lying states. Various matrix-induced radiationless population transfer channels have been identified.

  4. Using Uncertainty Principle to Find the Ground-State Energy of the Helium and a Helium-like Hookean Atom

    ERIC Educational Resources Information Center

    Harbola, Varun

    2011-01-01

    In this paper, we accurately estimate the ground-state energy and the atomic radius of the helium atom and a helium-like Hookean atom by employing the uncertainty principle in conjunction with the variational approach. We show that with the use of the uncertainty principle, electrons are found to be spread over a radial region, giving an electron…

  5. Spectra of helium clusters with up to six atoms using soft-core potentials

    SciTech Connect

    Gattobigio, M. [Universite de Nice-Sophia Antipolis, Institut Non-Lineaire de Nice, CNRS, 1361 route des Lucioles, F-06560 Valbonne (France); Kievsky, A.; Viviani, M. [Istituto Nazionale di Fisica Nucleare, Largo Pontecorvo 3, I-56100 Pisa (Italy)

    2011-11-15

    In this paper, we investigate small clusters of helium atoms using the hyperspherical harmonic basis. We consider systems with A=2,3,4,5,6 atoms with an interparticle potential which does not present a strong repulsion at short distances. We use an attractive Gaussian potential that reproduces the values of the dimer binding energy, the atom-atom scattering length, and the effective range obtained with one of the widely used He-He interactions, the Aziz and Slaman potential, called LM2M2. In systems with more than two atoms, we consider a repulsive three-body force that, by construction, reproduces the trimer binding energy of the LM2M2 potential. With this model, consisting of the sum of a two- and three-body potential, we have calculated the spectrum of clusters formed by four, five, and six helium atoms. We have found that these systems present two bound states, one deep and one shallow, close to the threshold fixed by the energy of the (A-1)-atom system. Universal relations between the energies of the excited state of the A-atom system and the ground-state energy of the (A-1)-atom system are extracted, as well as the ratio between the ground state of the A-atom system and the ground-state energy of the trimer.

  6. Atomic impact experiments with free helium-3 and helium-4 clusters

    Microsoft Academic Search

    Jürgen Gspann

    1995-01-01

    Free helium clusters with of the order of 103 to 107 atoms have been predicted to reach final temperatures of about 0.4 K in the case of4He, and of 0.15 K in the case of3He. In the first case, the clusters have to be expected to be superfluid, in the latter case to be normalfluid. Impact experiments with cesium atoms,

  7. The Helium Atom and Isoelectronic Ions in Two Dimensions

    ERIC Educational Resources Information Center

    Patil, S. H.

    2008-01-01

    The energy levels of the helium atom and isoelectronic ions in two dimensions are considered. The difficulties encountered in the analytical evaluation of the perturbative and variational expressions for the ground state, promote an interesting factorization of the inter-electronic interaction, leading to simple expressions for the energy. This…

  8. ALIGNMENT OF METASTABLE HELIUM ATOMS BY UNPOLARIZED RESONANCE RADIATION

    Microsoft Academic Search

    P. A. Franken; F. D. Colegrove

    1958-01-01

    Experiments in which helium atoms in the ³S⁠metastable ; state were aligned by the action of unpolarized optical resonance radiation are ; reported. The alignment was detected by resonance methods; the observed line ; widths are of the order of a milligauss with a raw signal-to-noise ratio of ; approximates 1OO: 1. The simplest experimental arrangement is described and

  9. The helium atom in a strong magnetic field

    Microsoft Academic Search

    W. Becken; P. Schmelcher; F. K. Diakonos

    1999-01-01

    We investigate the electronic structure of the helium atom in a magnetic field between B = 0 and 0953-4075\\/32\\/6\\/018\\/img1. The atom is treated as a nonrelativistic system with two interacting electrons and a fixed nucleus. Scaling laws are provided connecting the fixed-nucleus Hamiltonian to the one for the case of finite nuclear mass. Respecting the symmetries of the electronic Hamiltonian

  10. Similarity between Positronium-Atom and Electron-Atom Scattering

    NASA Astrophysics Data System (ADS)

    Fabrikant, I. I.; Gribakin, G. F.

    2014-06-01

    We employ the impulse approximation for a description of positronium-atom scattering. Our analysis and calculations of Ps-Kr and Ps-Ar collisions provide a theoretical explanation of the similarity between the cross sections for positronium scattering and electron scattering for a range of atomic and molecular targets observed by S. J. Brawley et al. [Science 330, 789 (2010)].

  11. Zeeman deceleration of electron-impact-excited metastable helium atoms

    NASA Astrophysics Data System (ADS)

    Dulitz, Katrin; Tauschinsky, Atreju; Softley, Timothy P.

    2015-03-01

    We present experimental results that demonstrate—for the first time—the Zeeman deceleration of helium atoms in the metastable 23S1 state. A more than 40% decrease of the kinetic energy of the beam is achieved for deceleration from 490 m s?1 to a final velocity of 370 m s?1. Metastable atom generation is achieved with an electron-impact-excitation source whose performance is enhanced through an additional discharge-type process which we characterize in detail. Metastable helium is efficiently generated even in a mixture of other noble gases that have much lower excitation energies. Comparison of deceleration data at different electron beam pulse durations confirms that a matching between the initial particle distribution and the phase-space acceptance of the decelerator is crucial for the production of a decelerated packet with a well-defined velocity distribution. The experimental findings are in good agreement with three-dimensional numerical particle trajectory simulations.

  12. Quantum entanglement for helium atom in the Debye plasmas

    NASA Astrophysics Data System (ADS)

    Lin, Yen-Chang; Fang, Te-Kuei; Ho, Yew Kam

    2015-03-01

    In the present work, we present an investigation on quantum entanglement of the two-electron helium atom immersed in weakly coupled Debye plasmas, modeled by the Debye-Hückel, or screened Coulomb, potential to mimic the interaction between two charged particles inside the plasma. Quantum entanglement is related to correlation effects in a multi-particle system. In a bipartite system, a measurement made on one of the two entangled particles affects the outcome of the other particle, even if such two particles are far apart. Employing wave functions constructed with configuration interaction B-spline basis, we have quantified von Neumann entropy and linear entropy for a series of He 1,3Se and 1,3Po states in plasma-embedded helium atom.

  13. Ground State Hyperfine Structure of Muonic Helium Atom

    E-print Network

    A. A. Krutov; A. P. Martynenko

    2008-07-21

    On the basis of the perturbation theory in the fine structure constant $\\alpha$ and the ratio of the electron to muon masses we calculate one-loop vacuum polarization and electron vertex corrections and the nuclear structure corrections to the hyperfine splitting of the ground state of muonic helium atom $(\\mu e ^4_2He)$. We obtain total result for the ground state hyperfine splitting $\\Delta \

  14. Atomic masses of tritium and helium-3.

    PubMed

    Myers, E G; Wagner, A; Kracke, H; Wesson, B A

    2015-01-01

    By measuring the cyclotron frequency ratios of (3)He(+) to HD(+) and T(+) to HD(+), and using HD(+) as a mass reference, we obtain new atomic masses for (3)He and T. Our results are M[(3)He]=3.016?029?322?43(19)??u and M[T]=3.016?049?281?78(19)??u, where the uncertainty includes an uncertainty of 0.12 nu in the mass reference. Allowing for cancellation of common systematic errors, we find the Q value for tritium ? decay to be (M[T]-M[(3)He])c(2)=18?592.01(7)??eV. This allows an improved test of systematics in measurements of tritium ? decay that set limits on neutrino mass. PMID:25615466

  15. Atomic Masses of Tritium and Helium-3

    NASA Astrophysics Data System (ADS)

    Myers, E. G.; Wagner, A.; Kracke, H.; Wesson, B. A.

    2015-01-01

    By measuring the cyclotron frequency ratios of 3He+ to HD+ and T+ to HD+ , and using HD+ as a mass reference, we obtain new atomic masses for 3He and T. Our results are M [3He]=3.016 029 322 43 (19 ) u and M [T ]=3.016 049 281 78 (19 ) u , where the uncertainty includes an uncertainty of 0.12 nu in the mass reference. Allowing for cancellation of common systematic errors, we find the Q value for tritium ? decay to be (M [T ]-M [3He])c2=18 592.01 (7 ) eV . This allows an improved test of systematics in measurements of tritium ? decay that set limits on neutrino mass.

  16. Spectroscopy of lithium atoms and molecules on helium nanodroplets.

    PubMed

    Lackner, Florian; Poms, Johannes; Krois, Günter; Pototschnig, Johann V; Ernst, Wolfgang E

    2013-11-21

    We report on the spectroscopic investigation of lithium atoms and lithium dimers in their triplet manifold on the surface of helium nanodroplets (He(N)). We present the excitation spectrum of the 3p ? 2s and 3d ? 2s two-photon transitions for single Li atoms on He(N). The atoms are excited from the 2S(?) ground state into ?, ?, and ? pseudodiatomic molecular substates. Excitation spectra are recorded by resonance enhanced multiphoton ionization time-of-flight (REMPI-TOF) mass spectroscopy, which allows an investigation of the exciplex (Li*–He(m), m = 1–3) formation process in the Li–He(N) system. Electronic states are shifted and broadened with respect to free atom states, which is explained within the pseudodiatomic model. The assignment is assisted by theoretical calculations, which are based on the Orsay–Trento density functional where the interaction between the helium droplet and the lithium atom is introduced by a pairwise additive approach. When a droplet is doped with more than one alkali atom, the fragility of the alkali–He(N) systems leads preferably to the formation of high-spin molecules on the droplets. We use this property of helium nanodroplets for the preparation of Li dimers in their triplet ground state (13?u(+)). The excitation spectrum of the 23?g(?? = 0–11) ? 13?u(+)(?? = 0) transition is presented. The interaction between the molecule and the droplet manifests in a broadening of the transitions with a characteristic asymmetric form. The broadening extends to the blue side of each vibronic level, which is caused by the simultaneous excitation of the molecule and vibrations of the droplet (phonons). The two isotopes of Li form 6Li2 and 7Li2 as well as isotope mixed 6Li7Li molecules on the droplet surface. By using REMPI-TOF mass spectroscopy, isotope-dependent effects could be studied. PMID:23895106

  17. PREFACE: Atom-surface scattering Atom-surface scattering

    NASA Astrophysics Data System (ADS)

    Miret-Artés, Salvador

    2010-08-01

    It has been a privilege and a real pleasure to organize this special issue or festschrift in the general field of atom-surface scattering (and its interaction) in honor of J R Manson. This is a good opportunity and an ideal place to express our deep gratitude to one of the leaders in this field for his fundamental and outstanding scientific contributions. J R Manson, or Dick to his friends and colleagues, is one of the founding fathers, together with N Cabrera and V Celli, of the 'Theory of surface scattering and detection of surface phonons'. This is the title of the very well-known first theoretical paper by Dick published in Physical Review Letters in 1969. My first meeting with Dick was around twenty years ago in Saclay. J Lapujoulade organized a small group seminar about selective adsorption resonances in metal vicinal surfaces. We discussed this important issue in surface physics and many other things as if we had always known each other. This familiarity and warm welcome struck me from the very beginning. During the coming years, I found this to be a very attractive aspect of his personality. During my stays in Göttingen, we had the opportunity to talk widely about science and life at lunch or dinner time, walking or cycling. During these nice meetings, he showed, with humility, an impressive cultural background. It is quite clear that his personal opinions about history, religion, politics, music, etc, come from considering and analyzing them as 'open dynamical systems'. In particular, with good food and better wine in a restaurant or at home, a happy cheerful soirée is guaranteed with him, or even with only a good beer or espresso, and an interesting conversation arises naturally. He likes to listen before speaking. Probably not many people know his interest in tractors. He has an incredible collection of very old tractors at home. In one of my visits to Clemson, he showed me the collection, explaining to me in great detail, their technical properties; all of them were ready for use! We cannot imagine him without his two old-fashioned Mercedes, also in his collection. He also has technical skills in construction and music and always has time for jogging. I would finally say that he is an even-tempered person. In brief, mens sana in corpore sano 1 . Dick is a theorist bound to experimental work, extremely intuitive and very dedicated. In his long stays outside Clemson, he always visited places where experiments were being carried out. He has been, and still is, of great help to experimental PhD students, postdocs or senior scientists in providing valuable advice and suggestions towards new measurements. Plausible interpretations of their results developing theoretical models or always searching for good agreement with experiment are two constants in his daily scientific work. Experimental work is present in most of his 150 papers. One of the main theoretical challenges in this field was to develop a formalism where the plethora of experimental results reported in the literature were accommodated. His transition matrix formalism was also seminal in the field of atom-surface scattering. Elastic and inelastic (single and double phonon) contributions were determined as well as the multiphonon background. This work was preceded by a theory for diffuse inelastic scattering and a posterior contribution for multiphonon scattering, both with V Celli. In a similar vein, a theory of molecule-surface scattering was also derived and, more recently, a theory for direct scattering, trapping and desorption. Very interesting extensions to scattering with molten metal and liquid surfaces have also been carried out. Along with collaborators he has studied energy accommodation and sticking coefficients, providing a better understanding of their meaning. G Armand and Dick proposed the well-known corrugated Morse potential as an interaction potential model providing reliable results of diffraction patterns and selective adsorption resonances. This proposal was, in a certain sense, the result of many previous studies carried out by t

  18. Similarity between positronium-atom and electron-atom scattering.

    PubMed

    Fabrikant, I I; Gribakin, G F

    2014-06-20

    We employ the impulse approximation for a description of positronium-atom scattering. Our analysis and calculations of Ps-Kr and Ps-Ar collisions provide a theoretical explanation of the similarity between the cross sections for positronium scattering and electron scattering for a range of atomic and molecular targets observed by S.?J. Brawley et al. [Science 330, 789 (2010)]. PMID:24996087

  19. Experimental study of {mu}-atomic and {mu}-molecular processes in pure helium and deuterium-helium mixtures

    SciTech Connect

    Bystritsky, V.M.; Boreiko, V.F.; Gerasimov, V.V.; Pavlov, V.N.; Sandukovsky, V.G.; Stolupin, V.A.; Volnykh, V.P. [Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Czaplinski, W.; Popov, N.P.; Wozniak, J. [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, PL-30059 Cracow (Poland); Filipowicz, M. [AGH University of Science and Technology, Faculty of Fuels and Energy, PL-30059 Cracow (Poland); Huot, O.; Knowles, P.E.; Schaller, L.A.; Schneuwly, H. [Department of Physics, University of Fribourg, CH-1700 Fribourg (Switzerland); Mulhauser, F. [University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

    2005-03-01

    We present experimental results of {mu}-atomic and {mu}-molecular processes induced by negative muons in pure helium and helium-deuterium mixtures. The experiment was performed at the Paul Scherrer Institute (Switzerland). We measured relative intensities of muonic x-ray K series transitions in ({mu}{sup 3,4}He){sup *} atoms in pure helium as well as in helium-deuterium mixtures. The d{mu}{sup 3}He radiative decay probabilities for two different helium densities in D{sub 2}+{sup 3}He mixture were also determined. Finally, the q{sub 1s}{sup He} probability for a d{mu} atom formed in an excited state to reach the ground state was measured and compared with theoretical calculations using a simple cascade model.

  20. A four-body approach to electron-impact single ionization of helium atoms

    NASA Astrophysics Data System (ADS)

    Ghanbari-Adivi, Ebrahim; Abdollahi-Tadi, Rayhaneh

    2013-12-01

    A four-body approach based on the three-Coulomb distorted wave (3CDW) model is applied to study of the electron-impact single ionization of helium atoms. Triply differential cross sections (TDCS) are calculated for different values of the incident and ejection energies and various amounts of the scattering angles. The ejection angular distribution of the TDCS in general exhibits two peaks, binary and recoil peaks. The obtained results are compared with the available experimental data as well as other theoretical predictions. The comparison shows a good agreement between the present calculations and the measurements. Also, the obtained results are compatible with the other theories.

  1. Electronic Relaxation Processes of Transition Metal Atoms in Helium Nanodroplets

    NASA Astrophysics Data System (ADS)

    Kautsch, Andreas; Lindebner, Friedrich; Koch, Markus; Ernst, Wolfgang E.

    2014-06-01

    Spectroscopy of doped superfluid helium nanodroplets (He_N) gives information about the influence of this cold, chemically inert, and least interacting matrix environment on the excitation and relaxation dynamics of dopant atoms and molecules. We present the results from laser induced fluorescence (LIF), photoionization (PI), and mass spectroscopy of Cr and Cu doped He_N. From these results, we can draw a comprehensive picture of the complex behavior of such transition metal atoms in He_N upon photo-excitation. The strong Cr and Cu ground state transitions show an excitation blueshift and broadening with respect to the bare atom transitions which can be taken as indication for the solvation inside the droplet. From the originally excited states the atoms relax to energetically lower states and are ejected from the He_N. The relaxation processes include bare atom spin-forbidden transitions, which clearly bears the signature of the He_N influence. Two-color resonant two-photon ionization (2CR2PI) also shows the formation of bare atoms and small Cr-He_n and Cu-He_n clusters in their ground and metastable states ^c. Currently, Cr dimer excitation studies are in progress and a brief outlook on the available results will be given. C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, 2011. A. Kautsch, M. Koch, and W. E. Ernst, J. Phys. Chem. A, 117 (2013) 9621-9625, DOI: 10.1021/jp312336m F. Lindebner, A. Kautsch, M. Koch, and W. E. Ernst, Int. J. Mass Spectrom. (2014) in press, DOI: 10.1016/j.ijms.2013.12.022 M. Koch, A. Kautsch, F. Lackner, and W. E. Ernst, submitted to J. Phys. Chem. A

  2. Ionization of highly excited helium atoms in an electric field

    SciTech Connect

    van de Water, W.; Mariani, D.R.; Koch, P.M.

    1984-11-01

    We present detailed measurements of ionization of highly excited triplet helium atoms in a static electric field. The atoms were prepared in states with energy E close to the saddle-point threshold E = -2(F(a.u.))/sup 1/2/. The electric field F was sufficiently strong for the states to be characterized by total spin S and absolute value of the magnetic quantum number M/sub L/. For M/sub L/ = 0 states the experiments measured ionization properties of adiabatic states. In another case, Vertical BarM/sub L/Vertical Bar = 2, they predominantly measured those of diabatic states. In both cases the ionization rate was found to be a highly nonmonotonic function of the field strength. The observations are analyzed in terms of a theory of the helium density of states in an electric field. A companion paper (D. A. Harmin, Phys. Rev. A 30, 2413 (1984)) develops in detail the general theory, which uses quantum defects to parametrize the effect of the core interaction. The agreement between measured and calculated ionization curves is good, indicating that the field ionization of a nonhydrogenic atom can now be understood in a detailed, quantitative, and predictive sense.

  3. Electron correlation in fast ion-impact single ionization of helium atoms

    NASA Astrophysics Data System (ADS)

    Ghanbari-Adivi, E.; Eskandari, S.

    2015-01-01

    A four-body distorted-wave approximation is applied for theoretical analysis of the fully differential cross sections (FDCS) for proton-impact single ionization of helium atoms in their ground states. The nine-dimensional integrals for the partial amplitudes are analytically reduced to closed-form expressions or some one-dimensional integrals which can be easily calculated numerically. Calculations are performed in the scattering and perpendicular planes. The influence of the target static electron correlations on the process is investigated using a number of different bound-state wave functions for the ground state of the helium targets. An illustrative computation is performed for 75-keV proton-helium collisions and the obtained results are compared with experimental data and other theoretical predictions. Although for small momentum transfers, the comparison shows a reasonable agreement with experiments in the scattering and perpendicular planes, some significant discrepancies are still present at large momentum transfers in these planes. However, our results are compatible and for some cases, better than those of the other sophisticated calculations.

  4. Positronium-atom scattering at low energies

    NASA Astrophysics Data System (ADS)

    Fabrikant, I. I.; Gribakin, G. F.

    2014-11-01

    A pseudopotential for positronium-atom interaction, based on electron-atom and positron-atom phase shifts, is constructed, and the phase shifts for Ps-Kr and Ps-Ar scattering are calculated. This approach allows us to extend the Ps-atom cross sections, obtained previously in the impulse approximation [I. I. Fabrikant and G. F. Gribakin, Phys. Rev. Lett. 112, 243201 (2014), 10.1103/PhysRevLett.112.243201], to energies below the Ps ionization threshold. Although experimental data are not available in this low-energy region, our results describe well the tendency of the measured cross sections to drop with decreasing velocity at v <1 a.u. Our results show that the effect of the Ps-atom van der Waals interaction is weak compared to the polarization interaction in electron-atom and positron-atom scattering. As a result, the Ps scattering length for both Ar and Kr is positive, and the Ramsauer-Townsend minimum is not observed for Ps scattering from these targets. This makes Ps scattering quite different from electron scattering in the low-energy region, in contrast to the intermediate energy range from the Ps ionization threshold up to v ˜2 a.u., where the two are similar.

  5. Application of cold beam of atoms and molecules for studying luminescence of oxygen atoms stimulated by metastable helium

    NASA Astrophysics Data System (ADS)

    Khmelenko, V. V.; Mao, S.; Meraki, A.; Wilde, S. C.; McColgan, P. T.; Pelmenev, A. A.; Boltnev, R. E.; Lee, D. M.

    2014-12-01

    We describe a method for creating a high flux beam of cold atoms and molecules. By using this beam method, spectroscopic studies of the afterglow of oxygen-helium gas mixtures at cryogenic temperatures were performed. The cooling by helium vapor of a helium jet containing trace amounts of oxygen after passing through a radiofrequency discharge zone led to the observation of strong emissions from atomic oxygen. The effect results from the increased efficiency of energy transfer from metastable helium atoms and molecules to the atomic oxygen in the cold dense helium vapor. The effect might find application for the detection of small quantities of impurities in helium gas as well as possible laser action.

  6. Binding of two helium atoms in confined geometries

    SciTech Connect

    Kilic, S. [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik] [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik; [Univ. of Split (Croatia). Faculty of Natural Sciences; Krotscheck, E.; Zillich, R. [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik] [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik

    1999-08-01

    The authors carry out a comprehensive study of the binding of two helium atoms in unrestricted and, in particular, in restricted geometries in both two and three dimensions. Besides the well known binding of the {sup 4}He dimer in unrestricted geometry in two and three dimensions, the authors also find weakly bound states of the {sup 3}He-{sup 4}He molecule and the {sup 3}He dimer in 2 dimensions. Furthermore, any combination of two {sup 4}He or {sup 3}He atoms can form a molecule if their motion is sufficiently confined. The calculations are carried out by numerically solving the Schroedinger equation as well as by constructing a suitable variational wave function.

  7. Electron scattering in helium for Monte Carlo simulations Alexander V. Khrabrov and Igor D. Kaganovich

    E-print Network

    Kaganovich, Igor

    to be determined), where E is the energy of the electron, r is the total cross-section, and h is the scatter- ing September 2012) An analytical approximation for differential cross-section of electron scattering on helium IN HELIUM The differential scattering cross-section of an electron on the potential /ðr� ¼ V0 a r e�r=a (1

  8. Photoionization Spectroscopy of Isolated cr Atoms in Ultracold Helium Nanodroplets

    NASA Astrophysics Data System (ADS)

    Kautsch, Andreas; Hasewend, Matthias; Ratschek, Martin; Koch, Markus; Ernst, Wolfgang E.

    2012-06-01

    Recently we succeeded in doping Cr atoms to He nanodroplets (HeN) at 0.4 Kand carried out resonance ionization mass spectroscopy (RIMS). Here we present resonant two-photon ionization (R2PI) measurements in the wavelength range from 350 to 361 nm (27700 - 28600 cm-1, 3.43 - 3.54 eV). As one of several possible ionization pathways we allocate a first excitation step to the y7Po ? a7S3 transition, happening inside the HeN. Due to the interaction with the surrounding He this excitation appears broadened in the spectra and gives the possibility to obtain detailed information about the perturbation upon electronic excitation of the Cr atom in HeN. Subsequently, the dopant atom leaves the HeN and is ionized in the gas phase where discrete free atom autoionization levels are populated leading to additional sharp spectral features. Future investigations with two photon two color ionization and selective electron energy ionization as well as quantum chemistry calculations will be discussed. M. Ratschek, M. Koch, and W. E. Ernst, J. Chem. Phys., in press (2012) C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, 2011.

  9. LBNL-42730 1 Collisional Perturbation of States in Atomic Ytterbium by Helium and Neon

    E-print Network

    Pines, Alexander

    LBNL-42730 1 Collisional Perturbation of States in Atomic Ytterbium by Helium and Neon D in atomic ytterbium by helium and neon buffer gases are reported. We find upper limits for the quenching and neon. PACS numbers: 34, 11.30.Er, 42.62.Fi (Submitted to Phys. Rev. A) 1. INTRODUCTION The 6s2 1 S0 6s

  10. Study of Injection of Helium into Supersonic Air Flow Using Rayleigh Scattering

    NASA Technical Reports Server (NTRS)

    Seaholtz, Richard G.; Buggele, Alvin E.

    1997-01-01

    A study of the transverse injection of helium into a Mach 3 crossflow is presented. Filtered Rayleigh scattering is used to measure penetration and helium mole fraction in the mixing region. The method is based on planar molecular Rayleigh scattering using an injection-seeded, frequency-doubled ND:YAG pulsed laser and a cooled CCD camera. The scattered light is filtered with an iodine absorption cell to suppress stray laser light. Preliminary data are presented for helium mole fraction and penetration. Flow visualization images obtained with a shadowgraph and wall static pressure data in the vicinity of the injection are also presented.

  11. Dynamic polarizabilities of rare-earth-metal atoms and dispersion coefficients for their interaction with helium atoms

    E-print Network

    Chu, Xi

    Dynamic polarizabilities of rare-earth-metal atoms and dispersion coefficients; published 29 March 2007 The dynamic scalar and tensor polarizabilities of the rare-earth-metal atoms coefficients for the interactions of the rare-earth-metal atoms with helium atoms. The static polarizabilities

  12. Formation of Triplet Positron-helium Bound State by Stripping of Positronium Atoms in Collision with Ground State Helium

    NASA Technical Reports Server (NTRS)

    Drachman, Richard J.

    2006-01-01

    Formation of triplet positron-helium bound state by stripping of positronium atoms in collision with ground state helium JOSEPH DI RlENZI, College of Notre Dame of Maryland, RICHARD J. DRACHMAN, NASA/Goddard Space Flight Center - The system consisting of a positron and a helium atom in the triplet state e(+)He(S-3)(sup e) was conjectured long ago to be stable [1]. Its stability has recently been established rigorously [2], and the values of the energies of dissociation into the ground states of Ps and He(+) have also been reported [3] and [4]. We have evaluated the cross-section for this system formed by radiative attachment of a positron in triplet He state and found it to be small [5]. The mechanism of production suggested here should result in a larger cross-section (of atomic size) which we are determining using the Born approximation with simplified initial and final wave functions.

  13. Rearrangement and annihilation in antihydrogen-atom scattering

    SciTech Connect

    Jonsell, Svante [Department of Physics, Swansea University, Singleton Park, Swansea SA2 8PP (United Kingdom)

    2008-08-08

    I review some results for annihilation and rearrangement processes in low-energy antihydrogen-hydrogen and antihydrogen-helium scattering. For the strong nuclear force results using a {delta}-function potential are compared to a scattering length approach. It is found that the {delta}-function potential does not give correct annihilation cross sections in the case of antihydrogen-helium scattering. Problem associated with the use of the Born-Oppenheimer approximation for rearrangement calculations are reviewed.

  14. SURFACE EFFECTS ON NEUTRON SCATTERING IN HELIUM FILMS B. LAMBERT, D. SALIN

    E-print Network

    Paris-Sud XI, Université de

    L-377 SURFACE EFFECTS ON NEUTRON SCATTERING IN HELIUM FILMS B. LAMBERT, D. SALIN Laboratoire d'Ultrasons in the form of a cylindrical surface of 1.5 m radius in the horizontal plane, thus focussing one sharp energy

  15. Simulations of the effect of final state interactions on the scattering reponses of helium droplets

    E-print Network

    Yang, Jian

    1996-01-01

    SIMULATIONS OF THE EFFECT OF FINAL STATE INTERACTIONS ON THE SCATTERING RESPONSES OF HELIUM DROPLETS A Thesis by JIAN YANG Submitted to the Office of Graduate Studies of Texas AgrM University in partial fulfillment of the requirements... for the degree of MASTER OF SCIENCE December 1996 Major Subject: Physics SIMULATIONS OF THE EFFECT OF FINAL STATE INTERACTIONS ON THE SCATTERING RESPONSES OF HELIUM DROPLETS A Thesis by JIAN YANG Submitted to Texas AihM University in partial fulfillment...

  16. Rayleigh Scattering at Atoms with Dynamical Nuclei

    E-print Network

    J. Froehlich; M. Griesemer; B. Schlein

    2005-09-05

    Scattering of photons at an atom with a dynamical nucleus is studied on the subspace of states of the system with a total energy below the threshold for ionization of the atom (Rayleigh scattering). The kinematics of the electron and the nucleus is chosen to be non-relativistic, and their spins are neglected. In a simplified model of a hydrogen atom or a one-electron ion interacting with the quantized radiation field in which the helicity of photons is neglected and the interactions between photons and the electron and nucleus are turned off at very high photon energies and at photon energies below an arbitrarily small, but fixed energy (infrared cutoff), asymptotic completeness of Rayleigh scattering is established rigorously. On the way towards proving this result, it is shown that, after coupling the electron and the nucleus to the photons, the atom still has a stable ground state, provided its center of mass velocity is smaller than the velocity of light; but its excited states are turned into resonances. The proof of asymptotic completeness then follows from extensions of a positive commutator method and of propagation estimates for the atom and the photons developed in previous papers. The methods developed in this paper can be extended to more realistic models. It is, however, not known, at present, how to remove the infrared cutoff.

  17. Importance of considering helium excited states in He+ scattering by an aluminum surface

    NASA Astrophysics Data System (ADS)

    Iglesias-García, A.; García, Evelina A.; Goldberg, E. C.

    2014-11-01

    The He+/Al system is a very interesting projectile-surface combination which was thought initially as an example of a pure Auger neutralization mechanism. Then, because of the measured reionization explained by the antibonding interaction of the projectile state with the core target states, the resonant charge exchange with the band states was considered as another important contribution to the neutralization. Nevertheless, by only considering the neutralization to the ground state of helium, the measured ion survival probability is still overestimated. On the other hand, measurements of electron emission from an Al surface bombarded by He positive ions suggested the possibility of occupied excited states of helium due to the ion-surface collision. In this work, we also include the excited states of He within the time-dependent scattering process in which both neutralization mechanisms, resonant and Auger, are simultaneously contemplated. Our starting point is a multiorbital Anderson Hamiltonian projected over the selected space of ground and excited atomic configurations. An extra term related to the Auger mechanism is added to this Hamiltonian. A difference with previous works is that this approach includes the electron spin and, therefore, the spin fluctuation statistics in the charge-exchange process is correctly taken into account. We find a notable improvement in the agreement with the experiments and also that the interference between both mechanisms is not dramatic.

  18. Measurement of a Long Electronic Spin Relaxation Time of Cesium Atoms in Superfluid Helium

    SciTech Connect

    Furukawa, T.; Izumi, H.; Shimoda, T. [Department of Physics, Graduate School of Science, Osaka University, Osaka 560-0043 (Japan); Matsuo, Y.; Fukuyama, Y.; Kobayashi, T. [RIKEN, 2-1, Hirosawa, Wako-shi, Saitama 351-0198 (Japan); Hatakeyama, A. [Institute of Physics, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Tokyo 153-8902 (Japan)

    2006-03-10

    The longitudinal electronic spin relaxation time of Cs atoms optically polarized in superfluid helium (He II, 1.5 K) has been measured with special care to cope with a serious decrease in the number of Cs atoms in the observation region. This decrease, mainly caused by helium convection in introducing the atoms into He II by laser sputtering, was significantly reduced using a new atom implantation method. Combined with a careful correction for the number of atoms, we have determined the relaxation time to be 2.24(19) s or longer, roughly twice as long as that in solid He.

  19. Three-body recombination of cold helium atoms

    NASA Astrophysics Data System (ADS)

    Suno, H.; Esry, B. D.; Greene Burke, Chris H., Jr.

    2002-05-01

    Three-body recombination is an important loss mechanism for Bose-Einstein condensates. Previous investigations( B.D. Esry, C.H. Greene, and J.P. Burke, Jr., Phys. Rev. Lett. 83), 1751 (1999); E. Nielsen and J.H. Macek, ibid. 83, 1566 (1999); P.F. Bedaque, E. Braaten, and H.-W. Hammer, ibid. 85, 908 (2000). have been limited to the ultracold limit where only the J=0 symmetry needed to be considered. This work(H. Suno, B.D. Esry, C.H. Greene, and J.P. Burke, Jr., accepted in Phys. Rev. A) extends these studies and treats not only J=0 but also J>0 states, so that the recombination rate K3 at finite collision energies can be calculated. In addition, the rates for the time-reversed process, namely collision-induced dissociation, are also obtained. In particular we study the case of ground-state helium atoms, including collisions of both ^4He and ^3He.

  20. Inelastic scattering of atoms in a double well

    SciTech Connect

    Annibale, E. S. [Instituto de Fisica, Universidade de Sao Paulo, 05508-090, Sao Paulo (Brazil); Institut fuer Physik, Universitaet Augsburg, D-86135, Augsburg (Germany); Fialko, O. [Institut fuer Physik, Universitaet Augsburg, D-86135, Augsburg (Germany); Centre for Theoretical Chemistry and Physics, Massey University (Albany Campus), Private Bag 102904, North Shore MSC, Auckland 0745 (New Zealand); Ziegler, K. [Institut fuer Physik, Universitaet Augsburg, D-86135, Augsburg (Germany)

    2011-04-15

    We study a mixture of two light spin-1/2 fermionic atoms and two heavy atoms in a double-well potential. Inelastic scattering processes between both atomic species excite the heavy atoms and renormalize the tunneling rate and the interaction of the light atoms (polaron effect). The effective interaction of the light atoms changes its sign and becomes attractive for strong inelastic scattering. This is accompanied by a crossing of the energy levels from singly occupied sites at weak inelastic scattering to a doubly occupied and an empty site for stronger inelastic scattering. We are able to identify the polaron effect and the level crossing in the quantum dynamics.

  1. Neutron-scattering investigation of the excitation spectrum of liquid helium

    SciTech Connect

    Kalinin, I. V. [Institute of Physics and Power Engineering (Russian Federation)], E-mail: kaliv@ippe.ru; Lauter, H. [Institut Laue-Langevin (France); Puchkov, A. V. [Institute of Physics and Power Engineering (Russian Federation)

    2007-07-15

    The results of the investigation of the temperature evolution of the scattering law S(Q, {omega}) of superfluid helium measured in the wave-vector range 0.3 < Q < 0.8 A{sup -1} and helium temperatures from 1.0 to 2.2 K are reported. The investigations have been performed on the high-flux reactor at the Institut Laue-Langevin (France) with the IN6 neutron inelastic-scattering spectrometer. The deviation of the experimental scattering law of liquid helium from the damping harmonic oscillator model, which was previously observed independently in the experiments with the IN6 spectrometer and with the DIN-2PI spectrometer (at the IBR-2 reactor, Dubna, Russia) and were more recently called extrapeak, has been corroborated. The temperature dependence of the extrapeak parameters has been determined. This dependence makes it possible to propose hypotheses on the nature of the extrapeak.

  2. Introduction to Density Functional Theory: Calculations by Hand on the Helium Atom

    ERIC Educational Resources Information Center

    Baseden, Kyle A.; Tye, Jesse W.

    2014-01-01

    Density functional theory (DFT) is a type of electronic structure calculation that has rapidly gained popularity. In this article, we provide a step-by-step demonstration of a DFT calculation by hand on the helium atom using Slater's X-Alpha exchange functional on a single Gaussian-type orbital to represent the atomic wave function. This DFT…

  3. Scattering of electrons from neon atoms

    NASA Technical Reports Server (NTRS)

    Dasgupta, A.; Bhatia, A. K.

    1984-01-01

    Scattering of electrons from neon atoms is investigated by the polarized-orbital method. The perturbed orbitals calculated with use of the Sternheimer approximation lead to the polarizability 2.803 a(0)-cube in fairly good agreement with the experimental value 2.66 a(0)-cube. Phase shifts for various partial waves are calculated in the exchange, exchange-adiabatic, and polarized-orbital approximations. They are compared with the previous results. The calculated elastic differential, total, and momentum-transfer cross sections are compared with the experimental results. The polarized-orbital approximation yields results which show general improvement over the exchange-adiabatic approximation.

  4. Collisional lasing on a self-terminating transition of a helium atom

    SciTech Connect

    Bel'skaya, E V; Bokhan, P A; Zakrevskii, D E; Lavrukhin, M A [Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)

    2011-01-24

    Laser on a self-contained transition of a helium atom is studied under excitation of the helium mixture with molecular gases by single long-duration (up to 700ns) or double nanosecond pulses. In He - H{sub 2}O and He - NH{sub 3} mixtures, no limitations were found on the pulse repetition rate and the laser pulse duration obtained was equal to that of the pump pulse. (lasers and amplifiers)

  5. Excitation of autoionizing states of helium-like ions by scattering of high-energy particles

    SciTech Connect

    Mikhailov, A. I.; Mikhailov, I. A.; Nefiodov, A. V., E-mail: anef@thd.pnpi.spb.ru [B. P. Konstantinov Petersburg Nuclear Physics Institute (Russian Federation); Plunien, G. [Technische Universitaet Dresden, Institut fuer Theoretische Physik (Germany)] [Technische Universitaet Dresden, Institut fuer Theoretische Physik (Germany)

    2013-03-15

    The cross sections for two-electron excitations of helium-like atomic systems into the autoionizing 2s{sup 2} ({sup 1}S)- and 2p{sup 2} ({sup 1}S)-states by collisions with high-energy electrons and photons are deduced. The evaluations are performed to the leading order of non-relativistic perturbation theory. The analytical formulas for cross sections are obtained in the form of universal scalings. A comparison of our theoretical predictions with available theoretical and experimental results for the helium atom is made.

  6. The role of correlation in the ground state energy of confined helium atom

    SciTech Connect

    Aquino, N. [Departamento de Física, Universidad Autónoma Metropolitana-Iztapalapa, Apartado Postal 55-534, 09340 México Distrito Federal (Mexico)

    2014-01-14

    We analyze the ground state energy of helium atom confined by spherical impenetrable walls, and the role of the correlation energy in the total energy. The confinement of an atom in a cavity is one way in which we can model the effect of the external pressure on an atom. The calculations of energy of the system are carried out by the variational method. We find that the correlation energy remains almost constant for a range values of size of the boxes analyzed.

  7. Purification of helium in atomic and molecular gases by cataphoresis

    Microsoft Academic Search

    D. S. Remer; F. H. Shair

    1971-01-01

    The separation of gas mixtures by cataphoresis in a DC glow discharge was experimentally investigated as a function of the discharge current, the total gas pressure, and the initial composition of the gas mixture. The electric field, degree of ionization, and reactor geometry were also considered. Gases under investigation included binary mixtures of helium with argon, neon, nitrogen, oxygen, carbon

  8. Small-angle scattering of neutrons on normal and superfluid liquid helium

    NASA Astrophysics Data System (ADS)

    Tsipenyuk, Yu. M.; Kirichek, O.; Petrenko, O.

    2013-09-01

    Experiments on small-angle scattering of neutrons on liquid helium at temperatures of 1.0-5 K at the ISIS pulsed neutron source (England) are reported. Detailed measurements of the angular distribution of the scattered neutrons reveal a significant change in the temperature dependence of the second moment of the pairwise correlation function (the first derivative of the angular distribution for small scattering angles). At high temperatures the angular distribution of the scattered neutrons follows the classical description for small-angle scattering, but at temperatures below the ?-point, quantum mechanical behavior is observed (scattering of neutrons on quantum fluctuations). It is confirmed experimentally that over the entire temperature range the neutron scattering cross section at zero angle is determined by classical thermodynamic fluctuations in the density.

  9. The Effects of the Pauli Exclusion Principle in Determining the Ionization Energies of the Helium Atom and Helium-Like Ions

    ERIC Educational Resources Information Center

    Deeney, F. A.; O'Leary, J. P.

    2012-01-01

    For helium and helium-like ions, we have examined the differences between the values of the ionization energies as calculated from the Bohr theory and those measured in experiments. We find that these differences vary linearly with the atomic number of the system. Using this result, we show how the Bohr model for single-electron systems may be…

  10. Three-body recombination in cold helium-helium-alkali-metal-atom collisions

    SciTech Connect

    Suno, Hiroya; Esry, B. D. [The Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001 (Japan); Department of Physics, Kansas State University, Manhattan, Kansas 66506 (United States)

    2009-12-15

    Three-body recombination in helium-helium-alkali-metal collisions at cold temperatures is studied using the adiabatic hyperspherical representation. The rates for the three-body recombination processes {sup 4}He+{sup 4}He+X->{sup 4}He+{sup 4}HeX and {sup 4}He+{sup 4}He+X->{sup 4}He{sub 2}+X, with X={sup 7}Li, {sup 23}Na, {sup 39}K, {sup 85}Rb, and {sup 133}Cs, are calculated at nonzero collision energies by including not only zero total angular momentum, J=0, states but also J>0 states. The three-body recombination rates show a relatively weak dependence on the alkali-metal species, differing from each other only by about one order of magnitude, except for the {sup 4}He-{sup 4}He-{sup 23}Na system.

  11. Evidence of scattering of bulk elementary excitations in isotopically pure liquid helium-II at low temperatures

    NASA Astrophysics Data System (ADS)

    Zakharenko, A. A.

    2010-07-01

    This short report is concerned with experimental investigations of bulk elementary excitations (BEEs) in the isotopically pure liquid helium-II at low temperatures below 100 mK. The evidence of BEEs? scattering is introduced in this work. Two identical Au-heaters were used to generate BEEs. The first pulsed heater generates BEE beams to record them. The second heater serves to generate BEE beams in order to scatter the first beams, operating delay time between pulses of the heaters. Experimental signals were recorded by several bolometers situated both above and below the liquid surface: scattered BEEs are travelling in the liquid from the pulsed heater to the bolometer; scattered BEEs, reaching the liquid surface, evaporate 4He-atoms detected by two bolometers positioned in a vacuum; scattered signals are reflected from the liquid surface back to the liquid and are detected by the other bolometer situated in the liquid. It is manifested that the experimental results showed a dramatic decrease in peaks of recorded signals. Also, signal losses for different heater powers were calculated.

  12. Resonant two-photon ionization spectroscopy of Al atoms and dimers solvated in helium nanodroplets

    NASA Astrophysics Data System (ADS)

    Krasnokutski, Serge A.; Huisken, Friedrich

    2015-02-01

    Resonant two-photon ionization (R2PI) spectroscopy has been applied to investigate the solvation of Al atoms in helium droplets. The R2PI spectra reveal vibrational progressions that can be attributed to Al-Hen vibrations. It is found that small helium droplets have very little chance to pick up an aluminum atom after collision. However, the pick-up probability increases with the size of the helium droplets. The absorption band that is measured by monitoring the ions on the mass of the Al dimer is found to be very little shifted with respect to the Al monomer band (˜400 cm-1). However, using the same laser wavelength, we were unable to detect any Aln photoion with n larger than two.

  13. Resonant two-photon ionization spectroscopy of Al atoms and dimers solvated in helium nanodroplets.

    PubMed

    Krasnokutski, Serge A; Huisken, Friedrich

    2015-02-28

    Resonant two-photon ionization (R2PI) spectroscopy has been applied to investigate the solvation of Al atoms in helium droplets. The R2PI spectra reveal vibrational progressions that can be attributed to Al-Hen vibrations. It is found that small helium droplets have very little chance to pick up an aluminum atom after collision. However, the pick-up probability increases with the size of the helium droplets. The absorption band that is measured by monitoring the ions on the mass of the Al dimer is found to be very little shifted with respect to the Al monomer band (?400 cm(-1)). However, using the same laser wavelength, we were unable to detect any Aln photoion with n larger than two. PMID:25725735

  14. ETUDE DES ATOMES METASTABLES DE L'HELIUM ET DU NEON PRESENTS DANS LES DECHARGES LUMINESCENTES Laboratoire de Physique des Milieux Ioniss -Universit Paul Sabatier -31 -Toulouse.

    E-print Network

    Boyer, Edmond

    ETUDE DES ATOMES METASTABLES DE L'HELIUM ET DU NEON PRESENTS DANS LES DECHARGES LUMINESCENTES A investigated metastable helium and neon atoms by means of o p t i c a l absorption. This results, supplemented

  15. Elastic scattering of relativistic electrons by screened atomic nuclei

    Microsoft Academic Search

    S. Lin; N. Sherman; J. K. Percus

    1963-01-01

    The effect of screening by atomic electrons on the scattering of ; relativistic electrons by heavy atoms was computed numerically using different ; screening raodels. Exponential and Hartree potentials were used to simulate the ; screening. The asymmetry factor S( theta ) and the differential scattering cross ; section d sigma ( theta )\\/d OMEGA were computed at 15 degree

  16. TOPICAL REVIEW: Differential cross sections for photo-double-ionization of the helium atom

    Microsoft Academic Search

    J. S. Briggs; V. Schmidt

    2000-01-01

    A rather complete understanding is emerging of the process of full fragmentation of the helium atom following absorption of a single photon. In this review the major experimental and theoretical advances that have led to our understanding of this simplest photo-double-ionization process, particularly with respect to multiply differential cross sections, are described.

  17. Hydrogen Atom and Helium Ion Spatial and Momentum Distribution Functions Illustrate the Uncertainty Principle

    E-print Network

    Rioux, Frank

    the Uncertainty Principle Frank Rioux|SJU The uncertainty principle is revealed by a comparison of the coordinate and momentum wave functions for the hydrogen atom (z=1) and helium ion (z=2) clearly illustrate the uncertainty principle. 0 2 4 6 r 2 1 r

  18. Threshold effects in positron scattering from isoelectronic series of atoms and molecules

    NASA Astrophysics Data System (ADS)

    Machacek, J. R.; Buckman, S. J.; Sullivan, J. P.

    2014-10-01

    The observation of features, often referred to as "Wigner cusps" in a scattering cross section at the opening of a new scattering channel has been widely reported in electron scattering, and has been attributed to strong coupling between the two scattering channels. Recently a series of cusps were observed in positron scattering from the noble gases [A. C. L. Jones et al., Phys. Rev. Lett. 105, 073201 (2010), 10.1103/PhysRevLett.105.073201]. In this case, the strong opening of the positronium formation cross section resulted in a cusplike feature, or bump, in the total elastic scattering cross section. The positronium formation channel is typically the largest partial scattering cross section in the region of the electronic excitation and ionization thresholds in most atoms and molecules, and it is plausible that similar features may exist in other atomic and molecular species. We have undertaken measurements of the isoelectronic targets of helium—H2, and neon—H2O, NH3, and CH4, in an effort to better understand the mechanisms leading to these threshold features.

  19. Exploiting Universality in Atoms with Large Scattering Lengths

    SciTech Connect

    Braaten, Eric

    2012-05-31

    The focus of this research project was atoms with scattering lengths that are large compared to the range of their interactions and which therefore exhibit universal behavior at sufficiently low energies. Recent dramatic advances in cooling atoms and in manipulating their scattering lengths have made this phenomenon of practical importance for controlling ultracold atoms and molecules. This research project was aimed at developing a systematically improvable method for calculating few-body observables for atoms with large scattering lengths starting from the universal results as a first approximation. Significant progress towards this goal was made during the five years of the project.

  20. Plateau Effects in Laser-Assisted Electron-Atom Scattering

    Microsoft Academic Search

    M. V. Frolov; Anthony F. Starace; A. V. Flegel; N. L. Manakov

    2003-01-01

    A quasienergy state analysis of electron-atom scattering in an intense, elliptically-polarized laser field is presented, modeling the atom by a zero-range potential. We obtain exact analytic expressions for the differential cross section dsigman for electron scattering with emission or absorption of n-photons [1]. Well-known approximate results [2] follow from our exact results in the limit that the atomic potential is

  1. Brillouin scattering measurements of the velocity and attenuation of high frequency sound waves in superfluid helium

    Microsoft Academic Search

    R. L. St. Peters; T. J. Greytak; G. B. Benedek

    1970-01-01

    We have measured, from the Brillouin spectrum of scattered laser light, the velocity and attenuation of thermally driven high frequency first sound in liquid helium under its saturated vapor pressure between 1.25°K and the lambda point. The sound wavevector was fixed at 2.0339 × 105 cm-1; the frequency varied from 768 MHz at our lowest temperature to 709 MHz near

  2. Laser-modified electron scattering from a slowly ionising atom

    NASA Technical Reports Server (NTRS)

    Fiordilino, E.; Mittleman, M. H.

    1983-01-01

    When an electron scatters from an atom in the presence of a laser field which is resonant with an atomic transition, off-shell effects enter into the cross section. These only become significant at higher laser intensities where the atom may also be ionised by the laser. Cross-sections are obtained for electron-atom scattering in which these off-shell effects appear and in which the slow ionisation of the atom by the laser is included. Experiments are suggested in which simplifications can occur and which still retain these 'exotic' effects.

  3. Interaction of positronium with helium atoms — the classical treatment of the 5-body collision system

    NASA Astrophysics Data System (ADS)

    T?kési, Károly; DuBois, Robert D.; Mukoyama, Takeshi

    2014-09-01

    The interaction between positronium and a helium atom is studied using the 5-body classical trajectory Monte Carlo method. We present the total cross sections for the dominant channels, namely for single ionization of the target, and ionization of the projectile, resulting from pure ionization and also from electron transfer (capture or loss) processes for 1-5.7 a.u. incident velocities of the positronium atom. Our results were compared with the calculated data using hydrogen projectiles having the same velocities as well as with the experimental data in collisions between H and He [R.D. DuBois, Á. Kövér, Phys. Rev. A 40, 3605 (1989)]. We analyze the similarities and deviations for ionization of helium atoms by positronium and hydrogen projectile impact. Contribution to the Topical Issue "Electron and Positron Induced Processes", edited by Michael Brunger, Radu Campeanu, Masamitsu Hoshino, Oddur Ingólfsson, Paulo Limão-Vieira, Nigel Mason, Yasuyuki Nagashima and Hajime Tanuma.

  4. Entanglement Interferometry for Precision Measurement of Atomic Scattering Properties

    Microsoft Academic Search

    Artur Widera; Olaf Mandel; Markus Greiner; Susanne Kreim; Theodor W. Hänsch; Immanuel Bloch

    2004-01-01

    We report on a matter wave interferometer realized with entangled pairs of trapped 87Rb atoms. Each pair of atoms is confined at a single site of an optical lattice potential. The interferometer is realized by first creating a coherent spin superposition of the two atoms and then tuning the interstate scattering length via a Feshbach resonance. The selective change of

  5. The velocity dependence of the absolute total ionization cross section for collisions of argon atoms with singlet and triplet metastable helium atoms

    Microsoft Academic Search

    M. R. Woodard

    1977-01-01

    The velocity dependence of the absolute total ionization cross section of argon atoms upon impact with selected metastable states of helium atoms was measured using a low voltage D. C. discharge as the source of the excited atoms, and a rotating slotted disk selector for velocity selection of the excited atoms. Selection of the electronic spin state of the excited

  6. A novel spacetime concept for describing electronic motion within a helium atom

    E-print Network

    Kunming Xu

    2007-05-30

    Euclidean space and linear algebra do not characterize dynamic electronic orbitals satisfactorily for even the motion of both electrons in an inert helium atom cannot be defined in reasonable details. Here the author puts forward a novel two-dimensional spacetime model from scratch in the context of defining both electrons in a helium atom. Space and time are treated as two orthogonal, symmetric and complementary quantities under the atomic spacetime. Electronic motion observed the rule of differential and integral operations that were implemented by dynamic trigonometric functions. It is demonstrated that the atomic spacetime is not a linear vector space with Newtonian time, and within which calculus has non-classical definition, and complex wave functions have fresh physical significances. This alternative approach is original, informative and refreshing but still compatible with quantum mechanics in the formulation. The description of electronic resonance in helium is also comparable with classical mechanics such as an oscillating pendulum and with classical electromagnetism such as an LC oscillator. The study has effectively unified complex function, calculus, and trigonometry in mathematics, and provided a prospect for unifying particle physics with classical physics on the novel spacetime platform.

  7. Zero-energy neutron-triton and proton-Helium-3 scattering with \\eftnopi

    E-print Network

    Johannes Kirscher

    2011-05-18

    Model-independent constraints for the neutron-triton and proton-Helium-3 scattering lengths are calculated with a leading-order interaction derived from an effective field theory without explicit pions. Using the singlet neutron-proton scattering length, the deuteron, and the triton binding energy as input, the predictions $\\ants=9.2\\pm2.6 $fm, $\\antt=7.6\\pm1.6 $fm, $\\aphes=3.6\\pm0.32 $fm, and $\\aphet=3.1\\pm 0.23 $fm are obtained. The calculations employ the resonating group method and include the Coulomb interaction when appropriate. The theoretical uncertainty is assessed via a variation of the regulator parameter of the short-distance interaction from $400 $MeV to $1.6 $GeV. The phase-shift and scattering-length results for the proton-Helium-3 system are consistent with a recent phase shift analysis and with model calculations. For neutron-triton, the results for the scattering lengths in both singlet and triplet channels are significantly smaller than suggested by R-matrix and partial-wave-analysis extractions from data. For a better understanding of this discrepancy, the sensitivity of the low-energy four-body scattering system to variations in the neutron-neutron and proton-proton two-nucleon scattering lengths is calculated. Induced by strong charge-symmetry-breaking contact interactions, this dependence is found insignificant. In contrast, a strong correlation between the neutron-triton scattering length and the triton binding energy analogous to the Phillips line is found.

  8. Investigating the dynamics of laser induced sparks in atmospheric helium using Rayleigh and Thomson scattering

    NASA Astrophysics Data System (ADS)

    Nedanovska, E.; Nersisyan, G.; Morgan, T. J.; Hüwel, L.; Murakami, T.; Lewis, C. L. S.; Riley, D.; Graham, W. G.

    2015-01-01

    We have used optical Rayleigh and Thomson scattering to investigate the expansion dynamics of laser induced plasma in atmospheric helium and to map its electron parameters both in time and space. The plasma is created using 9 ns duration, 140 mJ pulses from a Nd:YAG laser operating at 1064 nm, focused with a 10 cm focal length lens, and probed with 7 ns, 80 mJ, and 532 nm Nd:YAG laser pulses. Between 0.4 ?s and 22.5 ?s after breakdown, the electron density decreases from 3.3 × 1017 cm-3 to 9 × 1013 cm-3, while the temperature drops from 3.2 eV to 0.1 eV. Spatially resolved Thomson scattering data recorded up to 17.5 ?s reveal that during this time the laser induced plasma expands at a rate given by R ˜ t0.4 consistent with a non-radiative spherical blast wave. This data also indicate the development of a toroidal structure in the lateral profile of both electron temperature and density. Rayleigh scattering data show that the gas density decreases in the center of the expanding plasma with a central scattering peak reemerging after about 12 ?s. We have utilized a zero dimensional kinetic global model to identify the dominant particle species versus delay time and this indicates that metastable helium and the He2+ molecular ion play an important role.

  9. Zero-energy neutron-triton and proton-Helium-3 scattering with \\eftnopi

    E-print Network

    Kirscher, Johannes

    2011-01-01

    Model-independent constraints for the neutron-triton and proton-Helium-3 scattering lengths are calculated with a leading-order interaction derived from an effective field theory without explicit pions. Using the singlet neutron-proton scattering length, the deuteron, and the triton binding energy as input, the predictions $\\ants=9.2\\pm2.6 $fm, $\\antt=7.6\\pm1.6 $fm, $\\aphes=3.6\\pm0.32 $fm, and $\\aphet=3.1\\pm 0.23 $fm are obtained. The calculations employ the resonating group method and include the Coulomb interaction when appropriate. The theoretical uncertainty is assessed via a variation of the regulator parameter of the short-distance interaction from $400 $MeV to $1.6 $GeV. The phase-shift and scattering-length results for the proton-Helium-3 system are consistent with a recent phase shift analysis and with model calculations. For neutron-triton, the results for the scattering lengths in both singlet and triplet channels are significantly smaller than suggested by R-matrix and partial-wave-analysis extrac...

  10. Scattering and absorption of ultracold atoms by nanotubes

    E-print Network

    Jetter, B; Schneeweiss, P; Gierling, M; Scheel, S; Günther, A; Fortágh, J; Judd, T E

    2012-01-01

    We study cold atoms scattering from static and vibrating nanotubes. We find the scattering potential calculations for dielectric tubes can be greatly simplified with a modified pairwise summation approach. Quantum reflection of atoms from a nanotube is shown to become important if a Bose-Einstein condensate is used. Non-trivial absorption of atoms by nanotubes, as seen in experiments, is explained by inter-atomic interactions and quantum pressure. Natural nanotube vibrations do not significantly reduce condensate fractions, but lower frequency oscillations can dramatically heat the cloud.

  11. Chaotic scattering of atoms at a standing laser wave

    E-print Network

    S. V. Prants

    2012-05-20

    Atoms, propagating across a detuned standing laser wave, can be scattered in a chaotic way even in the absence of spontaneous emission and any modulation of the laser field. Spontaneous emission masks the effect in some degree, but the Monte Carlo simulation shows that it can be observed in real experiments by the absorption imaging method or depositing atoms on a substrate. The effect of chaotic scattering is explained by a specific behavior of the dipole moments of atoms crossing the field nodes and is shown to depend strongly on the value of the atom-laser detuning.

  12. Creation evidence of the second non-dispersive Zakharenko wave by helium atomic beams in superfluid helium-II at low temperatures

    NASA Astrophysics Data System (ADS)

    Zakharenko, A. A.

    2007-10-01

    In this work, the experimental results of the creation of the second non-dispersive Zakharenko wave (C_{ph}=C_{g} ? 0) in the negative roton branch (the so-called second sound) of the bulk elementary excitations (BEEs) energy spectra are introduced. Several BEE signals detected by a bolometer situated in the isotopically pure liquid helium-II at low temperatures ˜100 mK are shown, which give evidence of negative roton creation in the liquid by helium atomic beams striking the liquid surface. The negative roton signals were clearly distinguished by the following ways: the negative roton signal created by helium atomic beams appeared earlier than the positive roton signal created by the beams, and presence of both positive and negative roton signals together. It is natural that the negative roton creation by the beams requires the ^{4}He-atom energies ˜12 K, while the positive roton creation by the atomic beams requires energies ˜35 K. Therefore, successive increase in the heater power resulting in an increase in the ^{4}He-atom energies gives solid evidence that the negative rotons are first created in the liquid by the helium atomic beams.

  13. Optical and electron spin resonance studies of xenon-nitrogen-helium condensates containing nitrogen and oxygen atoms.

    PubMed

    Boltnev, Roman E; Bykhalo, Igor B; Krushinskaya, Irina N; Pelmenev, Alexander A; Khmelenko, Vladimir V; Mao, Shun; Meraki, Adil; Wilde, Scott C; McColgan, Patrick T; Lee, David M

    2015-03-19

    We present the first observations of excimer XeO* molecules in molecular nitrogen films surrounding xenon cores of nanoclusters. Multishell nanoclusters form upon the fast cooling of a helium jet containing small admixtures of nitrogen and xenon by cold helium vapor (T = 1.5 K). Such nanoclusters injected into superfluid helium aggregate into porous impurity-helium condensates. Passage of helium gas with admixtures through a radio frequency discharge allows the storage of high densities of radicals stabilized in impurity-helium condensates. Intense recombination of the radicals occurs during destruction of such condensates and generates excited species observable because of optical emission. Rich spectra of xenon-oxygen complexes have been detected upon destruction of xenon-nitrogen-helium condensates. A xenon environment quenches metastable N((2)D) atoms but has a much weaker effect on the luminescence of N((2)P) atoms. Electron spin resonance spectra of N((4)S) atoms trapped in xenon-nitrogen-helium condensates have been studied. High local concentrations of nitrogen atoms (up to 10(21) cm(-3)) stabilized in xenon-nitrogen nanoclusters have been revealed. PMID:25353614

  14. Rydberg States of rb and cs Atoms on Helium Nanodroplets: a Rydberg-Ritz Analysis

    NASA Astrophysics Data System (ADS)

    Lackner, Florian; Krois, Gunter; Ernst, Wolfgang E.

    2013-06-01

    Rydberg series of Rb and Cs atoms on the surface of helium nanodroplets (He_{N}) have been studied by resonance enhanced multi-photon ionization spectroscopy and laser induced fluorescence spectroscopy. The recorded excitation spectra are analyzed by using a Rydberg-Ritz approach. The dependence of the quantum defects on the principal quantum number within a Rydberg series gives insight into the interaction between the alkali atom's valence electron and the superfluid helium droplet. For higher excited states a screening of the valence electron from the alkali atom core by the helium droplet is observed. For lower states the strength of the screening effect decreases and the quantum defects are found to lie closer to free atom values. In addition, the large spin-orbit (SO) constant of the Cs-He_{N} nP(^{2}?) states allows a detailed study of the influence of the helium droplet on the SO splitting as function of the principal quantum number. Within the pseudo-diatomic picture the alkali-He_{N} system represents a diatomic molecule. The coupling of the Cs valence electrons spin and the orbital angular momentum with the intermolecular axis, which is defined by the connection between the droplet center and the alkali nucleus, depends on the strength of the atomic SO interaction. While the splitting of the 6^{2}P_{1/2}(^{2}?_{1/2}) and 6^{2}P_{3/2}(^{2}?_{3/2}) components has an atom-like character (Hund's case (c) coupling), the SO splitting of higher n states is lower than the atomic value (Hund's case (a) coupling). C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in: Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, (2011) F. Lackner, G. Krois, M. Theisen, M. Koch, and W.E. Ernst, Phys. Chem. Chem. Phys., 13, 18781-18788 (2011) F. Lackner, G. Krois, and W.E. Ernst, J. Phys. Chem. Lett., 3, 1404-1408 (2012)

  15. Atomic delay in helium, neon, argon and krypton

    NASA Astrophysics Data System (ADS)

    Palatchi, Caryn; Dahlström, J. M.; Kheifets, A. S.; Ivanov, I. A.; Canaday, D. M.; Agostini, P.; DiMauro, L. F.

    2014-12-01

    Photoionization by an eXtreme UltraViolet (XUV) attosecond pulse train (APT) in the presence of an infrared pulse (RABBITT method) conveys information about the atomic photoionization delay. By taking the difference of the spectral delays between pairs of rare gases (Ar,He), (Kr,He) and (Ne,He) it is possible to eliminate in each case the larger group delay (‘attochirp’) associated with the APT itself and obtain the Ar, Kr and Ne Wigner delays referenced to model calculations of the He delay. In this work we measure how the delays vary as a function of XUV photon energy but we cannot determine the absolute delay difference between atoms due to lack of precise knowledge of the initial conditions. The extracted delays are compared with several theoretical predictions and the results are consistent within 30 as over the energy range from 10 to 50 eV. An ‘effective’ Wigner delay over all emission angles is found to be more consistent with our angle-integrated measurement near the Cooper minimum in Ar. We observe a few irregular features in the delay that may be signatures of resonances. .

  16. Proposed method for laser spectroscopy of pionic helium atoms to determine the charged-pion mass

    E-print Network

    Masaki Hori; Anna Sótér; Vladimir I. Korobov

    2014-04-30

    Metastable pionic helium ($\\pi{\\rm He}^+$) is a three-body atom composed of a helium nucleus, an electron occupying the $1s$ ground state, and a negatively charged pion $\\pi^-$ in a Rydberg state with principal- and orbital angular momentum quantum numbers of $n\\sim \\ell+1\\sim 16$. We calculate the spin-independent energies of the $\\pi{\\rm ^3He}^+$ and $\\pi{\\rm ^4He}^+$ isotopes in the region $n=15$--19. These include relativistic and quantum electrodynamics corrections of orders $R_{\\infty}\\alpha^2$ and $R_{\\infty}\\alpha^3$ in atomic units, where $R_{\\infty}$ and $\\alpha$ denote the Rydberg and fine structure constants. The fine-structure splitting due to the coupling between the electron spin and the orbital angular momentum of the $\\pi^-$, and the radiative and Auger decay rates of the states are also calculated. Some states $(n,\\ell)=(16,15)$ and $(17,16)$ retain nanosecond-scale lifetimes against $\\pi^-$ absorption into the helium nucleus. We propose to use laser pulses to induce $\\pi^-$ transitions from these metastable states, to states with large ($\\sim 10^{11}$ s$^{-1}$) Auger rates. The $\\pi{\\rm He}^{2+}$ ion that remains after Auger emission of the $1s$ electron undergoes Stark mixing with the $s$, $p$, and $d$ states during collisions with the helium atoms in the experimental target. This leads to immediate nuclear absorption of the $\\pi^-$. The resonance condition between the laser beam and the atom is thus revealed as a sharp spike in the rates of neutrons, protons, deuterons, and tritons that emerge....(continued)

  17. Precise laser spectroscopy of the antiprotonic helium atom and CPT test on antiproton mass and charge

    E-print Network

    H. Yamaguchi; J. Eades; R. S. Hayano; M. Hori; D. Horvath; T. Ishikawa; B. Juhasz; J. Sakaguchi; H. A. Torii; E. Widmann; T. Yamazaki

    2003-03-19

    We have measured twelve transition frequencies of the antiprotonic helium atom (pbar-He+) with precisions of 0.1--0.2 ppm using a laser spectroscopic method. The agreement between the experiment and theories was so good that we can put a limit on the proton-antiproton mass (or charge) difference. The new limit is expected to be much smaller than the already published value, 60 ppb.

  18. Quantum turbulence: from superfluid helium to atomic Bose-Einstein condensates

    Microsoft Academic Search

    Makoto Tsubota

    2009-01-01

    This article reviews recent developments in quantum fluid dynamics and quantum turbulence (QT) for superfluid helium and atomic Bose–Einstein condensates. Quantum turbulence was discovered in superfluid He in the 1950s, but the field moved in a new direction starting around the mid-1990s. Quantum turbulence is comprised of quantised vortices that are definite topological defects arising from the order parameter appearing

  19. Scattering properties of weakly bound dimers of fermionic atoms

    Microsoft Academic Search

    Dmitry Petrov; Christophe Salomon; Georgy Shlyapnikov

    2005-01-01

    We consider weakly bound diatomic molecules (dimers) formed in a two-component atomic Fermi gas with a large positive scattering length for the interspecies interaction. We develop a theoretical approach for calculating atom-dimer and dimer-dimer elastic scattering and for analyzing the inelastic collisional relaxation of the molecules into deep bound states. This approach is based on the single-channel zero-range approximation, and

  20. Absorption spectrum of atomic impurities in isotopic mixtures of liquid helium

    NASA Astrophysics Data System (ADS)

    Mateo, David; Hernando, Alberto; Barranco, Manuel; Mayol, Ricardo; Pi, Martí

    2011-05-01

    We theoretically describe the absorption spectrum of atomic impurities in isotopic mixtures of liquid helium within a zero-temperature density functional approach. Two situations are considered. In the first one, the absorption spectrum of Na atoms attached to He41000-He3N3 droplets with N3 values from 100 to 3000 is presented as a case study of an impurity that does not dissolve into helium droplets. In the second one, the absorption spectrum of Mg atoms in liquid He3-He4 mixtures is presented as a case study of an impurity dissolved into liquid helium. We have found that the absorption spectrum of the impurity is rather insensitive to the isotopic composition because the line shift is mostly affected by the total He density around the impurity, not by its actual composition. For bulk liquid mixtures, results are presented as a function of pressure at selected values of the He3 concentration. The results for isotopically pure He3 and He4 liquids doped with Mg are compared with available experimental data.

  1. Helium in chirped laser fields as a time-asymmetric atomic switch

    SciTech Connect

    Kaprálová-Ž?ánská, Petra Ruth, E-mail: kapralova@jh-inst.cas.cz [Department of Radiation and Chemical Physics, Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8 (Czech Republic); J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, 182 23 Prague 8 (Czech Republic); Moiseyev, Nimrod, E-mail: nimrod@tx.technion.ac.il [Schulich Faculty of Chemistry and Faculty of Physics, Technion – Israel Institute of Technology, Haifa 32000 (Israel)

    2014-07-07

    Tuning the laser parameters exceptional points in the spectrum of the dressed laser helium atom are obtained. The weak linearly polarized laser couples the ground state and the doubly excited P-states of helium. We show here that for specific chirped laser pulses that encircle an exceptional point one can get the time-asymmetric phenomenon, where for a negative chirped laser pulse the ground state is transformed into the doubly excited auto-ionization state, while for a positive chirped laser pulse the resonance state is not populated and the neutral helium atoms remains in the ground state as the laser pulse is turned off. Moreover, we show that the results are very sensitive to the closed contour we choose. This time-asymmetric state exchange phenomenon can be considered as a time-asymmetric atomic switch. The optimal time-asymmetric switch is obtained when the closed loop that encircles the exceptional point is large, while for the smallest loops, the time-asymmetric phenomenon does not take place. A systematic way for studying the effect of the chosen closed contour that encircles the exceptional point on the time-asymmetric phenomenon is proposed.

  2. Negative ion productions in high velocity collision between small carbon clusters and Helium atom target

    NASA Astrophysics Data System (ADS)

    M, Chabot; K, Béroff; T, Pino; G, Féraud; N, Dothi; Padellec A, Le; G, Martinet; S, Bouneau; Y, Carpentier

    2012-11-01

    We measured absolute double capture cross section of Cn+ ions (n=1,5) colliding, at 2.3 and 2.6 a.u velocities, with an Helium target atom and the branching ratios of fragmentation of the so formed electronically excited anions Cn-*. We also measured absolute cross section for the electronic attachment on neutral Cn clusters colliding at same velocities with He atom. This is to our knowledge the first measurement of neutral-neutral charge exchange in high velocity collision.

  3. Absolute number densities of helium metastable atoms determined by atomic absorption spectroscopy in helium plasma-based discharges used as ambient desorption/ionization sources for mass spectrometry

    NASA Astrophysics Data System (ADS)

    Reininger, Charlotte; Woodfield, Kellie; Keelor, Joel D.; Kaylor, Adam; Fernández, Facundo M.; Farnsworth, Paul B.

    2014-10-01

    The absolute number densities of helium atoms in the 2s 3S1 metastable state were determined in four plasma-based ambient desorption/ionization sources by atomic absorption spectroscopy. The plasmas included a high-frequency dielectric barrier discharge (HF-DBD), a low temperature plasma (LTP), and two atmospheric-pressure glow discharges, one with AC excitation and the other with DC excitation. Peak densities in the luminous plumes downstream from the discharge capillaries of the HF-DBD and the LTP were 1.39 × 1012 cm- 3 and 0.011 × 1012 cm- 3, respectively. Neither glow discharge produced a visible afterglow, and no metastable atoms were detected downstream from the capillary exits. However, densities of 0.58 × 1012 cm- 3 and 0.97 × 1012 cm- 3 were measured in the interelectrode regions of the AC and DC glow discharges, respectively. Time-resolved measurements of metastable atom densities revealed significant random variations in the timing of pulsed absorption signals with respect to the voltage waveforms applied to the discharges.

  4. Proposed method for laser spectroscopy of pionic helium atoms to determine the charged-pion mass

    NASA Astrophysics Data System (ADS)

    Hori, Masaki; Sótér, Anna; Korobov, Vladimir I.

    2014-04-01

    Metastable pionic helium (?He+) is a three-body atom composed of a helium nucleus, an electron occupying the 1s ground state, and a negatively charged pion ?- in a Rydberg state with principal and orbital angular momentum quantum numbers of n ˜?+1˜16. We calculate the spin-independent energies of the ?3He+ and ?4He+ isotopes in the region n =15-19. These include relativistic and quantum electrodynamics corrections of orders R??2 and R??3 in atomic units, where R? and ? denote the Rydberg and fine structure constants. The fine-structure splitting due to the coupling between the electron spin and the orbital angular momentum of the ?- and the radiative and Auger decay rates of the states are also calculated. Some states (n,?)=(16,15) and (17,16) retain nanosecond-scale lifetimes against ?- absorption into the helium nucleus. We propose the use of laser pulses to induce ?- transitions from these metastable states to states with large (˜1011 s-1) Auger rates. The ?He2+ ion that remains after Auger emission of the 1s electron undergoes Stark mixing with the s, p, and d states during collisions with the helium atoms in the experimental target. This leads to immediate nuclear absorption of the ? -. The resonance condition between the laser beam and the atom is thus revealed as a sharp spike in the rates of neutrons, protons, deuterons, and tritons that emerge. A resonance curve is obtained from which the ?He+ transition frequency can in principle be determined with a fractional precision of 10-8-10-6 provided the systematic uncertainties can be controlled. By comparing the measured ?He+ frequencies with the calculated values, the ?- mass may be determined with a similar precision. The ?He+ will be synthesized by allowing a high-intensity (>108 s-1) beam of ?-produced by a cyclotron to come to rest in a helium target. The precise time structure of the ?- beam is used to ensure a sufficient rate of coincidence between the resonant laser pulses and the ?He+ atoms.

  5. Thomson scattering in the average-atom approximation.

    PubMed

    Johnson, W R; Nilsen, J; Cheng, K T

    2012-09-01

    The average-atom model is applied to study Thomson scattering of x-rays from warm dense matter with emphasis on scattering by bound electrons. Parameters needed to evaluate the dynamic structure function (chemical potential, average ionic charge, free electron density, bound and continuum wave functions, and occupation numbers) are obtained from the average-atom model. The resulting analysis provides a relatively simple diagnostic for use in connection with x-ray scattering measurements. Applications are given to dense hydrogen, beryllium, aluminum, and titanium plasmas. In the case of titanium, bound states are predicted to modify the spectrum significantly. PMID:23031036

  6. Dynamics of entanglement between two atomic samples with spontaneous scattering

    SciTech Connect

    Di Lisi, Antonio; De Siena, Silvio; Illuminati, Fabrizio [Dipartimento di Fisica 'E. R. Caianiello', Universita di Salerno, INFM-UdR di Salerno, INFN Sezione di Napoli, Gruppo Collegato di Salerno, Via. S. Allende, I-84081 Baronissi, SA (Italy)

    2004-07-01

    We investigate the effects of spontaneous scattering on the evolution of entanglement of two atomic samples, probed by phase-shift measurements on optical beams interacting with both samples. We develop a formalism of conditional quantum evolutions and present a wave function analysis implemented in numerical simulations of the state vector dynamics. This method allows us to track the evolution of entanglement and to compare it with the predictions obtained when spontaneous scattering is neglected. We provide numerical evidence that the interferometric scheme to entangle atomic samples is only marginally affected by the presence of spontaneous scattering and should thus be robust even in more realistic situations.

  7. Scattering properties of weakly bound dimers of fermionic atoms

    SciTech Connect

    Petrov, D.S. [ITAMP, Harvard-Smithsonian Center for Astrophysics, and Harvard-MIT Center for Ultracold Atoms, Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106-4030 (United States); Russian Research Center Kurchatov Institute, Kurchatov Square, 123182 Moscow (Russian Federation); Salomon, C. [Laboratoire Kastler-Brossel, Ecole Normale Superieure, 24 rue Lhomond, 75005 Paris (France); Shlyapnikov, G.V. [Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106-4030 (United States); Russian Research Center Kurchatov Institute, Kurchatov Square, 123182 Moscow (Russian Federation); Laboratoire Physique Theorique et Modeles Statistique, Universite Paris Sud, Batiment 100, 91405 Orsay (France); Van der Waals-Zeeman Institute, University of Amsterdam, Valckenierstraat 65/67, 1018 XE Amsterdam (Netherlands)

    2005-01-01

    We consider weakly bound diatomic molecules (dimers) formed in a two-component atomic Fermi gas with a large positive scattering length for the interspecies interaction. We develop a theoretical approach for calculating atom-dimer and dimer-dimer elastic scattering and for analyzing the inelastic collisional relaxation of the molecules into deep bound states. This approach is based on the single-channel zero-range approximation, and we find that it is applicable in the vicinity of a wide two-body Feshbach resonance. Our results draw prospects for various interesting manipulations of weakly bound dimers of fermionic atoms.

  8. Probing helium nano-bubble formation in tungsten with grazing incidence small angle x-ray scattering

    NASA Astrophysics Data System (ADS)

    Thompson, M.; Kluth, P.; Doerner, R. P.; Kirby, N.; Corr, C.

    2015-04-01

    Helium nano-bubble formation in plasma facing materials has emerged as a major concern for the next-step fusion experiment ITER, where helium plasmas will be used during the tokamak's start-up phase. Here, we demonstrate that grazing incidence small-angle x-ray scattering is a powerful technique for the analysis of helium nano-bubble formation in tungsten. We measured helium bubbles with sizes between 1.5–2.5 nm in tungsten exposed to helium plasma at 700 °C, where a smaller number of larger bubbles were also observed. Depth distributions can be estimated by taking successive measurements across a range of x-ray incidence angles. Compared with traditional approaches in the field, such as transmission electron microscopy, this technique provides information across a much larger volume with high statistical precision, whilst also being non-destructive.

  9. Theory of direct scattering of neutral and charged atoms

    NASA Technical Reports Server (NTRS)

    Franco, V.

    1979-01-01

    The theory for direct elastic and inelastic collisions between composite atomic systems formulated within the framework of the Glauber approximation is presented. It is shown that the phase-shift function is the sum of a point Coulomb contribution and of an expression in terms of the known electron-hydrogen-atom and proton-hydrogen-atom phase shift function. The scattering amplitude is reexpressed, the pure Coulomb scattering in the case of elastic collisions between ions is isolated, and the exact optical profile function is approximated by a first-order expansion in Glauber theory which takes into account some multiple collisions. The approximate optical profile function terms corresponding to interactions involving one and two electrons are obtained in forms of Meijer G functions and as a one-dimensional integral, and for collisions involving one or two neutral atoms, the scattering amplitude is further reduced to a simple closed-form expression.

  10. A discrete variable representation for electron-hydrogen atom scattering

    SciTech Connect

    Gaucher, L.F.

    1994-08-01

    A discrete variable representation (DVR) suitable for treating the quantum scattering of a low energy electron from a hydrogen atom is presented. The benefits of DVR techniques (e.g. the removal of the requirement of calculating multidimensional potential energy matrix elements and the availability of iterative sparse matrix diagonalization/inversion algorithms) have for many years been applied successfully to studies of quantum molecular scattering. Unfortunately, the presence of a Coulomb singularity at the electrically unshielded center of a hydrogen atom requires high radial grid point densities in this region of the scattering coordinate, while the presence of finite kinetic energy in the asymptotic scattering electron also requires a sufficiently large radial grid point density at moderate distances from the nucleus. The constraints imposed by these two length scales have made application of current DVR methods to this scattering event difficult.

  11. Dynamics of molecular and polymeric interfaces probed with atomic beam scattering and scanning probe imaging.

    PubMed

    Brown, Ryan D; Tong, Qianqian; Becker, James S; Freedman, Miriam A; Yufa, Nataliya A; Sibener, S J

    2012-01-01

    The scattering of atomic and molecular beams from well-characterized surfaces is a useful method for studying the dynamics of gas-surface interactions, providing precise information on the energy and momentum exchange which occur in such encounters. We apply this technique to new systems including disordered films of macromolecules, complex interfaces of macromolecular systems, and hybrid organic-semiconductor interfaces. Time-lapse atomic force microscopy studies of diblock copolymer structural evolution and fluctuations complement the scattering data to give a more complete understanding of dynamical processes in these complex disordered films. Our new scattering findings quantitatively characterize changes in interfacial dynamics including confinement in thin films of poly(methyl methacrylate) and changes in the physical properties of poly(ethylene terephthalate) films as they transform from the glassy to their semicrystalline phase. Further measurements on a hybrid organic-semiconductor interface, methyl-terminated silicon (111), reveal that the surface thermal motion and gas-surface energy accommodation are dominated by local molecular vibrations while the interfacial lattice dynamics remain accessible through helium scattering. High temperature atomic force microscopy allows direct, real-time visualization of structural reorganization and defect migration in poly(styrene)-block-poly(methyl methacrylate) films, revealing details of film reorganization and thermal annealing. Moreover, we employed lithographically created channels to guide the alignment of polymer microdomains. This, in turn, allows direct observation of the mechanisms for diffusion and annihilation of dislocation and disclination defects. In summary, this paper elaborates on the power of combining atom scattering and scanning probe microscopy to interrogate the vibrational dynamics, energy accommodation, energy flow, and structural reorganization in complex interfaces. PMID:23230775

  12. Entanglement interferometry for precision measurement of atomic scattering properties

    E-print Network

    Artur Widera; Olaf Mandel; Markus Greiner; Susanne Kreim; Theodor W. Hänsch; Immanuel Bloch

    2003-10-30

    We report on a two-particle matter wave interferometer realized with pairs of trapped 87Rb atoms. Each pair of atoms is confined at a single site of an optical lattice potential. The interferometer is realized by first creating a coherent spin-mixture of the two atoms and then tuning the inter-state scattering length via a Feshbach resonance. The selective change of the inter-state scattering length leads to an entanglement dynamics of the two-particle state that can be detected in a Ramsey interference experiment. This entanglement dynamics is employed for a precision measurement of atomic interaction parameters. Furthermore, the interferometer allows to separate lattice sites with one or two atoms in a non-destructive way.

  13. Time-resolved Thomson scattering on high-intensity laser-produced hot dense helium plasmas

    NASA Astrophysics Data System (ADS)

    Sperling, P.; Liseykina, T.; Bauer, D.; Redmer, R.

    2013-02-01

    The introduction of brilliant free-electron lasers enables new pump-probe experiments to characterize warm and hot dense matter states, i.e. systems at solid-like densities and temperatures of one to several hundred eV. Such extreme conditions are relevant for high-energy density studies such as, e.g., in planetary physics and inertial confinement fusion. We consider here a liquid helium jet pumped with a high-intensity optical short-pulse laser that is subsequently probed with brilliant soft x-ray radiation. The optical short-pulse laser generates a strongly inhomogeneous helium plasma which is characterized with particle-in-cell simulations. We derive the respective Thomson scattering spectrum based on the Born-Mermin approximation for the dynamic structure factor considering the full density and temperature-dependent Thomson scattering cross section throughout the target. We observe plasmon modes that are generated in the interior of the target and study their temporal evolution. Such pump-probe experiments are promising tools to measure the important plasma parameters density and temperature. The method described here can be applied to various pump-probe scenarios by combining optical lasers, soft x-rays and hard x-ray sources.

  14. Spectroscopic studies of impurity-helium condensates containing stabilized N and O atoms

    NASA Astrophysics Data System (ADS)

    Krushinskaya, I. N.; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. D.

    2012-12-01

    We present optical spectra of impurity-helium condensates during the process of their formation by injection of gas mixtures N2-Rg-He (Rg=Ne, Kr) into bulk superfluid helium after passing through a RF discharge. Atomic lines of He, Ne, Kr, N, O atoms as well as bands (1+ and 2+ systems of N2) are present in the spectral range 320-1100 nm studied in these experiments. We also detected spectra emitted by the samples during their destruction, stimulated by warming through the temperature range 1.5-15 K The luminescence spectra of the N-N2-He and N-N2-Ne-He samples contain only intense N(2D-4S) (?-group) and O(1D-1S) (?-group) lines. For the N-N2-Ne-He sample we observed the transformation of spectra of the ?-group. In thermo-stimulated luminescence spectra of the N-N2-Kr-He samples, the intense ?-group of O atoms and M-bands of NO molecules were found. Differences in the spectra obtained during destruction of N-N2-Ne-He and N-N2-Kr-He samples may be explained by a different shell structure of the nanoclusters formed during sample preparation.

  15. Bragg scattering of slow atoms from a standing light wave

    Microsoft Academic Search

    S. Kunze; S. Dürr; G. Rempe

    1996-01-01

    Slow atoms from a magneto-optical trap are used to study diffraction from a near-resonant standing-wave light field. Long interaction times make it possible to observe unidirectional Bragg scattering. In particular, the Pendellösung interference effect between two resonant momentum states is demonstrated for first- and second-order diffraction. The oscillation frequency of second-order scattering shows a transition from a four-photon type process

  16. Elastic scattering of electrons from Rb, Cs and Fr atoms

    NASA Astrophysics Data System (ADS)

    Gangwar, R. K.; Tripathi, A. N.; Sharma, L.; Srivastava, R.

    2010-04-01

    Differential, integrated elastic, momentum-transfer and total cross sections as well as differential S, T and U spin parameters for scattering of electrons from rubidium, caesium and francium atoms in the incident energy range up to 300 eV are calculated using a relativistic Dirac equation. The projectile electron-target atom interaction is represented by both real and complex parameter-free optical potentials for obtaining the solution of a Dirac equation for scattered electrons. The Dirac-Fock wavefunctions have been used to represent the Rb, Cs and Fr target atoms. The results of differential cross sections and spin asymmetry parameter S for e-Rb and e-Cs have been compared with the available experimental and theoretical results. Detailed results are reported for the elastic scattering of electrons from the ground states of a francium atom for the first time in the wide range of incident electron energies. The results of electron-Fr elastic scattering show the similar features to those obtained in the case of e-Rb and e-Cs elastic scattering.

  17. Ultra-precise single-ion atomic mass measurements on deuterium and helium-3

    NASA Astrophysics Data System (ADS)

    Zafonte, S. L.; Van Dyck, R. S., Jr.

    2015-04-01

    The former University of Washington Penning Trap Mass Spectrometer (UW-PTMS), now located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, was used in the decade before the move to determine new values for the deuteron atomic mass, M (2H+) = 2.013?553 212?745(40) u, and the deuterium atomic mass, M (2H) = 2.014?101 778?052(40) u, both of which are now more than an order-of-magnitude more accurate than the previous best 1994-MIT measurements of these quantities. The new value for the deuteron’s mass can then be used with the accepted 2010-CODATA proton mass and the most recent 1999-measurement of the 2.2 MeV gamma-ray binding energy of the deuteron to refine the neutron’s mass to mn = 1.008?664 916?018(435) u which has about half the uncertainty relative to the value computed using that previous 1994-MIT deuterium measurement. As a result, further improvements of mn must now come from a more accurate determination of the wavelength of this gamma ray. In this same period of time, this spectrometer has also been used to determine new values for the helion atomic mass, M (3He2+) = 3.014?932 246?668(43) u, and the neutral helium-3 atomic mass, M (3He) = 3.016?029 321?675(43) u, which are both about 60 times more accurate than the 2006-SMILETRAP measurements, but disagree with the 4.4-times less-accurate 2015-Florida-State measurements by 0.76 nu. It is expected that these helium-3 results will be used in the future 3H/3He mass ratio (to be determined by the Heidelberg, Germany version of the old UW-PTMS) in order to generate a more accurate value for the tritium atomic mass.

  18. Electron elastic scattering off a semifilled-shell atom: The Mn atom

    NASA Astrophysics Data System (ADS)

    Dolmatov, V. K.; Amusia, M. Ya.; Chernysheva, L. V.

    2013-10-01

    The impact of both exchange interaction and electron correlation, as well as their combined impact, on electron elastic scattering off a semifilled-shell Mn(⋯3d54s2, 6S) atom are theoretically studied in the electron energy range of ?=0-25 eV. Corresponding elastic-scattering phase shifts ??(?) as well as partial ??(?) and total ?(?) cross sections are found to be subject to a strong correlation impact. The latter is shown to drastically differ for oppositely spin-polarized scattered electrons in some cases, thereby bringing significant differences in corresponding ??(?)s, ??(?)s, and ?(?)s between these electrons. This is proven to be an inherent feature of electron scattering off a semifilled-shell atom in general. Electron correlation is accounted for in the framework of the self-energy part ? of the Green function of a scattered electron concept. The latter is calculated both in the second-order perturbation theory in the Coulomb interelectron interaction as well as beyond it by solving the Dyson equation for ?. The significance of the “Dyson” correlation corrections in e-+Mn scattering is unraveled. They are shown to noticeably increase the inherent differences between elastic-scattering phase shifts and cross sections of spin-up (?) and spin-down (?) polarized electrons scattered off a spin-polarized Mn atom, in some cases. In particular, the existence of a narrow resonant maximum in ??(?) near ??8 eV but the absence of such in ??(?) in e-+Mn scattering is predicted.

  19. Formation of the muonic helium atom /alpha particle-muon-electron/ and observation of its Larmor precession

    NASA Technical Reports Server (NTRS)

    Souder, P. A.; Casperson, D. E.; Crane, T. W.; Hughes, V. W.; Lu, D. C.; Yam, M. H.; Orth, H.; Reist, H. W.; Zu Putlitz, G.

    1975-01-01

    Experiments are described in which it proved possible to form the muonic helium atom by stopping polarized negative muons in a helium gas with a 2% xenon admixture at a pressure of 14 atm. The observed Larmor precession amplitudes are plotted against the gyromagnetic ratio for both muons and antimuons stopped in He + 2% Xe. In addition, a non-zero residual polarization of 0.06 plus or minus 0.01 was measured for muons stopped in pure helium gas, which corresponds to a depolarization factor of 18 plus or minus 3.

  20. Photoionisation of a helium atom involving autoionisation states coupled by a circularly polarised laser field

    SciTech Connect

    Gryzlova, E V [Department of Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation); Magunov, A I [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Rotter, I [Max-Planck-Institut fur Physik komplexer Systeme (Germany); Strakhova, S I [D.V. Skobel'tsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

    2005-01-31

    The rotating wave approximation is used to obtain parametric expressions for the resonance cross section for the atomic ground state ionisation by linearly polarised probe radiation in the vicinity of an autoionisation state coupled resonantly to another autoionisation state through circularly polarised laser radiation. Calculations are made for the 2s2p {sup 1}P and 2s3d {sup 1}D states of the helium atom. It is shown that the structure of the photoionisation cross-section spectrum formed for circularly polarised laser radiation differs qualitatively from the structure formed in the case of linear polarisation. The dependence of this structure on the intensity and frequency of laser radiation and the direction of polarisation of the probe radiation is studied. (interaction of laser radiation with matter. laser plasma)

  1. Communication: Angular momentum alignment and fluorescence polarization of alkali atoms photodetached from helium nanodroplets

    SciTech Connect

    Hernando, Alberto; Beswick, J. Alberto; Halberstadt, Nadine [LCAR-IRSAMC, Université Toulouse 3 - Paul Sabatier and CNRS, 31062 Toulouse (France)] [LCAR-IRSAMC, Université Toulouse 3 - Paul Sabatier and CNRS, 31062 Toulouse (France)

    2013-12-14

    The theory of photofragments angular momentum polarization is applied to the photodetachment of an electronically excited alkali atom from a helium nanocluster (N = 200). The alignment of the electronic angular momentum of the bare excited alkali atoms produced is calculated quantum mechanically by solving the excited states coupled equations with potentials determined by density functional theory (DFT). Pronounced oscillations as a function of excitation energy are predicted for the case of Na@(He){sub 200}, in marked contrast with the absorption cross-section and angular distribution of the ejected atoms which are smooth functions of the energy. These oscillations are due to quantum interference between different coherently excited photodetachment pathways. Experimentally, these oscillations should be reflected in the fluorescence polarization and polarization-resolved photoelectron yield of the ejected atoms, which are proportional to the electronic angular momentum alignment. In addition, this result is much more general than the test case of NaHe{sub 200} studied here. It should be observable for larger droplets, for higher excited electronic states, and for other alkali as well as for alkali-earth atoms. Detection of these oscillations would show that the widely used pseudo-diatomic model can be valid beyond the prediction of absorption spectra and could help in interpreting parts of the dynamics, as already hinted by some experimental results on angular anisotropy of bare alkali fragments.

  2. Communication: Angular momentum alignment and fluorescence polarization of alkali atoms photodetached from helium nanodroplets

    NASA Astrophysics Data System (ADS)

    Hernando, Alberto; Beswick, J. Alberto; Halberstadt, Nadine

    2013-12-01

    The theory of photofragments angular momentum polarization is applied to the photodetachment of an electronically excited alkali atom from a helium nanocluster (N = 200). The alignment of the electronic angular momentum of the bare excited alkali atoms produced is calculated quantum mechanically by solving the excited states coupled equations with potentials determined by density functional theory (DFT). Pronounced oscillations as a function of excitation energy are predicted for the case of Na@(He)200, in marked contrast with the absorption cross-section and angular distribution of the ejected atoms which are smooth functions of the energy. These oscillations are due to quantum interference between different coherently excited photodetachment pathways. Experimentally, these oscillations should be reflected in the fluorescence polarization and polarization-resolved photoelectron yield of the ejected atoms, which are proportional to the electronic angular momentum alignment. In addition, this result is much more general than the test case of NaHe200 studied here. It should be observable for larger droplets, for higher excited electronic states, and for other alkali as well as for alkali-earth atoms. Detection of these oscillations would show that the widely used pseudo-diatomic model can be valid beyond the prediction of absorption spectra and could help in interpreting parts of the dynamics, as already hinted by some experimental results on angular anisotropy of bare alkali fragments.

  3. Communication: angular momentum alignment and fluorescence polarization of alkali atoms photodetached from helium nanodroplets.

    PubMed

    Hernando, Alberto; Beswick, J Alberto; Halberstadt, Nadine

    2013-12-14

    The theory of photofragments angular momentum polarization is applied to the photodetachment of an electronically excited alkali atom from a helium nanocluster (N = 200). The alignment of the electronic angular momentum of the bare excited alkali atoms produced is calculated quantum mechanically by solving the excited states coupled equations with potentials determined by density functional theory (DFT). Pronounced oscillations as a function of excitation energy are predicted for the case of Na@(He)200, in marked contrast with the absorption cross-section and angular distribution of the ejected atoms which are smooth functions of the energy. These oscillations are due to quantum interference between different coherently excited photodetachment pathways. Experimentally, these oscillations should be reflected in the fluorescence polarization and polarization-resolved photoelectron yield of the ejected atoms, which are proportional to the electronic angular momentum alignment. In addition, this result is much more general than the test case of NaHe200 studied here. It should be observable for larger droplets, for higher excited electronic states, and for other alkali as well as for alkali-earth atoms. Detection of these oscillations would show that the widely used pseudo-diatomic model can be valid beyond the prediction of absorption spectra and could help in interpreting parts of the dynamics, as already hinted by some experimental results on angular anisotropy of bare alkali fragments. PMID:24329048

  4. Estimates of Intra-Beam Scattering in Atomic Beam Sources

    NASA Astrophysics Data System (ADS)

    Stancari, M.; Ciullo, G.; Atutov, S.; Barion, L.; Capiluppi, M.; Contalbrigo, M.; Dalpiaz, P. F.; Giordano, F.; Lenisa, P.; Statera, M.; Wang, M.

    2005-08-01

    The intensity of atomic beam sources has reached a limit in recent years of around 1017 atoms/s, limiting in turn the luminosity of HEP experiments utilizing polarized gas targets inside storage rings. It has been suggested that this intensity limit is a result of intra-beam scattering, although this has not been decisively proven. A method to estimate these losses, based upon the calculated beam density, has been developed. The first results are compared with data from both the molecular beam of the Ferrara SpinLab test bench and the atomic beam of the HERMES source.

  5. Rubidium Atoms on Helium Droplets: Analysis of AN Exotic Rydberg Complex

    NASA Astrophysics Data System (ADS)

    Lackner, Florian; Krois, Günter; Koch, Markus; Ernst, Wolfgang E.

    2012-06-01

    Rubidium atoms on the surface of superfluid helium droplets have been excited into Rydberg states. The excitation spectrum of the Rb-He_N system has been recorded from the 5^2D state manifold up to the ionization threshold by resonant three-photon-ionization time-of-flight spectroscopy. The observation of droplet size dependent shifts of excited states with respect to bare atom states is explained by a decreased quantum defect and a lowered ionization threshold. Within the scope of a Rydberg model we demonstrate that quantum defects and ionization thresholds are constant for each specific Rydberg series, which confirms the Rydberg character of excited Rubidium states on helium droplets. A set of six Rydberg series could be identified. Individual Rydberg states are observed with effective principle quantum numbers up to n* ? 19 and l ? 3, for which the expectation value of the electron orbital radius is about ten times larger than the droplet radius. M. Theisen, F. Lackner, G. Krois, and W.E. Ernst, J. Phys. Chem. Lett., 2, 2778-2782 (2011) F. Lackner, G. Krois, M. Theisen, M. Koch, and W.E. Ernst, Phys. Chem. Chem. Phys., 13, 18781-18788 (2011) J.E. Murphy, J.M. Berg, A.J. Merer, N.A. Harris, and R.W. Field, Phys. Rev. Lett. 65, 1861 (1990)

  6. How accurately does the free complement wave function of a helium atom satisfy the Schrödinger equation?

    PubMed

    Nakashima, Hiroyuki; Nakatsuji, Hiroshi

    2008-12-12

    The local energy defined by Hpsi/psi must be equal to the exact energy E at any coordinate of an atom or molecule, as long as the psi under consideration is exact. The discrepancy from E of this quantity is a stringent test of the accuracy of the calculated wave function. The H-square error for a normalized psi, defined by sigma2 identical with psi|(H-E)2|psi, is also a severe test of the accuracy. Using these quantities, we have examined the accuracy of our wave function of a helium atom calculated using the free complement method that was developed to solve the Schrödinger equation. Together with the variational upper bound, the lower bound of the exact energy calculated using a modified Temple's formula ensured the definitely correct value of the helium fixed-nucleus ground state energy to be -2.903,724,377,034,119,598,311,159,245, 194,4 a.u., which is correct to 32 digits. PMID:19113607

  7. Dynamics of entanglement between two atomic samples with spontaneous scattering

    Microsoft Academic Search

    Antonio Di Lisi; Silvio De Siena; Fabrizio Illuminati

    2004-01-01

    We investigate the effects of spontaneous scattering on the evolution of entanglement of two atomic samples, probed by phase-shift measurements on optical beams interacting with both samples. We develop a formalism of conditional quantum evolutions and present a wave function analysis implemented in numerical simulations of the state vector dynamics. This method allows us to track the evolution of entanglement

  8. Electron properties in an atmospheric helium plasma jet determined by Thomson scattering

    NASA Astrophysics Data System (ADS)

    Hübner, S.; Santos Sousa, J.; Puech, V.; Kroesen, G. M. W.; Sadeghi, N.

    2014-10-01

    In this work we present Thomson scattering measurements on a nanosecond pulsed high voltage dielectric barrier discharge (DBD)-like helium plasma jet, operated in ambient air. With the low detection limit offered by a triple grating spectrograph equipped with a high quantum efficiency intensified charge-coupled device (ICCD) camera, temporally and spatially resolved electron densities and mean energies have been mapped. 7?kV peak with 250?ns width pulses at 20?kHz are applied to the inner cylindrical shaped electrode of a DBD. This results in a peculiar hollow electron density profile in the vicinity of the jet nozzle with maximum values of ne = 5 × 1018?m?3 and mean energies of up to 2.5?eV. Further downstream, the profile collapses radially and contracts. A much higher electron density is found (2 × 1019?m?3) while the mean energy is lower (0.5?eV).

  9. Elastic scattering of electrons by gadolinium and barium atoms

    NASA Astrophysics Data System (ADS)

    Miloshevsky, G. V.; Tolkach, V. I.; Rozin, S.; Shani, G.

    2000-08-01

    Total and differential cross-sections for elastic scattering of electrons from gadolinium and barium atoms in a wide energy range were calculated. In the low- and intermediate-energy regions, the phase theory of elastic scattering was used. At low incident energies (<10 eV), an additional polarization potential was introduced. At high incident energies, the Born approximation (keV range) and the Rutherford formula (MeV range) were applied. Our results are in rather good agreement with experimental data of Romanyuk et al. (Pis'ma Zh. Eksp. Teor. Fiz. 32 (1980) 472) for elastic scattering of very-low-energy electrons from barium atoms which confirm its reliability. This agreement is important because these experimental results are in serious disagreement with theoretical calculations of Szmytkowski and Sienkiewicz (Phys. Rev. A 50 (1994) 4007).

  10. Photon scattering from strongly driven atomic ensembles

    SciTech Connect

    Jin Luling [Max-Planck Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Department of Physics, Northwest University, Xi'an 710069, Shaanxi (China); Evers, Joerg; Macovei, Mihai [Max-Planck Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany)

    2011-10-15

    The second-order correlation function for light emitted from a strongly and near-resonantly driven dilute cloud of atoms is discussed. Because of the strong driving, the fluorescence spectrum separates into distinct peaks, for which the spectral properties can be defined individually. It is shown that the second-order correlations for various combinations of photons from different spectral lines exhibit bunching together with super-Poissonian or sub-Poissonian photon statistics, tunable by the choice of the detector positions. Additionally, a Cauchy-Schwarz inequality is violated for photons emitted from particular spectral bands. The emitted light intensity is proportional to the square of the number of particles, and thus can potentially be intense. Three different averaging procedures to model ensemble disorder are compared.

  11. Ultra-low-temperature reactions of C(³P?) atoms with benzene molecules in helium droplets.

    PubMed

    Krasnokutski, Serge A; Huisken, Friedrich

    2014-12-01

    The reaction of carbon atoms with benzene has been investigated in liquid helium droplets at T = 0.37 K. We found an addition of the carbon atom to form an initial intermediate complex followed by a ring opening and the formation of a seven-membered ring. In contrast to a previous gas phase study, the reaction is frozen after these steps and the loss of hydrogen does not occur. A calorimetric technique was applied to monitor the energy balance of the reaction. It was found that more than 267 kJ mol(-1) were released in this reaction. This estimation is in line with quantum chemical calculations of the formation energy of a seven-membered carbon ring. It is suggested that reactions of this kind could be responsible for the low abundance of small polycyclic aromatic hydrocarbon molecules in the interstellar medium. We also found the formation of weakly bonded water-carbon adducts, in which the carbon atom is linked to the oxygen atom of the water molecule with a binding energy of about 33.4 kJ mol(-1). PMID:25481143

  12. On the size and structure of helium snowballs formed around charged atoms and clusters of noble gases.

    PubMed

    Bartl, Peter; Leidlmair, Christian; Denifl, Stephan; Scheier, Paul; Echt, Olof

    2014-09-18

    Helium nanodroplets doped with argon, krypton, or xenon are ionized by electrons and analyzed in a mass spectrometer. HenNgx(+) ions containing up to seven noble gas (Ng) atoms and dozens of helium atoms are identified; the high resolution of the mass spectrometer combined with advanced data analysis make it possible to unscramble contributions from isotopologues that have the same nominal mass but different numbers of helium or Ng atoms, such as the magic He20(84)Kr2(+) and the isobaric, nonmagic He41(84)Kr(+). Anomalies in these ion abundances reveal particularly stable ions; several intriguing patterns emerge. Perhaps most astounding are the results for HenAr(+), which show evidence for three distinct, solid-like solvation shells containing 12, 20, and 12 helium atoms. This observation runs counter to the common notion that only the first solvation shell is solid-like but agrees with calculations by Galli et al. for HenNa(+) [J. Phys. Chem. A 2011, 115, 7300] that reveal three shells of icosahedral symmetry. HenArx(+) (2 ? x ? 7) ions appear to be especially stable if they contain a total of n + x = 19 atoms. A sequence of anomalies in the abundance distribution of HenKrx(+) suggests that rings of six helium atoms are inserted into the solvation shell each time a krypton atom is added to the ionic core, from Kr(+) to Kr3(+). Previously reported strong anomalies at He12Kr2(+) and He12Kr3(+) [Kim , J. H.; et al. J. Chem. Phys. 2006, 124, 214301] are attributed to a contamination. Only minor local anomalies appear in the distributions of HenXex(+) (x ? 3). The distributions of HenKr(+) and HenXe(+) show strikingly similar, broad features that are absent from the distribution of HenAr(+); differences are tentatively ascribed to the very different fragmentation dynamics of these ions. PMID:24128371

  13. Recent progress in electron scattering from atoms and molecules

    SciTech Connect

    Brunger, M. J. [Centre for Antimatter-Matter Studies, CAPS, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia and Institute of Mathematical Sciences, University of Malaya, Kuala Lumpur (Malaysia); Buckman, S. J. [Institute of Mathematical Sciences, University of Malaya, Kuala Lumpur, Malaysia and Centre for Antimatter-Matter Studies, AMPL, Australian National University, Canberra, ACT 0200 (Australia); Sullivan, J. P.; Palihawadana, P. [Centre for Antimatter-Matter Studies, AMPL, Australian National University, Canberra, ACT 0200 (Australia); Jones, D. B. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001 (Australia); Chiari, L.; Pettifer, Z. [Centre for Antimatter-Matter Studies, CAPS, Flinders University, GPO Box 2100, Adelaide, SA 5001 (Australia); Silva, G. B. da [Centre for Antimatter-Matter Studies, CAPS, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia and Universidade Federal de Mato Grosso, Barra do Garças, Mato Grosso (Brazil); Lopes, M. C. A. [Centre for Antimatter-Matter Studies, CAPS, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia and Departamento de Fisica, Universidade Federal de Juiz de Fora, Juiz de Fora, MG (Brazil); Duque, H. V. [Departamento de Fisica, Universidade Federal de Juiz de Fora, Juiz de Fora, MG (Brazil); Masin, Z.; Gorfinkiel, J. D. [Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA (United Kingdom); Garcia, G. [Instituto de Fisica Fundamental, CSIC, Madrid E-28006 (Spain); Hoshino, M.; Tanaka, H. [Department of Physics, Sophia University, Tokyo, 102-8554 (Japan); Limão-Vieira, P. [Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal)

    2014-03-05

    We present and discuss recent results, both experimental and theoretical (where possible), for electron impact excitation of the 3s[3/2 ]{sub 1} and 3s?[1/2 ]{sub 1} electronic states in neon, elastic electron scattering from the structurally similar molecules benzene, pyrazine, and 1,4-dioxane and excitation of the electronic states of the important bio-molecule analogue ?-tetrahydrofurfuryl alcohol. While comparison between theoretical and experimental results suggests that benchmarked cross sections for electron scattering from atoms is feasible in the near-term, significant further theoretical development for electron-molecule collisions, particularly in respect to discrete excitation processes, is still required.

  14. Partial Wave Dispersion Relations: Application to Electron-Atom Scattering

    NASA Technical Reports Server (NTRS)

    Temkin, A.; Drachman, Richard J.

    1999-01-01

    In this Letter we propose the use of partial wave dispersion relations (DR's) as the way of solving the long-standing problem of correctly incorporating exchange in a valid DR for electron-atom scattering. In particular a method is given for effectively calculating the contribution of the discontinuity and/or poles of the partial wave amplitude which occur in the negative E plane. The method is successfully tested in three cases: (i) the analytically solvable exponential potential, (ii) the Hartree potential, and (iii) the S-wave exchange approximation for electron-hydrogen scattering.

  15. Learning Approach on the Ground State Energy Calculation of Helium Atom

    SciTech Connect

    Shah, Syed Naseem Hussain [Department of Physics, Federal Urdu University of Art, Sciences and Technology, Gulshan Campus Gulshan-e-Iqbal, University Road Karachi-75300 (Pakistan)

    2010-07-28

    This research investigated the role of learning approach on the ground state energy calculation of Helium atom in improving the concepts of science teachers at university level. As the exact solution of several particles is not possible here we used approximation methods. Using this method one can understand easily the calculation of ground state energy of any given function. Variation Method is one of the most useful approximation methods in estimating the energy eigen values of the ground state and the first few excited states of a system, which we only have a qualitative idea about the wave function.The objective of this approach is to introduce and involve university teacher in new research, to improve their class room practices and to enable teachers to foster critical thinking in students.

  16. Double-electron capture in collision of fast alpha particles with helium atoms

    NASA Astrophysics Data System (ADS)

    Ghanbari-Adivi, Ebrahim; Ghavaminia, Hoda

    2014-11-01

    A four-body boundary-corrected first-order Jackson-Schiff approximation (JS1-4B) is developed to calculate the differential and integral cross-sections (DCSs) for double-electron exchange in collision of fast alpha ions with helium atoms in their ground states. The influence of the static electron correlations on cross-sections is taken into account through choosing the different wave functions to describe the initial and final bound states of the electrons. The quantum-mechanical post and prior transition amplitudes for double charge exchange are derived in terms of two-dimensional real integrals which can be calculated numerically. The validity and utility of the applied approach is critically assessed in comparison with the available experimental data for differential and integral cross-sections. The present calculations are also compared with the results obtained from the other theories.

  17. Cavity-Modified Collective Rayleigh Scattering of Two Atoms

    NASA Astrophysics Data System (ADS)

    Reimann, René; Alt, Wolfgang; Kampschulte, Tobias; Macha, Tobias; Ratschbacher, Lothar; Thau, Natalie; Yoon, Seokchan; Meschede, Dieter

    2015-01-01

    We report on the observation of cooperative radiation of exactly two neutral atoms strongly coupled to the single mode field of an optical cavity, which is close to the lossless-cavity limit. Monitoring the cavity output power, we observe constructive and destructive interference of collective Rayleigh scattering for certain relative distances between the two atoms. Because of cavity backaction onto the atoms, the cavity output power for the constructive two-atom case (N =2 ) is almost equal to the single-emitter case (N =1 ), which is in contrast to free-space where one would expect an N2 scaling of the power. These effects are quantitatively explained by a classical model as well as by a quantum mechanical model based on Dicke states. We extract information on the relative phases of the light fields at the atom positions and employ advanced cooling to reduce the jump rate between the constructive and destructive atom configurations. Thereby we improve the control over the system to a level where the implementation of two-atom entanglement schemes involving optical cavities becomes realistic.

  18. Penning ionization of argon by metastable helium atoms : a study of the energy and angular distributions of the ejected electrons

    E-print Network

    Paris-Sud XI, Université de

    L-271 Penning ionization of argon by metastable helium atoms : a study of the energy and angular'ionisation Penning de l'argon par l'hélium dans les états métastables 2 1S et 2 3S est réalisée. Les spectres en. 2014 Experimental measurements are reported for the Penning ionization of an argon target by impact

  19. Spin Ordering on the Niobium OXIDE(100) Surface Measured by Elastic Metastable Helium Scattering.

    NASA Astrophysics Data System (ADS)

    Swan, Anna K.

    Magnetic insulating solids show a rich variety of electron spin ordering configurations due to the existence of several competing magnetic coupling mechanisms. Calculations indicate that spin ordering on the 2-dimensional surface of a solid may differ from the 3-dimensional bulk spin arrangement. However, the lack of suitable experimental probes has greatly limited the study of spin ordering on solid surfaces. In this thesis, I present a novel experimental technique that is capable of measuring surface long-range spin ordering using elastic scattering of metastable He 2^3S atoms (ESMA). I also present results from the first application of this technique, the determination of the spin ordering on a NiO(100) surface. ESMA is based on the spin dependent de-excitation probability of the He 2^3S atoms (He*) at a magnetic surface. The electronic metastable 2^3S state of He is very long lived in vacuum, but on impact with a surface a large fraction of the metastable atoms de-excite to the electronic ground state. However, on an insulating surface with localized spins, the local nature of the atom-surface interaction together with Auger selection rules will prevent the de -excitation of a He* atom with a spin orientation parallel to the local surface electron spin. Thus, a periodic arrangement of the local surface moments leads to a periodic modulation of the elastically scattered He* beam which is manifested in the corresponding diffraction pattern. Application of this technique to the NiO(100) surface reveals a spin structure that is quite different from the bulk anti-ferromagnetic arrangement. The data suggests the presence of a frozen spin wave arrangement on the surface, where the surface spin ordering has acquired a longer super-periodicity in a high symmetry direction, due to a spatial precession of the spins around the spin directions defined by the bulk ordering. In order to better understand these results, I have developed a model of the scattering process that includes the effect of a spatially modulated attenuation of the metastable He* beam due to the spin dependent de-excitation probability of the He* atoms. The results show good qualitative agreement with the NiO(100) data, and demonstrate that a small spatial modulation of the de-excitation probability over the surface will give rise to corresponding diffraction peaks.

  20. Measurements of scattering processes in negative ion-atom collisions

    SciTech Connect

    Kvale, T.J.

    1992-01-01

    This Technical Progress Report describes the progress made on the research objectives during the past twelve months. This research project is designed to provide measurements of various scattering processes which occur in H{sup {minus}} collisions with atomic (specifically, noble gas and atomic hydrogen) targets at intermediate energies. These processes include: elastic scattering,single- and double-electron detachment, and target excitation/ionization. For the elastic and target inelastic processes where H{sup {minus}} is scattered intact, the experimental technique of Ion Energy-Loss Spectroscopy (IELS) will be employed to identify the final target state(s). In most of the above processes, cross sections are unknown both experimentally and theoretically. The measurements in progress will provide either experimentally-determined cross sections or set upper limits to those cross sections. In either case, these measurements will be stringent tests of our understanding in energetic negative ion-atom collisions. This series of experiments required the construction of a new facility and the initial ion beam was accelerated through the apparatus in April 1991.

  1. J-matrix calculation of electron-helium S-wave scattering

    SciTech Connect

    Konovalov, D. A.; Fursa, D. V.; Bray, I. [Discipline of Information Technology, School of Business, James Cook University, Townsville, Queensland 4811 (Australia); ARC Centre for Antimatter-Matter Studies, Curtin University, GPO Box U1987, Perth, Western Australia 6845 (Australia)

    2011-09-15

    The J-matrix approach to electron-atom scattering is revised by merging it with the Fano's multiconfiguration interaction matrix elements [U. Fano, Phys. Rev. 140, A67 (1965)]. The revised method is then applied to the S-wave model of the e-He scattering problem demonstrating remarkable computational efficiency and accuracy. In particular, the method is in complete agreement with the convergent-close-coupling elastic, 2{sup 1,3}S excitation and single ionization cross sections for impact energies in the range 0.1-1000 eV. The S-wave resonance structures in the elastic and 2{sup 1,3}S excitation cross sections are highlighted.

  2. 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. Shimamhura and M. Kimura

    NASA Astrophysics Data System (ADS)

    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 was aimed at discussing some new aspects related to the metastability of hadronic helium atoms which had been discovered when negative kaons, negative pions and antiprotons were stopped in liquid helium. The delayed fraction, time spectrum shape and lifetimes were the observables. Further experimental studies are in progress, 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 and Russell: (1) the atomic core polarization effect; (2) the structure and radiative lifetimes; (3) the non-statistical distribution of the angular momentum and an estimate of the delayed fraction; and (4) the isotope effect, though the title represents only (1). 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.

  3. Scattering of cold-atom coherences by hot atoms: frequency shifts from background-gas collisions.

    PubMed

    Gibble, Kurt

    2013-05-01

    Frequency shifts from background-gas collisions currently contribute significantly to the inaccuracy of atomic clocks. Because nearly all collisions with room-temperature background gases that transfer momentum eject the cold atoms from the clock, the interference between the scattered and unscattered waves in the forward direction dominates these frequency shifts. We show they are ? 10 times smaller than in room-temperature clocks and that van der Waals interactions produce the cold-atom background-gas shift. General considerations allow the loss of the Ramsey fringe amplitude to bound this frequency shift. PMID:23683186

  4. Neutral atom lithography using the 389 nm transition in metastable helium

    NASA Astrophysics Data System (ADS)

    Reeves, Jason

    Resist based neutral atom lithography with metastable 23 S1 Helium (He*) has been used to produce small structures in both gold and palladium. A beam of He* from a reverse flow, DC discharge source is collimated by the bichromatic optical force followed by three optical molasses velocity compression stages. The He* beam then crosses a region where a mechanical or optical mask creates the desired pattern. In the first experiments, a self assembled monolayer (SAM) of nonanethiol is grown on a gold coated silicon wafer and then exposed to the bright, collimated beam of He* after a nickel micro mesh mask. The mesh protects parts of the SAM from the 20 eV of internal energy deposited by the impact of a He* atom onto the sample surface. The pattern of the mesh is transferred into the ˜200 A gold layer with a standard selective etch that removes the gold from under the damaged SAM molecules. The samples were analyzed with an Atomic Force Microscope and Scanning Electron Microscope. The second set of experiments were performed using an optical mask to pattern a gold coated silicon wafer. In the optical mask, the He* atoms experience the dipole force while traversing a standing light wave of lambda1 = 1083 nm light tuned 490 MHz above the 23S1 ? 23P2 transition or, in separate experiments, lambda 2 = 389 nm light tuned 80 MHz below the 23S1 ? 33P2 transition. Using the optical masks, He* can be focused or channeled into parallel lines separated by lambda/2 by varying the intensity of the standing light wave. The small structures created by the 389 nm optical mask began approaching the gold surface granularity. A ˜ 200A layer of palladium on silicon was chosen as the palladium granularity is much smaller and the SAM of nonanethiol will still form on the surface. Experiments using a nickel micro mesh as a mechanical mask have demonstrated similar features to those in gold.

  5. Scattering processes in antiprotonic hydrogen - hydrogen atom collisions

    E-print Network

    V. P. Popov; V. N. Pomerantsev

    2006-01-11

    The elastic scattering, Stark transitions and Coulomb deexcitation of excited antiprotonic hydrogen atom in collisions with hydrogenic atom have been studied in the framework of the fully quantum-mechanical close-coupling method for the first time. The total cross sections $\\sigma_{nl \\to n'l'}(E)$ and averaged on the initial angular momentum $l$ cross sections $\\sigma_{n\\to n'}(E)$ have been calculated for the initial states of $(\\bar{p}p)_{n}$ atoms with the principal quantum number $n=3 - 14 $ and at the relative energies $E=0.05 - 50$ eV. The energy shifts of the $ns$ states due to the strong interaction and relativistic effects are taken into account. Some of our results are compared with the semiclassical calculations.

  6. First $?K$ atom lifetime and $?K$ scattering length measurements

    E-print Network

    B. Adeva; L. Afanasyev; Y. Allkofer; C. Amsler; A. Anania; S. Aogaki; A. Benelli; V. Brekhovskikh; T. Cechak; M. Chiba; P. Chliapnikov; C. Ciocarlan; S. Constantinescu; P. Doskarova; D. Drijard; A. Dudarev; M. Duma; D. Dumitriu; D. Fluerasu; A. Gorin; O. Gorchakov; K. Gritsay; C. Guaraldo; M. Gugiu; M. Hansroul; Z. Hons; S. Horikawa; Y. Iwashita; V. Karpukhin; J. Kluson; M. Kobayashi; V. Kruglov; L. Kruglova; A. Kulikov; E. Kulish; A. Kuptsov; A. Lamberto; A. Lanaro; R. Lednicky; C. Mariñas; J. Martincik; L. Nemenov; M. Nikitin; K. Okada; V. Olchevskii; M. Pentia; A. Penzo; M. Plo; T. Ponta; P. Prusa; G. Rappazzo; A. Romero Vidal; A. Ryazantsev; V. Rykalin; J. Schacher; A. Sidorov; J. Smolik; S. Sugimoto; F. Takeutchi; L. Tauscher; T. Trojek; S. Trusov; T. Urban; T. Vrba; V. Yazkov; Y. Yoshimura; M. Zhabitsky; P. Zrelov

    2014-03-04

    The results of a search for hydrogen-like atoms consisting of $\\pi^{\\mp}K^{\\pm}$ mesons are presented. Evidence for $\\pi K$ atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen in terms of characteristic $\\pi K$ pairs from their breakup in the same target ($178 \\pm 49$) and from Coulomb final state interaction ($653 \\pm 42$). Using these results the analysis yields a first value for the $\\pi K$ atom lifetime of $\\tau=(2.5_{-1.8}^{+3.0})$ fs and a first model-independent measurement of the S-wave isospin-odd $\\pi K$ scattering length $\\left|a_0^-\\right|=\\frac{1}{3}\\left|a_{1/2}-a_{3/2}\\right|= \\left(0.11_{-0.04}^{+0.09} \\right)M_{\\pi}^{-1}$ ($a_I$ for isospin $I$).

  7. Electron-helium and electron-neon scattering cross sections at low electron energies using a photoelectron source

    NASA Technical Reports Server (NTRS)

    Kumar, Vijay; Subramanian, K. P.; Krishnakumar, E.

    1987-01-01

    Absolute electron-helium and electron-neon scattering cross sections have been measured at low electron energies using the powerful technique of photoelectron spectroscopy. The measurements have been carried out at 17 electron energies varying from 0.7 to 10 eV with an accuracy of + or - 2.7 percent. The results obtained in the present work have been compared with other recent measurement and calculations.

  8. Four-body charge transfer processes in collisions of bare projectile ions with helium atoms

    NASA Astrophysics Data System (ADS)

    Jana, S.; Mandal, C. R.; Purkait, M.

    2015-02-01

    Single-electron capture by a bare ion from a helium atom at intermediate and high energies in the framework of four-body distorted wave (DW-4B) approximation in both prior and post form has been considered. In the entrance channel, the initial bound state wave function is distorted by the incoming projectile ion, and the corresponding distortion is related to the Coulomb continuum states of the active electron and the residual target ion in the field of the projectile ion respectively. Continuum states of the active electron and the projectile ion in the field of the residual target ion are also included in the exit channel. It may be mentioned that the effect of dynamic electron correlation is explicitly taken into account through the complete perturbation potential. The total single-electron capture cross sections are obtained by summing over all contributions up to n = 3 shells and sub-shells respectively. In addition, the differential cross sections for alpha particle–helium collision are calculated at impact energies of 60, 150, 300, 450, and 630 keV amu?1, respectively. The cross sections exhibit a monotonically decreasing angular dependence, with clear peak structures around 0.1 to 0.2 mrad being found at low impact energies. The current theoretical results, both in prior and post forms of the transition amplitude for symmetric and asymmetric collision, are compared with the available theoretical and experimental results. Current computed results have been found to be satisfactory in comparison with other theoretical and experimental findings.

  9. Esr Spectra of Alkali-Metal Atoms on Helium Nanodroplets: a Theoretical Model for the Prediction of Helium Induced Hyperfine Structure Shifts

    NASA Astrophysics Data System (ADS)

    Hauser, Reas W.; Filatov, Michael; Ernst, Wolfgang E.

    2013-06-01

    We predict He-droplet-induced changes of the isotropic HFS constant a_{HFS} of the alkali-metal atoms M = Li, Na, K and Rb on the basis of a model description. Optically detected electron spin resonance spectroscopy has allowed high resolution measurements that show the influence of the helium droplet and its size on the unpaired electron spin density at the alkali nucleus. Our theoretical approach to describe this dependence is based on a combination of two well established techniques: Results of relativistic coupled-cluster calculations on the alkali-He dimers (energy and HFS constant as functions of the binding length) are mapped onto the doped-droplet-situation with the help of helium-density functional theory. We simulate doped droplets He_{N} with N ranging from 50 to 10000, using the diatomic alkali-He-potential energy curves as input. From the obtained density profiles we evaluate average distances between the dopant atom and its direct helium neighborhood. The distances are then set in relation to the variation of the HFS constant with binding length in the simplified alkali-He-dimer model picture. This method yields reliable relative shifts but involves a systematic absolute error. Hence, the absolute values of the shifts are tied to one experimentally determined HFS constant for ^{85}Rb-He_{N = 2000}. With this parameter choice we obtain results in good agreement with the available experimental data for Rb and K^{a,b} confirming the predicted 1/N trend of the functional dependence^{c}. M. Koch, G. Auböck, C. Callegari, and W. E. Ernst, Phys. Rev. Lett. 103, 035302-1-4 (2009) M. Koch, C. Callegari, and W. E. Ernst, Mol. Phys. 108 (7), 1005-1011 (2010) A. W. Hauser, T. Gruber, M. Filatov, and W. E. Ernst, ChemPhysChem (2013) online DOI: 10.1002/cphc.201200697

  10. Atomic form factors, incoherent scattering functions, and photon scattering cross sections

    Microsoft Academic Search

    J. H. Hubbell; Wm. J. Veigele; E. A. Briggs; R. T. Brown; D. T. Cromer; R. J. Howerton

    1975-01-01

    Tabulations are presented of the atomic form factor, F (?,Z), and the incoherent scattering function, S (x,Z), for values of x (=sin &Vthgr;\\/2)\\/?) from 0.005 A??1 to 109 A??1, for all elements A=1 to 100. These tables are constructed from available state-of-the-art theoretical data, including the Pirenne formulas for Z=1, configuration-into action results by Brown using Brown-Fontana and Weiss correlated

  11. Energy-loss contribution to grazing scattering of fast He atoms from a silver surface

    NASA Astrophysics Data System (ADS)

    Ríos Rubiano, C. A.; Bocan, G. A.; Juaristi, J. I.; Gravielle, M. S.

    2014-03-01

    The energy lost by helium atoms axially scattered from a Ag(110) surface is studied in order to investigate the influence of dissipative processes on fast atom diffraction spectra. In this work inelastic projectile distributions are evaluated within a semiclassical formalism that includes dissipative effects due to electron-hole excitations through a friction force. For incidence along the [11¯2] and [11¯0] directions the model predicts the presence of multiple peaks in the energy-loss spectrum for a given impact energy. But these structures are completely washed out when the experimental dispersion of the incident beam is taken into account, giving rise to a smooth energy-loss distribution. Simulations including the experimental energy spread are in fairly good agreement with available experimental data for the [11¯2] channel. In addition, our results suggest that inelastic processes produce an almost constant background in the transverse momentum distribution, except in the extremes of the momentum range where classical rainbow maxima appear. By adding elastic and inelastic contributions, experimental diffraction patterns are well reproduced.

  12. Scattering of positrons and electrons by alkali atoms

    NASA Technical Reports Server (NTRS)

    Stein, T. S.; Kauppila, W. E.; Kwan, C. K.; Lukaszew, R. A.; Parikh, S. P.; Wan, Y. J.; Zhou, S.; Dababneh, M. S.

    1990-01-01

    Absolute total scattering cross sections (Q sub T's) were measured for positrons and electrons colliding with sodium, potassium, and rubidium in the 1 to 102 eV range, using the same apparatus and experimental approach (a beam transmission technique) for both projectiles. The present results for positron-sodium and -rubidium collisions represent the first Q sub T measurements reported for these collision systems. Features which distinguish the present comparisons between positron- and electron-alkali atom Q sub T's from those for other atoms and molecules (room-temperature gases) which have been used as targets for positrons and electrons are the proximity of the corresponding positron- and electron-alkali atom Q sub T's over the entire energy range of overlap, with an indication of a merging or near-merging of the corresponding positron and electron Q sub T's near (and above) the relatively low energy of about 40 eV, and a general tendency for the positron-alkali atom Q sub T's to be higher than the corresponding electron values as the projectile energy is decreased below about 40 eV.

  13. Dynamic correlation in high-harmonic generation for helium atoms in intense visible lasers

    E-print Network

    G. A. McKenna; R. Nepstad; J. F. McCann; D. Dundas

    2009-05-20

    We investigate the effect of dynamic electron correlation on high-harmonic generation in helium atoms using intense visible light (\\lambda=390nm). Two complementary approaches are used which account for correlation in an approximate manner: time-dependent density-functional theory and a single-active-electron model. For intensities I~10^{14} W/cm^2, the theories are in remarkably good agreement for the dynamic polarization and harmonic spectrum. This is attributed to a low-frequency collective mode together with a high-frequency single-electron response due to the nuclear singularity, both of which dominate electron correlation effects. A time-frequency analysis is used to study the timing and emission spectrum of attosecond bursts of light. For short pulses, we find a secondary maximum below the classical cut-off. The imprint of the carrier-envelope-phase, for the time-integrated spectral density appears at frequencies above the high-frequency drop-off, consistent with previous studies in the infrared \\lambda~800nm.

  14. Penning ionization electron spectroscopy of hydrogen sulfide by metastable helium and neon atoms.

    PubMed

    Falcinelli, Stefano; Candori, Pietro; Bettoni, Marta; Pirani, Fernando; Vecchiocattivi, Franco

    2014-08-21

    The dynamics of the Penning ionization of hydrogen sulfide molecules by collision with helium and metastable neon atoms, occurring in the thermal energy range, has been studied by analyzing the energy spectra of the emitted electrons obtained in our laboratory in a crossed beam experiment. These spectra are compared with the photoelectron spectra measured by using He(I) and Ne(I) photons under the same experimental conditions. In this way we obtained the negative energy shifts for the formation of H2S(+) ions in the first three accessible electronic states by He*(2(3,1)S1,0) and Ne*((3)P2,0) Penning ionization collisions: the 2b1 (X?(2)B1) fundamental one, the first 5a1 (Ã(2)A1), and the second 2b2 (B?(2)B2) excited states, respectively. The recorded energy shifts indicate that in the case of He* and Ne*-H2S the autoionization dynamics depends on the features of the collision complex and is mainly driven by an effective global attraction that comes from a balance among several non covalent intermolecular interaction components. This suggests that the Penning ionization should take place, in a specific range of intermolecular distances, as we have already observed in the case of Penning ionization of water molecules [Brunetti, B. G.; Candori, P.; Falcinelli, S.; Pirani, F.; Vecchiocattivi, F. J. Chem. Phys. 2013, 139, 164305-1-164305-8]. PMID:24796487

  15. Coulomb-gauge electrodynamics analysis of two-photon exchange in electron-atom scattering. II. Interaction at all distances beyond atomic dimensions

    NASA Astrophysics Data System (ADS)

    Au, C. K.

    1988-07-01

    We follow up on our previous analysis of the two-photon exchange potential in the scattering of a light point-charged particle by a neutral system (electron-atom scattering) by examining all the time-ordered Feynman diagrams involved. In a close parallel with the work of J. F. Babb and L. Spruch [Phys. Rev. A 36, 456 (1987)] on Rydberg states of helium, the present analysis on scattering is valid for all distances larger than the atomic radius (R>a). In the dipole approximation, we reproduce the potential obtained by G. Feinberg and J. Sucher [Phys. Rev. A 27, 1958 (1983)] using a more powerful covariant field-dispersion-theory technique. We give simple expressions for the additional nonadiabatic and multipole corrections in the two-Coulomb-photon exchange channel and also give the lowest nonadiabatic and energy-dependent corrections to the retardation potentials. These potentials are valid for all R>a. The implication of these additional correction potentials in the study of heliumlike Rydberg states is briefly discussed.

  16. Low-Energy Elastic Electron Scattering by Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Zatsarinny O.; Bartschat, K.; Tayal, S. S.

    2006-01-01

    The B-spline R-matrix method is employed to investigate the low-energy elastic electron scattering by atomic oxygen. Flexible non-orthogonal sets of radial functions are used to construct the target description and to represent the scattering functions. A detailed investigation regarding the dependence of the predicted partial and total cross sections on the scattering model and the accuracy of the target description is presented. The predicted angle-integrated elastic cross sections are in good agreement with experiment, whereas significant discrepancies are found in the angle-differential elastic cross sections near the forward direction. .The near-threshold results are found to strongly depend on the treatment of inner-core short-range correlation effects in the target description, as well as on a proper account of the target polarizability. A sharp increase in the elastic cross sections below 1 eV found in some earlier calculations is judged to be an artifact of an unbalanced description of correlation in the N-electron target structure and the (N+l)-electron-collision problems.

  17. Physics of Polarized Scattering at Multi-level Atomic Systems

    NASA Astrophysics Data System (ADS)

    Stenflo, J. O.

    2015-03-01

    The symmetric peak observed in linear polarization in the core of the solar sodium D1 line at 5896 Å has remained enigmatic since its discovery nearly two decades ago. One reason is that the theory of polarized scattering has not been experimentally tested for multi-level atomic systems in the relevant parameter domains, although the theory is continually being used for the interpretation of astrophysical observations. A laboratory experiment that was set up a decade ago to find out whether the D1 enigma is a problem of solar physics or quantum physics revealed that the D1 system has a rich polarization structure in situations where standard scattering theory predicts zero polarization, even when optical pumping of the m state populations of the hyperfine-split ground state is accounted for. Here we show that the laboratory results can be modeled in great quantitative detail if the theory is extended to include the coherences in both the initial and final states of the scattering process. Radiative couplings between the allowed dipole transitions generate coherences in the initial state. Corresponding coherences in the final state are then demanded by a phase closure selection rule. The experimental results for the well understood D2 line are used to constrain the two free parameters of the experiment, collision rate and optical depth, to suppress the need for free parameters when fitting the D1 results.

  18. Physics of polarized scattering at multi-level atomic systems

    E-print Network

    Stenflo, Jan

    2015-01-01

    The symmetric peak observed in linear polarization in the core of the solar sodium D$_1$ line at 5896 \\AA\\ has remained enigmatic since its discovery nearly two decades ago. One reason is that the theory of polarized scattering has not been experimentally tested for multi-level atomic systems in the relevant parameter domains, although the theory is continually being used for the interpretation of astrophysical observations. A laboratory experiment that was set up a decade ago to find out whether the D$_1$ enigma is a problem of solar physics or quantum physics revealed that the D$_1$ system has a rich polarization structure in situations where standard scattering theory predicts zero polarization, even when optical pumping of the $m$ state populations of the hyperfine-split ground state is accounted for. Here we show that the laboratory results can be modeled in great quantitative detail if the theory is extended to include the coherences in both the initial and final states of the scattering process. Radiat...

  19. Relativistic Corrections to the Zeeman Effect in Hydrogen-Like Atoms, Positronium, and Helium-Like Atoms.

    NASA Astrophysics Data System (ADS)

    Anthony, John Michael

    An approximately relativistic theory of bound states which ensures the Poincare invariance of atomic systems to relative order (v/c)^2 is used to derive the Zeeman interaction Hamiltonians correct to order alpha^3 and to all orders in m_{rm e}/m _{rm N} for arbitrary two body systems and three body systems. Previously neglected radiative corrections of order alpha^3 and recoil corrections of order alpha ^3m_{rm e} /m_{rm N} are also included. For neutral systems, the linear Zeeman Hamiltonians are unitarily equivalent to the linear Zeeman Hamiltonians obtained by other authors in the past. Explicit analytic expressions for the g_{rm J} and g_{rm I} factors of hydrogen-like atoms are given and verify the results of Grotch and Kashuba. The positronium ground state g factor calculated here agrees exactly with previous calculations. The terms of order m_{rm e}/m_{rm N} , alpha^2, alpha^3, and alpha^2 m_{rm e}/m _{rm N} of the three -body linear Zeeman Hamiltonian are used to calculate the g factors for n = 2 ^4He and ^3He. The effect of the finite mass of the nucleus on the wavefunction is accounted for in the work presented here. The 2^3S _1 g_{rm J} factor is in excellent agreement with the results of Grotch and Hegstrom and experimental results. It is the first time that corrections of order alpha ^3 and alpha^2m _{rm e}/m _{rm N} have been used to calculate the 2^3P_ {rm J} and 2^1P _1 helium g factors. Three different wavefunction are used to derive the 2^3 P_{rm J} and 2^1P_1 g factors for ^4He and ^3He. The most accurate is a 125 term configuration interaction wavefunction utilizing 12 nonlinear parameters. The resulting g'_{rm s} factor agrees exactly with the results of Lewis and Hughes (to order alpha^2). The g' _{rm L} factor obtained is a significant improvement over the results of Lewis and Hughes. The linear Zeeman Hamiltonian, the zero field relativistic Hamiltonian correct to order alpha ^5, and the leading order quadratic Zeeman Hamiltonian are used in degenerate perturbation theory to solve for the energy eigenvalues of hydrogen, positronium, and ^4He for various values of the external magnetic field.

  20. Bragg scattering as a probe of atomic wave functions and quantum phase transitions in optical lattices.

    PubMed

    Miyake, Hirokazu; Siviloglou, Georgios A; Puentes, Graciana; Pritchard, David E; Ketterle, Wolfgang; Weld, David M

    2011-10-21

    We have observed Bragg scattering of photons from quantum degenerate ^{87}Rb atoms in a three-dimensional optical lattice. Bragg scattered light directly probes the microscopic crystal structure and atomic wave function whose position and momentum width is Heisenberg limited. The spatial coherence of the wave function leads to revivals in the Bragg scattered light due to the atomic Talbot effect. The decay of revivals across the superfluid to Mott insulator transition indicates the loss of superfluid coherence. PMID:22107532

  1. Cold magnetically trapped 2Dg scandium atoms. II. Scattering dynamics

    NASA Astrophysics Data System (ADS)

    Karman, Tijs; Groenenboom, Gerrit C.

    2014-11-01

    The binary collision dynamics of 2Dg ,3 /2 ground state scandium atoms is studied from first principles. We employ 30 coupled diabatic ab initio potentials in a coupled-channels study of the scattering dynamics of cold and ultracold scandium atoms in external magnetic fields. Due to the long-ranged magnetic dipolar interaction, the field dependence of the cross section does not follow the threshold laws derived by Volpi and Bohn [Phys. Rev. A 65, 052712 (2002), 10.1103/PhysRevA.65.052712]. In the field-free case, the near-threshold cross section is independent of the collision energy, and hence the cross section does not follow the well-established Wigner threshold laws. The observed threshold behavior is explained in the Born approximation. For energies above 1 ? K , inelastic collisions are driven by the anisotropic nonrelativistic electronic interaction. For energies below 100 ? K , the ratio of elastic-to-inelastic collisions is likely to be favorable for evaporative cooling. Both anisotropy in the long-range interaction and in the short-range potential contribute to large cross sections for inelastic collisions at higher energies and lead to a small ratio of elastic-to-inelastic collisions. This is in agreement with the large rates for Zeeman relaxation of submerged-shell atoms observed experimentally. The effect of the uncertainty in the ab initio potential is sampled by scaling the reduced mass and is found to have little influence on the conclusions drawn from this work.

  2. Double photoionization of helium with synchrotron x-rays: Proceedings

    SciTech Connect

    Not Available

    1994-01-01

    This report contains papers on the following topics: Overview and comparison of photoionization with charged particle impact; The ratio of double to single ionization of helium: the relationship of photon and bare charged particle impact ionization; Double photoionization of helium at high energies; Compton scattering of photons from electrons bound in light elements; Electron ionization and the Compton effect in double ionization of helium; Elimination of two atomic electrons by a single energy photon; Double photoionization of helium at intermediate energies; Double Photoionization: Gauge Dependence, Coulomb Explosion; Single and Double Ionization by high energy photon impact; The effect of Compton Scattering on the double to single ionization ratio in helium; and Double ionization of He by photoionization and Compton scattering. These papers have been cataloged separately for the database.

  3. Total Cross Section Measurements for the Scattering of Polarized Neutrons from Polarized HELIUM-3.

    NASA Astrophysics Data System (ADS)

    Keith, Christopher Douglas

    The first measurements of polarized neutron--polarized ^3He scattering in the few MeV region have been performed. Measurements of the total cross section difference Deltasigma_{T } have been obtained for incident neutron energies 1-10 MeV. The experiment was performed with both beam and target spins in the horizontal plane, transverse to the incident beam momentum. The results are sensitive to the excited state structure of the alpha particle and are compared to phase-shift predictions based on a number of analyses of the n-^3He system. The Deltasigma_{T} results are in agreement with a recent R-matrix analysis of A = 4 scattering and reaction data, and lend support to the ^4He level scheme derived from that analysis. None of the analyses considered here are able to simultaneously reproduce both the current results and previous measurements of the unpolarized total cross section. The experiment was performed at the Triangle Universities Nuclear Laboratory and its Polarized Target Facility. The polarized neutron beam is produced as a secondary beam through polarization-transfer reactions with polarized protons and deuterons. The beams of polarized charged particles are obtained from the TUNL Atomic Beam Polarized Ion Source and accelerated by a tandem Van de Graaff. The beam polarization is monitored by a carbon-foil polarimeter located after the accelerator. A statically-polarized target of solid ^3He was developed for the experiment. A 0.4 mole sample of solid ^3He is grown under a pressure of 45.5 bars at 1 K and cooled to 12 mK with a ^3He-^4 He dilution refrigerator. A 7 Tesla superconducting split-coil magnet is used to polarize the nuclear spins to nearly 40%. The temperature is determined by two independent thermometric standards: ^{60} Co gamma-ray anisotropy and the ^3He melting curve. For temperatures below 20 mK, agreement between the two methods is better than 2%. We observe no heating in the target due to neutron or gamma-ray induced reactions. The density of the 2.16 cm long ^3He sample is 2.0times10^{22} atoms/cm^3, two orders of magnitude greater than any current gas target of polarized ^3He. The target is well-suited for a variety of nuclear physics experiments in which a dense target of polarized ^3He is desirable.

  4. Superelastic electron scattering from laser-excited cesium atoms

    SciTech Connect

    Slaughter, D. S.; Karaganov, V.; Brunger, M. J.; Teubner, P. J. O. [School of Chemistry, Physics and Earth Sciences, Flinders University, GPO Box 2100, Adelaide, 5001 (Australia); Bray, I. [ARC Centre for Antimatter-Matter Studies, Curtin University, Perth, 6845 (Australia); Bartschat, K. [Department of Physics and Astronomy, Drake University, Des Moines, Iowa 50311 (United States)

    2007-06-15

    We present results from a joint experimental and theoretical investigation of superelastic electron scattering from laser-excited Cs atoms in the (6p){sup 2}P{sub 3/2} state. Comparison of the measured pseudo-Stokes parameters P{sub 1}, P{sub 2}, and P{sub 3} and the total degree of polarization P{sup +} for incident energies of 5.5 eV and 13.5 eV, respectively, with theoretical predictions based upon a nonrelativistic convergent close-coupling method and a 24-state semirelativistic Breit-Pauli R-matrix approach indicates that driving channel coupling to convergence for these observables is more important than accounting for relativistic effects.

  5. Inelastic cross sections for positron scattering from atomic hydrogen

    SciTech Connect

    Weber, M.; Hofmann, A.; Raith, W.; Sperber, W. [Bielefeld Univ. (Germany). Fakultaet fuer Physik; Jacobsen, F.; Lynn, K.G. [Brookhaven National Lab., Upton, NY (United States)

    1994-12-31

    Positronium formation (Ps) cross sections for positrons impinging on atomic hydrogen were measured in the impact energy range from 13eV to 255eV at the High Intensity Positron (HIP) beam at Brookhaven National Laboratory (BNL). The Ps-formation cross section was found to rise rapidly from the threshold at 6.8eV to a maximum value of (2.98 {plus_minus} 0.18) {times} 10{sup {minus}16} cm{sup 2} for {approx} 15eV positrons. By 75eV it drops below the detection limit of 0.17 {times} 10{sup {minus}16} cm{sup 2} which is the present level of statistical uncertainty. The experiment was modified to enable the measurement of doubly differential scattering cross sections.

  6. Rayleigh Scattering Cross Section Redward of Ly$?$ by Atomic Hydrogen

    E-print Network

    Hee-Won Lee; Hee Il Kim

    2004-02-02

    We present a low energy expansion of the Kramers-Heisenberg formula for atomic hydrogen in terms of $(\\omega/\\omega_l)$, where $\\omega_l$ and $\\omega$ are the angular frequencies corresponding to the Lyman limit and the incident radiation, respectively. The leading term is proportional to $(\\omega/\\omega_l)^4$, which admits a well-known classical interpretation. With higher order terms we achieve accuracy with errors less than 4 % of the scattering cross sections in the region $\\omega/\\omega_l\\le 0.6$. In the neighboring region around Ly$\\alpha$ ($\\omega/\\omega_l >0.6$), we also present an explicit expansion of the Kramers-Heisenberg formula in terms of $\\Delta\\omega\\equiv (\\omega-\\omega_{Ly\\alpha})/\\omega_{Ly\\alpha}$. The accuracy with errors less than 4 % can be attained for $\\omega/\\omega_l \\ge 0.6$ with the expansion up to the fifth order of $\\Delta\\omega$. We expect that these formulae will be usefully applied to the radiative transfer in high neutral column density regions, including the Gunn-Peterson absorption troughs and Rayleigh scattering in the atmospheres of giants.

  7. Positron scattering from hydrogen atom embedded in dense quantum plasma

    SciTech Connect

    Bhattacharya, Arka [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India)] [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India); Kamali, M. Z. M. [Centre for Foundation Studies in Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)] [Centre for Foundation Studies in Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ghoshal, Arijit [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India) [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India); Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ratnavelu, K. [Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)] [Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)

    2013-08-15

    Scattering of positrons from the ground state of hydrogen atoms embedded in dense quantum plasma has been investigated by applying a formulation of the three-body collision problem in the form of coupled multi-channel two-body Lippmann-Schwinger equations. The interactions among the charged particles in dense quantum plasma have been represented by exponential cosine-screened Coulomb potentials. Variationally determined hydrogenic wave function has been employed to calculate the partial-wave scattering amplitude. Plasma screening effects on various possible mode of fragmentation of the system e{sup +}+H(1s) during the collision, such as 1s?1s and 2s?2s elastic collisions, 1s?2s excitation, positronium formation, elastic proton-positronium collisions, have been reported in the energy range 13.6-350 eV. Furthermore, a comparison has been made on the plasma screening effect of a dense quantum plasma with that of a weakly coupled plasma for which the plasma screening effect has been represented by the Debye model. Our results for the unscreened case are in fair agreement with some of the most accurate results available in the literature.

  8. Laser spectroscopy of Ag and Au atoms immersed in superfluid helium and its applications to investigate nuclear structures

    NASA Astrophysics Data System (ADS)

    Furukawa, Takeshi; Matsuo, Yukari; Hatakeyama, Atsushi; Kobayashi, Tohru; Asahi, Koichiro; Shimoda, Tadashi; Orochi Collaboration

    2011-01-01

    We have been developing a new nuclear laser spectroscopic method “OROCHI” for determining spins and moments of exotic RIs. It is the method based on the combination of superfluid helium as a stopper of radioactive isotope (RI) beam and in situ laser spectroscopy of RI atoms. This unique method will enable us to measure nuclear spins and electromagnetic moments of extremely low yield RI (less than 1 particle per second). For applying this method to stable Ag and Au isotopes, we have measured optical absorption spectra of these elements. Optical pumping of those atoms has also been attempted with pumping lasers tuned to the measured absorption lines. Details of this laser spectroscopy method in He II “OROCHI” and the development for applying OROCHI to Ag and Au atoms are presented.

  9. Probing a cold surface with slow heavy-atom scattering: Experimental results and theoretical calculations

    E-print Network

    Burke, Kieron

    Probing a cold surface with slow heavy-atom scattering: Experimental results and theoretical manuscript received 20 September 2001; published 2 January 2002 Slow heavy atoms scattering from cold, which is slow and strong, it is typically much more complex.2 In the common case of a light particle

  10. Scattering of Polarized Radiation by Atoms in Magnetic and Electric Fields

    E-print Network

    Yee Yee Oo; K. N. Nagendra; Sharath Ananthamurthy; G. Ramachandran

    2005-09-26

    The polarization of radiation by scattering on an atom embedded in combined external quadrupole electric and uniform magnetic fields is studied theoretically. Analytic formulae are derived for the scattering phase matrix. Limiting cases of scattering under Zeeman effect, and Hanle effect in weak magnetic fields are discussed.

  11. Photo-ionization of the helium atom close to the double ionization threshold: towards the Ericson regime

    E-print Network

    Benoit Gremaud; Dominique Delande

    1998-02-04

    We calculate the photo-ionization cross-section from the ground state of the helium atom, using the complex rotation method and diagonalization of sparse matrices. This produces directly the positions and widths of the doubly excited 1Po resonances together with the photo-ionization cross-section. Our calculations up to the N=9 threshold are in perfect agreement with recent experimental data and show the transition from a regular structure at low energy to a chaotic one at high energy, where various resonances strongly overlap.

  12. Differential elastic scattering cross sections for 54.9eV positrons incident on helium

    NASA Technical Reports Server (NTRS)

    Chaplin, R. L.; Diana, L. M.; Brooks, D. L.

    1990-01-01

    Absolute differential elastic scattering cross sections measured with the 3-m, high resolution, time-of-flight spectrometer are presented for 54.9eV positrons incident on He. Five point moving average differential cross sections are plotted against average scattering angles which range from 14 to 36 deg. Also the averages of five differential cross sections which have adjacent values of scattering angle are plotted versus the corresponding averages of the scattering angles. The curve fitted to these data is shaped like the theoretical curve but has its minimum and its maximum at scattering angles that are about 4 deg higher and 15 deg lower respectively than predicted by theory.

  13. Dissipative light scattering by a trapped atom approaching electromagnetically-induced-transparency conditions

    SciTech Connect

    Roghani, Maryam; Breuer, Heinz-Peter; Helm, Hanspeter [Institute of Physics, Albert-Ludwigs University, Hermann-Herder Strasse 3, D-79104 Freiburg (Germany)

    2010-03-15

    We study the time dependence of the spectrum of inelastically scattered radiation from a trapped atom. The atom is illuminated by two lasers tuned to the electromagnetically induced transparency (EIT) of the free atom. For counterpropagating laser beams, rapid removal of vibrational energy is observed as the atom approaches near-EIT conditions. We show that the imbalance in the sidebands of the scattered radiation spectrum explains quantitatively the cooling of the center-of-mass motion of the trapped atom. We also examine parameters critical for EIT cooling in situations far from the Lamb-Dicke limit.

  14. Dissipative light scattering by a trapped atom approaching electromagnetically-induced-transparency conditions

    NASA Astrophysics Data System (ADS)

    Roghani, Maryam; Breuer, Heinz-Peter; Helm, Hanspeter

    2010-03-01

    We study the time dependence of the spectrum of inelastically scattered radiation from a trapped atom. The atom is illuminated by two lasers tuned to the electromagnetically induced transparency (EIT) of the free atom. For counterpropagating laser beams, rapid removal of vibrational energy is observed as the atom approaches near-EIT conditions. We show that the imbalance in the sidebands of the scattered radiation spectrum explains quantitatively the cooling of the center-of-mass motion of the trapped atom. We also examine parameters critical for EIT cooling in situations far from the Lamb-Dicke limit.

  15. Exchange and polarization effects on elastic electron-atom/ion scattering

    E-print Network

    Kaganovich, Igor

    Exchange and polarization effects on elastic electron-atom/ion scattering (aka. a small part approaches Needed for modeling and simulations : · accurate atomic and molecular data (, d/d, , rates physics · atomic physics · molecular physics · beam-surface interactions #12;0 ( ) ( ) ( ) ( ) e e e i i i

  16. Measurements of Electron Energy Distribution and Metastable Atom Density in the Afterglow of an RF ICP Discharge in Helium

    NASA Astrophysics Data System (ADS)

    Blessington, Jon; Dejoseph, Charles, Jr.; Demidov, Vladimir; Koepke, Mark

    2006-10-01

    In previous work [1], it was shown that even a small number of nonlocal fast electron, which do not significantly affect the overall mean electron energy, can dramatically change the plasma and near-wall sheath properties. In this work, Langmuir probe measurements of electron density, temperature, energy distribution functions (EEDF), metastable atom density and their temporal evolution in the afterglow of low-pressure (50 mTorr) helium rf ICP discharges have been carried out. The experimental setup is described in [2]. The primary focus of this work is the investigation of the high energy portion of the EEDF which shows peaks corresponding to electrons with energies 14.4 and 19.8 eV. These peaks arise from electrons produced in Penning ionization with metastable helium atoms and metastable-electron collisions of second kind. This fast component of the EEDF can be controlled independently on the slow electrons, which is a direct consequence of the EEDF nonlocality. [1] V. Demidov et al. PRL 95, 215002 (2005). [2] W. Guo et al., PSST 10, 43 (2002).

  17. Characteristics of the Interstellar Helium by the He I 58.4-nm Optical Observation

    NASA Astrophysics Data System (ADS)

    Yamazaki, A.; Yoshikawa, I.; Shiomi, K.; Nakamura, M.; Miyake, W.

    2001-05-01

    There is a region with high-density helium gas in shape of a corn in the solar system, which is called the helium cone. The helium atoms originate from the local interstellar medium (LISM), and are injected into the heliosphere with the interstellar wind. The solar gravity force and radiation pressure decide the helium density distribution in the helium cone. Therefore the velocity, the density, and the temperature of the interstellar helium is estimated from the helium density distribution in the helium cone. An eXtreme Ultra-Violet (XUV) scanner has been built for Japanese first Mars Explorer, Planet-B. The scanner has detected the He I 58.4-nm emission resonantly scattered by the helium atoms in the helium cone on the Planet-B's cruise orbit to Mars. The He I emission rate is estimated from the helium cone formation model under the condition that the velocity vector of the interstellar wind and the loss rate (ionization rate) of helium atom in the interplanetary space are constant. The best agreement between the observation and the model gives the LISM parameters.

  18. Phase-operation for conduction electron by atomic-scale scattering via single point-defect

    SciTech Connect

    Nagaoka, Katsumi, E-mail: NAGAOKA.Katsumi@nims.go.jp; Yaginuma, Shin [International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Nakayama, Tomonobu [International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-0044 (Japan)

    2014-03-17

    In order to propose a phase-operation technique for conduction electrons in solid, we have investigated, using scanning tunneling microscopy, an atomic-scale electron-scattering phenomenon on a 2D subband state formed in Si. Particularly, we have noticed a single surface point-defect around which a standing-wave pattern created, and a dispersion of scattering phase-shifts by the defect-potential against electron-energy has been measured. The behavior is well-explained with appropriate scattering parameters: the potential height and radius. This result experimentally proves that the atomic-scale potential scattering via the point defect enables phase-operation for conduction electrons.

  19. Light scattering from ultracold atoms in optical lattices as an optical probe of quantum statistics

    SciTech Connect

    Mekhov, Igor B. [Institut fuer Theoretische Physik, Universitaet Innsbruck, Innsbruck (Austria); Faculty of Physics, St. Petersburg State University, St. Petersburg (Russian Federation); Maschler, Christoph; Ritsch, Helmut [Institut fuer Theoretische Physik, Universitaet Innsbruck, Innsbruck (Austria)

    2007-11-15

    We study off-resonant collective light scattering from ultracold atoms trapped in an optical lattice. Scattering from different atomic quantum states creates different quantum states of the scattered light, which can be distinguished by measurements of the spatial intensity distribution, quadrature variances, photon statistics, or spectral measurements. In particular, angle-resolved intensity measurements reflect global statistics of atoms (total number of radiating atoms) as well as local statistical quantities (single-site statistics even without optical access to a single site) and pair correlations between different sites. As a striking example we consider scattering from transversally illuminated atoms into an optical cavity mode. For the Mott-insulator state, similar to classical diffraction, the number of photons scattered into a cavity is zero due to destructive interference, while for the superfluid state it is nonzero and proportional to the number of atoms. Moreover, we demonstrate that light scattering into a standing-wave cavity has a nontrivial angle dependence, including the appearance of narrow features at angles, where classical diffraction predicts zero. The measurement procedure corresponds to the quantum nondemolition measurement of various atomic variables by observing light.

  20. Ultra-low-temperature reactions of C(3P0) atoms with benzene molecules in helium droplets

    NASA Astrophysics Data System (ADS)

    Krasnokutski, Serge A.; Huisken, Friedrich

    2014-12-01

    The reaction of carbon atoms with benzene has been investigated in liquid helium droplets at T = 0.37 K. We found an addition of the carbon atom to form an initial intermediate complex followed by a ring opening and the formation of a seven-membered ring. In contrast to a previous gas phase study, the reaction is frozen after these steps and the loss of hydrogen does not occur. A calorimetric technique was applied to monitor the energy balance of the reaction. It was found that more than 267 kJ mol-1 were released in this reaction. This estimation is in line with quantum chemical calculations of the formation energy of a seven-membered carbon ring. It is suggested that reactions of this kind could be responsible for the low abundance of small polycyclic aromatic hydrocarbon molecules in the interstellar medium. We also found the formation of weakly bonded water-carbon adducts, in which the carbon atom is linked to the oxygen atom of the water molecule with a binding energy of about 33.4 kJ mol-1.

  1. Interacting double dark resonances in a hot atomic vapor of helium

    SciTech Connect

    Kumar, S.; Ghosh, R. [School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067 (India); Laupretre, T.; Bretenaker, F.; Goldfarb, F. [Laboratoire Aime Cotton, CNRS-Universite Paris Sud 11, F-91405 Orsay Cedex (France)

    2011-08-15

    We experimentally and theoretically study two different tripod configurations using metastable helium ({sup 4}He*), with the probe field polarization perpendicular and parallel to the quantization axis, defined by an applied weak magnetic field. In the first case, the two dark resonances interact incoherently and merge together into a single electromagnetically induced transparency peak with increasing coupling power. In the second case, we observe destructive interference between the two dark resonances inducing an extra absorption peak at the line center.

  2. Detection of individual atoms in helium buffer gas and observation of their real-time motion

    NASA Technical Reports Server (NTRS)

    Pan, C. L.; Prodan, J. V.; Fairbank, W. M., Jr.; She, C. Y.

    1980-01-01

    Single atoms are detected and their motion measured for the first time to our knowledge by the fluorescence photon-burst method in the presence of large quantities of buffer gas. A single-clipped digital correlator records the photon burst in real time and displays the atom's transit time across the laser beam. A comparison is made of the special requirements for single-atom detection in vacuum and in a buffer gas. Finally, the probability distribution of the bursts from many atoms is measured. It further proves that the bursts observed on resonance are due to single atoms and not simply to noise fluctuations.

  3. Elastic scattering of polarized protons on helium three at 800 MeV

    SciTech Connect

    Azizi, A.

    1985-07-01

    A set of spin dependent parameters and cross sections has been measured for polarized p-/sup 3/He elastic scattering over the range of q .7 to 4.2 fm/sup -1/. The experiment was done at the Los Alamos Meson Physics Facility (LAMPF) using the High Resolution Spectrometer (HRS) with a polarized proton beam at .8 GeV. The focal plane polarimeter of the HRS was used to determine the spin direction of the scattered proton. Since /sup 3/He is one of the simplest nuclei, polarized p-/sup 3/He scattering provides a very sensitive test of multiple scattering theories. The theoretical analysis was done by using two different wave functions for /sup 3/He as input to the multiple scattering theory. The theoretical calculations and experimental data together will give us useful information about nucleon-nucleon amplitudes and also help us to obtain a better understanding of the scattering process. 68 refs., 55 figs., 9 tabs.

  4. Scattering of low-energy electrons and positrons by atomic beryllium: Ramsauer–Townsend effect

    NASA Astrophysics Data System (ADS)

    Reid, David D.; Wadehra, J. M.

    2014-11-01

    Total cross sections for the scattering of low-energy electrons and positrons by atomic beryllium in the energy range below the first inelastic thresholds are calculated. A Ramsauer–Townsend minimum is seen in the electron scattering cross sections, while no such effect is found in the case of positron scattering. A minimum total cross section of 0.016 a02 at 0.0029 eV is observed for the electron case. In the limit of zero energy, the cross sections yield a scattering length of ?0.61 a0 for electron and +13.8 a0 for positron scattering.

  5. Intershell correlations in nonresonant Compton scattering of an X-ray photon by an atom

    SciTech Connect

    Hopersky, A. N., E-mail: hopersky_vm_1@rgups.ru; Nadolinsky, A. M.; Ikoeva, K. Kh.; Khoroshavina, O. A. [Rostov State Railway University (Russian Federation)

    2011-11-15

    The role of intershell correlations in nonresonant Compton scattering of an X-ray photon by a free multielectron atom is studied theoretically for the Ar atom. The results of calculation are of a predictive nature. The developed mathematical formalism is general in nature and can be applied to a wide set of elements from the Periodic Table, for which the description of the wavefunctions of scattering states in the nonrelativistic Hartree-Fock approximation remains correct.

  6. The total cross section for electron scattering by atomic hydrogen

    Microsoft Academic Search

    T. T. Scholz; H. R. J. Walters; P. G. Burke

    1990-01-01

    An accurate total cross section for electron scattering by H(1s) in the intermediate energy regime of 1.0-3.7 Ryd is constructed by the addition of the best cross sections for elastic scattering, bound-state excitation, and ionization that are currently available. The theoretical cross sections arising from intermediate energy R-matrix (IERM) calculations are used for elastic scattering and n = 2 excitation.

  7. Theory of direct scattering, trapping, and desorption in atom-surface collisions Guoqing Fan1

    E-print Network

    Manson, Joseph R.

    Theory of direct scattering, trapping, and desorption in atom-surface collisions Guoqing Fan1 and J desorbs in a distribution at equilibrium with the surface temperature. In this paper a scattering theory is developed, using an iterative algorithm and classical mechanics for the collision process, which describes

  8. Low-energy electron-atom scattering: The case of near degeneracy

    SciTech Connect

    Feinberg, G.; Sucher, J.; Amado, R.

    1986-07-28

    We study low-energy elastic electron scattering from an atomic or molecular target for the case where the initial state of the target is close in energy to target states of opposite parity. We show that under these circumstances there is a range of small scattering angles in which the angular distribution varies rapidly. Experimental tests are suggested.

  9. X-ray-photon scattering by an excited and ionized atom

    NASA Astrophysics Data System (ADS)

    Hopersky, Alexey N.; Nadolinsky, Alexey M.; Novikov, Sergey A.; Yavna, Victor A.

    2015-02-01

    The scattering process of an x-ray photon by an excited and ionized many-electron atom with attosecond photon-electron contact interaction is theoretically investigated. The results of the authors' recent work [Hopersky et al., Phys. Rev. A 88, 032704 (2013), 10.1103/PhysRevA.88.032704] are generalized for the cases of (a) arbitrary energy of the photon that prepares the scattering state and (b) the scattering of the photon by the continuous spectrum electron of the ionization state of the atom. The atom of Ne is considered as the object of the study. Along with the effects of normal Compton and elastic scattering, the existence of anomalous inelastic scattering is predicted. It may be assumed that this effect will become a basis for an experimental method of increasing the energy of the photons generated, for example, by a free-electron x-ray laser. It is determined that during the elastic scattering of a photon by an electron of the continuous spectrum, along with the known contribution from the jl Bessel function over the l =0 harmonic (Thomson scattering), there is also a contribution from Bessel functions with harmonics l ?[1 ;? ) . The experimental discovery and application of the anomalous Compton photon scattering effect directly by the atomic electron of the continuous spectrum have their own practical interest.

  10. Temperature Dependence in Rainbow Scattering of Hyperthermal Ar Atoms from LiF(001)

    E-print Network

    Hayes, W W

    2015-01-01

    Recent experiments have reported measurements of rainbow scattering features in the angular distributions of hyperthermal Ar colliding with LiF(001) [Kondo et al., J. Chem. Phys. 122, 244713 (2005)]. A semiclassical theory of atom-surface collisions recently developed by the authors that includes multiphonon energy transfers is used to explain the temperature dependence of the measured scattered angular distribution spectra.

  11. Influence of coherent Raman scattering on coherent population trapping in atomic sodium vapor

    SciTech Connect

    Wong, Vincent; Bennink, Ryan S.; Marino, Alberto M.; Boyd, Robert W.; Stroud, C.R. Jr.; Narducci, F.A. [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); EO Sensors Division, Naval Air Systems Command, Patuxent River, Maryland 20670 (United States)

    2004-11-01

    We study how coherent Stokes and anti-Stokes Raman scattering influence coherent population trapping. In an experiment using an atomic sodium vapor cell we observe induced transparency, induced absorption, and gain features, all of subnatural linewidth. The electromagnetically induced resonance is a peak or a dip depending on which side of the optical transition the fields are tuned to, and thus whether coherent anti-Stokes Raman scattering or coherent Stokes Raman scattering is the dominant process.

  12. Higher-Order Stark Effect on Magnetic Fine Structure of the Helium Atom

    Microsoft Academic Search

    Aleksandr Magunov; Vitaly Ovsiannikov; Vitaly Pal’chikov; Victor Pivovarov; Gebhard von Oppen

    2001-01-01

    We have calculated the scalar and tensor dipole polarizabilities (?) and hyperpolarizabilities (?) of excited 1s2p\\u000a 3\\u000a P}in0}, 1s2p\\u000a 3\\u000a P\\u000a 2- states of helium. Our theory includes fine structure of triplet sublevels. Semiempirical and accurate electron-correlated\\u000a wave functions have been used to determine the static values of ? and ?. Numerical calculations are carried out using sums of oscillator

  13. Advances in the helium-jet coupled on-line mass separator RAMA. [Recoil Atom Mass Analyzer

    SciTech Connect

    Moltz, D M; Aysto, J; Cable, M D; Parry, R F; Haustein, P E; Wouters, J M; Cerny, J

    1980-01-01

    General improvements to the on-line mass separator RAMA (Recoil Atom Mass Analyzer) have yielded a greater reliability and efficiency for some elements. A new utilitarian helium-jet chamber has been installed to facilitate quick target and degrader foil changes in addition to a new ion source holder. A higher efficiency hollow-cathode, cathode-extraction ion source, for lower melting point elements (< 1200/sup 0/C) has also been designed. Tests with the beta-delayed proton emitter /sup 37/Ca showed a factor of five increase in yield over the old hollow-cathode, anode-extraction source. A differentially-pumped-tape drive system compatible with both ..gamma..-..gamma.. and ..beta..-..gamma.. experiments has been incorporated into the general detection system. All major operating parameters will soon be monitored by a complete stand-alone microprocessor system which will eventually be upgraded to a closed-loop control system.

  14. Electron Diffraction of Superfluid Helium Droplets

    PubMed Central

    2014-01-01

    We present experimental results of electron diffraction of superfluid helium droplets and droplets doped with phthalocyanine gallium chloride and discuss the possibility of performing the same experiment with a laser aligned sample. The diffraction profile of pure droplets demonstrates dependence on the nozzle temperature, that is, on the average size of the droplets. Larger clusters demonstrate faster decay with increasing momentum transfer, whereas smaller clusters converge to isolated gas phase molecules at source temperatures of 18 K and higher. Electron diffraction of doped droplets shows similar modified molecular scattering intensity as that of the corresponding gas phase molecules. On the basis of fittings of the scattering profile, the number of remaining helium atoms of the doped droplets is estimated to be on the order of hundreds. This result offers guidance in assessing the possibility of electron diffraction from laser aligned molecules doped in superfluid helium droplets. PMID:24920997

  15. LIF Measurements on an Atomic Helium Beam in the Edge of a Fusion Plasma--possible derivation of the electron density

    SciTech Connect

    Krychowiak, M.; Koenig, R.; Klinger, T. [Max-Planck-Institut fuer Plasmaphysik, EURATOM-Association, Wendelsteinstrasse 1, D-17491 Greifswald (Germany); Mertens, Ph.; Schweer, B.; Brezinsek, S.; Schmitz, O.; Samm, U. [Institut fuer Energieforschung (IEF 4-Plasmaphysik), FZ Juelich, EURATOM-Association, TEC, Wilhelm-Johnen-Strasse D-52428 Juelich (Germany); Brix, M. [UKEA, JET- Experimental Department, EURATOM-Association, Culham Science Centre, ABINGDON, Oxfordshire, OX14 3DB (United Kingdom)

    2008-03-19

    Local values of the electron density and temperature in the edge of a fusion plasma can be derived with high space and time resolution by the use of line radiation of atomic helium beams. The accuracy of this method is mainly limited by the uncertainties in the collisional-radiative model which is needed in order to obtain both plasma parameters from the measured relative intensities of atomic helium lines. Combination of a helium beam with a pulsed high-power laser provides a possibility of n{sub e} measurement which does not require a detailed knowledge of the collisional-radiative model. The method relies on resonant laser pumping of some levels and analyzing their fluorescence after the end of the laser pulse. Such measurements were already performed in low temperature plasmas with some content of atomic helium [1,2,3]. In this paper, we discuss the applicability of this method in the fusion edge plasma in the density range of {approx}10{sup 12}-10{sup 13} cm{sup -3} when exciting helium atoms with a laser at the wavelength of {lambda} = 388.9 nm tuned to the triplet transition 2{sup 3}S-vector3{sup 3}P deg. and observing the fluorescence light at the laser wavelength and at {lambda} = 587.6 nm(3{sup 3}D-vector2{sup 3}P deg.). A first test measurement at the TEXTOR tokamak in Juelich performed by use of an excimer-pumped dye laser in connection with a thermal helium beam is shown and discussed.

  16. Classical Theory of Atom Scattering from Corrugated Surfaces W. W. Hayes

    E-print Network

    Manson, Joseph R.

    in the collision of an atomic projectile with a surface which is either ordered or disordered. This theory the theory reproduces the well-known eikonal approximation for elastic collisions, provides a simpleClassical Theory of Atom Scattering from Corrugated Surfaces W. W. Hayes Physical Sciences

  17. Langmuir-Taylor surface ionization of alkali (Li, Na, K) and alkaline earth (Ca, Sr, Ba) atoms attached to helium droplets

    Microsoft Academic Search

    F. Stienkemeier; M. Wewer; F. Meier; H. O. Lutz

    2000-01-01

    A beam of superfluid helium droplets (HeN, N~104) doped with alkali and alkaline earth atoms is detected by Langmuir-Taylor surface ionization. We measured detection efficiencies and time constants as a function of the temperature of a hot rhenium surface. Compared to results on free K, Na, and Ba atoms we find practically no differences in the detection properties; apparently the

  18. Scattering properties of weakly-bound dimers of Fermi atoms

    NASA Astrophysics Data System (ADS)

    Petrov, Dmitry

    2005-03-01

    We discuss the behavior of weakly bound bosonic dimers formed in a two-component Fermi gas with a large positive scattering length for the interspecies interaction. We present a theoretical approach for solving a few-body scattering problem and describe the physics of dimer-dimer elastic and inelastic scattering. We explain why these diatomic molecules, while in the highest ro-vibrational level, are characterized by remarkable collisional stability. Co-authors are Christophe Salomon, LKB, Ecole Normale Superieure, Paris, France; Georgy Shlyapnikov, LPTMS, University of South Paris, Orsay, France.

  19. Cavity-Enhanced Light Scattering in Optical Lattices to Probe Atomic Quantum Statistics

    SciTech Connect

    Mekhov, Igor B. [Institut fuer Theoretische Physik, Universitaet Innsbruck, Innsbruck (Austria); V. A. Fock Institute of Physics, St. Petersburg State University, St. Petersburg (Russian Federation); Maschler, Christoph; Ritsch, Helmut [Institut fuer Theoretische Physik, Universitaet Innsbruck, Innsbruck (Austria)

    2007-03-09

    Different quantum states of atoms in optical lattices can be nondestructively monitored by off-resonant collective light scattering into a cavity. Angle resolved measurements of photon number and variance give information about atom-number fluctuations and pair correlations without single-site access. Observation at angles of diffraction minima provides information on quantum fluctuations insensitive to classical noise. For transverse probing, no photon is scattered into a cavity from a Mott insulator phase, while the photon number is proportional to the atom number for a superfluid.

  20. Parity-Odd Atomic Multipoles in X-ray Scattering and Absorption

    NASA Astrophysics Data System (ADS)

    Lovesey, Stephen William; Balcar, Ewald

    2010-10-01

    Scattering of x-rays enhanced by an electric dipole-electric quadrupole (E1-E2) event probe parity-odd atomic multipoles at the heart of many current theories of complex materials, e.g., Mott-Hubbard insulators and multiferroics. We achieve a complete decomposition of the E1-E2 scattering amplitude at spin-orbit split states in terms of atomic multipoles, albeit unfamiliar composite atomic operators built with electron position, spin and orbital variables. In consequence, one has clear insight as to the physical makeup of quantities that determine structure factors for Bragg diffraction enhanced by resonant ions that occupy sites devoid of inversion symmetry.

  1. The Scattering of Gas Atoms from Solid Surfaces

    ERIC Educational Resources Information Center

    Walton, Alan J.

    1977-01-01

    Traditional undergraduate courses in gas kinetic theory encourage the view that in all collisions between a gas atom and a surface, the angle of incidence of the gas atom equals its angle of reflection. This article illustrates and explains the incorrectness in assuming specular reflection and zero dwell time. (Author/MA)

  2. Deep Inelastic Electron Scattering Off the Helium and Tritium Mirror Nuclei

    SciTech Connect

    Holt, Roy J. [Physics Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Petratos, Gerassimos G. [Department of Physics, Kent State University, Kent, OH 44242 (United States)

    2011-09-21

    We discuss a possible measurement of the ratio of nucleon structure functions, F{sub 2}{sup n}/F{sub 2}{sup p}, and the ratio of up to down quark distributions, u/d, at large Bjorken x, by performing deep inelastic electron scattering from the {sup 3}H and {sup 3}He mirror nuclei with the 11 GeV upgraded beam of Jefferson Lab. The measurement is expected to be almost free of nuclear effects, which introduce a significant uncertainty in the extraction of these two ratios from deep inelastic scattering off the proton and deuteron. The results are expected to test perturbative and non-perturbative mechanisms of spin-flavor symmetry breaking in the nucleon, and constrain the structure function parametrizations needed for the interpretation of high energy collider and neutrino oscillations data. The precision of the expected data can also test models of the nuclear EMC effect and provide valuable input for its full explanation.

  3. Resonant atom-dimer collisions in cesium: Testing universality at positive scattering lengths

    NASA Astrophysics Data System (ADS)

    Zenesini, A.; Huang, B.; Berninger, M.; Nägerl, H.-C.; Ferlaino, F.; Grimm, R.

    2014-08-01

    We study the collisional properties of an ultracold mixture of cesium atoms and dimers close to a Feshbach resonance near 550 G in the regime of positive s-wave scattering lengths. We observe an atom-dimer loss resonance that is related to Efimov's scenario of trimer states. The resonance is found at a value of the scattering length that is different from a previous observation at low magnetic fields. This indicates nonuniversal behavior of the Efimov spectrum for positive scattering lengths. We compare our observations with predictions from effective field theory and with a recent model based on the van der Waals interaction. We present additional measurements on pure atomic samples in order to check for the presence of a resonant loss feature related to an avalanche effect, as suggested by observations in other atomic species. We could not confirm the presence of such a feature.

  4. Kinematically complete experiments for positron-impact ionization of helium atoms at the NEPOMUC facility

    NASA Astrophysics Data System (ADS)

    Pflüger, T.; Holzwarth, M.; Senftleben, A.; Ren, X.; Dorn, A.; Ullrich, J.; Hargreaves, L. R.; Lohmann, B.; Slaughter, D. S.; Sullivan, J. P.; Lower, J. C.; Buckman, S. J.

    2011-01-01

    Positron impact ionization of helium is studied with fully resolved momentum vectors of all continuum particles. An imaging multi-particle momentum spectrometer (reaction microscope) detecting all final state particles over the full solid angle was applied. This apparatus was connected to the NEPOMUC facility delivering intense positron beams tuneable over a large energy range with good beam quality. At 80 eV impact energy about 5000 triple coincidence events were collected. Cross sections as function of the longitudinal particle momentum show strong differences compared to respective electron impact ionization data most likely originating from the reversed post collision interaction in both cases. Calculations using the 3 Coulomb wavefunction method show clear discrepancies from the experimental results.

  5. Helium-rich white dwarf atmospheres: the non-symmetric ion-atom absorption processes

    NASA Astrophysics Data System (ADS)

    Sre?kovi?, V. A.; Mihajlov, A. A.; Ignjatovi?, Lj M.; Dimitrijevi?, M. S.

    2014-12-01

    Here, the processes of photo-association and absorption charge-exchange in He+H+ collisions together with the process of molecular ion HeH+ photo-dissociation are considered as factors of influence on the opacity of the atmospheres of helium-rich white dwarfs in the far UV region. It is shown that they should be taken into account even in the cases of the atmospheres of white dwarfs with H:He =10?5. Also, it is established that in the cases of white dwarfs with H:He gtrsim 10?4, especially when H:He ? 10?3, these processes have to be included ab initio in the corresponding models of their atmospheres.

  6. Measurements of Total Cross-Sections for Positron - and Electron-Alkali Atom Scattering and of Positronium Formation Cross-Sections for Argon and Potassium Atoms

    Microsoft Academic Search

    Sonal P. Parikh

    1992-01-01

    We have measured total cross sections (Q _{rm T}'s) for positrons (e^+'s) and electrons (e ^-'s) scattering from potassium (K) and rubidium (Rb) atoms and for e^-'s scattering from lithium (Li) and cesium (Cs) atoms, using a beam transmission technique. Our measured e^--alkali atom Q_{rm T}'s show a monotonic decrease with increasing energy for all the alkali atoms. Our measured

  7. Non-reactive scattering of excited exotic hydrogen atoms

    E-print Network

    G. Ya. Korenman; V. P. Popov; V. N. Pomerantsev

    2005-04-27

    The Coulomb deexcitation of light exotic atoms in collisions with hydrogen atoms has been studied in the framework of the fully quantum-mechanical close-coupling method for the first time. The calculations of the $l$-averaged cross sections have been performed for $(\\mu p)_n$ and $(\\mu d)_n$ atoms in the states with the principal quantum number $n=3 \\div 8$ and relative energies region $E=0.01 \\div 100$ eV. The obtained results reveal the new $n$ and $E$ dependences of the Coulomb deexcitation cross sections. The large fraction (up to $\\sim$ 36%) of the transition with $\\Delta n > 1$ is also predicted.

  8. Relativistic Corrections to the Zeeman Effect in Hydrogen-Like Atoms, Positronium, and Helium-Like Atoms

    Microsoft Academic Search

    John Michael Anthony

    1993-01-01

    An approximately relativistic theory of bound states which ensures the Poincare invariance of atomic systems to relative order (v\\/c)^2 is used to derive the Zeeman interaction Hamiltonians correct to order alpha^3 and to all orders in m_{rm e}\\/m _{rm N} for arbitrary two body systems and three body systems. Previously neglected radiative corrections of order alpha^3 and recoil corrections of

  9. New quantum gravity effect, dark energy, accelerating universe, black hole and experimental scheme using superfluid Helium and atom interferometer

    E-print Network

    Hongwei Xiong

    2011-01-03

    Considerable attention has been focused on Verlinde's recent work, claiming that Newton's gravity is not a fundamental force. In a recent work (arXiv:1012.5858), we give further the logic basis and basic clues to derive the Newton's gravity, inertia law and Einstein's weak equivalence principle. In this work, we show that if the gravity is not a fundamental force, in special case, it could be repulsive when quantum wavepacket effect is considered. This quantum gravity effect leads to several physical effects: (1) It is consistent with the universe with accelerating expansion, if the gravity and quantum effect of the fluctuating 'vacuum' (dark energy) is considered. The role of the cosmological constant is naturally interpreted when the gravity and quantum effect of the whole 'vacuum' background is considered. (2) It leads to new idea about black hole information paradox, no-hair theorem and Hawking radiation. (3) With a sphere full of superfluid Helium, we propose a feasible experimental scheme to test our idea with an atom interferometer placed in the sphere. Our calculations show that the accuracy Delta g/g below 10^(-8) could be used to test our idea, which satisfies the present experimental technique of atom interferometer.

  10. Inelastic and reactive scattering of hyperthermal atomic oxygen from amorphous carbon

    NASA Technical Reports Server (NTRS)

    Minton, Timothy K.; Nelson, Christine M.; Brinza, David E.; Liang, Ranty H.

    1991-01-01

    The reaction of hyperthermal oxygen atoms with an amorphous carbon-13 surface was studied using a modified universal crossed molecular beams apparatus. Time-of-flight distributions of inelastically scattered O-atoms and reactively scattered CO-13 and CO2-13 were measured with a rotatable mass spectrometer detector. Two inelastic scattering channels were observed, corresponding to a direct inelastic process in which the scattered O-atoms retain 20 to 30 percent of their initial kinetic energy and to a trapping desorption process whereby O-atoms emerge from the surface at thermal velocities. Reactive scattering data imply the formation of two kinds of CO products, slow products whose translational energies are determined by the surface temperature and hyperthermal (Approx. 3 eV) products with translational energies comprising roughly 30 percent of the total available energy (E sub avl), where E sub avl is the sum of the collision energy and the reaction exothermicity. Angular data show that the hyperthermal CO is scattered preferentially in the specular direction. CO2 product was also observed, but at much lower intensities than CO and with only thermal velocities.

  11. Energy Levels in Helium and Neon Atoms by an Electron-Impact Method.

    ERIC Educational Resources Information Center

    Taylor, N.; And Others

    1981-01-01

    Electronic energy levels in noble gas atoms may be determined with a simple teaching apparatus incorporating a resonance potentials tube in which the electron beam intensity is held constant. The resulting spectra are little inferior to those obtained by more elaborate electron-impact methods and complement optical emission spectra. (Author/SK)

  12. Robust quantum gates on neutral atoms with cavity-assisted photon-scattering

    E-print Network

    L. -M. Duan; B. Wang; H. J. Kimble

    2005-05-09

    We propose a scheme to achieve quantum computation with neutral atoms whose interactions are catalyzed by single photons. Conditional quantum gates, including an $N$-atom Toffoli gate and nonlocal gates on remote atoms, are obtained through cavity-assisted photon scattering in a manner that is robust to random variation in the atom-photon coupling rate and which does not require localization in the Lamb-Dicke regime. The dominant noise in our scheme is automatically detected for each gate operation, leading to signalled errors which do not preclude efficient quantum computation even if the error probability is close to the unity.

  13. Quasi-Free Scattering of Protons from HELIUM-3 at Intermediate Energies.

    NASA Astrophysics Data System (ADS)

    Bracco, Angela

    Quasi-free scattering of protons from ('3)He at intermediate energies has been studied. Two sets of experiments have been carried out at the TRIUMF cyclotron laboratory. The first set of experiments concerned the study of two-nucleon wavefunctions in ('3)He. The ('3)He(p,2p)np reaction was studied in a quasi-free scattering arrangement characterized by P(' )(recoil) = 0 and various excitation energies E(recoil) of the unobserved p-n pair. Data were obtained at 250 and 400 MeV at symmetric and asymmetric angle pairs. The ('3)He spectral function deduced in the framework of the plane wave impulse approximation (PWIA) is compared to the predictions of Faddeev and variational calculations. Comparisons are also made with p-n relative motion momentum distributions calculated using plane waves for the p-n pair and Irving, Irving-Gunn, and Khanna wave functions for ('3)He. The second set of experiments concerned the study of the proton-deuteron relative motion momentum distribution in ('3)He. Since the PWIA predicts the same relative motion momentum distributions extracted from the ('3)He(p,2p)d and ('3)He(p,pd)p reactions, a comparison of the results of the two reactions is made. The ('3)He(p,2p)d reaction was measured at 300 and 450 MeV for recoil momenta larger than 350 MeV/c and the ('3)He(p,pd)p at 450 MeV for recoil momenta between 0 and 480 MeV/c. The present momentum distributions are compared to the existing ('3)He(p,pd)p and ('3)He(e,e'p)d results and to spectral functions calculated using either variational techniques or Faddeev equations.

  14. Electron capture by large helium droplets

    Microsoft Academic Search

    Ulrich Henne; J. Peter Toennies

    1998-01-01

    The attachment of electrons to large helium droplets containing up to 108 atoms produced in supercritical liquid free jet expansions has been investigated in a crossed beam scattering experiment. Negative cluster ions were formed in collisions with electrons from a nearly monoenergetic (deltaE~0.25 eV) electron beam with energies Eel=1.0-100 eV and were subsequently size selected by electrostatic deflection. Depending on

  15. Quenching of the resonance 5s(3P1) state of krypton atoms in collisions with krypton and helium atoms

    NASA Astrophysics Data System (ADS)

    Zayarnyi, D. A.; L'dov, A. Yu; Kholin, I. V.

    2014-11-01

    The processes of collision quenching of the resonance 5s[3/2]1o(3P1) state of the krypton atom are studied by the absorption probe method in electron-beam-excited high-pressure He – Kr mixtures with a low content of krypton. The rate constants of plasmochemical reactions Kr* + Kr + He ? Kr*2 + He [(4.21 ± 0.42) × 10-33 cm6 s-1], Kr* + 2He ? HeKr* + He [(4.5 ± 1.2) × 10-36 cm6 s-1] and Kr* + He ? products + He [(2.21 ± 0.22) × 10-15 cm3 s-1] are measured for the first time. The rate constants of similar reactions are refined for krypton in the metastable 5s[3/2]2o (3P2) state.

  16. 2s Hyperfine Structure in Hydrogen Atom and Helium3 Ion

    Microsoft Academic Search

    Savely G. Karshenboim; D. I. Mendeleev

    The usefulness of study of hyperfine splitting in the hydrogen atom is limited on a level of 10 ppm by our knowledge of the\\u000a proton structure. One way to go beyond 10 ppm is to study a specific difference of the hyperfine structure intervals ?\\u000a v2 - ?\\u000a v1. Nuclear effects for are not important this difference and it is

  17. Characterization of helium surface-wave plasmas at intermediate pressures (5–50?Torr): temperatures and density of metastable atoms in the 23s level

    NASA Astrophysics Data System (ADS)

    Hamdan, Ahmad; Margot, Joëlle; Vidal, François; Matte, Jean-Pierre

    2015-01-01

    A stationary surface wave discharge is studied in helium gas at intermediate pressure. By optical emission spectroscopy, rotational temperatures derived from impurities molecular bands have been studied, as well as the excitation temperature from the Boltzmann plot method of helium lines, as a function of gas pressure, absorbed power and axial position. The rotational temperature of OH molecules is supposed to be in thermal equilibrium with the plasma gas and is used for determining its temperature. The influence of the tube diameter has also been studied; it was observed that the tubes with smaller diameter lead to higher gas temperature. By optical absorption spectroscopy, the density of metastable atoms (in 23s level) has been studied as a function of the parameters. An important dependence on the gas pressure has been observed. Indeed, a one order of magnitude reduction is obtained when the pressure increases from 5 to 50?Torr. The density of metastable atoms remains constant as a function of power and almost all along the plasma column. Finally, a collisional-radiative model was used to compare the experimental to the theoretical results of the density of metastable atoms providing at the same time estimations of the density and the temperature of the electrons as well as the density of helium (atomic and molecular) ions. Results showed a good agreement when the tube diameter is large, but for smaller tubes, the agreement was obtained only for the higher gas pressures.

  18. Imaging Nonequilibrium Atomic Vibrations with X-ray Diffuse Scattering

    SciTech Connect

    Trigo, M.; Chen, J.; Vishwanath, V.H.; /SLAC; Sheu, Y.M.; /Michigan U.; Graber, T.; Henning, R.; /U. Chicago; Reis, D; /SLAC /Stanford U., Appl. Phys. Dept.; ,

    2011-03-03

    We use picosecond x-ray diffuse scattering to image the nonequilibrium vibrations of the lattice following ultrafast laser excitation. We present images of nonequilibrium phonons in InP and InSb throughout the Brillouin-zone which remain out of equilibrium up to nanoseconds. The results are analyzed using a Born model that helps identify the phonon branches contributing to the observed features in the time-resolved diffuse scattering. In InP this analysis shows a delayed increase in the transverse acoustic (TA) phonon population along high-symmetry directions accompanied by a decrease in the longitudinal acoustic (LA) phonons. In InSb the increase in TA phonon population is less directional.

  19. Light Scattering for Thermometry of Fermionic Atoms in an Optical Lattice

    SciTech Connect

    Ruostekoski, J. [School of Mathematics, University of Southampton, Southampton, SO17 1BJ (United Kingdom); Foot, C. J.; Deb, A. B. [Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX1 3PU (United Kingdom)

    2009-10-23

    We propose a method of using off-resonant light scattering to measure the temperature of fermionic atoms tightly confined in a two-dimensional optical-lattice potential. We show that fluctuations of the intensity in the far-field diffraction pattern arising from thermal correlations of the atoms can be accurately detected above the shot noise by collecting photons scattered in a forward direction, with the diffraction maxima blocked. The sensitivity of this method of thermometry is enhanced by an additional harmonic trapping potential.

  20. Extracting low-energy electron-atom scattering parameters from ionic measurements

    NASA Astrophysics Data System (ADS)

    Macri, P.; Barrachina, R. O.

    2003-05-01

    We analyze different methods to extract from ionic measurements electron-atom scattering parameters, such as the scattering length. Different generalizations of O'Malley et al.'s modified effective range theory, such as for instance Fabrikant's approach or the multichannel theory of Watanabe and Greene, are used in the literature to fit the experimental data. In this communication we propose a different approach that provides a significant improvement over other methods on a much broader range of energies. We discuss its applicability in the case of negative ion photodetachment and in coincidence measurements of electron capture and loss to the continuum in atomic collisions.

  1. Measurement of effective atomic number of gunshot residues using scattering of gamma rays

    NASA Astrophysics Data System (ADS)

    Y?lmaz, Demet; Tur?ucu, Ahmet; Uzuno?lu, Zeynep; Korucu, Demet

    2014-09-01

    Better understanding of gunshot residues and the major elemental composition would be valuable to forensic scientists for their analysis work and interpretation of results. In the present work, the effective atomic numbers of gunshot residues (cartridge case, bullet core, bullet jacket and gunpowder) were analyzed using energy dispersive X-ray analysis (EDX). The scattering of 59.54 keV gamma rays is studied using a high-resolution HPGe detector. The experiment is performed on various elements with atomic number in the 4?Z?82. The intensity ratio of coherent to Compton scattered peaks, corrected for photo-peak efficiency of gamma detector and absorption of photons in the sample and air, is plotted as a function of atomic number and constituted a best-fit-curve. From this fit-curve, the respective effective atomic numbers of gunshot residues are determined.

  2. A design for a pinhole scanning helium microscope

    NASA Astrophysics Data System (ADS)

    Barr, M.; Fahy, A.; Jardine, A.; Ellis, J.; Ward, D.; MacLaren, D. A.; Allison, W.; Dastoor, P. C.

    2014-12-01

    We present a simplified design for a scanning helium microscope (SHeM) which utilises almost entirely off the shelf components. The SHeM produces images by detecting scattered neutral helium atoms from a surface, forming an entirely surface sensitive and non-destructive imaging technique. This particular prototype instrument avoids the complexities of existing neutral atom optics by replacing them with an aperture in the form of an ion beam milled pinhole, resulting in a resolution of around 5 microns. Using the images so far produced, an initial investigation of topological contrast has been performed.

  3. Influence of nearly resonant light on the scattering length in low-temperature atomic gases

    Microsoft Academic Search

    P. O. Fedichev; Y. M. Kagan; G. V. Shlyapnikov; J. T. M. Walraven

    1996-01-01

    We develop the idea of manipulating the scattering length $a$ in\\u000alow-temperature atomic gases by using nearly resonant light. As found, if the\\u000aincident light is close to resonance with one of the bound $p$ levels of\\u000aelectronically excited molecule, then virtual radiative transitions of a pair\\u000aof interacting atoms to this level can significantly change the value and even

  4. Simple approximation to thermal attenuation in low energy atom-surface scattering: Single phonon processes

    Microsoft Academic Search

    J. R. Manson; G. Armand

    1987-01-01

    We consider a simple approximation to the general theory of thermal attenuation of elastic peaks as a function of surface temperature in low energy atom-surface scattering. The results illustrate the complexity of the strongly interacting atom-surface system, yet provide simple closed form expressions which are no more difficult to apply than a standard Debye-Waller factor. Very good agreement is obtained

  5. Transition in electron scattering mechanism in atomic layer deposited Nb:TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Niemelä, Janne-Petteri; Hirose, Yasushi; Hasegawa, Tetsuya; Karppinen, Maarit

    2015-01-01

    We characterized transport and optical properties of atomic layer deposited Nb:TiO2 thin films on glass substrates. These promising transparent conducting oxide (TCO) materials show minimum resistivity of 1.0 × 10-3 ? cm at 300 K and high transmittance in the visible range. Low-temperature (2-300 K) Hall measurements and the Drude fitting of the Vis-NIR optical spectra indicate a transition in the scattering mechanism from grain boundary scattering to intra-grain scattering with increasing Nb content, thus underlining enhancement of the grain size in the low doping regime as the key for further improved TCO properties.

  6. Positron scattering from hydrogen atom with screened Coulomb potentials

    SciTech Connect

    Ghoshal, Arijit [Department of Mathematics, Burdwan University, Golapbag, Burdwan 713 104, West Bengal, India and Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Nayek, Sujay [Department of Mathematics, Burdwan University, Golapbag, Burdwan 713 104, West Bengal (India); Kamali, M. Z. M. [Centre for Foundation Studies in Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ratnavelu, K. [Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)

    2014-03-05

    Elastic positron-hydrogen collisions with screened Coulomb potentials have been investigated using a second-order distorted wave Born approximation in the momentum space. Two types of potentials have been considered, namely, static screened Coulomb potential and exponential cosine-screened Coulomb potential. Using a simple variationally determined hydrogenic wave function it has been possible to obtain the scattering amplitude in a closed form. A detailed study has been made on the differential and total cross sections in the energy range 20–300 eV.

  7. X-ray measurements in helium-like atoms increased discrepancy between experiment and theoretical QED

    NASA Astrophysics Data System (ADS)

    Chantler, C. T.; Payne, A. T.; Gillaspy, J. D.; Hudson, L. T.; Smale, L. F.; Henins, A.; Kimpton, J. A.; Takacs, E.

    2014-12-01

    A recent 15 parts per million (ppm) experiment on muonic hydrogen ({{p}+}{{? }-}) found a major discrepancy with quantum electrodynamics (QED) and independent nuclear size determinations. Here we find a significant discrepancy in a different type of exotic atom: a medium-Z nucleus with two electrons. Investigation of the data collected is able to discriminate between available QED formulations and reveals a pattern of discrepancy of almost six standard errors of experimental results from the most recent theoretical predictions, with a functional dependence proportional to Zn where n? 4. In both the muonic and highly charged systems, the sign of the discrepancy is the same, with the measured transition energy higher than predicted. Some consequences are possible or probable, and some are more speculative. This may give insight into effective nuclear radii, the Rydberg, the fine-structure constant, or unexpectedly large QED terms.

  8. Crossed-molecular-beams reactive scattering of oxygen atoms

    SciTech Connect

    Baseman, R.J.

    1982-11-01

    The reactions of O(/sup 3/P) with six prototypical unsaturated hydrocarbons, and the reaction of O(/sup 1/D) with HD, have been studied in high-resolution crossed-molecular-beams scattering experiments with mass-spectrometric detection. The observed laboratory-product angular and velocity distributions unambiguously identify parent-daughter ion pairs, distinguish different neutral sources of the same ion, and have been used to identify the primary products of the reactions. The derived center-of-mass product angular and translational energy distributions have been used to elucidate the detailed reaction dynamics. These results demonstrate that O(/sup 3/P)-unsaturated hydrocarbon chemistry is dominated by single bond cleavages, leading to radical products exclusively.

  9. Positron scattering from hydrogen atom embedded in weakly coupled plasma

    SciTech Connect

    Ghoshal, Arijit [Department of Mathematics, Burdwan University, Golapbag, Burdwan 713 104, West Bengal (India); Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Kamali, M. Z. M. [Centre for Foundation Studies in Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ratnavelu, K. [Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)

    2013-01-15

    The positron-hydrogen collision problem in weakly coupled plasma environment has been investigated by applying a formulation of the three-body collision problem in the form of coupled multi-channel two-body Lippmann-Schwinger equations. The interactions among the charged particles in the plasma have been represented by Debye-Huckel potentials. A simple variational hydrogenic wave function has been employed to calculate the partial-wave scattering amplitude. Plasma screening effects on various possible mode of fragmentation of the system e{sup +}+H(1s) during the collision, such as 1s{yields}1s and 2s{yields}2s elastic collisions, 1s{yields}2s excitation, positronium formation, elastic proton-positronium collisions, have been reported. Furthermore, a detailed study has been made on differential and total cross sections of the above processes in the energy range 13.6-350 eV of the incident positron.

  10. On neutrino-atom scattering in searches for neutrino magnetic moments

    E-print Network

    Konstantin A. Kouzakov; Alexander I. Studenikin; Mikhail B. Voloshin

    2011-02-03

    In the experimental searches for neutrino magnetic moments using germanium detectors one studies the ionization channel in the neutrino-atom scattering. We find that the so-called stepping approximation to the neutrino-impact ionization is exact in the semiclassical limit, and that the deviations from this approximation are very small.

  11. Atom-dimer scattering and stability of Bose and Fermi mixtures

    NASA Astrophysics Data System (ADS)

    Cui, Xiaoling

    2014-10-01

    Motivated by a recent experiment by the Ecole Normale Supérieure de Lyon (ENS) group on the mixture of Bose and Fermi superfluids [I. Ferrier-Barbut et al., Science 345, 1035 (2014), 10.1126/science.1255380], we investigate the effective scattering between a bosonic atom and a molecule (dimer) of fermion atoms. It is found that the mean-field prediction of the atom-dimer scattering length (aad), as simply given by the boson-fermion scattering length (abf), generically fails. Instead, aad crucially depends on the ratio between abf and aff (the fermion-fermion scattering length), and in addition it log-periodically depends on the three-body parameter. We identify the universal parameters in characterizing aad for a wide range of aff in the molecular side of the fermion-fermion Feshbach resonance, and further demonstrate that the atom-dimer many-body system can become unstable against either phase separation or collapse as tuning aff. Our results have some implications for the ENS experiment.

  12. Kinematical rainbow and elastic focusing effects in atom-surface scattering S. Miret-Artes

    E-print Network

    Manson, Joseph R.

    Kinematical rainbow and elastic focusing effects in atom-surface scattering S. Miret in elastic surface diffraction are reported. First, a kinematical rainbow KR condition, a special case of the well-known rainbow singularity, is examined and shown to be a two-dimensional counterpart of the glory

  13. Charge-transfer reactions in atom scattering from ionic surfaces: A time-dependent wavepacket approach

    E-print Network

    Zeiri, Yehuda

    Charge-transfer reactions in atom scattering from ionic surfaces: A time-dependent wavepacket with the electrostatic image charge in the metal surface, as indicated in Fig. 1(a). For low workfunction surfaces resonant with the valence band of the surface, but the image attraction is small (at least for singly-charged

  14. Beyond the single-atom response in absorption lineshapes: Probing a dense, laser-dressed helium gas with attosecond pulse trains

    E-print Network

    Liao, Chen-Ting; Camp, Seth; Schafer, Kenneth J; Gaarde, Mette B

    2015-01-01

    We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and subsequently to the appearance of new, narrow features in the absorption line.

  15. Surface structure of alanine on Cu(110) via grazing scattering of fast atoms and molecules

    NASA Astrophysics Data System (ADS)

    Seifert, J.; Busch, M.; Meyer, E.; Winter, H.

    2014-02-01

    We have studied structures of the chiral amino acid alanine adsorbed on Cu(110) via low-energy electron diffraction (LEED) as well as scattering of fast light atoms and molecules. The adsorption process was controlled in situ by the intensity of specularly reflected 2-keV He atoms. For projectile energies less than 1 keV, we applied the method of fast atom diffraction for studies on the structure of adsorbed alanine molecules on an atomically flat Cu(110) surface with focus on a p(3×2) adsorbate phase. The results are consistent with LEED and explain distortions in LEED patterns via an elongated surface unit cell with incommensurate c(3.16×2) symmetry of parts of the adsorbate. From triangulation using fast atoms via the azimuthal rotation of the target surface, the positions of protruding methyl groups are derived.

  16. Low energy ion scattering by atomic steps on the single crystal surface

    NASA Astrophysics Data System (ADS)

    Dzhurakhalov, A. A.; Kutliev, U. O.; Umarov, F. F.

    2004-05-01

    The energy, angular distributions and trajectories of particles scattered on surfaces of Ni(100) and Cu(100), with both ideal and damaged, and semi-infinite and isolated atomic steps, have been calculated. It has been shown that from the correlation between the experimental and calculated energy distributions of the scattered particles, one may determine the spatial extension of the isolated atomic steps and the distance between them on the single crystal surface damaged by ion bombardment. The energy and angular distributions of ions dechanneled from semi-infinite steps on the GaP(100) surface have been presented. It has been shown that the dechanneling ions form the characteristic peaks in the angular and energy distributions of the scattered particles.

  17. Second order classical perturbation theory for atom surface scattering: Analysis of asymmetry in the angular distribution

    SciTech Connect

    Zhou, Yun, E-mail: zhou.yun.x@gmail.com; Pollak, Eli, E-mail: eli.pollak@weizmann.ac.il [Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot (Israel)] [Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot (Israel); Miret-Artés, Salvador, E-mail: s.miret@iff.csic.es [Instituto de Fisica Fundamental, Consejo Superior de Investigaciones Cientificas, Serrano 123, 28006 Madrid (Spain)] [Instituto de Fisica Fundamental, Consejo Superior de Investigaciones Cientificas, Serrano 123, 28006 Madrid (Spain)

    2014-01-14

    A second order classical perturbation theory is developed and applied to elastic atom corrugated surface scattering. The resulting theory accounts for experimentally observed asymmetry in the final angular distributions. These include qualitative features, such as reduction of the asymmetry in the intensity of the rainbow peaks with increased incidence energy as well as the asymmetry in the location of the rainbow peaks with respect to the specular scattering angle. The theory is especially applicable to “soft” corrugated potentials. Expressions for the angular distribution are derived for the exponential repulsive and Morse potential models. The theory is implemented numerically to a simplified model of the scattering of an Ar atom from a LiF(100) surface.

  18. Antihydrogen-hydrogen elastic scattering at thermal energies using an atomic-orbital technique

    SciTech Connect

    Sinha, Prabal K.; Chaudhuri, Puspitapallab; Ghosh, A.S. [Department of Physics, Bangabasi College, 19, Raj Kumar Chakravorty Sarani, Kolkata 700 009 (India); Instituto de Fisica 'Gleb Wataghin', Universidade Estadual de Campinas, 13083-970 Campinas, Sao Paulo (Brazil); Department of Theoretical Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032 (India)

    2003-05-01

    In view of the recent interest in the trapping of antihydrogen atom H(bar sign), at very low temperatures, H-bar-H scattering has been investigated at low incident energies using a close-coupling model with the basis set H-bar(1s,2s,2p-bar)+H(1s,2s,2p-bar). The predicted s-wave elastic phase shifts, scattering length, and effective range are in a good agreement with the other recent predictions of Jonsell et al. and of Armour and Chamberlain. The results indicate that the atomic orbital expansion model is suitable to study the H-bar-H scattering at ultracold temperatures.

  19. Second order classical perturbation theory for atom surface scattering: Analysis of asymmetry in the angular distribution

    NASA Astrophysics Data System (ADS)

    Zhou, Yun; Pollak, Eli; Miret-Artés, Salvador

    2014-01-01

    A second order classical perturbation theory is developed and applied to elastic atom corrugated surface scattering. The resulting theory accounts for experimentally observed asymmetry in the final angular distributions. These include qualitative features, such as reduction of the asymmetry in the intensity of the rainbow peaks with increased incidence energy as well as the asymmetry in the location of the rainbow peaks with respect to the specular scattering angle. The theory is especially applicable to "soft" corrugated potentials. Expressions for the angular distribution are derived for the exponential repulsive and Morse potential models. The theory is implemented numerically to a simplified model of the scattering of an Ar atom from a LiF(100) surface.

  20. Coulomb excitation of helium atoms in collisions with highly charged ions

    NASA Astrophysics Data System (ADS)

    Tschersich, M.; Drozdowski, R.; Busch, M.; Skogvall, B.; von Oppen, G.

    1999-12-01

    Collisional excitation of He atoms by 65 and 80 MeV 40Arq+ ions (q = 6,13,14) was investigated by measuring the intensities Iicons/Journals/Common/lambda" ALT="lambda" ALIGN="MIDDLE"/>(Fz) of He I spectral lines at 401 nm and 447 nm as functions of an electric field -30 < Fz < +30 kV cm-1 applied parallel and antiparallel to the ion beam. Well resolved signals of singlet-triplet anticrossings 0953-4075/32/23/309/img1" ALT="(img) with n = 4 and 5 were measured for both field directions in addition to smooth intensity variations of the 0953-4075/32/23/309/img2" ALT="(img) lines with n = 7 and 5. The asymmetric signal structure indicates a highly coherent excitation of states with different angular momenta. For comparison, some supplementary measurements of I447 for proton impact are also reported. The results are discussed within the framework of saddle dynamics and the Paul-trap model. They confirm the Janev-Presnyakov scaling law valid for electric dipole Coulomb excitation, according to which the excitation process is essentially determined by the scaled energies E0 = Eion/(Aicons/Journals/Common/cdot" ALT="cdot" ALIGN="TOP"/> q) of the projectile.

  1. Strong-field spatial intensity-intensity correlations of light scattered from regular structures of atoms

    E-print Network

    M. Macovei; J. Evers; C. H. Keitel

    2007-02-14

    Photon correlations and cross-correlations of light scattered by a regular structure of strongly driven atoms are investigated. At strong driving, the scattered light separates into distinct spectral bands, such that each band can be treated as independent, thus extending the set of observables. We focus on second-order intensity-intensity correlation functions in two- and multi-atom systems. We demonstrate that for a single two-photon detector as, e.g., in lithography, increasing the driving field intensity leads to an increased spatial resolution of the second-order two-atom interference pattern. We show that the cross-correlations between photons emitted in the spectral sidebands violate Cauchy-Schwartz inequalities, and that their emission ordering cannot be predicted. Finally, the results are generalized for multi-particle structures, where we find results different from those in a Dicke-type sample.

  2. Time dependent integral equation approaches to quantum scattering: Comparative application to atom-rigid rotor multichannel scattering

    NASA Astrophysics Data System (ADS)

    Sharafeddin, Omar A.; Kouri, Donald J.; Judson, Richard S.; Hoffman, David K.

    1992-04-01

    In this paper we generalize earlier work on potential scattering to atom-rigid rotor scattering. We compare six approaches including the interaction picture, modified Cayley, amplitude density, and symmetric split operator methods. All methods derive from the integral equation form of the time-dependent Schrödinger equation. The methods were tested using the standard Lester-Bernstein model potential. All methods were found to perform well with the same parameters. Fast Fourier transforms were not used in these methods, and an average execution time for a 16 channel problem on CRAY YMP supercomputer was about 45 s. This single calculation yields results at any energy significantly contained in the initial packet. In the present study, the S matrix was computed at a total of 42 energies, but results could have been obtained at many more energies without a large increase in computing time. Timing results for one of the methods are reported for 25, 64, 144, and 256 coupled channels.

  3. Collisional lasing on a self-terminating transition 2{sup 1}P{sup o}{sub 1} - 2{sup 1}S{sub 0} in helium atom

    SciTech Connect

    Bel'skaya, E V; Bokhan, P A; Zakrevskii, D E; Lavrukhin, M A [A.V. Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)

    2012-02-28

    Lasing on a self-terminating transition 2{sup 1}P{sup o}{sub 1} - 2{sup 1}S{sub 0} ({lambda} = 2.058 {mu}m) in helium atom is studied for a single- and double-pulse operation regimes under electron beam pumping in pure helium and its mixtures with H{sub 2}, N{sub 2}, O{sub 2}, CO{sub 2}, H{sub 2}O, NH{sub 3}, and N{sub 2}O. In pure helium, the maximal pulse duration is {approx}50 ns, which agrees with the calculated value. Recovery of lasing in the second pulse is observed at a time delay between the pulses of longer than 1.25 {mu}s. In adding CO{sub 2}, N{sub 2}O, NH{sub 3}, and H{sub 2}O, the relaxation rate for population of the metastable state He(2{sup 1}S{sub 0}) increases, which makes the delay, needed for recovering lasing, shorter up to pulse merging in the case of H{sub 2}O. At the exciting pulse base-level duration of 1.2 {mu}s, in mixtures of helium with NH{sub 3} and H{sub 2}O, laser pulses with a duration of {approx}0.8 {mu}s are observed, which testifies that collisional quasi-cw lasing occurs. Mechanisms of collisional lasing are discussed.

  4. Coherent and spontaneous Rayleigh-Brillouin scattering in atomic and molecular gases and gas mixtures

    SciTech Connect

    Vieitez, M. O.; Duijn, E. J. van; Ubachs, W. [Laser Centre, Vrije Universiteit, De Boelelaan 1081, NL-1081 HV Amsterdam (Netherlands); Witschas, B. [Deutsches Zentrum fuer Luft- und Raumfahrt DLR, Institut fuer Physik der Atmosphaere, Oberpfaffenhofen (Germany); Meijer, A.; Wijn, A. S. de; Dam, N. J. [Institute of Molecules and Materials, Applied Molecular Physics, Radboud University, NL-6500 HC Nijmegen (Netherlands); Water, W. van de [Physics Department, Eindhoven University of Technology, Postbus 513, NL-5600 MB Eindhoven (Netherlands)

    2010-10-15

    We study Rayleigh-Brillouin scattering in gases of N{sub 2}, O{sub 2}, and SF{sub 6} molecules, Kr atoms, and He-Xe and He-CO{sub 2} mixtures at pressures ranging from 1 to 3 bar and using two different experimental setups. In one setup, we measure spectra of light scattered by thermal density fluctuations (spontaneous Rayleigh-Brillouin scattering); in the second setup density waves are induced in the overlap region of two counterpropagating laser beams (coherent Rayleigh-Brillouin scattering). We compare measured spectra to the Tenti models and to a recent model for mixtures. We find new values of the bulk viscosity, which is a parameter in line-shape models that allows for internal degrees of freedom. Both experiments agree on the value of the bulk viscosity. Our results indicate a need for new line-shape models for mixtures of molecules with internal degrees of freedom.

  5. Ultracold scattering of Rb atoms and bound states of Rb2

    NASA Astrophysics Data System (ADS)

    Geltman, Sydney

    2006-11-01

    The most accurate theoretical potentials available for the interaction of a pair of ground-state Rb atoms are used to evaluate their ultracold scattering properties. The close relation between the zero-energy scattering phase shifts and the number of bound states in the potential, by Levinson's theorem, is used to assign absolute values to the l = 0, 1 and 2 phase shifts. The number of bound states is compared with those resulting from detailed spectroscopic studies on the singlet potential and photoassociation results on the triplet potential. We review the scattering formulae needed to satisfy the Pauli principle for the fermion nuclei of 85Rb and 87Rb and their single unpaired electrons, for all possible initial hyperfine states. Scattering lengths are evaluated and their sensitivity to details of the asymptotic potentials is demonstrated.

  6. A comparative study on total reflection X-ray fluorescence determination of low atomic number elements in air, helium and vacuum atmospheres using different excitation sources

    NASA Astrophysics Data System (ADS)

    Misra, N. L.; Kanrar, Buddhadev; Aggarwal, S. K.; Wobrauschek, Peter; Rauwolf, M.; Streli, Christina

    2014-09-01

    A comparison of trace element determinations of low atomic number (Z) elements Na, Mg, Al, P, K and Ca in air, helium and vacuum atmospheres using W L?1, Mo K? and Cr K? excitations has been made. For Mo K? and W L?1 excitations a Si (Li) detector with beryllium window was used and measurements were performed in air and helium atmospheres. For Cr K? excitation, a Si (Li) detector with an ultra thin polymer window (UTW) was used and measurements were made in vacuum and air atmospheres. The sensitivities of the elemental X-ray lines were determined using TXRF spectra of standard solutions and processing them by IAEA QXAS program. The elemental concentrations of the elements in other solutions were determined using their TXRF spectra and pre-determined sensitivity values. The study suggests that, using the above experimental set up, Mo K? excitation is not suited for trace determination of low atomic number element. Excitation by WL?1 and helium atmosphere, the spectrometer can be used for the determination of elements with Z = 15 (P) and above with fairly good detection limits whereas Cr K? excitation with ultra thin polymer window and vacuum atmosphere is good for the elements having Z = 11 (Na) and above. The detection limits using this set up vary from 7048 pg for Na to 83 pg for Ti.

  7. An x ray scatter approach for non-destructive chemical analysis of low atomic numbered elements

    NASA Technical Reports Server (NTRS)

    Ross, H. Richard

    1993-01-01

    A non-destructive x-ray scatter (XRS) approach has been developed, along with a rapid atomic scatter algorithm for the detection and analysis of low atomic-numbered elements in solids, powders, and liquids. The present method of energy dispersive x-ray fluorescence spectroscopy (EDXRF) makes the analysis of light elements (i.e., less than sodium; less than 11) extremely difficult. Detection and measurement become progressively worse as atomic numbers become smaller, due to a competing process called 'Auger Emission', which reduces fluorescent intensity, coupled with the high mass absorption coefficients exhibited by low energy x-rays, the detection and determination of low atomic-numbered elements by x-ray spectrometry is limited. However, an indirect approach based on the intensity ratio of Compton and Rayleigh scattered has been used to define light element components in alloys, plastics and other materials. This XRS technique provides qualitative and quantitative information about the overall constituents of a variety of samples.

  8. February 1, 1994 / Vol. 19, No. 3 / OPTICS LETTERS Spin relaxation of optically trapped atoms by light scattering

    E-print Network

    Heinzen, Daniel J.

    February 1, 1994 / Vol. 19, No. 3 / OPTICS LETTERS Spin relaxation of optically trapped atoms of optically trapped atoms that is due to light scattering from the trap laser. We observe relaxation times greater than 2 s for ground-state hyperfine-levelpopulations of 85 Rb atoms trapped in an optical dipole

  9. Theoretical Studies of Energy and Momentum Exchange in Atomic and Molecular Scattering from Surfaces

    SciTech Connect

    Joseph R. Manson

    2005-06-30

    The contributions that we have made during the grant period of DE-FG02-98ER45704 can be placed into six different categories: (1) advances in the Theory of Molecule-Surface Scattering, (2) advances in the Theory of Atom-Surface Scattering, (3) utilization of scattering theory to Extract Physical Information about Surfaces, (4) Gas-Surface Interactions, (5) Ion Scattering from surfaces and (6) Scanning Tunneling Microscopy (STM). These six topics are discussed below as individual listings under the title 'IV. Detailed description of research accomplishments'. These advances show that we have made significant progress on several scientific problems in atomic and molecular surface scattering during the course of this grant as well as contributions to other areas. It is also noted that this work, although fundamentally theoretical, is marked by its strong motivation to explain current experimental measurements. This was an important secondary goal in the proposed work. We have developed theory that is useful to experimentalists in the explanation and analysis of their experimental data.

  10. Towards weighing individual atoms by high-angle scattering of electrons

    E-print Network

    Argentero, G; Kotakoski, J; Eder, F R; Meyer, J C

    2015-01-01

    We consider theoretically the energy loss of electrons scattered to high angles when assuming that the primary beam can be limited to a single atom. We discuss the possibility of identifying the isotopes of light elements and of extracting information about phonons in this signal. The energy loss is related to the mass of the much heavier nucleus, and is spread out due to atomic vibrations. Importantly, while the width of the broadening is much larger than the energy separation of isotopes, only the shift in the peak positions must be detected if the beam is limited to a single atom. We conclude that the experimental case will be challenging but is not excluded by the physical principles as far as considered here. Moreover, the initial experiments demonstrate the separation of gold and carbon based on a signal that is related to their mass, rather than their atomic number.

  11. Towards weighing individual atoms by high-angle scattering of electrons.

    PubMed

    Argentero, G; Mangler, C; Kotakoski, J; Eder, F R; Meyer, J C

    2015-04-01

    We consider theoretically the energy loss of electrons scattered to high angles when assuming that the primary beam can be limited to a single atom. We discuss the possibility of identifying the isotopes of light elements and of extracting information about phonons in this signal. The energy loss is related to the mass of the much heavier nucleus, and is spread out due to atomic vibrations. Importantly, while the width of the broadening is much larger than the energy separation of isotopes, only the shift in the peak positions must be detected if the beam is limited to a single atom. We conclude that the experimental case will be challenging but is not excluded by the physical principles as far as considered here. Moreover, the initial experiments demonstrate that the separation of gold and carbon based on a signal that is related to their mass, rather than their atomic number. PMID:25522869

  12. Spectral theory of quantum memory and entanglement via Raman scattering of light by an atomic ensemble

    E-print Network

    O. S. Mishina; D. V. Kupriyanov; J. H. Muller; E. S. Polzik

    2007-02-27

    We discuss theoretically quantum interface between light and a spin polarized ensemble of atoms with the spin >= 1 based on an off-resonant Raman scattering. We present the spectral theory of the light-atoms interaction and show how particular spectral modes of quantum light couple to spatial modes of the extended atomic ensemble. We show how this interaction can be used for quantum memory storage and retrieval and for deterministic entanglement protocols. The proposed protocols are attractive due to their simplicity since they involve just a single pass of light through atoms without the need for elaborate pulse shaping or quantum feedback. As a practically relevant example we consider the interaction of a light pulse with hyperfine components of D1 line of 87Rb. The quality of the proposed protocols is verified via analytical and numerical analysis.

  13. Electron atomic scattering factors, Debye-Waller factors and the optical potential for high-energy electron diffraction.

    PubMed

    Peng, Lian-Mao

    2005-06-01

    High-energy electrons may be elastically and inelastically scattered by a solid. To a good approximation the effect of inelastic scattering on the elastically scattered electrons may be taken into account using the concept of the complex optical potential. The optical potential may be calculated using electron atomic scattering factors and Debye-Waller factors, which in turn can be evaluated numerically using Hartree Fock atomic wave functions and shell models of lattice dynamics. The numerical electron atomic scattering factors have been parameterized using five Gaussian functions for all the neutral atoms of the periodic table and for 106 important ions, and the temperature-dependent Debye-Waller B-factors have been fitted by using fourth degree polynomial regression fitting for 19 compounds with the sodium chloride structure, 5 compounds with the cesium chloride structure, 17 compounds with the zinc-blend structure and 68 elemental crystals. PMID:16076864

  14. Measurements of ultra-low-energy electron scattering cross sections of atoms and molecules

    SciTech Connect

    Kitajima, M.; Shigemura, K.; Kurokawa, M. [Department of Chemistry, Tokyo Institute of Technology, 152-8551 Tokyo (Japan); Odagiri, T. [Department of Physics, Sophia University, 102-8554 Tokyo, Japan and Department of Chemistry, Tokyo Institute of Technology, 152-8551 Tokyo (Japan); Kato, H.; Hoshino, M.; Tanaka, H. [Department of Physics, Sophia University, 102-8554 Tokyo (Japan); Ito, K. [Photon Factory, Institute of Materials Structure Science, 305-0801 Tsukuba (Japan)

    2014-03-05

    A new experimental technique for the total cross section measurements of ultra-low energy electron collisions with atoms and molecules utilizing the synchrotron radiation is presented. The technique employs a combination of the penetrating field technique and the threshold photoionization of rare gas atoms using the synchrotron radiation as an electron source in order to produce a high resolution electron beam at very low energy. Absolute total cross sections for electron scattering from He, Ne, Ar, Kr, and Xe in the energy region from extremely low electron energy to 20 eV are presented.

  15. Scattering of Stark-decelerated OH radicals with rare-gas atoms

    NASA Astrophysics Data System (ADS)

    Scharfenberg, L.; Gubbels, K. B.; Kirste, M.; Groenenboom, G. C.; van der Avoird, A.; Meijer, G.; van de Meerakker, S. Y. T.

    2011-11-01

    We present a combined experimental and theoretical study on the rotationally inelastic scattering of OH (X2?3/2, J = 3 / 2, f) radicals with the collision partners He, Ne, Ar, Kr, Xe, and D2 as a function of the collision energy between ~70 cm-1 and 400 cm-1. The OH radicals are state selected and velocity tuned prior to the collision using a Stark decelerator, and field-free parity-resolved state-to-state inelastic relative scattering cross sections are measured in a crossed molecular beam configuration. For all OH-rare gas atom systems excellent agreement is obtained with the cross sections predicted by coupled channel scattering calculations based on accurate ab initio potential energy surfaces. This series of experiments complements recent studies on the scattering of OH radicals with Xe [J.J. Gilijamse, S. Hoekstra, S.Y.T. van de Meerakker, G.C. Groenenboom, G. Meijer, Science 313, 1617 (2006)], Ar [L. Scharfenberg, J. K?os, P.J. Dagdigian, M.H. Alexander, G. Meijer, S.Y.T. van de Meerakker, Phys. Chem. Chem. Phys. 12, 10660 (2010)], He, and D2 [M. Kirste, L. Scharfenberg, J. K?os, F. Lique, M.H. Alexander, G. Meijer, S.Y.T. van de Meerakker, Phys. Rev. A 82, 042717 (2010)]. A comparison of the relative scattering cross sections for this set of collision partners reveals interesting trends in the scattering behavior.

  16. Theory of Direct Scattering, Trapping and Desorption in Atom-Surface Collisions

    E-print Network

    Guoqing Fan; J. R. Manson

    2008-04-10

    When gas atoms or molecules collide with clean and ordered surfaces, under many circumstances the energy-resolved scattering spectra exhibit two clearly distinct features due to direct scattering and to trapping in the physisorption well with subsequent desorption. James Clerk Maxwell is credited with being the first to describe this situation by invoking the simple assumption that when an impinging gas beam is scattered from a surface it can be divided into a part that exchanges no energy and specularly reflects and another part that equilibrates or accommodates completely and then desorbs with an equilibrium distribution. In this paper a scattering theory is developed, using an iterative algorithm and classical mechanics for the collision process, that describes both direct scattering and trapping-desorption of the incident beam. The initially trapped fraction of particles can be followed as they continue to make further interactions with the surface until they are all eventually promoted back into the positive energy continuum and leave the surface region. Consequently, this theory allows a rigorous test of the Maxwell assumption and determines the conditions under which it is valid. The theory also gives quantitative explanations of recent experimental measurements which exhibit both a direct scattering contribution and a trapping-desorption fraction in the energy-resolved spectra.

  17. Spacelab 2 measurement of the solar coronal helium abundance

    NASA Astrophysics Data System (ADS)

    Gabriel, A. H.; Culhane, J. L.; Patchett, B. E.; Breeveld, E. R.; Lang, J.; Parkinson, J. H.; Payne, J.; Norman, K.

    1995-07-01

    The abundance of helium relative to hydrogen has been measured with the 'Coronal Helium Abundance Spacelab Experiment' (CHASE) from the space shuttle Challenger in 1985. Previous solar measurements have proved difficult due to the temperature-sensitivity of the electron excitation rates for the observed lines. In this approach, scattered Lyman Alpha radiation of helium and hydrogen formed in the corona were measured with a grazing-incidence spectrometer and compared with the intensity of the illuminating flux from the solar chromosphere. The abundance ratio by number of atoms was found to be 0.070 with an uncertainty of 0.011. Scattered light in the telescope is the main source of error.

  18. Total cross sections for positron scattering from argon atoms at intermediate energies

    Microsoft Academic Search

    S. P. Khare; Ashok Kumar; Kusum Lata

    1986-01-01

    A model complex potential is employed to obtain integrated elastic cross sections, absorption cross sections, and total cross sections for positron scattering from argon atoms in 100-800 eV energy range. The total cross sections are found to be in good agreement with the experimental data for E>=300 eV and lower than the corresponding electron cross sections over the whole energy

  19. Absolute electron-scattering total cross section measurements for noble gas atoms and diatomic molecules

    Microsoft Academic Search

    Czeslaw Szmytkowski; Krzysztof Maciag; Grzegorz Karwasz

    1996-01-01

    Absolute electron-scattering total cross sections for noble gas atoms (He, Ne, Ar, Kr, and Xe) and H2, N2, CO, NO, and O2 molecules have been measured at impact energies between 0.5 and 250 eV by the linear transmission method with the same experimental set-up for all the investigated targets. Generally, our total cross sections have been found to be in

  20. Simultaneous characterization of protein coated iron oxide nanoparticles with nuclear inelastic scattering and atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Marx, J.; Huang, H.; Faus, I.; Rackwitz, S.; Wolny, J. A.; Schlage, K.; Ulber, R.; Wille, H.-C.; Schünemann, V.

    2014-04-01

    Bovine serum albumin coated magnetic iron oxide nanoparticles (IONPs), which were synthesized using a co-precipitation method with 57Fe have been subject to a combined study using atomic force microscopy (AFM) and nuclear inelastic scattering (NIS). The obtained partial density of vibrational states (pDOS) shows evidence for lattice stiffening and a pronounced mode at 23 meV compared to thin film magnetite at room temperature.

  1. Photon antibunching upon scattering by an atomic Bose-Einstein condensate

    SciTech Connect

    Ilichev, L. V., E-mail: leonid@iae.nsk.su; Chapovsky, P. L. [Russian Academy of Sciences, Siberian Branch, Institute of Automation and Electrometry (Russian Federation)

    2010-05-15

    Antibunching of photodetections from different modes is shown to arise when two quantized light modes are scattered by an atomic Bose-Einstein condensate. This effect appears because of the uncertainty in the position of the condensate wave function relative to the optical lattice formed by the light beams. It is shown how the information contained in the history of photodetections leads to a spatial localization of the condensate wave function.

  2. Novel Algorithms for Quantum Simulation of 3 D Atom-Diatom Reactive Scattering

    Microsoft Academic Search

    Ashot S. Gevorkyan; Gabriel G. Balint-kurti; Alexander V. Bogdanov; Gunnar Nyman

    2007-01-01

    A new approach is described to the evaluation of the S-matrix in three-dimensional atom-diatom reactive quantum scattering theory. A theory based on natural collision coordinates\\u000a is developed, where the reaction coordinate can be viewed as fulfilling the same role as time in a time-dependent formulation.\\u000a By writing the full wavefunction in coupled-channel form it is proved that the 3D multi-channel

  3. Coherent and stochastic contributions of compound resonances in atomic processes: electron recombination, photoionization and scattering

    E-print Network

    V. V. Flambaum; M. G. Kozlov; G. F. Gribakin

    2015-03-04

    In open-shell atoms and ions, processes such as photoionization, combination (Raman) scattering, electron scattering and recombination, are often mediated by many-electron compound resonances. We show that their interference (neglected in the independent-resonance approximation) leads to a coherent contribution, which determines the energy-averaged total cross sections of electron- and photon-induced reactions obtained using the optical theorem. On the other hand, the partial cross sections (e.g., electron recombination, or photon Raman scattering) are dominated by the stochastic contributions. Thus, the optical theorem provides a link between the stochastic and coherent contributions of the compound resonances. Similar conclusions are valid for reactions via compound states in molecules and nuclei.

  4. Study of effective atomic number of breast tissues determined using the elastic to inelastic scattering ratio

    NASA Astrophysics Data System (ADS)

    Antoniassi, M.; Conceição, A. L. C.; Poletti, M. E.

    2011-10-01

    In this work we have measured Compton and Rayleigh scattering radiation from normal (adipose and fibroglandular), benign (fibroadenoma) and malignant (ductal carcinoma) breast tissues using a monoenergetic beam of 17.44 keV and a scattering angle of 90° ( x=0.99 Å -1). A practical method using the area of Rayleigh and Compton scattering was used for determining the effective atomic number ( Zeff) of the samples, being validated through measurements of several reference materials. The results show that there are differences in the distributions of Zeff of breast tissues, which are mainly related to the elemental composition of carbon ( Z=6) and oxygen ( Z=8) of each tissue type. The results suggest that is possible to use the method to characterize the breast tissues permitting study histological features of the breast tissues related to their elemental composition.

  5. Light scattering and dissipative dynamics of many fermionic atoms in an optical lattice

    NASA Astrophysics Data System (ADS)

    Sarkar, S.; Langer, S.; Schachenmayer, J.; Daley, A. J.

    2014-08-01

    We investigate the many-body dissipative dynamics of fermionic atoms in an optical lattice in the presence of incoherent light scattering. Deriving and solving a master equation to describe this process microscopically for many particles, we observe contrasting behavior in terms of the robustness against this type of heating for different many-body states. In particular, we find that the magnetic correlations exhibited by a two-component gas in the Mott insulating phase should be particularly robust against decoherence from light scattering, because the decoherence in the lowest band is suppressed by a larger factor than the time scales for effective superexchange interactions that drive coherent dynamics. Furthermore, the derived formalism naturally generalizes to analogous states with SU(N) symmetry. In contrast, for typical atomic and laser parameters, two-particle correlation functions describing bound dimers for strong attractive interactions exhibit superradiant effects due to the indistinguishability of off-resonant photons scattered by atoms in different internal states. This leads to rapid decay of correlations describing off-diagonal long-range order for these states. Our predictions should be directly measurable in ongoing experiments, providing a basis for characterizing and controlling heating processes in quantum simulation with fermions.

  6. Magnetic Field Effects on the 1083 nm Atomic Line of Helium. Optical Pumping of Helium and Optical Polarisation Measurement in High Magnetic Field

    Microsoft Academic Search

    E. Courtade; F. Marion; P.-J. Nacher; G. Tastevin; K. Kiersnowski; T. Dohnalik

    2002-01-01

    The structure of the excited $2^{3}$S and $2^{3}$P triplet states of $^{3}$He\\u000aand $^{4}$He in an applied magnetic field B is studied using different\\u000aapproximations of the atomic Hamiltonian. All optical transitions (line\\u000apositions and intensities) of the 1083 nm $2^{3}$S-$2^{3}$P transition are\\u000acomputed as a function of B. The effect of metastability exchange collisions\\u000abetween atoms in the ground

  7. The ionization degree of Ar atoms single scattered from pure metal and alloy surfaces

    SciTech Connect

    Abdulkasimov, F.B.; Ferleger, V.K. [Arifov Inst. of Electronics, Tashkent (Uzbekistan)

    1996-12-31

    A procedure of deflection of backscattered neutral atoms with low energy E{sub o} = (250 {divided_by} 3,000) eV based on neutral ionization by electron impact has been developed. The ionization degrees {eta}{sup +} of Ar atoms single scattered at the angle {Theta} = 138{degree} from V and VI period metal polycrystal surfaces as well as inelastic energy losses Q have been measured. It has been found that both {eta}{sup +} and Q changed nonmonotonically within each period. It has been shown that for the elements of the same group under otherwise equal conditions {eta}{sup +} at the scattering from V period elements appeared to be always higher than those for the VI period. It has been established that at scattering from MoRe alloy surface {eta}{sup +} in peaks of single scattering from Mo and Re the metal target values coincided with corresponding values measured for pure Mo and Re metal targets. Using the results obtained one could draw some conclusions about the dependence of the charge state on the target structure.

  8. Scattering of hyperthermal argon atoms from clean and D-covered Ru(0001) surfaces.

    PubMed

    Ueta, Hirokazu; Gleeson, Michael A; Kleyn, Aart W

    2011-01-21

    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°) near-specular peaks and additional off-specular features. The energy distributions show an oscillatory behavior as a function of outgoing angle. In comparison, scattered Ar atoms from a Ag(111) surface exhibit a broad angular intensity distribution and an energy distribution that qualitatively tracks the binary collision model. The features observed for Ru, which are most evident when scattering from the clean surface at 180 K and from the Ru(0001)-(1×1)D surface, are consistent with rainbow scattering. The measured TOF profiles cannot be adequately described with a single shifted Maxwell-Boltzmann distribution. They can be fitted by two components that exhibit complex variations as a function of outgoing angle. This suggests at least two significantly different site and?or trajectory dependent energy loss processes at the surface. The results are interpreted in terms of the stiffness of the surface and highlight the anomalous nature of the apparently simple hcp(0001) ruthenium surface. PMID:21261381

  9. Influence of Nearly Resonant Light on the Scattering Length in Low-Temperature Atomic Gases

    SciTech Connect

    Fedichev, P.O.; Kagan, Y.; Shlyapnikov, G.V.; Walraven, J.T. [Van der Waals--Zeeman Institute, University of Amsterdam, Valckenierstraat 65-67, 1018 XE Amsterdam (The Netherlands)] [Van der Waals--Zeeman Institute, University of Amsterdam, Valckenierstraat 65-67, 1018 XE Amsterdam (The Netherlands); [Russian Research Center, Kurchatov Institute, Kurchatov Square, 123182 Moscow (Russia); [Ecole Normale Superieure, Paris, 75231 (France)

    1996-09-01

    We develop the idea of manipulating optically the scattering length {ital a} in low-temperature atomic gases. If the incident light is close to resonance with one of the bound {ital p} levels of electronically excited molecules, virtual radiative transitions of a pair of interacting atoms to this level can significantly change the value and even reverse the sign of {ital a}. The decay of the gas due to photon recoil and dueto photoassociation can be minimized by selecting the frequency detuning and the Rabi frequency. Our calculations show the feasibility of optical manipulations of trapped Bose condensates through a light-induced change in the mean field interaction between atoms, which is illustrated for {sup 7}Li. {copyright} {ital 1996 The American Physical Society.}

  10. Changes in the Atomic Structure through Glass Transition Observed by X-Ray Scattering

    SciTech Connect

    Egami, Takeshi [ORNL

    2012-01-01

    The glass transition involves a minor change in the internal energy, and yet the physical and mechanical properties of a glass change dramatically. In order to determine the evolution of the atomic structure through the glass transition, we employed in-situ synchrotron X-ray scattering measurements as a function of temperature on a model material: Zr-Cu-Al metallic glass. We found that the thermal expansion at the atomic level is smaller than the macroscopic thermal expansion, and significantly increases above the glass transition temperature. The observed changes in the pair-distribution function (PDF) are explained in terms of the fluctuations in the local atomic volume and their change through the glass transition.

  11. Fission-fusion correlations for swelling and microstructure in stainless steels: effect of the helium-to-displacement-per-atom ratio

    SciTech Connect

    Odette, G.R.; Maziaz, P.J.; Spitznagel, J.A.

    1981-01-01

    The initial irradiated structural materials data base for fusion applications will be developed in fission reactors. Hence, this data may need to be adjusted using physically-based procedures to represent behavior in fusion environments, viz. - fission-fusion correlations. Such correlation should reflect a sound mechanistic understanding, and be verified in facilities which most closely simulate fusion conditions. In this paper we review the effects of only one of a number of potentially significant damage variables, the helium to displacement per atom ratio, on microstructural evolution in austenitic stainless steels. Dual-ion and helium preinjection data are analyzed to provide mechanistic guidance; these results appear to be qualitatively consistent with a more detailed comparison made between fast (EBR-II) and mixed (HFIR) spectrum neutron data for a single heat of 20% cold-worked 316 stainless steel. These two fission environments bound fusion (He/dpa ratios. A model calibrated to the fission reactor data is used to extrapolate to fusion conditions. Both the theory and broad empirical observation suggest that helium to dpa ratios have both a qualitative and quantitative influence on microstructural evolution; and that the very high and low ratios found in HFIR and EBR-II may not result in behavior which brackets intermediate fusion conditions.

  12. Atomic scattering as a probe of polymer surface and thin film dynamics M. A. Freedman, A. W. Rosenbaum, and S. J. Sibener*

    E-print Network

    Sibener, Steven

    . One area of interest is the effect of nanoconfinement and surface behavior on polymer properties.4 than previous methods used to study polymer surfaces. Even neutron and x-ray scattering techniques,10 It consists of a cryogenically cooled supersonic helium beam source and an ultrahigh- vacuum UHV scattering

  13. Elements & Compounds Atoms (Elements)

    E-print Network

    Frey, Terry

    #12;Elements & Compounds #12;Atoms (Elements) Molecules (Compounds) Cells Elements & Compounds #12;Nucleus Electrons Cloud of negative charge (2 electrons) Fig. 2.5: Simplified model of a Helium (He) Atom He 4.002602 2 Helium Mass Number (~atomic mass) = number of Neutrons + Protons = 4 for Helium Atomic

  14. Magnetoconductivity of two-dimensional electrons on liquid helium: Experiments in the fluid phase

    E-print Network

    Dykman, Mark

    Magnetoconductivity of two-dimensional electrons on liquid helium: Experiments in the fluid phase M manuscript received 25 November 1996 The magnetoconductivity (B) of two-dimensional electrons on liquid-particle magnetoconductivity. For both vapor-atom and ripplon scattering the results are in good agreement with a microscopic

  15. Helium Neon Laser

    NSDL National Science Digital Library

    Zollman, Dean

    This resource, part of the Spectroscopy Lab Suite, illustrates the physics of a Helium-Neon Laser. Students can create energy levels for both the He and Ne atoms. The basic processes for light emission, including collisions and level transitions, are shown. The atomic energy levels and the pumping energy can be adjusted to achieve an output spectrum similar to the measured physical spectrum.

  16. PHYSICAL REVIEW A 86, 062708 (2012) Atom-dimer scattering amplitude for fermionic mixtures with different masses

    E-print Network

    Leyronas, Xavier

    PHYSICAL REVIEW A 86, 062708 (2012) Atom-dimer scattering amplitude for fermionic mixtures with different masses: s-wave and p-wave contributions F. Alzetto,1 R. Combescot,1,2 and X. Leyronas1 1 a Feshbach resonance, as a function of the mass ratio, the fermion-dimer scattering amplitude in fermionic

  17. Existence and Born-Oppenheimer Asymptotics of the Total Scattering Cross-Section in Ion-Atom Collisions

    E-print Network

    Wang, Xue Ping

    Existence and Born-Oppenheimer Asymptotics of the Total Scattering Cross-Section in Ion then extract the leading term of the scattering cross-section in the Born-Oppenheimer limit. I Introduction-atom collision and suggested to use Born-Oppenheimer approximation to study the problem. Recall that it is well

  18. Empirical forms for the electron\\/atom elastic scattering cross sections from 0.1 to 30 keV

    Microsoft Academic Search

    R. Browning; T. Z. Li; B. Chui; Jun Ye; R. F. W. Pease; Z. Czyzewski; D. C. Joy

    1994-01-01

    Empirical forms have been found for the total and differential elastic scattering cross sections for electron\\/atom scattering. The cross sections are valid over the range 0.1-30 keV and across the periodic table. The empirical forms of the cross sections are derived from trends in tabulated Mott scattering cross sections. The form of the total cross section is similar to a

  19. Atomic Force Microscopy and Light Scattering of Small Unilamellar Actin-Containing Liposomes

    PubMed Central

    Palmer, Andre F.; Wingert, Philip; Nickels, Jonathan

    2003-01-01

    Three-dimensional networks of filamentous actin (F-actin) encapsulated inside phosphatidylcholine liposomes are currently being used in an effort to model the cytoskeleton and plasma membrane of eukaryotic cells. In this article, unilamellar lipid vesicles consisting of egg yolk-derived phosphatidylcholine encapsulating monomeric actin (G-actin) were made via extrusion in low ionic strength buffer (G-buffer). Vesicle shape and structure in these dispersions was studied using a combination of fluid-tapping atomic force microscopy, and multiangle static light scattering. After subjecting the liposome dispersion to high ionic strength polymerization buffer (F-buffer) containing K+ ions, atomic force microscopy imaging and light scattering of these liposomes indicated the formation of specialized structures, including an overall liposome structure transformation from spherical to torus, disk-shaped geometries and tubular assemblies. Several atomic force microscopy control measurements were made to ascertain that the specialized structures formed were not due to free G-actin and F-actin self-assembling on the sample surface, plain liposomes exposed to G- and F-buffer, or liposomes encapsulating G-actin. Liposomes encapsulating G-actin assumed mostly thin disk shapes and some large irregularly shaped aggregates. In contrast, liposomes encapsulating polymerized actin assumed mostly torus or disk shapes along with some high aspect ratio tubular structures. PMID:12885667

  20. Studies on scattering of fast H and He atoms from Fe films grown on Cu(0 0 1)

    Microsoft Academic Search

    M. Baron; T. Bernhard; M. Gruyters; H. Winter

    2006-01-01

    The structure of ultrathin epitaxial Fe films grown on Cu(001) at room temperature is investigated by grazing scattering of fast H and He atoms. By making use of ion beam triangulation, direct information on the atomic structure of the film and substrate surfaces are obtained. We discuss a new variant of this method based on the detection of the number

  1. Calculation of the total and total ionization cross sections for positron scattering on atomic hydrogen

    SciTech Connect

    Bray, I. (Electronic Structure of Materials Centre, The Flinders University of South Australia, G.P.O. Box 2100, Adelaide 5001 (Australia)); Stelbovics, A.T. (Centre for Atomic, Molecular and Surface Physics, School of Mathematical and Physical Sciences, Murdoch University, Perth 6150 (Australia))

    1994-04-01

    The total and total ionization cross sections for positron scattering on atomic hydrogen are calculated by applying the convergent-close-coupling method to the model where positronium-formation channels are omitted. This model accurately describes the physics of the scattering whenever the positronium formation cross section is negligible, in particular, above 100 eV for this system. The total ionization cross section results in this energy region are in excellent agreement with the recent measurements of Jones [ital et] [ital al]. [J. Phys. B 26, L483 (1993)], and so lie below the earlier measurements of Spicher [Phys. Rev. Lett. 64, 1019 (1990)], and the recent calculations of Acacia [ital et] [ital al]. [Phys. Rev. Lett. (to be published)]. The total cross section is in very good agreement with the recent measurements of Zhou [ital et] [ital al]. (unpublished) down to 30 eV.

  2. He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth

    SciTech Connect

    Not Available

    1992-01-01

    Investigations in this laboratory have focused on the surface structure and dynamics of ionic insulators and on epitaxial growth onto alkali halide crystals. In the later the homoepitaxial growth of NaCl/NaCl(001) and the heteroepitaxial growth of KBr/NaCl(001), NaCl/KBr(001) and KBr/RbCl(001) have been studied by monitoring the specular He scattering as a function of the coverage and by measuring the angular and energy distributions of the scattered He atoms. These data provide information on the surface structure, defect densities, island sizes and surface strain during the layer-by-layer growth. The temperature dependence of these measurements also provides information on the mobilities of the admolecules. He atom scattering is unique among surface probes because the low-energy, inert atoms are sensitive only to the electronic structure of the topmost surface layer and are equally applicable to all crystalline materials. It is proposed for the next year to exploit further the variety of combinations possible with the alkali halides in order to carry out a definitive study of epitaxial growth in the ionic insulators. The work completed so far, including measurements of the Bragg diffraction and surface dispersion at various stages of growth, appears to be exceptionally rich in detail, which is particularly promising for theoretical modeling. In addition, because epitaxial growth conditions over a wide range of lattice mismatches is possible with these materials, size effects in growth processes can be explored in great depth. Further, as some of the alkali halides have the CsCl structure instead of the NaCl structure, we can investigate the effects of the heteroepitaxy with materials having different lattice preferences. Finally, by using co-deposition of different alkali halides, one can investigate the formation and stability of alloys and even alkali halide superlattices.

  3. Atomic-scale dynamics inside living cells explored by neutron scattering

    PubMed Central

    Jasnin, Marion

    2009-01-01

    Single-particle neutron spectroscopy has contributed important experimental data on molecular dynamics in biological systems. The technique provides information on atomic and molecular motions in macromolecules on the picosecond to the nanosecond time scale, which are essential to biological function. Here, we report on recent neutron measurements performed directly in living cells by using isotope labelling to explore the dynamics of specific cellular components. The paper proposes an integrated view of results on atomic-scale cell water dynamics, internal and global macromolecular motions and solvent isotope effect on macromolecular dynamics. The work established the specific usefulness of the neutron scattering technique to get insight into biologically relevant dynamical features, in particular through comparative measurements. The method developed can now be applied to look for dynamical signatures related to cell characteristics in many different cell types and organelles. PMID:19586955

  4. Proton scattering by a hydrogen atom in an effectively two-body model

    SciTech Connect

    Pupyshev, V. V., E-mail: pupyshev@theor.jinr.ru [Joint Institute for Nuclear Research (Russian Federation)

    2013-02-15

    It is assumed that the total potential of proton interaction with a hydrogen atom is the sum of the short-range nuclear soft-core Reid potential and the long-range Thomas-Fermi potential. A quantum mechanical analysis of low-energy features of the phase shift and cross section for elastic proton scattering on a hydrogen atom is given for the case of zero total angular momentum. The calculations performed in the present study within a nonlinear version of the variable-phase approach ultimately revealed that, because of a long-range character of the asymptotic behavior of the Thomas-Fermi potential, the respective cross section at low energies oscillates but has a finite number of zeros.

  5. Exact quantum scattering calculations of transport properties: CH2(tilde{X}^3B1, tilde{a}^1A1)-helium

    NASA Astrophysics Data System (ADS)

    Dagdigian, Paul J.; Alexander, Millard H.

    2013-04-01

    Transport properties for collisions of methylene, in both its ground tilde{X}^3B_1 and low-lying tilde{a}^1A_1 electronic states, with helium have been computed using recently computed high-quality ab initio potential energy surfaces (PESs). Because of the difference in the orbital occupancy of the two electronic states, the anisotropies of the PESs are quite different. The CH2(tilde{a})-He PES is very anisotropic because of the strong interaction of the electrons on the helium atom with the unoccupied CH2 orbital perpendicular to the molecular plane, while the anisotropy of the CH2(tilde{X})-He PES is significantly less since this orbital is singly occupied in this case. To investigate the importance of the anisotropy on the transport properties, calculations were performed with the full potential and with the spherical average of the potential for both electronic states. Significant differences (over 20% for the tilde{a} state at the highest temperatures considered) in the computed transport properties were found.

  6. Ab initio molecular dynamics calculations on scattering of hyperthermal H atoms from Cu(111) and Au(111)

    NASA Astrophysics Data System (ADS)

    Kroes, Geert-Jan; Pavanello, Michele; Blanco-Rey, María; Alducin, Maite; Auerbach, Daniel J.

    2014-08-01

    Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction ("EF") model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated "post" ("p") the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy loss in the range 0.2-0.3 eV due to ehp excitation, which should be possible to observe. The average non-adiabatic energy losses for non-penetrative scattering exceed the adiabatic losses to phonons by 0.9-1.0 eV. This suggests that for scattering of hyperthermal H-atoms from coinage metals the dominant energy dissipation channel should be to ehp excitation. These predictions can be tested by experiments that combine techniques for generating H-atom beams that are well resolved in translational energy and for detecting the scattered atoms with high energy-resolution.

  7. Elastic scattering of an oxygen atom on a silicon atom in the 10-500 eV range of relative kinetic energies

    NASA Astrophysics Data System (ADS)

    Sycheva, A. A.; Balint-Kurti, G. G.; Palov, A. P.

    2014-11-01

    The potential of interaction between oxygen and silicon atoms in a range of interatomic distances within 0.75-11.5 au has been calculated from first principles (ab initio) using the multiconfigurational interaction (MRCI) method with the aug-pp-AVQZ basis set of atomic wave functions. An analytical approximation of the numerically calculated potential is presented. The elastic scattering of oxygen on silicon was studied in the 10-500 eV range of relative kinetic energies. The obtained differential, integral, and transport scattering cross sections and the proposed interatomic potential can be used in the field of nanotechnologies.

  8. Deuterium scattering from Rh(110) surface

    Microsoft Academic Search

    D. Cvetko; A. Morgante; A. Santaniello; F. Tommasini

    1996-01-01

    Thermal energy deuterium beam scattering (TEDS) from Rh(110) surface is reported and compared to helium atom scattering (HAS). Unlike for He, we find quite strong D2 off-specular diffraction. The D2 diffraction intensities are fairly isotropic along the [001] and [11¯0], reflecting the presence of a finite dissociation barrier in the potential energy surface (PES) rather than the anisotropic corrugation of

  9. Elastic differential cross sections for C4F6 isomers in the 1.5-200 eV energy electron impact: Similarities with six fluorine containing molecules and evidence of F-atom like scattering

    NASA Astrophysics Data System (ADS)

    Hoshino, M.; Limão-Vieira, P.; Anzai, K.; Kato, H.; Cho, H.; Mogi, D.; Tanioka, T.; Ferreira da Silva, F.; Almeida, D.; Blanco, F.; García, G.; Ingólfsson, O.; Tanaka, H.

    2014-09-01

    We report absolute elastic differential cross sections for electron interactions with the C4F6 isomers, hexafluoro-1,3-butadiene (1,3-C4F6), hexafluoro-2-butyne (2-C4F6), and hexafluorocyclobutene (c-C4F6). The incident electron energy range is 1.5-200 eV, and the scattered electron angular range for the differential measurements varies from 15° to 150°. In all cases the absolute scale of the differential cross section was set using the relative flow technique, with helium as the reference species. Atomic-like behaviour in these scattering systems is shown here for the first time, and is further investigated by comparing the elastic cross sections for the C4F6 isomers with other fluorinated molecules, such as SF6 and CnF6 (n = 2, 3, and 6). We note that for all the six-F containing molecules, the scattering process for electron energies above 30 eV is indistinguishable. Finally, we report results for calculations of elastic differential cross sections for electron scattering from each of these isomers, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements is found to be quite remarkable in all cases.

  10. Elastic differential cross sections for C?F? isomers in the 1.5-200 eV energy electron impact: similarities with six fluorine containing molecules and evidence of F-atom like scattering.

    PubMed

    Hoshino, M; Limão-Vieira, P; Anzai, K; Kato, H; Cho, H; Mogi, D; Tanioka, T; Ferreira da Silva, F; Almeida, D; Blanco, F; García, G; Ingólfsson, O; Tanaka, H

    2014-09-28

    We report absolute elastic differential cross sections for electron interactions with the C4F6 isomers, hexafluoro-1,3-butadiene (1,3-C4F6), hexafluoro-2-butyne (2-C4F6), and hexafluorocyclobutene (c-C4F6). The incident electron energy range is 1.5-200 eV, and the scattered electron angular range for the differential measurements varies from 15° to 150°. In all cases the absolute scale of the differential cross section was set using the relative flow technique, with helium as the reference species. Atomic-like behaviour in these scattering systems is shown here for the first time, and is further investigated by comparing the elastic cross sections for the C4F6 isomers with other fluorinated molecules, such as SF6 and CnF6 (n = 2, 3, and 6). We note that for all the six-F containing molecules, the scattering process for electron energies above 30 eV is indistinguishable. Finally, we report results for calculations of elastic differential cross sections for electron scattering from each of these isomers, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements is found to be quite remarkable in all cases. PMID:25273432

  11. Determination of carbon in aqueous solutions by atmospheric-pressure helium microwave induced plasma atomic emission spectrometry with gas-phase sample introduction technique.

    PubMed

    Matsumoto, Akihiro; Nakahara, Taketoshi

    2003-03-01

    A trace amount of carbon was determined by atmospheric-pressure helium microwave induced plasma atomic emission spectrometry (He-MIP-AES) with gas-phase sample introduction technique. This method was applied for the generation of a continuous flow of carbon dioxide by the acidification of carbonate ion and hydrogen carbonate ion for the determination of carbon. The generated carbon dioxide was separated from the solution by a simple gas-liquid separator, dried with a desiccant and swept into the MIP with helium carrier gas for analysis. Of the acids and drying agents investigated, hydrochloric acid for acidification and anhydrous calcium chloride as a desiccant were found to be the most appropriate for the generation of carbon dioxide. Under the optimized experimental conditions, the best attainable detection limits at C (I) 193.09 and C (I) 247.86 nm lines were 7.89 and 8.10 microg/l with linear dynamic ranges of 100 to 10,000 and 100 to 20,000 microg/l for carbon, respectively. The presence of many diverse elements and ions was found to cause a more or less depressing interference by the proposed technique. However, no interference was observed from the following elements and ions: Ca, K, Rb, Br-, Cl-, F- and I-. Finally, the present method has been applied to the determination of carbon in several water samples. PMID:12675347

  12. Photoionization of helium-like ions accompanied by the excitation of p-wave states of the residual atom

    SciTech Connect

    Mikhailov, A. I.; Nefiodov, A. V., E-mail: anef@thd.pnpi.spb.ru [Russian Academy of Sciences, Petersburg Nuclear Physics Institute (Russian Federation)

    2011-02-15

    The single-photon ionization of the ground state of a helium-like multicharged ion, which is accompanied by a simultaneous excitation of the residual ion to the np states, is studied using nonrelativistic pertubation theory with respect to the electron-electron interaction. Formulas describing the cross section for the process being studied are obtained. These formulas exhibit a scaling behavior in the target-nucleus charge number Z and in the principal quantum number n. Numerical calculations are performed for nonrelativistic energies including the near-threshold region.

  13. Gross Structure in the Spectra of Helium Ions Inelastically Scattered from Heavy Nuclei with Large Energy Loss

    Microsoft Academic Search

    G. Chenevert; N. S. Chant; I. Halpern; C. Glashausser; D. L. Hendrie

    1971-01-01

    Forward-angle spectra of alpha particles inelastically scattered from heavy nuclei at incident energies up to 90 MeV are found to exhibit a broad but conspicous plateau. The integrated cross section of this plateau constitutes about 25% of the total (alpha,alpha') cross section at an incident energy of 65 MeV. The total (alpha,alpha') cross section is, in turn, about 16 of

  14. Applications of Quantum Theory of Atomic and Molecular Scattering to Problems in Hypersonic Flow

    NASA Technical Reports Server (NTRS)

    Malik, F. Bary

    1995-01-01

    The general status of a grant to investigate the applications of quantum theory in atomic and molecular scattering problems in hypersonic flow is summarized. Abstracts of five articles and eleven full-length articles published or submitted for publication are included as attachments. The following topics are addressed in these articles: fragmentation of heavy ions (HZE particles); parameterization of absorption cross sections; light ion transport; emission of light fragments as an indicator of equilibrated populations; quantum mechanical, optical model methods for calculating cross sections for particle fragmentation by hydrogen; evaluation of NUCFRG2, the semi-empirical nuclear fragmentation database; investigation of the single- and double-ionization of He by proton and anti-proton collisions; Bose-Einstein condensation of nuclei; and a liquid drop model in HZE particle fragmentation by hydrogen.

  15. Atomic mass dependence of hadron production in semi-inclusive deep inelastic lepton-nucleus scattering

    E-print Network

    Li-Hua Song; Na Liu; Chun-Gui Duan

    2013-10-20

    Hadron production in lepton-nucleus deep inelastic scattering is studied in a quark energy loss model. The leading-order computations for hadron multiplicity ratios are presented and compared with the selected HERMES pions production data with the quark hadronization occurring outside the nucleus by means of the hadron formation time. It is found that the obtained energy loss per unit length is $0.440 \\pm 0.013$ GeV/fm for an outgoing quark by the global fit. It is confirmed that the atomic mass number dependence of hadron attenuation is theoretically and experimentally in good agreement with the $A^{2/3}$ power law for quark hadronization occurring outside the nucleus.

  16. Laser-Induced Optical Pumping Measurements of Cross Section for Fine- and Hyperfine-Structure Transitions in Sodium Induced by Collisions with Helium and Argon Atoms

    NASA Technical Reports Server (NTRS)

    Dobson, Chris C.; Sung, C. C.

    1999-01-01

    Optical pumping of the ground states of sodium can radically alter the shape of the laser-induced fluorescence excitation spectrum, complicating measurements of temperature, pressure, etc., which are based on these spectra. Modeling of the fluorescence using rate equations for the eight hyperfine states of the sodium D manifolds can be used to quantify the contribution to the ground state pumping of transitions among the hyperfine excited states induced by collisions with buffer gas atoms. This model is used here to determine, from the shape of experimental spectra, cross sections lor DELTA.F transitions of the P(sub 3/2) state induced by collisions with helium and argon atoms, for a range of values assumed for the P(sub 1/2), DELTA.F cross sections. The hyperfine cross sections measured using this method, which to our knowledge is novel, are compared with cross sections for transitions involving polarized magnetic substates m(sub F) measured previously using polarization sensitive absorption. Also, fine-structure transition cross sections were measured in the pumped vapor, giving agreement with previous measurements made in the absence of pumping.

  17. Laser Induced Optical Pumping Measurements of Cross Sections for Fine and Hyperfine Structure Transitions in Sodium Induced by Collisions with Helium Argon Atoms

    NASA Technical Reports Server (NTRS)

    Dobson, Chris C.; Sung, C. C.

    1998-01-01

    Optical pumping of the ground states of sodium can radically alter the shape of the laser induced fluorescence excitation spectrum, complicating measurements of temperature, pressure, etc., which are based on these spectra. Modeling of the fluorescence using rate equations for the eight hyperfine states of the sodium D manifolds can be used to quantify the contribution to the ground state pumping of transitions among the hyperfine excited states induced by collisions with buffer gas atoms. This model is used here to determine, from the shape of experimental spectra, cross sections for (Delta)F transitions of the P(sub 3/2) state induced by collisions with helium and argon atoms, for a range of values assumed for the P(sub 1/2), (Delta)F cross sections. The hyperfine cross sections measured using this method, which is thought to be novel, are compared with cross sections for transitions involving polarized magnetic substates, m(sub F), measured previously using polarization sensitive absorption. Also, fine structure transition ((Delta)J) cross sections were measured in the pumped vapor, giving agreement with previous measurements made in the absence of pumping.

  18. Absolute differential cross sections for the scattering of kilo-electron-volt O atoms

    NASA Astrophysics Data System (ADS)

    Smith, G. J.; Gao, R. S.; Lindsay, B. G.; Smith, K. A.; Stebbings, R. F.

    1996-03-01

    This paper reports measurements of absolute differential cross sections for the direct scattering of oxygen atoms by He, Ne, Ar, Kr, Xe, H2, N2, O2, CO, CO2, H2O, SO2, NH3, CH4, CF4, and SF6 targets. The measured cross sections include contributions from all elastic and inelastic processes that result in a fast neutral oxygen atom product. Cross sections are presented for 0.5- and 1.5-keV projectile energies over the laboratory angular range 0.2°-5°. When compared in the center-of-mass reference frame, these cross sections exhibit a high degree of similarity in both amplitude and angular dependence. The cross sections for N2, CO, CO2, and H2O are inverted using a partial-wave analysis to yield empirical interaction potentials, which can then be used to extrapolate the measurements down to lower energies. Using these potentials, cross sections are evaluated at 0.1 keV.

  19. Total cross sections for positrons scattered elastically from helium based on new measurements of total ionization cross sections

    NASA Technical Reports Server (NTRS)

    Diana, L. M.; Chaplin, R. L.; Brooks, D. L.; Adams, J. T.; Reyna, L. K.

    1990-01-01

    An improved technique is presented for employing the 2.3m spectrometer to measure total ionization cross sections, Q sub ion, for positrons incident on He. The new ionization cross section agree with the values reported earlier. Estimates are also presented of total elastic scattering cross section, Q sub el, obtained by subtracting from total scattering cross sections, Q sub tot, reported in the literature, the Q sub ion and Q sub Ps (total positronium formation cross sections) and total excitation cross sections, Q sub ex, published by another researcher. The Q sub ion and Q sub el measured with the 3m high resolution time-of-flight spectrometer for 54.9eV positrons are in accord with the results from the 2.3m spectrometer. The ionization cross sections are in fair agreement with theory tending for the most part to be higher, especially at 76.3 and 88.5eV. The elastic cross section agree quite well with theory to the vicinity of 50eV, but at 60eV and above the experimental elastic cross sections climb to and remain at about 0.30 pi a sub o sq while the theoretical values steadily decrease.

  20. Atmospheric helium capillary dielectric barrier discharge for soft ionization: determination of atom number densities in the lowest excited and metastable States.

    PubMed

    Horvatic, Vlasta; Müller, Saskia; Veza, Damir; Vadla, Cedomil; Franzke, Joachim

    2014-01-01

    The populations of the lowest excited helium states 2s 3S1, 2s 1S, 2p 3P0 J, and 2p 1P0 created in an atmospheric helium capillary dielectric barrier discharge were determined by means of optical emission spectroscopy. The emitted intensities of 388, 501, 587, and 667 nm lines were measured side-on and end-on with respect to the discharge axis. The comparison of optically thin side-on spectra with end-on spectra, which exhibited the absorption effects in the line kernels, enabled the determination of the average values of the number densities n1 in the considered He states along the plasma length L. The field of the theoretical profiles for a series of the n1L parameters pertinent to the experimental conditions was calculated for each line. By introducing the experimental data into the field of calculated curves, n1L corresponding to the particular state could be obtained. The measurements of the emission profiles were done as a function of the discharge voltage in the range covering homogeneous as well as filamentary DBD operation mode. Due to nonuniformity of the excited atom density distribution along the plasma, the values of n1 could be obtained only in the homogeneous operation mode where the nonuniformity was small. The following maximum values were found for the number densities in the investigated states: n1 av (2s 3S1) = (2.9 ± 1.1) × 1013 cm?3, n1 av (2s 1S) = (1.4 ± 0.5) × 1013 cm?3, n1 av (2p 3P0 J) = (1.1 ± 0.4) × 1013 cm?3, n1 av (2p 1P0) = (4.2 ± 1.6) × 1012 cm?3, and they represent the average populations along the plasma column in the capillary. PMID:24320177

  1. NON-ADIABATIC TREATMENT OF ELASTIC SCATTERING OF ELECTRONS BY ATOMIC HYDROGEN. Research Report No. CX37

    Microsoft Academic Search

    Omidvar

    1959-01-01

    The elastic scattering of electrons by atomic hydrogen including the ; effects of exchange and polarization is calculated. To include the exchange ; effect the total spin and space function of the incident and the bound electrons ; is made antisymmetric with respect to interchange of the two electrons. In this ; way an equation for the wave function of

  2. Proton and Helium Induced L Subshell Ionization Cross-Section Measurements of Medium to High Z Atoms

    Microsoft Academic Search

    Mark Francis Harrigan

    1986-01-01

    This thesis deals with the L subshell ionization of medium to high atomic number (Z) targets by proton and He('+) ion bombardment, and the subsequent filling of the inner shell vacancy by the production of X-rays. The L subshell ionization cross sections for antimony (Z = 51), gadolinium (Z = 64), tungsten (Z = 74) and gold (Z = 79)

  3. Possibility of giant enhancement of low-frequency non-resonant Rayleigh scattering by atomic systems within dense plasmas

    SciTech Connect

    Basu, Joyee, E-mail: joyeebasu@yahoo.com; Ray, Debasis, E-mail: ray.debasis@gmail.com [Department of Physics, Bengal Engineering and Science University, Shibpur, Howrah, West Bengal 711 103 (India)] [Department of Physics, Bengal Engineering and Science University, Shibpur, Howrah, West Bengal 711 103 (India)

    2014-03-15

    In this paper, we demonstrate the possibility of electron density-induced giant growth of non-resonant Rayleigh scattering of electromagnetic radiation (in the low-frequency limit) by atomic systems within dense plasmas. Non-relativistic quantum mechanical calculation is performed under electric dipole approximation, for elastic scattering of radiation by the ground states 1s of plasma-embedded hydrogen-like atomic ions treated within the framework of the ion-sphere model. The results indicate giant enhancement of the non-resonant (photon frequency ? being much smaller than the lowest resonance frequency ?{sub 1s?2p}) Rayleigh cross-section by an order of magnitude, at (atomic system-specific) high enough plasma electron densities under present consideration. The Z{sup ?8}-scaling of the non-resonant Rayleigh cross-section in free and isolated H-isoelectronic sequence of ions is shown to be broken in dense plasma environments.

  4. Inelastic helium scattering studies of the vibrational spectroscopy and dynamics of ordered Ar, Kr, and Xe multilayers physisorbed on Ag(111)

    NASA Astrophysics Data System (ADS)

    Gibson, K. D.; Sibener, S. J.

    1988-06-01

    This is the second of three papers discussing our studies of overlayers of Ar, Kr, and Xe physisorbed on Ag(111). All of these rare gases form ordered structures, which are azimuthally aligned but translationally incommensurate with the Ag substrate. In this paper, we discuss experiments in which we utilized the angle resolved time of flight of inelastically scattered 18 MeV He atoms to examine the surface dynamics of multilayer rare gas films along the ?¯-M¯ direction. This was done on a layer-by-layer basis for 2, 3, and ?20 layers for each of the rare gases. Unlike the monolayers, the vibrational modes observed for the multilayers show dispersion across the surface Brillouin zone, the amount of dispersion increasing with the number of adsorbed layers. These results reveal in detail how the surface dynamical properties of a thin film evolve towards those of a thick crystal as a function of increasing dimension. Lattice dynamics calculations, which utilize realistic gas phase pair potentials, reproduce the experimentally observed phonon dispersion relations quite well. We also examine the inelastic scattering probabilities and linewidths of the transitions. One of the more notable results is that the inelastic scattering probabilities vary by at most a factor of 2-3 across the entire surface Brillouin zone. Isothermal desorption measurements for the Xe overlayers are also discussed. Like the monolayer, the bilayer and trilayer exhibit nearly zeroth order desorption until ˜90% of the top layer has desorbed, where the desorption kinetics become first order.

  5. Low-energy electron-impact ionization of the helium atom using the multiconfiguration Hartree-Fock method

    SciTech Connect

    Saha, Hari P. [Physics Department, University of Central Florida, Orlando, Florida 32816 (United States)

    2010-10-15

    We have extended the multiconfiguration Hartree-Fock method for electron-impact ionization of atoms to investigate the effects of polarization and electron correlation of the target in the initial state. As a test case, the method is applied to calculate triple differential cross sections for electron-impact ionization of He atom at an excess energy of 2 eV for the coplanar {theta}{sub 12}={pi} geometry for equal and unequal energies of two final-state outgoing electrons. To determine the effects of electron correlation between the two outgoing electrons in the final state, the variationally determined screening potential approximation is used. It is found that target correlation in the initial state has smaller effect on the triple differential cross section but the polarization of the target by the incident electron has considerable effect on the triple differential cross section at low incident energy. The results are compared with absolute measurement and other available theoretical results.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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 × 109 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. Spatial profiles of electron and metastable atom densities in positive polarity fast ionization waves sustained in helium

    SciTech Connect

    Weatherford, Brandon R., E-mail: brweathe@gmail.com, E-mail: zax@esi-group.com, E-mail: evbarna@sandia.gov, E-mail: mjkush@umich.edu; Barnat, E. V., E-mail: brweathe@gmail.com, E-mail: zax@esi-group.com, E-mail: evbarna@sandia.gov, E-mail: mjkush@umich.edu [Sandia National Laboratories, Albuquerque, New Mexico 87185-1423 (United States); Xiong, Zhongmin, E-mail: brweathe@gmail.com, E-mail: zax@esi-group.com, E-mail: evbarna@sandia.gov, E-mail: mjkush@umich.edu; Kushner, Mark J., E-mail: brweathe@gmail.com, E-mail: zax@esi-group.com, E-mail: evbarna@sandia.gov, E-mail: mjkush@umich.edu [Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2122, USA. (United States)

    2014-09-14

    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{sup 9?}cm s{sup ?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.

  8. REVIEWS OF TOPICAL PROBLEMS: On the possibility of selecting molecules embedded in superfluid helium nanodroplets (clusters)

    NASA Astrophysics Data System (ADS)

    Makarov, Grigorii N.

    2006-11-01

    Methods for producing beams of nanometer-sized superfluid helium droplets and techniques for embedding single molecules and clusters in them open up many possibilities for spectroscopy, as well as providing insight into many physical and chemical processes occurring on the atomic and molecular level at extremely low temperatures (T <= 0.4 K). In this paper, results of investigations into the possibility of selecting molecules embedded in superfluid helium nanodroplets (clusters) are reviewed. The method proposed starts with the selective vibrational excitation of cluster-embedded molecules by intense IR laser radiation (which greatly reduces the size of the excited clusters), followed by size-separating the clusters via scattering the cluster beam from a crossing molecular (atomic) beam. It is shown that molecules of a particular isotope (component) composition can be selected with this method. The advantages and disadvantages of the method are discussed. Methods for creating and doping helium nanodroplets and some other examples of their applications are also outlined.

  9. On the Formation of (Anionic) Excited Helium Dimers in Helium Droplets

    PubMed Central

    2014-01-01

    Metastable atomic and molecular helium anions exhibiting high-spin quartet configurations can be produced in helium droplets via electron impact. Their lifetimes allow detection in mass spectrometric experiments. Formation of atomic helium anions comprises collision-induced excitation of ground state helium and concomitant electron capture. Yet the formation of molecular helium anions in helium droplets has been an unresolved issue. In this work, we explore the interaction of excited helium atoms exhibiting high-spin triplet configurations with ground state helium using the equation-of-motion coupled-cluster method. Transition barriers in the energetically lowest He*–He and He*––He interaction potentials prevent molecule formation at the extremely low temperatures present in helium droplets. In contrast, some excited states allow a barrier-free formation of molecular helium (anions). Moreover, we show that the necessary excitation energies pinpoint (higher) resonances in recently recorded mass spectra and emend the assignment of those resonances that have previously been assigned to electron-impact ionization of ground state helium necessitating subsequent double-electron capture. Embedding molecules or molecular clusters in helium droplets is a predestined experimental technique for the study of phenomena at very low temperatures. Profound knowledge about active processes in the helium environment is required for a proper assessment of experimental data. PMID:24866535

  10. Solving the electron and electron-nuclear Schroedinger equations for the excited states of helium atom with the free iterative-complement-interaction method

    SciTech Connect

    Nakashima, Hiroyuki; Hijikata, Yuh; Nakatsuji, Hiroshi [Quantum Chemistry Research Institute, JST CREST, Kyodai Katsura Venture Plaza 106, Goryo Oohara 1-36, Nishikyo-ku, Kyoto 615-8245 (Japan) and Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan)

    2008-04-21

    Very accurate variational calculations with the free iterative-complement-interaction (ICI) method for solving the Schroedinger equation were performed for the 1sNs singlet and triplet excited states of helium atom up to N=24. This is the first extensive applications of the free ICI method to the calculations of excited states to very high levels. We performed the calculations with the fixed-nucleus Hamiltonian and moving-nucleus Hamiltonian. The latter case is the Schroedinger equation for the electron-nuclear Hamiltonian and includes the quantum effect of nuclear motion. This solution corresponds to the nonrelativistic limit and reproduced the experimental values up to five decimal figures. The small differences from the experimental values are not at all the theoretical errors but represent the physical effects that are not included in the present calculations, such as relativistic effect, quantum electrodynamic effect, and even the experimental errors. The present calculations constitute a small step toward the accurately predictive quantum chemistry.

  11. New x-ray measurements in Helium-like Atoms increase discrepancy between experiment and theoretical QED

    E-print Network

    Christopher T. Chantler; Andrew T. Payne; John D. Gillaspy; Lawrence T. Hudson; Lucas F. Smale; Albert Henins; Justin A. Kimpton; Endre Takacs

    2014-05-28

    A recent 15 parts-per-million (ppm) experiment on muonic hydrogen found a major discrepancy with QED and independent nuclear size determinations. Here we find a significant discrepancy in a different type of exotic atom, a medium-Z nucleus with two electrons. Investigation of the data collected is able to discriminate between available QED formulations and reveals a pattern of discrepancy of almost 6 standard errors of experimental results from the most recent theoretical predictions with a functional dependence proportional to Z^n where n=4. In both the muonic and highly charged systems, the sign of the discrepancy is the same, with the measured transition energy higher than predicted. Some consequences are possible or probable, and some are more speculative. This may give insight into effective nuclear radii, the Rydberg, the fine-structure constant or unexpectedly large QED terms.

  12. Non-resonant elastic scattering of low-energy photons by atomic sodium confined in quantum plasmas

    NASA Astrophysics Data System (ADS)

    Ghosh, Avijit; Ray, Debasis

    2015-03-01

    The non-resonant elastic scattering of low-energy photons by the bound valence electron in the ground state 3s of atomic sodium confined in quantum plasmas is investigated theoretically. The incident photon energy is assumed to be much smaller than the 3s-3p excitation energy. The alkali atom sodium is first formulated as an effective one-electron problem in which the attractive interaction between the valence electron and the atomic ion core is simulated by a spherically symmetric model potential. The Shukla-Eliasson oscillatory exponential cosine screened-Coulomb potential model is then used to mimic the effective two-body (valence-core) interaction within quantum plasmas. Non-relativistic calculations performed within the electric dipole approximation indicate that the non-resonant elastic photon scattering cross-section undergoes a dramatic growth by several orders of magnitude as the quantum wave number increases. A qualitative explanation of this phenomenon is presented. In the absence of the oscillatory cosine screening term, a similar growth is observed at larger values of the quantum wave number. Our computed relevant atomic data are in very good agreement with the experimental as well as the previous theoretical data for the zero-screening (free atom) case, and with the very limited, accurate theoretical results available for the case of exponential screened-Coulomb two-body interaction, without the cosine screening term.

  13. Quenching of krypton atoms in the metastable 5s ({sup 3}P{sub 2}) state in collisions with krypton and helium atoms

    SciTech Connect

    Zayarnyi, D A; L'dov, A Yu; Kholin, I V [P N Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

    2013-08-31

    We have used the absorption probe method to study the processes of collisional quenching of the metastable 5s [3/2]{sup o}{sub 2}({sup 3}P{sub 2}) state of the krypton atom in electron-beam-excited high-pressure He – Kr mixtures with a low content of krypton. The rate constants of plasma-chemical reactions Kr* + Kr + He ? Kr*{sub 2}+He [(2.88 ± 0.29) × 10{sup -33} cm{sup 6} s{sup -1}], Kr* + 2He ? HeKr* + He [(4.6 ± 1.3) × 10{sup -36} cm{sup 6} s{sup -1}] and Kr* + He ? products + He [(1.51 ± 0.15) × 10{sup -15} cm{sup 3} s{sup -1}] are measured for the first time. The rate constants of similar reactions in the Ar – Kr mixture are refined. (active media)

  14. Measurement of differential atomic collision cross sections.

    NASA Technical Reports Server (NTRS)

    Fitzwilson, R. L.; Thomas, E. W.

    1971-01-01

    An apparatus for the study of differential angular scattering of atomic projectiles by gas targets is described. The design facilitates system alignment and provides for accurate reproducible location of components. The performance of the instrument is studied for scattering of H+ at 5-25 keV energies by helium and argon targets. Differential cross sections for elastic scattering and charge transfer are presented as well as total charge transfer cross sections. The coefficients for secondary electron ejection by impact of H and H+ on a metal surface are compared.

  15. Resonances in Mie scattering by an inhomogeneous atomic cloud R. Bachelard1,2

    E-print Network

    Boyer, Edmond

    of electro- magnetic radiation by spherical objects [1, 2]. Via calcu- lation of the electric and magnetic or in emulsions), Mie's full theory has to be used to find the scattering pattern. Mie scattering differs from

  16. Relationship Between the Atomic Pair Distribution Function and Small-Angle Scattering: Implications for Modeling of Nanoparticles

    Microsoft Academic Search

    S. Billinge; C. L. Farrowa

    2009-01-01

    The relationship between the equations used in the atomic pair distribution function (PDF) method and those commonly used in small-angle-scattering (SAS) analyses is explicitly shown. The origin of the sloping baseline, -4Ïrρâ, in PDFs of bulk materials is identified as originating from the SAS intensity that is neglected in PDF measurements. The nonlinear baseline in nanoparticles has the same origin,

  17. A MATLAB-based finite-element visualization of quantum reactive scattering. I. Collinear atom-diatom reactions

    SciTech Connect

    Warehime, Mick [Chemical Physics Program, University of Maryland, College Park, Maryland 20742-2021 (United States); Alexander, Millard H., E-mail: mha@umd.edu [Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021 (United States)

    2014-07-14

    We restate the application of the finite element method to collinear triatomic reactive scattering dynamics with a novel treatment of the scattering boundary conditions. The method provides directly the reactive scattering wave function and, subsequently, the probability current density field. Visualizing these quantities provides additional insight into the quantum dynamics of simple chemical reactions beyond simplistic one-dimensional models. Application is made here to a symmetric reaction (H+H{sub 2}), a heavy-light-light reaction (F+H{sub 2}), and a heavy-light-heavy reaction (F+HCl). To accompany this article, we have written a MATLAB code which is fast, simple enough to be accessible to a wide audience, as well as generally applicable to any problem that can be mapped onto a collinear atom-diatom reaction. The code and user's manual are available for download from http://www2.chem.umd.edu/groups/alexander/FEM.

  18. A MATLAB-based finite-element visualization of quantum reactive scattering. I. Collinear atom-diatom reactions

    NASA Astrophysics Data System (ADS)

    Warehime, Mick; Alexander, Millard H.

    2014-07-01

    We restate the application of the finite element method to collinear triatomic reactive scattering dynamics with a novel treatment of the scattering boundary conditions. The method provides directly the reactive scattering wave function and, subsequently, the probability current density field. Visualizing these quantities provides additional insight into the quantum dynamics of simple chemical reactions beyond simplistic one-dimensional models. Application is made here to a symmetric reaction (H+H2), a heavy-light-light reaction (F+H2), and a heavy-light-heavy reaction (F+HCl). To accompany this article, we have written a MATLAB code which is fast, simple enough to be accessible to a wide audience, as well as generally applicable to any problem that can be mapped onto a collinear atom-diatom reaction. The code and user's manual are available for download from http://www2.chem.umd.edu/groups/alexander/FEM.

  19. Paramagnetic Attraction of Impurity-Helium Solids

    NASA Technical Reports Server (NTRS)

    Bernard, E. P.; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. M.

    2003-01-01

    Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals.

  20. Measurements of scattering processes in negative ion-atom collisions. Technical progress report, 1 September 1991--31 August 1992

    SciTech Connect

    Kvale, T.J.

    1992-04-01

    This Technical Progress Report describes the progress made on the research objectives during the past twelve months. This research project is designed to provide measurements of various scattering processes which occur in H{sup {minus}} collisions with atomic (specifically, noble gas and atomic hydrogen) targets at intermediate energies. These processes include: elastic scattering,single- and double-electron detachment, and target excitation/ionization. For the elastic and target inelastic processes where H{sup {minus}} is scattered intact, the experimental technique of Ion Energy-Loss Spectroscopy (IELS) will be employed to identify the final target state(s). In most of the above processes, cross sections are unknown both experimentally and theoretically. The measurements in progress will provide either experimentally-determined cross sections or set upper limits to those cross sections. In either case, these measurements will be stringent tests of our understanding in energetic negative ion-atom collisions. This series of experiments required the construction of a new facility and the initial ion beam was accelerated through the apparatus in April 1991.

  1. Magnetoconductivity of two-dimensional electrons on liquid helium:Experiments in the fluid phase

    Microsoft Academic Search

    M. J. Lea; P. Fozooni; A. Kristensen; P. J. Richardson; K. Djerfi; M. I. Dykman; C. Fang-Yen; A. Blackburn

    1997-01-01

    The magnetoconductivity sigma(B) of two-dimensional electrons on liquid helium was measured from 0.25 to 1.3 K in the electron fluid phase in magnetic fields up to 8 T. In low magnetic fields B, sigma(0)\\/sigma(B)=1+(muB)2 as in the Drude model, where mu is the zero-field mobility due to scattering by 4He vapor atoms and ripplons, even for muB>>:1. The values of

  2. Universal nature and finite-range corrections in elastic atom-dimer scattering below the dimer breakup threshold

    E-print Network

    A. Kievsky; M. Gattobigio

    2013-06-07

    We investigate universal behavior in elastic atom-dimer scattering below the dimer breakup threshold calculating the atom-dimer effective-range function $ak\\cot\\delta$. Using the He-He system as a reference, we solve the Schr\\"odinger equation for a family of potentials having different values of the two-body scattering length $a$ and we compare our results to the universal zero-range form deduced by Efimov, $ak\\cot\\delta=c_1(ka)+c_2(ka)\\cot[s_0\\ln(\\kappa_*a)+\\phi(ka)]$, for selected values of the three-body parameter $\\kappa_*$. Using the parametrization of the universal functions $c_1,c_2,\\phi$ given in the literature, a good agreement with the universal formula is obtained after introducing a particular type of finite-range corrections. Furthermore, we show that the same parametrization describes a very different system: nucleon-deuteron scattering below the deuteron breakup threshold. Our analysis confirms the universal character of the process, and relates the pole energy in the effective-range function of nucleon-deuteron scattering to the three-body parameter $\\kappa_*$.

  3. Resonances in low-energy electron scattering on atomic Rb, Cs, and Fr.

    NASA Astrophysics Data System (ADS)

    Thumm, U.; Bahrim, C.; Fabrikant, I. I.

    2002-10-01

    Within the relativistic Dirac R-matrix method and a model based on an effective two-electron approach(U. Thumm and D.W. Norcross Phys.Rev.A 45, 6349 (1992).), we analyze the spectra of Rb^-, Cs^-, and Fr^- ions in electron scattering by Rb, Cs, and Fr targets at incident electron energies below 2.8 eV. Our calculations predict the same ^3P^o,e , ^3F^o, and ^1P^o resonances for all three anions(C. Bahrim, U. Thumm, and I.I. Fabrikant Phys.Rev.A 63, 042710 (2001); C. Bahrim and U. Thumm, Phys.Rev.A 64, 022716 (2001)) in calculations of angle-dependent, momentum transfer, and total cross sections. We discuss relativistic effects in the resonance profiles. Our 1^+ partial cross sections show pronounced Ramsauer-Townsend (RT) minima at 41/46/32 meV for Rb/Cs/Fr, caused by the strong atomic polarizability and related to a ^3S^e virtual state(C. Bahrim, U.Thumm, and I.I. Fabrikant, J. Phys. B 34, L195 (2001)). In the total converged cross section these RT minima are shifted to lower energies (4.6/1.1 meV for Rb/Cs, and below 1 meV for Fr) due to the nearby ^3P^o resonance. We also discuss our spin-flip and spin-exchange cross sections for e^- + Rb, Cs, and Fr collisions in comparison with experimental data.

  4. Treatment of ion-atom collisions using a partial-wave expansion of the projectile wavefunction

    SciTech Connect

    Foster, M [Los Alamos National Laboratory; Colgan, J [Los Alamos National Laboratory; Wong, T G [SANTA CLARA U; Madison, D H [MISSOURI U

    2008-01-01

    We present calculations of ion-atom collisions using a partial-wave expansion of the projectile wavefunction. Most calculations of ion-atom collisions have typically used classical or plane-wave approximations for the projectile wavefunction, since partial-wave expansions are expected to require prohibitively large numbers of terms to converge scattering quantities. Here we show that such calculations are possible using modern high-performance computing. We demonstrate the utility of our method by examining elastic scattering of protons by hydrogen and helium atoms, problems familiar to undergraduate students of atomic scattering. Application to ionization of helium using partial-wave expansions of the projectile wavefunction, which has long been desirable in heavy-ion collision physics, is thus quite feasible.

  5. A low energy bound atomic electron Compton scattering model for Geant4

    NASA Astrophysics Data System (ADS)

    Brown, J. M. C.; Dimmock, M. R.; Gillam, J. E.; Paganin, D. M.

    2014-11-01

    A two-body fully relativistic three-dimensional scattering framework has been utilised to develop an alternative Compton scattering computational model to those adapted from Ribberfors' work for Monte Carlo modelling of Compton scattering. Using a theoretical foundation that ensures the conservation of energy and momentum in the relativistic impulse approximation, this new model, the Monash University Compton scattering model, develops energy and directional algorithms for both the scattered photon and ejected Compton electron from first principles. The Monash University Compton scattering model was developed to address the limitation of the Compton electron directionality algorithms of other computational models adapted from Ribberfors' work. Here the development of the Monash University Compton scattering model, including its implementation in a Geant4 low energy electromagnetic physics class, G4LowEPComptonModel, is outlined. Assessment of the performance of G4LowEPComptonModel was undertaken in two steps: (1) comparison with respect to the two standard Compton scattering classes of Geant4 version 9.5, G4LivermoreComptonModel and G4PenelopeComptonModel, and (2) experimental comparison with respect to Compton electron kinetic energy spectra obtained from the Compton scattering of 662 keV photons off the K-shell of gold. Both studies illustrate that the Monash University Compton scattering model, and in turn G4LowEPComptonModel, is a viable replacement for the majority of computational models that have been adapted from Ribberfors' work. It was also shown that the Monash University Compton scattering model is able to reproduce the Compton scattering triply differential cross-section Compton electron kinetic energy spectra of 662 keV photons K-shell scattering off of gold to within experimental uncertainty.

  6. Collisions in a gas of metastable helium near quantum degeneracy

    NASA Astrophysics Data System (ADS)

    Seidelin, Signe; Gomes, Jose

    2005-05-01

    Experiments with an atomic cloud of metastable helium (He*) in the vicinity of Bose-Einstein condensation will be presented. The metastability of the atoms has opened the door for using new and original detection methods: due to their internal energy, the atoms can be detected electronically by means of a micro-channel plate. The use of He* is also interesting due to the presence of ionizing collisions in the sample. The He^+ ions produced in collisions between the metastable atoms can be detected in real- time, and the ion signal constitutes an alternative and useful diagnostic. In particular, this signal allows one to identify very precisely the Bose-Einstein condensation threshold. One of the advantages of using this signal to probe the cloud is its ``non-invasive'' nature: observing the ions does not at all alter the natural evolution of the cloud, in contrast to the ordinary detection technique which consists of releasing the atoms from the trap and then imaging the cloud. In the experiments to be discussed, by using this new diagnostics based on the ion signal, we have measured some important parameters governing both elastic and inelastic collisions: the ionizing rate constants and the scattering length for metastable helium.

  7. Electron-Atom Superelastic Scattering in Magnesium at Millielectron Volt Energies T. Baynard, A. C. Reber, R. F. Niedziela,| S. A. Darveau, B. Prutzman,# and R. S. Berry*,

    E-print Network

    Berry, R. Stephen

    Electron-Atom Superelastic Scattering in Magnesium at Millielectron Volt Energies T. Baynard, A. C energy dependence of magnesium from threshold to 1400 eV10 with an energy resolution of 250 meV. Similar

  8. Atomic interferometry as two-level particle scattering by a periodic potential

    Microsoft Academic Search

    Christian J. Bordé; Claus Lämmerzahl

    1999-01-01

    The beam splitting process of an atomic beam is described by an exactly solvable theory. We use exact plane wave solutions of an atomic two-level system interacting with laser beams and employ appropriate jump conditions between regions with and without laser beam. The transmission matrix as well as the reflection matrix are given explicitely. Also, the conditions for atom optical

  9. Effect of electron correlation in proton-helium collisions

    NASA Astrophysics Data System (ADS)

    Ghavaminia, H.

    2015-03-01

    The four-body Born approximation is applied in post form to calculate the differential and total cross-sections for single electron capture from helium atoms by impact of the fast protons in the intermediate energy range. Theoretical results are obtained for hydrogen formation in ground state using full correlated accurate wave function for helium. The present results are compared with the results obtained from one parameter uncorrelated wave function to provide a clear visualization for the effect of electron correlation on the cross-sections. Comparison between the results for different wave functions shows the sensitivity of the processes on the electron-electron correlation especially at small scattering angles. The results are also compared with experimental data. The present calculated results show a general agreement with experimental finding for differential cross-sections and pursue the excellent trend with the measurement and other theoretical findings for total cross-sections.

  10. Measurements of Total Cross Sections for Positrons and Electrons Colliding with Atomic Hydrogen and Measurements of Positronium Formation Cross Sections for Positron-Argon and - Scattering

    Microsoft Academic Search

    Shangjing Zhou

    1993-01-01

    We have made the first measurements of total cross sections for 5 to 302 eV positrons and 31 to 302 eV electrons scattered by atomic hydrogen. A beam-transmission technique is used where the positron and electron beam passes through a low temperature scattering cell containing a mixture of hydrogen atoms and molecules generated in an adjacent radio-frequency discharge region. We

  11. Atomic-resolution structural information from scattering experiments on macromolecules in solution

    NASA Astrophysics Data System (ADS)

    Köfinger, Jürgen; Hummer, Gerhard

    2013-05-01

    The pair-distance distribution function (PDDF) contains all structural information probed in an elastic scattering experiment of macromolecular solutions. However, in small-angle x-ray scattering (SAXS) or small-angle neutron scattering (SANS) experiments only their Fourier transform is measured over a restricted range of scattering angles. We therefore developed a mathematically simple and computationally efficient method to calculate the PDDFs as well as accurate scattering intensities from molecular dynamics simulations. The calculated solution scattering intensities are in excellent agreement with SAXS and wide-angle x-ray scattering (WAXS) experiments for a series of proteins. The corresponding PDDFs are remarkably rich in features reporting on the detailed protein structure. Using an inverse Fourier transform method, most of these features can be recovered if scattering intensities are measured up to a momentum transfer of q?2-3Å-1. Our results establish that high-precision solution scattering experiments utilizing x-ray free-electron lasers and third generation synchrotron sources can resolve subnanometer structural detail, well beyond size, shape, and fold.

  12. Atomic oxygen effects on thin film space coatings studied by spectroscopic ellipsometry, atomic force microscopy, and laser light scattering

    NASA Technical Reports Server (NTRS)

    Synowicki, R. A.; Hale, Jeffrey S.; Woollam, John A.

    1992-01-01

    The University of Nebraska is currently evaluating Low Earth Orbit (LEO) simulation techniques as well as a variety of thin film protective coatings to withstand atomic oxygen (AO) degradation. Both oxygen plasma ashers and an electron cyclotron resonance (ECR) source are being used for LEO simulation. Thin film coatings are characterized by optical techniques including Variable Angle Spectroscopic Ellipsometry, Optical spectrophotometry, and laser light scatterometry. Atomic Force Microscopy (AFM) is also used to characterize surface morphology. Results on diamondlike carbon (DLC) films show that DLC degrades with simulated AO exposure at a rate comparable to Kapton polyimide. Since DLC is not as susceptible to environmental factors such as moisture absorption, it could potentially provide more accurate measurements of AO fluence on short space flights.

  13. Protein Dynamics and Stability: The Distribution of Atomic Fluctuations in Thermophilic and Mesophilic Dihydrofolate Reductase Derived Using Elastic Incoherent Neutron Scattering

    Microsoft Academic Search

    Lars Meinhold; David Clement; Moeava Tehei; Roy Daniel; John L. Finneye; Jeremy C. Smith

    2008-01-01

    The temperature dependence of the dynamics of mesophilic and thermophilic dihydrofolate reductase is examined using elastic incoherent neutron scattering. It is demonstrated that the distribution of atomic displacement amplitudes can be derived from the elastic scattering data by assuming a (Weibull) functional form that resembles distributions seen in molecular dynamics simulations. The thermophilic enzyme has a significantly broader distribution than

  14. Helium isotopic abundance variation in nature

    SciTech Connect

    Holden, N.E.

    1993-08-01

    The isotopic abundance of helium in nature has been reviewed. This atomic weight value is based on the value of helium in the atmosphere, which is invariant around the world and up to a distance of 100,000 feet. Helium does vary in natural gas, volcanic rocks and gases, ocean floor sediments, waters of various types and in radioactive minerals and ores due to {alpha} particle decay of radioactive nuclides.

  15. Production of a Biomimetic Fe(I)-S Phase on Pyrite by Atomic-Hydrogen Beam-Surface Reactive Scattering

    PubMed Central

    Che, Li; Gardenghi, David J.; Szilagyi, Robert K.; Minton, Timothy K.

    2011-01-01

    Molecular beam-surface scattering and X-ray absorption spectroscopic experiments were employed to study the reaction of deuterium atoms with a pyrite, FeS2 (100), surface and to investigate the electronic and geometric structures of the resulting Fe-S phases. Incident D atoms, produced by a radio frequency plasma and expanded in an effusive beam, were directed at a pyrite surface held at various temperatures from ambient up to 200 °C. During exposure to the D-atom beam, D2S products were released with a thermal distribution of molecular speeds, indicating that the D atoms likely reacted in thermal equilibrium with the surface. The yield of D2S from the surface decreased approximately exponentially with exposure duration, suggesting that the surface accessible sulfur atoms were depleted, thus leaving an iron-rich surface. This conclusion is consistent with X-ray absorption measurements of the exposed surfaces, which indicated the formation of a layered structure, with elemental iron as the outermost layer on top of a formally Fe(I)-S phase as an intermediate layer and a formally Fe(II)-S2 bulk pyrite layer at lower depths. The reduced Fe(I)-S phase is particularly remarkable because of its similarity to the catalytically active sites of small molecule metalloenzymes, such as FeFe-hydrogenases and MoFe-nitrogenases. PMID:21526811

  16. Angular distributions of 5eV atomic oxygen scattered from solid surfaces on the LDEF satellite

    NASA Technical Reports Server (NTRS)

    Gregory, John C.; Peters, Palmer N.

    1992-01-01

    The angular distribution of 5eV atomic oxygen scattered off several smooth solid surfaces was measured by experiment A0114 which flew on board the Long Duration Exposure Facility (LDEF). Target surfaces were silver, vitreous carbon, and lithium fluoride crystal. The apparatus was entirely passive. It used the property of silver surfaces to absorb oxygen atoms with high efficiency; the silver is converted to optically transmissive silver oxide. A collimated beam of oxygen atoms is allowed to fall on the target surface at some pre-set angle. Reflected atoms are then intercepted by a silver film placed so that it subtends a considerable solid angle from the primary beam impact on the target surface. The silver films are evaporated onto flexible optically-clear polycarbonate sheets which are scanned later to determine oxygen uptake. While the silver detector cannot measure atom velocity or energy, its physical configuration allows easy coverage of large angular space both in the beam-plane (that which includes the incident beam and the surface normal), and in the azimuthal plane of the target surface.

  17. Simultaneous detection of surface coverage and structure of krypton films on gold by helium atom diffraction and quartz crystal microbalance techniques

    SciTech Connect

    Danisman, M. Fatih; Oezkan, Berrin [Department of Chemistry, Middle East Technical University, Ankara 06800 (Turkey)

    2011-11-15

    We describe a quartz crystal microbalance setup that can be operated at low temperatures in ultra high vacuum with gold electrode surfaces acting as substrate surface for helium diffraction measurements. By simultaneous measurement of helium specular reflection intensity from the electrode surface and resonance frequency shift of the crystal during film adsorption, helium diffraction data can be correlated to film thickness. In addition, effects of interfacial viscosity on the helium diffraction pattern could be observed. To this end, first, flat gold films on AT cut quartz crystals were prepared which yield high enough helium specular reflection intensity. Then the crystals were mounted in the helium diffractometer sample holder and driven by means of a frequency modulation driving setup. Different crystal geometries were tested to obtain the best quality factor and preliminary measurements were performed on Kr films on gold surfaces. While the crystal structure and coverage of krypton films as a function of substrate temperature could successfully be determined, no depinning effects could be observed.

  18. Atomically detailed lipid bilayer models for the interpretation of small angle neutron and X-ray scattering data.

    PubMed

    Fogarty, Joseph C; Arjunwadkar, Mihir; Pandit, Sagar A; Pan, Jianjun

    2015-02-01

    We present a new atom density profile (ADP) model and a statistical approach for extracting structural characteristics of lipid bilayers from X-ray and neutron scattering data. Models for five lipids with varying head and tail chemical composition in the fluid phase, 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC), 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylserine (POPS), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG), are optimized using a simplex based method to simultaneously reproduce both neutron and X-ray scattering data. Structural properties are determined using statistical analysis of multiple optimal model structures. The method and models presented make minimal assumptions regarding the atomic configuration, while taking into account the underlying physical properties of the system. The more general model and statistical approach yield data with well defined uncertainties, indicating the precision in determining density profiles, atomic locations, and bilayer structural characteristics. Resulting bilayer structures include regions exhibiting large conformational variation. Due to the increased detail in the model, the results demonstrate the possibility of a distinct hydration layer within the interfacial (backbone) region. PMID:25448879

  19. A study of pseudoresonances in the application of the Schwinger variational principle to electron scattering from atomic hydrogen

    NASA Technical Reports Server (NTRS)

    Weatherford, Charles A.; Odom, Gregory; Tucker, Roy

    1989-01-01

    The Schwinger variational principle is applied to s-wave electron-hydrogen atom scattering. Computationally, consistent with a recent paper by Apagyi et al. (1988), there are pseudoresonances at the static exchange level of approximation, but not at the static level. The T-matrix as well as the K-matrix version of the Schwinger principle is used with a real Slater basis, and the same results are obtained in both. The origin of the pseudoresonances from singularities in the separable potential that is effectively employed in the Lippman-Schwinger equation from which the Schwinger variational principle can be derived. The determination of the pseudoresonance parameters from the separable potential is computationally inexpensive and may be used to predict the pseudoresonance parameters for the scattering calculations so as to avoid them.

  20. High-resolution inelastic x-ray scattering to study the high-frequency atomic dynamics of disordered systems

    NASA Astrophysics Data System (ADS)

    Monaco, Giulio

    2008-06-01

    The use of momentum-resolved inelastic x-ray scattering with meV energy resolution to study the high-frequency atomic dynamics in disordered systems is here reviewed. The typical realization of this experiment is described together with some common models used to interpret the measured spectra and to extract parameters of interest for the investigation of disordered systems. With the help of some selected examples, the present status of the field is discussed. Particular attention is given to those results which are still open for discussion or controversial, and which will require further development of the technique to be fully solved. Such an instrumental development seems nowadays possible at the light of recently proposed schemes for advanced inelastic x-ray scattering spectrometers. To cite this article: G. Monaco, C. R. Physique 9 (2008).

  1. Communication: Semiclassical perturbation theory for the quantum diffractive scattering of atoms on thermal surfaces

    NASA Astrophysics Data System (ADS)

    Daon, Shauli; Pollak, Eli; Miret-Artés, S.

    2012-11-01

    Inspired by the semiclassical perturbation theory of Hubbard and Miller [J. Chem. Phys. 80, 5827 (1984), 10.1063/1.446609], we derive explicit expressions for the angular distribution of particles scattered from thermal surfaces. At very low surface temperature, the observed experimental background scattering is proportional to the spectral density of the phonons. The angular distribution is a sum of diffraction peaks and a broad background reflecting the spectral density. The theory is applied to measured angular distributions of Ne, Ar, and Kr scattered from a Cu(111) surface.

  2. Experiments with electron bubbles in liquid helium

    Microsoft Academic Search

    Ambarish Ghosh

    2005-01-01

    When a free electron is injected into liquid helium, it forms a microscopic bubble essentially free of helium atoms. The electron bubble is an excellent textbook example of a quantum mechanical particle confined in a potential well. The bubble is also a powerful tool to study superfluidity. In this dissertation, we describe various experiments on electron bubbles using standard ultrasonic

  3. Helium recovery process

    Microsoft Academic Search

    D. B. Crawford; M. Karafian

    1967-01-01

    In a process for the recovery of helium from natural gas by liquefaction of hydrocarbons and separation of gaseous helium, the gaseous mixture containing helium, carbon dioxide, nitrogen, and methane is cooled to separate a liquid fraction containing dissolved helium and a helium-enriched gaseous fraction. The helium is stripped from the liquid fraction into an overhead gaseous fraction which is

  4. Inelastic scattering of light by a cold trapped atom: Effects of the quantum center-of-mass motion

    E-print Network

    Marc Bienert; Wolfgang Merkel; Giovanna Morigi

    2005-11-16

    The light scattered by a cold trapped ion, which is in the stationary state of laser cooling, presents features due to the mechanical effects of atom-photon interaction. These features appear as additional peaks (sidebands) in the spectrum of resonance fluorescence. Among these sidebands the literature has discussed the Stokes and anti-Stokes components, namely the sidebands of the elastic peak. In this manuscript we show that the motion also gives rise to sidebands of the inelastic peaks. These are not always visible, but, as we show, can be measured in parameter regimes which are experimentally accessible.

  5. Accurate small and wide angle x-ray scattering profiles from atomic models of proteins and nucleic acids

    NASA Astrophysics Data System (ADS)

    Nguyen, Hung T.; Pabit, Suzette A.; Meisburger, Steve P.; Pollack, Lois; Case, David A.

    2014-12-01

    A new method is introduced to compute X-ray solution scattering profiles from atomic models of macromolecules. The three-dimensional version of the Reference Interaction Site Model (RISM) from liquid-state statistical mechanics is employed to compute the solvent distribution around the solute, including both water and ions. X-ray scattering profiles are computed from this distribution together with the solute geometry. We describe an efficient procedure for performing this calculation employing a Lebedev grid for the angular averaging. The intensity profiles (which involve no adjustable parameters) match experiment and molecular dynamics simulations up to wide angle for two proteins (lysozyme and myoglobin) in water, as well as the small-angle profiles for a dozen biomolecules taken from the BioIsis.net database. The RISM model is especially well-suited for studies of nucleic acids in salt solution. Use of fiber-diffraction models for the structure of duplex DNA in solution yields close agreement with the observed scattering profiles in both the small and wide angle scattering (SAXS and WAXS) regimes. In addition, computed profiles of anomalous SAXS signals (for Rb+ and Sr2+) emphasize the ionic contribution to scattering and are in reasonable agreement with experiment. In cases where an absolute calibration of the experimental data at q = 0 is available, one can extract a count of the excess number of waters and ions; computed values depend on the closure that is assumed in the solution of the Ornstein-Zernike equations, with results from the Kovalenko-Hirata closure being closest to experiment for the cases studied here.

  6. Accurate small and wide angle x-ray scattering profiles from atomic models of proteins and nucleic acids.

    PubMed

    Nguyen, Hung T; Pabit, Suzette A; Meisburger, Steve P; Pollack, Lois; Case, David A

    2014-12-14

    A new method is introduced to compute X-ray solution scattering profiles from atomic models of macromolecules. The three-dimensional version of the Reference Interaction Site Model (RISM) from liquid-state statistical mechanics is employed to compute the solvent distribution around the solute, including both water and ions. X-ray scattering profiles are computed from this distribution together with the solute geometry. We describe an efficient procedure for performing this calculation employing a Lebedev grid for the angular averaging. The intensity profiles (which involve no adjustable parameters) match experiment and molecular dynamics simulations up to wide angle for two proteins (lysozyme and myoglobin) in water, as well as the small-angle profiles for a dozen biomolecules taken from the BioIsis.net database. The RISM model is especially well-suited for studies of nucleic acids in salt solution. Use of fiber-diffraction models for the structure of duplex DNA in solution yields close agreement with the observed scattering profiles in both the small and wide angle scattering (SAXS and WAXS) regimes. In addition, computed profiles of anomalous SAXS signals (for Rb(+) and Sr(2+)) emphasize the ionic contribution to scattering and are in reasonable agreement with experiment. In cases where an absolute calibration of the experimental data at q = 0 is available, one can extract a count of the excess number of waters and ions; computed values depend on the closure that is assumed in the solution of the Ornstein-Zernike equations, with results from the Kovalenko-Hirata closure being closest to experiment for the cases studied here. PMID:25494779

  7. Accurate small and wide angle x-ray scattering profiles from atomic models of proteins and nucleic acids

    SciTech Connect

    Nguyen, Hung T. [BioMaPS Institute for Quantitative Biology, Rutgers University, Piscataway, New Jersey 08854 (United States); Pabit, Suzette A.; Meisburger, Steve P.; Pollack, Lois [School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853 (United States); Case, David A., E-mail: case@biomaps.rutgers.edu [BioMaPS Institute for Quantitative Biology, Rutgers University, Piscataway, New Jersey 08854 (United States); Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854 (United States)

    2014-12-14

    A new method is introduced to compute X-ray solution scattering profiles from atomic models of macromolecules. The three-dimensional version of the Reference Interaction Site Model (RISM) from liquid-state statistical mechanics is employed to compute the solvent distribution around the solute, including both water and ions. X-ray scattering profiles are computed from this distribution together with the solute geometry. We describe an efficient procedure for performing this calculation employing a Lebedev grid for the angular averaging. The intensity profiles (which involve no adjustable parameters) match experiment and molecular dynamics simulations up to wide angle for two proteins (lysozyme and myoglobin) in water, as well as the small-angle profiles for a dozen biomolecules taken from the BioIsis.net database. The RISM model is especially well-suited for studies of nucleic acids in salt solution. Use of fiber-diffraction models for the structure of duplex DNA in solution yields close agreement with the observed scattering profiles in both the small and wide angle scattering (SAXS and WAXS) regimes. In addition, computed profiles of anomalous SAXS signals (for Rb{sup +} and Sr{sup 2+}) emphasize the ionic contribution to scattering and are in reasonable agreement with experiment. In cases where an absolute calibration of the experimental data at q = 0 is available, one can extract a count of the excess number of waters and ions; computed values depend on the closure that is assumed in the solution of the Ornstein–Zernike equations, with results from the Kovalenko–Hirata closure being closest to experiment for the cases studied here.

  8. Coupling between positronium formation and elastic positron-scattering channels in the rare gases

    SciTech Connect

    Jay, P. M.; Coleman, P. G. [Department of Physics, University of Bath, Bath, BA2 7AY (United Kingdom)

    2010-07-15

    Measurements of elastic-scattering cross sections are presented for positron collisions with helium, neon, argon, krypton, and xenon around the threshold energy for positronium (Ps) formation. The elastic cross section falls slowly with increasing energy above the Ps formation threshold in helium and neon, whereas in argon, krypton, and xenon it exhibits an increase, which appears both more prominent and more sustained as the atomic number of the gas increases. It is proposed that this coupling is a result of an intermediate virtual Ps state that enhances branching into the (atom plus positron) final state.

  9. Low-energy electron elastic scattering from Mn, Cu, Zn, Ni, Ag, and Cd atoms

    SciTech Connect

    Felfli, Z.; Msezane, A. Z. [Department of Physics and Center for Theoretical Studies of Physical Systems, Clark Atlanta University, Atlanta, Georgia 30314 (United States); Sokolovski, D. [School of Mathematics and Physics, Queen's University of Belfast, Belfast, BT7 1NN (United Kingdom); Department of Chemical Physics, University of the Basque Country, Leioa (Spain)

    2011-05-15

    Electron elastic total cross sections (TCSs) for ground and excited Mn, Cu, Zn, Ni, Ag, and Cd atoms have been investigated in the electron-impact energy range 0 {<=}E{<=} 1 eV. The near-threshold TCSs for both the ground and excited states of these atoms are found to be characterized by Ramsauer-Townsend minima, shape resonances, and extremely sharp resonances corresponding to the formation of stable bound negative ions. The recently developed Regge-pole methodology where the crucial electron-electron correlations are embedded is employed for the calculations. From close scrutiny of the imaginary parts of the complex angular momenta, we conclude that these atoms form stable weakly bound ground and excited negative ions as Regge resonances through slow electron collisions. The extracted electron binding energies from the elastic TCSs of these atoms are contrasted with the available experimental and theoretical values.

  10. One-photon scattering by an atomic chain in a two-mode resonator: cyclic conditions

    PubMed Central

    2014-01-01

    In this work, a chain of N identical two-level atoms coupled with a quantized electromagnetic field, initially prepared via a single-photon Fock state, is investigated. The N-particle state amplitude of the system is calculated for several space configurations of the atoms in the Weisskopf-Wigner approximation. It was shown that the space configuration of an atomic chain, the total number of atoms, and even the available volume for the field modes define the behavior of the system state amplitude with time. Applying the condition of ‘cyclic bonds’, presented in this work, to the elaborated theory allows to describe the system time evolution, practically, for any space configuration. PMID:24860278

  11. Dynamics of surface-aligned photochemistry (theory). II. Localized H-atom scattering in the HBr(ad)/LiF(001)+h? system

    NASA Astrophysics Data System (ADS)

    Barclay, V. J.; Jack, D. B.; Polanyi, J. C.; Zeiri, Y.

    1992-12-01

    The angular and energy distributions of 1.1 and 2.6 eV H-atom scattering from a LiF(001) surface are compared for two different sources of hot H-atoms (1) localized H-atoms produced by the photolysis of HBr molecules adsorbed on the LiF surface; and (2) H-atoms from a beam at the same energy and angle of approach to the LiF surface as in (1). These distributions are the results of classical stochastic trajectories carried out on a 7×7 slab of LiF(001). The calculated angular distributions are compared with experimental distributions [E. B. D. Bourdon et al., J. Chem. Phys. 95, 1361 (1991)]. The computed effects of changing H-atom energy and surface temperature are also reported; localized scattering becomes increasingly nonspecular at lower photon energies, and broader at higher surface temperatures.

  12. Elastic electron-atom scattering in amplitude-phase representation with application to electron diffraction and spectroscopy

    SciTech Connect

    Rundgren, J. [Department of Theoretical Physics, Royal Institute of Technology (KTH), SE-106 91 Stockholm (Sweden)

    2007-11-15

    The amplitude-phase representation (APR) [W. E. Milne, Phys. Rev. 35, 863 (1930)] is applied to the relativistic radial Schroedinger equation corresponding to the Dirac equations with central potential. The initial conditions, hitherto unspecified, for the nonlinear second-order amplitude equation at the finite radius of a muffin-tin (MT) sphere are established by a semiconvergent method. This opens the possibility of using APR for the calculation of electron scattering phase shifts with a finite MT radius as well as with a large atomic radius, whereby the first wave node is phase of reference equal to a multiple of {pi}, adding nothing to the phase shifts. Furthermore, APR is used for benchmarking wave functions obtained by ordinary differential equation integration of the Dirac equations up to high energy and high orbital quantum number. The present APR procedure is discussed with reference to earlier numerical methods. To complete the physical picture, the paper ends with a discussion on exchange-correlation dependent scattering potential in MT spheres of optimized radii, a crystal potential model whose dependence on radii and energy dependent inner potential has recently been corroborated by low energy electron diffraction in oxides with many atoms per unit cell.

  13. Selection of anti-scatter grids for different imaging tasks: the advantage of low atomic number cover and interspace materials.

    PubMed

    Sandborg, M; Dance, D R; Carlsson, G A; Persliden, J

    1993-12-01

    A Monte Carlo computer program has been developed for the study of anti-scatter grids used in diagnostic radiology. The program estimates the scatter from soft tissue phantoms representative of either adult or paediatric examinations and uses dose increase, signal-to-noise ratio improvement and contrast improvement factors to study grid performance. It has been used to quantify the advantage of replacing grids with aluminium covers and interspaces by grids using materials of low atomic number for these components. Two approaches are used. First, the aluminium and low atomic number alternatives are compared for five grid ratios at fixed strip density and width and for tube potentials of 50, 70, 100 and 150 kV. Second, 44 commercially available grids are compared for three different imaging situations (lumbar spine, chest and paediatric). The results demonstrate that grids made with carbon fibre cover and cotton fibre interspace result in greater improvements in contrast and signal-to-noise ratio, and lower dose increase factors, than do grids made with aluminium. The dose reduction varies with irradiation conditions and is generally larger at lower tube potentials, higher grid ratios and lower strip densities. A typical reduction in mean absorbed dose in the patient is 30% in an adult lumbar spine (AP view) at 70 kV with a grid with 36 strips per centimetre and ratio 12. PMID:8293261

  14. Positron scattering by atomic hydrogen using optical potentials and with positronium formation

    NASA Technical Reports Server (NTRS)

    Walters, H. R. J.

    1990-01-01

    The scattering is considered of positrons by H(ls) in a two-state model which incorporates optical potentials. The model explicitly describes elastic scattering, i.e., positron + H(ls) yields positron + H(ls) and Ps(ls) yields Ps(ls) + p. The inelastic processes positron + H(ls) yields positron + H* Ps(ls) + p yields Ps* + p where * stands for a state other than ls, are implicitly taken into account through the optical potentials, which also allow for polarization of H(ls) and Ps(ls).

  15. Scope and limitations of high energy electron scattering in obtaining relevant structural information about atoms and molecules

    SciTech Connect

    Ketkar, S.N.

    1984-01-01

    During the course of this work experiments were undertaken to measure the scattering cross-sections for high energy electrons scattering from various target systems. The experiments can be broadly classified into two categories, one dealing with rather small systems and the other dealing with large systems (at least in the view of physicists). Although the experimental aspects, in so much as the experimental measurement of the intensities of the scattered electron is concerned, is the same for both the cases the motivation for performing the experiment is totally different. In the first case, simple atomic and molecular target systems, namely He, H/sub 2/ and D/sub 2/, are used. For such systems, good theoretical framework is available and critical comparisons of experimental cross sections are made with theoretical predictions. Attention is focussed mainly at small momentum transfer (up to 10A/sup -1/), and correlation and binding effects are studied. In the second case, somewhat larger molecular systems, namely naphthalene, anthraquinone, anthracene and dichromium tetraacetate are used. For such systems attention is focused at large momentum transfer (from 10 to 25 A/sup -1/) to obtain structural information about the molecules.

  16. Combined inelastic neutron scattering and solid state DFT study of dynamics of hydrogen atoms in trioctahedral 1M phlogopite

    SciTech Connect

    Smr?ok, ?ubomír [Institute of Inorganic Chemistry, Slovak Academy of Sciences, Bratislava, Slovak Republic; Kolesnikov, Alexander I [ORNL; Rieder, Milan [Czech Geological Survey, Praha, Czech Republic

    2012-01-01

    Inelastic neutron scattering (INS) was used to study vibrational dynamics of the hydrogen atoms in natural trioctahedral phlogopite, K0.93Na0.03(Mg2.47Fe0.22Al0.16Fe0.04Tl0.06)[Si2.84Al1.16]O10OH1.71F0.28Cl0.01, within the 50-1000 cm-1 energy range. The INS spectra collected using direct geometry spectrometer SEQUOIA at ORNL were interpreted by means of the solid-state DFT calculations covering both normal mode analysis and molecular dynamics. To optimize the structure and to calculate the vibrational modes under harmonic approximation both a hybrid PBE0 and the AM05 functional were used, while the molecular dynamics calculations (60ps/1fs) were performed only with the computationally less-demanding AM05 functional. The main contributions to the dominant band within ~750-550 cm-1 are symmetric and antisymmetric Mg-O-H bending modes, overlapping with the skeletal stretching and bending modes causing weaker secondary movements of H atoms of inner hydroxyl groups. Signatures of the Mg-O-H bending modes appear down to ~400 cm-1, where a region of octahedra deformation modes starts. These deformations cause just shallow movements of the hydrogen atoms and are mirrored by the modes with close vibrational energies. The region from ~330 cm-1 down to the low energy end of the spectrum portrays induced vibrations of the H atoms caused by deformation of individual polyhedra, translational vibrations of the parts of the 2:1 layer relative one to another, and librational and translational vibrations of the layer. The main difference between the INS spectrum of dioctahedral Al-muscovite and trioctahedral Mg-phlogopite is that the Mg-O-H modes are all assigned to in-plane vibrations of the respective hydrogen atoms.

  17. Measurements of helium 23S metastable atom density in low-pressure glow discharge plasmas by self-absorption spectroscopy of HeI 23S-23P transition

    NASA Astrophysics Data System (ADS)

    Shikama, Taiichi; Ogane, Shuhei; Ishii, Hidekazu; Iida, Yohei; Hasuo, Masahiro

    2014-08-01

    The helium 23S metastable atom densities are experimentally evaluated by self-absorption spectroscopy of the HeI 23S-23P transition spectra in two kinds of cylindrical glow discharge plasmas, which have different radii and are operated under different pressures of 300 and 20 Pa. The spectra are measured by using an interference spectroscopy system with a wavelength resolution of about 60 pm, and the relative intensities of the fine structure transitions are analyzed. It is found that the method is in principle applicable to plasmas with the pressure up to about the atmospheric pressure and electron density on the order of up to 1022 m-3. For a plasma with an absorption length of 10 mm and a spatially uniform temperature of 300 K, the method is sensitive to the metastable atom density roughly from 1016 to 1019 m-3.

  18. Nuclear forward scattering vs. conventional Mossbauer studies of atomically tailored Eu-based materials.

    SciTech Connect

    Konjhodzic, A.; Adamczyk, A.; Hasan, Z.; Alp, E. E.; Sturhahn, W.; Zhao, J.; Carroll, J. J.; Vagizov, F.; Univ. of Philadelphia; Youngstown State Univ.

    2006-01-01

    With the decrease in size of devices, rapid characterization of nano-devices is an inevitable necessity. It is shown that Moessbauer spectroscopy using synchrotron radiation from the advanced photon source provides such a tool of investigation. Results are presented and compared for conventional Moessbauer and Nuclear Forward Scattering for {sup 151}Eu-doped magnesium sulfide as an example, especially at low concentrations.

  19. Dynamics of hydrogen atoms in superoxide dismutase by quasielastic neutron scattering.

    PubMed Central

    Andreani, C; Filabozzi, A; Menzinger, F; Desideri, A; Deriu, A; Di Cola, D

    1995-01-01

    The low energy dynamic of the enzyme Cu,Zn superoxide dismutase have been investigated by means of quasielastic neutron scattering in the temperature range 4-320 K. Below 200 K the scattering is purely elastic, while above this temperature a pronounced decrease in the elastic intensity is observed, together with the onset of a small quasielastic component. This behavior is similar to that previously observed in other more flexible globular proteins, and can be attributed to transitions between slightly different conformational substates of the protein tertiary structure. The presence of only a small quasielastic component, whose intensity is < or = 25% of the total spectrum, is related to the high structural rigidity of this protein. PMID:7647254

  20. Low-energy electron scattering from Ca atoms and photodetachment of Ca{sup -}

    SciTech Connect

    Zatsarinny, Oleg; Bartschat, Klaus; Gedeon, Sergey; Gedeon, Viktor; Lazur, Vladimir [Department of Physics and Astronomy, Drake University, Des Moines, Iowa 50311 (United States); Department of Theoretical Physics, Uzhgorod State University, Uzhgorod 88000 (Ukraine)

    2006-11-15

    The B-spline R-matrix method is used to investigate electron scattering from neutral calcium and photodetachment of Ca{sup -} in the low-energy range from threshold to 4 eV. The multiconfiguration Hartree-Fock method with nonorthogonal orbital sets is employed for an accurate representation of the target wave functions. The close-coupling expansion includes 39 bound states of neutral calcium, covering all states from the ground state to 4s8s {sup 1}S. The present calculations yield good agreement with the few available experimental data for both elastic electron scattering and photodetachment of Ca{sup -}. The prominent resonance structure in the low-energy region is analyzed and discussed.

  1. Electron-impact excitation of the 6p7s {sup 3}P{sub 1} state of Pb atom at small scattering angles

    SciTech Connect

    Milisavljevic, S.; Rabasovic, M. S.; Sevic, D.; Marinkovic, B. P. [Institute of Physics, Pregrevica 118, 11080 Belgrade (Serbia); Pejcev, V. [Institute of Physics, Pregrevica 118, 11080 Belgrade (Serbia); Faculty of Natural Sciences, Radoja Domanovica 12, 34000 Kragujevac (Serbia); Filipovic, D. M. [Institute of Physics, Pregrevica 118, 11080 Belgrade (Serbia); Faculty of Physics, University of Belgrade, P. O. Box 368, 11001 Belgrade (Serbia); Sharma, Lalita; Srivastava, Rajesh [Department of Physics, Indian Institute of Technology, Roorkee 247667 (India); Stauffer, A. D. [Department of Physics and Astronomy, York University, Toronto, Canada M3J 1P3 (Canada)

    2007-05-15

    Electron-impact excitation of the 6p7s {sup 3}P{sub 1} state of Pb atom has been investigated both experimentally and theoretically. Differential cross sections (DCSs) were measured at incident electron energies of E{sub 0}=10, 20, 40, 60, 80, and 100 eV and small scattering angles up to 10 degree sign using a crossed electron-atom beam technique. The forward scattering function method has been used for determination of the absolute generalized oscillator strengths and DCS values. Corresponding relativistic distorted wave calculations have been performed and compared with experimental results.

  2. Sum rules and other properties involving resonance projection operators. [for optical potential description of electron scattering from atoms and ions

    NASA Technical Reports Server (NTRS)

    Berk, A.; Temkin, A.

    1985-01-01

    A sum rule is derived for the auxiliary eigenvalues of an equation whose eigenspectrum pertains to projection operators which describe electron scattering from multielectron atoms and ions. The sum rule's right-hand side depends on an integral involving the target system eigenfunctions. The sum rule is checked for several approximations of the two-electron target. It is shown that target functions which have a unit eigenvalue in their auxiliary eigenspectrum do not give rise to well-defined projection operators except through a limiting process. For Hylleraas target approximations, the auxiliary equations are shown to contain an infinite spectrum. However, using a Rayleigh-Ritz variational principle, it is shown that a comparatively simple aproximation can exhaust the sum rule to better than five significant figures. The auxiliary Hylleraas equation is greatly simplified by conversion to a square root equation containing the same eigenfunction spectrum and from which the required eigenvalues are trivially recovered by squaring.

  3. Characterisation of the polysaccharide produced by Acetobacter xylinum strain CR1/4 by light scattering and atomic force microscopy.

    PubMed

    Ridout, M J; Brownsey, G J; Gunning, A P; Morris, V J

    1998-11-01

    The molecular weight of the extracellular polysaccharide (CR1/4) produced by Acetobacter xylinum strain CR1/4 has been shown to be dependent upon growth conditions. Under normal growth conditions a high molecular weight polysaccharide ( > 1 x 10(6) Da) is produced. Maintaining the pH at 5 results in an order of magnitude increase in the total yield of polysaccharide, but also an order of magnitude decrease in molecular weight. Analysis of the CR1/4 polysaccharides by the techniques of atomic force microscopy and static light scattering suggests that they are double helices. In solution the molecules behave as stiff coils with a Kuhn statistical segment length of 325 nm. PMID:9849626

  4. ?-connectin studies by small-angle x-ray scattering and single-molecule force spectroscopy by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Marchetti, S.; Sbrana, F.; Toscano, A.; Fratini, E.; Carlà, M.; Vassalli, M.; Tiribilli, B.; Pacini, A.; Gambi, C. M. C.

    2011-05-01

    The three-dimensional structure and the mechanical properties of a ?-connectin fragment from human cardiac muscle, belonging to the I band, from I27 to I34, were investigated by small-angle x-ray scattering (SAXS) and single-molecule force spectroscopy (SMFS). This molecule presents an entropic elasticity behavior, associated to globular domain unfolding, that has been widely studied in the last 10 years. In addition, atomic force microscopy based SMFS experiments suggest that this molecule has an additional elastic regime, for low forces, probably associated to tertiary structure remodeling. From a structural point of view, this behavior is a mark of the fact that the eight domains in the I27-I34 fragment are not independent and they organize in solution, assuming a well-defined three-dimensional structure. This hypothesis has been confirmed by SAXS scattering, both on a diluted and a concentrated sample. Two different models were used to fit the SAXS curves: one assuming a globular shape and one corresponding to an elongated conformation, both coupled with a Coulomb repulsion potential to take into account the protein-protein interaction. Due to the predominance of the structure factor, the effective shape of the protein in solution could not be clearly disclosed. By performing SMFS by atomic force microscopy, mechanical unfolding properties were investigated. Typical sawtooth profiles were obtained and the rupture force of each unfolding domain was estimated. By fitting a wormlike chain model to each peak of the sawtooth profile, the entropic elasticity of octamer was described.

  5. Effects of Helium on Radiation Damage in Fusion Materials 7.On Helium Irradiation Damage in Non-Metallic Materials

    Microsoft Academic Search

    Shunsuke Muto

    2005-01-01

    Helium irradiation effects on non-metallic materials from an atomic to a macroscopic scale are reviewed from the viewpoint of fundamental lattice defects. Following a rough description of radiation damage phenomena in covalent and ionic materials, general but characteristic property changes associated with helium ion irradiation are introduced, taking the localized character of valence electrons incorporated in the atomic bonding into

  6. Sensitivity of ultracold-atom scattering experiments to variation of the fine-structure constant

    SciTech Connect

    Borschevsky, A.; Beloy, K. [Centre for Theoretical Chemistry and Physics, New Zealand Institute for Advanced Study, Massey University Auckland, Private Bag 102904, 0745 Auckland (New Zealand); School of Physics, University of New South Wales, Sydney 2052 (Australia); Flambaum, V. V. [School of Physics, University of New South Wales, Sydney 2052 (Australia); Centre for Theoretical Chemistry and Physics, New Zealand Institute for Advanced Study, Massey University Auckland, Private Bag 102904, 0745 Auckland (New Zealand); Schwerdtfeger, P. [Centre for Theoretical Chemistry and Physics, New Zealand Institute for Advanced Study, Massey University Auckland, Private Bag 102904, 0745 Auckland (New Zealand)

    2011-05-15

    We present numerical calculations for cesium and mercury to estimate the sensitivity of the scattering length to the variation of the fine-structure constant {alpha}. The method used follows the ideas of Chin and Flambaum [Phys. Rev. Lett. 96, 230801 (2006)], where the sensitivity to the variation of the electron-to-proton mass ratio {beta} was considered. We demonstrate that for heavy systems, the sensitivity to the variation of {alpha} is of the same order of magnitude as to the variation of {beta}. Near narrow Feshbach resonances, the enhancement of the sensitivity may exceed nine orders of magnitude.

  7. Bremsstrahlung in the scattering of low-energy electrons by neutral atomic systems. [in atmosphere of sun and cool stars

    NASA Technical Reports Server (NTRS)

    Gould, R. J.

    1985-01-01

    By elementary methods, the cross section for electron-atom and electron-molecule bremsstrahlung is computed in the limit when the incident electron energy is much less than Ry. The procedure employs the classical soft-photon emission probability formula for general (h/2pi)(omega), yielding a simple expression for the bremsstrahlung cross section in terms of the total elastic scattering cross section. The validity of the method is discussed, and results are compared with more elaborate and accurate calculations. Comparison is made with ('free-free') opacity calculations for the associated process at the temperature (6300 K) of the solar atmosphere. For chi sub omega = (h/2pi)(omega)/kT = 1, the computed absorption coefficient is within 2, 7, and 12 percent of accurate calculations for scatterings by H, He, and H2, respectively. The general dependence of the opacity on chi sub omega is described well by the simple formula, although the error is larger for higher chi sub omega; it is suggested that the inaccuracy at high frequencies is due to the failure of the soft-photon approximation.

  8. Atomic dynamics in molten AlCu alloys of different compositions and at different temperatures by cold neutron scattering

    NASA Astrophysics Data System (ADS)

    Dahlborg, U.; Besser, M.; Kramer, M. J.; Morris, J. R.; Calvo-Dahlborg, M.

    2013-03-01

    The atomic motions in molten Al1-xCux (x=0.10, 0.171 and 0.25) around the eutectic composition (x=0.171) were studied by cold neutron inelastic scattering at three different temperatures (973 K, 1173 K and 1373 K). An alloy of eutectic composition containing the 63Cu isotope was also studied. Self-diffusion coefficients for the Cu ions were determined from the width of quasielastic peaks and were found to decrease slightly with increasing Cu concentration. Longitudinal current correlation functions Jl(Q,E) exhibit at all temperatures and at all compositions a shoulder at energies below 10 meV and one main maximum at higher energies. These features can be interpreted in terms of excitations of acoustic and optic nature. The shape of Jl(Q,E) is sensitive to composition, being considerably more structured for larger Cu content. This can be coupled to the existence of a prepeak in the measured zeroth moment of dynamic scattering function indicating an increased chemical ordering with increasing Cu concentration for all temperatures. Indications for an existence of a liquid-liquid phase transition are presented.

  9. Atomic Probing Structures of Electrolytes at Graphene Surface: Insights from X-ray Scattering and Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Zhou, Hua; Fenter, Paul; Ganesh, Panchapakesan; Kent, Paul; Jiang, Deen; Chialvo, Ariel; Fulvio, Pasquale; Dai, Sheng; Feng, Guang; Rouha, Michael; Cummings, Peter; Presser, Volker; McDonough, Jake; Gogotsi, Yuri; Wander, Matthew; Shuford, Kevin

    2012-02-01

    The interactions of electrolyte fluids with carbon-based electrodes control many complex interfacial processes encountered in electrochemical energy storage systems. However, our knowledge of the atomic/nanoscale reactivity at interfaces of electrolytes with electrodes remain scares due to the incomplete understanding of interfacial structures and processes in-situ and real-time encountered in real operation conditions. In this talk, we will present our efforts to obtain a molecular-scale perspective of the interactions of electrolytes with carbon surfaces near ``real world'' conditions. Structures of various electrolytes including slat aqueous and ionic liquids on atomically flat graphene (epitaxially grown on a SiC substrate), an ideal model fluid-solid interface system, were investigated by coupling high-resolution interface X-ray scattering techniques with molecular modeling-simulation approaches. These results provide a base-line for understanding relevant electrolyte/carbon interactions and will lead to fundamentally new insights and provide unique tests of atomistic fluid-solid interface models for energy storage systems.

  10. Energy transfer in O collisions with He isotopes and helium escape from Mars

    NASA Astrophysics Data System (ADS)

    Bovino, S.; Zhang, P.; Kharchenko, V.; Dalgarno, A.

    2010-12-01

    Helium is one of the dominant constituents in the upper atmosphere of Mars [1]. Thermal (Jeans’) escape of He is negligible on Mars [2] and major mechanism of escape is related to the collisional ejection of He atoms by energetic oxygen. Collisional ejection dominates over ion-related mechanisms [3] and evaluation of the escape flux of neutral He becomes an important issue. The dissociative recombination of O2+ is considered to be the major source of energetic oxygen atoms [4]. We report accurate data on energy-transfer collisions between hot oxygen atoms and the atmospheric helium gas. Angular dependent scattering cross sections for elastic collisions of O(3P) and O(1D) atoms with helium gas have been calculated quantum mechanically and found to be surprisingly similar. Cross sections, computed for collisions with both helium isotopes, 3He and 4He, have been used to construct the kernel of the Boltzmann equation, describing the energy relaxation of hot oxygen atoms. Computed rates of energy transfer in O + He collisions have been used to evaluate the flux of He atoms escaping from the Mars atmosphere at different solar conditions. We have identified atmospheric layers mostly responsible for production of the He escape flux. Our results are consistent with recent data from Monte Carlo simulations of the escape of O atoms: strong angular anisotropy of atomic cross sections leads to an increased transparency of the upper atmosphere for escaping O flux [5] and stimulate the collisional ejection of He atoms. References [1] Krasnopolsky, V. A., and G. R. Gladstone (2005), Helium on Mars and Venus: EUVE observations and modeling, Icarus, 176, 395. [2] Chassefiere E. and F. Leblanc (2004), Mars atmospheric escape and evolution; interaction with the solar wind, Planetary and Space Science, 52, 1039 [3] Krasnopolsky, V. (2010), Solar activity variations of thermospheric temperatures on Mars and a problem of CO in the lower atmoshpere, Icarus, 207, 638. [4] Fox, J. L. (1995), On the escape of oxygen and hydrogen from Mars, Geophy. Rev. Lett., 20, 1847. [5] Krestyanikova, M. A. and V. I. Shematovich (2006), Stochastic models of hot planetary and satellite coronas: a hot oxygen corona of Mars, Solar System Research, 40, 384.

  11. Note: Mechanical etching of atomic force microscope tip and microsphere attachment for thermal radiation scattering enhancement

    SciTech Connect

    Brissinger, D.; Parent, G., E-mail: gilles.parent@univ-lorraine.fr; Lacroix, D. [Université de Lorraine, LEMTA, UMR 7563, BP70239, 54500 Vandoeuvre-lés-Nancy (France)] [Université de Lorraine, LEMTA, UMR 7563, BP70239, 54500 Vandoeuvre-lés-Nancy (France)

    2013-12-15

    This Note describes a mechanical etching technique which can be used to prepare silicon tips used in atomic force microscopy apparatus. For such devices, dedicated tips with specific shapes are now commonly used to probe surfaces. Yet, the control of the tip morphology where characteristic scales are lower than 1 ?m remains a real challenge. Here, we detail a controlled etching process of AFM probes apex allowing micrometer-sized sphere attachment. The technique used and influent parameters are discussed and SEM images of the achieved tips are given. Deceptive problems and drawbacks that might occur during the process are also covered.

  12. The spatio-temporal distribution of He (23S1) metastable atoms in a MHz-driven helium plasma jet is influenced by the oxygen/nitrogen ratio of the surrounding atmosphere

    NASA Astrophysics Data System (ADS)

    Winter, J.; Santos Sousa, J.; Sadeghi, N.; Schmidt-Bleker, A.; Reuter, S.; Puech, V.

    2015-04-01

    The density of helium He (23S1) metastable atoms is measured in a 1.6 mm diameter MHz-driven atmospheric pressure helium plasma jet by laser absorption spectroscopy with spatial and temporal resolution. The surrounding atmosphere of the jet is varied from pure oxygen to pure nitrogen with a gas shielding device. The highest metastable density of 1.3 × 1013 cm?3 is obtained in the center of the jet close to the nozzle exit at normal atmospheric air conditions. Within 0.3 mm in the radial direction and 2 mm in the axial direction, the He metastable density drops below the detection limit. The obtained He metastable lifetime is almost independent of the shielding gas composition. By analyzing the diffusion of shielding gas species into the effluent it is concluded that their density is too low to explain the observed He metastable lifetime. Instead, impurities from the feed gas, especially water molecules, are more likely to be responsible. However, a drastic change in metastable He density is observed when decreasing the amount of oxygen in the shielding gas. The lower the oxygen amount, the lower the metastable He density. For pure nitrogen, no He metastables are detected at all. By exchanging nitrogen with argon, a similar behavior is observed. Thus, it is concluded that it is the absence of ambient oxygen rather than the elevated presence of nitrogen, which is responsible for the observed decrease in the He (23S1) density.

  13. Atomic Mass Dependence of Hadron Production in Deep Inelastic Scattering on Nuclei

    E-print Network

    A. Accardi; D. Grunewald; V. Muccifora; H. J. Pirner

    2005-10-27

    Hadron production in lepton-nucleus deep inelastic scattering is studied in an absorption model. In the proposed model, the early stage of hadronization in the nuclear medium is dominated by prehadron formation and absorption, controlled by flavor-dependent formation lengths and absorption cross sections. Computations for hadron multiplicity ratios are presented and compared with the HERMES experimental data for pions, kaons, protons and antiprotons. The mass-number dependence of hadron attenuation is shown to be sensitive to the underlying hadronization dynamics. Contrary to common expectations for absorption models, a leading term proportional to A^{2/3} is found. Deviations from the leading behavior arise at large mass-numbers and large hadron fractional momenta.

  14. Detection of Negative Charge Carriers in Superfluid Helium Droplets: The Metastable Anions He*– and He2*–

    PubMed Central

    2014-01-01

    Helium droplets provide the possibility to study phenomena at the very low temperatures at which quantum mechanical effects are more pronounced and fewer quantum states have significant occupation probabilities. Understanding the migration of either positive or negative charges in liquid helium is essential to comprehend charge-induced processes in molecular systems embedded in helium droplets. Here, we report the resonant formation of excited metastable atomic and molecular helium anions in superfluid helium droplets upon electron impact. Although the molecular anion is heliophobic and migrates toward the surface of the helium droplet, the excited metastable atomic helium anion is bound within the helium droplet and exhibits high mobility. The atomic anion is shown to be responsible for the formation of molecular dopant anions upon charge transfer and thus, we clarify the nature of the previously unidentified fast exotic negative charge carrier found in bulk liquid helium. PMID:25068008

  15. Gain and continuous-wave laser oscillation on the 1315 nm atomic iodine transition pumped by an air-helium electric discharge

    E-print Network

    Carroll, David L.

    Gain and continuous-wave laser oscillation on the 1315 nm atomic iodine transition pumped by an air on the 1315 nm transition of atomic iodine using the energy transferred to I 2 P1/2 from O2 a1 produced American Institute of Physics. DOI: 10.1063/1.2957678 The classical chemical oxygen iodine laser COIL re

  16. Growing metal nanoparticles in superfluid helium

    NASA Astrophysics Data System (ADS)

    Yang, Shengfu; Ellis, Andrew M.; Spence, Daniel; Feng, Cheng; Boatwright, Adrian; Latimer, Elspeth; Binns, Chris

    2013-11-01

    Helium droplets provide a cold and confined environment where atomic and/or molecular dopants can aggregate into clusters and nanoparticles. In particular, the sequential addition of different materials to helium droplets can lead to the formation of a wide range of nanoparticles, including core-shell nanoparticles, which can then be deposited onto a surface. Here we briefly discuss the fundamental properties of helium droplets and then address their implications for the formation of clusters and nanoparticles. Several key experiments on atomic and molecular clusters will be highlighted and new results obtained for nanoparticles formed in this way will be presented. Finally, the versatility, the limitations and new possibilities provided by superfluid helium droplets in nanoscience and nanotechnology will be addressed.

  17. Requirements, possible alternatives & international NEUTRON SCATTERING

    E-print Network

    Dimeo, Robert M.

    Requirements, possible alternatives & international NEUTRON SCATTERING DETECTORS for Rob Dimeo NIST neutron scattering instruments are the most demanding require background low #12;#12;The Helium-3 Supply Crisis ­ Alternative Techniques to Helium-3 based Detectors for Neutron Scattering Applications

  18. Investigation of electron-atom/molecule scattering resonances: Two complex multiconfigurational self-consistent field approaches

    NASA Astrophysics Data System (ADS)

    Samanta, Kousik; Yeager, Danny L.

    2015-01-01

    Resonances are temporarily bound states which lie in the continuum part of the Hamiltonian. If the electronic coordinates of the Hamiltonian are scaled ("dilated") by a complex parameter, ? = ?ei? (?, ? real), then its complex eigenvalues represent the scattering states (resonant and non-resonant) while the eigenvalues corresponding to the bound states and the ionization and the excitation thresholds remain real and unmodified. These make the study of these transient species amenable to the bound state methods. We developed a quadratically convergent multiconfigurational self-consistent field method (MCSCF), a well-established bound-state technique, combined with a dilated Hamiltonian to investigate resonances. This is made possible by the adoption of a second quantization algebra suitable for a set of "complex conjugate biorthonormal" spin orbitals and a modified step-length constraining algorithm to control the walk on the complex energy hypersurface while searching for the stationary point using a multidimensional Newton-Raphson scheme. We present our computational results for the 2P Be- shape resonances using two different computationally efficient methods that utilize complex scaled MCSCF (i.e., CMCSCF). These two methods are to straightforwardly use CMCSCF energy differences and to obtain energy differences using an approximation to the complex multiconfigurational electron propagator. It is found that, differing from previous computational studies by others, there are actually two 2P Be- shape resonances very close in energy. In addition, N2 resonances are examined using one of these methods.

  19. Formation of hydrogen atom in 2s state in proton–sodium inelastic scattering

    NASA Astrophysics Data System (ADS)

    Sabbah, A. Elkilany

    2015-03-01

    The inelastic collision of protons with sodium atoms are treated for the first time within the framework of the coupled-static and frozen core approximations. The method is used for calculating partial and total cross-sections with the assumption that only two channels (elastic and hydrogen formation in 2s state) are open. In each case, the calculations are carried out for seven values of the total angular momentum ?(0 ? ? ? 6). The target is described using the Clementi Roetti wave functions within the framework of the one valence electron model. We use Lipmann–Swinger equation to solve the derived equations of the problem, then apply an iterative numerical method to obtain the code of computer to calculate iterative partial cross-sections. This can be done through calculating the reactance matrix at different values of considered energies to obtain the transition matrix that gives partial and total cross sections. The present results for total hydrogen (2s state) formation cross sections are in agreement with results of other available ones in wide range of incident energy.

  20. Application of Lna Lasers to Helium Optical Pumping

    Microsoft Academic Search

    James Gregory Lynn

    1990-01-01

    Electron spin-polarized helium 2^3 S_1 metastable atoms are a valuable probe of spin-dependent phenomena. Helium metastable atoms can be polarized by illumination with circularly -polarized 1.083 mum 2^3 S_1 rightarrow 2^3P_{0,1,2 } resonance radiation in a process known as optical pumping. Metastable atom polarizations obtained in this manner have been limited by the low intensity of optical pumping radiation available

  1. [Atomic beam studies of the interaction of hydrogen with transition metal surfaces

    SciTech Connect

    Not Available

    1992-01-01

    We have constructed two experimental facilities during the term of this grant. In the first three years we constructed a helium atom scattering (HAS) facility with both elastic (EHAS) and inelastic (IHAS) scattering measurement capabilities to investigate the structural and dynamical aspects of solid surfaces and thin films. A pioneering surface metastable atom magnetic diffraction (SMAMD) facility was constructed and developed over the past four years, which makes possible the investigation of long-range electron spin-ordering on the surfaces of insulating magnetic crystals. The following were studied: H overlayers and Ag, Cu on Pd(111), reconstructed Au(111), and NiO(100).

  2. Expansion coefficients of scattering parameters in quantum thermodynamic perturbation theory

    SciTech Connect

    Buendia, E.; Guardiola, R. (Departamento de Fisica Moderna, Universidad de Granada Granada, Spain, 18071 (ES)); De Llano, M. (Physics Department, North Dakota State University, Fargo, North Dakota 58105)

    1989-07-01

    We tabulate the expansion coefficients of various scattering parameters associated with several interparticle pair potentials used in the quantum thermodynamic perturbation theory of strongly coupled, many-particle substances. The expansion is in powers or the attractive part of the pair potential. The potential is divided into repulsive and attractive parts according to several methods in vogue both in classical and in quantum equation-of-state studies of condensed-matter systems. Results are reported for several interparticle potentials of helium-3 and -4 atoms, of the three electron spin-polarized isotopes of atomic hydrogen, and of the nucleon.

  3. NIST Form Factor, Attenuation, and Scattering Tables

    NSDL National Science Digital Library

    The National Institute of Standards and Technology has published the article, NIST Form Factor, Attenuation, and Scattering Tables. This paper describes and computes "the primary interactions of x-rays with isolated atoms from Z=1(hydrogen) to Z=92(uranium) within a self-consistent Dirac-Hartree-Fock framework." Sections included in the paper are Introduction and Importance of Form Factors, Form Factors and Standard Definitions, Available Tabulations and Basis of Current Formalism, Basic Transform Equations, Avoidance of Singularities, Avoidance of Imprecision, Integration Precision Requirements, Choice of Interpolation Formalism, and Results for Hydrogen and Helium, among others.

  4. Scattering processes in Bose-Einstein condensed systems

    NASA Astrophysics Data System (ADS)

    Wynveen, Aaron Sundby

    Unambiguous proof of the existence of Bose condensation in superfluid helium has long eluded researchers ever since condensation was hypothesized to be responsible for superfluidity sixty years ago. Both experimentalists and theorists have been stymied in this effort due to the complexity of this system. Our group has predicted, though, a means by which Bose condensation may be directly probed via a condensate mediated transmission process. Experiments in which helium beams are transmitted through a superfluid to provide information concerning the condensate nature of helium have been undertaken by our group. In the context of these experiments, we have carried out theoretical and computational studies of this process in weakly interacting systems in which calculations may be readily performed. These studies have demonstrated that there exists effective transparency of the condensate to the scattering atoms in these weakly interacting systems similar to that predicted for helium. Dissipation, which may screen the condensate mediated process, has also been shown to be negligible in the weakly interacting systems. Simulations of the helium beams used in the transmission experiments have also been developed. By combining gas dynamics with a hydrodynamic simulation, we have been able to explore a broader range of experimental regimes and thus were able to simulate the anomalous signals observed in the beam experiments. A full characterization of these beams is necessary for correct interpretation of the transmitted signals, and the results of the simulations have led to beneficial modifications to the transmission experiment. And finally, we have presented another means by which condensation may be studied in helium by analyzing the motion of small helium drops through a background helium vapor.

  5. Protein Dynamics and Stability: The Distribution of Atomic Fluctuations in Thermophilic and Mesophilic Dihydrofolate Reductase Derived Using Elastic Incoherent Neutron Scattering

    PubMed Central

    Meinhold, Lars; Clement, David; Tehei, Moeava; Daniel, Roy; Finney, John L.; Smith, Jeremy C.

    2008-01-01

    The temperature dependence of the dynamics of mesophilic and thermophilic dihydrofolate reductase is examined using elastic incoherent neutron scattering. It is demonstrated that the distribution of atomic displacement amplitudes can be derived from the elastic scattering data by assuming a (Weibull) functional form that resembles distributions seen in molecular dynamics simulations. The thermophilic enzyme has a significantly broader distribution than its mesophilic counterpart. Furthermore, although the rate of increase with temperature of the atomic mean-square displacements extracted from the dynamic structure factor is found to be comparable for both enzymes, the amplitudes are found to be slightly larger for the thermophilic enzyme. Therefore, these results imply that the thermophilic enzyme is the more flexible of the two. PMID:18310248

  6. Protein Dynamics and Stability: The Distribution of Atomic Fluctuations in Thermophilic and Mesophilic Dihydrofolate Reductase Derived Using Elastic Incoherent Neutron Scattering

    SciTech Connect

    Meinhold, Lars [University of Heidelberg; Clement, David [University of Waikato, New Zealand; Tehei, M [University of Waikato, New Zealand; Daniel, R. M. [University of Waikato, New Zealand; Finney, J.L. [University College, London; Smith, Jeremy C [ORNL

    2008-11-01

    The temperature dependence of the dynamics of mesophilic and thermophilic dihydrofolate reductase is examined using elastic incoherent neutron scattering. It is demonstrated that the distribution of atomic displacement amplitudes can be derived from the elastic scattering data by assuming a (Weibull) functional form that resembles distributions seen in molecular dynamics simulations. The thermophilic enzyme has a significantly broader distribution than its mesophilic counterpart. Furthermore, although the rate of increase with temperature of the atomic mean-square displacements extracted from the dynamic structure factor is found to be comparable for both enzymes, the amplitudes are found to be slightly larger for the thermophilic enzyme. Therefore, these results imply that the thermophilic enzyme is the more flexible of the two.

  7. Differential cross-section for positronium formation in electron-atomic hydrogen collisions

    NASA Technical Reports Server (NTRS)

    Drachman, R. J.; Omidvar, K.; Mcguire, J. H.

    1976-01-01

    The L=0 and 1 partial wave amplitudes obtained by a two-state coupled static approximation with correlation with the L greater than or equal to 2 Born amplitudes were combined to obtain the differential cross section for positronium formation in electron-atomic hydrogen collisions. For positron energies of 0.64 and 0.75 ryd, minima at the scattering angles of 57 deg and 51 deg are found. Total cross sections for positronium formation for low and intermediate impact energies are given. Measurement of the differential cross section for the process positron + helium yields positronium + helium ion for the detection of possible minima is suggested.

  8. New power source from fractional quantum energy levels of atomic hydrogen that surpasses internal combustion

    Microsoft Academic Search

    R. L. Mills; P. Ray; B. Dhandapani; M. Nansteel; X. Chen; J. He

    2002-01-01

    Extreme ultraviolet (EUV) spectroscopy was recorded on microwave discharges of helium with 2% hydrogen. Novel emission lines were observed with energies of q·13.6eV where q=1,2,3,4,6,7,8,9, or 11 or these lines inelastically scattered by helium atoms wherein 21.2eV was absorbed in the excitation of He (1s2) to He (1s12p1). These lines were identified as hydrogen transitions to electronic energy levels below

  9. Polarization phase matrices for radiation scattering on atoms in external magnetic fields: The case of forbidden transitions in astrophysics

    E-print Network

    Oo, Yee Yee; Sampoorna, M; Nagendra, K N; Ramachandran, G

    2008-01-01

    Using a quantum electrodynamical approach, we derive the scattering phase matrices for polarized radiation involving forbidden line transitions and in the presence of an external magnetic field. The case of (J=0->2->0) scattering is considered as an example. The non-magnetic Rayleigh scattering phase matrix is also presented. The Stokes profiles in a single scattering event are computed for the strong field (Zeeman) and weak field (Hanle) limits, covering also the regime of intermediate field strengths (Hanle- Zeeman).

  10. Polarization phase matrices for radiation scattering on atoms in external magnetic fields: The case of forbidden transitions in astrophysics

    E-print Network

    Yee Yee Oo; Phyu Phyu San; M. Sampoorna; K. N. Nagendra; G. Ramachandran

    2008-05-26

    Using a quantum electrodynamical approach, we derive the scattering phase matrices for polarized radiation involving forbidden line transitions and in the presence of an external magnetic field. The case of (J=0->2->0) scattering is considered as an example. The non-magnetic Rayleigh scattering phase matrix is also presented. The Stokes profiles in a single scattering event are computed for the strong field (Zeeman) and weak field (Hanle) limits, covering also the regime of intermediate field strengths (Hanle- Zeeman).

  11. Core scattering of quadratic Zeeman orbits in barium

    SciTech Connect

    Liu Hongping; Zhan Mingsheng [State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China); Center for Cold Atom Physics, Chinese Academy of Sciences, Wuhan 430071 (China); Quan Wei; Shen Li [State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China); Center for Cold Atom Physics, Chinese Academy of Sciences, Wuhan 430071 (China); Graduate School of Chinese Academy of Sciences, Beijing 100080 (China); Connerade, Jean-Patrick [Quantum Optics and Laser Science Group, Blackett Laboratory, Imperial College, London SW7 2BW (United Kingdom); State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China)

    2007-07-15

    We report a method to uncover the peaks due to scattering of quadratic Zeeman orbits by the atomic core of a many-electron atom. The method is experimental, and consists in identifying the supernumerary peaks in the scaled-energy spectra by comparing them with the corresponding hydrogenic calculations using closed-orbit theory. The scaled actions of the observed additional peaks correspond to combining the scaled actions of individual closed orbits, except for a small blueshift, which is explainable as a core-induced interaction, depending on the penetration of the orbits. Our method is related to earlier theoretical studies of helium, but can be applied to any experimentally accessible atom, including those with large cores. We show that, for barium, core-scattering processes do indeed occur, and that they are confined to a specific portion of the scaled-energy spectrum.

  12. Rethermalizing collisions between magnetically trapped metastable neon atoms

    NASA Astrophysics Data System (ADS)

    Mogendorff, V. P.; Claessens, B. J.; Kuppens, S. J. M.; Vredenbregt, E. J. D.; Beijerinck, H. C. W.

    2002-05-01

    The successful Bose-Einstein Condensation (BEC) of alkali atoms has stimulated several groups to extend the range to metastable rare gas atoms. In 2001 this resulted in the achievement of BEC with metastable helium atoms (He^*) [1,2]. The only other rare gas atom suitable for achieving BEC is neon. The goal of our group is BEC of metastable neon (Ne^*). A condensate of metastable rare gas atoms is of special interest because their large internal energy enables real time diagnostics of the sample during condensation, giving new insight into the dynamics of the phase transition. Crucial for achieving BEC is a large (positive) scattering length. For He^* a good estimate of the order of magnitude of the scattering length was known. For neon no such theoretical estimate exists, therefore, experimental data on the value of the scattering length is necessary to determine whether or not BEC is feasible for Ne^*. In recent thermalization experiments involving two RF-knives, similar to the scheme used by Aspect et al. [3], we have observed rethermalizing collisions in our magnetic trap. Moreover, preliminary measurements point in the direction of a large absolute value of the scattering length. In this presentation we will discuss these thermalization experiments, and hope to present a value of the scattering length. [1] A. Robert et al., Science 292, 461 (2001). [2] F.P. Dos-Santos et al., Phys. Rev. Lett. 86, 3459 (2001). [3] A. Browaeys et al., Phys. Rev. A. 64, 034703 (2001).

  13. Equation of state of metallic helium

    SciTech Connect

    Shvets, V. T., E-mail: tarval@breezein.net [Odessa State Academy of Refrigeration (Ukraine)

    2013-01-15

    The effective ion-ion interaction, free energy, pressure, and electric resistance of metallic liquid helium have been calculated in wide density and temperature ranges using perturbation theory in the electron-ion interaction potential. In the case of conduction electrons, the exchange interaction has been taken into account in the random-phase approximation and correlations have been taken into account in the local-field approximation. The solid-sphere model has been used for the nuclear subsystem. The diameter of these spheres is the only parameter of this theory. The diameter and density of the system at which the transition of helium from the singly ionized to doubly ionized state occurs have been estimated by analyzing the pair effective interaction between helium atoms. The case of doubly ionized helium atoms has been considered. Terms up to the third order of perturbation theory have been taken into account in the numerical calculations. The contribution of the third-order term is significant in all cases. The electric resistance and its temperature dependence for metallic helium are characteristic of simple divalent metals in the liquid state. The thermodynamic parameters-temperature and pressure densities-are within the ranges characteristic of the central regions of giant planets. This makes it possible to assume the existence of helium in the metallic state within the solar system.

  14. Elastic cross sections for electron scattering from GeF4: predominance of atomic-F in the high-energy collision dynamics.

    PubMed

    Kato, H; Suga, A; Hoshino, M; Blanco, F; García, G; Limão-Vieira, P; Brunger, M J; Tanaka, H

    2012-04-01

    We report absolute differential cross sections (DCSs) for elastic electron scattering from GeF(4). The incident electron energy range was 3-200 eV, while the scattered electron angular range was typically 15°-150°. In addition, corresponding independent atom model (IAM) calculations, within the screened additivity rule (SCAR) formulation, were also performed. Those results, particularly for electron energies above about 10 eV, were found to be in good quantitative agreement with the present experimental data. Furthermore, we compare our GeF(4) elastic DCSs to similar data for scattering from CF(4) and SiF(4). All these three species possess T(d) symmetry, and at each specific energy considered above about 50 eV their DCSs are observed to be almost identical. These indistinguishable features suggest that high-energy elastic scattering from these targets is virtually dominated by the atomic-F species of the molecules. Finally, estimates for the measured GeF(4) elastic integral cross sections are derived and compared to our IAM-SCAR computations and with independent total cross section values. PMID:22482558

  15. Helium on Venus - Implications for uranium and thorium

    NASA Technical Reports Server (NTRS)

    Prather, M. J.; Mcelroy, M. B.

    1983-01-01

    Helium is removed at an average rate of 10 to the 6th atoms per square centimeter per second from Venus's atmosphere by the solar wind following ionization above the plasmapause. The surface source of helium-4 on Venus is similar to that on earth, suggesting comparable abundances of crustal uranium and thorium.

  16. Spectroscopic studies of OCS-doped 4He clusters with 9-72 helium atoms: observation of broad oscillations in the rotational moment of inertia.

    PubMed

    McKellar, A R W; Xu, Yunjie; Jäger, Wolfgang

    2007-08-01

    High-resolution spectra of HeN-OCS clusters with N up to 39 in the microwave region and up to 72 in the infrared region were observed with apparatus-limited line widths of about 15 kHz and 0.001 cm(-1), respectively. The cold (approximately 0.2 K) clusters were produced in pulsed supersonic jet expansions of very dilute OCS + He mixtures and probed using a microwave Fourier transform spectrometer or a tunable infrared diode laser spectrometer. Consistent analyses of the microwave and infrared data yield band origins for the carbonyl stretching vibration, together with rotational parameters for the ground and excited vibrational states. The rotational constant, B, passes through a minimum at N = 9 and then rises as the He atoms uncouple from the OCS rotational motion as a result of superfluid effects. There are broad unexpected oscillations in B, with maxima at N = 24 and 47 and minima at N = 36 and 62. The change in B upon vibrational excitation, which is negative for the OCS molecule, converges to positive values for N > 15. These results help to bridge the gap between individual molecules and bulk matter with atom-by-atom resolution over a significant range of cluster sizes. PMID:17455923

  17. A portable helium sniffer

    USGS Publications Warehouse

    Friedman, Irving; Denton, E.H.

    1976-01-01

    A portable helium sniffer has been developed for field use. The instrument is mounted in a four-wheel-drive pickup truck and can detect 50 parts per billion of helium in soil gas. The usefulness of helium sniffing in soil is being investigated as a prospecting tool in gas, oil, uranium, and geothermal prospecting as well as in earthquake prediction.

  18. Tungsten Helium cooled Target

    E-print Network

    McDonald, Kirk

    Rotating Tungsten Helium cooled Target RoTHeTa Cyril Kharoua Daniela Ene, Ferenc Mezei, Etam Noah 2011 Some history >Granular Tungsten target helium cooled was first proposed by Peter Sievers for a MW a rotating wheel, fitted with tungsten rods and cooled with helium is a viable solution... #12;Page 4Cyril

  19. Helium-Recycling Plant

    NASA Technical Reports Server (NTRS)

    Cook, Joseph

    1996-01-01

    Proposed system recovers and stores helium gas for reuse. Maintains helium at 99.99-percent purity, preventing water vapor from atmosphere or lubricating oil from pumps from contaminating gas. System takes in gas at nearly constant low back pressure near atmospheric pressure; introduces little or no back pressure into source of helium. Concept also extended to recycling of other gases.

  20. Rapidly pulsed helium droplet source

    SciTech Connect

    Pentlehner, Dominik; Riechers, Ricarda; Dick, Bernhard; Slenczka, Alkwin [Institute for Physical and Theoretical Chemistry, University of Regensburg, 93053 Regensburg (Germany); Even, Uzi; Lavie, Nachum; Brown, Raviv; Luria, Kfir [Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv (Israel)

    2009-04-15

    A pulsed valve connected to a closed-cycle cryostat was optimized for producing helium droplets. The pulsed droplet beam appeared with a bimodal size distribution. The leading part of the pulse consists of droplets suitable for doping with molecules. The average size of this part can be varied between 10{sup 4} and 10{sup 6} helium atoms, and the width of the distribution is smaller as compared to a continuous-flow droplet source. The system has been tested in a single pulse mode and at repetition rates of up to 500 Hz with almost constant intensity. The droplet density was found to be increased by more than an order of magnitude as compared to a continuous-flow droplet source.

  1. Warm Breeze from the Starboard Bow: a New Population of Neutral Helium in the Heliosphere

    NASA Astrophysics Data System (ADS)

    Kubiak, M. A.; Bzowski, M.; Sokó?, J. M.; Swaczyna, P.; Grzedzielski, S.; Alexashov, D. B.; Izmodenov, V. V.; Möbius, E.; Leonard, T.; Fuselier, S. A.; Wurz, P.; McComas, D. J.

    2014-08-01

    We investigate the signals from neutral helium atoms observed in situ from Earth orbit in 2010 by the Interstellar Boundary Explorer (IBEX). The full helium signal observed during the 2010 observation season can be explained as a superposition of pristine neutral interstellar He gas and an additional population of neutral helium that we call the Warm Breeze. The Warm Breeze is approximately 2 times slower and 2.5 times warmer than the primary interstellar He population, and its density in front of the heliosphere is ~7% that of the neutral interstellar helium. The inflow direction of the Warm Breeze differs by ~19° from the inflow direction of interstellar gas. The Warm Breeze seems to be a long-term, perhaps permanent feature of the heliospheric environment. It has not been detected earlier because it is strongly ionized inside the heliosphere. This effect brings it below the threshold of detection via pickup ion and heliospheric backscatter glow observations, as well as by the direct sampling of GAS/Ulysses. We discuss possible sources for the Warm Breeze, including (1) the secondary population of interstellar helium, created via charge exchange and perhaps elastic scattering of neutral interstellar He atoms on interstellar He+ ions in the outer heliosheath, or (2) a gust of interstellar He originating from a hypothetic wave train in the Local Interstellar Cloud. A secondary population is expected from models, but the characteristics of the Warm Breeze do not fully conform to modeling results. If, nevertheless, this is the explanation, IBEX-Lo observations of the Warm Breeze provide key insights into the physical state of plasma in the outer heliosheath. If the second hypothesis is true, the source is likely to be located within a few thousand AU from the Sun, which is the propagation range of possible gusts of interstellar neutral helium with the Warm Breeze characteristics against dissipation via elastic scattering in the Local Cloud. Whatever the nature of the Warm Breeze, its discovery exposes a critical new feature of our heliospheric environment.

  2. Thermodynamic properties of hydrogen-helium plasmas

    NASA Technical Reports Server (NTRS)

    Nelson, H. F.

    1971-01-01

    The thermodynamic properties of an atomic hydrogen-helium plasma are calculated and tabulated for temperatures from 10,000 to 100,000 K as a function of the mass fraction ratio of atomic hydrogen. The tabulation is for densities from 10 to the minus 10th power to 10 to the minus 6th power gm/cu cm and for hydrogen mass fraction ratios of 0, 0.333, 0.600, 0.800, and 1.0, which correspond to pure helium, 50 percent hydrogen per unit volume, 75 percent hydrogen per unit volume, 89 percent hydrogen per unit volume, and pure hydrogen plasmas, respectively. From an appended computer program, calculations can be made at other densities and mass fractions. The program output agrees well with previous thermodynamic property calculations for limiting cases of pure hydrogen and pure helium plasmas.

  3. Atomic charge-exchange between semi-relativistic ( v/ c = 0.49) helium ions and targets from carbon to lead

    NASA Astrophysics Data System (ADS)

    Meharchand, R.; Akimune, H.; van den Berg, A. M.; Fujita, Y.; Fujiwara, M.; Galès, S.; Harakeh, M. N.; Hashimoto, H.; Hayami, R.; Hitt, G. W.; Itoh, M.; Kawabata, T.; Kawase, K.; Kinoshita, M.; Nakanishi, K.; Nakayama, S.; Okumura, S.; Shimbara, Y.; Uchida, M.; Yamagata, T.; Yosoi, M.; Zegers, R. G. T.

    2007-11-01

    Ratios of equilibrium charge-state yields for singly to doubly ionized 3He ions at an energy of 420 MeV were measured using the Grand Raiden magnetic spectrometer at RCNP. Targets with atomic numbers of 6, 12, 28, 40, 50 and 82 were used. It is found that theoretical calculations for atomic electron-capture and stripping cross sections, which have been successful in describing the data up to beam energies of 200 MeV, are also applicable at this higher energy. However, where at the lower energies the stripping cross sections were calculated with a combination of models by Bohr and Gillespie, the best description of the data at E( 3He) = 420 MeV is obtained when using only the model by Gillespie. The experimental results are also compared with calculations using the code CHARGE, originally developed for fast, heavy ( Z > 29) projectiles, to test the extrapolation to low- Z projectiles. It is found that the code underestimates the production of singly-charged 3He ions, in particular for heavier target nuclei.

  4. Helium in the Universe.

    NASA Astrophysics Data System (ADS)

    Tayler, R. J.

    1995-02-01

    The element helium was discovered on Earth in March 1895, although its existence had been suggested much earlier by J.N. Lockyer after unidentified spectral lines had been observed in a solar eclipse in 1868. Helium plays a major role in astronomy and cosmology. As a radioactive decay product, it helped to establish the great age of the Earth. Nuclear reactions, producing helium from hydrogen, power most stars and nuclear reactions involving helium are important in late stages of stellar evolution. All stars and gas clouds appear to contain substantial amounts of helium and this observation, together with the discovery and properties of the cosmic microwave radiation, is one of the two factors leading to the current popularity of the hot big-bang cosmological theory. Because helium is such a strongly bound nucleus, a single secure identification of a star or a gas cloud devoid of helium would cause great difficulties for the theory.

  5. On the Formation of the Resonance Lines of Helium in the Sun

    NASA Astrophysics Data System (ADS)

    Pietarila, Anna; Judge, Philip G.

    2004-05-01

    To investigate the cause of anomalously bright resonance lines of helium in the Sun, we have studied the magnitude of the enhancements and some proposals made to explain them. Calculations in new semiempirical solar models indicate that the resonance lines of helium are enhanced by factors of 2-5 for He I and between 2 and 9 for He II, depending on the elemental abundances assumed. These enhancements are substantially less than earlier work has suggested, with the differences arising from radiative transfer not only in helium lines but also in lines of less abundant elements. Photon scattering, even with small line center optical depths (of order unity or less) throughout the transition region, is shown to significantly modify line intensities and their center-to-limb variation. This effect has important consequences both for our analysis and also for the analysis of solar EUV lines in general, including emission measure analyses. We have re-examined some proposals to explain the enhancements based on the ``ionizing plasma'' picture. The proposals include explicit heating (the ``burst'' picture) and heating via advection (diffusive and/or flowing models and the ``velocity redistribution'' [VR] proposal). We argue that the original VR mechanism must be modified to include kinetic effects for helium atoms, which reduce the effects of VR. The VR mechanism also naturally predicts helium lines that are blue-shifted relative to lines less sensitive to VR, which contradicts observations for the He I 584 Å line. Ionizing plasma models also potentially lead to enhancement of ?n>=1 transitions (n is the principal quantum number) in other atoms and ions. Existing observational evidence for enhanced ?n>=1 transitions in other ions is weak. We conclude that the ionizing plasma scenarios are not the sole cause of the helium enhancement. Instead, in a companion paper, we propose that the thermodynamic properties of noble gases in the upper chromosphere will lead to enhancement of their spectral lines if cross-field diffusion into coronal plasma is important. Finally, we show that, surprisingly, multifluid flows of the kind computed by Fontenla and colleagues can reproduce observed intensities of several lines of C and Si and may contain a resolution to the helium enhancement problem.

  6. Hyperfine structure in hydrogen and helium ion

    Microsoft Academic Search

    Savely G. Karshenboima; D. I. Mendeleev

    The hyperfine structure (HFS) intervals of the ground state in a number of neutral atoms and singly charged ions can be measured with a high accuracy. However, theory even in the case of the simplest of them (such as hydrogen isotopes and the helium-3 ion) is essentially af- fected by nuclear structure effects which contribute from 30 to 200 ppm

  7. Cryogenic liquid-jet breakup in two-fluid atomizers

    NASA Technical Reports Server (NTRS)

    Ingebo, Robert D.

    1991-01-01

    A two-fluid atomizer was used to study the breakup of liquid-nitrogen jets in nitrogen, argon, and helium atomizing gas flows. A scattered-light scanner particle sizing instrument previously developed at NASA Lewis Research Center was further developed and used to determine characteristic drop diameters for the cryogenic sprays. In the breakup regime of aerodynamic-stripping, i.e., sonic-velocity conditions, the following correlation of the reciprocal Sauter mean diameter, D(sub 32)exp -1, with the atomizing-gas flowrate, W(g), was obtained: D(sub 32)exp -1 = k(sub c)(W(g)exp 1.33), where k(sub c) is a proportionality constant evaluated for each atomizing gas. Values of k(sub c) = 120, 220, and 1100 were obtained for argon, nitrogen, and helium gasflows, respectively. The reciprocal Sauter mean diameter and gas flowrate have the units of 1/cm and g/sec, respectively. In the regime of capillary-wave breakup, or subsonic conditions, it was found that D(sub 32)exp -1 = k(g)(W(g)exp 0.75), where k = 270, 390, and 880 for argon, nitrogen, and helium gasflows, respectively.

  8. The local interstellar helium density

    NASA Technical Reports Server (NTRS)

    Freeman, J.; Paresce, F.; Bowyer, S.; Lampton, M.; Stern, R.; Margon, B.

    1977-01-01

    During the Apollo-Soyuz Test Project, an extreme-ultraviolet telescope observed the region of the sky from which the interstellar medium approaches the sun. The instrument had a tin filter whose bandpass included the 584-A line of neutral helium. The observations set an upper bound for the number density of neutral helium in the local interstellar medium of 0.004 + or - 0.0022 per cu cm, which is significantly lower than previously reported. The stated error is dominated by the present uncertainty in the solar 584-A flux, which is taken to be approximately 200 million photons/sq cm per sec at earth's orbit. The result is not consistent with previous resonant-scattering Ly-alpha observations of interstellar hydrogen passing through the solar system, which generally yield a hydrogen number density of about 0.1 per cu cm, unless interstellar helium is locally depleted below its cosmic abundance. The result is consistent with cosmic abundances if the much lower average hydrogen densities inferred from recent column-density measurements to nearby hot stars are in fact representative of the immediate solar neighborhood.

  9. High-resolution infrared spectroscopy: Jet-cooled halogenated methyl radicals and reactive scattering dynamics in an atom + polyatom system

    NASA Astrophysics Data System (ADS)

    Whitney, Erin Sue

    This thesis describes a series of projects whose common theme comprises the structure and internal energy distribution of gas-phase radicals. In the first two projects, shot noise-limited direct absorption spectroscopy is combined with long path-length slit supersonic discharges to obtain first high-resolution infrared spectra for jet-cooled CH2F and CH2Cl in the symmetric and antisymmetric CH2 stretching modes. Drawing motivation from the question of the equilibrium structures of halogen-substituted methyl radicals, spectral assignment yields refined lower and upper state rotational constants, as well as fine-structure parameters from least-square fits to the sub-Doppler lineshapes for individual transitions. High-level CCSD(T) calculations extrapolated to the complete basis set (CBS) limit confirm the existence of a non-planar (theta=29°) CH2F equilibrium structure with a 132 cm-1 barrier to planarity and a vibrational bend frequency of 276 cm-1. Similar calculations for CH 2Cl predict a slightly nonplanar equilibrium structure (theta=11°) with a vibrationally adiabatic one-dimensional treatment of the bend coordinate yielding a fundamental anharmonic frequency (393 cm-1). Both sets of calculations are in excellent agreement with previous studies. More interesting, however, are the unexpected intensity ratios of the symmetric vs. antisymmetric bands for CH2F and the absence of an antisymmetric band for CH2Cl. While a simple bond-dipole picture predicts a ratio of 1:3 for the symmetric vs. antisymmetric intensities, the experimentally observed value for CH2F is ˜2:1. This ratio is confirmed by DFT [B3LYP/aug-cc-pVTZ] calculations in a novel albeit indirect probe of the effective non-planarity for CH2F. For CH2Cl, similar DFT calculations predict a 30-fold decrease between the intensity of the symmetric and antisymmetric CH2 stretches, leading to the postulation of a nearly perfect cancellation of antisymmetric stretch intensity transition moment with chlorination. These two projects are followed by an investigation utilizing a well-characterized radical source, F, in a reaction with ethane to form HF and ethyl radical. The non-radical HF product is detected directly through similar high-resolution infrared absorption methods as described above, and its analysis is used to make inferences about the internal energy redistribution of the other radical fragment, ethyl. State-to-state reaction dynamics under single collision conditions are interpreted in the context of a simple impulsive model based on conservation of linear/angular momentum yields predictions in good agreement with experiment. Deviations from the model indicate only minor excitation of the ethyl vibrations, in contrast with a picture of extensive intramolecular vibrational energy flow but consistent with Franck-Condon excitation of the methylene CH2 bending mode. The results suggest a relatively simple dynamical picture for exothermic atom + polyatomic scattering, i.e., that of early barrier dynamics in atom + diatom systems but modified by impulsive recoil coupling at the transition state between translational/rotational degrees of freedom.

  10. Detailed and Simplified Nonequilibrium Helium Ionization in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Golding, Thomas Peter; Carlsson, Mats; Leenaarts, Jorrit

    2014-03-01

    Helium ionization plays an important role in the energy balance of the upper chromosphere and transition region. Helium spectral lines are also often used as diagnostics of these regions. We carry out one-dimensional radiation-hydrodynamics simulations of the solar atmosphere and find that the helium ionization is set mostly by photoionization and direct collisional ionization, counteracted by radiative recombination cascades. By introducing an additional recombination rate mimicking the recombination cascades, we construct a simplified three-level helium model atom consisting of only the ground states. This model atom is suitable for modeling nonequilibrium helium ionization in three-dimensional numerical models. We perform a brief investigation of the formation of the He I 10830 and He II 304 spectral lines. Both lines show nonequilibrium features that are not recovered with statistical equilibrium models, and caution should therefore be exercised when such models are used as a basis for interpretating observations.

  11. Comparison of classical and quantal calculations of helium three-body recombination

    NASA Astrophysics Data System (ADS)

    Pérez-Ríos, Jesús; Ragole, Steve; Wang, Jia; Greene, Chris H.

    2014-01-01

    A general method to study classical scattering in n-dimension is developed. Through classical trajectory calculations, the three-body recombination is computed as a function of the collision energy for helium atoms, as an example. Quantum calculations are also performed for the J? = 0+ symmetry of the three-body recombination rate in order to compare with the classical results, yielding good agreement for E ? 1 K. The classical threshold law is derived and numerically confirmed for the Newtonian three-body recombination rate. Finally, a relationship is found between the quantum and classical three-body hard hypersphere elastic cross sections which is analogous to the well-known shadow scattering in two-body collisions.

  12. Comparison of classical and quantal calculations of helium three-body recombination

    SciTech Connect

    Pérez-Ríos, Jesús, E-mail: jperezri@purdue.edu; Greene, Chris H. [Physics Department, Purdue University, West Lafayette, Indiana 47907 (United States)] [Physics Department, Purdue University, West Lafayette, Indiana 47907 (United States); Ragole, Steve [Joint Quantum Institute, University of Maryland, College Park, Maryland 20742 (United States)] [Joint Quantum Institute, University of Maryland, College Park, Maryland 20742 (United States); Wang, Jia [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States)] [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States)

    2014-01-28

    A general method to study classical scattering in n-dimension is developed. Through classical trajectory calculations, the three-body recombination is computed as a function of the collision energy for helium atoms, as an example. Quantum calculations are also performed for the J{sup ?} = 0{sup +} symmetry of the three-body recombination rate in order to compare with the classical results, yielding good agreement for E ? 1 K. The classical threshold law is derived and numerically confirmed for the Newtonian three-body recombination rate. Finally, a relationship is found between the quantum and classical three-body hard hypersphere elastic cross sections which is analogous to the well-known shadow scattering in two-body collisions.

  13. Differential Single-Capture Cross Sections for Fast Alpha-Helium Collisions

    NASA Astrophysics Data System (ADS)

    Ghanbari-Adivi, Ebrahim; Ghavaminia, Hoda

    2014-08-01

    A four-body theoretical study of the single charge transfer process in collision of energetic alpha ions with helium atoms in their ground states is presented. The model utilizes the Coulomb-Born distorted wave approximation with correct boundary conditions to calculate the single-electron capture differential and integral cross sections. The influence of the dynamic and static electron correlations on the capture probability is investigated. The results of the calculations are compared with the recent experimental measurements for differential cross sections and with the other theoretical manipulations. The results for scattering at extreme forward angles are in good agreement with the experimental measurements, but in other scattering angles the agreement is poor. However, the present four-body results for integral cross sections are in excellent agreement with the experimental data.

  14. Tritium-helium effects in metals

    SciTech Connect

    Caskey, G.R. Jr.

    1985-01-01

    Investigations of helium effects in metals at the Savannah River Laboratory have been carried out by introducing helium by radioactive decay of tritium. This process does not create concurrent radiation damage, such as accompanies ion implantation and (n,..cap alpha..) reactions. The process has its own peculiarities, however, which partially mask and interact with the helium effect of interest. The distribution and local concentration of helium and tritium, which are responsible for changes in mechanical properties and fracture mode, are controlled by the large difference in solubility and diffusivity between the two atoms and by their differing interaction energies with lattice defects, impurities, and internal boundaries. Furthermore, in all investigations with helium generated from tritium decay, some tritium and deuterium are always present. Consequently, property changes include tritium-helium interaction effects to some extent. Results of investigations with several austenitic stainless steels, Armco iron, and niobium single crystals illustrate the variety of phenomena and some of the complex interactions that can be encountered.

  15. The role of symmetry in the theory of inelastic high-energy electron scattering and its application to atomic-resolution core-loss imaging.

    PubMed

    Dwyer, C

    2015-04-01

    The inelastic scattering of a high-energy electron in a solid constitutes a bipartite quantum system with an intrinsically large number of excitations, posing a considerable challenge for theorists. It is demonstrated how and why the utilization of symmetries, or approximate symmetries, can lead to significant improvements in both the description of the scattering physics and the efficiency of numerical computations. These ideas are explored thoroughly for the case of core-loss excitations, where it is shown that the coupled angular momentum basis leads to dramatic improvements over the bases employed in previous work. The resulting gains in efficiency are demonstrated explicitly for K-, L- and M-shell excitations, including such excitations in the context of atomic-resolution imaging in the scanning transmission electron microscope. The utilization of other symmetries is also discussed. PMID:25541390

  16. He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth. Progress report, May 1, 1991--April 30, 1992

    SciTech Connect

    Not Available

    1992-05-01

    Investigations in this laboratory have focused on the surface structure and dynamics of ionic insulators and on epitaxial growth onto alkali halide crystals. In the later the homoepitaxial growth of NaCl/NaCl(001) and the heteroepitaxial growth of KBr/NaCl(001), NaCl/KBr(001) and KBr/RbCl(001) have been studied by monitoring the specular He scattering as a function of the coverage and by measuring the angular and energy distributions of the scattered He atoms. These data provide information on the surface structure, defect densities, island sizes and surface strain during the layer-by-layer growth. The temperature dependence of these measurements also provides information on the mobilities of the admolecules. He atom scattering is unique among surface probes because the low-energy, inert atoms are sensitive only to the electronic structure of the topmost surface layer and are equally applicable to all crystalline materials. It is proposed for the next year to exploit further the variety of combinations possible with the alkali halides in order to carry out a definitive study of epitaxial growth in the ionic insulators. The work completed so far, including measurements of the Bragg diffraction and surface dispersion at various stages of growth, appears to be exceptionally rich in detail, which is particularly promising for theoretical modeling. In addition, because epitaxial growth conditions over a wide range of lattice mismatches is possible with these materials, size effects in growth processes can be explored in great depth. Further, as some of the alkali halides have the CsCl structure instead of the NaCl structure, we can investigate the effects of the heteroepitaxy with materials having different lattice preferences. Finally, by using co-deposition of different alkali halides, one can investigate the formation and stability of alloys and even alkali halide superlattices.

  17. Helicity-Resolved Raman Scattering of MoS2, MoSe2, WS2, and WSe2 Atomic Layers.

    PubMed

    Chen, Shao-Yu; Zheng, Changxi; Fuhrer, Michael S; Yan, Jun

    2015-04-01

    The two-fold valley degeneracy in two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs) (Mo,W)(S,Se)2 is suitable for "valleytronics", the storage and manipulation of information utilizing the valley degree of freedom. The conservation of luminescent photon helicity in these 2D crystal monolayers has been widely regarded as a benchmark indicator for charge carrier valley polarization. Here we perform helicity-resolved Raman scattering of the TMDC atomic layers. In drastic contrast to luminescence, the dominant first-order zone-center Raman bands, including the low energy breathing and shear modes as well as the higher energy optical phonons, are found to either maintain or completely switch the helicity of incident photons. In addition to providing a useful tool for characterization of TMDC atomic layers, these experimental observations shed new light on the connection between photon helicity and valley polarization. PMID:25719859

  18. Investigation of sonic/subsonic air-blast atomization using Rayleigh- and Mie-scattering visualization techniques

    E-print Network

    Kim, Tae-Kyun

    1996-01-01

    blurred images containing misleading information and to enhance the image resolution, the need for instantaneous planar cuts for tomographic view has long been recognized. Rayleigh- and Mie-scattering methods using a short-pulsed laser sheet are one... of the inethods which satisfy these requirements. The methods provide tomographical images and minimize the image blur. The Rayleigh scattering uses the moisture in the gas as natural seeding to visualize sonic/supersonic gas jets. Most moisture in the gas jet...

  19. Quantum Theory of Reactive Scattering and Adsorption at Surfaces

    NASA Astrophysics Data System (ADS)

    Groß, Axel

    The interaction of atoms and molecules with surfaces is of great technological relevance [1]. Both advantageous and harmful processes can occur at surfaces. Catalytic reactions at surfaces represent a desired process while corrosion is an unwanted process. If light atoms and molecules such as hydrogen or helium are interacting with the surface, then quantum effects in the interaction dynamics between the incoming beam and the substrate have to be taken into account. First of all there are quantum effects in the energy transfer to the substrate vibrations, the phonons. While classically there will always be an energy loss of the incident particles to the substrate, quantum mechanically there is a certain probability for elastic scattering, i.e., without any energy transfer between the substrate and the scattered particles. This has also important consequences on the sticking probabilities of weakly bound species such as rare gases at low kinetic energies.

  20. Structure and dynamics of few-helium clusters using soft-core potentials

    NASA Astrophysics Data System (ADS)

    Kievsky, A.; Viviani, M.; Gattobigio, M.; Romero-Redondo, C.; Garrido, E.

    2014-04-01

    In this work we investigate the structure and dynamics of small clusters of Helium atoms. We consider bound states of clusters having A = 2, 3, 4, 5, 6 atoms and continuum states in the three-atom system. Motivated by the fact that the He-He system has a very large scattering length a compared to the range r 0 of the He-He potential ( r 0/ a < 1/10), we propose the use of a soft-core interparticle potential. We use an attractive gaussian potential that reproduces the values of the dimer binding energy and the atomatom scattering length obtained with one of the widely used He-He interactions, the LM2M2 potential. In addition, we include a repulsive three-body force to reproduce the trimer binding energy. With this model, consisting in the sum of a two- and a three-body potential, we show the spectrum of the four, five, and sixparticle systems and phase-shifts and inelasticities in the three-atom system. Comparisons to calculations using realistic He-He potentials are given. In addition some universal relations are explored.

  1. White-light cavity based on coherent Raman scattering via normal modes of a coupled cavity-and-atom system

    SciTech Connect

    Zhang Jiepeng; Hernandez, Gessler; Zhu Yifu [Department of Physics, Florida International University, Miami, Florida 33199 (United States); Wei Xiaogang [Department of Physics, Florida International University, Miami, Florida 33199 (United States); College of Physics, Jilin University, Changchun 130023 (China)

    2010-03-15

    We describe a white-light cavity scheme based on a cavity quantum electrodynamics system that consists of multiple three-level atoms confined in an optical cavity and coherently driven by a free-space, circularly polarized field. A linearly polarized field is coupled into the cavity mode and its two circular components induce coherent Raman transitions through the normal modes of the coupled atom-cavity system. One circular component of the cavity field experiences anomalous dispersion which enables broadband light transmission through the cavity. We present the experimental demonstration of the broadband light transmission through an optical cavity coupled to cold Rb atoms.

  2. [Atomic beam studies of the interaction of hydrogen with transition metal surfaces]. Technical progress report, August 1, 1985--July 30, 1992

    SciTech Connect

    Not Available

    1992-12-31

    We have constructed two experimental facilities during the term of this grant. In the first three years we constructed a helium atom scattering (HAS) facility with both elastic (EHAS) and inelastic (IHAS) scattering measurement capabilities to investigate the structural and dynamical aspects of solid surfaces and thin films. A pioneering surface metastable atom magnetic diffraction (SMAMD) facility was constructed and developed over the past four years, which makes possible the investigation of long-range electron spin-ordering on the surfaces of insulating magnetic crystals. The following were studied: H overlayers and Ag, Cu on Pd(111), reconstructed Au(111), and NiO(100).

  3. Free-energy model for fluid helium at high density

    E-print Network

    Christophe Winisdoerffer; Gilles Chabrier

    2004-12-06

    We present a semi-analytical free-energy model aimed at characterizing the thermodynamic properties of dense fluid helium, from the low-density atomic phase to the high-density fully ionized regime. The model is based on a free-energy minimization method and includes various different contributions representative of the correlations between atomic and ionic species and electrons. This model allows the computation of the thermodynamic properties of dense helium over an extended range of density and temperature and leads to the computation of the phase diagram of dense fluid helium, with its various temperature and pressure ionization contours. One of the predictions of the model is that pressure ionization occurs abruptly at $\\rho \\simgr 10$ g cm$^{-3}$, {\\it i.e.} $P\\simgr 20$ Mbar, from atomic helium He to fully ionized helium He$^{2+}$, or at least to a strongly ionized state, without He$^{+}$ stage, except at high enough temperature for temperature ionization to become dominant. These predictions and this phase diagram provide a guide for future dynamical experiments or numerical first-principle calculations aimed at studying the properties of helium at very high density, in particular its metallization. Indeed, the characterization of the helium phase diagram bears important consequences for the thermodynamic, magnetic and transport properties of cool and dense astrophysical objects, among which the solar and the numerous recently discovered extrasolar giant planets.

  4. PURIFICATION OF HELIUM COOLANT

    Microsoft Academic Search

    K. Oshima; K. Naito; K. Nishida

    1963-01-01

    The literature from 1955 to 1961 on the purification of helium coolant, ; especially on the separatiqn of fission gases, is reviewed. The principle of gas ; purification, the separation of radioactive and nonradioactive gases, and ; purification systems for helium coolant are covered. 184 references. (D.C.W.)

  5. Global operators for delta functions - Extension to scattering states and the inclusion of spin. [in atomic physics

    NASA Technical Reports Server (NTRS)

    Sucher, J.; Drachman, R. J.

    1979-01-01

    The paper presents an extension of the identities of Hiller, Sucher, and Feinberg for the evaluation of bound-state matrix elements of delta function operators, to scattering states. Attention is given to the technical difficulties encountered in the application of the scattering-state identities and how they can be overcome, including infrared singularities which arise if Coulomb forces are present and the velocity of the incident particle is small. In addition, both the scattering and bound-state identities are generalized to include spin-dependent contact interactions and spin-dependent Hamiltonians. Finally, it is stressed that the identities can be used to improve the accuracy of calculations of interest for diverse physical phenomena, ranging from positron annihilation to hyperfine structure.

  6. 48 CFR 52.208-8 - Required Sources for Helium and Helium Usage Data.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... false Required Sources for Helium and Helium Usage Data. 52.208-8...208-8 Required Sources for Helium and Helium Usage Data. As prescribed...clause: Required Sources for Helium and Helium Usage Data (APR 2002)...

  7. Elastic scattering of tritons by helium-4

    SciTech Connect

    Jarmie, N.; Correll, F.D.; Brown, R.E.; Hardekopf, R.A.; Ohlsen, G.G.

    1980-11-01

    Angular distributions of the differential cross section and of the analyzing power have been measured for the /sup 4/He(t,t)/sup 4/He reaction at 19 energies from 6 to 17 MeV. The relative errors of the cross section and analyzing power range from 2.0 to 2.5% and 0.005 to 0.01, respectively, and the scale errors are 1% in each case. Complete data tables are presented, and the experimental procedure is described for the present measurements and for earlier cross-section measurements. Graphs of the data are presented, as well as the curves resulting from an energy-independent phase-shift analysis.

  8. Improved helium line formation for EHe stars

    E-print Network

    N. Przybilla; K. Butler; U. Heber; C. S. Jeffery

    2005-12-06

    Quantitative analyses of extreme helium stars to date face the difficulty that theory fails to reproduce the observed helium lines in their entirety, wings and line cores. Here, we demonstrate how the issues can be resolved using state-of-the-art non-LTE line formation for these chemically peculiar objects. Two unique B-type objects are discussed in detail, the pulsating variable V652 Her and the metal-poor star HD144941. The improved non-LTE computations for helium show that analyses assuming LTE or based on older non-LTE model atoms can predict equivalent widths, for the HeI 10830A transition in particular, in error by up to a factor ~3. Our modelling approach also succeeds in largely resolving the general mismatch for effective temperatures of EHe stars derived from ionization equilibria and from spectral energy distributions.

  9. Synthesis-atomic structure-properties relationships in metallic nanoparticles by total scattering experiments and 3D computer simulations: case of Pt-Ru nanoalloy catalysts.

    PubMed

    Prasai, Binay; Ren, Yang; Shan, Shiyao; Zhao, Yinguang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian; Petkov, Valeri

    2015-04-24

    An approach to determining the 3D atomic structure of metallic nanoparticles (NPs) in fine detail and using the unique knowledge obtained for rationalizing their synthesis and properties targeted for optimization is described and exemplified on Pt-Ru alloy NPs of importance to the development of devices for clean energy conversion such as fuel cells. In particular, PtxRu100-x alloy NPs, where x = 31, 49 and 75, are synthesized by wet chemistry and activated catalytically by a post-synthesis treatment involving heating under controlled N2-H2 atmosphere. So-activated NPs are evaluated as catalysts for gas-phase CO oxidation and ethanol electro-oxidation reactions taking place in fuel cells. Both as-synthesized and activated NPs are characterized structurally by total scattering experiments involving high-energy synchrotron X-ray diffraction coupled to atomic pair distribution functions (PDFs) analysis. 3D structure models both for as-synthesized and activated NPs are built by molecular dynamics simulations based on the archetypal for current theoretical modelling Sutton-Chen method. Models are refined against the experimental PDF data by reverse Monte Carlo simulations and analysed in terms of prime structural characteristics such as metal-to-metal bond lengths, bond angles and first coordination numbers for Pt and Ru atoms. Analysis indicates that, though of a similar type, the atomic structure of as-synthesized and respective activated NPs differ in several details of importance to NP catalytic properties. Structural characteristics of activated NPs and data for their catalytic activity are compared side by side and strong evidence found that electronic effects, indicated by significant changes in Pt-Pt and Ru-Ru metal bond lengths at NP surface, and practically unrecognized so far atomic ensemble effects, indicated by distinct stacking of atomic layers near NP surface and prevalence of particular configurations of Pt and Ru atoms in these layers, contribute to the observed enhancement of the catalytic activity of PtxRu100-x alloy NPs at x ? 50. Implications of so-established relationships between the atomic structure and catalytic activity of Pt-Ru alloy NPs on efforts aimed at improving further the latter by tuning-up the former are discussed and the usefulness of detailed NP structure studies to advancing science and technology of metallic NPs - exemplified. PMID:25874741

  10. Imbibition of Liquid Helium in Aerogels

    NASA Astrophysics Data System (ADS)

    Spathis, P.; Delga, A.; Malheiro, C.; Wolf, P. E.

    2013-06-01

    We report optical measurements of the imbibition of liquid helium in a sample of silica aerogel with 90 % porosity. Both direct imaging and light scattering experiments were performed to determine the dynamics and the properties of the liquid-gas interface in both the normal and superfluid phases of liquid helium. In the normal phase, a classical Lucas Washburn behavior is observed for the rise of the imbibition front while the behavior in the superfluid phase is markedly different, as the fluid invades the sample from all sides with a constant speed. In both phases, the interface is rough, leading to light scattering. In addition, condensation ahead of the imbibition front is observed at low temperature in the superfluid phase.

  11. Total Cross Sections for Inelastic Scattering of Charged Particles by Atoms and Molecules. IV. Positive Lithium Ion

    Microsoft Academic Search

    Yong-Ki Kim; Mitio Inokuti

    1970-01-01

    The Born cross sections for several important discrete excitations of Li+ from its ground state have been calculated with correlated wave functions. By extrapolation, cross sections for higher excitations have also been determined. Subtraction of the sum sigmaex of these excitation cross sections from the total inelastic-scattering cross section sigmatot obtained through a sum rule for the Bethe cross sections

  12. Effects of dark atom excitations

    E-print Network

    Jean-René Cudell; Maxim Yu. Khlopov; Quentin Wallemacq

    2014-11-06

    New stable quarks and charged leptons may exist and be hidden from detection, as they are bound by Coulomb interaction in neutral dark atoms of composite dark matter. This possibility leads to fundamentally new types of indirect effects related to the excitation of such dark atoms followed by their electromagnetic de-excitation. Stable -2 charged particles, bound to primordial helium in O-helium (OHe) atoms, represent the simplest model of dark atoms. Here we consider the structure of OHe atomic levels which is a necessary input for the indirect tests of such composite dark matter scenarios, and we give the spectrum of electromagnetic transitions from the levels excited in OHe collisions.

  13. Two-photon spectroscopy of antiprotonic helium

    NASA Astrophysics Data System (ADS)

    Barna, Dániel

    2014-04-01

    The precision of laser spectroscopy of antiprotonic helium (a helium atom with one of its electrons replaced by an antiproton) has improved by almost 4 orders of magnitude over its 20 years of history. Experimental transition frequencies can be compared to 3-body QED calculations to derive the antiproton-electron mass ratio. In the latest measurements of the Asacusa experiment at CERN, two-photon transitions of antiprotonic helium were excited using two counter-propagating laser beams. This method reduces the Doppler-broadening caused by the thermal motion of the atoms, and allowed us to measure the transition frequencies with a fractional precision of 2.5-5 parts in 109. From these frequencies, we derived an antiproton-electron mass ratio of 1836.1526736(23). Our precision approaches that of the experimental value of the proton-electron mass ratio, and agrees with the latter within errors. Assuming CPT symmetry (i.e. mp=m_{overline {p}}), we further derived the electron's atomic mass as m e = 0.0005485799091(7)u from the more accurately known atomic mass of the proton.

  14. Observation of a superfluid component within solid helium.

    PubMed

    Lauter, H; Apaja, V; Kalinin, I; Kats, E; Koza, M; Krotscheck, E; Lauter, V V; Puchkov, A V

    2011-12-23

    We demonstrate by neutron scattering that a localized superfluid component exists at high pressures within solid helium in aerogel. Its existence is deduced from the observation of two sharp phonon-roton spectra which are clearly distinguishable from modes in bulk superfluid helium. These roton excitations exhibit different roton gap parameters than the roton observed in the bulk fluid at freezing pressure. One of the roton modes disappears after annealing the samples. Comparison with theoretical calculations suggests that the model that reproduces the observed data best is that of superfluid double layers within the solid and at the helium-substrate interface. PMID:22243164

  15. 3He NMR studies on helium-pyrrole, helium-indole, and helium-carbazole systems: a new tool for following chemistry of heterocyclic compounds.

    PubMed

    Radula-Janik, Klaudia; Kupka, Teobald

    2015-02-01

    The (3)He nuclear magnetic shieldings were calculated for free helium atom and He-pyrrole, He-indole, and He-carbazole complexes. Several levels of theory, including Hartree-Fock (HF), Second-order Møller-Plesset Perturbation Theory (MP2), and Density Functional Theory (DFT) (VSXC, M062X, APFD, BHandHLYP, and mPW1PW91), combined with polarization-consistent pcS-2 and aug-pcS-2 basis sets were employed. Gauge-including atomic orbital (GIAO) calculated (3)He nuclear magnetic shieldings reproduced accurately previously reported theoretical values for helium gas. (3)He nuclear magnetic shieldings and energy changes as result of single helium atom approaching to the five-membered ring of pyrrole, indole, and carbazole were tested. It was observed that (3)He NMR parameters of single helium atom, calculated at various levels of theory (HF, MP2, and DFT) are sensitive to the presence of heteroatomic rings. The helium atom was insensitive to the studied molecules at distances above 5?Å. Our results, obtained with BHandHLYP method, predicted fairly accurately the He-pyrrole plane separation of 3.15?Å (close to 3.24?Å, calculated by MP2) and yielded a sizable (3)He NMR chemical shift (about -1.5?ppm). The changes of calculated nucleus-independent chemical shifts (NICS) with the distance above the rings showed a very similar pattern to helium-3 NMR chemical shift. The ring currents above the five-membered rings were seen by helium magnetic probe to about 5?Å above the ring planes verified by the calculated NICS index. PMID:25228253

  16. Photoionization of Alkali-Doped Helium Nanodroplets

    NASA Astrophysics Data System (ADS)

    Theisen, Moritz; Lackner, Florian; Krois, Günter; Koch, Markus; Ernst, Wolfgang E.

    2012-06-01

    Superfluid helium droplets (He_N) provide a cold, weakly-interacting environment for the investigation of weakly bound molecules. Whereas the host-dopant interaction is weak for neutral molecules, ion impurities may be surrounded by frozen shells of polarized helium atoms. An extreme example of the different behavior is given by alkali metal impurities that stay at the surface of the droplet as neutrals but immerse into the droplet as cations releasing a considerable amount of binding energy. We report measurements of the photoionization efficiency for the rubidium-He_N and cesium-He_N systems and find that the ionization threshold is lowered compared with the free atoms and is in good agreement with Rydberg state spectroscopy of these systems. The corresponding energy shift increases when going from heavy to light alkali metals and from small to large helium droplets. Both effects can be explained by the difference in polarization energies associated with submerged alkali metal cations. The findings agree qualitatively well with recent calculations of helium snowball formation around alkali metal cations. M. Theisen, F. Lackner, G. Krois, and W. E. Ernst, J. Phys. Chem. Lett. 2, 2778 (2011). F. Lackner, G. Krois, M. Theisen, M. Koch, and W. E. Ernst, Phys. Chem. Chem. Phys. 13, 18781 (2011). D. E. Galli, D. M. Ceperley, and L. Reatto, J. Phys. Chem. A 115, 7300 (2011).

  17. Leakage detection method using helium

    Microsoft Academic Search

    H. Ishii; H. Morishita; K. Seki; T. Yamazaki

    1983-01-01

    A means is disclosed for detecting helium which has flowed into a system by substitution for air at a leaking location and mixed with the remaining gases, and after the helium gas permeates a helium permeable membrane as a sample gas so that the air component unnecessary for detection is suppressed, the helium gas enters the space of a mass

  18. Scattering of Antiprotons by Nuclei (Atoms) in the Range of Low Energies $E\\lesssim 10^5$ eV. Mirror Reflection, Diffraction, and Channeling of Antiprotons in Crystals

    E-print Network

    V. G. Baryshevsky

    2014-04-01

    Studying antiproton scattering by nuclei (atoms) in the range of low energies, we found out that the increase in the antiproton-nucleus scattering amplitude through Coulomb interaction provides the possibility to investigate spin-dependent processes accompanying the interaction of antiprotons with nuclei (polarized or unpolarized) by means of mirror reflection of antiprotons from the vacuum-matter boundary, diffraction and channeling (surface diffraction and channeling) of antiprotons in crystals.

  19. Electron spectroscopy of doubly-excited helium-like ions

    Microsoft Academic Search

    S. Ohtani; Y. Kanai; I. Yamada; H. A. Sakaue; Y. Awaya; T. Kambara; T. Nabeshima; N. Nakamura; H. Suzuki; T. Takayanagi; K. Wakiya; A. Danjo; M. Yoshino

    1991-01-01

    Spectroscopic investigations of electrons coming from doubly-excited states of helium-like C and B ions have been made with zero-degree spectroscopies. These excited states are produced by two-electron capture collisions of bare ions with helium atoms. Electrons from the configurations of 2lnl' are observed in a wide energy range. Total angular momentum distributions in the double-electron transfer collisions are briefly discussed.

  20. Core helium flash

    SciTech Connect

    Cole, P.W.; Deupree, R.G.

    1980-01-01

    The role of convection in the core helium flash is simulated by two-dimensional eddies interacting with the thermonuclear runaway. These eddies are followed by the explicit solution of the 2D conservation laws with a 2D finite difference hydrodynamics code. Thus, no phenomenological theory of convection such as the local mixing length theory is required. The core helium flash is violent, producing a deflagration wave. This differs from the detonation wave (and subsequent disruption of the entire star) produced in previous spherically symmetric violent core helium flashes as the second dimension provides a degree of relief which allows the expansion wave to decouple itself from the burning front. Our results predict that a considerable amount of helium in the core will be burned before the horizontal branch is reached and that some envelope mass loss is likely.

  1. The Descending Helium Balloon

    ERIC Educational Resources Information Center

    Helseth, Lars Egil

    2014-01-01

    I describe a simple and fascinating experiment wherein helium leaks out of a rubber balloon, thereby causing it to descend. An estimate of the volumetric leakage rate is made by measuring its rate of descent.

  2. Multiple scattering of slow ions in a free-electron gas

    NASA Astrophysics Data System (ADS)

    Archubi, Claudio D.; Arista, Néstor R.

    2005-12-01

    We study the influence of electronic scattering on the angular distributions of ions and atoms moving through a free-electron gas. We present a general formulation based on the multiple-scattering formalism, using two alternative descriptions: a linear approach based on Lindhard’s dielectric function, and a nonlinear treatment based on density functional calculations. We obtain analytical expressions for the multiple-scattering function and for the half-width of the distribution. We show the results of several calculations for slow hydrogen and helium and their isotopes. We analyze the results and obtain analytical approximations for all of the cases. The magnitude of the electronic effects on the multiple scattering distribution is determined and compared with previous estimations.

  3. Thermodynamic properties of helium

    SciTech Connect

    Sychev, V.V.; Vasserman, A.A.; Kozlov, A.D.; Spiridonov, G.A.; Tsymarnyi, V.A.

    1987-01-01

    This volume offers reliable data on the thermodynamic properties of helium over a wide variety of conditions. Spanning temperatures between the lambda line and 1500 K and pressures up to 100 MPa, these data are vital to helium extraction from natural gases and to the design of cryogenic apparatus. The equations of state are considered along with the construction of a single equation of state. 175 references.

  4. Topography, complex refractive index, and conductivity of graphene layers measured by correlation of optical interference contrast, atomic force, and back scattered electron microscopy

    SciTech Connect

    Vaupel, Matthias, E-mail: Matthias.vaupel@zeiss.com; Dutschke, Anke [Training Application Support Center, Carl Zeiss Microscopy GmbH, Königsallee 9-21, 37081 Göttingen (Germany); Wurstbauer, Ulrich; Pasupathy, Abhay [Department of Physics, Columbia University New York, 538 West 120th Street, New York, New York 10027 (United States); Hitzel, Frank [DME Nanotechnologie GmbH, Geysostr. 13, D-38106 Braunschweig (Germany)

    2013-11-14

    The optical phase shift by reflection on graphene is measured by interference contrast microscopy. The height profile across graphene layers on 300?nm thick SiO{sub 2} on silicon is derived from the phase profile. The complex refractive index and conductivity of graphene layers on silicon with 2?nm thin SiO{sub 2} are evaluated from a phase profile, while the height profile of the layers is measured by atomic force microscopy. It is observed that the conductivity measured on thin SiO{sub 2} is significantly greater than on thick SiO{sub 2}. Back scattered electron contrast of graphene layers is correlated to the height of graphene layers.

  5. Helium-Charged La-Ni-Al Thin Films Deposited by Magnetron Sputtering

    SciTech Connect

    Shi Liqun [Fudan University (China); Chen Deming [Chinese Academy of Sciences (China); Xu Shilin [Fudan University (China); Liu Chaozhu [Fudan University (China); Hao Wanli [China Academy of Engerineering Physics (China); Zhou Zhuyin [Fudan University (China)

    2005-07-15

    An advanced implantation of low energy helium-4 atoms during the La-Ni-Al film growth by adopting magnetron sputtering with Ar/He mixture gases is discussed. Both proton backscattering spectroscopy (PBS) and elastic recoil detection (ERD) analyses were adopted to measure helium concentration of the films and distribution in the near-surface region. Helium atoms with a high concentration incorporate evenly in deposited film. The introduction of the helium with no extra irradiation damage is expected by choosing suitable deposition conditions. It was found that amorphous and crystalline LaNi{sub 5}-type structures can be achieved when sputtered with pure Ar and Ar/He mixture gases at room temperature, respectively. Thermal desorption experiments proposes that a part of hydrogen atoms are bound to trapped helium at crystal and releases together with helium. Only a small fraction of helium is released from the helium-vacancy clusters in lower temperature range and most of helium is released from small size helium bubbles in the high temperature range.

  6. Quantum Scattering

    Microsoft Academic Search

    E. B. Manoukian

    Significant progress has been made over the years in physics through scattering experiments. The discovery of the atomic nucleus, the visible tracks of particles observed in cloud chambers, the determination of the structure of matter, the emergence of the endless variety of particles by accelerators and the extraction of information on their interactions, are just a few of the examples

  7. {beta}-connectin studies by small-angle x-ray scattering and single-molecule force spectroscopy by atomic force microscopy

    SciTech Connect

    Marchetti, S.; Carla, M.; Gambi, C. M. C. [Department of Physics, University of Florence and CNISM Via G. Sansone 1, IT-50019, Sesto Fiorentino, Florence (Italy); Sbrana, F.; Vassalli, M. [Biophysics Institute of the National Research Council, Via De Marini 6, Genova (Italy); Toscano, A.; Pacini, A. [Department of Anatomy, Histology, and Forensic Medicine, University of Florence, Florence (Italy); Fratini, E. [Department of Chemistry and Consorzio Interuniversitario per lo Sviluppo dei Sistemi a Grande Interfase (CSGI), University of Florence, Via della Lastruccia 3, IT-50019, Sesto Fiorentino, Florence (Italy); Tiribilli, B. [Complex System Institute of the National Research Council (ISC-CNR), Sesto Fiorentino, Florence (Italy)

    2011-05-15

    The three-dimensional structure and the mechanical properties of a {beta}-connectin fragment from human cardiac muscle, belonging to the I band, from I{sub 27} to I{sub 34}, were investigated by small-angle x-ray scattering (SAXS) and single-molecule force spectroscopy (SMFS). This molecule presents an entropic elasticity behavior, associated to globular domain unfolding, that has been widely studied in the last 10 years. In addition, atomic force microscopy based SMFS experiments suggest that this molecule has an additional elastic regime, for low forces, probably associated to tertiary structure remodeling. From a structural point of view, this behavior is a mark of the fact that the eight domains in the I{sub 27}-I{sub 34} fragment are not independent and they organize in solution, assuming a well-defined three-dimensional structure. This hypothesis has been confirmed by SAXS scattering, both on a diluted and a concentrated sample. Two different models were used to fit the SAXS curves: one assuming a globular shape and one corresponding to an elongated conformation, both coupled with a Coulomb repulsion potential to take into account the protein-protein interaction. Due to the predominance of the structure factor, the effective shape of the protein in solution could not be clearly disclosed. By performing SMFS by atomic force microscopy, mechanical unfolding properties were investigated. Typical sawtooth profiles were obtained and the rupture force of each unfolding domain was estimated. By fitting a wormlike chain model to each peak of the sawtooth profile, the entropic elasticity of octamer was described.

  8. Analytical complex at the PIK reactor for studying the supra-atomic structure and dynamics of materials by neutron scattering

    SciTech Connect

    Lebedev, V. M., E-mail: lebedev@pnpi.spb.ru; Lebedev, V. T.; Ivanova, I. N.; Orlova, D. N. [Russian Academy of Sciences, St. Petersburg Nuclear Physics Institute (Russian Federation)

    2011-12-15

    A project of the center for studying reactor materials and solving problems of materials science is presented which will be equipped with the following neutron instruments: a small-angle Membrana diffractometer, a spin-echo spectrometer, and a time-of-flight spectrometer. It is proposed to irradiate materials in the PIK reactor core and use neutron-scattering tools to analyze the structure and dynamics of these materials and investigate radiative defects in the complete experimental cycle (initial material-irradiation-strength tests, thermal loads, and other effects) using materials science techniques.

  9. Fluorine atom abstraction by Si(100). I. Experimental

    NASA Astrophysics Data System (ADS)

    Tate, M. R.; Gosalvez-Blanco, D.; Pullman, D. P.; Tsekouras, A. A.; Li, Y. L.; Yang, J. J.; Laughlin, K. B.; Eckman, S. C.; Bertino, M. F.; Ceyer, S. T.

    1999-08-01

    In the interaction of low energy F2 with Si(100) at 250 K, a dissociative chemisorption mechanism called atom abstraction is identified in which only one of the F atoms is adsorbed while the other F atom is scattered into the gas phase. The dynamics of atom abstraction are characterized via time-of-flight measurements of the scattered F atoms. The F atoms are translationally hyperthermal but only carry a small fraction (˜3%) of the tremendous exothermicity of the reaction. The angular distribution of F atoms is unusually broad for the product of an exothermic reaction. These results suggest an "attractive" interaction potential between F2 and the Si dangling bond with a transition state that is not constrained geometrically. These results are in disagreement with the results of theoretical investigations implying that the available potential energy surfaces are inadequate to describe the dynamics of this gas-surface interaction. In addition to single atom abstraction, two atom adsorption, a mechanism analogous to classic dissociative chemisorption in which both F atoms are adsorbed onto the surface, is also observed. The absolute probability of the three scattering channels (single atom abstraction, two atom adsorption, and unreactive scattering) for an incident F2 are determined as a function of F2 exposure. The fluorine coverage is determined by integrating the reaction probabilities over F2 exposure, and the reaction probabilities are recast as a function of fluorine coverage. Two atom adsorption is the dominant channel [P2=0.83±0.03(95%, N=9)] in the limit of zero coverage and decays monotonically to zero. Single atom abstraction is the minor channel (P1=0.13±0.03) at low coverage but increases to a maximum (P1=0.35±0.08) at about 0.5 monolayer (ML) coverage before decaying to zero. The reaction ceases at 0.94±0.11(95%, N=9) ML. Thermal desorption and helium diffraction confirm that the dangling bonds are the abstraction and adsorption sites. No Si lattice bonds are broken, in contrast to speculation by other investigators that the reaction exothermicity causes lattice disorder.

  10. Helium Diffusion in Olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.

    2011-12-01

    Diffusion of helium has been characterized in natural Fe-bearing olivine (~Fo90) and synthetic forsterite. Polished, oriented slabs of olivine were implanted with 3He, at 100 keV at a dose of 5x1015/cm2 or at 3.0 MeV at a dose of 1x1016/cm2. A set of experiments on the implanted olivine were run in 1-atm furnaces. In addition to the one-atm experiments, experiments on implanted samples were also run at higher pressures (2.6 and 2.7 GPa) to assess the potential effects of pressure on He diffusion and the applicability of the measured diffusivities in describing He transport in the mantle. The high-pressure experiments were conducted in a piston-cylinder apparatus using an "ultra-soft" pressure cell, with the diffusion sample directly surrounded by AgCl. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. This direct profiling method permits us to evaluate anisotropy of diffusion, which cannot be easily assessed using bulk-release methods. For diffusion in forsterite parallel to c we obtain the following Arrhenius relation over the temperatures 250-950°C: D = 3.91x10-6exp(-159 ± 4 kJ mol-1/RT) m2/sec. The data define a single Arrhenius line spanning more than 7 orders of magnitude in D and 700°C in temperature. Diffusion parallel to a appears slightly slower, yielding an activation energy for diffusion of 135 kJ/mol and a pre-exponential factor of 3.73x10-8 m2/sec. Diffusion parallel to b is slower than diffusion parallel to a (by about two-thirds of a log unit); for this orientation an activation energy of 138 kJ/mol and a pre-exponential factor of 1.34x10-8 m2/sec are obtained. This anisotropy is broadly consistent with observations for diffusion of Ni and Fe-Mg in olivine. Diffusion in Fe-bearing olivine (transport parallel to b) agrees within uncertainty with findings for He diffusion in forsterite. The higher-pressure experiments yield diffusivities in agreement with those from the 1-atm experiments, indicating that the results reported here can be reasonably applied to modeling He transport in the upper mantle. The insensitivity of He diffusion to pressure over the investigated range of conditions suggests that compression of the mineral lattice is not sufficient to significantly influence migration of the relatively small helium atoms, which likely diffuse via crystal interstices. The He diffusivities in this work are generally consistent with results from the study of Futagami et al. (1993), who measured He diffusion in natural olivine by outgassing 4He implanted samples, and with the diffusivities measured by bulk-release of 4He and 3He by Shuster et al. (2003), but are about 2 orders of magnitude slower than the recent findings of Tolstikhin et al. (2010) and Blard et al. (2008) . An up-temperature extrapolation of our data also show reasonable agreement with the higher-temperature measurements of Hart (1984). Blard et al. (2008) GCA 72, 3788-3803; Futagami et al. (1993) GCA 57, 3177-3194; Hart (1984) EPSL 70, 297-302; Shuster et al.( 2003) EPSL 217, 19-32; Tolstikhin et al. (2010) GCA 74, 1436-1447

  11. Using X-ray absorption spectra to monitor specific radiation damage to anomalously scattering atoms in macromolecular crystallography.

    PubMed

    Oliéric, V; Ennifar, E; Meents, A; Fleurant, M; Besnard, C; Pattison, P; Schiltz, M; Schulze-Briese, C; Dumas, P

    2007-07-01

    Radiation damage in macromolecular crystals is not suppressed even at 90 K. This is particularly true for covalent bonds involving an anomalous scatterer (such as bromine) at the 'peak wavelength'. It is shown that a series of absorption spectra recorded on a brominated RNA faithfully monitor the extent of cleavage. The continuous spectral changes during irradiation preserve an 'isosbestic point', each spectrum being a linear combination of 'zero' and 'infinite' dose spectra. This easily yields a good estimate of the partial occupancy of bromine at any intermediate dose. The considerable effect on the near-edge features in the spectra of the crystal orientation versus the beam polarization has also been examined and found to be in good agreement with a previous study. Any significant influence of the (C-Br bond/beam polarization) angle on the cleavage kinetics of bromine was also searched for, but was not detected. These results will be useful for standard SAD/MAD experiments and for the emerging 'radiation-damage-induced phasing' method exploiting both the anomalous signal of an anomalous scatterer and the 'isomorphous' signal resulting from its cleavage. PMID:17582167

  12. Spectroscopy of barium attached to superfluid helium clusters

    NASA Astrophysics Data System (ADS)

    Stienkemeier, F.; Meier, F.; Lutz, H. O.

    To complement the data on absorption spectra of alkaline earth atoms attached to superfluid helium clusters we are reporting on barium atoms attached to 4HeN. The absorption spectrum of the lowest singlet transition is blue-shifted and strongly broadened compared to the corresponding unperturbed Ba (6s6p1Po1?6s21S0) transition in accord with the observations on Sr and Ca added to HeN [F. Stienkemeier, F. Meier, and H.O. Lutz: J. Chem. Phys. 107(24), 10816 (1997)]. Moreover, we compare the asymptotic values of shift and width of the excitation spectrum with increasing helium cluster size He ( 1000 up to 10000) to those found for barium atoms in bulk liquid helium.

  13. SPIN POLARIZED HELIUM3, A PLAYGROUND IN MANY DOMAINS OF PHYSICS

    Microsoft Academic Search

    M. LEDUC

    1990-01-01

    This article gives a survey of the different methods which can be used to polarize the nuclear spin of helium-3. These techniques are particularly discussed in relation to the production of polarized helium-3 targets for nuclear physics experiments, such as electron or proton scattering and neutron spin filters. Some emphasis is given to the development of new powerful solid state

  14. Effective atomic numbers of blue topaz at different gamma-rays energies obtained from Compton scattering technique

    SciTech Connect

    Tuschareon, S., E-mail: tuscharoen@hotmail.com; Limkitjaroenporn, P., E-mail: tuscharoen@hotmail.com; Kaewkhao, J., E-mail: tuscharoen@hotmail.com [Center of Excellence in Glass Technology and Materials Science (CEGM), Nakhon Pathom Rajabhat University, Nakhon Pathom, 73000, Thailand and Science Program, Faculty of Science and Technology, Nakhon Pathom Rajabhat University, Nakhon Pathom, 73000 (Thailand)

    2014-03-24

    Topaz occurs in a wide range of colors, including yellow, orange, brown, pink-to-violet and blue. All of these color differences are due to color centers. In order to improve the color of natural colorless topaz, the most commonly used is irradiated with x- or gamma-rays, indicated that attenuation parameters is important to enhancements by irradiation. In this work, the mass attenuation coefficients of blue topaz were measured at the different energy of ?-rays using the Compton scattering technique. The results show that, the experimental values of mass attenuation coefficient are in good agreement with the theoretical values. The mass attenuation coefficients increase with the decrease in gamma rays energies. This may be attributed to the higher photon interaction probability of blue topaz at lower energy. This result is a first report of mass attenuation coefficient of blue topaz at different gamma rays energies.

  15. Effective atomic numbers of blue topaz at different gamma-rays energies obtained from Compton scattering technique

    NASA Astrophysics Data System (ADS)

    Tuschareon, S.; Limkitjaroenporn, P.; Kaewkhao, J.

    2014-03-01

    Topaz occurs in a wide range of colors, including yellow, orange, brown, pink-to-violet and blue. All of these color differences are due to color centers. In order to improve the color of natural colorless topaz, the most commonly used is irradiated with x- or gamma-rays, indicated that attenuation parameters is important to enhancements by irradiation. In this work, the mass attenuation coefficients of blue topaz were measured at the different energy of ?-rays using the Compton scattering technique. The results show that, the experimental values of mass attenuation coefficient are in good agreement with the theoretical values. The mass attenuation coefficients increase with the decrease in gamma rays energies. This may be attributed to the higher photon interaction probability of blue topaz at lower energy. This result is a first report of mass attenuation coefficient of blue topaz at different gamma rays energies.

  16. Model for the charge-transfer probability in helium nanodroplets following electron-impact ionization

    SciTech Connect

    Ellis, Andrew M.; Yang Shengfu [Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)

    2007-09-15

    A theoretical model has been developed to describe the probability of charge transfer from helium cations to dopant molecules inside helium nanodroplets following electron-impact ionization. The location of the initial charge site inside helium nanodroplets subject to electron impact has been investigated and is found to play an important role in understanding the ionization of dopants inside helium droplets. The model is consistent with a charge migration process in small helium droplets that is strongly directed by intermolecular forces originating from the dopant, whereas for large droplets (tens of thousands of helium atoms and larger) the charge migration increasingly takes on the character of a random walk. This suggests a clear droplet size limit for the use of electron-impact mass spectrometry for detecting molecules in helium droplets.

  17. Cold Atoms

    NASA Astrophysics Data System (ADS)

    Bellac, Michel Le

    2014-11-01

    This chapter and the following one address collective effects of quantum particles, that is, the effects which are observed when we put together a large number of identical particles, for example, electrons, helium-4 or rubidium-85 atoms. We shall see that quantum particles can be classified into two categories, bosons and fermions, whose collective behavior is radically different. Bosons have a tendency to pile up in the same quantum state, while fermions have a tendency to avoid each other. We say that bosons and fermions obey two different quantum statistics, the Bose-Einstein and the Fermi-Dirac statistics, respectively. Temperature is a collective effect, and in Section 5.1 we shall explain the concept of absolute temperature and its relation to the average kinetic energy of molecules. We shall describe in Section 5.2 how we can cool atoms down thanks to the Doppler effect, and explain how cold atoms can be used to improve the accuracy of atomic clocks by a factor of about 100. The effects of quantum statistics are prominent at low temperatures, and atom cooling will be used to obtain Bose-Einstein condensates at low enough temperatures, when the atoms are bosons.

  18. Laser-Driven Nanoplasmas in Doped Helium Droplets: Local Ignition and Anisotropic Growth

    NASA Astrophysics Data System (ADS)

    Mikaberidze, Alexey; Saalmann, Ulf; Rost, Jan M.

    2009-03-01

    Doping a helium nanodroplet with only a tiny xenon cluster of a few atoms sparks complete ionization of the droplet at laser intensities below the ionization threshold of helium atoms. As a result, the intrinsically inert and transparent droplet turns into a fast and strong absorber of infrared light. Microscopic calculations reveal a two-step mechanism to be responsible for the dramatic change: Avalanchelike ionization of the helium atoms on a femtosecond time scale, driven by field ionization due to the quickly charged xenon core, is followed by resonant absorption enabled by an unusual cigar-shaped nanoplasma within the droplet.

  19. A kinematically complete experiment for positron impact ionization of helium at the positron beam facility NEPOMUC

    NASA Astrophysics Data System (ADS)

    Dorn, A.; Holzwarth, M.; Pflueger, Th.; Senftleben, A.; Ren, X.; Ullrich, J.; Hargreaves, L.; Lohmann, B.; Slaughter, D.; Sullivan, J.; Lower, J.; Buckman, S.

    2011-11-01

    In the project presented ionizing collisions of positrons with simple atoms and molecules will be explored in unprecedented detail. By combining presently available high-intensity positron sources with an efficient multi-particle imaging spectrometer (reaction microscope) fully differential benchmark cross sections (FDCS) will become available to critically test theory and to advance our understanding of few-body quantum dynamics. Here the results of a pilot experiment on positron impact ionization of helium at the NEPOMUC positron beam facility are presented. Momentum distributions of the ionized electron and the scattered projectile along the incoming projectile beam axis are presented for E0 = 80 eV and compared to respective electron impact results. For positron impact the electron momentum distribution is shifted significantly forward compared to the electron impact case indicating the reversed post-collision interaction in both cases. In future FDCS will be obtained also at the Australian Positron Beamline Facility.

  20. Study of zinc-induced changes in lymphocyte membranes using atomic force microscopy, luminescence, and light scattering methods

    NASA Astrophysics Data System (ADS)

    Filimonenko, D. S.; Khairullina, A. Ya.; Yasinskii, V. M.; Kozlova, N. M.; Zubritskaja, G. P.; Slobozhanina, E. I.

    2011-07-01

    Changes in the surface structure of lymphocyte membranes exposed to various concentrations of zinc ions are studied. It is found by atomic force microscopy that increasing the concentration of zinc ions leads to a reduction in the correlation length of the autocorrelation function of the roughness profile of a lymphocyte compared to control samples; this may indicate the existence of fine structure in the membrane surface. Fluorescence markers are used to observe a reduction in the microviscosity of the lipids in the outer monolayer of the lipid bilayer after lymphocytes are exposed to Zn ions, as well as the exposure of phosphatidylserine on the surface membrane, and the oxidation of HS-groups of membrane proteins. Calculations of the absorption coefficients of lymphocytes modified with zinc reveal the existence of absorption bands owing to the formation of metal-protein complexes and zinc oxide nanoparticles. These results indicate significant changes in the structural and functional state of lymphocyte membranes exposed to zinc ions.

  1. Mixed quantum/classical theory for inelastic scattering of asymmetric-top-rotor + atom in the body-fixed reference frame and application to the H2O + He system

    NASA Astrophysics Data System (ADS)

    Semenov, Alexander; Dubernet, Marie-Lise; Babikov, Dmitri

    2014-09-01

    The mixed quantum/classical theory (MQCT) for inelastic molecule-atom scattering developed recently [A. Semenov and D. Babikov, J. Chem. Phys. 139, 174108 (2013)] is extended to treat a general case of an asymmetric-top-rotor molecule in the body-fixed reference frame. This complements a similar theory formulated in the space-fixed reference-frame [M. Ivanov, M.-L. Dubernet, and D. Babikov, J. Chem. Phys. 140, 134301 (2014)]. Here, the goal was to develop an approximate computationally affordable treatment of the rotationally inelastic scattering and apply it to H2O + He. We found that MQCT is somewhat less accurate at lower scattering energies. For example, below E = 1000 cm-1 the typical errors in the values of inelastic scattering cross sections are on the order of 10%. However, at higher scattering energies MQCT method appears to be rather accurate. Thus, at scattering energies above 2000 cm-1 the errors are consistently in the range of 1%-2%, which is basically our convergence criterion with respect to the number of trajectories. At these conditions our MQCT method remains computationally affordable. We found that computational cost of the fully-coupled MQCT calculations scales as n2, where n is the number of channels. This is more favorable than the full-quantum inelastic scattering calculations that scale as n3. Our conclusion is that for complex systems (heavy collision partners with many internal states) and at higher scattering energies MQCT may offer significant computational advantages.

  2. Mixed quantum/classical theory for inelastic scattering of asymmetric-top-rotor + atom in the body-fixed reference frame and application to the H?O + He system.

    PubMed

    Semenov, Alexander; Dubernet, Marie-Lise; Babikov, Dmitri

    2014-09-21

    The mixed quantum/classical theory (MQCT) for inelastic molecule-atom scattering developed recently [A. Semenov and D. Babikov, J. Chem. Phys. 139, 174108 (2013)] is extended to treat a general case of an asymmetric-top-rotor molecule in the body-fixed reference frame. This complements a similar theory formulated in the space-fixed reference-frame [M. Ivanov, M.-L. Dubernet, and D. Babikov, J. Chem. Phys. 140, 134301 (2014)]. Here, the goal was to develop an approximate computationally affordable treatment of the rotationally inelastic scattering and apply it to H2O + He. We found that MQCT is somewhat less accurate at lower scattering energies. For example, below E = 1000 cm(-1) the typical errors in the values of inelastic scattering cross sections are on the order of 10%. However, at higher scattering energies MQCT method appears to be rather accurate. Thus, at scattering energies above 2000 cm(-1) the errors are consistently in the range of 1%-2%, which is basically our convergence criterion with respect to the number of trajectories. At these conditions our MQCT method remains computationally affordable. We found that computational cost of the fully-coupled MQCT calculations scales as n(2), where n is the number of channels. This is more favorable than the full-quantum inelastic scattering calculations that scale as n(3). Our conclusion is that for complex systems (heavy collision partners with many internal states) and at higher scattering energies MQCT may offer significant computational advantages. PMID:25240355

  3. Cryogenic and Simulated Fuel Jet Breakup in Argon, Helium and Nitrogen Gas Flows

    NASA Technical Reports Server (NTRS)

    Ingebo, Robert D.

    1995-01-01

    Two-phase flow atomization of liquid nitrogen jets was experimentally investigated. They were co-axially injected into high-velocity gas flows of helium, nitrogen and argon, respectively, and atomized internally inside a two-fluid fuel nozzle. Cryogenic sprays with relatively high specific surface areas were produced, i.e., ratios of surface area to volume were fairly high. This was indicated by values of reciprocal Sauter mean diameters, RSMD's, as measured with a scattered- light scanning instrument developed at NASA Lewis Research Center. Correlating expressions were derived for the three atomizing gases over a gas temperature range of 111 to 422 K. Also, the correlation was extended to include waterjet breakup data that had been previously obtained in simulating fuel jet breakup in sonic velocity gas flow. The final correlating expression included a new dimensionless molecular-scale acceleration group. It was needed to correlate RSMD data, for LN2 and H2O sprays, with the fluid properties of the liquid jets and atomizing gases used in this investigation.

  4. Fort St. Vrain helium circulator auxiliary systems: dynamic performance evaluation and acceptance tests

    Microsoft Academic Search

    1976-01-01

    The purpose of the tests described is to show that the dynamic performance of the Fort St. Vrain helium circulator auxiliary systems satisfies all the guidelines and criteria established and agreed to by Public Service Company of Colorado (PSC), Proto-Power, and General Atomic Company (GA). Specifically, it is shown that transfers to and from backup bearing water and helium purification

  5. Effects of Rayleigh scattering on the CMB and cosmic structure

    NASA Astrophysics Data System (ADS)

    Alipour, Elham; Sigurdson, Kris; Hirata, Christopher M.

    2015-04-01

    During and after recombination, in addition to Thomson scattering with free electrons, photons also couple to neutral hydrogen and helium atoms through Rayleigh scattering. This coupling influences both cosmic microwave background (CMB) anisotropies and the distribution of matter in the Universe. The frequency dependence of the Rayleigh cross section breaks the thermal nature of CMB temperature and polarization anisotropies and effectively doubles the number of variables needed to describe CMB intensity and polarization statistics, while the additional atomic coupling changes the matter distribution and the lensing of the CMB. We introduce a new method to capture the effects of Rayleigh scattering on cosmological power spectra. Rayleigh scattering modifies CMB temperature and polarization anisotropies at the ˜1 % level at 35 GHz (scaling ??4 ), and modifies matter correlations by as much as ˜0.3 %. We show the Rayleigh signal, especially the cross-spectra between the thermal (Rayleigh) E -polarization and Rayleigh (thermal) intensity signal, may be detectable with future CMB missions even in the presence of foregrounds, and how this new information might help to better constrain the cosmological parameters.

  6. Communication: Barium ions and helium nanodroplets: Solvation and desolvation

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaohang; Drabbels, Marcel

    2012-08-01

    The solvation of Ba+ ions created by the photoionization of barium atoms located on the surface of helium nanodroplets has been investigated. The excitation spectra corresponding to the 6p 2P1/2 ? 6s 2S1/2 and 6p 2P3/2 ? 6s 2S1/2 transitions of Ba+ are found to be identical to those recorded in bulk He II [H. J. Reyher, H. Bauer, C. Huber, R. Mayer, A. Schafer, and A. Winnacker, Phys. Lett. A 115, 238 (1986)], indicating that the ions formed at the surface of the helium droplets become fully solvated by the helium. Time-of-flight mass spectra suggest that following the excitation of the solvated Ba+ ions, these are being ejected from the helium droplets either as bare Ba+ ions or as small Ba+Hen (n < 20) complexes.

  7. Cavitation pressure in liquid helium

    Microsoft Academic Search

    Frederic Caupin; Sebastien Balibar

    2001-01-01

    Recent experiments have suggested that, at low enough temperature, the homogeneous nucleation of bubbles occurs in liquid helium near the calculated spinodal limit. This was done in pure superfluid helium 4 and in pure normal liquid helium 3. However, in such experiments, where the negative pressure is produced by focusing an acoustic wave in the bulk liquid, the local amplitude

  8. Helium, its extraction and purification

    Microsoft Academic Search

    R. W. Wilson; H. R. Newson

    1967-01-01

    This is a general discussion of the extraction of helium from natural gas as practiced in the existing helium plants. Several phases of the helium extraction process, such as the refrigeration systems, and methods of carbon dioxide and water removal, are similar to those in natural gas processing. It is concluded that in cryogenic processes solid desiccants are more suited

  9. Free-energy model for fluid helium at high density

    E-print Network

    Winisdoerffer, C; Winisdoerffer, Christophe; Chabrier, Gilles

    2004-01-01

    We present a semi-analytical free-energy model aimed at characterizing the thermodynamic properties of dense fluid helium, from the low-density atomic phase to the high-density fully ionized regime. The model is based on a free-energy minimization method and includes various different contributions representative of the correlations between atomic and ionic species and electrons. This model allows the computation of the thermodynamic properties of dense helium over an extended range of density and temperature and leads to the computation of the phase diagram of dense fluid helium, with its various temperature and pressure ionization contours. One of the predictions of the model is that pressure ionization occurs abruptly at $\\rho \\simgr 10$ g cm$^{-3}$, {\\it i.e.} $P\\simgr 20$ Mbar, from atomic helium He to fully ionized helium He$^{2+}$, or at least to a strongly ionized state, without He$^{+}$ stage, except at high enough temperature for temperature ionization to become dominant. These predictions and this ...

  10. Photonic, Electronic and Atomic Collisions

    NASA Astrophysics Data System (ADS)

    Fainstein, Pablo D.; Lima, Marco Aurelio P.; Miraglia, Jorge E.; Montenegro, Eduardo C.; Rivarola, Roberto D.

    2006-11-01

    Plenary. Electron collisions - past, present and future / J. W. McConkey. Collisions of slow highly charged ions with surfaces / J. Burgdörfer ... [et al.]. Atomic collisions studied with "reaction-microscopes" / R. Moshammer ... [et al.]. Rydberg atoms: a microscale laboratory for studying electron-molecule tnteractions / F. B. Dunning -- Collisions involvintg photons. Quantum control of photochemical reaction dynamics and molecular functions / M. Yamaki ... [et al.]. Manipulating and viewing Rydberg wavepackets / R. R. Jones. Angle-resolved photoelectrons as a probe of strong-field interactions / M. Vrakking. Ultracold Rydberg atoms in a structured environment / I. C. H. Liu and J. M. Rost. Synchrotron-radiation-based recoil ion momentum spectroscopy of laser cooled and trapped cesium atoms / L. H. Coutinho. Reconstruction of attosecond pulse trains / Y. Mairesse ... [et al.]. Selective excitation of metastable atomic states by Femto- and attosecond laser pulses / A. D. Kondorskiy. Accurate calculations of triple differential cross sections for double photoionization of the hygrogen molecule / W. Vanroose ... [et al.]. Double and triple photoionization of Li and Be / J. Colgan, M. S. Pindzola and F. Robicheaux. Few/many body dynamics in strong laser fields / J. Zanghellini and T. Brabec. Rescattering-induced effects in electron-atom scattering in the presence of a circularly polarized laser field / A. V. Flegel ... [et al.]. Multidimensional photoelectron spectroscopy / P. Lablanquie ... [et al.]. Few photon and strongly driven transitions in the XUV and beyond / P. Lambropoulos, L. A. A. Nikolopoulos and S. I. Themelis. Ionization dynamics of atomic clusters in intense laser pulses / U. Saalmann and J. M. Rost. On the second order autocorrelation of an XUV attosecond pulse train / E. P. Benis ... [et al.]. Evidence for rescattering in molecular dissociation / I. D. Williams ... [et al.]. Photoionizing ions using synchrotron radiation / R. Phaneuf. Photo double ionization of fixed in space deuterium molecules / T. Weber ... [et al.]. Coherence and intramolecular scattering in molecular photoionization / U. Becker. Experimental observation of interatomic coulombic decay in neon dimers / T. Jahnke ... [et al.]. Ionization by short UV laser pulses: secondary ATI peaks of the electron spectrum / V. D. Rodríguez, E. Cormier and R. Gayet. Molecular frame photoemission in photoionization of H[symbol] and D[symbol]: the role of dissociation on autoionization of the Q[symbol] and Q[symbol] doubly excited states / D. Dowek, M. Lebech and J. C. Houver. 3p photoemission of 3d transition metals - atoms, molecules and clusters / M. Martins -- Collisions involving electrons. Spin-resolved collisions of electrons with atoms and molecules / G. F. Hanne. Calculation of ionization and excitation processes using the convergent close-coupling method / D. V. Fursa, I. Bray and A. T. Stelbovics. The B-spline R-matrix method for electron and photon collisions with atoms and ions / O. Zatsarinny and K. Bartschat. Absolute angle-differential cross sections for excitation of neon atoms electrons of energy 16.6-19.2 eV / M. Allan ... [et al.]. Studies of QED and nuclear size effects with highly charged ions in an EBIT / J. R. Crespo López-Urrutia ... [et al.]. Recombination of astrophysically relevant ions: Be-like C, N, and O / M. Fogle ... [et al.]. Dissociation and excitation of molecules and molecular ions by electron impact / A. E. Orel and J. Royal state-selective X-ray study of the radiative recombination of U[symbol] ions with cooling electrons / M. Pajek ... [et al.]. Electron collisions with trapped, metastable helium / L. J. Uhlmann ... [et al.]. Non-dipole effects in electron and photon impact ionization / N. L. S. Martin. Electron driven processes in atmospheric behaviour / L. Campbell, M. J. Brunger and P. J. 0. Teubner. Calculation of excitation and ionization for electron-molecule collisions at intermediate energies / J. D. Gorfinkiel. Absolute total cross sections for electron-CH[symbol] scattering at intermediate en

  11. Disintegration of Atomic Nuclei

    Microsoft Academic Search

    H. S. Allen

    1932-01-01

    THE epoch-making results as to the disintegration of atomic nuclei recently obtained in the Cavendish Laboratory serve to recall the experiments of Prof. J. N. Collie and his fellow-workers made twenty years ago. In some of these experiments it was thought that helium and neon were produced by sending powerful electric discharges through exhausted tubes. Sir William Ramsay observed the

  12. Development of a polarized Helium-3 ion source for RHIC using the electron beam ion source

    E-print Network

    Epstein, Charles Samuel

    2013-01-01

    This thesis presents my work on the design and development of a source of polarized Helium-3 ions for the Relativistic Heavy Ion Collider at Brookhaven National Lab, Upton, NY. The 3He atoms will be polarized using the ...

  13. Spin-orbit interaction and large inelastic rates in bismuth-helium collisions S. E. Maxwell,1,* M. T. Hummon,1

    E-print Network

    Krems, Roman

    Spin-orbit interaction and large inelastic rates in bismuth-helium collisions S. E. Maxwell,1,* M experimental and theoretical study of cold collisions between bismuth and helium atoms in strong magnetic properties. Here, we present a study of a very different system: cold collisions of helium and bismuth

  14. Laser ionization and spectroscopy of Cu in superfluid helium nanodroplets

    PubMed Central

    Lindebner, Friedrich; Kautsch, Andreas; Koch, Markus; Ernst, Wolfgang E.

    2014-01-01

    Mass and optical spectroscopic methods are used for the analysis of copper (Cu) atoms and clusters doped to helium nanodroplets (HeN). A two-color resonant two-photon ionization scheme is applied to study the Cu 2P1/2,3/2??2S1/2 ground state transition. The absorption is strongly broadened for Cu atoms submerged inside helium nanodroplets and a comparison with computed literature values is provided. An observed ejection of the dopant from the droplet is triggered upon excitation, populating energetically lower states. The formation of Cun clusters up to Cu7 inside helium nanodroplets was observed by means of electron impact ionization mass spectroscopy.

  15. Towards atomic resolution in sodium titanate nanotubes using near-edge X-ray-absorption fine-structure spectromicroscopy combined with multichannel multiple-scattering calculations

    PubMed Central

    Krüger, Peter; Lagos, Maureen J; Ke, Xiaoxing; Van Tendeloo, Gustaaf; Ewels, Chris; Umek, Polona; Guttmann, Peter

    2012-01-01

    Summary Recent advances in near-edge X-ray-absorption fine-structure spectroscopy coupled with transmission X-ray microscopy (NEXAFS–TXM) allow large-area mapping investigations of individual nano-objects with spectral resolution up to E/?E = 104 and spatial resolution approaching 10 nm. While the state-of-the-art spatial resolution of X-ray microscopy is limited by nanostructuring process constrains of the objective zone plate, we show here that it is possible to overcome this through close coupling with high-level theoretical modelling. Taking the example of isolated bundles of hydrothermally prepared sodium titanate nanotubes ((Na,H)TiNTs) we are able to unravel the complex nanoscale structure from the NEXAFS–TXM data using multichannel multiple-scattering calculations, to the extent of being able to associate specific spectral features in the O K-edge and Ti L-edge with oxygen atoms in distinct sites within the lattice. These can even be distinguished from the contribution of different hydroxyl groups to the electronic structure of the (Na,H)TiNTs. PMID:23213642

  16. A Reusable Surface-Enhanced Raman Scattering (SERS) Substrate Prepared by Atomic Layer Deposition of Alumina on a Multi-Layer Gold and Silver Film

    SciTech Connect

    Dai, Sheng [ORNL; Mahurin, Shannon Mark [ORNL; John, Joshy [ORNL; Sepaniak, Michael [University of Tennessee, Knoxville (UTK)

    2011-01-01

    A thermally stable, reusable surface-enhanced Raman scattering (SERS) substrate consisting of a gold/silver bi-layer film with a protective alumina coating is reported. The film is synthesized by thermally evaporating sequential layers of gold and silver followed by coating an ultra-thin alumina layer using atomic layer deposition. The use of gold as the foundational layer improves the thermal stability of the metal bi-layer film while providing the additional ability to tune the SERS response. Deposition of the thin alumina overlayer on the bi-layer film creates a SERS substrate capable of enduring multiple high-temperature exposures to 400 C with minimal loss of enhancement capabilities. We demonstrate the multi-use capability of the substrate by measuring the SERS spectrum of rhodamine 6G followed by a thermal treatment at 400 C to remove the analyte. A representative substrate was used to acquire SERS spectra of rhodamine 6G up to five repeat measurements, thus establishing the reusability of this relatively simple, inexpensive, and stable substrate.

  17. Surface-enhanced Raman scattering and atomic force microscopy of brass electrodes in sulfuric acid solution containing benzotriazole and chloride ion

    SciTech Connect

    Rubim, J.C.; Kim, J.; Henderson, E.; Cotton, T.M. (Instituto de Quimica da Universidade de Sao Paulo (Brazil) Ames Lab., IA (United States) Iowa State Univ., Ames (United States))

    1993-01-01

    Three different methods were used to roughen brass (Cu/Zn = 67/33) electrodes in 0.5 M H[sub 2]SO[sub 4] containing 1.0 mM benzotriazole (BTAH): (1) polarization at +0.05 V vs. saturated calomel for 5 min; (2) immersion in the above solution for six hours; and (3) oxidation-reduction cycling in the presence of chloride ion. The surfaces prepared by the first two methods exhibited surface-enhanced Raman scattering (SERS) spectra of the polymeric complex [Cu(I)BTA][sub s]. The SERS spectrum obtained from electrodes prepared by the third method is very similar to that of [Cu(I)CIBTAH][sub 4]. Examination of the electrodes by atomic force microscopy (AFM) showed that a large number of grain boundary sites are formed by the roughening processes. This effect is attributed to the loss of zinc, which occurs during corrosion of the mirror-like, polished brass electrode surface in the sulfuric acid solution. 11 refs., 5 figs.

  18. Surface enhanced Raman scattering, natural bond orbitals and Mulliken atomic charge distribution in the normal modes of diethyldithiocarbamate cadmium (II) complex, [Cd(DDTC)2].

    PubMed

    Téllez Soto, C A; Costa, A C; Versiane, O; Lemma, T; Machado, N C F; Mondragón, M A; Martin, A A

    2015-07-01

    Theoretical and experimental bands have been assigned to the Fourier Transform Infrared (FT-IR) and FT-Raman spectra of the bis(diethyldithiocarbamate)Cd(II) complex, abbreviated as ([Cd(DDTC)2]). The calculations and spectral interpretation have been based on the DFT/B3LYP method, infrared and Raman second derivative spectra, and band deconvolution analysis to assist in the assignment of observed fundamentals. This study validated the unusual pseudo tetrahedral molecular structure formed around the Cd(II) cation. Surface-enhanced Raman scattering (SERS) was used to determine the interactions of the normal-modes of the diethyldithiocarbamate cadmium (II) complex on nano-structured silver surfaces. Natural bond orbital (NBO) analysis was also carried out to study the Cd(II) hybridization causing the pseudo tetrahedral geometry of the framework of the [Cd(DDTC)2] complex, and to confirm the charge transfer mechanisms through second order perturbation theory analysis of the Fox Matrix. In order to find out the electronic dispersion of the Mulliken atomic charges (MAC) in the normal modes, we calculated the MAC for each normal mode and correlated these values with the SERS effect. Experimental UV-Vis spectra were obtained and charge transfer bands were assigned. Good agreement between the calculated and experimental values for the vibrational and UV-Vis spectra was obtained. PMID:25813176

  19. OPTICAL PUMPING OF HELIUM IN THE ³S⁠METASTABLE STATE

    Microsoft Academic Search

    F. D. Colegrove; P. A. Franken

    1960-01-01

    The alignment of He⁴ atoms in the (n = 2, metastable) ³Si\\/; sub 1\\/ state is described. Metastable atoms are produced by a r-f discharge in a ; glass tube containing a few nim of pure helium, and the one micron pumping light ; (2³P-2 ³S) is provided by a helium lamp. A resonance signal is ; obtained froni radio

  20. First Observation of Negative Ions in Suprafluid Helium

    Microsoft Academic Search

    Asiz Kasimov; Klaus Jungmann; Gisbert Zu Putlitz; Christiane Zuehlke

    2000-01-01

    Atoms and ions immersed in suprafluid ^4He render the possibility to investigate fundamental interactions of the foreign object with the helium host and to study intrinsic properties of the quantum fluid. Among the major goals is a clearification of the not very well understood nature of elementary ecitations known as rotons. These microprobes form two basically different defect structures: Depending

  1. Quantum mechanicallycomplete measurements in electron impact excitation of helium

    E-print Network

    , experimentally the goal has only been CP500, The Physics of Electronic and Atomic Collisions, edited by Y://proceedings.aip.org/proceedings/cpcr.jsp #12;attained for the 21 ? and 3! P states of helium. Reviews have been given by, for example, Andersen emitted after the excitation process. Earlier studies of the 3*D excitation process made observations

  2. Thermal conduction energy loss in a helium afterglow

    Microsoft Academic Search

    B. V. Donovan; M. C. Sexton

    1970-01-01

    A free-space microwave interferometer (35 GHz) is used to monitor the acoustic standing waves excited by the ionizing discharge in low-pressure helium afterglows. From the frequency of these waves, the decaying gas temperature is evaluated. Theoretical calculations, based on heat loss by atom thermal conduction only, give very good agreement with the experimental results over a wide range of plasma

  3. Helium mobility in SON68 borosilicate nuclear glass: A nuclear reaction analysis approach

    NASA Astrophysics Data System (ADS)

    Bès, R.; Sauvage, T.; Peuget, S.; Haussy, J.; Chamssedine, F.; Oliviero, E.; Fares, T.; Vincent, L.

    2013-11-01

    The 3He behavior in the non active R7T7 type borosilicate glass called SON68 has been investigated using the implantation method to introduce helium in the material. Nuclear Reaction Analysis (NRA) was performed to follow the helium concentration depth profile evolution as a function of annealing time and temperature. In addition, in situ Transmission Electron Microscopy (TEM) has been implemented to study the formation of helium bubbles during both implantation and annealing processes. Numerical modeling with two different approaches is proposed and discussed to investigate the helium mobility mechanisms. Our study reveals for helium incorporation by implantation at low temperature the presence of several helium populations with disparate diffusivities. The most mobile helium fraction would be attributed to atomic diffusion. The corresponding activation energy value (0.61 eV) extracted from Arrhenius graphs is in good agreement with literature data. The results also highlight that the damages associated to helium sursaturation are the source of small helium clusters formation, with a reduced mobility instead of the atomic mobility measured by the infusion technique. Small cavities that support this assumption have been observed by TEM at low temperature.

  4. Lifetime of a Chemically Bound Helium Compound

    NASA Technical Reports Server (NTRS)

    Chaban, Galina M.; Lundell, Jan; Gerber, R. Benny; Kwak, Dochan (Technical Monitor)

    2001-01-01

    The rare-gas atoms are chemically inert, to an extent unique among all elements. This is due to the stable electronic structure of the atoms. Stable molecules with chemically bound rare-gas atoms are, however, known. A first such compound, XePtF6, W2S prepared in 1962 and since then a range of molecules containing radon, xenon and krypton have been obtained. Most recently, a first stable chemically bound compound of argon was prepared, leaving neon and helium as the only elements for which stable chemically bound molecules are not yet known. Electronic structure calculations predict that a metastable species HHeF exists, but significance of the result depends on the unknown lifetime. Here we report quantum dynamics calculations of the lifetime of HHeF, using accurate interactions computed from electronic structure theory. HHeF is shown to disintegrate by tunneling through energy barriers into He + HF and H + He + F the first channel greatly dominating. The lifetime of HHeF is more than 120 picoseconds, that of DHeF is 14 nanoseconds. The relatively long lifetimes are encouraging for the preparation prospects of this first chemically bound helium compound.

  5. Quantum mechanics of one- and two-electron atoms

    Microsoft Academic Search

    H. A. Bethe; E. E. Salpeter

    1977-01-01

    Calculations are presented pertaining to hydrogen- and helium-like atoms and their comparisons with experiments. Mainly low-brow explicit derivations are given rather than more elegant but more difficult formalisms. A large fraction is devoted to the Dirac theory of the electron and to radiative effects including relevant experiments treated from the practical point of view. The hydrogen and helium atoms without

  6. Applications of Groundwater Helium

    USGS Publications Warehouse

    Kulongoski, Justin T.; Hilton, David R.

    2011-01-01

    Helium abundance and isotope variations have widespread application in groundwater-related studies. This stems from the inert nature of this noble gas and the fact that its two isotopes ? helium-3 and helium-4 ? have distinct origins and vary widely in different terrestrial reservoirs. These attributes allow He concentrations and 3He/4He isotope ratios to be used to recognize and quantify the influence of a number of potential contributors to the total He budget of a groundwater sample. These are atmospheric components, such as air-equilibrated and air-entrained He, as well as terrigenic components, including in situ (aquifer) He, deep crustal and/or mantle He and tritiogenic 3He. Each of these components can be exploited to reveal information on a number of topics, from groundwater chronology, through degassing of the Earth?s crust to the role of faults in the transfer of mantle-derived volatiles to the surface. In this review, we present a guide to how groundwater He is collected from aquifer systems and quantitatively measured in the laboratory. We then illustrate the approach of resolving the measured He characteristics into its component structures using assumptions of endmember compositions. This is followed by a discussion of the application of groundwater He to the types of topics mentioned above using case studies from aquifers in California and Australia. Finally, we present possible future research directions involving dissolved He in groundwater.

  7. One-dimensional fluid simulations of a helium - xenon filled ac colour plasma flat panel display pixel

    Microsoft Academic Search

    Ramana Veerasingam; Robert B. Campbell; Robert T. McGrath

    1997-01-01

    One-dimensional (1D) fluid simulations are used to model a helium-xenon filled ac plasma display pixel. The model includes four levels for helium atomic states, seven levels for xenon atomic states and a xenon dimer state. The model also includes VUV emission including photon trapping due to collisional broadening from the resonant atomic xenon at wavelengths of 129 nm and 147

  8. Signature of helium segregation in hydrogen-helium mixtures

    NASA Astrophysics Data System (ADS)

    Hamel, Sebastien; Morales, Miguel A.; Schwegler, Eric

    2011-10-01

    The conductivity and reflectivity of mixtures of hydrogen and helium under high pressure are calculated using first-principles molecular dynamics and the Kubo-Greenwood formula. Hydrogen-helium mixtures have been predicted to undergo demixing below a certain critical temperature. The impact of phase segregation of helium on the optical properties of the mixtures is explored. The change in reflectivity upon demixing is found to vary with frequency with larger variation at higher frequency.

  9. Evolution of defects in silicon carbide implanted with helium ions

    NASA Astrophysics Data System (ADS)

    Zhang, Chonghong; Song, Yin; Yang, Yitao; Zhou, Chunlan; Wei, Long; Ma, Hongji

    2014-05-01

    Effects of accumulation of radiation damage in silicon carbide are important concerns for the use of silicon carbide in advanced nuclear energy systems. In the present work lattice damage in silicon carbide crystal (4H type) implanted with 100 keV 4He+ ions was investigated with Rutherford backscattering spectrometry in channeling geometry (RBS/c) and positron beam Doppler broadening spectrometry (PBDB). Helium implantation was performed at the specimen temperature of 510 K to avoid amorphization of the SiC crystal. Fluences of helium ions were selected to be in the range from 1 × 1016 to 3 × 1016 ions cm-2, around the dose threshold for the formation of observable helium bubbles under transmission electron microscopes (TEM). The RBS/c measurements show distinctly different annealing behavior of displaced Si atoms at doses below or above the threshold for helium bubble formation. The RBS/c yield in the peak damage region of the specimen implanted to 3 × 1016 He-ions cm-2 shows an increase on the subsequently thermal annealing above 873 K, which is readily ascribed to the extra displacement of Si atoms due to helium bubble growth. The RBS/c yield in the specimen implanted to a lower ion fluence of 1.5 × 1016 He-ions cm-2 decreases monotonously on annealing from ambient temperatures up to 1273 K. The PBDB measurements supply evidence of clustering of vacancies at temperatures from 510 to 1173 K, and dissociation of vacancy clusters above 1273 K. The similarity of annealing behavior in PBDB profiles for helium implantation to 1 × 1016 and 3 × 1016 ions cm-2 is ascribed to the saturation of trapping of positrons in vacancy type defects in the damaged layers in the specimens helium-implanted to the two dose levels.

  10. Mixed quantum/classical theory for inelastic scattering of asymmetric-top-rotor + atom in the body-fixed reference frame and application to the H{sub 2}O + He system

    SciTech Connect

    Semenov, Alexander [Chemistry Department, Wehr Chemistry Building, Marquette University, Milwaukee, Wisconsin 53201-1881 (United States); PSL Research University, Observatoire de Paris, Sorbonne Universités, UPMC Univ Paris 06, ENS, UCP, CNRS, UMR8112, LERMA, 5 Place Janssen, 92195 Meudon (France); Dubernet, Marie-Lise [PSL Research University, Observatoire de Paris, Sorbonne Universités, UPMC Univ Paris 06, ENS, UCP, CNRS, UMR8112, LERMA, 5 Place Janssen, 92195 Meudon (France); Babikov, Dmitri, E-mail: dmitri.babikov@mu.edu [Chemistry Department, Wehr Chemistry Building, Marquette University, Milwaukee, Wisconsin 53201-1881 (United States)

    2014-09-21

    The mixed quantum/classical theory (MQCT) for inelastic molecule-atom scattering developed recently [A. Semenov and D. Babikov, J. Chem. Phys. 139, 174108 (2013)] is extended to treat a general case of an asymmetric-top-rotor molecule in the body-fixed reference frame. This complements a similar theory formulated in the space-fixed reference-frame [M. Ivanov, M.-L. Dubernet, and D. Babikov, J. Chem. Phys. 140, 134301 (2014)]. Here, the goal was to develop an approximate computationally affordable treatment of the rotationally inelastic scattering and apply it to H{sub 2}O + He. We found that MQCT is somewhat less accurate at lower scattering energies. For example, below E = 1000 cm{sup ?1} the typical errors in the values of inelastic scattering cross sections are on the order of 10%. However, at higher scattering energies MQCT method appears to be rather accurate. Thus, at scattering energies above 2000 cm{sup ?1} the errors are consistently in the range of 1%–2%, which is basically our convergence criterion with respect to the number of trajectories. At these conditions our MQCT method remains computationally affordable. We found that computational cost of the fully-coupled MQCT calculations scales as n{sup 2}, where n is the number of channels. This is more favorable than the full-quantum inelastic scattering calculations that scale as n{sup 3}. Our conclusion is that for complex systems (heavy collision partners with many internal states) and at higher scattering energies MQCT may offer significant computational advantages.

  11. Determining the Source of Neutral Helium in the Corona from Spectropolarimetric Observations with SOLARC

    Microsoft Academic Search

    Meghan Cassidy

    2009-01-01

    On the summit of Haleakala, spectropolarimetic ground observations from the coronagraph of the Scattered-light Observatory for Limb Active Regions and Coronae (SOLARC) and infrared imaging spectropolarimeter detect a spectrally resolved surface brightness flux at the 10830 Å wavelength. The polarization signal indicates scattered light off of He I particles. Under investigation is the origin of this neutral helium. Its presence

  12. Helium jet dispersion to atmosphere

    NASA Technical Reports Server (NTRS)

    Khan, Hasna J.

    1986-01-01

    On the event of loss of vacuum guard of superinsulated helium dewar, high rate of heat transfer into the tank occurs. The rapid boiling of liquid helium causes the burst disk to rupture at four atmospheres and consequently the helium passes to the atmosphere through vent lines. The gaseous helium forms a vertical buoyant jet as it exits the vent line into a stagnant environment. Characterization of the gaseous jet is achieved by detailed analysis of the axial and radial dependence of the flow parameters.

  13. Helium cryopumping for fusion applications

    SciTech Connect

    Sedgley, D.W.; Batzer, T.H.; Call, W.R.

    1988-05-01

    Large quantities of helium and hydrogen isotopes will be exhausted continuously from fusion power reactors. This paper summarizes two development programs undertaken to address vacuum pumping for this application: (i) A continuous duty cryopump for pumping helium and/or hydrogen species using charcoal sorbent and (ii) a cryopump configuration with an alternative shielding arrangement using charcoal sorbent or argon spray. A test program evaluated automatic pumping of helium, helium pumping by charcoal cryosorption and with argon spray, and cryosorption of helium/hydrogen mixtures. The continuous duty cryopump pumped helium continuously and conveniently. Helium pumping speed was 7.7 l/s/cm/sup 2/ of charcoal, compared to 5.8 l/s/cm/sup 2/ for the alternative pump. Helium speed using argon spray was 18% of that obtained by charcoal cryosorption in the same (W-panel) pump. During continuous duty cryopump mixture tests with helium and hydrogen copumped on charcoal, gas was released sporadically. Testing was insufficient to explain this unacceptable event.

  14. Hydrogen Production Using the Modular Helium Reactor

    SciTech Connect

    E. A. Harvego; S. M. Reza; M. Richards; A. Shenoy

    2005-05-01

    The high-temperature characteristics of the Modular Helium Reactor (MHR) make it a strong candidate for the production of hydrogen using either thermochemical or high-temperature electrolysis (HTE) processes. Using heat from the MHR to drive a Sulfur-Iodine (S-I) thermochemical hydrogen process has been the subject of a DOE sponsored Nuclear Engineering Research Initiative (NERI) project lead by General Atomics, with participation from the Idaho National Engineering and Environmental Laboratory (INEEL) and Texas A&M University. While the focus of much of the initial work was on the S-I thermochemical production of hydrogen, recent activities have also included development of a preconceptual design for an integral HTE hydrogen production plant driven by the process heat and electricity produced by a 600 MWt MHR. This paper describes RELAP5-3D analyses performed to evaluate alternative primary system cooling configurations for the MHR to minimize peak reactor vessel and core temperatures while achieving core helium outlet temperatures in the range of 900 oC to 1000 oC, needed for the efficient production of hydrogen using either the S-I thermochemical or HTE process. The cooling schemes investigated are intended to ensure peak fuel temperatures do not exceed specified limits under normal or transient upset conditions, and that reactor vessel temperatures do not exceed ASME code limits for steady-state or transient conditions using standard LWR vessel materials. Preconceptual designs for both an S-I thermochemical and HTE hydrogen production plant driven by a 600 MWt MHR at helium outlet temperatures in the range of 900 oC to 1000 oC are described and compared. An initial SAPHIRE model to evaluate the reliability, maintainablility, and availability of the S-I hydrogen production plant is also discussed, and plans for future assessments of conceptual designs for both a S-I thermochemical and HTE hydrogen production plant coupled to a 600 MWt modular helium reactor are described.

  15. A configurational study of helium clusters doped with He(?-) and He2 (?.).

    PubMed

    Rodríguez-Cantano, Rocío; González-Lezana, Tomás; Villarreal, Pablo; Gianturco, Franco A

    2015-03-14

    Helium clusters doped with electronically excited atomic and molecular helium anions He(?-) and He2 (?-) at T = 0.4 K are studied by means of path integral Monte Carlo calculations. Geometry and energetics of the systems with up to 32 solvating He atoms are characterised. The interactions between the anions and the neutral He atoms have been described by fitting previously reported ab initio points to analytical expressions. The HeN-He(?-) clusters with N > 6 display a structure defined by a bipyramid which completely solvates the atomic anion, whereas the rest of surrounding He atoms form a dimple around that initial cage. On the contrary, the structures observed for the HeN-He2 (?-) clusters clearly show the dopant located outside the helium droplet, thereby confirming the heliophobic character of He2 (?-). PMID:25770536

  16. Swelling and structure of vanadium-base alloys irradiated in the dynamic helium charging experiment

    SciTech Connect

    Chung, H.M.; Loomis, B.A.; Smith, D.L.

    1994-08-01

    Combined effects of dynamically charged helium and neutron damage on density change, void distribution, and microstructural evolution of V-4Cr-4Ti alloy have been determined after irradiation to 18--31 dpa at 425--600 C in the Dynamic Helium Charging Experiment (DHCE), and the results were compared with those from a non-DHCE in which helium generation and negligible. For specimens irradiated to {approx}18-31 dpa at 500--600 with a helium generation rate of 0.4--4.2 appm He/dpa, only a few helium bubbles were observed at the interface of grain matrices and some of the Ti(O,N,C) precipitates, and no microvoids or helium bubbles were observed either in grain matrices or near grain boundaries. Under these conditions, dynamically produced helium atoms seem to be trapped in the grain matrix without significant bubble nucleation or growth, and in accordance with this, density changes from DHCE and non-DHCE (negligible helium generation) were similar for comparable fluence and irradiation temperature. Only for specimens irradiated to {approx}31 dpa at 425 C, when helium was generated at a rage of 0.4--0.8 appm helium/dpa, were diffuse helium bubbles observed in limited regions of grain matrices and near {approx}15% of the grain boundaries in densities significantly lower than those in the extensive coalescences of helium bubbles typical of other alloys irradiated in tritium-trick experiments. Density changes of specimens irradiated at 425 C in the DHCE were significantly higher than those from non-DHCE irradiation. Microstructural evolution in V-4Cr-4Ti was similar for DHCE and non-DHCE except for helium bubble number density and distribution. As in non-DHCE, the irradiation-induced precipitation of ultrafine Ti{sub 5}Si{sub 3} was observed for DHCE at >500 C but not at 425 C.

  17. Differential elastic electron scattering cross sections for CCl4 by 1.5-100 eV energy electron impact.

    PubMed

    Limão-Vieira, P; Horie, M; Kato, H; Hoshino, M; Blanco, F; García, G; Buckman, S J; Tanaka, H

    2011-12-21

    We report absolute elastic differential, integral and momentum transfer cross sections for electron interactions with CCl(4). The incident electron energy range is 1.5-100 eV, and the scattered electron angular range for the differential measurements varies from 15°-130°. The absolute scale of the differential cross section was set using the relative flow technique with helium as the reference species. Comparison with previous total cross sections shows good agreement. Atomic-like behaviour in this scattering system is shown here for the first time, and is further investigated by comparing the CCl(4) elastic cross sections to recent results on the halomethanes and atomic chlorine at higher impact energies [H. Kato, T. Asahina, H. Masui, M. Hoshino, H. Tanaka, H. Cho, O. Ingólfsson, F. Blanco, G. Garcia, S. J. Buckman, and M. J. Brunger, J. Chem. Phys. 132, 074309 (2010)]. PMID:22191877

  18. Proton and helium cyclotron anisotropy instability thresholds in the magnetosheath

    NASA Technical Reports Server (NTRS)

    Gary, S. Peter; Convery, Patrick D.; Denton, Richard E.; Fuselier, Stephen A.; Anderson, Brian J.

    1994-01-01

    Both the protons and the helium ions of the terrestrial magnetosheath typically display T (sub perpendicular) greater than T (sub parallel), where perpendicular to and parallel to denote directions perpendicular and parallel to the background magnetic field. Observations of the highly compressed magnetosheath show an inverse correlation between these ion temperature anisotropies and the parallel proton beta. Computer simulations have demonstrated that these correlations are due to wave-particle scattering by electromagnetic ion cyclotron anisotropy instabilities. These correlations correspond to linear theory thresholds of the proton cyclotron and the helium cyclotron instabilities. This paper uses linear Vlasov theory and the assumption of a constant maximum growth rate to obtain closed-form expressions for these thresholds as a function of the relative helium density and the parallel proton beta in a parameter model of the magnetosheath.

  19. Effective interactions, elementary excitations, and transport in the helium liquids

    SciTech Connect

    Pines, D.

    1986-01-01

    Polarization potentials, the self-consistent fields which describe the primary consequences of the strong atom-atom interaction in the helium liquids, are developed for liquid /sup 4/He and /sup 3/He. Emphasis is placed on the common physical origin of the effective interactions in all helium liquids, and the hierarchy of physical effects (very short-range atomic correlations, zero point motion, and the Pauli principle) which determine their strength is reviewed. An overview is then given of the application of polarization potential theory to experiment, including the phonon-maxon-roton spectra of /sup 4/He and /sup 3/He-/sup 4/He mixtures, the phonon-maxon spectrum of normal and spin-polarized /sup 3/He, and the transport properties of superfluid /sup 4/He and of normal and spin-polarized /sup 3/He.

  20. Compact hydrogen/helium isotope mass spectrometer

    DOEpatents

    Funsten, Herbert O. (Los Alamos, NM); McComas, David J. (Los Alamos, NM); Scime, Earl E. (Morgantown, WV)

    1996-01-01

    The compact hydrogen and helium isotope mass spectrometer of the present invention combines low mass-resolution ion mass spectrometry and beam-foil interaction technology to unambiguously detect and quantify deuterium (D), tritium (T), hydrogen molecule (H.sub.2, HD, D.sub.2, HT, DT, and T.sub.2), .sup.3 He, and .sup.4 He concentrations and concentration variations. The spectrometer provides real-time, high sensitivity, and high accuracy measurements. Currently, no fieldable D or molecular speciation detectors exist. Furthermore, the present spectrometer has a significant advantage over traditional T detectors: no confusion of the measurements by other beta-emitters, and complete separation of atomic and molecular species of equivalent atomic mass (e.g., HD and .sup.3 He).