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1

Accurate Determination of the Scattering Length of Metastable Helium Atoms Using Dark Resonances between Atoms and Exotic Molecules  

E-print Network

a new measurement of the s-wave scattering length a of spin-polarized helium atoms in the 2 3S1Accurate Determination of the Scattering Length of Metastable Helium Atoms Using Dark Resonances helium atoms in the 2 3 S1 state [1,2], several esti- mates for their s-wave scattering length a were

Cohen-Tannoudj, Claude

2

Helium atom scattering investigation of the Sb(111) surface  

NASA Astrophysics Data System (ADS)

The Sb(111) surface was studied with helium atom scattering (HAS). Elastic HAS at different energies of the incident helium beam (15.3, 21.9, 28.4 meV) was applied for structural investigations. The lattice constants derived from the positions of the observed diffraction peaks up to third order were found to be in perfect agreement with previous structure determinations of Sb(111). The observed diffraction patterns with clear peaks up to second order were used to model the electronic surface corrugation with the GR method. As an estimation for the attractive part of the interaction potential a well depth of (4.0 ± 0.5) meV was found. Best fit results were obtained with a corrugation height of 12-13% of the lattice constant, which is rather large compared to other surfaces with metallic character. Intensity measurements of the specular peak as a function of incident energy were analysed to determine the distribution of terraces on the surface. The results show a quite flat Sb(111) surface and a step height of 3.81 Å of the remaining terraces.

Mayrhofer-Reinhartshuber, M.; Tamtögl, A.; Kraus, P.; Ernst, W. E.

2013-10-01

3

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

E-print Network

Feasibility of measuring surface electron spin dynamics by inelastic scattering of metastable helium atoms M. El-Batanouny, G. Murthy, and C. R. Willis Department of Physics, Boston University January 1998 The application of inelastic scattering of monoenergetic beams of metastable 23 S helium

Kais, Sabre

4

Elastic and inelastic helium atom scattering at a cleaved mica sheet  

Microsoft Academic Search

A mica sheet has been cleaved in situ in a UHV beam scattering apparatus. The diffraction of the helium atoms shows sharp Bragg peaks. In the ?100? and ?110? directions of the hexagonal surface the intensities of the Bragg peaks are analysed in terms of a sinusoidal corrugation. With hard wall scattering calculations (Kirchhoff-Eikonal approximation) the corrugation is found to

G. Brusdeylins; D. Schmicker

1995-01-01

5

Scattering of H(1s) off metastable helium atom at thermal energies  

SciTech Connect

Quantal calculations for scattering of ground-state antihydrogen by metastable (n=2S) helium atoms have been performed using the nonadiabatic, atomic orbital expansion technique at thermal energies. The zero-energy elastic cross sections of the present systems are much greater than the corresponding value for the ground-state helium target. The low-energy elastic cross section for the singlet metastable helium [He(2 {sup 1}S)] target is higher than the corresponding value when the target is in the metastable triplet state [He(2 {sup 3}S)].

Sinha, Prabal K.; Ghosh, A. S. [Department of Physics, Bangabasi College, 19, Raj Kumar Chakravorty Sarani, Kolkata 700 009 (India); Department of Theoretical Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032 (India)

2006-06-15

6

Atomic scattering from an adsorbed monolayer solid with a helium beam that penetrates to the substrate  

SciTech Connect

Diffraction and one-phonon inelastic scattering of a thermal energy helium atomic beam are evaluated in the situation that the target monolayer lattice is so dilated that the atomic beam penetrates to the interlayer region between the monolayer and the substrate. The scattering is simulated by propagating a wavepacket and including the effect of a feedback of the inelastic wave onto the diffracted wave, which represents a coherent re-absorption of the created phonons. Parameters are chosen to be representative of an observed p(1 Multiplication-Sign 1) commensurate monolayer solid of H{sub 2}/NaCl(001) and a conjectured p(1 Multiplication-Sign 1) commensurate monolayer solid of H{sub 2}/KCl(001). For the latter, there are cases where part of the incident beam is trapped in the interlayer region for times exceeding 50 ps, depending on the spacing between the monolayer and the substrate and on the angle of incidence. The feedback effect is large for cases of strong transient trapping.

Hansen, F. Y. [Department of Chemistry, Technical University of Denmark, IK-207-DTU, DK-2800 Lyngby (Denmark); Bruch, L. W. [Department of Physics, University of Wisconsin-Madison, 1150 University Avenue, Madison, Wisconsin 53706 (United States); Dammann, B. [Department of Informatics and Mathematical Modeling, Technical University of Denmark, 321-DTU, DK 2800 Lyngby (Denmark)

2013-03-14

7

Breakdown of atomic superposition for the helium scattering potential of c(2×2) oxygen on nickel (001)  

NASA Astrophysics Data System (ADS)

Self-consistent calculations of the charge density of the c(2×2) phase of oxygen on nickel (001) (i) give a helium scattering potential which in excellent agreement with the shape, height and width of that obtained by Rieder by fitting his atom-surface scattering data: (ii) justify th use of a hard-wall fit because of a 4.2 Å -1 averrage softness parameter; and (iii) rule out superposition of atomic or ionic charge densities for this and similar systems.

Godby, R. W.; Garcia, N.

1985-11-01

8

Breakdown of atomic superposition for the helium scattering potential of c(2×2) oxygen on nickel (001)  

NASA Astrophysics Data System (ADS)

Self-consistent calculations of the charge density of the c(2×2) phase of oxygen on nickel (001) (i) give a helium scattering potential which is in excellent agreement with the shape, height and width of that obtained by Rieder by fitting his atom-surface scattering data; (ii) justify the use of a hard-wall fit because of a 4.2 Å -1 average softness parameter; and (iii) rule out superposition of atomic or ionic charge densities for this and similar systems.

Godby, R. W.; Garcia, N.

9

The scattering of low energy helium ions and atoms from a copper single crystal. Elastic and inelastic effects  

Microsoft Academic Search

The scattering of 4–10 keV Helium ions from a copper surface can be described reasonably well with elastic, single collisions, even for fairly small scattering angles. However, in a more refined analysis of the experimental results, deviations from this behaviour are observed. Measurements of the energy and the width (FWHM) of the surface peak have been performed. The general behaviour

L. K. Verhey; B. Poelsema; A. L. Boers

1976-01-01

10

Ab initio interaction potentials and scattering lengths for ultracold mixtures of metastable helium and alkali-metal atoms  

E-print Network

We have obtained accurate ab initio quartet potentials for the diatomic metastable triplet helium + alkali-metal (Li, Na, K, Rb) systems, using all-electron restricted open-shell coupled cluster singles and doubles with noniterative triples corrections [CCSD(T)] calculations and accurate calculations of the long-range $C_6$ coefficients. These potentials provide accurate ab initio quartet scattering lengths, which for these many-electron systems is possible, because of the small reduced masses and shallow potentials that results in a small amount of bound states. Our results are relevant for ultracold metastable triplet helium + alkali-metal mixture experiments.

Dariusz K?dziera; ?ukasz Mentel; Piotr S. ?uchowski; Steven Knoop

2015-01-05

11

Ab initio interaction potentials and scattering lengths for ultracold mixtures of metastable helium and alkali-metal atoms  

E-print Network

We have obtained accurate ab initio quartet potentials for the diatomic metastable triplet helium + alkali-metal (Li, Na, K, Rb) systems, using all-electron restricted open-shell coupled cluster singles and doubles with noniterative triples corrections [CCSD(T)] calculations and accurate calculations of the long-range $C_6$ coefficients. These potentials provide accurate ab initio quartet scattering lengths, which for these many-electron systems is possible, because of the small reduced masses and shallow potentials that results in a small amount of bound states. Our results are relevant for ultracold metastable triplet helium + alkali-metal mixture experiments.

K?dziera, Dariusz; ?uchowski, Piotr S; Knoop, Steven

2015-01-01

12

Interpretation of helium atom scattering from isolated CO molecules on copper (001) based on an exact quantum mechanical model  

Microsoft Academic Search

The previously reported scattering of He atoms from isolated CO molecules on Cu(001) has been reinterpreted using an exact quantum mechanical model assuming a hard hemisphere on a hard flat surface. From a best fit of all the observed oscillations for each incident energy an effective radius for the hemisphere is determined. The radius increases from a=2.4 to 4.4 Å

B. H. Choi; K. T. Tang; J. P. Toennies

1997-01-01

13

Helium Atom Scattering from KTa0:7Nb0:3O3 (001): Anomalous Surface reflectivity with varying surface temperature and helium wave vector  

SciTech Connect

Helium atom diraction experiments have been carried out on the (001) surface of KTaO3 doped with 30% Nb. The surfaces were produced by cleaving single crystals of the material in situ. After the samples were thermally cycled, the angular distributions measured in the <100> azimuth, but not those in the <110> azimuth, revealed half-order diraction peaks. These indicate the formation of small (21) surface domains. The scans of the specular and Bragg diraction peak intensities as the sample temperatures were varied from about 325K to 60-80K and back to 325K showed large hysteresis particularly in the <100> azimuth. In addition, these scans showed a distinct intensity dip at about 85K, which is far removed from any bulk phase transition temperature of this material. Most curious, the specular re ectivity of the surface was found to be a strong function of the He wavevector, decreasing rapidly as the wavevector was varied above or below an optimum value.

Fatema, Rifat [Florida State University; Trelenberg, T. W. [Florida State University; Van Winkle, David [Florida State University; Skofronick, J. G. [Florida State University; Safron, Sanford A. [Florida State University; Flaherty, F. A. [Valdosta State University, Valdosta, GA; Boatner, Lynn A [ORNL

2011-01-01

14

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)

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.

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

1985-01-01

15

The Structure of the Helium Atom  

Microsoft Academic Search

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

Irving Langmuir

1921-01-01

16

Electron scattering in helium for Monte Carlo simulations  

SciTech Connect

An analytical approximation for differential cross-section of electron scattering on helium atoms is introduced. It is intended for Monte Carlo simulations, which, instead of angular distributions based on experimental data (or on first-principle calculations), usually rely on approximations that are accurate yet numerically efficient. The approximation is based on the screened-Coulomb differential cross-section with energy-dependent screening. For helium, a two-pole approximation of the screening parameter is found to be highly accurate over a wide range of energies.

Khrabrov, Alexander V.; Kaganovich, Igor D. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2012-09-15

17

Interaction of Helium Rydberg State Atoms with Superfluid Helium  

NASA Astrophysics Data System (ADS)

The pair potentials between ground state helium and Rydberg He atoms are calculated by the full configuration interaction electronic structure method for both the electronic singlet and the triplet manifolds. The obtained pair potentials are validated against existing experimental molecular and atomic data. Most states show remarkable energy barriers at long distances ( Å), which can effectively stabilize He against the formation of He at low nuclear kinetic energies. Bosonic density functional theory calculations, based on the calculated pair potential data, indicate that the triplet ground state He reside in spherical bubbles in superfluid helium with a barycenter radius of 6.1 Å at the liquid saturated vapor pressure. The pressure dependency of the relative He absorption line blue shift in the liquid was obtained through both the statistical line broadening theory as well as the dynamic adiabatic following method. The pronounced difference between the results from the static and dynamic models is attributed to the dynamic Jahn-Teller effect that takes places in the electronically excited state within the dephasing time of 150 fs. Transient non-thermalized liquid surroundings near He may contribute to an artificial reduction in the absorption line blue shift by up to 30 cm.

Fiedler, Steven L.; Eloranta, Jussi

2014-03-01

18

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.

19

Searching for dark matter with helium atom  

E-print Network

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.

Imre Ferenc Barna

2006-08-10

20

Classical Helium Atom with Radiation Reaction  

E-print Network

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.

G. Camelio; A. Carati; L. Galgani

2011-11-24

21

Classical helium atom with radiation reaction  

NASA Astrophysics Data System (ADS)

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.

Camelio, G.; Carati, A.; Galgani, L.

2012-06-01

22

Classical helium atom with radiation reaction  

SciTech Connect

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.

Camelio, G. [Universita degli Studi di Milano, Corso di Laurea in Fisica, Via Celoria 16, I-20133 Milano (Italy); Carati, A.; Galgani, L. [Dipartimento di Matematica, Universita degli Studi di Milano, Via Saldini 50, I-20133 Milano (Italy)

2012-06-15

23

Classical helium atom with radiation reaction.  

PubMed

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. PMID:22757518

Camelio, G; Carati, A; Galgani, L

2012-06-01

24

Elastic Collisions of Interstellar Helium Atoms with Solar Wind Ions  

NASA Astrophysics Data System (ADS)

Relative motion of the Sun with respect to the surrounding local interstellar medium (LISM) results in entering of interstellar helium atoms into the heliosphere. These atoms have been experimentally studied in detail by observing their glow, measuring as pickup ions, and by directly detecting them on the Ulysses and IBEX space missions. Local helium fluxes in the heliosphere are characterized by angular and velocity distributions determined by the velocity, temperature, and number density of helium in the LISM. Dynamics of atom propagation to an observational point in the gravitational field of the sun and atom losses are well understood. The observed far wings of directional distributions of interstellar helium fluxes show higher intensities than predicted by conventional theoretical models. This wing enhancement, the helium flux halo (in contrast to the flux core), could be caused, in part, by elastic collisions of interstellar helium atoms with solar wind ions. This presentation evaluates elastic collisions of inflowing interstellar helium atoms with solar wind protons and alpha-particles leading to the helium flux halo.

Gruntman, M.

2013-12-01

25

Atomic origins of solid helium bubbles in tungsten  

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

26

Elastic collisions of interstellar helium atoms with solar wind protons  

NASA Astrophysics Data System (ADS)

Relative motion of the Sun with respect to the surrounding local interstellar medium results in entering of interstellar helium atoms into the heliosphere. Current models of helium flowing into the solar system do not include elastic collisions of atoms with solar wind ions. It was predicted in 1986, without quantitative elaboration, that such collisions would enhance wings of directional distributions of helium atom fluxes. This paper focuses on a theoretical treatment of elastic collisions of interstellar He atoms with the solar wind protons resulting in increased wing intensities, called the helium flux halo in contradistinction to the flux core. We concentrate on directional distributions of He atom intensities at 1 AU from the Sun for observers at rest and moving with the Earth and confirm the formation of the flux halo. We show that the collision-produced halo would often dominate He atom intensities at angles larger than 30°-35° from the maximum intensity direction in the flux core. A comparison with direct measurements of interstellar helium atom fluxes is beyond the scope of this paper.

Gruntman, Mike

2013-04-01

27

Convergent close-coupling calculations of positron scattering on metastable helium  

SciTech Connect

The convergent close-coupling method has been applied to positron scattering on a helium atom in the 2 {sup 3}S metastable state. For this system the positronium (Ps) formation channel is open even at zero scattering energy making the inclusion of the Ps channels especially important. Spin algebra is presented for the general case of arbitrary spins. A proof is given of the often-used assumption about the relationship between the amplitudes for ortho-positronium and para-positronium formation. The cross sections for scattering from 2 {sup 3}S are shown to be significantly larger than those obtained for the ground state.

Utamuratov, R.; Kadyrov, A. S.; Fursa, D. V.; Bray, I.; Stelbovics, A. T. [ARC Centre for Antimatter-Matter Studies, Department of Applied Physics, Curtin University, Perth 6152 (Australia)

2010-10-15

28

Atomic resonance and scattering  

SciTech Connect

Experiments were conducted in the following areas: mapping of energy levels of a Rydberg lithium atom in a strong magnetic field in the vicinity of a crossing between levels from different principle quantum numbers, electrodynamics in a cavity, resonance enhanced multiphoton ionization, velocity dependence of rotational rainbow structure in Na2-Ar, high precision mass measurement on single ions using cyclotron resonance, low temperature energy transfer, trapping of neutral atoms, and vibrationally inelastic collisions.

Kleppner, D.; Pritchard, D.E.; Ahmad-Bitar, R.; Ducas, T.; Kelleher, D.; Ligare, M.; Lyyra, A.M.; Moskowitz, P.; Saenger, K.L.; Smith, N.

1984-01-01

29

Dynamic atom optics to produce ultraslow, ultracold helium atoms: design study and possible applications  

Microsoft Academic Search

Atoms, unlike photons, travel at velocities readily attainable in the laboratory, making possible novel atom optical devices based on optical elements which move relative to the atomic beam. We report design studies of a device to accelerate or decelerate and simultaneously monochromatize a helium atomic beam. A helium supersonic free-jet (v equals 950 m\\/s, (Delta) v equals 5 m\\/s, FWHM)

R. B. Doak; K. Kevern; Andrew Chizmeshya; Rudolf David; George Comsa

1997-01-01

30

Observation of the spin polarization of Cs atoms during optical orientation of metastable helium atoms in alkali-helium plasma  

NASA Astrophysics Data System (ADS)

We are the first to experimentally observe a magnetic-resonance signal of 62 S 1/2 Cs atoms by absorption of light from a helium lamp that was used to optically orient metastable 23 S 1 He atoms. The amplitude of the cesium signal proved to be almost three orders of magnitude lower than the amplitude of the magnetic resonance of 23 S 1 He atoms. Particular features of the creation and observation of the collisional polarization of cesium under conditions of alkali-helium plasma have been discussed.

Dmitriev, S. P.; Dovator, N. A.; Kartoshkin, V. A.; Okunevich, A. I.

2014-02-01

31

The Weakest Link: Bonding between Helium Atoms  

ERIC Educational Resources Information Center

A highly simplified model for helium dimers that reproduces their essential features without the need for elaborate computation is presented. The He-He potential is predicted to have minimum of 10.9 K at a nuclear separation of 5.61 bohrs.

Lohr, Lawrence L.; Blinder, S. M.

2007-01-01

32

Helium atom in an external electric field: Exact diagonalization  

NASA Astrophysics Data System (ADS)

An exact diagonalization method is applied to solve the quantum-mechanical problem of spinless helium atom in an external electric field of arbitrary magnitude. The basis set for two-electron problem is built from different pair combinations ?nalama(?ra)?nblbmb(?rb) of orthonormalized single-particle hydrogen-like wave functions ?nml(r) belonging to any possibly bound states of the individual a- and b-electrons in the Coulomb central field renormalized by the scale parameter ? > 0. Within the selected basis the matrix elements of the total Hamiltonian allows an exact analytical representation in the form of finite numerical sums. The diagonalization procedure is performed by Jacobi algorithm for N × N square Hermitian matrix built on the basis of dimension N = 25. The systematics and the numerical values of the low-lying energy levels at zero field are in good agreement with known experimental data. The field dependences of low-lying levels (Stark effect) and polarizability in the ground state of helium atom are presented. It is shown that even extremely high external fields lead only to shifting or splitting of existing low levels, without disturbance of their systematics. Typically, no new low-energy excitation can be created under external electric field of moderate intensity. Radical reconstruction in spectrum of individual helium atoms can be expected in condensed helium phases where each atom is deeply affected by interaction fields from neighbors. This result should be taken into account at interpretation of electrodynamic experiments on superfluid helium.

Antsygina, T. N.; Chishko, K. A.

2014-09-01

33

Spectroscopy of barium atoms in liquid and solid helium matrices  

SciTech Connect

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.

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

2011-08-15

34

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

ERIC Educational Resources Information Center

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…

Harbola, Varun

2011-01-01

35

Classical limit states of the helium atom  

Microsoft Academic Search

The classical simplicity and intuitive appeal of Bohr's atomic model have given the classical hydrogen atom an important and pervasive role in atomic physics. Even today, the Bohr model remains as a cornerstone underlying quan- tum mechanics. However, the precise role of this classical foundation has been debated since the early days of quantum theory. Recently, a series of experimental

J. A. West; Z. D. Gaeta; C. R. Stroud

1998-01-01

36

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

SciTech Connect

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.

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

37

The Helium Atom and Isoelectronic Ions in Two Dimensions  

ERIC Educational Resources Information Center

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…

Patil, S. H.

2008-01-01

38

Photoionization of atoms and molecules. [of hydrogen, helium, and xenon  

NASA Technical Reports Server (NTRS)

A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.

Samson, J. A. R.

1976-01-01

39

Revised Primordial Helium Abundance Based on New Atomic Data  

Microsoft Academic Search

We have derived a primordial helium abundance of Yp=0.2477+\\/-0.0029, based on new atomic physics computations of the recombination coefficients of He I and of the collisional excitation of the H I Balmer lines together with observations and photoionization models of metal-poor extragalactic H II regions. The new atomic data increase our previous determination of Yp by 0.0086, a very significant

Manuel Peimbert; Valentina Luridiana; Antonio Peimbert

2007-01-01

40

Ultrafast probing of ejection dynamics of Rydberg atoms and molecular fragments from electronically excited helium nanodroplets  

SciTech Connect

The ejection dynamics of Rydberg atoms and molecular fragments from electronically excited helium nanodroplets are studied with time-resolved extreme ultraviolet ion imaging spectroscopy. At excitation energies of 23.6 {+-} 0.2 eV, Rydberg atoms in n= 3 and n= 4 states are ejected on different time scales and with significantly different kinetic energy distributions. Specifically, n= 3 Rydberg atoms are ejected with kinetic energies as high as 0.85 eV, but their appearance is delayed by approximately 200 fs. In contrast, n= 4 Rydberg atoms appear within the time resolution of the experiment with considerably lower kinetic energies. Major features in the Rydberg atom kinetic energy distributions for both principal quantum numbers can be described within a simple elastic scattering model of localized perturbed atomic Rydberg atoms that are expelled from the droplet due to their repulsive interaction with the surrounding helium bath. Time-dependent kinetic energy distributions of He{sub 2}{sup +} and He{sub 3}{sup +} ions are presented that support the formation of molecular ions in an indirect droplet ionization process and the ejection of neutral Rydberg dimers on a similar time scale as the n= 3 Rydberg atoms.

Buenermann, Oliver; Kornilov, Oleg; Neumark, Daniel M. [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Chemistry, University of California, Berkeley, California 94720 (United States); Haxton, Daniel J.; Gessner, Oliver [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Leone, Stephen R. [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Chemistry, University of California, Berkeley, California 94720 (United States); Department of Physics, University of California, Berkeley, California 94720 (United States)

2012-12-07

41

Luminescence of nitrogen and neon atoms isolated in solid helium  

NASA Astrophysics Data System (ADS)

Investigations of metastable N( 2D) and Ne( 3P 2) atoms isolated in solid helium have been carried out for the first time. The luminescence spectra and kinetics in the impurity helium solid phase (IHSP), with impurity centers N 2, Ne, Ar, and Kr, show the sensitizing influence of a neighboring heavy particle on the forbidden N( 2D- 4S) transition. The extremely long-lived (??10 4s) hyperbolically decaying afterglow and thermoluminescence of this transition have been observed in the IHSP. Thermoluminescence studies allowed the determination of the energy barrier for pair fusion of neighboring centers. In agreement with calculations the energy barrier of this process which determines the IHSP stability turns out to be E1 = 40 ± 4 K. The activation energy of the long-lived afterglow stage was found to be E2 ? 7 K, close to the energy of vacancy formation in solid helium. By using laser-induced fluorescence, Ne( 3P 2) atoms have been detected in superfluid helium and in the IHSP for the first time. Within an experimental accuracy of 0.18 Å their spectral lines were unshifted and unbroadened with respect to the gas-phase values.

Boltnev, R. E.; Gordon, E. B.; Khmelenko, V. V.; Krushinskaya, I. N.; Martynenko, M. V.; Pelmenev, A. A.; Popov, E. A.; Shestakov, A. F.

1994-12-01

42

Giant helium dimers produced by photoassociation of ultracold metastable atoms.  

PubMed

We produce giant, purely long-range helium dimers by photoassociation of metastable helium atoms in a magnetically trapped, ultracold cloud. The photoassociation laser is detuned close to the atomic 2(3)S1-2(3)P0 line and produces strong heating of the sample when resonant with molecular bound states. The temperature of the cloud serves as an indicator of the molecular spectrum. We report good agreement between our spectroscopic measurements and our calculations of the five bound states belonging to a 0(+)(u) purely long-range potential well. These previously unobserved states have classical inner turning points of about 150a(0) and outer turning points as large as 1150a(0). PMID:12935015

Léonard, J; Walhout, M; Mosk, A P; Müller, T; Leduc, M; Cohen-Tannoudji, C

2003-08-15

43

Ground State Hyperfine Structure of Muonic Helium Atom  

E-print Network

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 \

A. A. Krutov; A. P. Martynenko

2008-07-21

44

Atomic masses of tritium and helium-3.  

PubMed

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

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

2015-01-01

45

Atomic Masses of Tritium and Helium-3  

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

46

Similarity between positronium-atom and electron-atom scattering  

E-print Network

We employ the impulse approximation for description of positronium-atom scattering. Our analysis and calculations of Ps-Kr and Ps-Ar collisions provide 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)].

Fabrikant, I I

2015-01-01

47

Spectroscopy of lithium atoms and molecules on helium nanodroplets.  

PubMed

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

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

2013-11-21

48

Spectroscopy of Lithium Atoms and Molecules on Helium Nanodroplets  

PubMed Central

We report on the spectroscopic investigation of lithium atoms and lithium dimers in their triplet manifold on the surface of helium nanodroplets (HeN). We present the excitation spectrum of the 3p ? 2s and 3d ? 2s two-photon transitions for single Li atoms on HeN. 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*–Hem, m = 1–3) formation process in the Li–HeN 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–HeN 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

2013-01-01

49

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

NASA Astrophysics Data System (ADS)

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.

Ghanbari-Adivi, Ebrahim; Abdollahi-Tadi, Rayhaneh

2013-12-01

50

PREFACE: Atom-surface scattering Atom-surface scattering  

NASA Astrophysics Data System (ADS)

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

Miret-Artés, Salvador

2010-08-01

51

A comparative study of helium atom diffusion via an interstitial mechanism in nickel and palladium  

Microsoft Academic Search

At low temperatures, helium atoms diffuse primarily by an interstitial mechanism due to the lower activation energy. Using a modified analytic embedded-atom model (MAEAM) and the molecular dynamics method, a study of the interstitial diffusion for helium atoms in perfect nickel and palladium was performed. Consequently, the diffusion coefficient was calculated from the jump-frequency method. The temperature dependency of the

Jixing Xia; Wangyu Hu; Jianyu Yang; Bingyun Ao; Xiaolin Wang

2006-01-01

52

Binding of two helium atoms in confined geometries  

SciTech Connect

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.

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

53

Zeeman deceleration of electron-impact-excited metastable helium atoms  

E-print Network

We present experimental results that demonstrate - for the first time - the Zeeman deceleration of helium atoms in the metastable 2^3S_1state. A more than 40% decrease of the kinetic energy of the beam is achieved for deceleration from 490 m/s to a final velocity of 370 m/s. 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. 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.

Dulitz, Katrin; Softley, Timothy P

2015-01-01

54

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

NASA Astrophysics Data System (ADS)

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.

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

55

Luminescence of oxygen atoms stimulated by metastable helium at cryogenic temperatures.  

PubMed

We present investigations of the afterglow of oxygen-helium gas mixtures at cryogenic temperatures. The cooling of a helium jet containing trace amounts of oxygen after passing through a radio frequency discharge zone led to the observation of strong emissions from atomic oxygen. The effect results from the increasing efficiency of energy transfer from metastable helium atoms and molecules to oxygen impurities in the cold dense helium vapor. This effect might find an application for the detection of small quantities of the impurities in helium gas. PMID:24237513

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

2013-11-01

56

Helium atoms in chromium-rich Fe-Cr alloys - Ab initio results  

NASA Astrophysics Data System (ADS)

Helium generation in Fe-Cr alloys degrades the material by causing swelling and eventually the nucleation of bubbles. When the alloys are used as construction materials the resulting embrittlement is especially undesirable. The effects of helium atoms in pure iron have been recently elucidated by ab initio calculations. The different magnetic behavior - ferromagnetic for iron and anti-ferromagnetic for chromium - makes simple extrapolation to alloys and pure chromium uncertain. In the present study helium in pure chromium as well as chromium alloys with a small concentration of iron is investigated by ab initio density-functional theory calculations. The results indicate that interstitial helium atoms occupy the tetrahedral site in pure chromium. A pair of interstitial helium atoms have binding energies of about 0.3-0.6 eV when they are first or second nearest neighbors. When a substitutional iron atom is involved, the binding energy goes up to 1 eV. The formation energy of a substitutional helium atom is slightly higher (about 0.2 eV) when a substitutional iron atom is close by. The same holds for two helium atoms sitting in a vacancy, but then the energy difference is roughly twice as large. A substitutional helium atom is relatively strongly bound to a substitutional iron atom, with a binding energy of about 0.3 eV.

Henriksson, K. O. E.

2009-12-01

57

Photoionization Spectroscopy of Isolated cr Atoms in Ultracold Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

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.

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

2012-06-01

58

Attenuation of Scattered Thermal Energy Atomic Oxygen  

NASA Technical Reports Server (NTRS)

The attenuation of scattered thermal energy atomic oxygen is relevant to the potential damage that can occur within a spacecraft which sweeps through atomic oxygen in low Earth orbit (LEO). Although there can be significant oxidation and resulting degradation of polymers and some metals on the external surfaces of spacecraft, there are often openings on a spacecraft such as telescope apertures, vents, and microwave cavities that can allow atomic oxygen to enter and scatter internally to the spacecraft. Atomic oxygen that enters a spacecraft can thermally accommodate and scatter to ultimately react or recombine on surfaces. The atomic oxygen that does enter a spacecraft can be scavenged by use of high erosion yield polymers to reduce its reaction on critical surfaces and materials. Polyoxymethylene and polyethylene can be used as effective atomic oxygen scavenging polymers.

Banks, Bruce A.; Seroka, Katelyn T.; McPhate, Jason B.; Miller, Sharon K.

2011-01-01

59

Electronic interaction anisotropy between open-shell lanthanide atoms and helium from cold collision experiment  

E-print Network

Electronic interaction anisotropy between open-shell lanthanide atoms and helium from cold and helium is extremely small. The interaction of the rare-earth atoms with He gives rise to several shells submerged under the filled 6s electronic orbitals, resulting in large electronic spin and orbital

Krems, Roman

60

Positronium-atom scattering at low energies  

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

61

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

NASA Technical Reports Server (NTRS)

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.

Seaholtz, Richard G.; Buggele, Alvin E.

1997-01-01

62

Symmetric And Non-Symmetric Muonic Helium Atoms Studies  

SciTech Connect

The ground state hyperfine structure and other properties are calculated for muonic helium atoms ({sup 3}He{sup +2}{mu}{sup -}e{sup -} or {sup 4}He{sup +2}{mu}{sup -}e{sup -}) with the use of some local properties of the wave functions in the domains where two particles are close to each other or far away. Simple wave functions incorporating these properties with one variational parameter is developed. The calculated values for hyperfine structure, energy and average interparticle distances in ground state are compared with the correlation function hyper-spherical harmonic method and multibox variational approach. The obtained results are very close to the values calculated by mentioned methods, giving strong indications that the proposed wave functions provide relatively accurate values.

Mohammadi, S. [Physics Department, Payame Noor University, Mashad 91735 (Iran, Islamic Republic of)

2011-10-28

63

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

NASA Technical Reports Server (NTRS)

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.

Drachman, Richard J.

2006-01-01

64

Theoretical survey on positronium formation and ionisation in positron atom scattering  

NASA Technical Reports Server (NTRS)

The recent theoretical studies are surveyed and reported on the formation of exotic atoms in positron-hydrogen, positron-helium and positron-lithium scattering specially at intermediate energy region. The ionizations of these targets by positron impact was also considered. Theoretical predictions for both the processes are compared with existing measured values.

Basu, Madhumita; Ghosh, A. S.

1990-01-01

65

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

E-print Network

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

Chu, Xi

66

Classical limit states of the helium atom J. A. West,1,2  

E-print Network

and intuitive appeal of Bohr's atomic model have given the classical hydrogen atom an important and pervasive role in atomic physics. Even today, the Bohr model remains as a cornerstone underlying quan- tum for the simplest such atom, helium, this extension is nontrivial because the old quantum theory of Bohr was never

Stroud, Carlos R.

67

Linewidths in bound state resonances for helium scattering from Si(111)-(1 × 1)H  

Microsoft Academic Search

Helium-3 spin-echo measurements of resonant scattering from the Si(111)-(1 × 1)H surface, in the energy range 4-14 meV, are presented. The measurements have high energy resolution yet they reveal bound state resonance features with uniformly broad linewidths. We show that exact quantum mechanical calculations of the elastic scattering, using the existing potential for the helium\\/Si(111)-(1 × 1)H interaction, cannot reproduce

F. E. Tuddenham; H. Hedgeland; J. Knowling; A. P. Jardine; D. A. MacLaren; G. Alexandrowicz; J. Ellis; W. Allison

2009-01-01

68

X-ray observation of a helium atom and placing a nitrogen atom inside He@C60 and He@C70.  

PubMed

Single crystal X-ray analysis has been used as a powerful method to determine the structure of molecules. However, crystallographic data containing helium has not been reported, owing to the difficulty in embedding helium into crystalline materials. Here we report the X-ray diffraction study of He@C60 and the clear observation of a single helium atom inside C60. In addition, the close packing of a helium atom and a nitrogen atom inside fullerenes is realized using two stepwise insertion techniques, that is, molecular surgery to synthesize the fullerenes encapsulating a helium atom, followed by nitrogen radio-frequency plasma methods to generate the fullerenes encapsulating both helium and nitrogen atoms. Electron spin resonance analysis reveals that the encapsulated helium atom has a small but detectable influence on the electronic properties of the highly reactive nitrogen atom coexisting inside the fullerene, suggesting the potential usage of helium for controlling electronic properties of reactive species. PMID:23462997

Morinaka, Yuta; Sato, Satoru; Wakamiya, Atsushi; Nikawa, Hidefumi; Mizorogi, Naomi; Tanabe, Fumiyuki; Murata, Michihisa; Komatsu, Koichi; Furukawa, Ko; Kato, Tatsuhisa; Nagase, Shigeru; Akasaka, Takeshi; Murata, Yasujiro

2013-01-01

69

Probing crystalline insulator surfaces with neutral helium atom scattering: A study of mixed potassium tantalate/niobate and thin films of potassium chloride and p-quaterphenyl on sodium chloride(001)  

NASA Astrophysics Data System (ADS)

Results from experiments using a thermal-energy beam of helium atoms as a probe in studying three crystalline insulator surfaces are presented. The primary focus is the simple ferroelectric perovskite, KTa1- xNbxO3 (or KTN when not specifying an Nb concentration) with x = 0.06, 0.10, 0.20, 0.30, and 0.52. Thin films of KCl and p-quaterphenyl grown onto NaCl(001) were also studied. Extending an earlier work on potassium tantalate (KTaO3), freshly cleaved (001) surfaces of niobium-doped potassium tantalate (KTN) were studied. While KTaO3 is an incipient ferroelectric undergoing no bulk phase changes, KTN, with Nb concentration greater than ˜1.5%, is a tunable ferroelectric, existing in several bulk phases depending on the temperature of the material. A metastable feature observed in KTN immediately after cleaving results in satellite peaks around the specular peak which decay over time. Also, small, broad half-order peaks were observed when the surface temperature was cycled between 50 K and 270 K for the first time. Surface hysteresis effects and responses to electric fields were also studied. Surface dispersion curves for the two high-symmetry directions are given for various Nb doping levels and substrate temperatures. This work compares the above phenomena to similar occurrences observed previously in KTaO3, and notes how the responses differ as a function of niobium doping. Also building on previous experience, the growth of KCl on NaCl was studied. Several recent works have focused on the physical interpretation of 3/4-order peaks observed during LEED investigations of this system. A HAS study of this system revealed, at best, a weak indication of several n/4-order peaks, but at film thicknesses well above those reported. In our first attempt to examine the surfaces of films of large organic molecules using HAS, p-quaterphenyl (p-4P) was deposited onto an NaCl surface held at 300K. Diffraction intensities from the NaCl were reduced but produced no other effects. However, cooling the surface to 50 K revealed many smaller diffraction peaks from the p-4P in addition to the larger NaCl peaks. The organic film peaks were isotropic, appearing as a two-dimensional diffraction powder pattern.

Trelenberg, Thomas Walter

70

Method and means for helium/hydrogen ratio measurement by alpha scattering  

NASA Technical Reports Server (NTRS)

An apparatus for determining helium to hydrogen ratios in a gaseous sample is presented. The sample is bombarded with alpha particles created by a self contained radioactive source and scattering products falling within a predetermined forward scattering angular range impact a detector assembly. Two detectors are mounted in tandem, the first completely blocking the second with respect to incident scattering products. Alpha particle/hydrogen or alpha particle/helium collisions are identified by whether scattering product impacts occur simultaneously in both detectors or only in the first detector. Relative magnitudes of the two pulses can be used to further discriminate against other effects such as noise and cosmic ray events.

Whitehead, A. B.; Tombrello, T. A. (inventors)

1980-01-01

71

Ps-atom scattering at low energies  

E-print Network

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 [Phys. Rev. Lett. 112, 243201 (2014)], 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 $venergy region, in contrast to the inter...

Fabrikant, I I

2015-01-01

72

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

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

73

Scattering laser light on cold atoms: Toward multiple scattering signals from single-atom responses  

SciTech Connect

We deduce the coherent backscattering signal from two distant laser-driven atoms using single-atom equations. The background and interference components of the double scattering spectrum obtained by this alternative approach agree exactly with the results of the standard master equation treatment. In contrast to the master equation, however, the new approach is suitable for the generalization to a large number of atomic scatterers.

Wellens, Thomas; Geiger, Tobias; Shatokhin, Vyacheslav; Buchleitner, Andreas [Institut fuer Physik, Albert-Ludwigs-Universitaet Freiburg, Hermann-Herder-Str. 3, D-79104 Freiburg (Germany)

2010-07-15

74

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

SciTech Connect

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.

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

75

Semiempirical potentials for positron scattering by atoms  

SciTech Connect

We report calculations of differential and integral cross sections for positron scattering by noble gas and alkaline-earth atoms within the same methodology. The scattering potentials are constructed by scaling adiabatic potentials so that their minima coincide with the covalent radii of the target atoms. Elastic differential and integral cross sections are calculated for Ne, Ar, Be, and Mg, and the results are very close to experimental and best theoretical data. Particularly, elastic differential cross sections for Be and Mg at low energies are reported.

Assafrao, Denise; Walters, H. R. J.; Arretche, Felipe; Dutra, Adriano; Mohallem, J. R. [Departamento de Fisica, Universidade Federal do Espirito Santo, 29075-910, Vitoria, ES (Brazil); Department of Applied Mathematics and Theoretical Physics, Queen's University, Belfast, BT7 1NN (United Kingdom); Departamento de Fisica, Universidade do Estado de Santa Catarina, 89223-100, Joinville, SC (Brazil); Laboratorio de Atomos e Moleculas Especiais, Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, PO Box 702, 30123-970, Belo Horizonte, MG (Brazil)

2011-08-15

76

Metastable Helium: A New Determination of the Longest Atomic Excited-State Lifetime  

NASA Astrophysics Data System (ADS)

Exited atoms may relax to the ground state by radiative decay, a process which is usually very fast (of order nanoseconds). However, quantum-mechanical selection rules can prevent such rapid decay, in which case these “metastable” states can have lifetimes of order seconds or longer. In this Letter, we determine experimentally the lifetime of the longest-lived neutral atomic state—the first excited state of helium (the 2S13 metastable state)—to the highest accuracy yet measured. We use laser cooling and magnetic trapping to isolate a cloud of metastable helium (He*) atoms from their surrounding environment, and measure the decay rate to the ground 1S01 state via extreme ultraviolet (XUV) photon emission. This is the first measurement using a virtually unperturbed ensemble of isolated helium atoms, and yields a value of 7870(510) seconds, in excellent agreement with the predictions of quantum electrodynamic theory.

Hodgman, S. S.; Dall, R. G.; Byron, L. J.; Baldwin, K. G. H.; Buckman, S. J.; Truscott, A. G.

2009-07-01

77

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

ERIC Educational Resources Information Center

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…

Baseden, Kyle A.; Tye, Jesse W.

2014-01-01

78

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

SciTech Connect

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)

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

79

MISSE Scattered Atomic Oxygen Characterization Experiment  

NASA Technical Reports Server (NTRS)

An experiment designed to measure the atomic oxygen (AO) erosion profile of scattered AO was exposed to Low Earth Orbital (LEO) AO for almost four years as part of the Materials International Space Station Experiment 1 and 2 (MISSE 1 and 2). The experiment was flown in MISSE Passive Experiment Carrier 2 (PEC 2), Tray 1, attached to the exterior of the International Space Station (ISS) Quest Airlock. The experiment consisted of an aperture disk lid of Kapton H (DuPont) polyimide coated on the space exposed surface with a thin AO durable silicon dioxide film. The aperture lid had a small hole in its center to allow AO to enter into a chamber and impact a base disk of aluminum. The AO that scattered from the aluminum base could react with the under side of the aperture lid which was coated sporadically with microscopic sodium chloride particles. Scattered AO erosion can occur to materials within a spacecraft that are protected from direct AO attack but because of apertures in the spacecraft the AO can attack the interior materials after scattering. The erosion of the underside of the Kapton lid was sufficient to be able to use profilometry to measure the height of the buttes that remained after washing off the salt particles. The erosion pattern indicated that peak flux of scattered AO occurred at and angle of approximately 45 from the incoming normal incidence on the aluminum base unlike the erosion pattern predicted for scattering based on Monte Carlo computational predictions for AO scattering from Kapton H polyimide. The effective erosion yield for the scattered AO was found to be a factor of 0.214 of that for direct impingement on Kapton H polyimide.

Banks, Bruce A.; deGroh, Kim K.; Miller, Sharon K.

2006-01-01

80

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

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…

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

2012-01-01

81

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

SciTech Connect

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.

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

2014-01-14

82

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

NASA Astrophysics Data System (ADS)

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.

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

2013-09-01

83

Atom-interferometric studies of light scattering  

SciTech Connect

We have used an echo-type atom interferometer that manipulates laser-cooled atoms in a single ground state to investigate the effect of light scattering from pulsed and continuous-wave light. The interferometer uses two off-resonant standing-wave pulses applied at times t=0 and t=T to diffract and recombine momentum states separated by 2({Dirac_h}/2{pi})k at t=2T. Matter wave interference is associated with the formation of a density grating with period {lambda}/2 in the vicinity of this echo time. The grating contrast is measured by recording the intensity of coherently backscattered light. The interferometer is perturbed by an additional pulse applied at t=2T-{delta}T or by continuous-wave background light. If the additional pulse is a standing wave, the momentum states interfering at t=2T are displaced and the grating contrast can be completely recovered due to constructive interference. In this case, the contrast shows a periodic modulation at the atomic recoil frequency as a function of {delta}T. In a recent work, it was shown that the atomic recoil frequency can be measured easily and precisely when using coherence functions to model the signal shape. This paper provides an alternative description of the signal shape through an analytical calculation of echo formation in the presence of an additional standing-wave pulse. Using this treatment, it is possible to model the effects of spontaneous emission and spatial profile of the laser beam on the signal shape. Additionally, the theory predicts scaling laws as a function of the pulse area and the number of additional standing-wave pulses. These scaling laws are investigated experimentally and can be exploited to improve precision measurements of the atomic recoil frequency. We also show that coherence functions can be used to make a direct measurement of the populations of momentum states associated with the ground state under conditions where the Doppler-broadened velocity distribution of the sample is much larger than the recoil velocity. These measurements are consistent with Monte Carlo wave-function simulations. If the additional pulse is a traveling wave, we find that the grating contrast measured as a function of {delta}T can be modeled by a quasiperiodic coherence function as in previous experiments that utilized atomic beams. In this work, we investigate the dependence of the photon scattering rate on the intensity and detuning of the traveling wave. We also study the effects of perturbing the interferometer with continuous-wave light and find that the dependence of the photon scattering rate on the intensity and detuning of the perturbing field is consistent with expectations.

Beattie, S.; Barrett, B.; Chan, I.; Mok, C.; Kumarakrishnan, A. [Department of Physics and Astronomy, York University, Toronto, Ontario, M3J 1P3 (Canada); Yavin, I. [Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08544 (United States)

2009-07-15

84

Atom-molecule scattering with the average wavefunction method  

NASA Astrophysics Data System (ADS)

The average wavefunction method (AWM) is applied to atom-molecule scattering. In its simplest form the labor involved in solving the AWM equations is equivalent to that involved for elastic scattering in the same formulation. As an initial illustration, explicit expressions for the T-matrix are derived for the scattering of an atom and a rigid rotor. Results are presented for low-energy scattering and corrections to the Born approximation are clearly evident. In general, the AWM is particularly suited to polyatom scattering due to its reduction of the potential in terms of a separable atom-atom potential.

Singh, Harjinder; Dacol, Dalcio K.; Rabitz, Herschel

1987-08-01

85

Spin exchange cross sections for collisions of metastable helium atoms with lithium atoms in the ground state  

NASA Astrophysics Data System (ADS)

The spin exchange and chemi-ionization cross sections for the metastable helium atom-lithium atom in the ground state system have been calculated. Using data on the interaction potentials obtained in this study, the spin exchange cross sections are determined for the first time for the He(23 S 1)-Li(22 S 1/2) system in the interval of collision energies from 5 × 10-3 to 16 eV.

Kartoshkin, V. A.

2007-12-01

86

Exchange and correlation Kohn–Sham functionals for the helium atom: locality and homogeneity  

Microsoft Academic Search

The locality and homogeneous nature of the exchange and correlation functionals for the ground state of the helium atom, in the Kohn–Sham formulation, are revisited. Our analysis is focused on the integrands of both functionals, although the integrated quantities are compared with previous results. Both functionals are not local, and the correlation functional is not homogeneous. To study the non-locality,

Federico Moscardó; J. C. Sancho-Garc??a

1998-01-01

87

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

E-print Network

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

Rioux, Frank

88

Thomson scattering in low temperature helium plasmas of a magnetic multipole plasma source  

NASA Astrophysics Data System (ADS)

Measurements of electron density and temperature of helium plasmas in a cw running magnetic multipole plasma source by repetitively laser-pulsed 90° Thomson scattering are reported. This is the first experiment in which this technique has been applied to such plasmas. Measurements are performed at a helium gas pressure of pg = 5 Pa, the discharge voltage was Ud = 100 V, the discharge current was 5 A leq Id leq 30 A, and the cathode heating current was 80 A leq Ih leq 140 A. Electron energy distribution functions obtained from the Thomson scattering spectra are studied. The obtained plasma parameters are electron temperature 1.5 eV leq kTe leq 5 eV and density 1012 cm-3 leq ne leq 4 × 1012 cm-3, respectively. The sensitivity of detection of the experiment is in the range of 109 electrons and the accuracy of the electron temperature and electron density are specified to 15% and 20%, respectively. In addition, the neutral density and helium gas temperature are obtained from the Rayleigh component of the scattered spectra. Langmuir probe measurements are performed under the same plasma conditions and a comparison of the results with Thomson scattering shows good agreement between the two diagnostics.

Maurmann, S.; Kadetov, V. A.; Kahlil, A. A. I.; Kunze, H.-J.; Czarnetzki, U.

2004-10-01

89

Characterization of mixed atomic clusters of helium and spin-aligned tritium  

Microsoft Academic Search

Atomic clusters of three or more spin-aligned tritium atoms are predicted to be bound [1]. Since the tritium dimer (triplet) is not bound, formation of pure spin-aligned tritium clusters might prove challenging. Here we consider the possibility of forming small spin-aligned tritium clusters on the surface of larger helium clusters. To this end, we present a preliminary characterization of mixed

Gabriel Hanna; Doerte Blume

2004-01-01

90

THE INTERACTION OF HELIUM ATOMS WITH EDGE DISLOCATIONS IN ?-Fe  

SciTech Connect

Formation energies, binding energies, and the migration of interstitial He atoms at and near the center of an a/2<111>{110} edge dislocation in ?-Fe are determined using molecular dynamics and conjugate gradient relaxation methods. Results are compared as a function of the distance of the interstitial He atoms from the center of the dislocation and the amount of excess volume around the dislocation. Interstitial He atoms have negative binding energy on the compression side of the dislocation and strong positive binding energy on the tension side. Even at low temperatures, interstitial He atoms in the vicinity of the dislocation easily migrate to positions near the center of the dislocation, where they form crowdion interstitials with binding energies in excess of 2 eV.

Heinisch, Howard L.; Gao, Fei; Kurtz, Richard J.

2004-06-30

91

Spectroscopy of antiprotonic helium atoms and its contribution to the fundamental physical constants  

PubMed Central

Antiprotonic helium atom, a metastable neutral system consisting of an antiproton, an electron and a helium nucleus, was serendipitously discovered, and has been studied at CERN’s antiproton decelerator facility. Its transition frequencies have recently been measured to nine digits of precision by laser spectroscopy. By comparing these experimental results with three-body QED calculations, the antiproton-to-electron massratio was determined as 1836.152674(5). This result contributed to the CODATA recommended values of the fundamental physical constants. PMID:20075605

Hayano, Ryugo S.

2010-01-01

92

Neutron scattering study of the excitation spectrum of solid helium at ultra-low temperatures  

Microsoft Academic Search

There has been a resurgence of interest in the properties of solid helium due to the recent discovery of non-classical rotational\\u000a inertia (NCRI) in solid 4He by Chan and coworkers below 200 mK which they have interpreted as a transition to a ‘supersolid’ phase. We have carried\\u000a out a series of elastic and inelastic neutron scattering measurements on single crystals

Elizabeth Blackburn; John Goodkind; Sunil K. Sinha; Collin Broholm; John Copley; Ross Erwin

2008-01-01

93

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

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

94

A helium film coated quasi-parabolic mirror to focus a beam of ultra-cold spin polarized atomic hydrogen  

Microsoft Academic Search

A 350 mK helium-4-coated mirror was used to increase the intensity of an ultra-cold electron-spin-polarized atomic hydrogen beam. The mirror uses the observed specular reflection of atomic hydrogen from a superfluid-helium-covered surface. A quasi-parabolic polished copper mirror was installed with its focus at the 5 mm diameter exit aperture of an atomic hydrogen stabilization cell in the gradient of an

V. G. Luppov; W. A. Kaufman; K. M. Hill; R. S. Raymond; A. D. Kirsch

1993-01-01

95

Coulomb holes and correlation potentials in the helium atom  

Microsoft Academic Search

In this paper we investigate Coulomb correlation effects in the He atom by studying the structure of the static and dynamic Coulomb hole charge distributions as determined by the analytical 39-parameter correlated wave function of Kinoshita. The static Coulomb hole, which is defined in terms of the radial electron-electron distribution function, shows that as a result of Coulomb repulsion there

Marlina Slamet; Viraht Sahni

1995-01-01

96

Iteration wave function for describing the (e, 2e) spectrum of the helium atom  

NASA Astrophysics Data System (ADS)

The wave function of the ground state of the helium atom is derived by the variational-iteration technique with the Hylleraas-Eckart momentum representation of the wave function as a first approximation. This function is used to calculate the ratios of the differential cross sections ?(n=2)/?(n=1) and ?(2p)/?(2s) for helium ionized by an electron impact. The calculation is conducted in the plane-wave impulse approximation for symmetric noncoplanar kinematics of the (e, 2e) process. The results are compared with previous calculations in which variational wave functions of the configurational interaction type were used. Good agreement with the existing experimental data for ?(n=2)/?(n=1) is obtained. The results are generalized to helium ions.

Ippolitov, I. I.; Katyurin, S. V.; Glinkin, O. B.

1986-12-01

97

The Dynamics of Atom-Surface Interactions Involving HELIUM(2(1)S), HELIUM(2(3)P) and Electron-Spin HELIUM(2(3)S) Atoms  

Microsoft Academic Search

For several years Metastable Atom Deexcitation Spectroscopy (MDS) has been employed as a probe of surface electronic structure offering unparalleled surface specificity. In MDS a thermal-energy beam of rare-gas metastable atoms is directed at the surface under study, and the energy distribution of electrons ejected as a result of metastable atom deexcitation is measured. However, correct interpretation of the data

David Michael Oro

1994-01-01

98

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

E-print Network

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.

Kunming Xu

2007-05-30

99

Velocity Analysis of Potassium Atoms Scattered by Magnesium Oxide  

Microsoft Academic Search

A beam of potassium atoms is scattered by an MgO crystal and the magnetic velocity analyzer used to determine the distribution in velocity of the scattered atoms. The resulting velocity spectrum agrees very well with that calculated on the assumption of a Maxwell distribution characteristic of the temperature of the crystal although the crystal temperature was varied over a wide

A. Ellett; V. W. Cohen

1937-01-01

100

Kinematic coupling in continuum atomic scattering  

NASA Astrophysics Data System (ADS)

I present here a new three-body wavefunction which is a product of five Kinematically Coupled Coulomb waves. The KC5C wavefunction is valid through second order in all scattering regions and satisfies all asymptotic boundary conditions of the Schrödinger equation. The Brauner, Briggs and Klar (BBK) and Alt and Mukhanedzhanov (AM) continuum state wavefunction models are developed here within a unified notation. The new, Kinematic Coupling model incorporates aspects of both of these previous models and combines the reduced charge potential, discussed in the AM model, with the kinetic energy and allows me to retain the exact three-body Hamiltonian by introducing an exact interaction potential. With this, I assert a triple product form for the wavefunction, which incorporates the known continuum Coulomb eigenstates of the asymptotic Hamiltonian in the region ?? and a third unknown function. This ansatz is then substituted into the exact Schrödinger equation and I find solutions that match smoothly with the Redmond-Merkuriev 3C wavefunction in region ?O, where all of the particles are far apart. I also find that a symmetric and complete description of the local momenta arises naturally. Unlike the local momenta of the AM model however, these depend on the conjugate coordinates and yield both distortion and coupling effects. The strength of the Kinematic Coupling model is then illustrated by showing that it contains the appropriate two-body coalescence, and reproduces and improves upon the results of the BBK and AM models in the region ??, where two of the particles remain close. Moreover, because the distortion terms are vanishingly small at large radial separations and all energies, and identically zero along curves that are determined by the TDCS scattering angles, the KC5C wavefunction may be extended into the interior region. While the Kinematic Coupling framework indicates why the paradigm 3C wavefunction is so successful at describing both electron-ion scattering and some photo-ionization processes, I find that local effects may be important in heavy ion-atom scattering events. This point is illustrated by consideration of the H**2 continuum state, which is relevant in the breakup (H+3) *-->H++H**2-->H ++H++H- , studied by Wiese. I show that the local distortion effects provide an explanation for the observed asymmetry in the experimental data and thus illustrate the importance and validity of the local momenta herein formulated. I suggest that the KC5C wavefunction replace the paradigm 3C wavefunction and that the local distortion be treated as a vector potential, thus making the local momenta a necessary gauge constraint in a complete description of the three-body Coulomb interaction.

Schillaci, Michael Jay

1999-12-01

101

Exploiting Universality in Atoms with Large Scattering Lengths  

SciTech Connect

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.

Braaten, Eric

2012-05-31

102

Optical and Electron Spin Resonance Studies of Xenon-Nitrogen-Helium Condensates Containing Nitrogen and Oxygen Atoms.  

PubMed

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

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

2014-11-11

103

Zero-energy neutron-triton and proton-Helium-3 scattering with EFT(??)  

NASA Astrophysics Data System (ADS)

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 triton binding energy as input, the predictions as(t-n)=9.2±2.6 fm, at(t-n)=7.6±1.6 fm, asC(He3-p)=3.6±0.32 fm, and atC(He3-p)=3.1±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.

Kirscher, Johannes

2013-04-01

104

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

E-print Network

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.

Johannes Kirscher

2011-05-18

105

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

106

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

E-print Network

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...

Kirscher, Johannes

2011-01-01

107

Atomic delay in helium, neon, argon and krypton  

NASA Astrophysics Data System (ADS)

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. .

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

2014-12-01

108

Discrete Visible Luminescence of Helium Atoms and Molecules Desorbing from Helium Clusters: The Role of Electronic, Vibrational, and Rotational Energy Transfer  

SciTech Connect

Discrete visible and near-infrared luminescence of a beam of photoexcited helium clusters is reported. The emission lines are attributed to free helium atoms and molecules desorbing from clusters in electronically excited states. Depending on the excitation energy, various atomic and molecular singlet and triplet states are involved in the relaxation process. With increasing cluster size the intensity of molecular transitions becomes dominant. The temperature of ejected molecules could be estimated to T{sub vib}{approximately}2500 K and T{sub rot}{approximately}450 K and is much higher than that of the cluster itself. {copyright} {ital 1997} {ital The American Physical Society}

von Haeften, K.; von Pietrowski, R.; Moeller, T. [Hamburger Synchrotronstrahlungslabor HASYLAB Deutsches Elektronen Synchroton DESY, Hamburg, Notkestr. 85, 22603 Hamburg (Germany)] [Hamburger Synchrotronstrahlungslabor HASYLAB Deutsches Elektronen Synchroton DESY, Hamburg, Notkestr. 85, 22603 Hamburg (Germany); Joppien, M.; Moussavizadeh, L. [II. Institute fuer Experimentalphysik, Universitaet Hamburg (Germany)] [II. Institute fuer Experimentalphysik, Universitaet Hamburg (Germany); de Castro, A.R. [Laboratorio National de Luz Sincrotron, Campinas 13081-90 (Brazil)] [Laboratorio National de Luz Sincrotron, Campinas 13081-90 (Brazil)

1997-06-01

109

Desorption Dynamics of Heavy Alkali Metal Atoms (Rb, Cs) off the Surface of Helium Nanodroplets  

E-print Network

We present a combined ion imaging and density functional theory study of the dynamics of the desorption process of rubidium and cesium atoms off the surface of helium nanodroplets upon excitation of the perturbed $6s$ and $7s$ states, respectively. Both experimental and theoretical results are well represented by the pseudodiatomic model for effective masses of the helium droplet in the desorption reaction of m_eff/m_He~10 (Rb) and 13 (Cs). Deviations from this model are found for Rb excited to the 6p state. Photoelectron spectra indicate that the dopant-droplet interaction induces relaxation into low-lying electronic states of the desorbed atoms in the course of the ejection process.

von Vangerow, J; Stienkemeier, F; Mudrich, M; Leal, A; Mateo, D; Hernando, A; Barranco, M; Pi, M

2014-01-01

110

Atomic Hydrogen in Contact with a Helium Surface: Bose Condensation, Adsorption Isotherms, and Stability  

Microsoft Academic Search

The energy of interacting spin-polarized atomic hydrogen (H?) on a helium surface and the density dependence of the adsorption energy have been calculated, permitting a realistic determination of the adsorption isotherms. Surface interactions are shown to allow Bose-Einstein condensation in the gas. At the Bose-Einstein condensation the surface coverage attains a maximum which is essentially independent of the isotherm temperature.

Isaac F. Silvera; Victor V. Goldman

1980-01-01

111

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

E-print Network

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)

Masaki Hori; Anna Sótér; Vladimir I. Korobov

2014-04-30

112

LIF measurements on an atomic helium beam in the edge of a fusion plasma  

NASA Astrophysics Data System (ADS)

A method for the absolute measurement of population densities of selected atomic helium levels, which has been applied on the tokamak TEXTOR at the Forschungszentrum Jülich in Germany, is presented. The method is based on the resonant excitation of selected levels by a high-power, narrow-band, pulsed laser beam saturating the optical pumping process. Observation of the fluorescence response is performed at the laser wavelength and elsewhere in the spectrum: this gives information on collisional population transfer between some excited levels. Data analysis, as required for the derivation of absolute population densities, includes due consideration of the Zeeman splitting of spectral lines in a strong magnetic field. The first results of the measured population densities are compared with those provided by simulation based on the collisional-radiative model for atomic helium in the edge of fusion plasmas. This code has been extended to include the laser interaction with atomic helium, in order to simulate the measured time traces of radiation from the laser-perturbed levels. A combination of this simulation procedure with laser-induced fluorescence measurements is suggested as a possible method for determining the electron density in the edge plasma.

Krychowiak, M.; Mertens, Ph; König, R.; Schweer, B.; Brezinsek, S.; Schmitz, O.; Brix, M.; Samm, U.; Klinger, T.

2008-06-01

113

JOURNAL DE PHYSIQUE Colloque C 3, supplkment au no 10, Tome 31, Octobre 1970,page C 3 -29 THE SCATTERING OF LIGHT FROM LIQUID HELIUM  

E-print Network

THE SCATTERING OF LIGHT FROM LIQUID HELIUM W. F. VINEN and J. M. VAUGHAN Department of Physics, University of Birmingham, England Abstract. -A review is given of the scattering of light by superfluid helium. A brief situation that obtains in the neighbourhood of the &point. 1. Introduction. - A liquid scatters light

Paris-Sud XI, Université de

114

Resonances in rotationally inelastic scattering of OH(X2?) with helium and neon.  

PubMed

We present detailed calculations on resonances in rotationally and spin-orbit inelastic scattering of OH (X(2)?, j = 3/2, F(1), f) radicals with He and Ne atoms. We calculate new ab initio potential energy surfaces for OH-He, and the cross sections derived from these surfaces compare well with the recent crossed beam scattering experiment of Kirste et al. [Phys. Rev. A 82, 042717 (2010)]. We identify both shape and Feshbach resonances in the integral and differential state-to-state scattering cross sections, and we discuss the prospects for experimentally observing scattering resonances using Stark decelerated beams of OH radicals. PMID:22502519

Gubbels, Koos B; Ma, Qianli; Alexander, Millard H; Dagdigian, Paul J; Tanis, Dick; Groenenboom, Gerrit C; van der Avoird, Ad; van de Meerakker, Sebastiaan Y T

2012-04-14

115

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

NASA Astrophysics Data System (ADS)

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.

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

2012-11-01

116

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)

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.

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

2014-10-01

117

Light scattering by ultracold atoms in an optical lattice  

SciTech Connect

We investigate theoretically light scattering of photons by ultracold atoms in an optical lattice in the linear regime. A full quantum theory for the atom-photon interactions is developed as a function of the atomic state in the lattice along the Mott-insulator-superfluid phase transition, and the photonic-scattering cross section is evaluated as a function of the energy and of the direction of emission. The predictions of this theory are compared with the theoretical results of a recent work on Bragg scattering in time-of-flight measurements [A.M. Rey et al., Phys. Rev. A 72, 023407 (2005)]. We show that, when performing Bragg spectroscopy with light scattering, the photon recoil gives rise to an additional atomic site-to-site hopping, which can interfere with ordinary tunneling of matter waves and can significantly affect the photonic-scattering cross section.

Rist, Stefan [Departament de Fisica, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Spain); Menotti, Chiara [CNR-INFM BEC, and Dipartimento di Fisica, Universita di Trento, I-38050 Povo (Italy); Morigi, Giovanna [Departament de Fisica, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Spain); Theoretische Physik, Universitaet des Saarlandes, D-66041 Saarbruecken (Germany)

2010-01-15

118

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

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

119

Metastable atoms and the electron distribution function in a helium discharge positive column  

NASA Astrophysics Data System (ADS)

The influence of chemo-ionization processes on the shape of the electron distribution function (EDF) is investigated both by solving the Boltzmann equation and by measurements in a dc low-pressure (0.3 Torr) low-current (i = 10 - 80 mA) helium discharge. Probes were used to measure EDFs, electron densities and the axial and radial electric field strengths. The concentrations of metastable helium atoms in triplet and singlet states were measured using an optical absorption method. For calculating distribution functions the kinetic equation was solved analytically in local and nonlocal approximations. Good agreement is achieved between experiment and the nonlocal approximation for electron energies above 5 eV. Chemo-ionization is found to influence the high-energy tail of the EDF and thus the rates of electron impact excitation and ionization.

Alexandrov, V. M.; Flender, Ute; Kolokolov, N. B.; Rykova, O. V.; Wiesemann, K.

1996-08-01

120

Scattering in Flatland: Efficient Representations via Wave Atoms  

E-print Network

This paper presents a numerical compression strategy for the boundary integral equation of acoustic scattering in two dimensions. These equations have oscillatory kernels that we represent in a basis of wave atoms, and ...

Demanet, Laurent

121

Simple theory of atom-surface scattering  

SciTech Connect

The theory of the scattering of a beam of particles by a corrugated surface potential is shown to simplify dramatically in the semiclassical limit if the corrugation is not too strong and the direction of the incoming beam is close to the surface normal. It is shown that in any scattering event by a potential of quite general form the scattering amplitude is dominated by the potential corrugation near vanishing potential. For a weakly corrugated Morse potential, it is found that under near-normal-incidence conditions the classical scattering cross section is identical to the corresponding cross section for scattering by a hard corrugated wall with the same corrugation. Quantum-mechanical effects appear as small oscillations about the Kirchoff scattering amplitude. It is proposed that the observation of pronounced neon diffraction from Ni(110) and Pd(110), reported recently, may be reasonably explained if the corrugation function is defined at vanishing potential rather than at the classical turning points.

Maniv, T.; Cohen, M.H.

1986-04-15

122

Ab initio potential energy curve for the helium atom pair and thermophysical properties of the dilute helium gas. II. Thermophysical standard values for low-density helium  

Microsoft Academic Search

A helium–helium interatomic potential energy curve determined from quantum-mechanical ab initio calculations and described with an analytical representation considering relativistic retardation effects (R. Hellmann, E. Bich, and E. Vogel, Molec. Phys. (in press)) was used in the framework of the quantum-statistical mechanics and of the corresponding kinetic theory to calculate the most important thermophysical properties of helium governed by two-body

Eckard Bich; Robert Hellmann; Eckhard Vogel

2007-01-01

123

Magnetic Dichroism of Potassium Atoms on the Surface of Helium Nanodroplets  

SciTech Connect

The population ratio of Zeeman sublevels of atoms on the surface of superfluid helium droplets (T=0.37 K) has been measured. Laser induced fluorescence spectra of K atoms are measured in the presence of a moderately strong magnetic field (2.9 kG). The relative difference between the two states of circular polarization of the exciting laser is used to determine the electron spin polarization of the ensemble. Equal fluorescence levels indicate that the two spin sublevels of the ground-state K atom are equipopulated, within 1%. Thermalization to 0.37 K would give a population ratio of 0.35. We deduce that the rate of spin relaxation induced by the droplet must be <520/s. For the K{sub 2} triplet dimer we find instead full thermalization of the spin.

Nagl, Johann; Auboeck, Gerald; Callegari, Carlo; Ernst, Wolfgang E. [Institute of Experimental Physics, TU Graz, Petersgasse 16, 8010 Graz (Austria)

2007-02-16

124

Millimeter-Wave Spectra of Carbon Monoxide Solvated with Helium Atoms  

NASA Astrophysics Data System (ADS)

Millimeter-wave spectra of He_N-CO (^{12}C^{16}O, ^{13}C^{16}O, ^{12}C^{18}O, ^{13}C^{18}O) clusters with N up to 10, produced in a molecular expansion, were observed using intracavity OROTRON jet spectrometer in the frequency range of 110-150 GHz. The R(0) transitions were detected, which correspond to the known b-type (K = 1 - 0) R(0) lines of the binary system, He_1-CO. Further, the a-type (K = 0 - 0) rotational transitions of He_N-CO (N = 7, 8) in the frequency range of 20-40 GHz were measured combining OROTRON spectrometer with a double resonance technique. The isotopic shifts of the cluster transitions show remarkably smooth behavior with N from 1 to 6 and become rather scattering for N ? 7. The dependence of the rotational constant (cluster moment of inertia) and of the shift of the CO fundamental vibration on the number of He atoms in cluster were obtained for He_N-CO isotopologues from the analysis of their infrared spectra and very recent microwave data for the normal He_N-^{12}C^{16}O isotopologue. This study explores the microscopic evolution of superfluidity, which becomes apparent even in such small clusters as He_4-CO. The obtained results are compared with those from recent quantum Monte-Carlo calculations. and used to further interpret recent infrared measurements of CO in helium nanodroplets. J. Tang, A. R. W. McKellar, J. Chem. Phys. 119, 763 (2003) A. R. W. McKellar, J. Chem. Phys. 121, 6868 (2004) A. R. W. McKellar, J. Chem. Phys. 125, 164328 (2006). L. A. Surin, A. V. Potapov, B. S. Dumesh, S. Schlemmer, Y. Xu, P. L. Raston, and W. Jäger, Phys. Rev. Lett. 101, 233401 (2008) T. Škrbi?, S. Moroni, and S. Baroni, J. Phys. Chem. A 111, 7640 (2007). K. von Haeften, S. Rudolph, I. Simanovski, M. Havenith, R. E. Zillich, and K. B. Whaley, Phys. Rev. B 73, 054502 (2006).

Surin, L. A.; Giesen, T. F.; Schlemmer, S.; Potapov, A. V.; Dumesh, B. S.

2009-06-01

125

Optical Pumping and Electron Spin Resonance of Single 87Rb Atoms on Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

Our recent development of electron spin resonance (ESR) spectroscopy on superfluid helium nanodroplets (HeN) provides a sensitive tool to investigate interactions between a surface located alkali-metal atom and an ESR silent species inside the droplet. Highest sensitivity is expected for alkali-metal atoms with large hyperfine coupling. We present hyperfine resolved ESR spectra of single 87Rb (hyperfine constant a_HFS = 3417 MHz) atoms isolated on HeN. In accordance with our previous work on 85Rb (AHFS= 1012 MHz) we find a droplet size dependent increase of AHFS between 400 and 450 ppm, due to the electronic perturbation by the helium environment. The process of optical pumping and of optical detection on HeN is investigated in detail in order to optimize the ESR signal. A simple model for optical pumping on HeN is presented, which agrees well with the experimental results. M. Koch, G. Auböck, C. Callegari, and W.E. Ernst, Phys. Rev. Lett. 103, 035302 (2009) A. Volk, J. Poms, M. Koch, and W.E. Ernst, J. Phys. Chem. A, in press

Koch, Markus; Poms, Johannes; Volk, Alexander; Ernst, Wolfgang E.

2011-06-01

126

Two photon laser spectroscopy of antiprotonic helium atoms at CERN's AD  

NASA Astrophysics Data System (ADS)

The ASACUSA collaboration of CERN has carried out two-photon laser spectroscopy of antiprotonic helium atoms using counter-propagating ultraviolet laser beams. This excited some non-linear transitions of the antiproton at the wavelengths ? = 139.8-197.0 nm, in a way that reduced the thermal Doppler broadening of the observed resonances. The resulting narrow spectral lines allowed the measurement of three transition frequencies with fractional precisions of 2.3-5 parts in 109. By comparing these values with three-body QED calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23). We briefly review these results.

Hori, M.

2014-06-01

127

Dynamics of entanglement between two atomic samples with spontaneous scattering  

SciTech Connect

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.

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

128

Matter-wave scattering and guiding by atomic arrays  

SciTech Connect

We investigate the possibility that linear arrays of atoms can guide matter waves, much as fiber optics guide light. We model the atomic line as a quasi-one-dimensional array of s-wave point scatterers embedded in two-dimensions. Our theoretical study reveals how matter-wave guiding arises from the interplay of scattering phenomena with bands and conduction along the array. We discuss the conditions under which a straight or curved array of atoms can guide a beam focused at one end of the array.

Vaishnav, J. Y. [Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Walls, J. D. [Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138 (United States); Apratim, M. [Department of Electrical Engineering, Indian Institute of Technology, Kharagpur 721302 (India); Heller, E. J. [Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138 (United States)

2007-07-15

129

Coherent scattering by a spherical medium of resonant atoms  

SciTech Connect

We consider the problem of coherent resonant scattering of electromagnetic waves by a spherical medium of two-level atoms. The frequency dependence of the scattering amplitudes and cross sections reveals a complex structure of narrow peaks and dips. We relate these scattering resonances to the cooperative emission resonances characteristic of a sphere. We find the scattering to show considerable interference between the electric and magnetic multipole contributions, particularly in the lower multipole orders. This interference tends to enhance anisotropies in the differential scattering cross section even for small spheres. For such spheres, the peak values of the resonant contributions of the low-order multipoles to the total scattering cross section can increase with multipole order, in contrast to the usual decrease seen in nonresonant scattering.

Prasad, Sudhakar; Glauber, Roy J. [Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131 (United States); Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States)

2011-06-15

130

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

NASA Technical Reports Server (NTRS)

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.

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

131

Reversal of Photon-Scattering Errors in Atomic Qubits  

E-print Network

Spontaneous photon scattering by an atomic qubit is a notable example of environment-induced error and is a fundamental limit to the fidelity of quantum operations. In the scattering process the qubit loses its distinctive and coherent character owing to its entanglement with the photon. Using a single trapped ion we show that by utilizing the information carried by the photon we are able to coherently reverse this process and correct for the scattering error. We further used quantum process tomography to characterize the photon-scattering error and its correction scheme and demonstrate a correction fidelity greater than 85% whenever a photon was measured.

Nitzan Akerman; Shlomi Kotler; Yinnon Glickman; Roee Ozeri

2012-09-11

132

How Accurately Does the Free Complement Wave Function of a Helium Atom Satisfy the Schroedinger Equation?  

SciTech Connect

The local energy defined by H{psi}/{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 {sigma}{sup 2}{identical_to}<{psi}|(H-E){sup 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 Schroedinger 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.

Nakashima, Hiroyuki; Nakatsuji, Hiroshi [Quantum Chemistry Research Institute, JST, CREST, Kyodai Katsura Venture Plaza 106, Goryo Oohara 1-36, Nishikyo-ku, Kyoto 615-8245 (Japan)

2008-12-12

133

Double-charge-transfer cross sections in inelastic collisions of bare ions with helium atoms  

SciTech Connect

Double-charge-transfer cross sections into singly and doubly excited states for collisions of {alpha} particles with helium atoms have been studied in the energy range of 50 to 500 keV/amu. We have also studied the double electron capture cross sections into ground states for collisions of {sup 7}Li{sup 3+} and {sup 10}B{sup 5+} with helium atoms. In our study we have applied the four-body boundary corrected continuum intermediate state approximation. The intermediate continuum states of each electron and static correlations of the electrons have been taken into account in this formalism. Present calculated results for total charge transfer cross sections for the reaction {alpha}+He and Li{sup 3+}+He compare favorably well with the existing experimental and other theoretical predictions. Due to the nonavailability of any theoretical and experimental finding for the reaction B{sup 5+}+He, the energy variation of capture cross sections into the ground state of B{sup 5+} ion has been shown within the same energy range. However, charge transfer cross sections into singly and doubly excited states of He are compared with the available theoretical observations only due to nonavailability of any experimental result. In this case as well, agreement is very encouraging.

Purkait, M. [Department of Physics, Ramakrishna Mission Residential College, Narendrapur, Kolkata-700 103 (India); Sounda, S.; Dhara, A.; Mandal, C. R. [Department of Physics, Jadavpur University, Kolkata-700 032 (India)

2006-10-15

134

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

135

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

SciTech Connect

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.

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

136

Solvation and Spectral Line Shifts of Chromium Atoms in Helium Droplets Based on a Density Functional Theory Approach  

PubMed Central

The interaction of an electronically excited, single chromium (Cr) atom with superfluid helium nanodroplets of various size (10 to 2000 helium (He) atoms) is studied with helium density functional theory. Solvation energies and pseudo-diatomic potential energy surfaces are determined for Cr in its ground state as well as in the y7P, a5S, and y5P excited states. The necessary Cr–He pair potentials are calculated by standard methods of molecular orbital-based electronic structure theory. In its electronic ground state the Cr atom is found to be fully submerged in the droplet. A solvation shell structure is derived from fluctuations in the radial helium density. Electronic excitations of an embedded Cr atom are simulated by confronting the relaxed helium density (?He), obtained for Cr in the ground state, with interaction pair potentials of excited states. The resulting energy shifts for the transitions z7P ? a7S, y7P ? a7S, z5P ? a5S, and y5P ? a5S are compared to recent fluorescence and photoionization experiments. PMID:24906160

2014-01-01

137

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

NASA Astrophysics Data System (ADS)

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).

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

2014-10-01

138

Rubidium D1 and D2 atomic lines’ pressure broadened by ground-state helium atoms  

NASA Astrophysics Data System (ADS)

Full quantum calculations are performed to determine the spectral broadening of the rubidium D1 and D2 lines induced by collisions with helium perturbers. The potential curves of the low-lying RbHe molecular states, as well as the corresponding transition dipole moments, are generated theoretically with ab initio methods based on SA-CASSCF-MRCI calculations, including the spin-orbit effects. The absorption and emission coefficients at wavelengths lying between 650 and 950\\;nm and temperatures ranging from 100 to 3000 K are determined. The absorption profile reveals it is dominated by the free-free transitions, whereas the emission spectral shape arises from the free-free and bound-free transitions. The resulting red- and blue-wing profiles are compared with previous experimental and theoretical works.

Bouhadjar, F.; Alioua, K.; Bouazza, M. T.

2014-09-01

139

Atom-diatom scattering dynamics of spinning molecules.  

PubMed

We present full quantum mechanical scattering calculations using spinning molecules as target states for nuclear spin selective atom-diatom scattering of reactive D+H2 and F+H2 collisions. Molecules can be forced to rotate uni-directionally by chiral trains of short, non-resonant laser pulses, with different nuclear spin isomers rotating in opposite directions. The calculations we present are based on rotational wavepackets that can be created in this manner. As our simulations show, target molecules with opposite sense of rotation are predominantly scattered in opposite directions, opening routes for spatially and quantum state selective scattering of close chemical species. Moreover, two-dimensional state resolved differential cross sections reveal detailed information about the scattering mechanisms, which can be explained to a large degree by a classical vector model for scattering with spinning molecules. PMID:25591357

Eyles, C J; Floß, J; Averbukh, I Sh; Leibscher, M

2015-01-14

140

Emergence of a measurement basis in atom-photon scattering  

E-print Network

The process of quantum measurement has been a long standing source of debate. A measurement is postulated to collapse a wavefunction onto one of the states of a predetermined set - the measurement basis. This basis origin is not specified within quantum mechanics. According to the theory of decohernce, a measurement basis is singled out by the nature of coupling of a quantum system to its environment. Here we show how a measurement basis emerges in the evolution of the electronic spin of a single trapped atomic ion due to spontaneous photon scattering. Using quantum process tomography we visualize the projection of all spin directions, onto this basis, as a photon is scattered. These basis spin states are found to be aligned with the scattered photon propagation direction. In accordance with decohernce theory, they are subjected to a minimal increase in entropy due to the photon scattering, while, orthogonal states become fully mixed and their entropy is maximally increased. Moreover, we show that detection of the scattered photon polarization measures the spin state of the ion, in the emerging basis, with high fidelity. Lastly, we show that while photon scattering entangles all superpositions of pointer states with the scattered photon polarization, the measurement-basis states themselves remain classically correlated with it. Our findings show that photon scattering by atomic spin superpositions fulfils all the requirements from a quantum measurement process.

Yinnon Glickman; Shlomi Kotler; Nitzan Akerman; Roee Ozeri

2012-06-18

141

Observation of cooperative Mie scattering from an ultracold atomic cloud  

SciTech Connect

Scattering of light at a distribution of scatterers is an intrinsically cooperative process, which means that the scattering rate and the angular distribution of the scattered light are essentially governed by bulk properties of the distribution, such as its size, shape, and density, although local disorder and density fluctuations may have an important impact on the cooperativity. Via measurements of the radiation pressure force exerted by a far-detuned laser beam on a very small and dense cloud of ultracold atoms, we are able to identify the respective roles of superradiant acceleration of the scattering rate and of Mie scattering in the cooperative process. They lead, respectively, to a suppression or an enhancement of the radiation pressure force. We observe a maximum in the radiation pressure force as a function of the phase shift induced in the incident laser beam by the cloud's refractive index. The maximum marks the borderline of the validity of the Rayleigh-Debye-Gans approximation from a regime, where Mie scattering is more complex. Our observations thus help to clarify the intricate relationship between Rayleigh scattering of light at a coarse-grained ensemble of individual scatterers and Mie scattering at the bulk density distribution.

Bender, H.; Stehle, C.; Slama, S.; Zimmermann, C. [Physikalisches Institut, Eberhardt-Karls-Universitaet Tuebingen, D-72076 Tuebingen (Germany); Kaiser, R. [Institut Non Lineaire de Nice, CNRS, Universite de Nice Sophia-Antipolis, F-06560 Valbonne (France); Piovella, N. [Dipartimento di Fisica, Universita Degli Studi di Milano, Via Celoria 16, I-20133 Milano (Italy); Courteille, Ph. W. [Physikalisches Institut, Eberhardt-Karls-Universitaet Tuebingen, D-72076 Tuebingen (Germany); Institut Non Lineaire de Nice, CNRS, Universite de Nice Sophia-Antipolis, F-06560 Valbonne (France); Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, 13560-970 Sao Carlos, SP (Brazil)

2010-07-15

142

Optimization of polarized helium-3 neutron spin filters for neutron scattering  

Microsoft Academic Search

Nuclear spin-polarized 3He gas has been widely used in neutron scattering experiments. Spin-exchange optical pumping (SEOP) is one of the primary methods to produce polarized 3He. In SEOP, 3He is polarized via spin exchange collisions with optically pumped rubidium (Rb) atoms. At Indiana University, we have developed a boat system and a compact system based on the SEOP method to

Chenyang Jiang

2010-01-01

143

Strong-field Kapitza-Dirac scattering of neutral atoms.  

PubMed

Laser induced strong-field phenomena in atoms and molecules on the femtosecond (fs) time scale have been almost exclusively investigated with traveling wave fields. In almost all cases, approximation of the strong electromagnetic field by an electric field purely oscillating in time suffices to describe experimental observations. Spatially dependent electromagnetic fields, as they occur in a standing light wave, allow for strong energy and momentum transfer and are expected to extend strong-field dynamics profoundly. Here we report a strong-field version of the Kapitza-Dirac effect for neutral atoms where we scatter neutral He atoms in an intense short pulse standing light wave with fs duration and intensities well in the strong-field tunneling regime. We observe substantial longitudinal momentum transfer concomitant with an unprecedented atomic photon scattering rate greater than 10(16)s(-1). PMID:24702358

Eilzer, S; Zimmermann, H; Eichmann, U

2014-03-21

144

On the Size and Structure of Helium Snowballs Formed around Charged Atoms and Clusters of Noble Gases  

PubMed Central

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 He2084Kr2+ and the isobaric, nonmagic He4184Kr+. 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. A2011, 115, 730021568337] 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+ [KimJ. H.; et al. J. Chem. Phys.2006, 124, 21430116774401] 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

2013-01-01

145

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

PubMed

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

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

2014-09-18

146

Effect of electron correlation on high-order-harmonic generation of helium atoms in intense laser fields: Time-dependent generalized pseudospectral approach in hyperspherical coordinates  

E-print Network

Effect of electron correlation on high-order-harmonic generation of helium atoms in intense laser. The procedure is applied to the investigation of high-order-harmonic generation HHG of helium atoms states and the role of the individual spin orbital can- not be explicitly treated. The recent development

Chu, Shih-I

147

Fluxes of energetic neutral helium atoms from the heliosheath and the IBEX Ribbon  

NASA Astrophysics Data System (ADS)

Full sky maps of energetic neutral hydrogen atoms (H ENA) obtained with the Interstellar Boundary Explorer revealed a bright, arc-like Ribbon, which dominates over the heliosheath emission on large swaths of the sky. We simulate the emission of helium ENA from the heliosheath and the IBEX Ribbon. To estimate the heliosheath signal, we use a set of simple models of the heliosphere, where we take the newest results from the Voyagers spacecraft into account. We simulate the evolution of energy spectra of ?-particles and He+ ions using a number of binary interactions of He ions with plasma and neutral background in the heliosheath. The suprathermal ions from this distribution are a source of emerging He ENA flux, which we calculate. The fluxes in the observer frame are corrected for the Compton-Getting effect and the re-ionization losses on the path to detector. We conclude that the highest intensities should be expected from the heliospheric tail. For 1 keV He ENA, they are ~ 0.5 - 10 (cm2 ssrkeV )-1, depending on the employed model, whereas the expected intensities in the forward and flank sectors of the heliosphere in models with the heliosheath thickness ~ 25 AU do not exceed 0.02 (cm2 ssrkeV )-1 and 0.2 (cm2 ssrkeV )-1, respectively. For assessment of the IBEX Ribbon emission we compare the He ENA emissions from two models of the Ribbon origin previously developed to explain the hydrogen emission. In the first one, the Ribbon ENAs are produced outside the heliopause from the ionized neutral solar wind in the direction where the local interstellar magnetic field is perpendicular to the line-of-sight. The second model proposes the ENA production at the interface between the Local Interstellar Cloud (LIC) and the Local Bubble (LB). In the first model, the expected intensity is ~ 0.014 (cm2 ssrkeV )-1, i.e., of the order of the emission from the forward sector of the heliosphere, whereas in the second model, the intensity is ~ 2 - 7 (cm2 ssrkeV )-1. If the IBEX Ribbon requires a source population of ENAs leaving the heliosphere, then the Ribbon should not be visible in He ENA because of the insufficient supply of the He ENA from the neutralized ?-particles from the solar wind. Full-sky measurements of He ENA could create a possibility of distinction between proposed models of the Ribbon origin. We check that He ENA have a potential to probe distant sources of ENA production owing to the expected long mean free path against ionization and elastic scattering (up to 8000 AU for 1 keV/n He) in the interstellar medium.

Swaczyna, Pawel; Grzedzielski, Stan; Bzowski, Maciej

2014-05-01

148

Enhanced ion backscattering near 180/sup 0/ scattering angles in the two-atom scattering model. [Ion scattering from solids  

SciTech Connect

An analytical two-atom scattering model has been developed to treat the recent discovery of the enhancement near 180/sup 0/ of Rutherford backscattering yields from disordered solids. In contrast to conventional calculations of Rutherford backscattering that treat scattering from a single atom only (the backscattering atom), the present model includes the interaction of a second atom lying between the target surface and the backscattering atom. The projectile ion makes a glancing collision with this second atom both before and after it is backscattered. A weighted average is made over all possible positions of this second atom. The model predicts an enhancement effect whose physical origin arises from the tolerance of path for those ions whose ingoing and outgoing trajectories lie in the vicinity of the critical impact parameter. Results using Moliere scattering show how the yield enhancement depends on ion energy, backscattering depth, exit angle, scattering potential, atomic numbers of the projectile and target, and target density. In the model the critical impact parameter and critical angle play important roles. It is shown that these quantities depend on a single dimensionless parameter and formulas accurate to better than 1% are given for them.

Oen, O.S.

1982-08-01

149

Learning Approach on the Ground State Energy Calculation of Helium Atom  

SciTech Connect

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.

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

150

Optically-Detected Magnetic Resonance of Alkali Atoms Isolated on Helium Nano-Droplets  

NASA Astrophysics Data System (ADS)

Sharp, hyperfine-resolved, ESR spectra of alkali atoms isolated on helium nanodroplets are measured by optically-detected magnetic resonance (ODMR). A net spin polarization is created inside a magnetic field (B=0.2 to 4.2 T) by a pump laser beam. Microwave radiation in a resonant cavity at 9.4 GHz causes a spin transition which is detected by a probe laser beam. For ultimate precision the spectrum of free atoms is concurrently measured and serves as a reference. The shift of the ESR lines on the droplet with respect to free atoms directly reflects the distortion of the valence-electron wavefunction due to the He nanodroplet. While the electron g-factor remains unchanged within experimental uncertainties (<5 ppm), the increase of the hyperfine constant (typically +400 ppm) is consistent with an increase of the Fermi contact interaction. We are able to follow this change as a function of droplet size attesting the sensitivity of the method for the measurement of chemical shifts. The observation of Rabi oscillations indicates a long decoherence time and proves our ability to perform coherent manipulation of the spin.

Koch, Markus; Callegari, Carlo; Ernst, Wolfgang E.

2009-06-01

151

Dynamics of entanglement between two atomic samples with spontaneous scattering  

Microsoft Academic Search

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

Antonio Di Lisi; Silvio De Siena; Fabrizio Illuminati

2004-01-01

152

Scattering of atoms on a Bose-Einstein condensate  

SciTech Connect

We study the scattering properties of a Bose-Einstein condensate held in a finite depth well when the incoming particles are identical to the ones in the condensate. We calculate phase shifts and corresponding transmission and reflection coefficients, and we show that the transmission times can be negative, i.e., the atomic wave packet seemingly leaves the condensate before it arrives.

Poulsen, Uffe V.; Moelmer, Klaus [QUANTOP-Danish National Research Center for Quantum Optics, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2003-01-01

153

Emergence of a measurement basis in atom-photon scattering.  

PubMed

After measurement, a wave-function is postulated to collapse on a predetermined set of states--the measurement basis. Using quantum process tomography, we show how a measurement basis emerges in the evolution of the electronic spin of a single trapped atomic ion after spontaneous photon scattering and detection. This basis is determined by the excitation laser polarization and the direction along which the photon was detected. Quantum tomography of the combined spin-photon state reveals that although photon scattering entangles all superpositions of the measurement-basis states with the scattered photon polarization, the measurement-basis states themselves remain classically correlated with it. Our findings shed light on the process of quantum measurement in atom-photon interactions. PMID:23471403

Glickman, Yinnon; Kotler, Shlomi; Akerman, Nitzan; Ozeri, Roee

2013-03-01

154

Electron shell ionization of atoms with classical, relativistic scattering.  

PubMed

We investigate forward scattering of ionization from neon, argon, and xenon in ultrahigh intensities of 2 × 10(19) W/cm(2). Comparisons between the gases reveal the energy of the outgoing photoelectron determines its momentum, which can be scattered as far forward as 45° from the laser wave vector k(laser) for energies greater than 1 MeV. The shell structure in the atom manifests itself as modulations in the photoelectron yield and the width of the angular distributions. We arrive at an agreement with theory by using an independent electron model for the atom, a dipole approximation for the bound state interaction, and a relativistic, three-dimensional, classical radiation field including the laser magnetic field. The studies provide the atomic physics within plasmas, radiation, and particle acceleration in ultrastrong fields. PMID:25167403

Ekanayake, N; Luo, S; Grugan, P D; Crosby, W B; Camilo, A D; McCowan, C V; Scalzi, R; Tramontozzi, A; Howard, L E; Wells, S J; Mancuso, C; Stanev, T; Decamp, M F; Walker, B C

2013-05-17

155

LIF measurements for validation of collisional-radiative modelling of atomic helium in the edge of a fusion plasma  

NASA Astrophysics Data System (ADS)

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 (CR) model which is needed in order to obtain both plasma parameters from the measured relative intensities of atomic helium lines. Laser-induced fluorescence spectroscopy on a thermal helium beam in the edge plasma of the tokamak TEXTOR in Jülich was applied to validate the CR model of helium. By use of a high-power, pulsed laser system (a dye laser pumped by an excimer laser) several laser excitation schemes starting from the n=2 levels have been tried. The fluorescence light was observed at the laser wavelength and elsewhere in the spectrum providing information on population densities of initial levels as well as on collisional population transfer between excited levels. This paper summarises the results of the measurements, showing principal limits and possible improvements of this experimental validation method of the CR model of the diagnostic helium beam.

Krychowiak, M.; Mertens, Ph; König, R.; Schweer, B.; Brezinsek, S.; Schmitz, O.; Brix, M.; Samm, U.; Wolf, R.; Klinger, T.

2010-05-01

156

Resonances in rotationally inelastic scattering of OH(X2) with helium and Koos B. Gubbels, Qianli Ma, Millard H. Alexander, Paul J. Dagdigian, Dick Tanis et al.  

E-print Network

Resonances in rotationally inelastic scattering of OH(X2) with helium and neon Koos B. Gubbels of OH(X2 ) with helium and neon Koos B. Gubbels,1,2,a) Qianli Ma,3 Millard H. Alexander,4 Paul J; published online 11 April 2012) We present detailed calculations on resonances in rotationally and spin

157

X and Rb Atoms on Helium Nanodroplets: is the Van Der Waals Attraction Strong Enough to Form a Molecule?  

NASA Astrophysics Data System (ADS)

Chemical reactions in the cold environment of a helium nanodroplet currently attract high interest and can be spectroscopically observed with typical molecular beam techniques. In order to estimate the influence of surrounding helium on the van der Waals interaction between heliophilic and heliophobic dopants that could be investigated in our lab with ESR spectroscopy, we apply density-functional theory to simulate a double-dotation of He-clusters with Rb and Xe atoms. Simulations of a double-doped He_{N} droplet with N = 500 show that the alkali metal atom stays on the surface, whereas the Xe atom sits in the middle of the droplet. The van der Waals attraction between Rb and Xe is not strong enough to compensate the separation of the heliophilic Xe and the heliophobic Rb caused by the helium droplet: a potential barrier of 23.4 K has to be overcome, which is to be compared with the 0.4 K internal temperature of the droplet. 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) M. Koch, C. Callegari, and W. E. Ernst, Mol. Phys. 108 (7), 1005-1011 (2010) J. Poms, A. W. Hauser, and W. E. Ernst, Phys. Chem. Chem. Phys. 14, 15158-15165 (2012)

Poms, Johannes; Hauser, Andreas W.; Ernst, Wolfgang E.

2013-06-01

158

A helium film coated quasi-parabolic mirror to focus a beam of ultra-cold spin polarized atomic hydrogen  

SciTech Connect

A 350 mK helium-4-coated mirror was used to increase the intensity of an ultra-cold electron-spin-polarized atomic hydrogen beam. The mirror uses the observed specular reflection of atomic hydrogen from a superfluid-helium-covered surface. A quasi-parabolic polished copper mirror was installed with its focus at the 5 mm diameter exit aperture of an atomic hydrogen stabilization cell in the gradient of an 8 T solenoid field. The four-coned mirror shape, which was designed specifically for operation in the gradient, increased the beam intensity focused by a sextupole magnet into a compression tube detector by a factor of about 7.5.

Luppov, V.G.; Kaufman, W.A.; Hill, K.M.; Raymond, R.S.; Kirsch, A.D. (Randall Laboratory, University of Michigan, Ann Arbor, Michigan 48109-1120 (United States))

1993-12-05

159

Shifts in the ESR Spectra of Alkali-Metal Atoms (Li, Na, K, Rb) on Helium Nanodroplets  

PubMed Central

He-droplet-induced changes of the hyperfine structure constants of alkali-metal atoms are investigated by a combination of relativistically corrected ab initio methods with a simulation of the helium density distribution based on He density functional theory. Starting from an accurate description of the variation of the hyperfine structure constant in the M–He diatomic systems (M=Li, Na, K, Rb) as a function of the interatomic distance we simulate the shifts induced by droplets of up to 10 000 4He atoms. All theoretical predictions for the relative shifts in the isotropic hyperfine coupling constants of the alkali-metal atoms attached to helium droplets of different size are then tied to a single, experimentally derived parameter of Rb. PMID:23125112

Hauser, Andreas W; Gruber, Thomas; Filatov, Michael; Ernst, Wolfgang E

2013-01-01

160

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

161

A database method for binary atomic scattering angle calculation  

NASA Astrophysics Data System (ADS)

Calculation of the classical binary atomic scattering angle is a critical factor in computer simulations of ion beam interactions with matter. Different approaches intended for more accurate results with sufficient speed have been reported in the literature. This paper presents an approach using database evaluation. This approach has been tested and found to be extremely fast (18 times faster than the Biersack-Haggmark's Magic-Formula for scattering [Nucl. Instr. and Meth. 174 (1980) 257]), and its accuracy is better than 0.5%. This database takes only 216 kB of computer memory.

Yuan, B.; Yu, P. C.; Tang, S. M.

1993-11-01

162

Electron scattering by laser-excited barium atoms  

NASA Technical Reports Server (NTRS)

Inelastic and superelastic scattering of 30- and 100-eV electrons by laser-excited 6s 6p 1P and subsequent cascade-populated 6s 6p 3P, 6s 5d 1D, and 6s 5d 3D Ba atoms have been observed. Absolute differential cross sections for the singlet and relative scattering intensities for the triplet species have been determined in the 5 to 20 deg angular region. Under the present conditions excitations dominate over deexcitations.

Register, D. F.; Trajmar, S.; Jensen, S. W.; Poe, R. T.

1978-01-01

163

Recent progress in electron scattering from atoms and molecules  

SciTech Connect

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.

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

164

Cavity-Modified Collective Rayleigh Scattering of Two Atoms  

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

165

Inversion problem for ion-atom differential elastic scattering.  

NASA Technical Reports Server (NTRS)

The paper describes a practical application of Remler's (1971) method by which one constructs a set of phase shifts from high resolution measurements of the differential elastic scattering of protons by rare-gas atoms. These JWKB phase shifts are then formally inverted to determine the corresponding intermolecular potentials. The validity of the method is demonstrated by comparing an intermolecular potential obtained by direct inversion of experimental data with a fairly accurate calculation by Wolniewicz (1965).

Rich, W. G.; Bobbio, S. M.; Champion, R. L.; Doverspike, L. D.

1971-01-01

166

Scattering processes in antiprotonic hydrogen - hydrogen atom collisions  

E-print Network

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.

V. P. Popov; V. N. Pomerantsev

2006-01-11

167

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

E-print Network

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 $I$).

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

168

Cooperative scattering and radiation pressure force in dense atomic clouds  

SciTech Connect

Atomic clouds prepared in ''timed Dicke'' states, i.e. states where the phase of the oscillating atomic dipole moments linearly varies along one direction of space, are efficient sources of superradiant light emission [Scully et al., Phys. Rev. Lett. 96, 010501 (2006)]. Here, we show that, in contrast to previous assertions, timed Dicke states are not the states automatically generated by incident laser light. In reality, the atoms act back on the driving field because of the finite refraction of the cloud. This leads to nonuniform phase shifts, which, at higher optical densities, dramatically alter the cooperative scattering properties, as we show by explicit calculation of macroscopic observables, such as the radiation pressure force.

Bachelard, R. [University of Nova Gorica, School of Applied Sciences, Vipavska 11c SI-5270 Ajdovscina (Slovenia); Piovella, N. [Dipartimento di Fisica, Universita Degli Studi di Milano, Via Celoria 16, I-20133 Milano (Italy); Courteille, Ph. W. [Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, 13560-970 Sao Carlos, SP (Brazil)

2011-07-15

169

Femtosecond quantum fluid dynamics of helium atom under an intense laser field  

SciTech Connect

A comprehensive, nonperturbative, time-dependent quantum mechanical (TDQM) approach is proposed for studying the dynamics of a helium atom under an intense, ultrashort (femtoseconds) laser pulse. The method combines quantum fluid dynamics (QFD) and density functional theory. It solves a single generalized nonlinear Schroedinger equation of motion (EOM), involving time and three space variables, which is obtained from two QFD equations, namely, a continuity equation and an Euler-type equation. A highly accurate finite difference scheme along with a stability analysis is presented for numerically solving the EOM. Starting from the ground-state Hartree-Fock density for He at t = 0, the EOM yields the time-dependent (TD) electron density, effective potential surface, difference density, difference effective potential, ground-state probability, {l_angle}r{r_angle}, magnetic susceptibility, polarizability, flux, etc. By a Fourier transformation of the TD dipole moment along the linearly polarized-field direction, the power and rate spectra for photoemission are calculated. eleven mechanistic routes for photoemission are identified, which include high harmonic generation as well as many other spectral transitions involving ionized, singly excited, doubly excited (autoionizing), and continuum He states, based on the evolution of the system up to a particular time. Intimate connections between photoionization and photoemission are clearly observed through computer visualizations. Apart from being consistent with current experimental and theoretical results, the present results offer certain predictions on spectral transitions which are open to experimental verification.

Dey, B.K. [Panjab Univ., Chandigarh (India). Dept. of Chemistry] [Panjab Univ., Chandigarh (India). Dept. of Chemistry; Deb, B.M. [Panjab Univ., Chandigarh (India). Dept. of Chemistry] [Panjab Univ., Chandigarh (India). Dept. of Chemistry; [Jawaharial Nehru Centre for advanced Scientific Research, Bangalore (India)

1998-10-05

170

Primordial helium recombination. III. Thomson scattering, isotope shifts, and cumulative results  

SciTech Connect

Upcoming precision measurements of the temperature anisotropy of the cosmic microwave background at high multipoles will need to be complemented by a more complete understanding of recombination, which determines the damping of anisotropies on these scales. This is the third in a series of papers describing an accurate theory of He i and He ii recombination. Here we describe the effect of Thomson scattering, the {sup 3}He isotope shift, the contribution of rare decays, collisional processes, and peculiar motion. These effects are found to be negligible: Thomson and {sup 3}He scattering modify the free electron fraction x{sub e} at the level of severalx10{sup -4}. The uncertainty in the 2{sup 3}P{sup o}-1{sup 1}S rate is significant, and for conservative estimates, gives uncertainties in x{sub e} of order 10{sup -3}. We describe several convergence tests for the atomic level code and its inputs, derive an overall C{sub l} error budget, and relate shifts in x{sub e}(z) to the changes in C{sub l}, which are at the level of 0.5% at l=3000. Finally, we summarize the main corrections developed thus far. The remaining uncertainty from known effects is {approx}0.3% in x{sub e}.

Switzer, Eric R.; Hirata, Christopher M. [Department of Physics, Princeton University, Princeton, New Jersey, 08544 (United States); School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540 (United States)

2008-04-15

171

The Helium Resonant Scattering in the Corona and Heliosphere (HERSCHEL) Suborbital Investigation: an Overview  

NASA Astrophysics Data System (ADS)

Although solar elemental abundances have historically been assumed to be representative of cosmic abundances, the advent of measurements from space-borne platforms has provided evidence that solar abundances vary with location within the sun and the heliosphere. The HERSCHEL investigation achieves imaging observations of the hydrogen, helium and electron components of the solar corona in order to establish a link between the variations in helium abundance in the solar chromosphere and and variations in the helium abundance in the solar wind. Three different aspects of this observation are achieved in the three separate instruments constituting the HERSCHEL payload. The mutual support of these three components leads to a measurement of the coronal helium abundance with the minimal a priori assumptions.

Moses, Daniel

172

Elastic Scattering of Protons and Pions from Polarized HELIUM-3 at Intermediate Energies  

NASA Astrophysics Data System (ADS)

A novel cryogenic technique has been used to produce polarized ^3He targets with a relative density of up to p = 12 atmospheres (or ~ 3 times 10^ {20} ^3He atoms/cm ^3; p = 1 atmosphere corresponds to 760 Torr or 101.3 kPa pressure at 273 K). In these targets the ^3He nuclei are polarized by spin exchange collisions with optically pumped rubidium atoms. From transmission measurements at wavelengths of 790-800 nm, pressure shifts, linewidths and lineshape asymmetries for the Rb 5S_{1/2} to 5P_{1/2} D1 transition have been determined. The Rb spin destruction rate was found to exhibit a quadratic increase versus ^3 He pressure: this might indicate the importance of Rb-^3He-^3He collision processes. The transmission results for circularly polarized light are well described by a model which predicts the dependence of the average Rb polarization on Rb density, ^3He pressure, light intensity and cell geometry. The Rb - ^3 He spin exchange cross section, < sigma_{Se^nu}> = 6.1 times 10^ {-20} cm^3s ^{-1}, was found to be independent of ^3He pressure up to p = 12.1 atmospheres. Maximum ^3He polarizations of up to 70% were achieved with cells of 35 cm ^3 volume containing ^3He at p = 7-10 atmospheres. This target has been used to measure cross sections and spin observables in elastic scattering of both pions and protons from polarized ^3He. Angular distributions of cross sections and the spin observables A_{OOON}, A_ {OONO}, and A_{OONN } have been measured for the elastic scattering of polarized protons from polarized ^3He at incident proton energies of 200, 290, 400 and 500 MeV. Measurements were made at 12 angles in the range 24^ circ-73^circ for most of the energies. The results are compared to two nonrelativistic microscopic momentum space optical model calculations. One calculation utilizes the Distorted Wave Impulse Approximation (DWIA) formalism whereas the second uses the Distorted Wave Born Approximation (DWBA). The overall agreement with the data is poor. For the target related spin observables (A_{OOON} and A_{OONN} the DWBA calculation represents a significant improvement over the DWIA model but the observables are poorly described whereas the beam related asymmetry (A_{OONO }) is well described. The measurement of elastic scattering of 100 MeV pi^+ from a polarized ^3He target is, together with recent measurements on the spin-1/2 nuclei ^{13}C and ^{15}N, the world's database for pion scattering from polarized spin-1/2 complex nuclei (A > 2). Measurements have been made at lab angles of 60^circ, 80^circ and 100^ circ, with the largest value A_ {y} = 0.89 +/- 0.12 occurring at 80^circ near a cross section minimum. This asymmetry is the largest observed to date in pion scattering from a spin-1 over 2 nucleus. The A_{y } data are qualitatively reproduced by a schematic model. However agreement with the data is significantly improved when realistic three-body Faddeev wave functions and a full nonlocal DWIA reaction model is used.

Larson, Bart William

173

Scattering cross sections for rotational excitation of N2, O2, and CH4 molecules in collisions with He atoms  

NASA Astrophysics Data System (ADS)

The decomposition of an energy dissipation spectrum was studied using two crossed neutral molecular beams. Scattering of a nearly monochromatic helium atomic beam gives rotary transitions with 1 meV energy difference. The measure of collisions between He and excited rotary states of N2, O2, and H4 as separated transitions in a flight path spectrum over a large angular range is obtained. Together with the angular distribution of the scattered intensity, the flight path spectrum provides relative, double, differential efficiency cross sections, that show diffraction oscillations of angular dependance in all cases. Comparison of measured results with theoretical calculated differential cross sections in accordance with the exact close-coupling method shows good conformity.

Kohl, K. H.

1982-12-01

174

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

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

175

Double photoionization of helium with synchrotron x-rays: Proceedings  

SciTech Connect

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.

Not Available

1994-01-01

176

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

Microsoft Academic Search

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

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

1975-01-01

177

All-order relativistic many-body theory of low-energy electron-atom scattering  

NASA Astrophysics Data System (ADS)

A generalization of the box-variational method is developed to describe particle scattering with the Dirac equation. The method is applied to extract phase shifts from all-order single + double relativistic many-body perturbation theory calculations of the electron-helium, electron-neon, and electron-krypton systems. Comparisons with experimental elastic and momentum transfer cross sections are made. Agreement at the 1% to 2% level is achieved for helium and neon. The scattering length for krypton is 4% smaller in magnitude than experimental estimates derived from swarm experiments.

Cheng, Yongjun; Tang, Li Yan; Mitroy, J.; Safronova, M. S.

2014-01-01

178

Physics of polarized scattering at multi-level atomic systems  

E-print Network

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...

Stenflo, Jan

2015-01-01

179

Low-Energy Elastic Electron Scattering by Atomic Oxygen  

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

180

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

SciTech Connect

Investigations have focused primarily on surface structure and dynamics of ionic insulators, epitaxial growth onto alkali halide crystals and multiphoton studies. The surface dynamics of RbCl has been re-examined. We have developed a simple force constant model which provides insight into the dynamics of KBr overlayers on NaCl(001), a system with a large lattice mismatch. The KBr/NaCl(001) results are compared to Na/Cu(001) and NaCl/Ge(001). We have completed epitaxial growth experiments for KBr onto RbCl(001). Slab dynamics calculations using a shell model for this system with very small lattice mismatch are being carried out in collaboration with Professor Manson of Clemson University and with Professor Schroeder in Regensburg, Germany. Extensive experiments on multiphoton scattering of helium atoms onto NaCl and, particularly, LiF have been carried out and the theory has been developed to a rather advanced stage by Professor Manson. This work will permit the extraction of more information from time-of-flight spectra. It is shown that the theoretical model provides a very good description of the multiphoton scattering from organic films. Work has started on self-assembling organic films on gold (alkyl thiols/Au(111)). We have begun to prepare and characterize the gold crystal; one of the group members has spent two weeks at the Oak Ridge National Laboratory learning the proper Au(111) preparation techniques. One of our students has carried out neutron scattering experiments on NiO, measuring both bulk phonon and magnon dispersion curves.

Not Available

1992-01-01

181

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

NASA Astrophysics Data System (ADS)

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 ne 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 ˜1012-1013 cm-3 when exciting helium atoms with a laser at the wavelength of ? = 388.9 nm tuned to the triplet transition 23S?33P ° and observing the fluorescence light at the laser wavelength and at ? = 587.6 nm(33D?23P °). A first test measurement at the TEXTOR tokamak in Jülich performed by use of an excimer-pumped dye laser in connection with a thermal helium beam is shown and discussed.

Krychowiak, M.; Mertens, Ph.; Schweer, B.; Brezinsek, S.; König, R.; Schmitz, O.; Brix, M.; Klinger, T.; Samm, U.

2008-03-01

182

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

NASA Astrophysics Data System (ADS)

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.

Karman, Tijs; Groenenboom, Gerrit C.

2014-11-01

183

Electroweak constraints from atomic parity violation and neutrino scattering  

SciTech Connect

Precision electroweak physics can provide fertile ground for uncovering new physics beyond the standard model (SM). One area in which new physics can appear is in so-called 'oblique corrections', i.e., next-to-leading-order expansions of bosonic propagators corresponding to vacuum polarization. One may parametrize their effects in terms of quantities S and T that discriminate between conservation and nonconservation of isospin. This provides a means of comparing the relative contributions of precision electroweak experiments to constraints on new physics. Given the prevalence of strongly T-sensitive experiments, there is an acute need for further constraints on S, such as provided by atomic parity-violating experiments on heavy atoms. We evaluate constraints on S arising from recently improved calculations in the Cs atom. We show that the top quark mass m{sub t} provides stringent constraints on S within the context of the SM. We also consider the potential contributions of next-generation neutrino scattering experiments to improved (S,T) constraints.

Hobbs, Timothy; Rosner, Jonathan L. [Department of Physics, Indiana University, Bloomington, Indiana 47405 (United States); Enrico Fermi Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637 (United States)

2010-07-01

184

The Influence of Atomic Model on Scattering Polarization Profile  

NASA Astrophysics Data System (ADS)

The diagnostic of magnetic field is very important in solar physics. Stokes parameters I, Q, U, and V can give a complete description of the state of polarization of a beam of light. By inversion of Stokes parameters, the magnetic field in the sun can be obtained. In the recent decades, the diagnostic of magnetic field has been almost based on the Zeeman effect in presence of a strong magnetic field. But in the quiet sun region, the turbulent magnetic field strength is usually less than 100 Gs. Because the Hanle effect is sensitive to a weak magnetic field, it can provide a diagnostic tool for a weak magnetic field. However, it is not easy to obtain the weak field with this effect, and a complete understanding of the polarization mechanism is needed. This paper focuses on the influence of different atomic models on the scattering polarization and Hanle effect. We adopt the seven-, four-, and two-level atomic models to investigate the theoretical linear polarization profiles of MgI b triplet so that we can probe the magnetic field more precisely. In this calculation, we use a typical temperature of 5755 K, corresponding to the temperature of MgI b triplet formation region. It does find that the results for the seven- and four-level atomic models are almost the same. The polarization degrees are nearly unaffected by the populations of MgI atom's levels above the transition levels. There is a big difference between the results from the two- and multi-level atomic models. For the two-level atomic model, the b_4 line is not affected by the Hanle effect in the lower level. But for the multi-level atomic models, it does. And the lower level Hanle effect of b_2 line in the multi-level approximation is much more obvious than that in the two-level approximation. This study is thus useful to produce the theoretical profiles for diagnosing a weak magnetic field, and finally b_2 line is the most suitable candidate for the purpose.

Li, H.; Qu, Z. Q.

2014-09-01

185

Attosecond XUV absorption spectroscopy of doubly excited states in helium atoms dressed by a time-delayed femtosecond infrared laser  

NASA Astrophysics Data System (ADS)

In the present paper, we investigate the time-resolved transient absorption spectroscopy of doubly excited states of helium atoms by solving the time-dependent two-electron Schrödinger equation numerically based on a one-dimensional model. The helium atoms are subjected to an extreme ultraviolet (XUV) attosecond pulse and a time-delayed infrared (IR) few-cycle laser pulse. A superposition of doubly excited states populated by the XUV pulse is identified, which interferes with the direct ionization pathway leading to Fano resonance profiles in the photoabsorption spectrum. In the presence of an IR laser, however, the Fano line profiles are strongly modified: A shifting, splitting, and broadening of the original absorption lines is observed when the XUV attosecond pulse and infrared few-cycle laser pulse overlap in time, which is in good agreement with recent experimental results. At certain time delays, we observe symmetric Lorentz, inverted Fano profiles, and even negative absorption cross sections indicating that the XUV light can be amplified during the interaction with atoms. We further prove that the above pictures are general for different doubly excited states by suitably varying the frequency of the IR field to coherently couple the corresponding states.

Yang, Z. Q.; Ye, D. F.; Ding, Thomas; Pfeifer, Thomas; Fu, L. B.

2015-01-01

186

A helium-film-coated quasi-parabolic mirror to focus a beam of ultra-cold spin-polarized atomic hydrogen  

SciTech Connect

A 350 mK helium-4 coated mirror was used to increase the intensity of an ultra-cold electron-spin-polarized atomic hydrogen beam. The mirror uses the observed specular reflection of atomic hydrogen from a superfluid-helium-covered surface. A quasi-parabolic polished copper mirror was installed with its focus at the 5 mm diameter exit aperture of an atomic hydrogen stabilization cell in the gradient of an 8 T solenoid. The four-coned mirror shape, which was designed specifically for operation in the gradient, increased the beam intensity focused by a sextupole magnet into a compression tube detector more than seven-fold.

Luppov, V.G.; Kaufman, W.A.; Hill, K.M. [and others

1993-04-01

187

Scattering of high-velocity Ar atoms by CO2, OCS, and CS2  

NASA Technical Reports Server (NTRS)

Fast Ar beams have been scattered by room-temperature CO2, OCS, and CS2 to obtain average atom-molecule potentials. The results are consistent with other scattering measurements on similar systems, and are also in excellent agreement with available theoretical calculations based on an electron-gas model. Decomposition of the atom-molecule potentials into constituent atom-atom potentials shows that such a representation can be utilized with fair accuracy but that a definite discrepancy exists.

Amdur, I.; Peters, W. A.; Jordan, J. E.; Mason, E. A.

1976-01-01

188

Rayleigh scattering from n=3 states of hydrogenlike atoms  

NASA Astrophysics Data System (ADS)

An exact analytic evaluation of the Kramers-Heisenberg matrix elements for Rayleigh scattering from n=3 states of hydrogenlike atoms is performed in the nonrelativistic dipole approximation, using the Green's function method. The results are given separately for each subshell. The possibility of 3 s?3 d transitions is also considered. The dependence on the photon energy is contained in six invariant amplitudes. The formulas needed for the evaluation of the various cross sections are presented. The numerical results are contained in tables from which partial and total cross sections can be easily built, covering the energy range from zero up to 20 times the K threshold energy. In the vicinity of Balmer ? frequency the cross section is large and comparable with that for excited n=2 states, confirming an earlier hypothesis of Röhr. At other energies the cross sections for n=2 and n=3 states are comparable, too. The results should be useful in plasma diagnostics.

Florescu, Viorica; Cionga, Aurelia

1985-06-01

189

Inelastic cross sections for positron scattering from atomic hydrogen  

SciTech Connect

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.

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

190

Laser assisted electron-atom scattering in critical geometries  

NASA Astrophysics Data System (ADS)

We investigate the scattering of electrons off of neutral targets in the presence of a linearly polarized, low frequency laser field. The laser has large enough extent for the wavefunction to be treated in the Floquet expansion. The scattering geometries of interest are small angles where momentum transfer is nearly perpendicular to the field, and the Kroll Watson approximation breaks down. We use the eigenchannel R matrix method to solve the Schr"odinger equation, employing Hamiltonians in both the length and the velocity gauges in different regions. The target atom is represented by a model potential including a screened coulomb term near the origin and a longer range induced dipole interaction. The short range reaction matrix in the Kramers-Henneberger (acceleration) representation is found by matching the velocity gauge R matrix to spherical Gordon-Volkov states, and from this the cross section is derived. Experiments have shown emission and absorption cross sections at small angles to be much higher than the approximation predicts, and we hope to gain insight into the cause of this phenomenon.

Morrison, Nathan; Greene, Chris H.

2012-06-01

191

Positron scattering from hydrogen atom embedded in dense quantum plasma  

SciTech Connect

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.

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

192

The Surface Lattice Dynamics of Crystalline Ionic Insulators via Helium Atom Spectroscopy  

NASA Astrophysics Data System (ADS)

A recently constructed high-resolution He atom scattering (HAS) instrument has been used to carry out experiments on several ionic insulating surfaces--namely RbI (001), MgO (001), and NiO (001). The HAS technique is nearly an ideal probe for measuring the low-energy surface vibrational modes or dispersion curves (2-50 meV) of a crystalline surface with extremely high resolution (< 0.5 meV). Each mode consists of a quantized wave vibration called a surface phonon which has a characteristic frequency, omega, and wavevector, Q. Experimentally, the surface dispersion curves can be mapped over the entire irreducible Brillouin zone by measuring omega(Q) versus Q. The shapes of these curves are directly affected by the atomic force constants. Therefore, the measured surface lattice dynamics leads to an evaluation of the surface forces of crystals. Recently, there has been an increased interest in the heavier, more polarizable alkali halides, RbI (001) for example, since theoretical calculations predict relaxation-induced modes that are surface localized and well-separated from the bulk bands. The results for RbI (001) experimentally confirm the predicted relaxation-induced modes. MgO (001) and NiO (001) represent the first HAS results performed on ionic insulating crystals in our laboratory that are not alkali halide crystals. MgO (001) is an interesting surface since it is a well-known catalyst and a common substrate material used for making thin films. NiO (001) is also interesting since it is an antiferromagnet, and the possibility of coupling between the intrinsic crystalline magnetic field and the surface phonon modes exists. The lattice dynamical results for these two surfaces are also given. The results from earlier HAS studies on MgO (001) were extended and later corroborated by independent HAS observations. The results for the NiO (001) represent the first experimental surface dynamical measurements for this crystal, and they are compared with bulk theoretical and experimental results as well as HAS dynamical measurements from the Ni(001) + c-(2 x 2)O surface, where oxygen is chemisorbed on the Ni (001) surface.

Brug, William Patrick

193

Atomic vibrations in iron nanoclusters: Nuclear resonant inelastic x-ray scattering and molecular dynamics simulations  

E-print Network

Atomic vibrations in iron nanoclusters: Nuclear resonant inelastic x-ray scattering and molecular-assembled, isolated 57 Fe nanoclusters was studied by nuclear resonant inelastic x-ray scattering and molecular of the experimental nanoclusters were investigated by atomic force microscopy, high resolution transmission electron

Kik, Pieter

194

Eikonal approximation in atom-surface scattering: Effects of a corrugated attractive well J. R. Manson  

E-print Network

for the scattering of atomic beams from surfaces, is extended to include a periodic corrugation of the leading edgeEikonal approximation in atom-surface scattering: Effects of a corrugated attractive well J. R for estimating small effects of corrugation of the attractive physisorption potential on the diffraction spectra

Manson, Joseph R.

195

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

E-print Network

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

Burke, Kieron

196

Interacting double dark resonances in a hot atomic vapor of helium  

SciTech Connect

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.

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

197

Precise Measurements of S-Wave Scattering Phase Shifts with a Juggling Atomic Clock  

NASA Astrophysics Data System (ADS)

We demonstrate an interferometric scattering technique that allows highly precise measurements of s-wave scattering phase shifts. We collide two clouds of cesium atoms in a juggling fountain clock. The atoms in one cloud are prepared in a coherent superposition of the two clock states and the atoms in the other cloud are prepared in one of the F,mF ground states. When the two clouds collide, the clock states experience s-wave phase shifts as they scatter off of the atoms in the other cloud. We detect only the scattered part of the clock atom's wavefunction for which the relative phase of the clock coherence is shifted by the difference of the s-wave phase shifts. In this way, we unambiguously observe the differences of scattering phase shifts. These phase shifts are independent of the atomic density to lowest order, enabling measurements of scattering phase shifts with atomic clock accuracy. Recently, we have observed the changes in scattering phase shifts as a function of magnetic field over a range of values where Feshbach resonances may be expected and where inelastic scattering channels open and close. A number of these measurements will precisely test and tightly constrain our knowledge of cesium-cesium interactions. With such knowledge, future measurements may place stringent limits on the time variation of fundamental constants, such as the electron-proton mass ratio, by precisely probing phase shifts near a Feshbach resonance.

Gensemer, Steven; Hart, Russell; Martin, Ross; Xu, Xinye; Legere, Ronald; Gibble, Kurt; Kokkelmans, Servaas

2009-03-01

198

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

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

199

Total scattering cross sections and interatomic potentials for neutral hydrogen and helium on some noble gases  

SciTech Connect

Measurements of energy-dependent scattering cross sections for 30 to 1800 eV D incident on He, Ne, Ar, and Kr, and for 40 to 850 eV He incident on He, Ar, and Kr are presented. They are determined by using the charge-exchange efflux from the Princeton Large Torus tokamak as a source of D or He. These neutrals are passed through a gas-filled scattering cell and detected by a time-of-flight spectrometer. The cross section for scattering greater than the effective angle of the apparatus (approx. =20 mrad) is found by measuring the energy-dependent attenuation of D or He as a function of pressure in the scattering cell. The interatomic potential is extracted from the data.

Ruzic, D.N.; Cohen, S.A.

1985-04-01

200

Elastic scattering of polarized protons on helium three at 800 MeV  

SciTech Connect

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.

Azizi, A.

1985-07-01

201

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

E-print Network

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

Kaganovich, Igor

202

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

SciTech Connect

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.

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

203

HIPPO: A supersonic helium jet gas target for nuclear astrophysics  

NASA Astrophysics Data System (ADS)

A high density supersonic helium jet gas target has been developed for the newly installed St. George Recoil Mass Separator, at the Nuclear Science Laboratory, University of Notre Dame. The jet's properties for both helium and nitrogen have been studied by means of elastic scattering and energy loss experiments. The helium jet's full width at half maximum was found to be 2.1 mm, assuming axially symmetric gas expansion with a maximum target thickness of (2.67±0.16)×1017 atoms/cm2 at 1500 mbar of inlet pressure, and well confined within the jet region.

Kontos, Antonios; Schürmann, Daniel; Akers, Charles; Couder, Manoel; Görres, Joachim; Robertson, Daniel; Stech, Ed; Talwar, Rashi; Wiescher, Michael

2012-02-01

204

Deep Inelastic Electron Scattering Off the Helium and Tritium Mirror Nuclei  

SciTech Connect

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.

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

205

Electron loss to the Continuum in the Projectile ionization for Positronium - Helium atom collision  

E-print Network

The dynamics of the electron loss to the continuum (ELC) from the light neutral projectile positronium (Ps) atom in collision with the He atom is studied in the framework of the post collisional Coulomb Distorted Eikonal Approximation (CDEA). Both the fully differential (TDCS) and the double differential (DDCS) cross sections are investigated in the intermediate and high incident energies. Results are compared with the existing experiment and other theories, where possible.

Roy, Susmita

2008-01-01

206

Effects of coupled atomic states on the resonance scattering of radiation  

E-print Network

The excitation and decay probabilities for resonance scattering of radiation from an atom with two coupled excited states in an external static field are calculated as a function of time and frequency. Various oscillatory terms are found...

Srivastava, Rajendra P.; Fontana, Peter R.

1974-01-01

207

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

E-print Network

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 a.u. 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 a.u. for electron and +13.8 a.u. for positron scattering.

Reid, David D

2014-01-01

208

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

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

209

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

SciTech Connect

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.

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

210

Microscopic theory of scattering of weak electromagnetic radiation by a dense ensemble of ultracold atoms  

SciTech Connect

Based on the developed quantum microscopic theory, the interaction of weak electromagnetic radiation with dense ultracold atomic clouds is described in detail. The differential and total cooperative scattering cross sections are calculated for monochromatic radiation as particular examples of application of the general theory. The angular, spectral, and polarization properties of scattered light are determined. The dependence of these quantities on the sample size and concentration of atoms is studied and the influence of collective effects is analyzed.

Sokolov, I. M., E-mail: IMS@IS12093.spb.edu; Kupriyanov, D. V. [St. Petersburg State Technical University (Russian Federation); Havey, M. D. [Old Dominion University, Department of Physics (United States)

2011-02-15

211

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

Microsoft Academic Search

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

H. Richard Ross

1993-01-01

212

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

E-print Network

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.

Hongwei Xiong

2011-01-03

213

Precise Measurements of S-Wave Scattering Phase Shifts with a Juggling Atomic Clock  

NASA Astrophysics Data System (ADS)

We demonstrate an interferometric scattering technique that allows highly precise measurements of s-wave scattering phase shifts. We collide two clouds of cesium atoms in a juggling fountain clock. The atoms in one cloud are prepared in a coherent superposition of the two clock states and the atoms in the other cloud in an F,mF state. After the two clouds collide, we detect the scattered part of the clock atom's wavefunction for which the phase of the clock coherence is shifted by the difference of the s-wave phase shifts. In this way, we unambiguously observe the differences of scattering phase shifts. These phase shifts are independent of the atomic density to lowest order, enabling measurements of scattering phase shifts with clock accuracy. Recently, we have observed the changes in scattering phase shifts as a function of magnetic field over a range where Feshbach resonances may be expected and inelastic scattering channels open and close. Measurements like these will tightly constrain our knowledge of cesium-cesium interactions. With such knowledge, future measurements may place stringent limits on the time variation of fundamental constants, such as the electron-proton mass ratio, by precisely probing phase shifts near a Feshbach resonance.

Gensemer, Steven; Hart, Russell; Martin, Ross; Xu, Xinye; Legere, Ronald; Gibble, Kurt; Kokkelmans, Servaas

2009-04-01

214

2s Hyperfine Structure in Hydrogen Atom and Helium3 Ion  

Microsoft Academic Search

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

Savely G. Karshenboim; D. I. Mendeleev

215

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)

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.

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

2015-01-01

216

Experimental Determination of the Turning Point of Thermal Energy Helium Atoms above a Cu(001) Surface  

NASA Astrophysics Data System (ADS)

The effective height of CO islands above a Cu(001) surface has been determined to be 2.3 Å from six interference maxima in the energy dependence of a specularly scattered He beam. Calculations of the He-CO-Cu potential and a best fit of the data show that the He-Cu(001) potential, recently predicted by Chizmeshya and Zaremba, must be shifted outwards by 0.64+/-0.2 Å. Since the position of this potential is based on the electron spillout predicted by the jellium model, its use in the case of Cu(001) must be re-examined.

Ellis, J.; Hermann, K.; Hofmann, F.; Toennies, J. P.

1995-07-01

217

Kaonic hydrogen atom and kaon-proton scattering length  

E-print Network

Kaonic hydrogen is studied with various realistic potentials in an accurate numerical approach based on Sturmian functions. The kaon-proton scattering length extracted from the 1s energy shift of the kaonic hydrogen by applying the Deser-Trueman formula is severely inconsistent with the one derived by directly solving the scattering Schoedinger equation. We pay special attention to the recent measurement of the energy shift and decay width of the 1s kaonic hydrogen state by the DEAR Collaboration. After taking into account the large discrepancy between the extracted and directly-evaluated scattering lengths, we found theoretical predictions of most chiral SU(3) based models for the kaonic hydrogen decay width are consistent with the DEAR data. We warn the SIDDHARTA collaboration that it may not be reasonable to extract kaon-nucleon scattering lengths, by using the Coulomb-interaction corrected Deser-Truemab formula, from the planned measurement of kaonic hydrogen.

Y. Yan

2009-05-29

218

Optical tuning of the scattering length of cold alkaline-earth-metal atoms  

SciTech Connect

It is possible to tune the scattering length for the collision of ultracold {sup 1}S{sub 0} ground-state alkaline-earth-metal atoms using an optical Feshbach resonance. This is achieved with a laser far detuned from an excited molecular level near the frequency of the atomic intercombination {sup 1}S{sub 0}-{sup 3}P{sub 1} transition. Simple resonant-scattering theory, illustrated by the example of {sup 40}Ca, allows an estimate of the magnitude of the effect. Unlike alkali metal species, large changes of the scattering length are possible while atom loss remains small, because of the very narrow linewidth of the molecular photoassociation transition. This raises prospects for control of atomic interactions for a system without magnetically tunable Feshbach resonance levels.

Ciurylo, R. [Atomic Physics Division, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8423, Gaithersburg, Maryland 20899-8423 (United States); Instytut Fizyki, Uniwersytet Mikolaja Kopernika, ul. Grudziadzka 5/7, 87-100 Torun (Poland); Tiesinga, E.; Julienne, P.S. [Atomic Physics Division, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8423, Gaithersburg, Maryland 20899-8423 (United States)

2005-03-01

219

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

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

220

Interatomic potentials from rainbow scattering of keV noble gas atoms under axial surface channeling  

NASA Astrophysics Data System (ADS)

For grazing scattering of keV Ne and Ar atoms from a Ag(1 1 1) and a Cu(1 1 1) surface under axial surface channeling conditions we observe well defined peaks in the angular distributions for scattered projectiles. These peaks can be attributed to "rainbow-scattering" and are closely related to the geometry of potential energy surfaces which can be approximated by the superposition of continuum potentials along strings of atoms in the surface plane. The dependence of rainbow angles on the scattering geometry provides stringent tests on the scattering potentials. From classical trajectory calculations based on universal (ZBL), adjusted Moliere (O'Connor and Biersack), and individual interatomic potentials we obtain corresponding rainbow angles for comparison with the experimental data. We find good overall agreement with the experiments for a description of trajectories based on adjusted Moliere and individual potentials, whereas the agreement is poorer for potentials with ZBL screening.

Schüller, A.; Wethekam, S.; Mertens, A.; Maass, K.; Winter, H.; Gärtner, K.

2005-04-01

221

Multimode entanglement of light and atomic ensembles via off-resonant coherent forward scattering  

SciTech Connect

Quantum theoretical treatment of coherent forward scattering of light in a polarized atomic ensemble with an arbitrary angular momentum is developed. We consider coherent forward scattering of a weak radiation field interacting with a realistic multilevel atomic transition. Based on the concept of an effective Hamiltonian and on the Heisenberg formalism, we discuss the coupled dynamics of the quantum fluctuations of the polarization Stokes components of propagating light and of the collective spin fluctuations of the scattering atoms. We show that in the process of coherent forward scattering, this dynamics can be described in terms of a polariton-type spin wave created in the atomic sample. Our work presents a general example of an entangling process in the system of collective quantum states of light and atomic angular momenta, previously considered only for the case of spin-(1/2) atoms. We use the developed general formalism to test the applicability of the spin-(1/2) approximation for modeling the quantum nondemolishing measurement of atoms with a higher angular momentum.

Kupriyanov, D.V.; Mishina, O.S.; Sokolov, I.M.; Julsgaard, B.; Polzik, E.S. [Department of Theoretical Physics, State Polytechnic University, 195251 St. Petersburg (Russian Federation); QUANTOP-Danish Quantum Optics Center, Niels Bohr Institute, 2100 Copenhagen (Denmark)

2005-03-01

222

Non-reactive scattering of excited exotic hydrogen atoms  

E-print Network

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.

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

2005-01-13

223

Monitoring nano-flow rate of water by atomic emission detection using helium radio-frequency plasma.  

PubMed

Recently, high-performance nano-scale flow pumping systems have been developed for micro and miniaturized analysis systems. A novel device capable of measuring and monitoring nanoliter scale flow rates has been required for the further development of the pumping system. In this study, an atomic emission detector using helium radio-frequency plasma (RFP-AED) was used for the measurement of the nanoliter scale flow rate of water by quantitatively detecting the emission from hydrogen in the water molecules. Monitoring nano-flow rates of water in the range up to 1.0 microl min(-1), and the change in the flow rate by the indication of the ratio of the emissions of H (656.3 nm) and He (667.8 nm) were successful. At present, the lowest flow rate that could be determined reproducibly was 4 nl min(-1) calculated as five times the standard deviation of the background noise. Additionally, similar evaluations for the deviation of each flow rate by using the RFP-AED and a flow-injection system were produced. PMID:12866864

Nakagama, Tatsuro; Maeda, Tsuneaki; Uchiyama, Katsumi; Hobo, Toshiyuki

2003-06-01

224

Inelastic and reactive scattering of hyperthermal atomic oxygen from amorphous carbon  

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

225

Compton scattering of an X-ray photon by an open-shell atom  

SciTech Connect

A nonrelativistic quantum theory for the nonresonant Compton scattering of an X-ray photon by a free many-electron atom with an open shell in the ground state has been constructed in the single-configuration Hartree-Fock approximation outside the impulse approximation widely used in the literature. The transition to an atom with closed shells reproduces the results obtained previously in [6, 7]. The results of a test calculation for atoms with open (Ti, Fe) and closed (Zn) 3d core shells are presented. The effects of the radial relaxation of one-electron states in the field of core vacancies have been taken into account. The results of the calculation agree well with the experimental results [15, 16]. It has been established that the results of the impulse approximation in the investigated X-ray photon energy ranges disagree with those of our theory not only quantitatively but also qualitatively. In particular, the impulse approximation near the elastic (Thomson and Rayleigh) scattering line leads to a gross overestimation of the contributions from the deep atomic shells involved in the inelastic photon scattering only virtually to the scattering probability. The presented theory is general in character and its applicability to a particular element of the Mendeleev table with an open core shell or to a many-electron atomic ion is limited only by the requirement that the nonrelativistic Hartree-Fock approximation be properly used in describing the scattering-state wave functions.

Hopersky, A. N., E-mail: hopersky_vm_1@rgups.ru; Nadolinsky, A. M. [Rostov State University of Transport Communication (Russian Federation)

2012-09-15

226

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

NASA Astrophysics Data System (ADS)

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.

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

227

He atom surface scattering: Surface dynamics of insulators, overlayers and crystal growth. Progress report, May 1, 1992--April 30, 1993  

SciTech Connect

Investigations have focused primarily on surface structure and dynamics of ionic insulators, epitaxial growth onto alkali halide crystals and multiphoton studies. The surface dynamics of RbCl has been re-examined. We have developed a simple force constant model which provides insight into the dynamics of KBr overlayers on NaCl(001), a system with a large lattice mismatch. The KBr/NaCl(001) results are compared to Na/Cu(001) and NaCl/Ge(001). We have completed epitaxial growth experiments for KBr onto RbCl(001). Slab dynamics calculations using a shell model for this system with very small lattice mismatch are being carried out in collaboration with Professor Manson of Clemson University and with Professor Schroeder in Regensburg, Germany. Extensive experiments on multiphoton scattering of helium atoms onto NaCl and, particularly, LiF have been carried out and the theory has been developed to a rather advanced stage by Professor Manson. This work will permit the extraction of more information from time-of-flight spectra. It is shown that the theoretical model provides a very good description of the multiphoton scattering from organic films. Work has started on self-assembling organic films on gold (alkyl thiols/Au(111)). We have begun to prepare and characterize the gold crystal; one of the group members has spent two weeks at the Oak Ridge National Laboratory learning the proper Au(111) preparation techniques. One of our students has carried out neutron scattering experiments on NiO, measuring both bulk phonon and magnon dispersion curves.

Not Available

1992-11-01

228

Scattering amplitude of ultracold atoms near the p-wave magnetic Feshbach resonance  

SciTech Connect

Most of the current theories on the p-wave superfluid in cold atomic gases are based on the effective-range theory for the two-body scattering, where the low-energy p-wave scattering amplitude f{sub 1}(k) is given by f{sub 1}(k)=-1/[ik+1/(Vk{sup 2})+1/R]. Here k is the incident momentum, V and R are the k-independent scattering volume and effective range, respectively. However, due to the long-range nature of the van der Waals interaction between two colliding ultracold atoms, the p-wave scattering amplitude of the two atoms is not described by the effective-range theory [J. Math. Phys. 4, 54 (1963); Phys. Rev. A 58, 4222 (1998)]. In this paper we provide an explicit calculation for the p-wave scattering of two ultracold atoms near the p-wave magnetic Feshbach resonance. We show that in this case the low-energy p-wave scattering amplitude f{sub 1}(k)=-1/[ik+1/(V{sup eff}k{sup 2})+1/(S{sup eff}k)+1/R{sup eff}] where V{sup eff}, S{sup eff}, and R{sup eff} are k-dependent parameters. Based on this result, we identify sufficient conditions for the effective-range theory to be a good approximation of the exact scattering amplitude. Using these conditions we show that the effective-range theory is a good approximation for the p-wave scattering in the ultracold gases of {sup 6}Li and {sup 40}K when the scattering volume is enhanced by the resonance.

Zhang Peng [Exploratory Research for Advanced Technology, Macroscopic Quantum Project, Japan Science and Technology, Tokyo 113-8656 (Japan); Department of Physics, Renmin University of China, Beijing 100872 (China); Naidon, Pascal [Exploratory Research for Advanced Technology, Macroscopic Quantum Project, Japan Science and Technology, Tokyo 113-8656 (Japan); Ueda, Masahito [Exploratory Research for Advanced Technology, Macroscopic Quantum Project, Japan Science and Technology, Tokyo 113-8656 (Japan); Department of Physics, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033 (Japan)

2010-12-15

229

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

E-print Network

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.

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

2005-05-09

230

Multiphoton effects in laser-assisted ionization of a helium atom by electron impact  

NASA Astrophysics Data System (ADS)

The dynamics of the electron impact multiphoton ionization of a He atom in the presence of an intense laser field ( n ? _e, 2 e) is studied theoretically for laser polarization (\\vert\\vert^l) and perpendicular (bot^r) to the incident momentum. The triple differential (TDCS) as well as the double differential (DDCS) cross sections are studied for the coplanar asymmetric geometry. The results are compared with the only available kinematically complete experiment at high incident energy (1000 eV). Significant laser modification (enhancement) is noted due to multiphoton effects in the present binary and recoil peak intensities of the TDCS for both the geometries, in qualitative agreement with the experiment. In the single photon case, the net effect of the laser field is to suppress the field free (FF) TDCS as well as the DDCS in the zeroth order approximation of the ejected electron wave function (CV), while in the first order (MCV), the cross sections are found to be enhanced. The CV multiphoton cross sections obey the famous Kroll Watson (KW) sum rule while the latter does not hold good in the corresponding MCV approximation.

Ghosh Deb, S.; Sinha, C.

2010-11-01

231

Asymmetric superradiant scattering and abnormal mode amplification induced by atomic density distortion.  

PubMed

The superradiant Rayleigh scattering using a pump laser incident along the short axis of a Bose-Einstein condensate with a density distortion is studied, where the distortion is formed by shocking the condensate utilizing the residual magnetic force after the switching-off of the trapping potential. We find that very small variation of the atomic density distribution would induce remarkable asymmetrically populated scattering modes by the matter-wave superradiance with long time pulse. The optical field in the diluter region of the atomic cloud is more greatly amplified, which is not an ordinary mode amplification with the previous cognition. Our numerical simulations with the density envelop distortion are consistent with the experimental results. This supplies a useful method to reflect the geometric symmetries of the atomic density profile by the superradiance scattering. PMID:23787626

Wang, Zhongkai; Niu, Linxiao; Zhang, Peng; Wen, Mingxuan; Fang, Zhen; Chen, Xuzong; Zhou, Xiaoji

2013-06-17

232

Exciton-Polariton scattering for defect detection in cold atom Optical Lattices  

E-print Network

We study the effect of defects in the Mott insulator phase of ultracold atoms in an optical lattice on the dynamics of resonant excitations. Defects, which can either be empty sites in a Mott insulator state with one atom per site or a singly occupied site for a filling factor two, change the dynamics of Frenkel excitons and cavity polaritons. While the vacancies in first case behave like hard sphere scatters for excitons, singly occupied sites in the latter case can lead to attractive or repulsive scattering potentials. We suggest cavity polaritons as observation tool of such defects, and show how the scattering can be controlled in changing the exciton-photon detuning. In the case of asymmetric optical lattice sites we present how the scattering effective potential can be detuned by the cavity photon polarization direction, with the possibility of a crossover from a repulsive into an attractive potential.

Hashem Zoubi; Helmut Ritsch

2007-10-29

233

Imaging Nonequilibrium Atomic Vibrations with X-ray Diffuse Scattering  

SciTech Connect

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.

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

234

Imaging nonequilibrium atomic vibrations with x-ray diffuse scattering.  

PubMed

We use picosecond x-ray diffuse scattering to image the nonequilibrium vibrations in 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 phonons. In InSb the increase in TA phonon population is less directional. PMID:21580798

Trigo, M; Chen, J; Vishwanath, V H; Sheu, Y M; Graber, T; Henning, R; Reis, D A

2010-12-15

235

Matter-Wave Scattering from Ultracold Atoms in an Optical Lattice  

SciTech Connect

We study matter-wave scattering from an ultracold, many-body atomic system trapped in an optical lattice. The angular cross section of the target lattice for a matter wave is determined and is demonstrated to have a strong dependence on the many-body phase, superfluid, or Mott insulator. Analytical approaches are employed deep in the superfluid and Mott-insulator regimes, while intermediate points in the phase transition are treated numerically. Matter-wave scattering offers a convenient method for nondestructively probing the quantum many-body phase transition of atoms in an optical lattice.

Sanders, Scott N. [Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Harvard University, Cambridge, Massachusetts 02138 (United States); Mintert, Florian [Albert-Ludwigs-Universitaet Freiburg, Hermann-Herder-Strasse 3, 79104 Freiburg (Germany); Heller, Eric J. [Harvard University, Cambridge, Massachusetts 02138 (United States)

2010-07-16

236

Impact of anisotropic atomic motions in proteins on powder-averaged incoherent neutron scattering intensities  

SciTech Connect

This paper addresses the question to which extent anisotropic atomic motions in proteins impact angular-averaged incoherent neutron scattering intensities, which are typically recorded for powder samples. For this purpose, the relevant correlation functions are represented as multipole series in which each term corresponds to a different degree of intrinsic motional anisotropy. The approach is illustrated by a simple analytical model and by a simulation-based example for lysozyme, considering in both cases the elastic incoherent structure factor. The second example shows that the motional anisotropy of the protein atoms is considerable and contributes significantly to the scattering intensity.

Kneller, Gerald R. [Centre de Biophys. Moleculaire, CNRS, Rue Charles Sadron, 45071 Orleans (France); Synchrotron Soleil, L'Orme de Merisiers, 91192 Gif-sur-Yvette (France); Universite d'Orleans, Chateau de la Source-Av. du Parc Floral, 45067 Orleans (France); Chevrot, Guillaume [Centre de Biophys. Moleculaire, CNRS, Rue Charles Sadron, 45071 Orleans (France); Synchrotron Soleil, L'Orme de Merisiers, 91192 Gif-sur-Yvette (France)

2012-12-14

237

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

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

238

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

E-print Network

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 independent-resonance approximation) leads to a coherent contribution, which determines the energy-averaged total cross sections of electron- and photon-induced reactions found from the optical theorem. On the other hand, the partial cross sections (e.g., electron recombination, combination photon scattering) are dominated by the stochastic contributions. Thus, the optical theorem provides a link between the stochastic and coherent contributions of the compound resonances.

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

2014-04-16

239

Multiphonon resonances in the Debye-Waller factor of atom surface scattering.  

PubMed

He atom surface scattering by dispersionless phonons is treated employing coupled channel (CC) calculations. At low energies, they predict a behavior opposite to perturbative Born or "exponentiated" Born approximation: strong resonant phonon stimulated elastic and inhibited inelastic scattering. The corresponding resonances have not been observed in earlier CC results since these have considered only the temperature dependence of the Debye-Waller factor at higher energy or omitted the attractive well. The resonances can be interpreted in terms of bound states in the attractive well with several excited vibrational quanta. They may be observable for, e.g., He scattering by a cold Xe/Cu surface. PMID:14995320

Brenig, W

2004-02-01

240

Positron scattering from hydrogen atom with screened Coulomb potentials  

SciTech Connect

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.

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

241

Differential cross sections for positron scattering from alkali atoms  

SciTech Connect

Close-coupling calculations for differential cross sections for elastic and inelastic positron-alkali scattering at incident energies between 1 eV and 100 eV will be presented. Particular emphasis is placed on excitation of the resonant (ns){sup 2}S {yields} (np){sup 2}P{sup o} and the optically forbidden (ns){sup 2}S {yields} (n{prime}d){sup 2}D transitions. The results will be compared with first order DWBA calculations to assess the importance of channel coupling in the theoretical description of these collision processes.

DeVries, K.M.; Bartschat, K.; McEachran, R.P. [and others

1993-05-01

242

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)

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.

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

2014-09-01

243

Photochemistry of adsorbed molecules. XV. Localized atomic scattering in the photolysis of HI/LiF(001) and HI/NaF(001)  

E-print Network

Photochemistry of adsorbed molecules. XV. Localized atomic scattering in the photolysis of HI has shown evidence of ``localized atomic scatter- ing'' LAS .5­8 For both adsorbates, the H-atom have compared the ``elastic'' H atom angular-scattering, Pel , of HI ad photolyzed at 248 nm for Li

Zeiri, Yehuda

244

Imbedded matrix Green's functions in atomic and molecular scattering theory  

NASA Astrophysics Data System (ADS)

This paper presents a general, simple, and unified treatment of Green's function approaches to the solution of the sets of coupled second order differential equations encountered in the theory of inelastic and reactive scattering. The standard scalar theory of Sturm-Liouville problems is extended to systems of equations without recourse to spectral resolutions of the Green's operator. A nonstandard approach to invariant imbedding is then developed to yield the most general kind of recursion relation for Wigner R matrices possible; the R-matrix propagation of Light and Walker and the variable interval-variable step algorithm of Parker, Schmalz, and Light are shown to be particularly simple examples of this more general scheme. Extensions and simplifications are offered. Also recurrence relations, stabilization of solutions, adiabatic and diabatic representations, and the use of nonorthogonal bases are all treated in a transparent manner.

Lill, J. V.; Schmalz, T. G.; Light, J. C.

1983-04-01

245

Imbedded matrix Green's functions in atomic and molecular scattering theory  

SciTech Connect

This paper presents a general, simple, and unified treatment of Green's function approaches to the solution of the sets of coupled second order differential equations encountered in the theory of inelastic and reactive scattering. The standard scalar theory of Sturm--Liouville problems is extended to systems of equations without recourse to spectral resolutions of the Green's operator. A nonstandard approach to invariant imbedding is then developed to yield the most general kind of recursion relation for Wigner R matrices possible; the R-matrix propagation of Light and Walker and the variable interval-variable step algorithm of Parker, Schmalz, and Light are shown to be particularly simple examples of this more general scheme. Extensions and simplifications are offered. Also recurrence relations, stabilization of solutions, adiabatic and diabatic representations, and the use of nonorthogonal bases are all treated in a transparent manner.

Lill, J.V.; Schmalz, T.G.; Light, J.C.

1983-04-01

246

THE SCATTERING OF A POTASSIUM ATOMIC BEAM BY A CROSSED BEAM OF BROMINE MOLECULES  

Microsoft Academic Search

A study was made of the scattering of crossed molecular beams for the ; determinntion of information on intermolecular forces and chemical reaction cross ; sections. A high resolution molecular beam apparatus was constructed to study ; the interaction of a monoenergetic beam of potassium atoms with a crossed beam of ; bromine molecules. The device incorporates resistance heated ovens,

1960-01-01

247

Atom-dimer scattering and stability of Bose and Fermi mixtures  

NASA Astrophysics Data System (ADS)

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.

Cui, Xiaoling

2014-10-01

248

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

E-print Network

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

Manson, Joseph R.

249

Energy transfer in O collisions with He isotopes and Helium escape from Mars  

NASA Astrophysics Data System (ADS)

Accurate data on energy-transfer collisions between hot oxygen atoms and the atmospheric helium gas on Mars, are reported. Anisotropic 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. Atmospheric layers mostly responsible for production of the He escape flux are identified. Our results demonstrate that strong angular anisotropy of scattering cross sections increases the collisional ejection of light atoms and is critical in the evaluation of He escape from Mars, Venus and Earth.

Bovino, S.; Zhang, P.; Gianturco, F. A.; Dalgarno, A.; Kharchenko, V.

2011-01-01

250

Impact Collision Ion Scattering Spectroscopy Applied to the Determination of Atomic Surface Structure  

NASA Astrophysics Data System (ADS)

The technique of impact collision ion scattering spectroscopy (ICISS) was used to investigate the atomic structure and low energy ion scattering dynamics from various surfaces. A new formalism for calculating the three-dimensional cross section for an ion to scatter sequentially and classically from two atoms has been developed. This method can be used to assist in the interpretation of ICISS data in terms of quantitative surface-structure models. Shadowing and blocking effects for energetic ions scattering from more than one atom are shown to be special cases of rainbow scattering. Even at keV energies and above, the cross section at the critical angle for scattering must be evaluated by quantum or semi-classical means to avoid the singularity in the classically calculated cross sections. In an ICISS investigation of the Ag(110) surface, a surface flux peak analysis demonstrated that the surface was not a complete monolayer, but rather contained 10-15% random vacancies. Subsurface Li^+ scattering results confirmed the oscillatory relaxation of the first two atomic layers of the surface, with Delta_{12} = -7.5% and Delta_{23} = 4.0%. Modeling of the neutralization mechanism for the He^+ scattering gave a best fit time-dependent Auger neutralization time constant of 0.84 +/- 0.08 fs. A neutralization study of 5 keV He^+ ions scattered from Au adatoms on the Si(111)- sqrt{3} x sqrt {3}-Au surface showed the He^+ ICISS data contained false shadowing features that were actually the result of local neutralization effects. Good agreement was obtained for a radially dependent ion-atom neutralization theory with rate R = Aexp (-ar) , where A and a are 15.5 fs^{ -1} and 1.94 A^{-1} , respectively. A detailed examination of the Si(111)- sqrt{3} x sqrt{3 })-Ag surface was also made. The 5 keV Li ^+ ICISS data gave evidence for Ag island formation at single monolayer coverages of silver, while the LEED, AES and LEIS data showed that at relatively high coverages of Ag (35 ML) small areas of sqrt {3} x sqrt{3} character were still present. Nine structurally different models of the sqrt{3} surface were tested and compared to the experimental ICISS results, with only the honeycomb-chained-trimer and missing-top-layer models found to be consistent with the Li^+ ICISS results.

Daley, Richard Stephen

1990-08-01

251

Spacelab 2 measurement of the solar coronal helium abundance  

NASA Astrophysics Data System (ADS)

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.

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

1995-07-01

252

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

NASA Astrophysics Data System (ADS)

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.

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

2004-05-01

253

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

NASA Astrophysics Data System (ADS)

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.

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

2014-01-01

254

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

SciTech Connect

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.

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

255

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

E-print Network

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.

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

2007-02-14

256

Beam guiding system for Rutherford scattering diagnostic at TEXTOR  

NASA Astrophysics Data System (ADS)

A beam guiding system for a neutral beam probe diagnostics is developed for implementation at the Textor experiment. Energetic helium atoms scattered on the plasma ions provided information about the local ion temperature. Time resolution is attained by sampling scattered particles measured individually by a time of flight analyzer.

Cosler, A.; Vanderven, H. W.; Barbian, E. P.; Bertschinger, G.; Vanblokland, A. A. E.; Kemmereit, E.

1988-11-01

257

Quantitative study of two- and three-dimensional strong localization of matter waves by atomic scatterers  

SciTech Connect

We study the strong localization of atomic matter waves in a disordered potential created by atoms pinned at the nodes of a lattice, for both three-dimensional (3D) and two-dimensional (2D) systems. The localization length of the matter wave, the density of localized states, and the occurrence of energy mobility edges (for the 3D system), are numerically investigated as a function of the effective scattering length between the atomic matter wave and the pinned atoms. Both positive and negative matter wave energies are explored. Interesting features of the density of states are discovered at negative energies, where maxima in the density of bound states for the system can be interpreted in terms of bound states of a matter wave atom with a few pinned atomic scatterers. In 3D we found evidence of up to three mobility edges, one at positive energies, and two at negative energies, the latter corresponding to transitions between extended and localized bound states. In 2D, no mobility edge is found, and a rapid exponential-like increase of the localization length is observed at high energy.

Antezza, Mauro; Castin, Yvan; Hutchinson, David A. W. [Laboratoire Kastler Brossel, Ecole Normale Superieure, CNRS and UPMC, 24 rue Lhomond, F-75231 Paris (France); Jack Dodd Centre for Quantum Technology, Department of Physics, University of Otago, Dunedin 9016 (New Zealand)

2010-10-15

258

Quantum fluid dynamics based current-density functional study of a helium atom in a strong time-dependent magnetic field  

Microsoft Academic Search

.  \\u000a Evolution of the helium atom in a strong time-dependent (TD) magnetic field\\u000a (B) of strength up to 1011 G is investigated through a quantum fluid\\u000a dynamics (QFD) based current-density functional theory (CDFT). The\\u000a TD-QFD-CDFT computations are performed through numerical solution of a\\u000a single generalized nonlinear Schrödinger equation employing vector\\u000a exchange-correlation potentials and scalar exchange-correlation density\\u000a functionals that depend both on

2011-01-01

259

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

SciTech Connect

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.

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

1981-01-01

260

Observation of suppression of light scattering induced by dipole-dipole interactions in a cold atomic ensemble  

E-print Network

We study the emergence of collective scattering in the presence of dipole-dipole interactions when we illuminate a cold cloud of rubidium atoms with a near-resonant and weak intensity laser. The size of the atomic sample is comparable to the wavelength of light. When we gradually increase the atom number from 1 to 450, we observe a broadening of the line, a small red shift and, consistently with these, a strong suppression of the scattered light with respect to the noninteracting atom case. Numerical simulations, which include the internal atomic level structure, agree with the data.

J. Pellegrino; R. Bourgain; S. Jennewein; Y. R. P. Sortais; S. D. Jenkins; J. Ruostekoski; A. Browaeys

2014-10-08

261

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

NASA Technical Reports Server (NTRS)

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.

Ross, H. Richard

1993-01-01

262

Helium Neon Laser  

NSDL National Science Digital Library

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.

Zollman, Dean

263

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

E-print Network

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

Heinzen, Daniel J.

264

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

SciTech Connect

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.

Joseph R. Manson

2005-06-30

265

Towards weighing individual atoms by high-angle scattering of electrons  

E-print Network

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.

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

2015-01-01

266

s-wave elastic scattering of antihydrogen off atomic alkali-metal targets  

SciTech Connect

We have investigated the s-wave elastic scattering of antihydrogen atoms off atomic alkali-metal targets (Li, Na, K, and Rb) at thermal energies (10{sup -16}-10{sup -4} a.u.) using an atomic orbital expansion technique. The elastic cross sections of these systems at thermal energies are found to be very high compared to H-H and H-He systems. The theoretical models employed in this study are so chosen to consider long-range forces dynamically in the calculation. The mechanism of cooling suggests that Li may be considered to be a good candidate as a buffer gas for enhanced cooling of antihydrogen atoms to ultracold temperature.

Sinha, Prabal K.; Ghosh, A. S. [Department of Physics, Bangabasi College, 19, Raj Kumar Chakravorty Sarani, Kolkata 700 009 (India); Department of Theoretical Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700 032 (India)

2006-03-15

267

Neutrino scattering on atomic electrons in searches for the neutrino magnetic moment.  

PubMed

The scattering of a neutrino on atomic electrons is considered in the situation where the energy transferred to the electrons is comparable to the characteristic atomic energies, as relevant to the current experimental search for the neutrino magnetic moment. The process is induced by the standard electroweak interaction as well as by the possible neutrino magnetic moment. Quantum-mechanical sum rules are derived for the inclusive cross section at a fixed energy deposited in the atomic system, and it is shown that the differential over the energy transfer cross section is given, modulo very small corrections, by the same expression as for free electrons, once all possible final states of the electronic system are taken into account. Thus, the atomic effects effectively cancel in the inclusive process. PMID:21231219

Voloshin, M B

2010-11-12

268

Measurements of molecule diffusion on surfaces using neutron and helium spin echo  

Microsoft Academic Search

We present a new approach to gain detailed surface-molecule potential information by combining neutron and helium atom scattering. First results are presented for a prototype study of benzene molecule diffusion on graphite surfaces. The measurements show good agreement and confirm the transferability of the results between the two methods. Future instrumental improvements are described that will improve the sensitivity of

Peter Fouquet; Holly Hedgeland; Andrew Jardine; Gil Alexandrowicz; William Allison; John Ellis

2006-01-01

269

TOPICAL REVIEW: Helium spin-echo spectroscopy: studying surface dynamics with ultra-high-energy resolution  

Microsoft Academic Search

Spin-echo measurements offer a major step forward in the technique of helium atom surface scattering. The experimental energy transfer resolution has been improved by several orders of magnitude, and has resulted in an expansion in the range of surface systems which can be studied. We describe the measurements within a double Fourier transform formalism, which by using appropriately selected 'tilted

G. Alexandrowicz; A. P. Jardine

2007-01-01

270

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

SciTech Connect

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.

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

271

Light-scattering detection of quantum phases of ultracold atoms in optical lattices  

SciTech Connect

Ultracold atoms loaded on optical lattices can provide unprecedented experimental systems for the quantum simulations and manipulations of many quantum phases. However, so far, how to detect these quantum phases effectively remains an outstanding challenge. Here, we show that the optical Bragg scattering of cold atoms loaded on optical lattices can be used to detect many quantum phases, which include not only the conventional superfluid and Mott insulating phases, but also other important phases, such as various kinds of charge density wave (CDW), valence bond solid (VBS), CDW supersolid (CDW-SS) and Valence bond supersolid (VB-SS).

Ye Jinwu [Department of Physics, Capital Normal University, 100048 Beijing (China); Department of Physics and Astronomy, Mississippi State University, P. O. Box 5167, Mississippi State, MS, 39762 (United States); Zhang, J. M.; Liu, W. M. [Institute of Physics, Chinese Academy of Sciences, 100080 Beijing (China); Zhang Keye; Li Yan; Zhang Weiping [Department of Physics, East China Normal University, 200062 Shanghai (China)

2011-05-15

272

Photon antibunching upon scattering by an atomic Bose-Einstein condensate  

SciTech Connect

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.

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

273

Scattering Theory of Kondo Mirages and Observation of Single Kondo Atom Phase Shift  

Microsoft Academic Search

We explain the origin of the Kondo mirage seen in recent quantum corral\\u000aScanning Tunneling Microscope (STM) experiments with a scattering theory of\\u000aelectrons on the surfaces of metals. Our theory combined with experimental data\\u000aprovides the first direct observation of a single Kondo atom phase shift. The\\u000aKondo mirage at the empty focus of an elliptical quantum corral is

Gregory A. Fiete; Jesse S. Hersch; Eric J. Heller; H. C. Manoharan; C. P. Lutz; D. M. Eigler

2001-01-01

274

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

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

275

Analytic description of elastic electron-atom scattering in an elliptically polarized laser field  

NASA Astrophysics Data System (ADS)

An analytic description of laser-assisted electron-atom scattering (LAES) in an elliptically polarized field is presented using time-dependent effective range (TDER) theory to treat both electron-laser and electron-atom interactions nonperturbatively. Closed-form formulas describing plateau features in LAES spectra are derived quantum mechanically in the low-frequency limit. These formulas provide an analytic explanation for key features of the LAES differential cross section. For the low-energy region of the LAES spectrum, our result generalizes the Kroll-Watson formula to the case of elliptic polarization. For the high-energy (rescattering) plateau in the LAES spectrum, our result generalizes prior results for a linearly polarized field valid for the high-energy end of the rescattering plateau [Flegel , J. Phys. BJPAPEH0953-407510.1088/0953-4075/42/24/241002 42, 241002 (2009)] and confirms the factorization of the LAES cross section into three factors: two field-free elastic electron-atom scattering cross sections (with laser-modified momenta) and a laser field-dependent factor (insensitive to the scattering potential) describing the laser-driven motion of the electron in the elliptically polarized field. We present also approximate analytic expressions for the exact TDER LAES amplitude that are valid over the entire rescattering plateau and reduce to the three-factor form in the plateau cutoff region. The theory is illustrated for the cases of e-H scattering in a CO2-laser field and e-F scattering in a midinfrared laser field of wavelength ?=3.5?m, for which the analytic results are shown to be in good agreement with exact numerical TDER results.

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

2013-01-01

276

Electron-indium atom scattering and analysis of electron and optical spectra  

NASA Astrophysics Data System (ADS)

Experimental study of indium atom using electron and optical spectroscopy is presented in this paper. Both experimental techniques including experimental setups are described. Differential and integrated cross sections on elastic and inelastic electron scattering by indium atom are measured using electron spectrometer. The measurements are performed at incident electron energies of E0 = 10, 20, 40, 60, 80 and 100 eV within the large scattering angles ranging from 10° to 150° in steps of 10°. The experimental results are presented and comparison with the values predicted by calculated optical potentials method is conducted, showing good agreement. The differential cross sections (DCSs) for electron-impact excitation of the resonant state 6s 2S1/2 of Indium atom are measured at small and large angles. The forward scattering function method has been used for normalizing the generalized oscillator strengths (GOS) to determine optical oscillator strength and obtaining the absolute DCS values. Optical spectrum of In I and In II lines has been acquired by a streak camera. The experimental results regarding indium lines obtained by time resolved laser induced breakdown spectroscopy (LIBS) could be useful for obtaining the important plasma parameters such as temperature, electron density as well as plasma-expansion velocity and plasma starting times.

Rabasovi?, Maja S.

2014-12-01

277

Dynamics of surface-aligned photochemistry (theory). II. Localized H-atom scattering in the HBr(ad)/LiF(OOl)+hv system  

E-print Network

Dynamics of surface-aligned photochemistry (theory). II. Localized H-atom scattering in the HBr sourcesof hot H-atoms ( 1) localized H-atoms producedby the photolysis of HBr moleculesadsorbedon the Li distributions of 1.1 and 2.6 eV H-atom scattering from a LiF(OO1) surfaceare compared for two different

Zeiri, Yehuda

278

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

SciTech Connect

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.

Egami, Takeshi [ORNL

2012-01-01

279

Investigation of sonic/subsonic air-blast atomization using Rayleigh- and Mie-scattering visualization techniques  

E-print Network

To examine the jet mixing in air-blast twin fluid atomization, the sonic and supersonic air jet developments have been exclusively visualized using the Rayleigh scattering principle and the development of liquid spray has been separately visualized...

Kim, Tae-Kyun

1996-01-01

280

Atomic scattering spectroscopy for determination of the polarity of semipolar AlN grown on ZnO  

SciTech Connect

Determination of the polarity of insulating semipolar AlN layers was achieved via atomic scattering spectroscopy. The back scattering of neutralized He atoms on AlN surfaces revealed the atomic alignment of the topmost layers of semipolar AlN and the ZnO substrate. Pole figures of the scattering intensity were used to readily determine the polarity of these wurtzite-type semipolar materials. In addition, we found that +R-plane AlN epitaxially grows on ?R-plane ZnO, indicating that the polarity flips at the semipolar AlN/ZnO interface. This polarity flipping is possibly explained by the appearance of ?c and m-faces on the ?R ZnO surfaces, which was also revealed by atomic scattering spectroscopy.

Kobayashi, Atsushi; Ohta, Jitsuo [Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505 (Japan)] [Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505 (Japan); Ueno, Kohei; Oshima, Masaharu [Department of Applied Chemistry, The University of Tokyo, Tokyo 113-8656 (Japan) [Department of Applied Chemistry, The University of Tokyo, Tokyo 113-8656 (Japan); Synchrotron Radiation Research Organization, The University of Tokyo, Tokyo 113-8656 (Japan); Fujioka, Hiroshi, E-mail: hfujioka@iis.u-tokyo.ac.jp [Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505 (Japan) [Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505 (Japan); CREST, Japan Science and Technology Agency (JST), Tokyo 102-0076 (Japan)

2013-11-04

281

Ejection of quasi-free electron pairs from the helium atom ground state by single photon absorption  

E-print Network

We investigate single photon double ionization (PDI) of helium at photon energies of 440 and 800 eV. We observe doubly charged ions with close to zero momentum corresponding to electrons emitted back-to-back with equal energy. These slow ions are the unique fingerprint of an elusive quasi-free PDI mechanism predicted by Amusia et al. nearly four decades years ago [J. Phys. B 8, 1248, (1975)] . It results from the non-dipole part of the electromagnetic interaction. Our experimental data are in excellent agreement with calculations performed using the convergent close coupling and time dependent close coupling methods.

Schöffler, M S; Waitz, M; Trinter, F; Jahnke, T; Lenz, U; Jones, M; Belkacem, A; Landers, A; Pindzola, M S; Cocke, C L; Colgan, J; Kheifets, A; Bray, I; Schmidt-Böcking, H; Dörner, R; Weber, Th

2012-01-01

282

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

PubMed Central

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

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

2003-01-01

283

Partial wave expansion of ion-atom elastic scattering in solids  

NASA Astrophysics Data System (ADS)

Elastic scattering cross sections of keV protons in solids ( Z = 3-82) are calculated using the partial wave expansion technique and the "muffin-tin" bound-atom potential. The differential cross sections for small scattering angles of less than 10° are smaller than those with the Ziegler-Biersack-Littmark potential at all energies and for all solids, although, for larger angles, the two cross sections agree with each other. The mean free paths of the protons in the solids, obtained from the total cross sections, decrease very slowly with decreasing energy. Furthermore, at low energies they approach half the nearest-neighbor distance, which is taken as the radius of the augmented plane wave sphere in the muffin-tin model of crystalline solids.

Ohya, K.; Kawata, J.; Mori, I.

1992-04-01

284

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

SciTech Connect

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.

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

285

Theory of negative-ion conversion of neutral atoms in grazing scattering from alkali halide surfaces  

NASA Astrophysics Data System (ADS)

The theoretical approach proposed by Borisov et al. [Phys. Rev. Lett. 77, 1893 (1996)] to treat negative-ion conversion of neutral atoms at ionic crystal surfaces is described in detail. Due to the localization of the valence-band electrons at the anionic sites of the crystal, the conversion process is viewed as a result of successive binary collisions between the projectile and the negatively charged sites at the surface. Parameter-free calculations of F- formation in grazing scattering from LiF(100) and KI(100) are performed using a model in which all sites of the crystal lattice but one, the active site, are represented by eventually polarizable point charges. Parallel velocity thresholds for negative-ion formation, relative efficiency of the negative-ion formation for LiF and KI crystals, and dependences of this efficiency on the scattering angle correspond well to the experimental results.

Borisov, A. G.; Sidis, V.

1997-10-01

286

The helium atom consists of a nucleus with charge +2e and no spin, and two electrons, each with charge e and spin h. In this problem, treat the nucleus as a fixed (immovable) source of  

E-print Network

The helium atom consists of a nucleus with charge +2e and no spin, and two electrons, each with charge ­e and spin ½h. In this problem, treat the nucleus as a fixed (immovable) source of electric field. Also, ignore the spin-orbit interaction and other fine structure and hyperfine effects. (a) Write

Ha, Taekjip

287

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

SciTech Connect

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.

Not Available

1992-01-01

288

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

SciTech Connect

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.

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

2013-02-15

289

Quantum scattering of distinguishable bosons using an ultracold-atom collider  

SciTech Connect

We describe an implementation of a magnetic collider for investigating cold collisions between ultracold atomic clouds in different spin states, and we use this to study scattering involving both even- and odd-order partial waves. Our method relies on the axial asymmetry of a double-well magnetic trap to selectively prepare the spin state in each cloud. We measure the energy dependence of s, p, and d partial-wave phase shifts in collisions up to 300 {mu}K between {sup 87}Rb atoms in the 5S{sub 1/2},F=1,m{sub F}=-1 and 5S{sub 1/2},F=2,m{sub F}=1 states.

Mellish, Angela S.; Wilson, Andrew C. [Department of Physics, University of Otago, Dunedin (New Zealand); Kjaergaard, Niels [Department of Physics, University of Otago, Dunedin (New Zealand); Niels Bohr Institute, University of Copenhagen, Copenhagen (Denmark); QUANTOP, Danish National Research Foundation Center for Quantum Optics, Copenhagen (Denmark); Julienne, Paul S. [National Institute of Standards and Technology, 100 Bureau Drive, Stop 8423, Gaithersburg, Maryland 20899-8423 (United States)

2007-02-15

290

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

PubMed

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. PMID:25106598

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

2014-08-01

291

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)

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.

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

2014-11-01

292

Hartree-Fock Values of Coupling Constants, Polarizabilities, Susceptibilities and Radii for the Neutral Atoms, Helium to Nobelium  

Microsoft Academic Search

Presented here are the values, obtained with Hartree-Fock functions, for ; the spin --orbit, magnetic-dipole, and electric-quadrupole coupling constants, ; electric-dipole polarizabilities, magnetic excited states of the neutral atoms ; from He to No. (auth);

S. Fraga; J. Karwowski; K. M. S. Saxena

1973-01-01

293

Photoabsorption profile and satellite features of the potassium 4s?4p transition perturbed by ground-state helium atoms  

NASA Astrophysics Data System (ADS)

Quantal calculations are performed to determine the absorption profile of the broadened potassium resonance line 4p?4s in its far wings provoked by helium perturbers. First, the X2?+, A2?, and B2?+ potentials, as well as the transition dipole moments, are carefully computed through ab initio methods, based on state-averaged complete active space self-consistent field multireference configuration interaction (SA-CASSCF-MRCI) calculations involving the Davidson and basis-set superposition error (BSSE) corrections. The data are then used to generate the KHe photoabsorption spectra and to examine their behavior with temperature. The theoretical profile is dominated by the free-free transitions and exhibits, in the vicinity of the wavelength position of 693 nm, a satellite peak in the blue wing attributed to the B?X transitions. The results are compared with previous theoretical and experimental investigations and, in general, good agreement is found.

Boutarfa, H.; Alioua, K.; Bouledroua, M.; Allouche, A.-R.; Aubert-Frécon, M.

2012-11-01

294

ASPIN: An all spin scattering code for atom molecule rovibrationally inelastic cross sections  

NASA Astrophysics Data System (ADS)

We present in this work a new computational code for the quantum calculation of integral cross sections for atom-molecule (linear) scattering processes. The atom is taken to be structureless while the molecule can be in its singlet, doublet, or triplet spin states and can be treated as either a rigid rotor or a rovibrational target. All the relevant state-to-state integral cross sections, and their sums over final states, can be calculated with the present code, for which we also describe in detail the various component routines. Program summaryProgram title: ASPIN Catalogue identifier: AEBO_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBO_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 99 596 No. of bytes in distributed program, including test data, etc.: 1 267 615 Distribution format: tar.gz Programming language: Fortran/MPI Computer: AMD OPTERON COMPUTING SYSTEMS, model TYAN GX28 (B2882) Operating system: SuSE LINUX Professional 9 RAM: 128 GB Classification: 2.6 External routines: LAPACK/BLAS Nature of problem: Scattering of a diatomic molecule in its ?1, ?2, or ?3 spin states with an atom in its S1 state. Partial and integral cross sections. Solution method: The coupled channel equations that describe the scattering process are solved through the propagation of the reactance K matrix employing a modification of the Variable Phase Method [1-3]. Restrictions: Depending on the vib-rotational base used the problem may or may not fit into available RAM memory because all the runtime relevant quantities are stored on RAM memory instead of on disk. Additional comments: Both serial and parallel implementations of the program are provided. The CPC Librarian was not able to successfully run the parallel version. Running time: For simple and converged calculations a usual running time is in the order of a few minutes in the computer mentioned above, being shorter for the singlet and longer for the triplet. References: [1] F. Calogero, Variable Phase Approach to Potential Scattering, New York, 1967. [2] A. Degasperis, Il Nuovo Cimento 34 (1964) 1667. [3] C. Zemach, Il Nuovo Cimento 33 (1964) 939.

López-Durán, D.; Bodo, E.; Gianturco, F. A.

2008-12-01

295

Ion-reversibility studies in amorphous solids using the two-atom scattering model. [Rutherford backscattering from disordered solids  

SciTech Connect

An analytical two-atom scattering model has been developed to treat the recent discovery of the enhancement near 180/sup 0/ of Rutherford backscattering yields from disordered solids. In contrast to conventional calculations of Rutherford backscattering that treat scattering from a single atom only (the backscattering atom), the present model includes the interaction of a second atom lying between the target surface and the backscattering plane. The projectile ion makes a glancing collision with this second atom both before and after it is backscattered. The model predicts an enhancement effect whose physical origin arises from the tolerance of path for those ions whose inward and outward trajectories lie in the vicinity of the critical impact parameter. Results using Moliere scattering show how the yield enhancement depends on ion energy, backscattering depth, exit angle, scattering potential, atomic numbers of the projectile and target, and target density. In the model the critical impact parameter and critical angle play important roles. It is shown that these quantities depend on a single dimensionless parameter and analytical expressions for them are given which are accurate to better than 1%.

Oen, O.S.

1981-06-01

296

The Kondo Effect in Atom-Surface Scattering: Dynamical 1/N Approach  

NASA Astrophysics Data System (ADS)

The Kondo effect may be observable in certain atom-surface scattering experiments, in particular those involving charge transfer to alkaline-earth atoms. By combining the Keldysh method with the NCA approximation to solve the dynamical Newns-Anderson model in the U arrow ? limit, Shao et al. found an anomalously strong surface-temperature dependence of the outgoing charge state fractions.(H. Shao, P. Nordlander and D. Langreth, Phys. Rev. Lett. 77), 948 (1996). The effect cannot be explained within a simple single-particle picture. To test this result, and to analyze a more realistic model with finite Coulomb interaction energy U and with excited atomic states, we employ the dynamical 1/N approach.(A. Onufriev and J. B. Marston, Phys. Rev. B 53), 13340 (1996). The approach is equivalent to systematically expanding the many-body wavefunction in the number of particle-hole pairs. We recover the qualitative features that Shao et al. found; however, local heating of the surface at the impact site may make experimental identification more difficult than previously suggested. We comment on the differences between the two theoretical approaches, and on issues facing experimentalists in efforts to find the Kondo effect.

Merino, Jaime; Marston, Brad

1998-03-01

297

Cross sections of discrete-level excitation of noble-gas atoms in Compton scattering  

NASA Astrophysics Data System (ADS)

The differential cross section in angle and the total cross sections for the excitation of atomic discrete levels in Compton scattering are investigated. Results are presented for the valent np-n,(n+1)d and np-(n+1),(n+2)p levels of the outer subshells of the noble-gas atoms Ne, Ar, Kr, and Xe, covering the range of the momentum transferred to the atom up to 8 a.u., which is sufficiently large for the calculation of the total Compton excitation cross sections. Calculations were performed in one-electron Hartree-Fock approximation and with many-electron effects taken into account in the random-phase approximation with exchange for monopole, dipole, quadrupole, and octupole transitions. Contributions from higher multipoles proved to be unimportant and many-electron effects were found to be quite noticeable in the differential cross section, while almost negligible in the total excitation cross sections. We conclude that the contributions of discrete excitations are comparable to those of the ionization process.

Amusia, M. Ya.; Chernysheva, L. V.; Felfli, Z.; Msezane, A. Z.

2002-06-01

298

Diffusion jumps of single atoms into vacancies in an iron monolayer studied by nuclear resonant scattering  

NASA Astrophysics Data System (ADS)

We study the structure of a model surface, i.e., an Fe monolayer on W(110) by nuclear resonant scattering of x rays. We conclude that at room temperature the structure is nearly perfect, whereas when increasing the temperature up to 770 K an increasing fraction of the Fe atoms feels the appearance of defects manifested by a beat structure due to an electric field gradient. The field gradient is caused by an asymmetry of the neighborhood of part of the atoms and attributable to an increasing fraction of vacancies in the monolayer. With increasing temperature the beat structure gets smeared due to the onset of dynamics in the surface, i.e., the motion of the defects and consequently of the atoms. From the temperature dependence of the amplitude of the beat we deduce the vacancy concentration, thus the vacancy formation energy [0.17(5) eV] and from the broadening with less accuracy we deduce the vacancy migration energy [0.16(6) eV] resulting in 0.33(11) eV for the activation energy of diffusion.

Vogl, G.; Partyka-Jankowska, E.; Zaj?c, M.; Chumakov, A. I.

2009-09-01

299

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

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

300

Manipulation of p-Wave Scattering of Cold Atoms in Low Dimensions Using the Magnetic Field Vector  

NASA Astrophysics Data System (ADS)

It is well known that the magnetic Feshbach resonances of cold atoms are sensitive to the magnitude of the external magnetic field. Much less attention has been paid to the direction of such a field. In this work we calculate the scattering properties of spin polarized fermionic atoms in reduced dimensions, near a p-wave Feshbach resonance. Because of the spatial anisotropy of the p-wave interaction, the scattering has a nontrivial dependence on both the magnitude and the direction of the magnetic field. In addition, we identify an inelastic scattering process which is impossible in the isotropic-interaction model; the rate of this process depends considerably on the direction of the magnetic field. Significantly, an Einstein-Podolsky-Rosen entangled pair of identical fermions may be produced during this inelastic collision. This work opens a new method to manipulate resonant cold atomic interactions.

Peng, Shi-Guo; Tan, Shina; Jiang, Kaijun

2014-06-01

301

Determination of Atomic Scattering Factors of B.C.C. Metals by the Critical-Voltage Method  

Microsoft Academic Search

The critical-voltage effect in electron diffraction has been applied to the 400 reflexion of b.c.c. metals, V, Cr, Fe and Nb, and the X-ray atomic scattering factors fx for the first-order reflexion 200 have been determined from the measured values of critical voltages Ec by many-beam calculations. The results are compared with X-ray experimental data and theoretical scattering factors for

Osamu Terasaki; Yuji Uchida; Denjiro Watanabe

1975-01-01

302

On the formation of (anionic) excited helium dimers in helium droplets.  

PubMed

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

Huber, Stefan E; Mauracher, Andreas

2014-08-21

303

Doubly differential spectra of scattered protons in ionization of atomic hydrogen  

SciTech Connect

We have measured and calculated doubly differential cross sections for ionization of atomic hydrogen using 75-keV proton impact for fixed projectile energy losses as a function of scattering angle. This collision system represents a pure three-body system and thus offers an accurate test of the theoretical description of the few-body dynamics without any complications presented by electron correlation in many-electron targets. Comparison between experiment and several theoretical models reveals that the projectile-target nucleus interaction is best described by the operator of a second-order term of the transition amplitude. Higher-order contributions in the projectile-electron interaction, on the other hand, are more appropriately accounted for in the final-state wave function.

Schulz, M.; Laforge, A. C.; Egodapitiya, K. N.; Alexander, J. S. [Department of Physics and LAMOR, Missouri University of Science and Technology, Rolla, Missouri 65409 (United States); Hasan, A. [Department of Physics, UAE University, Post Office Box 17551, Alain, Abu Dhabi (United Arab Emirates); Ciappina, M. F. [Institute of High Performance Computing, 1 Fusionopolis Way, 16-16, Connexis 138632 (Singapore); Roy, A. C. [School of Mathematical Sciences, Ramakrishna Mission, Vivekananda University, Belur Math 711202 (India); Dey, R. [Max Planck Institut fuer Plasmaphysik, Boltzmannstrasse 2, D-85748 Garching (Germany); Samolov, A.; Godunov, A. L. [Department of Physics, Old Dominion University, Norfolk, Virginia 23529 (United States)

2010-05-15

304

Nonadiabatic semiclassical scattering: Atom--diatom collisions in self-consistent matrix propagator formalism  

SciTech Connect

The self-consistent matrix propagator method of Laing and Freed is extended to treat semiclassical nonadiabatic scattering in the collinear atom--diatom system. Applications are made to a model system in which diabatic surfaces are parallel, so the nonadiabatic transitions are not well localized in space, thereby introducing difficulties in some previous nonadiabatic semiclassical methods. In the self-consistent matrix propagator method nonadiabatic transitions occur at the boundaries of Magnus regions, and the relative phases, associated with trajectories undergoing transitions at different boundaries, must accurately be determined. This necessitates the determination of the absolute phases of the uniformized classical S matrix, a phase which is unnecessary in single potential surface semiclassical scattering. Semiclassical calculations are compared with full close coupled quantum calculations of Schmalz. The agreement is very good even at relatively low energies. The largest errors enter, as anticipated, for highly classically forbidden transitions whose overall probabilities are, however, rather small. The self-consistent matrix propagator method becomes simpler to apply and more accurate as the total energy increases, i.e., as the fully quantum calculations become prohibitively large. The method has the physical appeal that the self-consistent trajectories follow essentially adiabatic surfaces in strongly interacting regions and diabatic surfaces in weakly interacting regions, with a self-consistent interpolation between these regions.

Herman, M.F.; Freed, K.F.

1983-05-15

305

Nonadiabatic semiclassical scattering: Atom-diatom collisions in self-consistent matrix propagator formalism  

NASA Astrophysics Data System (ADS)

The self-consistent matrix propagator method of Laing and Freed is extended to treat semiclassical nonadiabatic scattering in the collinear atom-diatom system. Applications are made to a model system in which diabatic surfaces are parallel, so the nonadiabatic transitions are not well localized in space, thereby introducing difficulties in some previous nonadiabatic semiclassical methods. In the self-consistent matrix propagator method nonadiabatic transitions occur at the boundaries of Magnus regions, and the relative phases, associated with trajectories undergoing transitions at different boundaries, must accurately be determined. This necessitates the determination of the absolute phases of the uniformized classical S matrix, a phase which is unnecessary in single potential surface semiclassical scattering. Semiclassical calculations are compared with full close coupled quantum calculations of Schmalz. The agreement is very good even at relatively low energies. The largest errors enter, as anticipated, for highly classically forbidden transitions whose overall probabilities are, however, rather small. The self-consistent matrix propagator method becomes simpler to apply and more accurate as the total energy increases, i.e., as the fully quantum calculations become prohibitively large. The method has the physical appeal that the self-consistent trajectories follow essentially adiabatic surfaces in strongly interacting regions and diabatic surfaces in weakly interacting regions, with a self-consistent interpolation between these regions.

Herman, Michael F.; Freed, Karl F.

1983-05-01

306

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

SciTech Connect

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.

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

307

Low photon scattering rates and large optical depths of atoms in donut modes of hollow core optical fibers  

NASA Astrophysics Data System (ADS)

We have guided cold rubidium atoms in blue-detuned hollow optical modes of a hollow fiber. These higher order modes allow large optical depth, low scattering rates, and efficient use of guide laser power. Atoms are transported through a 3-cm-long hollow fiber with a 100 micron diameter using the first three optical modes of the fiber. We compare guiding properties in the red-detuned, fundamental HE11 mode with the blue-detuned TE01 (first order) and HE12 (second order) modes. Using guide laser powers below 50 mW and detunings below 1.5 nm, we have directly measured recoil scattering rates in the three different guides and found that atoms in the HE12 mode typically have a 10x lower recoil scattering rate compared to the red-detuned HE11 mode for equal guide peak intensity. Furthermore, we have observed optical depths of ˜20 for the blue-detuned guides with recoil scattering rates below 10 Hz. We will discuss our ongoing experiments using the atoms in these guides. This work supported by the Office of Naval Research and the Defense Advanced Research Projects Agency.

Pechkis, Joseph A.; Fatemi, Fredrik K.

2012-06-01

308

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

Microsoft Academic Search

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

Omidvar

1959-01-01

309

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

E-print Network

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.

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

2014-05-15

310

ELSEPA—Dirac partial-wave calculation of elastic scattering of electrons and positrons by atoms, positive ions and molecules  

NASA Astrophysics Data System (ADS)

The FORTRAN 77 code system ELSEPA for the calculation of elastic scattering of electrons and positrons by atoms, positive ions and molecules is presented. These codes perform relativistic (Dirac) partial-wave calculations for scattering by a local central interaction potential V(r). For atoms and ions, the static-field approximation is adopted, with the potential set equal to the electrostatic interaction energy between the projectile and the target, plus an approximate local exchange interaction when the projectile is an electron. For projectiles with kinetic energies up to 10 keV, the potential may optionally include a semiempirical correlation-polarization potential to describe the effect of the target charge polarizability. Also, for projectiles with energies less than 1 MeV, an imaginary absorptive potential can be introduced to account for the depletion of the projectile wave function caused by open inelastic channels. Molecular cross sections are calculated by means of a single-scattering independent-atom approximation in which the electron density of a bound atom is approximated by that of the free neutral atom. Elastic scattering by individual atoms in solids is described by means of a muffin-tin model potential. Partial-wave calculations are feasible on modest personal computers for energies up to about 5 MeV. The ELSEPA code also implements approximate factorization methods that allow the fast calculation of elastic cross sections for much higher energies. The interaction model adopted in the calculations is defined by the user by combining the different options offered by the code. The nuclear charge distribution can be selected among four analytical models (point nucleus, uniformly charged sphere, Fermi's distribution and Helm's uniform-uniform distribution). The atomic electron density is handled in numerical form. The distribution package includes data files with electronic densities of neutral atoms of the elements hydrogen to lawrencium ( Z=1-103) obtained from multiconfiguration Dirac-Fock self-consistent calculations. For comparison purposes, three simple analytical approximations to the electron density of neutral atoms (corresponding to the Thomas-Fermi, the Thomas-Fermi-Dirac and the Dirac-Hartree-Fock-Slater models) are also included. For calculations of elastic scattering by ions, the electron density should be provided by the user. The exchange potential for electron scattering can be selected among three different analytical approximations (Thomas-Fermi, Furness-McCarthy, Riley-Truhlar). The offered options for the correlation-polarization potential are based on the empirical Buckingham potential. The imaginary absorption potential is calculated from the local-density approximation proposed by Salvat [Phys. Rev. A 68 (2003) 012708]. Program summaryTitle of program:ELSEPA Catalogue identifier: ADUS Program summary URL:http://cpc.cs.qub.ac.uk/cpc/summaries/ADUS Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland License provisions: none Computer for which the program is designed and others in which it is operable: Any computer with a FORTRAN 77 compiler Operating systems under which the program has been tested: Windows XP, Windows 2000, Debian GNU/Linux 3.0r0 (sarge) Compilers:Compaq Visual Fortran v6.5 (Windows); GNU FORTRAN, g77 (Windows and Linux) Programming language used: FORTRAN 77 No. of bits in a word: 32 Memory required to execute with typical data: 0.6 Mb No. of lines in distributed program, including test data, etc.:135 489 No. of bytes in distributed program, including test data, etc.: 1 280 006 Distribution format: tar.gz Keywords: Dirac partial-wave analysis, electron elastic scattering, positron elastic scattering, differential cross sections, momentum transfer cross sections, transport cross sections, scattering amplitudes, spin polarization, scattering by complex potentials, high-energy atomic screening functions Nature of the physical problem: The code calculates differential cross sections, total cross sections and transport cross sections for

Salvat, Francesc; Jablonski, Aleksander; Powell, Cedric J.

2005-01-01

311

Paramagnetic Attraction of Impurity-Helium Solids  

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

312

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

SciTech Connect

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.

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

313

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

NASA Astrophysics Data System (ADS)

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 ?1s-2p) Rayleigh cross-section by an order of magnitude, at (atomic system-specific) high enough plasma electron densities under present consideration. The Z-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.

Basu, Joyee; Ray, Debasis

2014-03-01

314

Quantum simulations of helium clusters with ionic and open shell dopants  

E-print Network

+He) and halogen atoms and ions interacting with helium, in particular iodine. Spin-orbit coupling betweenQuantum simulations of helium clusters with ionic and open shell dopants Marius Lewerenz ·Helium-helium interaction is of weak van der Waals type, closed shell atoms of very low polarisability

Boyer, Edmond

315

Interaction-induced dipoles of hydrogen molecules colliding with helium atoms: a new ab initio dipole surface for high-temperature applications.  

PubMed

We report new ab initio results for the interaction-induced dipole moments ?? of hydrogen molecules colliding with helium atoms. These results are needed in order to calculate collision-induced absorption spectra at high temperatures; applications include modeling the radiative profiles of very cool white dwarf stars, with temperatures from 3500 K to 9000 K. We have evaluated the dipoles based on finite-field calculations, with coupled cluster methods in MOLPRO 2006 and aug-cc-pV5Z (spdfg) basis sets for both the H and He centers. We have obtained values of ?? for eight H(2) bond lengths ranging from 0.942 a.u. to 2.801 a.u., for 15 intermolecular separations R ranging from 2.0 a.u. to 10.0 a.u., and for 19 different relative orientations. In general, our values agree well with earlier ab initio results, for the geometrical configurations that are treated in common, but we have determined more points on the collision-induced dipole surface by an order of magnitude. These results make it possible to calculate transition probabilities for molecules in excited vibrational states, overtones, and rotational transitions with ?J > 4. We have cast our results in the symmetry-adapted form needed for absorption line shape calculations, by expressing ?? as a series in the spherical harmonics of the orientation angles of the intermolecular vector and of a unit vector along the H(2) bond axis. The expansion coefficients depend on the H(2) bond length and the intermolecular distance R. For large separations R, we show that the ab initio values of the leading coefficients converge to the predictions from perturbation theory, including both classical multipole polarization and dispersion effects. PMID:22299884

Li, Xiaoping; Mandal, Anirban; Miliordos, Evangelos; Hunt, Katharine L C

2012-01-28

316

VELOCITY DEPENDENCE OF THE DIFFERENTIAL CROSS SECTIONS, AND POTENTIAL WELL DEPTHS FROM ATOMIC BEAM SCATTERING MEASUREMENTS: K-Hg AND Cs-Hg SYSTEMS  

Microsoft Academic Search

Measurements of the velocity dependence of the angular intensity ; distribution of potassium and cesium atomic beams scattered by a crossed atomic ; beam of mercury are presented. The alkali atomic beam was velocity-selected, ; having a triangular velocity distribution with a halfintensity width of 0.047 of ; the peak velocity. The alkali velocity could be varied over the range

F. A. Morse; R. B. Bernstein

1962-01-01

317

Atomic vibrations in iron nanoclusters : nuclear resonant inelastic x-ray scattering and molecular dynamics simulations.  

SciTech Connect

The lattice vibrational dynamics of supported, self-assembled, isolated {sup 57}Fe nanoclusters was studied by nuclear resonant inelastic x-ray scattering and molecular dynamics calculations. The morphological and structural properties and the chemical state of the experimental nanoclusters were investigated by atomic force microscopy, high resolution transmission electron microscopy, and x-ray photoelectron spectroscopy. The measured and calculated vibrational densities of states (VDOSs) reveal an enhancement of the low- and high-energy phonon modes and provide experimental and theoretical proof of non-Debye-like behavior in the low-energy region of the VDOS. Experimentally, this effect was found to depend on the nature of the surface shell (oxide or carbide) of the core/shell nanoclusters. According to the calculations for supported isolated pure Fe nanoclusters, the non-Debye-like behavior appears not only in the surface shell but also in the bcc-Fe core of the nanocluster due to the hybridization of surface and bulk modes.

Cuenya, B. R.; Naitabdi, A.; Croy, J.; Sturhahn, W.; Zhao, J. Y.; Alp, E. E.; Meyer, R.; Sudfeld, D.; Schuster, E.; Keune, W.; X-Ray Science Division; Univ. of Central Florida; Univ. Duisburg-Essen

2007-11-01

318

Diffraction of helium from Cu(110), (113), (115) and (117); Interaction potential and surface crystallography  

NASA Astrophysics Data System (ADS)

We present data obtained by helium scattering on different faces of copper: (110), (113), (115) and (117). It is shown that they are well fitted by model potentials, a corrugated Morse (CMP) for all faces and a modified form (MCMP) for the low corrugated (110) and (113) faces. Then, the isopotentials Z E( R) , representing the effective corrugation for an incident helium atom of energy E are compared to those resulting from a method of superposition of atomic densities calculated in two different ways. So, starting from the tables of atomic wave functions given by Clementi and Roetti, a good agreement is obtained with experiment, provided that the proportionality constant between the potential and the electronic density is taken to be ? = 600 eV03.

Gorse, D.; Salanon, B.; Fabre, F.; Kara, A.; Perreau, J.; Armand, G.; Lapujoulade, J.

1984-11-01

319

Multiple scattering of matter waves: An analytic model of the refractive index for atomic and molecular gases  

SciTech Connect

We present an analytic model of the refractive index for matter waves propagating through atomic or molecular gases. The model, which combines the Wentzel-Kramers-Brillouin (WKB) treatment of the long-range attraction with the Fraunhofer model treatment of the short-range repulsion, furnishes a refractive index in compelling agreement with recent experiments of Jacquey et al. [Phys. Rev. Lett. 98, 240405 (2007)] on Li atom matter waves passing through dilute noble gases. We show that the diffractive contribution, which arises from scattering by a two-dimensional 'hard core' of the potential, is essential for obtaining a correct imaginary part of the refractive index.

Lemeshko, Mikhail; Friedrich, Bretislav [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin (Germany)

2010-08-15

320

Diffusion by atomic place exchange in ultrathin iron films on Ag(100): an ion scattering spectroscopy study  

NASA Astrophysics Data System (ADS)

The surface composition of ultrathin (0-10 ML) iron films deposited on a well defined Ag(100) substrate at 140 K has been investigated by ion scattering spectroscopy. The data unambiguously show the occurrence of intermixing. The concentration of Ag at the surface decreases rather rapidly with the film thickness but it is still relevant (˜ 10%) even in the case of the thickest layer. The data are interpreted in terms of an atomic place exchange between silver and incident iron atoms at the surface of the growing film.

Canepa, M.; Magnano, E.; Campora, Andrea; Cantini, P.; Salvietti, M.; Mattera, L.

1996-05-01

321

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

PubMed

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. PMID:25028010

Warehime, Mick; Alexander, Millard H

2014-07-14

322

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

NASA Astrophysics Data System (ADS)

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.

Warehime, Mick; Alexander, Millard H.

2014-07-01

323

Ion temperature measurements in tokamak plasmas by Rutherford scattering  

NASA Astrophysics Data System (ADS)

A Rutherford scattering diagnostic has been applied at the TEXTOR tokamak to obtain spatially and temporally resolved information on the temperature of the bulk ions in the plasma. In the experimental setup, a helium atomic beam (30-keV, 12-mA equivalent current) passes vertically through the plasma core. A small part of the injected atoms is scattered elastically by the thermally moving plasma ions. The ion temperature in the scattering volume can be determined from the broadening of the energy spectrum of the scattered particles. Energy analysis of the scattered atoms is performed by a mass-selective time-of-flight analyzer detecting the particles at an observation angle which is selectable between 3° and 8°. Coincidence techniques have been successfully applied in this detector for rejection of background events triggered by detections of neutrons and gamma radiation. Ion temperature profiles were measured on a shot-to-shot basis by shifting the cross section of the diagnostic beam and the observational volume of the analyzer through the plasma. The ion temperatures measured in ohmic deuterium plasmas were found to be in reasonable agreement with those obtained from passive neutral particle analysis. Up to now, ion temperatures have been measured throughout the complete discharge with an accuracy of 8% and a time and space resolution of 100 ms and 0.10 m at a scattering angle of 7°. Deuteron density profiles could be deduced from the scattering yield measured at different radial positions in the plasma. The ratio of the isotopes, hydrogen and deuterium, was determined from their separate contributions to the spectrum of helium particles scattered on hydrogen and deuterium. Although theoretical predictions showed that the majority of the probing helium atoms loses one of its electrons during the elastic scattering process on multiply charged carbon and oxygen ions, contributions from impurities to the observed experimental spectrum are shown to appear dominant for impure plasmas.

van Blokland, A. A. E.; Barbian, E. P.; Donné, A. J. H.; van der Grift, A. F.; Grimbergen, T. W. M.; Oyevaar, Th.; Schüller, F. C.; Tammen, H. F.; van der Ven, H. W.; Vijverberg, T. F.; de Winter, F. D. A.; Bertschinger, G.; Cosler, A.; Korten, M.

1992-06-01

324

Rutherford backscattering oscillation in scanning helium-ion microscopy  

SciTech Connect

Scanning helium-ion microscopy (SHIM) yields high-resolution imaging and is capable of surface elemental analysis at the nanometer scale. Here we examine recently discovered SHIM backscattered intensity oscillations versus the target atomic number. These oscillations are contrary to the expected monotonic increase of the backscattered helium-ion (He{sup +}) rate with the atomic number of elemental samples. We explore the ion-sample interaction via numerical simulations for a variety of scattering geometries and confirm the presence of oscillations. The oscillations are attributed to the atomic rather than the nuclear structure of the target. To that end, we study the link (near anticorrelation) between backscatter rate and He{sup +} beam stopping power, both versus the target atomic number. This leads us to ascribe the origin of the backscatter oscillation to the ''Z{sub 2}-oscillations'' of the stopping power in ion-beam physics, with the latter being rooted in the valence electron configuration of elemental targets.

Kostinski, Sarah; Yao, Nan [Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544 (United States)

2011-03-15

325

A low energy bound atomic electron Compton scattering model for Geant4  

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

326

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

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

Berry, R. Stephen

327

Screening Effects on Nonrelativistic Bremsstrahlung in the Scattering of Electrons by Neutral Atoms  

NASA Technical Reports Server (NTRS)

Atomic screening effects on nonrelativistic electron-atom bremsstrahlung radiation are investigated using a simple analytic solution of the Thomas-Fermi model for many-electron atoms. The Born approximation is assumed for the initial and final states of the projectile electron. The results show that the screening effect is important in the soft radiation region and is decreasing with increasing radiation. These results help provide correct information about the behavior of bound electrons in the target atom in bremsstrahlung processes.

Jung, Young-Dae; Lee, Kun-Sang

1995-01-01

328

Spin-orbit corrections of order m{alpha}{sup 6} to the fine structure of the (37,35) state in the {sup 4}He p antiprotonic helium atom  

SciTech Connect

Precise numerical calculation of radiofrequency intervals between hyperfine sublevels of the (37,35) state of the antiprotonic helium-4 atom is presented. Theoretical consideration includes the QED corrections of order m{alpha}{sup 6} to the electron spin-orbit interaction. Only the leading order contribution in the electron-to-antiproton and electron-to-{alpha} particle mass ratios is considered, so the {alpha} particle and antiproton are treated nonrelativistically. The effective Hamiltonian is derived using the formalism of the nonrelativistic quantum electrodynamics.

Korobov, Vladimir I.; Zhong Zhenxiang [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Science, 430071 Wuhan (China)

2009-10-15

329

Differential cross sections for scattering of 0.5-, 1.5-, and 5.0 keV oxygen atoms by He, N2, and O2  

NASA Technical Reports Server (NTRS)

This paper reports measurements of absolute scattering cross sections, differential in angle, for collisions of ground-state oxygen atoms with He, N2, and O2. Data are presented for scattering of 0.5-, 1.5-, and 5.0-keV oxygen-atom projectiles in the range of laboratory frame angles between 0.06 and 5 deg. These measurements provide information relevant to calculations of the aeronomic consequences of O(+) precipitation in the earth's upper atmosphere.

Schafer, D. A.; Newman, J. H.; Smith, K. A.; Stebbings, R. F.

1987-01-01

330

Theoretical investigation of rotationally inelastic collisions of the methyl radical with helium.  

PubMed

Rotationally inelastic collisions of the CH(3) molecule in its ground X(2)A(2)'' electronic state have been investigated. We have determined a potential energy surface (PES) for the interaction of rigid CH(3), frozen at its equilibrium geometry, with a helium atom, using a coupled-cluster method that includes all single and double excitations, as well as perturbative contributions of connected triple excitations [RCCSD(T)]. The anisotropy of the PES is dominated by repulsion of the helium by the hydrogen atoms. The dissociation energy D(e) was computed to equal 27.0 cm(-1). At the global minimum, the helium atom lies in the CH(3) plane between two C-H bonds at an atom-molecule separation R = 6.52 bohr. Cross sections for collision-induced rotational transitions have been determined through quantum scattering calculations for both nuclear spin modifications. Rotationally inelastic collisions can cause a change in the rotational angular momentum n and its body-frame projection k. Because of the anisotropy of the PES due to the hydrogen atoms, there is a strong propensity for ?k = ±3 transitions. Thermal rate constants for state-specific total collisional removal have also been determined. PMID:21842932

Dagdigian, Paul J; Alexander, Millard H

2011-08-14

331

Impurity condensation in liquid and solid helium  

NASA Astrophysics Data System (ADS)

It is shown from an analysis of x-ray structural and IR spectroscopic studies that when impurity particles are introduced into liquid or solid helium, the clusters formed in the cold part of a gas jet have a pronounced spatial separation of impurities with different volatility. In particular, in the condensation of partially dissociated diatomic molecules the atoms are highly concentrated near and on the surface of the clusters. Segregation of this kind is preserved in the condensate in liquid helium, which consists of clusters stuck together into a porous structure; in solid helium clusters are isolated. The presence of high concentrations of atoms in the surface layer at the boundary with condensed helium explains the specifics of condensate behavior observed by methods of optical spectroscopy, ESR, and thermometry. An experimental strategy is developed for detecting the formation of an impurity-helium solid.

Gordon, E. B.

2004-10-01

332

Incoherent scattering of 59.54 keV gamma rays by selected elements in the atomic region 29<=Z<=74  

Microsoft Academic Search

Incoherent scattering cross-sections for 11 moderate to high atomic number elements have been experimentally determined using 59.54 keV gamma rays emitted by the radionuclide 241Am. Measurements were performed using a standard back-scattering geometry set up to obtain scattering angles of 145 deg, 154 deg and 165 deg. Resulting photon momentum transfers were in the range 4.58<=x<=4.76 Å-1. High purity (better

I. S. Elyaseery; A. Shukri; C. S. Chong; A. A. Tajuddin; D. A. Bradley

1999-01-01

333

Angular distributions of 5eV atomic oxygen scattered from solid surfaces on the LDEF satellite  

NASA Technical Reports Server (NTRS)

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.

Gregory, John C.; Peters, Palmer N.

1992-01-01

334

Atomically detailed lipid bilayer models for the interpretation of small angle neutron and X-ray scattering data.  

PubMed

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

Fogarty, Joseph C; Arjunwadkar, Mihir; Pandit, Sagar A; Pan, Jianjun

2015-02-01

335

Energy-related atomic and molecular structure and scattering studies. Annual progress report, July 1, 1980-June 30, 1981  

SciTech Connect

The basic goals of this program concern the experimental determination of properties of atoms and molecules and molecular clusters that are important in a wide range of energy-related processes, in particular, measurements of polarizabilities of highly polar molecules and their polymers, and of a number of important atomic elements distributed through the periodic table, as well as of the scattering of low-energy electrons by these same systems. The most significant scientific accomplishment of the program during the past year has been the completion of measurements of the dc electric dipole polarizabilities of a number of alkali halide dimers ((KCl)/sub 2/, (RbCl)/sub 2/, (CsCl)/sub 2/, (KF)/sub 2/, and (CsF)/sub 2/). An experiment was completed to measure the total cross sections for the scattering of low-energy electrons by atomic lithium, a very significant experimental test of a relatively simple, many-body system, which is amenable to elaborate computational determination.

Bederson, B.

1981-02-01

336

Thermal stability of helium-vacancy clusters in iron  

NASA Astrophysics Data System (ADS)

Molecular dynamics calculations were performed to evaluate the thermal stability of helium-vacancy clusters (He nV m) in Fe using the Ackland Finnis-Sinclair potential, the Wilson-Johnson potential and the Ziegler-Biersack-Littmark-Beck potential for describing the interactions of Fe-Fe, Fe-He and He-He, respectively. Both the calculated numbers of helium atoms, n, and vacancies, m, in clusters ranged from 0 to 20. The binding energies of an interstitial helium atom, an isolated vacancy and a self-interstitial iron atom to a helium-vacancy cluster were obtained from the calculated formation energies of clusters. All the binding energies do not depend much on cluster size, but they primarily depend on the helium-to-vacancy ratio ( n/ m) of clusters. The binding energy of a vacancy to a helium-vacancy cluster increases with the ratio, showing that helium increases cluster lifetime by dramatically reducing thermal vacancy emission. On the other hand, both the binding energies of a helium atom and an iron atom to a helium-vacancy cluster decrease with increasing the ratio, indicating that thermal emission of self-interstitial atoms (SIAs) (i.e. Frenkel-pair production), as well as thermal helium emission, may take place from the cluster of higher helium-to-vacancy ratios. The thermal stability of clusters is decided by the competitive processes among thermal emission of vacancies, SIAs and helium, depending on the helium-to-vacancy ratio of clusters. The calculated thermal stability of clusters is consistent with the experimental observations of thermal helium desorption from ?-Fe during post-He-implantation annealing.

Morishita, K.; Sugano, R.; Wirth, B. D.; Diaz de la Rubia, T.

2003-04-01

337

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)

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.

Shikama, Taiichi; Ogane, Shuhei; Ishii, Hidekazu; Iida, Yohei; Hasuo, Masahiro

2014-08-01

338

A study of pseudoresonances in the application of the Schwinger variational principle to electron scattering from atomic hydrogen  

NASA Technical Reports Server (NTRS)

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.

Weatherford, Charles A.; Odom, Gregory; Tucker, Roy

1989-01-01

339

Peculiarities of elastic scattering of intermediate-energy electrons related to their capture at quasi-stationary levels of an atom in a continuous spectrum  

NASA Astrophysics Data System (ADS)

A theoretical model of electron scattering on an atom is constructed to study elastic atomic scattering of intermediate-energy electrons. The proposed model is based upon the combined Mensing potential with two spheres of atomic electrons, which admits analytical solutions of the radial Schröbinger equation. A procedure for matching the parameters of this scatterer to an approximate electrostatic potential of an atom in the form of a screened Coulomb potential has been determined. The screening radius of the latter potential has been calculated proceeding from the properties corresponding to the Thomas-Fermi method. A model of a scatterer determined according to the aforementioned procedure can be used to calculate the energy dependence of the cross section of elastic electron scattering on some atoms with s, p, and d shells representing elements neighboring zirconium. The main result is the establishment of factors responsible for the appearance of maxima on the energy dependences of the cross section of elastic electron scattering. These maxima are related to the resonant trapping of impinging electrons by quasi-stationary levels in a continuous spectrum.

Libenson, B. N.

2014-05-01

340

Interaction potentials for multi-electron atoms in front of a LiF (0 0 1) surface from rainbow scattering  

NASA Astrophysics Data System (ADS)

Pairwise interaction potentials for multi-electron atoms moving in front of a LiF (0 0 1) surface are investigated theoretically and experimentally. From angular distributions of fast He, N, S, Cl and Kr atoms grazingly scattered under axial surface channeling conditions, rainbow angles are experimentally determined for a wide range of energies for the motion normal to the surface plane. These angles are used as a benchmark to probe the pairwise potential model. In the simulations the scattering process is described by means of the surface eikonal approximation, while the atom-surface interaction is derived by adding binary interatomic potentials that include the proper asymptotic limit.

Gravielle, M. S.; Miraglia, J. E.; Schüller, A.; Winter, H.

2013-12-01

341

Molecular dynamics simulations of cumulative helium bombardments on tungsten surfaces  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations were performed to study the cumulative bombardments of low-energy (60-200 eV) helium atoms on tungsten surfaces. The behaviour of helium and the response of tungsten surface were investigated. The helium incident energy and tungsten temperature play important roles on the formation and growth of helium clusters. The temperature can promote the coalescence of helium clusters and increase the size of the helium clusters. The rupture of the helium clusters has also been observed. During the formation of helium clusters, the interstitial tungsten atoms are produced and evolve into bundles of <1 1 1> crowdions, which would be constrained around the helium clusters for a long time. However, they will finally move onto the top surface along the <1 1 1> direction, which results in stacking the tungsten atoms on the surface. The complex combination effects of the helium clusters and the interstitial atoms result in the growth of the surfaces. Besides, several tungsten atoms were ejected from tungsten surfaces.

Li, Min; Cui, Jiechao; Wang, Jun; Hou, Qing

2014-10-01

342

Formation of DNA nanoparticles in the presence of novel polyamine analogues: a laser light scattering and atomic force microscopic study  

Microsoft Academic Search

We synthesized a pentamine (3-3-3-3) and two hex- amine (3-3-3-3-3 and 3-4-3-4-3) analogues of the natural polyamine, spermine (3-4-3) and studied their effectiveness in condensing pGL3 plasmid DNA, using light scattering and atomic force micro- scopic (AFM) techniques. The midpoint concentra- tion of the polyamines on pGL3 condensation (EC50) was 11.3, 10.6, 1.5, 0.49 and 0.52 mM, respectively, for 3-4-3,

Veena Vijayanathan; Thresia Thomas; Thomas Antony; Akira Shirahata; T. J. Thomas

2004-01-01

343

On the inversion of the atomic beam scattering data in the Eikonal approximation  

NASA Astrophysics Data System (ADS)

The inversion method of Celli, Garcia and Rieder requires some a-priori knowledge about the phases of the dominant scattering amplitudes. A perturbational method will be introduced here which is evaluated in the Eikonal approximation, but can in principle be extended to the Helmholtz equation. It is based on the observation that the expansion coefficients PG( n) of the scattering intensities with respect to ki, the incident wave vector, are functions of the corrugation amplitudes and phase differences and fulfill certain sum rules. If these coefficients are determined by several measurements with varying scattering parameters, then the lowest PG( n) for n = 2,3.4 are sufficient for finding the essentially unique surface profile function. As an example, simulated surface domain structure scattering data will be inverted.

Schlup, W. A.

1989-04-01

344

Strong directional out-of-plane scattering in multiple ionizing highly charged ion-atom collisions  

SciTech Connect

The azimuthal ({phi}{sub r}) and polar angle ({theta}{sub r}) scattering of projectiles in coincidence with recoil ions has been studied for 0.53 MeV/u F{sup 8+} + Ne. For high degree of ionization of the target we find the resultant transverse momentum of all electrons emitted into the continuum to increase with the number of ejected electrons and to have a direction mostly not co-planar with the scattering plane.

Gonzalez, A.; Hagmann, S.; Quinteros, T. [Kansas State Univ., Manhattan, KS (United States). J.R. MacDonald Lab.; Kraessig, B. [Freiburg Univ. (Germany). Fakultaet fuer Physik; Koch, R.; Schmidt-Boecking, H. [Frankfurt Univ. (Germany). Inst. fuer Kernphysik; Skutlartz, A. [East Carolina Univ., Greenville, NC (United States)

1990-12-31

345

Strong directional out-of-plane scattering in multiple ionizing highly charged ion-atom collisions  

SciTech Connect

The azimuthal ([phi][sub r]) and polar angle ([theta][sub r]) scattering of projectiles in coincidence with recoil ions has been studied for 0.53 MeV/u F[sup 8+] + Ne. For high degree of ionization of the target we find the resultant transverse momentum of all electrons emitted into the continuum to increase with the number of ejected electrons and to have a direction mostly not co-planar with the scattering plane.

Gonzalez, A.; Hagmann, S.; Quinteros, T. (Kansas State Univ., Manhattan, KS (United States). J.R. MacDonald Lab.); Kraessig, B. (Freiburg Univ. (Germany). Fakultaet fuer Physik); Koch, R.; Schmidt-Boecking, H. (Frankfurt Univ. (Germany). Inst. fuer Kernphysik); Skutlartz, A. (East Carolina Univ., Greenville, NC (United States))

1990-01-01

346

Accurate treatment of the scattering and atomic states in the K-d system  

NASA Astrophysics Data System (ADS)

The low-energy K-d scattering amplitudes were calculated. A “chirally motivated” KbarN-?? potential was constructed and used as an input in the three-body Faddeev-type AGS equations. The 1s level shift and width of kaonic deuterium were then calculated using an optical two-body K--d potential, which reproduces the three-body results on K-d scattering.

Shevchenko, N. V.

2013-09-01

347

Energy-related atomic and molecular structure and scattering studies. Annual progress report, July 1, 1979-June 30, 1980  

SciTech Connect

The basic goals of this program concern the experimental determination of properties of atoms and simple molecules that are important in a wide range of energy-related processes. In particular we have initiated measurements of polarizabilities of highly polar molecules and dimers, and of a number of atoms distributed through the periodic table, and, of the scattering of low energy electrons by highly polar molecules. For this latter series of measurements an entirely new apparatus has been designed and its external components have been completed. A new electron optics assembly has also been designed and is currently under construction. Details of all these projects are presented; analysis and data of the polarizability measurements are also given.

Bederson, B.

1980-03-01

348

He/Ar-atom scattering from molecular monolayers: C60/Pt(111) and graphene/Pt(111).  

PubMed

Supersonic He and Ar atomic beam scattering from C(60) and graphene monolayers adsorbed on a Pt(111) surface are demonstrated in order to obtain detailed insight into a gas-molecule collision that has not been studied in detail so far. The effective masses and phonon spectral densities of the monolayers seen by different projectiles are discussed based on classical models such as the hard cube model and the recently developed smooth surface model. Large effective masses are deduced for both the monolayers, suggesting collective effects of surface atoms in the single collision event. The effective Debye temperature of graphene was found to be similar to that reported in highly oriented pyrolytic graphite (HOPG), indicating that the graphene is decoupled well from the Pt substrate. A much smaller Debye-Waller factor was found for the C(60) layer, probably reflecting the strong C(60)-Pt(111) interaction. PMID:21399342

Yamada, Y; Sugawara, C; Satake, Y; Yokoyama, Y; Okada, R; Nakayama, T; Sasaki, M; Kondo, T; Oh, J; Nakamura, J; Hayes, W W

2010-08-01

349

Helium superfluidity. Shapes and vorticities of superfluid helium nanodroplets.  

PubMed

Helium nanodroplets are considered ideal model systems to explore quantum hydrodynamics in self-contained, isolated superfluids. However, exploring the dynamic properties of individual droplets is experimentally challenging. In this work, we used single-shot femtosecond x-ray coherent diffractive imaging to investigate the rotation of single, isolated superfluid helium-4 droplets containing ~10(8) to 10(11) atoms. The formation of quantum vortex lattices inside the droplets is confirmed by observing characteristic Bragg patterns from xenon clusters trapped in the vortex cores. The vortex densities are up to five orders of magnitude larger than those observed in bulk liquid helium. The droplets exhibit large centrifugal deformations but retain axially symmetric shapes at angular velocities well beyond the stability range of viscous classical droplets. PMID:25146284

Gomez, Luis F; Ferguson, Ken R; Cryan, James P; Bacellar, Camila; Tanyag, Rico Mayro P; Jones, Curtis; Schorb, Sebastian; Anielski, Denis; Belkacem, Ali; Bernando, Charles; Boll, Rebecca; Bozek, John; Carron, Sebastian; Chen, Gang; Delmas, Tjark; Englert, Lars; Epp, Sascha W; Erk, Benjamin; Foucar, Lutz; Hartmann, Robert; Hexemer, Alexander; Huth, Martin; Kwok, Justin; Leone, Stephen R; Ma, Jonathan H S; Maia, Filipe R N C; Malmerberg, Erik; Marchesini, Stefano; Neumark, Daniel M; Poon, Billy; Prell, James; Rolles, Daniel; Rudek, Benedikt; Rudenko, Artem; Seifrid, Martin; Siefermann, Katrin R; Sturm, Felix P; Swiggers, Michele; Ullrich, Joachim; Weise, Fabian; Zwart, Petrus; Bostedt, Christoph; Gessner, Oliver; Vilesov, Andrey F

2014-08-22

350

Phonon scattering rates and atomic ordering in Ag1-xSb1+xTe2+x(x=0,0.1,0.2) investigated with inelastic neutron scattering and synchrotron diffraction  

NASA Astrophysics Data System (ADS)

The phonon dispersions and scattering rates of the thermoelectric material Ag1-xSb1+xTe2+x(x=0,0.1,0.2) were measured with inelastic neutron scattering, as function of both temperature T and off stoichiometry x. In addition, detailed measurements of diffuse scattering were performed with both neutron and synchrotron x-ray diffraction. The results show that phonon scattering rates are large and weakly dependent on T or x, and the lattice thermal conductivity calculated from these scattering rates and group velocities is in good agreement with bulk transport measurements. We also find that the scattering rates and their temperature dependence cannot be accounted for with common models of phonon scattering by anharmonicity or point defects. The diffuse scattering measurements show a pervasive, complex signal, with several distinct components. In particular, broad superstructure reflections indicate a short-range ordering of the Ag and Sb cations on their sublattice. Single-crystal Bragg peak intensities also reveal large static atomic displacements, compatible with results from Rietveld refinement of neutron powder diffraction data. Our results indicate that a complex nanostructure, arising from multiple variants of nanoscale anisotropic superstructures of cations, and large atomic displacements, is likely responsible for the strong phonon scattering.

Ma, J.; Delaire, O.; Specht, E. D.; May, A. F.; Gourdon, O.; Budai, J. D.; McGuire, M. A.; Hong, T.; Abernathy, D. L.; Ehlers, G.; Karapetrova, E.

2014-10-01

351

Accurate small and wide angle x-ray scattering profiles from atomic models of proteins and nucleic acids.  

PubMed

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

Nguyen, Hung T; Pabit, Suzette A; Meisburger, Steve P; Pollack, Lois; Case, David A

2014-12-14

352

One-photon scattering by an atomic chain in a two-mode resonator: cyclic conditions.  

PubMed

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

Sizhuk, Andrii S; Yezhov, Stanislav M

2014-01-01

353

One-photon scattering by an atomic chain in a two-mode resonator: cyclic conditions  

PubMed Central

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

2014-01-01

354

Positron scattering by atomic hydrogen using optical potentials and with positronium formation  

NASA Technical Reports Server (NTRS)

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).

Walters, H. R. J.

1990-01-01

355

Experiments with electron bubbles in liquid helium  

NASA Astrophysics Data System (ADS)

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 techniques. By using a focused sound wave, we create a region in liquid helium where the pressure was negative. The bubble becomes unstable, and can grow without limit when the ambient pressure is lower than some critical value. This macroscopic bubble can then be detected by light scattering. The critical pressure of the bubble depends on many factors. For example, a bubble containing an electron in an excited state has a lower magnitude of critical pressure, and is therefore easier to explode than a bubble with the electron in the ground state. Similarly, bubbles trapped on vortices are easier to explode than normal, untrapped bubbles. In our experiments, we injected electrons in liquid helium by either a field emission tip or a radioactive beta source. We investigated the different experimental conditions under which the bubbles were trapped on vortices. We measured the difference of critical pressures between bubbles on and off vortices as a function of temperature. In the course of our experiments, we were able to detect electrons that were formed by the Penning ionization of dimers. At temperatures lower than 1 K, we have discovered new objects that can be exploded very easily. These objects depend on different experimental parameters in a complicated way, and are not completely understood. In a second series of experiments, we used infrared radiation to excite the electron bubbles. By analyzing the data carefully, we estimated the lifetime of these excited state bubbles; and concluded that the decay mechanism is non-radiative in nature. We also studied the effect of infrared radiation on bubbles trapped on vortices. Finally, we measured the current arising from the secondary ionization of the beta particles emitted from a radioactive source. The current had an interesting dependence on different experimental parameters, especially temperature and electric field.

Ghosh, Ambarish

356

Helium-surface interaction potential: Determination and applications  

NASA Astrophysics Data System (ADS)

Extensive interest in the field of elastic helium atom-surface scattering is due to encouraging progress made for surface structure determination. An important ingredient in this development is a reliable atom-surface interaction potential. We briefly review the theoretical activity in this area and present our results for the He-Cu(110) interaction potential. From these studies we conclude that the Esbjerg-Nørskov relation between helium-surface repulsive potential and the surface charge density works well. The addition of the Zaremba-Kohn attractive part to the calculated repulsive part completely specifies the total interaction potential. We also reconcile different values for the Cu(110) corrugation obtained with and without using the Esbjerg-Nørskov relation. For application purposes we find that the Esbjerg-Nørskov relation with charge densities derived from atomic superposition is more convenient to use. We illustrate this by examining chemisorption of oxygen on Ni(001). For this a p(2 × 2) structure at low exposures changes to a c(2 × 2) at higher exposures. There have been conflicting suggestions about the vertical height for oxygen in the two phases. We compare our calculated corrugations with Rieder's data and conclude that in both phases oxygen is at a vertical distance of about 0.9 Å. Chlorine adsorption on Ag(001) is another system for which He diffraction work of Cardillo et al. has clearly distinguished between two competing structural alternatives. Another application is taken to show how helium diffraction can give site specific information. Here we study the He-H/Pt(111) system and demonstrate that H chemisorbs on a three-fold hcp site at a vertical distance of about 1 Å on Pt(111). As a last example, we present some new results for the Cu(110)-O(2 × 1) system. In particular, we show that He diffraction results are in agreement with the recent findings of EXAFS measurements.

Batra, Inder P.

1984-12-01

357

Mean free path of inelastic electron scattering in elemental solids and oxides using transmission electron microscopy: Atomic number dependent oscillatory behavior  

SciTech Connect

Mean free path of inelastic electron scattering {lambda} has been measured with a 200 keV transmission electron microscope for the majority of stable elemental solids and their oxides. An oscillating behavior vs atomic number Z has been revealed, such that within one row of the Periodic Table, the minimum (maximum) of {lambda} is observed for elements with completed (empty) outer d shells. A significantly weaker {lambda}(Z) dependence is observed for the oxides. The {lambda}(Z) variation is ascribed to the three major factors: atomic density, number of 'free' electrons per atom, and contribution of atomic core-loss transitions.

Iakoubovskii, Konstantin; Mitsuishi, Kazutaka; Nakayama, Yoshiko; Furuya, Kazuo [Quantum Dot Research Center, National Institute for Materials Science, 3-13 Sakura, Tsukuba 305-0005 (Japan); High Voltage Microscopy Station, National Institute for Materials Science, 3-13 Sakura, Tsukuba 305-0005 (Japan)

2008-03-01

358

Nuclear forward scattering vs. conventional Mossbauer studies of atomically tailored Eu-based materials.  

SciTech Connect

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.

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

359

hal-00120114,version2-23Feb2007 Lifetime of weakly-bound dimers of ultracold metastable helium studied by  

E-print Network

between two 23 S1 spin polarized helium atoms. This inhibition has a limit set by spin relaxation pro- sociation, our group studied exotic molecules in which two spin-polarized metastable helium atoms are bound between two spin-polarized 23 S1 helium atoms, v = 14 being the least- bound vibrational state

Paris-Sud XI, Université de

360

Detection of Negative Charge Carriers in Superfluid Helium Droplets: The Metastable Anions He*– and He2*–  

PubMed Central

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

2014-01-01

361

Ion temperature measurements by means of Rutherford scattering at TEXTOR  

NASA Astrophysics Data System (ADS)

Rutherford scattering of neutral particles from a diagnostic beam is a method for local and time-resolved measurements of the ion temperature. Energetic helium atoms are injected into the plasma and become elastically scattered by plasma ions. Energy and momentum conservation determine the energy distribution of the scattered particles. The ion temperature can be deduced from the width of this distribution. This paper deals with the Rutherford scattering diagnostic which has been recently installed at TEXTOR. The diagnostic consists of two main components: a monoenergetic probing beam (He, 35 keV, 10 mA) injected into the plasma and a time-of-flight analyzer for the determination of the energy of scattered particles. The scattering angle can be adjusted in the range from 3° to 8°.

van Blokland, A. A. E.; Barbian, E. P.; Grimbergen, T. W. M.; Oyevaar, Th.

1990-10-01

362

Resonant Raman Scattering and Atomic Force Microscopy of InGaAs/GaAs Multilayer Nanostructures with Quantum Dots  

SciTech Connect

The transition from two-dimensional (2D) pseudomorphic growth to the three-dimensional (3D) (nanoisland) growth in In{sub x}Ga{sub 1-} {sub x}As/GaAs multilayer structures grown by molecular-beam epitaxy was investigated by atomic force microscopy, photoluminescence, and Raman scattering. The nominal In content x in In{sub x}Ga{sub 1-x}As was varied from 0.20 to 0.50. The thicknesses of the deposited In{sub x}Ga{sub 1-x}As and GaAs layers were 14 and 70 monolayers, respectively. It is shown that, at these thicknesses, the 2D-3D transition occurs at x {>=} 0.27. It is ascertained that the formation of quantum dots (nanoislands) does not follow the classical Stranski-Krastanov mechanism but is significantly modified by the processes of vertical segregation of In atoms and interdiffusion of Ga atoms. As a result, the In{sub x}Ga{sub 1-x}As layer can be modeled by a 2D layer with a low In content (x < 0.20), which undergoes a transition into a thin layer containing nanoislands enriched with In (x > 0.60). For multilayer In{sub x}Ga{sub 1-x}As structures, lateral alignment of quantum dots into chains oriented along the [1-bar10] direction can be implemented and the homogeneity of the sizes of quantum dots can be improved.

Valakh, M.Ya.; Strelchuk, V.V.; Kolomys, A.F. [Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kiev, 03028 (Ukraine); Mazur, Yu.I.; Wang, Z.M.; Xiao, M.; Salamo, G.J. [University of Arkansas, Department of Physics, 72701 Arkansas (United States)

2005-01-01

363

Raman scattering of an ultrashort resonance test pulse in an atomic gas  

Microsoft Academic Search

Stokes free induction, photon echo, and anti-Stokes free induction arising in a gas after the passage of an ultrashort test pulse are studied. The pulse is delayed relative to ultrashort biharmonic pumping and is in resonance with the allowed atomic transition adjacent to the Raman transition. A physical interpretation is given for the present nonstationary four-photon process and the cubic

A. I. Alekseev; O. V. Zhemerdeev

1987-01-01

364

Optically pumped helium - a spin dependent probe  

Microsoft Academic Search

In the 25 years since the first optical pumping experiments in helium were reported, there have been an astonishing variety of applications. We describe briefly the use of spin-polarized helium to measure interplanetary magnetic fields, to probe spin-dependent nuclear and atomic collisions, to investigate surface properties of materials, and to study the quantum properties of a spin-polarized Fermi system. Il

L. D. Schearer

1985-01-01

365

Shallow and diffuse spin-orbit potential for proton elastic scattering from neutron-rich helium isotopes at 71 MeV/nucleon  

E-print Network

Vector analyzing powers for proton elastic scattering from 8He at 71 MeV/nucleon have been measured using a solid polarized proton target operated in a low magnetic field of 0.1 T. The spin-orbit potential obtained from a phenomenological optical model analysis is found to be significantly shallower and more diffuse than the global systematics of stable nuclei, which is an indication that the spin-orbit potential is modified for scattering involving neutron-rich nuclei. A close similarity between the matter radius and the root-mean-square radius of the spin-orbit potential is also identified.

S. Sakaguchi; T. Uesaka; N. Aoi; Y. Ichikawa; K. Itoh; M. Itoh; T. Kawabata; T. Kawahara; Y. Kondo; H. Kuboki; T. Nakamura; T. Nakao; Y. Nakayama; H. Sakai; Y. Sasamoto; K. Sekiguchi; T. Shimamura; Y. Shimizu; T. Wakui

2013-02-18

366

Shallow and diffuse spin-orbit potential for proton elastic scattering from neutron-rich helium isotopes at 71 MeV/nucleon  

E-print Network

Vector analyzing powers for proton elastic scattering from 8He at 71 MeV/nucleon have been measured using a solid polarized proton target operated in a low magnetic field of 0.1 T. The spin-orbit potential obtained from a phenomenological optical model analysis is found to be significantly shallower and more diffuse than the global systematics of stable nuclei, which is an indication that the spin-orbit potential is modified for scattering involving neutron-rich nuclei. A close similarity between the matter radius and the root-mean-square radius of the spin-orbit potential is also identified.

Sakaguchi, S; Aoi, N; Ichikawa, Y; Itoh, K; Itoh, M; Kawabata, T; Kawahara, T; Kondo, Y; Kuboki, H; Nakamura, T; Nakao, T; Nakayama, Y; Sakai, H; Sasamoto, Y; Sekiguchi, K; Shimamura, T; Shimizu, Y; Wakui, T

2013-01-01

367

A summary of the low angle x-ray atomic scattering factors which have been measured by the critical voltage effect in High Energy Electron Diffraction (HEED)  

SciTech Connect

A tabulated summary of all the accurate (/approximately/0.1%) low-angle x-ray atomic scattering (form) factors which have been determined by the systematic critical voltage technique in HEED is presented. For low atomic number elements (Z/approx lt/40) the low angle form factors can be significantly different to best free atom values, and so the best band structure calculated and/or x-ray measured form factors consistent with the critical voltage measurements are also indicated. At intermediate atomic numbers Zapprox. =40..-->..50 only the very low-angle form factors appear to be different to the best free atom values, and even then only by a small amount. For heavy elements (Z/approx lt/70) the best free atom form factors appear to agree very closely with the critical voltage measured values and so, in this case, critical voltage measurements give very accurate measurements of Debye-Waller factors. 48 refs.

Fox, A.G.; Fisher, R.M.

1987-08-01

368

Absolute differential cross sections for the elastic scattering of electrons from atomic hydrogen at low incident energies  

NASA Astrophysics Data System (ADS)

Absolute differential cross sections for electrons elastically scattered from atomic hydrogen have been measured at low incident energies. The measurements were facilitated by the moveable nozzle source recently developed in our lab. Data taken at the incident energies of 20 eV, 40 eV, and 100 eV, and spanning the angular range of 10^rc to 120^rc will be presented. The results will be compared to the earlier measurements of Williams(Joseph Callaway and J. F. Williams, Phys. Rev. A) 12, 2312 (1975), J. F. Williams, J. Phys. B 8, 2191 (1975) and Shyn(T. W. Shyn and S. Y. Cho, Phys. Rev. A) 40, 1315 (1989), T. W. Shyn and Alan Grafe, Phys. Rev. A 46, 2949 (1992), and the theoretical calculations of Bray(Igor Bray, Phys. Rev. A) 46, 6995 (1992). Funded by the National Science Foundation under Grant # NSF-RUI-PHY-0096808.

James, Kenneth; Leonard, Linda; Proctor, Stephanie; Childers, J. G.; Khakoo, Murtadha A.

2003-05-01

369

Effect of optical pumping and Raman scattering on the degenerate four-wave mixingin coherently pumped rubidium atoms  

NASA Astrophysics Data System (ADS)

We present an experimental study of cw degenerate four-wave mixing (DFWM) in Doppler-broadened rubidium atoms coupled by an additional coherent field. The coupling field and the DFWM fields were arranged in a ?-type configuration from the rubidium D2 transitions. We found that the presence of the coherent coupling field modifies the DFWM emission:mfat lower intensities of the coupling field, the DFWM emission is enhanced; at higher intensities of the coupling field, the DFWM is reduced. The observed effect of the coupling laser on the DFWM emission may be explained by the direct competition between the resonance-enhanced two-photon Raman scattering and the optical-pumping-enhanced DFWM emission.

Zhu, Yifu; Wasserlauf, T. N.; Sanchez, Paul

1997-01-01

370

CCMR: Characterization of Organic semiconductor thin films: In situ synchrotron x-ray scattering and ex situ atomic force microscopy  

NSDL National Science Digital Library

Our group studies the growth of organic semiconductor thin films, to better understand the connection between thin film morphology, crystal structure, and electronic device properties. Conventionally, thin films of organic semiconductors are deposited using thermal evaporation. However, the use of supersonic molecular beams to deposit thin films allows the incident kinetic energy of the organic semiconductor to be tuned in the range of 4-16 eV. The organic semiconductor thin films are characterized using in situ real time synchrotron x-ray scattering, and ex situ atomic force microscopy (AFM). My research experience this summer primarily consisted of analyzing x-ray data and studying the morphology of the thin films deposited on various dielectrics (self-assembled monolayers, SAMs) of varying chain length using AFM.

Greer, Douglas

2009-08-15

371

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)

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.

Berk, A.; Temkin, A.

1985-01-01

372

X-ray scattering for the atomic structure of a barium-induced Si(111)-3 × 2 surface  

NASA Astrophysics Data System (ADS)

We have investigated the atomic arrangement of a barium (Ba)-induced Si(111)-3×2 surface by using surface-sensitive synchrotron X-ray scattering. In-plane fractional-order reflections obtained from three rotational domains of 3×1 symmetry have been used to examine several competing structural models including the honeycomb-chain-channel (HCC) and the double-?-bonded chain (D?C) models. By fitting two different data sets, both the goodness-of-the fits ?2 and the residuum R-factor strongly favor the HCC over the D?C model. We conclude that a Ba-paired HCC structure with a 1/3 monolayer of Ba coverage best describes the Ba-induced 3×2 surface with a Ba-Ba interatomic spacing d = 1.93 Å.

Kim, N. D.; Kang, T. S.; Je, J. H.; Kim, H. J.; Noh, D. Y.; Chung, J. W.

2008-04-01

373

Atomistic simulation of helium bubble nucleation in palladium  

Microsoft Academic Search

A palladium crystal has been constructed with 11808 atoms. 55 helium atoms occupied the octahedral position of palladium crystal are introduced and retained in a spherical region. Molecular dynamic simulations are performed in a constant temperature and constant volume ensemble (NVT) with temperature controlled by Nose–Hoover thermostat. The interactions between palladium atoms are described with modified analytic embedded atom method

Liang Wang; Wangyu Hu; Shifang Xiao; Jianyu Yang; Huiqiu Deng

2009-01-01

374

Sensitivity of ultracold-atom scattering experiments to variation of the fine-structure constant  

NASA Astrophysics Data System (ADS)

We present numerical calculations for cesium and mercury to estimate the sensitivity of the scattering length to the variation of the fine-structure constant ?. The method used follows the ideas of Chin and Flambaum [Phys. Rev. Lett. PRLTAO0031-900710.1103/PhysRevLett.96.230801 96, 230801 (2006)], where the sensitivity to the variation of the electron-to-proton mass ratio ? was considered. We demonstrate that for heavy systems, the sensitivity to the variation of ? is of the same order of magnitude as to the variation of ?. Near narrow Feshbach resonances, the enhancement of the sensitivity may exceed nine orders of magnitude.

Borschevsky, A.; Beloy, K.; Flambaum, V. V.; Schwerdtfeger, P.

2011-05-01

375

Sensitivity of ultracold-atom scattering experiments to variation of the fine-structure constant  

SciTech Connect

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.

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

376

Sensitivity to alpha-variation in ultracold atomic-scattering experiments  

E-print Network

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 ideas 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 variation of alpha is of the same order of magnitude as to variation of beta. Near narrow Feshbach resonances the enhancement of the sensitivity may exceed nine orders of magnitude.

Borschevsky, A; Flambaum, V V; Schwerdtfeger, P

2011-01-01

377

A refined He-LiF(001) potential from selective adsorption resonances measured with high-resolution helium spin-echo spectroscopy  

Microsoft Academic Search

The authors have developed a new experimental approach for measuring gas-surface selective adsorption resonances with much higher energy resolution and over a wider range of kinematic conditions than has previously been possible. The technique involves using a 3He spin-echo spectrometer as a Fourier transform helium atom scattering apparatus. The authors applied the technique to the He-LiF(001) system. They developed a

D. J. Riley; A. P. Jardine; S. Dworski; G. Alexandrowicz; P. Fouquet; J. Ellis; W. Allison

2007-01-01

378

Atomic dynamics in molten AlCu alloys of different compositions and at different temperatures by cold neutron scattering  

SciTech Connect

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.

Dahlborg, U. [University of Rouen; Besser, M. [Ames Laboratory; Kramer, Matthew J. [Ames Laboratory; Morris, J. R. [Oak Ridge National Laboratory; Calvo-Dahlborg, M. [University of Rouen

2013-12-21

379

Metastable helium density probe for remote plasmas  

SciTech Connect

Helium metastable atom density was spatially determined by a modified electrostatic probe in a remote plasma. The probe structure was similar to that of a guard ring probe. Opposite polarity voltages were applied to the inner probe and the guard ring to shield both electrons and ions from the vicinity of the inner probe. Therefore, the inner probe current is due to secondary electrons generated by the de-exciting helium metastable atom flux. The photoelectron current was removed by shielding and orienting the probe 90 deg. to the direction of the plasma-generated photon flux. Helium metastable atom density on the order of 10{sup 7} cm{sup -3} was measured. Limitations on the use of this technique are revealed by comparisons with simulated metastable distributions.

Miura, Naoto; Hopwood, Jeffrey [Department of Electrical and Computer Engineering, Tufts University, 161 College Ave., Medford, Massachusetts 02155 (United States)

2009-11-15

380

Note: Mechanical etching of atomic force microscope tip and microsphere attachment for thermal radiation scattering enhancement  

SciTech Connect

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.

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

381

Requirements, possible alternatives & international NEUTRON SCATTERING  

E-print Network

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

Dimeo, Robert M.

382

A Measurement of the neutron electric form factor at very large momentum transfer using polaried electrions scattering from a polarized helium-3 target  

SciTech Connect

Knowledge of the electric and magnetic elastic form factors of the nucleon is essential for an understanding of nucleon structure. Of the form factors, the electric form factor of the neutron has been measured over the smallest range in Q{sup 2} and with the lowest precision. Jefferson Lab experiment 02-013 used a novel new polarized {sup 3}He target to nearly double the range of momentum transfer in which the neutron form factor has been studied and to measure it with much higher precision. Polarized electrons were scattered off this target, and both the scattered electron and neutron were detected. G{sup n}{sub E} was measured to be 0.0242 ± 0.0020(stat) ± 0.0061(sys) and 0.0247 ± 0.0029(stat) ± 0.0031(sys) at Q{sup 2} = 1.7 and 2.5 GeV{sup 2}, respectively.

Aidan Kelleher

2010-10-01

383

Three-dimensional strong localization of matter waves by scattering from atoms in a lattice with a confinement-induced resonance  

SciTech Connect

The possibility of using ultracold atoms to observe strong localization of matter waves is now a subject of great interest, as undesirable decoherence and interactions can be made negligible in these systems. It was proposed that a static-disordered potential can be realized by trapping atoms of a given species in randomly chosen sites of a deep three-dimensional (3D) optical lattice with no multiple occupation. We analyze in detail the prospects of this scheme for observing localized states in 3D for a matter wave of a different atomic species that interacts with the trapped particles and that is sufficiently far detuned from the optical lattice to be insensitive to it. We demonstrate that at low energy a large number of 3D strongly localized states can be produced for the matter wave, if the effective scattering length describing the interaction of the matter wave with a trapped atom is of the order of the mean distance between the trapped particles. Such high values of the effective scattering length can be obtained by using a Feshbach resonance to adjust the free-space interspecies scattering length and by taking advantage of confinement-induced resonances induced by the trapping of the scatterers in the lattice.

Massignan, Pietro; Castin, Yvan [Niels Bohr Institutet, Universitetsparken 5, DK-2100 Copenhagen O (Denmark); and Laboratoire Kastler Brossel, Ecole Normale Superieure, 24 rue Lhomond, 75005 Paris (France); Laboratoire Kastler Brossel, Ecole Normale Superieure, 24 rue Lhomond, 75005 Paris (France)

2006-07-15

384

Reactive scattering of a supersonic alkali atom beam: K+Br2 BrCN, SnCl4, PCl3, CCl4, CH3I  

Microsoft Academic Search

Angular distribution measurements of reactive scattering of a supersonic potassium atom beam by a series of molecules are reported with initial kinetic energy (˜ 5 kcal mole-1) above the thermal energy range. The narrow Laval nozzle velocity distribution gives improved resolution over thermal energy measurements. Total reaction cross sections are found to decrease with energy. Differential reaction cross sections for

J. C. Whitehead; D. R. Hardin; R. Grice

1972-01-01

385

Inelastic and Reactive Scattering Dynamics of Hyperthermal Oxygen Atoms on Ionic Liquid Surfaces: [emim][NTf{sub 2}] and [C{sub 12}mim][NTf{sub 2}  

SciTech Connect

Collisions of hyperthermal oxygen atoms, with an average translational energy of 520 kJ mol{sup -1}, on continuously refreshed ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([emim][NTf{sub 2}]) and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C{sub 12}mim][NTf{sub 2}]), were studied with the use of a beam-surface scattering technique. Time-of-flight and angular distributions of inelastically scattered O and reactively scattered OH and H{sub 2}O were collected for various angles of incidence with the use of a rotatable mass spectrometer detector. For both O and OH, two distinct scattering processes were identified, which can be empirically categorized as thermal and non-thermal. Non-thermal scattering is more probable for both O and OH products. The observation of OH confirms that at least some reactive sites, presumably alkyl groups, must be exposed at the surface. The ionic liquid with the longer alkyl chain, [C{sub 12}mim][NTf{sub 2}], is substantially more reactive than the liquid with the shorter alkyl chain, [emim][NTf{sub 2}], and proportionately much more so than would be predicted simply from stoichiometry based on the number of abstractable hydrogen atoms. Molecular dynamics models of these surfaces shed light on this change in reactivity. The scattering behavior of O is distinctly different from that of OH. However, no such differences between inelastic and reactive scattering dynamics have been seen in previous work on pure hydrocarbon liquids, in particular the benchmark, partially branched hydrocarbon, squalane (C{sub 30}H{sub 62}). The comparison between inelastic and reactive scattering dynamics indicates that inelastic scattering from the ionic liquid surfaces takes place predominantly at non-reactive sites that are effectively stiffer than the reactive alkyl chains, with a higher proportion of collisions sampling such sites for [emim][NTf{sub 2}] than for [C{sub 12}mim][NTf{sub 2}].

Wu Bohan; Zhang Jianming; Minton, Timothy K. [Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717 (United States); McKendrick, Kenneth G. [School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom); Slattery, John M. [Department of Chemistry, University of York, Heslington, York YO10 5DD (United Kingdom); Yockel, Scott; Schatz, George C. [Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113 (United States)

2011-05-20

386

Helium diffraction from adsorbate-covered surfaces: A study of the O-Ni(001) system  

NASA Astrophysics Data System (ADS)

Elastic helium-atom-surface scattering is currently being used to obtain important structural information from adsorbate-covered surfaces. Since our earlier work on helium diffraction from p(2×2) and c(2×2) phases of oxygen on Ni(001) there have been three new developments. These are (i) the suggestion by Rieder of a prolate charge distribution on oxygen, (ii) the pseudobridge site proposal of Demuth et al., and (iii) the self-consistent calculation of the helium-surface interaction potential due to Lang and Nørskov. In this paper we present results for a wide range of calculational parameters for the c(2×2) phase of oxygen on Ni(001) and comment on the above developments. Specifically, based on the results in (iii), we are able to explore the implications of the use of the Esbjerg-Nørskov-Lang relation with and without helium averaged surface-charge density. We conclude that the prolate charge distribution produces a shape function in better agreement with experiment. Changes in corrugation coefficients introduced by shifting to the pseudobridge site from the centered site are noted to be small.

Batra, Inder P.; Barker, J. A.

1984-05-01

387

Investigation of electron-atom/molecule scattering resonances: Two complex multiconfigurational self-consistent field approaches  

NASA Astrophysics Data System (ADS)

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.

Samanta, Kousik; Yeager, Danny L.

2015-01-01

388

Variational Method for Two-Electron Atoms  

ERIC Educational Resources Information Center

Proposes a simple two-parameter trial wave function for the helium atom and helium-like ions. Shows that a variational calculation for the ground-state energy yields better results than the usual one-parameter example. (MLH)

Srivastava, M. K.; Bhaduri, R. K.

1977-01-01

389

Gain and continuous-wave laser oscillation on the 1315 nm atomic iodine transition pumped by an air-helium electric discharge  

E-print Network

American Institute of Physics. DOI: 10.1063/1.2957678 The classical chemical oxygen iodine laser COIL re investigations into an electrically driven oxygen-iodine laser ElectricOIL that was demonstrated by Carroll et alGain and continuous-wave laser oscillation on the 1315 nm atomic iodine transition pumped by an air

Carroll, David L.

390

Helium on Venus - Implications for uranium and thorium  

NASA Technical Reports Server (NTRS)

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.

Prather, M. J.; Mcelroy, M. B.

1983-01-01

391

State-to-state three-atom time-dependent reactive scattering in hyperspherical coordinates.  

PubMed

We present a time-dependent, hyperspherical wave packet method for calculating three-atom state-to-state S-matrix elements. The wave packet is propagated in time using adiabatically adjusting, principal axes hyperspherical coordinates that treat all arrangement channels equivalently, allowing the simultaneous analysis of the products in all three arrangement channels. We take advantage of the symmetry of the potential energy surface and decompose the initial wave packet into its component irreducible representations, propagating each component separately. Each irreducible representation component of the wave packet is analyzed by projecting it onto the hyperspherical basis at a fixed, asymptotic hyperradius, and irreducible representation dependent S-matrix elements are obtained by matching the hyperspherical projections to symmetry-adapted Jacobi coordinate boundary conditions. We obtain arrangement channel-dependent S-matrix elements as linear combinations of the irreducible representation dependent elements. State-to-state H + H(2) and F + H(2) results for zero total angular momentum are presented. PMID:23406125

Crawford, Jeff; Parker, Gregory A

2013-02-01

392

Fine-structure effects in relativistic calculations of the static polarizability of the helium A. Derevianko and W. R. Johnson  

E-print Network

of spin­ spin mixing of helium levels with different values of orbital angular momentum L but the sameFine-structure effects in relativistic calculations of the static polarizability of the helium atom and 1s3p 3 P2 of the helium atom. The calculations of the reduced matrix elements for the resonant terms

Johnson, Walter R.

393

Electron-capture processes of low-energy Si3+, Si4+, and Si5+ ions in collisions with helium atoms  

Microsoft Academic Search

Single- and double-electron-capture cross sections for Siq+ (q=3, 4, and 5) ions in collisions with He atoms have been measured at collision energies of a few hundred to a few thousand eV. The observed cross sections for single-electron capture are found to be of the order of 10-15 cm2, relatively independent of the collision energy, and are generally in agreement

H. Tawara; K. Okuno; C. W. Fehrenbach; C. Verzani; M. P. Stockli; B. D. Depaola; P. Richard; P. C. Stancil

2001-01-01

394

Spin-orbit interaction and large inelastic rates in bismuth-helium collisions S. E. Maxwell,1,* M. T. Hummon,1  

E-print Network

Spin-orbit interaction and large inelastic rates in bismuth-helium collisions S. E. Maxwell,1,* M in heavy atoms. Collisions between paramagnetic atoms and helium can change the spin orientation experimental and theoretical study of cold collisions between bismuth and helium atoms in strong magnetic

Krems, Roman

395

Differential cross-section for positronium formation in electron-atomic hydrogen collisions  

NASA Technical Reports Server (NTRS)

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.

Drachman, R. J.; Omidvar, K.; Mcguire, J. H.

1976-01-01

396

The influence of superfluidity on impurities condensation in liquid helium  

NASA Astrophysics Data System (ADS)

All major aspects of the influence of superfluidity in He II on the processes of condensation of impurities suspended in it have been analyzed. Particular attention is given to the recently discovered phenomenon of impurities coalescence catalysis by quantized vortices in superfluid helium. The presence of quantized vortices not only tremendously accelerates the condensation process for any substance introduced into liquid helium but also gives rise to a completely new product—long and thin nanowires. The role of local overheating, which accompanies coalescence of particles inside superfluid helium, in formation of morphology and structure of impurity-helium condensates, including molecular crystals containing stabilized active atoms, is elucidated.

Gordon, E. B.

2012-11-01

397

Helium vs. Proton Induced Displacement Damage in Electronic Materials  

NASA Technical Reports Server (NTRS)

In this project, the specific effects of displacement damage due to the passage of protons and helium nuclei on some typical electronic materials will be evaluated and contrasted. As the electronic material absorbs the energetic proton and helium momentum, degradation of performance occurs, eventually leading to overall failure. Helium nuclei traveling at the same speed as protons are expected to impart more to the material displacement damage; due to the larger mass, and thus momentum, of helium nuclei compared to protons. Damage due to displacement of atoms in their crystalline structure can change the physical properties and hence performance of the electronic materials.

Ringo, Sawnese; Barghouty, A. F.

2010-01-01

398

Electron-hydrogen-atom elastic and inelastic scattering with screened Coulomb interaction around the n=2 excitation threshold  

NASA Astrophysics Data System (ADS)

The effects of Coulomb interaction screening on electron-hydrogen-atom elastic and excitation scattering around the n=2 threshold have been investigated by using the R-matrix method with pseudostates. The elastic and excitation collision strengths show dramatic changes when the interaction screening length D varies from ? to 3.8 a.u., as a result of the convergence of 1,3S Feshbach resonances to the varying 2s threshold and of the transformation of 1,3P and 1D Feshbach resonances into shape-type resonances when they pass across the 2s and 2p threshold at certain critical value of D, respectively [S. B. Zhang , Phys. Rev. Lett. 104, 023203 (2010)]. The resonance parameters for a large number of D in the range D=?-3.8 a.u. are presented. It is observed that the 1,3P and 1D resonance contributions to the elastic and excitation collision strengths decrease rapidly with decreasing D after the resonance passes the critical D value. The contribution of a 1Se Feshbach resonance to the elastic or excitation collision strength changes into a cusp after the resonance merges into its parent 2s state and immerses into the background with the further decrease of D.

Zhang, Song Bin; Wang, Jian Guo; Janev, R. K.

2010-03-01

399

Warm Breeze from the Starboard Bow: a New Population of Neutral Helium in the Heliosphere  

NASA Astrophysics Data System (ADS)

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.

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

400

Coupled-channel study of rotational excitation of a rigid asymmetric top by atom impact: (HâCO,He) at interstellar temperatures. [cross section convergence, quantum mechanics, pumping model, resonance, Maxwell--Boltzmann distribution, statistical, equilibrium  

Microsoft Academic Search

A quantum mechanical scattering study is carried out to test a collisional pumping model for cooling the 6 and 2 cm doublets of interstellar formaldehyde. The Arthurs and Dalgarno formalism is extended to the collision of an s-state atom with a rigid asymmetric top molecule and applied to rotational excitation of ortho formaldehyde by helium impact. Using a previously determined

B. J. Garrison; W. A. Jr. Lester

1976-01-01

401

The local interstellar helium density  

NASA Technical Reports Server (NTRS)

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.

Freeman, J.; Paresce, F.; Bowyer, S.; Lampton, M.; Stern, R.; Margon, B.

1977-01-01

402

Photoionization of helium atoms irradiated with intense vacuum ultraviolet free-electron laser light. Part I. Experimental study of multiphoton and single-photon processes  

SciTech Connect

The interaction of He atoms with intense vacuum-ultraviolet light of a free-electron laser is investigated using time-of-flight mass spectroscopy and photoelectron spectroscopy. The atoms were irradiated with 100 fs pulses at 95 nm wavelength, which corresponds to {approx}13 eV photon energy. The ionization of He atoms is observed at a peak intensity of 10{sup 10}-10{sup 13} W/cm{sup 2}, which is due both to nonlinear multiphoton ionization with the fundamental wavelength and single-photon ionization with third harmonic radiation of the free-electron laser. The observation of two sharp photoelectron peaks in the kinetic energy spectra, that are separated by the photon energy, is in agreement with the numerical solution of the time-dependent Schroedinger equation. The calculation was done using the fully quantized field and a limited but representative set of basis states. The ionization rate dependence on the laser peak intensity indicates that: (a) The low-energy peak in the photoelectron spectra is mainly due to two-photon absorption of the fundamental, but (b) the high-energy peak at 15.4 eV is probably due to third harmonic FEL radiation. The theoretically predicted contribution from three-photon absorption of the fundamental is of about the same order of magnitude and could not be separated from the third harmonic background signal. Particularly, the photoelectron spectra and He{sup +} time-of-flight data give evidence that the intensity of third harmonic light is high enough to perform single-shot spectroscopy on gas phase samples.

Laarmann, T.; Guertler, P.; Laasch, W.; Schulz, J.; Wabnitz, H.; Moeller, T. [Hamburger Synchrotronstrahlungslabor HASYLAB at Deutsches Elektronen Synchrotron DESY, Notkestr. 85, 22607 Hamburg (Germany); Castro, A.R.B. de [Laboratorio Nacional de Luz Sincrotron LNLS 13084-971 Campinas SP (Brazil) and Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas IFGW-UNICAMP 13083-970 Campinas SP (Brazil)

2005-08-15

403

Double electron capture by protons from helium  

Microsoft Academic Search

The double electron capture process for protons passing through helium is studied using the impact parameter method in the atomic state expansion. The effect of the translatory motion of the electrons and the Pauli principle have been incorporated. Permanent address: Department of Physics, Jadavpur University, Calcutta - 32, India.

K. Roy; S. C. Mukherjee; D. P. Sural

1975-01-01

404

Hyperfine structure in hydrogen and helium ion  

Microsoft Academic Search

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

Savely G. Karshenboima; D. I. Mendeleev

405

The connection between multi-state resonant charge transfer dynamics and many-electron states in atom--metal surface scattering  

NASA Astrophysics Data System (ADS)

For Li+ and Na+ scattering from clean and cesium-covered Cu(001) surfaces, we have measured probabilities to form different final electronic states in the scattered flux as a function of the Cs-induced work-function shift [Delta][phi]. Specifically, positive and negative ion yields for 400 eV Li+ scattering, and the relative yields of excited neutral Li(2p) and Na(3p) for 400 and 100 eV Li+ and 1320 eV Na+ scattering were measured. As we lowered the work function from its clean (metal) surface value, we observed a monotonic decrease in the Li+ yield, a monotonic increase in the Li+ yield, and a peak in the minority Li(2p) channel yield (and the Na(3p) yield). The major trends in the Li/Cu(001) data (and likewise in the Na/Cu(001) data) can be reproduced by use of a multi-state model, developed by Marston and co-workers, of resonant charge transfer. Here we present a new, straightforward explanation of these trends, based upon an examination of the many-electron states of the atom--metal system. Much of the charge transfer dynamics can be understood through the ground state of the interacting Li/Cu(001) system, since the `atom probabilities'--the probabilities that the Li is a Li+, Li(2s), Li(2p), or Li+-tend to equilibrate towards their ground-state values throughout the atom's trajectory. In each of our experiments, the velocity is low enough that the Li/Cu(001) system electronically equilibrates close to the surface, where the atom--metal couplings are large; at small atom--metal separations z, the Li atom probabilities therefore track their ground-state values. As the atom moves along its outgoing trajectory, the couplings decrease exponentially, and eventually the atom probabilities lose track of their ground-state values. Qualitative arguments, based upon general principles of quantum mechanics, allow us to understand the dependence of the ground-state probabilities on the work function [phi] and z. To comprehend the origin of the Li(2p) peak we must consider both the ground-state probabilities and the conditions under which the dynamical probabilities lose track of their ground-state values.

Dahl, E. B.; Behringer, E. R.; Andersson, D. R.; Cooper, B. H.

1998-03-01

406

Dynamics of small mobile helium clusters near tungsten surfaces  

NASA Astrophysics Data System (ADS)

We report the results of a systematic atomic-scale analysis of the dynamics of small mobile helium clusters in tungsten, near tungsten surfaces. These helium clusters are attracted to tungsten surfaces due to an elastic interaction force that drives surface segregation. As the clusters migrate toward the surface, trap mutation and cluster dissociation are activated at rates higher than in the bulk. These kinetic processes are responsible for important structural, morphological, and compositional features in plasma-exposed tungsten, including surface adatoms, near-surface immobile helium-vacancy complexes, and retained helium content. Detailed results are presented for di-helium and tri-helium clusters near low-Miller-index tungsten surfaces.

Hu, Lin; Hammond, Karl D.; Wirth, Brian D.; Maroudas, Dimitrios

2014-08-01

407

Helium in the Martian atmosphere - Thermal loss considerations  

NASA Technical Reports Server (NTRS)

Helium concentrations in the Martian atmosphere are estimated assuming that the helium production on Mars (comparable to its production on earth) via the radioactive decay of uranium and thorium is in steady state equilibrium with its thermal escape. Although nonthermal losses would tend to reduce the estimated concentrations, these concentrations are not necessarily an upper limit since higher production rates and/or a possibly lower effective exospheric temperature over the solar activity cycle could increase them to even higher values. The computed helium concentration at the Martian exobase (200 km) is 8 million atoms/cu cm. Through the lower exosphere, the computed helium concentrations are 30-200 times greater than the Mariner-measured atomic hydrogen concentrations. It follows that helium may be the predominant constituent in the Martian lower exosphere and may well control the orbital lifetime of Mars-orbiting spacecraft.

Levine, J. S.; Keating, G. M.; Prior, E. J.

1974-01-01

408

Helium diffusion behavior and its retention in LaNiAl alloy from molecular dynamic simulations  

NASA Astrophysics Data System (ADS)

Molecular dynamic method has been used to investigate the diffusion behavior of helium atom in the LaNiAl alloy system. The results have shown that diffusion coefficient of helium atom increases as the temperature increases from 300 to 1500 K, which indicates that helium atom gets more active via thermal desorption. The diffusion coefficient in LaNi5 and LaNi4Al are about 1.5 × 10-5 and 1.1 × 10-6 cm2/s at 1300 K, respectively, and the diffusion barrier of He are 1.45 and 0.52 eV, respectively. The helium diffusion is shown to be enhanced with temperature increasing. Compared with metallic La, Ni, Al and Pd, the simulation result implies that helium atom is more stable and difficult to diffuse in LaNi5 and LaNi4Al alloys, which are the most promising materials for helium retention in experiments. Our results indicate the correlation between diffusion behavior of helium atom and capacity of materials for helium retention. Therefore, it can be considered as a feasible method to evaluate the helium retention capacity of materials via determining the diffusion properties of interstitial helium atom.

Wang, Liang; Hu, Wangyu; Deng, Huiqiu

2011-07-01

409

Surface-scattering study of the interaction potential of He atoms with the step edges of the Cu(211) and Cu(511) vicinal surfaces  

SciTech Connect

The diffraction intensities of He atoms scattered from vicinal Cu(211) and Cu(511) surfaces have been measured with a high angular resolution over a wide range of incident energies from 8 to 82 meV. Close-coupling scattering calculations with a corrugated Morse potential were performed to obtain the corrugation parameters for the first three complex Fourier coefficients. The energy-dependent corrugation profiles determined from the best fit indicate that the corrugation predicted by a simple hard-sphere model is considerably smeared out at the small electron densities far from the surface probed by the He atoms. A comparison with Eikonal calculations demonstrates that hard corrugated wall Eikonal models are not adequate for the structural analysis of stepped surfaces. {copyright} {ital 1996 The American Physical Society.}

Miret-Artes, S.; Toennies, J.P.; Witte, G. [Max-Planck-Institut fuer Stroemungsforschung, Bunsenstrasse 10, D-37073 Goettingen (Germany)] [Max-Planck-Institut fuer Stroemungsforschung, Bunsenstrasse 10, D-37073 Goettingen (Germany)

1996-08-01

410

Study of the real part (f') of anomalous scattering factors for the elements of atomic number from Z = 64 to 73 using HPGe detector  

NASA Astrophysics Data System (ADS)

The real part ( f') of the anomalous scattering factors for the targets of atomic number ranging from Z = 64 to 73 (Gd, Dy, Yb, Hf and Ta) are determined using low-energy external bremsstrahlung (EB) radiations. In this method, the EB photons are produced by beta particles from a weak beta source of 90Sr - 90Y in a nickel foil. The emitted EB photons are incident on the elemental targets of our study and the transmitted spectrum of the emerging photons from the target is measured using an ORTEC-made High-Purity Germanium (HPGe) detector coupled to an 8 K multichannel analyzer. The transmitted spectra show a sharp decrease in intensity at the K shell binding energies of the target atoms. The regions around the decreased portion have been used to determine the real part of the anomalous scattering factors. The experimentally measured values are found to be in good agreement with the available theoretical values.

Hosur, Savita B.; Naik, L. R.; Badiger, N. M.

2013-05-01

411

Protein Dynamics and Stability: The Distribution of Atomic Fluctuations in Thermophilic and Mesophilic Dihydrofolate Reductase Derived Using Elastic Incoherent Neutron Scattering  

SciTech Connect

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.

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

412

A Study of the Surface Properties of the Mixed Crystal KTa_xNb_1-xO3 (KTN) Using Helium Atom Scattering  

NASA Astrophysics Data System (ADS)

Experimental results, from the study of the KTN surface properties, are presented. The measurements from in situ cleaved samples include ranges of x from 0.06 to 0.52, different substrate temperatures (80-375 K), and different beam energies (29 and 38 meV). The observations include: i) an initial metastable structure which forms on cleaving but disappears quickly with time, ii) measurements of steps on the surface which do not always reflect the unit cell dimension, iii) surface structure related to the bulk structural phase transitions which occur at different sample temperatures, iv) a competition between the Ta and Nb doping levels leading to structures emerging from microstructure domains, v) large hysteresis especially for x=0.52, and vi) a collection of surface dynamical results. The latter includes an Einstein mode at approximately 14 meV believed due to vibration of the K ions. There is also an overtone of this mode at about 27 meV which is weak in intensity. A second Einstein mode near 6 meV is observed at room temperature and for the x=0.52 sample shows dispersion going from the Einstein behavior at 80 K to a dispersive form at 190 K.

Skofronick, J. G.; Trelenberg, T. W.; Akhadov, E. A.; Safron, S. A.; van Winkle, D. H.; Boatner, L. A.; Flaherty, F. A.

2002-03-01

413

A Study of the Surface Properties of the Mixed Crystal KTa_xNb_1-xO3 (KTN) Using Helium Atom Scattering  

Microsoft Academic Search

Experimental results, from the study of the KTN surface properties, are presented. The measurements from in situ cleaved samples include ranges of x from 0.06 to 0.52, different substrate temperatures (80-375 K), and different beam energies (29 and 38 meV). The observations include: i) an initial metastable structure which forms on cleaving but disappears quickly with time, ii) measurements of

J. G. Skofronick; T. W. Trelenberg; E. A. Akhadov; S. A. Safron; D. H. van Winkle; L. A. Boatner; F. A. Flaherty

2002-01-01

414

Coinage metal exciplexes with helium atoms: a theoretical study of M*(2L)He(n) (M = Cu, Ag, Au; L = P,D).  

PubMed

The structure and energetics of exciplexes M*((2)L)He(n) (M = Cu, Ag and Au; L = P and D) in their vibrational ground state are studied by employing diffusion Monte Carlo (DMC). Interaction potentials between the excited coinage metals and He atoms are built using the Diatomics-in-Molecule (DIM) approach and ab initio potential curves for the M((2)L)-He dimers. Extending our previous work [Cargnoni et al., J. Phys. Chem. A, 2011, 115, 7141], we computed the dimer potential for Au in the (2)P and (2)D states, as well for Cu and Ag in the (2)D state, employing basis set superposition error-corrected Configuration Interaction calculations. We found that the (2)? potential correlating with the (2)P state of Au is substantially less binding than for Ag and Cu, a trend well supported by the M(+) ionic radiuses. Conversely, the interaction potentials between a (n - 1)d(9)ns(2 2)D metal and He present a very weak dependency on M itself or the projection of the angular momentum along the dimer axis. This is due to the screening exerted by the ns(2) electrons on the hole in the (n - 1)d shell. Including the spin-orbit coupling perturbatively in the DIM energy matrix has a major effect on the lowest potential energy surface of the (2)P manifold, the one for Cu allowing the formation of a "belt" of five He atoms while the one for Au being completely repulsive. Conversely, spin-orbit coupling has only a weak effect on the (2)D manifold due to the nearly degenerate nature of the diatomic potentials. Structural and energetic results from DMC have been used to support experimental indications for the formation of metastable exciplexes or the opening of non-radiative depopulation channels in bulk and cold gaseous He. PMID:24072257

Cargnoni, Fausto; Ponti, Alessandro; Mella, Massimo

2013-11-14

415

PHYS 385 Lecture 27 -Poly-electron atoms 27 -1 2003 by David Boal, Simon Fraser University. All rights reserved; further copying or resale is strictly prohibited.  

E-print Network

's important: · helium atom by approximation · spin wavefunctions for helium Text: Gasiorowicz, Chap. 18 Helium is helium. The relevant coordinates for the helium atom can be defined as The Hamiltonian operator,2) as o(1,2) = o(1)o(2) where spin-statistics are ignored for the moment. The single particle wavefunction

Boal, David

416

Elastic cross sections for electron scattering from GeF4: Predominance of atomic-F in the high-energy collision dynamics  

NASA Astrophysics Data System (ADS)

We report absolute differential cross sections (DCSs) for elastic electron scattering from GeF4. 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 GeF4 elastic DCSs to similar data for scattering from CF4 and SiF4. All these three species possess Td 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 GeF4 elastic integral cross sections are derived and compared to our IAM-SCAR computations and with independent total cross section values.

Kato, H.; Suga, A.; Hoshino, M.; Blanco, F.; García, G.; Limão-Vieira, P.; Brunger, M. J.; Tanaka, H.

2012-04-01

417

Dynamic response of target electrons on elastic scattering cross sections for heavy-ion impact on a high-Z atom  

NASA Astrophysics Data System (ADS)

Large-angle elastic scattering cross sections were measured for medium energy He+ and Ne+ ions impact on Ni, Sb, and Hf atoms and the results are compared with those calculated using screened interatomic potentials. As the screened Coulomb potential, we employed the Molière, Ziegler-Biersack-Littmark (ZBL), and that calculated numerically by solving the Poisson equation applied to the Hartree-Fock (HF) atomic model. For He+ impact, the ZBL and HF (He2+ is assumed) potentials reproduced well the observed scattering cross sections but the Molière potential underestimated them significantly. Surprisingly, however, for Ne+ impact on Sb and Hf, the observed scattering cross sections were much larger than those calculated from all the above screened interatomic potentials, although Ne10+ was assumed for the HF potential. In a large-angle collision, a projectile heavy ion attracts the target electrons to distort the electron cloud and as a result it changes the electric field upon the projectile. The observed scattering cross sections are reproduced well by assuming a simple model that the center of gravity of the target electrons slightly shifts toward the projectile by 0.09 0.12 Å for Hf and 0.066 0.070 Å for Sb from the nucleus.

Hoshino, Yasushi; Kido, Yoshiaki

2003-07-01

418

Comparison of classical and quantal calculations of helium three-body recombination  

SciTech Connect

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.

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

419

Atom Builder  

NSDL National Science Digital Library

This website allows the user to build their own Carbon Atom out of elementary particles (up quarks, down quarks, and electrons). As protons, neutrons, and electrons are added to the atom, the atom changes from one element to another. From hydrogen the atom changes into helium, then lithium, and on up through the Periodic table until it finally becomes carbon. If, while being built, the balance between protons, neutrons, and electrons is not sufficiently maintained, the atom will either become radioactive and decay, or become so ionized that it will attach itself to a molecule outside the building area. In either case, the user must start over. The activity is over when the atom changes into carbon. Read the guides for assistance.

2010-12-22

420

An Ordered State of Dislocations in Solid Helium  

NASA Astrophysics Data System (ADS)

An ordered state of dislocations, see e.g. [1], is disclosed from neutron inelastic scattering data taken from solid helium at 40mK and a pressure of about 30bar. A characteristic feature is the phonon gap at the origin of about 0.15 meV, which reveals the non-equilibrium state of stressed helium created by rapid cooling with the blocked-capillary method. Energy gain scattering starts to appear at a temperature of 0.5 K that underlines the non-equilibrium state of stressed helium and the non-applicability of the detailed balance. The increasing thermal occupation of phonon-states observed as increasing intensity in energy gain scattering builds to a phase transition close to 1.4K. The creation of a helium single crystal with hcp-structure in thermal equilibrium [2] is observed at this temperature. This phase transition is in agreement with the vanishing quasi two-dimensional superfluid helium in solid helium confined in aerogel around 1.3K [3]. The event of the ``supersolid'' transition around 100mK is not observed in the two neutron scattering experiments.[4pt] [1] G. S"oyler, et. al., Phys. Rev. Lett. 103, 175301 (2009)[0pt] [2] E. Blackburn, et. al., PRAMANA 71, 673 (2008)[0pt] [3] H.Lauter, et. al., Phys. Rev. Lett. 107, 265301 (2011)

Lauter, Hans Jochen; Krotscheck, Eckhard; Kats, Efim; Herwig, Kenneth; Podlesnyak, Andrey; Souleymane, Diallo; Henry, Glyde; Savici, Andreii

2013-03-01

421

Cryogenic liquid-jet breakup in two-fluid atomizers  

NASA Technical Reports Server (NTRS)

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.

Ingebo, Robert D.

1991-01-01

422

Status of electron temperature and density measurement with beam emission spectroscopy on thermal helium at TEXTOR  

NASA Astrophysics Data System (ADS)

Beam emission spectroscopy on thermal helium is used at the TEXTOR tokamak as a reliable method to obtain radial profiles of electron temperature Te(r, t) and electron density ne(r, t). In this paper the experimental realization of this method at TEXTOR and the status of the atomic physics employed as well as the major factors for the measurement's accuracy are evaluated. On the experimental side, the hardware specifications are described and the impact of the beam atoms on the local plasma parameters is shown to be negligible. On the modeling side the collisional-radiative model (CRM) applied to infer ne and Te from the measured He line intensities is evaluated. The role of proton and deuteron collisions and of charge exchange processes is studied with a new CRM and the impact of these so far neglected processes appears to be of minor importance. Direct comparison to Thomson scattering and fast triple probe data showed that for high densities ne > 3.5 × 1019 m-3 the Te values deduced with the established CRM are too low. However, the new atomic data set implemented in the new CRM leads in general to higher Te values. This allows us to specify the range of reliable application of BES on thermal helium to a range of 2.0 × 1018 < ne < 2.0 × 1019 m-3 and 10 eV < Te < 250 eV which can be extended by routine application of the new CRM.

Schmitz, O.; Beigman, I. L.; Vainshtein, L. A.; Schweer, B.; Kantor, M.; Pospieszczyk, A.; Xu, Y.; Krychowiak, M.; Lehnen, M.; Samm, U.; Unterberg, B.; TEXTOR Team

2008-11-01

423

Neutron scattering studies of short-range order, atomic displacements, and effective pair interactions in a null-matrix Ni0.5262Pt0.48 crystal  

NASA Astrophysics Data System (ADS)

The best known exception to the Heine-Sampson and Bieber-Gauthier arguments for ordering effects in transition metal alloys (similar to the Hume-Rothery rules) is a NiPt alloy, whose phase diagram is similar to that of the CuAu system. Using neutron scattering we have investigated the local atomic order in a null-matrix Ni0.5262Pt0.48 single crystal. In a null-matrix alloy, the isotopic composition is adjusted so that the average neutron scattering length vanishes ( Ni62 has a negative scattering length nearly equal in magnitude to that of Pt). Consequently, all contributions to the total scattering depending on the average lattice are suppressed. The only remaining components of the elastic scattering are the short-range order (SRO) and size effect terms. These data permit the extraction of the SRO parameters (concentration-concentration correlations) as well as the displacement parameters (concentration-displacement correlations). Using the Krivoglaz-Clapp-Moss theory, we obtain the effective pair interactions (EPIs) between near neighbors in the alloy. The results can be used by theorists to model the alloy in the context of the electronic theory of alloy phase stability, including a preliminary evaluation of the local species-dependent displacements. Our maps of V(q) , the Fourier transform of the EPIs, show very similar shapes in the experimental and reconstructed data. This is of importance when comparing to electronic structure calculations.

Rodriguez, J. A.; Moss, S. C.; Robertson, J. L.; Copley, J. R. D.; Neumann, D. A.; Major, J.

2006-09-01

424

The Primordial Helium Abundance  

Microsoft Academic Search

I present a brief review on the determination of the primordial helium abundance by unit mass, Yp. I discuss the importance of the primordial helium abundance in: (a) cosmology, (b) testing the standard big bang nucleosynthesis, (c) studying the physical conditions in H II regions, (d) providing the initial conditions for stellar evolution models, and (e) testing the galactic chemical

Manuel Peimbert

2008-01-01

425

Metastable helium spectroscopy on simple metals: Comparison between low and high work function substrates  

NASA Astrophysics Data System (ADS)

In this work we investigate the deexcitation process of a slow metastable helium atom (He*) in its triplet state on simple metal surfaces. We compute the electronic properties of the interacting He*-metal (jellium-like) system, using the embedding Green's function method, within the framework of density functional theory. The Auger deexcitation rates are calculated at different distances from the surface using the Fermi golden rule, and the energy distribution of the emitted electrons is obtained by integrating the Auger rates along the classical trajectory followed by the atom in the scattering process. We present the results for three metal surfaces (Al, Na, and Cs) which are sufficiently different to span the distinct deexcitation mechanisms taking place when the He* interacts with the surface: resonant ionization + Auger neutralization for high work function substrates, and Auger deexcitation for low work function ones. Our results for the deexcitation spectral profiles are in good agreement with the experimental ones.

Trioni, M. I.; Butti, G.; Bonini, N.; Brivio, G. P.

2005-08-01

426

Quantitative study of two-and three-dimensional strong localization of matter waves by atomic scatterers  

E-print Network

Quantitative study of two- and three-dimensional strong localization of matter waves by atomic study the strong localization of atomic matter waves in a disordered potential created by atoms pinned at the nodes of a lattice, for both three-dimensional (3D) and two-dimensional (2D) systems. The localization

Paris-Sud XI, Université de

427

Observation of Collective Friction Forces due to Spatial Self-Organization of Atoms: From Rayleigh to Bragg Scattering  

E-print Network

Observation of Collective Friction Forces due to Spatial Self-Organization of Atoms: From Rayleigh demonstrate that emission-induced self-organization of two-level atoms can effect strong damping of the sample's center-of-mass motion. When illuminated by far-detuned light, cold cesium atoms assemble into a density

Vuletic, Vladan

428

Analysis of decomposition of impurity-helium solid phase  

NASA Astrophysics Data System (ADS)

The elemental composition of the impurity-helium solid phase (IHSP) grown by injecting of a gas jet containing Ne, Ar, Kr, and Xe atoms and N2 molecules into superfluid HeII is studied. The measured stoichiometric ratios S=NHe/NIm are much larger than the values predicted by the model of frozen together monolayer helium clusters. The theoretical possibility of freezing together of two-layered clusters is justified in the continual model of the helium subsystem of IHSP which fills the space between rigid impurity centers. Regularities of decomposition of "dry" samples (extracted from liquid helium) are analyzed in the temperature range 1.5-12 K under pressures from 10 to 500 torr. Two stages of sample decomposition are discovered: a slow stage accompanied by cooling and a rapid stage accompanied by heat release. These results suggest the presence of two types of helium in IHSP, viz., weakly bound and strongly bound helium which can be attributed respectively to the second and first coordination spheres of helium formed around heavy impurity particles. A tendency to elevation of the thermal stability of impurity-helium (IH) samples upon an increase in the mass of impurity center has been observed. An increase in the helium vapor pressure above the samples also increases their stability. It is found that the decomposition of IH samples containing nitrogen atoms in the temperature range 3-4.5 K is accompanied with luminescence induced by recombination of atoms. This indicates the possibility of a wide range of chemical reactions in solidified helium.

Boltnev, R. E.; Gordon, E. B.; Krushinskaya, I. N.; Martynenko, M. V.; Pelmenev, A. A.; Popov, E. A.; Khmelenko, V. V.; Shestakov, A. F.

1997-07-01

429

HERSCHEL Sounding Rocket Mission Observations of the Helium Corona  

NASA Astrophysics Data System (ADS)

The HERSCHEL (Helium Resonant Scattering in the Corona and Heliosphere) investigation successfully obtained unprecedented images of the helium and hydrogen components of the solar corona out to 3 solar radii during a suborbital flight on 14 September 2009. Preliminary analysis of these observations indicates the spatial distribution of the helium abundance and outflow velocity provides powerful diagnostics for the source and dynamics of the slow solar wind during the time of solar minimum activity. An analysis of co-temporal STEREO EUVI data to derive the temperature of low coronal structures associated with the regions of enhanced helium abundance observed by HERSCHEL provides evidence the relative first ionization potential (FIP) of helium and hydrogen may play an important role in the observed abundance distribution. NRL was supported by the Office of Naval Research and NASA under NDPRS6598G.

Newmark, Jeffrey; Moses, J.; Antonucci, E.; Fineschi, S.; Abbo, L.; Telloni, D.; Auchere, F.; Barbey, N.; Romoli, M.

2010-05-01

430

Elastic scattering of tritons by helium-4  

SciTech Connect

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.

Jarmie, N.; Correll, F.D.; Brown, R.E.; Hardekopf, R.A.; Ohlsen, G.G.

1980-11-01

431

(3) He NMR studies on helium-pyrrole, helium-indole, and helium-carbazole systems: a new tool for following chemistry of heterocyclic compounds.  

PubMed

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. Copyright © 2014 John Wiley & Sons, Ltd. PMID:25228253

Radula-Janik, Klaudia; Kupka, Teobald

2015-02-01

432

Exotic Atoms and Muonium  

NASA Astrophysics Data System (ADS)

In exotic atoms, one of the atomic electrons is replaced by a negatively charged particle, whereas muonium consists of a positive muon and an electron. After a general review of the theoretical and experimental aspects, the present knowledge of this field is summarized. These include muonium and the application of the muon spin resonance method in solid-state physics and chemistry, muonic hydrogen atoms, muonic molecules and muon-catalyzed fusion, pionic hydrogen atoms and their use in chemistry, testing quantum electrodynamics on heavy muonic atoms, measuring particle and nuclear properties using hadronic atoms, and testing basic symmetry principles with antiprotonic helium atoms and antihydrogen.

Horváth, D.

433

Photoionization of Alkali-Doped Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

Superfluid helium droplets (He_N) provide a cold, weakly-interacting environment for the investigation of weakly bound molecules. Whereas the host-dopant interaction is weak for neutral molecules, ion impurities may be surrounded by frozen shells of polarized helium atoms. An extreme example of the different behavior is given by alkali metal impurities that stay at the surface of the droplet as neutrals but immerse into the droplet as cations releasing a considerable amount of binding energy. We report measurements of the photoionization efficiency for the rubidium-He_N and cesium-He_N systems and find that the ionization threshold is lowered compared with the free atoms and is in good agreement with Rydberg state spectroscopy of these systems. The corresponding energy shift increases when going from heavy to light alkali metals and from small to large helium droplets. Both effects can be explained by the difference in polarization energies associated with submerged alkali metal cations. The findings agree qualitatively well with recent calculations of helium snowball formation around alkali metal cations. M. Theisen, F. Lackner, G. Krois, and W. E. Ernst, J. Phys. Chem. Lett. 2, 2778 (2011). F. Lackner, G. Krois, M. Theisen, M. Koch, and W. E. Ernst, Phys. Chem. Chem. Phys. 13, 18781 (2011). D. E. Galli, D. M. Ceperley, and L. Reatto, J. Phys. Chem. A 115, 7300 (2011).

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

2012-06-01

434

He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth. Progress report, May 1, 1991--April 30, 1992  

SciTech Connect

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.

Not Available

1992-05-01

435

The Descending Helium Balloon  

ERIC Educational Resources Information Center

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.

Helseth, Lars Egil

2014-01-01

436

Superfluidity of helium-3  

Microsoft Academic Search

This article presents a phenomenological dynamic phase transition theory–modeling and analysis–for liquid helium-3. We derived two new models, for liquid helium-3 with or without applied field, by introducing three wave functions and using a unified dynamical Ginzburg–Landau model. The analysis of these new models leads to predictions of existence of (1) a metastable region, (2) a new phase C in

Tian Ma; Shouhong Wang

2008-01-01

437

Superfluid helium tanker instrumentation  

Microsoft Academic Search

An instrumentation system for a 1992 Space Shuttle flight demonstration of superfluid-helium tanker and transfer technology is presented. The system measures helium temperatures, pressures, flow rates and mass and the amount of liquid or vapor present. It consists of analog and digital portions which provide a fault-tolerant, compact, relatively lightweight, space-qualified electronics system. The data-processing hardware and software are ground-commandable,

C. E. Woodhouse; A. Kashani; A. T. Lukemire

1989-01-01

438

H-He elastic scattering at low energies: Contribution of nonzero partial waves  

SciTech Connect

The present study reports the nonzero partial wave elastic cross sections together with s-wave results for the scattering of an antihydrogen atom off a gaseous helium target at thermal energies (up to 10{sup -2} a.u.). We have used a nonadiabatic atomic orbital method having different basis sets to investigate the system. The consideration of all the significant partial waves (up to J=24) reduces the oscillatory nature present in the individual partial wave cross section. The added elastic cross section is almost constant up to 10{sup -7} a.u. and then decreases steadily and very slowly with increasing energy.

Sinha, Prabal K.; Ghosh, A.S. [Department of Physics, Bangabasi College, 19, Raj Kumar Chakravorty Sarani, Kolkata 700 009 (India); Department of Theoretical Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700 032 (India)

2005-01-01

439

Helium liquefaction using cryorefrigerators  

NASA Astrophysics Data System (ADS)

A two-stage Gifford-McMahon refrigerator with a Joule-Thomson (J-T) stage connected in series, was extended to a small helium liquefier. The plant can operate automatically. Helium is liquefied within the J-T cycle, directly after the J-T valve, into a 3l tank. This liquid He is used for the indirect cooling of an externally accessible sample chamber, either by using helium contact gas, or by means of liquid He condensed from an external helium gas source. The second design is meant for laboratory applications. The liquid helium tank is not incorporated in the J-T cycle, but thermally connected to the J-T stage of the refrigerator. The He gas from an external source is then condensed into the 2l tank. The liquid helium is accessible via a top-loading sample tube. The refrigerating capacity of both devices is 2W at 4.5K. The cleaning procedures for the He gas to be condensed into the tanks, and the production of temperatures below 4.2K in the He bath are described.

Forth, Hans-Joachim

1986-12-01

440

High-field harmonic generation in helium  

SciTech Connect

We observe harmonics of 526-nm laser light up to the 45th order, 11.7 nm, in helium. We discuss the extension of the harmonic plateau with increasing laser intensity. The data suggest that the highest harmonic order produced depends on the highest intensity seen by the atom before photoionization. Harmonics are generated predominantly from neutrals. Harmonic generation from ions is weak owing to poor phase matching between the fundamental and harmonic fields at high electron densities.

Crane, J.K.; Perry, M.D.; Herman, S. (Laser Program, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 (United States)); Falcone, R.W. (Department of Physics, University of California, Berkeley, Berkeley, California 94720 (United States))

1992-09-15