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1

Scattering of helium atoms from rare-gas-plated graphite  

SciTech Connect

Accurate close-coupling calculations are performed for helium interacting with rare-gas-plated graphite. The atom-surface potentials used in this study are based upon pairwise additivity of atom-atom interactions, and the role of three-body forces is explored. Comparison between theoretical calculations which in turn include and exclude three-body forces indicates that experimental data are sensitive to three-body forces. Further comparison between theoretical calculations and experimental data for helium scattering from either krypton- or xenon-plated graphite yields semiquantitative agreement. Inasmuch as there are no adjustable parameters employed in the input potentials, it is concluded that these systems are well understood.

Schwartz, C.

1986-08-15

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

Helium atom scattering from isolated CO molecules on copper(001) A. P. Graham, F. Hofmann, and J. P. Toennies  

E-print Network

Helium atom scattering from isolated CO molecules on copper(001) A. P. Graham, F. Hofmann, and J. P 1996 Angular distributions have been measured for helium atoms scattering from isolated CO molecules with difficulties. Helium atom scattering HAS , on the other hand, can, at least for simple systems, also detect

Manson, Joseph R.

4

Helium atom scattering from isolated CO molecules on copper(001) A. P. Graham, F. Hofmann, and J. P. Toennies  

E-print Network

Helium atom scattering from isolated CO molecules on copper(001) A. P. Graham, F. Hofmann, and J. P 1996! Angular distributions have been measured for helium atoms scattering from isolated CO molecules with difficulties. Helium atom scattering ~HAS!, on the other hand, can, at least for simple systems, also detect

Manson, Joseph R.

5

Atomic hydrogen modification of copper surfaces studied by helium atom scattering  

NASA Astrophysics Data System (ADS)

The structure and bonding of single crystal copper surfaces under irradiation by H atoms is investigated by helium atom scattering under UHV conditions. The effect of H atoms on Cu?Cu bonding is deduced from the temperature dependence of the intensity of the specular He reflection from a clean Cu(110) surface and for irradiation with an effusive H atom beam. The Debye temperature deduced from the attenuation of the specular reflection decreases from 340 ± 10 K to 287 ± 10 K upon exposure to hydrogen atoms, implying a decrease in the surface Rayleigh phonon frequency by the H?Cu interaction. Also, the chemical reduction of a Cu(100)-(2 2× 2) R45°- O surface by irradiation with H atoms at 723 K is investigated. H atoms are shown to be an effective means for removing oxide impurities from Cu surfaces.

Miyake, T.; Petek, H.

1997-11-01

6

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

NASA Astrophysics Data System (ADS)

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 × 1) commensurate monolayer solid of H2/NaCl(001) and a conjectured p(1 × 1) commensurate monolayer solid of H2/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.; Bruch, L. W.; Dammann, B.

2013-03-01

7

Positronium formation in the n = 2 level in positron scattering from hydrogen and helium atoms  

SciTech Connect

A distorted-wave model (Phys. Rev. A 27, 1904 (1983); 28, 2180 (1983)) is applied to calculate the formation of positronium in the n = 2 states in e/sup +/ scattering from hydrogen and helium atoms. The incident wave is represented by a polarized-orbital method. The first-Born-approximation results of the 2p-excited-state capture cross section in the case of helium is reported for the first time. The first Born approximation is found to be unsuitable for prediction of the rearrangement processes. The present total (ground- and excited-state) positronium-formation cross sections have been compared with the corresponding observed values of Fornari et al. (Phys. Rev. Lett. 51, 2276 (1983)) and of Charlton et al. (J. Phys. B 16, L465 (1983)).

Khan, P.; Mazumdar, P.S.; Ghosh, A.S.

1985-03-01

8

Vibrational dynamics and surface structure of Bi(111) from helium atom scattering measurements.  

PubMed

The Bi(111) surface was studied by elastic scattering of helium atoms at temperatures between 118 and 423 K. The observed diffraction patterns with clear peaks up to third order were used to model the surface corrugation using the eikonal approximation as well as the GR method. Best fit results were obtained with a rather large corrugation height compared to other surfaces with metallic character. The corrugation shows a slight enhancement of the surface electron density in between the positions of the surface atoms. The vibrational dynamics of Bi(111) were investigated by measurements of the Debye-Waller attenuation of the elastic diffraction peaks and a surface Debye temperature of (84 ± 8) K was determined. A decrease of the surface Debye temperature at higher temperatures that was recently observed on Bi nanofilms could not be confirmed in the case of our single-crystal measurements. PMID:22354901

Mayrhofer-Reinhartshuber, M; Tamtögl, A; Kraus, P; Rieder, K H; Ernst, W E

2012-03-14

9

Reconstruction of the CoGa(100) surface studied by thermal-energy helium-atom scattering, LEED, and AES  

NASA Astrophysics Data System (ADS)

The surface structure of CoGa(100) has been studied by means of thermal-energy helium-atom scattering (TEAS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). A c(4×2) surface reconstruction is revealed by LEED and TEAS measurements. Sometimes this reconstruction is mixed with a (5×5) reconstruction, which is found to be due to a very minor contamination with oxygen. Only double-layer steps are found on the surface. Above 500 K, the reconstructed layer starts to disorder, but short-range ordering in this layer is still observed until 700 K. Near 900 K, segregation of Co is observed with AES. The increase of the cobalt concentration is consistent with filling up the 0.25 ML, necessary for the c(4×2) reconstruction, to a completed monolayer at 900 K. This interpretation implies that the surface is always terminated by Co.

Pan, F. M.; Pflitsch, Ch.; David, R.; Verheij, L. K.; Franchy, R.

2001-03-01

10

Approximating the Helium Wavefunction in Positronium-Helium Scattering  

NASA Technical Reports Server (NTRS)

In the Kohn variational treatment of the positronium- hydrogen scattering problem the scattering wave function is approximated by an expansion in some appropriate basis set, but the target and projectile wave functions are known exactly. In the positronium-helium case, however, a difficulty immediately arises in that the wave function of the helium target atom is not known exactly, and there are several ways to deal with the associated eigenvalue in formulating the variational scattering equations to be solved. In this work we will use the Kohn variational principle in the static exchange approximation to d e t e e the zero-energy scattering length for the Ps-He system, using a suite of approximate target functions. The results we obtain will be compared with each other and with corresponding values found by other approximation techniques.

DiRienzi, Joseph; Drachman, Richard J.

2003-01-01

11

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

SciTech Connect

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

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

1997-07-01

12

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

E-print Network

-spin systems is consid- ered. The study is based on a calculation of the differential inelastic reflection to experimental studies. In this paper we examine the possibility of extending the applicability of He* atom atoms (He*) from surfaces of magnetic insulators to study the dynamical properties of surface electron

Kais, Sabre

13

Positronium and Electron Scattering on Helium  

NASA Technical Reports Server (NTRS)

A recent work [1] establishes experimentally that Positronium scattering by atoms of various elements is surprisingly close in total cross-section to that of an isolated electron of the same velocity. In this work we will look at the scattering of Ps on Helium and compare it to a determination of the scattering of an e- with the same element. For both the Ps scattering and the e- scattering on He, we assume the symmetrization of the e- with the closed shell He electrons is the dominant interaction. A local effective potential employed in [2] and [3] is used to model the electron exchange and cross- sections are determined for a set of partial waves. For the Ps scattering we include as a secondary effect the Van der Waals interaction. For single e- scattering of He, we also employ a short range Coulomb potential and dispersion as contributing effects. Results of the cross-sections determined in each case are then compared

DiRienzi, Joseph

2011-01-01

14

Helium-antihydrogen scattering at low energies  

NASA Astrophysics Data System (ADS)

We calculate cross sections for helium-antihydrogen scattering for energies up to 0.01 atomic unit. Our calculation includes elastic scattering, direct antiproton-alpha particle annihilation and rearrangement into He^+\\bar p and ground-state positronium. Elastic scattering is calculated within the Born-Oppenheimer approximation using the potential calculated by Strasburger et al (2005 J. Phys. B: At. Mol. Opt. Phys. 38 3091). Matrix elements for rearrangement are calculated using the T-matrix in the distorted wave approximation, with the initial state represented by Hylleraas-type functions. The strong force, leading to direct annihilation, was included as a short-range boundary condition in terms of the strong-force scattering length.

Jonsell, S.; Armour, E. A. G.; Plummer, M.; Liu, Y.; Todd, A. C.

2012-03-01

15

Precision spectroscopy of the helium atom.  

SciTech Connect

Persistent efforts in both theory and experiment have yielded increasingly precise understanding of the helium atom. Because of its simplicity, the helium atom has long been a testing ground for relativistic and quantum electrodynamic effects in few-body atomic systems theoretically and experimentally. Comparison between theory and experiment of the helium spectroscopy in 1s2p{sup 3}P{sub J} can potentially extract a very precise value of the fine structure constant a. The helium atom can also be used to explore exotic nuclear structures. In this paper, we provide a brief review of the recent advances in precision calculations and measurements of the helium atom.

Hu, S.-M.; Lu, Z.-T.; Yan, Z.-C.; Physics; Univ. of Science and Technology of China; Univ. of Chicago; Univ. of New Brunswick

2009-06-01

16

Positronium and electron scattering on Helium  

NASA Astrophysics Data System (ADS)

A recent work [1] establishes experimentally that Positronium scattering by atoms of various elements is surprisingly close in total cross-section to that of an isolated electron of the same velocity. In this work we will look at the scattering of Ps on Helium and compare it to a determination of the scattering of an e- with the same element. For both the Ps scattering and the e- scattering on He, we assume the symmetrization of the e- with the closed shell He electrons is the dominant interaction. A local effective potential employed in [2] and [3] is used to model the electron exchange and cross- sections are determined for a set of partial waves. For the Ps scattering we include as a secondary effect the Van der Waals interaction. For single e- scattering of He, we also employ a short range Coulomb potential and dispersion as contributing effects. Results of the cross-sections determined in each case are then compared. [4pt] [1] S. J. Bromley, S. Armitage, J. Beale, D. E. Leslie, A. I. Williams, G. Laricchia, Science 330, 789 (2010)[0pt] [2] R. J. Drachman, S.K. Houston, J. Phys. B: At. Mol. Phys. 3 1657 (1970)[0pt] [3] J. Di Rienzi, R. J. Drachman, J. Phys. B. 36 2409 (2003)

di Rienzi, Joseph; Drachman, Richard

2011-06-01

17

Characterisation and O 2 titration of CO islands on Pt 100: helium atom scattering and reactive sticking probability measurements  

NASA Astrophysics Data System (ADS)

Thermal energy atom scattering (TEAS) has been used simultaneously with molecular beam adsorption and thermal desorption to probe the lateral distribution of CO on a Pt 100 single-crystal surface. On the initial hex-R phase at 350 K, (1 × 1) island growth occurs at a constant local coverage ( ?(1 × 1)CO) of 0.4 ML. However, during desorption the surface remains wholly in the (1 × 1) state until ( ?(1 × 1)CO) ? 0.25 ML. Subsequent reconstruction to hex occurs at a constant local coverage of 0.19 ML in the remaining (1 × 1) domains. Hysteresis is not observed for the pre-prepared (1 × 1) surface, on which a random CO distribution is observed during adsorption. The scattering cross-section ? for a single CO molecule on the hex-R and (1 × 1) surfaces at 350 K has been determined as 71 ± 10 and 130 ± 18Å 2 respectively. The behaviour during oxidation of (1 × 1)-CO islands on the initial hex-R surface prepared by either adsorption or desorption is found to be consistent with the TEAS data. The first sticking probabilities for O 2 and CO on the CO ad-freed and O ad-freed (1 × 1) phase of Pt 100 are also reported.

Pasteur, A. T.; Guo, X.-C.; Ali, T.; Gruyters, M.; King, D. A.

1996-11-01

18

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

19

Positronium formation in positron-helium scattering  

SciTech Connect

The positronium-formation cross sections in positron-helium scattering have been calculated with the use of a distorted-wave polarized-orbital method from the threshold to 100 eV. The results with and without the matrix elements involving the distorted target wave functions are found to differ appreciably. The results of the first Born approximation are not expected to be correct even at the incident-positron energy 100 eV. The measured values at 20 eV are found to be less than (1/2) of the present predicted values. The sharp rise of the formation cross section within the ore-gap region as observed by Charlton et al. has also been noticed by us. The minimum in the differential cross section has been found at all energies as in the case of hydrogen atom.

Khan, P.; Ghosh, A.S.

1983-10-01

20

Second Sound Scattering in Superfluid Helium  

Microsoft Academic Search

Focusing cavities are used to study the scattering of second sound in liquid helium II. The special geometries reduce wall interference effects and allow measurements in very small test volumes. In a first experiment, a double elliptical cavity is used to focus a second sound wave onto a small wire target. A thin film bolometer measures the side scattered wave

Thomas Rosgen

1985-01-01

21

A comparative study of the He-Sb(111) interaction potential from close-coupling calculations and helium atom scattering experiments  

NASA Astrophysics Data System (ADS)

The exact elastic close-coupling formalism is used to compare the performance of several interaction potentials suggested in literature for describing the measured elastic diffraction peak intensities in helium scattering experiments. The coupling parameters have been analytically calculated for the corrugated Morse potential on a hexagonal surface structure and adapted for usage with similar interaction potentials. The potentials used have been fitted to previously known bound state energies complemented by two additional levels which are found by improving energy resolution. It is established that the shifted Morse potential reproduces the experimental He-Sb(111) bound state more closely than the other considered potential shapes. The performance of several interaction potentials in describing the elastic scattering intensities is presented and discussed. Morse and Morse-related potentials provide the best compromise for the description of elastic scattering intensities. The different effects of the potential shape were determined by comparing the calculated scattering intensities.

Kraus, Patrick; Mayrhofer-Reinhartshuber, Michael; Gösweiner, Christian; Apolloner, Florian; Miret-Artés, Salvador; Ernst, Wolfgang E.

2014-12-01

22

Field Ionization detection of supersonic helium atom beams  

NASA Astrophysics Data System (ADS)

Field ionization detectors (FID) may offer near-unity detection efficiency and nanoscale spatial resolution. To date, FID detection of molecular beams has been limited to effusive beams of broad Maxwellian velocity distributions. We report FID measurements on monoenergetic helium beams, including intensity measurements and time-of-flight measurements. The FID tips were carefully prepared and characterized in a field ionization microscope prior to use. With the supersonic helium beam we find a much smaller effective detection area ( 50 sq. nm) than was reported in the effusive helium beam experiments ( 200,000 sq. nm). This suggests that the FID ionization yield depends strongly on energy loss by the impinging atom during its initial collision with the FID surface: Our thermal energy, monoenergetic helium beam atoms likely lose little or no energy upon scattering from the clean tungsten FID surface, allowing the scattered atoms to escape the FID polarization field and therby reducing the ionization yield. To improve signal levels, inelastic scattering might be enhanced by use of lower beam velocities (present in the tails of a Maxwellian) or by adsorbing an overlayer on the FID tip (present at cryogenic tip temperatures). These factors likely explain the higher detection yields measured in the effusive beam experiments.

Doak, R. B.

2003-10-01

23

Long range forces between atomic impurities in liquid helium  

E-print Network

Long range forces between atomic impurities in liquid helium J. Dupont-Roc Laboratoire Kastler in a polarizable medium. We show that atomic impurities in liquid helium may indeed realize repulsive forces embedded in liquid helium, super uid or not. Solid helium have also been used. Successful theoretical

24

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.

25

Classical Helium Atom with Radiation Reaction G. Camelio,1  

E-print Network

Classical Helium Atom with Radiation Reaction G. Camelio,1 A. Carati,2 and L. Galgani2 1) Universit November 2011) We study a classical model of Helium atom in which, in addition to the Coulomb forces be singular with respect to that of Lebesgue. PACS numbers: 05.45.-a, 41.60.-m Keywords: classical Helium atom

Carati, Andrea

26

Helium in confinement: the filling A Neutron Scattering investigation.  

E-print Network

Helium in confinement: the filling parameter. A Neutron Scattering investigation. Francesco Albergamo Institut Laue-Langevin, France Helium in confinement: the filling parameter. ­ p.1/13 #12;outline introduction and motivation Helium in confinement: the filling parameter. ­ p.2/13 #12;outline introduction

Glyde, Henry R.

27

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

28

A simple design for a helium scattering apparatus  

NASA Astrophysics Data System (ADS)

We have designed a simple helium scattering apparatus for gas-surface scattering experiments. The effusive source is a glass multicapillary array, operated at large Knudsen numbers which produces a highly collimated thermal He beam (FWHM ? 3°) with a Maxwellian velocity distribution. The detector is a Bayard Alpert ionization gauge, mounted in a tube that is separated from the main UHV chamber via a second multicapillary array. This setup allows one to select only those He atoms that are reflected by the sample in the specular direction and thus to measure the reflectivity of the surface. Examples of its performance are presented for the adsorption of CO on Ru(001), and for thermal annealing of a Ru(001) surface sputtered with argon ions at different energies.

Maier, F.; Kneitz, S.; Koschel, H.; Steinrück, H.-P.

1997-04-01

29

Antiprotonic Helium — An Exotic Hydrogenic Atom  

Microsoft Academic Search

The antiprotonic helium,\\u000a \\u000a\\u000a\\u000a\\u000a\\u000a\\u000a[`<\\/font\\u000a>(\\\\textp)] \\\\texte\\\\textHe\\\\text2 + ( = [`<\\/font\\u000a>(\\\\textp)] \\\\textHe\\\\text + )\\u000a\\\\overline {\\\\text{p}} {\\\\text{e}}{\\\\text{He}}^{\\\\text{2}} + \\\\left( { = \\\\overline {\\\\text{p}} {\\\\text{He}}^{\\\\text{ + }} } \\\\right)\\u000a\\u000a \\u000a , is a peculiar metastable atom, interfacing between matter and antimatter. A series of metastable states are composed of\\u000a the He nucleus, one electron in the ground 1s configuration and one antiproton

Toshimitsu Yamazaki

2001-01-01

30

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

31

Helium nanobubble release from Pd surface: An atomic simulation  

SciTech Connect

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

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

2011-02-14

32

Atoms in boxes: From confined atoms to electron-atom scattering  

NASA Astrophysics Data System (ADS)

We show that both confined atoms and electron-atom scattering can be described by a unified basis set method. The central idea behind this method is to place the atom inside a hard potential sphere, enforced by a standard Slater type basis set multiplied by a cutoff factor. For confined atoms, where the wall is placed close to the atomic nucleus, we show how the energy of the highest occupied atomic orbital and the static polarizability of helium and neon atoms evolve with the confinement radius. To our knowledge, these are the first confined atom polarizability calculations that include correlation for many-electron atoms, through the use of time-dependent density-functional theory. By placing the atom in a large spherical box, with a wall outside the electron density, we obtain scattering phase shifts using a recently developed method [M. van Faassen, A. Wasserman, E. Engel, F. Zhang, and K. Burke, Phys. Rev. Lett. 99, 043005 (2007)]. We show that the basis set method gives identical results to previously obtained phase shifts for e-H and e-He+ scattering.

van Faassen, Meta

2009-09-01

33

Neutron scattering study of elementary excitations in liquid helium-3  

Microsoft Academic Search

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

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

1976-01-01

34

Positron-alkali atom scattering  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

35

Atomic capture of negative muons and hadrons in Helium  

NASA Astrophysics Data System (ADS)

Collisions of slow negative heavy particles M with He atoms are considered using the semiclassical approximation for quantum coupling equations taking into account the two-particle channel M + He and the ionization channels M + He(+) + e. The ionization and atomic-capture cross sections are calculated. The kinetic characteristics of slowing-down and atomic capture of the particles in helium are obtained. The results for stopping power and slowing-down time of muons in helium are compared with the experimental data.

Dolinov, V. K.; Korenman, G. Ya.; Moskalenko, I. V.; Popov, V. P.

36

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

37

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

E-print Network

Electron scattering in helium for Monte Carlo simulations Alexander V. Khrabrov and Igor D://scitation.aip.org/termsconditions. Downloaded to IP: 198.35.3.245 On: Fri, 14 Feb 2014 17:06:57 #12;Electron scattering in helium for Monte September 2012) An analytical approximation for differential cross-section of electron scattering on helium

Kaganovich, Igor

38

Shift and broadening of resonance lines of antiprotonic helium atoms in solid helium  

E-print Network

We have estimated the shift and broadening of the resonance lines in the spectrum of antiprotonic helium atoms $\\bar{p}\\mathrm{He}^{+}$ implanted in solid helium $^4$He. The application of the response function for crystalline helium has enabled determination of the contributions from the collective degrees of freedom to the shift and broadening. It occurs that the broadening due to the collective motion is negligible compared to the natural line width. The available pair-correlation functions for crystalline $^4$He have been applied for estimating the resonance-line shift due to collisions of $\\bar{p}\\mathrm{He}^{+}$ atom with the surrounding $^4$He atoms. The dependence of the line shift, which has been calculated in the quasistatic limit, on the solid-$^4$He density is nonlinear.

Adamczak, Andrzej

2014-01-01

39

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

40

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

41

Quantum Field Theory and the Helium Atom: 101 Years Later  

E-print Network

Helium was first isolated on Earth in 1895, by Sir William Ramsey. One hundred and one years later, it seems like a good time to review our current theoretical understanding of the helium atom. Helium has played an important role in the development of both quantum mechanics and of quantum field theory. The early history of helium is sketched. Various aspects of the modern theory are described in some detail, including (1) the computation of fine structure to order \\alpha^2 Ry and \\alpha^3 Ry, (2) the decay of metastable states, and (3) Rydberg states and long-range forces. A brief survey is made of some of the recent work on the quantum field theory of He and He-like ions.

J. Sucher

1996-12-11

42

Deeply Virtual Compton Scattering off Helium  

NASA Astrophysics Data System (ADS)

Deeply Virtual Compton Scattering (DVCS) is privileged tool to access the partonic structure of hadrons encoded via the so-called Generalized Parton Distributions (GPDs). Similarly to the scattering of light by a material, DVCS provides information about the dynamics and the spatial structure of hadrons. Whether the target nucleus remains intact or not after the reaction, DVCS off a nuclear target allows to address the partonic structure of the nucleus as well as the partonic structure of nucleons embedded in the nuclear medium. Adding transverse degrees of freedom to conventional deep inelastic scattering, these exclusive channels are expected to bring sensitive information about the origin of the EMC effect. The eg6 experiment at the Jefferson Laboratory did explore nuclear DVCS off ^4He. The experimental asymmetry of the DVCS reaction with respect to the electron beam polarization was measured for the coherent and incoherent channels with the CLAS detector, complemented with a small angle electromagnetic calorimeter and a radial time projection chamber. This talk reviews the experimental methods and techniques of the eg6 run, and discusses the preliminary results of DVXS measurements.

Voutier, Eric

2012-03-01

43

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

E-print Network

In this work 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 inter-particle 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 LM2M2 potential. 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 in 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.

M. Gattobigio; A. Kievsky; M. Viviani

2011-06-20

44

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

Microsoft Academic Search

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

Jürgen Gspann

1995-01-01

45

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

46

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

47

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

NASA Astrophysics Data System (ADS)

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 He2+ and He3+ 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.

Bünermann, Oliver; Kornilov, Oleg; Haxton, Daniel J.; Leone, Stephen R.; Neumark, Daniel M.; Gessner, Oliver

2012-12-01

48

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

49

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

50

Further Examination of a Simplified Model for Positronium-Helium Scattering  

NASA Technical Reports Server (NTRS)

While carrying out investigations on Ps-He scattering we realized that it would be possible to improve the results of a previous work on zero-energy scattering of ortho-positronium by helium atoms. The previous work used a model to account for exchange and also attempted to include the effect of short-range Coulomb interactions in the close-coupling approximation. The 3 terms that were then included did not produce a well-converged result but served to give some justification to the model. Now we improve the calculation by using a simple variational wave function, and derive a much better value of the scattering length. The new result is compared with other computed values, and when an approximate correction due to the van der Waals potential is included the total is consistent with an earlier conjecture.

DiRienzi, J.; Drachman, Richard J.

2012-01-01

51

Temperature dependence in atom-surface scattering  

NASA Astrophysics Data System (ADS)

It is shown that a straightforward measure of the temperature dependence of energy resolved atom-surface scattering spectra measured under classical conditions can be related to the strength of the surface corrugation. Using classical perturbation theory combined with a Langevin bath formalism for describing energy transfer, explicit expressions for the scattering probabilities are obtained for both two-dimensional, in-plane scattering and full three-dimensional scattering. For strong surface corrugations results expressed as analytic closed-form equations for the scattering probability are derived which demonstrate that the temperature dependence of the scattering probability weakens with increasing corrugation strength. The relationship to the inelastic rainbow is briefly discussed.

Pollak, Eli; Manson, J. R.

2012-03-01

52

Ab initio potential energy curve for the helium atom pair and thermophysical properties of dilute helium gas. I. Helium-helium interatomic potential  

Microsoft Academic Search

A helium–helium interatomic potential energy curve was determined from quantum-mechanical ab initio calculations. Very large atom-centred basis sets including a newly developed d-aug-cc-pV8Z basis set supplemented with bond functions and ab initio methods up to full CI were applied. The aug-cc-pV7Z basis set of Gdanitz (J. Chem. Phys. 113, 5145 (2000)) was modified to be more consistent with the aug-cc-pV5Z

Robert Hellmann; Eckard Bich; Eckhard Vogel

2007-01-01

53

Probing helium interfaces with light scattering : from fluid mechanics to statistical physics  

E-print Network

We have investigated the formation of helium droplets in two physical situations. In the first one, droplets are atomised from superfluid or normal liquid by a fast helium vapour flow. In the second, droplets of normal liquid are formed inside porous glasses during the process of helium condensation. The context, aims, and results of these experiments are reviewed, with focus on the specificity of light scattering by helium. In particular, we discuss how, for different reasons, the closeness to unity of the index of refraction of helium allows in both cases to minimise the problem of multiple scattering and obtain results which it would not be possible to get using other fluids.

Pierre-Etienne Wolf; Fabien Bonnet; Sylvain Perraud; Laurent Puech; Bernard Rousset; Pierre Thibault

2008-07-10

54

Ionization of helium atoms under the effect of the antineutrino magnetic moment  

SciTech Connect

Differential cross sections for inelastic antineutrino interaction with a helium atom are calculated. It is shown that, in the energy-transfer range extending up to 1 keV, the cross sections in question are considerably enhanced in the electromagnetic-interaction channel in relation to the cross sections for elastic scattering on a free electron. Absolute cross-section values are of interest in searches for the antineutrino magnetic moment, provided that its value in Bohr magneton units falls within the range (10{sup -13}-10{sup -12}){sub Micro-Sign B}.

Martemyanov, V. P., E-mail: vpmar@kiae.ru; Tsinoev, V. G. [Russian Research Centre Kurchatov Institute (Russian Federation)

2011-12-15

55

Polarization Potential in Electron-Atom Scattering.  

National Technical Information Service (NTIS)

The polarization potential for electron-atom scattering is investigated analytically in momentum space. Contributions from discrete and continuum excitations are treated in detail. The equivalent-local polarization potential V(P) is derived, and calculate...

I. E. McCarthy, B. C. Saha, A. T. Stelbovics

1981-01-01

56

Re-Examination of a Simplified Model for Positronium-Helium Scattering  

NASA Technical Reports Server (NTRS)

Using a local effective potential to account for electron exchange, R J Drachman and S K Houston analyzed the zero-energy scattering of ortho-positronium by helium atoms in 1970. The idea was to use the existing static-exchange results to fit the parameters of the local potential and then to use the potential in a variational target-elastic calculation. The results were remarkably good, both for the scattering length and the annihilation parameter. Recently, however, a rigorous target-elastic calculation by Blackwood et al disagreed so strongly with these old results that we have undertaken a re-examination. We find that the assumption made in the earlier work, that the direct potential is negligible compared with the exchange potential, is not quantitatively correct. But the original idea that omission of the direct potential might compensate approximately for the omission of the van der Waals potential still seems reasonable.

Drachman, Richard J.; DiRienzi, Joseph

2003-01-01

57

Re-examination of a Simplified Model for Positronium-Helium Scattering  

NASA Technical Reports Server (NTRS)

Using a local effective potential to account for electron exchange, R J Drachman and S K Houston analyzed the zero-energy scattering of ortho-positronium by helium atoms in 1970. The idea was to use the existing static-exchange results to fit the parameters of the local potential and then to use the potential in a variational target-elastic calculation. The results were remarkably good, both for the scattering length and the annihilation parameter. Recently, however, a rigorous target-elastic calculation by Blackwood et al disagreed so strongly with these old results that we have undertaken a re-examination. We find that one of the apparently trivial assumptions of the local potential method is much more important than previously believed.

DiRienzi, Joseph; Drachman, Richard J.

2003-01-01

58

Toward improved photon-atom scattering predictions  

SciTech Connect

Photon-atom scattering is important in a variety of applications, but scattering from a composite system depends on the accurate characterization of the scattering from an isolated atom or ion. We have been examining the validity of simpler approximations of elastic scattering in the light of second-order S-matrix theory. Partitioning the many-body amplitude into Rayleigh and Delbrueck components, processes beyond photoionization contribute. Subtracted cross sections for bound-bound atomic transitions, bound pair annihilation, and bound pair production are required in anomalous scattering factors for: (1) convergence of the dispersion integral; (2) agreement with predictions of the more sophisticated S-matrix approach; (3) satisfying the Thomas-Reiche-Kuhn sum rule. New accurate tabulations of anomalous scattering factors have been prepared for all Z, for energies 0--10,000 keV, within the independent particle approximation (IPA) using a Dirac-Slater model of the atom. Separately, experimental atomic photoabsorption threshold information has been used to modify these IPA predictions for improved comparison with experiment.

Kissel, L.

1994-10-21

59

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

60

Alkali-Metal Atoms as Spin Labels on Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

We have recently achieved electron spin resonance (ESR) of single alkali-metal atoms isolated on helium (He) nanodroplets A two-laser pump/probe setup for optically detected magnetic resonance is applied, which is based on magnetic circular dichroism to selectively address spin states. The influence of the helium droplet on the alkali-metal valence-electron wave function is directly noticeable as a shift of the ESR transitions with respect to that of free atoms. This perturbation depends on the size of the droplets and can be modeled with an increase of the hyperfine constant, that is an increase of the Fermi contact interaction. After careful characterization of the Rb--He-droplet system the method is being developed into a more universal diagnostic tool to study spin dynamics. ESR silent species located inside the droplet can be investigated by utilizing the surface Rb atom as spin label, and the droplet size is a convenient handle to control the distance between the two. In case of species with a nuclear spin (e.g., 129Xe) spin exchange between the optically pumped Rb atom and the nuclear spin can be studied. We are also extending our method to study magnetically active materials of technological importance, such as Cr, Cu, and small clusters thereof, and we strive to present the first results at the meeting. M. Koch, G. Auböck, C. Callegari, and W.E. Ernst, Phys. Rev. Lett. 103, 035302 (2009) M. Koch, J. Lanzersdorfer, C. Callegari, J.S. Muenter, and W.E. Ernst, J. Phys. Chem. A 113, 13347 (2009) M. Koch, C. Callegari, and W.E. Ernst, Mol. Phys., in press.

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

2010-06-01

61

Electron scattering by atomic chains: Multiple-scattering effects  

NASA Astrophysics Data System (ADS)

Multiple-scattering effects of electrons traveling along atomic chains are shown to be important and useful for surface structure determination, especially in the medium-energy range (200-1000 eV). This applies to techniques based on diffraction of elastic electrons, such as medium-energy electron diffraction, as well as to techniques based on the angle-resolved detection of ``secondary'' electrons such as photoelectrons, Auger electrons, and other electrons. Two new methods for computing multiple-scattering amplitudes for chains are derived and used to show how multiple scattering along chains of atoms produces focusing, defocusing, amplification, and layer-dependent enhancements that can be put to effective use in structure determination. Strong forward-focusing peaks along internuclear axes are dominant under many conditions: this is a single-scattering effect. However, multiple scattering can totally defocus such forward-focused peaks, while other interference effects produce additional scattering peaks that do not have the direction of an internuclear axis. In addition, it follows that surface composition analysis by conventional Auger-electron spectroscopy can be quite sensitive to the incident direction of the electron beam used to produce Auger emission.

Xu, M.-L.; Barton, J. J.; van Hove, M. A.

1989-04-01

62

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

63

Rayleigh Scattering at Atoms with Dynamical Nuclei  

E-print Network

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

J. Froehlich; M. Griesemer; B. Schlein

2005-09-05

64

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

SciTech Connect

The dynamic scalar and tensor polarizabilities of the rare-earth-metal atoms are calculated with time-dependent density functional theory. The frequency-dependent polarizabilities at imaginary frequencies are used to determine the isotropic and orientation-dependent van der Waals coefficients for the interactions of the rare-earth-metal atoms with helium atoms. The static polarizabilities are compared with other theoretical values and with experimental results. The agreement is satisfactory in most cases but there are some exceptions where the discrepancy between theory and experiment is significant. The derived isotropic van der Waals coefficients range between 37 and 50 E{sub H}a{sub 0}{sup 6} and the orientation-dependent coefficients between 2 and -1 E{sub H}a{sub 0}{sup 6}. Thus the ratio of elastic to inelastic scattering cross sections is expected to be substantial and any one of the rare-earth-metal atoms is an excellent candidate for trapping and cooling in a He gas.

Chu, Xi; Dalgarno, Alexander; Groenenboom, Gerrit C. [Department of Chemistry, University of Montana, Missoula, Montana 59812 (United States); ITAMP, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States); Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 1, 6525ED, Nijmegen (Netherlands)

2007-03-15

65

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

66

Classical Helium Atom with Radiation Reaction Universit`a degli Studi di Milano, Corso di Laurea in Fisica,  

E-print Network

Classical Helium Atom with Radiation Reaction G. Camelio Universit`a degli Studi di Milano, Corso: November 24, 2011) Abstract We study a classical model of Helium atom in which, in addition to the Coulomb (see for example Refs. 1­8), in this paper we take into account, for the case of the Helium atom

Galgani, Luigi

67

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

68

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

NASA Astrophysics Data System (ADS)

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.

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

2013-03-01

69

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 for their interaction with helium atoms Xi Chu Department of Chemistry, University of Montana, Missoula, Montana 59812; published 29 March 2007 The dynamic scalar and tensor polarizabilities of the rare-earth-metal atoms

Chu, Xi

70

Photoabsorption by Ultracold Atoms and the Scattering Length  

Microsoft Academic Search

It is shown that photoabsorption in a gas of ultracold atoms depends on the sign and magnitude of the scattering length in the scattering of a pair of atoms. Measurements of fluorescence in 7Li are interpreted to show that the triplet scattering length is negative and the singlet scattering length is positive.

R. Côté; A. Dalgarno; Y. Sun; R. G. Hulet

1995-01-01

71

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

72

Lars Onsager Prize Talk: Quantum fluids: from liquid helium to cold atoms  

Microsoft Academic Search

The study of quantum liquids has led to ideas and concepts of broad applicability. I shall illustrate this by examples from the physics of liquid helium-3, heavy-fermion compounds, quark-gluon plasmas and cold atomic gases.

Christopher Pethick

2008-01-01

73

Atom and photon measurement in cooperative scattering by cold atoms  

E-print Network

In this paper, we study cooperative scattering of low intensity light by a cloud of N two-level systems. We include the incident laser field driving these two-level systems and compute the radiation pressure force on the center of mass of the cloud. This signature is of particular interest for experiments with laser cooled atoms. Including the complex coupling between dipoles in a scalar model for dilute clouds of two-level systems, we obtain expression for cooperative scattering forces taking into account the collective Lamb shift. We also derive the expression of the radiation pressure force on a large cloud of two-level systems from an heuristic approach and show that at lowest driving intensities this force is identical for a product and an entangled state.

Tom Bienaime; Marco Petruzzo; Daniele Bigerni; Nicola Piovella; Robin Kaiser

2012-01-16

74

Determination of surface corrugation amplitude from classical atom scattering  

E-print Network

from classical atom scattering W. W. Hayes Physical Sciences Department, Greenville Technical College height variation of the corrugation function for scattering of atoms under classical conditions can be determined by a measurement of the maximum intensity in energy-resolved scattering spectra as a function

Manson, Joseph R.

75

Relating Temperature Dependence of Atom Scattering Spectra to Surface Corrugation  

E-print Network

Relating Temperature Dependence of Atom Scattering Spectra to Surface Corrugation W. W. Hayes of the surface corrugation can be directly related to the temperature dependence of atom scattering spectra atomic mass, piz is the surface-normal component of the incident momentum, TS is the temperature, k

Manson, Joseph R.

76

Accurate Atomic Transition Probabilities for Hydrogen, Helium, and Lithium W. L. Wiese and J. R. Fuhra...  

E-print Network

Accurate Atomic Transition Probabilities for Hydrogen, Helium, and Lithium W. L. Wiese and J. R September 2009 We have carried out a comprehensive tabulation of the atomic transition probabilities probabilities of lines between different principal quantum numbers. © 2009 by the U. S. Secretary of Commerce

Magee, Joseph W.

77

The muonic helium atom as a classical three-body problem T.J.Stuchi 1 , A.C.B.Antunes 1 and M.A.Andreu 2  

E-print Network

The muonic helium atom as a classical three-body problem T.J.Stuchi 1 , A.C.B.Antunes 1 and M problem of the muonic helium atom, a helium atom with one of its electrons replaced by a muon. Firstly, we establish the connection of the model with the one-dimensional frozen planetary approximation of the helium

Barcelona, Universitat de

78

Principles and procedures for determining absolute differential electron-molecule (atom) scattering cross sections  

NASA Technical Reports Server (NTRS)

Procedures and calibration techniques for measuring the absolute elastic and inelastic differential cross sections (DCS) for electron impact on molecular (atomic) species are described and illustrated by examples. The elastic DCS for the molecule under study is first determined by calibration against helium using the relative flow technique. The second step involves the production of energy-loss spectra for the instrument response function, the unfolding of overlapping inelastic structures and the normalization of inelastic intensities to the elastic cross sections. It is concluded that this method of determining absolute differential electron-molecule (atom) scattering cross sections is generally applicable and provides reliable results.

Nickel, J. C.; Zetner, P. W.; Shen, G.; Trajmar, S.

1989-01-01

79

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

80

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

81

Excited Muonic Atom Scattering: New Adiabatic Approach  

NASA Astrophysics Data System (ADS)

Two adiabatic approaches: Born-Oppenheimer (BO) [1, 2] and hyperradial adiabatic (HA) [3] are frequently used for (x?) n (n?2) muonic atom scattering. In both cases the Coriolis coupling operator has the same form and is treated within the close-coupling scheme. Recently, we have developed a symmetry-adapted version of the HA approach [4] (SAHA) in which Coriolis couplings are calculated as the “fast” component of the dynamics. In SAHA the adiabatic problem should be solved for any pair of the total angular momentum J and total parity p repeatedly but the number of adiabatic states (and the number of channels in the close-coupling calculations) is reduced by J-factor.

Matveenko, A. V.

2001-12-01

82

Excitation of metastable argon and helium atoms by electron impact  

NASA Technical Reports Server (NTRS)

Using a time-of-flight method, the excitation of argon and helium metastables by electron impact is investigated in the energy range from threshold to about 50 eV. The secondary-electron yields of the metastable detector used are reviewed in detail. The effect of metastable recoil is also discussed. Comparisons with data from other investigators are presented.

Borst, W. L.

1974-01-01

83

Thermal desorption from ordered chemisorbed phases studied by helium scattering: Oxygen on Ag(110)  

NASA Astrophysics Data System (ADS)

We relate the helium specular beam intensity during adsorbate desorption (He desorption curve) to the instantaneous surface coverage. In this way the He desorption curve is shown to provide a picture of the desorption process which can be fruitfully compared to the one coming from thermal desorption mass spectra (TDS), obtained under strictly comparable experimental conditions. We tested the combination of thermal energy atom scattering (TEAS) and TDS in the case of the associative desorption from long range ordered O(2×1)-Ag(110) phase. Using the so-called overlap approach and assuming intense adsorbate-adsorbate (and vacancy-vacancy) attractions along Ag-O-Ag rows we obtain an instantaneous coverage which is in good agreement with TDS results. He desorption curves confirm the extreme sharpness of the desorption transition further indicating that the tails of the TDS peak bear small contributions from oxygen which did not belong to the O(2×1) phase. Opportunities and limitations inherent to the use of the He desorption curve (and its first derivative) as a marker of the temperature position and sharpness of the desorption transition are also addressed.

Canepa, M.; Terreni, S.; Narducci, E.; Mattera, L.

1999-01-01

84

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

85

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

86

Helium AtomSCF-LCAO Calculation of the (1s)2 Ground State of the  

NSDL National Science Digital Library

Using a double-zeta basis of Slater-type orbitals [STOs], this Java applet calculates the single determinant singlet ground state 1s2 wavefunction of the helium atom. The doubly occupied orbital is expanded in terms of two basis functions, 1s and 1s`.

87

Electron Scattering Redistribution Effect on Atomic Line Polarization  

NASA Astrophysics Data System (ADS)

The scattering of line photons on free electrons modifies the polarization of the atomic spectral lines. Hence it is important to treat scattering by electrons as a redistribution process and to study in detail its effect on line formation. The numerically difficult problem of evaluation and the use of angle-dependent atomic and electron scattering redistribution functions in the line transfer equation is considered. Two numerical methods, namely approximate lambda iteration and scattering expansion method, are used to solve the relevant polarized transfer problem. A study of the polarized line formation in a standard two-level atom picture including an exact treatment of electron scattering redistribution shows the importance of the latter in the analysis of polarized line profiles emitted by solar and stellar atmospheres. The effect of electron scattering turns out to be extremely important in the interpretation of very far wing line polarization of solar and stellar spectral lines.

Supriya, H. D.; Nagendra, K. N.; Ravindra, B.; Sampoorna, M.

2014-10-01

88

Metastable Atom Production in a Helium Gas Discharge  

NASA Astrophysics Data System (ADS)

A simple theoretical model of the positive column of a steady-state glow discharge in a magnetic field has been developed for the pressure range of 0-30 mT. By considering the processes of atom excitation by electron impact, and metastable collisions with ground and metastable states we can predict the rate of metastable atom effusion out of an anode slit. The atoms come from direct electron excitation and also from an established metastable population. The rate of effusion is predicted as a function of pressure, discharge current and voltage, and magnetic field strength. The results are compared with experimental measurements of metastable atom flux obtained using Time Of Flight spectroscopy.

Benitez, J. F.; Faxas, M.; Pacheco, A.; Quintero, L.; Rojas, J.; Salem, A.; Hardy, K.

2002-10-01

89

Metastable Atom Production in a Helium Gas Discharge  

Microsoft Academic Search

A simple theoretical model of the positive column of a steady-state glow discharge in a magnetic field has been developed for the pressure range of 0-30 mT. By considering the processes of atom excitation by electron impact, and metastable collisions with ground and metastable states we can predict the rate of metastable atom effusion out of an anode slit. The

J. F. Benitez; M. Faxas; A. Pacheco; L. Quintero; J. Rojas; A. Salem; K. Hardy

2002-01-01

90

Low-energy scattering of antihydrogen by helium and molecular hydrogen  

SciTech Connect

In this paper, we describe in detail calculations that we have carried out of cross sections for rearrangement processes in very low-energy helium+antihydrogen (H-bar) scattering that result in He{sup +}p-bar+Ps or Hep-bar+e{sup +} or {alpha}p-bar+Ps{sup -}. The interaction between the leptons is taken into account very accurately. Results are presented for all three processes. A description is also given of a preliminary calculation of elastic and antiproton annihilation cross sections for very low-energy H{sub 2}+H-bar scattering.

Armour, E. A. G.; Todd, A. C.; Liu, Y.; Gregory, M. R. [School of Mathematical Sciences, Nottingham University, Nottingham NG7 2RD (United Kingdom); Jonsell, S. [Department of Physics, University of Wales Swansea, Swansea SA2 8PP (United Kingdom); Plummer, M. [CLRC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom)

2008-08-08

91

Planar Rayleigh scattering results in helium-air mixing experiments in a Mach-6 wind tunnel.  

PubMed

Planar Rayleigh scattering measurements with an argon-fluoride excimer laser are performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach-6 facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross-sectional area (5 cm x 10 cm) of the flow field in the absence of clusters. PMID:20733871

Shirinzadeh, B; Hillard, M E; Balla, R J; Waitz, I A; Anders, J B; Exton, R J

1992-10-20

92

The effect of Compton scattering on the double to single ionization ratio in helium  

SciTech Connect

The ratio of double to single ionization in Helium produced by photon impact has been measured for photon energies from 2.1 to 5.5 keV. The measurements suggest that a significant contribution to the single ionization cross section is caused by Compton scattering for energies greater than {approximately} 3.8 keV. After accounting for the ionizing Compton scattering the measured ratio is not inconsistent with recent calculations of the asymptotic limit of the ionization ratio caused by photoabsorption which predict a limit near 1.66%.

Bartlett, R.J. [Los Alamos National Lab., NM (United States); Sagurton, M. [SFA, Inc., Landover, MD (United States); Samson, J.A.R.; He, Z.X. [Nebraska Univ., Lincoln, NE (United States)

1993-10-01

93

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

94

The Spectral Decomposition of the Helium atom two-electron configuration in terms of Hydrogenic orbitals  

E-print Network

The two electron configuration in the Helium atom is known to very high precision. Yet, we tend to refer to this configuration as a $1s\\uparrow 1s\\downarrow$ singlet, where the designations refer to Hydrogen orbitals. The high precision calculations utilize basis sets that are suited for high accuracy and ease of calculation, but do not really aid in our understanding of the electron configuration in terms of product states of Hydrogen orbitals. Since undergraduate students are generally taught to think of Helium, and indeed, the rest of the periodic table, in terms of Hydrogenic orbitals, we present in this paper a detailed spectral decomposition of the two electron ground state for Helium in terms of these basis states. The $1s\\uparrow 1s\\downarrow$ singlet contributes less than 93% to the ground state configuration, with other contributions coming from both bound and continuum Hydrogenic states.

Hutchinson, J; Marsiglio, F

2012-01-01

95

Photoionization of helium nanodroplets doped with rare gas atoms  

NASA Astrophysics Data System (ADS)

Photoionization of He droplets doped with rare gas atoms (Rg =Ne, Ar, Kr, and Xe) was studied by time-of-flight mass spectrometry, utilizing synchrotron radiation from the Advanced Light Source from 10to30eV. High resolution mass spectra were obtained at selected photon energies, and photoion yield curves were measured for several ion masses (or ranges of ion masses) over a wide range of photon energies. Only indirect ionization of the dopant rare gas atoms was observed, either by excitation or charge transfer from the surrounding He atoms. Significant dopant ionization from excitation transfer was seen at 21.6eV, the maximum of He 2pP1 absorption band for He droplets, and from charge transfer above 23eV, the threshold for ionization of pure He droplets. No Ne+ or Ar+ signal from droplet photoionization was observed, but peaks from HenNe+ and HenAr+ were seen that clearly originated from droplets. For droplets doped with Rg =Kr or Xe, both Rg+ and HenRg+ ions were observed. For all rare gases, Rg2+ and HenRgm+ (n,m?1) were produced by droplet photoionization. Mechanisms of dopant ionization and subsequent dynamics are discussed.

Kim, Jeong Hyun; Peterka, Darcy S.; Wang, Chia C.; Neumark, Daniel M.

2006-06-01

96

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

97

Helium self-interstitial atom interaction in ?-iron  

NASA Astrophysics Data System (ADS)

The effect of He impurities on the properties and behavior of self-interstitial atom (SIA) clusters in ?-Fe has been simulated by atomistic molecular dynamics (MD) and molecular statics (MS) simulation techniques using semi-empirical interatomic potentials and compared to ab initio electronic structure calculations. The MD simulations reveal many interactions between He and SIA clusters, including a spontaneous SIA-substitutional He recombination and replacement mechanism that ejects He into interstitial positions and a strong interaction between He, in either interstitial or substitutional positions, with SIA and SIA clusters and also with other He atoms. The MS calculations reveal relatively small interaction trapping radii of about 1 nm between interstitial He and SIA cluster complexes, but strong binding energies from 1.3 to 4.4 eV, depending on cluster size and interaction geometry. The comparisons between the ab initio and semi-empirical interactions are in generally good agreement and indicate that the He-point defect interactions in bcc Fe are well represented by considering the displacement (strain) field interactions amongst the defects.

Ventelon, Lisa; Wirth, Brian; Domain, Christophe

2006-06-01

98

Determination of ?? scattering lengths from measurement of ?? atom lifetime  

NASA Astrophysics Data System (ADS)

The DIRAC experiment at CERN has achieved a sizeable production of ?? atoms and has significantly improved the precision on its lifetime determination. From a sample of 21 227 atomic pairs, a 4% measurement of the S-wave ?? scattering length difference |a-a||syst-0.0073+0.0078)M?-1 has been attained, providing an important test of Chiral Perturbation Theory.

Adeva, B.; Afanasyev, L.; Benayoun, M.; Benelli, A.; Berka, Z.; Brekhovskikh, V.; Caragheorgheopol, G.; Cechak, T.; Chiba, M.; Chliapnikov, P. V.; Ciocarlan, C.; Constantinescu, S.; Costantini, S.; Curceanu (Petrascu), C.; Doskarova, P.; Dreossi, D.; Drijard, D.; Dudarev, A.; Ferro-Luzzi, M.; Fungueiriño Pazos, J. L.; Gallas Torreira, M.; Gerndt, J.; Gianotti, P.; Goldin, D.; Gomez, F.; Gorin, A.; Gorchakov, O.; Guaraldo, C.; Gugiu, M.; Hansroul, M.; Hons, Z.; Hosek, R.; Iliescu, M.; Karpukhin, V.; Kluson, J.; Kobayashi, M.; Kokkas, P.; Komarov, V.; Kruglov, V.; Kruglova, L.; Kulikov, A.; Kuptsov, A.; Kuroda, K. I.; Lamberto, A.; Lanaro, A.; Lapshin, V.; Lednicky, R.; Leruste, P.; Levi Sandri, P.; Lopez Aguera, A.; Lucherini, V.; Maki, T.; Manuilov, I.; Marin, J.; Narjoux, J. L.; Nemenov, L.; Nikitin, M.; Nunez Pardo, T.; Okada, K.; Olchevskii, V.; Pazos, A.; Pentia, M.; Penzo, A.; Perreau, J. M.; Plo, M.; Ponta, T.; Rappazzo, G. F.; Riazantsev, A.; Rodriguez, J. M.; Rodriguez Fernandez, A.; Romero Vidal, A.; Ronjin, V. M.; Rykalin, V.; Saborido, J.; Santamarina, C.; Schacher, J.; Schuetz, C.; Sidorov, A.; Smolik, J.; Takeutchi, F.; Tarasov, A.; Tauscher, L.; Tobar, M. J.; Trojek, T.; Trusov, S.; Utkin, V.; Vázquez Doce, O.; Vlachos, S.; Voskresenskaya, O.; Vrba, T.; Willmott, C.; Yazkov, V.; Yoshimura, Y.; Zhabitsky, M.; Zrelov, P.

2011-10-01

99

Thomson scattering in the average-atom approximation.  

PubMed

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

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

2012-09-01

100

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

101

Thomson scattering in the average-atom approximation  

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

102

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

103

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

104

Desorption dynamics of heavy alkali metal atoms (Rb, Cs) off the surface of helium nanodroplets.  

PubMed

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 meff/mHe ? 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. PMID:24911255

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

2014-08-21

105

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

106

Scattering properties of weakly bound dimers of fermionic atoms  

SciTech Connect

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

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

2005-01-01

107

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

108

Doubly excited states of the hydrogen negative ion and helium atom in astrophysical plasmas  

SciTech Connect

The nonthermal effects on the doubly excited resonance states of the hydrogen negative ion and helium atom are investigated in Lorentzian astrophysical plasma environments using highly correlated Hylleraas-type wave functions in the framework of the stabilization method. Resonance parameters (resonance position and width) are reported for the first time as functions of the spectral index and plasma parameter. The screening effects are more pronounced in the stronger screening region.

Jiang Pinghui [Center for Theoretical Atomic and Molecular Physics, Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080 (China); College of Electrical and Information Engineering, Heilongjiang Institute of Technology, Harbin 150050 (China); Kar, Sabyasachi; Zhou, Y. [Center for Theoretical Atomic and Molecular Physics, Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080 (China)

2013-01-15

109

Theory of direct scattering of neutral and charged atoms  

NASA Technical Reports Server (NTRS)

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

Franco, V.

1979-01-01

110

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

NASA Astrophysics Data System (ADS)

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

Kaprálová-Žánská, Petra Ruth; Moiseyev, Nimrod

2014-07-01

111

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

112

Photoabsorption and Compton scattering in ionization of helium at high photon energies  

SciTech Connect

Production of singly and doubly charged helium ions by impact of keV photons is studied. The ratio R{sub ph} = {sigma}{sub ph}{sup ++}/{sigma}{sub ph}{sup +} for photoabsorption is calculated in the photon-energy range 2--18 keV using correlated initial- and final- state wave functions. Extrapolation towards asymptotic photon energies yields R{sub ph}({omega} {yields} {infinity}) = 1.66% in agreement with previous predictions. Ionization due to Compton scattering, which becomes comparable to photoabsorption above {omega} {approximately} 3 keV, is discussed.

Andersson, L.R.; Burgdoerfer, J. [Oak Ridge National Lab., TN (United States)]|[Tennessee Univ., Knoxville, TN (United States). Dept. of Physics and Astronomy

1993-10-01

113

Quantum scattering of fast atoms and molecules on surfaces.  

PubMed

We present evidence for the diffraction of light keV atoms and molecules grazingly scattered on LiF(001) and NaCl(001) surfaces. At such energies, the de Broglie wavelength is 2 orders of magnitude smaller that the mean thermal atomic displacement in the crystal. Thus, no coherent scattering was expected and interaction of keV atoms with surfaces is routinely treated with classical mechanics. We show here that well-defined diffraction patterns can be observed indicating that, for grazing scattering, the pertinent wavelength is that associated with the slow motion perpendicular to the surface. The experimental data are well reproduced by an ab initio calculation. PMID:17358491

Rousseau, P; Khemliche, H; Borisov, A G; Roncin, P

2007-01-01

114

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...

Hori, Masaki; Korobov, Vladimir I

2014-01-01

115

A Complete Version of the Glauber Theory for Elementary Atom - Target Atom Scattering and Its Approximations  

E-print Network

A general formalism of the Glauber theory for elementary atom (EA) - target atom (TA) scattering is developed. A second-order approximation of its complete version is considered in the framework of the optical-model perturbative approach. A `potential' approximation of a second-order optical model is formulated neglecting the excitation effects of the TA. Its accuracy is evaluated within the second-order approximation for the complete version of the Glauber EA-TA scattering theory.

Olga Voskresenskaya; Alexander Tarasov

2011-08-21

116

Strong-Field Kapitza-Dirac Scattering of Neutral Atoms  

NASA Astrophysics Data System (ADS)

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 1016s-1.

Eilzer, S.; Zimmermann, H.; Eichmann, U.

2014-03-01

117

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

118

Atom and Atom scattering at too low energies  

E-print Network

A modified static exchange model is introduced to study cold-atomic interaction. It includes the effect of long-range van der Waals interaction in addition to short-range exchange force. The model is applied at first on Ps-H system to study the Feshbach resonances e.g. the s-wave elastic phase shifts and the corresponding cross sections. These are compared with the data obtained using the static exchange model. A very interesting features are observed when we vary the interatomic separation i.e. the strength of dipole-dipole interaction.

Ray, Hasi

2012-01-01

119

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

120

Free atoms at finite temperature: coherent and incoherent scattering functions  

NASA Astrophysics Data System (ADS)

We calculate the coherent and incoherent scattering functions for free atoms at finite temperature. This is performed within a finite-temperature Thomas-Fermi method recently proposed by us, which avoids — artificial — confining cells of the Wigner-Seitz type.

Castaño, F.; Membrado, M.; Pacheco, A. F.; Sabadell, M. A.; Sañudo, J.

1994-12-01

121

Classical theory for asymmetric in-plane atom surface scattering  

NASA Astrophysics Data System (ADS)

In-plane atom surface scattering perturbation theory within a generalized Langevin equation formalism is proposed to account for the asymmetry found in angular distributions of heavy rare gas atoms scattered by corrugated surfaces. We show that when the surface corrugation is represented in terms of the first two (sine) Fourier components, one finds an asymmetric angular distribution. This asymmetry reflects the ratchetlike form of the effective corrugation. Adding in higher-order terms can also increase the number of rainbow scattering angles. Three rainbows are found for a second-order sine term in the corrugation, four symmetrically spaced rainbow angles are found when adding in a second-order cosine term to the corrugation. Analytic expressions for the angular distribution are derived in terms of a Morse oscillator model. The theory accounts well for the asymmetry and predicts its disappearance as the incident scattering angle is increased. It also features a decrease in the distance between the rainbow angles as the angle of incidence is increased and as the incident energy is increased. The theory is successfully applied to the experimental results of Kondo [Eur. Phys. J. D 38, 129 (2006)] for the scattering of Ar on LiF(100) and the results of Amirav [J. Chem. Phys. 87, 1796 (1987)] for the scattering of Xe on Ge(100) and Ar and Kr on Ag(100).

Pollak, Eli; Moix, Jeremy M.; Miret-Artés, Salvador

2009-10-01

122

Positron scattering and annihilation on noble-gas atoms  

NASA Astrophysics Data System (ADS)

Positron scattering and annihilation on noble-gas atoms is studied ab initio using many-body theory methods for positron energies below the positronium formation threshold. We show that in this energy range, the many-body theory yields accurate numerical results and provides a near-complete understanding of the positron-noble-gas atom system. It accounts for positron-atom and electron-positron correlations, including the polarization of the atom by the positron and the nonperturbative effect of virtual positronium formation. These correlations have a large influence on the scattering dynamics and result in a strong enhancement of the annihilation rates compared to the independent-particle mean-field description. Computed elastic scattering cross sections are found to be in good agreement with recent experimental results and Kohn variational and convergent close-coupling calculations. The calculated values of the annihilation rate parameter Zeff (effective number of electrons participating in annihilation) rise steeply along the sequence of noble-gas atoms due to the increasing strength of the correlation effects, and agree well with experimental data.

Green, D. G.; Ludlow, J. A.; Gribakin, G. F.

2014-09-01

123

Inelastic scattering of hydroxyl radicals with helium and argon by velocity-map imaging.  

PubMed

The hydroxyl radical (OH) is one of the most interesting molecules in molecular dynamics. In particular, inelastic collisions of free radicals such as OH are profoundly important in environments ranging from combustion to astrochemistry. However, measuring the velocities of OH molecules in specific internal quantum states has proven to be very difficult. A method that can provide this important information is velocity-map imaging. Although this technique is very widely applicable in principle, it does require a sensitive and selective laser-ionization scheme. Here we show that, under the right conditions, velocity-map imaging can be applied to the study of the inelastic scattering of OH using crossed-molecular-beam methods. We measure fully quantum-state-specified product angular distributions for OH collisions with helium and argon. The agreement between exact close-coupling quantum scattering calculations on ab initio potential energy surfaces and experimental data is generally very satisfactory, except for scattering in the most forward directions. PMID:23174977

Sarma, Gautam; Marinakis, Sarantos; ter Meulen, J J; Parker, David H; McKendrick, Kenneth G

2012-12-01

124

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

125

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

126

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

127

Wave functions and two-electron probability distributions of the Hooke's-law atom and helium  

SciTech Connect

The Hooke's-law atom (hookium) provides an exactly soluble model for a two-electron atom in which the nuclear-electron Coulombic attraction has been replaced by a harmonic one. Starting from the known exact position-space wave function for the ground state of hookium, we present the momentum-space wave function. We also look at the intracules, two-electron probability distributions, for hookium in position, momentum, and phase space. These are compared with the Hartree-Fock results and the Coulomb holes (the difference between the exact and Hartree-Fock intracules) in position, momentum, and phase space are examined. We then compare these results with analogous results for the ground state of helium using a simple, explicitly correlated wave function.

O'Neill, Darragh P.; Gill, Peter M. W. [School of Chemistry, University of Nottingham, Nottingham NG7 2RD, (United Kingdom)

2003-08-01

128

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

129

Electron elastic scattering off a spin-polarized Cr atom  

NASA Astrophysics Data System (ADS)

Electron elastic scattering off a spin-polarized Cr(...3d54s1, 7S) atom is theoretically studied in the region of electron energies up to 15 eV using both a one-electron "spin-polarized" Hartree-Fock approximation and a multielectron spin-polarized random-phase approximation with exchange. It is found that scattering phase shifts of oppositely spin-polarized incoming electrons and corresponding cross sections of the scattering reactions significantly differ from each other, in general, even without accounting for spin-orbit interaction. This is shown to be associated with the presence of two semifilled 3d5 and 4s1 subshells in the Cr configuration which induce considerably different exchange in the interaction of oppositely spin-polarized incoming electrons with the atom target. The importance of electron correlation in the e-+Cr elastic-scattering process is revealed. Moreover, correlation is shown to induce strong differences between scattering of oppositely spin-polarized electrons off Cr. A physically transparent interpretation for the latter is provided.

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

2014-09-01

130

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

131

Electron Scattering From Laser Excited Ba and Yb Atoms  

NASA Astrophysics Data System (ADS)

Inelastic and elastic electron scattering out of the excited states of Ba and Yb has been studied at low collision energies. We present measurements (at 10 eV and 20 eV collision energies) of differential cross sections and orientation parameters for elastic scattering out of the 6 ^1P1 and 5 D levels of Ba and for inelastic scattering out of the 6 ^3P1 level of Yb to higher lying ^3D and ^3S levels. Collision studies are carried out using a momentum selected incident electron beam with momentum resolved scattered electron detection and excited atomic target populations generated by resonant laser radiation. To a good approximation, Ba and Yb are heavy two-electron systems comprising filled, approximately inert cores ([Xe] for Ba and [Xe]4f^14 for Yb) with two-electron 6s^2 valence configurations (in the ground state). Theoretical determinations of low-energy electron scattering parameters for these atoms, based on convergent close coupling and first order perturbative formalisms, have met with success in many cases. Such calculations have been applied to inelastic scattering from 6S, 5D and 6P target states in Ba and the 6S ground state in Yb (refs 1,2). Extension of previous experimental investigations to the new scattering processes described in this work will further test the efficacy of available theoretical methods. 1. I. Bray et al. J.Phys.B:At.Mol.Opt.Phys. 35 R117 (2002) 2. B Predojevic et al. J. Phys. B: At. Mol. Opt. Phys. 38 3489 (2005)

Zetner, Peter; Hein, Jeff

2007-06-01

132

Temperature and Atomic Oxygen Effects on Helium Leak Rates of a Candidate Main Interface Seal  

NASA Technical Reports Server (NTRS)

Helium leak tests were completed to characterize the leak rate of a 54 in. diameter composite space docking seal design in support of the National Aeronautics and Space Administration s (NASA's) Low Impact Docking System (LIDS). The evaluated seal design was a candidate for the main interface seal on the LIDS, which would be compressed between two vehicles, while docked, to prevent the escape of breathable air from the vehicles and into the vacuum of space. Leak tests completed at nominal temperatures of -30, 20, and 50 C on untreated and atomic oxygen (AO) exposed test samples were examined to determine the influence of both test temperature and AO exposure on the performance of the composite seal assembly. Results obtained for untreated seal samples showed leak rates which increased with increased test temperature. This general trend was not observed in tests of the AO exposed specimens. Initial examination of collected test data suggested that AO exposure resulted in higher helium leak rates, however, further analysis showed that the differences observed in the 20 and 50 C tests between the untreated and AO exposed samples were within the experimental error of the test method. Lack of discernable trends in the test data prevented concrete conclusions about the effects of test temperature and AO exposure on helium leak rates of the candidate seal design from being drawn. To facilitate a comparison of the current test data with results from previous leak tests using air as the test fluid, helium leak rates were converted to air leak rates using standard conversion factors for viscous and molecular flow. Flow rates calculated using the viscous flow conversion factor were significantly higher than the experimental air leakage values, whereas values calculated using the molecular flow conversion factor were significantly lower than the experimentally obtained air leak rates. The difference in these sets of converted flow rates and their deviation from the experimentally obtained air leak rate data suggest that neither conversion factor can be used alone to accurately convert helium leak rates to equivalent air leak rates for the test seals evaluated in this study; other leak phenomena, including permeation, must also be considered.

Penney, Nicholas; Wasowski, Janice L.; Daniels, Christopher C.

2011-01-01

133

Scattering approach to dispersive atom-surface interactions  

SciTech Connect

We develop the scattering approach for the dispersive force on a ground state atom on top of a corrugated surface. We present explicit results to first order in the corrugation amplitude. A variety of analytical results are derived in different limiting cases, including the van der Waals and Casimir-Polder regimes. We compute numerically the exact first-order dispersive potential for arbitrary separation distances and corrugation wavelengths, for a Rubidium atom on top of a silicon or gold corrugated surface. We consider in detail the correction to the proximity force approximation, and present a very simple approximation algorithm for computing the potential.

Dalvit, Diego [Los Alamos National Laboratory; Messina, Riccardo [LAB KASTLER BROSSEL; Maia Neto, Paulo [INSTITUTO DE FISICA UFRJ; Lambrecht, Astrid [LAB KASTLER BROSSEL; Reynaud, Serge [LAB KASTLER BROSSEL

2009-01-01

134

Coherence effects in scattering order expansion of light by atomic clouds  

E-print Network

We interpret cooperative scattering by a collection of cold atoms as a multiple scattering process. Starting from microscopic equations describing the response of $N$ atoms to a probe light beam, we represent the total scattered field as an infinite series of multiple scattering events. As an application of the method, we obtain analytical expressions of the coherent intensity in the double scattering approximation for Gaussian density profiles. In particular, we quantify the contributions of coherent backward and forward scattering.

Rouabah, Mohamed-Taha; Bachelard, Romain; Courteille, Philippe W; Kaiser, Robin; Piovella, Nicola

2014-01-01

135

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

136

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

137

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

PubMed

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

Gibble, Kurt

2013-05-01

138

Scattering of Cold-Atom Coherences by Hot Atoms: Frequency Shifts from Background-Gas Collisions  

NASA Astrophysics Data System (ADS)

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

Gibble, Kurt

2013-05-01

139

Diffusion coefficient of krypton atoms in helium gas at low and moderate temperatures  

NASA Astrophysics Data System (ADS)

In the present work, using the Chapman-Enskog method for dilute gases, the diffusion coefficients of ground krypton atoms in a very weakly ionized helium buffer gas are revisited. The calculations are carried out quantum mechanically in the range of low and moderate temperatures. The 1 ?+ potential-energy curve via which Kr approaches He is constructed from the most recent ab initio energy points. The reliable data points used in the construction are smoothly connected to adequate long- and short-range forms. The calculations of the classical second virial coefficients and the Boyle temperature of the helium-krypton mixture are also discussed. These coefficients and their variations in terms of temperature are analysed by adopting the constructed HeKr potential and the Lennard-Jones form that fits it. The diffusion and elastic cross sections are also explored and the resonance features they exhibit are closely examined. The variation law of the diffusion coefficients with temperature is determined for typical values of density and pressure. The coefficients show excellent agreement with the available experimental data; the discrepancies do not exceed 5%.

Bouazza, M. T.; Bouledroua, M.

140

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

2005-12-30

141

Elastic electron scattering from inert-gas atoms  

SciTech Connect

We present a comprehensive set of theoretical values for differential, total, and momentum transfer cross sections for elastic scattering of electrons by inert-gas atoms, for energies below 1 keV. In addition, we also provide Sherman function values for the xenon atom at various energies. The present work includes a critical analysis of most available experimental and theoretical data, and systematic investigations on the effect of various choices for the atomic central, exchange, and polarization potential that we used in our calculations. The objective of the present work is to employ a relatively simple and semiempirical approach with a minimum number of adjustable parameters, which could generate a reliable set of cross sections for a wide range of energies. The present data are in very good agreement with prior accurate experimental and theoretical values.

Adibzadeh, Mehrdad [Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606-3390 (United States)]. E-mail: ma4j@virginia.edu; Theodosiou, Constantine E. [Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606-3390 (United States)

2005-09-01

142

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

143

Excitation of {sup 1}S and {sup 3}S Metastable Helium Atoms to Doubly Excited States  

SciTech Connect

We present spectra of triplet and singlet metastable helium atoms resonantly photoexcited to doubly excited states. The first members of three dipole-allowed {sup 1,3}P{sup o} series have been observed and their relative photoionization cross sections determined, both in the triplet (from 1s2s {sup 3}S{sup e}) and singlet (from 1s2s {sup 1}S{sup e}) manifolds. The intensity ratios are drastically different with respect to transitions from the ground state. When radiation damping is included the results for the singlets are in agreement with theory, while for triplets spin-orbit interaction must also be taken into account.

Alagia, M. [CNR-ISMN Sezione Roma, Piazzale A. Moro 5, I-00185 Roma (Italy); Laboratorio Nazionale TASC, CNR-INFM, I-34012 Trieste (Italy); Coreno, M. [CNR-IMIP, Montelibretti, I-00016 Roma (Italy); Farrokhpour, H.; Omidyan, R.; Tabrizchi, M. [Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Franceschi, P. [Dipartimento di Fisica, Universita di Trento, I-38050 Povo (Tunisia) (Italy); Mihelic, A.; Zitnik, M. [Jozef Stefan Institute, P.O. Box 3000, SI-1001 Ljubljana (Slovenia); Moise, A.; Prince, K. C.; Richter, R. [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza, Trieste (Italy); Soederstroem, J. [Department of Physics, Uppsala University, Box 530, S-75121 Uppsala (Sweden); Synchrotron SOLEIL, l'Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex (France); Stranges, S. [Dipartimento di Chimica, Universita'La Sapienza', I-00185 Roma (Italy); Laboratorio Nazionale TASC, CNR-INFM, I-34012 Trieste (Italy)

2009-04-17

144

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

145

Absorption non-symmetric ion-atom processes in helium-rich white dwarf atmospheres  

NASA Astrophysics Data System (ADS)

In this work, the processes of absorption charge exchange and photoassociation in He+H+ collisions, together with the process of ion HeH+ photodissociation, are considered as factors influencing the opacities of the atmospheres of helium-rich white dwarfs in the far-UV and extreme ultraviolet (EUV) regions. It is shown that they should be taken into account even in the case of atmospheres of white dwarfs with H:He = 10-5. It is then established that in the case of white dwarfs with H:He ? 10-4, particularly when H:He ? 10-3, these processes have to be included ab initio in the corresponding models of their atmospheres, since in the far-UV and EUV regions they become dominant with respect to known symmetric ion-atom absorption processes.

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

2014-04-01

146

Role of electron wavepacket interference in the optical response of helium atoms  

NASA Astrophysics Data System (ADS)

Attosecond control of the optical response of helium atoms to extreme ultraviolet radiation in the presence of moderately strong infrared laser light has been recently demonstrated both by employing attosecond pulse trains (APTs) and single attosecond pulses. In the case of APTs the interference between different transiently bound electron wavepackets excited by consecutive attosecond light bursts in the train was indicated as the predominant mechanism leading to the control. We studied the same physical system with transient absorption spectroscopy using elliptically polarized infrared pulses or APTs with a varying number of pulses down to a single pulse. Our new results are not consistent with this kind of wavepacket interference being the dominant mechanism and show that its role in the control over the photoabsorption probability has to be rediscussed.

Lucchini, Matteo; Herrmann, Jens; Ludwig, André; Locher, Reto; Sabbar, Mazyar; Gallmann, Lukas; Keller, Ursula

2013-10-01

147

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

SciTech Connect

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

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

2011-09-15

148

Cs atoms on helium nanodroplets and the immersion of Cs{sup +} into the nanodroplet  

SciTech Connect

We report the non-desorption of cesium (Cs) atoms on the surface of helium nanodroplets (He{sub N}) in their 6{sup 2}P{sub 1/2} ({sup 2}{Pi}{sub 1/2}) state upon photo-excitation as well as the immersion of Cs{sup +} into the He{sub N} upon photo-ionization via the 6{sup 2}P{sub 1/2} ({sup 2}{Pi}{sub 1/2}) state. Cesium atoms on the surface of helium nanodroplets are excited with a laser to the 6{sup 2}P states. We compare laser-induced fluorescence (LIF) spectra with a desorption-sensitive method (Langmuir-Taylor detection) for different excitation energies. Dispersed fluorescence spectra show a broadening of the emission spectrum only when Cs-He{sub N} is excited with photon energies close to the atomic D{sub 1}-line, which implies an attractive character of the excited state system (Cs*-He{sub N}) potential energy curve. The experimental data are compared with a calculation of the potential energy curves of the Cs atom as a function of its distance R from the center of the He{sub N} in a pseudo-diatomic model. Calculated Franck-Condon factors for emission from the 6{sup 2}P{sub 1/2} ({sup 2}{Pi}{sub 1/2}) to the 6{sup 2}S{sub 1/2} ({sup 2}{Sigma}{sub 1/2}) state help to explain the experimental data. The stability of the Cs*-He{sub N} system allows to form Cs{sup +} snowballs in the He{sub N}, where we use the non-desorbing 6{sup 2}P{sub 1/2} ({sup 2}{Pi}{sub 1/2}) state as a springboard for ionization in a two-step ionization scheme. Subsequent immersion of positively charged Cs ions is observed in time-of-flight mass spectra, where masses up to several thousand amu were monitored. Only ionization via the 6{sup 2}P{sub 1/2} ({sup 2}{Pi}{sub 1/2}) state gives rise to a very high yield of immersed Cs{sup +} in contrast to an ionization scheme via the 6{sup 2}P{sub 3/2} ({sup 2}{Pi}{sub 3/2}) state. When resonant two-photon ionization is applied to cesium dimers on He droplets, Cs{sub 2}{sup +}-He{sub N} aggregates are observed in time-of-flight mass spectra.

Theisen, Moritz; Lackner, Florian; Ernst, Wolfgang E. [Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz (Austria)

2011-08-21

149

Observation of correlated X-ray scattering at atomic resolution  

PubMed Central

Tools to study disordered systems with local structural order, such as proteins in solution, remain limited. Such understanding is essential for e.g. rational drug design. Correlated X-ray scattering (CXS) has recently attracted new interest as a way to leverage next-generation light sources to study such disordered matter. The CXS experiment measures angular correlations of the intensity caused by the scattering of X-rays from an ensemble of identical particles, with disordered orientation and position. Averaging over 15 496 snapshot images obtained by exposing a sample of silver nanoparticles in solution to a micro-focused synchrotron radiation beam, we report on experimental efforts to obtain CXS signal from an ensemble in three dimensions. A correlation function was measured at wide angles corresponding to atomic resolution that matches theoretical predictions. These preliminary results suggest that other CXS experiments on disordered ensembles—such as proteins in solution—may be feasible in the future. PMID:24914148

Mendez, Derek; Lane, Thomas J.; Sung, Jongmin; Sellberg, Jonas; Levard, Clément; Watkins, Herschel; Cohen, Aina E.; Soltis, Michael; Sutton, Shirley; Spudich, James; Pande, Vijay; Ratner, Daniel; Doniach, Sebastian

2014-01-01

150

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

151

Deceleration and trapping of a fast supersonic beam of metastable helium atoms with a 44-electrode chip decelerator  

NASA Astrophysics Data System (ADS)

A surface-electrode decelerator consisting of 44 electrodes has been used to decelerate supersonic beams of helium Rydberg atoms moving with an initial velocity of 1200 m/s. Prior to the deceleration, the helium atoms were excited from the 1s2s1S0 metastable state to selected Rydberg-Stark states with a narrow-band tunable UV laser. Complete deceleration could be achieved over a distance of 36 mm and in 60 ?s, corresponding to an acceleration of -2.0×107 m/s2. After deceleration, the atoms were held in stationary electric traps above the chip surface, reaccelerated off the chip, and detected by pulsed electric-field ionization. The decelerator was also used to generate helium Rydberg-atom beams with a final velocity tunable between 0 and 1200 m/s. Transitions between low- and high-field-seeking Rydberg-Stark states were observed during trap loading and are attributed to adiabatic Landau-Zener dynamics at electric fields exceeding the Inglis-Teller field. By comparing the experimental results with the results of particle-trajectory simulations, the velocity distribution of the decelerated atoms was found to be characterized by temperatures ranging between 50 and 200 mK, depending on the magnitude of the electric dipole moment of the Rydberg-Stark states selected prior to the deceleration.

Allmendinger, P.; Agner, J. A.; Schmutz, H.; Merkt, F.

2013-10-01

152

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

153

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

154

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

155

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

PubMed

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

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

2014-08-21

156

Disalignment rates of the neon 2p5 and 2p10 atoms due to helium atom collisions measured at temperatures between 77 and 294 K  

NASA Astrophysics Data System (ADS)

Using a positive column of helium-neon glow discharge plasma at several temperatures between 77 and 294 K, the disalignment rates of excited neon atoms in the 2p5 and 2p10 (in Paschen notation) levels are measured by a polarization-resolved laser-induced fluorescence technique. For the 2p10 case, the disalignment rate due to radiation reabsorption is evaluated from the optical thickness of the plasma measured by a self-absorption method, and then is subtracted from the disalignment rate measured. From the slope of the obtained disalignment rate plotted against the helium atom density we determine the rate coefficients due to helium atom collisions. These rate coefficients are compared with the results of quantum multi-channel close-coupling calculations using the modified long-range potentials proposed by Bahrim and Khadilkar (2009 Phys. Rev. A 79 042715) from the original potentials of Hennecart and Masnou-Seeuws (1985 J. Phys. B: At. Mol. Phys. 18 657). Our present experiment agrees excellently with the theory for the 2p5 level at any temperatures between 77 and 294 K, and for the 2p10 state only at 294 K. Below 294 K, the experimental rate coefficients for the 2p10 state show a more rapid decrease with the decrease in temperature than the theory predicts.

Matsukuma, H.; Shikama, T.; Hasuo, M.

2011-04-01

157

Entanglement entropies in the ground states of helium-like atoms  

E-print Network

We examine the entanglement in the ground states of helium and helium-like ions using an original Hylleraas expansion. The von Neumann and linear entropies of the reduced density matrix are accurately computed by performing the Schmidt decomposition of the S singlet spatial wavefunctions. The results presented are more accurate than currently available in published literature.

Przemyslaw Koscik; Anna Okopinska

2014-04-18

158

Coherent effects in the incoherent channel of resonant radiation scattering from excited atoms  

SciTech Connect

Scattering of a resonance electromagnetic field from excited atoms cannot be described by the semiclassical theory of radiation operating with nonquantized electromagnetic fields. Field quantization effects are manifested in this case on the macroscopic level and lead to evolution of statistical properties of radiation in the course of scattering. It is found that a combined process coupling elastic scattering from an atom and induced emission from the same atom, which cannot be studied by the methods of the standard perturbation theory, plays a significant role in this effect. The process of combined scattering in extended media exhibits coherent properties that cannot be described by the standard refractive index.

Veklenko, B. A., E-mail: veklenkoba@yandex.ru [Moscow Power Engineering Institute (Technical University) (Russian Federation)

2011-05-15

159

Atom-surface scattering under classical conditions Andre Muis and J. R. Manson  

E-print Network

Atom-surface scattering under classical conditions Andre´ Muis and J. R. Manson Department Classical limit expressions of the differential reflection coefficient for atomiclike projectiles scattering from a surface are compared with recent experiments for the scattering of 200-eV Na ions from Cu 001

Manson, Joseph R.

160

Assessment of passive decay heat removal in the General Atomics Modular Helium Reactor  

E-print Network

that began in the 1950?s. The concept features a helium gas cooled reactor with a graphite moderated prismatic core that contains TRISO fuel. This study evaluates the passive decay heat removal capabilities of the MHR under abnormal conditions, more... that began in the 1950?s. The concept features a helium gas cooled reactor with a graphite moderated prismatic core that contains TRISO fuel. This study evaluates the passive decay heat removal capabilities of the MHR under abnormal conditions, more...

Cocheme, Francois Guilhem

2005-02-17

161

Pressure shifts and electron scattering in atomic and molecular gases  

NASA Astrophysics Data System (ADS)

The authors focus on one aspect of Rydberg electron scattering, namely number density effects in molecular gases. The recent study of Rydberg states of CH3I and C6H6 perturbed by H2 is the first attempt to investigate number density effects of a molecular perturber on Rydberg electrons. Highly excited Rydberg states, because of their 'large orbital' nature, are very sensitive to the surrounding medium. Photoabsorption or photoionization spectra of CH3I have also been measured as a function of perturber pressure in 11 different binary gas mixtures consisting of CH3I and each one of eleven different gaseous perturbers. Five of the perturbers were rare gases (He, Ne, Ar, Kr, Xe) and six were non-dipolar molecules (H2, CH4, N2, C2H6, C3H8). The goal of this work is to underline similarities and differences between atomic and molecular perturbers. The authors first list some results of the molecular study.

Rupnik, K.; McGlynn, S. P.; Asaf, U.

162

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

163

Phonon scattering and thermal conductance properties in two coupled graphene nanoribbons modulated with bridge atoms  

NASA Astrophysics Data System (ADS)

The phonon scattering and thermal conductance properties have been studied in two coupled graphene nanoribbons connected by different bridge atoms by using density functional theory in combination with non-equilibrium Green's function approach. The results show that a wide range of thermal conductance tuning can be realized by changing the chemical bond strength and atom mass of the bridge atoms. It is found that the chemical bond strength (bridge atom mass) plays the main role in phonon scattering at low (high) temperature. A simple equation is presented to describe the relationship among the thermal conductance, bridge atom, and temperature.

Tan, Shi-Hua; Tang, Li-Ming; Chen, Ke-Qiu

2014-05-01

164

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

SciTech Connect

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

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

2010-03-15

165

Positive effect of scattering strength of a microtoroidal cavity on atomic entanglement evolution  

SciTech Connect

We show that the rough surface of a microtoroidal cavity (scattering strength) can play a constructive role by studying the entanglement of two atoms surrounding the cavity. Analytical results show that appropriate surface roughness can enhance the atomic entanglement. In particular, the rough surface can also compensate for the loss of maximal entanglement during the evolution caused by cavity leakage and atomic spontaneous emission.

Jin Jiasen; Yu Changshui; Pei Pei; Song Heshan [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)

2010-04-15

166

Magnetic effects of critical scattering and atomic short range order in PtCo alloys  

NASA Astrophysics Data System (ADS)

Neutron scattering is a powerful method for studying the atomic and magnetic properties of materials. In particular, neutron diffuse scattering is often used to obtain a microscopic characterization of the atomic and magnetic moment distribution of alloys. The spatial correlations between moment fluctuations are measured with unpolarized neutrons while the polarized neutron cross sections measures the moment fluctuations at a site that are correlated with a concentration fluctuation at a neighbor site. In both cases, these correlations are affected by chemical short range order, and in the case of unpolarized neutron diffuse scattering, they are affected also by several other components that appear in the diffuse scattering such as thermal vibrations and spatial fluctuations due to the inhomogeneity of the magnetization in the alloy. In this work, a method is presented to analyze the unpolarized neutron diffuse scattering in alloys, taking into account all the components that affect the magnetic scattering, obtaining several atomic and magnetic ordering characteristics of these alloys.

Parra, R. E.; Gonzalez, A. C.

1998-11-01

167

Comment on ‘The spectral decomposition of the helium atom two-electron configuration in terms of hydrogenic orbitals’  

NASA Astrophysics Data System (ADS)

Brief remarks are made concerning Hutchinson et al 's paper (2013 Eur. J. Phys. 34 111) about the ground configuration of the helium atom and the importance of continuum states. The purpose of our comment is twofold: firstly, to indicate that even when using a good basis set, obtained using the self-consistent Hartree-Fock method, the contribution of other bound states and continuum ones is of some importance to calculate energy levels; and secondly, to emphasize that continuum states can be of great importance to satisfy several rigorous sum rules.

Di Rocco, Héctor O.

2013-03-01

168

Effect of charge polarization on inelastic scattering - Differential and integral cross sections for excitation of the 2/super 1/S state of helium by electron impact.  

NASA Technical Reports Server (NTRS)

Experimental differential scattering cross sections for excitation of helium by electron impact from its ground state to its 2(super 1)S state are presented at four incident electron energies in the range from 26 to 55.5 eV for scattering angles between 10 and 70 deg and at 81.6 eV for scattering angles between 10 and 80 deg. These cross sections are normalized and compared with results predicted by the Born approximation, the polarized Born approximation, and several other first-order approximations in which direct excitation is calculated in the Born approximation and exchange scattering in various Ochkur-like approximations.

Rice, J. K.; Truhlar, D. G.; Cartwright, D. C.; Trajmar, S.

1972-01-01

169

He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth. Progress report, May 1, 1991--April 30, 1994  

SciTech Connect

This progress report describes work carried out in the study of surface structure and dynamics of ionic insulators, the microscopic interactions controlling epitaxial growth and the formation of overlayers, and energy exchange in multiphonon surface scattering. The approach used is to employ high resolution helium atom scattering to study the geometry and structural features of the surfaces. Experiments have been carried out on the surface dynamics of RbCl and preliminary studies done on CoO and NiO. Epitaxial growth and overlayer dynamics experiments on the systems NaCl/NaCl(001), KBr/NaCl(001), NaCl/KBr(001) and KBr/RbCl(001) have been performed. They have collaborated with two theoretical groups to explore models of overlayer dynamics with which to compare and to interpret their experimental results. They have carried out extensive experiments on the multiphonon scattering of helium atoms from NaCl and, particularly, LiF. Work has begun on self-assembling organic films on gold and silver surfaces (alkyl thiols/Au(111) and Ag(111)).

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

1994-04-01

170

A Search for Wigner Cusps and Resonances in Positron Scattering by Atoms and Molecules  

NASA Astrophysics Data System (ADS)

Detailed elastic cross-section measurements in the vicinity of the positronium (Ps) formation threshold for He, Ne, Ar, Kr and Xe show a cusp-like feature, made visible by a small and localised depression of between (2 to 15%) of the cross-section value. Other near-threshold structures such as scattering resonances have been demonstrated in close-coupling and convergent-close-coupling calculations for helium. This investigation is undertaken to explicitly search for the presence or otherwise of scattering structures using a high efficiency (~ 1 % statistical uncertainty) and high resolution (< 70 meV) transmission based apparatus.

Caradonna, P.; Makochekanwa, C.; Jones, A.; Machacek, J. R.; Sullivan, J. P.; Buckman, S. J.

2012-11-01

171

Scattering of /sup 4/He atoms grazing the liquid-/sup 4/He surface  

SciTech Connect

Measurements of the scattering of /sup 4/He atoms grazing the surface of liquid /sup 4/He show that the reflectivity approaches unity as the perpendicular wave vector tends to zero, in agreement with theoretical predictions.

Nayak, V.U.; Edwards, D.O.; Masuhara, N.

1983-03-28

172

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

173

Frequency-doubled scattering of symmetry-breaking surface-state electrons on liquid Helium  

E-print Network

Any systems with symmetry-breaking eigenstates can effectively radiate photons with doubled frequency of the incident light, which is known as the second harmonic generation. Here, we study the second-order nonlinear effects with the system of surface-state electrons on liquid Helium. Due to the symmetry-breaking eigenstates, we show that a Rabi oscillation between two levels of the surface-state electrons can be realized beyond the usual resonant driving. Consequently, an electromagnetic field with the doubled frequency of the applied driving could be effectively radiated. This can be regarded as a frequency-doubled fluorescence, and interestingly, it works in the unusual Terahertz range.

Miao Zhang; Wenzhi Jia; Lianfu Wei

2010-12-28

174

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

175

Supersonic beam formation and helium-scattering from GaAs(110)  

Microsoft Academic Search

The author describes (1) his contributions to the science of supersonic beam formation, (2) the results of a ⁴He-scattering study from ion-damaged GaAs(110) surfaces, and (3) some preliminary results of 4He-scattering from MBE-grown GaAs(100). In our study of supersonic beam formation, we measure the angular distribution of flux from electron microscope apertures used as supersonic nozzles. This allows (1) the

1989-01-01

176

Supersonic Beam Formation and Helium-Scattering from Gallium ARSENIDE(110)  

Microsoft Academic Search

We describe (1) our contributions to the science of supersonic beam formation, (2) the results of a ^4He-scattering study from ion-damaged GaAs(110) surfaces, and (3) some preliminary results of ^4He-scattering from MBE-grown GaAs(100). In our study of supersonic beam formation, we measure the angular distribution of flux from electron microscope apertures used as supersonic nozzles. This allows (1) the ideal

Bradley Duane Weaver

1989-01-01

177

Diffraction of fast atomic projectiles during grazing scattering from a LiF(001) surface.  

PubMed

Light atoms and molecules with energies from 300 eV to 25 keV are scattered under a grazing angle of incidence from a LiF(001) surface. For impact of neutral projectiles along low index directions for strings of atoms in the surface plane we observe a defined pattern of intensity spots in the angular distribution of reflected particles which is consistently described using concepts of diffraction theory and specific features of grazing scattering of atoms from insulator surfaces. Experimental results for scattering of H, D, 3He, and 4He atoms as well as H2 and D2 molecules can be unequivocally referred to atom diffraction with de Broglie wavelengths as low as about 0.001 Angstroms. PMID:17358490

Schüller, A; Wethekam, S; Winter, H

2007-01-01

178

The measurement of angular differential cross sections at the SSL Atomic Scattering Facility  

NASA Technical Reports Server (NTRS)

The design of the SSL Atomic Scattering Facility (ASF) located at the NASA/Marshall Space Flight Center as well as some of the initial experiments to be performed with it, are covered. The goal is to develop an apparatus capable of measuring angular differential cross sections (ADCS) for the scattering of 2 to 14 eV atomic oxygen from various gaseous targets. At present little is known about atomic oxygen scattering with kinetic energies of a few eV. This apparatus is designed to increase the understanding of collisions in this energy region. Atomic oxygen scattering processes are of vital interest to NASA because the space shuttle as well as other low earth orbit satellites will be subjected to a flux of 5 eV atomic oxygen on the ram surfaces while in orbit. The primary experiments will involve the measurements of ADCS for atomic oxygen scattering from gaseous targets (in particular, molecular nitrogen). These, as well as the related initial experiments involving thermal He scattering from N2 and O2 targets will be described.

Kvale, Thomas J.

1988-01-01

179

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

180

Interacting double dark resonances in a hot atomic vapor of helium  

E-print Network

We experimentally and theoretically study two different tripod configurations using metastable helium ($^4$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 EIT 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.

S. Kumar; T. Lauprêtre; R. Ghosh; F. Bretenaker; F. Goldfarb

2011-04-18

181

Comparison of atomic oxygen measurements by incoherent scatter and satellite-borne mass spectrometer techniques  

NASA Technical Reports Server (NTRS)

Atomic oxygen densities determined by the incoherent scatter technique are compared to densities deduced from satellite-borne mass spectrometer measurements and are found to agree within experimental error. The diurnal variations inferred from the incoherent scatter measurements do show, however, some departure from diurnal variations found by modeling the mass spectrometer results. Some implications of these departures are briefly discussed.

Hedin, A. E.; Alcayde, D.

1974-01-01

182

Left-right asymmetry for scattering of polarized electrons from thallium and lead atoms  

Microsoft Academic Search

Polarized electrons were scattered elastically and inelastically from unpolarized thallium and lead atoms. The left-right scattering asymmetry has been measured for energies ranging from 2.5 to 14 eV at scattering angles between 35' and 125'. The influence of the electronic configuration of the valence electrons on the results of the asymmetry function is discussed. For elastic collisions no clear-cut conclusions

H. Geesmann; M. Bartsch; G. F. Hanne; J. Kessler

1991-01-01

183

Quantum optics in waveguides with resonant atoms: Multi-photon scattering  

Microsoft Academic Search

Quantum scattering of photons inside a one-dimensional waveguide caused by a number of closely located resonant two-level\\u000a atoms is studied using the theory of integrable quantum systems. The multi-particle wave function of scattered photons is\\u000a represented as a sum of terms of different degrees of “entanglement.” For two-photon scattering we discuss explicitly differences\\u000a in photon correlations for the single two-level

V. I. Yudson; P. Reineker

2010-01-01

184

The helium trimer with soft-core potentials  

E-print Network

The helium trimer is studied using two- and three-body soft-core potentials. Realistic helium-helium potentials present an extremely strong short-range repulsion and support a single, very shallow, bound state. The description of systems with more than two helium atoms is difficult due to the very large cancellation between kinetic and potential energy. We analyze the possibility of describing the three helium system in the ultracold regime using a gaussian representation of a widely used realistic potential, the LM2M2 interaction. However, in order to describe correctly the trimer ground state a three-body force has to be added to the gaussian interaction. With this potential model the two bound states of the trimer and the low energy scattering helium-dimer phase shifts obtained with the LM2M2 potential are well reproduced.

A. Kievsky; E. Garrido; C. Romero-Redondo; P. Barletta

2011-01-10

185

Hyperthermal Ar atom scattering from a C(0001) surface.  

PubMed

Experiments and simulations on the scattering of hyperthermal Ar from a C(0001) surface have been conducted. Measurements of the energy and angular distributions of the scattered Ar flux were made over a range of incident angles, incident energies (2.8-14.1 eV), and surface temperatures (150-700 K). In all cases, the scattering is concentrated in a narrow superspecular peak, with significant energy exchange with the surface. The simulations closely reproduce the experimental observations. Unlike recent experiments on hyperthermal Xe scattering from graphite [Watanabe et al., Eur. Phys. J. D 38, 103 (2006)], the angular dependence of the energy loss is not approximated by the hard cubes model. The simulations are used to investigate why parallel momentum conservation describes Xe scattering, but not Ar scattering, from the surface of graphite. These studies extend our knowledge of gas-surface collisional energy transfer in the hyperthermal regime, and also demonstrate the importance of performing realistic numerical simulations for modeling such encounters. PMID:18554044

Gibson, K D; Sibener, S J; Upadhyaya, Hari P; Brunsvold, Amy L; Zhang, Jianming; Minton, Timothy K; Troya, Diego

2008-06-14

186

Interaction potentials for fast atoms in front of Al surfaces probed by rainbow scattering  

NASA Astrophysics Data System (ADS)

Rainbow scattering for grazing-angle incidence of atoms at surfaces along low-indexed channeling directions provides a sensitive probe of quasistatic atom-surface potentials. The dependence of the rainbow angle on the kinetic energy for the projectile motion perpendicular to the surface, E? , varies with the electronic structure of the projectile as well as the crystallographic face of the aluminum surface. Comparison between experiment and classical Monte Carlo trajectory simulations demonstrates that the superposition of binary atom-atom potentials fails to adequately represent the equipotential surfaces. Ab initio atom-surface potentials based on density-functional theory are required to reach satisfactory agreement with experiment.

Tiwald, P.; Schüller, A.; Winter, H.; Tökesi, K.; Aigner, F.; Gräfe, S.; Lemell, C.; Burgdörfer, J.

2010-09-01

187

Z dependence of electron scattering by single atoms into annular dark-field detectors.  

PubMed

A simple parameterization is presented for the elastic electron scattering cross sections from single atoms into the annular dark-field (ADF) detector of a scanning transmission electron microscope (STEM). The dependence on atomic number, Z, and inner reciprocal radius of the annular detector, q(0), of the cross section ?(Z,q(0)) is expressed by the empirical relation [see formula in text] where A(q(0)) is the cross section for hydrogen (Z = 1), and the detector is assumed to have a large outer reciprocal radius. Using electron elastic scattering factors determined from relativistic Hartree-Fock simulations of the atomic electron charge density, values of the exponent n(Z,q(0)) are tabulated as a function of Z and q(0), for STEM probe sizes of 1.0 and 2.0 Å. Comparison with recently published experimental data for single-atom scattering [Krivanek et al. (2010). Nature 464, 571-574] suggests that experimentally measured exponent values are systematically lower than the values predicted for elastic scattering from low-Z atoms. It is proposed that this discrepancy arises from the inelastic scattering contribution to the ADF signal. A simple expression is proposed that corrects the exponent n(Z,q(0)) for inelastic scattering into the annular detector. PMID:22051035

Treacy, Michael M J

2011-12-01

188

Two-atom model in enhanced ion backscattering near 180/sup 0/ scattering angles  

SciTech Connect

The recent discovery by Pronko, Appleton, Holland, and Wilson of an unusual enhancement of the yield of ions backscattered through angles close to 180/sup 0/ from the near surface regions of solids is investigated using a two-atom scattering model. The model predicts an enhancement effect in amorphous solids 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. Predictions are given of the dependence of the yield enhancement on the following parameters: ion energy, backscattering depth, exit angle, scattering potential, atomic numbers of projectile and target, and atomic density of target.

Oen, O.S.

1981-06-01

189

Supersonic Beam Formation and Helium-Scattering from Gallium ARSENIDE(110)  

NASA Astrophysics Data System (ADS)

We describe (1) our contributions to the science of supersonic beam formation, (2) the results of a ^4He-scattering study from ion-damaged GaAs(110) surfaces, and (3) some preliminary results of ^4He-scattering from MBE-grown GaAs(100). In our study of supersonic beam formation, we measure the angular distribution of flux from electron microscope apertures used as supersonic nozzles. This allows (1) the ideal on-axis beam intensity to be calculated and a comparison to be made with effusive beams (a fourfold intensity enhancement occurs), and allows (2) accurate calculations of flow rates through the differential stages of a supersonic beam source. We also study (3) beam attenuation due to collisions with background gases, and show how skimmer-beam interference and condensation are avoided. The contributions (1)-(3) allow specification of the operating parameters leading to maximum beam signal. ^4He-beams are then used in comparing scattering intensities from clean and Ar^+ ion-damaged GaAs(110). We find that the average residual surface damage due to single ion impacts decreases from small groups of defects (vacancies and adatoms) at low sample temperature T during bombardment to isolated monovacancies at higher T. This decrease occurs even in the absence of thermal annealing, and is possibly due to the T-dependent accommodation of adatom energy by the crystal. We also show ^4He -scattering data from MBE-grown As-stabilized (2 x 4) reconstructed GaAs(100). The scattering intensity decays with a time constant of ~1 hour, about 100 times faster than a (110) surface under comparable vacuum conditions, but the cause of this instability is unknown.

Weaver, Bradley Duane

190

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

191

Effective-range corrections to three-body recombination for atoms with large scattering length  

SciTech Connect

Few-body systems with large scattering length a have universal properties that do not depend on the details of their interactions at short distances. The rate constant for three-body recombination of bosonic atoms of mass m into a shallow dimer scales as ({Dirac_h}/2{pi})a{sup 4}/m times a log-periodic function of the scattering length. We calculate the leading and subleading corrections to the rate constant, which are due to the effective range of the atoms, and study the correlation between the rate constant and the atom-dimer scattering length. Our results are applied to {sup 4}He atoms as a test case.

Hammer, H.-W.; Laehde, Timo A.; Platter, L. [Helmholtz-Institut fuer Strahlen- und Kernphysik (Theorie), Universitaet Bonn, 53115 Bonn (Germany); Department of Physics, University of Washington, Seattle, Washington 98195-1560 (United States); Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701 (United States)

2007-03-15

192

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

SciTech Connect

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

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

1980-01-01

193

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

194

An Introduction to the Helium Ion Microscope  

NASA Astrophysics Data System (ADS)

A new microscope has been developed that uses a beam of helium ions which is focused and scanned across the sample. In principle, and in its applications, it is similar to a traditional scanning electron microscope (SEM). However, the source technology, the sample interaction, and the contrast mechanisms are distinctly different. The helium ion source offers high brightness (4×109 A/cm2sr) and a small energy spread (?E/E˜3×10-5), and hence allows the beam to be focused to small probe sizes (as small as 0.25 nm). As the beam interacts with the sample, the beam penetrates relatively deeply before it diverges and hence there is a narrow sample interaction region near the surface. The helium beam generates secondary electrons, scattered helium atoms (ions and neutrals), and other detectable particles from which images can be generated or analysis can be performed.

Notte, John; Ward, Bill; Economou, Nick; Hill, Ray; Percival, Randy; Farkas, Lou; McVey, Shawn

2007-09-01

195

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

SciTech Connect

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

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

2008-03-19

196

LIGHT SCATTERED FROM TWO ATOMS W. M. Itano, U. Eichmann,  

E-print Network

polarizer P was inserted before D2. Another lens system formed a real image of the ions on another imaging are present only in one polarization of the scattered light. The polarization dependence is related-cooled to temperatures of a few millikelvins with a beam of linearly polarized, continuous-wave light. Cooling

197

Electron Diffraction of Superfluid Helium Droplets  

PubMed Central

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

2014-01-01

198

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

199

Wave functions and two-electron probability distributions of the Hooke's-law atom and helium  

Microsoft Academic Search

The Hooke's-law atom (hookium) provides an exactly soluble model for a two-electron atom in which the nuclear-electron Coulombic attraction has been replaced by a harmonic one. Starting from the known exact position-space wave function for the ground state of hookium, we present the momentum-space wave function. We also look at the intracules, two-electron probability distributions, for hookium in position, momentum,

Darragh P. ONeill; Peter M. W. Gill

2003-01-01

200

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

201

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

202

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

203

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

204

Transverse momentum transfer in atom-light scattering  

NASA Astrophysics Data System (ADS)

We predict a photon Hall effect in the optical cross section of atomic hydrogen, which is caused by the interference between an electric-quadrupole transition and an electric-dipole transition from the ground state to 3D3/2 and 3P3/2. This induces a magnetotransverse acceleration comparable to a fraction of g.

van Tiggelen, B. A.; Nussle, A.; Rikken, G. L. J. A.

2013-06-01

205

Low energy electron scattering from atoms: Search for nanocatalysts  

NASA Astrophysics Data System (ADS)

Manipulating the structure and the dynamics of metallic nanoparticles, attractive due to their optical, electronic and magnetic properties, including applications in catalysis, requires a fundamental understanding of the dynamic processes at the atomic level. The fundamental mechanism of catalysis at the atomic scale has already been proposed and demonstrated in Au, Pd and Au-Pd catalysis of H2O2 through the scrutiny of low energy electron elastic total cross sections (TCSs) [1]. The use of mixed precious metal catalysts can produce even higher activities compared to Au alone [2]. Here the interplay between negative ion resonances and Ramsauer-Townsend minima that characterize low energy electron TCSs for Au is identified as the fundamental signature of nanoscale catalysts. Calculated electron elastic TCSs for Ag, Pt, Pd, Ru and Y atoms are presented as illustrations. The recent complex angular momentum methodology is used for the calculations [3]. It is concluded that these atoms are suitable candidates for nanocatalysts individually or in combinations. [4pt] [1] A.Z. Msezane et al, J. Phys. B 43, 201001 (2010); EurophysicsNews 6, 11 (2010) [0pt] [2] D.T. Thompson, Nano Today 2, 40 (2007) [0pt] [3] D. Sokolovski et al, Phys. Rev. A 76, 012705 (2007)

Msezane, A. Z.; Felfli, Z.; Sokolovski, D.

2011-06-01

206

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

207

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

208

Inelastic atomic scattering by high-energy photons and charged particles  

Microsoft Academic Search

The first-order cross section for Compton scattering is expressed in terms of the cross section for scattering by fast charged particles in the plane-wave Born approximation as a function of the momentum, Q, transferred by the projectile to the atomic electron(s). As an example of this relationship, the high-energy photon limit for the ratio of double to single ionization by

J. Burgdoerfer; L. R. Andersson; J. H. McGuire; T. Ishihara

1994-01-01

209

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

210

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

211

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

ERIC Educational Resources Information Center

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

Taylor, N.; And Others

1981-01-01

212

Multiple x-ray scattering in multi-atom resonant photoemission  

NASA Astrophysics Data System (ADS)

Multi-atom resonant photoemission (MARPE) occurs when the photon energy is tuned to a core-level absorption edge of an atom neighboring the atom from which the photoelectron is being emitted, with the emitting level having a lower binding energy than the resonant level. Large peak intensity enhancements of 30-100oxides, in a metallic system, metal halides, and adsorbate systems. A theoretical model for the effect based on an extension of normal intraatomic resonant photoemission theory has also been developed and succesfully applied to MnO. The equivalence of that model with a single X-ray scattering picture is discussed in this paper. Furthermore, the extension to multiple X-ray scattering is shown to be relevant in the correct quatitative analysis of the effect. Finally, the role of such multi-atom effects in anomalous X-ray absorption and intraatomic resonant photoemission is studied.

Garcia de Abajo, F. Javier; Labute, Monte; Fadley, Charles S.; van Hove, Michel A.

2000-03-01

213

LETTER TO THE EDITOR: Positronium-hydrogen atom elastic scattering at medium energies  

NASA Astrophysics Data System (ADS)

We study the elastic scattering of positronium atoms by hydrogen atoms at medium energies using partial-wave Born-Oppenheimer (BO) exchange amplitudes and report accurate BO cross sections in the energy range 0 to 60 eV. The present BO results agree with a 22-state R-matrix and a five-state coupled-channel model potential calculation, but disagree strongly with a conventional close-coupling calculation as well as its input BO amplitudes at medium energies.

Adhikari, Sadhan K.; Mandal, Puspajit

2000-10-01

214

Scattering of helium nozzle beams from LiF/001/ and NaCl/001/ crystal surfaces. I - Elastic and inelastic transitions  

NASA Technical Reports Server (NTRS)

Nozzle-type atomic beams and time-of-flight detection methods are employed in studies of the scattering of thermal-energy He-4 atoms from LiF (001) and NaCl (001) surfaces under conditions where diffraction is observed and where substantial inelastic scattering occurs. Intensity and speed-distribution measurements are obtained for the portion of the scattering within the plane of incidence. For these measurements, incident-beam orientation with respect to target (polar angle and azimuth), incident-beam de Broglie wavelength (0.38-0.60 A), and crystal temperature (300-1000 K) are varied. For LiF, the measured intensity distributions exhibit sharp peaks comprised essentially of elastically scattered atoms and corresponding to up to third-order diffraction, inelastic scattering in the form of local dispersion about each of the elastic peaks, and a component of nominally diffuse scattering distributed below and between the peaks. For NaCl, the same general types of scattering are observed, with elastic scattering less prevalent, intensity peaks not as sharp, and dispersions of inelastic scattering harder to resolve.

Bledsoe, J. R.; Fisher, S. S.

1974-01-01

215

Single- and multiphonon atom-surface scattering in the quantum regime  

NASA Astrophysics Data System (ADS)

Recent developments and achievements in the theoretical interpretation of inelastic scattering of thermal energy beams of He and other noble gas atoms from surfaces are reviewed, with a special emphasis on the successful interpretation of multiphonon He atom scattering (HAS) experiments. These developments have been stimulated by the remarkable successes of HAS time-of-flight spectroscopy in revealing information on the low-energy dynamics of the various surfaces, adlayers and isolated adsorbates. The diversity of the developed theoretical approaches reflects also the diversity of the various observables that have been assessed under the different experimental conditions. To aid the systematization and cross-correlation among the different model descriptions we first present a short outline of their characteristics and main achievements. Although many of these theories have been improved and refined in the course of time, a unified approach was required for a fully quantum treatment of elastic (diffractive or diffuse) and inelastic (single- and multiphonon) atom-surface scattering processes on an equivalent footing. A substantial progress towards this end has been made in recent years by going beyond the standard semiclassical and perturbation methods in the analyses of HAS experiments. The present review focuses on the development of one such approach based on the so-called scattering spectrum formalism in which the quantum scattering amplitudes are calculated by using cumulant or linked cluster expansion in terms of the correlated and uncorrelated scattering events. This formalism is equally well suited for making a passage to perturbative quantum-mechanical and nonperturbative semiclassical treatments of inelastic atom-surface scattering. Using the developed formalism we first establish the relevant approximations for calculating the scattering spectra and examine their validity for the scattering conditions typical of HAS. In the next step the formalism is applied to benchmark systems to interpret the scattering data which intermingledly depend on the vibrational dynamics of the investigated surfaces per se and on the projectile-surface interaction potentials. A very good agreement between experimental results and theoretical predictions for HAS from surfaces characteristic of the different types of surface vibrational dynamics is obtained in all studied scattering regimes. This demonstrates a broad applicability of the developed formalism in the interpretations of inelastic HAS experiments and in the assessments of phonon-mediated energy transfer in gas-surface collisions.

Gumhalter, Branko

2001-09-01

216

Precision measurement of laser RF double resonance spectra with an effective compensation of residual magnetic field. For nuclear laser spectroscopy of RI atoms in superfluid helium  

NASA Astrophysics Data System (ADS)

We have been developing a novel laser spectroscopy method-"OROCHI" for radioisotopes trapped in superfluid helium. This new method is expected to determine nuclear spins and moments of exotic nuclei by precise measurement of Zeeman and hyperfine splitting of atoms using laser double resonance method. Its feasibility has been confirmed by means of a series of experiments with various stable atoms in superfluid helium, while the accuracy of experimental results is found strongly affected by external magnetic field. In order to obtain reliable and accurate results for atomic spectra with "OROCHI" method, based on laser RF double resonance spectroscopy of on-line experiment, we performed off-line test experiments for Rb in helium buffer gas. In this test experiment, we used three mutually orthogonal coils to effectively compensate for laboratory residual magnetic field and subsequently observed precise laser RF double resonance spectra of atoms which affords us accurate nuclear spin value. By comparison of those results, we could make clear the effect of residual magnetic field on experimental results. The details of "OROCHI" method and test experiments are presented.

Yang, X. F.; Furukawa, T.; Fujita, T.; Imamura, K.; Matsuo, Y.

2014-06-01

217

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

218

Flux measurements of alkali atoms diffusing via multiple surface scattering in a silanated glass tube  

Microsoft Academic Search

Alkali atoms that are diffusing away from a source via multiple surface scattering in a nonstick coated glass tube are monitored by laser fluorescence. Densities are measured by fluorescence intensity and weak-field absorption, and small asymmetries in the line shape provide a measurement of the flux. Average velocities as small as 0.3% of the thermal velocity can be resolved using

Michael A Waxman; Tyler Morgus; Alan D Streater

2002-01-01

219

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.

220

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

E-print Network

Classical Theory of Atom Scattering from Corrugated Surfaces W. W. Hayes Physical Sciences phonon transfers. In the classical limit the theory produces an expression that includes the effects A theory based in the semiclassical eikonal approximation is developed to describe energy trans- fer

Manson, Joseph R.

221

PHYSICAL REVIEW B 89, 045406 (2014) Classical and semiclassical theories of atom scattering from corrugated surfaces  

E-print Network

PHYSICAL REVIEW B 89, 045406 (2014) Classical and semiclassical theories of atom scattering from or disordered. This theory is extended from the quantum mechanical regime to the classical regime of complete to further expressions for multiple-phonon transfers. In the classical limit, the theory produces

Manson, Joseph R.

222

Towards non-classical light storage via atomic-vapor Raman scattering  

E-print Network

evidence for storage of a photon-number-squeezed state of light. The scheme is based on spontaneous Raman to store photons for long times, one approach to a practical quantum memory is to reversibly transferTowards non-classical light storage via atomic-vapor Raman scattering C. H. van der Wala,b, M. D

van der Wal, Caspar H.

223

Near threshold measurements of positron scattering from atoms and molecules  

NASA Astrophysics Data System (ADS)

Positron interaction with matter has many applications in such fields as material science, astronomy and condensed matter. Previous positron scattering experiments, which have typically had a resolution of 0.4 eV or greater, have provided important information. However they have been unable to probe threshold behaviors and resolve specific vibrational and electronic transitions. The continued development of a buffer-gas trap has led to a high resolution (i.e., 25 meV), low energy positron beam (i.e., E<=0.1 eV) with which to do these measurements. [1,2] A brief description will be presented of the current experimental setup and discussion of new analysis techniques to measure differential elastic, integral inelastic, grand total and total positronium cross sections. Current data and comparisons to theory will also be discussed. Work supported by NSF and ONR. [1] Gilbert et al., Appl. Phys. Lett. 70 1944 (1997) [2] Gilbert et al., Phys. Rev. Lett. 82 5032 (1999) Present addresses: * Photon Factory, High Energy Accelerator Research Organization, Japan ** Research School of Physical Sciences and Engineering, Australian National University, Australia

Marler, J. P.; Sullivan, J. P.; Buckman, S. J.; Gilbert, S. J.; Surko, C. M.

2002-05-01

224

A Zeeman-effect based scatter correction system for non-dispersive atomic fluorescence spectrometry  

NASA Astrophysics Data System (ADS)

A Zeeman-effect based method of correcting for the scattering of source radiation in atomic fluorescence spectrometry (AFS) is described. The magnetic field is applied to the atomization cell in a direction transverse to the source and detected beams. Both polarized and field modulated Zeeman AFS are examined. Fluorescence signals corrected for scattering are derived from differences in the measured light intensities caused by changes in the incident light polarization and/or field intensity. Results are given for the determination of Cd in an Al matrix, and for Cd, Hg, and Zn in NBS fly ash, orchard leaves, and river sediment. The scatter corrected values obtained by this method are in agreement with certified values.

Naranjit, D. A.; Radziuk, B. H.; Van Loon, J. C.

225

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

226

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

227

Sensitive Polarization Dependence for Helium Rydberg Atoms Driven by Strong Microwave Fields  

NASA Astrophysics Data System (ADS)

We prepare n^3S He Rydberg atoms with selected values n>=25 in a fast beam using CO2 lasers and double-resonance excitation. They then fly through a TE_121 mode cavity, exposing them to a half-sine pulse (about 350 field osc.) of 9.904 GHz electric field whose polarization can be varied: linear (LP), elliptical (EP), and circular (CP). Making EP close to LP can lead to substantial changes in microwave-power-dependent transitions to nearby bound states. In at least one case, a sharp dip in the LP signal( W. van de Water et al., Phys. Rev. A 42), 572 (1990) is transformed by EP into a pattern reminiscent of Stueckelberg oscillations, previously observed with LP at higher frequencies.( S. Yoakum et al., Phys. Rev. Lett. 69), 1919 (1992) Calculations suggest that pulse-shape-induced dynamics at Floquet avoided-crossing(s) explain the LP behavior. Changing the field to EP clearly must modify this behavior. We will discuss this kind of data as well as the polarization dependence of microwave ionization of n^3S He Rydberg atoms.

Zelazny, S. A.; Bellermann, M. R. W.; Smith, L. L.; Koch, P. M.

1996-05-01

228

Temperature Dependence in Atom-Surface Scattering Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovoth, Israel  

E-print Network

Temperature Dependence in Atom-Surface Scattering Eli Pollak Chemical Physics Department, Weizmann measure of the temperature dependence of energy resolved atom-surface scattering spectra measured under conditions of higher translational energies, larger surface temperatures and partic- ularly for heavier mass

Manson, Joseph R.

229

Near-Resonant Rayleigh Scattering Method for Measurements of Alkali Atomic Density in Combustion Gas Plasmas  

NASA Astrophysics Data System (ADS)

This paper reports the development of a non-intrusive, space-resolved method for density measurements of alkali atoms in combustion gas plasmas. A sodium density of over 1014 cm-3 in an air-acetylene flame was measured using a near-resonant Rayleigh scattering (NRRS) method, in which the wavelength of the incident laser was detuned from the resonance line of the sodium atoms in order to avoid reabsorption of the scattered signal light. The results agree fairly well with those obtained by the spectral absorption method and the Na reference cell method. The results show that the NRRS method described here can also be used to measure atomic densities of the order of 1016 cm-3, typical values in an open-cycle MHD power-generation plasma.

Watanabe, Yukio; Ikegami, Tomoaki; Nishiyama, Toshio; Akazaki, Masanori

1984-07-01

230

Continuous-flow determination of aqueous sulfur by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry with gas-phase sample introduction  

Microsoft Academic Search

A simple continuous-flow generation of volatile hydrogen sulfide and sulfur dioxide by acidification of aqueous sulfide and sulfite ions, respectively, is described for the determination of low concentrations of sulfur by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry (MIP-AES) in the normal ultraviolet (UV) and vacuum ultraviolet (VUV) regions of the spectrum. For measuring spectral lines in the VUV region,

Taketoshi Nakahara; Toshio Mori; Satoru Morimoto; Hiroshi Ishikawa

1995-01-01

231

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

232

Rayleigh scatter in kilovoltage x-ray imaging: is the independent atom approximation good enough?  

NASA Astrophysics Data System (ADS)

Monte Carlo simulation is the gold standard method for modelling scattering processes in medical x-ray imaging. General-purpose Monte Carlo codes, however, typically use the independent atom approximation (IAA). This is known to be inaccurate for Rayleigh scattering, for many materials, in the forward direction. This work addresses whether the IAA is sufficient for the typical modelling tasks in medical kilovoltage x-ray imaging. As a means of comparison, we incorporate a more realistic 'interference function' model into a custom-written Monte Carlo code. First, we conduct simulations of scatter from isolated voxels of soft tissue, adipose, cortical bone and spongiosa. Then, we simulate scatter profiles from a cylinder of water and from phantoms of a patient's head, thorax and pelvis, constructed from diagnostic-quality CT data sets. Lastly, we reconstruct CT numbers from simulated sets of projection images and investigate the quantitative effects of the approximation. We show that the IAA can produce errors of several per cent of the total scatter, across a projection image, for typical x-ray beams and patients. The errors in reconstructed CT number, however, for the phantoms simulated, were small (typically < 10 HU). The IAA can therefore be considered sufficient for the modelling of scatter correction in CT imaging. Where accurate quantitative estimates of scatter in individual projection images are required, however, the appropriate interference functions should be included.

Poludniowski, G.; Evans, P. M.; Webb, S.

2009-11-01

233

The helium atom in metallic electron gases: a comparative study based on screened Schrödinger Hamiltonians  

NASA Astrophysics Data System (ADS)

In the presence of an environment of mobile charges, the bound-state Schrödinger Hamiltonian for an embedded He atom differs from its vacuum form. The central problem of incorporating screening in the nucleus-bound-electron and bound-electron-bound-electron terms of this Hamiltonian is investigated here for the He ground state in a comparative manner by using two models, and the same product form of 1s-type parametric hydrogenic functions to perform exploratory variational calculations. Both models employ induced charge densities in the corresponding Poisson equations with a fixed point-like nucleus, but the underlying charge-density response of the host system is generated by differently chosen perturbations. These are the point-charge nucleus and the nucleus-bound-electron charge distribution as external perturbations. The repulsive bound-electron-bound-electron interaction in the Hamiltonian is modelled by a parametric Yukawa-type potential. Using the consistent variational results for the binding energies and wavefunctions, the charge-state-dependent stopping power of a metallic target for slowly moving He is briefly discussed.

Nagy, I.; Aldazabal, I.; Glasser, M. L.

2012-05-01

234

Measurements of metastable atom density using energies and densities of energetic "fast" electrons detected in the electron energy distribution function associated with the afterglow plasma produced by a radio frequency inductively coupled plasma helium d.  

E-print Network

??In this work, electron density, electron temperature, electron energy distribution function (EEDF), and metastable atom density in the afterglow of low-pressure (50 mTorr) helium radio-frequency… (more)

Blessington, Jon C.

2007-01-01

235

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

236

Observation of Suppression of Light Scattering Induced by Dipole-Dipole Interactions in a Cold-Atom Ensemble  

NASA Astrophysics Data System (ADS)

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 number of atoms from 1 to ˜450, we observe a broadening of the line, a small redshift and, consistently with these, a strong suppression of the scattered light with respect to the noninteracting atom case. We compare our data to numerical simulations of the optical response, which include the internal level structure of the atoms.

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

2014-09-01

237

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

PubMed

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 number of atoms from 1 to ?450, we observe a broadening of the line, a small redshift and, consistently with these, a strong suppression of the scattered light with respect to the noninteracting atom case. We compare our data to numerical simulations of the optical response, which include the internal level structure of the atoms. PMID:25302887

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

2014-09-26

238

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

E-print Network

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

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

2006-11-22

239

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.

240

An atomic layer deposition chamber for in situ x-ray diffraction and scattering analysis  

NASA Astrophysics Data System (ADS)

The crystal structure of thin films grown by atomic layer deposition (ALD) will determine important performance properties such as conductivity, breakdown voltage, and catalytic activity. We report the design of an atomic layer deposition chamber for in situ x-ray analysis that can be used to monitor changes to the crystal structural during ALD. The application of the chamber is demonstrated for Pt ALD on amorphous SiO2 and SrTiO3 (001) using synchrotron-based high resolution x-ray diffraction, grazing incidence x-ray diffraction, and grazing incidence small angle scattering.

Geyer, Scott M.; Methaapanon, Rungthiwa; Johnson, Richard W.; Kim, Woo-Hee; Van Campen, Douglas G.; Metha, Apurva; Bent, Stacey F.

2014-05-01

241

An atomic layer deposition chamber for in situ x-ray diffraction and scattering analysis.  

PubMed

The crystal structure of thin films grown by atomic layer deposition (ALD) will determine important performance properties such as conductivity, breakdown voltage, and catalytic activity. We report the design of an atomic layer deposition chamber for in situ x-ray analysis that can be used to monitor changes to the crystal structural during ALD. The application of the chamber is demonstrated for Pt ALD on amorphous SiO2 and SrTiO3 (001) using synchrotron-based high resolution x-ray diffraction, grazing incidence x-ray diffraction, and grazing incidence small angle scattering. PMID:24880424

Geyer, Scott M; Methaapanon, Rungthiwa; Johnson, Richard W; Kim, Woo-Hee; Van Campen, Douglas G; Metha, Apurva; Bent, Stacey F

2014-05-01

242

QED effects in scattering processes involving atomic bound states: Radiative recombination  

NASA Astrophysics Data System (ADS)

The standard perturbative expansion of the S matrix cannot generally be used in the treatment of atomic scattering processes, involving atomic bound states, due to the special type of singularity that can appear here. It is demonstrated in the present paper that as a consequence of the optical theorem for free particles the effective Hamiltonian is closely related to the total cross section, a relation that is valid also when bound states are present. This implies that methods designed for structure calculations also can be used in dynamical processes. We have found that the covariant-evolution-operator technique that we have developed for structure calculations is here particularly useful. This is a consequence of the fact that the regular part of this operator (the Green's operator), running over all times, is essentially equal to the effective Hamiltonian and therefore directly related to the scattering cross section. In this paper the procedure is demonstrated for the case of radiative recombination.

Lindgren, Ingvar; Salomonson, Sten; Holmberg, Johan

2014-06-01

243

Diffraction of swift atoms after grazing scattering from metal surfaces: N/Ag(111) system  

SciTech Connect

Diffraction patterns produced by grazing scattering of fast N atoms from a Ag(111) surface are investigated by employing the surface eikonal approximation. This method is a distorted-wave theory that takes into account the coherent addition of contributions coming from different projectile paths. In the model the projectile-surface potential is obtained from an accurate density-functional theory calculation. The dependence of the scattered projectile spectra on impact energy and incidence channel is analyzed, and possible incident direction and energy range for the observation of the interference patterns are predicted. In addition, it is found that as a result of the high reactivity of N atoms, asymmetries of the surface potential might be detected through their effects on diffraction patterns.

Gravielle, M. S. [Instituto de Astronomia y Fisica del Espacio (CONICET-UBA) and Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires (Argentina); Bocan, G. A. [Centro Atomico Bariloche, Comision Nacional de Energia Atomica, and Consejo Nacional de Investigaciones Cientificas y Tecnicas, S.C. de Bariloche, Rio Negro (Argentina); Diez Muino, R. [Donostia International Physics Center (DIPC) and Centro de Fisica de Materiales CSIC-UPV/EHU, San Sebastian (Spain)

2010-11-15

244

Elastic scattering of high-energy electrons by dopant atoms within a crystal in transmission electron microscopy.  

PubMed

A Bloch-wave model of dopant-atom scattering is developed using perturbation theory for parallel illumination in a transmission electron microscope. Dopant-atom scattering causes a change in the Bloch-wave excitations, with transitions from one Bloch state to another being governed by the amplitudes of the Bloch states at the dopant-atom position. The scattering mechanisms therefore depend on whether the dopant atom is substitutional or interstitial as well as the orientation of the crystal. The model is used to calculate the electron wavefunction for substitutional and interstitial Mo atoms in [111]- and [001]-oriented body-centred cubic Fe and the results overall are consistent with multislice simulations. However, subtle differences are also observed. For example, in the Bloch-wave model the phase change of the incident electrons (with respect to the perfect crystal) due to dopant-atom scattering varies with the crystallographic orientation while in multislice theory the phase change is constant. This is likely to be due to the assumptions made in the Bloch-wave model, such as neglect of elastic diffuse scattering. Apart from providing a fundamental understanding of dopant-atom scattering, the model can also potentially be extended to analyse dopant-atom imaging in a scanning transmission electron microscope. PMID:18931417

Mendis, B G

2008-11-01

245

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

246

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

247

Scattering of He atoms from surface defects by grazingangle diffraction beams D. Far as, 2 M. Patting, 1 K.H. Rieder, 1 and J. R. Manson 3  

E-print Network

Scattering of He atoms from surface defects by grazing­angle diffraction beams D. Far� â?? as, 2 M the scattering of He atoms from surfaces can be observed at grazing final angles of up to # f #90° with respect to the surface normal. For He atom scattering from Rh#311# under conditions in which a diffraction beam exits

Manson, Joseph R.

248

Classical Helium Model  

NSDL National Science Digital Library

The EJS Classical Helium Model is an example of a three-body problem that is similar to the gravitational three-body problem of a heavy sun and two light planets. The important difference is that the helium atom's two electrons repel one another, unlike the planetary case where the intraplanetary interaction is attractive. The EJS Classical Helium Model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_mech_orbits_ClassicalHelium.jar file will run the program if Java is installed.

Christian, Wolfgang

2009-03-14

249

The Effect of Electron Multiple Scattering and Far Atomic Shells on the Angular Distribution of Auger- and Photoelectrons Emitted by Adsorbed Atoms  

NASA Astrophysics Data System (ADS)

A Theoretical description of the angle-resolved specta of rapid Auger- and photoelectrons emitted by absorbed atoms is presented. The effects of electron multiple-scattering and far atomic shells on the angular distribution of photoelectrons with kinetic energy 317 eV emitted by one Cu-monolayer on Ni-surface are studied.

Vedrinskii, R. V.; Bugaev, L. A.

1992-01-01

250

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

SciTech Connect

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

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

1996-09-01

251

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

252

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

253

Compton scattering of energetic photons by light atoms in the presence of a low-frequency electromagnetic field  

Microsoft Academic Search

We consider the influence of a weak low-frequency electromagnetic field on Compton scattering of a high-energy photon by an electron which is initially bound in the ground state of a light atomic target. It is shown that this influence can be very substantial for the Compton scattering with a large (on the target scale) momentum transfer to the target when

A B Voitkiv; N Grün; J Ullrich

2003-01-01

254

Self-Consistent Model of Roton Cluster Excitations in Liquid Helium II  

E-print Network

We have proposed a model of roton cluster excitations in liquid helium~II based on a Schr\\"odinger-type equation with a self-consistent confining potential. We have derived an equation for the number of atoms in roton excitations, which can be treated as quantum $3{\\rm D}$ solitons, depending on vibrational quantum numbers. It is shown that the smallest roton cluster is in the symmetric vibrational quantum state and consists of 13 helium atoms. We have also used a modified Born approximation to calculate the $s$-scattering length for helium atoms. This allows us to calculate all parameters of Landau's roton excitation spectrum, in agreement to high accuracy with experimental measurements from neutron scattering.

V. I. Kruglov; M. J. Collett

2006-05-18

255

Comparative studies on ionizations in Ps-atom scattering using the Coulomb-Born approximation  

NASA Astrophysics Data System (ADS)

Three different types of ionization in Ps-He scattering are studied using the Coulomb-Born approximation. Two different approaches are used to orthogonalize the continuum Coulomb wavefunctions. The non-unitarity problem discussed by McAlinden et al (McAlinden M T, MacDonald F G R S and Walters H R J 1996 Can. J. Phys. 74 434) in Ps-atom scattering has been overcome in the present analytical methodology. All the important elastic and inelastic channels for both the atoms are taken into consideration. Comparison of the ionization cross sections with other atomic targets reveals the importance of van der Waals forces through the shifting of peak positions in agreement with the predicted strengths (Martin D W and Fraser P A 1980 J. Phys. B: At. Mol. Phys. 13 3383). The possibility of an additional channel is suggested from a comparison of the total cross section curve with experiment.

Ray, Hasi

2002-08-01

256

Ionization of He atoms during grazing scattering from a metal surface  

SciTech Connect

We present a theoretical analysis of experimental data on ion fractions and polar angular distributions for He atoms and ions produced during grazing scattering of keV neutral He atoms from an atomically clean and flat Al(111) surface. The discussion focuses on the mechanism of Auger ionization for which we have recently presented the first quantitative treatment by an ab initio method [S. Wethekam, Diego Valdes, R. C. Monreal, and H. Winter, Phys. Rev. B 78, 033105 (2008)]. Auger ionization, the inverse process of Auger neutralization, is a dynamical process that converts kinetic energy from the projectile to electronic excitations. We calculate Auger ionization rates and perform molecular-dynamics and Monte Carlo simulations of trajectory and charge state of scattered projectiles. We achieve quantitative agreement with experimental ion fractions and angular distributions. This demonstrates that Auger ionization is an efficient mechanism of ionization. We also discuss the sensitivity of the results on the theoretical input used in the simulations and give an estimate on the contribution of resonant processes.

Wethekam, S.; Winter, H. [Institut fuer Physik, Humboldt-Universitaet zu Berlin, Newtonstr. 15, D-12489 Berlin (Germany); Valdes, Diego; Monreal, R. C. [Departamento de Fisica Teorica de la Materia Condensada C-V, Universidad Autonoma de Madrid, E-28049 Madrid (Spain)

2009-05-15

257

All-atom ensemble modeling to analyze small angle X-ray scattering of glycosylated proteins  

PubMed Central

Summary The flexible and heterogeneous nature of carbohydrate chains often renders glycoproteins refractory to traditional structure determination methods. Small Angle X-ray scattering (SAXS) can be a useful tool for obtaining structural information of these systems. All-atom modeling of glycoproteins with flexible glycan chains was applied to interpret the solution SAXS data for a set of glycoproteins. For simpler systems (single glycan, with a well defined protein structure), all-atom modeling generates models in excellent agreement with the scattering pattern, and reveals the approximate spatial occupancy of the glycan chain in solution. For more complex systems (several glycan chains, or unknown protein substructure), the approach can still provide insightful models, though the orientations of glycans become poorly determined. Ab initio shape reconstructions appear to capture the global morphology of glycoproteins, but in most cases offer little information about glycan spatial occupancy. The all-atom modeling methodology is available as a webserver at http://modbase.compbio.ucsf.edu/allosmod-foxs. PMID:23473666

Guttman, Miklos; Weinkam, Patrick; Sali, Andrej; Lee, Kelly K.

2013-01-01

258

Recent investigations of silk fibers utilizing x-ray scattering and atomic force microscopy  

NASA Astrophysics Data System (ADS)

Silks from the mulberry silkworm, Bombyx mori, and the golden-orb spider, Nephila clavipes, are materials that possess respectable properties. Even pitted against the high performance fibers of Kevlar, polyethylene, and carbon, the advantages of some of nature's fibers are clear. The tensile strength of the golden-orb spider dragline is of the same order of magnitude as many synthetic fibers, yet the dragline's compressive strength as a percentage of its tensile strength is greater. The spider's ampullate glands, responsible for the manufacture of the dragline, also excel. The spider spins its fiber from a liquid crystalline solution that is water based versus the solutions at high temperatures containing volatile solvents that are required for current synthetic fibers. Understanding the morphology of silks will provide the basis for improved manufacturing and better performing synthetic fibers. The studies presented here have centered on the use of small-angle x-ray scattering, SAXS, to describe the large-scale morphology of silk fibers. We have determined minimum scattering dimensions on the order of 150-300 nm. A detailed analysis of the Porod scattering region has revealed correlation lengths of the same magnitude. Both of these dimensions are similar to with direct atomic force microscopy, AFM, measurements of nanofibers found in samples of abraded or peeled silk. The incorporation of discrete Fourier transform theory and AFM topographic information has yielded results in general agreement with measured SAXS patterns. This incorporation allows the materials scientist a way of visualizing the relationship between a material and its resulting scattering function. We have also found that x-ray scattering gives insight to new periodic distances of the morphology of golden-orb dragline. All of these studies yield a more complete view of the silk morphology and give a new method of model building from scattering experiments.

Miller, Lance D.

259

HELIUM, SOLID 1 Helium, Solid  

E-print Network

HELIUM, SOLID 1 Helium, Solid Henry R. Glyde Introduction Helium was first solidified at the famous focused on the melting curve, the specific heat, and the thermal conductivity of solid helium as a test criterion of melting does not hold in solid helium. This pioneering work up to 1957 is elegantly

Glyde, Henry R.

260

Diffuse scattering measurements of static atomic displacements in crystalline binary solid solutions  

SciTech Connect

Diffuse x-ray scattering from crystalline solid solutions is sensitive to both local chemical order and local bond distances. In short-range ordered alloys, fluctuations of chemistry and bond distances break the long-range symmetry of the crystal within a local region and contribute to the total energy of the alloy. Recent use of tunable synchrotron radiation to change the x-ray scattering contrast between elements has greatly advanced the measurement of bond distances between the three kinds of atom pairs found in crystalline binary alloys. The estimated standard deviation on these recovered static displacements approaches {+-}0.001 {angstrom} (0.0001 nm) which is an order of magnitude more precise than obtained with EXAFS. In addition, both the radial and tangential displacements can be recovered to five near neighbors and beyond. These static displacement measurements provide new information which challenges the most advanced theoretical models of binary crystalline alloys. 29 refs., 8 figs., 2 tabs.

Ice, G.E.; Sparks, C.J.; Jiang, X.; Robertson, L.

1997-09-01

261

Electron impact excitation of the 6s 2S 1/2 state of In atom at small scattering angles  

NASA Astrophysics Data System (ADS)

We measured the differential cross sections (DCSs) for the electron-impact excitation of the resonance transition 5p 2P 1/2-6s 2S 1/2 of In atom at small scattering angles using a crossed electron-atom beam technique. The incident electron energies were E0 = 10, 20, 40, 60, 80 and 100 eV, while the small scattering angles ranged from 1° to 10° in steps of 1°. The forward scattering function method has been used for normalizing the generalized oscillator strengths (GOS) to the known optical oscillator strength and obtaining the absolute DCS values.

Rabasovi?, M. S.; Toši?, S. D.; Ševi?, D.; Pej?ev, V.; Filipovi?, D. M.; Marinkovi?, B. P.

2009-01-01

262

Near-threshold emission of electrons during grazing scattering of keV Ne atoms from an Al(111) surface  

SciTech Connect

The number of electrons emitted during grazing scattering of Ne atoms with kilo-electron-volt energies from an Al(111) surface is recorded in coincidence with the energy loss of scattered projectiles. Irrespective of the total projectile energies used, we observe a pronounced increase of total electron emission yields when the energy for motion normal to the surface exceeds about 25 eV. Based on energy loss spectra and classical computer simulations of projectile trajectories we attribute electron emission under these scattering conditions to a promotion mechanism in binary collisions between Ne and Al target atoms resulting in single and double excitations of projectiles.

Matulevich, Y.; Lederer, S.; Winter, H. [Institut fuer Physik, Humboldt Universitaet zu Berlin, Brook-Taylor-Str. 6, D-12489 Berlin (Germany)

2005-01-15

263

Near-threshold emission of electrons during grazing scattering of keV Ne atoms from an Al(111) surface  

NASA Astrophysics Data System (ADS)

The number of electrons emitted during grazing scattering of Ne atoms with kilo-electron-volt energies from an Al(111) surface is recorded in coincidence with the energy loss of scattered projectiles. Irrespective of the total projectile energies used, we observe a pronounced increase of total electron emission yields when the energy for motion normal to the surface exceeds about 25eV . Based on energy loss spectra and classical computer simulations of projectile trajectories we attribute electron emission under these scattering conditions to a promotion mechanism in binary collisions between Ne and Al target atoms resulting in single and double excitations of projectiles.

Matulevich, Y.; Lederer, S.; Winter, H.

2005-01-01

264

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

265

Effects of coupled atomic states on the resonance scattering of radiation  

E-print Network

) E; = (E: + Eb)/2 - k , - ie)a + yb)/4 - ( R + i l ) E; = Eb-(i/2)r E; = E; EfjTects of coupled atomic states 915 where In equation (20) R is the real part and I the imaginary part of the expression. The real part produces an energy shift... and suppresses the other. t Present address : Physics Department, University of New Brunswick, Fredericton, New Brunswick, Canada. 91 1 912 R P Sricastava and P R Fontana 2. General theory The resonance scattering of radiation is calculated by considering...

Srivastava, Rajendra P.; Fontana, Peter R.

1974-01-01

266

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

PubMed

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

Jasnin, Marion

2009-10-01

267

Double ionization of helium in the 8--25keV x-ray energy range% (Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract W-31-109ENG38)  

Microsoft Academic Search

X rays in the keV energy regime interact only very weakly with helium atoms. Starting at about 6 keV x-ray energy, the absorption of x rays becomes less important in the ionization of helium than Compton scattering. Whereas for photoabsorption the high-energy asymptotic value for the fraction of helium double ionization is practically reached for keV x rays, the fraction

B. Krässig; R. W. Dunford; D. S. Gemmell; S. Hasegawa; E. P. Kanter; S. H. Southworth; L. Young; T. Weber; H. Schmidt-Böcking; W. Schmitt

1998-01-01

268

X-Ray Radiation from Nonlinear Thomson Scattering of an Intense Femtosecond Laser on Relativistic Electrons in a Helium Plasma  

E-print Network

X-Ray Radiation from Nonlinear Thomson Scattering of an Intense Femtosecond Laser on Relativistic November 2003) We have generated x-ray radiation from the nonlinear Thomson scattering of a 30 fs=1:5 J laser beam on plasma electrons. A collimated x-ray radiation with a broad continuous spectrum peaked

Umstadter, Donald

269

Path-integral theory of the scattering of ⁴He atoms at the surface of liquid ⁴He  

Microsoft Academic Search

The path-integral theory of the scattering of a ⁴He atom near the free surface of liquid ⁴He, which was originally formulated by Echenique and Pendry, has been recalculated with use of a physically realistic static potential and atom-ripplon interaction outside the liquid. The static potential and atom-ripplon interaction are based on the variational calculation of Edwards and Fatouros. An important

D. R. Swanson; D. O. Edwards

1988-01-01

270

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

NASA Astrophysics Data System (ADS)

Evolution of the helium atom in a strong time-dependent (TD) magnetic field ( B) of strength up to 1011 G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schrödinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >109 G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >109 G, the conventional TD-DFT based approach differs "dynamically" from the CDFT based approach under similar computational constraints.

Vikas, Hash(0x125f4490)

2011-02-01

271

Atomic-scale Modeling of Interactions of Helium, Vacancies and Helium-vacancy Clusters with Screw Dislocations in Alpha-Iron  

SciTech Connect

The interactions of He and vacancy defects with <111> screw dislocations in alpha-Fe are modeled using molecular statics, molecular dynamics and transition state energy determinations. The formation energies and binding energies of interstitial He atoms, vacancies and He-vacancy clusters near and within dislocations in alpha-Fe are determined at various locations relative to the dislocation core. Using the dimer transition state method the migration energies and trajectories of the He and vacancy defects near and within the screw dislocation are also determined. Both interstitial He atoms and single vacancies are attracted to and trapped in the dislocation core region, and they both migrate along the dislocation line with a migration energy of about 0.4 eV, which is about half the migration energy of vacancies in the perfect crystal and about five times the migration energy for interstitial He in the perfect crystal. Divacancies and He-divacancy complexes have migration properties within the dislocation core that are similar to those in the perfect crystal, although the stability of these defects within the dislocation may be somewhat less than in the perfect crystal.

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

2010-05-01

272

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

2010-08-13

273

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

274

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

PubMed

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

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

2014-09-28

275

Path-integral theory of the scattering of /sup 4/He atoms at the surface of liquid /sup 4/He  

SciTech Connect

The path-integral theory of the scattering of a /sup 4/He atom near the free surface of liquid /sup 4/He, which was originally formulated by Echenique and Pendry, has been recalculated with use of a physically realistic static potential and atom-ripplon interaction outside the liquid. The static potential and atom-ripplon interaction are based on the variational calculation of Edwards and Fatouros. An important assumption in the path-integral theory is the ''impulse approximation'': that the motion of the scattered atom is very fast compared with the motion of the surface due to ripplons. This is found to be true only for ripplons with wave vectors smaller than q/sub m/approx.0.2 A/sup -1/. If ripplons above q/sub m/ made an important contribution to the scattering of the atom there would be a substantial dependence of the elastic reflection coefficient on the angle of incidence of the atom. Since this is not observed experimentally, it is argued that ripplons above q/sub m/ give a negligible effect and should be excluded from the calculation. With this modification the theory gives a good fit to the experimental reflection coefficient as a function of the momentum and angle of incidence of the atom. The new version of the theory indicates that there is a substantial probability that an atom may reach the surface of the liquid without exciting any ripplons. The theory is not valid when the atom enters the liquid but analysis of the experiments shows that, once inside the liquid, the atom has a negligible chance of being scattered out again.

Swanson, D.R.; Edwards, D.O.

1988-02-01

276

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

277

The s-wave pi d scattering length from pi d atom using effective field theory  

E-print Network

The pi- d atom strong energy-level shift in the 1s state is derived by using the effective field theory. Taking into account the large value of radius of pionic deuterium and short radius of strong interaction between pion and deuteron we have considered deuteron as particle described by vector field. Pion is described by scalar field. To obtain non-relativistic Hamiltonian for pi d system Foldy-Wouthuysen transformation has been derived for the vector field. The strong interaction between pion and deuteron has been taken at the zero-range approach. We have found the Deser type formula for relation between the strong energy-level shift and the s-wave pi d scattering length.

B. F. Irgaziev; B. A. Fayzullaev

2004-04-23

278

Time-dependent approach to transport and scattering in atomic and mesoscopic physics  

SciTech Connect

Transport and scattering phenomena in open quantum-systems with a continuous energy spectrum are conveniently solved using the time-dependent Schroedinger equation. In the time-dependent picture, the evolution of an initially localized wave-packet reveals the eigenstates and eigenvalues of the system under consideration. We discuss applications of the wave-packet method in atomic, molecular, and mesoscopic systems and point out specific advantages of the time-dependent approach. In connection with the familiar initial value formulation of classical mechanics, an intuitive interpretation of transport emerges. For interacting many-particle systems, we discuss the efficient calculation of the self-consistent classical transport in the presence of a magnetic field.

Kramer, Tobias [Institut fuer Theoretische Physik, Universitaet Regensburg, 93040 Regensburg (Germany)

2011-03-21

279

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

NASA Technical Reports Server (NTRS)

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

Malik, F. Bary

1995-01-01

280

Continuous-flow determination of aqueous sulfur by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry with gas-phase sample introduction  

NASA Astrophysics Data System (ADS)

A simple continuous-flow generation of volatile hydrogen sulfide and sulfur dioxide by acidification of aqueous sulfide and sulfite ions, respectively, is described for the determination of low concentrations of sulfur by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry (MIP-AES) in the normal ultraviolet (UV) and vacuum ultraviolet (VUV) regions of the spectrum. For measuring spectral lines in the VUV region, the monochromator and the enclosed external optical path between the MIP source and the entrance slit of the monochromator have both been purged with nitrogen to minimize oxygen absorption below 190 nm. Sulfur atomic emission lines at 180.73, 182.04 and 217.05 nm have been selected as the analytical lines. Of the various acids examined, 1.0 M hydrochloric acid is the most favorable for both the generation of hydrogen sulfide from sulfide ions and sulfur dioxide from sulfite ions. Either generated hydrogen sulfide or sulfur dioxide is separated from the solution in a simple gas-liquid separator and swept into the helium stream of a microwave-induced plasma for analysis. The best attainable detection limits (3 ? criterion) for sulfur at 180.73 nm were 0.13 and 1.28 ng ml -1 for the generation of hydrogen sulfide and sulfur dioxide, respectively, with the corresponding background equivalent concentrations of 20.9 and 62.2 ng ml -1 in sulfur concentration. The typical analytical working graphs obtained under the optimized experimental conditions were rectilinear over approximately four orders of magnitude in sulfur concentration. The present method has been successfully applied to the recovery test of the sulfide spiked to waste water samples and to the determination of sulfite in some samples of commercially available wine.

Nakahara, Taketoshi; Mori, Toshio; Morimoto, Satoru; Ishikawa, Hiroshi

1995-06-01

281

Scattering of electron vortex beams on a magnetic crystal: Towards atomic-resolution magnetic measurements  

NASA Astrophysics Data System (ADS)

Use of electron vortex beams (EVB), that is, convergent electron beams carrying an orbital angular momentum (OAM), is a novel development in the field of transmission electron microscopy. They should allow measurement of element-specific magnetic properties of thin crystals using electron magnetic circular dichroism (EMCD)—a phenomenon similar to the x-ray magnetic circular dichroism. Recently, it has been shown computationally that EVBs can detect magnetic signal in a scanning mode only at atomic resolution. In this follow-up work, we explore in detail the elastic and inelastic scattering properties of EVBs on crystals, as a function of beam diameter, initial OAM, acceleration voltage, and beam displacement from an atomic column. We suggest that for a 10-nm layer of bcc iron oriented along (001) zone axis, an optimal configuration for a detection of EMCD is an EVB with OAM of 1? and a full width at half maximum diffraction-limited beam diameter of 1.6 Å, acceleration voltage 200 kV, and an annular detector with inner and outer radii of 7 and 44 mrad, respectively.

Rusz, Ján; Bhowmick, Somnath; Eriksson, Mattias; Karlsson, Nikolaj

2014-04-01

282

Thin film growth and the scattering of atoms from surface island defects  

NASA Astrophysics Data System (ADS)

We investigate the potential energy surface and dynamics of atoms impinging upon pyramidal defects on fcc (100) and (111) surfaces. Illustrative molecular dynamics trajectory results are used to highlight the subtleties of the growth processes. Homoatomic systems of both Cu and Pd are considered in order to determine the influence of extreme differences in bonding coordination variation, i.e. the binding energy per atom decreases by a factor of 3.3 from Cu(bulk) to Cu 2 but more dramatically by a factor of 7.5 for Pd(bulk) to Pd 2. We find that stable adsorption sites on pyramidal facets only exist for three layer high (and higher) facets, but even these sites are not as energetically favorable as those at the pyramid's base. This single energetic effect can promote a Stranski-Krastanov type growth pattern, with a critical roughness of no less than three layers being required before a 3D growth mechanism can propagate in a surface temperature regime where post impact diffusion is small compared to the deposition rate. The transition to 3D growth at the minimum possible roughness would be found for Pd on the (100) face where sticking to the sides of even the three layer pyramid is a high probability event, at a low enough temperature to make post-impact diffusion negligible. However, for the Cu system, we find that the "downward funneling" mechanism smoothed the growth for the three layer pyramid and is still important for the five layer pyramid, indicating that Cu will exhibit layer-by-layer like growth even past three layers. A comparison of scattering simulations from defects show that the growth mode is diffusion limited on the fcc (100) crystal face, but becomes dominated by impact induced disruption of the original structure for a (111) surface. This implies that the (111) surface will grow more smoothly as a new atom displaces pre-adsorbed atoms more easily, an effect that is not included in the "downward funneling" model. The ratio of the diatomic molecule's binding energy to the bulk cohesive energy is shown to provide good insight into the preferred growth mechanism. As the ratio increases, at least in the range spanned by typical metals, the film grows more layer-by-layer like on the (100) surface and less layer-by-layer like on the (111) surface. On the (100) surface, stronger low coordination bonding makes the defect structures less able to adsorb the impacting atom on the sloped faces, increasing the effectiveness of "downward funneling." On the (111) surface, stronger low coordination bonding inhibits impact disruption of the defects, decreasing this important smoothing mechanism.

Halstead, David M.; DePristo, Andrew E.

1993-05-01

283

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

284

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

285

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

286

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

287

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

288

Field ionization of helium in a supersonic beam: kinetic energy of neutral atoms and probability of their field ionization.  

PubMed

High detection efficiency combined with spatial resolution on a nm-scale makes the field ionization process a promising candidate for spatially resolved neutral particles detection. The effective cross-sectional area sigma(eff) can serve as a measure for the effectiveness of such a field ion detector. In the present contribution, we combine quantum-mechanical calculations of the field-modified electron density distribution near the tungsten tip surface and of the resulting local field distributions, performed using the functional integration method, with a classical treatment of the atom trajectories approaching the tip in order to calculate the sigma(eff) values for ionization of free He atoms over an apex of a tungsten field emitter tip. The calculated values are compared with experimental data for supersonic He atomic beams at two different temperatures 95 and 298K. PMID:19167823

Holst, B; Piskur, J; Kostrobiy, P P; Markovych, B M; Suchorski, Y

2009-04-01

289

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

290

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

291

Nonvariational calculation of the relativistic, finite-size, and QED corrections for the 2 1S excited state of the helium atom  

NASA Astrophysics Data System (ADS)

Relativistic and QED corrections are calculated by using a direct solution of the Schrödinger equation for the 2 1S excited state of the helium atom obtained with the correlation-function hyperspherical-harmonic method. Our extremely accurate nonvariational results for relativistic, QED, and finite-size corrections coincide exactly (up to 0.000 03 cm-1) with the values obtained in precision variational calculations of Drake [Nucl. Instrum. Methods Phys. Res. B 5, 2207 (1988)] and Baker, Hill, and Morgan [in Relativistic, Quantum Electrodynamic and Weak Interaction Effects in Atoms, edited by Walter Johnson, Peter Mohr, and Joseph Sucher, AIP Conf. Proc. No. 189 (AIP, New York, 1989), p. 123] for both infinite and finite nuclear masses. This confirms that a discrepancy of 0.0033 cm-1 between theory and experiment is not a result of an inaccuracy of variational wave functions, but is rooted in our inadequate knowledge of the QED operators. A better understanding of the different QED contributions to the operators (such as, for example, a more precise estimate of the Bethe logarithm) is therefore needed to explain the discrepancy.

Haftel, M. I.; Mandelzweig, V. B.

1994-05-01

292

Entanglement in helium  

E-print Network

Using a configuration-interaction variational method, we accurately compute the reduced, single-electron von Neumann entropy for several low-energy, singlet and triplet eigenstates of helium atom. We estimate the amount of electron-electron orbital entanglement for such eigenstates and show that it decays with energy.

Giuliano Benenti; Stefano Siccardi; Giuliano Strini

2012-04-30

293

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

NASA Astrophysics Data System (ADS)

Fast ionization waves (FIWs), often generated with high voltage pulses over nanosecond timescales, are able to produce large volumes of ions and excited states at moderate pressures. The mechanisms of FIW propagation were experimentally and computationally investigated to provide insights into the manner in which these large volumes are excited. The two-dimensional structure of electron and metastable densities produced by short-pulse FIWs sustained in helium were measured using laser-induced fluorescence and laser collision-induced fluorescence diagnostics for times of 100-120 ns after the pulse, as the pressure was varied from 1 to 20 Torr. A trend of center-peaked to volume-filling to wall-peaked electron density profiles was observed as the pressure was increased. Instantaneous FIW velocities, obtained from plasma-induced emission, ranged from 0.1 to 3 × 109 cm s-1, depending on distance from the high voltage electrode and pressure. Predictions from two-dimensional modeling of the propagation of a single FIW correlated well with the experimental trends in electron density profiles and wave velocity. Results from the model show that the maximum ionization rate occurs in the wavefront, and the discharge continues to propagate forward after the removal of high voltage from the powered electrode due to the potential energy stored in the space charge. As the pressure is varied, the radial distribution of the ionization rate is shaped by changes in the electron mean free path, and subsequent localized electric field enhancement at the walls or on the centerline of the discharge.

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

2014-09-01

294

Scattering of /sup 4/He atoms off the surface of liquid /sup 4/He at grazing angles of incidence  

SciTech Connect

The measurement of the elastic reflection coefficient for /sup 4/He atoms incident on the surface of liquid /sup 4/He are described. The elastic reflection coefficient, R(k,theta), was measured by varying the speed, v = h-bar k/m, of the incident atoms and the angle of incidence, theta. The range of the wavevector, k, was 0.2 A/sup -1/ to 0.7 A/sup -1/. The angle of incidence was varied from 53/sup 0/ to 87/sup 0/ with respect to the normal to the liquid /sup 4/He surface. A heat pulse applied to a graphite film resistor generates a beam of /sup 4/He atoms. The power of the atoms condensing on the surface of a graphite film resistor, used as a bolometer, was measured for the direct beam and for a beam reflected off the liquid surface. A comparison of the reflected and the direct power allows the computation of the reflection coefficient as a function of the time of flight. The elastic reflection coefficient was found to be a function of the perpendicular component of the momentum. The range of the perpendicular component of the wavevector, k/sub z/, was extended to 0.01 A/sup -1/. The results for k/sub z/ between 0.05 A/sup -1/ to 0.4 A/sup -1/ are in agreement with the measurements of Edwards et al. (1975a). The reflection rises to 20% for k/sub z/ equal to 0.01 A/sup -1/. This agrees with the variational theory of Edwards and Fatouros (1978) in which the trial wave function is unsymmetrized and the incident /sup 4/He atom scatters from a one-dimensional effective potential. The elastic scattering, for k/sub z/ small, is due to scattering from the long-range Van der Waals interaction between the incident atom and the liquid. The scattering appears to be essentially elastic and there is no evidence for any significant inelastic scattering. Our apparatus is however relatively insensitive to diffuse inelastic scattering.

Nayak, V.U.

1982-01-01

295

Physics 139B Fall 2009 The Variational Computation of the Ground State Energy of Helium  

E-print Network

Physics 139B Fall 2009 The Variational Computation of the Ground State Energy of Helium I. Introduction to the variational computation The Hamiltonian for the two-electron system of the helium atom is state energy of the helium atom. The ground state wave function of the helium atom is of the form: 1 2

California at Santa Cruz, University of

296

Physics 216 Spring 2012 The Variational Computation of the Ground State Energy of Helium  

E-print Network

Physics 216 Spring 2012 The Variational Computation of the Ground State Energy of Helium I. Introduction to the variational computation The Hamiltonian for the two-electron system of the helium atom is state energy of the helium atom. The ground state wave function of the helium atom is of the form: 1 2

California at Santa Cruz, University of

297

Energy harvesting in doped helium nano-droplets  

NASA Astrophysics Data System (ADS)

We report the observation of sequential Penning ionization of dopants by metastable helium atoms in helium nano-droplets resulting in doubly charged ions. Strong charge induced dipole-interaction between the excited helium atom and the target ion provides a high probability for the transfer of the internal energy of the excited helium atom to the dopant ion. This process may also lead subsequently to a Coulomb explosion of molecular or cluster dopants.

Zöttl, Samuel; Schöbel, Harald; Bartl, Peter; Leidlmair, Christian; Daxner, Matthias; Denifl, Stephan; Märk, Tilmann D.; Scheier, Paul; Spångberg, Daniel; Mauracher, Andreas; Bohme, Diethard K.

2012-11-01

298

Comparison of the measured X-ray yields of kaonic helium-3 and helium-4.  

E-print Network

??Kaonisches Helium ist ein exotisches Atom,? ?welches sich besonders zur Untersuchung der starken Wechselwirkung bei niedrigen Energien eignet.? ?Die starke Wechselwirkung zwischen Kaon und Heliumkern… (more)

Wünschek, Barbara

2012-01-01

299

Energy-related atomic and molecular structure and scattering studies. Progress report, July 1, 1981-December 31, 1982  

SciTech Connect

The basic goals of this program remain the experimental determination of fundamental properties of atoms and molecules, and of molecular clusters, and their use as benchmarks in comparison with computed properties based on theoretical models. In particular we are continuing our measurements of polarizabilities of highly polar molecules and their polymers, and of a number of important atomic elements, particularly several with high-Z. In a parallel program we are performing electron-scattering experiments on these systems. For the scattering program an entirely new apparatus has been designed and constructed. Preliminary scattering measurements have been made, and a summary of these and of problems encountered in this work is presented. Our recently completed alkali-halide dimer polarizability measurements have led to a combined theoretical-experimental determination of alkali halide monomer polarizabilities: the first available values for these important parameters. Our absolute electron-atomic lithium cross section has enabled us to calibrate earlier measurements of electron-Li/sub 2/ cross sections.

Bederson, B.

1982-06-30

300

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

PubMed Central

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

2014-01-01

301

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

302

Characterization of helium/argon working gas systems in a radiofrequency glow discharge atomic emission source. Part I: Optical emission, sputtering and electrical characteristics  

NASA Astrophysics Data System (ADS)

Studies are performed to determine the influence of discharge gas composition (helium/argon working gas mixtures) on the analyte emission signal intensities, sputtering rates, and DC-bias characteristics of an analytical radiofrequency glow discharge atomic emission spectroscopy (RF-GD-AES) source. As the partial pressure of He is increased from 0 to 15 torr, increased emission intensity is observed for a range of bulk and trace elements in NIST 1250 SRM (low alloy steel), regardless of the base pressure of Ar in the source (5 and 9 torr). In contrast to increases in analyte emission intensity of up to 300%, counterindicative decreases in the sputtering rates on the order of about 30-50% are observed. The magnitude of these effects depends on both the partial pressure of helium introduced to the source and the total pressure of the He and Ar gases. Use of relative emission yield (REY) to normalize changes in emission intensity to sputtering rates indicates that excitation efficiencies increase under these conditions. Increases in average electron energy and temperature appear to control this response. Decreases in both analyte emission intensities and sputter rates occur with increasing He partial pressure when the total pressure in the cell remains fixed (11 torr in these studies). Emission yields for the fixed pressure, mixed gas plasmas decrease as the partial pressure of He (He/Ar ratio) in the RF-GD source increases. In this case, decreases in electron number densities appear to dictate the lower REYs. Measurement of DC-bias values at the sample surface provide understanding with respect to the observed changes in sputtering rates as well as suggest the origins of changes in plasma electron energetics. Use of a diamond stylus profilometer provides both the quantitative sputter rate information as well as qualitative insights into the use of mixed gas plasmas for enhanced depth profiling capabilities. The analyte emission characteristics of these mixed gas plasmas can be further understood by examining fundamental Langmuir probe data for pure He and mixed Ar/He plasmas, which are presented in the following companion paper.

Christopher, Steven J.; Hartenstein, Matthew L.; Marcus, R. Kenneth; Belkin, Mikhail; Caruso, Joseph A.

1998-08-01

303

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

304

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

PubMed

The pair-distance distribution function (PDDF) contains all structural information probed in an elastic scattering experiment of macromolecular solutions. However, in small-angle x-ray scattering (SAXS) or small-angle neutron scattering (SANS) experiments only their Fourier transform is measured over a restricted range of scattering angles. We therefore developed a mathematically simple and computationally efficient method to calculate the PDDFs as well as accurate scattering intensities from molecular dynamics simulations. The calculated solution scattering intensities are in excellent agreement with SAXS and wide-angle x-ray scattering (WAXS) experiments for a series of proteins. The corresponding PDDFs are remarkably rich in features reporting on the detailed protein structure. Using an inverse Fourier transform method, most of these features can be recovered if scattering intensities are measured up to a momentum transfer of q?2-3Å(-1). Our results establish that high-precision solution scattering experiments utilizing x-ray free-electron lasers and third generation synchrotron sources can resolve subnanometer structural detail, well beyond size, shape, and fold. PMID:23767571

Köfinger, Jürgen; Hummer, Gerhard

2013-05-01

305

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

NASA Astrophysics Data System (ADS)

The pair-distance distribution function (PDDF) contains all structural information probed in an elastic scattering experiment of macromolecular solutions. However, in small-angle x-ray scattering (SAXS) or small-angle neutron scattering (SANS) experiments only their Fourier transform is measured over a restricted range of scattering angles. We therefore developed a mathematically simple and computationally efficient method to calculate the PDDFs as well as accurate scattering intensities from molecular dynamics simulations. The calculated solution scattering intensities are in excellent agreement with SAXS and wide-angle x-ray scattering (WAXS) experiments for a series of proteins. The corresponding PDDFs are remarkably rich in features reporting on the detailed protein structure. Using an inverse Fourier transform method, most of these features can be recovered if scattering intensities are measured up to a momentum transfer of q?2-3Å-1. Our results establish that high-precision solution scattering experiments utilizing x-ray free-electron lasers and third generation synchrotron sources can resolve subnanometer structural detail, well beyond size, shape, and fold.

Köfinger, Jürgen; Hummer, Gerhard

2013-05-01

306

Quantum theory of a micromaser operating on the atomic scattering from a resonant standing wave  

E-print Network

We study the amplification of a resonant standing-wave light field due to the interaction with a beam of monovelocity two-level atoms moving in the Raman-Nath regime and in the Bragg regime. The atomic density is low so that, at most, one atom...

Saif, F.; Le Kien, F.; Zubairy, M. Suhail

2001-01-01

307

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

308

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/LiF(001) and HI/NaF(001) V. J. Barclay,a) W.-H. Hung,b) W. J. Keogh,c) R. Ku¨hnemuth, J. C. Polanyi, G have compared the ``elastic'' H atom angular-scattering, Pel , of HI ad photolyzed at 248 nm for Li

Zeiri, Yehuda

309

Speckle Patterns with Atomic and Molecular de Broglie Waves  

SciTech Connect

We have developed a nozzle source that delivers a continuous beam of atomic helium or molecular hydrogen having a high degree of transverse coherence and with adequate optical brightness to enable new kinds of experiments. Using this source we have measured single slit diffraction patterns and the first ever speckle-diffraction patterns using atomic and molecular de Broglie waves. Our results suggest fruitful application of coherent matter beams in dynamic scattering and diffractive imaging at short wavelength and with extreme surface sensitivity.

Patton, Forest S.; Deponte, Daniel P.; Kevan, Stephen D. [Department of Physics, University of Oregon, Eugene, Oregon 97403-1274 (United States); Elliott, Greg S. [Department of Physics, University of Puget Sound, Tacoma, Washington 98416 (United States)

2006-07-07

310

Production of a Biomimetic Fe(I)-S Phase on Pyrite by Atomic-Hydrogen Beam-Surface Reactive Scattering  

PubMed Central

Molecular beam-surface scattering and X-ray absorption spectroscopic experiments were employed to study the reaction of deuterium atoms with a pyrite, FeS2 (100), surface and to investigate the electronic and geometric structures of the resulting Fe-S phases. Incident D atoms, produced by a radio frequency plasma and expanded in an effusive beam, were directed at a pyrite surface held at various temperatures from ambient up to 200 °C. During exposure to the D-atom beam, D2S products were released with a thermal distribution of molecular speeds, indicating that the D atoms likely reacted in thermal equilibrium with the surface. The yield of D2S from the surface decreased approximately exponentially with exposure duration, suggesting that the surface accessible sulfur atoms were depleted, thus leaving an iron-rich surface. This conclusion is consistent with X-ray absorption measurements of the exposed surfaces, which indicated the formation of a layered structure, with elemental iron as the outermost layer on top of a formally Fe(I)-S phase as an intermediate layer and a formally Fe(II)-S2 bulk pyrite layer at lower depths. The reduced Fe(I)-S phase is particularly remarkable because of its similarity to the catalytically active sites of small molecule metalloenzymes, such as FeFe-hydrogenases and MoFe-nitrogenases. PMID:21526811

Che, Li; Gardenghi, David J.; Szilagyi, Robert K.; Minton, Timothy K.

2011-01-01

311

Resolution and transfer width of thermal energy atomic scattering from solid surfaces (TEAS)  

NASA Astrophysics Data System (ADS)

The resolution of TEAS has been investigated as a function of energy spread of atomic beam. The model calculations have been executed within the framework of time dependent Schrödinger equation. The energy spread of realistic atomic beam has been taken into account by a wave-packet. The wave-packet describes the atomic beam as an ensemble of independent particles by quantum mechanics. Taking ideally periodic surface the resolution of diffraction peaks increases when the energy spread is decreased. This fact underlines the higher efficiency of the supersonic atomic source than the effusive atomic source. Furthermore the transfer width of experimental equipment increases—when the atomic beam monochromaticity is also increased—according to the concept of the transfer width. The relation between the transfer width and the size of the period of the surface topography significantly determines the resolution of the diffraction pattern.

Varga, G.

1999-04-01

312

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

313

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

314

The Formation Energies and Binding Energies of Helium Vacancy Cluster: Comparative Study in Ni and Pd  

NASA Astrophysics Data System (ADS)

Molecular dynamics calculations are performed to calculate the formation energy for helium in Ni-vacancy and Pd-vacancy clusters. The binding energies of helium and metal self-interstitial atoms (SIA) to the helium-vacancy cluster are also determined. The comparison of these energies indicates that helium to vacancy ratio (He/V) for helium in Pd is much higher.

Yang, Jianyu; Ao, Bingyun; Hu, Wangyu; Wang, Xiaolin

2006-01-01

315

Towards helium-3 neutron polarizers  

NASA Astrophysics Data System (ADS)

With a large absorption cross-section entirely due to antiparallel spin capture, polarized helium-3 is presently the most promising broad-band polarizer for thermal and epithermal neutrons. Immediate interest was raised amongst the neutron community when a dense gaseous 3He polarizer was used for the first time in 1988, on a pulsed neutron beam at Los Alamos. With 20 W of laser power on a 30 cm long, 8.6 atm target, 40% 3He polarization was achieved in a recent polarized electron scattering experiment at SLAC. In this technique the 4He nuclei are polarized directly at an appropriate high pressure through spin-exchange collisions with a thick, optically pumped rubidium vapor. A different and competitive approach is being presently developed at Mainz University in collaboration with ENS Paris and now the ILL. A discharge is established in pure 3He at low pressure producing excited metastable atoms which can be optically pumped with infra-red light. Highly effective exchange collision with the atoms remaining in the ground state quickly produces 75% polarization at 1.5 mbar. A truly non-magnetic system then compresses the polarized gas up to several bars as required. The most recent machine comprises a two-stage glass-titanium compressor. In less than 1 h it can inflate a 100 cm 3 target cell with three bars of polarized gas. The very long relaxation times (several days) now being obtained at high pressure with a special metallic coating on the glass walls, the polarized cell can be detached and inserted in the neutron beam as polarizer. We expect 50% 3He-polarization to be reached soon, allowing such filters to compete favorably with existing Heusler-crystal polarizers at thermal and short neutron wavelengths. It must be stressed that such a system based on a 3He polarization factory able to feed several passive, transportable, polarizers is well matched to neutron scattering needs.

Tasset, F.

1995-02-01

316

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

SciTech Connect

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

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

2008-01-01

317

Friction-Induced Energy-Loss Rainbows in Atom Surface Scattering  

NASA Astrophysics Data System (ADS)

The rainbow is due to extrema of the angular deflection function of light impinging on water drops. Generically, extrema of suitably defined deflection functions lead to rainbows. These include angular and rotational rainbows in surface scattering and more. Here we introduce the concept of an “energy-loss deflection function” for scattering of particles from a periodic surface whose extrema lead to a new form—the “energy-loss rainbow” which appears as multiple maxima in the final energy distribution of the scattered particle. Energy-loss rainbows are caused by frictional phonon effects which induce structure in the energy-loss distribution instead of “washing it out.” We provide evidence that they have been observed in Ne scattering on self-assembled monolayers.

Moix, Jeremy M.; Pollak, Eli; Miret-Artés, Salvador

2010-03-01

318

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

319

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

320

Xray Dispersion and Scattering in the Average-Atom Model of a Plasma  

E-print Network

of Nevada, Reno 09 2 #12;Average Atom & Static Conductivity Example Aluminum: density 0.27 gm/cc T = 5 e and Conductivity Consider an applied electric field: E(t) = F ^z sin t A(t) = F ^z cos t The time dependent Schr Average-Atom & Static Conductivity (Ziman) R Kubo-Greenwood Formula (Infrared Catastrophe) R "Proper

Johnson, Walter R.

321

Resonant Raman scattering and atomic force microscopy of InGaAs\\/GaAs multilayer nanostructures with quantum dots  

Microsoft Academic Search

The transition from two-dimensional (2D) pseudomorphic growth to the three-dimensional (3D) (nanoisland) growth in InxGa1?x\\u000a As\\/GaAs multilayer structures grown by molecular-beam epitaxy was investigated by atomic force microscopy, photoluminescence,\\u000a and Raman scattering. The nominal In content x in InxGa1?x\\u000a As was varied from 0.20 to 0.50. The thicknesses of the deposited InxGa1?x\\u000a As and GaAs layers were 14 and 70

M. Ya. Valakh; V. V. Strelchuk; A. F. Kolomys; Yu. I. Mazur; Z. M. Wang; M. Xiao; G. J. Salamo

2005-01-01

322

Simultaneous detection of surface coverage and structure of krypton films on gold by helium atom diffraction and quartz crystal microbalance techniques  

SciTech Connect

We describe a quartz crystal microbalance setup that can be operated at low temperatures in ultra high vacuum with gold electrode surfaces acting as substrate surface for helium diffraction measurements. By simultaneous measurement of helium specular reflection intensity from the electrode surface and resonance frequency shift of the crystal during film adsorption, helium diffraction data can be correlated to film thickness. In addition, effects of interfacial viscosity on the helium diffraction pattern could be observed. To this end, first, flat gold films on AT cut quartz crystals were prepared which yield high enough helium specular reflection intensity. Then the crystals were mounted in the helium diffractometer sample holder and driven by means of a frequency modulation driving setup. Different crystal geometries were tested to obtain the best quality factor and preliminary measurements were performed on Kr films on gold surfaces. While the crystal structure and coverage of krypton films as a function of substrate temperature could successfully be determined, no depinning effects could be observed.

Danisman, M. Fatih; Oezkan, Berrin [Department of Chemistry, Middle East Technical University, Ankara 06800 (Turkey)

2011-11-15

323

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

324

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

325

Helium effects on displacement cascades in ?-iron  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations have been performed to investigate the effects of helium on the displacement cascades in ?-iron. Besides conventional analysis tools, a new graphical representation of the data based on ternary plots has been introduced. Results show that the production of defects and their subsequent clustering appear to be greatly influenced by the presence of helium. Calculations reveal that the location of helium atoms, substitutional or interstitial, plays a major role. Compared to pure iron, interstitial helium atoms increase the amount of Frenkel pairs generated during the cascades. Conversely, substitutional helium atoms tend to decrease this production. However, in both cases, it is observed that helium atoms stabilize larger self-interstitial clusters, due to a strong binding energy. These simulations show that helium atoms trap self-interstitial clusters and would thus slow down their subsequent migration. Some helium-vacancy clusters are generated in the core of the displacement cascades but also grow at the periphery of self-interstitial clusters. It is shown that results greatly depend on the irradiation temperature.

Lucas, G.; Schäublin, R.

2008-10-01

326

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

327

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

NASA Astrophysics Data System (ADS)

A new method is introduced to compute X-ray solution scattering profiles from atomic models of macromolecules. The three-dimensional version of the Reference Interaction Site Model (RISM) from liquid-state statistical mechanics is employed to compute the solvent distribution around the solute, including both water and ions. X-ray scattering profiles are computed from this distribution together with the solute geometry. We describe an efficient procedure for performing this calculation employing a Lebedev grid for the angular averaging. The intensity profiles (which involve no adjustable parameters) match experiment and molecular dynamics simulations up to wide angle for two proteins (lysozyme and myoglobin) in water, as well as the small-angle profiles for a dozen biomolecules taken from the BioIsis.net database. The RISM model is especially well-suited for studies of nucleic acids in salt solution. Use of fiber-diffraction models for the structure of duplex DNA in solution yields close agreement with the observed scattering profiles in both the small and wide angle scattering (SAXS and WAXS) regimes. In addition, computed profiles of anomalous SAXS signals (for Rb+ and Sr2+) emphasize the ionic contribution to scattering and are in reasonable agreement with experiment. In cases where an absolute calibration of the experimental data at q = 0 is available, one can extract a count of the excess number of waters and ions; computed values depend on the closure that is assumed in the solution of the Ornstein-Zernike equations, with results from the Kovalenko-Hirata closure being closest to experiment for the cases studied here.

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

2014-12-01

328

1D scattering experiments with ultra-cold atoms: transient enhancement of high momenta  

NASA Astrophysics Data System (ADS)

During the scattering of a particle from a repulsive potential, the particle can exhibit an enhancement of high momentum components. This effect is transient in the sense that it only exists when there is an overlap between the particle's wavefunction and the scattering potential, and is inherently a quantum mechanical phenomenon. This effect has been shown to be strongest for scattering potentials that are weak such that the wavepacket is entirely transmitted [1]. In our experiment we use an ultra-cold gas interacting with a thin optical dipole barrier to observe this effect. If time permits, we will discuss experiments in progress to investigate tunneling of our ultra-cold gas in 1D. [4pt] [1] S. Brouard and J. G. Muga , Phys. Rev. Lett. 81, 2621-2625 (1998)

Chang, Rockson; Ellenor, Chris; Siercke, Mirco; Potnis, Shreyas; Steinberg, Aephraim

2011-06-01

329

Low-energy electron elastic scattering from Mn, Cu, Zn, Ni, Ag, and Cd atoms  

SciTech Connect

Electron elastic total cross sections (TCSs) for ground and excited Mn, Cu, Zn, Ni, Ag, and Cd atoms have been investigated in the electron-impact energy range 0 {<=}E{<=} 1 eV. The near-threshold TCSs for both the ground and excited states of these atoms are found to be characterized by Ramsauer-Townsend minima, shape resonances, and extremely sharp resonances corresponding to the formation of stable bound negative ions. The recently developed Regge-pole methodology where the crucial electron-electron correlations are embedded is employed for the calculations. From close scrutiny of the imaginary parts of the complex angular momenta, we conclude that these atoms form stable weakly bound ground and excited negative ions as Regge resonances through slow electron collisions. The extracted electron binding energies from the elastic TCSs of these atoms are contrasted with the available experimental and theoretical values.

Felfli, Z.; Msezane, A. Z. [Department of Physics and Center for Theoretical Studies of Physical Systems, Clark Atlanta University, Atlanta, Georgia 30314 (United States); Sokolovski, D. [School of Mathematics and Physics, Queen's University of Belfast, Belfast, BT7 1NN (United Kingdom); Department of Chemical Physics, University of the Basque Country, Leioa (Spain)

2011-05-15

330

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

331

Magnesium cluster film synthesis by helium nanodroplets.  

PubMed

Atomic and molecular clusters are a unique class of substances with properties that differ greatly from those of the bulk or single atoms due to changes in surface to volume ratio and finite size effects. Here, we demonstrate the ability to create cluster matter films using helium droplet mediated cluster assembly and deposition, a recently developed methodology that condenses atoms or molecules within liquid helium droplets and then gently deposits them onto a surface. In this work, we examine magnesium nanocluster films, which exhibit growth behavior comparable to low-energy cluster beam methods, and demonstrate physical properties and morphology dependent on helium droplet size. PMID:23927262

Emery, Samuel B; Rider, Keith B; Little, Brian K; Schrand, Amanda M; Lindsay, C Michael

2013-08-01

332

Matter-wave scattering and guiding by atomic arrays J. Y. Vaishnav,1,  

E-print Network

Department of Electrical Engineering, Indian Institute of Technology, Kharagpur 721302, India Received 8-wave guiding arises from the interplay of scattering phenomena with bands and conduction along the array. We of electromagnetic waves in a photonic crystal comprised of aluminum rods see, e.g., 1 . Although the problem

Heller, Eric

333

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

334

Scattering of light and acoustic disturbances in the atomic iodine laser  

SciTech Connect

An analysis is presented of the medium refractive index gradients and associated acoustic disturbances (ripples) observed in photolytically pumped atomic iodine laser oscillators. Coupled equations representing acoustic waves with a heating source, atomic iodine laser pumping and chemistry and the laser field are derived and used to evaluate the time-dependent growth rate of the instabilities in the oscillator. The theoretical, linearized model is found to be capable of accounting for growing instabilities, and the predicted scale size of the disturbance is in agreement with observations.

Riley, M.E.

1983-07-01

335

Helium tables.  

NASA Technical Reports Server (NTRS)

These tables are intended to provide a standard method and to facilitate the calculation of the quantity of "Standard Helium" in high pressure containers. The research data and the formulas used in the preparation of the tables were furnished by the Research Laboratory of Physical Chemistry, of the Massachusetts Institute of Technology.

Havill, Clinton H

1928-01-01

336

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

337

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

338

Magnetic Neutron Scattering from Atoms Dissolved in Ferromagnetic Iron and Nickel  

Microsoft Academic Search

Recent experimental results giving the distribution of the magnetic-moment disturbance associated with solute atoms in ferromagnetic iron and nickel are summarized. The disturbances around transition elements dissolved in iron are of two quite different forms dependent on whether the element concerned lies to the right or to the left of iron in the periodic table. This suggests a dependence on

G. G. Low

1968-01-01

339

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

340

Helium Spectra in Atonic Mechanics  

NASA Astrophysics Data System (ADS)

In our model of the helium atom, we postulate that the angular momentum of each electron divided by equals an integer, n, plus a fraction,?n. By minimizing the energy the energy of the helium atom, we find that the ?n values are a function of the total angular momenta, J, irrespective of the integer, n. We thus obtain a set of ?n values for the singlet and triplet states of helium. The ?n values are related to fractals. In our model, we made adjustments to the electron mass so that the calculated energy values agree with the seventeen values for the singlet 1s-ns configurations listed in NIST Atomic Spectra Database Levels Data. The adjustments to the electron mass were usually very close to unity except for the ground state for which the adjustment was ˜5%. (Adjustments like these suggest that we may be able to study three-body effects with spectral accuracy.) By doing this, we had good agreement with all of the NIST spectral values for helium (191 lines of He I, and 243 lines of He II). This conceptually and mathematically simple procedure can be used for other atoms.

Phillips, Alfred, Jr.

2008-03-01

341

Chemical and displacement atomic pair correlations in crystalline solid solutions recovered by anomalous x-ray scattering in Fe-Ni alloys  

SciTech Connect

Short-range pair correlations of atoms in crystalline solid solutions consist of both chemical and displacement correlations. Measurement of these pair correlations is fundamental to understanding the properties of solid solutions. We discuss anomalous scattering techniques which have provided an important advance in our ability to recover these pair correlations and to model the local atomic arrangements in crystalline solid solutions of Fe-Ni alloys.

Ice, G.E.; Sparks, C.J. [Oak Ridge National Lab., TN (United States); Shaffer, L.B. [Anderson Univ., Anderson, IN (United States). Dept. of Physics

1992-12-31

342

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

343

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

NASA Astrophysics Data System (ADS)

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.; Besser, M.; Kramer, M. J.; Morris, J. R.; Calvo-Dahlborg, M.

2013-03-01

344

Bremsstrahlung in the scattering of low-energy electrons by neutral atomic systems. [in atmosphere of sun and cool stars  

NASA Technical Reports Server (NTRS)

By elementary methods, the cross section for electron-atom and electron-molecule bremsstrahlung is computed in the limit when the incident electron energy is much less than Ry. The procedure employs the classical soft-photon emission probability formula for general (h/2pi)(omega), yielding a simple expression for the bremsstrahlung cross section in terms of the total elastic scattering cross section. The validity of the method is discussed, and results are compared with more elaborate and accurate calculations. Comparison is made with ('free-free') opacity calculations for the associated process at the temperature (6300 K) of the solar atmosphere. For chi sub omega = (h/2pi)(omega)/kT = 1, the computed absorption coefficient is within 2, 7, and 12 percent of accurate calculations for scatterings by H, He, and H2, respectively. The general dependence of the opacity on chi sub omega is described well by the simple formula, although the error is larger for higher chi sub omega; it is suggested that the inaccuracy at high frequencies is due to the failure of the soft-photon approximation.

Gould, R. J.

1985-01-01

345

Thermal evolution of helium in magnetron sputtered titanium films  

NASA Astrophysics Data System (ADS)

Helium-containing titanium films synthesized by magnetron sputtering method were investigated using thermal desorption spectrometry (TDS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Helium evolution behaviors under thermal treatment from room temperature to 1500 °C were characterized. Four peaks appeared in TDS at around 100, 420, 700, and 1250 °C were identified and attributed to helium desorption from the specimen surface, substitutional helium (helium atom in a vacancy), small HemVn clusters with different helium-to-vacancy ratios, and helium bubbles or voids, respectively. The helium evolution under thermal treatment composed of two coexisting and competing processes, where the faster process dominated in relevant temperature range, i.e. helium diffusion and release at low temperatures, and bubble or void formation at high temperatures. Three characteristic temperatures in TDS were identified in description of the phenomenon.

Zhang, Jinchao; Cheng, Chun; Wu, Erdong; Xiong, Liangyin; Liu, Shi

2014-10-01

346

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

347

Contrast-Matched Small-Angle Xray Scattering from a Heavy-Atom-Labeled Protein in Structure Determination: Application to a Lead-  

E-print Network

on a protein incorporating specific heavy-atom labels in 65% aqueous sucrose buffer can dramatically enhance using aqueous SAXS and RDC data alone. Moreover, we show that the correct structural solution can sucrose solution as a solvent.3 Contrast-matched scattering profiles arise from only a small number

Clore, G. Marius

348

Electron Bubbles in Liquid Helium  

E-print Network

When an electron (or positronium atom) is injected into liquid helium with nearly zero energy, a bubble quickly forms around it. This phenomenon (which also occurs in liquid hydrogen, liquid neon and possibly in solid helium) lowers the mobility of the electron to a value similar to that for a positive ion. We estimate the radius of the bubble at zero pressure and temperature based on the zero point energy of the electron. If the liquid is held in a state of negative pressure, the bubble will expand beyond the radius at zero pressure. We also estimate the negative pressure such that a bubble once formed will grow without limit.

Kirk T. McDonald

2003-12-03

349

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

350

Roughness of free surfaces of bulk amorphous polymers as studied by x-ray surface scattering and atomic force microscopy  

NASA Astrophysics Data System (ADS)

The morphology of free surfaces of polyetherimide (PEI) samples has been characterized using atomic force microscopy in noncontact mode (NC-AFM), x-ray reflectivity (XRR), and x-ray diffuse scattering (XDS). PEI slabs have been prepared by molding pellets onto float glass. In order to characterize the roughness and morphology mathematically, we considered the surfaces as being self-affine with a rms roughness ? and Hurst coefficient H up to a finite correlation length ?. NC-AFM topographs with ?=61+/-6.3 Å showed the presence of blobs on the surface having a slight tendency to form clusters. These features are reflected in the height-height correlation function which shows the presence of ``strong'' short-range (?1=1064 Å, H1=0.46) and ``weak'' long-range (?2=14537 Å, H2=0.99) correlations. The detection of the specularly reflected contribution in XRR scans only gives access to ?, the lateral fluctuations being averaged out over the coherence area. Scans in XDS include the detection of the diffuse (off-specular) scattering arising from lateral correlations in the surface fluctuations profile and are hence sensitive to ?, ?, and H. The XDS data have been analyzed by simultaneous fits using the distorted-wave Born approximation up to the first order. Calculations were performed using previously published approximations. Best fits to the experimental data provided strongly different correlations length values (7570 Å<=?<=1245 Å) indicating that the estimation of the latter by XDS is somewhat ambiguous. This is in agreement with the strong discrepancy between the correlation lengths determined with x rays and NC-AFM, which can be accounted for by the limits of the perturbation theory for interfaces with high rms roughnesses.

Stone, V. W.; Jonas, A. M.; Nysten, B.; Legras, R.

1999-08-01

351

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.

352

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

353

Physics 216 Spring 2012 The Variational Computation of the Ground State Energy of Helium  

E-print Network

Physics 216 Spring 2012 The Variational Computation of the Ground State Energy of Helium I. Introduction to the variational computation The Hamiltonian for the two­electron system of the helium atom is principle to compute the ground state energy of the helium atom. The ground state wave function

California at Santa Cruz, University of

354

Physics 139B Fall 2009 The Variational Computation of the Ground State Energy of Helium  

E-print Network

Physics 139B Fall 2009 The Variational Computation of the Ground State Energy of Helium I. Introduction to the variational computation The Hamiltonian for the two­electron system of the helium atom is principle to compute the ground state energy of the helium atom. The ground state wave function

California at Santa Cruz, University of

355

Global architecture of human poly(A)-specific ribonuclease by atomic force microscopy in liquid and dynamic light scattering.  

PubMed

Deadenylation is the initial and often rate-limiting step in the main pathways of eukaryotic mRNA decay. Poly(A)-specific ribonuclease (PARN) is a eukaryotic enzyme that efficiently degrades mRNA poly(A) tails. Structural and functional studies have shown that human PARN is composed of at least three functional domains, i.e. the catalytic nuclease domain and two RNA binding domains, the R3H and the RNA recognition motif (RRM), respectively. However, the complete structure of the full length protein is still unknown. We have investigated the global architecture of human PARN by atomic force microscopy (AFM) imaging in buffered milieu and report for the first time the dimensions of the full length protein at subnanometer resolution. The AFM images of single PARN molecules reveal compact ellipsoidal dimers (10.9 × 7.6 × 4.6nm). The dimeric form of PARN was confirmed by dynamic light scattering (DLS) measurements that rendered a molecular weight of 161 kDa, in accordance with previous crystal structures of PARN fragments showing a dimeric composition. We discuss a putative internal arrangement of three functional domains within the full length PARN dimer. PMID:21741754

Niedzwiecka, Anna; Lekka, Malgorzata; Nilsson, Per; Virtanen, Anders

2011-10-01

356

Microscopic study on proton elastic scattering of helium and lithium isotopes at energy range up to 160 MeV/nucleon.  

NASA Astrophysics Data System (ADS)

The proton elastic scattering data on 4,6,8 He and 6,7,9,11Li nuclei at energies below 160 MeV/nucleon are analyzed using the optical model. The optical potential (OP) is taken microscopically, with few and limited fitting parameters, using the single folding model for the real part and high-energy approximation (HEA) for the imaginary one. Clear dependencies of the volume integrals on energy and rms radii are obtained from the results. The calculated differential and the reaction cross sections are in good agreement with the available experimental data. In general, this OP with few and limited fitting parameters, which have a systematic behavior with incident energy and matter radii, successfully describes the proton elastic scattering data with stable and exotic light nuclei at energies up to 160 MeV/nucleon.

Farag, M. Y. H.; Esmael, E. H.; Maridi, H. M.

2014-03-01

357

NIST Form Factor, Attenuation, and Scattering Tables  

NSDL National Science Digital Library

The National Institute of Standards and Technology has published the article, NIST Form Factor, Attenuation, and Scattering Tables. This paper describes and computes "the primary interactions of x-rays with isolated atoms from Z=1(hydrogen) to Z=92(uranium) within a self-consistent Dirac-Hartree-Fock framework." Sections included in the paper are Introduction and Importance of Form Factors, Form Factors and Standard Definitions, Available Tabulations and Basis of Current Formalism, Basic Transform Equations, Avoidance of Singularities, Avoidance of Imprecision, Integration Precision Requirements, Choice of Interpolation Formalism, and Results for Hydrogen and Helium, among others.

358

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

359

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

360

Scattering from Materials BRENT FULTZ  

E-print Network

Scattering from Materials BRENT FULTZ Schematic drawing of the ARCS spectrometer, proposed by scattering methods using x-rays, electrons, neutrons, and -rays. Coherent elastic scattering, for example, reveals atom arrangements. Coherent inelastic scattering provides the energy-wavelength relationships

361

[Atomic beam studies of the interaction of hydrogen with transition metal surfaces  

SciTech Connect

We have constructed two experimental facilities during the term of this grant. In the first three years we constructed a helium atom scattering (HAS) facility with both elastic (EHAS) and inelastic (IHAS) scattering measurement capabilities to investigate the structural and dynamical aspects of solid surfaces and thin films. A pioneering surface metastable atom magnetic diffraction (SMAMD) facility was constructed and developed over the past four years, which makes possible the investigation of long-range electron spin-ordering on the surfaces of insulating magnetic crystals. The following were studied: H overlayers and Ag, Cu on Pd(111), reconstructed Au(111), and NiO(100).

Not Available

1992-01-01

362

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

363

Modeling the Interaction of Helium with Dislocations and Grain Boundaries in Alpha-Iron  

SciTech Connect

Molecular statics, molecular dynamics and the dimer method of potential surface mapping are being used to study the fate of helium in the vicinity of dislocations and grain boundaries in alpha-iron. Even at very low temperatures interstitial helium atoms can migrate to dislocations and grain boundaries, where they are strongly bound. The binding energies of helium to these microstructural features, relative to the perfect crystal, and the migration energies of helium diffusing within them have a strong correlation to the excess atomic volume that exists in these extended defects. Helium atom migration energies within the dislocations and grain boundaries studied are in the range of 0.4 – 0.5 eV. Helium “kick out” mechanisms have been identified within dislocations and grain boundaries by which interstitial helium atoms replace an Fe lattice atom, creating a stable He-vacancy complex that may be a nucleation site for a He bubble.

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

2006-09-01

364

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

E-print Network

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

Carroll, David L.

365

Conference on Atomic and Molecular Reactions and Structure, Flinders University of South Australia, Bedford Park, Australia, February 1982, Proceedings  

NASA Astrophysics Data System (ADS)

Topics discussed include electron-photon coincidence studies in sodium, 'Wannier-ridge' resonances as a new class of atomic states, stepwise electron-laser excitation studies of atoms, intermediate-energy electron scattering by atomic hydrogen, and the pulsed electron beam time-of-flight method for measuring absolute total cross sections for atomic helium. Also examined are electron coincidence spectroscopy as applied to momentum space chemistry, rotational and vibrational transitions in molecular collisions, infrared laser spectroscopy of molecular beams, the infrared absorption spectrum of water, and the electrostatic and relaxation effects in the ionization of intermolecular complexes.

366

Comparison of surface roughness of polished silicon wafers measured by light scattering topography, soft-x-ray scattering, and atomic-force microscopy  

Microsoft Academic Search

Chemomechanically polished silicon wafers are used in a wide range of technologies. In many of these applications, the desired properties are influenced by the Si surface mor- phology. Improvement of polishing methods to increase Si wafer surface quality has been a continuing goal of silicon manufacturers. Among the various methods used for the characterization of microroughness, light scattering topogra- phy

C. Teichert; J. F. Mackay; D. E. Savage; M. G. Lagally; M. Brohl; P. Wagner

1995-01-01

367

Helium-Recycling Plant  

NASA Technical Reports Server (NTRS)

Proposed system recovers and stores helium gas for reuse. Maintains helium at 99.99-percent purity, preventing water vapor from atmosphere or lubricating oil from pumps from contaminating gas. System takes in gas at nearly constant low back pressure near atmospheric pressure; introduces little or no back pressure into source of helium. Concept also extended to recycling of other gases.

Cook, Joseph

1996-01-01

368

A portable helium sniffer  

USGS Publications Warehouse

A portable helium sniffer has been developed for field use. The instrument is mounted in a four-wheel-drive pickup truck and can detect 50 parts per billion of helium in soil gas. The usefulness of helium sniffing in soil is being investigated as a prospecting tool in gas, oil, uranium, and geothermal prospecting as well as in earthquake prediction.

Friedman, Irving; Denton, E.H.

1976-01-01

369

Possible Stimulation of Nuclear ? Decay by Superfluid Helium  

NASA Astrophysics Data System (ADS)

It is suggested that superfluid helium (condensate of He4 atoms) may stimulate nuclear ? decay in a situation when an ? emitter moves through superfluid helium with fine-tuned velocity, so that the backward-emitted ? particle is at rest in the laboratory frame. It is shown that the probability of stimulated ? decay in this case may be sizable enough to be detected.

Barabanov, A. L.

2009-08-01

370

Experiments on solid Helium-4  

NASA Astrophysics Data System (ADS)

This thesis presents data on experiments done with hcp 4He. The main focus is on the possibility of superfluidity inside solid 4He. The presence of superfluidity inside the solid should be manifested by a flow through the solid. The aim of these experiments was to search for a D.C. flow, characterize it and determine if the flow is due to superfluidity. A cell was designed that exploits the properties of helium in confined geometries to provide an interface between superfluid liquid helium, and hcp solid helium at pressures greater than the bulk melting curve. This interface allowed for a direct injection of atoms into the solid from the superfluid. With this cell, two different methods can be used to induce flow. In the first method, mass is injected directly into one side of the solid, while the pressure of the other side is monitored for a response. In the second method, flow is induced by changing the temperature of liquid reservoirs connected to the solid through porous Vycor glass. In addition to observing flow, it is also seen that a fountain pressure exists between the two liquid reservoirs connected to each other through the Vycor, and solid helium. Using this same design, the growth of solid helium was also studied at pressure higher than the bulk melting curve. Here, the solid cannot grow along a free surface, since off the melting curve the cell is supposed to be completely filled with solid. Near the melting curve, transients of 1--5 mK are seen in the temperature along with pressure drops ? 160 mbar. These transients are shown to probably be due to the solidification of metastable liquid regions imbedded in the solid. Off the melting curve, growth of the solid continues, and this growth is studied in the context of, "isochoric compressibility."

Ray, Michael William

371

The Effects of Rayleigh Scattering on the CMB and Cosmic Structure  

E-print Network

During and after recombination, in addition to Thomson scattering with free electrons, photons also coupled to neutral hydrogen and helium atoms through Rayleigh scattering. This coupling influences both CMB anisotropies and the distribution of matter in the Universe. The frequency-dependence of the Rayleigh cross section breaks the thermal nature of CMB temperature and polarization anisotropies and effectively doubles the number of variables needed to describe CMB intensity and polarization statistics, while the additional atomic coupling changes the matter distribution and the lensing of the CMB. We introduce a new method to capture the effects of Rayleigh scattering on cosmological power spectra. Rayleigh scattering modifies CMB temperature and polarization anisotropies at the $\\sim\\!1 \\%$ level at $353 {\\rm GHz}$ (scaling $\\propto \

Alipour, Elham; Hirata, Christopher M

2014-01-01

372

Prolongation structures and matter-wave solitons in F=1 spinor Bose-Einstein condensate with time-dependent atomic scattering lengths in an expulsive harmonic potential  

NASA Astrophysics Data System (ADS)

In this paper, the integrability and matter-wave solitons in a system of three component Gross-Pitaevskii equation arising from the context of F=1 spinor Bose-Einstein condensate with time-dependent atomic scattering lengths in an expulsive harmonic potential are investigated by similarity transformation, prolongation technique and Riemann-Hilbert formulation. As a result, some new exact nonautonomous matter-wave soliton solutions with varying amplitudes and speeds are obtained. It is shown that there exist two integrable systems and exact N-matter-wave solitons in spin-1 Bose-Einstein condensates with time-dependent s-wave scattering lengths. The collision dynamics of the two matter-wave solitons are analyzed and the shape changing interaction phenomena are found.

Wang, Deng-Shan; Ma, Yu-Quan; Li, Xiang-Gui

2014-10-01

373

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

NASA Astrophysics Data System (ADS)

Herein the authors report on the demonstration of gain and a continuous-wave laser on the 1315nm transition of atomic iodine using the energy transferred to I(P1/22) from O2(a?1) produced by a radio-frequency-excited electric discharge sustained in a dry air-He-NO gas mixture. Active oxygen and nitrogen species were observed downstream of the discharge region. Downstream of the discharge, cold gas injection was employed to raise the gas density and lower the temperature of the continuous gas flow. Gain of 0.0062%cm-1 was obtained and the laser output power was 32mW in a supersonic flow cavity.

Woodard, B. S.; Zimmerman, J. W.; Benavides, G. F.; Carroll, D. L.; Verdeyen, J. T.; Palla, A. D.; Field, T. H.; Solomon, W. C.; Davis, S. J.; Rawlins, W. T.; Lee, S.

2008-07-01

374

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

375

Molecule condensate production from an atomic Bose-Einstein condensate via Feshbach scattering in an optical lattice: Gap solitons  

SciTech Connect

We propose a scheme for making a Bose-Einstein condensate (BEC) of molecules from a BEC of atoms in a strongly confining two-dimensional optical lattice and a weak one-dimensional optical lattice in the third dimension. The stable solutions obtained for the order parameters take the form of a different type of gap soliton, with both atomic and molecular BECs, and also standard gap solitons with only a molecular BEC. The strongly confining dimensions of the lattice stabilize the BEC against inelastic energy transfer in atom-molecule collisions. The solitons with atoms and molecules may be obtained by starting with an atomic BEC, and gradually tuning the resonance by changing the external magnetic-field strength until the desired atom-molecule soliton is obtained. A gap soliton of a BEC of only molecules may be obtained nonadiabatically by starting from an atom-only gap soliton, far from a Feshbach resonance and adjusting the magnetic field to near Feshbach resonance. After a period of time in which the dimer field grows, change the magnetic field such that the detuning is large and negative and Feshbach effects wash out, turn off the optical lattice in phase with the atomic BEC, and turn on an optical lattice in phase with the molecules. The atoms disperse, leaving a gap soliton composed of a molecular BEC. Regarding instabilities in the dimension of the weak optical lattice, the solitons which are comprised of both atoms and molecules are sometimes stable and sometimes unstable--we present numerically obtained results. Gap solitons comprised of only molecules have the same stability properties as the standard gap solitons: stable from frequencies slightly below the middle of the band gap to the top, and unstable below that point. Instabilities are only weakly affected by the soliton velocities, and all instabilities are oscillatory.

Tasgal, Richard S.; Menabde, G. [Departments of Chemistry and Electro-Optics, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105 (Israel); Band, Y. B. [Departments of Chemistry and Electro-Optics, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105 (Israel); Atomic Physics Division, A267 Physics, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

2006-11-15

376

Thermodynamic properties of hydrogen-helium plasmas  

NASA Technical Reports Server (NTRS)

The thermodynamic properties of an atomic hydrogen-helium plasma are calculated and tabulated for temperatures from 10,000 to 100,000 K as a function of the mass fraction ratio of atomic hydrogen. The tabulation is for densities from 10 to the minus 10th power to 10 to the minus 6th power gm/cu cm and for hydrogen mass fraction ratios of 0, 0.333, 0.600, 0.800, and 1.0, which correspond to pure helium, 50 percent hydrogen per unit volume, 75 percent hydrogen per unit volume, 89 percent hydrogen per unit volume, and pure hydrogen plasmas, respectively. From an appended computer program, calculations can be made at other densities and mass fractions. The program output agrees well with previous thermodynamic property calculations for limiting cases of pure hydrogen and pure helium plasmas.

Nelson, H. F.

1971-01-01

377

Superfluid Helium 3: Link Between Condensed Matter Physics and Particle Physics  

Microsoft Academic Search

The discovery of the superfluid phases of Helium 3 in 1971 opened the door to one of the most fascinating systems known in condensed matter physics. Superfluidity of Helium 3, originating from pair condensation of Helium 3 atoms, turned out to be the ideal test ground for many fundamental concepts of modern physics, such as macroscopic quantum phenomena, (gauge-)symmetries and

D. Vollhardt; P. Woelfle

2000-01-01

378

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

379

Combined inelastic neutron scattering and solid state density functional theory study of dynamics of hydrogen atoms in muscovite 2M1  

SciTech Connect

Inelastic neutron scattering (INS) was used to study dynamics of the hydrogen atoms in natural 2M1 muscovite in the 150-1200 cm-1 energy range. The resultant INS spectra are interpreted by means of solid state density functional theory calculations covering both normal mode analysis and molecular dynamics that include anharmonic conributions. While signatures of the Al-O-H bending modes were found over the whole energy transfer range, the dominant contributions were observed between 800-1000 cm-1. The modes assigned to the in-plane movements of the respective hydrogen atoms are well-defined and always appear at high energies. In contrast, the modes corresponding to the out-of-plane movements are spread over large energy transfer ranges; extending down to the region of external (lattice) modes. The positions of the high-energy modes contributing to the INS band at ~907 cm-1 depend on the distance of respective hydrogen atoms to the nearest oxygen atom of the basal net and its polarity.

Smr?ok, ?ubomír [Institute of Inorganic Chemistry, Slovak Academy of Sciences, Bratislava, Slovak Republic; Rieder, Milan [Czech Geological Survey, Praha, Czech Republic; Kolesnikov, Alexander I [ORNL; Granroth, Garrett E [ORNL

2011-01-01

380

White-light cavity based on coherent Raman scattering via normal modes of a coupled cavity-and-atom system  

SciTech Connect

We describe a white-light cavity scheme based on a cavity quantum electrodynamics system that consists of multiple three-level atoms confined in an optical cavity and coherently driven by a free-space, circularly polarized field. A linearly polarized field is coupled into the cavity mode and its two circular components induce coherent Raman transitions through the normal modes of the coupled atom-cavity system. One circular component of the cavity field experiences anomalous dispersion which enables broadband light transmission through the cavity. We present the experimental demonstration of the broadband light transmission through an optical cavity coupled to cold Rb atoms.

Zhang Jiepeng; Hernandez, Gessler; Zhu Yifu [Department of Physics, Florida International University, Miami, Florida 33199 (United States); Wei Xiaogang [Department of Physics, Florida International University, Miami, Florida 33199 (United States); College of Physics, Jilin University, Changchun 130023 (China)

2010-03-15

381

Low-energy antiproton interaction with helium  

NASA Astrophysics Data System (ADS)

An ab initio potential for the interaction of the neutral helium atom with antiprotons and protons is calculated using the Born-Oppenheimer approximation. Using this potential, the annihilation cross section for antiprotons in the energy range 0.01 ?eV to 1 eV is calculated.

Gibbs, W. R.

1997-11-01

382

Energy-Related Atomic and Molecular Structure and Scattering Studies. Progress Report, July 1, 1981-December 31, 1982.  

National Technical Information Service (NTIS)

The basic goals of this program remain the experimental determination of fundamental properties of atoms and molecules, and of molecular clusters, and their use as benchmarks in comparison with computed properties based on theoretical models. In particula...

B. Bederson

1982-01-01

383

Detailed and Simplified Nonequilibrium Helium Ionization in the Solar Atmosphere  

NASA Astrophysics Data System (ADS)

Helium ionization plays an important role in the energy balance of the upper chromosphere and transition region. Helium spectral lines are also often used as diagnostics of these regions. We carry out one-dimensional radiation-hydrodynamics simulations of the solar atmosphere and find that the helium ionization is set mostly by photoionization and direct collisional ionization, counteracted by radiative recombination cascades. By introducing an additional recombination rate mimicking the recombination cascades, we construct a simplified three-level helium model atom consisting of only the ground states. This model atom is suitable for modeling nonequilibrium helium ionization in three-dimensional numerical models. We perform a brief investigation of the formation of the He I 10830 and He II 304 spectral lines. Both lines show nonequilibrium features that are not recovered with statistical equilibrium models, and caution should therefore be exercised when such models are used as a basis for interpretating observations.

Golding, Thomas Peter; Carlsson, Mats; Leenaarts, Jorrit

2014-03-01

384

Differential Single-Capture Cross Sections for Fast Alpha-Helium Collisions  

NASA Astrophysics Data System (ADS)

A four-body theoretical study of the single charge transfer process in collision of energetic alpha ions with helium atoms in their ground states is presented. The model utilizes the Coulomb-Born distorted wave approximation with correct boundary conditions to calculate the single-electron capture differential and integral cross sections. The influence of the dynamic and static electron correlations on the capture probability is investigated. The results of the calculations are compared with the recent experimental measurements for differential cross sections and with the other theoretical manipulations. The results for scattering at extreme forward angles are in good agreement with the experimental measurements, but in other scattering angles the agreement is poor. However, the present four-body results for integral cross sections are in excellent agreement with the experimental data.

Ghanbari-Adivi, Ebrahim; Ghavaminia, Hoda

2014-08-01

385

Double ionization of helium by photons and charged particles  

Microsoft Academic Search

We discuss double ionization of helium by charged particles, photoionization, and Compton scattering. With the help of an analysis of the cross section as a function angular momentum transfer (partial waves) or momentum transfer, distant Coulomb collisions can be related to photoionization while hard Coulomb collisions can be related to Compton scattering. Within this framework, accurate tests for recent photoionization

J. Burgdoerfer; Y. Qiu; J. Wang; J. H. McGuire

1997-01-01

386

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.

387

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

388

Deposition of mass-selected clusters studied by thermal energy atom scattering and low-temperature scanning tunneling microscopy: An experimental setup  

NASA Astrophysics Data System (ADS)

We present an experimental setup for the investigation of the processes occurring during the deposition of mass-selected clusters on a well-defined surface. The sample is analyzed in situ by two complementary methods: thermal energy atom scattering (TEAS) and scanning tunneling microscopy (STM). TEAS is used to study the dynamical processes during the deposition and to gather statistical information about the resulting structures on the surface. Subsequent STM measurements allow us to investigate the collision outcome on an atomic scale. The setup is highly versatile and guarantees ultra-high-vacuum conditions and cryogenic temperatures (?30 K) of the sample at all times even during sample transfer. Clusters are produced in a CORDIS-type cluster source. A new compact multichannel effusive He source in combination with a new Wien-filter-based He detector are used for TEAS measurements. The new low-temperature STM allows measurements in a temperature range between 8 and 450 K. Atomic resolution on the Pt(111) surface is regularly observed at Tsample=8 K. The performances of the setup are illustrated by STM images obtained after the deposition of Ag7+ clusters with Ekin=95 and 1000 eV on bare Pt(111) and by measurements made of the deposition of Ag7+ clusters with Ekin=20 eV in a Xe-rare-gas matrix adsorbed on Pt(111).

Jödicke, Harald; Schaub, Renald; Bhowmick, Ashok; Monot, René; Buttet, Jean; Harbich, Wolfgang

2000-07-01

389

Atomic layer deposition-based tuning of the pore size in mesoporous thin films studied by in situ grazing incidence small angle X-ray scattering.  

PubMed

Atomic layer deposition (ALD) enables the conformal coating of porous materials, making the technique suitable for pore size tuning at the atomic level, e.g., for applications in catalysis, gas separation and sensing. It is, however, not straightforward to obtain information about the conformality of ALD coatings deposited in pores with diameters in the low mesoporous regime (<10 nm). In this work, it is demonstrated that in situ synchrotron based grazing incidence small angle X-ray scattering (GISAXS) can provide valuable information on the change in density and internal surface area during ALD of TiO2 in a porous titania film with small mesopores (3-8 nm). The results are shown to be in good agreement with in situ X-ray fluorescence data representing the evolution of the amount of Ti atoms deposited in the porous film. Analysis of both datasets indicates that the minimum pore diameter that can be achieved by ALD is determined by the size of the Ti-precursor molecule. PMID:25363826

Dendooven, Jolien; Devloo-Casier, Kilian; Ide, Matthias; Grandfield, Kathryn; Kurttepeli, Mert; Ludwig, Karl F; Bals, Sara; Van Der Voort, Pascal; Detavernier, Christophe

2014-12-21

390

[Atomic beam studies of the interaction of hydrogen with transition metal surfaces]. Technical progress report, August 1, 1985--July 30, 1992  

SciTech Connect

We have constructed two experimental facilities during the term of this grant. In the first three years we constructed a helium atom scattering (HAS) facility with both elastic (EHAS) and inelastic (IHAS) scattering measurement capabilities to investigate the structural and dynamical aspects of solid surfaces and thin films. A pioneering surface metastable atom magnetic diffraction (SMAMD) facility was constructed and developed over the past four years, which makes possible the investigation of long-range electron spin-ordering on the surfaces of insulating magnetic crystals. The following were studied: H overlayers and Ag, Cu on Pd(111), reconstructed Au(111), and NiO(100).

Not Available

1992-12-31

391

The Primordial Helium Abundance  

E-print Network

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 evolution models.

Manuel Peimbert

2008-11-18

392

Solvation of intrinsic positive charge in superfluid helium.  

PubMed

On the basis of electronic structure calculations, the structure of intrinsic positive charge solvated in superfluid helium is identified as triatomic He3(+) ion, which is bound to the surrounding ground state helium atoms through the charge–charge induced dipole interaction in a pairwise additive manner. Bosonic density functional theory calculations show that this ion forms the well-known Atkins’ snowball solvation structure where the first rigid helium shell is effectively disconnected from the rest of the liquid. Evaluation of the total energy vs helium droplet size N shows distinct regions related to the completion of solvent shells near N = 16 and N = 47. These regions can be assigned to magic numbers observed in positively charged helium droplets appearing at N = 15 and in the range between 20 and 50 helium atoms. The calculated added mass for the positive ion in bulk superfluid helium (18 mHe) is much smaller than the previous experiments suggest (30–40 mHe), indicating that there may be yet some unidentified additional factor contributing to the measured effective mass. Both previous experiments and the present calculations agree on the effective mass of the negative charge (240–250 mHe). The main difference between the solvated negative and positive charges in liquid helium is that the latter forms a chemically bound triatomic molecule surrounded by highly inhomogeneous liquid structure whereas the former remains as a separated charge with a smoothly varying liquid density around it. PMID:24654777

Mateo, David; Eloranta, Jussi

2014-08-21

393

Scattering of Antiprotons by Nuclei (Atoms) in the Range of Low Energies $E\\lesssim 10^5$ eV. Mirror Reflection, Diffraction, and Channeling of Antiprotons in Crystals  

E-print Network

Studying antiproton scattering by nuclei (atoms) in the range of low energies, we found out that the increase in the antiproton-nucleus scattering amplitude through Coulomb interaction provides the possibility to investigate spin-dependent processes accompanying the interaction of antiprotons with nuclei (polarized or unpolarized) by means of mirror reflection of antiprotons from the vacuum-matter boundary, diffraction and channeling (surface diffraction and channeling) of antiprotons in crystals.

V. G. Baryshevsky

2014-04-01

394

Analytical complex at the PIK reactor for studying the supra-atomic structure and dynamics of materials by neutron scattering  

SciTech Connect

A project of the center for studying reactor materials and solving problems of materials science is presented which will be equipped with the following neutron instruments: a small-angle Membrana diffractometer, a spin-echo spectrometer, and a time-of-flight spectrometer. It is proposed to irradiate materials in the PIK reactor core and use neutron-scattering tools to analyze the structure and dynamics of these materials and investigate radiative defects in the complete experimental cycle (initial material-irradiation-strength tests, thermal loads, and other effects) using materials science techniques.

Lebedev, V. M., E-mail: lebedev@pnpi.spb.ru; Lebedev, V. T.; Ivanova, I. N.; Orlova, D. N. [Russian Academy of Sciences, St. Petersburg Nuclear Physics Institute (Russian Federation)

2011-12-15

395

The solubility and diffusion coefficient of helium in uranium dioxide  

Microsoft Academic Search

The solubility and diffusion coefficient of helium in the single-crystal UO2 samples were determined by a Knudsen-effusion mass-spectrometric method. The measured helium solubilities were found to lie within the scatter of the available data, but to be much lower than those for the polycrystalline samples. The diffusion analysis was conducted based on a hypothetical equivalent sphere model and the simple

Kunihisa Nakajima; Hiroyuki Serizawa; Noriko Shirasu; Yoshinori Haga; Yasuo Arai

2011-01-01

396

Effects of dark atom excitations  

E-print Network

New stable quarks and charged leptons may exist and be hidden from detection, as they are bound by Coulomb interaction in neutral dark atoms of composite dark matter. This possibility leads to fundamentally new types of indirect effects related to the excitation of such dark atoms followed by their electromagnetic de-excitation. Stable -2 charged particles, bound to primordial helium in O-helium (OHe) atoms, represent the simplest model of dark atoms. Here we consider the structure of OHe atomic levels which is a necessary input for the indirect tests of such composite dark matter scenarios, and we give the spectrum of electromagnetic transitions from the levels excited in OHe collisions.

Cudell, Jean-René; Wallemacq, Quentin

2014-01-01

397

A Preliminary Report on X-Ray Photoabsorption Coefficients andAtomic Scattering Factors for 92 Elements in the 10-10,000 eVRegion  

SciTech Connect

Based on currently available photoabsorption measurements and recent theoretical calculations by Doolen and Liberman (Physica Scripta 36, 77 (1987)), a revised (from ADNDT 27, 1 (1982)) best-fit determination of the photoabsorption cross sections is presented here for the elements Z=1 to Z=92 in the 10-10,000 eV range. The photoabsorption data used include those described in the Lockheed and DOE listings of research abstracts for the past ten years and those which have been recently added to the comprehensive NBS Measured Data Base (NBSIR 86-3461, Hubbell et al.). The best-fit curves are compared with both the compilation of measurements and the calculations by Doolen and Liberman. Using the photoabsorption curves, the atomic scattering factors have been calculated for the energy range 50-10,000 eV and are also presented in this report.

Henke, B.L.; Davis, J.C.; Gullikson, E.M.; Perera, R.C.C.

1988-11-01

398

A preliminary report on x-ray photoabsorption coefficients and atomic scattering factors for 92 elements in the 10--10,000 eV region  

SciTech Connect

Based on currently available photoabsorption measurements and recent theoretical calculations by Doolen and Liberman, a revised best-fit determination of the photoabsorption cross sections is presented here for the elements Z = 1 to Z = 92 in the 10--10,000 eV range. The photoabsorption data used include those described in the Lockheed and DOE listings of research abstracts for the past ten years and those which have been recently added to the comprehensive NBS Measured data Base. The best-fit curves are compared with both the compilation of measurements and the calculations by Doolen and Liberman. Using the photoabsorption curves, the atomic scattering factors have been calculated for the energy range 50--10,000 eV and are also presented in this report.

Henke, B.L.; Davis, J.C.; Gullikson, E.M.; Perera, R.C.C.

1988-11-01

399

In Situ Synchrotron Based X-ray Fluorescence and Scattering Measurements During Atomic Layer Deposition: Initial Growth of HfO2 on Si and Ge Substrates  

SciTech Connect

The initial growth of HfO{sub 2} was studied by means of synchrotron based in situ x-ray fluorescence (XRF) and grazing incidence small angle x-ray scattering (GISAXS). HfO{sub 2} was deposited by atomic layer deposition (ALD) using tetrakis(ethylmethylamino)hafnium and H{sub 2}O on both oxidized and H-terminated Si and Ge surfaces. XRF quantifies the amount of deposited material during each ALD cycle and shows an inhibition period on H-terminated substrates. No inhibition period is observed on oxidized substrates. The evolution of film roughness was monitored using GISAXS. A correlation is found between the inhibition period and the onset of surface roughness.

K Devloo-Casier; J Dendooven; K Ludwig; G Lekens; J DHaen; C Detavernier

2011-12-31

400

{beta}-connectin studies by small-angle x-ray scattering and single-molecule force spectroscopy by atomic force microscopy  

SciTech Connect

The three-dimensional structure and the mechanical properties of a {beta}-connectin fragment from human cardiac muscle, belonging to the I band, from I{sub 27} to I{sub 34}, were investigated by small-angle x-ray scattering (SAXS) and single-molecule force spectroscopy (SMFS). This molecule presents an entropic elasticity behavior, associated to globular domain unfolding, that has been widely studied in the last 10 years. In addition, atomic force microscopy based SMFS experiments suggest that this molecule has an additional elastic regime, for low forces, probably associated to tertiary structure remodeling. From a structural point of view, this behavior is a mark of the fact that the eight domains in the I{sub 27}-I{sub 34} fragment are not independent and they organize in solution, assuming a well-defined three-dimensional structure. This hypothesis has been confirmed by SAXS scattering, both on a diluted and a concentrated sample. Two different models were used to fit the SAXS curves: one assuming a globular shape and one corresponding to an elongated conformation, both coupled with a Coulomb repulsion potential to take into account the protein-protein interaction. Due to the predominance of the structure factor, the effective shape of the protein in solution could not be clearly disclosed. By performing SMFS by atomic force microscopy, mechanical unfolding properties were investigated. Typical sawtooth profiles were obtained and the rupture force of each unfolding domain was estimated. By fitting a wormlike chain model to each peak of the sawtooth profile, the entropic elasticity of octamer was described.

Marchetti, S.; Carla, M.; Gambi, C. M. C. [Department of Physics, University of Florence and CNISM Via G. Sansone 1, IT-50019, Sesto Fiorentino, Florence (Italy); Sbrana, F.; Vassalli, M. [Biophysics Institute of the National Research Council, Via De Marini 6, Genova (Italy); Toscano, A.; Pacini, A. [Department of Anatomy, Histology, and Forensic Medicine, University of Florence, Florence (Italy); Fratini, E. [Department of Chemistry and Consorzio Interuniversitario per lo Sviluppo dei Sistemi a Grande Interfase (CSGI), University of Florence, Via della Lastruccia 3, IT-50019, Sesto Fiorentino, Florence (Italy); Tiribilli, B. [Complex System Institute of the National Research Council (ISC-CNR), Sesto Fiorentino, Florence (Italy)

2011-05-15

401

Double K-shell photoionization of atomic beryllium  

SciTech Connect

Double photoionization of the core 1s electrons in atomic beryllium is theoretically studied using a hybrid approach that combines orbital and grid-based representations of the Hamiltonian. The {sup 1} S ground state and {sup 1} P final state contain a double occupancy of the 2s valence shell in all configurations used to represent the correlated wave function. Triply differential cross sections are evaluated, with particular attention focused on a comparison of the effects of scattering the ejected electrons through the spherically symmetric valence shell with similar cross sections for helium, representing a purely two-electron target with an analogous initial-state configuration.

Yip, F. L. [Departamento de Quimica, Modulo 13, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Martin, F. [Departamento de Quimica, Modulo 13, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Instituto Madrilen (tilde sign)o de Estudios Avanzados en Nanociencia, Cantoblanco, E-28049 Madrid (Spain); McCurdy, C. W. [Department of Chemistry, University of California, Davis, California 95616 (United States); Lawrence Berkeley National Laboratory, Chemical Sciences, and Ultrafast X-ray Science Laboratory, Berkeley, California 94720 (United States); Rescigno, T. N. [Lawrence Berkeley National Laboratory, Chemical Sciences, and Ultrafast X-ray Science Laboratory, Berkeley, California 94720 (United States)

2011-11-15

402

SPECIAL TOPIC: HELIUM NANODROPLETS Experimental studies of helium droplets  

E-print Network

SPECIAL TOPIC: HELIUM NANODROPLETS Experimental studies of helium droplets J. A. Northbya) Physics September 2001 In this report I will review experimental studies of free helium droplets, with the exception of spectroscopic studies of helium droplets that contain impurities. This particular topic, as well as theoretical

Northby, Jan A.

403

Stable anatase TiO2 coating on quartz fibers by atomic layer deposition for photoactive light-scattering in dye-sensitized solar cells  

NASA Astrophysics Data System (ADS)

Quartz fibers provide a unique high surface-area substrate suitable for conformal coating using atomic layer deposition (ALD), and are compatible with high temperature annealing. This paper shows that the quartz fiber composition stabilizes ALD TiO2 in the anatase phase through TiO2-SiO2 interface formation, even after annealing at 1050 °C. When integrated into a dye-sensitized solar cell, the TiO2-coated quartz fiber mat improves light scattering performance. Results also confirm that annealing at high temperature is necessary for better photoactivity of ALD TiO2, which highlights the significance of quartz fibers as a substrate. The ALD TiO2 coating on quartz fibers also boosts dye adsorption and photocurrent response, pushing the overall efficiency of the dye-cells from 6.5 to 7.4%. The mechanisms for improved cell performance are confirmed using wavelength-dependent incident photon to current efficiency and diffuse light scattering results. The combination of ALD and thermal processing on quartz fibers may enable other device structures for energy conversion and catalytic reaction applications.

Kim, Do Han; Koo, Hyung-Jun; Jur, Jesse S.; Woodroof, Mariah; Kalanyan, Berç; Lee, Kyoungmi; Devine, Christina K.; Parsons, Gregory N.

2012-07-01

404

Ions and ionic compounds in helium nanodroplets  

NASA Astrophysics Data System (ADS)

In this thesis, ions in liquid helium nanodroplets are studied via electron impact mass spectrometry and a new technique called Optically Selected Mass Spectrometry (OSMS), which combines mass spectrometry and infrared spectroscopy. Electron impact of a helium nanodroplet results in ionization of a helium atom, followed by rapid charge migration that can ultimately result in charge transfer to a solute species. This process can be described quantitatively in terms of the influence of the electrostatic potential between the charge and the embedded molecule on the trajectory of the migrating charge. Vibrationally hot molecular ions formed via charge transfer are found to be effectively cooled by the helium environment on a timescale competitive with fragmentation. Comparisons with gas-phase results for the ions studied herein reveals that the ions are cooled via a highly non-thermal mechanism that appears to be generally applicable. High resolution infrared spectroscopy is used to examine a number of ionic compounds, namely alkali halide salts, bound to an HCN chromophore. The rotationally resolved spectra were used to obtain accurate molecular constants for these helium solvated complexes, including the large permanent electric dipole moments. The vibrational frequency shifts are in good agreement with theory, and the data suggests that the fundamental properties of these systems can be understood in terms of the size of the ions and the electrostatic moments of the molecules.

Lewis, William K.

405

Effective atomic numbers of blue topaz at different gamma-rays energies obtained from Compton scattering technique  

NASA Astrophysics Data System (ADS)

Topaz occurs in a wide range of colors, including yellow, orange, brown, pink-to-violet and blue. All of these color differences are due to color centers. In order to improve the color of natural colorless topaz, the most commonly used is irradiated with x- or gamma-rays, indicated that attenuation parameters is important to enhancements by irradiation. In this work, the mass attenuation coefficients of blue topaz were measured at the different energy of ?-rays using the Compton scattering technique. The results show that, the experimental values of mass attenuation coefficient are in good agreement with the theoretical values. The mass attenuation coefficients increase with the decrease in gamma rays energies. This may be attributed to the higher photon interaction probability of blue topaz at lower energy. This result is a first report of mass attenuation coefficient of blue topaz at different gamma rays energies.

Tuschareon, S.; Limkitjaroenporn, P.; Kaewkhao, J.

2014-03-01

406

Correlation of Excess Enthalpy and HELIUM-4 Production:. a Review  

NASA Astrophysics Data System (ADS)

Three different sets of experiments conducted in the Navy Laboratory (NAWCWD) at China Lake, California (1990-1994) clearly established that helium-4 is the main fusion product in the Pd/D2O + LiOD electrolysis system. A correlation between excess enthalpy and excess helium-4 was measured in 18 out of 21 experiments. The observation of no excess enthalpy was correlated with no excess helium in 12 out of 12 experiments. Thus, 30 out of 33 experiments agree with the hypothesis that the excess enthalpy produced in cold fusion studies is correlated with helium-4 production: D + D ? 4He+23.8 MeV. Furthermore, the measured rate of helium-4 production was always in the appropriate range of 1010-1012 atoms/s/W of excess power.

Miles, M. H.

2005-12-01

407

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

408

Structures, energetics, and dynamics of helium adsorbed on isolated fullerene ions.  

PubMed

Helium adsorbed on C(60)(+) and C(70)(+) exhibits phenomena akin to helium on graphite. Mass spectra suggest that commensurate layers form when all carbon hexagons and pentagons are occupied by one He each, but that the solvation shell does not close until 60 He atoms are adsorbed on C(60)(+), or 62 on C(70)(+). Molecular dynamics simulations of C(60)He(n)(+) at 4 K show that the commensurate phase is solid. Helium added to C(60)He(32)(+) will displace some atoms from pentagonal sites, leading to coexistence of a registered layer of immobile atoms interlaced with a nonregistered layer of mobile atoms. PMID:22401228

Leidlmair, Christian; Wang, Yang; Bartl, Peter; Schöbel, Harald; Denifl, Stephan; Probst, Michael; Alcamí, Manuel; Martín, Fernando; Zettergren, Henning; Hansen, Klavs; Echt, Olof; Scheier, Paul

2012-02-17

409

Structures, Energetics, and Dynamics of Helium Adsorbed on Isolated Fullerene Ions  

NASA Astrophysics Data System (ADS)

Helium adsorbed on C60+ and C70+ exhibits phenomena akin to helium on graphite. Mass spectra suggest that commensurate layers form when all carbon hexagons and pentagons are occupied by one He each, but that the solvation shell does not close until 60 He atoms are adsorbed on C60+, or 62 on C70+. Molecular dynamics simulations of C60Hen+ at 4 K show that the commensurate phase is solid. Helium added to C60He32+ will displace some atoms from pentagonal sites, leading to coexistence of a registered layer of immobile atoms interlaced with a nonregistered layer of mobile atoms.

Leidlmair, Christian; Wang, Yang; Bartl, Peter; Schöbel, Harald; Denifl, Stephan; Probst, Michael; Alcamí, Manuel; Martín, Fernando; Zettergren, Henning; Hansen, Klavs; Echt, Olof; Scheier, Paul

2012-02-01

410

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

411

The descending helium balloon  

NASA Astrophysics Data System (ADS)

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

2014-07-01

412

Modeling Two-Charge State Helium Plasmas  

NASA Astrophysics Data System (ADS)

A computational model for the flow of energetic helium ions and atoms through a background neutral helium gas is being developed. The essence of the method is to consider atomic reactions as creating a new source of ions or neutrals if the energy or charge state of the resulting particle is changed. A set of conservation equations in a two-dimensional (position -- energy) phase space is formulated. Atomic reactions that lead to ions being born with zero kinetic energy are modeled with a 1-D Volterra integral equation [1] that can quickly be solved numerically by finite differences. Atomic reactions leading to ions being born with finite kinetic energy are formulated as source terms in the position-energy phase space. The conservation equations are solved iteratively using the solution to the Volterra equation as a starting point. The current work focuses on multiple-pass, 1-D ion flow through neutral gas in a nearly transparent anode and cathode pair in planar, cylindrical, and spherical geometry for application to ^3He-^3He and D-^3He inertial electrostatic experiments.[4pt] [1] G.A. Emmert and J.F. Santarius, ``Atomic and Molecular Effects on Spherically Convergent Ion Flow I: Single Atomic Species,'' Phys. Plasmas 17, 013502 (2010)

Emmert, Gilbert; Santarius, John

2012-10-01

413

Possible stimulation of nuclear alpha decay by superfluid helium.  

PubMed

It is suggested that superfluid helium (condensate of (4)He atoms) may stimulate nuclear alpha decay in a situation when an alpha emitter moves through superfluid helium with fine-tuned velocity, so that the backward-emitted alpha particle is at rest in the laboratory frame. It is shown that the probability of stimulated alpha decay in this case may be sizable enough to be detected. PMID:19792793

Barabanov, A L

2009-08-28

414

Possible stimulation of nuclear alpha-decay by superfluid helium  

E-print Network

It is suggested that superfluid helium (condensate of 4-He atoms) may stimulate nuclear alpha-decay in a situation when an alpha-emitter moves through superfluid helium with fine-tuned velocity, so that the backward-emitted alpha-particle is at rest in the laboratory frame. It is shown that the probability of stimulated alpha-decay in this case may be sizable enough to be detected.

A. L. Barabanov

2009-02-26

415

Scintillation of liquid helium for low-energy nuclear recoils  

NASA Astrophysics Data System (ADS)

The scintillation properties of liquid helium upon the recoil of a low-energy helium atom are discussed in the context of the possible use of this medium as a detector of dark matter. It is found that the prompt scintillation yield in the range of recoil energies from a few keV to 100 keV is somewhat higher than that obtained by a linear extrapolation from the measured yield for a 5-MeV ? particle. A comparison is made of both the scintillation yield and the charge separation by an electric field for nuclear recoils and for electrons stopped in helium.

Ito, T. M.; Seidel, G. M.

2013-08-01

416

Mixed quantum/classical theory for inelastic scattering of asymmetric-top-rotor + atom in the body-fixed reference frame and application to the H2O + He system.  

PubMed

The mixed quantum/classical theory (MQCT) for inelastic molecule-atom scattering developed recently [A. Semenov and D. Babikov, J. Chem. Phys. 139, 174108 (2013)] is extended to treat a general case of an asymmetric-top-rotor molecule in the body-fixed reference frame. This complements a similar theory formulated in the space-fixed reference-frame [M. Ivanov, M.-L. Dubernet, and D. Babikov, J. Chem. Phys. 140, 134301 (2014)]. Here, the goal was to develop an approximate computationally affordable treatment of the rotationally inelastic scattering and apply it to H2O + He. We found that MQCT is somewhat less accurate at lower scattering energies. For example, below E = 1000 cm(-1) the typical errors in the values of inelastic scattering cross sections are on the order of 10%. However, at higher scattering energies MQCT method appears to be rather accurate. Thus, at scattering energies above 2000 cm(-1) the errors are consistently in the range of 1%-2%, which is basically our convergence criterion with respect to the number of trajectories. At these conditions our MQCT method remains computationally affordable. We found that computational cost of the fully-coupled MQCT calculations scales as n(2), where n is the number of channels. This is more favorable than the full-quantum inelastic scattering calculations that scale as n(3). Our conclusion is that for complex systems (heavy collision partners with many internal states) and at higher scattering energies MQCT may offer significant computational advantages. PMID:25240355

Semenov, Alexander; Dubernet, Marie-Lise; Babikov, Dmitri

2014-09-21

417

Mixed quantum/classical theory for inelastic scattering of asymmetric-top-rotor + atom in the body-fixed reference frame and application to the H2O + He system  

NASA Astrophysics Data System (ADS)

The mixed quantum/classical theory (MQCT) for inelastic molecule-atom scattering developed recently [A. Semenov and D. Babikov, J. Chem. Phys. 139, 174108 (2013)] is extended to treat a general case of an asymmetric-top-rotor molecule in the body-fixed reference frame. This complements a similar theory formulated in the space-fixed reference-frame [M. Ivanov, M.-L. Dubernet, and D. Babikov, J. Chem. Phys. 140, 134301 (2014)]. Here, the goal was to develop an approximate computationally affordable treatment of the rotationally inelastic scattering and apply it to H2O + He. We found that MQCT is somewhat less accurate at lower scattering energies. For example, below E = 1000 cm-1 the typical errors in the values of inelastic scattering cross sections are on the order of 10%. However, at higher scattering energies MQCT method appears to be rather accurate. Thus, at scattering energies above 2000 cm-1 the errors are consistently in the range of 1%-2%, which is basically our convergence criterion with respect to the number of trajectories. At these conditions our MQCT method remains computationally affordable. We found that computational cost of the fully-coupled MQCT calculations scales as n2, where n is the number of channels. This is more favorable than the full-quantum inelastic scattering calculations that scale as n3. Our conclusion is that for complex systems (heavy collision partners with many internal states) and at higher scattering energies MQCT may offer significant computational advantages.

Semenov, Alexander; Dubernet, Marie-Lise; Babikov, Dmitri

2014-09-01

418

The helium fine-structure controversy  

E-print Network

There is presently disagreement between theory and experiment as well as between different theoretical calculations concerning the fine-structure splitting of the lowest P state of the neutral helium atom. We believe that we have found a minor error in the formulas used by Drake et al. (Can. J. Phys. 80, 1195 (2002)) in their calculations, and we may have an explanation how the error has occurred. To what extent this might resolve (part of) the discrepancy is not known at present.

Ingvar Lindgren

2008-10-05

419

Helium Diffusion in Olivine  

NASA Astrophysics Data System (ADS)

Diffusion of helium has been characterized in natural Fe-bearing olivine (~Fo90) and synthetic forsterite. Polished, oriented slabs of olivine were implanted with 3He, at 100 keV at a dose of 5x1015/cm2 or at 3.0 MeV at a dose of 1x1016/cm2. A set of experiments on the implanted olivine were run in 1-atm furnaces. In addition to the one-atm experiments, experiments on implanted samples were also run at higher pressures (2.6 and 2.7 GPa) to assess the potential effects of pressure on He diffusion and the applicability of the measured diffusivities in describing He transport in the mantle. The high-pressure experiments were conducted in a piston-cylinder apparatus using an "ultra-soft" pressure cell, with the diffusion sample directly surrounded by AgCl. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. This direct profiling method permits us to evaluate anisotropy of diffusion, which cannot be easily assessed using bulk-release methods. For diffusion in forsterite parallel to c we obtain the following Arrhenius relation over the temperatures 250-950°C: D = 3.91x10-6exp(-159 ± 4 kJ mol-1/RT) m2/sec. The data define a single Arrhenius line spanning more than 7 orders of magnitude in D and 700°C in temperature. Diffusion parallel to a appears slightly slower, yielding an activation energy for diffusion of 135 kJ/mol and a pre-exponential factor of 3.73x10-8 m2/sec. Diffusion parallel to b is slower than diffusion parallel to a (by about two-thirds of a log unit); for this orientation an activation energy of 138 kJ/mol and a pre-exponential factor of 1.34x10-8 m2/sec are obtained. This anisotropy is broadly consistent with observations for diffusion of Ni and Fe-Mg in olivine. Diffusion in Fe-bearing olivine (transport parallel to b) agrees within uncertainty with findings for He diffusion in forsterite. The higher-pressure experiments yield diffusivities in agreement with those from the 1-atm experiments, indicating that the results reported here can be reasonably applied to modeling He transport in the upper mantle. The insensitivity of He diffusion to pressure over the investigated range of conditions suggests that compression of the mineral lattice is not sufficient to significantly influence migration of the relatively small helium atoms, which likely diffuse via crystal interstices. The He diffusivities in this work are generally consistent with results from the study of Futagami et al. (1993), who measured He diffusion in natural olivine by outgassing 4He implanted samples, and with the diffusivities measured by bulk-release of 4He and 3He by Shuster et al. (2003), but are about 2 orders of magnitude slower than the recent findings of Tolstikhin et al. (2010) and Blard et al. (2008) . An up-temperature extrapolation of our data also show reasonable agreement with the higher-temperature measurements of Hart (1984). Blard et al. (2008) GCA 72, 3788-3803; Futagami et al. (1993) GCA 57, 3177-3194; Hart (1984) EPSL 70, 297-302; Shuster et al.( 2003) EPSL 217, 19-32; Tolstikhin et al. (2010) GCA 74, 1436-1447

Cherniak, D. J.; Watson, E. B.

2011-12-01

420

Cold Atoms  

NASA Astrophysics Data System (ADS)

This chapter and the following one address collective effects of quantum particles, that is, the effects which are observed when we put together a large number of identical particles, for example, electrons, helium-4 or rubidium-85 atoms. We shall see that quantum particles can be classified into two categories, bosons and fermions, whose collective behavior is radically different. Bosons have a tendency to pile up in the same quantum state, while fermions have a tendency to avoid each other. We say that bosons and fermions obey two different quantum statistics, the Bose-Einstein and the Fermi-Dirac statistics, respectively. Temperature is a collective effect, and in Section 5.1 we shall explain the concept of absolute temperature and its relation to the average kinetic energy of molecules. We shall describe in Section 5.2 how we can cool atoms down thanks to the Doppler effect, and explain how cold atoms can be used to improve the accuracy of atomic clocks by a factor of about 100. The effects of quantum statistics are prominent at low temperatures, and atom cooling will be used to obtain Bose-Einstein condensates at low enough temperatures, when the atoms are bosons.

Bellac, Michel Le

2014-11-01

421

SPIN POLARIZED HELIUM3, A PLAYGROUND IN MANY DOMAINS OF PHYSICS  

Microsoft Academic Search

This article gives a survey of the different methods which can be used to polarize the nuclear spin of helium-3. These techniques are particularly discussed in relation to the production of polarized helium-3 targets for nuclear physics experiments, such as electron or proton scattering and neutron spin filters. Some emphasis is given to the development of new powerful solid state

M. LEDUC

1990-01-01

422

The solubility and diffusion coefficient of helium in uranium dioxide  

NASA Astrophysics Data System (ADS)

The solubility and diffusion coefficient of helium in the single-crystal UO 2 samples were determined by a Knudsen-effusion mass-spectrometric method. The measured helium solubilities were found to lie within the scatter of the available data, but to be much lower than those for the polycrystalline samples. The diffusion analysis was conducted based on a hypothetical equivalent sphere model and the simple Fick's law. The helium diffusion coefficient was determined by using the pre-exponential factor and activation energy as the fitting parameters for the measured and calculated fractional releases of helium. The optimized diffusion coefficients were in good agreement with those obtained by a nuclear reaction method reported in the past. It was also found that the pre-exponential factors of the determined diffusion coefficients were much lower than those analyzed in terms of a simple interstitial diffusion mechanism.

Nakajima, Kunihisa; Serizawa, Hiroyuki; Shirasu, Noriko; Haga, Yoshinori; Arai, Yasuo

2011-12-01

423

Creep properties of Hastelloy-X in impure helium environments  

SciTech Connect

In impure helium environments, Hastelloy-X is susceptible to carburization and oxidation. These effects are investigated separately, and are related to the creep behavior of the alloy. Experiments were carried out at 900/sup 0/C in both helium and air. Carburization resulted in a slight increase of the creep strength up to the onset of the tertial creep. Suppression of the creep crack growth by oxidation was confirmed using notched plate specimens of Inconel alloy 600 and Hastelloy-X. Although the difference of creep strength in air and in helium was very small and considered to be inclusive in the usual scatter, a pessimistic ratio of rupture stress in helium to that in air was estimated to be 0.9.

Nakanishi, T.; Kawakami, H.

1984-08-01

424

Model for the charge-transfer probability in helium nanodroplets following electron-impact ionization  

SciTech Connect

A theoretical model has been developed to describe the probability of charge transfer from helium cations to dopant molecules inside helium nanodroplets following electron-impact ionization. The location of the initial charge site inside helium nanodroplets subject to electron impact has been investigated and is found to play an important role in understanding the ionization of dopants inside helium droplets. The model is consistent with a charge migration process in small helium droplets that is strongly directed by intermolecular forces originating from the dopant, whereas for large droplets (tens of thousands of helium atoms and larger) the charge migration increasingly takes on the character of a random walk. This suggests a clear droplet size limit for the use of electron-impact mass spectrometry for detecting molecules in helium droplets.

Ellis, Andrew M.; Yang Shengfu [Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)

2007-09-15

425

Note: a new design for a low-temperature high-intensity helium beam source.  

PubMed

A high-intensity supersonic beam source is a key component of any atom scattering instrument, affecting the sensitivity and energy resolution of the experiment. We present a new design for a source which can operate at temperatures as low as 11.8 K, corresponding to a beam energy of 2.5 meV. The new source improves the resolution of the Cambridge helium spin-echo spectrometer by a factor of 5.5, thus extending the accessible timescales into the nanosecond range. We describe the design of the new source and discuss experiments characterizing its performance. Spin-echo measurements of benzene/Cu(100) illustrate its merit in the study of a typical slow-moving molecular adsorbate species. PMID:23464267

Lechner, B A J; Hedgeland, H; Allison, W; Ellis, J; Jardine, A P

2013-02-01

426

Towards atomic resolution in sodium titanate nanotubes using near-edge X-ray-absorption fine-structure spectromicroscopy combined with multichannel multiple-scattering calculations  

PubMed Central

Summary Recent advances in near-edge X-ray-absorption fine-structure spectroscopy coupled with transmission X-ray microscopy (NEXAFS–TXM) allow large-area mapping investigations of individual nano-objects with spectral resolution up to E/?E = 104 and spatial resolution approaching 10 nm. While the state-of-the-art spatial resolution of X-ray microscopy is limited by nanostructuring process constrains of the objective zone plate, we show here that it is possible to overcome this through close coupling with high-level theoretical modelling. Taking the example of isolated bundles of hydrothermally prepared sodium titanate nanotubes ((Na,H)TiNTs) we are able to unravel the complex nanoscale structure from the NEXAFS–TXM data using multichannel multiple-scattering calculations, to the extent of being able to associate specific spectral features in the O K-edge and Ti L-edge with oxygen atoms in distinct sites within the lattice. These can even be distinguished from the contribution of different hydroxyl groups to the electronic structure of the (Na,H)TiNTs. PMID:23213642

Kruger, Peter; Lagos, Maureen J; Ke, Xiaoxing; Van Tendeloo, Gustaaf; Ewels, Chris; Umek, Polona; Guttmann, Peter

2012-01-01

427

Atomistic simulation of helium-defect interaction in alpha-iron  

NASA Astrophysics Data System (ADS)

Molecular dynamics (MD) methods are utilized to study the formation of vacancy clusters created by displacement cascades in ?-Fe containing different concentrations of substitutional He atoms. Primary knock-on atom energies, Ep, from 500eV to 20keV are considered at a temperature of 100K, and the results are compared with those performed in pure ?-Fe. There are distinct differences in the number and size of vacancy clusters within displacement cascades with and without substitutional helium atoms. It is found that many large vacancy clusters can be formed within cascade cores in ?-Fe with helium atoms, in contrast to a few small vacancy clusters observed in pure ?-Fe. The number and size of helium/vacancy clusters generally increase with increasing helium concentration and PKA energy. One of the striking results is that the number of self-interstitial atoms (SIAs) and the size of interstitial clusters are much smaller than those in pure ?-Fe.

Yang, L.; Zu, X. T.; Xiao, H. Y.; Gao, F.; Heinisch, H. L.; Kurtz, R. J.; Liu, K. Z.

2006-02-01

428

Cryogenic and Simulated Fuel Jet Breakup in Argon, Helium and Nitrogen Gas Flows  

NASA Technical Reports Server (NTRS)

Two-phase flow atomization of liquid nitrogen jets was experimentally investigated. They were co-axially injected into high-velocity gas flows of helium, nitrogen and argon, respectively, and atomized internally inside a two-fluid fuel nozzle. Cryogenic sprays with relatively high specific surface areas were produced, i.e., ratios of surface area to volume were fairly high. This was indicated by values of reciprocal Sauter mean diameters, RSMD's, as measured with a scattered- light scanning instrument developed at NASA Lewis Research Center. Correlating expressions were derived for the three atomizing gases over a gas temperature range of 111 to 422 K. Also, the correlation was extended to include waterjet breakup data that had been previously obtained in simulating fuel jet breakup in sonic velocity gas flow. The final correlating expression included a new dimensionless molecular-scale acceleration group. It was needed to correlate RSMD data, for LN2 and H2O sprays, with the fluid properties of the liquid jets and atomizing gases used in this investigation.

Ingebo, Robert D.

1995-01-01

429

$?^4$ Ry corrections to singlet states of helium  

E-print Network

Corrections of order $\\alpha^4$Ry are calculated for the singlet states $1^1S_0$ and $2^1S_0$ of the helium atom. The result for $1^1S_0$ state is in slight disagreement with that of Korobov and Yelkhovsky in [Phys. Rev. Lett. {\\bf 87}, 193003 (2001)]. The results obtained lead to a significant improvement of transition frequencies between low lying levels of the helium atom. In particular theoretical predictions for the $2^1S_0 - 1^1S_0$ transition are found to be in disagreement with experimental values.

Krzysztof Pachucki

2006-07-07

430

Helium dilution refrigeration  

E-print Network

. The refrigerator was then leak tested on a Veeco NS-9 Helium Leak Detector. A small leak was found at the capillary joint between the still and mixing cham'oer and repaired. No other leaks were detectable on the most sensitive scale of the detector. 6.... The refrigerator was then leak tested on a Veeco NS-9 Helium Leak Detector. A small leak was found at the capillary joint between the still and mixing cham'oer and repaired. No other leaks were detectable on the most sensitive scale of the detector. 6...

McKee, Thomas Raymond

2012-06-07

431

Elements & Compounds Atoms (Elements)  

E-print Network

;Nucleus Electrons Cloud of negative charge (2 electrons) Fig. 2.5: Simplified model of a Helium (He) Atom (with ball-and-stick model superimposed) Unbonded Electron pair Water (H2O) Methane (CH4) (b) Molecular Electron distribution diagram Fig. 2.9: Electrons are distributed in shells of orbitals. Each orbital

Frey, Terry

432

Cavitation pressure in liquid helium  

Microsoft Academic Search

Recent experiments have suggested that, at low enough temperature, the homogeneous nucleation of bubbles occurs in liquid helium near the calculated spinodal limit. This was done in pure superfluid helium 4 and in pure normal liquid helium 3. However, in such experiments, where the negative pressure is produced by focusing an acoustic wave in the bulk liquid, the local amplitude

Frederic Caupin; Sebastien Balibar

2001-01-01

433

Mining for Helium Jurriaan Hage  

E-print Network

Mining for Helium Jurriaan Hage Peter van Keeken Department of Information and Computing Sciences-year functional programming course using the Helium compiler. The mining of such a collection is not trivial a type error. 1 #12;1 Introduction and motivation When the Helium compiler for learning Haskell

Utrecht, Universiteit

434

Communication: Barium ions and helium nanodroplets: Solvation and desolvation  

NASA Astrophysics Data System (ADS)

The solvation of Ba+ ions created by the photoionization of barium atoms located on the surface of helium nanodroplets has been investigated. The excitation spectra corresponding to the 6p 2P1/2 ? 6s 2S1/2 and 6p 2P3/2 ? 6s 2S1/2 transitions of Ba+ are found to be identical to those recorded in bulk He II [H. J. Reyher, H. Bauer, C. Huber, R. Mayer, A. Schafer, and A. Winnacker, Phys. Lett. A 115, 238 (1986)], indicating that the ions formed at the surface of the helium droplets become fully solvated by the helium. Time-of-flight mass spectra suggest that following the excitation of the solvated Ba+ ions, these are being ejected from the helium droplets either as bare Ba+ ions or as small Ba+Hen (n < 20) complexes.

Zhang, Xiaohang; Drabbels, Marcel

2012-08-01

435

Photodissociation of alkyl iodides in helium nanodroplets. II. Solvation dynamics.  

PubMed

The solvation dynamics of nonthermal species in liquid helium has been investigated by photolyzing alkyl iodide molecules, CH3I, C2H5I, and CF3I, embedded in helium nanodroplets. Iodine and CH3 fragments are found to leave the droplets solvated by a finite number of helium atoms, this in contrast to C2H5 and CF3 fragments. The speed distributions of the IHeN and CH3HeN complexes show a prominent correlation with the degree of solvation N. It is argued that this correlation is caused by a dynamical adjustment of the solvation structure size to the relative speed of the traveling fragments as they pass through the helium bath. The absence of C2H5HeN and CF3HeN complexes is attributed to the large internal energy of these alkyl fragments which leads to a rapid destruction of any possibly formed complexes. PMID:17887834

Braun, Andreas; Drabbels, Marcel

2007-09-21

436

Photodissociation of alkyl iodides in helium nanodroplets. II. Solvation dynamics  

NASA Astrophysics Data System (ADS)

The solvation dynamics of nonthermal species in liquid helium has been investigated by photolyzing alkyl iodide molecules, CH3I, C2H5I, and CF3I, embedded in helium nanodroplets. Iodine and CH3 fragments are found to leave the droplets solvated by a finite number of helium atoms, this in contrast to C2H5 and CF3 fragments. The speed distributions of the IHeN and CH3HeN complexes show a prominent correlation with the degree of solvation N. It is argued that this correlation is caused by a dynamical adjustment of the solvation structure size to the relative speed of the traveling fragments as they pass through the helium bath. The absence of C2H5HeN and CF3HeN complexes is attributed to the large internal energy of these alkyl fragments which leads to a rapid destruction of any possibly formed complexes.

Braun, Andreas; Drabbels, Marcel

2007-09-01

437

Helium liquefaction plant  

Microsoft Academic Search

In a helium liquefaction plant, a compressor includes first, second and third stages and a precooling section includes first, second and third turboexpanders in series between high and low pressure lines of a heat exchanger. A portion of the medium pressure gas at the output of the second turboexpander is directed back through the heat exchanger and mixed with the

Toscano

1981-01-01

438

Retention of implanted hydrogen and helium in martensitic stainless steels and their effects on mechanical properties  

Microsoft Academic Search

Martensitic stainless steels are candidate materials for the target structure of the European Spallation Source (ESS). Hydrogen and helium produced by nuclear transmutation in the proton beam and in the energetic neutron field cause changes of material properties in addition to those caused by atomic displacement. The present work presents results of diffusion and retention of hydrogen and helium, derived

P. Jung; C. Liu; J. Chen

2001-01-01

439

Non-ending helium story  

SciTech Connect

Why an adequate supply of helium is of importance to cryoengineering is obvious to everyone present at this conference. Why there is a non-ending helium problem - or more specifically why helium supply problems have arisen in the past, why they may arise again in the future, what are those problems and what solutions appear to exist - is more complicated. To answer these questions this paper is divided into three sections: resource availability, the demand for helium and the supply of helium. 17 refs.

Hammel, E.F.; Krupka, M.C.; Williamson, K.D. Jr.

1986-01-01

440

Development of a polarized Helium-3 ion source for RHIC using the electron beam ion source  

E-print Network

This thesis presents my work on the design and development of a source of polarized Helium-3 ions for the Relativistic Heavy Ion Collider at Brookhaven National Lab, Upton, NY. The 3He atoms will be polarized using the ...