Manson, Joseph R.
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.
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
Laser-assisted inelastic scattering of electrons by helium atoms
NASA Astrophysics Data System (ADS)
Agueny, H.; Makhoute, A.; Dubois, A.; Ajana, I.; Rahali, G.
2015-07-01
The differential cross section for electron-impact excitation of helium atoms in the presence of a linearly polarized laser field is calculated. The interaction of the laser field with both the projectile electron and the target atom is treated in a fully nonperturbative way, while the electron-atom interaction is treated within the first Born approximation. We are interested in studying two cases where the photon energy of the laser field is chosen to be far from resonance and when it matches with 2 1S ?2 1P and 3 1S ?3 1P transition frequencies. The agreement between perturbative and nonperturbative results is good, except close to the resonance where the perturbative cross sections diverge while the nonperturbative ones predict no maximum of the cross sections. Another interesting effect is the presence of an avoided crossing of the Floquet pseudoenergies at resonance.
Graphene on Ni(111): Electronic Corrugation and Dynamics from Helium Atom Scattering
2015-01-01
Using helium atom scattering, we have studied the structure and dynamics of a graphene layer prepared in situ on a Ni(111) surface. Graphene/Ni(111) exhibits a helium reflectivity of ?20% for a thermal helium atom beam and a particularly small surface electron density corrugation ((0.06 ± 0.02) Å peak to peak height). The Debye–Waller attenuation of the elastic diffraction peaks of graphene/Ni(111) and Ni(111) was measured at surface temperatures between 150 and 740 K. A surface Debye temperature of ?D = (784 ± 14) K is determined for the graphene/Ni(111) system and ?D = (388 ± 7) K for Ni(111), suggesting that the interlayer interaction between graphene and the Ni substrate is intermediary between those for strongly interacting systems like graphene/Ru(0001) and weakly interacting systems like graphene/Pt(111). In addition we present measurements of low frequency surface phonon modes on graphene/Ni(111) where the phonon modes of the Ni(111) substrate can be clearly observed. The similarity of these findings with the graphene/Ru(0001) system indicates that the bonding of graphene to a metal substrate alters the dynamic properties of the graphene surface strongly and is responsible for the high helium reflectivity of these systems. PMID:26617683
NASA Astrophysics Data System (ADS)
Chern, G.; Skofronick, J. G.; Brug, W. P.; Safron, S. A.
1989-06-01
A helium-atom surface-scattering instrument, employing a time-of-flight technique to observe inelastically scattered He atoms, has been used to measure the surface-phonon dispersion curves of the KBr(001) surface. Data were collected in the two high-symmetry directions, <100> and <110>, over the entire Brillouin zone for a target temperature of ~115 K and incident He wave vector ki~=7 Å-1. The results show important differences from some theoretical predictions of shell-model calculations that use parameters obtained by fitting bulk dispersion curves. In addition, the measured surface dispersion curves of KBr and of RbCl (reported previously) deviate from ``mirror-symmetry'' behavior, unlike their bulk dispersion curves.
NASA Astrophysics Data System (ADS)
Hansen, F. Y.; Bruch, L. W.; Dammann, B.
2013-03-01
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.
Positronium formation in the n = 2 level in positron scattering from hydrogen and helium atoms
Khan, P.; Mazumdar, P.S.; Ghosh, A.S.
1985-03-01
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)).
Helium Atom Scattering from Graphene Grown on Rh(111) K.D. Gibson and S. J. Sibener*
Sibener, Steven
Helium Atom Scattering from Graphene Grown on Rh(111) K.D. Gibson and S. J. Sibener* The James superlattice that appears as a series of hills and valleys in scanning tunneling microscopy. On Rh(111 aligned with the Rh(111) surface lattice vectors, but the Rh and graphene lattice constants
Hansen, F. Y.; Bruch, L. W.; Dammann, B.
2013-03-14
Diffraction and one-phonon inelastic scattering of a thermal energy helium atomic beam are evaluated in the situation that the target monolayer lattice is so dilated that the atomic beam penetrates to the interlayer region between the monolayer and the substrate. The scattering is simulated by propagating a wavepacket and including the effect of a feedback of the inelastic wave onto the diffracted wave, which represents a coherent re-absorption of the created phonons. Parameters are chosen to be representative of an observed p(1 Multiplication-Sign 1) commensurate monolayer solid of H{sub 2}/NaCl(001) and a conjectured p(1 Multiplication-Sign 1) commensurate monolayer solid of H{sub 2}/KCl(001). For the latter, there are cases where part of the incident beam is trapped in the interlayer region for times exceeding 50 ps, depending on the spacing between the monolayer and the substrate and on the angle of incidence. The feedback effect is large for cases of strong transient trapping.
Hansen, F Y; Bruch, L W; Dammann, B
2013-03-14
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. PMID:23514511
Helium-atom-scattering measurements of surface-phonon dispersion curves of the C(111)-H(1×1) surface
NASA Astrophysics Data System (ADS)
Lange, Gerrit; Toennies, J. Peter
1996-04-01
The surface-phonon dispersion curves of the hydrogen-terminated diamond (111)-(1×1) surface have been measured by inelastic helium-atom scattering. By using a very high incident-beam energy of 80.5 meV, the Rayleigh-wave dispersion curve could be observed throughout the entire Brillouin zone. The measured zone-boundary energies at the K¯ point are 64.4 and 70.6 meV, respectively. The data lie about 5% above the Rayleigh-wave dispersion curve obtained from semiempirical total-energy calculations.
NASA Astrophysics Data System (ADS)
Bunjes, N.; Luo, N. S.; Ruggerone, P.; Toennies, J. P.; Witte, G.
1994-09-01
An intense longitudinal-surface-phonon resonance in addition to the Rayleigh mode is observed on Ag(001) by inelastic helium-atom scattering (HAS). This mode, which is only barely visible by electron-energy-loss spectroscopy, is similar to the one previously detected by HAS for Cu(001). This observation provides additional evidence for the pseudocharge model previously invoked to explain the anomalous longitudinal resonance observed in several metal surfaces by HAS. The observed differences between Cu(001) and Ag(001) are also shown to be consistent with the pseudocharge model.
Approximating the Helium Wavefunction in Positronium-Helium Scattering
NASA Technical Reports Server (NTRS)
DiRienzi, Joseph; Drachman, Richard J.
2003-01-01
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.
Safron, S.A.; Skofronick, J.G.
1997-07-01
Over the twelve years of this grant from the U.S. Department of Energy, DE-FG05-85ER45208, the over-reaching aims of this work have been to explore and to attempt to understand the fundamental physics and chemistry of surfaces and interfaces. The instrument we have employed m in this work is high-resolution helium atom scattering (HAS) which we have become even more convinced is an exceptionally powerful and useful tool for surface science. One can follow the evolution of the development and progress of the experiments that we have carried out by the evolution of the proposal titles for each of the four three-year periods. At first, m in 1985-1988, the main objective of this grant was to construct the HAS instrument so that we could begin work on the surface vibrational dynamics of crystalline materials; the title was {open_quotes}Helium Atom-Surface Scattering Apparatus for Studies of Crystalline Surface Dynamics{close_quotes}. Then, as we became more interested m in the growth of films and interfaces the title m in 1988-1991 became {open_quotes}Helium Atom Surface Spectroscopy: Surface Lattice Dynamics of Insulators, Metal and Metal Overlayers{close_quotes}. In 1991-1994, we headed even more m in this direction, and also recognized that we should focus more on insulator materials as very few techniques other than helium atom scattering could be applied to insulators without causing surface damage. Thus, the proposal title became {open_quotes}Helium Atom-Surface Scattering: Surface Dynamics of Insulators, Overlayers and Crystal Growth{close_quotes}. M in the final period of this grant the title ended up {open_quotes}Investigations of the Dynamics and Growth of Insulator Films by High Resolution Helium Atom Scattering{close_quotes} m in 1994-1997. The list of accomplishments briefly discussed in this report are: tests of the shell model; multiphoton scattering; physisorbed monolayer films; other surface phase transitions; and surface magnetic effects.
Helium atom scattering study of the interaction of water with the BaF2(111) surface
NASA Astrophysics Data System (ADS)
Vogt, Jochen
2007-06-01
The interaction of water with the BaF2(111) single crystal surface is investigated using the helium atom scattering technique. It is found that H2O forms a long-range ordered two-dimensional (2D) phase with (1×1) translational symmetry already after an exposure of 3L (1L =10-6Torrs) at temperatures below 150K. The activation energy for desorption of the saturated 2D phase, which is assigned to a bilayer, is estimated to be 46±2kJmol-1, corresponding to a desorption temperature of 165K. The desorption of multilayers was observed at 150K, consistent with a binding energy of 42±2kJmol-1. Before completion and after desorption of the saturated 2D phase, a superstructure consistent with a disordered (?3 ×?3 )R30° lattice has been observed, which is attributed to the first layer of water with a coverage of one molecule per surface unit cell, in accordance with recent theoretical studies. Desorption of this phase is observed at temperatures above 200K, consistent with an unexpectedly strong bonding of the molecules to the substrate.
NASA Astrophysics Data System (ADS)
Farzaneh, Maryam
This thesis presents the results of elastic and inelastic helium-atom scattering (HAS) measurements from the insulating Sr2CuO2 Cl2(001) surface. Elastic HAS provided diffraction patterns which contain information about the surface periodicity and the topology of the surface charge density. Inelastic HAS, implemented via time-of-flight techniques, determined the corresponding surface phonon dispersion curves and was used to characterize surface vibrational modes. Elastic HAS revealed a surface periodicity consistent with the bulk termination, which suggests that the surface is non-polar and stable. This seems to favor one of the two surface candidates that may be exposed by the process of in-situ surface cleaving, namely SrCl and not CuO2. In order to interpret the experimental phonon dispersion data, lattice dynamical calculations based on the shell model were carried out for the bulk and the two surface terminations of SrCl and CuO2. From the bulk calculations, appropriate model parameters were derived that were subsequently extended to a surface dynamical model via a slab method. Comparison between the experimental data and theoretical results for two different slabs with SrCl and CuO2 terminations showed that the experimental data conform exclusively with the SrCl surface modes. Finally I report on a theoretical investigation of the anomalous magnetic properties of the CoO(001) surface. Recent experimental studies of the temperature-dependent antiferromagnetic ordering of the CoO(001) surface, using metastable He-atom scattering, revealed an anomalous enhancement in the sublattice magnetization with increasing temperature that straddles the bulk Neel temperature ( TbN ) of 290 K. I developed a Bogolyubov variational mean-field model based on a model Hamiltonian for the CoO(001) system by taking exchange, crystal field and magnetoelastic interactions into account. This model revealed that the enhancement in magnetization is closely related to the low-lying spin excited states on the CoO surface, and reproduced the observed anomalies.
Positronium and Electron Scattering on Helium
NASA Technical Reports Server (NTRS)
DiRienzi, Joseph
2011-01-01
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
2015-01-01
Elastic and inelastic close-coupling (CC) calculations have been used to extract information about the corrugation amplitude and the surface vibrational atomic displacement by fitting to several experimental diffraction patterns. To model the three-dimensional interaction between the He atom and the Bi(111) surface under investigation, a corrugated Morse potential has been assumed. Two different types of calculations are used to obtain theoretical diffraction intensities at three surface temperatures along the two symmetry directions. Type one consists of solving the elastic CC (eCC) and attenuating the corresponding diffraction intensities by a global Debye–Waller (DW) factor. The second one, within a unitary theory, is derived from merely solving the inelastic CC (iCC) equations, where no DW factor is necessary to include. While both methods arrive at similar predictions for the peak-to-peak corrugation value, the variance of the value obtained by the iCC method is much better. Furthermore, the more extensive calculation is better suited to model the temperature induced signal asymmetries and renders the inclusion for a second Debye temperature for the diffraction peaks futile. PMID:26257838
Atom lithography with metastable helium
Allred, Claire S.; Reeves, Jason; Corder, Christopher; Metcalf, Harold
2010-02-15
A bright metastable helium (He*) beam is collimated sequentially with the bichromatic force and three optical molasses velocity compression stages. Each He* atom in the beam has 20 eV of internal energy that can destroy a molecular resist assembled on a gold coated silicon wafer. Patterns in the resist are imprinted onto the gold layer with a standard selective etch. Patterning of the wafer with the He{sup *} was demonstrated with two methods. First, a mesh was used to protect parts of the wafer making an array of grid lines. Second, a standing wave of {lambda}=1083 nm light was used to channel and focus the He* atoms into lines separated by {lambda}/2. The patterns were measured with an atomic force microscope establishing an edge resolution of 80 nm. Our results are reliable and repeatable.
Capture of slow antiprotons by helium atoms
Shevchenko, N.V.; Revai, J.
2005-10-26
A consistent quantum mechanical calculation of partial cross sections leading to different final states of antiprotonic helium atom was performed. Calculations were carried out for a wide range of antiprotonic helium states and incident energies of the antiproton below the first ionization threshold of the He atom.
NASA Astrophysics Data System (ADS)
Chern, Gung
The alkali halide surfaces were the first for which full surface phonon dispersion curves were measured. Most of the early work was mainly concerned with the low-energy modes for the lighter alkali halides, such as LiF and NaF, and a full survey of a more representative sampling of these crystals was never made. A recent theoretical calculation has also suggested that relaxation effects might provide interesting features on the surface phonon modes especially for the optical modes of the heavier compounds. The work of this dissertation is an effort to measure the surface dynamics of other, usually heavier, alkali halide crystals. This work describes measurements on the surfaces of RbCl(001), RbBr(001), KBr(001), and NaI(001) with the inelastic He atom scattering technique. The energy gain or loss and the momentum change is measured by the time of flight method. For the four crystals, the surface phonon dispersion curves are obtained along both high symmetry directions. The general agreement between the theory and the experimental results is very good. Some new features of the surface vibration have been found. First, the optical mode, crossing resonance and acoustic modes were clearly seen from the KBr surface over the entire zone. The strong interaction coupling between the He and the optical mode is rather unique. Secondly, crossing resonances (S_8 mode) were observed for the KBr, RbBr and NaI surfaces. This observation suggests that this mode is a general feature of all the alkali halide surfaces. The origin of this mode might be due to the perpendicular polarized bulk acoustic motion. Thirdly, NaI results show that bound-state resonance effects could strongly enhance the bulk mode especially when there is a high density of phonon states. Finally, there is no experimental evidence supporting any surface relaxation effects. In fact, the experimental results seem to agree better with the unrelaxed calculations. In addition to the inelastic scattering measurements, we also did angular distribution, low pressure He beam scattering and a temperature-dependent dynamical study. Information such as the surface corrugation, He-surface potential, bound state energies, the surface Debye-Waller temperature and a measure of multi-phonon contributions can be obtained from these experimental results.
Positronium formation in positron-helium scattering
Khan, P.; Ghosh, A.S.
1983-10-01
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.
Flaherty, F. A.; Trelenberg, T. W.; Li, J. A.; Fatema, R.; Skofronick, J. G.; Van Winkle, D. H.; Safron, S. A.; Boatner, L. A.
2015-07-13
The structure and dynamics of cleaved (001) surfaces of potassium tantalates doped with niobium, KTa1-xNbxO? (KTN), with x ranging from 0% to 30%, were measured by helium atom scattering (HAS). Through HAS time-of-flight (TOF) experiments, a dispersionless branch (Einstein phonon branch) with energy of 13-14 meV was observed across the surface Brillouin zone in all samples. When this observation is combined with the results from earlier experimental and theoretical studies on these materials, a consistent picture of the stable surface structure emerges: After cleaving the single-crystal sample, the surface should be composed of equal areas of KO and TaO?/NbO? terraces.more »The data, however, suggest that K? and O²? ions migrate from the bulk to the surface, forming a charged KO lattice that is neutralized primarily by additional K? ions bridging pairs of surface oxygens. This structural and dynamic modification at the (001) surface of KTN appears due to its formally charged KO(-1) and TaO?/NbO?(+1) layers and avoids a “polar catastrophe.” This behavior is contrasted with the (001) surface behavior of the fluoride perovskite KMnF? with its electrically neutral KF and MnF? layers.« less
Flaherty, F. A.; Trelenberg, T. W.; Li, J. A.; Fatema, R.; Skofronick, J. G.; Van Winkle, D. H.; Safron, S. A.; Boatner, L. A.
2015-07-13
The structure and dynamics of cleaved (001) surfaces of potassium tantalates doped with niobium, KTa_{1-x}Nb_{x}O? (KTN), with x ranging from 0% to 30%, were measured by helium atom scattering (HAS). Through HAS time-of-flight (TOF) experiments, a dispersionless branch (Einstein phonon branch) with energy of 13-14 meV was observed across the surface Brillouin zone in all samples. When this observation is combined with the results from earlier experimental and theoretical studies on these materials, a consistent picture of the stable surface structure emerges: After cleaving the single-crystal sample, the surface should be composed of equal areas of KO and TaO?/NbO? terraces. The data, however, suggest that K? and O²? ions migrate from the bulk to the surface, forming a charged KO lattice that is neutralized primarily by additional K? ions bridging pairs of surface oxygens. This structural and dynamic modification at the (001) surface of KTN appears due to its formally charged KO(-1) and TaO?/NbO?(+1) layers and avoids a “polar catastrophe.” This behavior is contrasted with the (001) surface behavior of the fluoride perovskite KMnF? with its electrically neutral KF and MnF? layers.
Electron scattering in helium for Monte Carlo simulations
Khrabrov, Alexander V.; Kaganovich, Igor D.
2012-09-15
An analytical approximation for differential cross-section of electron scattering on helium atoms is introduced. It is intended for Monte Carlo simulations, which, instead of angular distributions based on experimental data (or on first-principle calculations), usually rely on approximations that are accurate yet numerically efficient. The approximation is based on the screened-Coulomb differential cross-section with energy-dependent screening. For helium, a two-pole approximation of the screening parameter is found to be highly accurate over a wide range of energies.
NASA Astrophysics Data System (ADS)
Kraus, Patrick; Mayrhofer-Reinhartshuber, Michael; Gösweiner, Christian; Apolloner, Florian; Miret-Artés, Salvador; Ernst, Wolfgang E.
2014-12-01
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.
Spectral properties of endohedrally confined helium atom
NASA Astrophysics Data System (ADS)
Fang, Shuai-Shuai; Hao-Xue, Qiao
2015-08-01
Based on the B-spline basis method, the properties of the helium atom confined inside an endohedral environment, such as buckminster fullerene, are studied. In our calculations, the endohedral environment is a parabolic potential well. In this situation, the phenomenon of “mirror collapse” is exhibited for energy levels of a confined helium atom. The “giant resonance” of oscillator strength of the dipole transition emerges with the variation of depth of the confining well. The physical mechanisms of these phenomena are analyzed in this paper. Project supported by the National Natural Science Foundation of China (Grant No. 11274246.)
Depolarized collision-induced light scattering by gaseous helium
NASA Astrophysics Data System (ADS)
Guillot-Noël, Christophe; Chrysos, Michael; LeDuff, Yves; Rachet, Florent
2000-02-01
We have carried out a joint study, experimental and theoretical, of the binary depolarized collision-induced light scattering spectrum by gaseous helium at room temperature. The intensities from helium pairs, calibrated on an absolute scale, have been measured in the much extended, previously unexplored, 5-680 cm-1 spectral domain. A critical analysis of the spectrum has been made by using ab initio anisotropy models available in the literature. Quantum-mechanical computations have enabled us to determine the spectral response of the pair polarizability terms which compose the most up-to-date anisotropy data (Moszynski et al 1996 J. Chem. Phys. 104 6997). The conclusion has been drawn that internuclear distances shorter than the helium atomic diameter are probed via the very far wing of our spectrum.
Commuting operators for the helium atom
NASA Astrophysics Data System (ADS)
Gottdiener, Luis
2015-11-01
We show that for the helium atom with electrostatic repulsion between electrons, the operators for the z component and the square of the total angular momentum commute with the Hamiltonian, and therefore quantum numbers M and L can be used to label the energy eigenstates. This fact is used but not proved in most quantum mechanics textbooks.
Classical Helium Atom with Radiation Reaction G. Camelio,1
Carati, Andrea
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
Helium-helium scattering in vacuum and in liquid helium-3
NASA Astrophysics Data System (ADS)
Hjort, Hans Henrik
1999-08-01
The diffusion coefficient D and the thermal diffusion ratio kT for dilute 4He in liquid 3He at low T are calculated from Fermi liquid theory. The temperature dependence of DT and kT/c is linear and related to the coefficients in the expansion of the scattering amplitude a34 in scalar combinations of the quasiparticle momenta. At T = 0, kT/c is smaller by a few percent than in previous calculations; previously the effect of 1T on the 3He distribution function was neglected. By measuring the ratio of two capacitors, the thickness of a 4He superfluid film under liquid 3He can be measured accurately. I have calculated the relation between the capacitance ratio and the thickness and 4He content of the film. The calculation, which includes the effects of pressure and concentration gradients caused by the van der Waals potential, was used to interpret the recent solubility and diffusion data of He et al. I have also developed a program to deduce D, the diffusion coefficient for 4He in liquid 3He, from the time-dependent measurements of He et al. An alternating Crank-Nicholson algorithm was used to solve the diffusion equation in cylindrical coordinates. The boundary condition depends on the thickness of the superfluid 4He film, which changes as 4He dissolves in or out of the liquid over the course of an experiment. The solution was used to fit D and several other parameters to the data using the Levenberg-Marquardt method. A scaling method for calculating the multiple scattering between and within beams of helium atoms is presented. The number of atoms N in the beams is reduced by a large factor ? while the collision cross-section ? is increased by ? so that the trajectories of all the scaled atoms can be calculated numerically. As an example of the method, I show that a low temperature atomic beam experiment to measure ? for 4He- 4He at low energies, is quite practicable; by using low intensity beams, the cross-section can be measured as a function of the relative velocity vr.
Sibener, Steven
Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH3Si 111 surfaces were measured using helium atom scattering. The elastic diffraction patterns exhibited is consistent with the interaction between the helium atoms and SiCH3 bending modes. These experiments have
Polarizability of the pionic helium atom
NASA Astrophysics Data System (ADS)
Korobov, V. I.; Bekbaev, A. K.; Aznabayev, D. T.; Zhaugasheva, S. A.
2015-12-01
The static dipole polarizability of metastable states in pionic helium atoms is studied. We use the complex coordinate rotation method to properly take account of the resonant nature of the states. Our calculation shows that the (17, 14) states both in 3He and 4He are not stable due to strong collisional quenching. This explains the absence of signal in the PiHe experiment at the Paul Scherer Institute, Switzerland while studying the (16, 15) \\to (17, 14) transition.
Helium in confinement: the filling A Neutron Scattering investigation.
Glyde, Henry R.
Helium in confinement: the filling parameter. A Neutron Scattering investigation. Francesco Albergamo Institut Laue-Langevin, France Helium in confinement: the filling parameter. Â p.1/13 #12;outline introduction and motivation Helium in confinement: the filling parameter. Â p.2/13 #12;outline introduction
Searching for dark matter with helium atom
Imre Ferenc Barna
2006-08-10
With the help of the boost operator we can model the interaction between a weakly interacting particle(WIMP) of dark matter(DAMA) and an atomic nuclei. Via this "kick" we calculate the total electronic excitation cross section of the helium atom. The bound spectrum of He is calculated through a diagonalization process with a configuration interaction (CI) wavefunction built up from Slater orbitals. All together 19 singly- and doubly-excited atomic sates were taken with total angular momenta of L=0,1 and 2. Our calculation may give a rude estimation about the magnitude of the total excitation cross section which could be measured in later scintillator experiments. The upper limit of the excitation cross section is $9.7\\cdot 10^{-8}$ barn.
Metastable Aluminum Atoms Floating on the Surface of Helium Nanodroplets.
Jeffs, Jay; Besley, Nicholas A; Stace, Anthony J; Sarma, Gautam; Cunningham, Ethan M; Boatwright, Adrian; Yang, Shengfu; Ellis, Andrew M
2015-06-12
Metal atoms have proved to be sensitive probes of the properties of superfluid helium nanodroplets. To date, all experiments on the doping of helium droplets have concentrated on the attachment of metal atoms in their ground electronic states. Here we report the first examples of metal atoms in excited states becoming attached to helium nanodroplets. The atoms in question are aluminum, and they have been generated by laser ablation in a metastable quartet state, which attaches to and remains on the surface of helium droplets. Evidence for a surface location comes from electronic spectra, which consist of very narrow absorption profiles that show very small spectral shifts. Supporting ab initio calculations show there to be an energy incentive for a metastable Al atom to remain on the surface of a helium droplet rather than move to the interior. The results suggest that helium droplets may provide a method for the capture and transport of metastable excited atomic and molecular species. PMID:26196800
NASA Technical Reports Server (NTRS)
Sharma, P. K.; Knuth, E. L.
1977-01-01
Spatial and energy distributions of helium atoms scattered from an anodized 1235-0 aluminum surface as well as the tangential and normal momentum accommodation coefficients calculated from these distributions are reported. A procedure for calculating drag coefficients from measured values of spatial and energy distributions is given. The drag coefficient calculated for a 6061 T-6 aluminum sphere is included.
Harmonic oscillator model for the helium atom
Carlsen, Martin
2015-01-01
A harmonic oscillator model in four dimensions is presented for the helium atom to estimate the distance to the inner and outer electron from the nucleus, the angle between electrons and the energy levels. The method is algebraic and is not based on the choice of correct trial wave function. Three harmonic oscillators and thus three quantum numbers are sufficient to describe the two-electron system. We derive a simple formula for the energy in the general case and in the special case of the Wannier Ridge. For a set of quantum numbers the distance to the electrons and the angle between the electrons are uniquely determined as the intersection between three surfaces. We show that the excited states converge either towards ionization thresholds or towards extreme parallel or antiparallel states and provide an estimate of the ground state energy.
Classical Helium Atom with Radiation Reaction
G. Camelio; A. Carati; L. Galgani
2011-11-24
We study a classical model of Helium atom in which, in addition to the Coulomb forces, the radiation reaction forces are taken into account. This modification brings in the model a new qualitative feature of a global character. Indeed, as pointed out by Dirac, in any model of classical electrodynamics of point particles involving radiation reaction one has to eliminate, from the a priori conceivable solutions of the problem, those corresponding to the emission of an infinite amount of energy. We show that the Dirac prescription solves a problem of inconsistency plaguing all available models which neglect radiation reaction, namely, the fact that in all such models most initial data lead to a spontaneous breakdown of the atom. A further modification is that the system thus acquires a peculiar form of dissipation. In particular, this makes attractive an invariant manifold of special physical interest, the zero--dipole manifold, that corresponds to motions in which no energy is radiated away (in the dipole approximation). We finally study numerically the invariant measure naturally induced by the time--evolution on such a manifold, and this corresponds to studying the formation process of the atom. Indications are given that such a measure may be singular with respect to that of Lebesgue.
Helium nanobubble release from Pd surface: An atomic simulation
Wang, Liang; Hu, Wangyu; Deng, Huiqiu; Xiao, Shifang; Yang, Jianyu; Gao, Fei; Heinisch, Howard L.; Hu, Shilin
2011-02-14
Molecular dynamic simulations of helium atoms escaping from a helium-filled nano-bubble near the surface of crystalline palladium reveal unexpected behavior. Significant deformation and cracking near the helium bubble occur initially, and then a channel forms between the bubble and the surface, providing a pathway for helium atoms to propagate towards the surface. The helium atoms erupt from the bubble in an instantaneous and volcano-like process, which leads to surface deformation consisting of cavity formation on the surface, along with modification and atomic rearrangement at the periphery of the cavity. The present simulation results show that, near the palladium surface, there is a helium-bubble-free zone, or denuded zone, with a typical thickness of about 3.0 nm. Combined with experimental measurements and continuum-scale evolutionary model predictions, the present atomic simulations demonstrate that the thickness of the denuded zone, which contains a low concentration of helium atoms, is somewhat larger than the diameter of the helium bubbles in the metal tritide. Furthermore, a relationship between the tensile strength and thickness of metal film is also determined.
ENERGY RELAXATION OF HELIUM ATOMS IN ASTROPHYSICAL GASES
Lewkow, N. R.; Kharchenko, V.; Zhang, P.
2012-09-01
We report accurate parameters describing energy relaxation of He atoms in atomic gases, important for astrophysics and atmospheric science. Collisional energy exchange between helium atoms and atomic constituents of the interstellar gas, heliosphere, and upper planetary atmosphere has been investigated. Energy transfer rates, number of collisions required for thermalization, energy distributions of recoil atoms, and other major parameters of energy relaxation for fast He atoms in thermal H, He, and O gases have been computed in a broad interval of energies from 10 meV to 10 keV. This energy interval is important for astrophysical applications involving the energy deposition of energetic atoms and ions into atmospheres of planets and exoplanets, atmospheric evolution, and analysis of non-equilibrium processes in the interstellar gas and heliosphere. Angular- and energy-dependent cross sections, required for an accurate description of the momentum-energy transfer, are obtained using ab initio interaction potentials and quantum mechanical calculations for scattering processes. Calculation methods used include partial wave analysis for collisional energies below 2 keV and the eikonal approximation at energies higher than 100 eV, keeping a significant energy region of overlap, 0.1-2 keV, between these two methods for their mutual verification. The partial wave method and the eikonal approximation excellently match results obtained with each other as well as experimental data, providing reliable cross sections in the astrophysically important interval of energies from 10 meV to 10 keV. Analytical formulae, interpolating obtained energy- and angular-dependent cross sections, are presented to simplify potential applications of the reported database. Thermalization of fast He atoms in the interstellar gas and energy relaxation of hot He and O atoms in the upper atmosphere of Mars are considered as illustrative examples of potential applications of the new database.
Almost fully polarized collision-induced light scattering in helium
NASA Astrophysics Data System (ADS)
Chrysos, M.; Rachet, F.; Guillot-Noël, C.; Le Duff, Y.
2001-04-01
For the first time in collision-induced light scattering (CILS), a CCD camera has been implemented for the detection of the He2 far spectral wing. We have thus been able to detect signals as low as one photoelectron per pixel and per week, i.e. signals weaker than the electronic noise of our detection device. With our recorded experimental spectra, depolarized and isotropic ones, the frequency domain probed by the thus far available in the literature experimental spectra has greatly been extended up to ?=680 cm-1 and 1200 cm-1 respectively. The depolarization ratio has been found to attain values as low as 0.03 in the helium far wing, that is the signature of an almost fully polarized spectrum. This is a finding thus far unique in CILS by inert gases. Comparison with quantum mechanical computations (where use of up-to-date ab initio incremental polarizabilities has been made) has clearly shown that the origin of this striking property is an almost perfect, probably accidental, destructive interference between polarization and exchange spectral components in the depolarized intensities. In addition, what has been found is that the interference takes place in a very small interval of interatomic distances that are shorter than the diameter of the helium atom.
Method for laser spectroscopy of metastable pionic helium atoms
NASA Astrophysics Data System (ADS)
Hori, M.; Sótér, A.; Aghai-Khozani, H.; Barna, D.; Dax, A.; Hayano, R. S.; Murakami, Y.; Yamada, H.
2015-08-01
The PiHe collaboration is currently attempting to carry out laser spectroscopy of metastable pionic helium atoms using the high-intensity ? - beam of the ring cyclotron facility of the Paul Scherrer Institute. These atoms are heretofore hypothetical three-body Coulomb systems each composed of a helium nucleus, a ? - occupying a Rydberg state, and an electron occupying the 1s ground state. We briefly review the proposed method by which we intend to detect the laser spectroscopic signal. This complements our experiments on metastable antiprotonic helium atoms at CERN.
Calculating helium atomic excited states in coordinate space
NASA Astrophysics Data System (ADS)
Hall, Shane; Siegel, P. B.
2015-12-01
Two coupled Schrödinger equations are used to calculate excited states of atomic helium. Using product state functions for the two-electron state, the shooting method is used to numerically determine the energies of the allowed singlet and triplet levels. The calculations agree well with the data, and the coordinate-space basis yields Schrödinger equations for helium that are familiar to students who have used similar methods for the hydrogen atom.
Atomic capture of negative muons and hadrons in Helium
NASA Astrophysics Data System (ADS)
Dolinov, V. K.; Korenman, G. Ya.; Moskalenko, I. V.; Popov, V. P.
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.
The Weakest Link: Bonding between Helium Atoms
ERIC Educational Resources Information Center
Lohr, Lawrence L.; Blinder, S. M.
2007-01-01
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.
Heuristic theory of positron-helium scattering.
NASA Technical Reports Server (NTRS)
Drachman, R. J.
1971-01-01
An error in a previous modified adiabatic approximation (Drachman, 1966), due to a lack of generality in the form of the short-range correlation part of the wave function for L greater than zero, is corrected heuristically by allowing the monopole suppression parameter to depend on L. An L-dependent local potential is constructed to fit the well-known positron-hydrogen s, p, and d wave phase shifts below the rearrangement threshold. The same form of potential yields a positron-helium cross-section in agreement with a recent experimental measurement near threshold.
Helium atom in an external electric field: Exact diagonalization
NASA Astrophysics Data System (ADS)
Antsygina, T. N.; Chishko, K. A.
2014-09-01
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.
ERIC Educational Resources Information Center
Harbola, Varun
2011-01-01
In this paper, we accurately estimate the ground-state energy and the atomic radius of the helium atom and a helium-like Hookean atom by employing the uncertainty principle in conjunction with the variational approach. We show that with the use of the uncertainty principle, electrons are found to be spread over a radial region, giving an electron…
Positron-alkali atom scattering
NASA Technical Reports Server (NTRS)
Mceachran, R. P.; Horbatsch, M.; Stauffer, A. D.; Ward, S. J.
1990-01-01
Positron-alkali atom scattering was recently investigated both theoretically and experimentally in the energy range from a few eV up to 100 eV. On the theoretical side calculations of the integrated elastic and excitation cross sections as well as total cross sections for Li, Na and K were based upon either the close-coupling method or the modified Glauber approximation. These theoretical results are in good agreement with experimental measurements of the total cross section for both Na and K. Resonance structures were also found in the L = 0, 1 and 2 partial waves for positron scattering from the alkalis. The structure of these resonances appears to be quite complex and, as expected, they occur in conjunction with the atomic excitation thresholds. Currently both theoretical and experimental work is in progress on positron-Rb scattering in the same energy range.
Quantum Field Theory and the Helium Atom: 101 Years Later
J. Sucher
1996-12-11
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.
Spin physics with laser-pumped helium atoms
Schearer, L.D.
1993-05-01
With the development of new, tunable lasers at 1083 nm, direct optical pumping of the triplet metastable atoms of helium yields an almost perfectly aligned ensemble. In {sup 3}He the hyperflne interaction and collisions transfer the orientation to the groundstate nuclear spins. The optical pumping process in {sup 3}He is extraordinarily efficient- nearly 2.5 nuclei are oriented per absorbed photon at turn-on. Applications to magnetometry, the production of spin-polarized electron and ion beams, and the development of polarized neutron beams and dense targets will be discussed. The progress of the UNI-Mainz experiment to measure the electric and magnetic form factors of the neutron will be described. In this experiment the polarized {sup 3}He target is mechanically compressed to several atmospheres with minimal loss of nuclear polarization. Extension of this dense nuclear target for use as a neutron spin filter is also in progress. We will also describe the status of our experiment to observe scattering asymmetries of polarized electrons by chiral molecules. Progress on the development of a compact, moderate current, polarized e-beam will be discussed.
Spectra of helium clusters with up to six atoms using soft-core potentials
Gattobigio, M.; Kievsky, A.; Viviani, M.
2011-11-15
In this paper, we investigate small clusters of helium atoms using the hyperspherical harmonic basis. We consider systems with A=2,3,4,5,6 atoms with an interparticle potential which does not present a strong repulsion at short distances. We use an attractive Gaussian potential that reproduces the values of the dimer binding energy, the atom-atom scattering length, and the effective range obtained with one of the widely used He-He interactions, the Aziz and Slaman potential, called LM2M2. In systems with more than two atoms, we consider a repulsive three-body force that, by construction, reproduces the trimer binding energy of the LM2M2 potential. With this model, consisting of the sum of a two- and three-body potential, we have calculated the spectrum of clusters formed by four, five, and six helium atoms. We have found that these systems present two bound states, one deep and one shallow, close to the threshold fixed by the energy of the (A-1)-atom system. Universal relations between the energies of the excited state of the A-atom system and the ground-state energy of the (A-1)-atom system are extracted, as well as the ratio between the ground state of the A-atom system and the ground-state energy of the trimer.
The Helium Atom and Isoelectronic Ions in Two Dimensions
ERIC Educational Resources Information Center
Patil, S. H.
2008-01-01
The energy levels of the helium atom and isoelectronic ions in two dimensions are considered. The difficulties encountered in the analytical evaluation of the perturbative and variational expressions for the ground state, promote an interesting factorization of the inter-electronic interaction, leading to simple expressions for the energy. This…
Interaction potential between a helium atom and metal surfaces
NASA Technical Reports Server (NTRS)
Takada, Y.; Kohn, W.
1985-01-01
By employing an S-matrix theory for evanescent waves, the repulsive potential between a helium atom and corrugated metal surfaces has been calculated. P-wave interactions and intra-atomic correlation effects were found to be very important. The corrugation part of the interaction potential is much weaker than predicted by the effective-medium theory. Application to Cu, Ni, and Ag (110) surfaces gives good agreement with experiment without any adjustable parameters.
Photoionization of atoms and molecules. [of hydrogen, helium, and xenon
NASA Technical Reports Server (NTRS)
Samson, J. A. R.
1976-01-01
A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.
Average-Atom Thomson Scattering
Johnson, Walter R.
-Atom Approximation W. R. Johnson, Notre Dame J. Nilsen & K. T. Cheng, LLNL The cross section for Thomson scattering Average-Atom Model Divide plasma into WS cells with a nucleus and Z electrons p2 2 - Z r + V a(r) = a a(r) V(r) = VKS(n(r), r) n(r) = nb(r) + nc(r) 4r2nb(r) = nl 2(2l+1) 1+exp[( nl -Âµ)/kBT] Pnl(r)2 Z = r
Rioux, Frank
Hydrogen Atom and Helium Ion Spatial and Momentum Distribution Functions Illustrate for oneelectron species such as the hydrogen atom and the helium ion. The coordinate 1s wave function for the hydrogen atom (z=1) and helium ion (z=2) clearly illustrate the uncertainty principle. 0 2 4 6 r 2 1 r
Simulations of the effect of final state interactions on the scattering reponses of helium droplets
Yang, Jian
1996-01-01
We study the effect of final state interactions (FSI) on the scattering responses of Helium droplets. By computing the s-wave component of the one-body density matrix of a Helium droplet, we find strong similarity between ...
Elastic Scattering Properties of Ultracold Strontium Atoms
NASA Astrophysics Data System (ADS)
Zhang, Ji-Cai; Zhu, Zun-Lue; Liu, Yu-Fang; Sun, Jin-Feng
2011-12-01
We investigate the elastic scattering properties of strontium atoms at ultracold temperatures. The scattering parameters, such as s-wave scattering lengths, effective ranges and p-wave scattering lengths, are calculated for all stable isotope combinations of Sr atoms by the quantal method and semiclassical method, respectively. Good agreements are obtained. The scattering parameters are very sensitive to small changes of the reduced mass. Due to the repulsive interisotope and intraisotope s-wave scattering length and large elastic cross sections, 84Sr—86Sr mixture is a good candidate to realize Bose—Bose quantum degenerate atomic gases.
Quantum entanglement for helium atom in the Debye plasmas
Lin, Yen-Chang; Fang, Te-Kuei; Ho, Yew Kam
2015-03-15
In the present work, we present an investigation on quantum entanglement of the two-electron helium atom immersed in weakly coupled Debye plasmas, modeled by the Debye-Hückel, or screened Coulomb, potential to mimic the interaction between two charged particles inside the plasma. Quantum entanglement is related to correlation effects in a multi-particle system. In a bipartite system, a measurement made on one of the two entangled particles affects the outcome of the other particle, even if such two particles are far apart. Employing wave functions constructed with configuration interaction B-spline basis, we have quantified von Neumann entropy and linear entropy for a series of He {sup 1,3}S{sup e} and {sup 1,3}P{sup o} states in plasma-embedded helium atom.
Ground State Hyperfine Structure of Muonic Helium Atom
A. A. Krutov; A. P. Martynenko
2008-07-21
On the basis of the perturbation theory in the fine structure constant $\\alpha$ and the ratio of the electron to muon masses we calculate one-loop vacuum polarization and electron vertex corrections and the nuclear structure corrections to the hyperfine splitting of the ground state of muonic helium atom $(\\mu e ^4_2He)$. We obtain total result for the ground state hyperfine splitting $\\Delta \
Further Examination of a Simplified Model for Positronium-Helium Scattering
NASA Technical Reports Server (NTRS)
DiRienzi, J.; Drachman, Richard J.
2012-01-01
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.
Electron impact excitation of helium atom
NASA Astrophysics Data System (ADS)
Han, Xiao-Ying; Zeng, De-Ling; Gao, Xiang; Li, Jia-Ming
2015-08-01
A method to deal with the electron impact excitation cross sections of an atom from low to high incident energies are presented. This method combines the partial wave method and the first Born approximation (FBA), i.e., replacing the several lowest partial wave cross sections of the total cross sections within FBA by the corresponding exact partial wave cross sections. A new set of codes are developed to calculate the FBA partial wave cross sections. Using this method, the convergent e-He collision cross sections of optical-forbidden and optical-allowed transitions at low to high incident energies are obtained. The calculation results demonstrate the validity and efficiency of the method. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB921501 and 2013CB922200), the National Natural Science Foundation of China (Grant Nos. 11274035, 11275029, 11328401, 11371218, 11474031, 11474032, and 11474034), and the Foundation of Development of Science and Technology of Chinese Academy of Engineering Physics (Grant Nos. 2013A0102005 and 2014A0102005).
Probing helium interfaces with light scattering : from fluid mechanics to statistical physics
Pierre-Etienne Wolf; Fabien Bonnet; Sylvain Perraud; Laurent Puech; Bernard Rousset; Pierre Thibault
2008-07-10
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.
PREFACE: Atom-surface scattering Atom-surface scattering
NASA Astrophysics Data System (ADS)
Miret-Artés, Salvador
2010-08-01
It has been a privilege and a real pleasure to organize this special issue or festschrift in the general field of atom-surface scattering (and its interaction) in honor of J R Manson. This is a good opportunity and an ideal place to express our deep gratitude to one of the leaders in this field for his fundamental and outstanding scientific contributions. J R Manson, or Dick to his friends and colleagues, is one of the founding fathers, together with N Cabrera and V Celli, of the 'Theory of surface scattering and detection of surface phonons'. This is the title of the very well-known first theoretical paper by Dick published in Physical Review Letters in 1969. My first meeting with Dick was around twenty years ago in Saclay. J Lapujoulade organized a small group seminar about selective adsorption resonances in metal vicinal surfaces. We discussed this important issue in surface physics and many other things as if we had always known each other. This familiarity and warm welcome struck me from the very beginning. During the coming years, I found this to be a very attractive aspect of his personality. During my stays in Göttingen, we had the opportunity to talk widely about science and life at lunch or dinner time, walking or cycling. During these nice meetings, he showed, with humility, an impressive cultural background. It is quite clear that his personal opinions about history, religion, politics, music, etc, come from considering and analyzing them as 'open dynamical systems'. In particular, with good food and better wine in a restaurant or at home, a happy cheerful soirée is guaranteed with him, or even with only a good beer or espresso, and an interesting conversation arises naturally. He likes to listen before speaking. Probably not many people know his interest in tractors. He has an incredible collection of very old tractors at home. In one of my visits to Clemson, he showed me the collection, explaining to me in great detail, their technical properties; all of them were ready for use! We cannot imagine him without his two old-fashioned Mercedes, also in his collection. He also has technical skills in construction and music and always has time for jogging. I would finally say that he is an even-tempered person. In brief, mens sana in corpore sano 1 . Dick is a theorist bound to experimental work, extremely intuitive and very dedicated. In his long stays outside Clemson, he always visited places where experiments were being carried out. He has been, and still is, of great help to experimental PhD students, postdocs or senior scientists in providing valuable advice and suggestions towards new measurements. Plausible interpretations of their results developing theoretical models or always searching for good agreement with experiment are two constants in his daily scientific work. Experimental work is present in most of his 150 papers. One of the main theoretical challenges in this field was to develop a formalism where the plethora of experimental results reported in the literature were accommodated. His transition matrix formalism was also seminal in the field of atom-surface scattering. Elastic and inelastic (single and double phonon) contributions were determined as well as the multiphonon background. This work was preceded by a theory for diffuse inelastic scattering and a posterior contribution for multiphonon scattering, both with V Celli. In a similar vein, a theory of molecule-surface scattering was also derived and, more recently, a theory for direct scattering, trapping and desorption. Very interesting extensions to scattering with molten metal and liquid surfaces have also been carried out. Along with collaborators he has studied energy accommodation and sticking coefficients, providing a better understanding of their meaning. G Armand and Dick proposed the well-known corrugated Morse potential as an interaction potential model providing reliable results of diffraction patterns and selective adsorption resonances. This proposal was, in a certain sense, the result of many previous studies carried out by t
Ionization of highly excited helium atoms in an electric field
van de Water, W.; Mariani, D.R.; Koch, P.M.
1984-11-01
We present detailed measurements of ionization of highly excited triplet helium atoms in a static electric field. The atoms were prepared in states with energy E close to the saddle-point threshold E = -2(F(a.u.))/sup 1/2/. The electric field F was sufficiently strong for the states to be characterized by total spin S and absolute value of the magnetic quantum number M/sub L/. For M/sub L/ = 0 states the experiments measured ionization properties of adiabatic states. In another case, Vertical BarM/sub L/Vertical Bar = 2, they predominantly measured those of diabatic states. In both cases the ionization rate was found to be a highly nonmonotonic function of the field strength. The observations are analyzed in terms of a theory of the helium density of states in an electric field. A companion paper (D. A. Harmin, Phys. Rev. A 30, 2413 (1984)) develops in detail the general theory, which uses quantum defects to parametrize the effect of the core interaction. The agreement between measured and calculated ionization curves is good, indicating that the field ionization of a nonhydrogenic atom can now be understood in a detailed, quantitative, and predictive sense.
Similarity between positronium-atom and electron-atom scattering.
Fabrikant, I I; Gribakin, G F
2014-06-20
We employ the impulse approximation for a description of positronium-atom scattering. Our analysis and calculations of Ps-Kr and Ps-Ar collisions provide a theoretical explanation of the similarity between the cross sections for positronium scattering and electron scattering for a range of atomic and molecular targets observed by S.?J. Brawley et al. [Science 330, 789 (2010)]. PMID:24996087
Entanglement in helium atom confined in an impenetrable cavity
Przemyslaw Koscik; Jayanta K. Saha
2015-10-15
We explore ground-state entanglement properties of helium atom confined at the center of an impenetrable spherical cavity of varying radius by using explicitly correlated Hylleraas-type basis set. Results for the dependencies of the von Neumann and linear entanglement entropic measures on the cavity radius are discussed in details. Some highly accurate numerical results for the von Neumann and linear entropy are reported for the first time. It is found that the transition to the strong confinement regime is manifested by the entropies as an appearance of the inflection points on their variations.
Entanglement in helium atom confined in an impenetrable cavity
NASA Astrophysics Data System (ADS)
Ko?cik, Przemys?aw; Saha, Jayanta Kumar
2015-11-01
We explore ground-state entanglement properties of helium atom confined at the center of an impenetrable spherical cavity of varying radius by using explicitly correlated Hylleraas-type basis set. Results for the dependencies of the von Neumann and linear entanglement entropic measures on the cavity radius are discussed in details. Some highly accurate numerical results for the von Neumann and linear entropy are reported for the first time. It is found that the transition to the strong confinement regime is manifested by the entropies as an appearance of the inflection points on their variations.
Coherently enhanced Raman scattering in atomic vapor
Chun-Hua Yuan; L. Q. Chen; Jietai Jing; Z. Y. Ou; Weiping Zhang
2010-07-06
We present a scheme to obtain the coherently enhanced Raman scattering in atomic vapor which is induced by a spin wave initially written by a weak write laser. The enhancement of Raman scattering is dependent on the number and the spatial distribution of the flipped atoms generated by the weak write laser. Such an enhanced Raman scattering may have practical applications in quantum information, nonlinear optics and laser spectroscopy because of its simplicity.
Re-examination of a Simplified Model for Positronium-Helium Scattering
NASA Technical Reports Server (NTRS)
DiRienzi, Joseph; Drachman, Richard J.
2003-01-01
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.
Re-Examination of a Simplified Model for Positronium-Helium Scattering
NASA Technical Reports Server (NTRS)
Drachman, Richard J.; DiRienzi, Joseph
2003-01-01
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.
Binding of two helium atoms in confined geometries
Kilic, S.; Krotscheck, E.; Zillich, R.
1999-08-01
The authors carry out a comprehensive study of the binding of two helium atoms in unrestricted and, in particular, in restricted geometries in both two and three dimensions. Besides the well known binding of the {sup 4}He dimer in unrestricted geometry in two and three dimensions, the authors also find weakly bound states of the {sup 3}He-{sup 4}He molecule and the {sup 3}He dimer in 2 dimensions. Furthermore, any combination of two {sup 4}He or {sup 3}He atoms can form a molecule if their motion is sufficiently confined. The calculations are carried out by numerically solving the Schroedinger equation as well as by constructing a suitable variational wave function.
Revised Primordial Helium Abundance Based on New Atomic Data
NASA Astrophysics Data System (ADS)
Peimbert, Manuel; Luridiana, Valentina; Peimbert, Antonio
2007-09-01
We have derived a primordial helium abundance of Yp=0.2477+/-0.0029, based on new atomic physics computations of the recombination coefficients of He I and of the collisional excitation of the H I Balmer lines together with observations and photoionization models of metal-poor extragalactic H II regions. The new atomic data increase our previous determination of Yp by 0.0086, a very significant amount. By combining our Yp result with the predictions made by the standard big bang nucleosynthesis model, we find a baryon-to-photon ratio, ?, in excellent agreement both with the ?-value derived by the primordial deuterium abundance value observed in damped Ly? systems and with the one obtained from the WMAP observations.
Attenuation of Scattered Thermal Energy Atomic Oxygen
NASA Technical Reports Server (NTRS)
Banks, Bruce a.; Seroka, Katelyn T.; McPhate, Jason B.; Miller, Sharon K.
2011-01-01
The attenuation of scattered thermal energy atomic oxygen is relevant to the potential damage that can occur within a spacecraft which sweeps through atomic oxygen in low Earth orbit (LEO). Although there can be significant oxidation and resulting degradation of polymers and some metals on the external surfaces of spacecraft, there are often openings on a spacecraft such as telescope apertures, vents, and microwave cavities that can allow atomic oxygen to enter and scatter internally to the spacecraft. Atomic oxygen that enters a spacecraft can thermally accommodate and scatter to ultimately react or recombine on surfaces. The atomic oxygen that does enter a spacecraft can be scavenged by use of high erosion yield polymers to reduce its reaction on critical surfaces and materials. Polyoxymethylene and polyethylene can be used as effective atomic oxygen scavenging polymers.
LBNL-42730 1 Collisional Perturbation of States in Atomic Ytterbium by Helium and Neon
Budker, Dmitry
LBNL-42730 1 Collisional Perturbation of States in Atomic Ytterbium by Helium and Neon D in atomic ytterbium by helium and neon buffer gases are reported. We find upper limits for the quenching and neon. PACS numbers: 34, 11.30.Er, 42.62.Fi (Submitted to Phys. Rev. A) 1. INTRODUCTION The 6s2 1 S0 6s
Theoretical survey on positronium formation and ionisation in positron atom scattering
NASA Technical Reports Server (NTRS)
Basu, Madhumita; Ghosh, A. S.
1990-01-01
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.
NASA Technical Reports Server (NTRS)
Drachman, Richard J.
2006-01-01
Formation of triplet positron-helium bound state by stripping of positronium atoms in collision with ground state helium JOSEPH DI RlENZI, College of Notre Dame of Maryland, RICHARD J. DRACHMAN, NASA/Goddard Space Flight Center - The system consisting of a positron and a helium atom in the triplet state e(+)He(S-3)(sup e) was conjectured long ago to be stable [1]. Its stability has recently been established rigorously [2], and the values of the energies of dissociation into the ground states of Ps and He(+) have also been reported [3] and [4]. We have evaluated the cross-section for this system formed by radiative attachment of a positron in triplet He state and found it to be small [5]. The mechanism of production suggested here should result in a larger cross-section (of atomic size) which we are determining using the Born approximation with simplified initial and final wave functions.
Symmetric And Non-Symmetric Muonic Helium Atoms Studies
Mohammadi, S.
2011-10-28
The ground state hyperfine structure and other properties are calculated for muonic helium atoms ({sup 3}He{sup +2}{mu}{sup -}e{sup -} or {sup 4}He{sup +2}{mu}{sup -}e{sup -}) with the use of some local properties of the wave functions in the domains where two particles are close to each other or far away. Simple wave functions incorporating these properties with one variational parameter is developed. The calculated values for hyperfine structure, energy and average interparticle distances in ground state are compared with the correlation function hyper-spherical harmonic method and multibox variational approach. The obtained results are very close to the values calculated by mentioned methods, giving strong indications that the proposed wave functions provide relatively accurate values.
Optical detection of nonradiating alkali atoms in solid helium.
Eichler, T; Müller-Siebert, R; Nettels, D; Kanorsky, S; Weis, A
2002-03-25
We have detected by optical means nonfluorescing 85Rb and 87Rb atoms implanted in a body centered cubic 4He crystal. In contrast to cesium the resonance fluorescence of rubidium is strongly quenched by the helium matrix, and the weak resonance absorption of the two Rb isotopes was detected using a double resonance technique. From a comparative study of the (optically detected) magnetic resonance spectra of 85Rb, 87Rb, and 133Cs we infer their effective g(F) factors and conclude that they are not perturbed by the He matrix at a level of 2 x 10(-4). We show further that optical pumping of Rb proceeds via depopulation, whereas for Cs it proceeds via repopulation. PMID:11909454
Chu, Xi
Dynamic polarizabilities of rare-earth-metal atoms and dispersion coefficients; published 29 March 2007 The dynamic scalar and tensor polarizabilities of the rare-earth-metal atoms coefficients for the interactions of the rare-earth-metal atoms with helium atoms. The static polarizabilities
Toward improved photon-atom scattering predictions
NASA Astrophysics Data System (ADS)
Kissel, Lynn
1995-05-01
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 Delbrück components, processes beyond photoionization contribute. Subtracted cross sections for bound-bound atomic transitions and bound pair annihilation 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.
Toward improved photon-atom scattering predictions
NASA Astrophysics Data System (ADS)
Kissel, Lynn
1994-10-01
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.
Galgani, Luigi
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
Positronium formation for positron scattering from helium ion
NASA Astrophysics Data System (ADS)
Zhi Zhang, Yong; Yu, Rong Mei; Xia Li, Shu; Song, Xiu Dan; Jiao, Li Guang
2015-09-01
Positronium (Ps) formation processes from helium ions by positron impact are studied using the two-channel two-center eikonal final state-continuum initial distorted wave method. The Ps(n = 1 and 2) and total Ps formation cross sections are calculated from the threshold to the high energy region, and the results are compared with other theoretical calculations available in the literature. It is found that the present results agree reasonably well with the close-coupling calculations, while other predictions, such as the Coulomb-Born approximation, the optical potential method, and the recent classical trajectory Monte Carlo method (Naginey 2014 Phys. Rev. A 89, 062704), are all much higher in the entire energy region. The maximum positions of the Ps(n) formation cross sections in our present work are in good agreement with the wave vector matching model of (Charlton 2014 J. Phys. B: At. Mol. Opt. Phys. 39, 4575). Finally, we discuss the scaling law of the Ps(n) formation cross sections with respect to the principal quantum number n of the Ps atom.
NASA Astrophysics Data System (ADS)
Trelenberg, Thomas Walter
Results from experiments using a thermal-energy beam of helium atoms as a probe in studying three crystalline insulator surfaces are presented. The primary focus is the simple ferroelectric perovskite, KTa1- xNbxO3 (or KTN when not specifying an Nb concentration) with x = 0.06, 0.10, 0.20, 0.30, and 0.52. Thin films of KCl and p-quaterphenyl grown onto NaCl(001) were also studied. Extending an earlier work on potassium tantalate (KTaO3), freshly cleaved (001) surfaces of niobium-doped potassium tantalate (KTN) were studied. While KTaO3 is an incipient ferroelectric undergoing no bulk phase changes, KTN, with Nb concentration greater than ˜1.5%, is a tunable ferroelectric, existing in several bulk phases depending on the temperature of the material. A metastable feature observed in KTN immediately after cleaving results in satellite peaks around the specular peak which decay over time. Also, small, broad half-order peaks were observed when the surface temperature was cycled between 50 K and 270 K for the first time. Surface hysteresis effects and responses to electric fields were also studied. Surface dispersion curves for the two high-symmetry directions are given for various Nb doping levels and substrate temperatures. This work compares the above phenomena to similar occurrences observed previously in KTaO3, and notes how the responses differ as a function of niobium doping. Also building on previous experience, the growth of KCl on NaCl was studied. Several recent works have focused on the physical interpretation of 3/4-order peaks observed during LEED investigations of this system. A HAS study of this system revealed, at best, a weak indication of several n/4-order peaks, but at film thicknesses well above those reported. In our first attempt to examine the surfaces of films of large organic molecules using HAS, p-quaterphenyl (p-4P) was deposited onto an NaCl surface held at 300K. Diffraction intensities from the NaCl were reduced but produced no other effects. However, cooling the surface to 50 K revealed many smaller diffraction peaks from the p-4P in addition to the larger NaCl peaks. The organic film peaks were isotropic, appearing as a two-dimensional diffraction powder pattern.
Scattering properties of dark atoms and molecules
NASA Astrophysics Data System (ADS)
Cline, James M.; Liu, Zuowei; Moore, Guy D.; Xue, Wei
2014-02-01
There has been renewed interest in the possibility that dark matter exists in the form of atoms, analogous to those of the visible world. An important input for understanding the cosmological consequences of dark atoms is their self-scattering. Making use of results from atomic physics for the potentials between hydrogen atoms, we compute the low-energy elastic scattering cross sections for dark atoms. We find an intricate dependence upon the ratio of the dark proton to the dark electron mass, allowing for the possibility to "design" low-energy features in the cross section. Dependences upon other parameters, namely the gauge coupling and reduced mass, scale out of the problem by using atomic units. We derive constraints on the parameter space of dark atoms by demanding that their scattering cross section not exceed bounds from dark matter halo shapes. We discuss the formation of molecular dark hydrogen in the Universe and determine the analogous constraints on the model when the dark matter is predominantly in molecular form.
Parametric Amplification of Scattered Atom Pairs
Campbell, Gretchen K.; Mun, Jongchul; Boyd, Micah; Streed, Erik W.; Ketterle, Wolfgang; Pritchard, David E.
2006-01-20
We have observed parametric generation and amplification of ultracold atom pairs. A {sup 87}Rb Bose-Einstein condensate was loaded into a one-dimensional optical lattice with quasimomentum k{sub 0} and spontaneously scattered into two final states with quasimomenta k{sub 1} and k{sub 2}. Furthermore, when a seed of atoms was first created with quasimomentum k{sub 1} we observed parametric amplification of scattered atoms pairs in states k{sub 1} and k{sub 2} when the phase-matching condition was fulfilled. This process is analogous to optical parametric generation and amplification of photons and could be used to efficiently create entangled pairs of atoms. Furthermore, these results explain the dynamic instability of condensates in moving lattices observed in recent experiments.
Random scattering by atomic density fluctuations in optical lattices.
Blaauboer, M; Kurizki, G; Akulin, V M
2001-04-16
We investigate hitherto unexplored regimes of probe scattering by atoms trapped in optical lattices: weak scattering by effectively random atomic density distributions and multiple scattering by arbitrary atomic distributions. Both regimes are predicted to exhibit a universal semicircular scattering line shape for large density fluctuations, which depend on temperature and quantum statistics. PMID:11328012
Random Scattering by Atomic Density Fluctuations in Optical Lattices
NASA Astrophysics Data System (ADS)
Blaauboer, M.; Kurizki, G.; Akulin, V. M.
2001-04-01
We investigate hitherto unexplored regimes of probe scattering by atoms trapped in optical lattices: weak scattering by effectively random atomic density distributions and multiple scattering by arbitrary atomic distributions. Both regimes are predicted to exhibit a universal semicircular scattering line shape for large density fluctuations, which depend on temperature and quantum statistics.
Atomic-scale mechanisms of helium bubble hardening in iron
NASA Astrophysics Data System (ADS)
Osetsky, Yuri N.; Stoller, Roger E.
2015-10-01
Generation of helium due to (n,?) transmutation reactions changes the response of structural materials to neutron irradiation. The whole process of radiation damage evolution is affected by He accumulation and leads to significant changes in the material's properties. A population of nanometric He-filled bubbles affects mechanical properties and the impact can be quite significant because of their high density. Understanding how these basic mechanisms affect mechanical properties is necessary for predicting radiation effects. In this paper we present an extensive study of the interactions between a moving edge dislocation and bubbles using atomic-scale modeling. We focus on the effect of He bubble size and He concentration inside bubbles. We found that ability of bubbles to act as an obstacle to dislocation motion is close to that of voids when the He-to-vacancy ratio is in the range from 0 to 1. A few simulations made at higher He contents demonstrated that the interaction mechanism is changed for over-pressurized bubbles and they become weaker obstacles. The results are discussed in light of post-irradiation materials testing.
Atomic-scale mechanisms of helium bubble hardening in iron
Osetskiy, Yury N.; Stoller, Roger E.
2015-06-03
Generation of helium due to (n,?) transmutation reactions changes the response of structural materials to neutron irradiation. The whole process of radiation damage evolution is affected by He accumulation and leads to significant changes in the material s properties. A population of nanometric He-filled bubbles affects mechanical properties and the impact can be quite significant because of their high density. Understanding how these basic mechanisms affect mechanical properties is necessary for predicting radiation effects. In this paper we present an extensive study of the interactions between a moving edge dislocation and bubbles using atomic-scale modeling. We focus on the effect of He bubble size and He concentration inside bubbles. Thus, we found that ability of bubbles to act as an obstacle to dislocation motion is close to that of voids when the He-to-vacancy ratio is in the range from 0 to 1. A few simulations made at higher He contents demonstrated that the interaction mechanism is changed for over-pressurized bubbles and they become weaker obstacles. The results are discussed in light of post-irradiation materials testing.
Atomic-scale mechanisms of helium bubble hardening in iron
Osetskiy, Yury N.; Stoller, Roger E.
2015-06-03
Generation of helium due to (n,?) transmutation reactions changes the response of structural materials to neutron irradiation. The whole process of radiation damage evolution is affected by He accumulation and leads to significant changes in the material s properties. A population of nanometric He-filled bubbles affects mechanical properties and the impact can be quite significant because of their high density. Understanding how these basic mechanisms affect mechanical properties is necessary for predicting radiation effects. In this paper we present an extensive study of the interactions between a moving edge dislocation and bubbles using atomic-scale modeling. We focus on the effectmore »of He bubble size and He concentration inside bubbles. Thus, we found that ability of bubbles to act as an obstacle to dislocation motion is close to that of voids when the He-to-vacancy ratio is in the range from 0 to 1. A few simulations made at higher He contents demonstrated that the interaction mechanism is changed for over-pressurized bubbles and they become weaker obstacles. The results are discussed in light of post-irradiation materials testing.« less
Sibener, Steven
Atomic scattering as a probe of polymer surface and thin film dynamics M. A. Freedman, A. W that for highly nanoconfined films, polymer-substrate interactions influence vibrational dynamics at the polymer found helium atom scattering to be a sensitive probe of the vibrational dynamics of the polymer thin
Lars Onsager Prize Talk: Quantum fluids: from liquid helium to cold atoms
NASA Astrophysics Data System (ADS)
Pethick, Christopher
2008-03-01
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.
NASA Technical Reports Server (NTRS)
Huang, K.-N.
1977-01-01
A computational procedure for calculating correlated wave functions is proposed for three-particle systems interacting through Coulomb forces. Calculations are carried out for the muonic helium atom. Variational wave functions which explicitly contain interparticle coordinates are presented for the ground and excited states. General Hylleraas-type trial functions are used as the basis for the correlated wave functions. Excited-state energies of the muonic helium atom computed from 1- and 35-term wave functions are listed for four states.
Scattered Atomic Oxygen Effects on Spacecraft Materials
NASA Technical Reports Server (NTRS)
Banks, Bruce A.; Miller, Sharon K. R.; deGroh, Kim K.; Demko, Rikako
2003-01-01
Low Earth orbital (LEO) atomic oxygen cannot only erode the external surfaces of polymers on spacecraft, but can cause degradation of surfaces internal to components on the spacecraft where openings to the space environment exist. Although atomic oxygen attack on internal or interior surfaces may not have direct exposure to the LEO atomic oxygen flux scattered impingement can have serious degradation effects where sensitive interior surfaces are present. The effects of atomic oxygen erosion of polymer interior to an aperture on a spacecraft is simulated using Monte Carlo computational techniques. A 2-dimensional model is used to provide quantitative indications of the attenuation of atomic oxygen flux as a function of distance into a parallel walled cavity. The degree of erosion re1ative is compared between the various interior locations and the external surface of a LEO spacecraft.
NASA Astrophysics Data System (ADS)
Rachet, Florent; Chrysos, Michael; Guillot-Noël, Christophe; Le Duff, Yves
2000-03-01
Contrary to what has been observed thus far collision-induced light scattering (CILS) can be completely polarized. This exceptional behavior characterizes the very far wing of the binary CILS spectrum by gaseous helium. This conclusion is drawn from an experimental study of the depolarization ratio of He 2 in a much extended, previously unexplored, spectral domain. Our analysis shows that this property, unique thus far, is mainly due to an almost perfect cancellation between polarization and exchange pair polarizability contributions to the depolarized spectrum, taking place at internuclear distances shorter than the atomic diameter.
The application of laser Rayleigh scattering to gas density measurements in hypersonic helium flows
NASA Technical Reports Server (NTRS)
Hoppe, J. C.; Honaker, W. C.
1979-01-01
Measurements of the mean static free-stream gas density have been made in two Langley Research Center helium facilities, the 3-inch leg of the high-Reynolds-number helium complex and the 22-inch hypersonic helium tunnel. Rayleigh scattering of a CW argon ion laser beam at 514.5 nm provided the basic physical mechanism. The behavior of the scattered signal was linear, confirmed by a preliminary laboratory study. That study also revealed the need to introduce baffles to reduce stray light. A relatively simple optical system and associated photon-counting electronics were utilized to obtain data for densities from 10 to the 23rd to 10 to the 25th per cu m. The major purpose, to confirm the applicability of this technique in the hypersonic helium flow, was accomplished.
Barcelona, Universitat de
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
Ground-State Entanglement Properties of Helium Atom in a Finite Spherical Cavity
NASA Astrophysics Data System (ADS)
Ko?cik, Przemys?aw; Saha, Jayanta K.
2015-10-01
The effects of the spatial confinement on the ground-state entanglement properties of the helium atom have been studied. The finite oscillator potential is used to represent the confining potential. The transition to the free atom regime and the harmonic confinement regime are discussed in detail in dependence of the control parameters of the system.
Introduction to Density Functional Theory: Calculations by Hand on the Helium Atom
ERIC Educational Resources Information Center
Baseden, Kyle A.; Tye, Jesse W.
2014-01-01
Density functional theory (DFT) is a type of electronic structure calculation that has rapidly gained popularity. In this article, we provide a step-by-step demonstration of a DFT calculation by hand on the helium atom using Slater's X-Alpha exchange functional on a single Gaussian-type orbital to represent the atomic wave function. This DFT…
A novel spacetime concept for describing electronic motion within a helium atom
Xu, Kunming
2006-01-01
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 mechani...
MISSE Scattered Atomic Oxygen Characterization Experiment
NASA Technical Reports Server (NTRS)
Banks, Bruce A.; deGroh, Kim K.; Miller, Sharon K.
2006-01-01
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.
Collisional lasing on a self-terminating transition of a helium atom
Bel'skaya, E V; Bokhan, P A; Zakrevskii, D E; Lavrukhin, M A
2011-01-24
Laser on a self-contained transition of a helium atom is studied under excitation of the helium mixture with molecular gases by single long-duration (up to 700ns) or double nanosecond pulses. In He - H{sub 2}O and He - NH{sub 3} mixtures, no limitations were found on the pulse repetition rate and the laser pulse duration obtained was equal to that of the pump pulse. (lasers and amplifiers)
ERIC Educational Resources Information Center
Deeney, F. A.; O'Leary, J. P.
2012-01-01
For helium and helium-like ions, we have examined the differences between the values of the ionization energies as calculated from the Bohr theory and those measured in experiments. We find that these differences vary linearly with the atomic number of the system. Using this result, we show how the Bohr model for single-electron systems may be…
The role of correlation in the ground state energy of confined helium atom
Aquino, N.
2014-01-14
We analyze the ground state energy of helium atom confined by spherical impenetrable walls, and the role of the correlation energy in the total energy. The confinement of an atom in a cavity is one way in which we can model the effect of the external pressure on an atom. The calculations of energy of the system are carried out by the variational method. We find that the correlation energy remains almost constant for a range values of size of the boxes analyzed.
Excitation of helium atoms in collisions with plasma electrons in an electric field
Smirnov, B. M.
2013-01-15
The rate constants are evaluated for excitation of helium atoms in metastable states by electron impact if ionized helium is located in an external electric field and is supported by it, such that a typical electron energy is small compared to the atomic excitation energy. Under these conditions, atomic excitation is determined both by the electron traveling in the space of electron energies toward the excitation threshold and by the subsequent atomic excitation, which is a self-consistent process because it leads to a sharp decrease in the energy distribution function of electrons, which in turn determines the excitation rate. The excitation rate constant is calculated for the regimes of low and high electron densities, and in the last case, it is small compared to the equilibrium rate constant where the Maxwell distribution function is realized including its tail. Quenching of metastable atomic states by electron impact results in excitation of higher excited states, rather than transition to the ground electron state for the electric field strengths under consideration. Therefore, at restricted electron number densities, the rate of emission of resonant photons of the wavelength 58 nm, which results from the transition from the 2{sup 1}P state of the helium atom to the ground state, is close to the excitation rate of metastable atomic states. The efficiency of atomic excitation in ionized helium, i.e., the part of energy of an electric field injected in ionized helium that is spent on atomic excitation, is evaluated. The results exhibit the importance of electron kinetics for an ionized gas located in an electric field.
Effect of static electric field on cross sections in antiproton impact ionization of atomic helium
NASA Astrophysics Data System (ADS)
Pandey, Mukesh Kumar; Ho, Y. K.
2012-10-01
We report the effect of static electric fields in different geometrical features on the collisional ionization of helium atoms by antiproton. The Classical Trajectory Monte Carlo (CTMC) method with a model interaction potential has been used to simulate the differential and total ionization cross sections in antiproton-helium atom collisions in the energy range of 10-500 keV with and without electric fields. The calculated ionization cross sections are in reasonable agreement with the recently reported experimental and theoretical results. The effects of the external electric fields are seen to be quite prominent.
NASA Astrophysics Data System (ADS)
Perez-Rios, Jesus; Ragole, Steve; Wang, Jia; Greene, Chris H.
2014-05-01
A general method to study classical scattering in n-dimensions is developed. Through classical trajectory calculations the new method is applied to compute the three-body recombination rate as a function of the collision energy for helium atoms, as an example. Quantum calculations are also performed for the J? = 0+ symmetry of the three-body recombination rate in order to compare with the classical results, yielding good agreement for E ~ 1 K. The classical threshold law is derived and numerically confirmed for the three-body recombination rate. Finally, a relationship is found between the quantum and classical three-body elastic cross section which exhibits a similarity to the well-known shadow scattering in two-body collisions. This work was supported by DOE, Office of Science.
Scattering of electrons from neon atoms
NASA Technical Reports Server (NTRS)
Dasgupta, A.; Bhatia, A. K.
1984-01-01
Scattering of electrons from neon atoms is investigated by the polarized-orbital method. The perturbed orbitals calculated with use of the Sternheimer approximation lead to the polarizability 2.803 a(0)-cube in fairly good agreement with the experimental value 2.66 a(0)-cube. Phase shifts for various partial waves are calculated in the exchange, exchange-adiabatic, and polarized-orbital approximations. They are compared with the previous results. The calculated elastic differential, total, and momentum-transfer cross sections are compared with the experimental results. The polarized-orbital approximation yields results which show general improvement over the exchange-adiabatic approximation.
NASA Astrophysics Data System (ADS)
Belhabib, T.; Desgardin, P.; Sauvage, T.; Erramli, H.; Barthe, M. F.; Garrido, F.; Carlot, G.; Nowicki, L.; Garcia, P.
2015-12-01
Helium behaviour in irradiated uranium dioxide may play an important role in the mechanical stability of nuclear fuels during and after its use in nuclear power plants. Helium migration mechanisms in bulk UO2 have already been the subject of theoretical studies but there is a lack of experimental data relating to the most stable location in the crystal. To this end, we have studied uranium dioxide samples implanted with helium ions at low fluence before and after thermal annealing in the range 600 and 800 °C. UO2 single crystals were implanted with 50 keV-3He ions at the fluence of 1 × 1015 at cm-2 and the location in the lattice of helium atoms was investigated using NRA (Nuclear Reaction Analysis) based on the reaction of 3He with deuterons (3He (d,p) 4He) in a channelling mode, recording angular scans across axes and planes. Furthermore, the uranium sub-lattice was analysed by the classical RBS method. After implantation, the experimental angular scans recorded across the main crystallographic axes and along major planes show that the helium atoms in their large majority occupy octahedral interstitial sites. No modification of the occupied crystallographic site was found after annealing at 600 °C. Conversely, no crystallographic relationship between matrix and helium signals was revealed following annealing at 800 °C. The latter feature is likely related to the clustering of implanted helium atoms into gas-filled bubbles. These experimental results have been quantified and interpreted using Monte Carlo simulations with the McChasy code.
Similarity between Positronium-Atom and Electron-Atom Scattering I. I. Fabrikant
Gribakin, Gleb
energy is much smaller than the ionization energies of the noble-gas atoms and many small molecules (suchSimilarity between Positronium-Atom and Electron-Atom Scattering I. I. Fabrikant Department of positronium-atom scattering. Our analysis and calculations of Ps-Kr and Ps-Ar collisions provide a theoretical
Diffraction electron-atom scattering in an intense low-frequency laser field
Jaron, A.; Kaminski, J.Z.
1997-12-01
An explanation of discrepancies between predictions of the Kroll-Watson theory and cross sections measured in the Wallbank-Holmes experiments on electron-atom scattering in the presence of a powerful low-frequency laser field is presented. Our model calculations for helium and argon as target atoms come out to be in good agreement with experimental results; i.e., obtained cross sections are by many orders of magnitude larger than those predicted by the Kroll-Watson theory. A mechanism responsible for such a substantial increase of the calculated cross sections is found to be due to the diffraction scattering of electrons by atomic obstacles. {copyright} {ital 1997} {ital The American Physical Society}
Version 3.0 Nuclear polarizability of helium isotopes in atomic transitions
Pachucki, Krzysztof
. These are relativistic and QED effects, finite nuclear mass and, to some extent, finite nuclear size. There is also 4 He + [1, 2], where the polarizability cor rection is about 1% of the finite nuclear size effectVersion 3.0 Nuclear polarizability of helium isotopes in atomic transitions K. Pachucki 1 and A
Assessment of passive decay heat removal in the General Atomics Modular Helium Reactor
Cocheme, Francois Guilhem
2005-02-17
The purpose of this report is to present the results of the study and analysis of loss-of-coolant and loss-of-flow simulations performed on the Modular Helium Reactor developed by General Atomics using the thermal-hydraulics ...
Variational Calculation on the Helium Atom Using a Trigonometric Trial Wave Function Frank Rioux
Rioux, Frank
Variational Calculation on the Helium Atom Using a Trigonometric Trial Wave Function Frank Rioux Chemistry Department CSB|SJU Trigonometric Trial Wave Function: r ,( ) 3 3 3 sech r( ):= Demonstrate the wave function is normalized. 0 r r ,( )2 4 r 2 d assume 0>, simplify 1 The terms
Variational Calculation on the Helium Atom Using a Hydrogenic Trial Wave Function Frank Rioux
Rioux, Frank
Variational Calculation on the Helium Atom Using a Hydrogenic Trial Wave Function Frank Rioux Chemistry Department CSB|SJU Gaussian Trial Wave Function: r ,( ) 3 exp - r( ):= Demonstrate the wave function is normalized. 0 r r ,( )2 4 r 2 d assume 0>, simplify 1 The terms
THE INTERACTION OF HELIUM ATOMS WITH EDGE DISLOCATIONS IN ?-Fe
Heinisch, Howard L.; Gao, Fei; Kurtz, Richard J.
2004-06-30
Formation energies, binding energies, and the migration of interstitial He atoms at and near the center of an a/2<111>{110} edge dislocation in ?-Fe are determined using molecular dynamics and conjugate gradient relaxation methods. Results are compared as a function of the distance of the interstitial He atoms from the center of the dislocation and the amount of excess volume around the dislocation. Interstitial He atoms have negative binding energy on the compression side of the dislocation and strong positive binding energy on the tension side. Even at low temperatures, interstitial He atoms in the vicinity of the dislocation easily migrate to positions near the center of the dislocation, where they form crowdion interstitials with binding energies in excess of 2 eV.
Spectroscopy of antiprotonic helium atoms and its contribution to the fundamental physical constants
Hayano, Ryugo S.
2010-01-01
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
NASA Astrophysics Data System (ADS)
Saha, H. P.
1993-08-01
The multiconfiguration Hartree-Fock method for continuum wave functions has been used to calculate the scattering length and phase shifts over extremely low energies ranging from 0 to 1 eV very accurately for electron-helium scattering. The scattering length is calculated very accurately with wave functions computed exactly at zero energy, resulting in an upper bound of 1.1784. The electron correlation and polarization of the target by the scattering electron, which are very important in these calculations, have been taken into account in an accurate ab initio manner through the configuration-interaction procedure by optimizing both bound and continuum orbitals simultaneously at each kinetic energy of the scattered electron. Detailed results for scattering length, differential, total, and momentum-transfer cross sections obtained from the phase shifts are presented. The present scattering length is found to be in excellent agreement with the experimental result of Andrick and Bitsch [J. Phys. B 8, 402 (1975)] and the theoretical result of O'Malley, Burke, and Berrington [J. Phys. B 12, 953 (1979)]. There is excellent agreement between the present total cross sections and the corresponding experimental measurements of Buckman and Lohmann [J. Phys. B 19, 2547 (1986)]. The present momentum-transfer cross sections also show remarkable agreement with the experimental results of Crompton, Elford, and Robertson [Aust. J. Phys. 23, 667 (1970)].
Saha, H.P. )
1993-08-01
The multiconfiguration Hartree-Fock method for continuum wave functions has been used to calculate the scattering length and phase shifts over extremely low energies ranging from 0 to 1 eV very accurately for electron-helium scattering. The scattering length is calculated very accurately with wave functions computed exactly at zero energy, resulting in an upper bound of 1.1784. The electron correlation and polarization of the target by the scattering electron, which are very important in these calculations, have been taken into account in an accurate [ital ab] [ital initio] manner through the configuration-interaction procedure by optimizing both bound and continuum orbitals simultaneously at each kinetic energy of the scattered electron. Detailed results for scattering length, differential, total, and momentum-transfer cross sections obtained from the phase shifts are presented. The present scattering length is found to be in excellent agreement with the experimental result of Andrick and Bitsch [J. Phys. B 8, 402 (1975)] and the theoretical result of O'Malley, Burke, and Berrington [J. Phys. B 12, 953 (1979)]. There is excellent agreement between the present total cross sections and the corresponding experimental measurements of Buckman and Lohmann [J. Phys. B 19, 2547 (1986)]. The present momentum-transfer cross sections also show remarkable agreement with the experimental results of Crompton, Elford, and Robertson [Aust. J. Phys. 23, 667 (1970)].
Correlation enhanced phase sensitive Raman scattering in atomic vapors
Chun-Hua Yuan; L. Q. Chen; Z. Y. Ou; Weiping Zhang
2013-05-25
We theoretically propose a method to enhance Raman scattering by injecting a seeded light field which is correlated with the initially prepared atomic spin wave. Such a light-atom correlation leads to an interference in the Raman scattering. The interference is sensitive to the relative phase between the seeded light field and initially prepared atomic spin wave. For constructive interference, the Raman scattering is greatly enhanced. Such an enhanced Raman scattering may find applications in quantum information, nonlinear optics and optical metrology due to its simplicity.
Exploiting Universality in Atoms with Large Scattering Lengths
Braaten, Eric
2012-05-31
The focus of this research project was atoms with scattering lengths that are large compared to the range of their interactions and which therefore exhibit universal behavior at sufficiently low energies. Recent dramatic advances in cooling atoms and in manipulating their scattering lengths have made this phenomenon of practical importance for controlling ultracold atoms and molecules. This research project was aimed at developing a systematically improvable method for calculating few-body observables for atoms with large scattering lengths starting from the universal results as a first approximation. Significant progress towards this goal was made during the five years of the project.
Double scattering of intense laser light by two atoms
Vyacheslav Shatokhin; Tobias Geiger; Thomas Wellens; Andreas Buchleitner
2010-03-31
This paper analyzes coherent backscattering of intense laser light by two randomly placed distant atoms. Starting from the general two-atom master equation, we analytically derive the elastic and inelastic background and interference components of the double scattering spectrum. By expressing the final results in terms of single-atom observables, the two-atom problem is shown to be equivalent to a description in terms of single atoms under bichromatic driving.
A novel spacetime concept for describing electronic motion within a helium atom
Kunming Xu
2007-05-30
Euclidean space and linear algebra do not characterize dynamic electronic orbitals satisfactorily for even the motion of both electrons in an inert helium atom cannot be defined in reasonable details. Here the author puts forward a novel two-dimensional spacetime model from scratch in the context of defining both electrons in a helium atom. Space and time are treated as two orthogonal, symmetric and complementary quantities under the atomic spacetime. Electronic motion observed the rule of differential and integral operations that were implemented by dynamic trigonometric functions. It is demonstrated that the atomic spacetime is not a linear vector space with Newtonian time, and within which calculus has non-classical definition, and complex wave functions have fresh physical significances. This alternative approach is original, informative and refreshing but still compatible with quantum mechanics in the formulation. The description of electronic resonance in helium is also comparable with classical mechanics such as an oscillating pendulum and with classical electromagnetism such as an LC oscillator. The study has effectively unified complex function, calculus, and trigonometry in mathematics, and provided a prospect for unifying particle physics with classical physics on the novel spacetime platform.
Zero-energy neutron-triton and proton-Helium-3 scattering with \\eftnopi
Johannes Kirscher
2011-05-18
Model-independent constraints for the neutron-triton and proton-Helium-3 scattering lengths are calculated with a leading-order interaction derived from an effective field theory without explicit pions. Using the singlet neutron-proton scattering length, the deuteron, and the triton binding energy as input, the predictions $\\ants=9.2\\pm2.6 $fm, $\\antt=7.6\\pm1.6 $fm, $\\aphes=3.6\\pm0.32 $fm, and $\\aphet=3.1\\pm 0.23 $fm are obtained. The calculations employ the resonating group method and include the Coulomb interaction when appropriate. The theoretical uncertainty is assessed via a variation of the regulator parameter of the short-distance interaction from $400 $MeV to $1.6 $GeV. The phase-shift and scattering-length results for the proton-Helium-3 system are consistent with a recent phase shift analysis and with model calculations. For neutron-triton, the results for the scattering lengths in both singlet and triplet channels are significantly smaller than suggested by R-matrix and partial-wave-analysis extractions from data. For a better understanding of this discrepancy, the sensitivity of the low-energy four-body scattering system to variations in the neutron-neutron and proton-proton two-nucleon scattering lengths is calculated. Induced by strong charge-symmetry-breaking contact interactions, this dependence is found insignificant. In contrast, a strong correlation between the neutron-triton scattering length and the triton binding energy analogous to the Phillips line is found.
NASA Astrophysics Data System (ADS)
Nedanovska, E.; Nersisyan, G.; Morgan, T. J.; Hüwel, L.; Murakami, T.; Lewis, C. L. S.; Riley, D.; Graham, W. G.
2015-01-01
We have used optical Rayleigh and Thomson scattering to investigate the expansion dynamics of laser induced plasma in atmospheric helium and to map its electron parameters both in time and space. The plasma is created using 9 ns duration, 140 mJ pulses from a Nd:YAG laser operating at 1064 nm, focused with a 10 cm focal length lens, and probed with 7 ns, 80 mJ, and 532 nm Nd:YAG laser pulses. Between 0.4 ?s and 22.5 ?s after breakdown, the electron density decreases from 3.3 × 1017 cm-3 to 9 × 1013 cm-3, while the temperature drops from 3.2 eV to 0.1 eV. Spatially resolved Thomson scattering data recorded up to 17.5 ?s reveal that during this time the laser induced plasma expands at a rate given by R ˜ t0.4 consistent with a non-radiative spherical blast wave. This data also indicate the development of a toroidal structure in the lateral profile of both electron temperature and density. Rayleigh scattering data show that the gas density decreases in the center of the expanding plasma with a central scattering peak reemerging after about 12 ?s. We have utilized a zero dimensional kinetic global model to identify the dominant particle species versus delay time and this indicates that metastable helium and the He2+ molecular ion play an important role.
Zero-energy neutron-triton and proton-Helium-3 scattering with \\eftnopi
Kirscher, Johannes
2011-01-01
Model-independent constraints for the neutron-triton and proton-Helium-3 scattering lengths are calculated with a leading-order interaction derived from an effective field theory without explicit pions. Using the singlet neutron-proton scattering length, the deuteron, and the triton binding energy as input, the predictions $\\ants=9.2\\pm2.6 $fm, $\\antt=7.6\\pm1.6 $fm, $\\aphes=3.6\\pm0.32 $fm, and $\\aphet=3.1\\pm 0.23 $fm are obtained. The calculations employ the resonating group method and include the Coulomb interaction when appropriate. The theoretical uncertainty is assessed via a variation of the regulator parameter of the short-distance interaction from $400 $MeV to $1.6 $GeV. The phase-shift and scattering-length results for the proton-Helium-3 system are consistent with a recent phase shift analysis and with model calculations. For neutron-triton, the results for the scattering lengths in both singlet and triplet channels are significantly smaller than suggested by R-matrix and partial-wave-analysis extrac...
Johnson, Alexis M; Lancaster, Diane K; Faust, Jennifer A; Hahn, Christine; Reznickova, Anna; Nathanson, Gilbert M
2014-11-01
Atomic and molecular solutes evaporate and dissolve by traversing an atomically thin boundary separating liquid and gas. Most solutes spend only short times in this interfacial region, making them difficult to observe. Experiments that monitor the velocities of evaporating species, however, can capture their final interactions with surface solvent molecules. We find that polarizable gases such as N2 and Ar evaporate from protic and hydrocarbon liquids with Maxwell-Boltzmann speed distributions. Surprisingly, the weakly interacting helium atom emerges from these liquids at high kinetic energies, exceeding the expected energy of evaporation from salty water by 70%. This super-Maxwellian evaporation implies in reverse that He atoms preferentially dissolve when they strike the surface at high energies, as if ballistically penetrating into the solvent. The evaporation energies increase with solvent surface tension, suggesting that He atoms require extra kinetic energy to navigate increasingly tortuous paths between surface molecules. PMID:26278769
Light scattering by ultracold atoms in an optical lattice
Stefan Rist; Chiara Menotti; Giovanna Morigi
2009-12-03
We investigate theoretically light scattering of photons by ultracold atoms in an optical lattice in the linear regime. A full quantum theory for the atom-photon interactions is developed as a function of the atomic state in the lattice along the Mott-insulator -- superfluid phase transition, and the photonic scattering cross section is evaluated as a function of the energy and of the direction of emission. The predictions of this theory are compared with the theoretical results of a recent work on Bragg scattering in time-of-flight measurements [A.M. Rey, {\\it et al.}, Phys. Rev. A {\\bf 72}, 023407 (2005)]. We show that, when performing Bragg spectroscopy with light scattering, the photon recoil gives rise to an additional atomic site to site hopping, which can interfere with ordinary tunneling of matter waves and can significantly affect the photonic scattering cross section.
Light scattering by ultracold atoms in an optical lattice
Rist, Stefan; Menotti, Chiara; Morigi, Giovanna
2010-01-15
We investigate theoretically light scattering of photons by ultracold atoms in an optical lattice in the linear regime. A full quantum theory for the atom-photon interactions is developed as a function of the atomic state in the lattice along the Mott-insulator-superfluid phase transition, and the photonic-scattering cross section is evaluated as a function of the energy and of the direction of emission. The predictions of this theory are compared with the theoretical results of a recent work on Bragg scattering in time-of-flight measurements [A.M. Rey et al., Phys. Rev. A 72, 023407 (2005)]. We show that, when performing Bragg spectroscopy with light scattering, the photon recoil gives rise to an additional atomic site-to-site hopping, which can interfere with ordinary tunneling of matter waves and can significantly affect the photonic-scattering cross section.
Helium in chirped laser fields as a time-asymmetric atomic switch
Kaprálová-Ž?ánská, Petra Ruth; Moiseyev, Nimrod
2014-07-07
Tuning the laser parameters exceptional points in the spectrum of the dressed laser helium atom are obtained. The weak linearly polarized laser couples the ground state and the doubly excited P-states of helium. We show here that for specific chirped laser pulses that encircle an exceptional point one can get the time-asymmetric phenomenon, where for a negative chirped laser pulse the ground state is transformed into the doubly excited auto-ionization state, while for a positive chirped laser pulse the resonance state is not populated and the neutral helium atoms remains in the ground state as the laser pulse is turned off. Moreover, we show that the results are very sensitive to the closed contour we choose. This time-asymmetric state exchange phenomenon can be considered as a time-asymmetric atomic switch. The optimal time-asymmetric switch is obtained when the closed loop that encircles the exceptional point is large, while for the smallest loops, the time-asymmetric phenomenon does not take place. A systematic way for studying the effect of the chosen closed contour that encircles the exceptional point on the time-asymmetric phenomenon is proposed.
CASCADE CALCULATION OF EXOTIC HELIUM ATOMS -- s-orbit vs. p-orbit absorption rates
NASA Astrophysics Data System (ADS)
Koike, T.; Akaishi, Y.
2000-09-01
We construct a new model for the Stark-mixing process of exotic helium atoms using the impact-parameter method, and compared it with a phenomenological one used so far (sliding transition model). It turns out that the sliding transition model is justified only for low-n states and largely overestimates the Stark-mixing transition rate at high-n states. As a result of the atomic-cascade calculation, the s-(p-)orbit absorption rates in our new model are considerably smaller (larger) than those in the phenomenological one, although both our new model and old one well reproduce the experimental x-ray yields.
Haberfehlner, Georg; Thaler, Philipp; Knez, Daniel; Volk, Alexander; Hofer, Ferdinand; Ernst, Wolfgang E.; Kothleitner, Gerald
2015-01-01
Structure, shape and composition are the basic parameters responsible for properties of nanoscale materials, distinguishing them from their bulk counterparts. To reveal these in three dimensions at the nanoscale, electron tomography is a powerful tool. Advancing electron tomography to atomic resolution in an aberration-corrected transmission electron microscope remains challenging and has been demonstrated only a few times using strong constraints or extensive filtering. Here we demonstrate atomic resolution electron tomography on silver/gold core/shell nanoclusters grown in superfluid helium nanodroplets. We reveal morphology and composition of a cluster identifying gold- and silver-rich regions in three dimensions and we estimate atomic positions without using any prior information and with minimal filtering. The ability to get full three-dimensional information down to the atomic scale allows understanding the growth and deposition process of the nanoclusters and demonstrates an approach that may be generally applicable to all types of nanoscale materials. PMID:26508471
Haberfehlner, Georg; Thaler, Philipp; Knez, Daniel; Volk, Alexander; Hofer, Ferdinand; Ernst, Wolfgang E; Kothleitner, Gerald
2015-01-01
Structure, shape and composition are the basic parameters responsible for properties of nanoscale materials, distinguishing them from their bulk counterparts. To reveal these in three dimensions at the nanoscale, electron tomography is a powerful tool. Advancing electron tomography to atomic resolution in an aberration-corrected transmission electron microscope remains challenging and has been demonstrated only a few times using strong constraints or extensive filtering. Here we demonstrate atomic resolution electron tomography on silver/gold core/shell nanoclusters grown in superfluid helium nanodroplets. We reveal morphology and composition of a cluster identifying gold- and silver-rich regions in three dimensions and we estimate atomic positions without using any prior information and with minimal filtering. The ability to get full three-dimensional information down to the atomic scale allows understanding the growth and deposition process of the nanoclusters and demonstrates an approach that may be generally applicable to all types of nanoscale materials. PMID:26508471
Hauser, Andreas W; Volk, Alexander; Thaler, Philipp; Ernst, Wolfgang E
2015-04-28
Collision times for the coinage metal atoms Cu, Ag and Au in He-droplets are derived from helium density functional theory and molecular dynamics simulations. The strength of the attractive interaction between the metal atoms turns out to be less important than the mass of the propagating metal atoms. Even for small droplets consisting of a few thousand helium atoms, the collision times are shortest for Cu, followed by Ag and Au, despite the higher binding energy of Au2 compared to Cu2. PMID:25812719
Volk, Alexander; Thaler, Philipp
2015-01-01
Collision times for the coinage metal atoms Cu, Ag and Au in He-droplets are derived from helium density functional theory and molecular dynamics simulations. The strength of the attractive interaction between the metal atoms turns out to be less important than the mass of the propagating metal atoms. Even for small droplets consisting of a few thousand helium atoms, the collision times are shortest for Cu, followed by Ag and Au, despite the higher binding energy of Au2 compared to Cu2. PMID:25812719
NASA Astrophysics Data System (ADS)
Oro, David Michael
1994-01-01
For several years Metastable Atom Deexcitation Spectroscopy (MDS) has been employed as a probe of surface electronic structure offering unparalleled surface specificity. In MDS a thermal-energy beam of rare-gas metastable atoms is directed at the surface under study, and the energy distribution of electrons ejected as a result of metastable atom deexcitation is measured. However, correct interpretation of the data requires detailed knowledge of the dynamics of the deexcitation process. In the present work spin -labeling techniques, specifically the use of electron-spin -polarized metastable He(2^3S) atoms, coupled with spin analysis of the ejected electrons, are used to probe the dynamics of He(2^3S) deexcitation at a variety of surfaces. Such measurements, coupled with studies of the deexcitation of He(2 ^1S) and He(2^3P) atoms at Cu(100) and Au(100) show that each species deexcites exclusively through resonance ionization followed by Auger neutralization. The data also provide the first direct confirmation of spin correlation in the Auger neutralization of ions outside a paramagnetic surface. Two proposed models for spin correlation are discussed and potential experimental tests for distinguishing between them are suggested. Studies of SPMDS at surfaces comprising layers of Ar or Xe atoms frozen onto a cryogenically cooled substrate are described and exhibit behavior similar to that observed in gas phase Penning ionization studies indicating that ejection results, in part, from surface Penning ionization (SPI). For Xe, however, additional features are observed and can be attributed to resonance ionization of the incident excited atoms followed by neutralization of the resulting He^+ ions through an interaction involving neighboring Xe atoms in the film. These results provide a rare example of a surface at which the rates for resonance ionization and Auger deexcitation are comparable. Also, the data show that the electron yield from both films is substantially higher than that from atomically clean metal surfaces. Potential experimental applications of the large spin correlation in He(2^3S) deexcitation at Cu and Au, and of deexcitation at Xe(100) and Ar(100) films are discussed.
Scattering in Flatland: Efficient Representations via Wave Atoms
Demanet, Laurent
This paper presents a numerical compression strategy for the boundary integral equation of acoustic scattering in two dimensions. These equations have oscillatory kernels that we represent in a basis of wave atoms, and ...
Symmetry descriptors for Si wafer characterisation for scanning helium atomic beam microscopy mirror
NASA Astrophysics Data System (ADS)
Galas, J.; Litwin, D.; Sitarek, S.; Surma, B.; Piatkowski, B.
2007-05-01
The Scanning Helium Atom Microscope is a new technique currently under development which has potential to become a powerful tool in life science, material engineering and other fields of science. One of the most important components of the microscope is a specially shaped mirror that focuses the helium atom beam onto a sample's surface. The mirror quality affects the diameter of the focused beam and consequently the microscope resolution. Thus, the mirror surface roughness and its shape must be controlled accurately. The mirror is formed from a very thin Si crystal membrane that is deformed under a precise electric field. The Si membrane production process is a complex issue and it is very difficult to obtain membranes of uniform thickness: some remaining thickness variations are always present. These variations affect the mirror shape generated by the electrostatic field and prevent optimal focusing of the helium beam. Here, our aim is to characterize the typical thickness variations observed in membranes. We find that whilst the perfectly symmetric membrane is very difficult to produce, it is possible to define criteria for the selection of the best subset of membranes from a larger production run. Our characterization and selection via "symmetry descriptors" will ultimately diminish aberrations in He focusing. In the paper, the "symmetry descriptors" will be defined, rationalised and discussed in detail.
The role of projectile double scattering in positron atom collisions
NASA Astrophysics Data System (ADS)
T?kési, K.
2007-03-01
We present the doubly differential cross sections of the ionization for positron and hydrogen atom collisions at 50 eV impact energy. We treat the collision problem in the framework of the full and reduced three-body classical trajectory Monte Carlo (CTMC) model. The role of projectile double scattering in light projectile and atom collisions are discussed.
Niemi, K.; Reuter, S.; Graham, L. M.; Waskoenig, J.; Gans, T.
2009-10-12
Absolute atomic oxygen ground state densities in a radio-frequency driven atmospheric pressure plasma jet, operated in a helium-oxygen mixture, are determined using diagnostic based modeling. One-dimensional numerical simulations of the electron dynamics are combined with time integrated optical emission spectroscopy. The population dynamics of the upper O 3p {sup 3}P ({lambda}=844 nm) atomic oxygen state is governed by direct electron impact excitation, dissociative excitation, radiation losses, and collisional induced quenching. Absolute values for atomic oxygen densities are obtained through comparison with the upper Ar 2p{sub 1} ({lambda}=750.4 nm) state. Results for spatial profiles and power variations are presented and show excellent quantitative agreement with independent two-photon laser-induced fluorescence measurements.
Millimeter-Wave Spectra of Carbon Monoxide Solvated with Helium Atoms
NASA Astrophysics Data System (ADS)
Surin, L. A.; Giesen, T. F.; Schlemmer, S.; Potapov, A. V.; Dumesh, B. S.
2009-06-01
Millimeter-wave spectra of He_N-CO (^{12}C^{16}O, ^{13}C^{16}O, ^{12}C^{18}O, ^{13}C^{18}O) clusters with N up to 10, produced in a molecular expansion, were observed using intracavity OROTRON jet spectrometer in the frequency range of 110-150 GHz. The R(0) transitions were detected, which correspond to the known b-type (K = 1 - 0) R(0) lines of the binary system, He_1-CO. Further, the a-type (K = 0 - 0) rotational transitions of He_N-CO (N = 7, 8) in the frequency range of 20-40 GHz were measured combining OROTRON spectrometer with a double resonance technique. The isotopic shifts of the cluster transitions show remarkably smooth behavior with N from 1 to 6 and become rather scattering for N ? 7. The dependence of the rotational constant (cluster moment of inertia) and of the shift of the CO fundamental vibration on the number of He atoms in cluster were obtained for He_N-CO isotopologues from the analysis of their infrared spectra and very recent microwave data for the normal He_N-^{12}C^{16}O isotopologue. This study explores the microscopic evolution of superfluidity, which becomes apparent even in such small clusters as He_4-CO. The obtained results are compared with those from recent quantum Monte-Carlo calculations. and used to further interpret recent infrared measurements of CO in helium nanodroplets. J. Tang, A. R. W. McKellar, J. Chem. Phys. 119, 763 (2003) A. R. W. McKellar, J. Chem. Phys. 121, 6868 (2004) A. R. W. McKellar, J. Chem. Phys. 125, 164328 (2006). L. A. Surin, A. V. Potapov, B. S. Dumesh, S. Schlemmer, Y. Xu, P. L. Raston, and W. Jäger, Phys. Rev. Lett. 101, 233401 (2008) T. Škrbi?, S. Moroni, and S. Baroni, J. Phys. Chem. A 111, 7640 (2007). K. von Haeften, S. Rudolph, I. Simanovski, M. Havenith, R. E. Zillich, and K. B. Whaley, Phys. Rev. B 73, 054502 (2006).
Dynamics of entanglement between two atomic samples with spontaneous scattering
Di Lisi, Antonio; De Siena, Silvio; Illuminati, Fabrizio
2004-07-01
We investigate the effects of spontaneous scattering on the evolution of entanglement of two atomic samples, probed by phase-shift measurements on optical beams interacting with both samples. We develop a formalism of conditional quantum evolutions and present a wave function analysis implemented in numerical simulations of the state vector dynamics. This method allows us to track the evolution of entanglement and to compare it with the predictions obtained when spontaneous scattering is neglected. We provide numerical evidence that the interferometric scheme to entangle atomic samples is only marginally affected by the presence of spontaneous scattering and should thus be robust even in more realistic situations.
Theory of direct scattering of neutral and charged atoms
NASA Technical Reports Server (NTRS)
Franco, V.
1979-01-01
The theory for direct elastic and inelastic collisions between composite atomic systems formulated within the framework of the Glauber approximation is presented. It is shown that the phase-shift function is the sum of a point Coulomb contribution and of an expression in terms of the known electron-hydrogen-atom and proton-hydrogen-atom phase shift function. The scattering amplitude is reexpressed, the pure Coulomb scattering in the case of elastic collisions between ions is isolated, and the exact optical profile function is approximated by a first-order expansion in Glauber theory which takes into account some multiple collisions. The approximate optical profile function terms corresponding to interactions involving one and two electrons are obtained in forms of Meijer G functions and as a one-dimensional integral, and for collisions involving one or two neutral atoms, the scattering amplitude is further reduced to a simple closed-form expression.
NASA Technical Reports Server (NTRS)
Liu, S. M.; Knuth, E. L.
1976-01-01
Three major areas were experimentally studied: (1) energy transfer in collisions of satellite-speed (700 m/sec) helium atoms with a cleaned satellite-type aluminum surface was investigated using the molecular-beam technique. Spatial and energy distributions of reflected helium atoms were measured and analyzed, (2) The gross accommodation coefficient for a satellite-speed (7000 m/sec) helium beam entering a 2-inch-diameter aluminum spherical cavity was determined by measuring the exit velocity distribution of the leaving helium atoms using a metastable time-of-flight method. Results indicate that the 7000-m/sec satellite-speed helium atoms entering the cavity gain full accommodation with the room-temperature inner surface of the sphere through a large number of collisions before leaving the spherical cavity; and (3) the feasibility of producing a satellite-speed atomic hydrogen beam by arc-heating, for use in studies of interactions of satellite-surfaces with hydrogen atoms under laboratory conditions, was investigated. It was found that a stable arc-heated molecular hydrogen beam can be obtained using the arc-heater, and that a partially dissociated hydrogen beam can be produced. Photographs of laboratory equipment are shown.
Atomic Scattering Polarization. Observations, Modeling, Predictions
NASA Astrophysics Data System (ADS)
Bueno, J. Trujillo; Alemán, T. Del Pino; Belluzzi, L.
2015-10-01
This paper highlights very recent advances concerning the identification of new mechanisms that introduce polarization in spectral lines, which turn out to be key for understanding some of the most enigmatic scattering polarization signals of the solar visible spectrum. We also show a radiative transfer prediction on the scattering polarization pattern across the Mg ii h & k lines, whose radiation can only be observed from space.
A discrete variable representation for electron-hydrogen atom scattering
Gaucher, L.F.
1994-08-01
A discrete variable representation (DVR) suitable for treating the quantum scattering of a low energy electron from a hydrogen atom is presented. The benefits of DVR techniques (e.g. the removal of the requirement of calculating multidimensional potential energy matrix elements and the availability of iterative sparse matrix diagonalization/inversion algorithms) have for many years been applied successfully to studies of quantum molecular scattering. Unfortunately, the presence of a Coulomb singularity at the electrically unshielded center of a hydrogen atom requires high radial grid point densities in this region of the scattering coordinate, while the presence of finite kinetic energy in the asymptotic scattering electron also requires a sufficiently large radial grid point density at moderate distances from the nucleus. The constraints imposed by these two length scales have made application of current DVR methods to this scattering event difficult.
Ultra-precise single-ion atomic mass measurements on deuterium and helium-3
NASA Astrophysics Data System (ADS)
Zafonte, S. L.; Van Dyck, R. S., Jr.
2015-04-01
The former University of Washington Penning Trap Mass Spectrometer (UW-PTMS), now located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, was used in the decade before the move to determine new values for the deuteron atomic mass, M (2H+) = 2.013?553 212?745(40) u, and the deuterium atomic mass, M (2H) = 2.014?101 778?052(40) u, both of which are now more than an order-of-magnitude more accurate than the previous best 1994-MIT measurements of these quantities. The new value for the deuteron’s mass can then be used with the accepted 2010-CODATA proton mass and the most recent 1999-measurement of the 2.2 MeV gamma-ray binding energy of the deuteron to refine the neutron’s mass to mn = 1.008?664 916?018(435) u which has about half the uncertainty relative to the value computed using that previous 1994-MIT deuterium measurement. As a result, further improvements of mn must now come from a more accurate determination of the wavelength of this gamma ray. In this same period of time, this spectrometer has also been used to determine new values for the helion atomic mass, M (3He2+) = 3.014?932 246?668(43) u, and the neutral helium-3 atomic mass, M (3He) = 3.016?029 321?675(43) u, which are both about 60 times more accurate than the 2006-SMILETRAP measurements, but disagree with the 4.4-times less-accurate 2015-Florida-State measurements by 0.76 nu. It is expected that these helium-3 results will be used in the future 3H/3He mass ratio (to be determined by the Heidelberg, Germany version of the old UW-PTMS) in order to generate a more accurate value for the tritium atomic mass.
NASA Technical Reports Server (NTRS)
Souder, P. A.; Casperson, D. E.; Crane, T. W.; Hughes, V. W.; Lu, D. C.; Yam, M. H.; Orth, H.; Reist, H. W.; Zu Putlitz, G.
1975-01-01
Experiments are described in which it proved possible to form the muonic helium atom by stopping polarized negative muons in a helium gas with a 2% xenon admixture at a pressure of 14 atm. The observed Larmor precession amplitudes are plotted against the gyromagnetic ratio for both muons and antimuons stopped in He + 2% Xe. In addition, a non-zero residual polarization of 0.06 plus or minus 0.01 was measured for muons stopped in pure helium gas, which corresponds to a depolarization factor of 18 plus or minus 3.
Analytical evaluation of atomic form factors: Application to Rayleigh scattering
NASA Astrophysics Data System (ADS)
Safari, L.; Santos, J. P.; Amaro, P.; Jänkälä, K.; Fratini, F.
2015-05-01
Atomic form factors are widely used for the characterization of targets and specimens, from crystallography to biology. By using recent mathematical results, here we derive an analytical expression for the atomic form factor within the independent particle model constructed from nonrelativistic screened hydrogenic wave functions. The range of validity of this analytical expression is checked by comparing the analytically obtained form factors with the ones obtained within the Hartee-Fock method. As an example, we apply our analytical expression for the atomic form factor to evaluate the differential cross section for Rayleigh scattering off neutral atoms.
Quantum interference in attosecond transient absorption of laser-dressed helium atoms
Shaohao Chen; Mengxi Wu; Mette B. Gaarde; Kenneth J. Schafer
2013-01-04
We calculate the transient absorption of an isolated attosecond pulse by helium atoms subject to a delayed infrared (\\ir) laser pulse. With the central frequency of the broad attosecond spectrum near the ionization threshold, the absorption spectrum is strongly modulated at the sub-\\ir-cycle level. Given that the absorption spectrum results from a time-integrated measurement, we investigate the extent to which the delay-dependence of the absorption yields information about the attosecond dynamics of the atom-field energy exchange. We find two configurations in which this is possible. The first involves multi photon transitions between bound states that result in interference between different excitation pathways. The other involves the modification of the bound state absorption lines by the IR field, which we find can result in a sub-cycle time dependence only when ionization limits the duration of the strong field interaction.
Wave functions and two-electron probability distributions of the Hooke's-law atom and helium
O'Neill, Darragh P.; Gill, Peter M. W.
2003-08-01
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.
Inelastic scattering of hydroxyl radicals with helium and argon by velocity-map imaging.
Sarma, Gautam; Marinakis, Sarantos; ter Meulen, J J; Parker, David H; McKendrick, Kenneth G
2012-12-01
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
Hernando, Alberto; Beswick, J. Alberto; Halberstadt, Nadine
2013-12-14
The theory of photofragments angular momentum polarization is applied to the photodetachment of an electronically excited alkali atom from a helium nanocluster (N = 200). The alignment of the electronic angular momentum of the bare excited alkali atoms produced is calculated quantum mechanically by solving the excited states coupled equations with potentials determined by density functional theory (DFT). Pronounced oscillations as a function of excitation energy are predicted for the case of Na@(He){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.
2014-01-01
The interaction of an electronically excited, single chromium (Cr) atom with superfluid helium nanodroplets of various size (10 to 2000 helium (He) atoms) is studied with helium density functional theory. Solvation energies and pseudo-diatomic potential energy surfaces are determined for Cr in its ground state as well as in the y7P, a5S, and y5P excited states. The necessary Cr–He pair potentials are calculated by standard methods of molecular orbital-based electronic structure theory. In its electronic ground state the Cr atom is found to be fully submerged in the droplet. A solvation shell structure is derived from fluctuations in the radial helium density. Electronic excitations of an embedded Cr atom are simulated by confronting the relaxed helium density (?He), obtained for Cr in the ground state, with interaction pair potentials of excited states. The resulting energy shifts for the transitions z7P ? a7S, y7P ? a7S, z5P ? a5S, and y5P ? a5S are compared to recent fluorescence and photoionization experiments. PMID:24906160
Modified atomic decay rate near absorptive scatterers at finite temperature
NASA Astrophysics Data System (ADS)
Suttorp, L. G.; van Wonderen, A. J.
2015-07-01
The change in the decay rate of an excited atom that is brought about by extinction and thermal-radiation effects in a nearby dielectric medium is determined from a quantum-mechanical model. The medium is a collection of randomly distributed thermally excited spherical scatterers with absorptive properties. The modification of the decay rate is described by a set of correction functions for which analytical expressions are obtained as sums over contributions from the multipole moments of the scatterers. The results for the modified decay rate as a function of the distance between the excited atom and the dielectric medium show the influence of absorption, scattering and thermal-radiation processes. Some of these processes are found to be mutually counteractive. The changes in the decay rate are compared to those following from an effective-medium theory in which the discrete scatterers are replaced by a continuum.
Observation of cooperative Mie scattering from an ultracold atomic cloud
Bender, H.; Stehle, C.; Slama, S.; Zimmermann, C.; Kaiser, R.; Piovella, N.; Courteille, Ph. W.
2010-07-15
Scattering of light at a distribution of scatterers is an intrinsically cooperative process, which means that the scattering rate and the angular distribution of the scattered light are essentially governed by bulk properties of the distribution, such as its size, shape, and density, although local disorder and density fluctuations may have an important impact on the cooperativity. Via measurements of the radiation pressure force exerted by a far-detuned laser beam on a very small and dense cloud of ultracold atoms, we are able to identify the respective roles of superradiant acceleration of the scattering rate and of Mie scattering in the cooperative process. They lead, respectively, to a suppression or an enhancement of the radiation pressure force. We observe a maximum in the radiation pressure force as a function of the phase shift induced in the incident laser beam by the cloud's refractive index. The maximum marks the borderline of the validity of the Rayleigh-Debye-Gans approximation from a regime, where Mie scattering is more complex. Our observations thus help to clarify the intricate relationship between Rayleigh scattering of light at a coarse-grained ensemble of individual scatterers and Mie scattering at the bulk density distribution.
Elastic scattering of electrons from Rb, Cs and Fr atoms
NASA Astrophysics Data System (ADS)
Gangwar, R. K.; Tripathi, A. N.; Sharma, L.; Srivastava, R.
2010-04-01
Differential, integrated elastic, momentum-transfer and total cross sections as well as differential S, T and U spin parameters for scattering of electrons from rubidium, caesium and francium atoms in the incident energy range up to 300 eV are calculated using a relativistic Dirac equation. The projectile electron-target atom interaction is represented by both real and complex parameter-free optical potentials for obtaining the solution of a Dirac equation for scattered electrons. The Dirac-Fock wavefunctions have been used to represent the Rb, Cs and Fr target atoms. The results of differential cross sections and spin asymmetry parameter S for e-Rb and e-Cs have been compared with the available experimental and theoretical results. Detailed results are reported for the elastic scattering of electrons from the ground states of a francium atom for the first time in the wide range of incident electron energies. The results of electron-Fr elastic scattering show the similar features to those obtained in the case of e-Rb and e-Cs elastic scattering.
Temperature and Atomic Oxygen Effects on Helium Leak Rates of a Candidate Main Interface Seal
NASA Technical Reports Server (NTRS)
Penney, Nicholas; Wasowski, Janice L.; Daniels, Christopher C.
2011-01-01
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.
Determination of $??$ scattering lengths from measurement of $?^+?^-$ atom lifetime
B. Adeva; L. Afanasyev; M. Benayoun; A. Benelli; Z. Berka; V. Brekhovskikh; G. Caragheorgheopol; T. Cechak; M. Chiba; P. V. Chliapnikov; C. Ciocarlan; S. Constantinescu; S. Costantini; C. Curceanu; P. Doskarova; D. Dreossi; D. Drijard; A. Dudarev; M. Ferro-Luzzi; J. L. Fungueiriño Pazos; M. Gallas Torreira; J. Gerndt; P. Gianotti; D. Goldin; F. Gomez; A. Gorin; O. Gorchakov; C. Guaraldo; M. Gugiu; M. Hansroul; Z. Hons; R. Hosek; M. Iliescu; V. Karpukhin; J. Kluson; M. Kobayashi; P. Kokkas; V. Komarov; V. Kruglov; L. Kruglova; A. Kulikov; A. Kuptsov; K. I. Kuroda; A. Lamberto; A. Lanaro; V. Lapshin; R. Lednicky; P. Leruste; P. Levi Sandri; A. Lopez Aguera; V. Lucherini; T. Maki; I. Manuilov; J. Marin; J. L. Narjoux; L. Nemenov; M. Nikitin; T. Nunez Pardo; K. Okada; V. Olchevskii; A. Pazos; M. Pentia; A. Penzo; J. M. Perreau; M. Plo; T. Ponta; G. F. Rappazzo; A. Riazantsev; J. M. Rodriguez; A. Rodriguez Fernandez; A. Romero Vidal; V. M. Ronjin; V. Rykalin; J. Saborido; C. Santamarina; J. Schacher; C. Schuetz; A. Sidorov; J. Smolik; F. Takeutchi; A. Tarasov; L. Tauscher; M. J. Tobar; T. Trojek; S. Trusov; V. Utkin; O. Vázquez Doce; S. Vlachos; O. Voskresenskaya; T. Vrba; C. Willmott; V. Yazkov; Y. Yoshimura; M. Zhabitsky; P. Zrelov
2011-10-03
The DIRAC experiment at CERN has achieved a sizeable production of $\\pi^+\\pi^-$ atoms and has significantly improved the precision on its lifetime determination. From a sample of 21227 atomic pairs, a 4% measurement of the S-wave $\\pi\\pi$ scattering length difference $|a_0-a_2| = (.0.2533^{+0.0080}_{-0.0078}|_\\mathrm{stat}.{}^{+0.0078}_{-0.0073}|_\\mathrm{syst})M_{\\pi^+}^{-1}$ has been attained, providing an important test of Chiral Perturbation Theory.
Probe Scattering by Fluctuating Multi-Atom Ensembles in Optical Lattices
NASA Astrophysics Data System (ADS)
Blaauboer, M.; Kurizki, G.; Akulin, V. M.
We investigate probe scattering by fluctuating ensembles of atoms trapped in optical lattices: weak scattering by effectively random atomic density distributions and multiple scattering by arbitrary atomic distributions. Both regimes are predicted to exhibit a universal semicircular scattering lineshape for large density fluctuations, which depend on temperature and quantum statistics.
2013-01-01
Helium nanodroplets doped with argon, krypton, or xenon are ionized by electrons and analyzed in a mass spectrometer. HenNgx+ ions containing up to seven noble gas (Ng) atoms and dozens of helium atoms are identified; the high resolution of the mass spectrometer combined with advanced data analysis make it possible to unscramble contributions from isotopologues that have the same nominal mass but different numbers of helium or Ng atoms, such as the magic He2084Kr2+ and the isobaric, nonmagic He4184Kr+. Anomalies in these ion abundances reveal particularly stable ions; several intriguing patterns emerge. Perhaps most astounding are the results for HenAr+, which show evidence for three distinct, solid-like solvation shells containing 12, 20, and 12 helium atoms. This observation runs counter to the common notion that only the first solvation shell is solid-like but agrees with calculations by Galli et al. for HenNa+ [J. Phys. Chem. A2011, 115, 730021568337] that reveal three shells of icosahedral symmetry. HenArx+ (2 ? x ? 7) ions appear to be especially stable if they contain a total of n + x = 19 atoms. A sequence of anomalies in the abundance distribution of HenKrx+ suggests that rings of six helium atoms are inserted into the solvation shell each time a krypton atom is added to the ionic core, from Kr+ to Kr3+. Previously reported strong anomalies at He12Kr2+ and He12Kr3+ [KimJ. H.; et al. J. Chem. Phys.2006, 124, 21430116774401] are attributed to a contamination. Only minor local anomalies appear in the distributions of HenXex+ (x ? 3). The distributions of HenKr+ and HenXe+ show strikingly similar, broad features that are absent from the distribution of HenAr+; differences are tentatively ascribed to the very different fragmentation dynamics of these ions. PMID:24128371
Bartl, Peter; Leidlmair, Christian; Denifl, Stephan; Scheier, Paul; Echt, Olof
2014-09-18
Helium nanodroplets doped with argon, krypton, or xenon are ionized by electrons and analyzed in a mass spectrometer. HenNgx(+) ions containing up to seven noble gas (Ng) atoms and dozens of helium atoms are identified; the high resolution of the mass spectrometer combined with advanced data analysis make it possible to unscramble contributions from isotopologues that have the same nominal mass but different numbers of helium or Ng atoms, such as the magic He20(84)Kr2(+) and the isobaric, nonmagic He41(84)Kr(+). Anomalies in these ion abundances reveal particularly stable ions; several intriguing patterns emerge. Perhaps most astounding are the results for HenAr(+), which show evidence for three distinct, solid-like solvation shells containing 12, 20, and 12 helium atoms. This observation runs counter to the common notion that only the first solvation shell is solid-like but agrees with calculations by Galli et al. for HenNa(+) [J. Phys. Chem. A 2011, 115, 7300] that reveal three shells of icosahedral symmetry. HenArx(+) (2 ? x ? 7) ions appear to be especially stable if they contain a total of n + x = 19 atoms. A sequence of anomalies in the abundance distribution of HenKrx(+) suggests that rings of six helium atoms are inserted into the solvation shell each time a krypton atom is added to the ionic core, from Kr(+) to Kr3(+). Previously reported strong anomalies at He12Kr2(+) and He12Kr3(+) [Kim , J. H.; et al. J. Chem. Phys. 2006, 124, 214301] are attributed to a contamination. Only minor local anomalies appear in the distributions of HenXex(+) (x ? 3). The distributions of HenKr(+) and HenXe(+) show strikingly similar, broad features that are absent from the distribution of HenAr(+); differences are tentatively ascribed to the very different fragmentation dynamics of these ions. PMID:24128371
Fluxes of energetic neutral helium atoms from the heliosheath and the IBEX Ribbon
NASA Astrophysics Data System (ADS)
Swaczyna, Pawel; Grzedzielski, Stan; Bzowski, Maciej
2014-05-01
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.
Generalized pseudopotential approach for electron-atom scattering.
NASA Technical Reports Server (NTRS)
Zarlingo, D. G.; Ishihara, T.; Poe, R. T.
1972-01-01
A generalized many-electron pseudopotential approach is presented for electron-neutral-atom scattering problems. A calculation based on this formulation is carried out for the singlet s-wave and p-wave electron-hydrogen phase shifts with excellent results. We compare the method with other approaches as well as discuss its applications for inelastic and rearrangement collision problems.
Learning Approach on the Ground State Energy Calculation of Helium Atom
Shah, Syed Naseem Hussain
2010-07-28
This research investigated the role of learning approach on the ground state energy calculation of Helium atom in improving the concepts of science teachers at university level. As the exact solution of several particles is not possible here we used approximation methods. Using this method one can understand easily the calculation of ground state energy of any given function. Variation Method is one of the most useful approximation methods in estimating the energy eigen values of the ground state and the first few excited states of a system, which we only have a qualitative idea about the wave function.The objective of this approach is to introduce and involve university teacher in new research, to improve their class room practices and to enable teachers to foster critical thinking in students.
NASA Astrophysics Data System (ADS)
Urabe, Keiichiro; Muneoka, Hitoshi; Stauss, Sven; Sakai, Osamu; Terashima, Kazuo
2015-10-01
Cryoplasmas, which are plasmas whose gas temperatures are below room temperature (RT), have shown dynamic changes in their physical and chemical characteristics when the gas temperature in the plasmas (Tgp) was decreased from RT. In this study, we measured the temporal behavior of helium metastable (Hem) atoms generated in a parallel-plate dielectric barrier discharge at ambient gas temperatures (Tga) of 300, 100, and 14 K and with a gas density similar to atmospheric conditions by laser absorption spectroscopy. The increments of Tgp to Tga were less than 20 K. We found from the results that the Hem lifetime and maximum density become longer and larger over one order of magnitude for lower Tga. The reasons for the long Hem lifetime at low Tga are decreases in the rate coefficients of three-body Hem quenching reactions and in the amounts of molecular impurities with boiling points higher than that of He.
Speckle intensity correlations of photons scattered by cold atoms
Müller, Cord A; Miniatura, Christian
2015-01-01
The irradiation of a dilute cloud of cold atoms with a coherent light field produces a random intensity distribution known as laser speckle. Its statistical fluctuations contain information about the mesoscopic scattering processes at work inside the disordered medium. Following up on earlier work by Assaf and Akkermans [Phys.\\ Rev.\\ Lett.\\ \\textbf{98}, 083601 (2007)], we analyze how static speckle intensity correlations are affected by an internal Zeeman degeneracy of the scattering atoms. It is proven on general grounds that the speckle correlations cannot exceed the standard Rayleigh law. On the contrary, because which-path information is stored in the internal atomic states, the intensity correlations suffer from strong decoherence and become exponentially small in the diffusive regime applicable to an optically thick cloud.
Peach, Gillian; Whittingham, Ian B.; Beams, Timothy J.
2004-09-01
We analyze a system of two colliding ultracold atoms under strong harmonic confinement from the viewpoint of quantum defect theory and formulate a generalized self-consistent method for determining the allowed energies. We also present two highly efficient computational methods for determining the bound state energies and eigenfunctions of such systems. The perturbed harmonic oscillator problem is characterized by a long asymptotic region beyond the effective range of the interatomic potential. The first method, which is based on quantum defect theory and is an adaptation of a technique developed by one of the authors (G.P.) for highly excited states in a modified Coulomb potential, is very efficient for integrating through this outer region. The second method is a direct numerical solution of the radial Schroedinger equation using a discrete variable representation of the kinetic energy operator and a scaled radial coordinate grid. The methods are applied to the case of trapped spin-polarized metastable helium atoms. The calculated eigenvalues agree very closely for the two methods, and with the eigenvalues computed using the generalized self-consistent method.
In-Situ Lattice Polarization Measurement by Atomic Wave Scattering
NASA Astrophysics Data System (ADS)
Schmidt, Felix; Bauer, Michael; Kindermann, Farina; Lausch, Tobias; Mayer, Daniel; Widera, Artur
2015-05-01
Optical dipole traps and lattices have become indispensable tools in atomic physics and atom optics. Especially the accurate alignment of the beam polarization is crucial, because a deviation from purely linear polarization will result in state dependent AC-stark vector light shifts, which are proportional to the atoms' magnetic mF substates. Such shifts can be either utilized as a tool for state dependent atomic transport and the creation of artificial gauge fields, or, in contrast, could cause unwanted dephasing in quantum information processing and spectroscopic experiments. Here, we present an in-situ measurement method of an optical lattice's polarization purity by employing the Kapitza-Dirac effect - the scattering of atoms by a standing light wave: We create a Rubidium-87 (Rb) BEC and shine in an optical lattice at 790 nm that is tuned in between the D1 and D2 lines of Rb. At this wavelength, the scalar dipole potentials of both lines counteract and ideally cancel out, yielding a high sensitivity to vector light shifts for different mF states. By analysing the scattering of Rb atoms in the residual potential for different mF states, we can extract the lattice polarization with high accuracy below 10-3.
Cs atoms on helium nanodroplets and the immersion of Cs{sup +} into the nanodroplet
Theisen, Moritz; Lackner, Florian; Ernst, Wolfgang E.
2011-08-21
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.
Miyake, Hirokazu
We have observed Bragg scattering of photons from quantum degenerate 87Rb atoms in a three-dimensional optical lattice. Bragg scattered light directly probes the microscopic crystal structure and atomic wave function whose ...
Phonon dispersion curves of the Ge(111)-c(2×8) surface determined by He atom scattering
NASA Astrophysics Data System (ADS)
Lobo, J.; Farías, D.; Hulpke, E.; Toennies, J. P.; Michel, E. G.
2006-07-01
The phonon dispersion curves of the Ge(111)-c(2×8) surface have been measured using high-resolution helium atom scattering. Experimental data points were obtained along two high-symmetry directions of the surface at room temperature and at 170K . The main features are explained by a (2×2) geometrical backfolding of the Rayleigh wave. The experimental phonon density of states obtained is qualitatively similar to the phonon density of states of the Si(111)-(7×7) surface.
NASA Astrophysics Data System (ADS)
Agueny, Hicham
2015-07-01
We present results for single and double electron captures in intermediate energies H+ and 2H+ projectiles colliding with a helium target. The processes under investigations are treated using a nonperturbative semiclassical approach in combination with Eikonal approximation to calculate the scattering differential cross sections. The latter reveals pronounced minima and maxima in the scattering angles, in excellent agreement with the recent experimental data. It turns out that the present structure depends strongly on the projectile energy and shows only slight variations with different capture channels. The observed structure demonstrates the analogy of atomic de Broglie's matter-wave scattering with ?d B=1.3 -3.2 ×10-3 a.u. and Fraunhofer-type diffraction of light waves.
Recent progress in electron scattering from atoms and molecules
Brunger, M. J.; Buckman, S. J.; Sullivan, J. P.; Palihawadana, P.; Jones, D. B.; Chiari, L.; Pettifer, Z.; Silva, G. B. da; Lopes, M. C. A.; Duque, H. V.; Masin, Z.; Gorfinkiel, J. D.; Garcia, G.; Hoshino, M.; Tanaka, H.; Limão-Vieira, P.
2014-03-05
We present and discuss recent results, both experimental and theoretical (where possible), for electron impact excitation of the 3s[3/2 ]{sub 1} and 3s?[1/2 ]{sub 1} electronic states in neon, elastic electron scattering from the structurally similar molecules benzene, pyrazine, and 1,4-dioxane and excitation of the electronic states of the important bio-molecule analogue ?-tetrahydrofurfuryl alcohol. While comparison between theoretical and experimental results suggests that benchmarked cross sections for electron scattering from atoms is feasible in the near-term, significant further theoretical development for electron-molecule collisions, particularly in respect to discrete excitation processes, is still required.
Recent progress in electron scattering from atoms and molecules
NASA Astrophysics Data System (ADS)
Brunger, M. J.; Buckman, S. J.; Sullivan, J. P.; Palihawadana, P.; Jones, D. B.; Chiari, L.; Pettifer, Z.; da Silva, G. B.; Lopes, M. C. A.; Duque, H. V.; Masin, Z.; Gorfinkiel, J. D.; Garcia, G.; Hoshino, M.; Tanaka, H.; Limão-Vieira, P.
2014-03-01
We present and discuss recent results, both experimental and theoretical (where possible), for electron impact excitation of the 3s[3/2]1 and 3s'[1/2]1 electronic states in neon, elastic electron scattering from the structurally similar molecules benzene, pyrazine, and 1,4-dioxane and excitation of the electronic states of the important bio-molecule analogue ?-tetrahydrofurfuryl alcohol. While comparison between theoretical and experimental results suggests that benchmarked cross sections for electron scattering from atoms is feasible in the near-term, significant further theoretical development for electron-molecule collisions, particularly in respect to discrete excitation processes, is still required.
Electron scattering by laser-excited barium atoms
NASA Technical Reports Server (NTRS)
Register, D. F.; Trajmar, S.; Jensen, S. W.; Poe, R. T.
1978-01-01
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.
NASA Technical Reports Server (NTRS)
Kumar, Vijay; Subramanian, K. P.; Krishnakumar, E.
1987-01-01
Absolute electron-helium and electron-neon scattering cross sections have been measured at low electron energies using the powerful technique of photoelectron spectroscopy. The measurements have been carried out at 17 electron energies varying from 0.7 to 10 eV with an accuracy of + or - 2.7 percent. The results obtained in the present work have been compared with other recent measurement and calculations.
Luppov, V.G.; Kaufman, W.A.; Hill, K.M.; Raymond, R.S.; Kirsch, A.D. )
1993-12-05
A 350 mK helium-4-coated mirror was used to increase the intensity of an ultra-cold electron-spin-polarized atomic hydrogen beam. The mirror uses the observed specular reflection of atomic hydrogen from a superfluid-helium-covered surface. A quasi-parabolic polished copper mirror was installed with its focus at the 5 mm diameter exit aperture of an atomic hydrogen stabilization cell in the gradient of an 8 T solenoid field. The four-coned mirror shape, which was designed specifically for operation in the gradient, increased the beam intensity focused by a sextupole magnet into a compression tube detector by a factor of about 7.5.
Two-photon double ionization of the helium atom by ultrashort pulses
Palacios, Alicia; Horner, Daniel A; Rescigno, Thomas N; McCurdy, C William
2010-05-14
Two-photon double ionization of the helium atom was the subject of early experiments at FLASH and will be the subject of future benchmark measurements of the associated electron angular and energy distributions. As the photon energy of a single femtosecond pulse is raised from the threshold for two-photon double ionization at 39.5 eV to beyond the sequential ionization threshold at 54.4 eV, the electron ejection dynamics change from the highly correlated motion associated with nonsequential absorption to the much less correlated sequential ionization process. The signatures of both processes have been predicted in accurate \\textit{ab initio} calculations of the joint angular and energy distributions of the electrons, and those predictions contain some surprises. The dominant terms that contribute to sequential ionization make their presence apparent several eV below that threshold. In two-color pump probe experiments with short pulses whose central frequencies require that the sequential ionization process necessarily dominates, a two-electron interference pattern emerges that depends on the pulse delay and the spin state of the atom.
Scattering approach to dispersive atom-surface interactions
Dalvit, Diego; Messina, Riccardo; Maia Neto, Paulo; Lambrecht, Astrid; Reynaud, Serge
2009-01-01
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.
Cavity-modified collective Rayleigh scattering of two atoms.
Reimann, René; Alt, Wolfgang; Kampschulte, Tobias; Macha, Tobias; Ratschbacher, Lothar; Thau, Natalie; Yoon, Seokchan; Meschede, Dieter
2015-01-16
We report on the observation of cooperative radiation of exactly two neutral atoms strongly coupled to the single mode field of an optical cavity, which is close to the lossless-cavity limit. Monitoring the cavity output power, we observe constructive and destructive interference of collective Rayleigh scattering for certain relative distances between the two atoms. Because of cavity backaction onto the atoms, the cavity output power for the constructive two-atom case (N=2) is almost equal to the single-emitter case (N=1), which is in contrast to free-space where one would expect an N^{2} scaling of the power. These effects are quantitatively explained by a classical model as well as by a quantum mechanical model based on Dicke states. We extract information on the relative phases of the light fields at the atom positions and employ advanced cooling to reduce the jump rate between the constructive and destructive atom configurations. Thereby we improve the control over the system to a level where the implementation of two-atom entanglement schemes involving optical cavities becomes realistic. PMID:25635545
Cavity-Modified Collective Rayleigh Scattering of Two Atoms
René Reimann; Wolfgang Alt; Tobias Kampschulte; Tobias Macha; Lothar Ratschbacher; Natalie Thau; Seokchan Yoon; Dieter Meschede
2015-01-15
We report on the observation of cooperative radiation of exactly two neutral atoms strongly coupled to the single mode field of an optical cavity, which is close to the lossless-cavity limit. Monitoring the cavity output power, we observe constructive and destructive interference of collective Rayleigh scattering for certain relative distances between the two atoms. Because of cavity backaction onto the atoms, the cavity output power for the constructive two-atom case ($N=2$) is almost equal to the single-emitter case ($N=1$), which is in contrast to free-space where one would expect an $N^2$ scaling of the power. These effects are quantitatively explained by a classical model as well as by a quantum mechanical model based on Dicke states. We extract information on the relative phases of the light fields at the atom positions and employ advanced cooling to reduce the jump rate between the constructive and destructive atom configurations. Thereby we improve the control over the system to a level where the implementation of two-atom entanglement schemes involving optical cavities becomes realistic.
Carrier Injection and Scattering in Atomically Thin Chalcogenides
NASA Astrophysics Data System (ADS)
Li, Song-Lin; Tsukagoshi, Kazuhito
2015-12-01
Atomically thin two-dimensional chalcogenides such as MoS2 monolayers are structurally ideal channel materials for the ultimate atomic electronics. However, a heavy thickness dependence of electrical performance is shown in these ultrathin materials, and the device performance normally degrades while exhibiting a low carrier mobility as compared with corresponding bulks, constituting a main hurdle for application in electronics. In this brief review, we summarize our recent work on electrode/channel contacts and carrier scattering mechanisms to address the origins of this adverse thickness dependence. Extrinsically, the Schottky barrier height increases at the electrode/channel contact area in thin channels owing to bandgap expansion caused by quantum confinement, which hinders carrier injection and degrades device performance. Intrinsically, thin channels tend to suffer from intensified Coulomb impurity scattering, resulting from the reduced interaction distance between interfacial impurities and channel carriers. Both factors are responsible for the adverse dependence of carrier mobility on channel thickness in two-dimensional semiconductors.
Scattering of cold-atom coherences by hot atoms: frequency shifts from background-gas collisions.
Gibble, Kurt
2013-05-01
Frequency shifts from background-gas collisions currently contribute significantly to the inaccuracy of atomic clocks. Because nearly all collisions with room-temperature background gases that transfer momentum eject the cold atoms from the clock, the interference between the scattered and unscattered waves in the forward direction dominates these frequency shifts. We show they are ? 10 times smaller than in room-temperature clocks and that van der Waals interactions produce the cold-atom background-gas shift. General considerations allow the loss of the Ramsey fringe amplitude to bound this frequency shift. PMID:23683186
Rengelink, R J; Vassen, W
2015-01-01
High precision spectroscopy on the $2 \\ ^3 S \\rightarrow 2 \\ ^1 S$ transition is possible in ultracold optically trapped helium but the accuracy is limited by the ac-Stark shift induced by the optical dipole trap. To overcome this problem, we have built a trapping laser system at the predicted magic wavelength of 319.8 nm. Our system is based on frequency conversion using commercially available components and produces over 2 W of power at this wavelength. With this system, we show trapping of ultracold atoms, both thermal ($\\sim0.2 \\ \\mathrm{\\mu K}$) and in a Bose-Einstein condensate, with a trap lifetime of several seconds, mainly limited by off-resonant scattering.
Scattering processes in antiprotonic hydrogen - hydrogen atom collisions
V. P. Popov; V. N. Pomerantsev
2006-01-11
The elastic scattering, Stark transitions and Coulomb deexcitation of excited antiprotonic hydrogen atom in collisions with hydrogenic atom have been studied in the framework of the fully quantum-mechanical close-coupling method for the first time. The total cross sections $\\sigma_{nl \\to n'l'}(E)$ and averaged on the initial angular momentum $l$ cross sections $\\sigma_{n\\to n'}(E)$ have been calculated for the initial states of $(\\bar{p}p)_{n}$ atoms with the principal quantum number $n=3 - 14 $ and at the relative energies $E=0.05 - 50$ eV. The energy shifts of the $ns$ states due to the strong interaction and relativistic effects are taken into account. Some of our results are compared with the semiclassical calculations.
First $?K$ atom lifetime and $?K$ scattering length measurements
B. Adeva; L. Afanasyev; Y. Allkofer; C. Amsler; A. Anania; S. Aogaki; A. Benelli; V. Brekhovskikh; T. Cechak; M. Chiba; P. Chliapnikov; C. Ciocarlan; S. Constantinescu; P. Doskarova; D. Drijard; A. Dudarev; M. Duma; D. Dumitriu; D. Fluerasu; A. Gorin; O. Gorchakov; K. Gritsay; C. Guaraldo; M. Gugiu; M. Hansroul; Z. Hons; S. Horikawa; Y. Iwashita; V. Karpukhin; J. Kluson; M. Kobayashi; V. Kruglov; L. Kruglova; A. Kulikov; E. Kulish; A. Kuptsov; A. Lamberto; A. Lanaro; R. Lednicky; C. Mariñas; J. Martincik; L. Nemenov; M. Nikitin; K. Okada; V. Olchevskii; M. Pentia; A. Penzo; M. Plo; T. Ponta; P. Prusa; G. Rappazzo; A. Romero Vidal; A. Ryazantsev; V. Rykalin; J. Schacher; A. Sidorov; J. Smolik; S. Sugimoto; F. Takeutchi; L. Tauscher; T. Trojek; S. Trusov; T. Urban; T. Vrba; V. Yazkov; Y. Yoshimura; M. Zhabitsky; P. Zrelov
2014-03-04
The results of a search for hydrogen-like atoms consisting of $\\pi^{\\mp}K^{\\pm}$ mesons are presented. Evidence for $\\pi K$ atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen in terms of characteristic $\\pi K$ pairs from their breakup in the same target ($178 \\pm 49$) and from Coulomb final state interaction ($653 \\pm 42$). Using these results the analysis yields a first value for the $\\pi K$ atom lifetime of $\\tau=(2.5_{-1.8}^{+3.0})$ fs and a first model-independent measurement of the S-wave isospin-odd $\\pi K$ scattering length $\\left|a_0^-\\right|=\\frac{1}{3}\\left|a_{1/2}-a_{3/2}\\right|= \\left(0.11_{-0.04}^{+0.09} \\right)M_{\\pi}^{-1}$ ($a_I$ for isospin $I$).
Cooperative scattering and radiation pressure force in dense atomic clouds
Bachelard, R.; Piovella, N.; Courteille, Ph. W.
2011-07-15
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.
Nephtali Garrido; Hector H. Hernandez
2012-01-19
We put to the test an effective three-dimensional electrostatic potential, obtained effectively by considering an electrostatic source inside a (5+$p$)-dimensional braneworld scenario with $p$ compact and one infinite spacial extra dimensions in the RS II-$p$ model, for $p=1$ and $p=2$. This potential is regular at the source and matches the standard Coulomb potential outside a neighborhood. We use variational and perturbative approximation methods to calculate corrections to the ground energy of the Helium atom modified by this potential, by making use of a 6 and 39-parameter trial wave function of Hylleraas type for the ground state. These corrections to the ground-state energy are compared with experimental data for Helium atom in order to set bounds for the extra dimensions length scale. We find that these bounds are less restrictive than the ones obtained by Morales et. al. through a calculation using the Lamb shift in Hydrogen.
Dynamics of the helium atom close to the full fragmentation threshold: Ionization excitation
Bouri, C.; Selles, P.; Malegat, L.; Teuler, J.M.; Njock, M. Kwato; Kazansky, A.K.
2005-10-15
The hyperspherical R-matrix method with semiclassical outgoing waves, designed to provide accurate double-ionization cross sections, is extended to allow for the computation of ionization-excitation data of comparable quality. Accordingly, it appears now as a complete method for treating the correlated dynamics of two-electron atoms, in particular above their full fragmentation threshold. Cross sections {sigma}{sub n} and asymmetry parameters {beta}{sub n} are obtained for single photoionization of helium with excitation of the residual ion up to as high a level as n=50 at 0.1 eV above the double-ionization threshold. These data are extrapolated to infinite values of n in order to check widespread assumptions regarding this limit. Our data are found consistent with the assumed n{sup -3} dependence of the partial ionization cross sections. However, the {beta}{sub {infinity}}=-0.636 obtained still lies far from the -1 value expected at the double-ionization threshold.
Scattering of wave packets on atoms in the Born approximation
NASA Astrophysics Data System (ADS)
Karlovets, D. V.; Kotkin, G. L.; Serbo, V. G.
2015-11-01
It has recently been demonstrated experimentally that 200 -300 keV electrons with the unusual spatial profiles can be produced and even focused to a subnanometer scale—namely, electrons carrying nonzero orbital angular momentum and also the so-called Airy beams. Since the wave functions of such electrons do not represent plane waves, the standard Born formula for scattering of them off a potential field is no longer applicable and, hence, needs modification. In the present paper, we address the generic problem of elastic scattering of a wave packet of a fast nonrelativistic particle off a potential field. We obtain simple and convenient formulas for a number of events and an effective cross section in such a scattering, which represent generalization of the Born formula for a case when finite sizes and spatial inhomogeneity of the initial packet should be taken into account. As a benchmark, we consider two simple models corresponding to scattering of a Gaussian wave packet on a Gaussian potential and on a hydrogen atom, and perform a detailed analysis of the effects brought about by the limited sizes of the incident beam and by the finite impact parameter between the potential center and the packet's axis.
Optical Manipulation of Light Scattering in Cold Atomic Rubidium
Olave, R G; Kemp, Kasie; Roof, S J; Balik, S; Havey, M D; Sokolov, I M; Kupriyanov, D V
2014-01-01
A brief perspective on light scattering in dense and cold atomic rubidium is presented. We particularly focus on the influence of auxiliary applied fields on the system response to a weak and nearly resonant probe field. Auxiliary fields can strongly disturb light propagation; in addition to the steady state case, dynamically interesting effects appear clearly in both the time domain, and in the optical polarization dependence of the processes. Following a general introduction, two examples of features found in such studies are presented. These include nonlinear optical effects in (a) comparative studies of forward- and fluorescence-configuration scattering under combined excitation of a control and probe field, and (b) manipulation of the spatial structure of the optical response due to a light shifting strong applied field.
Optical Manipulation of Light Scattering in Cold Atomic Rubidium
NASA Astrophysics Data System (ADS)
Olave, R. G.; Win, A. L.; Kemp, K.; Roof, S. J.; Balik, S.; Havey, M. D.; Sokolov, I. M.; Kupriyanov, D. V.
2015-06-01
A brief perspective on light scattering in dense and cold atomic rubidium is presented. We particularly focus on the influence of auxiliary applied fields on the system response to a weak and nearly resonant probe field. Auxiliary fields can strongly disturb light propagation; in addition to the steady state case, dynamically interesting effects appear clearly in both the time domain, and in the optical polarization dependence of the processes. Following a general introduction, two examples of features found in such studies are presented. These include nonlinear optical effects in (a) comparative studies of forward- and fluorescence-configuration scattering under combined excitation of a control and probe field, and (b) manipulation of the spatial structure of the optical response due to a light shifting strong applied field.
NASA Astrophysics Data System (ADS)
Matsukuma, H.; Shikama, T.; Hasuo, M.
2011-04-01
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.
Double photoionization of helium with synchrotron x-rays: Proceedings
Not Available
1994-01-01
This report contains papers on the following topics: Overview and comparison of photoionization with charged particle impact; The ratio of double to single ionization of helium: the relationship of photon and bare charged particle impact ionization; Double photoionization of helium at high energies; Compton scattering of photons from electrons bound in light elements; Electron ionization and the Compton effect in double ionization of helium; Elimination of two atomic electrons by a single energy photon; Double photoionization of helium at intermediate energies; Double Photoionization: Gauge Dependence, Coulomb Explosion; Single and Double Ionization by high energy photon impact; The effect of Compton Scattering on the double to single ionization ratio in helium; and Double ionization of He by photoionization and Compton scattering. These papers have been cataloged separately for the database.
Scattering of positrons and electrons by alkali atoms
NASA Technical Reports Server (NTRS)
Stein, T. S.; Kauppila, W. E.; Kwan, C. K.; Lukaszew, R. A.; Parikh, S. P.; Wan, Y. J.; Zhou, S.; Dababneh, M. S.
1990-01-01
Absolute total scattering cross sections (Q sub T's) were measured for positrons and electrons colliding with sodium, potassium, and rubidium in the 1 to 102 eV range, using the same apparatus and experimental approach (a beam transmission technique) for both projectiles. The present results for positron-sodium and -rubidium collisions represent the first Q sub T measurements reported for these collision systems. Features which distinguish the present comparisons between positron- and electron-alkali atom Q sub T's from those for other atoms and molecules (room-temperature gases) which have been used as targets for positrons and electrons are the proximity of the corresponding positron- and electron-alkali atom Q sub T's over the entire energy range of overlap, with an indication of a merging or near-merging of the corresponding positron and electron Q sub T's near (and above) the relatively low energy of about 40 eV, and a general tendency for the positron-alkali atom Q sub T's to be higher than the corresponding electron values as the projectile energy is decreased below about 40 eV.
Physics of Polarized Scattering at Multi-level Atomic Systems
NASA Astrophysics Data System (ADS)
Stenflo, J. O.
2015-03-01
The symmetric peak observed in linear polarization in the core of the solar sodium D1 line at 5896 Å has remained enigmatic since its discovery nearly two decades ago. One reason is that the theory of polarized scattering has not been experimentally tested for multi-level atomic systems in the relevant parameter domains, although the theory is continually being used for the interpretation of astrophysical observations. A laboratory experiment that was set up a decade ago to find out whether the D1 enigma is a problem of solar physics or quantum physics revealed that the D1 system has a rich polarization structure in situations where standard scattering theory predicts zero polarization, even when optical pumping of the m state populations of the hyperfine-split ground state is accounted for. Here we show that the laboratory results can be modeled in great quantitative detail if the theory is extended to include the coherences in both the initial and final states of the scattering process. Radiative couplings between the allowed dipole transitions generate coherences in the initial state. Corresponding coherences in the final state are then demanded by a phase closure selection rule. The experimental results for the well understood D2 line are used to constrain the two free parameters of the experiment, collision rate and optical depth, to suppress the need for free parameters when fitting the D1 results.
Low-Energy Elastic Electron Scattering by Atomic Oxygen
NASA Technical Reports Server (NTRS)
Zatsarinny O.; Bartschat, K.; Tayal, S. S.
2006-01-01
The B-spline R-matrix method is employed to investigate the low-energy elastic electron scattering by atomic oxygen. Flexible non-orthogonal sets of radial functions are used to construct the target description and to represent the scattering functions. A detailed investigation regarding the dependence of the predicted partial and total cross sections on the scattering model and the accuracy of the target description is presented. The predicted angle-integrated elastic cross sections are in good agreement with experiment, whereas significant discrepancies are found in the angle-differential elastic cross sections near the forward direction. .The near-threshold results are found to strongly depend on the treatment of inner-core short-range correlation effects in the target description, as well as on a proper account of the target polarizability. A sharp increase in the elastic cross sections below 1 eV found in some earlier calculations is judged to be an artifact of an unbalanced description of correlation in the N-electron target structure and the (N+l)-electron-collision problems.
Ultracold neutron production and up-scattering in superfluid helium between 1.1 K and 2.4 K
K. K. H. Leung; S. Ivanov; F. M. Piegsa; M. Simson; O. Zimmer
2015-07-27
Ultracold neutrons (UCNs) were produced in a 4 liter volume of superfluid helium using the PF1B cold neutron beam facility at the Institut Laue-Langevin and then extracted to a detector at room temperature. With a converter temperature of 1.08 K the number of accumulated UCNs was counted to be $91,\\!700 \\pm 300$. From this, we derive a volumetric UCN production rate of $(6.9 \\pm 1.7)\\,\\mathrm{cm^{-3}\\,s^{-1}}$, which includes a correction for losses in the converter during UCN extraction caused by a short storage time, but not accounting for UCN transport and detection efficiencies. The up-scattering rate of UCNs due to excitations in the superfluid was studied by scanning the temperature between 1.2-2.4 K. Using the temperature-dependent UCN production rate calculated from inelastic neutron scattering data in the analysis, the only UCN up-scattering process found to be present was from two-phonon scattering. Our analysis rules out contributions from the other scattering processes to $\\lesssim 10\\%$ of their predicted levels.
He atom surface scattering: Surface dynamics of insulators, overlayers and crystal growth
NASA Astrophysics Data System (ADS)
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.
Plasmon enhanced Raman scattering effect for an atom near a carbon nanotube.
Bondarev, I V
2015-02-23
Quantum electrodynamics theory of the resonance Raman scattering is developed for an atom in a close proximity to a carbon nanotube. The theory predicts a dramatic enhancement of the Raman intensity in the strong atomic coupling regime to nanotube plasmon near-fields. This resonance scattering is a manifestation of the general electromagnetic surface enhanced Raman scattering effect, and can be used in designing efficient nanotube based optical sensing substrates for single atom detection, precision spontaneous emission control, and manipulation. PMID:25836436
Manson, Joseph R.
and not by the smaller Mg ions. Since the repulsive force on an incoming atomic scattering projectile is due to Pauli to the oxygen atom. However, in the well one would also expect a strong corrugation of the at- tractive
Vilà, Arnau; González, Miguel; Mayol, Ricardo
2016-01-21
The capture dynamics of a Ne atom by a superfluid helium nanodroplet (((4)He)N=1000; T = 0.37 K), Ne + ((4)He)N? Ne@((4)He)N', was investigated using a quantum approach (TDDFT (helium) + quantum wave packet (Ne)) at zero angular momentum and a rather wide range of Ne atom initial mean velocities (?v0?: 90-1300 m s(-1)). This is probably the first quantum dynamics study focusing on the pick up process and the evolution of the dopant inside the nanodroplet and the second more detailed investigation on this topic. For ?v0? = 210 m s(-1) and above the atom is always captured, but for lower velocities the probability of capture is somewhat below the unity and decreases as ?v0? diminishes. The main energy exchange begins with the collision of the atom with the nanodroplet surface, and the excess of energy placed in the doped nanodroplet is progressively released by the evaporation of a small amount of (4)He atoms. Once the atom has entered into the nanodroplet its mean position follows an oscillatory trajectory, due to multiple sequential collisions with the inner surface of the nanodroplet, and its mean velocity reaches values which are below Landau's critical velocity. This probably corresponds to the general behavior of nanodroplets with a bulk-like region when moderate collision energies (i.e., similar to the ones considered here) are involved. In the future we hope to investigate the influence of angular momentum on the mechanism of the pick up process, using the same quantum dynamics method. PMID:26688071
Luppov, V.G.; Kaufman, W.A.; Hill, K.M.
1993-04-01
A 350 mK helium-4 coated mirror was used to increase the intensity of an ultra-cold electron-spin-polarized atomic hydrogen beam. The mirror uses the observed specular reflection of atomic hydrogen from a superfluid-helium-covered surface. A quasi-parabolic polished copper mirror was installed with its focus at the 5 mm diameter exit aperture of an atomic hydrogen stabilization cell in the gradient of an 8 T solenoid. The four-coned mirror shape, which was designed specifically for operation in the gradient, increased the beam intensity focused by a sextupole magnet into a compression tube detector more than seven-fold.
Inelastic cross sections for positron scattering from atomic hydrogen
Weber, M.; Hofmann, A.; Raith, W.; Sperber, W.; Jacobsen, F.; Lynn, K.G.
1994-12-31
Positronium formation (Ps) cross sections for positrons impinging on atomic hydrogen were measured in the impact energy range from 13eV to 255eV at the High Intensity Positron (HIP) beam at Brookhaven National Laboratory (BNL). The Ps-formation cross section was found to rise rapidly from the threshold at 6.8eV to a maximum value of (2.98 {plus_minus} 0.18) {times} 10{sup {minus}16} cm{sup 2} for {approx} 15eV positrons. By 75eV it drops below the detection limit of 0.17 {times} 10{sup {minus}16} cm{sup 2} which is the present level of statistical uncertainty. The experiment was modified to enable the measurement of doubly differential scattering cross sections.
Positron scattering from hydrogen atom embedded in dense quantum plasma
Bhattacharya, Arka; Kamali, M. Z. M.; Ghoshal, Arijit; Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur ; Ratnavelu, K.
2013-08-15
Scattering of positrons from the ground state of hydrogen atoms embedded in dense quantum plasma has been investigated by applying a formulation of the three-body collision problem in the form of coupled multi-channel two-body Lippmann-Schwinger equations. The interactions among the charged particles in dense quantum plasma have been represented by exponential cosine-screened Coulomb potentials. Variationally determined hydrogenic wave function has been employed to calculate the partial-wave scattering amplitude. Plasma screening effects on various possible mode of fragmentation of the system e{sup +}+H(1s) during the collision, such as 1s?1s and 2s?2s elastic collisions, 1s?2s excitation, positronium formation, elastic proton-positronium collisions, have been reported in the energy range 13.6-350 eV. Furthermore, a comparison has been made on the plasma screening effect of a dense quantum plasma with that of a weakly coupled plasma for which the plasma screening effect has been represented by the Debye model. Our results for the unscreened case are in fair agreement with some of the most accurate results available in the literature.
NASA Astrophysics Data System (ADS)
Yamazaki, Toshimitsu; Morita, Norio; Hayano, Ryugo S.; Widmann, Eberhard; Eades, John
2002-08-01
Antiprotonic helium, a neutral three-body system p¯e -He2+ (= p¯He+) , produced when antiprotons ( p¯) are captured in various phases of helium, comprises a series of long-lived ( ? ?s lifetime) states in which the p¯ orbits the helium nucleus in a localized trajectory with large principal and orbital quantum numbers ( n, l). Typically, n? M ?/m e?38 and l? n-1, where M ? is the reduced mass of the p¯-He system, whereas the electron occupies the ground 1s orbital. Because the p¯ moves slowly compared to the electron, this system possesses a dual character as both an exotic atom and a peculiar diatomic molecule, and is often called an antiprotonic helium atom-molecule, or atomcule for short. Its unique character of being metastable among p¯-containing atomic systems has permitted it to be studied with high-resolution laser spectroscopic techniques, yielding rich information on its formation, structure and decay. We first discuss the discovery at KEK Japan of the unexpectedly long survival time of p¯'s in liquid helium and the consequent systematic studies at the CERN LEAR facility of delayed annihilation time spectra of p¯'s stopped in various phases of helium. Theoretical models are introduced to explain the longevity and to predict the characteristic properties of antiprotonic helium. Laser spectroscopic studies have advanced and clarified the structure of the atomcule. These provide high-precision data on the transition energies which can be compared with advanced theories on the three-body Coulomb system. The latter now include QED effects to ppm precision, while the hyperfine structure has also been investigated experimentally and theoretically. Chemical physics aspects of antiprotonic helium are also described, including such environment-dependent effects as the dependence of its transition frequencies and level lifetimes on the phase and density of the surrounding helium, and the quenching of state populations by surrounding foreign atoms and molecules at impurity-level concentrations. The future scope of experiments on antiprotonic helium is discussed.
Elastic scattering of electrons by strontium and barium atoms
Szmytkowski, R.; Sienkiewicz, J.E. )
1994-11-01
Differential, total, and momentum transfer cross sections for the elastic scattering of low- and intermediate-energy (0.2--100 eV) electrons by Sr and Ba atoms were calculated in the relativistic polarized orbital approximation. A static part of the projectile-target interaction potential was generated by solving the Dirac-Hartree-Fock (DHF) equations for the isolated target. A polarization potential was obtained by solving the coupled DHF equations for the target perturbed by an electric field produced by the projectile. Only the dipole term in the polarization potential was included in scattering calculations. For low angular momenta (0[le][ital l][le]5) relativistic phase shifts were extracted by solving a continuum state DHF equation in an inner region, where exchange between the projectile and the target electrons was important, and then a relativistic variable phase (RVP) equation in an outer region, where exchange was negligible. For intermediate angular momenta (6[le][ital l][le]17) exchange was neglected and the phase shifts were calculated by solving the RVP equation in the whole configuration space. Higher ([ital l][ge]18) phase shifts were obtained using the Born approximation and their contributions to scattering amplitudes and cross sections were evaluated analytically. At low energies (0.2--10 eV) our total cross sections for both Sr and Ba atoms differ seriously from experimental data of Romanyuk, Shpenik, and Zapesochnyi (Pis'ma Zh. Eksp. Teor. Fiz. 32, 472 (1980) [JETP Lett. 32, 452 (1980)]). At energies up to 60 eV our differential cross section for Ba differs both in magnitude and shape from experimental data of Jensen, Register, and Trajmar [J. Phys. B 11, 2367 (1968)] but quite satisfactorily reproduces shapes of curves measured recently by Wang, Trajmar, and Zetner [J. Phys. B (to be published)]. At energies above 80 eV the agreement between the present results and the data of Jensen, Register, and Trajmar is much more satisfactory.
Scattering of two-level atoms by delta lasers: Exactly solvable models in atom optics
D. Seidel; J. G. Muga; G. C. Hegerfeldt
2006-07-18
We study the scattering of two-level atoms at narrow laser fields, modeled by a $\\delta$-shape intensity profile. The unique properties of these potentials allow us to give simple analytic solutions for one or two field zones. Several applications are studied: a single $\\delta$-laser may serve as a detector model for atom detection and arrival-time measurements, either by means of fluorescence or variations in occupation probabilities. We show that, in principle, this ideal detector can measure the particle density, the quantum mechanical flux, arrival time distributions or local kinetic energy densities. Moreover, two spatially separated $\\delta$-lasers are used to investigate quantized-motion effects on Ramsey interferometry.
The helium trimer with soft-core potentials
A. Kievsky; E. Garrido; C. Romero-Redondo; P. Barletta
2011-01-10
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.
NASA Astrophysics Data System (ADS)
Furukawa, Takeshi
2014-09-01
We have been developing a new laser spectroscopy technique named as OROCHI (Optical RI-atom Observation in Condensed Helium as Ion-catcher) for measurements of nuclear spins and electromagnetic moments of low yield exotic radioisotopes (RIs). In this technique, we use superfluid helium (He II) liquid as a stopping material of RI beam in which in-situ laser spectroscopy of the RI atoms stopped in He II is carried out. The characteristic features of He II, i.e. high trapping efficiency of He II liquid for accelerated ion beams and the characteristics of atomic spectra in He II, enables us to measure the nuclear spins and moments of the extremely low yield RIs. So far, we have demonstrated the feasibility of our method to deduce the nuclear spins and moments with stable Rb, Cs, Ag and Au isotopes supplied into He II by laser sputtering technique. In addition, we have also succeeded in observing laser-radiowave/microwave double resonance signals of 84-87Rb atoms injected into He II as energetic ion beam. In these on-line experiment, the 84-87Rb isotope beams (intensity: up to 105 particles/s) were provided with RIPS beamline in RIKEN, and introduced into He II filled in a cryostat. Special care was taken in controlling the stopping position of injected Rb isotopes. Aluminum energy degraders of varied thickness from 0 to 0.8 mm were placed upstream of the beam injection window of the He II cryostat for optimizing the stopping position The 84-87Rb atoms stopped and then neutralized in He II were optically pumped and polarized with circularly polarized pumping laser light whose wavelength were tuned to 780 nm, D1 absorption line of Rb atoms in He II. The polarized atoms were subjected to irradiation of radiowave or microwave, and then we demonstrated the double resonance spectroscopy for observing the Zeeman transition of 84-87Rb atoms and the hyperfine transition of 87Rb, respectively In this presentation we will show the details of OROCHI technique and the present status of our development, in particular the result of the recent on-line experiment.
Compton scattering of two x-ray photons by an atom
NASA Astrophysics Data System (ADS)
Hopersky, Alexey N.; Nadolinsky, Alexey M.; Novikov, Sergey A.
2015-11-01
The process of inelastic nonresonant two x-ray free-electron laser (XFEL) photon Compton scattering by a free atom is theoretically investigated. The object of the study is the He atom. We obtain the absolute values and the shape of the double differential scattering cross section. The quantum effect of creation of "hot" scattered photons with maximum energy 2 ? ? -I1 s is predicted (? ? is the energy of the incident XFEL photon on the atom, and I1 s is the energy of the ionization threshold of an atomic 1 s2 shell).
Light scattering from ultracold atomic gases in optical lattices at finite temperature
Douglas, James S.; Burnett, Keith
2011-09-15
We study light scattering from atoms in optical lattices at finite temperature. We examine the light scattered by fermions in the noninteracting regime and by bosons in the superfluid and Mott insulating regimes. We extend previous theoretical studies to include the full band structure of the optical lattice. We find that light scattering that excites atoms out of the lowest band leads to an increase in light scattering away from the classical diffraction peaks and is largely temperature independent. This additional light scattering leads to lower efficiency of temperature measurements based on photon counting.
NASA Astrophysics Data System (ADS)
Lidar (Hamburger), Daniel A.
1998-08-01
The sudden approximation (SA) for scattering of atoms from surfaces is generalized to allow for double collision events and scattering from time-dependent quantum liquid surfaces. The resulting new schemes retain the simplicity of the original SA, while requiring little extra computational effort. The results suggest that inert atom (and in particular He) scattering can be used profitably to study hitherto unexplored forms of complex surface disorder.
Inter-atomic force constants of BaF{sub 2} by diffuse neutron scattering measurement
Sakuma, Takashi Makhsun,; Sakai, Ryutaro; Xianglian; Takahashi, Haruyuki; Basar, Khairul; Igawa, Naoki; Danilkin, Sergey A.
2015-04-16
Diffuse neutron scattering measurement on BaF{sub 2} crystals was performed at 10?K and 295?K. Oscillatory form in the diffuse scattering intensity of BaF{sub 2} was observed at 295?K. The correlation effects among thermal displacements of F-F atoms were obtained from the analysis of oscillatory diffuse scattering intensity. The force constants among neighboring atoms in BaF{sub 2} were determined and compared to those in ionic crystals and semiconductors.
NASA Astrophysics Data System (ADS)
Rachet, Florent; Le Duff, Yves; Guillot-Noël, Christophe; Chrysos, Michael
2000-06-01
We measured the polarized binary collision-induced light scattering spectrum from room-temperature gaseous helium over the greatly extended spectral domain ?=5-1200 cm-1, and then deduced the isotropic spectrum that we report in the interval ?=100-1200 cm-1. Our experimental results were calibrated on an absolute scale. These data were compared to those from quantum-mechanical computations, where use of advanced induced-polarizability incremental traces was made. This comparison enabled us to check several trace models and to show that for certain ab initio ones the computed spectra agree well with our measurements. As was borne out from our computations the main contributions to the spectral intensities come from the exchange component of the incremental trace and its negative mixing with the rest of the trace components.
Electron elastic scattering off A @C60 : The role of atomic polarization under confinement
NASA Astrophysics Data System (ADS)
Dolmatov, V. K.; Amusia, M. Ya.; Chernysheva, L. V.
2015-10-01
The present paper explores possible features of electron elastic scattering off endohedral fullerenes A @C60 . It focuses on how dynamical polarization of the encapsulated atom A by an incident electron might alter scattering off A @C60 compared to the static-atom-A case, as well as how the C60 confinement modifies the impact of atomic polarization on electron scattering compared to the free-atom case. The aim is to provide researchers with a "relative frame of reference" for understanding which part of the scattering processes could be due to electron scattering off the encapsulated atom and which could be due to scattering off the C60 cage. To meet the goal, the C60 cage is modeled by an attractive spherical potential of a certain inner radius, thickness, and depth which is a model used frequently in a great variety of fullerene studies to date. Then, the Dyson equation for the self-energy part of the Green's function of an incident electron moving in the combined field of an encapsulated atom A and C60 is solved in order to account for the impact of dynamical polarization of the encaged atom upon e +A @C60 scattering. The Ba@C60 endohedral is chosen as the case study. The impact is found to be significant, and its utterly different role compared to that in e +Ba scattering is unraveled.
Roghani, Maryam; Breuer, Heinz-Peter; Helm, Hanspeter
2010-03-15
We study the time dependence of the spectrum of inelastically scattered radiation from a trapped atom. The atom is illuminated by two lasers tuned to the electromagnetically induced transparency (EIT) of the free atom. For counterpropagating laser beams, rapid removal of vibrational energy is observed as the atom approaches near-EIT conditions. We show that the imbalance in the sidebands of the scattered radiation spectrum explains quantitatively the cooling of the center-of-mass motion of the trapped atom. We also examine parameters critical for EIT cooling in situations far from the Lamb-Dicke limit.
Yu, Shengrui; Su, Shu; Dai, Dongxu; Yuan, Kaijun; Yang, Xueming
2015-04-21
The state-to-state dynamics of high-n Rydberg H-atom scattering with para-H2 at the collision energies of 0.45 and 1.07 eV have been studied using the H-atom Rydberg tagging time-of-flight technique. Both the inelastic scattering and reactive scattering are observed in the experimental time-of-flight spectra. The products H2(v', j' = odd) come only from reactive scattering and present clearly forward-backward asymmetric angular distributions, which differ from those of the corresponding ion-molecule reaction. The products H2(v', j' = even), however, come from both reactive scattering and inelastic scattering. Simulating the rotational distribution from reactive scattering, we found that most of the H2(v', j' = even) products come from inelastic scattering. The angular distributions of the product H2(v', j' = even) are consistent with what is predicted by the conventional textbook mechanism of inelastic scattering, and are a little different from those of the corresponding ion-molecule inelastic scattering. These results suggest that the effect of Rydberg electron could not be neglected in describing the differential cross sections of H* + para-H2 scattering. From the simulation, the branching ratios of the inelastic scattering channel were determined to be 66% and 79% at the collision energies of 0.45 and 1.07 eV, respectively. PMID:25162182
degenerate 87 Rb atoms in a three- dimensional optical lattice. Bragg scattered light directly probes development is the realization of single-site resolution of atoms in two-dimensional optical lattices [7 scale. We have applied this technique to ultra- cold atoms in a three-dimensional optical lattice
Safron, S.A.; Skofronick, J.G.
1994-04-01
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)).
Interacting double dark resonances in a hot atomic vapor of helium
S. Kumar; T. Lauprêtre; R. Ghosh; F. Bretenaker; F. Goldfarb
2011-07-17
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.
Interacting double dark resonances in a hot atomic vapor of helium
Kumar, S.; Ghosh, R.; Laupretre, T.; Bretenaker, F.; Goldfarb, F.
2011-08-15
We experimentally and theoretically study two different tripod configurations using metastable helium ({sup 4}He*), with the probe field polarization perpendicular and parallel to the quantization axis, defined by an applied weak magnetic field. In the first case, the two dark resonances interact incoherently and merge together into a single electromagnetically induced transparency peak with increasing coupling power. In the second case, we observe destructive interference between the two dark resonances inducing an extra absorption peak at the line center.
Chaotic walking and fractal scattering of atoms in a tilted optical lattice
S. V. Prants; V. O. Vitkovsky
2012-05-20
Chaotic walking of cold atoms in a tilted optical lattice, created by two counter propagating running waves with an additional external field, is demonstrated theoretically and numerically in the semiclassical and Hamiltonian approximations. The effect consists in random-like changing the direction of atomic motion in a rigid lattice under the influence of a constant force due to a specific behavior of the atomic dipole-moment component that changes abruptly in a random-like manner while atoms cross standing-wave nodes. Chaotic walking generates a fractal-like scattering of atoms that manifests itself in a self-similar structure of the scattering function in the atom-field detuning, position and momentum spaces. The probability distribution function of the scattering time is shown to decay in a non-exponential way with a power-law tail.
On the behavior of scattering phases in collisions of electrons with multi-atomic objects
M. Ya. Amusia; L. V. Chernysheva
2015-02-19
We have studied the energy dependence of several first scattering phases with multi-atomic object. As concrete examples representing the general trends endohedrals Neon inside C60 and Argon inside C60 are considered. It appeared that the presence of an inner atom, either Ne or Ar, qualitatively affects the scattering phases, in spite of the fact that the fullerene consists of 60 carbon atoms, while the atom staffed inside is only one. Calculations are performed in the one-electron Hartree-Fock (HF) and random phase approximation with exchange (RPAE) for the inner atom while the fullerenes shell is substituted by static potential without and with the polarization potential. It appeared that the total endohedral scattering phase is simply a sum of atomic, Ne or Ar, and fullerenes C60 phases, contrary to the intuitive assumption that the total phases on C60 and Neon inside C60 or Ar inside C60 has to be the same.
NASA Astrophysics Data System (ADS)
Denkelmann, R.; Maurmann, S.; Lokajczyk, T.; Drepper, P.; Kunze, H.-J.
1999-10-01
We present experimentally obtained rate coefficients for electron-atom collisions for icons/Journals/Common/Delta" ALT="Delta" ALIGN="TOP"/> n = 0 transitions of neutral helium. Results for the dipole-allowed transitions 3 3S-3 3P, 3 3P-3 3D, 3 1S-3 1P, 3 1D-3 1P, 4 1S-4 1P and 4 1D-4 1P are given for an electron temperature range of 3-7 eV. For the transitions 3 3S-3 3P and 3 3P-3 3D results down to temperatures below 1 eV were obtained. The measurements were performed in a magnetic multipole plasma source by a laser perturbation method. The plasma parameters were measured by employing a Langmuir probe. The electron density was in the range of 1011 to several 1012 cm-3 at helium filling pressures of a few Pascal. The results are compared with the theoretical and experimental data available in the literature.
Phase-operation for conduction electron by atomic-scale scattering via single point-defect
Nagaoka, Katsumi Yaginuma, Shin; Nakayama, Tomonobu
2014-03-17
In order to propose a phase-operation technique for conduction electrons in solid, we have investigated, using scanning tunneling microscopy, an atomic-scale electron-scattering phenomenon on a 2D subband state formed in Si. Particularly, we have noticed a single surface point-defect around which a standing-wave pattern created, and a dispersion of scattering phase-shifts by the defect-potential against electron-energy has been measured. The behavior is well-explained with appropriate scattering parameters: the potential height and radius. This result experimentally proves that the atomic-scale potential scattering via the point defect enables phase-operation for conduction electrons.
NASA Astrophysics Data System (ADS)
Swaczyna, P.; Grzedzielski, S.; Bzowski, M.
2014-12-01
Expected fluxes of energetic neutral helium atoms (He ENA) emitted from the heliosheath and created by the Ribbon secondary ENA mechanism are relatively small for the directions of the nose and flanks of the heliosphere. The mean free path against ionization in the Local Interstellar Cloud (LIC) for the He ENA reaches ~8,000 AU for atoms of energy ~5 keV, i.e., about 10 times higher than the mean free path against ionization for hydrogen atoms for the same energy. Thus observation of potential sources in the Local Interstellar Medium by an ENA detector could be possible for distances over a dozen thousand AU. This includes a potential to observe processes at the LIC boundary, to which the closest distance is likely smaller than 10,000 AU. Measurements of He ENA could potentially be used to bridge the gap between direct in situ sampling of our Galactic environment, available from Ulysses and IBEX, and the parsec-scale telescopic observations of interstellar absorption lines. Estimates of the expected heliospheric emission of He ENA are taken from a simple model of the heliosphere, for which we have obtained results consistent with HSTOF observation of He ENA. We use analytical model of the secondary ENA emission with a simple heliolatitude dependence in the supersonic solar wind. For the extraheliospheric sources, we examine simple He ENA production models on distant (<~0.1 pc) boundary layer. One such model, proposed earlier as an extraheliospheric source for the IBEX Ribbon at the hypothetic interface between the LIC and the Local Bubble, is now extended to provide estimates of the fluxes at a wider energy range, from a few to a few tens of keV, taking various distances to the interface into account. Including an appropriate mass spectrometer in the IMAP energetic neutral atom detector will give opportunity to distinguish helium atoms from the general ENA flux. This added capability would provide IMAP with a potential to discover possible enhancements in the He ENA fluxes other than from the heliotail direction, which could enable studying kinetic non-equilibrium processes operating in the "dark gap" region currently inaccessible for observations by IBEX and by traditional astrophysical techniques. These processes are potentially ubiquitous in the interstellar medium.
Advances in the helium-jet coupled on-line mass separator RAMA. [Recoil Atom Mass Analyzer
Moltz, D M; Aysto, J; Cable, M D; Parry, R F; Haustein, P E; Wouters, J M; Cerny, J
1980-01-01
General improvements to the on-line mass separator RAMA (Recoil Atom Mass Analyzer) have yielded a greater reliability and efficiency for some elements. A new utilitarian helium-jet chamber has been installed to facilitate quick target and degrader foil changes in addition to a new ion source holder. A higher efficiency hollow-cathode, cathode-extraction ion source, for lower melting point elements (< 1200/sup 0/C) has also been designed. Tests with the beta-delayed proton emitter /sup 37/Ca showed a factor of five increase in yield over the old hollow-cathode, anode-extraction source. A differentially-pumped-tape drive system compatible with both ..gamma..-..gamma.. and ..beta..-..gamma.. experiments has been incorporated into the general detection system. All major operating parameters will soon be monitored by a complete stand-alone microprocessor system which will eventually be upgraded to a closed-loop control system.
Fukushi, K. ); Willie, S.N.; Sturgeon, R.E. )
1993-02-01
Inorganic and organic mercury were determined by helium-microwave induced plasma-atomic emission spectrometry following cold vapor generation. Whereas only inorganic mercury was reduced by stannous ion in an acidic medium, both inorganic and organic mercury (total mercury) were reduced by stannous ion in the presence of cupric ion in a basic medium. Organic mercury was determined as the difference between total and inorganic mercury. Detection limits for inorganic and organic mercury were 11 and 10 pg, respectively. The accuracy of the proposed method was verified through the determination of inorganic, total and organic mercury in two marine biological standard reference materials, DORM-1 and TORT-1. 21 refs., 1 fig., 4 tabs.
Electron elastic scattering off high spin atoms: the Cr and Mn case
NASA Astrophysics Data System (ADS)
Dolmatov, V.; Amusia, M.; Chernysheva, L.
2014-05-01
The Cr(... 3d5 4s1 , 7 S) and Mn(... 3d5 4s2 , 6 S) atoms belong to the cohort of high spin atoms, owing to their semifilled 3d5 and 4s1 (in Cr) subshells. The current understanding of low-energy electron scattering off such atoms is rudimentary. Here, we scrutinize the impacts of electron correlation, exchange, and electron spin-polarization on elastic scattering phase shifts and total cross sections of e- + Cr and e- + Mn scattering, as well as Wigner time delays of the scattering processes in question, in the electron energy interval where most interesting effects occur, E = 0 -15 eV. We also provide an update to our earlier calculated results for e- + Mn scattering. The findings of this work identify some of the most intrinsic properties of electron elastic scattering off semifilled shell atoms. As in, a ``spin-polarized'' Hartree-Fock approximation, random phase approximation with exchange, and the Dyson theory for the self-energy part of the Green function of a scattered electron have been blended in together in order to advance into the understanding of electron scattering off semifilled shell atoms. Supported by the NSF grant PHY-1305085.
Das, J.N.; Paul, S.; Chakrabarti, K.
2004-04-01
Here we report a set of converged cross-section results for double photoionization of helium atoms obtained in the hyperspherical partial wave theory for equal energy sharing kinematics at 6 eV energy above threshold. The calculated cross section results are generally in excellent agreement with the absolute measured results of Doerner et al. [Phys. Rev. 57, 1074 (1998)].
Matter-Wave Scattering from Ultracold Atoms in an Optical Lattice
Sanders, Scott N.
We study matter-wave scattering from an ultracold, many-body atomic system trapped in an optical lattice. The angular cross section of the target lattice for a matter wave is determined and is demonstrated to have a strong ...
Chu, Shih-I; Dalgarno, A.
1975-08-01
The effective close-coupling method of Rabitz is tested and used to calculate the angular distributions of the elastic and inelastic scattering of molecular hydrogen in collision with atomic hydrogen when rotational transitions may occur...
Scattering of low-energy electrons and positrons by atomic beryllium: Ramsauer-Townsend effect
Reid, David D
2014-01-01
Total cross sections for the scattering of low-energy electrons and positrons by atomic beryllium in the energy range below the first inelastic thresholds are calculated. A Ramsauer-Townsend minimum is seen in the electron scattering cross sections, while no such effect is found in the case of positron scattering. A minimum total cross section of 0.016 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.
Theory of light and atom scattering in the Bose-Einstein condensate of a dilute gas
Avetisyan, Ya. A.; Trifonov, E. D.
2006-11-15
A semiclassical theory of superradiant light scattering from a Bose-Einstein condensate of a dilute gas is developed without recourse to the mean field approximation. The dynamics and spectrum of superradiant field, as well as the kinetics of formation of coherent atomic states with various translational momenta are calculated. The results are qualitatively consistent with experimental data for atoms scattered in the backward direction relative to that of the exciting laser beam propagation.
Sokolov, I. M. Kupriyanov, D. V.; Havey, M. D.
2011-02-15
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.
I. M. Sokolov; D. V. Kupriyanov; M. D. Havey
2011-02-18
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.
Intershell correlations in nonresonant Compton scattering of an X-ray photon by an atom
Hopersky, A. N. Nadolinsky, A. M.; Ikoeva, K. Kh.; Khoroshavina, O. A.
2011-11-15
The role of intershell correlations in nonresonant Compton scattering of an X-ray photon by a free multielectron atom is studied theoretically for the Ar atom. The results of calculation are of a predictive nature. The developed mathematical formalism is general in nature and can be applied to a wide set of elements from the Periodic Table, for which the description of the wavefunctions of scattering states in the nonrelativistic Hartree-Fock approximation remains correct.
Atomic effects in heavy-ion elastic scattering
Casandjian, J.M.; Mittig, W.; Villari, A.C.C.; Auger, G.; Beunard, R.; Bianchi, L.; Ciffre, J.L.; Wieleczko, J.P.; Lepine-Szily, A.; Menchaca-Rocha, A.; Foti, A. Orr, N.A. Plagnol, E. Siemssen, R.H.
1997-11-01
Angular distributions of a {sup 208}Pb beam on {sup 208}Pb thin targets at very small angles were measured. The shape of the experimental distribution is not Gaussian, indicating a plural scattering regime rather than multiple scattering. The distribution was well reproduced by a Monte Carlo simulation of the straggling process. For the first time we observed and quantified the influence of the production of electrons during the scattering. This effect was observed in the angular correlation of the scattered {sup 208}Pb nuclei detected in kinematic coincidence and also in the limiting angle of the {sup 208}Pb scattered in a {sup 107,109}Ag target. This effect introduces a spread in the scattered angle which is of the same order of magnitude as the angular straggling. {copyright} {ital 1997} {ital The American Physical Society}
The measurement of angular differential cross sections at the SSL Atomic Scattering Facility
NASA Technical Reports Server (NTRS)
Kvale, Thomas J.
1988-01-01
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.
X-ray-photon scattering by an excited and ionized atom
NASA Astrophysics Data System (ADS)
Hopersky, Alexey N.; Nadolinsky, Alexey M.; Novikov, Sergey A.; Yavna, Victor A.
2015-02-01
The scattering process of an x-ray photon by an excited and ionized many-electron atom with attosecond photon-electron contact interaction is theoretically investigated. The results of the authors' recent work [Hopersky et al., Phys. Rev. A 88, 032704 (2013), 10.1103/PhysRevA.88.032704] are generalized for the cases of (a) arbitrary energy of the photon that prepares the scattering state and (b) the scattering of the photon by the continuous spectrum electron of the ionization state of the atom. The atom of Ne is considered as the object of the study. Along with the effects of normal Compton and elastic scattering, the existence of anomalous inelastic scattering is predicted. It may be assumed that this effect will become a basis for an experimental method of increasing the energy of the photons generated, for example, by a free-electron x-ray laser. It is determined that during the elastic scattering of a photon by an electron of the continuous spectrum, along with the known contribution from the jl Bessel function over the l =0 harmonic (Thomson scattering), there is also a contribution from Bessel functions with harmonics l ?[1 ;? ) . The experimental discovery and application of the anomalous Compton photon scattering effect directly by the atomic electron of the continuous spectrum have their own practical interest.
Analysis of an atom laser based on the spatial control of the scattering length
Carpentier, Alicia V.; Michinel, Humberto; Rodas-Verde, Maria I.; Perez-Garcia, Victor M.
2006-07-15
In this paper we analyze atom lasers based on the spatial modulation of the scattering length of a Bose-Einstein condensate. We demonstrate, through numerical simulations and approximate analytical methods, the controllable emission of matter-wave bursts and study the dependence of the process on the spatial shape of the scattering length along the axis of emission. We also study the role of an additional modulation of the scattering length in time.
Hongwei Xiong
2011-01-03
Considerable attention has been focused on Verlinde's recent work, claiming that Newton's gravity is not a fundamental force. In a recent work (arXiv:1012.5858), we give further the logic basis and basic clues to derive the Newton's gravity, inertia law and Einstein's weak equivalence principle. In this work, we show that if the gravity is not a fundamental force, in special case, it could be repulsive when quantum wavepacket effect is considered. This quantum gravity effect leads to several physical effects: (1) It is consistent with the universe with accelerating expansion, if the gravity and quantum effect of the fluctuating 'vacuum' (dark energy) is considered. The role of the cosmological constant is naturally interpreted when the gravity and quantum effect of the whole 'vacuum' background is considered. (2) It leads to new idea about black hole information paradox, no-hair theorem and Hawking radiation. (3) With a sphere full of superfluid Helium, we propose a feasible experimental scheme to test our idea with an atom interferometer placed in the sphere. Our calculations show that the accuracy Delta g/g below 10^(-8) could be used to test our idea, which satisfies the present experimental technique of atom interferometer.
Nuclear spin relaxation times in hydrogen-helium and methane-helium slush at 4 MHz using pulsed NMR
NASA Astrophysics Data System (ADS)
Hamida, J. A.
2005-03-01
We compare the nuclear spin-lattice and nuclear spin-spin relaxation times observed for small grains of hydrogen suspended in liquid helium (hydrogen-helium ``slush'') with that of methane-helium ``slush.'' The transport properties of these ``slush'' materials are critical to NASA's goal of realizing atomic propellant designs for future spacecraft. Atoms of active propellants are stored cryogenically in a host matrix such as hydrogen (H2) or methane (CH4) to prevent recombination while liquid helium is ideal for holding the host matrix and for easy transportation. The host matrix must therefore be stable in liquid helium. We find that for hydrogen ``slush,'' NMR rate is consistent with scattering at grain boundaries due to the large electric quadrupole moment of hydrogen; on the other hand the ``slush'' rate for methane is consistent with internal diffusion as opposed to surface scattering. We conclude that for atomic propellants, methane is a better host than hydrogen because grains of methane are better isolated from the helium bath.
A study of atom localization in an optical lattice by analysis of the scattered light
Christoph I Westbrook; Christophe Jurczak; Gerhard Birkl; Bruno Desruelle; William D. Phillips; Alain Aspect
2012-01-13
We present an experimental study of a four beam optical lattice using the light scattered by the atoms in the lattice. We use both intensity correlations and observations of the transient behavior of the scattering when the lattice is suddenly switched on. We compare results for 3 different configurations of the optical lattice. We create situations in which the Lamb-Dicke effect is negligible and show that, in contrast to what has been stated in some of the literature, the damping rate of the 'coherent' atomic oscillations can be much smaller than the inelastic photon scattering rate.
Scattering properties of weakly-bound dimers of Fermi atoms
NASA Astrophysics Data System (ADS)
Petrov, Dmitry
2005-03-01
We discuss the behavior of weakly bound bosonic dimers formed in a two-component Fermi gas with a large positive scattering length for the interspecies interaction. We present a theoretical approach for solving a few-body scattering problem and describe the physics of dimer-dimer elastic and inelastic scattering. We explain why these diatomic molecules, while in the highest ro-vibrational level, are characterized by remarkable collisional stability. Co-authors are Christophe Salomon, LKB, Ecole Normale Superieure, Paris, France; Georgy Shlyapnikov, LPTMS, University of South Paris, Orsay, France.
Energy Levels in Helium and Neon Atoms by an Electron-Impact Method.
ERIC Educational Resources Information Center
Taylor, N.; And Others
1981-01-01
Electronic energy levels in noble gas atoms may be determined with a simple teaching apparatus incorporating a resonance potentials tube in which the electron beam intensity is held constant. The resulting spectra are little inferior to those obtained by more elaborate electron-impact methods and complement optical emission spectra. (Author/SK)
The Scattering of Gas Atoms from Solid Surfaces
ERIC Educational Resources Information Center
Walton, Alan J.
1977-01-01
Traditional undergraduate courses in gas kinetic theory encourage the view that in all collisions between a gas atom and a surface, the angle of incidence of the gas atom equals its angle of reflection. This article illustrates and explains the incorrectness in assuming specular reflection and zero dwell time. (Author/MA)
Kaonic hydrogen atom and kaon-proton scattering length
Y. Yan
2009-05-29
Kaonic hydrogen is studied with various realistic potentials in an accurate numerical approach based on Sturmian functions. The kaon-proton scattering length extracted from the 1s energy shift of the kaonic hydrogen by applying the Deser-Trueman formula is severely inconsistent with the one derived by directly solving the scattering Schoedinger equation. We pay special attention to the recent measurement of the energy shift and decay width of the 1s kaonic hydrogen state by the DEAR Collaboration. After taking into account the large discrepancy between the extracted and directly-evaluated scattering lengths, we found theoretical predictions of most chiral SU(3) based models for the kaonic hydrogen decay width are consistent with the DEAR data. We warn the SIDDHARTA collaboration that it may not be reasonable to extract kaon-nucleon scattering lengths, by using the Coulomb-interaction corrected Deser-Truemab formula, from the planned measurement of kaonic hydrogen.
Wang, Xue Ping
Existence and Born-Oppenheimer Asymptotics of the Total Scattering Cross-Section in Ion-Atom-Ping.Wang@math.univ-nantes.fr Abstract We prove the #12;niteness of the total scattering cross-section for ion-atom collisions.e. the atom. Under more restrictive assumptions, we show that some e#11;ective interaction in Born
Momentum density of hcp and liquid helium-4 by inelastic neutron scattering
Hilleke, Russell Otto
1983-01-01
A measurement of the momentum density in hcp and liquid /sup 4/He by inelastic neutron scattering is reported. Using the Low Resolution Medium Energy Chopper Spectrometer at the Intense Pulsed Neutron Source at Argonne National Laboratory, momentum transfers in the range 12 to 22.5 A/sup -1/ were attained. At these momentum transfers, the momentum density of the sample is related to the dynamic structure factor by the impulse approximation. The measured momentum distribution is Gaussian and the kinetic energy is larger than proposed by existing theories. Data were taken on two solid samples, the first was a 19.45 cm/sup 3//mole hcp solid, the second was 18.20 cm/sup 3// mole; both solid samples were maintained at 1.70 K during data collection. Data were also taken on a liquid sample with a molar volume of 18.20 cm/sup 3//mole at 4.00 K. At 1.70 K the two solid samples are essentially in their ground states so that the measurement is of the ground state momentum density. The liquid sample was included to see if the difference between the liquid and solid momentum density at the same molar volume was observable.
Atomic scattering factors for K-shell and L-shell ionization by fast electrons
Oxley; Allen
2000-09-01
Atomic scattering factors have been calculated for K-shell ionization for elements in the range Z = 6 (carbon) to Z = 50 (tin) and for L-shell ionization in the range Z = 20 (calcium) to Z = 60 (neodymium). The calculations are based on relativistic Hartree-Fock wave functions for the atomic bound states and Hartree-Slater wave functions for the continuum wave functions. The results are presented in tabular form such that accurate values of the scattering factors can be obtained by cubic spline interpolation for incident electron energies between 50 and 400 keV and for scattering vectors with magnitude s = sin straight theta / lambda up to 2.5 A(-1) (2straight theta is the scattering angle and lambda the wavelength of the incident electrons). A separate parameterization of the form factors is given for 2.5 atomic scattering factors in an exponential form has been obtained by fitting the calculated form factors in the region s scattering factors are suitable for the calculation of ionization cross sections for use in atom location by channelling-enhanced microanalysis (ALCHEMI). PMID:10967525
Inelastic and reactive scattering of hyperthermal atomic oxygen from amorphous carbon
NASA Technical Reports Server (NTRS)
Minton, Timothy K.; Nelson, Christine M.; Brinza, David E.; Liang, Ranty H.
1991-01-01
The reaction of hyperthermal oxygen atoms with an amorphous carbon-13 surface was studied using a modified universal crossed molecular beams apparatus. Time-of-flight distributions of inelastically scattered O-atoms and reactively scattered CO-13 and CO2-13 were measured with a rotatable mass spectrometer detector. Two inelastic scattering channels were observed, corresponding to a direct inelastic process in which the scattered O-atoms retain 20 to 30 percent of their initial kinetic energy and to a trapping desorption process whereby O-atoms emerge from the surface at thermal velocities. Reactive scattering data imply the formation of two kinds of CO products, slow products whose translational energies are determined by the surface temperature and hyperthermal (Approx. 3 eV) products with translational energies comprising roughly 30 percent of the total available energy (E sub avl), where E sub avl is the sum of the collision energy and the reaction exothermicity. Angular data show that the hyperthermal CO is scattered preferentially in the specular direction. CO2 product was also observed, but at much lower intensities than CO and with only thermal velocities.
Compton scattering of an X-ray photon by an open-shell atom
Hopersky, A. N. Nadolinsky, A. M.
2012-09-15
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.
Potentials for High-Energy Scattering from Hydrogenlike Atoms
Reading, John F.
1970-01-01
contains the essential difficulties of electron-, muon-, or proton-hydrogen scattering at high energies. The wave equation describing the motion is [- (8/2m, )~?'+H, + V(r, H)] g =EN, where H, = ?(5'/2m, )&'?-e /r- IVO and V(r, 8)= e'[(I/H) I/I R ?r... perturbs the bound system from which it is scattering. The projectile is considered initially to be moving along the Z axis at some impact parameter 8; we define y, as e iks~ where k= (2mkE/h ) fan@' e V ? ?+H + V(r H) p =P. p2~ ~ m ezP If we...
Ground State Properties of Cold Bosonic Atoms at Large Scattering Lengths
Song Junliang; Zhou Fei
2009-07-10
In this Letter, we study bosonic atoms at large scattering lengths using a variational method where the condensate amplitude is a variational parameter. We further examine momentum distribution functions, chemical potentials, the speed of sound, and spatial density profiles of cold bosonic atoms in a trap in this limit. The latter two properties turn out to bear similarities to those of Fermi gases. The estimates obtained here are applicable near Feshbach resonances, particularly when the fraction of atoms forming three-body structures is small and can be tested in future cold atom experiments.
Ultralow energy scattering of a He atom off a He dimer
Kolganova, E.A.; Motovilov, A.K.; Sofianos, S.A.
1997-09-01
We present a mathematically rigorous method suitable for bound-state and scattering process calculations for various three-atomic or molecular systems where the underlying forces are of a hard-core nature. We employed this method to calculate the binding energies and the ultra-low-energy scattering phase shifts below as well as above the breakup threshold for the three-He-atom system. The method has proved to be highly successful and suitable for solving the three-body bound-state and scattering problem in configuration space and thus it paves the way to study various three-atomic systems, and to calculate important quantities such as the cross sections, recombination rates, etc. {copyright} {ital 1997} {ital The American Physical Society}
Light scattering for thermometry of fermionic atoms in an optical lattice
J. Ruostekoski; C. J. Foot; A. B. Deb
2009-09-02
We propose a method for measuring the temperature of fermionic atoms in an optical lattice potential from the intensity of the scattered light in the far-field diffraction pattern. We consider a single-component gas in a tightly-confined two-dimensional lattice, illuminated by far off-resonant light driving a cycling transition. Our calculations show that thermal correlations of the fermionic atoms generate fluctuations in the intensity of the diffraction pattern of light scattered from the atomic lattice array and that this signal can be accurately detected above the shot noise using a lens to collect photons scattered in a forward direction (with the diffraction maxima blocked). The sensitivity of the thermometer is enhanced by an additional harmonic trapping potential.
Scattering of coherent states on a single artificial atom
B. Peropadre; J. Lindkvist; I. -C. Hoi; C. M. Wilson; J. J. Garcia-Ripoll; P. Delsing; G. Johansson
2012-10-08
In this work we theoretically analyze a circuit QED design where propagating quantum microwaves interact with a single artificial atom, a single Cooper pair box. In particular, we derive a master equation in the so-called transmon regime, including coherent drives. Inspired by recent experiments, we then apply the master equation to describe the dynamics in both a two-level and a three-level approximation of the atom. In the two-level case, we also discuss how to measure photon antibunching in the reflected field and how it is affected by finite temperature and finite detection bandwidth.
Inelastic scattering of electrons by metastable hydrogen atoms in a laser field
NASA Astrophysics Data System (ADS)
Buica, Gabriela
2015-09-01
The inelastic scattering of fast electrons by metastable hydrogen atoms in the presence of a linearly polarized laser field is theoretically studied in the domain of field intensities below 1010 W/cm2. The interaction of the hydrogen atom with the laser field is described by first-order time-dependent perturbation theory, while the projectile electrons interacting with the laser field are described by the Gordon-Volkov wave functions. An analytic expression is obtained for the differential scattering cross section in the first-order Born approximation for laser-assisted inelastic e--H (2 s ) scattering for the 2 s ?n l excitation. Detailed analytical and numerical results are presented for inelastic scattering accompanied by one-photon absorption, and the angular dependence and resonance structure of the differential cross sections are discussed for the 2 s ?4 l excitation of metastable hydrogen.
Exciton-Polariton scattering for defect detection in cold atom Optical Lattices
Hashem Zoubi; Helmut Ritsch
2007-10-29
We study the effect of defects in the Mott insulator phase of ultracold atoms in an optical lattice on the dynamics of resonant excitations. Defects, which can either be empty sites in a Mott insulator state with one atom per site or a singly occupied site for a filling factor two, change the dynamics of Frenkel excitons and cavity polaritons. While the vacancies in first case behave like hard sphere scatters for excitons, singly occupied sites in the latter case can lead to attractive or repulsive scattering potentials. We suggest cavity polaritons as observation tool of such defects, and show how the scattering can be controlled in changing the exciton-photon detuning. In the case of asymmetric optical lattice sites we present how the scattering effective potential can be detuned by the cavity photon polarization direction, with the possibility of a crossover from a repulsive into an attractive potential.
Design and construction of a sample preparation chamber for atomic beam scattering
Nielsen, C.
1992-05-18
A new type of atomic beam scattering spectrometer was built to advance the usefulness of the atomic beam scattering technique as a surface dynamics probe. The facility was not only built to investigate the typical alkali halide samples such as NaCl, NaF, and LiF, but also to investigate metallic surfaces. Metal samples are more complicated to study, due to their reactive surfaces and the sample preparation process. A surface analysis chamber was constructed as an attachment to the scattering facility to treat samples under ultra high vacuum (UHV) and then transfer these samples into the scattering facility. This surface analysis chamber is referred to as the sample preparation chamber and is the basis for this thesis.
Liao, Chen-Ting; Camp, Seth; Schafer, Kenneth J; Gaarde, Mette B
2015-01-01
We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and subsequently to the appearance of new, narrow features in the absorption line.
Liao, Chen-Ting; Sandhu, Arvinder; Camp, Seth; Schafer, Kenneth J; Gaarde, Mette B
2015-04-10
We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and subsequently, to the appearance of new, narrow features in the absorption line. PMID:25910116
Chen-Ting Liao; Arvinder Sandhu; Seth Camp; Kenneth J. Schafer; Mette B. Gaarde
2015-03-09
We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and subsequently to the appearance of new, narrow features in the absorption line.
Temperature dependence in rainbow scattering of hyperthermal Ar atoms from LiF(001)
NASA Astrophysics Data System (ADS)
Hayes, W. W.; Manson, J. R.
2015-11-01
Recent experiments have reported measurements of rainbow scattering features in the angular distributions of hyperthermal Ar colliding with LiF(001) [Kondo et al., J. Chem. Phys. 122, 244713 (2005)]. A theory of atom-surface collisions recently developed by the authors, based on the eikonal approximation, that includes multiphonon energy transfers is used to explain the temperature dependence of the measured scattered angular distribution spectra.
Nucleon Polarizabilities: from Compton Scattering to Hydrogen Atom
Hagelstein, Franziska; Pascalutsa, Vladimir
2015-01-01
We review the current state of knowledge of the nucleon polarizabilities and of their role in nucleon Compton scattering and in hydrogen spectrum. We discuss the basic concepts, the recent lattice QCD calculations and advances in chiral effective-field theory. On the experimental side, we review the ongoing programs aimed to measure the nucleon (scalar and spin) polarizabilities via the Compton scattering processes, with real and virtual photons. A great part of the review is devoted to the general constraints based on unitarity, causality, discrete and continuous symmetries, which result in model-independent relations involving nucleon polarizabilities. We (re-)derive a variety of such relations and discuss their empirical value. The proton polarizability effects are presently the major sources of uncertainty in the assessment of the muonic hydrogen Lamb shift and hyperfine structure. Recent calculations of these effects are reviewed here in the context of the "proton-radius puzzle". We conclude with summary...
Imaging Nonequilibrium Atomic Vibrations with X-ray Diffuse Scattering
Trigo, M.; Chen, J.; Vishwanath, V.H.; Sheu, Y.M.; Graber, T.; Henning, R.; Reis, D; ,
2011-03-03
We use picosecond x-ray diffuse scattering to image the nonequilibrium vibrations of the lattice following ultrafast laser excitation. We present images of nonequilibrium phonons in InP and InSb throughout the Brillouin-zone which remain out of equilibrium up to nanoseconds. The results are analyzed using a Born model that helps identify the phonon branches contributing to the observed features in the time-resolved diffuse scattering. In InP this analysis shows a delayed increase in the transverse acoustic (TA) phonon population along high-symmetry directions accompanied by a decrease in the longitudinal acoustic (LA) phonons. In InSb the increase in TA phonon population is less directional.
Light Scattering for Thermometry of Fermionic Atoms in an Optical Lattice
Ruostekoski, J.; Foot, C. J.; Deb, A. B.
2009-10-23
We propose a method of using off-resonant light scattering to measure the temperature of fermionic atoms tightly confined in a two-dimensional optical-lattice potential. We show that fluctuations of the intensity in the far-field diffraction pattern arising from thermal correlations of the atoms can be accurately detected above the shot noise by collecting photons scattered in a forward direction, with the diffraction maxima blocked. The sensitivity of this method of thermometry is enhanced by an additional harmonic trapping potential.
Direct measurement of the Wigner time delay for the scattering of light by a single atom.
Bourgain, R; Pellegrino, J; Jennewein, S; Sortais, Y R P; Browaeys, A
2013-06-01
We have implemented the Gedanken experiment of an individual atom scattering a wave packet of near-resonant light, and measured the associated Wigner time delay as a function of the frequency of the light. In our apparatus, the atom behaves as a two-level system and we have found delays as large as 42 ns at resonance, limited by the lifetime of the excited state. This delay is an important parameter in the problem of collective near-resonant scattering by an ensemble of interacting particles, which is encountered in many areas of physics. PMID:23722804
Measurement of effective atomic number of gunshot residues using scattering of gamma rays
NASA Astrophysics Data System (ADS)
Y?lmaz, Demet; Tur?ucu, Ahmet; Uzuno?lu, Zeynep; Korucu, Demet
2014-09-01
Better understanding of gunshot residues and the major elemental composition would be valuable to forensic scientists for their analysis work and interpretation of results. In the present work, the effective atomic numbers of gunshot residues (cartridge case, bullet core, bullet jacket and gunpowder) were analyzed using energy dispersive X-ray analysis (EDX). The scattering of 59.54 keV gamma rays is studied using a high-resolution HPGe detector. The experiment is performed on various elements with atomic number in the 4?Z?82. The intensity ratio of coherent to Compton scattered peaks, corrected for photo-peak efficiency of gamma detector and absorption of photons in the sample and air, is plotted as a function of atomic number and constituted a best-fit-curve. From this fit-curve, the respective effective atomic numbers of gunshot residues are determined.
{ital Ab initio} study of the anomalies in the He-atom-scattering spectra of H/Mo(110) and H/W(110)
Kohler, B.; Ruggerone, P.; Scheffler, M.
1997-11-01
Helium-atom-scattering (HAS) studies of the H-covered Mo(110) and W(110) surfaces reveal a twofold anomaly in the respective dispersion curves. In order to explain this unusual behavior we performed density-functional theory calculations of the atomic and electronic structure, the vibrational properties, and the spectrum of electron-hole excitations of those surfaces. Our work provides evidence for hydrogen-adsorption induced Fermi-surface nesting. The respective nesting vectors are in excellent agreement with the HAS data and recent angle resolved photoemission experiments of the H-covered alloy system Mo{sub 0.95}Re{sub 0.05}(110). Also, we investigated the electron-phonon coupling and discovered that the Rayleigh phonon frequency is lowered for those critical wave vectors. Moreover, the smaller indentation in the HAS spectra can be clearly identified as a Kohn anomaly. Based on our results for the susceptibility and the recently improved understanding of the He-scattering mechanism we argue that the larger anomalous dip is due to a direct interaction of the He atoms with electron-hole excitations at the Fermi level. {copyright} {ital 1997} {ital The American Physical Society}
Positron scattering from hydrogen atom with screened Coulomb potentials
Ghoshal, Arijit; Nayek, Sujay; Kamali, M. Z. M.; Ratnavelu, K.
2014-03-05
Elastic positron-hydrogen collisions with screened Coulomb potentials have been investigated using a second-order distorted wave Born approximation in the momentum space. Two types of potentials have been considered, namely, static screened Coulomb potential and exponential cosine-screened Coulomb potential. Using a simple variationally determined hydrogenic wave function it has been possible to obtain the scattering amplitude in a closed form. A detailed study has been made on the differential and total cross sections in the energy range 20–300 eV.
Comment on ``Semiempirical potentials for positron scattering by atoms''
NASA Astrophysics Data System (ADS)
Sullivan, J. P.; Machacek, J. R.; Buckman, S. J.; Bray, I.
2012-03-01
In their recent paper, Assafräo [D. Assafräo, H. R. J. Walters, F. Arretche, A. Dutra, and J. R. Mohallem, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.022713 84, 022713 (2011)] use a scaled adiabatic potential to calculate total and differential cross sections for positron scattering from a variety of targets. They claimed that the results are “very close to experimental and best theoretical data.” A brief examination of the recent literature on this subject demonstrates, however, that comparisons with several important and recent results have not been made, and that such comparisons clearly affect the accuracy of their conclusions.
Nucleon Polarizabilities: from Compton Scattering to Hydrogen Atom
Franziska Hagelstein; Rory Miskimen; Vladimir Pascalutsa
2015-12-15
We review the current state of knowledge of the nucleon polarizabilities and of their role in nucleon Compton scattering and in hydrogen spectrum. We discuss the basic concepts, the recent lattice QCD calculations and advances in chiral effective-field theory. On the experimental side, we review the ongoing programs aimed to measure the nucleon (scalar and spin) polarizabilities via the Compton scattering processes, with real and virtual photons. A great part of the review is devoted to the general constraints based on unitarity, causality, discrete and continuous symmetries, which result in model-independent relations involving nucleon polarizabilities. We (re-)derive a variety of such relations and discuss their empirical value. The proton polarizability effects are presently the major sources of uncertainty in the assessment of the muonic hydrogen Lamb shift and hyperfine structure. Recent calculations of these effects are reviewed here in the context of the "proton-radius puzzle". We conclude with summary plots of the recent results and prospects for the near-future work.
Search for Elastic Coherent Neutrino Scattering off Atomic Nuclei at the Kalinin Nuclear Power Plant
NASA Astrophysics Data System (ADS)
Akimov, D. Yu.; Belov, V. A.; Bolozdynya, A. I.; Burenkov, A. A.; Efremenko, Yu. V.; Etenko, A. V.; Kaplin, V. A.; Khromov, A. V.; Konovalov, A. M.; Kovalenko, A. G.; Kumpan, A. V.; Melikyan, Yu. A.; Rudik, D. G.; Sosnovtsev, V. V.
We propose to detect and study neutrino neutral elastic coherent scattering off atomic nuclei with two-phase emission detector with liquid xenon as a target medium. One of the possible experimental site is a Kalinin Nuclear Power Plant (KNPP) situated in the Russian Federation. In this paper we discuss the design of the detector and expected signals and background for this site.
Positron scattering from hydrogen atom embedded in weakly coupled plasma
Ghoshal, Arijit; Kamali, M. Z. M.; Ratnavelu, K.
2013-01-15
The positron-hydrogen collision problem in weakly coupled plasma environment has been investigated by applying a formulation of the three-body collision problem in the form of coupled multi-channel two-body Lippmann-Schwinger equations. The interactions among the charged particles in the plasma have been represented by Debye-Huckel potentials. A simple variational hydrogenic wave function has been employed to calculate the partial-wave scattering amplitude. Plasma screening effects on various possible mode of fragmentation of the system e{sup +}+H(1s) during the collision, such as 1s{yields}1s and 2s{yields}2s elastic collisions, 1s{yields}2s excitation, positronium formation, elastic proton-positronium collisions, have been reported. Furthermore, a detailed study has been made on differential and total cross sections of the above processes in the energy range 13.6-350 eV of the incident positron.
Zhou, Yun Pollak, Eli; Miret-Artés, Salvador
2014-01-14
A second order classical perturbation theory is developed and applied to elastic atom corrugated surface scattering. The resulting theory accounts for experimentally observed asymmetry in the final angular distributions. These include qualitative features, such as reduction of the asymmetry in the intensity of the rainbow peaks with increased incidence energy as well as the asymmetry in the location of the rainbow peaks with respect to the specular scattering angle. The theory is especially applicable to “soft” corrugated potentials. Expressions for the angular distribution are derived for the exponential repulsive and Morse potential models. The theory is implemented numerically to a simplified model of the scattering of an Ar atom from a LiF(100) surface.
Continetti, R.E.; Balko, B.A.; Lee, Y.T.
1989-02-01
A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H/sub 2/ /minus/> DH + H and the substitution reaction D + C/sub 2/H/sub 2/ /minus/> C/sub 2/HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible. 18 refs., 9 figs.
M. Macovei; J. Evers; C. H. Keitel
2007-02-14
Photon correlations and cross-correlations of light scattered by a regular structure of strongly driven atoms are investigated. At strong driving, the scattered light separates into distinct spectral bands, such that each band can be treated as independent, thus extending the set of observables. We focus on second-order intensity-intensity correlation functions in two- and multi-atom systems. We demonstrate that for a single two-photon detector as, e.g., in lithography, increasing the driving field intensity leads to an increased spatial resolution of the second-order two-atom interference pattern. We show that the cross-correlations between photons emitted in the spectral sidebands violate Cauchy-Schwartz inequalities, and that their emission ordering cannot be predicted. Finally, the results are generalized for multi-particle structures, where we find results different from those in a Dicke-type sample.
Atomic and molecular diamagnetic susceptibilities from Compton scattering data
NASA Astrophysics Data System (ADS)
Gadre, Shridhar R.; Pathak, Rajeev K.
1990-04-01
A procedure is proposed for the extraction of molar Larmor diamagnetic susceptibilities ?L=-N0e2
Glyde, Henry R.
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
NASA Astrophysics Data System (ADS)
Vieitez, M. O.; van Duijn, E. J.; Ubachs, W.; Witschas, B.; Meijer, A.; de Wijn, A. S.; Dam, N. J.; van de Water, W.
2010-10-01
We study Rayleigh-Brillouin scattering in gases of N2, O2, and SF6 molecules, Kr atoms, and He-Xe and He-CO2 mixtures at pressures ranging from 1 to 3 bar and using two different experimental setups. In one setup, we measure spectra of light scattered by thermal density fluctuations (spontaneous Rayleigh-Brillouin scattering); in the second setup density waves are induced in the overlap region of two counterpropagating laser beams (coherent Rayleigh-Brillouin scattering). We compare measured spectra to the Tenti models and to a recent model for mixtures. We find new values of the bulk viscosity, which is a parameter in line-shape models that allows for internal degrees of freedom. Both experiments agree on the value of the bulk viscosity. Our results indicate a need for new line-shape models for mixtures of molecules with internal degrees of freedom.
Vieitez, M. O.; Duijn, E. J. van; Ubachs, W.; Witschas, B.; Meijer, A.; Wijn, A. S. de; Dam, N. J.; Water, W. van de
2010-10-15
We study Rayleigh-Brillouin scattering in gases of N{sub 2}, O{sub 2}, and SF{sub 6} molecules, Kr atoms, and He-Xe and He-CO{sub 2} mixtures at pressures ranging from 1 to 3 bar and using two different experimental setups. In one setup, we measure spectra of light scattered by thermal density fluctuations (spontaneous Rayleigh-Brillouin scattering); in the second setup density waves are induced in the overlap region of two counterpropagating laser beams (coherent Rayleigh-Brillouin scattering). We compare measured spectra to the Tenti models and to a recent model for mixtures. We find new values of the bulk viscosity, which is a parameter in line-shape models that allows for internal degrees of freedom. Both experiments agree on the value of the bulk viscosity. Our results indicate a need for new line-shape models for mixtures of molecules with internal degrees of freedom.
An x ray scatter approach for non-destructive chemical analysis of low atomic numbered elements
NASA Technical Reports Server (NTRS)
Ross, H. Richard
1993-01-01
A non-destructive x-ray scatter (XRS) approach has been developed, along with a rapid atomic scatter algorithm for the detection and analysis of low atomic-numbered elements in solids, powders, and liquids. The present method of energy dispersive x-ray fluorescence spectroscopy (EDXRF) makes the analysis of light elements (i.e., less than sodium; less than 11) extremely difficult. Detection and measurement become progressively worse as atomic numbers become smaller, due to a competing process called 'Auger Emission', which reduces fluorescent intensity, coupled with the high mass absorption coefficients exhibited by low energy x-rays, the detection and determination of low atomic-numbered elements by x-ray spectrometry is limited. However, an indirect approach based on the intensity ratio of Compton and Rayleigh scattered has been used to define light element components in alloys, plastics and other materials. This XRS technique provides qualitative and quantitative information about the overall constituents of a variety of samples.
Theoretical Studies of Energy and Momentum Exchange in Atomic and Molecular Scattering from Surfaces
Joseph R. Manson
2005-06-30
The contributions that we have made during the grant period of DE-FG02-98ER45704 can be placed into six different categories: (1) advances in the Theory of Molecule-Surface Scattering, (2) advances in the Theory of Atom-Surface Scattering, (3) utilization of scattering theory to Extract Physical Information about Surfaces, (4) Gas-Surface Interactions, (5) Ion Scattering from surfaces and (6) Scanning Tunneling Microscopy (STM). These six topics are discussed below as individual listings under the title 'IV. Detailed description of research accomplishments'. These advances show that we have made significant progress on several scientific problems in atomic and molecular surface scattering during the course of this grant as well as contributions to other areas. It is also noted that this work, although fundamentally theoretical, is marked by its strong motivation to explain current experimental measurements. This was an important secondary goal in the proposed work. We have developed theory that is useful to experimentalists in the explanation and analysis of their experimental data.
O. S. Mishina; D. V. Kupriyanov; J. H. Muller; E. S. Polzik
2007-02-27
We discuss theoretically quantum interface between light and a spin polarized ensemble of atoms with the spin >= 1 based on an off-resonant Raman scattering. We present the spectral theory of the light-atoms interaction and show how particular spectral modes of quantum light couple to spatial modes of the extended atomic ensemble. We show how this interaction can be used for quantum memory storage and retrieval and for deterministic entanglement protocols. The proposed protocols are attractive due to their simplicity since they involve just a single pass of light through atoms without the need for elaborate pulse shaping or quantum feedback. As a practically relevant example we consider the interaction of a light pulse with hyperfine components of D1 line of 87Rb. The quality of the proposed protocols is verified via analytical and numerical analysis.
Suppressed grain-boundary scattering in atomic layer deposited Nb:TiO2 thin films
NASA Astrophysics Data System (ADS)
Niemelä, Janne-Petteri; Hirose, Yasushi; Shigematsu, Kei; Sano, Masahito; Hasegawa, Tetsuya; Karppinen, Maarit
2015-11-01
We have fabricated high-quality thin films of the transparent conducting anatase Nb:TiO2 on glass substrates through atomic layer deposition, and a subsequent reductive heat treatment of the as-deposited amorphous films. Hall-effect measurements and Drude-fitting of the Vis-NIR spectra indicate that for lightly doped films deposited at temperatures around 170 °C, grain boundary scattering becomes negligible and the mobility is predominately limited by phonon-electron scattering inherent to the anatase lattice and by impurities. Simultaneously, such lighter doping leads to reduced plasma absorption, thereby improving material's performance as a transparent conductor.
Measurements of ultra-low-energy electron scattering cross sections of atoms and molecules
Kitajima, M.; Shigemura, K.; Kurokawa, M.; Odagiri, T.; Kato, H.; Hoshino, M.; Tanaka, H.; Ito, K.
2014-03-05
A new experimental technique for the total cross section measurements of ultra-low energy electron collisions with atoms and molecules utilizing the synchrotron radiation is presented. The technique employs a combination of the penetrating field technique and the threshold photoionization of rare gas atoms using the synchrotron radiation as an electron source in order to produce a high resolution electron beam at very low energy. Absolute total cross sections for electron scattering from He, Ne, Ar, Kr, and Xe in the energy region from extremely low electron energy to 20 eV are presented.
An atomic layer deposition chamber for in situ x-ray diffraction and scattering analysis
Geyer, Scott M.; Methaapanon, Rungthiwa; Kim, Woo-Hee; Bent, Stacey F.; Johnson, Richard W.; Van Campen, Douglas G.; Metha, Apurva
2014-05-15
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 SiO{sub 2} and SrTiO{sub 3} (001) using synchrotron-based high resolution x-ray diffraction, grazing incidence x-ray diffraction, and grazing incidence small angle scattering.
An atomic layer deposition chamber for in situ x-ray diffraction and scattering analysis.
Geyer, Scott M; Methaapanon, Rungthiwa; Johnson, Richard W; Kim, Woo-Hee; Van Campen, Douglas G; Metha, Apurva; Bent, Stacey F
2014-05-01
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
An atomic layer deposition chamber for in situ x-ray diffraction and scattering analysis
NASA Astrophysics Data System (ADS)
Geyer, Scott M.; Methaapanon, Rungthiwa; Johnson, Richard W.; Kim, Woo-Hee; Van Campen, Douglas G.; Metha, Apurva; Bent, Stacey F.
2014-05-01
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.
Light-scattering detection of quantum phases of ultracold atoms in optical lattices
Ye Jinwu; Zhang, J. M.; Liu, W. M.; Zhang Keye; Li Yan; Zhang Weiping
2011-05-15
Ultracold atoms loaded on optical lattices can provide unprecedented experimental systems for the quantum simulations and manipulations of many quantum phases. However, so far, how to detect these quantum phases effectively remains an outstanding challenge. Here, we show that the optical Bragg scattering of cold atoms loaded on optical lattices can be used to detect many quantum phases, which include not only the conventional superfluid and Mott insulating phases, but also other important phases, such as various kinds of charge density wave (CDW), valence bond solid (VBS), CDW supersolid (CDW-SS) and Valence bond supersolid (VB-SS).
Diffraction of swift atoms after grazing scattering from metal surfaces: N/Ag(111) system
Gravielle, M. S.; Bocan, G. A.; Diez Muino, R.
2010-11-15
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.
Electron-indium atom scattering and analysis of electron and optical spectra
NASA Astrophysics Data System (ADS)
Rabasovi?, Maja S.
2014-12-01
Experimental study of indium atom using electron and optical spectroscopy is presented in this paper. Both experimental techniques including experimental setups are described. Differential and integrated cross sections on elastic and inelastic electron scattering by indium atom are measured using electron spectrometer. The measurements are performed at incident electron energies of E0 = 10, 20, 40, 60, 80 and 100 eV within the large scattering angles ranging from 10° to 150° in steps of 10°. The experimental results are presented and comparison with the values predicted by calculated optical potentials method is conducted, showing good agreement. The differential cross sections (DCSs) for electron-impact excitation of the resonant state 6s 2S1/2 of Indium atom are measured at small and large angles. The forward scattering function method has been used for normalizing the generalized oscillator strengths (GOS) to determine optical oscillator strength and obtaining the absolute DCS values. Optical spectrum of In I and In II lines has been acquired by a streak camera. The experimental results regarding indium lines obtained by time resolved laser induced breakdown spectroscopy (LIBS) could be useful for obtaining the important plasma parameters such as temperature, electron density as well as plasma-expansion velocity and plasma starting times.
V. V. Flambaum; M. G. Kozlov; G. F. Gribakin
2015-05-13
In open-shell atoms and ions, processes such as photoionization, combination (Raman) scattering, electron scattering and recombination, are often mediated by many-electron compound resonances. We show that their interference (neglected in the independent-resonance approximation) leads to a coherent contribution, which determines the energy-averaged total cross sections of electron- and photon-induced reactions obtained using the optical theorem. In contrast, the partial cross sections (e.g., electron recombination, or photon Raman scattering) are dominated by the stochastic contributions. Thus, the optical theorem provides a link between the stochastic and coherent contributions of the compound resonances. Similar conclusions are valid for reactions via compound states in molecules and nuclei.
NASA Astrophysics Data System (ADS)
Lee, Y.; Combi, M. R.; Tenishev, V.; Bougher, S. W.
2011-12-01
The production of energetic particles results in the formation of hot atom coronas on the Martian atmosphere. Being the most important reaction for the exosphere on Mars, dissociative recombination (DR) of O2+ ion is the dominant source of the production of hot atomic oxygen, which occurs mostly deep in the dayside thermosphere of Mars. As noted by Krestyanikova and Shematovitch [2005], the collision cross sections are critical parameters. The two different assumptions for scattering collision cross sections are: (1) considering total cross section and scattering collisions as elastic hard sphere encounters [Nagy et al. 1981], and (2) using the distribution of scattering angles in the center-of-mass frame. In this study, the DR of O2+ is assumed to be the only source of hot oxygen in the Martian thermosphere. The total and differential cross sections are obtained separately to calculate the hot oxygen fluxes from Martian upper atmosphere. The two different approximations for the O + O collision cross section are compared to study how they affect the calculation of hot oxygen escape fluxes. One assumes a single total cross section and hard sphere scattering. The other uses the scattering angle dependent differential scattering cross section of Kharchencko et al. [2000]. To describe self-consistently the exosphere and the upper thermosphere, a combination of our 3D Direct Simulation Monte Carlo (DSMC) model [Valeille, A., Combi, M., Bougher, S., Tenishev, V., Nagy, A., 2009. J. Geophys. Res. 114, E11006. doi:10.1029/2009JE003389] and the 3D Mars Thermosphere General Circulation Model (MTGCM) [Bougher, S., Bell, J., Murphy, J., Lopez-Valverde, M., Withers, P., 2006. Geophys. Res. Lett. 32, doi: 10.1029/2005GL024059. L02203] is used. Profiles of density and temperature, atmospheric loss rates and return fluxes as functions of the Solar Zenith Angle (SZA) are studied using the model for the cases considered. Comparisons of DSMC model outputs will be made with those from other recent exosphere model studies.
NASA Astrophysics Data System (ADS)
Beijerinck, H. C. W.; van der Kam, P. M. A.; Thijssen, W. J. G.; Verster, N. F.
1980-01-01
The scattering amplitude is investigated for small angles ?* ? 8.5, with ?* = ?/? o a reduced scattering angle. The scaling angle is ? o = (4?/ k2Q3) 1/2, with k the wavenumber and Q3 the total cross section due to the attractive branch of the intermolecular potential. Both pure inverse power potentials and realistic intermolecular potentials are investigated. The method used is a least-square curve fit of the real and imaginary parts of quantum-mechanically calculated scattering amplitudes f(?) with suitable model functions. The shape of these model functions is partially based on the classical and semiclassical results for small angle scattering. For the shape of the attractive contribution to the differential cross section ? 3(?) in the case of an inverse power potential we give a new model function that describe the quantum oscillations (diffraction) modulating the classical result ? e1(?) HE for the differential cross section in the high energy approximation, i.e. the approximation of a straight line trajectory. The first order correction on this straight line approximation is also derived and incorporated in our model function. For s = 6 and 2.5 ? ?* ? 8.5 we find a description of ? 3(?)/? e1(?) HE with a rms deviation of 2.3 × 10 -3. For the shape of the differential cross section at small angles we give a second, new semi-empirical model functions, ? 3(?)/? 3(0) = [1 -1 c1 sin ( c2?* 2) + c3?* 2] -(3 + 1)/3, with s the power of the potential. The asymptotic behaviour of this function for ?* ? 1 and ?* ? is in good agreement with the corresponding semiclassical and classical results. For s = 6 the parameters are c1 = 3.75, c2 = 0.556, and c3 = 2.94, resulting in a description of ? 3(?)/? 3(0) with a rms deviation of 0.9 × 10 -3 for ?* ? 4.0. A simple and accurate model function for the phase angle ? a(?) = arg( f(?)) enables us to include the glory behaviour in the case of a realistic intermolecular potential. For the analysis of the differential cross section of a realistic potential a suitable model function for the glory contribution is added, resulting in a description of ?(?)/?(0) with a rms deviation of 3 × 10 -3 for ?* ? 4.0. A universal set of parameters is presented that can be used for predicting the differential cross section for a realistic intermolecular potential. It is also shown that the velocity dependency of the attractive and the glory contribution to the imaginary part of the scattering amplitude for ?* = 0, i.e. the total cross section, can be effectively used for predicting the small angle behaviour of the differential cross section.
Changes in the Atomic Structure through Glass Transition Observed by X-Ray Scattering
Egami, Takeshi
2012-01-01
The glass transition involves a minor change in the internal energy, and yet the physical and mechanical properties of a glass change dramatically. In order to determine the evolution of the atomic structure through the glass transition, we employed in-situ synchrotron X-ray scattering measurements as a function of temperature on a model material: Zr-Cu-Al metallic glass. We found that the thermal expansion at the atomic level is smaller than the macroscopic thermal expansion, and significantly increases above the glass transition temperature. The observed changes in the pair-distribution function (PDF) are explained in terms of the fluctuations in the local atomic volume and their change through the glass transition.
Umstadter, Donald
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
Kim, Tae-Kyun
1996-01-01
To examine the jet mixing in air-blast twin fluid atomization, the sonic and supersonic air jet developments have been exclusively visualized using the Rayleigh scattering principle and the development of liquid spray has been separately visualized...
Atomic scattering spectroscopy for determination of the polarity of semipolar AlN grown on ZnO
Kobayashi, Atsushi; Ohta, Jitsuo; Ueno, Kohei; Oshima, Masaharu; Synchrotron Radiation Research Organization, The University of Tokyo, Tokyo 113-8656 ; Fujioka, Hiroshi; CREST, Japan Science and Technology Agency , Tokyo 102-0076
2013-11-04
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.
Krasnokutski, Serge A. Huisken, Friedrich
2014-12-07
The reaction of carbon atoms with benzene has been investigated in liquid helium droplets at T = 0.37 K. We found an addition of the carbon atom to form an initial intermediate complex followed by a ring opening and the formation of a seven-membered ring. In contrast to a previous gas phase study, the reaction is frozen after these steps and the loss of hydrogen does not occur. A calorimetric technique was applied to monitor the energy balance of the reaction. It was found that more than 267 kJ mol{sup ?1} were released in this reaction. This estimation is in line with quantum chemical calculations of the formation energy of a seven-membered carbon ring. It is suggested that reactions of this kind could be responsible for the low abundance of small polycyclic aromatic hydrocarbon molecules in the interstellar medium. We also found the formation of weakly bonded water-carbon adducts, in which the carbon atom is linked to the oxygen atom of the water molecule with a binding energy of about 33.4 kJ mol{sup ?1}.
Neutrons on a surface of liquid helium
P. D. Grigoriev; O. Zimmer; T. Ziman; A. D. Grigoriev
2015-09-21
We investigate the possibility of ultracold neutron (UCN) storage in quantum states defined by the combined potentials of the Earth's gravity and the neutron optical repulsion by a horizontal surface of liquid helium. We analyse the stability of the lowest quantum state, which is most susceptible to perturbations due to surface excitations, against scattering by helium atoms in the vapor and by excitations of the liquid, comprised of ripplons, phonons and surfons. This is an unusual scattering problem since the kinetic energy of the neutron parallel to the surface may be much greater than the binding energies perpendicular. The total scattering time constant of these UCNs at 0.7 K is found to exceed one hour, and rapidly increasing with decreasing temperature. Such low scattering rates should enable high-precision measurements of the scheme of discrete energy levels, thus providing improved access to short-range gravity. The system might also be useful for neutron beta-decay experiments. We also sketch new experimental concepts for level population and trapping of UCNs above a flat horizontal mirror.
Neutrons on a surface of liquid helium
Grigoriev, P D; Ziman, T; Grigoriev, A D
2015-01-01
We investigate the possibility of ultracold neutron (UCN) storage in quantum states defined by the combined potentials of the Earth's gravity and the neutron optical repulsion by a horizontal surface of liquid helium. We analyse the stability of the lowest quantum state, which is most susceptible to perturbations due to surface excitations, against scattering by helium atoms in the vapor and by excitations of the liquid, comprised of ripplons, phonons and surfons. This is an unusual scattering problem since the kinetic energy of the neutron parallel to the surface may be much greater than the binding energies perpendicular. The total scattering time constant of these UCNs at 0.7 K is found to exceed one hour, and rapidly increasing with decreasing temperature. Such low scattering rates should enable high-precision measurements of the scheme of discrete energy levels, thus providing improved access to short-range gravity. The system might also be useful for neutron beta-decay experiments. We also sketch new ex...
LRO-LAMP Observations of Lunar Exospheric Helium
NASA Astrophysics Data System (ADS)
Grava, Cesare; Retherford, Kurt D.; Hurley, Dana M.; Feldman, Paul D.; Gladstone, Randy; Greathouse, Thomas K.; Cook, Jason C.; Stern, Alan; Pryor, Wayne R.; Halekas, Jasper S.; Kaufmann, David E.
2015-11-01
We present results from Lunar Reconnaissance Orbiter’s (LRO) UV spectrograph LAMP (Lyman-Alpha Mapping Project) campaign to study the lunar atmosphere. Two kinds of off-nadir maneuvers (lateral rolls and pitches towards and opposite the direction of motion of LRO) were performed to search for resonantly scattering species, increasing the illuminated line-of-sight (and hence the signal from atoms resonantly scattering the solar photons) compared to previously reported LAMP “twilight observations” [Cook & Stern, 2014]. Helium was the only element distinguishable on a daily basis, and we present latitudinal profiles of its line-of-sight column density in December 2013. We compared the helium line-of-sight column densities with solar wind alpha particle fluxes measured from the ARTEMIS (Acceleration, Reconnection, Turbulence, & Electrodynamics of Moon’s Interaction with the Sun) twin spacecraft. Our data show a correlation with the solar wind alpha particle flux, confirming that the solar wind is the main source of the lunar helium, but not with a 1:1 relationship. Assuming that the lunar soil is saturated with helium atoms, our results suggest that not all of the incident alpha particles are converted to thermalized helium, allowing for a non-negligible fraction (~50 %) to escape as suprathermal helium or simply backscattered from the lunar surface. We also support the finding by Benna et al. [2015] and Hurley et al. [2015], that a non-zero contribution from endogenic helium, coming from radioactive decay of 232Th and 238U within the mantle, is present, and is estimated to be (4.5±1.2) x 106 He atoms cm-2 s-1. Finally, we compare LAMP-derived helium surface density with the one recorded by the mass spectrometer LACE (Lunar Atmospheric Composition Experiment) deployed on the lunar surface during the Apollo 17 mission, finding good agreement between the two measurements. These LRO off-nadir maneuvers allow LAMP to provide unique coverage of local solar time and latitude of the lunar exospheric helium, allowing for a better understanding of the temporal and spatial structure of the lunar exosphere.
PROPERTIES OF THE DIFFUSE NEUTRAL HELIUM IN THE INNER HELIOSPHERE
Moise, E.; Raymond, J.; Kuhn, J. R.
2010-10-20
Sensitive SOLARC imaging spectropolarimetric observations from Haleakala reveal a diffuse coronal surface brightness in the He I 1083 nm line. A series of observations suggests that this signal originates from an 'inner source' of neutral helium atoms in the solar corona. Here, we explore the possibility that this cold coronal component originates from helium ions that are neutralized by the near-Sun dust and subsequently excited to the metastable 1s2s {sup 3} S state, which then scatters photons from the solar disk. This picture suggests a deficit of coronal dust inside about 2-4 R{sub sun} in order to account for both the flat radial brightness distribution and the small velocity line width of the observations. We find a strong correlation between the polarized He brightness and coronal white light brightness that supports the argument that electronic collisional excitation of the metastable helium triplet level is responsible for our polarization signal.
Theory of negative-ion conversion of neutral atoms in grazing scattering from alkali halide surfaces
NASA Astrophysics Data System (ADS)
Borisov, A. G.; Sidis, V.
1997-10-01
The theoretical approach proposed by Borisov et al. [Phys. Rev. Lett. 77, 1893 (1996)] to treat negative-ion conversion of neutral atoms at ionic crystal surfaces is described in detail. Due to the localization of the valence-band electrons at the anionic sites of the crystal, the conversion process is viewed as a result of successive binary collisions between the projectile and the negatively charged sites at the surface. Parameter-free calculations of F- formation in grazing scattering from LiF(100) and KI(100) are performed using a model in which all sites of the crystal lattice but one, the active site, are represented by eventually polarizable point charges. Parallel velocity thresholds for negative-ion formation, relative efficiency of the negative-ion formation for LiF and KI crystals, and dependences of this efficiency on the scattering angle correspond well to the experimental results.
Bray, I. ); Stelbovics, A.T. )
1994-04-01
The total and total ionization cross sections for positron scattering on atomic hydrogen are calculated by applying the convergent-close-coupling method to the model where positronium-formation channels are omitted. This model accurately describes the physics of the scattering whenever the positronium formation cross section is negligible, in particular, above 100 eV for this system. The total ionization cross section results in this energy region are in excellent agreement with the recent measurements of Jones [ital et] [ital al]. [J. Phys. B 26, L483 (1993)], and so lie below the earlier measurements of Spicher [Phys. Rev. Lett. 64, 1019 (1990)], and the recent calculations of Acacia [ital et] [ital al]. [Phys. Rev. Lett. (to be published)]. The total cross section is in very good agreement with the recent measurements of Zhou [ital et] [ital al]. (unpublished) down to 30 eV.
Analysis of scattering mechanisms in zinc oxide films grown by the atomic layer deposition technique
NASA Astrophysics Data System (ADS)
Krajewski, Tomasz A.; Dybko, Krzysztof; Luka, Grzegorz; Wachnicki, Lukasz; Kopalko, Krzysztof; Paszkowicz, Wojciech; Godlewski, Marek; Guziewicz, Elzbieta
2015-07-01
In this work, the analysis of the temperature-dependent electrical conductivity of highly crystalline zinc oxide (ZnO) thin films obtained by the Atomic Layer Deposition (ALD) method is performed. It is deduced that the most important scattering mechanisms are: scattering by ionized defects (at low temperatures) as well as by phonons (mainly optical ones) at higher temperatures. Nevertheless, the role of grain boundaries in the carrier mobility limitation ought to be included as well. These conclusions are based on theoretical analysis and temperature-dependent Hall mobility measurements. The presented results prove that existing models can explain the mobility behavior in the ALD-ZnO films, being helpful for understanding their transport properties, which are strongly related both to the crystalline quality of deposited ZnO material and defects in its lattice.
Stefano Zippilli; Giovanna Morigi; Helmut Ritsch
2007-03-20
When N driven atoms emit in phase into a high-Q cavity mode, the intracavity field generated by collective scattering interferes destructively with the pump driving the atoms. Hence atomic fluorescence is suppressed and cavity loss becomes the dominant decay channel for the whole ensemble. Microscopically 3D light-intensity minima are formed in the vicinity of the atoms that prevent atomic excitation and form a regular lattice. The effect gets more pronounced for large atom numbers, when the sum of the atomic decay rates exceeds the rate of cavity losses and one would expect the opposite behaviour. These results provide new insight into recent experiments on collective atomic dynamics in cavities.
NASA Astrophysics Data System (ADS)
Feng, Y.; Xia, H.; Shrestha, S.; Conibeer, G.
2015-11-01
Intrigued by the high demand of fast design and development of nanoscale electronic devices, electronic transport across atomic dimensions becomes an important theoretical and computational problem. In this paper we present a tight-binding based model specially tailed for calculating realistic tunneling structures with scattering region dimensions of several nanometers. The proposed model allows for a proper treatment of the electron-phonon coupling effects in a tractable manner. By greatly reducing the complexity of the phonon-involved problem down to a quadratic level, transmission calculation for large-scale systems, including both planar structures and quantum wire structures, becomes practically feasible.
Electron scattering and dephasing rate of Rydberg atoms in a plasma
NASA Astrophysics Data System (ADS)
Gocke, C.; Röpke, G.
2006-04-01
Rydberg atoms can be considered as mesoscopic systems at the interface between quantum and classical behaviour. The interaction with the surroundings (bath) becomes essential and leads to dephasing of the wavefunction. An important process in Rydberg plasmas is the collision with free charge carriers. Transition rates due to Coulomb interaction are considered in the Born approximation and are shown to coincide with the dephasing time according to linear response theory for mesoscopic devices. We point out that this description of the dephasing process relies on weak coupling between the Rydberg states and the bath and becomes invalid, if strong scattering is of importance.
Effects of coupled atomic states on the resonance scattering of radiation
Srivastava, Rajendra P.; Fontana, Peter R.
1974-01-01
et a1 1969, Hansch et a1 1971). In most resonance fluo- rescence calculations the details of the frequency response and the time dependence of the scattering process have been integrated out. In this paper the full frequency and time response...- and Two-Electron Atoms (Berlin: Springer- Breit G 1933 Rev. mod. Phys. 5 91-140 Brewer R G, Kelly M T and Javan A 1969 Phys. Rev. Lett. 23 559-63 Fontana P R and Srivastava R P 1973 Phys. Rev. A 7 1866-9 Hansch T W, Levenson M D and Schawlow A L 1971...
Generalized Pseudo-potentials for Higher Partial Wave Scattering and Applications to Trapped Atoms
NASA Astrophysics Data System (ADS)
Stock, Rene; Silberfarb, Andrew; Deutsch, Ivan H.; Bolda, Eric L.
2004-05-01
We derive a generalized zero range pseudo-potential for all partial waves. Fermi's original s-wave pseudo-potential is widely used for calculating the mean field energy shift for interacting ultracold atoms. Generalizations of this pseudo-potential to p-wave scattering would be very useful, e.g., for studying ultra-cold collisions of identical Fermions. We derive a proper pseudo-potential for all higher partial waves based on a delta-shell potential in the limit as the shell radius approaches zero, thereby taking into account the higher multipoles not captured by a delta-function at the origin. We apply this correct form to study atoms in harmonic traps interacting via short-range potentials, deriving analytic expressions for the energy eigenstates and eigenvalues.
Hoshino, M; Limão-Vieira, P; Anzai, K; Kato, H; Cho, H; Mogi, D; Tanioka, T; Ferreira da Silva, F; Almeida, D; Blanco, F; García, G; Ingólfsson, O; Tanaka, H
2014-09-28
We report absolute elastic differential cross sections for electron interactions with the C4F6 isomers, hexafluoro-1,3-butadiene (1,3-C4F6), hexafluoro-2-butyne (2-C4F6), and hexafluorocyclobutene (c-C4F6). The incident electron energy range is 1.5-200 eV, and the scattered electron angular range for the differential measurements varies from 15° to 150°. In all cases the absolute scale of the differential cross section was set using the relative flow technique, with helium as the reference species. Atomic-like behaviour in these scattering systems is shown here for the first time, and is further investigated by comparing the elastic cross sections for the C4F6 isomers with other fluorinated molecules, such as SF6 and CnF6 (n = 2, 3, and 6). We note that for all the six-F containing molecules, the scattering process for electron energies above 30 eV is indistinguishable. Finally, we report results for calculations of elastic differential cross sections for electron scattering from each of these isomers, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements is found to be quite remarkable in all cases. PMID:25273432
NASA Astrophysics Data System (ADS)
Kroes, Geert-Jan; Pavanello, Michele; Blanco-Rey, María; Alducin, Maite; Auerbach, Daniel J.
2014-08-01
Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction ("EF") model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated "post" ("p") the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy loss in the range 0.2-0.3 eV due to ehp excitation, which should be possible to observe. The average non-adiabatic energy losses for non-penetrative scattering exceed the adiabatic losses to phonons by 0.9-1.0 eV. This suggests that for scattering of hyperthermal H-atoms from coinage metals the dominant energy dissipation channel should be to ehp excitation. These predictions can be tested by experiments that combine techniques for generating H-atom beams that are well resolved in translational energy and for detecting the scattered atoms with high energy-resolution.
Kroes, Geert-Jan; Pavanello, Michele; Blanco-Rey, María; Alducin, Maite; Auerbach, Daniel J
2014-08-01
Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction ("EF") model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated "post" ("p") the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy loss in the range 0.2-0.3 eV due to ehp excitation, which should be possible to observe. The average non-adiabatic energy losses for non-penetrative scattering exceed the adiabatic losses to phonons by 0.9-1.0 eV. This suggests that for scattering of hyperthermal H-atoms from coinage metals the dominant energy dissipation channel should be to ehp excitation. These predictions can be tested by experiments that combine techniques for generating H-atom beams that are well resolved in translational energy and for detecting the scattered atoms with high energy-resolution. PMID:25106598
Kroes, Geert-Jan Pavanello, Michele; Blanco-Rey, María; Alducin, Maite
2014-08-07
Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction (“EF”) model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated “post” (“p”) the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy loss in the range 0.2-0.3 eV due to ehp excitation, which should be possible to observe. The average non-adiabatic energy losses for non-penetrative scattering exceed the adiabatic losses to phonons by 0.9-1.0 eV. This suggests that for scattering of hyperthermal H-atoms from coinage metals the dominant energy dissipation channel should be to ehp excitation. These predictions can be tested by experiments that combine techniques for generating H-atom beams that are well resolved in translational energy and for detecting the scattered atoms with high energy-resolution.
Capture of Superfluid Helium by Porous Structures
NASA Astrophysics Data System (ADS)
Boltnev, R. E.; Bykhalo, I. B.; Ivashin, S. V.; Krushinskaya, I. N.; Mezhov-Deglin, L. P.
2008-02-01
We have studied superfluid helium capture in a sample of silica aerogel of 98.2% porosity in the temperature range from 1.22 K up to 1.89 K. The high retention of He in the aerogel sample corresponds to a similar phenomenon in impurity-helium condensates, in which very high values of the ratio of helium atoms to impurity atoms (up to 60) have been seen. We have observed that removing the aerogel sample from superfluid helium in a cylindrical glass beaker caused a decrease of the helium level corresponding to the geometrical volume of the sample (?1 cm3). This observation has allowed us to conclude that superfluid helium is completely captured by the porous sample. Superfluid helium filling aerogel and impurity-helium samples (porous structures) serves as a dispersive medium of gel-like samples which interacts strongly with impurity nanoclusters forming the dispersing system.
Giuliano Benenti; Stefano Siccardi; Giuliano Strini
2013-05-01
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.
ASPIN: An all spin scattering code for atom molecule rovibrationally inelastic cross sections
NASA Astrophysics Data System (ADS)
López-Durán, D.; Bodo, E.; Gianturco, F. A.
2008-12-01
We present in this work a new computational code for the quantum calculation of integral cross sections for atom-molecule (linear) scattering processes. The atom is taken to be structureless while the molecule can be in its singlet, doublet, or triplet spin states and can be treated as either a rigid rotor or a rovibrational target. All the relevant state-to-state integral cross sections, and their sums over final states, can be calculated with the present code, for which we also describe in detail the various component routines. Program summaryProgram title: ASPIN Catalogue identifier: AEBO_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBO_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 99 596 No. of bytes in distributed program, including test data, etc.: 1 267 615 Distribution format: tar.gz Programming language: Fortran/MPI Computer: AMD OPTERON COMPUTING SYSTEMS, model TYAN GX28 (B2882) Operating system: SuSE LINUX Professional 9 RAM: 128 GB Classification: 2.6 External routines: LAPACK/BLAS Nature of problem: Scattering of a diatomic molecule in its ?1, ?2, or ?3 spin states with an atom in its S1 state. Partial and integral cross sections. Solution method: The coupled channel equations that describe the scattering process are solved through the propagation of the reactance K matrix employing a modification of the Variable Phase Method [1-3]. Restrictions: Depending on the vib-rotational base used the problem may or may not fit into available RAM memory because all the runtime relevant quantities are stored on RAM memory instead of on disk. Additional comments: Both serial and parallel implementations of the program are provided. The CPC Librarian was not able to successfully run the parallel version. Running time: For simple and converged calculations a usual running time is in the order of a few minutes in the computer mentioned above, being shorter for the singlet and longer for the triplet. References: [1] F. Calogero, Variable Phase Approach to Potential Scattering, New York, 1967. [2] A. Degasperis, Il Nuovo Cimento 34 (1964) 1667. [3] C. Zemach, Il Nuovo Cimento 33 (1964) 939.
NASA Astrophysics Data System (ADS)
Smith, Adam H.
The ^3He nucleus has attracted considerable interest among both experimental and theoretical physicists. As a three body system this nucleus is calculable with Faddeev techniques and this serves as an important test of our knowledge of nuclear physics. Faddeev techniques result in detailed predictions which show small corrections to simple models which have the spin of the ^3 He nucleus totally carried by the neutron. This has resulted in many proposals to use polarized ^3He as a polarized neutron target. Measurements of spin dependent scattering from polarized ^3 He are used to test the calculations and on a more practical level explore the conditions under which polarized ^3He can be used as an effective polarized neutron target. We have used a laser optically-pumped polarized ^3He target with a polarized proton beam in the Indiana University Cooler light ion storage ring to measure the spin observables in vec p-{buildrellongrightarrowover{ ^3He}} scattering at beam energies of 197, 299 and 414 MeV. This represents the first experiment in the world to utilize this type of target in a storage ring. The experimental apparatus covered an angular range of 21^circ to 67^circ in the laboratory and simultaneously detected both elastic and quasielastic reactions. We have extracted the beam analyzing powers, target analyzing powers and spin correlation coefficients at all three beam energies for the two quasielastic reactions, {buildrellongrightarrowover {^3He}}(vec p, 2p) and {buildrellongrightarrow over{^3He}}(vec p, pn), and the elastic {buildrel longrightarrowover{^3He }}(vec p, p^3rm He) reaction. The large acceptance allowed us to use the quasielastic data to identify regions of phase space where it is possible to test the Faddeev calculations and also verify that polarized ^3He may serve as an effective polarized neutron target. The elastic scattering data have also pointed out deficiencies in current p-^3 He elastic scattering theories.
Semiclassical multi-phonon theory for atom-surface scattering: Application to the Cu(111) system
Daon, Shauli; Pollak, Eli
2015-05-07
The semiclassical perturbation theory of Hubbard and Miller [J. Chem. Phys. 80, 5827 (1984)] is further developed to include the full multi-phonon transitions in atom-surface scattering. A practically applicable expression is developed for the angular scattering distribution by utilising a discretized bath of oscillators, instead of the continuum limit. At sufficiently low surface temperature good agreement is found between the present multi-phonon theory and the previous one-, and two-phonon theory derived in the continuum limit in our previous study [Daon, Pollak, and Miret-Artés, J. Chem. Phys. 137, 201103 (2012)]. The theory is applied to the measured angular distributions of Ne, Ar, and Kr scattered from a Cu(111) surface. We find that the present multi-phonon theory substantially improves the agreement between experiment and theory, especially at the higher surface temperatures. This provides evidence for the importance of multi-phonon transitions in determining the angular distribution as the surface temperature is increased.
Merritt, J M; Miller, R E; K\\"upper, Jochen; Merritt, Jeremy M.; Miller, Roger E.
2006-01-01
Rotationally resolved infrared spectra are reported for the X-HCN (X = Cl, Br, I) binary complexes solvated in helium nanodroplets. These results are directly compared with that obtained previously for the corresponding X-HF complexes [J. M. Merritt, J. K\\"upper, and R. E. Miller, PCCP, 7, 67 (2005)]. For bromine and iodine atoms complexed with HCN, two linear structures are observed and assigned to the $^{2}\\Sigma_{1/2}$ and $^{2}\\Pi_{3/2}$ ground electronic states of the nitrogen and hydrogen bound geometries, respectively. Experiments for HCN + chlorine atoms give rise to only a single band which is attributed to the nitrogen bound isomer. That the hydrogen bound isomer is not stabilized is rationalized in terms of a lowering of the isomerization barrier by spin-orbit coupling. Theoretical calculations with and without spin-orbit coupling have also been performed and are compared with our experimental results. The possibility of stabilizing high-energy structures containing multiple radicals is discussed, ...
NASA Technical Reports Server (NTRS)
Dobson, Chris C.; Sung, C. C.
1999-01-01
Optical pumping of the ground states of sodium can radically alter the shape of the laser-induced fluorescence excitation spectrum, complicating measurements of temperature, pressure, etc., which are based on these spectra. Modeling of the fluorescence using rate equations for the eight hyperfine states of the sodium D manifolds can be used to quantify the contribution to the ground state pumping of transitions among the hyperfine excited states induced by collisions with buffer gas atoms. This model is used here to determine, from the shape of experimental spectra, cross sections lor DELTA.F transitions of the P(sub 3/2) state induced by collisions with helium and argon atoms, for a range of values assumed for the P(sub 1/2), DELTA.F cross sections. The hyperfine cross sections measured using this method, which to our knowledge is novel, are compared with cross sections for transitions involving polarized magnetic substates m(sub F) measured previously using polarization sensitive absorption. Also, fine-structure transition cross sections were measured in the pumped vapor, giving agreement with previous measurements made in the absence of pumping.
NASA Technical Reports Server (NTRS)
Dobson, Chris C.; Sung, C. C.
1998-01-01
Optical pumping of the ground states of sodium can radically alter the shape of the laser induced fluorescence excitation spectrum, complicating measurements of temperature, pressure, etc., which are based on these spectra. Modeling of the fluorescence using rate equations for the eight hyperfine states of the sodium D manifolds can be used to quantify the contribution to the ground state pumping of transitions among the hyperfine excited states induced by collisions with buffer gas atoms. This model is used here to determine, from the shape of experimental spectra, cross sections for (Delta)F transitions of the P(sub 3/2) state induced by collisions with helium and argon atoms, for a range of values assumed for the P(sub 1/2), (Delta)F cross sections. The hyperfine cross sections measured using this method, which is thought to be novel, are compared with cross sections for transitions involving polarized magnetic substates, m(sub F), measured previously using polarization sensitive absorption. Also, fine structure transition ((Delta)J) cross sections were measured in the pumped vapor, giving agreement with previous measurements made in the absence of pumping.
Cerkic, A.; Milosevic, D. B.
2006-03-15
Using the example of electron-atom scattering in a strong laser field, it is shown that the oscillatory structure of the scattered electron spectrum can be explained as a consequence of the interference of the real electron trajectories in terms of Feynman's path integral. While in previous work on quantum-orbit theory the complex solutions of the saddle-point equations were considered, we show here that for the electron-atom scattering with much simpler real solutions a satisfactory agreement with the strong-field-approximation results can be achieved. Real solutions are applicable both for the direct (low-energy) and the rescattering (high-energy) plateau in the scattered electron spectrum. In between the plateaus and beyond the rescattering cutoff good results can be obtained using the complex (quantum) solutions and the uniform approximation. The interference of real solutions is related to the recent attosecond double-slit experiment in time.
Radioactive transitions in the helium isoelectronic sequence
NASA Technical Reports Server (NTRS)
Dalgarno, A.
1971-01-01
The principles of the atomic spectrum theory are used to quantitatively analyze radiation transitions in two-electron helium-like atomic systems. Quantum theoretical methods, describing absorption and emission of a single photon in a radiative transition between two stationary states of an atomic system, reproduced the energy level diagram for the low lying states of helium. Reliable values are obtained from accurate variationally determined two-electron nonrelativistic wave functions for radiative transition probabilities of 2 3p states in the helium isoelectric sequence, and for the 2 1s and 2 3s1 states of the helium sequence.
NASA Technical Reports Server (NTRS)
Diana, L. M.; Chaplin, R. L.; Brooks, D. L.; Adams, J. T.; Reyna, L. K.
1990-01-01
An improved technique is presented for employing the 2.3m spectrometer to measure total ionization cross sections, Q sub ion, for positrons incident on He. The new ionization cross section agree with the values reported earlier. Estimates are also presented of total elastic scattering cross section, Q sub el, obtained by subtracting from total scattering cross sections, Q sub tot, reported in the literature, the Q sub ion and Q sub Ps (total positronium formation cross sections) and total excitation cross sections, Q sub ex, published by another researcher. The Q sub ion and Q sub el measured with the 3m high resolution time-of-flight spectrometer for 54.9eV positrons are in accord with the results from the 2.3m spectrometer. The ionization cross sections are in fair agreement with theory tending for the most part to be higher, especially at 76.3 and 88.5eV. The elastic cross section agree quite well with theory to the vicinity of 50eV, but at 60eV and above the experimental elastic cross sections climb to and remain at about 0.30 pi a sub o sq while the theoretical values steadily decrease.
NASA Astrophysics Data System (ADS)
Hansen, Jens-Ole
1995-01-01
We report a measurement of the spin-dependent asymmetries A_{T^' } and A_{TL^' } in ^3vec He(vec e, e^') quasielastic scattering at momentum transfer Q^2~ 0.2(GeV/c) ^2 and beam energy 370 MeV. The data were acquired at the MIT-Bates Linear Accelerator Center using a metastability-exchange optically-pumped polarized ^3He gas target, with which an average luminosity of ~10 ^{33}cm^ {-2}s^{-1} and an average polarization of 37% was achieved. The scattered electrons were detected in single-arm mode with the One Hundred Inch Proton Spectrometer (OHIPS) and the Medium Energy Pion Spectrometer (MEPS), each equipped with an x-y drift chamber, three planes of plastic scintillators, and a Cerenkov detector. Two spectrometers were used to measure both responses simultaneously. Background from the target walls used between 5% and 15%. As a check of the experimental procedure, a sample of elastic data was also collected. The experiment improves the statistical precision of the existing quasielastic data set by a factor of three. The result for the transverse asymmetry, -10.92 +/- 1.23 (stat.) +/- 0.81 (syst.) %, is well reproduced by recent calculations based on the Plane Wave Impulse Approximation (PWIA). The magnetic elastic form factor of the neutron, G_sp{M}{n}, was extracted from the data using the PWIA models. The result agrees with the dipole prediction as well as with data obtained in elastic electron scattering from deuterium at comparable Q^2. The transverse-longitudinal asymmetry, A _{TL^'}, was determined to be +1.60 +/- 0.55 (stat.) +/- 0.12 (syst.)%. The PWIA prediction for A_{TL^'} ranges from 2.1% and 2.9%, where the variation is due to the uncertainty in the nucleon-nucleon potential, nucleon form factors, and off-shell prescription. The overprediction of the data by 1-2.5sigma may indicate that final-state interactions (or other processes) play an important role for the inclusive reaction mechanism at this Q^2, as has been observed for the unpolarized longitudinal response function. In the absence of a theory for this reaction which includes final-state interactions, no reliable extraction of the neutron electric form factor, G_sp{E }{n}, is possible at present at this Q^2. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.).
On the Formation of (Anionic) Excited Helium Dimers in Helium Droplets
2014-01-01
Metastable atomic and molecular helium anions exhibiting high-spin quartet configurations can be produced in helium droplets via electron impact. Their lifetimes allow detection in mass spectrometric experiments. Formation of atomic helium anions comprises collision-induced excitation of ground state helium and concomitant electron capture. Yet the formation of molecular helium anions in helium droplets has been an unresolved issue. In this work, we explore the interaction of excited helium atoms exhibiting high-spin triplet configurations with ground state helium using the equation-of-motion coupled-cluster method. Transition barriers in the energetically lowest He*–He and He*––He interaction potentials prevent molecule formation at the extremely low temperatures present in helium droplets. In contrast, some excited states allow a barrier-free formation of molecular helium (anions). Moreover, we show that the necessary excitation energies pinpoint (higher) resonances in recently recorded mass spectra and emend the assignment of those resonances that have previously been assigned to electron-impact ionization of ground state helium necessitating subsequent double-electron capture. Embedding molecules or molecular clusters in helium droplets is a predestined experimental technique for the study of phenomena at very low temperatures. Profound knowledge about active processes in the helium environment is required for a proper assessment of experimental data. PMID:24866535
Applications of Quantum Theory of Atomic and Molecular Scattering to Problems in Hypersonic Flow
NASA Technical Reports Server (NTRS)
Malik, F. Bary
1995-01-01
The general status of a grant to investigate the applications of quantum theory in atomic and molecular scattering problems in hypersonic flow is summarized. Abstracts of five articles and eleven full-length articles published or submitted for publication are included as attachments. The following topics are addressed in these articles: fragmentation of heavy ions (HZE particles); parameterization of absorption cross sections; light ion transport; emission of light fragments as an indicator of equilibrated populations; quantum mechanical, optical model methods for calculating cross sections for particle fragmentation by hydrogen; evaluation of NUCFRG2, the semi-empirical nuclear fragmentation database; investigation of the single- and double-ionization of He by proton and anti-proton collisions; Bose-Einstein condensation of nuclei; and a liquid drop model in HZE particle fragmentation by hydrogen.
The s-wave pi d scattering length from pi d atom using effective field theory
B. F. Irgaziev; B. A. Fayzullaev
2004-04-23
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.
Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms
Song, Lei; Avoird, Ad van der; Karman, Tijs; Groenenboom, Gerrit C.; Balakrishnan, N.
2015-05-28
We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 ? 30 to v? = 0, j? are calculated using the close coupling method for collision energies between 0.1 and 15?000 cm{sup ?1} based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ? 3 to v? = 0, j? are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H–CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H–CO collisions in astrophysical models.
Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms
NASA Astrophysics Data System (ADS)
Song, Lei; Balakrishnan, N.; van der Avoird, Ad; Karman, Tijs; Groenenboom, Gerrit C.
2015-05-01
We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 - 30 to v' = 0, j' are calculated using the close coupling method for collision energies between 0.1 and 15 000 cm-1 based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ? 3 to v' = 0, j' are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H-CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H-CO collisions in astrophysical models.
NASA Astrophysics Data System (ADS)
Yonemori, Seiya; Kamakura, Taku; Ono, Ryo
2014-10-01
Atmospheric-pressure plasmas are of emerging interest for new plasma applications such as cancer treatment, cell activation and sterilization. In those biomedical processes, reactive oxygen/nitrogen species (ROS/RNS) are said that they play significant role. It is though that active species give oxidative stress and induce biomedical reactions. In this study, we measured OH, NO, O and N atoms using laser induced fluorescence (LIF) measurement and found that voltage polarity affect particular ROS. When negative high voltage was applied to the plasma jet, O atom density was tripled compared to the case of positive applied voltage. In that case, O atom density was around 3 × 1015 [cm-3] at maximum. In contrast, OH and NO density did not change their density depending on the polarity of applied voltage, measured as in order of 1013 and 1014 [cm-3] at maximum, respectively. From ICCD imaging measurement, it could be seen that negative high voltage enhanced secondary emission in plasma bullet propagation and it can affect the effective production of particular ROS. Since ROS/RNS dose can be a quantitative criterion to control plasma biomedical application, those measurement results is able to be applied for in vivo and in vitro plasma biomedical experiments. This study is supported by the Grant-in-Aid for Science Research by the Ministry of Education, Culture, Sport, Science and Technology.
NASA Astrophysics Data System (ADS)
Man?ev, I.; Milojevi?, N.; Belki?, Dž.
2015-03-01
The four-body boundary-corrected first Born (CB1-4B) approximation is used to compute cross sections for single electron capture from helium targets by fully stripped ions. The projectile ions are H+, He2+, Li3+, Be4+, B5+, C6+, N7+, O8+, and F9+. An extensive list of theoretical state-to-state cross sections in these collisions at energies ranging from 20 to 10 000 keV/amu is given. This list includes the state-selective cross sections Qnlm for each individual triple of the usual quantum numbers { n , l , m } of the final hydrogen-like states alongside Qnl and Qn for the pertinent sub-shells and shells where the respective summations over m and { l , m } have been carried out. The maximal value of the principal quantum number n was chosen to vary from 4 (H+) to 10 (F9+) so as to satisfy the condition n ?ZP, where ZP is the nuclear charge of the projectile. Usually, the largest cross sections stem from those values of n that match the projectile charge (n =ZP) . The total cross sections for capture summed over all the quantum numbers { n , l , m } are also tabulated. The overall goal of this study is to fill in lacunae in the existing databases of charge exchange cross sections that are needed in several inter-disciplinary fields. For example, in particle transport physics, which is of utmost importance in such emerging branches as hadron therapy, these cross sections constitute a part of the multifaceted input data for stochastic simulations of energy losses of multiply charged ions in matter, including tissue. Other significant uses of the present data are anticipated in charge exchange diagnostics within thermonuclear research project as well as in applications covering the relevant parts of plasma physics and astrophysics.
Weatherford, Brandon R. E-mail: zax@esi-group.com E-mail: mjkush@umich.edu; Barnat, E. V. E-mail: zax@esi-group.com E-mail: mjkush@umich.edu; Xiong, Zhongmin E-mail: zax@esi-group.com E-mail: mjkush@umich.edu; Kushner, Mark J. E-mail: zax@esi-group.com E-mail: mjkush@umich.edu
2014-09-14
Fast ionization waves (FIWs), often generated with high voltage pulses over nanosecond timescales, are able to produce large volumes of ions and excited states at moderate pressures. The mechanisms of FIW propagation were experimentally and computationally investigated to provide insights into the manner in which these large volumes are excited. The two-dimensional structure of electron and metastable densities produced by short-pulse FIWs sustained in helium were measured using laser-induced fluorescence and laser collision-induced fluorescence diagnostics for times of 100–120 ns after the pulse, as the pressure was varied from 1 to 20 Torr. A trend of center-peaked to volume-filling to wall-peaked electron density profiles was observed as the pressure was increased. Instantaneous FIW velocities, obtained from plasma-induced emission, ranged from 0.1 to 3×10?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.
Scattering of NH3 and ND3 with rare gas atoms at low collision energy.
Loreau, J; van der Avoird, A
2015-11-14
We present a theoretical study of elastic and rotationally inelastic collisions of NH3 and ND3 with rare gas atoms (He, Ne, Ar, Kr, Xe) at low energy. Quantum close-coupling calculations have been performed for energies between 0.001 and 300 cm(-1). We focus on collisions in which NH3 is initially in the upper state of the inversion doublet with j = 1, k = 1, which is the most relevant in an experimental context as it can be trapped electrostatically and Stark-decelerated. We discuss the presence of resonances in the elastic and inelastic cross sections, as well as the trends in the inelastic cross sections along the rare gas series and the differences between NH3 and ND3 as a colliding partner. We also demonstrate the importance of explicitly taking into account the umbrella (inversion) motion of NH3 in order to obtain accurate scattering cross sections at low collision energy. Finally, we investigate the possibility of sympathetic cooling of ammonia using cold or ultracold rare gas atoms. We show that some systems exhibit a large ratio of elastic to inelastic cross sections in the cold regime, which is promising for sympathetic cooling experiments. The close-coupling calculations are based on previously reported ab initio potential energy surfaces for NH3-He and NH3-Ar, as well as on new, four-dimensional, potential energy surfaces for the interaction of ammonia with Ne, Kr, and Xe, which were computed using the coupled-cluster method and large basis sets. We compare the properties of the potential energy surfaces corresponding to the interaction of ammonia with the various rare gas atoms. PMID:26567658
Scattering of NH3 and ND3 with rare gas atoms at low collision energy
NASA Astrophysics Data System (ADS)
Loreau, J.; van der Avoird, A.
2015-11-01
We present a theoretical study of elastic and rotationally inelastic collisions of NH3 and ND3 with rare gas atoms (He, Ne, Ar, Kr, Xe) at low energy. Quantum close-coupling calculations have been performed for energies between 0.001 and 300 cm-1. We focus on collisions in which NH3 is initially in the upper state of the inversion doublet with j = 1, k = 1, which is the most relevant in an experimental context as it can be trapped electrostatically and Stark-decelerated. We discuss the presence of resonances in the elastic and inelastic cross sections, as well as the trends in the inelastic cross sections along the rare gas series and the differences between NH3 and ND3 as a colliding partner. We also demonstrate the importance of explicitly taking into account the umbrella (inversion) motion of NH3 in order to obtain accurate scattering cross sections at low collision energy. Finally, we investigate the possibility of sympathetic cooling of ammonia using cold or ultracold rare gas atoms. We show that some systems exhibit a large ratio of elastic to inelastic cross sections in the cold regime, which is promising for sympathetic cooling experiments. The close-coupling calculations are based on previously reported ab initio potential energy surfaces for NH3-He and NH3-Ar, as well as on new, four-dimensional, potential energy surfaces for the interaction of ammonia with Ne, Kr, and Xe, which were computed using the coupled-cluster method and large basis sets. We compare the properties of the potential energy surfaces corresponding to the interaction of ammonia with the various rare gas atoms.
NASA Astrophysics Data System (ADS)
Dolmatov, Valeriy; Amusia, Miron; Chernysheva, Larissa
2015-05-01
A recent work has provided the initial insight into electron elastic scattering off endohedral atoms A @C60 . There, the atom A and C60 cage were regraded as non-polarizable targets. A question of how lifting the rigid- A-rigid-C60 constrain can affect e + A @C60 scattering has remained open. The present study provides a partial insight into the problem. It accounts for polarization of the atom by incoming electrons in the presence of rigid C60. This is an interesting in itself topic of study from the point of view of basic science. The Dyson theory for the self-energy part of the Green function ?e(?) of an electron moving in the field of A confined inside of rigid C60 is employed in the study. The function ?e(?) is regarded in the framework of the RPAE theory. The e + Ne @C60 elastic scattering is chosen as a case study. The s, p, d, f, g, and h phase shifts and partial (and total) electron elastic-scattering cross sections are calculated with and without accounting for ?e(?) . Calculated results provide the first insight into the confinement-correlation impact upon e + A @C60 elastic scattering. Supported by the NSF grant PHY-1305085.
NASA Astrophysics Data System (ADS)
Salvat, Francesc; Jablonski, Aleksander; Powell, Cedric J.
2005-01-01
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
Datz, S.; Hippler, R.; Andersen, L.H.; Dittner, P.F.; Knudsen, H.; Krause, H.F.; Miller, P.D.; Pepmiller, P.L.; Rosseel, T.; Stolterfoht, N.
1987-01-01
We have investigated charge transfer in collisions of energetic (0.1 - 1 MeV/nucleon) highly charged ions with helium atoms with the principal aim clarifying the nature of two-electron processes. The sensitivity of partial charge-changing cross sections (i.e., single- and double-charge transfer, transfer ionization (TI), and single and double ionization) to core configuration and scaling rules for one- and two-electron processes were investigated with iodine ions (q = 5+ ..-->.. 26+) and uranium ions (q = 17+ ..-->.. 44+) using an ion-charge state, recoil-ion coincidence method. Using zero-degree electron spectroscopy in coincidence with charge transfer, we found that at the higher energies, as in the case of 0.1 MeV/nucleon ions previously reported, TI involves the transfer of two electrons to a higher correlated state followed by loss of one electron to the continuum. In addition, we observe very high Rydberg electrons in coincidence with TI, implying a possible up-down correlation in the pair transfer. In addition, we made measurements of VUV photons emitted at the collision in coincidence with He/sup +/ and He/sup 2 +/ recoils. The results show that TI leads to capture into lower n states than single-charge transfer. 15 refs., 10 figs.
NASA Astrophysics Data System (ADS)
Nakashima, Hiroyuki; Hijikata, Yuh; Nakatsuji, Hiroshi
2008-04-01
Very accurate variational calculations with the free iterative-complement-interaction (ICI) method for solving the Schrödinger equation were performed for the 1sNs singlet and triplet excited states of helium atom up to N =24. This is the first extensive applications of the free ICI method to the calculations of excited states to very high levels. We performed the calculations with the fixed-nucleus Hamiltonian and moving-nucleus Hamiltonian. The latter case is the Schrödinger equation for the electron-nuclear Hamiltonian and includes the quantum effect of nuclear motion. This solution corresponds to the nonrelativistic limit and reproduced the experimental values up to five decimal figures. The small differences from the experimental values are not at all the theoretical errors but represent the physical effects that are not included in the present calculations, such as relativistic effect, quantum electrodynamic effect, and even the experimental errors. The present calculations constitute a small step toward the accurately predictive quantum chemistry.
Basu, Joyee Ray, Debasis
2014-03-15
In this paper, we demonstrate the possibility of electron density-induced giant growth of non-resonant Rayleigh scattering of electromagnetic radiation (in the low-frequency limit) by atomic systems within dense plasmas. Non-relativistic quantum mechanical calculation is performed under electric dipole approximation, for elastic scattering of radiation by the ground states 1s of plasma-embedded hydrogen-like atomic ions treated within the framework of the ion-sphere model. The results indicate giant enhancement of the non-resonant (photon frequency ? being much smaller than the lowest resonance frequency ?{sub 1s?2p}) Rayleigh cross-section by an order of magnitude, at (atomic system-specific) high enough plasma electron densities under present consideration. The Z{sup ?8}-scaling of the non-resonant Rayleigh cross-section in free and isolated H-isoelectronic sequence of ions is shown to be broken in dense plasma environments.
Average-atom treatment of relaxation time in X-ray Thomson scattering from warm-dense matter
Johnson, Walter R
2016-01-01
The influence of finite relaxation times on Thomson scattering from warm-dense plasmas is examined within the framework of the average-atom approximation. To this end, the Lindhard dielectric function, commonly used to evaluate the free-electron contribution to the Thomson cross section, is replaced by the Mermin dielectric function, which includes relaxation time explicitly. The relaxation time, which is evaluated by treating the average atom as an impurity in a uniform electron gas, depends critically on the transport cross section, which is evaluated in terms of scattering phase shifts in the average-atom potential. For the examples considered here, the calculated relaxation rates agree well, over a wide range of plasma densities and temperatures, with values inferred from the Ziman formula for the static conductivity and also with rates inferred from a fit to the frequency-dependent conductivity. Transport cross sections determined by the phase-shift analysis are compared with cross sections evaluated in ...
Arai, Toshikazu; Mitsui, Tomoyuki; Yayama, Hideki
2006-09-07
We have measured the temperature dependence of the electron attachment reaction rate of atomic hydrogen (H) on a liquid 4He surface in applied magnetic fields of 0-5 T at 0.2-0.6 K. The measured surface state electron (SSE) losses are faster at lower temperatures for a given magnetic field. This behavior can be qualitatively understood, since the surface coverage of adsorbed H is large at low temperature and the collisions between H and SSE are frequent. However, the reaction is faster than expected based on the collision frequency argument. The measured reaction rate coefficient Ke is strongly temperature dependent. We observe that, as the temperature is lowered, Ke increases by several orders of magnitude. This indicates that some additional effect enhances electron attachment at low temperature. We discuss a possible reaction mechanism between H and SSE.
Paramagnetic Attraction of Impurity-Helium Solids
NASA Technical Reports Server (NTRS)
Bernard, E. P.; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. M.
2003-01-01
Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals.
NASA Astrophysics Data System (ADS)
Falcinelli, Stefano; Bartocci, Alessio; Cavalli, Simonetta; Pirani, Fernando; Vecchiocattivi, Franco
2015-10-01
A combined analysis of both new (energy spectra of emitted electrons) and previously published (ionization cross sections) experimental data, measured under the same conditions and concerning electronically excited lighter noble gas -NH3 collisional autoionization processes, is carried out. Such an analysis, performed by exploiting a formulation of the full potential energy surface both in the real and imaginary parts, provides direct information on energetics, structure, and lifetime of the intermediate collision complex over all the configuration space. The marked anisotropy in the attraction of the real part, driving the approach of reagents, and the selective role of the imaginary component, associated to the charge transfer coupling between entrance and exit channels, suggests that reactive events occur almost exclusively in the molecular hemisphere containing the nitrogen lone pair. Crucial details on the stereo-dynamics of elementary collisional autoionization processes are then obtained, in which the open shell nature of the disclosed ionic core of metastable atom plays a crucial role. The same analysis also suggests that the strength of the attraction and the anisotropy of the interaction increases regularly along the series Ne*(3P), He*(3S), He*(1S)-NH3. These findings can be ascribed to the strong rise of the metastable atom electronic polarizability (deformability) along the series. The obtained results can stimulate state of the art ab initio calculations focused on specific features of the transition state (energetics, structure, lifetime, etc.) which can be crucial for a further improvement of the adopted treatment and to better understand the nature of the leading interaction components which are the same responsible for the formation of the intermolecular halogen and hydrogen bond.
Falcinelli, Stefano; Bartocci, Alessio; Cavalli, Simonetta; Pirani, Fernando; Vecchiocattivi, Franco
2015-10-28
A combined analysis of both new (energy spectra of emitted electrons) and previously published (ionization cross sections) experimental data, measured under the same conditions and concerning electronically excited lighter noble gas -NH3 collisional autoionization processes, is carried out. Such an analysis, performed by exploiting a formulation of the full potential energy surface both in the real and imaginary parts, provides direct information on energetics, structure, and lifetime of the intermediate collision complex over all the configuration space. The marked anisotropy in the attraction of the real part, driving the approach of reagents, and the selective role of the imaginary component, associated to the charge transfer coupling between entrance and exit channels, suggests that reactive events occur almost exclusively in the molecular hemisphere containing the nitrogen lone pair. Crucial details on the stereo-dynamics of elementary collisional autoionization processes are then obtained, in which the open shell nature of the disclosed ionic core of metastable atom plays a crucial role. The same analysis also suggests that the strength of the attraction and the anisotropy of the interaction increases regularly along the series Ne(*)((3)P), He(*)((3)S), He(*)((1)S)-NH3. These findings can be ascribed to the strong rise of the metastable atom electronic polarizability (deformability) along the series. The obtained results can stimulate state of the art ab initio calculations focused on specific features of the transition state (energetics, structure, lifetime, etc.) which can be crucial for a further improvement of the adopted treatment and to better understand the nature of the leading interaction components which are the same responsible for the formation of the intermolecular halogen and hydrogen bond. PMID:26520512
Tizei, Luiz H G; Iizumi, Yoko; Okazaki, Toshiya; Nakanishi, Ryo; Kitaura, Ryo; Shinohara, Hisanori; Suenaga, Kazu
2016-01-01
Single atom localization and identification is crucial in understanding effects which depend on the specific local environment of atoms. In advanced nanometer scale materials, the characteristics of individual atoms may play an important role. Here, we describe spectroscopic experiments (electron energy loss spectroscopy, EELS, and Energy Dispersed X-ray spectroscopy, EDX) using a low voltage transmission electron microscope designed towards single atom analysis. For EELS, we discuss the advantages of using lower primary electron energy (30keV and 60keV) and higher energy losses (above 800eV). The effect of atomic movement is considered. Finally, we discuss the possibility of using atomically resolved EELS and EDX data to measure the fluorescence yield for X-ray emission. PMID:26550931
Zayarnyi, D A; L'dov, A Yu; Kholin, I V
2013-08-31
We have used the absorption probe method to study the processes of collisional quenching of the metastable 5s [3/2]{sup o}{sub 2}({sup 3}P{sub 2}) state of the krypton atom in electron-beam-excited high-pressure He – Kr mixtures with a low content of krypton. The rate constants of plasma-chemical reactions Kr* + Kr + He ? Kr*{sub 2}+He [(2.88 ± 0.29) × 10{sup -33} cm{sup 6} s{sup -1}], Kr* + 2He ? HeKr* + He [(4.6 ± 1.3) × 10{sup -36} cm{sup 6} s{sup -1}] and Kr* + He ? products + He [(1.51 ± 0.15) × 10{sup -15} cm{sup 3} s{sup -1}] are measured for the first time. The rate constants of similar reactions in the Ar – Kr mixture are refined. (active media)
Eden, S.; Tabet, J.; Samraoui, K.; Louc, S.; Farizon, B.; Farizon, M.; Ouaskit, S.; Maerk, T. D.
2006-02-15
Absolute dissociation cross sections are reported for H{sub n}{sup +} clusters of varied mass (n=3,5,...,35) following collisions with He atoms at 60 keV/amu. Initial results have been published previously for a smaller range of cluster sizes [Ouaskit et al., Phys. Rev. A 49, 1484 (1994)]. The present extended study includes further experimental results, reducing the statistical errors associated with the absolute cross sections. The previously suggested quasilinear dependence of the H{sub n}{sup +} dissociation cross sections upon n is developed with reference to expected series of geometrical shells of H{sub 2} molecules surrounding a H{sub 3}{sup +} core. Recent calculations identify n=9 as corresponding to the first closed H{sub 2} shell [e.g., Stich et al., J. Chem. Phys. 107, 9482 (1997)]. Recurrence of the distinct characteristics observed in the dissociation-cross-section dependence upon cluster size around n=9 provides the basis for the presently proposed subsequent closed shells at n=15, 21, 27, and 33, in agreement with the calculations of Nagashima et al. [J. Phys. Chem. 96, 4294 (1992)].
Experimental studies on kaonic atoms at DA{Phi}NE
Okada, S.; Bazzi, M.; Berucci, C.; Bragadireanu, A. M.; Clozza, A.; Corradi, G.; Curceanu, C.; D'Uffizi, A.; Guaraldo, C.; Iliescu, M.; Sandri, P. Levi; Lucherini, V.; Pietreanu, D.; Piscicchia, K.; Lener, M. Poli; Rizzo, A.; Vidal, A. Romero; Sbardella, E.; Scordo, A.; Sirghi, D. L.
2011-10-21
We have measured the K-series x-rays of kaonic hydrogen atoms to determine the strong-interaction energy-level shift and width of the 1s atomic state with significant improvements over the previous experiments. The measurement offers a unique possibility to precisely determine the complex K{sup -}p S-wave scattering length. We have also measured kaonic x-ray spectra with several gaseous targets : deuterium, helium-3 and helium-4. In this paper, we present an overview of this experiment and preliminary spectra of those kaonic x-rays.
NASA Astrophysics Data System (ADS)
Klyavin, O. V.; Nikolaev, V. I.; Smirnov, B. I.; Khabarin, L. V.; Chernov, Yu. M.; Shpe?zman, V. V.
2008-08-01
The specific features of the mechanodynamic penetration of helium under plastic deformation into fcc (Cu) and bcc (Fe, Nb) metals with different initial defect structures (single-crystal, nanocrystalline, and porous samples) are investigated. The intensity of mechanodynamic penetration into these metals is shown to depend on the type of bonding (metallic or covalent), which determines the degree of localization of the plastic flow of these metals, as well as on the type of defect structure and on the character of plastic flow (dislocation deformation, twinning, grain-boundary sliding). Curves of helium extraction from samples at different strains are obtained. It is found that the helium release exhibits a wide variety of peaks depending on the degree and character of plastic deformation of the metals under investigation. This suggests that the metals contain different types of helium traps, which determine the content of helium and the specific features of its release in the temperature range studied.
Introduction of nickel surface layer atoms into silicon
NASA Astrophysics Data System (ADS)
Duplii, S. A.; Pelikhatyi, N. M.; Steshenko, S. A.
1989-07-01
Results of experimental studies of the process of introduction of nickel atoms into silicon upon irradiation of layered Ni-Si structures by argon ions are presented. Following irradiation, specimen composition was studied using back scattering of helium ions. Processing of the back scattering spectra was performed by an improved method using an analytical approach. The effects of annealing temperature and dosage on the process of formation of the suicide NiSi are studied.
RNA and its ionic cloud: solution scattering experiments and atomically detailed simulations.
Kirmizialtin, Serdal; Pabit, Suzette A; Meisburger, Steve P; Pollack, Lois; Elber, Ron
2012-02-22
RNA molecules play critical roles in many cellular processes. Traditionally viewed as genetic messengers, RNA molecules were recently discovered to have diverse functions related to gene regulation and expression. RNA also has great potential as a therapeutic and a tool for further investigation of gene regulation. Metal ions are an integral part of RNA structure and should be considered in any experimental or theoretical study of RNA. Here, we report a multidisciplinary approach that combines anomalous small-angle x-ray scattering and molecular-dynamics (MD) simulations with explicit solvent and ions around RNA. From experiment and simulation results, we find excellent agreement in the number and distribution of excess monovalent and divalent ions around a short RNA duplex. Although similar agreement can be obtained from a continuum description of the solvent and mobile ions (by solving the Poisson-Boltzmann equation and accounting for finite ion size), the use of MD is easily extended to flexible RNA systems with thermal fluctuations. Therefore, we also model a short RNA pseudoknot and find good agreement between the MD results and the experimentally derived solution structures. Surprisingly, both deviate from crystal structure predictions. These favorable comparisons of experiment and simulations encourage work on RNA in all-atom dynamic models. PMID:22385853
Winter, H.; Mertens, A.; Auth, C.; Borisov, A.G.
1996-09-01
Fast positive ions and atoms with energies ranging from some 100 eV to 100 keV are scattered under a grazing angle of incidence from a clean and flat (100) surface of a monocrystalline KI sample. We observe for halogen projectiles an almost complete negative-ion conversion, i.e., negative-ion fractions up to 98.5{percent}. Our data show a characteristic dependence on the projectile velocity, which provides important additional information on the mechanisms of formation of negative ions in the scattering from the surface of an insulator. {copyright} {ital 1996 The American Physical Society.}
Ultracold Metastable HELIUM-4 and HELIUM-3 Gases
NASA Astrophysics Data System (ADS)
Vassen, W.; Jeltes, T.; McNamara, J. M.; Tychkov, A. S.; Hogervorst, W.; van Leeuwen, K. A. H.; Krachmalnicoff, V.; Schellekens, M.; Perrin, A.; Chang, H.; Boiron, D.; Aspect, A.; Westbrook, C. I.
2008-04-01
We discuss our work to obtain a condensate containing more than 107 atoms and the first degenerate Fermi gas in a metastable state. Sympathetic cooling with Helium-4 is used to cool 106 Helium-3 atoms to a temperature T/TF < 0.5. The ultracold bosonic and fermionic gases have been used to observe the Hanbury Brown and Twiss effect for both isotopes, showing bunching for the bosons and antibunching for the fermions. A proposal for high resolution spectroscopy at 1.557 ?m, connecting both metastable states directly, is discussed at the end.
Zayarnyi, D A; L'dov, A Yu; Kholin, I V
2014-11-30
The processes of collision quenching of the resonance 5s[3/2]{sub 1}{sup o}({sup 3}P{sub 1}) state of the krypton atom are studied by the absorption probe method in electron-beam-excited high-pressure He – Kr mixtures with a low content of krypton. The rate constants of plasmochemical reactions Kr* + Kr + He ? Kr*{sub 2} + He [(4.21 ± 0.42) × 10{sup -33} cm{sup 6} s{sup -1}], Kr* + 2He ? HeKr* + He [(4.5 ± 1.2) × 10{sup -36} cm{sup 6} s{sup -1}] and Kr* + He ? products + He [(2.21 ± 0.22) × 10{sup -15} cm{sup 3} s{sup -1}] are measured for the first time. The rate constants of similar reactions are refined for krypton in the metastable 5s[3/2]{sub 2}{sup o} ({sup 3}P{sub 2}) state. (laser applications and other topics in quantum electronics)
Non-resonant elastic scattering of low-energy photons by atomic sodium confined in quantum plasmas
Ghosh, Avijit Ray, Debasis
2015-03-15
The non-resonant elastic scattering of low-energy photons by the bound valence electron in the ground state 3s of atomic sodium confined in quantum plasmas is investigated theoretically. The incident photon energy is assumed to be much smaller than the 3s-3p excitation energy. The alkali atom sodium is first formulated as an effective one-electron problem in which the attractive interaction between the valence electron and the atomic ion core is simulated by a spherically symmetric model potential. The Shukla-Eliasson oscillatory exponential cosine screened-Coulomb potential model is then used to mimic the effective two-body (valence-core) interaction within quantum plasmas. Non-relativistic calculations performed within the electric dipole approximation indicate that the non-resonant elastic photon scattering cross-section undergoes a dramatic growth by several orders of magnitude as the quantum wave number increases. A qualitative explanation of this phenomenon is presented. In the absence of the oscillatory cosine screening term, a similar growth is observed at larger values of the quantum wave number. Our computed relevant atomic data are in very good agreement with the experimental as well as the previous theoretical data for the zero-screening (free atom) case, and with the very limited, accurate theoretical results available for the case of exponential screened-Coulomb two-body interaction, without the cosine screening term.
Speckle Patterns with Atomic and Molecular de Broglie Waves
Patton, Forest S.; Deponte, Daniel P.; Kevan, Stephen D.; Elliott, Greg S.
2006-07-07
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.
Li, Xiaoping; Mandal, Anirban; Miliordos, Evangelos; Hunt, Katharine L C
2012-01-28
We report new ab initio results for the interaction-induced dipole moments ?? of hydrogen molecules colliding with helium atoms. These results are needed in order to calculate collision-induced absorption spectra at high temperatures; applications include modeling the radiative profiles of very cool white dwarf stars, with temperatures from 3500 K to 9000 K. We have evaluated the dipoles based on finite-field calculations, with coupled cluster methods in MOLPRO 2006 and aug-cc-pV5Z (spdfg) basis sets for both the H and He centers. We have obtained values of ?? for eight H(2) bond lengths ranging from 0.942 a.u. to 2.801 a.u., for 15 intermolecular separations R ranging from 2.0 a.u. to 10.0 a.u., and for 19 different relative orientations. In general, our values agree well with earlier ab initio results, for the geometrical configurations that are treated in common, but we have determined more points on the collision-induced dipole surface by an order of magnitude. These results make it possible to calculate transition probabilities for molecules in excited vibrational states, overtones, and rotational transitions with ?J > 4. We have cast our results in the symmetry-adapted form needed for absorption line shape calculations, by expressing ?? as a series in the spherical harmonics of the orientation angles of the intermolecular vector and of a unit vector along the H(2) bond axis. The expansion coefficients depend on the H(2) bond length and the intermolecular distance R. For large separations R, we show that the ab initio values of the leading coefficients converge to the predictions from perturbation theory, including both classical multipole polarization and dispersion effects. PMID:22299884
NASA Astrophysics Data System (ADS)
Li, Xiaoping; Mandal, Anirban; Miliordos, Evangelos; Hunt, Katharine L. C.
2012-01-01
We report new ab initio results for the interaction-induced dipole moments ?? of hydrogen molecules colliding with helium atoms. These results are needed in order to calculate collision-induced absorption spectra at high temperatures; applications include modeling the radiative profiles of very cool white dwarf stars, with temperatures from 3500 K to 9000 K. We have evaluated the dipoles based on finite-field calculations, with coupled cluster methods in MOLPRO 2006 and aug-cc-pV5Z (spdfg) basis sets for both the H and He centers. We have obtained values of ?? for eight H2 bond lengths ranging from 0.942 a.u. to 2.801 a.u., for 15 intermolecular separations R ranging from 2.0 a.u. to 10.0 a.u., and for 19 different relative orientations. In general, our values agree well with earlier ab initio results, for the geometrical configurations that are treated in common, but we have determined more points on the collision-induced dipole surface by an order of magnitude. These results make it possible to calculate transition probabilities for molecules in excited vibrational states, overtones, and rotational transitions with ?J > 4. We have cast our results in the symmetry-adapted form needed for absorption line shape calculations, by expressing ?? as a series in the spherical harmonics of the orientation angles of the intermolecular vector and of a unit vector along the H2 bond axis. The expansion coefficients depend on the H2 bond length and the intermolecular distance R. For large separations R, we show that the ab initio values of the leading coefficients converge to the predictions from perturbation theory, including both classical multipole polarization and dispersion effects.
Caballero-Benitez, Santiago F
2015-01-01
Quantum trapping potentials for ultracold gases change the landscape of classical properties of scattered light and matter. The atoms in a quantum many-body correlated phase of matter change the properties of light and vice versa. The properties of both light and matter can be tuned by design and depend on the interplay between long-range (nonlocal) interactions mediated by an optical cavity and short-range processes of the atoms. Moreover, the quantum properties of light get significantly altered by this interplay, leading the light to have nonclassical features. Further, these nonclassical features can be designed and optimised.
Lemeshko, Mikhail; Friedrich, Bretislav
2010-08-15
We present an analytic model of the refractive index for matter waves propagating through atomic or molecular gases. The model, which combines the Wentzel-Kramers-Brillouin (WKB) treatment of the long-range attraction with the Fraunhofer model treatment of the short-range repulsion, furnishes a refractive index in compelling agreement with recent experiments of Jacquey et al. [Phys. Rev. Lett. 98, 240405 (2007)] on Li atom matter waves passing through dilute noble gases. We show that the diffractive contribution, which arises from scattering by a two-dimensional 'hard core' of the potential, is essential for obtaining a correct imaginary part of the refractive index.
The atomic scale structure of CXV carbon: wide-angle x-ray scattering and modeling studies.
Hawelek, L; Brodka, A; Dore, J C; Honkimaki, V; Burian, A
2013-11-13
The disordered structure of commercially available CXV activated carbon produced from finely powdered wood-based carbon has been studied using the wide-angle x-ray scattering technique, molecular dynamics and density functional theory simulations. The x-ray scattering data has been converted to the real space representation in the form of the pair correlation function via the Fourier transform. Geometry optimizations using classical molecular dynamics based on the reactive empirical bond order potential and density functional theory at the B3LYP/6-31g* level have been performed to generate nanoscale models of CXV carbon consistent with the experimental data. The final model of the structure comprises four chain-like and buckled graphitic layers containing a small percentage of four-fold coordinated atoms (sp(3) defects) in each layer. The presence of non-hexagonal rings in the atomic arrangement has been also considered. PMID:24140935
Scaling functions applied to three-body recombination of Cesium-133 atoms
L. Platter; J. R. Shepard
2009-05-07
We demonstrate the implications of Efimov physics in the recently measured recombination rate of Cesium-133 atoms. By employing previously calculated results for the energy dependence of the recombination rate of Helium-4 atoms, we obtain three independent scaling functions that are capable of describing the recombination rates over a large energy range for identical bosons with large scattering length. We benchmark these and previously obtained scaling functions by successfully comparing their predictions with full atom-dimer phase shift calculations with artificial Helium-4 potentials yielding large scattering lengths. Exploiting universality, we finally use these functions to determine the 3-body recombination rate of Cesium-133 atoms with large positive scattering length, compare our results to experimental data obtained by the Innsbruck group and find excellent agreement.
Farrow, Christopher L; Billinge, Simon J L
2009-05-01
The relationship between the equations used in the atomic pair distribution function (PDF) method and those commonly used in small-angle-scattering (SAS) analyses is explicitly shown. The origin of the sloping baseline, -4pirrho0, in PDFs of bulk materials is identified as originating from the SAS intensity that is neglected in PDF measurements. The nonlinear baseline in nanoparticles has the same origin, and contains information about the shape and size of the nanoparticles. PMID:19349667
Scattering of a particle with spin by atomic chain as null test of T-violating P-even magnetism
S. L. Cherkas
2000-03-17
T-odd P-even long-range electromagnetic interaction of a particle of spin 1/2 with the nucleus is considered. Though matrix element of the interaction is zero for the particles on mass shell, nevertheless, null test exists for the interaction. The test consists in measuring of the spin-dependent T-odd P-even forward elastic scattering amplitude of a particle of spin 1/2 by atomic chain (axis) in a crystall.
Scattering of high-velocity He atoms by C/CH3/4 and Si/CH3/4
NASA Technical Reports Server (NTRS)
Amdur, I.; Marcus, A. B.; Jordan, J. E.; Mason, E. A.
1976-01-01
Fast helium beams are employed to probe short-range potentials in tetramethylmethane and tetramethylsilane, and throw light on the relations between these more complex reactions and such reactions as He-CH4 and He-SiH4. Earlier work on scattering of helium and argon beams by polyatomic molecules (fluorinated methanes, sulfur hexafluoride, silane, germane) are at variance with these results, as neither of the above systems can be represented as a cluster of four CH4 molecules, Effective He-H potentials based on scattering data are identical for the two systems studied but are much larger than the corresponding CH4 potential. A model in which centers of force are located along the bonds rather than at the nuclei is suggested for further testing.
Cryogenic Design and Operation of Liquid Helium in Electron Bubble Chamber
Ju, Y. L.; Dodd, J. R.; Willis, W. J.; Jia, L. X.
2006-04-27
We are developing a new cryogenic neutrino detector: electron bubble chamber, using liquid helium as the detecting medium, for the detection of low-energy neutrinos (<1 MeV), from the Sun. The program focuses in particular on the interactions of neutrinos scattering off atomic electrons in the detecting medium of liquid helium, resulting in recoil electrons which can be measured. We designed and constructed a small test chamber with 1.5L active volume to start the detector R and D, and performed experimental proofs of the operation principle. The test chamber is a stainless steel cylinder equipped with five optical windows and ten high voltage cables. To shield the liquid helium chamber against the external heat loads, the chamber is made of double-walled jacket cooled by a pumped helium bath and is built into a LN2/LHe cryostat, equipped with 80 K and 4 K radiation shields. A needle valve for vapor helium cooling was used to provide a 1.7{approx}4.5 K low temperature environments. The paper gives an introduction to the liquid helium solar neutrino detector, presents the cryogenic design and operation of the small test chamber.
Warehime, Mick; Alexander, Millard H.
2014-07-14
We restate the application of the finite element method to collinear triatomic reactive scattering dynamics with a novel treatment of the scattering boundary conditions. The method provides directly the reactive scattering wave function and, subsequently, the probability current density field. Visualizing these quantities provides additional insight into the quantum dynamics of simple chemical reactions beyond simplistic one-dimensional models. Application is made here to a symmetric reaction (H+H{sub 2}), a heavy-light-light reaction (F+H{sub 2}), and a heavy-light-heavy reaction (F+HCl). To accompany this article, we have written a MATLAB code which is fast, simple enough to be accessible to a wide audience, as well as generally applicable to any problem that can be mapped onto a collinear atom-diatom reaction. The code and user's manual are available for download from http://www2.chem.umd.edu/groups/alexander/FEM.
NASA Technical Reports Server (NTRS)
Cooper, J.
1983-01-01
The study of spectral line shapes has traditionally been mainly concerned with the measurement and interpretation of absorption or emission profiles. Often only the line widths are studied. The present investigation has the objective to evaluate the additional information which can be obtained by scattering light (usually from a laser) from an atomic system which is being perturbed by collisions. A scattering experiment is discussed. The scattered light consists of two components, a (coherent) Rayleigh component and a redistributed (fluorescent) component. In order to obtain the absorption spectrum, questions regarding the probability of photon absorption are considered. By observing the fluorescence subsequent to absorption during a collision it is found possible to obtain information on the evolution of the system from the point of absorption to the completion of the collision. The information on the intracollisional evolution is the justification for the title of the study, namely 'Why half a collision is better than a whole one'.
Warehime, Mick; Alexander, Millard H
2014-07-14
We restate the application of the finite element method to collinear triatomic reactive scattering dynamics with a novel treatment of the scattering boundary conditions. The method provides directly the reactive scattering wave function and, subsequently, the probability current density field. Visualizing these quantities provides additional insight into the quantum dynamics of simple chemical reactions beyond simplistic one-dimensional models. Application is made here to a symmetric reaction (H+H2), a heavy-light-light reaction (F+H2), and a heavy-light-heavy reaction (F+HCl). To accompany this article, we have written a MATLAB code which is fast, simple enough to be accessible to a wide audience, as well as generally applicable to any problem that can be mapped onto a collinear atom-diatom reaction. The code and user's manual are available for download from http://www2.chem.umd.edu/groups/alexander/FEM. PMID:25028010
In-situ synchrotron X-ray scattering study of thin film growth by atomic layer deposition.
Park, Yong Jun; Lee, Dong Ryeol; Lee, Hyun Hwi; Lee, Han-Bo-Ram; Kim, Hyungjun; Park, Gye-Choon; Rhee, Shi-Woo; Baik, Sunggi
2011-02-01
We report an atomic layer deposition chamber for in-situ synchrotron X-ray scattering study of thin film growth. The chamber was designed for combined synchrotron X-ray reflectivity and two-dimensional grazing-incidence X-ray diffraction measurement to do a in-situ monitoring of ALD growth. We demonstrate ruthenium thermal ALD growth for the performance of the chamber. 10, 20, 30, 50, 70, 100, 150 and 250-cycled states are measured by X-ray scattering methods during ALD growth process. Growth rate is calculated from thickness values and the surface roughness of each state is estimated by X-ray reflectivity analysis. The crystal structure of initial growth state is observed by Grazing-incidence X-ray diffraction. These results indicate that in-situ X-ray scattering method is a promising analysis technique to investigate the initial physical morphology of ALD films. PMID:21456240
NASA Astrophysics Data System (ADS)
Del Lama, L. S.; Soares, L. D. H.; Antoniassi, M.; Poletti, M. E.
2015-06-01
The Rayleigh to Compton scattering ratio (R/C) has been used as a reliable quantitative method for materials analysis, especially biological ones Unlike the conventional transmission method, which is sensitive to linear attenuation coefficients, the R/C ratio is more useful for situations where the ? variations are small and the atomic number variations become more significant. In the present study, gamma rays from an 241Am source with an energy of 59.54 keV were used to determine the effective atomic numbers for several materials considering the conventional total cross-section based method (ZeffATTEN) and also the intensity ratio between elastic (Rayleigh) and inelastic (Compton) scattered photons (ZeffR/C). Common liquid and solid compounds used as phantoms for investigation of radiation interaction effects on biological tissues were analyzed. This work aimed to use the R/C method in choosing the most suitable phantom to simulate biological tissues, considering two different experimental conditions: attenuation and scattering. The Rayleigh to Compton scattering ratio was shown to be a complementary approach to assist in the selection of appropriate tissue substitute materials.
Macco, Bart; Knoops, Harm C M; Kessels, Wilhelmus M M
2015-08-01
Hydrogen-doped indium oxide (In2O3:H) has recently emerged as an enabling transparent conductive oxide for solar cells, in particular for silicon heterojunction solar cells because its high electron mobility (>100 cm(2)/(V s)) allows for a simultaneously high electrical conductivity and optical transparency. Here, we report on high-quality In2O3:H prepared by a low-temperature atomic layer deposition (ALD) process and present insights into the doping mechanism and the electron scattering processes that limit the carrier mobility in such films. The process consists of ALD of amorphous In2O3:H at 100 °C and subsequent solid-phase crystallization at 150-200 °C to obtain large-grained polycrystalline In2O3:H films. The changes in optoelectronic properties upon crystallization have been monitored both electrically by Hall measurements and optically by analysis of the Drude response. After crystallization, an excellent carrier mobility of 128 ± 4 cm(2)/(V s) can be obtained at a carrier density of 1.8 × 10(20) cm(-3), irrespective of the annealing temperature. Temperature-dependent Hall measurements have revealed that electron scattering is dominated by unavoidable phonon and ionized impurity scattering from singly charged H-donors. Extrinsic defect scattering related to material quality such as grain boundary and neutral impurity scattering was found to be negligible in crystallized films indicating that the carrier mobility is maximized. Furthermore, by comparison of the absolute H-concentration and the carrier density in crystallized films, it is deduced that <4% of the incorporated H is an active dopant in crystallized films. Therefore, it can be concluded that inactive H atoms do not (significantly) contribute to defect scattering, which potentially explains why In2O3:H films are capable of achieving a much higher carrier mobility than conventional In2O3:Sn (ITO). PMID:26168056
Danisman, M. Fatih; Oezkan, Berrin
2011-11-15
We describe a quartz crystal microbalance setup that can be operated at low temperatures in ultra high vacuum with gold electrode surfaces acting as substrate surface for helium diffraction measurements. By simultaneous measurement of helium specular reflection intensity from the electrode surface and resonance frequency shift of the crystal during film adsorption, helium diffraction data can be correlated to film thickness. In addition, effects of interfacial viscosity on the helium diffraction pattern could be observed. To this end, first, flat gold films on AT cut quartz crystals were prepared which yield high enough helium specular reflection intensity. Then the crystals were mounted in the helium diffractometer sample holder and driven by means of a frequency modulation driving setup. Different crystal geometries were tested to obtain the best quality factor and preliminary measurements were performed on Kr films on gold surfaces. While the crystal structure and coverage of krypton films as a function of substrate temperature could successfully be determined, no depinning effects could be observed.
Berry, R. Stephen
Electron-Atom Superelastic Scattering in Magnesium at Millielectron Volt Energies T. Baynard, A. C energy dependence of magnesium from threshold to 1400 eV10 with an energy resolution of 250 meV. Similar
A low energy bound atomic electron Compton scattering model for Geant4
NASA Astrophysics Data System (ADS)
Brown, J. M. C.; Dimmock, M. R.; Gillam, J. E.; Paganin, D. M.
2014-11-01
A two-body fully relativistic three-dimensional scattering framework has been utilised to develop an alternative Compton scattering computational model to those adapted from Ribberfors' work for Monte Carlo modelling of Compton scattering. Using a theoretical foundation that ensures the conservation of energy and momentum in the relativistic impulse approximation, this new model, the Monash University Compton scattering model, develops energy and directional algorithms for both the scattered photon and ejected Compton electron from first principles. The Monash University Compton scattering model was developed to address the limitation of the Compton electron directionality algorithms of other computational models adapted from Ribberfors' work. Here the development of the Monash University Compton scattering model, including its implementation in a Geant4 low energy electromagnetic physics class, G4LowEPComptonModel, is outlined. Assessment of the performance of G4LowEPComptonModel was undertaken in two steps: (1) comparison with respect to the two standard Compton scattering classes of Geant4 version 9.5, G4LivermoreComptonModel and G4PenelopeComptonModel, and (2) experimental comparison with respect to Compton electron kinetic energy spectra obtained from the Compton scattering of 662 keV photons off the K-shell of gold. Both studies illustrate that the Monash University Compton scattering model, and in turn G4LowEPComptonModel, is a viable replacement for the majority of computational models that have been adapted from Ribberfors' work. It was also shown that the Monash University Compton scattering model is able to reproduce the Compton scattering triply differential cross-section Compton electron kinetic energy spectra of 662 keV photons K-shell scattering off of gold to within experimental uncertainty.
Rutherford backscattering oscillation in scanning helium-ion microscopy
Kostinski, Sarah; Yao, Nan
2011-03-15
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.
Screening Effects on Nonrelativistic Bremsstrahlung in the Scattering of Electrons by Neutral Atoms
NASA Technical Reports Server (NTRS)
Jung, Young-Dae; Lee, Kun-Sang
1995-01-01
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.
Quantum theory of a micromaser operating on the atomic scattering from a resonant standing wave
Saif, F.; Le Kien, F.; Zubairy, M. Suhail
2001-01-01
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...
The mutual influence of reactive and non-reactive scattering channels in atom--molecule collisions.
NASA Astrophysics Data System (ADS)
Simbotin, I.; Côté, R.; Dalgarno, A.
2008-05-01
In this work, we study D+H2 collisions for the main purpose of understanding the influence of the reactive scattering channels on the non-reactive scattering channels. We will present a detailed quantitative comparison between the results of full calculations (including rearrangement) and non-reactive calculations. We perform this comparison by artificially eliminating the possibility of rearrangement and by allowing only for inelastic scattering.
NASA Technical Reports Server (NTRS)
Synowicki, R. A.; Hale, Jeffrey S.; Woollam, John A.
1992-01-01
The University of Nebraska is currently evaluating Low Earth Orbit (LEO) simulation techniques as well as a variety of thin film protective coatings to withstand atomic oxygen (AO) degradation. Both oxygen plasma ashers and an electron cyclotron resonance (ECR) source are being used for LEO simulation. Thin film coatings are characterized by optical techniques including Variable Angle Spectroscopic Ellipsometry, Optical spectrophotometry, and laser light scatterometry. Atomic Force Microscopy (AFM) is also used to characterize surface morphology. Results on diamondlike carbon (DLC) films show that DLC degrades with simulated AO exposure at a rate comparable to Kapton polyimide. Since DLC is not as susceptible to environmental factors such as moisture absorption, it could potentially provide more accurate measurements of AO fluence on short space flights.
Angular distributions of 5eV atomic oxygen scattered from solid surfaces on the LDEF satellite
NASA Technical Reports Server (NTRS)
Gregory, John C.; Peters, Palmer N.
1992-01-01
The angular distribution of 5eV atomic oxygen scattered off several smooth solid surfaces was measured by experiment A0114 which flew on board the Long Duration Exposure Facility (LDEF). Target surfaces were silver, vitreous carbon, and lithium fluoride crystal. The apparatus was entirely passive. It used the property of silver surfaces to absorb oxygen atoms with high efficiency; the silver is converted to optically transmissive silver oxide. A collimated beam of oxygen atoms is allowed to fall on the target surface at some pre-set angle. Reflected atoms are then intercepted by a silver film placed so that it subtends a considerable solid angle from the primary beam impact on the target surface. The silver films are evaporated onto flexible optically-clear polycarbonate sheets which are scanned later to determine oxygen uptake. While the silver detector cannot measure atom velocity or energy, its physical configuration allows easy coverage of large angular space both in the beam-plane (that which includes the incident beam and the surface normal), and in the azimuthal plane of the target surface.
Coupling between positronium formation and elastic positron-scattering channels in the rare gases
Jay, P. M.; Coleman, P. G.
2010-07-15
Measurements of elastic-scattering cross sections are presented for positron collisions with helium, neon, argon, krypton, and xenon around the threshold energy for positronium (Ps) formation. The elastic cross section falls slowly with increasing energy above the Ps formation threshold in helium and neon, whereas in argon, krypton, and xenon it exhibits an increase, which appears both more prominent and more sustained as the atomic number of the gas increases. It is proposed that this coupling is a result of an intermediate virtual Ps state that enhances branching into the (atom plus positron) final state.
Park, Y. J.; Lee, D. R.; Baik, S.
2011-12-23
Due to the excellent conformality of ALD, it is not only adopted thin film, but also has been adopted for the fabrication of nanostructures. The surface reaction of ALD process is dependent on the substrate condition, thus the study on initial stage of ALD process is crucial to achieve controllable film growth. By the way, because of quite low scattering intensity of initial ultra thin layer, the high flux Synchrotron Radiation is needed. Synchrotron radiation x-ray scattering measurements allow us to investigate the atomic structure evolution of a few nanometer thickness films at the initial growth stage, nondestructively. Ru and TaN ALD films were grown. The thickness, roughness, and electron density were estimated by X-Ray Reflectivity (XRR) analysis. The island structures and its coverage also were estimated.
Inelastic scattering of light by a cold trapped atom: Effects of the quantum center-of-mass motion
Marc Bienert; Wolfgang Merkel; Giovanna Morigi
2005-11-16
The light scattered by a cold trapped ion, which is in the stationary state of laser cooling, presents features due to the mechanical effects of atom-photon interaction. These features appear as additional peaks (sidebands) in the spectrum of resonance fluorescence. Among these sidebands the literature has discussed the Stokes and anti-Stokes components, namely the sidebands of the elastic peak. In this manuscript we show that the motion also gives rise to sidebands of the inelastic peaks. These are not always visible, but, as we show, can be measured in parameter regimes which are experimentally accessible.
Helicity-resolved Raman scattering of MoS?, MoSe?, WS?, and WSe? atomic layers.
Chen, Shao-Yu; Zheng, Changxi; Fuhrer, Michael S; Yan, Jun
2015-04-01
The two-fold valley degeneracy in two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs) (Mo,W)(S,Se)2 is suitable for "valleytronics", the storage and manipulation of information utilizing the valley degree of freedom. The conservation of luminescent photon helicity in these 2D crystal monolayers has been widely regarded as a benchmark indicator for charge carrier valley polarization. Here we perform helicity-resolved Raman scattering of the TMDC atomic layers. In drastic contrast to luminescence, the dominant first-order zone-center Raman bands, including the low energy breathing and shear modes as well as the higher energy optical phonons, are found to either maintain or completely switch the helicity of incident photons. In addition to providing a useful tool for characterization of TMDC atomic layers, these experimental observations shed new light on the connection between photon helicity and valley polarization. PMID:25719859
Bederson, B.
1980-03-01
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.
Coherent backscattering of light with nonlinear atomic scatterers T. Wellens,1,2
Kaiser, Robin
a speckle pattern 7 indicating that phase coher- ence is preserved by the scattering process. Theoretical-localization regime suppression of diffusive behavior has been pre- dicted, provided phase coherence is preserved over
Strong directional out-of-plane scattering in multiple ionizing highly charged ion-atom collisions
Gonzalez, A.; Hagmann, S.; Quinteros, T. . J.R. MacDonald Lab.); Kraessig, B. . Fakultaet fuer Physik); Koch, R.; Schmidt-Boecking, H. . Inst. fuer Kernphysik); Skutlartz, A. )
1990-01-01
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.
Strong directional out-of-plane scattering in multiple ionizing highly charged ion-atom collisions
Gonzalez, A.; Hagmann, S.; Quinteros, T.; Kraessig, B.; Koch, R.; Schmidt-Boecking, H.; Skutlartz, A.
1990-12-31
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.
NASA Astrophysics Data System (ADS)
Liu, Ya-Wei; Mei, Xiao-Xun; Kang, Xu; Yang, Ke; Xu, Wei-Qing; Peng, Yi-Geng; Hiraoka, Nozomu; Tsuei, Ku-Ding; Zhang, Peng-Fei; Zhu, Lin-Fan
2014-01-01
The high-resolution x-ray-scattering technique is used to study the elastic scattering of atoms and molecules in the gas phase. The elastic squared form factor, which is the square of the Fourier transformation of the electron density distribution in position space and reveals the pure electronic structure of atoms and molecules in the ground state, of molecular hydrogen is measured at an incident photon energy of about 9889 eV and an energy resolution of about 70 meV. Although it is generally thought that the x-ray-scattering technique is identical to high-energy electron scattering, at least for elastic scattering these two techniques have an apparent difference, i.e., the pure electronic structure of a molecule in the ground state can be determined by x-ray scattering while it cannot be obtained by the high-energy electron impact method due to the interference between the scattering of separate nuclei and of the electrons in the target. The present experimental results match the theoretical calculations very well, which demonstrates that high-resolution x-ray scattering is a powerful tool to study the electronic structure of atoms and molecules in the ground state.
NASA Astrophysics Data System (ADS)
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
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.
Precision spectroscopy of Helium
Cancio, P.; Giusfredi, G.; Mazzotti, D.; De Natale, P.; De Mauro, C.; Krachmalnicoff, V.; Inguscio, M.
2005-05-05
Accurate Quantum-Electrodynamics (QED) tests of the simplest bound three body atomic system are performed by precise laser spectroscopic measurements in atomic Helium. In this paper, we present a review of measurements between triplet states at 1083 nm (23S-23P) and at 389 nm (23S-33P). In 4He, such data have been used to measure the fine structure of the triplet P levels and, then, to determine the fine structure constant when compared with equally accurate theoretical calculations. Moreover, the absolute frequencies of the optical transitions have been used for Lamb-shift determinations of the levels involved with unprecedented accuracy. Finally, determination of the He isotopes nuclear structure and, in particular, a measurement of the nuclear charge radius, are performed by using hyperfine structure and isotope-shift measurements.
Study of Impurity-Helium Condensates Formed by Multishell Nanoclusters
Mao, Shun
2014-12-17
. Impurity-helium condensates (IHCs) containing nitrogen and krypton atoms immersed in super fluid 4He have been studied via a CW electron spin resonance (ESR) technique. It was found that the addition of krypton atoms to the nitrogen-helium gas mixture used...
Nguyen, Hung T.; Pabit, Suzette A.; Meisburger, Steve P.; Pollack, Lois; Case, David A.
2014-12-14
A new method is introduced to compute X-ray solution scattering profiles from atomic models of macromolecules. The three-dimensional version of the Reference Interaction Site Model (RISM) from liquid-state statistical mechanics is employed to compute the solvent distribution around the solute, including both water and ions. X-ray scattering profiles are computed from this distribution together with the solute geometry. We describe an efficient procedure for performing this calculation employing a Lebedev grid for the angular averaging. The intensity profiles (which involve no adjustable parameters) match experiment and molecular dynamics simulations up to wide angle for two proteins (lysozyme and myoglobin) in water, as well as the small-angle profiles for a dozen biomolecules taken from the BioIsis.net database. The RISM model is especially well-suited for studies of nucleic acids in salt solution. Use of fiber-diffraction models for the structure of duplex DNA in solution yields close agreement with the observed scattering profiles in both the small and wide angle scattering (SAXS and WAXS) regimes. In addition, computed profiles of anomalous SAXS signals (for Rb{sup +} and Sr{sup 2+}) emphasize the ionic contribution to scattering and are in reasonable agreement with experiment. In cases where an absolute calibration of the experimental data at q = 0 is available, one can extract a count of the excess number of waters and ions; computed values depend on the closure that is assumed in the solution of the Ornstein–Zernike equations, with results from the Kovalenko–Hirata closure being closest to experiment for the cases studied here.
NASA Astrophysics Data System (ADS)
Nguyen, Hung T.; Pabit, Suzette A.; Meisburger, Steve P.; Pollack, Lois; Case, David A.
2014-12-01
A new method is introduced to compute X-ray solution scattering profiles from atomic models of macromolecules. The three-dimensional version of the Reference Interaction Site Model (RISM) from liquid-state statistical mechanics is employed to compute the solvent distribution around the solute, including both water and ions. X-ray scattering profiles are computed from this distribution together with the solute geometry. We describe an efficient procedure for performing this calculation employing a Lebedev grid for the angular averaging. The intensity profiles (which involve no adjustable parameters) match experiment and molecular dynamics simulations up to wide angle for two proteins (lysozyme and myoglobin) in water, as well as the small-angle profiles for a dozen biomolecules taken from the BioIsis.net database. The RISM model is especially well-suited for studies of nucleic acids in salt solution. Use of fiber-diffraction models for the structure of duplex DNA in solution yields close agreement with the observed scattering profiles in both the small and wide angle scattering (SAXS and WAXS) regimes. In addition, computed profiles of anomalous SAXS signals (for Rb+ and Sr2+) emphasize the ionic contribution to scattering and are in reasonable agreement with experiment. In cases where an absolute calibration of the experimental data at q = 0 is available, one can extract a count of the excess number of waters and ions; computed values depend on the closure that is assumed in the solution of the Ornstein-Zernike equations, with results from the Kovalenko-Hirata closure being closest to experiment for the cases studied here.
Quick, C.R. Jr.; Moore, D.S.
1983-01-01
Coherent anti-Stokes Raman spectroscopy (CARS) is being utilized to investigate the rovibrational energy distributions produced by reactive and nonreactive collisions of translationally hot atoms with simple molecules. Translationally hot H atoms are produced by ArF laser photolysis of HBr. Using CARS we have monitored, in a state-specific and time-resolved manner, rotational excitation of HBr (v = 0), vibrational excitation of HBr and H/sub 2/, rovibrational excitation of H/sub 2/ produced by the reaction H + HBr ..-->.. H/sub 2/ + Br, and Br atom production by photolysis of HBr.
NASA Astrophysics Data System (ADS)
Barclay, V. J.; Jack, D. B.; Polanyi, J. C.; Zeiri, Y.
1992-12-01
The angular and energy distributions of 1.1 and 2.6 eV H-atom scattering from a LiF(001) surface are compared for two different sources of hot H-atoms (1) localized H-atoms produced by the photolysis of HBr molecules adsorbed on the LiF surface; and (2) H-atoms from a beam at the same energy and angle of approach to the LiF surface as in (1). These distributions are the results of classical stochastic trajectories carried out on a 7×7 slab of LiF(001). The calculated angular distributions are compared with experimental distributions [E. B. D. Bourdon et al., J. Chem. Phys. 95, 1361 (1991)]. The computed effects of changing H-atom energy and surface temperature are also reported; localized scattering becomes increasingly nonspecular at lower photon energies, and broader at higher surface temperatures.
NASA Astrophysics Data System (ADS)
Rao, D. V.; Takeda, T.; Itai, Y.; Akatsuka, T.; Seltzer, S. M.; Hubbell, J. H.; Cesareo, R.; Brunetti, A.; Gigante, G. E.
Atomic Rayleigh scattering cross-sections for low, medium and high Z atoms are measured in vacuum using X-ray tube with a secondary target as an excitation source instead of radioisotopes. Monoenergetic K? radiation emitted from the secondary target and monoenergetic radiation produced using two secondary targets with filters coupled to an X-ray tube are compared. The K? radiation from the second target of the system is used to excite the sample. The background has been reduced considerably and the monochromacy is improved. Elastic scattering of K? X-ray line energies of the secondary target by the sample is recorded with Hp Ge and Si (Li) detectors. A new approach is developed to estimate the solid angle approximation and geometrical efficiency for a system with experimental arrangement using X-ray tube and secondary target. The variation of the solid angle is studied by changing the radius and length of the collimators towards and away from the source and sample. From these values the variation of the total solid angle and geometrical efficiency is deduced and the optimum value is used for the experimental work. The efficiency is larger because the X-ray fluorescent source acts as a converter. Experimental results based on this system are compared with theoretical estimates and good agreement is observed in between them.
Double Scattering Effects in the Ionization Spectrum Produced by Single Energetic Atomic Collisions
Suarez, S.; Barrachina, R.O.; Meckbach, W.
1996-07-01
We present experimental evidence of double scattering processes in the ionization of hydrogenic projectiles by single collisions with He targets at intermediate energies. We observe a distinctive shoulder in the electron velocity distribution in the forward direction at a velocity approximately 3 times greater than the velocity of the projectile. We interpret this structure as due to the emission of projectile electrons which have undergone two consecutive binary scattering processes: one with the target in first place, followed by a second one with the projectile nucleus. {copyright} {ital 1996 The American Physical Society.}
Positron scattering by atomic hydrogen using optical potentials and with positronium formation
NASA Technical Reports Server (NTRS)
Walters, H. R. J.
1990-01-01
The scattering is considered of positrons by H(ls) in a two-state model which incorporates optical potentials. The model explicitly describes elastic scattering, i.e., positron + H(ls) yields positron + H(ls) and Ps(ls) yields Ps(ls) + p. The inelastic processes positron + H(ls) yields positron + H* Ps(ls) + p yields Ps* + p where * stands for a state other than ls, are implicitly taken into account through the optical potentials, which also allow for polarization of H(ls) and Ps(ls).
Smr?ok, ?ubomír; Kolesnikov, Alexander I; Rieder, Milan
2012-01-01
Inelastic neutron scattering (INS) was used to study vibrational dynamics of the hydrogen atoms in natural trioctahedral phlogopite, K0.93Na0.03(Mg2.47Fe0.22Al0.16Fe0.04Tl0.06)[Si2.84Al1.16]O10OH1.71F0.28Cl0.01, within the 50-1000 cm-1 energy range. The INS spectra collected using direct geometry spectrometer SEQUOIA at ORNL were interpreted by means of the solid-state DFT calculations covering both normal mode analysis and molecular dynamics. To optimize the structure and to calculate the vibrational modes under harmonic approximation both a hybrid PBE0 and the AM05 functional were used, while the molecular dynamics calculations (60ps/1fs) were performed only with the computationally less-demanding AM05 functional. The main contributions to the dominant band within ~750-550 cm-1 are symmetric and antisymmetric Mg-O-H bending modes, overlapping with the skeletal stretching and bending modes causing weaker secondary movements of H atoms of inner hydroxyl groups. Signatures of the Mg-O-H bending modes appear down to ~400 cm-1, where a region of octahedra deformation modes starts. These deformations cause just shallow movements of the hydrogen atoms and are mirrored by the modes with close vibrational energies. The region from ~330 cm-1 down to the low energy end of the spectrum portrays induced vibrations of the H atoms caused by deformation of individual polyhedra, translational vibrations of the parts of the 2:1 layer relative one to another, and librational and translational vibrations of the layer. The main difference between the INS spectrum of dioctahedral Al-muscovite and trioctahedral Mg-phlogopite is that the Mg-O-H modes are all assigned to in-plane vibrations of the respective hydrogen atoms.
NASA Astrophysics Data System (ADS)
Smr?ok, L'ubomír; Kolesnikov, Alexander I.; Rieder, Milan
2012-10-01
Inelastic neutron scattering (INS) was used to study the vibrational dynamics of the hydrogen atoms in natural trioctahedral phlogopite, K0.93Na0.03(Mg2.47Fe0.22Al0.16Fe0.04Tl0.06)[Si2.84Al1.16]O10OH1.71F0.28Cl0.01, within the 50-1,000 cm-1 energy range. The INS spectra collected using direct geometry spectrometer SEQUOIA (ORNL) were interpreted by means of the solid-state DFT calculations covering both normal mode analysis and molecular dynamics. To optimize the structure and to calculate the vibrational modes under harmonic approximation, both a hybrid PBE0 and the AM05 functional were used, while the molecular dynamics calculations (60 ps/1 fs) were performed only with the computationally less-demanding AM05 functional. The main contributions to the dominant band within ~750-550 cm-1 are symmetric and antisymmetric Mg-O-H bending modes, overlapping with the skeletal stretching and bending modes causing weaker secondary movements of H atoms of inner hydroxyl groups. Signatures of the Mg-O-H bending modes appear down to ~400 cm-1, where a region of octahedra deformation modes starts. These deformations cause just shallow movements of the hydrogen atoms and are mirrored by the modes with close vibrational energies. The region from ~330 cm-1 down to the low-energy end of the spectrum portrays induced vibrations of the H atoms caused by deformation of individual polyhedra, translational vibrations of the parts of the 2:1 layer relative one to another, and librational and translational vibrations of the layer. The main difference between the INS spectrum of dioctahedral Al-muscovite and trioctahedral Mg-phlogopite is that the Mg-O-H modes are all assigned to in-plane vibrations of the respective hydrogen atoms.
NASA Astrophysics Data System (ADS)
Ko, Chung-Ting; Yang, Po-Shuan; Han, Yin-Yi; Wang, Wei-Cheng; Huang, Jhih-Jie; Lee, Yen-Hui; Tsai, Yi-Jen; Shieh, Jay; Chen, Miin-Jang
2015-07-01
Plasmonic silver nanostructures and a precise ZnO cover layer prepared by capacitively coupled plasma atomic layer deposition (ALD) were exploited to enhance the Raman scattering from nanoscale ultrathin films on a Si substrate. The plasmonic activity was supported by a nanostructured Ag (nano-Ag) layer, and a ZnO cover layer was introduced upon the nano-Ag layer to spectrally tailor the localized surface plasmon resonance to coincide with the laser excitation wavelength. Because of the optimized dielectric environment provided by the precise growth of ZnO cover layer using ALD, the intensity of Raman scattering from nanoscale ultrathin films was significantly enhanced by an additional order of magnitude, leading to the observation of the monoclinic and tetragonal phases in the nanoscale ZrO2 high-K gate dielectric as thin as ?6 nm on Si substrate. The excellent agreement between the finite-difference time-domain simulation and experimental measurement further confirms the so-called {{?ft| {\\overset{\\scriptscriptstyle\\rightharpoonup}{E}} \\right|}4} dependence of the surface-enhanced Raman scattering. This technique of plasmonic enhancement of Raman spectroscopy, assisted by the nano-Ag layer and optimized dielectric environment prepared by ALD, can be applied to characterize the structures of ultrathin films in a variety of nanoscale materials and devices, even on a Si substrate with overwhelming Raman background.
A Quantum Scattering Interferometer
Hart, R A; Legere, R; Gibble, K; Hart, Russell A.; Xu, Xinye; Legere, Ronald
2007-01-01
The collision of two ultra-cold atoms results in a quantum-mechanical superposition of two outcomes: each atom continues without scattering and each atom scatters as a spherically outgoing wave with an s-wave phase shift. The magnitude of the s-wave phase shift depends very sensitively on the interaction between the atoms. Quantum scattering and the underlying phase shifts are vitally important in many areas of contemporary atomic physics, including Bose-Einstein condensates, degenerate Fermi gases, frequency shifts in atomic clocks, and magnetically-tuned Feshbach resonances. Precise measurements of quantum scattering phase shifts have not been possible until now because, in scattering experiments, the number of scattered atoms depends on the s-wave phase shifts as well as the atomic density, which cannot be measured precisely. Here we demonstrate a fundamentally new type of scattering experiment that interferometrically detects the quantum scattering phase shifts of individual atoms. By performing an atomic...
Mertens, A.; Auth, C.; Winter, H.; Borisov, A.G.
1997-02-01
Fast alkali atoms and ions are scattered with keV energies under grazing incidence from the surface of the alkali halides LiF(100), KCl(100), KI(100), and the scattered beams are analyzed with respect to their charge fractions. From our experiments we find no evidence for occupied or unoccupied electronic surface states within the band gap of the insulator. {copyright} {ital 1997} {ital The American Physical Society}
Wetting Behavior of HELIUM-4 and HELIUM-3-HELIUM -4 Mixtures on a Cesium Surface.
NASA Astrophysics Data System (ADS)
Ketola, Kurt Stephen
1995-01-01
In 1991, it was predicted that ^4 {rm He} wouldn't wet a Cs surface at low enough temperatures. This was a surprising prediction since it had been thought that ^4{ rm He} would wet all surfaces since the interaction energy between two helium atoms is extremely weak compared to the interaction energy between a helium atom and most substrates. However, the large size of the electron shell of cesium causes the binding energy of a helium atom to a cesium surface to be weak, even compared to the binding energy of a helium atom to a liquid helium "substrate". We have examined the wetting behavior of ^4{rm He} on a cesium substrate using third sound techniques. This experiment was one of the first to show that the wetting behavior of ^4{rm He} on cesium was fundamentally different than that seen before on any other substrate. Our idea was to see if thickness/temperature waves (third sound) generated in a superfluid helium film adsorbed to a strong-binding surface would propagate across an adjacent Cs surface. If there was no superfluid present on the Cs surface, then there should be no transmission of the third sound waves across the Cs. We observed a transition from nonpropagation of third sound to propagation of third sound as a function of the helium vapor pressure in the cell. This was the first observation of a prewetting transition for any system and it indicated that there must be a wetting transition at some lower temperature which must be first-order. After completing the third sound experiments, we turned our attention to studying the wetting of ^3{rm He}- ^4{rm He} mixtures on Cs using quartz crystal microbalance techniques. This work was motivated by theoretical work which predicted that ^3{rm He}- ^4{rm He} mixtures of sufficiently high ^3{rm He} concentration would wet cesium at temperatures where pure ^4 {rm He} would not. Wetting would be induced by the ^3{rm He} at the liquid-vapor interface, which would reduce the liquid-vapor surface tension. We have observed the predicted transition for ^3{rm He}-^4{rm He} mixtures on cesium from nonwetting to wetting as the temperature is lowered, and we have measured the dependence of this reentrant wetting temperature on the ^3 {rm He} concentration.
A positron trap and beam apparatus for atomic and molecular scattering experiments.
Sullivan, J P; Jones, A; Caradonna, P; Makochekanwa, C; Buckman, S J
2008-11-01
An instrument has been designed and constructed to provide new insights into fundamental, low energy positron scattering processes. The design is based on the Surko trap system and produces a pulsed positron beam with an energy resolution of as good as 54 meV. The design and operation of the apparatus is explained, while the first experimental results from this apparatus have been demonstrated in recent publications. PMID:19045887
Francoual, S; Strempfer, J; Warren, J; Liu, Y; Skaugen, A; Poli, S; Blume, J; Wolff-Fabris, F; Canfield, P C; Lograsso, T
2015-09-01
The resonant scattering and diffraction beamline P09 at PETRA III at DESY is equipped with a 14?T vertical field split-pair magnet. A helium-3 refrigerator is available that can be fitted inside the magnet's variable-temperature insert. Here the results of a series of experiments aimed at determining the beam conditions permitting operations with the He-3 insert are presented. By measuring the tetragonal-to-orthorhombic phase transition occurring at 2.1?K in the Jahn-Teller compound TmVO4, it is found that the photon flux at P09 must be attenuated down to 1.5 × 10(9)?photons?s(-1) for the sample to remain at temperatures below 800?mK. Despite such a reduction of the incident flux and the subsequent use of a Cu(111) analyzer, the resonant X-ray magnetic scattering signal at the Tm LIII absorption edge associated with the spin-density wave in TmNi2B2C below 1.5?K is intense enough to permit a complete study in magnetic field and at sub-Kelvin temperatures to be carried out. PMID:26289272
Confined helium on Lagrange meshes.
Baye, D; Dohet-Eraly, J
2015-11-25
The Lagrange-mesh method has the simplicity of a calculation on a mesh and can have the accuracy of a variational method. It is applied to the study of a confined helium atom. Two types of confinement are considered. Soft confinements by potentials are studied in perimetric coordinates. Hard confinement in impenetrable spherical cavities is studied in a system of rescaled perimetric coordinates varying in [0,1] intervals. Energies and mean values of the distances between electrons and between an electron and the helium nucleus are calculated. A high accuracy of 11 to 15 significant figures is obtained with small computing times. Pressures acting on the confined atom are also computed. For sphere radii smaller than 1, their relative accuracies are better than 10(-10). For larger radii up to 10, they progressively decrease to 10(-3), still improving the best literature results. PMID:25732054
Xray Dispersion and Scattering in the Average-Atom Model of a Plasma
Johnson, Walter R.
Average-Atom & Static Conductivity (Ziman) R Kubo-Greenwood Formula (Infrared Catastrophe) R "Proper: = 2e2 3 d3 p (2)3 - f E v 2 p (Ziman formula) University of Nevada, Reno 09 6 #12;Example Comparison with Experiment 0.01 0.1 1 Density (gm/cc) 0.0001 0.0010 0.0100 0.1000 Resistivity(-cm) Ziman BSM D&K K&K Al T=20
S. Sakaguchi; T. Uesaka; N. Aoi; Y. Ichikawa; K. Itoh; M. Itoh; T. Kawabata; T. Kawahara; Y. Kondo; H. Kuboki; T. Nakamura; T. Nakao; Y. Nakayama; H. Sakai; Y. Sasamoto; K. Sekiguchi; T. Shimamura; Y. Shimizu; T. Wakui
2013-02-18
Vector analyzing powers for proton elastic scattering from 8He at 71 MeV/nucleon have been measured using a solid polarized proton target operated in a low magnetic field of 0.1 T. The spin-orbit potential obtained from a phenomenological optical model analysis is found to be significantly shallower and more diffuse than the global systematics of stable nuclei, which is an indication that the spin-orbit potential is modified for scattering involving neutron-rich nuclei. A close similarity between the matter radius and the root-mean-square radius of the spin-orbit potential is also identified.
Sensitivity of ultracold-atom scattering experiments to variation of the fine-structure constant
Borschevsky, A.; Beloy, K.; Flambaum, V. V.; Schwerdtfeger, P.
2011-05-15
We present numerical calculations for cesium and mercury to estimate the sensitivity of the scattering length to the variation of the fine-structure constant {alpha}. The method used follows the ideas of Chin and Flambaum [Phys. Rev. Lett. 96, 230801 (2006)], where the sensitivity to the variation of the electron-to-proton mass ratio {beta} was considered. We demonstrate that for heavy systems, the sensitivity to the variation of {alpha} is of the same order of magnitude as to the variation of {beta}. Near narrow Feshbach resonances, the enhancement of the sensitivity may exceed nine orders of magnitude.
NASA Technical Reports Server (NTRS)
Gould, R. J.
1985-01-01
By elementary methods, the cross section for electron-atom and electron-molecule bremsstrahlung is computed in the limit when the incident electron energy is much less than Ry. The procedure employs the classical soft-photon emission probability formula for general (h/2pi)(omega), yielding a simple expression for the bremsstrahlung cross section in terms of the total elastic scattering cross section. The validity of the method is discussed, and results are compared with more elaborate and accurate calculations. Comparison is made with ('free-free') opacity calculations for the associated process at the temperature (6300 K) of the solar atmosphere. For chi sub omega = (h/2pi)(omega)/kT = 1, the computed absorption coefficient is within 2, 7, and 12 percent of accurate calculations for scatterings by H, He, and H2, respectively. The general dependence of the opacity on chi sub omega is described well by the simple formula, although the error is larger for higher chi sub omega; it is suggested that the inaccuracy at high frequencies is due to the failure of the soft-photon approximation.
Atomistic simulation of helium bubble nucleation in palladium
NASA Astrophysics Data System (ADS)
Wang, Liang; Hu, Wangyu; Xiao, Shifang; Yang, Jianyu; Deng, Huiqiu
2009-09-01
A palladium crystal has been constructed with 11808 atoms. 55 helium atoms occupied the octahedral position of palladium crystal are introduced and retained in a spherical region. Molecular dynamic simulations are performed in a constant temperature and constant volume ensemble (NVT) with temperature controlled by Nose-Hoover thermostat. The interactions between palladium atoms are described with modified analytic embedded atom method (MAEAM), the interactions between palladium atom and helium atom are in the form of Morse potential, and the interactions between helium atoms are in the form of L-J potential function. With the analysis of the radial distribution function (RDF) and microstructure, it reveals that some of helium atoms form a series of clusters with different size, and the nucleation core is random at low temperature, and which is the embryo of helium bubble. Increasing temperature can accelerate the process of bubble nucleation, and the clusters will aggregate and coalesce into a bigger one in which there are no palladium atoms, and it is considered as a helium bubble.
Clore, G. Marius
with a given scattering profile. On the other hand, direct refinement against SAXS/WAXS data in combination profiles is generally restricted to low- resolution shape and size information that, on its own, cannot lead to unique 3-D structures of biological macromolecules comparable to all-atom models derived from X
Rotational state-changing cold collisions of hydroxyl ions with helium
Hauser, Daniel; Carelli, Fabio; Spieler, Steffen; Lakhmanskaya, Olga; Endres, Eric S; Kumar, Sunil S; Gianturco, Franco; Wester, Roland
2015-01-01
Cold molecules are important for many applications, from fundamental precision measurements, quantum information processing, quantum-controlled chemistry, to understanding the cold interstellar medium. Molecular ions are known to be cooled efficiently in sympathetic collisions with cold atoms or ions. However, little knowledge is available on the elementary cooling steps, because the determination of quantum state-to-state collision rates at low temperature is prohibitively challenging for both experiment and theory. Here we present a method to manipulate molecular quantum states by non-resonant photodetachment. Based on this we provide absolute quantum scattering rate coefficients under full quantum state control for the rotationally inelastic collision of hydroxyl anions with helium. Experiment and quantum scattering theory show excellent agreement without adjustable parameters. Very similar rate coefficients are obtained for two different isotopes, which is linked to several quantum scattering resonances a...
Second-order Born calculation of laser-assisted single ionization of helium by electrons
NASA Astrophysics Data System (ADS)
Makhoute, Abdelkader; Ajana, Imane; Khalil, Driss; Chaddou, Souhaila
2015-06-01
The Born approximation has been extended to second-order Born amplitude in order to describe the laser-assisted single ionization of helium atom by impact of electrons. In this study, we have used a Sturmian basis expansion to perform detailed calculations of the scattering amplitudes. We discuss the influence of varying the incident energy on the angular distribution of the ejected electron. From analysis of the results, we find that second-order calculation is significantly different from the first-order calculation at low incoming energies. It means that the process of the laser-assisted single ionization of helium by slow incident electron requires a double interaction of this electron with the target.
Aidan Kelleher
2010-10-01
Knowledge of the electric and magnetic elastic form factors of the nucleon is essential for an understanding of nucleon structure. Of the form factors, the electric form factor of the neutron has been measured over the smallest range in Q{sup 2} and with the lowest precision. Jefferson Lab experiment 02-013 used a novel new polarized {sup 3}He target to nearly double the range of momentum transfer in which the neutron form factor has been studied and to measure it with much higher precision. Polarized electrons were scattered off this target, and both the scattered electron and neutron were detected. G{sup n}{sub E} was measured to be 0.0242 ± 0.0020(stat) ± 0.0061(sys) and 0.0247 ± 0.0029(stat) ± 0.0031(sys) at Q{sup 2} = 1.7 and 2.5 GeV{sup 2}, respectively.
Elastic scattering and rotational excitation of nitrogen molecules by sodium atoms
NASA Astrophysics Data System (ADS)
Loreau, Jérôme; Zhang, Peng; Dalgarno, Alexander
2011-11-01
A quantal study of the rotational excitation of nitrogen molecules by sodium atoms is carried out. We present the two-dimensional potential energy surface of the NaN2 complex, with the N2 molecule treated as a rigid rotor. The interaction potential is computed using the spin unrestricted coupled-cluster method with single, double, and perturbative triple excitations (UCCSD(T)). The long-range part of the potential is constructed from the dynamic electric dipole polarizabilities of Na and N2. The total, differential, and momentum transfer cross sections for rotationally elastic and inelastic transitions are calculated using the close-coupling approach for energies between 5 cm-1 and 1500 cm-1. The collisional and momentum transfer rate coefficients are calculated for temperatures between 100 K and 300 K, corresponding to the conditions under which Na-N2 collisions occur in the mesosphere.
Elastic scattering and rotational excitation of nitrogen molecules by sodium atoms.
Loreau, Jérôme; Zhang, Peng; Dalgarno, Alexander
2011-11-01
A quantal study of the rotational excitation of nitrogen molecules by sodium atoms is carried out. We present the two-dimensional potential energy surface of the NaN(2) complex, with the N(2) molecule treated as a rigid rotor. The interaction potential is computed using the spin unrestricted coupled-cluster method with single, double, and perturbative triple excitations (UCCSD(T)). The long-range part of the potential is constructed from the dynamic electric dipole polarizabilities of Na and N(2). The total, differential, and momentum transfer cross sections for rotationally elastic and inelastic transitions are calculated using the close-coupling approach for energies between 5 cm(-1) and 1500 cm(-1). The collisional and momentum transfer rate coefficients are calculated for temperatures between 100 K and 300 K, corresponding to the conditions under which Na-N(2) collisions occur in the mesosphere. PMID:22070297
Fano Resonances observed in Helium Nanodroplets
LaForge, A C; Jabbari, G; Gokhberg, K; Kryzhevoi, N V; Krishnan, S R; Hess, M; O'Kee?e, P; Ciavardini, A; Prince, K C; Richter, R; Moshammer, R; Cederbaum, L S; Pfeifer, T; Stienkemeier, F; Mudrich, M
2015-01-01
Doubly-excited Rydberg states of helium (He) nanodroplets have been studied using synchrotron radiation. We observed Fano resonances related to the atomic N = 2,0 series as a function of droplet size. Although similar qualitatively to their atomic counterparts, the resonance lines are broader and exhibit a shift in energy which increases for the higher excited states. Furthermore, additional resonances are observed which are not seen in atomic systems. We discuss these features in terms of delocalized atomic states perturbed by the surrounding He atoms and compare to singly excited droplets.
NASA Technical Reports Server (NTRS)
Vidali, G.; Li, W.; Dowben, P. A.; Karimi, M.; Hutchings, C. W.; Lin, J.; Moses, C.; Ila, D.; Dalins, I.
1990-01-01
We used ABS, LEED and angle-resolved photo-electron spectroscopy (ARPES) to study bilayer films of Hg on Cu(001). In the surface temperature range of 180 to 330 K, the first Hg layer forms two ordered phases, a c(2x2) (with coverage-0.5 of Cu(001)) and a high density (partially commensurate) c(4x4) (coverage-0.62). ARPES data show that there is little or no dispersion of the 5d band of Hg. ABS data show that this layer is not flat, with in-registry Hg atoms lying about 0.15 below the not-in-registry Hg atoms. From ABS we find that the second layer forms a completely registered c(4x4) phase. From ARPES we obtain that the second layer has an electronic structure, particularly the 5d levels, characteristic of bulk mercury. Preliminary results of calculations of the structure of the bilayer are given.
Helium P-State Energies and Quantum Defect Analysis
NASA Astrophysics Data System (ADS)
Valdez, Travis; Peck, Ryan; Drake, Gordon W. F.
2015-05-01
Quantum defects provide a simple and accurate method of extending known atomic energies for low principal quantum number n to higher n up to the series limit, and including the scattering phase shift beyond. We will present new calculations of improved accuracy for the 1 snp1 P and 3 P states of helium up to n = 12 , based on variational calculations in Hylleraas coordinates. The results will be used to determine accurate values for the coefficients in the quantum defect expansion, ? =?0 +?2 /n*2 +?4 /n*4 + ... , where n* = n - ? . We will also test the usual assumption that only the even powers of 1 /n* need be included. In addition, we will study the effectiveness of a unitary transformation in reducing the numerical linear dependence of the basis set for large basis sets. Research supported by the Natural Sciences and Engineering Research Council of Canada.
Variational Method for Two-Electron Atoms
ERIC Educational Resources Information Center
Srivastava, M. K.; Bhaduri, R. K.
1977-01-01
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)
[Atomic beam studies of the interaction of hydrogen with transition metal surfaces
Not Available
1992-01-01
We have constructed two experimental facilities during the term of this grant. In the first three years we constructed a helium atom scattering (HAS) facility with both elastic (EHAS) and inelastic (IHAS) scattering measurement capabilities to investigate the structural and dynamical aspects of solid surfaces and thin films. A pioneering surface metastable atom magnetic diffraction (SMAMD) facility was constructed and developed over the past four years, which makes possible the investigation of long-range electron spin-ordering on the surfaces of insulating magnetic crystals. The following were studied: H overlayers and Ag, Cu on Pd(111), reconstructed Au(111), and NiO(100).
Equation of state of metallic helium
Shvets, V. T.
2013-01-15
The effective ion-ion interaction, free energy, pressure, and electric resistance of metallic liquid helium have been calculated in wide density and temperature ranges using perturbation theory in the electron-ion interaction potential. In the case of conduction electrons, the exchange interaction has been taken into account in the random-phase approximation and correlations have been taken into account in the local-field approximation. The solid-sphere model has been used for the nuclear subsystem. The diameter of these spheres is the only parameter of this theory. The diameter and density of the system at which the transition of helium from the singly ionized to doubly ionized state occurs have been estimated by analyzing the pair effective interaction between helium atoms. The case of doubly ionized helium atoms has been considered. Terms up to the third order of perturbation theory have been taken into account in the numerical calculations. The contribution of the third-order term is significant in all cases. The electric resistance and its temperature dependence for metallic helium are characteristic of simple divalent metals in the liquid state. The thermodynamic parameters-temperature and pressure densities-are within the ranges characteristic of the central regions of giant planets. This makes it possible to assume the existence of helium in the metallic state within the solar system.
Formation of hydrogen atom in 2s state in proton-sodium inelastic scattering
NASA Astrophysics Data System (ADS)
Sabbah, A. Elkilany
2015-03-01
The inelastic collision of protons with sodium atoms are treated for the first time within the framework of the coupled-static and frozen core approximations. The method is used for calculating partial and total cross-sections with the assumption that only two channels (elastic and hydrogen formation in 2s state) are open. In each case, the calculations are carried out for seven values of the total angular momentum ?(0 ? ? ? 6). The target is described using the Clementi Roetti wave functions within the framework of the one valence electron model. We use Lipmann-Swinger equation to solve the derived equations of the problem, then apply an iterative numerical method to obtain the code of computer to calculate iterative partial cross-sections. This can be done through calculating the reactance matrix at different values of considered energies to obtain the transition matrix that gives partial and total cross sections. The present results for total hydrogen (2s state) formation cross sections are in agreement with results of other available ones in wide range of incident energy.
NASA Technical Reports Server (NTRS)
Cook, Joseph
1996-01-01
Proposed system recovers and stores helium gas for reuse. Maintains helium at 99.99-percent purity, preventing water vapor from atmosphere or lubricating oil from pumps from contaminating gas. System takes in gas at nearly constant low back pressure near atmospheric pressure; introduces little or no back pressure into source of helium. Concept also extended to recycling of other gases.
Friedman, Irving; Denton, E.H.
1976-01-01
A portable helium sniffer has been developed for field use. The instrument is mounted in a four-wheel-drive pickup truck and can detect 50 parts per billion of helium in soil gas. The usefulness of helium sniffing in soil is being investigated as a prospecting tool in gas, oil, uranium, and geothermal prospecting as well as in earthquake prediction.
NASA Astrophysics Data System (ADS)
Miller, Michael Allen
1995-01-01
This dissertation presents the results of a study of the two-body and three-body breakup of polarized ^3{rm He} induced by quasi -elastic scattering of polarized protons. The analyzing powers, A_{n0} and A _{0n}, and the spin correlation parameter, A_{nn}, were measured for the quasi-elastic scattering reactions ^3vec{rm He}(vec{ rm p}, 2p), ^3vec {rm He}(vec{rm p}, pd) and ^3vec{rm He}(vec{rm p}, 2pd) at 197.3 MeV. The measurements were carried out using an internal metastability exchange optically pumped polarized ^3{rm He} target and the polarized proton beam of the Cooler storage ring at the Indiana University Cyclotron Facility. These were the first measurements made with an internal polarized target and a circulating polarized beam. The results are used to study the effective polarizations of protons and deuterons in ^3vec{rm He } and to explore the two-body and three-body breakup channels of the vec{rm p} + ^3vec{rm He} reaction.
Simple derivation of helium Lamb shift Krzysztof Pachucki z
Pachucki, Krzysztof
Simple derivation of helium Lamb shift Krzysztof Pachucki z Institute of Theoretical Physics, Warsaw University, Hoâ??za 69, 00Â681 Warsaw, Poland. Abstract. A simple derivation of Lamb shift a complete expression for the Lamb shift in the helium atom using the BetheÂ Salpeter formalism [3]. However
Helium on Venus - Implications for uranium and thorium
NASA Technical Reports Server (NTRS)
Prather, M. J.; Mcelroy, M. B.
1983-01-01
Helium is removed at an average rate of 10 to the 6th atoms per square centimeter per second from Venus's atmosphere by the solar wind following ionization above the plasmapause. The surface source of helium-4 on Venus is similar to that on earth, suggesting comparable abundances of crustal uranium and thorium.
Thermal desorption behavior of helium in aged titanium tritide films
NASA Astrophysics Data System (ADS)
Cheng, G. J.; Shi, L. Q.; Zhou, X. S.; Liang, J. H.; Wang, W. D.; Long, X. G.; Yang, B. F.; Peng, S. M.
2015-11-01
The desorption behavior of helium in TiT(1.5?1.8)-x3Hex film samples (x = 0.0022-0.22) was investigated by thermal desorption technique in vacuum condition in this paper. The thermal helium desorption spectrometry (THDS) of aging titanium tritide films prepared by electron beam evaporation revealed that, depending on the decayed 3He concentration in the samples, there are more than four states of helium existing in the films. The divided four zones in THDS based on helium states represent respectively: (1) the mobile single helium atoms with low activation energy in all aging samples resulted from the interstitial sites or dissociated from interstitial clusters, loops and dislocations, (2) helium bubbles inside the grain lattices, (3) helium bubbles in the grain boundaries and interconnected networks of dislocations in the helium concentration of 3Hegen/Ti > 0.0094, and (4) helium bubbles near or linked to the film surface by interconnected channel for later aging stage with 3Hegen/Ti > 0.18. The proportion of helium desorption in each zone was estimated, and dissociated energies of helium for different trapping states were given.
Differential cross-section for positronium formation in electron-atomic hydrogen collisions
NASA Technical Reports Server (NTRS)
Drachman, R. J.; Omidvar, K.; Mcguire, J. H.
1976-01-01
The L=0 and 1 partial wave amplitudes obtained by a two-state coupled static approximation with correlation with the L greater than or equal to 2 Born amplitudes were combined to obtain the differential cross section for positronium formation in electron-atomic hydrogen collisions. For positron energies of 0.64 and 0.75 ryd, minima at the scattering angles of 57 deg and 51 deg are found. Total cross sections for positronium formation for low and intermediate impact energies are given. Measurement of the differential cross section for the process positron + helium yields positronium + helium ion for the detection of possible minima is suggested.
NASA Astrophysics Data System (ADS)
Blanpied, Gary; Kumar, Sankaran; Dorroh, Dustin; Morgan, Craig; Blanpied, Isabelle; Sossong, Michael; McKenney, Shawn; Nelson, Beth
2015-06-01
Reported is a new method to apply cosmic-ray tomography in a manner that can detect and characterize not only dense assemblages of heavy nuclei (like Special Nuclear Materials, SNM) but also assemblages of medium- and light-atomic-mass materials (such as metal parts, conventional explosives, and organic materials). Characterization may enable discrimination between permitted contents in commerce and contraband (explosives, illegal drugs, and the like). Our Multi-Mode Passive Detection System (MMPDS) relies primarily on the muon component of cosmic rays to interrogate Volumes of Interest (VOI). Muons, highly energetic and massive, pass essentially un-scattered through materials of light atomic mass and are only weakly scattered by conventional metals used in industry. Substantial scattering and absorption only occur when muons encounter sufficient thicknesses of heavy elements characteristic of lead and SNM. Electrons are appreciably scattered by light elements and stopped by sufficient thicknesses of materials containing medium-atomic-mass elements (mostly metals). Data include simulations based upon GEANT and measurements in the HMT (Half Muon Tracker) detector in Poway, CA and a package scanner in both Poway and Socorro NM. A key aspect of the present work is development of a useful parameter, designated the "stopping power" of a sample. The low-density regime, comprising organic materials up to aluminum, is characterized using very little scattering but a strong variation in stopping power. The medium-to-high density regime shows a larger variation in scattering than in stopping power. The detection of emitted gamma rays is another useful signature of some materials.
Glaz, W.; Bancewicz, T.; Godet, J.-L.; Maroulis, G.; Haskopoulos, A.
2006-04-15
The collision-induced (CI) first hyperpolarizability tensor for the He-Ne pair composed of the lightest noble gas elements has been obtained on the grounds of an ab initio method as a function of the interatomic distance R. Collision-induced hyper-Rayleigh (CIHR) spectra scattered in mixtures of such atoms at temperatures of 95 and 295 K are computed in absolute units both quantum mechanically and classically for the frequency shifts up to 1000 cm{sup -1}. The spectral features of the CIHR profiles due to the vector b{sub 1} and septor b{sub 3} parts of the hyperpolarizability tensor are discussed. The quantum character of computed spectra, especially significant at lower temperatures, has been found out. The integrated intensities of the spectra have been evaluated and used as a criterion of the reliability of the computed profiles. The frequency-dependent depolarization ratio of the CIHR spectra was evaluated and discussed. The properties of the resulting HR profiles have been compared with the depolarized CI Rayleigh spectrum of the He-Ne pair.
Neutral Atom Microscopy: A New Surface Imaging Probe
NASA Astrophysics Data System (ADS)
Witham, Philip; Sanchez, Erik
2012-02-01
Recent advances have made microscopy using scanned neutral atom beams a practical reality. This technique is also called Atomic DeBroglie Microscopy, Neutral Beam Microscopy, and Scanning Helium Microscopy. Using thermal energy (under 70 meV) gas particles with neutral charge results in a probe beam that scatters from the first atomic layer of samples, with little chance of beam damage. The technique presented eliminates any need to focus the beam by using an aperture in close proximity to the sample, and has produced the first published images from gas scattering. Resolution has reached 0.6 ?m and much higher resolution is possible^1. Now that NAM is a reality, a great deal of research can be done to show what it is uniquely useful for, and to explain the image contrast mechanisms. Molecular beam experiments show a wide range of surface properties that may be possible to image with such a microscope, some that are difficult to see otherwise. For example, thermal helium has a strong scattering interaction with surface hydrogens. Imaging un-coated surfaces with high electric fields is possible and imaging through high magnetic fields has been demonstrated. Recent image results and the basic instrument design will be presented. ^1 A simple approach to neutral atom microscopy, Rev. Sci. Instrum. 82, 103705 (2011)
Development of a Polarized Helium-3 Ion Source for RHIC
NASA Astrophysics Data System (ADS)
Epstein, Charles; Milner, Richard; Maxwell, James; Alessi, James; Pikin, Alexander; Zelenski, Anatoli
2012-10-01
A polarized Helium-3 beam in RHIC would enable new, unique, high-energy QCD studies of neutron structure with existing polarized proton beams, as well as fundamental tests of the standard model in a future electron-ion collider eRHIC. An MIT-BNL collaboration is developing a polarized Helium-3 ion source for RHIC, and initial construction is underway. Helium-3 atoms will first be polarized through metastability exchange optical pumping and then transferred to the RHIC Electron Beam Ion Source (EBIS). Fully stripped Helium-3 ions would be extracted from EBIS and their polarization measured at low energies before acceleration in RHIC.
Helium vs. Proton Induced Displacement Damage in Electronic Materials
NASA Technical Reports Server (NTRS)
Ringo, Sawnese; Barghouty, A. F.
2010-01-01
In this project, the specific effects of displacement damage due to the passage of protons and helium nuclei on some typical electronic materials will be evaluated and contrasted. As the electronic material absorbs the energetic proton and helium momentum, degradation of performance occurs, eventually leading to overall failure. Helium nuclei traveling at the same speed as protons are expected to impart more to the material displacement damage; due to the larger mass, and thus momentum, of helium nuclei compared to protons. Damage due to displacement of atoms in their crystalline structure can change the physical properties and hence performance of the electronic materials.
Warm Breeze from the Starboard Bow: a New Population of Neutral Helium in the Heliosphere
NASA Astrophysics Data System (ADS)
Kubiak, M. A.; Bzowski, M.; Sokó?, J. M.; Swaczyna, P.; Grzedzielski, S.; Alexashov, D. B.; Izmodenov, V. V.; Möbius, E.; Leonard, T.; Fuselier, S. A.; Wurz, P.; McComas, D. J.
2014-08-01
We investigate the signals from neutral helium atoms observed in situ from Earth orbit in 2010 by the Interstellar Boundary Explorer (IBEX). The full helium signal observed during the 2010 observation season can be explained as a superposition of pristine neutral interstellar He gas and an additional population of neutral helium that we call the Warm Breeze. The Warm Breeze is approximately 2 times slower and 2.5 times warmer than the primary interstellar He population, and its density in front of the heliosphere is ~7% that of the neutral interstellar helium. The inflow direction of the Warm Breeze differs by ~19° from the inflow direction of interstellar gas. The Warm Breeze seems to be a long-term, perhaps permanent feature of the heliospheric environment. It has not been detected earlier because it is strongly ionized inside the heliosphere. This effect brings it below the threshold of detection via pickup ion and heliospheric backscatter glow observations, as well as by the direct sampling of GAS/Ulysses. We discuss possible sources for the Warm Breeze, including (1) the secondary population of interstellar helium, created via charge exchange and perhaps elastic scattering of neutral interstellar He atoms on interstellar He+ ions in the outer heliosheath, or (2) a gust of interstellar He originating from a hypothetic wave train in the Local Interstellar Cloud. A secondary population is expected from models, but the characteristics of the Warm Breeze do not fully conform to modeling results. If, nevertheless, this is the explanation, IBEX-Lo observations of the Warm Breeze provide key insights into the physical state of plasma in the outer heliosheath. If the second hypothesis is true, the source is likely to be located within a few thousand AU from the Sun, which is the propagation range of possible gusts of interstellar neutral helium with the Warm Breeze characteristics against dissipation via elastic scattering in the Local Cloud. Whatever the nature of the Warm Breeze, its discovery exposes a critical new feature of our heliospheric environment.
WARM BREEZE FROM THE STARBOARD BOW: A NEW POPULATION OF NEUTRAL HELIUM IN THE HELIOSPHERE
Kubiak, M. A.; Bzowski, M.; Sokó?, J. M.; Swaczyna, P.; Grzedzielski, S.; Alexashov, D. B.; Izmodenov, V. V.; Möbius, E.; Leonard, T.; Fuselier, S. A.; McComas, D. J.; Wurz, P.
2014-08-01
We investigate the signals from neutral helium atoms observed in situ from Earth orbit in 2010 by the Interstellar Boundary Explorer (IBEX). The full helium signal observed during the 2010 observation season can be explained as a superposition of pristine neutral interstellar He gas and an additional population of neutral helium that we call the Warm Breeze. The Warm Breeze is approximately 2 times slower and 2.5 times warmer than the primary interstellar He population, and its density in front of the heliosphere is ?7% that of the neutral interstellar helium. The inflow direction of the Warm Breeze differs by ?19° from the inflow direction of interstellar gas. The Warm Breeze seems to be a long-term, perhaps permanent feature of the heliospheric environment. It has not been detected earlier because it is strongly ionized inside the heliosphere. This effect brings it below the threshold of detection via pickup ion and heliospheric backscatter glow observations, as well as by the direct sampling of GAS/Ulysses. We discuss possible sources for the Warm Breeze, including (1) the secondary population of interstellar helium, created via charge exchange and perhaps elastic scattering of neutral interstellar He atoms on interstellar He{sup +} ions in the outer heliosheath, or (2) a gust of interstellar He originating from a hypothetic wave train in the Local Interstellar Cloud. A secondary population is expected from models, but the characteristics of the Warm Breeze do not fully conform to modeling results. If, nevertheless, this is the explanation, IBEX-Lo observations of the Warm Breeze provide key insights into the physical state of plasma in the outer heliosheath. If the second hypothesis is true, the source is likely to be located within a few thousand AU from the Sun, which is the propagation range of possible gusts of interstellar neutral helium with the Warm Breeze characteristics against dissipation via elastic scattering in the Local Cloud. Whatever the nature of the Warm Breeze, its discovery exposes a critical new feature of our heliospheric environment.
Damping of quantum interference of electrons on helium
NASA Astrophysics Data System (ADS)
Herman, D.; Karakurt, I.; Mathur, H.; Dahm, A. J.
2003-07-01
The damping of weak localization of electrons on helium is investigated. From previously measured magnetoresistivity line shapes, we are able to separately extract the damping due to electron-electron interaction and helium vapor-atom motion. We verify the theoretical prediction that vapor-atom motion reduces the interference contribution of paths as a squeezed exponential of their duration, rather than as a simple exponential.
NASA Astrophysics Data System (ADS)
Dunne, James Andrew
1995-01-01
Polarized electrons of energies 19.42, 22.67, and 25.5 GeV were scattered off a polarized ^3 He target at SLAC's End Station A to measure the spin asymmetry of the neutron. From this asymmetry, the spin dependent structure function g_1^ {rm n}(x) was determined over a range in x from 0.03 to 0.6 with an average Q^2 of 2 (GeV/C)^2. The value of the integral of g_1^{rm n} over x is intlimits _sp{0}{1}g_1^{ rm n}(x)dx = -0.036 +/- 0.009. The results were interpreted in the framework of the Quark Parton Model (QPM) and used to test the Ellis-Jaffe and Bjorken sum rules. The value of the integral is 2.6 standard deviations from the Ellis -Jaffe prediction while the Bjorken sum rule was found to be in agreement with this data and proton data from SMC and E-143.
Meinhold, Lars; Clement, David; Tehei, M; Daniel, R. M.; Finney, J.L.; Smith, Jeremy C
2008-11-01
The temperature dependence of the dynamics of mesophilic and thermophilic dihydrofolate reductase is examined using elastic incoherent neutron scattering. It is demonstrated that the distribution of atomic displacement amplitudes can be derived from the elastic scattering data by assuming a (Weibull) functional form that resembles distributions seen in molecular dynamics simulations. The thermophilic enzyme has a significantly broader distribution than its mesophilic counterpart. Furthermore, although the rate of increase with temperature of the atomic mean-square displacements extracted from the dynamic structure factor is found to be comparable for both enzymes, the amplitudes are found to be slightly larger for the thermophilic enzyme. Therefore, these results imply that the thermophilic enzyme is the more flexible of the two.
NASA Astrophysics Data System (ADS)
Hosur, Savita B.; Naik, L. R.; Badiger, N. M.
2013-05-01
The real part ( f') of the anomalous scattering factors for the targets of atomic number ranging from Z = 64 to 73 (Gd, Dy, Yb, Hf and Ta) are determined using low-energy external bremsstrahlung (EB) radiations. In this method, the EB photons are produced by beta particles from a weak beta source of 90Sr - 90Y in a nickel foil. The emitted EB photons are incident on the elemental targets of our study and the transmitted spectrum of the emerging photons from the target is measured using an ORTEC-made High-Purity Germanium (HPGe) detector coupled to an 8 K multichannel analyzer. The transmitted spectra show a sharp decrease in intensity at the K shell binding energies of the target atoms. The regions around the decreased portion have been used to determine the real part of the anomalous scattering factors. The experimentally measured values are found to be in good agreement with the available theoretical values.
Detailed and simplified nonequilibrium helium ionization in the solar atmosphere
Golding, Thomas Peter; Carlsson, Mats; Leenaarts, Jorrit E-mail: mats.carlsson@astro.uio.no
2014-03-20
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.
Ray, Hasi
2015-01-01
The static-exchange model (SEM) and the modified static-exchange model (MSEM) recently introduced by Ray [1] is applied to study the elastic collision between two hydrogen-like atoms when both are in ground states considering the system as a four-body Coulomb problem in the center of mass frame, in which all the Coulomb interaction terms in direct and exchange channels are treated exactly. The SEM includes the non-adiabatic short-range effect due to electron-exchange. The MSEM added in it, the long-range effect due to induced dynamic dipole polarizabilities between the atoms e.g. the Van der Waals interaction. Applying the SEM code in different H-like two-atomic systems, a reduced mass dependence on scattering length is observed. Again applying the MSEM code on H(1s)-H(1s) elastic scattering and varying the minimum values of interatomic distance, the dependence of scattering length on the effective interatomic potential consistent with the existing physics are observed. Both these basic findings in low and co...
Helium diffusion in uranium and plutonium oxides
NASA Astrophysics Data System (ADS)
Ronchi, C.; Hiernaut, J. P.
2004-02-01
Samples of UO 2, (U,Pu)O 2 and PuO 2 containing up to several 100 at. ppm helium were submitted to thermal annealing in a Knudsen-cell provided with a mass spectrometer. Gas release was measured on line with a great accuracy. In the examined materials helium was created by ?-decay of plutonium or laboratory infused at high temperature and high pressure. The selected samples exhibited different types of lattice damage, including reactor burn-up and high ?-radiation doses. Analysis of helium release as a function of temperature enabled the elementary diffusion processes to be investigated and the atomic diffusion coefficient to be deduced for a defined state of helium-in-solid. The helium diffusion coefficient has the expression: D=8×10 -7exp(-46 kcal mol -1/RT) m2 s-1, however, the enthalpy of diffusion increases to 70 kcal mol -1 in high burn-up fuel where helium is apparently stabilised in uranium/oxygen vacancy clusters.
Minerals Yearbook 1989: Helium
Leachman, W.D.
1989-01-01
Grade-A helium (99.995% or better) sales volume in the United States by private industry and the Bureau of Mines was 2,083 million cubic feet (MMcf) in 1989. Grade-A helium exports by private producers were 796 MMcf, for total sales of 2,879 MMcf of U.S. helium. The price of Grade-A helium, f.o.b. plant, was about $37.50 per thousand cubic feet (Mcf) for both the Bureau and private industry. The Bureau price for bulk liquid helium was $45.00 per Mcf with additional costs for container services and rent. The liquid helium price for private industry was also about $45.00 per Mcf with some producers posting surcharges to the price.
Cargnoni, Fausto; Ponti, Alessandro; Mella, Massimo
2013-11-14
The structure and energetics of exciplexes M*((2)L)He(n) (M = Cu, Ag and Au; L = P and D) in their vibrational ground state are studied by employing diffusion Monte Carlo (DMC). Interaction potentials between the excited coinage metals and He atoms are built using the Diatomics-in-Molecule (DIM) approach and ab initio potential curves for the M((2)L)-He dimers. Extending our previous work [Cargnoni et al., J. Phys. Chem. A, 2011, 115, 7141], we computed the dimer potential for Au in the (2)P and (2)D states, as well for Cu and Ag in the (2)D state, employing basis set superposition error-corrected Configuration Interaction calculations. We found that the (2)? potential correlating with the (2)P state of Au is substantially less binding than for Ag and Cu, a trend well supported by the M(+) ionic radiuses. Conversely, the interaction potentials between a (n - 1)d(9)ns(2 2)D metal and He present a very weak dependency on M itself or the projection of the angular momentum along the dimer axis. This is due to the screening exerted by the ns(2) electrons on the hole in the (n - 1)d shell. Including the spin-orbit coupling perturbatively in the DIM energy matrix has a major effect on the lowest potential energy surface of the (2)P manifold, the one for Cu allowing the formation of a "belt" of five He atoms while the one for Au being completely repulsive. Conversely, spin-orbit coupling has only a weak effect on the (2)D manifold due to the nearly degenerate nature of the diatomic potentials. Structural and energetic results from DMC have been used to support experimental indications for the formation of metastable exciplexes or the opening of non-radiative depopulation channels in bulk and cold gaseous He. PMID:24072257
Cargnoni, Fausto; Mella, Massimo
2011-06-30
We report a theoretical investigation of the solution properties of Cu and Ag atoms dissolved in He clusters. Employing our recent ab initio ground state pair potential for Me-He (Me = Ag, Cu), we simulated the species Me@He (n) (n = 2-100) by means of diffusion Monte Carlo (DMC) obtaining exact information on their energetics and the structural properties. In particular, we investigated the sensitivity of structural details on the well depth of the two interaction potentials. Whereas Ag structures the first He solvation layer similarly, to some extent, to a positive ion such as Na(+), Cu appears to require the onset of a second solvation shell for a similar dense structure to be formed despite an interaction well of 28.4 ?hartree. An additional signature of the different solution behavior between Ag and Cu appears also in the dependence of the energy required to evaporate a single He atom on the size of the MeHe(n) clusters. The absorption spectrum for the (2)P ? (2)S excitation of the metals was also simulated employing the semi-classical Lax approximation to further characterize Me@He(n) (n = 2-100) using novel accurate interaction potentials between He and the lowest (2)P state of Ag and Cu in conjunction with the Diatomic-in-Molecules approach. The results indicated that Ag exciplexes should not form via a direct vertical excitation into an attractive region of the excited manifolds and that there is an interesting dependence of the shape of the Cu excitation bands on the local structure of the first solvation shell. PMID:21425774
NASA Astrophysics Data System (ADS)
Prasai, Binay; Wilson, A. R.; Wiley, B. J.; Ren, Y.; Petkov, Valeri
2015-10-01
The extent to which current theoretical modeling alone can reveal real-world metallic nanoparticles (NPs) at the atomic level was scrutinized and demonstrated to be insufficient and how it can be improved by using a pragmatic approach involving straightforward experiments is shown. In particular, 4 to 6 nm in size silica supported Au100-xPdx (x = 30, 46 and 58) explored for catalytic applications is characterized structurally by total scattering experiments including high-energy synchrotron X-ray diffraction (XRD) coupled to atomic pair distribution function (PDF) analysis. Atomic-level models for the NPs are built by molecular dynamics simulations based on the archetypal for current theoretical modeling Sutton-Chen (SC) method. Models are matched against independent experimental data and are demonstrated to be inaccurate unless their theoretical foundation, i.e. the SC method, is supplemented with basic yet crucial information on the length and strength of metal-to-metal bonds and, when necessary, structural disorder in the actual NPs studied. An atomic PDF-based approach for accessing such information and implementing it in theoretical modeling is put forward. For completeness, the approach is concisely demonstrated on 15 nm in size water-dispersed Au particles explored for bio-medical applications and 16 nm in size hexane-dispersed Fe48Pd52 particles explored for magnetic applications as well. It is argued that when ``tuned up'' against experiments relevant to metals and alloys confined to nanoscale dimensions, such as total scattering coupled to atomic PDF analysis, rather than by mere intuition and/or against data for the respective solids, atomic-level theoretical modeling can provide a sound understanding of the synthesis-structure-property relationships in real-world metallic NPs. Ultimately this can help advance nanoscience and technology a step closer to producing metallic NPs by rational design.The extent to which current theoretical modeling alone can reveal real-world metallic nanoparticles (NPs) at the atomic level was scrutinized and demonstrated to be insufficient and how it can be improved by using a pragmatic approach involving straightforward experiments is shown. In particular, 4 to 6 nm in size silica supported Au100-xPdx (x = 30, 46 and 58) explored for catalytic applications is characterized structurally by total scattering experiments including high-energy synchrotron X-ray diffraction (XRD) coupled to atomic pair distribution function (PDF) analysis. Atomic-level models for the NPs are built by molecular dynamics simulations based on the archetypal for current theoretical modeling Sutton-Chen (SC) method. Models are matched against independent experimental data and are demonstrated to be inaccurate unless their theoretical foundation, i.e. the SC method, is supplemented with basic yet crucial information on the length and strength of metal-to-metal bonds and, when necessary, structural disorder in the actual NPs studied. An atomic PDF-based approach for accessing such information and implementing it in theoretical modeling is put forward. For completeness, the approach is concisely demonstrated on 15 nm in size water-dispersed Au particles explored for bio-medical applications and 16 nm in size hexane-dispersed Fe48Pd52 particles explored for magnetic applications as well. It is argued that when ``tuned up'' against experiments relevant to metals and alloys confined to nanoscale dimensions, such as total scattering coupled to atomic PDF analysis, rather than by mere intuition and/or against data for the respective solids, atomic-level theoretical modeling can provide a sound understanding of the synthesis-structure-property relationships in real-world metallic NPs. Ultimately this can help advance nanoscience and technology a step closer to producing metallic NPs by rational design. Electronic supplementary information (ESI) available: XRD patterns, TEM and 3D structure modelling methodology. See DOI: 10.1039/c5nr04678e
Comparison of classical and quantal calculations of helium three-body recombination
NASA Astrophysics Data System (ADS)
Pérez-Ríos, Jesús; Ragole, Steve; Wang, Jia; Greene, Chris H.
2014-01-01
A general method to study classical scattering in n-dimension is developed. Through classical trajectory calculations, the three-body recombination is computed as a function of the collision energy for helium atoms, as an example. Quantum calculations are also performed for the J? = 0+ symmetry of the three-body recombination rate in order to compare with the classical results, yielding good agreement for E ? 1 K. The classical threshold law is derived and numerically confirmed for the Newtonian three-body recombination rate. Finally, a relationship is found between the quantum and classical three-body hard hypersphere elastic cross sections which is analogous to the well-known shadow scattering in two-body collisions.
Comparison of classical and quantal calculations of helium three-body recombination
Pérez-Ríos, Jesús Greene, Chris H.; Ragole, Steve; Wang, Jia
2014-01-28
A general method to study classical scattering in n-dimension is developed. Through classical trajectory calculations, the three-body recombination is computed as a function of the collision energy for helium atoms, as an example. Quantum calculations are also performed for the J{sup ?} = 0{sup +} symmetry of the three-body recombination rate in order to compare with the classical results, yielding good agreement for E ? 1 K. The classical threshold law is derived and numerically confirmed for the Newtonian three-body recombination rate. Finally, a relationship is found between the quantum and classical three-body hard hypersphere elastic cross sections which is analogous to the well-known shadow scattering in two-body collisions.
Cryogenic liquid-jet breakup in two-fluid atomizers
NASA Technical Reports Server (NTRS)
Ingebo, Robert D.
1991-01-01
A two-fluid atomizer was used to study the breakup of liquid-nitrogen jets in nitrogen, argon, and helium atomizing gas flows. A scattered-light scanner particle sizing instrument previously developed at NASA Lewis Research Center was further developed and used to determine characteristic drop diameters for the cryogenic sprays. In the breakup regime of aerodynamic-stripping, i.e., sonic-velocity conditions, the following correlation of the reciprocal Sauter mean diameter, D(sub 32)exp -1, with the atomizing-gas flowrate, W(g), was obtained: D(sub 32)exp -1 = k(sub c)(W(g)exp 1.33), where k(sub c) is a proportionality constant evaluated for each atomizing gas. Values of k(sub c) = 120, 220, and 1100 were obtained for argon, nitrogen, and helium gasflows, respectively. The reciprocal Sauter mean diameter and gas flowrate have the units of 1/cm and g/sec, respectively. In the regime of capillary-wave breakup, or subsonic conditions, it was found that D(sub 32)exp -1 = k(g)(W(g)exp 0.75), where k = 270, 390, and 880 for argon, nitrogen, and helium gasflows, respectively.
Metal tritides helium emission
Beavis, L.C.
1980-02-01
Over the past several years, we have been measuring the release of helium from metal tritides (primarily erbium tritide). We find that qualitatively all tritides of interest to us behave the same. When they are first formed, the helium is released at a low rate that appears to be related to the amount of surface area which has access to the outside of the material (either film or bulk). For example, erbium tritide films initially release about 0.3% of the helium generated. Most tritide films emit helium at about this rate initially. At some later time, which depends upon the amount of helium generated, the parent occluding element and the degree of tritium saturation of the dihydride phase the helium emission changes to a new mode in which it is released at approximately the rate at which it is generated (for example, we measure this value to be approx. = .31 He/Er for ErT/sub 1/./sub 9/ films). If erbium ditritide is saturated beyond 1.9 T/Er, the critical helium/metal ratio decreases. For example, in bulk powders ErT/sub 2/./sub 15/ reaches critical release concentration at approx. = 0.03. Moderate elevation of temperature above room temperature has little impact on the helium release rate. It appears that the process may have approx. = 2 kcal/mol activation energy. The first helium formed is well bound. As the tritide ages, the helium is found in higher energy sites. Similar but less extensive measurements on scandium, titanium, and zirconium tritides are also described. Finally, the thermal desorption of erbium tritides of various ages from 50 days to 3154 days is discussed. Significant helium is desorbed along with the tritium in all but the youngest samples during thermodesorption.
Laser spectroscopic measurement of helium isotope ratios.
Wang, L.-B.; Mueller, P.; Holt, R. J.; Lu, Z.-T.; O'Connor, T. P.; Sano, Y.; Sturchio, N.; Univ. of Illinois; Univ. of Tokyo; Univ. of Illinois at Chicago
2003-06-13
A sensitive laser spectroscopic method has been applied to the quantitative determination of the isotope ratio of helium at the level of {sup 3}He/{sup 4}He = 10{sup -7}--10{sup -5}. The resonant absorption of 1083 nm laser light by the metastable {sup 3}He atoms in a discharge cell was measured with the frequency modulation saturation spectroscopy technique while the abundance of {sup 4}He was measured by a direct absorption technique. The results on three different samples extracted from the atmosphere and commercial helium gas were in good agreement with values obtained with mass spectrometry. The achieved 3{sigma} detection limit of {sup 3}He in helium is 4 x 10{sup -9}. This demonstration required a 200 {mu}L STP sample of He. The sensitivity can be further improved, and the required sample size reduced, by several orders of magnitude with the addition of cavity enhanced spectroscopy.
Electrical conductivity and thermopower of metallic helium
NASA Astrophysics Data System (ADS)
Shvets, V. T.; Kozitskii, S. V.
2013-04-01
The pair effective interionic interaction, electrical resistance, and thermopower of liquid metallic helium have been calculated over wide temperature and density ranges using the perturbation theory for the potential of electron-ion interaction. For conduction electrons, the random-phase approximation has been used taking into account the exchange interaction and correlations in the local-field approximation. The nuclear subsystem has been described by the hard-sphere model. The sphere diameter is the only parameter of the theory. The diameter and the system density at which helium is transformed from the singly ionized to doubly ionized state have been estimated based on an analysis of the pair effective interaction between helium nuclei. The case of doubly ionized helium atoms has been considered. The numerical calculations have been performed taking into account the perturbation theory in terms up to the third order. In all cases, the role of the third-order correction is significant. In the case of metallic helium, the values of the electrical resistance and its temperature dependence are characteristic of divalent simple liquid metals, as well as the dependences of the thermopower on the density and temperature.
Elastic scattering of tritons by helium-4
Jarmie, N.; Correll, F.D.; Brown, R.E.; Hardekopf, R.A.; Ohlsen, G.G.
1980-11-01
Angular distributions of the differential cross section and of the analyzing power have been measured for the /sup 4/He(t,t)/sup 4/He reaction at 19 energies from 6 to 17 MeV. The relative errors of the cross section and analyzing power range from 2.0 to 2.5% and 0.005 to 0.01, respectively, and the scale errors are 1% in each case. Complete data tables are presented, and the experimental procedure is described for the present measurements and for earlier cross-section measurements. Graphs of the data are presented, as well as the curves resulting from an energy-independent phase-shift analysis.
Not Available
1992-12-31
We have constructed two experimental facilities during the term of this grant. In the first three years we constructed a helium atom scattering (HAS) facility with both elastic (EHAS) and inelastic (IHAS) scattering measurement capabilities to investigate the structural and dynamical aspects of solid surfaces and thin films. A pioneering surface metastable atom magnetic diffraction (SMAMD) facility was constructed and developed over the past four years, which makes possible the investigation of long-range electron spin-ordering on the surfaces of insulating magnetic crystals. The following were studied: H overlayers and Ag, Cu on Pd(111), reconstructed Au(111), and NiO(100).
Correlation of Excess Enthalpy and HELIUM-4 Production:. a Review
NASA Astrophysics Data System (ADS)
Miles, M. H.
2005-12-01
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.
Solvation of Na+, K+, and Their Dimers in Helium
An der Lan, Lukas; Bartl, Peter; Leidlmair, Christian; Jochum, Roland; Denifl, Stephan; Echt, Olof; Scheier, Paul
2012-01-01
Helium atoms bind strongly to alkali cations which, when embedded in liquid helium, form so-called snowballs. Calculations suggest that helium atoms in the first solvation layer of these snowballs form rigid structures and that their number (n) is well defined, especially for the lighter alkalis. However, experiments have so far failed to accurately determine values of n. We present high-resolution mass spectra of Na+Hen, K+Hen, Na2+Hen and K2+Hen, formed by electron ionization of doped helium droplets; the data allow for a critical comparison with several theoretical studies. For sodium and potassium monomers the spectra indicate that the value of n is slightly smaller than calculated. Na2+Hen displays two distinct anomalies at n=2 and n=6, in agreement with theory; dissociation energies derived from experiment closely track theoretical values. K2+Hen distributions are fairly featureless, which also agrees with predictions. PMID:22374575
ERIC Educational Resources Information Center
Helseth, Lars Egil
2014-01-01
I describe a simple and fascinating experiment wherein helium leaks out of a rubber balloon, thereby causing it to descend. An estimate of the volumetric leakage rate is made by measuring its rate of descent.
Noncavitating Pump For Liquid Helium
NASA Technical Reports Server (NTRS)
Hasenbein, Robert; Izenson, Michael; Swift, Walter; Sixsmith, Herbert
1996-01-01
Immersion pump features high efficiency in cryogenic service. Simple and reliable centrifugal pump transfers liquid helium with mass-transfer efficiency of 99 percent. Liquid helium drawn into pump by helical inducer, which pressurizes helium slightly to prevent cavitation when liquid enters impeller. Impeller then pressurizes liquid. Purpose of pump to transfer liquid helium from supply to receiver vessel, or to provide liquid helium flow for testing and experimentation.
Modeling Two-Charge State Helium Plasmas
NASA Astrophysics Data System (ADS)
Emmert, Gilbert; Santarius, John
2012-10-01
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)
Possible stimulation of nuclear alpha-decay by superfluid helium
A. L. Barabanov
2009-09-03
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.
Optimized Helium-Brayton Power Conversion for Fusion Energy Systems
Zhao Haihua; Fukuda, Grant; Abbott, Ryan P.; Peterson, Per F.
2005-04-15
This paper presents an overview and a few point designs for multiple-reheat helium Brayton cycle power conversion systems using molten salts (or liquid metals or direct helium cooling). All designs are derived from the General Atomics GT-MHR power conversion unit (PCU). The important role of compact, offset fin heat exchangers for heat transfer to the power cycle helium, and the potential for these to be fabricated from carbon-coated composite materials that would have lower potential for fouling, are discussed. Specific links are made to the ITER TBM and laser IFE blanket design, and to Z-Pinch/HIF thick-liquid IFE.
The helium fine-structure controversy
Ingvar Lindgren
2008-10-05
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.
NASA Astrophysics Data System (ADS)
Takeuchi, Wataru
2016-01-01
The rainbow angles corresponding to pronounced peaks in the angular distributions of scattered projectiles with small angle, attributed to rainbow scattering (RS), under axial surface channeling conditions are strongly dependent on the interatomic potentials between projectiles and target atoms. The dependence of rainbow angles on normal energy of projectile energy to the target surface that has been experimentally obtained by Schüller and Winter (SW) (2007) for RS of He, Ne and Ar atoms from a Ag(1 1 1) surface with projectile energies of 3-60 keV was evaluated by the three-dimensional computer simulations using the ACOCT code based on the binary collision approximation with interatomic pair potentials. Consequently, the ACOCT results employing the Moliere pair potential with screening length correction close to adjustable one of O'Connor and Biersack (OB) formula are almost in agreement with the experimental ones, being self-consistent with the SW's ones analyzed by computer simulations of classical trajectory calculations as RS from corrugated equipotential planes based on continuum potentials including the Moliere pair potential with screening length correction of the OB formula.
Mass Superflux in Solid Helium: What Limits the Flux?
NASA Astrophysics Data System (ADS)
Hallock, Robert; Vekhov, Yegor
2015-03-01
The thermo-mechanical effect in superfluid helium is used to create a chemical potential difference, ?? , across a superfluid-filled vertical Vycor rod. This rod separates a bulk liquid superfluid helium reservoir, R 1 , on the top of the Vycor at T 1 = 1 . 46 - 1 . 51 K and solid hcp 4He on the bottom at TC = 0 . 1 - 0 . 8 K. Two in situ capacitance pressure gauges, C 1 and C 2 , are placed at the ends of the horizontal cylindrical solid helium sample (1.84 cm3, 25 . 9 - 26 . 4 bar) and located at different distances from the position of the Vycor rod in the solid helium, 10 and 31 mm, respectively. A T 1 decrease/increase changes ?? and leads to a solid helium pressure increase/decrease detected by both Cs. The rate of pressure change is slower at the further gauge, C 2 , than at the nearer one, C 1 . This behavior is interpreted as due to the presence of a mass flux bottleneck inside the solid helium sample. We believe, e.g. in the case of a T 1 decrease, that helium atoms emerge from the Vycor rod, perhaps migrate along the superfluid core of edge dislocations in solid helium and adsorb on them. This is the so-called ``syringe-effect'' or superclimb of edge dislocations. The dependence on temperature will be discussed. Work supported by NSF DMR 12-05217.
Prasai, Binay; Ren, Yang; Shan, Shiyao; Zhao, Yinguang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian; Petkov, Valeri
2015-05-01
An approach to determining the 3D atomic structure of metallic nanoparticles (NPs) in fine detail and using the unique knowledge obtained for rationalizing their synthesis and properties targeted for optimization is described and exemplified on Pt-Ru alloy NPs of importance to the development of devices for clean energy conversion such as fuel cells. In particular, PtxRu100-x alloy NPs, where x = 31, 49 and 75, are synthesized by wet chemistry and activated catalytically by a post-synthesis treatment involving heating under controlled N2-H2 atmosphere. So-activated NPs are evaluated as catalysts for gas-phase CO oxidation and ethanol electro-oxidation reactions taking place in fuel cells. Both as-synthesized and activated NPs are characterized structurally by total scattering experiments involving high-energy synchrotron X-ray diffraction coupled to atomic pair distribution functions (PDFs) analysis. 3D structure models both for as-synthesized and activated NPs are built by molecular dynamics simulations based on the archetypal for current theoretical modelling Sutton-Chen method. Models are refined against the experimental PDF data by reverse Monte Carlo simulations and analysed in terms of prime structural characteristics such as metal-to-metal bond lengths, bond angles and first coordination numbers for Pt and Ru atoms. Analysis indicates that, though of a similar type, the atomic structure of as-synthesized and respective activated NPs differ in several details of importance to NP catalytic properties. Structural characteristics of activated NPs and data for their catalytic activity are compared side by side and strong evidence found that electronic effects, indicated by significant changes in Pt-Pt and Ru-Ru metal bond lengths at NP surface, and practically unrecognized so far atomic ensemble effects, indicated by distinct stacking of atomic layers near NP surface and prevalence of particular configurations of Pt and Ru atoms in these layers, contribute to the observed enhancement of the catalytic activity of PtxRu100-x alloy NPs at x ? 50. Implications of so-established relationships between the atomic structure and catalytic activity of Pt-Ru alloy NPs on efforts aimed at improving further the latter by tuning-up the former are discussed and the usefulness of detailed NP structure studies to advancing science and technology of metallic NPs - exemplified. PMID:25874741
NASA Astrophysics Data System (ADS)
Cherniak, D. J.; Watson, E. B.
2011-12-01
Diffusion of helium has been characterized in natural Fe-bearing olivine (~Fo90) and synthetic forsterite. Polished, oriented slabs of olivine were implanted with 3He, at 100 keV at a dose of 5x1015/cm2 or at 3.0 MeV at a dose of 1x1016/cm2. A set of experiments on the implanted olivine were run in 1-atm furnaces. In addition to the one-atm experiments, experiments on implanted samples were also run at higher pressures (2.6 and 2.7 GPa) to assess the potential effects of pressure on He diffusion and the applicability of the measured diffusivities in describing He transport in the mantle. The high-pressure experiments were conducted in a piston-cylinder apparatus using an "ultra-soft" pressure cell, with the diffusion sample directly surrounded by AgCl. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. This direct profiling method permits us to evaluate anisotropy of diffusion, which cannot be easily assessed using bulk-release methods. For diffusion in forsterite parallel to c we obtain the following Arrhenius relation over the temperatures 250-950°C: D = 3.91x10-6exp(-159 ± 4 kJ mol-1/RT) m2/sec. The data define a single Arrhenius line spanning more than 7 orders of magnitude in D and 700°C in temperature. Diffusion parallel to a appears slightly slower, yielding an activation energy for diffusion of 135 kJ/mol and a pre-exponential factor of 3.73x10-8 m2/sec. Diffusion parallel to b is slower than diffusion parallel to a (by about two-thirds of a log unit); for this orientation an activation energy of 138 kJ/mol and a pre-exponential factor of 1.34x10-8 m2/sec are obtained. This anisotropy is broadly consistent with observations for diffusion of Ni and Fe-Mg in olivine. Diffusion in Fe-bearing olivine (transport parallel to b) agrees within uncertainty with findings for He diffusion in forsterite. The higher-pressure experiments yield diffusivities in agreement with those from the 1-atm experiments, indicating that the results reported here can be reasonably applied to modeling He transport in the upper mantle. The insensitivity of He diffusion to pressure over the investigated range of conditions suggests that compression of the mineral lattice is not sufficient to significantly influence migration of the relatively small helium atoms, which likely diffuse via crystal interstices. The He diffusivities in this work are generally consistent with results from the study of Futagami et al. (1993), who measured He diffusion in natural olivine by outgassing 4He implanted samples, and with the diffusivities measured by bulk-release of 4He and 3He by Shuster et al. (2003), but are about 2 orders of magnitude slower than the recent findings of Tolstikhin et al. (2010) and Blard et al. (2008) . An up-temperature extrapolation of our data also show reasonable agreement with the higher-temperature measurements of Hart (1984). Blard et al. (2008) GCA 72, 3788-3803; Futagami et al. (1993) GCA 57, 3177-3194; Hart (1984) EPSL 70, 297-302; Shuster et al.( 2003) EPSL 217, 19-32; Tolstikhin et al. (2010) GCA 74, 1436-1447
In situ controlled modification of the helium density in single helium-filled nanobubbles
David, M.-L. Pailloux, F.; Alix, K.; Mauchamp, V.; Pizzagalli, L.; Couillard, M.; Botton, G. A.
2014-03-28
We demonstrate that the helium density and corresponding pressure can be modified in single nano-scale bubbles embedded in semiconductors by using the electron beam of a scanning transmission electron microscope as a multifunctional probe: the measurement probe for imaging and chemical analysis and the irradiation source to modify concomitantly the pressure in a controllable way by fine tuning of the electron beam parameters. The control of the detrapping rate is achieved by varying the experimental conditions. The underlying physical mechanisms are discussed; our experimental observations suggest that the helium detrapping from bubbles could be interpreted in terms of direct ballistic collisions, leading to the ejection of the helium atoms from the bubble.
Precise tests of x-ray scattering theories in the Compton regime.
Dunford, R. W.; Gemmell, D. S.; Kanter, E. P.; Krassig, B.; Southworth, S. H.; Young, L.
1999-01-15
The authors report two experiments intended to test the accuracy of state-of-the-art theoretical predictions for x-ray scattering from low-Z atoms. The first one deals with the differential x-ray scattering cross sections in Ne and He from 11-22 keV and the Ne Compton-to-Rayleigh scattering ratio in this energy range. It was found that, in order to be consistent with the experimental results, an accurate description at low Z must include nonlocal exchange, electron correlation, and dynamic effects. The second experiment concerns the ratio of helium double-to-single ionization for Compton scattering in the 8-28 keV energy range where published experimental and theoretical results so far fail to give a consistent picture. The progress of the experiment and the data analysis is reported.
Seely, D.G.; Bross, S.W.; Gaus, A.D.; Edwards, J.W.; Schultz, D.R.; Gay, T.J.; Park, J.T.; Peacher, J.L. )
1992-02-01
Angular-differential cross sections for charge transfer with simultaneous emission of a photon in collisions of protons with helium atoms have been measured. The incident proton energies were 25, 50, and 100 keV and the center-of-mass scattering angles were between 0 and 2.0 mrad. In the experiment, hydrogen atoms that scattered through an angle {theta} were detected in coincidence with photons emitted perpendicular to the scattering plane with a wavelength between 1140 and 1400 A. Differential cross sections for capture into the 2{ital p} state of the hydrogen atom were determined from the variation in the coincidence signal with {theta}. The experimental results are compared with the results of a classical trajectory Monte Carlo (CTMC) simulation and with the results of a calculation for H(2{ital p}) capture using the Coulomb-Brinkman-Kramers (CBK) approximation. The agreement between the experimental results and the CTMC calculation is good at all three energies while the agreement between the shape of the data and the CBK calculation is good at 50 and 100 keV.
Band, Yehuda B.
in an optical lattice: Gap solitons Richard S. Tasgal,1 G. Menabde,1 and Y. B. Band1,2 1 Departments-dimensional optical lattice and a weak one-dimensional optical lattice in the third dimension. The stable solutions and negative and Feshbach effects wash out, turn off the optical lattice in phase with the atomic BEC, and turn
NASA Astrophysics Data System (ADS)
Smilgies, D.-M.; Toennies, J. P.
1988-10-01
Analytic expressions are derived to calculate the instrumental width of the phonon energy-loss peaks obtained in a helium atom inelastic scattering apparatus used in the measurement of surface phonon dispersion curves at single crystals. The formulas take into account all the kinematic effects arising from the velocity distribution of the incident beam, the angular resolution of the instrument, as well as the finite time resolution of the time-of-flight detection system. Implications for the optimal design parameters are discussed.
Laser-driven nanoplasmas in doped helium droplets: Local ignition and anisotropic expansion
Mikaberidze, Alexey; Rost, Jan M
2009-01-01
Doping a helium nanodroplet with a tiny xenon cluster of a few atoms only, sparks complete ionization of the droplet at laser intensities below the ionization threshold of helium atoms. As a result, the intrinsically inert and transparent droplet turns into a fast and strong absorber of infrared light. Microscopic calculations reveal a two-step mechanism to be responsible for the dramatic change: Avalanche-like ionization of the helium atoms on a femtosecond time scale, driven by field ionization due to the quickly charged xenon core is followed by resonant absorption enabled by an unusual cigar-shaped nanoplasma within the droplet.
Gayone, J.E.; Pregliasco, R.G.; Sanchez, E.A.; Grizzi, O.
1997-08-01
We have used ion-scattering spectrometry with time-of-flight analysis (TOF) to study the atomic structure of a GaAs(110) surface exposed to atomic hydrogen. The TOF spectra of ions plus neutrals acquired for 6 keV Ne{sup +} backscattering from both As and Ga top-layer atoms show a strong dependence on the projectile incidence direction and on the hydrogen exposure. The variations in the quasisingle backscattered intensity derived from the TOF spectra were analyzed with a code that calculates shadowing and focusing regions in a two-atom model. Measurements as a function of the hydrogen exposure indicate that the surface derelaxes approaching the ideal bulk termination. At the beginning of the adsorption the fraction of the surface that undergoes derelaxation increases very fast with exposure. At higher exposures, the rate of derelaxation becomes slower and the TOF spectra tend to a steady state. From Ne quasisingle backscattered intensities, measured as a function of the incident angle, we have determined that the spacing between the top As and Ga layers is reduced from ({Delta}Z=0.66{plus_minus}0.08) {Angstrom} for the clean surface to ({Delta}Z=0.0{plus_minus}0.08) {Angstrom} for intermediate exposures (2000 L H{sub 2}). At this exposure we have found a spacing between the first and second layers of (1.8{plus_minus}0.1) {Angstrom}. At higher exposures the results indicate a small counter-relaxation. {copyright} {ital 1997} {ital The American Physical Society}
$?^4$ Ry corrections to singlet states of helium
Krzysztof Pachucki
2006-07-07
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.
Radiative transfer in cylindrical threads with incident radiation VI. A hydrogen plus helium system
Gouttebroze, Pierre
2009-01-01
Spectral lines of helium are commonly observed on the Sun. These observations contain important informations about physical conditions and He/H abundance variations within solar outer structures. The modeling of chromospheric and coronal loop-like structures visible in hydrogen and helium lines requires the use of appropriate diagnostic tools based on NLTE radiative tranfer in cylindrical geometry. We use iterative numerical methods to solve the equations of NLTE radiative transfer and statistical equilibrium of atomic level populations. These equations are solved alternatively for the hydrogen and helium atoms, using cylindrical coordinates and prescribed solar incident radiation. Electron density is determined by the ionization equilibria of both atoms. Two-dimension effects are included. The mechanisms of formation of the principal helium lines are analyzed and the sources of emission inside the cylinder are located. The variations of spectral line intensities with temperature, pressure, and helium abundan...
Fluorine atom abstraction by Si(100). I. Experimental
NASA Astrophysics Data System (ADS)
Tate, M. R.; Gosalvez-Blanco, D.; Pullman, D. P.; Tsekouras, A. A.; Li, Y. L.; Yang, J. J.; Laughlin, K. B.; Eckman, S. C.; Bertino, M. F.; Ceyer, S. T.
1999-08-01
In the interaction of low energy F2 with Si(100) at 250 K, a dissociative chemisorption mechanism called atom abstraction is identified in which only one of the F atoms is adsorbed while the other F atom is scattered into the gas phase. The dynamics of atom abstraction are characterized via time-of-flight measurements of the scattered F atoms. The F atoms are translationally hyperthermal but only carry a small fraction (˜3%) of the tremendous exothermicity of the reaction. The angular distribution of F atoms is unusually broad for the product of an exothermic reaction. These results suggest an "attractive" interaction potential between F2 and the Si dangling bond with a transition state that is not constrained geometrically. These results are in disagreement with the results of theoretical investigations implying that the available potential energy surfaces are inadequate to describe the dynamics of this gas-surface interaction. In addition to single atom abstraction, two atom adsorption, a mechanism analogous to classic dissociative chemisorption in which both F atoms are adsorbed onto the surface, is also observed. The absolute probability of the three scattering channels (single atom abstraction, two atom adsorption, and unreactive scattering) for an incident F2 are determined as a function of F2 exposure. The fluorine coverage is determined by integrating the reaction probabilities over F2 exposure, and the reaction probabilities are recast as a function of fluorine coverage. Two atom adsorption is the dominant channel [P2=0.83±0.03(95%, N=9)] in the limit of zero coverage and decays monotonically to zero. Single atom abstraction is the minor channel (P1=0.13±0.03) at low coverage but increases to a maximum (P1=0.35±0.08) at about 0.5 monolayer (ML) coverage before decaying to zero. The reaction ceases at 0.94±0.11(95%, N=9) ML. Thermal desorption and helium diffraction confirm that the dangling bonds are the abstraction and adsorption sites. No Si lattice bonds are broken, in contrast to speculation by other investigators that the reaction exothermicity causes lattice disorder.
Chluba, Jens
2015-01-01
We present the first fast and detailed computation of the cosmological recombination radiation released during the hydrogen (redshift z ~ 1300) and helium (z ~ 2500 and z ~ 6000) recombination epochs, introducing the code CosmoSpec. Our computations include important radiative transfer effects, 500-shell bound-bound and free-bound emission for all three species, the effects of electron scattering and free-free absorption as well as interspecies (HeII --> HeI --> HI) photon feedback. The latter effect modifies the shape and amplitude of the recombination radiation and CosmoSpec improves significantly over previous treatments of it. Utilizing effective multilevel atom and conductance approaches, one calculation takes only ~ 15 seconds on a standard laptop as opposed to days for previous computations. This is an important step towards detailed forecasts and feasibility studies considering the detection of the cosmological recombination lines and what one may hope to learn from the ~ 6.1 photons emitted per hydro...
Cryogenic and Simulated Fuel Jet Breakup in Argon, Helium and Nitrogen Gas Flows
NASA Technical Reports Server (NTRS)
Ingebo, Robert D.
1995-01-01
Two-phase flow atomization of liquid nitrogen jets was experimentally investigated. They were co-axially injected into high-velocity gas flows of helium, nitrogen and argon, respectively, and atomized internally inside a two-fluid fuel nozzle. Cryogenic sprays with relatively high specific surface areas were produced, i.e., ratios of surface area to volume were fairly high. This was indicated by values of reciprocal Sauter mean diameters, RSMD's, as measured with a scattered- light scanning instrument developed at NASA Lewis Research Center. Correlating expressions were derived for the three atomizing gases over a gas temperature range of 111 to 422 K. Also, the correlation was extended to include waterjet breakup data that had been previously obtained in simulating fuel jet breakup in sonic velocity gas flow. The final correlating expression included a new dimensionless molecular-scale acceleration group. It was needed to correlate RSMD data, for LN2 and H2O sprays, with the fluid properties of the liquid jets and atomizing gases used in this investigation.
Nuclear reaction analysis of helium migration in silicon carbide
Miro, Sandrine; Costantini, Jean-Marc; Haussy, Jacques; Beck, Lucile; Vaubaillon, Sylvain; Pellegrino, Stephanie; Meis, Constantin; Grob, J J; Zhang, Yanwen; Weber, William J
2011-01-01
4H-SiC and 6H-SiC single crystals were implanted at room temperature with 3-MeV 3He ions at a fluence of 1x1016 cm-2. Analysis of helium migration was carried out with the 3He(d, p)4He nuclear reaction. No clear thermally-activated migration in the end-of-range (EOR) region is found below 1100 C, meaning that helium is strongly trapped probably in helium-vacancy clusters. At 1100 C and above, a fraction of 3He atoms remains trapped in the clusters, but a significant fraction is detrapped into a broad distribution, which is slightly shifted towards the sample surface. Helium detrapping from the EOR region increases with increasing annealing time and temperature. Moreover, the helium content is not conserved, since a significant fraction of 3He atoms is released out of the sample. Helium out-gassing actually increases with increasing annealing time and temperature, up to about 40% at 1150 C. No clear difference is found between the 4H-SiC and 6H-SiC polytypes.
Vaupel, Matthias Dutschke, Anke; Wurstbauer, Ulrich; Pasupathy, Abhay; Hitzel, Frank
2013-11-14
The optical phase shift by reflection on graphene is measured by interference contrast microscopy. The height profile across graphene layers on 300?nm thick SiO{sub 2} on silicon is derived from the phase profile. The complex refractive index and conductivity of graphene layers on silicon with 2?nm thin SiO{sub 2} are evaluated from a phase profile, while the height profile of the layers is measured by atomic force microscopy. It is observed that the conductivity measured on thin SiO{sub 2} is significantly greater than on thick SiO{sub 2}. Back scattered electron contrast of graphene layers is correlated to the height of graphene layers.
K Devloo-Casier; J Dendooven; K Ludwig; G Lekens; J DHaen; C Detavernier
2011-12-31
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.
Marchetti, S.; Carla, M.; Gambi, C. M. C.; Sbrana, F.; Vassalli, M.; Toscano, A.; Pacini, A.; Fratini, E.; Tiribilli, B.
2011-05-15
The three-dimensional structure and the mechanical properties of a {beta}-connectin fragment from human cardiac muscle, belonging to the I band, from I{sub 27} to I{sub 34}, were investigated by small-angle x-ray scattering (SAXS) and single-molecule force spectroscopy (SMFS). This molecule presents an entropic elasticity behavior, associated to globular domain unfolding, that has been widely studied in the last 10 years. In addition, atomic force microscopy based SMFS experiments suggest that this molecule has an additional elastic regime, for low forces, probably associated to tertiary structure remodeling. From a structural point of view, this behavior is a mark of the fact that the eight domains in the I{sub 27}-I{sub 34} fragment are not independent and they organize in solution, assuming a well-defined three-dimensional structure. This hypothesis has been confirmed by SAXS scattering, both on a diluted and a concentrated sample. Two different models were used to fit the SAXS curves: one assuming a globular shape and one corresponding to an elongated conformation, both coupled with a Coulomb repulsion potential to take into account the protein-protein interaction. Due to the predominance of the structure factor, the effective shape of the protein in solution could not be clearly disclosed. By performing SMFS by atomic force microscopy, mechanical unfolding properties were investigated. Typical sawtooth profiles were obtained and the rupture force of each unfolding domain was estimated. By fitting a wormlike chain model to each peak of the sawtooth profile, the entropic elasticity of octamer was described.