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Journal Cover Atoms
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  This is an Open Access Journal Open Access journal
   ISSN (Online) 2218-2004
   Published by MDPI Homepage  [147 journals]
  • Atoms, Vol. 4, Pages 26: Evaluation of State-Resolved Reaction
           Probabilities and Their Application in Population Models for He, H, and H2

    • Authors: Dirk Wünderlich, Ursel Fantz
      First page: 26
      Abstract: Population models are a prerequisite for performing qualitative analysis of population densities measured in plasmas or predicting the dependence of plasma emission on parameter variations. Models for atomic helium and hydrogen as well as molecular hydrogen in low-pressure plasmas are introduced. The cross-sections and transition probabilities used as input in the atomic models are known very accurately, and thus a benchmark of these models against experiments is very successful. For H2, in contrast, significant deviations exist between reaction probabilities taken from different literature sources. The reason for this is the more complex internal structure of molecules compared to atoms. Vibrationally resolved models are applied to demonstrate how these deviations affect the model results. Steps towards a consistent input data set are presented: vibrationally resolved Franck–Condon factors, transition probabilities, and ionization cross-sections have been calculated and are available now. Additionally, ro-vibrational models for selected transitions are applied successfully to low-density, low-temperature plasmas. For further improving the accuracy of population models for H2, however, it is necessary to establish a comprehensive data set for ro-vibrationally resolved excitation cross-sections based on the most recent calculation techniques.
      PubDate: 2016-09-29
      DOI: 10.3390/atoms4040026
      Issue No: Vol. 4, No. 4 (2016)
  • Atoms, Vol. 4, Pages 19: Prospects for Precise Measurements with Echo Atom

    • Authors: Brynle Barrett, Adam Carew, Hermina Beica, Andrejs Vorozcovs, Alexander Pouliot, A. Kumarakrishnan
      First page: 19
      Abstract: Echo atom interferometers have emerged as interesting alternatives to Raman interferometers for the realization of precise measurements of the gravitational acceleration g and the determination of the atomic fine structure through measurements of the atomic recoil frequency ω q . Here we review the development of different configurations of echo interferometers that are best suited to achieve these goals. We describe experiments that utilize near-resonant excitation of laser-cooled rubidium atoms by a sequence of standing wave pulses to measure ω q with a statistical uncertainty of 37 parts per billion (ppb) on a time scale of ∼50 ms and g with a statistical precision of 75 ppb. Related coherent transient techniques that have achieved the most statistically precise measurements of atomic g-factor ratios are also outlined. We discuss the reduction of prominent systematic effects in these experiments using off-resonant excitation by low-cost, high-power lasers.
      PubDate: 2016-06-27
      DOI: 10.3390/atoms4030019
      Issue No: Vol. 4, No. 3 (2016)
  • Atoms, Vol. 4, Pages 20: Neutrons and Gamma-Ray Dose Calculations in
           Subcritical Reactor Facility Using MCNP

    • Authors: Ned Xoubi
      First page: 20
      Abstract: In nuclear experimental, training and teaching laboratories such as a subcritical reactor facility, huge measures of external radiation doses could be caused by neutron and gamma radiation. It becomes imperative to place the health and safety of staff and students in the reactor facility under proper scrutiny. The protection of these individuals against ionization radiation is facilitated by expected dose mapping and shielding calculations. A three-dimensional (3D) Monte Carlo model was developed to calculate the dose rate from neutrons and gamma, using the ANSI/ANS-6.1.1 and the ICRP-74 flux-to-dose conversion factors. Estimation for the dose was conducted across 39 areas located throughout the reactor hall of the facility and its training platform. It was found that the range of the dose rate magnitude is between 7.50 E−01 μSv/h and 1.96 E−04 μSv/h in normal operation mode. During reactor start-up/shut-down mode, it was observed that a large area of the facility can experience exposure to a significant radiation field. This field ranges from 2.99 E+03 μSv/h to 3.12 E+01 μSv/h. There exists no noticeable disparity between results using the ICRP-74 or ANSI/ANS-6.1.1 flux-to-dose rate conversion factors. It was found that the dose rate due to gamma rays is higher than that of neutrons.
      PubDate: 2016-06-30
      DOI: 10.3390/atoms4030020
      Issue No: Vol. 4, No. 3 (2016)
  • Atoms, Vol. 4, Pages 21: Analysis of Polarizability Measurements Made with
           Atom Interferometry

    • Authors: Maxwell Gregoire, Nathan Brooks, Raisa Trubko, Alexander Cronin
      First page: 21
      Abstract: We present revised measurements of the static electric dipole polarizabilities of K, Rb, and Cs based on atom interferometer experiments presented in [Phys. Rev. A 2015, 92, 052513] but now re-analyzed with new calibrations for the magnitude and geometry of the applied electric field gradient. The resulting polarizability values did not change, but the uncertainties were significantly reduced. Then, we interpret several measurements of alkali metal atomic polarizabilities in terms of atomic oscillator strengths fik, Einstein coefficients Aik, state lifetimes τk, transition dipole matrix elements Dik, line strengths Sik, and van der Waals C6 coefficients. Finally, we combine atom interferometer measurements of polarizabilities with independent measurements of lifetimes and C6 values in order to quantify the residual contribution to polarizability due to all atomic transitions other than the principal ns-npJ transitions for alkali metal atoms.
      PubDate: 2016-07-06
      DOI: 10.3390/atoms4030021
      Issue No: Vol. 4, No. 3 (2016)
  • Atoms, Vol. 4, Pages 22: Atomic Structure Calculations and Study of Plasma
           Parameters of Al-Like Ions

    • Authors: Arun Goyal, Indu Khatri, Avnindra Singh, Man Mohan, Rinku Sharma, Narendra Singh
      First page: 22
      Abstract: In the present paper, the spectroscopic properties and plasma characteristics of Al-like ions are investigated in an extensive and detailed manner by adopting the GRASP2K package based on fully relativistic Multi-Configuration Dirac–Hartree–Fock (MCDHF) wave-functions in the active space approximation. We have presented energy levels for Al-like ions for Valence-Valence (VV) and Core-Valence (CV) correlations under the scheme of active space. We have also provided radiative data for E1 transitions for Al-like ions and studied the variation of the transition wavelength and transition probability for electric dipole (E1) Extreme Ultraviolet (EUV) transitions with nuclear charge. Our calculated energy levels and transition wavelengths match well with available theoretical and experimental results. The discrepancies of the GRASP2K code results with CIV3 and RMPBT (Relativistic Many Body Perturbation Theory) results are also discussed. The variations of the line intensity ratio, electron density, plasma frequency and plasma skin depth with plasma temperature and nuclear charge are discussed graphically in detail for optically thin plasma in Local Thermodynamic Equilibrium (LTE). We believe that our obtained results may be beneficial for comparisons and in fusion and astrophysical plasma research.
      PubDate: 2016-07-11
      DOI: 10.3390/atoms4030022
      Issue No: Vol. 4, No. 3 (2016)
  • Atoms, Vol. 4, Pages 23: Scalar Aharonov–Bohm Phase in Ramsey Atom
           Interferometry under Time-Varying Potential

    • Authors: Atsuo Morinaga, Motoyuki Murakami, Keisuke Nakamura, Hiromitsu Imai
      First page: 23
      Abstract: In a Ramsey atom interferometer excited by two electromagnetic fields, if atoms are under a time-varying scalar potential during the interrogation time, the phase of the Ramsey fringes shifts owing to the scalar Aharonov–Bohm effect. The phase shift was precisely examined using a Ramsey atom interferometer with a two-photon Raman transition under the second-order Zeeman potential, and a formula for the phase shift was derived. Using the derived formula, the frequency shift due to the scalar Aharonov–Bohm effect in the frequency standards utilizing the Ramsey atom interferometer was discussed.
      PubDate: 2016-08-02
      DOI: 10.3390/atoms4030023
      Issue No: Vol. 4, No. 3 (2016)
  • Atoms, Vol. 4, Pages 24: Electron Impact Excitation of F-Like W LXVI

    • Authors: Kanti Aggarwal
      First page: 24
      Abstract: Electron impact excitation collision strengths are calculated for all transitions among 113 levels of the 2s 2 2p 5 , 2s2p 6 , 2s 2 2p 4 3ℓ, 2s2p 5 3ℓ, and 2p 6 3ℓ configurations of F-like W LXVI. For this purpose, Dirac Atomic R-matrix Code (DARC) has been adopted and results are listed over a wide energy range of 1000 to 6000 Ryd. For comparison purposes, analogous calculations have also been performed with the Flexible Atomic Code (FAC), and the results obtained are comparable with those from DARC.
      PubDate: 2016-07-26
      DOI: 10.3390/atoms4030024
      Issue No: Vol. 4, No. 3 (2016)
  • Atoms, Vol. 4, Pages 25: Decoherence Spectroscopy for Atom Interferometry

    • Authors: Raisa Trubko, Alexander Cronin
      First page: 25
      Abstract: Decoherence due to photon scattering in an atom interferometer was studied as a function of laser frequency near an atomic resonance. The resulting decoherence (contrast-loss) spectra will be used to calibrate measurements of tune-out wavelengths that are made with the same apparatus. To support this goal, a theoretical model of decoherence spectroscopy is presented here along with experimental tests of this model.
      PubDate: 2016-08-17
      DOI: 10.3390/atoms4030025
      Issue No: Vol. 4, No. 3 (2016)
  • Atoms, Vol. 4, Pages 12: Obtaining Atomic Matrix Elements from Vector
           Tune-Out Wavelengths Using Atom Interferometry

    • Authors: Adam Fallon, Charles Sackett
      First page: 12
      Abstract: Accurate values for atomic dipole matrix elements are useful in many areas of physics, and in particular for interpreting experiments such as atomic parity violation. Obtaining accurate matrix element values is a challenge for both experiment and theory. A new technique that can be applied to this problem is tune-out spectroscopy, which is the measurement of light wavelengths where the electric polarizability of an atom has a zero. Using atom interferometry methods, tune-out wavelengths can be measured very accurately. Their values depend on the ratios of various dipole matrix elements and are thus useful for constraining theory and broadening the application of experimental values. To date, tune-out wavelength measurements have focused on zeros of the scalar polarizability, but in general the vector polarizability also contributes. We show here that combined measurements of the vector and scalar polarizabilities can provide more detailed information about the matrix element ratios, and in particular can distinguish small contributions from the atomic core and the valence tail states. These small contributions are the leading error sources in current parity violation calculations for cesium.
      PubDate: 2016-03-30
      DOI: 10.3390/atoms4020012
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 13: Multi-Configuration Dirac–Hartree–Fock
           (MCDHF) Calculations for B-Like Ions

    • Authors: Indu Khatri, Arun Goyal, Avnindra Singh, Man Mohan
      First page: 13
      Abstract: Relativistic configuration interaction results are presented for several B-like ions (Ge XXVIII, Rb XXXIII, Sr XXXIV, Ru XL, Sn XLVI, and Ba LII) using the multi-configuration Dirac–Hartree–Fock (MCDHF) method. The calculations are carried out in the active space approximation with the inclusion of the Breit interaction, the finite nuclear size effect, and quantum electrodynamic corrections. Results for fine structure energy levels for 1s22s22p and 2s2p2 configurations relative to the ground state are reported. The transition wavelengths, transition probabilities, line strengths, and absorption oscillator strengths for 2s22p–2s2p2 electric dipole (E1) transitions are calculated. Both valence and core-valence correlation effects were accounted for through single-double multireference (SD-MR) expansions to increasing sets of active orbitals. Comparisons are made with the available data and good agreement is achieved. The values calculated using core–valence correlation are found to be very close to other theoretical and experimental values. The behavior of oscillator strengths as a function of nuclear charge is studied. We believe that our results can guide experimentalists in identifying the fine-structure levels in their future work.
      PubDate: 2016-05-06
      DOI: 10.3390/atoms4020013
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 14: Atom Interferometry in the Presence of an
           External Test Mass

    • Authors: Boris Dubetsky, Stephen Libby, Paul Berman
      First page: 14
      Abstract: The influence of an external test mass on the phase of the signal of an atom interferometer is studied theoretically. Using traditional techniques in atom optics based on the density matrix equations in the Wigner representation, we are able to extract the various contributions to the phase of the signal associated with the classical motion of the atoms, the quantum correction to this motion resulting from atomic recoil that is produced when the atoms interact with Raman field pulses and quantum corrections to the atomic motion that occur in the time between the Raman field pulses. By increasing the effective wave vector associated with the Raman field pulses using modified field parameters, we can increase the sensitivity of the signal to the point where such quantum corrections can be measured. The expressions that are derived can be evaluated numerically to isolate the contribution to the signal from an external test mass. The regions of validity of the exact and approximate expressions are determined.
      PubDate: 2016-04-21
      DOI: 10.3390/atoms4020014
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 15: Novel Ion Trap Design for Strong Ion-Cavity

    • Authors: Alejandro Márquez Seco, Hiroki Takahashi, Matthias Keller
      First page: 15
      Abstract: We present a novel ion trap design which facilitates the integration of an optical fiber cavity into the trap structure. The optical fibers are confined inside hollow electrodes in such a way that tight shielding and free movement of the fibers are simultaneously achievable. The latter enables in situ optimization of the overlap between the trapped ions and the cavity field. Through numerical simulations, we systematically analyze the effects of the electrode geometry on the trapping characteristics such as trap depths, secular frequencies and the optical access angle. Additionally, we simulate the effects of the presence of the fibers and confirm the robustness of the trapping potential. Based on these simulations and other technical considerations, we devise a practical trap configuration that isviable to achieve strong coupling of a single ion.
      PubDate: 2016-04-26
      DOI: 10.3390/atoms4020015
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 16: The Faddeev-Merkuriev Differential Equations
           (MFE) and Multichannel 3-Body Scattering Systems

    • Authors: Chi Hu
      First page: 16
      Abstract: Numerical implementation of the modified Faddeev Equation (MFE) is presented in some detail. The Faddeev channel wave function displays unique properties of each and every open channel, respectively. In particular, near resonant energies, the structures of the resonances are beautifully displayed, from which, the life-time of the resonances can be determined by simply using the uncertainty principle. The phase shift matrix, or the K-matrix, provides unique information for each and every resonance. This information enables the identification of the physical formation mechanism of the Gailitis resonances. A few of these resonances, previously known as the mysterious shape resonances, have occurred in a number of different collision systems. The Gailitis resonances are actually produced by a quantized Stark-effect within the various collision systems. Since the Stark-effect is a universal phenomenon, the Gailitis resonances are expected to occur in much broader classes of collision systems. We will present the results of a precision calculation using the MFE method in sufficient detail for interested students who wish to explore the mysteries of nature with a powerful theoretical tool.
      PubDate: 2016-05-03
      DOI: 10.3390/atoms4020016
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 17: Series of Broad Resonances in Atomic Three-Body

    • Authors: Daniel Diaz, Zoltan Papp, Chi-Yu Hu
      First page: 17
      Abstract: We re-examine the series of resonances found earlier in atomic three-body systems by solving the Faddeev-Merkuriev integral equations. These resonances are rather broad and line up at each threshold with gradually increasing gaps. This lining up takes place in the same way for all thresholds and is irrespective of the spatial symmetry. We relate these resonances to the Gailitis mechanism, which is a consequence of the polarization potential.
      PubDate: 2016-06-20
      DOI: 10.3390/atoms4020017
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 18: A Wigner Function Approach to Coherence in a
           Talbot-Lau Interferometer

    • Authors: Eric Imhof, James Stickney, Matthew Squires
      First page: 18
      Abstract: Using a thermal gas, we model the signal of a trapped interferometer. This interferometer uses two short laser pulses, separated by time T, which act as a phase grating for the matter waves. Near time 2 T , there is an echo in the cloud’s density due to the Talbot-Lau effect. Our model uses the Wigner function approach and includes a weak residual harmonic trap. The analysis shows that the residual potential limits the interferometer’s visibility, shifts the echo time of the interferometer, and alters its time dependence. Loss of visibility can be mitigated by optimizing the initial trap frequency just before the interferometer cycle begins.
      PubDate: 2016-06-22
      DOI: 10.3390/atoms4020018
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 5: Acknowledgement to Reviewers of Atoms in 2015

    • Authors: Atoms Editorial Office
      First page: 5
      Abstract: The editors of Atoms would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2015. [...]
      PubDate: 2016-01-22
      DOI: 10.3390/atoms4010005
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 6: Two Photon Processes in an Atom Confined in
           Gaussian Potential

    • Authors: Sonia Lumb, Shalini Lumb, Vinod Prasad
      First page: 6
      Abstract: Transitions of an atom under the effect of a Gaussian potential and loose spherical confinement are studied. An accurate Bernstein-polynomial (B-polynomial) method has been applied for the calculation of the energy levels and radial matrix elements. The transition probability amplitudes, transparency frequencies, and resonance enhancement frequencies for transitions to various excited states have been evaluated. The effect of the shape of confining potential on these spectral properties is studied.
      PubDate: 2016-02-17
      DOI: 10.3390/atoms4010006
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 7: Guest Editor’s Notes on the “Atoms” Special
           Issue on “Perspectives of Atomic Physics with Trapped Highly Charged

    • Authors: Elmar Träbert
      First page: 7
      Abstract: The study of highly charged ions (HCI) was pursued first at Uppsala (Sweden), by Edlén and Tyrén in the 1930s. Their work led to the recognition that the solar corona is populated by such ions, an insight which forced massive paradigm changes in solar physics. Plasmas aiming at controlled fusion in the laboratory, laser-produced plasmas, foil-excited swift ion beams, and electron beam ion traps have all pushed the envelope in the production of HCI. However, while there are competitive aspects in the race for higher ion charge states, the real interest lies in the very many physics topics that can be studied in these ions. Out of this rich field, the Special Issue concentrates on atomic physics studies that investigate highly charged ions produced, maintained, and/or manipulated in ion traps. There have been excellent achievements in the field in the past, and including fairly recent work, they have been described by their authors at conferences and in the appropriate journals. The present article attempts an overview over current lines of development, some of which are expanded upon in this Special Issue.
      PubDate: 2016-02-24
      DOI: 10.3390/atoms4010007
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 8: Second Order Stark-Effect Induced Gailitis
           Resonances in e + Ps and p + 7Li

    • Authors: Chi Hu, Zoltan Papp
      First page: 8
      Abstract: We present a detailed comparison between the first order Stark-effect induced Gailitis resonance in e+ + H (n = 2) and the second order Stark-effect induced resonance in e + Ps (n = 1). Common characteristics as well as differences of these resonances will be identified. These results will be used to assess the presence of Gailitis resonances in the scattering of proton on the ground state of 7Li atom. During the lifetime of the Gailitis resonance, nuclear fusion is enhanced by the resonant entry of the proton into the nucleus of 7Li via a compound nuclear energy level of 8Be*.
      PubDate: 2016-02-26
      DOI: 10.3390/atoms4010008
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 9: Merkuriev Cut-off in e+ − H Multichannel
           Scattering Calculations

    • Authors: Vitaly Gradusov, Vladimir Roudnev, Sergey Yakovlev
      First page: 9
      Abstract: We present the results of positron-Hydrogen multichannel scattering calculations performed on the base of Faddeev-Merkuriev equations. We discuss an optimal choice of the Merkuriev’s Coulomb splitting parameters. Splitting the Coulomb potential in two-body configuration space is applicable for a limited energy range. Splitting the potential in three-body configuration space makes it possible to perform calculations in a broader range of energies and to optimize the numerical convergence. Scattering cross sections for zero total angular momentum for all processes between the positronium formation threshold and the third excitation threshold of the Hydrogen atom are reported.
      PubDate: 2016-03-01
      DOI: 10.3390/atoms4010009
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 10: Relativistic Ionization of Hydrogen Atoms by
           Positron Impact

    • Authors: Amal Chahboune, Bouzid Manaut, Elmostafa Hrour, Souad Taj
      First page: 10
      Abstract: Relativistic triple differential cross-sections (TDCS) for ionization of hydrogen atoms by positron impact have been calculated in the symmetric coplanar geometry. We have used Dirac wave functions to describe free electron’s and positron’s sates. The relativistic formalism is examined by taking the non relativistic limit. Present results are compared with those for the corresponding electron-impact case. In the first Born approximation, we found that the TDCS for positron impact ionization exceeds that for electron impact for all energies in accordance with the result obtained by several other theories.
      PubDate: 2016-03-04
      DOI: 10.3390/atoms4010010
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 11: Fundamental Features of Quantum Dynamics Studied
           in Matter-Wave Interferometry—Spin Weak Values and the Quantum

    • Authors: Stephan Sponar, Tobias Denkmayr, Hermann Geppert, Yuji Hasegawa
      First page: 11
      Abstract: The validity of quantum-mechanical predictions has been confirmed with a high degree of accuracy in a wide range of experiments. Although the statistics of the outcomes of a measuring apparatus have been studied intensively, little has been explored and is known regarding the accessibility of quantum dynamics. For these sorts of fundamental studies of quantum mechanics, interferometry using neutron matter-waves in particular, provides almost ideal experimental circumstances. In this device quantum interference between spatially separated beams occurs on a macroscopic scale. Recently, the full determination of weak-values of neutrons 1 2 - spin adds a new aspect to the study of quantum dynamics. Moreover, a new counter-intuitive phenomenon, called quantum Cheshire Cat, is observed in an interference experiment. In this article, we present an overview of these experiments.
      PubDate: 2016-03-11
      DOI: 10.3390/atoms4010011
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 1, Pages 1: Welcome to Atoms: A New Open Access Journal

    • Authors: James Babb
      Pages: 1 - 1
      Abstract: There is no doubt that it is an exciting time to be studying quantum properties of atoms, molecules, and nuclei. Increasingly deep connections between long-established fields: “atomic physics”, “molecular physics”, “chemical physics”, “nuclear physics”, “scattering theory”, “nuclear magnetic resonance”, “quantum optics”, etc., are blurring old research labels. Atoms is a new open access journal with a broad scope that will aim to capture some of these exciting changes and developments, with a quantum flavor. The Editorial Board's collective expertise spans the fields involved and reflects the international communities active in these areas.
      PubDate: 2012-12-17
      DOI: 10.3390/atoms1010001
      Issue No: Vol. 1, No. 1 (2012)
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