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   ISSN (Online) 2218-2004
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  • Atoms, Vol. 5, Pages 15: Shannon Information Entropy in Position Space for
           the Ground and Singly Excited States of Helium with Finite Confinements

    • Authors: Jen-Hao Ou, Yew Ho
      First page: 15
      Abstract: We provide benchmark values for Shannon information entropies in position space for the ground state and ls2s 1Se excited state of helium confined with finite confinement potentials by employing the highly correlated Hylleraas-type wave functions. For the excited state, a “tilt” (small oscillation) on the curve of Shannon entropy as a function of width size for the confinement potential is observed. Justified by the behavior of the electron density, the localization or delocalization of the helium wave functions confined with repulsive and attractive finite oscillator (FO) potentials are examined.
      PubDate: 2017-03-24
      DOI: 10.3390/atoms5020015
      Issue No: Vol. 5, No. 2 (2017)
       
  • Atoms, Vol. 5, Pages 16: Multiconfiguration Dirac-Hartree-Fock
           Calculations with Spectroscopic Accuracy: Applications to Astrophysics

    • Authors: Per Jönsson, Gediminas Gaigalas, Pavel Rynkun, Laima Radžiūtė, Jörgen Ekman, Stefan Gustafsson, Henrik Hartman, Kai Wang, Michel Godefroid, Charlotte Froese Fischer, Ian Grant, Tomas Brage, Giulio Del Zanna
      First page: 16
      Abstract: Atomic data, such as wavelengths, spectroscopic labels, broadening parameters and transition rates, are necessary for many applications, especially in plasma diagnostics, and for interpreting the spectra of distant astrophysical objects. The experiment with its limited resources is unlikely to ever be able to provide a complete dataset on any atomic system. Instead, the bulk of the data must be calculated. Based on fundamental principles and well-justified approximations, theoretical atomic physics derives and implements algorithms and computational procedures that yield the desired data. We review progress and recent developments in fully-relativistic multiconfiguration Dirac–Hartree–Fock methods and show how large-scale calculations can give transition energies of spectroscopic accuracy, i.e., with an accuracy comparable to the one obtained from observations, as well as transition rates with estimated uncertainties of a few percent for a broad range of ions. Finally, we discuss further developments and challenges.
      PubDate: 2017-04-14
      DOI: 10.3390/atoms5020016
      Issue No: Vol. 5, No. 2 (2017)
       
  • Atoms, Vol. 5, Pages 17: P-Wave Positron-Hydrogen Scattering,
           Annihilation, and Positronium Formation

    • Authors: Anand Bhatia
      First page: 17
      Abstract: In a previous paper (Bhatia A.K. 2016), a hybrid theory for the scattering of positrons from hydrogen atoms was applied to calculate S-wave phase shifts, annihilation, and positronium formation cross sections. This approach is now being applied to calculate P-wave positron-hydrogen scattering. The present results, obtained using short-range correlation functions along with long-range correlations in the Schrödinger equation at the same time, agree very well with the results obtained in an earlier calculation by Bhatia et al. (1974), using the Feshbach projection operator formalism. In these earlier calculations, the correction due to the long-range correlations was applied to the variational results. In spite of the fact that this ad hoc correction destroyed the variational bound, the final results have been considered accurate. Annihilation cross-sections, positronium formation cross-sections, calculated in the distorted-wave approximation, are also presented.
      PubDate: 2017-04-18
      DOI: 10.3390/atoms5020017
      Issue No: Vol. 5, No. 2 (2017)
       
  • Atoms, Vol. 5, Pages 1: Acknowledgement to Reviewers of Atoms in 2016

    • Authors: Atoms Editorial Office
      First page: 1
      Abstract: The editors of Atoms would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...]
      PubDate: 2017-01-10
      DOI: 10.3390/atoms5010001
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 2: An Investigation on the He−(1s2s2 2S)
           Resonance in Debye Plasmas

    • Authors: Arijit Ghoshal, Yew Ho
      First page: 2
      Abstract: The effect of Debye plasma on the 1 s 2 s 2 2 S resonance states in the scattering of electron from helium atom has been investigated within the framework of the stabilization method. The interactions among the charged particles in Debye plasma have been modelled by Debye–Huckel potential. The 1 s 2 s excited state of the helium atom has been treated as consisting of a H e + ionic core plus an electron moving around. The interaction between the core and the electron has then been modelled by a model potential. It has been found that the background plasma environment significantly affects the resonance states. To the best of our knowledge, such an investigation of 1 s 2 s 2 2 S resonance states of the electron–helium system embedded in Debye plasma environment is the first reported in the literature.
      PubDate: 2017-01-11
      DOI: 10.3390/atoms5010002
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 3: Combining Multiconfiguration and Perturbation
           Methods: Perturbative Estimates of Core–Core Electron Correlation
           Contributions to Excitation Energies in Mg-Like Iron

    • Authors: Stefan Gustafsson, Per Jönsson, Charlotte Froese Fischer, Ian Grant
      First page: 3
      Abstract: Large configuration interaction (CI) calculations can be performed if part of the interaction is treated perturbatively. To evaluate the combined CI and perturbative method, we compute excitation energies for the 3 l 3 l ′ , 3 l 4 l ′ and 3 s 5 l states in Mg-like iron. Starting from a CI calculation including valence and core–valence correlation effects, it is found that the perturbative inclusion of core–core electron correlation halves the mean relative differences between calculated and observed excitation energies. The effect of the core–core electron correlation is largest for the more excited states. The final relative differences between calculated and observed excitation energies is 0.023%, which is small enough for the calculated energies to be of direct use in line identifications in astrophysical and laboratory spectra.
      PubDate: 2017-01-12
      DOI: 10.3390/atoms5010003
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 4: High-Precision Measurements of the Bound
           Electron’s Magnetic Moment

    • Authors: Sven Sturm, Manuel Vogel, Florian Köhler-Langes, Wolfgang Quint, Klaus Blaum, Günter Werth
      First page: 4
      Abstract: Highly charged ions represent environments that allow to study precisely one or more bound electrons subjected to unsurpassed electromagnetic fields. Under such conditions, the magnetic moment (g-factor) of a bound electron changes significantly, to a large extent due to contributions from quantum electrodynamics. We present three Penning-trap experiments, which allow to measure magnetic moments with ppb precision and better, serving as stringent tests of corresponding calculations, and also yielding access to fundamental quantities like the fine structure constant α and the atomic mass of the electron. Additionally, the bound electrons can be used as sensitive probes for properties of the ionic nuclei. We summarize the measurements performed so far, discuss their significance, and give a detailed account of the experimental setups, procedures and the foreseen measurements.
      PubDate: 2017-01-21
      DOI: 10.3390/atoms5010004
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 5: Hyperfine Structure and Isotope Shifts in Dy II

    • Authors: Dylan Del Papa, Richard Holt, S. Rosner
      First page: 5
      Abstract: Using fast-ion-beam laser-fluorescence spectroscopy (FIBLAS), we have measured the hyperfine structure (hfs) of 14 levels and an additional four transitions in Dy II and the isotope shifts (IS) of 12 transitions in the wavelength range of 422–460 nm. These are the first precision measurements of this kind in Dy II. Along with hfs and IS, new undocumented transitions were discovered within 3 GHz of the targeted transitions. These atomic data are essential for astrophysical studies of chemical abundances, allowing correction for saturation and the effects of blended lines. Lanthanide abundances are important in diffusion modeling of stellar interiors, and in the mechanisms and history of nucleosynthesis in the universe. Hfs and IS also play an important role in the classification of energy levels, and provide a benchmark for theoretical atomic structure calculations.
      PubDate: 2017-01-20
      DOI: 10.3390/atoms5010005
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 6: JJ2LSJ Transformation and Unique Labeling for
           Energy Levels

    • Authors: Gediminas Gaigalas, Charlotte Fischer, Pavel Rynkun, Per Jönsson
      First page: 6
      Abstract: The JJ2LSJ program, which is important not only for the GRASP2K package but for the atom theory in general, is presented. The program performs the transformation of atomic state functions(ASFs) from a jj-coupled CSF basis into an LSJ-coupled CSF basis. In addition, the program implements a procedure that assigns a unique label to all energy levels. Examples of how to use the JJ2LSJ program are given. Several cases are presented where there is a unique labeling problem.
      PubDate: 2017-01-27
      DOI: 10.3390/atoms5010006
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 7: Core Effects on Transition Energies for 3dk
           Configurations in Tungsten Ions

    • Authors: Charlotte Fischer, Gediminas Gaigalas, Per Jönsson
      First page: 7
      Abstract: Allenergylevelsofthe3dk,k=1,2,...,8,9,configurationsfortungstenions,computedusing the GRASP2K fully relativistic code based on the variational multiconfiguration Dirac–Hartree–Fock method, are reported. Included in the calculations are valence correlation where all 3s,3p,3d orbitals are considered to be valence orbitals, as well as core–valence and core–core effects from the 2s,2p subshells. Results are compared with other recent theory and with levels obtained from the wavelengths of lines observed in the experimental spectra. It is shown that the core correlation effects considerably reduce the disagreement with levels linked directly to observed wavelengths, but may differ significantly from the NIST levels, where an unknown shift of the levels could not be determined from experimental wavelengths. For low values of k, levels were in good agreement with relativistic many-body perturbation levels, but for 2 < k < 8, the present results were in better agreement with observation.
      PubDate: 2017-02-08
      DOI: 10.3390/atoms5010007
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 8: Calculation of Rates of 4p–4d Transitions in
           Ar II

    • Authors: Alan Hibbert
      First page: 8
      Abstract: Recent experimental work by Belmonte et al. (2014) has given rates for some 4p–4d transitions that are significantly at variance with the previous experimental work of Rudko and Tang (1967) recommended in the NIST tabulations. To date, there are no theoretical rates with which to compare. In this work, we provide such theoretical data. We have undertaken a substantial and systematic configuration interaction calculation, with an extrapolation process applied to ab initio mixing coefficients, which gives energy differences in agreement with experiment. The length and velocity forms give values that are within 10%–15% of each other. Our results are in sufficiently close agreement with those of Belmonte et al. that we can confidently recommend that their results are much more accurate than the early results of Rudko and Tang, and should be adopted in place of the latter.
      PubDate: 2017-02-21
      DOI: 10.3390/atoms5010008
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 9: The Cu II Spectrum

    • Authors: Alexander Kramida, Gillian Nave, Joseph Reader
      First page: 9
      Abstract: New wavelength measurements in the vacuum ultraviolet (VUV), ultraviolet and visible spectral regions have been combined with available literature data to refine and extend the description of the spectrum of singly ionized copper (Cu II). In the VUV region, we measured 401 lines using a concave grating spectrograph and photographic plates. In the UV and visible regions, we measured 276 lines using a Fourier-transform spectrometer. These new measurements were combined with previously unpublished data from the thesis of Ross, with accurate VUV grating measurements of Kaufman and Ward, and with less accurate older measurements of Shenstone to construct a comprehensive list of ≈2440 observed lines, from which we derived a revised set of 379 optimized energy levels, complemented with 89 additional levels obtained using series formulas. Among the 379 experimental levels, 29 are new. Intensities of all lines observed in different experiments have been reduced to the same uniform scale by using newly calculated transition probabilities (A-values). We combined our calculations with published measured and calculated A-values to provide a set of 555 critically evaluated transition probabilities with estimated uncertainties, 162 of which are less than 20%.
      PubDate: 2017-02-24
      DOI: 10.3390/atoms5010009
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 10: The Role of the Hyperfine Structure for the
           Determination of Improved Level Energies of Ta II, Pr II and La II

    • Authors: Laurentius Windholz
      First page: 10
      Abstract: For the determination of improved energy levels of ionic spectra of elements with large values of nuclear magnetic dipole moment (and eventually large values of nuclear quadrupole moments), it is necessary to determine the center of gravity of spectral lines from resolved hyperfine structure patterns appearing in highly resolved spectra. This is demonstrated on spectral lines of Ta II, Pr II and La II. Blend situations (different transitions with accidentally nearly the same wave number difference between the combining levels) must also be considered.
      PubDate: 2017-02-28
      DOI: 10.3390/atoms5010010
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 11: Resonance Transitions in the Spectra of the
           Ag6+–Ag8+ Ions

    • Authors: Alexander Ryabtsev, Edward Kononov
      First page: 11
      Abstract: The spectrum of silver, excited in a vacuum spark, was recorded in the region 150–350 Å on a 3-m grazing incidence spectrograph. The resonance 4dk–(4dk−15p + 4dk−14f + 4p54dk+1) was studied in the Ag6+–Ag8+ spectra (Ag VII–Ag IX) with k = 5–3, respectively. Several hundred lines were identified with the aid of the Cowan code and orthogonal operator technique calculations. The energy levels were found and the transition probabilities were calculated.
      PubDate: 2017-03-04
      DOI: 10.3390/atoms5010011
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 12: Spectral Analysis of Moderately Charged Rare-Gas
           Atoms

    • Authors: Jorge Reyna Almandos, Mónica Raineri
      First page: 12
      Abstract: This article presents a review concerning the spectral analysis of several ions of neon, argon, krypton and xenon, with impact on laser studies and astrophysics that were mainly carried out in our collaborative groups between Argentina and Brazil during many years. The spectra were recorded from the vacuum ultraviolet to infrared regions using pulsed discharges. Semi-empirical approaches with relativistic Hartree–Fock and Dirac-Fock calculations were also included in these investigations. The spectral analysis produced new classified lines and energy levels. Lifetimes and oscillator strengths were also calculated.
      PubDate: 2017-03-07
      DOI: 10.3390/atoms5010012
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 13: Direct Observation of the M1 Transition between
           the Ground Term Fine Structure Levels of W VIII

    • Authors: Momoe Mita, Hiroyuki Sakaue, Daiji Kato, Izumi Murakami, Nobuyuki Nakamura
      First page: 13
      Abstract: We present a direct observation of the M1 transition between the fine structure splitting in the 4 f 13 5 s 2 5 p 6 2 F ground term of W VIII. The spectroscopic data of few-times ionized tungsten ions are important for the future ITER diagnostics, but there is a serious lack of data. The present study is part of an ongoing effort to solve this problem. Emission from the tungsten ions produced and trapped in a compact electron beam ion trap is observed with a Czerny–Turner visible spectrometer. Spectra in the EUV range are also observed at the same time to help identify the previously-unreported visible lines. The observed wavelength 574.47 ± 0.03 nm (air), which corresponds to the fine structure splitting of 17,402.5 ± 0.9 cm − 1 , shows reasonable agreement with the previously reported value 17,410 ± 5 cm − 1 obtained indirectly through the analysis of EUV spectra [Ryabtsev et al., Atoms 3 (2015) 273].
      PubDate: 2017-03-08
      DOI: 10.3390/atoms5010013
      Issue No: Vol. 5, No. 1 (2017)
       
  • Atoms, Vol. 5, Pages 14: Electroweak Decay Studies of Highly Charged
           Radioactive Ions with TITAN at TRIUMF

    • Authors: Kyle Leach, Iris Dillmann, Renee Klawitter, Erich Leistenschneider, Annika Lennarz, Thomas Brunner, Dieter Frekers, Corina Andreoiu, Anna Kwiatkowski, Jens Dilling
      First page: 14
      Abstract: Several modes of electroweak radioactive decay require an interaction between the nucleus and bound electrons within the constituent atom. Thus, the probabilities of the respective decays are not only influenced by the structure of the initial and final states in the nucleus, but can also depend strongly on the atomic charge. Conditions suitable for the partial or complete ionization of these rare isotopes occur naturally in hot, dense astrophysical environments, but can also be artificially generated in the laboratory to selectively block certain radioactive decay modes. Direct experimental studies on such scenarios are extremely difficult due to the laboratory conditions required to generate and store radioactive ions at high charge states. A new electron-beam ion trap (EBIT) decay setup with the TITAN experiment at TRIUMF has successfully demonstrated such techniques for performing spectroscopy on the radioactive decay of highly charged ions.
      PubDate: 2017-03-21
      DOI: 10.3390/atoms5010014
      Issue No: Vol. 5, No. 1 (2017)
       
  • 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 27: Positron-Hydrogen Scattering, Annihilation, and
           Positronium Formation

    • Authors: Anand Bhatia
      First page: 27
      Abstract: In previous papers (Bhatia A.K. 2007, 2012) a hybrid theory for the scattering of electrons from a hydrogenic system was developed and applied to calculate scattering phase shifts, Feshbach resonances, and photoabsorption processes. This approach is now being applied to the scattering of positrons from hydrogen atoms. Very accurate phase shifts, using the Feshbach projection operator formalism, were calculated previously (Bhatia A.K. et al. 1971 and Bhatia et al. 1974a). The present results, obtained using shorter expansions in the correlation function, along with long-range correlations in the Schrödinger equation, agree very well with the results obtained earlier. The scattering length is also calculated and the present results are compared with the previous results. Annihilation cross-sections, and positronium formation cross-sections, calculated in the distorted-wave approximation, are also presented.
      PubDate: 2016-11-04
      DOI: 10.3390/atoms4040027
      Issue No: Vol. 4, No. 4 (2016)
       
  • Atoms, Vol. 4, Pages 28: Decoherence in Excited Atoms by Low-Energy
           Scattering

    • Authors: Diego Quiñones, Benjamin Varcoe
      First page: 28
      Abstract: We describe a new mechanism of decoherence in excited atoms as a result of thermal particles scattering by the atomic nucleus. It is based on the idea that a single scattering will produce a sudden displacement of the nucleus, which will be perceived by the electron in the atom as an instant shift in the electrostatic potential. This will leave the atom’s wave-function partially projected into lower-energy states, which will lead to decoherence of the atomic state. The decoherence is calculated to increase with the excitation of the atom, making observation of the effect easier in Rydberg atoms. We estimate the order of the decoherence for photons and massive particles scattering, analyzing several commonly presented scenarios. Our scheme can be applied to the detection of weakly-interacting particles, like those which may be the constituents of Dark Matter, the interaction of which was calculated to have a more prominent effect that the background radiation.
      PubDate: 2016-12-09
      DOI: 10.3390/atoms4040028
      Issue No: Vol. 4, No. 4 (2016)
       
  • Atoms, Vol. 4, Pages 29: Rovibrationally Resolved Time-Dependent
           Collisional-Radiative Model of Molecular Hydrogen and Its Application to a
           Fusion Detached Plasma

    • Authors: Keiji Sawada, Motoshi Goto
      First page: 29
      Abstract: A novel rovibrationally resolved collisional-radiative model of molecular hydrogen that includes 4,133 rovibrational levels for electronic states whose united atom principal quantum number is below six is developed. The rovibrational X 1 Σ g + population distribution in a SlimCS fusion demo detached divertor plasma is investigated by solving the model time dependently with an initial 300 K Boltzmann distribution. The effective reaction rate coefficients of molecular assisted recombination and of other processes in which atomic hydrogen is produced are calculated using the obtained time-dependent population distribution.
      PubDate: 2016-12-20
      DOI: 10.3390/atoms4040029
      Issue No: Vol. 4, No. 4 (2016)
       
  • Atoms, Vol. 4, Pages 30: Cross Sections and Rate Coefficients for
           Vibrational Excitation of HeH+ Molecule by Electron Impact

    • Authors: Mehdi Ayouz, Viatcheslav Kokoouline
      First page: 30
      Abstract: Cross sections and thermally-averaged rate coefficients for vibration (de-)excitation of HeH + by an electron impact are computed using a theoretical approach that combines the multi-channel quantum defect theory and the UK R-matrix code. Fitting formulas with a few numerical parameters are derived for the obtained rate coefficients. The interval of applicability of the formulas is from 40 to 10,000 K.
      PubDate: 2016-12-20
      DOI: 10.3390/atoms4040030
      Issue No: Vol. 4, No. 4 (2016)
       
  • Atoms, Vol. 4, Pages 31: Spectrum and Energy Levels of Four-Times Ionized
           Yttrium (Y V)

    • Authors: Joseph Reader
      First page: 31
      Abstract: The analysis of the spectrum of four-times-ionized yttrium, Y V, was extended to provide a large number of new spectrum lines and energy levels. The new analysis is based on spectrograms made with sliding-spark discharges on 10.7 m normal- and grazing-incidence spectrographs. The measurements cover the region 184–2549 Å. The results revise levels for this spectrum by Zahid-Ali et al. (1975) and by Ateqad et al. (1984). Five hundred and seventy lines were classified as transitions between 23 odd-parity and 90 even-parity levels. The 4s24p5, 4s4p6, 4s24p44d, 5s, 5p, 5d, 6s configurations are now complete. Results for the 4s24p46d and 7s configurations are tentative. Ritz-type wavelengths were determined from the optimized energy levels, with uncertainties as low as ±0.0004 Å. The observed configurations were interpreted with Hartree-Fock calculations and least-squares fits of the energy parameters to the observed levels. Oscillator strengths for all classified lines were calculated with the fitted parameters. The results are compared with values for the level energies, percentage compositions, and transition probabilities from recent ab initio theoretical calculations. The ionization energy was revised to 607,760 ± 300 cm−1 (75.353 ± 0.037 eV).
      PubDate: 2016-12-21
      DOI: 10.3390/atoms4040031
      Issue No: Vol. 4, No. 4 (2016)
       
  • Atoms, Vol. 4, Pages 19: Prospects for Precise Measurements with Echo Atom
           Interferometry

    • 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
           Coupling

    • 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
           Systems

    • 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
           Ions”

    • 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
           Cheshire-Cat

    • 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)
       
 
 
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