25 Matching Results

Search Results

Advanced search parameters have been applied.

In Pursuit of Highly Accurate Atomic Lifetime Measurements of Multiply Charged Ions

Description: Accurate atomic lifetime data are useful for terrestrial and astrophysical plasma diagnostics. At accuracies higher than those required for these applications, lifetime measurements test atomic structure theory in ways complementary to spectroscopic energy determinations. At the highest level of accuracy, the question arises whether such tests reach the limits of modern theory, a combination of quantum mechanics and QED, adn possibly point to physics beyond the Standard Model. If high-precision atomic lifetime measurements, especially on multiply charged ions, have not quite reached this high accuracy yet, then what is necessary to attain this goal?
Date: June 1, 2009
Creator: Trabert, E
Partner: UNT Libraries Government Documents Department

Spectroscopy of Argon Excited in an Electron Beam Ion Trap

Description: Argon is one of the gases best investigated and most widely used in plasma discharge devices for a multitude of applications that range from wavelength reference standards to controlled fusion experiments. Reviewing atomic physics and spectroscopic problems in various ionization stages of Ar, the past use and future options of employing an electron beam ion trap (EBIT) for better and more complete Ar data in the x-ray, EUV and visible spectral ranges are discussed.
Date: April 18, 2005
Creator: Trabert, E
Partner: UNT Libraries Government Documents Department

Spectroscopy of ions using fast beams and ion traps

Description: A knowledge of the spectra of ionized atoms is of importance in many fields. They can be studied in a wide variety of light sources. In recent years techniques coming under the broad heatings of fast beams and ion traps have been used extensively for such investigations. This article considers the advantages that various techniques have for particular applications.
Date: October 1, 2004
Creator: Pinnington, E. H. & Trabert, E.
Partner: UNT Libraries Government Documents Department

Isoelectronic trends of line strength data in the Li and Be isoelectronic sequences

Description: The decays of the 2p J = 1/2 and J = 3/2 levels of Li-like ions and of the 2s2p {sup 1,3}P{sub 1}{sup 0} levels of Be-like ions can be used as simple-atom test beds for experimental lifetime measurements and for the development of accurate calculations of the transition rates. They have summarized and filtered the experimental data in order to obtain consistent data sets and isoelectronic trends that can be compared to theoretical predictions. The graphical presentation of line strength data enables direct comparison and evaluation of the merit of data along extended isoelectronic sequences. From this, the precision that is necessary in future meaningful experiments can be deduced.
Date: March 1, 2006
Creator: Trabert, E & Curtis, L J
Partner: UNT Libraries Government Documents Department

Measurement of the two-loop Lamb shift in lithiumlike U89+

Description: Using the SuperEBIT electron beam ion trap we have measured the 2s{sub 1/2}-2p{sub 1/2} transitions in U{sup 88+} and U{sup 89+}. The value of 280.645 {+-} 0.015 eV for Li-like U{sup 89+} improves the available precision by nearly an order of magnitude and establishes a new benchmark for testing QED, including higher-order contributions, within a fractional accuracy of better than 3 x 10{sup -4}. From our measurement, we infer a value for both the 2s and 1s two-loop Lamb shift, yielding excellent agreement with recent calculations of the 1.26 eV 1s two-loop Lamb shift in U{sup 91+}.
Date: April 1, 2005
Creator: Beiersdorfer, P; Chen, H; Thorn, D B & Trabert, E
Partner: UNT Libraries Government Documents Department

Prominent Soft X-ray Lines of Sr-like Au41+ in Low-energy EBIT Spectrum

Description: Relativistic multireference M{o}ller-Plesset perturbation theory has been employed to calculate with high accuracy the energy levels and transition probabilities of Cu- to Sr-like gold ions. The many-body calculations were carried out to identify the unassigned blended lines in the 35-40 angstroms region of the low-energy EBIT spectrum of the gold ions. Most of the prominent lines in the 35-40 angstroms region were identified as the emission lines in Sr-like gold.
Date: March 27, 2007
Creator: Vilkas, M J; Ishikawa, Y & Trabert, E
Partner: UNT Libraries Government Documents Department

Observation of hyperfine mixing in measurements of a magnetic octupole decay in isotopically pure nickel-like 129Xe and 132Xe ions

Description: We present measurements of high statistical significance of the rate of the magnetic octupole (M3) decay in nickel-like ions of isotopically pure {sup 129}Xe and {sup 132}Xe. On {sup 132}Xe, an isotope with zero nuclear spin and therefore without hyperfine structure, the lifetime of the metastable level was established as (15.06 {+-} 0.24) ms. On {sup 129}Xe, an additional fast (2.7 {+-} 0.1 ms) decay component was established that represents hyperfine mixing with a level that decays by electric quadrupole (E2) radiation.
Date: December 21, 2006
Creator: Trabert, E; Beiersdorfer, P & Brown, G V
Partner: UNT Libraries Government Documents Department

Relativistic multireference many-body perturbation theory calculations on Au64+ - Au69+ ions

Description: Many-body perturbation theory (MBPT) calculations are an adequate tool for the description of the structure of highly charged multi-electron ions and for the analysis of their spectra. They demonstrate this by way of a re-investigation of n=3, {Delta}n=0 transitions in the EUV spectra of Na-, Mg-, Al-like, and Si-like ions of Au that have been obtained previously by heavy-ion accelerator based beam-foil spectroscopy. They discuss the evidence and propose several revisions on the basis of the multi-reference many-body perturbation theory calculations of Ne- through P-like ions of Au.
Date: March 31, 2006
Creator: Vilkas, M J; Ishikawa, Y & Trabert, E
Partner: UNT Libraries Government Documents Department

Relativistic multireference many-body perturbation theory calculations on F-, Ne-, Na-, Mg-, Al-, Si-, and P-like xenon ions

Description: Many-Body Perturbation Theory (MBPT) has been employed to calculate with high wavelength accuracy the extreme ultraviolet (EUV) spectra of F-like to P-like Xe ions. They discuss the reliability of the new calculations using the example of EUV beam-foil spectra of Xe, in which n = 3, {Delta}n = 0 transitions of Na-, Mg-, Al-like, and Si-like ions have been found to dominate. A further comparison is made with spectra from an electron beam ion trap, that is, from a device with a very different (low density) excitation balance.
Date: December 22, 2005
Creator: Vilkas, M J; Ishikawa, Y & Trabert, E
Partner: UNT Libraries Government Documents Department

Relativistic Multireference Many-body Perturbation Theory for Open-shell Ions with Multiple Valence Shell Electrons: the Transition Rates and Lifetimes of the Excited Levels in Chlorinelike Fe X

Description: A recently developed relatistic multireference many-body perturbation theory based on multireference configuration-interaction wavefunctions as zeroth order wavefunctions is outlined. The perturbation theory employs a general class of configuration-interaction wve functions as reference functions, and thus is applciable to multiple open valence shell systems with near degeneracy of a manifold of strongly interacting configurations. Multireference many-body perturbation calculations are reported for the ground and excited states of chlorine-like Fe X in which the near degeneracy of a manifold of strongly interacting configurations mandates a multireference treatment. Term energies of a total of 83 excited levels arising from the 3s{sup 2}3p{sup 5}, 3s3p{sup 6}, 3s{sup 2}3p{sup 4}3d, 3s3p{sup 5}3d, and 3s{sup 2}3p{sup 3}3d{sup 2} configurations of the ion are evaluated to high accuracy. Transition rates associated with E1/M1/E2/M2/E3 radiative decays and lifetimes of a number of excited levels are calculated and compared with laboratory measurements to critically evaluate recent experiments.
Date: September 30, 2009
Creator: Ishikawa, Y; Santana, J A & Trabert, E
Partner: UNT Libraries Government Documents Department

Relativistic Many-body Moller-Plesset Perturbation Theory Calculations of the Energy Levels and Transition Probabilities in Na- to P-like Xe Ions

Description: Relativistic multireference many-body perturbation theory calculations have been performed on Xe{sup 43+}-Xe{sup 39+} ions, resulting in energy levels, electric dipole transition probabilities, and level lifetimes. The second-order many-body perturbation theory calculation of energy levels included mass shifts, frequency-dependent Breit correction and Lamb shifts. The calculated transition energies and E1 transition rates are used to present synthetic spectra in the extreme ultraviolet range for some of the Xe ions.
Date: March 27, 2007
Creator: Vilkas, M J; Ishikawa, Y & Trabert, E
Partner: UNT Libraries Government Documents Department

Soft-X-ray spectra of highly charged Os, Bi, Th, and U ions in an electron beam ion trap

Description: Systematic variation of the electron-beam energy in an electron-beam ion trap has been employed to produce soft-X-ray spectra of Os, Bi, Th, and U with highest charge states ranging up to Ni-like ions. Guided by relativistic atomic structure calculations, the strongest lines have been identified with {Delta}n = 0 (n = 4 to n' = 4) transitions in Rb- to Cu-like ions. The rather weak 4p-4d transitions are much less affected by QED contributions than the dominant 4s-4p transitions. Our wavelength measurements consequently provide benchmarks with and (almost) without QED. Because the radiative corrections are not very sensitive to the number of electrons in the valence shell, our data, moreover, provide benchmarks for the evaluation of electron-electron interactions.
Date: December 3, 2004
Creator: Trabert, E.; Beiersdorfer, P.; Fournier, K. B. & Chen, M. H.
Partner: UNT Libraries Government Documents Department

Electric-dipole 5s - 5p Transitions in Promethiumlike Ions

Description: The 5s-5p electric-dipole resonance transitions in highly ionized promethiumlike ions have been studied applying relativistic multi-reference Moeller-Plesset second-order perturbation theory. The transition wavelengths are determined to within 0.2 {angstrom} in the more highly charged ions, where the level degeneracies are small. For somewhat lighter ions a very large reference space was used in order to account for the many degeneracies. In order to calculate transition probabilities and lifetimes, correlation corrections have been added to the transition operator in the next order. The contributions from the higher orders of the theory, that is, frequency-dependent Breit correction, Lamb shift, and mass shifts, have been estimated. The results are used to re-assess spectroscopic data from beam-foil, electron beam ion trap, and tokamak observations.
Date: February 29, 2008
Creator: Vilkas, M J; Ishikawa, Y & Trabert, E
Partner: UNT Libraries Government Documents Department

L-Shell Spectroscopy of Au as a Temperature Diagnostic Tool

Description: In order to develop plasma diagnostic for reduced-size hot hohlraums under laser irradiation, they have studied the L-shell emission from highly charged gold ions in the SuperEBIT electron beam ion trap. The resolving power necessary to identify emission features from individual charge states in a picket fence pattern has been estimated, and the observed radiation features have been compared with atomic structure calculations. They find that the strong 3d{sub 5/2} {yields} 2p{sub 3/2} emission features are particularly useful in determining the charge state distribution and average ion charge <Z>, which are strongly sensitive to the electron temperature.
Date: March 27, 2008
Creator: Trabert, E; Hansen, S B; Beiersdorfer, P; Brown, G V; Widmann, K & Chung, H K
Partner: UNT Libraries Government Documents Department

Magnetic-Field Sensitive Line Ratios in EUV and Soft X-ray Spectra

Description: We discovered a class of lines that are sensitive to the strength of the ambient magnetic field, and present a measurement of such a line in Ar IX near 49 {angstrom}. Calculations show that the magnitude of field strengths that can be measured ranges from a few hundred gauss to several tens of kilogauss depending on the particular ion emitting the line.
Date: April 24, 2006
Creator: Beiersdorfer, P; Scofield, J; Brown, G V; Chen, H; Trabert, E & Lepson, J K
Partner: UNT Libraries Government Documents Department

Forbidden line wavelengths and transition probabilities measured using an electron beam ion trap (EBIT)

Description: Several coronal lines posed a long-standing riddle to earth-bound spectroscopists, until - following up on a suggestion by Grotrian (1937) - B. Edlen (1942) confirmed that their wavenumbers indeed corresponded to fine structure intervals in the ground configurations of highly charged ions like Fe X and Fe XI. This in turn caused turmoil in solar physics, because the corona must be much hotter than the underlying chromosphere in order to produce such ions. X-ray and EUV spectra of the sun became available after World War II, by observations from sounding rockets and satellites. These spectra confirmed the presence of the highly charged ions. Laboratory observation of the (electric-dipole) forbidden lines, however, had to wait for the development of low-density plasma discharges like the tokamak fusion experiments, because in regular light sources, collisions would likely quench such long-lived levels. Since then, a fair number of forbidden transitions has been observed in the laboratory, and forbidden lines are being valued for plasma diagnostics. While forbidden transitions in light ions are often found in astrophysical light sources, similar transitions in highly charged heavy ions like Kr will be important for plasma machines like ITER, in which Kr will likely be used for radiative cooling and will therefore also be available for detailed diagnostics.
Date: September 10, 1998
Creator: Beiersdorfer, P.; Gillaspy, J. D.; Serpa, F. G.; Trabert, E. & Utter, S. B.
Partner: UNT Libraries Government Documents Department

Investigation of the 2p3/2-3d5/2 line emission of Au53+ -- Au69+ for diagnosing high energy density plasmas

Description: Measurements of the L-shell emission of highly charged gold ions were made under controlled laboratory conditions using the SuperEBIT electron beam ion trap, allowing detailed spectral observations of lines from ironlike Au{sup 53+} through neonlike Au{sup 69+}. Using atomic data from the Flexible Atomic Code, we have identified strong 3d{sub 5/2} {yields} 2p{sub 3/2} emission features that can be used to diagnose the charge state distribution in high energy density plasmas, such as those found in the laser entrance hole of hot hohlraum radiation sources. We provide collisional-radiative calculations of the average ion charge <Z> as a function of temperature and density, which can be used to relate charge state distributions inferred from 3d{sub 5/2} {yields} 2p{sub 3/2} emission features to plasma conditions, and investigate the effects of plasma density on calculated L-shell Au emission spectra.
Date: January 29, 2008
Creator: Brown, G V; Hansen, S B; Trabert, E; Beiersdorfer, P; Widmann, K; Chen, H et al.
Partner: UNT Libraries Government Documents Department