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Self-energies and the interactions of particles with surfaces

Description: We have in this paper reviewed the method of treating many-body problems by means of an effective interaction self-energy. We have developed an alternatvie approach to the self-energy which is simpler and more straight-forward than standard methods, and we have illustrated its use with two examples of a charge interacting with a metal surface. In each case the self-energy produces the classical image potential together with corrections due to quantum mechanical effects. This method has also been successfully applied to the problem of an atom interacting with a surface. Corrections to the Van der Waals dispersion force are obtained, and via the non-conservative imaginary parts to /summation//sub i/(z) we discuss transition rates and energy exchange. 14 refs., 1 fig.
Date: January 1, 1987
Creator: Manson, J.R.; Ritchie, R.H.; Echenique, P.M. & Gras-Marti, A.
Partner: UNT Libraries Government Documents Department

The Los Alamos bright sources: Review of the physics and the diagnostic technology

Description: The investigation of many interesting physical phenomena in nature requires the generation of high-energy-density fields. To produce energy densities exceeding 10/sup 7/ J/cm/sup 3/ requires focusing a very powerful, very bright, short pulse laser. This talk will present a review of the physics that will be investigated with one such laser system, will describe the laser used, will describe the laser diagnostics, and will describe the physics diagnostics. The talk will emphasize the areas of research that will help the diagnostics of different aspects of these bright sources, and their interactions, especially the diagnostics of hot small volumes in picosecond time scales. 15 refs., 7 figs.
Date: January 1, 1989
Creator: Kyrala, G.A.; Schappert, G.T.; Jones, L.A.; Lee, P.H.Y.; Casperson, D.E.; Cobble, J.A. et al.
Partner: UNT Libraries Government Documents Department

The optical properties of beryllium

Description: We review the published data on the optical properties of beryllium for the spectral region from 0.03 to 300 eV. In the visible and infrared spectral regions, where published data from various authors show very large variations, we have performed experiments that identify the most probable sources of error, and use this information to select the best data from published sources. The effects of surface oxide overlayers have also been studied. In the far infrared spectral region, where only normal incidence reflectance data are available, and in the extreme ultraviolet, where only transmission data are available, there is insufficient information to fully determine the optical properties at each photon energy. Between 0.06 and 26 eV, however, a normal incidence reflectance curve is fully determined. This curve has been used for a Kramers{endash}Kronig analysis to determine the optical properties in this spectral range. 10 refs., 13 figs., 3 tabs.
Date: February 1, 1990
Creator: Arakawa, E.T. (Oak Ridge National Lab., TN (USA)); Callcott, T.A. & Chang, Yun-ching (Oak Ridge National Lab., TN (USA) Tennessee Univ., Knoxville, TN (USA). Dept. of Physics)
Partner: UNT Libraries Government Documents Department

Calculation of emission and absorption spectra of LTE plasma by the STA (Super Transition Array) method

Description: Recent improvements in the Super Transition Array (STA) method for calculating Bound-Bound (BB) and Bound-Free (BF) emission and absorption spectra for LTE plasma are described and illustrated. The method accounts for all possible BB and BF radiative transitions in the plasma. Full detailed first order quantum relativistic treatment is used for calculating transition energies and probabilities. The enormous number of configurations are divided into sets of superconfigurations comprised of a collection of energetically grouped configurations. The contribution of the transition array between two superconfigurations to a specific one-electron transition is then represented by a Gaussian whose moments are calculated accurately using a technique that bypasses the necessity of direct summation over all the levels involved. The calculation of these moments involves the populations of the configurations given by their statistical weights and the Boltzmann factor. For each configuration within the super configuration we use zeroeth order energies in the Boltzmann factor corrected by a super configuration averaged first order term. The structure of the spectrum is increasingly revealed by splitting each STA into a number of smaller STAs. When the spectrum converges it describes the detailed UTA' structure, where each configuration-to-configuration array is represented by a separate Gaussian with first order energy in the Boltzmann factor. Convergence is reached with only a few thousand STAs, at most, which makes the calculations practical. It should be pointed out that in this treatment the STA moments are obtained by summing over all level-to-level transitions, rather than configuration-to-configuration average transitions. 4 refs., 9 figs.
Date: January 11, 1991
Creator: Bar-Shalon, A.; Oreg, J. (Israel Atomic Energy Commission, Beersheba (Israel). Nuclear Research Center-Negev) & Goldstein, W.H. (Lawrence Livermore National Lab., CA (USA))
Partner: UNT Libraries Government Documents Department

Symposium commemorating the 25th anniversary of elements 99 and 100. [Lawrence Berkeley Lab. , January 23, 1978]

Description: Separate abstracts were prepared for five of the contributions to this symposium. The four remaining ones have already been cited in ERA and may be located by reference as the entry CONF-780134-- in the Report Number Index. (RWR)
Date: April 1, 1979
Creator: Seaborg, G.T. & Webb, C. (eds.)
Partner: UNT Libraries Government Documents Department

Depolarization due to the resonance tail during a fast resonance jump

Description: The mechanism of depolarization due to a fast resonance jump is studied. The dominant effect for cases of interest is not dependent on the rate of passage through resonance, but rather on the size of the resonance jump as compared to the width, epsilon, of the resonance. The results are applied to a calculation of depolarization in the AGS at Brookhaven National Laboratory.
Date: January 1, 1980
Creator: Ruth, R D
Partner: UNT Libraries Government Documents Department

Systematics of energy levels and other properties of highly charged ions

Description: Our knowledge of energy levels and other properties of highly charged ions is often required to interpret the complex phenomena which occurs in collisions of these highly charged ions. In this paper we report on our initial efforts to understand the systematics of the properties of highly charged ions. This effort is based on the use of (relatively) simple central-field calculations, which, as shall be shown, are surprisingly accurate for highly charged ions. We stress the point of view that diverse observable data can be represented in terms of a small set of key numerical parameters (e.g., phase shifts, oscillator strength densities, and amplitudes at the nucleus). The variation of such parameters from one ion species to another lends itself to easy and instructive mapping using realistic atomic models. By mapping these parameters throughout the periodic system and for all ionic charges, one can establish trends that will form a reliable basis for predicting unmeasured properties of ions. In addition, this survey is useful for establishing to what extent such well-known spectral features as Cooper zeros and shape resonances, so important in neutral atoms, control the spectral behavior of ions. 14 refs., 3 figs.
Date: January 1, 1986
Creator: Manson, S. T.; Inokuti, M. & Theodosiou, C. E.
Partner: UNT Libraries Government Documents Department

Atomic spectrum of neptunium. [Tables]

Description: A description and interpretation of the atomic spectrum of neptunium are given. Wavelengths were measured for 6096 spectrum lines in the range 3793 to 38,812 cm/sup -1/ (26,353 to 2575 A), of which 2526 were classified as transitions between 329 odd levels and 130 even levels of neutral neptunium (Np I). The data are presented in five tables.
Date: May 1, 1976
Creator: Fred, M.; Tomkins, F. S.; Blaise, J. E.; Camus, P. & Verges, J.
Partner: UNT Libraries Government Documents Department

Many-electron effects in photoelectron spectroscopy. [Deviations from Koopman's one-electron model, satellite structure, configuration interaction, mechanisms]

Description: The deviations from Koopmans' one-electron model of photoionization which lead to satellite structure in the photoelectron spectrum are examined within the formalism of configuration interaction (CI). The mechanisms which contribute to satellite intensity may be classified as continuum state configuration interaction, final ionic state configuration interaction, and initial state configuration interaction. The discussion centers around the last two mechanisms, these being the prime contributors to the satellite intensity well above threshold. Specific examples of theoretical ''spectra'' are presented for the F(1s) region of HF and the 1s region of neon. The agreement between theory and experiment is found to be excellent. In these two instances, initial state configuration interaction contributions increase the satellite intensity and are of nearly equal importance to the final ionic state mixing.
Date: June 1, 1976
Creator: Martin, R. L.
Partner: UNT Libraries Government Documents Department

Multiphoton spectroscopy in heavy elements

Description: Some recently discovered regularities in the spectra of heavy elements which are also applicable to the analysis of the spectra of lighter atoms are described. It is pointed out that stepwise resonant multiphoton methods are irreplaceable tools in the study of high lying states in a complex atomic system. Systematic applications of these methods has permitted regularities to be observed which also hold for the lighter elements. It is noted that greatly increased understanding of the excited state structure of heavy atoms is not possible. 8 references. (JFP)
Date: May 3, 1977
Creator: Solarz, R. W.; Paisner, J. A. & Worden, E. F.
Partner: UNT Libraries Government Documents Department

High resolution autoionization spectra in atomic uranium

Description: High resolution (less than or equal to .5 cm/sup -1/) autoionization spectra of atomic uranium has been observed from newly identified odd parity levels between 32,660 and 34,165 cm/sup -1/. Photoionization cross sections are presented.
Date: November 17, 1975
Creator: Paisner, J. A.; Solarz, R. W.; Carlson, L. R.; May, C. A. & Johnson, S. A.
Partner: UNT Libraries Government Documents Department

Equation of state of dense argon; a comparison of shock and static studies. [R]

Description: In the present paper we report new diamond anvil cell (DAC) measurements for room temperature solid argon to 800 kbars. This isotherm is in excellent agreement with one predicted from a theoretical analysis of shockwave data. These results are important for several reasons. First they demonstrate agreement between shock and static techniques even in cases where shock temperatures are extremely high and a large thermal correction is required to reduce the Hugoniot to an isotherm. Secondly the results suggest that solid argon may provide a useful pressure standard up to 3 Mbar. 12 refs., 3 figs.
Date: July 1, 1985
Creator: Ross, M.; Mao, H.K.; Bell, P.M. & Xu, J.A.
Partner: UNT Libraries Government Documents Department

Correlation in photodetachment

Description: Electron correlation plays a major role in all aspects of the photodetachment of an electron from a negative ion. Photodetachment measurements are well suited to investigate the relatively short range forces associated with correlation due to the absence of the long range Coulomb interaction. Measurements of electron affinities, asymmetry parameters and cross sections are described to illustrate the influence of correlation on photodetachment. 25 refs., 4 figs.
Date: January 1, 1991
Creator: Pegg, D.J. (Oak Ridge National Lab., TN (USA) Tennessee Univ., Knoxville, TN (USA). Dept. of Physics)
Partner: UNT Libraries Government Documents Department

Absolute wavelength measurement and fine structure determination in /sup 7/Li II

Description: The energy levels of two-electron atoms continue to provide rigorous tests of relativistic quantum theory, and of correlation effects within a multi-particle system. These interactions are determined perturbatively, with several approximations, and theoretical results often differ. It is critical to provide precise measurements of absolute wavelengths connecting these atomic energy levels to obtain a resolution of the precision of the different parts of such complex calculations. In this work, we report a high precision optical measurements in the 1s2s /sup 3/S - 1s2p /sup 3/P multiplet of Li II using fast-beam laser spectroscopy. A collinear interaction using both parallel and antiparallel laser and ion beams allows both for precise elimination of large Doppler shifts, and for a strong kinematic narrowing of the observed resonances, as compared with thermal beam experiments. The wavelengths of the observed resonance fluorescence radiation are determined by comparing them with simultaneously recorded saturated absorption profiles of molecular iodine hyperfine components. In turn, the absolute wavelengths of the iodine lines are obtained from precisely calibrated Fabry-Perot etalon fringes in a separate experiment. The final precision of the Li II wavelengths is 5 parts in 10/sup 9/, which is at a level of precision of 80 ppM of the QED corrections in the transition. 3 refs., 1 figs., 1 tab.
Date: January 1, 1985
Creator: Riis, E.; Berry, H.G.; Poulsen, O.; Lee, S.A. & Tang, S.Y.
Partner: UNT Libraries Government Documents Department

High resolution krypton M/sub 4,5/ x-ray emission spectra

Description: High resolution M/sub 4,5/ (3d ..-->.. 4p) x-ray emission spectra from a krypton plasma were measured using a recently developed grazing-incidence reflection-grating monochromator/spectrometer with very high flux rates at extreme ultraviolet and soft x-ray wave lengths. The nominal resolving power of the instrument, E/..delta..E, is about 300 in this energy range (approx.80 eV). Three dipole-allowed 3d ..-->.. 4p emission lines were observed at 80.98 eV, 80.35 eV and 79.73 eV. A broad peak at about 82.3 eV is tentatively assigned to transitions resulting from Kr/sup 2 +/, and effects of excitation energy on M/sub 4,5/ x-ray emission were observed. 9 refs., 3 figs., 1 tab.
Date: October 1, 1987
Creator: Perera, R.C.C.; Hettrick, M.C. & Lindle, D.W.
Partner: UNT Libraries Government Documents Department

Lattice dynamics of the heavy Fermion compound UBe/sub 13/

Description: UBe/sub 3/ has unusual electronic and magnetic properties due to a narrow band of U 5f states near the Fermi energy. We have used EXAFS to compare the interatomic forces in UBe/sub 13/ with those in ThBe/sub 13/, which has the same structure but no 5f electrons. From measurements made over the range 10 to 308 K, we have determined the temperature dependences of the mean square relative displacements (MSRD's) for the first actinide-beryllium and actinide-actinide shells in each material. The MSRD's for the corresponding shells in the two compounds were found to be quite similar. The thermal motion of the nearest-neighbor actinide-actinide pairs is shown to be due entirely to a single Einstein mode, the square of whose frequency is proportional to the actinide-Be force constant. We conclude that the presence or absence of 5f electrons on the actinide has very little effect on the actinide-beryllium bonding. 9 refs., 5 figs.
Date: January 1, 1986
Creator: Tranquada, J.M.; Heald, S.M.; Pick, M.A.; Fisk, Z. & Smith, J.L.
Partner: UNT Libraries Government Documents Department

Third-harmonic generation and multiphoton ionization spectroscopy

Description: Nonlinear phenomena, such as multiphoton excitation (MPE) processes leading to ionization and third-harmonic generation (THG) in gases have become the issue of extensive studies over recent years. Studies in rare gases in particular have resulted in several interesting observations in this respect. Thus, it has been established that three-photon resonantly enhanced multiphoton ionization (MPI) in the vicinity of states which are single photon optically coupled to the ground state may occur in efficient competition with THG. The present work demonstrates several new effects which may appear when third-harmonic radiation is present during MPI.
Date: January 1, 1987
Creator: Fotakis, C.; Stockdale, J.A.D. & Proctor, M.J.
Partner: UNT Libraries Government Documents Department

Slow positron study of positronium formation and diffusion in crystalline and amorphous ice

Description: The aim of the present work has been to study the interaction of low energy positrons and of Ps with a molecular solid. As a first example we have chosen ice which has been extensively investigated both by conventional positron annihilation methods as well as by many other techniques. Unlike in metals, positrons injected into most molecular solids may have a certain probability to form Ps in the bulk of the material. The process by which Ps is formed in condensed molecular materials has been a matter of strong debate. According to the Ore model of Ps formation, which is recognized as being valid for low density gases, the positron during its slowing down picks off an electron from a molecule with which it simultaneously forms Ps. For energies below E/sub L/ = I-6.8 eV, where I is the lowest ionisation energy and 6.8 eV is the Ps binding energy in vacuum, this process is not energetically possible. Above an energy E/sub u/ approx. I the model predicts a reduction of the yield of stable Ps, because of rapid slowing down of the positron by ionisation or by splitting up again of a Ps atom which may have been formed. The energy range E/sub L/ less than or equal to E approximately less than E/sub u/ is the so-called Ore gap in gases. In the present work both crystalline and amorphous ice have been studied using positrons of energies in the range 0 to 4.5 keV. The experimental methods used were determination of the yields of 3..gamma..-annihilations as well as Doppler broadening measurements in the temperature range 45 to 150 K. The main results obtained were a determination of the Ps diffusion constant, and a demonstration that in the present experiments one contribution to the total Ps yield comes from ...
Date: October 1, 1984
Creator: Lynn, K.G.; Eldrup, M.; Vehanen, A. & Schultz, P.J.
Partner: UNT Libraries Government Documents Department

Experiments on few-electron very high-Z ions

Description: The measurement of the Lamb shift in heliumlike uranium and outlines future experimental tests of QED using few-electron very high atomic number (Z) ions are presented. A discussion of the possibility of using ultrarelativistic atomic collisions to produce very heavy leptons is also presented. 38 refs., 4 figs., 1 tab.
Date: July 1, 1986
Creator: Gould, H. & Munger, C.
Partner: UNT Libraries Government Documents Department

Photoionization and photorecombination cross sections of non-hydrogenic states in plasmas

Description: We use Hartree-Slater self-consistent-field wave functions to compute photoionization and photorecombination cross sections and rates for partially ionized iron atoms, both in their isolated state and in a plasma environnment. The calculated cross sections are fitted to analytic expressions so that the photoionization and recombination rates can be given in closed forms. Our analytic representation satisfy the requirement that the oscillator-strength sums S/sub 0/, S/sub 1/, and S/sub 2/ must converge.
Date: September 1, 1986
Creator: Rozsnyai, B.F. & Jacobs, V.L.
Partner: UNT Libraries Government Documents Department

Recoil saturation of the self-energy in atomic systems

Description: Within the framework of the general self-energy problem for the interaction of a projectile with a many-body system, we consider the dispersion force between two atoms or between a charge and an atom. Since the Born-Oppenheimer approximation is not made, this is a useful approach for exhibiting non-adiabatic effects. We find compact expressions in terms of matrix elements of operators in the atomic displacement which are not limited by multipole expansions. 7 refs.
Date: January 1, 1988
Creator: Manson, J.R. & Ritchie, R.H.
Partner: UNT Libraries Government Documents Department

Atlas of uranium emission intensities in a hollow cathode discharge

Description: The uranium emission spectrum from a hollow cathode discharge is displayed from 11,000 to 26,000 cm/sup -1/. This atlas lists 4928 spectral lines of uranium; 3949 are classified to the neutral spectrum and 431 are classified to the singly ionized spectrum. Listed wavenumbers are accurate to +-0.003 cm/sup -1/ and the listed relative intensities to +-8%. The richness of the spectrum makes this atlas useful for wavenumber calibration of lasers, spectrographs, and monochromators to an accuracy of 1 part in 10/sup 7/. This atlas is also useful as a guide to the uranium spectrum, and relative oscillator strengths (gf values) can be calculated from the intensities to a precision of +-20%.
Date: July 1, 1980
Creator: Palmer, B.A.; Keller, R.A. & Engleman, R. Jr.
Partner: UNT Libraries Government Documents Department