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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

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

Static magnetic ordering of CeCu/sub 2. 1/Si/sub 2/ found by muon spin relaxation

Description: Zero- and longitudinal-field muon spin relaxation measurements on a poly-crystal sample of a heavy-fermion superconductor CeCu/sub 2.1/Si/sub 2/ (T/sub c/ = 0.7 K) have revealed an onset of static magnetic ordering below T )approximately) 0.8 K. The line shapes of the observed spectra in zero field indicate a wide distribution of static random local fields at muon sites, suggesting that the ordering is either spin glass or incommensurate spin-density-wave state. The observed width of the random local field at T = 0.05 K corresponds to a small averaged static moment of the order of 0.1 ..mu../sub B/ per formula unit.
Date: January 1, 1988
Creator: Uemura, Y.J.; Kossler, W.J.; Yu, X.H.; Schone, H.E.; Kempton, J.R.; Stronach, C.E. et al.
Partner: UNT Libraries Government Documents Department

Tests of quantum electrodynamics in few-electron very high-Z ions

Description: This article discusses our measurement of the Lamb shift in heliumlike uranium and outlines future tests of QED using few- electron very high atomic number (Z) ions. Our recently reported Lamb shift value of 70.4 (8.1) eV for the one- electron Lamb shift in uranium is in agreement with the theoretical value of 75.3 (0.4) eV. The experimental value was extracted from a beam-foil time-of-flight measurement of the 54.4 (3.3) ps lifetime of the 1s2p/sub 1/2/ /sup 3/P/sub 0/ state of heliumlike uranium. 24 refs., 5 figs., 1 tab.
Date: August 1, 1986
Creator: Gould, H. & Munger, C.T.
Partner: UNT Libraries Government Documents Department

Considerations for the use of synchrotron radiation sources to measure sub-keV x-ray photoabsorption cross sections in transmission

Description: Sub-keV x-ray photoabsorption cross section measurements in transmission have been made using synchrotron radiation beam lines on the VUV storage ring at the National Synchrotron Light Source (NSLS) and on the SPEAR storage ring at Stanford. The experimental considerations associated with making absolute measurements are reviewed, along with techniques for resolving difficulties. Suggestions for future measurements are included.
Date: February 1, 1988
Creator: Tirsell, K.G. & Del Grande, N.K.
Partner: UNT Libraries Government Documents Department

Radiative transition probabilities for the B /sup 1/PI - X /sup 1/SIGMA/sup +/ and B /sup 1/PI - A /sup 1/SIGMA/sup +/ of /sup 7/LiH

Description: The recently reported (J. Chem. Phys. 66, 5412 (1977)) hybrid potential curves for the X /sup 1/..sigma../sup +/ and A /sup 1/..sigma../sup +/ states of LiH and the herein reported hybrid potential curve for the B /sup 1/Pi state of LiH are combined with the ab initio transition moments of Docken and Hinze (J. Chem. Phys. 57, 4936 (1972)) to calculate radiative transition probabilities between all B /sup 1/Pi (v' less than or equal to 2) and all X /sup 1/..sigma../sup +/ (v'' less than or equal to 23) and A /sup 1/..sigma../sup +/ (v'' less than or equal to 26) vibrational levels of /sup 7/LiH. The strongest single emission band found is the B /sup 1/Pi (v' = 2) ..-->.. X /sup 1/..sigma../sup +/ (v'' = 23) band between the highest ''long-range'' levels in each potential. For all B /sup 1/Pi levels, the emission is dominated by B ..-->.. X rather than B ..-->.. A emission.
Date: January 1, 1978
Creator: Zemke, W.T.; Way, K.R. & Stwalley, W.C.
Partner: UNT Libraries Government Documents Department

Nonlinear materials for frequency conversion

Description: Two figures of merit, the threshold power (P/sub th/) and the limiting volume (V/sub min/) can be used to compare the relative efficiency and economy of new harmonic generating crystals. The properties of barium metaborate and L-Arginine phosphate are used to illustrate the effect of nonlinearity, birefringence, and damage threshold on these figures of merit.
Date: March 22, 1988
Creator: Velsko, S.P. & Eimerl, D.
Partner: UNT Libraries Government Documents Department

Two-photon (VUV + visible) resonance ionization spectroscopy of molecular hydrogen

Description: Two-photon transitions have been examined in molecular hydrogen using coherent vacuum ultraviolet (VUV) photons at a fixed wavelength of 118 nm and a tunable photon from a dye laser. Though the VUV intensity is very weak (/approximately/100 nJ per pulse) it was utilized very efficiently since most VUV photons in the ionoization region were absorbed. This is the first time that coherent VUV light has been employed with tunable visible light for the production of two-photon spectra and the measurement of two-photon rates. A new parameter is proposed for direct comparison of the data from various two-photon experiments. 4 refs., 2 figs., 1 tab.
Date: April 1, 1988
Creator: McCann, M.P.; Chen, C.H. & Payne, M.G.
Partner: UNT Libraries Government Documents Department