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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

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

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

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

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

Davydov solutions at 300 kelvin: The final search

Description: The original proposal by Professor A.S. Davydov of a soliton mechanism for localization and transport of energy along linear chain molecules provided the impetus for several research efforts which have explored the properties of these nonlinear entities in differing degrees of realism. The general conclusion from all of this work is that the nonlinear equations of motion which have been used to describe these systems have soliton-like solutions when they are solved in the deterministic limit. This limit corresponds to the absolute zero of temperature, because it ignores the influence of random thermal perturbations on the system. However, the questions of existence and importance of the Davydov soliton remain controversial when non-zero temperature effects are taken into account, because numerical simulations and theoretical calculations done by independent research groups have reached diametrically opposed conclusions. Our 1985 paper was the first to simulate thermal perturbations at biologically relevant temperature (300 K). Since publishing that paper, we have done simulations for collisions of phonon wave packets with Davydov solitons and have also taken into account the presence of multiple quanta of the high frequency oscillator field in the Davydov equations of motion. We present these results here. However, for the major question about the temperature effects on the Davydov soliton, our conclusions remain unchanged. 5 refs., 6 figs., 1 tab.
Date: January 1, 1989
Creator: Lomdahl, P.S. & Kerr, W.C.
Partner: UNT Libraries Government Documents Department

Laser-based diagnostics for density, temperature, velocity, and dissociation fraction in high temperature hydrogen flows

Description: This paper is essentially a review of the current state of the art in hydrogen atom and hydrogen molecule diagnostics. This paper contains some of our own results and ideas along with results from many other laboratories. This is not intended to be an exhaustive review; instead it summarizes some techniques which we believe are ideally suited as diagnostics for high temperature hydrogen which are of paramount importance for the Space Exploration Initiative (SEI). 31 refs., 1 fig.
Date: January 1, 1991
Creator: Sappey, A.D. & Funk, D.J.
Partner: UNT Libraries Government Documents Department

Determining desorption pre-exponential factors from temperature-programmed desorption spectra when the surface is nonuniform

Description: To find desorption pre-exponential factors from temperature-programmed desorption (TPD) spectra, we develop procedures using both the TPD spectra and their derivatives. First, an approximate method is derived using peak temperatures. This method is formally identical with one used for determining pre-exponential factors and desorption activation energies when desorptions are energetically uniform. The method can be used when the pre-exponential factor is constant. We next develop an iterative process that also uses peak temperatures, and again is usable when the pre-exponential factor is constant. This iterative approach should give more exact values of pre-exponential factors than the approximate approach. Using the first derivatives of TPD spectra over the entire range of temperatures leads to a second iterative process. This last procedure allows determination of energy-dependent pre-exponential factors. 8 refs., 13 figs.
Date: March 15, 1991
Creator: Brown, L.F. & Chemburkar, R.M.
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

Inverse problems SVD and pseudo SVD

Description: Physical experiments often gives rise to integral equations of the first kind. If the detection equipment can be adjusted that fact can lead to a kernel function that depends on one or more parameters. We address the general question of how to choose those parameters in such a way as to make the integral operator as well-conditioned as possible, thus optimizing the experiment. Attention is focused on the condition number of the discretized kernel and on its principal singular vector. Several examples are given and some preliminary general results are obtained.
Date: January 1, 1990
Creator: Faber, V.; Wing, G.M. & Zahrt, J.
Partner: UNT Libraries Government Documents Department

Collective vector method for calculation of E1 moments in atomic transition arrays

Description: The CV (collective vector) method for calculating E1 moments for a transition array is described and applied in two cases, herein denoted Z26A and Z26B, pertaining to two different configurations of iron VI. The basic idea of the method is to create a CV from each of the parent (''initial state'') state-vectors of the transition array by application of the E1 operator. The moments of each of these CV's, referred to the parent energy, are then the rigorous moments for that parent, requiring no state decomposition of the manifold of daughter state-vectors. Since, in cases of practical interest, the daughter manifold can be orders of magnitude larger in size than the parent manifold, this makes possible the calculation of many moments higher than the second in situations hitherto unattainable via standard methods. The combination of the moments of all the parents, with proper statistical weighting, then yields the transition array moments from which the transition strength distribution can be derived by various procedures. We describe two of these procedures: (1) The well-known GC (Gram-Charlier) expansion in terms of Hermite polynomials, (2) The Lanczos algorithm or Stieltjes imaging method, also called herein the delta expansion. Application is made in the cases of Z26A (50 lines) and Z26B (5523 lines) and the relative merits and shortcomings of the two procedures are discussed. 10 refs., 15 figs., 2 tabs.
Date: October 1, 1985
Creator: Bloom, S.D. & Goldberg, A.
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

Electronic properties of Ar and Xe under pressure

Description: A simple model for calculating ground- and excited-state properties of molecular and rare-gas crystals is presented. The electrons are considered to be tightly bound to their molecular or atomic sites and the effects of the crystal potential, calculated with local-density functionals, are treated as a perturbation of the molecules or atoms. Results for Ar to 500 kbar show that the ground-state atoms compress as the pressure is increased and that there is a gradual increase in exciton energies. Preliminary results on ground-state Xe to 1.5 Mbar show that, to about 1 Mbar, the electronic distributions of the Xe atoms compress, but beyond that there is a slight expansion.
Date: January 1, 1983
Creator: LeSar, R.
Partner: UNT Libraries Government Documents Department

High-resolution absorption spectrum of the 6/sup 1/S/sub 0/. -->. 6/sup 3/P/sub 1/ transition in mercury with a cw dye laser. Revision 1

Description: Using a stabilized single-frequency commercial dye laser and an external cavity doubling crystal, we have measured the isotope shifts of mercury for the 6/sup 1/S/sub 0/ ..-->.. 6/sup 3/P/sub 1/ transition with an accuracy of 4 MHz. We describe the method for generating single-frequency light at 2537 A and compare the results of our measurements of the isotope shifts with previous work. 4 refs., 1 fig., 1 tab.
Date: January 1, 1985
Creator: Crane, J.K.; Erbert, G.V.; Mostek, S.D.; Kerlin, R.C. & Paisner, J.A.
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

H/degree/ temperature and density measurements in a Penning surface-plasma H/sup minus/ ion source

Description: Using vacuum ultraviolet laser-absorption spectroscopy, the H/degree/ density and temperature are measured as a function of discharge current and H/sub 2/-gas flow in both the plasma column and the drift region between the plasma column and the emitter in the 4X source. For typical source operating parameters, the atom temperature is 1.5 eV in the plasma column and 0.6 eV in the drift region; the atom density, 7 /times/ 10/sup 14/ cm/sup /minus/3/ in the plasma column and 4 /times/ 10/sup 14/ cm/sup /minus/3/ in the drift region. Separate measurements give 2% for the ratio of H/sub 2/ molecules in the first vibrational level to the total H/sub 2/ density. 8 refs., 6 figs., 1 tab.
Date: January 1, 1989
Creator: Smith, H.V. Jr.; Allison, P.; Pitcher, E.J.; Stevens, R.R. Jr.; Worth, G.T.; Stutzin, G.C. et al.
Partner: UNT Libraries Government Documents Department

Quenching of Einstein's A-coefficients by photons

Description: We present evidence for the quenching of Einstein A-coefficients in an Ar-ion laser discharge due to the presence of a high intensity laser flux. The reduction in spontaneous emission intensity when lasing occurs was found to be dependent on the Einstein A-coefficient for transitions originating from the same upper level. 9 refs., 3 figs.
Date: May 1, 1989
Creator: Aumayr, F.; Hung, J. & Suckewer, S.
Partner: UNT Libraries Government Documents Department

Quenching of Einstein A-Coefficients in plasmas and lasers

Description: The coefficient of spontaneous emission (Einstein A-coefficient) is considered to be one of the basic constants of a given transition in atom or ion. The formula for the Einstein A-coefficient was derived in the pioneering works of Weisskopf and Wigner (WW) based on Dirac's theory of light. More recently, however, it was noted in several papers that the rate of spontaneous radiative decay can deviate significantly from the WW expression in certain conditions, for example in a laser cavity. A different type of change in A- coefficients was inferred from measurements of changes in the intensity branching ratio of spectral lines in a plasma. A change of branching ratio of up to a factor of 10 was observed in CIV for 3p-3s (580.1--581.2nm) and 3p-2s (31.2-nm) transitions when the electron density changed from approximately N{sub e} {approx} 1 {times} 10{sup 18} to 5 {times} 10{sup 18} cm{sup {minus}3}. This effect was also observed in CIII and NV. An initial theoretical approach to the problem based on the integration of the Schroedinger equation with the ion Coulomb potential modified by the electron cloud within the Debye radius was unsuccessfully in predicting the experimental observations. The effect of quenching of spontaneous emission coefficients was observed also in an Ar-ion laser as a function of the intracavity power density (photon density) for lines originating from the same upper level as the lasing line. Measurements of these line profiles absorption for different lasing conditions and related discussions are also presented. 14 refs., 6 figs.
Date: March 1, 1991
Creator: Suckewer, S. (Princeton Univ., NJ (USA). Plasma Physics Lab. Princeton Univ., NJ (USA). Dept. of Mechanical and Aerospace Engineering)
Partner: UNT Libraries Government Documents Department

Quenching of Einstein-coefficients by photons

Description: Experimental evidence is presented for the change of Einstein's A- coefficients for spontaneous transitions from the upper laser level of argon ion laser discharge due to the presence of the high- intensity laser flux. To demonstrate that this quenching effect cannot be attributed to a reduction in self-absorption of the strong spontaneous emission line, absorption and line profile measurements have been performed. Computer modelling of the reduction of self absorption due to Rabi splitting also indicated that this effect is too small to explain the observed quenching of spontaneous line emissions. 13 refs., 11 figs.
Date: March 1, 1991
Creator: Aumayr, F. (Technische Univ., Vienna (Austria). Inst. fuer Allgemeine Physik); Lee, W.; Skinner, C.H. & Suckewer, S. (Princeton Univ., NJ (USA). Plasma Physics Lab.)
Partner: UNT Libraries Government Documents Department

Very high resolution saturation spectroscopy of lutetium isotopes via c-w single-frequency laser resonance ionization mass spectrometry

Description: In this paper, we discuss the use of Resonance Ionization Mass Spectrometry (RIMS) to perform isotopically selective saturation spectroscopy of lutetium isotopes. Utilizing this technique, it is shown that accurate measurements of the relative frequencies of hyperfine (HF) components for different isotopes easily can be made without the need for an isotopically enriched sample. The precision with which the HF splitting constants can be determined is estimated to be approx.5 times greater than in previous work.
Date: January 1, 1987
Creator: Fearey, B.L.; Parent, D.C.; Keller, R.A. & Miller, C.M.
Partner: UNT Libraries Government Documents Department