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Physics with bottled antiprotons

Description: The same beam cooling techniques that has allowed for high luminosity antiproton experiments at high energy also provides the opportunity for experiments at ultra-low energy. Through a series of deceleration stages, antiprotons collected and cooled at the peak momentum for production can be made available at thermal or sub-thermal energies. In particular, the Los Alamos collaboration is developing an RFQ-pulsed ion trap beam line for the antiproton gravitational mass experiment (PS200) at LEAR that will provide beams of antiprotons in the energy range 0.001 to 1000.0 eV. Antiprotons at these energies make these fundamental particles available for experiments in condensed matter and atomic physics. The recent speculation that antiprotons may form metastable states in some forms of normal matter could open many new avenues of basic and applied research. 5 refs.
Date: January 1, 1986
Creator: Hynes, M.V. & Campbell, L.C.
Partner: UNT Libraries Government Documents Department

Surface and adsorbate structural studies by photoemission in the h. nu. = 50-500 eV range

Description: The present status of photoelectron spectroscopy in the 50-500 eV range is discussed in relation to its application to surface science. Instrumentation aspects of synchrotron radiation sources are reviewed. The direct transition model is shown to be applicable in this range with some limitations. Cooper minima and adsorbate sensitivity enhancement for h..nu.. > 100 eV are reviewed. A new effect--condensed phase photoelectron asymmetry--is noted. Finally, photoelectron diffraction - another new effect - is described and evaluated.
Date: August 1, 1979
Creator: Shirley, D.A.
Partner: UNT Libraries Government Documents Department

Indirect processes in electron-impact ionization of multiply-charged ions

Description: Recent research efforts have assembled a steadily increasing array of measurements and calculations of electron impact ionization of multiply-charged ions. Significant disagreement is often found, however, between experimental results and theory due to the influence of a number of indirect processes observed in the experiments but not included in the calculations. Some of the most important of these indirect ionization processes are described and examples are discussed. New data for electron impact single-ionization of Kr/sup 2 +/ are presented in the energy range from below threshold (36 eV) to 1500 eV, and compared to related measurements and to theory.
Date: January 1, 1984
Creator: Gregory, D.C.
Partner: UNT Libraries Government Documents Department

Progress in Beam Focusing and Compression for Target Heating and Warm Dense Matter Experiments

Description: The Heavy-Ion Fusion Sciences Virtual National Laboratory is pursuing an approach to target heating experiments in the warm dense matter regime, using space-charge-dominated ion beams that are simultaneously longitudinally bunched and transversely focused. Longitudinal beam compression by large factors has been demonstrated in the Neutralized Drift Compression Experiment (NDCX) with controlled ramps and forced neutralization. Using an injected 30 mA K{sup +} ion beam with initial kinetic energy 0.3 MeV, axial compression leading to {approx}50X current amplification and simultaneous radial focusing to a few mm have led to encouraging energy deposition approaching the intensities required for eV-range target heating experiments. We discuss the status of several improvements to NDCX to reach the necessary higher beam intensities, including: beam diagnostics, greater axial compression via a longer velocity ramp; and plasma injection improvements to establish a plasma density always greater than the beam density, expected to be > 10{sup 13} cm{sup -3}.
Date: April 17, 2009
Creator: Seidl, Peter; Anders, A.; Bieniosek, F.M.; Barnard, J.J.; Cohen, R.H.; Coleman, J.E. et al.
Partner: UNT Libraries Government Documents Department

TART calculations using the new 2021 energy group cross section library compared with B. Czirr's resonance self-shielding experiments

Description: Results from calculations using a 2021-energy-group cross section library with sufficient energy definition in the lower energy range to resolve the known resorances in /sup 239/Pu and /sup 235/U are compared with flat-plate resorance self-shielding experimental data. The results are somewhat ambiguous. The lower energy ranges appear to agree better with experimental data for small areal densities, but disagree more as the areal density increases. (20 figures) (RWR)
Date: November 13, 1973
Creator: Bacon, L.
Partner: UNT Libraries Government Documents Department

A Preliminary Report on X-Ray Photoabsorption Coefficients andAtomic Scattering Factors for 92 Elements in the 10-10,000 eVRegion

Description: Based on currently available photoabsorption measurements and recent theoretical calculations by Doolen and Liberman (Physica Scripta 36, 77 (1987)), a revised (from ADNDT 27, 1 (1982)) best-fit determination of the photoabsorption cross sections is presented here for the elements Z=1 to Z=92 in the 10-10,000 eV range. The photoabsorption data used include those described in the Lockheed and DOE listings of research abstracts for the past ten years and those which have been recently added to the comprehensive NBS Measured Data Base (NBSIR 86-3461, Hubbell et al.). The best-fit curves are compared with both the compilation of measurements and the calculations by Doolen and Liberman. Using the photoabsorption curves, the atomic scattering factors have been calculated for the energy range 50-10,000 eV and are also presented in this report.
Date: November 1, 1988
Creator: Henke, B.L.; Davis, J.C.; Gullikson, E.M. & Perera, R.C.C.
Partner: UNT Libraries Government Documents Department

Statistical properties of the S-wave resonances of {sup 235}U

Description: The resonance parameters of {sup 235}U in the energy range 0 eV to 2.25 keV were obtained from a generalized least squares analysis of a large set of experimental data using the Reich-Moore formalism in the fitting code SAMMY. The aim of the present paper is to present the statistical properties of the s-wave resonance parameters generated from this study.
Date: June 1, 1997
Creator: Leal, L.C.; Derrien, H. & Larson, N.M.
Partner: UNT Libraries Government Documents Department

Neutron total and capture cross section measurements and resonance parameter analysis of tungsten from 0.01 eV to 200 eV

Description: Natural tungsten metal was measured using neutron time-of-flight spectroscopy at the Rensselaer Polytechnic Institute (RPI) Gaerttner Laboratory linear accelerator to determine the tungsten resonance parameters. Three separate measurements were performed: transmission, capture, and self-indication. Previous measurements did not employ all three experiment types and used less sophisticated methods. The current work improves on the published tungsten data base and reduces resonance parameter uncertainties.
Date: June 15, 1998
Creator: Werner, C.J.; Block, R.C.; Slovacek, R.E.; Overberg, M.E.; Moretti, B.E.; Burke, J.A. et al.
Partner: UNT Libraries Government Documents Department

Reactions of ions with atomic and molecular free radicals. Progress report, May 1, 1979-April 30, 1980

Description: A very detailed study of the microscopic dynamics of the reaction D/sub 2//sup +/ + F(/sup 2/p) ..-->.. FD/sup +/ + D, over the range of relative kinetic energy from 0.001 eV to 25 eV is reported. At very low collision energy, the total reaction cross section is governed by long-range forces - principally the charge-quadrupole interaction, which favors reactions on PI-type potential energy surfaces in the covalent interaction region. At high collision energies, a clear transition to reactions on a strongly repulsive potential energy surface is observed. The change in reaction dynamics is evident from the shape of the energy dependence of the total reaction cross section, and from a shift in the product angular distribution from 0/sup 0/ toward 180/sup 0/ in the center-of-mass coordinate system.
Date: January 1, 1980
Creator: Gentry, W.R.
Partner: UNT Libraries Government Documents Department

Dynamics of nonreactive inelastic ion--molecule collisions

Description: Thesis. A tandem electrostatic energy analyzer molecular beam apparatus was built for studying low energy inelastic 180 deg scattering of alkali ions from molecules. A beam of essentially monoenergetic ions is produced by a first analyzer and is focused on the center of a scattering cell containing essentially stationary molecules. Ions which are not significantly deflected in their laboratory motion after collisions with the molecules are energy analyzed with a second analyzer.'Ine scattered beam intensity detected at a particular final laboratory energy is attributable to collisions resulting in a distinct amount of inelasticity. The Na/sup +/ H/sub 2/, HD, D/sub 2/ scattering was studied in the relative energy range of 0.74 to 30. eV. The Na/sup +/ -- D/sub 2/ system shows predominantly vibrationally elastic scattering below 8 eV relative energy. Above 8 eV the most probable inelasticity observed increases monotonically with the initial collision energy and is comparable to excitation to higher vibrational levels. At 17 eV this inelasticity is 3.92 eV. Classical trajectory calculations are used to study the contribution of different collision orientations to the scattering spectra. It is found that collisions in which the projectile approaches the molecule along the bisector of its bond yield the most significant contribution to the backscattering spectra. It is shown that all backscattering can be accounted for by considering only zero impact parameter collisions. The results of trajectory calculations using a dumbbell repulsive ion molecule interaction potential on collisions restricted to zero impact parameter are fit to the experimental data. Through the discrepancies in the fit it is found that the ratio of the stiffness of the interaction potential along the collinear axis to that in the molecular bisector plane is greater than that ratio for the dumbbell potential. (auth)
Date: August 1, 1973
Creator: Dimpfl, W.L.
Partner: UNT Libraries Government Documents Department

Developing a 500-eV proton beam

Description: Tests have been carried out which indicate that H- intensity limitations in lamb-shift polarized ion sources result from large diveregence in the 500-eV H+ ion beam. Intensity limitations due to other effects are not yet measurable.
Date: January 1, 1983
Creator: Chamberlin, E.P.; Benage, J.F. Jr. & Williams, H.E.
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

New neutron capture and transmission measurements for {sup 134,136}Ba at ORELA and their impact on s-process nucleosynthesis calculations

Description: We have made high-resolution neutron capture and transmission measurements on isotopically enriched samples of {sup 134}Ba and {sup 136}Ba at the Oak Ridge Electron Linear Accelerator (ORELA) in the energy range from 20 eV to 500 keV. Previous measurements had a lower energy limit of 3 - 5 keV, which is too high to determine accurately the Maxwellian-averaged capture cross section at the low temperatures (kT {approx} 6 - 12 keV) favored by the most recent stellar models of the {ital s}-process. Our results for the astrophysical reaction rates are in good agreement with the most recent previous measurement at the classical {ital s}-process temperature, kT = 30 keV, but show significant differences at lower 40 temperatures. We discuss the astrophysical implications of these differences.
Date: October 1, 1996
Creator: Koehler, P.E.; Spencer, R.R.; Winters, R.R.; Guber, K.H.; Harvey, J.A.; Hill, N.W. et al.
Partner: UNT Libraries Government Documents Department

Final report for the Sept. 1997 - Jan. 2000 period of Contract No. DE-FG02-97ER54445. Fundamental science of high-density fluorocarbon plasmas

Description: This report describes the results obtained during the two and a half years of work on the contract ''Fundamental Science of High-Density Fluorocarbon Plasmas.'' This program established critical elements of the scientific knowledge base of high-density fluorocarbon plasmas used for SiO{sub 2} patterning. To this end the authors characterized the species that exist in the gas phase and the processes that occur at relevant surfaces in contact with the plasma using complementary diagnostic instrumentation for plasma and surface characterization at two universities. By moving diagnostics from one university to the other, the full spectrum of diagnostics was applied to a single plasma reactor and fluorocarbon plasma etching process. The results of these measurements were correlated with data obtained when patterning SiO{sub 2} using identical conditions. In parallel, a reactive beam scattering system was employed to establish the consequences of the interaction of mass- and energy-resolved low-energy (20 to 300 eV) ions with SiO{sub 2} and resist surfaces.
Date: February 1, 2001
Creator: Oehrlein, G.S.; Anderson, H.M. & Cecchi, J.L.
Partner: UNT Libraries Government Documents Department

Beam Compression in Heavy-Ion Induction Linacs

Description: The Heavy-Ion Fusion Sciences Virtual National Laboratory is pursuing an approach to target heating experiments in the Warm Dense Matter regime, using space-charge-dominated ion beams that are simultaneously longitudinally bunched and transversely focused. Longitudinal beam compression by large factors has been demonstrated in the LBNL Neutralized Drift Compression Experiment (NDCX) experiment with controlled ramps and forced neutralization. The achieved peak beam current and energy can be used in experiments to heat targets and create warm dense matter. Using an injected 30 mA K{sup +} ion beam with initial kinetic energy 0.3 MeV, axial compression leading to {approx}50x current amplification and simultaneous radial focusing to beam radii of a few mm have led to encouraging energy deposition approaching the intensities required for eV-range target heating experiments. We discuss experiments that are under development to reach the necessary higher beam intensities and the associated beam diagnostics.
Date: January 1, 2009
Creator: Seidl, P.A.; Anders, A.; Bieniosek, F.M.; Barnard, J.J.; Calanog, J.; Chen, A.X. et al.
Partner: UNT Libraries Government Documents Department

DOPPLER BROADENING OF THE TOTAL, FISSION, CAPTURE, AND SCATTERING NEUTRON CROSS SECTIONS OF Pu-241

Description: ABS>The cross sections were calculated by the Reich-Moore multilevel formula from 0.02 to 11 ev and were convoluted with Doppler functions corresponding to various sample temperatures. The cross sections are tabulated vs neutron energy for temperatures of 27, 500, 1000, 2000, and 3000 deg C. (D.C.W.)
Date: December 16, 1963
Creator: Marshall, N.H. & Simpson, O.D.
Partner: UNT Libraries Government Documents Department

High-resolution neutron capture and transmission measurements and the stellar neutron capture cross sections of {sup 116,120}Sn

Description: Improved astrophysical reaction rates for {sup 116,120}Sn(n, {gamma}) are of interest because nucleosynthesis models have not been able to reproduce the observed abundances in this mass region. For example, previous s-process calculations have consistently underproduced the s-only isotope {sup 116}Sn. Also, these studies have resulted in residual reprocess abundances for the tin isotopes which are systematically larger than predicted by reprocess calculations. It has been suggested that these problems could be solved by reducing the solar tin abundance by 10-20%, but there is no experimental evidence to justify this renormalization. Instead, it is possible that the problem lies in the (n,T) cross sections used in the reaction network calculations or in the s-process models. One reason to suspect the (n, {gamma}) data is that previous measurements did not extend to low enough energies to determine accurately the Maxwellian-averaged capture cross sections at the low temperatures (kT=6-8 keV) favored by the most recent stellar models of the s process. Also, the two most recent high-precision measurements of the {sup 120}Sn(n, {gamma}) cross section are in serious disagreement. Because of its small size, this cross section could affect (via the s-process branching at {sup 121}Sn) the relative abundances of the three s-only isotopes of Te.
Date: June 1, 1997
Creator: Koehler, P.E.; Spencer, R.R. & Guber, K.H.
Partner: UNT Libraries Government Documents Department