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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

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

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

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

Silicon photodiode characterization from 1 eV to 10 keV

Description: Silicon photodiodes offer a number of advantages over conventional photocathode type soft x-ray detectors in pulsed power experiments. These include a nominally flat response, insensitivity to surface contamination, low voltage biasing requirements, sensitivity to low energy photons, excellent detector to detector response reproducibility, and ability to operate in poor vacuum or gas backfilled experiments. Silicon photodiodes available from International Radiation Detectors (IRD), Torrance, California have been characterized for absolute photon response from 1 eV to 10 keV photon energy, time response, and signal saturation levels. The authors have assembled individually filtered photodiodes into an array designated the XUV-7. The XUV-7 provides seven photodiodes in a vacuum leak tight, electrically isolated, low noise, high bandwidth, x-ray filtered assembly in a compact package with a 3.7 cm outside diameter. In addition they have assembled the diodes in other custom configurations as detectors for spectrometers. Their calibration measurements show factor of ten deviations from the silicon photodiode theoretical flat response due to diode sensitivity outside the center `sensitive area`. Detector response reproducibility between diodes appears to be better than 5%. Time response measurements show a 10-90% rise time of about 0.1 nanoseconds and a fall time of about 0.5 nanoseconds. Silicon photodiodes have proven to be a versatile and useful complement to the standard photocathode detectors for soft x-ray measurement and are very competitive with diamond for a number of applications.
Date: October 1, 1997
Creator: Idzorek, G.C. & Bartlett, R.J.
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

Spectroscopic Characterization of Post-Cluster Argon Plasmas During the Blast Wave Expansion

Description: In this work we present temperature diagnostics of an expanding laser-produced argon plasma. A short-pulse (35fs) laser with an intensity of I = 10{sup 17}W/cm{sup 2} deposits {approx} 100 mJ of energy into argon clusters. This generates a hot plasma filament that develops into a cylindrically expanding shock. We develop spectral diagnostics for the temperatures of the argon plasma in the shock region and the preionized region ahead of the shock. A collisional-radiative model is applied to explore line intensity ratios derived from Ar II - Ar IV spectra that are sensitive to temperatures in a few eV range. The results of hydrodynamic simulations are employed to derive a time dependent radiative transport calculation that generates the theoretical emission spectra from the expanding plasma.
Date: May 30, 2002
Creator: Ching, H,-K.; Fournier, K.B.; Edwards, M.J.; Scott, H.A.; Cattolica, R.; Ditmire, T. et al.
Partner: UNT Libraries Government Documents Department

Element-specific soft x-ray magneto-optic rotation studies of magnetic films and multilayers

Description: Tunable multilayer linear polarizers extend magneto-optic rotation techniques that directly sense polarization changes into the 50--1,000 eV range. The resonant response at atomic core levels yields element-specific magnetic signals that can be much larger than the analogous signal in the visible. A tunable multilayer polarimeter is described, and examples of its use in early Kerr rotation hysteresis studies of Fe films and Fe/Cr multilayers are given.
Date: May 1, 1996
Creator: Kortright, J.B. & Rice, M.
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

Calculation of resonance self shielding in $sup 239$Pu

Description: The 2000-group TART code and the ENDL cross section library were used to calculate the fissions as a function of depth in the flat Pu plate experiment of Czirr and Bramblett (Nucl. Sci. Eng., fissions with the Pu target in to the number with the target out; secondary fissions in the target do not contribute. Results from experiment and Monte Carlo calculations are given for thicknesses from 0.06 to 3.13 g/cm/sup 2/ in nine energy groups from 2.15 eV to 10 keV. It was found that the TART 2000-group structure was it adequate since vast increases in the number of groups did not change the results. Where the total and fission cross section data are well known, the calculations and experiment were in reasonably good agreement. The only region of disagreement was in the unresolved resonance region above 300 eV. (11 figures, 1 table) (RWR)
Date: January 15, 1974
Creator: Plechaty, E. F. & Cullen, D. E.
Partner: UNT Libraries Government Documents Department

Theoretical research on charge exchange of uranum ions at thermal energies

Description: The cross section for resonant charge transfer in U$sup +$-U collisions is calculated as a function of the energy in the center-of-mass coordinate frame. The computed value decreases monotonically from approximately 300 A$sup 2$ at 0.025 eV to 100 A$sup 2$ at 50 eV. The latter value would be appropriate for ions of energy 100 eV moving through a gas of neutral atoms at thermal velocities. (auth)
Date: January 1, 1975
Creator: Bardsley, J N
Partner: UNT Libraries Government Documents Department

Spectra of $gamma$-rays from capture of 2 eV to 9 x 10$sup 4$ eV neutrons by $sup 181$Ta

Description: Using new experimental techniques, the spectra of $gamma$-rays from the capture of neutrons by $sup 181$Ta were measured at the Livermore 100-MeV linac for neutrons from 2 eV to 9 x 10$sup 4$ eV with a (Ge(Li)-NaI) three-crystal spectrometer. Individual primary $gamma$-ray lines were resolved to 1778-keV excitation in $sup 182$Ta. Neutron resonances were resolved to 200-eV neutron energy. Data analysis techniques and codes were developed to extract positions and intensities of resolved transitions from the large data matrices accumulated in this experiment. Techniques were developed to unfold the unresolved $gamma$- ray spectra using the simple response of the three-crystal spectrometer. The resolved transition data were used to place 110 states with spin and parity assignments in the $sup 182$Ta level diagram below 1780-keV excitation. A set of 1240 E1 transition strengths were analyzed to extract 1.38 +- 0.11 degrees of freedom for the most likely chisquared fit to the distribution of widths. The E1 strength function was extracted for E/sub gamma/ = 4 to 6 MeV and compared with previous results. The $gamma$-ray spectra for E/sub gamma/ = 1.5 to 6.1 MeV were unfolded for neutron energy groups between 20 and 9 x 10$sup 4$ eV. Below 5-MeV $gamma$-ray energy no dependence of the spectral shape on neutron energy was observed. (30 figures, 4 tables) (auth)
Date: April 30, 1976
Creator: Stelts, M.L.
Partner: UNT Libraries Government Documents Department