Digital Commons Network^™

Differential Cross Sections For Ionization Of Water Vapor By High-Velocity Bare Ions And Electrons, J. H. Miller, W. E. Wilson, S. T. Manson, M. Eugene Rudd

M. Eugene Rudd Publications

A semiempirical model of single differential cross sections (SDCS) for ionization of water vapor by fast electrons and bare ions is presented. At low secondary-electron energy, the model is based on an asymptotic expansion of the first Born approximation with coefficients, that are independent of projectile properties, evaluated from experimental photoabsorption and protonimpact ionization data. As the secondary-electron energy increases, the model converges to a binary-encounter approximation. Comparisons with measured differential, total, and dissociative cross sections for ionization of water by fast electrons are used to test the model. For primary electrons with energy greater than about 500 eV, agreement …

Temporary Anion States Of Polyatomic Hydrocarbons, Kenneth D. Jordan, Paul Burrow

Paul Burrow Publications

Contents

I. Introduction

II. Electron Transmission Spectroscopy

A. Background

B. Interpretation of Transmission Data

III. Alkenes, Dienes, and Polyenes

A. Ethylene and Alkyl-Substituted Ethylenes

B. Butadiene, Hexatriene, and Octatetraene

C. Other Conjugated Dienes

D. Cyclooctatetraene

E. Nonconjugated Dienes

IV. Alkynes

A. Acetylene and Alkyl-Substituted Acetylenes

B. Cyclic Acetylenes

C. Butadiyne and 2,4-Hexadiyne

V. Aromatic Systems

A. Benzene and Alkyl-Substituted Benzenes

B. Naphthalene, Anthracene, and Tetracene

C. Styrene and cis- and trans-Stilbene

D. Biphenyls

E. Triptycene, Dibenzonorbornadiene, and Related Compounds

VI. Halogen-Containing Compounds

A. Saturated Compounds

B. Unsaturated Compounds

VII. Conclusions

VIII. Acknowledgment

IX. References

X. Bibliography of Studies …

Positronium Formation From Li And Na Atoms By Use Of Pseudopotential, Sultana N. Nahar, J M. Wadehra

Physics and Astronomy Faculty Research Publications

The differential and total cross sections for the formation of positronium in its ground state from Li and Na atoms by the impact of intermediate-energy positrons are calculated in the first Born and distorted-wave Born approximations. Hellmann-type pseudopotentials are used to represent the alkali-metal ion cores. The difference in the use of pseudopotentials and the static potential for the core representation for evaluating various rearrangement cross sections is discussed.

Thermal And Structural Stability Of Cosputtered Amorphous TaXCu1-X Alloy Thin Films On Gaas, J.E. Oh, John A. Woollam, K.D. Aylesworth, David J. Sellmyer, J.J. Pouch

David Sellmyer Publications

The thermal and chemical stabilities of amorphous-metal diffusion barrier films are of importance in high-temperature semiconductor device applications. The reaction characteristics of the barrier constituents with the surrounding elements as well as the crystallization temperature determine the thermal stability of an amorphous-alloy diffusion barrier. We report that suitable thin films of Ta-Cu have been prepared over a wide range of compositions, by cosputter deposition onto GaAs and fused-quartz substrates. The amorphous nature and crystallization behavior of the films have been monitored by x-ray diffraction and van der Pauw resistivity measurements. Films were found to be amorphous over the range of …

A Criterion For Vortex Breakdown, R. E. Spall, T. B. Gatski, C. E. Grosch

CCPO Publications

A criterion for the onset of vortex breakdown over a wide range of the Reynolds number is proposed. Based upon previous experimental, theoretical, and numerical studies, as well as a new numerical study, an appropriately defined local Rossby number is used to delineate the region where breakdown occurs. Comparisons are made with previously suggested criticality parameters and the unique features of the proposed Rossby number parameter are shown. A number of previous theoretical studies concentrating on inviscid standing‐wave analyses for trailing wing‐tip vortices are reviewed and reinterpreted, along with the previous numerical and experimental studies, in terms of the Rossby …

Errata: First-Principles Theoretical Explanation Of Incommensurate Behavior In Rb2Znc4, V. Katanant, P.J. Edwardson, John Hardy, L. L. Boyer

John R. Hardy Papers

Figures 2(a) and 2(b) of this paper have been inadvertently interchanged; thus, the caption for Fig. 2(a) relates to Fig. 2(b) and the caption for Fig. 2(b) relates to Fig. 2(a).

Exact Evaluation And Recursion Relations Of Two-Center Harmonic Oscillator Matrix Elements, P. J. Drallos, J. M. Wadehra

Physics and Astronomy Faculty Research Publications

Using vibrational wave functions of two relatively displaced harmonic oscillators of arbitrary frequencies, Franck–Condon overlap integrals and matrix elements of x^l, exp(−2cx), and exp(−cx^2) (x is the internuclear separation) are obtained. Useful three‐term, four‐term, and five‐term recursion relations among these matrix elements are derived. It is shown that all of the relevant matrix elements can be obtained from a mere knowledge of the lowest two Franck–Condon overlap integrals. Results are illustrated by computation of Franck–Condon factors for the A ^1∑^+_u –X ^1∑^+_g and the B ^1Π_u –X ^1∑^+_g systems of ^7Li_2.

Search For The S Meson In Antiproton-Proton Interactions, William J. Fickinger, R. Marino, D. K. Robinson

Faculty Scholarship

The interaction between antiprotons and protons has been studied in the range 1910 to 1990 MeV center-of-mass energy in a drift-chamber experiment at the Brookhaven Alternating Gradient Synchrotron. The total cross section has been determined at eleven different incident momenta, and the elastic cross section between 8 and 30 deg in the laboratory has been measured with an energy resolution of about 5 MeV. The cross section for annihilation into charged mesons has also been measured, with the same resolution. There is no evidence in any of these channels for the existence of a narrow resonance.

Polarizing Beam Splitters For Infrared And Millimeter Waves Using Single-Layer-Coated Dielectric Slab Or Unbacked Films, R. M.A. Azzam

Electrical Engineering Faculty Publications

No abstract provided.

Calculation Of Electron Capture Cross Sections Of Collisions Of Be ²⁺ On H, A. E. Wetmore, H. R. Cole, Ronald E. Olson

Physics Faculty Research & Creative Works

Using the perturbed stationary state method, including electron translation factors, the authors have calculated electron capture cross sections for the helium-like ions Be²⁺ and B³⁺ incident on ground-state atomic hydrogen. The molecular structure calculation employs pseudo-potentials to represent the inactive K-shell electrons on the incident ions. The calculated cross sections vary rapidly in the 107 cm s-1 velocity range (E approximately 1 keV amu-1). The calculations show preferential transfer to the Be⁺(2s) and the B²⁺(2p) product states. The calculations for B³⁺+H are in good agreement with experimental measurements of Cradall et al …

Double Electron Transitions In Collisions Between Multiply Charged Ions And Helium Atoms, Ronald E. Olson, A. E. Wetmore, M. L. Mckenzie

Physics Faculty Research & Creative Works

A semiclassical model for He is applied to the study of multiply charged ions colliding with He at intermediate energies. Single and double-electron capture and ionisation and capture-ionisation reactions are studied for incident-ion charge states q=+1 to +50 at 1 MeV amu-1. For charge states q>or approximately=+10, single electron capture is found to be dominated by a two-electron transition in which one electron is captured and the other is ionised.

Negative Ion Drift Velocities In Mixtures Of Methane And Sulphur Hexafluoride, M. C. Cornell, Ian M. Littlewood

Physics Faculty Research & Creative Works

The velocities of negative ions drifting in mixtures of methane and Sulphur hexafluoride have been measured. Measurements were made as a function of gas composition, reduced electric field strength between 3 and 185 Td, and total gas pressure in the range 100-600 Torr at 300K. The data indicate that SF 6- (SF6) ions are the dominant ion in all of the gas mixtures studied. Extrapolation of the data using Blanc's Law was used to determine the velocity of Sulphur hexafluoride ions drifting in pure methane.

Photoconductivity Parameters In Lithium Niobate, Robert Gerson, J. F. Kirchhoff, L. E. Halliburton, D. A. Bryan

Physics Faculty Research & Creative Works

Measurements on a variety of doped (magnesium and/or iron) and undoped lithium niobate crystals in the oxidized state demonstrate an Arrhenius dependence of dark conductivity on reciprocal temperature between 460 and 590 K. All of the crystals had roughly the same conductivity and activation energy (1.21 eV) over the temperature range, implying that all have about the same free-carrier concentration and mobility. The enhanced photoconductivity of magnesium-doped lithium niobate is attributed to a greatly reduced trapping cross section of Fe³⁺ for electrons, the smaller cross section being due to a changed substitutional site for Fe³⁺. The Fe …

Magnetic Relaxation In Fe-(Sio2) Granular Films, Gang Xiao, Sy_Hwang Liou, A. Levy, J.N. Taylor, C. L. Chien

Sy-Hwang Liou Publications

Magnetic relaxation of granular Fe-(SiO₂) solids with low metal-volume fraction has been studied by employing dc SQUID (superconducting quantum interference device) magnetometry and Mössbauer spectroscopy with the characteristic measuring time differing by nine orders of magnitude. The blocking temperatures (T_B), extrapolated to zero external field as measured by the two techniques maintain a constant ratio of 0.35 independent of samples. Arrhenius law was found adequate in describing the relaxation process, with a well-defined relaxation-time constant of τ₀≃10^-13 sec. A cusp in the susceptibility is observed at T_B, below which irreversible difference …

Photorefraction In Batio3, Stephen Ducharme

Stephen Ducharme Publications

This thesis summarizes the results of experimental investigations of the photorefractive properties of melt-grown BaTiO₃ single crystals. Three basic photorefractive material properties are studied: (1) the effective density of photorefractive charges, (2) the photoconductivity of the photorefractive charges, and (3) the relative contributions of electron and hole photoconduction. Volume holographic measurement techniques are used: two-beam energy coupling, four-wave mixing, and erasure of volume holograms. The photorefractive properties were altered experimentally by chemically reducing or oxidizing a BaTiO₃ crystal. I have extended the “hopping conduction” model of photorefractive transport to include simultaneous electron and hole photoconduction. The extension of …

Determination Of Phenomenological Optical Model Parameters For Neutrons On 208Pb From 4 To 150 Mev, Randy L. Schutt

Masters Theses

Phenomenological o p tic a l model parameters for neutrons incident on ²⁰⁸Pb have been determined for neutron energies from 4 to 150 MeV using the code SNOOPY-8. Neutron total cross sections from 4 to 150 MeV and angular distributions for elastic scattering from 13.5 to 40.0 MeV were utilized. Analyses of total and differential cross sections were performed at a number of energies to determine energy dependent expressions for the real strengths of the central potential, imaginary surface potential, and imaginary volume potential. These energy dependent expressions for V, W_d, and W_S were found to …

The Fricke Dosimeter As A 1-Hit Detector, Robert Katz, G. L. Sinclair, M. P. R. Waligorski

Robert Katz Publications

A fit to the experimental data for the response of the Fricke dosimeter to energetic heavy ions is obtained using a calculation of the relative effectiveness of a 1-hit detector, from track theory. We use 2 fitted parameters, the target size, a₀, which may be thought to represent a “diffusion length,” and E₀, the dose of gamma-rays at which there is an average of one hit per target (the D-37 dose), and a new algorithm for the average radial distribution of dose in liquid water from the passing ion. The G value for ions is then …

The Radial Distribution Of Dose Around The Path Of A Heavy Ion In Liquid Water, M. P. R. Waligorski, R. N. Hamm, Robert Katz

Robert Katz Publications

Monte Carlo calculations of the radial distribution of dose in liquid water, incorporating energy deposition due to primary excitations and ionizations, have been performed for protons of energy 1, 10, 20, 50, and 100 MeV. By combining these results with earlier semi-empirical formulae used in track structure theory calculations, a corrected analytic formulation has been developed which on radial integration closely reproduces the value of stopping power for protons in the energy range 0.1–1000 MeV. After including a β-dependent ‘effective charge’ formula, this corrected formulation is tested against all published measurements of radial distribution of dose from energetic ions in …

Beyond The Rigid-Ion Approximation With Spherically Symmetric Ions, L. L. Boyer, M. J. Mehl, J. L. Feldman, John R. Hardy, J. W. Flocken, C. Y. Fong

John R. Hardy Papers

In our recent Letter we introduced an ab initio model for spherically symmetric charge relaxation of ions in a crystal, called potential-induced breathing (PIB), and demonstrated its importance in the calculation of elastic constants. We also investigated the splitting of the longitudinal optic (LO) and transverse optic (TO) mode frequencies, which results from the macroscopic field associated with longitudinal modes. In the discussion immediately before and after Eq. (5) we argued, incorrectly, that the only contributions to the LO-TO splitting from PIB were from terms involving S_k, the derivative of the self-energy of the kth ion with …

Thin-Film Beam Splitter That Reflects Light As A Half-Wave Retarder And Transmits It Without Change Of Polarization: Application To A Michelson Interferometer, R. M.A. Azzam

Electrical Engineering Faculty Publications

The refractive index n₁ of a transparent layer of quarter-wave optical thickness coating a transparent substrate of refractive index n₂ can be chosen to produce half-wave retardation (HWR) in reflection and no change of polarization in refraction at any angle of incidence ø. The function n₁(ø, n₂), and the associated polarization-independent reflectance of the film-substrate system R(ø, n₂) are determined. Such a coated surface can be used as a beam splitter with excellent characteristics (e.g., split fractions that do not depend on source polarization, a split beam whose polarization is identical …

Equilibrium Properties Of Short Field-Reversed Configurations, Ross L. Spencer, M. Tuszewski

Faculty Publications

Some features of short field-reversed configuration (FRC) equilibria relevant to transport and stability are studied numerically and analytically. It is shown that magnetic field curvature effects significantly increase the FRC magnetization for plasma elongations epsilon is less than or equal to 4.

Two-Step Stabilization Of Autoionizing States, J. Greg Story, Linn D. Van Woerkom, William E. Cooke

Physics Faculty Research & Creative Works

A two-step process using internal conversion and fluorescence to stabilize the 6P_3/211d autoionizing state of barium has been observed. The internal conversion produces very highly excited autoionizing Rydberg states, which then emit fluorescence to produce singly excited, bound states. Inclusion of this process should bring calculations closer to agreement with recent measurements of dielectronic recombination.

Experimental Test Of Higher-Order Electron-Capture Processes In Collisions Of Fast Protons With Atomic Hydrogen, Hans G. Vogt, Reinhold S. Schuch, Edson L B Justiniano, Michael Schulz, W. Schwab

Physics Faculty Research & Creative Works

We present measurements of the angular distribution of fast hydrogen atoms formed by electron capture of 2.8- and 5.0-MeV protons in atomic hydrogen. In the angular region of the Thomas peak (0.47 mrad) the experimental results obtained with this pure three-body collision system are in reasonable agreement with a strong-potential Born calculation and the impulse approximation, but not with other higher-order theories.

First-Principles Theoretical Explanation Of Incommensurate Behavior In Rbznc4, V. Katkanant, P. J. Edwardson, John R. Hardy, L. L. Boyer

John R. Hardy Papers

We have carried out an ab initio theoretical study of the potential energy and molecular dynamics of Rb₂ZnCl₄. These calculations demonstrate that the incommensurate transition in this compound is caused by the relaxation of imperfect-hexagonal spirals of highly unstable ZnCl₄^2- ions. This leads to angstrom-size displacements with essentially zero energy change. We argue that such "latent" (or imperfect) symmetry could be the general cause of incommensurate transitions in insulators.

Asymmetry In The Magnetoconductance Of Metal Wires And Loops, A. D. Benoit, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb

Faculty Publications

Universal conductance fluctuations in wires and Aharonov-Bohm oscillations in loops are not symmetric about H=0. The observation of asymmetry in the periodic oscillations is possible when the phase-coherence length of the wave function is comparable to the separation of the voltage probes. In both cases, four-probe measurements yield resistances which depend on lead configuration. The asymmetries appear like Hall voltages, and are consistent with Onsager's relations.

Multicritical Points In An Ising Random-Field Model, Miron Kaufman, Philip E. Klunzinger, A. Khurana

Physics Faculty Publications

The phase diagram of the mean-field Ising model in a random field obeying a symmetric three-peak distribution is determined. This distribution is relevant to diluted antiferromagnets in a uniform magnetic field. The phase diagram includes a fourth-order point, tricritical points, ordered critical points, critical end points, and a double critical end point. An ordered phase persists for arbitrarily large random fields at low temperatures.

Semiconducting/Semi-Insulating Reversibility In Bulk Gaas, David C. Look, Phil W. Yu, W. M. Theis, W. Ford, G. Mathur, J. R. Sizelove, D. H. Lee, S. S. Li

Physics Faculty Publications

Bulk, liquid-encapsulated Czochralski GaAs may be reversibly changed from semiconducting (ρ~1 Ω cm) to semi-insulating (ρ~10⁷ Ω cm) by slow or fast cooling, respectively, following a 5 h, 950°C soak in an evacuated quartz ampoule. This effect has been studied by temperature-dependent Han-effect, photoluminescence, infrared absorption, mass spectroscopy, and deep level transient spectroscopy measurements. Except for boron, the samples are very pure, with carbon and silicon concentrations less than 3 X 10¹⁴ cm^-3. Donor and acceptor concentrations, on the other hand, are in the mid 10¹⁵ cm^-3 range, which means …

Semiconducting/Semi-Insulating Reversibility In Bulk Gaas, David C. Look, Phil W. Yu, W. M. Theis, W. Ford, G. Mathur, J. R. Sizelove, D. H. Lee, S. S. Li

Physics Faculty Publications

Bulk, liquid‐encapsulated Czochralski GaAs may be reversibly changed from semiconducting (ρ∼1 Ω cm) to semi‐insulating (ρ∼10⁷ Ω cm) by slow or fast cooling, respectively, following a 5 h, 950 °C soak in an evacuated quartz ampoule. This effect has been studied by temperature‐dependent Hall‐effect, photoluminescence, infrared absorption, mass spectroscopy, and deep level transient spectroscopy measurements. Except for boron, the samples are very pure, with carbon and silicon concentrations less than 3×10¹⁴ cm⁻³. Donor and acceptor concentrations, on the other hand, are in the mid 10¹⁵ cm⁻³ range, which means that …

Effects Of Second Sound On Acoustic Trasmission At The Solid-Liquid 4He Interface, Matthew J. Moelter, M. B. Manning, C. Elbaum

Physics

We have calculated the reflection and transmission coefficients of acoustic waves propagating across a solid-liquid interface of ⁴He, using an extension of the treatment of Castaing and Nozières in which we include pressure changes associated with second sound. These calculations account well for the experimental results obtained over the temperature range 0.83 K≤ T ≤1.46 K and provide an alternative explanation to the one we offered previously for the lack of agreement between experiment and the theory of Castaing and Nozières.

Measurement Of The Lifetime Of The Metastable 5d3/226d3/2, J=0 Autoionizing State Of Barium, Linn D. Van Woerkom, J. Greg Story, William E. Cooke

Physics Faculty Research & Creative Works

We report a measurement of the lifetime of the metastable 5d_3/226d_3/2, J=0 autoionizing state of barium. We have determined the lifetime to be 190(10) ns.