Digital Commons Network^™

Ionization Of H And He+ By Electrons And Positrons Colliding At Near-Threshold Energies, A. E. Wetmore, Ronald E. Olson

Physics Faculty Research & Creative Works

Ionization cross sections for the four combinations of electrons and positrons on H and He+ have been calculated at energies near the threshold for ionization using the classical trajectory Monte Carlo method. In addition, charge-exchange (positronium formation) cross sections have been calculated for the positron-impact collisions. The ionization cross sections compare well with the predictions of the Wannier and Klar models and experimental observations. Our results indicate that the Wannier-type threshold behavior may extend to higher energies than was previously thought. In addition, we have calculated two of the collision parameters, the angle and the relative separation between the escaping …

Static And Dynamic Properties Of Polystyrene In Good Solvents: Ethylbenzene And Tetrahydrofuran, K. Venkataswamy, Alexander M. Jamieson, Rolfe G. Petschek

Faculty Scholarship

We report static and dynamic light scattering studies of polystyrenes of narrow molecular weight distribution in ethylbenzene (EtPh) and tetrahydrofuran (THF) as solvents. These experiments generate values for z-average radius of gyration, (Rg)₂, weight-average second osmotic virial coefficient, A₂, z-average translational diffusion coefficients, (Dt)z, and hence the diffusion virial coefficients, kD, and the z-average of the inverse frictional radius, 〈Rf-1〉z. The results show that while for a specific molecular weight the 〈Rg〉z values in THF are similar to our experimental values in ethylbenzene and to literature values in benzene or toluene, the A2 values, as well as hydrodynamic radii, are …

Angular And Energy Dependence Of Cross Sections For Ejection Of Electrons From Water Vapor. I. 50-2000-Ev Electron Impact, M. A. Bolorizadeh, M. Eugene Rudd

M. Eugene Rudd Publications

We have measured the angular and energy distribution of the absolute cross sections for ejection of electrons from water vapor by electrons incident at 50-2000 eV. The angular range was 15° to 150° and the range of secondary electron energies was from 2 eV to an energy equal to the primary energy minus the first ionization potential. Electron energies were analyzed with a parallel-plate electrostatic analyzer with a resolution of 1.1%. Generally good agreement is obtained with the data of Opal et al. [J. Chem. Phys. 55, 4100 (1971)l at 500 eV except at the extremes of their angular range. …

Fock-Tani Transformation And A First-Order Theory Of Charge Transfer, P. C. Ojha, M. D. Girardeau, J. D. Gilbert, Jack C. Straton

Physics Faculty Publications and Presentations

A unitary (Fock-Tani) transformation of the second-quantized Hamiltonian breaks the interaction into its component parts, e.g., elastic scattering, inelastic scattering, rearrangement interaction, etc. The interaction for a particular process is ‘‘weaker’’ than the overall interaction; this is reflected in certain orthogonality corrections which appear in a perturbation expansion of the T-matrix element. As a result, the internuclear potential makes a negligible contribution of order m_e/m_p to the first-order amplitude for charge transfer. We find very good agreement with experimental and the best available theoretical results for the total cross section for the reaction p+H(1s)→H(1s)+p for …

The Homodyne Interferometer And Its Use In Finding The Optical Properties Of Graphite, Steven Randle Frey

Masters Theses

"An interferometer based on the principle of homodyning can be used to measure the reflectance of solid samples at microwave frequencies. These measurements provide the low frequency values needed for a Kramers-Kronig analysis. This analysis yields the complex dielectric function, e₁⁺ ie₂, and complex index of refraction, n + ik, of the solid. 2 This interferometer was tested on a pressed pellet sample of powdered Dixon 200-10 graphite and yielded satisfactory results. Also investigated were two different methods of signal modulation: mechanical chopping and a rotating wire grid polarizer" Abstract, p. ii

Nonadiabatic Theory Of Fine-Structure Branching Cross Sections For Na-He, Na-Ne, And Na-Ar Optical Collisions, Linda L. Vahala, P. S. Julienne, Mark D. Havey

Electrical & Computer Engineering Faculty Publications

The nonadiabatic close-coupled theory of atomic collisions in a radiation field is generalized to include electron spin and is used to consider the weak-field Na–rare-gas (RG) optical collision Na(²S_1/2)+RG+nhν μNa(²P_j)+RG+(n-1)hν. The effects of detuning and incident energy on the branching into the atomic Na 3p²P_3/2 and 3p²P_1/2 states are examined. The cross sections σ(j) are found to have a strong asymmetry between red and blue detuning as well as a complex threshold and resonance structure dependence on energy. A partial cross-section analysis …

Structural And Topological Contributions To The Electronic Properties Of Inhomogeneous Media (Fractal, Electrode, Impedance), Michael Kramer

Dissertations, Theses, and Capstone Projects

Recent theoretical developments in the theory of inhomogeneous media have enabled Physicists to explore various properties of random composites. We demonstrate how these techniques can be applied to the treatment of electrochemical systems, specifically porous structures. A Random Network Model is introduced to represent the porous electrode immersed in electrolyte, and using numerical simulation the a.c. impedance behavior of the system is explored. We explore how various compositional and structural parameters contribute to the electrical properties of the system. The topology of our model is analyzed, and the effect of fractal structures on impedance behavior is considered. To examine the …

A Study Of Electron-Ion And Ion-Ion Recombination In Atmospheric Gas Discharges, Michael Corbin Cornell

Doctoral Dissertations

"In separate experiments, the electron-ion recombination rate, Y_ei, has been measured in CO₂ and in mixtures of He, CO₂, and N₂; and the ion-ion recombination rate, Y_ii, has been measured in SF6 and in mixtures of SF₆ and CH₄. The rate constant was determined by analyzing the rising edge of the discharge current pulse. Measurements were made as functions of reduced electric field strength, gas pressure, and gas composition.

In the electron-ion recombination study, Y_ei in CO₂ and in mixtures containing N₂ and CO_{2 …}

Total Refraction At Oblique Incidence By A Transparent Bilayer Coating On A High-Index Transparent Or Absorbing Substrate, R. M.A. Azzam, Karim Javily

Electrical Engineering Faculty Publications

Transparent bilayer coatings that produce total refraction (TR) of obliquely incident monochromatic light into an underlying substrate are considered. When the substrate is transparent, it is shown that TR takes place without any accompanying change of polarization. Totally refracting bilayers are realizable in the IR where high-refractive-index substrates are available. This is illustrated by a BaF₂–ZnSe bilayer on a Ge substrate at a 10.6-μm (CO₂-laser) wavelength and 45° angle of incidence. Limited changes of the angle of incidence, wavelength, and refractive indices and thicknesses of the two films of the bilayer are introduced, and their effects …

Polarization Asymmetry In The Photodisintegration Of The Deuteron, M. P. De Pascale, G. Giordano, G. Matone, D. Babusci, R. Bernabei, Oleksa-Myron Bilaniuk, L. Casano, S. D'Angelo, M. Mattioli, P. Picozza, D. Prosperi, C. Schaerf, S. Frullani, B. Girolami

Physics & Astronomy Faculty Works

The reaction ²(γ,p)n has been studied using a monochromatic and polarized gamma ray beam at energies E(γ)=19.8, 29.0, 38.6, and 60.8 MeV. The beam of an intensity ∼4×10⁵ γ/sec was obtained by Compton back scattering of mode-locked laser light off electron bunches in the Adone storage ring. Photoneutron yields were measured at nine neutron angles thetan≃15, 30, 45, 60, 90, 120, 135, 150, and 165 deg in the center of mass (c.m.) for E(γ)=19.8, 29.0, and 38.6 MeV, and at thetan≃30, 60, 90, 120, and 150 deg c.m. for E(γ)=60.8 MeV. The polarization independent component Iₒ(theta) of the differential cross …

Direct Memory Acquisition Of Fast Analog Signals, Syed Javaid Iqbal

Masters Theses

A fast data transfer computer circuit is developed using the direct memory acquisition (DMAC) technique. For this purpose Z-80 microcomputer ·chips, manufactured by Ziolog, were used. The direct memory acquisition circuitry was developed in several stages and required both hardware and software development. An erasable programmable read only memory (EPROM) programmer was built for reading and loading the system program. The design, construction, and testing of the DMAC system are discussed in detail and an example of the use of this system for collecting data is given.

(E,2e) Spectroscopic Investigations Of The Spectral Momentum Densities Of Thin Carbon Films, John Robert Dennison

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

An (e,2e) electron scattering spectrometer has been constructed and used for the first time to investigate the spectral momentum density of the valence bands of a solid target. This technique provides fundamental information about the electronic structure of both crystalline and amorphous solids. The three fundamental quantities, the band structure, electron density of states, and electron momentum distribution can be simultaneously derived from the measured (e,2e) cross section.

A review of single electron and (e,2e) scattering theory is given with an emphasis on scattering from solids. The effects of multiple scattering are discussed and a method of deconvoluting those effects …

Absorption Cross-Sections Of Sodium Diatomic Molecules, Zeng-Shevan Fong

Physics Theses & Dissertations

The absorption cross sections of sodium dimers were studied using a heat pipe over operating in the non-heat-pipe mode. Three wavelength regions were observed. They are in the red, the green-blue, and the near ultraviolet regions. The absorption cross section depends on the wavelength of the incident light. Representative peak values for the v"=0 progression in the red and green-blue regions are 2.59 A sup 2 (average value) and 11.77 A sup 2 (T_ave=624 K). The value for the C greater than X transitions is several tenths A sup 2. The cross sections were measured from absorption spectra …

Physics Of Some Environmental Aspects Of Energy, David W. Hafemeister

Physics

Approximate numerical estimates are carried out on the following environmental effects from energy production and conservation: (1) The greenhouse effect caused by increased CO₂ in the atmosphere; (2) Loss of coolant accidents in nuclear reactors; (3) Increased radon concentrations in buildings with very low air infiltration rates; (4) Acid rain from the combustion of fossil fuels; and (5) Explosions of liquified natural gas (LNG).

Energy Conservation In Large Buildings, A. Rosenfeld, David W. Hafemeister

Physics

As energy prices rise, newly energy aware designers use better tools and technology to create energy efficient buildings. Thus the U.S. office stock (average age 20 years) uses 250 kBTU/ft² of resource energy, but the guzzler of 1972 uses 500 (up × 2), and the 1986 ASHRAE standards call for 100–125 (less than 25% of their 1972 ancestors). Surprisingly, the first real cost of these efficient buildings has not risen since 1972. Scaling laws are used to calculate heat gains and losses of buildings to obtain the ΔT(free) which can be as large as 15–30 °C (30–60 °F) for …

A Chronology Of Energy Conservation And Production, David W. Hafemeister

Physics

No abstract provided.

Clayton Et Al. Respond, C.E. Clayton, C. Joshi, C. Darrow, Donald P. Umstadter

Donald Umstadter Publications

Clayton et al. Respond: The authors of the Comment are quite correct when they point out that the ruby-laser scattering system used in our study can only respond to beat-excited density fluctuations with k_y = k₂, where the CO₂ (ruby) beam propagates in the z (y) direction.

Investigation Of The Appropriateness Of Sensitized Luminescence To Determine Exciton Motion Parameters In Pure Molecular Crystals, Vasudev M. Kenkre, Paul Ernest Parris, Dankward B. Schmid

Physics Faculty Research & Creative Works

A wealth of experimental data has been collected over the years regarding the sensitized luminescence of molecular crystals. Indeed, such observations have played a primary role in attempts to characterize the dynamical aspects of exciton transport in these materials. Nonetheless, as has been noted previously, serious questions of interpretation remain concerning the relationship between primary experimental observables and microscopic parameters which govern exciton transport and capture. In the past these questions have led to an uncertainty, not always acknowledged, in the values of exciton diffusion constants reported in the literature. On the other hand, careful analysis of some recent experiments …

Temperature Dependence Of The Normal-Metal Aharonov-Bohm Effect, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb

Faculty Publications

The amplitude of h/e periodic oscillations in the magnetoresistance of very small normal-metal (Au) rings, as well as the harmonic h/2e, have been studied as a function of temperature. The amplitudes depend on the temperature T roughly as T-^1/2, as expected from the averaging of conduction channels in the absence of inelastic scattering, but may not be entirely consistent with this model. At the lowest T, the size of the fluctuations in the conductance is about ΔG∼e²/h, as predicted recently.

Ionization Cross Sections For 10-300-Kev/U And Electron-Capture Cross Sections For 5-150-Kev/U 3He2+ Ions In Gases, M. Eugene Rudd, T. V. Goffe, A. Itoh

M. Eugene Rudd Publications

Cross sections for production of positive and negative charge for 10-300-keV/u He²⁺ ions on He, Ne, Ar, Kr, H₂, N₂, CO, O₂, CH₄, N₂O, and C0₂ were measured by the transverse-field method. Single- and double-electron-capture cross sections at 5-150 keV/u for the same targets were measured by the method of deflection of different charge-state components of the beam after passing through a known length of target gas. A secondary-emission detector was used to detect the neutral component of the beam. A small least-squares adjustment of the cross sections …

Electron Production In Proton Collisions: Total Cross Sections, M. Eugene Rudd, Y-K. Kim, D. H. Madison, J. W. Gallagher

M. Eugene Rudd Publications

Existing data on the ionization of neutral atoms and molecules by proton impact are reviewed, and electron production cross-section data are collected. The three major experimental methods are discussed and possible sources of error identified. Some theoretical cross sections are discussed, and well-established methods of relating them to measured cross sections are reviewed. A mathematical equation is fitted to the weighted experimental data for each target, and these fits are adjusted to be consistent with appropriate theoretical calculations and with electron impact and photoionization data. Recommended values of total cross sections for proton-impact ionization are given.

Electron Production In Proton Collisions: Total Cross Sections, M. Eugene Rudd, Yongki Kim, Don H. Madison, Jean W. Gallagher

Physics Faculty Research & Creative Works

Existing data on the ionization of neutral atoms and molecules by proton impact are reviewed, and electron production cross-section data are collected. The three major experimental methods are discussed and possible sources of error identified. Some theoretical cross sections are discussed, and well-established methods of relating them to measured cross sections are reviewed. A mathematical equation is fitted to the weighted experimental data for each target, and these fits are adjusted to be consistent with appropriate theoretical calculations and with electron impact and photoionization data. Recommended values of total cross sections for proton-impact ionization are given.

Angular Differential Cross Sections For The Excitation Of 11S Helium To The 21S And 21P States By 25- To 100-Kev-Proton Impact, T. J. Kvale, D. G. Seely, D. M. Blakenship, E. Redd, Timothy J. Gay, M. Kimura, E. Rille, J. L. Peacher, J. T. Park

Timothy J. Gay Publications

Angular differential cross sections for the proton-impact excitation of ground-state helium (1¹S) to the 2¹S and 2¹P states have been measured for the first time in the energy range 25 to 100 keV with use of the energy-loss technique. The data indicate that, for very small scattering angles, at 25 keV the 2¹S differential cross section is greater than the 2¹P differential cross section. For impact energies greater than 50 keV, the 2¹P differential cross section clearly dominates over the 21S cross section in the very small scattering …

Time-Dependent Magnetic Structures Of The Superconducting Mixed Ternary System Ho(Rh₁₋ₓirₓ)₄B₄, Steven E. Lambert, M. Brian Maple, Oran Allan Pringle, Herbert A. Mook

Physics Faculty Research & Creative Works

Magnetic structures have been determined by netron diffraction for several compositions in the superconducting mixed ternary system Ho(Rh_1-xIr_x)₄B₄. Two features previously reported to occur in the heat capacity for some compositions are shown to correspond to successive magnetic transitions. For x=0.30 and 0.45, neutron diffraction peaks for the lowest temperature structure develop over a timescale of many hours. The results are discussed in terms of magnetic frustration.

Angular Differential Cross Sections For The Excitation Of 1¹S Helium To The 2¹S And 2¹P States By 25- To 100-Kev-Proton Impact, Thomas J. Kvale, Denver G. Seely, D. M. Blankenship, E. Redd, Timothy Gay, Mineo Kimura, Eduard P. Rille, Jerry Peacher, John T. Park

Physics Faculty Research & Creative Works

Angular differential cross sections for the proton-impact excitation of ground-state helium (1¹S) to the 2¹S and 2¹P states have been measured for the first time in the energy range 25 to 100 keV with use of the energy-loss technique. The data indicate that, for very small scattering angles, at 25 keV the 2¹S differential cross section is greater than the 2¹P differential cross section. For impact energies greater than 50 keV, the 2¹P differential cross section clearly dominates over the 2¹S cross section in the very …

Birefringence Measurements Of The Uniaxial-Stress Dependence Of The Incommensurate Phase Transition In K2Seo4, D. P. Billesbach, F. G. Ullman, John R. Hardy

John R. Hardy Papers

The uniaxial-stress dependence of the incommensurate-phase-transition temperature (at 130 K) in K₂SeO₄ was measured along all three crystal axes by observation of the anomalies in the birefringence caused by the structure change. The results for the c-axis-stress dependence (- 17.0±0.2 K/kbar) agree with previous studies of other workers. This experiment has also provided the first direct measurements of the a-axis- and b-axis-stress dependences (+ 3.1 ±0.2 K/kbar and +7.7± 0.2 K/kbar, respectively). Also, a value of -6.2±0.3 K/kbar was calculated from these data for the dependence of the transition temperature on hydrostatic pressure. This …

Emerging Technologies For Verification Of Arms Control Treaties, David W. Hafemeister

Physics

Progress in the technical means of monitoring to verify compliance to arms control treaties is discussed in the following areas: Real-time surveillance with charge-coupled devices in the visible and infrared; image enhancement with digital 1 image processing and with adaptive optics; imaging with radars based on satellites and on the ground; seismic monitoring with high frequency discrimination and with unattended in-country seismic stations; and nuclear weapons test monitoring with the global positioning satellite system.

Low Temperature Tunneling Dynamics In Condensed Media, Paul Ernest Parris, Robert J. Silbey

Physics Faculty Research & Creative Works

There has been considerable interest recently in the low temperature dynamics of condensed phase tunneling phenomena. In this paper we consider the interplay between quasiparticle transport and vibrational relaxation; the former taking place via tunneling in a double well potential, and the latter occurring due to interactions of the tunneling system with a harmonic bath. Taking the system-bath interactions to be linear in the bath coordinates, and explicitly allowing for a vibrationally excited well, we present a unified treatment of the weak and strong coupling regimes and obtain reduced equations of motion for the tunneling particle position operator. Solutions are …

Cross Sections For Ionization Of Gases By 10-2000-Kev He+ Ions And For Electron Capture And Loss By 5-350-Kev He+ Ions, M. Eugene Rudd, T. V. Goff, A. Itoh, R. D. Dubois

M. Eugene Rudd Publications

Cross sections for production of positive and negative charge for 10-2000-keV He⁺ ions on He, Ne, Ar, Kr, H₂, N₂, CO, O₂, CH₄, and CO₂ were measured by the transverse-field method. Electron-capture and -loss cross sections for 5-350-keV He⁺ ions on the same targets were measured by the method of beam deflection of various charge states after passing through a known length of target gas. Secondary-emission detectors were used to detect neutral, singly charged, and doubly charged beam components. The equation σ₊- σ_- = σ_{10 …}

Incident Beam Polarization For Laser Doppler Velocimetry Employing A Sapphire Cylindrical Window, James A. Lock, Harold J. Schock

Physics Faculty Publications

For laser Doppler velocimetry studies employing sapphire windows as optical access ports, the birefringency of sapphire produces an extra beam intersection volume which serves to effectively smear the acquired velocity flow field data. It is shown that for a cylindrical window geometry, the extra beam intersection volume may be eliminated with minimal decrease in the fringe visibility of the remaining intersection volume by suitably orienting the polarizations of the initial laser beams. For horizontally incident beams, these polarizations were measured at three intersection locations within the cylinder. It was found that the measured polarization angles agreed with the theoretical predictions.