Physical Sciences and Mathematics Commons^™

Gamma-Ray Optical Studies Of ⁷³Ge And ⁵⁷Fe, Walter Carlton Mcdermott Iii

Physics Theses & Dissertations

The research described herein is among the first attempts to test one of the more popular theories for development of a gamma-ray laser. This work is a "marriage" between the Borrmann effect, which is a consequence of the dynamical theory of x-ray diffraction, and time-filtering which comes from time-domain Mossbauer spectroscopy.

Our experiments involved the search for a nuclear Borrmann effect and the subsequent time-filtering effect using ⁵⁷Fe and ⁷³Ge. In both cases, no nuclear Borrmann effect was observed; however, the methodology and criteria necessary for such an observation with any isotope were documented. The procedures necessary for …

Wavelength Modulation Spectroscopy With Diode Lasers, Ying Lu

Electrical & Computer Engineering Theses & Dissertations

Wavelength Modulation Spectroscopy is a non-intrusive technique which enables several parameters such as concentration, velocity, and temperature of a target specie to be measured. The method involves a modulation of a probe laser beam and detection at the fundamental, or any harmonic frequency, by a phase-sensitive apparatus. The theory of wavelength modulation is discussed. Effects of the finite value of the wavelength modulation index, together with the effects of any residual amplitude modulation that often occurs simultaneously in a diode laser, are included. It is shown that there are several advantages in using detection harmonics orders greater than the second. …

Two-Photon Quantum Interference Polarization Spectroscopy: Measurements Of Transition Matrix Elements In Atomic Rubidium, Alexander I. Beger

Physics Theses & Dissertations

The estimation of the adequacy of theoretical calculations on the atomic structure requires availability of the precise experimental data on radiative properties of the atoms. Such data is also required in astronomy and some important areas of technology. The lack of precision of traditional spectroscopic studies of atom presents a fundamental obstacle for progress in these areas. For example, in atomic rubidium, the best precision of the traditional spectroscopic results is on the order of about 1 - 5%, which does not allow for clear assessment of the latest sophisticated theoretical calculations on atomic rubidium structure, with emphasis on different, …

Electron Beam Emission From A Ferroelectric Cathode, Crystal Briana Garland

Electrical & Computer Engineering Theses & Dissertations

The electron beam emission from a LTZ-2 (lead titanate-zirconate) ferroelectric cathode was characterized. The purpose was to determine the operation range for this type of electron emitter. The experimental apparatus consisted of a high voltage driving circuit with a charging voltage up to 30kV. A solid-state SCR switch is used to generate the high voltage pulse which induces a polarization change. Current densities on the order of 80A/cm² 30kV were achieved. The electron beam profile is Guassian. At long anode-cathode distances the measured current densities were found to be above Child-Langmuir space charge limits. The large current densities and …

Pion Absorption On Polarized Lithium-7 At 165 Mev, Thomas A. Greco

Physics Theses & Dissertations

Pion absorption is not well understood. Cross section data alone does not provide a complete description since the cross section tends to be sensitive only to the spin-independent terms in the transition amplitude. Polarization observables are thus necessary to complete the picture. In this experiment, analyzing powers for the reaction ^7→Li(π⁺,pp)⁵He at T_π = 165 MeV were measured at the Paul Scherrer Institut, Switzerland. The emitted protons were detected with the SUSI spectrometer at 38° in coincidence with an array of five scintillator telescopes centered around the quasi-free angle for absorption on a nucleon …

Η Production In Peripheral Heavy-Ion Collisions, Alec Schramm, Daniel Reeves

Alec J Schramm

We estimate the impact parameter dependence of the production cross section for ηc and ηb mesons in peripheral heavy-ion collisions. Total and elastic γγ cross sections are calculated in an equivalent photon approximation.

Background Paper On "Power Line Fields And Public Health", David W. Hafemeister

Physics

No abstract provided.

Laser Injection Of Ultrashort Electron Pulses Into Wakefield Plasma Waves, Donald P. Umstadter, J.K. Kim, E. Dodd

Donald Umstadter Publications

A novel laser-plasma-based source of relativistic electrons is described. It involves a combination of orthogonally directed laser beams, which are focused in a plasma. One beam excites a wakefield electron plasma wave. Another locally alters the trajectory of some of the electrons in such a way that they can be accelerated and trapped by the wave. With currently available table-top terawatt lasers, a single ultrashort-duration electron bunch can be accelerated to multi-MeV energies in a fraction of a millimeter, with femtosecond synchronization between the light pulse, the electron bunch, and the plasma wave. Both analytical and numerical-simulation results are presented.

Signal Averaging X-Ray Streak Camera With Picosecond Jitter, Anatoly Maksimchuk, M. Kim, J. Workman, G. Korn, J. Squier, D. Du, Donald Umstadter, G. Mourou, M. Bouvier

Donald Umstadter Publications

We have developed an averaging picosecond x-ray streak camera using a dc-biased photoconductive switch as a generator of a high-voltage ramp. The streak camera is operated at a sweep speed of up to 8 ps/mm, shot-to-shot jitter is less than ±1 ps. The streak camera has been used to measure the time history of broadband x-ray emission from an ultrashort pulse laser-produced plasma. Accumulation of the streaked x-ray signals significantly improved the signal-to-noise ratio of the data obtained.

Long-Range Order And Magnetic Properties Of MnXPt1 – X Thin Films, Kurt W. Wierman, Roger D. Kirby

Roger Kirby Publications

Thin films of Mn_xPt_1–x (x = 0.18, 0.22, 0.25, 0.30, 0.34) were prepared by magnetron sputtering onto quartz substrates. After annealing in vacuum for 1 h at 850°C, X-ray diffraction indicates that the films have the Cu₃Au cubic structure (a = 3.87 Å) and are highly textured with the (111) axis along the film normal. These samples have a high degree of long-range order, as indicated by the ratio of the intensities of the superlattice (100) and fundamental (200) X-ray diffraction reflections. We report here the results of magnetic and magnetooptical measurements …

Optical Electron Polarimetry With Heavy Noble Gases, Timothy J. Gay, J. E. Furst, K. W. Trantham, W. M. K. P. Wijayaratna

Timothy J. Gay Publications

We have measured the polarization of fluorescence emitted by the noble gases He, Ne, Ar, Kr, and Xe following impact excitation by polarized electrons. In He, the 3³P→2³S transition was studied; in the heavy noble gases the np⁵ (n+1) p ³D³→np⁵ (n+1) s³P² transitions were analyzed. We investigated these transitions as candidates for efficient optical electron polarimetry and found that, because of their larger excitation cross sections and analyzing power, the heavy noble gases are superior to He, which had been used …

Chemical Wave Propagation In Hele-Shaw Cells And Porous Media, D. A. Vasquez, J. W. Wilder, Boyd F. Edwards

All Physics Faculty Publications

Chemical waves induce density gradients in fluids which may lead to convection. This paper studies the convective effects on chemical waves propagating in porous media or in fluids confined between two parallel vertical walls. Chemical waves in the iodate–arsenous acid system are modeled with a one variable reaction‐diffusion equation. The fluid flow is modeled using Darcy’s law. A linear stability analysis on convectionless fronts shows a transition to convection. The full nonlinear equations describing the convective front are solved numerically on a vertical slab. Convective fronts propagate faster than convectionless fronts. Near the onset of convection, the fronts are raised …

Spectroscopy Of Atoms Confined To The Single Node Of A Standing Wave In A Parallel-Plate Cavity, V. Sandoghar, C. I. Sukenik, S. Haroche, E. A. Hinds

Physics Faculty Publications

We have performed spectroscopy on sodium atoms that are optically channeled in the single node of a laser standing wave set up across a parallel-plate cavity. Using this technique we have extended our previous measurement of the Lennard-Jones van der Waals energy-level shift [Sandoghdar et al., Phys. Rev. Lett. 68, 3432 (1992)] down to a cavity width of ~500 nm. We discuss the applications of this technique to the precise measurement of atom-surface distances.

A Magnetic Neutron Diffraction, And Mössbauer Spectral Study Of The Ce₂Fe₁₇₋ₓalₓ Solid Solutions, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, Zhongbo Hu, William B. Yelon, Fernande Grandjean, K. H. J. Buschow

Chemistry Faculty Research & Creative Works

The magnetic properties of a series of Ce₂Fe_17-xAl_x solid solutions with x equal to 0.00, 0.88, 2.06, 2.81, 3.98, 5.15, 6.08, 7.21, 8.20, 9.08, 9.84, and 10.62 have been studied by magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. The compounds crystallize in the rhombohedral Th₂Zn₁₇-type structure. Magnetization studies indicate that the Curie temperature increases uniformly from 238 K for Ce₂Fe₁₇ to 384 K for Ce₂Fe₁₄Al₃ and then decreases at higher aluminum content. Powder neutron diffraction results, obtained at 295 K, indicate that aluminum …

Linear And Non-Linear Preprocessing Of Wavefront Sensor Slope Measurements For Improved Adaptive Optics Performance, Dennis A. Montera

Theses and Dissertations

New methods for preprocessing wavefront sensor (WFS) slope measurements are presented. Methods are developed to improve the accuracy of WFS slope measurements, as well as estimating key atmospheric and system parameters from the slope signals. Both statistical and artificial neural network solutions are investigated. Also, new atmospheric models for generating slope and phase data with the proper spatial and temporal statistics are developed. The experiments in improving the accuracy of WFS slope measurements include reducing the WFS slope measurement error and compensating for adaptive optics system time delay through temporal slope prediction. The experiments in key parameter estimation include estimating …

A Statistical Study Of Transient Events In The Outer Dayside Magnetosphere, Jeff Sanny, D. G. Sibeck, C. C. Venturini, C. T. Russell

Physics Faculty Works

The AMPTE CCE satellite frequently observed transient (1 ≤ τ ≤ 8 min) events marked by magnetic field strength increases and bipolar magnetic field signatures (peak-to-peak amplitudes ≥ 4 nT) while in the outer dayside magnetosphere. We report a survey of 59 prominant events observed from August to November 1984. The bipolar signatures and minimum variance analysis reveal that most events move poleward and antisunward, except in the immediate vicinity of local noon. Here the motion of the events appears to be better governed by the spiral/orthospiral interplanetary magnetic field (IMF) orientation than magnetic curvature forces associated with IMF By. …

Scanning Local‐Acceleration Microscopy, Nancy Burnham, A. Kulik, G. Gremaud, P. Gallo, F. Oulevey

Nancy A. Burnham

By adapting a scanning force microscope to operate at frequencies above the highest tip–sample resonance, the sensitivity of the microscope to materials’ properties is greatly enhanced. The cantilever’s behavior in response to high‐frequency excitation from a transducer underneath the sample is fundamentally different than to its low‐frequency response. In this article, the motivations, instrumentation, theory, and first results for this technique are described.

Non-Traditional Techniques In Teaching Science For General Students, Gary Lewis, Ben Golden, Gail Schiffer, Diane Willey

Gary C. Lewis

No abstract provided.

Materials’ Properties Measurements: Choosing The Optimal Scanning Probe Microscope Configuration, Nancy Burnham, G Gremaud, A Kulik, P Gallo, F Oulevey

Nancy A. Burnham

Rheological models are used to represent different scanning probe microscope configurations. The solutions for their static and dynamic behavior are found and used to analyze which scanning probe microscope configuration is best for a given application. We find that modulating the sample at high frequencies results in the best microscope behavior for measuring the stiffness of rigid materials, and that by modulating the tip at low frequencies and detecting the motion of the tip itself (not its position relative to the tip holder) should be best for studying compliant materials in liquids.

Tabletop Laser Accelerators Are On The Way, Phillip F. Schewe, Ben Stein, Donald P. Umstadter

Donald Umstadter Publications

The goal here is to use high electric fields in plasmas to accelerate electrons to 100-GeV energies over distances of meters rather than kilometers. This should promote the development of new particle colliders and x-ray sources. The predicted high acceleration gradients in plasmas have been achieved in recent years, but could only be used with external electron injection from a conventional source. Now scientists at the University of Michigan (Donald Umstadter, 313-764-2284) have made progress in eliminating conventional electron sources altogether. In a preliminary experiment, by simply focusing a laser into a plasma, the Michigan scientists have extracted a collimated …

Ultraviolet And Electron Radiation Induced Fragmentation Of Adsorbed Ferrocene, Dulip Welipitiya, A. Green, J.P. Woods, Peter A. Dowben, Brian W. Robertson, Dongjin Byun, Jiandi Zhang

Peter Dowben Publications

From thermal desorption spectroscopy we find that ferrocene, Fe(C₅H₅)₂, adsorbs and desorbs associatively on Ag(100). Photoemission results indicate that the initially adsorbed surface species closely resembles that of molecular ferrocene. The shift in photoemission binding energies relative to the gas phase is largely independent of the molecular orbital. We find that ultraviolet light does lead to partial fragmentation of the ferrocene and that the molecular fragments are much more strongly bound to the surface than the associatively adsorbed ferrocene. Since fragmentation occurs only in the presence of incident radiation, selective area deposition from this …

New Model For Electron-Impact Ionization Cross Sections Of Molecules, W. Hwang, Y.-K. Kim, M. Eugene Rudd

M. Eugene Rudd Publications

A theoretical model for electron-impact ionization cross sections, which has been developed primarily for atoms and atomic ions, is applied to neutral molecules. The new model combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses minimal theoretical data for the ground state of the target molecule, which are readily available from public-domain molecular structure codes such as GAMESS. The theory is called the binary encounter Bethe (BEB) model, and does not, in principle, involve any adjustable parameters. Applications to 19 molecules, including H₂, NO, CH₂, C₆H₆, and SF …

Consequences Of Supergravity With Gauged U(1)R Symmetry, Diego Castano, D. Z. Freedman, C. Manuel

Chemistry and Physics Faculty Articles

The structure of gauged R-supergravity Lagrangians is reviewed, and we consider models with a hidden sector plus light fields of the MSSM. A simple potential for the hidden sector is presented which has a global minimum with zero cosmological constant and spontaneously broken SUSY and R-symmetry. The U(1)_R vector multiplet acquires a Planck scale through the Higgs mechanism, and it decouples at low energy. Due to very interesting cancellations, the U(1)_RD-terms also drop out at low energy. Thus no direct effects of the gauging of R-symmetry remain in the low-energy effective Lagrangian, …

C-Axis Oriented (Hg,Ti)-Based Superconducting Films With TC≥125 K, F. Foong, B. Bedard, Q.L. Xu, Sy_Hwang Liou

Sy-Hwang Liou Publications

Thin films with mostly (Hg,Tl) ₁Ba₂Ca₃Cu₂O_{8+ δ} [(Hg,Tl)-1223] phase have been fabricated by radio frequency magnetron sputtering of precursor films and post-annealing method. The doping of a small amount of thallium in the film is helpful to the formation of the three-layer CuO₂ compound. These films have a highly oriented structure with the c-axis perpendicular to the film surface. Resistivity measurements show that the films after annealing at 300 °C for 1 h in O₂ have the superconducting transition temperature of T_c (onset)=133 K and T_c (zero)=127 …

Rapidity Gaps Between Jets In Photoproduction At Hera, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. Repond, R. Stanek, R. L. Talaga, H. Zhang, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, R. Bruni, G. Cara Romeo, G. Castellini, M. Chiarini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, I. Gialas, R. Giusti, G. Iacobucci, G. Laurenti, G. Levi, A. Margotti, T. Massam, R. Nania, Margarita C. K. Mattingly

Faculty Publications

Photoproduction events which have two or more jets have been studied in the Wγp range 135 GeV < Wγp < 280 GeV with the ZEUS detector at HERA. A class of events is observed with little hadronic activity between the jets. The jets are separated by pseudorapidity intervals (Δη) of up to four units and have transverse energies greater than 6 GeV. A gap is defined as the absence between the jets of particles with transverse energy greater than 300 MeV. The fraction of events containing a gap is measured as a function of Δη. It decreases exponentially as expected for processes in which colour is exchanged between the jets, up to a value of Δη ∼ 3, then reaches a constant value of about 0.1. The excess above the exponential fall-off can be interpreted as evidence for hard diffractive scattering via a strongly interacting colour singlet object.

Evidence Favoring Molybdenum−Carbon Bond Formation In Xanthine Oxidase Action: 17O- And 13C-Endor And Kinetic Studies, Barry D. Howes, Robert C. Bray, Raymond L. Richards, Nigel A. Turner, Brian Bennett, David J. Lowe

Physics Faculty Research and Publications

The reaction mechanism of the molybdoenzyme xanthine oxidase has been further investigated by ¹³C and ¹⁷O ENDOR of molybdenum(V) species and by kinetic studies of exchange of oxygen isotopes. Three EPR signal-giving species were studied:  (i) Very Rapid, a transient intermediate in substrate turnover, (ii) Inhibited, the product of an inhibitory side reaction with aldehyde substrates, and (iii) Alloxanthine, a species formed by reaction of reduced enzyme with the inhibitor, alloxanthine. The Very Rapid signal was developed either with [8-¹³C]xanthine or with 2-oxo-6-methylpurine using enzyme equilibrated with [¹⁷O]H₂O. The Inhibited signal was …

Heat-Capacity And Magnetic Measurements On The Y(Ni2-XCoX)B2C System, C. C. Hoellwarth, P. Klavins, R. N. Shelton

Physics

We have performed field-and temperature-dependent magnetization, resistivity, and heat-capacity measurements on polycrystalline samples of the Y(Ni_2-xCo_x)B₂C system with 0.0≤x≤0.4. Values of T_c ,x₀,H_c2,Θ_D,λ and N(E_d) were determined for various samples. We observe that Θ_D increases with x, while all the other parameters decrease with x. The T_c vs x data can be described using the BCS theory and the measured values of N(E_f)and Θ_D. The results suggest that the decrease in T_c is due to the decrease in …

Low Energy Electron Scattering From Ch3Cl, X. Shi, V.K. Chan, Gordon A. Gallup, Paul Burrow

Paul Burrow Publications

Differential cross section measurements for the elastic scattering of electrons from CH₃Cl at energies from 0.5 to 9.5 eV are reported for scattering angles of 30° and 100°. The angular scattering dependence is determined at selected energies over this range. At energies below 1.0 eV, the cross sections are in excellent agreement with calculations using the Born dipole approximation. At large angles and higher energies, the scattering is dominated by a ²A₁ temporary negative ion state near 3.5 eV. Energy loss data at 3.5, 5.0, and 8.5 eV are reported and the relative contributions of various …

Response To ‘‘Comment On ‘A Paradox Involving The Second Law Of Thermodynamics’ ’’ [Phys. Plasmas 2, 1893 (1995)], D. P. Sheehan

Physics and Biophysics: Faculty Scholarship

No abstract provided.

Photodetachment Of Li- From The Li 3S Threshold To The Li 6S Threshold, Cheng Pan, Anthony F. Starace, Chris H. Greene

Anthony F. Starace Publications

Eigenchannel R-matrix calculations (including effects of long-range multipole interactions beyond the reaction volume) for Li^- photodetachment partial cross sections from the vicinity of the Li 3s threshold to the Li 6s threshold (3.8 eV ≤ħω≤ 5.65 eV) are presented. Excellent agreement with the relative total cross section measurements of U. Berzinsh et al. [Phys. Rev. Lett. 74, 4795 (1995)] in the vicinity of the Li 3s and Li 3p thresholds is found. The calculated resonance structures are analyzed in detail. In particular, the energy region between the Li 4s and Li 5 …