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Cross Section, Robert Katz

Robert Katz Publications

In radiobiology the term cross section is used in ways that depart from its original physical meaning. Some of these conceptual extensions represent significant distortions of the original concept. These distortions lead to the misinterpretation of experimental findings.

Near-100% Production Of The Excited Be+ 1s22p Ion From Decay Of Be 1s2S22p, C. Denise Caldwell, Mark G. Flemming, Manfred O. Krause, Peter Van Der Meulen, Cheng Pan, Anthony F. Starace

Anthony F. Starace Publications

In examining the decay of photon-produced Be 1s2s²np(¹P), n=2,3, we discovered that the vastly predominant decay mode is to the final excited ionic states Be⁺ 1s²np, rather than the ground state. For n=2, the 2p ion accounts for 95% of the total production, with Be⁺ 1s²3p the other main contributor. For n=3, 3p is predominant, again with a very small fraction of 2s. The result for n=2 occurs as a consequence of the similarity between the 2s and …

Oxidation-Reduction Behavior Of Undoped And Sr-Doped Lamno3: Defect Structure, Electrical Conductivity, And Thermoelectric Power, J. H. Kuo, Harlan U. Anderson, Don M. Sparlin

Materials Science and Engineering Faculty Research & Creative Works

Seebeck coefficient and electrical conductivity measurements were performed for undoped and Sr-doped LaMnO₃ as a function of temperature and oxygen partial pressure. The results of electrical conductivity showed typical p-type behavior. As reduction proceeded, the electrical conductivity of these LaMnO₃-based perovskites decreased with P 1 4O₂. The analysis of the electrical conductivity data was performed by extending the defect model from a previous thermogravimetric (TG) study. The measured Seebeck coefficients were found to be positive except for the most reducing conditions when the decomposition into multiple phases occurred. The Heikes formula was adopted to interpret …

Enhanced Polarization Of Electron Spins In He4 By Simultaneous Optical Pumping With Circularly And Linearly Polarized Resonance Radiation, Laird D. Schearer, Padetha Tin

Physics Faculty Research & Creative Works

The polarization of helium (2³S₁) metastable atoms saturates at 50% when the ensemble is optically pumped with the D0 (2³S₁-2³P₀) transition. We have obtained polarizations approaching 100% with a simple, straightforward modification to the conventional experimental arrangement. The addition of a small amount of -polarized D₀ light incident on the cell perpendicular to the defining field direction doubles the polarization produced by circularly polarized + light along the field direction. A simple rate-equation model illustrates the enhancement. © 1990 The American Physical Society.

Subshell Electron Capture In Collisions Of Fully Stripped Ions With He And H2 At Intermediate Energies, L. Meng, C. O. Reinhold, Ronald E. Olson

Physics Faculty Research & Creative Works

Classical phase-space models of the hydrogen molecule and helium are utilized to study shell and subshell electron-capture processes in collisions of fully stripped ions on charge states from 1 to 15 with H2 and He at intermediate impact energies (20200 keV/amu). Autoionization after double electron capture is approximated and is found to be an important channel for high projectile charges. The resulting (n,l) distributions for proton impact of He and H₂ as well as total capture cross sections are found to be in very good agreement with experimental data. l distributions for high projectile charges are also analyzed for …

State-Selective Capture In Collisions Between Ions And Ground- And Excited-State Alkali-Metal Atoms, J. Pascale, Ronald E. Olson, C. O. Reinhold

Physics Faculty Research & Creative Works

Total cross sections for state-selective electron capture in collisions between ions and alkali-metal atoms have been calculated by means of a three-body classical-trajectory Monte Carlo (CTMC) method using model potentials to describe the electron ionic-core interactions. Calculations have been performed for Na⁺-Na(28d) collisions and for N⁵⁺ and Ar⁸⁺-Cs(6s) collisions. The collision velocity range corresponds to 0.5vp/ve2, where vp is the projectile velocity in the laboratory frame and ve is the initial orbital velocity of the electron bound to the alkali-metal core. In the case of Na₊+Na(28d) collisions, calculations of the final n,l,m distributions …

Enhanced Radiative Auger Emission From Lithiumlike S13+16, E. M. Bernstein, M. W. Clark, C. S. Oglesby, J. A. Tanis, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, B. M. Johnson, K. W. Jones

Physics Faculty Research & Creative Works

The radiative Auger emission (RAE) from 0.946.25-MeV/u ₁₆S¹³⁺ (lithiumlike) projectiles excited in collisions with He target atoms has been measured. For these highly stripped ions the intensity of RAE photons relative to K x-ray emission is enhanced by about a factor of five compared with theoretical calculations and an earlier experimental measurement for S ions with few electron vacancies. The enhancement of RAE for S¹³⁺ is qualitatively similar to results reported previously for lithiumlike ₂₃V²⁰⁺; however, some differences between S and V are evident. © 1990 The American Physical Society.

Physical Properties Of Coarse Aerosol Particles And Haze Elements In Polluted Urban-Marine Environment, Josef Podzimek

Physics Faculty Research & Creative Works

Measurements of coarse particles (with r ≥ 1.0 μm) with the aid of a cascade impactor and of particle (droplet) identification in sensitized gelatine layers reveal their mean concentration of about 1.5 cm-3 during the months of May and June 20 km west from Napoli in Italy. Haze particles (droplets) are usually featured by insoluble core and many small particles deposited on their surface. Sea salt aerosol does not play a dominant role in the haze element formation at this site of measurement. © 1990.

Experimental And Theoretical Study Of The Electron Spectra In 66.7350-Kev/U C++He Collisions, L. H. Toburen, R. (Robert) D. Dubois, C. O. Reinhold, D. R. Schultz, Ronald E. Olson

Physics Faculty Research & Creative Works

Measurements of the differential and total cross sections for production of free electrons are reported for collisions of 66.7350-keV/u C+ ions with He. The experimental data are compared with theoretical calculations that include electron emission from both target and projectile using the classical-trajectory Monte Carlo method and the independent-electron approximation. Good agreement is observed between theory and experiment, and structures appearing in the electron spectra can be explained in terms of either, or both, target and projectile ionization. © 1990 The American Physical Society.

Binary Nucleation Of Ethanol And Water, John L. Schmitt, J. Whitten, G. W. Adams, R. A. Zalabsky

Physics Faculty Research & Creative Works

The authors have used a fast expansion cloud chamber to measure binary homogeneous nucleation rates in several ethanol-water mixtures as a function of temperature, ethanol and water activities and nucleation rate. Data (ethanol and water activities) are presented for a range in nucleation rate from 10 3 to 105 drops/cm3 s from 263 to 293 K for mixtures having mole ratios (ethanol/water) of 10, 4, 0.1, 0.01, and 0.001. A comparison of the extensive data set to other data in the literature shows good agreement. We find current theory, as expected, is unable to accurately predict the data at low …

Rotational Effects In The Continuous Vacuum-Ultraviolet Fluorescence Spectrum Of H2 Associated With Spontaneous Dissociation, H. Schmoranzer, T. Noll, E. Roueff, H. Abgrall, Ronald James Bieniek

Physics Faculty Research & Creative Works

The effects of rotational-vibrational interaction, and of rotational coupling between the B 2p u+1 and C 2p u1 electronic states, on the B X fluorescence continuum of H2 associated with spontaneous dissociation were investigated spectroscopically using monochromatized synchrotron radiation for selective excitation of rovibronic states. The rotational shifts and perturbations in the modulated continua intensities observed agree well with close-coupling and Jeffreys-Wentzel-Kromers-Brillouin (JWKB) calculations also performed and are explained in terms of nonadiabatic coupling effects and rainbow-interference structures. A straightforward experimental technique is described to detect mixed electronic states. © 1990 The American Physical Society.

Application Of The Results Of Carbon Pellet Modeling To The Problem Of Plasma Penetration, L. L. Vahala, A. G. El Cashlan, G. A. Gerdin, P. B. Parks

Electrical & Computer Engineering Faculty Publications

The assumptions of the evaporation model for low-Z pellets interacting with magnetic fusion plasmas developed by Parks are tested. These assumptions are that the vapor density profile in the region adjacent to the pellet surface falls off with radial distance as r^-α , where 5 <α<6, and that the ionization time for the transition between charge states ז_f (i.e., for r < ~3 sonic radii). The first assumption is tested by solving a two-parameter eigenvalue problem for the evaporation cloud in the region interior to the sonic radius; the results are found to be consistent with the low-Z evaporation model. The second assumption, that ז_zi «ז_f, is tested at the sonic radius using the results from atomic physics and the low-Z evaporation model. It is found that indeed ז_zi «ז_f for plasmas with parameters close to thermonuclear conditions (e.g. CIT), but not for those of smaller Tokamaks such as …

Measurement Of Magnetic Fluctuations By O-X Mode Conversion, L. L. Vahala, G. Vahala, N. Bretz

Electrical & Computer Engineering Faculty Publications

The possibility of measuring magnetic fluctuations in a fusion plasma is considered by examining the O→X mode conversion. Under certain conditions and with good angular resolution, this mode conversion can be attributed to the presence of magnetic fluctuations even though the level of these fluctuations is much lower than that of density fluctuations. Some nonideal effects such as mode polarization mismatch at the plasma edge are also discussed.

Influence Of Copper Doping On The Performance Of Optically Controlled Gaas Switches, St. T. Ko, V. K. Lakdawala, K. H. Schoenbach, M. S. Mazzola

Electrical & Computer Engineering Faculty Publications

The influence of the copper concentration in silicon-doped gallium arsenide on the photoionization and photoquenching of charge carriers was studied both experimentally and theoretically. The studies indicate that the compensation ratio (N_Cu/N_Si) is an important parameter for the GaAs:Si:Cu switch systems with regard to the turn-on and turn-off performance. The optimum copper concentration for the use of GaAs:Si:Cu as an optically controlled closing and opening switch is determined.

The Effects Of Prisms Learning Cycle Strategies On Achievement, Integrated Process Skills, And Attitudes Towards Physics Of High School Physics Students When Referenced To Kolb’S Learning Style Inventory, Michael P. Kelly

Dissertations and Theses @ UNI

This study asked the question: Is the gain in physics achievement, process skills, and attitudes toward physics, using the PRISMS teaching strategy, different among high school physics students in the four cognitive learning modes identified by the Kolb Learning Styles Inventory (LSI)? In this study a group of high school physics students were tested for gains in scores in the three areas mentioned in the statement of the problem. This treatment group was taught using PRISMS teaching strategies. Their learning styles were classified according to the Kolb LSI. The procedure followed for this study included administration of the Kolb LSI …

Undergraduate Elementary Education Students’ Understanding Of The Particulate Nature Of Matter, Pushpa Pandey

Dissertations and Theses @ UNI

This study was descriptive in nature and investigated preservice elementary teachers' understanding of the particulate nature of matter. Twenty-two sophomore elementary education majors were interviewed using the interview-about-events technique. Students were asked to observe and offer explanations for some common physical and chemical changes such as melting, evaporating, condensing, dissolving, and burning. Next, the students' model of matter was probed and they were asked to provide a description of each event using their conceptual model. The results indicated that the majority of students (82%) accepted that matter is made of particles. However, only 56% of these students believed that particles …

Undergraduate Elementary Education Students’ Concepts Of Light, Deborah Lynn Orr

Dissertations and Theses @ UNI

The purpose of the study was to describe some ideas that future elementary school teachers have about light and shadows. Twenty-five freshmen and sophomores in elementary education were interviewed using the Interview-About-Instances technique developed by Osborne and Gilbert. Students were asked to explain specific instances of sources and non-sources of light, the distance light travels, and the role of light in vision. Students defined the word "shadow" and predicted where shadows could be in particular situations. The results of this study indicate that many students lack factual information or have misconceptions concerning light propagation. Fifty-six percent of the students in …

Advanced Infrared Optically Black Baffle Materials, David D. Allred, Ronald D. Seals, C. M. Egert

Faculty Publications

Infrared optically black baffle surfaces are an essential component of many advanced optical systems. All internal surfaces in advanced infrared optical sensors that require stray light management to achieve resolution are of primary concern in baffle design. Current industrial materials need improvements to meet advanced optical sensor systems requirements for optical, survivability, and endurability. Baffles are required to survive and operate in potentially severe environments. Robust diffuse-absorptive black surfaces, which are (1) thermally and mechanically stable to threats of x-ray, launch, and in-flight maneuver conditions, with specific densities to allow an acceptable weight load, (2) handleable during assembly, (3) cleanable, …

Annealing Behavior Of The Photoluminescence Lines In Cdte And Znx Cd1-X Te Single Crystals, David D. Allred, A. Reyes-Mena, Jesus González-Hernández, Elías López-Cruz, Worth P. Allred

Faculty Publications

The main lines in the photoluminescence spectra of Zn1Cd1-xTe single crystals grown by a modified Bridgman method in the compositional range of 0≤X≤0.25 have been identified. All crystals show only near-band-edge emission. To assist in the identification, various samples with different compositions were annealed under a Cd atmosphere. In the pure crystals, the prominent (A°, X) bound exciton line, as well as the doublet at longer wavelengths, disappear after the annealing. In contrast, the treatments do not change significantly the PL spectra of the mixed crystals.

Characterization Of Metal/Carbon Multilayers By Raman Spectroscopy, David D. Allred, Qi Wang, Jesus González-Hernández

Faculty Publications

Laser Raman spectroscopy has been found to be useful for characterizing amorphous semiconductor multilayers, especially the interfaces of multilayers. Recently, we have extended this technique to the characterization of magnetron sputtered multilayers commonly used as reflectors in soft x-ray optics. Unlike the multilayers previously studied which contained only semiconductors and dielectrics, these are generally semiconductor/metal multilayers. We report here on the Raman characterization of the most common class of multilayers used in soft x-ray optics, those that contain a high density metal like tungsten interspersed with layers of carbon. In all of the metal/carbon multilayers the dominate feature in the …

Deposition Of Zinc Selenide By Atomic Layer Epitaxy For Multilayer X-Ray Optics, J.K. Shurtleff, David D. Allred, R. T. Perkins, J. M. Thorne

Faculty Publications

Thin film deposition techniques currently being used to produce multilayer x-ray optics (MXOs) have difficulty producing smooth, uniform multilayers with d-spacings less than about twelve angstroms. We are investigating atomic layer epitaxy (ALE) as an alternative to these techniques. ALE is a chemical vapor deposition technique which deposits an atomic layer of material during each cycle of the deposition process. The thickness of a film deposited by ALE depends only on the number of cycles. Multilayers deposited by ALE should be smooth and uniform with precise d-spacings which makes ALE an excellent technique for producing multilayer x-ray optics. We have …

Diffuse Absorbing Beryllium Coatings Produced By Magnetron Sputtering, David D. Allred, C. M. Egert

Faculty Publications

Beryllium coatings with varying thicknesses and columnar grain sizes were deposited by low temperature magnetron sputtering and wet chemically etched to enhance diffuse absorption of light. After etching these coatings exhibited a matte black surface finish and low specular reflectance (below 2%) in the IR up to a critical wavelength dependent upon the original grain size of the coating. Extremely thick coatings (350 µm) with original grain sizes of 10 to 12 µm were produced which exhibited specular reflectances below 0.5% up to 50 µm wavelength and a Lambertian BRDF at 10.6 µm averaging 4.3x10-3 ster-1. Scanning electron micrographs are …

Design Of High Performance Soft X-Ray Windows, Raymond T. Perkins, David D. Allred, Larry V. Knight, James M. Thorne

Faculty Publications

X-ray windows are used in sources and detectors to separate the neighborhood of the x-ray generation or detection from the use environment. While each use has its own requirements, there are some principles that should be used in designing an optimal x-ray window. Because x-rays are absorbed to some extent by all materials, minimizing absorption is one criterion in preparing windows. Also, for most uses there is a pressure difference across the window so that ensuring pinhole-free structure and sufficient mechanical strength to support the differential is another criterion for window design. Traditionally, absorption is minimized by fabricating the window …

A Theoretical And Experimental Study Of The Three-Ring Electrostatic Electron Lens, Thomas Anthony Sommer

Dissertations and Theses

A theoretical and experimental study of the three-ring electrostatic lens is presented. The lens consists of three isolated ring-shaped conductors, equally spaced along a common axis of symmetry. When appropriate potentials are applied to the conductors an electric field is produced near the axis which is capable of focusing a collimated beam of electrons. In the theoretical study the charge density method is used to find a closed-form solution for the field. This method approximates the field by replacing each ring with an infinitely thin hoop of uniform charge. The radial and axial equations of motion are then solved numerically, …

Dielectric Response Spectrum Of A Damped One- Dimensional Double-Well Oscillator, John W. Flocken, R. A. Guenther, John R. Hardy, L. L. Boyer

Physics Faculty Publications

The characteristic features of the dielectric response spectrum associated with the condensation of a "soft" phonon mode during a ferroelectric phase transition can be reproduced by an oscillator moving in a damped linear double-well potential. The behavior of the response function below the transition temperature T, can be simulated by introducing a linear mean-field coupling which destroys the symmetry of the well. Potentials derived from physically realistic parameters are shown to result in dielectric responses which are in order-of-magnitude agreement with experimental values.

Dielectric Response Spectrum Of A Damped One-Dimensional Double-Well Oscillator, J. W. Flocken, R. A. Guenther, John R. Hardy, L. L. Boyer

John R. Hardy Papers

The characteristic features of the dielectric response spectrum associated with the condensation of a "soft" phonon mode during a ferroelectric phase transition can be reproduced by an oscillator moving in a damped linear double-well potential. The behavior of the response function below the transition temperature T_c can be simulated by introducing a linear mean-field coupling which destroys the symmetry of the well. Potentials derived from physically realistic parameters are shown to result in dielectric responses which are in order-of-magnitude agreement with experimental values.

Adiabatic Population Transfer In A Three-Level System Driven By Delayed Laser Pulses, J. R. Kuklinski, U. Gaubatz, Foek T. Hioe, K Bergmann

Physics Faculty/Staff Publications

We give a simple analytic solution that describes a novel method for population transfer in a three-level system driven by delayed pulses and which accounts for recent experimental results. This solution describes a procedure that is counter intuitive, and yet it is shown to be, in fact, one of the simplest solutions for multilevel systems arising from the adiabatic theorem. Its possible application to many-level systems is suggested.

Observability Of Atmospheric Glories And Supernumerary Rainbows, James A. Lock

Physics Faculty Publications

The finite spatial coherence width of sunlight at the Earth imposes restrictions on the production of scattering phenomena based on the interference of light waves. With the spatial coherence properties of sunlight taken into account, the visibility of the supernumerary rainbow sequence adjacent to the primary rainbow and the radii of the water droplets that produce the optimum glory intensity were calculated. A substantial reduction was found in the contrast of all the supernumeraries beyond the first few, and the peak observability of the glory occurred for water droplets with radii between 10 and 20 µm.

Calculation Of Electron Scattering For 4He In A Continuum Shell Model, Ming Yu

Masters Theses

Calculations for the electroexcitation of the ⁴He, O+ state have been performed within the context of recoil corrected continuum shell model. Approximations previously employed for inelastic scattering with the recoil corrected continuum shell model are eliminated in the work. The O+ state exhausts only 10% of the energy weighted sum rule and previous shell model calculations for the excitation of this state produce about ten times too much strength. This difficulty is alleviated by the use translationally invariant wave functions and the application of continuum boundary conditions for this particle unbound state. The structure of the O+ state is …

Relativistic And Non-Relativistic Nuclear Charge Form Factors, Tao Wang

Masters Theses

This thesis presents an examination that the two nuclear charge form factors, relativistic and non-relativistic, are equivalent approximately in an appreciable range. The relativistic one is contributed by both vector charge density and tensor charge density. And the non-relativistic charge form factor is contributed by the nuclear densities from experimental electron scattering cross section, these densities are fundamental to much of nuclear structure physics.

The Dirac equation is used to calculate the vector charge density and tensor density, because the charge density from the analysis of the experimental data may be compared with proton charge densities obtained from various models …