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Electron Capture At Very Small Scattering Angles From Atomic Hydrogen By 25-125-Kev Protons, Paul J. Martin, D. M. Blankenship, Thomas J. Kvale, E. Redd, Jerry Peacher, John T. Park

Physics Faculty Research & Creative Works

Differential cross sections for electron capture in collisions between protons and hydrogen atoms have been experimentally determined for incident proton energies of 25, 60, and 125 keV in the center-of-mass scattering-angle range of 0-3 mrad. The experimental results compare more favorably with the results of both a multistate and a two-state calculation than with the results of a continuum distorted-wave-approximation calculation. There is no evidence of a Jackson-Schiff-type minimum.

Detection Of Vibrationally Excited Nitrogen By Trapped Electron And Electron Transmission Methods, J.A. Michejda, L.J. Dube, Paul Burrow

Paul Burrow Publications

Two techniques for detection of vibrationally excited nitrogen using low-energy electron scattering are described. The first technique uses the trapped electron method to observe excitation from N₂^ν into the B³П_g state near threshold. From the known Franck-Condon factors, the contribution from excited vibrational levels may be unfolded. The second technique employs the electron transmission method to detect sharp structure in the total scattering cross section resulting from the formation of temporary negative ions. Because of uncertainties in the total scattering cross sections from each of the vibrational levels, the transmission method is less accurate than …

A Critical Study Of Nonlinear Echo Phenomena, Monish Ranjan Chatterjee

Electrical and Computer Engineering Faculty Publications

The present thesis attempts to give a concise and critical account of the evolution of the echo phenomena over the last thirty years. Starting with spin and photon echoes, which were among the earliest to be observed and studied, the thesis explores the experimental findings and the models proposed in connection with the more contemporary echo experiments, viz. those involving electroacoustic or polarization echoes in single and polycrystalline piezoelectric materials and in powders. Although the investigations regarding the various mechanisms of short and long term echo formation are by no means complete, a coherent picture is beginning to emerge as …

Rare-Earth-Rich Metallic Glasses. I. Magnetic Hysteresis, George C. Hadjipanayis, David J. Sellmyer, B. Brandt

David Sellmyer Publications

An anomalous magnetic behavior has been observed in rare-earch-rich metallic glasses of the composition (R₇₅Au₂₅)_100-xB_x where R denotes Pr, Gd, Tb, Er and x=0,10. The observed hysteresis in all samples except Gd at liquid-helium temperatures is due to the large anisotropy which develops below the ordering temperature. High-field-magnetization measurements up to 220 kOe were used to determine the spontaneous magnetization and the magnetic anisotropy constant which was found to be of order 10⁸ erg/cm³ for the Tb and Er glasses. These parameters were used together with the observed remanence ratio to …

Rare-Earth-Rich Metallic Glasses. Ii. Magnetic Viscosity, George C. Hadjipanayis, David J. Sellmyer

David Sellmyer Publications

Magnetic viscosity measurements on amorphous Tb₇₅Au₂₅ and (Er₆₅Fe₃₅)₉₀B₁₀ alloys are presented in the temperature range of 1.3 to 30 K. The magnetization in a steady magnetic field is found to follow a logarithmic time dependence for times up to 400 s suggesting a spectrum of activation energies. The magnetic viscosity parameters were used to investigate the temperature dependence of the observed large coercive fields and to study intrinsic temperature and thermal activation effects. It is found that the large change of the coercive field at very low temperatures is mainly …

Energy Dependence Of Alignment In Foil Collision-Excited N=3 States Of He I, Timothy J. Gay, H. G. Berry, R. Deserio, H. P. Garnir, R. M. Schectman, N. Schaffel, R. D. Hight, D.J. Burns

Timothy J. Gay Publications

We have measured the beam-foil collision-induced alignment of the 3p ¹P, 3p ³P, 3d ¹D, and 3d ³D states of He I for He+ beam energies between 30 and 1300 keV. The alignment of all four states is found to vary with beam-current density as well as energy. The number of secondary electrons emitted per incident ion, γ, has also been measured as a function of foil temperature and beam energy between 400 and 1400 keV. The rate of change of both alignment and γ with foil temperature exhibits …

Ionization By Low And Intermediate Energy Ion And Neutral Beams, M. Eugene Rudd

M. Eugene Rudd Publications

One of the most important basic processes that take place in collisions of atomic systems is ionization resulting in the emission of electrons. A complete understanding of this process is complicated by the fact that electron emission can take place via a number of mechanisms, some of which are related. Simple measurements of the cross section for electron ejection as a function of projectile velocity does not usually provide enough information to unravel the various mechanisms. But cross sections which are differential in the angle and energy of the ejected electrons, which are now available for protons on a variety …

Renormalization Of The Vortex Diffusion Constant In Superfluid Films, Rolfe G. Petschek

Faculty Scholarship

We study the dynamics of vortices in superfluid helium films, using a phenomenological Langevin equation to account for diffusive as well as convective motion of vortices. We show that in the long-wavelength limit, dynamic screening effects give rise to a renormalization of the diffusion constant, while the convective parameter remains unchanged. The critical behavior is analyzed with renormalization-group methods. In the limit TTc-, we find a universal cusp singularity for the diffusion constant, reaching a finite value at Tc.

University-School Cooperation, Herman Feshbach, Robert Fuller

Robert G. Fuller Publications

We have a growing concern with the deterioration in both the quality and quantity of secondary physics education in the US. These concerns have recently been addressed by an APS panel chaired by Gertrude S. Goldhaber.

Molecular Effects In Beam-Foil Collision-Induced Alignment Of He I, Timothy J. Gay, H. G. Berry, R. Deserio

Timothy J. Gay Publications

We have measured the alignment of beam-foil collision-excited states of He I produced by bombarding carbon foils of various (1.3-110 μg/cm²) areal densities with beams of He⁺ and HeH⁺. In addition, we have measured the total light yield of several transitions in He I, He II, and H as a function of foil thickness using beams of HeH⁺ ions. Experiments were done with He-foil exit energies of 125, 500, 550, and 650 keV. He I alignment decreases in all cases for the thinnest foils when molecular projectiles are used. Total light intensities generally increase …

Magnetic Properties Of Rare Earth-Gallium-Iron Glasses, S.G. Cornelison, David J. Sellmyer, George C. Hadjipanayis

David Sellmyer Publications

Results of magnetic susceptibility, high-field magnetization, and Mössbauer effect are reported for several R-Ga and R-Ga-Fe metallic glasses, where R = Pr and Tb. Magnetic ordering temperatures, effective moments, and coercive forces were determined. In certain cases the data indicate that the low temperature states of magnetic order are asperomagnetic or spin-glass-like. For (Pr₈₀Ga₂₀)₈₀Fe₂₀, several anomalies were observed including a large coercive field (45 kOe) at 100 K. Journal of Applied Physics is copyrighted by The American Institute of Physics.

Ammonia Adsorption And Decomposition On A Ni(Ll0) Surface, M. Grunze, M. Golze, R.K. Driscoll, Peter A. Dowben

Peter Dowben Publications

We report UPS/XPS results for ammonia adsorption and decomposition on a Ni(1 10)-surface. At T < 130 K molecular adsorption of NH ₃ is observed to proceed with an initial sticking coefficient of s ₀-0.1. Increasing the temperature of the nickel surface above 150 K results in partial dissociation of the adsorbed NH ₃ molecules. The intermediate species are tentatively identified by their photoelectron spectra as NH-fragments. At temperatures above 350 K only atomic nitrogen is observed to populate the surface after NH ₃-exposures. Our data show a similar reactivity of the Ni(ll0) surface in the NH ₃-decomposition reaction as found on iron-single crystal …

Angular Differential And Total Cross Sections For The Excitation Of Atomic Hydrogen To Its N=2 State By Helium Ions, John E. Aldag, Jerry Peacher, Paul J. Martin, V. C. Sutcliffe, Jacob M. George, E. Redd, Thomas J. Kvale, D. M. Blankenship, John T. Park

Physics Faculty Research & Creative Works

Differential cross sections for 15-100 keV He⁺ excitation of atomic hydrogen to its n=2 level have been determined for c.m. angles from 0 to 8 mrad. The differential cross sections are obtained from an analysis of the angular distribution of the scattered ions which have lost an energy corresponding to the excitation of the target to its n=2 level. The shape of the differential cross section changes rapidly with increasing incident energy. At 15 keV, the differential cross section falls off by a factor of 5 in 6 mrad. At 100 keV, the differential cross section decreases by nearly …

Raman Investigation Of The Charge-Density-Wave Mixed-Crystal System 1t-Tas2-XSeX, J.R. Duffey, Roger D. Kirby

Roger Kirby Publications

The results of Raman scattering measurements on the mixed-crystal system 1T- TaS_2-xSe_x in the commensurate charge-density-wave state are reported. In the pure compounds, our measurements indicate that a strong LA-TA phonon interaction at the distortion wave-vector results in additional coupled charge-density-wave-lattice excitations. These excitations can be followed over the whole range of concentrations in the mixed crystals. The concentration dependences of the mode frequencies are treated using an effective oscillator model.

Landau Free Energy Form At The F Point Of The Roverline3 Structure, Dorian M. Hatch, Daniel L. Decker

Faculty Publications

A free energy form compatible with the F point of the trigonal D63d(Roverline3c) symmetry is constructed. It is a function of the order parameter, elastic strain, and the stress. The resulting free energy exhibits a close formalistic analogy to the stressed cubic perovskite structures and their associated multicriticality.

Effect Of Polarization And Absorption On Differential Cross Sections And Angular Correlation Parameters For Electron Excitation Of Helium, M. E. Stewart, Don H. Madison

Physics Faculty Research & Creative Works

The effects of local polarization and absorption potentials on differential cross sections and angular correlation parameters are studied within the distorted-wave approximation for electron excitation of the 2 ¹P state of helium. For examining the effect of local polarization, we have compared a recent numerical self-consistent adiabatic polarization potential for helium with the commonly used hydrogenic adiabatic polarization potential. Different radial regions for the polarization potential were studied to determine their contribution to the overall effect of polarization. Calculations are also presented which show the effects of different strengths for a local absorption potential.

Resonant Structure In The Π⁺ Π⁺Π‾ Π‾ System Between 1.5 And 1.9 Gev, F. A. Dibianca, William J. Fickinger, J. A. Malko, D. K. Robinson

Faculty Scholarship

Resonant structure is studied in the 1.5-to-1.9-GeV mass region of the neutral four-pion system in the reaction π+n→pπ+π+π-π- at 6 GeV/c incident momentum. The ρ0 and A2± content are determined as a function of the four-pion mass. The 4π mass spectrum is best fitted by two resonances, both of which decay predominantly into ρ0π+π-, each with evidence for an appreciable A2π component.

Four-Color And Hβ Photometry Of The Galactic Cluster Ngc 7790, Edward G. Schmidt

Edward Schmidt Publications

Observations have been obtained on the four-color and Hβ system of 16 stars in the field of NGC 7790. These represent virtually all of the stars which are in the B-star region of the cluster color-magnitude diagram. I discuss the membership of these stars and find three which are possibly field stars. The remaining stars indicate a true distance modulus of 11.98 ± 0.13 for the cluster and a color excess of E(b – y) = 0.403.

Observation Of The Transition From Semiconductor To High-Tc Superconductor In (Snxeu1-X)Ymo6s8 Under High Pressure, D. W. Harrison, K. C. Lim, J. D. Thompson, C. Y. Huang, Paul D. Hambourger, H. L. Luo

Physics Faculty Publications

Pressure-induced high-temperature superconductivity is observed in semiconducting (Sn_xEu_1-x)_yMo₆S₈, where 0<~x<~0.1 and y=1.0 and 1.2, having a carrier concentration ≃10¹⁹/cm³ at 4.2 K as determined from Hall-effect measurements. Above a threshold pressure ≃7 kbar, superconductivity appears with dT_c/dP≃2 K/kbar. The maximum superconducting temperature (T_c∼10 K), reached at ∼ 12 kbar, represents the highest pressure-induced T_c in any semiconductor. For P>~13 kbar, the temperature-dependent resistance appears metallic.

Electron-Spin-Resonance Modes And The Edwards-Anderson Theory Of The Spin-Glass State, S. E. Barnes

Physics Articles and Papers

It is shown that the ESR modes observed in Cu: Mn alloys can be explained in terms of an Edwards-Anderson-type theory for a spin-glass when an anisotropy energy is included. Unlike other theories, the present one involves the conventional form for this anisotropy, U_K=Ksin²θ, where θ is the angle the local microscopic magnetization makes with the symmetry rather than equilibrium direction. The present theory is distinguished by a predicted, but as yet unobserved, angular dependence of single-crystal samples with axial symmetry.

Driven "Portulum": A Rolling Ball As A Simple Oscillating System, Laurence A. Marschall

Physics and Astronomy Faculty Publications

A classroom demonstration, a variation of the simple swinging pendulum, is described. In our "portulum," a ball, driven by short blasts of air, rolls along a curved tube. The design of this device, its construction, and its usefulness to the teaching of physics are discussed. It is also shown that the oscillations of the rolling ball have the same mathematical form as the oscillations of the ball swinging along the same path, but with a lower frequency.

Wave Demonstration Device, Glen T. Clayton, Harry D. Downing, Thomas O. Callaway

Faculty Publications

Students often have difficulty gaining an understanding of wave motion without effective demonstrations being performed in the lecture. Many excellent approaches utilizing ripple tanks, waves on a spring, chain, rope, etc., are customarily employed. Perhaps the most well-known device for demonstrating many of the effects of wave motion is the shive or bell wave motion machine.¹ The purpose of the present note is to describe a simple, inexpensive device which can be easily constructed by a teacher or student and can be used to demonstrate many of the properties of wave motion.

Elevated Electron Temperatures In The Auroral E Layer Measured With The Chatanika Radar, Vincent B. Wickwar, C. Lathuillere, W. Kofman, G. Lejeune

All Physics Faculty Publications

An extensive series of spectral measurements has been made in the auroral E region with the Chatanika incoherent scatter radar. Becasue of the small scale length for variations of electron density, temperatures, and ion-neutral collisions we used the operating mode with the best possible range resolution—9 km. About 5% of the time the data exhibited an unusual spectral shape that was most pronounced at 105 and 110 km. Instead of being almost Gaussian with only a small hint of two peaks, the spectra are much wider, with two well-developed peaks. After carefully considering the validity of the measurements and their …

Energization Of Ionospheric Ions By Electrostatic Hydrogen Cyclotron Waves, Nagendra Singh, Robert W. Schunk, Jan Josef Sojka

All Physics Faculty Publications

Interactions between ionospheric ions and a monochromatic electrostatic hydrogen cyclotron wave were studied numerically for conditions corresponding to the auroral plasma. Strong heating of the minority ions He⁺, He⁺⁺, and O⁺ were observed. The fraction of the initial ion population which underwent heating was found to strongly depend on the mass, charge, and initial temperature of the ion species.

A Numerical Investigation Of A Certain One-Dimensional Ising Model, Jimmy Green

Masters Theses & Specialist Projects

The model is a linear chain in which each spin interacts with its 2r nearest neighbors, the interaction energy being proportional to 1/r. Using a method similar to that of Montroll, the partition function of the model in the thermodynamic limit is shown to be related to the largest eigenvalue of a certain matrix. The largest eigenvalue of the matrix is determined numerically for 3 < r < 12.

Also, a correct method is demonstrated for evaluating an improper limit of the model, in which the interaction range is set to the chain length before the limit of an infinite number of spins is …

Theoretical Predictions For Ion Composition In The High-Latitude Winter F-Region For Solar Minimum And Low Magnetic Activity, Jan Josef Sojka, W. John Raitt, Robert W. Schunk

All Physics Faculty Publications

We combined a simple plasma convection model with an ionospheric-atmospheric density model in order to study the ion composition in the high-latitude winter F-region at solar minimum for low geomagnetic activity. Our numerical study produced time-dependent, 3-dimensional, ion density distributions for the ions NO+, O2 +, N2 +, O+, N+, and He+. We covered the high-latitude ionosphere above 54°N magnetic latitude and at altitudes between 160 and 800 km for a time period of 1 complete day. From our study we found the following (1) The ion composition exhibits a significant variation with latitude, local time, altitude, and universal time. …

A Theoretical Study Of The High-Latitude Winter F Region At Solar Minimum For Low Magnetic Activity, Jan Josef Sojka, W. J. Raitt, Robert W. Schunk

All Physics Faculty Publications

We combined a simple plasma convection model with an ionospheric-atmospheric composition model in order to study the high-latitude winter F region at solar minimum for low magnetic activity. Our numerical study produced time dependent, three-dimensional ion density distributions for the ions NO+, O2 +, N2 +, O+, N+, and He+. We covered the high-latitude ionosphere above 54°N magnetic latitude and at altitudes between 160 and 800 km for a time period of one complete day. The main result we obtained was that high-latitude ionospheric features, such as the ‘main trough,’ the ‘ionization hole,’ the ‘tongue of ionization,’ the ‘aurorally produced …

Small Angle Neutron Scattering From High Impact Polystyrene, Oran Allan Pringle

Faculty Research & Creative Works

"It is difficult to imagine a world without plastics. Although the development of most modern plastic materials took place after 1930, such mat􀃞ria1s are so common today that the word "plastic" is often used as an adjective to connote cheapness or lack of substance. Nevertheless, it 1s important to remember that for many uses plastics offer technical and cost advantages over other materials. "Wood warps and rots, iron rusts and much glass is brittle, yet no one disputes the enormous value of the s e mate r i a 1 s. " although plastic (Bryd son, 1970, p. 7.) Similarly, …

How Do College Students Solve Proportion Problems?, Melvin C. Thorton, Robert Fuller

Robert G. Fuller Publications

Problems which could be solved using proportional reasoning were administered nationwide by college faculty to their own science classes during a three year period. The reasoning of more than 8000 students covering three sections of the country was classified as concrete, transitional, or formal using Piagetian categories. Data from the West closely replicated that from the Midwest on similar metric conversion tasks. Student performance changed noticeably with a different problem format. The percentages of students using a ratio formula, ratio attempt, or intuitive methods of solution held approximately constant over time, task, and section of the country. The data shows …

Hall Effect At High Pressure In (Snxeu1-X)1.2mo6s8, Paul D. Hambourger, C. Y. Huang, H. L. Luo

Physics Faculty Publications

No abstract provided.