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Physics Faculty Research & Creative Works

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Articles 1861 - 1890 of 1961

Full-Text Articles in Physical Sciences and Mathematics

Eikonal Distorted-Wave Calculation For The Excitation Of H By He, Jerry Peacher, Richard H. Shields Jun 1974

Eikonal Distorted-Wave Calculation For The Excitation Of H By He, Jerry Peacher, Richard H. Shields

Physics Faculty Research & Creative Works

The eikonal distorted-wave Born approximation developed recently by Chen, Joachain, and Watson is applied to hydrogen excitation by helium impact in the intermediate-energy range. The differential and total cross sections for the excitation of the hydrogen atom to the 2s, 2p±, or 2p0 state by helium impact are presented. These results are compared to experiment and previous calculations. The differential cross section for the excitation of hydrogen to the 2s state compares well with the experimental data of Thomas and Sauers in shape and slope, but has a discrepancy in magnitude.

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Pb And Bi L-Subshell Ionization Cross-Section Ratios Versus Proton Bombarding Energy From 0.5 To 4 Mev, Don H. Madison, A. B. Baskin, C. E. Busch, Stephen M. Shafroth Feb 1974

Pb And Bi L-Subshell Ionization Cross-Section Ratios Versus Proton Bombarding Energy From 0.5 To 4 Mev, Don H. Madison, A. B. Baskin, C. E. Busch, Stephen M. Shafroth

Physics Faculty Research & Creative Works

Experimental ratios of L-subshell cross sections are given for ionization of lead and bismuth by 0.5-4-MeV-proton bombardment. The ratio of the LII to LI cross sections exhibits a maximum near 1.75 MeV. Individual subshell cross sections are obtained from the experimental ratios and previous total-cross-section data. These subshell ratios and cross sections are compared with the theoretical predictions of the plane-wave Born approximation using nonrelativistic hydrogenic wave functions, of the binary-encounter approximation scaled from Mg K-shell cross sections, and of the binary-encounter approximation scaled from cross sections obtained using L-shell velocity distributions. It was found that both approximations …

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Eikonal Approximation Applied To Atom-Atom Excitation At Intermediate Energies: Excitation Of H By H, Richard H. Shields, Jerry Peacher Feb 1974

Eikonal Approximation Applied To Atom-Atom Excitation At Intermediate Energies: Excitation Of H By H, Richard H. Shields, Jerry Peacher

Physics Faculty Research & Creative Works

The eikonal distorted-wave Born approximation (DWBA) developed recently by Chen, Joachain, and Watson is applied to atom-atom excitation in the intermediate energy range. In this paper the excitation of a hydrogen atom to the 2s, 2p±, or 2p0 state by hydrogen impact is considered. Differential cross sections are presented. Total cross sections are presented and compared to previous calculations. It is shown that the eikonal DWBA results for the total cross section approach the two-state distortion-approximation results in the limit of high energy and very-small-angle scattering.

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Diffusion-Controlled Intrachain Reactions Of Polymers. I Theory, Gerald Wilemski, Marshall Fixman Feb 1974

Diffusion-Controlled Intrachain Reactions Of Polymers. I Theory, Gerald Wilemski, Marshall Fixman

Physics Faculty Research & Creative Works

A theory of diffusion-controlled intramolecularly catalyzed reactions of polymer chains in dilute solution is formulated. A closure approximation yields a soluble integral equation for (essentially) the transient rate of the reaction. The time dependent solution consists of a sum of simple exponential terms whose coefficients and decay constants can be readily calculated. The theory is also applied to luminescence quenching and ring-chain interconversion.

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Diffusion-Controlled Intrachain Reactions Of Polymers. Ii Results For A Pair Of Terminal Reactive Groups, Gerald Wilemski, Marshall Fixman Feb 1974

Diffusion-Controlled Intrachain Reactions Of Polymers. Ii Results For A Pair Of Terminal Reactive Groups, Gerald Wilemski, Marshall Fixman

Physics Faculty Research & Creative Works

The formulas and results of the preceding paper are used to calculate the rate of reaction between reactive groups attached to the ends of a polymer chain. Extensive numerical calculations have been made for both transient rate processes and steady state luminescence quenching. The results are restricted to chains in dilute solution, in either the free draining or nondraining limits and with no excluded volume forces present. A discussion of the qualitative effects of excluded volume forces on the results is included. The results suggest that experimental studies of these processes may be feasible.

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Charge Transfer Between O Ions And O2 Molecules In The Ground State And Singlet Delta Excited State, R. F. Mathis, William R. Snow Jan 1974

Charge Transfer Between O Ions And O2 Molecules In The Ground State And Singlet Delta Excited State, R. F. Mathis, William R. Snow

Physics Faculty Research & Creative Works

A crossed-beam apparatus has been used to study charge transfer between O- ions and O2 molecules in the ground state and in the metastable, singlet delta, excited state. The energy of the incident ions ranged from 10 to 10000 eV. The cross section for charge transfer between O - and ground state O2 was found to have a maximum of 7.8X10-16 cm2 at about 5 keV. At the lower energies there is good agreement with the previous measurements of Snow et al. and Rutherford and Turner who also used crossed beam techniques. The cross section for charge transfer between O- …

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Structural Strain In Small Prenucleation Water Clusters, Donald E. Hagen Jan 1974

Structural Strain In Small Prenucleation Water Clusters, Donald E. Hagen

Physics Faculty Research & Creative Works

A method is developed for incorporating strain energy into a microphysical treatment of small prenucleation water clusters. The molecules are arranged in a clathrate-cage structure, and this structure is allowed to relax to minimize the strain energy resulting from hydrogen bond stretching and bending. The method is applied to various cluster sizes up to 130 molecules and the results are compared with the classical liquid drop model. The effect of anharmonic terms in the interaction is included.

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Optical Pumping In A Flowing Helium Afterglow With Additive Metal Impurity Atoms, Laird D. Schearer Jan 1974

Optical Pumping In A Flowing Helium Afterglow With Additive Metal Impurity Atoms, Laird D. Schearer

Physics Faculty Research & Creative Works

It is demonstrated that in a Penning collision of optically oriented metastable helium atoms with an impurity metal atom such as barium, both the longitudinal and transverse components of spin angular momentum are conserved. This results in a polarization of the ion which may be detected by optical emission in the case of excited ion levels or absorption for the ground states. A series of experiments is described which demonstrates the spin dependence of the Penning-collision process. The magnetic resonance of excited-state ions may be observed directly; from the resonance-linewidth radiative lifetimes may be measured. © 1974 The American Physical …

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Measurements Of The Average Electric Dipole Polarizabilities Of The Alkali Dimers, Robert W. Molof, Thomas M. Miller, Henry L. Schwartz, Benjamin Bederson, John T. Park Jan 1974

Measurements Of The Average Electric Dipole Polarizabilities Of The Alkali Dimers, Robert W. Molof, Thomas M. Miller, Henry L. Schwartz, Benjamin Bederson, John T. Park

Physics Faculty Research & Creative Works

The average electric dipole polarizabilities of the homonuclear alkali dimers have been measured in an electric deflection experiment. The molecular results are normalized to the corresponding atomic polarizabilities by comparing deflections of atomic and molecular alkali beams passing through an inhomogenous electrostatic field. The average polarizabilities in units of 10-24 cm3 are: Li2(990°K), 34±3; Na2(736°K), 30±3; K2(569°K), 61±5; Rb2(534°K), 68±7; Cs2(515°K), 91±7. Copyright © 1974 American Institute of Physics.

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Evaluation Of Model For The Contributin Of Phonon-Induced Tunneling To Donor Esr Spectral Narrowing In Germanium, David L. Meier, William F. Parks, Edward Boyd Hale Jan 1974

Evaluation Of Model For The Contributin Of Phonon-Induced Tunneling To Donor Esr Spectral Narrowing In Germanium, David L. Meier, William F. Parks, Edward Boyd Hale

Physics Faculty Research & Creative Works

The model commonly assumed to explain the narrowing of the ESR spectra of donor impurities in germanium is examined in detail. This model combines the Anderson line-narrowing theory with the Miller and Abrahams theory for the phonon-induced tunneling (hopping) of an electron between impurities. The predictions of this model are found to be in drastic disagreement with experimental results now available. It is shown that the narrowed linewidth should depend strongly on donor concentration, acceptor concentration, and temperature. Future spin-resonance experiments in highly compensated samples may show the effects of hopping, but no evidence now exists which indicates that hopping …

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Fresnel Drag In Uniformly Moving Media, William F. Parks, J. T. Dowell Jan 1974

Fresnel Drag In Uniformly Moving Media, William F. Parks, J. T. Dowell

Physics Faculty Research & Creative Works

A general first-order formula is derived for the Fresnel-drag effect in a uniformly moving medium with a plane surface. The two classical equations due to Lorentz and Laub are shown to be special cases corresponding to different experimental arrangements. The recent experiment of Bilger and Zavodny on Fresnel drag in a ring laser is discussed. © 1974 The American Physical Society.

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Dispersion Curves For Surface Electromagnetic Waves With Damping, Ralph William Alexander, G. S. Kovener, Robert John Bell Jan 1974

Dispersion Curves For Surface Electromagnetic Waves With Damping, Ralph William Alexander, G. S. Kovener, Robert John Bell

Physics Faculty Research & Creative Works

The Recent Observation of Back bending in the Dispersion Curves of Surface Plasmons on Silver Can Be Explained by Use of Fresnel's Equations. in the Presence of Damping, the Results of Attenuated-Total-Reflection Measurements Can Be Displayed as Dispersion Curves Either with or Without Back bending. the Measurements for Silver with Back Bending Are Expected for Experiments in Which the Frequency is Fixed, and the Propagation Constant (Or Angle of Incidence) is Swept. © 1974 the American Physical Society.

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On The Lambda Transition In Solid Orthohydrogen, Harry A. Brown Jan 1974

On The Lambda Transition In Solid Orthohydrogen, Harry A. Brown

Physics Faculty Research & Creative Works

No abstract provided.

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Erratum: Radiative And Predissociative Lifetimes Of The A ²Σ+ State Of Oh, Richard A. Anderson, R. A. Sutherland Dec 1973

Erratum: Radiative And Predissociative Lifetimes Of The A ²Σ+ State Of Oh, Richard A. Anderson, R. A. Sutherland

Physics Faculty Research & Creative Works

No abstract provided.

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Properties Of Microwave Cavities Containing Magnetic Resonant Samples, Kathy A. Rages, Robert E. Sawyer, Edward Boyd Hale Dec 1973

Properties Of Microwave Cavities Containing Magnetic Resonant Samples, Kathy A. Rages, Robert E. Sawyer, Edward Boyd Hale

Physics Faculty Research & Creative Works

Properties of TE011 cylindrical, microwave cavities containing cylindrical samples of various radii and dielectric constants are calculated. The properties considered are the resonant frequency, quality factor (Q), relevant magnetic filling factor for spin transitions (ε), and a signal sensitivity factor (Qε) for a lossless sample. Sample sizes range from zero radius to full cavity radius with some experimental data on less than full length samples. The choice of dielectric constants ranges from one to sixteen. The data are presented in dimensionless form since they will be of use to other ESR experimentalists. It is shown that use of large samples …

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Electron Spin Resonance In Argon-Ion-Implanted Silicon, Keh Chang Chu, Weiler R. Hurren, Edward Boyd Hale, John Reigle Dec 1973

Electron Spin Resonance In Argon-Ion-Implanted Silicon, Keh Chang Chu, Weiler R. Hurren, Edward Boyd Hale, John Reigle

Physics Faculty Research & Creative Works

A new paramagnetic center with g = 2.0029 is observed, in both n- and p-type silicon after they are heavily implanted (higher than 1017 ions/cm2) with 150-keV argon ions. © 1973 American Institute of Physics.

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Distorted-Wave Approximation And Its Application To The Differential And Integrated Cross Sections For Electron-Impact Excitation Of The 2¹P State Of Helium, Don H. Madison, W. Neil Shelton Feb 1973

Distorted-Wave Approximation And Its Application To The Differential And Integrated Cross Sections For Electron-Impact Excitation Of The 2¹P State Of Helium, Don H. Madison, W. Neil Shelton

Physics Faculty Research & Creative Works

Theoretical results are given for the application of the distorted-wave approximation to electron-atom impact excitation for transitions from an L-S coupled initial state to an arbitrarily coupled final state. Expressions for the differential cross section and spin polarization of the emitted electrons are given for unpolarized electron beams incident upon unpolarized atoms. These results are applied to excitation of helium from its ground state to the 1s2p1P1 excited state for incident-electron energies between 26.5 and 300 eV. The results are compared with previous theoretical and experimental works. It is found that the distorted-wave calculation is superior to …

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Spin Polarization And Differential Cross Section For Electron-Impact Excitation Of The 6s6p ¹P₁ State Of Mercury: Distorted-Wave Treatment, Don H. Madison, W. Neil Shelton Feb 1973

Spin Polarization And Differential Cross Section For Electron-Impact Excitation Of The 6s6p ¹P₁ State Of Mercury: Distorted-Wave Treatment, Don H. Madison, W. Neil Shelton

Physics Faculty Research & Creative Works

The results of the distorted-wave theory for electron-impact excitation of atoms are applied to the excitation of the 6s6p 1P1 state of mercury. The spin polarization and the differential cross section are given for unpolarized incident electron beams with energies between 25 and 180 eV. The distorted-wave results are compared with experimental data, and good agreement is found for both the spin polarization and differential cross section.

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Note On The Poisson Distribution, I. Adawi Jan 1973

Note On The Poisson Distribution, I. Adawi

Physics Faculty Research & Creative Works

No abstract provided.

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Production Of Metastable Ions In Cesium-Atom-Electron Collisions, Kaare J. Nygaard, Yu Bong Hahn Jan 1973

Production Of Metastable Ions In Cesium-Atom-Electron Collisions, Kaare J. Nygaard, Yu Bong Hahn

Physics Faculty Research & Creative Works

The structure in the total electron-impact ionization cross section in cesium can be partially accounted for by the mechanisms of autoionization and excitation ionization of 5p electrons. For electron energies above 17 eV a large fraction of the ions are metastable and can de detected by Auger emission from a metal surface. The experiment was performed in a cesium-atom-electron crossed-beam apparatus, and the metastable ions were counted with a channel electron multiplier. The metastable-ion count rate was a factor of 100 higher than that due to photons from atomic and ionic transitions. We have measured the over-all excitation function for …

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Total Electron Impact Ionization Cross Section In Rubidium From Threshold To 250 Ev, Kaare J. Nygaard, Yu Bong Hahn Jan 1973

Total Electron Impact Ionization Cross Section In Rubidium From Threshold To 250 Ev, Kaare J. Nygaard, Yu Bong Hahn

Physics Faculty Research & Creative Works

A study of ionization in rubidium has been made in a crossed atom-electron beam apparatus. At an electron energy of about 10 eV there is a maximum in the cross section corresponding to the maximum probability for removal of the 5s valence electron. At 16.5 eV we have observed a new peak that is caused by the mechanism of autoionization. For energies below 30 eV there is a good agreement, both in shape and magnitude, between the present measurements and the empirical formula of Lotz. The over-all uncertainty in the measurements is ± 12% which is mostly accounted for by …

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On The Effect Of Cesium In Photoionization Laser Plasmas, Kaare J. Nygaard Jan 1973

On The Effect Of Cesium In Photoionization Laser Plasmas, Kaare J. Nygaard

Physics Faculty Research & Creative Works

A number of photoionization mechanisms and how they can be used to generate large-volume laser plasmas are discussed. Reaction rates for two-step photoionization of the cesium atoms as well as formation of molecular ions (Cs2+) are estimated. The necessary cross-section data were obtained from related research in thermionic energy converters. © 1973, IEEE. All rights reserved.

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Penning Ionization Of Zn And Cd By Noble-Gas Metastable Atoms, L. A. Riseberg, William F. Parks, Laird D. Schearer Jan 1973

Penning Ionization Of Zn And Cd By Noble-Gas Metastable Atoms, L. A. Riseberg, William F. Parks, Laird D. Schearer

Physics Faculty Research & Creative Works

The Penning-ionization cross sections for He, Ne, Ar, and Kr metastable atoms with Zn and Cd have been measured in a pulsed afterglow. Within the framework of existing theories we have determined those parameters which are of importance in collisions of this type. We find that our data are internally consistent if the cross sections are proportional to the cube of the "hard-sphere" radii and the effects of selection rules are included. A theoretical basis for this dependence is suggested. © 1973 The American Physical Society.

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Absolute Differential Elastic- And Inelastic-Scattering Cross Sections In 25-140 Kev He+ + He Collisions, Victor Pol, Walter Kauppila, John T. Park Jan 1973

Absolute Differential Elastic- And Inelastic-Scattering Cross Sections In 25-140 Kev He+ + He Collisions, Victor Pol, Walter Kauppila, John T. Park

Physics Faculty Research & Creative Works

Data obtained as energy-loss spectra at angles from 0 to 7.3x10-3 rad (c.m.) with typical energy-loss resolution of 0.7 eV and angular resolution of 2x10-3 rad (c.m.) were used to calculate average differential cross sections dσdΩav for elastic scattering, direct excitation of the individual He(n=2) states, and direct excitation of the He+(n=2) states. The total cross section for excitation of the He(n=2) states obtained by integrating the differential cross sections was found to be 20x10-18 cm2 at 25 keV (lab) decreasing to 7x10-18 cm2 at 140 keV. At incident lab energies below 100 keV the He(2S2) and He(2P3) states dominate …

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Molecular Beam Measurements Of Total Collision Cross Sections Of H 22o, William R. Snow, J. T. Dowell, J. G. Chevrenak, H. E. Berek Jan 1973

Molecular Beam Measurements Of Total Collision Cross Sections Of H 22o, William R. Snow, J. T. Dowell, J. G. Chevrenak, H. E. Berek

Physics Faculty Research & Creative Works

The total cross section for H22O-H22O scattering is measured with a supersonic nozzle beam system. The primary beam has a narrow velocity distribution, and the velocity is varied by control of the nozzle temperature. Velocities are determined by time-of-flight techniques. Cross sections obtained are averages over a Maxwellian distribution of the target molecules. Data at three velocities are presented. The cross sections for H2O are surprisingly small, for example, 3.07 x10-14 cm2 at 1x105 cm/sec, indicating little contribution from the dipole-dipole interaction.

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Laser Scattering Measurements Of Droplet Growth In Binary Mixtures. Ii. H2o And Argon H2o And Helium, M. A. Viettit, Burton Schuster Jan 1973

Laser Scattering Measurements Of Droplet Growth In Binary Mixtures. Ii. H2o And Argon H2o And Helium, M. A. Viettit, Burton Schuster

Physics Faculty Research & Creative Works

Water droplet growth rates in a Wilson cloud chamber were measured in Ar-H2O and He-H2O media. These rates were determined in the size range 0.45-10.0 u.m by detection of oscillations in the intensity of polarized light from a He-Ne laser source scattered at 30° by the droplet population. Pressure and initial temperature were measured in the chamber for use in the computation of three droplet growth theories for comparison to experiment. Experiments were conducted in supersaturations ranging from 1.04 to 3.45.

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General Theory Of Diffusion-Controlled Reactions, Gerald Wilemski, Marshall Fixman Jan 1973

General Theory Of Diffusion-Controlled Reactions, Gerald Wilemski, Marshall Fixman

Physics Faculty Research & Creative Works

A formal mathematical description of diffusion-controlled bimolecular reactions is presented. The theory is completely general with respect to the kinds of reaction processes that may be considered. Besides the presentation of the general formalism, the paper also contains several examples illustrating the application of the theory to a simple many-particule system for simple catalytic bimolecular reactions, including fluorescence quenching. The manner in which approximate solutions may be obtained is also outlined.

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Gaas Laser Experiments For The Undergraduate Laboratory, R. E. Robert, Daniel J. Jones, Kaare J. Nygaard Jan 1973

Gaas Laser Experiments For The Undergraduate Laboratory, R. E. Robert, Daniel J. Jones, Kaare J. Nygaard

Physics Faculty Research & Creative Works

No abstract provided.

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Chemical Shift Parameters For Shallow Donors In Semiconductors, Edward Boyd Hale Jan 1973

Chemical Shift Parameters For Shallow Donors In Semiconductors, Edward Boyd Hale

Physics Faculty Research & Creative Works

A model for a shallow donor impurity in a semiconductor is used to calculate two relationships and several conditions involving the chemical shift parameters. The model is based on the standard effective mass form for the donor electron wave function, the existence of a potential in the chemical cell which may be real, pseudo, or rather general in nature, and a few somewhat restrictive approximations. The parameters, Δ, δ and Λ are theoretically calculated and are shown to be related if the approximations are valid. These parameters determine the 1S multiplet level structure and it is shown how properties of …

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Possible Applications Of Surface Electromagnetic Waves To Measure Absorption Coefficients, Ralph William Alexander, Robert John Bell, C. A. Ward, James Roger Weaver, I. L. Tyler, B. Fischer Jan 1973

Possible Applications Of Surface Electromagnetic Waves To Measure Absorption Coefficients, Ralph William Alexander, Robert John Bell, C. A. Ward, James Roger Weaver, I. L. Tyler, B. Fischer

Physics Faculty Research & Creative Works

We Show that Surface Electromagnetic Waves Can Probably Be Used to Measure the Absorption Coefficients of Materials overlaying Metals. the Proposed Experimental Method is Illustrated in the Infrared Frequency Range using Water, Teflon, and Polyethylene as Sample Materials.

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