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Articles 17971 - 18000 of 18253

Full-Text Articles in Physics

Associative Detachment: H+H-2*+E, Joseph C.Y. Chen, Jerry Peacher Apr 1968

Associative Detachment: H+H-→2*+E, Joseph C.Y. Chen, Jerry Peacher

Physics Faculty Research & Creative Works

The process of associative detachment in the (H,H-) collision system is investigated at energies below 12 eV. In this energy region, the interaction potential between H and H- has recently been determined. The energy dependence of the cross section is calculated with explicit allowance for the production of "hot" hydrogen molecules. It is observed that associative detachment provides a possible mechanism for generating an inverted population of the residual molecule such as H2.


New Superconvergent Dispersion Relations For The Forward Πn Crossing-Even Amplitude, David J. George, Barbara N. Hale, Arnold Tubis Apr 1968

New Superconvergent Dispersion Relations For The Forward Πn Crossing-Even Amplitude, David J. George, Barbara N. Hale, Arnold Tubis

Physics Faculty Research & Creative Works

A Liu-Okubo-type dispersion relation is derived for the crossing-even pion-nucleon forward elastic scattering amplitude T(+). Two subtractions are made, one at the physical scattering threshold and the other at a previously determined zero of T(+) on the imaginary axis of the complex ω (pion lab energy) plane. The dispersion relation is well satisfied over the whole allowed range of the Liu-Okubo parameter. Moreover, it is nearly saturated by low-energy scattering for a considerable range of the parameter. It should thus serve as an extremely sensitive test of the low-energy scattering data when such data become more accurately known.


Electrical Conductivity Of Potassium Chloride, Robert Fuller, Michael H. Reilly, Charles L. Marquardt, John C. Wells Mar 1968

Electrical Conductivity Of Potassium Chloride, Robert Fuller, Michael H. Reilly, Charles L. Marquardt, John C. Wells

Robert G. Fuller Publications and Presentations

The electrical conductivity of potassium chloride is discussed within the framework of a four-defect model of the crystal. The four defects are mobile anion and cation vacancies and immobile divalent cation impurities and divalent cation impurity-cation vacancy complexes. The Teltow formulation of the four-defect mode1 fails to describe precisely the measured electrical conductivity of KCl over the entire intrinsic and extrinsic range.


Interaction Potential Between The Ground States Of H And H-, Joseph C.Y. Chen, Jerry Peacher Mar 1968

Interaction Potential Between The Ground States Of H And H-, Joseph C.Y. Chen, Jerry Peacher

Physics Faculty Research & Creative Works

An investigation of the interaction potential for H and H- in both ungerade and gerade modes is carried out by a semiempirical method in which the recently observed isotope effect in dissociative attachment of electrons to hydrogen molecules is used. The interaction obtained is complex, and the imaginary parts of the interaction account for electron emissions during the course of the interaction. A comparison of the present result with other calculations is presented. The isotope effect in dissociative attachment is also discussed. It is shown that the ratios of the survival probabilities alone do not provide an adequate approximation for ...


A Method For Measuring Magnetization To High Pressures, C. R. Johansen, Mark H. Nelson, J. H. Gardner Mar 1968

A Method For Measuring Magnetization To High Pressures, C. R. Johansen, Mark H. Nelson, J. H. Gardner

Faculty Publications

A partially successful attempt has been made to measure the magnetic moment per unit volume of ferromagnetic materials as a function of pressure to the 100-kbar region. The apparatus, an early version of which has been described previously, consists basically of two opposed Bridgman flat anvils of alumina. One anvil also acts as a dielectric-filled microwave resonant cavity for an x-band spectrometer, allowing electron spin resonance studies to be made to high pressure. The sample to be studied is placed in contact with the anvil-cavity and covered with a pressure-transmitting medium which in turn is encircled by a flat pyrophyllite ...


Projected Hartree Product Wavefunctions, Gordon A. Gallup Feb 1968

Projected Hartree Product Wavefunctions, Gordon A. Gallup

Gordon Gallup Publications

A method for performing a restricted configuration interaction calculation on atoms or molecules based on the use of Young operators from the symmetric groups is discussed and its relation to some other types of calculations is pointed out. The method in its most general form can be said to be an extension of the independent particle approach which represents the wavefunction in terms of the n best possible one-particle orbitals for the n-particle system. Illustrations are given for the hydrogen molecule, the helium atom, and the allyl radical. ©1968 American Institute of Physics


Mössbauer Effect In 57Fe In Copper And The Spin‐Compensated State, B. B. Schwartz, D. J. Kim, Richard B. Frankel, N. A. Blum Feb 1968

Mössbauer Effect In 57Fe In Copper And The Spin‐Compensated State, B. B. Schwartz, D. J. Kim, Richard B. Frankel, N. A. Blum

Physics

The results of Mössbauer experiments on dilute Fe in Cu in high external magnetic fields (42–146 kOe) are presented here as evidence for significant destruction of the spin‐compensated state by a magnetic field for which μH0∼kTK, where kTK is on the order of the energy change associated with the formation of the spin‐compensated state.


Magnetic‐Field Dependence Of The Hyperfine Field At Fe In Dilute Fe-Pd Alloys, N. A. Blum, Richard B. Frankel Feb 1968

Magnetic‐Field Dependence Of The Hyperfine Field At Fe In Dilute Fe-Pd Alloys, N. A. Blum, Richard B. Frankel

Physics

No abstract provided.


Nonadiabatic Long-Range Forces, A. Dalgarno, Gordon W. F. Drake, G. A. Victor Jan 1968

Nonadiabatic Long-Range Forces, A. Dalgarno, Gordon W. F. Drake, G. A. Victor

Physics Publications

A general expression is obtained for the leading long-range correction to the static interaction of a slowly moving charged or neutral system at a large distance from a spherically symmetric atom, and precise estimates are presented of the magnitude for the systems H, HeA (1S1,2S1,A and A 2S3), Ne, Ar, Kr, Xe, Li+A (1S1,2S1,A and A 2S3), Li, Na, K, Rb, Cs, H2, N2, and CH4. © 1968 The American Physical Society.


Energy Spectra Of Auto-Ionizing Electrons In Oxygen, M. Eugene Rudd, Kenneth Smith Jan 1968

Energy Spectra Of Auto-Ionizing Electrons In Oxygen, M. Eugene Rudd, Kenneth Smith

M. Eugene Rudd Publications

Experimental and theoretical data are presented showing the energy spectra of auto-ionizing electrons from atomic oxygen. The experimental data were obtained by bombarding oxygen gas with 100-keV H+ and He+ ions; the theoretical results were obtained in a close-coupling calculation which coupled the 4S, 2D, and 2P terms of the ground-state configuration of O+ in electron-O+ scattering.


Optimum Spacing Of Square And Circular Coil Pairs, M. Eugene Rudd, J. R. Craig Jan 1968

Optimum Spacing Of Square And Circular Coil Pairs, M. Eugene Rudd, J. R. Craig

M. Eugene Rudd Publications

In a previous note Crownfield pointed out that the magnetic field along the axis of a coil pair is within a prescribed uniformity over a substantially longer region than that given by the Helmholtz spacing if a somewhat larger spacing is used. In the note, values of coil spacing and length of uniform field region are given for a few desired uniformities, but only for a particular "thick" coil pair, i.e., one with cross-sectional dimensions comparable to the spacing. Many coil pairs, such as those used to annul the earth's field over the region occupied by some apparatus ...


Excitation Of Auto-Ionizing Levels In Neon By Ion Impact, A. K. Edwards, M. Eugene Rudd Jan 1968

Excitation Of Auto-Ionizing Levels In Neon By Ion Impact, A. K. Edwards, M. Eugene Rudd

M. Eugene Rudd Publications

Auto-ionizing states of neutral and singly ionized neon were produced by bombarding neon gas with H+, He+, and Ne+ ions in the 150-250-keV energy range. Sixty lines in the electron spectrum were found, of which 43 have been classified into 13 Rydberg series. Ten of these series were previously unreported. Auger electrons from one- and two-vacancy states are also reported. Relative intensities of all transitions are listed.


Nuclear Spin-Lattice Relaxation Measurements By Tone-Burst Modulation, David C. Look, Donald R. Locker Jan 1968

Nuclear Spin-Lattice Relaxation Measurements By Tone-Burst Modulation, David C. Look, Donald R. Locker

Physics Faculty Publications

No abstract provided.


Luminescence Of F Centers In Alkali Halides Under Hydrostatic Pressure, A. D. Brothers, David W. Lynch Dec 1967

Luminescence Of F Centers In Alkali Halides Under Hydrostatic Pressure, A. D. Brothers, David W. Lynch

Physics and Astronomy Publications

F-center luminescence spectra have been measured at 78°K in NaCl, KCl, KBr, KI, RbCl, and CsBr under hydrostatic pressure to 3.5 kbar. From a comparison between the shift of the emission peak with pressure and the shift with temperature, it is concluded that most of the latter arises from the electron-lattice interaction and not from thermal expansion. This is the opposite of the conclusion for F-center absorption, for which thermal expansion dominates the temperature coefficient of the peak energy. The halfwidth of the function W(E), the probability per unit time of emitting a photon with energy between ...


Survival Probability In Dissociative Attachment, Joseph C.Y. Chen, Jerry Peacher Nov 1967

Survival Probability In Dissociative Attachment, Joseph C.Y. Chen, Jerry Peacher

Physics Faculty Research & Creative Works

The survival probability in dissociative attachment is investigated with special attention to the (e, H2 ) system. It is shown that the simple expression for the dissociative-attachment cross section, as given by the product of a capture cross section and a survival probability, is equivalent to the s -wave approximation for the g → g dissociative attachment. This expression, however, does not constitute an approximation for the g → u dissociative attachment, since the parity of the initial rotational states of H2 is always opposite to that of the relative angular momentum states of H and H- and the capture cross ...


Very High Pressure Effects Upon The Epr Spectrum Of Ruby, H. Mark Nelson, D. B. Larson, J. H. Gardner Sep 1967

Very High Pressure Effects Upon The Epr Spectrum Of Ruby, H. Mark Nelson, D. B. Larson, J. H. Gardner

Faculty Publications

The variation in the electron paramagnetic resonance (EPR) spectrum of ruby as a function of pressure has been observed to beyond 70 kbar for a magnetic field orientation parallel to the crystalline c axis. The data can be interpreted in terms of the usual spin Hamiltonian, where the spectroscopic splitting factor g|| has the same value as at ambient pressures, but where the zero-field splitting deltaincreases in a linear fashion from 0.38 to 0.43 cm. The experimental apparatus has been described previously, although important improvements in the pressure seal and in the pressure calibration have been made and ...


Mössbauer Study Of Ferrimagnetic Ordering In Nickel Ferrite And Chromium-Substituted Nickel Ferrite, J. Chappert, Richard B. Frankel Sep 1967

Mössbauer Study Of Ferrimagnetic Ordering In Nickel Ferrite And Chromium-Substituted Nickel Ferrite, J. Chappert, Richard B. Frankel

Physics

Mössbauer-effect measurements in external magnetic fields show that the magnetic structure of ferrimagnetic NiFe2O4 is the collinear Néel type. NiFe0.3Cr1.7O4 is shown to have a triangular structure with θA=20±10° and θB=50±4°.


High-Field Magnetoresistance Of Ordered Beta Brass , David J. Sellmyer, J. Ahn, J.-P. Jan Sep 1967

High-Field Magnetoresistance Of Ordered Beta Brass , David J. Sellmyer, J. Ahn, J.-P. Jan

David Sellmyer Publications

The magnetoresistance of several single-crystal specimens of ordered β-brass has been investigated in fields up to 150 kG. The purity of the samples is sufficiently high (ρ2954.2≃400) that the high-field condition is satisfied. The results indicate that ordered β-brass is an uncompensated metal and that its Fermi surface is multiply connected. Strong open orbits were observed when the field was in {110} or {100} planes, and this behavior is compatible with the Fermi-surface model predicted by augmented-plane-wave and Green's-function energy-band calculations. Evidence for the existence of higher-order open orbits and two-dimensional regions of open ...


Room-Temperature Second-Order Raman Spectra Of Csc1, Csbr, And Csi, A. M. Karo, John R. Hardy Aug 1967

Room-Temperature Second-Order Raman Spectra Of Csc1, Csbr, And Csi, A. M. Karo, John R. Hardy

John R. Hardy Papers

The room-temperature Raman spectra of CsC1, CsBr, and CsI have been computed from a simple, combined density-of-states approximation. Calculations have been made for four different model potential functions and compared with experiment in the cases of CsBr and CsI. In this way it is found that one of the variations, called the DD(-) model, is the most satisfactory. The agreement with the observed spectra is surprisingly close when one considers that no allowance has been made for variations in the elements of the Raman polarizability tensor.


Noise In Cadmium Sulfide & Cadmium Selenide Photoconductive Cells, Edward Foster Aug 1967

Noise In Cadmium Sulfide & Cadmium Selenide Photoconductive Cells, Edward Foster

Masters Theses & Specialist Projects

The primary object of this investigation is to design a system, including equipment and procedures, that can be used to evaluate the noise characteristics of photoconductive cells. The data once collected must be in a comprehensive and useful form. The secondary object is to use this system to evaluate a large number of cells of various types and to compare their noise profiles in a manner such that definite conclusions can be drawn concerning the absolute noise levels and profiles generated by the various cell types and the relations that may exist between the cells' noise output and the way ...


Fe1+ And Fe2+ Hyperfine Fields In Mgo And Cao, J. Chappert, Richard B. Frankel, N. A. Blum Jul 1967

Fe1+ And Fe2+ Hyperfine Fields In Mgo And Cao, J. Chappert, Richard B. Frankel, N. A. Blum

Physics

Hyperfine interactions have been measured for Fe1+ and Fe2+ in MgO and CaO. The core polarization fields per spin moment are −127 kOeμB for both Fe1+ and Fe2+.


Evaluation Of The Dispersion Relations Of Photoproduction, Paul Finkler Jul 1967

Evaluation Of The Dispersion Relations Of Photoproduction, Paul Finkler

Paul Finkler Papers

A modification of the Omnes method is used to solve the singular integral equations for the 3-3 partialwave amplitudes of photoproduction. The effects of multipion production are assumed to be negligible. The method requires a knowledge of the phase at all energies. Consequently, it is necessary to treat the corresponding pion-nucleon scattering problem to determine the eBect of the high-energy behavior of the phase on the solution for the scattering amplitude at low energies. The sharply resonant nature of the problen suggests an approximation in the form of solution, rather than in the Born terms, which leads to relatively simple ...


Anion Contributions To The Electrical Conductivity Of Alkali Chlorides, Robert Fuller, M.H. Reilly Jul 1967

Anion Contributions To The Electrical Conductivity Of Alkali Chlorides, Robert Fuller, M.H. Reilly

Robert G. Fuller Publications and Presentations

The measured electrical conductivity of pure RbCl is separated into the usual anion and cation contributions with activation energies of 2.55 and 1.58 eV, respectively. By comparison with corresponding results for KC1 and NaCl it is found that the alkali-chloride anion and cation activation energies differ most for nearly equal anion and cation radii. We conclude from this anomalous trend that an extension of conventional theory is required.


Effect Of Bound States On The Excitation Spectrum Of A Heisenberg Ferromagnet At Low Temperature, Richard Silberglitt, A. Brooks Harris Jul 1967

Effect Of Bound States On The Excitation Spectrum Of A Heisenberg Ferromagnet At Low Temperature, Richard Silberglitt, A. Brooks Harris

Department of Physics Papers

A compact expression for the energy shift and inverse lifetime (energy width) of spin waves in a Heisenberg ferromagnet at low temperatures is given. The two-particle bound states are observable via the resonance they cause in the self-energy of spin waves.


Temperature And Pressure Dependence Of The Optical Absorption And Luminescence Of A Defect In Tlcl, A. D. Brothers, David W. Lynch Jul 1967

Temperature And Pressure Dependence Of The Optical Absorption And Luminescence Of A Defect In Tlcl, A. D. Brothers, David W. Lynch

Physics and Astronomy Publications

The luminescence associated with an absorption band at about 3.0 eV in chalcogen-doped TlCl has been observed. The temperature and pressure coefficients of the positions of the absorption and emission peaks have been found to have "anomalous" negative signs. The temperature coefficient of the absorption peak is dominated by the effect of thermal expansion, the band shifting toward the blue as the lattice expands. The emission peak exhibits very little temperature dependence. Some arguments are presented in favor of interpreting this band as an exciton band associated with an anion vacancy (α band) instead of an F band. Lattice ...


F Band In X- And Electron-Irradiated Caf2, David A. Patterson, Robert Fuller Jun 1967

F Band In X- And Electron-Irradiated Caf2, David A. Patterson, Robert Fuller

Robert G. Fuller Publications and Presentations

This Letter reports an investigation using pulsed electron irradiation to determine if the low efficiency of F-band coloration in calcium fluoride is caused by the instability of the F center. No transient F centers were seen in times as short as 2 x 10-7 sec. It is concluded that the inherent efficiency of F-band coloration in CaF2 is small compared with similar processes in alkali halides and a possible reason for this is discussed.

Calcium fluoride has been extensively studied and is found to be more difficult to color than alkali halides and to have absorption ...


Integral Series Solution Of The Schrödinger Equation For The Helium Atom, W. Byers Brown, Ronald White Jun 1967

Integral Series Solution Of The Schrödinger Equation For The Helium Atom, W. Byers Brown, Ronald White

Center for Advanced Mineral and Metallurgical Processing (CAMP)

No abstract provided.


Analytic Power-Series Solution Of The Schrödinger Equation For The Helium Atom, W. Byers Brown, Ronald White Jun 1967

Analytic Power-Series Solution Of The Schrödinger Equation For The Helium Atom, W. Byers Brown, Ronald White

Center for Advanced Mineral and Metallurgical Processing (CAMP)

No abstract provided.


Mössbauer Evidence For A Spin-Compensated State In Dilute Fe-Cu Alloys, Richard B. Frankel, N. A. Blum, Brian B. Schwartz, Duk Joo Kim Jun 1967

Mössbauer Evidence For A Spin-Compensated State In Dilute Fe-Cu Alloys, Richard B. Frankel, N. A. Blum, Brian B. Schwartz, Duk Joo Kim

Physics

No abstract provided.


Inelastic Collisions Of The Second Kind Between Electrons And Excited Mercury Atoms, Paul Burrow Jun 1967

Inelastic Collisions Of The Second Kind Between Electrons And Excited Mercury Atoms, Paul Burrow

Paul Burrow Publications

The relative cross section for inelastic collisions of the second kind between electrons and mercury atoms in the excited 3P1 state was measured as a function of electron energy. Excited atoms were produced by absorption of the 2537 Å resonance line from a mercury arc. A low-energy beam of electrons was produced using the retarding potential difference method. Scattered electrons which gained kinetic energy were detected by passing them through a potential barrier which reflected unscattered electrons. The data are in good agreement with the cross section computed by applying detailed balancing to the known cross section for ...