bluuebunny/crossref_metadata_2025 huggingface dataset:
Noise in Transverse-Field Traveling-Wave Tubes
Authors: Wade G. , Amo K. , Watkins D. A.
Published: April 2005

From theoretical considerations of the fluctuations in an electron beam, an expression for the noise figure of a transverse-field amplifier is derived. There are found to be three statistically uncorrelated sources of noise in the beam of such a tube—(1) that arising from the fluctuations in the transverse emission velocity of electrons in a direction normal to the surface of the beam, (2) that arising from fluctuations in the transverse emission velocity of electrons in a direction parallel to the surface of the beam, and (3) that arising from fluctuations in the mean position of the beam and depending on its thickness. The analysis shows that the use of a collimator is required to give low noise figures. This is illustrated by the following example: for a tube designed to operate at 1000 mc with a collimator whose width is 0.004 in., the theoretical noise figure is 2 db. Without the collimator, the noise figure would be 11 db.
Measurement of Temperatures in Flames of Complex Structure by Resonance Line Radiation. II. Sodium Line Reversal by High-Resolution Spectroscopy
Authors: Strong H. M. , Bundy F. P.
Published: April 2005

Sodium line reversal temperature measurement by low resolving power spectroscopic instruments on complex flame structures gives temperatures intermediate between the highest and lowest temperature in the line of sight. An apparatus is described which was designed especially for determining the temperature structure in a complex flame by a modified sodium line reversal technique. Experimental data testing the validity of the method and a description of how it may be applied to complex flames is given.
Anisotropy of Diffusion in Grain Boundaries
Authors: Couling S. R. L. , Smoluchowski R.
Published: April 2005

Grain boundary penetrations of radioactive silver into copper bicrystals having a common cubic direction have been measured using an autoradiographic technique. Diffusion occurred along directions forming an angle φ=0°, 45°, and 90° with the common cubic direction. For very low angles of disorientation Θ, no preferential intergranular penetration was observed; for low and intermediate relative orientations, grain boundary diffusion was found to be most rapid along the common direction (φ=0°); for high angles of misfit, little anisotropy of boundary diffusion was detected. The observed asymmetry about Θ=45° of the curves of grain boundary penetration versus Θ is in agreement with the known dependence of the density of boundary dislocations on the angle between grains and on grain boundary direction. The anisotropy measurements may be qualitatively explained in terms of the distribution and relative amounts of elongated areas of ``fit'' and ``misfit'' in the grain boundary, and they confirm the earlier proposed model of grain boundaries in the region of angles where the simple dislocation model does not apply.
On the Effect of Integration in a Pulsed Radar, Randomly Modulated Carrier
Authors: Stone W. M.
Published: April 2005

The method of Marcum for finding the probability density function associated with a pulsed radar with integration and a square law detector is extended to include the case of a randomly modulated sinusoidal signal. Two mathematical procedures are developed, the well-known Edgeworth asymptotic series and a convergent series suggested by Varma. Sets of curves are drawn for probability of detection vs average signal-to-noise power ratio.

Some previous work has shown very high values for probability of detection resulting if it is assumed necessary to detect only one out of many pulses. Such probability levels are reduced if a slowly varying random amplitude of signal is postulated.
Theoretical Efficiency of the Thermionic Energy Converter
Authors: Houston J. M.
Published: April 2005

An analysis of the efficiency of the thermionic energy converter is given in terms of Vc and Va, which represent the potential differences between the top of the potential barrier between the electrodes and the Fermi levels of cathode and anode, respectively. The analysis applies to all vacuum converters, and to gas-filled converters when the gas pressure is low enough so that the electron mean free path is greater than the cathode-anode spacing. In special cases, the analysis may also apply at higher gas pressures. It is shown (with certain assumptions) that optimum values of Va and Vc exist. For Va, the optimum is determined by the onset of thermionic emission from the anode to the cathode. For Vc, the optimum is determined principally by radiation losses. It is concluded that no fundamental reason exists why efficiencies of 30% or more cannot be realized in converting heat to electricity by this method.
Calculation of the Performance of a High-Vacuum Thermionic Energy Converter
Authors: Webster H. F.
Published: April 2005

The performance of a high-vacuum thermionic energy converter has been evaluated from Langmuir's 1923 paper on the thermionic diode. The results are presented in the form of a generalized set of curves which show output voltage as a function of current drawn from the device. These general curves have then been applied to a few specific cases to determine what cathode-anode spacings, and cathode and anode properties will be required to produce a practical energy converter.
Depolarized Components of Light Scattered by Glasses. I. Measurements on Twelve Optical Glasses
Authors: Goldstein Martin
Published: April 2005

Measurements were made of Rayleigh's ratio and the depolarization ratios ρv and ρh on twelve optical glasses. Within an estimated error of ±5%, the ratio ρh equals unity in eleven of them, in apparent contradiction to the work of other investigators. It is concluded that light scattering does not distinguish a glass from a liquid.
Depolarized Components of Light Scattered by Glasses. II. Influence of Nonannealable Strains on the Scattering
Authors: Goldstein Martin
Published: April 2005

Light scattering measurements on twelve optical glasses revealed that most have depolarization ratios ρh=1 within experimental error. A theory postulating the existence of a type of nonannealable strain in glasses, proposed by Mueller to account for some observations giving ρh less than one, is recast in a form enabling an estimate of the magnitude of the effect to be made. It is found that in most cases the effect predicted is within present experimental error. If, however, an appreciable part of the glass consisted of domains of some of the crystalline forms of silica, ρh could be reduced significantly below one by this type of strain. The fact that ρh is unity in vitreous silica is an argument against the existence of such domains.
Diffusion of Interstitial Solutes in the Group V Transition Metals
Authors: Powers R. W. , Doyle Margaret V.
Published: April 2005

Mechanical relaxation measurements are used extensively to obtain information on the diffusion rate of interstitial solute atoms in body-centered cubic metals. Such studies have been stimulated by a model, developed by J. L. Snoek, which yielded a relationship between a relaxation time, an experimental parameter, and the diffusion coefficient of the solute atom. Although Snoek's model was confirmed very well for solid solutions of carbon or nitrogen in α-iron, a number of anomalies were observed when relaxation studies were extended to the group V transition metals.

An extensive experimental study has been made of the factors that influence relaxation times. The anomalous behavior of the group VA metals can be accommodated within the framework of Snoek's model by taking account of the specific nature of solid solutions based on these metals.

Diffusion data obtained by a variety of relaxation techniques are presented for oxygen, nitrogen, and carbon in vanadium, niobium (columbium), and tantalum. These data are in agreement with those obtained by the more conventional concentration gradient techniques in the few instances where such information is available. The pattern of activation energies suggest that lattice strain considerations alone are insufficient to explain the activation process involved in interstitial diffusion.
Ohmic Aluminum-n-Type Silicon Contact
Authors: Matlow Sheldon L. , Ralph Eugene L.
Published: April 2005

A method of making an ohmic alloyed contact to n-type silicon using aluminum has been developed. In the usual procedures for alloying aluminum to silicon a regrowth region of β-aluminum-silicon alloy is formed which is monocrystalline with the parent silicon. As a result of the junction formed between the n-type silicon and the p-type regrowth, the contact is rectifying. However, by the careful control of the heating and cooling cycles, it is possible to prevent the deposition of the β phase onto the surface of the parent silicon. Thus, an ohmic contact is obtained. The theory of the process is discussed. By this technique it has been possible to develop a ``ruggedized'' solar energy converter for use in space vehicles.
Elastic Moduli of Single-Crystal Gallium Arsenide
Authors: Bateman T. B. , McSkimin H. J. , Whelan J. M.
Published: April 2005

Velocities of propagation of high-frequency ultrasonic waves and the adiabatic elastic moduli for single-crystal gallium arsenide are reported. Data at 25°C were obtained in the range of 20–180 mc/sec.

The elastic moduli based on a density of 5.307 g/cm3 in units of 1012 dynes/cm2 are c11 = 1.188±0.14%; c12 = 0.538±0.36%; c44 = 0.5940±0.14%.
Distribution Coefficients and Carrier Mobilities in InSb
Authors: Strauss Alan J.
Published: April 2005

The following distribution coefficients have been measured for InSb crystals pulled from the melt at an extraction rate of 1.3 cm/hr and rotation rate of 130 rpm: Cd, 0.26; Zn, 3.38; Se, 0.17; Te, 0.54. The distribution coefficient for zinc has been found to vary with extraction and rotation rates in the manner predicted by the theory of Burton, Prim, and Slichter. Hall mobilities at 77°K have been measured for uncompensated samples containing impurity concentrations between 1015 and 1019 cm−3. Mobilities calculated from scattering theory are in moderately good agreement with the experimental values for n-type samples, but the agreement is considerably less satisfactory for p-type samples.
Glass, a Disturbing Factor in Physical Electronics Measurements
Authors: Bills D. G. , Evett A. A.
Published: April 2005

Evidence has been obtained that Pyrex and other glasses are not desirable construction materials in certain types of physical investigations such as clean surface experiments and measurements involving small ion or electron currents produced at low pressures. Pyrex appears to decompose at temperatures above about 350°C liberating water vapor and decomposition products which are not readily pumped out of a vacuum system. Pyrex also appears to chemically sputter in the presence of gaseous ions such as nitrogen or oxygen, thus liberating contamination into the system which is not readily removed. Sodium and potassium have been identified among the decomposition products and it is well known that these atoms are desorbed as ions from many metal surfaces when the surface is heated. Thus decomposition and sputtering of glass can produce spurious ion currents under certain conditions. The decomposition products can possibly account for insulating films on metal electrodes which charge up or polarize under charge bombardment.
Observations of Charged-Particle Tracks in Solids
Authors: Price P. B. , Walker R. M.
Published: April 2005

The characteristics of tracks produced by fission fragments have been studied by transmission electron microscopy in the following layer structure materials: molybdenite (MoS2), talc, clinochlore, jefferisite, and various micas including biotite, phlogopite, muscovite, and synthetic fluor-phlogopite. The measured track widths showed little correlation with the decomposition temperatures and it was concluded that the track formation cannot be described by a simple thermal spike model. The absence of any new rings or spots in the electron diffraction pattern of a heavily irradiated sample led to the conclusion that the tracks themselves consisted of a disordered region and not of a definable new crystalline phase. In many of the materials the tracks faded during observation in the beam. Although this fading could be eliminated by using a cold stage, it was not caused simply by the thermal instability of tracks; some materials which showed rapid track fading retained tracks to higher temperatures in external annealing experiments than did those in which no fading occurred. Annealing experiments also showed that tracks served to nucleate the high temperature decomposition of natural micas in a manner analogous to that previously reported for synthetic mica. The results of experiments in which Al absorbers were placed between a fission source and mica samples were interpreted as indicating that only particles with masses ≳ 30 are capable of forming visible tracks. This conclusion is consistent with the negative results of other irradiations in which mica samples were bombarded with 4-MeV alpha particles, 150-MeV oxygen nuclei, and 3-BeV protons. Experimental observations of the interaction of dislocations with tracks are also presented.
Measurements of Detonation Pressure
Authors: Cook M. A. , Keyes R. T. , Ursenbach W. O.
Published: April 2005

The ``aquarium technique'' is applied in the experimental determination of the equation of state for water and Lucite. Results for water are compared with similar results obtained by other methods. Measurements of the peak pressures in the detonation waves are presented for explosives of various types and rates of reaction. The peak pressures were found to be the Chapman-Jouguet or ``detonation'' pressures of the thermohydrodynamic theory. There was no evidence whatever for the ``spike'' of the Zeldovich-von Neumann model even though conditions were such that this spike would have been detected by the method employed if it were actually present, at least in the large diameter, nonideal explosives of maximum reaction zone length.
Formation Conditions and Structure of Thin Epitaxial Germanium Films on Single-Crystal Substrates
Authors: Sloope Billy W. , Tiller Calvin O.
Published: April 2005

An experimental investigation of the effects of formation conditions on the structural characteristics of thin Ge films vacuum deposited onto synthetic single crystals of CaF2, NaCl, NaF, and MgO is reported. Formation conditions include substrate temperature during deposition, rate of deposition, and heat treatment. The amorphous to crystalline transformation of Ge was found to occur in the 300–350°C substrate temperature range. It is shown that single-crystal films, 1500 Å thick, can be formed on CaF2 substrates at temperatures between 450° and 700°C by proper choice of rate of deposition. Crystalline structure, porosity, complexity of imperfections, and film adhesion are dependent on the rate of deposition and deposition temperature.
Power Density of Optimally Focused Space-Charge-Limited Electron Beams
Authors: Schwarz Helmut
Published: April 2005

Factors affecting the power density of optimally bundled electron beams used for the welding, cutting, and machining of solid material are described. The power density and spot size of these beams are expressed as a function of acceleration voltage, beam current, and electron optical characteristics of the system. Assuming that the spherical aberration of the beam-focusing lens system limits the spot size of the space-charge-limited beam, the power density under optimum conditions increases approximately with the fifth power of the acceleration voltage, and decreases with the 7/4 power of the beam current.

A criterion is also given which enables one to determine whether the electron beam at its impact on the workpiece is space-charge-limited or not. Some considerations are given to the neutralization of the electron space charge by ions originating from the background pressure of the vacuum system.
Theories of Birefringence Induced in Liquids by Ultrasonic Waves
Authors: Hilyard N. C. , Jerrard H. G.
Published: April 2005

Some liquids and solutions become doubly refracting and behave as uniaxial crystals when traversed by acoustic waves of high frequency. In many aspects the induced birefringence is analogous to birefringence due to flow. Theories for this behavior are presented and discussed in detail. For liquids and solutions of flexible macromolecules the birefringence is proportional to the square root of the acoustic intensity and to the frequency of the wave, but for colloidal solutions it varies directly as the intensity and is independent of frequency. It is shown that from measurements of the birefringence, values of relaxation times and diffusion constants can be obtained. The method has a number of advantages over flow birefringence studies and in common with the latter does not depend on the possession of a permanent dipole moment by the molecules.
Optimization of Efficiency of a Cesium-Diode Converter
Authors: Sanathanan C. K.
Published: April 2005

When the inter-electrode spacing is very small in an alkali-metal vapor diode, plasma heat transfer cannot be neglected. An efficiency analysis very similar to that of Schock includes this effect and compares it to that due to radiation loss. In the analysis the heat-transfer coefficient h[W/(cm)2(°K)] is given values 0, 0.005, and 0.01. This range is based on the experimental values of h obtained in potassium and cesium diodes. The greatest effect of h on efficiency is found theoretically to occur when the electron-emitter work function or output voltage is larger than the optimum value for a particular temperature.
A Variable Composition, High Field Superconducting Solenoid
Authors: Riemersma H. , Hulm J. K. , Venturino A. J. , Chandrasekhar B. S.
Published: April 2005

In previous work we described the fabrication of cold-worked niobium plus 25% zirconium wire and the use of such wire to construct a solenoid in which a field of 58±1 kG was achieved under loss-free superconducting conditions. We have continued these experiments with other compositions and find that the critical current in short samples at 21 000 G and 4.2°K decreases with increasing zirconium content for the compositions investigated, namely, Nb+25% Zr, Nb+33% Zr, and Nb+50% Zr. Kunzler observed that the magnetic field required to destroy the supercurrent in these alloys increased with increasing zirconium concentration in the same range of compositions. This behavior led us to build a new solenoid composed of several concentric sections with the lowest composition (25% Zr) on the outside and the highest composition (50% Zr) on the inside. Experiments with this coil are discussed.
Emission of Negative Ions from Metal Surfaces Bombarded by Positive Cesium Ions
Authors: Krohn Victor E.
Published: April 2005

High yields (>1%) of negative metal ions, usually including clusters of metal atoms and oxides, have been observed from targets of Cu, Ag, Au, Be, Cd, Al, Sn, Ta, W, and Ni bombarded by a beam of positive cesium ions. The increase observed in the negative-ion yields when an auxiliary beam of neutral cesium was directed at a copper target indicates that the presence of cesium on the target was an important factor in the production of large numbers of negative ions. From targets of aluminum and tin, respectively, the Al2− and Sn2− yields were an order of magnitude greater than the corresponding single-atom yields.
Direct Observation of Crystal Imperfections in KCl Single Crystal by Electron Microscope
Authors: Hibi Tadatosi , Yada Keiji
Published: April 2005

The processes of change of a thin KCl single crystal due to electron irradiation were observed by means of an electron microscope and electron diffraction. It was found that under weak electron irradiation loop structures first appeared and then disappeared showing a lot of small bright specks over the whole crystal. In this stage, each diffraction spot had streaks in 〈100〉 directions. Under intense electron irradiation bright squares appeared initially without the appearance of loop structures. In this stage, the diffraction pattern was a perfect net-like pattern. It was found that by using the replica technique, loop structures and large squares appeared in the crystal, and also that by using the dark-field image method the contrast of loop structures and bright squares was due to Bragg reflection, which had resulted from the formation of voids and cubic cavities in the crystal, respectively. From the experimental results, the mechanism of coagulation of vacancies in KCl crystal with electron irradiation is discussed.
Traveling-Wave Harmonic Generation Along Nonlinear Transmission Lines
Authors: Auld B. A. , DiDomenico M. , Pantell R. H.
Published: April 2005

A perturbation solution is developed for determining the steady-state response of nonlinear TEM transmission lines and nonlinear cylindrical waveguides of arbitrary cross section. The nonlinear medium which is considered in this analysis is comprised of both nonlinear reactance and nonlinear resistance; and can be physically realized in the ferroelectric ceramic material composed of 73% BaTiO3 and 27% SrTiO3. From the results of the perturbation analysis and the known large signal microwave characteristics of this material, the properties of traveling-wave harmonic generation in ferroelectric ceramics are investigated. To assess the characteristics of ferroelectric traveling-wave harmonic generators, an example is worked out for an S-band rectangular waveguide completely filled with the above mentioned ceramic and excited in the TE10 mode at the fundamental frequency of 3 kMc. The predicted behavior of this device is then compared with the experimental characteristics of a cavity-type ferroelectric harmonic generator in order to determine the advantages and disadvantages of each type of device. The comparison brings out the superiority of the resonant system and indicates ways of improving the distributed system. Finally, based upon the treatment of the waveguide problem, the processes of frequency and mode conversion in nonlinear waveguides are discussed, both in general and with regard to the example of the rectangular guide.
Optical Constants of Germanium
Authors: Nodvik J. S.
Published: April 2005

A check on the over-all consistency of calculated values of the optical constants n and k for Ge is obtained by using these in a dispersion relation to evaluate the free electron plasma frequency.
Mechanism of Friction
Authors: Walton D.
Published: April 2005

The lack of observable adhesion between most metal surfaces in air has been explained in the past by invoking the effect of released elastic stresses. In this work, the effect of released elastic stresses on adhesion has been investigated experimentally by evaporating thin films of gold on substrates of different hardness and measuring the adhesion as a function of the load. It has been found that the magnitude of the released elastic stresses is insufficient to account for the lack of observable adhesion in air. In the case of copper, it was found that adhesion became observable when the oxide film on the surface was ruptured. It was concluded that a protective film formed in the atmosphere prevented adhesion. It is suggested, therefore, that a class of frictional phenomena exists which cannot be explained by the adhesion theory. For electropolished Cu surfaces in particular, it is found that a mechanism based on plastic deformation may account for the frictional force observed where the oxide remains intact.
Thermoelectric Phenomena Associated with Electron-Field Emission
Authors: Levine Paul H.
Published: April 2005

The equilibrium temperature distribution in an ideal metal rod, one end of which is subjected to an intense electric field, is studied. Particular attention is focused on the case where the emitting end cools down, and the necessary conditions for this effect are derived. Viewed as a ``heat pump,'' the maximum rate of heat flow as a function of emitter temperature is derived, and it is found that rates in excess of 0.1 cal/sec/cm2 are possible at room temperature if the emitter work function is less than an electron volt.
Measurement of the Thermal Diffusivity of Thermoelectric Materials
Authors: McNeill D. J.
Published: April 2005

A simple modification of Angstrom's classical method for the determination of the thermal diffusivity of thermoelectric materials is described. Using the Peltier heat generated at the junction of the specimen and a current lead as a periodic heat source, symmetrical temperature variations may be established in the specimen and the diffusivity derived from the propagation constants of the variations. Results of measurements at room temperature on lead telluride are presented.
Point Defects in p-Type Germanium as Introduced by Deformation, Quenching, and Electron Bombardment
Authors: Hobstetter J. N. , Renton C. A.
Published: April 2005

In order to compare point defect formation in germanium through different modes of production, Hall measurements have been made on germanium after different treatments. The same starting material was used in all experiments, namely, 5 ohm-cm p-type germanium. Markedly different behavior was observed. For the electron bombarded material, the number of carriers is reduced at all temperatures below room temperature, while the quenched material shows an increase at all temperatures. The deformed material exhibits intermediate behavior, with the carrier concentration increased at high temperatures and decreased at low temperatures. This is accounted for by an energy level scheme similar to that of James and Lark-Horovitz.
Influence of F-Center Concentration on the Electrification of the Dust of KCl Monocrystals Irradiated with β Rays
Authors: Nikliborc Jan , Szaynok Anna
Published: April 2005

The electrification of the dust of KCl monocrystals irradiated with β rays is influenced by 3 factors: absorption of electrons in the crystal, creation of F centers, and secondary emission. The F-center concentration in crystals irradiated with β rays for various irradiation times was measured spectrophotometrically. Based on the F-center model and with the help of statistical calculations the relationship between the F-center concentration in the crystal and the surface charge due to F centers was found.
Temperature Distribution in a Hollow Cylindrical Cup with a Stem
Authors: Lehman Guy W.
Published: April 2005

An approximate analytical approach for determining the temperature distribution in a hollow cylindrical cup of radius C, having a base thickness H, with a stem of radius A, and length L, is given. The outer radial surface of the cup is held at a temperature T0 and the temperature at the bottom of the stem is Ts. All other surfaces are adiabatic. This geometrical arrangement is used to observe marker motion under the influence of a large thermal gradient in a thermal diffusion experiment described in the following paper. In this setup, only the sink temperature Ts and the temperature at the bottom of the cup Tm can be measured. Equations are presented which enable one to calculate the temperature and its gradient along the axis of this arrangement with relative ease for the physically important case A/C<¼. In the region along the axis above the cup-stem interface, the temperature at any point is given in terms of Tm, Ts, and functions which depend only upon the ratio A/H. A table of these functions is presented for the cases πA/H=0.4, 0.8, and 1.2.
Thermodynamics of a Superconducting Energy Converter
Authors: Chester Marvin
Published: April 2005

A thermodynamic analysis is given for an energy conversion process which employs the phase transition in a superconductor. The conversion process is a cyclic one. An expression for the conversion efficiency is obtained. Quantitative estimates are calculated from the formula for several superconducting materials. These indicate that conversion efficiencies as high as 44% may be obtainable under ideal conditions.
Energy of Formation of a Vacancy in Copper
Authors: Amar Henri
Published: April 2005

The quantum-mechanical calculations of Huntington and Seitz, of Huntington, and of Brooks led to a value of about 1 ev for the formation energy of a vacancy in copper. After a brief outline of these calculations, it is shown that in the light of recent experimental and theoretical work, the contributions of the electrostatic self-energy and Fermi energy of the valence electron must be corrected. These corrections lead to a final value of about 2 ev.
Mechanism for Dislocation Pinning in the Alkali Halides
Authors: Bauer Charles L. , Gordon Robert B.
Published: April 2005

Changes in the elastic modulus and internal friction of plastically deformed rocksalt, caused by changes in the mean free length of oscillating dislocation segments, have been observed during x-irradiation at temperatures ranging from 10° to 300°K. The rates at which the modulus and damping changes occur during irradiation are found to be independent of temperature; but during irradiation at helium temperature, the magnitude of the effects are smaller. This decrease in magnitude has been shown to be due to the absence of thermal unpinning. Explanations of the pinning process based on the diffusion of point defects to dislocations appear to be ruled out by the rapidity of the low temperature modulus change.

The dislocation pinning produced by irradiation of NaCl, KCl, KBr, and KI at low temperatures is found to be reversible when the crystals are subjected to illumination in, or near, the visible. The wavelength of the illumination which produces the maximum unpinning increases as the lattice constant increases; the effect disappears when the crystals are warmed to room temperature. However, at all temperatures, bleaching a deformed and partially irradiated crystal with F light causes a further modulus increase. The pinning point produced by low temperature irradiation is identified as a dislocation jog in close association with an F center whose absorption band is displaced towards the red by the dislocation strain field. Ionization of the F center results in recombination of its vacancy with the jog; warmup allows the F center to diffuse beyond recombination range.
Perturbation of Electron Flow
Authors: Kent Gordon
Published: April 2005

A perturbation analysis of single stream, quasi-static, nonrelativistic electron flow is developed, based on the nonlinear equation for the velocity field. The analysis is applicable to electron beams originating from a cathode at which the magnetic field is tangential. The consistent development of perturbation theory from the velocity field viewpoint makes unnecessary the tenuous physical arguments usually employed and resolves some of the related controversy. The surface charge and current usually assumed to replace the perturbed flow boundary are shown to be an interpretation justified by the rigorous application of the theory. The generality of the formulation makes simple the writing of the differential equation for the first order perturbation of any flow satisfying the stated conditions.
Back-Scattering of Megavolt Electrons from Thick Targets
Authors: Wright Kenneth A. , Trump John G.
Published: April 2005

Measurements are reported of the number and energy of the electrons which rebound from thick metal targets bombarded at normal incidence by monoenergetic electrons of from 1 to 3 Mev. The ratio of back-scattered to incident electron current, measured for twelve metal targets, was found to vary from 0.47 for 1-Mev electrons incident on U to 0.01 for 3-Mev electrons on Be. The total energy scattered backward from targets of Al, Cu, and Pb bombarded with 1- to 3.5-Mev electrons was determined by calorimetric methods. This energy diminished from 34% of the incident energy for Pb bombarded with 1-Mev electrons to 1% for Al bombarded with 3.5-Mev electrons. The dependence of the number and energy of the back-scattered electrons on the atomic number of the target and on the incident electron energy is discussed.
Determination of the Orientation of Metal Grains by a New Kossel Line Technique
Authors: Heise B. H.
Published: April 2005

The orientation of surface grains in a thick crystalline specimen can be determined by means of a Kossel line technique. In this work the Kossel lines are recorded on a cylindrical film coaxial with the electron beam of an electron probe microanalyzer. These Kossel lines are analyzed by a mathematical technique to reveal the orientation of a grain. The technique will also yield a rough crystal analysis of unknown materials; therefore, it may be useful in analyzing inclusions and precipitates in solid specimens.
Optimized Method for Correcting Smearing Aberrations: Complex X-Ray Spectra
Authors: Porteus J. O.
Published: April 2005

The problem considered is one of obtaining a true spectrum from an observed spectrum containing the effects of finite resolution and noise. The finite resolution gives rise to a smearing aberration which may be represented by the convolution or fold of the true spectrum with a smearing function. The noise introduces an uncertainty which deserves careful consideration if a meaningful correction for the smearing aberration is to be effected.

In this paper an optimized practical solution to this problem is developed for the case of complex x-ray spectra as measured with modern high-precision spectrometers. The solution is based on the conventional Fourier transform solution of the convolution integral and is evaluated by means of a high-speed digital computer. The noise term is handled by a modification of the Wiener smoothing theory in which the stationarity condition is relaxed to permit application to complex x-ray spectra. Introduction of the inherent line shape permits easy evaluation of the required autocorrelation properties of the spectrum. Special consideration is given to the complicating difficulty of long ``tails'' or ``wings'' on the smearing functions encountered in x-ray spectroscopy. The corrected Cl K emission and absorption spectra of crystalline potassium chloride are presented as examples of the correction. Although the present solution was developed for the specific purpose indicated, it may be applied immediately to perform smearing corrections or differentiation of any data adequately represented by the present model and assumption regarding the errors. One possible additional application is the differentiation of electron energy-loss spectra recorded by the retarding field method.
Exploding Wire as Fast Dynamic Pinch
Authors: Katzenstein Jack , Sydor Michael
Published: April 2005

The high-current electric discharge through fine wires is studied under experimental conditions in which the interaction of the discharge with its self-magnetic field is dominant. When the wire is composed of an element or elements of low atomic number, the discharge is found to have many of the characteristics of pinch discharges in gases. A capacitor bank of 1.75 μf and a voltage rating of 100 kv was used with a switching spark gap and circuit of very low parasitic inductance. The parasitic inductance of the condensers and circuit was measured to be 0.05 μh while the ringing frequency of the discharge was 370 kc. Wires of copper, aluminum, polyethylene, lithium, and lithium-lithium hydride were exploded. The discharge was photographed with streak and framing cameras and oscillograms taken of the discharge current and its time rate of change. Wires composed of lithium-lithium deuteride were observed to give neutron yields of the order of 106 per shot. The neutron yields were measured with a silver-foil activation counter.
Cratering of Lead by Oblique Impacts of Hypervelocity Steel Pellets
Authors: Bryan George M. , Pugh Emerson M.
Published: April 2005

The volume and shape of craters produced in lead by the impact of steel pellets at 3 km/sec have been studied as functions of the angle of incidence for angles up to 70° from the normal. It is found that crater volume is linear in the cosine of the angle of incidence, and that it is directly proportional to the kinetic energy of the pellet for a given angle of incidence. Consideration of energy and momentum conservation leads to a plausible interpretation of this behavior. It is also found that the relation between the depth and the (transverse) diameter is consistent with the concept of a radial ``afterflow'' superimposed on a primary penetration which obeys the density law of penetration by fluid jets.
Solutions for the Infinite Layer and the Half-Space for Quasi-Static Consolidating Elastic and Viscoelastic Media
Authors: Freudenthal A. M. , Spillers W. R.
Published: April 2005

Solutions are presented for an infinite viscoelastic consolidating layer and an elastic and viscoelastic consolidating half-space considering the quasi-static response. The analogous coupled thermoelastic problems and applications in the field of secondary consolidation are discussed.
Low-Frequency Negative Resistance in Thin Anodic Oxide Films
Authors: Hickmott T. W.
Published: April 2005

Negative resistance and large current densities have been observed in the direct-current—voltage characteristics of five metal-oxide-metal sandwiches prepared from evaporated metal films. The systems studied and their voltages for maximum current are: Al-SiO-Au, 3.1 V; Al-Al2O3-Au, 2.9 V; Ta-Ta2O5-Au, 2.2 V; Zr-ZrO2-Au, 2.1 V; and Ti-TiO2-Au, 1.7 V. For aluminum oxide, which has been most extensively studied, the voltage for maximum current is independent of film thickness for films between 150 and 1000 Å thick; the phenomenon is not field dependent. Peak-to-valley ratios of 30:1 and current densities of 10 A/cm2 are typical. Maximum current densities at peak voltage are 25 A/cm2; minimum current densities are 0.01 A/cm2. Switching time from peak current to valley current is <0.5 μsec but negative resistance is not found for 60-cycle voltages. Establishment of the dc characteristics and dependence on temperature and atmosphere are described. Electron emission from aluminum oxide sandwiches can occur at 2.5 V. Space-charge-limited currents in the insulator provide a possible mechanism for the current-voltage curves and large currents below the voltage for maximum current through the oxide films. The mechanism responsible for negative resistance is uncertain.
Thermodynamics of Surface Films
Authors: Carabateas E. N.
Published: April 2005

A relation between the surface coverage and the surface potential of an adsorbed film is developed from a thermodynamic argument. It is found that the proper variables to be used in the theory of films are the temperature of the surface and the saturation temperature corresponding to the pressure of the vapor in equilibrium with the surface. The analysis is applied to the experimental data of Taylor and Langmuir for cesium on tungsten with good results. In the Appendix an estimate of the range over which the surface forces extend is obtained by means of a simple microscopic model.
Debris Mechanism of Strain-Hardening
Authors: Gilman J. J.
Published: April 2005

Strain-hardening caused by ``debris'' produced by multiple cross-glide is discussed. This form of strain-hardening is often linearly proportional to strain, because the debris concentration increases in proportion to strain. The rate of debris production should be sensitive to the applied stress, crystal structure, and crystal orientation as is observed.

The debris mechanism is the only one that explains the self-hardening of isolated half-loops. It also explains the negative temperature dependence of strain-hardening at low temperatures, unlike other theories.

The cross-gliding that leads to debris production is influenced by free surfaces which exert a cross-glide force on obliquely incident dislocations, and which cause extended dislocations to become contracted so they can more easily cross-glide.
Yield Points and Delay Times in Single Crystals
Authors: Johnston W. G.
Published: April 2005

Stress-strain curves and transient creep curves for single crystals are obtained from calculations based on the observed behavior of dislocations in LiF, and the strain rate equation, ε̇=bnv. The pronounced yield drops and apparent ``delay times'' predicted by the calculations are observed experimentally. This agreement between calculation and experiment implies that further consideration of the calculations may give some insight into the yield point and transient creep behavior of single crystals. Several parameters are varied in the calculation in order to determine the effect of such things as testing machine speed, machine hardness, rate of dislocation multiplication, work-hardening rate, number of mobile dislocations initially present, and the dependence of dislocation velocity on stress. The parameter that most strongly influences the yield points and transient creep behavior of a given material is n0, the number of mobile dislocations initially present. The wide range of observed yield point and transient creep behavior of various materials can be rationalized in terms of how dislocation velocity varies with stress; the less sensitive is the velocity to the applied stress, the more pronounced will be the yield drop or delay time. The calculation is applicable only when n0≠0; and the yield points and yield drops develop continuously and relatively gradually as dislocation motion and multiplication begin before the upper yield point is reached. The upper yield stress is not closely related to the stress required to unpin dislocations. It is necessary to distinguish between this type of yield point, which is commonly observed, and the Cottrell type of yield point in which dislocation motion begins at the upper yield stress, and in which the upper yield stress is related to the unpinning stress.
Ignition of a Thermionic Cathode Arc
Authors: White John E.
Published: April 2005

Ignition of a thermionic cathode discharge in mercury vapor at the low applied potential of 2.4 V is shown to be the result of a potential minimum in space 0.8 V below the cathode, and of a favorable contact potential difference. Good emitters require more voltage to fire than high work function cathodes. Using an argon buffer gas at about 3.5 mm Hg pressure, ignition is easiest with an added Hg vapor pressure of 1.85 mm. Adequate pressure is required because of the two-stage ionization which produces ignition. This process applies also to the noble gases, and requires that ignition cannot occur with electron energy less than half the ionization potential.
Interaction of Parallel Dislocations in a Hexagonal Crystal
Authors: Chou Y. T.
Published: April 2005

Based on the theory of anisotropic elasticity, the stress field of a single dislocation, the force between two parallel dislocations, and the stress field of various types of infinite dislocation walls and arrays are fully analyzed for a hexagonal crystal.

The attraction sector of an edge dislocation with respect to another edge dislocation of the same sign is no longer the half-quadrant as in the isotropic case. For graphite crystals the attraction sector is about 70° instead of 45°.

The force between two parallel screw dislocations is not central. A tangential component exists, being zero along x and y axes. The tangential force will retard the formation of screw dislocation arrays along any plane except those parallel or normal to the basal plane. Cross slip may be aided or opposed by this force, depending on the direction of applied stress.

The stress field of an infinite dislocation wall or array, either parallel or normal to the basal plane, has similar characteristics to those from isotropic treatment, although their magnitudes and geometries may differ considerably.

Numerical data of six important material constants are tabulated for many common hexagonal crystals.
Temperature Variation of Saturation Magnetization of Gamma-Ferric Oxide
Authors: Brown William Fuller , Johnson Clark E.
Published: April 2005

The temperature variation of the saturation magnetization of a γ-ferric oxide sample has been interpreted by use of Néel's molecular-field model, with neglect of A-A and B-B interactions. The parameters assumed are: j of the Brillouin function= 52; a net moment of 1.25 Bohr magnetons per iron atom; ratio of the number of atoms on A sites to the number on B sites, 8/(40/3)=3/5. From these parameters the function M/M∞=G(T/θ) was calculated numerically; M=magnetization at temperature T, M∞=magnetization at T=0, θ=Curie temperature. The data fit the theoretical curve very well if θ is assigned the value 1020°K.
Scattering Theory for Finite-Beam Incidence
Authors: Lynch P. J. , Altshuler S.
Published: April 2005

The Schiff small-angle approximation for plane-wave scattering by a dielectric is integrated over an appropriate angular distribution of incident plane waves in order to represent finite-beam scattering. The intensity distribution near the forward direction where incident and scattered waves interfere can now be expressed in a meaningful way. If the radius of the incident beam is not large relative to the dimensions of the scattering system, the scattered wave is seriously modified. A simple definition of cross section is chosen, and an extended optical theorem for total cross sections is derived.
Direct Observation of Imperfections in Semiconductor Crystals by Anomalous Transmission of X Rays
Authors: Schwuttke G. H.
Published: April 2005

An experimental technique for the direct observation of imperfections in single crystals is described. It is based on the anomalous transmission effect of x rays observed in crystals of high perfection. The parallel beam method previously used only for the mapping of dislocations has been improved so that large area x-ray topographs are recorded. It can now be applied to the detection of impurities, segregation, and precipitation effects in semiconductor materials. Microsegregation of oxygen in silicon, precipitation of copper in silicon, and arsenic segregation in germanium were used to study the influence of segregation and precipitation on the anomalous transmission. Working conditions of x-ray diffraction microscopy are discussed, and it is shown that segregation phenomena produce typical impurity contrast which is reflection-dependent if the impurities are in solid solution. For precipitated impurities, this relation does not exist.
Use of Frustrated Total Internal Reflection to Measure Film Thickness and Surface Reliefs
Authors: Harrick N. J.
Published: April 2005

When total internal reflection of light occurs, radiation penetrates beyond the reflecting surface into the rarer medium where the intensity decreases with distance from the interface in an exponential manner. Since the degree of coupling to this radiation can be controlled by adjusting the proximity of another object to this interface, it is possible to utilize this phenomenon in the measurement of film thickness and to obtain high contrast images of surface reliefs.
Conversion of GaAs to GaP by Solid-State Diffusion
Authors: Stone Louis E.
Published: April 2005

The formation of discrete phase GaP by diffusion of phosphorus into GaAs at pressures of 10 to 30 atm and temperatures of 800° to 900°C is described. X-ray data identifying GaP are given. A mechanism is postulated for the step-like concentration gradients observed. Striae supporting this hypothesis were observed and are illustrated. Epitaxial growth as a factor is considered but not believed a significant factor based on microscopy and experimental environment.
Spin-Wave Instability at Large Precession Angles
Authors: Schlömann Ernst
Published: April 2005

Second-order instability of z-directed spin waves is investigated for the case of thin disks, assuming that the precession angle is very large. It is found that for large precession angles, the buildup rate of the spin-wave population is proportional to the transverse magnetic moment and the square root of the transverse demagnetizing factor.