bluuebunny/crossref_metadata_2025 huggingface dataset:
Pyromagnetic Effect: A Method for Determining Curie Points
Authors: Chynoweth A. G.
Published: April 2005

A dynamic technique has been developed for studying the pyromagnetic effect (the change in the intensity of magnetization, I, with temperature, T). The thermal transients produced in a crystal of gadolinium iron garnet when subjected to brief, intense, flashes of light, result in transient changes in the intensity of magnetization. The magnitude of the signal picked up by the detector coil is determined by the pyromagnetic coefficient (dI/dT), and the rate of change of the temperature. No externally applied magnetic field is necessary to obtain these signals and, furthermore, the net state of magnetization of the crystal is determined nondestructively. As (dI/dT) possesses a very sharp peak at the Curie point, the latter can be determined simply and with some precision; the actual temperature change produced in the crystal by the light can be kept to a small fraction of a degree. The Curie point for gadolinium iron garnet was found to be 564±3°K. The technique may prove to be useful for studying the behavior of (dI/dT) at low temperatures.
Some Observations on Creep in Zinc Single Crystals
Authors: Stüwe H. P.
Published: April 2005

A concentrated load, applied to the surface of a Zn single crystal, produces a hexagonal dimple if this surface is parallel to the basal plane of the crystal lattice. The rim of these dimples is formed by six sets of edge dislocations moving into the six slip directions with increasing loading time, thus causing the dimple to grow. The dimple contours can be photographed with a microfocus x-ray tube. Measurements of a large number of dimples showed:

(1) For a given loading time, dimple size increases linearly with the applied load.

(2) For a given load, dimple size increases with loading time until the shear stress at the dimple rim has been lowered to a value characteristic for the material used, below which creep velocity is either zero or extremely low.

(3) This critical shear stress is independent of temperature.

(4) It depends on the impurity concentration of the crystal in the way predicted by the model of Cottrell.
Cleavage Cracks and Dislocations in LiF Crystals
Authors: Gilman J. J. , Knudsen C. , Walsh W. P.
Published: April 2005

It is shown that dislocations are nucleated ahead of the tips of cracks that move slower than ∼6×103 cm/sec in LiF crystals. The motion of cracks that move slower than ∼3×103 cm/sec is unstable; that is, the velocity oscillates.

About 2×105 cm/sec is the terminal velocity for (100) cleavage cracks in LiF.

For constant driving force, cracks move more slowly in crystals with high dislocation densities than in relatively perfect crystals.
Method for Making Successive Replicas of the Same Spot
Authors: Fourie J. T.
Published: April 2005

A technique is described in which use is made of the slit type electron microscope specimen carrier for replicating successively the same spot on a metal sample. The main advantage is that no specialized apparatus is required. By using the slit type specimen carrier a relatively large undisturbed field of view is obtained. A series of electron micrographs showing the formation and growth of slip lines on an α-brass single crystal is used to demonstrate the capabilities of the method.
Use of an Electro-Optical Method to Determine Detonation Temperatures in High Explosives
Authors: Gibson F. C. , Bowser M. L. , Summers C. R. , Scott F. H. , Mason C. M.
Published: April 2005

A method has been devised for sampling the optical radiation from the interior of a detonating solid-explosive charge by introducing a transparent plastic rod axially into the charge at the time of fabrication. The radiation was analyzed by a grating spectrograph, using four bands 100 A wide and 600 A apart. The radiation intensities were used to calculate the color temperatures within the detonating explosive. The apparatus was calibrated by a radio-frequency-excited lamp known to have gray-body radiation. The explosive charges were vacuum-impregnated with propane to replace the air in the intergranular voids to eliminate light emission from the air shock.
Electron Mirror Microscopy of Patterns Recorded on Magnetic Tape
Authors: Mayer Ludwig
Published: April 2005

This paper deals with the utilization of electron mirror microscopy for the observation of magnetic patterns recorded on magnetic tapes. Experimental evidence is presented demonstrating that, contrary to a statement in the literature, electron mirror microscopy can provide micrographs of magnetic patterns written on magnetic tapes. Successful utilization of the principle of electron mirror microscopy for depiction of magnetic patterns on magnetic tapes may have general significance with respect to magnetic memory systems in the event that evaporated magnetic films do become available. The high resolving power of the electron mirror microscope and the fact that it is an electronic device suggests further experimentation aimed at an all-electronic, fast-reading magnetic memory system with large storage capacity.
Excitation of Short Infrared Pulses with High Repetition Rate by Electron Bombardment of Cuprous Oxide
Authors: Frerichs Rudolf , Weichman Frank
Published: April 2005

The infrared emission of Cu2O under electron-bombardment was investigated. Lamps containing an electron-bombarded Cu2O target emit a single band between 0.8 and 1.4 μ. They can be very accurately pulsed with the help of a built-in grid. The efficiency at 6500 v is about 4 to 5% of the electrical input. With improved cooling of the target such lamps should form a powerful source for repetitive μsec pulses of the near infrared spectral region which can be observed with photoemissive tubes and image converters.
Maser Oscillator with One Beam through Two Cavities
Authors: Wells Willard H.
Published: April 2005

A two-cavity beam type of maser is studied by a geometrical representation of the Schrödinger equation developed by Feynman, Vernon, and Hellwarth. By this method complicated effects may be readily visualized. As an example, the qualitative explanation will be developed for the experimental observation that a cavity in a maser will oscillate simultaneously at two frequencies (differing by 1000–5000 cps) under certain conditions when the beam is first passed through another cavity. A possible amplifier application is noted.
Ultrasonic Interferometer for the Measurement of the Temperature Dependence of Elastic Constants
Authors: Espinola R. P. , Waterman P. C.
Published: April 2005

An ultrasonic interferometer method for relatively precise measurement of changes in velocities in solids is described; fractional velocity changes as small as 5×10−6 can be detected by this method. Application of the interferometer to specimens in which the temperature is varied yields the temperature dependence of the appropriate adiabatic elastic stiffness constants. Some results are reported for steel, fused silica, and single crystals of KBr, KCl, and LiF.
Zeros of Gaussian Noise
Authors: White Gerald M.
Published: April 2005

For many years statisticians and research workers in communication theory have been interested in the problem of the ``zeros'' i.e., the statistics of the times a random function crosses through its average value. At present very few of the desired results are amenable to analytic or numerical solution; therefore, an experiment was designed for generating and measuring the zeros of Gaussian noise having various spectral shapes. This article contains several experimentally determined distributions and statistics. Those that could be checked with numerical calculations {e.g., P[+z(t)|+z(0)], the probability of finding a zero in an increment of time Δt, t seconds after a zero has occurred} agreed closely with their calculated values. The others, e.g., W(N,T), the number of zeros in an increment of time T, verified what would be intuitively expected. The article also briefly outlines the equipment used in this investigation.
Energy Distribution Half-Widths for Field Emission Electrons
Authors: Murphy E. L.
Published: April 2005

The results of a numerical treatment of the dependence of half-widths of electron energy distribution on temperature, field, and work function are presented for the electrons emitted from a metal at temperatures and fields within the extended field emission range. For the distribution, the width of the peak at half maximum and the partial widths from peak to half-maximum on either side are presented graphically as a function of one parameter depending on temperature, field, and work function. The peak energy can also be determined in terms of this parameter.
Apparent Temperatures of Some Terrestrial Materials and the Sun at 4.3-Millimeter Wavelengths
Authors: Straiton A. W. , Tolbert C. W. , Britt C. O.
Published: April 2005

This paper describes a 4.3-mm radiometer and measurements made with it of the apparent temperature of various terrestrial materials, the attenuation through the atmosphere and the temperature of the sun. Materials whose apparent temperatures were measured included water, wood, metal, grass, asphalt, gravel and asbestos. Since their apparent temperatures are dependent upon their reflectivity, these data are interpreted in terms of the background reflected by the materials.

The attenuation vertically through a clear sky ranged between 1.6 and 2.3 db. The sun, of optical disk size, was found to be between 104 and 1.2×104°K on May 3 and June 17, 1957.
Master Amplifier Characteristics for Transmission and Reflection Cavities
Authors: Stich Malcolm L.
Published: April 2005

The noise temperature, band width, and gain modulation characteristics of a transmission maser are obtained as a function of iris coupling for fixed desired gain and other parameters. It is found with the help of a characteristic curve that certain of these characteristics can be optimized at the expense of others. The same functions are compared in the case of a reflection maser. The reflection maser is shown to be superior in most respects, although the same noise temperature may be attained with the transmission maser at a substantial sacrifice in band width and gain modulation. The reflection maser is also limited by the availability of good circulators, while a transmission maser can be made independent of load. A figure of merit for both types of maser amplifiers is obtained. This is Q0Z, where Q0 is the unloaded cavity Q; Z is given by Z=4πξχ0−Q0−1; ξ is the filling factor; and χ0 is the negative rf susceptibility. When the cavity band width is much less than the susceptibility band width, an auxilliary figure of merit is Z.
Spectral Characteristics of the Radiation Emitted by Electrons Accelerated in a Synchrotron
Authors: Tomboulian D. H. , Bedo D. E.
Published: April 2005

Expressions are developed for the average power radiated by a high-energy electron moving in a circular orbit. The instantaneous electron energy E(t) is assumed to vary with the time in accordance with E(t)Emsin2(πt/2T). Spectral distributions are obtained corresponding to the radiation emitted over a partial or full acceleration interval. The numerical results predicted from the general relations are examined for a particular value of the peak energy Em=6.0 Bev and the orbital radius R=86.14 ft. In the case of these parameters, the continuous spectrum attains a peak at 0.36 A. Other numerical calculations, related to the case where the radiation is collected only over the low-energy portion of the acceleration interval, indicate that it is feasible to utilize the continuum as a source for measurements in problems of interest to astrophysics and solid state spectroscopy.
Diffusion of Tungsten in Nickel and Reaction at Interface with SrO
Authors: Allison Herbert W. , Moore George E.
Published: April 2005

Diffusion rates of tungsten in single crystal and polycrystalline nickel were measured at temperatures between 1100°C and 1275°C by using radioactive tungsten185 and a sectioning technique. Grain boundary diffusion was observed by use of radioautographs. A simple vacancy mechanism accounts for nearly all of the diffusion; some refinement is required for the transport observed at greater depths.

The rate of reaction of polycrystalline 4.9% tungsten-nickel alloy with SrO was measured by the hydrogen evolution technique at temperatures between 830°C and 1280°C. The rate indicates that the production of Sr in amounts up to 200 μg cm−2 is not limited by diffusion of tungsten in the nickel core.
High Q Quartz Crystals at Low Temperatures
Authors: White Donald L.
Published: April 2005

The Q (quality factor) of natural quartz was measured from 4.2°K to over 100°K. The quartz was in a high precision AT crystal unit vibrating on overtones of the thickness shear at about 6.3 mc and 8.8 mc.

At higher temperatures the Q varied rapidly with temperature, but did not depend on the particular mode of vibration.

At low temperatures (say less than 10°K) the Q also depended on the mode of vibration. At these low temperatures the Q became very large—a record of 55 million was observed on one mode at 4.2°K. Apparently another loss mechanism dominates at low temperatures, and very likely this mechanism may not be intrinsic to quartz. The mounting structure or gold electrodes may be the primary source of energy loss in the liquid helium temperature range.
Some Aspects of the Thermal Desorption of a Boundary Lubricant
Authors: Kingsbury E. P.
Published: April 2005

An expression is developed relating friction coefficient in a boundary lubricated sliding system to temperature, heat of adsorption, and sliding velocity. Frictional and wear phenomena are shown to be double exponential functions of temperature and single exponential functions of sliding velocity. Experimental confirmation is obtained and a simple method is indicated for measuring the heat of a adsorption as a function of temperature.
Diffusion and Elastic Collision Losses of the ``Fast Electrons'' in Plasmas
Authors: Medicus G.
Published: April 2005

(I) When the energy spectrum of plasma electrons consists of two clearly separable groups—a high-energy, primary, non-Maxwellian, and a low-energy, secondary, Maxwellian one—the characteristic linear part of the corresponding probe curves, extrapolated to plasma potential, directly determines the random current density of the fast group. With a hemispherical anode and a hollow hot cathode near its center, in Ne of about 1 mm Hg pressure, the flow of the fast group at low diode currents follows closely the spherical case of diffusion. The experimental data, by means of the diffusion law, can be evaluated for the mean free path l of the fast electrons. It is found that l is independent of the plasma density and is about equal to the value calculated from the cross-section function for 10–16 volt electrons in Ne.

(II) The Diffusion law being applicable, the elastic collision losses of the fast group can be calculated. They are found to be relatively small compared to the total energy losses of the fast electrons. The results will be used in an attempt to determine the energy transfer from the fast group to the Maxwellian group, to be described in a subsequent paper.

The most remarkable result is the low interaction of the fast group with the Maxwellian group at low total plasma densities where the partial density of the slow group is always comparable to or even much higher than that of the fast group.
Investigation of the Perveances and Beam Profiles of an Aperture Disk Emission System
Authors: Harrison E. R.
Published: April 2005

Argon ion beams are used for determining experimentally the perveances and the associated beam profiles of a series of electrode structures consisting of coaxial aperture disks. The results are of particular interest in the design of ion sources. Since, fundamentally, there is little difference between electron guns and ion sources, the results should also be of interest in the design and study of electron guns. Electron guns producing convergent beams, and designed on the Pierce principle of rectilinear flow, require electrodes whose shape is not always easy to reproduce or the most convenient to use. If the principle of rectilnear motion is abandoned, it is found experimentally that the perveance in many cases is little affected by the adoption of the much simpler electrode system of coaxial aperture disks. Perveance is the ratio of the output current to the32 power of the input voltage.
Diffraction by a Perfectly Absorbing Thin Screen
Authors: Derwin C. C.
Published: April 2005

A plane screen only one-eighth wavelength thick which absorbed 99% of the intensity of normally incident microwave was constructed using glass with an electrically conducting surface. Comparative measurements were made of the diffraction pattern in and near slits in ``perfectly absorbing thin screens'' and ``perfectly reflecting thin screens.'' It was found that the diffraction pattern of the slits on the side of the screens opposite the source was the same for both screens at distances greater than a half-wavelength. Even in the planes of the slits the diffraction patterns for these two screens differed by less than the experimental error for slits wider than one wavelength.
Domain Observations on Iron Whiskers
Authors: DeBlois R. W. , Graham C. D.
Published: April 2005

Ferromagnetic domain walls have been observed by standard methods on iron whiskers. The whiskers are square in cross section, generally 20 to 60 microns on a side, and up to one cm long. The whiskers are single crystals with the axis in a 〈100〉 direction and the faces nearly perfect {100} planes. The domain patterns are exceptionally clear and simple. Several characteristic patterns have been described and represented with three-dimensional models; a feature common to many patterns is the V line, which consists of two plane walls meeting in a V with its apex at the whisker surface. The effects of applied fields and applied stresses on the domain structures have been studied, and some observations have been made on whiskers small enough to approach a single-domain state.
Studies of High-Velocity Impact in Wax
Authors: Partridge William S. , Clay Wallace G.
Published: April 2005

Penetration of wax pellets into wax targets was found to vary linearly with the cube root of the pellet mass and the pellet velocity up to velocities in excess of twice the sonic velocity in the wax target. The crater area varies directly as the impact velocity, but there is a marked increase in the constant of proportionality above the target sonic velocity. The volume of the crater per unit energy of the pellet was found to be 2.23×10−8 m3/joule for the lower velocity range and above the target sonic velocity the value was found to be 2.75×10−8 m3/joule.

It was observed that a large part of the crater volume is created by deformation of the target material and that only a small part is due to ejection of the target material.
Shear Rate Dependence of the Viscosity and Elastic Compliance of Polymer Melts—Correspondence with a Hydrodynamic Theory of Viscoelastic Flow
Authors: Boyd Richard H.
Published: April 2005

The variation of viscosity and elastic compliance with shear rate of several typical polymer melts has been measured. The results are compared with the predictions of a hydrodynamic flow theory proposed by Y. H. Pao [J. Appl. Phys. 28, 591 (1957)]. The agreement is satisfactory.
Study of Order in Annealed and Irradiated Alpha Brass by Lattice Parameter Measurements
Authors: Feder R. , Nowick A. S. , Rosenblatt D. B.
Published: April 2005

The increase in short-range order in alpha brass (25% and 30% Zn) produced by thermal treatment or neutron irradiation is accompanied by a measurable decrease in lattice parameter (up to 0.02%). The equilibrium values of the lattice parameter decrease markedly with annealing temperature in the lower range of the measurements, i.e., in the vicinity of 125°C. The activation energies calculated from the kinetics of the lattice parameter changes are 40.7 kcal/mole for the 25% Zn alloy, and 39.5 kcal/mole for the 30% Zn alloy, in agreement with results of anelastic measurements and electrical resistivity studies. From thermodynamic data it is estimated that a decrease in lattice parameter of 0.01% corresponds to an increase of about 0.05 in the Bethe short range order parameter.
Simplified Theory of One-Carrier Currents with Field-Dependent Mobilities
Authors: Lampert Murray A.
Published: April 2005

A general method is presented for the calculation of steady-state, one-carrier currents in nonmetallic solids where the mobility is field dependent. The analysis includes the effects of space charge and trapping. The essential mathematical step is the representation of the electric-field intensity as a polynomial in the drift velocity. Detailed applications are made to semiconductor and insulator problems. A new mobility function of convenient mathematical form is proposed for the case that the carrier has a constant mean free path. Some very general properties of the current flow are established by geometric analysis.
Application of the Ion Bombardment Cleaning Method to Titanium, Germanium, Silicon, and Nickel as Determined by Low-Energy Electron Diffraction
Authors: Farnsworth H. E. , Schlier R. E. , George T. H. , Burger R. M.
Published: April 2005

The ion-bombardment cleaning method has been successfully applied to the (100) faces of germanium, silicon, and nickel, and to the (0001) face of titanium. Conditions and precautions necessary for the production of clean surfaces are described. Tests have been made for contamination from the ambient during the cleaning procedure for germanium. It has been shown that contamination approximating one-half monolayer does not occur under the conditions which were obtained, and that the method is capable of producing surfaces which are atomically clean.

Results for clean (100), (111), and (110) germanium faces and the (100) silicon face indicate that the atomic positions in the surface planes are not the same as the corresponding positions in the bulk structure. For (100) nickel and (0001) titanium, the positions of the atoms in the surface planes are in agreement with x-ray data. In the case of titanium, an unidentified surface structure was present until after several cycles of alternate heating and ion bombardment. In the case of nickel, a double-spaced surface monolayer and in some cases a single-spaced, simple-square structure, attributed to carbon, was present until after several cycles of alternate heating and ion bombardment.
Orientation Dependence of Ultrasonic Attenuation in Zinc
Authors: Waterman P. C.
Published: April 2005

The attenuation of plane elastic waves in the megacycle region is investigated for several different propagation directions in single crystalline zinc. Results are in qualitative agreement with the losses predicted theoretically due to dislocation damping and thermoelastic effects, and in addition losses not accounted for by the available theory are observed.
Preventing Conductivity Fluctuations during Growth of a Semiconducting Crystal
Authors: Pfann W. G. , Hobstetter J. N. , Indig G. S.
Published: April 2005

Fluctuations in the electrical conductivity of an extrinsic semiconductor arising from fluctuations in the growth conditions of the crystal can be eliminated by adding to the melt a critical concentration of a suitable donor or acceptor. Useful solute combinations are those for which one of the two characteristics; (a) the conductivity type and (b) the sign of (1−k), where k is the distribution coefficient, must be opposite and the other the same for the two solutes. The critical ratio of melt concentrations, (C2/C1), is equal to (dk1/df)/(dk2/df), where f denotes growth rate, and subscript 1 denotes the major solute. Expressions are derived for the critical ratio, for the effects of deviations from it, and for the optimum characteristics of solute combinations.
Radiation Effects from (n,α) Reactions in Boron Glass and Energy of the Reacting Neutrons
Authors: Mylonas C. , Truell R.
Published: April 2005

The damage produced in neutron irradiated boron glass by the products of the (n,α) reaction appears as a pronounced optical birefringence. This birefringence is shown to be due to macroscopic stresses resulting from volume contraction of the glass. The variation of strain with depth from the glass surface is found to fit to a remarkable degree the space rate of decay of radiation of suitable velocity distribution and random direction. This permits the determination of the neutron velocity by one-velocity theory, or of the most probable velocity for a Maxwellian neutron distribution; in addition the average volume contraction corresponding to a single neutron-boron reaction is found to be equal to 3.6×10−19 cm3 per (n,α) reaction.
Neutron Multiplication in Small Spheres of Fissionable Material
Authors: Bendt P. J. , Peterson R. E.
Published: April 2005

Central-source neutron multiplication measurements have been made on small spheres of U233, U235, U238, and Pu239. Measurements were made on four sizes of spheres, varying approximately from 1 in. to 2.5 in. in diameter. In the case of U233, only one sphere, 1.245 in. in diameter, was available. The three neutron sources, mock-fission, Po–Li, and Po–Be, were 0.4-in. diameter spheres. They have widely different neutron spectra. Multiplications were measured with a flat-response long counter, and with U235, U238, and Np237 spiral fission chambers, under conditions such that the error introduced by room-scattered neutrons was negligible. Results of the multiplication measurements are given. The measurements have been analyzed to obtain the leakage spectra from the spheres in terms of three velocity groups. The Np237 and U238 fission chambers serve as threshold detectors defining the lower energy of the second and third velocity groups, respectively.
Production of Cadmium Sulfide Crystals by Coevaporation in a Vacuum
Authors: Miller R. J. , Bachman C. H.
Published: April 2005

Apparatus was developed by which beams of cadmium and of sulfur were simultaneously directed to a common point on a temperature controlled substrate in a demountable vacuum apparatus. Cadmium sulfide crystals were obtained. The various types of crystals: spiroidals, globules, ribbons, and needles are described together with the conditions tending to produce each type. Crystal size can be increased by repeated exposure to the beams.
Diffusion of Indium in Tin Single Crystals
Authors: Sawatzky Anton
Published: April 2005

The rate of diffusion of indium in single crystals for two orientations has been measured using the radio-active isotope In114. The diffusion coefficients in the directions parallel to the a axis and c axis are given by the Arrhenius relations Da=34.1 exp(−25 800/RT) cm2 sec−1 and Dc=12.2 exp(−25 600/RT) cm2 sec−1, respectively. The anisotropy is discussed in terms of the vacancy mechanism of diffusion.
Thermoelastic Dissipation due to High-Speed Dislocations
Authors: Weiner J. H.
Published: April 2005

The thermoelastic dissipation due to an edge dislocation moving at an arbitrary speed is calculated analytically and numerical results presented. It is found that, at usual stress levels, this mechanism has only a minor effect in limiting dislocation speed.
Calculation of the Transmission Factor in X-Ray Scattering
Authors: Sawada M. , Shaw C. H.
Published: April 2005

Analytical equations have been derived for the transmission factor applicable to the case of a rather weakly absorbing sample of circular cross section and larger than the x-ray beam. Calculations are presented for liquid nitrogen and it is shown that under certain practicable conditions the transmission factor is constant for a rather wide range of the scattering angle.
Mechanism of Cataphoretic Segregation in Inert Gas Glow Discharges
Authors: Loeb Leonard B.
Published: April 2005

The collection of a minority gas species at the cathode in a glow discharge, termed cataphoresis, appears not to have been completely successfully explained. Observation indicates that in all cases, the minority gas segregated at the cathode, must be capable of being very effectively ionized by the vehicular gas. The recent discovery of the effective creation of ion complexes such as NeHe+ and NeA+ in pressure dependent reactions above some mm of Hg pressure by Oskam, the independent direct observation of these ions and the production of ions such as HeH+, NeH+, and AH+ with 1% H2 in the inert gas by Weimer, using the effusion mass spectrometer of Pahl, render a basis for the extension of the Druyvesteyn theory developed for metallic ions in inert gas to the general process, aid in the explanation of the Hg-Xe anomaly observed by Kenty, and indicate certain needed corrections which are acting to make the process more efficient.
Ferromagnetic Resonance in Thin Magnetic Films at Radio Frequencies
Authors: Hasty Turner E. , Boudreaux Lee J.
Published: April 2005

Ferromagnetic resonance in thin films has been extended to the radio-frequency region of from 1–20 Mc. Theoretical expressions governing this resonance condition are given along with experimental results. It is found that resonance in this region affords an excellent means of measuring the anisotropy field Hk. Films with compositions near 80% Fe—20% Ni were studied by this technique. The anisotropy field of these films was found to be around 5 oe. The width of the absorption line varied from 0.6 to 2.4 oe, depending on the composition of the film. The minimum linewidth was found to occur for the composition of minimum magnetostriction.
On the Possibility of Detecting Shock-Induced Second-Order Phase Transitions in Solids. The Equation of State of Invar
Authors: Curran D. R.
Published: April 2005

First-order phase changes in shock-loaded solids have been previously detected from the formation of multiple-wave structures in the solids. It is shown theoretically that a multiple-shock structure under shock loading also may be produced by a second-order phase transition. Accordingly, the possibility of detecting shock-induced demagnetization of ferromagnetic metals and alloys is discussed and an experimental attempt to detect such a demagnetization in shock-loaded Invar (64 Fe, 36 Ni) is reported. Extrapolation of data by Patrick suggests a Curie point transition in Invar in the neighborhood of 50 kbar. The Hugoniot equation of state of Invar has been obtained over a pressure range of 35 to 160 kbar. No double-shock structure was observed, but a decrease in compressibility observed in the neighborhood of 60 kbar is thought to be evidence of demagnetization.
``Anomalous'' Electron Double Diffraction
Authors: Haase O. , Heidenreich R. D.
Published: April 2005

Double diffraction of electrons by tandem foils of polycrystalline MgO and single crystal silicon is demonstrated. The patterns are very similar irrespective of which foil the electrons pass through first. The effect is explained by elastic bending of the thin, silicon crystal. The relationship between the double diffraction features, Kikuchi lines, and angular distortion of the crystal is discussed.
Dislocation Etch Pits on the Basal Plane of Zinc Crystals
Authors: Rosenbaum H. S. , Saffren M. M.
Published: April 2005

An etch pit technique has been developed that reveals the sites of dislocations which intersect the basal plane surface of zinc crystals. Pits can be formed by either Cl2, HCl, Br2, HBr, or HI dissolved in an appropriate organic solvent. Etchants made with Cl2 or HCl produce hexagonal pyramidal pits whose edges are parallel to 〈101̄0〉 directions; but Br2, BHr, or HI etchants produce hexagonal pits whose edges are parallel to 〈112̄0〉 directions. The technique is useful for observing glide which occurs on nonbasal planes. The dislocation etch pits are seen to form a ``polygonization'' pattern in a crystal that was annealed after deformation. A discussion is presented on the mechanism of etch pit formation and the factors which might determine the shape of the pits.
Superconductor-Transition Switching Time Measurements Using a Superconductive Radio-Frequency Mixer
Authors: Feucht Donald L. , Woodford James B.
Published: April 2005

The transition properties of thin superconducting tin films are determined through measurements on a new device, the superconductive radio-frequency mixer. An equivalent circuit for this device is presented which permits the prediction of mixer performance using static transmission curves for the particular films employed. Experimental transmission curves and their characteristics are discussed. The measured mixer performance is compared with theoretical performance for operation in the frequency range of 240 to 840 Mc. It is shown that the transition speed of the superconducting thin films can be determined and that film-switching times are at least as short as 0.625 nsec.
Noise in InSb Photodiodes
Authors: Pagel B. R. , Petritz R. L.
Published: April 2005

Experimental investigation of noise generation in InSb infrared photodiodes is reported. Minimum noise occurs when the diode is biased to zero potential. Noise spectra taken on seven photodiodes determined the white noise level above 1 kc. The experimental value of white noise is compared with the noise induced by random fluctuations in background radiation. The photonoise is calculated from 〈i2〉/Δf=2qIPHfor an equivalent noise generator. The photoinduced current IPH is measurable directly for zero bias potential. The total measured white noise is of the order of one decibel above the calculated photoinduced noise. Thus the photoinduced noise is the primary source observed, and InSb photodiodes closely approach the ideal case of being background-limited infrared detectors.
Single and Double Pile-Up of Dislocations in MgO Crystals
Authors: Chou Y. T. , Whitmore R. W.
Published: April 2005

A quantitative analysis has been made of elastic interactions in three types of pile-up groups of dislocations in MgO crystals; (i) single pile-up, (ii) double pile-up on two orthogonal slip planes, and (iii) double pile-up on two slip planes intersecting at 120°. The equilibrium positions of dislocations in these groups are given. It is found that the stress concentration factor is highest in type (iii) and lowest in type (i). The number of dislocations in the pile-up groups sufficient to raise the tip stress to 1000σ0 is 1000 in type (i), about 120, determined by extrapolation, in type (ii), and 62 in type (iii).
Attainment of Ultrahigh Vacua, Reduction in Surface Desorption, and the Adsorption of Hydrogen by Evaporated Molybdenum
Authors: Hunt Angus L. , Damm Charles C. , Popp Earl C.
Published: April 2005

Deposition of molybdenum by vaporization from simple hairpin filaments has been found to reduce pressures in both unbaked and moderately baked stainless steel vacuum systems to 4×10−10 mm Hg. A deposit of 300 mg from a single filament, 0.050 in. in diameter and 6 in. long, has maintained an unbaked 85-liter volume at pressures below 10−9 mm Hg for over 40 hr with the aid of a small well-trapped diffusion pump. For a substrate area of 8×103 cm2, the initial pumping speed of a molybdenum deposit was found to be as high as 105 liters/sec for hydrogen and 8×104 liters/sec for deuterium. The sticking probability for either hydrogen or deuterium on this deposit is estimated at 0.3.

A similar system, baked at 200°C for several days while pumped by an oil-free ion pump, attained 2×10−10 mm Hg with molybdenum evaporation. When the ion pump was valved off, the pressure in this 75-liter system remained at 2×10−10 mm Hg for two weeks with no external pumping.
X-Ray Polarizer
Authors: Cole H. , Chambers F. W. , Wood C. G.
Published: April 2005

In the Borrmann effect, or the anomalous transmission, by diffraction, of x rays through perfect crystals, one state of polarization of the x-ray beam is preferentially absorbed. Since this happens in the ``transmitted'' as well as in the diffracted beam, a simple polarizer-monochromator is possible in the sense that insertion and rotation of the polarizer does not sensibly change the line of action of the x-ray beam. We have used as our ``Borrmann crystal'' a single-crystal slab of dislocation-free germanium approximately 30 mils thick and cut for symmetric Laue diffraction from the 220 planes. The details of the rotating crystal holder, an analysis of the polarization, comments on the double-crystal geometrical effects, and an example of the use of the polarizer-monochromator to study the polarization term in Bragg diffraction are presented.
Effect of Electron Bombardment on the Near-Infrared Fluorescence of Single-Crystal CdS
Authors: Kulp B. A.
Published: April 2005

Under electron bombardment at 40°C, two fluorescence bands in the near infrared are observed in many CdS crystals. The bands are at about 8500 A and 1.05 μ. The 8500-A band is reduced in intensity by electron bombardment at 100 and 275 Kev and by exposure to x radiation. The 1.05−μ band is not greatly affected by these irradiations. Heat treatment for ½ hr at 200°C partially restores the 8500-A band. The effect is interpreted as a redistribution of electrons over the existing defects. The defect responsible for the 8500-A band is believed to be copper in a particular ionization state. The 1.05−μ band is observed to appear after heat treatment at 200°C if it is not present originally. This fact makes the origin of this latter band uncertain.
Calculations of the Thermoelectric Parameters and the Maximum Figure of Merit for Acoustical Scattering
Authors: Testardi Louis R.
Published: April 2005

The calculations of Chasmar and Stratton [R. P. Chasmar and R. Stratton, J. Electronic and Control 7, 52 (1959)] for the determination of the maximum thermoelectric figure of merit are extended for the case of acoustical scattering. Graphical data are presented for the determination of the material parameter, the optimum values of several quantities, and the degradation of the figure of merit for nonoptimum conditions. The variations of the Seebeck coefficient and the electrical conductivity computed from exact statistics are compared with experimental results for several alloys of thermoelectric interest. Good agreement is found except for high electrical conductivities. Other anomalies are noted.
Fast-Risetime Excitation Scheme to Achieve Nonequilibrium and Amplifying Carrier Distributions
Authors: Dousmanis George C.
Published: April 2005

A technique is suggested for creating anisotropic and emissive carrier distributions in semiconductors or other crystals at low temperatures. As an example, application of the technique in the re-entrant (negative-mass) regions of heavy holes in germanium and silicon, in conjunction with cyclotron resonance using circularly polarized microwaves, is discussed. These distributions are expected to be short-lived (of order 0.2 to 5 mμsec), but more anisotropic than those obtained so far in these regions by applying steady-state optical excitation alone. The nonequilibrium distributions would be created by excitations (pulsing, for example) with risetime shorter than the carrier-phonon scattering time. Recently, the increasing purity of materials and speed of electronic instruments have approached the theoretical requirements of this method.
Semiconducting Stress Transducers Utilizing the Transverse and Shear Piezoresistance Effects
Authors: Pfann W. G. , Thurston R. N.
Published: April 2005

Principles of a varied group of new semiconducting, piezoresistive stress and strain transducers are outlined. These devices have in common the utilization of the transverse or shear piezoresistive effect. One group of devices consists of gauges in the form of a thin rectangular sheet which is bonded to the test piece, and whose resistance change can be expressed as a simple function of the principal stresses in the gauge. Two special gauges in this group are described. In one, the resistance change is proportional to the sum of the principal biaxial stresses for any orientation of the gauge on the test piece. In the other, the resistance change is proportional only to longitudinal stress components, being independent of transverse stress components. Also described are: a four-terminal gauge for complete determination of biaxial stresses, full-bridge gauges made from a single crystal, load cells of low compliance, new torque transducers, and diffusion techniques for making some of the foregoing. The devices are illustrated in terms of germanium and silicon but extension to other semiconductors is straightforward.
Effect of Hydrostatic Pressure on the High-Temperature Steady-State Creep of Lead
Authors: Butcher B. M. , Ruoff A. L.
Published: April 2005

The activation energy and activation volume for the creep of high-purity lead were obtained by the method of rapidly varying the temperature and pressure. The activation energy was found to be 1.18±0.03 ev and the activation volume was found to be (24.2±0.6)×10−24 cc or 0.80 atomic volume.
Emission Fluctuations of Tungsten-Based Barium Dispenser Cathodes
Authors: Brodie I.
Published: April 2005

Emission fluctuations in five different types of tungsten-based barium dispenser cathodes have been measured as functions of both frequency and current density. Two of the cathodes were of the L variety and the remainder of the ``impregnated'' variety. The L cathode spectra show that the emission fluctuations are caused by fluctuations in the number of adsorbed atoms on the tungsten emitting surface. The amplitude of the fluctuations is governed by the average surface coverage and theoretical studies indicate that the shape of the spectra is governed by the diffusion processes by which the surface is replenished.

The results from the impregnated cathodes indicate that the contribution of the impregnant in the pore ends to the total noise is only significant when the pore ends supply an appreciable fraction of the total emission from the cathode, the majority of the surface, which is barium activated tungsten, behaving as an L cathode surface.
Growth of Stannic Oxide Crystals from the Vapor Phase
Authors: Marley J. A. , MacAvoy T. C.
Published: April 2005

Single crystals of stannic oxide up to 30×4×2 mm have been prepared by a high temperature vapor deposition technique. Using high purity SnO2 powder, crystallization and growth were studied under both neutral and oxidizing conditions. Neutral carrier gases, with the exception of helium, encouraged the formation of voids and inclusions. However, the use of a helium-oxygen system was found to eliminate these defects. An explanation is offered for this behavior. Three distinct variations in the crystalline habit of SnO2 have been observed, apparently dependent upon the temperature at which growth occurred.
Theory of Electron Collection of Spherical Probes
Authors: Medicus G.
Published: April 2005

The theory of spherical probes based on the impact parameter of the carriers is given. Fields outside the sheath are neglected, which is justified for electron collection. The results are obtained more directly than by Mott-Smith and Langmuir. General results such as the transition from impact parameter limitation to sheath limitation for the spherical case, not previously treated in the literature, are derived. The case of a uniformly accelerated half-Maxwellian (as opposed to a Maxwellian with drift) is treated in detail; the case of a pure Maxwellian superimposed on the accelerated half-Maxwellian and the superposition of two different accelerated half-Maxwellians is discussed briefly.
Properties of Single-Domain Particles of Cobalt-Nickel
Authors: Falk R. B. , Hooper G. D.
Published: April 2005

Single-domain particles of cobalt-nickel have been prepared by electrodeposition into mercury, and the intrinsic coercive force observed as a function of particle composition. A marked increase in coercive force occurred in particles having a composition of 87.5% cobalt–12.5% nickel. On the basis of the spherical structure of the particles observed in electron micrographs and from the constancy of the coercive force with packing, crystal anisotropy was assumed to be the principal factor contributing to the coercivity of the cobalt-nickel particles. An intrinsic coercive force of 1750 oe was achieved, and a minimum crystal anisotropy of −2.4×106 ergs/cc calculated at −196°C for the above composition. Magnets were prepared with a maximum magnetic energy of 1.3×106 gauss-oe.
Improved Representation of Calculated Surface Mobilities in Semiconductors. I. Minority Carriers
Authors: Grover N. B. , Goldstein Y. , Many A.
Published: April 2005

A simple and convenient representation is given of calculated values of minority carrier surface mobility over the range of practical interest of surface potential from depletion to strong inversion layers for an extended range of material resistivity and temperature.
Improved Representation of Calculated Surface Mobilities in Semiconductors. II. Majority Carriers
Authors: Goldstein Y. , Grover N. B. , Many A. , Greene R. F.
Published: April 2005

Improved representation is given of calculated values of majority carrier surface mobility. For extrinsic material the semiconductor effectively constitutes a single-carrier system. The surface mobility is then independent of the bulk potential and can be expressed as a function of the potential barrier Vs by a single family of curves over the entire range of interest of surface potential, material resistivity, and temperature.
Low-Temperature Thermoelectric Power of the Rare-Earth Metals
Authors: Born H. J. , Legvold Sam , Spedding F. H.
Published: April 2005

The Seebeck coefficients (thermoelectric powers) of yttrium, lanthanum, and 11 of the rare earths have been measured for the temperature range 7° to 300°K. The transitions reported by other investigators on specific heat, magnetic moment, and resistivity at the magnetic ordering temperatures are, in many instances, visible also in the curves of thermoelectric power (TEP) vs temperature. The Néel temperature is evidenced by a change in slope in the TEP vs T curve. The ferro-antiferro transition temperature is obvious only in the case of dysprosium and appears as a sharp drop in the curve. With the exception of samarium and ytterbium, the TEP's of the metals are negative throughout most of the temperature range covered, and, with the same exceptions, the TEP curves have about the same slope near room temperature.
A Method for the Measurement of Short Minority Carrier Diffusion Lengths in Semiconductors
Authors: Goodman Alvin M.
Published: April 2005

A method is presented whereby short minority carrier diffusion lengths in semiconductors may be determined by measuring the variation of surface photovoltage as a function of optical absorption coefficient. The method does not depend upon the specific form of the relationship between the surface photovoltage and the density of the excess minority carriers injected at the bulk edge of the surface space charge region. Only capacitive contacts to the sample are needed for the measurement. The method has been used to determine the minority carrier diffusion length in both n and p type gallium arsenide.
High-Temperature Kilocycle Internal Friction in Al2O3 Single Crystals
Authors: Huber R. J. , Baker G. S. , Gibbs P.
Published: April 2005

Dislocation damping in Al2O3 single crystals has been measured to 1850°C. Undeformed specimens show no damping greater than δ = 10−5. Deformed specimens have an exponentially rising damping above 1450°C with an activation energy of 100–120 kcal/mole. The damping is amplitude independent at least to 10−5 strain amplitude. Dislocation densities and distributions for the specimens were determined by surface etching.