bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron Trajectories in a Nonuniform Axially Symmetric Magnetic Field
Authors: Dunn D. A. , Holaday R. E.
Published: April 2005

Electrons injected along the flux lines of a spatially varying, axially symmetric magnetic field that is increasing in the direction of electron motion will follow approximately helical trajectories about the flux lines. If the field increases too rapidly, the electrons will not be able to penetrate the magnetic field beyond a certain point and will be turned back by the magnetic mirror formed by the increasing field. For more slowly varying fields, the electrons can penetrate the mirror with a large fraction of their energy in axial velocity. The equations of motion for electrons in a sinusoidally varying magnetic field have been solved on a computer, and the results are presented in graphical form. An application of this field configuration as a device for converging a hollow cylindrical electron beam has been tested, and measured area convergences of 15 to 1 have been obtained by photographing a movable carbon screen collector that is heated by the beam. The beam is started out with a conventional parallel flow gun immersed in the magnetic field. As the beam leaves the first accelerating electrode it enters the region of increasing magnetic field. It then shrinks in diameter and thickness, and hence in area, approximately in proportion to the increase in the magnetic field. The actual area convergence will be less than this increase by an amount depending on the length and rate of the magnetic field taper.
Role of Crystal Structure in Diffusion. II. Activation Energies for Diffusion in Closest-Packed Structures
Authors: Azároff Leonid V.
Published: April 2005

The effect of available diffusion paths on activation energies are considered for silver iodide, zinc oxide, and bismuth selenide. It is shown that the energy in β-AgI should be nearly twice that in γ-AgI because the Ag atoms in tetrahedral sites first must be displaced to octahedral voids before voidal diffusion can occur in the beta modification. The 2:1 ratio between the self-diffusion energies of Zn determined by radioactive tracer and electrical conductivity measurements in ZnO is similarly explained. It is also shown that the difference between the activation energies for diffusion in BiSe and Bi2Se3 can be used to determine the formation energy of vacancies in BiSe. The agreement between these predictions and experimentally determined values attests that qualitatively accurate explanations can be based on considerations of the crystal structure.
Properties of High-Resistivity Gallium Arsenide Compensated with Diffused Copper
Authors: Blanc Joseph , Bube Richard H. , MacDonald Harold E.
Published: April 2005

Low-resistivity n-type GaAs crystals with silicon donors are compensated with diffused copper to produce high-resistivity crystals in a manner which is amenable to semiquantitative description in terms of a simple thermodynamic model. The high-resistivity GaAs:Cu crystals are subjected to photoelectronic analysis, including room temperature Hall and photo-Hall measurements, to obtain information about the effects of deep-lying imperfections on the properties of the initial n-type GaAs. In addition to three deep donors previously reported, five acceptors are revealed. A 0.42-ev acceptor level, when compensated, provides a long electron lifetime resulting in high n-type photosensitivity at low temperatures. Evidence for effects on the electron mobility is obtained for compensated deep donor levels, important mainly in high-resistivity n-type material, and for compensated acceptors lying 0.22 ev above the valence band, important mainly at low temperatures.
Thermal Conductivity of Porous Media. I. Unconsolidated Sands
Authors: Woodside W. , Messmer J. H.
Published: April 2005

The problem of determining the effective thermal conductivity of a two-phase system, given the conductivities and volume fractions of the components, is examined. Equations are described which have been proposed as solutions to this problem, including those of Maxwell, de Vries, and Kunii and Smith, the weighted geometric mean equation, and an equation based on a three-element resistor model found applicable to the analogous electrical conductivity problem. Experimental results are presented for five unconsolidated samples: three quartz sand packs, a glass bead pack, and a lead shot pack. The method of conductivity measurement using the transient line heat source (thermal conductivity probe) is described. Data are reported showing the variation of effective thermal conductivity with porosity, solid particle conductivity, saturating fluid conductivity, and the pressure of the saturating gas. From considerations based on the kinetic theory of gases, it is shown that the characteristic dimension of the pore space, with respect to heat conduction in the gas occupying this space, is smaller than the mean particle diameter by a factor of roughly 100. The thermal conductivity equations which best represent the observed data are those of de Vries, and Kunii and Smith, and a slightly modified version of the resistor model equation.
Fields in Cavity-Excited Accelerators
Authors: Cristal E. G. , Van Bladel J.
Published: April 2005

Field configuration and resonant frequency are determined for the lowest azimuthally-independent mode of a coaxial cavity surrounding a circular tube, Several values of the width of the coupling gap are considered, and the central problem consists in determining the tangential electric field Et in that gap. It was found that the fields near the axis of the accelerator are quite insensitive to the actual profile of Et, and that satisfactory results are obtained by assuming Et to be constant. The problem is repeated for a parallel plane configuration, with the purpose of investigating the influence of the flattening of the cavity. Computations show that the two configurations yield fairly similar results.
Effect of Temperature on the Exoemission of Electrons from Abraded Aluminum Surfaces
Authors: Pimbley W. T. , Francis E. E.
Published: April 2005

A model and resulting theory for the exoemission of electrons from metal surfaces are presented. The model states that the exoemission is governed by the diffusion of vacancies in the metal, vacancies created by the abrasion. A vacancy, upon diffusing to the surface, may give up its energy to an electron. However, when in the same event, a photon also transfers its energy to the electron, the electron may be emitted. Experiments performed show the exoemission decay to be composed of two exponential decays. Both exponential decay constants vary with temperature according to the equation: k=Fe−E/RT. Here, F is a constant and E is an activation energy which, measured, approximates 5.6 kcal/mole. A comparison between experiment and theory give the theory corroboration.
Nonbasal Glide in Dislocation-Free Cadmium Crystals. I. The (101̄1) [12̄10] System
Authors: Price P. B.
Published: April 2005

Electron-transparent dislocation-free platelets of cadmium were deformed in tension parallel to the basal plane, inside an electron microscope, in the temperature range from +25° to −150°C. At high strain rates the crystals twinned. At low strain rates (≲10−2 sec−1) the glide system depended on α, the angle between the tensile axis and a close-packing direction. For 0≤α≲20° pyramidal glide on the (112̄2) [1̄1̄23] system occurred. For 20°≲α≤30° a new glide system, (101̄1) [12̄10], was identified which has not yet been observed in large cadmium crystals. Edge dislocations with a ⅓[12̄10] Burgers vector moved across the entire crystal on (101̄1) planes without multiplying or forming obstacles to further glide. Occasionally, at high strain, fracture occurred on a (101̄1) plane. The observations suggested that, in the temperature range studied, the flow stress for (101̄1) [12̄10] glide was considerably lower than that for prismatic glide on the (101̄0) [12̄10] system, slightly higher than that for (112̄2) [1̄1̄23] glide, and independent of strain for a given temperature.
Characteristics of the Annealing Kinetics of Tin Films Deposited at 88°K
Authors: Priest J. , Chiou C. , Caswell H. L.
Published: April 2005

The electrical resistance of evaporated, high purity tin films deposited at 88°K decreases rapidly in two temperature regions as determined by isothermal annealing studies. One pronounced annealing peak occurs at 110°K and has an activation energy of 0.34±0.06 ev. The second much less pronounced peak at 180°K has an activation energy of 0.74±0.10 ev.

The annealing characteristics of five pure films varying in thickness from 960 A to 4100 A and a film deposited in a high partial pressure of N2 are quite reproducible. The presence of O2 during evaporation, however, drastically altered the annealing kinetics and increased the activation energy at any given temperature. The defect resistivity at the time of evaporation was the same for all five pure films and a film deposited in a high partial pressure of N2, but is about 75% higher for the film deposited in the presence of O2.
Saturation Effects in Ferrite Frequency Doublers Operating in the Uniform Precession Mode
Authors: Auld B. A.
Published: April 2005

Three distinct saturation mechanisms occurring in ferrite frequency doublers are described. An approximate nonlinear equation of motion, including the effect of the reaction field, is obtained and solved for a particular case. The effects of the system parameters on conversion efficiency are discussed. Restrictions on the validity of the analysis due to transverse and longitudinally pumped spin waves are examined.
Unified Performance Calculations for Thermoelectric Cooling
Authors: Watanabe Akinori
Published: April 2005

A normalization of practical quantities has yielded systematic forms for performance calculations of an idealized couple composed of temperature-independent parameters. The normalized quantities can be expressed by only three parameters at most instead of six, i.e., normalized current and two types of normalized temperature difference. Effects of contact resistance, current ripple, and heat leak on practical quantities are also considered as functions of the same parameters. Proposed graphs herein of performance quantities and their variations with above effects are given respectively, including no fixed parameters. The temperature difference normalized by its maximum is recommended as ``figure of performance'' as a criterion for an operating couple.
Photoeffects in Silicon Surface-Barrier Diodes
Authors: Tuzzolino A. J. , Hubbard E. L. , Perkins M. A. , Fan C. Y.
Published: April 2005

Silicon surface-barrier photodiodes have been fabricated and the steady-state and time-varying photoresponse have been measured. The photodiodes are operated in the reverse-bias, or photoconductive mode at room temperature and do not require encapsulation. The average steady-state photosensitivity is 0.31 μa/μw (λ=5461 A) and 0.065 μa/μw (λ=2537 A) with approximately 50 A of gold on the sensitive area. With no gold on the sensitive area, the photosensitivity is 0.37 μa/μw and 0.13 μa/μw, respectively. The photoresponse is uniform over the sensitive area (0.1 to 2.5 cm2) to within a few percent, depending on the wavelength. The high-frequency cutoff is limited by the photodiode capacitance and load resistance. Cutoff frequencies greater than 100 kcps have been obtained. The operating characteristics of these devices are reported for six wavelengths lying in the range of approximately 0.2 to 0.6 μ. The possibility of using photodiodes of this type in combination with a scintillator crystal for detecting charged particles is discussed.
Specific Friction Force in a Graphite Brush Contact as a Function of the Temperature in the Contact Spots
Authors: Holm Else
Published: April 2005

Measurements by different workers have indicated that the friction coefficient μ of a graphite brush contact decreases with rising contact temperature T. If P = mechanical load, Ab = load bearing area and F = friction force, the average pressure is p̄ = P/Ab and the specific friction force ψ = F/Ab. Hence μ = F/P = ψ/p̄. It will be shown in this paper that the measured μ(T) effect during smooth sliding is caused by the decrease of ψ with rising T.

The specific friction force is a function of the character of the sliding surface alone, and μ is, in addition, a function of the actual pressure in Ab. It is shown that sliding, after a relatively short time, leads to a stage during which Ab, thus also p̄, remains practically constant for more than 10 hr. The (μ,T) test begins when such an ``initial stage,'' defined by μ=μ0, T = T0 and constant contact voltage U, has been reached. It involves T increasing above T0 and then decreasing to T0 again, whereby the time of the test is short enough for constancy of p̄. During a perfect (μ,T) test, the forward and reversed curves agree with each other indicating that Ab has remained constant.

For all sliding stages with constant p̄, the relationship mentioned above can be written: μ(T) = constψ(T), which makes it possible to study ψ as a function of T by studying μ as a function of T. The decrease of ψ with rising T is explained by assuming that adherence bonds in Ab are broken or loosened by T according to a probability exp(−φ/kT) = exp(−11600 φ/T) with φ in ev. The measured, strong dependence on T results from the activation energy φ=0.07 to 0.1 ev between the graphite ``platelets'' being of the order of kT. Hence it is expected that μ and ψ are inversely proportional to the probability factor. It was found that at constant Ab up to about 500°K (the upper limit measured): ψ(T)ψ(T0)=μ(T)μ(T0)=exp[11600[open pi](1T−1T0)]gives a very good agreement in the case of graphite members when the binding energy is assumed to be φ=0.09 ev. For these contacts, ψ decreases from 0.12 to about 0.065 ton/cm2; simultaneously μ decreases from 0.13 at 115°C to 0.07 at about 200°C. This has been found at atmospheric air pressure with dew point about 279°K and also in vacuum of 10−4 mm Hg with dew point about 75°K. With a copper and gold ring at atmospheric air pressure, the (μ,T) curves have a somewhat steeper slope and agreement with theory requires ψ=0.12 or 0.10 ev, respectively.

At temperatures of about 500°K, μ and ψ decrease very slowly and may reach a lower limit at temperatures when the chemisorbed gases on the graphite platelets begin to evaporate.
Etch Pit Studies on ZnS Crystals
Authors: Czyzak S. J. , Manthuruthil J. C. , Reynolds D. C.
Published: April 2005

Etch pits and x-ray studies have been made on several ZnS crystals. Etch pit geometries have indicated, in some cases, a mixed cubic-hexagonal structure. This has been confirmed by x-ray analysis. A model to explain the x-ray and etch pit data is presented.
Investigation of the Coercive Forces of Ni, Fe, and Ni–Fe Films during Evaporation
Authors: Behrndt Klaus H.
Published: April 2005

The dependence of the coercive force of Ni, Fe, and Ni–Fe films upon film thickness and amount of trapped gas was evaluated in vacuo. The magneto-optic Kerr effect was utilized for this investigation. Although the penetration depth of light into the film material was determined to be 150±25 A, measurements of Hc could commence for film thicknesses <100 A. It was found that the coercive force Hc is independent of film thickness if the content of trapped gas, as indicated by the p/r (residual gas pressure over deposition rate) ratio is very small, e.g., 5×10−8 torr/A/sec for Ni films. At higher p/r ratios, the coercive force of Ni films displays initially a steep rise which is followed by a shallow minimum, while in Ni–Fe films a maximum appears at about 750 A. The different behavior of Fe films is ascribed to higher gas absorption on this material rather than a principal change in the mechanism of the coercive force. A hypothesis is proposed as explanation for the observed effects.
On the Problem of Pulsed Oscillations in Ruby Maser
Authors: Makhov George
Published: April 2005

It is shown by means of a semiquantitative nonlinear analysis that elementary interaction between an inverted electron spin system and a resonant cavity does not give rise to the pulsed mode of operation of the ruby maser oscillator. It is suggested that the additional nonlinearity necessary for the existence of such a mode resides in the ``distant ENDOR,'' the interaction between the chromium electrons and the Al27 nuclei.
Experimental Determination of the Anisotropy Distribution in Ferromagnetic Powders
Authors: Flanders P. J. , Shtrikman S.
Published: April 2005

A technique to determine the anisotropy distribution in a ferromagnetic powder consisting of uniaxial particles has been developed. This technique can be used for samples with randomly oriented particles as well as with oriented samples. In principle it eliminates incoherent magnetization reversals which led to errors in previous methods. It involves saturating the material in a magnetic field and then making torque measurements at an angle several degrees away from the saturating direction. In these measurements the torque on the specimen as a function of magnetic field is recorded as the field is cycled from zero to a specified field and then reduced to zero. This cycling procedure is continued, gradually increasing the maximum applied field upon subsequent cycles until the magnetic field exceeds the highest anisotropy field of the particles in the distribution. For elongated γ-Fe2O3 particles this technique gives length-to-width distributions which approach those observed by the electron microscope technique. These results are compared to those obtained by remanence measurements which give smaller values of anisotropy constants, indicating the importance of incoherent magnetization reversals, when the remanence is acquired.
Anisotropic Thermal Expansion of Single Crystals of Thallium, Yttrium, Beryllium, and Zinc at Low Temperatures
Authors: Meyerhoff R. W. , Smith J. F.
Published: April 2005

The anisotropic thermal expansion of the hexagonal elements, thallium, yttrium, beryllium, and zinc, has been measured. The temperature range for the thallium, yttrium, and zinc measurements was 4.2−273.2°K, while for beryllium the range was 77−273.2°K. Dimensional changes were detected by an interferometric technique, and the movement of the interference fringes was detected with a photomultiplier tube. From the measured values of ΔL/L0 the coefficients of thermal expansion and the c/a ratios of the metals were calculated as a function of temperature. A review of previous measurements of the thermal expansion of these metals is also included.
Evidence for a Selenium Donor Level above the Principal Conduction Band Edge in GaSb
Authors: Bate R. T.
Published: April 2005

Low-temperature Hall coefficient and resistivity data on selenium-doped GaSb are interpreted under the assumption that selenium introduces a donor level above the principal [000] conduction band minimum. The postulated level is associated with electrons in [111] valleys localized in hydrogen-like orbits around selenium atoms. The results at 77°K are consistent with the assumption that impurity scattering is dominant and that a selenium donor level is located about 0.07 ev above the principal conduction band edge at 77°K. The low-temperature data on tellurium-doped samples are also discussed.
Mechanical Behavior of Sapphire Whiskers at Elevated Temperatures
Authors: Brenner S. S.
Published: April 2005

The tensile behavior of sapphire whiskers was measured at temperatures ranging from 25–2030°C. At room temperature, the tensile strength of the whiskers is size dependent and varies from several hundred thousand psi to 1 500 000 psi. With increasing temperature the strength decreases and becomes less size dependent. The whiskers exhibit delayed fracture above 630°C, the time to fracture being exponentionally related to the applied stress. Delayed fracture occurs in both hydrogen and oxygen atmospheres and hence is not believed to be due to stress corrosion. The mechanical behavior of the whiskers has been rationalized by assuming that they are essentially dislocation free and that failure occurs by thermally activated crack propagation preceded, at high temperatures, by localized dislocation nucleation.
Elastic Wave Propagation in Piezoelectric Semiconductors
Authors: Hutson A. R. , White Donald L.
Published: April 2005

A plane elastic wave propagating in a piezoelectric crystal may be accompanied by longitudinal electric fields which provide an additional elastic stiffness. When the crystal is also semiconducting, these fields produce currents and space charge resulting in acoustic dispersion and loss. A linear theory of this effect is developed, taking into account drift, diffusion, and trapping of carriers for both extrinsic and intrinsic semiconductors. Conductivity modulation sets an upper limit on strain amplitude for a linear theory. The directional characteristics and the magnitude of the effects are illustrated for CdS and GaAs. The Appendix treats the interaction of an arbitrary acoustic plane wave with the electromagnetic fields in a piezoelectric crystal (based on a treatment by Kyame [J. J. Kyame, J. Acoust. Soc. Am. 21, 159 (1949); 26, 990 (1954).]) and further shows explicitly that only the effects of longitudinal electric fields need be considered.
Comparison of Several Methods for the Photographic Detection of Thermal Neutron Images
Authors: Berger Harold
Published: April 2005

Several methods of photographic detection of thermal neutron images have been studied and compared with regard to photographic speed, relative neutron-gamma response, and image sharpness qualities. All these comparisons have been made using a low gamma content, monochromatic neutron beam (1.05 A) having an intensity of 3×105 neutrons/cm2-sec. The fastest speed, best neutron-gamma response of the direct exposure methods, and good image sharpness have been obtained by using a direct exposure method employing a B-10 loaded scintillator and type F x-ray film. Gadolinium and rhodium intensifier screens with type KK film have also yielded good results by the direct exposure method (film and intensifier screens exposed to the neutron beam together). Results are also reported for the use of indium, cadmium, silver, and gold screens. The transfer method, in which the photographic film is exposed only to the radioactive decay radiation of an image-carrying metallic screen, and not to the neutron beam itself, has been found useful not only because no effect on the image is produced by gamma radiation in the neutron beam, but also because improved image sharpness has been obtained. In the cases of indium and gold (the two materials which have been found useful for the transfer method in the neutron flux available for this study), the improved image resolution obtained with the transfer method has been shown to result from the fact that the high energy prompt (n,γ) radiation is not detected on the film.
Kinking and the Fracture of Ionic Solids
Authors: Stokes R. J. , Johnston T. L. , Li C. H.
Published: April 2005

A single crystal undergoing plastic bending develops constraints due to the gradient in lateral contraction across the beam. These constraints result in lateral stresses which may be relieved by the process of anticlastic kinking. Anticlastic kink boundaries in rocksalt structure solids consist of arrays of {121}〈110〉 edge dislocations formed by the interaction of two systems of {110}〈110〉 glide dislocations, one system being responsible for slip in the main part of the crystal beam, the other confined to its corner.

Temperature affects the structure of kink boundaries and their subsequent role in initiating fracture.

I. At high temperatures (∼0.3 Tm). The resultant edge dislocations in the boundary can move over their {121} slip planes and the kinks become sharp. The resultant dislocations are ineffective barriers to slip and the crystals are ductile.

II. At low temperatures (∼0.1–0.2 Tm). The resultant edge dislocations are immobile and the kinks consist of a diffuse array. The resultant dislocations provide strong barriers to slip and cracks nucleate at the kink boundary.

III. At very low temperatures (∼0.1 Tm). Fracture occurs before the second set of {110}〈110〉 glide dislocations have been activated to generate anticlastic kinks. Relaxation of the lateral stress results in a complex fracture.
Preparation and Some Properties of Tantalum Carbide
Authors: Eckstein Bernard H. , Forman Ralph
Published: April 2005

Small tantalum carbide objects may be made by heating the objects made from tantalum in dilute hydrocarbon atmospheres at temperatures >2000°K. Carburization proceeds quite rapidly above 2300°K by diffusion of carbon initially deposited on the surface into the metal, principally along grain boundaries, to form a thin layer of Ta2C which is quickly converted to the TaC. The latter has a tensile strength of 21–25 kg/mm2, a work function φ=3.17 ev, an emissivity of 0.40–0.46 between 2400° and 3500°K, rising with increasing temperature, and a resistivity ρ=102+0.0178 T (°K) ohm cm between 1400° and 3500°K.
Charged Right Circular Cylinder
Authors: Smythe W. R.
Published: April 2005

A paper with the above title appeared in this Journal in 1956 giving the charge distribution on, and capacitance of, an electrified right circular solid conducting cylinder for length-to-diameter ratios of 0.25 to 4. Much more accurate values, calculated for the range 0.125 to 8 on a digital computer, are tabulated in the present paper. Over this range the capacitance is given to 0.2% accuracy by the formula C=[0.708+0.615(b/a)0.76]×10−10a farads,where 2b is the length and a the radius. A spherical harmonic expansion for the potential outside the circumscribed sphere is given.
Anomalous Magnetic Films
Authors: Cohen Mitchell S.
Published: April 2005

A study of three types of anomalous nickel-iron magnetic films has been made: high coercive-force films, which have unusually large hysteresigraph values of wall and rotational coercive forces; rotatable initial-susceptibility films, for which the value of the initial susceptibility as found from low-field hysteresigraph measurements is determined by previously-applied high magnetic fields; and mottled films, whose high-field hysteresis loops show low remanence and a high wall coercive force, and whose Bitter patterns have a spotted or mottled appearance. Anomalous films have been produced by a variety of techniques. In general, for a given technique, a mild treatment yielded high coercive-force films, a moderate treatment gave rotatable initial-susceptibility films, and a drastic treatment produced mottled films. The techniques used were evaporation at slow rates at high substrate temperatures, evaporation on aggregated metal deposits, electroplating on annealed gold films, and annealing normal films. According to a qualitative model postulated to explain these results, these production techniques cause the formation of small, scattered inhomogeneities which have high values of randomly oriented magnetic anisotropy associated with them. As the production technique becomes more drastic, the density and anisotropy values of these anisotropy centers increase, causing the gradual transition from high coercive-force films through rotatable initial-susceptibility films to mottled films. It is concluded that inhomogeneous strain in conjunction with magnetostriction is a likely cause of anisotropy centers. It is thought that ``rotatable anisotropy'' films discussed by previous workers are closely related to the films investigated in the present study.
Significance of Fatigue in Lead Oxide Vidicon Target
Authors: Bigelow J. E. , Haq K. E.
Published: April 2005

To understand ``fatigue'' or ``burn-in'' in the target of a PbO Vidicon, experiments have been made with sandwich cells of evaporated PbO. It has been demonstrated by using chopped radiation that as the PbO layer fatigues, there is an increase in short term dark conductivity. Further, it has been shown that the phenomenon is associated with loss of oxygen from the surface of the crystals during irradiation with photons. A surface chemistry model similar to one proposed by Morrison and Melnick in connection with ZnO is used to explain the observed results.
On the Observation of Transient Space-Charge-Limited Currents in Insulators
Authors: Silver M. , Mark P. , Olness D. , Helfrich W. , Jarnagin R. C.
Published: April 2005

The conditions for the observation of space-charge-limited (SCL) transient current pulses in insulators are examined. A parameter α=2tr/τ (tr=space-charge-free transit time and τ=response time of the circuit) is defined, whose value determines the extent to which the pulses are distorted from their ideal shape. For α>100, the pulses are undistorted. For 20<α<100, the pulse shape becomes distorted from the ideal case and for α<20, pulses begin to be indistinguishable. It is shown that carrier transport in any insulator may be investigated by transient SCL current measurements provided that trapping is not too severe and that ohmic contact formation (either transient or steady-state) is possible.
The Theory of Čerenkov Effect Based on Lorentz Transformations
Authors: Zelby Leon W.
Published: April 2005

The method of calculating rf excitation by the Čerenkov effect using Lorentz transformations, first used by Nag and Sayied in the case of a single electron and an infinite dielectric medium, was extended to a modulated electron beam in the presence of a finite dielectric boundary. A relation between the Čerenkov effect and Roentgen surface current was pointed out.
Electric Characteristics of Gamma-Ray Irradiated Shielding Window Glass
Authors: Yamamoto Kakuji , Tsuchiya Masao
Published: April 2005

Induced color of shielding window glass of various kinds by γ-ray irradiation is studied. With Co60−1 kc as radiation source, 23°±3°C as irradiation temperature, 105 R/h as exposure dose rate and 105−107 R as total exposure dose, the coloration increases gradually.

Volume resistivity of glass and its change by gamma-ray irradiation are measured. 100 V dc is applied to a sheet of glass sandwiched between two electrodes to measure the change of its electric resistance with time. The quantity of induced space charge by radiation is calculated by time integration of the current which is obtained from reciprocal of the resistance. Resistance of high density glass is found to become minimum—hence the current becomes maximum—at the exposure dose of 106 R and increases as the dose increases, but resistance of medium density glass decreases gradually. Change of the resistance is exponential and the charge is always positive at any dose. This testifies that glass is electrized by radiation. On the other hand, linearity is established between the quantity of space charge and the dose in a range of 105 to 4×106 R. This suggests the possibility of the electrization to be utilized for dosimetry.

The above not only demonstrates the physical properties of shielding window glass and the effect of radiation on it but seems to help to find the means of preventing the breakdown by radiation of glass.
Statistical Aspects of Ferromagnetic Nucleation-Field Theory
Authors: Brown William Fuller
Published: April 2005

It has been shown by DeBlois that surface flaws decrease the magnitude of the nucleation field of iron whiskers below the ideal theoretical value Hn0=2K1/Ms. It is assumed here that the number of flaws in area S is determined by a Poisson distribution, with mean number λS (λ=const); that each flaw independently has a magnitude x (in magnetic field intensity units) that is a random variable with distribution function F(x); and that the nucleation field magnitude is Hn=Hn0—xm, where xm is the magnitude of the largest flaw on the surface of the specimen, or of a part of it that may be regarded as physically independent. The distribution of observed nucleation fields is then calculated; for large λS, it has an asymptotic form independent of the precise form of F(x), provided F(x) satisfies certain rather general conditions, and identical with the form obtained when F(x)=1—eμx (μ=const). Comparison with data of DeBlois and Bean gives a fair fit, with λ≈2×103 cm−2. A particle of surface area 10−8 cm2, and with this same λ, would be practically certain to have no flaws; with a λ 5000 times as large, it would have probability 0.9 of flawlessness. These conclusions are consistent with the relatively much greater success of ideal crystal theory for fine particles than for bulk material.
dc Electroluminescence in Zinc Sulfide Films
Authors: Thornton W. A.
Published: April 2005

Thin films of ZnS:Cu, Mn, Cl have been excited by direct current and the response to voltage reversal and unidirectional square pulses studied. Emission-current-voltage relations are considered and the results compared with information on ac-excited phosphors of this type. The results indicate that applications of dc excited films in solid-state devices depend on their good brightness at low voltage and high discrimination ratio.
Compositional Requirements of Square-Loop Memory Core Ferrites
Authors: Wiechec W. , Kelley C. M.
Published: April 2005

Experimental evidence indicates that Mn3+ and Cu2+ are responsible for squareness in ferrites. Ferrites for memory core use appear to have optimum characteristics when 0.28 atoms per formula molecule are in octahedral sites. A number of square-loop compositions containing up to seven metal elements were made, verifying the above requirement.
Extraordinary Hall Effect in Paramagnetic Gold Alloys
Authors: Blue M. D.
Published: April 2005

The Hall coefficient of alloys of up to 5% Ni, Co, Fe, and Mn in Au has been measured from 4.2°K to room temperature. The Hall coefficients are strongly temperature dependent in these alloys and have been fitted to an equation of the form R=R0+R1χ, where R0 is close to the value for the Hall coefficient of pure Au, and χ the magnetic susceptibility, is the source of most of the temperature dependence. Values for R1 are compared to the extraordinary coefficients of ferromagnetic metals.
Anisotropy in the Superconductivity of Deformed Re Single Crystals
Authors: Hauser J. J.
Published: April 2005

Single crystals of rhenium with a resistivity ratio (ρ300°K/ρ4.2°K) of approximately 1500 were grown by the floating-zone technique. The crystals were then deformed by tension. Samples were selected where the deformation took place primarily on one slip system, i.e., on the (101̄0) slip plane along the <1̄21̄0> slip direction.

Measurements of the resistance were made to determine the variation of the critical current with applied magnetic field. The deformed samples revealed an anisotropy in the transition field (the transition field being the field at which the smallest measureable amount of normality is observed) increasing with decreasing current as one approaches the range where filamentary conduction is important. The transition field was a minimum when the field was perpendicular to the active slip plane. The anisotropy at low current disappeared upon annealing the samples at 2700°C for 1.5 h and only the demagnetization effects remained. These results can be interpreted in terms of the anisotropic dislocation density introduced by this particular deformation.
Results of an Ultrasonic Measurement Survey
Authors: Einspruch Norman G. , Truell Rohn
Published: April 2005

Results of an ultrasonic measurement survey in which nine groups made compressional wave transit time measurements on a given sample of fused silica are presented. Seven of the nine reports agreed within 0.3%, and it is suggested that discrepancies in published values of elastic constants of a given material may be due to variations in the samples themselves.
Diode Measurements with Thick Chloride Layers on Nickel
Authors: Anderson J. R.
Published: April 2005

The formation of a thick chloride layer on the surface of a nickel anode has been found to result in a diode characteristic curve which, in addition to lateral displacement due to the surface potential, shows marked nonparallelism with respect to the diode characteristic for the clean surface. This behavior has been interpreted in terms of the electrical conductance of the chloride layer and it suggests a general method for the measurement of the electrical properties of thin insulating layers on metal surfaces. Confirmatory conductance measurements have been made with bulk nickel chloride. Some kinetic data have been obtained for the formation of thick cloride layers on the surface of nickel and a technique is described for the preparation of uncontaminated sintered nickel films of small area. It is concluded that the conductivity of stoichiometric nickel chloride is ≲10−15 Ω−1 cm−1 at room temperature, but that after heating in vacuum the conductivity rises and feeble semiconductivity results, with an activation energy for conduction of about 16 kcal mole−1. Both the conductance and the surface potential for a chloride layer on nickel increase on heating in vacuum and it is suggested that this is due to the incorporation of nickel from the substrate.
Exact Solutions for Space-Charge Flow in Spherical Coordinates with Application to Magnetron Injection Guns
Authors: Dryden V. W.
Published: April 2005

Here are presented some forms of axially symmetric space-charge flow from a cone cathode in the presence of a magnetic field which are interesting for the design of electron guns, since the resulting flow is axial and laminar. The method of computation is presented and recent results are discussed. A discussion of the future of this study is also given.
A Rapid X-Ray Method for the Determination of Substructure Characteristics
Authors: Weissmann S. , Gorman L. A. , Zwell L.
Published: April 2005

An x-ray diffraction method is described by which the substructure characteristics and dislocation densities of crystalline materials can be rapidly determined. The method is based on spatial tracing of reflection images and their extrapolation onto the specimen surface using the method of least squares.
High Magnetic Field Research
Authors: Lax Benjamin
Published: April 2005

The use of high magnetic fields as a research tool for a wide variety of physical phenomena is clearly recognized today and the subject of an International Symposium at Cambridge this fall. Another important step in promoting research with the help of large magnetic fields has been the sponsorship of the M. I. T. National Magnet Laboratory by the Air Force. This paper will review the highlights of the conference which included papers on research in plasma physics, low temperatures, solid state and the latest developments for generating high magnetic fields. The plans and objectives of the National Magnet Laboratory and description of the physical facilities will be presented. In addition, a brief review will be given of a number of experiments already performed in the existing Magnet Laboratory at M. I. T.
Modification of Spin Screw Structure due to Anisotropy Energy and Applied Magnetic Field
Authors: Nagamiya Takeo
Published: April 2005

Recent development in the theory of screw structure of spins and its modification due to anisotropy energy and applied magnetic field is reviewed, with reference to neutron diffraction work on rare-earth metals and MnAu2.
Threshold Properties of Partially Switched Ferrite Cores
Authors: Shahan V. T. , Gutwin O. A.
Published: April 2005

A switching threshold relaxation effect has been observed which is detrimental to high-speed selection of partially switched (time-limited switching) ferrite memory cores. This paper discusses this threshold effect as determined by measurements on cores of 1- to 5-oe coercivity. Two aspects of switching threshold are observed: A static threshold (Hf) which is effective at a time long after switching, and a relaxation effect which is a reduction in threshold immediately after switching. The reduction is considerable and may limit the amplitude of the digit-disturb field that a core may withstand to a small fraction of the coercive force. A first approximation to the switching threshold dependence on time may be given as: Ht=Hf(1-e−3t/τ) for t>0. This representation is reasonably accurate for most ferrite cores, although a sum of exponentials is necessary for an improved description. The ratio of the static threshold to the coercivity (Hf/Hc) is influenced by the duration and polarity (relative to the switching field) of the disturb field, the amplitude of the switching field, the flux state, the ambient temperature, and the ferrite composition. The static threshold of a core switched to the 50% flux state by a 10-nsec pulse may be only half the value of the threshold after switching to the 50% state with a 2-μsec pulse. The relaxation time also depends on the above mentioned parameters (except relative polarity) and, in addition, is influenced by the coercivity of the sample, lower coercivity samples having longer relaxation times. Measurements at ambient temperatures ranging from −195°C to near the Curie temperature (+250°C) show the product of coercivity and relaxation time to be nearly constant for a given core. The relaxation time is a maximum at the 40–50% flux state and approaches zero at the major loop remanent flux states.
Magneto-Optically Measured High-Speed Switching of Sandwich Thin Film Elements
Authors: Suits J. C. , Pugh E. W.
Published: April 2005

A technique employing the Kerr magneto-optic effect has been used for measuring switching times as short as 10 nsec in thin ferromagnetic films, both individually and when coupled together in a sandwich structure. The switching speed of individual 1-mm-diam Permalloy bits has been found to be dependent on film thickness, the thicker bits switching more slowly. It was further observed that the time to switch 90% of a film is much more sensitive to film thickness than the time to switch 50% of the same film. When two similar films, magnetized in a head-to-tail fashion, are placed on either side of a drive line strip, the time to switch 50% of the films is essentially the same as for individual bits. However, the time required to switch 90% of the material is considerably shorter for sandwich elements than for the corresponding single bits. These results suggest that the slower switching of thick bits may be attributed to an incoherent rotational mechanism associated with the inhomogeneous demagnetizing field.
Permalloy-Sheet Transfluxor-Array Memory
Authors: Briggs G. R. , Tuska J. W.
Published: April 2005

Annealed molybdenum Permalloy sheets of ⅛−1 mil thickness have been photoetched to form transfluxor-element memory arrays utilizing inhibited-flux storage. Operating characteristics are summarized for single elements switched in 21 nsec−3.2 μsec. Some findings are: one to zero information flux ratios of 5:1 to 16:1, one to disturb noise flux ratios greater than 30:1, and Sw values of 1.7 to 0.14 oe μsec. In addition, operation is possible over a temperature range of −70° to +150°C without drive-current compensation. Also, for a ⅛-mil thick element switched in times less than 0.1 μsec, Sw values less than 0.2 oe μsec are obtained, indicating that fast switching may occur partially by uniform flux rotation. Array photoetching is described. Arrays containing 128 and 1152 elements have been fabricated. The latter permit a storage density of 250 000 bits/cu in. to be attained. The arrays receive a stress-relief treatment which results in a signal uniformity of ±3%. Photofabrication of windings has been accomplished also. This process generates continuous windings linking the transfluxor apertures.
Anisotropy of the Hyperfine Interaction in Magnetite
Authors: Boyd E. L. , Slonczewski J. C.
Published: April 2005

This paper describes effects of anisotropy of the hyperfine interaction on nuclear magnetic resonance in a ferromagnetic or ferrimagnetic material. It is shown how the line shape in a polycrystalline sample depends on whether the excitation is through domains or domain walls. The absorption spectrum of Fe57 in powdered magnetite (Fe3O4) is observed, and the results show that, in this case, the excitation is predominantly through domains. They also establish a value for the hyperfine anisotropy on octahedral sites.
Nuclear Resonance in Ferromagnetic Alloys
Authors: Kushida Toshimoto , Silver A. H. , Koi Yoshitaka , Tsujimura Akira
Published: April 2005

The internal fields Hi in ferromagnetic alloys were measured at both the solvent and the solute nuclei at magnetic and nonmagnetic atoms using NMR techniques. Co59 resonances in Co-rich alloys (Co-Fe, -Ni, -Cu, -Cr, -Mn, -Al) have fine structures which depend on the kind and the concentration of impurity metals. Similar structures are found for the Fe57 resonances in Fe-rich alloys. These structures are tentatively interpreted as caused by the anisotropy of Hi at the nearest neighbors. The Co59 resonance is also observed in Fe-rich Co-Fe alloys, and it is found that Hi seen at the Co site is lower by about 50 koe than that at the Fe site. The Co59 line width is about 400 kc for (Fe+1% Co) alloy. Both the temperature and the pressure dependences of the Co59 frequency were measured. Hi at Cu63 and Cu65 was measured in Co-rich Co-Cu and in Fe-rich Fe-Cu ferromagnetic alloys. The magnitude of these internal fields at Cu and their observed pressure dependence are, at least, not inconsistent with the contention that the observed Hi is mainly produced by the 4s conduction-electron polarization, although Hi at the Cu nucleus, 217.7 koe for Fe-Cu alloy and 157.5 koe for Co-Cu alloy, is considerably higher than the usual theoretical prediction.
Hyperfine Fields, Spin Orbit Coupling, and Nuclear Magnetic Moments of Rare-Earth Ions
Authors: Watson R. E. , Freeman A. J.
Published: April 2005

An investigation is presented of the related problems of hyperfine fields, spin orbit coupling, and the determination of nuclear magnetic moments, all of which are strongly dependent on the 4f charge distributions in the rare earths and play an important role in Mössbauer, NMR, paramagnetic resonance, and optical absorption measurements. The discussion is based on a set of conventional approximate nonrelativistic Hartree-Fock wave functions which were determined for nine ions of the series. Results are presented, and the various approximations and assumed relationships between these quantities (listed in the title) are discussed in the light of comparisons between theoretical predictions and experiment.
Magnetic Hyperfine Interaction and Electronic Relaxation in Sm3+ in EuIG
Authors: Caspari M. E. , Frankel S. , Wood G. T.
Published: April 2005

The attenuation and rotation of the integral correlation of the 1415−122 kev γ-γ cascade following the K capture of Eu152 was measured in neutron irradiated polycrystalline samples EuIG from −25°C to above the Néel temperature with and without magnetizing field perpendicular to the counter plane. The existence of time-dependent hyperfine interactions of short relaxation times was taken into account in the evaluation of the average component of the effective hyperfine field 〈Hintz〉 along the direction of the magnetizing field. The sign, magnitude, and temperature dependence of 〈Hintz〉 was in excellent agreement with that calculated from molecular field theory under the assumption that the electronic configuration of Sm152 following the K capture of Eu152 was that of the Sm3+ ion. The contribution to the magnetic hyperfine field arising from exchange between the 4f and inner core s electrons was found to be small compared with that from the orbital and spin moments of the 4f shell. The absolute magnitude of the hyperfine field was 4.7×106 oe. Under the assumption that the time-dependent interactions are largely magnetic, the electronic relaxation time was found to be 3.2×10−12 sec at 400°C and varied inversely with the absolute temperature.