摘要:

Experiments are described in which minority carrier lifetime and resistivity of germanium are altered by the addition of copper by diffusion, under conditions where extraneous chemical contamination is minimized. This copper is then gettered by heating the samples in contact with liquid lead or gold, and the resistivity and lifetime are substantially restored. The gettering process in interpreted in terms of the low distribution coefficient of copper in the ternary system which copper and germanium form with the getter.

ISSN:0021-8979    

DOI:10.1063/1.1721894

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Low magnetic saturation ferrites suitable for microwave applications can be prepared in the magnesium aluminum ferrite system. These ferrites can be prepared to possess also relatively high permeabilities at carrier frequencies. Curie temperatures, coercive forces, magnetic saturations at 25°C, and initial permeabilities at 0.1 megacycle/sec for such materials are given.

ISSN:0021-8979    

DOI:10.1063/1.1721895

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A study of aging in cold‐worked Al&sngbnd;Ag and Al&sngbnd;Zn alloys during the first stage of precipitation was made, by means of small‐angle x‐ray scattering. (a) The rate of growth of the Ag or Zn clusters was very little affected by cold‐work. (b) Evidence was found that the amount of clustered solute is not altered by aging. (c) The clusters were deformed by cold‐work, giving rise to an anisotropic small‐angle scattering. This cannot be explained by large amounts of glide taking place in a limited number of slip planes, but rather speaks in favor of zones of homogeneous deformation. The deformation of precipitated particles by cold‐work is a new and powerful means of investigating the mechanism of plastic deformation in the interior of a material.

ISSN:0021-8979    

DOI:10.1063/1.1721896

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The observed losses in a ferromagnetic core are always greater than those calculated on the basis of a homogeneous permeability. In a magnetization process by domain‐boundary displacements the permeability is certainly not homogeneous, but attains extreme values in the domain walls. As a result of this concentration of the changes in magnetic flux the dispersion curves of the initial permeability as a function of frequency show a shift of the dispersion region towards lower frequencies with increasing domain size. This is the well‐known eddy‐current anomaly encountered in laminated cores. An electric‐circuit model was utilized to determine the eddy‐current distribution and domain‐boundary motion in a number of idealized cases.

ISSN:0021-8979    

DOI:10.1063/1.1721897

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The reduction of cathodoluminescence efficiency of phosphors has been observed after bombarding with H+, H2+, He+, Ne+, N2, and A+ions having energies from 1 to 25 kev. Detectable deterioration could be observed after a bombardment of less than 10−9coul/mm2of ions (5×1011ions/cm2). The deterioration could be annealed out at temperatures between 450° and 700°C. Results indicate that light 25‐kev ions probably penetrate 0.1&mgr; to 0.2&mgr; into the phosphor.

ISSN:0021-8979    

DOI:10.1063/1.1721898

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The velocity dispersion in fused quartz and in Armco iron was investigated by measuring the resonant frequency of small cylinders using quartz crystals on the ends as drivers and detectors. With x‐cut crystals and y‐cut crystals the computed velocities of the dilatational waves in the range 2.0–5.0 Mc and shear waves in the range 1.5–3.0 Mc decrease with frequency. This decrease in both cases is regarded as unreasonably large and is ascribed primarily to sample geometry. Simple standing plane waves, either dilatational or shear, cannot satisfy the boundary conditions in a free cylinder. A mosaic crystal was then constructed of sectors of y‐cut crystals such that the driver generated and the detector transmitted only torsional waves. With these crystals and viscous coupling between the crystals and sample, the velocity in fused quartz was constant within ±1 m/s for the frequency range 0.6–3.0 Mc. The velocity in Armco iron was constant within ±2 m/s in the range 0.5–1.5 Mc and decreased about 10 m/s in the range 1.5–3.0 Mc.

ISSN:0021-8979    

DOI:10.1063/1.1721899

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Studies of electron mobility in silver halide crystals have been carried out by Haynes and Shockley by means of ultrashort light and voltage pulses applied simultaneously to large, single crystals of these materials. Their apparatus made use of a radar‐type, pulse‐forming network discharged through mercury spark‐gap tubes. An apparatus for carrying out this same type of experiment has been developed using an air‐driven turbine with a mirror and a spark‐gap switch. Repetitive light pulses of 3.33‐microsecond duration and voltage pulses of 10 kv and about 20‐microsecond duration can be applied to a crystal at a rate of 500 per second. The light and voltage pulses can be initiated simultaneously or at controlled time intervals. The simplicity and practicality of this type of apparatus for electron mobility and photolysis studies on the silver halides are illustrated by experimental results. Light pulses from a mercury arc release photoconduction electrons in the surface of a silver chloride crystal. The voltage pulse pulls the liberated electrons in a straight column for varying distances through the crystal, where they become trapped. This is shown by the direct photolysis along the column in the crystal. Also, print‐out silver specks produced in large photographic grains are displaced to one side of the grains by the voltage pulses applied during exposure. The displacement is in the direction that electrons are pulled in the applied field. By separation of the light pulse and voltage pulse in time, the mean lifetime of the photoliberated electrons can be studied. The lifetime of the electrons was found to be approximately 10 microseconds, of the same order as that of electrons in large, wellannealed single crystals of silver chloride.

ISSN:0021-8979    

DOI:10.1063/1.1721900

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A hollow cylindrical single crystal of pure aluminum was deformed by detonating an explosive charge that had been placed axially within the crystal. The approximate strain rate achieved was 105sec−1. The object of the test was to relate the pattern of deformation to the stresses set up by the explosive and the crystallographic axes of the crystal. The reaction of the cylinder was markedly different from the reaction which would be exhibited by a similarly shaped cylinder of polycrystalline material. The deformation was non‐uniform with both the fracturing and the plastic flow exhibiting a twofold symmetry that could be unambiguously related to the orientation of stress with respect to the crystallographic axes and their associated slip systems.

ISSN:0021-8979    

DOI:10.1063/1.1721901

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Reversal of magnetization in square‐loop metallic tapes is described in terms of the domain geometry and the dependence of this geometry upon the applied magnetic field wave shape. For a steady field whose amplitude is slightly greater than the coercive force, the reversal is accomplished by growth of a single axial domain originating at the thin tape edge. For steady fields of much greater amplitude, the reversal domain grows in from all tape surfaces. Because of the finite nucleation time required to establish the reversal domain, short duration, high amplitude field pulses can be used to investigate the mechanism of nucleation of the high field reversal domain configuration. A model which accounts for the nucleation process is suggested. The compatability of this model with various experimental results is presented. From these results an understanding of the high field reversal‐domain configuration and the kinetics of the nucleation and growth of these domains in lamellar materials is obtained. An auxiliary result obtained is the value of the ``intrinsic mobility'' of a domain wall which for a 65 Permalloy specimen is determined to be about 100 cm/sec oe.

ISSN:0021-8979    

DOI:10.1063/1.1721902

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

By utilizing the method of pulsed nuclear magnetic resonance, radio‐frequency energy in the form of pulses can be stored serially in a sample of nuclear spins and recalled at an arbitrary later time within the memory or relaxation time of the spin sample. Weak pulses of radio‐frequency energy condition the nuclear spins to start precessing in phase. After they become completely out of phase, a strong recollection pulse brings about a phase reversal of precession and produces a series of spin echoes in a sequence corresponding to direct or reverse order of input pulses. The echo amplitudes in such a series are given as a function of the number and strength of the input pulses and the conditions for maximum storage capacity in a spin ensemble are determined. The maximum specific storage capacity in liquids is expressed in terms of the thermal noise of the detecting apparatus, the effect of self‐diffusion of the molecules, and the relaxation times. The origin of undesired spin echoes arising from the interaction of input pulses is discussed, and means for eliminating these echoes by frequency and magnetic field modulation are discussed and applied. Extensive use is made of a magnetic field modulation technique to destroy undesired echoes, and to permit novel types of recall of serially stored groups of pulses. Whereas Fernbach and Proctor [J. Appl. Phys.26, 170 (1955)] have demonstrated multiple pulse storage under conditions which reproduce the input pulse shape, the present investigation is concerned with the storage of a maximum number of pulses whose shape is ideally determined by the nuclear spin band width. In practice, the order of 1000 rf pulses can be stored and recalled by this method in a proton sample several cc in volume within a memory time of 10 to 50 milliseconds. Large specific storage capacities expected for existing long relaxation time liquids are not realized because of excessive self‐diffusion.

ISSN:0021-8979    

DOI:10.1063/1.1721903

出版商:AIP    

年代:1955

数据来源: AIP