摘要:

Using the experimentally determined temperature and field‐dependent electrical conductivity for NaCl, we have solved numerically the one‐dimensional heat‐transport equation, with and without current continuity requirements, to obtain the breakdown fields. The results are consistent with experiment.

ISSN:0021-8979    

DOI:10.1063/1.1658481

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The use of freely suspended LiTaO3pyroelectric detectors for wide‐band application is severely hampered by mechanical resonances of the detector (typically several hundred kHz) which are excited by the incident radiation. These resonances give rise to slowly decaying oscillatory piezoelectric signals superimposed on the pyroelectric signal. It is shown that by suitable mounting of the detector films these resonances can be entirely eliminated, thereby increasing the useful bandwidth of the devices to at least several hundred MHz. In addition, it is shown that when the incident radiation is modulated at a mechanical resonance frequency of a freely suspended LiTaO3detector, considerable enhancement of the current and voltage response is obtained. The experimental results are found to be in reasonable agreement with results calculated for LiTaO3by including thermal expansion in the equations of motion of a pyroelectric crystal.

ISSN:0021-8979    

DOI:10.1063/1.1658482

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The extent to which various factors contribute to smoothing of the classical small‐angle x‐ray scattering curve in the subsidiary peak region is examined. The effects of finite chromatic and angular resolutions and of shape and size distribution of heterogeneities are determined and discussed. Two methods of obtaining quantitative size data from curves exhibiting asymptotic behavior are discussed. An analysis is presented to show the validity of a method first suggested by Bragg from an empirical evaluation. A new method using an intercept of the extrapolated asymptotic curve is described. The significance of the effective mean heterogeneity dimensions found is discussed. It is shown how correlation with analysis of data for the Guinier region can be used to estimate the spread of heterogeneity size distributions.

ISSN:0021-8979    

DOI:10.1063/1.1658483

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The theory of electrons scattered by light in the presence of a thin dielectric slab is developed and applied to some recent experiments of Schwarz and Hora. The experimental results are explained and some new effects predicted.

ISSN:0021-8979    

DOI:10.1063/1.1658484

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Single crystals of TiCx(x=0.84) were exposed to a carbon source at temperatures near 2000°C. The penetration of carbon into the structure, reflected in a gradient in the value ofx, was evaluated with the electron microprobe analyzer. The chemical diffusivityD˜was then determined using the Boltzmann‐Matano method of analysis. The experimental value ofD˜was found to increase with decreasing carbon vacancy concentration, 1−x, and to have the average value of 220 exp (−97 700/RT) cm2/sec. This value ofD˜is in good agreement with one generated from Sarian's14C tracer measurements on TiC crystals and DePoorter's semitheoretical model for activity. Because of the abundance of vacancies in the carbon fcc sublattice of TiCx, the experimental activation energy represents an energy of motion only. Lower experimental values for the diffusion activation energy have been obtained by other workers with the phase‐boundary advance method. The present work shows that the difference between the activation energy measured by the tracer method and that measured by the phase‐boundary advance technique cannot be ascribed to the influence of a chemical gradient. Hence it is probably due to grain‐boundary short circuiting.

ISSN:0021-8979    

DOI:10.1063/1.1658485

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A nondestructive x‐ray diffraction technique has been developed to analyze small diffusion zones. This technique constitutes a new approach to the study of one‐dimensional volume diffusion and only requires intensity measurements from two different reflections. It has the distinct advantages of permitting a determination of both the concentration profile and the atomic arrangements associated with the diffusion zone. Data for the Cu&sngbnd;Ni system is presented to provide an example of the technique. The composition profile resulting from the interdiffusion of an 8‐&mgr; Ni deposit and a Cu single crystal at 900°C for 45 min was determined. Good agreement was found between these experimental results and a composition curve calculated from DaSilva‐Mehl diffusion coefficients. It has also been found that volume diffusion significantly increases the degree of crystalline misorientation along the diffusion zone. The structure of the as‐plated Ni deposits on a Cu single crystal was found to undergo a large misorientation change, initially, but maintained a relatively constant degree of epitaxy for longer diffusion times.

ISSN:0021-8979    

DOI:10.1063/1.1658486

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A circular waveguide partially filled with dielectric is considered as the deflecting structure for a relativistic particle separator. The cutoff wavelengths and normalized phase velocity versus frequency characteristics are presented. The expressions for power, losses, deflecting fields, and transverse deflecting forces are also given. Our investigation shows that the dominant (HEM11) mode of the structure can be used as a transverse deflecting mode for synchronous particles in a relativistic particle separator.

ISSN:0021-8979    

DOI:10.1063/1.1658487

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The gas‐breakdown threshold or the minimum power density required to ionize a gas with 10.6‐&mgr;‐wave‐length radiation has been examined using the radiation of aQ‐switched CO2laser. The studies show that the focused beam cannot initiate the breakdown process for intensities as high as 109W/cm2. If an initial low degree of ionization is provided by an external source, the subsequent growth of the breakdown is in agreement with a cascade model as evidenced by the experimentally determined gas pressure and laser‐radiation frequency dependence.

ISSN:0021-8979    

DOI:10.1063/1.1658488

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A detailed picture of the behavior of cesium oxide as a low work‐function coating on III‐V semiconductors and on silver has been obtained. Measurement of required cesium and oxygen exposure for optimum photoyield shows that the compound normally formed is close to CS2O, with variations in required exposure for very thin and very thick layers. By making simultaneous Kelvin work‐function, photoyield‐threshold, and thickness measurements, it was possible to establish that the CS2O, ann‐type semiconductor, forms a heterojunction or Schottky barrier with its substrate. This provides a band bending which produces a gradual lowering of the vacuum level with increasing thickness to an ultimate work function of 0.6 eV. The photoyield and dark current from the substrate are limited by the interfacial barrier at the heterojunction. This barrier is 1.00±0.05 eV for a silver substrate and 1.23±0.03 eV for GaSb. The band‐bending distance in the CS2O is about 50 Å and the hot electron scattering distance is 9 Å. These data have been used in an improved calculation of the maximum &Ggr; escape probability and requisite CS2O thickness for electron emission from III‐V semiconductors of different bandgaps. Electron emission from CS2O induced by an oxygen overpressure was also measured. CSOH is compared with CS2O as a work‐function lowering coating.

ISSN:0021-8979    

DOI:10.1063/1.1658489

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A creation model has been developed to interpret the behavior of Bostick plasmoids in the plane of the discharge. The plasmoids are formed by pulsed unidirectional current discharges across the electrodes of a button gunin vacuo(10−6Torr). The model is that of a vacuum arc which expands in the form of a thin, highly conducting torus by virtue of the interaction of the surge current with its self‐induced magnetic field. When the current no longer flows, the plasma of the arc continues to move by virtue of its own inertia. The plasmoid speeds directly away from the button gun have been determined experimentally from time of arrival measurements to moveable electrostatic probes, and are found to increase monotonically from 20 to 100 km/sec for a corresponding source voltage range of 2.5–17.5 kV. The measured velocity &ngr;′ of any point on the plasma which subtends an angle &thgr; to the direction of forward motion at the button‐gun source is given byv′=⟨I⟩(&agr;/&pgr;&rgr;)1/2cos&thgr;, where ⟨I⟩ is the average surge current, &rgr; is the measured mass per unit length (line density) of the genetic plasmoid and &agr; is a theoretically calculated constant. The line density &rgr; of the plasmoid has been shown theoretically to be a constant and its magnitude has been measured to be 10−9kg/m and hence the massMof the plasmoid is deduced theoretically to be given by:M=⟨I⟩&tgr;(&agr;&pgr;&rgr;)1/2, where &tgr; is the duration of the current pulse. This formula predicts the plasmoid mass to increase from 0.05 to 0.2 &mgr;g for the current range of interest and the predicted mass is verified to within 16% by a novel experimental technique.

ISSN:0021-8979    

DOI:10.1063/1.1658490

出版商:AIP    

年代:1970

数据来源: AIP