摘要:

In an earlier analysis of the effect of magnetic fields on thermionic diodes, numerical results indicated that under certain conditions the fraction of emitted electrons reaching the collector equals the sine of the angle at which the magnetic field intersects the emitting surface. An analytic proof of this relation has since been found and is presented here.

ISSN:0021-8979    

DOI:10.1063/1.1728485

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The ion, electron and atom number densities, and electron temperatures of a cesium plasma generated in a diode have been measured by spectroscopic techniques. The theoretical bases for these techniques are outlined. The errors involved in applying these theories to heavy atom collision‐dominated plasmas are discussed. Working equations for the electron, ion and atom temperatures, and number densities are developed. Among the working equations developed and applied are those for the determination of the electron number density from the continuum intensity and Stark broadening. Temperatures in the cesium plasma were 0.7 ev with ion and electron number densities of the order of 1015cm−3. The agreement of cesium pressure computed from the spectroscopically determined temperatures and number densities and that from vapor pressure curves strongly suggest the existence of thermal equilibrium. The agreement in the values of electron number densities determined from continuum intensity and Stark broadening measurements justify the approximations made in applying these theories to the cesium plasma.

ISSN:0021-8979    

DOI:10.1063/1.1728524

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Tensile stress strain curves were obtained for single crystals of lithium fluoride. The specimens were elongated at room temperature along a ⟨100⟩ axis. The number of slip‐band sources was controlled by surface treatment. Both the yield stress and the flow stress in the plastic range were found to depend on the number of active slip bands. The shapes of the stress‐strain curves were related to the behavior of individual dislocations in lithium fluoride.

ISSN:0021-8979    

DOI:10.1063/1.1728468

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Observations have been made of the low‐frequency fluctuations occurring in hot‐cathode dc mercury‐vapor discharges at a pressure of approximately 1 &mgr;. A spectrum analyzer was employed to study frequency spectra from three widely differing experimental tubes and to determine the effects of variations in tube geometry, electrode spacing, and anode current. Similar measurements were also made at points along a long discharge column with the aid of a capacitive probe sliding on the outside of the tube. The character of the spectrum is markedly dependent on tube geometry, substantially independent of column length and position along the column, and may be coarse or contain relatively pure frequency components. Two mechanisms observed involved frequency variation proportional to the square and cube roots of anode current, and possible explanations are given. There is, however, evidence for the existence of other basic mechanisms of generation.

ISSN:0021-8979    

DOI:10.1063/1.1728477

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Measurements have been made of the impedance/frequency characteristics of a hot‐cathode, dc, mercury‐vapor plasma at a pressure of approximately 1 &mgr;. The experimental tube contained a directly‐heated cathode from a commercial mercury‐vapor rectifier and provided a discharge column 80 cm long. Bridge techniques were used to obtain impedance loci extending to 2 Mc/sec for several values of anode current. These appeared to normalize, the magnitudes of the components being approximately inversely proportional to current. A basic equivalent circuit can be deduced, its parameters being dependent on physical processes occurring in the discharge. Prominent frequency components of the low‐frequency voltage fluctuations present in the tube appear to be closely related to the impedance characteristics.

ISSN:0021-8979    

DOI:10.1063/1.1728488

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

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.

ISSN:0021-8979    

DOI:10.1063/1.1728521

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A pulsed probe has been used to measure certain parameters of a time varying plasma in mercury vapor. Langmuir probe characteristics have been obtained by pulsing the probe voltage to successively higher values for &mgr;sec intervals at specific times relative to a repetitive discharge pulse. Curves showing the time dependence of the plasma potential, electron temperature, and electron density relative to this pulse are presented. The probe characteristics do not exhibit a sharp break at the plasma potential. This is related to a disturbance of the plasma by the probe. A novel and precise technique for determining the actual plasma potential is described. This technique depends upon the abrupt appearance of a spike on the leading edge of the probe current pulse.

ISSN:0021-8979    

DOI:10.1063/1.1728522

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

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.

ISSN:0021-8979    

DOI:10.1063/1.1728523

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

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.

ISSN:0021-8979    

DOI:10.1063/1.1728525

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

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 3×105neutrons/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,&ggr;) radiation is not detected on the film.

ISSN:0021-8979    

DOI:10.1063/1.1728526

出版商:AIP    

年代:1962

数据来源: AIP