摘要:

Measurements of the currents leaving thin films of uranium dioxide undergoing a known rate of fission have determined the secondary electron yield due to fission fragments emerging from the films. This yield was found to vary from about 570 to 300 electrons per fragment over a film thickness from 0.1 to 3 microns. The ratio of charge carried by the secondary electrons emitted from the surface to the charge carried by fission fragments was also determined. This ratio varies slowly with film thickness, from 28 for a 0.1‐micron coating to about 21 for a 3‐micron coating. The behavior of the charge ratio and secondary electron yield with coating thickness is in qualitative agreement with theory.

ISSN:0021-8979    

DOI:10.1063/1.1728810

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A review is given of the energy band structures in a number of relatively well understood semiconductors, including Si and Ge, the Group III–V compounds, the IV–VI compounds (lead salts), CdAs2, and Bi2Te3, and of the experimental methods which have been used in determining these band structures. This review is directed particularly toward the interests of those engaged in applied research and development of semiconductor devices which depend more or less specifically on band structure properties for their operation. It is also meant to provide a single source of the latest available energy band information for those engaged in basic research on semiconductors and for students.

ISSN:0021-8979    

DOI:10.1063/1.1728811

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

At microwave frequencies, ferroelectric ceramics behave as nonlinear dielectrics and exhibit large signal scalar nonlinear characteristics in both the dielectric constant and the rf conductivity. The nonlinear behavior of a ceramic of 73% BaTiO3‐27% SrTiO3has been used to construct a harmonic generator operating from 3 kMc to 9 kMc. An efficiency of 8.5% for a peak input power of 2200 w was attained. In addition, a new measurement technique has been developed for measuring the large signal properties of this ceramic as well as for other nonlinear materials. This technique makes explicit use of the anharmonic response of a resonant system that contains a nonlinear element. The analysis of both the harmonic generator and the nonlinear resonant system takes into account nonlinear reactance as well as nonlinear resistance. For temperatures about 30°C above the Curie temperature (the Curie temperature for the ceramic composed of 73% BaTiO3‐27% SrTiO3is approximately 20°C) the large signal dielectric constant and rf conductivity were found to be given by the expressions &egr;′(|E|)=&egr;0[2200−7.5×10−11|E|2] farad/m, and &sgr;(|E|) =&ohgr;&egr;0[160+29×10−12|E|2] mhos/m, where |E| is in volts per meter. These results were obtained at 3 kMc and are valid up to field strengths of 20 kv/cm.

ISSN:0021-8979    

DOI:10.1063/1.1728812

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The scattering and absorption of an obliquely incident, plane electromagnetic wave by an infinite, cylindrically symmetrical region characterizable by a complex dielectric ``constant'' is determined by application of the Born approximation for the case of dielectric ``constant'' near unity. Differential‐scattering cross sections and absorption cross sections are derived as a function of angle of incidence, angle of polarization, and integrals over the inhomogeneous region. The expressions for the scattered fields are compared to the expansion of an exact solution for the homogeneous dielectric cylinder in the limit of dielectric constant near unity. The approximate expressions agree exactly. Of singular notability in this respect is the fact that polarization is altered in the Born approximation by the appearance of dyadic terms in the propagation equation in the region of inhomogeneity, while the exact solution requires the generation of cross‐polarized waves to satisfy boundary conditions.

ISSN:0021-8979    

DOI:10.1063/1.1728813

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The pulsed Townsend discharge technique for the determination of electron attachment coefficients of electronegative gases is examined for situations where the ion density is sufficiently high that space charge effects must be considered. The equations of motion for the ions are solved to yield a first‐order differential equation for a parametric function, in terms of which the current and boundary position may be expressed. For the particular case of interest, an initial distribution which decays exponentially from the cathode, an exact solution for the current is obtained by numerical evaluation of this function. Comparison with experiment shows excellent qualitative and fair quantitative agreement.

ISSN:0021-8979    

DOI:10.1063/1.1728814

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The ferroelectric and pyroelectric properties of mineral and synthetic colemanite were investigated. It is shown that the synthetic compound, prepared by the controlled dehydration of higher order calcium borates, has a much lower Curie temperature than mineral colemanite. The substitutional impurity concentration of strontium for calcium in natural colemanite is proposed to be primarily responsible for its higher Curie temperature. The occurrence of a double dielectric anomaly in some specimens of mineral colemanite is described and it is shown that the temperature at which the lower anomaly occurs is consistent with the ferroelectric transition observed in the synthetic compound while the upper anomaly is characteristic of the more common calcium‐strontium‐borate pentahydrates.

ISSN:0021-8979    

DOI:10.1063/1.1728815

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Fission fragment tracks observed in electron microscope studies of platinum and palladium films are interpreted in terms of thermal processes involving melting and vaporization. The results require that the energy lost by the fragment be converted into thermal energy over the entire volume of the track in a time short enough that little of it is conducted away. A model in which free electrons disperse the energy over this volume is used to account for the width and structures of the tracks.

ISSN:0021-8979    

DOI:10.1063/1.1728816

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Amplitude dependent dislocation damping was measured in LiF. It was found that average dislocation velocities comparable to those present during plastic deformation occur under periodic stresses more than an order of magnitude below the macroscopic yield stress. This implies that the impediments to dislocation motion effective in plastic deformation are localized at widely separated points along the dislocation.

ISSN:0021-8979    

DOI:10.1063/1.1728817

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Trap depths and densities can be determined from the analysis of the dependence of space‐charge‐limited currents on applied electric field in insulators. Values obtained from space‐charge‐limited current measurements are compared with those obtained from thermally stimulated currents and from photocurrent decay on the same crystal of cadmium sulfide. The results indicate that gross errors in trap depth and density can be made if it is simply assumed that the rapid rise in current toward the trap‐free curve with increasing applied voltage always occurs when the traps are filled. Although this may sometimes be true, it is also possible for such a rapid rise to result from field ionization of the traps, or even in certain cases from the onset of double injection. Even if the latter effects occur, however, proper analysis of the space‐charge‐limited current data permits an evaluation of trap depth and density which is completely consistent with independent measurements of thermally stimulated current and photocurrent decay.

ISSN:0021-8979    

DOI:10.1063/1.1728818

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The initial slope of the correlation function &ggr;(r) is proportional to the specific surface of the scattering sample in principle, and is equal to zero in practice. In this paper, a simple model is investigated which illustrates the problem. Calculations are carried out to show how surface areas may be obtained from scattering data.

ISSN:0021-8979    

DOI:10.1063/1.1728819

出版商:AIP    

年代:1962

数据来源: AIP