摘要:

Micrographic techniques have been used to study dislocations, point defect clusters, and cavities in neutron‐irradiated LiF crystals.No evidence of inhomogeneous damage caused by ``thermal or displacement spikes'' was found. However, a uniform etching effect was found for doses greater than ∼1015nvt. The etching is believed to be caused by clusters of point defects greater than 2 A but less than 50 A in size. This agrees with previous x‐ray results. The defect clusters decrease in number and increase in size with increasing annealing temperatures. At temperatures greater than ∼400°C only (110) dislocation loops remain and these disappear above ∼600°C. Electron bombardment causes a similar effect.The as‐grown dislocation structure of LiF is not affected by neutron bombardment. However, it becomes increasingly difficult to move fresh dislocations in crystals given neutron doses greater than ∼1012nvt. The hardening is independent of dislocation velocity and temperature and hence cannot be caused by Cottrellpinning of dislocations. The color changes that accompany hardening suggest that it is caused by defect clusters rather than single defects.At annealing temperatures above ∼600°C crystallographic cavities appear in LiF crystals. They are rectangular parallelepipeds with (100) sides. Evidence is presented to show that the cavities are not caused by fission gases but probably by loss of fluorine from the crystals.

ISSN:0021-8979    

DOI:10.1063/1.1723322

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

An expression is developed relating friction coefficient in a boundary lubricated sliding system to temperature, heat of adsorption, and sliding velocity. Frictional and wear phenomena are shown to be double exponential functions of temperature and single exponential functions of sliding velocity. Experimental confirmation is obtained and a simple method is indicated for measuring the heat of a adsorption as a function of temperature.

ISSN:0021-8979    

DOI:10.1063/1.1723323

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The diffusion coefficients for hydrogen in mild steel have been measured in the temperature range of 25° to 90°C. A mass spectrometer was used to study the movement of hydrogen through thin steel plates. Two methods of measuring diffusion have been used; the rate of approach to equilibrium when hydrogen is supplied to the plate, and the rate of outgassing when the source of hydrogen is removed. Two decidedly different sets of diffusion coefficients were obtained by the two methods. The first method gave diffusion coefficients which agree very well with values obtained by others at higher temperatures while the outgassing method, which was more reproducible, gave values considerably lower. These results are compared with those of other investigators.

ISSN:0021-8979    

DOI:10.1063/1.1723324

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The ratio of the diffusion coefficients for hydrogen and deuterium in steel have been measured in the temperature range of 26°C to 86°C. A mixture of the two gases was introduced into the steel by abrasion in a mixture of normal and heavy water. The diffusion coefficients were measured simultaneously for the two using the mass spectrometer to observe the rate of evolution of the gases from the steel. The ratio of the diffusion coefficients was found to be constant within the limits of experimental error over the entire temperature range and had a value of 1.37±0.02. The ratio of the permeation rates was found to vary with the temperature. The results are compared with those of other investigators.

ISSN:0021-8979    

DOI:10.1063/1.1723325

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Measurements have been made of the coefficients of friction for graphite and some graphite‐based materials which are of interest for nuclear reactor application. Static and kinetic friction coefficients have been measured as a function of surface conditioning and temperature up to a maximum temperature of 2450°C. In addition, the effects of force, stress, anisotropy, refractory coating, and uranium loading were studied. The most significant effect was found to be caused by the conditioning of the contact surfaces by polishing action, and this was more pronounced in the static than the kinetic friction coefficient. The friction coefficients increase with temperature. Other effects studied had negligible influence.

ISSN:0021-8979    

DOI:10.1063/1.1723326

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

(I) When the energy spectrum of plasma electrons consists of two clearly separable groups—a high‐energy, primary, non‐Maxwellian, and a low‐energy, secondary, Maxwellian one—the characteristic linear part of the corresponding probe curves, extrapolated to plasma potential, directly determines the random current density of the fast group. With a hemispherical anode and a hollow hot cathode near its center, in Ne of about 1 mm Hg pressure, the flow of the fast group at low diode currents follows closely the spherical case of diffusion. The experimental data, by means of the diffusion law, can be evaluated for the mean free pathlof the fast electrons. It is found thatlis independent of the plasma density and is about equal to the value calculated from the cross‐section function for 10–16 volt electrons in Ne.(II) The Diffusion law being applicable, the elastic collision losses of the fast group can be calculated. They are found to be relatively small compared to the total energy losses of the fast electrons. The results will be used in an attempt to determine the energy transfer from the fast group to the Maxwellian group, to be described in a subsequent paper.The most remarkable result is the low interaction of the fast group with the Maxwellian group at low total plasma densities where the partial density of the slow group is always comparable to or even much higher than that of the fast group.

ISSN:0021-8979    

DOI:10.1063/1.1723327

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Argon ion beams are used for determining experimentally the perveances and the associated beam profiles of a series of electrode structures consisting of coaxial aperture disks. The results are of particular interest in the design of ion sources. Since, fundamentally, there is little difference between electron guns and ion sources, the results should also be of interest in the design and study of electron guns. Electron guns producing convergent beams, and designed on the Pierce principle of rectilinear flow, require electrodes whose shape is not always easy to reproduce or the most convenient to use. If the principle of rectilnear motion is abandoned, it is found experimentally that the perveance in many cases is little affected by the adoption of the much simpler electrode system of coaxial aperture disks. Perveance is the ratio of the output current to the32power of the input voltage.

ISSN:0021-8979    

DOI:10.1063/1.1723328

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Rectifying junctions may be made by heating silicon‐aluminum or silicon‐boron alloys in contact withn‐type silicon carbide. The measured solubility of carbon in liquid silicon is consistent with the view that these junctions are produced by an alloying and regrowth mechanism. Nonrectifying contacts may be made in an analogous manner using silicon‐phosphorous alloys. Visible radiation is emitted uniformly over the rectifying junctions when current is passed in the forward direction, with a quantum efficiency of the order of 10−6. Current flow in the reverse direction is associated with the appearance of ``blue spots,'' similar in appearance to the points of light that are often observed when silicon junctions are biased in the avalanche region.

ISSN:0021-8979    

DOI:10.1063/1.1723329

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Measurements were made of the diffraction pattern in slits ranging in width from 0.2 to 2.5 wavelengths. Microwave radiation of 10.4 and 16 cm was used. Ratios of intensity in the slit to the intensity of the unperturbed beam were found for plane polarized radiation incident on the conducting slit screen. Comparison with diffraction patterns in the plane of circular apertures was made. A peak of intensity was found for the slit width of one‐half wavelength and a plateau was observed in the plot of intensityvsslit width in the region of width equal to one wavelength. A theory involving multiple reflections from the edges was utilized to explain the variations of intensity in the plane of the slit. The electric field was studied when polarized parallel and also perpendicular to the slit edges. A high intensity was found near the edges when the electric field was polarized perpendicular to them.

ISSN:0021-8979    

DOI:10.1063/1.1723330

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

A plane screen only one‐eighth wavelength thick which absorbed 99% of the intensity of normally incident microwave was constructed using glass with an electrically conducting surface. Comparative measurements were made of the diffraction pattern in and near slits in ``perfectly absorbing thin screens'' and ``perfectly reflecting thin screens.'' It was found that the diffraction pattern of the slits on the side of the screens opposite the source was the same for both screens at distances greater than a half‐wavelength. Even in the planes of the slits the diffraction patterns for these two screens differed by less than the experimental error for slits wider than one wavelength.

ISSN:0021-8979    

DOI:10.1063/1.1723331

出版商:AIP    

年代:1958

数据来源: AIP