摘要:

It is considered common knowledge by many workers in the field of detonation phenomena that transparent plastics quickly go opaque under strong shock wave attack. In this paper high‐speed photographs are shown, and it is seen that Lucite and Plexiglas do not go opaque until shattered by tension waves. The behavior of plate glass is somewhat similar. By adjustment of dimensions and lighting, events can be observed with good photographic quality through the shock front for an undetermined length of time.

ISSN:0021-8979    

DOI:10.1063/1.1777084

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The field strength required for field evaporation of tungsten and for best image conditions in the field ion microscope is measured by comparison with field electron emission of the same emitter. The evaporation field is independent of emitter radius except for radii below 150 A where the influence of free surface energy becomes noticeable. The field for the best conditions of a helium ion image of a typical emitter of 1000 A radius is 440 Mv/cm. This field increases gradually with decreasing tip radius, so that the ratio of evaporation field to best image field for tungsten decreases from 1.27 at 1000 A radius to 1.0 at about 40 A radius. The radius dependence of this ratio can be calculated by assuming that the time a hopping atom spends in the critical ionization zone is a constant fraction of the ionization time. Practical implications are that large tip radii are preferable for easily evaporating emitter materials, and small radii may be useful when field evaporation is to be studied under best image conditions.

ISSN:0021-8979    

DOI:10.1063/1.1777085

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A generalized derivation of the broadening of powder pattern lines by stacking faults has been carried through allowing for fault planes of arbitrary dimensions. A minimum dimension for the fault planeTminis obtained from the measurable effective particle sizesDe(111) andDe(200). Values ofTminof the order of 200 A are obtained for samples of filings of copper, &agr; brass, and silver. The results suggest that, in the drastic cold work involved in filings, the stacking faults tend to extend over rather large distances comparable to the coherent domain dimensions.

ISSN:0021-8979    

DOI:10.1063/1.1777086

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Nickel (110) surfaces, in clean and nearly clean conditions, have been studied by low‐energy electron diffraction. When free from foreign atoms, the surface (110) plane of atoms has the normal arrangement expected for such a plane. Very slight contamination by oxygen (and perhaps other atoms) results, in some cases, in an arrangement of the topmost layer of atoms in which nickel and oxygen (or another atom) alternate along each [100] line and also along each [110] line. Study of such a surface has shown that the superficial half‐layer of nickel atoms is displaced toward the bulk of the crystal by about 0.10 A.

ISSN:0021-8979    

DOI:10.1063/1.1777087

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Temperatures of about 20 000°K with ion densities ranging from 1017to 1018cm−3have been produced in helium by means of explosive‐driven shocks. Helium was used because of its relatively simple structure, but this choice eliminated usual shock methods because of the high sound speed and high ionization potential. Shock waves having sufficient strength and planarity were obtained by reflecting against a glass plate initially strong shock waves produced by high explosives. Equilibrium calculations based on smear camera velocities of accurately plane shocks were used to determine the state of the gas behind the reflected shock wave.The light emitted consisted of a continuum on which were superimposed shifted and broadened lines of the normal helium spectrum and forbidden lines as well. Time‐resolved spectrograms showed evidence of a measurable relaxation time at the shock front but no evidence of significant radiative cooling of the gas behind the shock.Under the conditions of these experiments, it was demonstrated that a quantitative prediction of the behavior of the helium states with principal quantum numbers 2, 3, and 4 requires consideration of the effects of electrons as well as ions.

ISSN:0021-8979    

DOI:10.1063/1.1777088

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

We have calculated the magnetization curves of an infinite ferromagnetic cylinder with negative uniaxial anisotropy. The cylinder axis is a hard magnetocrystalline direction and the basal plane is an easy plane. The applied field lies along the cylinder axis. The distribution of the magnetization corresponds to the azimuthally symmetric mode denoted as ``magnetization curling.'' With the present choice of anisotropy, stable solutions for the distribution can be obtained through partial reversal of the magnetization.

ISSN:0021-8979    

DOI:10.1063/1.1777089

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

We have determined the solute contribution &rgr;i(T,c) of the solutes Cr, Mn, Fe, Co, and Ni in copper and of the solutes Mn, Fe, and Co in gold over the temperature range 4° to 1200°K and over a wide range of solute concentrations. The parameter &rgr;i(T,c) for a given solute is defined here as the difference &rgr;i(T,c) =&rgr;alloy(T,c)—&rgr;solvent(T). The temperature dependence of &rgr;iis quite complicated for several of the solutes, in particular, Fe and Co. For example, in an alloy containing 0.05 at.%Fe in copper this quantity &rgr;Feexhibits a minimum at 25°K and a maximum at 65°K. Alloys of Fe in gold exhibit a broad maximum in &rgr;Feat temperatures between 70° and 200°K, depending upon the iron concentration. In all the alloys investigated, except for Ni in copper, &rgr;idecreases with increasing temperature in the region of high temperatures (above about 500°K).

ISSN:0021-8979    

DOI:10.1063/1.1777090

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The resistivity, Hall coefficient, and Seebeck coefficient of single crystals of PbTe were investigated in the range from 77° to 900°K using a capsuling arrangement which prevented tellurium loss from the specimens at elevated temperatures. The low temperature properties obtained agree with the data reported in the literature. The thermal energy gap obtained from the high temperature measurements cannot, however, be brought into agreement with the energy gap determined from room temperature absorption measurements by considering solely the excitation of electron‐hole pairs across the energy gap at elevated temperatures. Rather, it is necessary to include the carriers generated by defect formation at elevated temperatures. Both Schottky‐Wagner and Frenkel defects are present, the activation energies for formation of the two types of defects being related by the equationEF=½ES+0.55 ev≃0.7 ev.

ISSN:0021-8979    

DOI:10.1063/1.1777091

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The temperature of a blackbody source which emits continuous radiation with a spectral peak in the range 0.6 to 8 kev in photon energy (soft x rays) may be determined by analyzing an absorption experiment. The technique employed here may be useful for the analysis of other continuous radiation distributions of soft x rays (e.g., free‐free continuum radiation from plasma discharges and deceleration radiation from thick targets). Use is made of the approximation that over a limited energy region the absorption coefficient varies inversely with the cube of the spectral energy. The following equation,I(x)=I0(1+C1x logex+C2x+C3x43),neglecting terms of magnitudeC4x5/3or less for thin absorbers, describes the relative dependence of the transmitted x‐ray intensityI(x) on the absorber thicknessxfor a blackbody spectrum of incident intensityI0. The constantsC1throughC3are related in a known manner to the temperature of the blackbody source for a given absorber material. Similarly, the equation,I(x)=I0D1x7/8(1+D2x−1/4) exp(−D3x1/4),neglecting terms of magnitudeD4x−1/2or less for thick absorbers, describes the transmission of a blackbody spectrum characterized by a source temperature which may be determined from the constantsD1throughD3.

ISSN:0021-8979    

DOI:10.1063/1.1777092

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Previous work has shown the existence of some structurally forbidden reflections in the electron diffraction patterns of (100) oriented polycrystalline films. These films were deposited under ultra‐high vacuum conditions. A continuation of this work has resulted in the observation of these and other forbidden reflections in the diffraction patterns of two other kinds of films: (001) oriented single crystals containing deformation twins and (100) oriented single crystals. The existence of these strong reflections is probably due to strong dynamic interactions between the electron beam and the crystal lattice.

ISSN:0021-8979    

DOI:10.1063/1.1777093

出版商:AIP    

年代:1961

数据来源: AIP