摘要:

The natural stable isotopes of forty‐three elements, comprising 177 different nuclides, have been enriched; the goal is to enrich 257 isotopes of fifty‐nine elements. The isotopic enrichments, the operation of the production mass spectrographs including a listing of best charge materials, a brief review of the chemical and analytical problems, a tabulation of the best compounds of the separated isotopes for mass spectrometer analyses, and a listing of some of the major uses of separated isotopes have been included in this survey of the electromagnetic isotope separation program.

ISSN:0021-8979    

DOI:10.1063/1.1721144

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The complete field plot obtained by ``relaxation'' was used to determine electron trajectories for parallel incidence at heights up to one‐third the bore diameter, from a numerical integration of the trajectory equation using the method of differences. The accuracy attained in this method yields cardinal points to within one percent. It was found that the focal lengthfnfor a ray of heightrnwas given byfn=f0−brn2, wherebis a constant; also, because of the curvature of the principal planes, the distancednto the midplane follows a lawdn=c−drn2wherecanddare constants. A consequence of this is that for the same variation in focal length, the greater the curvature of the principal plane the larger the spherical aberration of the lens.The trajectory tracings indicate that spherical aberration is small at heights up to one‐twelfth the bore diameter, but increases with height till at a value of one‐third the bore, the percentage change in focal length has decreased by some 40 percent. Confirmation of focal properties was obtained using the lens in a single stage electron microscope and examining the pincushion distortion in the image of a gauze object.Evaluation of the spherical aberration using the weak lens approximation of Scherzer leads to gross errors both in magnitude and variation, e.g., the aberration does not remain constant with voltage ratio. The experimental data with the electron microscope indicate little or no change in aberration with increase in the power of the lens; this does not agree with the results of the mathematical analysis of Ramberg.

ISSN:0021-8979    

DOI:10.1063/1.1721145

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

When a germaniump—njunction biased in the forward direction has a reverse voltage suddenly applied, a large transient current flows during the ``recovery time.'' A proposed mechanism for this current involving diffusion of stored minority carriers to the barrier is compared with experimental results. Since the current is related to the diode forward direction characteristics these are examined. Finally a variable time delay utilizing the recovery current effect is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1721146

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

An approximate integral recursion formula is developed which gives a relation between the probability that a photon will be transmitted through a slab of finite thickness with exactlyk+1 collisions and the probability that it will be transmitted with exactlykcollisions, where the latter probability is known for suitable ranges of slab thickness, of incident energy, and of incident angle. A similar formula also exists for the expected energy transmitted. The two recursion formulas have been used to calculate the transmissions with one, two, and three scatterings for photons incident on slabs of lead and of iron, and from these calculated transmissions the ``build‐up'' factors have been estimated. The build‐up factor for normally incident photons of 1 to 20 mc2are given for lead slabs and for iron slabs having a thickness of 0 to 20 mfp.A second method, which considers the transmission through a thick slab as a succession of transmissions through thin slabs, is used to check the estimates of the build‐up factor obtained by the first method. This second method provides additional information in the form of the distributions of the transmitted photons.Finally, some transmission and reflection values for thin slabs of the Compton scatterer are presented along with some results for air which are obtained by the second (thin‐slab) method.

ISSN:0021-8979    

DOI:10.1063/1.1721147

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Microphone carbon has been produced by deposition of pyrolytic carbon films over the surfaces of small spherules of silica. The properties of contacts between these spherules are shown to be dependent on the structure and geometry of the carbon surface as determined by electron diffraction and microscopic studies. The graphite‐like crystallites in pyrolytic carbon surfaces are more or less preferentially oriented with their basal planes parallel to the surface, and the contact properties depend systematically on the degree of orientation. This is explained in terms of the anisotropy in properties of these crystallites which are closely approximated by those of single crystal graphite which were determined. The contact resistance and its temperature coefficient and the ``burning voltage'' for carbon contacts are explicable on this basis. However, the microphonic sensitivity of carbon contacts is independent of the surface structure and depends only on the surface geometry.

ISSN:0021-8979    

DOI:10.1063/1.1721148

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Equations and graphs are presented of the resonant wavelength and quality factor of elliptical resonant cavities operating in the TE111mode. Both components of this mode are treated and distinctive characteristics of each are shown as a function of eccentricity of the cavity.

ISSN:0021-8979    

DOI:10.1063/1.1721149

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The relationship proposed by Ferry and his co‐workers for the effects of frequency and temperature on the dynamic properties of certain polymers is shown to lead to a method for calculating the activation energy of viscous flow from relaxation, creep, and dynamic test data, the results agreeing with those obtained in steady‐state flow. The Ferry reduction explains, and is supported by, observed increases in dynamic modulus and viscosity with increasing temperature.

ISSN:0021-8979    

DOI:10.1063/1.1721150

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The method of a double camera for electron diffraction here described consists in taking two diffraction patterns simultaneously so that the wavelength of electrons applied to an ``unknown'' is exactly to that for the reference.

ISSN:0021-8979    

DOI:10.1063/1.1721151

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Simple equations are developed which permit the calculation of the trap depth and frequency factor of first‐order glow curves from the temperatures of the peak and the half‐height. The equation for the trap depth does not depend explicitly on the frequency factor or the heating rate and is accurate to 5 percent over a wide range. Application is made to theoretical glow curves and to an experimental glow curve obtained from the thermoluminescence of ice.

ISSN:0021-8979    

DOI:10.1063/1.1721152

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Internal friction peaks resulting from sodium ion diffusion in three kinds of soda glasses have been observed in the temperature range 100° to 200°C for transverse and torsional frequencies between 20 to 400 cps. The heat of activation for sodium ion diffusion was found to range between 17 000–21 000 cal/mole and might probably be slightly dependent on the sodium content. The results obtained were confirmed by electrical resistivity measurements. For quartz glass and for soda glass having Na2O content less than 4 percent, the internal friction peak of the type discussed here could not be noticed, thus indicating that below a minimum Na2O content of about 4 percent, ionic sodium diffusion does not contribute to the anelastic behavior.

ISSN:0021-8979    

DOI:10.1063/1.1721153

出版商:AIP    

年代:1953

数据来源: AIP