摘要:

A hot‐cathode magnetron ionization gauge capable of measuring pressures as low as 10−14Torr has been described in previous publications. The low‐pressure limit of this gauge has been extended by the addition of an electron multiplier ion detector. The ions generated in the magnetron gauge are focused onto the first dynode of the multiplier by an electrostatic lens system. The multiplier gain is high enough to permit the use of an ion counting technique for the measurement of very low pressures. The lens system focuses the ions from the gauge into a beam that passes through two limiting apertures before striking the first dynode. This arrangement prevents the soft x rays generated at the magnetron gauge anode from falling directly on the first dynode. The x‐ray photoemission from the first dynode has been reduced by a factor of 50 000 below that observed for the magnetron gauge alone. Measurements of sensitivity and x‐ray photocurrent indicate that this device should have a linear response down to pressures of 2×10−17Torr. Ability to measure low pressures with the gauge appears to be limited by the inherent dark current of the multiplier. The gauge may be used to advantage for the measurement of higher pressures by operating at reduced emission current levels to minimize pumping and degassing effects. Photoemission from the first dynode caused by incident light from the magnetron gauge filament has been reduced to values below the x‐ray photoemission by the use of a lanthanum hexaboride cathode which operates at only 675°C. This low operating temperature reduces the problem of gas reactions with the filament. Radiation from gas molecules excited by electron impact in the magnetron gauge has been observed in the 10−9Torr pressure range.

ISSN:0034-6748    

DOI:10.1063/1.1718411

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A new replica technique for electron microscopy of fracture surfaces is described, which can reveal the relationship between the microstructural features of metals and alloys and the detailed topography of their fracture surfaces. This etch‐shadow extraction replica technique combines in one replica the salient features of shadowed‐surface replicas and precipitate‐extraction replicas. Thus a bridge is provided between the fracture topography, which is governed mainly by the effects of fracture‐velocity changes, and the significant microstructural features such as precipitates, grain boundaries, etc.

ISSN:0034-6748    

DOI:10.1063/1.1718412

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

An apparatus for the measurement of contact angles of corrosive liquids by the tilting‐plate method as a function of temperature (−30 to 140°F) and pressure (5 to 100 psia) is described.

ISSN:0034-6748    

DOI:10.1063/1.1718413

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

This report describes an electronic voltmeter which has high input impedance and good thermal stability even though it is constructed entirely with solid‐state components. The system is built around a phase‐locked oscillator system which inherently has a perfect integrator within its control loop; as a result, the steady‐state series error is zero. A discussion of system operation and results obtained from an experimental model of the voltmeter are given. First the system is described and an elementary analysis is given. Experimental results and other possible uses then follow.

ISSN:0034-6748    

DOI:10.1063/1.1718414

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Measurements have been made of the density of charged‐particle tracks in the Brookhaven 20‐in. hydrogen bubble chamber as a function of particle velocity and chamber operating conditions. The track densitymis given by the functionA(Ps)n&bgr;−2where, at 27°K,A=7.5×10−8bubbles/cm of track,n=5.4, andPsis the superheat pressure in psia in the chamber. The pressure superheat dependence &Dgr;m/(m&Dgr;Ps)≅10% per psia; for tracks at different temperatures but with the same pressure superheat, the temperature dependence &Dgr;m/(m&Dgr;T) is in the range 5–15% per 0.1°K, over the region of normal chamber operation. Macroscopic bubbles grow at the rate 0.21 mm msec−½, until they are quenched by chamber recompression in proportion to their degree of internal energy. The measured track density dependencies are consistent with the view that bubbles originate on stopped secondary electrons produced in close collision processes, where distant collision influence is suppressed by the density effect much more for hydrogen than for the heavier bubble chamber liquids. It is shown that formation and growth of bubbles to critical size may be understood in terms of conventional fluid dynamics provided the expansion is extremely rapid. The secondary electron energies required for bubble formation at 27°K range from 80 to 292 eV depending on the superheat of the chamber.

ISSN:0034-6748    

DOI:10.1063/1.1718415

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Thermistor probes were built capable of resolving 0.01°C temperature differences in times as short as 0.02 sec, as shown by direct measurement. An approximately linear relation of output signal to temperature, and insensitivity to variations in water velocity require careful choices of circuit resistances and operating power dissipation. Preliminary tests at sea illustrated the importance of eliminating the velocity effect, but also showed that small thermal microstructures could be detected with the new probes.

ISSN:0034-6748    

DOI:10.1063/1.1718416

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

An apparatus for tensile testing in vacuum to 5400°F is described. A load‐elongation curve is plotted during testing of a standard specimen at a selected nominal strain rate between 0.005 and 5.0 in./in./min. The load train design provides that the grips, as well as the specimen, are in the furnace hot zone. The specimen is heated by radiation from an induction‐heated susceptor, and its temperature is uniform within the limits of detection of an optical pyrometer.

ISSN:0034-6748    

DOI:10.1063/1.1718417

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A transistorized automatic data recording system has been developed to provide more reliable instrumentation for the cosmic‐ray physicist. The system includes a counting rate integrator, a memory circuit, an electronic clock, and a serial‐to‐decimal converter. Besides reliability, small size, and low power consumption, the system can give both BCD and decimal output which are automatically punched on IBM cards.

ISSN:0034-6748    

DOI:10.1063/1.1718418

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A method of forming small holes in certain materials is described. The material is first exposed to massive, high energy particles such as fission fragments and is then immersed in a chemical etching solution which dissolves the damaged material along the paths of the particles. With this technique it is possible to form holes which are as small as 25 Å in diameter and are up to ∼10 &mgr; long. The hole diameters can be increased at will from the minimum size by continued etching. A density of up to ∼1011holes/cm2can be attained by a short irradiation in a typical reactor. The holes can be accurately aligned by collimating a beam of fission fragments. Fine holes have been formed in this way in a number of nonmetallic materials including glass, mica, and other silicate minerals.

ISSN:0034-6748    

DOI:10.1063/1.1718419

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Pattern reproduction problems arising with the use of image converters operating at high light levels in gated regimes in the microsecond range are examined. Potential gradients developed across the finite resistance of the photocathode are ascertained to be the mechanism causing distortion. Theoretical formulas are derived to describe the photocathode potential for the case of homogeneous illumination and to estimate the influence of such extraneous fields on the electron‐optical imaging. Three methods of remedy are discussed, one of which is supported by theoretical and experimental evidence presented in the paper.

ISSN:0034-6748    

DOI:10.1063/1.1718420

出版商:AIP    

年代:1963

数据来源: AIP