摘要:

A superconducting magnetic flux detector which can detect changes in flux as small as 10−11G·cm2is now in use in a small number of low temperature laboratories. We describe here how the devices work, how they are made, how they can be used for practical measurements of magnetic susceptibilities or fields, and how they can be made even more sensitive. The devices can easily be used in work other than low temperature physics and should find widespread application.

ISSN:0034-6748    

DOI:10.1063/1.1684651

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An electrostatic analyzer is discussed which has no fringe field effects. The basic idea is to form the equipotential surfaces around an ideal conductor for which the Dirichlet problem can be exactly solved. It is just the case of any spherical conducting cap, in particular, any hemispherical cap: The equipotential surfaces, in the portion interesting for the trajectory of the particles, are very near to spherical surfaces so that the focusing properties of the ideal hemispherical condenser are still valid. The external surface can act as the container so that another source of perturbation of the electric field is eliminated. The computed and experimental response of the analyzer shows satisfactory agreement for several different geometrical conditions, within the limits due to the expected uncertainties. Some further applications are also mentioned in view of making simultaneous measurements in different energy bands, as well as of determining, in favorable conditions, the potential of the external electrode when it is not zero, which can be the case of an analyzer on board a satellite.

ISSN:0034-6748    

DOI:10.1063/1.1684652

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A device has been developed to find the change in calibration of a torsion load cell when the cell is under hydrostatic pressure. The change in calibration was found to depend upon load as well as pressure. The correction was found to vary between 10 and 20% at 10 kilobars, being higher for the lower stresses.

ISSN:0034-6748    

DOI:10.1063/1.1684653

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A microwave probe is described which allows the electron density profile in a supersonic constricted arc jet plasma to be measured. Peak electron densities of 6×1013/cm3have been measured near the edge of the jet stream, with the electron density decreasing toward the center.

ISSN:0034-6748    

DOI:10.1063/1.1684654

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A technique has been developed by which a microcrack may be propagated in a controlled manner through a small slab, with simultaneous microscopic observation of the path of the crack and the force changes occurring during propagation. For studies of grain boundaries effects, specimens require grain sizes at least as large as specimen thickness (∼50 &mgr;) in order to define the effect of a single boundary on the crack path. Crack behavior may be observed by means of optical microscopy and would be suitable for scanning or transmission electron microscopy. Application of the technique to ceramic bicrystals indicates strong crack pinning points within the individual crystals as well as at the grain boundaries. In polycrystalline materials, these pinning points result in a start‐stop process which is repeated numerous times.

ISSN:0034-6748    

DOI:10.1063/1.1684655

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A technique has been developed which offers a significant improvement in the measurement of the loss in low loss materials having dielectric constants ≥4. The device consists of a cutoff section of circular waveguide concentrically loaded with a rod of the dielectric to be measured. The principal advantage of the technique is that by proper choice of sample and waveguide dimensions one can minimize the effect of resistive losses due to the metal walls. This is achieved by using the sample rod essentially as a section of dielectric waveguide in which the major fraction of the energy is confined to the rod. Both the reduction in wall losses and the simplicity of the design make the use of the waveguides fabricated from lower conductivity, high melting point metals much more attractive for measurement of low loss ceramic dielectrics at high temperatures. Results are reported for single crystal sapphire.

ISSN:0034-6748    

DOI:10.1063/1.1684656

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A method of using the scanning electron microscope (SEM) to measure the thickness of thin films in inaccessible locations is described. Emphasis is placed on the calibrations of the SEM necessary to obtain good reproducible data and comparisons are made between thickness measurements made using the SEM and interferometric techniques. Actual measurements in the 10 000–15 000 Å range have been made with errors of 2–5%.

ISSN:0034-6748    

DOI:10.1063/1.1684657

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Incandescent solids at temperatures above 1500 K radiate sufficient energy to allow optical pyrometry with a precision of 2 K or less in 1 msec. An instrument system has been built which achieves accuracy of a few kelvins. The sensitivity is 0.4 K when making 1200 measurements/sec near 2000 K or it can be increased as required to 0.01 K with a measurement rate of 1/sec. The system permits dynamic measurement of high temperature thermal properties of refractory metals with better accuracy than has been obtained by methods using slow heating.

ISSN:0034-6748    

DOI:10.1063/1.1684658

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Of the various kinds of doped germanium investigated for low temperature resistance thermometry, arsenic doping has been found most satisfactory in providing adequate sensitivity over the temperature range from less than 1 to a little over 100 K. Such sensors are highly reproducible as well as sensitive, but for accurate thermometry it has been a disadvantage that the relationship between sensor resistanceRand absolute temperatureTcannot be expressed accurately in analytic form. However, the relationship can be expressed within close limits over wide temperature ranges by polynomials of the formlog10R=i=0nAj(log10T)i.For an optimum representation, it is necessary to make judicious choices both of the polynomial degree and the temperature range. Insistence on a single polynomial over the entire 1–100 K range produces a solution with spurious oscillations of rms amplitude some 0.3% of the absolute temperature. Such spurious oscillations can be reduced to an amplitude of a few parts in 104of temperature by using one polynomial for the 1–20 K range and a second polynomial forT≳15 K(thus affording a small overlap region between the two polynomials). The markedly inferior results of using different temperature ranges and a different polynomial regression procedure are illustrated.

ISSN:0034-6748    

DOI:10.1063/1.1684659

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The application of a correlation method for the measurement of gas (vapor) bubble velocity in liquid flow is described. Contrary to previous similar procedures an optical method (laser light) is used for the bubble (or void) detection. First experimental results are reported.

ISSN:0034-6748    

DOI:10.1063/1.1684660

出版商:AIP    

年代:1970

数据来源: AIP