摘要:

Several related methods for determining the calibration formula of a continuously scanning bridge circuit using on‐line data are analyzed and discussed. High‐resolution resistance thermometry requires a sensitive, accurate conversion of off‐balance voltage measurements to resistance measurements. The objective is to properly determine the relationR=f(V,RB,Ci), whereVis the bridge output‐voltage,RBis a balance resistance, and theCiare unknown coefficients that depend onRBand other fixed circuit parameters. Linearization to the formR = RB + C1(RB)Vcan yield a fairly accurate conversion fromV(t) toR(t). IfR˙(t) or higher derivatives are required, linearization leads to systematic errors and a more sophisticated method is needed. From the analysis of three techniques for determining corrective terms, we conclude that parameterization of a model for the bridge circuit is the most satisfactory procedure. An empirical, self‐consistent method is useful if the circuit model is unknown or extremely complicated. Calibration data from a high‐resolution specific‐heat experiment were used to test the various methods.

ISSN:0034-6748    

DOI:10.1063/1.1686146

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We have devised, constructed, and tested in flight a scheme which permits the ends (near the anode seals) as well as the bottom and sides of an x‐ray astronomy proportional counter to be protected by anticoincidence guard counters. A rocket‐borne test has shown that the non‐x‐ray background is reduced by an additional factor of about 30 when the end guard counter feature is added.

ISSN:0034-6748    

DOI:10.1063/1.1686147

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A large desorption cryostat particularly suited for measurement of the properties of cryogenic materials between 1.5 and 60K is described. In the difficult range above 20K temperature control and uniformity remains excellent. For measurements above 20K either hydrogen or helium may be used as the adsorptive. The temperature range of the cryostat may be extended to 120K with the use of nitrogen as the adsorptive.

ISSN:0034-6748    

DOI:10.1063/1.1686148

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A technique for the magnetic suspension of small (< 1 mm diam) superconducting niobium spheres is described in which the restoring forces (shape of the applied field) can be conveniently adjusted and low losses in the translational modes of oscillation easily obtained. The suspension was developed for use in an experiment designed to detect the existence of fractional electric charge but is applicable to other experimental situtations as well. A typical sphere is suspended with a vertical period of oscillation of 1.5 sec and a Q of 3000. Adjustments can be made over the period range 0.6 to 9 sec and Q's as high as 8000 have been achieved.

ISSN:0034-6748    

DOI:10.1063/1.1686149

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A supersonic molecular beam source was attached to an electron diffraction unit in order to study molecular structures and cluster structures. Because the density in a molecular beam is only a few times 1012molecules per cm3, it was necessary to lower the pressure in the diffraction chamber to 5×10−8Torr and to eliminate the back‐scattered electrons at largesvalues. This was accomplished by means of a very deep (45 mm) beam‐stop and a mask. Liquid helium cryopumping makes it possible to reduce the beam source bulkiness which, in turn, permits the placement of the scattering point as close as possible to the source (about 55 mm from the nozzle). Thus a target of the highest density is obtained, while a wide range of scattering is permitted. Reliable diffraction data have been obtained out tos= 45 Å−1. The main components of the diffraction unit are described, as is also the supersonic molecular beam source. A discussion is presented on the use of the apparatus.

ISSN:0034-6748    

DOI:10.1063/1.1686150

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Single crystals of n‐type Bi2Se3grown by the Bridgman technique are found to make excellent Hall effect magnetometers capable of repeated cycling to liquid helium temperatures. Plots of Hall resistivity, &rgr;yx, versus magnetic fieldBto 11 tesla deviate from linearity by less than ±0.8% for all temperatures between 1.1 and 300 K. Furthermore, the slope of the &rgr;yxversusBcurve varies by less than 2% in the region 1.1 to 78 K.

ISSN:0034-6748    

DOI:10.1063/1.1686151

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A technique is described whereby the shape of the first derivative electron spin resonance (ESR) spectra observed for &ggr;‐irradiated glycylglycine can be used in ESR experiments to estimate the microwave magnetic fieldH1in the 40–1000 mG range. The ratio of the minor to major derivative peak heights of the glycylglycine doublet is found to vary withH1. Slow passage progressive saturation studies are included in an attempt to explain the phenomenon. The technique provides a means of measuringH1, without knowing effective cavity Q, incident power, or the field concentrating effects of quartz inserts and is proposed as an interlaboratory ESR microwave power comparison standard.

ISSN:0034-6748    

DOI:10.1063/1.1686152

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A useful thin‐film passive dosimeter system has been developed through use of a poly(halo)styrene matrix doped with malachite green methoxide as an indicator. Extensive characterization studies of the chlorostyrene dosimeters have been completed and the range of conditions under which they are useful has been defined. Exposure to radiation causes development of a blue color (absorption at 630 and 430 nm) which has an optical density proportional to dose over the range 104−107rad and may be calibrated to above 3×107rad. No effects of dose rate have been observed between 102and 1015rad/sec, and no effects of photon energy between 2 keV x‐rays and 1 MeV gamma rays. Of the environmental parameters studied, only extraneous uv light, temperature, and a few noxious gases have a significant effect on the performance of the dosimeters. Oxygen has only a small effect (a few percent) at low dose rates, but acidic gases such as NO2, SO2, and HCl will first color, then bleach the films. The rate and ultimate amount of coloration are dependent on temperature, but this effect is negligible from 0 to 35°C. These films have an indefinite shelf life at room temperature in the absence of light and corrosive gases, and the small effects of oxygen and temperature can be compensated for in the calibration for a particular application.

ISSN:0034-6748    

DOI:10.1063/1.1686153

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Using a magnetically retracted pedestal, small targets of a solid material can be accurately positioned at the focus of a laser pulse. The particular system to be described is relatively inexpensive, has proved capable of holding a vacuum of the order of 10−8Torr, and has provided successful firings in more than 95% percent of the attempts. It has the added advantage of being easily adaptable to a variety of applications, such as toroidal confinement devices, mirror or minimum B machines, Z and &THgr; pinch systems and plasma focus devices.

ISSN:0034-6748    

DOI:10.1063/1.1686154

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We describe a method of accurately measuring the secondary electron yield of solids over the entire incident energy range of 0–1000 eV in less than 30 msec using a commercial LEED/Auger system. Particular attention is paid to the region of low‐energy incident electrons (Ep=0 to 100 eV), and the spatial and energy resolution there are considered. The method is fast enough to see temporal changes in yield on the scale of hundreds of milliseconds. Criteria for measuring the yield of semi‐insulators are considered, as well as measurements of fine structure in the yield nearEp=0 eV.

ISSN:0034-6748    

DOI:10.1063/1.1686155

出版商:AIP    

年代:1973

数据来源: AIP