摘要:

Apparatus and methods have been devised for the rapid and precise determination of the Boltzmann temperature of oxide coated cathodes in scanning beam tubes. The measuring apparatus comprises a digital voltmeter connected between cathode and collector of the tube under test by means of a high input resistance amplifier connected to have unity gain, and a variable shunt from cathode to collector consisting of tap switches and 20 precisely calibrated resistors having values from 104to 2×1010&OHgr;. The 19 temperatures determined by the 20 retarding potentials measured with this apparatus are computed on a GE 265 calculator. The interfering side effects which are encountered in practical measurements, viz., contact potential drift, contact potential instability, Ohmic and non‐Ohmic leakages, collector thermionic and photoelectric emission, heater‐to‐collector emission, and interelectrode potential minimum, nonuniform geometry, and poorly activated cathodes, are discussed, and the means taken to overcome these effects described in detail. The use of a magnetic field parallel to the electric field to effect collimation is described. It is shown that a very high field may be required to obtain the correct temperature in tubes with nonuniform geometry. It is estimated that in most cases the electron temperature can be measured with an absolute probable error of 1.7°, and that the relative probable error is approximately an order of magnitude lower.

ISSN:0034-6748    

DOI:10.1063/1.1684462

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The spreading resistance probe technique of measuring resistivity in epitaxial layers requires precise control of the parameters that affect the area of contact and damage under the probe. The effects of these parameters on the measurements are described and the design of a semiautomatic probe is presented. The probe can be lowered with the same velocity during each measurement and theIRdrop across the contacts is kept independent of resistivity. The mechanical design and the electronics of the probe are discussed in detail. The reproducibility of the measurements is found to be independent of resistivity in the constant voltage mode and is compared with the customary constant current mode. The (3&sgr;) multioperator reproducibility of the measurements is better than ±0.39% for n‐type silicon and ±0.65% for p‐type silicon.

ISSN:0034-6748    

DOI:10.1063/1.1684463

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Resolution in the photoemission energy analyzer is investigated theoretically for the case of a finite emitter in a spherically symmetric retarding field with a magnetic field present. Resolution errors shift and broaden structure in measured energy distribution curves by an amount which is energy dependent. The analysis is applicable to the spherical capacitor analyzer, the screened emitted geometry, the multiscreened LEED system, and others. Electrolytic tank measurements show field distortions caused by a flat emitter, the emitter support, and the window aperture. Spherical symmetry is restored to a configuration with a large emitter or support structure by surrounding the emitter with a screened, field‐free region. An explanation is given for the reasonable resolution obtained for any small emitter completely enclosed by a collector. Distortion of measured electron energy distributions caused by reverse photoemission, reflected electrons, and fringing fields at the emitter is also discussed.

ISSN:0034-6748    

DOI:10.1063/1.1684464

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An apparatus allowing deformation experiments under hydrostatic pressure up to 15 kilobars is described. The pressure environment is a gas. The load measurement is performed under pressure and the load vs elongation curve is directly recorded during the test.

ISSN:0034-6748    

DOI:10.1063/1.1684465

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Improvement of the signal‐to‐noise (S/N) ratio of cw NMR spectrometers by cooling circuit components to liquid helium temperature is discussed. Criteria for design of a low temperature circuit using a twin‐T bridge and MOSFET amplifier are presented. A liquid helium temperature spectrometer for operation at 16 MHz which improves S/N ratio by a factor of 5 over conventional techniques is described.

ISSN:0034-6748    

DOI:10.1063/1.1684466

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The thermal expansion or magnetostriction of wires controlled by a feedback circuit is used to compensate for the effect of environmental disturbance on a movable platform. The system provides linear control of the platform position to plus or minus a few angstroms and angular control to plus or minus a few milliarc‐seconds.

ISSN:0034-6748    

DOI:10.1063/1.1684467

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The design and application of high temperature thermal analysis equipment is described in this paper. Radiation emitted from the inductively heated samples impinges on an ir semiconductor device, the output of which is amplified and displayed on an X‐Y two‐pen recorder. Small heat effects associated with condensed state phase transitions can readily be detected using the techniques of thermal analysis (TA), derivative analysis (DA), or differential thermal analysis (DTA). Solid state transformations found in thorium dicarbide are illustrated using the various TA techniques. Data presented for phase changes in the uranium present in hypostoichiometric uranium dioxide show that isothermal enthalpy changes of <7 cal can be detected by the TA apparatus when using the DA mode of operation.

ISSN:0034-6748    

DOI:10.1063/1.1684468

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An alpha emitter (241Am) deposited externally as a thin source on a small NaI(Tl) crystal has been employed as a miniature light pulser. Applications include photomultiplier tube calibration and stabilization, and high precision light collection efficiency mappings for design optimization of scintillation and Cˇerenkov detectors. Improved resolution has been reported by Menefee and Cho [IEEE Trans. Nucl. Sci.NS‐13,No. 3, 159 (1966)] for NaI(Tl) crystals doped internally with241Am.

ISSN:0034-6748    

DOI:10.1063/1.1684469

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An instrument is described for the measurement of the dichroism produced in solutions of macromolecules by pulsed electric fields. Measurements can be made with monochromatic radiation in the wavelength range from 240 to 600 nm. The pulse generation equipment employed is similar to that used by previous workers but the optics and signal detection system are novel and allow a direct measurement of the dichroism. The relation between the output signal of the apparatus and the dichroism of the sample is derived. Representative experimental data from a study of tobacco mosaic virus are presented to demonstrate the performance of the apparatus. Limitations of the instrument are noted and possible improvements are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1684470

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Simultaneous Q‐switching of two independent ruby lasers has been achieved by a single rotating prism. Frequencies of the two lasers are independently tuned. A difference frequency in the range of approximately 0–50 cm−1could be obtained.

ISSN:0034-6748    

DOI:10.1063/1.1684471

出版商:AIP    

年代:1970

数据来源: AIP