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Mar 1973

Volume 44, Issue 3, pp. 265-350

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A New Retarding Field Electron Spectrometer with Differential Output

I. Lindau, J. C. Helmer, and J. Uebbing

Rev. Sci. Instrum. 44, 265 (1973); http://dx.doi.org/10.1063/1.1686105 (10 pages) | Cited 20 times

Online Publication Date: 6 November 2003

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We describe the construction and performance of a new electron spectrometer for analysis of low kinetic energy electrons, 0–2000 eV. The design of the analyzer is based on computer calculations and combines many favorable properties of both the retarding and the deflection energy analyzer. The energy analyzer consists of a set of electrodes with cylindrical symmetry and a planar retarding field grid followed by an electrode system with postmonochromatic action. Therefore a differential spectrum is obtained directly. The performance of the analyzer is discussed in terms of resolution, sensitivity, luminosity, and signal‐to‐background. The resolution achieved is 0.5%, with a resolution of 30 meV, making it possible to resolve and study electronic vibrational levels in atoms and molecules. A few spectra of nitrogen and argon are shown as representative of the performance of the new analyzer.

Field Spinning Zeeman Modulation in Microwave Spectroscopy with Cosine Distribution Magnets

R. Claude Woods

Rev. Sci. Instrum. 44, 274 (1973); http://dx.doi.org/10.1063/1.1686106 (8 pages) | Cited 4 times

Online Publication Date: 6 November 2003

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The technique of field spinning Zeeman modulation in microwave spectroscopy has been extended to long cylindrical absorption cells by using orthogonal pairs of cosine distribution magnets. This magnet configuration permits economical application of the field spinning approach to rather long path length, large diameter cells with substantial homogeneity of the field. Fields adequate for microwave spectroscopy may be obtained even within a metallic (preferably austenitic stainless steel) cylindrical vacuum chamber. The solutions of Maxwell's equations for an idealization of the latter situation of an intervening conducting layer are presented, so that with the formulas given here, one may easily calculate available field as a function of geometry, amplifier power, modulation frequency, and circuit parameters. Two new microwave spectrometers have been constructed using such magnets, and our experiences with applying the field spinning technique to them will be discussed. Because the absorption cells are discharge tubes, we will consider the effects which the presence of the plasma has on the field spinning modulation method. While the plasma does give rise to the complication of a nonflat base line, it will be demonstrated that this can be held to quite manageable levels over a wide range of conditions. The spurious baseline fluctuation is likely to be observed in other configurations of Zeeman modulation of a plasma sample and appears to be related to a modulation of the plasma density and the resultant change in its refractive index.

A Microwave Spectrometer with an Internal Glow Discharge

R. Claude Woods

Rev. Sci. Instrum. 44, 282 (1973); http://dx.doi.org/10.1063/1.1686107 (7 pages) | Cited 16 times

Online Publication Date: 6 November 2003

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A microwave spectrometer which utilizes the positive column of a dc glow discharge as its sample region has been constructed and operated successfully. This instrument employs free space microwave propagation through a large industrial Pyrex pipe, along with Zeeman modulation, and is intended for the study of transient paramagnetic molecules which are likely to be found in active discharges. This spectromenter features no mechanical tuning, instantaneous broad band width, resolution limited by Doppler broadening, and sensitivity comparable to that of conventional Stark modulated waveguide cells. Extensive observations primarily of the microwave spectrum of the OH radical in a water vapor discharge, have been made in order to delineate the range of application of this technique and to determine the effects of various operating parameters on the spectrum observed. Although the glow discharge is an extremely complicated phenomenon and is capable of manifesting its complexities in the behavior of our spectrometer, a wide range of conditions exist in which the presence of the plasma in the transmission path has negligible impact on the microwave spectrometer signal. Theoretical considerations of basic plasma physics will be employed to support the proposition that this is not unexpected and that a wide range of microwave spectroscopic studies of plasma samples are possible.

A Sampling Unit for an X ‐ Y Recorder

Todd I. Smith

Rev. Sci. Instrum. 44, 288 (1973); http://dx.doi.org/10.1063/1.1686108 (3 pages) | Cited 3 times

Online Publication Date: 6 November 2003

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An inexpensive sampling circuit is described which allows high frequency repetitive signals to be plotted on an x ‐ y recorder. The minimum sample width of 100 nsec is short enough that the effective high frequency 3 dB down point is about 6 MHz. The circuit includes provisions for signal averaging which allows significant improvement in the signal‐to‐noise ratio in many situations.

Design of a Thermal Reference System for Use in Thermography

John A. Charles and John E. Francis

Rev. Sci. Instrum. 44, 291 (1973); http://dx.doi.org/10.1063/1.1686109 (4 pages) | Cited 1 time

Online Publication Date: 6 November 2003

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Increased interest in the use of the scanning infrared camera as both a diagnostic and research tool by the medical profession has led to the need for an external temperature reference. The scanning infrared camera detects the infrared radiation leaving a surface and converts the energy into a visual image which is photographed and termed a thermogram. This paper presents a thermal reference made by constructing an extended surface or fin in such a way as to produce a linear temperature profile down the fin axis. A fin was made following the theoretical model and tested. The resulting fin was quite linear and provides an excellent thermal reference.

Short Sample Testing of Very High Current Superconductors

John R. Purcell and Henri DesPortes

Rev. Sci. Instrum. 44, 295 (1973); http://dx.doi.org/10.1063/1.1686110 (3 pages) | Cited 1 time

Online Publication Date: 6 November 2003

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An apparatus is described for ``short sample'' testing at high currents using the induced current method. Primary currents of 100 A would produce up to 16 000 A secondary current. The method of measuring the secondary current and results are given.

Analytical Fit of the Transfer Function of a Logarithmic Electrometer and Correction for Ambient Temperature Variations

Raymond W. Huggins

Rev. Sci. Instrum. 44, 297 (1973); http://dx.doi.org/10.1063/1.1686111 (4 pages) | Cited 3 times

Online Publication Date: 6 November 2003

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An analytical fit has been derived for the transfer function of a logarithmic electrometer utilizing a p‐n junction diode as a feedback loop element. Elementary semiconductor theory has been used to describe the diode current‐voltage characteristic, and the diode ohmic resistance and an external parallel resistance have been included in the circuit analysis. A temperature correction has been applied to account for a difference in the temperature of the diode during calibration and during the taking of data. The analytical fit with temperature correction is believed to be accurate to better than 10% of the absolute current input over seven current decades.

A Method of Measuring Thermal Conductivity in the Presence of Extraneous Heat Currents and the Thermal Conductivity of Brass at Low Temperatures

R. L. Cappelletti and M. Ishikawa

Rev. Sci. Instrum. 44, 301 (1973); http://dx.doi.org/10.1063/1.1686112 (4 pages) | Cited 8 times

Online Publication Date: 6 November 2003

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A modification of the absolute, longitudinal, steady‐state method of measuring thermal conductivity at low temperatures using one calibrated thermometer is described. By this method the effects due to any type of constant extraneous heating are completely canceled. The method is applied to measure the thermal conductivity of machined brass between 0.3 and 2 K.

An Optical Distance Measuring Instrument

John M. Payne

Rev. Sci. Instrum. 44, 304 (1973); http://dx.doi.org/10.1063/1.1686113 (3 pages) | Cited 3 times

Online Publication Date: 6 November 2003

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This paper describes an instrument that measures the transit time of a modulated light beam out and back over the path whose length is required. The instrument has a digital readout and an rms (1σ) accuracy of ±0.08 mm on a single measurement over ranges up to 60 m. The measurement time is 2.7 sec.

A High Speed X‐Radiographic Camera for Use in the Electron Beam Environment

Donald Scribner Wood

Rev. Sci. Instrum. 44, 307 (1973); http://dx.doi.org/10.1063/1.1686114 (4 pages)

Online Publication Date: 6 November 2003

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A high‐speed X‐radiographic camera to radiograph blowoff products from materials subjected to high‐energy deposition by pulsed electron beams is described. Information obtained is average material density as a function of time and distance from the sample surface and is used to improve predictive hydrodynamic models. The camera design overcomes the difficult diagnostic problems of intense background radiation (bremsstrahlung), scattered electrons and electromagnetic interference usually associated with the electron beam environment. Conventional x‐ray film is mounted on a disk which rotates inside of a shielded housing. Data are recorded through a slit in the housing near the edge of the film disk (polar coordinate geometry) in either a flash (framing) or continuous (streak) mode. X‐ray energies used were 20–30 keV. Maximum speed of the film past the slit is approximately 0.04 cm∕μsec.

An Automatic Recording Device for Zimm‐Crothers Viscometer

J. C. Bernengo, C. Marion, and B. Roux

Rev. Sci. Instrum. 44, 311 (1973); http://dx.doi.org/10.1063/1.1686115 (3 pages) | Cited 5 times

Online Publication Date: 6 November 2003

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A high precision, easy to build, digital recording system has been adapted on a commerical Zimm‐Crothers rotating viscometer. It allows intrinsic viscosity measurements on very diluted nucleic acid solutions.

High Temperature Density Measuring Apparatus Using the Photon Attenuation Technique

F. E. LeVert, I. G. Dillon, and H. J. Tarng

Rev. Sci. Instrum. 44, 313 (1973); http://dx.doi.org/10.1063/1.1686116 (3 pages) | Cited 2 times

Online Publication Date: 6 November 2003

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Equipment has been designed and developed that allows one to use the gamma attenuation technique to measure the densities of metals at high temperatures. Saturated liquid density values have been measured from room temperature up to 1841°C. The density values obtained by this technique compare very well with those measured by other methods.

A Nanovolt‐Level MOSFET Reversing Switch for Low Temperature Applications

Jack R. Anderson and Donald R. Zrudsky

Rev. Sci. Instrum. 44, 316 (1973); http://dx.doi.org/10.1063/1.1686117 (6 pages) | Cited 1 time

Online Publication Date: 6 November 2003

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A remote reversing switch is presented, which is operable at low temperatures and useful for eliminating thermal lead voltages by means of an average. It utilizes four n‐channel enhancement mode MOSFET's with the channels connected in a balanced bridge configuration. Input signal reversal is achieved by gating on alternate pairs of transistors. The use of sapphire heat sinks for all channel leads is critical to the achievement of a switch resolution of better than ±2 nV, measured at 4.2, 77, and 300 K. The switch was also used as a remote chopping element for a phase‐synchronized dc to ac inversion, again at 4.2, 77, and 300 K with resolution approaching the limits of the equipment used to test its performance. The small size, infinitesimal power dissipation, predicted immunity to large magnetic fields, and almost perfect isolation of the driving circuit from the desired signal makes this reversing switch superior to any other device which has previously been used for such purposes.

An Improved Infrared In Situ Cell for Gas Adsorption Studies

A. Igarashi, Y. Ogino, and S. Onodera

Rev. Sci. Instrum. 44, 321 (1973); http://dx.doi.org/10.1063/1.1686118 (2 pages) | Cited 3 times

Online Publication Date: 6 November 2003

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A simple infrared cell was developed to study gas adsorption on a catalyst. The main body of the cell was made of Pyrex glass. Windows were attached to the cell body by means of O‐ring seals with water‐cooled brass rings. A heating assembly with tungsten windings was set in the cell. This cell could be used at temperatures up to 450°C, either under vacuum to a pressure of 10−6 Torr or in any controlled atmosphere.

Derivation of Second Order Geometric Factor G

J. T. C. Kan

Rev. Sci. Instrum. 44, 323 (1973); http://dx.doi.org/10.1063/1.1686119 (3 pages) | Cited 8 times

Online Publication Date: 6 November 2003

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The geometric factor G is a major parameter in determining differential cross sections with a gas target. Silverstein has calculated G for several detector aperture geometries with a finite sized, but parallel incident beam. Critchfield and Dodder have calculated G for a parallel‐edge front aperture and circular back aperture with a divergent incident beam. In this article, G is calculated for a parallel edge front aperture and a rectangular back aperture with a divergent incident beam. The present calculation follows the method outlined by Critchfield and Dodder and employs a convenient combination and slight modification of their notation and that of Silverstein.

A Servo‐Controlled Axial Fatigue Machine with Strain Rate Feedback for Testing Polymers and Composites

C. K. H. Dharan and A. D. Colvin

Rev. Sci. Instrum. 44, 326 (1973); http://dx.doi.org/10.1063/1.1686120 (5 pages) | Cited 2 times

Online Publication Date: 6 November 2003

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An inexpensive servo‐controlled electrohydraulic fatigue machine, capable of a maximum load of 22.2 kN (5000 lbf) and a maximum servo‐controlled strain rate of 0.2 sec−1, is described. Its primary capability is to perform load and strain‐range controlled fatigue tests conducted at constant strain rate feedback. In addition, the machine is capable of performing constant strain rate tensile tests and closed loop stress relaxation tests. The results of some initial fatigue tests are presented.

Optical Fiber Breaking Stress Distributions Obtained by a Cantilever Method

M. J. Saunders

Rev. Sci. Instrum. 44, 330 (1973); http://dx.doi.org/10.1063/1.1686121 (4 pages) | Cited 1 time

Online Publication Date: 6 November 2003

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A description is given of a cantilever apparatus to determine the mechanical strength and elastic modulus of optical fibers. This test method overcomes the problem of fiber breakage in the jaws of tensile machines. Young's modulus, the breaking stress distribution, and values of the breaking radius of curvature and strain are presented for fused quartz fibers.
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Hall Probe Loop for Nulling Induced Voltages from ac Magnetic Fields

V. M. Cottles and A. M. Hermann

Rev. Sci. Instrum. 44, 334 (1973); http://dx.doi.org/10.1063/1.1686122 (2 pages)

Online Publication Date: 6 November 2003

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A simple Hall probe loop which can be adjusted to null induced voltages from ac magnetic fields is described. With its use induced voltages have been reduced to the microvolt region allowing Hall effect measurements without the use of bucking voltages in low mobility materials.

A Two Frequency ac Hall Apparatus for Measurements in Metals

J. Yahia and G. Perluzzo

Rev. Sci. Instrum. 44, 335 (1973); http://dx.doi.org/10.1063/1.1686123 (3 pages) | Cited 3 times

Online Publication Date: 6 November 2003

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A novel and simple two frequency ac Hall apparatus is described and some results obtained using it are presented.

Elimination of Need for Special Purpose Switches in Accurate Four‐Terminal Circuitry

E. Zair and A. J. Greenfield

Rev. Sci. Instrum. 44, 337 (1973); http://dx.doi.org/10.1063/1.1686124 (1 page)

Online Publication Date: 6 November 2003

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An arrangement is suggested which avoids the need for specialized, high‐priced, bulky switches in four‐terminal resistance circuitry.

Temperature Control Using a Platinum Resistance Sensor

G. D. Brabson and A. A. Fannin

Rev. Sci. Instrum. 44, 338 (1973); http://dx.doi.org/10.1063/1.1686125 (1 page)

Online Publication Date: 6 November 2003

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A platinum resistance sensor can be used in conjunction with a resistance bridge to generate an error signal that is proportional to the difference between the actual and desired temperatures. The magnitude of the error signal, 0.4 mV∕°C, is 10 times that generated by a Chromel‐Alumel thermocouple.

Logarithmic Readout Attachment for Double‐Beam Spectrophotometers

J. R. Shepherd and H. R. Hedgpeth

Rev. Sci. Instrum. 44, 338 (1973); http://dx.doi.org/10.1063/1.1686126 (2 pages)

Online Publication Date: 6 November 2003

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The described attachment will process the output from a manual readout spectrophotometer, take the log10 of reference minus the log of the signal (log10 Io∕I), and feed that to a recorder.

Differences Between ac and dc Determinations of Germanium Thermometer Resistances

C. A. Swenson and P. C. F. Wolfendale

Rev. Sci. Instrum. 44, 339 (1973); http://dx.doi.org/10.1063/1.1686127 (3 pages) | Cited 7 times

Online Publication Date: 6 November 2003

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The resistances of several germanium thermometers are found to differ for ac and dc measurements. At 300 K, these differences are frequency independent from roughly 5 to 103 Hz. The ac resistances always are smaller, and the approximate temperature differences (Tdc − Tac) vary from 100 mk at 77 K to 0.2 mK below 17 K.

Inexpensive High Vacuum Feedthroughs

S. Gerber and D. Post

Rev. Sci. Instrum. 44, 341 (1973); http://dx.doi.org/10.1063/1.1686128 (2 pages) | Cited 2 times

Online Publication Date: 6 November 2003

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Rigid coaxial cable has been used to construct simple, inexpensive high vacuum coaxial and coaxial push pull rotary motion feedthroughs.

Magnetic and Electrostatic Deflectors for Charged‐Particle Beams

W. Haeberli

Rev. Sci. Instrum. 44, 342 (1973); http://dx.doi.org/10.1063/1.1686129 (2 pages) | Cited 1 time

Online Publication Date: 6 November 2003

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It is often assumed that uniform electrostatic or magnetic fields are required if all particles in a parallel beam of ions of finite diameter are to be deflected through the same angle. It is shown that the nonuniform field caused even by very short electrodes or pole pieces produces uniform deflection under certain conditions.
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