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Review of Scientific Instruments

Issue 3 • Date Mar 1967

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Displaying Results 1 - 25 of 47
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Some Techniques for Sensitive Magnetic Measurements Using Superconducting Circuits and Magnetic Shields

    Page(s): 311 - 318
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    A new superconducting circuit has been used in a sensitive magnetic susceptibility apparatus to detect changes in magnetic susceptibility as small as 10-10 cgs/g in a 104 Oe field, and in a low field magnetometer with which magnetic fields as low as 5×10-7 Oe have been measured. A low field superconducting shield for testing sensitive magnetometers has been developed and used to provide stable magnetic fields of less than 10-6 Oe, maintained stably for as long as six days. The measured attenuation of externally applied axial field changes is shown to be a factor of about 31 per shield radius. The stability of the persistent field of a Nb‐25% Zr superconducting solenoid, observed over an 8 h period, indicated an average drift in the persistent solenoid field of less than one part in 1010/sec. Also, the attenuation of various high field magnetic shields of Nb‐25% Zr foil was measured. View full abstract»

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  • Fast Carbon Bolometer for Observing Thermal Pulses

    Page(s): 318 - 321
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    A carbon bolometer, used as a high speed thermometer for observing heat pulses in solids at low temperatures, is described. In conjunction with a KCl substrate, the carbon bolometer was compared with a thin film superconducting bolometer. The carbon bolometer was found to have a frequency response flat to at least 2.5 kHz. View full abstract»

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  • Fatigue Apparatus for Extreme High Vacuum

    Page(s): 322 - 325
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    A constant amplitude, reverse bend stress fatigue testing device is described which permits simultaneous testing of up to eight specimens at extremely low pressure levels below 10-10 Torr. The vibratory force was provided by an electromagnetic exciter with vibration frequencies in the range of 50–200 cps. Fatigue tests with 1100‐H14 aluminum showed that a substantial increase in the cyclic fracture life was obtained in high vacuum as compared to the fatigue behavior in unit atmosphere of air. The fatigue life improvement increased proportionally with the cyclic stress frequency. View full abstract»

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  • Method of Producing and Measuring Charged Single Droplets

    Page(s): 325 - 327
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    A method is discussed for producing and measuring the electric charge on single droplets pulsed out of a main stream of droplets which were produced by periodic mechanical excitation of a jet of liquid. With this method, charges on the order of 100 electrons can be measured on the single droplets. View full abstract»

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  • Effect of High Pressure On a Strain Gauge Load Cell

    Page(s): 328 - 331
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    A load cell employing foil strain gauges is described for measuring small uniaxial loads (5×104 to 2×106 dynes) applied magnetically to develop bending stresses in crystals under hydrostatic pressures up to 15 kbar. Two calibration methods of direct loading at pressure were used—a magnetically operated plunger and dead weight loading. It was established that the change in gauge output (the ``pressure effect'') during increase of pressure at no‐load is in keeping with previous work. However, the gauge factor, as determined by the load cell response after balancing at pressure, decreases with increasing pressure. For the strain gauges used here, the decrease is approximately linear and at 10 kbar is as much as 20%. View full abstract»

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  • Measurements of Beam Divergence of Q‐Switched Ruby Laser Rods

    Page(s): 331 - 334
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    A method of measuring beam divergence is reported that provides simultaneous variable intensity multiple exposures of the laser output on Polaroid film, and does not require densitometer tracings of the exposures to establish the beam divergence. Using this technique, beam divergence as a function of power output of 12 ``Q‐switched'' ruby rods is reported. Inference is made that the active divergence of a ruby rod is the sum of the passive beam divergence of that rod plus the divergence due to radial mode structure. Thermal distortion probably contributes very little to the beam divergence. View full abstract»

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  • Plane Layer Type Apparatus for Gas Thermal Conductivity Measurements

    Page(s): 335 - 339
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    A simple plane horizontal layer type apparatus is described for measuring thermal conductivities of gases over a wide pressure range. Experimental results obtained with argon, nitrogen, and air indicate that thermal conductivities and thermal accommodation coefficients can be determined with the apparatus within about 2% accuracies at pressures ranging from free molecule to continuum conditions. View full abstract»

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  • 100 kHz Homodyne, 35 GHz Reflection‐Cavity Spectrometer with Phase‐Lock of the Reference Signal and Low Frequency Field Modulation

    Page(s): 339 - 347
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    A 35 GHz, reflection‐cavity type microwave spectrometer is described. We use a 35 GHz ferrite modulator in the signal arm to produce a double sideband (±100 kHz) suppressed carrier signal to reduce the 1/f microwave crystal noise. Solid metal cavities and low frequency modulation of the externally applied magnetic field are used to reduce leakage from the cavity, thereby reducing susceptibility to microphonics and allowing more freedom in the choice of cavity modes suitable for a wide variety of experiments with metallic or dielectric samples. This instrument employs a 35 GHz ferrite phase shifter to phase lock the microwave signal in the reference arm of the bridge for observation of absorption signals An analogous scheme for phase‐locking at dispersion signals is also suggested. A narrow passband, low noise, active filter, with a Q factor of approximately 106, is used as part of a feedback loop around the 100 kHz receiver. This minimizes the possibility of saturation of the receiver due to less than critical coupling to the microwave cavity. Practical advantages of the present unit in low temperature spectroscopy, particularly with regard to helium bubbling and helium level change, are stressed. Comparative sensitivity tests of this unit with the standard 200 Hz magnetic field modulation systems show that, at cavity power levels smaller than 5 mW, a factor of ten improvement can be attained. At higher microwave power levels the improvement available is hampered by microphonics in the bridge. The theoretical analysis of the microwave bridge operation, of various key components, and of the electronic system is presented in the text and in the appendices. View full abstract»

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  • Focusing of Charged Particles with Hemispherical Grids

    Page(s): 348 - 352
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    A theoretical analysis has been carried out to determine the trajectories of charged particles incident upon a pair of concentric spherical grids, where the inner grid is maintained at a large accelerating potential with respect to the outer grid. The results show that under certain conditions a beam of charged particles incident on the outer grid is sharply focused inside the inner grid. These results were confirmed experimentally using hemispherical grids and electron beams. View full abstract»

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  • New Microwave Interferometric Device Using Lecher Wires for High Spatial Resolution

    Page(s): 352 - 354
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    The following describes a Lecher system with finlines for providing the transition to waveguides which is suitable for incorporation in microwave interferometers. This device gives a spatial resolution perpendicular to the wires which is smaller than the wire separation, even for 4 mm waves, i.e. smaller than λ/2. View full abstract»

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  • Four‐Stage Mass Spectrometer of Large Radius

    Page(s): 355 - 359
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    A research mass spectrometer has been constructed comprising four analyzing elements; two electrostatic and two magnetic 90° lenses, each with a mean radius of curvature of 50.8 cm. The instrument can be programmed for the mass and energy resolution of both primary and secondary ion species, making the spectrometer an attractive tool for studies of sputtering, charge exchange, and dissociation phenomena. A high isotopic abundance sensitivity (∼108/1) has also been achieved, a figure of merit that is important in nuclear measurements and special tracer applications. View full abstract»

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  • Contactless Measurement of Resistivity of Slices of Semiconductor Materials

    Page(s): 360 - 367
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    In this resistivity measurement, a pair of semicircular measuring electrodes is connected to a series or parallel resonance circuit composed of an inductance L and a variable capacitance C. A sample is coupled capacitively with the electrode with no direct contact. The authors' method is similar to the Q meter method in principle, but uses a comparative measurement. Some analyses of this method and the experimental results are reported: (1) the measurable range of resistivity is limited by an electrode structure and a frequency, (2) the resistivity measurement over a range as wide as 0.3 to 1500 Ω‐cm can be carried out by using both the series and the parallel resonance circuits, (3) for a thin sample below 3 mm in thickness, the resistivity can be measured by using a calibration, (4) the influence of different surface treatments is not seen if the surface remains flat. View full abstract»

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  • Double Mechanical Heat Switch for Calorimetry Below 1°K

    Page(s): 368 - 370
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    A double mechanical heat switch suitable for calorimetry in the 0.2 to 5°K range is described. The lowest temperatures are achieved by adiabatic demagnetization of a paramagnetic salt. One switch makes or breaks contact between the salt and the bath, whereas the other is between the salt and the specimen. The performance of the device is illustrated by the description of an experiment in which 1.8 moles of pure magnesium metal was cooled from 1.4 to 0.15°K in 35 min. On opening the thermal switch, a temperature rise of 0.03°K was observed. View full abstract»

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  • Properties of Gold‐Chromium Alloy Pressure Gauges

    Page(s): 371 - 374
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    The pressure and temperature dependence of the electrical resistance of the alloy Au+2.1% Cr have been measured. After low temperature heat treatment, the resistance of this alloy passes through a minimum as a function of temperature. As pressure is increased, the temperature at which the resistance minimum occurs becomes progressively higher. Metallographic study shows that a necessary condition for the occurrence of this resistance minimum is the formation of a finely dispersed second phase. As a material for electrical resistance pressure gauges, the gold‐chromium alloy is characterized by low temperature sensitivity, absence of shift of the zero‐pressure resistance, and nearly linear and reasonably large pressure response. However, it also displays hysteresis during pressure cycling and a tendency for the pressure calibration to drift. View full abstract»

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  • Particle‐Beam Profiling System

    Page(s): 375 - 376
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    A system using a 25.4 cm square wire spark chamber with acoustic readout and storage oscilloscope to display a particle‐beam profile is described. The instrument was built for an experiment at the Stanford Linear Accelerator Center. View full abstract»

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  • Measurement of Radiant Energy Emitted by Xenon Flashlamps

    Page(s): 377 - 381
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    Two types of radiometer were used to measure the radiant energy produced by high energy helical xenon flashlamps operating in the pulse mode. Metal cylinders plated with platinum black are accurate to 2%, but can be used only at low incident energy and power. Graphite slugs are less accurate because of uncertainties in the reflectivity of graphite, but are more durable, and have been used successfully at incident radiant energy of 126 J/cm2 and peak power of 50×103 W/cm2. View full abstract»

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  • High Speed Electromagnetic Shutter

    Page(s): 382 - 383
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    A high speed electromagnetically driven shutter has been constructed and used. This shutter is of the closed‐open‐closed variety, and is characterized by highly reproducible open duration time and negligible jitter. The shutter action is obtained when a thin plate carrying an open slit slides past a fixed slit. The moving slit is driven by the mutual repulsion of two parallel conductors carrying current in opposite directions. The present model has a total open time of 35 μsec, but this can easily be reduced by modifications of the shutter geometry. The application of this instrument to short duration absorption spectroscopy is described. View full abstract»

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  • Measurement of Dielectric Constant and Loss Factor of Powder Materials in the Microwave Region

    Page(s): 384 - 386
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    A system has been developed to measure the dielectric properties of powder materials using X band microwave frequencies. The measurement is conducted in a microwave cavity oscillating in the TM012 mode and resonant at 9.4kMc. Relatively small amounts of material are needed, and samples are introduced into the cavity using a quartz tube. The limitation of the perturbation theory as a basis for computation is examined experimentally. The suitability of different equations correlating the apparent dielectric constant of the powder material with the intrinsic values of the solid (crystalline or fused solids) is demonstrated by the data. View full abstract»

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  • Goniometer Assembly for NQR Zeeman Studies

    Page(s): 387 - 389
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    The study of Zeeman splitting of NQR lines in single crystals at times provides information about the nature of certain chemical bonds. Such analyses require a goniometer to orient the crystal with respect to the magnetic field. The description of a goniometer which is easily constructed and is sufficiently accurate for many studies is given. View full abstract»

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  • Two Directional Beam Convergence by Sector Shaped Uniform Magnetic Field

    Page(s): 390 - 394
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    In order to increase the ion transmission in a mass spectrometer, an ion optical system which renders the output ion beam from a magnet parallel to the median plane is proposed, and its general design formulae and processes are presented. The characteristics and the merits of the present system over the conventional two directional beam focusing arrangement are discussed and some numerical examples are given. View full abstract»

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  • Measurement of Contact Resistance

    Page(s): 395 - 397
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    An instrument for measuring the long term quality of electrical connecting devices is described. The parameter which controls this property is the contact resistance. In the instrument described, the contact and bulk resistance are separated by utilizing the difference in thermal response time between a contact spot and bulk metal. The circuits, mode of operation, and applications of the instrument are discussed. Contact resistance can be measured within 5% in most electronic connectors, switches, and relays. View full abstract»

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  • Theoretical Main Beam Profiles for the Kratky Small Angle Camera

    Page(s): 398 - 404
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    A geometrical procedure is developed for determining the theoretical profile of the main beam intensity for the Kratky low angle x‐ray diffraction camera. Agreement of experimental and theoretical profiles for a variety of camera geometries is excellent. In contrast to an estimation of the beam width by extrapolation, which may be misleading under certain circumstances, the experimental determination of the entire profile provides an accurate check of the camera alignment for all operating conditions. Furthermore, the area under the theoretical profile furnishes a relative measure of the total useful main beam intensity. This information may be used to determine the optimum values of the camera parameters for operation at any desired maximum resolution. View full abstract»

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  • Ion Tracer Anemometer for the Measurement of Low Density Air Flow

    Page(s): 405 - 409
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    A density independent anemometer for use at altitudes between 20 and 50 km has been developed and successfully operated on an air sampling research balloon flight. Its operation is based on the pulsed generation of ions within the air stream and their subsequent detection at a measured distance. Closed loop retriggering of the electric discharge results in a pulse train whose frequency varies directly with the air velocity. Semiconductor circuitry is used throughout, including an automatic discharge restarting circuit. Designed for monitoring velocities between 5 and 50 m/sec, the instrument range can be conveniently extended in both directions by suitable repositioning of the anemometer probes. View full abstract»

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  • New Experimental Method for Perturbation Measurements in Cavity Resonators

    Page(s): 410 - 414
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    We present a new experimental equipment for field strength measurements in low Q cavity resonators by means of the perturbation method. The main part of this equipment is an admittance meter which enables us to perform both amplitude and direction measurements by an extremum method. View full abstract»

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Aims & Scope

Review of Scientific Instruments, published by the American Institute of Physics, is devoted to scientific instruments, apparatus, and techniques.

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Editor
Albert T. Macrander
Argonne National Laboratory