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Review of Scientific Instruments

Issue 5 • Date May 1971

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Displaying Results 1 - 25 of 55
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • A Low Temperature Glass‐Ceramic Capacitance Thermometer

    Page(s): 561 - 566
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    Dielectric measurements are reported on capacitance thermometers based on SrTiO3 crystallized from glass at 1100 and 1200°C. Multilayer experimental units, approximately 5×2×1 mm, were fabricated using pilot plant facilities and measured from 1.7 to 300 K. If both the capacitance and loss tangent are measured, the range of the 1100°C crystallized thermometer is from at least 1.7 to 300 K. For capacitance measurement alone, the thermometer range is below 72 K, and in this range the capacitance varies smoothly and monotonically with temperature, becoming linear below 5.2 K. The sensitivity is largest in this linear region and averages 250 pF·K-1 for the 1100°C crystallized thermometers. The self‐heating at 4.2 K is about 70 pW (5 kHz, 7 mV) and decreases with decreasing temperature. The effect of a magnetic field on the thermometer was measured in an open Dewar of liquid helium at four frequencies in fields up to 80 kG. The measured changes were ≤±1 mK and are interpreted as fluctuations in the bath temperature rather than an intrinsic magnetocapacitance effect. The response time between 4.2 and 300 K is at least 70 K·sec-1. The main disadvantage of the thermometer is a transient (∼30 min) capacitance instability which is equivalent to a ≤30 mK change before stabilization. Once stabilized, the thermometer repeats to about ±2 mK when compared to a germanium thermometer, and repeats to ±13 mK on cyclically plunging into liquid helium (15 cycles) in the unstabilized case. This instability is apparently due to helium migration into the unencapsulated sensor body. The polar properties of glass crystallized SrTiO3, on which the thermometer is based, are briefly discussed, and comparisons are made with two other capacitance thermometers reported in the literature. View full abstract»

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  • Studies of a Glass‐Ceramic Capacitance Thermometer between 0.025 and 2.4 K

    Page(s): 567 - 570
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    Capacitance measurements from 0.025 to 2.4 K are reported for capacitance thermometers (made from an SrTiO3 glass‐ceramic crystallized at 1100 and 1203°C), two of which were the ones reported in the previous article. It was found that the 1200‐type thermometer has a useful thermometric range down to 0.06 K and a linear C‐T region down to 0.5 K. The 1100‐type thermometer has a useful range down to 0.110 K and a linear region down to 1.1 K. The measured data do not appear to be influenced by self‐heating or adiabatic correction effects. Both thermometers display an unexpected increase in capacitance with decreasing temperature below their monotonically decreasing ranges. The 1100‐type thermometer displays the more pronounced increase, with C∝T-1 from 0.100 to 0.025 K. It is argued that this T-1 behavior is due to the onset of an ultralow temperature phase transition in the glass crystallized SrTiO3, and the possibility of using this effect to achieve adiabatic depolarization cooling is discussed. View full abstract»

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  • Studies of a Glass‐Ceramic Capacitance Thermometer in an Intense Magnetic Field at Low Temperatures

    Page(s): 571 - 573
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    The effect of an intense magnetic field on an 1100‐type capacitance thermometer (made from an SrTiO3 glass‐ceramic crystallized at 1100°C) was accurately measured at five temperatures between 1.5 and 4.2 K. At each manostatically maintained temperature, the capacitance changes were measured five times between B=0 and B=14 T, and it was found that these changes did not exceed the measurement uncertainty, ±0.3 pF≅±1 mK. Similar results were obtained on a second 1100‐type thermometer. Some suggestions are made for the use of this type of thermometer in magnetic field experiments. View full abstract»

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  • Simulating Atmospheric Radio Noise from Low Frequency through High Frequency

    Page(s): 574 - 577
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    Generally it is too costly or otherwise not feasible to conduct performance tests on a radio communication system under conditions of actual atmospheric radio noise because this noise is nonstationary. Accurate simulation of desired conditions solves this difficulty. Magnetic tape recordings were made of atmospheric radio noise from low frequency through high frequency. The recordings were computer analyzed and were used as a model for the design of an atmospheric noise simulator. The simulation is valid and accurate for the limited available data base. View full abstract»

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  • Measurement of the Thermal Pressure Coefficient (∂P/∂T)v of Molten Salts

    Page(s): 578 - 580
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    A method for the determination of the thermal pressure coefficient (∂P/∂T)v or γv for molten salts up to 400°C and 400 bars is described. The results, which are considered to be accurate to ±3%, are compared with previous work. View full abstract»

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  • Refrigerating Vapor Bath

    Page(s): 580 - 583
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    A simple and inexpensive refrigerating vapor bath has been developed for the purpose of cooling gas line traps. The cooling medium in the bath is the cold vapor from liquid nitrogen. The temperature regulation range is from -196 to ∼0°C. For a glass‐isolated stainless steel gas trap the liquid nitrogen consumption rate was less than ½ liter/24 h at temperatures between -130 and -196°C. View full abstract»

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  • A Comparison of Ta, W, and Pt‐8%W Surface Ionization Detectors for Fast Potassium Atom Detection

    Page(s): 583 - 586
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    Data are presented which describe and compare the behavior of Ta, W, and Pt‐8%W surface ionization detectors for fast potassium atom detection. The potassium atom energy in these experiments covered the range from thermal energy to 500 eV. View full abstract»

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  • A Low Cost Versatile Arc Melter

    Page(s): 587 - 588
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    We have designed and built an arc melter which uses an inexpensive Pyrex pipe cross for a controlled atmosphere chamber. An argon jet has been incorporated into the electrode holder which provides both dynamic flushing and rapid quenching capabilities. View full abstract»

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  • Paired Comparison Tests of the Relative Signal Detected by Capacitive and Floating Langmuir Probes in Turbulent Plasma from 0.2 to 10 MHz

    Page(s): 589 - 594
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    Paired comparison measurements of the spectrum of electrostatic potential fluctuations in a steady state turbulent plasma confined in a magnetic mirror geometry have been made with capacitive and floating Langmuir probes over the frequency range from 0.2 to 10.0 MHz. For the experimental conditions investigated (5×107≤ne≤5×108/cm3, 8≤Te≤38 eV, 350≤Ti≤930 eV, Bmax=1.0 T), no significant difference in the relative frequency response was observed below 4.0 MHz. At about this frequency, however, the signal detected by the floating Langmuir probe dropped off relative to that of the capacitive probe. The source resistance of the turbulent fluctuations sensed by the Langmuir probe was about 400 Ω. At higher frequencies (from 7.0 to 10.0 MHz) a signal was detected by the floating Langmuir probe that was not detected by the capacitive probe. This spurious signal may be confused with the turbulent fluctuations of the plasma in the absence of paired comparison tests. View full abstract»

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  • Corona Discharge Anemometer and Its Operational Hypothesis

    Page(s): 595 - 600
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    The paper presents an outline of the physical mechanism of corona discharge between a highly stressed anode and a large plate cathode as applied to the operation of a new type of anemometer. An operational hypothesis is proposed for the anemometer with reference to its kinematic and electrostatic principles of performance. Experimental results are presented to justify the hypothesis and the calibration of the probe. A discussion of the probe sensitivity to yaw of gas stream is included. View full abstract»

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  • Measurement of the Index of Refraction of Some Molten Ionic Salts

    Page(s): 600 - 602
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    A simple method for measuring the index of refraction of molten salts is described. The indices of CaCl2, KBr, NaCl, and KCl are given at wavelengths ranging from 4000 to 7000 Å. Dispersion curves are given. Comparison is made with values obtained by another method. View full abstract»

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  • A Solid State Light Pen and Computer Interface for the Tektronix 611 Storage Oscilloscope

    Page(s): 602 - 605
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    A solid state light pen has been developed to accommodate the phosphor characteristics of the Tektronix 611 storage oscilloscope. Computer interfacing for the 'scope includes remote control of the storage mode and expansion of both X and Y axes by a factor of 1–8 with variable trace positioning. View full abstract»

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  • A Thermistor Anemometer for the Measurement of Very Low Air Velocities

    Page(s): 606 - 609
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    A new thermistor anemometer is described for measuring low air velocities of 0–100 cm/sec. A theoretical performance curve (anemometer output vs air velocity) was calculated for the instrument. When compared with the experimental performance data, good correlation existed. Several characteristics of the anemometer were investigated experimentally. The instrument displayed excellent sensitivity and good stability (reproducibility of the calibration curve at a given ambient temperature). The output was not affected by the air flow direction. The anemometer output was affected by changes in ambient temperature, and the use of calibration curves for various ambient temperatures is suggested. View full abstract»

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  • A Precision Variable Luminance Source for Photometric Applications

    Page(s): 610 - 612
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    A variable luminance source having precise photometric characteristics is described. The instrument utilizes the principle of the integrating sphere, efficiently using the flux from a 45 W quartz‐halogen lamp to provide luminances from 1 to 500 fL in a continuous range. The color temperature was kept within ±100 K over the entire luminance range by geometric means without the introduction of aberrative optical elements. Luminance uniformity and stability of ±2.5 and ±0.5%, respectively, were maintained over a 42 mm output aperture for the tungsten spectrum from 0.4 to 1.4 μ. View full abstract»

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  • Resistance of a Silicon Bronze at Low Temperatures

    Page(s): 612 - 613
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    A specially prepared silicon bronze is shown to be quite insensitive to magnetic field and temperature change at liquid helium temperatures. The temperature coefficient of resistance is of the order of a few parts per million per degree over the range 2–10 K and the change in resistance at a flux density of 1 T (104 G) is about 10 ppm. View full abstract»

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  • Polymers at Low Temperatures: Increasing Thermal Diffusivity in Specific Heat Measurements

    Page(s): 614 - 615
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    The thermal diffusivity of samples of powdered high polymers can be increased (at least in the temperature range 1–20 K) by compressing them with copper powder. Hence thermal relaxation times in specific heat measurements can be decreased. The specific heat of the copper is relatively small and is well known. Calorimeter vessels are then unnecessary. View full abstract»

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  • Circuit for Approximate Computation of Reciprocal of Time Delay to Maximum Cross Correlation

    Page(s): 616 - 618
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    A circuit was developed to measure the inverse time delay to maximum cross correlation between two stationary time varying voltages. The first voltage is delayed in a sample‐and‐hold circuit whose sampling frequency is swept. When the delay between the two signals is smaller than a quarter of the period of the fundamental, the sample‐and‐hold voltage is directly multiplied with the downstream voltage. When the delay is greater than a quarter of the period of the fundamental, the sample‐and‐hold signal is multiplied by the sample‐and‐hold value of the second signal, sampled at the same rate, 180° later. The filtered product for both cases has a maximum when the sampling frequency is inversely proportional to twice the delay to maximum cross correlation. View full abstract»

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  • Apparatus to Rotate Samples Rapidly at Temperatures Less than 2 K in High Transverse Magnetic Fields

    Page(s): 618 - 625
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    A system is described that allows rapid rotation of a sample at speeds up to 103 rps at temperatures less than 2 K in large transverse magnetic fields. It uses an He gas turbine with hydrostatic He gas bearings. A very compact, efficient counterflow heat exchanger was developed to cool the bearing and drive gas to 15 K. The system was developed specifically to produce high proton polarizations using the spin refrigerator technique, but is applicable to other experimental situations requiring high speed rotation at low temperatures in large transverse magnetic fields. View full abstract»

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  • An Apparatus for Magnetic Measurements at High Pressure

    Page(s): 626 - 629
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    A nonmagnetic high pressure cell capable of being used for a variety of magnetic measurements to over 100 kilobars is described. A Bridgman anvil type of cell, it has a 3–5 mm3 sample volume and is suitable for both pulsed and wide line nuclear magnetic resonance (NMR) measurements. In addition to a detailed description of the apparatus used for wide line NMR measurements, the use of the high pressure cell for magnetoresistance and susceptibility measurements is described. View full abstract»

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  • A Wien Filter for Use as an Energy Analyzer with an Electron Microscope

    Page(s): 630 - 637
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    An electron optical system is described which is suitable for energy loss analysis in an electron microscope. A focusing spectrometer of the Wien type has been added underneath the column of a Hitachi HU11A electron microscope. After passing through the microscope, the electrons are slowed down before entering the spectrometer and reaccelerated to the detection point. Appropriate control of the electron trajectories into the Wien analyzer is achieved with a quadrupole field lens which makes it possible to use a long entrance slit. The energy resolution of the analyzer is limited by the width of the entrance slit which is adjusted to match the beam spread (1.5 eV). It can be made large (250 μ) compared with that of the Möllenstedt analyzer (5 μ), thereby passing much higher intensity through the analyzer and increasing the system flexibility. View full abstract»

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  • Improved Method of Spinning Rotors to High Speeds at Low Temperature

    Page(s): 637 - 639
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    A technique is described for spinning rotors of almost any size up to rotational speeds limited only by their strength, at liquid helium temperatures. The rotor is spun on the lower end of a long vertical stainless steel hypodermic needle tube shaft which connects to an air turbine drive above the apparatus. Electrical leads from the rotor are brought out through the hollow shaft and liquid mercury contacts. A convenient low noise system of liquid mercury electrical connections is described. View full abstract»

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  • Precision Beam Location

    Page(s): 640 - 643
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    A method for precise positioning of a beam on a given target is described. The technique employs a time dependent bias applied to the relative target beam position and frequency tuned detection of an associated flux that is coherently sensitive to changes in the primary beam. A location reference is determined which is the centroid of the convolution product of the target shape function and the beam profile function. View full abstract»

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  • The Behavior of Type K Thermocouples in Temperature Measurement: The Chromel P‐Alumel Thermocouples

    Page(s): 644 - 653
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    A study has been made on the origin of internal errors of type K and particularly of Chromel P‐Alumel thermocouples. Physical and chemical nonuniformities fixed in the materials and subsequent modifications occurring in the system set a lower limit to the error band within which it is not legitimate to expect any better degree of accuracy. Effects of chemical attack, ordering, and cold work were specially considered. It appears that a kinetic model accounting for time dependence may be envisaged. Some basic recommendations are made for all cases. View full abstract»

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  • A Miniature Turbulence Gauge Utilizing Aerodynamic Lift

    Page(s): 653 - 656
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    An advanced version of the aerofoil probe turbulence gauge is described. The new device uses an axisymmetric lifting body sensor of 2.4 mm diameter coupled directly to a miniature preamplifier unit (6.35 mm diam). The output voltage varies linearly with the v or w component of turbulence. The device has uniform sensitivity and good signal‐to‐noise ratio over a nominal frequency range of 10–10 000 Hz. A discussion of calibration procedures and application considerations is included. View full abstract»

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

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Albert T. Macrander
Argonne National Laboratory