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Review of Scientific Instruments

Issue 6 • Date Jun 1964

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Displaying Results 1 - 25 of 44
  • Orbitron Ionization Gauge

    Page(s): 661 - 665
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    An ion gauge with high ionization efficiency and low input power is described. In this gauge, called the orbitron, electrons are injected by a small tungsten filament into the electrostatic field between two concentric cylinders, with energies and angular momenta such that a relatively long mean free path is achieved. Only 4 μA electron current is needed to produce the same ion current obtained from 8 mA emission in a conventional Bayard‐Alpert gauge. X‐ray and photocurrents are held to low values by locating the ion collector remotely from the main source of light and x rays. The ion current is linear with pressure below 1×10-5 Torr and has been tested down to 5×10-11 Torr. The lower pressure limit has not yet been determined. View full abstract»

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  • Vibrating Membrane Electrometer with High Conversion Gain

    Page(s): 666 - 668
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    A vibrating membrane transducer is used as the sensing element for a high sensitivity electrometer. The method of operation provides an increased conversion gain by using a special circuit in which the electrometer current controls the displacement amplitude of a membrane forced to vibrate at its resonant frequency. The experimental transducer produces an alternating output voltage, is small and rugged, and has a conversion gain three orders of magnitude greater than electrometer transducers in current use. View full abstract»

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  • Plastic Scintillator Response to 1–10 keV Photons

    Page(s): 669 - 672
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    The linearity and absolute detection efficiency of several different plastic scintillator‐phototube combinations have been determined for photon energies between 1 and 10 keV. Fluorescent x‐ray techniques were used to provide monochromatic photon beams which were allowed to impinge on the scintillator or, alternately, on a proportional counter monitor. Indications were obtained of nonlinear photoelectron/photon response for photons having energies less than a few keV. Clearly nonlinear behavior was obtained for conversion efficiencies expressed as photoelectrons/keV of photon energy absorbed. View full abstract»

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  • Nanosecond Pulsing for Van de Graaff Accelerators

    Page(s): 672 - 679
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    A pulsed ion source capable of delivering 10‐mA proton bursts with durations of approximately 1 nsec is described. Critical design constraints are discussed and used to illustrate the general procedure for meeting various experimental requirements. The system consists of a Duo‐Plasmatron ion source, a lens‐chopper combination, and a klystron buncher which uses the entire accelerator as a drift path to produce bunched ion bursts at the target. The equipment has been fitted into the terminal of the ORNL 3‐MV Van de Graaff accelerator. Since no accessory bunching magnets are used, ion bursts can be delivered to many different target stations. An external diverter system is used to vary the repetition rate from 106 sec-1 down to 3×104 sec-1. View full abstract»

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  • Probes for High Temperature Nuclear Magnetic Resonance

    Page(s): 680 - 682
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    Two designs are described for single coil NMR probes and furnaces with the Varian wide line spectrometer (V‐4210) to temperatures up to 1000°C. Their application to molten salt systems is outlined. View full abstract»

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  • ``On‐Line'' Operation of a Digital Computer in Nuclear Physics Experiments

    Page(s): 682 - 690
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    The instrumentation necessary for coupling a commercial digital computer to several nuclear physics experiments in an ``on-line'' operation has been designed and constructed. Multiparameter experiments utilizing the ``on-line'' operation include fission fragment mass ratio measurements, neutron time-of-flight measurements, and the measurement of prompt ν¯ for fissionable materials. View full abstract»

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  • Cesium Vapor Dispenser

    Page(s): 691 - 693
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    A simple dispenser of cesium vapor was investigated to determine its utility as a stable and controllable source of cesium vapor for long life applications. The dispenser is basically a container filled with a mixture of cesium chromate and silicon powder. The powder reacts when it is heated to temperatures near 1000°K, and it releases a cesium vapor stream through a slit. The cesium vapor release rate was found to be stable and controllable by adjustments of the powder temperature. A constant and stable cesium flux could, therefore, be maintained over periods of many hours. At temperatures below 800°K the powder mixture is inert. This permits conventional bake‐out of the device and provides a convenient source of cesium vapor in demountable vacuum systems. These dispensers have been used successfully in experimental energy converters, cesiated cathode tubes, and in demountable vacuum systems. View full abstract»

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  • Gamma‐Ray Detection Efficiency and Image Resolution in Sodium Iodide

    Page(s): 693 - 697
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    Photoelectric, Compton, and photopeak efficiencies have been calculated at several gamma‐ray energies for large flat sodium iodide crystals in which the thickness ranges from ⅛-2 in. Also, the loss of position resolution by gamma‐ray scattering within the scintillator is calculated, since this is of interest in the design of gamma‐ray imaging devices like the scintillation camera. An examination of the data shows the advantage of using low energy gamma rays for imaging whenever possible. They are efficiently detected by solid sodium iodide scintillators ½ in. thick, and there is little loss of resolution due to scattering of gamma rays in the scintillator. In the higher energy range, a choice must be made between a thin scintillator with its relatively good position resolution and low detection efficiency, or a thick crystal with higher detection efficiency and less satisfactory resolution. View full abstract»

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  • Wideband Feedback Coherence Control for Superregenerative NQR Spectrometers

    Page(s): 698 - 700
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    A description is given of a wideband feedback coherence control system for superregenerative NQR spectrometers. By making use of a servo motor to adjust the oscillator grid bias, increases in rf searching band are possible. As an example, a bandwidth of 30 Mc around a center frequency of 70 Mc has been obtained. The sensitivity of the circuit to nuclear quadrupole resonance signals is high. The spectrometer will operate unattended. View full abstract»

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  • Errors in Noise Measurements due to the Finite Amplitude Range of the Measuring Instrument

    Page(s): 701 - 703
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    Systematic errors are introduced when amplitude measurements of Gaussian random noise are made with practical instruments having finite amplitude ranges. Graphs are presented which should assist in designing experiments to minimize these errors and in correcting existing data. View full abstract»

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  • Vibration Method for the Elastic Constants of Small Plates

    Page(s): 703 - 707
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    A method is described in which a clamped mode of vibration is used in order that the driving force may exceed the weight of the specimen. A supported cantilever plate is vibrated in flexural and torsional modes by driving the support. An approximate solution of the vibration equation is used to calculate the elastic constants from the resonant frequencies. The solution is expressed in terms of the ratio of the resonant frequency of the unknown specimen to that of a standard of the same length and width, to reduce the precision required in specification of the support location. This method was applied in a radiation effects study to measure the Young's moduli of small ceramic plates within 3–5%. The accuracy was limited in this instance by the dimensional tolerances of the specimens. View full abstract»

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  • Gamma‐Ray Pair Spectrometry from 20–650 MeV

    Page(s): 708 - 712
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    Two pair spectrometers have been developed to measure gamma‐ray spectra over a range from 20 to 650 MeV with good resolution. One is a conventional 180° spectrometer to measure the lower energies; the other, for high energies, utilizes a circular geometry. An expression for the absolute efficiency is given in terms of the geometry, magnetic field, and pair‐production cross section. The effects of geometry, electron scattering, and radiation straggling on the efficiency and resolution function are considered. All these factors are then used to provide the proper normalization for the experimental spectra over the range of energies measured. The counting data are stored in a magnetic‐core device, then read out on punched cards. A computer program analyzes the data and makes all the necessary corrections and subtractions. These spectrometers have been used in experiments with neutral pions at cyclotron energies. View full abstract»

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  • High Pressure Polymorphic Transitions Studied by Audio‐ and Radio‐Frequency Techniques

    Page(s): 713 - 719
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    Volume and resistivity changes associated with polymorphic transitions in solids under pressure have been studied by an ac inductive method. A small coil is wound over a core of the sample, and the electrical impedance of the coil determined as a function of pressure to 65 kbar. The coil method was demonstrated in three electrically different operating regions: large skin depth, small skin depth, and an intermediate case. With large skin depth, the inductance of the coil reflects the volume of the sample core. With small skin depth, the reactance and resistance of the coil represent a mixture of volume and resistivity information, but the data may be easily analyzed to yield resistivity alone. In the intermediate case, volume and resistivity are separately displayed by the inductance and resistance, respectively. The coil method offers the advantage that volumetric transitions may be studied remotely, with no moving mechanical indicators. The sensitivity to volume change was demonstrated to be at least 0.1%. View full abstract»

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  • Charge Analyzer for Aerosols and Sprays

    Page(s): 719 - 723
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    A charge analyzer is described that permits the rapid and convenient charge analysis of aerosols and sprays emerging from a nozzle at a high flow velocity. The charged particles are deposited on two collector electrodes. The rate of charge deposition is measured by means of a recording voltmeter, one for each electrode. The amount of material deposited is determined by weighing on a microbalance. Measurements have been conducted with several materials at flow rates between 1.5 and 15 m/sec. Such data are presented. View full abstract»

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  • Zone‐Melting Apparatus for Alkali Metal Cyanides and Alkali Metal Halides

    Page(s): 724 - 727
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    A zone‐melting apparatus is described that can be largely assembled from commercially available components. Details of a technique are given for zone refining alkali metal cyanides and halides in reinforced, flexible metal boats. View full abstract»

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  • Thermal Stability Apparatus for Liquid Propellants

    Page(s): 727 - 728
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    A thermal stability test apparatus for liquid propellants is described which consists of a closed chamber that can be maintained at fixed elevated temperatures. The sample can be rapidly pumped directly into the chamber by means of a remotely operated, syringe‐type pump. A check valve, incorporated into the pump, sealed off the bomb after the liquid was injected. Time from injection to ignition can be recorded. The method offers the advantage that no container or capsule intervenes between the heating medium and the sample, and there are no temperature lags due to the intermediate wall. View full abstract»

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  • Device for the Precise Measurement of Small Temperature Changes

    Page(s): 729 - 732
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    A device capable of measuring temperature with a precision corresponding to a standard deviation of about 14 microdegrees at room temperature has been designed and constructed. The device employs a thermistor as the temperature‐sensing element in an ac bridge. The bridge imbalance, after being amplified, is detected by two phase‐sensitive detectors phase‐shifted 90° with respect to each other to insure that both the resistive and reactive components of the bridge elements are balanced. View full abstract»

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  • Fast‐Acting Superconducting Power Switches

    Page(s): 733 - 737
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    Superconducting switches operating on the basis of superconducting‐to‐normal transitions are considered as a means of initiating high power pulsed discharges from inductive energy storage systems. An analysis of transition times, power losses, and design techniques is presented. Thermally and magnetically activated switches, consisting of long, noninductively wound 0.005‐in. Nb‐25% Zr wires, with normal resistances in the kilohm region, have been tested. A linear representation of the reappearance of resistance during a superconducting‐to‐normal transition yielded values up to 105 Ω/sec. A mathematical analysis, which is in good agreement with experimental results, is given. Factors influencing the rate of increase of resistance are reviewed. View full abstract»

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  • Monitoring the Magnetostriction of Thin Films During Vacuum Deposition

    Page(s): 738 - 741
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    A device has been constructed which monitors the magnetostriction of magnetic films prepared by vacuum deposition techniques. The substrate upon which the film is deposited is stressed mechanically during deposition, thereby applying alternate tensile and compressive states of strain to the depositing film. A localized alternating magnetic field is employed as an anisotropy orienting field and is used also to switch the state of magnetization of the film. The substrate is strained at a low repetition rate, and the depositing film is switched magnetically at a high rate. The periodic stress application to the film and the associated strain‐induced anisotropy modulate the flux reversal output; the resulting signal is detected by a pickup coil. The phase and amplitude of the modulated signal are a function of the magnetostriction and the corresponding film composition. The monitor is mounted in the vapor path so that a representative film element is deposited on the stressed substrate. Zero magnetostriction of the sample, as determined by the monitor, has been found to correspond to zero magnetostriction of arrays of film elements deposited at the same time. The monitor makes possible automatic control of magnetostriction through control of source composition. View full abstract»

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  • System for Measuring the Dynamic Properties of Materials

    Page(s): 742 - 746
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    A system is described which facilitates a detailed study of the response of materials to shock loading under conditions of uniaxial strain. The uniaxial strain loading is produced by a flat projectile plate driven into a target plate by a gas gun. The resulting motion of the free surface of the target plate is monitored by the shorting of a resistance wire which is inclined at a slight angle to the free surface. An accurate time base relates the free surface data to the time of impact. The measured free surface motion may be used to determine the dynamic stress‐strain behavior of the material. View full abstract»

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  • Preparation of CrBr3 Samples

    Page(s): 747 - 748
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    It has been difficult to shape the various samples needed for ferromagnetic resonance, optical, and microwave optical experiments on chromium tribromide. These difficulties have been largely overcome by a technique in which the crystals, rigidly immobilized, are sheared over an edge while immersed in liquid nitrogen. View full abstract»

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  • Low Cost Digital Tape Store

    Page(s): 751 - 752
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    First Page of the Article
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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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Meet Our Editors

Editor
Albert T. Macrander
Argonne National Laboratory