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Review of Scientific Instruments

Issue 4 • Date Apr 1979

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Displaying Results 1 - 25 of 26
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • High‐resolution scanning transmission electron microscope at Johns Hopkins

    Page(s): 403 - 410
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    The scanning transmission electron microscope constructed at Johns Hopkins follows the general layout of the first instrument at the University of Chicago. It is currently operating at 50 kV with a resolution of about 3 Å. Its detector scheme consists of scintillation crystals coupled to photomultipliers in such a way as to eliminate introduction of unnecessary statistical noise. A unique alignment scheme utilizes the spherical aberration of the objective lens. View full abstract»

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  • Construction of a Čerenkov light source

    Page(s): 411 - 417
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    A radiation source has been developed and implemented from Čerenkov emission that is intended to provide an intense continuum from the infrared to 600 Å. Parasitic use of the primary electron beam at the Stanford Linear Accelerator Center (SLAC) together with a novel optical geometry for light collection can give a focused and tunable ultraviolet beam with 104 kW/m2∙sr brightness, 10-2 spectral purity, and with the pulsed, 5 ps time structure of the SLAC electron beam. Measurements of emission characteristics in the visible part of the spectrum correlate closely with the predicted performance. View full abstract»

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  • Simple apparatus for measuring the dynamic shear modulus of cylindrical specimens

    Page(s): 418 - 420
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    An apparatus is decribed which has been used to determine the shear modulus of cylindrical specimens vibrating in the torsional mode. The specimens are maintained in self‐excited vibration by an eddy‐current driver, an eddy‐current pickup, and a feed back circuit consisting of a phase‐locked‐loop and an amplitude control module. The system has a frequency stability of 1 part in 106 for high‐Q materials (a few thousand) in the audio range. In addition, it can automatically track frequency changes of a few percent with negligible error in phase or frequency. View full abstract»

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  • Pulsed blowdown—electron gun facility for low‐temperature and high‐pressure supersonic flow electronic transition lasers

    Page(s): 421 - 424
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    The design of a small compact pulsed blowdown apparatus coupled to a cold cathode electron gun is described. This system allows the excitation of a gas mixture in supersonic flow at temperatures of 80 and 120 K and density of 1 amagat with a maximum electron beam current density of 20 A cm-2 at 300 kV and pulse length of 0.5 μs. With this facility it has been possible, using aerodynamic cooling, to achieve high‐power, long‐pulse ultraviolet laser operation in a high‐pressure active medium on XeF and Ne ii ion transitions. A strong increase in fluorescence intensity was also obtained for numerous atomic lines and molecular bands of interest for the developement of high‐power, high‐efficiency, visible and ultraviolet lasers. View full abstract»

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  • ESR dual sample cavities for Q‐band and for spectrometers with small magnets

    Page(s): 425 - 427
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    Dual sample cavities are described in which the standard sample sees both the primary modulation field and also an opposing secondary modulation field from a very small adjacent compensation coil. Both primary and secondary fields are at the same modulation frequency. The geometry permits solution of dual sample cavity design problems at Q‐band, where the microwave cavity is small relative to the volume of space occupied by the primary modulation field and at X‐band when magnets with a small volume of homogeneous field are employed. View full abstract»

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  • Cylindrical crossed‐coil NMR limb blood flowmeter

    Page(s): 428 - 434
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    A nuclear magnetic resonance (NMR) flowmeter has been developed for noninvasive measurement of upper extremity blood flow in humans. Flow through major arteries and veins is determined by placing the arm into a 12.5‐cm i.d. crossed‐coil detector structure, contained in a 0.075 T (750 G) steady detector field. Venous flow is measured by passage of a demagnetized bolus of blood, generated by periodic application of a radio‐frequency tagger field upstream from the detector. The self tag technique is applied to arterial flow. Detector output is a direct function of the pulsatile component of arterial volume flow, within the range of linear operation. Consideration has been given in flowmeter design to sensitivity, long term stability, and ease of operation. View full abstract»

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  • Explosively triggered gas‐dielectric crowbar switch

    Page(s): 435 - 437
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    A gas‐insulated gap switch with an unusually high standoff‐to‐trigger voltage ratio is described. Designed to standoff 500 kV when pressurized with SF6 at 1.5 MPa (212 psi), the switch was triggered with as little as 19.3 kV across the gap by firing a shaped charge from one electrode toward the opposite electrode. Similar air‐insulated and SF6‐insulated gaps pressurized to 83 kPa (12 psi) and designed to standoff 50 and 150 kV, respectively, were triggered with 15.4 kV across the gap by firing an ordinary RP‐2 detonator from one electrode toward the other. View full abstract»

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  • New difference reflectance methods for study of small interfacial effects

    Page(s): 438 - 441
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    Two sensitive differential optical techniques useful for study of small reflectance or absorptive differences between two interfaces are described. The first scheme employs a mechanically chopped light beam impinging on an arrangement of symmetrical dual cells to allow detection of differential reflectances ΔR/R≪10-3. The second is a polarization‐modulated beam‐split laser version of the same method yielding approximately the same sensitivity. Representative measurements of voltage‐induced reflectance changes at liquid–solid interfaces using these methods are given. View full abstract»

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  • Extension of the application of the shorted quartz gauge

    Page(s): 442 - 444
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    Shorted guard‐ring quartz gauges 12.7 mm in diameter and 3.2 mm thick were shock loaded by AL 6061 and copper impactors to stresses of 42 and 58 kilobars, respectively. Distortion of the current output was observed only at the 58 kilobar stress; at 42 kilobars the current profile conforms closely to the stress profile. Comparison of present data with previous studies demonstrates: (a) The present results lie on a smooth extension of an earlier calibration by Hayes and Gupta. (b) When only the current peak at the shock front is considered, the present data lie close to Graham’s curve for shunted gauges. An example of application of the shorted gauge at 40 kilobars to monitor a stress relaxing profile in LiF is also described. View full abstract»

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  • Programmable digital pulse generator for proton enhanced 13C high resolution NMR in solids

    Page(s): 445 - 449
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    A programmable pulse generator is described for NMR spectrometers. The pulse generator can operate either in a single cycle mode where up to 16 pulses can be given sequentially or, in the double cycle mode, a programmable number (⩽15) of these pulses can be repeated n times (n⩽99) before the rest of the 16 pulses are completed. The length of all these pulses can be programmed, manually or by computer. As an example the programming of the pulse generator for a multiple contact proton enhanced 13C NMR experiment is given. View full abstract»

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  • New beam postion monitor by detecting wall currents

    Page(s): 450 - 453
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    A new type of beam postion monitor has been designed and bench tested. The results agreed well with the expected performance. Tests with the proton beam showed that this monitor was applicable to our accelerator. View full abstract»

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  • Simple method to measure the thermal conductivity of technical superconductors, e.g., NbTi

    Page(s): 454 - 457
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    A technique is described which allows the measurement of the thermal conductivity κ of superconductors below Tc without the use of a thermometer, if Tc is known. The method is particularly adapted to technical superconductors of poor thermal conductivity. It is convenient to use as sample a superconducting wire or band provided with a high conductivity matrix of a normal metal, which has to be removed from the test length. The stabilized ends of the sample are thermally anchored to a heat sink of variable temperature T. A current I flowing through the conductor holds the middle part of the test length in the normal state due to Joule heating. The length of the normal section and hence the voltage appearing on the sample are a functions of I and FκdT. The variation of the temperature of the heat sink then allows the determination of κ (T). Results for two NbTi samples are included. View full abstract»

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  • Rapid investigation of sedimentation phenomena by vibrational force field

    Page(s): 458 - 463
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    A new method for the rapid investigation of sedimentation phenomena of fine particles is developed by using the force due to a vibrational acceleration. The small displacement of the particle with respect to the wall of the container, which is produced by the vibration, is measured by the interference between the light scattered by the particle and that of the cell wall. The interference is detected as a beat note in the scattered‐light intensity, and displayed as a time‐autocorrelation of the photocurrent, the analysis of which gives the sedimentation coefficient and the dispersion. View full abstract»

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  • New magnetic command system for a 200‐kA circuit breaker with 10‐μs current transfer time

    Page(s): 464 - 465
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    We present improvements of the previously described command system of a 200‐kA circuit breaker with 10‐μs current transfer time. It uses the magnetic pressure produced by a high‐current pulse sent through two flat conductors instead of a coaxial circuit. The necessary command current is cut in half and the standoff voltage is higher. View full abstract»

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  • Improved 10B‐loaded liquid scintillator with pulse‐shape discrimination

    Page(s): 466 - 471
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    An improved 10B‐loaded liquid scintillator solution has been developed containing trimethylborate, 1‐methylnaphthalene, and 9,10‐diphenylanthracene. Cells up to 5 cm in diameter by 15.2 cm long have been prepared and tested with 10B‐loadings up to 7.2% by weight (80% trimethylborate). The solution has excellent light output and pulse‐shape discrimination properties and is stable at temperatures as low as -17°C. Neutron efficiency calculations are also presented. View full abstract»

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  • 6Li‐loaded liquid scintillators with pulse shape discrimination

    Page(s): 472 - 477
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    Excellent pulse height and pulse shape discrimination performance has been obtained for liquid scintillators containing as much as 10 wt.% 6Li‐salicylate dissolved in a toluene‐methanol solvent system using naphthalene and 9,10 diphenylanthracene as intermediate and secondary solutes. This solution has improved performance at higher 6Li‐loading than solutions in dioxane‐water solvent systems, and remains stable at temperatures as low as -10°C. Cells as large as 5 cm in diameter and 15.2 deep have been prepared which have a higher light output for slow neutron detection than 10B‐loaded liquids. Neutron efficiency calculations are also presented. View full abstract»

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  • Use of variable pH interface to a mass spectrometer for the measurement of dissolved volatile compounds

    Page(s): 478 - 481
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    A wide variety of dissolved chemicals can be measured continuously with some specificity by directly interfacing a relatively inexpensive mass spectrometer to a solution. Specifically, we describe the construction and initial use of a membrane interace to a mass spectrometer which allows the continuous measurement of the concentration of dissolved volatile compounds in buffered aqueous solution. In addition to volatile compounds that do not dissociate appreciably at pH 7 (e.g., ethanol, ethylene glycol), volatile acids and bases, such as acetic acid or ammonia, can be measured with the interface is operated within the range 1⩽pH⩽12. We also discuss the sensitivity of the system to variations in flow rate and describe a satisfactory method for providing sufficiently constant flow rates. View full abstract»

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  • Pneumatic hydrogen pellet injection system for the ISX tokamak

    Page(s): 482 - 487
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    We describe the design and operation of the solid hydrogen pellet injection system used in plasma refueling experiments on the ISX tokamak. The gun‐type injector operates on the principle of gas dynamic acceleration of cold pellets confined laterally in a tube. The device is cooled by flowing liquid helium refrigerant, and pellets are formed in situ. Room temperature helium gas at moderate pressure is used as the propellant. The prototype device injected single hydrogen pellets into the tokamak discharge at a nominal 330 m/s. The tokamak plasma fuel content was observed to increase by (0.5–1.2) ×1019 particles subsequent to pellet injection. A simple modification to the existing design has extended the performance to 1000 m/s. At higher propellant operating pressures (28 bars), the muzzle velocity is 20% less than predicted by an idealized constant area expansion process. View full abstract»

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  • 100‐MHz noise spectrometer

    Page(s): 488 - 496
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    The design, construction, and performance of a 100‐MHz noise spectrometer are described. Basically a 100‐MHz bridge, this system uses the properties of a double balanced mixer to enable the experimenter to determine spectral densities of fluctuations in the real or imaginary parts of a sample impedance, as well as the real part of the cross‐spectral density. Calibration circuits and techniques are described. The results of measurements on commercial 50‐Ω terminators demonstrate fluctuations of both the real and the imaginary parts of the impedance and partial correlation between them. View full abstract»

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  • Versatile electron spectrometer for surface studies

    Page(s): 497 - 501
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    An electron spectrometer is described which is designed to measure a variety of electron spectra of solid surfaces in ultrahigh vacuum. The instrument is capable of the high‐energy resolution (10–15 meV) required for vibrational inelastic electron scattering from atoms and molecules on surfaces. It has also been designed to carry out angle‐resolved photoemission measurements, Auger electron spectroscopy, and energy‐loss measurements of electronic excitations. The performance of the instrument in these modes of operation is discussed. View full abstract»

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  • Thermal expansion of a fused quartz tube in a dimensional stability test facility

    Page(s): 502 - 506
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    A facility to monitor the dimensional stability of structures of arbitrary size or shape under varying temperature and pressure conditions is described. Real‐time linear displacements are measured with a modified Michelson laser interferometer to a resolution of less than one part in 107 and an accuracy of ∼2 parts in 107 for ∼1 m gauge lengths. Verification of the system accuracy with a quartz tube required considerations of its fabrication and compositional characteristics. View full abstract»

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  • Electronic detector for conducting particles and fibrils

    Page(s): 507 - 508
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    When small airborne conducting particles and fibrils strike a conducting surface with an electric charge distribution on it, they acquire charge and are repelled from the surface. If the conducting surface is connected to a power supply of constant potential, a charging pulse is observed as each particle or fibril makes contact with the surface. A collection of such charging pulses can be processed by a pulse height analyzer to yield information about the size and frequency of conducting airborne particles. View full abstract»

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  • Simple, reliable, and sensitive interferometer for the measurement of the refractive index of liquids as a function of temperature

    Page(s): 509 - 510
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    We describe a very simple and inexpensive interferometer setup which provides high accuracy measurements of the refractive index (n) of liquids with temperature. A standard deviation σ (n) =5.4×10-7 has been observed in isooctane liquid when fitting n to a linear temperature variation. View full abstract»

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  • Image reduction to submicrometer dimensions by asymmetric crystal reflection of x rays

    Page(s): 510 - 512
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    An image‐reduction method utilizing asymmetric Bragg reflection is demonstrated by 9.5‐fold and 22.6‐fold one‐dimensional reductions of a 30 cell/mm gold mesh having a web width of 8μm. Applicability of the method to microphotolithography is suggested. 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