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Review of Scientific Instruments

Issue 8 • Date Aug 1953

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Displaying Results 1 - 25 of 28
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Microwave Frequency Standard

    Page(s): 565 - 568
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    Here described is a high stability UHF source which is used as a microwave frequency standard. Frequency measurement requires the use of a calibrated communication receiver to measure the difference between a known harmonic of the UHF source and the unknown microwave frequency. Frequencies as high as 27 kmc have been measured and the frequency stability is approximately 1 part per million. View full abstract»

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  • The Measurement of Distortion in Nuclear Emulsions

    Page(s): 569 - 572
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    A quantitative study of distortion in nuclear emulsions, based on a method of measuring and calculating distortion to known accuracy, has been made. The method has been applied to a study of variations in fixing washing and drying procedures. Distortion reduction up to one‐half was found to occur with the use of a concentrated sodium sulfate hypo solution. The reduction of vertical shrinkage and the use of thicker emulsions also appear to reduce distortion. The method of distortion measurement is accurate to better than 10 percent using sea‐level cosmic‐ray background tracks as a distortion indicator. View full abstract»

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  • Double Focusing of Charged Particles by a System of Two Magnets with Nonuniform Fields

    Page(s): 573 - 585
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    Equations are obtained for the focusing by a system of two magnets with nonuniform fields such that n≫0 in the first magnet and n≪0 in the second. For each magnet a lens equation is set up, and then the system of the two magnets is itself treated as a thick lens. It is shown that for very large n, there is in general one object distance for which double focusing takes place. The theory is also applied to deflecting systems with moderate values of n, and it is shown that the entrance and exit angles can be reduced to values of the order of 20° even for small deflections (20°) of the charged particle. View full abstract»

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  • An Aerosol Analyzer

    Page(s): 586 - 588
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    Described is a simple device for measuring the total mass and total charge of a powder cloud. The instrument consists of a sensitive electrometer circuit and a metallic collection chamber. The powder is collected on a filter paper sealed between two aluminum tubes which, if their length is three times greater than their diameter, provides sufficient shielding of the charge collected on the filter paper to justify assumption of an ``Ice Pail.'' The shielding error is less than 0.5 percent. A null‐reading circuit is used with a Cenco electrometer. The necessary counter voltage for the null‐reading circuit is supplied by a potentiometer circuit, and a vacuum‐tube voltmeter is used to measure the voltage. Because it is desired to obtain explicitly the mass and charge of a given cloud of particles rather than the ratio of charge to mass, enough mass must be collected for weighing and, in addition, the total charge measured. This is to be accomplished without disturbing appreciably the normal flow rate of powder from the aerosol generator. View full abstract»

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  • The Theory of the Fixed Frequency Cyclotron

    Page(s): 589 - 601
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    The theory of the fixed frequency cyclotron is developed and illustrated at each step with numerical results for an example. The conditions for ion transmission with respect to horizontal motion are derived, and it is shown that they are satisfied by all ions in most cyclotrons. A more correct and more complete focusing formula than that found in the literature is derived and used to integrate the vertical motion. It is characterized by a region in which the net force is defocusing causing the ions to diverge exponentially from the median plane. The theory is applied to find the maximum energy attainable as a function of dee voltage and magnetic field fall‐off. The problem of orbital precession is treated quite generally, and equations for calculating the center of curvature as a function of time are derived. Some considerations in the magnetic field design are presented. A proof is given that ions experience strong radial grouping. The effect of ion source ``feelers'' is discussed. View full abstract»

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  • Effect of Space Charge on Saturation Properties of Ionization Chambers

    Page(s): 602 - 605
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    Experiments on cylindrical ionization chambers operating at high‐current densities showed that more voltage was required to produce saturation when the central electrode was negative than when it was positive with respect to the outer cylinder. An analysis is made which indicates this phenomenon might be explained by the positive ion space charge. Under the condition of uniform ionization density within the chamber, a relation is developed for the ratio of voltages required to overcome the space charge for the two collection polarities. Also, approximate analyses are made for the cases of the ionizing particles originating at the surface of either electrode. There is only rough agreement between the calculations and experimental data. View full abstract»

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  • A High‐Intensity Pulsed Ion Source

    Page(s): 606 - 610
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    A pulsed cold cathode ion source, giving peak proton currents in excess of one milliampere and average currents up to 50 microamperes, is described. The source is based on the Penning discharge using axial extraction of the ions. Some discussion of the discharge mechanism and the role of the cathode material is included. Installation and operation of this source in the Berkeley 4‐mv Van de Graaff and its performance in that machine is discussed. View full abstract»

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  • Measurements of Scintillation Lifetimes

    Page(s): 611 - 616
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    A pulsed x‐ray method for measuring the decay time of luminescence of organic scintillators is described. The design of the x‐ray tube and the arrangement of the accompanying electrical apparatus is outlined. Particular care was taken to minimize the time dispersion effect of the apparatus and to increase the pulse size of the scintillation in order that statistical fluctuations would be minimized. The luminescence decay curves for anthracene, stilbene, and diphenylacetylene scintillators are shown. View full abstract»

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  • A Pulsed Mass Spectrometer with Time Dispersion

    Page(s): 616 - 617
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    An improved design of a pulsed mass spectrometer using linear time of flight analysis has been completed. A peak width of two mass units at mass 40 has been achieved as well as a linear mass scale. View full abstract»

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  • A Fast Coincidence‐Anticoincidence Analyzer

    Page(s): 618 - 620
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    A modified Rossi circuit has been extended to a form in which it allows the recording of as many as six coincidence and four anticoincidence pulses with a resolving time of 3×10-9 second. All input pulses are negative and of any amplitude ≫ 3 volts. A complete schematic is given of the circuit which has operated for six months without possibility of adjustment. View full abstract»

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  • Molecular Models of Amino Acids, Peptides, and Proteins

    Page(s): 621 - 627
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    A set of accurate scale models has been developed for use in studies of the structures of amino acids, peptides, and proteins. Models representing atoms or groups of atoms built from hard wood to the scale 1 in.=1A are connected by a clamping device which maintains desired molecular configurations. These accurate models have been used as substitutes for calculation in investigations of the probable configuration of the polypeptide chain in proteins. Analogous models constructed of rubber‐like plastic to the scale 1 in.=2A and connected by snap fasteners are designed for qualitative studies of protein structure. View full abstract»

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  • The Adaptation of the Norelco High‐Angle Spectrometer to the Measurement of the X‐Ray Diffraction of Fibers

    Page(s): 627 - 631
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    The use of the North American Philips spectrometer for the radial and azimuthal scanning of the transmitted x‐ray diffraction of rayon tire yarns involved a change in the slit system from convergent to divergent, design of a rotating sample holder, a reproducible sample preparation and positioning, and calibration and control checks which guarantee that the x‐ray intensity remain constant to ±2 percent as automatically recorded by the rate meter. Typical data are presented and compared with data obtained photographically. View full abstract»

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  • Circuit for a Radio‐Frequency Spectrometer

    Page(s): 632 - 634
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    A circuit is described for amplitude stabilization of a regenerative detector for use in nuclear magnetic resonance experiments. A remotely located two‐stage dc amplifier converts variations in oscillator grid leak voltage into compensating changes in plate supply potential. The stabilizer circuit adds little stray capacity and does not appreciably affect the oscillator design. The level of oscillation is adjustable from zero to approximately 0.3 volt peak rf signal at the detector grid. Once set, it remains essentially constant over the tuning range (4.8 to 6.3 Mc/sec). A noise figure of 2 or better is obtained. Circuit parameters for the regenerative detector and the stabilizer are given. View full abstract»

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  • Design and Performance of a Radio‐Frequency Ion Source

    Page(s): 635 - 638
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    Tests were made on a 27‐megacycle, inductively coupled, radio‐frequency ion source standardized in design for use at the Los Alamos Scientific Laboratory. Total deuteron beam current and probe current characteristics were found, in tests made before installation, as a function of gas pressure of the discharge, rf power input, probe voltage, and extraction system geometry to determine the best values of these variables to use. These characteristics showed a maximum total beam current of 600 μa to be obtained with roughly 200 watts of rf power input. Tests made after installation in an accelerator gave 92 percent monatomic deuteron beams of up to 80 percent the strength found under similar conditions in the tests made before installation. A platinum‐coated envelope gave a triatomic beam of about one‐eighth the strength of the monatomic beam obtained with an uncoated envelope. The source has been used at 150‐psi external pressure in a Van de Graaff tank. View full abstract»

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  • A Regulator for a 20‐ to 250‐Kilovolt Cockcroft‐Walton Accelerator

    Page(s): 638 - 640
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    A regulator has been built to hold the accelerating potential of a Cockcroft‐Walton accelerator to within 0.015 percent of any preset potential in the range of 20–250 kilovolts. The regulator is a degenerative type where the error signal is amplified by a galvanometer‐phototube dc amplifier system which controls a variable impedance transformer in series with the high‐voltage power transformer primary. The regulator is very simple to put into operation. Its action is independent of the potential desired; therefore the range of operation could easily be extended. View full abstract»

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  • Recent Developments in the Production of Halogen‐Quenched Geiger‐Müller Counting Tubes

    Page(s): 641 - 643
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    Geiger‐Müller tubes have been constructed which use visibly transparent nonmetallic electrically conducting films as cathodes. These tubes have the following advantages: (1) a long plateau; (2) no photosensitivity; (3) an almost indefinite operating life; (4) immunity from damage arising from heavy discharges; (5) straightforward filling procedure devoid of any ``passivising'' or saturating techniques; (6) good response to ionizing radiation throughout the length of the counter; (7) freedom from use of critical materials such as copper or stainless steel No. 446 which require special cleaning and polishing procedures. View full abstract»

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  • Apparatus for Nuclear Magnetic Resonance

    Page(s): 644 - 652
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    Apparatus and procedures are described for the high‐resolution measurement of resonance shifts and for the observation of broad line shapes. Included are a discussion of magnet design and a summary of empirical results obtained in the construction and field homogenization of two large permanent magnets. Narrow, complex resonance lines, with components separated by as little as a milligauss, are resolved by a combination of homogeneous applied magnetic field, small samples, and slow‐sweep field modulation. Broad absorption line shapes are plotted at fixed frequency by a system incorporating a regenerative oscillator, a narrow band amplifier, a recording potentiometer, and an electronic control for varying the applied magnetic field linearly in time. A simple cryostat provides stable temperatures from 85° to 500°K. In the case of samples with short spin‐lattice relaxation times, such as the metals, improved signal‐to‐noise ratios are obtained by adjusting the oscillator to super‐regenerative operation and observing the frequency modulation associated with the dispersive component of the resonance. View full abstract»

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  • Apparatus for Crystal Pulling in Vacuum Using a Graphite Resistance Furnace

    Page(s): 652 - 655
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    A vacuum furnace is described for use in pulling large single crystals of germanium from a melt. The heating element in this furnace is a resistance heated split graphite cylinder. View full abstract»

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  • A Fast Neutron Coincidence Spectrometer

    Page(s): 656 - 660
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    A fast neutron coincidence spectrometer of high efficiency has been constructed applicable to the approximate energy range of 1 Mev to 20 Mev. Design considerations and the working model are discussed. To illustrate the operation of such an instrument, the line spectra of the gamma‐rays from Co60 and of 3.3‐ Mev D‐D Neutrons are presented. Discrimination between gamma‐rays and neutrons is obtained by utilizing the difference in the time of flight of the two particles. In conclusion possible improvements are suggested. View full abstract»

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  • An Inexpensive Recording Differential Manometer Suitable for Reaction Kinetics Measurements

    Page(s): 661 - 664
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    A differential manometer which photographically records pressure as a function of time is described. A fluorescent lamp in conjunction with a simple louver system provides a sharp image of the interface between indicator liquid and gas. The instrument can be used to study reactions whose half‐lives range from a few seconds to several hours. View full abstract»

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  • On Energy Resolution with Proportional Counters

    Page(s): 664 - 668
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    The shape of a proportional counter pulse due to an extended track of ionization is determined, before and after passing through a linear pulse amplifier, for various values of track extension and positive ion collection time. It is found that the maximum height of the amplifier output pulse is essentially independent of the length and orientation of the track in the counter, provided the time of collection of the outermost electrons is not longer than the amplifier time constant. View full abstract»

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  • Construction of a Universal Electron Diffraction Microscope and its Optical Features

    Page(s): 669 - 675
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    A universal electron diffraction microscope, as we call it, consists of three stage electron lens and two specimen chambers and functions both as an electron microscope and as an electron diffraction unit. This instrument can be used in the following seven ways: (1) Electron microscope; range of magnification between 800 and 20 000 times can be covered continuously. (2) Electron microdiffraction unit; electron diffraction pattern characteristic of any small area of a specimen under microscopic observation can be revealed by a switch. (3) Dark‐field electron microscopic image. (4) High‐resolution electron diffraction unit. (5) Effective camera length of electron diffraction is variable from 0 to 250 cm. (6) Shadow micrographs of the specimen used in (4) can be directly obtained. (7) Shadow microdiffraction (probe diffraction); dark‐field microscopic image appears in each diffraction spot. The specimen in the second chamber can be heated at any temperature up to about 800°C and on which two kinds of substances can be evaporated, and this evaporation gun can also be used for charge neutralization. View full abstract»

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  • A Vacuum Anemometer

    Page(s): 676 - 682
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    A vacuum anemometer is described for indicating or measuring the streaming of gases and vapors in vacuum. The device is particularly useful for measuring the projective vapor emission from liquid surfaces and the flow of gas through pipes, for instance, between a vessel and a pump. The anemometer consists of a propeller mounted on a shaft supported by jeweled bearings, the propeller being driven by the stream of gas. To measure the speed of the propeller, a small ac generator is incorporated in the device, and the output is indicated by an electronic voltmeter. Under conditions of heavy electrical braking, it is shown that the speed is directly proportional to the pressure, independent of the nature of the gas and of its molecular weight. The instrument is rugged, insensitive to vibration, stable, and readily calibrated. It has low inertia and responds rapidly to a change in the momentum of the stream of incident molecules. Sources of error are discussed and typical performance data are reported. View full abstract»

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  • A Sensitive Respirometer for the Measurement of Rapid Changes in Metabolism of Oxygen

    Page(s): 683 - 695
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    A respirometer used to study the oxygen metabolism of peripheral nerve is described. The theory of its operation and its operating characteristics are given. The respirometer consists essentially of the nerve trunk itself, placed symmetrically across the tip of a polarized platinum microelectrode which is flush with the floor of the chamber. The sides of the nerve are exposed to moist gas of known oxygen content; the top surface of the nerve is covered. The current to the platinum electrode measures the concentration of oxygen in the nerve at the electrode tip. In the steady state the oxygen concentration near the electrode is determined by: (1) the configuration of the system, (2) the oxygen content of the gas phase, (3) the diffusion coefficient of oxygen in the tissue, and (4) the rate of oxygen consumption by the tissue. Starting from the steady state, any change in rate of oxygen uptake may be followed directly during the first 45 to 60 seconds of such a change; during this time the change is equal to the negative of the rate of change of oxygen concentration at the electrode tip. Slow, prolonged changes in respiratory rate may be followed, within limitations determined by the diffusion characteristics of the system and by slow drift in electrode calibration. It is estimated that changes in rate of oxygen uptake as small as 0.3 mm3 O2/cc hr (0.6 percent of the rate of uptake by resting frog nerve) can be reproducibly detected. 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