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Review of Scientific Instruments

Issue 5 • Date May 1958

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Displaying Results 1 - 25 of 36
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Sensitive, Quantitative Recording X‐Ray Spectrometer

    Page(s): 343 - 348
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    A spectrometer has been developed with the object of achieving a high diffraction efficiency, low background, and stability and convenience in operation. A mechanism is used to position the detector and crystal in relation to the sample, for determining extended spectra by Johann's and Cauchois' methods. Sample‐chambers with radiation shielding walls are used, and the outlet for fluorescent radiation is designed for reducing background. Microsamples can be used to simplify the evaluation of quantitative results. A vacuum‐chamber has been designed for further reducing background. 4×7 cm crystal lamellae on glass supports are prepared from blocks of NaCl or LiF and bent cylindrically for line focusing, or double‐curved for point‐focusing to increase the intensity at particular wavelengths, the focusing always being aberration‐free. The equipment has been calibrated for microquantitative determination of 30 elements, and an absolute sensitivity of 2×10-10 g has been achieved for the elements CoZn. View full abstract»

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  • Temperature‐Regulated Bismuth Resistor for Magnetic‐Field Measurements

    Page(s): 349 - 354
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    The magnetoresistance effect of the metal bismuth has been used in measuring magnetic induction for many years. This report describes significant features of the electrical and mechanical design of an electrically temperature‐regulated resistor assembly and associated equipment. Commercial ductile bismuth wire was successfully used in a small probe. Useful resolution of 2 gauss in fields above 5000 gauss was readily attained. Limitations and advantages of bismuth resistors as devices for measuring magnetic induction are discussed briefly. Some data from the use of the first units are presented. View full abstract»

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  • Electronic Integrator with Immediate Digital Output

    Page(s): 355 - 359
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    A method is presented for instantaneously obtaining a numerical value proportional to the area of a recurring voltage transient. The underlying principle is the summation of pulses from a generator whose repetition rate is a linear function of the instantaneous input voltage. The technique allows accurate gating to reduce the effects of unwanted signal and noise and has a high order of stability and linearity. The particular device actually constructed and tested was designed to measure the area of the roughly triangular voltage change, about 1 msec in duration, produced by ventral root nerve fibers activated in a monosynaptic reflex. View full abstract»

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  • Photoelectric Flow Birefringence Instrument of High Sensitivity

    Page(s): 360 - 367
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    We have modified a conventional concentric‐cylinder flow birefringence instrument (built by the Rao Instrument Company) by adding a photocell and a rotating disk that scans the annulus with a moving spot of light. In this way the optical intensity pattern formed in the image of the annulus by the combination of polarizer, analyzer, and quarter‐wave plate is converted into an electrical wave which is then analyzed by an electronic device. Full advantage can be taken of the increased sensitivity to birefringence caused by the presence of the quarter‐wave plate, since the presence of a bright background, so disturbing to the eye, is not important to the photocell. In effect, the system is converted to a linear dependence on the magnitude of the birefringence, instead of the quadratic one found in the conventional method of observation. The sensitivity is in fact increased by about a factor of ten over the same instrument used in the conventional way, and at the same time the measurements are made independent of the visual judgment of the experimenter. The linearity of the system also has considerable advantages when extraneous sources of birefringence are present, as is commonly the case. View full abstract»

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  • Electronic Ultra‐High Vacuum Pump

    Page(s): 367 - 370
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    An ultra‐high vacuum pump has been developed based on the combined effects of ionization, excitation and sputtering. A cold‐cathode discharge in magnetic field is employed with no hot filaments nor moving parts. The ultimate vacuum attainable is not yet known but is probably below 2×10-10 mm Hg. A pumping speed of about 10 liters/sec for air has been recorded at 1×10-7 mm Hg. The pump replaces liquid nitrogen‐trapped oil diffusion pumps for pumping microwave tubes. View full abstract»

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  • Low‐Noise 30‐Mc Amplifier

    Page(s): 371 - 374
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    A low‐noise 30‐Mc amplifier with Western Electric Type 416B triodes used in a cascode circuit is described. The theoretical noise figure of the amplifier, with the optimum value of source resistance, is 1.06 or 0.26 db. The amplifier is being used to study noise in semiconductors. View full abstract»

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  • Production of Beams of Polarized Protons by the Acceleration of Protons Derived from Polarized Hydrogen Molecules

    Page(s): 374 - 376
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    A conventional Stern‐Gerlach separation of hydrogen molecules is proposed for the supplying of a radio‐frequency or PIG ion source of standard type to produce microampere beams of polarized protons for acceleration in electrostatic accelerators, cyclotrons, etc. The long nuclear relaxation time of molecular hydrogen gas allows the accumulation of polarized protons (as molecules) for the production of microampere average beams by means of a pulsed ion source. The polarized protons after acceleration have the energy‐ and angular‐spread characteristic of the machine with which they were accelerated. There is no apparent reason why polarized H- may not be produced in the same strong‐field rf ion source, accelerated in a weak field to preserve polarization and stripped in a tandem machine, all without significant depolarization. View full abstract»

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  • Rocking‐Bomb Calorimeter for Measuring Heats of Solution

    Page(s): 377 - 380
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    A calorimeter designed for measuring the heats of rapid reactions such as dissolution and hydrolysis near room temperature is described. The instrument consists of a sealed copper bomb suspended in an evacuated submarine immersed in a thermostat; stirring is accomplished by rocking the assembly through an arc of 150°. Measurements of the heat of solution of potassium chloride in water at 25.00°C have been performed. View full abstract»

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  • Easily Mounted Aluminum Oxide Foils for Windows and Backings

    Page(s): 380 - 382
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    The well‐known difficulties with preparation, handling, and mounting of thin foils are avoided by the use of aluminum oxide foils (25 to 250 μg/cm2, or 700 to 7000 A thickness) which are grown on a solid piece of mechanically shaped aluminum that serves also as the necessary robust frame. These foils have excellent properties for an application in the spectroscopy of particle and quantum radiation. A simple method for the mechanical and chemical preparation will be described. The foils are gas tight, smooth, and withstand a considerable pressure. A formula describes the relation between breaking pressure, diameter, and thickness for circular shaped foils. View full abstract»

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  • Fast and Sensitive Magnetic Susceptometer for the Study of Rapid Biochemical Reactions

    Page(s): 383 - 391
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    A Rankine balance type magnetic susceptometer of much greater sensitivity than previously obtained and combined for the first time with a flow system for the study of chemical reactions is described. The instrument can detect in one measurement a change in volume magnetic susceptibility of 5×10-12 emu. The response time is adjustable down to a fraction of a second by means of an electronic servo system. The time resolution of the flow system is presently limited by the flushing time of the cell to five seconds. A time resolution of hundredths of a second is feasible, as is the detection, in one measurement taking a second, of a change of 1.5×10-12 emu corresponding to the rms Brownian force arising from air resistance to the motion of the magnet. View full abstract»

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  • Improved Instrument for the Measurement of Linear Pyrolysis Rates of Solids

    Page(s): 392 - 395
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    An improved instrument has been designed and constructed for the measurement of the linear decomposition and sublimation rates of solid substances. This instrument, which is provided with automatic recording devices, eliminates many of the shortcomings of the earlier prototypes and makes possible the determination of linear rates with a precision of 1%. Important new features include (1) an integral heating element and thermocouple assembly; (2) stainless‐steel and Plexiglas construction throughout; (3) heavy, solid‐copper electrical‐conductor supports for the heating element; and (4) a precision position‐sensing potentiometer. The use of cut strands of Plexiglas 55 is recommended for periodic standardization and calibration of the instrument. View full abstract»

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  • Method of Measuring Sound Velocity Amplitude in Tubes over the Audio and near Ultrasonic Range

    Page(s): 396 - 398
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    A method of measuring the velocity amplitude of sound waves propagated in hollow tubes is described. A conducting quartz fiber is stretched across a cross section of the tube where the latter is pervaded by the magnetic field of a permanent magnet. The potential difference across the oscillating fiber is recorded on an oscilloscope. Velocity amplitudes have been measured for frequencies up to about 20 000 cps. An approximate relation is derived for the velocity amplitude as a function of the generated potential. It has been found that the method is much freer from disturbances over the above frequency range than a similar method in which the cooling effect by the sound wave on a current heated wire or fiber is used. Some observations made during the production of quartz fibers sputtered with gold are reported. View full abstract»

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  • Vapor Pressure Apparatus

    Page(s): 399 - 400
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    A vapor pressure apparatus has been developed which has certain manipulative and accuracy advantages over the well‐known isoteniscope. A reliable criterion for complete degassing is inherent in the apparatus. Since degassing is required only once for a series of determinations at various temperatures, the apparatus is well adapted where the amount of sample is limited. The useful temperature range of this apparatus is between the freezing point of mercury (-38.9°C) and the temperature at which the vapor pressure of mercury becomes appreciable (∼0.1 mm at 80°C). The apparatus may not be used if the sample reacts chemically with mercury. View full abstract»

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  • Electronic Computer for Mass Identification of Particles

    Page(s): 401 - 404
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    This paper describes a circuit for identifying protons, deuterons, and tritons. The identification is accomplished by obtaining the product of the energy and the initial space rate of energy loss. The product is modified so that each type of particle gives a unique result in the form of an output pulse having an amplitude nearly proportional to the mass of the particle. The circuit as given is capable of handling input pulses as narrow as 1 μsec, although shorter pulses may be used if some test features are eliminated. The multiplying operation is performed by QK‐329 tubes, using the principle of difference of squares. View full abstract»

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  • Range of 14‐Mev Protons in Nuclear Emulsion

    Page(s): 404 - 405
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    Neutrons, produced by the reaction H3(d,n)He4, gave proton recoils in nuclear emulsion whose ranges were used to obtain a calibration point on the range‐energy relation. The range for 13.94±0.10‐Mev protons in emulsion of density 3.815 g/cm3 is 995.9±2.1 μ. View full abstract»

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  • Efficiencies of Sodium Iodide Crystals

    Page(s): 406 - 410
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    Efficiencies for monoenergetic gamma rays, emanating from an axial point source and incident on sodium iodide crystals of 1.5 in. diameter and of various heights, have been calculated by numerical integration methods. The crystals considered are right circular cylinders of heights 0.125, 0.25, 0.375, 0.50, 0.75, 1.5, 2.0, and 3.0 in. Seventeen photon energies in the range from 0.025 to 10.0 Mev were used. Fourteen distances from source to crystal face in the range 0.1 to 50.0 cm were used. Efficiencies for crystals of diameters other than 1.5 in. may be obtained from these results. Relative photoelectric efficiencies were not calculated. View full abstract»

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  • Swept Frequency Eddy‐Current Device to Measure Overlay Thickness

    Page(s): 411 - 415
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    A new instrument is described which enables nondestructive measurements to be made of film and overlay thicknesses. It utilizes the change in electrical impedance of a composite sample resulting from differences in the thickness of the material being measured to cut off a swept‐frequency oscillator at a frequency determined by that thickness. Operating frequencies from 200 kc to 20 Mc have been used with frequency‐sweep widths, or deviations, up to 10% to measure overlay thicknesses ranging from 0.00005 to 0.007 in. on composite samples in which the conductivity‐to‐permeability ratio of the base and overlay differ by at least a factor of two. Equations are developed to illustrate the conditions for which a reactance‐tube oscillator is employed in a unique manner to make the measurement automatic. View full abstract»

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  • Photoproton Scintillation Spectrometer

    Page(s): 415 - 419
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    An apparatus is described for the measurement of the energy and angular distribution of protons from (γ, p) reactions. A method is presented for obtaining energy spread of 3% for protons of 3 to 15 Mev with a NaI scintillator of 1‐in. diam aperture. Energy calibration of the detector with monoenergetic protons gives an energy vs pulse‐height line having an intercept of 0.46±0.10 Mev. The ratio of α particle to proton energy for equal pulse heights is found to be 1.93±0.04 for 4.48‐Mev α particles. A CsI scintillator, similarly mounted, yields an intercept of -0.17±0.15 Mev and an α‐proton energy ratio of 1.66±0.07 for 5.3‐Mev α particles. A modification of the phoswich to provide discrimination against electrons is described. View full abstract»

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  • Gearing System for a Continually‐Aligned Two‐Crystal X‐Ray Spectrometer

    Page(s): 420 - 422
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    A two crystal x‐ray spectrometer which is able to scan continuously through Bragg angles of 10°–45° has been put into operation. The appropriate angular changes of the components, first pointed out by Allison, are effected through a planetary gear system. The unit in use is adapted to a Norelco goniometer. View full abstract»

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  • Furnace for the Growth of Naphthalene and Anthracene Crystals

    Page(s): 423 - 424
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    A furnace for the growth of naphthalene (mp 80°C) and anthracene (mp 217°C) crystals from the melt by the Bridgman method is described. Crystals up to 15 mm diam by 3 ft may be grown. The furnace is simple in construction, and very convenient and reliable in operation. View full abstract»

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  • Compact Curved‐Crystal X‐Ray Spectrometer

    Page(s): 425 - 426
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    A curved‐crystal spectrometer has been designed with all the mechanism except the crystal and detector arms contained in a box 6×7×3½ inches. Three sets of arms are provided for focusing circles of 10‐, 20‐, and 40‐cm radius. Either automatic drive at from ½ to 8 degrees 2θ per minute or manual scanning may be used. Precision‐cut commercial gears result in accurate positioning and less than 0.01° 2θ backlash in the drive mechanism. Thus the spectrometer is satisfactory for use with rather perfect crystals such as quartz as well as with the alkali halides. Interchange of crystals and alignment of new crystals is simple and rapid. View full abstract»

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  • Respirator Suitable for both Small and Large Laboratory Animals

    Page(s): 427 - 428
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    A respirator with cycling rates from 5 to 80 cycles per minute is described. The inspiration‐expiration ratio is adjustable. Four animals may be respirated simultaneously. Operation is quiet, with only one moving part in the multiple valve assembly. Manual operation is possible in event of power failure. View full abstract»

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  • Quartz Helix Magnetic Susceptibility Balance Using the Curie‐Cheneveau Principle

    Page(s): 429 - 432
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    A quartz spring balance is described which can be used to measure the magnetic susceptibility of submilligram amounts of sample. The magnetic field is supplied by a moving permanent magnet, and the susceptibility is determined by the deflection of the spring observed in a measuring microscope. The apparatus is calibrated by a comparison standard (platinum) and results are shown for platinum, nickel aluminate, lead, manganese, and sucrose. A precision of better than 2% can be obtained on submilligram amounts of paramagnetic substances having a magnetic susceptibility of from 1 to 50×10-6 emu/g. On weakly paramagnetic or diamagnetic substances comparable precision can be obtained on less than 10 mg amounts of sample. View full abstract»

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  • Simple Etching Cutter

    Page(s): 433
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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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Editor
Albert T. Macrander
Argonne National Laboratory