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Review of Scientific Instruments

Issue 9 • Date Sep 1963

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Displaying Results 1 - 25 of 33
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • High Intensity Source of 20‐keV Hydrogen Atoms

    Page(s): 963 - 970
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    A continuous source of energetic hydrogen atoms has been developed for use in a plasma experiment. The mechanical design and some operating characteristics of the ion source are described, as well as the beam focusing and neutralizing system. An output of 65‐mA power equivalent of 20‐keV hydrogen atoms has been measured on a 2.0×6.3 cm target located 350 cm from the ion source. View full abstract»

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  • Use of an Analog‐to‐Digital Converter in Pulsed Nuclear Resonance

    Page(s): 971 - 975
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    The use, in pulsed nuclear resonance experiments, of a voltage‐to‐frequency converter and an electronic counter to act as an integrator for the observed signals is described. Because measurements of this type are free of most subjective influences, they improve upon continued replication. Data are obtainable in a form which may easily be processed by a digital computer. Increased accuracy and sensitivity are the result. Sample T1 determinations are presented. The relaxation in a sample showing a single T1 is followed to within one part in 104 of equilibrium. Remarks are made concerning the design and use of a calibration equation capable of accounting for the behavior of a vacuum tube diode detector biased for linear operation. View full abstract»

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  • Simple Transistorized Logarithmic Time Base

    Page(s): 975 - 977
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    A time base is described which allows the spot of a cathode ray tube to be deflected at a rate proportional to the logarithm of the time. The circuit requires the use of two transistors, one of which serves as a conversion stage and the other as an amplifier stage. Two different sets of component values are given to cover a range of either two or three decades. The performance of the time base and its limitations in respect to temperature variations and supply voltage fluctuations are discussed. View full abstract»

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  • Device for the Measurement of Friction at Ultrahigh Vacuum

    Page(s): 978 - 980
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    A friction measurement device has been developed which permits continuous measurement of static and kinetic coefficient of friction at ultrahigh vacuum. Sliding motion inside the vacuum chamber is accomplished by using a disk rotated by a zero‐leakage, direct‐drive rotary seal. The coefficient of friction is measured using a strain‐gauge system which is compatible with the ultrahigh vacuum test environment. An example of the type of results obtained with the device is given. The apparatus has been continuously operated at pressures in the 10-10 Torr region. View full abstract»

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  • Photodiode as a Sensitive Temperature Probe

    Page(s): 981 - 983
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    A temperature probe capable of reading temperature deviations of ±0.005°F or less at ambient temperatures has been developed using the large temperature coefficient of the reverse current of a Sylvania 1N77B photodiode. The photodiode case, a 0.072‐in.‐diam×0.80‐in.‐long glass cylinder, makes possible a small but very rugged probe assembly. View full abstract»

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  • Liquid‐Helium Temperature Regulator

    Page(s): 984 - 987
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    An electronic regulator is described that is capable of controlling the temperature of a liquid‐helium bath within ±10 μdeg for a few minutes and reducing long‐term drift to less than 40 μdeg/h. With occasional adjustment, the temperature can be indefinitely maintained within ±10 μdeg. The circuit is designed to be used with a resistance thermometer bridge previously described. The error signal from the bridge is displayed on a meter, so that the bridge can be balanced without use of an oscilloscope and the performance of the regulator can be continuously monitored. View full abstract»

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  • Two‐Component Microbalance for Measuring the Forces on Ion‐Bombarded Surfaces

    Page(s): 988 - 991
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    A two‐component null‐type microbalance has been developed to measure forces due to ion bombardment on a surface. The balance employs the principle of the attracted disk electrometer. The sensitivity can be adjusted by simply changing the location of the center of gravity. Measurements of a few micrograms of force in two perpendicular directions can be made simultaneously. View full abstract»

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  • Optical Cells for the Observation of Raman Scattering in Gases at Medium Pressures

    Page(s): 992 - 993
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    Recent investigations of the broadening and shift of isotropic Raman lines of compressed hydrogen have demonstrated the effects of intermolecular forces on intramolecular motions. This paper describes two cells suitable for such experiments in the low to medium density range. The first is a cell for use at 85°K and 100 atm, which is similar in design to a conventional Raman source. The second cell, for use at room temperature and at pressures up to 1000 atm, utilizes the large compressive strength of glass and is an improved version of a cell reported previously. High resolution Raman spectra of the Q1 branch of hydrogen have been obtained in the range 25 to 400 times standard density both at liquid air and room temperature. View full abstract»

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  • Electrodeless Determination of Electrical Conductivities of Melts at Elevated Temperatures

    Page(s): 994 - 996
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    An electrodeless method for measuring the electrical conductivities of metallic and semiconductor melts at elevated temperatures is described. The transformer ``eddy current'' method, which was capable of measuring conductivities from one to greater than 10 000 (Ω‐cm)-1, was used. The system was calibrated with Hg at 25°C and tested with Hg to 300°C and Bi to 550°C. The specific conductivities of various compositions of BiBiI3 solutions were measured at 500°C and compared with those measured by an electrode method. The accuracy of the method decreased with decreasing conductivity. View full abstract»

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  • Photomultiplier Gain Stabilization Circuit

    Page(s): 997 - 1001
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    A simple method is described for the gain stabilization of a photomultiplier in which the stabilization system does not interfere with the fast pulse spectrum to be measured. The functioning principle consists in sending a low frequency (77 Hz) and very low intensity light pulse, which gives a modulation of the photomultiplier thermionic noise, on the photocathode together with the scintillation light. The modulation frequency is then selected on the anode by a special filter. The signal obtained in this way is used to trigger a feedback circuit, which makes the photomultiplier gain constant by suitably varying its voltage. View full abstract»

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  • Nanosecond Scintillation Coincidence Spectrometer System with High Reliability

    Page(s): 1001 - 1006
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    A low‐energy scintillation coincidence system capable of few‐nanosecond resolution and very low timing jitter is described. Saturating circuit techniques are used to make the performance nearly independent of tube parameters, resulting in stable and reliable performance over periods of months. View full abstract»

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  • New Instrument for Measuring Evaporation; Application to Evaporation of Water through Thin Films

    Page(s): 1006 - 1009
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    A new instrument quickly and accurately determines evaporation rates of water. A probe passes helium over a small area of the water surface; the vapor picked up by the helium returns through the probe and is continuously measured by a thermal conductivity cell. Accuracy and repeatability are within 1% absolute. The apparatus is sensitive to a change in evaporation rate of less than 1%; response is 5 to 20 sec, depending upon the magnitude of the step change. The instrument, called an evaporometer, is especially useful for rapidly screening water‐evaporation retardants and for determining evaporation rates through monomolecular films spread on the water surface of the film balance. Evaporation rate vs film pressure isotherms, determined simultaneously with pressure vs area isotherms, should yield additional information about the composition and structure of the monolayers. Although the evaporometer was developed for the determination of water evaporation, it is adaptable to nonaqueous liquids. View full abstract»

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  • Sensitive Tritium Counting with a Propane Proportional Counting System

    Page(s): 1010 - 1014
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    Comparison of the minimum detectable amount of tritium by different counting devices shows that proportional gas counting is the most sensitive method at the present time. A new method of tritium proportional gas counting using propane as counting gas is described. The propane is formed by hydrogenation of propyne with palladium oxide as a catalyst. Using a 2.5‐liter counter filled with propane at 2.2 atm pressure requires a sample size of half a mole of H2O or H2. For a background of 5.3 cpm, this results in a minimum detectable concentration, without isotopic enrichment of tritium, of 3 TU equal to ±2σ for a counting time of 1000 min. View full abstract»

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  • Radio‐Frequency Excited Plasma Tunnel for Laboratory Studies of Supersonic Plasma Flow Fields

    Page(s): 1015 - 1019
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    A description is given of a supersonic, low density plasma tunnel employing rf excitation of the gas stream. The facility, which has been designed to be of laboratory proportions, provides clean, supersonic plasma streams at velocities up to about Mach 2. The static stream pressures available are in the range from about 0.1 to 10 Torr and jets up to 2 or 3 cm in diameter are produced. A discussion of the important design features is given and the application of this facility to several studies of supersonic plasma flow fields is described. View full abstract»

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  • Retractable Low Temperature Targets for High Energy Physics Experiments

    Page(s): 1019 - 1022
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    A system is described which allows as many as five different low temperature targets to be positioned vertically inside a vacuum system. The targets normally contain liquid hydrogen or deuterium. The vertical travel is obtained by using a bellows system in such a way that the over‐all external height of the system is constant. A maximum travel of 4 in. can be obtained. View full abstract»

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  • Particle Size Classifier for the Subsieve Range

    Page(s): 1023 - 1025
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    A particle size classifier for dry powders in aerosol form, based on the combined classifying mechanisms of impaction, adhesion, and the characteristic trajectories of particles, has been developed and extensively tested with a variety of powders. Continuous classification has been achieved for powders the diameters of which are predominantly below 50 μ by impacting the aerosol cloud onto a moving surface and recovering those fractions resulting from the aforementioned mechanisms. Partial separation of powder mixtures is sometimes possible when the components have widely differing physical properties. View full abstract»

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  • Electronic Variable Delay for Tracing Characteristic Curves of Coincidence Circuits and Time‐to‐Height Converters

    Page(s): 1026 - 1028
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    Automatic tracing of characteristic curves of coincidence circuits and time‐to‐height converters has been accomplished by utilizing a tunnel diode circuit, which provides an electrically controlled time delay continuously varying from 30 to 65 nsec. An input pulse starts a current ramp through the tunnel diode, which generates an output pulse on triggering. The moment of triggering, however, is programmed by a control voltage which dictates the instantaneous value of the initial current flowing through the tunnel diode. Measurements of the delay vs control voltage relationship show no deviation from linearity greater than the experimental error of ±15 psec. Time jitter, characterized by the full width at half‐maximum of the output‐pulse time distribution, is less than 30 psec. A coincidence resolution curve displayed on the screen of an oscilloscope and a height‐vs‐time curve of a time‐to‐height converter traced by an X‐Y recorder are shown. View full abstract»

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  • Absolute Differential Radiometer

    Page(s): 1028 - 1034
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    A radiometer is described which is calibrated on an absolute basis from its geometric and physical parameters. An estimated 3% accuracy is achieved using common handbook values for the physical parameters. Experiment confirms the calibration, including predicted dependence of sensitivity on temperature. The instrument gives integrated response to diffuse thermal radiation exchanged between surfaces at normal room temperature. When used with a commercial microvoltmeter, the present device measures net heat fluxes ranging from 0.1 to 100 Btu/h‐ft2. It responds quickly to changes in incident flux and reaches equilibrium within about 1 min. It is sufficiently rugged and stable for practical field work and is suggested as a tool for research and teaching. View full abstract»

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  • Interaction of Fission Fragments with Organic Scintillators

    Page(s): 1035 - 1040
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    A pulse‐shape discriminator circuit was used for the measurement of the pulse heights of the slow components of light pulses from organic scintillators excited by different types of particles: electrons, protons, alpha particles, and fission fragments. Three types of organic scintillators were employed: a crystal (stilbene), a liquid (7 g PPO and 0.5 g M2‐POPOP in 1 liter of toluene), and a plastic (NE‐150). The relationship of the pulse heights of the slow components for excitation with electrons, protons, and alpha particles was similar for all three scintillators. However, fission fragments produced a slow component pulse height similar to protons in stilbene and the plastic but more like electrons in the liquid. The pulse‐height distributions of total light pulses from the scintillators excited by the alpha and spontaneous fission emissions of Cf252 were measured. The alpha‐particle and fission‐event spectra were resolved only with the liquid scintillator giving a pulse‐height spread of the fission distribution peak of 40%. From the maximum of the fission sepctra it was calculated that the most probable energy of fission produced the same pulse height as an electron with 1/75th that energy would produce. The alpha particles and the fission events were counted with 100% efficiency and a value of 31.0±0.5 was obtained for the alpha to fission disintegration ratio of Cf252. View full abstract»

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  • Pressure Measurements Below 10-10 Torr with Bayard‐Alpert and Magnetron Gauges

    Page(s): 1041 - 1043
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    Below 1×10-10 Torr, pressure measurement by means of Bayard‐Alpert type ion gauges is complicated by the existence of a current associated with soft ``x‐rays.'' The precise measurement of a true ion current requires precise determination of the so‐called x‐ray limit of each gauge. The present work describes the use of a Bayard‐Alpert gauge containing a modulating electrode (after the design of Redhead) to measure pressures below 10-10 Torr. Magnetron‐type gauges, which do not have x‐ray limitations, were then compared directly with the Bayard‐Alpert gauges. In addition, gauge comparisons were carried out in a dynamic system involving pressure ratios across a capillary. Both series of experiments showed that the output current of the magnetron gauge was a power function (exponent 1.6) below approximately 2×10-10 Torr (N2). In the latter work it was possible to make measurements to below 1×10-12 Torr N2 equivalent. View full abstract»

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  • Apparatus for Electron Spin Resonance Studies at Very High Pressures

    Page(s): 1043 - 1046
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    Apparatus for studying electron paramagnetic resonance in solids under pressure to 60 kilobars and beyond has been developed. The high pressures are produced between dielectric Bridgman anvils, one of which serves as a microwave resonance cavity. The instrument makes possible the study, by EPR techniques, of paramagnetic atoms or ions subject to stresses which might be expected to induce changes in their electronic structure. View full abstract»

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  • Deformation‐Free Acid Drilling of Single Crystals

    Page(s): 1049 - 1050
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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