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Review of Scientific Instruments

Issue 12 • Date Dec 1972

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Displaying Results 1 - 25 of 42
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Thermometric Properties of Carbon‐Impregnated Porous Glass at Low Temperatures

    Page(s): 1743 - 1747
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    Samples (4.8×1.6×1.0 mm) were cut from a plate of carbon‐impregnated porous glass, encapsulated in He‐filled Pt cans as two‐lead devices, and their thermometric properties measured from 2 to 400 K. This material has a large sensitivity (R77/R300≅2.0, R4.2/R300≅130) combined with a relatively small resistivity (R4.2≃2100 Ω, R77≃34 Ω, R300≃17 Ω, for the samples' size), and d lnR/d lnT is smooth and monotonic over this temperature range. Repeatability of the two‐lead device is ≃±0.8 mK at 4.2 K and ≪±60 mK at 77 K, and no evidence of isothermal aging was observed. The magnetoresistance was measured at 4.2 K in fields up to 30 kG and found to be approximately twice as large as for carbon radio resistors at 4.2 K. Curve‐fitting studies were made over increasingly larger temperature intervals (2–5, 2–10,…, 2–200 K) based on the equation log R=A+BT-P, and it was found that in each interval the R-T data could be fitted to better than 1% of the upper temperature. An interesting scaling relation was found between the R-T curves of the units, such that at each temperature, Ri=bRjm for the ith and jth units, where b and m are constants. This scaling could permit a two‐point calibration transfer. It is postulated that the broad‐range thermometric properties of this material derive from the high‐purity carbon filaments deposited in the ∼40 Å pore‐size porous glass. View full abstract»

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  • New Instrumentation for Research on Vibrotactile Sensitivity of the Tongue

    Page(s): 1748 - 1751
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    The need for a reliable instrument for vibrotactile stimulation of the tongue is presented. A signal delivery and signal monitoring instrumentation system as well as an appropriate method and apparatus for holding and positioning the test structure is described. The system is capable of controlling those spatial and psychophysical parameters affecting vibratory study of the tongue. View full abstract»

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  • A Field Mill for Tethered Balloons

    Page(s): 1751 - 1754
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    An instrument is described for obtaining time averages of the resultant of the vertical and one horizontal component of electric field in the lower atmosphere. This instrument is designed to be suspended from a tethered balloon and to telemeter the desired data to an operator by means of an audio pulse width modulation technique which requires the operator to be equipped only with a hand‐held AM receiver and a stopwatch. The net self‐charge on the field mill is maintained at or near zero by means of a 210Po alpha source. If we assume that the horizontal component of the electric field is small compared with the vertical, the field mill system can be used to observe the average vertical atmospheric electric field profile produced by the electrode effect near the ocean surface. View full abstract»

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  • Sweep Generator for MOS Analysis

    Page(s): 1755 - 1757
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    A sweep generator is described which provides an output voltage of triangular wave shape variable in frequency from 0–1.6 Hz, variable in peak‐to‐peak amplitude from 0–100 V, and variable in offset from zero by dc voltages up to ±150 V. The waveform is stable and linear, and the sweep voltage can be held at any point on the waveform for moderate periods of time (minutes) without significant change in voltage, and can be held indefinitely at either peak value of the waveform. View full abstract»

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  • An Improved ac Bridge Circuit for Use in Four‐Terminal Resistance Thermometry

    Page(s): 1758 - 1762
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    Details are given of an improved version of the ac Kelvin bridge first described by Ekin and Wagner [Rev. Sci. Instrum. 41, 1109 (1970)]. Battery‐operated operational amplifiers with highly superior noise performance at 33 Hz were used for the voltage followers required to make the bridge compatible with four‐leaded germanium resistance thermometers. A discussion of bridge operation, accuracy limitations, and final performance characteristics is presented, including a confirmation of the design objective to accurately measure a ΔT of 0.5 mK at 4.2 K, with a 1 mV germanium sensor excitation and a 1 Hz detector bandwidth. View full abstract»

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  • Heater Lead Error in Calorimetry

    Page(s): 1762 - 1765
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    A summary of previous work is followed by an examination of the effects of radiation from heater leads. Solutions of the exact differential equation for particular experimental configurations have been obtained by a numerical method. For certain simple situations the solutions can be checked against partial or complete analytical solutions of the equation. It is shown that even for low temperature calorimeters a large part of the electrical energy dissipated in heater leads may be radiated unless the lead resistance is kept very low. If a significant part of the total energy supplied to the calorimeter is radiated, systematic errors may arise because, for a given calorimeter heating rate, the heater lead radiation loss will differ in the ``full'' and ``empty calorimeter'' experiments. View full abstract»

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  • A Versatile 60 kV Switching System for Pulsed Excitation of Lasers

    Page(s): 1765 - 1768
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    A fast switching high voltage system capable of handling 60 kV is described. The system utilizes a sealed‐off pressurized hydrogen spark gap as a switching device. A versatile silicone rubber coupling module makes different high voltage components easily interchangeable without the need of draining off any insulation liquid. The system was used to build a laser, which emits radiation pulses of a few nanoseconds duration at a wavelength ranging from 337 nm in the ultraviolet region of the spectrum to 9.0 μ in the infrared. The uv pulses contain enough energy to permit pumping of a tunable rhodamine 6 G dye laser. View full abstract»

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  • A Device for the Removal of Temperature Gradients in NMR Spinning Tubes

    Page(s): 1769 - 1771
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    A simple paddle device is described for the removal of temperature gradients in liquids contained in high resolution NMR spinning tubes. Experiments show that this accessory reduces temperature gradients to less than 0.10°C along the length of the liquid without any impairment in spectrometer resolution or sensitivity. The device is readily adaptable to most conventional high resolution NMR spectrometers. View full abstract»

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  • Secondary‐Ion Collection System for an Ion Microprobe Analyzer of High Mass Resolution

    Page(s): 1771 - 1772
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    An optical system by which about 10% of the secondary ions produced by an ion microprobe are collected into the acceptance phase space of a mass spectrometer, of mass resolution over 10 000, is described. The crucial feature is that the specimen stage is divided into sections of different potential, so that the secondaries can be steered when they are at low velocities. View full abstract»

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  • Thruster Characterization Using a Thrust Balance

    Page(s): 1773 - 1774
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    A procedure is described which enables thrusters to be characterized in a continuous manner in a relatively short time. The method should be particularly suitable for electric thrusters with variable thrust. View full abstract»

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  • A Simplified Graphical Evaluation of High‐Frequency and Quasistatic Capacitance‐Voltage Curves

    Page(s): 1775 - 1777
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    High‐frequency and quasistatic capacitance‐voltage curves of metal silicon‐dioxide silicon capacitors can be evaluated quickly by the use of only two graphs to give doping density, flat band voltage, and density of interface states at selected points in the band gap. View full abstract»

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  • A Technique for Measuring Equilibrium Thermodynamic States of Liquid Metals at High Temperatures and Pressures

    Page(s): 1777 - 1784
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    This paper presents a method for overcoming temperature and pressure limitations inherent in conventional techniques for measuring equilibrium thermodynamic data. The method can be applied to conducting materials that can be resistively heated and that do not dissociate in the liquid phase; and it is thus particularly suitable for investigating pure liquid‐metal thermodynamic data. The technique has been applied extensively to lead at temperatures exceeding 5000 K and at pressures up to 2 kilobars. A cylindrical material specimen 1 mm in diameter and 25 mm long is interposed between two current leads and mounted axially concentric with a high‐pressure cell. After the cell is pressurized with helium, a current pulse from the overdamped discharge of a high‐voltage capacitor bank heats the wire at such a rate that its expansion is nearly isobaric. The energy deposited in a central segment of the sample is computed by integrating the product of the current flowing in the segment with the resistive voltage developed across it. With these data, sample resistance can also be calculated during a major portion of the time that current flows. Because mounting constraints limit sample expansion to the radial dimension, the equilibrium volume is calculated from the expanded diameter, which is measured by means of pulsed x‐radiography. View full abstract»

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  • An Elevated Temperature Torsional Fatigue Testing Fixture

    Page(s): 1784 - 1785
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    A simple fixture that can be used with any closed‐loop tensile testing system for torsional cyclic testing is described. This fixture was successfully used for low cycle fatigue and crack growth rate studies of high‐strength steels both at ambient and elevated temperatures. The unique design of this fixture is that by using the output of the torque cell as the feedback to the servocontroller of the hydraulic tensile testing machine, the applied torque remains independent of all machine variables and the tests can be programmed to follow any torque/time profile. View full abstract»

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  • Continuous Measurement of Internal Friction and Modulus with a Regenerative Feedback Loop and Composite Oscillator

    Page(s): 1786 - 1789
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    Continuous measurement of the internal friction and modulus defect in covalent crystals has been obtained by using a regenerative feedback loop in conjunction with the Marx composite oscillator technique. This system was designed specifically for the rapid measurement of strain‐dependent internal friction at elevated temperatures; however, it can readily be used to measure automatically the internal friction in a variety of systems. View full abstract»

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  • Beam Current and Position Monitor for the Astron Accelerator

    Page(s): 1789 - 1792
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    A beam current and position monitoring system very similar to one developed for the Berkeley ERA accelerator has been developed for use on the Astron accelerator. Beam current measurements are accurate to less than 2%. At beam currents above 500 A beam displacements less than 1 mm off‐axis can be observed. The beam current and position at any two of 30 locations in the accelerator and transport section can be simultaneously monitored on either of two oscillograph systems. The current sensors do not interfere with the beam propagation and are outside the vacuum system for easy maintenance and calibration. View full abstract»

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  • Instrumentation for In Situ Electron Microscope Studies of Sputtered Thin Film Growth

    Page(s): 1793 - 1796
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    An assembly has been constructed for the investigation of the nucleation and growth of ion beam‐sputtered thin films inside the transmission electron microscope. A commercial microscope has been modified to allow a dynamic investigation of the formation of films on electron‐transparent substrates. The resolution of the microscope is not significantly impaired by the apparatus; the resolution during deposition is generally 15–25 Å. To date silver, gold, niobium, and silicon have been successfully deposited. View full abstract»

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  • Intensified Ultraviolet Analyzing Lamp for Flash Photolysis

    Page(s): 1797 - 1799
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    An intensifier is described which increases the light level of an Osram 150 W xenon lamp by a factor of up to 30 at 350 nm, and holds it constant to 0.02% of the brightened level for 10 msec. Control for longer times is possible. This precision of control is possible only when the light level seen by a photomultiplier is used to regulate the intensified level. If two photomultipliers are used, one to observe the transient absorption signals and the other to control the light level, then the light level can be held constant to about 0.1%. This limitation is not due to the intensifier circuit, but to the difficulty of optically matching two beams and two photomultipliers. View full abstract»

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  • A Programmable Digital Pulser for NMR

    Page(s): 1800 - 1803
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    A programmable digital pulser for pulsed NMR applications employing inexpensive integrated circuits is described. This pulser employs two types of modules, one master clock and several counters. The required pulse sequence determines the number of counters to be front‐panel interconnected. The master clock module simultaneously provides crystal‐controlled clock pulses with periods from 10-7 to 1 sec in decade steps. These pulses are used by the counter modules to generate either time delays or pulses with a maximum resolution of five digits. View full abstract»

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  • A Method for Performing High Precision Lattice Parameter Change Measurements on Quenched Aluminum

    Page(s): 1804 - 1810
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    Experimental techniques to measure x‐ray lattice parameter changes to 1 ppm in quenched aluminum single crystal foils are described. Included in the description is a cryostat designed to allow the mounting of a sample cooled to liquid nitrogen temperature after quenching. X‐ray diffraction measurements are performed on the sample at liquid nitrogen temperature. In between successive measurements, the sample is annealed at temperatures up to 260°C. The measurement of simultaneous lattice parameter and Bragg line shape changes is shown to be possible for quenched samples. View full abstract»

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  • Measurement of the Dielectric Constant and Loss Tangent of Multilayer Specimen and Its Application

    Page(s): 1811 - 1813
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    This paper describes a measuring technique for the dielectric constant and loss tangent of multilayer specimens at above 1 MHz by the apparatus devised for the varying gap immersion method. The method permits the measurement of a dielectric film formed on a substrate. Specimens that cannot be immersed directly in a liquid can be placed in a pouch. Since the method does not require conventional micrometer measurements of thickness of the specimen, the substrate, and the pouch, it improves the accuracy of the measurements. By this method, a whole measurement of a specimen can be done in several minutes with an accuracy of 0.5% and 5% for the dielectric constant and the loss tangent, respectively, of a low‐loss specimen of polymeric film several hundred microns thick. The thickness of the specimen can also be calculated from the measured data to within 1 μ. View full abstract»

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  • An Intense Microsecond Flash Lamp

    Page(s): 1814 - 1818
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    A flash lamp system for flash photolysis is described which produces an intense flash of short duration and little afterglow. The discharge takes place in the space formed by placing a solid quartz rod on the axis of a cylindrical quartz tube. When the system dissipates 600 J of electrical energy, it produces a flash in xenon, at 25 Torr, which has a width of 0.9 μsec at half‐height and the afterglow decays to less than 1% of its maximum value within 4.4 μsec from the start of the flash. By surrounding the lamps with a filter solution, noise generated by standing waves in the cell can be eliminated. Methods for eliminating other types of noise are presented. View full abstract»

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  • Operation of a Grid‐Shuttered Image Converter Tube in the Picosecond Region

    Page(s): 1819 - 1829
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    Experiments have been carried out to investigate the performance of a standard, commercial, image converter tube (RCA C73435) in the picosecond region. Using a multikilovolt subnanosecond‐rise time pulse generator, switched by a laser‐triggered spark gap, to generate the deflection pulses, streak velocities of 1.6×1010 cm/sec and a streak‐limited resolution of ≪5 psec have been obtained. Photocathode saturation and space charge effects are avoided with the use of low cathode currents, and, in order that photographic records can be obtained on high‐speed film, a high‐gain (106), four‐stage magnetically focused image intensifier (EMI 9694) is optically coupled to the screen of the image converter tube. The over‐all response time of the camera is also dependent on the transit time spread of the photoelectrons between the cathode and the screen and this is reduced by the application of accelerating voltages of 2500 V to the ICT grid. Evaluation of the camera system has been undertaken with the 1.06 μ fundamental output of a mode‐locked neodymium glass laser. Mode‐locked pulses of ∼6 psec duration were resolved. View full abstract»

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  • Frequency Sweep Adiabatic Fast Passage on the Varian HA‐100

    Page(s): 1830 - 1831
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    A modification of the Varian HA‐100 NMR spectrometer to permit frequency sweep adiabatic fast passage measurements of T1 is described. The spectrometer can be operated in the lock mode making signal averaging possible. View full abstract»

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  • Rotating Magnetic Field Control for Bubble‐Domain Experiments

    Page(s): 1831 - 1833
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    We describe a method of generating a magnetic field whose direction can be rotated in a fixed plane. Such fields are required in microscopic studies of bubble‐domain device operation. With the apparatus described here, the field is rotated in synchronism with the setting of a special 360°‐rotation potentiometer. The field is produced by orthogonal coils which are driven with currents derived from the sine and cosine function outputs of this special potentiometer. 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