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Review of Scientific Instruments

Issue 6 • Date Jun 1981

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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
  • Magnetically suspended cross‐correlation chopper in molecular beam‐surface experiments

    Page(s): 789 - 796
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    The advantages of the cross‐correlation time of flight (TOF) method when applied to surface scattering experiments under ultrahigh vacuum conditions are demonstrated in comparison with the conventional TOF method. The principle of the cross‐correlation TOF technique including the deconvolution procedure and statistical accuracy given by this method is discussed. The main parts of the spectrometer: chopper blade, magnetic rotor suspension and drive, and data acquisition system are described followed by the test of the TOF spectrometer, and by an illustration of the efficiency of this technique by means of TOF distributions measured for hydrogen molecules desorbing from metal surfaces. View full abstract»

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  • Polarized He (23S) thermal metastable atom source

    Page(s): 797 - 801
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    A source of polarized He (23S) metastable atoms is described that provides a thermal energy beam with a flux of the order of ∼1014 metastables s-1 steradian-1 at a polarization Pz∼50%. The polarization of the beam can be simply reversed, or modulated, without changing the beam trajectory or flux. The beam contains no significant admixtures of He(21S) atoms, photons, or fast neutrals and is suitable for use in a wide variety of collision and surface physics experiments. View full abstract»

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  • Multiple crossing devices for laser‐molecular beam spectroscopy

    Page(s): 802 - 803
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    The construction of a multipass device for laser‐molecular beam spectroscopy is described. The device increases signal to noise ratios by a factor of 10 does not contribute to the width of the signal, and in addition provides an indication of the orthogonality of laser and molecular beams. View full abstract»

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  • Mass spectrometric analyzer for individual aerosol particles

    Page(s): 804 - 809
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    A new analytical instrument has been developed to give real‐time chemical composition and size data on individual aerosol particles. It separates the particles from the entraining gases by means of aerodynamic nozzles and differential pumping, so that they enter the high vacuum region as a collimated beam. Each arriving particle is flash vaporized, the vapor ionized, and the ions analyzed by a quadrupole mass spectrometer. The instrument has been tested with several inorganic and organic aerosols and has yielded mass spectral peaks corresponding to a series of fragment ions. The more stable compounds yielded the parent ion as well. Particles 0.9 μm in diameter are readily detected with signal‐to‐noise ratios of 12:1 on the dominant peak. On this basis, the small‐size sensitivity limit is well under 0.5 μm diameter and, with design improvements, can probably be extended to 0.1 μm or smaller. View full abstract»

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  • Performance of the new high mass resolution time of flight atom probe

    Page(s): 810 - 818
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    Detectability and mass resolution of a newly built high mass resolution time‐of‐flight atom probe were examined. In order to maximize the detectability, the specimen tip apex, the probe hole, and the entering side of the energy‐compensating deflector were aligned by a laser beam. Transmittance of ions through the deflector and mass resolution were optimized varying the combinations of deflector electrode voltages. The detectability, defined as the ratio of the number of all atoms in the area aimed by the probe hole to the number of field evaporated ions arriving at the detector, was found to be dependent on the crystallographic plane and its aimed area, possibly due to the rolling motion of the field evaporating atoms in a certain preferable direction. The observed detectability ranges from only 10% at the central area of the W (011) plane, which is dark in a multiatom‐layer desorption image, to 91% at the (011) plane side of the W(114) plane, which is significantly higher than the maximum detectability limited by the effective area of a chevron detector, 55%. Thus, the overall detectability might be as high as 50% and the transmittance would be nearly 100%. The mass resolution Δm/m was 1/1100 at half peak height which was comparable to the theoretically expected mass resolution limited by the pulse width and the time resolution of the timer, 5 ns, and each of the detected W ions was clearly discriminated corresponding to each W isotope. The atom probe also successfully demonstrated its unique capability of the atomic layer‐by‐layer mass analysis providing the ultimately fine depth profile. View full abstract»

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  • Fast electronics for time‐of‐flight measurements

    Page(s): 819 - 824
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    High speed circuitry for measurement of particle flight times over the range from 15 ns to ≪1 μs with event rates as high as 105 s-1 was developed for use in a time‐of‐flight field‐ionization mass spectrometer for neutral particles. The circuits were designed for space flight applications and have low power consumption (∼2 W), low weight (≪50 g), and small physical size (6×13 cm). The circuitry is easily interfaced with standard pulse height analysis equipment or a microprocessor. View full abstract»

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  • Double‐reflection x‐ray spectrometer for pulsed‐source diagnostics

    Page(s): 825 - 830
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    The mirror technique provides a promising new soft x‐ray, energy‐resolving capability. Mirrors have the uncommon but very useful characteristic of behaving as low‐pass filters. If x‐ray absorption is low, then the change in reflection across the critical cutoff energy at a particular mirror angle is quite sharp and can be used to resolve x‐ray spectra with energy resolution comparable to solid‐state detectors. The properties of mirrors that enable them to resolve x‐ray spectra have been incorporated into a two‐mirror intermediate‐resolution x‐ray spectrometer, which is described here. The instrument is capable of measuring pulsed‐source x‐ray spectra between a few tenths and about 8 keV. View full abstract»

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  • Copper activation counter calibration using solid state track detectors

    Page(s): 831 - 834
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    A simple procedure has been developed in laser fusion diagnostics to calibrate, in situ, a copper‐activation detector for 14.1 MeV DT neutrons. By mounting thin solid state track detectors in front of the copper‐activation detector, one can measure the fluence of DT alpha particles and thus also determine the neutron fluence. An inferred alpha particle yield from this measurement can then be utilized to calibrate the copper‐activation detector. View full abstract»

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  • Novel charged particle analyzer for momentum determination in the multichanneling mode: I. Design aspects and electron/ion optical properties

    Page(s): 835 - 839
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    We present a novel electrostatic, energy‐dispersive particle analyzer whose astigmatism can be used to measure the polar angle distribution of charged particles originating in a sample spot, in a multichanneling mode. The analyzer consists of a toroidal prism and a truncated conical lens, both coaxial on an axis through the particle source. The toroidal prism is used in an unusual way, in that the axial radius of the central equipotential surface varies from infinity to a certain minimal value for varying deflection angles in the prism. We develop design criteria for an analyzer using this principle, suitable for measurements on solid samples. The energy resolution of the analyzer lies between those of a 127 ° cylindrical and of a 180 ° spherical analyzer. Angular resolutions of ≪2.6 ° (FWHM) can be achieved. View full abstract»

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  • Fast digital data acquisition and on‐line processing system for an HB5 scanning transmission electron microscope

    Page(s): 840 - 848
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    The Fast Digital Data Acquisition System (FDDAS) links a Vacuum Generator’s HB5 Scanning Transmission Electron Microscope and a PDP‐11/34 minicomputer, to enable high‐speed collection and storage of digitized images for analysis, processing, and display, either in real time (using hardware) or later (via software). The FDDAS hardware consists of a digital scan generator, a programmable quad scaler with quad discriminator, an on‐line processor with digital gray level generator, an analog to digital converter, and a joystick. These devices are interconnected as addressable locations on the FDDAS bus line, the ’’System Bus,’’ on which they can act as data sources or sinks. The FDDAS also contains the circuitry for interfacing the system bus to the PDP‐11 UNIBUS, allowing it to read or write image data into the computer at memory cycle speeds. The FDDAS software consists of data transfer, data reformatting, and test pattern generation modules which are linked in an overlay structure and designed to execute under Digital Equipment Corporation’s RT11 operating system. View full abstract»

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  • Statistical analysis of the noise in fluorescence measurements by the sampling technique

    Page(s): 849 - 851
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    Analysis of the statistical distribution of the noise in fluorescence measurements by the sampling technique is presented. The experimental results indicate that Poisson statistics are predominant. Least squares analysis of a fluorescence decay is performed by using correct standard deviations of the experimental points. The χ2 test is applied to evaluate the goodness of the fit for two interpolating functions. View full abstract»

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  • Passively mode‐locked Nd:glass laser oscillator optimized for TEM00 selectivity and long term stability and reliability

    Page(s): 852 - 857
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    A passively mode‐locked Nd:glass laser oscillator optimized for TEM00 selectivity and long term stability and reliability is presented. The important aspects of the optimized design are explained in detail. A detailed alignment procedure is also included. This laser oscillator is capable of producing TEM00, bandwidth‐limited, ≃9 picosecond pulses for ⩾12 hours. View full abstract»

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  • Mössbauer spectroscopy cell for in situ catalyst characterization and reaction kinetics studies at high pressures

    Page(s): 858 - 862
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    A stainless steel cell with beryllium windows has been used for carrying out in situ Mössbauer spectroscopy studies (with a vertical γ‐ray beam) at pressures up to 6.8 MPa and temperatures up to 773 K. The downflow of gas through the powdered catalyst sample minimizes bulk gas phase concentration gradients in the cell above the catalyst layer, and this allows reaction kinetics measurements to be routinely analyzed. Incorporation of a prereactor and/or postreactor makes it possible to model longitudinal variations of catalyst states in a packed catalyst bed. View full abstract»

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  • Adjustable long duration high‐intensity point light source

    Page(s): 863 - 868
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    A new long duration high‐intensity point light source with adjustable light duration and a small light spot locally stable in time has been developed. The principle involved is a stationary high‐temperature plasma flow inside a partly constrained capillary of a coaxial spark gap which is viewed end on through a terminating Plexiglas window. The point light spark gap is operated via a resistor by an artificial transmission line. Using two exchangeable inductance sets in the line, two ranges of photoduration 10–130 μs and 100–600 μs can be covered. For a light spot size of 1.5 mm diameter the corresponding peak light output amounts to 5×106 and 1.6×106 candelas, respectively. Within these ranges the duration is controlled by an ignitron crowbar to extinguish the plasma. The adjustable photoduration is very useful for the application of continuous writing rotating mirror cameras, thus preventing multiple exposures. The essentially uniform exposure within the visible spectral range makes the new light source suitable for color cinematography. View full abstract»

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  • Influence of velocity gradients on measurements of velocity and streamwise vorticity with hot‐wire X‐array probes

    Page(s): 869 - 879
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    An analysis and measurement of the effects of the streamwise velocity gradients, ∂U/∂y and ∂U/∂z, on the velocity components, U, v, and w, and the streamwise vorticity component, ωx, measured in turbulent flow with a pair of orthogonal hot‐wire X arrays, is presented. It is shown that these gradients, which can have the same order of magnitude instantaneously as the mean shear stress at the wall, cause extremely large errors in the measured instantaneous cross‐stream velocity and streamwise vorticity components. View full abstract»

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  • Simple single phase and homogeneous multiphase bidirectional flowmeter

    Page(s): 880 - 882
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    The flowmeter described is based upon the bending of a slender spring steel beam in a fluid stream. The pressure exerted on the beam is determined by attaching strain gauges to the beam. The direction of flow can be determined by the sign of the bridge current when inbalance occurs, singe the gauges will change from the tension to the compression mode. The flowmeter may be used with corrosive and hot fluids since coated beams may be used, and for increased sensitivity silicon strain gauges with temperature compensation can be used, and the system may then be used for determining gas flow rates. View full abstract»

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  • New capacitive micromanometer

    Page(s): 883 - 887
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    The theory, design, and preliminary test results of a new capacitive micromanometer for differential pressure measurement are presented. A U‐tube manometer and two cylindrical cross capacitors are used to transduct pressure variation to capacitance variation linearly. The change in capacitance is measured with the help of a 2‐winding transformer ratio bridge employing an 8‐decade Inductive Voltage Divider (IVD). The value of differential pressure is obtained with a resolution of 60 m Pa in terms of the IVD ratio readings. The unit constructed can measure pressures from very low values to 10 k Pa. It is considered that the proposed system can be developed as a primary standard for the measurement of low range differential pressures. View full abstract»

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  • Measurement and simulation of thermistor response time in the millisecond range

    Page(s): 888 - 894
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    The Finite Element Simulation Technique (FEST) has been applied to the design of hermetically‐sealed thermistors with millisecond response times. These thermistors are used in stopped‐flow calorimeters developed especially for investigations of biological reactions. FEST is also used to reconstruct the reaction kinetics obtained with these thermistors by correcting for their finite sensor response times and temperature loss. View full abstract»

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  • Application of a digital computer to data acquisition and shield temperature control of a high‐temperature, adiabatic calorimeter

    Page(s): 895 - 901
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    The use of a digital computer, operating under real‐time, time‐sharing mode, for the operation of a high‐temperature (300–1300 K), adiabatic calorimeter is described. The specimen temperature and power to the specimen heater are logged continuously, from which the heat capacity is calculated for specified temperature intervals (e.g., 20 K). The determinate error in the calculated heat capacity is about ±0.6%. The temperature control of the adiabatic shields is quite comparable with that obtained previously with analog controllers. The temperature difference between the specimen and a shield can be maintained to about ±0.1 K. The heat capacity of a pure titanium specimen has been measured from 320 to 1020 K using the computer and also using the analog control. No discernible difference in results can be seen. The heat capacity data scatter about ±1% from a smooth curve fitted through the 325 data points. View full abstract»

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  • Electronic analogs of double‐junction and single‐junction SQUIDs

    Page(s): 902 - 914
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    We describe electronic analogs of a double‐junction (dc) SQUID and a single‐junction (rf) SQUID that are simple to construct and operate, and are considerably more flexible than those previously reported. The Josephson junction analog is based on the Resistively‐Shunted Junction (RSJ) model, and uses a novel method based on a sample‐and‐hold circuit to generate the sin ϑ ’’supercurrent.’’ Examples are shown of the single‐junction I–V characteristics, threshold curves of critical current vs applied flux and I–V curves for the double‐junction SQUID analog, and rf SQUID characteristics as a function of applied flux and rf drive current. Other applications of the analogs, including the incorporation of a nonsinusoidal current‐phase relation, are discussed. View full abstract»

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  • Minicomputer‐based test system for analyzing the electronic components of a large scale scientific research instrument

    Page(s): 915 - 921
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    Large scale research experiments often require the use of highly specialized and sophisticated electronic equipment including computer‐based data acquisition systems capable of gathering large amounts of data over very short time intervals. Equipment malfunctions can mean a loss of experimental data integrity and valuable research time. A diagnostic test system has been developed to monitor the electronic equipment of such an experiment, the Fast Neutron Hodoscope at the Transient Reactor Test Facility in Idaho. The system allows hodoscope electronics designers at Argonne National Laboratory in Illinois, and hodoscope maintenance engineers in Idaho, to observe simultaneously digital and analog signals from the hodoscope electronics while the hodoscope is in operation. The diagnostic test system can be controlled either locally by the engineers at the research site in Idaho or remotely by the designers in Illinois via a computer to computer telephone link between the two sites. As a result potential equipment problems as well as actual failures can often be pinpointed and corrected with minimal lost time and cost to the research program. View full abstract»

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  • Large signal testing of fusible links

    Page(s): 922 - 925
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    Large signal testing of fusible links is accomplished by passing a destructive constant current level through the item and terminating the heating at a preset voltage level or pulse duration. Testing at currents typical of functioning levels provides insight as to performance and quality. View full abstract»

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  • Bulk conductivity measurement of paper by a new in situ pressure cell

    Page(s): 926 - 932
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    In this report a new bulk conductivity cell design is described which can be used to characterize both conductivized and nonconductive paper. By the use of optically flat stainless steel electrodes under a pressure of 115 bars during the conductivity measurement, it is shown that the contact resistance between the paper sample and the electrodes is reduced to negligible proportions. The effect of paper surface morphology on the contact resistance during the measurement of bulk conductivity was studied by a comparison between the polished stainless steel electrodes and electrodes composed of liquid Galium Indium, which make intimate contact with the paper surface. Bulk conductivity measurements were determined for paper samples having different basis weights and different degrees of calendering. The results obtained with the pressurized stainless steel electrodes for these paper samples indicate that the contact resistance is essentially eliminated for all the papers studied by using an applied pressure of 115 bars. View full abstract»

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  • Microautomatic data acquisition system

    Page(s): 933 - 935
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    We have built a system for collecting, accumulating, and computing data from optical‐type measurements, by coupling a commercial desk computer (TEXAS TI59 with PRINTER PC 100 C) to the experimental apparatus through a simple, but effective, interface. Our purpose is to use the full computing capability of a microcomputer such as TI59 on line with the experimental apparatus. 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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Editor
Albert T. Macrander
Argonne National Laboratory