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Review of Scientific Instruments

Issue 3 • Date Mar 1988

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Displaying Results 1 - 25 of 32
  • Inelastic x‐ray scattering with fluorescence coincidence detection using a pulsed synchrotron source

    Page(s): 407 - 413
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    We describe a system used to measure the spectrum of x rays scattered inelastically from K‐shell electrons using a coincidence technique. The source of the x rays was a pulsed synchrotron source. We describe fast–slow coincidence logic adapted for use with a pulsed source of fluctuating intensity, describe in detail the background subtraction and statistical noise in the measurement, and present the results of measurements made with the system. The precautions used to avoid detector‐to‐detector scattering are also described. The combination of high source intensity and coarse time resolution (due to the pulsed nature of the source) put us in the regime for much of the scattered x‐ray spectrum, in which the number of accidental coincidences greatly exceeded the number of true signal counts. We show that in this case significant reductions in statistical uncertainty may not be achieved by further increases in source intensity. View full abstract»

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  • Calibration of pulsed x‐ray spectra

    Page(s): 414 - 419
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    A new technique has recently been described for the absolute calibration of intense sources of pulsed radiation in the 0.2–1‐MeV range of photon energies. An x‐ray activation technique, it depended upon the storage of samples of the irradiating spectrum in the form of populations of nuclei excited to isomeric states with lifetimes of seconds to hours. Accuracy was dependent upon the precision assumed for tabulated values of nuclear parameters. Described here is an extension of this technique to the larger range of photon energies, 0.2–1.5 MeV and to intensities from 1012 keV/keV to 1016 keV/keV using the target nuclei 79Br and 77Se. In this work self‐consistency of the nuclear parameters was directly determined. Important changes were found to be necessary for improved accuracy, particularly over the larger ranges of experimental variables being considered. Values of the now‐consistent set of nuclear parameters are reported. View full abstract»

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  • High precision alignment of x‐ray transmission diffraction gratings

    Page(s): 420 - 422
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    Gold transmission diffraction gratings used for x‐ray spectroscopy must often be aligned rotationally to within submilliradian accuracy of an instrument axis. Currently, these gratings have a high line density (grating periods less than 300 nm) so conventional techniques (such as optical imaging or diffraction) which have been used previously to determine the grating orientation cannot work. Other techniques (such as polarization effects) give ≪1‐mrad accuracy. We describe here a simple technique that allows one to produce an optically observable alignment mark that is oriented parallel to the grating direction within a few microradians. We ‘‘write’’ a line, ∼0.01‐mm wide, directly on the grating by exposing an electron‐beam‐sensitive coating of polymethylmethacrylate (PMMA) on the grating while driving the grating through the beam of a scanning electron microscope (SEM). The direction of motion is made parallel to the grating lines by controlling the stage motion with a joystick while inspecting the grating in the SEM. Using the joystick, one can ‘‘follow’’ a single grating line from end to end. The SEM written line is made a permanent addition to the grating by ion‐beam etching or gold microplating, and can later be used for in situ alignment verification. Our lines have been made parallel to the original grating lines to approximately ±5 μrad; this alignment can be extended to ±1 μrad. Standard optical techniques can be used to align the grating with respect to an arbitrary instrument axis. This technique works equally well with transmission and reflection gratings. View full abstract»

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  • Low‐pressure, automated, sample packing unit for diffuse reflectance infrared spectrometry

    Page(s): 423 - 426
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    An automatic, low‐pressure packing unit has been designed with control of packing time and pressure to prepare powder samples for diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This unit also provides a polished packing surface that ensures constant measurement height of the sample in the spectrometer. Use of this unit coupled with sample rotation during measurement and control of particle size and size distribution, provides excellent precision in obtaining DRIFTS spectra. For example, repackings by a single person or by several untrained people gave coefficients of variation from 0.8% to 2.3% for each digital spectral value for a coal sample and from 1.3% to 3.7% for thymol blue, a sharp spectral featured organic, rather than the 15%–30% normally found for repackings of the same sample. Thus representative DRIFTS spectra can be obtained quickly and efficiently from a powder sample with a single spectrum using this low‐pressure, mechanical packing device, control of particle parameters, and sample rotation as opposed to previous efforts requiring the repacking of several samples and averaging of the spectra. View full abstract»

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  • Plasma emission spectroscopy with an optical fiber probe

    Page(s): 427 - 429
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    We have developed an optical fiber probe which is well suited for measuring localized light emission in plasmas. The plasma emission intensity distribution along the axis of a parallel‐plate rf glow discharge has been used as an example for comparing measurements between the optical fiber probe and the standard lens‐slit system. View full abstract»

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  • Nanoradian sensitivity Kerr effect apparatus

    Page(s): 430 - 433
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    The shot‐noise limit to the sensitivity of ellipsometric phase shift measurements with a laser beam power of a few mW is of the order of 10-9 rad. An apparatus is described that realizes shot‐noise‐limited performance for dc Kerr effect birefringence measurements. View full abstract»

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  • Electronic device for the analysis of electron diffraction patterns

    Page(s): 434 - 437
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    Using a video camera, a video digitizer, and a microcomputer, an image processing system is assembled to determine the locations of electron diffraction spots on photographic negatives of electron diffraction patterns. This system can help to reduce the measurement time to one third when compared with conventional manual methods and produces results with better accuracy and less operator fatigue. View full abstract»

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  • System for simultaneous count/current measurement with a dual‐mode photon/particle detector

    Page(s): 438 - 442
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    A microcomputer‐based control system for a dual‐output Channeltron (TM) detector has been developed and implemented. This system is capable of collecting ion current and ion‐counting information simultaneously. Ion current and ion‐counting data are scaled in software and provide consistent ion intensity values from both outputs. Calculation of the ion current/ion count rate ratio at each peak in the mass spectrum allows the system to compensate for variations in gain from peak to peak. The data collection system maximizes the data collection rate and extends the useful dynamic range of electron multiplier‐based detection to nine orders of magnitude with no change in any of the multiplier conditions. Measurement of such a wide range of ion intensities in a single spectrum is particularly useful for applications in tandem mass spectrometry. View full abstract»

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  • Ion source for production of metastable He+(2S1/2) ions

    Page(s): 443 - 447
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    The construction and performance of an electron bombardment ion source designed to produce a beam of low‐energy (100–400 eV) singly ionized helium (He+) with a significant fraction of ions in the metastable 2S1/2 state is described. The source operates in the fringe field of a magnet and injects ions along the field lines into the center of the magnet. He+ currents of up to 70 μA with small beam energy spread (3 eV) are obtained. A typical metastable fraction is 0.08% for small He+ currents (2–5 μA). View full abstract»

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  • Low power, 3.2‐cm, efficient microwave electron cyclotron resonant ion source

    Page(s): 448 - 452
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    Design improvements in a microwave (2.45‐GHz) plasma disk ion source have resulted in a compact, efficient, and low power ion source capable of delivering ion beam current densities in excess of 10 mA/cm2 . The ion source has been designed for a 3.2‐cm‐diam double graphite extraction grid set. Ion beam extraction was studied using argon and oxygen discharges with input gas flows of 1–5 standard cubic centimeters per minute (sccm) and input powers under 150 W. Ion beam currents of 20 to over 40 mA were obtained at extraction potentials of 1600 V. Double Langmuir probe measurements were made for argon, and by using a free‐fall diffusion model, extracted beam current densities were shown to be consistent with measured discharge electron and ion densities. These experiments demonstrate the ability of microwave plasma technology to produce high beam current densities for both inert and chemically reactive gases. The compact electron cyclotron resonant microwave ion source shows significant improvements in efficiency, lifetime, and ion beam current densities over earlier designs and over similar size conventional broad beam dc and rf ion sources. View full abstract»

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  • Small multicusp H- source

    Page(s): 453 - 456
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    High‐quality H- beams have been generated from a multicusp source equipped with a permanent magnet filter. It is shown that a large improvement in H- yield can be achieved by employing a small multicusp source, fabricated with the proper wall material and extraction chamber length. From this small source, H- current densities higher than 250 mA/cm2 have been extracted from a 1‐mm‐diam aperture for a discharge voltage of 150 V and a discharge current of 450 A. When the source is operated with deuterium, the extractable negative ion current density is reduced by approximately 30%. View full abstract»

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  • Thomson parabola ion energy analyzer with a coincident and jitter‐free applied electric field ramp

    Page(s): 457 - 459
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    A simple Thomson parabola ion energy analyzer for intense pulsed ion beam is demonstrated. Beam ions collimated by two apertures, are deflected by a time ramping electric field and a static magnetic field. The ramping electric field is produced with a stacked cable pulser powered by a voltage divider of the pulse power generator. As there is no additional switching tube and no high‐voltage generator other than the main machine, the analyzer has an electric field ramp that is coincident and has no jitter with the ion beam. A temporal history of ion beam energy is measured as an example and a reasonable agreement with the measured diode voltage is obtained. View full abstract»

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  • Magnetic surface mapping with highly transparent screens on the Auburn torsatron

    Page(s): 460 - 466
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    In stellarator‐type magnetic confinement devices (of which the torsatron is one), the magnetic field is produced entirely by external, current‐carrying coils. Two methods for mapping magnetic surfaces in the Auburn torsatron were tested and compared, both of which involve the use of highly transparent screens. The first method consists of coating the screen with a phosphor that emits light when struck by electrons emitted by an electron gun. A pattern representative of a magnetic surface is formed on the screen, and this pattern is recorded photographically. The second method uses an uncoated screen to collect electrons emitted from an emissive probe, which is scanned over a poloidal cross section of the torus. Under certain conditions, the collected current is a constant over a particular magnetic surface so that a contour plot of the current versus position is equivalent to a plot of the magnetic surfaces. Parametric studies of the two methods are presented, and the effectiveness of each technique is discussed. View full abstract»

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  • Automatic system for the control of batch‐produced 11CO2 for continuous labeling experiments

    Page(s): 467 - 469
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    A system for storage and continuous dispensing of constant activity 11CO2 from batch production is described. The system has been used successfully to maintain constant activity levels for 2‐h plant tracer kinetic experiments. This development now allows any existing cyclotron facility to supply a radioisotope stream continuously from a short batch irradiation. It requires no modification for use with other isotopes such as N‐13 or O‐15 in gaseous form and can be used in other biological and clinical investigations as well as the plant physiology investigations for which it was developed. View full abstract»

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  • Apparatus for the measurement of compressibility isotherms of gases up to 10 kbar: Experimental data for argon at 298.15 K

    Page(s): 470 - 476
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    An apparatus for the measurement of compressibility isotherms of gases up to pressures of 10 kbar and at temperatures between 273 and 350 K is described. It is based on a gas expansion method in which the pressure distortion of the experimental volume is evaluated by calibration with the measuring gas at lower pressures. The apparatus can easily be adapted for isochoric measurements over a wide temperature range. Measurements on argon at 298.15 K show that the method is capable of giving a precision of 0.02%–0.06% for the density, 0.1% for the pressure, and 2 mK for the temperature. View full abstract»

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  • Characteristics of a thermal gas flowmeter

    Page(s): 477 - 479
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    The characteristics of a thermo tube type thermal gas flowmeter were analyzed and experimental results were described. The output of this flowmeter is temperature difference between two points along an electrically heated capillary. An analytical expression of its outputs was derived assuming a simple flow condition. An experimental prototype was constructed. The temperature distribution was measured and the outputs were obtained for three kinds of gases: nitrogen, carbon dioxide, and argon. Those outputs were compared with theoretical ones, and those agree well in the case of small flow rate. The relationship among temperature difference, mass flow rate, and specific heat of gas was discussed. View full abstract»

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  • In situ magnetization loop tracer for thin‐film growth

    Page(s): 480 - 483
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    A thin‐film loop tracer is described which is straightforward to construct, rugged, has a sensitivity of at least 10-6 emu at fields to 3000 Oe, and a bandwidth of 1 megacycle. The device is readily adaptable for in situ ultrahigh‐vacuum measurements. View full abstract»

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  • Rapid separation of fine particles with narrow size distribution

    Page(s): 484 - 485
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    In a rotating tube with steady (laminar) flow (RSF) or with alternate flow (RAF) method for separation of fine particles, a simple and practical formula giving the relationship between the particle velocity (RSF velocity) along the tube length and parameter Aω0/V0 is derived, where A is the tube radius, ω0 is its angular velocity, and V0 is the sedimentation velocity of a particle. The chromatographic classification by these helical orbit sedimentation methods with laminar flow have been investigated with the formula in detail. In the flow methods the lowest size for biological and chemical samples with density ρ(≳1.05 g/cm3) is estimated as ∼10 μm when the tube with 2–4 mm i.d. and length L∼1 m is used. View full abstract»

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  • High‐accuracy oxygen polarograph for photosynthetic systems

    Page(s): 486 - 491
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    A new system is presented here, whose design is based on the electrochemical phenomena occurring on the platinum electrode that we examined before [P. Meunier and R. Popovic (unpublished)]. The architecture of the system is articulated around an IBM‐PC computer which controls the polarization of the electrodes, the triggering of the flash lamp, and the acquisition of data. The potentiostat circuit and new electrode design improve the response of the electrode to a rise time of 4 ms and a decay time constant of 21 ms, without the signal being distorted by filters and without using the first derivative of the signal. This polarograph shows a 50‐dB signal‐to‐noise ratio (0.3% error) during experiments with the motile algae Dunaliella tertiolecta. The determination of amplitudes of oxygen production is performed with third‐order cubic spline interpolations, after subtraction of the current base line. The resulting accuracy and reproducibility will enable researchers to attain a higher degree of refinement in the quantification of properties of the oxygen evolving complex. View full abstract»

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  • Automated system for relative sound velocity and ultrasonic attenuation measurements

    Page(s): 492 - 495
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    In order to facilitate measurements of ultrasonic velocity and attenuation, we have developed an automated version of the phase sensitive technique with quadrature detection. The technique is outlined and the precision of relative transit time or velocity measurements that can be obtained from it is analyzed. We describe the computer‐controlled experimental setup and report relative velocity and attenuation results obtained on a single crystal of pure KZnF3 . The temperature dependence of the elastic constants C11 and C44 calculated from these results agree very well with that obtained from echo overlap measurements performed on the same crystal. The relative error on the present velocity measurements is Δv/v∼10-5 . View full abstract»

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  • Four‐probe single‐crystal holder for conductivity measurements

    Page(s): 496 - 497
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    The development and testing of a four‐probe small single‐crystal holder for conductivity studies down to liquid‐helium temperature is described. A single crystal of the reactive sodide, Na+C222∙Na, was successfully mounted, but its resistance was too high to permit determination of the conductivity. The method should be useful for single‐crystal conductivity measurements of reactive and/or thermally unstable crystals. View full abstract»

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  • Small oven for obtaining temperatures to 1350 °C

    Page(s): 497 - 498
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    A small, inexpensive oven capable of achieving a temperature of 1350 °C with a power consumption of less than 1 kW is described. The oven has a working volume which is roughly 10×6×12 cm. It has been used for bonding gold to sapphire substrates, but would be suitable for use in any application which requires elevated temperatures in a working volume of 500–1000 cm3. View full abstract»

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  • Time response of small side‐on photomultiplier tubes in time‐correlated single‐photon counting measurements

    Page(s): 499 - 501
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    The position‐dependent time response of eight small side‐on type photomultiplier tubes (Hamamatsu R928 and R955) has been investigated. Using the method of time‐correlated single‐photon counting relative transit times, single‐photon response widths and relative quantum yields have been determined. This characterization provides the basis for the proper selection and use of fast photomultiplier tubes in single‐photon counting experiments. View full abstract»

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  • Optical alignment device for x‐ray diffraction systems

    Page(s): 501 - 502
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    A device is described which enables x‐ray diffraction systems to be aligned optically using a collimated laser beam to mimic the x‐ray beam path through the system. Alignment using the device is faster and safer than the conventional procedures. View full abstract»

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  • Dark‐field microscopy of transparent objects with a bright‐field objective

    Page(s): 502 - 503
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    Described is a simple modification of a standard bright‐field objective to produce dark‐field imagery of transparent objects. 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