bluuebunny/crossref_metadata_2025 huggingface dataset:
Versatile pulse programmer for nuclear magnetic resonance
Authors: Adduci D. J. , Gerstein B. C.
Published: March 2003

A microprocessor-based pulse programmer for pulsed NMR applications employing digital integrated circuit and microprocessor techniques is described. The pulse programmer was designed to be completely general with the capability to quickly and easily program any desired pulse sequence. Pulse sequenching and timing information is entered through any standard ASCII terminal using a programming language developed specifically for NMR. A resident text editor provides for easy pulse sequence modifications as well as a program library feature. A language translator and run-time monitor transform this general hardware system into a ’’smart’’ pulse programmer capable of extended programming functions.
All-metal automated Toepler pump for laboratory use
Authors: Baker R. W. , Buxton T. L. , Ellefson R. E.
Published: March 2003

An all-metal automated Toepler pump has been developed with improved safety and reliability over the traditional glass pump. New applications cited include the preparation of standard gas mixtures and the transfer of gas for vapor phase reactions.
Design and characteristics of a cell for photoacoustic spectroscopy of condensed matter
Authors: Ducharme D. , Tessier A. , Leblanc R. M.
Published: March 2003

We describe a photoacoustic cell which is simple to use, easy to construct, and which gives a great sensitivity, expressed as a signal-to-noise ratio of 3000. Calibration of the cell indicates that it can be used with confidence as a general purpose photoacoustic cell.
Soldering multifilamentary Nb3Sn conductors
Authors: Broach J. Thomas , Lee W. David
Published: March 2003

A method is described for making solder connections to a commercial Nb3Sn multifilamentary conductor.
Electrical feedthrough for gas pressures up to 10 000 bar and low temperatures
Authors: Schouten J. A. , Trappeniers N. J. , Goedegebuure W.
Published: March 2003

An electrical gas-tight feedthrough is described which is suitable for use at pressures up to 10 000 bar and temperatures down to −180 °C. The capacitance of the feedthrough is about 20 pF.
Streak camera-TV system with improved S/N ratio incorporating a digital video recorder directly interfaced to a computer
Authors: Schmidt K. H. , Gordon S.
Published: March 2003

By incorporating a digital video recorder, a streak camera system previously developed for recording time-resolved transient absorption and emission spectra was greatly improved with respect to reproducibility and accuracy. The requirements for on-line computer time were also reduced.
Air-borne laser induced fluorescence system for measuring OH and other trace gases in the parts-per-quadrillion to parts-per-trillion range
Authors: Davis D. D. , Heaps W. S. , Philen D. , Rodgers M. , McGee T. , Nelson A. , Moriarty A. J.
Published: March 2003

Described in detail is a laser induced fluorescence system which has been successfully interfaced with two aircraft sampling platforms (i.e., Sabreliner jet and an L-188C Electra). This system, which has been under development for four years, presently consists of the following major components: (1) a Nd–Yag laser driven oscillator–amplifier dye laser; (2) a sampling manifold with associated fluorescence detection optics; (3) an OH calibration chamber; (4) a laser beam steering assembly; and (5) sampling electronics and data processing hardware. During the last three years, this system has been flown some 50 000 air miles making tropospheric OH radical measurements over the latitude range of 70 °N to 57 °S. OH concentrations measured during these flights have ranged from 30 parts-per-quadrillion (3.7×105 molecules/cm3) at altitudes of 6 km to 0.8 parts-per-trillion (2.0×107 molecules/cm3) at 0.5 km. Computations have been completed which indicate that the existing aircraft system with modest modifications should also be capable of detecting natural tropospheric levels of NO, SO2, CH2O, NO2, HNO2, NO3, H2O2, and CS2 by using both conventional laser-induced fluorescence methodology and multiphoton techniques.
Electrohydraulic fatigue apparatus for testing at cryogenic temperature
Authors: Liaw P. K. , Baker J.
Published: March 2003

A closed-loop electrohydraulic fatigue apparatus was constructed for testing from above room temperature to 77 K. Several important improvements in the electronics of the reference function generator and the servo controller over previous apparatus are described. The electronics allows cool-down of the specimen to 77 K at zero stress, correction for thermal contraction, and then cyclic fatigue testing under strain control, all without interruption of hydraulic power.
New cavity perturbation technique for microwave measurement of dielectric constant
Authors: Sen Susanta , Saha P. K. , Nag B. R.
Published: March 2003

A new cavity perturbation technique is presented for microwave measurement of dielectric constant, which uses a modified cylindrical reentrant cavity. Though suitable for only low dielectric constants, the method has the advantages, (a) sample area does not appear in the calculations, (b) only the ratio of frequency shifts due to two samples of same area and different thickness is involved, and (c) calibration of the measuring system with known dielectric is not necessary.
Further laboratory studies and stratospheric flight of a mass spectrometer beam system
Authors: Mauersberger K. , Finstad R.
Published: March 2003

A gas expansion system combined with a mass spectrometer has been tested and flown successfully in the stratosphere. Through a sequence of orifices and high speed pumping, gas particles were formed into a molecular beam and analyzed by a sensitive mass spectrometer. During two balloon flights, vertical profiles of all major atmospheric constituents as well as O3, CO2, H2O and others were obtained. Gases such as 38Ar and 16O17O provided in-flight calibration standards. The sensitivity of the system was such that gases with mixing ratios of 10 ppb at an ambient pressure of about 10 mbar were detectable.
Screw-fastened joints for thermal contact at low temperatures
Authors: Lau K. M. , Zimmermann W.
Published: March 2003

Electrical resistance measurements at 4.2 K on simple screw-fastened joints between two pieces of bare copper, between two pieces of gold-plated copper, and between two pieces of silver indicate the potential usefulness of such joints for thermal contact down to millikelvin temperatures.
Electronic stabilization system for an oscillating vane pressure gauge
Authors: Hainsworth D. W. , Dyksterhuis F. H.
Published: March 2003

An electronic stabilization system for an oscillating vane pressure gauge is described. A new continuous drive method is used, obviating the necessity for reliance on mechanical filtering by the vane to produce stable oscillation amplitude. The parameter, damping coefficient, can be measured as being proportional to dc voltage. The dc correction signal is generated with attention to system stability so that stable operation is achieved quickly. Experimental results showing proportionality between the dc correction voltage and damping ratio are presented.
Single photon x-ray detection with a CCD image sensor
Authors: Catura R. C. , Smithson R. C.
Published: March 2003

Individual x rays of 5.9 and 22.4 keV have been detected and energy analyzed in single pixels of a CCD image sensor. The results indicate the CCD operates as an array of tiny Si solid state detectors providing both high spatial resolution and x-ray energy discrimination. These devices will prove useful sensors at the focus of future x-ray telescopes.
System for dispensing and continuously measuring the flow of solid particles into a hot high pressure gas flow
Authors: Goin K. L. , McClure J. G.
Published: March 2003

A system for dispensing and continuously measuring the flow of solid particles into a hot high-pressure gas flow for times up to 1 h is described. A differential pressure across an orifice is used to force the particle flow. A strain gauge load cell is used to continuously sense the weight of the container from which the particles are being dispensed. Calibration results are included for flows of 100-μm-diam glass spheres through several orifices at rates from 1 to 15 g/s.
Apparatus for studying fretting fatique in vacuum
Authors: Poon C. , Hoeppner D. W.
Published: March 2003

Recent investigations on the mechanism of fretting fatigue have indicated that mechanical damage, not chemical corrosion, has the largest effect in decreasing structural component life. Since there is no general agreement on the mechanism of fretting fatigue, an experiment has been designed to evaluate statistically the relative role of the mechanical process and the chemical process in reducing fatigue life. An initial step was to develop an apparatus that allows fretting fatigue tests to be performed in both laboratory air and vacuum environments. A detailed discussion of the experimental apparatus and experimental procedure are presented in this paper. Also typical test results are presented. It is found that fretting fatigue in vacuum is about ten times slower than that in laboratory air. Fractographic analysis of the wear surface indicated that less severe fretting damage occurred in the vacuum environment.
Differential light detector
Authors: Hofmann K. P. , Emeis D.
Published: March 2003

A sensitive differential light detector is described which consists of two antiparallel silicon photovoltaic diodes and a current-to-voltage converter. The device is optimized to the detection of small differences in intensity. The noise and signal transfer features are considered, and an application example is given.
New fully bakeable and moveable vacuum seal between stainless steel and Al2O3 ceramic
Authors: Langenwalter M. , Grössl M. , Märk T. D.
Published: March 2003

The current paper describes a simple construction which allows the monitoring of the radial dependence of the extracted and mass identified ion currents in a hollow cathode stationary afterglow apparatus at any time during the afterglow. The main feature of the monitoring device is a fully bakeable and moveable vacuum seal between polished stainless steel and polished Al2O3 ceramic.
Ion wave excitation with an array of wire probes
Authors: Schott L.
Published: March 2003

A simple and inexpensive method to excite compressive ion acoustic waves with relative amplitudes δn/n≲0.45 is described.
Comparison of circuits for linearizing the temperature indications of thermistors
Authors: Hoge Harold J.
Published: March 2003

Eight circuits designed for producing a signal that is a linear function of temperature change, utilizing a single thermistor as the temperature-sensitive element, are examined. All are found equal in linearizing capability, including five circuits containing operational amplifiers. This finding does not apply to certain linearizing circuits such as those containing logarithmic amplifiers, some of which may be expected to have a linearizing capability greater than that of the circuits examined.
Superconducting accelerometer using niobium-on-sapphire rf resonator
Authors: Blair David G.
Published: March 2003

An accelerometer is described which uses a rf niobium-on-sapphire resonator as its sensor element. The accelerometer uses a magnetically levitated spool as a test mass and the spool modulates the inductance of the resonator; its position is servo controlled to maintain the resonator at the external rf excitation frequency. The accelerometer has high sensitivity over the full audio frequency range, but is optimized for frequencies between 100 Hz and 1 kHz, where the calculated displacement sensitivity approaches 10−15 cm for a 1 Hz measurement bandwidth. The system noise sources are analyzed and possible improvements are discussed.
Heat capacity measurements by means of thermal relaxation method in medium temperature range
Authors: Hatta Ichiro
Published: March 2003

The thermal relaxation method is used to measure heat capacities of small samples in the temperature range around room temperature. The calorimeter is designed to measure under heat exchange gas and a steplike excess heat is applied to the sample by irradiation from a lamp.
Versatile digital lock-in detection technique: Application to spectrofluorometry and other fields
Authors: Cova S. , Longoni A. , Freitas I.
Published: March 2003

A digital lock-in detection technique which overcomes some practical limitations of the analog lock-in amplifiers is described. An example of implementation is given, based on multichannel pulse analyzers. Some representative results are reported for two typical application fields of lock-in techniques, namely optical spectrometry and semiconductor profiling with C–V techniques. Advantages and limitation of the technique are discussed as well as adaptation to various modulation waveforms.
Geometries and focal properties of two electron-lens systems useful in low-energy electron or ion scattering
Authors: Chutjian Ara
Published: March 2003

Geometries and focal properties are given for two types of electron-lens systems commonly needed in electron scattering. One is an electron gun which focuses electrons from a thermionic emitter onto a fixed point (target) over a wide range of final energies. The other is an electron analyzer system which focuses scattered electrons of variable energy onto a fixed position (e.g., the entrance plane of an analyzer) at fixed energy with a zero final beam angle. Analyzer-system focusing properties are given for superelastic, elastic, and inelastically-scattered electrons. Computer calculations using recent, accurate tube-lens focal properties are used to compute lens voltages, locations and diameters of all pupils and windows, and filling factors and asymptotic rays throughout each lens system. Focus voltages as a function of electron energy and energy change are given, and limits of operation of each system discussed. Both lens systems have been in routine use for several years, and good agreement has been consistently found between calculated and operating lens voltages.
Some characteristics of tungsten filaments operated as cathodes in a gas discharge
Authors: Ehlers K. W. , Leung K. N.
Published: March 2003

Some physical properties of tungsten filaments, when operated as cathodes in a gas discharge, are presented. For a 0.1524-cm-diam tungsten wire, the initiation of a discharge is found to be dependent on the filament geometry. The effect of connecting the discharge power supply to either the positive or negative leg of the filament is examined. When the emission current becomes a sizable fraction of the filament heater current, the filament does not emit uniformly. The temperature distribution indicates that the majority of the electrons are emitted from the negative leg of the filament.
Capacitance measuring circuit for water waves
Authors: Popil R. , Curzon F. L.
Published: March 2003

A simple, reliable, integrated circuit is described which is used to measure standing water waves of amplitudes ranging from less than 1 mm. The circuit has a high dynamic range and is linear for changes in water depth of several centimeters. The sensitivity of this capacitance measuring device is 38 mV/mm of wave amplitude, enabling small amplitude waves to be readily detected.
Effect of finite analyzer size on the distribution functions measured in field-free plasmas
Authors: DeNeef C. P. , Theiss A. J.
Published: March 2003

Ideal, gridded, planar electrostatic retarding field analyzers correctly measure isotropic velocity distributions in field-free plasmas if the grid and collector are infinite. However, the finite apertures in practical analyzers block some particles that have sufficient momentum to be collected. We calculated the resulting error in the measured distribution function for a range of analyzer sizes when a Maxwellian distribution enters the analyzer.
Voltage multiplication circuit for starting uv source gas discharge lamps
Authors: Chapman R. , Moore S. E.
Published: March 2003

Gas discharge lamps need a momentary high voltage to initiate their operation but normal operation only requires a much lower operating voltage. Circuit design parameters are presented, together with a practical arrangement, so that the HV trigger pulse may be derived in an economical manner from the normal operating power source.
Circuit for maintaining constant phototube current in polarization modulation spectroscopy
Authors: Modine F. A.
Published: March 2003

A description is given of a control circuit that maintains a constant direct current from a photomultiplier tube. The circuit is useful in spectroscopic applications employing ligh modulation at high frequencies.
Simple bridge detector for use with a low-temperature capacitance thermometer, and thermometer performance limits
Authors: Prober D. E.
Published: March 2003

A simple high-resolution bridge circuit for use with a glass–ceramic capacitance thermometer is described. This circuit allows a linear readout of capacitance changes and has better than 1 mK resolution and short-term stability. Performance limits of the thermometer itself are also reported. Irreproducibility of thermometer calibration upon thermal cycling can be as large as 0.3 K, and changes in the calibration slope dC/dT are also observed. The bridge circuit described partially compensates for these shifts in dC/dT.
High-resolution scanning transmission electron microscope at Johns Hopkins
Authors: Wiggins J. W. , Zubin J. A. , Beer M.
Published: March 2003

The scanning transmission electron microscope constructed at Johns Hopkins follows the general layout of the first instrument at the University of Chicago. It is currently operating at 50 kV with a resolution of about 3 Å. Its detector scheme consists of scintillation crystals coupled to photomultipliers in such a way as to eliminate introduction of unnecessary statistical noise. A unique alignment scheme utilizes the spherical aberration of the objective lens.
Construction of a Čerenkov light source
Authors: Rothbart G. B. , Sheppard J. C. , Piestrup M. A. , Powell R. A. , Pantell R. H. , Gearhart R. A.
Published: March 2003

A radiation source has been developed and implemented from Čerenkov emission that is intended to provide an intense continuum from the infrared to 600 Å. Parasitic use of the primary electron beam at the Stanford Linear Accelerator Center (SLAC) together with a novel optical geometry for light collection can give a focused and tunable ultraviolet beam with 104 kW/m2⋅sr brightness, 10−2 spectral purity, and with the pulsed, 5 ps time structure of the SLAC electron beam. Measurements of emission characteristics in the visible part of the spectrum correlate closely with the predicted performance.
Extension of the application of the shorted quartz gauge
Authors: Rosenberg Gideon
Published: March 2003

Shorted guard-ring quartz gauges 12.7 mm in diameter and 3.2 mm thick were shock loaded by AL 6061 and copper impactors to stresses of 42 and 58 kilobars, respectively. Distortion of the current output was observed only at the 58 kilobar stress; at 42 kilobars the current profile conforms closely to the stress profile. Comparison of present data with previous studies demonstrates: (a) The present results lie on a smooth extension of an earlier calibration by Hayes and Gupta. (b) When only the current peak at the shock front is considered, the present data lie close to Graham’s curve for shunted gauges. An example of application of the shorted gauge at 40 kilobars to monitor a stress relaxing profile in LiF is also described.
New beam postion monitor by detecting wall currents
Authors: Satoh Kohtaro
Published: March 2003

A new type of beam postion monitor has been designed and bench tested. The results agreed well with the expected performance. Tests with the proton beam showed that this monitor was applicable to our accelerator.
6Li-loaded liquid scintillators with pulse shape discrimination
Authors: Greenwood L. R. , Chellew N. R. , Zarwell G. A.
Published: March 2003

Excellent pulse height and pulse shape discrimination performance has been obtained for liquid scintillators containing as much as 10 wt.% 6Li-salicylate dissolved in a toluene-methanol solvent system using naphthalene and 9,10 diphenylanthracene as intermediate and secondary solutes. This solution has improved performance at higher 6Li-loading than solutions in dioxane-water solvent systems, and remains stable at temperatures as low as −10°C. Cells as large as 5 cm in diameter and 15.2 deep have been prepared which have a higher light output for slow neutron detection than 10B-loaded liquids. Neutron efficiency calculations are also presented.
Pneumatic hydrogen pellet injection system for the ISX tokamak
Authors: Milora S. L. , Foster C. A.
Published: March 2003

We describe the design and operation of the solid hydrogen pellet injection system used in plasma refueling experiments on the ISX tokamak. The gun-type injector operates on the principle of gas dynamic acceleration of cold pellets confined laterally in a tube. The device is cooled by flowing liquid helium refrigerant, and pellets are formed in situ. Room temperature helium gas at moderate pressure is used as the propellant. The prototype device injected single hydrogen pellets into the tokamak discharge at a nominal 330 m/s. The tokamak plasma fuel content was observed to increase by (0.5–1.2) ×1019 particles subsequent to pellet injection. A simple modification to the existing design has extended the performance to 1000 m/s. At higher propellant operating pressures (28 bars), the muzzle velocity is 20% less than predicted by an idealized constant area expansion process.
Image reduction to submicrometer dimensions by asymmetric crystal reflection of x rays
Authors: Mardix S. , Lang A. R.
Published: March 2003

An image-reduction method utilizing asymmetric Bragg reflection is demonstrated by 9.5-fold and 22.6-fold one-dimensional reductions of a 30 cell/mm gold mesh having a web width of 8μm. Applicability of the method to microphotolithography is suggested.
Measurement of pressure at the wavy gas–liquid interface
Authors: Kordyban Eugene , Cuker Seymour
Published: March 2003

A method for measuring the pressure in gas at the wave surface has been developed and is presented here. This method utilizes a sensor which follows the wave surface; the pressure fluctuations usually present under such conditions have been minimized by the use of a swivel joint and special tubing configuration.
Simple calibrated gas feed system
Authors: Horwitz C. M.
Published: March 2003

Constant calibrated gas flow is needed in vacuum processes such as plasma etching and sputtering. It is shown that capillary tubes combined with a simple pressure regulator can give satisfactory results. Typical calibrations for different capillary lengths, diameters, and for different gas types (A, N2, H2, He, CH4, CCl2F2, CHClF2) are given. Agreement with viscous flow theory is good, and over a 100:1 range in flowrate the resettability and variability in flowrate varies from ±2% to ±20%.
Constant-current supply of 3 ppm stability and resettability; application for a SQUID
Authors: Levy B. , Greenfield A. J.
Published: March 2003

We describe a new design for a constant-current supply which is stable and resettable to 3 ppm over a period of one week, even in the presence of ambient temperature changes of several degrees. These characteristics are achieved by utilizing a digital-to-analog converter for providing a changeable, yet extremely stable, reference voltage. Seven full-scale current ranges are available between 0.1 and 100 mA. It is also shown that this constant-current supply is suitable even for use with a SQUID, meeting all of the exacting requirements for such use.
Improved grid holders for an all-purpose electron microscope specimen stage
Authors: Warble C. E.
Published: March 2003

The general requirements necessary for a specimen grid holder (cup) to meet the rather stringent demands set by an all-purpose specimen stage are discussed. Two models made from platinum or aluminum are described, which provide for the grid to be either on or off the axes of tilt, and allow the cup and grid to be ultrasonically cleaned. The stability, tilt movements, anticontamination, and furnace characteristics of the cups have proved to be excellent.
Bridge for measurement of low resistance
Authors: Matey J. R. , Dierker S. B. , Anderson A. C.
Published: March 2003

A simple four-terminal bridge of low power dissipation and high resolution is used to measure small resistances at low temperatures.
Microprocessor-controlled inhalation system for repeated exposure of animals to aerosols
Authors: Carpenter R. L. , Barr F. P. , Leydig R. L. , Rajala R. E.
Published: March 2003

A microprocessor-controlled inhalation exposure system (MCIES) has been built to automate aerosol generation and sampling while controlling exposure time for animal toxicity studies. The system has a time resolution of 0.1 s and automatically sequences the exposure events from initiation to temination of the exposure. The operator is required to preset all airflows, read in a paper tape containing the time sequence of events, and initiate the automatic sequence by closing a switch.
Microcomputer-based multiplexer for performing depth profiling with an Auger electron spectrometer
Authors: Oppenheimer J. L.
Published: March 2003

A microcomputer-based instrument for the automated profiling of samples with an Auger electron spectrometer and Ion Gun is described. The instrument records the changing heights of spectral peaks as it controls spectrometer scanning over predefined windows. Interactive front panel controls are used to set up a run and control profiling operations. The generated data is stored on a magnetic disk for later analysis and plotting. Implementation of the device using an LSI-11 microcomputer and interfacing hardware is detailed, along with the characteristics of the fortran iv driving software. An exploration of future capabilities and applications of the multiplexer is also given.
Gas consumption characteristics of a recirculating HF-laser
Authors: Willis C. , Dosi M. , James D. J.
Published: March 2003

The gas consumption characteristics of a recirculating HF TE-laser have been defined. The stoichiometry varies from close to H2:SF6:1:1 at low H2 concentration to 3:1 above 30% H2. The output energy shows a broad maximum in its dependence on pressure and H2 concentration and, as a result fairly stable output can be maintained with recirculation using only a simple make-up control system.
Frequency-following reference oscillator for a two-phase lock-in amplifier
Authors: Brown B. L.
Published: March 2003

The circuit for a frequency-following oscillator is described for use in obtaining a commensurate reference for a two-phase lock-in amplifier. This device is useful in tracking signals which drift slowly in frequency and which are apt to be either intermittent or momentarily small in amplitude, as in the Brownian motion of a mechanical oscillator. Digital hysteresis is used to reduce the number of tracking corrections made when the signal and the reference oscillator are close in frequency and to increase the number of corrections when they are not.
Atomic hydrogen beam source: a convenient, extended cavity, microwave discharge design
Authors: Murphy Edmond J. , Brophy John H.
Published: March 2003

An extended cavity design of a microwave discharge source for production of intense beams of atomic, radical, and metastable species in vacuo is described. The extended cavity enables the discharge to be run at the beam source nozzle while the power connection and tuning elements remain conveniently outside the apparatus. This design minimizes wall recombination losses to produce intense atomic hydrogen beams with considerably less engineering than previous discharge sources.
Precision field averaging NMR magnetometer for low and high fields, using flowing water
Authors: Pendlebury J. M. , Smith K. , Unsworth P. , Greene G. L. , Mampe W.
Published: March 2003

The separated oscillatory field magnetic resonance technique (Ramsey technique) has been employed with flowing water as a volume averaging magnetometer. Polarization and detection were performed in high fields, external to the volume over which the magnetic field was to be averaged. An accuracy of a few parts in 107 at a nominal field of 18 G was obtained. The technique is applicable, using standard equipment, for the measurement of fields ranging from kilogauss down to milligauss.
Measurement of H− density in plasma by photodetachment
Authors: Bacal M. , Hamilton G. W. , Bruneteau A. M. , Doucet H. J. , Taillet J.
Published: March 2003

Techniques have been developed for measurement of the density of H− in a plasma by photodetachment. Photodetachment is detected by the increase in electron density with no change in positive ion density after a light pulse from a ruby laser. The authenticity of photodetachment signals can be assured by their comparison with known cross sections for photodetachment of H−. Interpretations of photodetachment data are less ambiguous than probe interpretations because photodetachment is not affected by the mass of positive ions and is not limited in usefulness by the Debye distance. Photodetachment measurements with time resolution and spatial resolution are straightforward.
Improved servo-polarimeter
Authors: Primak William , Monahan Emmet
Published: March 2003

A servo-polarimeter utilizing a rotating plastic film as a modulator has been modified to improve stability and sensitivity. The birefringence in a sample being scanned by moving it past a slit can now be determined to better than 3×10−9.
Low-cost digital system for control of a retarding potential energy analyzer
Authors: Harrison A. R. , Hodge L. A. , Mahan A. H. , Dunning F. B.
Published: March 2003

A simple, low-cost digital system is described which is used in conjuction with a conventional retarding potential analyzer to measure the energy distribution of the electrons in a beam.
Effects of 1-MeV gamma radiation on a multi-anode microchannel array detector tube
Authors: Timothy J. G. , Bybee R. L.
Published: March 2003

The response of a multi-anode microchannel array (MAMA) detector tube to 1-MeV gamma radiation from a 60Co source was evaluated. The measured detection efficiency of the microchannel plate (MCP) was 2.2 × 10−2 counts/photon and no permanent degradation of MCP performance was observed after exposure to a total dose of 106 rads.
Dynamic characteristics of a simple constant-temperature hot-wire anemometer
Authors: Lu S. S.
Published: March 2003

A simple constant-temperatue hot-wire anemometer has been analyzed and tested in a shock tube and by electronic tests. In the derivation of the governing equations, the finite open-loop gain of an operational amplifier is considered. The measured values of the natural frequency and the damping coefficient for the anemometer system are in satisfactory agreement with the theory. For short probe cables, the frequency response is found to be limited by the finite open-loop gain of the amplifier.
Measurement of concentration and study of recombination of atomic hydrogen by Wrede–Harteck method
Authors: Kumar Vijay , Krishnakumar E.
Published: March 2003

The dissociation efficiency of molecular hydrogen was measured using a Wrede–Harteck gauge, at nine different pressures from 0.2 to 1 Torr with discharge/flow tubes of different sizes. The maximum dissociation efficiency was measured at 0.4 to 0.5 Torr pressure of molecular hydrogen. The effect of recombination of hydrogen atoms on the walls of the flow system and in the gas volume was considered in detail and the dissociation efficiency in the discharge region was calculated. Also, γ, the fraction of surface collisions leading to recombination, was measured by the same method and was found to be 6.4×10−5 and 4.3×10−4 for clean Pyrex and quartz tubes, respectively. This may be a new and relatively accurate method for measuring γ for atomized gases in discharge tubes of different materials.
Low-cost method for stabilization of a CO2 laser for use in far infrared laser pumping
Authors: Lund Mark W. , Cogan J. N. , Davis Jeffrey A.
Published: March 2003

A simple and inexpensive technique for stabilization of a CO2 laser used to optically pump a far infrared waveguide laser is discussed. The technique uses the fact that the output power of the CO2 laser varies as the output frequency is swept through the Doppler profile of the emission line. Stabilization is obtained by adjusting the mirror separation and forcing the output power to remain constant at the level corresponding to the desired pump frequency.
Use of sodium silicate as an ultrasonic transducer bond
Authors: Matey James R. , Ross D. L.
Published: March 2003

Sodium silicate may be used to make reliable transducer bonds for ultrasonics experiments near room temperature.
Quasi-quadrature interferometer for plasma density radial profile measurements
Authors: Lowenthal D. D. , Hoffman A. L.
Published: March 2003

A cw Mach Zehnder multichannel interferometer has been developed to measure time-dependent fractional fringe shifts with an accuracy of one-fortieth fringe. The design is quasi-quadrature in that known phase shifts, introduced in the reference beam, are time multiplexed with the normal reference beam. This technique requires only one detector per interferometer channel as compared to two detectors for most quadrature designs. The quadrature information makes the sense of density changes unambiguous, it automatically calibrates the instrument during the plasma event, and it makes fringe shift measurements virtually independent of fringe contrast fluctuations caused by plasma refractive and/or absorptive effects. The interferometer optical design is novel in that the electro-optic crystal used to introduce the 90° phase shifts is located in the common 2-mm-diam HeNe entrance beam to the interferometer, by exploiting polarization techniques, rather than in the expanded 1–2-cm reference beam itself. This arrangement greatly reduces the size, cost, and high-voltage requirements for the phase modulating crystal.
Resonant torsional apparatus for contactless measurements of electrical conductivity and magnetic susceptibility of solids
Authors: Hendrickson J. R. , Philbrook John
Published: March 2003

We have constructed a torsional resonance apparatus for contact-free measurements of the electrical conductivity of solids. Owing to its use of modulation spectroscopy, the technique achieves considerable enhancement of sensitivity compared to previous contactless methods. Conductivities in the range 10−5 mho/cm to 10−6 mho/cm can now be measured by the contactless technique. Measurements of magnetic susceptibility as low as 10−12 can be made. This sensitivity allows for investigation of magnetic impurities as dilute as 1 part in 107. In samples which display both phenomena of electrical conductivity and magnetic susceptibility, the two effects can be sorted out via analysis of frequency and/or temperature dependence. The present apparatus has potential for considerable improvement.
Rogowski coils: theory and experimental results
Authors: Nassisi V. , Luches A.
Published: March 2003

The theory is given of the voltage output of a Rogowski coil excited by a current pulse flowing along the axis of the coil. In this theory the Rogowski coil is considered as a delay line. The results do not differ from those obtained usually by considering the coil as a voltage source dφ/dt with an inductive output impedance. Details are also given of the design of two Rogowski coils and their working modes are fully analyzed.
High-resolution dc-voltage-biased ac conductance bridge for tunnel junction measurements
Authors: Moody M. V. , Paterson J. L. , Ciali R. L.
Published: March 2003

A simple, low-cost conductance bridge circuit, which provides high-resolution measurements of dI/dV and d2I/dV2 for a voltage-biased load, is presented. A resolution in dI/dV for a 90-Ω tunnel junction of several parts in 105 has been measured using a 35-μV-rms modulation level and a 1-s postdetection time constant (Bn=0.25 Hz). The output impedance of the voltage source and the error in the conductance measurement are discussed. The output impedance of the circuit with an AD119 operational amplifier is 0.02 Ω. A detailed discussion of Johnson-Nyquist, tunnel junction, and amplifier noise is presented.
Shock tube coupled to the time-of-flight mass spectrometer via a molecular beam sampling system
Authors: Krizancic I. , Haluk M. , Cho S. H. , Trass O.
Published: March 2003

A method for continuous mass spectrometric analysis of high-temperature reacting gas mixtures is described. The apparatus consists of a unique combination of three devices: the shock tube, the time-of-flight mass spectrometer, and the supersonic molecular beam. The driven section of the shock tube constitutes the reservoir of a supersonic molecular beam by which gas is continuously extracted from the reaction zone and introduced through a two-stage high-capacity vacuum system into the ionization region of the mass spectrometer. The shock tube and the mass spectrometer are coupled at right angles to one another. This configuration avoids excessive pressure buildup in the mass spectrometer system. The apparatus has an estimated mass resolution of 100 amu, a frequency range of 10–100 kHz, and can be operated over a wide range of shock conditions during the complete high-temperature pulse.
Optically coupled wide bandwidth dc isolation amplifier
Authors: Gay James G. , Iddings C. K.
Published: March 2003

We describe a general purpose optically coupled dc isolation amplifier with voltage gain of 100, 20-V peak-to-peak output swing, and response from dc to well over 250 kHz. Components used are all standard, commercially available items.
Method of forming an inexpensive high-temperature metal foil seal
Authors: Chou Mau-Song , Zawadzkas Gerald A.
Published: March 2003

A method for forming a thin metal foil seal capable of withstanding temperatures up to 500 °C and pressures up to 150 psig has been developed. The seal is formed by seam welding with an inexpensive electric marker.
Versatile, isotopically specific hydrogen halide TEA pin laser
Authors: Horwitz Alexander B. , Leone Stephen R.
Published: March 2003

A practical, easily constructed design for a laboratory hydrogen/deuterium halide chemical TEA laser is presented. Typical output energies in excess of 50 mJ/pulse broadband and 5 mJ/pulse on single lines are easily obtained. Isotopically specific oscillation on the v=1→0 band of single isotopes of H35Cl–H37Cl, D35Cl–D37Cl, H79Br–H81Br, and D79Br–D81Br is demonstrated. The ease of conversion from one laser species to the next and the flexible design provide a highly versatile device for laboratory problems in chemical and physical dynamics. Major advances in the development of laboratory HCl and HBr chemical TEA lasers are also reviewed.
Submicrometer particle detector and size analyzer
Authors: Litton C. D. , Graybeal L. , Hertzberg M.
Published: March 2003

A new instrument is described for measuring concentrations of submicrometer particulates with diameters ranging from 0.005 to 1.0 μm and concentrations as low as 750 particles per cm3 at small diameters and 25 particles per cm3 at the larger diameters. Developed by the Bureau of Mines, the instrument is capable of obtaining size distributions of the sampled particulates using an electrical mobility classification which requires voltages of less than 1000 V over the entire size range. The instrument is normally operated by 115 V ac, but it contains an internal rechargeable battery pack for up to 25 h of continuous dc operation. It has been designed primarily as an incipient fire detector, but can be used as a suspended particulate monitor and size analyzer or as a laboratory instrument for studying combustion aerosols. Representative data are presented, indicating potential uses of the instrument.
Mach one impact test apparatus utilizing an 18.4-mm-bore gas gun with a novel decelerating device
Authors: Coppa A. P. , Selden G. F. , Mehan R. L.
Published: March 2003

The design and operation of a helium-gas-driven gun capable of operation to Mach one is described in this report. The gun utilizes a unique tapered-tube decelerator that captures the sabot and prevents gas discharge from the muzzle. This feature makes it possible to operate the gun in a normal laboratory environment without excessive safety precautions.
Capacitance determination of the area thermal expansion of dielectric crystals
Authors: Legge J. C. , Robinson M. C. , Shapiro M. M.
Published: March 2003

Both the area thermal expansion and the dielectric constant of a solid insulator are determined by a capacitance technique in which the change in area of a capacitor is first caused by the variation with temperature of the dimensions of the dielectric, and then by the variation over the same temperature range of the dimensions of copper electrodes, the same sample being used in both cases. This method is particularly convenient for small, flat crystals under hydrostatic pressure and for anisotropic crystals. It is believed that a similar method could be used to measure the compressibility. The apparatus and calculations are described, and the results of a test run on the thermal expansion of NaCl are compared with previous data. Between 77 and 250 K, the measured linear thermal expansion L (T)/L (300) of NaCl agrees with the results of a Fabry–Perot etalon experiment to within 0.03%, giving differences in the coefficient of linear expansion of 10% in the worst case.
Digital feedback stabilization of a single-axial-mode CO2 TEA laser
Authors: Tsao Jeffrey Y. , Sharp R. C. , Yablonovitch E.
Published: March 2003

We have achieved long-term stability in producing high-power single-axial-mode CO2 laser pulses with a hybrid oscillator (TEA laser + low-pressure section) by using a novel digital feedback system that electronically adjusts cavity length.
Precision axial translator with high stability
Authors: Bösch M. A.
Published: March 2003

We describe a new type of translator which is inherently stable against torsion and twisting. This concentric translator is also ideally suited for precise axial motion with clearance of the center line.
Stable sinusoidal driver circuit for tuning fork choppers
Authors: Podolske James
Published: March 2003

A circuit is presented which can drive tuning fork choppers, such as the Bulova L40 and L2 series. The advantages of this circuit over the factory-supplied 5A-type driver are better drive-amplitude stability, freedom from drift due to line-voltage variations, and a cleaner, transient-free sinusoidal reference signal. Test results indicate an improvement in long-term stability by as much as a factor of 4.
A convenient standard for low-field susceptibility calibration
Authors: Rosenbaum J. , Larson E. , Hoblitt R. , Fickett F. R.
Published: March 2003

Finely ground mixtures of magnetic iron oxide and glass provide a convenient calibration standard of moderate accuracy (∼5%) for low-field (<0.5 kA/m) magnetic susceptibility measurements. The use of powders allows fabrication of standards of nearly any shape and size. For our mixtures, which range from 0.063 to 11.8% iron oxide by weight, the susceptibility values vary from 2.65×10−7 to 5.77×10−5 m3/kg, and are nearly linear with iron oxide concentration.
Long-lived rotating targets
Authors: Picot A.
Published: March 2003

The target used inside an accelerator, even if rotating, is damaged by the beam and must be frequently replaced. We describe a simple method permitting the use of a rotating target over its full area, and improving its life by a factor of 10.
A mass spectrometer for analyzing hydrogen-ion species
Authors: Ehlers K. W. , Leung K. N. , Williams M. D.
Published: March 2003

The design of a compact, high-resolution 180 ° magnetic deflection mass spectrometer for the study of positive and negative hydrogen-ion species is described.
Measurement of turbulent fluctuations in high-speed flows using hot wires and hot films
Authors: Acharya Mukund
Published: March 2003

A hot wire has a limited life in high-speed wind-tunnel flows because it is typically subjected to large dynamic loads. As a consequence hot films and modified hot wires are frequently used for turbulence measurements in such flows. However, the fluctuation sensitivities of such probes are reduced because of various factors, leading to erroneous results. This paper described the results of tests on some sensors in both subsonic and supersonic boundary-layer flows. A simple technique to determine dynamic calibration correction factors for the sensitivities is also presented.
Glass windows for hydrostatic pressures of 45 kbar
Authors: Lavergne A. , Whalley E.
Published: March 2003

Unprotected glass windows can be used at hydrostatic pressures up to at least 45 kbar on a 0.5-mm-diam aperture, and up to 40 kbar on a 0.8-mm-diam aperture.
A microprocessor-controlled photon counter for pulsed optically detected magnetic resonance
Authors: Power R. K. , Nishimura A. M.
Published: March 2003

In pulsed optically detected magnetic resonance (ODMR) spectroscopy, a lock-in amplifier is used to monitor the signal which is phase-matched to the duty cycle of an applied sequence of pulses. However, since the desired signals reside atop a much larger amplitude-modulated signal, lock-in amplification methods are difficult to use. Commerically available photon counters are of limited use, because the pulsed ODMR method requires sequential counting over several time intervals, often with minimum time delay between the intervals. The multiaccumulator photon counter described here is capable of such sequential counting over as many as four intervals. The microprocessor which controls the counter algebraically manipulates the photon counts during each of the duty cycles. The result is an inexpensive yet versatile photon counter which is suited for pulsed ODMR and other applications in which sequential counting is necessary.
Highly-reliable temperature sensor using rf-sputtered SiC thin film
Authors: Wasa Kiyotaka , Tohda Takao , Kasahara Yukio , Hayakawa Shigeru
Published: March 2003

A SiC thin-film thermistor for high-temperature use has been developed by using rf-sputtered SiC thin films. This thermistor can be used for industrial and consumer use within an operating temperature range of −100 to 450 °C. By using SiC thin films, the thermistor maintains high electrical stability. The resistance change is less than 3% after exposure to heat at 400 °C for 2000 h. In addition, the film growth technique made possible the production of a high-accuracy thermistor, i.e., thermistor coefficient <±0.5%, thermistor resistance <±1.5%.
A simple and sensitive apparatus for measuring the magnetization of small ferrite samples
Authors: Peuzin J. C. , Girod S. , Rebreyend J. C.
Published: March 2003

This paper describes an apparatus which allows the routine measurement of the magnetization of small ferrite samples using the well-known extraction method. In contrast to the classical extraction method, however, this device makes use of a high-permeability magnetic circuit that serves both to apply the bias field and to collect the sample flux. This design, together with a signal sampling technique, allows an unusually high sensitivity for this type of method (magnetic moment resolution is 5×10−5 μem). The apparatus is described in detail and a brief theory of its function is given. Finally, the device usefulness is illustrated by some measurement results referring to Ga YIG spheres that are used in ferrimagnetic resonators.
Use of 13CO2 in high-power pulsed TEA-lasers
Authors: Willis C. , Hackett P. A. , Parsons J. M.
Published: March 2003

The use of 13CO2 in carbon dioxide lasers enhances the available spectral range very significantly but is prohibitively expensive if gas flow through the laser is required. A TEA CO2 laser equipped with a gas recirculation system is described. This reduces gas costs to negligible levels even for expensive isotopic mixtures.