bluuebunny/crossref_metadata_2025 huggingface dataset:
Convenient fast pulsed molecular beam valve
Authors: Adams Thomas E. , Rockney Bennett H. , Morrison Richard J. S. , Grant Edward R.
Published: March 2003

We describe a fast electromagnetic valve for generation of a pulsed supersonic molecular beam. The valve produces 70 μs pulses with typical intensities in the neighborhood of 1×1022 molecules sr−1 s−1 at frequencies to 35 Hz. It is triggered by a low voltage–low current pulsed power supply which activates externally-mounted coils, minimizing problems of heat dissipation and electrical and magnetic interference. It also features a corrosion resistant gas reservoir isolated from the driving mechanism by a stainless steel bellows.
New approach to improve performances of electron spectrometers
Authors: Dubé D. , Roy D. , Ballu Y.
Published: March 2003

In addition to the deflection of the charged particles during their passage through an electrostatic deflector, it is proposed to impose a gradual retardation along their path, so that they leave the instrument at lower energy. By means of a new figure of merit involving the usual optical characteristics (dispersion, aberration, and magnification), it is shown that this principle can improve the performances of electron spectrometers, taking the 127° cylindrical electrostatic analyzer as an example. Calculations of energy transmission functions show that, at constant energy resolution, an increase of about 100% in the transmitted intensity may be expected for a retardation factor of 10. Further considerations on the space charge in a monochromator show that, since the charge density is mainly concentrated at the entrance and relatively unaffected by the retardation, the principle could be efficient for electron monochromators, too.
Microprocessor driven ultrafast multichannel event counter
Authors: Maurin T. , Devos F.
Published: March 2003

In this paper we describe a multichannel counter which can be very helpful in a wide range of physical measurements: time constants of very fast relaxation phenomena (from 1 ns to 10 μs), time interval between event occurrences (from 3.5 ns to 21.5 μs), phase measurements on periodic signals, event-time histogram construction (up to 65536 events on each channel), etc. Its larger number of channels, 6143 (3×211−1) permits covering a wide range of time constants while preserving its ultimate time resolution (3.5 ns). The sampling technique we used introduces no parasitic counting, so that it is able to record very short transient signals.
New method for the calibration of vacuum gauges
Authors: Labrune Jean-Claude , Théobald Jean-Gérard
Published: March 2003

A method for determining vacuum ionization gauge coefficients is described. It uses a molecular beam collision technique.
Measurement of very small phase differences
Authors: Schauer F.
Published: March 2003

A simple method is presented to measure very small phase differences in the range of microradians between two ac voltages. The voltages are combined linearly and one of them is adjusted in amplitude such that the output is a minimum. This minimum voltage is proportional to the phase shift to be measured. The method is applicable from power to radio frequencies.
Capacitive pressure gauge for use inside a sample cell
Authors: Morii Yukio , Adams E. D.
Published: March 2003

A small, self-contained capacitive pressure gauge for use inside a sample cell is described. A similar gauge with plates constructed of epoxy with a metal film coating is suitable for use within a NMR cell.
Radio frequency atomic hydrogen beam source
Authors: Slevin J. , Stirling W.
Published: March 2003

A simple, convenient rf discharge source for the production of an intense beam of hydrogen atoms is described. The design and operation is such that the discharge tube can be operated over a period of several thousand hours, producing an intense beam with dissociation ∼95%.
Estimation of heating rate using a calorimetric probe
Authors: Mehta R. C.
Published: March 2003

This paper presents a thermal analysis of a calorimetric probe. Heat-transfer rates to the instrument are estimated from measurements of temperature and rate of temperature change using energy conservation considerations. An example is given, and comparisons are made which show fairly good agreement with experimental results.
Improved 50 ps photodiode
Authors: Ramsey J. M. , Whitten W. B.
Published: March 2003

The construction of an inexpensive 50-ps rise-time photodiode is discussed. The temporal response of the photodiode is made insensitive to the quality of focus of the incoming light through a relatively simple procedure. Quantum efficiencies of up to 5.9% at 514 nm were measured.
Novel bandwidth measurement system for short-fiber lengths
Authors: Presby H. M. , Marcuse D. , Bodeep G.
Published: March 2003

A system assembled from commercially available units for measuring the bandwidth of short lengths of multimode optical fibers is described. A light pulser which generates a 75-ps FWHM pulse from a laser diode emitting at 820 nm is utilized as the fiber excitation source. An ultrahigh-speed photodiode with a rise time of approximately ∼50 ps is used for detecting the output pulse, which is then displayed on a sampling oscilloscope. A photograph of the pulse is digitized and analyzed to give the fiber bandwidth using a unique video-based and computer-operated arrangement. The bandwidths of 100 m lengths of graded-index fiber were measured with a repeatability of a few percent. The results compared favorably with independent measurements made with a standard dispersion test set.
Improved source of cold plasma electrons and negative ions
Authors: Hershkowitz Noah , Intrator Tom
Published: March 2003

A cold electron plasma has been produced, with a greater latitude in neutral pressure and plasma density than previously, by drifting plasma through an improved magnetic cusp cage. The motion across this cage has been characterized as a two-step process. First, the plasma between the cusps cools off as it loses contact with the primary ionizing electrons which are confined at the cusps and, second, the cold plasma electrons experience a ∇B×B drift across the cage barrier magnetic field. Large ambipolar fields are also seen across the region. A two-component, positive ion (Ar+)–negative ion (SF6−) plasma was created with the ratio of electron density (ne) to positive ion density (n+) continuously variable from 10−3<ne/n+<1.
Two-dimensional spatial distribution of volume emission from line integral data
Authors: Navarro A. P. , Paré V. K. , Dunlap J. L.
Published: March 2003

A method is presented for determining the two-dimensional (2-D) spatial distribution of the volume emission intensity [E = f(r,ϑ)] in a plasma from line integral data obtained by arrays of collimated detectors looking through the plasma along different chords. Subject to the assumption that E can be represented by 𝒥m [fm(r)cos mϑ +gm(r)sin mϑ] with only a few terms m, expressions are developed that separate harmonic contributions to the line integrals, a numerical procedure is outlined for inversion of these contributions to obtain the factors fm(r) and gm(r), and the formulas that result are presented for m = 0 through m = 5. This method was developed for application to data from arrays of soft x-ray detectors on the Impurity Study Experiment (ISX-B) tokamak. One use would be comparison of the soft x-ray volume emission contours with other measures of plasma shape. Simulations of these shape determinations were performed, using as input, a pressure profile representing a calculated MHD equilibrium for a D-shaped plasma in ISX-B. The results of these simulations are shown and the determination of the poloidal structure of MHD perturbations in the plasma is also illustrated.
Automatic recording of conductivity variations at rf frequencies: Application to nonstationary plasmas
Authors: Vialle M. , Fitaire M. , Margot J. , Pointu A. M. , Wartski L.
Published: March 2003

A simple device using a Phase-Locked Loop is described which allows automatic recording of the frequency and the quality factor of a rf cavity used to study a nonstationary dielectric medium.
Digital temperature control and measurement system
Authors: Strem R. B. , Das B. K. , Greer S. C.
Published: March 2003

We describe an automated digital temperature control and measurement system with a temperature resolution of about 1 mK and operating in the temperature range −40° to +70 °C.
Simultaneous measurements of thermopower, thermal conductivity, and electrical resistivity between 1.2 and 350 K
Authors: Chaussy J. , Guessous A. , Mazuer J.
Published: March 2003

We described a fast-cooling cryostat with a novel cooling system using a nitrogen heat pipe. The principal feature of the cryogenic assembly is an evacuated calorimeter containing a heat sink which can be maintained successively at 1, 4.2, and 77 K during the experiment. This allows sample regulation from 1.5 to 350 K. An electronic circuit including noise filters and nanovoltmeters is used to measure the electrical resistivity, thermal conductivity, and thermoelectric power of conducting or semiconducting materials. We used a commercially available Au–Fe–chromel couple as the working thermocouple. First, we calibrated it against germanium and platinum resistance thermometers, and compared the thermoelectric scale so obtained with previous calibrations. We report a preliminary test on pure lead which enabled us to obtain the absolute thermoelectric powers of AuFe and chromel and also to estimate the parasitic radiative heat transfer during thermal conductivity measurements. We also report the three transport properties of the title for an amorphous Ce0.3Al0.7 alloy prepared by sputtering a crystalline CeAl3 compound. The thermal conductivity and electrical resistivity were essentially those associated with amorphous materials. The thermoelectric power exhibited structure at low temperatures which suggests that a weak magnetism appeared in this glassy structure formed from the typical Kondo compound CeAl3.
3-sample, 6-lead Bridgman anvil assembly for resistivity measurements to 100 Kbar
Authors: Rajan K. Govinda , Sastry V. Sankara , Khanna Rita
Published: March 2003

An analysis of the mechanical behavior of gaskets in a Bridgman anvil under high pressure clearly reveals an inherent source of nonreproducibility in the stress system from run to run. This problem has been shown to be overcome by designing a 3-sample, 6-lead cell in which a calibrant is also mounted along with the sample. The cell is described, and results on pure antimony clearly establish that the structural transition in antimony (at room temperature) occurs, at exactly the high bismuth transition pressure.
Application of Fourier transform-NMR spectroscopy to submicrosecond time-resolved detection in laser flash photolysis experiments
Authors: Miller R. J. , Closs G. L.
Published: March 2003

The physical principles that are the foundation of the time-resolved experiment are summarized by means of a general expression for the experimental observable—the free induction decay: the reaction dynamics are treated within the framework of the radical pair theory of chemically induced dynamic nuclear polarization (CIDNP) in a strong magnetic field. The basic instrumentation used consists of a pulsed nitrogen laser and a commercial, high-resolution Fourier transform-NMR spectrometer operating at a resonant frequency of 60 MHz. Modifications to the NMR spectrometer are described that provide for kinetic experiments with a time resolution of 1.2×10−7s and a spectral resolution on the order of hertz. Selected results from the flash photolysis of two ketones that react by Norrish type I cleavage are reported and discussed to exemplify the information obtainable with this new technique. The advantages and the limitations of NMR detection in flash photolysis experiments are considered.
Gaseous breakdown studies using a modified image converter streak camera
Authors: Hong Siu-Ping , Shinoda Yuji , Schiller N.H.
Published: March 2003

The temporal and spatial information of gaseous breakdowns occurring from the nanosecond to millisecond time scales are important to the basic understanding and applications of gaseous discharges. A streak camera is an ideal tool for acquiring both time- and space-dependent data simultaneously. However, there are several problems associated with using a conventional streak camera for gaseous breakdown studies. Modifications have been made specifically to solve these problems, while the features of the original streak camera are preserved. A signal overlapping problem has been eliminated by extending the dead time to 70 ms. Streak camera response times have been minimized by adjusting the bias voltages. One streak range has been extended to 7 ms to cover the entire event of a gaseous discharge. The modifications and experimental evaluation of the modified streak camera will be presented.
Photoelectron spectroscopy of supersonic molecular beams
Authors: Pollard J. E. , Trevor D. J. , Lee Y. T. , Shirley D. A.
Published: March 2003

A high-resolution photoelectron spectrometer which uses molecular beam sampling is described. Photons from a rare-gas resonance lamp or UV laser are crossed with the beam from a differentially pumped supersonic nozzle source. The resulting photoelectrons are collected by an electrostatic analyzer of a unique design consisting of a 90° spherical sector preanalyzer, a system of lenses, and a 180° hemispherical deflector. A multichannel detection system based on dual microchannel plates with a resistive anode position encoder provides an increase in counting efficiency by a factor of 12 over the equivalent single channel detector. The apparatus has demonstrated an instrumental resolution of better than 10 meV FWHM, limited largely by the photon source linewidth. A quadrupole mass spectrometer is used to characterize the composition of the molecular beam. Extensive differential pumping is provided to protect the critical surfaces of the analyzer and mass spectrometer from contamination. Because of the near elimination of Doppler and rotational broadenings, the practical resolution is the highest yet obtained in molecular PES.
Anomalous variations in dark pulse rate in GaP first dynode PMTs at constant temperature
Authors: Yamashita Mikio
Published: March 2003

The temporal dependence of dark pulse rate in RCA 8850 tubes has been examined at different high voltages at constant temperatures. The experimental results reveal explicitly that at higher applied voltages considerable amount of luminescence occurs possibly as a result of charge buildup on the dynodes, thus causing an anomalous increase in dark pulse rate. For tubes of this type, and under specific operating conditions, the phenomenon might introduce a large unsuspected error in photon counting and in low-level scintillation counting experiments.
Metastable ion source
Authors: Holt R. A. , Rosner S. D. , Gaily T. D. , Adam A. G.
Published: March 2003

A very low-pressure magnetically-focused electron bombardment ion source is described which produces substantial quantities of ions in highly excited metastable states. Using the laser–fluorescence technique, we have measured a 2s3S1 metastable content of 0.6%–2.3% in a 0.4 μA, 5 keV beam of 7Li+. The source design can be applied to essentially any ionic species and offers the additional advantage of relatively low energy spread.
Criterion of goodness of fit for deconvolution calculations
Authors: Irvin J. A. , Quickenden T. I. , Sangster D. F.
Published: March 2003

A quantitative statistical test for ascertaining the goodness of fit in deconvolution analysis is presented and is compared with two currently used tests. The new test is generally applicable and unlike the latter tests, still holds when significant random errors occur in both the measured excitation pulse and the measured luminescence curve. One of the existing tests involves a convenient, but subjective assessment of the randomness of a plot of weighted residuals and the new quantitative text is used to evaluate the scope of this subjective approach.
Static characteristics of the three-grid modulated Bayard–Alpert gauge in intermittent-grid-modulation mode
Authors: Kanaji Toru , Urano Toshio
Published: March 2003

A new modulation mode, intermittent-grid-modulation mode, was applied to a specially prepared three-grid Bayard–Alpert gauge which has two additional concentric grids inside the electron collector grid (G1). With this mode, the modulation factors for the noise currents are very small, so that only the signal current corresponding to pressure is singled out, and the modulation can be repeated automatically without significant difficulties. Potentials of the filament and G1 are kept constant at 400 and 500 V, respectively. The innermost grid (G3) was also kept at a constant potential of 300 V to keep a stationary emission of the x-ray photoelectrons from the ion collector. To modulate the true ion current, the potential of the intermittent grid (G2) was changed manually (on:350 V/off:50 V). In the ’’on’’ and ’’off’’ states, all the thermal electrons bombard only G1, and the pressure change induced by the change of the electron stimulated gas desorption rate was not detected. The collector currents in both states for various pressures were measured, and it was confirmed that the difference, Ion−Ioff, was proportional to the pressure down to the lower pressure limit [8×10−9Pa (6×10−11Torr)] of the vacuum system employed in this study. However, the lowest measurable pressure of this gauge is believed to be much lower than this value. The modulation factor k for the true ion current was about 0.81, and the sensitivity S was about 1.3×10−2/Pa.
New fluorescence detection system for x-ray absorption spectroscopy
Authors: Cramer Stephen P. , Scott Robert A.
Published: March 2003

The design and performance of a 24-channel fluorescence detection system for use in x-ray absorption spectroscopy are discussed, and comparisons are drawn with other detection systems currently in use. Each channel of the current system consists of a NaI scintillation detector with a filter and collimator arrangement designed to reduce the scatter and filter fluorescence background. Given a sufficiently intense and stable x-ray source, this apparatus can record a useful EXAFS spectrum for an element (Z⩾23) at 100 ppm concentration in approximately 30 minutes. The new design permits the study of plate-like samples (such as molybdenum enzyme solutions) unsuitable for previously described slit assemblies. Breaking the detection system up into discrete elements also allows (1) optimization of filter thickness for each direction, (2) use of a weighting scheme to optimize the total S/N, and (3) operation at high total count rates, while retaining the advantages of pulse counting electronics. The relative merits of filters and crystal monchromators are discussed quantitatively, using the two criteria of efficiency and selectivity. It is shown that practical filters and barrel monochromators give similar performance over a 100-fold concentration range, for a given solid angle, and that the 20-fold solid angle advantage of the multielement approach makes it the design of choice for many cases. Finally, the construction of an array of solid-state detectors with the appropriate filters and collimating elements is proposed as a device capable of yielding unprecedented performance in x-ray absorption spectroscopy.
Towards picosecond resolution with single-photon avalanche diodes
Authors: Cova S. , Longoni A. , Andreoni A.
Published: March 2003

Avalanche p–n photodiodes with uniform breakdown over the junction area are known to be capable of single-photon detection. An experimental study has been performed on the temporal resolution of these single-photon avalanche diodes (SPADs) in measurements of the shape of ultrashort light pulses. By using an active-quenching circuit, pulsed operation of the device has been obtained in accurately controlled conditions, avoiding spurious effects met in previous passive-quenching circuits. Laser pulses with durations down to 150 ps FWHM have been used; the results obtained show that the resolution is remarkably better than this value. Performances and limitations of SPADs are discussed; temporal resolutions of a few tens of picoseconds may be expected.
Improved spectrophotometric cell for hydrothermal solutions
Authors: Susak Nicholas J. , Crerar David A. , Forseman Theodore C. , Haas John L.
Published: March 2003

A simple, inexpensive spectrophotometric cell was designed for use with aqueous solutions for which temperature is a maximum of 325°C and pressure, 28 MPa. The cell has an internal volume of 5 ml and a path length of 1.31 cm. Each furnace assembly is 120 mm in diameter × 150 mm high and will fit into most commercial spectrophotometers. Temperature is controlled by a standard set-point controller and a balancing circuit that is used to maintain the temperature of the sample and reference cell within 1°C of each other at any temperature.
CW far-infrared laser-scattering apparatus for plasma wave studies
Authors: Peebles W. A. , Luhmann N. C. , Mase A. , Park H. , Semet A.
Published: March 2003

A description of the design and construction of the first cw far-infrared laser-scattering apparatus for the study of the frequency and wavenumber spectra of plasma density fluctuations is given. Scattering results from both a controlled laboratory plasma and the UCLA Microtor tokamak are discussed.
Modified variable temperature control unit for NMR spectrometers
Authors: Yoshida Nobuyuki , Kumano Masafumi , Ikenoue Tsuneo
Published: March 2003

A variable temperature control unit for NMR spectrometers was modified to improve the accuracy of the temperature setting and to suppress the drift and fluctuation of the sample temperature within ±0.1 °C.
Low-frequency tunable (1–1.8 GHz) electron spin resonance resonator and spectrometer
Authors: Dahlberg E. D. , Dodds S. A.
Published: March 2003

We describe a tunable low-frequency Electron Spin Resonance spectrometer suitable for operation in the liquid helium temperature range. The resonator is a one-quarter wavelength piece of stripline, whose frequency can be set anywhere in the band from 1–1.8 GHz. The microwave bridge uses a solid-state oscillator and commerically available components.
Fiber optics link to a solar spectrophotometer
Authors: Valente Marques C. , Santos Lemos J. , Ribau Teixeira M. , Manuel Leirão M. , Carvalho Rodrigues F. , Pinto Peixoto J.
Published: March 2003

A solar spectrophotometer with a dioptric imaging system linked to the monochromator by an optical fiber affords a lightweight, easily movable setup for the use in remote locations. Such a system is described in this note.
Compact electrooptically Q-switched CO2 waveguide laser
Authors: Marcus S.
Published: March 2003

A compact electrooptically Q-switched waveguide CO2 laser, with the electrooptic crystal mounted within the waveguide, has been built and operated. Unlike most electrooptically Q-switched CO2 lasers, it requires neither intracavity wavelength selection, nor a polarizing element, nor a waveplate.
Intensity-modulated display for synchronous test interpretation
Authors: Lach Lawrence E.
Published: March 2003

In certain synchronous testing or measurement applications, intensity modulation of the display scope can be used to good advantage. An example is presented in which the synchronous measurement of a thermal transient is simplified by a logical scope display in which three time variables are simultaneously displayed through intensity modulation.
Source plasma characteristics of the coaxial duoPIGatron ion source
Authors: Horiike Hiroshi , Akiba Masato , Arakawa Yoshihiro , Matsuda Shinzaburo , Sakuraba Junji
Published: March 2003

A new variation of the duoPIGatron ion source, the coaxial duoPIGatron ion source, has been built and tested. A distinctive feature of this source is the coaxially-shaped intermediate electrode formed by a magnetic center pole and an intermediate electrode chamber. The source generated a dense and uniform plasma over a grid of 18.5 cm diameter and produced ion beams of 30 A at 30 kV stably and efficiently. The coaxial intermediate electrode worked well at a fixed ratio between the center pole coil current and source coil current, indicating that the magnetic nozzle has successfully connected the cathode with source plasma region. An increase of the applied magnetic field did not affect the density profile, and it raised the arc efficiency. The arc efficiency reached 1.5 A/kW at the source coil current of 30 A when the operation of the source was most stable. The ion species fraction was measured and the proton ratio was increased to 70% from 60% of the modified duoPIGatron.
Subnanosecond fluorescence-lifetime measuring system using single photon counting method with mode-locked laser excitation
Authors: Kinoshita Shuichi , Ohta Hironobu , Kushida Takashi
Published: March 2003

A simple fluorescence decay-time measuring system with single photon counting technique is described which uses, besides an undumped cw mode-locked laser as an exciting source, a compact side-on photomultiplier and IC comparators instead of a head-on photomultiplier and a constant-fraction discriminator. This system gives time behavior of fluorescence in the subnanosecond region or less with sufficient accuracy within a time as short as several seconds. The performance of this system is studied and factors to broaden the response time are discussed.
High-resolution solenoid coil nuclear magnetic resonance probe for superconducting magnet spectrometers
Authors: Bailey J. Terry , Rosanske Richard C. , Levy George C.
Published: March 2003

A broadband probe having a tuning range of 20 to 65 MHz has been designed and built specifically to give maximum sensitivity per unit volume of sample. This is accomplished through use of a solenoid rf coil instead of the usual Helmholtz coil found in commercial probes for superconducting magnet systems. Improvement in signal-to-noise ratios approaches a factor of 3. Probe design considerations and construction materials are described.
Continuous flow reflux oven as the source of an effusive molecular Cs beam
Authors: Swenumson R. D. , Even U.
Published: March 2003

The design and the operation of a continuous flow reflux (CFR) oven used for the formation of an effusive Cs molecular beam which is compatible with ultrahigh vacuum (10−9 Torr) conditions are described. The CFR oven operation utilizes capillary action to recycle the unused part of the Cs molecular beam. A possibility of extending the principle to supersonic beam pressures is discussed.
Bow-shaped toroidal magnet coils
Authors: Bonanos Peter
Published: March 2003

A constant-tension coil whose structural pathway resembles an archer’s bow is described. This shape permits the construction of demountable high-field toroidal magnets with joints at the inner major radius where they are most useful. The support arrangement redistributes the coil tension to maintain the joints under compression and ensure reliable performance.
Electrical resistivity measurements of conductors in the diamond-window, high-pressure cell
Authors: Mao H. K. , Bell P. M.
Published: March 2003

The electrical resistance measurement of metallic conducting materials can be done in situ in a diamond-window, high-pressure cell with a four-lead arrangement designed to avoid contact and lead-wire resistances. Variants of the general method include designs for long (several cm) and short (less than 1 mm) length of samples material, and for the use of solid and fluid pressure-transmitting media.
Measurement of contact resistance of an ohmic contact applied to a high resistivity photoconductor
Authors: Mathur V. K. , Chang C. S. , Lee Chi H.
Published: March 2003

A technique is described to estimate the contact resistance of an ohmic contact, under dynamic conditions, applied to a high resistivity photoconductor. It has been used to estimate the contact resistance of an ohmic contact (Au–Ge) applied to a semiinsulating Cr-doped GaAs (p≊108 W cm).
Novel method of compensating shunts for measuring kiloampere pulsed currents
Authors: Chatterjee U. K. , Shikarkhane N. S. , Nundy U.
Published: March 2003

A simple method of compensating an inductive strip shunt is to use another shunt in series with it, with equal inductance but lesser resistance. When the voltages induced in these shunts are subtracted in a compensating circuit, the compensated shunt acts like a pure resistance. A compensated shunt of thin tantalum foil, having an effective resistance of 200 mW, was made.
Sample chamber for mapping chemical microstructure
Authors: Hendricks Lloyd J.
Published: March 2003

A sample collection system for collecting microsamples under an inert atmosphere by laser pyrolysis for chemical analysis is described. Samples collected are about 10–100 micrograms. Hence the system can be used to map the chemical microstructure of heterogeneous materials with grain or layer dimensions of the order of millimeters on down to hundredths of a millimeter.
Application of a simple automatic null method for vapor pressure measurements by the torsion-Knudsen effusion-recoil technique
Authors: Tomiska Josef
Published: March 2003

A description is given for a null method apparatus for continuous determination of vapor pressure by the ’’Torsion-Knudsen Effusion-Recoil’’ technique. The compensation system can be operated manually or automatically and is based on an industrial core-magnet moving-coil galvanometer with two windings (10 and 4000 ohms). The significant advantages of the method are: (a) there is constant sensitivity over the entire pressure range of Knudsen effusion conditions; (b) there is negligible mass load of the torsion element (max. 0.5 g); (c) it is possible to switch the integrated damping on or off at any time desired; (d) system oscillations can be initiated by current pulses; and (e) calibration of the torsion element can be done under high vacuum with improved accuracy. Precision of torsion calibration attained is 0.1%. Resolution is limited by the current measurement and is about 0.6%–0.9% of the picoammeter range.
Transient method to measure the thermal conductivity of high-temperature melts using a liquid-metal probe
Authors: Hoshi M. , Omotani T. , Nagashima A.
Published: March 2003

A transient instrument with a liquid metal in-glass probe to measure the thermal conductivity of high-temperature melts has been developed. A wire heat source in the conventional hot-wire method was replaced by a mercury thread contained in a glass capillary. This modification has made it possible to apply the transient method to electrically conducting liquids at high temperature. Satisfactory results were obtained for HTS (Heat Transfer Salt) in the temperature range 457–580 K.
High-stability function generator
Authors: Bruschi L. , Storti R. , Torzo G.
Published: March 2003

We describe a voltage-controlled function generator that works in the audio frequency range and gives a sinusoidal signal with an amplitude stable within ±50 ppm. An internal phase shifter, frequency independent, gives eight square wave reference signals, where phase angles are integer multiples of π/4 with respect to the sine wave.
Simple and fast technique for measuring dielectric constant of polymers at microwave frequencies
Authors: Jamwal K. K. S. , Dhar Atula
Published: March 2003

A simple, fast technique for accurate measurement of dielectric constant of polymers at microwave frequencies is presented. The measurement of the wavelength of the microwave signal on the surface of the dielectric rod with the diameter D = λg directly determines the dielectric constant. Results for teflon, perspex, nylon, etc. in the X band (8.5–12.8 GHz) are also presented.
Mössbauer spectroscopy cell for i
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i
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u catalyst characterization and reaction kinetics studies at high pressures
Authors: Shen W. M. , Dumesic J. A. , Hill C. G.
Published: March 2003

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.
Magnetically suspended cross-correlation chopper in molecular beam-surface experiments
Authors: Comsa G. , David R. , Schumacher B. J.
Published: March 2003

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.
Polarized He (23S) thermal metastable atom source
Authors: Riddle T. W. , Onellion M. , Dunning F. B. , Walters G. K.
Published: March 2003

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.
Automatic recording quartz spring balance with an image sensor
Authors: Hayashi K. , Nakamura M. , Miyauchi K. , Yamamoto I.
Published: March 2003

An automatic recording quartz spring balance is improved by using image sensor techniques. Two kinds of arrangement of the image sensor are examined. The weighing error is less than 0.15% for the maximum load. Stability against a zero point shift is excellent. Merits of this balance are discussed in comparison with previous automatic recording balances. Especially the balance system is simple in mechanism.
Dynamics of a digital automatic gain control for Gaussian signals
Authors: Egau P. C.
Published: March 2003

A simple digital automatic gain control loop, suitable for stabilizing the level of a slowly varying Gaussian signal in single-channel or multichannel applications is described. The probabilities of the excursion levels of the feedback control signal are derived and presented in normalized charts. These enable tradeoff between the signal level accuracy and the magnitude of the gain change steps to be readily accomplished and the corresponding increase in signal rms deviation due to the control signal to be determined.
Very low noise cooled audiofrequency preamplifier for gravitational research
Authors: Bordoni F. , Maggi G. , Ottaviano A. , Pallottino G. V.
Published: March 2003

We describe a low-frequency amplifier whose front end, realized with field effect transistors, is cooled at the temperature of 150 K. The results of the measurement of the noise voltage and of the noise current are given as a function of both frequency and temperature. The amplifier has an optimum noise temperature of 25 mK at 1.8 kHz with a source resistance of 390 kΩ and has been used in connection with a gravitational wave antenna of the Rome group.
Microprocessor control of an oxygen electrode system
Authors: Volpicelli Richard , Prydekker Ralph , Hagar William
Published: March 2003

A technique is described for acquisition and analysis of measurements made with a Clark oxygen electrode. An RCA 1802 microprocessor (ELF) system was modified to provide automatic control with an increase in accuracy. Cost is nominal and installation is straightforward. In our application, we continuously monitored the oxygen content in cultures of respiring algae. The linear changes in oxygen concentration with time were analyzed by a least squares fit program to give the slope representing rate of respiration. This program continually processes the data and retains only the essential information from the least squares program, thereby reducing data storages drastically. The system is initiated with one start key and automatically stores and computes the input data. The program may be terminated manually at any time—usually when the standard error of the mean is less than one percent of the slope value. An eight-digit readout displays the values for the slope, standard error, standard deviation, and correlation coefficient.
Heat pipe oven of well-defined column density
Authors: Scheingraber H. , Vidal C. R.
Published: March 2003

A modification of the concentric heat-pipe oven is presented which exceeds the conventional heat pipe oven because of a better defined column density and a significantly shorter warm-up time for achieving stable operation. Similar to the conventional concentric heat-pipe oven, the modified version provides metal-vapor–noble gas mixtures with adjustable partial pressures. As an example, third harmonic experiments have been carried out in a strontium–xenon mixture and phase-matching curves have been measured which demonstrate the well-defined column density.
Molecular beam facility for studying mass spectrometer performance
Authors: Ballenthin John O. , Nier Alfred O.
Published: March 2003

An apparatus is described which produces neutral gas beams in the velocity range from thermal to 6 km/s. This facility makes possible studies simulating the motion of instruments through tenuous atmospheres. The use of the apparatus in studying the response of an open-source mass spectrometer similar to those carried on high-speed spacecraft, such as earth satellites or planetary probes for investigating ambient atmospheric composition, is examined. Experiments performed included ones of response of an open source mass spectrometer when: (a) the instrument was in a normal mode of operation; (b) the instrument’s ion source potentials were adjusted so as to reject gas particles which struck instrument surfaces; (c) the gas beam was restricted so that selected portions of the ion source were struck; and (d) the gas beam struck the ion source at angles other than normal incidence.
Study of microwave self-detecting oscillators
Authors: Rupp L. W.
Published: March 2003

Several microwave circuits incorporating a BARITT device as both source and detector have been investigated as electron-spin-resonance spectrometers. Interesting mode interaction effects are observed in hybrid geometries. A novel, very compact structure exhibits particularly high ESR sensitivity.
Geometrically focused neutral beam accelerators
Authors: Molvik A. W. , Munger R. H. , Duffy T. J. , Correll D. L.
Published: March 2003

A more reliable 40 kV, 65 A power supply drain at 0.4 A/cm2, neutral-beam accelerator was developed for the Tandem Mirror Experiment (TMX). Multiple slotted aperture grids of 60% transparency are fabricated from refractory metal wires mounted to form a spherical surface. This geometrically focuses the beam by aiming individual beamlets at the center of curvature of the spherical grid (r = 3.2 m). We attain greater reliability and faster conditioning with geometrical focusing than with the previous technique of electrostatically steering beamlets to a common point. Electrostatic steering, accomplished by offsetting grid wires, is satisfactory if the offset of a beamlet is much less than the distance from the beamlet to the grids. It was found that Pierce Angle entrance grids performed better if sharper edged. A redesigned accelerator grid support structure reduced the number of ceramic-to-metal vacuum joints, and eliminated O rings between precisely aligned parts. The suppressor grid feedthrough is required to withstand a maximum voltage of 15 kV occurring during breakdown, greatly exceeding the operating voltage of 1.5 kV. Convenient fabrication and assembly techniques have been developed. Assembly of accelerators and plasma sources in a clean room appears to reduce the conditioning time. Following the successful testing of the prototype, eight 40 kV accelerators were built for TMX. Furthermore, ten 20 kV versions were built that are modifiable to 40 kV by exchanging the entrance grid.
Ramsauer-type apparatus for absolute total cross-section measurements at intermediate energy
Authors: Dalba G. , Fornasini P. , Grisenti R. , Lazzizzera I. , Ranieri G. , Zecca A.
Published: March 2003

The paper presents an apparatus designed for the absolute measurement of total electron–atom and electron–molecule cross sections at intermediate energy. This is the first reported instrument capable of measurements at energies higher than 1 KeV. The construction and operation of the apparatus are described. The performance of the apparatus is discussed for two configurations. The first was used to measure the already published data for He, N2, NO, and O2. New measurements for the e−–He system extending to 2000 eV are presented and discussed: these data were obtained with the second (improved angular resolution) setup.
Versatile high temperature flow reactor for kinetic and spectroscopic studies
Authors: Gersh Michael E. , Silver Joel A. , Zahniser Mark S. , Kolb Charles E. , Brown Robert G. , Gozewski Conrad M. , Kallelis Spiros , Wormhoudt Joda C.
Published: March 2003

A high temperature flow reactor has been constructed to perform kinetic and spectroscopic studies on species at temperatures between 300 and 1500 K. The species in the flow reactor may be detected or studied using: laser-induced fluorescence, resonance fluorescence, infrared absorption, ultraviolet absorption, chemiluminescence, or molecular beam mass spectrometry. The features of the apparatus are described in detail, and the initial spectroscopic and kinetic studies are discussed.
Isothermal, isobaric, elevated temperature, high-pressure, flow calorimeter
Authors: Christensen J. J. , Hansen L. D. , Izatt R. M. , Eatough D. J. , Hart R. M.
Published: March 2003

An isothermal, isobaric, flow calorimeter suitable for measuring either endothermic or exothermic heats of mixing from 273 to 423 K and from 0.1 to 40.5 MPa is described. Energy effects from 0.15 to 30 J/min can be measured to an accuracy of ±0.5% for standard test systems at a constant temperature through the use of an automatically controlled heater and a constant cooling Peltier device. The calorimeter was tested by measuring the heat of mixing of water-ethanol at 383 K and 1 MPa and was found to produce data in good agreement with published literature values.
Method for phase-shift determination from measured collision cross sections
Authors: Arnow M. , Jones D. R.
Published: March 2003

A method which determines phase shifts from experimentally measured collision cross-section data by means of a linear regression analysis is discussed. This method also provides a means to normalize the measured data. An application to low energy electron-helium scattering data is included.
Device for the measurement of 227 Ac in solid samples
Authors: Crawford D. J. , Frazier W. K. , Reynolds B. A. , Patch K. D. , Haywood F. F. , Goldsmith W. A. , Perdue P. T. , Berven B. A.
Published: March 2003

A technique has been developed for the determination of 227Ac concentration in soil samples. Emanating 219Rn is introduced into an air stream and passed through a two-filter decay tube similar to that reported by Thomas and LeClare for 222Rn [Health Phys. 18, 113 (1970)]. Experimental tests and theoretical calculations indicate the technique to be sensitive at a level of 2 pCi/g with a 95% confidence level. Relevant empirical and theoretical considerations are discussed.
Curved-channel microchannel array plates
Authors: Timothy J. Gethyn
Published: March 2003

Microchannel array plates (MCPs) in which the channels are curved to inhibit ion-feedback, in an identical manner to that employed in a conventional channel electron multiplier, have been fabricated and their performance characteristics have been evaluated. These devices represent a major advance in MCP technology since a single curved-channel MCP can be operated stably at high gain in the pulse-counting mode. Gains of greater than 106 electrons pulse−1 have been obtained at applied potentials of the order of 2000 V with maximum count-rate capabilities exceeding 105 counts mm−2s−1 and lifetimes exceeding 2.5×1011 counts mm−2.
Magnetic effects in high current ion beams
Authors: Cottrell G. A.
Published: March 2003

It is known that, in intense ion beams being developed for use in neutral injection, the space charge of the ions is almost totally compensated by electrons. In the limit of total compensation, it is shown that there is a critical ion current, Ic, above which transport is no longer emittance but magnetic self-field dominated. A Monte Carlo model of beam neutralization in the presence of the self-field is presented and applied to the example of the JET injectors. Results show a foreshortening of the injector focus, a rise in beamlet emittance, and an increase in the angular divergence (of order 0.1°) in high current neutral injectors. It is shown that, because of stochastic neutralization effects, there is a fundamental limit to the ability to focus an injector uniquely.
Catalytic converters for closed-cycle operation of isotopic CO2 TEA lasers
Authors: Sorem Michael S. , Faulkner George
Published: March 2003

Long-term operation of high-power rare isotope CO2 TEA lasers operating with high CO2 concentrations (20%–25%) has been achieved using a variety of Pt and Pt-coated catalysts to drive the CO+1/2O2→CO2 recombination reaction. The problem of oxygen exchange between 18O substituted CO2 species (628, 828, 838, etc.) and the heated catalysts, or their supporting substrates, has been studied closely. It was found that Pt over an aluminum washcoat on a stainless steel substrate provided good catalytic activity with negligible oxygen exchange, if the Pt to Al2O3 mass ratio was near unity. Catalytic converter performance was analyzed for a typical laboratory CO2 TEA laser (Lumonics 103) with a measured O2 generation rate of ∼0.15 liter Torr per liter of discharge volume per pulse. The laser output was correlated to the catalytic converter operating temperature, as well as the equilibrium O2 concentration. Laser performance was typically degraded for O2 concentrations in the discharge in excess of 0.1%.
Scanner for measuring fine sea-surface structures
Authors: Wu Jin , Haimbach S. P. , Hsu Y.-H. L.
Published: March 2003

An optical scanner using the principle of light reflection has been designed for determining directional slope distributions of the wind-disturbed water surface. The instrument has been tested successfully in the laboratory and could be used in the field. Some sample results along with procedures for data analysis are also presented.
AUTOSEP, an automated system for the quantitative ion exchange separation of plutonium from impurities
Authors: Freeman Brian P. , Weiss Jon R. , Pietri Charles E.
Published: March 2003

The anion exchange separation of interfering impurities from plutonium in the Dowex-1 8 N HNO3 system is a reliable purification method. An automated system, AUTOSEP, based on this manual procedure has been developed for greater productivity. Samples, in groups of ten, each containing 5–10 mg of plutonium are processed automatically in this system. AUTOSEP incorporates a means of programming reagent delivery, adjustment of the sample to the plutonium (IV) oxidation state via Fe(II) reduction/HNO3 oxidation, plutonium sorption on the resin in 8 N HNO3, washing of the resin bed with 8 N HNO3 to remove impurities, elution of the purified plutonium with 0.36 N HCl–0.01 N HF, and waste effluent disposal. The reagents are delivered by gravity from a module whose only moving parts are rotary valves. The eluted plutonium solutions are collected for subsequent controlled-potential coulometric analysis. The average recovery of plutonium determined by controlled-potential coulometry using this apparatus was 100.00% with a relative standard deviation of 0.10%.