bluuebunny/crossref_metadata_2025 huggingface dataset:
More efficient channel electron multiplier by coating of the cone with a high secondary electron yield material
Authors: Manalio A. A. , Burin K. , Rothberg G. M.
Published: March 2003

The efficiency of channel electron multipliers (CEM) falls drastically at energies of the incident electrons greater than a few KeV. For conversion Electron Mössbauer Spectroscopy (CEMS) the conversion electron energies are far greater than a few KeV, and the CEM efficiency at 7 KeV, for example, is about 10% determined in our laboratory. The efficiency can be improved by increasing the secondary electron yield of the detector cone. To find a coating material, a study of relative secondary electron yields was carried out using a scanning microscope. The results of the study indicate that the detector efficiency should improve by more than a factor of 3 when the cone is coated with MgO. Experimentally, the efficiency of the coated detector is in fact more than 3 times that of the uncoated detector.
Long-term operation of a sealed waveguide CO2 laser
Authors: Pace Paul , Cruickshank James
Published: March 2003

A mass spectrometer has been utilized to study the gas composition during operation of a CO2 laser using a BeO waveguide. The results indicate that the use of a drying agent to absorb water vapor has allowed us to achieve lifetimes in excess of 5000 h in sealed waveguide lasers.
Optimization of homogeneous electromagnetic coil systems: Application to whole-body NMR imaging magnets
Authors: Saint-Jalmes Hervé , Taquin Jacques , Barjhoux Yves
Published: March 2003

The design of an air-cored electomagnetic coil system is a very specific problem because of one essential feature: every characteristic parameter of the field produced is mainly determined by the geometry of the current-bearing conductors. Various methods are presented to overcome the mathematical and computational difficulty of homogeneity optimization. Linearization of the field equations allows solving them with a pocket calculator, with some significant design restrictions. Nonlinear resolution and full system simulation can be performed at a computer center or on a scientifically-oriented microcomputer system, both possibilities having their own advantages and tradeoffs. As an example, the optimization of a whole-body NMR imaging magnet is presented. Compensation of field inhomogeneities up to the 14th order allows a drastic reduction of magnet size and power consumption. A sketch of the procedures and results at three different levels—pocket calculator, microcomputer, and computer center—is presented.
Versatile pulsed rf heterodyne spectrometer
Authors: Gibson A. A. V. , Owers-Bradley J. R. , Calder I. D. , Ketterson J. B. , Halperin W. P.
Published: March 2003

We present the design of a versatile rf heterodyne spectrometer covering a 100 kHz to 190 MHz frequency range, which has been useful in nuclear magnetic resonance and acoustic experiments over its whole range. Commercial instruments were used wherever possible: two units, an rf pulse generator, and a 30-MHz IF amplifier/detector were constructed and are described in detail. Also, we briefly outline application to ultrasound and NMR measurements and interfacing to a minicomputer-based data processing system.
Precision abrasion mass spectrometry: Instrumental method for determination of the quantitative distribution of volatile compounds trapped in polymeric materials
Authors: Grayson M. A. , Theby E. A. , Lippold K. O.
Published: March 2003

An instrument to mass spectrometrically analyze volatile compounds trapped or formed in an intractable solid matrix such as a polymer or resin-fiber composite is described. Samples are precisely abraded inside the ion-source housing of a time-of-flight mass spectrometer, and the evolved compounds are mass analyzed. By use of appropriate data acquisition and analysis techniques, either qualitative or quantitative information about the indigenous volatile compounds can be obtained. In the latter case, distribution profiles of the trapped compound(s) can be measured. Typical results for water in an epoxy resin and the pertinent experimental variables in obtaining accurate distribution profiles are discussed.
Self-balancing high-precision ac Wheatstone bridge for observing diffusion processes in electrolyte solutions
Authors: Kiggen H. J. , Laumen H.
Published: March 2003

To observe long-time diffusion experiments in electrolyte solutions a self-balancing ac Wheatstone bridge has been built up. The bridge has six decimal places of controllable R and C decades; a resolution of 10−6 is achieved. The balancing of the bridge is done by a microcomputer system.
Low energy x-ray preionization source for discharge excited lasers
Authors: Levatter Jeffrey I. , Li Zaizguang
Published: March 2003

A low voltage (50 kV), low energy (3 J) x-ray preionization source has been developed specifically for avalanche discharge laser preionization. The new device uses a single stage high-voltage capacitor switched by a gradient grid hydrogen thyratron that drives a cold-cathode electron beam. Intense x-ray emission is produced by allowing the e beam to impact a high Z target foil. The entire system can operate up to 35 Hz repetition rate and produce an electron preionization density of ∼108 cm−3 in most rare-gas/halide laser gas mixtures.
New wide angle, high transmission energy analyzer for secondary ion mass spectrometry
Authors: Siegel M. W. , Vasile M. J.
Published: March 2003

A conically tapered resistive disk with a single conducting hemisphere is used to effect the same energy selection as a pair of concentric hemispheres. The combination of this energy filter with a quadrupole mass spectrometer produces a secondary ion mass spectrometry (SIMS) instrument with a high total transmission attributable to its open geometry and lack of restricting apertures. An approximate form for the energy filter-mass spectrometer combined transmission function is constructed for operating conditions pertaining experimentally, and the theory and experiment are shown to be in good agreement. For a primary beam spot large compared with the electrical entrance aperture of the quadrupole, the energy bandwidth increases linearly with the spot diameter, and the transmission increases quadratically with the mass bandwidth and inverse quadratically with the spot diameter. The overall transmission (absolute sensitivity) is typically on the order of 5×10−4 in the static mode, and would be much higher (∼12% for typical applications) in the dynamic mode with small spot rastering. Static mode ion transmissions are measured for Cu+, Al+, Si+, and Ni+ at the peak of the kinetic energy distribution with an energy bandwidth of less than 3 eV. The instrument is used to study the copper surface in the static mode at current densities as low as 1.5×10−9A/cm2, using 90° incidence for the primary ions, with energies as low as 500 eV. The kinetic distribution of Cu+ ions is only weakly dependent upon primary ion energy over the range 500 eV to 3 keV. The Cu+ distributions show a 13-eV halfwidth and a maximum at 10 eV, while the Cu2+ ion kinetic energy distribution has a 10-eV halfwidth and a maximum at 7 eV. Molecular ions ejected from a copper surface after a plasma oxidation are CuOH+,Cu2O+ Cu2OH+, and Cu2(C2H2)+. These ions have kinetic energy distributions with ∼7 eV half-widths and peaks at ∼5 eV. The aforementioned measurements are made with an energy resolution of less than 3 eV, which is compatible with a mass resolution equal to the mass number of at least 250 amu.
Ion optics improvements to a multiple aperture ion source
Authors: Gardner W. L. , Whealton J. H. , Barber G. C. , Blue C. W. , Dagenhart W. K. , Haselton H. H. , Kim J. , Menon M. M. , Ponte N. S. , Ryan P. M. , Schechter D. E. , Stirling W. L. , Tsai C. C. , Wright R. E.
Published: March 2003

Experimental comparison is made of four plasma grids, each with a specific aperture geometry, in an attempt to improve the ion optics of a multiple aperture ion source. It is clearly shown that a simple notch geometry outperforms the other candidates with a high transmission efficiency (∼68%) to a 2° target at high perveance (∼9.6 μperv).
Visual method for determining the elastic buckling strength of glass microspheres
Authors: Milewski John V.
Published: March 2003

To meet specific fuel filling requirements, it is important to know the buckling properties of microspheres used in laser fusion targets. A visual technique for determining the room temperature elastic buckling strength of microspheres is described.
Laser-Doppler system for rapid scanning of flow fields
Authors: Durst F. , Lehmann B. , Tropea C.
Published: March 2003

A plane mirror mounted on an optical scanner was used to deflect the outgoing beams of a laser-Doppler anemometer operated in backscatter mode, thus permitting, through movement of the mirror, rapid scanning of the measuring control volume throughout the flowfield. Furthermore, the use of a zoom lens element in the transmitting optics enabled the depth range of measurement to be extended without the need to mechanically traverse the system. The signal analysis for a scanning LDA is considered for the case of mean and fluctuating velocity measurements and the effects of the inherent spatial averaging is examined. The analysis yields results that are confirmed by measurements made in a simple coaxial air jet using a transient recorder-based signal processing system. Several improvements to the present system are suggested and the applicability of the scanning LDA in turbulence research is discussed.
Rocket-borne spectrometer to measure the near infrared absorption spectrum of the upper atmosphere
Authors: Matsuzaki A. , Nakamura Y. , Itoh T.
Published: March 2003

A new type of spectrometer has been developed for performing a rocket measurement of the near infrared (NIR) absorption spectrum of the upper atmosphere. The spectrometer is based on multichannel spectroscopy with the use of a one-dimensional solid state image sensor. The time of scanning for a spectrum is 10 ms which is much shorter than a usual mechanical scanning. This spectrometer which was borne on the S-310-8 rocket measured the NIR absorption spectrum of atmospheric constituents such as O2 and H2O with negligible distortion due to the rocket motion. A PCM (pulse code modulation) transmission is preferable in order to obtain a large amount of data in the spectrum measurement. The PCM data processing system is also described.
Nonvisual measurement of collapse field in small-bubble garnets
Authors: Smith A. B. , Bekebrede W. R. , Kestigian M.
Published: March 2003

We describe a nonvisual apparatus for directly measuring the collapse field of any bubble-domain material regardless of bubble diameter. We employ an optical technique utilizing the Faraday effect. Laser light is passed through the sample and polarizer and is then directed onto a photodetector. The bias field applied to the sample includes an ac component which modulates the bubble diameter and hence causes an ac output from the photodetector. The collapse field is determined by increasing the dc component of the bias field until the ac photodetector output due to the bubble modulation drops to zero. Although this method is straightforward in principle, a number of special measures are necessary to make rapid and accurate measurements. We discuss how the optimum optical wavelength and power for these measurements are determined by the magneto-optic and absorption characteristics of bubble garnets. We also describe the means to achieve the essential requirement of low laser noise. Finally, we present typical results obtained with our technique on a garnet material having 1.4 μm stripes. These data demonstrate that accuracies of ∼1% are readily achieved with measurement times of less than one minute.
Electronic method of determining the strength of suspensions in colloidal sols
Authors: Neelakantaswamy P. S. , Gnanaprakasam S.
Published: March 2003

A simple electronic method for measuring strength of suspension (dispersed phase) in the dispersion medium of a colloidal sol is described. Using a VHF (very high frequency) resonant circuit as a sensor, the damping resulting from resonance perturbation is measured when the sensor is suitably coupled to the colloidal system. The measured electrical signal is related quantitatively to the suspension strength. The merits of this instrumentation in terms of simplicity, economy, and linearity are compared with those of a corresponding microwave system. On the basis of the principle described here, an electronic meter that could measure the dry rubber content (DRC) in fresh, natural rubber latex has been successfully developed. Relevant theoretical considerations and experimental results are presented.
High temperature ultrahigh vacuum infrared window seal
Authors: Manuccia T. J. , Peele J. R. , Geosling C. E.
Published: March 2003

An alkali halide-to-metal high vacuum window sealing method is described which is usable to 275 °C with a combined leak plus outgas rate of <3×10−10 atm-cm3/s. This seal is usable for static laser photolysis of low pressure, reactive gaseous samples, since the only materials to come into sample contact are stainless steel, lead, and the alkali halide window. This method has also been successfully used to seal stainless steel to stainless steel.
Single pulse switchout system for a passively mode-locked Q-switched Nd:YAG laser
Authors: Matsushima Isao , Kasai Takeshi , Yano Masaaki
Published: March 2003

A new optical switchout device for a passively mode-locked Q-switched laser is presented. This device can switch out a single pulse with energy at a preset level. The stability of the switched out single-pulse energy is greater than the input pulse train. This is achieved by means of a high speed comparator and avalanche transitor chains. A single pulse of ±13% energy stability is obtained from the pulse train of our Nd:YAG laser oscillator with a ±25% fluctuation. The maximum repetition frequency of 2 kHz is sufficient not only for this kind of laser but also for other applications. The life of the avalanche transistors used here is more than one million shots. The possibility of further improvements in output stability is also discussed.
Design of high speed cylindrical NMR sample spinners
Authors: Doty F. David , Ellis Paul D.
Published: March 2003

Simple approximate solutions to compressible fluid flow problems are used to arrive at useful design equations for high-speed spinning on cylindrical air bearings for NMR studies of solids. The optimum radial clearance is shown to depend on the 1/3 power of the rotor diameter, and is 0.027 mm for a 12-mm rotor, with a surface speed of one half the speed of sound, c. The required air bearing hole diameter is about 0.3 mm with a square root dependence on the rotor diameter. A few general comments are made concerning turbine design, and a simple combination impulse-reaction type is described which offers some improvement in drive efficiency. Drive air flow is shown to depend approximately on the square root of the rotor volume for a surface speed 0.5 c. Relevant data for a number of high strength materials including hard ceramics are tabulated, and limiting speeds are calculated. The design equations are verified for 8 and 12 mm rotors made from Al2O3 with wall thicknesses equal to 6% of the diameter.
A new pressure jump cell for direct microscopic observations
Authors: Wenzel J. , Schneider G. M.
Published: March 2003

A pressure jump autoclave for direct microscopic investigations is described. In the instrument, the pressure jump principle with rupture diaphragm is realized in a simple manner by use of Swagelok standard parts, which may easily be adapted to other types of autoclaves. Up to now the cell has been used for the investigation of aging processes in liquid–liquid precipitates, but the instrument can also be suited for other purposes.
Design and calibration of the fast ion diagnostic experiment detector on the poloidal divertor experiment
Authors: Kaita R. , Goldston R. J. , Meyerhofer D. , Eridon J.
Published: March 2003

A special purpose charge-exchange analyzer was constructed to measure the spatial distribution of hot-plasma ions, as a function of energy and time, in the poloidal divertor experiment (PDX). The fast neutrals produced by charge exchange within the tokamak are reionized as they pass through a helium stripping cell in the detector. The energies of these ions are determined by the trajectories they follow between cylindrical deflection plates which are set at known electrostatic potentials. We describe the technique used to calibrate the response of this system as it depends on the energies and the masses of the particles which are being detected.
Time of flight analysis of metastable products from a gas discharge
Authors: Hardy K. A. , Sheldon J. W.
Published: March 2003

The performance of a metastable atomic beam TOF machine as a thermal plasma diagnostic apparatus is described. The machine consists of two differentially pumped chambers, one containing a hot-cathode, low-voltage discharge and the other a channeltron electron multiplier to detect Auger electrons produced by the metastable atoms. Data acquisition and analysis is by a computer-based pulse height analyzer. The utility of the machine is demonstrated with a discharge in neon.
Theoretical analysis of space-charge effects in photochron streak cameras
Authors: Niu H. , Sibbett W.
Published: March 2003

The influence of space-charge effects on the nature and extent of intensity-dependent temporal broadening in picosecond and subpicosecond streak images has been investigated analytically. The results indicate that the limitations on the dynamic range of electron-optical streak cameras result primarily from space-charge effects which are most serious in regions of the streak tubes where the photoelectrons travel with low velocities for relatively long times. The predicted values of dynamic range have been found to be in reasonable agreement with experimental measurements for Photochron I and Photochron II streak cameras. Theoretical estimates of the dynamic range of the Photochron IV streak camera which is currently being developed have also been included.
Intensity stabilized pulsed analyzing lamp for ultraviolet transient spectrometry
Authors: Fenger Jo/rgen
Published: March 2003

This report describes an apparatus for increasing the light intensity of a Varian VIX-150 UV xenon lamp. The increase is a factor 100 times greater at 220 nm. The light pulse width can be varied from 1 to 10 ms. The intensity of the light pulse can be controlled in two different modes: (1) the light flux from the lamp is kept constant by means of a parallel close-loop control on a small fraction, 10%, of the radiated flux from the lamp. The intensity variation of a 10-ms light pulse detected by a photomultiplier used for detecting the transient absorption signal can be held constant to within 5%. The accuracy is not limited by the lamp intensifier, but by a lack of precision in optical alignment of the absorption spectrometer; (2) the photomultiplier for the transient absorption signal controls the light intensity. During the first period of the light pulse the photomultiplier signal acts to provide feedback for the lamp intensifier and a constant light level is then obtained. In the subsequent period a hold circuit continues to keep the light level constant. Within the hold period the feedback signal from the photomultiplier is switched off and it continues as the detector for the transient absorption signal. In this mode of operation, a useful light pulse of 1 ms is obtained; the intensity variation is within 3%.
Fatigue in photomultipliers due to excitation by pulsed light sources
Authors: López R. J. , Rebolledo M. A.
Published: March 2003

In this paper the fatigue produced by pulsed light sources on an RCA C31034 photomultiplier connected to a photon-counting system is studied experimentally. This fatigue is compared to that obtained when utilizing a continuous light source with the same mean intensity value. It is found that the fatigue produced by the pulsed source is of the same order as that produced by the continuous source, even though pulses are very distant between them. This is explained assuming that when fatigue magnitude decreases the relaxation velocity of the fatigue decreases as well.
Telephone monitoring of an unattended computer-controlled experiment
Authors: Cohn Charles E.
Published: March 2003

The status of an experiment can be monitored by telephone with the aid of a digital speech synthesizer and a telephone coupler.
Improved cell design for pulsed dye lasers
Authors: Roncin Jean-Yves , Damany Henri
Published: March 2003

A clean demountable dye cell is described which is more advantageous than the usual commercial cuvettes for obtaining good quality light beams from pulsed dye lasers.
Laser interferometer for high temperature isothermal length changes over long time periods
Authors: Drotning W. D.
Published: March 2003

A laser interferometer for high precision isothermal length change measurements over long periods of time at high temperatures is described. An example is presented of the length change of a solid material near 500 K measured over several hours. The operating range of the device is from ambient temperature to 900 K, with an ultimate length change resolution of 10 nm. The critical optical alignment of the interferometer is performed and maintained by a minicomputer using an auto-alignment control feature. Particular emphasis has been placed on long term system stability (measurement time scales greater than a few minutes) for studies of the high temperature isothermal behavior of solid materials as a function of time. To account for small temperature fluctuations in these measurements, a technique is presented for correction of the results for sample length changes induced by thermal expansion.
A/D converter sampling rate multiplier
Authors: Roth J. A. , Jelatis G. J. , Maynard J. D.
Published: March 2003

We describe here a simple and inexpensive circuit which operates with a moderately fast (hardware limited to 35 kHz in our particular case) A/D converter in a minicomputer to produce as much as sixteen times higher sampling rates for repetitive signals. The sampling window of 512 points may be delayed by as much as fifteen window widths. The circuit connects externally to the minicomputer, requiring no internal modifications, and hence can be used with any A/D converter–computer system.
Noise isolation switch for commercial broadband power amplifiers used in pulsed NMR
Authors: Sears R. E. J.
Published: March 2003

A simple, quarter wave line diode switch for use in pulsed NMR is described. This switch isolates the receiver from the noise produced by a commercial broadband and high-gain, power amplifier.
High-sensitivity ZnO-semiconductor detector for atomic hydrogen beams
Authors: Hishinuma Naoshi
Published: March 2003

A procedure which highly sensitizes a ZnO-crystal surface to atomic hydrogen is described. The lower limit of detection achieved with the sensitized detector was about 6×108 atoms cm−2 s−1.
Mode converter for electron cyclotron resonance heating of toroidal plasmas
Authors: Motley R. W. , Hsuan H. , Glanz J.
Published: March 2003

A method is proposed for improving the efficiency of cyclotron resonance heating of a toroidal plasma by ordinary mode radiation from the outside of the torus. Radiation not absorbed in the first pass is reflected from the inside of the torus by a corrugated surface which rotates the polarization by 90 °, so that a secondary source of extraordinary waves is created in the high field, accessible region of the plasma.
Calibration of piezoelectric-driven mirrors for laser resonators
Authors: Varwig R. L. , Sandstrom R. L. , Wang C. P.
Published: March 2003

A new technique for measuring small displacements of piezoelectric-driven mirrors has been applied to the calibration of piezoelectric-driven mirror systems for laser resonator cavities. In this technique, a wave-front sensor that includes an acousto–optic modulator and uses optical heterodyning measures the phase change when a mirror, driven by the piezoelectric translator, moves. Measurements obtained by means of this technique have been compared with measurements obtained with the traditional interferometer methods and have proven to be more precise. The increased precision was attributed to higher signal-to-noise ratios typically obtained with frequency-modulated, relative to amplitude-modulated, systems where intensity fluctuations exist in the system. The increased signal-to-noise ratio is advantageous when, as frequency increases, the output voltage from the driving power amplifier falls off. For a given amplifier, frequency–response data of the piezoelectric driver–mirror combination can be determined at higher frequencies. In this case, the frequency has been extended from 15–40 kHz.
Split-ring resonator for use in magnetic resonance from 200–2000 MHz
Authors: Hardy W. N. , Whitehead L. A.
Published: March 2003

A novel high Q resonator is described that is suitable for magnetic resonance in the frequency region 200–2000 MHz, where ordinary cavities are generally too bulky and solenoidal coils impractical.
Use of the ac mutual inductance bridge for measuring diamagnetism and paramagnetic temperature dependence
Authors: Hockman A. J. , Sena F. J. , Gentile P. S.
Published: March 2003

The use of the ac mutual inductance technique has been extended to include temperature measurements (78–300 K) for paramagnetic compounds with as few as one unpaired electron per formula unit. Calibration data for the coil are described using three cobalt compounds. The technique has also been adapted to the study of diamagnetism by using a control solvent to modify the calibration ratio.
Simultaneous measurement of the thermal conductivity and the thermal diffusivity of liquids by the transient hot-wire method
Authors: Nagasaka Y. , Nagashima A.
Published: March 2003

The paper describes a method and an instrument to measure the thermal conductivity and the thermal diffusivity of liquids simultaneously by the transient hot-wire method. Though the principle of this method has formerly been known, the practical application to fluids has been enabled only by high-precision measurement. In the present method, the thermal conductivity can be determined from the slope of the temperature rise against time of electrically-heated wire and the thermal diffusivity can be obtained from the slope and the absolute temperature rise. In this instrument, the absolute temperature rise, which is detected as voltage change of an unbalanced bridge, is recorded by a high-precision digital system. This method has been tested by measuring toluene in the temperature range 0 °–80 °C at atmospheric pressure. The accuracy of the thermal conductivity measurement is estimated as ±0.5%, whereas that of the thermal diffusivity measurement is ±5%.
Simple heat flux meter
Authors: Andretta A. , Bartoli B. , Coluzzi B. , Cuomo V. , De Stefano S.
Published: March 2003

A small heat flux meter, with short response time, useful to measure local heat fluxes typically found in solar energy and natural radiative cooling work is described. Utilizing recording instruments normally used for temperature measurement with thermocouples, the meter assures an accuracy of at least 10%. The calibration constant measured with two different calibration devices is given.
Apparatus for high-pressure and low-temperature experiments
Authors: Golopentia D. A. , Ruoff A. L.
Published: March 2003

A new type of apparatus for high-pressure experiments at low temperature (1.5 °K) is presented. It uses a flat diamond anvil with a spherical indentor. It utilizes a load ring placed under the sample, so that the load (and hence pressure) can be measured in situ at low temperature. The apparatus was successfully used to investigate the high-conductivity state of sulphur. It can be used to investigate other thin film samples.
Particle sizing by electrical single particle aerodynamic relaxation time analyzer
Authors: Renninger R. G. , Mazumder M. K. , Testerman M. K.
Published: March 2003

An aerosol particle size analyzer based on a laser Doppler velocimeter (LDV) has been developed to measure the aerodynamic diameter da of individual particles and droplets in real time. The particles are electrically charged and then passed through a 40-kHz electric field. The phase lag φ of the particle motion with respect to the field is measured by the LDV. A microcomputer determines da from φ and stores the aerodynamic size distribution of the sampled particulates. The analyzer has counted and sized particles at a maximum rate of 200 particles/s in the size range of 0.3–5.0 μm in aerodynamic diameter.
Determining the electron energy distribution near the plasma potential in the earth’s ionosphere
Authors: Sharp William E. , Hays Paul B. , Cutler James R. , Dobbs Michael E.
Published: March 2003

A determination of the plasma potential using an electrostatic analyzer is described in which the potential difference between the instrument slit system and surrounding plasma is minimized. Data obtained from rocket-borne instrumentation demonstrate the viability of this technique for electron fluxes between thermal energies (∼0.5 V) and suprathermal energies (many volts).
Afterpulses in a photomultiplier tube poisoned with helium
Authors: Bartlett D. F. , Duncan A. L. , Elliott J. R.
Published: March 2003

A five-inch photomultiplier tube (RCA ♯4522) was run continuously for eight weeks surrounded by a pure helium atmosphere. Although some evidence of afterpulsing was seen as early as the end of the first week, the fraction of pulses having afterpulses did not reach 15% until after four weeks. The gain of the tube was unaffected by the helium until about the sixth week when suddenly the gain dropped by a factor of 10. The temporal distribution of the afterpulses (600–1200 ns) is readily explained by the voltage distribution between the cathode and the first dynode.
New fast Fourier transform algorithm for linear system analysis applied in molecular beam relaxation spectroscopy
Authors: Schütte Joachim
Published: March 2003

The well-known FFT (Fast Fourier Transform) algorithm of Cooley and Tukey has found widespread application in the field of numerical Fourier transforms and related problems. Nevertheless, the FFT algorithm has to be treated with caution, because in order to avoid aliasing in the frequency domain, it is restricted to the transform of bandlimited functions. A new algorithm has been developed that still has the FFT characteristics, but that is no longer confined to bandlimited functions. The new algorithm has been tested in the case of MBRS (Molecular Beam Relaxation Spectroscopy) linear system analysis.
Correlator for measuring picosecond pulses—a new design
Authors: Ketkar S. N. , Keto J. W. , Holder C. H.
Published: March 2003

We present a new design for an autocorrelator to measure pulsewidths of picosecond light pulses. This device gives a real time display of the pulsewidths, enabling one to align precisely synchronously-pumped mode-locked dye lasers for optimum performance.
Instrument to measure stratospheric ozone with high resolution
Authors: Aimedieu Patrick , Barat Jean
Published: March 2003

We describe an ozonosonde based on a homogeneous chemiluminescent reaction of olefins with ozone, allowing ozone measurements at all altitudes accessible to stratospheric balloons. The ozone–olefin reaction, which is bimolecular, gives a signal proportional to ozone mixing ratio. Typical response at 100 mb (∼16 km) with ethylene is 104 counts s−1 ppm−1. With 2-methyl 2-butene, one can extend the measurements to 1 mb. At 2 mb (43 km), we typically find 2×104 counts s−1 ppm−1. The time constant is 1 s, and the statistical noise of the reaction (∼1%) allows the use of the instrument to make accurate relative measurements for dynamical studies of the stratosphere. Two versions of the instrument have been flown successfully six times. We present a flight profile between 200 mb (∼12 km) and 12 mb (∼30 km), and also measurements at 2.5 mb (41 km) float level.
Automatic shutter controller for molecular beam epitaxy
Authors: Stanchak C. M. , Morkoç H. , Witkowski L. C. , Drummond T. J.
Published: March 2003

The molecular beam epitaxy (MBE) crystal growth technique utilizes thermal molecular beams which are stabilized by constant temperature control and controlled manually by metal shutters. Through the addition of an automated programmable shutter control system, the capabilities of the MBE system are enhanced. Two examples of automatic control of the shutters to grow epitaxial GaAs–AlGaAs layers are described. By changing the simple settings on the control units, the growth schedule can be easily altered to allow for the optimization of crystal structures used for innovative devices and basic research.
New type of position sensitive photomultiplier
Authors: Kuroda Kei-ichi , Sillou Daniel , Takeutchi Fujio
Published: March 2003

A position sensitive photomultiplier of a new concept is presented which is based on the scaling property of the equation of motion describing electrons moving inside electric and magnetic fields. The idea has been fully supported by a test using a prototype having ten stages of specially designed dynodes. A gain of 105–106, and a spatial resolution of ∼3.4 mm (FWHM) in two-dimensional space have been obtained. The time resolution is comparable or superior to that of most conventional photomultipliers. An example of data handling of signals coming from divided anode cells showed a possibility of reconstructing impact light position with a precision of a few hundred microns.
Practical method of improving the uniformity of magnetic fields generated by single and double Helmholtz coils
Authors: Kaminishi Katsuji , Nawata Shigenori
Published: March 2003

Design possibilities of single and double Helmholtz coils of rectangular cross section have been investigated for the purpose of generating magnetic fields which have the same or even better uniformity as compared to that achieved with the idealized coils of negligible winding cross section. It is shown that the optimum dimensions of coil configuration can be determined by means of numerical analysis, even under such practical conditions that the ratio of thickness to width of winding cross section and the turn ratio of the coil pairs should be ratios of relatively small integers. It is also suggested that the balancing method provides a possible means of extending the uniform region one and a half times as much as that achieved with the idealized coils of negligible winding cross section.
Design and operation of a magnetic osmometer
Authors: Crouch Thomas H.
Published: March 2003

Presented here is a detailed description of a magnetic osmometer as well as the theory of its operation. This instrument has the pressure sensor and is placed on the dialysate side of a semipermeable membrane and is capable of measuring pressure changes as low as 1×10−3 cm of water. The stability of the system is greatly enhanced by maintaining contact with a large thermally stable atmosphere. This eliminates ordinary pressure fluctuations encountered when the system is left open to the normal atmosphere. Measurements with bovine serum albumin at concentrations of 86 mg/ml (1.3 mM) were made with an absolute error of ±15% and standard error of ±5% in the pressure difference of 0.0032 cm of water. The molecular weight of this protein was determined to within ±0.4% of the value known from the amino acid sequence. The design presented here facilitates sample changes and requires less than one milliliter of solution per measurement.
Methods for the blind adjustment of the apertures of an electron beam device
Authors: Schulz W. , Schulz B.
Published: March 2003

An electrical method for the adjustment of an electron beam without optical accessories is described. This method also allows a determination of the beam diameter, the axial brightness, and the astigmatism.
Thermal conductivity and specific heat of a glass–epoxy composite at temperatures below 4 K
Authors: Walker F. J. , Anderson A. C.
Published: March 2003

The thermal conductivity and specific heat of the glass–cloth reinforced epoxy laminate G-10, as well as the cryogenic grade G-10 CR, have been measured over the temperature range 0.1–4 K.
Design for high-temperature oven for spectroscopy experiments
Authors: Soltanolkotabi M. , Gupta R.
Published: March 2003

Design of an oven suitable for atomic spectroscopy experiments on low vapor pressure elements is described. This oven can heat samples to about 1000 °C without producing significant magnetic fields, without condensation of the sample along optical paths, and with very little optical background.
Vacuum UV window system for shock tubes bakeable to high temperature
Authors: Lifshitz Assa , Bidani Menashe , Carroll Harvey F.
Published: March 2003

A novel double-window system for shock tubes useful with vacuum UV atomic resonance absorption spectrometry is described. This system allows the shock tube to be baked to 400 °C under high vacuum.
Modified mixed-gas flow method for controlling the oxygen partial pressure in a furnace, using a CO2–CO system
Authors: Kimizuka Noboru , Takayama Eiji
Published: March 2003

The oxygen partial pressure in a furnace can be controlled precisely even at lower temperature (550°–900 °C), with a CO2–CO mixture preheated on an iron-containing alumina catalyst for establishing chemical equilibrium in the gas phase. It was found that a CO2–CO system is more practical than a CO2–H2 system because the optimum temperature of the catalyst is nearly equal to the main furnace temperature and does not depend on the mixing ratio of the gases.
New method for determination of surface tension of liquids
Authors: Ohsawa Toshihiko , Ozaki Tadao
Published: March 2003

A new method of quickly and precisely measuring the surface tension of liquids and solutions is described. Utilizing the fact that the size of the bubbles formed from a gas flowing out of a nozzle is dependent on the nozzle diameter and the surface tension of the liquid used, the surface tension of a liquid can be determined by simply counting the number of bubbles formed from a gas flowing out at a constant flow rate or by measuring the period of bubble formation. The expected accuracy of the method is below 0.1% of variance. An evident correlation between the period of bubble formation and the surface tension was shown with several kinds of liquids which differ in surface tension. Changes in surface tension with varied degree of neutralization were determined in an aqueous solution of polyacrylic acid (PAA), 20–30 points of measurement with an accuracy of about 0.1% could be easily obtained within one hour.
Angle-resolved electron spectrometer with multidetection
Authors: Hansson G. V. , Goldberg B. , Bachrach R. Z.
Published: March 2003

A high-resolution, angle-resolved photoemission electron spectrometer has been built which incorporates a position-sensitive multidetection system. The spectrometer is a 180 ° hemispherical electrostatic deflection analyzer utilizing preretardation, 1.5 ° angle-resolving optics mounted on a two-axis angular manipulator. Combined with the sample holder, independent control of the polar and azimuthal angles of both the sample and detector are available. The multidetection spectrometer collects through a PDP-11 based data acquisition and control system up to 32 resolution elements per spectral frame.
Microwave spectrometer for the detection of transient gaseous species
Authors: Kolbe W. F. , Zollner Wolf-Dieter , Leskovar B.
Published: March 2003

A microwave spectrometer and associated apparatus for the detection of unstable free radical species is described. The spectrometer, which operates over a frequency range from 66 to 73 GHz, consists of a tunable Fabry–Perot resonator followed by superhetrodyne detection for high sensitivity at low power levels. The resonator tuning is accomplished by means of a computer-controlled stepping motor and by a piezoelectric tranducer which also permits the use of source modulation and phase sensitive detection at 100 Hz. The sensitivity of the spectrometer is adequate to permit the detection of rotational transitions with absorption coefficients as small as 2×10−9 cm−1. The operation of the spectrometer is demonstrated by the detection of the two free radical species OH and SO. In the case of OH, a number of L-doubling transitions, previously unobserved, are reported.
Microwave electron spin resonance spectrometer with operation to 54 mK in a dilution refrigerator
Authors: Sanny J. , Clark W. G.
Published: March 2003

A 9.5-GHz electron spin resonance ESR spectrometer which operates in conjuction with a helium dilution refrigerator down to 54 mK is described. Instead of the conventional waveguide and cavity arrangement, coaxial and superconducting twisted pair transmission lines are used to bring the microwave power into the mixing chamber, where a tiny coil surrounds the sample. This low Q, high-filling factor configuration has a sensitivity about the same as that of a conventional high Q cavity with a small filling factor. Several suggestions for further development and improvement are presented.
Flexible Fourier multinuclear magnetic resonance spectrometer
Authors: Brondeau J. , Diter B. , Canet D.
Published: March 2003

This paper presents an easy-to-build Fourier multinuclear magnetic resonance spectrometer operating, in the present case, below 100 MHz but readily adaptable to any magnet system. Receiver and transmitter are essentially made of commercially available wide-band components. Some dedicated homemade circuits, necessary to the proper operation of the system, are described. A probe head has been especially designed for the observation of nuclei resonating between 6 and 36 MHz (nitrogen 14 to phosphorus 31), in addition to proton and fluorine (90 MHz and 84.6 MHz), without removing the sample and/or changing the spectrometer configuration. Interchangeable inserts are built in such a way that the measuring channel on the one hand, and the stabilization–decoupler channels on the other hand, are separated through the use of two orthogonal coils. Tuning and matching networks, which involve, for the measuring channel, homemade nonmagnetic capacitors variable in a large range, are described. The flexibility and the ease of operation of the apparatus are outlined.
High-temperature calorimetry (1000°–1500 °C): new calorimeter detectors, procedures of mixing, and automatic data exploitation
Authors: Hatem G. , Gaune P. , Bros J. P. , Gehringer F. , Hayer E.
Published: March 2003

New calorimetric detectors for measurements of enthalpies of formation of liquid ionic and metallic systems in the temperature range 1000°–1500 °C have been designed and assembled. Much attention was paid in designing these new detectors in order to obtain reliable data. The mixing method, used with a stirring device, allows avoidance of parasitic thermal effects, and therefore improves the accuracy of the measured heat of mixing. The acquisition and treatment system of the calorimetric data is described.
Capacitance voltage divider for high-voltage pulse measurement
Authors: Edson W. A. , Oetzel G. N.
Published: March 2003

A circuit capable of dividing 250 kV pulses by a ratio of 100,000 has been built and tested. It permits use of standard oscilloscopes to view high-speed transients that have components between 200 kHz and 200 MHz. The design is an adaptation of the guard ring principle, commonly used in electrostatic measurements.
Technique for measurement of fast exponentially-decaying signals
Authors: Garver W. P.
Published: March 2003

An accurate yet inexpensive technique for measuring time constants of fast exponentially-decaying signals is described. Two discriminators are set at different levels and the difference between the corresponding triggering times gives the time constant.
Interfacing a 32 K commodore PET computer with digital/analog and analog/digital converters
Authors: DeRosa F. , Jedju T. M.
Published: March 2003

A procedure for interfacing a 32 K PET Computer with digital-to-analog and analog-to-digital converters is documented.
Large acceptance angle retarding-potential analyzers
Authors: Molvik Arthur W.
Published: March 2003

Electrostatic retarding-potential gridded analyzers have been used to measure the current and the axial energy distributions of ions escaping along magnetic field lines in the 2XIIB magnetic fusion experiment at Lawrence Livermore National Laboratory (LLNL). Two analyzers are discussed: a large scanning analyzer with a movable entrance aperture that can measure ion losses from a different segment of the plasma diameter on each shot, and a smaller analyzer that mounts in 5-cm-diam. ports. Careful electromagnetic shielding and grounding were necessary in order to reduce spurious signals. Accurate measurements of ion current require grids that attenuate the plasma flow and isolate it from the analyzer grid potentials, several techniques to suppress secondary and primary electrons, and consideration of the space-charge limits as well as techniques to increase these limits. Accurate measurements of ion energy require, in addition, confining large-angle ion orbits within the analyzer by an axial magnetic field, limiting the sweep rate of the ion-repeller grid, and aligning the analyzer so that it is normal to the magnetic field lines. (The analyzers are also used on the Tandem Mirror Experiment, TMX, where the angular acceptance requirements are reduced). The analyzers measure the axial energy, which in 2XIIB and TMX is much greater than the transverse energy. Several pitfalls and their cures are identified in the design, construction, and operation of these analyzers.
Magnet system of the 500 MHz NMR spectrometer at the Francis Bitter National Magnet Laboratory: I. Design and development of the magnet
Authors: Williams J. E. C. , Neuringer L. J. , Bobrov E. , Weggel R. , Ruben D. J. , Harrison W. G.
Published: March 2003

A high field nuclear magnetic resonance spectrometer has been put into operation at the MIT, Francis Bitter National Magnet Laboratory. The spectrometer is built around a high homogeneity magnet, the design field of which was 11.74 T, and which in fact operates in persistent mode at a field of 11.71 T. The magnet is wound using niobium–titanium superconductor cooled to 2.3 K and is housed in a special dewar designed to permit continuous subatmospheric cryogenic operation and to minimize helium consumption. This and a companion paper describe the analysis, design, and construction of the magnet.
Magnet system of the 500 MHz NMR spectrometer at the Francis Bitter National Magnet Laboratory: II. Disturbances, quenches, and training
Authors: Williams J. E. C. , Bobrov E. S.
Published: March 2003

Mechanical disturbances in the NMR magnet winding, some of which resulted in premature quenching, have been monitored. The history of disturbances and quenches is presented. Their nature as well as the training of the winding are interpreted in terms of a comprehensive static and dynamic analysis of the mechanical behavior of the magnet. The analysis accurately predicts the measured deflections of the magnet, and more significantly, critical events in the sequence of training quenches. In particular a repeated quench was shown to be caused by slippage of the winding on the core tube. It was successfully overcome by a change in the field pattern of the magnet. Training quenches are interpreted as the result of axial tensile stress developed locally within the winding.