bluuebunny/crossref_metadata_2025 huggingface dataset:
Design for a combustible gas measuring circuit
Authors: Fredericks George E. , Scott Ronald S.
Published: March 2003

A circuit for a combustible gas detector is described and the properties of the transducer that affect the design of the circuit are discussed. The transducer is a novel device made from a mixture of metal oxides. Evidence is presented to show that the transducer operates through the enhancement of surface conductivity due to reduction of the metal oxide surface.
Simple, high precision technique for orienting single crystals
Authors: Deutsch Moshe , Freund Isaac
Published: March 2003

A simple, non-photographic technique for highly precise orientation of single crystals has been developed and used to obtain an alignment accuracy of 10″. The method is directly extendable to an ultimate accuracy of a small fraction of a second of arc.
Specimen holder for energy dispersive x-ray analysis in the transmission electron microscope
Authors: Sprys J. W.
Published: March 2003

A specimen holder constructed of magnesium and poly-methyl-methacrylate for use in the transmission electron microscope (TEM) is described which can be used for energy dispersive spectrometry (EDS). The holder is designed to eliminate unwanted detectable x-ray radiation from the body of the holder and to permit EDS analysis with only a 3 ° sample tilt toward the x-ray detector. The specimen holder incorporates two tilt axes which allow examination of materials for both EDS and TEM analysis simultaneously.
Afterpulsing in the Bendix M-306 magnetic multiplier
Authors: Khayrallah George
Published: March 2003

A fast method for studying afterpulsing is described, and its application in measuring the Bendix M-306 magnetic multiplier afterpulsing time-spectrum is presented.
Low noise and drift by parallel amplifiers
Authors: Sundqvist B. , Bäckström G.
Published: March 2003

A low noise and low drift amplifier has been constructed using several monolithic operational amplifiers in parallel. It is shown that each amplifier may be connected by only three resistors. An input noise of 0.15 μV (p–p) in the band 0.1–10 Hz was obtained with six amplifiers, and the noise is expected to decrease as N−1/2 as the number of units is increased.
Electromagnetic generation of Rayleigh waves at MHz frequencies
Authors: Moran T. J. , Lin M. J. , Buchholtz F. , Thomas R. L.
Published: March 2003

A contactless method of generating ultrasonic Rayleigh waves at MHz frequencies in metals using the electromagnetic generation technique is described. The method requires the use of photographic printed circuit techniques for the production of the meander coil transducers. Excellent efficiency is achieved and insertion losses are as low as 78 dB in aluminum with an external magnetic field of 5 kG and a frequency of 4.75 MHz.
Automatic digital microwave hygrometer
Authors: Hasegawa Saburo , Stokesberry Daniel P.
Published: March 2003

This hygrometer is designed to measure the humidity of atmospheric air over the vapor pressure range 3–7400 Pa (0.03–74 mbar). The instrument is an adaptation of a microwave refractometer using two cavities operating at 12 GHz. One cavity is exposed to the moist test air and the other is exposed to the same air sample with all the water vapor removed. Both cavities are maintained at the same fixed temperature in a thermostated oven and at the same total pressure. The difference in frequency between the cavities is automatically nulled by a tuning probe in the sampling cavity. The instrument was calibrated by two independent methods. One involved the measurement of the resonance frequency of the sampling cavity as a function of probe penetration and using this in a theoretically derived equation for vapor pressure. The second involved the measurement of the probe penetration as an empirical function of known vapor pressure of a test gas. These two methods yielded results which agreed on the average to better than 0.5% for vapor pressures up to 3050 Pa (30.5 mbar).
Variable low temperature EPR cavity
Authors: Perlson B. D. , Weil J. A.
Published: March 2003

An EPR cavity system, operating in the range 12 K to room temperature, is described. Sample cooling is accomplished with a Displex helium gas refrigerator, operating for arbitrarily long periods with the use of only electricity. The system permits accurate rotation and manipulation of single crystal samples throughout its operating range.
Probe for the measurement of magnetic fields with sub-nanosecond resolution
Authors: Serov R. , Richardson M. C. , Burtyn P.
Published: March 2003

A double coil differential magnetic probe has been specifically devised for the measurement of magnetic fields with high temporal and spatial resolution. Having a response time of <1 nsec, a sensitivity of 0.3 V nsec G−1, and high discrimination (≳300) to all other types of background interference, it is well suited to the analysis of magnetic fields associated with plasmas produced by ultrashort laser pulses.
Semiautomatic permeance tester for thick magnetic films
Authors: Calcagno Paul A. , Thompson David A.
Published: March 2003

An apparatus has been developed for the measurement of the permeance (effective permeability–thickness product) of magnetic films for frequencies 1–100 MHz and permeances up to 20 000 μ with an accuracy of ±100 μ. This is suitable for permalloy films in the 0.5–5 μ thickness range, which are used in thin film recording heads operating in this frequency range.
Large volume TEA CO2 amplifier
Authors: Domey Jacques
Published: March 2003

A 15×15 cm cross section, 50 cm long, TEA CO2 amplifier using a reliable and simple discharge system is described. This system permits external control of the width of the discharge and is easily scalable. The spatial distribution of the small signal gain over the cross section of the amplifier is investigated. An average small signal gain coefficient of 0.022 cm−1 is obtained at an input energy density of 100 J/liter. Measurement of the saturated energy gain is reported. The small signal gain has also been measured on a smaller cross section but more heavily excited amplifier, using a similar discharge system.
Apparatus for measuring rapidly varying electric fields in plasmas
Authors: Mendel C. W.
Published: March 2003

A system is described which can measure plasma electric fields on nanosecond time and submillimeter distance scales. The measurement is made by observing the time dependent deflection of a 10−7 A beam of 22 keV He+ ions. The measurement does not perturb the plasma.
Oxidized BN: An excellent source material for producing boron ion beams
Authors: De Keersmaecker R.
Published: March 2003

Several solid source loading materials for the production of a boron ion beam with a hot filament hollow cathode ion source are compared. As far as easy handling and large B+ currents are concerned, oxidized boron nitride is shown to be an excellent choice. Currents of 80 μA 11B+ are routinely obtained at the target from an oxidized BN source.
Demountable optical windows using heat shrinkable tubing
Authors: Zitter R. N. , Koster D. F.
Published: March 2003

Heat shrinkable tubing provides a new way of mounting optical windows on systems that is simple and quick and permits fast and easy removal.
Electromagnetic levitation facility incorporating electron beam
Authors: Wouch G. , Okress E. C. , Frost R. T. , Rutecki D. J.
Published: March 2003

An electromagnetic levitation apparatus incorporating an electron beam for auxiliary heating and melting has been developed for experiments on containerless vacuum purification and undercooled solidification of high melting materials. Stable levitation of 10-g specimens of molten tungsten has been achieved and a variety of containerless solidification experiments is being performed, including pure polycrystalline castings and single tungsten crystals grown from the undercooled levitated melts.
Bonded electrodes for use on the external surfaces of spacecraft
Authors: Kendall B. R. F. , Weeks J. O.
Published: March 2003

A new bonding process is described which is suitable for applying electrodes to the external surfaces of spacecraft and sounding rockets. A polyimide material containing small, uniform glass spheres provides the necessary insulation and mechanical strength. The bonded electrodes are simple to construct and are shown to have good electrical, vacuum, and thermal properties.
Technique for conductivity measurements on single crystals of organic materials
Authors: Coleman L. B.
Published: March 2003

A technique is described for making four probe conductivity measurements on small, fragile single crystals of organic compounds. Physical constraint of the sample is minimal, allowing repeated thermal cycling.
Machining hyperbolic electrodes with a straight edged tool
Authors: Blair J. Morris
Published: March 2003

A method is given for designing a milling machine cutting tool for forming hyperbolic electrode surfaces. The cutting edge of the tool is a straight line. Its orientation and spacing with respect to the axis of rotation of the tool have a simple relationship to the size of the hyperbola to be formed.
Design and properties of position-sensitive proportional counters using resistance–capacitance position encoding
Authors: Borkowski C. J. , Kopp M. K.
Published: March 2003

The construction and signal processing methods of several experimental gas-filled, position-sensitive proportional counters (PSPCs) using resistance–capacitance (RC) position encoding are described, and guidelines for the design and operation of these counters are given. Using these guidelines, we were able to improve the spatial resolution and shorten the signal processing time; for example, the intrinsic spatial uncertainty in the position measurement was reduced to 28 μ FWHM for alpha particles and 100 μ FWHM for low-energy x rays (2–6 keV). Also, the signal processing time was reduced to 0.6 μsec without seriously degrading the spatial resolution. These results have widened the field of application of the RC position encoding method for position measurements of low-energy photons, neutrons, and charged particles in a wide variety of nuclear physics experiments, in nuclear medicine imaging, and in low-dose, medium-resolution radiography.
Minicomputer applications in solid state physics: Automated instrumentation for the de Haas–van Alphen effect
Authors: Alles H. G. , Higgins R. J.
Published: March 2003

A computer-assisted measurement system is described which has been optimized for the precise measurements of the amplitudes, phases, and frequencies of the de Haas–van Alphen oscillations. System software, architecture, and control concepts are described which have general utility in computer-controlled and automated measurements. The system is made flexible for a broad class of experiments by partitioning control functions, by providing efficient control parameter handling and editing, and by utilizing program chaining. The experimeter’s role is enhanced with an interface control board which allows the manual control and flexibility essential in a research laboratory.
Ultrahigh pressure diamond-anvil cell and several semiconductor phase transition pressures in relation to the fixed point pressure scale
Authors: Piermarini G. J. , Block S.
Published: March 2003

A diamond-anvil type optical cell of improved design has produced static pressures in gasketed samples up to 500 kilobar as measured by the ruby fluorescence technique. The ruby R1 line pressure shift is linear to 291 kilobar, and the maximum measured shift is extrapolated to 500 kilobar assuming continued linearity of the pressure dependence. The ultimate pressure capability of this diamond cell has not been established. Transition pressures in the semiconductors Si, ZnSe, ZnS, and GaP measured by the ruby method indicate that the revised 1970 fixed point scale and the ruby (NaCl) scale diverge above 135 kilobar and disagreement may be by as much as a factor of 2 in the 500 kilobar range with the ruby scale defining the lower pressure.
Method for measuring coincidences in the presence of a high level of accidental coincidences
Authors: Suchannek Rudolf G. , Young Stephen J. , Sheridan J. Roger
Published: March 2003

An electronic system was developed for coincidence measurements in the presence of a high level of accidental coincidences, assuming the true coincidence rate is constant. This system eliminates the distortions produced by the use of two independent coincidence modules for measuring accidental coincidences na and the sum of accidental and real coincidences ns. The two quantities are measured by the same coincidence module during successive periods of 40 msec. The system was tested under conditions such that the accidental coincidence counts exceeded the number of real coincidences by a factor of 102. The accuracy of the measurement of real coincidences was limited only by statistical fluctuations of accidental coincidences.
Prealignment of gas laser cavities
Authors: Hernqvist K. G. , Firester A. H.
Published: March 2003

A method of coarse alignment and fine tuning of the cavity of a gas laser is presented. The laser cavity to be aligned is treated as a Fabry–Perot cavity, and its transmission of a frequency-swept laser is maximized. An experiment is described showing that this fine-tuning procedure results in maximum power output when the laser is operated. The method is particularly well-suited to laser manufacturing.
Programmable control unit for a balloon-borne quadrupole mass spectrometer
Authors: Arijs E. , Nevejans D.
Published: March 2003

For the measurement of the ionic composition of the atmosphere a reprogrammable control unit for a quadrupole mass filter has been constructed. The heart of this unit consists of two programmable read only memories which allows the choice of 16 different measuring jobs by six telecontrol channels. The underlying principles as well as the performance of the unit are described.
High pressure–low temperature apparatus for electrical conductivity measurements
Authors: Jones R. E. , Anderson G. C. , Keeler W. J.
Published: March 2003

Equipment is described for electrical measurements under hydrostatic pressures to 30 kilobar over the low to room temperature range. The piston and cylinder type pressure vessel of the high-pressure cryostat is actuated directly by a hydraulic ram at room temperature. Thermal isolation is achieved through use of long tension and compression members. Details about the self-stressing, double-walled cylinder are provided. Both the Bi I–II transition and an n–InSb manometer have been used for pressure calibration.
Selective removal of either metastable species from a mixed 3P0,2 rare-gas metastable beam
Authors: Dunning F. B. , Cook T. B. , West W. P. , Stebbings R. F.
Published: March 2003

A tunable cw laser has been used to selectively remove either of the two metastable species, 3P0,2, which are initially present in a neon metastable beam. The method is applicable to other rare gases and provides the opportunity for separate investigation of effects due to atoms in either the 3P0 or 3P2 state.
Microwave Hall measurment techniques on low mobility semiconductors and insulators. I. Analysis
Authors: Sayed Mohamed M. , Westgate Charles R.
Published: March 2003

The relationships of microwave Hall mobilities and microwave conductivities in a semiconductor, placed at the center of a dual mode TE111 cavity, are expressed in terms of the loaded and unloaded voltage reflection coefficients, the sample and the cavity dimensions, the ratio of the output power to the input power of the cavity, and the magnetic field. Scattering
New technique for determining the heating effects of the electron beam on metal foils in an electron microscope
Authors: Lewis William F. , Marti Jordi , Paul David I.
Published: March 2003

We have devised a new method for determining the heating effects of the electron beam on metal foils in a transmission electron microscope. Thin specimens of tin, lead, and zinc were melted in the electron microscope using the combination of heat from the electron beam in ’’normal’’ usage and a previously calibrated heating cartridge. The temperature rise due to the electron beam heating was the difference between the melting temperature of the metal foil and the ’’temperature contribution’’ of the heating element. For a given beam current the temperature rise of the metal foils due to be beam was determined to within ±10 °C using this technique. This technique appears to be valid provided the beam current is kept at the same constant value during calibration and operation.
Theoretical limitations and extensions of a modulation technique for lineshape analysis
Authors: Hanisch Robert J. , Hughes Gregory P. , Merrill John R.
Published: March 2003

The technique of differentiation by modulating the independent variable of an experimental signal and its application to increasing the accuracy of experimental measurements has been studied via a computer simulation. The modulation derivative (the approximate derivative obtained using this method) has been found to be accurate to 1% or better when the amplitude of modulation is 5% or less of the full width of the transfer function. The dependence of the width and amplitude of the first and second modulation derivatives upon the amplitude of modulation has been studied, and methods have been found for ascertaining the width of the transfer function and its first derivative without using the small amplitudes of modulation usually necessary. The approach described is general and is applicable to any experiment where the modulation technique can be utilized.
Measurement of the quantum efficiency of an electron multiplier as a function of incident proton energy
Authors: Cho Z. H. , Singh M. , Mohabbatizadeh A. , Chai J. , Cheung H. , Sackerlotzky O. H.
Published: March 2003

The quantum efficiency (QE) of an electron multiplier tube with oxidized Cu–Be dynodes was measured for incident protons over the energy region of 0.5–2 MeV at beam currents of 0.1–0.5 nA. The QE is relatively constant with energy up to 1.4 MeV. At higher energy the QE is inverse proportionally to incident energy, dropping to about half the peak value at 2.0 MeV. The proton beam was obtained from a Van de Graaff accelerator at UCLA.
Digital light scattering photometer
Authors: Lee S. P. , Tscharnuter W. , Chu B.
Published: March 2003

We have constructed a three-channel digital (ratio) photometer using TTL integrated circuit. Each channel has its own separate scaler and timer with eight-digit counting capacities. The instrument is particularly useful for precise determinations of correlation lengths of critical fluid systems and for size studies of small macromolecules in solution. It has an estimated resolution of 13 Å and 17 Å in the correlation length for λ0 = 4880 Å and 6328 Å, respectively. The instrument overlaps comfortably with the size ranges accessible by means of small angle scattering of x-rays.
Technique for sampling gases in hollow microspheres
Authors: Ebner M. A. , Rensel W. B.
Published: March 2003

A simple technique is described for inserting single gas-filled laser fusion pellets into high-vacuum systems for qualitative gas analysis.
Small effect of hydrostatic pressure on the emf of the Chromel/Alumel thermocouple between 4.2 and 300 K
Authors: Diatschenko V. , Chu C. W.
Published: March 2003

The hydrostatic pressure effect on the emf of the Chromel/Alumel thermocouple has been found to be very small between 4.2 and 300 K up to 22 kilobar. This makes the Chromel/Alumel thermocouple the best temperature sensor yet for high-pressure and low-temperature study.
Electrical resistance of Evanohm under pressure
Authors: Andersson P. , Bäckström G.
Published: March 2003

The electrical resistance of Evanohm wire has been determined as a function of hydrostatic pressure. A Teflon cell with a novel type of electrical feedthrough was used to contain the fluid medium. The resistance was found to decrease approximately linearly by 0.3% up to 27 kilobar. The remarkably small variation of its resistance with temperature and pressure makes Evanohm a suitable material for strain measurements under pressure.
High pressures with supported opposed steel anvils
Authors: Ruoff Arthur L. , Wanagel John
Published: March 2003

It is shown that opposed, supported maraging steel anvils are capable of generating pressures in excess of the upper bismuth transition at 75 kilobar, and in excess of the InAs transition at 85 kilobar, or more than four times the compressive yield stress of the material.
Time-resolved pinhole camera for observation of nanosecond-duration x–uv plasma emission
Authors: Johnson David J. , Stephanakis Stavros J. , Boller John R.
Published: March 2003

A vacuum diode with a rear-mounted Pilot-B scintillator has been coupled with a conventional evacuated pinhole camera. The cathode of the diode is fabricated from 2-μ thick polycarbonate (Kimfol) with a 200-Å aluminum layer on the rear surface. Incident photons with energies above the carbon K edge (284 eV) are highly absorbed in the polycarbonate, but photons with energies below the K edge are absorbed in the aluminum and produce photoelectrons. This yields a photoelectron sensitivity which is peaked at approximately 275 eV. The photoelectrons are accelerated by a 10-kV cathode potential to an aluminum anode coating on the scintillator, and scintillation photons are observed with an image converter camera. Streak photographs of exploded-wire x–uv radiation taken with this system are presented.
Plasma-cathode electron gun
Authors: Bayless J. R.
Published: March 2003

The plasma-cathode electron gun is a new type of electron source which is suitable for applications requiring a large area, high-energy electron beam. It employs a plasma generated within a cold low-voltage, hollow-cathode discharge as the source of electrons. Plasma cathode devices are characterized by their simplicity and versatility, and they offer a number of advantages over other designs. An electron gun producing a beam with dimensions of 5×125 cm has been developed for use with high-power cw gas lasers. This device has been operated at beam energies of 150 keV and cw beam current densities of 0.1–0.2 mA/cm2.
High-sensitivity appearance potential spectrometer for the detection of photons, electrons, and ions
Authors: Kluge A.
Published: March 2003

A versatile appearance potential spectrometer has been developed to detect photons and electrons, emitted during electron bombardment, for determining the binding energies of the electrons of surface atoms. Primary currents down to 50 μA yield good signals for the detection of electrons. Furthermore, the detection of desorbed ions can be used for measuring the threshold energy of ion emission. A special preamplifier is used for a high signal-to-noise ratio.
Technique for rapid Faraday susceptibility measurements
Authors: Szofran F. R. , Burmester W. L. , Sellmyer D. J. , Rubin L. G.
Published: March 2003

An apparatus is described which permits the rapid acquisition and computer analysis of temperature-dependent Faraday susceptibility data. The apparatus utilizes a relatively inexpensive, three-channel, data-acquisition system.
Simple technique for observing ferrimagnetic resonance in magnetic-bubble garnet films
Authors: Vella-Coleiro G. P.
Published: March 2003

A very simple microwave spectrometer has been used to make ferrimagnetic resonance measurements in magnetic-bubble garnet films. The simplicity of the technique makes it well suited for routine measurements of gyromagnetic ratios, damping parameters, and anisotropy constants in bubble materials.
Apparatus for high-pressure, low-temperature, neutron-scattering measurements
Authors: Kleb R. , Copley J. R. D.
Published: March 2003

We describe an apparatus which is designed for neutron-scattering studies of single crystals under hydrostatic pressures up to 5 kilobar and at temperatures between 77 and ∼300 K. The safety features of the system are emphasized.
Design of stopped-flow NMR rapid-mixing cells
Authors: Grimaldi John J. , Sykes Brian D.
Published: March 2003

The design and construction of two rapid-mixing apparatuses which can be accommodated within the probes of commercial NMR spectrometers are described. The principal features of the cells described are applicable to the construction of stopped-flow cells for any NMR spectrometer.
Hydrogen leak detector using a Pd-gate MOS transistor
Authors: Stiblert L. , Svensson C.
Published: March 2003

A small, battery-operated hydrogen leak detector using a palladium-gate MOS transistor as sensing element has been developed. It is shown to have a sensitivity of 1 ppm hydrogen in air and response and recovery times of a few seconds. The fast response was obtained by operating the sensing element at 150 °C.
Laser temperature-jump spectrophotometer using stimulated Raman effect in H2 gas for the study of nanosecond fast chemical relaxation times
Authors: Ameen Syed
Published: March 2003

A laser temperature-jump spectrophotometer for the study of chemical relaxation times with a heating time of about 18 nsec is described. The stimulated Raman effect in hydrogen gas at 80-atm pressure produces a frequency shift of a neodymium-glass laser from 1.06 to 1.89 μ, at which the absorbance of water is very high. The use of H2 as a Raman active material for the frequency shifting, instead of liquid N2 previously used, is emphasized, which eliminates the need for low-temperature storage facilities and creates the possibilities for generation of other wavelengths, by using a mixture of gases and varying the pressures to obtain other absorption frequencies for the heating of the solvent molecules. For aqueous solutions heated by 1.89-μ radiation pulses, a special spacer cell is described, which allows maximum coaxial overlap between the laser pulse and the analyzing beam. For other nonaqueous solvents a multireflection cell is constructed. The H2 Raman-shifted pulse is narrowed from a 28-nsec half-width of the original 1.06-μ Nd+3-glass laser to 15-nsec half-width at 1.89 μ. The conversion efficiency of usually about 20% is increased to about 40% using a multistage H2 gas Raman cell device, in which the scattering focal volume is increased.
Sub-nanosecond metal-oxide-semiconductor pressure switch for the terapascal range
Authors: Kalibjian R. , Brier R. L.
Published: March 2003

A solid-state sensor has been developed to give a signal risetime of 1 nsec in the TPa pressure range. For applications requiring a high signal-to-noise ratio, the sensor is operated reliably in the switch mode with a 50-V bias voltage. The pressure sensor can also be operated in the shock-induced polarization mode giving 2-nsec FWHM signals with 0.6-V amplitude.
Automated nonselective measurement of T1ρ by Fourier transform NMR
Authors: Freeman Walter J. , Leipert Thomas K. , Dalrymple David L. , Noggle Joseph H.
Published: March 2003

A simple, computer automated method for measuring rotating frame relaxation times (T1ρ) for many line spectra on modified commercial NMR spectrometers is discussed. Sources of error and critical instrumental parameters are identified. Adjustment of the various parameters of the pulsed rf system is more critical than for T1 but perhaps less so than for T2 measurements.
Mechanical opening system for vacuum tubes in space environment
Authors: Arends H. J. , Gonfalone A. A.
Published: March 2003

A clean opening system for a vacuum tube is discussed. This system presents the following advantages: before closure, the tube can be baked to temperatures of the order of 350 °C. Once sealed a high vacuum can be maintained inside, and the opening of the tube can be done in a high vacuum environment without degradation of the vacuum. This is achieved by cutting a fine membrane holding a cover. Different parts of the system have been tested successfully.
Improved method for LEED intensity measurements
Authors: Felter T. E. , Estrup P. J.
Published: March 2003

Faster and more accurate measurements of low level light sources such as LEED spot intensities are described. The method uses image intensification in a conventional spot photometer.
New crossed-beam apparatus for the study of ion–molecule collision processes
Authors: Vestal M. L. , Blakley C. R. , Ryan P. W. , Futrell J. H.
Published: March 2003

A new crossed-beam apparatus for the study of ion–molecule collision processes is described. Among the novel features of this apparatus are a high pressure ’’chemical ionization’’ ion source, an apertureless exponential ion deceleration lens, a product ion mass/energy analyzer that can be scanned in angle through nearly a full octant of a sphere, and a supersonic nozzle molecular beam source. The high pressure source can be used to produce vibrationally relaxed ground state reactant ions, and the deceleration lens produces focused ion beams with energies as low as 0.1 eV at intensities equal to the space-charge limit.
Application of a glass-sealed Langmuir probe to ionosphere study
Authors: Oyama Koh-ichiro , Hirao Kunio
Published: March 2003

A glass-sealed Langmuir probe was developed to get accurate information on the ionospheric plasma. An electrode sealed in a glass tube is first baked in low pressure and tipped off the pumping system to keep the electrode surface clean. An essential advantage of the glass-sealed Langmuir probe is that it will not require the rapid sweeping of a probe voltage for reliable data acquisition. It is noted that the glass-sealed Langmuir probe is strongly recommended for the measurement of energy distribution of thermal electrons by the second harmonic method.
New ’’wall-less’’ ionization chamber for air dose measurement
Authors: Varma M. N. , Baum J. W.
Published: March 2003

A simple mesh wall ionization chamber (representing a ’’wall-less’’ ionization chamber) is described for air dose measurement. The effects of insulators and air circulation in the vicinity of the chamber were studied. An outer shield mesh placed around the collecting chamber eliminates the adverse effects of air circulation and electrostatic disturbances around the detector. The detector can be used effectively to measure that component of dose due to low energy electrons or x rays which are normally stopped by the walls of conventional dose measuring instruments. The mesh ion chamber is particularly useful in measuring dose distribution in and around a radiation field. This chamber approximates a free air ion chamber that can be used at low, as well as high, energies once electron equilibrium is achieved. The chamber was tested using 137Cs gamma radiations and gives good agreement with a model 570 Victoreen R meter.
Lifetime of a fast, high-voltage vacuum spark gap
Authors: Avraham E. Bar , Porat Y.
Published: March 2003

The operation of a fast, high-voltage vacuum spark gap is affected by the pumping speed after each shot. A simple means to prolong the gap lifetime is proposed.
High pressure calorimetry as applied to piezothermal analysis
Authors: Pruzan Philippe , Minassian Léon Ter , Figuiere Pierre , Szwarc Henri
Published: March 2003

This paper describes an apparatus which can be used to determine bulk thermal expansion coefficients of liquids as a function of temperature and pressure up to 10 kilobar in a temperature range from −20° to 100 °C. The principle of the method consists in measuring the heat of compression by a step by step procedure. The apparatus is a Joule twin calorimeter which is composed of a high pressure vessel and a reference cylinder. Temperature differences between these two components can be detected at better than 10−5 K by means of a gas thermometer, thus providing high sensitivity. Results are given for liquid n-hexane and ethyl alcohol.
Rocket-borne double focusing analyzer for particle spectroscopy in the lower magnetosphere
Authors: Crifo J. F. , Prange R. , Cornic C. , Salvetat P.
Published: March 2003

We describe a rocket-borne instrument for measurement of the low energy electron and proton distribution function in the magnetosphere. It consists of an optimized programmable electrostatic toroidal analyzer as an energy selector, coupled with an electron multiplier as a particle detector, and of the associated electronics. Much attention has been paid to the experimental calibration of the instrument which gives us some understanding of the real behavior of the detector and the way it influences the analyzer properties.
Precise temperature control for growth of silicon crystals
Authors: Lee S. P. , Lue J. T. , Yang Y. T. , Yu H. Y.
Published: March 2003

An automatic temperature controller for a three-phase, grid-controlled induction furnace, which can maintain the oven temperature at the silicon melting point with a stability of ±0.4 °C for 2 h of operation, has been described.
Ionization-type smoke detectors
Authors: Simon Frank N. , Rork Gerald D.
Published: March 2003

A simple model is developed to determine quantitative relations among operating parameters applicable to the design of ionization-type smoke detectors. The model permits the adjustable parameters of operating current, radioisotope source intensity, and cell geometry to be specified for ambient pressure response and optimum sensitivity to smoke particulates. Specific ionization has been measured for two sources (3H and 63Ni) as a function of pressure as required by the model. Experimental agreement with the model presented shows its validity for design evaluation of ionization cells for smoke detection and possibly other special applications with particulates.
Tungsten dendrite–thorium carbide cathode
Authors: Glascock H. H.
Published: March 2003

A new method, the capillary method, is described here for fabricating ThC cathodes. Each cathode consists of W–Re tubing containing a W-dendrite matrix filled with dense ThC–W eutectic. Hundreds of these cathodes have been used as sources for electron guns which require zero field emission capability of several A/cm2 for thousands of hours. The effective work function of this cathode can be expressed as φ=2.93+2.15×10−4 T between 1750 and 2350 K.
Elimination of reflection errors in emissometers by using alternate apertures
Authors: Deardorff D. K.
Published: March 2003

Modifications to an existing vacuum emissometer are described that allow mathematical elimination of reflection errors of the specimen–window–specimen–detector type. Normal total emittance in the range 20–600 °C can be determined. Successive radiance readings Ls and Ls′ are obtained using alternate full- and reduced-size apertures. A separate run on a blackbody crucible allows determination of the corresponding LBB and LBB′ values at the same temperature. The equation for true emittance is shown to be ε=Ls−Ls′/LBB−LBB′.
New quantitative schlieren technique
Authors: Pandya T. P. , Saxena A. K. , Srivastava B. C.
Published: March 2003

A new technique—adapting the rings and brushes assembly—for quantitative schlieren studies is described. Examples of its possible application are given, and a typical case is discussed in detail.
Thermal drive apparatus for direct vacuum tunneling experiments
Authors: Thompson W. A. , Hanrahan S. F.
Published: March 2003

A thermal drive apparatus is described which has been used for direct vacuum tunneling experiments where two electrodes are brought to within 10–20 Å of each other. This drive has shown excellent stability against low-frequency vibrations and appears to have less than 1-Å instability over periods of hours.
Versatile, space-saving Dewars utilizing a simple valve seal
Authors: Foner S. , McNiff E. J.
Published: March 2003

Dewars with a minimal vacuum space utilizing a simple valve arrangement and permitting a minimum loss of working volume are discussed. Dewars with a difference between the inner and outer diameter as small as 1.5 mm have been constructed.
Chemical kinetic studies by a new small pressure perturbation method
Authors: Clegg R. M. , Maxfield B. W.
Published: March 2003

The construction and operation of a repetitive pressure perturbation apparatus to study rapid chemical relaxation kinetics is reported. The reaction progress is monitored by measuring light absorption, light scattering, or fluorescence. This new instrument allows the application of small pressure perturbations (0.01–5.0 atm), which is a feature of special interest when studying reactions that are sensitive to small changes in free energy (e.g., quasi-phase changes in biomembranes and conformational changes in macromolecules). Repetitive application of the pressure perturbation and averaging of consecutive measurements greatly enhances the sensitivity and allows the use of such small pressure perturbations. The time range available for kinetic studies is 20 μsec to several minutes. Examples of the performance of the new apparatus are given, and the theoretical analysis is discussed insofar as it differs from conventional relaxation techniques.
Current inversion impedance converter using operational amplifiers
Authors: Sancholuz Arturo G.
Published: March 2003

A current inversion impedance converter that requires three amplifiers is presented. The residual error in the g parameters is negligible for practical applications. The network is short circuit stable at one port and open circuit stable at the other. A novel application of the circuit is also briefly described.
Design of a bent beam electron gun for evaporation
Authors: Banerjee A. , Barthwal S. K. , Chopra K. L.
Published: March 2003

This note describes the design and fabrication of a simple 6 kW bent beam electron gun for vacuum deposition of thin films.
Hadamard transform infrared astronomical imaging device
Authors: Slingerland J.
Published: March 2003

A 255 picture element imaging device for astronomical applications in the J and K atmospheric windows (1.5- to 1.8-μ and 2.0- to 2.4-μ wavelength, respectively) is described. Spatial information is optically encoded and detected by a LN2-cooled detector. Electronic decoding is achieved during measurement by means of a special purpose computer. Under seeing and scintillation noise limited conditions a multiplex advantage of a factor of 8 is attained.
Design of a synchrotron radiation facility for Orsay’s ACO storage ring : LURE
Authors: Guyon P. M. , Depautex C. , Morel G.
Published: March 2003

The LURE synchrotron radiation facility is described. We emphasize the scientific and technological considerations that led to our practical choice of transfer optics, vacuum equipment, and fail safe system based on the use of an acoustical delay line. Characteristics of the vacuum beam lines are given as well as the actual performance of the system as a practical light source.
On the sample holders for the superconducting magnetometer
Authors: Cerdonio M. , Messana C. , Gramaccioni C.
Published: March 2003

A simple modification of the sample holders for our superconducting magnetometer is described. It eliminates the holder contribution from the total signal.
Pressure control of rf bias for sputtering
Authors: Kochel L. J.
Published: March 2003

A method of simultaneously controlling vacuum pressure and substrate bias using only a pressure controller is described for an rf bias sputtering system in which the bias is developed through substrate tuning.
Simple, rapid slit alignment procedure
Authors: Deutsch Moshe , Freund Isaac
Published: March 2003

A simple, rapid means of accurately aligning a slit parallel to the line focus of an x-ray tube is described.
Improved sensitivity for the superconducting ’’chopper’’ amplifier
Authors: Friedberg C. B. , Galfo C. H.
Published: March 2003

A heterodyning modulation technique is described which results in an improved sensitivity for the superconducting chopper amplifier. Dc sensitivities of 3×10−12 V were obtained in a 1 Hz noise bandwidth. An experimental comparison of various modulation schemes is presented.
Sensitive instrument to measure the friction between single fibers in various media
Authors: Landwehr Robert C.
Published: March 2003

A sensitive instrument is described that measures the frictional and normal forces while nearly parallel fibers are rubbed in various media at normal forces down to 1 mg and rubbing speeds slow enough to ensure continuous contact. Typical frictional output traces are shown for human hair and coarse mohair fibers in water. The instrument detects scale engagement of keratin fibers.
Calibration of rare-earth x-ray intensifying screens in the 15–70 keV energy range for use on pulsed x-ray sources
Authors: Birks L. S. , Sandelin J. W. , Dozier C. M.
Published: March 2003

Rare-earth screens (Rarex types B and BG) were calibrated against Kodak No-Screen x-ray film using pulsed x radiation. Type B screen, which contains only an yttrium compound, is over 50 times more sensitive than No-Screen film in the energy range above 17 keV and is the preferred screen, of the two tested, in the energy range below 50 keV. Type BG screen, which contains yttrium and gadolinium compounds, is 1.5 times less sensitive than type B below 50 keV (the Gd absorption edge) but 3.5 times more sensitive above 50 keV. All of the calibrations were accomplished with monochromatic x rays from secondary fluorescers. The results should be accurate for pulses of shorter duration than 1 msec, which is the decay time of the screens.
Balloon-borne stratospheric grab-sampling system
Authors: Schmeltekopf A. L. , Goldan P. D. , Harrop W. J. , Thompson T. L. , Albritton D. L. , MacFarland M. , Sapp A. E. , Henderson W. R.
Published: March 2003

A lightweight balloon-borne grab-sampling system for determining mixing ratios <10−9 of chlorocarbons and other minor constituents in the stratosphere is described. The all-metal system consists of five sampling spheres and associated valves, which are opened and closed at selected altitudes by on-board electronics during a parachute descent. The construction features, operating techniques, and experimental tests are given. In the latter, particular attention has been given to the problem of surface adsorption in ambient-pressure in situ sampling of trace stratospheric constituents at these low mixing ratios.
Intense accelerated metal ion beam utilizing laser blowoff
Authors: Friichtenicht J. F. , Utterback N. G. , Valles J. R.
Published: March 2003

An intense pulsed beam of energetic metal ions has been produced by electrically accelerating ions extracted from a laser-produced plasma. A pulsed laser focused on a metal surface in a vacuum provides the expanding metal plasma. The plasma is intercepted by a pair of shaped grids located at a distance where the plasma cloud has become collisionless. An electric field between the grids accelerates and focuses the ions. Electrons from a heated filament are introduced into the ion stream in an effort to neutralize the space charge spreading of the ion beam (plasma). Ion beams were produced with energies from 1 to 10 keV. Ion fluences per pulse in the fast beam have reached 1013 cm−2, and 1012 ions per pulse have been injected through a cylindrical channel 0.8 cm diam×2.0 cm long. The beam pulse lengths were typically less than 20 μsec. Aluminum has been used principally but the method should be applicable to a wide range of materials.
Automatic recording capillary viscometer for the study of polymeric reactions
Authors: Kilp T. , Houvenaghel-Defoort B. , Panning W. , Guillet J. E.
Published: March 2003

An automatic viscometer and sampling system suitable for monitoring changes in the molecular weight of polymers in solution is described. Automation provides significant increases in precision and accuracy. The instrument can be used to follow degradation or polymerization reactions induced by radiation, heat, or chemical reaction. Examples are given of its application to the study of photolytic and chemical degradation of polymers.
Studies of the hollow discharge duoplasmatron as a source of H− ions
Authors: Kobayashi M. , Prelec K. , Sluyters Th.
Published: March 2003

A parametric study was made of the pulsed hollow discharge duoplasmatron, operating as a negative hydrogen ion source in the pure hydrogen mode and in the mixed hydrogen–cesium mode. Effects of the arc current, gas pressure, and the magnetic field on the extracted H− current were investigated for different electrode geometries and potentials. In the hydrogen mode a maximum H− beam current of 11 mA was obtained from an anode extraction aperture of 2.45-mm diameter, with a normalized emittance of 0.1π cm mrad. In the mixed hydrogen–cesium mode an H− beam current of 60 mA was obtained from the same aperture. At a current of 40 mA the normalized emittance was 0.23π cm mrad. An analysis of the results points to the volume production of H− ions in the hydrogen mode and to the surface production in the hydrogen–cesium mode.
Measurement of thermal expansion at high temperatures by laser interferometry of two fibers
Authors: Hollenberg G. W. , Sharpe W. N.
Published: March 2003

Thermal expansion is determined by measuring interferometrically the relative displacement of two fibers attached to specimens. Coherent monochromatic light from a laser incident upon the two adjacent fibers produces a Fraunhofer fringe pattern. Relative displacement of the fibers can then be determined by monitoring the motion of the fringe pattern. The technique was applied to the measurement of thermal expansion of ceramics in air to 1150 °C and of graphites in vacuum to 1900 °C.
Effect of scattered light on temperature measurement by optical pyrometry
Authors: Einziger R. E. , Mundy J. N.
Published: March 2003

The difficulties associated with the use of optical pyrometry for temperature measurement in an electron-beam furnace are discussed. Light from the filaments producing the electron beam may be scattered into the optical pyrometer. A procedure has been developed that allows a determination of the required correction to the optical pyrometer reading which will take into account the scattered-light effect and also the error introduced by the correction. The problems associated with the use of thermocouples at high voltage in an electron-beam furnace are also evaluated.
Soft recovery of shocked specimens for dynamic fracture studies
Authors: Holt W. H. , Mock W.
Published: March 2003

A system that permits the soft recovery of specimens shock loaded with a gas gun has been designed for dynamic fracture studies. Post-impact damage to the specimen is minimized via the in-flight capture of the projectile and flyer disk. The system has been tested for projectile velocities up to 0.32 mm/μsec.
Compact telemeter for plasma losses on isolated surfaces
Authors: Nonn Paul D.
Published: March 2003

Two infrared light-beam telemeters for reading currents between 1×10−6 and 5×10−4 A at frequencies from dc to 100 kHz are described. One design is currently in use aboard the isolated rings of the Wisconsin levitated octupole for measuring the flux of plasma to collectors on the ring surface from the stable confinement region around the ring. This device is triggered from outside the vacuum vessel and applies a 20 V bias to the striped plasma collectors. Each telemeter is completely contained within a 1 cm diam by 12 cm long case and, although buried in the solid aluminum rings, can be removed and serviced through airlocks. A second telemeter design, a more versatile but much more complex predecessor, is powered by capacitors that are charged by a bank of solar cells, which are illuminated by a light source outside the plasma containment zone in controlled patterns to select bias from 0 to 50 V in 10 steps. Elaborate precautions were taken to avoid anticipated possible interference from plasma light, large magnetic fields, and high microwave fields.
Uniaxial stress apparatus for an EPR X-band spectrometer
Authors: Szumowski J. , Falkowski K.
Published: March 2003

A simple system for examining the influence of uniaxial stress on the X-band EPR spectrum has been designed and fabricated. The system is capable of applying a compressive uniaxial stress up to 3500 kg/cm2, permits investigation of the angular dependence of the EPR spectra, and can operate in the temperature range of 80–400 K.