bluuebunny/crossref_metadata_2025 huggingface dataset:
National facilities for research in the physics of condensed matter
Authors: Vineyard George H. , Falicov L. M.
Published: March 2003

Brief descriptions are given of 23 national facilities in the U. S. that are of importance to research in the physics of condensed matter. These facilities range from nuclear reactors and synchrotron sources to high-voltage electron microscopes and facilities for the preparation of special materials and submicron structures. They take a variety of forms and are located in several kinds of institutions, but are alike in being available to qualified scientists from other laboratories. The primary purpose, size, major experimental equipment, and method of operation are described for each facility.
Measurement of vacuum space potential by an emissive probe
Authors: Cho M. H. , Chan C. , Hershkowitz N. , Intrator T.
Published: March 2003

Using the inflection point method of interpreting emissive probes, it is shown that it is possible to measure the electric space potential established between two parallel metal plates in a vacuum.
Digital differential depth meter
Authors: Woodward B.
Published: March 2003

This diver-portable instrument measures relative depths to a precision of ±0.02 m in real time by using two sensitive pressure sensors. It fulfills a need by diver scientists to measure relative water depths in any underwater current in which diving is possible, but without being encumbered by unwieldy equipment such as was used previously. Typical applications include the measurement of stratigraphic levels on sea-bed sites of historical, biological, and geological interest.
Closed-cycle gaseous alkyl-iodide (C3F7I) supply system
Authors: Schlie L. A. , Rathge R. D.
Published: March 2003

A completely passive closed-cycle flowing alkyl-iodide (C3F7I) gaseous supply system which provides a high purity and fixed pressure of gaseous C3F7I at a well-regulated flow velocity is reported. Its employment produces an extreme cost saving and the generated flowing gas can easily be coupled with cw atomic iodine photolysis lasers to produce excellent results. The low-temperature evaporation/condensation baths (<0 °C) freeze out all of the excited atomic iodine quenchers H2O and I2 present in liquid C3F7I.
Transmission grating velocimeter for particles electric mobility measurements
Authors: Delatour E. , Hanss M.
Published: March 2003

A novel optical velocimeter has been designed in order to measure with a high resolution electrophoretic mobility distributions of suspended particles. It uses a transmission grating on which the dark-field image of the particles is focused. A spectral analysis of the transmitted time-modulated light intensity allows the determination of the velocity spectrum. The principle, a description of the apparatus, and some results are given. The velocity resolution is significantly better than with the laser Doppler techniques for different reasons which are discussed.
An efficient digital phase-sensitive detector for use in electron-spin-resonance spectroscopy
Authors: Vistnes A. I. , Wormald D. I. , Isachsen S. , Schmalbein D.
Published: March 2003

A digital phase-sensitive detector for a modified Bruker electron-spin-resonance (ESR) spectrometer, equipped with an Aspect 2000 minicomputer is described. Magnetic field modulation is derived from a clock in the computer, which makes it possible to perform the data acquisition fully synchronously with the modulation. The resulting high phase accuracy makes it possible to compress the data to a single modulation period before the Fourier transformation. Both the in-phase and the phase-quadrature signals (of the first or second harmonic) are recorded simultaneously. The system is so efficient that the data processing including the Fourier transformation is approximately 1000 times faster than a previously reported digital phase-sensitive detector system for ESR [T. Watanabe et al., Appl. Spectrosc. 34, 456 (1980)].
Double focusing ion mass spectrometer of cylindrical symmetry
Authors: Coplan M. A. , Moore John H. , Hoffman R. A.
Published: March 2003

A mass spectrometer consisting of an electric sector followed by a magnetic sector is described. The geometry is a cylindrically symmetric generalization of the Mattauch–Herzog spectrometer. With its large annular entrance aperture and a position-sensitive detector the instrument provides a large geometric factor and 100% duty factor making it appropriate for spacecraft experiments.
Optical length determinations in the diamond-anvil cell
Authors: Scott Cassie , Jeanloz Raymond
Published: March 2003

Sample dimensions can be measured optically at high pressures to a precision of about 65 nm. Using an image-shearing device and a gasketed diamond-anvil cell, linear strains can be determined to about one part in 103 for typical sample dimensions (∼100 μm). This technique complements x-ray diffraction measurements in that optical length determinations are rapid, and can be applied to samples that are amorphous or of low atomic number. Compressibility at high temperatures and creep deformation under nonhydrostatic stresses can also be measured optically. We illustrate this method by successfully measuring the hydrostatic compression of gold to 7 GPa, using some of the smallest samples for which length changes have been determined at high pressures (∼40 μm).
New viscosity measurement: The oscillating magnetically suspended sphere
Authors: Leyh Carl , Ritter Rogers C.
Published: March 2003

A vertically oscillating spherical buoy, magnetically suspended, is used in a new measurement of viscosity. Thus far it has been applied only to transparent, dilute aqueous biomolecular solutions of 0.5-ml volume. With a different position transducer and sufficient attention to the hydrodynamics, it is possible that these limitations could be transcended. In the method, the phase lag of the motion relative to a sinusoidal magnetic driving force is measured with a phase-lock amplifier. This has been effective with amplitudes of motion from 100 Å to 1.8×10−3 cm. At the lowest amplitude noise reduces the precision, but different position sensors could improve that. Motion with larger amplitude risks invoking more complicated boundary layer effects, but has not been necessary thus far for precision at the level of two or three parts in 103 relative viscosity. This level of precision has been confirmed with aqueous sucrose and propanol solutions, and the output versus viscosity is linear at least to this level. Practical difficulties in the design of an instrument with such small volume has been our present limitation, both in precision and in the lack of ease of data taking. In this paper we present a simplified theory of operation, the design of the instrument, results of calibration runs, noise behavior and estimated limitations, and a discussion of improvements which might increase the precision about a factor of 10.
Axial magnetic field extraction-type microwave ion source with a permanent magnet
Authors: Ishikawa Junzo , Takeiri Yasuhiko , Takagi Toshinori
Published: March 2003

We have developed a new type of microwave ion source which has an axial magnetic field generated by a permanent magnet. By the combination of the permanent magnet and ferromagnetic materials, a closed magnetic circuit is formed through an ion extraction electrode. This axial magnetic field is utilized both for the high-density plasma production by the electron- cyclotron resonance process and for the high efficient ion extraction by transporting the generated ions along the magnetic force lines. The continuous ion beams of 2–3 mA are delivered from the extraction aperture (2 mm in diameter) when various gases (Ar, N2, CO2), metal vapors (Cs, Rb), and reactive gas (O2) are used. Extremely low impurities are present in the extracted ion beam. An ion beam with low emittance of 10−8 m rad order and high brightness of 1011 A m−2 rad−2 order is obtained. The size of this ion source is 50 mm in diameter and 65 mm in height. The discharge power of the microwave with the frequency of 2.45 GHz is 7 to 30 W. Thus, a high-current microwave ion source with compact structure and low power consumption is realized.
Energy deposition measurements of a large-diameter, intense relativistic electron beam for high-power gas laser excitation
Authors: Suzuki Tadashi , Kannari Fumihiko , Obara Minoru , Fujioka Tomoo
Published: March 2003

Measurements of electron-beam (e-beam) energy deposition in gaseous medium by a segmented totally stopping calorimeter and a pressure jump method are described, both of which gave the same values. Typical e-beam parameters are 2 MV, 80 kA, and 65 ns (FWHM). The e-beam cross-sectional area is 10 cm in diameter. First, the radial distribution of the e-beam current generated from the field-emission diode as a function of the axial magnetic field was measured. Next, for applications to longitudinal excitation of the high-power gas lasers, the e-beam energy deposition characteristics are measured in N2 for the propagation distance up to 2.3 m in terms of the axial magnetic field, the N2 gas pressure, and the radial e-beam distribution. As a result, the axial field equivalent to the self-magnetic field of the electron beam can acceptably control the e-beam generation and propagation uniformities.
Mie scattering functions for milk fat globules
Authors: Nallasamy M.
Published: March 2003

Mie scattering functions for milk fat globules seeded in water for laser Doppler measurements are presented.
Note on the design of simple indium O-ring seals
Authors: Turkington R. R. , Harris-Lowe R. F.
Published: March 2003

Various different applications of indium O-ring seals are briefly reviewed. A critical factor in the construction of any indium pressure-type seal is the finish of the surface cold welding to the indium. We present the results of some tests on surface finishes achieved by machining and grinding, which indicate certain conditions which ensure the integrity of the seal. Specifically, we find that if the metal surface has to be ground, it should be ground, and then polished to a surface granularity of less than 5  μ. This condition can be obtained using a grinding powder with a mesh size of 3200 or greater. Alternatively, careful surface preparation using a lathe furnishes an equally satisfactory finish, provided no attempt is made to ‘‘improve’’ the surface using emery paper, etc. In the latter case, the fine helical pattern imparted by the lathe is essential for the fabrication of a reliable seal.
Apparatus for measuring Seebeck coefficients of high-resistance semiconducting films
Authors: Trakalo M. , Moore C. J. , Leslie J. D. , Brodie D. E.
Published: March 2003

An apparatus is described for measuring Seebeck coefficients in semiconducting thin-film samples with resistances as high as 1011 Ω. A temperature gradient ΔT is produced across the sample by means of differential optical heating of the ends of the sample. The Seebeck voltage ΔV is measured using a specially designed amplifier circuit with an input impedance of 1013 Ω. The Seebeck coefficient is obtained from the slope of the plot of ΔV vs ΔT.
High-temperature, cyclic-loading stage for the scanning electron microscope
Authors: Nagy Andrew , Campbell John B. , Davidson D. L.
Published: March 2003

A stage for the ETEC Corp. SEM has been designed and constructed, which is capable of cyclicly loading a specimen up to 4000 N at temperatures up to at least 750 °C. The specimen is symmetrically loaded so that it may be observed dynamically under high resolution. Loading frequencies from static up to 4 Hz may be used, with a resolution of about 50 nm on the specimen for static loading and 100 nm for dynamic (TV scan rate) observation in the secondary electron mode. Load is applied with a closed-loop, servocontrolled hydraulic system. Heating is by resistive elements surrounding the specimen grips. Extensive radiative shielding is used for heat containment, with leakage extracted by liquid cooling of the pull rods and outer shielding.
Fabrication and leak-tight furnace brazing of intricate objects
Authors: Swift G. W. , Migliori A. , Wheatley John , Waller C. R. , Suazo G.
Published: March 2003

An extremely compact crossflow heat exchanger has been constructed by hydrogen furnace brazing together a stack of hundreds of chemically milled stainless-steel sheets. The resulting structure is leak tight and very strong, but fluid channels as small as 51 μm are not plugged by excess brazing material. The construction technique is easily adapted to mass production and should be useful for structures of an intricate but repetitive three-dimensional nature.
Extraction of H− beams from a magnetically filtered multicusp source
Authors: York R. L. , Stevens Ralph R. , Leung K. N. , Ehlers K. W.
Published: March 2003

H− ions produced by volume processes have been extracted from a multicusp source operated with a magnetic filter and accelerated to form a high-quality beam. It was found that the H− beam current increased almost linearly with the discharge current. An H− ion current density of 38 mA/cm2 was obtained with a discharge current of approximately 350 A. The accelerated beam was mass analyzed and the emittance of the H− component was measured. The electron component and the percentage of ion impurity in the extracted beam were also determined.
Fast chopped neutral beam technique for measurement of central ion temperature and central neutral atom density on the WEGA Tokamak
Authors: Hess W. R. , Gregory B. C. , Gormezano C.
Published: March 2003

This paper describes some details and results of an active neutral beam diagnostic mounted on the WEGA Tokamak and used in conjunction with a single-channel neutral particle energy analyzer. The beam diagnostic permits temporal resolution over a 40-ms interval of the Tokamak discharge during which lower hybrid heating is applied. The central ion temperature was measured to be 270 eV before heating and 340 eV during 178 kW of heating. In addition, the central neutral atom density was deduced from experimental results to be (1.5±1)×1014 m−3 using this active measurement technique. The relative efficiency of the charge-exchange analyzer measured using the active beam is in good agreement with independent calibration.
Surface fluctuation spectroscopy: Comments on experimental technique and capillary ripple theory
Authors: Mann J. Adin , Edwards Robert V.
Published: March 2003

We comment on several aspects of the light scattering technology that have been developed in our laboratory. In particular we show that Shih’s [Rev. Sci. Instrum. 55, XXX (1984)] data is consistent once beam propagation is taken into account fully and a small error in the grating constants corrected. The result is that we can make a stronger statement concerning the correspondence between theory and experiment for both the center frequency and width of the spectrum of capillary wave fluctuations at the liquid/vapor interface. We discuss questions of optimal design of the optical system and detection system for these measurements. We collect a set of dimensionless groups that are useful for the design of experiments.
Simple water-cooled mirror for high-power lamps
Authors: Curzon F. L. , Kjo/rvel A. , Camm D. M. , Halpin N. P. , Curzon A. E.
Published: March 2003

A mirror is described which endures illumination levels approaching 1 MW m−2. It has high reflectivity (>90%) and does not deteriorate even after several hours exposure to high illumination levels. It is inexpensive and easily replaced in the event of damage.
Turbine drive sample spinner for x-ray diffraction
Authors: Renault Jacques
Published: March 2003

A new sample spinner is described which is driven with a jet of air or other gas. The spinner features ease of mounting, rapid sample changing, and the ability to run at high revolutions per minute. The reproducibility of intensities with successive specimen remounting is better than 1%, and the standard deviation of d spacings measured for the 11 silicon peaks is 0.0005 A.
Ion deflection air flow meter with constant deflection
Authors: Janka K.
Published: March 2003

An air flow meter based on a constant deflection of ions is presented. The constant deflection is achieved by controlling the ion flight time between electrodes by adjusting the voltage of one electrode. The meter is shown to have some desirable properties: (a) linear response, (b) the capability of measuring low air velocities, and (c) insensitivity to aerosol particles in the air. Experimental measurements have been carried out in the range 1 cm/s–10 m/s.
Inexpensive apparatus for generating, standardizing, and dispensing sulfurous acid
Authors: Schein Daniel B. , Lee Tracy L. , Hokama Jane , Zeitlin Harry
Published: March 2003

The design, construction, and use of an inexpensive sulfurous acid production flask is described. The advantages of the design are the ease with which the solution can be dispensed and standardized, as well as the availability of inexpensive glassware to construct the apparatus. Standard iodometric techniques are utilized to standardize the generated sulfurous acid solutions to a precision of three significant figures. Two alternative designs are discussed.
Measurement of an obliquely incident soft x-ray with a microchannel plate
Authors: Arata Yoshiaki , Miyake Shoji , Kishimoto Hiroaki , Abe Nobuyuki
Published: March 2003

A 4-keV soft x ray is measured using a microchannel plate (MCP) and a visible light multichannel analyzer. A transparent photocathode is mounted in close contact with the front surface of the MCP to compensate for the reduction in gain of the obliquely incident soft x ray. Favorable improvement in sensitivity was obtained even at a large incident angle without reduction in the resolving power.
Modified high-pressure ac calorimetric technique
Authors: Jin X. C. , Hor P. H. , Wu M. K. , Chu C. W.
Published: March 2003

A modified high-pressure ac calorimetric technique has been developed by using a ‘‘plus–minus’’ square wave as the heating source. Because of the absence of a second-harmonic component in the heating source, the spurious signal in the ac specific heat is thus totally removed. The sensitivity of the technique is, therefore, improved as evidenced by the successful detection of the many phase transitions in CeSb under high pressure.
Simple system for high-pressure EPR measurements on aqueous samples
Authors: Cannistraro S.
Published: March 2003

We describe a simple high-pressure (up to 600 bars) device for EPR measurements of liquid samples which fits in the standard microwave cavities of X-band spectrometers.
Radio-frequency susceptibility apparatus for measuring small superconducting samples
Authors: Dalrymple B. J. , Prober D. E.
Published: March 2003

A radio-frequency magnetic susceptibility apparatus is described, which is capable of measuring the superconducting transition temperature of individual samples with volumes as small as 2×10−8 cm3 (mass ≂0.1 μg) with a signal-to-noise ratio of 20. The system uses phase-sensitive detection and operates between 1 and 10 MHz. Measurements in large dc magnetic fields ∼150 kG are also possible. Detailed information concerning construction and operation is provided.
High-temperature resonance cell for laser spectroscopy on low vapor pressure elements
Authors: Kluge H.-J. , Kremmling H. , Streib J. , Wallmeroth K.
Published: March 2003

A novel resonance cell system is described for laser spectroscopy on small samples of low vapor pressure elements. Temperatures of up to 1500 °C are reached with a cell made of sapphire allowing fluorescence and absorption spectroscopy in the spectral region 0.17 μm≤λ≤5 μm. The cell, with a small volume of 0.8 cm3, is designed for a fast sample change. The system has been applied to measurements of the isotope shift of radioactive Au isotopes.
Study of dynamical light scattering in phase separating 3He–4He mixtures using linear photodiode arrays
Authors: Sinha Dipen N. , Hoffer James K.
Published: March 2003

Experimental techniques to study dynamical light scattering phenomena in phase separating 3He–4He liquid mixtures are described. Commercially available self-scanning 512-element linear photodiode arrays are used to record ‘‘snapshots’’ of small-angle light scattering patterns with high angular resolution at time intervals as short as 2 ms. Logic circuitry developed for interfacing the photodiode arrays with a digital oscilloscope recorder is described in detail.
Construction and tuning of a monophoton decay fluorometer with high- resolution capabilities
Authors: Small Enoch W. , Libertini Louis J. , Isenberg Irvin
Published: March 2003

A fluorescence decay instrument, assembled largely from commercially available components, is described. This system incorporates a tunable picosecond laser system as an excitation source, energy windowing to minimize artifacts due to pulse pile up and sample alternation to compensate for long-term instrumental drift. The instrument was tested for its ability to resolve multiple exponential decays using methods of moments analysis. By examining the flatness of λ-invariance plots and the accuracy of recovered decay parameters, proper tuning of electronic components and definition of a range of reasonable counting rates was possible. Errors of significance to the resolution of closely spaced decays are discussed. A number of examples are shown for resolutions that are generally regarded as difficult, including two, three, and four components.
Some performance characteristics of a new discriminator for x-ray position-sensitive detectors
Authors: Morgue Michel , Gabriel André
Published: March 2003

Proportional position-sensitive counters using a delay line system are generally used in x-ray analysis. A new fast discriminator, linked to the end of the detector, has interesting performance characteristics.
Azimuthal integration of scattered light intensity using a conical lens
Authors: Pine David J.
Published: March 2003

A simple optical scheme using a conical lens to perform azimuthal integration of light collected in a light scattering experiment is described. A substantial increase in the signal-to-noise ratio of the scattered light intensity is achieved. The scheme is particularly useful in nonequilibrium experiments such as spinodal decomposition, where the angular distribution of scattered light varies slowly in time and is peaked in the forward direction.
Optical interferometric liquid gate plate positioner
Authors: Gaylord T. K. , Guest C. C.
Published: March 2003

A mechanical, three degree-of-freedom, index-matching, liquid-gate, photographic-glass-plate positioner is described that maintains a fixed optical path length (constant phase) over a 50-mm clear aperture. Such a device is needed in critical interferometric applications such as laser holographic nondestructive testing and laser optical data processing.
Theory and design of a tunable pulsed dye laser cryogenic photocalorimeter
Authors: Cooper Thomas M. , Schmidt Hartland H. , Murray Lionel P. , Birge Robert R.
Published: March 2003

A tunable-pulsed dye laser cryogenic (77 K) photocalorimeter is described. The photocalorimeter consists of a four-element Calvet conduction calorimeter connected via fiber-optics light guides to a flashlamp pumped tunable dye laser. The present arrangement makes possible the study of many photochemical reactions where the extent of reaction cannot be measured by conventional techniques. A theoretical model of heat flow in the calorimeter produced by laser excitation is described. We demonstrate that the output signal generated by absorption of a laser pulse can be fit to a set of exponentials and that the peak height is linearly proportional to the integrated signal for short pulse-width lasers. A method is developed for the use of this technique to measure enthalpy changes associated with photochemical reactions. Optimum experimental conditions for the measurement of the photochemical response function are described, along with a discussion of sources of random and systematic error. Calibration experiments using steady-state heating and laser pulses are described, followed by sample data obtained from calorimetric measurements of the primary step in the photocycle of light adapted bacteriorhodopsin.
UHV cell for Raman studies of gases adsorbed on metals
Authors: Arunkumar K. A. , Marzouk H. A. , Bradley E. B.
Published: March 2003

We describe a UHV Raman cell for the study by laser Raman spectroscopy of gases adsorbed at low coverages on smooth metal surfaces. Provision is made for three samples, and the sample temperature is controlled from 100 to 800 K. The cell also contains a residual gas analyzer, an argon-ion sputter gun for cleaning the samples, and ports for observation of right-angle and oblique Raman scattering. Displayed are Raman spectra of CO on Ni(111) adsorbed from the chamber residual gases and Raman spectra of CH3COCH3 adsorbed on the same single crystal at 10 L exposure.
Simultaneous determination of vapor–liquid equilibria and saturated densities up to 45 MPa and 433 K
Authors: Fontalba F. , Richon D. , Renon H.
Published: March 2003

A new apparatus to simultaneously measure vapor–liquid equilibria and volumetric properties of coexisting phases is presented. It was especially designed to study hydrocarbon–carbon dioxide mixtures up to 45 MPa and 433 K. Tests have been performed on isopentane–carbon dioxide mixtures. Comparison of the new results to those from literature shows that the just developed apparatus gives reliable data. Reproducibility tests have displayed very small data dispersion.
Integrated dc SQUID magnetometer with a high slew rate
Authors: Wellstood Frederick , Heiden C. , Clarke John
Published: March 2003

We have fabricated a magnetometer in which the thin-film superconducting pick-up loop and dc SQUID are integrated on a single silicon chip. The magnetometer, which is intended primarily for geophysical applications, has a magnetic field sensitivity of typically 5×10−15 T Hz−1/2 at frequencies above about 10 Hz, and 2×10−14/( f /1 Hz)1/2 T Hz−1/2 at lower frequencies. The dynamic range is ±2×107 Hz1/2 and the maximum slew rate is about 4×10−3 T s−1 at 6 kHz. This high slew rate enables the magnetometer to be operated in a flux-locked loop for long periods of time without losing lock.
Vacuum insulated siphon for a continuously filled cold plate
Authors: Parpia J. M. , Rhodes T. L.
Published: March 2003

The construction of a vacuum insulated siphon for filling the cold plate of a dilution refrigeration cryostat is described. The siphon allows the pickup of liquid helium from the main liquid-helium bath at a level 30 cm below the main flange of the dilution refrigeration insert.
Modified automatic echo selection logic for ultrasonic attenuation measurement system
Authors: Pathak L. , Seshadri V. R.
Published: March 2003

Modifications required in the circuit described by Pathak et al. [Rev. Sci. Instrum. 54, 482 (1983)] to make it select any two echoes rather than two successive echoes for ultrasonic attenuation measurement are described in this note.
High-temperature specimen holder for use with the PHI model 2100 specimen introduction/reaction chamber
Authors: White C. L. , Dimas R. , Losch W.
Published: March 2003

A high-temperature specimen holder for use with a commercially available rapid specimen introduction device on an Auger electron spectroscopy system is described. Necessary (nondestructive) modifications to the specimen carousel are also included. Use of the specimen holder allows rapid transfer of specimens for in situ heating to approximately 1000° C during Auger analysis, while retaining conventional capabilities of the commercial system for ambient temperature analysis.
Direct comparison of copper, silver, and palladium heat exchangers for cooling 3He
Authors: Berg R. F. , Ihas G. G.
Published: March 2003

The heat transport between liquid 3He and five different small metal particle ‘‘sintered’’ sponges are directly compared in the temperature range from 7 to 70 mK through measurements on five cells which are identical in every way except for the nature of the sponge. Fine (0.1–1 μm) powders of copper, silver, and palladium are formed into sponges that are bonded to the walls of a copper container using various packing and heat-treatment techniques. Each container, fitted with a resistance thermometer and heater and filled with liquid 3He at a pressure varying from 3 to 15 bars, is then used as a heat exchanger between a dilution refrigerator and the 3He. The palladium sponge, per unit surface area, has the lowest thermal resistance (R) to liquid 3He, but is the most difficult heat exchanger to make. The silver sponge, per unit volume, has the lowest R and is by far the simplest heat exchanger to build, requiring only cold packing with no heat treatment, yet performs as well or better than those discussed previously in the literature.
Passive level indicator and valve for transferring LN2
Authors: Goodrich R. G.
Published: March 2003

A gas thermometer operated diaphragm valve for controling LN2 transfers is described. The value uses the pressure variation of air or N2 between 77 K and ambient temperature to open and close the vent line of a self-pressuring storage Dewar.
Selection of dwell time when using a lock-in amplifier in a sequence of measurements
Authors: DiJulio S. S. , Knuth E. L.
Published: March 2003

A procedure for selecting, for a previously chosen value of the time constant of the lock-in amplifier, the value of the dwell time at a new measurement location so as to reduce the total time required to complete the sequence of measurements is presented. Results of an application to profile measurements in flames are included.
Hybrid absorber-foil technique to measure the electron temperature of 0.1–10-keV plasmas
Authors: Cardozo N. J. Lopes
Published: March 2003

The soft x-ray absorber-foil technique for electron-temperature measurements is considered. The idea is introduced to compare the signals of a surface-barrier diode and an x-ray-sensitive photodiode rather than those of two identical detectors. The contrasting characteristics of the two detector types gives rise to an improvement of the temperature resolution by a factor 2 (at 0.4 keV) to 10 (at 10 keV).
General purpose photon-counting minicomputer interface
Authors: Smith D. D. , Thompson N. L. , Axelrod D.
Published: March 2003

A general purpose photon-counting interface for use with a minicomputer (NOVA 3/12) is described. This device is capable of signal averaging and autocorrelating digitized data with sample time intervals of fixed or variable duration. Means are provided for experimental control and graphical display of results. Suggestions are given for minor modifications resulting in an even greater performance range.
High-performance coaxial EPR cavity for investigations at elevated temperatures and pressures
Authors: Goldberg Ira B. , McKinney Ted M.
Published: March 2003

A microwave cavity suitable for heating a sample to temperatures above 800 °C within 15 s at gas pressures above 17.5 MPa is reported. The cavity is coaxial and operates in the TE011 mode at frequencies between 9 and 10 GHz. The heating element is constructed of nickel–chromium (i.e., Chromel) wire. It consists of two concentric helices wound in opposite senses (directions) and connected in series so as to minimize the magnetic field generated by the heater current. The heater is potted in magnesium oxide–phosphate ceramic and placed inside of a cylinder made from 50-μm copper foil which provides uniform temperature distribution and shields the heater from the microwave field. This assembly then serves as the heating element and the coaxial conductor of the cavity. The diameter of the coaxial heater assembly is approximately 7 mm. The sample is confined by a cylindrical quartz cuvette which surrounds the coaxial conductor. Sample thicknesses of 0.2 to 1.0 mm can be used. Heating from room temperature to 800 °C requires between 15 and 20 s. Operating pressures up to 17 MPa have been used, although the structural design limit of the brass or beryllium copper walls is greater than 22 MPa. Modulation coils are placed in recessed areas of the cavity walls and covered with a thin layer of copper. Cooling water flows through channels cut into the walls to maintain constant microwave parameters. Q factors of 8000 –12 000 can be obtained depending on the sample.
Vacuum spark as a reproducible x-ray source
Authors: Wong C. S. , Lee S.
Published: March 2003

The operational characteristics of a laser-initiated vacuum spark is studied with reference to its x-ray emission. The present system employs a fast capacitor bank (current rise time=1 μs) with input energy of 4.4 kJ. The studies here show that for such a system, the system parameters can be adjusted for satisfactory optimum operation with respect to x-ray emission reproducibility. It is observed that intense x-ray point sources are obtained consistently by choosing the right V–d combination, where V is the discharge voltage in kilovolts and d is the electrode separation in millimeters. For the present system, this combination is found to be 20–5 and a x-ray reproducibility of better than 80% has been achieved in this system.
Instrumentation at pulsed neutron sources
Authors: Carpenter J. M. , Lander G. H. , Windsor C. G.
Published: March 2003

Scientific investigations involving the use of neutron beams have been centered at reactor sources for the last 35 years. Recently, there has been considerable interest in using the neutrons produced by accelerator driven (pulsed) sources. Such installations are in operation in England, Japan, and the United States. In this article a brief survey is given of how the neutron beams are produced and how they can be optimized for neutron scattering experiments. A detailed description is then given of the various types of instruments that have been, or are planned, at pulsed sources. Numerous examples of the scientific results that are emerging are given. An attempt is made throughout the article to compare the scientific opportunities at pulsed sources with the proven performance of reactor installations, and some familiarity with the latter and the general field of neutron scattering is assumed. New areas are being opened up by pulsed sources, particularly with the intense epithermal neutron beams, which promise to be several orders of magnitude more intense than can be obtained from a thermal reactor.
Multiformat electronic cell sorting system: II. Design and construction
Authors: Tyrer Harry W.
Published: March 2003

The design, construction, and evaluation of a computer-controlled electronic cell sorting device is described; the computer performs all cell data analysis and sorting functions. The primary advantage is that the functions are programmable and, hence, any data analysis or sorting format can be implemented (within the constraints of the physical system). The software that has been developed is highly modular and can be manipulated to perform different functions. In our present configuration, the device analyzes data from each cell on a cell-by-cell basis, performs the sorting function, stores the cell data for off-line analysis, and provides a real-time display (histogram) of cell data.
Simple plethysmograph for measuring respiration rates in rats with lung damage
Authors: Feaster Gene R. , Kimler Bruce F. , Henderson Sheri D. , Mansfield Carl M.
Published: March 2003

In order to measure respiration rates in rats irradiated to the whole thorax, a plethysmograph involving a microphone with extended low-frequency response and an airtight, whole-body chamber has been constructed. The microphone response to the respiration pressure waves created by the rats placed in the chamber is markedly greater in amplitude than the response to laboratory sounds and animal noises; thereby filtering complexities are avoided. The output from the microphone went to a frequency counter for measurement of the number of pressure waves per unit time. Control, unirradiated rats, between the ages of 3 and 18 months, demonstrated a respiration rate in the range of 130–160 breaths per minute. Rats that received thoracic radiation doses greater than 12 Gy displayed increased respiration rates and occasional abnormal respiration patterns. These results demonstrate that this whole-body plethysmograph incorporating a sensitive microphone and simple electronics can be used for the measurement of respiration functions in rats with lung damage.
Directly heated lanthanum hexaboride filaments
Authors: Leung K. N. , Pincosy P. A. , Ehlers K. W.
Published: March 2003

Some physical properties of lanthanum hexaboride filaments, when operated as cathodes in a gas discharge, are presented. These directly heated hairpin-shaped filaments have been tested in different types of ion sources and are shown to be capable of long-pulse or cw discharge operations. The design of a shaped lanthanum hexaboride filament for the purpose of further extension of lifetime is also described.
Characteristics of a hollow cathode ion source with magnetic multipole semicylindrical arc chamber
Authors: Tanaka Shigeru , Akiba Masato , Mizuhashi Kiyoshi , Ohara Yoshihiro , Okumura Yoshikazu
Published: March 2003

An ion source with a hollow cathode set at a position where no backstreaming electrons can arrive has been proposed and fabricated. The arc chamber is a magnetically line-cusped semicylinder (i.e., semicircular cross section) whose axis is perpendicular to the ion beam axis and the hollow cathode is positioned on the extended line of the cylinder axis. Preliminary experiments were made on this source. The highest arc and gas efficiencies obtained were 0.64 A/kW and about 70%, respectively, and a proton ratio of 85% was attained. In addition, the fraction of metal impurities in the beam was measured to be negligibly small. These source performances are comparable to those of the conventional tungsten-filament magnetic multipole line-cusp sources for neutral beam injectors.
Temperature control of a cryogenic torsion pendulum
Authors: Phillips Peter R.
Published: March 2003

This paper describes a method of maintaining a constant level of liquid helium in a container over a 5-day period by continuously transferring liquid from a supply tank. The technique uses no valves and minimizes vibration and disturbances of the temperature distribution.
Programmable data-acquisition and stepping motor control system
Authors: Whiting Douglas , Williams Arthur
Published: March 2003

The implementation of a compact, inexpensive, programmable stepping motor controller and data-acquisition system based on the Zilog Z-80 microprocessor is described, including its basic hardware and software configurations. While originally designed to facilitate data acquisition from scanning x-ray diffractometers, the units have proven to be quite versatile and have been applied to a variety of instrumentation requiring automatic data acquisition and mechanical control.
Ozone dosimetry for calibration of power deposition in nuclear pumped lasers
Authors: Elsayed-Ali H. E. , Miley G. H.
Published: March 2003

Ozone yield from the irradiation of O2–SF6 mixtures has been utilized for calibration of power deposition in boron-10 coated tubes used in nuclear pumped laser experiments. Laser experiments using such tubes have previously relied solely on theoretical calculations. Results obtained from an O2–SF6 dosimeter show reasonable agreement with recent theoretical calculations and, because of its simplicity and accuracy, the use of this dosimeter is proposed for calibration of nuclear pumped laser sources.
High-resolution light spot localization with photodiode arrays
Authors: Bertani D. , Cetica M. , Ciliberto S. , Francini F.
Published: March 2003

We describe two analog electronic techniques to determine the position of a light spot on a linear photodiode array by detecting its intensity peak or its centroid. The position was detected with an accuracy of 1 and 3.5 μm by the two methods, respectively, using a 16-μm center-to-center array. As an example, the displacement of a mirror was measured with a sensitivity of 0.05 μm.
Photoacoustic measurement of the thermal properties of liquids
Authors: Quimby R. S. , Chang Y. S.
Published: March 2003

A new technique is demonstrated for measuring the thermal diffusivity of liquids. In this method laser light is absorbed at a given distance below the surface of the liquid, and the photoacoustic signal is measured as a function of this distance. Good agreement of the measured value for ethylene glycol [(9.5±1.0)×10−4 cm2/s] with previously determined values is obtained provided that thermal expansion in the liquid is taken into account. The data agree well with a theory based on McDonald and Wetsel’s composite piston model of the photoacoustic effect, allowing for the first time the direct separation of the mechanical piston and thermal piston contributions to the photoacoustic signal. This technique also has the potential for measuring the thermal expansion coefficients of liquids.
New lens system for surface vibrational spectroscopy at high impact energies
Authors: Strong R. L. , Erskine J. L.
Published: March 2003

The design, characterization, and performance of a new lens system which permits high-resolution electron energy-loss spectroscopy (EELS) studies at high energies is described. The lens system can be adapted to most existing EELS instruments and extends the impact energy range to 300 eV. Electron ray-tracing techniques are used to characterize operating modes of one of the more common EELS optics designs as well as the new lens configuration. The results presented in this paper demonstrate some limitations of matrix optics approaches and the applicability of electron ray-tracing techniques for characterizing the transmission properties, angular profiles, image sizes, and operating modes of EELS spectrometers.
Vibration isolation for broadband gravitational wave antennas
Authors: Saulson Peter R.
Published: March 2003

We discuss an active vibration isolation system which is a prototype of an isolation system for an interferometric gravitational wave antenna. Particular attention is paid to factors which limit the isolation which can be achieved. We were able to reduce the effective resonant frequency of the test mass to 0.04 Hz. Between 3 and 8 Hz, this was sufficient to bring the motion of the test mass within a factor of 2 of its Brownian motion amplitude.
Fourier-analyzing coil arrays for pulsed relativistic electron beam experiments
Authors: Ekdahl C. A.
Published: March 2003

Arrays of flux detection coils can be used in pulsed relativistic electron beam experiments to Fourier analyze in azimuth the magnetic fields resulting from beam or net currents. In propagation experiments using the beam generated with the IBEX accelerator the displacement perturbations of the initially injected beam were determined using arrays sensitive to the first azimuthal harmonic of the azimuthal magnetic field. These arrays were found to be capable of easily resolving 120-MHz oscillations of the beam centroid with amplitude less than 0.1 mm.
Compact Thomson spectrometer
Authors: Rhee M. J.
Published: March 2003

Particle dynamics and collimation in the Thomson spectrometer system are discussed. A compact spectrometer which consists of a unique pinhole arrangment, a pair of permanent magnets, and CR-39 detector is described with a few practical calibration techniques. Applications including analysis of charge-to-mass ratio and construction of charge state resolved energy spectra are discussed with experimental examples.
Methods for a precision measurement of ionic masses and appearance energies using the pulsed-laser time-of-flight atom probe
Authors: Tsong T. T. , Liou Y. , McLane S. B.
Published: March 2003

An attempt has been made to use the pulsed-laser time-of-flight atom probe for a precision measurement of ionic masses and the critical energy deficits, or the appearance energies, of field emitted ions. For this purpose methods for determining accurately the flight-path constant and the time-delay constant of the atom probe have been devised. Using 300-ps laser pulses and a digital electronic timer of 1-ns resolution and a flight path of slightly over 4 m, ionic masses of pulsed-laser field desorbed gaseous ions can be measured with an accuracy of better than 0.0005 to 0.003 amu for ions of low to intermediate masses. For multiply charged field evaporated heavy metal ions, the accuracy is not as good due mainly to the very limited number of ions which can be collected at a given low emitter voltage. The accuracy of measuring the critical energy deficit depends on the emitter voltage, and the mass and the charge of the ions. It ranges from ∼0.3 eV for singly charged, heavy gas ions at a low emitter voltage to a few electron volts for multiply charged metal ions at a high emitter voltage. The precision of this instrument in these measurements can be further improved by over a factor of 10 simply by using laser pulses of shorter duration and an electronic timer of better resolution. These units are now commercially available. Using this pulsed-laser field ion emission technique, those solids which can be formed into a field ion emitter and those gases which can be field adsorbed on an emitter surface can be studied. The technique also has a very high sensitivity.
High-pressure NMR probe head for low temperatures
Authors: Huber H. , Mali M. , Roos J. , Brinkmann D.
Published: March 2003

A nuclear-magnetic-resonance probe head for investigations under hydrostatic pressures up to 7 kbar is described. Helium gas is used as the pressure transmitting medium allowing low-temperature measurements. Compact design allows for use in small bore superconducting magnets. As a first result the discovery of a new high-pressure phase in the superionic conductor RbAg5I5 is presented.
Microcomputer-controlled furnace for obtaining dynamic thermogravimetric measurements
Authors: Gleixner R. A. , Green M. J.
Published: March 2003

A cyclic thermogravimetric apparatus has been developed for reliable measurement of the equilibrium decomposition pressures of metal carbonates. The measurement technique involves suspending a sample from a microbalance inside a reaction vessel which in turn is supported vertically inside a furnace. An atmosphere of argon and carbon dioxide flows through the reaction vessel and the furnace temperature is varied periodically about a preset temperature, while the mass and temperature of the sample are monitored. The equilibrium decomposition temperature for a given partial pressure of CO2 is the mean temperature of that temperature cycle which produces a symmetrical mass variation with no net mass change. The method for controlling the furnace using a Rockwell AIM-65 microcomputer is described in detail. The equilibrium pressure of calcium carbonate, which has been studied extensively by other workers, was measured to test the performance of the system.
Improved method for the discrete fast Fourier transform
Authors: Sorella S. , Ghosh S. K.
Published: March 2003

A new algorithm is proposed here for the discrete fast Fourier transform with greatly reduced aliasing which is known to be inherent in the conventional algorithm of Cooley and Tukey, unless the function is band limited and the sampling frequency satisfies the Nyquist condition. Like the algorithm recently proposed by Schütte and extended by Mäkinen in this journal, this is also based on the polynomial expansion of the function to be transformed but more general in formulation and less restrictive than theirs. Its power is demonstrated with a few non-band-limited functions that can be exactly transformed with chosen limits as usually met in different experimental situations. In all cases tried, this yields, in general, much improved accuracy in comparison to others at little or no corresponding increase of computation time.