bluuebunny/crossref_metadata_2025 huggingface dataset:
Random array grid collimators
Authors: Fenimore E. E. , Blake R. L.
Published: March 2003

X-ray collimators using grid patterns which are random offer several significant advantages over collimators using periodic grids. In particular, random array grid collimators (RAGC’s) eliminate the requirement that there be very closely spaced grids if a wide field of obscuration outside the central peak is desired. The RAGC should be less susceptible to systematic off-axis leaks, and the RAGC has a better high energy response than a periodic grid collimator. The random array technique can also be used to produce converging or diverging collimators. A general theory is presented which predicts the angular response of a RAGC. It is shown that pure random arrays have two problems: there are strong wings in the response function and the patterns are not self-supporting. Restrictions on the randomness of the pattern are suggested which eliminate these problems but at the price of putting an upper limit on the available throughput. However, even in the worst case, the upper limit for a two-dimensional collimator is as high as 23%. In other cases, throughputs the order of 40% are possible with two-dimensional collimators and of 50% with one-dimensional collimators. These techniques can provide 10 arc second two-dimensional collimators with a large collecting area. Suggestions are presented for easing the fabrication effort of the grids.
Comparison of multiple-scan direct and lock-in detection in magnetic resonance: Application to nuclear acoustic resonance
Authors: Ashton G. R. , Hsu D. K. , Leisure R. G.
Published: March 2003

Theoretical expressions are derived for the signal-to-noise ratios in magnetic resonance experiments for the lock-in and multiple-scan direct detection schemes. Effects of noise character, post-spectrometer filters, and modulation frequency are included in the analysis. The theoretical results are found to be in good agreement with experiment for the specific case of nuclear acoustic resonance in a metal single crystal.
An apparatus for the measurement of the rates of emanation of radon from rock specimens and powders
Authors: McCorkell R. H. , Brameld M. P.
Published: March 2003

Specimens are placed in sealed chambers to which scintillation cells are attached and radon concentrations, R, are measured in the air of the chambers at intervals thereafter by inserting the cells into scintillation counters. The Rn emanation rate is calculated from the rate at which R increases, or from the maximum R reached. Uncertainties are estimated to be 10%–25%, detection limits 10−19 Ci cm−2 s−1 or 5×10−19 Ci g−1 s−1. Effects of disequlibrium in the Rn decay chain, or the diffusion rate of Rn, and of Rn leakage are considered. Powdering a rock usually has little effect on its emanation rate per gram.
Laser-heated high-temperature EPR spectroscopy
Authors: Yager T. A. , Kingery W. D.
Published: March 2003

A CO2 laser-heated sample holder for an EPR spectrometer capable of temperatures above 1200°C is described. Since only the sample is heated, this system permits rapid temperature changes and rotation of the magnet around the sample. The spectra of MgO containing Fe3+ and Cr3+ at room temperature and 1200°C are presented.
Surface ionization source for heavy ions
Authors: Rasser B. , Pearson D. I. C. , Remy M.
Published: March 2003

An ion source using the surface ionization process is described. Elements whose ionization potentials are below or around 6 eV may be ionized in the source. The element vapour to be ionized is passed through one or more rhenium grids on which surface ionization occurs. The source is tested for different elements—lithium, indium, rare earths, uranium—the latter corresponding to the upper limit of the ionization potential range. The properties and performance of the source are studied. Currents from many tens of μA to many mA have been extracted, depending on the source element.
Low energy ion beam transport by permanent magnets
Authors: Ehlers K. W. , Leung K. N.
Published: March 2003

The guiding of a 300 eV divergent hydrogen ion beam by a surface magnetic field generated by samarium cobalt magnets has been investigated. It was found that magnets arranged in a multi-ring-cusp configuration produced the best beam transport efficiency.
Small solid-particle ejector
Authors: Hwang C. C.
Published: March 2003

This paper presents the description of a pneumatically-operated particle ejector and its performance under atmospheric ambient conditions. The ejected 100-μ particles are observed to remain an aggregate for approximately 10 ms prior to dispersion. The particles move at the initial velocity for a short initial period. This observation can be verified by a mathematical analysis. The instant of time at which the particles leave the ejector can be determined within approximately 1 ms.
Techniques for very low energy electron diffraction
Authors: Price G. L.
Published: March 2003

LEED intensity curves between 0–50 eV contain sharp peaks due to electronic surface resonances. Successful comparison with theory requires an accurate knowledge of the incidence angles and energy resolution ≲0.15 eV. It is shown that these requirements can be achieved with a conventional LEED system. The resolution was obtained by doubly modulating the four grid retarding optics and the electron gun. The incidence angles were found with a simple photographic technique.
Constant current test method for fuseable links
Authors: Rosenthal L. A. , Beck P. M.
Published: March 2003

Discharging a capacitor through a constant current ballast into a fuse device provides a repeatable method for fuse characterization. The energy required to burn out the device is easily calculated from the area under the voltage trace. A simple, novel circuit provides this constant current pulse which is self-terminating.
Contactless conductivity measurements with a rotating sample magnetometer
Authors: Flanders P. J. , Shtrikman S.
Published: March 2003

A contactless method for measuring the electrical conductivity σ is described. In this method the conductivity is measured through the voltage induced in coils by the sample which rotates in a steady magnetic field. The dependence of the signal on sample geometry is studied and compared with experiment. The method is argued to be advantageous compared to the standard induction type techniques for contactless conductivity measurements.
Spectrometer for soft x-ray emission studies of liquid metals and metallic vapors
Authors: Hague C. F. , Laporte D.
Published: March 2003

An x-ray spectrometer based on the Johann bent-crystal principle is described. An entrance slit system has been adopted which provides excellent protection of the diffracting crystal from metallic vapors. Such an arrangement also provides improved resolution and dispenses with the need for a thin film window between the x-ray source and spectrometer tank. Resolution comparable to a two plane-crystal instrument has been attained and systematic studies of the soft x-ray emissions from liquid metals and alloys and metallic vapors undertaken.
Measurements of picosecond light pulses with a two-photon photoconductivity detector
Authors: Mak Paul S. , Davis Christopher C. , Forster Barry J. , Lee Chi H.
Published: March 2003

An optical detector that can measure the pulse width of a picosecond light pulse from a mode-locked Nd-glass laser has been developed. The detector was constructed with seven spatially separated CdS0.5Se0.5 crystals which exhibited two-photon conductivity when illuminated with 1.06 μm optical radiation. A seven-channel peak detector and display system were used in conjunction with the two-photon detector to record picosecond pulses on a single-shot basis. For the laser used the measured correlation curve yielded a pulse width of 10 ps with a contrast ratio of 2.8:1.
Charge exchange measurements in helium using a double tandem accelerator-decelerator source of low energy highly stripped oxygen ions
Authors: Bayfield J. E. , Gardner L. D. , Gulkok Y. Z. , Saylor T. K. , Sharma S. D.
Published: March 2003

Cross sections for Oq+-He single electron capture have been measured for 5⩽q⩽8 within the energy range 15 to 100 keV per amu. High energy positive ions were injected into an EN tandem Van de Graaff operated at a negative voltage, producing even higher energy for foil stripping to high charge states, followed by ion deceleration to reduce the ion energy by as much as a factor of 50.
Simple technique for the flat smooth mounting of thin foils
Authors: Holt W. H. , Blackmon C. M.
Published: March 2003

A simple technique for the wrinkle-free mounting of thin foils is described and example results presented. The uniformity of the stretching is also discussed.
Fusion target evaluation by buoyancy analysis
Authors: Crawley Richard L. , Steinman David A.
Published: March 2003

Projected inertial confinement fusion reactors will require tens of targets per second. This paper describes a device which can measure the diameter and wall thickness of these targets in a precise, simple and rapid fashion.
Microcomputer controlled integrator for Calvet-type twin calorimeters
Authors: Dickens K. J. , Kleppa O. J. , Yokokawa H.
Published: March 2003

An improved integration method has been developed for use with Calvet-type differential calorimeters. The new integrator is based on a voltage-to-frequency converter combined with a digital system interfaced to a microcomputer. The microcomputer provides programmed control of the integrator and, with little or no operator intervention, calculates the total heat effect making corrections for background and baseline drift. With this method a calorimetric precision of the order of ±0.1% has been achieved in experiments carried out at 651°C. This is about one order of magnitude of improvement over graphical methods and about a factor of 3 better than the analog integration techniques which we have used previously.
Performance characteristics of a small dilution refrigerator using a centering device
Authors: Fagaly R. L. , Bohn R. G.
Published: March 2003

A centering device has been used on a small dilution refrigerator to reduce vibrational heating by an order of magnitude. The refrigeration capability with the device is shown to approach the expected value for a given temperature.
High pressure and low temperature cell for x-ray diffuse scattering studies
Authors: Moudden A. H. , Gatebois L. , Denoyer F. , Lambert M.
Published: March 2003

We present the details of design and construction of a high pressure cell for x-ray diffuse scattering experiments up to 5 kbar and down to 77 °K. Exciting preliminary results on thiourea are presented as a test of its performance.
New position-sensitive hard x-ray spectrometer
Authors: Yin Lo I , Trombka Jacob I. , Seltzer Stephen M.
Published: March 2003

A new prototype Lixiscope (Low intensity x-ray imaging scope) is described. In addition to good spatial and temporal resolution in the 20 keV to 200 keV region, it is capable of single-photon counting, imaging, as well as good energy resolution. The new device is well-suited for future low-flux applications in astronomy, medicine, and industry.
Some properties of Nuclepore filters
Authors: Chen Tar-pin , DiPirro Michael J. , Bhattacharyya Bidyut , Gasparini Francis M.
Published: March 2003

We present the results of various measurements we have made to characterize Nuclepore filters. These include nitrogen and helium adsorption isotherms, heat capacity and SEM studies of pore size distribution and pore density.
Pressure distribution in gaskets of high pressure devices
Authors: Kamarád J.
Published: March 2003

The values of the coefficient of internal friction μ and the yield stress σ0 of materials which are used in gaskets of high pressure devices, are given. The mathematical expressions, based on the analysis of the real pressure distribution in the gasket of Bridgman anvils enables one to calculate the gasket geometry and the forces acting on the pistons of the high pressure devices.
Electron energy loss microanalysis system with high collection efficiency
Authors: Johnson Dale E.
Published: March 2003

An electron energy loss spectrometry system is described in which the lenses of an electron microscope are used with a straight edge magnetic sector energy analyzer to significantly improve the performance over that of the magnetic sector alone. An order of magnitude improvement in performance is demonstrated experimentally with two orders of magnitude improvement in performance predicted to be possible. The design, construction, and interfacing of the magnetic sector analyzer to the electron microscope are described.
New method of studying the low surface pressures of monolayer at air/water interface
Authors: Munger Gaétan , Leblanc Roger M.
Published: March 2003

The determination of the properties of gaseous films at air/water interface requires very special techniques as far as the measurements of the surface pressure are concerned. We have designed an apparatus based upon the characteristics of Langmuir trough. The measuring system consists of a lamp, three optics fibers and two high-gain phototransistors. The surface pressure that have been measured (accurately with great ease) range from 0.0010–0.1500±0.00005 mN m−1 or ±0.1%. One successful application of the apparatus had been the determination of the molecular weight of proteins such as the bovine serum albumin, egg albumin, bovine rhodopsin, and cytochrome c.
Intense 3 ns neutron source
Authors: Chang J. , Leeper R. J.
Published: March 2003

A 3 ns pulsed beam-target neutron source has been developed to simulate a thermonuclear neutron burst from an inertial confinement fusion target. The yield from the neutron source is equivalent to an isotropic source producing ∼3×106 D–D and ∼2×107 D–T neutrons into 4 π steradians per pulse. The unique features of this source include simplicity of design, ease of operation, multiple shot capability, and above all compactness which permits easy portability and in situ applications. The use of these sources for characterizing the impulse response of heavily shielded scintillation neutron time-of-flight detectors operating in the mean-level detection mode is discussed.
Multicusp negative ion source
Authors: Ehlers K. W. , Leung K. N.
Published: March 2003

The characteristics of a steady state, surface conversion, multiline-cusp negative ion source have been investigated for the production of high-energy neutral beams. With the presence of cesium, this source has been operated at a neutral pressure of 1×10−3 Torr to generate a H− ion current greater than 400 mA. The percentage of impurities in the self-extracted negative ion beam has been analyzed by a mass spectrometer. A technique for reducing the background electron density at the source exit is also presented.
Flash x-ray tube for diffraction studies on a two-stage light-gas gun
Authors: Johnson Quintin , Mitchell A. C. , Smith Ian D.
Published: March 2003

A flash x-ray tube has been fabricated and has been driven by a Blumlein pulse generator to peak voltages of 60 to 80 kV and peak anode currents of 8 to 10 kA. The pulse width, dependent upon the anode-cathode spacing, can be made ∼80-ns wide, and a small spot or line focus is possible. These features make the device useful for flash x-ray diffraction studies. Current in the diode region exceeds the calculated space-charge limited values, probably because of neutralization of charge by plasma ejected from the cathode during the initial phase of the discharge.
Digital data acquisition and analysis of striated muscle diffraction patterns with a direct memory access microprocessor system
Authors: Roos Kenneth P. , Baskin Ronald J. , Lieber Richard L. , Cline James W. , Paolini Paul J.
Published: March 2003

A microprocessor based data acquisition computing system has been developed to examine dynamic changes in light diffraction patterns from single skeletal muscle fibers. A significant improvement in digital data acquisition rate compared to previous designs has been achieved by utilizing a fast dedicated analog to digital converter and direct memory access data storage. Diffraction patterns from muscle fibers are imaged onto a 256 element charge-coupled device. The analog output of a full 256 point frame of data may be digitized and stored in 2.2 ms (128 point half frame in 1.1 ms) with a spatial resolution of up to 5.0 nm/sarcomere. This computing system can transfer up to 28 full frames of data as one continuous block directly between the CCD and memory leaving the CPU free for experimental control and closed-loop processing. The computing system calibrates and analyzes diffraction data under sofware control for sarcomere length, dispersion, and peak intensity. The operation of this data acquisition computing system is superior to previous digital designs with its increased data acquisition rate and to analog designs with its data manipulation, analysis, experimental control, and processing capabilities.
Compact 0.1 TW CO2 laser system
Authors: Tan K. O. , James D. J. , Nilson J. A. , Burnett N. H. , Alcock A. J.
Published: March 2003

A 3 atm, 9×9×100 cm3 uv preionized self-sustained discharge module has been used as the basis for a compact nanosecond pulse CO2 laser system. Up to 60 J has been extracted from the device in an ∼600 ps pulse. The high degree of gain uniformity and fast gain risetime demonstrated by the present device point to some potential advantages in the incorporation of large aperture uv preionized self-sustained CO2 discharges into high irradiance target interaction laser systems.
Computer controlled absorption spectrometer for gas phase samples
Authors: Arndt F. W. , Huber J.Robert
Published: March 2003

A computer controlled absorption spectrometer featuring a rotating tube which contains the sample and reference cells is described. The high sensitivity of this instrument makes it suitable for dilute gasphase absorption measurements.
Apparatus for the continuous measurement of changes in ultrasonic velocity
Authors: Simpson A. M. , Roger W. A. , Jericho M. H.
Published: March 2003

In measuring the velocity of sound in materials with plate-like of fibrous geometries, in thin foils, or in materials with high attenuation, the only clear signal is often after a single transit through the sample. A system is described which allows continuous measurements of changes of acoustic propagation time through such samples with a resolution of 0.2 ns. In some circumstances, the resolution can be improved to 15 ps.
Computer controlled apparatus for measuring contact electrification of polymers
Authors: Hennecke Manfred
Published: March 2003

An on-line computer controlled apparatus for measuring the contact electrification of polymers due to subsequent intermittent contacts is developed. The utilization of measuring probes and metal contact pins instead of the plotter pens of a programmable four-colour plotter renders it possible to simultaneously perform contacting experiments on more than one polymer specimen. The parameters of the contact electrification experiment are input separately for each specimen by the computer’s keyboard and can be changed during the experimental run.
Proportional response photon counter
Authors: Mitra S. , Sinha A. K. , Roy S. C.
Published: March 2003

A scintillation counter whose detection efficiency is linearly proportional to the energy of the interacting photon has been developed by combining a suitable filter with a conventional NaI(Tl) crystal. A general theory has been developed from which the material and optimum filter thickness for a particular crystal valid for a certain photon energy range can be obtained. Experimental verification of the theoretical prediction has been made for five different photon energies.
Intensity dependent time resolution and dynamic range of photochron picosecond streak cameras II. Linear photoelectric recording
Authors: Bradley D. J. , Bryant S. F. , Sibbett W.
Published: March 2003

By using an optical multichannel analyser to replace film as the recording medium a completely linear recording streak camera has been constructed with a time resolution of less than 3 ps, and an improved dynamic range of ∼150. It has also been found possible to dispense with an image intensifier and still achieve a dynamic range of ∼25, while retaining a temporal resolution of ∼4 ps.
An apparatus for measuring the thermal conductivity of cast insulation materials
Authors: Wilkins Christine A. , Ash Robert L.
Published: March 2003

A steady-state apparatus has been developed for measuring the thermal conductivity of cast materials. The design has employed a novel thermal symmetry arrangement which can permit total electrical isolation of the test material from its surroundings.
A method for rapid calculations of electron trajectories in multi-element electrostatic cylinder lenses
Authors: Fink J. , Kisker E.
Published: March 2003

A computer program is described, which permits rapid calculations of paraxial electron trajectories in multielement electrostatic cylinder lens systems. The method uses a ’’unified’’ data set for the electric potential of tube lenses with arbitrary voltage ratios, rather than solving Laplace’s equation numerically, thereby shortening the program coding drastically. With this program computer optimizations of long lens systems with respect to beam divergence and beam diameter can also be performed. Examples are given of the design of a multi-element zoom lens and of the calculation of electron trajectories in 250 V acceleration tube with 36 electrodes.
Efficient photon correlator for measuring transient waveforms of very weak fluorescence
Authors: Aoki Tadashi , Sakurai Katsumi
Published: March 2003

An efficient photon correlator has been developed for the measurements of the temporal change of a very weak fluorescence. It was designed by using a TTL integrated circuit which is standard and easily available. Data acquired by an electric circuit were processed and accumulated in the memory of a computer. The system operates in a delayed counting mode and its temporal resolution is 25 ns.
High current-density electrodes suitable for laser doppler electrophoresis
Authors: Uzgiris E. E.
Published: March 2003

The principal electrode problems associated with laser Doppler electrophoresis in high salt conditions and at high current densities (pH drift, colloidal particle ejection, and gas bubbling) have been solved through the use of hybrid electrodes that are platinized Ag/AgCl or by the use of platinized Ag. For salt conditions well below physiological saline an agarose gel overcoating on either of these electrode types has been useful for containing the increased tendency for the ejection of colloidal particles.
Status of carbon resistors for low temperature thermometry
Authors: Rubin L. G.
Published: March 2003

Carbon resistor brand identification and availability problems are discussed.
Measurement of temperature
Authors: Hudson R. P.
Published: March 2003

A general review of thermometry is presented. Topics covered include the concept of temperature and temperature scales; the International Practical Temperature Scale (IPTS); the roles played by the Advisory Committee on Thermometry and its parent International Committe on Weights and Measures; anticipated improvements in an extension of the IPTS; recent advances in primary thermometry; and current developments of practice (including fixed points and interpolation devices, and practical temperature measurements at the secondary level).
A single-coil triple resonance probe for NMR experiments
Authors: Kan S. , Fan M. , Courtieu J.
Published: March 2003

A single-coil triple-tuned NMR probe designed to simultaneously stimulate 1H, 2H and 13C resonances is described. Isolation between the 1H and 13C channels is higher that obtained by the cross-coil system and the 1H decoupling efficiency is significantly increased. The basic idea can be applied to design probes for observing resonances of various other nuclei either in liquid or solid state.
Stability data for germanium resistance thermometers at three temperatures
Authors: Besley L. M.
Published: March 2003

Twenty-four germanium resistance thermometers have been cycled 30 times between 15 K and 300 K with resistance measurements being made at 15 K, 20 K and 27 K on each cycle. Stabilities ranging from 0.1 mK to 10 mK at 20 K were observed with both drifts and jumps in the resistance of some thermometers. In most cases, the proportional changes in the resistance of a particular thermometer were the same at each of the three test temperatures. The effect of possible strain introduced by an epoxy heat sink on the thermometer was found to be insignificant.
Simple pulse generator for a powerful modulator
Authors: Spagnolo Bernardo
Published: March 2003

A pulse generator circuit with pulse length 2.5 μs, peak voltage 1 kV, pulse repetition frequency 25–300 Hz, is described. This pulser may be used as a trigger for the thyratron of a ’’line-type modulator’’.
Measurements of the dielectric constant parallel to the surface of films
Authors: Hirota Sumio
Published: March 2003

A method for the measurement of the dielectric constant parallel to a film surface is formulated. The distribution of electric charge and capacity were calculated as a function of the geometry of electrodes and the dielectric constant of the film. A concept of residual capacity was introduced to obtain the dielectric constant of the film from the observed capacity. Two sort of experiments was used to see if the method is sufficient in measurement of the dielectric constant parallel to film surface, and find the error in both cases was less than 10%. An example of the anisotropy of dielectric constant is shown in the case of a roll oriented nylon 12 film.
A three axis computer controlled low field magnet for optical and magnetic resonance studies
Authors: Erickson L. E.
Published: March 2003

A low field magnet system is described which is suitable for optical and magnetic resonance experiments. It consists of three pairs of orthogonal Helmholtz coils, whose currents are controlled by a microcomputer to provide a magnetic field with a specific field and direction. Earth’s field compensation is programmed. The field magnitude is accurate to 0.1 G and direction to 0.3 deg for fields greater than 5 G. The maximum field is 50 G.
A technique to prepare metallic multi-point field emission sources
Authors: Okuyama F.
Published: March 2003

A technique is proposed which enables one to fabricate multi-point field emission sources of bakeable structure. The technique is based on the cathodic growth of metallic needle crystal from metal crabonyl vapors and has so far been confirmed to provide emission sources of W, Mo, and Mo2C. The field emission sources prepared by this technique are highly resistive to thermal treatment and actually yield field ions possessing satisfactory intensities when used as the ion sources of a field ion mass spectrometer. It is believed that the application of these field emission sources is not restricted to mass spectrometry but can be extended to other ion and electron optical systems. The technique may thus open new areas in field emission technology.
An automated relaxation calorimeter with extended temperature range
Authors: Griffing B. F. , Shivashankar S. A.
Published: March 2003

A computer-automated thermal relaxation calorimeter for use in the temperature range 4–380 K is described. The system can be utilized to make absolute measurements on fairly small (20 mg.) samples which may be of low thermal conductivity. A new hybrid sweep-decay mode of operation for measuring heats of transition is demonstrated.
Properties of pulsed gas lasers pumped by LC inversion circuit made of BaTiO3 and SrTiO3 series ceramic capacitors
Authors: Matsumoto Koji , Sueoka Kazuhiko , Obara Minoru , Fujioka Tomoo , Yamamoto Hirotaka
Published: March 2003

Properties of pulsed gas lasers pumped by LC inversion circuit made of BaTiO3 and SrTiO3 series ceramic capacitors were experimentally investigated. The effects of a decrease in capacitance at higher charging voltages on TEA CO2 and TE N2 laser performances were clarified in terms of discharge voltage, current, power pulse, real stored energy and the energy deposited into the discharge load. Laser performances of the TEA CO2 and TE N2 lasers with the SrTiO3 series capacitor used as an energy storage element of the LC inversion circuit were found to be superior to that of the BaTiO3 series capacitor used.
A simple pulsed valve for use in supersonic nozzle experiments
Authors: Otis Charles E. , Johnson Philip M.
Published: March 2003

Gas pulses having a typical duration of 500–600 μs are produced by a nozzle which uses a fuel injector valve as its primary component.
Liquid nitrogen cooled laser rod holder design
Authors: Gettemy Don , Barnes Norman P. , Griggs Ed
Published: March 2003

A reliable Ho:YLF laser system has been successfully developed. Problems encountered in laser-rod and support-system design were unique and most difficult to solve. These problems include holding a fragile laser rod having nonisotropic thermal expantion with vacuum tight seals which can be thermally cycled. Experimentally proven solutions are described which should help others in developing new solid-state laser systems.
Method of characterization of dielectric or semiconductor materials using an optically pumped far infrared waveguide laser
Authors: Decoster Didier , Depret Jacques
Published: March 2003

A method of measurement of the absorption coefficient of a material is presented using a CO2 optically pumped far infrared waveguide laser which has been specially developed for this purpose. This method permits the elimination of the instability effects due to the basic design concept of the laser. It is used to measure the absorption coefficient of a few mesogeneous substances in order to deduce their order parameters.
Photophoretic spectrometer
Authors: Arnold Stephen , Amani Yaquob , Orenstein Albert
Published: March 2003

An instrument is described which measures the spectral dependence of the radiometric (photophoretic) force on a micron-sized particle in a static configuration. This spectrometer consists of a servo-stabilized Millikan chamber which can be used as a photophoretic balance over the spectral range from 200 nm to 1000 nm. Spectra may be taken in a vacuum as small as 10−4 torr. The action spectrum of the photophoretic force on a crystallite of CdS is used as an example. The pressure dependence of the force at 500 nm is consistant with a radiometric mechanism.
Fast digital apparatus for capacitance transient analysis
Authors: Wagner Elmar E. , Hiller Don , Mars Dan E.
Published: March 2003

The analysis of transient phenomena originating from relaxation processes is a tool for material and device characterization. The time constants of the transients provide information about the energy levels involved, and the transient amplitude is coupled to the density of occupied states. A convenient method for the analysis of exponential transients is the use of correlation-spectroscopic techniques. An example is deep level transient spectroscopy, a capacitance method for the study of deep impurities in semiconductors. The correlation with a weighting function is in this case conventionally made by hardwired instruments. We demonstrate here how shortcomings of this method can be avoided and higher flexibility can be achieved by separating the signal processing from the data acquisition. The hardware is a high-resolution capacitance measurement system with a resolution of 0.002 pF in capacitance and 5 μs in time. As a result of the measurement, which is considerably faster than analog methods, a data array describes the response of the sample with regard to time and temperature. Several signal processing routines are applied to the data to filter out specific information.
Real time digital spectral analysis as a plasma fluctuation diagnostic
Authors: Schoenberg Kurt F.
Published: March 2003

A real time digital spectral analysis system, applicable to broad band plasma fluctuations, is presented. The system digitally records plasma potential fluctuations on a pair of matched electrostatic probes, and subsequently outputs the cross power spectral density and phase via an on-line computer graphics display. The spectral analysis system and its experimental accuracy are discussed. Using the Lawrence Berkeley Laboratory ten amp neutral beam ion source, several examples demonstrating the systems application to plasma wave detection are given.
Experimental techniques for determining the structure of high frequency waves impressed on an intense relativistic electron beam
Authors: Davis H. A. , Cornet Edward
Published: March 2003

Techniques developed to measure the amplitude, wavelength and azimuthal mode structure of high frequency (a few hundred MHz) waves impressed on an intense relativistic electron beam are described. The details of a wave probe array, two different signal processing schemes and data reduction methods are discussed. Sample data illustrating the use of these techniques, including a multi-probe wavelength measurement made on a single machine firing are presented.
Optically isolated electronic trigger system for experiments on a subnanosecond time scale with a pulsed Van de Graaff electron accelerator
Authors: Luthjens L. H. , Vermeulen M. J. W. , Hom M. L.
Published: March 2003

An optically isolated electronic trigger system for a pulsed Van de Graaff electron accelerator, producing an external pretrigger pulse 75 ns before arrival of the electron pulse at the target, is described. The total time jitter between trigger signal and electron pulse is 50 ps. The measurement of optical and electrical transients on a subnanosecond time scale with a sequential sampling oscilloscope is demonstrated. The contribution of various parts of the equipment to the total jitter is discussed. Those contributions to the jitter due to the electron transit time fluctuations in the accelerator assuming a constant acceleration voltage gradient and to the shot noise in the photomultiplier detector of the trigger system are calculated to be 5 ps and 12 to 21 ps respectively. Comparison with the experimental results leads to the conclusion that a considerable part of the total jitter may be attributed to acceleration voltage gradient fluctuations, to accelerator vibrations and possibly to density fluctuations in the insulation gas. Possible improvements of the trigger system are discussed. The apparatus is used for pulse radiolysis experiments with subnanosecond time resolution down to 100 ps in combination with subnanosecond time duration electron pulses.
Synchronized flash light source optical detection for electric field-jump relaxation experiments
Authors: Savage C. R. , Herrmann U. , Sumdani G. , Schelly Z. A.
Published: March 2003

An electric field-jump apparatus is constructed, with a synchronized Xe flash lamp for photometric monitoring of chemical relaxations. The instrument is especially useful for the investigation of linear macromolecules, where the analyzing light beam must be linearly polarized. A video amplifier is used in conjunction with the photomultiplier, providing for fast rise time and low noise of the detection system.
Preparation of large-area monocrystalline silicon thin windows
Authors: Cheung N. W.
Published: March 2003

A procedure suitable for laboratory practice is described to prepare large-area self-supporting silicon thin crystals with (100), (110) and (111) orientations. Windows up to 2 cm in diameter and 2000 Å in thickness can be produced. Variation in the thickness across the sample can be as low as ±60 Å as measured by 4He+ backscattering spectrometry.
TV-rate histogram equalization processor for the electron microscope
Authors: Matsuda Jin-ichi , Horiguchi Akira , Ura Katsumi
Published: March 2003

A fast (NTSC TV-rate), low cost, simple histogram equalization processor is described. In this apparatus, the histogram equalization processing is carried out by the table look-up method at TV-rate. The characteristics of the processor, and its applications to the real time and on-line processing of weak contrast images from the Ultra-High Voltage Electron Microscope (Osaka University) are described. With this apparatus, equilevel processing, level compression, and level slicing may also be easily carried out.
Constriction resistance measuring system for residential branch circuit connections
Authors: Laug Owen B.
Published: March 2003

A constriction resistance measuring system was designed for evaluating the performance of residential branch wiring circuit connections. The measurement system separates the bulk from the constriction resistance by utilizing the nonlinear voltage-current behavior of a connection. The method overcomes some of the past problems with the nonlinear technique by employing a pulse stimulus current coupled to a high-speed data acquisition system under computer control. A least squares nonlinear fit program is used to obtain the best fit of the voltage-current data to an equation which serves as the nonlinear model. The model was verified by simulating connections with a ’’true 4-wire crossed rod’’ measurement technique. Measurements on connections formed with aluminium and copper conductors agree closely with the parameters predicted by the model. The method is shown to have the ability to accurately measure the constriction resistance of practical connectors in the presence of widely changing values of bulk resistance. A modification of the technique is proposed and shown to have a potential threefold increase in sensitivity.
High-field titanium-wafer vacuum pump
Authors: Van Dyck R. S. , Schwinberg P. B.
Published: March 2003

A new style of sputter-ion Penning discharge pump has been designed, built and tested using helium and hydrogen as background gases. This pump has been shown to operate reliably and stably in the magnetic field extremes of 0.5 and 51 kG. Anode potential must exceed 2000 V and still higher potentials assure the ability to efficiently pump noble gases. At 51 kG, the current/pressure ratio for this test pump with ∼1.2 cm3 of total cell volume ranges from 500 to 100 A/Torr for a pressure range of approximately 2×10−7 to 4×10−11 Torr (uncorrected) respectively.
High input impedance wideband rf preamplifier for SQUIDs
Authors: Pang C. S. , Falco Charles M. , Schuller Ivan K.
Published: March 2003

We describe a wideband rf preamplifier with high input impedance designed for operation of superconducting quantum interference devices (SQUIDs).
Modified pulsed valve for supersonic jet applications
Authors: Auerbach A. , McDiarmid R.
Published: March 2003

The modification of a commercial, pulsed, piezoelectric valve to enhance its applicability as a moderately rapid (∼0.3 ms), pulsed, supersonic molecular beam source is described.
Use of a microwave delay line to reduce the dead time in electron spin echo envelope spectroscopy
Authors: Davis J. L. , Mims W. B.
Published: March 2003

Echo envelope spectrometry, a method for obtaining the electron–nuclear superhyperfine spectrum by transforming the electron spin echo decay envelope into the frequency domain, is limited in its effectiveness by the presence of an appreciable dead time following the microwave transmitter pulses. We describe here a simple passive addition to the microwave circuit which can reduce the dead time by 1.5:1. The performance of an electron spin echo spectrometer with and without this accessory is compared.
New type of ultrafast circuit breaker: its principle and performance
Authors: Caupers P. , Rioux C. , Rioux-Damidau F.
Published: March 2003

The replacement of conventional voltage sources by inductive storage techniques in high-voltage pulse generation requires the successful operation of a suitable circuit breaker. The proposed device is composed of two different parts, the mechanical switch and the energy absorber. The magnetically activated mechanical switch operates in nitrogen under pressure and requires a low command energy (10%–15% of the primary stored energy). We present the mechanical switch basic principle and its performances, namely its restriking voltage and the parameters which affect it. The complete circuit breaker (switch plus energy absorber) can be used to open successfully currents up to 70 kA in times less than 10 μs. The restriking voltage (here, 40 kV after 20 μs) is proportional to the number of knives and can be improved by having longer conductors and a large number of knives. The switch jitter is very low (≃1 μs).
0.5-MHz bandwidth, voltage-programmable current source for light-emitting-diode testing
Authors: Abbas Daniel C.
Published: March 2003

In the evaluation of light-emitting diodes we frequently wish to know how various device characteristics, such as the intensity of light emitted, vary as a function of the current flowing through the device. It is often advantageous to be able to measure these characteristics while using pulsed current excitation. A current source is described, the output of which is proportional to an input voltage. The current source has a 0.5-MHz bandwidth and is suitable for being driven in a pulsed mode with rise and fall times of 650 ns with a 50-Ω load. It can supply up to 250 mA continuously and up to 500 mA peak current.
Simple mechanical device for fine angular adjustments
Authors: Abachi H. , Bedos H. , Malbrunot P.
Published: March 2003

A means of making very fine and reproducible angular adjustments with a simple and strong mechanical arrangement is described. This device mainly consists of three differential screws. Moreover, as all parts of this mechanism can be made of the same metal, it is well adapted to used in extreme physical conditions (low or high temperatures, high pressures, corrosive media ...).
All glass mixing device for reactions under pressures in the 10 kbar range
Authors: le Noble W. J. , Wedinger R. , Schlott R.
Published: March 2003

A simple device is described which permits the mixing of solutions under pressure while both remain separate from the hydraulic fluid. The device combines features of the optical cell we have described earlier and of a mixing device described by Eckert; however, unlike the latter, it has no aluminum or teflon parts and is usable over a pressure range an order of magnitude wider.
Photoionization quantometer for absolute intensity measurements of vacuum ultraviolet and soft x-ray radiation from laser plasma
Authors: Bobashev S. V. , Shmaenok L. A.
Published: March 2003

Design and parameters of the photoionization quantometer are given. It is a combination of photoionization chamber with time-of-flight mass spectrometer. The quantometer is an absolute detector of radiation in the wavelength interval (100–0.1 nm) due to the fact that photoionization and electron-impact ionization cross sections of gases are used for absolute measurements. The quantometer is suitable for measurements of the number of photons in radiation pulses. The minimum number of photons detectable for a single pulse increases from 106 cm−2 puls−1 at 100 nm up to 1011 cm−2 puls−1 for 0.1 nm. The quantometer has been used for vacuum ultraviolet and soft x-ray radiation measurements in the laser plasma experiment. An improved variant of the quantometer is presented which provides the absolute measurements of soft x-ray radiation for laser plasma having continuous spectrum. The inaccuracy of measurements does not exceed 25% for soft x ray.
High-temperature diamond-anvil pressure cell for single-crystal studies
Authors: Hazen Robert M. , Finger Larry W.
Published: March 2003

The miniature, single-crystal, diamond-anvil pressure cell of Merrill and Bassett [Rev. Sci. Instrum. 45, 290 (1974)] has been adapted for x-ray crystallographic studies at sustained temperatures and pressures up to 450 °C at 30 kbar.
Characterization of self-heating effects in a superconducting bolometer with the superfluid helium film
Authors: Hansen G. M. , Telschow K. L.
Published: March 2003

The static and dynamic response characteristics of a thin-film aluminum superconducting transition-edge bolometer are presented with particular attention paid to self-heating effects. Criteria are developed for correct operation of the bolometer for heat-pulse detection and ’’in situ’’ tests are presented to meet these criteria in a given experimental arrangement. The use of the superfluid helium film near its onset transition and the propagation of Third sound waves within this film are shown to aid greatly the characterization of the bolometer response. The results indicate that in order to guarantee correct bolometer response both heat-pulse and static resistance measurements must be compared.
Ultrahigh vacuum specimen holder with rapid cooling mechanism
Authors: Nakanishi Shigemitsu , Horiguchi Tetsuo
Published: March 2003

A simple mechanism capable of rapidly cooling a specimen in ultrahigh vacuum (from 400°–185°C in a few minutes) is described. Its principle feature is that the specimen holder can conveniently be made to contact and separate from a liquid nitrogen (LN) reservoir. This allows the specimen both to be rotated at cooling temperatures and be heated at low LN boil-off rates. The measured LN holding time with the specimen under experimental conditions reached about two hours and the temperature of the cooled specimen was kept constant (within a few degrees) even during its rotary movements. The mechanism can easily be combined with most rotary- and translational-motion feedthroughs available commercially. Versatile modifications of the manipulating facilities are possible within the basic design principles.
Voltage and current measurements for fast pulsed high current discharges
Authors: Pack J. L. , Liberman I.
Published: March 2003

A method for correcting for the inductance in a fast pulsed discharge circuit yields accurate discharge voltage and power input waveforms. An economic fast current shunt is described.
Rate sensing servo amplifier for increasing stability of servo controlled leak valves
Authors: Twist James R.
Published: March 2003

A servo amplifier is described which increases the stability of the series 213 and series 216 Granville–Phillips servo controlled leak valve. The amplifier provides increased immunity from 60 Hz noise through filtering, negative feedback via a rate sensing circuit, and adjustable gain.
Absorbed current electron spin polarization detector
Authors: Pierce D. T. , Girvin S. M. , Unguris J. , Celotta R. J.
Published: March 2003

The principle of spin analysis by means of measurement of the spin dependent absorption of a polarized electron beam is presented. The spin dependent signal is enhanced relative to the spin averaged signal at an energy near which the secondary yield is unity. Both the collected charge method and the zero-crossing method are described for situations where the polarization can and cannot be reversed. A statistical analysis of the uncertainty in the polarization determination by each method is given. Annealed, evaporated Au films are shown to be suitable for the detecting surface of this spin detector. The figure of merit is derived and found for Au films to be comparable to the very best Mott detectors, but the electron optical acceptance is smaller. The applications for which this simple compact spin detector are especially suited are discussed.
Response of a chevron microchannel plate to 2.5 and 14 MeV neutrons
Authors: Medley S. S. , Persing R.
Published: March 2003

The response of a large area (4.6×13 cm) multianode channel electron multiplier array (CEMA) detector to energetic neutrons was investigated. The measured neutron detection efficiencies of the chevron microchannel plate (MCP) were 1.7×10−3 and 6.4×10−3 counts/neutron, respectively, for 2.5 MeV-DD and 14 MeV-DT neutrons. The apparently higher efficiency observed for the 14 MeV neutrons is attributed to neutron-induced background gamma radiation.